JP2715178B2 - Ink and ink jet recording method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ink-jet ink (hereinafter sometimes simply referred to as “ink”), and more specifically, to fly an ink from the orifice of a recording head by the action of thermal energy. The present invention relates to an ink jet recording method for performing recording.

(Prior Art) The ink jet recording method generates less noise at the time of recording, can easily cope with colorization, and can obtain a high-resolution recorded image at high speed by using a highly integrated head. It has the advantage that.

In such an ink jet recording method, an ink obtained by dissolving various water-soluble dyes in water or a mixture of water and an organic solvent is used. However, when water-soluble dyes are used, these water-soluble dyes are inherently inferior in light fastness, so that the light fastness of a recorded image often becomes a problem.

Further, since the dye is water-soluble, water resistance of a recorded image often becomes a problem. That is, when rain, sweat, or water for eating and drinking is applied to the recorded image, the recorded image may bleed or disappear.

On the other hand, there is a similar problem in stationery using a dye such as a ballpoint pen, and various water-based pigment inks for stationery have been proposed in order to solve such problems of light resistance and water resistance. In order to put the water-based pigment ink into practical use, studies have been made on dispersion stability, prevention of ink solidification at the pen tip, and prevention of wear of the ball of a ballpoint pen.

Examples include JP-A-58-080368 and JP-A-61-20.
No. 0182, JP-A-61-247774, JP-A-61-2727
No. 8, JP-A-62-000568, JP-A-62-101671
JP-A-62-101672, JP-A-1-249869, JP-A-1-301760 and the like. Recently, a large number of ballpoint pens and markers using water-based pigment inks have been marketed as commercial products.

(Problems to be Solved by the Invention) However, a conventional aqueous pigment ink for stationery using carbon black is applied to ink jet recording by a method of performing recording by flying ink by the action of thermal energy from an orifice of a recording head. When used, there is a problem that a remarkable trouble occurs in the ejection stability and printing failure occurs.

In particular, in the case of ink jet recording in which recording is performed by applying thermal energy and discharging droplets, when a conventional pigment ink is used, when a pulse is applied to the ink, a deposit is formed on the thin film resistor by the heat, In some cases, ejection of liquid droplets cannot respond to an applied pulse due to incomplete bubbling of ink, causing non-ejection.

That is, in order to stably eject the ink from the nozzle tip, the ink has the performance of foaming in a desired volume on the thin-film resistor, and furthermore, the foaming and defoaming can be repeated in a desired time. There must be. However, conventional stationery inks do not satisfy these performances, so that the above-described various inconveniences have occurred when the ink is filled in an ink jet recording apparatus to perform recording.

In addition, when a pigment ink dispersion is used for inkjet recording, prevention of solidification at the tip of the recording head due to long-term storage is an important technical issue, and the composition of the ink is important in designing a reliable pigment ink. Is an important point.

Further, some of the conventional pigment inks have excellent dischargeability in a relatively short time, but the discharge becomes unstable when the driving conditions of the recording head are changed or continuous discharge is performed for a long time. And finally there is a problem that the ink is not discharged.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, to perform stable ejection even when the driving conditions are changed or used for a long time, and to provide excellent long-term storage stability. Another object of the present invention is to provide an ink in which solidification of ink at the head end is eliminated and an ink jet recording method using the same.

Further, an object of the present invention is to provide an ink and an ink jet recording method capable of always performing stable high-speed recording, and obtaining a recorded image having excellent fastness such as water resistance and light resistance when printed on uncoated paper. To provide.

(Means for Solving the Problems) The above object is achieved by the present invention described below.

That is, the present invention relates to an aqueous liquid composition comprising at least 3 to 20% by weight of carbon black, 10 to 90% by weight of water and 0.1 to 5% by weight of a water-soluble resin, A transition temperature (Tg) of 50 ° C. or higher, and the amount of the water-soluble resin dissolved in the composition is 2% by weight
An ink-jet ink utilizing thermal energy for ink ejection, and an ink-jet recording method using the ink, characterized in that:

(Function) In the aqueous pigment ink using carbon black, the present inventors have proposed a method for increasing the resolubility of the solidified ink in order to prevent the ink from solidifying at the tip of the head and causing various problems. After careful examination, the glass transition temperature (Tg) of the water-soluble resin contained in the ink was 50
When the temperature is higher than ° C, it has been found that the ink solidified by drying can be redissolved with the ink itself, and various problems at the leading end of the recording head can be solved.

That is, the aqueous pigment ink generally agglomerates when dried, and cannot be easily redissolved unlike the ink using the dye ink. It must be redispersed using sound waves or the like.

The solidification of the ink at the tip of the recording head can be improved to some extent by increasing the airtightness of the cap, or by periodically cleaning the face surface of the recording head with a wiper or the like.

However, providing a washing unit or the like with a high alkali in the apparatus leads to an increase in cost, and furthermore, it is not a preferable solution since it is dangerous for a user of the printer to touch the high alkali solution.

Thus, the present inventors have studied various means for improving the resolubility of the solidified ink by improving the constituent elements of the ink, and by including the water-soluble resin as described above as a pigment dispersion resin. It was found that the re-solubility of the ink was significantly improved.

That is, the ink attached to the face surface of the recording head is
Dissolution of water and low-boiling point contained in the ink evaporates quickly, leaving a pigment dispersion and a high-boiling-point solvent.The solidified ink formed at this time has a Tg of the water-soluble resin contained therein.
When the temperature is lower than 50 ° C., although the reason is not clear, the surface is hardened into a film and cannot be easily dissolved again. However, when a water-soluble resin having a Tg of 50 ° C. or higher is used, the surface of the solidified material is soft and the solidified material can be redissolved by the ink itself.

Further, the properties generally required for ink-jet inks include physical properties such as viscosity, surface tension, and pH of the ink, but a dispersion system such as an aqueous pigment ink satisfies these physical properties. In many cases, the foaming of the ink was unstable.

Accordingly, the present inventors have conducted intensive studies on the performance of an aqueous pigment ink which is stable to heat and capable of optimal foaming. As a result, the amount of the water-soluble resin dissolved in the ink is reduced to 2% of the total amount of the ink. By controlling the amount to be not more than 1% by weight, preferably not more than 1% by weight, the ink foams accurately on the thin film resistor under any driving conditions, and further, deposits are generated on the thin film resistor over a long period of time. Not found.

That is, if a large amount of excess water-soluble resin is present in the ink with respect to the pigment, the ink does not foam even when given heat energy is applied to the thin-film resistor, or the excess heat is generated by pulse application. The water-soluble resin becomes insoluble and deposits on the thin film resistor, which causes non-discharge and printing disorder.

The dissolved water-soluble resin referred to in the present invention refers to a resin that is not adsorbed on a pigment in an ink but is dissolved in a liquid medium.

Preferred Embodiment Next, the present invention will be described in more detail with reference to preferred embodiments.

As the carbon black used in the present invention, No. 230
0, No.900, MCF88, No.33, No.40, No.45, No.52, MA
7, MA8, ♯2200B (Mitsubishi Chemical), RAVEN1255 (Colombia), REGAL400R, REGALE330R, REGAL660R, MOGU
LL (Cabot), Color Black FW1, Color Black
FW18, Color Black S170, Color Black S150, Printex
Commercial products such as 35, Printex U (made by Degussa), and those newly manufactured for this purpose can also be used.
Further, two or more of these carbon blacks can be used in combination.

The content of carbon black in the ink used in the present invention is preferably in the range of 3 to 20% by weight in weight ratio.

The water-soluble resin contained as a dispersant for carbon black in the present invention is soluble in an aqueous solution in which an amine or a base is dissolved, and any resin can be used as long as the Tg is 50 ° C. or higher. 3,000 to 30,000, more preferably 5,000 to 15,000. It is also possible to use two or more water-soluble resins in combination.

Specifically, styrene-acrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer, styrene-maleic acid copolymer, styrene-maleic acid-alkyl acrylate copolymer, styrene-methacrylic Acid copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-alkyl acrylate copolymer, styrene-maleic An acid half ester copolymer, a vinyl naphthalene-acrylic acid copolymer, a vinyl naphthalene-maleic acid copolymer, or a salt thereof may be used.

The water-soluble resin is 0.1 to 5% by weight based on the total amount of the ink.
, Preferably in the range of 0.3 to 2% by weight.
Such a water-soluble resin may be added separately from the dispersant when preparing the ink after the dispersion treatment.

The Tg of the water-soluble resin is measured using a differential thermal analysis (DTA) or a differential calorimetry (DSC).

The ink of the present invention improves the solubility of the water-soluble resin,
In order to further improve the long-term storage property, it is preferable that the entire ink is preferably adjusted to be neutral or alkaline. However, in this case, the pH is preferably in the range of 7 to 10, because it may cause corrosion of various members used in the ink jet recording apparatus which is a strong alkali.

Examples of the pH adjuster used in this case include amines or bases, for example, various organic amines such as diethanolamine and triethanolamine, and hydroxides of alkali metals such as sodium hydroxide, lithium hydroxide and potassium hydroxide. An inorganic alkali agent, an organic acid, a mineral acid, or the like is used.

As described above, carbon black, a water-soluble resin, an amine and the like are dispersed or dissolved in an aqueous medium.

An aqueous medium suitable for the ink of the present invention is a mixed solvent of water and a water-soluble organic solvent. As the water, not deionized water but general water containing various ions is used. Is preferred.

Examples of the water-soluble organic solvent used by mixing with water include, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol. Alkyl alcohols having 1 to 4 carbon atoms; amides such as dimethylformamide and dimethylacetamide; ketones or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylenes such as polyethylene glycol and polypropylene glycol Glycols; ethylene glycol, propylene glycol, butylene glycol, triethylene glycol,
Alkylene glycols wherein the alkylene group contains 2 to 6 carbon atoms, such as 1,2,6-hexatriol, thiodiglycol, hexylene glycol, diethyl glycol;
Glycerin; lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, and triethylene glycol monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, 1,3 -Dimethyl-2-imidazolidinone.

Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are particularly preferable.

Also, among these many water-soluble organic solvents, the polyhydric alcohol or its alkyl ether is preferably contained in the ink of the present invention in an amount of 0.001 to 10% by weight of the whole ink.

In the ink of the present invention, in order to obtain higher ejection stability, it is effective to add ethyl alcohol or isopropyl alcohol to an aqueous medium of 3% by weight to 15% by weight.

This is presumably because the addition of ethyl alcohol or isopropyl alcohol can more stably foam the ink on the thin film resistor.

However, if ethyl alcohol or isopropyl alcohol is added in excess, the print quality of printed matter is impaired, so that a more appropriate addition concentration is 3% by weight to 10% by weight.

Another effect of the addition of ethyl alcohol or isopropyl alcohol to the dispersion is that the generation of bubbles during dispersion can be suppressed and efficient dispersion can be performed.

The content of these water-soluble organic solvents in the ink of the present invention is generally in the range of 3 to 50% by weight, preferably in the range of 3 to 40% by weight based on the total weight of the ink.

The water used is in the range of 10 to 90% by weight, preferably 30 to 80% by weight of the total weight of the ink.

The main components constituting the ink of the present invention are as described above, but in order to obtain an ink having other desired physical properties, a surfactant, a humectant, an antifoaming agent, a preservative, and the like are used as necessary. Or a commercially available water-soluble dye or the like can be added.

As the humectant, any of those conventionally used can be used, but urea, thiourea and derivatives thereof are preferable. The amount added is in the range of 2 to 10% by weight, preferably in the range of 2 to 5% by weight of the total weight of the ink.

Surfactants include anionic surfactants such as fatty acid salts, higher alcohol sulfates, liquid fatty oil sulfates, alkylallyl sulfonates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene alkyl esters. There are nonionic surfactants such as oxyethylene sorbitan alkyl esters,
One or more of these can be appropriately selected and used.

The amount used varies depending on the dispersant, but is preferably 0.01 to 5% by weight based on the total amount of the ink.
It is preferable to determine the amount of the surfactant to be added so that the surface tension of the ink is 30 dyne / cm or more. This is because, if the surface tension of the ink is smaller than this value, an undesired situation such as printing distortion due to the wetting of the nozzle tip (shift of the landing point of the ink droplet on the recording paper) is caused in the ink jet recording method of the present invention. It is because.

Another feature of the ink of the present invention is that the amount of the water-soluble resin dissolved in the ink is 2% by weight or less, preferably 1% by weight or less of the total amount of the ink.
As a result, the ink is thermally stable, and the ink on the thin film resistor is accurately foamed under any driving conditions, and is useful for ink jet recording in which no deposit is generated on the thin film resistor for a long time. It can be ink.

That is, if a large amount of excess water-soluble resin is present in the ink with respect to the pigment, the ink does not foam or even heat is applied when applying a predetermined thermal energy on the thin-film resistor. The water-soluble resin becomes insoluble and deposits on the thin-film resistor, causing non-discharge and printing disorder.

One means of reducing the amount of such dissolved water-soluble resin is to make the ratio of pigment and water-soluble resin by weight at the time of making the ink.
It is to be adjusted in the range of 3: 1 to 10: 1, preferably 10: 3 to 10: 1.

Further, the total amount of the pigment and the water-soluble resin in the dispersion is preferably at least 10% by weight, and more preferably at most 30%. The reason is that if the water-soluble resin does not exist as a pigment having a certain concentration or more in the dispersion, the dispersion can be performed efficiently and the optimum dispersion state cannot be obtained.

As a method for preparing the ink of the present invention, first, a carbon black is added to an aqueous solution containing at least a dispersing resin, an amine or a base and water, and after stirring, dispersion is performed using a dispersing means described below, which is necessary. Centrifugation is performed accordingly to obtain a desired dispersion. Next, the above-mentioned components are added to the dispersion and stirred to obtain the ink of the present invention.

In particular, in order to reduce the amount of unadsorbed resin to 2% by weight or less,
In the preparation method, it is necessary to completely dissolve the resin in advance by stirring the aqueous solution containing the dispersed resin, the amine or the base, and water at 60 ° C. or more for 30 minutes or more.

Further, it is necessary to add the amount of the amine or base that dissolves the resin at least 1.2 times the amount calculated from the acid value of the resin. The amount of the amine or base is determined by the following equation.

It is also necessary to carry out premixing for 30 minutes or more before dispersing the aqueous solution containing the pigment.

This premixing operation improves the wettability of the pigment surface and promotes the adsorption of the resin to the pigment surface.

As amines added to the dispersion, organic amines such as monoethanolamine, diethanolamine, triethanolamine, aminomethylpropanol, and ammonia are preferable. As the base, sodium hydroxide, lithium hydroxide, potassium hydroxide and the like are preferable.

On the other hand, the disperser used in the present invention may be any commonly used disperser, and examples thereof include a ball mill, a roll mill, and a sand mill.

Among them, a high-speed sand mill is preferable, and examples thereof include a super mill, a sand glider, a bead mill, an agitator mill, a Glen mill, a Dyno mill, a pearl mill, and a Kobol mill (all trade names).

In the present invention, as a method for obtaining a pigment having a desired particle size distribution, the size of the pulverizing medium of the disperser is reduced, the filling rate of the pulverizing medium is increased, and the processing time is lengthened. Reduce the discharge speed. After the pulverization, a method such as classification using a filter or a centrifuge is used. Or a combination thereof.

In addition, as a method of measuring the amount of the non-adsorbed resin according to the present invention, the pigment component and the resin component adsorbed on the pigment are precipitated using an ultracentrifuge or the like, and the residual resin content contained in the supernatant liquid is determined. TOC (Total Organic Carbon, total organic carbon meter) or gravimetric method (method of evaporating the supernatant to dryness and measuring the amount of resin)
Etc. are preferably used.

The ink of the present invention is particularly preferably used in an ink jet recording method in which recording is performed by discharging droplets by the action of thermal energy, but it goes without saying that it can also be used for general writing instruments.

As a device suitable for performing recording using the ink of the present invention, there is a device that applies thermal energy corresponding to a recording signal to ink in a room of a recording head and generates droplets by the thermal energy.

FIG. 1-a and FIG.
This is shown in FIG.

The head 13 is formed by bonding a glass, ceramic or plastic plate having a groove 14 through which ink passes to a heating head 15 (the head is shown in the figure, but is not limited to this) used for thermal recording. Is obtained. The heating head 15 includes a protective film 16 formed of silicon oxide or the like, aluminum electrodes 17-1, 17-2, a heat-generating low antibody layer 18 formed of nichrome or the like, a heat storage layer 19, and a substrate 20 having good heat dissipation properties such as alumina. Consists of

The ink 21 reaches a discharge orifice (fine hole) 22 and forms a meniscus 23 by the pressure P.

Now, when an electric signal is applied to the electrodes 17-1 and 17-2, the area indicated by n of the heating head 15 generates heat rapidly, and bubbles are generated in the ink 21 in contact with the area, and the meniscus 23 Protrudes, the ink 21 is ejected, becomes a recording droplet 24 from the orifice 22, and flies toward the recording material 25. Second
The figure shows an external view of a multi-head in which a number of heads shown in FIG. 1-a are arranged. The multi-head is manufactured by closely contacting a gas plate 27 having a multi-groove 26 and a heating head 28 similar to that described with reference to FIG. 1-a.

FIG. 1-a is a cross-sectional view of the head 13 along the ink flow path, and FIG. 1-b is a cross-sectional view taken along line AB in FIG. 1-a.

FIG. 3 shows an example of an ink jet recording apparatus incorporating such a head.

In FIG. 3, reference numeral 61 denotes a blade as a wiping member, one end of which is held by a blade holding member to be a fixed end, and forms a cantilever. The blade 61 is disposed at a position adjacent to a recording area of the recording head, and in this example, is held in a form protruding into the movement path of the recording head. 62 is a cap and a blade
It is arranged at the home position adjacent to 61, moves in the direction perpendicular to the direction of movement of the print head, contacts the ejection port surface,
A structure for performing capping is provided. 63 is blade 61
Is an ink absorber provided adjacent to the blade 61.
Similarly to the above, the recording head is held in a form protruding into the movement path of the recording head. The blade 61, the cap 62, and the absorber 63 constitute an ejection recovery section 64, and the blade 61 and the absorber 63 remove water, dust, and the like from the ink ejection port surface.

Reference numeral 65 denotes a recording head which has ejection energy generating means and performs recording by ejecting ink to a recording material facing an ejection port surface provided with ejection ports, and 66 denotes a mounting of the recording head 65 and movement of the recording head 65. Is a carriage for performing the following. Carriage 66
Is slidably engaged with a guide shaft 67, and a part of the carriage 66 is connected to a belt 69 driven by a motor 68 (not shown). As a result, the carriage 66 can move along the guide shaft 67, and the recording head 65 can move the recording area and the area adjacent thereto.

Numeral 51 denotes a paper feed unit for inserting a recording material, and numeral 52 denotes a paper feed roller driven by a motor (not shown). With these configurations, the recording material is fed to a position facing the ejection port surface of the recording head, and as the recording proceeds, the discharge rollers 53
Is discharged to the paper discharge unit where.

In the above configuration, when the recording head 65 returns to the home position at the end of recording or the like, the cap 62 of the head recovery unit 64 is retracted from the movement path of the recording head 65, but the blade 61
Protrudes into the movement path. As a result, the recording head 65
Is wiped. When capping is performed with the cap 62 in contact with the ejection surface of the recording head 65,
The cap 62 moves so as to protrude into the movement path of the recording head.

When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as the position at the time of wiping described above. As a result, even in this movement, the ejection port surface of the recording head 65 is wiped.

The above-described movement of the print head to the home position is performed not only at the end of printing and at the time of ejection recovery, but also at predetermined intervals while the print head moves through the printing area for printing to the home position adjacent to the printing area. Then, the wiping is performed along with this movement.

FIG. 4 is a diagram showing an example of an ink cartridge containing ink supplied to the head via an ink supply tube. Here, reference numeral 40 denotes an ink bag storing the supply ink, and a rubber stopper 42 is provided at the tip of the ink bag. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. 44
Is an ink absorber for receiving waste ink.

The ink jet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated as described above, but is also suitably used in the one in which they are integrated as shown in FIG. .

In FIG. 5, reference numeral 70 denotes an ink jet cartridge, which contains an ink absorber impregnated with ink, and in which ink in the ink absorber is supplied from a head 71 having a plurality of orifices by ink droplets. Is discharged.

Reference numeral 72 denotes an air communication port for communicating the inside of the cartridge with the standby.

This ink jet cartridge 70 is used in place of the recording head shown in FIG. 3, and is detachable from the carriage 66.

(Examples) Next, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, "parts" and "%" are based on weight unless otherwise specified.

Example 1 (Preparation of pigment dispersion) Styrene-acrylic acid-ethyl acrylate copolymer (acid value 190, average molecular weight 15,700, Tg75 ° C) 2 parts Monoethanolamine 1.5 parts Ion-exchanged water 72.5 parts Diethylene glycol 5 parts And heated to 70 ° C in a water bath,
Dissolve the resin completely. 14 parts of carbon black (MCF-88, manufactured by Mitsubishi Kasei Corporation) and 5 parts of isopropyl alcohol were added to this solution, and after premixing for 30 minutes, a dispersion treatment was performed under the following conditions.

Disperser: Sand grinder (Igarashi Kikai Co., Ltd.) Grinding media: Zirconium beads (1 mm diameter) Filling ratio of grinding media: 50% (volume) Grinding time: 3 hours Further centrifugation (12000 rpm, 20 minutes) Then, coarse particles were removed to obtain a dispersion.

(Preparation of ink) 30 parts of the above dispersion 30 parts diethylene glycol 10 parts N-methylpyrrolidone 5 parts Styrene-methacrylic acid-ethyl acrylate copolymer monoethanolamine salt (acid value 162, average molecular weight 12200,
Tg76 ° C) 0.5 parts Isopropyl alcohol 5 parts Ion-exchanged water 49.5 parts The above ingredients are mixed, and the pH is adjusted to 8-ethanol with monoethanolamine.
Adjusted to 10 to obtain ink (A) of the present invention.

Example 2 (Preparation of pigment dispersion) Styrene-acrylic acid-butyl acrylate copolymer (acid value 195, average molecular weight 8000, Tg75 ° C) 3 parts Triethanolamine 2 parts Deionized water 68 parts Diethylene glycol 5 parts The above-mentioned components And heated to 70 ° C in a water bath,
Dissolve the resin completely. To this solution were added 5 parts of carbon black S170 (manufactured by Tegusa), 10 parts of MCF-88 (manufactured by Mitsubishi Kasei), and 7 parts of ethanol. After premixing for 30 minutes, the mixture was dispersed under the following conditions. Processing was performed.

Dispersing machine: Pearl mill (manufactured by Ashizawa Co., Ltd.) Grinding media: glass beads (1 mm diameter) Filling rate of grinding media: 50% (volume) Discharge speed: 100 ml / min. Further, centrifugation (12000 rpm, 20 minutes) is performed Then, coarse particles were removed to obtain a dispersion.

(Preparation of ink) 30 parts of the above dispersion 30 parts thiodiglyl 10 parts 1,3-dimethylimidazolidinone 10 parts Styrene-acrylic acid-butyl acrylate copolymer ammonium salt (acid value 189, average molecular weight 20,000, Tg74 ° C) 0.5 part 5 parts of ethanol 44.5 parts of ion-exchanged water Mix the above ingredients and adjust the pH to 8 to 8 with triethanolamine.
This was adjusted to 10 to obtain the ink (B) of the present invention.

Example 3 (Preparation of Pigment Dispersion) Styrene-acrylic acid-ethyl acrylate copolymer (acid value 168, average molecular weight 10100, Tg83 ° C) 3 parts Aminomethylpropanol 1.5 parts Ion-exchanged water 67.5 parts Diethylene glycol 5 parts And heated to 70 ° C in a water bath,
Dissolve the resin completely. 15 parts of carbon black MCF-88 (manufactured by Mitsubishi Kasei Corporation) and 5 parts of ethanol were added to this solution, and after premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Dispersing machine: Pearl mill (manufactured by Ashizawa Co., Ltd.) Grinding media: glass beads (1 mm diameter) Filling rate of grinding media: 50% (volume) Discharge speed: 100 ml / min. Further, centrifugation (12000 rpm, 20 minutes) is performed Then, coarse particles were removed to obtain a dispersion.

(Preparation of ink) 30 parts of the above dispersion liquid 20 parts of glycerin 5 parts of ethylene glycol 5 parts of ethanol 5 parts of ion-exchanged water 20 parts The above components were mixed, and the pH was adjusted to 8 to 10 with aminomethylpropanol. Ink (C) was obtained.

Example 4 (Preparation of Pigment Dispersion) Styrene-acrylic acid-α-methylstyrene-butyl methacrylate copolymer (acid value 205, average molecular weight 13000,
Tg72 ° C) 1 part Styrene-acrylic acid copolymer (acid value 180, average molecular weight 5000, Tg93 ° C) 3 parts Aminomethylpropanol 1.5 parts Ion-exchanged water 64.5 parts Diethylene glycol 5 parts Heated to
Dissolve the resin completely. To this solution, 10 parts of carbon black (MOGUL L, manufactured by Cabot Corporation), 8 parts of carbon black (REGAL660R, manufactured by Cabot Corporation), and 7 parts of ethanol were added, and after premixing for 30 minutes,
Dispersion processing was performed under the following conditions.

Disperser: Sand grinder (Igarashi Kikai Co., Ltd.) Grinding media: glass beads (1 mm diameter) Filling ratio of grinding media: 50% (volume) Grinding time: 3 hours Further centrifugation (12000 rpm, 20 minutes) Then, coarse particles were removed to obtain a dispersion.

(Preparation of ink) 30 parts of the above dispersion 30 parts of polyethylene glycol 300 15 parts of ethylene glycol 5 parts of ethanol 45 parts of ion-exchanged water After mixing the above components and adjusting the pH to 8 to 10 with aminomethylpropanol, The mixture was stirred for 1 hour to obtain the ink (D) of the present invention.

Comparative Example 1 In the composition of Example 1, the styrene-acrylic acid-ethyl acrylate copolymer used in the dispersion was replaced with the following water-soluble resin, and the other conditions were the same as in Example 1 to obtain a comparative example. Ink (E) was used.

Acrylic acid-butyl acrylate-methyl methacrylate copolymer (acid value 80, average molecular weight 10,000, Tg 48 ° C) Comparative Example 2 Styrene-acrylic acid-butyl acrylate copolymer used in the composition of Example 2 above An ink (F) of Comparative Example was obtained in the same manner as in Example 2 except that the coalesced product and the styrene-acrylic acid-butyl acrylate copolymer ammonium salt were replaced with the following water-soluble resin.

Acrylic acid-methacrylic acid-ethyl acrylate copolymer and its ammonium salt (acid value 110 average molecular weight 6000, T
g25 ° C.) Using the inks of the above Examples and Comparative Examples, the following tests were performed using an inkjet recording apparatus having an on-demand type multi-recording head.

T ₁ : Driving conditions and ejection stability Set the driving voltage to 25V, and set the frequency to 2KHz, 4
Under two conditions of KHz, printing was performed at room temperature, and the presence or absence of printing disorder, chipping, non-ejection, etc. was observed, and the ejection stability was evaluated.

A: Discharges cleanly from the first character, non-discharge during continuous printing,
There is no chipping or print disturbance.

B: The character portion was ejected in a clear manner, but several non-ejections occurred in the solid print portion.

C: Even in the character portion, when several characters are printed, non-ejection occurs, and the printing is disturbed to the extent that the characters cannot be read.

T ₂ : Clogging during reprinting after temporary stoppage of printing After filling the printer with the specified ink and printing alphanumeric characters continuously for 10 minutes, printing was stopped and left for 30 minutes without caps etc. Thereafter, alphanumeric characters were printed again, and determination was made based on the presence or absence of defective portions such as blurred or missing characters.

 A: There is no defective part from the first character.

 B: Part of the first character is blurred or missing.

 C: The first character cannot be printed at all.

T ₃ : Clogging recovery at the time of reprinting after printing is stopped for a long time After filling the printer with predetermined ink and printing alphanumeric characters continuously for 10 minutes, printing is stopped, and 60 ° C without cap etc. After standing for 10 days, a nozzle clogging recovery operation was performed, and the number of recovery operations until normal printing without character blurring, chipping, etc. was possible was determined.

 A: Normal printing is possible with 1 to 5 recovery operations.

 B: Normal printing is possible with 6 to 9 recovery operations.

 C: Normal printing is possible with 11 or more recovery operations.

T ₀ : Amount of dissolved water-soluble resin The obtained ink was centrifuged at 55,000 rpm for 5 hours with an ultra-high speed cooling centrifuge (manufactured by Beckman) to precipitate the pigment component and the resin component adsorbed on the pigment. After that, a certain amount of the supernatant is collected, dried and solidified in a vacuum dryer (60 ° C., 24 hours).
The percentage of the amount of the resin to the charged ink is calculated and defined as the residual resin concentration.

The evaluation results are shown in Table 1 below. For the evaluations in the table, the results based on the above criteria were described.

(Effect of the Invention) As described above, when applied to an ink jet printer, the ink of the present invention does not cause solidification of the ink at the tip of the head even when left for a long time, and is excellent in the robustness of printed matter. Needless to say, the density of the printed matter is high, and stable ejection can always be performed even when the driving conditions are changed or used for a long time, and the effect that the reliability is excellent is exhibited.

[Brief description of the drawings]

FIGS. 1-a and 1-b are a longitudinal sectional view and a transverse sectional view of a head portion of the ink jet recording apparatus. FIG. 2 is an external perspective view of a head obtained by multiplying the head shown in FIG. FIG. 3 is a perspective view showing an example of the ink jet recording apparatus. FIG. 4 is a longitudinal sectional view of the ink cartridge. FIG. 5 is a perspective view of the ink jet cartridge. 61: Wiping member 62: Cap 63: Ink absorber 64: Discharge recovery unit 65: Print head 66: Carriage

Claims (6)

(57) [Claims] An aqueous liquid composition comprising at least 3 to 20% by weight of carbon black, 10 to 90% by weight of water and 0.1 to 5% by weight of a water-soluble resin, wherein the water-soluble resin has a glass transition. A temperature (Tg) of 50 ° C. or more and an amount of the water-soluble resin dissolved in the composition of 2% by weight or less, wherein the ink for ink ejection uses thermal energy to eject ink. . 2. The ink-jet ink according to claim 1, wherein the ink-jet ink contains ethyl alcohol or isopropyl alcohol. 3. The ink-jet ink according to claim 1, wherein the pH value is in the range of 7 to 10. 4. The ink-jet ink according to claim 1, wherein the amount of the water-soluble resin dissolved in the composition is 1% by weight or less. 5. An ink jet recording method in which thermal energy is applied to ink to discharge the ink from an orifice, and the discharged ink is applied to a recording material to perform recording, wherein the ink is any one of claims 1 to 4. An ink jet recording method characterized by applying the above-described ink. 6. The ink jet recording method according to claim 5, wherein ink is ejected by an on-demand ink jet system.