JPH10237367A - Ink for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject ink capable of improving stability of dispersion into water, fixity of luster of image and prevention of nozzle clogging while maintaining high blackness and water resistance of carbon black, by mixing water with carbon black and a polyethyleneimine. SOLUTION: This ink comprises at least (A) water, (B) carbon black fine particles having >=1.5mmol/g surface active hydrogen content [e.g. having 20-200nm dispersion average particle diameter in ink, obtained by oxidizing acidic carbon black with a hypohalite in water] and (C) a polyethyleneimine (e.g. having 200-10,000 molecular weight). Preferably the ink contains 1-20wt.% based on the total of ink of the component C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous pigment ink applied to an ink jet recording method for performing recording by discharging from an ejection orifice and flying as droplets.

[0002]

2. Description of the Related Art Among the various recording methods known at present, a non-impact recording method with almost no noise during recording, high-speed recording is possible, and no special fixing process is required for plain paper. Attention has been paid to an ink jet recording method as a recording method capable of performing recording.

[0003] As an ink jet recording ink, an aqueous dye ink in which a water-soluble dye is dissolved in an aqueous medium is generally employed. When inkjet recording is performed using such an aqueous dye ink, the obtained recorded image is affected by the physical properties of the water-soluble dye, and its water resistance,
There is a disadvantage that the light resistance is poor. In particular, in the case of black ink, since there are few water-soluble dyes having good black color reproducibility, a black ink is made by mixing a plurality of dyes. There is a problem that the color tone changes. Further, the storage stability of the ink itself containing such a water-soluble dye is not so high.

Therefore, recently, an attempt has been made to apply an aqueous ink using a pigment such as carbon black to the ink jet recording system in place of such a dye-based ink. Since carbon black is insoluble in water, it is excellent in water resistance as compared with water-soluble dyes, and also excellent in light resistance.

[0005]

However, since carbon black does not dissolve in water, which is the medium of the ink, there arises a problem that it is difficult to finely disperse the carbon black in an aqueous medium and secure its stability. . Also, if a dispersant such as a water-soluble resin is added to improve the dispersion stability of carbon black, nozzle clogging may occur, or the viscosity may cause problems such as instability in continuous ejection. I will.

In order to solve such a problem, Japanese Patent Application Laid-Open No. H8-3498 discloses a method of adding a dispersant such as a water-soluble resin by using carbon black having a specific amount of surface active hydrogen. And that good water dispersibility can be obtained.

However, such a water-based ink in which carbon black is dispersed has a problem that the glossiness of an image is insufficient. The problem is that when a color image is reproduced together with the color ink, the image becomes matte black and the image becomes uncomfortable. Further, when an image is immersed in water, there arises a problem that carbon black is detached from the surface of the paper. This is presumably because the dye binds to the paper at the molecular level, whereas the carbon black has only a small amount of particles attached to the paper surface, and thus has a lower binding force to the paper than the dye.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an ink jet recording ink capable of obtaining an image having a high degree of blackening and excellent light fastness and water fastness.

Another object of the present invention is to provide an ink jet recording ink which is excellent in water dispersibility of fine particles dispersed in the ink and is capable of obtaining an image having excellent gloss and fixability. Things.

[0010]

SUMMARY OF THE INVENTION The present invention relates to an ink jet recording ink containing at least water, carbon black fine particles having a surface active hydrogen content of 1.5 mmol / g or more, and polyethyleneimine.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous pigment ink of the present invention contains at least water, fine carbon black particles and polyethyleneimine. The present invention provides a high effect particularly when used for a black pigment such as carbon black. When the present invention is used, while maintaining a high degree of blackening and water resistance of carbon black, the dispersion stability in water, the resulting image gloss and fixability without causing problems such as nozzle clogging. Can be improved. In the ink of the present invention, the carbon black has a surface active hydrogen content of 1.
Carbon black of 5 mmol / g or more is used.
Since carbon black having such a surface active hydrogen content has many hydroxyl groups and carboxyl groups having active hydrogen on the surface, the hydrophilicity of the carbon black itself is improved, and the surface area is further increased, such as a water-soluble dye. It is considered that it has chemical properties and has good water dispersibility.
The preferred surface active hydrogen content of carbon black is 1.
5 to 5.0 mmol / g, more preferably 2.0 to 5.0 mmol / g.
５5.0 mmol / g. If the surface active hydrogen content is below the above range, the dispersion stability of the carbon black particles in water becomes insufficient, and if the surface active hydrogen content exceeds the above range, the water dispersibility is the same, but the production cost is undesirably high.

The surface active hydrogen content of carbon black is measured by the Tweil method as follows. First, all the active hydrogens on the carbon black are exchanged for methyl groups by dropping a diethyl ether solution of diazomethane on the carbon black. Hydrocarbon iodide having a specific gravity of 1.7 is added to this carbon black, and the mixture is heated to vaporize methyl groups as methyl iodide. This gas of methyl iodide is trapped by a silver nitrate solution and precipitated as methyl silver iodide. The amount of methyl groups, ie, the amount of active hydrogen, is determined from the weight of the precipitate.

By using the above-mentioned carbon black, the dispersion average particle size of the carbon black fine particles in the ink is 20 to 200 nm, preferably 20 to 150 n.
m, more preferably 30 to 100 nm. If the dispersion average particle size of the carbon black is larger than 200 nm, sedimentation of the carbon black is likely to occur, and the temporal stability of the ink is impaired.

The carbon black used in the present invention is:
It is preferably produced by further oxidizing acidic carbon black with hypohalite in water. The carbon black thus produced has good dispersibility even without a dispersant, so that clogging of the ink nozzle portion is less likely to occur, and a clear image with a high degree of blackening can be obtained.

The acidic carbon black is a carbon black having a carboxyl group on the particle surface, and preferably has a pH of 6 or less, preferably 4 or less. The acidic carbon black is generally prepared by an oxidation method using an oxidizing agent (eg, nitric acid, ozone, hydrogen peroxide, nitrogen oxide, or the like), or a surface modification method such as a plasma treatment for a color such as furnace black. Obtained by appropriately oxidizing carbon black.

In order to further oxidize the acidic carbon black, a hypohalite is used. Specific examples include sodium hypochlorite and potassium hypochlorite, and sodium hypochlorite is particularly preferred in terms of reactivity. The oxidation of acidic carbon black is generally carried out by charging acidic carbon black and hypohalite having an effective halogen concentration of 10 to 30% with respect to the weight of carbon black in an appropriate amount of water for 5 hours or more, preferably 10 to 10 hours. 15 hours, 50 ° C
As mentioned above, it is preferably carried out by stirring at 95 to 105 ° C. The carbon black thus obtained is:
It has a surface active hydrogen content of 5 mmol / g or more.

Next, the product is filtered, and by-product salts are removed by washing with ion-exchanged water. Further, purification and concentration are performed using a separation membrane having a pore size of 0.01 μm or less such as a reverse osmosis membrane or an ultrafiltration membrane. The concentration is generally performed so that the carbon black content becomes a concentrated pigment dispersion of about 10 to 30% by weight with respect to water.

As described above, the surface active hydrogen content is 1.
Carbon black having an amount of 5 mmol / g or more is excellent in water dispersibility. However, there is a problem that an image obtained by an aqueous ink using this carbon black has insufficient gloss and fixability. Normally, when a water-soluble resin used as a dispersant for carbon black is added, glossiness and fixability are improved, but the effect of using the above carbon black, particularly nozzle clogging, is impaired.

The ink of the present invention has an improved fixability of carbon black on the paper surface by adding polyethyleneimine to the aqueous medium in addition to the carbon black particles. In addition, polyethyleneimine has a lower molecular weight than a water-soluble resin or the like, so that the ability to prevent clogging of the nozzle can be improved, and the gloss of an image by carbon black can be improved. In addition, since polyethyleneimine also has a chelating action and an antibacterial action, it also has an effect of improving the stability of the ink, such as the antifungal property of the aqueous ink.

The polyethyleneimine used in the present invention is a linear polymer represented by the following formula:-[CH ₂ CH ₂ NH]-, which has a branched chain containing a primary, secondary, or tertiary amino nitrogen. You may have. Usually, commercially available polyethyleneimine is a compound having a branch in the polymerization of ethyleneimine.
Polyethyleneimine having a molecular weight of 200 to 10,000, particularly 250 to 2,000 is preferably used. As long as the molecular weight is in this range and water-soluble, it can be used regardless of the degree of branching. Examples of the polyethyleneimine that can be used in the present invention include “Epomin” (registered trademark) SP-series manufactured by Nippon Shokubai Co., Ltd., those obtained by reacting polyethyleneimine with ethylene oxide, those obtained by reacting alcohol or amine, and the like. And derivatives thereof.

Polyethyleneimine is contained in the ink of the present invention in an amount of 1 to 20% by weight, preferably 3 to 15% by weight. If the amount of polyethyleneimine is less than 1% by weight, the effect of the present invention cannot be obtained. If the amount is more than 20% by weight, the viscosity of the ink becomes too high, so that the ink flight response and replenishment are reduced, and the fixing speed is slow. Is not preferred. The ink of the present invention may contain various known organic solvents and additives in addition to the water, carbon black and polyethyleneimine described above. It is preferable to include a water-soluble organic solvent in order to adjust the moisturizing property, surface tension, viscosity, drying speed and the like of the ink. As the water-soluble organic solvent, one having 1 carbon atom such as ethanol, isopropanol and butanol.
To 4 alkyl alcohols, alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol and triethylene glycol, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether and triethylene glycol Lower alkyl ethers of alkylene glycols such as monobutyl ether, pyrrolidones such as 2-pyrrolidone and N-methyl-2-pyrrolidone, glycerin and the like can be used. When these water-soluble organic solvents are contained, they are preferably contained in an amount of 1 to 30% by weight based on the total amount of the ink.

Further, resin fine particles having an ionic group may be added to the ink of the present invention. Such resin fine particles are excellent in dispersibility in an aqueous medium which is an ink medium and can improve abrasion resistance of an obtained image without causing a problem such as nozzle clogging. As the fine resin particles, any resin having an ionic group on its surface may be used. For example, various resins such as a polyester resin, a vinyl polymer, a polyurethane resin, a styrene resin, and a styrene-acryl copolymer are used. be able to. Examples of the ionic group include a sulfonic acid group, a carboxylic acid group, a sulfuric acid group, a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, an alkali metal base or an ammonium base thereof, and a primary to tertiary amine group. Examples thereof include an alkali metal carboxylate, an ammonium carboxylate, an alkali metal sulfonic acid and an ammonium sulfonate, and particularly preferred are an alkali metal sulfonate and an ammonium sulfonate in view of the stability of aqueous dispersion. . The introduction of the ionic group described above may be achieved by adding a monomer having an ionic group during the synthesis of the resin fine particles.

The fine resin particles have an average particle size of 0.0
It is desirable to use one having a thickness of 1 to 1.0 μm, preferably 0.03 to 0.8 μm, more preferably 0.05 to 0.6 μm. This is because if the average particle size is small, the effect of improving the friction resistance is reduced, and if the average particle size is large, the aqueous dispersion stability of the resin fine particles after long-term storage tends to be low. The resin fine particles are 0.01 to
It is preferable to contain 15% by weight, preferably 0.1 to 10% by weight, more preferably 0.2 to 5% by weight. If the content of the resin particles is too large, the nozzle may be clogged or the degree of blackening of the image may be reduced. If the content is too small, the effect of the addition becomes insufficient.

Further, a small amount of a water-soluble polymer compound may be contained so as to prevent clogging in order to impart glossiness to the image and improve fixability. Examples of the water-soluble polymer compound include polyvinylpyrrolidone, a water-soluble acrylic resin, polyvinyl alcohol, and polysaccharides.

It is preferable that the pH of the ink is adjusted to 8 to 10 in order to improve the storage stability of the ink. NaHCO ₃ , Na ₂ B ₄ O ₇ ,
Examples thereof include alkanolamines such as ethanolamine, diethanolamine and triethanolamine, and hydroxides of alkali metals such as potassium hydroxide and lithium hydroxide.

Further, the water-based pigment ink of the present invention contains a known viscosity modifier, a fungicide and a rust inhibitor, an ultraviolet absorber, an antioxidant, a dispersant, a dispersion stabilizer, a surfactant, a metal ion sequestration. An additive such as an agent (chelating agent) can be appropriately selected and used in an appropriate amount.

The water-based ink of the present invention, when used for recording by an ink jet system, is excellent in the fastness (light fastness and water fastness) of characters and figures recorded on a paper surface, and can be used even when immersed again in water. It does not flow out and has excellent fixability, does not fade even when exposed to sunlight, and has excellent light fastness. Further, it is excellent in glossiness required when a color image is reproduced in combination with a color ink.

[0028]

【Example】

(Production Example 1 of Carbon Black Dispersion) Carbon Black (MA-100, PH 3.5, manufactured by Mitsubishi Chemical Corporation) 300
g was thoroughly mixed with 1000 ml of water, and 450 g of sodium hypochlorite (effective chlorine concentration: 12%) was added dropwise thereto.
The mixture was stirred at 100 to 105 ° C for 10 hours. The obtained slurry was filtered and washed with water. This pigment wet cake is added to water 30
The suspension was re-dispersed in 00 ml and desalted with a reverse osmosis membrane until the electrolysis reached 0.2 μs. Further, this pigment dispersion was concentrated to a pigment concentration of 20% by weight to obtain a carbon black dispersion A.

The resulting carbon black dispersion was acidified with aqueous hydrochloric acid, purified again by membrane, concentrated, dried and pulverized to obtain carbon black powder. The surface active hydrogen content of this carbon black was 2.8 mmol / g.

(Production Example 2 of Carbon Black Dispersion) After 300 g of carbon black (MA-8, PH 3.5, manufactured by Mitsubishi Chemical Corporation) was well mixed in 1000 ml of water, sodium hypochlorite (effective chlorine concentration) was added thereto. (12%) 450 g was added dropwise, and the mixture was stirred at 100 to 105 ° C for 8 hours. The obtained slurry was filtered and washed with water. This pigment wet cake was redispersed in 3000 ml of water, and desalted with a reverse osmosis membrane until the electrolysis reached 0.2 μs. Further, this pigment dispersion was concentrated to a pigment concentration of 20% by weight to obtain a carbon black dispersion B.

A powder of carbon black was obtained from the obtained carbon black dispersion in the same manner as in Production Example 1.
The surface active hydrogen content of this carbon black is 2.5 m
mol / g.

(Production Example of Resin Fine Particle Dispersion) In an autoclave equipped with a thermometer and a stirrer, 130 parts by weight of dimethyl terephthalate, 56 parts by weight of dimethyl isophthalate, 6 parts by weight of dimethyl ester of sodium sulfoisophthalate, and 159 of ethylene glycol Parts by weight, 30 parts by weight of tricyclodecane dimethanol and 0.1 part by weight of tetrabutoxytitanate are charged at 180 to 230 ° C. and 120 parts by weight.
The mixture was heated for one minute to perform a transesterification reaction. Then, the temperature of the reaction system was raised to 240 ° C., and the reaction was continued at a system pressure of 1 to 10 mmHg for 60 minutes to obtain a copolymerized polyester resin A. Next, 340 parts by weight of the obtained polyester resin, 150 parts by weight of methyl ethyl ketone, tetrahydrofuran 1
After dissolving 40 parts by weight at 80 ° C., water 680 at 80 ° C.
Was added to obtain an aqueous microdispersion of a copolymerized polyester having an average particle size of about 0.15 μm. Further, the obtained aqueous microdispersion was placed in a distillation flask and the fraction temperature was 100 ° C.
, And after cooling, water was added to bring the solids concentration to 1
0 wt% to obtain a resin fine particle dispersion.

Example 1 Carbon black dispersion A5
0 g, 2-pyrrolidone 8 g, isopropyl alcohol 2
g and 9 g of polyethyleneimine having a molecular weight of 600 (Epomin SP-006; manufactured by Nippon Shokubai Co., Ltd.) to obtain a water-based pigment ink by further adding water to make the total amount 100 g. The dispersion average particle size of carbon black in this ink was 150 nm. The average particle size of the carbon black was measured using a laser light diffusion type particle size distribution analyzer.

Next, when an image printed with this ink using an ink jet recording apparatus (MJ500C; manufactured by Epson Corporation) was immersed in water, it showed no flow of the pigment and was excellent in fixability. When the image was visually evaluated, the degree of blackening and the glossiness were satisfactory. Further, the ink ejection property was stable, the ink did not solidify in the nozzles, and no ejection failure occurred even in a print test several hours later. Further, even if this ink was stored at 50 ° C. for one month, no precipitate was generated, and even when a printing test was performed using this ink, the ejection of the ink was stable.

Example 2 Carbon black dispersion A5
0 g, 2-pyrrolidone 8 g, isopropyl alcohol 2
g and 6 g of polyethyleneimine having a molecular weight of 1200 (Epomin SP-012; manufactured by Nippon Shokubai Co., Ltd.) to obtain a water-based pigment ink by further adding water to make the total amount 100 g. The dispersion average particle size of carbon black in this ink was 150 nm.

The obtained ink was printed in the same manner as in Example 1, and the obtained image was immersed in water. As a result, there was no flow of the pigment and the fixability was excellent. When the image was visually evaluated, the degree of blackening and the glossiness were satisfactory.
Further, the ink ejection property was stable, the ink did not solidify in the nozzles, and no ejection failure occurred even in a print test several hours later. Also, apply this ink to 50
No precipitate was generated even after storage at 1 ° C. for one month, and the ejection of the ink was stable even in a printing test using this ink.

Example 3 Carbon black dispersion B5
0 g, 2-pyrrolidone 8 g, isopropyl alcohol 2
g and 6 g of polyethyleneimine having a molecular weight of 600 (Epomin SP-006; manufactured by Nippon Shokubai Co., Ltd.) to obtain a water-based pigment ink by further adding water to make the total amount 100 g. The dispersion average particle size of carbon black in this ink was 100 nm.

The obtained ink was printed in the same manner as in Example 1, and the obtained image was immersed in water. As a result, there was no flow of the pigment and the fixability was excellent. When the image was visually evaluated, the degree of blackening and the glossiness were satisfactory.
Further, the ink ejection property was stable, the ink did not solidify in the nozzles, and no ejection failure occurred even in a print test several hours later. Also, apply this ink to 50
No precipitate was generated even after storage at 1 ° C. for one month, and the ejection of the ink was stable even in a printing test using this ink.

Example 4 Carbon Black Dispersion A5
0 g, resin fine particle dispersion 10 g, 2-pyrrolidone 8 g,
Water was further added to 2 g of isopropyl alcohol and 9 g of polyethyleneimine having a molecular weight of 600 (Epomin SP-006; manufactured by Nippon Shokubai Co., Ltd.) to make the total amount 100 g, whereby an aqueous pigment ink was obtained. The dispersion average particle size of carbon black in this ink was 150 nm.

The obtained ink was printed in the same manner as in Example 1, and the obtained image was immersed in water. As a result, there was no flow of the pigment and the fixability was excellent. When the image was visually evaluated, the degree of blackening and the glossiness were satisfactory.
Further, the ink ejection property was stable, the ink did not solidify in the nozzles, and no ejection failure occurred even in a print test several hours later. Also, apply this ink to 50
No precipitate was generated even after storage at 1 ° C. for one month, and the ejection of the ink was stable even in a printing test using this ink. Further, even if the obtained image was strongly rubbed with a finger, the image was not disturbed and had excellent wear resistance.

Comparative Example 1 Carbon Black Dispersion A5
An aqueous pigment ink was obtained by further adding water to 0 g, 8 g of 2-pyrrolidone and 2 g of isopropyl alcohol to make the total amount 100 g.

The obtained ink was printed in the same manner as in Example 1, and when the obtained image was immersed in water, the flow of the pigment occurred and the fixability was poor. When the image was visually evaluated, the degree of blackening was satisfactory, but the glossiness was insufficient.

Comparative Example 2 Carbon Black Dispersion B5
An aqueous pigment ink was obtained by further adding water to 0 g, 8 g of 2-pyrrolidone and 2 g of isopropyl alcohol to make the total amount 100 g.

The obtained ink was printed in the same manner as in Example 1. When the obtained image was immersed in water, the flow of the pigment occurred, and the fixability was poor. When the image was visually evaluated, the degree of blackening was satisfactory, but the glossiness was insufficient.

Comparative Example 3 Carbon black (MA10
0, active hydrogen content 0.13 mmol / g, manufactured by Mitsubishi Chemical Corporation) 10 g, 2-pyrrolidone 8 g, isopropyl alcohol 2 g, and 6 g of polyethyleneimine having a molecular weight of 600 (Epomin SP-006; manufactured by Nippon Shokubai Co., Ltd.). The total amount was adjusted to 100 g to obtain an aqueous pigment ink. When the obtained ink was allowed to stand for more than ten minutes,
The supernatant was generated due to the sedimentation of the carbon black, and printing was impossible.

[0046]

According to the present invention, it is possible to provide an ink jet recording ink capable of obtaining an image having a high degree of blackening and excellent light fastness and water fastness.

Further, according to the present invention, it is possible to provide an ink jet recording ink which is excellent in water dispersibility of fine particles dispersed in the ink and has excellent gloss and fixability.

Claims (4)

[Claims] 1. An ink jet recording ink comprising at least water, carbon black fine particles having a surface active hydrogen content of 1.5 mmol / g or more, and polyethyleneimine. 2. The polyethyleneimine having a molecular weight of 20.
The ink for inkjet recording according to claim 1, wherein the number is from 0 to 10,000. 3. The ink for inkjet recording according to claim 2, wherein the content of the polyethyleneimine is 1 to 20% by weight based on the total amount of the ink. 4. The ink jet recording ink according to claim 1, wherein the dispersed average particle size of the carbon black fine particles in the ink is 200 nm or less.