JP2019203044A - Aqueous ink, ink cartridge and inkjet recording method - Google Patents

Abstract

To provide an aqueous ink which is excellent in color development of an image and scratch resistance.SOLUTION: There is provided an aqueous ink which comprises a self-dispersible pigment and wax particles, wherein the aqueous ink further comprises a polyoxyethylene alkyl ether, the content (mass%) of the polyoxyethylene alkyl ether is 0.20 times or more and 24.00 times or less in mass ratio (times) to the content (mass%) of the wax particles.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous ink, an ink cartridge, and an ink jet recording method.

  Examples of the color material of the water-based ink include dyes and pigments. In particular, by using an ink containing a pigment as a color material (hereinafter referred to as “pigment ink”), an image having excellent fastness can be obtained. In recent years, pigment inks have been used for recording images on a wide variety of recording media such as plain paper, glossy paper, and matte paper. When recording images on these various recording media, there is a demand for pigment inks that are excellent in color developability and scratch resistance of the images obtained. A pigment ink containing a self-dispersing pigment and wax particles has been proposed (see Patent Document 1). Also, a pigment ink containing a self-dispersing pigment, resin particles, and polyoxyethylene alkyl ether has been proposed (see Patent Document 2).

JP 2006-145313 A JP 2017-179284 A

  The present inventors have studied to record images on various recording media using the pigment inks described in Patent Documents 1 and 2. It has been found that when an image is recorded on a certain type of recording medium, the color developability and scratch resistance of the image may not be sufficiently obtained particularly in an area where the recording duty is low.

  Accordingly, an object of the present invention is to provide a water-based ink that is excellent in image color development and scratch resistance. Another object of the present invention is to provide an ink cartridge using the water-based ink and an ink jet recording method using the water-based ink.

  The present invention is a water-based ink containing a self-dispersing pigment and wax particles, wherein the water-based ink further contains a polyoxyethylene alkyl ether, and the content (mass%) of the polyoxyethylene alkyl ether is The present invention relates to a water-based ink having a mass ratio (times) to a content (mass%) of the wax particles of 0.20 times or more and 24.00 times or less.

  The present invention also relates to an ink cartridge comprising an ink and an ink storage portion that stores the ink, wherein the ink is a water-based ink having the above-described configuration.

  Furthermore, the present invention is an ink jet recording method for recording an image on a recording medium by ejecting ink from an ink jet recording head, wherein the ink is a water-based ink having the above-described configuration. Regarding the method.

  ADVANTAGE OF THE INVENTION According to this invention, the water-based ink excellent in the color development of an image and abrasion resistance, the ink cartridge using the said water-based ink, and the inkjet recording method can be provided.

It is sectional drawing which shows typically one Embodiment of the ink cartridge of this invention. FIG. 2 is a diagram schematically illustrating an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, in which (a) is a perspective view of a main part of the ink jet recording apparatus, and (b) is a perspective view of a head cartridge.

  Hereinafter, embodiments of the present invention will be described in detail. In the present invention, the water-based ink is hereinafter sometimes referred to as “ink”. Various physical property values are values at a temperature of 25 ° C. unless otherwise specified. Hereinafter, “reflected light” refers to reflected light of light incident on an image formed of a pigment. When light enters the image from the direction of 45 degrees, light that is reflected at the same angle of 45 degrees with respect to the image (hereinafter referred to as “regular reflection light”) is generated. This regular reflection light is a color component different from the original color of the pigment. Furthermore, not only specularly reflected light but also light diffused and reflected in various directions (hereinafter sometimes referred to as “diffused light”) is generated. This diffused light is the original color component of the pigment.

  When recording the image on the matte paper among the recording media, the present inventors cannot sufficiently obtain the color developability of the image and the scratch resistance when using the inks described in Patent Documents 1 and 2. Found that there is a case. As a result of the study by the present inventors, even when an image is recorded on a mat paper, in order to obtain the color developability and scratch resistance of the image, a self-dispersing pigment, wax particles, and polyoxyethylene alkyl ether are used. It has been found that it is important to use the ink that it contains. The reason is as follows.

  Compared to glossy paper, which is the same coated paper, matte paper has higher ink permeability because the ink-receiving layer has larger pores. Even in such a recording medium with high ink permeability, it is necessary to use a self-dispersing pigment in order to keep the pigment near the surface of the recording medium. When a resin-dispersed pigment is used as the pigment, even if ink adheres to the recording medium, the pigment is difficult to aggregate because the resin exists between the pigments. On the other hand, when a self-dispersing pigment is used as the pigment, if the ink adheres to the recording medium, the pigment is likely to aggregate, so that the pigment does not easily enter the pores of the ink receiving layer of the recording medium. Therefore, by using a self-dispersing pigment as the pigment, it is possible to keep the pigment near the surface of the recording medium.

  However, even when an ink containing a self-dispersing pigment is used, when an image is recorded on mat paper, the color developability of the image cannot be obtained. The matte paper has an ink receiving layer formed using an inorganic pigment having a large particle size. Therefore, the surface of the matte paper is less smooth than the glossy paper that is the same coated paper. When light is incident on the pigment attached to such a surface, the direction in which the light is incident varies, so the direction in which the light is reflected varies. As a result, specularly reflected light is also generated in various directions, so that the specularly reflected light easily enters the eyes of a person observing the image. Therefore, in an image recorded on mat paper, a color different from the original color of the pigment is easily recognized.

  In particular, in the region where the recording duty of the image is low, the amount of the pigment adhering to the recording medium is small compared to the region where the recording duty is high, so the amount of reflected light from the image is also small. For this reason, since the proportion of the regular reflection light in the reflected light is also increased, the regular reflection light easily enters the eyes of the person observing the image. As a result, it is easy to recognize a color different from the original color of the pigment, and the color developability of the image cannot be obtained.

  Therefore, in order to obtain color developability even in a region where the image recording duty is low, the ink is further added with wax particles. Compared to pigments, wax particles have a low refractive index and a low light reflectance. For this reason, it was thought that reflection of light other than diffused light that can be recognized as the original color of the pigment can be suppressed and color development can be improved. Furthermore, the present inventors considered that the color developability of the image is improved for the following reason.

  When light incident on the image hits particles such as pigments and wax particles, all generate reflected light. Even if a pigment layer composed of pigments and wax particles is formed on the recording medium, the total amount of particles that reflect light does not change compared to the case where a pigment layer composed only of pigments is formed. However, when a pigment layer composed of pigment and wax particles is formed on the recording medium, the proportion of the pigment in the pigment layer decreases. Here, the regular reflection light generated from the wax particles is white light. Therefore, the color developability of the image is hardly affected by the specularly reflected light generated from the resin particles. When a pigment layer composed of pigment and wax particles is formed, specular reflection light, which is a color component different from the original color of the pigment, in reflected light generated from an image is reduced. For this reason, it was estimated that the color developability of the image can be obtained even if the recording duty of the image is low and the amount of the pigment adhering to the recording medium is small. However, contrary to prediction, even when an ink containing a self-dispersing pigment and wax particles was used, the color development of the image could not be obtained in the region where the image recording duty was low.

  Furthermore, the present inventors can improve the scratch resistance of an image because the friction coefficient of the pigment layer composed of pigment and wax particles is reduced compared to the pigment layer composed only of the pigment. I thought. However, even when an ink containing a self-dispersing pigment and wax particles was used, the scratch resistance of the image could not be obtained. The reason why the color developability and scratch resistance of the image cannot be obtained is as follows.

  Generally, the self-dispersing pigment has a hydrophilic group for stable dispersion in the ink, but the wax particles are composed of oils and fats in which higher fatty acids and glycerin are esterified or hydrocarbons having a large number of carbon atoms. High hydrophobicity. Therefore, the hydrophilic group of the self-dispersing pigment and the hydrophobic wax particles are unlikely to interact with each other. As a result, even if the self-dispersing pigment stays near the surface of the recording medium, the wax particles enter the pores of the recording medium. In particular, in a region where the image recording duty is low, the amount of the pigment adhering to the recording medium is small, so that the sealing effect by the pigment is not sufficient, and the wax particles hardly stay near the surface of the recording medium. Even if the ink contains wax particles, if the wax particles enter the pores of the recording medium, the effect of the wax particles may not be exhibited, and the color developability and scratch resistance of the image may not be obtained. found.

  Therefore, in order to keep the wax particles near the surface of the recording medium, the ink further contains polyoxyethylene alkyl ether. Polyoxyethylene alkyl ether has a hydrophilic part and a hydrophobic part. The oxygen atom in the ethylene oxide group, which is the hydrophilic part of the polyoxyethylene alkyl ether, interacts with the hydrophilic group of the self-dispersing pigment, so that the polyoxyethylene alkyl ether is adsorbed on the self-dispersing pigment. Furthermore, since the alkyl group, which is the hydrophobic part of the polyoxyethylene alkyl ether, interacts with the wax particles in a hydrophobic manner, a self-dispersing pigment staying near the surface of the recording medium is passed through the polyoxyethylene alkyl ether through the wax. Particles adsorb. As a result, the wax particles do not enter the pores of the recording medium and can remain near the surface of the recording medium, so that it is possible to obtain image coloring and scratch resistance.

  Even if the polyoxyethylene polyoxypropylene alkyl ether described in Patent Document 1 is used in place of the polyoxyethylene alkyl ether, the color developability and scratch resistance of the image cannot be obtained. Since the propylene oxide group in the polyoxyethylene polyoxypropylene alkyl ether has a structure in which the carbon chain is branched, it tends to be sterically hindered compared to an ethylene oxide group that does not have a structure in which the carbon chain is branched. In addition, polyoxyethylene polyoxypropylene alkyl ethers having groups with branched carbon chains have low motility in the ink, so that polyoxyethylene alkyl ethers adsorb on the self-dispersing pigments and wax particles, respectively. It becomes difficult. For this reason, the wax particles hardly stay near the surface of the recording medium, and the color development and scratch resistance of the image cannot be obtained.

  Furthermore, content (mass%) of polyoxyethylene alkyl ether is 0.20 times or more and 24.00 times or less in mass ratio (times) to the content (mass%) of wax particles. When the ratio is less than 0.20 times, since the polyoxyethylene alkyl ether is less than the wax particles, the wax particles do not stay near the surface of the recording medium, and enter the pores of the recording medium. Colorability and scratch resistance cannot be obtained. When the ratio exceeds 24.00 times, the amount of polyoxyethylene alkyl ether is large relative to the wax particles. When ink adheres to the recording medium, a large amount of polyoxyethylene alkyl ether tends to be present near the surface of the recording medium, with the hydrophilic portion of the polyoxyethylene alkyl ether being oriented on the surface of the recording medium. Since the hydrophilicity of the surface of the recording medium is increased and the pigment is less likely to aggregate, the pigment itself enters the pores of the recording medium. For this reason, neither pigment nor wax particles remain near the surface of the recording medium, so that it is not possible to obtain image coloring and scratch resistance.

<Ink>
The ink contains a self-dispersing pigment, wax particles, and polyoxyethylene alkyl ether. Hereinafter, components that can be used in the ink will be described.

(Self-dispersing pigment)
As the self-dispersing pigment, it is preferable to use a pigment that binds an anionic group directly or through another atomic group to the particle surface of the pigment. As the pigment, it is preferable to use carbon black or an organic pigment. Moreover, a pigment can be used individually by 1 type or in combination of 2 or more types.

Examples of the anionic _group, -COOM, -SO 3 M, and the like _-PO 3 _{M 2.} Examples of M independently include a hydrogen atom; an alkali metal; ammonium (NH ₄ ); and an organic ammonium. Examples of the other atomic group (—R—) include an alkylene group; an arylene group; an amide group; a sulfonyl group; an imino group; a carbonyl group; an ester group; an ether group; The content (% by mass) of the self-dispersing pigment in the ink is preferably 1.00% by mass or more and 10.00% by mass or less based on the total mass of the ink.

[Volume average particle diameter]
The volume average particle diameter (nm) of the self-dispersing pigment is preferably 50 nm or more and 300 nm or less, and more preferably 50 nm or more and 200 nm or less. The volume average particle diameter can be determined by a dynamic light scattering method.

(Wax particles)
The ink contains wax particles. The wax particles are present in a state of being dispersed in the ink. Examples of the wax include natural wax and synthetic wax.

  Examples of natural waxes include petroleum waxes, plant waxes, and animal and plant waxes. Examples of petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum. Examples of plant waxes include carnauba wax, candelilla wax, rice wax, and wood wax. Examples of animal and plant waxes include lanolin and beeswax.

  Examples of synthetic waxes include synthetic hydrocarbon waxes and modified waxes. Examples of the synthetic hydrocarbon wax include polyolefin wax and Fischer-Tropsch wax. Examples of the modified wax include paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives.

  These waxes can be used singly or in combination of two or more. The wax particles are preferably formed of at least one of paraffin wax and polyolefin wax.

  The content (% by mass) of wax particles in the ink is preferably 0.01% by mass or more and 1.00% by mass or less, and 0.05% by mass or more and 0.50% by mass based on the total mass of the ink. More preferably, it is as follows.

(Dispersant)
The ink preferably contains a dispersant for dispersing the wax particles. That is, the wax particles are preferably dispersed in the ink using a dispersant. Examples of the dispersant include a surfactant; a resin having a hydrophilic group such as a sulfonic acid group or a carboxylic acid group; Examples of the resin having a hydrophilic group include a resin having a hydrophilic group graft-bonded; a resin having a unit derived from a hydrophilic monomer and a monomer having a hydrophobic portion; Can do.

  When polyoxyethylene alkyl ether that is a surfactant is used as a dispersant, polyoxyethylene alkyl ether that is a dispersant is also included in calculating the “content of polyoxyethylene alkyl ether”.

[Volume average particle diameter]
The volume average particle diameter (nm) of the wax particles is preferably 25 nm or more and 300 nm or less, and more preferably 30 nm or more and 100 nm or less. The volume average particle diameter (nm) of the self-dispersing pigment is preferably a ratio (times) to the volume average particle diameter (nm) of the wax particles and is preferably 0.30 times or more and 10.00 times or less. When the ratio is less than 0.30, the particle size of the self-dispersing pigment is too small with respect to the wax particles, so that light is easily reflected on the surface of the wax particles, and scattered light increases. Accordingly, since it is difficult to suppress reflection of light other than diffused light that can be recognized as the original color of the pigment, there is a case where the color developability of the image cannot be obtained sufficiently. If the ratio exceeds 10.00 times, the particle size of the self-dispersing pigment is too large for the wax particles, so that light is not easily reflected on the surface of the wax particles, and the color developability of the image may not be sufficiently obtained. is there.

[Acid value]
The acid value (mgKOH / g) of the wax particles is preferably 50 mgKOH / g or less. When the acid value exceeds 50 mgKOH / g, the hydrophilicity of the wax particles is increased, so that the hydrophobic portion of the polyoxyethylene alkyl ether and the wax particles are less likely to interact with each other in a hydrophobic manner. This makes it difficult for the wax particles to stay near the surface of the recording medium, so that sufficient color development and scratch resistance may not be obtained in some cases. The acid value of the wax particles can be determined by potentiometric titration. The acid value (mgKOH / g) of the wax particles is preferably 5 mgKOH / g or more.

(Polyoxyethylene alkyl ether)
The polyoxyethylene alkyl ether has a structure represented by R—O— (CH ₂ CH ₂ O) _n H. R is an alkyl group, and n is a positive integer. The alkyl group (R) in the polyoxyethylene alkyl ether is a hydrophobic site, and the ethylene oxide group (CH ₂ CH ₂ O) is a hydrophilic site. Thus, since polyoxyethylene alkyl ether has a hydrophobic part and a hydrophilic part, it can interact with each of a self-dispersion pigment and wax particles.

  In order to have a strong hydrophobic interaction with the wax particles, the carbon number of the alkyl group (R) in the polyoxyethylene alkyl ether is preferably 12 or more, and more preferably 16 or more. If the number of carbon atoms is less than 16, the polyoxyethylene alkyl ether is strongly hydrophobic and hardly interacts with the wax particles, so that the wax particles do not stay near the surface of the recording medium. You may not get enough. The carbon number is preferably 18 or less.

  Examples of the alkyl group (R) include a lauryl group, myristol group, cetyl group, palmitoleyl group, stearyl group, oleyl group, and linoleyl group. Of these, the alkyl group is preferably a saturated hydrocarbon group. The alkyl group is preferably a straight chain. n is preferably 4 or more and 30 or less.

  Among these, the polyoxyethylene alkyl ether preferably has an HLB value of 12.9 or more according to the Griffin method. Here, the HLB value according to the Griffin method is calculated from the formula amount of the ethylene oxide group of the polyoxyethylene alkyl ether and the molecular weight of the polyoxyethylene alkyl ether, the HLB value = 20 × (the formula amount of the ethylene oxide group of the polyoxyethylene alkyl ether) ) / (Molecular weight of polyoxyethylene alkyl ether). The HLB value indicates the degree of hydrophilicity or lipophilicity of polyoxyethylene alkyl ether in the range of 0.0 to 20.0. The lower the HLB value, the higher the lipophilicity (hydrophobicity) of the polyoxyethylene alkyl ether. On the other hand, the higher the HLB value, the higher the hydrophilicity of the polyoxyethylene alkyl ether.

  When the HLB value is 12.9 or more, the polyoxyethylene alkyl ether has high hydrophilicity and has a sufficient amount of ethylene oxide groups for hydrogen bonding with the hydrophilic group of the self-dispersing pigment. The HLB value is preferably 16.0 or less.

  The content (mass%) of the polyoxyethylene alkyl ether is preferably 0.03 times or more and 1.20 times or less in mass ratio (times) to the content (mass%) of the self-dispersing pigment. If the mass ratio is less than 0.03 times, the amount of polyoxyethylene alkyl ether is less than that of the self-dispersing pigment, so that the self-dispersing pigment is difficult to adsorb to the wax particles via the polyethylene alkyl ether. As a result, it is difficult to keep the wax particles near the surface of the recording medium, and the color development and scratch resistance of the image may not be sufficiently obtained. When the mass ratio exceeds 1.20 times, the amount of polyoxyethylene alkyl ether is larger than that of the self-dispersing pigment. When ink adheres to the recording medium, a large amount of polyoxyethylene alkyl ether tends to be present near the surface of the recording medium, with the hydrophilic portion of the polyoxyethylene alkyl ether being oriented on the surface of the recording medium. Since the hydrophilicity of the surface of the recording medium is increased and the pigment is less likely to aggregate, the pigment itself enters the pores of the recording medium. For this reason, since neither pigment nor wax particles remain near the surface of the recording medium, the color developability and scratch resistance of the image may not be sufficiently obtained.

(Aqueous medium)
The ink is an aqueous ink containing at least water as an aqueous medium. As water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the ink is preferably 10.00% by mass or more and 90.00% by mass or less, preferably 50.00% by mass or more and 90.00% by mass or less, based on the total mass of the ink. More preferably.

  The aqueous medium may further contain a water-soluble organic solvent. The water-soluble organic solvent is not particularly limited as long as it is water-soluble, and monohydric alcohol, polyhydric alcohol, (poly) alkylene glycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less based on the total mass of the ink.

(Other additives)
In addition to the above-described components, the ink may contain water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. You may make it contain. In addition, surfactants other than polyoxyethylene alkyl ethers, pH adjusters, antifoaming agents, rust preventives, antiseptics, fungicides, antioxidants, anti-reducing agents, evaporation are optionally added to the ink. Various additives such as an accelerator may be contained.

(Ink physical properties)
The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 5.0 mPa · s or less, and more preferably 1.0 mPa · s or more and 3.0 mPa · s or less. The static surface tension of the ink at 25 ° C. is preferably 28 mN / m or more and 45 mN / m or less. Further, the pH of the ink at 25 ° C. is preferably 5 or more and 9 or less.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink storage unit that stores the ink. And the ink accommodated in this ink accommodating part is the ink of this invention demonstrated above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage portion for storing ink. The ink storage portion is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other via a communication port 18. The absorber housing chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may have a form in which the entire amount of ink stored is held by an absorber without having an ink storage chamber for storing liquid ink. Further, the ink storage portion may have a form that does not have an absorber and stores the entire amount of ink in a liquid state. Furthermore, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method>
The ink jet recording method of the present invention is a method of recording an image on a recording medium by discharging the ink of the present invention described above from an ink jet recording head. Examples of the method for ejecting ink include a method for imparting mechanical energy to the ink and a method for imparting thermal energy to the ink. In the present invention, it is preferable that the recording head ejects ink by the action of thermal energy. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

  2A and 2B are diagrams schematically showing an example of an ink jet recording apparatus used in the ink jet recording method of the present invention. FIG. 2A is a perspective view of a main part of the ink jet recording apparatus, and FIG. 2B is a perspective view of a head cartridge. It is. The ink jet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set. While the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is conveyed in the sub-scanning direction by a conveying unit (not shown), whereby an image is recorded on the recording medium 32.

(recoding media)
The recording medium for recording an image using the ink of the present invention is preferably mat paper. The matte paper can be selected according to the purpose of use of the recorded matter on which the image is recorded. Examples of mat paper include art paper that makes use of the texture of the base material (drawing paper tone, canvas tone, Japanese paper tone, etc.) in order to express paintings, photographs, graphic images and the like according to preference. . The matte paper has an ink receiving layer on the surface. The ink receiving layer of matte paper has an inorganic pigment with a volume average particle diameter of 3.0 μm to 10.0 μm, and absorbs ink using voids formed by the inorganic pigment. Examples of inorganic pigments include silica, alumina, hydrated alumina, and calcium carbonate. Even if plain paper and glossy paper are used as the recording medium, the surface is not uneven, so that there is no problem that the color developability of the image cannot be obtained in a region where the recording duty is low.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. In addition, what is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
To a solution obtained by dissolving 5.00 g of concentrated hydrochloric acid in 5.50 g of water, 1.80 g of 4-amino-1,2-benzenedicarboxylic acid was added at a temperature of 5 ° C. In order to maintain the temperature at 10 ° C. or lower, a solution obtained by dissolving 1.80 g of sodium nitrite in 9.00 g of water was added to the solution obtained above while stirring in an ice bath. After stirring for 15 minutes, 6.00 g of carbon black having a specific surface area of 254 m ² / g and a DBP oil absorption of 180 mL / 100 g was added and mixed. Furthermore, after stirring for 15 minutes, the obtained slurry was filtered with a filter paper (standard filter paper No. 2, manufactured by Advantech), and the carbon black was sufficiently washed with water and dried in an oven at a temperature of 110 ° C. Water was added to the obtained carbon black to obtain a pigment dispersion 1 having a carbon black content (solid content) of 10.0%. The pigment dispersion 1 contained a self-dispersed pigment having —C ₆ H ₃ — (COONa) ₂ groups bonded to the particle surface. The volume average particle diameter (nm) of the pigment was 130 nm.

(Pigment dispersion 2)
To a solution obtained by dissolving 5.00 g of concentrated hydrochloric acid in 5.50 g of water, 1.24 g of 4-amino-1,2-benzenedicarboxylic acid was added at a temperature of 5 ° C. In order to maintain the temperature at 10 ° C. or lower, a solution obtained by dissolving 1.80 g of sodium nitrite in 9.00 g of water was added to the solution obtained above while stirring in an ice bath. After stirring for 15 minutes, 6.00 g of carbon black having a specific surface area of 180 m ² / g and a DBP oil absorption of 280 mL / 100 g was added and mixed. Further, after stirring for 15 minutes, the obtained slurry was filtered with a filter paper (standard filter paper No. 2, manufactured by Advantech), and the carbon black was sufficiently washed with water and dried in an oven at a temperature of 110 ° C. Water was added to the obtained carbon black to obtain a pigment dispersion 2 having a carbon black content (solid content) of 10.0%. Pigment dispersion 2 contained a self-dispersed pigment having —C ₆ H ₃ — (COONa) ₂ groups bonded to the particle surface. The volume average particle diameter (nm) of the pigment was 300 nm.

(Pigment dispersion 3)
To a solution obtained by dissolving 5.00 g of concentrated hydrochloric acid in 5.50 g of water, 0.96 g of 4-amino-1,2-benzenedicarboxylic acid was added at a temperature of 5 ° C. In order to maintain the temperature at 10 ° C. or lower, a solution obtained by dissolving 1.80 g of sodium nitrite in 9.00 g of water was added to the solution obtained above while stirring in an ice bath. After stirring for 15 minutes, 6.00 g of carbon black having a specific surface area of 140 m ² / g and a DBP oil absorption of 121 mL / 100 g was added and mixed. Further, after stirring for 15 minutes, the obtained slurry was filtered with a filter paper (standard filter paper No. 2, manufactured by Advantech), and the carbon black was sufficiently washed with water and dried in an oven at a temperature of 110 ° C. Water was added to the obtained carbon black to obtain a pigment dispersion 3 having a carbon black content (solid content) of 10.0%. The pigment dispersion 3 contained a self-dispersed pigment having —C ₆ H ₃ — (COONa) ₂ groups bonded to the particle surface. The volume average particle diameter (nm) of the pigment was 80 nm.

(Pigment dispersion 4)
Carbon black having a specific surface area of 254 m ² / g, DBP oil absorption of 180 mL / 100 g, and pH 3.0 was added to 1,000 mL of water and mixed. To this solution, 450 g of sodium hypochlorite (effective chlorine concentration is 12%) was dropped, and the temperature was maintained at 100 ° C. to 105 ° C. and stirred for 10 hours to obtain a slurry. The obtained slurry was filtered with a filter paper (standard filter paper No. 2, manufactured by Advantech), and the carbon black was sufficiently washed with water and dispersed in 3,000 mL of water to obtain a filtrate. The obtained filtrate is desalted using a reverse osmosis membrane until the electric conductivity becomes 0.2 μs / m, adjusted to pH 8 to 10, and then concentrated to have a carbon black content (solid content) of 10. A pigment dispersion 4 of 0.0% was obtained. The pigment dispersion 4 contained a self-dispersed pigment having —COONa groups bonded to the particle surface. The volume average particle diameter (nm) of the pigment was 130 nm.

(Pigment dispersion 5)
A pigment dispersion 5 having a Cab-O-Jet 450C (Cabot) content (solid content) of 10.0% was obtained. The pigment dispersion 5 includes C.I. I. A self-dispersing pigment in which a functional group containing a phosphonic acid group was bonded to the surface of the pigment blue 15: 4 particles was contained. The volume average particle diameter (nm) of the pigment was 113 nm.

(Pigment dispersion 6)
A pigment dispersion 6 having a Cab-O-Jet 465M (Cabot) content (solid content) of 10.0% was obtained. The pigment dispersion 6 includes C.I. I. The self-dispersing pigment in which a functional group including a phosphonic acid group is bonded to the surface of the pigment red 122 particle was included. The volume average particle diameter (nm) of the pigment was 105 nm.

(Pigment dispersion 7)
A pigment dispersion 7 having a Cab-O-Jet 470Y (Cabot) content (solid content) of 10.0% was obtained. The pigment dispersion 7 includes C.I. I. A self-dispersing pigment in which a functional group containing a phosphonic acid group was bonded to the surface of the pigment yellow 74 particles was contained. The volume average particle diameter (nm) of the pigment was 170 nm.

(Pigment dispersion 8)
10.0 parts of pigment, 50.0 parts of liquid containing resin, and 40.0 parts of ion-exchanged water were mixed. As the pigment, carbon black having a specific surface area of 254 m ² / g and a DBP oil absorption of 180 mL / 100 g was used. As the liquid containing the resin, the styrene-acrylic acid copolymer is neutralized with an equimolar amount of 10.0% sodium hydroxide aqueous solution with respect to the acid value of the copolymer, and the resin content is 20. A liquid that was 0% was used. The styrene-acrylic acid copolymer has an acid value of 200 mgKOH / g and a weight average molecular weight of 10,000. This mixture was dispersed for 5 hours while cooling with water using a batch type vertical sand mill (manufactured by IMEX) filled with 200.0 parts of zirconia beads having a particle diameter of 0.3 mm. Thereafter, the dispersion was centrifuged to remove coarse particles, and pressure filtration was performed with a cellulose acetate filter (manufactured by Advantech) having a pore size of 3.0 μm. By the above-described method, a pigment dispersion 8 (pigment content of 10.0% and resin content of 10.0%) in a state where the pigment was dispersed in water by the resin was obtained. The volume average particle diameter (nm) of the pigment was 130 nm.

<Preparation of dispersion of wax particles>
To a container equipped with a stirrer, a thermometer, and a temperature controller, wax particles shown in Table 1, an anionic surfactant potassium montanate, a potassium hydroxide aqueous solution, and ion-exchanged water as a dispersant were added. The temperature was raised to 160 ° C., stirred for 2 hours, and then cooled to a temperature of 40 ° C. to obtain a dispersion of wax particles having a wax particle (solid content) content of 10.0%. The volume average particle diameter and acid value of the wax particles were the values shown in Table 1. Polyethylene wax is one type of polyolefin wax.

<Preparation of dispersion of resin particles>
35.0 parts of styrene, 29.0 parts of butyl acrylate, 16.0 parts of butyl methacrylate, and 20.0 parts of methacrylic acid (total 100.0 parts) were mixed. 200.0 parts of ion-exchanged water and 2.0 parts of an emulsifier (sodium dodecylbenzene) were added to a flask equipped with a stirrer, a nitrogen inlet tube, a reflux condenser, and a thermometer. Nitrogen gas was introduced into the flask, 20.0 parts of the previously prepared monomer mixture was added with stirring, and the temperature was raised to 85 ° C. A liquid prepared by dissolving 80.0 parts of the previously prepared monomer mixture and 1.0 part of a polymerization initiator (potassium persulfate) in 20.0 parts of water was dropped into this flask over 3 hours. did. Thereafter, aging was performed for 2 hours to obtain a dispersion of resin particles having a resin particle content of 20.0%. The volume average particle diameter of the resin particles was 150 nm, and the acid value was 130 mgKOH / g.

[Acid value of wax particles and resin particles]
The method for measuring the acid value of the wax particles and the resin particles is as follows. Using a potentiometric automatic titrator (AT-510, manufactured by Kyoto Denshi Kogyo Co., Ltd.) equipped with a streaming potential titration unit (PCD-500), the acid value of urethane resin dissolved in tetrahydrofuran is measured by colloidal titration using the potential difference. did. At this time, an ethanol solution of potassium hydroxide was used as a titration reagent.

[Volume average particle diameter of pigment, wax particle, and resin particle]
Using a particle size analyzer (Nanotrack UPA-EX150, Nikkiso Co., Ltd.) by a dynamic light scattering method, a particle size of a pigment dispersion, a wax particle dispersion, and a resin particle dispersion diluted with pure water is used. Was measured. The measurement conditions were SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: true sphere, refractive index: 1.50.

<Preparation of ink>
After mixing each component described in Tables 2 and 3 and stirring sufficiently, pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare each ink. The polyoxyethylene alkyl ether used is as shown in Table 4. All the polyoxyethylene alkyl ethers shown in Table 4 are manufactured by Nikko Chemicals. NIKKOL PBC34 is a polyoxyethylene polyoxypropylene alkyl ether manufactured by Nikko Chemicals. Acetylenol E100 is an acetylene glycol surfactant manufactured by Kawaken Fine Chemicals. MegaFuck F-444 is a fluorinated surfactant made by DIC.

<Evaluation>
Each ink was filled in an ink cartridge, and set in an ink jet recording apparatus (PIXUS PRO-10, manufactured by Canon Inc.) equipped with a recording head for discharging the ink by thermal energy. The resolution of the inkjet recording apparatus is 2400 dpi × 1200 dpi. An image recorded under the condition of applying one 30.4 ng ink droplet to a unit area of 1/600 inch × 1/600 inch is defined as having a recording duty of 100%. A solid image having a recording duty of 40% and a low duty was recorded on matte paper (Photo Rag 188 g / m ² , manufactured by Hahnmuhle) using the inkjet recording apparatus. In the present invention, according to the following evaluation criteria, A or B is an acceptable level and C is an unacceptable level. The evaluation results are shown in Table 6. The volume average particle diameter (nm) of the inorganic pigment in the ink receiving layer of the matte paper is in the range of 3.0 μm to 10.0 μm.

(Color development)
The obtained image was subjected to color measurement as follows using a spectrophotometer (Spectrolino, manufactured by Gretag Macbeth) to evaluate the color developability. The measurement conditions were a light source D50 and a viewing angle of 2 °. When an ink having a pigment type of carbon black was used, the optical density of the image was measured to evaluate the color developability. When yellow ink, magenta ink, and cyan ink were used, the chroma C ^* of the image was measured to evaluate the color developability. Here, the saturation C ^* is obtained by measuring a ^* and b ^* based on the L ^* a ^* b ^* display system defined by the CIE (International Commission on Illumination), and C ^* = {(a ^* ) ² + (b ^* ) ² } It is a value calculated by the formula of ^1/2 . Evaluation criteria are listed in Table 5.

(Abrasion resistance)
The obtained image was dried at a temperature of 25 ° C. for 10 minutes, and then the surface of the solid image was lightly rubbed 10 times with a nail. Thereafter, the solid image was visually observed to evaluate scratch resistance.
A: The portion rubbed with the nail was not noticeable. B: The portion rubbed with the nail was conspicuous, but the white background of the recording medium was not visible. C: The white background of the portion rubbed with the nail was visible.

Using the ink jet recording apparatus equipped with the ink 24, the recording duty is 100% on Canon photographic paper / glossy gold (GL-101, manufactured by Canon) and matte paper (Photo Rag 188 g / m ² , manufactured by Hahnmuhle). A solid image was recorded. When recording an image on any recording medium, the evaluation rank of the color developability and scratch resistance of the image was an acceptable A rank.

  A solid image having a recording duty of 40% was recorded on Canon photographic paper / glossy gold (GL-101, manufactured by Canon) using the inkjet recording apparatus equipped with the ink 24. As a result, the evaluation rank of the color developability and scratch resistance of the image was an acceptable A rank. However, as described in Comparative Example 3, when a solid image having a recording duty of 40% is recorded on mat paper using the ink jet recording apparatus having the ink 24 mounted thereon, the evaluation rank of the color development property and scratch resistance of the image is recorded. Was an unacceptable level of C rank.

Claims (8)

A water-based ink containing a self-dispersing pigment and wax particles,
The water-based ink further contains polyoxyethylene alkyl ether;
The content (mass%) of the polyoxyethylene alkyl ether is 0.20 times or more and 24.00 times or less in mass ratio (times) to the content (mass%) of the wax particles. Water based ink.   The content (mass%) of the polyoxyethylene alkyl ether is 0.03 times or more and 1.20 times or less as a mass ratio (times) to the content (mass%) of the self-dispersing pigment. The water-based ink described.   The volume average particle diameter (nm) of the self-dispersing pigment is a ratio (times) to the volume average particle diameter (nm) of the wax particles, and is 0.30 times or more and 10.00 times or less. The water-based ink described.   The water-based ink according to any one of claims 1 to 3, wherein the polyoxyethylene alkyl ether has an HLB value by the Griffin method of 12.9 or more.   The water-based ink according to any one of claims 1 to 4, wherein the alkyl group of the polyoxyethylene alkyl ether has 16 or more carbon atoms.   The water-based ink according to any one of claims 1 to 5, wherein the wax particles have an acid value (mgKOH / g) of 50 mgKOH / g or less. An ink cartridge comprising ink and an ink containing portion for containing the ink,
An ink cartridge, wherein the ink is the water-based ink according to any one of claims 1 to 6. An inkjet recording method for recording an image on a recording medium by discharging ink from an inkjet recording head,
An ink jet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 6.