JP2015229730A - Ink, ink cartridge, and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ink that can record an image having excellent scratch resistance and color development.SOLUTION: There is provided inkjet ink containing a pigment, a resin particle, and an urethane resin. In the ink, the resin particle is formed of a copolymer having a unit (X) derived from α-olefin polymer, a unit (A) derived from α,β-ethylenic unsaturated acid monomer comprising maleic acid, and a unit (B) derived from α,β-ethylenic unsaturated monomer other than the α,β-ethylenic unsaturated acid monomer, the density of the α-olefin polymer is 850 kg/mor more and 960 kg/mor less, and the urethane resin comprises a poly(oxytetramethylene) structure.

Description

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

  In recent years, with the advancement of inkjet recording technology, it has become possible to record high-definition and color-developing images, such as those realized by silver salt photography and offset printing, relatively easily and inexpensively even in general households. It is coming.

  When a dye ink containing a dye is used as a coloring material, a good image can be obtained without graininess, but there is a problem that the fastness such as light resistance, water resistance, and gas resistance is inferior. For this reason, in recent years, pigment ink containing a pigment as a coloring material has been used. Examples of such a pigment ink include an ink containing a pigment dispersed with a water-soluble resin for the purpose of further improving the fastness such as the fixing property of the pigment to the recording medium and the scratch resistance of the image. Widely used. Furthermore, an ink has been proposed in which the fixability of pigment particles on a recording medium is improved by adding a urethane resin (Patent Document 1).

  In an image recorded with ink containing a pigment dispersed with such a resin, the recording layer is hardly scraped against light rubbing by a fingernail or the like, and the scratch resistance is improved to some extent. However, it does not have sufficient scratch resistance when the image is strongly rubbed with a fingernail or the like.

  Therefore, in order to improve the scratch resistance of the image, it has been proposed to apply ink using two types of waxes having different average particle diameters to the recording medium, and according to such proposal, it is said that the color developability is also improved. (Patent Document 2). In addition, an ink containing a pigment and a polyolefin wax such as a polyethylene wax has been proposed (Patent Document 3).

  By the way, polyolefin resin is known as a plastic that can be used for various industrial products. A polyolefin resin is a resin having a low specific gravity and excellent moldability, chemical resistance, water resistance, and the like. However, since polyolefin resin has low polarity, it is known that coating and adhesion are difficult resins. Accordingly, it is known to treat the surface of a polyolefin resin with an acid-modified polyolefin resin that has been modified with an acid to impart polarity. In addition, it is known that such an acid-modified polyolefin resin is used as a binder or an adhesive for ink or paint (Patent Document 4). Furthermore, a clear ink containing a modified polypropylene emulsion has been proposed (Patent Document 5).

Japanese Patent No. 3897268 JP 2007-277290 A JP 2005-48108 A JP 2009-40920 A JP 2003-335058 A

  Since the resin particles proposed in Patent Document 4 are made of a polyolefin resin, the surface energy of the recording layer can be lowered by using an ink containing the resin particles. Furthermore, it is possible to improve the scratch resistance of the recording layer by reducing the friction coefficient. However, as a result of investigations by the present inventors, it has been found that since the slipping property between the pigment particles increases, the binding property between the pigment particles decreases, and the pigment particles are easily peeled off from the recording layer.

  Further, even when the ink containing the modified polypropylene emulsion proposed in Patent Document 4 is used, the scratch resistance of the obtained image is still insufficient. Furthermore, the present inventors examined an ink containing the resin particles proposed in Patent Document 4 and the urethane resin proposed in Patent Document 1. As a result, it was found that the scratch resistance of the image was slightly improved by containing the urethane resin, but the color developability of the image was lowered depending on the type of the urethane resin.

  Accordingly, an object of the present invention is to provide an ink capable of recording an image having excellent scratch resistance and color developability. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using the ink.

The above object is achieved by the present invention described below. That is, according to the present invention, an inkjet ink containing a pigment, resin particles, and a urethane resin, wherein the resin particles contain a unit (X) derived from an α-olefin polymer and maleic acid. Unit (A) derived from α, β-ethylenically unsaturated acid monomer and α, β-ethylenically unsaturated monomer other than α, β-ethylenically unsaturated acid monomer A density of the α-olefin polymer is 850 kg / m ³ or more and 960 kg / m ³ or less, and the urethane resin has a poly (oxytetramethylene) structure. An ink-jet ink is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the ink which can record the image excellent in abrasion resistance and coloring property can be provided. In addition, according to the present invention, it is possible to provide an ink cartridge and an ink jet recording method using this ink.

  Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments. In the present specification, ink for ink jet may be referred to as “ink”. Various physical property values in this specification are values at 25 ° C. unless otherwise specified.

  When ink containing resin particles and urethane resin is used, the scratch resistance of the image is slightly improved, but the reason why the color developability of the image is lowered depending on the type of urethane resin is presumed as follows. .

  Since the resin particles formed from the acid-modified polyolefin form a film after being applied to the recording medium, the strength of the image can be improved. Furthermore, since the acid-modified polyolefin has a unit derived from an α-olefin polymer, it is considered that when applied to a recording medium together with ink, the energy of the image surface is lowered and slipperiness is imparted to the image surface. From the above two points, it is presumed that the use of an ink containing resin particles and urethane resin improves the scratch resistance of the image.

  However, when resin particles formed of acid-modified polyolefin are simply added to the ink, the hydrophobic acid-modified polyolefin and hydrophobic pigment particles interact strongly, and the resin is surrounded around the pigment particles in the image. Particles settle. For this reason, it is presumed that the sliding property between the pigment particles increases, the binding property between the pigment particles decreases, and the pigment particles are peeled off from the image.

  Accordingly, the present inventors have further included a urethane resin in the ink as a component for enhancing the fixability of the pigment particles to the recording medium, and the pigment particles having increased slip properties are bound to each other to thereby make the image scratch resistant. Tried to improve. However, it was found that the inclusion of a urethane resin synthesized by using polyethylene glycol as a polyol component proposed in Patent Document 1 slightly improves the scratch resistance of the image, but decreases the color developability.

  A urethane resin prepared using hydrophilic polyethylene glycol having a short alkylene group as a polyol component has a relatively high hydrophilicity. For this reason, it is presumed that the compatibility with hydrophobic resin particles and pigment particles is low, and the resin components are gathered together like a sea-island structure. By the way, since the α-olefin polymer has a small interaction between molecules and a low density, the acid-modified polyolefin itself has a low density. For this reason, the resin particle formed with the acid-modified polyolefin has a low refractive index. On the other hand, urethane resin has a higher refractive index than acid-modified polyolefin. For this reason, resin components in the ink gather together, and a sea-island structure having a difference in refractive index is formed in the image. Therefore, it is considered that light is irregularly scattered on the image, and the desired coloring component is reduced and the coloring property is lowered.

  The present inventors have examined a urethane resin that does not form the sea-island structure that generates irregular light scattering. As a result, it has been found that the use of a urethane resin having a poly (oxytetramethylene) structure in its molecular structure can improve the scratch resistance of the image without deteriorating the color developability. When the urethane resin containing a poly (oxytetramethylene) structure is used, the present inventors presume the reason why an image having excellent scratch resistance and color developability can be recorded.

  The urethane resin containing a poly (oxytetramethylene) structure interacts particularly strongly with the pigment particles, binds the pigment particles having increased slip properties, and improves the scratch resistance of the image. Furthermore, since the urethane resin containing a poly (oxytetramethylene) structure has high hydrophobicity, compatibility with hydrophobic resin particles is increased. For this reason, it is considered that the resin particles and the urethane resin form an image without forming a sea-island structure around the pigment particles, and both scratch resistance and color developability are compatible.

  On the other hand, it was found that when a urethane resin containing a structure in which the number of carbon atoms of the alkylene group is further increased (for example, a poly (oxypentamethylene) structure) is used, the scratch resistance of the image is lowered. This is considered because the interaction between the unit derived from the polyol component in the urethane resin and the pigment particles is weakened. From the above, it is considered that by using a urethane resin containing a poly (oxytetramethylene) structure, it is possible to record an image having excellent scratch resistance without deteriorating color developability.

<Ink>
The ink of the present invention is an ink-jet ink containing a pigment, resin particles, and a urethane resin. Hereinafter, components constituting the ink-jet ink of the present invention will be described in detail.

(Resin particles)
The ink of the present invention contains resin particles formed of a polyolefin-based copolymer. The copolymer includes a unit (X) derived from an α-olefin polymer, a unit (A) derived from an α, β-ethylenically unsaturated acid monomer, and the α, β-ethylenically unsaturated. And a unit (B) derived from an α, β-ethylenically unsaturated monomer other than the acid monomer.

  The α-olefin polymer constituting the unit (X) has an α-olefin unit such as an ethylene unit or a propylene unit as a main structural unit. The α-olefin polymer may be an ethylene homopolymer or a propylene homopolymer, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, and 4-methyl-1-pentene. The α-olefin copolymer may be used. However, since ethylene homopolymer has high hardness and high crystallinity, it has low meltability and solubility in organic solvents, and α, β-ethylenically unsaturated acid monomer and α, β-ethylene. May be difficult to modify with a photo-unsaturated monomer. For this reason, the α-olefin polymer is preferably a copolymer in which an ethylene unit or a propylene unit is a main constituent unit and another α-olefin is further copolymerized. Examples of such a copolymer include a random copolymer, a block copolymer, a graft copolymer, and a combination of these copolymers.

  The other α-olefin copolymerized with ethylene is preferably propylene or 1-butene from the viewpoint of versatility and copolymerizability. In particular, as the α-olefin polymer, a relatively low-density polyolefin having an ethylene unit and a propylene unit is preferable because it can form resin particles having good copolymerizability and good water dispersibility. .

  When the α-olefin polymer is a copolymer of ethylene and propylene, the content (% by mass) of ethylene units based on the total mass of the α-olefin polymer may be 5.0% by mass or more. preferable. Moreover, it is more preferable that it is 20.0 mass% or more, and it is especially preferable that it is 40.0 mass% or more. Moreover, it is preferable that it is 90.0 mass% or less, It is more preferable that it is 80.0 mass% or less, It is especially preferable that it is 60.0 mass% or less. The content of the ethylene unit and the propylene unit can be calculated from the absorption intensity of the infrared absorption spectrum, for example.

The density of the α-olefin polymer constituting the unit (X) is 850 kg / m ³ or more and 960 kg / m ³ or less, preferably 850 kg / m ³ or more and 940 kg / m ³ or less. By using an α-olefin polymer having a density within the above range, an image having a desired scratch resistance can be recorded. When the density of the α-olefin polymer is less than 850 kg / m ³ , the strength of the resin particles decreases, and the image scratch resistance decreases. On the other hand, when an α-olefin polymer having a density exceeding 960 kg / m ³ is used, the slipperiness of the surface of the recording layer is lowered, and an image having a desired scratch resistance cannot be recorded.

  The content of the unit (X) in the copolymer constituting the resin particles is preferably 40.0% by mass or more and 90.0% by mass or less based on the total mass of the resin particles. By using resin particles formed of a copolymer having a unit (X) content within the above range, an image having sufficient scratch resistance can be recorded.

  The α, β-ethylenically unsaturated acid monomer that becomes a constituent component of the unit (A) by polymerization is a monomer having an acid group (anionic group). Examples of the α, β-ethylenically unsaturated acid monomer include carboxylic acids such as (meth) acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic acid, and fumaric acid. Group-containing monomers and derivatives thereof; sulfones such as styrene sulfonic acid, sulfonic acid-2-propylacrylamide, (meth) acrylic acid-2-ethyl sulfonate, (meth) acrylamide-t-butylsulfone, and vinyl sulfonic acid Examples include monomers having an acid group and derivatives thereof; monomers having a phosphate group such as 2-phosphonic acid ethyl (meth) acrylate and vinylphosphonic acid, and derivatives thereof. The α, β-ethylenically unsaturated acid monomer may be a salt or an anhydride. Examples of the salt of the α, β-ethylenically unsaturated acid monomer include lithium salts, sodium salts, potassium salts, ammonium salts, and organic ammonium salts of the above monomers. In the present invention, from the viewpoint of copolymerizability with an α-olefin polymer, maleic acid that is likely to undergo a grafting reaction by hydrogen abstraction is used at least as an α, β-ethylenically unsaturated acid monomer. The maleic acid is preferably an anhydride.

  The acid value of the copolymer constituting the resin particles is preferably 90 mgKOH / g or more and 260 mgKOH / g or less. If the acid value of the copolymer is less than 90 mgKOH / g, the dispersibility in the liquid medium tends to be insufficient. On the other hand, when the acid value of the copolymer exceeds 260 mgKOH / g, the hydrophobicity of the resin particles decreases too much, and the scratch resistance of the image tends to decrease.

  In the copolymer forming the resin particles, the content of the unit (A) is preferably 0.10 times or more and 0.40 times or less in a ratio with respect to 100 parts by mass of the unit (X), and 0.20 times. More preferably, it is 0.40 times or more. When the ratio is less than 0.10 times, dispersibility in a liquid medium tends to be lowered, and storage stability and ejection stability tend to be lowered. On the other hand, when the ratio exceeds 0.40 times, it becomes easy to form a lump of hydrophilic components in the resin particles. For this reason, it becomes easy to form a microphase separation state along with the hydrophobic part of the unit (X), and the storage stability of the ink tends to be lowered.

  The weight average molecular weight of the α-olefin polymer is preferably 5,000 or more and 100,000 or less, more preferably 10,000 or more and 80,000 or less. When the α-olefin polymer has a weight average molecular weight of less than 5,000, the scratch resistance of the image tends to decrease. On the other hand, an α-olefin polymer having a weight average molecular weight exceeding 100,000 has low fluidity, so that it is uniform with α, β-ethylenically unsaturated acid monomer and α, β-ethylenically unsaturated monomer. It may be difficult to copolymerize. Accordingly, unreacted materials and by-products tend to be mixed into the ink.

  The α, β-ethylenically unsaturated monomer that becomes a constituent component of the unit (B) by polymerization is other than the α, β-ethylenically unsaturated acid monomer, that is, α, It is a β-ethylenically unsaturated monomer. Hereinafter, the “α, β-ethylenically unsaturated monomer having no acid group” may be simply referred to as “α, β-ethylenically unsaturated monomer”. Specific examples of the α, β-ethylenically unsaturated monomer include (meth) acrylic acid esters of aliphatic alcohols; monomers having aromatic groups; monomers having (poly) alkylene oxide groups. Can be mentioned.

  Specific examples of (meth) acrylic acid esters of aliphatic alcohols include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, (meth ) N-hexyl acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-lauryl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, (meth ) Hydroxypropyl acrylate and the like. Specific examples of the monomer having an aromatic group include benzyl (meth) acrylate, styrene, α-methylstyrene, and the like. Specific examples of the monomer having a (poly) alkylene oxide group include methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, and polypropylene glycol (meth) acrylate. Can do. These α, β-ethylenically unsaturated monomers can be used singly or in combination of two or more.

  The content of the unit (B) in the copolymer that forms the resin particles is preferably 0.30 times or more and 0.80 times or less in a ratio with respect to 100 parts by mass of the unit (X), and 0.40 times. More preferably, it is 0.70 times or less. When the ratio is less than 0.30 times, the adsorption force of the resin particles to the recording medium is lowered, and the image scratch resistance tends to be lowered. On the other hand, if the ratio exceeds 0.80, the ratio of the unit (X) in the hydrophobic portion of the copolymer constituting the resin particles is too low, and the image scratch resistance tends to be reduced. .

  As long as the effects of the present invention are not impaired, the copolymer that forms the resin particles may be “other units” other than the α, β-ethylenically unsaturated acid monomer and the α, β-ethylenically unsaturated monomer. It may have a unit derived from “body”. Examples of other monomers that can be used include crosslinkable unsaturated monomers having two or more polymerizable double bonds.

  The weight average molecular weight of the copolymer constituting the resin particles is preferably 3,000 or more and 100,000 or less, and more preferably 10,000 or more and 80,000 or less. By using a copolymer having a weight average molecular weight within the above range, resin particles having sufficient dispersibility in a liquid medium can be obtained.

  The volume average particle diameter of the resin particles is preferably 30 nm or more and 300 nm or less, and more preferably 40 nm or more and 250 nm or less. When the volume average particle diameter of the resin particles is less than 30 nm, the ratio of the resin particles penetrating into the recording medium increases and the ratio of the resin particles remaining on the surface of the recording medium decreases. For this reason, abrasion resistance may fall. On the other hand, when the volume average particle diameter of the resin particles exceeds 300 nm, the resin particles are likely to adhere to the ejection port of the recording head and the ink flow path. For this reason, the ejection stability required for the ink for inkjet may be lowered.

  In addition, the volume average particle diameter of the resin particles is, for example, a liquid whose content is about 0.02% by dispersing resin particles separated from ink in pure water, and a dynamic light scattering method. It can be measured using a particle size distribution measuring device. As a dynamic light scattering type particle size distribution measuring apparatus, for example, trade name “UPA-EX150” (manufactured by Nikkiso) can be used. The measurement conditions may be, for example, SetZero: 30 s, number of measurements: 3, measurement time: 180 seconds, refractive index: 1.5, and the like.

The resin particle content C _E (% by mass) in the ink is preferably 0.30% by mass or more and 5.00% by mass or less based on the total mass of the ink. If the content _CE of the resin particles is less than 0.30% by mass, a sufficient amount of the resin particles cannot remain on the recording medium, and the image scratch resistance may be lowered. On the other hand, when the content _CE of the resin particles exceeds 5.00% by mass, the ratio of the resin particles present around the pigment particles becomes excessive. For this reason, even if it contains a urethane resin, it becomes difficult to suppress the slipperiness between the pigment particles, and the scratch resistance of the image may be lowered.

(Method for producing resin particles)
The resin particles contained in the ink of the present invention can be obtained by modifying an α-olefin polymer with an α, β-ethylenically unsaturated acid monomer and an α, β-ethylenically unsaturated monomer. The modification of the α-olefin polymer can be performed by a known method such as a solution method, a melting method, and a kneading method.

  The solution method includes an α-olefin polymer heated to a temperature above the softening point and dissolved in an organic solvent, an α, β-ethylenically unsaturated acid monomer, and an α, β-ethylenically unsaturated monomer. Is reacted in the presence of a radical generator such as an organic peroxide. In the melting method, an α-olefin polymer heated and melted at a temperature above the softening point is mixed with an α, β-ethylenically unsaturated acid monomer and an α, β-ethylenically unsaturated monomer, This is a method of reacting in the presence of a radical generator such as an organic peroxide. The kneading method involves kneading a mixture of an α-olefin polymer, an α, β-ethylenically unsaturated acid monomer, an α, β-ethylenically unsaturated monomer, and a radical generator such as an organic peroxide. And kneading at a temperature equal to or higher than the softening point of the α-olefin polymer. As the kneading machine, for example, a Banbury mixer, a kneader, an extruder or the like can be used.

  As addition methods of α, β-ethylenically unsaturated acid monomer, α, β-ethylenically unsaturated monomer, and radical generator, batch addition, dilution in solution, addition by addition, and dropwise addition Can be selected as appropriate, such as continuous addition. The order of addition can also be selected as appropriate. The modification reaction of the α-olefin polymer may be performed in multiple stages. When performing the modification reaction of the α-olefin polymer in multiple stages, the respective reactors and methods can be used in appropriate combination. In addition, a decompression step is provided after completion of the reaction to remove residual α, β-ethylenically unsaturated acid monomer, α, β-ethylenically unsaturated monomer, radical generator and decomposition products thereof, organic solvent, etc. You can also

  The organic peroxide used as the radical generator is preferably a peroxide having a carbon atom in its skeleton. Among these, a peroxide capable of generating a radical having a hydrogen abstracting effect is preferable. Specific examples of the organic peroxide include ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxy ester, peroxydicarbonate, and alkyl peroxycarbonate. These organic peroxides can be used alone or in combination of two or more.

  Examples of the organic solvent used for modifying the α-olefin polymer by the solution method include saturated aliphatic hydrocarbons such as hexane, heptane, and octane; cyclohexane, methylcyclohexane, ethylcyclohexane, cycloheptane, and methylcyclohexane. Saturated alicyclic hydrocarbons such as heptane; alkylene glycol alkyl ether alkylates such as ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate; diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, etc. Dialkylene glycol alkyl ether alkylates: ethyl acetate, propyl acetate, butyl acetate, propio Esters that do not contain ethylenic double bonds such as ethyl acetate, propyl propionate, butyl propionate, ethyl butyrate, propyl butyrate, butyl butyrate; ethylenic double bonds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone Non-containing ketones; ethers containing no ethylenic double bond such as n-butyl ether, isobutyl ether, tetrahydrofuran, diethyl ether, ethylene glycol dialkyl ether, dioxane and the like. These organic solvents can be used alone or in combination of two or more.

  The reaction temperature for modifying the α-olefin polymer is not particularly limited. However, the α-olefin polymer is molten or organic so that the α, β-ethylenically unsaturated acid monomer, the α, β-ethylenically unsaturated monomer, and the organic peroxide are uniformly dispersed. It is preferable to modify at a temperature higher than the temperature at which the solvent dissolves. Specifically, it is preferable to denature at 100 ° C. or higher. Moreover, in order to suppress the fall of the molecular weight of the alpha olefin polymer by an organic peroxide, it is preferable not to modify | denature at too high temperature. Specifically, it is preferable to modify at 200 ° C. or lower.

  If the copolymer obtained by the polymerization reaction is dispersed in a dispersion medium, a dispersion containing resin particles can be obtained. For example, after the obtained copolymer is melted and a basic compound is added, a dispersion medium is further added and emulsified to obtain a dispersion of resin particles. A stabilizer for adjusting the stability can be added to the obtained dispersion. Examples of the stabilizer include compounds such as nitrosophenylhydroxy compounds, phosphite compounds, and pentaerythritol esters. These stabilizers can be used individually by 1 type or in combination of 2 or more types.

  Examples of emulsification methods include mechanical methods and phase inversion methods. The mechanical method is a method in which a copolymer melted at a high temperature is mixed with a basic compound, an organic solvent, and water, and an oil-in-water emulsion is produced through a homogenizer. In the phase inversion method, a copolymer melted at a high temperature, a basic compound, an organic solvent, and a part of water are mixed to form a water-in-oil emulsion, and then inverted water is added. This is a method of phase transition to an oil-in-water emulsion. Moreover, the mechanical method which forms an oil-in-water-type emulsion using a high-shear type rotary emulsification disperser can also be used.

  Basic compounds include alkali metals such as lithium hydroxide, sodium hydroxide and potassium hydroxide; alkaline earth metals such as calcium hydroxide; ammonia, methylamine, ethylamine, propylamine, butylamine, ethanolamine, diethanolamine, Amines such as ethanolamine, isopropylamine, propanolamine, 2-methyl-2-aminopropanol, N, N-dimethylethanolamine, N-methyldiethanolamine, dimethylamine, triethylamine, morpholine, N-methylmorpholine, N-ethylmorpholine There can be mentioned. These basic compounds can be used singly or in combination of two or more. The usage-amount of a basic compound is not specifically limited. Specifically, the amount that the pH of the dispersion of resin particles is 6 to 11 is preferable, and the amount that the pH is 7 to 9 is more preferable. When the pH of the dispersion is 6 to 11, anionic groups such as carboxylic acid groups in the copolymer constituting the resin particles are neutralized and can be stably dispersed.

  As the dispersion medium, water or a mixed solvent of water and an organic solvent can be used. The content of the organic solvent in the mixed solvent is preferably 50.0 parts by mass or less and more preferably 0.0 parts by mass or more with respect to 100.0 parts by mass of the unit (X). Examples of the organic solvent include methanol, ethanol, n-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, t-butanol, 1-pentanol and other alcohols; acetone, methyl ethyl ketone and other ketones; diethyl ether, Examples include ethers such as tetrahydrofuran; cellosolves such as 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol; alkylene glycols such as ethylene glycol, propylene glycol, and diethylene glycol; and polyhydric alcohols such as glycerin. . These organic solvents can be used alone or in combination of two or more. As the organic solvent, alcohols soluble in water at 25% by mass or more at 25 ° C. are preferable, and butanols are more preferable.

  The mixing ratio of the organic solvent and water in the mixed solvent can be arbitrarily selected. However, from the viewpoint of reducing the amount of the organic solvent used as much as possible, the organic solvent / water (mass ratio) is preferably 25/75 to 0/100.

  The resin (solid content) content in the dispersion of resin particles is not particularly limited. However, in consideration of handleability, the content (% by mass) of the resin (solid content) is preferably 1.0% by mass to 60.0% by mass, and preferably 10.0% by mass to 50.0% by mass. More preferably.

(Urethane resin)
The ink of the present invention contains a urethane resin containing a poly (oxytetramethylene) structure. Urethane resins used in ink jet inks usually have units derived from polyisocyanates, polyols, and diols having acid groups. Examples of the polyol include polyester polyol; polyether polyol; polycarbonate polyol and the like. The ink of the present invention contains a polyether-based urethane resin obtained using a polyether polyol having a poly (oxytetramethylene) structure as an essential component.

  The urethane resin containing a poly (oxytetramethylene) structure interacts particularly strongly with pigment particles whose slipperiness is increased by the resin particles, and can improve the scratch resistance of the recorded image. A urethane resin synthesized using a polyether polyol having an alkylene group having 3 or less carbon atoms (for example, a trimethylene group) is too hydrophilic to weaken the interaction with the pigment particles, resulting in image scratch resistance. Decreases. On the other hand, a urethane resin synthesized using a polyether polyol having an alkylene group having 5 or more carbon atoms (for example, a pentamethylene group) is too hydrophobic, so that the interaction between the urethane resins becomes strong. For this reason, the interaction between the urethane resin and the resin particles is weakened, and the color developability of the image is lowered.

  The number n of repeating oxytetramethylene units in the polyether polyol having a poly (oxytetramethylene) structure is preferably 10 or more and 40 or less. When the number of repetitions n is less than 10, the flexibility of the formed resin film is lowered and the image scratch resistance tends to be lowered. On the other hand, if the number of repetitions n exceeds 40, the resin film to be formed becomes too flexible and the image scratch resistance tends to decrease.

  As the polyisocyanate, aliphatic and aromatic polyisocyanates used for synthesizing general urethane resins can be suitably used. Further, as the diol having an acid group, a diol having an acid group such as a carboxy group, a sulfonic acid group, or a phosphoric acid group, which is used for synthesizing a general urethane resin, can be suitably used. . The diol having an acid group is preferably a short chain diol having less than 10 carbon atoms. Specific examples of the diol having an acid group include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutanoic acid. Of these, dimethylolpropionic acid and dimethylolbutanoic acid are preferred.

  The acid value of the urethane resin is preferably 20 mgKOH / g or more and 100 mgKOH / g or less. A urethane resin having an acid value of less than 20 mgKOH / g becomes too hydrophobic and the interaction between the urethane resins becomes strong, so that the color developability of the image may be lowered. On the other hand, since the urethane resin having an acid value exceeding 100 mgKOH / g has high hydrophilicity, the compatibility with the resin particles is lowered, and the color developability of the image may be lowered.

  The weight average molecular weight of the urethane resin is preferably 5,000 or more and 50,000 or less. When the weight average molecular weight of the urethane resin is less than 5,000, even if the urethane resin and the pigment particles interact with each other, the effect of binding the pigment particles may be slightly weak, so that the scratch resistance may be lowered. On the other hand, when the weight average molecular weight of the urethane resin exceeds 50,000, the compatibility between the urethane and the resin particles is lowered, and the color developability of the image may be lowered.

The content C _U (% by mass) of the urethane resin in the ink is preferably 0.02% by mass or more and 10.00% by mass or less based on the total mass of the ink, and is preferably 0.10% by mass or more and 5.00% by mass. More preferably, it is% or less. The content C _U of the urethane resin in the ink is within the above range, it is possible to urethane resin effectively interact with the pigment particles, resin particles, further improving the abrasion resistance and color development of the image.

The resin particle content C _E (% by mass) based on the total mass of the ink is 1.0 times the mass ratio (C _E / C _U ) to the urethane resin content C _U (% by mass). It is preferably 30.0 times or less. When the value of C _E / C _U is less than 1.0 times, the content of the urethane resin is relatively excessively large, there is a case where color of the image becomes insufficient. On the other hand, when the value of C _E / C _U is greater than 30.0, the content of the urethane resin is relatively excessively small, a urethane resin, weakened the interaction between the pigment particles and resin particles. For this reason, the scratch resistance of the image may decrease.

(Production method of urethane resin)
Examples of the method for producing the urethane resin include a one-shot method and a prepolymer method. The urethane resin used in the ink of the present invention may be produced by any method. The one-shot method is a method in which all raw materials are reacted at once. In the prepolymer method, a polyisocyanate and a diol having an acid group are reacted with a polyol dissolved in an organic solvent such as methyl ethyl ketone to form a urethane prepolymer, and then a chain extender is added to perform a chain extension reaction. How to do it.

(Pigment)
The ink of the present invention is a pigment ink containing a pigment. Examples of the pigment include inorganic pigments such as carbon black, calcium carbonate, and titanium oxide; organic pigments such as azo, phthalocyanine, and quinacridone. In addition to pigments, dyes may be used in combination for purposes such as toning.

The content C _P (% by mass) of the pigment in the ink is preferably 0.20% by mass or more and 10.00% by mass or less, and 0.50% by mass or more and 5.00% by mass based on the total mass of the ink. More preferably, it is% or less. The content C _P of the pigment in the ink is within the above range, it is possible to exhibit the basic properties as an ink for inkjet, such as discharge stability at a higher level.

The pigment content C _P (mass%) based on the total mass of the ink is 0.1 times or more as a mass ratio (C _P / C _U ) to the urethane resin content C _U (mass%). It is preferable that it is 10.0 times or less. C the value of _P / C _U By within the above range, the pigment particles can be sintered wearing the urethane resin in a more preferred state, it is possible to improve the scratch resistance of the image.

(Other resins)
The ink of the present invention can contain other resins in addition to the above resin particles. Other resins may be added as a dispersant for further stably dispersing the resin particles, or may be added as a component for improving fastness such as image marker resistance.

  Examples of other resins include acrylic acid resins. Examples of the resin include a block copolymer, a random copolymer, a graft copolymer, and salts thereof. Natural resins such as rosin can also be used. These resins may be an alkali-soluble resin that is soluble in an aqueous solution in which a base is dissolved, or may be resin particles formed from a resin obtained by emulsion polymerization or soap-free polymerization. Especially, as other resin, resin obtained using the above-mentioned (alpha), (beta) -ethylenically unsaturated acid monomer and (alpha), (beta) -ethylenically unsaturated monomer is preferable.

  The content (% by mass) of other resin in the ink is preferably 5.00% by mass or less based on the total mass of the ink. Further, the total of the content (mass%) of the resin particles and the content (mass%) of other resins is 0.30 mass% or more and 7.00 mass% or less based on the total mass of the ink. preferable.

(Aqueous medium)
The ink of the present invention preferably contains an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As water, it is preferable to use deionized water. The content (% by mass) of water in the ink is preferably 50.00% by mass or more and 95.00% by mass or less based on the total mass of the ink. 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. As the water-soluble organic solvent, any of those usable for ink-jet inks such as alcohols, glycols, glycol ethers and nitrogen-containing compounds can be used. These water-soluble organic solvents can be used alone or in combination of two or more.

(Other additives)
In addition to the above components, the ink of the present invention may contain a water-soluble organic compound that is solid at room temperature, such as urea, urea derivatives, trimethylolpropane, and trimethylolethane. The content (% by mass) of the water-soluble organic compound that is solid at room temperature in the ink is preferably 0.10% by mass or more and 20.00% by mass or less based on the total mass of the ink, and 3.00% by mass. More preferably, it is 10.00 mass% or less. If necessary, other water-soluble resins, surfactants, resins, pH adjusters, antifoaming agents, rust inhibitors, antiseptics, antifungal agents, antioxidants, anti-reducing agents, chelating agents, etc. Various additives may be included.

<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 the ink accommodating part is the ink of the present invention described above. As for the structure of the ink cartridge, the ink storage portion includes an ink storage chamber that stores liquid ink and a negative pressure generation member storage chamber that stores a negative pressure generation member that holds the ink therein by a negative pressure. The thing etc. can be mentioned. In addition, the ink cartridge may be provided with an ink storage portion that does not have an ink storage chamber for storing liquid ink but is configured to hold the entire amount of ink stored by the negative pressure generating member. 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 a method for ejecting ink include a method for applying mechanical energy to the ink and a method for applying thermal energy to the ink. In the present invention, it is particularly preferable to employ an ink jet recording method using thermal energy. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

  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.

<Synthesis of α-olefin polymer>
By vapor phase polymerization using a fluidized bed reactor described in “Example 1” of JP-A-11-100406, the polymerization pressure is a value shown in Table 1, and ethylene: propylene (mass ratio) = 50.0: 50.0 α-olefin polymers O1 to O5 were synthesized. Table 1 shows the density of the α-olefin polymer measured by a gas substitution method using a dry automatic densimeter (trade name “Acpic 1330-03”, manufactured by Micromeritics).

<Manufacture of modified polyolefin>
(Modified polyolefin PO1 to PO7)
In a 500 mL separable flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 100.0 parts of an α-olefin polymer of the type shown in Table 2 and diethylene glycol monoethyl ether acetate 100.0 I put a part. The mixture was melted in an oil bath maintained at 180 ° C. in a nitrogen atmosphere, and the temperature of the oil bath was adjusted with stirring so that the temperature in the system became 170 ° C. While stirring, add benzyl acrylate part, 5.0 parts maleic anhydride and 0.4 part di-t-butyl peroxide (trade name “Perbutyl D”, manufactured by NOF Corporation) in the amounts shown in Table 2. did. The system was kept at 170 ° C. and reacted for 30 minutes, and then the same amounts of benzyl acrylate, maleic anhydride, and di-t-butyl peroxide were added again. Similarly, benzyl acrylate, maleic anhydride, and di-t-butyl peroxide were added a total of 5 times every 30 minutes.

  The system was monitored by GPC (gel permeation chromatography) while maintaining the temperature in the system at 170 ° C., and the reaction was stopped when the weight average molecular weight of the reaction product reached the value shown in Table 2. The temperature in the system is lowered to 50 ° C., and the pressure in the flask is reduced by an aspirator for 1 hour to remove the solvent, unreacted monomer, di-t-butyl peroxide, and di-t-butyl peroxide decomposition products. Removed. After completion of the decompression, the reaction product was taken out and cooled to obtain a modified polyolefin modified with maleic anhydride and benzyl acrylate.

  In Table 2, the value of the ratio (part) of the unit derived from each of maleic anhydride, acrylic acid, and benzyl acrylate in the modified polyolefin with respect to 100.0 parts by mass of the α-olefin polymer is shown. Moreover, the weight average molecular weight of the modified polyolefin measured by GPC is also shown. Ml-A means maleic anhydride, AA means acrylic acid, and BzA means benzyl acrylate.

<Manufacture of resin particles>
In a 1000 mL separable flask equipped with a stirrer, a thermometer, and a reflux condenser, 100.0 g of modified polyolefins (PO1 to PO7) were put and melted in an oil bath maintained at 130 ° C. While maintaining the temperature of the oil bath at 130 ° C., an 8 mol / L potassium hydroxide aqueous solution was added so as to be 0.8 equivalent as a neutralization equivalent to the acid value, and then 80 ° C. with vigorous stirring. 300.0 g of ion exchange water was added in small portions. Although the viscosity in the system increased, the viscosity decreased when ion-exchanged water was continuously added. After cooling to an internal temperature of 30 ° C., the contents are filtered through a 100 mesh nylon filter cloth, and an aqueous dispersion of resin particles P1 to P7 having a resin (solid content) content of 20.0% Got. Table 3 shows the characteristics of the obtained resin particles P1 to P7.

<Manufacture of urethane resin>
(Urethane resin U1)
With reference to the description of “Synthesis Example 1” in JP-A-2005-290044, a urethane resin U1 containing a poly (oxytetramethylene) structure was synthesized. A four-necked flask equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a cooling tube was prepared. In this four-necked flask, 480.0 parts of poly (oxytetramethylene) glycol (n = 27.5, PTMG2000) having a number average molecular weight of 2,000, 240.0 parts of isophorone diisocyanate, and 0.007 part of dibutyltin dilaurate Put. The mixture was reacted at 100 ° C. for 1 hour in a nitrogen gas atmosphere, and then cooled to 65 ° C. or lower. 185.0 parts of dimethylolpropionic acid, 10.0 parts of neopentyl glycol, and 447.8 parts of methyl ethyl ketone were added and reacted at 80 ° C. for 16 hours. Monitoring by FT-IR, when the presence of isocyanate groups was no longer confirmed, 400.0 parts of methyl ethyl ketone and 100.0 parts of methanol were added to stop the reaction. Thereafter, methyl ethyl ketone and methanol were distilled off from the solution by heating under reduced pressure, and an appropriate amount of water was added. As a result, a liquid having an acid value of 82 mgKOH / g, a urethane resin U1 having a polystyrene-equivalent weight average molecular weight of 30,000, and a resin (solid content) content of 20.0% was obtained.

(Urethane resins U2-U5)
The synthesis was performed in the same manner as in the case of the urethane resin U1 except that the amounts of dimethylolpropionic acid and neopentyl glycol used were changed. Thus, the liquid containing the urethane resin U2-U5 which has the following weight average molecular weights (polystyrene conversion) and an acid value was obtained, respectively.
Urethane resin U2 Acid value 19 mgKOH / g, Weight average molecular weight 30,000
Urethane resin U3 Acid value 20 mgKOH / g, Weight average molecular weight 31,000
Urethane resin U4 Acid value 100 mgKOH / g, Weight average molecular weight 30,000
Urethane resin U5 Acid value 102 mgKOH / g, Weight average molecular weight 32,000

(Urethane resin U6-U10)
Instead of poly (oxytetramethylene) glycol having a number average molecular weight of 2,000, poly (oxytetramethylene) glycol having a number average molecular weight of 1,000 (n = 13.5, PTMG1000) was used. Further, synthesis was performed in the same manner as in the case of the urethane resin U1 except that the amounts of poly (oxytetramethylene) glycol, dimethylolpropionic acid, and neopentyl glycol were changed. Thus, the liquid containing the urethane resins U6-U10 which have the following weight average molecular weights (polystyrene conversion) and an acid value was obtained, respectively.
Urethane resin U6 Acid value 79 mgKOH / g, Weight average molecular weight 4,800
Urethane resin U7 Acid value 78 mgKOH / g, Weight average molecular weight 5,000
Urethane resin U8 Acid value 75 mgKOH / g, Weight average molecular weight 30,000
Urethane resin U9 Acid value 72 mgKOH / g, Weight average molecular weight 50,000
Urethane resin U10 Acid value 72 mgKOH / g, Weight average molecular weight 52,000

(Urethane resin U11)
A urethane resin U11 was obtained in the same manner as in the case of the urethane resin U1 except that polyethylene glycol (PEG 2000) having a number average molecular weight of 2,000 was used instead of poly (oxytetramethylene) glycol. The acid value of the obtained urethane resin U11 was 83 mgKOH / g, and the weight average molecular weight in terms of polystyrene was 30,000.

(Urethane resin U12)
Further, poly (oxypentamethylene) glycol (PPMG2000) having a number average molecular weight of 2,000 was used in place of poly (oxytetramethylene) glycol (PTMG2000). Otherwise, urethane resin U12 was obtained in the same manner as in the case of urethane resin U1 described above. The acid value of the obtained urethane resin U12 was 82 mgKOH / g, and the weight average molecular weight in terms of polystyrene was 31,000.

<Preparation of pigment dispersion>
20.0 parts of pigment, 50.0 parts of resin aqueous solution (solid content: 20.0%), and 60.0 parts of water were added to a bead mill with a filling rate of zirconia beads having a diameter of 0.3 mm of 80%. And dispersed for 5 hours at 1,800 rpm. As the bead mill, the trade name “LMZ2” (manufactured by Ashizawa Finetech) was used. As the pigment, carbon black (trade name “MA-100”, manufactured by Mitsubishi Chemical Corporation) was used. As the aqueous resin solution, an aqueous solution obtained by neutralizing a styrene-acrylic acid copolymer having an acid value of 210 mgKOH / g and a weight average molecular weight of 8,000 with a 10% aqueous sodium hydroxide solution was used. After the dispersion, the aggregated components were removed by centrifuging at 5,000 rpm for 30 minutes. Dilution with ion-exchanged water gave a pigment dispersion having a pigment content of 20.0%.

<Preparation of ink>
(Examples 1-21, Comparative Examples 1-7, Reference Example 1)
After mixing each component (unit:%) shown in the upper part of Tables 4-1 to 4-3, pressure filtration is performed with a membrane filter (trade name “HDCII filter”, manufactured by Pall) having a pore size of 2.5 μm. Ink was prepared. “Acetyleneol E100” is a nonionic surfactant manufactured by Kawaken Fine Chemicals. “Proxel GXL (S)” is an antibacterial agent manufactured by Avicia. Polyethylene glycol having a number average molecular weight of 600 was used. The lower part of Tables 4-1 to 4-3 shows ink characteristics.

<Evaluation>
The ink cartridge filled with each ink was mounted on an ink jet recording apparatus (trade name “PIXUS Pro 9500”, manufactured by Canon Inc.) that ejects ink by the action of thermal energy. In this embodiment, a solid image recorded by applying eight ink droplets having a mass per droplet of 3.5 nanograms to a unit area of 1/600 inch × 1/600 inch is recorded as “recording duty is 100%. Is defined. With this ink jet recording apparatus, a pattern including a solid image of 5 cm × 5 cm with a recording duty of 100% is recorded on a recording medium (trade name “Canon Photo Paper / Glossy Gold GL-101”, manufactured by Canon). Got. The obtained recorded matter was stored at room temperature for 24 hours, and then evaluated for the following scratch resistance and color developability. In the present invention, “A” and “B” are acceptable levels and “C” is unacceptable levels in the evaluation criteria for each item shown below.

(Abrasion resistance)
The surface of the recorded material (the surface of the solid image) was quickly rubbed 10 times with the back of the nail. Then, the surface of the recorded matter was visually observed, and scratch resistance was evaluated according to the following evaluation criteria. The results are shown in Table 5.
A: The recorded material was hardly scratched.
B: The recorded material was scratched, but was slight.
C: A noticeable scratch was attached to the recorded material.

(Color development (1))
For Examples 1 to 6, 11 to 21, Comparative Examples 1 to 6, and Reference Example 1, the optical density of the recorded matter (solid image) was measured using a spectrophotometer (trade name “Spectorolino”, manufactured by Gretag Macbeth). It was measured. The color developability was evaluated according to the following evaluation criteria. The results are shown in Table 5.
A: The optical density was 2.4 or more.
B: The optical density was 2.2 or more and less than 2.4.
C: The optical density was less than 2.2.

(Color development (2))
For the inks of Examples 7 to 10 and Comparative Example 7, the optical density of the recorded matter (solid image) was measured using a spectrophotometer (trade name “Spectorolino”, manufactured by Gretag Macbeth). Then, the optical density of the solid image recorded with the ink of Comparative Example 7 was used as a reference, and the color development was evaluated according to the following evaluation criteria. The results are shown in Table 5.
A: The difference from the optical density of the reference was less than 0.1.
B: The difference from the optical density of the reference was 0.1 or more and less than 0.2.
C: The difference from the optical density of the reference was 0.2 or more.

Claims (7)

An inkjet ink containing a pigment, resin particles, and a urethane resin,
The resin particles are a unit (X) derived from an α-olefin polymer, a unit (A) derived from an α, β-ethylenically unsaturated acid monomer containing maleic acid, and the α, β-ethylene. Formed by a copolymer having a unit (B) derived from an α, β-ethylenically unsaturated monomer other than the polymerizable unsaturated acid monomer,
The α-olefin polymer has a density of 850 kg / m ³ or more and 960 kg / m ³ or less,
An inkjet ink, wherein the urethane resin includes a poly (oxytetramethylene) structure. The resin particle content C _E (% by mass) based on the total mass of the ink is 1.0 times the mass ratio (C _E / C _U ) to the urethane resin content C _U (% by mass). The ink according to claim 1, which is 30.0 times or more. The pigment content C _P (% by mass) based on the total mass of the ink is 0.1 times or more in terms of a mass ratio (C _P / C _U ) to the urethane resin content C _U (% by mass). The ink according to claim 1, wherein the ink is 10.0 times or less.   The ink according to any one of claims 1 to 3, wherein an acid value of the urethane resin is 20 mgKOH / g or more and 100 mgKOH / g or less.   The ink according to any one of claims 1 to 4, wherein the urethane resin has a weight average molecular weight of 5,000 or more and 50,000 or less. An ink cartridge comprising ink and an ink containing portion for containing the ink,
The ink cartridge according to claim 1, wherein the ink is an ink according to claim 1. 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 ink according to any one of claims 1 to 5.