pigment dispersion

Abstract

To provide a pigment dispersion which has excellent dispersibility, is less likely to cause an increase in viscosity with time and has excellent dispersion stability.SOLUTION: There is provided a pigment dispersion containing a condensed polycyclic pigment having a maximum wavelength in the range of 450 to 700 nm in the transmission spectrum, a polyvinyl acetal resin containing a structural unit having an acetal group including an aryl group and an organic solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pigment dispersion that has excellent dispersibility, little increase in viscosity over time, and excellent dispersion stability. [Background technology]

[0002] Ink and paint are used in which pigments and other additives are blended with binder resin and dispersed in a solvent.

[0003] As the binder resin, polyvinyl acetal resins such as polyvinyl butyral resins are widely used, as they are excellent in film-forming properties, pigment dispersibility, adhesiveness, alcohol solubility, etc.

[0004] For example, Patent Documents 1 and 2 describe ink compositions that use polyvinyl acetal resins obtained by acetalizing a mixture of low-polymerization polyvinyl alcohol and high-polymerization polyvinyl alcohol. Furthermore, Patent Document 3 describes the use of a polyvinyl acetal resin as the resin in an ink for an oil-based ballpoint pen that uses a resin having a solubility in ethanol at 25° C. of more than 7% by weight. Patent Document 4 describes an oil-based ink containing fluorescent resin particles, a non-aqueous solvent, and a basic dispersant, in which the fluorescent resin particles contain a solid resin such as polyvinyl acetal. Furthermore, Patent Document 5 describes the use of a polyvinyl acetal resin as the resin in a non-aqueous inkjet ink containing a dye, a pigment, a resin, and an organic solvent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-114931 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-60427 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-172543 [Patent Document 4] Japanese Patent Application Publication No. 2018-90666 [Patent Document 5] International Publication No. 2019 / 103088 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even the inks described in Patent Documents 1 to 5 have problems such as insufficient pigment dispersibility and dispersion stability over time. In particular, phthalocyanine pigments have low polarity, making them difficult to adsorb through intermolecular interactions, resulting in insufficient dispersibility. Furthermore, phthalocyanine pigments have a bulky structure and a very large molecular weight, making it difficult to maintain a dispersed state, and problems such as ink clogging due to clumps formed by sedimentation occur.

[0007] An object of the present invention is to provide a pigment dispersion that has excellent dispersibility, little increase in viscosity over time, and excellent dispersion stability. [Means for solving the problem]

[0008] The present invention provides a pigment dispersion containing a fused polycyclic pigment having a maximum wavelength in the wavelength range of 450 to 700 nm in its transmission spectrum, a polyvinyl acetal resin containing a structural unit having an acetal group containing an aryl group, and an organic solvent. The present invention will be described in detail below.

[0009] As a result of extensive research, the present inventors have found that by using as a dispersant a polyvinyl acetal resin containing a structural unit having an acetal group containing an aryl group, it is possible not only to improve the dispersibility of a specific fused polycyclic pigment that is poor in dispersibility and difficult to maintain in a dispersed state, but also to suppress sedimentation over time, and have completed the present invention.

[0010] The pigment dispersion of the present invention contains a polyvinyl acetal resin. The polyvinyl acetal resin contains a structural unit having an acetal group containing an aryl group. By having the above structure, the dispersibility and dispersion stability of a specific pigment can be improved.

[0011] The aryl group may be monocyclic or polycyclic, and one or more hydrogen atoms of the aryl group may be substituted with an alkyl group, a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, a halogen atom, a nitro group, a phosphoric acid group, an acyl group, or a salt thereof. The aryl group preferably has 6 to 14 carbon atoms, and more preferably 6 to 10 carbon atoms.

[0012] When the aryl group is substituted with an alkyl group, the alkyl group preferably has 1 to 12 carbon atoms, and more preferably has 1 to 5 carbon atoms. Examples of the alkyl group include a methyl group, a trifluoromethyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, and an octadecyl group.

[0013] Examples of the monocyclic aryl group include alkylphenyl groups such as a phenyl group, an o-methylphenyl group, a m-methylphenyl group, a p-methylphenyl group, a dimethylphenyl group, a trimethylphenyl group, a tetramethylphenyl group, a pentamethylphenyl group, an o-trifluoromethylphenyl group, an o-ethylphenyl group, a m-ethylphenyl group, a p-ethylphenyl group, a diethylphenyl group, a triethylphenyl group, an o-propylphenyl group, a m-propylphenyl group, a p-propylphenyl group, an o-isopropylphenyl group, a m-isopropylphenyl group, and a p-isopropylphenyl group. The polycyclic aryl group may be a ring assembly type aryl group or a condensed polycyclic aryl group.The ring assembly type aryl group may include alkylbiphenyl groups such as biphenyl group, methylbiphenyl group, dimethylbiphenyl group, trimethylbiphenyl group, tetramethylbiphenyl group, ethylbiphenyl group, diethylbiphenyl group, triethylbiphenyl group, and tetraethylbiphenyl group.The condensed polycyclic aryl group may include alkylnaphthyl groups such as naphthyl group, methylnaphthyl group, ethylnaphthyl group, dimethylnaphthyl group, and diethylnaphthyl group, and alkylanthryl groups such as anthryl group, methylanthryl group, ethylanthryl group, dimethylanthryl group, and diethylanthryl group.

[0014] Examples of the structural unit having an acetal group containing an aryl group include the structural unit represented by the following formula (1).

[0015] [ka]

[0016] In formula (1), R 1 represents a single bond or an alkylene group, and R 2 represents an aryl group.

[0017] In the above formula (1), R 1 When R is an alkylene group, the lower limit of the number of carbon atoms in the alkylene group is preferably 1, and the upper limit is preferably 12. If the number of carbon atoms in the alkylene group exceeds 12, optimum strength may not be obtained. 1 When is an alkylene group, the upper limit of the number of carbon atoms in the alkylene group is more preferably 5.

[0018] In the above formula (1), R 1When is an alkylene group, examples of the alkylene group include linear alkylene groups such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, octamethylene, and decamethylene groups; branched alkylene groups such as methylmethylene, methylethylene, 1-methylpentylene, and 1,4-dimethylbutylene groups; Examples include branched alkylene groups and cyclic alkylene groups such as cyclopropylene, cyclobutylene, and cyclohexylene. Of these, linear alkylene groups such as methylene, ethylene, n-propylene, and n-butylene are preferred, with methylene and ethylene being more preferred.

[0019] Above R 2 The aryl group represented by the formula (I) preferably has 6 carbon atoms at the lower limit, 14 carbon atoms at the upper limit, and more preferably 10 carbon atoms at the upper limit.

[0020] In the polyvinyl acetal resin, the structural unit having an acetal group containing an aryl group is represented by the formula (1), R 1 is a single bond, R 2 is preferably an aryl group having 6 to 14 carbon atoms, and R 1 is a single bond, R 2 is more preferably an aryl group having 6 to 10 carbon atoms, and R 1 is a single bond, R 2 is more preferably a phenyl group, an alkylphenyl group, a naphthyl group, or a biphenyl group. The phenyl group, alkylphenyl group, naphthyl group, and biphenyl group may have some of their hydrogen atoms substituted with chlorine atoms.

[0021] In the polyvinyl acetal resin, the content of structural units having an acetal group containing an aryl group relative to all structural units is preferably 0.5 mol % in the lower limit and 10.0 mol % in the upper limit. By setting the content of the structural unit having an acetal group containing an aryl group within the above range, the dispersibility of the fused polycyclic pigment can be further improved. The more preferred lower limit of the content of the structural unit having an acetal group containing an aryl group is 1.5 mol %, and even more preferred lower limit is 2.5 mol %, and more preferred upper limit is 9.0 mol %, and even more preferred upper limit is 8.0 mol %. The content of the structural unit having an acetal group containing an aryl group can be measured by NMR or the like.

[0022] The polyvinyl acetal resin preferably further contains a structural unit having a chlorine atom. By including the structural unit having a chlorine atom, it is possible to further improve the adhesiveness and dispersibility, and also to further improve the dispersion stability.

[0023] The structural unit having a chlorine atom is not particularly limited as long as it has a structure having a chlorine atom, but examples thereof include a structure in which a chlorine atom is bonded via an acetal bond, a structure in which a chlorine atom or a chlorine atom-containing group is present in a side chain without an acetal bond, and the like, and a structure in which a chlorine atom is bonded via an acetal bond is preferred. Note that the structure in which a chlorine atom is bonded via an acetal bond also includes a case in which a chlorine atom is bonded via a further linking group other than an acetal bond.

[0024] When the structural unit having a chlorine atom has a structure in which the chlorine atom is bonded via an acetal bond (hereinafter, such a structural unit may be referred to as a "chlorinated-modified acetal bond unit"), the chlorinated-modified acetal bond unit includes not only the chlorinated-modified acetal bond unit not having an aryl group (hereinafter, also referred to as an "aryl-group-free chlorinated-modified acetal bond unit"), but also a structural unit having an acetal group containing the aryl group and a chlorine atom. The aryl group-free chlorinated modified acetal bond unit is preferably a constitutional unit represented by the following formula (2). The presence of such a structural unit allows an appropriate distance to be maintained between the main chain of the modified polyvinyl acetal resin and the chlorine atom, resulting in further improved adhesion and dispersibility, and further improved dispersion stability of the resulting pigment dispersion.

[0025] [ka]

[0026] In the above formula (2), R 3 represents a single bond or an alkylene group, and R 4 represents a chlorine atom, a chloroalkyl group, or a substituent represented by the following formula (3). Among them, R 3 is preferably a single bond, and R 4 is preferably a substituent represented by the following formula (3).

[0027] [ka]

[0028] In the above formula (3), R 5 represents a chlorine atom or a chloroalkyl group, and R 6 , R 7 each independently represents a hydrogen atom, a chlorine atom, or a chloroalkyl group. Among them, R 5 is preferably a chlorine atom, and R 6 is preferably a hydrogen atom, and R 7 is preferably a hydrogen atom.

[0029] The chloroalkyl group preferably has a carbon number of 1 or more and preferably 20 or less. The chloroalkyl group may be linear or branched. Examples of the chloroalkyl group include a chloromethyl group, a chloroethyl group, a chloropropyl group, and a chlorobutyl group.

[0030] The content of the chlorine atom-containing structural units (hereinafter also referred to as "chlorinated modified unit amount") relative to all structural units in the polyvinyl acetal resin is preferably 0.1 mol% or less. By setting the chlorinated modified unit amount to 0.1 mol% or more, adhesion and dispersibility can be further improved, and the dispersion stability of the resulting pigment dispersion can be further improved. A more preferred lower limit of the amount of chlorinated modified units is 0.5 mol %, and an even more preferred lower limit is 1.0 mol %. The upper limit of the amount of the chlorinated modified units is not particularly limited, but from the viewpoint of ease of handling during production, it is preferably 30 mol % or less. In addition, when the polyvinyl acetal resin contains both a chlorinated modified acetal bond unit and a structure having a chlorine atom or a chlorine atom-containing group in a side chain without an acetal bond, the amount of the chlorinated modified unit means the total amount of both.

[0031] The content of the chlorinated modified acetal bond units relative to all structural units in the polyvinyl acetal resin is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, even more preferably 1.0 mol% or more, and is preferably 30 mol% or less.

[0032] The content of the non-aryl group-containing chlorinated modified acetal bond units relative to all structural units in the polyvinyl acetal resin is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, and even more preferably 1.0 mol% or more, and is preferably 20 mol% or less, more preferably 15 mol% or less, and even more preferably 10 mol% or less.

[0033] The polyvinyl acetal resin preferably has a structural unit having an acetal group represented by the following formula (4), a structural unit having a hydroxyl group represented by the following formula (5), and a structural unit having an acetyl group represented by the following formula (6).

[0034] [ka]

[0035] In formula (4), R 8 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. Examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, and an octadecyl group.

[0036] In the polyvinyl acetal resin, the content of the structural units having an acetal group represented by the above formula (4) relative to all structural units is preferably 51.0 mol% in lower limit, more preferably 58.5 mol%, and more preferably 73.0 mol% in upper limit, more preferably 66.5 mol%.

[0037] The content of structural units having acetal groups relative to all structural units of the polyvinyl acetal resin (hereinafter also referred to as the total acetal group amount) is preferably 40.0 mol% at the lower limit, more preferably 60.0 mol%, and more preferably 81.5 mol% and more preferably 75.0 mol% at the upper limit, regardless of whether a single aldehyde or a mixed aldehyde is used for acetalization. The total amount of acetal groups in the polyvinyl acetal resin can be measured by NMR or the like.

[0038] The ratio (mol %) of the content of the structural units having an acetal group containing an aryl group relative to the total amount of acetal groups in the polyvinyl acetal resin ([content of structural units having an acetal group containing an aryl group / total amount of acetal groups] × 100) is preferably 0.70 mol %, more preferably 7.5 mol %, and more preferably 71.4 mol %, and more preferably 16.1 mol %.

[0039] The content of the structural unit having an acetoacetal group in the polyvinyl acetal resin is preferably 0 to 14.0 times, more preferably 0 to 4.0 times, the content of the structural unit having an acetal group containing an aryl group. By setting the amount within the above range, there is an advantage that the pigment can be broken down into finer particles by penetrating between the pigment particles. Furthermore, the content of the structural unit having a butyral group in the polyvinyl acetal resin is preferably 4.0 to 36.0 times, and more preferably 6.0 to 22.0 times, the content of the structural unit having an acetal group containing an aryl group. By setting the thickness within the above range, there is an advantage that an appropriate distance between pigment particles can be maintained and thickening over time can be suppressed.

[0040] In the polyvinyl acetal resin, the content of the structural unit having a hydroxyl group represented by the above formula (5) relative to all structural units (hereinafter also referred to as "hydroxyl group amount") is preferably 18.0 mol% in the lower limit and 45.0 mol% in the upper limit. By setting the content within the above range, there is an advantage that the compatibility with common solvents is good. The more preferred lower limit of the hydroxyl group amount is 23.0 mol %, and the more preferred upper limit is 38.0 mol %.

[0041] In the polyvinyl acetal resin, the content of the structural unit having an acetyl group represented by the above formula (6) relative to all structural units (hereinafter also referred to as "acetyl group amount") is preferably 0.05 mol% as a lower limit, more preferably 0.1 mol% as a lower limit, and even more preferably 0.5 mol% as a lower limit, and preferably 30.0 mol% as an upper limit, more preferably 15.0 mol% as an upper limit, and even more preferably 5.0 mol% as an upper limit.

[0042] The average degree of polymerization of the polyvinyl acetal resin is not particularly limited, but the preferred lower limit is 150 and the preferred upper limit is 1,000. When the average degree of polymerization of the polyvinyl acetal resin is 150 or more, a pigment dispersion having sufficient viscosity can be obtained, and when the average degree of polymerization of the polyvinyl acetal resin is 1000 or less, handling can be improved. The average degree of polymerization is more preferably 270 in the lower limit, even more preferably 350 in the lower limit, more preferably 600 in the upper limit, and even more preferably 500 in the upper limit.

[0043] The polyvinyl acetal resin can be prepared, for example, by acetalizing polyvinyl alcohol with an aldehyde having an aryl group.

[0044] Examples of the aldehyde having an aryl group include alkyl benzaldehydes such as benzaldehyde, o-methyl benzaldehyde, m-methyl benzaldehyde, p-methyl benzaldehyde, dimethyl benzaldehyde, trimethyl benzaldehyde, tetramethyl benzaldehyde, pentamethyl benzaldehyde, o-ethyl benzaldehyde, m-ethyl benzaldehyde, p-ethyl benzaldehyde, diethyl benzaldehyde, triethyl benzaldehyde, o-propyl benzaldehyde, m-propyl benzaldehyde, p-propyl benzaldehyde, o-isopropyl benzaldehyde, m-isopropyl benzaldehyde, and p-isopropyl benzaldehyde (cumin aldehyde); halogenated benzaldehydes such as p-chloro benzaldehyde and p-bromo benzaldehyde; Examples of the aldehyde include alkylbiphenylaldehydes such as biphenylaldehyde, methylbiphenylaldehyde, dimethylbiphenylaldehyde, trimethylbiphenylaldehyde, tetramethylbiphenylaldehyde, ethylbiphenylaldehyde, diethylbiphenylaldehyde, triethylbiphenylaldehyde, and tetraethylbiphenylaldehyde, alkylnaphthylaldehydes such as naphthylaldehyde, methylnaphthylaldehyde, ethylnaphthylaldehyde, dimethylnaphthylaldehyde, and diethylnaphthylaldehyde, and alkylanthraldehydes such as anthraldehyde, methylanthraldehyde, ethylanthraldehyde, dimethylanthraldehyde, and diethylanthraldehyde. These aldehydes may be used alone or in combination of two or more.

[0045] The acetalization can be carried out by a known method, and is preferably carried out in an aqueous solvent, a mixed solvent of water and an organic solvent compatible with water, or an organic solvent. Examples of the water-compatible organic solvent that can be used include alcohol-based organic solvents, aromatic organic solvents, aliphatic ester-based solvents, ketone-based solvents, lower paraffin-based solvents, ether-based solvents, amide-based solvents, and amine-based solvents. Examples of the alcohol-based organic solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol. Examples of the aromatic organic solvent include xylene, toluene, ethylbenzene, and methyl benzoate. Examples of the aliphatic ester solvent include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetoacetate, and ethyl acetoacetate. Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone, benzophenone, and acetophenone. Examples of the lower paraffin solvent include hexane, pentane, octane, cyclohexane, and decane. Examples of the ether solvent include diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol diethyl ether. Examples of the amide solvent include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and acetanilide. Examples of the amine solvent include ammonia, trimethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, N-methylaniline, N,N-dimethylaniline, and pyridine. These can be used alone or in combination of two or more solvents. Among these, ethanol, n-propanol, isopropanol, and tetrahydrofuran are particularly preferred from the viewpoints of solubility in the resin and ease of purification.

[0046] The acetalization is preferably carried out in the presence of an acid catalyst. The acid catalyst is not particularly limited, and examples thereof include mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; carboxylic acids such as formic acid, acetic acid, and propionic acid; and sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and paratoluenesulfonic acid. These acid catalysts may be used alone or in combination of two or more compounds. Among these, hydrochloric acid, nitric acid, and sulfuric acid are preferred, and hydrochloric acid is particularly preferred.

[0047] In addition, during the acetalization, an aldehyde other than the aldehyde having an aryl group (hereinafter also referred to as "other aldehyde") may be used in combination. The other aldehyde is not particularly limited, and examples thereof include aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butylaldehyde, isobutyraldehyde, n-valeraldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, n-heptylaldehyde, n-octylaldehyde, n-nonylaldehyde, n-decylaldehyde, and amylaldehyde. These aldehydes may be used alone or in combination of two or more.

[0048] Furthermore, when the polyvinyl acetal resin has a structural unit having a chlorine atom, examples of a method for producing the polyvinyl acetal resin having the structural unit having a chlorine atom include a method of acetalizing polyvinyl alcohol having a structural unit having a chlorine atom using an aldehyde having an aryl group, etc. Alternatively, a method of acetalizing a polyvinyl alcohol resin using an aldehyde having an aryl group, etc., and then adding a chlorine atom may be mentioned. Further examples include a method of acetalizing a polyvinyl alcohol resin using an aldehyde having an aryl group and an aldehyde having a chlorine atom, or an aldehyde equivalent, and a method of acetalizing a polyvinyl alcohol resin using an aldehyde having an aryl group and a chlorine atom, etc. Among these, a method of acetalizing a polyvinyl alcohol resin using an aldehyde having an aryl group and an aldehyde having a chlorine atom, or an aldehyde equivalent, and a method of acetalizing a polyvinyl alcohol resin using an aldehyde having an aryl group and a chlorine atom are preferred.

[0049] Examples of the aldehyde having a chlorine atom include 3-chloroacetaldehyde, dichloroacetaldehyde, trichloroacetaldehyde, 3-chloropropionaldehyde, and 4-chlorobutyraldehyde. The aldehyde equivalent having a chlorine atom is an aldehyde to which a protecting group has been added, or a compound that can be converted into an aldehyde by a commonly used method, and examples thereof include acetal, dichloroacetaldehyde diethyl acetal, aldehyde hydrate, etc. Examples of the aldehyde having a chlorine atom include chloroacetaldehyde dimethyl acetal, chloroacetaldehyde diethyl acetal, 2-chloromethyl-1,3-dioxolane, dichloroacetaldehyde dimethyl acetal, dichloroacetaldehyde diethyl acetal, 2,2-dichloromethyl-1,3-dioxolane, trichloroacetaldehyde dimethyl acetal, trichloroacetaldehyde diethyl acetal, trichloroacetaldehyde methyl acetal, and the like. chloroacetaldehyde dimethyl acetal, trichloroacetaldehyde ethyl hemiacetal, chloral hydrate, 2,2,2-trichloromethyl-1,3-dioxolane, 3-chloropropionaldehyde dimethyl acetal, 3-chloropropionaldehyde diethyl acetal, 2-(2-chloroethyl)-1,3-dioxolane, 4-chlorobutyraldehyde dimethyl acetal, 4-chlorobutyraldehyde diethyl acetal, 2-(3-chloropropyl)-1,3-dioxolane, and the like.

[0050] When the aryl group-containing aldehyde is used in combination with another aldehyde during the acetalization, the ratio (mol %) of the amount of the aryl group-containing aldehyde added to the total amount of aldehydes added ([amount of aryl group-containing aldehyde added / total amount of aldehydes added] × 100) is preferably 0.4 to 90.0 mol %. By setting the ratio of the amount of the aryl group-containing aldehyde added within the above preferred range, the ratio of structural units having an acetal group containing an aryl group in the obtained polyvinyl acetal resin can be set within a preferred range, thereby further improving the dispersibility of the fused polycyclic pigment.

[0051] When an aldehyde having an aryl group is used in combination with another aldehyde during the acetalization, the dispersibility-improving effect of the resulting polyvinyl acetal resin can be further enhanced, and therefore, a method in which all aldehydes are added simultaneously is preferred.

[0052] The amount of the total aldehyde added can be appropriately set depending on the total amount of acetal groups in the target polyvinyl acetal resin. In particular, an amount of 60 to 95 mol %, preferably 70 to 90 mol %, based on 100 mol % of polyvinyl alcohol is preferred because this allows the acetalization reaction to proceed efficiently and makes it easy to remove unreacted aldehyde.

[0053] In the pigment dispersion of the present invention, the content of the polyvinyl acetal resin is preferably 0.5% by weight at the lower limit, more preferably 0.85% by weight at the lower limit, and preferably 3.0% by weight at the upper limit, more preferably 2.0% by weight at the upper limit.

[0054] In the pigment dispersion of the present invention, the content of the polyvinyl acetal resin relative to 100 parts by weight of the fused polycyclic pigment preferably has a lower limit of 5 parts by weight and an upper limit of 20 parts by weight. By setting the content within the above range, dispersibility can be further improved. The lower limit of the content is more preferably 7 parts by weight, and the upper limit thereof is more preferably 16 parts by weight.

[0055] The pigment dispersion of the present invention contains a fused polycyclic pigment having a maximum wavelength in its transmission spectrum of 450 to 700 nm or more. The pigments mentioned above are difficult to disperse because of their low polarity and difficulty in adsorption through intermolecular interactions, and because the molecules are large, they settle quickly and are difficult to maintain in a dispersed state. In the pigment dispersion of the present invention, the dispersibility and dispersion stability of the pigment can be improved by using the pigment in combination with the polyvinyl acetal resin.

[0056] The above-mentioned fused polycyclic pigment has a maximum wavelength in the range of 450 to 700 nm in the transmission spectrum. The maximum wavelength in the transmission spectrum of the fused polycyclic pigment is preferably 470 to 570 nm, and more preferably 480 to 540 nm. The maximum wavelength can be measured using, for example, a spectrophotometer.

[0057] The fused ring pigment preferably has a maximum wavelength in its absorption spectrum of 400 to 1000 nm, more preferably 580 to 900 nm. The maximum wavelength can be measured using, for example, a spectrophotometer.

[0058] The lower limit of the number of aromatic rings in one molecule of the fused polycyclic pigment is preferably 1, more preferably 2, and the upper limit is preferably 6, more preferably 4. The aromatic ring is an aromatic hydrocarbon ring, and refers to a single ring or a single ring constituting a condensed ring. For example, a naphthalene ring contains two aromatic rings, and an anthracene ring contains three aromatic rings.

[0059] The molecular weight of the condensed polycyclic pigment is preferably 250 in the lower limit and 1,500 in the upper limit. Within the above range, there is an advantage that the polyvinyl acetal resin is easily adsorbed and the dispersed state is easily maintained. The lower limit of the molecular weight is more preferably 400, even more preferably 500, and more preferably 1,200.

[0060] Examples of the condensed polycyclic pigments include phthalocyanine-based, isoindolinone-based, quinophthalone-based, isoindoline-based, anthraquinone-based, diketopyrrolopyrrole-based, perylene-based, perinone-based, quinacridone-based, and dioxazine-based pigments.

[0061] Examples of the phthalocyanine pigment include metal phthalocyanine pigments and non-metal phthalocyanine pigments. Examples of metals contained in the metal phthalocyanine pigment include copper, nickel, cobalt, zinc, iron, silver, beryllium, magnesium, calcium, aluminum, indium, sodium, lithium, titanium, tin, lead, vanadium, chromium, and manganese. Of these, copper phthalocyanine pigments are preferred. Specific examples of the phthalocyanine pigments include copper phthalocyanine pigments such as CI Pigment Blue 15, CI Pigment Blue 15:1, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Blue 15:5, CI Pigment Blue 15:6, CI Pigment Blue 17:1, CI Pigment Green 7, CI Pigment Green 36, CI Pigment Green 37, and CI Pigment Green 42. Other examples include zinc phthalocyanine pigments such as CI Pigment Green 58, cobalt phthalocyanine pigments such as CI Pigment Blue 75, aluminum phthalocyanine pigments such as CI Pigment Blue 79, and metal-free phthalocyanine pigments such as CI Pigment Blue 16.

[0062] Examples of the isoindolinone pigments include CI Pigment Yellow 109, CI Pigment Yellow 110, CI Pigment Yellow 173, and CI Pigment Orange 61. Examples of the isoindoline pigments include CI Pigment Yellow 139, CI Pigment Yellow 185, CI Pigment Orange 66, CI Pigment Orange 69, and CI Pigment Red 260. Examples of the anthraquinone pigments include CI Pigment Yellow 24, CI Pigment Yellow 108, CI Pigment Orange 51, CI Pigment Red 168, CI Pigment Red 177, and CI Pigment Blue 60. Examples of the diketopyrrolopyrrole pigments include CI Pigment Orange 71, CI Pigment Orange 73, CI Pigment Red 254, CI Pigment Red 255, CI Pigment Red 264, CI Pigment Red 270, and CI Pigment Red 272. Examples of the perylene pigments include CI Pigment Red 123, CI Pigment Red 149, CI Pigment Red 178, CI Pigment Red 179, CI Pigment Red 190, CI Pigment Red 224, CI Pigment Violet 29, CI Pigment Black 31, and CI Pigment Black 32. Examples of the perinone pigments include CI Pigment Orange 43 and CI Pigment Red 194. Examples of the quinacridone pigments include CI Pigment Violet 19, CI Pigment Red 122, CI Pigment Red 202, CI Pigment Red 206, CI Pigment Red 207, CI Pigment Red 209, and CI Pigment Orange 48. Examples of the dioxazine pigment include CI Pigment Violet 23, CI Pigment Violet 37, and CI Pigment Blue 80.

[0063] The average particle size of the fused polycyclic pigment in the pigment dispersion preferably has a lower limit of 100 nm, more preferably 150 nm, and a preferred upper limit of 400 nm, more preferably 300 nm. The average particle size can be determined, for example, by measuring the D50 of the pigment in a pigment dispersion of 3% by weight or less using a particle size distribution measuring device or the like.

[0064] In the pigment dispersion of the present invention, the ratio of the number of aromatic rings contained in one molecule of the fused polycyclic pigment to the number of aromatic rings contained in one molecule of the polyvinyl acetal resin containing a structural unit having an acetal group containing an aryl group (number of aromatic rings in one molecule of the fused polycyclic pigment / number of aromatic rings in one molecule of the polyvinyl acetal resin) is preferably 0.05 to 3.5, and more preferably 0.1 to 2.8. Having the ratio within this range has the advantage of promoting the interaction between the aromatic rings in the fused polycyclic pigment and the aromatic rings in the polyvinyl acetal resin. The number of aromatic rings in one molecule of the polyvinyl acetal resin can be calculated based on the average degree of polymerization and the content of structural units having an aryl group.

[0065] In the pigment dispersion of the present invention, the ratio of the number of aromatic rings in the entire fused polycyclic pigment to the number of aromatic rings in the entire polyvinyl acetal resin (number of aromatic rings in the entire fused polycyclic pigment / number of aromatic rings in the entire polyvinyl acetal resin) is preferably 5.5 to 31.0, and more preferably 6.0 to 12.5. The ratio of the number of aromatic rings in the entire fused polycyclic pigment to the number of aromatic rings in the entire polyvinyl acetal resin can be calculated based on the content of the fused polycyclic pigment in the pigment dispersion of the present invention, the number of aromatic rings in one molecule of the fused polycyclic pigment, the content and molecular weight of the polyvinyl acetal resin, and the number of aromatic rings in one molecule of the polyvinyl acetal resin.

[0066] The pigment dispersion of the present invention contains an organic solvent.

[0067] Examples of the organic solvent include alcohols, polyhydric alcohols, glycol ethers, and esters. Examples of the alcohols include other higher alcohols such as ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, pentanol, hexanol, n-heptanol, 2-heptanol, octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, decanol, and cyclohexanol, as well as benzyl alcohol, terpineol, and dihydroterpineol. Examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, and phenyl glycol. Examples of the glycol ethers include propylene glycol monomethyl ether, propylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, butyl cellosolve, butyl carbitol, butyl triglycol, and methyl diglycol. Examples of the esters include methyl propionate, ethyl propionate, butyl propionate, methyl butanoate, ethyl butanoate, butyl butanoate, methyl pentanoate, ethyl pentanoate, butyl pentanoate, methyl hexanoate, ethyl hexanoate, butyl hexanoate, 2-ethylhexyl acetate, and 2-ethylhexyl butyrate. In addition, butyl cellosolve acetate, butyl carbitol acetate, terpineol acetate, dihydroterpineol acetate, etc. can also be used. Two or more of the above organic solvents may be mixed and used.

[0068] The organic solvent preferably has a boiling point of 75.0 to 250°C.

[0069] The lower limit of the content of the organic solvent in the pigment dispersion of the present invention is preferably 80% by weight, more preferably 83% by weight, and the upper limit is preferably 90% by weight, more preferably 88% by weight.

[0070] The content of water in the pigment dispersion of the present invention is preferably 3% by weight or less.

[0071] The pigment dispersion of the present invention may contain additives such as adhesion promoters, plasticizers, fillers, compatibilizers, surfactants, and thickeners, as long as the effects of the present invention are not impaired.

[0072] Examples of methods for preparing the pigment dispersion of the present invention include a method in which the fused polycyclic pigment, the polyvinyl acetal resin, the organic solvent, and additives added as needed are stirred and mixed.

[0073] The uses of the pigment dispersion of the present invention are not particularly limited, but it can be used for, for example, ink-jet inks, writing implements, stamps, and the like. [Effects of the Invention]

[0074] According to the present invention, it is possible to provide a pigment dispersion that has excellent dispersibility, little increase in viscosity over time, and excellent dispersion stability. DETAILED DESCRIPTION OF THE INVENTION

[0075] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0076] Example 1 (Preparation of Polyvinyl Acetal Resin) 200 g of polyvinyl alcohol was added to 1,800 g of pure water and dissolved by stirring for 2 hours at 90° C. This solution was cooled to 40° C., and 150 g of 35 wt % hydrochloric acid, 10 g of benzaldehyde, and 100 g of butylaldehyde were added thereto. The liquid temperature was maintained at 40° C. to carry out an acetalization reaction, and the reaction product was precipitated. The polyvinyl alcohol used had an average degree of polymerization of 450 and a degree of saponification of 98.0 mol %. Thereafter, the liquid temperature was maintained at 40°C for 3 hours to complete the reaction, and the mixture was neutralized, washed with water and dried in a conventional manner to obtain a powder of polyvinyl acetal resin. The obtained polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 13 Analysis using C-NMR (nuclear magnetic resonance spectroscopy) revealed that the structural unit (R 1 is a single bond, R 2 The content of butyral groups was 60.5 mol %, the content of hydroxyl groups was 34.6 mol %, and the content of acetyl groups was 2.0 mol %.

[0077] (Preparation of pigment dispersion) 2.25 g of the obtained polyvinyl acetal resin, 22.5 g of pigment, and 147.75 g of organic solvent were mixed and stirred with a stirrer for 1 hour to prepare a pigment dispersion. The pigment used was Pigment Blue 15:3 (manufactured by Resinocolor Kogyo Co., Ltd., phthalocyanine copper, molecular weight 576, average particle size 80 μm, maximum wavelength in absorption spectrum 602 nm, maximum wavelength in transmission spectrum 495 nm, number of aromatic rings per molecule 4), and the organic solvent used was benzyl alcohol (melting point -15°C, boiling point 205°C). The maximum wavelength in the transmission spectrum and the maximum wavelength in the absorption spectrum of the pigment were measured using a spectrophotometer (V-730, manufactured by JASCO Corporation).

[0078] Examples 2 to 5 Pigment dispersions were prepared in the same manner as in Example 1, except that the amount of polyvinyl acetal resin added was changed as shown in Table 1.

[0079] (Examples 6 to 13, 15, and 20, Comparative Examples 1 and 2) Pigment dispersions were prepared in the same manner as in Example 1, except that the type and amount of aldehyde added were changed as shown in Table 1.

[0080] Examples 14 and 16 The pigment used was Pigment Green 7 (manufactured by Resinocolor Kogyo Co., Ltd., chlorinated copper phthalocyanine, molecular weight 1127, average particle size 50 μm, maximum wavelength in absorption spectrum 858 nm, maximum wavelength in transmission spectrum 516 nm, number of aromatic rings per molecule 4). The type and amount of aldehyde added were changed as shown in Table 1. A pigment dispersion was prepared in the same manner as in Example 1, except for the above. In addition, the polyvinyl acetal resin obtained in Example 14 was dissolved in DMSO-d6 (dimethyl sulfoxide), 13 Analysis using C-NMR (nuclear magnetic resonance spectroscopy) revealed that the structural unit (R 1 is a single bond, R 2 The content of butyral groups was 60.5 mol %, the content of hydroxyl groups was 34.6 mol %, and the content of acetyl groups was 2.0 mol %.

[0081] Example 17 (Preparation of Polyvinyl Acetal Resin) 200 g of polyvinyl alcohol was added to 1,800 g of pure water and dissolved by stirring for 2 hours at 90° C. This solution was cooled to 40° C., and 150 g of 35 wt % hydrochloric acid, 10 g of benzaldehyde, 100 g of butylaldehyde, and 20 g of chloroacetaldehyde dimethyl acetal were added thereto. The liquid temperature was raised to and maintained at 50° C. to carry out an acetalization reaction, and the reaction product was precipitated. The polyvinyl alcohol used had an average degree of polymerization of 450 and a degree of saponification of 98.0 mol %. Thereafter, the liquid temperature was raised to 40°C and maintained for 3 hours to complete the reaction, and the mixture was neutralized, washed with water and dried in a conventional manner to obtain a powder of polyvinyl acetal resin. The obtained polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 H-NMR (nuclear magnetic resonance spectroscopy) and 13 Analysis using C-NMR (nuclear magnetic resonance spectroscopy) revealed that the structural unit (R 1 is a single bond, R 2 The content of chlorinated modified acetal bond units represented by formula (2) (where R 3 is a single bond, R 4 is a substituent represented by formula (3), in formula (3), R 5 is a chlorine atom, R 6 , R 7 The content of alkyl groups (whose atoms are hydrogen atoms) was 4.9 mol %. Furthermore, the amount of butyral groups was 55.6 mol %, the amount of hydroxyl groups was 34.6 mol %, and the amount of acetyl groups was 2.0 mol %.

[0082] (Preparation of pigment dispersion) A pigment dispersion was prepared in the same manner as in Example 1, except that the obtained polyvinyl acetal resin was used.

[0083] (Examples 18 to 19) The pigment used was Pigment Green 7 (manufactured by Resinocolor Kogyo Co., Ltd., chlorinated copper phthalocyanine, molecular weight 1127, average particle size 50 μm, maximum wavelength in absorption spectrum 858 nm, maximum wavelength in transmission spectrum 516 nm, number of aromatic rings per molecule 4). The type and amount of aldehyde added were changed as shown in Table 1. A pigment dispersion was prepared in the same manner as in Example 1, except for the above.

[0084] <Evaluation> The pigment dispersions obtained in the examples and comparative examples were evaluated as follows, and the results are shown in Table 1.

[0085] (1) Dispersibility The obtained pigment dispersion was diluted 100 times, and the particle diameter (D50) was measured using a particle diameter distribution measuring device (SALD-7100, manufactured by Shimadzu Corporation).

[0086] (2) Surface roughness The obtained pigment dispersion was coated onto a slide glass to a thickness of approximately 50 μm and dried at 80°C for 3 hours. After that, the arithmetic mean roughness Ra and maximum height roughness Rz were measured using a surface roughness measuring device (Tokyo Seimitsu Co., Ltd., Surfcom 1400G).

[0087] (3) Dispersion stability The obtained pigment dispersion was measured at 25°C and a shear rate of 20 s using a cone-plate type viscometer Gemini (manufactured by Bohlin Instruments). -1 The initial viscosity (Pa·s) was measured.

[0088] The viscosity (Pa·s) of the resulting pigment dispersion was measured in the same manner 30 days after the initial viscosity measurement to confirm the rate of change in viscosity (%), and evaluated according to the following criteria. ◎: Viscosity change rate is less than 10% ○: Viscosity change rate is 10% or more but less than 15% △: Viscosity change rate is 15% or more but less than 20% ×: Viscosity change rate is 20% or more, or viscosity decline due to sedimentation

[0089] [Table 1] [Industrial Applicability]

[0090] According to the present invention, it is possible to provide a pigment dispersion that has excellent dispersibility, little increase in viscosity over time, and excellent dispersion stability.

Claims

1. The ink contains a condensed polycyclic pigment having a maximum wavelength in the wavelength range of 450 to 700 nm in its transmission spectrum, a polyvinyl acetal resin containing a structural unit having an acetal group containing an aryl group, and an organic solvent; the condensed polycyclic pigment is a metal phthalocyanine pigment, A pigment dispersion comprising 5 to 20 parts by weight of a polyvinyl acetal resin containing a structural unit having an acetal group containing an aryl group, relative to 100 parts by weight of the condensed polycyclic pigment.

2. The pigment dispersion according to claim 1 , wherein the fused polycyclic pigment has a molecular weight of 400 or more and 1,500 or less.

3. 3. The pigment dispersion according to claim 1, wherein the content of the structural unit having an acetal group containing an aryl group in the polyvinyl acetal resin is 0.5 mol % or more and 10.0 mol % or less.

4. 4. The pigment dispersion according to claim 1, wherein the water content is 3% by weight or less.

5. The pigment dispersion according to any one of claims 1 to 4, wherein the content of the structural unit having an acetoacetal group in the polyvinyl acetal resin is from 0 to 14.0 times the content of the structural unit having an acetal group containing an aryl group, and the content of the structural unit having a butyral group is from 4.0 to 36.0 times the content of the structural unit having an acetal group containing an aryl group.

6. The pigment dispersion according to any one of claims 1 to 5, wherein the ratio of the number of aromatic rings contained in one molecule of the fused polycyclic pigment to the number of aromatic rings contained in one molecule of the polyvinyl acetal resin containing a structural unit having an acetal group containing an aryl group is 0.05 or more and 3.5 or less.

7. 7. The pigment dispersion according to claim 1, wherein the polyvinyl acetal resin has a hydroxyl group content of 18.0 mol % or more and 45.0 mol % or less.

8. 8. The pigment dispersion according to claim 1, wherein the polyvinyl acetal resin has an average degree of polymerization of 150 or more and 1,000 or less.

9. 9. The pigment dispersion according to claim 1, wherein the polyvinyl acetal resin has a total acetal group content of 40.0 mol % or more and 81.5 mol % or less.

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