JP5570542B2 - Black ink composition for aqueous inkjet - Google Patents

Description

  The present invention is a black for water-based inkjet that can obtain a high printing density even when printed on uncoated paper such as plain paper and offset paper, and has excellent scratch resistance of printed matter, and is excellent in ejection stability and storage stability. The present invention relates to an ink composition.

The ink jet printing / recording method is a printing / recording method in which ink droplets are directly ejected from a very fine nozzle onto a printing / recording substrate and adhered to obtain characters and images.
In the past, water-based inkjet printing methods have a problem that printing takes a long time because the print head is a scanning type, drying of an aqueous medium is slow, and expensive special paper is required to obtain a cosmetic print. It was considered unsuitable for the production of large quantities of printed matter.
However, on the other hand, it does not require a plate making process like a normal printing method, and even if it includes an electrophotographic method, it has the advantage that it can be printed with a very simple device configuration. It was mostly used at home.

  Therefore, if the above-mentioned problems of printing and drying time and printing paper cost can be solved, it is considered that there is sufficient value in competition with other printing methods in industrial applications such as office and commercial printing. It is done. For these reasons, in order to use the inkjet printing method for industrial purposes, recently, a technology for actively applying high-speed printing and low-cost printing paper from both the printing apparatus and ink has been studied. .

  A printed image by the ink jet printing method is composed of dots of ink droplets. Therefore, basically, in order to realize high-speed printing, it is necessary to eject many ink droplets to a predetermined place in a shorter time. Accordingly, first, from the surface of the printing apparatus, the problem is solved by increasing the number of nozzles that eject ink droplets, and a single-pass printing method using a fixed line head has been developed.

  In a printing method using a fixed printing line head, a series of nozzles are provided to cover the full width of the printed image in the vertical direction, and ink is selectively ejected while the printing substrate is fed without interruption. / Printed matter is produced by non-ejection. Therefore, in order to eject ink droplets to a predetermined position in the vertical direction of the printing flow, a printing method in which a scanning head having a small number of nozzles is moved and the feeding of the printing substrate needs to be stopped during that time. In comparison, faster printing is possible.

  However, in the ink jet printing method in which it is necessary to always fill the nozzle with ink before discharging the ink droplet, at least from when the ink droplet is discharged until the next ink droplet is discharged. A time lag occurs while the nozzle is filled with ink. In the meantime, the feeding of the printing substrate is continued, and if the feeding speed is too fast, the dot interval of the ink droplets is separated, and the printed matter cannot be manufactured. Therefore, it can be said that it is indispensable to quickly fill the nozzles with ink in order to increase the printing speed. Further, if a large area dot having a high color density can be formed with a single ink droplet, it is advantageous to increase the printing speed accordingly.

On the other hand, in industrial applications, emphasis is also placed on reducing the cost of printing materials, and the use of uncoated paper (printing paper) such as plain paper or ordinary offset paper as a printing substrate is being studied. In such printing paper, paper fibers are sparse, and an aqueous medium of ink penetrates deeply into the paper (fibers). At this time, if the coloring component of the ink also sinks into the paper together, the density and sharpness of the printed image are lowered. Moreover, if it spreads along a fiber on the surface of paper, a bleed will generate | occur | produce and both will impair the value of printed matter. Therefore, a countermeasure is required that does not cause a decrease in density and sharpness and bleeding.
In addition, the ink performance required by the original inkjet recording system, including storage stability, ejection reliability that allows stable ejection without causing nozzle clogging, droplet flying properties, and scratch resistance of printed matter Must be.

  As described above, in order to expand the application range of the ink jet printing method for industrial use, the ink is required to have a very high performance. However, there is an ink property to be considered in order to realize the required performance as a stage before specifically examining the ink material and composition. In particular, the viscosity of the ink is a very important property that affects various performances. For example, in order to quickly fill the nozzle with ink, it is necessary to keep the ink viscosity low, and lowering the viscosity also improves the expandability of the ink droplets. However, on the contrary, the permeability of the ink into the printing paper is increased, and the coloring component is likely to sink into the paper.

In view of this, a technique for preventing the coloring component from sinking into the paper by removing the aqueous medium at an early stage from the system while keeping the ink viscosity as low as possible has been developed.
(1) As such a technique, for example, a resin component necessary for film formation without using a water-soluble resin or an alkali-soluble resin as much as possible, which causes a high viscosity and delays the removal of the aqueous medium from the system. Is a method using a resin emulsion insoluble in water (see, for example, Patent Document 1),
(2) A method of separating an aqueous medium and a solid component when a droplet of ink printing has landed on the surface of the printing paper after applying a reaction liquid for aggregating the ink coloring material or resin to the printing paper in advance (for example, , See Patent Document 2)
Etc. have been proposed.

  By the way, recently, an ink having a high color density has been demanded so that a clearer printed matter can be obtained. With black ink, the optical density (OD value) of an image is 1.3 or more, and further 1.5. This may be required. In this case, for example, in the case of an ink containing about 5% by mass of carbon black, which is a pigment capable of imparting high blackness, as a practical content, the method (1) described above includes a resin emulsion insoluble in water. It is impossible to achieve such a high print density. The method of applying the reaction liquid (2) is extremely difficult, and even if it can be realized, there is a problem that extra materials and steps are required.

  Therefore, a method of increasing the carbon black content is used, but increasing the amount of carbon black as a solid content itself is a factor in increasing the viscosity of the ink. Further, since carbon black has a fine primary particle size and is porous and has a large specific surface area, it has poor dispersion stability, and it is necessary to adsorb / cover a large amount of dispersant and dispersing resin. These dispersing agents and dispersing resins cause the ink to become highly viscous and delay the release of the aqueous medium from the system, which is disadvantageous for increasing the printing speed. In order to keep the viscosity low, a low molecular weight dispersant is used as much as possible, or a method of aggregating (coating) the carbon black surface if it is a resin (for example, see Patent Documents 3 and 4). If the amount of carbon black is increased, the amount of the dispersant and the dispersing resin is increased accordingly, and an increase in viscosity is inevitable.

Therefore, the method of increasing the carbon black content increases the viscosity of the ink just to maintain the dispersion stability of the carbon black. Addition will be restricted. However, at this stage, only a dispersant and a dispersing resin necessary for maintaining the dispersion stability of carbon black are used, and a sufficient ink film cannot be formed. Naturally, when an external force is applied to the ink film due to rubbing or the like, it is in a state where it is easily peeled off from the printing paper, but it is possible to form an ink film having good scratch resistance while the remaining available solid components are restricted. The current situation is difficult.
As described above, while water-based inkjet printing methods are being used to increase the printing speed and use of uncoated paper such as plain paper and normal offset paper as printing paper, a high print density can be obtained and printed matter can be obtained. At present, it is difficult to obtain a black ink composition for water-based inkjet that has excellent scratch resistance and excellent ejection stability and storage stability.

Japanese Patent Laid-Open No. 06-145570 Japanese Patent Laid-Open No. 09-207424 JP 09-104834 A Republished WO2005 / 116147

  The present invention is a black ink composition for water-based ink jets that provides high printing density and excellent scratch resistance even when printed at high speed on uncoated paper (plain paper, offset paper), and is excellent in ejection stability and storage stability. The issue is to provide goods.

As a result of intensive studies to solve the above problems, the present inventors have invented the following black ink composition for water-based inkjet.
(1) An aqueous inkjet black ink composition containing at least carbon black, an alkali-soluble resin, a wax emulsion, a basic compound, and an aqueous medium, wherein the carbon black content is in the aqueous inkjet black ink composition 8-12% by mass, the wax emulsion has an average particle size of 150-200 nm, and is contained in an amount of 10-40 parts by mass with respect to 100 parts by mass of carbon black in terms of solid content. Black ink composition.
(2) The black ink composition for water-based inkjet according to (1), wherein the carbon black is a resin-coated carbon black coated with an alkali-soluble resin.
(3) The black ink composition for water-based inkjets according to any one of (1) or (2), wherein the wax emulsion is a nonionic polyalkylene wax emulsion.

  According to the black ink composition for water-based inkjet of the present invention, the printing after inkjet printing has a sufficiently high printing density, and has excellent scratch resistance, storage stability, and ejection stability. The effect can be demonstrated.

The inventors have increased the content of carbon black in the ink composition to 8 to 12% by mass as compared with conventional ink-jet inks, and added a wax emulsion having an average particle diameter of 150 to 200 nm to carbon black. A new black ink composition for water-based ink jet was developed by adding a specific amount to the above.
Specifically, if the wax emulsion has the above average particle diameter, good ejection stability can be maintained even when ink is ejected from a nozzle having a fine diameter by the ink jet printing method. On the other hand, the particle size of the wax emulsion is about 1.5 to 2 times the average particle size of a general pigment contained in ink jet printing ink.

After the ink has landed on the surface of the printing paper, the solid component is carried into the aqueous medium and penetrates into the paper (moves between the paper fibers). It can be said that it is easy to stay on the paper surface due to the great resistance from the paper fiber. Furthermore, since the wax emulsion surface is hydrophobic and the alkali-soluble resin is adsorbed on the pigment surface, the pigment has a higher affinity with the aqueous medium. Then, the aqueous medium immediately disappears from around the wax emulsion and the distance traveled ends short, whereas the pigment travels a longer distance. As these combined effects, it can be expected that a large amount of the wax emulsion is present on the surface side of the printing paper to exhibit high scratch resistance. In addition, even if the wax emulsion and the pigment are present at the same location, it can be expected that the wax emulsion protrudes to the surface side by an amount corresponding to the large particle size, and it can be used advantageously for imparting scratch resistance.
Based on such inference and expectation, the average particle diameter of the wax emulsion is set to 150 to 200 nm, and the content is fixed to 10 to 40 parts by mass with respect to 100 parts by mass of carbon black. The present inventors have found that the problems can be solved and have completed the present invention.

That is, the present invention provides (1) a black ink composition for aqueous inkjet containing at least carbon black, an alkali-soluble resin, a wax emulsion, a basic compound, and an aqueous medium, wherein the carbon black content is an aqueous inkjet. The wax emulsion has an average particle size of 150 to 200 nm and contains 10 to 40 parts by mass with respect to 100 parts by mass of carbon black in terms of solid content. The present invention relates to a black ink composition for water-based inkjet.
The present invention also relates to (2) the black ink composition for water-based inkjet according to (1), wherein the carbon black is a resin-coated carbon black coated with an alkali-soluble resin.
The present invention also relates to (3) the black ink composition for water-based inkjet according to any one of (1) or (2) above, wherein the wax emulsion is a nonionic polyalkylene wax emulsion.

Hereinafter, the black ink composition for water-based inkjet of the present invention will be specifically described for each component.
(Carbon black)
The carbon black used in the black ink composition for water-based inkjet of the present invention may be powdery or granular. Any of those conventionally used in inkjet can be used, but the smaller the average primary particle size, the more the colored image obtained has a tendency to improve the scratch resistance and gloss, and the average primary particle size is smaller than 18 nm. It is preferable that the thickness be 14 nm or less.

  The average primary particle diameter of carbon black means a value determined as follows. That is, first, when a carbon black aggregate image was photographed with a transmission electron microscope (TEM), the carbon black was adjusted to a concentration such that the aggregate images on the photograph did not overlap each other in chloroform. A sufficiently diluted dispersion is prepared. Next, it is spread on a mesh with a collodion film, dried, and photographed in that state to obtain a TEM photograph (magnification of 30,000 times after stretching). Then, a TEM photograph is read by a scanner, and an image signal is digitized, then input to a computer, and an area of each aggregate is obtained by image analysis. Furthermore, the average area of primary particles is obtained from the area of each aggregate and the number of aggregated primary particles, and the diameter of a circle having the same area is calculated as the average particle diameter of the primary particles. Finally, the average primary particle diameter of all the aggregates or a specific number of primary particles is arithmetically averaged to obtain the average primary particle diameter.

The content of carbon black in the black ink composition for aqueous inkjet is 8 to 12% by mass, preferably 10 to 12% by mass. When the content is less than 8% by mass, the density of the obtained image is low, and when it exceeds 12% by mass, there is a concern that the discharge stability of the aqueous inkjet black ink composition may be lowered.
Further, the carbon black to be used is preferably a specific surface area of 200 m ² / g or more, more preferably 230 m ² / g or more, more preferably 260 m ² / g or more, in terms of better scratch resistance and gloss of the resulting colored image. ² / g or more is particularly preferable.
The carbon black to be used may have any pH, but preferably has a pH of 6 to 10, more preferably 7 in terms of excellent storage stability of the black ink composition for aqueous inkjet. ~ 9.
The specific surface area of the carbon black described above refers to the nitrogen adsorption specific surface area measured according to JIS K6217, and the pH refers to the pH value measured according to JIS K6221.

As carbon black used in the present invention, Mitsubishi carbon black # 2600, # 2300, # 980, # 966, # 960, # 950, # 85 (above, manufactured by Mitsubishi Chemical Corporation), MONARCH-1100, -900 , -880, -800, Cabojet -300, -200 (above, manufactured by Cabot Corporation), Printex-95, -90, -85, -80, Hiblack-890, -600L (above, manufactured by Degussa), Raven- 2500U (above, manufactured by Colombian).
The carbon black content in the black ink composition for water-based inkjet of the present invention is preferably blended so as to be in the range of 8 to 12% by mass. If the carbon black content is less than 8% by mass, a high OD value cannot be obtained, and if the carbon black content is more than 12% by mass, the ejection stability and storage stability tend to decrease, such being undesirable.

(Alkali-soluble resin)
The alkali-soluble resin used in the black ink composition for water-based inkjet of the present invention is a copolymer that is used for dispersing pigments in ordinary inks and paints and is soluble in an aqueous medium in the presence of a basic compound. Resin can be used.
Examples of such an alkali-soluble resin include, for example, a polymer having a carboxyl group-containing monomer, preferably a hydrophobic group-containing monomer for improving the adsorptivity with a pigment, or other if necessary. A copolymer obtained by reacting with the polymerizable monomer can be used.
Examples of the monomer having a carboxyl group include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, 2-carboxyethyl (meth) acrylate, 2-carboxypropyl (meth) acrylate, and anhydrous. Maleic acid, maleic acid monoalkyl ester, citraconic acid, citraconic anhydride, citraconic acid monoalkyl ester and the like can be mentioned.

  Examples of the hydrophobic group-containing monomer for improving the adsorptivity with the pigment include a radically polymerizable unsaturated carboxylic acid such as (meth) acrylic acid as a monomer having a long-chain alkyl group. Alkyl esters having 8 or more carbon atoms (for example, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, 2-hydroxystearyl (meth) acrylate, etc.)), Alkyl vinyl ethers having 8 or more carbon atoms (for example, dodecyl vinyl ether), vinyl esters of fatty acids having 8 or more carbon atoms (for example, vinyl 2-ethylhexanoate, vinyl laurate, vinyl stearate, etc.), fat Cyclohexyl (meth) acrylate as a monomer having a cyclic hydrocarbon group DOO, etc., as the monomer having an aromatic hydrocarbon group, benzyl (meth) acrylate, styrene, alpha-styrene, and a styrene monomer such as vinyltoluene.

In addition, other polymerizable monomers used as necessary include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, (meth ) (Meth) acrylic acid such as butyl acrylate and hexyl (meth) acrylate, hydroxyethyl (meth) acrylate, acrylamide, N-methylolacrylamide and the like.
In the alkali-soluble resin obtained by copolymerizing the above monomers, when considering improvement of the solubility of the resin in an aqueous medium and prevention of a decrease in water resistance of the printed matter, preferably, the glass transition temperature is 10 to 10. 50 degreeC, acid value 100-300 mgKOH / g, and a mass mean molecular weight are 10,000-50,000. When the acid value of the alkali-soluble resin is less than 100 mgKOH / g, the solubility of the resin in an aqueous medium is lowered. On the other hand, when the acid value exceeds 300 mgKOH / g, there is a concern that the water resistance of the obtained printed matter is lowered.

  Moreover, when aiming at prevention of the fall of blocking resistance of a printed matter, and prevention of a fall of bend-proof property, the glass transition temperature of alkali-soluble resin shall be the range of 10-50 degreeC, Preferably it is the range of 20-45 degreeC. preferable. When the glass transition temperature of the alkali-soluble resin is less than 10 ° C., the blocking resistance of the printed matter obtained is lowered, whereas when it exceeds 50 ° C., the bending resistance may be lowered.

Furthermore, when further improving the scratch resistance of the printed matter, in order to prevent a decrease in the dispersibility of the carbon black, the weight average molecular weight of the alkali-soluble resin is preferably in the range of 10,000 to 50,000, More preferably, the weight average molecular weight of the alkali-soluble resin is in the range of 20,000 to 30,000.
When the weight average molecular weight of the alkali-soluble resin is less than 10,000, the dispersion stability of the carbon black and the scratch resistance of the resulting printed matter are lowered. On the other hand, when it exceeds 50,000, the carbon in the black ink composition for aqueous inkjet The dispersibility of black may also decrease.
The content of the alkali-soluble resin is generally 10 to 60 parts by mass, more preferably 15 to 50 parts by mass with respect to 100 parts by mass of carbon black contained in the black ink composition for aqueous inkjet. When the content of the alkali-soluble resin is less than the above range, the dispersibility of the carbon black in the aqueous medium may be lowered. On the other hand, exceeding the above range is not preferable because the viscosity increases.

Here, the glass transition temperature, acid value, and weight average molecular weight of the alkali-soluble resin described above can be determined by the following method.
<Glass transition temperature>
The glass transition temperature is a theoretical glass transition temperature obtained by the following wood equation.
Wood formula: 1 / Tg = W1 / Tg1 + W2 / Tg2 + W3 / Tg3 +... + Wx / Tgx
(Wherein Tg1 to Tgx are the glass transition temperatures of the respective homopolymers of monomers 1, 2, 3,... X constituting the alkali-soluble resin, and W1 to Wx are the monomers 1, 2, 3,. ..Each polymerization fraction of x, Tg represents the theoretical glass transition temperature (however, the glass transition temperature in the wood equation is an absolute temperature)

<Acid value>
The acid value is a theoretical acid value obtained by arithmetically determining the number of mg of potassium hydroxide theoretically required to neutralize 1 g of the alkali-soluble resin based on the composition of the monomer used for synthesizing the alkali-soluble resin. It is.

<Mass average molecular weight>
The mass average molecular weight can be measured by a gel permeation chromatography (GPC) method. As an example, chromatography can be performed using Water 2690 (manufactured by Waters) as a GPC apparatus and PLgel 5μ MIXED-D (manufactured by Polymer Laboratories) as a column, and the weight average molecular weight in terms of polystyrene can be obtained.

(Wax emulsion)
The wax emulsion used in the black ink composition for water-based inkjet of the present invention has an average particle diameter of 150 to 200 nm, preferably 160 to 180 nm.
When the average particle size of the wax emulsion is less than 150 nm, the scratch resistance is lowered. On the other hand, when it exceeds 200 nm, the discharge stability of the aqueous inkjet black ink composition is lowered, which is not preferable.
The wax emulsion used is preferably a nonionic emulsified modified paraffin wax emulsion, and more preferably a nonionic polyalkylene wax emulsion.

Specific examples of such a wax emulsion include AQUACE531 (mixed system, average particle size of 160 nm, manufactured by Big Chemie Japan Co., Ltd.).
The average particle diameter of the wax emulsion described above is a value measured by a dynamic light scattering method using a Microtrac UPA particle size distribution meter manufactured by Nikkiso Co., Ltd.
In the black ink composition for water-based inkjet of the present invention, the content of the wax emulsion is preferably in the range of 10 to 40 parts by mass (solid content) with respect to 100 parts by mass of carbon black. More preferably, it is within the range of (solid content).
When the content of the wax emulsion is less than 10 parts by mass, the scratch resistance tends to decrease. On the other hand, when the content exceeds 40 parts by mass, the discharge stability of the aqueous inkjet black ink composition decreases, which is not preferable.

(Basic compound)
The basic compound used in the black ink composition for aqueous inkjet of the present invention is used for dissolving the alkali-soluble copolymer in an aqueous medium. It can mix | blend so that it may become 0-4.0 mass%.
Examples of such basic compounds include inorganic basic compounds such as sodium hydroxide and potassium hydroxide, ammonia, methylamine, ethylamine, monoethanolamine, N, N-dimethylethanolamine, N, N-diethyl. Organic basic compounds such as ethanolamine, N, N-dibutylethanolamine, diethanolamine, N-methyldiethanolamine, triethanolamine, morpholine, N-methylmorpholine and N-ethylmorpholine can be used. These may be used alone or in combination of two or more.

(Aqueous medium)
Examples of the aqueous medium used in the aqueous inkjet black ink composition of the present invention include an aqueous medium composed of water and a water-soluble organic solvent.
The water is preferably ion-exchanged water or distilled water from which metal ions or the like have been removed.
Further, by including a water-soluble organic solvent, it may be possible to impart more excellent ink jet printing suitability in terms of storage stability, ejection stability, ink flying property, and the like. Examples of such water-soluble organic solvents include monoalcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, ketones, ethers, esters, nitrogen-containing compounds, and the like. These may be used alone or in combination of two or more.

  Specific examples of the monoalcohols include methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonyl alcohol, n-decanol, and these. Isomers, cyclopentanol, cyclohexanol and the like, and preferably an alcohol having an alkyl group with 1 to 6 carbon atoms.

  Specific examples of the polyhydric alcohol include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,2-pentanediol, 1,5-pentanediol, neopentyl glycol, 1, 2-hexanediol, 1,6-hexanediol, 1,2-cyclohexanediol, heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, glycerin, pentaerythritol, diethylene glycol, Examples include dipropylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, polypropylene glycol, and thiodiglycol.

  Specific examples of the lower alkyl ethers of the polyhydric alcohol include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol monopropyl ether, ethylene glycol isopropyl ether, ethylene glycol monobutyl ether. , Ethylene glycol isobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene A glycol monobutyl -n- butyl ether.

Examples of the ketones include acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diisopropyl ketone, cyclopentanone, and cyclohexanone.
Examples of the ethers include isopropyl ether, n-butyl ether, tetrahydrofuran, tetrahydropyran, 1,4-dioxane and the like.
Examples of the esters include propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, ethyl butyrate, dibutyl phthalate, dioctyl phthalate, and ε-caprolactone, ε- There are cyclic esters such as caprolactam.
Examples of the nitrogen-containing compound include urea, pyrrolidone, N-methyl-2-pyrrolidone, octyl pyrrolidone and the like.
Although content of the said water-soluble organic solvent is not specifically limited, 20-70 mass% is preferable in the black ink composition for water-based inkjets.

(Additive)
Furthermore, the black ink composition for water-based inkjet of the present invention includes a known pigment dispersant, surfactant, antifungal agent, rust inhibitor, thickener, antioxidant, ultraviolet absorber, storage according to the purpose. Additives such as property improvers, antifoaming agents, and PH adjusters can also be added.

(Method for producing black ink composition for water-based inkjet)
The method for producing the black ink composition for water-based inkjet of the present invention using the above components includes (1) an aqueous resin varnish obtained by dissolving an alkali-soluble resin in water in the presence of carbon black and a basic compound, and necessary. After mixing the pigment dispersant and the like, the carbon black is dispersed using various dispersing machines such as a ball mill, an attritor, a roll mill, a sand mill, an agitator mill, etc., and the remaining materials are added to form an aqueous inkjet. For preparing a black ink composition for use (hereinafter referred to as production method 1), (2) after carbon black is dispersed by the above-mentioned method, an acid precipitation method or ion exchange described in re-published WO2005 / 116147 A resin-coated pigment obtained by depositing an alkali-soluble resin on the pigment surface by means, etc., and then the obtained resin-coated pigment A method of neutralizing with a basic compound, redispersing in water using various dispersers (such as a high-speed stirrer), and adding the remaining materials to prepare a black ink composition for water-based inkjet (hereinafter manufacturing) (Described as Method 2).
Especially, a manufacturing method (2) is preferable from the point which the storage stability of the black ink composition for water-based inkjets becomes further favorable.
The black ink composition for water-based inkjet of the present invention thus obtained has an initial viscosity after production of 6.0 to 10.0 mmPa · s, preferably 7.0 to 9.0 mmPa · s.

(Printing method)
Next, a printing method using the aqueous inkjet black ink composition of the present invention will be described.
Examples of the substrate for printing of the black ink composition for water-based inkjet according to the present invention include coated paper such as art paper, inkjet exclusive paper, and inkjet glossy paper, as well as uncoated paper such as plain paper and offset paper.
For example, the black ink composition for water-based inkjet of the present invention is accommodated in an ink cartridge, and the ink cartridge is mounted on a single-pass inkjet recording apparatus and ejected from the nozzle onto the printing substrate. Thus, ink jet printing can be performed.
By using the aqueous black inkjet ink composition of the present invention, the printing density (OD value) is improved. In particular, even with uncoated paper in which a high printing density could not be obtained, the OD value can be set to 1.3 or more, and further, the OD value can be set to 1.5 or more, thereby obtaining an effect such that a clearer printed matter can be obtained. be able to.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited only to these examples. Unless otherwise specified, “%” means “% by mass”, and “part” means “part by mass”.

Black ink composition material for water-based inkjet
Carbon Black Printex 90 (average particle size 14 nm, specific surface area 300 m ^{2 /} g, pH 9.0, manufactured by Degussa)

Alkali-soluble resin (alkali-soluble resin A)
Acrylic acid / n-butyl acrylate / benzyl methacrylate / styrene copolymer (alkali-soluble resin B) having a glass transition temperature of 40 ° C., a weight average molecular weight of 30,000, and an acid value of 150 mgKOH / g
Acrylic acid / n-butyl acrylate / benzyl methacrylate / styrene copolymer (alkali-soluble resin C) having a glass transition temperature of 40 ° C., a weight average molecular weight of 30,000 and an acid value of 185 mg KOH / g
Acrylic acid / n-butyl acrylate / benzyl methacrylate / styrene copolymer having a glass transition temperature of 40 ° C., a weight average molecular weight of 20,000, and an acid value of 185 mg KOH / g

Wax emulsion AQUACER 531 (solid content 45%, nonionic emulsified modified paraffin wax, average particle size 160 nm, manufactured by Big Chemie Japan Co., Ltd.)
AQUACER 539 (solid content 35%, nonionic emulsified modified paraffin wax, average particle size 50 nm, manufactured by Big Chemie Japan Co., Ltd.)
Hitech E-6314 (solid content 35%, nonionic emulsified polyethylene wax, average particle size 100 nm, manufactured by Toho Chemical Co., Ltd.)
Hitech E-1000 (35% solids, nonionic emulsified polyethylene wax, average particle size 140 nm, manufactured by Toho Chemical Co., Ltd.)

Production of Black Ink Composition for Water-based Inkjet According to Production Method 1 Aqueous resin varnish B, carbon black, wax emulsion, glycerin, diethylene glycol, and ethylene oxide addition of acetylene glycol as a surfactant so as to have the mass ratio shown in Table 1 The product (Acetylenol E100, manufactured by Kawaken Fine Chemical Co., Ltd.) was stirred and mixed to obtain black ink compositions for aqueous inkjets of Examples 1 to 3 listed in Table 1.

Production of black ink composition for water-based inkjet by production method 2 Production of aqueous resin varnishes A to C in which alkali-soluble resins are dissolved in the presence of a basic compound (aqueous resin varnish A)
25 parts by mass of the alkali-soluble resin A was dissolved in a mixed solution of 3.2 parts by mass of sodium hydroxide and 71.8 parts by mass of water to obtain an aqueous resin varnish A having an alkali-soluble resin concentration of 25%. Obtained.
(Water-based resin varnish B)
25 parts by weight of the alkali-soluble resin B was dissolved in a mixed solution of 3.9 parts by weight of sodium hydroxide and 71.1 parts by weight of water to obtain an aqueous resin varnish B having an alkali-soluble resin concentration of 25%. Obtained.
(Water-based resin varnish C)
25 parts by mass of the alkali-soluble resin C was dissolved in a mixed solution of 3.9 parts by mass of sodium hydroxide and 71.1 parts by mass of water to obtain an aqueous resin varnish C having an alkali-soluble resin concentration of 25%. Obtained.

Preparation of black ink base for aqueous inkjet Addition and mixing of 48 parts by mass of water to 32 parts by mass of each of the above aqueous resin varnishes A to C, followed by addition of 20 parts by mass of carbon black, stirring and mixing, followed by kneading in a wet circulation mill Meat was prepared to prepare black ink bases A to C for aqueous inkjet.

Black ink composition for water-based inkjet After each of the above black ink bases A to C for water-based inkjet is diluted with water so that the pigment concentration becomes 5%, a cation exchange resin (DOWEX MONOSPHERE (H) 650C is added to the diluted solution. , Manufactured by Dow Chemical Co., Ltd.) was added and stirred, and ion exchange was performed until the pH was less than 4. Thus, resin-coated pigments A to C were obtained. Thereafter, the ion exchange resin was filtered through a mesh, and then suction filtered to obtain a water-containing cake (solid content 25%) containing the resin-coated pigments A to C.
To the water-containing cake containing the resin-coated pigments A to C, sodium hydroxide that neutralizes 80% of the alkali-soluble resin acid value in the resin-coated pigments A to C and water with a pigment concentration of 20% are added. After that, the mixture was stirred with a high-pressure emulsifying dispersion device: Gorin homogenizer (manufactured by APV GAULIN INK.) To obtain aqueous pigment dispersions A to C.
Next, the aqueous pigment dispersions A to C, wax emulsion, glycerin, diethylene glycol, ethylene oxide adduct of acetylene glycol as a surfactant (acetyleneol E100, Kawaken Fine Chemical Co., Ltd.) are used so that the mass ratios shown in Table 2 are obtained. The mixture was stirred and mixed to obtain black ink compositions for water-based inkjets of Examples 4 to 11 and Comparative Examples 1 to 6 described in Tables 2 and 3.

Examples 1 to 11 and Comparative Examples 1 to 11 were used by using a printer for evaluation in which a head manufactured by SPECTRA was mounted on the printing offset paper using the black ink composition for aqueous inkjets of Examples 1 to 11 and Comparative Examples 1 to 6. No. 6 black ink composition for water-based inkjet was printed.

Evaluation of Printed Material Evaluation is made by the following evaluation methods, and the results are shown in Table 1.
(Image density)
The solid image density (OD value) of each printed matter obtained by printing the aqueous inkjet black ink compositions of Examples 1 to 11 and Comparative Examples 1 to 6 was measured using a densitometer: SpectroEye (manufactured by X-Rite). did.

(Abrasion resistance)
A sample piece including a printed part at the center portion obtained by cutting each printed matter obtained by printing the aqueous ink-jet black ink composition of Examples 1 to 11 and Comparative Examples 1 to 6 into 2.5 cm × 25 cm is a Gakushin type scratch resistance test. Using a printing machine, the application paper was the same as that used for printing, and evaluation was made based on peeling of the surface of the rubbed sample piece and soiling of the application paper when rubbed 20 times each with a load of 200 g.
Evaluation Criteria A: No rubbing on the surface of the sample piece at the rubbed area, and no dirt on the backing paper. ○: No rubbing on the surface of the sample piece at the rubbing area, but the rubbing paper slightly dirty. Part of sample piece surface has linear paper peeling and the backing paper is dirty ×: Paper peeling is seen on almost the whole surface of the sample piece surface of the rubbing part, and the backing paper is dirty

(Storage stability of black ink composition for water-based inkjet)
About the black ink composition for water-based inkjets of Examples 1-11 and Comparative Examples 1-6, it took in a glass bottle, respectively, and measured the viscosity of 25 degreeC as initial viscosity using a viscometer (the Toki Sangyo company make, RE100L type). did. Then, it was sealed and stored at 60 ° C. for 1 month, and the viscosity after storage (25 ° C.) was measured with a viscometer. The storage stability was evaluated by the rate of change in viscosity (viscosity at 60 ° C., 1 month later−viscosity before storage / viscosity before storage).
Evaluation criteria A: Viscosity change rate of less than 5% B: Viscosity change rate of 5% or more and less than 10% Δ: Viscosity change rate of 10% or more and less than 20% ×: Viscosity change rate of 20% More than

(Discharge stability of black ink composition for water-based inkjet)
The black ink compositions for water-based inkjets of Examples 1 to 11 and Comparative Examples 1 to 6 are packed in an evaluation printer cartridge equipped with a SPECTRA head, printed on offset paper, and evaluated for ejection stability. went.
Evaluation criteria ◎: No printing disturbance, stable ejection ○: Printing disturbance, almost stable ejection Δ: Some printing disturbance, but ejection possible x: No ejection thing

According to the results of Examples 1 to 3, the aqueous inkjet black ink composition of the present invention has a scratch resistance and storage stability when the content of carbon black and wax emulsion changes within a predetermined range. In addition, it can be seen that the ejection stability is good and it has a stable property without being affected by the concentration of these components.
From the results of Examples 1 to 11, it can be said that the larger the content ratio of carbon black, the higher the image density of the printed matter.
In contrast to the results of Examples 1 to 3 using the aqueous ink jet black ink composition having a high resin concentration, the results of Examples 4 to 9 are any of scratch resistance, storage stability and ejection stability. It was good in one or more points, and Examples and 11 were comparable. This indicates that these properties are better when the carbon black surface is coated with an alkali-soluble resin that acts as a dispersant than when it is not, and that the amount of alkali-soluble resin used can be reduced. I mean.
Moreover, according to Examples 4-11, it turns out that the ink composition of this invention is excellent also in storage stability and initial stage viscosity.
As a result of Comparative Example 1, it is understood that the scratch resistance is insufficient when no wax emulsion is used.
From the result of Comparative Example 2, when the content of carbon black is small, the scratch resistance, storage stability and ejection stability are good, but the image density becomes small and the desired image density cannot be obtained. Further, as shown in Comparative Example 3, when the content of carbon black is excessive, all the properties of scratch resistance, storage stability and ejection stability are deteriorated.
4-6, when the average particle size of the wax is small, the image density, storage stability, and ejection stability are good, even if the wax solid content is appropriate. The rubability was poor.

Claims (2)

A resin-coated carbon black coated with an alkali-soluble resin, an alkali-soluble resin, a wax emulsion, a basic compound, and an aqueous inkjet black ink composition containing an aqueous medium, wherein the carbon black content is an aqueous inkjet black ink It is 8 to 12% by mass in the composition, and the wax emulsion has an average particle size of 160 to 200 nm, and is contained in an amount of 10 to 40 parts by mass with respect to 100 parts by mass of carbon black in terms of solid content. An aqueous inkjet black ink composition for uncoated paper and coated paper . The wax emulsion, nonionic polyalkylene wax emulsion in which claim 1 Symbol placement aqueous inkjet black ink composition.