JPH04126781A - Ink and method for ink jet recording using the same - Google Patents

Abstract

PURPOSE:To obtain an ink, excellent in preservation stability without solidifying at the tips of heads even when allowed to stand for a long period by blending two kinds of water-soluble resins having specific weight-average molecular weights in a specified proportion. CONSTITUTION:The objective ink is obtained by blending the first water-soluble resin, composed of monomers composed of styrene and/or derivatives thereof and monomers composed of (meth)acrylic acid, maleic acid and derivatives thereof and having 3000-20000 weight-average molecular weight and the second water-soluble resin having 20000-50000 weight-average molecular weight at (95:5)-(75:25) weight ratio of the first water-soluble resin : the second water-soluble resin in an amount of <=2wt.% dissolved therein with carbon black, a polyhydric alcohol and/or an alkyl ether thereof, an aliphatic monohydric alcohol and water.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an ink particularly suitable for an inkjet recording device, and more specifically to an ink for recording by ejecting ink from an orifice of a recording head by the action of thermal energy. The present invention relates to an ink and an inkjet recording method using the same.

(Prior Art and its Problems) In inkjet recording methods, proposals have been made to apply water-based pigment inks to inkjet recording in order to improve the water resistance and light resistance of recorded materials. Application of such water-based pigment inks has been tried and used in stationery such as ballpoint pens, but in order to put water-based pigment inks for stationery into practical use, it is necessary to improve dispersion stability, prevent ink from solidifying at the pen tip, and improve ballpoint pens. The main technical issue was preventing wear of the balls.

However, when conventional water-based pigment ink for stationery is used in an inkjet recording device that performs recording by ejecting recording liquid from the orifice of the recording head by the action of thermal energy, it causes significant problems in ejection stability. , which has the disadvantage of causing printing defects.

In particular, in inkjet recording devices that perform recording by ejecting droplets by applying thermal energy, when conventional water-based pigment ink for stationery is used, when a pulse is applied to the ink, the heat causes deposits to form on the thin film resistor. This results in the formation of particles, incomplete foaming of the ink, and the inability of droplet ejection to respond to applied pulses, resulting in non-ejection.

That is, in order to stably eject ink from the nozzle tip, the ink must be foamed to a desired volume on the thin film resistor, and
It must have the property of repeating foaming and defoaming in a desired amount of time, but since conventional water-based pigment inks for stationery do not satisfy these properties, they are inkjet ink that can be filled into an inkjet recording device and used for recording. If this is done, various inconveniences as described above will occur.

Furthermore, when using a dispersion system called pigment ink for inkjet recording, preventing solidification at the tip of the 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. This is a great point. In this respect as well, water-based pigment inks developed for conventional stationery do not provide sufficient reliability.

Furthermore, although some conventional water-based pigment inks have excellent ejection properties in a relatively short period of time, ejection failure may occur if the driving conditions of the recording head are changed or continuous ejection is performed for a long period of time. The problem also arises that it becomes stable and eventually stops being discharged.

In order to solve the problems of water-based pigment inks for ink-jet recording in the prior art as described above, the present inventors have already proposed the invention of water-based pigment ink for ink-jet recording.As a result, These inventions have made it possible for the first time to obtain ink with ejection stability suitable for inkjet recording devices.However,
There are still various insufficiencies in using these inks in an inkjet recording device, which is an actual product.

The first problem is that long-term storage stability in an ink cartridge, which is a container for storing ink, is not sufficient.

Therefore, the purpose of the present invention is to solve this problem, have excellent long-term storage stability, and at the same time, be able to always perform stable ejection even when the driving conditions of the device change or when used for a long time. An object of the present invention is to provide an ink for an inkjet recording device that eliminates the solidification of the ink.

The second problem with water-based pigment ink when used in an actual product inkjet recording device is the abrasion resistance of the printed matter, that is, the possibility of rubbing the printed matter against another paper, or rubbing the printed matter against another paper. Another problem is that when characters are traced over with a marker or the like, they become smudged.

Therefore, another object of the present invention is to provide an ink for an inkjet recording device that can improve the scratch resistance of the printed matter obtained.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides an ink containing carbon black, a water-soluble resin, a polyhydric alcohol and/or its alkyl ether, an aliphatic monohydric alcohol, and water, in which the amount of the water-soluble resin dissolved is 2% by weight. The water-soluble resin is at least one monomer selected from styrene and/or its derivatives, and one or more monomers selected from (meth)acrylic acid, maleic acid, and derivatives thereof. consisting of a weight average molecular weight of 3000 to 20
000, and the weight average molecular weight is 2.
0,000 to 50,000, and the weight ratio of the first water-soluble resin to the second water-soluble resin is 95:5 to 75:25; This is an inkjet recording method in which recording is performed by applying thermal energy to the ink and ejecting the ink as droplets from micropores.

(Function) By composing the water-soluble resin, which is one of the constituent components of the water-based pigment ink for inkjet recording, with two types of water-soluble resins having a specific weight average molecular weight in a specific ratio,
The ink of the present invention has excellent long-term storage stability, and does not solidify at the tip of the head even if left for a long time.

In addition, it has practical storage stability, and stable ejection is possible even when the driving conditions of the inkjet recording device vary or when the inkjet recording device is used for a long time.

Furthermore, the resulting printed matter not only has excellent fastness such as light resistance and water resistance, but also has excellent print quality with no problem in scratch resistance and practicality.

The essence of why the above-mentioned excellent actions and effects are exhibited in the ink of the present invention that uses two types of water-soluble resins with different weight average molecular weights is still not clear.
This is thought to be due to the following reasons.

First, since the first water-soluble resin has a low molecular weight, it has excellent adsorption properties to dispersed pigment particles having a small particle size.

On the other hand, the second water-soluble resin has a large molecular weight and is highly effective in adsorbing to pigment particles and increasing steric hindrance between particles to prevent agglomeration, thereby imparting weak structural viscosity to the ink and helping to prevent sedimentation. Also, for the same reason, when the ink is fixed on the recording paper, it is thought that it connects the particles and increases the binding property, contributing to the improvement of the scratch resistance.

As mentioned above, when two types of water-soluble resins with different weight average molecular weights are used in an ink, each resin exhibits functions according to its physical properties, so it is necessary to use a single resin with the average molecular weight of both. It is thought that superior functions will be exhibited that are different from those in the case where the

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments.

General physical properties required for ink for inkjet recording include particle formation performance, ejection properties, responsiveness, and the like. Therefore, from these points alone, it is preferable that the ink be a liquid with high surface tension and low viscosity.

However, when the solid content of an aqueous pigment dispersion ink is lowered to lower the viscosity, problems arise in that the print density becomes thinner, sedimentation occurs more quickly, and the printing performance and storage stability of the resulting prints deteriorate. - On the other hand, if the viscosity is increased (sedimentation is slowed down and the storage stability of the obtained printed matter is improved, but this causes other problems such as lowering of response frequency and deterioration of ejection stability).

Furthermore, the aqueous pigment inks for inkjet recording that have been proposed so far have a relatively small amount of resin component and have insufficient scratch resistance because the ink is fixed on the surface of the recording paper. On the other hand, if a friction-resistant binder is added, the abrasion resistance can be improved even if the ink is fixed on the surface of the recording paper. However, if the resin content is increased in this way, there is a problem that the discharge performance and responsiveness deteriorate.

The present inventors, in order to solve various problems of the prior art in water-based pigment ink for inkjet recording,
As a result of intensive research into dispersants that can improve storage stability and scratch resistance under the constraint of ensuring dischargeability with a dissolved water-soluble resin of 2% by weight or less, we found that two dispersants with different weight average molecular weights The inventors have discovered that the problems of the prior art can be solved by using different types of water-soluble resins as pigment dispersants, and have completed the present invention.

That is, the water-soluble resin contained as a dispersant for carbon black in the ink of the present invention is composed of two types: a first water-soluble resin and a second water-soluble resin as described below.

The above-mentioned first and second water-soluble resins are both copolymers of vinyl monomers, and the monomers contained as essential components in the water-soluble resin include 30 to 65% by weight of styrene monomers. and a carboxyl group-containing monomer in a range of 20 to 50% by weight.

The molecular weight of the first water-soluble resin is 3,000 to 20,000, preferably 5,000 to 12,000, and the molecular weight of the second water-soluble resin is 20,000 to 50,000, preferably 25,000 to 4,000, as measured by GPC in terms of styrene.
0000, and the weight ratio of the first water-soluble resin and the second water-soluble resin is 95:5 to 75:
The range is 25.

The styrenic monomers constituting the above water-soluble resin include:
For example, styrene, α-methylstyrene, vinyltoluene, etc. Examples of carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, and derivatives thereof include acrylic acid, methacrylic acid, maleic acid, and half esters of maleic acid. Examples of the alcohol component used for half-esterification include methanol, ethanol, propatool, n-butanol, and other higher alcohols.

In order to adjust physical properties such as softening point, the following monomers can be arbitrarily selected and copolymerized to be included in both the first and second water-soluble resins used in the present invention. , such monomers include 2-ethylhexyl acrylate, n-butyl acrylate, 4-hydroxybutyl acrylate, tert-butyl acrylate, methyl acrylate, ethyl acrylate, dimethylaminoethyl acrylate, 2-hydroxy acrylate, - (Meth)acrylic acid alkyl esters such as hydroxyethyl acrylate and methyl methacrylate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and isobutyl vinyl ether; N-vinylpyrrolidone, acrylamide, N-methylol acrylamide and the like.

The first and second water-soluble resins having two types of weight average molecular weights used in the present invention can be synthesized by solution polymerization using an ordinary radical initiator, and the molecular weight can be adjusted by using ethylene glycol as a solvent. , ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, etc., or by using known mercapto as a chain transfer agent. However, from the viewpoint of odor, the former is practically preferred.

The water-soluble resin having the above-mentioned structure is preferably contained in an amount of 0.1 to 5% by weight, more preferably 0.3 to 2% by weight, based on the total amount of the ink.

The carbon black used in the present invention includes No.
2300, No. 900, MCF88, No. 33
, No. 40, No. 45, No. 52,
MA? , MA8, #2200B (manufactured by Mitsubishi Kasei), RAVEN1255 (:lIO:/manufactured by Via), REGAL400R, REGAL330R, R
EGAL660R, MOGUL L (manufactured by Cabot), Co1or Black FWI, Co1
or BlackFWlg, Co1or Black
5170, Co1or Black 5150
Commercially available products such as , Pr1ntex 35, Pr1ntex U (manufactured by Degutsusa), and even products newly manufactured for the purpose of the present invention can be used. It is also possible to use two or more types of these carbon blacks in combination. The content of carbon black used in the present invention in the ink is preferably in the range of 3 to 20% by weight.

The ink of the present invention improves the solubility of water-soluble resin, and -
In order to make the layer excellent in long-term storage stability, it is preferable that the ink as a whole be adjusted to be neutral or alkaline. However, in this case, a strong alkali may cause corrosion of various members used in an inkjet recording device, so it is preferable that the pH is in the range of 7 to 10. The pH adjusters used in this case include amines or bases, various organic amines such as jetanolamine and triethanolamine, and alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide. Inorganic alkaline agents such as, organic acids, mineral acids, etc. are used.

As mentioned above, carbon black, water-soluble resin, amine, etc. are dispersed or dissolved in an aqueous medium.

A suitable aqueous medium for the ink of the present invention is a mixed solvent of water and a water-soluble organic solvent. It is preferable to do so.

In addition, water-soluble organic solvents used by mixing with water include:
For example, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, 5ec-butyl alcohol, tert-
Butyl alcohol, isobutyl alcohol, etc. with 1 carbon number
~4 alkyl alcohols; dimethylformamide,
Amides such as dimethylacetamide; ketones or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol, propylene glycol, butylene glycol , triethylene glycol, 1,2,6-hexadriol, thiodiglycol, hexylene glycol, diethylene glycol and other alkylene glycols containing 2 to 6 carbon atoms; glycerin; ethylene glycol monomethyl (or ethyl ) Lower alkyl ethers of polyhydric alcohols such as ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, 1,3-dimethyl-2=imidazolidinone etc.

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 preferred. Further, among these many water-soluble organic solvents, the alkaline regulator is an essential component, and is preferably contained in the ink of the present invention in an amount of 0.001 to 10% by weight based on the total ink.

In order to obtain even higher ejection stability in the ink of the present invention, it is effective to add an aliphatic monohydric alcohol such as ethyl alcohol or isopropyl alcohol to the aqueous medium at a ratio of 3% to 15% by weight. It is. This is considered to be because the addition of ethyl alcohol or isopropyl alcohol allows the ink to foam on the thin film resistor more stably. However, if too much ethyl alcohol or isopropyl alcohol is added, the quality of the printed matter will be impaired, so a more appropriate addition concentration is preferably 3% by weight to 10% by weight.

Another effect of adding ethyl alcohol or isopropyl alcohol to the dispersion liquid is that it suppresses the generation of bubbles during dispersion and enables efficient dispersion.

The content of the water-soluble organic solvent used in the ink of the present invention ranges from 3 to 50% by weight, preferably from 3 to 40% by weight, based on the total weight of the ink. or,
The water used ranges from 10 to 90% by weight, preferably from 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 with desired physical properties, surfactants, humectants, antifoaming agents, preservatives, etc. may be used as necessary. Alternatively, a commercially available water-soluble dye or the like may be added.

Incidentally, as the humectant, any conventionally used moisturizer can be used, but urea, thio base material, and their rust conductors are preferable. The amount added is in the range of 2 to 10% by weight, preferably 2 to 5% by weight, based on the total weight of the ink.

Examples of surfactants include anionic surfactants such as fatty acid salts, higher alcohol sulfate ester salts, liquid fatty oil sulfate ester salts, alkylaryl sulfonates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene alkyl ethers. There are nonionic surfactants such as oxyethylene 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. It is preferable to determine the amount of surfactant added. This is because if the surface tension of the ink is smaller than this, in the inkjet recording method of the present invention, undesirable situations such as print distortion (misalignment of the landing point of ink droplets on the recording paper) due to wetting of the nozzle tip may occur. This is because it will cause it.

Furthermore, another feature of the ink of the present invention is that the amount of water-soluble resin dissolved in the ink is 2% by weight or less, preferably 1% by weight or less, based on the total amount of the ink. As a result, inkjet recording is stable to heat, the ink foams accurately on the thin film resistor under any driving conditions of the recording device, and no deposits are generated on the thin film resistor even over long periods of time. It can be made into a useful ink.

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 predetermined amount of thermal energy is applied on the thin film resistor, or the excess water may be removed by the heat during pulse application. The water-soluble resin becomes an insoluble substance and is deposited on the thin film resistor, causing non-discharge and irregular printing.

Note that 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 creating the ink. Adjust to. Furthermore, if the pigment and water-soluble resin do not exist in the dispersion at a certain concentration or higher, dispersion cannot be performed efficiently and an optimal dispersion state cannot be obtained. Therefore, the total amount of the pigment and water-soluble resin in the dispersion is 10% or more as a standard, preferably 30%
% or less.

The method for preparing the ink of the present invention is to first add carbon black to an aqueous solution containing at least a water-soluble resin, an amine or a base, and water, stir it, and then disperse it using the dispersion means described below. Perform centrifugation according to the conditions to obtain the desired dispersion. Next, the components listed above are added to this dispersion and stirred to obtain the ink of the present invention.

In particular, the amount of dissolved water-soluble resin that is not adsorbed to the pigment is 2
In order to keep it below weight%, in the ink preparation method,
60% of an aqueous solution containing a water-soluble resin, amine or base, and water.
It is necessary to completely dissolve the resin in advance by stirring at a temperature of at least 30 minutes.

Further, it is necessary to add the amount of amine or base that dissolves the resin at least 1.2 times the amount determined by calculating the acid value of the water-soluble resin. The amount of amine or base is determined by the following formula.

Amount of amine or base (g) = Acid value of resin x Molecular weight of amine or base x Amount of resin (g) Furthermore, it is also necessary to perform premixing for at least 30 minutes 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. Further, as the base, sodium hydroxide, lithium hydroxide, potassium hydroxide, etc. are preferable.

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, a sand mill, and the like. Among these, high-speed sand mills are particularly preferred, and examples thereof 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 pigments 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 the discharge speed. Methods such as pulverization and classification using a filter, centrifuge, etc. are used, or a combination thereof.

In addition, as a method for measuring the amount of unadsorbed resin according to the present invention, the pigment component and the resin component adsorbed to the pigment are precipitated using an ultracentrifuge, and the amount of residual resin contained in this supernatant liquid is determined. TOC (Total Organic Carbon,
A total organic carbon meter), a gravimetric method (a method in which the supernatant is evaporated to dryness and the amount of resin is measured), etc. are preferably used.

The ink of the present invention is particularly suitable for use in an inkjet recording method 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.

Apparatuses suitable for performing recording using the ink of the present invention include an apparatus that applies thermal energy corresponding to a recording signal to the ink in the chamber of a recording head, and generates droplets using the thermal energy.

Examples of the head configuration, which is the main part, are shown in Figures 1-a and 1-b.
As shown in FIG.

The head 13 is made by bonding a glass, ceramic, or plastic plate, etc., having grooves 14 through which ink passes, and a heat-generating head 15 (the head is shown in the figure, but is not limited thereto) used for thermal recording. It can be obtained by

The heat generating head 15 has a protective film 1 formed of oxidized silicon or the like.
6. It consists of 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.

The ink 21 has reached a discharge orifice (micropore) 22, and a meniscus 23 is formed 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 suddenly generates heat, bubbles are generated in the ink 21 in contact with this area, and the pressure causes a meniscus. 23 protrudes, the ink 21 is ejected, becomes a recording droplet 24 from the orifice 22, and flies toward the recording material 25. FIG. 2 shows an external view of a multi-head in which a large number of heads shown in FIG. 1-a are arranged. The multi-head is manufactured by closely adhering a glass plate 27 having multi-grooves 26 and a heating head 28 similar to that explained in FIG. 1-a.

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

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

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, forming a cantilever shape. 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 moving direction 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 blade 61 and 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 denotes a recording head which has an ejection energy generating means and performs recording by ejecting ink onto a recording material facing the ejection orifice surface on which the ejection ports are arranged, and 66 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 6 driven by a motor 68.
9 (not shown). As a result, carriage 6
6 can be moved along the guide shaft 67, and the recording head 65 can move the recording area and its adjacent area.

Reference numeral 51 represents a paper feeding section for inserting recording material, and reference numeral 52 represents 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 is completed, the cap 62 of the head recovery section 64
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,
During this movement as well, 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 performed at the end of printing or when ejection is restored. 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:
It can be suitably used not only in the case where the head and ink cartridge are separate bodies as described above, but also in one in which they are integrated as shown in FIG.

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 shown in FIG. 3, and is detachable from the carriage 66.

(Example) Next, the present invention will be explained in more detail by giving examples and comparative examples. It should be noted that the terms in the text or % are based on weight unless otherwise specified.

Example 1 (Preparation of pigment dispersion) Styrene-acrylic acid-ethyl acrylate copolymer (weight ratio 50/35/15. Weight average molecular weight 9000)
3.0 parts styrene-acrylic acid-butyl acrylate copolymer (weight ratio 40/35/25, weight average molecular weight 32,000) 0.
5 parts monoethanolamine 2.0 parts ion exchange water 66.5 parts ethylene glycol 5. Part O: Mix the above ingredients,
Heat to 70°C in a water bath to completely dissolve the resin. Add carbon black (Mogul-L) to this solution.
, made by Cabrac ■) and 5 parts of ethanol were added.
After premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Dispersion machine: Sand grinder (manufactured by Igarashi Kikai ■) Grinding media: Glass peas (1 mm diameter) Filling rate of grinding media: 250% (volume) Grinding time: 4 hours After dispersion, centrifugation treatment (1200 Orpm, 30 minutes) was performed. , coarse particles were removed to prepare a dispersion.

(Preparation of ink) Above dispersion 30 parts diethylene glycol 10 parts ethylene glycol 5 parts ethanol
5 parts ion exchange water
50 parts of the above components were mixed, and the pH was adjusted to a range of 8 to 10 using monoethanolamine to obtain an ink (A) of the present invention.

Example 2 (Preparation of pigment dispersion) Styrene-α-methylstyrene-acrylic acid copolymer (
Molar ratio 45/20/35, weight average molecular weight 3000)
2.0 parts styrene-acrylic acid-
Butyl acrylate copolymer (weight ratio 35/35/30,
Weight average molecular weight 45000) 0.
5 parts Monoethanolamine 1.5 parts Ion-exchanged water 68.0 parts Ethylene glycol 5.0 parts A dispersion liquid was prepared in the same manner as in Example 1 except that carbon black was changed to MAloo (manufactured by Mitsubishi Kasei ■).

(Preparation of ink) Above dispersion 30 parts triethylene glycol 2 parts ethylene glycol 5 parts ethanol
5 parts ion exchange water
40 parts of the above components were mixed and the pH was adjusted to a range of 8 to 1O with monoethanolamine to obtain an ink (B) of the present invention.

Example 3 (Preparation of pigment dispersion) Styrene-maleic acid butyl alcohol half ester copolymer (weight ratio 55/45, weight average molecular weight 16)
000) 2.5 parts styrene-methacrylic acid-2-hydroxyethyl acrylate copolymer (weight ratio 35150/15, weight average molecular weight 50000
) 0.5 part monoethanolamine
2.0 parts ion exchange water 7
0.0 part ethylene glycol 5 parts Carbon black MCF-88 (manufactured by Mitsubishi Kasei ■) 15
A dispersion liquid was prepared in the same manner as in Example 1 except that the amount was changed to

(Preparation of ink) Above dispersion 30 parts diethylene glycol 20 parts thiodiglycol 7 parts ethanol
5 parts ion exchange water
38 parts of the above components were mixed, and the pH was adjusted to a range of 8 to 1O with monoethanolamine to obtain an ink (C) of the present invention.

Example 4 (Preparation of pigment dispersion) Styrene-methacrylic acid copolymer (weight ratio 7°/30,
Weight average molecular weight 18500) 3.0 parts Styrene-acrylic acid-2-hydroxyethyl acrylate-2-hydroxymethyl acrylate copolymer (weight ratio 50/3
0/IO/10, weight average molecular weight 29000)
0.5 part monoethanolamine
2.0 parts ion exchange water 66.5
Part ethylene glycol 5 parts Carbon black REGAL 660R (manufactured by Cabot ■)
A dispersion liquid was prepared in the same manner as in Example 1 except that .

(Preparation of ink) Above dispersion 30 parts triethylene glycol 20 parts 1,3-dimethylimidazolidinone 7 parts isopropyl alcohol
5 parts ion exchange water
38 parts of the above components were mixed and the pH was adjusted to a range of 8 to 10 using monoethanolamine to obtain an ink (D) of the present invention.

Comparative Example 1 In place of the two types of water-soluble resins in Example 1 above, 3 parts of styrene-acrylic acid-ethyl acrylate copolymer (weight ratio 15150/35, weight average molecular weight 3300) of one type of water-soluble resin An ink (E) of a comparative example was obtained in the same manner as in Example 1 except that

Comparative Example 2 In place of the two types of water-soluble resins in Example 1, styrene-acrylic acid-acrylic butyl copolymer (weight ratio 35/35/30, weight average molecular weight 32,000)3.
Ink (F) of a comparative example was obtained in the same manner as in Example 1 except that 0 parts of one kind of water-soluble resin was used.

(Evaluation) Using the inks of the above Examples and Comparative Examples, the following tests were conducted using an ink jet recording apparatus having a bubble jet recording head.

To: Amount of dissolved water-soluble resin
After centrifuging at 55,000 rpm for 5 hours to precipitate the pigment and the resin adsorbed on the pigment, a certain amount of the supernatant was collected and dried and solidified in a vacuum dryer (60° C., 24 hours). From this amount of resin, the percentage with respect to the charged ink is calculated and used as the residual resin concentration.

T1; Driving conditions and ejection stability The driving voltage is set to 25V, and the frequency is 2KH at each voltage.
Printing is performed at room temperature under two conditions: z and 4KHz.
The presence or absence of irregularities in printing, chipping, non-ejection, etc. was observed to evaluate ejection stability.

Discharges cleanly from the A knee character, fails to discharge during continuous printing,
There are no chips or irregularities in printing.

B: Letters were ejected clearly, but ejection failure occurred at several locations in solid print areas.

C: Even in the character part, when printing is performed in several places, non-ejection occurs, and the print becomes irregular (to the extent that the characters are impossible to read).

T2: Long-term storage ability A predetermined amount of each ink was injected and filled into an ink cassette (ink cassette for Canon bubble jet printer BJ-130), stored at 60°C for 3 months, and then the change in viscosity of the ink was measured. Observe the formation of precipitate.

Viscosity change; A: The viscosity change is ±1 cps or less.

B: Viscosity change is greater than ±1 cps, ±3 cps
It is as follows.

C: Viscosity change is greater than ±3 cps.

Precipitate generation; A: No precipitate was observed.

B: A slight amount of sediment is seen inside the bag, but there is no problem in practical use.

C: A large amount of precipitate was formed.

Ts: Scratchability The characters of the printed matter were slowly rubbed with an orange PILOT fluorescent spot lighter (manufactured by Pilot ■) to determine the stains around the characters, and the scratchability was evaluated as 1 or less.

8; There is no staining around the letters.

B: Stain is observed.

C: Significant staining occurred.

The evaluation results are shown in the table below. The evaluation in the table is based on the above criteria (results are listed).

Low Nl: Low (Evaluation Results) (Effects of the Invention) As explained above, when the ink of the present invention is applied to an inkjet printer, the ink does not solidify at the tip of the head even if left for a long time. .

Further, the ink of the present invention has practical storage stability and can be stably ejected even under fluctuations in driving conditions and long-term use.

Furthermore, the ink of the present invention has excellent reliability, and the printed matter obtained not only has excellent fastness such as light resistance and water resistance, but also has excellent practicality without any problems in scratch resistance. It can be done as a thing.

[Brief explanation of drawings]

1-a and 1-b are a vertical 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, and FIG. 5 is a perspective view of the inkjet cartridge. 61: Wiping member 62: Cap 63, Ink absorber 64: Ejection recovery section 65: Recording head 66: Carriage 1. -a Figure 2 Figure 4 Figure 5

Claims (8)

[Claims] (1) In the ink containing carbon black, a water-soluble resin, a polyhydric alcohol and/or its alkyl ether, an aliphatic monohydric alcohol, and water, the amount of the water-soluble resin dissolved is 2% by weight or less. , the water-soluble resin consists of at least one monomer selected from styrene and/or its derivatives, and one or more monomers selected from (meth)acrylic acid, maleic acid, and derivatives thereof. , a first water-soluble resin having a weight average molecular weight of 3,000 to 20,000; and a first water-soluble resin having a weight average molecular weight of 20,000 to 20,000.
50,000, and the weight ratio of the first water-soluble resin and the second water-soluble resin is 95:
An ink having a ratio of 5 to 75:25. (2) The ink according to claim 1, wherein the aliphatic monohydric alcohol is ethyl alcohol or isopropyl alcohol. (3) Content of aliphatic monohydric alcohol is 3 to 15% by weight
The ink according to claim 1, which is within the range of . (4) The ink according to claim 1, wherein the content of the polyhydric alcohol and/or its alkyl ether is in the range of 10 to 50% by weight. (5) In an inkjet recording method in which recording is performed by applying thermal energy to ink according to a recording signal and ejecting the ink as droplets from micropores, the ink may include carbon black, water-soluble resin, polyhydric alcohol, etc. or an alkyl ether thereof, an aliphatic monohydric alcohol, and water, and the amount of the water-soluble resin dissolved therein is 2% by weight or less, and the water-soluble resin contains at least styrene and/or A first compound having a weight average molecular weight of 3,000 to 20,000 and comprising one or more monomers selected from derivatives thereof and one or more monomers selected from (meth)acrylic acid, maleic acid, and derivatives thereof. It consists of a water-soluble resin and a second water-soluble resin having a weight average molecular weight of 20,000 to 50,000, and the weight ratio of the first water-soluble resin to the second water-soluble resin is 95:5 to 75:25. An inkjet recording method characterized by: (6) The inkjet recording method according to claim 5, wherein the aliphatic monohydric alcohol is ethyl alcohol or isopropyl alcohol. (7) Content of aliphatic monohydric alcohol is 3 to 15% by weight
The inkjet recording method according to claim 5, which falls within the range of. (8) The inkjet recording method according to claim 5, wherein the content of the polyhydric alcohol and/or its alkyl ether is in the range of 10 to 50% by weight.