JPH0418462A - Ink and method for ink jet recording with the same - Google Patents

Abstract

PURPOSE:To provide an ink giving printed products having excellent fastness (abrasion resistance) and high concentrations stably jetted for long periods even when driving conditions are changed, by adding specific amounts of a pigment and a microemulsion containing particles having specific particle sizes to an aqueous medium. CONSTITUTION:The objective ink contains a pigment and 0.5-10wt.% of a microemulsion having an average particle size of <=50nm in an aqueous medium [preferably water or a water-soluble organic solvent including a polyhydric alcohol (alkyl ether) and an aliphatic monohydric alcohol]. <=2wt.% of a water- soluble resin (preferably having a weight-average mol.wt. of 3000-30000) is preferably contained as a dispersing agent of the pigment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ink particularly suitable for inkjet printers, and furthermore, the present invention relates to ink suitable for inkjet printers, and furthermore, the present invention relates to an ink suitable for inkjet printers, and furthermore, ink droplets are ejected and blown from an orifice of a recording head by the action of thermal energy to print on uncoated paper. , relates to an inkjet recording method for recording on so-called plain paper.

[Conventional technology]

The inksheet recording method has the advantages of generating less noise during recording (and by using a highly integrated head, high-resolution recorded images can be obtained at high speed).

In such inkjet recording methods, various water-soluble dyes dissolved in water or a mixture of water and an organic solvent are used as inks.However, when water-soluble dyes are used, these Since the water-soluble dyes originally have poor light resistance, the light resistance of recorded images often becomes a problem.

Furthermore, since the ink is water-soluble, water resistance of recorded images often becomes a problem. That is, if a recorded image is exposed to rain, sweat, or drinking water, the recorded image may smudge or disappear.

On the other hand, similar problems exist in stationery using dyes such as hole pens, and various water-based pigment inks for stationery have been proposed to solve the problems of light resistance and water resistance. In order to put water-based pigment ink into practical use, examples of studies investigating dispersion stability, prevention of ink solidification at the pen tip, and prevention of wear on the ball of a ballpoint pen include JP-A-58-80368 and JP-A-61-200182. Publication, JP-A-61-24
7774, JP 61-272278, JP 62-568, JP 62-10167], JP 1011672, JP 1-249869
No. 1, No. 1-301760, and the like. Recently, hole pens and markers using water-based pigment inks have come onto the market as products.

[Problem that the invention seeks to solve]

However, when conventional water-based pigment ink for stationery is used in an inkjet recording device that performs recording by ejecting and flying ink droplets from the orifice of the recording head by the action of thermal energy, the ejection stability is significantly impaired. There was a drawback that printing defects occurred. In particular, when conventional pigment ink is used for recording by ejecting droplets by applying thermal energy, when a pulse is applied to the ink, the heat causes deposits to form on the thin film resistor, causing the ink to eject. Foaming may be incomplete and droplet ejection may not respond to the applied pulse, resulting in non-ejection. In other words,
In order for ink to be stably ejected from the nozzle tip, the ink must have the ability to foam to the desired volume on the thin film resistor and also have the ability to repeat foaming and defoaming in the desired time. However, since conventional stationery inks do not satisfy these performance requirements, various inconveniences as described above occur when an inkjet recording device is filled with the inks and used for recording.

In addition, as mentioned above, when using pigment ink as previously proposed for ink sheet recording, the fastness of printed matter is significantly improved compared to that using dye ink, but subsequent research has shown that A problem arose in that the abrasion resistance, particularly the scratch resistance, of the printed material was inferior to that printed using dye ink. In particular, if the pigment concentration is increased to increase print density, or if printing is done with ink designed to leave the pigment on the surface of the paper without penetrating, problems with the abrasion resistance of the printed material become serious. However, there is an inconvenience in that the printed matter is contaminated when rubbed with an eraser or strongly by hand.

On the other hand, to increase wear resistance, it is used for pigment dispersion.
It is possible to increase the content of the aqueous dispersion resin, but
This method has the disadvantage that the ink ejection stability is significantly impaired for reasons described below. Furthermore, by changing the type or amount of the solvent that makes up the ink, we can increase the permeability of the ink.
Although it is possible to improve abrasion resistance by penetrating pigment into paper, this is undesirable because it reduces the density of printed matter.

Furthermore, although some conventional water-based pigment inks have excellent ejection properties in a relatively short period of time, ejection becomes unstable when the driving conditions of the print head are changed or continuous ejection is performed for a long period of time. Eventually, the problem arises that it stops being discharged.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above, to achieve high density of printed matter when printed on non-coated paper, to have excellent abrasion resistance (scratch resistance), and to achieve ( The purpose of the present invention is to provide an ink with excellent long-term storage stability.

Another object of the present invention is to provide an ink that, when applied to an inkjet printer, can provide stable ejection at all times even when driving conditions fluctuate and the ink is used for long periods of time.

A further object of the present invention is to provide an inkjet recording method that enables stable high-speed recording at all times and that provides printed matter with excellent water resistance and light resistance when printed on uncoated paper.

[Means and effects for solving the problems] The above objects are achieved by the present invention as described below. That is, the present invention provides an ink containing a pigment and a microemulsion in an aqueous medium, the microemulsion having an average particle diameter of 50
nm or less, and its content is 0.5 nm or less based on the total weight of the ink.
Inkjet is an ink characterized by having a content in the range of 5 to 10% by weight, and performs recording by ejecting the ink as droplets from micropores by applying thermal energy to the ink according to a recording signal. This is a recording method.

The present invention will be explained in detail below.

The present inventors have intensively studied ways to increase the abrasion resistance (scratch resistance) of printed matter by inkjet recording using aqueous pigment inks, and have found that, among other things, 1) the average particle diameter is 5.
By using a microemulsion with a particle size of 0 nm or less, preferably 10 nm or more, and 2) furthermore, the content of the microemulsion being 0.5 to 10% (by weight) of the total weight of the ink, the abrasion resistance of printed matter can be improved. high quality, high print density,
Moreover, it was discovered that an ink with good dispersion stability could be obtained, leading to the present invention.

In general, microemulsions have high film properties, and by adding them to ink, they can provide prints with good abrasion resistance even on non-absorbing recording media.

However, when pigment ink containing microemulsions is created and ejected using an inkjet recording device, printing defects often occur depending on the ink creation conditions, making it impossible to obtain good printed matter. The inventors of the present invention conducted extensive research and found that the average particle size of the microemulsion added to the ink has a large effect on the ejection stability of the ink, leading to the present invention.

The inkjet recording device used in the present invention has a side of 5
Ink is ejected from fine ejection holes of 0 μm or less, and a filter of several microns is usually installed between the ink tank and the nozzle to prevent contaminants from clogging the tips of the ejection holes and causing ejection failure. is attached.

On the other hand, the pigment ink of the present invention is 0.2 μm to 0.05 μm.
It is composed of a dispersion of pigment molecules with a particle size of approximately 1.5 m and a dispersion resin, an aqueous solvent, and ion-exchanged water, etc. When a microemulsion is added to this, the number of particles in the ink increases and the ink becomes thicker. These particles interfere with each other as they pass through the filter, resulting in −
It is thought that the ink cannot pass through the filter at times, resulting in non-ejection.

In particular, the inkjet recording device used in the present invention is
Since the device is driven at a high frequency of 2 KHz or more, there is a very high possibility that such a phenomenon will occur.

Therefore, the present inventors investigated an ink that could prevent such phenomena and also have good abrasion resistance for printed matter.
It has been found that when the particle size of the microemulsion added is 50 nm or less, the occurrence of non-ejection is improved.

As the microemulsion used in the present invention, any microemulsion can be used as long as it is dispersed in water and satisfies the above performance.As a commercially available product, PB-300 (average particle size 2
3.1 nm), EAS-2 (average particle size 22 nm)
) (manufactured by Kao Corporation), and when newly created, the method is to use a hydrophobic monomer such as styrene, α-methylstyrene, or methyl methacrylate, and styrene sulfonic acid or vinylbenzenesulfonic acid. , vinyltoluenesulfonic acid, sulfonithyl methacrylate,
2-acrylamide 2-methylpropanesulfonic acid, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, acrylotrile, acrylamide, 4-vinylpyridine, N
%N-dimethylaminoethyl methacrylate, N5N-dimethylaminoethyl methacrylate monoester of maleic acid, etc. are dispersed in a water medium using potassium persulfate as an initiator using a soap-free emulsion polymerization method. Examples include methods for obtaining copolymers.

The amount of microemulsion used in the present invention is preferably in the range of 0.5 to 10% by weight based on the total ink. If the amount added is less than 0.5%, there will be no effect on abrasion resistance, and if it exceeds 10%, there will be the problem that a film will be formed during storage of the ink. Furthermore, it is preferably in the range of 1% to 5%.

The average particle diameter of the microemulsion can be measured using a particle size distribution measuring device that applies a dynamic light scattering method using laser light. The amount of pigment used in the present invention is preferably 3 to 20% by weight, preferably 3 to 12% by weight based on the total ink.

As the pigment used in the present invention, all conventionally known organic and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, general azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioisico pigments, isoindolinone pigments, quinophthaloni pigments, etc. Cyclic pigments, dye lakes such as basic dye lakes and acid dye lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, daylight fluorescent pigments, titanium oxide, iron oxide, carbon black, etc. Inorganic pigments include: Furthermore, any pigment not listed in the color index can be used as long as it can be dispersed in water.

In the present invention, the water-soluble resin (
As a dispersion resin), the weight average molecular weight is 3000 to 30
000 is preferable from the viewpoint of maintaining dispersion stability and reducing the viscosity of the ink. Furthermore, preferably 50
Anything in the range of 00 to 15,000 can be used, including styrene-acrylic acid copolymer, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer, styrene-maleic acid copolymer. Acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, vinyl Examples include naphthalene-maleic acid copolymers and salts thereof.

Various methods can be used to measure the weight average molecular weight of a water-soluble resin, but it is generally measured by GPC (Köl permeation chromatography) or the like.

The water-soluble resin is 0.1 to 5% by weight based on the total amount of ink,
It is preferably contained in a range of 0.3 to 2% by weight.

In the ink of the present invention, preferably the entire ink is adjusted to be neutral or alkaline, which improves the solubility of the water-soluble resin and provides a recording liquid with excellent long-term storage stability of the layer. Therefore, it is desirable. However, in this case, it is preferable that the pH be within the range of 7 to 10 since it may cause corrosion of various members used in the ink sheet recording device.

Examples of pH adjusting agents include various organic amines such as jetanolamine and triethanolamine, inorganic alkaline agents such as alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, organic acids, , mineral acids. As described above, the pigment and water-soluble resin are dispersed or dissolved in the water-soluble medium.

A suitable aqueous medium for the ink of the present invention is a mixed solvent of water and a water-soluble organic solvent, and as water, ion-exchanged water (deionized water) is used instead of ordinary water containing various ions. is preferred.

Examples of water-soluble organic solvents used in combination with water include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, 5eC-butyl alcohol, tert-buty alcohol, and isobutyl alcohol. Alkyl alcohols having 1-4 carbon atoms; amides such as dimethylformamide and dimethylacetamide; ketone or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylenes such as polyethylene glycol and polypropylene glycol Glycols; alkylene groups containing 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexandriol, thiodiglycol, hexylene glycol, diethylene glycol, etc. Glycols; glycerin; lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, Examples include 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 preferred.

Among these many water-soluble organic solvents, organic amine water is contained as an essential component in the ink of the present invention, preferably in an amount of 0.001 to IO% by weight of the entire ink.

In addition, the above-mentioned water-soluble organic solvents other than organic amines are selected as desired and are contained in appropriate amounts, but among them, polyhydric alcohols such as diethylene glycol, polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of alcohols are preferred.

Furthermore, in order to prevent the ink from solidifying at the nozzle tip during use and storage of the head, it is preferable that the content of polyhydric alcohol be 10% or more. moreover,
It has been found that it is effective to add 3% by weight or more of aliphatic monohydric alcohol, such as ethanol or isopropyl alcohol, in order to obtain stability in ejection. This is thought to be because the addition of these solvents allows the ink to foam on the thin film resistor more stably. However, adding too much of these solvents has the disadvantage of impairing the quality of printed matter, so a more appropriate concentration of these solvents is 3 to 10% by weight.
It is. Further, as an effect of these solvents, by adding these solvents to the dispersion liquid, generation of bubbles can be suppressed during dispersion, and efficient dispersion can be performed.

The content of the water-soluble organic solvent in the ink of the present invention is 10 to 50% by weight, preferably 10 to 40% by weight of the total weight of the ink.
% by weight, and the water used is 10% of the total weight of the ink.
-90% by weight, preferably 30-90% by weight.

In addition to the above-mentioned components, the ink of the present invention may contain surfactants, antifoaming agents, preservatives, etc., if necessary, in order to make the ink have desired physical properties. Commercially available water-soluble dyes can also be added.

Examples of surfactants include fatty acid salts, higher alcohol sulfate ester salts, liquid fatty oil sulfate ester salts, anionic surfactants such as alkylaryl sulfonates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxy There are nonionic surfactants such as ethylene sorbitan alkyl esters, and one or more of these can be appropriately selected and used.

The amount used varies depending on the dispersant, but it is preferably 0.01 to 5% by weight based on the total amount of the ink. At this time, it is preferable to determine the amount of the activator 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 exhibits a value smaller than this, in a recording method such as the present invention, undesirable situations such as print distortion (deviation of the landing point of ink droplets) due to wetting of the nozzle tip will occur. It is.

In general, the performance required for inkjet inks includes physical properties such as viscosity, surface tension, and pH, but in dispersion systems such as water-based pigment inks, even if these physical properties are satisfied, the ink's Foaming was often unstable.

Therefore, the present inventors conducted extensive research on the performance of water-based pigment inks that are thermally stable and capable of optimal foaming. It has been found that by setting the amount to 2% or less, preferably 1% or less, the ink foams accurately on the resistor under various driving conditions, and furthermore, no deposits are generated on the thin film resistor even over a long period of time. In other words, if there is a large amount of excess water-soluble resin in the ink relative to the pigment, the ink may not foam even if a certain amount of thermal energy is applied on the thin film resistor, or the excess water may be absorbed by the heat during pulse application. The water-soluble resin becomes an insoluble substance and accumulates on the thin film resistor, causing non-discharge and irregular printing.

The dissolved water-soluble resin refers to a resin that is not adsorbed to the pigment in the ink but is dissolved in the liquid medium. One way to reduce the amount of dissolved water-soluble resin is to adjust the ratio of pigment to water-soluble resin to a weight ratio of 3:1 to 10:1, preferably 10:3 to 10:1 when preparing the ink. It's about adjusting.

Further, the total amount of carbon black and water-soluble resin in the dispersion is preferably 10% or more, preferably 30% or less on a weight basis. The reason for this is that unless a certain concentration or higher of carbon black and water-soluble resin are present in the dispersion liquid, dispersion cannot be carried out efficiently and an optimum dispersion state cannot be obtained.

The method for producing the ink of the present invention is to first add a pigment to an aqueous solution containing at least a dispersion resin, an amine, and water, stir it, then disperse it using the dispersion means described below, and if necessary, centrifuge it. Treatment is carried out to obtain the desired dispersion. Next, the components listed above including the microemulsion are added to this dispersion and stirred to form an ink.

In particular, in order to reduce the amount of water-soluble resin dissolved in the ink (resin that is not adsorbed to the pigment) to 2% or less, in the preparation method, an aqueous solution containing resin, amine, and water is heated at 60°C or higher for 3 minutes. It is necessary to completely dissolve the resin in advance by stirring as described above.

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

The acid value of the resin is the amount of KOH (mg) that neutralizes the resin.
).

Furthermore, it is also necessary to perform 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 adsorption of the resin onto the pigment surface.

The amines added to the dispersion include monoethanolamine, jetanolamine, triethanolamine,
Organic amines such as aminomethylpropertool and ammonia are preferred.

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

Among these, high-speed sand mills are preferred, and examples include super mills, sand grinders, bead mills, agitator mills, grain mills, Dyno mills, pearl mills, and cobol mills (all trade names).

In the present invention, methods for obtaining a pigment having a desired particle size distribution include reducing the size of the grinding media of the dispersion machine, increasing the filling rate of the grinding media, lengthening the processing time, and slowing down the discharge speed. After crushing, methods such as classification using a filter or centrifugal separation are used. or a combination of these methods.

The method of measuring the amount of water-soluble resin dissolved in the ink according to the present invention is to precipitate the pigment component and the resin component adsorbed to the pigment using an ultracentrifuge or the like, and then collect the supernatant liquid. TOC (Total Or
(ganic carbon, total organic carbon meter), gravimetric method (method in which the supernatant is evaporated to dryness and the amount of resin is measured), etc. are preferably used.

The recording liquid of the present invention is particularly suitable for use in an inkjet recording system in which recording is performed by ejecting droplets under the action of thermal energy, but it goes without saying that it can also be used for general writing instruments.

A suitable recording device for recording using the ink of the present invention includes a device that applies thermal energy corresponding to a recording signal to a recording liquid in a chamber of a recording head and generates droplets using the energy.

An example of the configuration of the head, which is the main part, is shown in FIG. 1(a).

(b), shown in FIG.

The head 13 includes a glass, ceramic, or plastic plate having grooves 14 through which ink passes, and a heat generating head 15 used for thermal recording (a thin film head is shown in the figure, but is not limited to this). Obtained by gluing. The heating head 15 includes a protective film 16 made of silicon oxide or the like, aluminum electrodes 17-1, 17-2, a heating resistor layer 18 made of nichrome or the like, a heat storage layer 19, and a substrate 20 with good heat dissipation properties such as alumina. It consists of

The ink 21 has reached a discharge orifice (micropore) 22, and a meniscus 23 is formed by the pressure P.

Now, electrode 17-1. When an electrical signal is applied to 17-2,
The area indicated by n of the heating head 15 suddenly generates heat, bubbles are generated in the ink 21 in contact with this area, the meniscus 23 protrudes due to the pressure, and the ink 21 is ejected from the orifice 22 and becomes a recording droplet 24. It flies toward the recording medium 25. FIG. 2 shows an external view of the multi-head shown in FIG. 1(a) in which a large number of heads are arranged. The multi-head is assembled by bonding a glass plate 27 having multi-grooves 26 and a heating head 28 similar to that described in FIG. 1(a).

Note that FIG. 1(a) shows the head 13 along the ink flow path.
FIG. 1(b) is a sectional view taken along A-B in FIG. 1(a).
This is a cut plane along a line.

An example of an ink jet recording apparatus incorporating the head according to FIG. 3 is shown.

In FIG. 3, 61 is a blade as a wiping member, one end of which is held by a blade holding member and becomes a fixed end in the form of a cantilever. The blade 61 is disposed adjacent to the recording area of the recording head, and in this example, is held in a protruding form in the movement path of the recording head. A cap 62 is disposed at a home position adjacent to the blade 61, and is configured to move in a direction perpendicular to the direction of movement of the recording head and come into contact with the ejection port surface to perform capping. Furthermore, 63 is an ink absorber provided adjacent to the blade 61;
Like the blade 61, it is held in a protruding form in the movement path of the recording head. The above blade 61° cap 62
The absorber 63 constitutes an ejection recovery section 64, and the blade 61 and the absorber 63 remove moisture, dust, etc. from the ink ejection orifice surface.

Reference numeral 65 is a recording head that has an ejection energy generating means and performs recording by ejecting ink onto a recording material facing the ejection orifice surface on which ejection ports are arranged, and 66 is a recording head that mounts the print head 65 and moves the print head 65. It is a carriage for carrying out. The carriage 66 is slidably engaged with a guide shaft 67, and a portion of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. This allows the carriage 66 to move along the guide shaft 67, allowing the recording head 65 to move the recording area and its adjacent area.

Reference numeral 51 denotes a paper feeding section for inserting a recording material, and 52 a paper feed roller driven by a motor (not shown). With these configurations, the recording material is fed to a position facing the ejection opening surface of the recording head, and as recording progresses, the recording material is discharged to a paper discharge section provided with a paper discharge roller 53.

In the above configuration, when the recording head 65 returns to the home position after recording ends, etc., the cap 6 of the head recovery section 64
2 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port surface of the recording head 65 is wiped. Note that when the cap 62 contacts the ejection surface of the recording head 65 to perform capping, 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 in the same position as the wiping position described above. As a result, even during this movement, the ejection orifice surface of the recording head 65 is wiped.

The above-mentioned movement of the print head to the home position is not only done at the end of printing or when ejection is restored (also, while the print head moves to the print area for printing, it moves to the home position adjacent to the print area at predetermined intervals). 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, 40 is an ink bag containing supply ink, and a rubber stopper 42 is provided at the tip of the ink bag. By inserting a needle (not shown) into this plug 42,
The ink in the ink bag 40 can be supplied to the head. 44 is an ink absorber that receives waste ink.

The inkjet recording device used in the present invention includes:
The head and ink cartridge are not limited to separate units as described above, but a unit in which they are integrated as shown in FIG. 5 may also be suitably used.

In FIG. 5, 70 is an inkjet cartridge, which houses an ink absorber impregnated with ink. It is configured to be discharged as

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

This inkjet cartridge 70 is used in place of the recording head 65 shown in FIG. 3, and is detachable from the carriage 66.

〔Example〕

Next, the present invention will be specifically explained with reference to Examples.

Example 1 (Preparation of pigment dispersion) Styrene-acrylic acid-ethyl acrylate copolymer
5 parts (acid value 153, average molecular weight 10,000) monoethanolamine 1.5 parts ion exchange water
68.5 parts ethylene glycol
Mix 5 parts of the above ingredients and 7 parts in a water bath.
Heat to 0°C to completely dissolve the resin. At this time, if the concentration of the resin to be dissolved is low, it may not be completely dissolved, so when dissolving the resin, a high concentration solution may be prepared in advance and diluted to prepare the desired resin solution. Carbon black (MCF88, manufactured by Mitsubishi Kasei) 1
After adding 5 parts and 5 parts of ethanol and performing premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Dispersion machine...Sand grinder (manufactured by Igarashi Kikai) Grinding media...Zirconium beads 1mm 1 Filling rate of grinding media...50% (volume) Grinding time...3
Centrifugation treatment (1200 ORPM, 20 minutes) was further performed to remove coarse particles and obtain a dispersion.

(Preparation of ink) Above dispersion 50 parts ethylene glycol 8 parts diethylene glycol 10 parts ethanol
4 parts p PB-3001% ion exchange water 27 parts The above components were mixed and stirred for 1 hour to obtain ink (A).

Example 2 (Preparation of pigment dispersion) Styrene-maleic acid half ester-maleic anhydride copolymer 8 parts (acid value 2
05, average molecular weight 7000) Aminomethyl propatool 4 parts Ion-exchanged water 56 parts Diethylene glycol 5 parts The above components were mixed and heated to 70°C in a water bath to completely dissolve the resin component. To this solution, 20 parts of carbon black (SB6, manufactured by Degutsusa) and 7 parts of ethanol were added, premixing was performed for 30 minutes, and then dispersion treatment was performed under the following conditions.

Dispersion machine...Pearl mill (manufactured by Ashizawa) grinding media/
...Glass Peas l m Filling rate of m-diameter grinding media...50% (volume) Discharge speed -100 mj! /m
in.

Further, centrifugation treatment (1200 ORPM, 20 minutes) was performed to remove coarse particles and obtain a dispersion.

(Creating ink) The above dispersion EG300 Ethylene glycol ethanol PB-300 ion exchange water Mix the above ingredients, 30 copies Part 6 Call 10 copies 5th part Part 3 46 copies Stir for 1 hour, ink (B) I got it.

Example 3 (Preparation of pigment dispersion) Styrene-acrylic acid-butyl acrylate copolymer
6 parts (acid value 137, average molecular weight 11400) monoethanolamine 3 parts ion exchange water
66 parts ethylene glycol
Mix 5 parts of the above ingredients and soak in a water bath for 70 min.
Heat to ℃ to completely dissolve the resin. Add copper phthalocyanine blue (Heliogen Blue) to this solution.
D6700T.

After adding 15 parts (manufactured by BASF) and 5 parts of ethanol and performing premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Disperser: Sand grinder (manufactured by Igarashi Kikai) Grinding media: Zirconium beads 1 mm Filling rate of post-grinding media: 50% (volume) Grinding time:
- Centrifugation treatment (12,000 RPM, 20 minutes) was further performed for 3 hours to remove coarse particles and obtain a dispersion.

(Preparation of ink) Above dispersion 35 parts ethylene glycol 20 parts ethanol
4 parts EAS - 21 parts ion-exchanged water 58 parts The above components were mixed and stirred for 1 hour to obtain ink (C).

Comparative Example 1 PB-300 contained in the ink of Example 1 was replaced with E-5.
Ink (D) was obtained using the same formulation as in Example 1, except that ink was replaced with No. 5 (manufactured by Seiko Kagaku, emulsion of styrene acrylic acid copolymer, average particle size 139 nm).

Comparative Example 2 PB-300 contained in the ink of Example 2 was converted to E-2
Ink (E) was obtained using the same formulation as in Example 2, except that the ink was replaced with No. 34 (manufactured by Seiko Kagaku, emulsion made of styrene acrylic acid copolymer, average particle size 88 nm).

Comparative Example 3 An ink (
F) was obtained.

Comparative Example 4 Ink (G) was obtained using the same formulation as in Example 3, except that the content of PB-300 contained in the ink in Example 3 was changed to 0.2 parts.

Using each of the above inks, the following tests were conducted using a recording apparatus having an on-demand multi-head that ejects ink by applying thermal energy to the ink according to a recording signal.

Furthermore, the average particle size of the microemulsion was determined by ELS-
800 (electrophoretic light scattering photometer, manufactured by Otsuka Electronics).

TI= Driving conditions and ejection stability The driving voltage was set to 25V and 30V, and printing was performed at room temperature under two conditions at each voltage and a frequency of 2KHz.
The ejection stability was evaluated by observing the presence or absence of irregularities in printing, chipping, and non-ejection.

It discharges cleanly from the first Al character, and there are no discharge failures, chips, or print disturbances during continuous printing.

B: Letters are ejected neatly, but ejection failures are observed in several areas in solid print areas.

C: Significant disturbance in ejection occurs from the first character, making it impossible to read the printed matter.

T2: Test of abrasion resistance (scratch resistance) of printed matter NP-D
BJ130 printer for K paper and XEROX4024 paper (
Use an eraser (
Rub 5 times back and forth with a pressing force of 50g using Lion 8501).
The optical density before and after the test is measured using a Macbeth densitometer (RD918), and the residual rate is calculated.

T3: Long-term ink storage test After storing each ink at 40° C. for 4 weeks, visually observe the amount of precipitate attached to the bottom of the storage bottle.

A: No precipitate was observed.

B: A slight amount of precipitate is observed at the bottom of the bottle, but there is no practical problem. C: A large amount of precipitate is formed, and a film is formed on the surface of the ink.

TO: Amount of dissolved water-soluble resin The obtained ink was centrifuged at 5500 rpm for 5 hours using an ultra-high-speed refrigerated centrifuge (manufactured by Beckman) to sediment the pigment and the resin adsorbed on the pigment. A certain amount of the supernatant liquid is collected and dried and solidified in a vacuum dryer (60° C., 24 hours). The percentage of this resin amount to the charged ink is calculated and determined as the residual resin concentration.

Note that Table 1 describes the performance of the microemulsion used in this experiment. Furthermore, the evaluation results are shown in Table 2. Regarding the evaluations in the table, for T1 the ejection stability was the result based on the above criteria, for T2 the residual rate of the reflection density of the printed matter before and after the test, and for T3 the result of visual observation.

Table 1 Average particle size of microemulsion Table 2 Evaluation results [Effects] As explained above, the ink of the present invention has excellent fastness (scratch resistance) of printed matter when applied to inksheet printers. Of course, the density of printed matter is high (
, it is possible to always perform stable ejection even when driving conditions fluctuate or when used for a long time, and it also has the effect of being excellent in long-term storage stability.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are a longitudinal cross-sectional view and a cross-sectional view of a head section of an inkjet recording apparatus. FIG. 2 is an external perspective view of a multi-head head shown in FIG. 1. FIG. 3 is a perspective view showing an example of an inkjet recording device. FIG. 4 is a longitudinal sectional view of the ink cartridge. FIG. 5 is a perspective view of the inksheet cartridge. 61... Wiping member 62... Cap 63... Ink absorber 64... Ejection recovery section 65... Recording head 66... Carriage error diagram (b) error? mouth

Claims (12)

[Claims] (1) An ink containing a pigment and a microemulsion in an aqueous medium, in which the average particle diameter of the microemulsion is 50 nm or less, and the content thereof is in the range of 0.5 to 10% by weight of the total weight of the ink. An ink characterized by: (2) Claim (1) containing a water-soluble resin as a pigment dispersant
). (3) The amount of the water-soluble resin dissolved in the ink is 2
The ink according to claim 2, wherein the amount is not more than % by weight. (4) The ink according to claim (1), wherein the aqueous medium contains water and a water-soluble organic solvent. (5) The ink according to (4), wherein the water-soluble organic solvent contains a polyhydric alcohol and/or an alkyl ether thereof and an aliphatic monohydric alcohol. (6) The weight average molecular weight of the water-soluble resin is 3000 to 3
The ink according to claim (2), which is in the range of 0,000. (7) In an inkjet recording method in which recording is performed by ejecting ink as droplets from micropores by applying thermal energy to the ink according to a recording signal, the ink forms a pigment and a microemulsion in an aqueous medium. An inkjet recording method, characterized in that the average particle diameter of the microemulsion is 50 nm or less, and the content thereof is in the range of 0.5 to 10% by weight based on the total weight of the ink. (8) The inkjet recording method according to (7), wherein the ink contains a water-soluble resin as a pigment dispersant. (9) The amount of the water-soluble resin dissolved in the ink is
The inkjet recording method according to claim 8, wherein the content is 2% by weight or less. (10) The inkjet recording method according to (7), wherein the aqueous medium of the ink contains water and a water-soluble organic solvent. (11) The water-soluble organic solvent is a polyhydric alcohol and/or
or an alkyl ether thereof and an aliphatic monohydric alcohol. (12) The inkjet recording method according to item (8), wherein the weight average molecular weight of the water-soluble resin in the ink is in the range of 3,000 to 30,000.