Method for manufacturing a resin composition and resin composition

Abstract

To provide a method for producing a resin composition which can remarkably improve strength of a molding using a resin composition containing cellulose fibers.SOLUTION: A method for producing a resin composition using cellulose fibers (A), an aqueous crosslinking agent (B), a thermoplastic resin (C) reactive with the aqueous crosslinking agent (B), and a thermoplastic resin (D) as stating materials, includes: a step (I)of obtaining a dispersion by mixing and drying cellulose fibers (A) and an aqueous crosslinking agent (B) in the presence of water in a mass ratio of (A) to (B) of 100:0.5 to 30; and a step (II) of adding the thermoplastic resin (C) to the dispersion obtained in the step (I), and kneading the mixture, thereby reacting the aqueous crosslinking agent (B) with the thermoplastic resin (C).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a resin composition capable of improving the strength of a cellulose fiber composite resin molded body, and to the resin composition.

Background Art

[0002] Conventionally, fibrous additives such as glass fiber, carbon fiber, aramid fiber, and cellulose fiber have been used for the purpose of improving the strength of resin molded bodies. Among them, cellulose fiber has characteristics such as low density, high elastic modulus, and low linear thermal expansion coefficient. In addition, since cellulose fiber is "carbon neutral" and a sustainable resource, it is expected to be a material contributing to the reduction of environmental load. However, cellulose fiber is hydrophilic and resin is hydrophobic, and the strength of cellulose fiber may not be fully reflected in the molded body, possibly because of the poor adhesion between cellulose fiber and resin.

[0003] In cellulose fiber composite resin, in order to improve the strength of the molded body, methods have been proposed to improve the compatibility and interfacial strength between cellulose fiber and resin by hydrophobically modifying cellulose fiber or using a compatibilizer.

[0004] For example, as described in Patent Document 1, in a composite material composed of microfibrillated cellulose fiber and polyolefin such as polypropylene, it is widely known to use maleic acid-modified polypropylene as a compatibilizer or an interfacial reinforcing agent. However, its affinity with highly hydrophilic cellulose fiber is low, and the actual reinforcing effect is not satisfactory.

[0005] Furthermore, Patent Document 2 describes that in polylactic acid and polypropylene composite resins containing natural plant fibers, including cellulose fibers, using a modified propylene resin obtained by reacting a propylene resin having a group that reacts with a carbodiimide group with a carbodiimide group-containing compound results in a composite resin with excellent heat resistance and flexural strength. However, although the heat resistance of the polylactic acid resin composition has been improved, the improvement in flexural strength has not been sufficient.

[0006] Furthermore, Patent Document 3 describes that by using a resin composition for molding materials consisting of plant fibers, thermoplastic resins such as polyolefins, and compounds that react with carboxyl groups, a lightweight molded article with suppressed fogging and maintained strength can be obtained. However, the compounds that react with carboxyl groups are used to suppress the volatilization of organic acids and other substances contained in plant fibers, which are the cause of fogging, and do not improve the strength of the resulting molded article. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent Application Publication No. 2008 / 0146701 [Patent Document 2] Japanese Patent Publication No. 2008-88358 [Patent Document 3] International Publication No. 2020 / 230836 [Overview of the project] [Problems that the invention aims to solve]

[0008] In contrast, the present invention aims to provide a method for producing a resin composition that can dramatically improve the strength of a molded article using a resin composition containing cellulose fibers. [Means for solving the problem]

[0009] As a result of diligent research to solve the above problems, the inventors have found that a resin composition with high strength when molded can be obtained by mixing cellulose fibers with a specific aqueous crosslinking agent in the presence of water, drying the mixture, and then kneading and reacting it with a thermoplastic resin that is reactive with the aqueous crosslinking agent.

[0010] In other words, the means of the present invention that seeks to solve the above problems is, <1> A method for producing a resin composition, characterized by comprising the following steps (I) and (II), using cellulose fiber (A), aqueous crosslinking agent (B), thermoplastic resin (C) that is reactive with aqueous crosslinking agent (B), and thermoplastic resin (D) as starting materials. Step (I): In the presence of water, cellulose fibers (A) and an aqueous crosslinking agent (B) are mixed and dried to obtain a dispersion in a mass ratio of (A):(B) = 100:0.5~30. Step (II): The dispersion obtained in Step (I) is mixed with a thermoplastic resin (C) to react with the aqueous crosslinking agent (B) and the thermoplastic resin (C). <2> The aqueous crosslinking agent (B) is characterized by having at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, an epoxy group, a hydroxyl group, a carboxyl group, an amino group, and an isocyanate group. <1> Method for producing the resin composition described above, <3> The thermoplastic resin (C) is a polyolefin having at least one functional group selected from the group consisting of an anhydride group, a hydroxyl group, a carboxyl group, an epoxy group, and an amino group. <1> Method for producing the resin composition described above, <4> The thermoplastic resin (D) is characterized in that it is a polyolefin resin. <1> Method for producing the resin composition described above, <5> The above step (I) or step (II) is characterized by further adding a dihydrazide compound (E). <1> Method for producing the resin composition described above, <6> The above is characterized by further adding and kneading a thermoplastic resin (D) in step (II) or after step (II), thereby defibrating the cellulose fibers (A) into fine cellulose fibers (A') in the thermoplastic resin (D). <1> Method for producing the resin composition described above, <7>Cellulose fiber (A) and / or microcellulose fiber (A’), Thermoplastic resin (D), and Reactant (F) of aqueous crosslinking agent (B) and thermoplastic resin (C) having reactivity with aqueous crosslinking agent (B) A resin composition containing: The functional group involved in the reaction between the aqueous crosslinking agent (B) and the thermoplastic resin (C) is at least one selected from the group of the following combinations (1) to (8), and Based on 1 part by mass in total of cellulose fiber (A) and / or microcellulose fiber (A’), Thermoplastic resin (D): 0.5 to 100 parts by mass, Reactant (F): 0.01 to 1.5 parts by mass Characterized by containing, a resin composition, (1) Carbodiimide group and acid anhydride group (2) Carbodiimide group and carboxy group (3) Oxazoline group and acid anhydride group (4) Epoxy group and acid anhydride group (5) Hydroxy group and acid anhydride group (6) Carboxy group and acid anhydride group (7) Amino group and acid anhydride group (8) Isocyanate group and hydroxy group is.

Effect of the Invention

[0011] According to the method for producing the resin composition of the present invention, the strength of the molded body of the obtained resin composition can be dramatically improved.

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. Note that the following description is an example of an embodiment of the present invention and is not limited to this description.

[0013] <Raw Materials of Resin Composition> The manufacturing method of the resin composition of the present invention uses cellulose fiber (A), an aqueous crosslinking agent (B), a thermoplastic resin (C) reactive with the aqueous crosslinking agent (B), and a thermoplastic resin (D) as starting materials.

[0014] Cellulose fiber (A) is known to originate from plants (e.g., wood, bamboo, hemp, cotton, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., tunicates), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc., and any of them can be used in the present invention. Preferably, it is a cellulose fiber derived from a plant or a microorganism, more preferably a cellulose fiber derived from a plant. Among the cellulose fibers derived from plants, pulp (especially softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP)) is particularly preferred.

[0015] Also, the cellulose fiber (A) may be a modified cellulose in which the functional groups of cellulose are substituted and modified. For example, modified cellulose fibers esterified with acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhyd anhydride, valeric anhydride, hexanoic anhydride, decanoic anhydride, benzoic anhydride, stearic anhydride, etc., and polybasic acid anhydrides such as maleic anhydride, succinic anhydride, phthalic anhydride, alkyl or alkenyl succinic anhydride, maleic anhydride-modified polyolefin, maleic anhydride-modified polybutadiene, etc. may be used. Further, modified cellulose fibers adsorbed and modified on the cellulose surface using an acrylic resin and / or a styrene acrylic resin containing at least one monomer unit selected from the group consisting of (meth)acrylate-based monomers, (meth)acrylamide-based monomers, and styrene-based monomers may be used. The cellulose fiber (A) may be used alone or in combination of two or more.

[0016] Examples of aqueous crosslinking agents (B) include compounds containing at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, an epoxy group, a hydroxyl group, a carboxyl group, an amino group, an isocyanate group, a hydrazide group, a silanol group, and an aziridinyl group. Among these, compounds containing at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, an epoxy group, a hydroxyl group, a carboxyl group, an amino group, and an isocyanate group are preferred.

[0017] The aqueous crosslinking agent (B) is preferably water-soluble or water-dispersible in order to allow for easy mixing with cellulose fibers in the presence of water. In this invention, water-soluble or water-dispersible means that when dispersed in water with a solid content of 5% by mass, no precipitate forms after 24 hours at room temperature, and the visible light transmittance of the dispersion at a wavelength of 600 nm is 50%T or higher.

[0018] The aqueous crosslinking agent (B) only needs to have two or more functional groups in its molecule. The aqueous crosslinking agent having functional groups may be synthesized by known methods, or a commercially available functional group-containing compound may be used. Examples of commercially available carbodiimide group-containing compounds include Carbodilite V-02, SV-02, and V-04 from Nisshinbo Chemical Co., Ltd., examples of commercially available oxazoline group-containing compounds include Epocross WS-700 from Nippon Shokubai Co., Ltd., examples of commercially available epoxy group-containing compounds include Denacol EX-861 and EX-512 from Nagase ChemteX Corporation, examples of commercially available hydroxyl and carboxyl group-containing compounds include Pluscoat Z-687 and Z-730 from Go-o Chemical Industry Co., Ltd., examples of hydroxyl group-containing compounds include polyvinyl alcohol and cellulose derivatives, examples of carboxyl group-containing polymers include polyacrylic acid, examples of commercially available amino group-containing polymers include JEFFAMINEED-2003 from Huntsman, and examples of commercially available isocyanate group-containing polymers include Duranate WL70-100 from Asahi Kasei.

[0019] The aqueous crosslinking agent (B) can also be obtained by polymerizing an ethylenically unsaturated monomer having a functional group using a known method. Examples of ethylenically unsaturated monomers include those having an oxazoline group such as 2-vinyl-2-oxazoline, 4-methyl-2-vinyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2-vinyl-2-oxazoline, and 2-isopropenyl-2-oxazoline; an epoxy group such as glycidyl (meth)acrylate; a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, N-methylolacrylamide, and N-hydroxyethylacrylamide; a carboxyl group such as (meth)acrylic acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid, maleic acid, and fumaric acid; and an amino group such as 2-aminoethyl methacrylate and 4-aminostyrene. One type may be used alone, or two or more types may be used in combination.

[0020] The thermoplastic resin (C) that reacts with the aqueous crosslinking agent (B) can be a thermoplastic resin having a functional group that can react with the aqueous crosslinking agent (B), and is preferably a polyolefin having at least one functional group selected from the group consisting of an acid anhydride group, a hydroxyl group, a carboxyl group, an epoxy group, and an amino group. Among these, from the viewpoint of versatility, polyolefins having an acid anhydride group are preferred, and examples include maleic anhydride-modified polyolefins such as maleic anhydride-modified polyethylene and maleic anhydride-modified polypropylene. One type of polyolefin having a functional group may be used alone, or two or more types may be used in combination.

[0021] Functional groups may be contained within the main chain of the polyolefin, or they may be attached to the main chain of the polyolefin as side chains. One method for attaching functional groups as side chains to a polyolefin is to graft a polyolefin with an ethylenically unsaturated monomer having a functional group. Graft reactions can be carried out by known methods, such as a solution method in which the polyolefin is dissolved or uniformly dispersed in an organic solvent by raising the temperature above its softening point, and an ethylenically unsaturated monomer having a functional group and an organic peroxide are added and reacted; and a melt method in which the polyolefin is melted by raising the temperature above its softening point, and an ethylenically unsaturated monomer having a functional group and an organic peroxide are added, mixed, and reacted.

[0022] The main chain polyolefin may be a homopolymer such as polyethylene or polypropylene, or an olefin copolymer, but an α-olefin copolymer containing at least ethylene and / or propylene is preferred. Examples of α-olefins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-dodedecene, and 4-methyl-1-pentene. Examples of copolymers include random copolymers, block copolymers, graft copolymers, and mixtures thereof.

[0023] Examples of ethylenically unsaturated monomers used in the graft reaction include those having an acidic anhydride group such as maleic anhydride, itaconic anhydride, citraconic anhydride, and 2-methacryloyloxyethyl succinic acid; a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, N-methylolacrylamide, and N-hydroxyethylacrylamide; a carboxyl group such as (meth)acrylic acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid, maleic acid, and fumaric acid; an epoxy group such as glycidyl (meth)acrylate; and an amino group such as 2-aminoethyl methacrylate and 4-aminostyrene. One type may be used alone, or two or more types may be used in combination.

[0024] The amount of functional groups in the reactive thermoplastic resin (C) is not particularly limited, as long as it is sufficient to react with the aqueous crosslinking agent (B) to the extent that the effects of the present invention can be obtained. For example, in the case of maleic anhydride-modified polyolefin, the acid value is preferably in the range of 1 to 150 mg KOH / OH, and more preferably in the range of 5 to 100 mg KOH / OH.

[0025] The thermoplastic resin (D) is not particularly limited as long as it is commonly used in molded articles. Examples include polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyamides such as polyacetal, nylon 6, nylon 66, nylon 11, and nylon 12; polyesters such as polylactic acid, polyethylene terephthalate, and polybutylene terephthalate; chlorine resins such as polyvinyl chloride and polyvinylidene chloride; fluororesins such as polyvinyl fluoride and polyvinylidene fluoride; polystyrene; ABS resin; petroleum resin, coumarone resin; terpene resin; rosin resin; thermoplastic elastomers such as olefin-based elastomers, vinyl chloride-based elastomers, urethane-based elastomers, polyester-based elastomers, and polyamide-based elastomers; polycarbonates such as ionomer resins, polyacrylonitrile, ethylene-vinyl acetate resin, ethylene-vinyl alcohol resin, polypropylene carbonate, and polycarbonate diol; modified polyphenylene ether and methylpentene resin. One or more of these can be used in combination. Thermoplastic resins with a melting point or softening point of 220°C or lower are preferable because they have less thermal impact on cellulose fibers. Specifically, polyolefins are preferred, with polypropylene being the most preferred.

[0026] In the method for producing the resin composition of the present invention, it is preferable to further add a dihydrazide compound (E) as a starting material in step (I) or step (II) described later, in order to improve the strength of the molded article, which is the objective of the present invention. A dihydrazide compound (E) is a compound having two hydrazide groups in its molecule. It is believed that the dihydrazide compound (E) is adsorbed by the interaction of the hydrazide groups with the hydrophilic groups on the surface of the cellulose, and that the hydrophobic group located between the hydrazide groups imparts hydrophobicity to the cellulose. This hydrophobicity is thought to improve the compatibility between the cellulose fibers and the thermoplastic resin in the composite step with the thermoplastic resin described later, thereby further improving the mechanical properties of the molded article. From the viewpoint of imparting hydrophobicity to the cellulose fibers (A), it is preferable that the number of carbon atoms in the dihydrazide compound (E) is 6 to 12. In particular, sebacate dihydrazide, dodecanediose dihydrazide, isophthalic acid dihydrazide, etc. are preferred.

[0027] The present invention provides a method for producing a resin composition comprising: (I) a step of mixing and drying cellulose fibers (A) and an aqueous crosslinking agent (B) in the presence of water in a mass ratio of (A):(B)=100:0.5~30 to obtain a dispersion; and (II) a step of adding a thermoplastic resin (C) to the dispersion obtained in step (I) and kneading it to react the aqueous crosslinking agent (B) and the thermoplastic resin (C).

[0028] In step (I), the cellulose fibers (A) and the aqueous crosslinking agent (B) must be mixed in the presence of water in order to ensure uniform mixing. The proportion of water is usually preferably 0.5 to 100 parts by mass, and more preferably 1 to 80 parts by mass, per 1 part by mass of cellulose fibers (A). There are no particular restrictions on the mixing method as long as the cellulose fibers (A) and the aqueous crosslinking agent (B) are uniformly mixed. Fillers or the like may be mixed in addition to the cellulose fibers (A) during mixing.

[0029] In step (I), the cellulose fibers (A) and aqueous crosslinking agent (B) may be mixed with water in the presence of an organic solvent as needed. Examples of organic solvents that can swell the cellulose fibers include methanol, ethanol, isopropanol, n-propanol, t-butanol, acetone, diacetone alcohol, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methyl-2-pyrrolidone. These may be used individually or in combination of two or more as needed. The proportion of the organic solvent is preferably 1 to 100 parts by mass per 100 parts by mass of water, within the range that it is miscible with water.

[0030] The dispersion consisting of the cellulose fibers (A) and aqueous crosslinking agent (B) described above needs to be dried in order to knead and react with the thermoplastic resin (C). There are no particular restrictions on the drying method, as long as it can be dried at a temperature that does not cause aggregation or decomposition of the cellulose fibers (A) or aqueous crosslinking agent (B). Preferably, in order to suppress the shrinkage of the dispersion consisting of cellulose fibers (A) and aqueous crosslinking agent (B) during drying, it is preferable to use a method of dynamic drying under a reduced pressure atmosphere while stirring the contents, or to use a kneader equipped with equipment that can remove moisture or vent holes.

[0031] In step (II), the dispersion obtained in step (I) is mixed with the thermoplastic resin (C) while dispersing the cellulose fibers (A), and the aqueous crosslinking agent (B) is reacted with the thermoplastic resin (C) to form a reaction product (F) of the aqueous crosslinking agent (B) and the thermoplastic resin (C). There are no particular restrictions on the mixing method, and conventionally known methods can be used. Examples include single-screw mixers, twin-screw mixers, kneaders, Banbury mixers, pressure kneaders, roll mixers, etc. The mixer may be of the batch type or continuous type.

[0032] The mixing temperature should preferably be such that it promotes the reaction between the aqueous crosslinking agent (B) and the thermoplastic resin (C), and does not cause the cellulose fibers to deteriorate due to heat. Specifically, mixing is preferably carried out in the range of 100 to 250°C.

[0033] There are no particular restrictions on the order in which the thermoplastic resin (D) is added, but it is preferable to add it in or after step (II) in order to avoid inhibiting the uniform mixing of the cellulose fibers (A) and the aqueous crosslinking agent (B), and the reaction between the aqueous crosslinking agent (B) and the thermoplastic resin (C).

[0034] In step (I), the ratio of cellulose fibers (A) to aqueous crosslinking agent (B) must be in a mass ratio of (A):(B) = 100:0.5 to 30. If the amount of aqueous crosslinking agent (B) is less than 0.5 parts by mass per 100 parts by mass of cellulose fibers (A), the amount of aqueous crosslinking agent (B) relative to the cellulose fibers (A) will be insufficient, reducing the reactivity with the thermoplastic resin (C) and decreasing the compatibility between the cellulose fibers (A) and the thermoplastic resin (D), resulting in difficulty in obtaining sufficient strength for the molded article using the resin composition. Conversely, if the amount of aqueous crosslinking agent (B) is more than 30 parts by mass per 100 parts by mass of cellulose fibers (A), the excess (B) component will aggregate the cellulose fibers (A), worsening the dispersibility of the cellulose fibers (A) in steps (I) and beyond, making it difficult to obtain sufficient strength for the molded article using the resin composition.

[0035] In step (II), the mass ratio of the aqueous crosslinking agent (B) to the thermoplastic resin (C) is preferably (B):(C) = 1:0.1 to 100. If the mass ratio of the aqueous crosslinking agent (B) to the thermoplastic resin (C) is outside the above range, the unreacted excess components will act as plasticizers for the cellulose fibers (A), thus degrading the reinforcing effect.

[0036] In step (II) and / or after step (II), when adding and kneading the thermoplastic resin (D), it is preferable to defibrate some or all of the cellulose fibers (A) into fine cellulose fibers (A') in the thermoplastic resin (D). In the present invention, fine cellulose fibers (A') refer to fibers with a diameter of less than 1000 nm. From the viewpoint of reinforcing effect and moldability, the diameter is preferably 4 to 800 nm, more preferably 4 to 400 nm, and even more preferably 4 to 200 nm. In the present invention, the fiber diameter is confirmed by the following method. <How to check fiber diameter> A resin composition (or molded body) sample containing fine cellulose fibers (A') was wrapped in a 325-mesh stainless steel mesh and treated under xylene reflux at 140°C for 5 hours to dissolve the resin and extract the fibers. The resulting dried samples were then observed with a scanning electron microscope (e.g., JEOL Ltd., JSM-5610LV) at a magnification of 10,000x, and the fiber diameter of any given fiber was measured.

[0037] <Resin composition> In a preferred embodiment of the resin composition of the present invention, the composition contains cellulose fibers (A) and / or fine cellulose fibers (A'), a thermoplastic resin (D), and a reaction product (F) of an aqueous crosslinking agent (B) and a thermoplastic resin (C).

[0038] The resin composition obtained in the present invention comprises a reaction product (F) of an aqueous crosslinking agent (B) and a thermoplastic resin (C). In the reaction product (F), the combination of functional groups involved in the reaction between the aqueous crosslinking agent (B) and the thermoplastic resin (C) is preferably at least one selected from the group consisting of a carbodiimide group and an acid anhydride group, a carbodiimide group and a carboxyl group, an oxazoline group and an acid anhydride group, an epoxy group and an acid anhydride group, a hydroxyl group and an acid anhydride group, a carboxyl group and an acid anhydride group, an amino group and an acid anhydride group, and an isocyanate group and a hydroxyl group, and may be two or more. Particularly preferred combinations are a carbodiimide group and an acid anhydride group, and an oxazoline group and an acid anhydride group. Specific compound combinations include a carbodiimide group-containing compound and maleic anhydride-modified polypropylene, and an oxazoline group-containing compound and maleic anhydride-modified polypropylene.

[0039] The mass ratio of the total cellulose fibers (A) and fine cellulose fibers (A'), thermoplastic resin (D), and reactant (F) must be (A)+(A'):(D):(F)=1:0.5 to 100:0.01 to 1.5. If the amount of reactant (F) is 0.01 parts by mass or less per 1 part by mass of the total cellulose fibers (A) and fine cellulose fibers (A'), the effect of improving the dispersibility of the cellulose fibers (A) by the reactant (F) will not be sufficiently obtained, and the effect of improving the compatibility between the cellulose fibers (A) and the thermoplastic resin (D) will not be sufficiently obtained, resulting in a reduced reinforcing effect. If the amount of reactant (F) is 1.5 or more per 1 part by mass of cellulose fibers (A), the excess (F) component will act as a plasticizer in the molded article, making it difficult to obtain sufficient strength in the molded article using the resin composition.

[0040] The resin composition of the present invention may include, to the extent that it does not impede the effects of the present invention, resins other than thermoplastic resin (D); fibrous, granular, or plate-shaped fillers such as inorganic, organic, or metallic materials; crystallization nucleating agents; crosslinking agents; hydrolysis inhibitors; antioxidants; ultraviolet absorbers; surfactants; lubricants; waxes; colorants; stabilizers, etc., and one or more of these may be used in combination.

[0041] <Molded body> The resin composition of the present invention can be used to mold various molded products using conventionally known molding methods (for example, injection molding, extrusion molding, compression molding, blow molding, vacuum molding, foam molding, rotational molding, gas injection molding, etc.). It is particularly suitable for injection molding. Furthermore, the applications of molded articles using the resin composition of the present invention are not particularly limited, but include, for example, interior and exterior materials and casings for transportation machinery such as automobiles, motorcycles, bicycles, railways, drones, rockets, aircraft, and ships; energy machinery such as wind turbines and hydroelectric generators; home appliance casings such as air conditioners, refrigerators, vacuum cleaners, microwave ovens, AV equipment, digital cameras, and personal computers; electronic circuit boards; communication equipment casings such as mobile phones and smartphones; medical devices such as crutches and wheelchairs; shoes such as sneakers and business shoes; tires; balls for ball sports; ski boots; snowboards; golf clubs; protectors; fishing lines; fishing lures; and other sports equipment; outdoor equipment such as tents and hammocks; civil engineering and construction materials such as wire insulation, water pipes, and gas pipes; building materials such as pillars, flooring, decorative panels, window frames, and insulation materials; furniture such as bookshelves, desks, and chairs; industrial robots and household robots; filaments and support materials for 3D printers; packaging materials such as films and tapes; resin containers such as PET bottles; eyeglass frames; trash cans; and other household goods such as mechanical pencil cases. [Examples]

[0042] The following describes embodiments of the present invention. However, the present invention is not limited to these embodiments.

[0043] [Cellulose fiber (A)] The cellulose fiber (A) used as a raw material in this embodiment was either commercially available softwood bleached kraft pulp (A-1; hereinafter simply referred to as "cellulose fiber (A-1)") or commercially available cotton linter pulp (A-2).

[0044] [Manufacturing of resin compositions] (Example 1) <Process (I)> In a container equipped with a stirrer, 20 parts by mass of cellulose fiber (A-1) as cellulose fiber (A), 80 parts by mass of water, and 1 part by mass of a carbodiimide group-containing compound (B-1, Carbodilite SV-02 manufactured by Nisshinbo Chemical Co., Ltd., solid content 40% by mass) as an aqueous crosslinking agent (B) were added and mixed at 70°C. After that, the water was removed by distillation under reduced pressure to obtain a dispersion consisting of A-1 and B-1. <Process (II)> Next, 20.4 parts by mass of the dispersion, 6 parts by mass of maleic anhydride-modified polypropylene (C-1, Toyo Tac® PMAH1000P, manufactured by Toyobo Co., Ltd.) as thermoplastic resin (C), and 73.6 parts by mass of polypropylene resin (Prime Polypro® J108M, manufactured by Prime Polymer Co., Ltd., hereinafter sometimes simply referred to as "polypropylene resin") as thermoplastic resin (D) were placed in a Laboplast Mill (manufactured by Toyo Seiki Co., Ltd.), and melt-kneaded at a mixing temperature of 180°C and 100 revolutions per minute for 10 minutes to react B-1 and C-1, and to defibrate A-1 into fine cellulose to obtain a resin composition.

[0045] (Examples 2-3) A resin composition was obtained in accordance with the method described in Example 1, except that the type and amount of aqueous crosslinking agent (B) were changed as shown in Table 1.

[0046] (Comparative Example 1) A resin composition was obtained in accordance with the method described in Example 1, except that the aqueous crosslinking agent (B) was not used and the amount of each starting material was changed as shown in Table 1.

[0047] (Comparative Example 2) A resin composition was obtained in accordance with the method described in Example 1, except that a thermoplastic resin (C) that reacts with an aqueous crosslinking agent (B) was not used, and the amount of each starting material was changed as shown in Table 1.

[0048] (Example 4) <Process (I)> In a container equipped with a stirrer, 20 parts by mass of cellulose fiber (A-1) as cellulose fiber (A), 80 parts by mass of water, and 2.5 parts by mass of a carbodiimide group-containing compound (B-1, Carbodilite SV-02 manufactured by Nisshinbo Chemical Co., Ltd., solid content 40% by mass) as an aqueous crosslinking agent (B) were added and mixed at 70°C. After that, the water was removed by distillation under reduced pressure to obtain a dispersion consisting of A-1 and B-1. <Process (II)> Next, 21 parts by mass of the dispersion, 6 parts by mass of maleic anhydride-modified polypropylene (C-1, Toyo Tac® PMAH1000P manufactured by Toyobo Co., Ltd.) as thermoplastic resin (C), 69 parts by mass of polypropylene resin as thermoplastic resin (D), and 4 parts by mass of sebacate dihydrazide as dihydrazide compound (E) were placed in a Laboplast Mill (manufactured by Toyo Seiki Co., Ltd.), and melt-kneaded at a mixing temperature of 180°C and 100 revolutions per minute for 10 minutes to react B-1 and C-1, and to defibrate A-1 into fine cellulose to obtain a resin composition.

[0049] (Examples 5 and 6) A resin composition was obtained in accordance with the method described in Example 4, except that the type of cellulose fiber (A) and the timing of the addition of the dihydrazide compound (E) were changed as shown in Table 1.

[0050] [Table 1]

[0051] [Table 2]

[0052] Explanation of abbreviations in Tables 1 and 2 B-1: Nisshinbo Chemical Co., Ltd. Carbodilite SV-02, Solid content 40% by mass B-2: Nippon Shokubai Co., Ltd. Epocross WS-700, Solid content 25% by mass C-1: Toyo Tack (registered trademark) PMAH1000P manufactured by Toyobo Co., Ltd. PP: Prime Polymer Co., Ltd. "Prime Polypropylene (registered trademark) J108M" (mp: 170~175℃) SDH: Dihydrazide sebacate

[0053] <Evaluation of resin compositions> (Injection molding, measurement of bending properties) The obtained resin composition was used to form bar-type test specimens as described in JIS standard K7171 using a manual injection molding machine (manufactured by Imoto Seisakusho Co., Ltd.: Model 18D1). The bending strength was measured in accordance with JIS K7171 using a universal testing machine "Tensilon® RTM-50" manufactured by Orientec Co., Ltd. Table 2 shows the results of comparing the improvement rate of bending strength compared to the resin alone as an index. Strength [index] = (Strength of the example and comparative example) / (Strength of the resin alone) × 100

[0054] <Confirmation of the presence of fine cellulose fibers (A') in the resin composition> The resin composition obtained in the example was wrapped in a 325-mesh stainless steel mesh and treated under xylene reflux at 140°C for 5 hours to dissolve and remove the resin, and fine cellulose fibers (A') were extracted from the resin composition. When these were observed with a scanning electron microscope (SEM) at a magnification of 10,000x, the presence of fine cellulose fibers (A') having the fiber diameter defined in the present invention was confirmed. Furthermore, it was confirmed that fine cellulose fibers (A') were similarly present in the other examples as well.

[0055] A comparison of Examples 1-6 and Comparative Examples 1-2 shows that by satisfying all the conditions defined in the present invention, the present invention achieves the desired level of bending strength index of the resulting molded article, which is not achieved in the comparative examples that do not satisfy even one of the conditions.

Claims

1. A method for producing a resin composition, characterized by having the following steps (I) and (II), using cellulose fiber (A), aqueous crosslinking agent (B), polyolefin (C) which is reactive with aqueous crosslinking agent (B), and polyolefin (D) as starting materials. Step (I): In the presence of water, cellulose fibers (A) and an aqueous crosslinking agent (B) are mixed and dried to obtain a dispersion in a mass ratio of (A):(B) = 100:0.5 to 30. Step (II): The dispersion obtained in Step (I) is mixed with polyolefin (C) to react with the aqueous crosslinking agent (B) and polyolefin (C).

2. A method for producing the resin composition according to claim 1, characterized in that the aqueous crosslinking agent (B) has at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, an epoxy group, a hydroxyl group, a carboxyl group, an amino group, and an isocyanate group.

3. The method for producing the resin composition according to Claim 1, characterized in that the polyolefin (C) is a polyolefin having at least one functional group selected from the group consisting of an acid anhydride, a hydroxyl group, a carboxyl group, an epoxy group, and an amino group.

4. A method for producing a resin composition according to claim 1, characterized in that a dihydrazide compound (E) is further added in step (I) or step (II).

5. A method for producing a resin composition according to claim 1, characterized in that, in step (II) or after step (II), polyolefin (D) is further added and kneaded to defibrate cellulose fibers (A) into fine cellulose fibers (A') in the polyolefin (D).

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