JPH10204347A - Ink for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ink jet ink that is excellent in dispersibility in water of fine particles dispersed in the ink and gives an image having a high blackness and excellent resistances to light and water, by dispersing fine carbon black particles having a specified value or more active hydrogen content on the surface and fine resin particles in a water-base medium. SOLUTION: Fine resin particles in addition of fine carbon black particles are dispersed in a water-base medium to give this ink, which exhibits improved fixability of carbon black particles and abrasion resistance on a printing paper. Fine particles of a polyester resin, a vinyl resin, a styrene resin, etc., can be used, polyester resin particles being pref. in terms of dispersibility. The dipersibility of the resin particles is enhanced by incorporating ionic groups into the surfaces thereof. A carbon black having an active hydrogen content at the surface of 1.5mmol/g or higher is used. Such a carbon black is obtd. by oxidizing a carbon black with an oxidizing agent and further oxidizing the resultant acidic carbon black with a hypohalogenous acid salt in water.

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 capable of recording as an extremely useful recording method. In the ink-jet recording system, various methods have been proposed and commercialized with improvements, while others are still being put to practical use.

In this ink jet recording system, small droplets of a recording liquid called ink are caused to fly by various working principles,
The recording is performed by attaching it to a recording member such as paper. When ink-jet recording was performed using an aqueous dye ink obtained by dissolving a water-soluble black dye in water, the obtained recorded image was inferior in water resistance and light resistance depending on the physical properties of the water-soluble dye. There was a disadvantage that it became something. In particular, in the case of black ink, since there are few water-soluble dyes having good black color reproducibility,
Although black ink is made by mixing a plurality of dyes, there is a problem that if any of the dyes fades, the color tone of black 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. The pigment-based ink using carbon black has an advantage that the light resistance and water resistance of the obtained recorded image are extremely good as compared with the image using the dye-based recording liquid. Therefore, when this ink is used for an ink jet printer, high color developability and water resistance can be obtained, and various effects such as clear contours of characters and drawings can be obtained.

[0004]

However, since the carbon black particles printed on the paper surface by the ink jet printer are attached to the paper surface, there is a problem that the carbon black particles are easily peeled off when the paper surface is rubbed. Occurs. 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.

[0005] In addition, since carbon black does not dissolve in water, which is the medium of the ink, there is also a problem that it is difficult to finely disperse the carbon black in an aqueous medium and secure its stability.

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 can obtain an image having excellent friction resistance and glossiness. Is what you do.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an ink jet recording ink in which carbon black fine particles having a surface active hydrogen content of 1.5 mmol / g or more and resin fine particles are dispersed in at least an aqueous medium.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The aqueous pigment ink of the present invention contains at least water, carbon black fine particles and resin fine particles. The present invention provides a high effect particularly when used for a black pigment such as carbon black. When the present invention is used, dispersion stability in water, friction resistance, and glossiness can be improved while maintaining a high degree of blackening and water resistance of carbon black.

[0010] The ink of the present invention is an ink in which carbon black particles are dispersed in an aqueous medium and resin fine particles are dispersed, thereby enhancing the binding property of carbon black on the paper surface and increasing the friction resistance. Since the resin fine particles are dispersed separately from the carbon black particles, the resin fine particles do not cover the periphery of the carbon black particles and do not deteriorate the color developability. In addition, since the resin fine particles are solid, there is little change during storage or in the head of the ink jet printer, which is stable. . Further, the glossiness of the image due to the carbon black can be improved by the influence of the resin particles. In particular, when a dispersant such as a water-soluble resin is not added to the aqueous solvent, clogging in the ink nozzle portion is less likely to occur, and an image having high coloring property or blackening degree is obtained.

The resin fine particles used in the present invention include:
Various resins such as a polyester resin, a vinyl polymer, a polyurethane resin, a styrene resin, and a styrene-acrylic copolymer can be used. It has excellent properties and shows good characteristics.

The polyester resin comprises a polycarboxylic acid and a polyhydric alcohol. Examples of the polycarboxylic acid include aromatic dicarboxylic acids, aromatic oxycarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, Or higher polyhydric carboxylic acids, and the polyhydric alcohols include aliphatic polyhydric alcohols, alicyclic polyhydric alcohols, and aromatic polyhydric alcohols. it can.

Further, as the polyester resin, the main chain is polyester or polyester polyurethane,
Graft products whose side chains are radically polymerizable unsaturated monomers can also be used.

The resin fine particles exhibit water dispersibility by being constituted so as to contain an ionic group on the surface. The water dispersibility means a state generally called an emulsion or a colloidal dispersion. The ionic group dissociates in the aqueous medium to form an electric double layer at the interface between the resin particles and water. When the resin particles are present as microparticles in an aqueous system, electrostatic repulsion occurs due to the action of the electric double layer, and the microparticles are stably dispersed in the aqueous system. Examples of such an ionic group include a sulfonic acid group, a carboxylic acid group, a sulfuric acid group, a phosphoric acid group, a phosphonic acid group and a phosphinic acid group, or an alkali metal base or an ammonium base thereof, or a primary to tertiary amine group. And the like, and a carboxylic acid alkali metal base,
Ammonium carboxylate, alkali metal sulfonate and ammonium sulfonate are preferred, and alkali metal sulfonate and ammonium sulfonate are particularly preferred in view of water dispersion stability. 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.

When an alkali metal carboxylate or ammonium carboxylate is introduced as an ionic group into the fine particles of the polyester resin, a polyvalent carboxylic acid such as trimellitic acid is introduced into the system at the end of polymerization of the polyester. To add a carboxyl group to the terminal of the resin, and then neutralize it with ammonia, sodium hydroxide or the like to exchange the group with a carboxylate group. When an alkali metal sulfonate or ammonium sulfonate is introduced as an ionic group into the polyester resin fine particles, by containing a mono- or dicarboxylic acid having an alkali metal sulfonate or ammonium sulfonate, These ionic groups can be introduced into the polyester resin. Salts include ammonium ions, Li, N
a, K, Mg, Ca, Cu, Fe, etc., and particularly preferred are K and Na.

The average particle size of the resin fine particles used in the present invention is 0.01 to 1.0 μm, preferably 0.03 to 0.1 μm.
8 μm, more preferably in the range of 0.05 to 0.6 μm. If the average particle size of the resin particles is less than this range, it may not be possible to obtain a sufficient effect of improving the friction resistance. Phase separation may occur.

The specific gravity of the resin fine particles is 0.8-1.
1, preferably 0.93 to 1.00, more preferably 0.94 to 0.98. If the specific gravity is lower than this range, the ink may be phase-separated due to the floating of particles when the ink is stored for a long time, and if it is much higher, sedimentation may occur.

The fine resin particles are 0.01 to the total amount of the ink.
To 15% by weight, preferably 0.1 to 10% by weight, more preferably 0.2 to 5% by weight. When the content of the resin particles exceeds this range, the discharge nozzle of the ink jet printer head may be clogged or the degree of blackening of the carbon black may be reduced. May not be obtained. The total amount of the carbon black particles and the resin fine particles is 4 to 35% by weight of the total weight of the ink,
Preferably 5-20% by weight, more preferably 10-15%
It is contained in the range of weight%.

In the ink of the present invention, carbon black having a surface active hydrogen content of 1.5 mmol / g or more is used as carbon black. 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. By using such a carbon black, it is not necessary to use a dispersant for water of a pigment such as a water-soluble resin in combination, or the amount of the dispersant can be reduced. Problems such as clogging and loss of ink ejection stability can be solved. However, for this reason, the friction resistance of the ink tends to decrease, but in the present invention, the friction resistance is also improved because the above resin fine particles are used in combination.

The surface active hydrogen content of the carbon black is preferably 1.5 to 5.0 mmol / g, more preferably 2.0 to 5.0 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 the 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 15 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 a conventional oxidizing agent (eg, nitric acid, ozone, hydrogen peroxide, nitrogen oxide, or the like), or a surface modification method such as plasma treatment, for example, by a color such as furnace black. It is obtained by appropriately oxidizing carbon black for use.

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. The product is then filtered and the by-product salts are removed by washing with deionized 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. The obtained concentrated pigment dispersion is added to an aqueous medium and adjusted to an appropriate pigment concentration to obtain an ink. Preferably, both the carbon black and the resin fine particles are added to the aqueous medium as a concentrated dispersion, but one or both of them may be dried to form a powder, and then added to the aqueous medium. The ink of the present invention may contain various known organic solvents and additives in addition to the above-mentioned water, carbon black and resin fine particles. 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. Examples of the water-soluble organic solvent include alkyl alcohols having 1 to 4 carbon atoms such as ethanol, isopropanol and butanol, alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol and triethylene glycol, and polyalkylene glycols such as polyethylene glycol and polypropylene glycol. , Lower alkyl ethers of alkylene glycols such as ethylene glycol monoethyl ether, diethylene glycol monoethyl ether and triethylene glycol monobutyl ether; pyrrolidones such as 2-pyrrolidone and N-methyl-2-pyrrolidone; and glycerin. 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.

In order to impart gloss to an image, a water-soluble resin may be added in an appropriate amount so as not to cause clogging or impair the stability of the ink. Examples of such a water-soluble resin include polyvinyl pyrrolidone, a water-soluble acrylic resin, and polyvinyl alcohol.

It is preferable to adjust the pH of the ink to 8 to 10 in order to improve the storage stability of the ink. NaHCO3, Na2B4O7,
Examples thereof include alkanolamines such as ethanolamine, diethanolamine and triethanolamine, and hydroxides of alkali metals such as potassium hydroxide and lithium hydroxide.

Further, the aqueous pigment ink of the present invention may contain 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.

When the aqueous ink of the present invention is used for recording by an ink jet system, it is excellent in the fastness (light fastness and water fastness) of characters and figures recorded on paper, and the pigment component can be re-immersed in water again. It does not flow out and is water-resistant, does not fade even when exposed to sunlight, and has excellent light resistance. Further, even if the printed surface is rubbed, the pigment component does not peel off, and the rub resistance is excellent.

[0030]

【Example】

(Production Example 1 of Resin Fine Particle Dispersion) Dimethyl terephthalate 130 was placed in an autoclave equipped with a thermometer and a stirrer.
Parts by weight, dimethyl isophthalate 56 parts by weight, pentasodium sulfoisophthalic acid dimethyl ester 6 parts by weight, ethylene glycol 159 parts by weight, tricyclodecane dimethanol 30 parts by weight, tetrabutoxy titanate 0.1
A part by weight was charged and heated at 180 to 230 ° C. for 120 minutes 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, and 140 parts by weight of tetrahydrofuran were dissolved at 80 ° C., and 680 parts of water at 80 ° C. was added.
An aqueous microdispersion of a copolymerized polyester having an average particle size of about 0.15 μm was obtained. Further, the obtained aqueous microdispersion was placed in a distillation flask and distilled until the fraction temperature reached 100 ° C. After cooling, water was added to adjust the solid content concentration to 10% by weight to obtain a resin fine particle dispersion A.

(Production Example 2 of Resin Fine Particle Dispersion) Thermometer
In a reactor equipped with a stirrer, a reflux device, and a metering dropping device, 60 parts by weight of the polyester resin A and methyl ethyl ketone 3 were added.
The resin was dissolved in 6 parts by weight, heated and stirred under reflux. After the resin was completely dissolved, 24 parts by weight of isopropyl alcohol was added and heated again under reflux. Thereafter, a mixture of 8 parts by weight of ethyl acrylate, 12 parts by weight of acrylic acid, 2 parts by weight of octyl mercaptan, 1.2 parts by weight of azobisisobutylnitrile, 12 parts by weight of methyl ethyl ketone,
A solution dissolved in a mixed solution of 8 parts by weight of isopropyl alcohol was added dropwise to the polyester solution over 1.5 hours, and further reacted for 3 hours to obtain a graft.
After the graft solution was cooled to room temperature, 10 parts by weight of triethylamine was added to neutralize the solution, and 160 parts by weight of ion-exchanged water was added and stirred for 20 minutes. Thereafter, the solvent remaining in the medium was distilled off by heating to obtain an aqueous dispersion having a solid content concentration of 10% by weight, whereby a resin fine particle dispersion B was obtained. The average particle size of the resin fine particles in the resin fine particle dispersion was 0.05 μm.

(Production Example 1 of Carbon Black Dispersion) After 300 g of carbon black (MA-100, 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 10 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 A.

The obtained carbon black dispersion was acidified with aqueous hydrochloric acid, again subjected to membrane purification, concentration, drying and pulverization 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 carbon black powder 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.

Example 1 Carbon Black Dispersion A2
Water was added to 5 g, 10 g of the resin fine particle dispersion A, 5 g of ethanol and 5 g of 2-methylpyrrolidone to make the total amount 100 g, thereby obtaining an aqueous pigment ink. The carbon black dispersion average particle size of this ink is 150 n.
m. The average particle size of the carbon black was measured using a laser light diffusion type particle size distribution analyzer.

Next, this ink was printed using an ink jet recording apparatus (MJ500C; manufactured by Epson Corporation).
Even when the obtained image was strongly rubbed, the printed characters did not come off at all and had excellent rub resistance. When the image was immersed in water, there was no flow of the pigment, and the image was excellent in water resistance. When the image was visually evaluated, the degree of blackening and the glossiness were satisfactory. In addition, the ejection property of the ink is stable, and the ink does not solidify in the nozzle,
No ejection failure occurred in a printing 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. The image density of a solid image measured with a Macbeth reflection densitometer was 1.30,
Sufficient image density was obtained.

Example 2 Carbon Black Dispersion A2
Water was further added to 5 g, 10 g of the resin fine particle dispersion B, 5 g of ethanol and 5 g of 2-methylpyrrolidone to make the total amount 100 g, thereby obtaining an aqueous pigment ink. The dispersion average particle size of carbon black in this ink is 150
nm.

Next, this ink was printed using an ink jet recording apparatus (MJ500C; manufactured by Epson Corporation).
Even when the obtained image was strongly rubbed, the printed characters did not come off at all and had excellent rub resistance. When the image was immersed in water, there was no flow of the pigment, and the image was excellent in water resistance. When the image was visually evaluated, the degree of blackening and the glossiness were satisfactory. In addition, the ejection property of the ink is stable, and the ink does not solidify in the nozzle,
No ejection failure occurred in a printing 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. When the image density of the solid image was measured with a Macbeth reflection densitometer, it was 1.31.
Sufficient image density was obtained.

Example 3 Carbon Black Dispersion B2
Water was added to 5 g, 10 g of the resin fine particle dispersion A, 5 g of ethanol and 5 g of 2-methylpyrrolidone to make the total amount 100 g, thereby obtaining an aqueous pigment ink. The dispersion average particle size of carbon black in this ink is 100
nm.

Next, this ink was printed using an ink jet recording apparatus (MJ500C; manufactured by Epson Corporation).
Even when the obtained image was strongly rubbed, the printed characters did not come off at all and had excellent rub resistance. When the image was immersed in water, there was no flow of the pigment, and the image was excellent in water resistance. When the image was visually evaluated, the degree of blackening and the glossiness were satisfactory. In addition, the ejection property of the ink is stable, and the ink does not solidify in the nozzle,
No ejection failure occurred in a printing 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. When the image density of the solid image was measured with a Macbeth reflection densitometer, it was 1.31.
Sufficient image density was obtained.

Comparative Example 1 Carbon Black Dispersion A2
5 g, ethanol 5 g and 2-methylpyrrolidone 5 g
Was further added to make the total amount 100 g, whereby an aqueous pigment ink was obtained.

The obtained ink was printed using an ink jet recording apparatus (MJ500C; manufactured by Epson Corporation). When the obtained image is rubbed, some of the printed characters are peeled off,
It was confirmed that the friction resistance was insufficient.

Comparative Example 2 Carbon Black Dispersion B2
5 g, ethanol 5 g and 2-methylpyrrolidone 5 g
Was further added to make the total amount 100 g, whereby an aqueous pigment ink was obtained.

The obtained ink was printed using an ink jet recording apparatus (MJ500C; manufactured by Epson Corporation). When the obtained image is rubbed, some of the printed characters are peeled off,
It was confirmed that the friction resistance was insufficient.

Comparative Example 3 Carbon black (MA10
0, active hydrogen content 0.13 mmol / g, manufactured by Mitsubishi Chemical Corporation) 5 g, resin fine particle dispersion A 10 g, ethanol 5 g
Then, 5 g of 2-methylpyrrolidone and water were further added to make the total amount 100 g, whereby an aqueous pigment ink was obtained.

When the obtained ink was allowed to stand for several minutes,
The supernatant was generated due to the sedimentation of the carbon black, and printing was impossible.

[0048]

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 can obtain an image having excellent friction resistance and glossiness. it can.

Claims (5)

[Claims] 1. An ink jet recording ink comprising carbon black fine particles having a surface active hydrogen content of 1.5 mmol / g or more and resin fine particles dispersed in at least an aqueous medium. 2. The resin fine particles having an average particle size of 0.01 to 0.01.
2. The ink for ink-jet recording according to claim 1, wherein the thickness is 1.0 [mu] m. 3. The ink for ink-jet recording according to claim 2, wherein the resin fine particles are resin fine particles having an ionic group. 4. The ink for ink-jet recording according to claim 2, wherein said resin fine particles are polyester-based resin fine particles. 5. 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.