Method for producing resin composition

Abstract

To provide a method for producing a resin composition at low cost which enables production of a resin composition that is excellent in tensile strength and bending strength, and suppresses poor appearance by remaining of cellulose-derived fiber feeling.SOLUTION: A method for producing a resin composition includes: a first step of charging a raw material composition containing at least a cellulose fiber, a first thermoplastic resin, urea and a dispersion medium into a first kneader, heating the raw material composition in a temperature range of at least 100°C or higher and 130°C or lower while stirring, removing the dispersion medium, and obtaining a mixture; a second step of melting and kneading the mixture obtained in the first step with the first kneader or a second kneader, and obtaining a masterbatch; and a third step of kneading the masterbatch obtained in the second step, and a resin for dilution.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a resin composition. [Background technology]

[0002] Fine fibrous cellulose obtained by finely disintegrating plant fibers includes microfibril cellulose and cellulose nanofibers, and is a fine fiber with a fiber diameter of about 1 nm to several tens of μm. Fine fibrous cellulose is lightweight, has high strength, a high elastic modulus, and a low coefficient of linear thermal expansion, and is therefore suitable for use as a reinforcing material for resin compositions.

[0003] However, since fine fibrous cellulose is hydrophilic while resin is hydrophobic, there has been a problem with the dispersibility of the fine fibrous cellulose when it is used as a reinforcing material for resin.

[0004] In Patent Document 1, a cellulose raw material and urea are heat-treated to obtain a cellulose raw material in which some of the hydroxyl groups of the cellulose are substituted with carbamate groups, and this is then micronized by mechanical treatment to obtain fine fibrous cellulose. The fine fibrous cellulose obtained by this method is less hydrophilic than conventional fine fibrous cellulose and has a high affinity for low-polarity resins, etc., and therefore disperses highly uniformly in resins, giving rise to resin compositions with high tensile strength.

[0005] However, the manufacturing method of Patent Document 1 required many steps, such as drying at 105°C, heating at 140°C, and washing, to obtain a modified cellulose raw material. The manufacturing method as a whole required many steps, resulting in high costs. Furthermore, simply reducing the number of steps to reduce costs could result in poor appearance of the resulting resin composition due to the fibrous texture derived from cellulose remaining. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-1876 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a method for producing a resin composition at low cost, which can obtain a resin composition that is excellent in tensile strength and flexural strength and further suppresses poor appearance due to the remaining fibrous texture derived from cellulose. [Means for solving the problem]

[0008] The present invention provides the following: (1) A method for producing a resin composition, comprising: a first step of feeding a raw material composition containing at least cellulose fiber, a first thermoplastic resin, urea, and a dispersing medium into a first kneader, heating the raw material composition with stirring at a temperature in the range of at least 100°C to 130°C, and removing the dispersing medium to obtain a mixture; a second step of melt-kneading the mixture obtained in the first step in the first kneader or the second kneader to obtain a masterbatch; and a third step of kneading the masterbatch obtained in the second step with a diluent resin. (2) The method for producing a resin composition according to (1), wherein the first thermoplastic resin is a thermoplastic resin modified with a hydrophilic functional group. (3) The method for producing a resin composition according to (1) or (2), wherein the melt-kneading temperature in the second step is in the range of at least 135°C or higher and 220°C or lower. (4) The method for producing a resin composition according to any one of (1) to (3), wherein the amount of the dispersion medium added to the first kneader in the first step is an amount that results in a solids concentration of the cellulose fibers of 10% by mass to 50% by mass. (5) The method for producing a resin composition according to any one of (1) to (4), wherein the first kneader and the second kneader are both equipped with parts constituting a screw, and the relationship between the screw peripheral speed of the first kneader in the first step and the screw peripheral speed of the first kneader or the second kneader in the second step satisfies the following relationship: Screw peripheral speed in the first process ≧ Screw peripheral speed in the second process (6) The method for producing a resin composition according to (2), wherein in the first step, the raw material composition further contains a second thermoplastic resin that is a thermoplastic resin that is not modified with a hydrophilic functional group. (7) The method for producing a resin composition according to (2), wherein in the second step, a second thermoplastic resin that is a thermoplastic resin not modified with a hydrophilic functional group is further added to the first kneader or the second kneader and melt-kneaded together with the mixture. [Effects of the Invention]

[0009] According to the present invention, a resin composition can be obtained that is excellent in tensile strength and flexural strength and further suppresses poor appearance due to the remaining fibrous texture derived from cellulose, and a low-cost method for producing the resin composition can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] In the examples and comparative examples, the appearance evaluation result of the film is A. [Figure 2] This is an example in which the appearance evaluation result of the film is B in Examples and Comparative Examples. [Figure 3] This is an example in which the appearance evaluation result of the film is C in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] The method for producing the resin composition of the present invention will be described below. In the present invention, "to" includes the extreme values. That is, "X to Y" includes the values ​​X and Y at both ends.

[0012] (Method of producing resin composition) The method for producing a resin composition of the present invention includes a first step of feeding a raw material composition containing at least cellulose fibers, a first thermoplastic resin, urea, and a dispersion medium into a first kneader, heating the raw material composition with stirring at a temperature in the range of at least 100°C to 130°C, and removing the dispersion medium to obtain a mixture; a second step of melt-kneading the mixture obtained in the first step in the first kneader or the second kneader to obtain a masterbatch; and a third step of kneading the masterbatch obtained in the second step with a diluent resin.

[0013] (First process: Dry kneading process) In the first step, a raw material composition containing at least cellulose fibers, a first thermoplastic resin, urea, and a dispersion medium is charged into a first kneader, heated with stirring at a temperature in the range of at least 100°C to 130°C, and the dispersion medium is removed to obtain a mixture.

[0014] (Cellulose fiber (A)) The cellulose fiber (A) used in the present invention can be obtained by pulping a pulp raw material. The pulp raw material may be either wood or non-wood. Examples of wood raw materials used to produce wood pulp include softwood and hardwood. Examples of non-wood raw materials used to produce non-wood pulp include cotton, hemp, sisal, Manila hemp, flax, straw, bamboo, bagasse, and kenaf. The pulp raw materials (wood raw materials and non-wood raw materials) may be unbleached (before bleaching) or bleached (after bleaching).

[0015] The method for pulping wood raw materials is not particularly limited, and examples include pulping methods commonly used in the papermaking industry. Wood pulp can be classified by pulping method, and examples include chemical pulp obtained by cooking using methods such as the Kraft method, sulfite method, soda method, and polysulfide method; mechanical pulp (TMP) obtained by pulping using mechanical forces such as a refiner or grinder; semi-chemical pulp obtained by chemical pretreatment followed by mechanical pulping; recycled paper pulp; and deinked pulp.

[0016] The Canadian Standard Freeness of the cellulose fiber (A) used in the present invention is not particularly limited. A freeness of more than 600 mL is preferable from the viewpoint of contributing to cost reduction because the beating step can be omitted. The upper limit of the freeness is not particularly limited, but in reality it is 800 mL or less. The Canadian Standard Freeness of the cellulose fiber (A) can be measured according to JIS P 8121-2:2012.

[0017] The cellulose fibers (A) may be mechanically treated, from the viewpoint that uniform penetration and contact of urea with the cellulose in the cellulose fibers leads to improved strength of the final fiber-reinforced resin. By performing the mechanical treatment, the specific surface area of ​​the pulp is increased, and it is expected that the amount of urea reacted therewith will increase.

[0018] In the present invention, mechanical treatment generally refers to mixing fibers in a dispersion medium, typically water, and further pulverizing or fibrillating the fibers, and includes beating, defibrating, dispersing, etc. Pulverization refers to reducing the fiber length, fiber diameter, etc., and fibrillation refers to increasing the fluffiness of the fibers.

[0019] The cellulose fibers (A) used in the present invention may be chemically modified by acetylation, oxidation, esterification, etherification, or the like. However, the use of non-chemically modified cellulose fibers is preferred from the viewpoint of contributing to reducing environmental impact and cost, since the chemical modification step can be omitted.

[0020] (acetylated denaturation) The acetylated modified pulp that can be used in the present invention (sometimes simply referred to as "acetylated pulp") has the hydrogen atoms of the hydroxyl groups present on the surface of the cellulose in the pulp raw material substituted with acetyl groups (CH3-CO-). The substitution with acetyl groups increases hydrophobicity and reduces aggregation during drying, improving workability and facilitating dispersion and defibration in the resin after kneading. Furthermore, the substitution of highly reactive hydroxyl groups with acetyl groups suppresses thermal decomposition of cellulose, improving heat resistance during kneading. The degree of acetyl group substitution (DS) of the acetylated pulp is preferably adjusted to 0.4 to 1.3, more preferably 0.6 to 1.1, from the viewpoints of workability and maintaining the crystallinity of the cellulose fibers.

[0021] (Acetylation reaction) The acetylation reaction can be carried out in a short time by suspending the cellulose raw material in an anhydrous aprotic polar solvent capable of swelling the raw material, such as N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF), and using acetic anhydride, acetyl chloride, or another acetyl halide, in the presence of a base. The base used in this acetylation reaction is preferably pyridine, N,N-dimethylaniline, sodium carbonate, sodium bicarbonate, or potassium carbonate, with potassium carbonate being more preferred. Furthermore, the reaction can be carried out without the use of an anhydrous aprotic polar solvent or base by using an excess of an acetylating reagent such as acetic anhydride.

[0022] The acetylation reaction is preferably carried out, for example, at room temperature to 100°C with stirring. After the reaction treatment, drying under reduced pressure may be carried out to remove the acetylation reagent. If the target degree of acetyl group substitution has not been reached, the acetylation reaction and the subsequent drying under reduced pressure may be repeated any number of times.

[0023] (Washing) The acetylated pulp obtained by the acetylation reaction is preferably subjected to a washing treatment such as water replacement after the acetylation treatment.

[0024] (dehydration) The washing treatment may be carried out with dehydration as needed. Dehydration can be carried out by pressurized dehydration using a screw press or reduced-pressure dehydration by evaporation, but centrifugal dehydration is preferred from the viewpoint of efficiency. Dehydration is preferably carried out until the solid content in the solvent is about 10 to 60%.

[0025] (Dry) The acetylated pulp that can be used in the present invention may be dried after the dewatering step. The drying can be carried out using, for example, a microwave dryer, a blower dryer, or a vacuum dryer, but a dryer that can dry while stirring, such as a drum dryer, a paddle dryer, a Nauta mixer, or a batch dryer with a stirring blade, is preferred. When drying is carried out, the moisture content of the acetylated pulp is preferably 1 to 40%, more preferably 1 to 10%, and even more preferably 1 to 5%.

[0026] (oxidative modification) Oxidation can be carried out as known in the art. Oxidation improves handling during mechanical treatment to increase pulp consistency. For example, a method is available in which raw pulp is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a substance selected from the group consisting of bromides, iodides, and mixtures thereof. This method selectively oxidizes the primary hydroxyl group at C6 of the glucopyranose ring on the cellulose surface, generating a group selected from the group consisting of aldehyde, carboxyl, and carboxylate groups. Another example is ozone oxidation. This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring that constitutes cellulose, while also decomposing the cellulose chain.

[0027] An example of a method for measuring the amount of carboxyl groups is described below. 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose is prepared, and a 0.1 M aqueous solution of hydrochloric acid is added to adjust the pH to 2.5. A 0.05 N aqueous solution of sodium hydroxide is then added dropwise, and the electrical conductivity is measured until the pH reaches 11. The amount of carboxyl groups can be calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid, where the change in electrical conductivity is gradual. Amount of carboxyl groups [mmol / g oxidized cellulose] = a [mL] x 0.05 / mass of oxidized cellulose [g]

[0028] The amount of carboxyl groups in oxidized cellulose measured in this manner is preferably 0.1 mmol / g or more, more preferably 0.3 mmol / g or more, even more preferably 0.5 mmol / g or more, and even more preferably 0.8 mmol / g or more, based on the bone dry mass. The upper limit of this amount is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and even more preferably 2.0 mmol / g or less. Therefore, this amount is preferably 0.1 to 3.0 mmol / g, more preferably 0.3 to 2.5 mmol / g, even more preferably 0.5 to 2.5 mmol / g, and even more preferably 0.8 to 2.0 mmol / g.

[0029] (Etherification and Esterification) As etherification and esterification, modifications can be carried out by known methods such as carboxymethylation, phosphate esterification, phosphite esterification, and sulfate esterification.

[0030] (carboxymethylated) Carboxymethylation can be carried out as known in the art. Carboxymethylation improves handling during mechanical processing to increase pulp consistency. The degree of carboxymethyl substitution per glucose unit of carboxymethyl cellulose can be measured, for example, by the following method: 1) Accurately weigh out approximately 2.0 g of carboxymethyl cellulose (bone dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 2) Add 100 mL of nitric acid / methanol (a solution obtained by adding 100 mL of special-grade concentrated nitric acid to 1000 mL of methanol) and shake for 3 hours to convert the carboxymethyl cellulose salt (carboxymethyl cellulose) into hydrogen-type carboxymethyl cellulose. 3) Accurately weigh out approximately 1.5 g to 2.0 g of hydrogen-type carboxymethyl cellulose (bone dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 4) Wet the hydrogen-type carboxymethyl cellulose with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. 5) Back-titrate excess NaOH with 0.1N H2SO4 using phenolphthalein as an indicator. 6) Calculate the degree of carboxymethyl substitution (DS) by the following formula: A = [(100 × F' - (0.1N H2SO4) (mL) × F) × 0.1] / (bone-dry mass of hydrogen-form carboxymethyl cellulose (g)) DS=0.162×A / (1-0.058×A) A: The amount of 1N NaOH (mL) required to neutralize 1 g of hydrogen-type carboxymethyl cellulose F: Factor of 0.1N H2SO4 F': Factor of 0.1N NaOH

[0031] The degree of carboxymethyl substitution per anhydroglucose unit in carboxymethylated cellulose is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.10 or more. The upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.35 or less. Therefore, the degree of carboxymethyl group substitution is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and even more preferably 0.10 to 0.35.

[0032] (First thermoplastic resin (B1)) The first thermoplastic resin (B1) used in the present invention is not particularly limited as long as it is a general thermoplastic resin. However, the type of thermoplastic resin used can be appropriately selected taking into consideration the affinity of the diluent resin used as the base material with cellulose. For example, when a highly hydrophobic polyolefin is used as the diluent resin, it is preferable to use a thermoplastic resin modified with a hydrophilic functional group, preferably an acid-modified one, because it has a low affinity with cellulose. Here, "hydrophilic" refers to a good affinity with water and the cellulose surface. Examples of hydrophilic functional groups include hydroxyl groups, carboxy groups, carbonyl groups, amino groups, amide groups, and sulfo groups. Examples of such first thermoplastic resins (B1) include base-modified polyolefins and acid-modified polyolefins, among which maleic anhydride-modified polypropylene (MAPP) and maleic anhydride-modified polyethylene (MAPE). Furthermore, when a relatively low-hydrophobic polyamide resin is used as the diluent resin, the same polyamide resin as the diluent resin may be used as the first thermoplastic resin (B1) because of its high affinity with cellulose.

[0033] From the viewpoint of easy dispersibility, the melting point of the first thermoplastic resin (B1) used in the present invention is preferably equal to or lower than the melting point of the diluent resin (M) described below. For example, the melting point of maleic anhydride-modified polypropylene (MAPP) is 150°C, and the melting point of maleic anhydride-modified polyethylene (MAPE) is 120°C. For example, the melting point of polyamide resin (PA6) is 220°C. Furthermore, from the viewpoint of suppressing a decrease in drying efficiency and pulp defibration efficiency due to melting in the first step, the melting point of the first thermoplastic resin (B1) is preferably equal to or higher than the thermal decomposition temperature of urea (sometimes simply abbreviated as "decomposition temperature") described below. The thermal decomposition temperature of urea is 135°C.

[0034] When a thermoplastic resin modified with a hydrophilic functional group, preferably acid-modified, is used as the first thermoplastic resin (B1), such thermoplastic resin (B1) functions as a compatibilizing resin. A compatibilizing resin functions to uniformly mix and enhance adhesion between cellulose fibers with different hydrophobicities and the diluent resin (M), which will be described later. Factors determining the characteristics of a compatibilizing resin include, for example, the amount of dicarboxylic acid added and the weight-average molecular weight of the polyolefin resin used as the base material, in the case of maleic anhydride-modified polyolefin. Polyolefin resins with a high amount of dicarboxylic acid added enhance compatibility with hydrophilic polymers such as cellulose, but the molecular weight of the resin decreases during the addition process, resulting in reduced strength of molded products. The optimal balance of dicarboxylic acid addition is 20 to 100 mg KOH / g, more preferably 45 to 65 mg KOH / g. A low addition amount reduces the number of points in the resin where interaction occurs with the hydroxyl groups of cellulose and the hydroxyl groups and modified functional groups contained in the modified cellulose. Furthermore, if the amount added is too high, self-aggregation due to hydrogen bonding between carboxyl groups in the resin and a decrease in the molecular weight of the olefin resin used as the base material due to excessive addition reactions will result in an insufficient strength as a reinforced resin. The molecular weight of the polyolefin resin is preferably 35,000 to 250,000, and more preferably 50,000 to 100,000. If the molecular weight is lower than this range, the strength of the resin will decrease, while if it is higher than this range, the viscosity will increase significantly when melted, which will reduce workability during mixing and cause molding defects.

[0035] The amount of the first thermoplastic resin (B1) is not particularly limited, but is preferably 10 to 70 mass% and more preferably 20 to 50 mass% relative to the mass (100 mass%) of the cellulose fiber (A) excluding lignin. If the amount added exceeds 70 mass%, it exceeds the amount necessary to form an interface between the cellulose and the resin, and it is thought that the strength of the composite will decrease.

[0036] The first thermoplastic resin (B1) may be used singly or as a mixed resin of two or more kinds. When used as a graft material of one or more polymers and a polyolefin, the polyolefin resin constituting the graft material is not particularly limited, but polyethylene, polypropylene, polybutylene, etc. can be used from the viewpoint of ease of production of the graft material.

[0037] (Urea(C)) In the present invention, urea (C) is used as a low-molecular weight auxiliary that provides a primary amine, from the viewpoint of improving the strength of the resulting resin composition.

[0038] Urea has a thermal decomposition temperature of 135°C and decomposes into ammonia and isocyanic acid above this temperature. By kneading urea with cellulose fibers, the unmodified hydroxyl groups newly revealed from within the fibers react with the generated isocyanic acid, promoting the formation of urethane bonds. This is thought to enhance the hydrophobicity of cellulose fibers compared to untreated urea-treated fibers. Furthermore, by simultaneously melt-kneading the cellulose fibers with the first thermoplastic resin (B1) containing an acid anhydride, the newly introduced amino groups on the surface of the cellulose fibers by urea treatment interact with the carboxylic acid of the first thermoplastic resin (B1), forming a stronger composite between the cellulose fibers and the first thermoplastic resin (B1). Furthermore, the urea-derived compound may coat the fiber surface and harden it, potentially contributing to an improvement in the modulus of elasticity.

[0039] The amount of urea to be blended is not particularly limited, but from the viewpoint of preventing the fibers from agglomerating and the strength from decreasing due to the blending amount of urea being too large, the ratio of the mass of urea (C) to the mass of cellulose fiber (A) excluding lignin is preferably less than 0.8, more preferably 0.05 or more and less than 0.75, and even more preferably 0.1 or more and less than 0.7.

[0040] (dispersion medium) Examples of the dispersion medium include water and organic solvents, and a mixture thereof may also be used. From the viewpoints of compatibility with pulp and safety, water is preferred. The amount of dispersion medium is preferably such that the amount of cellulose fiber (hereinafter referred to as the solids concentration of cellulose fiber) relative to the total amount of cellulose fiber and dispersion medium fed into the kneader is 10 to 50 mass%, more preferably 20 to 40 mass%. If the solids concentration of the cellulose fiber at the start of kneading is too low below the above-mentioned lower limit, the drying load increases and drying becomes insufficient. As a result, the dispersion medium may be carried over into the mixture kneaded in the second step (masterbatch kneading step), and the strength of the final resin composition may decrease. If the solids concentration of the cellulose fiber at the start of kneading is too high above the above-mentioned upper limit, the penetration of the dispersion medium, such as urea-containing water, into the cellulose fibers is poor, resulting in non-uniformity.

[0041] In the first step, to suppress the decomposition of urea, which is expected to have the effect of inhibiting cellulose aggregation while removing water as a dispersant, the barrel temperature of the kneader is set to a temperature range of at least 100°C to 130°C, preferably 110°C to 130°C, from the viewpoint of being above the boiling point of water but below the decomposition temperature of urea, and the raw material composition is heated while stirring to remove the dispersant and obtain a mixture. If the heating temperature in the first step is too high, the urea will decompose, reducing the effect of the urea in the second step (masterbatch kneading step) described below and preventing successful kneading. Furthermore, if the urea, which inhibits aggregation by penetrating between cellulose particles, decomposes, agglomerates are more likely to remain.

[0042] In the first step, the dispersion medium is preferably removed until the solids concentration of the resulting mixture reaches 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less. As the removal of the dispersion medium progresses, a shear force is applied to the cellulose fibers containing the urea water, and the resulting resin composition has excellent strength.

[0043] In order to increase the number of contacts with the screw, the peripheral speed of the screw of the kneader in the first step is preferably 150 mm / sec or more and 1200 mm / sec or less, and more preferably 200 mm / sec or more and 1000 mm / sec or less. The peripheral speed of the screw can be calculated by the following formula. Screw peripheral speed = screw nominal diameter x screw rotation speed x pi ÷ 60

[0044] In the first step, the raw material composition is heated to a predetermined temperature while being stirred, for example, by a single-screw or multi-screw kneader (extruder). From the viewpoint of versatility, a twin-screw kneader is preferably used. Furthermore, the kneader (extruder) used in the first step is preferably equipped with parts constituting a screw.

[0045] In the method for producing a resin composition of the present invention, the raw material composition fed into the first kneader may further contain a second thermoplastic resin (B2). In this specification, this second thermoplastic resin (B2) may be referred to as a "binder resin."

[0046] (Second thermoplastic resin (B2)) The second thermoplastic resin (B2) must not be modified with a hydrophilic functional group. From the viewpoint of easy dispersibility, the melting point of the thermoplastic resin (B2) is preferably equal to or lower than the melting point of the diluent resin (M) described below. There are no particular lower limits, but considering use in components for automobiles, home appliances, etc., it is preferably 60°C or higher, and more preferably 80°C or higher.

[0047] Examples of the second thermoplastic resin (B2) include polyolefins such as homopolypropylene (hPP, melting point: 165°C), high-density polyethylene (HDPE, melting point: 132°C), low-density polyethylene (LDPE, melting point: 95 to 135°C), and linear low-density polyethylene (LLDPE, melting point: 124°C), and block copolymers such as block polypropylene (bPP, melting point: 160 to 165°C).

[0048] The amount of the second thermoplastic resin (B2) is not particularly limited, but is preferably 1 to 50 mass% and more preferably 5 to 40 mass% relative to the mass (100 mass%) of the cellulose fiber (A) excluding lignin, so as to suppress aggregation while not contributing to a decrease in the strength of the molded body. Furthermore, the amount of the second thermoplastic resin (B2) is preferably equal to or less than the amount of the first thermoplastic resin (B1) so as not to inhibit interface formation. Furthermore, the amount of the second thermoplastic resin (B2) is preferably equal to or less than the amount of urea (C) so as not to inhibit cellulose modification.

[0049] (Second process: Masterbatch mixing process) In the second step, the mixture obtained in the first step is melt-kneaded in a kneader that is the same as or different from the kneader used in the first step to obtain a masterbatch.

[0050] As the device for melt-kneading in the second step, a single-screw or multi-screw kneader (extruder) is preferably used. From the viewpoint of being able to melt-knead the cellulose fibers (A) with the first thermoplastic resin (B1) and the second thermoplastic resin (B2) used as needed, as well as having a strong kneading force that promotes nano-pulp formation, a multi-screw kneader (extruder) such as a twin-screw kneader (extruder) or a four-screw kneader (extruder) is preferably configured to include multiple kneading screws, rotors, etc.

[0051] The set temperature of the kneader barrel when kneading the masterbatch in the second step is not particularly limited, but the upper limit of the temperature range is preferably equal to or lower than the decomposition temperature of the cellulose fiber (A), and the lower limit of the temperature range is preferably equal to or higher than the lower of the melting temperature of the first thermoplastic resin (B1) or the decomposition temperature of urea. For example, when maleic anhydride-modified polypropylene is used as the first thermoplastic resin (B1), the melt-kneading temperature in the second step preferably ranges from at least 135°C to 220°C, more preferably from 135°C to 200°C, and even more preferably from 150°C to 180°C. Furthermore, for example, when polyamide resin (PA6) is used as the first thermoplastic resin (B1), the melt-kneading temperature in the second step preferably ranges from at least 135°C to 220°C, more preferably from 150°C to 210°C.

[0052] If the dispersant is not completely removed in the first step, when the masterbatch is kneaded in the second step, the thermal decomposition products of urea will react with the dispersant, such as water, instead of with the cellulose hydroxyl groups, resulting in waste of urea.

[0053] The peripheral screw speed of the kneader in the second step is preferably 45 mm / sec or more and 1000 mm / sec or less, more preferably 80 mm / sec or more and 800 mm / sec or less, from the viewpoint of the melt viscosity of the resin in which cellulose is dispersed.

[0054] Furthermore, the relationship between the screw peripheral speed of the kneader in the first step and the screw peripheral speed of the kneader in the second step preferably satisfies the following relationship, from the viewpoint of increasing the number of contacts when drying the dispersion medium in the first step and increasing the viscosity of the mixture in the second step after drying to enhance dispersion: Screw peripheral speed in the first process ≧ Screw peripheral speed in the second process

[0055] In the method for producing a resin composition of the present invention, when the diluent resin is relatively hydrophobic and a thermoplastic resin modified with a hydrophilic functional group, preferably acid-modified, is used as the first thermoplastic resin (B1), it is preferable to further use a second thermoplastic resin (B2), which is a thermoplastic resin that is not modified with a hydrophilic functional group, from the viewpoint of suppressing the occurrence of fibrous aggregation in the final resin composition.

[0056] In the method for producing a resin composition of the present invention, when a second thermoplastic resin (B2) (binder resin) is used, the binder resin may be included in the raw material composition in the first step as described above, or alternatively, the binder resin may be charged into a kneader in the second step and melt-kneaded together with the mixture obtained in the first step.

[0057] The method for producing a resin composition of the present invention may include a step of washing the masterbatch with water after the second step. The temperature of the water used for washing is preferably room temperature to 100°C, more preferably 50 to 100°C. After washing, it is preferable to dry the masterbatch until the water content reaches about 0.1 to 5%, from the viewpoints of preventing decomposition of the diluent resin (M) used as the base material and reducing the drying load during kneading.

[0058] (Third step: Dilution and kneading step) In the third step, the masterbatch obtained in the second step is kneaded with a diluent resin.

[0059] (Resin for dilution (M)) The diluent resin (M) used in the present invention may be any of the following general thermoplastic resins having a melting temperature of 250° C. or less. The diluent resin (M) may be used alone or in combination of two or more resins.

[0060] Common thermoplastic resins that can be used include polyolefin resins, polyamide resins, polyvinyl chloride, polystyrene, polyvinylidene chloride, fluororesins, (meth)acrylic resins, polyesters, polylactic acid, copolymer resins of lactic acid and esters, polyglycolic acid, acrylonitrile-butadiene-styrene copolymers (ABS resins), polyphenylene oxide, polyurethanes, polyacetals, vinyl ether resins, polysulfone resins, and cellulose resins (such as triacetylated cellulose and diacetylated cellulose).

[0061] As the polyolefin resin, polyethylene, polypropylene (hereinafter also referred to as "PP"), ethylene-propylene copolymer, polyisobutylene, polyisoprene, polybutadiene, etc. can be used.

[0062] Polyamide resins (PA) are also expected to interact with hydroxyl groups of cellulose that have not been affected by urea, making them suitable for use. Examples of PA include aliphatic PAs such as polyamide 6 (nylon 6, PA6), polyamide 11 (nylon 11, PA11), polyamide 12 (nylon 12, PA12), polyamide 66 (nylon 66, PA66), polyamide 46 (nylon 46, PA46), polyamide 610 (nylon 610, PA610), and polyamide 612 (nylon 612, PA612), as well as aromatic PAs composed of aromatic diamines such as phenylenediamine and aromatic dicarboxylic acids such as terephthaloyl chloride or isophthaloyl chloride, or derivatives thereof. From the viewpoint of high affinity with cellulose fibers and cellulose nanofibers, aliphatic PAs are preferred, with PA6, PA11, and PA12 being more preferred, and PA6 being particularly preferred. Furthermore, one type of polyamide resin may be used alone, or two or more types of polyamide resins may be mixed together.

[0063] The resins exemplified above can be used as homopolymers or as block copolymers containing resins having various known functions in a half amount or less.

[0064] When adding the diluent resin (M) and melt-kneading, the masterbatch and the diluent resin (M) may be mixed at room temperature without heating and then melt-kneaded, or they may be mixed while being heated and then melt-kneaded.

[0065] The equipment used for melt-kneading the diluent resin (M) can be the same as that used in the second step (masterbatch kneading step). The heating temperature during melt-kneading is preferably set within ±10°C of the minimum processing temperature recommended by the thermoplastic resin supplier for the diluent resin (M). By setting the temperature within this range, the pulp and resin can be uniformly mixed.

[0066] The resin composition produced by the production method of the present invention may further contain additives such as surfactants, polysaccharides such as starches and alginic acid, natural proteins such as gelatin, glue and casein, inorganic compounds such as tannin, zeolite, ceramics and metal powder, colorants, plasticizers, fragrances, pigments, flow control agents, leveling agents, conductive agents, antistatic agents, UV absorbers, UV dispersants, deodorizers, antioxidants, etc. The content of any additive may be appropriately determined within a range that does not impair the effects of the present invention.

[0067] According to the present invention, a resin composition can be obtained that is excellent in tensile strength and flexural strength and further suppresses poor appearance due to the remaining fibrous texture derived from cellulose, and a low-cost method for producing the resin composition can be provided.

[0068] (Application) The resin composition produced by the production method of the present invention can be used to produce molding materials and molded articles (molding materials and molded articles). Examples of the shape of the molded article include films, sheets, plates, pellets, powders, and various shapes such as three-dimensional structures. Molding methods that can be used include mold molding, injection molding, extrusion molding, blow molding, and foam molding.

[0069] The molded body (molded body) can be used not only in the field of fiber-reinforced plastics where matrix molded bodies (molded bodies) containing cellulose fibers are used, but also in fields where thermoplasticity and mechanical strength (tensile strength, etc.) are required.

[0070] They can be effectively used as interior, exterior and structural materials for transportation equipment such as automobiles, trains, ships and airplanes; cases, structural materials and internal parts for electrical appliances such as computers, televisions, telephones and watches; cases, structural materials and internal parts for mobile communication devices such as mobile phones; cases, structural materials and internal parts for portable music players, video players, printing equipment, copying equipment, sporting goods and the like; building materials; office equipment such as stationery, containers and the like. [Example]

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0072] (Measuring Canadian Standard Freeness (CSF)) The Canadian standard freeness of the cellulose fibers used in the examples and comparative examples was measured in accordance with JIS P 8121-2:2012.

[0073] (Measurement of lignin content) The lignin content of the cellulose fibers used in the examples and comparative examples was measured based on the Klason method, which is a commonly used quantitative method (Klason lignin).

[0074] (Measurement of tensile strength) 150 g of the pellet-like resin molded bodies obtained in the Examples, Comparative Examples, and Reference Examples were placed in a small molding machine ("MC15" manufactured by Xplore Instruments) and molded into dumbbell-shaped test specimens (Type A12, JIS K7139) at a heating barrel (cylinder) temperature of 200°C and a mold temperature of 40°C. The resulting test specimens were measured for modulus of elasticity, maximum stress (yield strength), and fracture displacement (strain and elongation until fracture) using a precision universal testing machine ("Autograph AG-Xplus" manufactured by Shimadzu Corporation) at a test speed of 1 mm / min and an initial gauge length of 30 mm. The modulus of elasticity and maximum stress were measured as the reinforcement ratio, where the modulus of elasticity and maximum stress of the dilution resin were set to 100, respectively. The results are shown in Tables 1, 2, and 3. The fracture displacement measurements are shown in Tables 1, 2, and 3.

[0075] (Measurement of bending strength) 150 g of the pellet-like resin molded body obtained in the Examples, Comparative Examples, and Reference Examples was placed in a small molding machine ("MC15" manufactured by Xplore Instruments) and molded into bar test specimens (4 mm thick, 80 mm parallel length) at a heating barrel (cylinder) temperature of 250°C and a mold temperature of 40°C. The elastic modulus, maximum stress, and fracture displacement of the obtained test specimens were measured using a precision universal testing machine ("Autograph AG-Xplus" manufactured by Shimadzu Corporation) at a test speed of 10 mm / min and a support distance of 64 mm. The elastic modulus and maximum stress were measured as reinforcement ratios, where the values ​​of the elastic modulus and maximum stress of the dilution resin were set to 100. The results are shown in Tables 1, 2, and 3. The fracture displacement measurements are shown in Tables 1, 2, and 3.

[0076] (density measurement) The density of the pellet-shaped resin molded bodies obtained in the Examples, Comparative Examples and Reference Examples was measured using a dry automatic density meter, Accupyc II 1340-10CC (manufactured by Shimadzu Corporation).

[0077] (Film appearance evaluation) 60 mg of the pellet-like resin molded product obtained in the Examples, Comparative Examples, and Reference Examples was pressed at 200°C to 2.5 MPa using a compression molding machine manufactured by Shinto Metal Industries Co., Ltd. to produce a film approximately 35 mm in diameter and 0.1 mm thick. The film was visually inspected for the presence or absence of fibrous material, and if present, its condition was evaluated according to the following criteria. The results are shown in Tables 2 and 3. A: No fibrous material is visible in the film (Figure 1). B: The fiber remains visible in the film, but the boundary with the resin matrix is ​​unclear (Figure 2). C: The fiber bundles are clearly visible in the film, and the boundary with the resin matrix is ​​clear (Figure 3).

[0078] (Materials used in the production of masterbatches and resin compositions) (A) Cellulose fiber (decomposition temperature: 299°C) (B1) First thermoplastic resin Maleic anhydride-modified polypropylene (MAPP): (Toyotack PMA-H1000P, manufactured by Toyobo Co., Ltd.: dicarboxylic acid addition amount 57 mg KOH / g, melting point: 150°C) (MAPP is a thermoplastic resin modified with hydrophilic functional groups.) Powdered polyamide resin (PA6): (Unitika powder, A1020LP, melting point: 220°C) (B2) Second thermoplastic resin: A thermoplastic resin that is not modified with a hydrophilic functional group (sometimes referred to as a "binder resin"). High-density polyethylene (HDPE): (HJ580 manufactured by Japan Polyethylene Co., Ltd., melting point: 134°C) (C) Urea: (Powder form: manufactured by Mitsui Chemicals) (M) Dilution resin Homopolypropylene (hPP): (PP MA04A manufactured by Japan Polypropylene Corporation, melting point: 165°C) High-density polyethylene (HDPE): (HJ580 manufactured by Japan Polyethylene Co., Ltd., melting point: 134°C) Polyamide resin (PA6): (1013B manufactured by Ube Industries, Ltd., melting point: 220°C) (antioxidant) Hindered phenolic antioxidant (Irganox 1010 manufactured by BASF Japan Ltd.)

[0079] Example 1 (Masterbatch manufacturing) Cellulose fiber 1 (unbeaten softwood unbleached kraft pulp (NUKP) (Canadian Standard Freeness >600 mL, lignin content 1% to 30% by mass) solids (26.4 g), 7.2 g of MAPP, 7.2 g of urea, and a dispersant of water sufficient to achieve a NUKP solids concentration of 50% by mass were mixed in a twin-screw mixer at 100°C to 130°C and a screw peripheral speed of 212 mm / sec to obtain a mixture with a solids concentration of 98.0% by mass (dry mixing). The entire mixture was mixed with 7.2 g of HDPE as a binder resin in a twin-screw mixer at a temperature of 180°C or less and a screw peripheral speed of 126 mm / sec to obtain a masterbatch (masterbatch mixing).

[0080] (Production of Resin Composition) 20 g of the obtained masterbatch was mixed with 80 g of diluent resin (hPP) and kneaded using a twin-screw kneader under heating conditions of 180°C or less. The molten mixture was then pelletized using a pelletizer to obtain a pellet-shaped resin composition (molded product) containing cellulose fiber 1, MAPP, urea-derived compound, HDPE, and diluent resin (hPP).

[0081] Example 2 Dry kneading was carried out in the same manner as in Example 1, except that in the production of the masterbatch, the amount of water used as a dispersion medium was changed to an amount such that the solid content concentration of NUKP became 40% by mass, and a mixture with a solid content concentration of 97.6% by mass was obtained. A masterbatch and a pellet-shaped resin composition (molded product) were obtained in the same manner as in Example 1, except that the obtained mixture was used.

[0082] Example 3 In producing the masterbatch, dry kneading was carried out in the same manner as in Example 1, except that the amount of water used as a dispersion medium was changed to an amount such that the solid content concentration of NUKP became 30% by mass, and a mixture with a solid content concentration of 98.3% by mass was obtained. A masterbatch and a pellet-shaped resin composition (molded product) were obtained in the same manner as in Example 1, except that the obtained mixture was used.

[0083] Example 4 Dry kneading was carried out in the same manner as in Example 1, except that in the production of the masterbatch, the amount of water used as a dispersion medium was changed to an amount such that the solid content concentration of NUKP became 20% by mass, and a mixture with a solid content concentration of 97.8% by mass was obtained. A masterbatch and a pellet-shaped resin composition (molded product) were obtained in the same manner as in Example 1, except that the obtained mixture was used.

[0084] Example 5 Dry kneading was carried out in the same manner as in Example 1, except that in the production of the masterbatch, the amount of water used as a dispersion medium was changed to an amount such that the solid content concentration of NUKP became 10% by mass, and a mixture with a solid content concentration of 96.8% by mass was obtained. A masterbatch and a pellet-shaped resin composition (molded product) were obtained in the same manner as in Example 1, except that the obtained mixture was used.

[0085] Example 6 Dry kneading was carried out in the same manner as in Example 1 to obtain a mixture with a solid content of 99.0% by mass. Using the obtained mixture, masterbatch kneading was carried out in the same manner as in Example 1, except that the screw peripheral speed was changed to 157 mm / sec. A pellet-shaped resin composition (molded product) was obtained in the same manner as in Example 1, except that the obtained masterbatch was used.

[0086] Example 7 Dry kneading was carried out in the same manner as in Example 2 to obtain a mixture with a solid content of 98.3% by mass. Using the obtained mixture, masterbatch kneading was carried out in the same manner as in Example 1, except that the screw peripheral speed was changed to 157 mm / sec. A pellet-shaped resin composition (molded product) was obtained in the same manner as in Example 1, except that the obtained masterbatch was used.

[0087] Example 8 Dry kneading was carried out in the same manner as in Example 3 to obtain a mixture with a solid content of 98.7% by mass. Using the obtained mixture, masterbatch kneading was carried out in the same manner as in Example 1, except that the screw peripheral speed was changed to 157 mm / sec. A pellet-shaped resin composition (molded product) was obtained in the same manner as in Example 1, except that the obtained masterbatch was used.

[0088] Example 9 Dry kneading was carried out in the same manner as in Example 4 to obtain a mixture with a solid content of 98.7% by mass. Using the obtained mixture, masterbatch kneading was carried out in the same manner as in Example 1, except that the screw peripheral speed was changed to 157 mm / sec. A pellet-shaped resin composition (molded product) was obtained in the same manner as in Example 1, except that the obtained masterbatch was used.

[0089] Example 10 (Production of cellulose fiber 2) Unbleached softwood kraft pulp (NUKP) with a solids concentration of 18% by mass was beaten three times using a single-disc refiner (manufactured by Kumagaya Riki Kogyo Co., Ltd., plate blade width: 4 mm, groove width: 5 mm) at a clearance of 0.25 mm until the Canadian standard freeness reached 233 mL, yielding cellulose fiber 2 with a moisture content of 20%. The lignin content of cellulose fiber 2 was 7.9% by mass.

[0090] (Masterbatch manufacturing) 26.1 g of cellulose fiber 2 (solids content: 20%), 7.2 g of MAPP, and 7.2 g of urea were dried and stirred in a twin-screw kneader at 100°C to 130°C and a screw peripheral speed of 212 mm / sec (dry kneading) to obtain a mixture with a solids concentration of 98.5% by mass. The entire amount of this mixture and 7.2 g of HDPE were kneaded in a twin-screw kneader at a temperature of 180°C or less and a screw peripheral speed of 126 mm / sec (masterbatch kneading) to obtain a masterbatch.

[0091] (Production of Resin Composition) 20 g of the obtained masterbatch was mixed with 80 g of diluent resin (hPP) and kneaded using a twin-screw kneader under heating conditions of 180°C or less. The molten mixture was then pelletized using a pelletizer to obtain a pellet-shaped resin composition (molded product) containing cellulose fiber 2, MAPP, urea-derived compound, HDPE, and diluent resin (hPP).

[0092] Example 11 Dry kneading was carried out in the same manner as in Example 10 to obtain a mixture with a solid content of 98.4% by mass. Using the obtained mixture, masterbatch kneading was carried out in the same manner as in Example 10, except that the screw peripheral speed was changed to 157 mm / sec. A pellet-shaped resin composition (molded product) was obtained in the same manner as in Example 10, except that the obtained masterbatch was used.

[0093] [Table 1]

[0094] As can be seen from Table 1, the resin compositions of Examples 1 to 11 were produced through the following steps: a first step (drying and kneading step) in which a raw material composition containing at least cellulose fiber, a thermoplastic resin modified with a hydrophilic functional group (MAPP) as a first thermoplastic resin, urea, and water as a dispersant was placed in a kneader and heated with stirring at a temperature ranging from 100°C to 130°C to dry and stir the mixture, remove the dispersant, and obtain a mixture; a second step (masterbatch kneading step) in which the resulting mixture was melt-kneaded in the kneader to obtain a masterbatch; and a third step (dilution and kneading step) in which the resulting masterbatch was kneaded with hPP as a diluent resin. All of these resin compositions had superior tensile strength (elastic modulus, maximum stress) and flexural strength (elastic modulus, maximum stress) compared to Reference Example 1, in which a test piece was produced using only the diluent resin (hPP).

[0095] Example 12 (Masterbatch manufacturing) A masterbatch was obtained in the same manner as in Example 3, except for the addition of an antioxidant. Specifically, 26.4 g of unbeaten softwood unbleached kraft pulp (NUKP) (Canadian Standard Freeness >600 mL, lignin content 1% by mass or more, 30% by mass or less) as cellulose fiber 1 (solid content), 7.2 g of MAPP, 7.2 g of urea, and 1.2 g of antioxidant as a dispersion medium, in an amount of water such that the NUKP solids concentration was 30% by mass, were dried and stirred in a twin-screw kneader under conditions of 100°C to 130°C and a screw peripheral speed of 212 mm / sec (dry kneading), to obtain a mixture with a solids concentration of 98.3% by mass. The entire amount of this mixture and 7.2 g of HDPE as a binder resin were kneaded in a twin-screw kneader under conditions of a temperature of 180°C or less and a screw peripheral speed of 126 mm / sec (masterbatch kneading), to obtain a masterbatch.

[0096] (Production of Resin Composition) 20.5 g of the obtained masterbatch was mixed with 79.5 g of diluent resin (hPP) and kneaded using a twin-screw kneader under heating conditions of 180°C or less. The molten mixture was then pelletized using a pelletizer to obtain a pellet-shaped resin composition (molded product) containing cellulose fiber 1, MAPP, urea-derived compound, HDPE, and diluent resin (hPP).

[0097] Example 13 A masterbatch was obtained in the same manner as in Example 12, except that the timing of adding HDPE as a binder resin was changed from masterbatch mixing to dry mixing. Specifically, during dry mixing, cellulose fiber 1, MAPP, urea, and water as a dispersion medium were added to HDPE and dry mixed using a twin-screw kneader under the same conditions as in Example 12, to obtain a mixture with a solid content of 98.6% by mass. This mixture was then kneaded using the twin-screw kneader under the same conditions as in Example 12 to obtain a masterbatch. A pellet-shaped resin composition (molded product) was obtained in the same manner as in Example 12, except that the obtained masterbatch was used.

[0098] Example 14 A pellet-shaped resin composition (molded body) containing cellulose fiber 1, MAPP, a urea-derived compound, HDPE, and a diluent resin (HDPE) was obtained in the same manner as in Example 12, except that HDPE was used instead of hPP as the diluent resin in the production of the resin composition.

[0099] Example 15 A pellet-shaped resin composition (molded body) containing cellulose fiber 1, MAPP, a urea-derived compound, HDPE, and a diluent resin (HDPE) was obtained in the same manner as in Example 13, except that HDPE was used instead of hPP as the diluent resin in the production of the resin composition.

[0100] (Comparative Example 1) (Masterbatch manufacturing) A masterbatch was obtained in the same manner as in Example 12, except that HDPE was not added as a binder resin, the dry kneading step and the masterbatch kneading step were not separated, and drying and masterbatch kneading were carried out simultaneously at 150°C. Note that, because the dry kneading step was not carried out, the masterbatch kneading was carried out in the presence of water, which resulted in a reaction between the water and urea, producing a foul odor (ammonia odor), and making the product less easy to work with.

[0101] (Production of Resin Composition) 20.5 g of the obtained masterbatch was mixed with 79.5 g of diluent resin (hPP) and kneaded using a twin-screw kneader under heating conditions of 180°C or less. The molten mixture was then pelletized using a pelletizer to obtain a pellet-shaped resin composition (molded product) containing cellulose fiber 1, MAPP, a urea-derived compound, and diluent resin (hPP).

[0102] (Comparative Example 2) A masterbatch with a solid content of 99.1% by mass was obtained in the same manner as in Comparative Example 1, except that 7.2 g of HDPE was added as a binder resin and kneaded. Since the dry kneading step was not performed, the masterbatch was kneaded in the presence of water, resulting in a reaction between the water and urea, which produced a foul odor (ammonia odor) and made the product less workable. A pellet-shaped resin composition (molded product) was obtained in the same manner as in Example 1, except that the obtained masterbatch was used.

[0103] (Comparative Example 3) (Preparation of dry mixture) 26.4 g of unbeaten softwood unbleached kraft pulp (NUKP) (Canadian Standard Freeness >600 mL, lignin content ≥1% by mass, ≤30% by mass) as cellulose fiber 1 (solids content), 7.2 g of MAPP, 7.2 g of urea, 7.2 g of HDPE as binder resin, 1.2 g of antioxidant, and a dispersing medium of water sufficient to achieve a NUKP solids concentration of 30% by mass were dried and stirred (dry-mixed) in a twin-screw mixer at a temperature of 105°C and a screw peripheral speed of 212 mm / sec to obtain a dry mixture with a solids concentration of 98.5% by mass. The resulting dry mixture was used in the next step without undergoing the masterbatch mixing process.

[0104] (Production of Resin Composition) 20.5 g of the obtained dry mixture was mixed with 79.5 g of diluent resin (hPP) and kneaded using a twin-screw kneader under heating conditions of 180°C or less. The molten mixture was then pelletized using a pelletizer to obtain a pellet-shaped resin composition (molded product) containing cellulose fiber 1, MAPP, urea-derived compound, HDPE, and diluent resin (hPP).

[0105] [Table 2]

[0106] As can be seen from Table 2, the resin compositions of Examples 12 to 15 were produced through the following steps: a first step (drying and kneading step) in which a raw material composition containing at least cellulose fiber, a thermoplastic resin modified with a hydrophilic functional group (MAPP) as a first thermoplastic resin, urea, and water as a dispersant was placed in a kneader and heated with stirring at a temperature ranging from 100°C to 130°C to dry and stir the mixture, remove the dispersant, and obtain a mixture; a second step (masterbatch kneading step) in which the mixture was melt-kneaded in the kneader to obtain a masterbatch; and a third step (dilution and kneading step) in which the masterbatch was kneaded with hPP or HDPE as a diluent resin. All of these resin compositions had superior tensile strength (elastic modulus, maximum stress) and flexural strength (elastic modulus, maximum stress) compared to Reference Examples 1 and 2, which used test pieces prepared using only the same type of diluent resin that did not contain cellulose fiber. Furthermore, the results of the film appearance evaluation were excellent compared to the resin compositions of Comparative Examples 1 to 3 in which the first step (dry kneading step) and the second step (masterbatch kneading step) were not separated.

[0107] Example 16 (Production of acetylated cellulose fiber 3) (beating treatment) Unbleached softwood kraft pulp (NUKP) with a solids concentration of 18% by mass was beaten three times using a single-disc refiner (Kumagaya Riki Kogyo Co., Ltd., plate blade width: 4 mm, groove width: 5 mm) at a clearance of 0.25 mm until the Canadian standard freeness reached 200 mL, yielding cellulose fibers with a solids concentration of 20%. The lignin content of the resulting cellulose fibers was 9% by mass.

[0108] (Acetylation treatment) 150 kg of the above-mentioned beaten cellulose fiber (30 kg solids) was placed in a mixer ("FM150L" manufactured by Nippon Coke & Engineering Co., Ltd.), and stirring was started. The mixture was then dehydrated under reduced pressure at 80°C. 20 kg of acetic anhydride was then added, and the mixture was reacted at 80°C for 1 hour. After the reaction, the mixture was dried under reduced pressure at 80°C and washed with water to obtain acetylated cellulose fiber (acetylated modified NUKP) 3. The acetylated cellulose fiber 3 was then placed in a dryer and dried under reduced pressure at 60 to 70°C. The moisture content of the obtained acetylated cellulose fiber 3 was measured using an infrared moisture meter. The moisture content was 2.3% by mass. The acetyl group substitution degree (DS) of the acetylated cellulose fiber 3 was 0.7.

[0109] (Masterbatch manufacturing) A mixture with a solids concentration of 98.5% by mass was obtained by drying and stirring 25 g of acetylated cellulose fiber 3 (solid content), 7 g of powdered polyamide resin, 6 g of urea, 2 g of antioxidant, and a dispersion medium of water in an amount sufficient to give a solids concentration of 30% by mass of acetylated cellulose fiber 3 in a twin-screw kneader at 100°C to 130°C and a screw peripheral speed of 212 mm / sec (dry kneading). The total amount of this mixture was mixed with the same polyamide resin as the dilution polyamide resin in a mass ratio of 3:2, and the mixture was kneaded in a twin-screw kneader at 190°C to 220°C and a screw peripheral speed of 126 mm / sec (masterbatch kneading) to give a masterbatch.

[0110] (Production of Resin Composition) 30 g of the obtained masterbatch was mixed with 60 g of diluent resin (polyamide resin: PA6) and kneaded using a twin-screw kneader under heating conditions of 220°C or less. The molten mixture was then pelletized using a pelletizer to obtain a pellet-shaped resin composition (molded product) containing acetylated cellulose fibers 3, powdered polyamide resin, urea-derived compound, and diluent resin (polyamide resin: PA6).

[0111] Comparative Example 4 (Masterbatch manufacturing) 25 g of acetylated cellulose fiber 3 (solid content), 39.6 g of powdered polyamide resin, and 2 g of antioxidant were mixed, and without performing a dry kneading process, the mixture was kneaded using a twin-screw kneader at a temperature of 220°C or less and a screw peripheral speed of 126 mm / sec (masterbatch kneading) to obtain a masterbatch with a solid content of 99.1 mass%.

[0112] A pellet-shaped resin composition (molded body) containing acetylated cellulose fiber 3, powdered polyamide resin, and diluent resin (polyamide resin: PA6) was obtained in the same manner as in Example 16, except that 30 g of the obtained masterbatch and 60 g of diluent resin (polyamide resin: PA6) were used.

[0113] [Table 3]

[0114] As can be seen from Table 3, the resin composition of Example 16 was produced through the following steps: a raw material composition containing at least acetylated cellulose fiber as the cellulose fiber, polyamide resin (PA6) as the first thermoplastic resin, urea, and water as the dispersant was placed in a kneader, and the mixture was dried and stirred by heating at a temperature range of at least 100°C to 130°C while stirring, to remove the dispersant and obtain a mixture; a second step (masterbatch kneading step) was melt-kneaded in the kneader to obtain a masterbatch; and a third step (dilution kneading step) was kneaded with polyamide resin (PA6) as the diluent resin. The resin composition of Example 16 had superior tensile strength (elastic modulus, maximum stress) and flexural strength (elastic modulus, maximum stress) compared to Reference Example 3, which used test pieces prepared using only the same type of diluent resin that did not contain cellulose fiber. Furthermore, compared to the resin composition of Comparative Example 4, which did not use urea, did not undergo the first step (dry kneading step), and underwent the second step (masterbatch kneading step), the resin composition had superior tensile strength (elastic modulus) and flexural strength (elastic modulus, maximum stress).

Claims

1. a first step of feeding a raw material composition containing at least cellulose fibers, a first thermoplastic resin, urea, and a dispersion medium into a first kneader, heating the raw material composition with stirring at a temperature in the range of at least 100°C to 130°C, and removing the dispersion medium to obtain a mixture; a second step of melt-kneading the mixture obtained in the first step in the first kneader or the second kneader to obtain a masterbatch; a third step of kneading the masterbatch obtained in the second step with a diluent resin, The method for producing a resin composition, wherein the melt-kneading temperature in the second step is within a temperature range of at least 135°C or higher and 220°C or lower.

2. The method for producing a resin composition according to claim 1 , wherein the first thermoplastic resin is a thermoplastic resin modified with a hydrophilic functional group.

3. 3. The method for producing a resin composition according to claim 1, wherein the amount of the dispersion medium added to the first kneader in the first step is an amount such that the solids concentration of the cellulose fibers is 10% by mass to 50% by mass.

4. The first kneader and the second kneader each include a part that constitutes a screw, The relationship between the screw peripheral speed of the first kneader in the first step and the screw peripheral speed of the first kneader or the second kneader in the second step satisfies the following relationship. The method for producing a resin composition according to any one of claims 1 to 3. Screw peripheral speed in the first process ≧ Screw peripheral speed in the second process

5. 3. The method for producing a resin composition according to claim 2, wherein in the first step, the raw material composition further contains a second thermoplastic resin that is a thermoplastic resin that is not modified with a hydrophilic functional group.

6. 3. The method for producing a resin composition according to claim 2, wherein in the second step, a second thermoplastic resin that is a thermoplastic resin not modified with a hydrophilic functional group is further added to the first kneader or the second kneader and melt-kneaded together with the mixture.

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