Pigment dispersion

Abstract

Provided is a pigment dispersion liquid in which a pigment is highly micro-dispersed, said pigment dispersion liquid being capable of producing an aqueous inkjet ink which is capable of recording an image having excellent color rendering properties, abrasion resistance, alcohol resistance, and adhesion to a non-absorbent substrate, and which has excellent discharge stability and redispersibility. A pigment dispersion for use in the preparation of an aqueous inkjet ink. The pigment dispersant is an A-B block copolymer containing a polymer chain A and a polymer chain B, having a number average molecular weight of 5000-15000, a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.2-1.6, and an acid value of 100 mgKOH / g or more, 30-70 mol% of the carboxyl groups derived from methacrylic acid are neutralized by ammonia, and 30-70 mol% of the carboxyl groups derived from methacrylic acid are neutralized by sodium hydroxide and / or potassium hydroxide.

Description

Technical Field

[0001] The present invention relates to pigment dispersions. Background Art

[0002] Printers and presses equipped with aqueous inkjet inks have expanded their applications across a wide range of fields, including personal, office, professional, recording, color display, and color photography, due to their advanced functionality. In particular, research into high-speed printers for industrial use is advancing. Furthermore, to address the challenges of high-speed printing and high-quality images, the ink droplets ejected from the printhead are being miniaturized. To achieve this, the pigments in the ink must be further miniaturized, and the miniaturized pigment particles must be microdispersed in the dispersion medium.

[0003] By using inks containing micronized pigments, it is possible to produce printed materials with improved vividness and color density, particularly improved chroma, an indicator of "color purity." Furthermore, when printed on processed paper for inkjet recording (photo paper, wide-format paper, etc.), the glossiness of the recorded images is improved. However, inks containing micronized pigments tend to penetrate the paper, resulting in a tendency for the color rendering of the image to deteriorate.

[0004] Furthermore, with high-speed printing, ink ejection stability is becoming increasingly important. Furthermore, if printing is temporarily stopped, ink can dry on the recording head, sometimes resulting in ejection failure. Therefore, ink must have good redispersibility—the ability for dried ink to dissolve easily in subsequent ink ejection and cleaning fluid, restoring the pigment dispersion to its original state.

[0005] On the other hand, printing is sometimes performed on non-absorbent recording media (substrates) such as plastic films in the industrial field. Furthermore, when printing images with excellent adhesion, wet abrasion resistance, dry abrasion resistance, and alcohol resistance (alcohol brush resistance) on non-absorbent substrates, inks are required that can form a durable coating film that is insoluble in various liquids. Specifically, inks are required to possess the contradictory properties of redispersibility (redispersibility) to quickly return to their original state even after drying, while also providing the durability to form a durable coating film that is insoluble in various liquids.

[0006] In addition, water-based inkjet ink uses black, yellow, magenta and cyan to reflect primary colors. Moreover, in order to expand the color range, colors such as orange, green and red are used, and in order to reflect good white on paper or film, white pigments such as titanium dioxide pigment are sometimes used. However, titanium dioxide pigment is an inorganic compound and therefore has a high specific gravity and is easily precipitated during long-term storage. Furthermore, titanium dioxide pigment sometimes forms lumps depending on the storage conditions, and therefore, the function of the ink is sometimes impaired. When the pigment in the ink has precipitated, it is necessary to stir the ink and restore the dispersed state of the pigment to its original state. However, if the precipitated pigment forms a lump, even if the ink is stirred, it is usually difficult to redisperse the pigment.

[0007] In order to enhance the durability of recorded images and improve the dispersibility of pigments, various inkjet inks have been proposed in which the configurations of the resins and surfactants to be blended have been studied (Patent Documents 1 to 5).

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent No. 5403313

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2008-45023

[0012] Patent Document 3: Japanese Patent No. 4157868

[0013] Patent Document 4: Japanese Patent Application No. 2009-515007

[0014] Patent Document 5: International Publication No. 2013 / 008691 Summary of the Invention

[0015] Problems to be solved by the invention

[0016] However, even with the inks proposed in Patent Documents 1 to 5, it is difficult to record images with excellent color development, abrasion resistance, alcohol resistance, and adhesion to non-absorbent substrates. Furthermore, even with these inks, ejection stability and redispersibility are not necessarily excellent, and there is room for improvement.

[0017] The present invention has been made in view of the problems of such prior art, and its object is to provide: a pigment dispersion liquid in which the pigment is highly finely dispersed and can be used to prepare the following aqueous inkjet ink, wherein the aqueous inkjet ink can record images with excellent color development, friction resistance, alcohol resistance and adhesion to non-absorbent substrates, and has excellent ejection stability and redispersibility.

[0018] Solutions for solving problems

[0019] That is, according to the present invention, the following pigment dispersion is provided.

[0020] [1] A pigment dispersion for preparing an aqueous inkjet ink, comprising a pigment, a dispersant, a water-soluble organic solvent, and water, wherein the dispersant is an AB block copolymer comprising a polymer chain A and a polymer chain B, having a number average molecular weight of 5,000 to 15,000, a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.2 to 1.6, and an acid value of 100 mgKOH / g or more, the polymer chain A being a polymer block comprising at least one structural unit (A-1) selected from the group consisting of methyl methacrylate and benzyl methacrylate, and at least one structural unit (A-2) selected from the group consisting of cyclohexyl methacrylate, dicyclopentyl methacrylate, and isobornyl methacrylate, wherein the structural unit (A-1) and the structural unit (A-2) are 2) has a total content of 70% by mass or more, a glass transition temperature of 50° C. or more, a number average molecular weight of 2,000 to 10,000, and a molecular weight distribution of 1.1 to 1.5, the polymer chain B is a polymer block comprising a structural unit (B-1) derived from methacrylic acid and a structural unit (B-2) derived from at least one selected from the group consisting of methyl methacrylate, benzyl methacrylate, and cyclohexyl methacrylate, the content of the structural unit (B-1) being 25 to 50% by mass, and the number average molecular weight being 2,000 to 10,000, and in the AB block copolymer, 30 to 70 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with ammonia, and 30 to 70 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with at least one of sodium hydroxide and potassium hydroxide.

[0021] [2] The pigment dispersion according to [1], wherein in the AB block copolymer, 40 to 60 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with ammonia, and 40 to 60 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with sodium hydroxide.

[0022] [3] The pigment dispersion according to [1] or [2], wherein the content of the pigment is 5 to 60% by mass, the content of the dispersant is 0.5 to 20% by mass, the content of the water-soluble organic solvent is 30% by mass or less, and the content of water is 20 to 80% by mass.

[0023] [4] The pigment dispersion according to any one of [1] to [3] above, wherein the water-soluble organic solvent is at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-N,N-dimethylpropionamide and 3-butoxy-N,N-dimethylpropionamide.

[0024] [5] The pigment dispersion according to any one of [1] to [4], wherein the pigment is at least one selected from the group consisting of a yellow pigment, a red pigment, a blue pigment, a green pigment, an orange pigment, a black pigment, and a white pigment; the yellow pigment is at least one selected from the group consisting of CI Pigment Yellow 74, 150, 155, and 180; the red pigment is at least one selected from the group consisting of CI Pigment Red 122, 202, 254, and 269 and solid solutions thereof; and CI Pigment Violet 19 and 23 and solid solutions thereof; the blue pigment is at least one selected from the group consisting of CI Pigment Blue 15:3, 15:4, and 15:6; the green pigment is at least one selected from the group consisting of CI Pigment Green 7, 36, and 58; the orange pigment is CI Pigment Orange 43; the black pigment is CI Pigment Black 7; and the white pigment is CI Pigment White 6.

[0025] Effects of the Invention

[0026] According to the present invention, there can be provided: a pigment dispersion liquid in which the pigment is highly finely dispersed and which can be used to prepare the following aqueous inkjet ink, wherein the aqueous inkjet ink can record images having excellent color development, friction resistance, alcohol resistance and adhesion to non-absorbent substrates, and is excellent in ejection stability and redispersibility. DETAILED DESCRIPTION

[0027] Pigment dispersion

[0028] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments. One embodiment of the pigment dispersion of the present invention is used to prepare an aqueous inkjet ink and contains a pigment, a dispersant, a water-soluble organic solvent, and water. The following describes the details of the pigment dispersion of this embodiment.

[0029] (pigment)

[0030] The pigment dispersion of this embodiment contains pigments in a micro-dispersed state. As pigments, conventionally known organic pigments and inorganic pigments used in aqueous inkjet inks can be used. As organic pigments, there can be mentioned color pigments such as phthalocyanine, azo, azomethine azo, azomethine, anthraquinone, pyrene / perylene, indigo / thioindigo, dioxazine, quinacridone, isoindoline, isoindolinone, diketopyrrolopyrrole, quinophthalone, and indanthrene pigments; and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. As inorganic pigments, there can be mentioned body pigments, titanium oxide pigments, iron oxide pigments, and spinel pigments.

[0031] Specific examples of pigments represented by color index (CI) numbers include: CI Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 97, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 175, 180, 181, 185, 191; CI Pigment Red 4, 5, 9, 23, 48, 49, 52, 53, 57, 97, 112, 122, solid solutions containing CI Pigment Red 122, 123, 144, 146, 147, 149, 150, 166, 168, 8, 170, 176, 177, 180, 184, 185, 192, 202, 207, 214, 215, 216, 217, 220, 221, 223, 224, 226, 227, 228, 238, 240, 242, 254, 255, 264, 269, 272; CI Pigment Violet 19, 23, 29, 30, 37, 40, 50; CI Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 22, 60, 64; CI Pigment Green 7, 36, 58; CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63; CI Pigment Black 7; CI Pigment White 6; etc.

[0032] Among them, from the viewpoints of color development, dispersibility and weather resistance, at least one selected from the group consisting of yellow pigments, red pigments, blue pigments, green pigments, orange pigments, black pigments and white pigments is preferred. Moreover, the yellow pigment is preferably at least one selected from the group consisting of CI Pigment Yellow 74, 150, 155 and 180. The red pigment is preferably at least one selected from the group consisting of CI Pigment Red 122, 202, 254, 269 and their solid solutions, and CI Pigment Violet 19, 23 and their solid solutions. The blue pigment is preferably at least one selected from the group consisting of CI Pigment Blue 15:3, 15:4 and 15:6. The green pigment is preferably at least one selected from the group consisting of CI Pigment Green 7, 36 and 58. The orange pigment is preferably CI Pigment Orange 43. The black pigment is preferably CI Pigment Black 7. The white pigment is preferably CI Pigment White 6.

[0033] Except for the case where the printed matter (image) requires hiding power, it is preferred to use organic particulate pigments. In the case of a printed matter that needs to show transparency with high clarity, it is preferred to use a pigment that has been micronized by wet grinding or dry grinding such as salt milling. If it is considered to avoid nozzle clogging, etc., it is preferred to use an organic pigment with a number average particle size of less than 0.2 μm and an inorganic pigment with a number average particle size of less than 0.4 μm, from which pigments with a particle size exceeding 1.0 μm are removed. By using a pigment with a number average particle size within the above range, the optical density, chromaticity, color development and print quality of the printed matter recorded can be improved, and the sedimentation of the pigment in the ink can be appropriately suppressed. The number average particle size of the pigment can be measured, for example, using an electron microscope, a light scattering particle size distribution meter, etc.

[0034] The pigment may be any of the following: untreated pigments; self-dispersible pigments with functional groups introduced onto their surfaces; surface-treated pigments such as coupling agents and activators, polymers, or encapsulated pigments. Furthermore, the pigment may be treated with a dispersant. For example, a dispersant may be present during pigment synthesis, pigmentation, or pigment micronization. The pigment may also be treated by mixing the dispersant and pigment in water, stirring to disperse them, and then precipitating them in a poor solvent or acid precipitation.

[0035] (Dispersant)

[0036] The dispersant is a component used to disperse the pigment in a liquid medium containing a water-soluble organic solvent and water, and is an AB block copolymer as follows: it contains a polymer chain A and a polymer chain B, has a number average molecular weight of 5000 to 15000, a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.2 to 1.6, and an acid value of 100 mgKOH / g or more.

[0037] The dispersant is an AB block copolymer comprising a polymer chain A (hereinafter, also referred to as "A chain") and a polymer chain B (hereinafter, also referred to as "B chain"). The A chain is a water-insoluble polymer block. In addition, the B chain is a water-soluble polymer block comprising a structural unit (B-1) derived from methacrylic acid, in which the carboxyl group derived from methacrylic acid is neutralized by an alkali. Since the A chain is a water-insoluble polymer block, it has high hydrophobicity and is adsorbed on hydrophobic pigments. Moreover, since the A chain is a water-insoluble polymer block, the AB block copolymer (dispersant) is not easily desorbed from the adsorbed pigment for a long time, and the micro-dispersed state of the pigment can be maintained. In addition, even when ejected in an inkjet manner, the A chain is not easily desorbed from the pigment, and therefore the ejection stability is also good. The B chain is a water-soluble polymer block. By means of the B chain, the aggregation of the pigment can be suppressed.

[0038] The polymer chain A (A chain) is a polymer block comprising at least one structural unit (A-1) selected from the group consisting of methyl methacrylate and benzyl methacrylate, and at least one structural unit (A-2) selected from the group consisting of cyclohexyl methacrylate, dicyclopentanyl methacrylate, and isobornyl methacrylate.

[0039] The total content of structural units (A-1) and (A-2) in chain A is 70% by mass or more, preferably 80% by mass or more, and more preferably 95% by mass or more. Chain A is a highly hydrophobic polymer block having an aromatic ring and a cycloalkyl ring, and therefore efficiently adsorbs to the pigment.

[0040] The glass transition temperature (Tg) of the A chain is 50°C or higher, preferably 55 to 155°C. That is, due to the high glass transition temperature, the A chain is a relatively hard polymer block. The glass transition temperature (Tg) of the A chain can be measured by thermal analysis. In addition, the glass transition temperature (Tg) of the A chain can also be easily obtained by calculation. Specifically, the glass transition temperature (°C) of the polymer copolymerized with the monomer of the x component is set to "T", the composition ratio (mass ratio) of each monomer is set to "W1, W2,...", and the glass transition temperature (°C) of the homopolymer of each monomer is set to "T1, T2,...". In this case, the glass transition temperature (T (°C)) of the polymer can be calculated according to the following formula (1).

[0041] 1 / T={W1 / (T1+273)}+{W2 / (T2+273)}+···…(1)

[0042] The glass transition temperature of the homopolymer of each monomer can be obtained from the website "https: / / polymer.nims.go.jp / ". For example, homopolymers of methyl methacrylate (Tg = 105°C), benzyl methacrylate (Tg = 54°C), cyclohexyl methacrylate (Tg = 83°C), dicyclopentanyl methacrylate (Tg = 120°C), and isobornyl methacrylate (Tg = 110°C) can be used.

[0043] The number average molecular weight (Mn) of the A chain is 2000 to 10000, preferably 3000 to 7000. If the Mn of the A chain is less than 2000, it becomes easy to desorb from the pigment. On the other hand, if the Mn of the A chain exceeds 10000, it will be granulated in an aqueous liquid medium and sometimes cannot be adsorbed on the pigment. By making Mn within the above range, the A chain dissolved or swollen in the aqueous liquid medium will be efficiently adsorbed on the pigment. It should be noted that the number average molecular weight (Mn) and weight average molecular weight (Mw) in this specification are values ​​converted to polystyrene measured by gel permeation chromatography (GPC).

[0044] The molecular weight distribution (PDI = weight average molecular weight / number average molecular weight) of the A chain is 1.1 to 1.5, preferably 1.2 to 1.45. That is, the A chain is a polymer block with relatively uniform molecular weight. By making the polymer molecular weight uniform, the content of high-molecular-weight polymers and low-molecular-weight polymers is reduced, resulting in a large number of polymer chains that contribute to pigment dispersibility, which is preferred.

[0045] The A chain may further contain other structural units in addition to the structural units (A-1) and (A-2) as needed. Examples of monomers constituting other structural units include: styrene; (meth)acrylates having alkyl or alkenyl groups, such as methyl (meth)acrylate, butyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; (meth)acrylates containing hydroxyl groups, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 3-hydroxypropyl (meth)acrylate; glycol ether (meth)acrylates, such as (poly)ethylene glycol monomethyl ether (meth)acrylate, (poly)ethylene glycol monoethyl ether (meth)acrylate, and (poly)propylene glycol monomethyl ether (meth)acrylate; (meth)acrylates containing amino groups, such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and tert-butylaminoethyl (meth)acrylate; and the like.

[0046] Polymer chain B (B chain) is a polymer block comprising a structural unit (B-1) derived from methacrylic acid and a structural unit (B-2) derived from at least one selected from the group consisting of methyl methacrylate, benzyl methacrylate, and cyclohexyl methacrylate. Furthermore, the B chain is a high-acid polymer block having a content of structural unit (B-1) of 25 to 50% by mass, preferably 26 to 40% by mass.

[0047] Since the B chain has a high acid value, it is a polymer block that is neutralized and dissolved in water. In addition, the surface of the non-absorbent substrates such as the film of the plastic is hydrogen-bonded with the carboxyl group, so that the adhesion to the printed film can be improved. And then, since the carboxyl group is neutralized, the hydration is high. Therefore, even if the pigments such as titanium oxide are precipitated, the aggregation of the pigment can be suppressed, and the original dispersion state can be restored by stirring alone. If the content of the structural unit (B-1) is less than 25% by mass, although the AB block copolymer is dissolved in water, the redispersibility and the adhesion of the printed film are reduced. On the other hand, if the content of the structural unit (B-1) exceeds 50% by mass, the polymerizability is reduced, and the hydrated part becomes more, so that the viscosity of the pigment dispersion is sometimes excessively increased.

[0048] The B chain is a polymer block comprising a structural unit (B-2) derived from at least one selected from the group consisting of methyl methacrylate, benzyl methacrylate, and cyclohexyl methacrylate. The inclusion of this structural unit (B-2) in the B chain allows it to have a high glass transition temperature (Tg), similar to the A chain, and contributes to improved adhesion to substrates and abrasion resistance.

[0049] If structural unit (B-2) is derived solely from cyclohexyl methacrylate, even if structural unit (B-1) is included in large quantities, the cyclohexyl group is highly hydrophobic, and therefore, even after neutralization, it may become difficult to dissolve in water. Therefore, structural unit (B-2) is preferably a structural unit derived from at least one of methyl methacrylate and benzyl methacrylate; or a structural unit derived from at least one of methyl methacrylate and benzyl methacrylate and cyclohexyl methacrylate. It should be noted that if benzyl methacrylate is used, since it has an aromatic ring, it can further improve the adhesion to non-absorbent substrates such as PET film.

[0050] The number average molecular weight (Mn) of the B chain is 2,000 to 10,000, preferably 3,000 to 7,000. If the Mn of the B chain is less than 2,000, the molecular weight is too low, making it difficult to dissolve and disperse the A chain in water. On the other hand, if the Mn of the B chain exceeds 10,000, the molecular weight is too high, and the viscosity of the pigment dispersion may become excessively high.

[0051] The number average molecular weight (Mn) of the AB block copolymer (dispersant) is 5,000 to 15,000, preferably 6,000 to 13,000. If the Mn of the AB block copolymer is less than 5,000, the molecular weight of either the A chain or the B chain may be extremely low, and dispersion stability may be reduced. On the other hand, if the Mn of the AB block copolymer exceeds 15,000, the molecular weight of either the A chain or the B chain may be extremely high, and the performance of each polymer block may not be fully exerted.

[0052] The molecular weight distribution (PDI = weight average molecular weight / number average molecular weight) of the AB block copolymer is 1.2 to 1.6, preferably 1.3 to 1.5. If the molecular weight distribution is outside the above range, a large amount of substances with molecular weights outside the range are contained, and the desired performance may not be achieved.

[0053] The acid value of the AB block copolymer is 100 mgKOH / g or more, preferably 105 to 150 mgKOH / g. If the acid value of the AB block copolymer is less than 100 mgKOH / g, the amount of the copolymer that dissolves in water decreases, and redispersibility may not be exhibited.

[0054] In the AB block copolymer, 30 to 70 mol% of the carboxyl groups derived from methacrylic acid are neutralized by ammonia. Furthermore, 30 to 70 mol% of the carboxyl groups derived from methacrylic acid are neutralized by at least one of sodium hydroxide and potassium hydroxide. That is, the AB block copolymer is neutralized by the volatile base and the base remaining in the form of the neutralized salt and ionized. A part of the carboxyl groups is neutralized by ammonia, which is a volatile base. If a printed matter (image) is recorded using ink prepared from a pigment dispersion of the AB block copolymer (dispersant), ammonia volatilizes and generates carboxyl groups. That is, the ionized carboxyl groups become water-insoluble carboxyl groups, and the coating film of the image becomes water-insoluble. Moreover, hydrophobic groups such as aromatic rings and cycloalkyl groups are present in the AB block copolymer, and therefore, the friction resistance and alcohol resistance of the image are improved.

[0055] In addition, although ammonia volatilizes, sodium salts and potassium salts exist in their original state after recording. That is, when the ink is dried on the recording head of the inkjet method, although ammonia volatilizes, sodium salts and potassium salts exist in their original state. Even if the ink dries on the recording head, the water-soluble organic solvent whose boiling point is above the specified temperature also remains. By the presence of sodium salts and potassium salts with carboxyl groups and water-soluble organic solvents, the dried ink is easily redissolved (redispersed) in the ink and cleaning liquid ejected next, thereby suppressing the clogging of the recording head caused by drying. In addition, by drying after printing, the water-soluble organic solvent is almost volatilized and water-soluble sodium salts and potassium salts are present. However, due to the presence of hydrophobic groups such as aromatic rings and cycloalkyl groups in the AB block copolymer, the friction resistance and alcohol resistance of the image can be maintained at a high level.

[0056] In an AB block copolymer, if less than 30 mol% of the carboxyl groups derived from methacrylic acid are neutralized with ammonia, the proportion of carboxyl groups neutralized with sodium hydroxide and potassium hydroxide becomes relatively high, thereby reducing the friction resistance of the printed material. On the other hand, if more than 70 mol% of the carboxyl groups derived from methacrylic acid in an AB block copolymer are neutralized with ammonia, the redispersibility (redispersibility) of the ink becomes insufficient. It should be noted that, in an AB block copolymer, preferably, 40-60 mol% of the carboxyl groups derived from methacrylic acid are neutralized with ammonia, and 40-60 mol% of the carboxyl groups derived from methacrylic acid are neutralized with sodium hydroxide.

[0057] Dispersant (AB block copolymer) can be manufactured according to the method known in the past. For example, preferably by living anionic polymerization, living cationic polymerization and living radical polymerization etc. have active polymerization method and manufacture. Wherein, from the viewpoints such as conditions, materials and devices, preferred living radical polymerization. Particularly preferably using organic compound as catalyst and using organic iodide as polymerization initiation compound RTCP method, RCMP method. These methods use safer commercially available compounds, do not use heavy metals, special compounds, in terms of cost and purification, are advantageous. And then, by making the growth end be tertiary iodine, thus can easily form the block structure with good precision with common equipment.

[0058] Any polymer block in chain A or chain B can be polymerized first. Chain A is preferably polymerized before chain B. If chain B is polymerized first, if the polymerization rate is less than 100%, structural units derived from residual monomers may be incorporated into the post-polymerized chain A. In this case, a large amount of methacrylic acid, a component of chain B, may be incorporated into chain A, potentially making chain A more soluble in water.

[0059] Preferably, solution polymerization is carried out in an organic solvent to manufacture the AB block copolymer, and more preferably, solution polymerization is carried out in an organic solvent identical to the water-soluble organic solvent compounded in the pigment dispersion. After polymerization, ammonia, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, etc. are added to neutralize the carboxyl group, and aqueous solution is carried out, thereby, a solution of the AB block copolymer can be obtained. In addition, after polymerization is carried out in an organic solvent, it is added to a poor solvent to precipitate the polymer. After the precipitated polymer is dispersed in water or water and a water-soluble organic solvent, ammonia, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, etc. are added to neutralize the carboxyl group, and aqueous solution is carried out, thereby, a solution of the AB block copolymer can also be obtained.

[0060] (Dispersion Medium)

[0061] The pigment dispersion of this embodiment contains a liquid medium containing water and a water-soluble organic solvent as a dispersion medium for the pigment. As the water, ion-exchanged water, distilled water, purified water, etc. are preferably used.

[0062] The water-soluble organic solvent functions not only as a moisturizing agent but also as an anti-drying agent, and also has the effect of improving wettability to plastic films. Examples of the water-soluble organic solvent include: alcohol solvents such as methanol, ethanol, and isopropanol; ketone solvents such as acetone; alkylene glycol solvents such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 3-methoxy-3-methyl-1-butanol, and 1,2-hexanediol; alkylene glycol monoalkyl ether solvents such as ethylene glycol methyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; glycerol solvents such as glycerol, diglycerol, and ethylene oxide adducts of glycerol; amide solvents such as 2-pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; urea solvents such as tetramethylurea and dimethylimidazolidinone; carbonate solvents such as ethylene carbonate and dimethyl carbonate; and the like.

[0063] From the viewpoint of moisturizing and preventing drying, the water-soluble organic solvent is preferably at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-N,N-dimethylpropionamide and 3-butoxy-N,N-dimethylpropionamide.

[0064] The dispersant is preferably produced by solution polymerization using a water-soluble organic solvent contained in a pigment dispersion or aqueous inkjet ink. If these water-soluble organic solvents are used as polymerization solvents, the polymer solution obtained by polymerization can be directly used to prepare the pigment dispersion, thereby simplifying the process.

[0065] (Other additives)

[0066] The pigment dispersion of this embodiment may contain other additives as needed. Examples of such additives include surfactants, preservatives, organic solvents other than the aforementioned water-soluble organic solvents, leveling agents, surface tension modifiers, pH adjusters, ultraviolet absorbers, light stabilizers, antioxidants, dyes, fillers, waxes, thickeners, defoamers, mildew inhibitors, antistatic agents, metal particles, and magnetic powders.

[0067] By making the pigment dispersion contain a surfactant, the surface tension of the pigment dispersion and the ink can be maintained within a specified range. It should be noted that the surface tension of the ink at 25°C is preferably 15 to 45 mN / m, more preferably 20 to 40 mN / m. Examples of surfactants include silicone-based, acetylene glycol-based, fluorine-based, alkylene oxide-based and hydrocarbon-based surfactants. Among them, silicone-based, acetylene glycol-based and fluorine-based surfactants are preferred. Surfactants usually sometimes cause ink foaming or cause ink to be repelled on the surface of the film. Therefore, it is preferable to appropriately control the amount of surfactant added to the pigment dispersion.

[0068] Examples of the preservative include sodium benzoate, benzimidazole, thiabendazole, potassium sorbate, sodium sorbate, sodium dehydroacetate, thiazolesulfonamide, and pyrithione.

[0069] (Pigment dispersion)

[0070] The content of the pigment in the pigment dispersion is preferably 5 to 60% by mass. When the pigment is an organic pigment, the content of the organic pigment in the pigment dispersion is preferably 5 to 30% by mass, more preferably 10 to 25% by mass. In addition, when the pigment is an inorganic pigment, the content of the inorganic pigment in the pigment dispersion is preferably 20 to 60% by mass, more preferably 30 to 50% by mass.

[0071] The content of the dispersant in the pigment dispersion is preferably 0.5 to 20% by mass. If the content of the pigment dispersant is less than 0.5% by mass, it becomes difficult to stably disperse the pigment. On the other hand, if the content of the pigment dispersant exceeds 20% by mass, the viscosity becomes excessively high and exhibits non-Newtonian viscosity, sometimes making it impossible to eject the ink in a straight line using an inkjet method.

[0072] The content of the dispersant is preferably determined based on the type of pigment, surface properties, particle size, etc. Specifically, the content of the pigment dispersant is preferably 5 to 50 parts by mass, more preferably 10 to 30 parts by mass, per 100 parts by mass of the organic pigment. Furthermore, the content of the pigment dispersant is preferably 1 to 20 parts by mass, more preferably 3 to 10 parts by mass, per 100 parts by mass of the inorganic pigment.

[0073] The content of the water-soluble organic solvent in the pigment dispersion is preferably 30% by mass or less, more preferably 0.5% to 20% by mass. If the content of the water-soluble organic solvent exceeds 30% by mass, the water-soluble organic solvent tends to remain in the printed film, which may cause blocking and reduce the image's physical properties such as water resistance and abrasion resistance. In addition, the viscosity of the pigment dispersion increases, and the dispersant may desorb from the pigment, causing aggregation.

[0074] The water content in the pigment dispersion is preferably 20 to 80% by mass. By forming an aqueous pigment dispersion containing an appropriate amount of water, an aqueous inkjet ink can be easily prepared.

[0075] If the content of surfactant in the pigment dispersion is too high, the pigment may tend to aggregate. Therefore, it is preferable to appropriately control the content of surfactant. The content of surfactant in the pigment dispersion is preferably 0 to 3.5% by mass, more preferably 0.01 to 2% by mass. In addition, the content of preservative in the pigment dispersion is preferably 0.05 to 2% by mass, more preferably 0.1 to 1% by mass.

[0076] Pigment dispersion liquid can be manufactured according to the method known in the past. For example, when pigment, dispersant, water and water-soluble organic solvent are mixed, stirring and dispersion treatment are carried out to obtain pre-pigment dispersion liquid. When mixing, stirring and dispersion treatment are carried out, known mixers, stirring devices and dispersing devices can be used in the past. As mixers, dissolvers, homogenizers etc. can be enumerated. As mixers and dispersing devices, kneaders, attritors, ball mills, vertical media dispersers and horizontal media dispersers filled with glass beads and zirconia beads, colloid mills, jet mills, high-pressure homogenizers, and ultrasonic dispersers etc. can be enumerated. In addition, as the medium filled in the media disperser, it is preferred to use beads below 1mm. By using such beads as the medium, the crystals and shapes of the pigment are not easily destroyed, and so-called gentle dispersion (soft dispersion) can be carried out.

[0077] The pigment is preferably dispersed until it becomes primary particles by the above-mentioned mixing, stirring and dispersion treatment. However, the pigment may also be aggregated into a desired particle size. The dispersion state of the pigment can be confirmed by conventionally known methods. For example, it can be confirmed by using an optical microscope, an electron microscope, a particle size distribution measuring instrument such as light scattering, or a spectrophotometer to measure absorbance. After the dispersion treatment, coarse particles can also be removed by centrifugal filtration, filter filtration, etc. Thereafter, other additives may be added as needed to obtain a pigment dispersion.

[0078] The physical properties of the pigment dispersion are appropriately designed based on the physical properties of the desired aqueous inkjet ink. The viscosity of the aqueous inkjet ink is adjusted to an appropriate viscosity for ejection from the nozzles of the recording head, depending on the type of pigment and other factors. For example, the viscosity of an ink containing an organic pigment at 25°C is preferably 2 to 10 mPa·s. Ink containing an inorganic pigment preferably has a viscosity of 5 to 30 mPa·s at 25°C.

[0079] The pH of the pigment dispersion at 25°C is preferably 7.0 to 10.0, more preferably 7.5 to 9.5. If the pH of the pigment dispersion is lower than 7.0, the dispersant may precipitate easily and the pigment may aggregate easily. On the other hand, if the pH of the pigment dispersion exceeds 10.0, the pigment dispersion becomes highly alkaline, which may make handling difficult. The surface tension of the pigment dispersion at 25°C is preferably 15 to 45 mN / m, more preferably 20 to 40 mN / m.

[0080] The pigment dispersion of this embodiment is useful as a pigment dispersion to be mixed with an aqueous inkjet ink. The inkjet ink can be used in inkjet printers for consumer use, industrial use, and printing and dyeing. Examples of the medium (recording medium) to be printed include plain paper; glossy paper; matte paper; films formed of polyesters such as PET, vinyl chloride, etc.; fibers such as cotton and polyester; metals such as aluminum plates, etc. By utilizing the ink prepared using the pigment dispersion of this embodiment, images with excellent color rendering properties can be recorded at high speed even for paper containing a large amount of inorganic fillers. In addition, the ink prepared using the pigment dispersion of this embodiment is suitable for high-speed printing and is therefore suitable for industrial label printing, package printing, and wide-format inkjet printers.

[0081] Example

[0082] Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limited to these Examples. It should be noted that "parts" and "%" in Examples and Comparative Examples are based on mass unless otherwise specified.

[0083] <Manufacturing of Pigment Dispersion>

[0084] (Manufacturing Example 1)

[0085] In a reaction vessel, 290.5 parts of diethylene glycol monobutyl ether (BDG), 290.5 parts of propylene glycol monomethyl ether (MPG), 5.4 parts of iodine, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured by FUJIFILM Wako Pure Chemical Corporation) 20.1 parts, 110.0 parts of benzyl methacrylate (BzMA), 132.0 parts of cyclohexyl methacrylate (CHMA), and 0.43 parts of N-iodosuccinimide (NIS) were placed. While nitrogen was flowing, the mixture was heated to 40°C and stirred, and polymerized for 4 hours to form an A chain (polymer). A portion of the obtained liquid was sampled, and the polymerization conversion rate, calculated from the non-volatile component reaching a constant at 180°C, was 99.2%. In addition, the sampled liquid was dissolved in acetone and analyzed by gas chromatography, and as a result, almost no monomer was detected. The molecular weight of the polymer was measured by gel permeation chromatography (GPC) using 0.1 mmol / L dimethylformamide as a developing solvent. The results showed that the number average molecular weight (Mn) of the polymer, as calculated as polystyrene, was 5000, and the molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 1.20.

[0086] A portion of the sampled liquid was added to a large amount of hexane and stirred thoroughly to obtain a white precipitate. The obtained precipitate was dried under reduced pressure and the residual solvent was distilled off. Then, the glass transition temperature (Tg) of the precipitate (polymer) measured by thermal analysis was 68.6°C. It should be noted that the Tg (calculated value) of the polymer (A chain) calculated according to the above formula (1) was 69.2°C, which was confirmed to be a substantially equivalent value.

[0087] 187.9 parts of BzMA and 125.2 parts of methacrylic acid (MAA) were added and polymerized for 3 hours to form a B chain and obtain an AB block copolymer. The content of structural units (structural units (B-1)) derived from MAA in the B chain (MMA content) was 40%. The solid content measured by sampling a portion of the reaction solution was 48.6%, and the polymerization rate calculated from the solid content was approximately 100%. The Mn of the AB block copolymer was 10700 and the PDI was 1.31. In addition, the Mn of the B chain ("Mn of the AB block copolymer" - "Mn of the A chain") was 5700.

[0088] A 0.5-portion sample of the reaction solution was placed in a conical beaker, and 40 mL of a 1 / 1 (mass ratio) mixture of toluene and ethanol was added to dissolve the mixture. Phenolphthalein was then added. The AB block copolymer was then titrated with a 0.1 mol / L potassium hydroxide ethanol solution to determine an acid value of 146.9 mgKOH / g. This was confirmed to be substantially the same as the acid value calculated from the monomer composition.

[0089] In a separate container, 44.2 parts of 28% ammonia water and 246.3 parts of water were placed to prepare an ammonia aqueous solution. Separately, in yet another container, 29.1 parts of sodium hydroxide and 261.4 parts of water were placed to prepare an aqueous sodium hydroxide solution. The sodium hydroxide aqueous solution and the ammonia aqueous solution were sequentially added to the reaction solution to neutralize the carboxyl groups derived from methacrylic acid and form an aqueous solution. Specifically, 50 mol% of the carboxyl groups were neutralized with ammonia, and the remaining 50 mol% of the carboxyl groups were neutralized with sodium hydroxide. Water was added to adjust the solids content to obtain a solution of Dispersant D-1 with a solids content of 25.0%.

[0090] (Manufacturing Examples 2 to 9, Comparative Manufacturing Examples 1 to 5)

[0091] Solutions of dispersants D-2 to 9 and comparative dispersants C-1 to 5 were obtained in the same manner as in Example 1, except that the types and amounts (unit: parts) of various materials shown in Tables 1 to 4 were used. The meanings of the abbreviations in the tables are shown below.

[0092] DCMA: dicyclopentyl methacrylate

[0093] IBXMA: Isobornyl methacrylate

[0094] MMA: methyl methacrylate

[0095] EHMA: 2-ethylhexyl methacrylate

[0096] ·PPG: Propylene glycol monopropyl ether

[0097] MTPG: tripropylene glycol monomethyl ether

[0098] MDPA: 3-methoxy-N,N-dimethylpropionamide

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103] Table 3

[0104]

[0105] Table 4

[0106]

[0107] <Manufacturing of Emulsion Adhesive>

[0108] (Reference Manufacturing Example)

[0109] A reaction vessel was charged with 131.7 parts of BDG, 0.5 parts of iodine, 2.6 parts of V-70, 44 parts of BzMA, 13 parts of 2-hydroxyethyl methacrylate (HEMA), and 0.11 parts of NIS. The mixture was heated to 40°C and stirred for 4 hours to polymerize. The polymerization yield, calculated from the solids content, was approximately 100%. GPC measurements of the polymer showed an Mn of 15,000 and a PDI of 1.31.

[0110] 52.8 parts of BzMA and 12.9 parts of MAA were added and polymerized for 4.5 hours to form a block copolymer. The polymerization rate reached approximately 100%, confirming that most of the monomers had polymerized. The block copolymer had an Mn of 23,000, a PDI of 1.45, and an acid value of 69.0 mgKOH / g.

[0111] A mixture of 10 parts 28% aqueous ammonia and 253.4 parts water was added to obtain a low-viscosity emulsion (emulsion adhesive) that was translucent, slightly yellowish, and transparent. The viscosity of the emulsion, measured with a B-type viscometer, was 79.6 mPa·s, and the solids content was 24.6%. The number average particle size of the emulsion particles was 115 nm.

[0112] <Manufacturing of Pigment Dispersion (1)>

[0113] (Example 1)

[0114] 60 parts of titanium oxide (trade name "CR-50", manufactured by Ishiharasangyo Kaisha, Ltd.), 12 parts of dispersant D-1, 6 parts of 1,2-hexanediol, and 22 parts of ion-exchanged water were mixed in a disperser and then dispersed using a horizontal bead mill (trade name "DYNO-MILL KDL Type A", manufactured by Shinmaru Enterprise Corporation) filled with 0.5 mm Ø zirconium oxide beads (filling ratio: 80%). After filtering with a 5 μm membrane filter to remove coarse particles, ion-exchanged water was added to adjust the concentration to obtain a white pigment dispersion W-1 with a pigment concentration of 50%. The number average particle size of the pigment in the resulting pigment dispersion W-1 was 295 nm. The resulting pigment dispersion W-1 had a viscosity of 13.5 mPa·s, a pH of 8.9, and a surface tension of 30.0 mN / m.

[0115] (Examples 2, 3, Comparative Example 1)

[0116] White pigment dispersions W-2, W-3, and CW-1 were obtained in the same manner as in Example 1 except that the dispersants shown in Table 5 were used. The physical properties of the obtained pigment dispersions are shown in Table 5.

[0117] <Evaluation(1)>

[0118] (Sedimentation recovery)

[0119] 1.5 g of a pigment dispersion diluted with water was placed in a 2 mL polypropylene microtube. Using a small centrifuge (trade name "DISKBOY FB-4000", manufactured by Kurabo Industries Ltd.), the mixture was centrifuged at 9000 rpm for 1 minute to form a hard lump at the bottom of the microtube. The microtube was held vertically with the formed hard lump forming the lower side and allowed to stand in the chamber for 30 minutes. Afterwards, the mixture was shaken and mixed by hand, and sedimentation recovery was evaluated according to the evaluation criteria shown below. The results are shown in Table 5. It should be noted that "◎" and "○" were considered qualified.

[0120] ◎: After several oscillations, the sedimentation disappears.

[0121] ○: After 10 shakes, sedimentation disappeared.

[0122] △: After 20 shakes, the sedimentation disappeared.

[0123] ×: The sediment does not disappear even when shaken.

[0124] (Redispersibility)

[0125] A pigment dispersion was added dropwise to a glass plate and placed in a constant temperature and humidity chamber set at 60°C and 40% humidity. After drying for 12 hours, pure water was added to the resulting dried product. The dried product with added water was observed visually and under a microscope, and its redispersibility was evaluated according to the following evaluation criteria. The results are shown in Table 5. It should be noted that "◎" and "○" were considered acceptable. Furthermore, the number average particle size of the redispersed pigment was measured. The results are shown in Table 5.

[0126] [Redispersibility (visual inspection)]

[0127] ◎: No aggregates or films, and the product is liquid.

[0128] ○: A small amount of aggregates were observed, but no film was found.

[0129] △: Agglomerates and films are present, but liquid is also present.

[0130] ×: Not redispersed.

[0131] [Redispersibility (microscope)]

[0132] ◎: No foreign matter such as aggregates.

[0133] ○: A small amount of aggregates were observed, but no film-like fragments or the like were found.

[0134] △: Aggregates and film-like fragments are visible.

[0135] ×: Many foreign objects.

[0136] Table 5

[0137]

[0138] *: Agglomerates are removed.

[0139] <Manufacturing of Pigment Dispersion (2)>

[0140] (Example 4)

[0141] A dispersion treatment was performed in the same manner as in Example 1 using 20 parts of copper phthalocyanine blue (CI Pigment Blue 15:3, trade name "A-220," manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), 28 parts of dispersant D-4, 1 part of BDG, and 51 parts of water. Ion-exchanged water was added to adjust the concentration, yielding a cyan pigment dispersion C-1 with a pigment concentration of 15%. The number average particle size of the pigment in the resulting pigment dispersion C-1 was 105 nm. The resulting pigment dispersion C-1 had a viscosity of 3.2 mPa·s, a pH of 8.6, and a surface tension of 40.5 mN / m.

[0142] (Examples 5 to 9, Comparative Examples 2 to 5)

[0143] Cyan pigment dispersions C-2 to C-6 and CC-1 to C-4 were obtained in the same manner as in Example 4 except that the dispersants shown in Tables 6 and 7 were used. The physical properties of the obtained pigment dispersions are shown in Tables 6 and 7.

[0144] <Evaluation (2)>

[0145] (Storage stability)

[0146] The pigment dispersion was stored at 70°C for one week. The number average particle size of the pigment, the viscosity of the pigment dispersion, and the pH of the pigment dispersion after storage were measured. The results are shown in Tables 6 and 7. Small changes in the number average particle size of the pigment and the viscosity of the pigment dispersion after storage were evaluated as "○" and large changes as "X". The results are shown in Tables 6 and 7.

[0147] (Redispersibility)

[0148] The same evaluation as that for "redispersibility" in the aforementioned "Evaluation (1)" was performed. The results are shown in Tables 6 and 7.

[0149] Table 6

[0150]

[0151] Table 7

[0152]

[0153] <Ink production (1)>

[0154] (Implementation Application Examples 1 to 6, Comparative Application Examples 1 and 2)

[0155] Pigment dispersions of the types shown in Table 8 were prepared. 40 parts of the pigment dispersion, 44 parts of water, 5 parts of 1,2-hexanediol, 10 parts of glycerin, and 1 part of a surfactant (trade name "SURFYNOL 465", manufactured by Nissin Chemical Industry Co., Ltd.) were mixed and thoroughly stirred, and then filtered through a membrane filter with a pore size of 10 μm to prepare inkjet inks IC-1 to 6, ICC-1, and 2.

[0156] <Evaluation (3)>

[0157] The prepared inks were filled into ink cartridges and installed in an inkjet printer (trade name "EM930C", manufactured by Seiko Epson Corporation). Using this inkjet printer, a solid image (print) with maximum print density was recorded on plain paper (paper containing a large amount of inorganic filler (calcium carbonate), trade name "Colorlok paper", manufactured by HP Inc.).

[0158] (Discharge stability)

[0159] The ejection failure during recording, such as ink non-ejection and ink scattering, was observed, and the ink ejection stability was evaluated according to the following evaluation criteria. The results are shown in Table 8. Note that "○" was considered acceptable.

[0160] ○: No ejection failure.

[0161] Δ: In addition to ink droplets, slight splashing was observed.

[0162] ×: No ejection during the process or ink scattering was observed.

[0163] (Appearance of printed matter)

[0164] The appearance of the recorded printed matter was visually observed and evaluated according to the following evaluation criteria. The obtained results are shown in Table 8. In addition, "○" was evaluated as passing.

[0165] ◯: No streaks or unevenness were observed, and the printed material was uniform.

[0166] ×: Streaks and unevenness were observed.

[0167] (Optical density)

[0168] The optical density (OD value) of the recorded image was measured five times using a densitometer (trade name "Macbeth RD-914", manufactured by Gretag Macbeth LLC.), and the average value was calculated.

[0169] Table 8

[0170] Implementation application examples 1 2 3 4 5 6 Comparative Application Examples 1 2 Ink Name 1C-1 IC-2 IC-3 IC-4 IC-5 IC-6 ICC-1 ICC-2 Pigment dispersion used C-1 C-2 C-3 C-4 C-5 C-6 CC-1 CC-4 Ejection stability 〇 O 〇 〇 〇 〇 〇 △ Appearance of printed material O 〇 〇 〇 〇 〇 〇 △ Optical density 1.41 1.38 1.43 1.40 1.38 1.38 1.26 1.39

[0171] <Ink Manufacturing (2)>

[0172] (Implementation Application Examples 7 to 12, Comparative Application Examples 3 to 5)

[0173] Pigment dispersions of the types shown in Table 9 were prepared. 16.0 parts of the emulsion binder prepared in Reference Preparation Example, 28.6 parts of the pigment dispersion, 18.0 parts of propylene glycol, 0.5 parts of a surfactant (trade name "SILFACE SAG503A", manufactured by Nissin Chemical Industry Co., Ltd.), 0.7 parts of polyethylene wax, and 36.2 parts of water were mixed and thoroughly stirred. The mixture was then filtered through a membrane filter with a pore size of 5 μm to prepare inkjet inks IC-7 to 12 and ICC-3 to 5 for film printing. The viscosities of the prepared inks are shown in Table 9.

[0174] <Evaluation (4)>

[0175] Prepare an inkjet printer equipped with a sheet heater (trade name "MMP825H," manufactured by MASTERMIND CO., LTD.) and the following types of substrates. Fill the prepared ink cartridges with each ink and install them in the prepared inkjet printer. Use this printer to record images (printed materials) on the following types of substrates. Specifically, after heating the substrate to a surface temperature of 55°C using the sheet heater, apply ink and print. Then, dry the substrate in a thermostatic chamber heated to 90°C for 10 minutes to obtain printed materials.

[0176] OPP film (polypropylene film, manufactured by Futamura Chemical Co., Ltd., thickness 50 μm)

[0177] PET film (polyethylene terephthalate film, manufactured by Futamura Chemical Co., Ltd., thickness 50 μm)

[0178] (Discharge stability, printed appearance)

[0179] The same evaluations as those for "discharge stability" and "appearance of printed matter" in the aforementioned "Evaluation (3)" were performed. The results are shown in Table 9.

[0180] (Adhesion)

[0181] After fully pressing the transparent tape against the recorded image, peel it off. Visually observe the peeling of the image from the substrate and evaluate the image's adhesion according to the following evaluation criteria. The results are shown in Table 9. "◎" and "○" are considered acceptable.

[0182] ◎: No peeling at all.

[0183] ○: Slightly peeled.

[0184] Δ: The peeled area is smaller than the non-peeled area.

[0185] ×: The peeled area is larger than the non-peeled area.

[0186] (Friction resistance (dry and wet friction resistance))

[0187] Using a Gakushin type rubbing color fastness tester (trade name "RT-300", manufactured by DAIEI KAGAKU SEIKI MFG.CO., LTD.), a dry rubbing test was conducted, in which a dry white cloth was moved back and forth 100 times with a 500g load, and a wet rubbing test was conducted, in which a white cloth moistened with water was moved back and forth 100 times with a 200g load. The peeling of the image after the rubbing test was visually observed, and the image's rubbing resistance (dry rubbing resistance and wet rubbing resistance) was evaluated according to the evaluation criteria shown below. The results are shown in Table 9. "◎," "○," and "△" were considered acceptable.

[0188] ◎: No peeling at all.

[0189] ○: Slightly peeled.

[0190] Δ: The peeled area is smaller than the non-peeled area.

[0191] ×: The peeled area is larger than the non-peeled area.

[0192] (Alcohol resistance)

[0193] Add a 70% ethanol solution to the image and let it sit for 10 seconds. After that, rub the image back and forth several times with a cotton swab. Measure the number of times the image peels off, and evaluate the image's alcohol resistance according to the following evaluation criteria. The results are shown in Table 9. "◎" and "○" are considered acceptable.

[0194] ◎: More than 20 times

[0195] ○: 10 to less than 20 times

[0196] △: 5 to less than 10 times

[0197] ×: Peeled off immediately ~ Less than 5 times

[0198] Table 9

[0199]

[0200] <Manufacturing of Pigment Dispersion (3)>

[0201] (Examples 10 to 15)

[0202] The following pigments were prepared. Pigment dispersions Y-1, M-1, Bk-1, R-1, G-1, and O-1 were obtained in the same manner as in Example 4, except that the prepared pigments were used in place of copper phthalocyanine blue. The physical properties of the resulting pigment dispersions are shown in Table 10.

[0203] Yellow pigment: CI Pigment Yellow 155, azo pigment, trade name "CFY6241", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0204] Magenta pigment: CI Pigment Red 122, quinacridone pigment, trade name "CFR-130", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0205] Black pigment: CI Pigment Black 7, carbon black, trade name "Raven 1200", manufactured by BIRLA

[0206] Red pigment: CI Pigment Red 254, diketopyrrolopyrrole pigment, trade name "CFR6742", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0207] Green pigment: CI Pigment Green 36, copper phthalocyanine halide pigment, trade name "CFG6450", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0208] Orange pigment: CI Pigment Orange 43, polycyclic condensed pigment, trade name "CFO6292", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0209] <Evaluation (5)>

[0210] (Storage stability, redispersibility)

[0211] The same evaluations as those for "storage stability" and "redispersibility" in the aforementioned "Evaluation (2)" were performed. The results are shown in Table 10.

[0212] Table 10

[0213]

[0214] <Ink Manufacturing (3)>

[0215] (Implementation Application Examples 13 to 18)

[0216] Inkjet inks IY-1, IM-1, IBk-1, IR-1, IG-1, and IO-1 were prepared in the same manner as in Example 1 except that the pigment dispersions shown in Table 11 were used.

[0217] <Evaluation (6)>

[0218] (Ejection stability, printed appearance, optical density)

[0219] The same evaluations as those for "discharge stability," "appearance of printed matter," and "optical density" in the aforementioned "Evaluation (3)" were performed. The results are shown in Table 11.

[0220] Table 11

[0221] Implementation application examples 1 13 14 15 16 17 18 Ink Name IC-1 IY-1 IM-1 IBk-1 IR-1 IG-1 IO-1 Pigment dispersion used C-1 Y-1 M-1 Bk-1 R-1 G-1 O-1 Ejection stability ○ ○ ○ ○ ○ ○ ○ Appearance of printed material 〇 〇 〇 〇 〇 〇 〇 Optical density 1.41 1.27 1.38 1.46 1.39 1.43 1.31

[0222] <Ink Manufacturing (4)>

[0223] (Implementation Application Examples 19 to 24)

[0224] Inkjet inks IY-2, IM-2, IBk-2, IR-2, IG-2, and IO-2 for thin film printing were prepared in the same manner as in Example 7, except that the pigment dispersions shown in Table 12 were used. The viscosities of the prepared inks are shown in Table 12.

[0225] <Evaluation (7)>

[0226] (Dispensing stability, printed appearance, adhesion, abrasion resistance, alcohol resistance)

[0227] The same evaluations as those for "discharge stability" and "appearance of printed matter" in "Evaluation (3)" and "adhesion," "friction resistance," and "alcohol resistance" in "Evaluation (4)" were performed. The results are shown in Table 12.

[0228] Table 12

[0229]

[0230] Industrial applicability

[0231] The pigment dispersion of the present invention is useful as a pigment dispersion for preparing an aqueous inkjet ink.

Claims

1. A pigment dispersion comprising a pigment, a dispersant, a water-soluble organic solvent and water for preparing an aqueous inkjet ink. The dispersant is an AB block copolymer comprising a polymer chain A and a polymer chain B, wherein the AB block copolymer has a number average molecular weight of 5,000 to 15,000, a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.2 to 1.6, and an acid value of 100 mgKOH / g or more. The polymer chain A is a polymer block comprising at least one structural unit (A-1) selected from the group consisting of methyl methacrylate and benzyl methacrylate, and at least one structural unit (A-2) selected from the group consisting of cyclohexyl methacrylate, dicyclopentanyl methacrylate, and isobornyl methacrylate, wherein the total content of the structural units (A-1) and (A-2) is 70% by mass or more, the polymer block has a glass transition temperature of 50° C. or more, a number average molecular weight of 2,000 to 10,000, and a molecular weight distribution of 1.1 to 1.5, The polymer chain B is a polymer block comprising a structural unit (B-1) derived from methacrylic acid and a structural unit (B-2) derived from at least one selected from the group consisting of methyl methacrylate, benzyl methacrylate, and cyclohexyl methacrylate, wherein the content of the structural unit (B-1) is 25 to 50% by mass, and the number average molecular weight of the polymer block is 2,000 to 10,000. In the AB block copolymer, 30 to 70 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with ammonia, and 30 to 70 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with at least one of sodium hydroxide and potassium hydroxide.

2. The pigment dispersion according to claim 1, wherein In the AB block copolymer, 40 to 60 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with ammonia, and 40 to 60 mol% of the carboxyl groups derived from the methacrylic acid are neutralized with sodium hydroxide.

3. The pigment dispersion according to claim 1 or 2, wherein The content of the pigment is 5 to 60% by mass. The content of the dispersant is 0.5 to 20% by mass. The content of the water-soluble organic solvent is 30% by mass or less, The water content is 20 to 80% by mass.

4. The pigment dispersion according to any one of claims 1 to 3, wherein The water-soluble organic solvent is at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-N,N-dimethylpropionamide and 3-butoxy-N,N-dimethylpropionamide.

5. The pigment dispersion according to any one of claims 1 to 4, wherein The pigment is at least one selected from the group consisting of yellow pigment, red pigment, blue pigment, green pigment, orange pigment, black pigment and white pigment, The yellow pigment is at least one selected from the group consisting of CI Pigment Yellow 74, 150, 155 and 180, The red pigment is at least one selected from the group consisting of CI Pigment Red 122, 202, 254, 269 and their solid solutions, and CI Pigment Violet 19, 23 and their solid solutions. The blue pigment is at least one selected from the group consisting of CI Pigment Blue 15:3, 15:4 and 15:6, The green pigment is at least one selected from the group consisting of CI Pigment Green 7, 36 and 58, The orange pigment is CI Pigment Orange 43, The black pigment is CI Pigment Black 7, The white pigment is CI Pigment White 6.

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