Method for producing oligomer dispersion of cellulose fiber, coating composition containing oligomer dispersion of cellulose fiber, and method for forming multi-layer coating film

Abstract

To provide a method for manufacturing a cellulose fiber oligomer dispersion having cellulose fibers with a lot of hydroxyl groups left uniformly and stably dispersed.SOLUTION: A method for manufacturing a cellulose fiber oligomer dispersion comprises steps of: mixing the aqueous dispersion of cellulose fibers (A) with a compound (B) having two or more reactive groups and having a solubility and boiling point in a specific range to obtain a mixture (i); removing water in the resultant mixture (i) to obtain a mixture (ii) including the cellulose fibers (A) and the compound (B); and mixing the resultant mixture (ii) with a compound (C) having one or more reactive groups having reactivity with the reactive groups in the compound (B) to form an oligomer by reacting the reactive groups in the compound (B) with the reactive groups in the compound (C).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing an oligomer dispersion of cellulose fibers, a coating composition containing the oligomer dispersion of cellulose fibers, and a method for forming a multilayer coating film.

Background Art

[0002] In recent years, in coating films, resin molded products, etc., in order to reduce the coefficient of thermal expansion and increase mechanical strength such as bending strength, blending of cellulose fibers has been widely carried out. Further, for the purpose of further improving the mechanical strength of cellulose fibers, cellulose nanofibers (CNF) obtained by defibrating cellulose fibers have been developed. As something obtained by defibrating cellulose fibers in the same manner as the above CNF, cellulose nanocrystals (CNC) are known. The above CNF and CNC are collectively referred to as nanocellulose.

[0003] However, since cellulose fibers have a large number of hydroxyl groups on the surface, the hydrogen bonding force is high, and even when blended in a normal resin composition or solvent, they do not disperse uniformly and aggregate. Therefore, the dispersibility, storage stability, coating film physical properties, transparency, and finish are insufficient, and it has been difficult to fully exhibit the performance of cellulose fibers.

[0004] Therefore, techniques for stabilizing cellulose fibers in a solution have been proposed. For example, in Patent Document 1, it has been proposed to make cellulose fibers less polar using a modification reaction such as an acylation reaction.

[0005] However, when such a modification reaction is used, processes such as washing are required, so the manufacturing process tends to be complicated, and there are also problems in terms of manufacturing cost. Furthermore, when the cellulose fibers are depolarized by such a modification reaction, the hydroxyl groups of the cellulose fibers are modified. On the other hand, various properties of the cellulose fibers, such as the function as a thickening property and the expression of high strength, are often derived from the hydroxyl groups of the cellulose fibers. Therefore, there is a problem that the depolarization of the cellulose fibers and the maintenance of the functions of the cellulose fibers are contradictory matters.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention aims to provide a method for producing an oligomer dispersion of cellulose fibers in which cellulose with many hydroxyl groups remaining in the cellulose fibers is uniformly and stably dispersed in the oligomer without using a modification reaction involving a complicated washing process or the like.

Means for Solving the Problems

[0008] Under such circumstances, as a result of intensive research by the present inventors, it has been found that by mixing two or more specific compounds capable of forming oligomers into an aqueous dispersion of cellulose fibers (A) through a dehydration process and then forming oligomers, the above object can be achieved, and the present invention has been completed.

[0009] According to the present invention, there are provided a method for producing an oligomer dispersion of cellulose fibers, a coating composition containing the oligomer dispersion of cellulose fibers, and a method for forming a multilayer coating film, including the following aspects.

[0010] [Aspect 1] The following steps (1) to (3): Step (1): A step of mixing an aqueous dispersion of cellulose fiber (A) with a compound (B) having two or more reactive groups, having a solubility in 100 g of water at 20 ° C of 100 g or more, and having a boiling point of 115 ° C or more to obtain a mixed liquid (i). Step (2): A step of removing water in the mixed liquid (i) obtained in the step (1) to obtain a mixed liquid (ii) containing the cellulose fiber (A) and the compound (B), and Step (3): A step of mixing the mixed liquid (ii) obtained in the step (2) with a compound (C) having one or more reactive groups having reactivity with the reactive groups in the compound (B), and reacting the reactive groups in the compound (B) with the reactive groups in the compound (C) to form an oligomer. A method for producing an oligomer dispersion of cellulose fiber, comprising: [Aspect 2] The method for producing an oligomer dispersion of cellulose fiber according to Aspect 1, wherein the solubility parameter value (SP value) of the compound (B) is in the range of 12 to 23 (cal / cm 3 ) 1 / 2 . [Aspect 3] The method for producing an oligomer dispersion of cellulose fiber according to Aspect 1 or 2, wherein the molecular weight of the compound (B) is in the range of 60 to 2000. [Aspect 4] The method for producing an oligomer dispersion of cellulose fiber according to any one of Aspects 1 to 3, wherein the compound (B) is a compound (B') having two or more active hydrogen groups, having a solubility in 100 g of water of 100 g or more, and having a boiling point of 115 ° C or more. [Aspect 5] The method for producing an oligomer dispersion of cellulose fiber according to Aspect 4, wherein the compound (B') is a compound (B'') having two or more hydroxyl groups, having a solubility in 100 g of water of 100 g or more, and having a boiling point of 115 ° C or more. [Aspect 6] The method for producing an oligomer dispersion of cellulose fibers according to embodiment 5, which includes reacting the hydroxyl group in the cellulose fiber (A), the hydroxyl group in the compound (B''), and the reactive group in the compound (C) in the step (3). [Embodiment 7] The method for producing an oligomer dispersion of cellulose fibers according to embodiment 5 or 6, wherein the compound (B'') is trimethylolpropane and / or glycerin. [Embodiment 8] The method for producing an oligomer dispersion of cellulose fibers according to any one of embodiments 1 to 7, wherein the compound (C) is a compound (C') having two or more carboxy groups or one or more carboxylic anhydride groups. [Embodiment 9] After the step (3), further, the following step (4), Step (4): A step of further mixing a compound (D) having one or more reactive groups reactive with the oligomers in the oligomer dispersion of cellulose fibers obtained in step (3) and reacting the oligomers with the compound (D). The method for producing an oligomer dispersion of cellulose fibers according to any one of embodiments 1 to 8, which includes this. [Embodiment 10] The method for producing an oligomer dispersion of cellulose fibers according to embodiment 9, wherein the compound (D) is a compound (D') having an epoxy group. [Embodiment 11] A paint composition containing an oligomer dispersion of cellulose fibers obtained by the production method according to any one of embodiments 1 to 10. [Embodiment 12] The paint composition according to embodiment 11, further containing a binder component (E). [Embodiment 13] The paint composition according to embodiment 12, wherein the binder component (E) contains a hydroxyl group-containing resin (E1) and a crosslinking agent (E2). [Embodiment 14] A method for forming a multilayer coating film by sequentially applying at least one layer of a colored base coat paint and at least one layer of a clear coat paint to an object to be coated, the method for forming a multilayer coating film including applying the coating composition according to any one of Aspects 11 to 13 as the clear coat paint.

Advantages of the Invention

[0011] According to the present invention, there is provided a method for producing an oligomer dispersion of cellulose fibers in which cellulose in which many hydroxyl groups of the cellulose fibers are left without using a modification reaction involving a complicated washing process or the like and which is uniformly and stably dispersed. The oligomer dispersion of cellulose fibers obtained according to the present invention exhibits good dispersibility without causing aggregation of the cellulose fibers and can be maintained without impairing various properties derived from the hydroxyl groups of the cellulose fibers. Therefore, the oligomer dispersion of cellulose fibers obtained according to the present invention can be suitably used, for example, as a reinforcing material or an additive for various resins and paints. In particular, when the oligomer dispersion of cellulose fibers obtained according to the present invention is used as a compounding component of a paint, the paint exhibits pseudoplasticity and can form a coating film excellent in finish and film physical properties.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present invention will be described in detail. It should be understood that the present invention is not limited to the following embodiments and includes various modified examples implemented without changing the gist of the present invention.

[0013] <Step (1)> In Step (1) of the present invention, an aqueous dispersion of cellulose fibers (A) and a compound (B) having two or more reactive groups, a solubility in 100 g of water at 20°C of 100 g or more, and a boiling point of 115°C or more are mixed to obtain a mixed liquid (i).

[0014] Aqueous dispersion of cellulose fiber (A) The aqueous dispersion of cellulose fiber (A) is one in which cellulose fibers are in a dispersed state in water. In the present invention, the cellulose fiber may be natural cellulose or regenerated cellulose. Further, as long as it has a hydroxyl group, it may be a semi-synthetic cellulose fiber or a modified cellulose fiber.

[0015] Natural cellulose fibers are those obtained by removing impurities through a purification process from naturally occurring cellulose fiber-containing substances. Examples of natural cellulose fiber-containing substances include wood such as softwood and hardwood, cotton such as cotton linter and cotton lint, squeezed pulp such as sugarcane and sugar beet, bast fibers such as flax, ramie, jute, and kenaf, leaf vein fibers such as sisal and pineapple, leaf stalk fibers such as abaca and banana, fruit fibers such as coconut husk, stem fibers such as bamboo, bacterial cellulose produced by bacteria, seaweeds such as valonia and scytosiphon, or tunicates of ascidians, etc.

[0016] Examples of regenerated cellulose fibers include rayon, cupra, etc. Examples of semi-synthetic cellulose fibers include acetate, etc.

[0017] As the modified cellulose fiber, those obtained by performing various chemical modifications on cellulose can be used. Examples of the types of chemical modifications include esterifications such as carboxymethylation, acylation, phosphorylation, oxidations such as carboxylation, sulfonation, fluorination, cationization, treatment with a silane coupling agent, etc.

[0018] In the present invention, the cellulose fiber can contain at least one nanocellulose material selected from cellulose nanofibers and cellulose nanocrystals.

[0019] Cellulose nanofibers can be obtained by known methods. For example, cellulose raw materials can be defibrated and refined until the fiber diameter becomes nanosized to obtain nanocellulose fibers. Examples of defibrating methods for cellulose raw materials include mechanical defibrating and chemical treatments such as treatment with an oxidation catalyst solution containing an N-oxyl compound.

[0020] The cellulose raw material is not particularly limited as long as it contains cellulose. Examples include various wood pulps, non-wood pulps, bacterial cellulose, regenerated cellulose, waste paper pulp, cotton, Valonia cellulose, and sea squirt cellulose. Also, various commercially available cellulose powders and microcrystalline cellulose powders may be used.

[0021] The average fiber diameter of the cellulose nanofibers is preferably 1 nm to 200 nm, more preferably 1 nm to 100 nm, and even more preferably 1 nm to 50 nm. The average fiber length of the cellulose nanofibers is preferably 10 to 10,000 nm, more preferably 20 to 2,000 nm, and particularly preferably 30 to 600 nm. The average aspect ratio of the cellulose nanofibers is preferably 3 to 10,000, and more preferably 5 to 1,000. Here, the average aspect ratio is the average fiber length / average fiber diameter. The average fiber diameter and average fiber length of the nanocellulose material can be measured, for example, by photographing the nanocellulose material with a microscope such as an atomic force microscope and measuring from the image. Also, the average fiber diameter and average fiber length of the nanocellulose material can be measured, for example, by measuring the fiber diameters and fiber lengths of 10 cellulose fibers and adopting the average value.

[0022] Cellulose nanocrystals can be obtained by known methods. For example, the amorphous part can be hydrolyzed and removed by treating the cellulose raw material with an acid such as sulfuric acid, and then cellulose nanocrystals can be obtained by mechanical defibrating.

[0023] The cellulose raw material is not particularly limited as long as it contains cellulose, and the same cellulose raw materials as those for the raw materials of cellulose nanofibers can be used. Also, the mechanical fibrillation treatment is not particularly limited, and conventionally known methods can be used, for example, methods using apparatuses such as high-pressure homogenizers, ultra-high-pressure homogenizers, ball mills, roll mills, cutter mills, planetary mills, jet mills, attritors, grinders, juice mixers, homomixers, ultrasonic homogenizers, nanojizers, underwater counter-collision, single-screw or twin-screw extruders, etc.

[0024] The average aspect ratio of the cellulose nanocrystals is preferably less than 50. The average fiber diameter of the cellulose nanocrystals is preferably 1 nm to 100 nm, more preferably 1 nm to 85 nm, and even more preferably 1 nm to 70 nm. Also, the average fiber length is preferably 30 to 500 nm, more preferably 40 to 300 nm. The average aspect ratio of the cellulose nanocrystals is preferably 15 to 50, more preferably 20 to 45.

[0025] Compound (B ) In the present invention, a cellulose fiber aqueous dispersion is mixed with a compound (B) having two or more reactive groups, having a solubility in 100 g of water at 20 °C of 100 g or more, and having a boiling point of 115 °C or more to obtain a mixed liquid (i).

[0026] The reactive group of compound (B) is not particularly limited as long as it can react with the reactive group of compound (C) described later to form an oligomer. Examples of such reactive groups include a hydroxyl group, an amino group, a polymerizable unsaturated group, an epoxy group which may be alicyclic, a (meth)acryloyl group, a mercapto group, a carboxy group, an alkoxy group, an isocyanate group, a silanol group, etc. Among them, from the viewpoint of the dispersibility of the cellulose fiber (A), an active hydrogen group such as a hydroxyl group or an amino group and a polymerizable unsaturated group are preferable, an active hydrogen group is more preferable, and a hydroxyl group is particularly preferable. In this specification, the polymerizable unsaturated group means an unsaturated group capable of radical polymerization, and examples thereof include a vinyl group, a (meth)acryloyl group, a (meth)acrylamide group, a vinyl ether group, an allyl group, a propenyl group, an isopropenyl group, a maleimide group, etc. Further, two or more reactive groups of compound (B) may be the same or different. In this specification, (meth)acryloyl means acryloyl or methacryloyl, (meth)acrylamide means acrylamide or methacrylamide, (meth)acrylate means acrylate or methacrylate, and (meth)acrylic acid means acrylic acid or methacrylic acid, respectively.

[0027] Compound (B) has a solubility of 100 g or more in 100 g of water at 20°C and a boiling point of 115°C or more. By using compound (B) having such solubility and boiling point, a dispersion in which cellulose fibers are uniformly dispersed in the oligomer can be obtained through the dehydration step in step (2) and the oligomer formation step in step (3) described later. The solubility of compound (B) in 100 g of water at 20°C is preferably 200 g or more, more preferably 300 g or more (including the case of miscibility). The boiling point is preferably 115 to 350°C, more preferably 130 to 300°C, and still more preferably 150 to 250°C.

[0028] As the compound (B) used herein, various organic compounds having two or more reactive groups can be used. For example, compounds having an amino group such as 1,2-ethanediamine and 1,6-hexanediamine; diols such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol, triols such as trimethylolpropane and glycerin and their polyoxyalkylene adducts, polyhydric alcohols having four or more hydroxyl groups such as pentaerythritol and their polyoxyalkylene adducts, etc., compounds having a hydroxyl group; compounds having an amino group and a hydroxyl group such as diethanolamine; compounds having a hydroxyl group and an acryloyl group such as 2-hydroxyethyl acrylate, etc. These compounds can be used alone or in combination of two or more.

[0029] Also, from the viewpoint of the dispersibility of the cellulose fiber (A), the solubility parameter value (SP value) of the compound (B) is preferably in the range of 12 to 23 (cal / cm 3 ) 1 / 2 , more preferably in the range of 12 to 22 (cal / cm 3 ) 1 / 2 , and particularly preferably in the range of 13 to 22 (cal / cm 3 ) 1 / 2 .

[0030] Here, the solubility parameter value is generally also called the SP value (solubility parameter value), and is a measure indicating the degree of hydrophilicity or hydrophobicity (polarity) of a solvent or a resin. Also, it is an important measure for judging the solubility and compatibility between a solvent and a resin, and between resins. Generally, when the solubility parameter values are close (the absolute value of the difference in solubility parameter values is small), the solubility and compatibility are good.

[0031] The solubility parameter (SP value) in the present invention is a value calculated by the following Fedors formula described in Polymer Engineering and Science, 14, No. 2, p. 147 (1974). SP = √{Σ(ΔE1) / Σ(ΔV1)} (In the formula, ΔE1 represents the cohesive energy per unit functional group (cal / mol), and ΔV1 represents the molar volume per unit functional group (cm 3 / mol).)

[0032] Also, the molecular weight of compound (B) is preferably in the range of 60 to 2000, and particularly preferably in the range of 90 to 1800, from the viewpoints of the dispersibility of cellulose fiber (A) and the handling of the oligomer dispersion. Among them, from the viewpoint of the water resistance of the coating film formed by the coating composition containing the oligomer dispersion of the cellulose fiber, the molecular weight of compound (B) is preferably in the range of 90 to 1000, and particularly preferably in the range of 90 to 200.

[0033] The compound preferably used as compound (B) is a compound (B') having two or more active hydrogen groups, a solubility in 100 g of water of 100 g or more, and a boiling point of 115°C or higher. Among them, the particularly preferably used compound is a compound (B'') having two or more hydroxyl groups, a solubility in 100 g of water of 100 g or more, and a boiling point of 115°C or higher. In the present specification, the solubility in 100 g of water is a value measured at a temperature of 20°C.

[0034] Examples of such compound (B'') include trimethylolpropane, glycerin, pentaerythritol, polyoxyalkylene adducts of trimethylolpropane, polyoxyalkylene adducts of glycerin, and polyoxyalkylene adducts of pentaerythritol. These can be used alone or in combination of two or more. Among them, from the viewpoint of the water resistance of the coating film formed by the coating composition containing the oligomer dispersion of the cellulose fiber, it is preferable to use trimethylolpropane and / or glycerin.

[0035] Mixture (i) Such a compound (B) is mixed with an aqueous dispersion of cellulose fibers (A) to obtain a mixed liquid (i). As means for mixing the aqueous dispersion of cellulose fibers (A) and the compound (B), there are no particular limitations, and for example, conventionally known mixing means such as stirring and ultrasonic treatment can be used. Also, the temperature during mixing is generally preferably in the range of 5 to 95°C.

[0036] <Step (2)> In step (2) of the present invention, water in the mixed liquid (i) obtained in step (1) is removed to obtain a mixed liquid (ii) containing cellulose fibers (A) and the compound (B).

[0037] As means for removing water in the mixed liquid (i), it can be appropriately selected and used from conventionally known dehydration means. Examples of such dehydration means include dehydration by heating and reduced pressure.

[0038] <Step (3)> In step (3) of the present invention, the mixed liquid (ii) obtained in step (2) is mixed with a compound (C) having one or more reactive groups having reactivity with the reactive groups in the compound (B), and the reactive groups in the compound (B) are reacted with the reactive groups in the compound (C) to form an oligomer.

[0039] Compound (C) The compound (C) to be mixed with the mixture (ii) has at least one reactive group having reactivity with the reactive group in the compound (B). The reactive group possessed by the compound (C) can be used without particular limitation as long as it can react with the reactive group in the compound (B) to form an oligomer. Examples of such reactive groups include a carboxy group, a carboxylic anhydride group, a polymerizable unsaturated group, an epoxy group, and an isocyanate group. Among them, reactive groups having reactivity with active hydrogen groups such as a hydroxy group and an amino group, for example, a carboxy group and a carboxylic anhydride group, are preferable, and a carboxylic anhydride group is particularly preferable. Further, the compound (C) is preferably a compound having two or more reactive groups having reactivity with the reactive group in the compound (B), or a compound having a reactive group having reactivity with the reactive group in the compound (B) and generating a reactive group having reactivity with the reactive group in the compound (B) by the reaction with the reactive group in the compound (B). When the compound (C) has two or more reactive groups, these reactive groups may be the same or different.

[0040] As such a compound (C), any organic compound having at least one reactive group having reactivity with the reactive group in the compound (B) can be used without particular limitation. Examples thereof include compounds having a carboxy group such as succinic acid, isophthalic acid, terephthalic acid, adipic acid, and dodecanedioic acid; and compounds having a carboxylic anhydride group such as phthalic anhydride, hexahydrophthalic anhydride, succinic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, and pyromellitic anhydride.

[0041] Among these, compounds having two or more carboxy groups or compounds having one or more carboxylic anhydride groups are preferably used, and compounds having one or more carboxylic anhydride groups are particularly preferably used.

[0042] From the viewpoint of handling the reaction product, the molecular weight of the compound (C) is preferably in the range of 50 to 500, and particularly preferably in the range of 60 to 300.

[0043] Formation of oligomer The mixture (ii) and the compound (C) are mixed, and the reactive groups in the compound (B) and the reactive groups in the compound (C) are reacted with each other, whereby an oligomer containing the compound (B) and the compound (C) as monomer units is formed. When the reactive group of the compound (C) has reactivity with the hydroxyl group in cellulose, in the formation of the oligomer, the reactive group in the compound (B) and the reactive group in the compound (C) may be reacted with each other, and the hydroxyl group in the cellulose fiber (A) and the reactive group in the compound (C) may also be reacted with each other. As the oligomer to be formed, from the viewpoint of the dispersibility of the cellulose fiber (A), preferably, an oligomer having an ester bond formed by the reaction of the hydroxyl group in the compound (B) and the carboxylic anhydride group in the compound (C) can be mentioned.

[0044] <Step (4)> In the production method of the present invention, after step (3), a compound (D) having a reactive group having reactivity with the oligomer in the oligomer dispersion of the cellulose fiber obtained in step (3) may be further mixed, and a step (step (4)) of reacting the oligomer with the compound (D) may be further provided. Thereby, an oligomer containing the compound (B), the compound (C) and the compound (D) as monomer units can be formed.

[0045] Compound D The compound (D) that can be used in step (4) has a reactive group having reactivity with the oligomer in the oligomer dispersion of the cellulose fiber obtained in step (3). As such a compound (D), various organic compounds that can react with the oligomer in the oligomer dispersion of the cellulose fiber obtained in step (3) to form an oligomer can be used. For example, a compound (D') having an epoxy group, a compound having a hydroxyl group, a compound having a primary amino group, a compound having a secondary amino group, etc. can be mentioned. Among these, from the viewpoint of the dispersibility of the cellulose fiber (A), it is preferable that the compound is a compound (D') having an epoxy group.

[0046] Examples of the compound (D’) having an epoxy group include aliphatic epoxy compounds such as butyl glycidyl ether, octyl glycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol butyl glycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, hexanediol diglycidyl ether, glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, diglycerin tetraglycidyl ether, glycidyl laurate, glycidyl neodecanoate; alicyclic epoxy compounds such as dicyclopentadiene dioxide, ethylene glycol diester of epoxycyclohexenecarboxylic acid, 3,4-epoxycyclohexylmethyl carboxylate, 3,4-epoxycyclohexenylmethyl-3’,4’-epoxycyclohexenecarboxylate, glycidyl ester of hexahydrophthalic acid; epoxy compounds obtained by the reaction of a polyphenol compound and epichlorohydrin and hydrogenated products thereof, aromatic or heterocyclic epoxy compounds such as diglycidyl phthalate, triglycidyl isocyanurate, tetraglycidyl diaminodiphenylmethane, etc. Among these, aliphatic epoxy compounds are preferred, and glycidyl neodecanoate is particularly preferred from the viewpoints of reducing the viscosity of the resulting oligomer dispersion and improving the compatibility with other paint components when blended into the paint composition.

[0047] From the viewpoint of handling the reaction product, the molecular weight of the compound (D) is preferably in the range of 100 to 500, and particularly preferably in the range of 200 to 400.

[0048] <Oligomer dispersion of cellulose fiber> By the production method including the above steps (1) to (3) or steps (1) to (4), an oligomer dispersion of cellulose fibers is obtained. In the obtained oligomer dispersion of cellulose fibers, the cellulose fibers exhibit good dispersibility without causing aggregation, and can be maintained without impairing various properties derived from the hydroxyl groups of the cellulose fibers. Therefore, the oligomer dispersion of cellulose fibers obtained by the present invention can be suitably used as a reinforcing material or an additive for various resins and paints. In particular, when the oligomer dispersion of cellulose fibers obtained by the present invention is used as a rheology control agent for a paint, the paint exhibits pseudoplasticity and can form a coating film excellent in finishability and film physical properties. Further, since the oligomer dispersion of cellulose fibers obtained by the present invention can be obtained as a dispersion containing no organic solvent, it has the advantage of being suitably used as a raw material for a solvent-free paint.

[0049] <Paint composition> As a blending component of the paint composition, the oligomer dispersion of cellulose fibers obtained by the production method of the present invention can be used. In this case, in the oligomer dispersion of cellulose fibers obtained by the production method of the present invention, since the cellulose with many hydroxyl groups of the cellulose fibers is uniformly and stably dispersed, the paint can exhibit pseudoplasticity and can form a coating film excellent in finishability and film physical properties.

[0050] As the binder component (E) of the coating composition, a resin composition containing a film-forming resin usually used in coatings can be used. As such a resin composition, a thermosetting resin composition can be preferably used. Specifically, for example, a combination of a base resin such as an acrylic resin, a polyester resin, an alkyd resin, or a urethane resin having a crosslinkable functional group such as a hydroxyl group, and a crosslinking agent such as a melamine resin, a urea resin, or a polyisocyanate compound (including a blocked form) can be used. These resin compositions can be used by dissolving or dispersing them in a solvent such as an organic solvent and / or water. There is no particular limitation on the ratio of the base resin to the crosslinking agent in the resin composition. Generally, the crosslinking agent can be used in the range of 10 to 100% by mass, preferably 20 to 80% by mass, more preferably 30 to 60% by mass, based on the total amount of the base resin solid content.

[0051] Particularly preferred binder components (E) include those containing a hydroxyl group-containing resin (E1) and a crosslinking agent (E2).

[0052] Examples of the hydroxyl group-containing resin (E1) include acrylic resins, polyester resins, urethane resins, epoxy resins, acrylic epoxy resins, silicone-modified polyester resins, silicone-modified acrylic resins, acrylic urethane resins, polyvinyl alcohol resins, and polyglycerin resins. Among these resins, a hydroxyl group-containing acrylic resin is particularly preferred in terms of weather resistance and water resistance. Also, a hydroxyl group-containing polyester resin can be preferably used in terms of smoothness and the like.

[0053] The hydroxyl group-containing acrylic resin is an acrylic resin having a hydroxyl group and can be synthesized by copolymerizing a polymerizable unsaturated monomer having a hydroxyl group and other polymerizable unsaturated monomers as constituent monomer components.

[0054] Examples of the polymerizable unsaturated monomer having a hydroxyl group include monoesterified products of (meth)acrylic acid and a divalent alcohol having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified products of the monoesterified products of (meth)acrylic acid and a divalent alcohol having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; (meth)acrylates having a polyoxyalkylene chain with a hydroxyl group at the molecular terminal. These can be used alone or in combination of two or more.

[0055] Examples of the other polymerizable unsaturated monomers include aromatic vinyl monomers such as styrene, vinyltoluene, and α-methylstyrene; methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, polyalkylene glycol (meth)acrylate, isobornyl (meth)acrylate, and (meth)acrylic acid. These can be used alone or in combination of two or more.

[0056] The hydroxyl value of the hydroxyl group-containing acrylic resin is usually in the range of 0.1 to 300 mgKOH / g, preferably in the range of 10 to 200 mgKOH / g, and the weight average molecular weight is usually in the range of 1,000 to 100,000, preferably in the range of 2,000 to 30,000.

[0057] In this specification, the number average molecular weight and the weight average molecular weight are values obtained by converting the retention time (retention volume) measured using gel permeation chromatography (GPC) into the molecular weight of polystyrene based on the retention time (retention volume) of standard polystyrene with a known molecular weight measured under the same conditions. Specifically, as the gel permeation chromatograph, "HLC8120GPC" (trade name, manufactured by Tosoh Corporation) is used, and as the columns, four columns of "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and "TSKgel G-2000HXL" (trade names, all manufactured by Tosoh Corporation) are used, and the measurement can be carried out under the conditions of a mobile phase of tetrahydrofuran, a measurement temperature of 40 °C, a flow rate of 1 mL / min and a detector RI.

[0058] The hydroxyl group-containing polyester resin can be produced by an esterification reaction and / or a transesterification reaction of an acid component and an alcohol component.

[0059] As the above acid component, in the production of the polyester resin, compounds usually used as the acid component can be used without particular limitation. As the above acid component, for example, alicyclic polybasic acids, aliphatic polybasic acids, aromatic polybasic acids, aromatic monocarboxylic acids, aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, lower alkyl esterified products of these acids, etc. can be used.

[0060] An alicyclic polybasic acid is generally a compound having one or more alicyclic structures (mainly 4- to 6-membered rings) and two or more carboxy groups in one molecule, an acid anhydride of the compound, and an esterified product of the compound.

[0061] An aliphatic polybasic acid is generally an aliphatic compound having two or more carboxy groups in one molecule, an acid anhydride of the compound, and an esterified product of the compound.

[0062] Aromatic polybasic acids generally include aromatic compounds having two or more carboxy groups in one molecule, acid anhydrides of the aromatic compounds, and esterified products of the aromatic compounds. Further, if necessary, aromatic monocarboxylic acids, aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, etc. can also be used.

[0063] As the above alcohol component, in the production of polyester resins, compounds usually used as alcohol components can be used without particular limitation, but those containing divalent alcohols such as alicyclic diols, aliphatic diols, aromatic diols, and polyhydric alcohols having three or more valences are preferred.

[0064] As the method for producing the above hydroxyl group-containing polyester resin, the above acid component and alcohol component can be reacted by a known method for production.

[0065] Further, the above hydroxyl group-containing polyester resin can also be modified with fatty acids, oils and fats, polyisocyanate compounds, epoxy compounds, etc. during the preparation of the resin, or after the esterification reaction and / or after the transesterification reaction.

[0066] From the viewpoint of finishability, the number average molecular weight of the hydroxyl group-containing polyester resin is usually 1,000 to 20,000, preferably in the range of 1,050 to 10,000, and more preferably 1,100 to 5,000. Also, from the viewpoint of the curability of the resulting coating film, the hydroxyl value of the hydroxyl group-containing polyester resin is usually 20 to 300 mgKOH / g, preferably in the range of 30 to 250 mgKOH / g, and more preferably 40 to 180 mgKOH / g.

[0067] Further, the crosslinking agent (E2) can be used without particular limitation as long as it can react with the hydroxyl groups of the hydroxyl group-containing resin (E1) by heating to cause curing. Examples thereof include polyisocyanate compounds, blocked polyisocyanate compounds, amino resins such as melamine resins, benzoguanamine resins, and urea resins.

[0068] As the mixing ratio of the hydroxyl group-containing resin (E1) and the crosslinking agent (E2), based on a total of 100 parts by mass of the solid content of both, in terms of the solid content, the hydroxyl group-containing resin (E1) is in the range of 60 to 95 parts by mass, particularly in the range of 70 to 90 parts by mass, and the crosslinking agent (E2) is in the range of 5 to 40 parts by mass, particularly in the range of 10 to 30 parts by mass, which is preferable from the viewpoints of coating film hardness and processability.

[0069] In addition, the coating composition may contain, if necessary, ordinary paint additives such as coloring pigments, extender pigments, thickeners, curing catalysts, ultraviolet absorbers, light stabilizers, defoamers, plasticizers, organic solvents, surface modifiers, anti-settling agents, etc., either alone or in combination of two or more.

[0070] The coating composition of the present invention can be prepared by mixing the various components described above in a solvent by ordinary coating means. As the above solvent, for example, organic solvents, water, etc. can be used. It is preferable to use an organic solvent as the above solvent.

[0071] Examples of the organic solvent include hydrocarbon solvents such as heptane, toluene, xylene, octane, and mineral spirit; ester solvents such as ethyl acetate, n-butyl acetate, isobutyl acetate, ethylene glycol monomethyl ether acetate, and diethylene glycol monobutyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, and isobutanol; ether solvents such as n-butyl ether, dioxane, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether; and aromatic petroleum solvents such as Swazol 310, Swazol 1000, and Swazol 1500 manufactured by Cosmo Oil Co., Ltd.

[0072] In addition, the paint composition of the present invention may be a so-called solvent-free paint in which the non-volatile content accounts for 90 to 100% by mass, preferably 95 to 100% by mass, more preferably 98 to 100% by mass of the total mass of the paint composition. In this specification, the non-volatile content means the residue excluding the volatile components, and the residue may be solid or liquid at normal temperature. For example, it refers to the residual components when the sample is treated at 105°C for 3 hours to remove the volatile components.

[0073] After forming a wet paint film (uncured paint film) by applying the paint composition of the present invention to an object to be painted, a cured paint film can be obtained by curing the wet paint film.

[0074] The object to be painted is not particularly limited, and examples thereof include the outer plate portion of an automobile body such as a passenger car, a truck, a motorcycle, and a bus; automobile parts; and the outer plate portion of household electrical products such as a mobile phone and an audio device. Among these, the outer plate portion of an automobile body and automobile parts are preferred.

[0075] The material of these objects to be painted is not particularly limited, and examples thereof include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, alloyed zinc (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, and epoxy resin, and plastic materials such as various FRPs; inorganic materials such as glass, cement, and concrete; wood; and fiber materials such as paper and cloth. Among these, metal materials and plastic materials are preferred.

[0076] The object to be painted may be one that has been subjected to surface treatment such as phosphate treatment, chromate treatment, or composite oxide treatment on the metal surface of the above-mentioned metal material or a metal body formed therefrom. Further, the object to be painted may be one in which an undercoat paint film and / or a middle coat paint film such as various electrodeposition paints are formed on the metal surface.

[0077] The coating method of the coating composition of the present invention is not particularly limited. For example, air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, etc. can be mentioned, and a wet coating film can be formed by these coating methods. Among these, methods such as air spray coating and rotary atomization coating are preferred. When coating, electrostatic application may be performed as necessary.

[0078] The curing of the wet coating film can be carried out by heating after coating the coating composition of the present invention on the object to be coated. The heating can be carried out by known heating means. For example, drying furnaces such as hot air furnaces, electric furnaces, and infrared induction heating furnaces can be used. The heating temperature is preferably about 60 to 180 °C, more preferably about 90 to 170 °C, and still more preferably about 110 to 160 °C. The heating time is not particularly limited, but usually, about 10 to 60 minutes is preferred, and about 20 to 40 minutes is more preferred.

[0079] The coating amount of the coating composition of the present invention can be appropriately set according to the coating purpose. Generally, as the cured film thickness, an amount of about 0.5 to 50 μm, preferably about 2 to 40 μm, more preferably about 5 to 30 μm, and even more preferably about 8 to 18 μm can be adopted.

[0080] <Multi-layer coating film forming method> The coating composition containing the oligomer dispersion of cellulose fibers obtained by the production method of the present invention may be used as a coating composition for forming a multi-layer coating film. For example, in a method of forming a multi-layer coating film by sequentially coating at least one layer of a colored base coat paint and at least one layer of a clear coat paint on an object to be coated, a multi-layer coating film can be formed by coating the coating composition of the present invention as a clear coat paint.

[0081] As the colored base coat paint used in the above multi-layer coating film forming method, for example, when the object to be coated is an automobile body, those known per se that are usually used in the coating of automobile bodies can be used.

[0082] Specifically, as the colored base coat paint composition, a substrate resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, or an epoxy resin having crosslinkable functional groups such as carboxy groups and hydroxyl groups, and an amino resin such as a melamine resin or a urea resin, and a crosslinking agent such as a blocked polyisocyanate compound are dissolved or dispersed in an organic solvent or water together with pigments such as colored pigments, extender pigments, and pearlescent pigments, a thickener, and optional other components to form a paint. Among them, a thermosetting paint using at least one selected from the group consisting of a hydroxyl group-containing polyester resin and a hydroxyl group-containing acrylic resin as the substrate resin and using a melamine resin as the curing agent can be preferably used.

[0083] When the paint composition of the present invention is used as a clear coat paint, as the binder component of the clear coat paint, for example, those known per se usually used in the painting of automobile bodies can be used. Specifically, for example, a substrate resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, an epoxy resin, or a fluororesin having crosslinkable functional groups such as hydroxyl groups, carboxy groups, epoxy groups, and silanol groups, and a crosslinking agent such as a melamine resin, a urea resin, a blocked polyisocyanate compound, a carboxy group-containing compound or resin, or an epoxy group-containing compound or resin can be contained as the binder component. Among them, an organic solvent-based thermosetting paint containing a carboxy group-containing resin and an epoxy group-containing resin, or a thermosetting paint containing a hydroxyl group-containing acrylic resin and an optionally blocked polyisocyanate compound is preferable. As the hydroxyl group-containing acrylic resin, various hydroxyl group-containing acrylic resins described in relation to the above hydroxyl group-containing resin (E1) can be preferably used.

[0084] In addition, the clear coat paint can contain, as necessary, coloring pigments, pearlescent pigments, dyes, matting agents, etc. to such an extent that transparency is not impaired, and further can appropriately contain extender pigments, ultraviolet absorbers, light stabilizers, defoamers, thickeners, rust preventives, surface modifiers, etc.

[0085] The clear coat paint can be applied by a method known per se, such as airless spraying, air spraying, a rotary atomizing coater, etc., and electrostatic application may be carried out during application.

[0086] The clear coat paint can be applied so that the cured film thickness is usually in the range of 10 to 80 μm, preferably 15 to 60 μm, more preferably 20 to 50 μm. Further, from the viewpoint of preventing the occurrence of coating film defects, etc., after the application of the clear coat paint, if necessary, an interval of about 1 to 60 minutes can be provided at room temperature, or preheating can be carried out at a temperature of about 40 to about 80 °C for about 1 to 60 minutes.

[0087] By heating a multilayer coating film including a colored base coat film and a clear coat film formed by applying a colored base coat paint and a clear coat paint to an object to be coated, a cured multilayer coating film can be formed. The heating means can be carried out, for example, by hot air heating, infrared heating, high-frequency heating, etc. The heating temperature is preferably 80 to 160 °C, more preferably 100 to 140 °C. Also, the heating time is preferably 10 to 60 minutes, more preferably 15 to 40 minutes. If necessary, before carrying out the heat curing, heating may be carried out directly or indirectly at a temperature of about 50 to about 110 °C, preferably about 60 to about 90 °C for about 1 to 60 minutes by preheating, air blowing, etc.

[0088] Further, for the heat curing of the colored base coat film and the clear coat film, a clear coat paint may be applied after the heat curing of the colored base coat film to form an uncured clear coat film, and then the uncured colored base coat film and the clear coat film may be heat cured, or after forming the uncured colored base coat film and the uncured clear coat film, a multilayer coating film including these two coating films may be cured at once by heat curing.

Example

[0089] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited thereto. In each example, "parts" and "%" are based on mass unless otherwise specified. Also, the film thickness of the coating film is based on the cured coating film.

[0090] Production Example 1 Into a reaction vessel equipped with a magnetic stirrer, 96 parts of deionized water was charged. While stirring the deionized water with the magnetic stirrer, 4 parts of "Celluforce NCC" (trade name, manufactured by Celluforce, cellulose nanocrystal powder) was gradually added, and then stirring was continued for 2 hours to obtain a cellulose nanocrystal aqueous dispersion (A-1) having a solid content concentration of 4%.

[0091] Example 1 Into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a water separator, 122 parts (solid content: 4.88 parts) of the cellulose nanocrystal aqueous dispersion (A-1) obtained in Production Example 1 and 134 parts (1.0 mol) of trimethylolpropane (solubility in 100 g of water at 20°C: 390 g, boiling point: 160°C, SP value: 15.9, molecular weight: 134) were charged. After heating to 110°C with stirring, the mixture was stirred at 110°C for 60 minutes to obtain a mixed solution (i-1) (Step (1)). Next, after heating the obtained mixed solution (i-1) to 110°C, while maintaining the temperature at 110°C, the pressure was reduced with an evaporator to remove the water brought in from the cellulose nanocrystal aqueous dispersion (A-1), and a mixed solution (ii-1) containing "Celluforce NCC" and trimethylolpropane was obtained (Step (2)). Next, while maintaining the obtained mixed solution (ii-1) at 110°C, 127 parts of a mixture of 77 parts (0.5 mol) of hexahydrophthalic anhydride (molecular weight: 154) and 50 parts (0.5 mol) of succinic anhydride (molecular weight: 100) was added to the mixed solution (ii-1), and the reaction was carried out at 110°C until the total acid value reached a total acid value at which the reaction rate of the acid anhydride group was 95% or more, to obtain an oligomer dispersion of cellulose fibers (step (3)).

[0092] Here, the total acid value when the reaction rate of the acid anhydride group is 95% or more is calculated as follows. First, the above total acid value is a value calculated with the carboxy group as 1 mol of acid group and the acid anhydride group as 2 mol of acid group, and the acid value described below is a value calculated with the carboxy group as 1 mol of acid group and the acid anhydride group as 1 mol of acid group. Therefore, the total acid value before the reaction of the mixture of 134 parts (1.0 mol) of trimethylolpropane, 77 parts (0.5 mol) of hexahydrophthalic anhydride, and 50 parts (0.5 mol) of succinic anhydride is (0.5 + 0.5)×2×1000×56.1 / (134 + 77 + 50) ≒ 430 mgKOH / g. And in the above mixture, when the reaction rate of the acid anhydride group reaches 95%, the total acid value, for calculating the carboxy group generated by the reaction as 1 mol of acid group, is (0.5 + 0.5)×(1×0.95 + 2×0.05)×1000×56.1 / (134 + 77 + 50) ≒ 226 mgKOH / g. Therefore, in Example 1, the total acid value when the reaction rate of the acid anhydride group is 95% or more is 226 mgKOH / g or less. For this reason, the above reaction was carried out until the total acid value reached 226 mgKOH / g or less.

[0093] Next, 228 parts (1 mol) of "Cardura E10P" (manufactured by HEXION, monoglycidyl neodecanoate, molecular weight 228) was added to the obtained oligomer dispersion of cellulose fibers, and the reaction was carried out until the acid value reached an acid value at which the reaction rate of the carboxyl group was 90% or more, to obtain an oligomer dispersion No. 1 of cellulose fibers. Here, the acid value when the reaction rate of the carboxyl group is 90% or more is calculated as follows. The acid value before the reaction of the mixture of 134 parts (1.0 mol) of trimethylolpropane, 77 parts (0.5 mol) of hexahydrophthalic anhydride, 50 parts (0.5 mol) of succinic anhydride, and 228 parts (1.0 mol) of "Cardura E10P" is considered that all acid anhydride groups in the above hexahydrophthalic anhydride and succinic anhydride are ring-opened to form carboxyl groups until the reaction is completed, so (0.5 + 0.5)×1×1000×56.1 / (134 + 77 + 50 + 228) ≒ 115 mgKOH / g. And in the above mixture, the acid value when the reaction rate of the carboxyl group reaches 90% is (0.5 + 0.5)×(100 - 90) / 100×1000×56.1 / (134 + 77 + 50 + 228) ≒ 11.5 mgKOH / g. Therefore, in Example 1, the acid value when the reaction rate of the carboxyl group is 90% or more is 11.5 mgKOH / g or less. For this reason, the above reaction was carried out until the acid value reached 11.5 mgKOH / g or less.

[0094] Examples 2 to 15 In Example 1, except that the blending composition was as shown in Tables 1 to 3 below, oligomer dispersions No. 2 to No. 15 of cellulose fibers were obtained in the same manner as in Example 1.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] (Note 1) "Reocristal I-2SX": Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., an aqueous dispersion of cellulose nanofibers, with a solid content of 2%.

[0099] Comparative Example 1 Into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and water separator, 139 parts (5.56 parts of solid content) of the cellulose nanocrystal aqueous dispersion (A-1) obtained in Production Example 1 and 202 parts (1.0 mol) of 1,12-dodecanediol (solubility in 100 g of water at 20°C: 1 g, boiling point: 189°C, molecular weight: 202) were charged. After heating to 110°C with stirring, the mixture was stirred at 110°C for 60 minutes to obtain a mixed liquid (i-16). When the obtained mixed liquid (i-16) was observed with the naked eye, aggregates were seen (Step (1)). Therefore, Steps (2) and subsequent steps were not carried out.

[0100] Regarding the oligomer dispersions of the cellulose fibers of Examples 1 to 15 obtained above and the dispersion of the cellulose fibers of Comparative Example 1 (mixed liquid (i-16)), evaluations were performed by the following test methods. The evaluation results are shown in Tables 1 to 3. (Test Method) Dispersibility: Each oligomer dispersion of cellulose fibers was observed with the naked eye, and the presence or absence of aggregates was evaluated according to the following criteria. A and B are the passing levels. A: No aggregates are seen B: Slight aggregates are seen C: A large amount of aggregates are seen

[0101] Production Example 2 - Production of Hydroxyl Group-Containing Resin (E1) Into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet tube, and a dropping device, 27 parts of "Swazol 1000" (trade name, manufactured by Cosmo Oil Co., aromatic organic solvent) and 5 parts of propylene glycol monomethyl ether acetate were charged, and the mixture was stirred at 150 °C while blowing nitrogen gas. A monomer mixture consisting of 20 parts of styrene, 32.5 parts of 2-hydroxypropyl acrylate, 46.5 parts of isobutyl methacrylate, 1.0 part of acrylic acid, and 1.5 parts of ditertiary amyl peroxide (polymerization initiator) was dropped into this mixture at a uniform rate over 4 hours. Then, it was aged at 150 °C for 1 hour and then cooled. Further, 34 parts of butyl acetate was added for dilution to obtain a hydroxyl group-containing acrylic resin (E1-1) solution with a solid content concentration of 60% by mass. The hydroxyl value of the obtained hydroxyl group-containing acrylic resin (E1-1) was 140 mgKOH / g, the acid value was 8.0 mgKOH / g, the weight average molecular weight was 10,000, and the glass transition temperature was 39 °C.

[0102] Example 16 - Production of Paint Composition 88.5 parts (solid content 53.1 parts) of the hydroxyl group-containing acrylic resin (E1-1) solution obtained in Production Example 1, 10.1 parts (solid content 10.1 parts, of which 0.1 part is the cellulose fiber (A) component and 10 parts is the oligomer component) of the oligomer dispersion of cellulose fibers No. 1 obtained in Example 1, and 0.4 parts (solid content 0.2 parts) of "BYK-300" (trade name, manufactured by BYK Chemie, surface conditioner, active ingredient 52%) were uniformly mixed to obtain a main agent. And 36.9 parts of "Sumidur N3300" (trade name, manufactured by Sumika Covestro Urethane Co., isocyanurate form of hexamethylene diisocyanate, solid content content 100%), which is a curing agent (crosslinking agent (E2)), were uniformly mixed immediately before painting. Further, butyl acetate was added to adjust the viscosity to 30 seconds according to Ford Cup No. 4 at 20 °C to obtain a paint composition (P-1).

[0103] Comparative Example 2 A paint composition (P-2) was produced in the same manner as in Example 1 except that the formulation composition was as shown in Table 2 below. However, since a large amount of aggregates were generated in the paint composition, the production of the following test plates was not carried out.

[0104] Preparation of Test Panel for Example 16 On a cold-rolled steel sheet sized 10 cm × 15 cm and subjected to zinc phosphate chemical conversion treatment, "Electron GT-10" (trade name, manufactured by Kansai Paint Co., Ltd., cationic electrodeposition paint) was electrodeposition-coated to a dry film thickness of 20 μm and then heated at 170 °C for 30 minutes to cure. Thereafter, on the electrodeposition coating film, "WP-306T" (trade name, manufactured by Kansai Paint Co., Ltd., polyester melamine resin-based waterborne intermediate paint) was electrostatically coated using a rotary atomization type electrostatic coater to a cured film thickness of 30 μm. After leaving it for 5 minutes, preheating was carried out at 80 °C for 3 minutes. Thereafter, heating was carried out at 140 °C for 30 minutes to obtain a test object to be coated. Next, on the test object to be coated, "WBC-713T No.202" (trade name, manufactured by Kansai Paint Co., Ltd., acrylic melamine resin-based waterborne base coat paint, black color) was electrostatically coated using a rotary atomization type electrostatic coater to a cured film thickness of 15 μm. After leaving it for 5 minutes, preheating was carried out at 80 °C for 3 minutes. Next, on the uncured base coat coating film, the paint composition (P-1) was electrostatically coated using a rotary atomization type electrostatic coater to a dry film thickness of 40 μm to form a clear coat coating film, and it was left for 7 minutes. Then, heating was carried out at 140 °C for 30 minutes to heat-cure the base coat coating film and the clear coat coating film, thereby preparing a test panel for Example 16.

[0105] Regarding the test panel obtained above, evaluation was carried out by the following test methods. The evaluation results are shown in Table 4 together with the paint compositions. (Test Method) Transparency: The test panel was observed with the naked eye, and the transparency was evaluated according to the following criteria. Pass: No aggregates are generated and it is transparent. Fail: A large amount of aggregates are generated.

[0106] [Table 4]

[0107] Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible.

Claims

1. The following steps (1) to (3): Step (1): A water dispersion of cellulose fiber (A) is mixed with a compound (B) having two or more reactive groups, a solubility in 100 g of water at 20 °C of 100 g or more, and a boiling point of 115 °C or more to obtain a mixed liquid (i). Step (2): Removing water in the mixed liquid (i) obtained in the above step (1) to obtain a mixed liquid (ii) containing the cellulose fiber (A) and the compound (B), and Step (3): Mixing the mixed liquid (ii) obtained in the above step (2) with a compound (C) having one or more reactive groups reactive with the reactive groups in the compound (B), and reacting the reactive groups in the compound (B) with the reactive groups in the compound (C) to form an oligomer. A method for producing an oligomer dispersion of cellulose fiber, comprising the above steps.

2. The solubility parameter value (SP value) of the compound (B) is in the range of 12 to 23 (cal / cm 3 ). 1 / 2 The method for producing an oligomer dispersion of cellulose fibers according to claim 1, wherein the method is within the range of

3. The method for producing an oligomer dispersion of cellulose fiber according to claim 1 or 2, wherein the molecular weight of the compound (B) is in the range of 60 to 2000.

4. The method for producing an oligomer dispersion of cellulose fiber according to any one of claims 1 to 3, wherein the compound (B) is a compound (B') having two or more active hydrogen groups, a solubility in 100 g of water of 100 g or more, and a boiling point of 115 °C or more.

5. The method for producing an oligomer dispersion of cellulose fiber according to claim 4, wherein the compound (B') is a compound (B'') having two or more hydroxyl groups, a solubility in 100 g of water of 100 g or more, and a boiling point of 115 °C or more.

6. The method for producing an oligomer dispersion of cellulose fiber according to claim 5, wherein in the above step (3), reacting the hydroxyl group in the cellulose fiber (A), the hydroxyl group in the compound (B''), and the reactive group in the compound (C) is included.

7. The method for producing an oligomer dispersion of cellulose fiber according to claim 5 or 6, wherein the compound (B'') is trimethylolpropane and / or glycerin.

8. The method for producing an oligomer dispersion of cellulose fiber according to any one of claims 1 to 7, wherein the compound (C) is a compound (C') having two or more carboxy groups or one or more carboxylic anhydride groups.

9. After the above step (3), further, the following step (4), Step (4): Further mixing a compound (D) having one or more reactive groups reactive with the oligomers in the dispersion liquid into the oligomer dispersion liquid of cellulose fibers obtained in step (3), and reacting the oligomers with the compound (D). A method for producing an oligomer dispersion liquid of cellulose fibers according to any one of claims 1 to 8, comprising the above steps.

10. The method for producing an oligomer dispersion liquid of cellulose fibers according to claim 9, wherein the compound (D) is a compound (D') having an epoxy group.

11. A method for producing a coating composition containing an oligomer dispersion liquid of cellulose fibers, comprising: The following steps (1) to (3): Step (1): Mixing an aqueous dispersion liquid of cellulose fibers (A) with a compound (B) having two or more reactive groups, having a solubility of 100 g or more in 100 g of water at 20°C, and having a boiling point of 115°C or more to obtain a mixed liquid (i). Step (2): Removing water in the mixed liquid (i) obtained in step (1) to obtain a mixed liquid (ii) containing the cellulose fibers (A) and the compound (B); and Step (3): Mixing the mixed liquid (ii) obtained in step (2) with a compound (C) having one or more reactive groups reactive with the reactive groups in the compound (B), and reacting the reactive groups in the compound (B) with the reactive groups in the compound (C) to form oligomers. A manufacturing method comprising the above steps.

12. The manufacturing method according to claim 11, wherein the coating composition further contains a binder component (E).

13. The manufacturing method according to claim 12, wherein the binder component (E) contains a hydroxyl group-containing resin (E1) and a crosslinking agent (E2).

14. A method for forming a multilayer coating film by sequentially coating at least one layer of a colored base coat paint and at least one layer of a clear coat paint on an object to be coated, comprising coating a coating composition produced by the manufacturing method according to any one of claims 11 to 13 as the clear coat paint.

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