US20050215664A1

US20050215664A1 - Ink jet ink

Info

Publication number: US20050215664A1
Application number: US11/070,714
Authority: US
Inventors: Hamdy Elwakil; Patrick McIntyre
Original assignee: Individual
Current assignee: EIDP Inc
Priority date: 2004-03-02
Filing date: 2005-03-02
Publication date: 2005-09-29
Also published as: AU2005219867A1; US7278730B2; PT1730244E; EP1730244B1; AU2005219867B2; JP2007526389A; JP4852031B2; WO2005085371A1; EP1730244A1; CN1926205A; ATE443739T1; CN1926205B; DE602005016785D1; ES2330654T3; US20050196560A1

Abstract

Disclosed is a non-aqueous inkjet ink containing certain titanium dioxide slurries, an associated inkjet ink set for inkjet printing, and a method of inkjet printing with the inkjet ink or ink set. The solvent and mixtures of solvents used for the dispersed titanium dioxide have a hydrogen bonding solubility parameter of greater than about 9. The inks have improved anti-settling properties with less pigment agglomeration and flocculation over time such that they can be utilized to prepare a stable inkjet ink. Also described is the use of this ink to print on colored or transparent surfaces.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application Ser. No. 60/549,607 (filed Mar. 2, 2004), the disclosure of which is incorporated by reference herein for all purposes as if fully set forth.

BACKGROUND OF THE INVENTION

1. Field of the Invention
This present invention pertains to a non-aqueous inkjet ink made from titanium dioxide and an associated inkjet ink set for inkjet printing. The invention also pertains to a method of inkjet printing with the ink and ink set. The inks utilized herein have improved anti-settling performance with less pigment agglomeration and flocculation over time such that they can be utilized as a stable inkjet ink. The white ink based on the titanium dioxide provides new means to digitally print white ink by itself, but also with other colors.
2. Description of the Related Art
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper or polymeric substrates, to form the desired image. The droplets are ejected from a printhead in response to electrical signals generated by a microprocessor.
Colored inkjet inks comprise one or more colorants that are dissolved (e.g., dyes) and/or dispersed (e.g., pigments and dispersed dyes) in the ink vehicle. The ink vehicle can be aqueous (significant amounts of water) or non-aqueous (predominantly organic liquid), and the ink is referred to as aqueous or non-aqueous ink accordingly.
Although aqueous ink is advantageous because water is especially environmentally friendly, there are many applications where aqueous ink is unsuitable and non-aqueous ink must be used. Many, if not most of these non-aqueous ink applications involve printed articles on hydrophobic substrates, and particularly printed articles on polymer substrates, which will be exposed to sunlight, and the preferred colorants in these applications are pigments because of their well-know advantage in fade resistance compared to dyes.
Dispersion of pigments in a non-aqueous vehicle is substantially different than dispersion in an aqueous vehicle. Generally, pigments that can be dispersed well in water do not disperse well in non-aqueous solvent, and vice versa.
Also, the demands of inkjet printing are quite rigorous and the standards of dispersion quality are high. Thus, pigments that may be “well dispersed” for other applications are often still inadequately dispersed for inkjet applications.
There is a need for improved pigment selection especially for a stable white ink for inkjet inks. In particular, there is a need for the white pigments that can be sufficiently stabilized in inkjet compatible formulations so that the resultant ink can be effectively jetted, even after being stored or otherwise unused for some period of time. In addition, the ability to use a white ink to complement other inks of an ink set can lead to improved images, especially when lighter tones and/or higher degrees of coverage or opacity are needed.
White inks are useful and provide good visibility when printed on transparent and colored surfaces. White printing on these surfaces is desirable in numerous end uses, such as the computer industry (printed circuit boards, computer chips), recording industry (tapes, film, etc.), packaging and automotive coatings. White ink may be used not only to detail and add decals to automobiles, but also to other motor vehicles, including trucks, planes and trains, as well as bicycles, etc. White ink may also be useful on other surfaces, such as plastics, wood, metal, glass, textiles, polymeric films and leather for both practical and ornamental purposes. Colored paper and cardboard can also be effectively printed with white ink.
White ink formulations typically contain a particulate white pigment dispersed in a solvent/resin system.
There are many patents and applications describing aspects of using a white ink in ink jet printing. U.S. Pat. No. 4,630,076 describes a color ink jet system with an additional white ink that is printed on top of the previously printed color dots, but does not provide a means to produce a stable useful white ink.
U.S. 2001/0020964 describes the use of a quickly drying white ink printed over another ink or adjacently. This use of white ink is particularly directed to use of the white ink with the black ink. No description of an effective ink jet white ink is provided.
U.S. Pat. No. 5,439,514 describes an aqueous ink which has both a colorant and a white inorganic material in the same ink.
U.S. Pat. No. 6,769,766 describes the need for a white UV ink for ink jet printers.
WO02/096654 provides a possible solution to the problem of the settling of the titanium dioxide by agitating the ink cartridge by having a continuous ink-flow subsystem to inhibit settling of solids out of suspension.
U.S. 2003/0052952 describes an inorganic phosphoric acid treated titanium dioxide that can be slurred to obtain an aqueous ink. Only modest ink stability is reported.
U.S. Pat. No. 6,433,038 describes an aqueous photocurable ink that has a anatase titanium dioxide as the colorant.
U.S. 2004/0246319, EP-A-1321497, EP-A-1388578 and WO00/049097 all describe inks that contain a polymerizable compound and a white pigment and/or titanium dioxide.
U.S. Pat. No. 4,680,580 describes a white ink with an inorganic white pigment, a binder resin, a solvent selected from an alcohol, ketone, ether or acetate ester and cyclohexanone, which are solvents for the binder and a conductive salt. This ink is primarily effective for continuous ink jet printers.
WO04/053002 discloses an opaque ink jet ink which has similar feature to U.S. Pat. No. 4,680,580, as it is an ink with a conductive component and suggested for utility with continuous ink jet printers.
Current white ink formulations are not acceptable for numerous applications, such as commercial drop-on-demand inkjet applications, primarily because of poor stability resulting in pigment settling and agglomeration. Poor stability may result in “nozzle outs” or plugging of the ink jet nozzles. For example, a typical print head on an industrial printer has 256 nozzles, each nozzle head having a diameter of about 50 microns in size. Large pigment particles and agglomerates may plug the nozzles. Poor stability also results in poor hiding, non-uniform coverage and poor clarity in the printed surface.
White ink formulations based on inorganic white pigments, such as titanium dioxide (TiO₂), may fail because of poor stabilization of the TiO₂pigment. Pigment agglomeration and flocculation are often at fault in poor performance of white inks, particularly white inkjet inks, due to settling and nozzle plugging problems.
As a result, there is a need for a white pigmented ink formulation for use in ink and inkjet systems that avoid the aforementioned negative attributes. The present invention meets these needs.

SUMMARY OF THE INVENTION

In one aspect of the present invention there is provided a non-aqueous inkjet ink comprising a non-aqueous liquid carrier having dispersed therein (a) a titanium dioxide pigment and (b) at least one dispersant for the titanium dioxide pigment, wherein:
(i) the non-aqueous liquid carrier comprises an organic solvent or a mixture of organic solvents,
(ii) the organic solvent or mixture of organic solvents has a hydrogen bonding solubility parameter based on Hansen solubility parameters of more than about 9,
(iii) the organic solvent or mixture of organic solvents in the non-aqueous liquid carrier are predominantly only non-reactive organic solvents; and
(iv) the conductivity of the ink is less than about 50 μmho/cm.
These inkjet inks may further comprise a variety of optional additives of the general type known to those of ordinary skill in the art, as part of the titanium dioxide slurry and/or added to the jet ink separately therefrom, such optional additives including, for example, other dispersants, binders, humectants and rheological modifiers.
Unexpectedly, by use of the dispersant in combination with the non-aqueous solvent mixture with a Hansen solubility parameter of greater than 9, settling of titanium dioxide particles is significantly reduced. Moreover, even when settling does occur, the settling is “soft” settling, meaning the titanium dioxide pigment can be readily re-dispersed and rejuvenated by low shear mixing so as not to result in plugging of inkjet printhead nozzles. Low shear mixing includes, for example, simple shaking (e.g., by hand or movement of the inkjet printhead), or stirring with an impeller or mixing blades at speeds of less than about 500 rpm wherein no grinding occurs. In contrast, “hard” settling occurs with many titanium dioxide slurries of the prior art. For most of the dispersant/solvent combinations, negligible soft settling is observed.
The titanium dioxide pigment used herein is white, thus the inkjet inks of the present invention are preferably white. Non-white colored inks can also be made by utilizing one or more additional colorants in the ink.
In accordance with another aspect of the present invention, there is provided an inkjet ink set comprising a plurality of colored, pigmented inks, at least one of which is a preferably white inkjet ink as set forth above.
The inkjet inks of the present invention are suitable, for example, for use in personal, business and industrial drop-on-demand inkjet printers, and numerous other printing applications. Furthermore, they can be used for printing a wide variety of substrates including non-white paper, transparencies, polymer substrates, textiles, etc.
The present invention thus also provides a method for inkjet printing onto a substrate, comprising the steps of:
(1) providing a drop-on demand inkjet printer that is responsive to digital data signals;
(2) loading the printer with a substrate to be printed;
(3) loading the printer with the above-mentioned inkjet ink or inkjet ink set; and
(4) printing onto the substrate using the inkjet ink set in response to the digital data signals.
A preferred substrate for the instant invention inkjet ink or inkjet ink set is a thermoplastic polymer substrate.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description. It is to be appreciated that certain features of the invention which are, for clarity, described above and below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. In addition, references in the singular may also include the plural (for example, “a” and “an” may refer to one, or one or more) unless the context specifically states otherwise. Further, reference to values stated in ranges include each and every value within that range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a non-aqueous ink, preferably a white ink, made from a particularly dispersed, stabilized titanium dioxide slurry. Inks made therefrom have improved stability to agglomeration upon storage. The ink utilizes at least one dispersant in amounts to stabilize and keep the pigments deflocculated over extended periods of time when the slurry is subsequently used in an ink formulation. As a result, the ultimate ink formulation provides desirable properties such as good hiding, uniform coverage, selective coverage, selective opacity, good chemical resistance and good clarity when applied to surfaces. The non-aqueous ink is especially useful for printing on polymeric substrates.
Titanium Dioxide Pigment
Titanium dioxide (TiO₂) pigment useful in the present invention may be in the rutile or anatase crystalline form. It is commonly made by either a chloride process or a sulfate process. In the chloride process, TiCl₄is oxidized to TiO₂particles. In the sulfate process, sulfuric acid and ore containing titanium are dissolved, and the resulting solution goes through a series of steps to yield TiO₂. Both the sulfate and chloride processes are described in greater detail in “The Pigment Handbook”, Vol. 1, 2nd Ed., John Wiley & Sons, NY (1988), the relevant disclosure of which is incorporated by reference herein for all purposes as if fully set forth.
The titanium dioxide particles can have a wide variety of average particle sizes of about 1 micron or less, depending on the desired end use application of the ink.
The titanium dioxide pigment is in and of itself white in color.
For applications demanding high hiding or decorative printing applications, the titanium dioxide particles preferably have an average size of less than about 1 micron (1000 nanometers). Preferably, the particles have an average size of from about 50 to about 950 nanometers, more preferably from about 75 to about 750 nanometers, and still more preferably from about 100 to about 500 nanometers. These titanium dioxide particles are commonly called pigmentary TiO₂.
For applications demanding white color with some degree of transparency, the pigment preference is “nano” titanium dioxide. “Nano” titanium dioxide particles typically have an average size ranging from about 10 to about 200 nanometers, preferably from about 20 to about 150 nanometers, and more preferably from about 35 to about 75 nanometers. An ink comprising nano titanium dioxide can provide improved chroma and transparency, while still retaining good resistance to light fade and appropriate hue angle.
In addition, unique advantages may be realized with multiple particle sizes, such as opaqueness and UV protection. These multiple sizes can be achieved by adding both a pigmentary and a nano grade of TiO₂.
The titanium dioxide can be incorporated into an ink formulation via a slurry concentrate composition. The amount of titanium dioxide present in the slurry composition is preferably from about 15 wt % to about 80 wt %, based on the total slurry weight. For slurries wherein the majority of titanium dioxide particles are of a pigmentary size, and preferably those in which the average particle size is greater than about 200 nanometers up to about 1 micron, the amount of titanium dioxide in the slurry is preferably from about 50 wt % to about 75 wt %, based on the total weight of the slurry. For slurries wherein the majority of titanium dioxide particles are of “nano” size, and preferably those in which the average particle size is from about 10 nanometers to about 200 nanometers, the amount of titanium dioxide in the slurry is preferably from about 20 wt % to about 50 wt %, and more preferably from about 25 wt % to about 35 wt %, based on the weight of the slurry.
Alternatively, the titanium dioxide can be mixed with the dispersants, the solvent(s) and dispersed to obtain the final ink formulation in one step.
The titanium dioxide pigment may be substantially pure titanium dioxide or may contain other metal oxides, such as silica, alumina and zirconia. Other metal oxides may become incorporated into the pigment particles, for example, by co-oxidizing or co-precipitating titanium compounds with other metal compounds. If co-oxidized or co-precipitated metals are present, they are preferably present as the metal oxide in an amount from about 0.1 wt % to about 20 wt %, more preferably from about 0.5 wt % to about 5 wt %, and still more preferably from about 0.5 wt % to about 1.5 wt %, based on the total titanium dioxide pigment weight.
The titanium dioxide pigment may also bear one or more metal oxide surface coatings. These coatings may be applied using techniques known by those skilled in the art. Examples of metal oxide coatings include silica, alumina, alumina-silica and zirconia, among others. Such coatings may optionally be present in an amount of from about 0.1 wt % to about 10 wt %, and preferably from about 0.5 wt % to about 3 wt %, based on the total weight of the titanium dioxide pigment.
The titanium dioxide pigment may also bear one or more organic surface coatings, such as, for example, carboxylic acids, silanes, siloxanes and hydrocarbon waxes, and their reaction products with the titanium dioxide surface. The amount of organic surface coating, when present, generally ranges from about 0.01 wt % to about 6 wt %, preferably from about 0.1 wt % to about 3 wt %, more preferably about 0.5 wt % to about 1.5 wt %, and still more preferably about 1 wt %, based on the total weight of the pigment.
Dispersants
The polymeric dispersant or dispersants provide enhanced effects in stabilizing titanium dioxide pigment for inkjet ink and, furthermore, provide enhanced stability in the ink formulations. Suitable polymeric dispersants include cationic polymeric dispersants, and mixtures of two dispersants, one of which is a graft copolymer and another of which is a block copolymer.
If the polymeric dispersants (such as the block and graft copolymer dispersants) contain acid functionality, they can be used in their non-neutralized form. An option is to neutralize at least a portion of the acid-functional groups with a base such as ammonia, potassium hydroxide, sodium hydroxide, an amine, such as dimethyl ethyl amine, amino methyl propanol and the like, which forms a water-solubilizing group.
For the dispersants with amine-functional groups (cationic), they can be converted to their salt form by adding acids, organic chlorides, etc. An example of an added organic chloride is benzyl chloride.
An additional dispersant is a phosphated polymer that is different from the dispersants described above.
The inks of the present invention, and titanium dioxide slurry used in those inks, preferably have an overall dispersant to pigment weight ratio (D/P) of from about 0.0025:1 to about 0.25:1, preferably from about 0.05:1 to about 0.175:1, and more preferably from about 0.075:1 to about 0.14:1. The overall dispersant to pigment ratio is the sum total of D/P contributions from each dispersant present.
The dispersants to be used can be prepared by any of the known polymer preparation processes for the relevant type of polymer.
Note: All molecular weights referred to herein are determined by Gel Permeation Chromatography using polystyrene as a standard.
An example of a dispersant is a graft copolymer dispersant preferably having a weight average molecular weight of from about 4000 to about 100000, and more preferably from about 10000 to about 40000. The graft copolymer dispersants can be block or comb copolymers. The graft copolymer comprises from about 90% to about 50% by weight of a polymeric backbone and, correspondingly, from about 10% to about 50% by weight of polymeric side chains attached to the backbone (the backbone and side chains together being 100 wt %).
The polymeric backbone is a hydrophobic (relative to the side chains) adsorbing segment. The side chains are individually hydrophilic (relative to the backbone) stabilizing segments. The side chains are attached to the backbone at a single terminal point.
Backbone
As just indicated, the backbone of the graft copolymer dispersant is hydrophobic relative to the side chains. The backbone comprises polymerized hydrophobic monomers such as alkyl methacrylates and acrylates, and cycloaliphatic methacrylates and acrylates, such as those listed hereinafter. The backbone may still further comprise up to about 20% by weight, and preferably from about 1% to about 10% by weight, based on the weight of the graft copolymer, of polymerized ethylenically unsaturated acid monomers, such as those listed hereinafter, as well as up to about 30% by weight, based on the weight of the graft copolymer, of other polymerized ethylenically unsaturated monomers containing functional groups, such as those listed hereinafter.
The backbone of the graft copolymer has an affinity for the surface of the pigment used in the slurry and anchors the copolymer to the pigment, thus keeping the pigment dispersed and preventing the graft copolymer from returning to the liquid phase.
Typical alkyl acrylates and methacrylates that can be used have 1 to 12 carbon atoms, and preferably 1 to 8 carbon atoms, in the alkyl group, and include, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, 2-ethyl hexyl acrylate, 2-ethyl hexyl methacrylate, nonyl acrylate, nonyl methacrylate, lauryl acrylate, lauryl methacrylate and the like. Of these, the methacrylates are preferred.
Cycloaliphatic acrylates and methacrylates can also be used such as trimethylcyclohexyl acrylate, trimethylcyclohexyl methacrylate, t-butyl cyclohexyl acrylate, isobutylcyclohexyl methacrylate and the like. Again, methacrylates are preferred.
Examples of ethylenically unsaturated acid monomers include methacrylic acid, acrylic acid, itaconic acid, maleic acid and the like; and ethylenically unsaturated sulfonic and sulfinic acid and esters thereof, such as styrene sulfonic acid, acrylamido propane sulfonic acid, acrylamido methyl propane sulfonic acid and the like. When used, acrylic and methacrylic acid are preferred.
Examples of functional monomers (other than the ethylenically unsaturated acid monomers) include acrylamide, methacrylamide, methacrylonitrile, hydroxy ethyl acrylate, hydroxy ethyl methacrylate, t-butylamino ethyl methacrylate, diethyl amino ethyl acrylate, diethyl amino ethyl methacrylate, nitro phenol acrylate, nitro phenol methacrylate, phthalimido methyl acrylate and phthalimido methacrylate.
Side Chains
The side chains of the graft copolymer are hydrophilic (relative to the backbone) macromonomers that preferably have a weight average molecular weight of from about 1000 to about 30000, and more preferably from about 1500 to about 8000. The side chains preferably comprise from about 2% to about 100% by weight, more preferably from about 20% to about 60% by weight, based on the weight of the macromonomer, of polymerized ethylenically unsaturated acid monomers. The side chains are hydrophilic and keep the pigment uniformly dispersed in the slurry and resulting ink.
Alternatively, the side chains can have nonionic hydrophilic groups such as condensed alkylene oxides. The side chains can be a mixture of ionic and non-ionic groups or mixtures either in the same side chain or in different side chains.
The macromonomer contains a single terminal ethylenically unsaturated group, which is polymerized into the backbone of the graft copolymer.
Methacrylic acid is preferred as the ethylenically unsaturated acid monomer, particularly if it is the sole constituent of the macromonomer. Other acid monomers that can be used include ethylenically unsaturated carboxylic acids such as acrylic acid, itaconic acid, maleic acid and the like; and ethylenically unsaturated sulfonic and sulfinic acid and esters thereof, such as styrene sulfonic acid, acrylamido propane sulfonic acid, acrylamido methyl propane sulfonic acid and the like.
Up to about 80% by weight, based on the weight of the macromonomer, of other hydrophobic polymerized ethylenically unsaturated monomers can be present in the macromonomer, including the alkyl acrylates and methacrylates, cycloaliphatic acrylates and methacrylates listed above.
One preferred macromonomer contains from about 50% to about 80% by weight of polymerized methyl methacrylate, and from about 20% to about 50% by weight of polymerized methacrylic acid (100 wt % total), and has a weight average molecular weight of from about 2000 to about 5000.
The monomers constituting the macromonomer are preferably polymerized using a catalytic chain transfer agent that contains a Co⁺²group, i.e. a cobalt chain transfer agent, which ensures that the resulting macromonomer only has one terminal ethylenically unsaturated group which will polymerize with the backbone monomers to form the graft copolymer. Typically, in the first step of the process for preparing the macromonomer, the monomers are blended with an inert organic solvent, which is water miscible or water dispersible, and a cobalt chain transfer agent and heated usually to the reflux temperature of the reaction mixture. In subsequent steps additional monomers, cobalt chain transfer agent and a conventional azo type polymerization catalyst (such as 2,2′-azobis(2-methylbutanenitrile), 2,2′-azobis(2,4′-dimethylpentanenitrile) and 2,2′-azobis(2,4-dimethyl-4-methoxyvaleronitrile)) are added and polymerization is continued until a macromonomer is formed of the desired molecular weight. After macromonomer is formed, any solvent may be stripped off before additional processing to make the first dispersant graft copolymer.
Preferred cobalt chain transfer agents are described in U.S. Pat. No. 4,680,352 and U.S. Pat. No. 4,722,984 (the disclosures of which are incorporated by reference herein for all purposes as if fully set forth). Most preferred are pentacyanocobaltate (II), diaquabis(borondifluorodimethyl-glyoximato) cobaltate (II) and diaquabis(borondifluorophenylglyoximato) cobaltate (II). Typically these chain transfer agents are used at concentrations of from about 5 ppm to about 1000 ppm, based on the weight of the monomers used.
Example of a Preparation of a Dispersant
The graft copolymer used in the present invention is preferably prepared by the Special Chain Transfer (SCT) method as described in U.S. Pat. No. 5,231,131 (the disclosure of which is incorporated by reference herein as if fully set forth). By using this method, 100% graft copolymer can be efficiently prepared rather than a mixture of graft copolymer, low molecular weight backbone polymer and copolymerized macromonomer segments, as is generally been the case with other processes used for making graft copolymers. However, it should be recognized that the graft copolymer dispersant used in this invention is not restricted to any specific preparation technology. Graft dispersants of the structure and functionality described above made using other known polymerization techniques will also provide benefits of this invention and are thus contemplated to be within the scope of this invention.
To form the graft copolymer, backbone monomers are polymerized in the presence of solvent, polymerization catalyst and macromonomer prepared, for example, as described above. Any of the aforementioned azo type catalysts can be used, as can other suitable catalysts such as peroxides and hydroperoxides. Typical of such catalysts are di-tertiarybutyl peroxide, di-cumyl peroxide, tertiaryamyl peroxide, cumenehydroperoxide, di(n-propyl) peroxydicarbonate, peresters such as amyl peroxyacetate and the like. Polymerization is continued usually at the reflux temperature of the reaction mixture until a graft copolymer is formed of the desired molecular weight.
Typical solvents that can be used to form the macromonomer and/or the graft copolymer are ketones such as methyl ethyl ketone, isobutyl ketone, ethyl amyl ketone and acetone; alcohols such as methanol, ethanol and isopropanol; esters such as ethyl acetate; glycols such as ethylene glycol and propylene glycol; ethers such as tetrahydrofuran and ethylene glycol mono butyl ether; and the like.
After the graft copolymer is formed, the acid functionality thereon can be at least partially neutralized with an amine or an inorganic base such as ammonium hydroxide or sodium hydroxide, and then water is added to form a dispersion of the graft copolymer. Typical amines that can be used include amino methyl propanol, amino ethyl propanol, dimethyl ethyl amine, triethylamine and the like. A preferred amine for inkjet applications is dimethyl ethyl amine.
Typically, these dispersant graft copolymers and the other dispersants described below are used as from about 20% to about 60% solutions in typical solvents.
Particularly useful graft copolymers include the following:
a graft copolymer having a backbone of polymerized methyl acrylate and butyl acrylate, and side chains of a macromonomer having a weight average molecular weight of from about 2000 to about 5000, and containing from about 50% to about 80% by weight, based on the weight of the macromonomer, of polymerized methyl methacrylate and from about 20% to about 50% by weight, based on the weight of the macromonomer, of polymerized methacrylic acid;
a graft copolymer having a backbone of polymerized methyl acrylate, butyl acrylate and acrylamido methyl propane sulfonic acid, and side chains of the above macromonomer;
a graft copolymer having a backbone of polymerized methyl acrylate, butyl acrylate and acrylic acid, and side chains of the above macromonomer;
a graft copolymer having a backbone of polymerized ethyl acrylate, and side chains of the above macromonomer;
a graft copolymer having a backbone of polymerized ethyl acrylate, methyl acrylate and acrylic acid, and side chains of the above macromonomer; and
a graft copolymer having a backbone of polymerized ethyl acrylate and acrylic acid, and side chains of the above macromonomer.
Alternative Dispersant
Another dispersant is a block copolymer of type AB, ABA or ABC, or mixtures thereof. At least one of the blocks, A, B, or C is an adsorbing segment. At least one of the blocks, A, B, or C is a stabilizing segment. By “adsorbing segment” it is meant that the segment is designed to adsorb onto the surface of a titanium dioxide pigment, for example, by acid-base or other bonding interactions. By “stabilizing segment” it is meant that the segment is designed to provide a steric stabilization of the pigment particle against flocculation in a slurry composition. Generally, the adsorbing segments of the block copolymer are hydrophobic, in comparison to the stabilizing segment, and are designed to adhere to the pigment surface, while the stabilizing segments are generally hydrophilic, in comparison to the adsorbing segment, and are soluble in processing media, for example, media used in finishing crude titanium dioxide pigment.
The hydrophobic adsorbing segment preferably comprises polymerized ethylenically unsaturated hydrophobic monomers such as are listed hereinafter, and further comprises polymerized ethylenically unsaturated monomers having functional groups that enhance the pigment binding force. Monomers having functional groups are preferably present in an amount up to about 40% by weight, based on the total weight of the adsorbing segment. For example, monomers with acid functional groups may be incorporated in the hydrophobic portion to bind with basic groups on the titanium dioxide pigment surface. Monomers with amine groups may be incorporated in the hydrophobic portion to bind with acid groups that may be present on the titanium dioxide surface. Other monomers that have known affinity for titanium dioxide, such as monomers with silane groups, etc., may also be incorporated in the hydrophobic portion.
Suitable hydrophobic monomers that can be used to form the hydrophobic adsorbing segment include, but are not limited to, alkyl (meth)acrylates having 1 to 12 (and preferably 1 to 8) carbon atoms in the alkyl group (such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, lauryl methacrylate and the like, and any mixtures thereof). Cycloaliphatic (meth)acrylates can also be used (such as trimethylcyclohexyl methacrylate, isobutylcyclohexyl methacrylate and the like, as well as any mixtures thereof). Mixtures of any of the above may also be used.
Suitable monomers with acid groups that can be incorporated into the hydrophobic adsorbing segment to enhance the pigment binding force include ethylenically unsaturated carboxylic acids (such as acrylic acid and methacrylic acid). Methacrylic acid is preferred, particularly if it is the sole acid constituent.
Suitable monomers with amine groups include alkylaminoalkyl methacrylate monomers having 1 to 4 carbon atoms in the alkyl group (such as dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dipropylaminoethyl methacrylate, dibutylaminoethyl methacrylate) and the like.
As stated above, the stabilizing segment is preferably soluble in the selected (aqueous) processing medium encountered during crude pigment finishing and, therefore, primarily comprises polymerized ethylenically unsaturated hydrophilic monomers. Suitable hydrophilic monomers that can be used to form the stabilizing segment include monomers with acid groups (such as acrylic acid, methacrylic acid, 2-acrylamido-2-propane sulfonic acid, and the like, as listed hereinabove). The salts of these monomers can also be used to aid in dispersing the copolymer in the selected aqueous processing medium. Such salts can be formed by the addition of an amine (such as dimethyl ethyl amine or 2-amino methyl propanol) or an inorganic base (such as ammonium hydroxide or sodium hydroxide) to the polymer dispersant after it has been formed. In addition to the forgoing monomers, other commonly used hydrophobic monomers can be copolymerized into the stabilizing portion, provided they are used at a concentration that will not significantly change the solubility properties of the stabilizing portion in the selected processing medium. Some useful examples include the alkyl (meth)acrylates and other hydrophobic monomers listed hereinabove.
The block copolymer dispersant preferably has a number average molecular weight of from about 1000 to about 15000, and more preferably from about 2000 to about 5000. The adsorbing segment preferably has a number average molecular weight of from about 1000 to about 5000, and more preferably from about 1000 to about 3000. The stabilizing segment preferably has a number average molecular weight of from about 1000 to about 5000, and more preferably from about 1000 to about 3000.
The method of preparation of the second dispersant is not critical. Block copolymer dispersants of the structure and functionality described above made using known polymerization techniques will provide the benefits of this invention and are thus contemplated to be within the scope of this invention. The second dispersant may be prepared, for example, by using the Group Transfer Polymerization (GTP) method reported in U.S. Pat. No. 4,656,226; or the anionic polymerization method reported by Morton in Anionic Polymerization: Principles and Practice (New York: Academic Press, 1983) (the disclosures of which are incorporated by reference herein for all purposes as if fully set forth).
The GTP method is preferred. An advantage of the GTP process is the ability to make polymer dispersants with precise architecture and low polydispersity. Typically polydispersity of GTP polymers is between about 1.0 and about 1.25.
Phosphate-Containing Dispersant
Another optional dispersant is a phosphated polymer dispersant comprising a hydrophilic (relative to the adsorbing segment) stabilizing segment and a hydrophobic (relative to the stabilizing segment) adsorbing segment. The phosphated polymer can be a graft copolymer, a block copolymer or a random copolymer.
The adsorbing segment of the phosphated polymer mainly comprises polymerized ethylenically unsaturated hydrophobic monomers, such as alkyl (meth)acrylates, cycloaliphatic (meth)acrylates and aryl (meth)acrylates, such as are listed hereinafter. The term (meth)acrylate refers to both the acrylate and methacrylate esters. The adsorbing segment preferably further comprises from about 1% to about 20% by weight, and more preferably from about 1% to about 10% by weight, based on the total weight of the copolymer, of polymerized non-hydrophobic ethylenically unsaturated monomers that have attached thereto a phosphate anchoring group. It should be noted that it is not necessary that the phosphate group be incorporated in the hydrophobic segment of the polymer. Phosphate groups can be incorporated in the hydrophilic segment as well.
Examples of hydrophobic monomers that can be used to form the adsorbing segment include alkyl (meth)acrylates having 1 to 12 carbon atoms in the alkyl group, such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, lauryl methacrylate and the like, and any mixtures thereof. Cycloaliphatic (meth)acrylates can also be used such as trimethylcyclohexyl methacrylate, isobutylcyclohexyl methacrylate and the like, and any mixtures thereof. Mixtures of any of the above may also be used.
The hydrophilic stabilizing segment of the phosphated dispersant comprises polymerized ethylenically unsaturated hydrophilic monomers. Such monomers include acid-containing monomers, such as acrylic acid, methacrylic acid and 2-acrylamido-2-propane sulfonic acid; and non-ionic hydrophilic monomers. Additional examples of useful acid-containing monomers include itaconic acid, maleic acid and the like. Ethylenically unsaturated sulfonic, sulfinic, phosphoric or phosphonic acid and esters thereof also can be used, such as styrene sulfonic acid, vinyl phosphonic acid and its esters, and the like. Monomers containing acid functionality are selected, in part, on their theoretical ability to bind to the titanium oxide particles. Non-ionic hydrophilic monomers that are useful in the hydrophilic stabilizing segment include monoethylenically unsaturated poly(alkylene glycol) monomers, such as poly(ethylene glycol) mono (meth)acrylate, poly(ethylene glycol) alkyl ethers having 1 to 4 carbon atoms in the alkyl group (such as poly(ethylene glycol) methyl ether oligomers, supplied under the trade name Bisomer S20W by International Specialty Chemicals), and the like; and poly(alkoxylated) alkyl (meth)acrylates and the like. These monomers preferably have a weight average molecular weight of from about 200 to about 4000, and more preferably from about 200 to about 2000. A combination of nonionic and anionic stabilizing segments can also be favorable.
Phosphate groups can be incorporated into the adsorbing segment or the stabilizing segment by reacting the polymer with phosphoric acid or phosphorus pentoxide. Unreacted or residual phosphoric acid groups are preferably neutralized with amine or inorganic base when used for dispersing titanium dioxide pigment into water. The remainder of the polymer may be adjusted to improve dispersibility of the titanium dioxide pigment and make the copolymer more compatible with other components to form a stabilized pigment slurry.
Alternatively, phosphate groups may be incorporated into the polymer by reaction of a phosphorus containing reactive group with a monomer, macromonomer or polymer such that the resultant optional dispersant is a phosphate-substituted dispersant. An example of this strategy is forming a polymer having reactive hydroxyl groups, for example, by forming a copolymer with hydroxy alkyl methacrylates or acrylates, and subsequently reacting the hydroxy groups with phosphorus pentoxide. Neutralizing phosphoric acid groups with amine or inorganic base is preferable for aqueous titanium dioxide slurries.
Suitable monomers with phosphate groups that can also be used to introduce phosphate groups into the copolymer (adsorbing segment or stabilizing segment) include ethylenically unsaturated phosphate monomers (such as phosphorylated polyethylene glycol (meth)acrylate, phosphorylated hydroxy ethyl (meth)acrylate, and the like) or ethylenically unsaturated monomers containing alcohol groups (such as hydroxy alkyl (meth)acrylate) or epoxy groups (such as glycidyl acrylate and glycidyl (meth)acrylate) which are treated with one or more phosphorylating agents (such as phosphoric acid or phosphorous pentoxide) before or after polymerization to form phosphate groups where the epoxy or alcohol groups used to be.
The phosphated copolymer dispersant preferably has a number average molecular weight of from about 4000 to about 25000, and more preferably from about 5000 to about 20000. The adsorbing segment typically has a number average molecular weight of from about 2000 to about 10000, and preferably from about 4000 to about 7000. The stabilizing segment typically has a number average molecular weight of from about 2000 to about 15000, and preferably from about 4000 to about 7000. The adsorbing segment typically comprises from about 20% to about 80% by weight of the polymer, and correspondingly the stabilizing segment typically comprises from about 80% to about 20% by weight of the polymer (the adsorbing and stabilizing segments being 100 wt % total).
The forgoing dispersants may be prepared by a variety of well known solution polymerization techniques devised for a particular structure, such as by the GTP (Group Transfer Polymerization) method reported in previously incorporated U.S. Pat. No. 4,656,226; by the standard anionic or the free radical polymerization method reported in previously incorporated U.S. Pat. No. 4,656,226; or by the SCT method reported in previously incorporated U.S. Pat. No. 5,231,131.
The GTP method is traditionally used to form block copolymers. Using this method, it is generally recommended to block any acid or hydroxyl containing monomers to prevent side reactions during polymerization. Following polymerization, the acid and hydroxyl groups are unblocked by a reaction with alcohol or water.
The SCT method is traditionally used to form the macromonomer portion of a graft copolymer. Macromonomers can also be supplied by other means.
Standard anionic polymerization is oftentimes used to form random copolymers and may be used to prepare analogues of resins described herein.
Commercially available suitable dispersants include Disperbyk® 2000 and Disperbyk® 2001 (Byk Chemie, Wesel, Germany). These are described as modified acrylate block copolymers. The Disperbyk® 2000 has an amine value of 4 mg KOH/gm, and the Disperbyk® 2001 has an amine value of 29 mg KOH/gm and an acid value of 19 mg/KOH/gm.
A slurry formed from the titanium dioxide, the dispersant(s), and the solvent or mixture of solvents with a hydrogen bonding solubility parameter of greater than 9, is a stable slurry. When settling does occur, the settling is “soft” settling, meaning the titanium dioxide pigment can be readily re-dispersed and rejuvenated by low shear mixing. The pigment is also similarly stably dispersed when the slurry is formulated into inks, so as not to result in plugging of ink jet nozzles. Low shear mixing includes, for example, shaking by hand or stirring with an impeller or mixing blades at speeds of less than about 500 rpm wherein no grinding occurs. In contrast, “hard” settling occurs with many titanium dioxide slurries of the prior art. By “hard settling” it is meant the settling of titanium dioxide particles from the slurry cannot be re-dispersed to an acceptable level for ink jet inks.
Other dispersants described herein can be used singly in the non-aqueous solvents (which have a hydrogen bonding solubility parameter as described by Hansen solubility parameter) to produce stable titanium dioxide inks.
The inventive inks do not have added salts that increase the conductivity, which should be less than about 50 μmho/cm, and more preferably less than about 25 μmho/cm. Added salts can be detrimental to drop-on demand ink jet printer systems.
Liquid Carrier for Preparation of the Titanium Dioxide Slurries
The titanium dioxide slurry used in this invention comprises a non-aqueous liquid carrier. The carrier is preferably an organic solvent or mixture of organic solvents having a hydrogen bonding solubility parameter based on Hansen solubility parameters of more than about 9. This combination of dispersant and solvent leads to a peculiarly effective liquid carrier for the titanium dioxide pigment.
Optional Additives for the Titanium Dioxide Slurry
The titanium dioxide slurry used in the present invention may optionally comprise one or more additives that are compatible with the end use in inkjet inks.
For example, the titanium dioxide slurry may optionally comprise a humectant. A humectant may be considered a co-solvent. Typically, although not always, a humectant has a higher boiling point than the primary solvent, that is, the liquid carrier. A humectant is generally added to prevent drying during storage. Humectants may also help retard settling.
Humectants are especially useful additives to formulations that have a propensity for chalking. Chalking occurs when solvent (that is, liquid carrier for the slurries of this invention) evaporates, pigment, especially the titanium dioxide pigment, dries on surfaces, and sides of storage vessels and may flake off and fall back into the slurry. Chalking can be a serious problem. For example, if dried pigment agglomerates are introduced into an ink jet formulation, an unacceptable level of nozzle outs may occur. Humectants retard solvent evaporation and thereby retard chalking.
Examples of suitable humectants for use in this invention include polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol and 1,2,6-hexanetriol; glycol ethers such as dipropylene glycol monomethyl ether and propylene glycol normal propyl ether; and others including trimethylolpropane, trimethylolethane, glycerin, polyethylene glycol and dipropylene glycol. Ethylene glycol is preferred.
The titanium dioxide slurry may also optionally comprise a rheology modifier. A rheology modifier can be any known commercially available rheology modifiers, such as Solthix® thickeners available from Avecia. Other useful rheology modifiers include cellulose and synthetic hectorite clays. Synthetic hectorite has the formula:
[Mg_wLi_xSi₈O₂₀H_4-yF_z]²⁻
wherein w=3 to 6; x=0 to 3; y=0 to 4; z=12−2−e−x, wherein the negative lattice charge is balanced by counterions, and wherein the counterions are selected from the group consisting of Na⁺, K⁺, NH₄ ⁺, Li⁺, Mg²⁺, Ca²⁺, Ba²⁺, N(CH₃)₄ ⁺, and mixtures thereof. Synthetic hectorite clays are commercially available, for example, from Southern Clay Products, Inc., and include Laponite®; Lucenite SWN®, Laponite S®, Laponite XL®, Laponite RD® and Laponite RDS® brands of synthetic hectorite.
Preparation of Titanium Dioxide Slurry
The titanium dioxide slurry used in this invention can be prepared by mixing the components in a mixing vessel. Components can be added sequentially or simultaneously in any order. The following provides a typical process to prepare the slurry, but should not be considered limiting. Typically, a two-step process is used involving a first mixing step followed by a second grinding step. The first step comprises mixing all of the ingredients, that is, titanium dioxide pigment, dispersants, liquid carrier and any optional additives to provide a blended “pre-mix”. Mixing generally occurs in a stirred vessel. High-speed dispersers are particularly suitable for the mixing step. Preferably, the dispersants are combined before introducing into the mixture of other ingredients. The combined dispersants are typically added incrementally.
The second step comprises grinding of the pre-mix to produce a titanium dioxide slurry. Preferably grinding occurs by media milling although other techniques can be used. Following a grinding step, the slurry is filtered. Filtration can be performed using any means known in the art, and is typically accomplished by use of standard, commercially available filters between 1 and 10 microns in size.
After completion of the grinding or dispersing step, additional ink vehicle components can be added to prepare the final ink composition. Alternatively, all of the ink components can be added at the mixing step and the dispersing step is done with subsequent dilution.
Preparation of Inks
The inks of this invention are preferably made from the titanium dioxide slurries described above, by conventional process known to the art. That is, the titanium oxide slurry is processed by routine operations to become an ink which can be successfully jetted in an inkjet system.
Typically, in preparing an ink, all ingredients except the pigment slurry are first mixed together. After the other ingredients are mixed, the slurry is added. Common ingredients in ink formulations useful with the titanium dioxide slurries include one or more humectants, a co-solvent, one or more surfactants and biocide.
The titanium dioxide slurry used in this invention utilizes a dispersants in specific amounts to stabilize and keep the pigments deflocculated over long periods of time both in slurry form and when the slurry is subsequently used in an ink formulation. As a result, the white ink formulation is stable and non-flocculated or agglomerated and has other advantageous properties when applied to surfaces as an ink. The neutralization of the dispersants can depend on the final vehicle use in the ink, the printed substrate etc.
Alternatively, the ink may be prepared without the intervening step of preparing a pigment slurry. That is, the TiO₂pigment and other ingredients of the ink can be combined in any order and this mixture is subject to dispersing mixing. The intensity of the mixing can range from milling using a ball mill with or more intense dispersive mixing such as HSD, roll milling or media milling can be used to obtain the final ink formulation. There are no constraints on the milling media.
Ink Vehicle
The ink vehicle is non-aqueous. “Non-aqueous vehicle” refers a vehicle that is substantially comprised of a nonaqueous solvent or mixtures of such solvents, which solvents should predominantly preferably be polar.
An important limitation of the vehicle is that made up of solvent or a mixture of solvents that have a hydrogen solubility greater than 9 based on the Hansen Solubility Parameters (See Charles M Hansen, Solubility Parameters, CRC Press, 2000). The solubility parameters are calculated based on the solvent(s) only; dispersants, binders, etc. are not factored into the calculation.
Examples of polar solvents include alcohols, esters, ketones and ethers. Specific examples include mono- and di-alkyl ethers of glycols and polyglycols, such as monomethyl ethers of mono-, di- and tri-propylene glycols, and the mono-n-butyl ethers of ethylene, diethylene and triethylene glycols and glycerol and substituted glycerols.
Glycol ethers include ethylene glycol mono-methyl ether, ethylene glycol mono-ethyl ether, ethylene glycol mono-propyl ether, ethylene glycol monobutyl ether, diethylene glycol mono-methyl ether, diethylene glycol mono-ethyl ether, diethylene glycol mono-propyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol mono-methyl ether, propylene glycol mono-ethyl ether, propylene glycol mono-butyl ether, propylene glycol mono-propyl ether, dipropylene glycol mono-methyl ether, dipropylene glycol mono-ethyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-propyl ether, and dipropylene glycol mono-isopropyl ether.
Ether solvents include but are not limited to include dioxane, dimethyl ether, diethyl ethyl, di-isopropyl ether, tetrahydrofuran, glyme, diglyme, triglyme, and tetraglyme.
Heteroatom solvents include, but are not limited to amide solvents including dimethylacetamide and cyclic amines such as 2-pyrolidinone, N-methyl 2-pyrolidinone, and sulfur containing solvents including dimethyl sulfoxide and sulflone.
Polyhydroxyl solvents include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, trimethylol propane, butanediol, pentanediol and hexanediol.
A further optional limitation of the solvent and mixture of solvents is that it has a boiling point of greater than 125° C. at 0.1 kilopascals. It is routine to have ink components that are volatile and can evaporate after the ink is jetted onto the substrate. In the preferred application of these white inks, the ink components can be imbibed into the substrate without adversely affecting the resolution of the printed image.
For the instant invention no additional water should be added; however, no extraordinary drying of the components of the ink is required. Even when no water is deliberately added to the non-aqueous vehicle, some adventitious water may be carried into the formulation, but generally this will be no more than about 5%. Preferably, the non-aqueous ink of this invention will have no more than about 2%, and more preferably no more than about 1%, by weight of water based on the total weight of the non-aqueous vehicle.
The amount of non-aqueous vehicle in the ink (non-solids) is typically in the range of about 50% to about 99.8%, and preferably about 66% to about 95%, based on total weight of the ink.
The inks of the present invention are not considered to be UV-curable or photopolymerizable inks, as those terms are understood by those of ordinary skill in the relevant art (see, for example, previously incorporated U.S. 2004/0246319, EP-A-1321497, EP-A-1388578 and WO00/49097). The non-aqueous vehicle, therefore, should be comprised of predominantly “non-reactive” solvents. “Non-reactive” in this context means non-photopolymerizable. Preferably, the organic solvents of non-aqueous vehicle comprises substantially only non-reactive solvents, and the non-aqueous vehicle is substantially free of reactive components.
Other Ingredients
The inks may optionally contain one or more other ingredients such as, for example, surfactants, binders, bactericides, fungicides, algicides, sequestering agents, buffering agents, corrosion inhibitors, light stabilizers, anti-curl agents, thickeners, and/or other additives and adjuvants well-known in the relevant art.
These other ingredients may be formulated into the inks and used in accordance with this invention, to the extent that such other ingredients do not interfere with the stability and jettability of the ink, which may be readily determined by routine experimentation. The inks may be adapted by these additives to the requirements of a particular inkjet printer to provide an appropriate balance of properties such as, for instance, viscosity and surface tension, and/or may be used to improve various properties or functions of the inks as needed.
The amount of each ingredient must be properly determined, but is typically in the range of from about 0 to about 15% by weight and more typically from about 0.1% to about 10% by weight, based on the total weight of the ink.
Surfactants may be used and useful examples include ethoxylated acetylene diols (e.g. Surfynols® series from Air Products), ethoxylated primary (e.g. Neodol® series from Shell) and secondary (e.g. Tergitol® series from Union Carbide) alcohols, sulfosuccinates (e.g. Aerosol® series from Cytec), organosilicones (e.g. Silwet® series from Witco) and fluoro surfactants (e.g. Zonyl® series from DuPont). Surfactants, if used, are typically in the amount of from about 0.01 to about 5% and preferably from about 0.2 to about 2%, based on the total weight of the ink.
Binders may be also used and can be soluble or dispersed polymer(s), added to the ink to improve the adhesion of a pigment. Examples of polymers that can be used include poly(meth)acrylates, polyesters, polystyrene/acrylates, sulfonated polyesters, polyurethanes, polyimides and the like. When present, soluble polymer is advantageously used at levels of at least about 0.3%, and preferably at least about 0.6%, based on the total weight of the ink. Upper limits are dictated by ink viscosity or other physical limitations.
When the substrates used with the invention are porous, such as paper and textiles, binders can be added to reduce the penetration of the ink into the substrates. In other words with these additives, the ink will remain more on the surface of the porous substrate and the opacity hiding power and other printing parameters for the ink will be improved.
Ink Properties
Jet velocity, drop size and stability are greatly affected by the surface tension and the viscosity of the ink. Inkjet inks typically have a surface tension in the range of about 20 dyne/cm to about 60 dyne/cm at 25° C. Viscosity can be as high as 30 cps at 25° C., but is typically somewhat lower. The inks have physical properties compatible with a wide range of ejecting conditions, i.e., driving frequency of the piezo element, or ejection conditions for a thermal head, for either a drop-on-demand device or a continuous device, and the shape and size of the nozzle. The inks of this invention should have excellent storage stability for long periods so as not clog to a significant extent in an ink jet apparatus. Further, it should not alter the materials of construction of the ink jet printing device it comes in contact with, and be essentially odorless and non-toxic.
Although not restricted to any particular viscosity range or printhead, the inventive inks are suited to lower viscosity applications such as those required by higher resolution (higher dpi) printheads that jet small droplet volumes, e.g. less than about 20 pL. Thus the viscosity (at 25° C.) of the inventive inks can be less than about 8 cps.
The inks of this invention are sufficiently stable to be effective inkjet inks. When tested by heating the inks for one week at 70° C., the physical parameters of particle size and viscosity should be in normal bounds. The inks should also be printable from the desired printing system for multiple days, without any observable decrease in performance.
The conductivity was measured with an EC meter Model 1056 from Amber Science Inc., Eugene, Oreg.
Ink Set
Ink sets contain the ink described above and a plurality of other inks. The non-white inks of the ink set contain other colorants.
The additional colorant in the inks of the ink sets of the present invention is preferably a pigment. By definition, pigments do not form (to a significant degree) a solution in the vehicle and must be dispersed.
Traditionally, pigments are stabilized to dispersion by dispersing agents, such as polymeric dispersants or surfactants. More recently, though, so-called “self-dispersible” or “self-dispersing” pigments (hereafter “SDP(s)”) have been developed. As the name would imply, SDPs are dispersible in a vehicle without dispersants.
A preferred black pigment is carbon black.
Other pigments for inkjet applications are also generally well known. A representative selection of such pigments are found, for example, in U.S. Pat. No. 5,026,427, U.S. Pat. No. 5,086,698, U.S. Pat. No. 5,141,556, U.S. Pat. No. 5,169,436 and U.S. Pat. No. 6,160,370, the disclosures of which are incorporated by reference herein for all purposes as if fully set forth. The exact choice of pigment will depend upon color reproduction and print quality requirements of the application.
Dispersants to stabilize the additional pigments to dispersion are preferably polymeric because of their efficiency. Examples of typical dispersants for nonaqueous pigment dispersions include, but are not limited to, those sold under the trade names: Disperbyk (BYK-Chemie, USA), Solsperse (Avecia) and EFKA (EFKA Chemicals) polymeric dispersants.
Suitable pigments also include SDPs. SDPs for aqueous inks are well known. SDPs for non-aqueous inks are also known and include, for example, those described in U.S. Pat. No. 5,698,016, U.S. 2001003263, U.S. 2001004871 and U.S. 20020056403, the disclosures of which are incorporated by reference herein for all purposes as if fully set forth. The techniques described therein could be applied to the pigments of the present invention.
It is desirable to use small pigment particles for maximum color strength and good jetting. The particle size may generally be in the range of from about 0.005 micron to about 15 microns, is typically in the range of from about 0.005 to about 1 micron, is preferably from about 0.005 to about 0.5 micron, and is more preferably in the range of from about 0.01 to about 0.3 micron.
The levels of pigment employed in the instant inks, especially the non-white inks, are those levels that are typically needed to impart the desired OD to the printed image. Typically, the non-white pigment levels are in the range of from about 0.01 to about 10% by weight, based on the total weight of the ink.
The ink sets containing a white ink provide significant new breadth to printing capabilities. In one preferred embodiment, in addition to a white ink, the ink sets also contain a cyan, magenta and yellow ink. In addition to CMY, it may also be preferred that the ink sets further comprise a black ink.
In another preferred embodiment, the ink sets comprise a white ink and a black ink.
The method of printing in accordance with the invention comprises the steps of:

(a) providing an ink jet printer that is responsive to digital data signals;
(b) loading the printer with a substrate to be printed;
(c) loading the printer with the above-mentioned inks and/or ink sets;
(d) printing onto the substrate using the inkjet ink set in response to the digital data signals.

When printing on a transparent substrate, like polyvinyl butyral, it is sometimes desirable for the image to only appear on one side or be visible from both sides. If the image is to be visible only on one side, the white ink could be printed first and printed in the shape of the image and with adjustable opaqueness such that the image would only appear from one side. The opaqueness can be adjusted by a variety of means including changing the titanium dioxide concentration in the ink, printing multiple times, etc.
If the image is to be seen from both sides then the white ink can be use to provide more flexibility to the image through the use of white. Its inclusion in parts of the image can improve the whiteness of image areas, and the clarity of the image. Nanograde titanium dioxide with its better transparency may be preferred in this application.
When printing on textiles, the white ink of this invention can provide other benefits. Often when textiles are printed the ink will feather into the textile giving an indistinct boundary. The white ink could be use to print a small, imperceptible boundary to a design and making it appear to have a distinct boundary.
The titanium dioxide white ink, since it is stable, can be added to another ink to provide a pigmented ink with both a pigment and a titanium dioxide pigment. While a white ink/pigmented ink would be lighter than the pigmented ink, it would retain the covering power and other beneficial properties of a combined ink because of the inclusion of the white ink.
Printed Substrates
The inks and ink sets can be used to print many substrates including paper, especially colored papers, packaging materials, textiles and polymer substrates. The instant invention is particularly advantageous for printing on polymeric (non-porous) substrates such as polyvinyl butyral interlayer (including 15 and 30 mil thickness); spun bonded polyolefin (e.g. Tyvek®, DuPont); polyvinyl chloride; polyethylene terephthalate polyester; polyvinyl fluoride polymer, and the like.
A particularly preferred use for the ink sets of the present invention is the decorative printing of polyvinyl butyral interlayers used in safety or architectural glass applications, such as disclosed in commonly owned WO2004018197 entitled “Decorative Laminated Safety Glass”, the disclosure of which is incorporated by reference herein for all purposes as if fully set forth.

EXAMPLES

Various abbreviations used in these Examples, as well as the solubility parameter of certain solvents, are listed below in Table 1.

	TABLE 1


	Solubility
	Parameter
	of Solvents

DPM	Dipropylene glycol methyl ether	10.3
DPMA	Dipropylene glycol methyl ether	8
	acetate
TPnP	Tripropylene glycol propyl ether	8.1
DPnP	Dipropylene glycol propyl ether	9.2
TPM	Tripropylene glycol methyl ether	8.7
PNP	Propylene glycol n-propyl ether	12
PMA	Propylene glycol methyl ether acetate
DMAE	Dimethyl ethylamine
BzCl	Benzyl chloride
Cps	Centipoise
NBA	n-Butyl acrylate
MA	Methyl acrylate
AA	Acrylic acid
MAA	Methacrylic acid
MMA	Methyl methacrylate
NBMA	n-Butyl methacrylate
GMA	Glycidyl methacrylate
EHMA	2-Ethylhexyl methacrylate
BzMA	Benzyl methacrylate
DMAEMA	N,N-dimethylaminoethyl methacrylate
TBACB	Tetrabutylammonium m-chlorobenzoate

Methods

Titanium dioxide slurries were prepared from titanium dioxide pigments, dispersants, water and optional additives using a Dispermat® High Speed Disperser (HSD), available from VMA-Getzmann GMBH, to premix ingredients followed by media milling using an Eiger minimill, available from Eiger Machinery, Inc. Premixing of all slurry ingredients was performed using a Model AE5—CEX Dispermat operated typically at 2000 rpm with an attached 60 mm Cowels blade.
Slurry premix was loaded into a 1-liter stainless steel vessel for media milling. Slurry viscosity at a specific pigment loading was used to assess dispersant effectiveness. The most effective dispersant or combination of dispersants produced slurries with the lowest viscosity. Slurry viscosity was measured using a Brookfield viscometer and model RVTDV-II with measurements taken at 10 and 100 spindle rpm. Viscosity units are Centipoise (cps).
Titanium Dioxide Pigments
Commercially available titanium dioxide pigments were used. Two alumina-coated titanium dioxide pigments were used, R700 (available from E. I. duPont de Nemours and Company, Wilmington Del.) and RDI-S (available from Kemira Industrial Chemicals, Helsinki, Finland). A third titanium dioxide was used, P-25 (available from Degussa, Parsippany N.J.), which is an uncoated nano grade of titanium dioxide. Additional alumina and silica coated pigmentary and nanograde titanium dioxides were tested, including R-706 (available from E. I. duPont de Nemours and Company, Wilmington Del.) and W-6042 (a silica-alumina-treated nano grade titanium dioxide from Tayco Corporation, Osaka, Japan).
Ink Formulation and Evaluation
The inks were prepared by methods known to one skilled in the art, unless otherwise noted. One strategy was to prepare dispersions of the pigments (pigment slurries) and, in a separate step, the ink components were combined and mixed together by ball milling, media milling or other mixing means. In general, 0.8 to 1.0 micron zirconia was used for the milling. After the ink was milled, it was filtered through a 1-micron filter paper to remove the media. If the ink did not filter well, it was not tested in a printer. Alternatively, all of the ink components were combined and processed in dispersion equipment and filtered. In this case, the final filtered ink was obtained from the dispersion step.
Printing Tests
Any printer can be used to test these white inks. Unless otherwise noted, the examples described below were done using an Epson 3000 ink jet printer or a Mimaki JV3 wide format printer, and prints were made on various substrates. The white ink was used in place of the black ink and images were produced using PhotoShop Software. The substrates included polymeric sheets such as polyvinyl butyral interlayer (15, 30 ml thickness), Tyvek® JetSmart (available from E. I. duPont de Nemours and Company, Wilmington Del.), uncoated polyvinyl chloride, Tedlar® (available from E. I. duPont de Nemours and Company, Wilmington Del.), polyethylene terephthalate and Surlyn® (available from E. I. duPont de Nemours and Company, Wilmington Del.). In addition, textiles and paper were also used as substrates. Polyurethane was obtained from Deerfield Urethane, South Deerfield, Mass.
The jetting performance was rated GOOD if multiple prints that were all white could be printed without noticeable decrease in the white intensity. Images were also printed. These tests showed the inventive ink set provided desirable gamut, transparency and light-fastness.
Dispersant Preparation
The dispersants were used as 25% to 50% by weight solutions in common organic solvents. The amount of dispersant listed in the examples below was total weight of the added solution, not the active ingredients. Where ratios of dispersants to pigments are described, the ratio is given as active ingredients.
Dispersant 1—Graft Polymer Dispersant
Dispersant 1 was a graft polymer with a comb-like structure, and its molecular configuration was:
nBA/MA/AA (45.5/45.5/9)//MMA/MAA (71.25/28.75)
The above representation illustrates the polymer backbone made up 69% of the polymer (nBA/MA/AA). The notation (45.5/45.5/9) indicates the relative weight percents of each monomer, that is, 45.5 wt % nBA, 45.5 wt % MA and 9 wt % AA. The arms, which were the macromonomer, were 31% of the total polymer (MMA/MAA) wherein the monomers were utilized in relative weight percent amounts of 71.25 wt % and 28.75 wt %, respectively. In this representation of the dispersants, a double slash indicates a separation between blocks, and a single slash indicates a random copolymer within a block.
The acid groups on the polymer were neutralized with DMEA.
Dispersant 2—Block Copolymer Dispersants
The block dispersants were prepared using the GTP method disclosed in previously incorporated U.S. Pat. No. 4,656,226. One of these dispersants, Dispersant 2A, had a molecular configuration of:
nBMA/MAA//MAA 13/5//10.
In this representation, which is different from the representation for the graft copolymer, the notation 13/5//10 indicates a block copolymer with the respective number of monomers. That is, one block is a random copolymer having 13 monomer units of nBMA and 5 monomer units of MAA. The second block has 10 monomer units of MAA.
The second block copolymer dispersant, Dispersant 2B, had a molecular configuration of:
nBMA//MAA 13//10.
The notation 13//10 indicates 13 monomer units of nBMA and 10 monomer units of MAA in the block copolymer.
The third block copolymer dispersant, Dispersant 2C, had a molecular configuration of:
nBMA//MMA/MAA 10//5/10.
The notation 10//5/10 indicates one block was an nBMA polymer having 10 monomer units, and the other block was a random copolymer having 5 monomer units of MMA and 10 monomer units of MAA.
The fourth block copolymer dispersant, Dispersant 2D, was prepared by the following procedure.
While flushing a flask with N₂, 455.9 g THF and 18.86 g 1-methoxy-1-trimethysiloxy-2-methylpropene (methyl initiator) were added via addition funnel. 1.9541 g mesitylene and 0.6 mL of a 1 M solution of TBACB in acetonitrile (catalyst) were injected using two syringes, and the first monomer feed was started. 88.4 g nBMA, 176.4 g MMA, 88.4 g EHMA, 44.2 g BzMA and 76.6 g methacrylic acid 3-(trimethoxysilyl)propyl ester (A-174, Tokyo Kasei Kogyo Co. Ltd., Japan), the primary components of the A block, were added via addition funnel over a period of 60 min. The temperature was kept below 50° C. by cooling the reaction flask with an ice bath. At 70 min. from the start, the conversion was 95% or more for all monomers.
A second monomer feed (B block) of DMAEMA was started via the same addition funnel at 90 min from the start. 227.0 g of this monomer was added over a period of 30 min. The temperature rose to 58° C. during this feed. In parallel with the monomer feeds, a feed consisting of 0.6 mL TBACB in 5.0 g THF was fed to the reaction pot over 120 min. The reaction mixture was held for 2 hours while temperature dropped to 31.4° C. At this point, 93.2 g methanol was added to quench the reaction. Next, 425.4 g solvent was stripped out in three steps and replaced with 613.6 g PMA. The reaction mixture was cooled down to 94.4° C., and 75.3 g methanol and 525.0 g butoxyethanol were added. Then 164.4 g BzCl was added to quaternize the amino groups from the DMAEMA, and this solution was refluxed for six hours until the amine value decreased from an initial value of 0.656 mEq/g solution to 0.070 mEq/gram solution (equivalent to approx. 90% quaternization degree of the amino groups in the polymer).
The resulting polymer solution had a polymer solids content of 34.29 wt % and a calculated number average molecular weight of about 8134 g/mol. The AB block copolymer had the following mole ratio of constituents:
nBMA/MMA/EHMA/BzMA/A-174//DMAEMA-BzCl 10.1/28.7/4.1/7.2/5.0//23.6-21.2
wherein n-BMA/MMA/EHMA/BzMA/A-174 is the A-segment and DMAEMA is the B-segment of the polymer.
The fifth block copolymer dispersant, Dispersant 2E, had the following composition:
BMA/MMA/BzMA/EHMA//A-174/DMAEMA-BzCl 10.1/28.7/4.1/7.2//5.0/23.6-21.2
and was prepared in a manner similar to Dispersant 2D, but the A-174 was added in the B block.
The sixth block copolymer dispersant, Dispersant 2F, had the following composition:
BMA/MMA/BzMA/EHMA/MPEG550MA//DMAEMA-BzCl 10.3/29.3/4.2/7.4/3.2//24.0-21.6
and was prepared by a manner similar to Dispersant 2D except that the reactive monomer A-174 (76.6 g) was replaced by MPEG550MA (methyl-capped polyethylene glycol methacrylate monomer) (104.5g). The weight of MPEG550MA used was different in order to adjust for similar mole % of components in the final polymer.
Phosphate-Containing Dispersant—Dispersant 3
The third dispersant was a phosphated acrylic comb copolymer containing phosphate functionality in the pigment adsorbing backbone segment and prepared using a standard free radical polymerization approach. The resulting phosphated copolymer had the following composition:
nBA/MA/GMA-Phosphated (45.5/45.5/9)//Bisomer 20W
The weight ratio of the phosphated portion to the Bisomer was 60:40.
The phosphate polymer was prepared using the macromonomer, Bisomer 20W, available from International Specialty Chemicals, as the stabilizing arms of the polymer. This material is a macromonomer of poly(ethylene glycol monomethacrylate). It is nonionic with a molecular weight (Mw) of 2000 and provided the water-soluble functionality to the polymer. The Bisomer 20W macromonomer, along with other ingredients, were reacted in a vessel to form the macro branched graft copolymer.
The polymer was formed by charging a reactor equipped with a stirrer, thermocouple, condenser and nitrogen blanket, and heating the contents to reflux. To the reactor, the backbone monomers nBA, GMA and MA, and the Bisomer 20W macromonomer, were added with isopropanol as the solvent. The polymerization reaction was initiated by feeding the initiator 2,2′-azobis(2,4-dimethylvaleronitrile) (Vazo® 52 from E. I. du Pont de Nemours and Company, Wilmington, Del.) which was dissolved in a solution of methyl ethyl ketone and isopropanol. The phosphating was accomplished by an esterification of the epoxy groups on glycidyl methacrylate with phosphoric acid (H₃PO₄).
The resulting phosphated acrylic graft copolymer reached 99% conversion, ans was 45 wt % solids in a solution of water/isopropanol. The molecular weight of the polymer was obtained using GPC. The polymer was methylated prior to injection into the column. The GPC indicated a number average molecular weight of 4577 and a polydispersity of 2.64.
Binder Polymers
Binder Polymer 1 was a GTP monoblock having the following composition:
BMA/MMA/EHMA/BzMA/A-174 18.3/52.1/13.1/7.4/9.1
and was prepared by the following procedure.
While flushing a flask with N₂, 464.1 g THF and 18.90 g 1-methoxy-1-trimethysiloxy-2-methylpropene were added via addition funnel. 2.0823 g mesitylene and 0.6 mL of a 1 M solution of TBACB in acetonitrile were injected using two syringes and the monomer mixture feed was started. The monomer mixture consisted of 88.1 g nBMA, 176.3 g MMA, 88.1 g EHMA, 44.2 g BzMA and 77.6 g A-174, and was added via addition funnel over a period of 60 min. The temperature was kept below 50° C. by cooling the reaction flask with an ice bath. In parallel with the monomer feed, a feed consisting of 0.6 mL TBACB in 5.0 g THF was fed to the reaction pot. At 80 min. from the start, the conversion was 99% or more for all monomers. At this point, 92.2 g methanol was added to quench the reaction. Next, 423 g solvent was stripped out in three steps and replaced with 500.2 g PMA. The reaction mixture was cooled down to 92.2° C., and 75.7 g methanol and 450.7 g butoxyethanol were added.
The resulting polymer solution had a polymer solids content of 29.76 wt %. GPC results: measured number average molecular weight (Mn) 5330 g/mol, (theoretical 4449 g/mol), weight average molecular weight (Mw) 6191 g/mol, polydispersity 1.16.
Binder 2 was a GTP monoblock having the following composition:
BMA/MMA/EHMA/BzMA/MPEG-500MA 19.0/53.9/13.6/7.7/5.8
And was prepared in a manner similar to Binder 1 except the reactive monomer A-174 (77.6g) was replaced by MPEG550MA (104.5 g). The amount of MPEG550MA used was different to adjust for similar mole % of components in the final polymer.
Binder 3 was a GTP monoblock having the following composition:
BzMA/HEMA/ETEGMA/MAA 60/29/10/10
and was made in a manner similar to Binder 1.

Comparative Slurry Example 1

A titanium dioxide slurry premix was prepared by charging 138.45 g water, 1 g of 50% DMEA in water, 20 g of a 50:50 blend of Dispersant 1 and Dispersant 2B (37 wt % solids), 50 g ethylene glycol, 2 g Dehydran® 1620 and 720 g of R700 pigment into a 1-liter stainless steel vessel, and processing for 10 minutes at 2000 rpm using a Dispermat High Speed Disperser configured with a 60 mm Cowels blade. The premix was let down with 68.55 g water, stirring at 250 rpm for 5 minutes.
The premix was then processed on an Eiger Mini Mill, model MK II M250 VSE EXP for 15 minutes at 3250 rpm disc speed with a 480 g media charge of 0.8-1.0 mm zirconia. Grinding was continued for 30 minutes with sampling at 10, 15, 20 and 30 minutes to determine particle size. The final product was 72 wt % solids. Results are provided in Table 2 before and after let down

TABLE 2

Comparative Slurry Example 1

Particle Size vs. Milling Time

Median Particle

Particle size, Size

Grind Time <204 nm 50% 95%

10 minutes 30.82 240.2 395.9

15 minutes 18.68 235.9 293.8

20 minutes 26.42 246.7 380.9

Comparative Ink Example 1

Comparative Ink Example 1 was prepared by diluting Comparative Slurry Example 1 with water to obtain a titanium dioxide slurry with 15 wt % solids. This diluted slurry was converted into an ink with the following formulation.

TABLE 3


Comparative Ink Example 1 Formulation

	Comparative Slurry 1	40
	DPM	36.92
	DPnP	24.61
	BYK 348	0.5
	Pigment solids (Wt %)	6.00
	Viscosity (Cps)	7.56
	Surface Tension (Dyne/Cm)	26.37

	BYK 348 is a surfactant from Byk Chemie.

This ink could be printed. The aqueous content in this ink (>5 wt %) can lead to possible instability of the ink.

Comparative Slurry Examples 2 and 3

Comparative Slurry examples 2 and 3 were made in a manner similar to Comparative Slurry Example 1. Table 4 lists the compositions for the slurries

TABLE 4


Comparative Slurry Examples 2 and 3

Comparative Slurry EX

	2	3

Di Water	83.49	182.8
DMEA 50%	1.00	1.0
Dispersants 1/2B, 50%/50%	28.80
Dispersants 1/2C, 50%/50%		44.2
Ethylene Glycol	50.00	50.0
Dehydran ® 1620	2.00	2.0
PnP	103.51
Dispersant 3	20.00
Ti-Pure R700	720.00	720.0
Total	1008.80	1000.0

Comparative Ink Examples 2 and 3

The inks were made in a manner similar to Comparative Ink Example 1.

TABLE 5


Comparative Ink Examples 2 and 3

Comparative Ink Example

	2	3

Comparative Slurry Ex 2	35.0
Comparative Slurry Ex 3		35.0
DPM	48.8	48.8
DPMA	16.3	16.3
Total	100.00	100.00
Wt % Pigment	25.00	25.00
Viscosity (Cps)	6.38	NA
Surface Tension (Dyne/Cm)	29.68	NA
Filterability	Poor	Poor
Milling Time (hr)	72.0	72.0

	Jettability of the ink	Not Jetted

These inks were not filterable and never were jetted. This combination of dispersant, solvent and modest water present leads to inconsistent results when compared with the non-aqueous inks of the instant invention.

Slurry Example 1

Slurry Example 1 was prepared in a 100-gram batch by charging the ingredients listed in Table 8 into a plastic jar (250 ml capacity) and following these steps:
(1) In a 250 ml plastic bottle, the solvents (s) as well as the dispersants were added.
(2) The mixture was mixed until the dispersants dissolved completely in the solvents.
(3) The white pigment was added slowly to the container
(4) The contents were mixed well, then the zirconium media (0.8-1.0 mil zirconium media) was added.
(5) The plastic container was then added to a roller mill, the speed of which was adjusted to 35 rpm.

TABLE 6

Slurry Example 1, Composition

Slurry Ex 1

Disperbyk ® 2000 8.71

Dispersant 1/2B (50/50 wt %) 5.17

PnP 361.12

Ti-Pure R700 250.00

Total 625.00

Ink Example 1

Ink Example 1 was prepared using Slurry Ex 1 according to the following composition.

TABLE 7

Ink Ex 1

Ink Example 1

Slurry Example 1 60.00

DPnP 40.00

BYK 348 0.50

Total 100.50

% Pigment (Solid) 24.00

Viscosity (Cps) 6.79

Surface Tension (Dyne/Cm) 27.02

This ink was printed on polyvinyl butyral and the optical properties are reported in Table 8

TABLE 8


Ink Example 1, White Ink Printed Decorative Laminates

Number of
printing	Glass	% Trans-
passes	type	mission	% Haze	% Clarity

1	Clear	39.4	92.2	52.4
2	Clear	29.8	97.0	40.8
3	Clear	24.7	96.2	46.9
4	Clear	20.9	95.1	52.3
5	Clear	19.2	89.2	66.5
1	Starphire	37.4	91.4	50.9
2	Starphire	27.7	96.9	39.4
3	Starphire	22.9	95.8	45.0
4	Starphire	19.4	85.3	48.4
5	Starphire	17.3	85.8	69.8

The “Clear glass” is normal glass made by the float process, and it had a slightly green tint. The Starphire glass was the PPG “ultra-white” glass.
Test for Whiteness and Yellowness of White Ink Printed Substrates

The polyvinyl butyral decorative laminate used with Ink Example 1 was tested for whiteness as measured by ASTM E 313, and yellowness as measured by ASTM D1925. The Whiteness Index was 44.52, and the Yellowness Index was −2.2.

Ink Examples 2-4

Ink Examples 2-4 were prepared according to the following recipes in a manner similar to Slurry Example 1/Ink Example 1.

TABLE 9


Ink Examples 2-4

Ink Example

	2	3	4

Ti-Pure R700	25.0	25.0	25.0
DPM	73.5	73.5	73.5
Dispersant 3	1.5		0.8
Dispersant 1/2C, 50%/50%		1.5	0.8
Total	100.00	100.00	100.00
Wt % Pigment	25.00	25.00	25.00
Viscosity (Cps)	7.06	7.65	11.60
Surface Tension (Dyne/Cm)	29.12	29.37	29.41
Filterability	Very Good	Very Good	Very Good
Milling Time (hr)	18.0	18.0	18.0
Jetability of the ink	Excellent	Excellent	Excellent

Ink Examples 5-7

These inks were prepared according to the following recipes in a manner similar to Slurry Example 1/Ink Example 1.

TABLE 10


Ink Examples 5-7

	5	6	7

Ti-Pure R700	25.0	25.0	25.0
TPM	6.5
PPH		6.5
DPM	58.5	58.5	65.0
Disperbyk ® 2001	10.0	10.0	10.0
Total	100.0	100.0	100.0
Wt % Pigment (Solid)	25.00	25.00	25.00
Pigment/Dispersant	5	5	5
Viscosity (Cps)	7.35	8.22	6.84
Surface Tension (Dyne/Cm)	28.96	29.78	29.10
Filterability	Good	Good	Good
Media	0.8-1.0
	Zirconium
	Media
Milling Time (hour)	24.00	24.00	24.00
Ink Stability	Good	Good	Good
(minimum settling)
Consistency of print	Moderate	Good	Good
Jetability of the ink	Excellent	Excellent	Excellent

Ink Examples 8-10

TABLE 11


Ink Examples 8-10

	8	9	10

Ti-Pure R700	25.0	25.0	25.0
DPM	73.5	73.5	73.5
Dispersant 3	1.5	0.0	0.8
Dispersant 1	0.0	1.5	0.8
Total	100.0	100.0	100.0
Wt % Pigment (Solid)	25.00	25.00	25.00
Pigment/Dispersant	16.7	16.7	16.7
Viscosity (Cps)	7.06	7.65	11.6
Surface Tension (Dyne/Cm)	29.12	29.37	29.41

Ink Examples 11-22

These inks were prepared to test inks with varying dispersants and two examples (15 and 22) with added binder. The inks were aged for 7 days at 70° C. to do an accelerated test of ink stability. If the change in viscosity was less than ±20% difference, they were judged to be stable.

TABLE 12


Ink Examples 11-22

	11	12	13	14	15	15	17	18	19	20	21	22

Ti Pure R 700	20.0	20.0	20.0	20.0	20.0	20.0	20.0	20.0	20.0	20.0	20.0	20.0
P-25 Degussa (nano)	5.0	5.0	5.0	5.0	5.0	5.0	5.0	5.0	5.0	5.0	5.0	5.0
DPM	54.6	53.8	53.8	53.8	53.8	53.8	53.8	53.8	53.8	53.8	53.8	53.8
DPMA	18.2	17.9	17.9	17.9	17.9	17.9	17.9	17.9	17.9	17.9	17.9	17.9
Dispersant 1/2C 50:50	2.2	2.2		2.2		1.1	0.6
Dispersant 3		1.1	1.1				0.6	1.1
Disperbyk ® 2001			2.2	1.1	2.2	2.2	2.2	2.2	2.2	2.2	2.2	2.2
Binder 1					1.1
Dispersant 2D									1.1
Dispersant 2E										1.1
Dispersant 2F											1.1
Binder 2												1.1
Surface Tension	28.3	28.6	28.2	28.3	28.7	28.9	27.0	27.8	28.8	22.3	29.0	28.3
(Dyne/Cm)
Viscosity@ 60 rpm	9.4	7.7	5.4	5.6	4.8	5.3	5.2	5.3	4.8	5.1	5.1	5.0
(Cps)
7 Day Oven Aged
Viscosity@ 60 rpm	6.4	5.5	5.3	5.1	4.4	4.7	4.8	5.2	5.7	4.8	5.9	4.8
(Cps)

All of the tested inks were judged to be stable except that Ink Examples 11 and 12 were only marginally stable by this accelerated test.

Ink Examples 23-28

Inks 23-28 were similarly prepared as before to test binders and dispersants, and two examples (24 and 25) had added binder. The inks were aged for 7 days at 70° C. to do an accelerated test of ink stability. If the change in viscosity was less than ±20% difference they were judged to be stable.

TABLE 13


Ink Examples 23-28

	23	24	25	26	27	28

Ti Pure R 700	20.00	20.00	20.00	20.00	20.00	20.00
P-25 Degussa (nano)	5.00	5.00	5.00	5.00	5.00	5.00
DPM	54.60	54.60	54.60	54.60	54.60	54.60
DPMA	18.20	18.20	18.20	18.20	18.20	18.20
Disperbyk ® 2001	2.20	2.20	2.20	2.20	2.20	2.20
Binder 3		1.10
Binder 2			1.10
Dispersant 2E				1.10
Dispersant 2F					1.10
Dispersant 2D						1.10
Total	100.0	101.1	101.1	101.1	101.1	101.1
Filterability	Good	Good	Good	Good	Good	Good
Viscosity@ 60 rpm (Cps)	5.12	5.17	5.60	5.31	5.02	5.19
Surface Tension (Dyne/Cm)	28.80	29.06	28.90	28.88	28.89	28.93
Viscosity@ 60 rpm (Cps) After 7	5.10	4.50	5.30	5.20	5.10	4.50
days
Surface Tension (Dyne/Cm)	27.40	28.02	28.95	28.12	29.19	28.04
After 7 days
Particle Size: (microns, 50%)	0.2670	0.2592	0.2578	0.2570	0.2522	0.2760

All of these inks were judged stable based on the 70° C. accelerated aging test. These tests show the stability of the inks with single dispersants, two dispersants and a single dispersant with binder.

Ink Examples 28-32 and Comparative Ink Examples 4-6

These inks were prepared to demonstrate the importance of the hydrogen solubility parameter. Ink examples 28-32 and Comparative Ink Examples 4-6 are listed in Table 14. The calculated hydrogen solubility parameter is listed in the table. Thus, Ink Example 32 satisfies the limit of hydrogen solubility parameter of greater than 9, but Comparative Inks 4, 5 and 6 do not.

TABLE 14


Ink Examples 28-32 and Comparative Ink Examples 4-6

			Calculated			Particle
	Pigment	Ink Vehicle	Solubility	Disper-	Viscos-	Size	Ink
Example	(pph)	(pph)	Parameter	sant (pph)	ity (Cps)	(nm)	Stability

28	R700 (20)	DPM (72.8)	10.3	D2001	6.7	289.4	Good
	P-25 (5)	DPMA (0.0)		(2.2)
29	R700 (20)	DPM (63.5)	10.0	D2001	5.5	276.0	Good
	P-25 (5)	DPMA (9.3)		(2.2)
30	R700 (20)	DPM (54.6)	9.73	D2001	5	256.2	Good
	P-25 (5)	DPMA (18.2)		(2.2)
31	R700 (20)	DPM (45.5)	9.44	D2001	4.8	249.8	Good
	P-25 (5)	DPMA (27.3)		(2.2)
32	R700 (20)	DPM (36.4)	9.15	D2001	4.8	257.7	Good
	P-25 (5)	DPMA (36.4)		(2.2)
Comp	R700 (20)	DPM (18.2)	8.57	D2001	EEE	336.0	Poor
Ink 4	P-25 (5)	DPMA (54.6)		(2.2)
Comp	R700 (20)	DPM (9.1)	8.27	D2001	EEE	343	Poor
Ink 5	P-25 (5)	DPMA (63.5)		(2.2)
Comp	R700 (20)	DPM (0)	8.0	D2001	EEE	494.8	Poor
Ink 6	P-25 (5)	DPMA (72.8)		(2.2)

The ink stability observations were made by looking at the containers of the ink and observing settling or other apparent instability. Note that the particle size is larger for the Comparative inks, perhaps indicating that the dispersing effectiveness of the solvent mixture with hydrogen bonding solubility parameter of less than 9 is poorer.

Ink Examples 30 and 31 could separately be left in an ink cartridge for extended periods of time without degrading the printed image. That is, a printer with these inks could be left idle for several weeks and then restarted without concern that the ink had settled.
Test of Settling of Inks

Another measure of the stability of the titanium dioxide inks is to test the settling of the ink. Ink was placed in a cylindrical glass vial 1.6 cm in diameter and 5 cm high. After 45 days the vials were observed and the amount of settling recorded. The amount of clear liquid on top was recorded and the amount of white ink recorded. The less % clear observed the less settling is observed. A % clear of less than 5% is judged as very good, 5 to 10% as good, 10 to 20% as moderate. In each of these cases this was soft settling, and simple mixing could resuspend the ink. If the clear region was 20 to 40%, that was judged not acceptable for an ink. Anything more than 40% was judged as severe settling.

TABLE 15


Settling of the Inks

Ink ID	Clear/cm	White/cm	Total/cm	% Clear

Ink 23	0.4	4.5	4.9	8.2
Ink 24	0.5	4.0	4.5	11.1
Ink 25	0.5	4.0	4.5	11.1
Ink 26	0.7	4.5	5.2	13.5
Ink 28	0.5	2.4	2.9	17.2
Ink 29	0.5	4.0	4.5	11.1
Ink 30	0.2	3.5	3.7	5.4
Ink 31	0.1	4.0	4.1	2.4
Ink 32	0.5	4.0	4.5	11.1
Comp Ink 4	0.5	3.5	4.0	12.5
Comp Ink 5	1.5	3.5	5.0	30.0
Comp Ink 6	2.0	2.5	4.5	44.4

Inks 23-26 are combinations of different dispersants and in some cases additional binders. Inks 28-32 and Comparative Inks 4-6 are the inks with a variable ratio of DPM and DPMA. The Comparative Inks 5 and 6 clearly failed a stability test, and Comparative Ink 4 was moderate in settling performance.
Tests of the inventive ink demonstrate surprising stability for titanium dioxide inks.
Conductivity of the Inks

The conductivity of three inks were measured. For reference, the pure solvents DPM and DPMA have conductivities of 4.36 and 4.22 μmho/cm respectively.

TABLE 16


Conductivity of the Inks

Ink Example

	33	34	35

Titanium dioxide	Ti-Pure	Ti-Pure	Ti-Pure
	R-700, 30%	TS-6200	R706
DPM	50.8	50.8	50.8
DPMA	17.0	17.0	17.0
Viscosity	4.73	4.81	5.79
Surface Tension	28.79	29.02	27.78
Conductivity (μmho/cm)	5.14	5.00	4.37

The conductivities of the inventive inks were very low. The lack of any added salt or any other significant amount of charged species lead to these low values.
Printing Results on Polyvinyl Butyral and their Glass Laminates.

Ink Example 16 was printed on a sheet of polyvinyl butyral (PVB) using Mamiki JV3 printer. The white ink was printed alone and in combinations with other colors in two different modes.
Mode 1: The white ink was printed first then the color (CMYK) was printed on the top of it (overprinted). Mode 2: The white ink at 100% coverage was printed simultaneously printed with the other colors (CMYK).

The printed PVB was laminated according to techniques described in previously incorporated WO04/018197. The Adhesion (PSI) results are summarized in Table 17.

TABLE 17


Laminated Glass Print Properties

Color	Alone	Mode 1	Mode 2

White (50% coverage)	2920
White (100% coverage)	2511
Cyan	2285	2330	2031
Magenta	2375	2024	1881
Yellow	2247	2177	2039
Black	2589	2400	2249

The white ink did not adversely effect the adhesion performance of the laminate. Also printing in either of the modes still produced laminates with adhesion tests greater than 2000 psi.

Claims

1. A non-aqueous inkjet ink comprising a non-aqueous liquid carrier having dispersed therein (a) a titanium dioxide pigment and (b) at least one dispersant for the titanium dioxide pigment, wherein:

(i) the non-aqueous liquid carrier comprises an organic solvent or a mixture of organic solvents,

(ii) the organic solvent or mixture of organic solvents has a hydrogen bonding solubility parameter based on Hansen solubility parameters of more than about 9,

(iii) the organic solvent or mixture of organic solvents in the non-aqueous liquid carrier are predominantly only non-reactive organic solvents; and

(iv) the conductivity of the ink is less than about 50 μmho/cm.

2. The non-aqueous inkjet ink of claim 1, wherein the organic solvent or mixture of organic solvents has a boiling point of greater than 120° C. at 0.1 kpascals.

3. The non-aqueous inkjet ink of claim 1, wherein the organic solvent or mixture of organic solvents is predominantly comprised of polar solvents.

4. The non-aqueous inkjet ink of claim 1, wherein the at least one dispersant is a combination of dispersants comprising:

(1) a graft copolymer having a weight average molecular weight of from about 4000 to about 100000, comprising from about 90% to about 50% by weight of a polymeric backbone, and from about 10% to about 50% by weight of macromonomer side chains attached to the backbone, the polymeric backbone and macromonomer side chains comprising 100 wt % of the graft copolymer, wherein:

(i) the polymeric backbone is hydrophobic in comparison to the macromonomer side chains and comprises polymerized ethylenically unsaturated hydrophobic monomers and, optionally, up to about 20% by weight, based on the weight of the graft copolymer, of polymerized ethylenically unsaturated acid monomers; and

(ii) each of the macromonomer side chains individually is a hydrophilic polymer containing acids groups attached to the polymeric backbone at a single terminal point, and

(A) has a weight average molecular weight of from about 1000 to about 30000, and

(B) comprises from about 2% to about 100% by weight, based on the weight of the macromonomer side chain, of a polymerized ethylenically unsaturated acid monomer, and

(2) a block copolymer of type AB, ABA or ABC wherein at least one of the blocks in the block copolymer is an adsorbing segment, and wherein at least one of the blocks in the block copolymer is a stabilizing segment.

5. The non-aqueous inkjet ink of claim 1, which is white.

6. An inkjet ink set comprising a plurality of colored, pigmented inks, at least one of which is a first non-aqueous inkjet ink comprising a non-aqueous liquid carrier having dispersed therein (a) a titanium dioxide pigment and (b) at least one dispersant for the titanium dioxide pigment, wherein:

(iv) the conductivity of the ink is less than about 50 μmho/cm.

7. The inkjet ink set of claim 6, wherein the organic solvent or mixture of organic solvents has a boiling point of greater than 120° C. at 0.1 kpascals.

8. The inkjet ink set of claim 6, wherein the organic solvent or mixture of organic solvents in the first non-aqueous ink is predominantly comprised of polar solvents.

9. The inkjet ink set of claim 6, wherein the at least one dispersant in the first non-aqueous inkjet ink is a combination of dispersants comprising:

10. The inkjet ink set of claim 6, wherein the first non-aqueous inkjet ink is white.

11. The inkjet ink set of claim 10, further comprising a cyan ink, a magenta ink and a yellow ink.

12. The inkjet ink set of claim 10, further comprising a black ink.

13. The inkjet ink set of claim 11, further comprising a black ink.

14. A method for inkjet printing onto a substrate, comprising the steps of:

(1) providing a drop-on demand inkjet printer that is responsive to digital data signals;

(2) loading the printer with a substrate to be printed;

(3) loading the printer with an inkjet ink; and

(4) printing onto the substrate using the inkjet ink in response to the digital data signals,

wherein the inkjet ink is a first non-aqueous inkjet ink comprising a non-aqueous liquid carrier having dispersed therein (a) a titanium dioxide pigment and (b) at least one dispersant for the titanium dioxide pigment, wherein:

(iv) the conductivity of the ink is less than about 50 μmho/cm.

15. The method of claim 14, wherein the printer is loaded with an inkjet ink set comprising a plurality of colored, pigmented inks, at least one of which is the first non-aqueous inkjet ink.

16. The method of claim 14, wherein the substrate is a thermoplastic polymer substrate.