WO1996019542A1

WO1996019542A1 - Erasable ink composition containing polymer-encapsulated colorant and marking instrument containing the ink

Info

Publication number: WO1996019542A1
Application number: PCT/US1995/016288
Authority: WO
Inventors: David C. Villiger; Aiying Wang; Jeffery H. Banning; Wayne A. Chandler; Barry W. Chadwick
Original assignee: Bic Corporation
Priority date: 1994-12-20
Filing date: 1995-12-14
Publication date: 1996-06-27
Also published as: AU4518596A; AR000392A1; TW419511B

Abstract

An erasable ink composition contains a dispersion of particles of water-insoluble polymer-encapsulated colorant obtained from the emulsion polymerization of at least one emulsion-polymerizable monomer in the presence of colorant. The ink is intended for use in any of a variety of marking instruments, in particular, a ball-point pen.

Description

ERASABLE INK COMPOSITION CONTAINING POLYMER-ENCAPSULATED COLORANT AND MARKING INSTRUMENT CONTAINING THE INK

BACKGROUND OF THE INVENTION

This invention relates to an erasable ink composition and to a marking instrument, e.g., a ball-point pen, containing the composition. More particularly, this invention relates to an erasable ink composition containing a dispersion of a polymer-encapsulated colorant.

Numerous erasable ink compositions are known, e.g., those described in U.S. Patent Nos. 3,834,823, 3,875,105, 3,949,132, 4,097,290, 4,212,676, 4,227,930, 4,256,494, 4,297,260, 4,329,262, 4,329,264, 4,349,639, 4,357,431, 4,367,966, 4,368,076, 4,379,867, 4,389,499, 4,390,646, 4,391,927, 4,407,985, 4,410,643, 4,419,464, 4,441,928, 4,509,982, 4,525,216, 4,557,618, 4,578,117, 4,596,846, 4,606,769, 4,629,748, 4,687,791, 4,721,739, 4,738,725, 4,760,104, 4,786,198, 4,830,670, 4,954,174, 4,960,464, 5,004,763, 5,024,898, 5,037,702, 5,082,495, 5,114,479, 5,120,359, 5,160,369 and 5,217,255. These inks are formulated by mixing a colorant (taken herein to also include "pigment", "dye", "chro ophore" and other terms of similar meaning) with a variety of polymer and liquid carrier/solvent combinations thereby forming a flowable colorant/polymer matrix. The polymer component is chosen for its film forming properties and its ability to be readily removed from the substrate to which it is applied, e.g., cellulosic paper, through the abrasive action of an eraser. However, a common problem with these erasable ink compositions concerns the residual colorant which remains after erasure. Incomplete erasure may be attributed to inadequate removal of the colorant/polymer matrix from the paper substrate and/or migration of colorant into the pores of the substrate.

SUMMARY OF THE INVENTION

In accordance with the present invention, an erasable ink composition is provided which comprises a dispersion of particles of water-insoluble polymer- encapsulated colorant obtained by polymerizing under emulsion polymerization conditions at least one emulsion- polymerizable monomer in the presence of colorant, the erasable ink composition when applied to a substrate and upon drying thereon being (1) sufficiently adherent to a substrate as to resist flaking therefrom and (2) substantially erasable.

The colorant which is present with the emulsion polymerizable monomer at the time polymerization is effectuated may be present as solid colorant particles or in another embodiment be dissolved in the emulsion- polymerizable monomer (i.e., be monomer dissolvable).

Since the colorant is encapsulated by polymer in the erasable ink composition of this invention, there is little opportunity for it to separate from the polymer and migrate into a porous substrate. Thus, the erasable ink composition of this invention is apt to leave significantly less residual colorant following its erasure than known erasable ink compositions in which the colorant is merely physically combined with the polymer component(s) .

The expression "polymer-encapsulated colorant" shall be understood herein to refer to any association of colorant and polymer in which the colorant is physically bound or occluded by, or entrapped within, the polymer. The term "polymer-encapsulated colorant" excludes those materials in which colorant is bound to the polymer primarily through van der Waals forces, hydrogen bonding, ionic bonding and/or covalent bonding.

The expression "solid colorant particles" and equivalent expressions shall be understood herein to include any water-insoluble, solid particulate color-imparting substance which is chemically inert with respect to both the monomer and the resulting encapsulating polymer.

The expression "dissolved colorant" and equivalent expressions shall be understood herein to refer to any water-insoluble color-imparting substance which is soluble, or capable of being made soluble, in at least one of the monomers used in obtaining the colorant encapsulating polymer and which is chemically inert with respect to such monomer and the resulting polymer.

The term "dissolved" as applied to colorant herein shall be understood to include those cases in which: (1) colorant is dissolved directly in monomer in the absence of solvent(s) , (2) a solution of colorant is dissolved in monomer, (3) colorant is dissolved in a solution of monomer and (4) a solution of colorant is dissolved in a solution of monomer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The monomers employed in the practice of this invention include those of the hydrophobic and hydrophilic varieties. However, where hydrophilic monomers are employed, they must be copolymerized with a sufficient amount of hydrophobic monomer(s) and/or crosslinking monomer(s) as to provide a substantially water-insoluble polymer.

Examples of suitable hydrophobic monomers include monovinylidene aromatic monomers such as styrene, vinyl toluene, t-butyl styrene, chlorostyrene, vinylbenzyl chloride and vinyl pyridene; alkyl esters of a , β- ethylenically unsaturated acids such as ethyl acrylate, methyl methacrylate, butyl acrylate and 2-ethylhexyl acrylate; unsaturated esters of saturated carboxylic acids such as vinyl acetate, unsaturated halides such as vinyl chloride and vinylidene chloride; unsaturated nitriles such as aerylonitrile; dienes such as butadiene and isoprene; and the like. Of these monomers, the monovinylidene aromatics such as styrene and the alkyl acrylates such as butyl acrylate are preferred.

Illustrative of useful water-soluble monomers are ethylenically unsaturated carboxylic acids or their salts such as acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, itaconic acid and maleic acid; ethylenically unsaturated carboxamides such as acrylamide; vinyl pyrrolidone; hydroxyalkyl acrylates and methacrylates such as hydroxyethyl acrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate; aminoalkyl esters of unsaturated acids such as 2-aminoethyl methacrylate; epoxy functional monomers such as glycidyl methacrylate; sulfoalkyl esters of unsaturated acids such as 2-sulfoethyl methacrylate; ethylenically unsaturated quaternary ammonium compounds such as vinylbenzyl trimethyl ammonium chloride; and, vinyl sulfonic acids or their salts such as styrene sulfonic acid and sodium vinyl sulfonate.

It is critical, however, that such water-soluble monomers not be employed in amounts sufficient to render the resulting polymer soluble in water.

Suitable crosslinking monomers include ethylene dimethacrylate and divinylbenzene.

Particularly effective monomer recipes for the practice of this invention are those containing from about 20 to about 90 weight percent of styrene, from about 10 to about 80 weight percent of alkyl acrylate such as butyl acrylate and from about 0.01 to about 2 weight percent of the unsaturated carboxylic acids such as acrylic acid, with said weight percentages being based on the weight of total monomers. Suitable solid colorant particles for use in preparing the polymer-encapsulated colorant component of the erasable ink composition herein include particles of a wide variety of inorganic and organic pigments.

Useful inorganic pigments include C.I. (color index)Pigment Yellow—34, —36, —37, —42 and —48, C.I.Pigment Orange—21, C.I.Pigment Brown—6, C.I.Pigment Red—101, —105, -106, -107 and -108, C.I.Pigment Violet-14 and -16, C.I.Pigment Blue—27, —28, —29 and —35; C.I.Pigment Green—17, —18, —19 and —21, C.I.Pigment Black —6, —7, —9 and —10, C.I.Pigment White—l, —4 and —6, and the like.

Useful organic pigments include azo, anthraquinone, phthalocyanine, triphenylmethane, quinacridone and dioxazine pigments. Examples include C.I. (color index)Pigment Yellow-1, -2, -3, -5, —12, -13, -14, -15, -17 and -83, C.I.Vat Yellow-1, C.I.Pigment

Orange—1, —5, —13, —16, —17 and —24, C.I.Vat Orange—3, C.I.Pigment Red -1, -2, -3, -4, -5, -7, -9, -12, -22, -23, -37, —38, —48 Calcium Lake, —49 Barium Lake, —50, —51, -53 Barium Lake, —57 Calcium Lake, -58 Manganese Lake, -60 Barium Lake, —63 Calcium Lake, —63 Manganese Lake, —81, —83 Aluminum Lake, —88, —112 and —214, C.I.Pigment Violet—l, —3, -19 and -23, C.I.Vat Violet-2, C.I.Pigment Blue-1, -2, -15, —16 and —17; C.I.Vat Blue—4, C.I.Pigment Green—2, —7, —8 and —10, C.I.Pigment Brown—1, —2 and 5, C.I.Vat Brown—3, C.I.Pigment Black-1, and the like.

Mixtures of two or more of these and/or similar solid colorant particles can be used to provide virtually any desired color by regulating the proportions of the individual colorants therein. It is preferred to use colorants having a particle size of not greater than about 5 microns and it is particularly preferred to employ colorants having a particle size of from about 0.01 to about 3 microns. Those skilled in the art will recognize and appreciate that a wide variety of solid colorant particles can be employed in the practice of this invention, such colorants being included within the scope of this invention. The monomer-dissolvable colorant utilized in the practice of this invention must be soluble in the discontinuous monomer phase, either directly or through the use of solvent(s) , and substantially insoluble in the continuous aqueous phase of the dispersion which is formed prior to carrying out the emulsion polymerization operation. Suitable monomer-dissolvable colorants include inorganic and organic pigments and oil-soluble dyes. Oil-soluble dyes found to be useful generally include members of the class of solvent dyes including some basic dyes. A solvent dye can be defined by its solubility in an organic solvent or solvents, e.g., toluene or xylene. Basic dyes are slightly water-soluble, moderately colored materials which are convertible to strong chromophores via interaction with acids or acidic polymers,. Illustrative examples of dyes that can be used as colorants in the present invention are disclosed in U.S. Patent No. 5,114,479 and include Sudan Red 380, Sudan Blue 670, Baso Red 546, Baso Blue 688, Sudan Yellow 150, Baso Blue 645, Flexo Yellow 110, and Flexo Blue 630, all commercially available from BASF; Oil Red 235, commercially available from Passaic Color and Chemical; Morfast Yellow 101, commercially available from Morton; Nitro Fast Yellow B, commercially available from Sandoz; Macrolex Yellow 6G, commercially available from Mobay. Other useful water-insoluble, monomer soluble colorants are disclosed in U.S. Patent No. 5,203,913 and include Solvent Yellow 14, 16 and 21, Solvent Orange 45, 62, Solvent Red 1, 7, 8, 119 and 125, Solvent Blue 5, 14, 25 and 36 and Solvent Black 5 and 34. Mixtures of two or more of these colorants can be used to provide virtually any desired color by regulating the proportions of the individual colorants therein.

Further useful water-insoluble monomer-dissolvable colorants are described in U.S. Patent No. 4,874,832 and include dyestuff precursors selected from among the triphenylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds and spiropyran compounds and mixtures thereof. In particular, the following are suitable: triphenylmethane compounds: 3,3-bis- (p-dimethylaminophenyl)-6-dimethylaminophthalide ("crystal violet lactone") and 3,3-bis-(p-dimethyl-amino-phenyl)- phthalide ("malachite green lactone") , diphenyl-methane compounds: 4,4-bis-dimethylaminobenzhydryl benzyl ether, N- 2,4,5-trichlorophenylleucauramine, N-halogeno- phenylleucauramine, N-S-naphthylleucauramine, and N-2,4- dichlorophenylleucauramine; xanthene compounds: rhodamine-/3- anilinolactam, rhodamine-,5-(p-nitroaniline)-lactam, rhodamine-_/3-(p-chloroaniline)-lactam, 7-dimethyl-amine-2- methoxy-flouran, 7-diethylamine-3-methoxyfluoran, 7- diethylamine-3-methylfluoran, 7-diethylamine-3- chlorofluoran, 7-diethylamine-3-chloro-2-methylfluoran, 7- diethylamine-2,4-dimethylfluoran, 7-diethylamine-2,3- di ethylflouran, 7-diethylamine-(3-acetyl-methylamine)- fluoran, 7-diethyl-amine-3-methylfluoran, 3,7-diethyl- aminefluoran, 7-diethylamino-3-(dibenzylamine)-fluoran, 7- diethylamine-3-(methylbenzylamine)-fluorane) , 7- diethylamine-3-(dichloroethylamine)-flouran and 7- diethylamine-3-(diethylamine)-fluoran; thiazine compounds: N-benzoylleucomethylene blue, o-chlorobenzoylleucomethylene blue and p-nitrobenzoylleucomethylene blue; and spiro compounds: 3-methyl-2,2'-spiro-bis-(benzo(f)-chromene) .

Solvents which dissolve these dyestuff precursors include, e.g., chlorinated diphenyl, chlorinated paraffin, cottonseed oil, groundnut oil, silicone oil, tricresyl phosphate, monochlorobenzene, furthermore partially hydrogenated terphenyls, alkylated diphenyls, alkylated naphthalenes, aryl ethers, arylalkyl ethers, higher alkylated benzenes and others. Diluents, such as, for example, kerosine, n-paraffins and iso-paraffins, can be added to the solvents. .

In the practice of this invention, where solid colorant particles are employed an aqueous dispersion of solid colorant particles is first provided. The aqueous dispersion can be obtained employing any suitable method, e.g., that described in U.S. Patent No. 3,884,871, the contents of which are incorporated by reference herein. Thus, the colorant particles can be dispersed in water with the aid of one or more dispersing agents. Suitable dispersing agents include surface active agents (surfactants) and e ulsifiers, e.g., salts of fatty acids such as potassium oleate, metal alkyl sulfates such as sodium lauryl sulfate, salts of alkyl aryl sulfonic acids such as sodium dodecylbenzene sulfonate, polysoaps such as sodium polyacrylate and alkali metal salts of methyl methacrylate/2-sulfoethyl methacrylate copolymers and other sulfoalkyl acrylate copolymers, and other anionic surfactants such as the dihexyl ester of sodium sulfosuccinic acid; non-ionic surfactants such as the nonionic condensates of ethylene oxide with propylene oxide, ethylene glycol and/or propylene glycol; and cationic surfactants such as alkylamine-guanidine polyoxyethanols, as well as a wide variety of micelle generating substances described by D.C. Blackley in "Emulsion Polymerization", Wiley and Sons, Chapter 7 (1975) and other surfactants listed in McCutcheon's "Detergents and Emulsifers", 1980 Annual, North American Edition, Mccutcheon, Inc. , Morristown, N.J. Also included among the suitable surfactants are the surface active polymers (often called polysoaps) , e.g., those described in U.S. Patent No. 3,965,032, the contents of which are incorporated by reference herein. Of the suitable surfactants, the anionic varieties such as the potassium salts of functionalized oligomers, e.g., Polywet varieties available from Uniroyal Chemical, are preferred.- Such surface active agents or emulsifiers are employed in amounts sufficient to provide a stable dispersion of the monomer and dye in water. Preferably, such surface active agents are employed in concentrations in the range from about 0.2 to about 10, most preferably from about 1 to about 6, weight percent based on the aqueous phase.

It is advantageous to use well-dispersed colorant particles to provide desirable conditions for the encapsulation of individual colorant particles with polymer. If the colorant particles are permitted to flocculate or agglomerate, they may become coated by the polymer to form relatively large encapsulated aggregates. While erasable inks containing such aggregates are not excluded from the scope of this invention, it will be understood by those skilled in the art that large amounts of these agglomerates could be disadvantageous for some applications.

Good colorant dispersions in water can be obtained by first preparing a concentrated aqueous colorant slurry containing about 60-70 weight percent or more of colorant, adding a dispersing agent to the slurry and thoroughly mixing the resulting dispersion. If desired, the colorant particles can be wetted or coated with monomer(s) and/or copolymerizable anchoring agent(s) prior to forming the dispersion. If desired, the concentrated dispersion of colorant may thereafter be diluted, e.g., to a concentration of between 15 and 30 percent of colorant by weight, by addition of deionized water. Small amounts of additional dispersing agent can be added if desired.

The use of a copolymerizable anchoring agent can be advantageous in promoting the anchoring of the encapsulating polymer to the surfaces of the colorant particles during polymerization and insuring that all of the colorant particles are uniformly coated by the polymer. Suitable anchoring agents include organic vinyl monomers containing polar groups which are strongly adsorbed on the surfaces of the colorant particles. Representative polar groups include, e.g., —COOH, -S0₃H, —NH₂, -OH, -C0NH-, -C≡N, —CO—, —COO— and N0₂. Examples of useful anchoring agents include the acrylic and methacrylic acids and their sodium salts, hydroxyethylmethacrylate, aminoacrylates and sodium vinylsulfonate. These and similar anchoring agents will undergo copolymerization with the emulsion polymerizable monomers and thus become incorporated into the structure of the encapsulating polymer.

In the practice of this invention, where monomer- dissolvable colorant is employed a hydrophobic insoluble monomer/colorant solution is first provided, the solution then being dispersed in water to form an aqueous dispersion. The aqueous dispersion is thereafter subjected to emulsion polymerization conditions wherein the hydrophobic monomer undergoes polymerization to form polymer particles which encapsulate the colorant. Alternatively, aqueous dispersions of the monomer and colorant are separately formed and thereafter combined in a reactor and subjected to emulsion polymerization conditions to provide a composition containing polymer-encapsulated colorant. More particularly, the monomer/colorant solution can be obtained by dissolving both the monomer and the colorant in a suitable organic solvent. The monomer and colorant can be dissolved in different solvents so long as the solvents are water-insoluble and miscible with each other. Alternatively, the colorant can be directly dissolved in the monomer. The monomer/colorant solution is thereafter introduced to an aqueous solution of water- soluble surface active agent or emulsifier and subjected to agitation using a high shear mixing device such as a Waring blender, homogenizer and/or ultrasonic mixer to form the desired dispersion containing dispersed monomer/colorant solution droplets. Alternatively, separate dispersions of monomer and colorant, respectively, can be formed and thereafter combined under agitation in a polymerization reactor during polymerization. As another alternative, the dispersion can be formed by adding monomer to a preformed aqueous dispersion containing colorant dispersed therein or by adding colorant to a preformed aqueous dispersion containing monomer dispersed therein. In such instances the monomer and/or colorant will dissolve directly in the discontinuous phase. It is often desirable to add additional surfactant or emulsifier to the preformed dispersion of monomer or colorant prior to or simultaneous with the addition of monomer or colorant. Where the colorant is added to a preformed emulsion of monomer the colorant should dissolve within the discontinuous monomer phase.

The aqueous dispersions are typically formed by contacting the liquid monomer and colorant or solution(s) thereof with an aqueous solution of water-soluble surfactant or emulsifier thereby forming the dispersion. The dispersion can contain from about 70 to about 99.5, and preferably from about 80 to 98, weight percent total monomer and, correspondingly, from about 0.5 to about 30, and preferably from about 2 to about 10, weight percent total colorant.

The hydrophobic monomer is present in the emulsio in a proportion sufficient to enclose or encapsulate the colorant when the monomer is polymerized. Sufficient surface active agent and/or emulsifier is present in the emulsion to provide an aqueous dispersion which is sufficiently stable to be subjected to emulsion polymerization conditions. Preferably, the emulsion contains from about 1 to about 30 weight percent monomer, from about 0.1 to about.25 weight percent colorant and a remaining amount of the aqueous phase including surfactant and/or emulsifier, catalyst and the like. Typically, suitable surface active agents or emulsifiers include salts of fatty acids such as potassium oleate, metal alkyl sulfates such as sodium lauryl sulfate, salts of alkyl aryl sulfonic acids such as sodium dodecylbenzene sulfonate, polysoaps such as sodium polyacrylate and alkali metal salts of methyl methacrylate/2-sulfoethyl methacrylate copolymers and othe sulfoalkyl acrylate copolymers, and other anionic surfactants such as the dihexyl ester of sodium sulfosuccinic acid; non-ionic surfactants such as the nonionic condensates of ethylene oxide with propylene oxid ethylene glycol and/or propylene glycol; and cationic surfactants such as alkylamine-guanidine polyoxyethanols,. well as a wide variety of micelle generating substances described by D.C. Blackley in "Emulsion Polymerization", Wiley and Sons, Chapter 7 (1975) and other surfactants listed in McCutcheon's "Detergents and Emulsifers", 1980 Annual, North American Edition, McCutcheon, Inc., Morristown, N.J. Also included among the suitable surfactants are the surface active polymers (often called polysoaps) , e.g., those described in U.S. Patent No. 3,965,032. Of the suitable surfactants, the anionic varieties such as the potassium salts of functionalized oligomers, e.g., Polywet varieties sold by Uniroyal Chemical, are preferred. Such surface active agents or emulsifiers are employed in amounts sufficient to provide a stable dispersion of the monomer and dye in water. Preferably, such surface active agents are employed in concentrations in the range from about 0.2 to about 10, most preferably from about 1 to about 6, weight percent based on the aqueous phase.

The emulsion polymerization conditions employed in the practice of this invention are generally conventional free-radical type polymerizations carried out in the presence of a radical initiator such as a peroxygen compound, an azo catalyst, ultraviolet light and the like. Preferably, such polymerization is carried out in the presence of a water-soluble peroxygen compound at temperatures in the range of from about 50° to about 90°C. The emulsion is generally agitated during the polymerization period in order to maintain adequate feed transfer. The concentration is normally in the range of from about 0.005 to about 8, preferably from about 0.01 to about 5, weight percent based on total monomer. Examples of suitable catalysts include inorganic persulfate compounds such as sodium persulfate, potassium persulfate, ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl hydroperoxide, dibenzoyl peroxide and dilauroyl peroxide; azo catalysts such as azobisisobutyronitrile, and other common free-radical generating compounds. Also suitable are various forms of free-radical generating radiation means such as ultra-violet radiation, electron beam radiation and gamma radiation. Alternatively, a redox catalyst composition can be employed wherein the polymerization temperature ranges from about 25° to about 80°C. Exemplary redox catalyst compositions include a peroxygen compound as described hereinbefore, preferably potassium persulfate or t-butyl hydroperoxide, and a reducing component such as sodium metabisulfite and sodium formaldehyde hydrosulfite. It is also suitable to employ various chain transfer agents such as mercaptans, e.g., dodecyl mercaptan, dialkyl xanthogen disulfides, diaryl disulfides, and the like.

Following emulsion polymerization, the emulsion polymerizate can be withdrawn from the polymerization vesse and (1) the emulsion employed as, or in, the erasable ink o (2) the unreacted monomer and other volatiles can be remove to provide a concentrated emulsion which is then used as, o in, the erasable ink or (3) the polymer particles can be recovered from the aqueous continuous phase of the dispersion by conventional means such as drying under vacuu or spray drying and, following any optional post-recovery operation such as washing, redispersed in an appropriate aqueous dispersion medium to provide the erasable ink. The polymer-encapsulated colorant particles of th erasable ink composition of this invention will generally possess an average particle size of from about 25 to about 1000 nanometers and preferably from about 50 to about 250 nanometers. The fully formulated erasable ink composition, i.e., the aqueous dispersion of polymer-encapsulated colorant and any optional component(s) , can possess a relatively low viscosity, e.g., from about 1 to about 80,00 centipoises and preferably from about 3 to about 30,000 centipoises, or a relatively high viscosity, e.g., at least about 100,000 centipoises and preferably at least about

500,000 centipoises. It will, of course, be recognized tha when the erasable ink composition possesses such a high viscosity that it no longer readily flows solely under the influence of gravity, it becomes necessary to provide a pressurized delivery system for any marking instrument containing the ink.

To improve or optimize one or more functional characteristics of the erasable ink composition, one or more optional components can be added in the usual amounts to the composition, e.g., one or more natural and/or synthetic polymer latices, rheological modifiers, suspension agents, humectants, emulsifiers, surfactants, plasticizers, spreading agents, drying agents, release agents, parting agents, preservatives, antimicrobial agents, anticorrosion agents, antioxidants, coalescing aids, and the like.

With or without the addition of any optional component(s) , the erasable ink composition when applied to a substrate, and particularly a porous substrate such as a cellulosic paper, and upon drying thereon is (1) sufficiently adherent to the substrate as to resist flaking therefrom and (2) substantially erasable. Thus, the dry erasable ink composition of this invention applied to paper and evaluated by the adherency test described infra will generally exhibit less than about 30 weight percent flaking, preferably less than about 20 weight percent flaking and even more preferably less than about 10 weight percent flaking. Erasability values delta E*ab of the erasable ink composition herein as measured by ASTM D-2244-89 will generally be on the order of less than about 4.0, preferably less than about 3.5 and even more preferably less than about 3.0.

It is preferred that the erasable ink composition herein when evaluated by the smearability test described infra exhibit a subjectively determined low level of smear, e.g., a smear value of 2 or less and preferably a smear value of 1 (i.e., essentially no smearing). The erasable ink composition of this invention is intended to be used in any of a variety of marking instruments, and in particular, a ball-point pen.

The following examples are illustrative of the erasable ink composition of this invention.

EXAMPLES 1-4 ILLUSTRATING THE PREPARATION OF POLYMER-ENCAPSULATED COLORANT DERIVED FROM SOLID COLORANT PARTICLES

EXAMPLE 1

The following ingredients were placed in a reaction bottle and stirred:

Ingredient Amount (q) Water 56.00

Rosin Soap 2.00

Na₃PO₄ ^» 10H₂O 0 . 17

HEMA (Fe(II) complex of EDTA 0.02 from Hampshire) Sodium formaldehyde sulfoxyl 0.03

Dispersed Blue 69 (copper phthalocyanine from BASF) 4.00

Thereafter, the following ingredients were placed in the reaction bottle containing the above-identified ingredients and the bottle was capped:

Ingredient Amount (q)

Styrene 9.00 Dodecyl mercaptan 0.07

Butadiene (liquified) 25.00

A solution of cumene hydroperoxide (0.03g) in styrene (l.OOg) was then added to the reaction bottle via syringe. The reaction bottle was agitated for about 12 to about 24 hours at approximately 15°C to provide an emulsion polymerizate containing approximately 42.4 weight percent solids. The color of the resulting polymer-encapsulated colorant (dry) was blue. The average particle size (dry) of the polymer-encapsulated colorant was about 100 to about 300 nanometers. The calculated T_g for the polymer- encapsulated colorant was approximately -46°C.

EXAMPLE 2 A mini-emulsion was formed by mixing the following ingredients together and passing the mixture through a microfluidizer several times:

Ingredient Amount g )

Water 78. 88 Styrene 15. ,69

Sodium lauryl sulfate 0. 80

Hexadecane 2. ,52

TINT-AYD Blue PC (copper phthalocyanine from Daniels Products) 2.10

Thereafter, the following ingredients were placed in a reaction bottle and the bottle was capped:

Ingredient Amount ( )

Mini-emulsion (described above) 46.54

Water 37.50

Dodecyl mercaptan 0.07

Na₃PO₄-10H₂O 0.17

HEMA (FE(II) Complex of EDTA from Hampshire) 0.02

Sodium formaldehyde sulfoxyl 0.03

Butadiene (liquified) 25.00 A solution of cumene hydroperoxide (0.03g) in styrene (l.OOg) was then added to the reaction bottle via syringe. The reaction bottle was agitated for about 12 to about 24 hours at approximately 15°C to provide an emulsion polymerizate containing approximately 32.3 weight percent solids. The color of the resulting polymer-encapsulated colorant (dry) was blue. The average particle size (dry) o the polymer-encapsulated colorant was about 100 to about 300 nanometers. The calculated T. for the polymer- encapsulated colorant was approximately -53°C.

EXAMPLE 3 The following ingredients were placed in a reaction kettle and stirred at approximately 60°C: Ingredient Amount fg)

Water 238.0

Alipal EP-120 (Anionic

Surfactant from Rhόne-Poulenc) 9.7

Sipo DS-4 (Anionic Surfactant from Rhόne-Poulenc) 9.7

Aquis Phthalo Blue Pigment R/S BW-3521 (Heubach) 20.0

A pre-emulsion was formed by stirring the following ingredients together in a separate container at room temperature for 30 minutes:

Ingredient Amount (g) Water 190.0

Alipal EP-120 (Anionic surfactant from Rhδne-Poulenc) 29.6

Sipo DS-4 (Anionic surfactant from Rhδne-Poulenc) 9.7 Butyl acrylate 162.0

2-Ethyl hexyl acrylate 162.0

Acrylonitrile 42.0 The pre-emulsion (30g) was added to the reaction kettle at about 75°c and stirred for approximately 15 minutes. A solution of azo initiator (VA-61 from WAKO Chemicals) (0.03g) in water (6.1g) was added to the reaction kettle to initiate emulsion polymerization. The contents of the reaction kettle were stirred for approximately 15 minutes at about 60°C. The remaining portion of the pre- emulsion was introduced to an addition funnel and added dropwise to the reaction kettle over a 3 hour period at about 75°C. Similarly, an initiator solution formed by admixing water (48.3g), Alipal EP-120 (anionic surfactant from Rhδne-Poulenc) (1.9g) and azo initiator (VA-61 from WAKO Chemicals) (0.5g) was then placed in the addition funnel and added dropwise to the reaction kettle over the three hour period while maintaining the reaction kettle at about 75°C. After all additions were complete, the temperature of the reaction kettle was maintained at 80°C for approximately 1 hour. Thereafter, residual monomer remaining in the emulsion polymerizate was scavenged with four separate scavenger solutions of sodium formaldehyde sulfoxylate (Hydro AWC from Henkel) (0.15g) in water (lOg) and a 70% solution of t-butylhydroperoxide (0.30g) in water (5g) . The resulting emulsion polymerizate was neutralized to a slightly basic pH, i.e., from about 7.5 to about 8.5, utilizing Aqua Ammonia 28%. The color of the resulting polymer dye (dry) was blue. The average particle size of the polymer dye was about 120 nanometers. The calculated T_g for the polymer dye was approximately -61°C.

EXAMPLE 4

The following ingredients were placed in a reaction kettle and stirred at approximately 60°C:

Ingredient Amount (g) Water 273.3

Alipal EP-120 (Anionic

Surfactant from Rhόne-Poulenc) 4.0

Sipo DS-4 (Anionic Surfactant from Rhδne-Poulenc) 4.0 Iron sulfate (0.025M) 1.5

Aquis Phthalo Blue Pigment

R/S BW-3521 (Heubach) 20.0

A pre-emulsion was formed by admixing the following ingredients under stirring for 30 minutes at room temperature:

Ingredient Amount (g)

Water 213.7

Alipal EP-120 (Amine Surfactant from Rhόne-Poulenc) 9.7

Sipo DS-4 (Anionic Surfactant from Rhδne-Poulenc) 3.4 Acrylic acid 3.4

Itaconic acid 3.4

Butyl acrylate 190.2

2-Ethylhexylacrylate 190.2

Acrylonitrile 50.0

The pre-emulsion (30g) was added to the reaction kettle at about 60°C and stirred for approximately 15 minutes. A solution of ammonium persulfate (0.5g) in water (6.2g) and a solution of sodium bisulfate (0.3g) in water (6.2g) were added to the reaction kettle to initiate emulsion polymerization. The contents of the reaction kettle were stirred for approximately 15 minutes at about 60°C. An initiator solution formed by admixing water (49.8g) , Alipal EP-120 (anionic surfactant from Rhδne- Poulenc) (2.2g) and ammonium persulfate (0.8g) and an initiator solution formed by admixing water (49.8g) and sodium bisulfate (0.4g) were then placed in an addition funnel and added dropwise to the reaction kettle over a three hour period while maintaining the kettle at about 80°C. Similarly, the remaining portion of the pre-emulsion was introduced to an addition funnel and added dropwise to the reaction kettle over the 3 hour period while maintaining the temperature of the reaction kettle at 80°C. After all additions were complete_/ the temperature of the reaction kettle was maintained at 80°C for approximately 1 hour. Thereafter, residual monomer remaining in the emulsion polymerizate was scavenged with four separate scavenger solutions of sodium formaldehyde sulfoxylate (Hydro AWC from Henkel) (0.15g) in water (lOg) and a 70% solution of t-butylhydroperoxide (0.30g) in water (5g) . The resulting emulsion polymerizate was neutralized to a slightly basic pH, i.e., from about 7.5 to about 8.5, utilizing Aqua Ammonia 28%. The color of the resulting polymer- encapsulated colorant (dry) was blue. The calculated T_g for the polymer-encapsulated colorant was approximately -50°C.

The polymer-encapsulated colorants of Examples 1-4 can be directly employed as erasable ink compositions or be combined with one or more optional components as disclosed hereinabove prior to being employed as erasable ink compositions.

The properties of the erasable ink composition of Example 2 were evaluated. In particular, the color intensity, viscosity, adherency, erasability and smearability of the erasable ink composition were evaluated.

Color intensity was evaluated by a subjective visual evaluation of script. Adherency was determined by performing a drawdown on preweighed Linetta drawdown paper with approximately 0.8 of sample (spread over an area of inch x 1% inch) and drawn down with a #6 eater-bar. The sample was allowed to dry completely (approximately 5 minutes at room temperature) and the paper was weighed again. The paper was then crumpled by hand, any flakes were blown off and the paper was reweighed. This test was also performed with erasable ink made according to U.S. Patent Nos. 5,120,359 and 5,203,913 (Comparative Example 1).

Erasability was determined by performing an actua "WRITE-TEST" (similar to a spirograph wherein ink is applie in a circular arrangement on paper with some cross-over of ink occurring) with ball-point pens containing the erasable ink composition of Example 2 and the following commercially available pens which contain erasable ink: Pen Ink Color Comparative Example

Erasermate Blue 2

Erasermate 2 Blue 3 Scripto Blue 4

Scripto Red 5

The "WRITE-TEST" write-downs were then erased and reflectance measurements were performed on the erased portion of the paper versus an unblemished/untouched portio of the paper. A quantitative value was then obtained, i.e., delta E*ab from CIE lab measurement (described in ASTM D- 2244-89) . Lower values indicate more complete erasures. , Smearability was subjectively evaluated for the erasable ink composition of Example 2 and Comparative Examples 2-5 1-2 seconds after writing by attempting to smudge the ink with one's fingers. A smear value of 1 represents essentially no smearing and a smear value of 5 represents such a degree of smearing that legibility of the writing is significantly impaired. Table I below presents the properties of the erasable ink compositions:

Table I

Adherency

(Wt.% of Dried

Ink Composition Erasability

Color Viscosity Retained on Value Smear

Example Intensity (cps) the Paper) (delta E*ab) Value

3 Approx. 50% -3-10 100% 1.55 1 of Comparative Examples

Comp. Ex. 1 - - 63% - -

Comp. Ex. 2 - - - 3.3 2

Comp. Ex. 3 - - - 3.63 2

Comp. Ex. 4 - - - 5.38 3

Comp. Ex. 5 - - - - 4

As can be seen from the data presented in Table I, the erasable ink composition of Example 2 exhibited superior adherency, erasability and resistance to smear relative to the comparative examples. The erasable ink composition of this invention is highly adherent to substrates as to resist flaking therefrom, substantially erasable and substantially non-smearing.

EXAMPLES 5-7 ILLUSTRATING THE PREPARATION OF

POLYMER-ENCAPSULATED COLORANT DERIVED

FROM MONOMER DISSOLVED COLORANT

EXAMPLE 5

The following ingredients were placed in a reaction bottle and stirred:

Ingredient Amount (a)

Water 58.00 Rosin Soap 2 . 00

Na₃PO₄ - 10H₂O 0 . 17

HEMA (Fe(II) complex of EDTA 0.02 from Hampshire)

Sodium formaldehyde sulfoxyl 0.03

Ingredient Amount (a)

Styrene 9.00

Dodecyl mercaptan 0.07

Butadiene (liquified) 25.00

Solvent Blue 36 (ICI/Zeneca, 1.00 Wilmington, DE)

A solution of cumene hydroperoxide (0.03g) in styrene (l.OOg) was then added to the reaction bottle via syringe. The reaction bottle was agitated for about 12 to about 24 hours at approximately 15°C to provide an emulsion polymerizate containing approximately 39.8 weight percent solids. The color of the resulting polymer-encapsulated colorant (dry) was blue. The average particle size (dry) of the polymer-encapsulated colorant was about 100 to about 200 nanometers. The calculated T₈ for the polymer- encapsulated colorant was approximately -46°C.

EXAMPLE 6 The following ingredients were placed in a reaction kettle and stirred at approximately 60°C:

Ingredient Amount (q)

Water 260.4

Alipal EP-120 (Anionic

Surfactant from Rhδne-Poulenc) 3.2

Sipo DS-4 (Anionic Surfactant from Rhδne-Poulenc) 3.2

Ingredient Amount (q) Water 203.6

Alipal EP-120 (Amine

Surfactant from Rhδne-Poulenc) 9.0 Sipo DS-4 (Anionic Surfactant from Rhδne-Poulenc) 3.2

Acrylic acid 3.2 Itaconic acid 3.2

Butyl acrylate 162.0

2-Ethylhexylacrylate 162.0 Acrylonitrile 47.6

Solvent Yellow (the condensation product of N,N-dimethyl- aminobenzaldehyde and ethylhexylcyanoacetate) 9.5 The pre-emulsion (30g) was added to the reaction kettle at about 60°C and stirred for approximately 15 minutes. A solution of ammonium persulfate (0.6g) in water (6.1g) was added to the reaction kettle to initiate emulsio polymerization. The contents of the reaction kettle were stirred for approximately 15 minutes at about 60°C. An initiator solution formed by admixing water (48.3g), Alipal EP-120 (anionic surfactant from Rhδne-Poulenc) (l.9g) and ammonium persulfate (0.8g) was then placed in an addition funnel and added dropwise to the reaction kettle over a three hour period while maintaining the kettle at about 80°C. Similarly, the remaining portion of the pre-emulsion was introduced to the addition funnel and added dropwise to the reaction kettle over the 3 hour period while maintainin the temperature of the reaction kettle at 80°C. After all additions were complete, the temperature of the reaction kettle was maintained at 80°C for approximately 1 hour. Thereafter, residual monomer remaining in the emulsion polymerizate was scavenged with four separate scavenger solutions of sodium formaldehyde sulfoxylate (Hydro AWC fro Henkel) (0.15g) in water (lOg) and a 70% solution of t-butylhydroperoxide (0.30g) in water (5g) . The resulting emulsion polymerizate was neutralized to a slightly basic pH, i.e., from about 7.5 to about 8.5, utilizing Aqua Ammonia 28%. The emulsion polymerizate contained approximately 39.4 weight percent solids. The color of the resulting polymer-encapsulated colorant (dry) was yellow. The calculated T. for the polymer-encapsulated colorant was approximately -50°C. The polymer-encapsulated colorants of Examples 5- can be directly employed as erasable ink compositions or be combined with one or more optional components as disclosed hereinabove prior to being employed as erasable ink compositions. To further illustrate the erasable ink composition of this invention, the polymer-encapsulated colorant of Example 6 was combined with propylene glycol to provide an erasable ink composition (Example 7) containing 90 weight percent polymer-encapsulated colorant obtained from Example 2 and 10 weight percent propylene glycol.

The properties of the erasable ink composition of Example 7 were evaluated. In particular, the color intensity, viscosity, adherency, erasability and smearability of the erasable ink composition were evaluated.

Color intensity was evaluated by a subjective visual evaluation of script.

Adherency was determined by performing a drawdown on preweighed Linetta drawdown paper with approximately 0.8g of sample (spread over an area of h inch x X. inch) and drawn down with a #6 eater-bar. The sample was allowed to dry completely (approximately 5 minutes at room temperature) and the paper was weighed again. The paper was then crumpled by hand, any flakes were blown off and the paper was reweighed. This test was also performed with erasable ink made according to U.S. Patent Nos. 5,120,359 and 5,203,913 (Comparative Example 6).

Erasability was determined by performing an actual "WRITE-TEST" (similar to a spirograph wherein ink is applied in a circular arrangement on paper with some cross-over of ink occurring) with ball-point pens containing the erasable ink composition of Example 7 and the following commercially available pens which contain erasable ink: Pen Ink Color Comparative Example Erasermate Blue 7

Erasermate 2 Blue 8

Scripto Blue 9

Scripto Red 10 The "WRITE-TEST" write-downs were then erased and reflectance measurements were performed on the erased portion of the paper versus an unblemished/untouched portion of the paper. A quantitative value was then obtained, i.e., delta E*ab from CIE lab measurement (described in ASTM D- 2244-89) . Lower values indicate more complete erasures.

Smearability was subjectively evaluated for the erasable ink composition of Example 7 and Comparative Examples 6-10 1-2 seconds after writing by attempting to smudge the ink with one's fingers. A smear value of 1 represents essentially no smearing and a smear value of 5 represents such a degree of smearing that legibility of the writing is significantly impaired.

Table II below presents the properties of the erasable ink compositions:

Table I

Adherency (Wt. % of Dried Ink Composition Erasability

Color Viscosity Retained on Value Smear

Examde Intensitv reps) the Paper) (delta E*ab) Value

7 Comparable to -3-10 100% 3.56 1

Comparative

Examples

Comp. Ex. 6 - - 63% - -

Comp. Ex. 7 - - - 3.3 2

Comp. Ex. 8 - - - 3.63 2

Comp. Ex. 9 - - - 5.38 3

Comp. Ex. 10 - - - - 4

As can be seen from the data presented in Table II, the erasable ink composition of Example 7 exhibited superior adherency and resistance to smear and comparative. if not superior, color intensity and erasability relative to the comparative examples. The erasable ink composition of this invention is highly adherent to substrates as to resist flaking therefrom, substantially erasable and substantially non-smearing.

While this invention has been disclosed herein in connection with certain embodiments and certain procedural details, it is clear that changes, modifications or equivalents can be used by those skilled in the art. Accordingly, such changes within the principles of this invention are intended to be included within the scope of the claims below.

Claims

WHAT IS CLAIMED IS:

1. An erasable ink composition which comprises dispersion of particles of water-insoluble polymer- encapsulated colorant obtained by polymerizing under emulsion polymerization conditions at least one emulsion- polymerizable monomer in the presence of colorant, the erasable ink composition when applied to a substrate and upon drying thereon being (1) sufficiently adherent to a substrate as to resist flaking therefrom and (2) substantially erasable.

2. The erasable ink composition of Claim 1 wherein the colorant comprises solid colorant particles tha are insoluble in the emulsion polymerization medium and any component thereof.

3. The erasable ink composition of Claim 1 wherein the colorant is dissolved in the emulsion polymerizable monomer prior to polymerizing the emulsion polymerizable monomer.

4. The erasable ink composition of Claim 1 exhibiting less than about 30 weight percent flaking and an erasability value delta E*ab of less than about 4.0.

5. The erasable ink composition of Claim 1 wherein the monomer is at least one member of the group consisting of styrene, vinyl toluene, t-butyl styrene, chlorostyrene, vinyl benzyl chloride, vinyl pyridene, ethyl acrylate, methyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, butadiene and isoprene.

6. The erasable ink composition of Claim 2 wherein the solid colorant particles are wetted or coated with copolymerization monomer containing polar groups.

7. The erasable ink composition of Claim 6 wherein the copolymerizable monomer is at least one member of the group consisting of acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, aminoacrylate and sodium vinylsulfonate.

8. The erasable ink composition of Claim 3 wherein the colorant is -a water-insoluble solvent dye.

9. The erasable ink composition of one of Claims 1 to 8 further comprising at least one component selected from the group consisting of natural latices, synthetic latices, rheological modifiers, suspension agents, humectants, emulsifiers, surfactants, plasticizers, spreading agents, drying agents, release agents, parting agents, preservatives, antimicrobial agents, anticorrosion agents, antioxidants and coalescing aids.

10. A marking instrument containing the erasable ink composition of one of Claims 1 to 9.