Pigment dispersion, paint composition, painted article, method for manufacturing a painted article, and pigment dispersant

Abstract

To provide a pigment dispersion that exhibits good compatibility with various resins, and which allows for the preparation of paint compositions with good performance by mixing with resins. [Solution] A pigment dispersion comprising a resin having structural units (a) derived from a (meth)acrylic monomer containing a nitrogen atom and structural units (b) derived from an alkyd resin containing an unsaturated double bond, a pigment, and a dispersion medium. Also, a pigment dispersant comprising a resin having structural units (a) derived from a (meth)acrylic monomer containing a nitrogen atom and structural units (b) derived from an alkyd resin containing an unsaturated double bond.

Description

TECHNICAL FIELD

[0001] The present invention relates to a pigment dispersion, a coating composition, a coated article, a method for producing a coated article, and a pigment dispersant. More specifically, the present invention relates to a pigment dispersion containing a specific resin, a coating composition using the pigment dispersion, an article coated using the coating composition, a method for producing the coated article, and a pigment dispersant containing a specific resin.

BACKGROUND ART

[0002] Pigment dispersion technology is important for coloring materials such as coatings. Various studies on pigment dispersants and the like have been conducted so far. Examples of known documents related to pigment dispersion technology include the following Patent Documents 1 to 6.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0003]

PATENT DOCUMENT 1

PATENT DOCUMENT 2

PATENT DOCUMENT 3

PATENT DOCUMENT 4

PATENT DOCUMENT 5

PATENT DOCUMENT 6

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] One method for preparing paint compositions involves mixing a pigment dispersion, in which pigments are dispersed at a high concentration in a dispersion medium, with a binder resin to create a paint composition. This pigment dispersion, in which pigments are dispersed at a high concentration in a dispersion medium, is sometimes referred to as "seed pen" (meaning "paint seed") in the paint and coating industry.

[0005] When preparing paint compositions in this manner, the "compatibility" between the pigment dispersion and the binder resin can become an issue. If the "compatibility" between the pigment dispersed in the pigment dispersion (the pigment dispersed in the dispersion medium without settling or agglomerating due to the action of the pigment dispersant) and the binder resin is poor, the performance of the prepared paint may be insufficient. From a convenience standpoint, it is preferable for a single pigment dispersion to be compatible with various types of binder resins. However, binder resins have diverse structures and properties. Therefore, conventional pigment dispersions may be compatible with one binder resin but not with another.

[0006] This invention has been made in view of these circumstances. One of the objects of this invention is to provide a pigment dispersion that has good compatibility with various resins and that allows for the preparation of a paint composition with good performance by mixing with resins. [Means for solving the problem]

[0007] The inventors have completed the invention described below and solved the above problems.

[0008] 1. A resin having a structural unit (a) derived from a (meth)acrylic monomer containing a nitrogen atom, and a structural unit (b) derived from an alkyd resin containing an unsaturated double bond, Pigments and Dispersion medium and A pigment dispersion containing [a specific pigment]. 2. The pigment dispersion described in 1. The pigment dispersion, wherein the resin further has a structural unit (c1) derived from a monomer represented by the following general formula (C1). CH2=CR-COO-R a (C1) In general formula (C1), R is a hydrogen atom or a methyl group, R a is an alkyl group, a monocyclic or polycyclic cycloalkyl group, an aryl group or an aralkyl group, and these groups may be substituted with a hydroxy group. 3. The pigment dispersion according to 1. or 2., wherein the resin further has a structural unit (c2) derived from styrene or a styrene derivative, the pigment dispersion. 4. The pigment dispersion according to any one of 1. to 3., wherein the resin further comprises a structural unit (c3) derived from acrylic acid or methacrylic acid, the pigment dispersion. 5. The pigment dispersion according to any one of 1. to 4., wherein the nitrogen atom-containing (meth)acrylic monomer comprises a monomer represented by the following general formula (A1) or (A2), the pigment dispersion. CH2=CR-COO-L-NR 1 R 2 (A1) CH2=CR’-CO-NR 1 ’R 2 ’ (A2) In general formula (A1), R is a hydrogen atom or a methyl group, L is a divalent linking group, R 1 and R 2 are each independently a hydrogen atom or a monovalent organic group, and R 1 and R 2 may be bonded to each other to form a ring structure. In general formula (A2), R' is a hydrogen atom or a methyl group, R 1 ' and R 2' is independently a hydrogen atom or a monovalent organic group, R 1 'and R 2 The ' elements may combine to form a ring structure. 6. A pigment dispersion according to any one of 1. to 5., The alkyd resin containing the aforementioned unsaturated double bond is a pigment dispersion containing a maleic acid structure. 7. A pigment dispersion according to any one of 1. to 6., A pigment dispersion in which the proportion of the structural unit (a) in the resin is 0.05 to 10% by mass. 8. A pigment dispersion according to any one of 1. to 7., A pigment dispersion in which the proportion of the structural unit (b) in the resin is 7 to 30% by mass. 9. A pigment dispersion according to any one of 1. to 8., The dispersion medium is a pigment dispersion containing an organic solvent. 10. A paint composition which is a mixture of a pigment dispersion liquid described in any one of 1. to 9. and a binder resin. 11. A painted article painted with the paint composition described in 10. 12. A method for manufacturing a painted article, comprising a painting step of applying the paint composition described in 10. to the article. 13. A pigment dispersant comprising a resin having a structural unit (a) derived from a (meth)acrylic monomer containing a nitrogen atom and a structural unit (b) derived from an alkyd resin containing an unsaturated double bond. 14. A pigment dispersant as described in 13. The resin further comprises a pigment dispersant having a structural unit (c1) derived from a monomer represented by the following general formula (C1). CH2=CR-COO-R a (C1) In general formula (C1), R is a hydrogen atom or a methyl group. R a The group is an alkyl group, a monocyclic or polycyclic cycloalkyl group, an aryl group, or an aralkyl group, and these groups may be substituted with a hydroxyl group. 15. A pigment dispersant as described in 13. or 14., The resin further comprises a pigment dispersant having a structural unit (c2) derived from styrene or a styrene derivative. 16. A pigment dispersant described in any one of items 13 to 15, The resin further comprises a pigment dispersant containing structural units (c3) derived from acrylic acid or methacrylic acid. 17. A pigment dispersant described in any one of items 13 to 16, The (meth)acrylic monomer containing the nitrogen atom is a pigment dispersant comprising a monomer represented by the following general formula (A1). CH2=CR-COO-L-NR 1 R 2 (A1) CH2=CR-CO-NLNR 1 R 2 (A2) In general formula (A1), R is a hydrogen atom or a methyl group. L is a divalent linking group, R 1 and R 2 Each is independently a hydrogen atom or a monovalent organic group, and R 1 and R 2 They may combine to form a ring structure. In general formula (A2), R' is a hydrogen atom or a methyl group. R 1 'and R 2 ' is independently a hydrogen atom or a monovalent organic group, R 1 'and R 2 The ' elements may combine to form a ring structure. 18. A pigment dispersant described in any one of items 13 to 17, The alkyd resin containing the aforementioned unsaturated double bond is a pigment dispersant containing a maleic acid structure. 19. A pigment dispersant described in any one of items 13 to 18, A pigment dispersant wherein the ratio of the structural unit (a) in the resin is 0.05 to 10% by mass. 20. A pigment dispersant described in any one of items 13 to 18, A pigment dispersant wherein the ratio of the structural unit (b) in the resin is 7 to 30% by mass. [Effects of the Invention]

[0009] The pigment dispersion of the present invention exhibits good compatibility with various resins. By mixing the pigment dispersion of the present invention with a binder resin, a paint composition with good performance can be prepared. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below.

[0011] In this specification, the notation "X~Y" in descriptions of numerical ranges means "X or greater and Y or less" unless otherwise specified. For example, "1~5 mass%" means "1 mass% or greater and 5 mass% or less".

[0012] In this specification, when a group (atomic group) is not specified as substituted or unsubstituted, it includes both unsubstituted and substituted groups. For example, "alkyl group" includes not only unsubstituted alkyl groups but also substituted alkyl groups. In this specification, the term "(meth)acrylic" refers to a concept that encompasses both acrylic and methacrylic. The same applies to similar terms such as "(meth)acrylate." In this specification, the term "(meth)acrylic monomer" includes, unless otherwise specified, (meth)acrylic acid, (meth)acrylic acid esters, and monomers of amide compounds derived from (meth)acrylic acid, such as (meth)acrylamide. In this specification, unless otherwise specified, the term "organic group" refers to an atomic group obtained by removing one or more hydrogen atoms from an organic compound. For example, "monovalent organic group" refers to an atomic group obtained by removing one hydrogen atom from any organic compound.

[0013] <Pigment dispersion> The pigment dispersion of this embodiment is A resin having a structural unit (a) derived from a (meth)acrylic monomer containing a nitrogen atom, and a structural unit (b) derived from an alkyd resin containing an unsaturated double bond, Pigments and Dispersion medium and Includes.

[0014] For a single pigment dispersion to be compatible with various binder resins, it is considered necessary for the resin contained in the pigment dispersion to have a variety of chemical structures (elements, functional groups, etc.). If there is a chemical structure among these various structures that is compatible with the binder resin, the compatibility between the pigment dispersion and the binder resin is expected to improve.

[0015] In this embodiment, the resin in the pigment dispersion has structural units derived from alkyd resin, which is known to have relatively good compatibility with other components in the paint field, as well as structural units derived from (meth)acrylic monomer containing nitrogen atoms. These structural units have different structures and chemical properties from alkyd resin, which is presumed to contribute to good compatibility with various resins. Specifically, it can be interpreted that good compatibility is obtained with one binder resin primarily through the interaction of structural units derived from alkyd resins, and with another binder resin primarily through the interaction of structural units derived from nitrogen-containing (meth)acrylic monomers. Just to be clear, the binder resin may interact with both structural units derived from (meth)acrylic monomers containing nitrogen atoms and structural units derived from alkyd resins containing unsaturated double bonds.

[0016] Furthermore, as a secondary effect of the resin having the two structural components mentioned above, it is thought that the resin is also more likely to disperse various types of pigments well.

[0017] The description of the pigment dispersion of this embodiment will continue.

[0018] (resin) In the pigment dispersion of this embodiment, the resin has structural units (a) derived from a (meth)acrylic monomer containing a nitrogen atom and structural units (b) derived from an alkyd resin containing an unsaturated double bond.

[0019] The nitrogen atom-containing (meth)acrylic monomer that forms the basis of structural unit (a) preferably includes a monomer represented by the following general formula (A1) or (A2). CH2=CR-COO-L-NR 1 R 2 (A1) CH2=CR'-CO-NR 1 'R 2 (A2) In general formula (A1), R is a hydrogen atom or a methyl group. L is a divalent linking group, R 1 and R 2 Each is independently a hydrogen atom or a monovalent organic group, and R 1 and R 2 They may bond to form a ring structure. In general formula (A2), R' is a hydrogen atom or a methyl group. R 1 'and R 2 ' is independently a hydrogen atom or a monovalent organic group, R 1 'and R 2The ' elements may combine to form a ring structure.

[0020] In general formula (A1), the divalent linking group of L is usually a divalent organic group, preferably a linear or branched alkylene group, and more preferably a linear alkylene group. The total number of carbon atoms in L is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 3. In general formula (A1), R 1 and R 2 Examples of monovalent organic groups include alkyl groups, alicyclic groups, aryl groups, and aralkyl groups. A preferred monovalent organic group is an alkyl group. The total number of carbon atoms in the monovalent organic group is, for example, 1 to 10, preferably 1 to 6, and more preferably 1 to 3. R 1 and R 2 When atoms bond to form a ring structure, the ring skeleton may contain heteroatoms other than nitrogen atoms, or it may consist only of nitrogen atoms and carbon atoms. Specifically, the ring skeleton can be a pyrrolidine skeleton, a piperidine skeleton, a piperazine skeleton, a morpholine skeleton, etc. 1 and R 2 The ring that can be formed by the bonding of these atoms is preferably a 5-6 membered ring including the nitrogen atom. 1 and R 2 The rings that can be formed by the bonding of these atoms are usually saturated and do not contain unsaturated double bonds.

[0021] Preferred monomers that fit the general formula (A1) include dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate.

[0022] R in general formula (A2) 1 'and R 2 The specific form of ' is R in general formula (A1) as described above. 1 and R 2 It can be similar to that.

[0023] Specific examples of monomers that fit the general formula (A2) include N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, (meth)acryloylmorpholine, diacetone(meth)acrylamide, N,N-diethyl(meth)acrylamide, and N-[3-(dimethylamino)propyl](meth)acrylamide.

[0024] The resin may contain only one type of structural unit (a), or it may contain two or more types of structural units (a). Considering the balance of various performance characteristics, the ratio of structural unit (a) in the resin is preferably 0.05 to 10% by mass, and more preferably 0.1 to 5% by mass.

[0025] As the alkyd resin containing unsaturated double bonds that form the basis of structural unit (b), an alkyd resin modified with an oil such as a fatty acid is preferred. From the viewpoint of further improving dispersibility and compatibility with the binder resin, it is preferable to use an alkyd resin with an appropriate oil length. The oil length of the alkyd resin containing unsaturated double bonds is preferably 20-50%, more preferably 25-45%, and even more preferably 30-40%. Just to clarify, oil length is an indicator that shows the proportion of "fatty acids or oily components" contained in alkyd resin. Specifically, oil length can be calculated using the following formula. Oil content (%) = {(mass of fatty acids, oils, or fatty acid esters) / total weight of resin} × 100

[0026] Considering copolymerization with nitrogen-containing (meth)acrylic monomers, alkyd resins containing a maleic acid structure are preferred. The cis structure of maleic acid is considered advantageous for copolymerization with nitrogen-containing (meth)acrylic monomers. Examples of alkyd resins containing a maleic acid structure include Arakawa Chemical Industries' "ALUKIDIR" series, Harima Chemical Industries' "HALIFUTAR" series, and DIC's "ALUKIDIR" series. Of course, instead of using commercially available alkyd resins, it is also possible to synthesize and use an appropriate alkyd resin. Just to clarify, not all alkyd resins in the above-mentioned commercially available series have unsaturated double bonds; only some of the alkyd resins in these series do.

[0027] The resin may contain only one type of structural unit (b), or it may contain two or more types of structural units (a). Considering the balance of various performance characteristics, the ratio of structural unit (b) in the resin is preferably 7 to 30% by mass, more preferably 10 to 25% by mass, and even more preferably 10 to 20% by mass. From another perspective, in order to ensure performance, the ratio of structural units (b) in the resin is R AL When R is the ratio of all structural units other than structural unit (b), AL The value of / R is preferably 10 to 60% by mass, and more preferably 15 to 50% by mass.

[0028] The resin further, • The following structural unit (c1) is derived from a monomer represented by the general formula (C1), • Structural units (c2) derived from styrene or styrene derivatives, • Structural unit (c3) derived from acrylic acid or methacrylic acid It is preferable that the resin contains one or more of these structural units. It is believed that by further including one or more of these structural units in the resin, the interaction with the binder resin becomes even more diverse. This is expected to further enhance compatibility with various binder resins.

[0029] CH2=CR-COO-R a (C1) In general formula (C1), R is a hydrogen atom or a methyl group. R a The group is an alkyl group, a monocyclic or polycyclic cycloalkyl group, an aryl group, or an aralkyl group, and these groups may or may not be substituted with a hydroxyl group.

[0030] Specific examples of monomers represented by general formula (C1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-stearyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, and the like. Other specific examples of monomers represented by the general formula (C1) include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0031] When synthesizing resins, R is used as a monomer represented by the general formula (C1). a A combination of pigments with and without hydroxyl group substitutions may be used. This creates both low-polarity and high-polarity regions within the resin. This may lead to further improvements in the dispersibility of the pigment and the compatibility between the pigment dispersion and the binder resin. Furthermore, when synthesizing resins, R is used as a monomer represented by the general formula (C1). a Those in which are linear or branched alkyl groups, and R a It is also possible to use a combination of a monocyclic or polycyclic cycloalkyl group. This may allow for adjustment of the dispersibility of the pigment and the compatibility between the pigment dispersion and the binder resin.

[0032] If the resin contains structural unit (c1), the ratio of all structural units corresponding to structural unit (c1) in the resin is preferably 30 to 85% by mass, more preferably 40 to 80% by mass. If the resin contains a structural unit (c1) having a hydroxyl group, its proportion in the resin is preferably 1 to 20% by mass, more preferably 5 to 15% by mass. If the resin contains structural units (c1) that do not have a hydroxyl group, the proportion of such units in the resin is preferably 25 to 80% by mass, more preferably 30 to 70% by mass. By adjusting the content of each structural unit, a better balance of various performance characteristics can sometimes be achieved.

[0033] Examples of styrene or styrene derivatives that form the structural unit (c2) include styrene itself, α-methylstyrene, o-methylstyrene, m-methylstyrene, and p-methylstyrene.

[0034] If the resin contains structural units (c2), the ratio of structural units (c2) in the resin is preferably 3 to 25% by mass, more preferably 5 to 20% by mass.

[0035] When the resin contains structural units (c3), the ratio of structural units (c3) in the resin is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass.

[0036] The weight-average molecular weight of the resin is not particularly limited. The weight-average molecular weight should be adjusted considering factors such as the dispersibility of the pigment and its ease of dispersion in the dispersion medium.

[0037] Resins can usually be synthesized by radical polymerization. A specific example of polymerization is to gradually add monomers other than the alkyd resin and a radical polymerization initiator dropwise to a solution containing an alkyd resin with unsaturated double bonds. Alkyd resins containing unsaturated double bonds typically have a larger molecular weight and a smaller amount of unsaturated double bonds per unit mass compared to other monomers, which may make them less susceptible to radical polymerization. However, by gradually adding monomers other than the alkyd resin and a radical polymerization initiator dropwise to a solution containing the alkyd resin, the concentration of the alkyd resin in the reaction system can be increased while the concentrations of the other monomers can be decreased. This allows the alkyd resin to polymerize sufficiently, resulting in the desired resin.

[0038] Alternatively, the desired resin can likely be obtained by a dropwise polymerization method, in which all monomers, including the alkyd resin, and the radical polymerization initiator are added dropwise to the polymerization solvent little by little.

[0039] (Pigment) In this embodiment, there are no particular restrictions on the type or form of the pigment. Any pigment can be used as long as it can be dispersed in the dispersion medium by the resin described above.

[0040] Examples of pigments include known inorganic and organic pigments. Specifically, these include white pigments such as titanium dioxide (titanium white), zinc oxide, lead white, basic lead sulfate, lead sulfate, lithopone, zinc sulfide, and antimony white; black pigments such as carbon black, acetylene black, lamp black, graphite, iron black (black iron oxide), and aniline black; yellow pigments such as naphthol yellow S, Hansa yellow, pigment yellow L, benzidine yellow, permanent yellow, and pyrite (yellow iron oxide); and chromium orange, chromium vermilion, permanent orange, and imidazole. Examples include orange pigments such as iron oxide and amber; red pigments such as red iron oxide, red lead, permanent red, quinacridone red pigments, and diketopyrrolopyrrole red pigments; purple pigments such as cobalt purple, fast violet, methyl violet lake, and dioxazine pigments; blue pigments such as ultramarine, Prussian blue, cobalt blue, phthalocyanine blue, and indigo; and green pigments such as chrome green, pigment green B, and phthalocyanine green.

[0041] Furthermore, extender pigments can be cited as examples of pigments. Specifically, these include barita powder, barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, hydrated magnesium silicate, alumina white, gloss white, mica powder, etc. Other pigments not listed here can also be used without any particular restrictions.

[0042] Pigment median diameter D 50 While not particularly limited, the particle size is typically 0.01 to 50 μm, taking into account various properties such as color development and ease of dispersion as a pigment. 50 This can usually be determined based on particle size distribution measurement using laser diffraction / scattering. Also, for some commercially available pigments, the distributor is D 50 It may have a value of D. In that case, that value is D 50 It may be adopted as such.

[0043] The amount of pigment in the pigment dispersion can be adjusted as appropriate depending on the type of pigment and the desired color tone. Considering good dispersion of the pigment in the dispersion medium, the amount of pigment per 100 parts by mass of resin is preferably 5 to 300 parts by mass, more preferably 10 to 250 parts by mass, and even more preferably 20 to 200 parts by mass.

[0044] (dispersion medium) The dispersion medium is not particularly limited as long as the pigment and resin can exist stably in the pigment dispersion. In this embodiment, the dispersion medium usually contains an organic solvent. Specifically, it is preferable that 90% by mass or more of the dispersion medium is an organic solvent, more preferably 95% by mass or more is an organic solvent, and even more preferably 98% by mass or more is an organic solvent. Particularly preferable is that the dispersion medium does not contain water other than water, which is inevitably mixed in.

[0045] Examples of organic solvents that can be used as dispersion media include aromatic hydrocarbon solvents such as toluene and xylene, alcoholic solvents such as methanol, ethanol, isopropyl alcohol, n-butanol, and isobutanol, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, and esteric solvents such as ethyl acetate, propyl acetate, butyl acetate, and isobutyl acetate. As a dispersion medium, only one type of organic solvent may be used, or two or more types of organic solvents may be used.

[0046] The amount of dispersion medium is not particularly limited. However, considering its use as a "seed pen" as described above, the amount of dispersion medium used may be such that the concentration of nonvolatile components in the pigment dispersion is, for example, 40 to 100% by mass, preferably 50 to 90% by mass.

[0047] (Other optional components) The pigment dispersion of this embodiment may or may not contain any other components besides the resin, pigment, and dispersion medium. Optional components include surface modifiers (plasticizers, silicone compounds, waxes, defoamers, leveling agents, anti-smudge agents, etc., known in the paint field), fluidity modifiers, pigment dispersants (different from the resins mentioned above, e.g., wetting dispersants), UV absorbers, light stabilizers, antioxidants, magnetic powders, and charge control agents.

[0048] (Manufacturing of pigment dispersions) The pigment dispersion of this embodiment can be manufactured by mixing the above-mentioned resin, pigment, etc. When mixing, it is preferable to use an appropriate device (such as a shaker) to sufficiently disperse the pigment. Alternatively, beads (for example, steel beads) may be mixed together with the resin and pigment, and then the beads may be removed after the pigment has sufficiently dispersed.

[0049] <Paint composition> A paint composition can be manufactured by mixing the pigment dispersion described above with a binder resin. Any binder resin known in the art of paints and / or available on the market can be used without particular limitation. Furthermore, a paint containing the binder resin may be mixed with the pigment dispersion described above. From a practical standpoint, it is common practice to produce a desired paint composition by mixing a paint, such as a white paint, with the pigment dispersion described above. Specific examples of binder resins include alkyd resins, melamine resins, (meth)acrylic resins, and phthalic acid resins. Furthermore, paints containing binder resins include paints containing at least one of these resins and a colorant such as a pigment.

[0050] The mixing ratio of the pigment dispersion to the binder resin is not particularly limited and can be adjusted as appropriate depending on the appearance of the final coating film to be obtained. As an example, based on non-volatile components, the amount of binder resin per 1 part by mass of pigment dispersion is specifically 1 to 100 parts by mass, more specifically 2 to 50 parts by mass, and even more specifically 3 to 30 parts by mass.

[0051] When mixing the pigment dispersion and the binder resin, it is preferable to use, for example, a stirrer having a rotating blade to ensure that the pigment dispersion and the binder resin are thoroughly and uniformly mixed.

[0052] <Painted articles and methods for manufacturing the same> A painted article can be manufactured by applying the paint composition produced in the manner described above to an article. There are no specific limitations on the painting method. Appropriate painting methods and conditions should be selected according to the properties of the binder resin. Depending on the type of binder resin, additional treatments such as baking may be performed.

[0053] <Pigment dispersant> Up to this point, this embodiment has been described focusing on a "pigment dispersion" containing a specific resin, a pigment, and a dispersion medium. Apart from this perspective, it is also possible to consider the aforementioned agents containing specific resins as "pigment dispersants," that is, agents that have the function of dispersing pigments in a dispersion medium. A pigment dispersion can be prepared by mixing a pigment dispersant with some kind of pigment and dispersing it in a dispersion medium. Since the specific form of the resin has already been sufficiently explained, the specific form of the pigment dispersant will not be explained again.

[0054] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. [Examples]

[0055] Embodiments of the present invention will be described in detail based on examples and comparative examples. It should be noted that the present invention is not limited to these examples.

[0056] <Preparation of monomers and initiators> The following monomers and radical polymerization initiators were prepared.

[0057] ((meth)acrylic monomers) • Styrene (manufactured by Asahi Kasei Corporation, product name: Styrene monomer (SM)) n-butyl acrylate (manufactured by Toagosei Co., Ltd., product name: BA) • Isobornyl acrylate (manufactured by Changxing Materials Co., Ltd., product name: ETERMER70) • Ethyl acrylate (manufactured by Mitsubishi Chemical Corporation, product name: EA) • 2-hydroxyethyl methacrylate (manufactured by Nippon Shokubai Co., Ltd., product name: HEMA) • Methacrylic acid (manufactured by Mitsubishi Chemical Corporation, product name: MAA) • Dimethylaminoethyl methacrylate (manufactured by Mitsubishi Gas Chemical Company, product name: DAM)

[0058] (Alkyd resin and polyester resin (for examples and comparative examples)) Alkyd resin A (for the example) was synthesized using the following procedure. • Stage 1 A flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube was prepared. Into this flask, 20 parts by mass of tall oil fatty acids, 3 parts by mass of ethylene glycol, 10 parts by mass of glycerin, 5 parts by mass of pentaerythritol, 21 parts by mass of phthalic anhydride, 0.1 parts by mass of triphenyl phosphite, and 1 part by mass of butyl acetate were charged. The dehydration reaction was then carried out under a nitrogen atmosphere at 180°C for 2 hours and then at 220°C for 2 hours. • Stage 2 After the first step was completed, the temperature in the flask was lowered to 160°C, 1 part by mass of maleic anhydride was added, and the reaction was carried out at 170°C for 1 hour. • Dilution After the second reaction stage was complete, the temperature was lowered to 80°C, and 39 parts by mass of butyl acetate was added to dilute the solution. In this way, a resin solution containing alkyd resin (60% by mass of non-volatile components) was obtained.

[0059] Furthermore, alkyd resin B, alkyd resin C, and polyester resin (all resin solutions with a solid content of 60% by mass) were obtained in the same manner as described above for alkyd resin A, except that the substances and quantities used in the first stage were changed as shown in the table below, and the second stage was omitted. The table below also lists the oil length of each alkyd resin.

[0060] [Table 1]

[0061] (Radical polymerization initiator) • 2,2'-Azobis(2-methylbutyronitrile) (manufactured by Nippon Finechem Co., Ltd., product name: ABN-E)

[0062] <Synthesis of resins> (Synthesis Example 1) I followed these steps. (1) In a flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, 15 parts by mass of alkyd resin A and 48 parts by mass of butyl acetate were charged and the temperature was raised to 125°C while stirring. (2) A mixed solution (monomer solution) was prepared by adding 12 parts by mass of styrene, 15 parts by mass of n-butyl acrylate, 21 parts by mass of isobornyl acrylate, 24 parts by mass of ethyl acrylate, 8 parts by mass of 2-hydroxyethyl methacrylate, 1 part by mass of methacrylic acid, 0.5 parts by mass of dimethylaminoethyl methacrylate, and 4 parts by mass of 2,2'-azobis(2-methylbutyronitrile) to a separate container. (3) The prepared monomer solution was added dropwise to the flask over 3 hours and reacted at 125°C for 5 hours while stirring. In this way, a resin solution containing (meth)acrylic resin (60% by mass of non-volatile components) was obtained.

[0063] (Synthesis Examples 2-9 and Comparative Synthesis Examples 1-5) A resin solution containing (meth)acrylic resin was obtained in the same manner as in Synthesis Example 1, except that the type and amount of starting materials used were changed as shown in the table below. However, in Synthesis Example 2, not only were the type and amount of starting materials changed, but the specific dropwise addition procedure was also modified: (i) First, a mixture of the total amount of methacrylic acid listed in the table below and half the amount of the other monomers other than dimethylaminoethyl methacrylate was added dropwise into the flask and reacted; and after the addition was complete, (ii) a mixture of dimethylaminoethyl methacrylate listed in the table below and half the amount of the other monomers other than methacrylic acid was added dropwise into the flask and reacted. (This was intended to avoid the neutralization reaction between methacrylic acid and dimethylaminoethyl methacrylate during polymerization. However, given that the evaluation using the resin obtained in Synthesis Example 1, etc., was favorable (see below), it is thought that methacrylic acid and dimethylaminoethyl methacrylate will be incorporated into the polymer without neutralization even without adopting this method.) Furthermore, in Synthesis Example 5, not only were the type and amount of starting materials changed, but the synthesis procedure was also modified to include the dropwise addition of alkyd resin A. Specifically, in (1) of Synthesis Example 1, only 48 parts by mass of butyl acetate was placed in a flask and the temperature was raised to 125°C. In (2), a mixed solution (monomer solution) containing all the monomers (including alkyd resin) and initiators listed in the table was prepared.

[0064] The table below shows the types and amounts of monomers and initiators used, and R AL This section summarizes information regarding the value of / R (definition as described above) and special notes on the synthesis method. The values ​​for each monomer and initiator represent the amount used (parts by mass). However, for alkyd resins, the values ​​represent the amount used in terms of non-volatile components.

[0065] [Table 2]

[0066] <Rating> (Compatibility: Evaluation of cloudiness of the coating film) First, the resin obtained in the synthesis example and the binder resin were uniformly mixed so that they were equal in mass in terms of non-volatile components. The mixing was carried out over 20 minutes using an AS ONE tornado stirrer equipped with an AS ONE SUS disperser stirring blade. In this way, a composition for compatibility evaluation was prepared.

[0067] One of the following binder resins was used: • Alkyd resin: Alkyd resin A (manufactured in-house, 60% by mass of non-volatile components) synthesized using the above synthesis procedure. • Melamine resin: Melane 265 (manufactured by Resonaq, 60% by mass of non-volatile components) • Acrylic resin: Hitaloid (registered trademark) 3624B (manufactured by Resonaq Corporation, 60% by mass of non-volatile components)

[0068] The composition for compatibility evaluation was applied to the surface of a glass plate using a 6 mil applicator. It was then left to stand overnight at room temperature. The appearance of the resulting film was visually evaluated according to the following criteria. Less turbidity and greater transparency indicate that the resin obtained in the synthesis example and the binder resin are uniformly mixed (i.e., compatible) and have not separated. Evaluation criteria: 5. The exterior was transparent. 4. The exterior was almost transparent. 3: A slight cloudiness was observed on the exterior. 2: A cloudy appearance was observed. 1: Significant clouding was observed in the external appearance.

[0069] (Pigment dispersibility: Color separation evaluation) First, a pigment dispersion was manufactured. Specifically, it was manufactured using the following procedure. (1) Using the formulations shown in Table 3-1 below, the resin obtained in either the synthesis example or the comparative synthesis example, the dispersion medium (organic solvent), the pigment, and optionally a commercially available dispersant were mixed with steel beads (particle size: 2.38 mm) over a period of 2 hours. A rocking shaker (manufactured by Seiwa Giken Co., Ltd.) was used for mixing. After mixing was complete, the steel beads were removed. In this way, seven "pre" pigment dispersions were obtained for each resin obtained in either the synthesis example or the comparative synthesis example. (2) The pre-pigment dispersion obtained in (1) above, the resin obtained in the synthesis example or comparative synthesis example (the same as that used in (1) above), and an organic solvent as needed were mixed in the proportions shown in Table 3-2. The apparatus and conditions used for mixing were the same as in (1) above. (Supplement - Meaning of implementing (2): Since the optimal pigment concentration differs depending on the type of pigment, resin is added to adjust the concentration of non-volatile components.) As described above, seven pigment dispersions were prepared for each resin obtained in the synthesis example or comparative synthesis example. In other words, 14 resins × 7 colors = 98 pigment dispersions were prepared.

[0070] [Table 3]

[0071] Details of the pigments and commercially available dispersants in the table above are shown below. Pigments Black: Carbon black (manufactured by Mitsubishi Chemical Corporation, Mitsubishi Carbon Black #2900B, average diameter 15nm) Red: Red iron oxide (manufactured by Morishita Bengara Kogyo Co., Ltd., product name: MR-220A) Yellow: Yellow iron oxide (manufactured by Titanium Industries Co., Ltd., product name: TAROX®, synthetic iron oxide LL-XLO, average diameter 300 nm) Blue: Phthalocyanine pigment (manufactured by Sanyo Shikiso Co., Ltd., product name: CYANINE BLUE J-620) Green: Phthalocyanine pigment (BASF, product name: Heliogen® GREEN L 8730) Purple: Dioxazine pigment (Manufactured by Western Chemical Industries, product name: Carbazole Violet 1107, average diameter 8 μm) Orange: Isoindoline pigment (KIKUFINE ORANGE TC-360, manufactured by KIKUCHI COLASCO) • Commercially available dispersants DISPERBYK-180: Wetting and dispersing agent (manufactured by BYK, 100% active ingredient) DISPERBYK-2001: Wetting dispersant (manufactured by BYK, non-volatile content 46%) EFKA(registered trademark) PX 4320: Dispersant (manufactured by BASF, active ingredient <50%)

[0072] The manufactured pigment dispersion and the paint containing the binder resin were uniformly mixed in the ratios shown in the table below. A paint composition was then manufactured. The mixing was carried out over one hour using an AS ONE tornado stirrer equipped with an AS ONE SUS disperser stirring blade. The following types of paint containing binder resin were used: • Alkyd melamine resin paint (product name: High Merit, white paint manufactured by Natco Corporation) • Acrylic melamine resin paint (Product name: Acrylist (registered trademark) Hi, white paint manufactured by Natco Corporation) • Lacquer paint (Product name: Wide, manufactured by Natco Corporation, nitrocellulose lacquer white paint) • Acrylic lacquer paint (Product name: Eight, white paint manufactured by Natco Co., Ltd.) • Alkyd acrylic resin paint (product name: Speejit®, white paint manufactured by Natco Corporation) • Acrylic urethane resin paint (Product name: Stark (registered trademark) 1, white paint manufactured by Natco Corporation)

[0073] The manufactured paint composition was applied to a tin plate using an applicator. Before the applied paint composition dried, a line of the paint composition was dripped onto it using a glass rod. The mixture was then left to stand at room temperature for a sufficient amount of time. After that, the chromaticity of the dried paint film was measured in the areas where the paint composition had been dripped and where it had not, and the color difference ΔE was determined. A Konica Minolta CR-200 colorimeter was used to measure the chromaticity. The following evaluation criteria were used: A smaller ΔE indicates that the synthesized resin has a higher ability to disperse the pigment, and that the pigment is uniformly dispersed in the paint composition. Evaluation criteria: 5: ΔE was greater than or equal to 0 and less than 0.3. 4: ΔE was between 0.3 and 0.5. 3: ΔE was between 0.5 and 0.7. 2: ΔE was between 0.7 and 2. 1: ΔE was 2 or greater.

[0074] Furthermore, the coating film whose ΔE was evaluated above was subjected to a 3-day period at 40°C, and then its ΔE was evaluated again. The small change in ΔE before and after storage indicates that the pigment is stably dispersed by the resin.

[0075] The evaluation results are summarized in the table below. Just to be clear, let me add some explanation on how to read Tables 5-16. For example, in Table 5, if the number in the column immediately below "Synthesis Example 1" is 5, it means that the pigment dispersibility (color separation) evaluation result for "(i) a black pigment dispersion prepared using the resin of Synthesis Example 1 according to the formulations in Tables 3-1 and 3-2, and (ii) a white paint (alkyd melamine resin paint) mixed in a mass ratio of 2:8" was 5 on a 5-point scale. Note that the "mass ratio" here refers to the mixing ratio of the pigment dispersion, which may contain volatile solvents, and the white paint, which may contain volatile solvents, and not the mixing ratio in terms of non-volatile components. Furthermore, "flat base" in Table 5 and other sections specifically refers to a matte finish paint. Flat base is used by mixing it with glossy paint to achieve a matte effect without compromising color or transparency. Paint manufacturers offer multiple types of flat bases in their lineup, and sometimes specify the part number of the flat base needed to properly matte commercially available glossy paints. In this study, we used the flat base specified by the manufacturer for each white paint.

[0076] [Table 4]

[0077] [Table 5]

[0078] [Table 6]

[0079] [Table 7]

[0080] [Table 8]

[0081] [Table 9]

[0082] [Table 10]

[0083] [Table 11]

[0084] [Table 12]

[0085] [Table 13]

[0086] [Table 14]

[0087] [Table 15]

[0088] [Table 16]

[0089] <Discussion of Results> As shown in Tables 4-16, in the evaluations using the resins of synthesis examples 1-9, the compatibility and color separation evaluation results were all 3 or higher. In other words, the compatibility evaluation results show that the pigment dispersions produced using the resins of Synthesis Examples 1 to 9 exhibit good compatibility with various binder resins, including alkyd resins, melamine resins, and acrylic resins. Furthermore, the color separation evaluation results obtained using paint compositions produced with pigment dispersions manufactured using the resins of Synthesis Examples 1 to 9 were favorable, indicating that the resins of Synthesis Examples 1 to 9 possess good pigment dispersion capabilities.

[0090] In contrast, when resins synthesized without using alkyd resins containing unsaturated double bonds (comparative synthesis examples 1-4) were used, poor compatibility with some binder resins was obtained. Furthermore, when the resin did not have structural units (a) derived from (meth)acrylic monomers containing nitrogen atoms (comparative synthesis example 5), the dispersibility of the black pigment was unsatisfactory.

Claims

1. A resin having a structural unit (a) derived from a (meth)acrylic monomer containing a nitrogen atom, and a structural unit (b) derived from an alkyd resin containing an unsaturated double bond, Pigments and Dispersion medium and A pigment dispersion containing [a specific pigment].

2. A pigment dispersion according to claim 1, The resin further comprises a pigment dispersion having a structural unit (c1) derived from a monomer represented by the following general formula (C1). CH ２ =CR-COO-R ａ (C1) In general formula (C1), R is a hydrogen atom or a methyl group. R ａ The group is an alkyl group, a monocyclic or polycyclic cycloalkyl group, an aryl group, or an aralkyl group, and these groups may be substituted with a hydroxyl group.

3. A pigment dispersion according to claim 1 or 2, The resin further comprises a pigment dispersion having structural units (c2) derived from styrene or a styrene derivative.

4. A pigment dispersion according to claim 1 or 2, The resin further comprises a pigment dispersion containing structural units (c3) derived from acrylic acid or methacrylic acid.

5. A pigment dispersion according to claim 1 or 2, The (meth)acrylic monomer containing the nitrogen atom is a pigment dispersion comprising a monomer represented by the following general formula (A1) or (A2). CH ２ =CR-COO-L-NR １ R ２ (A1) CH ２ =CR’-CO-NR １ ’R ２ ’ (A2) In general formula (A1), R is a hydrogen atom or a methyl group. L is a divalent linking group, R １ and R ２ Each is independently a hydrogen atom or a monovalent organic group, R １ and R ２ They may combine to form a ring structure. In general formula (A2), R' is a hydrogen atom or a methyl group. R １ 'and R ２ ' is independently a hydrogen atom or a monovalent organic group, R １ 'and R ２ The ' elements may combine to form a ring structure.

6. A pigment dispersion according to claim 1 or 2, The alkyd resin containing the aforementioned unsaturated double bond is a pigment dispersion containing a maleic acid structure.

7. A pigment dispersion according to claim 1 or 2, A pigment dispersion in which the proportion of the structural unit (a) in the resin is 0.05 to 10% by mass.

8. A pigment dispersion according to claim 1 or 2, A pigment dispersion in which the proportion of the structural unit (b) in the resin is 7 to 30% by mass.

9. A pigment dispersion according to claim 1 or 2, The dispersion medium is a pigment dispersion containing an organic solvent.

10. A paint composition comprising a mixture of the pigment dispersion liquid according to claim 1 or 2 and a binder resin.

11. A painted article painted with the paint composition described in claim 10.

12. A method for manufacturing a painted article, comprising a painting step of applying the paint composition described in claim 10 to the article.

13. A pigment dispersant comprising a resin having a structural unit (a) derived from a (meth)acrylic monomer containing a nitrogen atom, and a structural unit (b) derived from an alkyd resin containing an unsaturated double bond.

14. A pigment dispersant according to claim 13, The resin further comprises a pigment dispersant having a structural unit (c1) derived from a monomer represented by the following general formula (C1). CH ２ =CR-COO-R ａ (C1) In general formula (C1), R is a hydrogen atom or a methyl group. R ａ The group is an alkyl group, a monocyclic or polycyclic cycloalkyl group, an aryl group, or an aralkyl group, and these groups may be substituted with a hydroxyl group.

15. A pigment dispersant according to claim 13 or 14, The resin further comprises a pigment dispersant having structural units (c2) derived from styrene or a styrene derivative.

16. A pigment dispersant according to claim 13 or 14, The resin further comprises a pigment dispersant containing structural units (c3) derived from acrylic acid or methacrylic acid.

17. A pigment dispersant according to claim 13 or 14, The (meth)acrylic monomer containing the nitrogen atom is a pigment dispersant comprising a monomer represented by the following general formula (A1). CH ２ =CR-COO-L-NR １ R ２ (A1) CH ２ =CR-CO-NLNR １ R ２ (A2) In general formula (A1), R is a hydrogen atom or a methyl group. L is a divalent linking group, R １ and R ２ Each is independently a hydrogen atom or a monovalent organic group, R １ and R ２ They may combine to form a ring structure. In general formula (A2), R' is a hydrogen atom or a methyl group. R １ 'and R ２ ' is independently a hydrogen atom or a monovalent organic group, R １ 'and R ２ The ' elements may combine to form a ring structure.

18. A pigment dispersant according to claim 13 or 14, The alkyd resin containing the aforementioned unsaturated double bond is a pigment dispersant containing a maleic acid structure.

19. A pigment dispersant according to claim 13 or 14, A pigment dispersant wherein the ratio of the structural unit (a) in the resin is 0.05 to 10% by mass.

20. A pigment dispersant according to claim 13 or 14, A pigment dispersant wherein the ratio of the structural unit (b) in the resin is 7 to 30% by mass.

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