Ink jet recording with an ink composition containing pigment

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loaded in an ink-jet recording apparatus to carry out INK JET RECORDING WITH AN INK recording. COMPOSITION CONTAINING PIGMENT Moreover, although some conventional water-based

pigment inks have a good performance when ejected BACKGROUND OF THE INVENTION 5 for a relatively short time, but such inks experienced

1. Field of the Invention problems such that ejection becomes unstable when The present invention relates to an ink suited for an drive conditions of a recording head are changed or ink

ink-jet printer, an ink-jet device making use of it and an is continuously ejected over a long period of time, fi

ink cartridge containing the ink. It also relates to an nally resulting in no ejection.

ink-jet recording process that makes a record on non- As a water-based pigment ink that can be preferably

coated paper, called plain paper, by causing ink to fly used in the above ink-jet recording, EP 0376284 A2

from orifices of a recording head by the action of heat discloses an ink characterized by having a superior

energy. ejection performance in ink-jet printers, response to

2. Related Background Art 15 variations of their drive conditions, stability in continuInk-jet recording systems have the advantages that ous ejection for a long period of time and restoration

they make less noise in the course of recording and a performance at the time of reprint after temporary stop

recorded image with a high resolution can be obtained of printing, and being particularly suited for ink-jet

at a high speed because of use of a highly integrated printers making use of heat energy. This ink, however,

head. Inks used in such ink-jet recording systems are 2Q is required to be more improved in its anti-sedimenta

those prepared by dissolving various kinds of water-sol- tion during long-term storage of ink, the stability in ink

uble dyes in water or in a mixed solution of water and an properties, and the response to higher-speed drive, organic solvent. When the water-soluble dyes are used,

however, light fastness of recorded images is often SUMMARY OF THE INVENTION

questioned because such water-soluble dyes have poor 25 Accordingly, an object of the present invention is to

light fastness by nature. provide an ink suited for ink-jet recording, that has

Water resistance of recorded images is also often eliminated the problems involved in the prior art dis

questioned because the ink is water-soluble. More spe- cussed above, enables always stable ejection regardless

cifically, if recorded images become wet with rain, 0f variations of drive conditions and even in its use for

sweat, or water from food and drink, they may become 30 a jong period of time, has a superior long-term storage

blurred or disappeared. stability, has also eliminated the problem of solidifica

Meanwhile, similar questions have arisen also with tion of ink at nozzle tips of a head) and has particularly

respect to writing implements such as ball-point pens superior stability in ink properties,

making use of dyes, and various water-based pigment Another object of the present invention is to provide

inks for writing materials have been proposed so that 35 an ink.jet recording process that enables always stable

the problems of light fastness and water resistance can hi h.s ed recording, and can obtain a recorded image

be settled. Examples of studies on dispersion stability, with rior festness such ^ water resistance ^ iight

prevention of ink solidification at pen points and pre- ... when characters

or the like are printed on non

vention of ball wear of ball-point pens for the purpose coated Daner

of putting water-based pigment inks into practical use 40 sm object Qf ^ t fa tQ

are seen in Japanese Patent Applications Laid-open No. ., ., _r .. _ , • r »i. • 1 1. •

58-80368, No. 61-200182, No. 61-247774 No. Provide an mk cartndge making use of the ink havmg

61-272278, No. 62-568, No. 62-101671, No. 62-101672, *he above superior properties and to proy.de an mk-jet

No. 1-249869, No. 1-301760, etc. Recently, ball-point devlce a"d M ^et recOT^B apparatus that have

pens or markers making use of water-based pigment 45 ... r«P°nse TMd make a record

inks have become commercially available. with a high image quality.

When, however, conventional water-based pigment Present invention provides an ink comprising a

inks for writing implements are applied in an ink-jet composition containing a pigment, a water-soluble resin

recording apparatus of the system that makes a record a h?u'd medlum' whereulJ the P'S1*"11 •?? ^

by causing ink to fly from orifices of a recording head 50 water-soluble resin are contained m said composition in

by the action of heat energy, there have been disadvan- 8 proportion of the weight Wr of the latter to the

tages such that serious difficulties may arise in ejection we,ght WP of the {°TMer' Wr/Wp, that satisfies the

stability, causing defective prints. In particular, in a following expression (I), system that makes a record by ejecting droplets by the

action of heat energy applied, use of the conventional 55 1.2 x DAR S Wr/Wp s 15 x DAR ®

pigment ink may cause the formation of deposits on a 100 100 thin-film resistor because of the heat generated when

pulses are applied to the ink, so that the ink may be wherein DAR denotes a value represented by the fol

imperfectly bubbled and the ejection of droplets can not lowing expression (II). respond to the applied pulses, often resulting in no ejec- 60

tion of ink. Namely, in order for an ink to be stably Minimum weight of w-eMOlable ^ (")

ejected from nozzle tips, the ink must have the perfor- = necessarv for dispersion of pigment 100

mances that it can be bubbled on a thin-film resistor to Weight of pigment form bubbles with the desired volume and also it can be

repeatedly bubbled and debubbled at the desired inter- 65 The present invention also provides an ink-jet recordvals. None of conventional inks for writing implements, ing process comprising applying a heat energy to an ink however, have satisfied such performances, and hence to eject said ink from an orifice in the form of ink dropvarious difficulties as stated above may occur when lets, and imparting said ink droplets to a recording me

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ranging from 3% by weight to 50% by weight, prefera- -continued

bly from 3% by weight to 40% by weight, of the total . , ,

... . , * i_ J • . Acid value of resin X Molecular weight of

weight of the ink. The water may be used m an amount amine or base y Weight of resin f»)

ranging from 10% by weight to 90% by weight, and 56,ooo preferably from 30% by weight to 80% by weight, of 5

the total weight of the ink. Before the aqueous solution containing the resin is

In addition to the above components, a surface active dispersed, it is also necessary to carry out stirring for 30

agent, a humectant, an anti-foaming agent, an antiseptic, minutes or more. This procedure improves the wettabil

etc. may be optionally added to the ink of the present ity of pigment surfaces and promotes adsorption of resin

invention in order to give an ink having the desired 10 to the pigment surfaces.

values of physical properties. It is also possible to add a The amine added in the dispersion may preferably

commerically available water-soluble dye. include organic amines such as monoethanolamine,

As the humectant, any of those conventionally used diethanolamine, triethanolamine, aminomethylpropanol

can be used. Preferred are urea, thiourea, and deriva- and ammonia. The base may preferably include sodium

tives of these. The humectant may be used preferably in 15 hydroxide, lithium hydroxide and potassium hydroxide,

an amount of 2% by weight to 10% by weight, and As for a dispersion machine used in the present inven

more preferably 2% by weight to 5% by weight, based tion, any dispersion machines commonly used can be

on the total weight of the ink. used, which includes, for example, a ball mill, a roll mill

The surface active agent may include anionic surface and a sand mill, active agents such as fatty acid salts, higher alcohol In particular, a high-speed type sand mill is preferred, sulfuric acid ester salts, liquid fatty oil sulfuric acid ester including, for example, Super Mill, Sand Grinder, salts and alkylallyl sulfonates, and nonionic surface Beads Mill, Agitator Mill, Grain Mill, DYNO-MILL, active agents such as polyoxyethylene alkyl ethers, Pearl Mill and CoBall-MILL (all trade names), polyoxyethylene alkyl esters and polyoxyethylene sor- ^ In the present invention, a pigment having the desired bitan alkyl esters, which can be used alone or in combi- particle size distribution can be obtained by a method nation of two or more kinds appropriately selected. The including a method in which the grinding media of the amount of the agent used may vary depending on the dispersion machine are made small in size, a method in dispersing agent. It may preferably be 0.01% by weight which the grinding media are packed at a large proporto 5% by weight based on the total weight of the ink. 3Q tion, a method in which the treatment time is made When added, the amount of the surface active agent longer, a method in which the discharge rate is made may preferably be so determined that the ink has a slower, and a method in which particles having been surface tension of not less than 30 dyne/cm. This is pulverized are classified using a filter or a centrifugal because, in the recording system as in the present inven- separator, which may also include a method comprising tion, a surface tension smaller than this value may cause 35 a combination of any of these methods, troubles such as print twists (defective ink-droplet im- The ink of the present invention can be particularly pacts) due to wetting of nozzle tips. Meanwhile, in preferably used in the ink-jet recording in which reorder to give an ink having the desired values of physi- cording is carried out by ejecting ink droplets by the cal properties, a water-soluble organic solvent, a pH action of heat energy. Needless to say, it can also be adjuster, an antifoaming agent, an antiseptic can be 40 used for usual writing implements, added. It is also possible to add a commerically avail- The apparatus suited to carry out recording by the able water soluble dye. use of the ink of the present invention may include an

The total amount of both the pigment and water-solu- apparatus in which a heat energy corresponding with a ble resin in the dispersant may preferably be not less recording signal is imparted to the ink held in the intethan 10% by weight and preferably not more than 30% 45 rior of a recording head so that ink droplets are generby weight. The reason therefore is that it is impossible ated by the action of the heat energy, to efficiently carry out dispersion to obtain an optimum FIGS. 1A, IB and 2 show an example of the constate of dispersion, unless the pigment and water-soluble struction of the head, which is a main component of the resin are present in the dispersion in a given concentra- apparatus.

tion or higher. 50 A head 13 is formed by bonding a glass, ceramic or The ink of the present invention can be prepared by a plastic plate or the like having a channel 14 through method as described below. First, the pigment is added which ink is passed, to a heating head 15 used in thermal to an aqueous solution containing at least a dispersion recording (the drawing shows a head, to which, howresin, an amine (or a base) and water, followed by stir- ever, is not limited). The heating head 15 is comprised ring. Thereafter the mixture is dispersed using the dis- 55 of a protective film 16 formed of silicon oxide or the persion means as described later, optionally followed by like, aluminum electrodes 17-1 and 17-2, a heating resiscentrifugal separation to give the desired dispersion. tor layer 18 formed of nichrome or the like, a heat accuNext, the components as described above are added to mulating layer 19, and a substrate 20 with good heat the resulting dispersion, followed by stirring to give the dissipation properties.

ink. 60 The ink 21 reaches an ejection orifice (a minute open

For the amine or base that dissolves the resin it is ing) 22 and a meniscus 23 is formed there by a pressure

necessary to be added in an amount 1.2 times or more P.

the amount determined by calculation based on the acid Now, upon application of electric signals to the elec

value of the resin. This amount can be determined by trodes 17-1 and 17-2, heat is abruptly generated at the the following expression. 65 region denoted by n in the thermal head 15, so that

bubbles are generated in the ink 21 coming into contact

Amount of amine or base (g) = with this region. The presure thus produced thrusts out

the meniscus 23 and the ink 21 is ejected from the orifice