Resin composition, molded body using same, and method for producing resin composition

Abstract

The resin composition is a melt-kneaded product of a mixture (α) containing a cellulose-based substance (A) and a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant, and a thermoplastic resin (C).

Description

Resin composition, molded article using the same, and method for producing resin composition

[0001] The present invention relates to a resin composition containing a cellulose-based material, a molded article using the same, and a method for producing the resin composition.

[0002] Fiber-reinforced plastics are lightweight and have excellent mechanical strength, and therefore are used in automotive exterior panels and interior materials, electrical equipment housings, building materials, etc. to reduce greenhouse gas emissions, and are expected to be one of the means for building a decarbonized society. In particular, increasing the strength of fiber-reinforced plastics and efficiently manufacturing them can reduce the amount of plastic and energy used, and are expected to be one of the means for efficiently reducing greenhouse gas emissions.

[0003] Japanese Patent Laid-Open Publication No. 63-33442 (Patent Document 1) discloses a polyolefin composition containing 10 to 97 wt% polyolefin, 3 to 90 wt% ethylene-vinyl ester copolymer or a copolymer of ethylene and an unsaturated carboxylic acid or a derivative thereof, and 10 to 120 wt% plant fibers primarily composed of fiberized cellulose per 100 wt% of the polyolefin and the copolymer combined. Japanese Patent Laid-Open Publication No. 2018-104650 (Patent Document 2) discloses a melt-molding resin composition containing a saponified ethylene-vinyl ester copolymer and a cellulose nanofiller, and also describes that the resin composition can contain other thermoplastic resins such as polyolefin resins. Japanese Patent Laid-Open Publication No. 2019-218450 (Patent Document 3) discloses a method for producing a cellulose resin composite containing cellulose and polypropylene resin, in which cellulose, polypropylene resin, acid-modified polyolefin resin, and polyvinyl alcohol having a viscosity coefficient of 0.20 or less are kneaded together in a water-containing state.

[0004] JP 63-33442 A JP 2018-104650 A JP 2019-218450 A

[0005] However, molded articles made from conventional resin compositions containing cellulosic fibers do not necessarily have sufficiently high mechanical strength.

[0006] The present invention has been made in consideration of the problems associated with the above-mentioned conventional technology, and aims to provide a resin composition containing a cellulose-based substance and a thermoplastic resin and capable of forming a molded body having excellent mechanical strength, a molded body made from the same, and a method for producing the resin composition.

[0007] As a result of extensive research to achieve the above object, the present inventors have found that a molded article having excellent mechanical strength can be obtained by using a resin composition obtained by melt-kneading a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant, with a thermoplastic resin (C), and have thus completed the present invention.

[0008] That is, the present invention provides the following aspects.

[0009] [1] A resin composition which is a melt-kneaded mixture of a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant, and a thermoplastic resin (C).

[0010] [2] The resin composition according to [1], wherein the mixture (α) further contains polyamines (D).

[0011] [3] The resin composition according to [2], wherein the mixture (α) further contains a carboxylic acid (E).

[0012] [4] The resin composition according to [2], which is a melt-kneaded product of the mixture (α) and a melt-kneaded product (β) containing the thermoplastic resin (C) and a carboxylic acid (E).

[0013] [5] The content of the polyvinyl acetate polymer emulsion (B) in the resin composition is 0.1 to 15 mass% in terms of polyvinyl acetate polymer. [1] The resin composition according to any one of [4] to [5].

[0014] [6] A molded article made of the resin composition according to any one of [1] to [5].

[0015] [7] A method for producing a resin composition, comprising: a step of preparing a mixture (α) by mixing a cellulose-based material (A) with a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant; and a step of melt-kneading the mixture (α) with a thermoplastic resin (C).

[0016] [8] The method for producing a resin composition according to [7], further comprising mixing a polyamine (D) into the mixture (α).

[0017] [9] The method for producing a resin composition according to [8], further comprising mixing a carboxylic acid (E) into the mixture (α).

[0018]

[10] The method for producing a resin composition according to [8], further comprising a step of melt-kneading the thermoplastic resin (C) and the carboxylic acid (E) to prepare a melt-kneaded product (β), wherein the mixture (α) and the melt-kneaded product (β) are melt-kneaded.

[0019]

[11] The method for producing a resin composition according to any one of [7] to

[10] , wherein the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B) are mixed together so that the content of the polyvinyl acetate polymer emulsion (B) in the resulting resin composition is 0.1 to 15 mass% in terms of polyvinyl acetate polymer.

[0020] Although the reason why a molded article made from the resin composition of the present invention has excellent mechanical strength is not entirely clear, the present inventors speculate as follows. That is, the resin composition of the present invention is a melt-kneaded mixture of the thermoplastic resin (C) and a mixture (α) containing the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B). It is speculated that in the mixture (α), the polyvinyl acetate polymer emulsion (B) (preferably, a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the cellulose-based material (A). It is speculated that when such a mixture (α) is melt-kneaded with the thermoplastic resin (C), the cellulose-based material (A) is highly dispersed in the thermoplastic resin (C) without aggregation due to the protective effect of the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhered to the surface of the cellulose-based material (A). Thereafter, as the melt-kneading is continued and the water is removed, it is presumed that a polyvinyl acetate polymer composition layer containing polyvinyl alcohol is formed on the surface of the cellulosic material (A) by the adhered polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer), as shown in FIG. 1A . Since the polyvinyl acetate polymer (vinyl acetate homopolymer) has hydrophobic methyl groups in its side chains, the formation of a polyvinyl acetate polymer composition layer on the surface of the cellulosic material (A) imparts hydrophobicity to the surface of the cellulosic material (A). As a result, the affinity between the thermoplastic resin (C) and the surface of the cellulosic material (A) is increased, and the cellulosic material (A) is highly dispersed in the thermoplastic resin (C). It is presumed that the molded article made from the resin composition of the present invention will have excellent mechanical strength.

[0021] Furthermore, when the resin composition of the present invention further contains the polyamines (D), it is presumed that in the mixture (α), the polyamines (D) adhere to the surface of the cellulose-based material (A) to form a polyamine (D) layer, and that the polyvinyl acetate polymer emulsion (B) (preferably a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the polyamine (D) layer. It is presumed that when such a mixture (α) and the thermoplastic resin (C) are melt-kneaded, the cellulose-based material (A) is not aggregated but is highly dispersed in the thermoplastic resin (C) due to the protective effect of the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhered to the surface of the polyamine (D) layer on the surface of the cellulose-based material (A). Thereafter, when the melt-kneading is continued and the water is removed, it is presumed that the polyamine (D) layer and the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhering to the surface of the cellulose-based material (A) form the polyamine (D) layer and a polyvinyl acetate polymer composition layer containing polyvinyl alcohol, as shown in Figure 1B. Since this polyvinyl acetate polymer composition layer is firmly adhered to the surface of the cellulose-based material (A) via the polyamine (D) layer, it is presumed that the mechanical strength of a molded article made from the resin composition of the present invention is improved.

[0022] Furthermore, when the resin composition of the present invention is a melt-kneaded mixture of the thermoplastic resin (C) and a mixture (α) containing the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), the polyamines (D), and the carboxylic acids (E), it is presumed that in the mixture (α), a layer of a reaction product of the polyamines (D) and the carboxylic acids (E) is formed on the surface of the cellulose-based material (A), and that the polyvinyl acetate polymer emulsion (B) (preferably a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the reaction product layer. It is presumed that when such a mixture (α) and the thermoplastic resin (C) are melt-kneaded, the cellulose-based material (A) is highly dispersed in the thermoplastic resin (C) without agglomeration due to the protective effect of the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhered to the surface of the reaction product layer on the surface of the cellulose-based material (A). Thereafter, when the melt-kneading is continued and the water is removed, it is presumed that a reaction product layer of the polyamines (D) and the carboxylic acids (E) and a polyvinyl acetate polymer composition layer containing polyvinyl alcohol are formed on the surface of the cellulosic material (A) by the reaction product layer and the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhering to the surface, as shown in Figure 1C. This polyvinyl acetate polymer composition layer is further firmly adhered to the surface of the cellulosic material (A) via the layer consisting of the reaction product of the polyamines (D) and the carboxylic acids (E), and therefore it is presumed that the mechanical strength of the molded article made from the resin composition of the present invention is further improved.

[0023] Furthermore, when the resin composition of the present invention is a melt-kneaded mixture of a mixture (α) containing the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamines (D), and a melt-kneaded mixture (β) containing the thermoplastic resin (C) and the carboxylic acids (E), it is presumed that in the mixture (α), the polyamines (D) adhere to the surface of the cellulose-based material (A) to form a polyamine (D) layer, and further, the polyvinyl acetate polymer emulsion (B) (preferably, a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the polyamine (D) layer. It is presumed that when such a mixture (α) and the melt-kneaded product (β) are melt-kneaded, the polyamines (D) on the surface of the cellulose-based material (A) react with the carboxylic acids (E), forming a layer of a reaction product of the polyamines (D) and the carboxylic acids (E) on the surface of the cellulose-based material (A), and that the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adheres to the surface of the reaction product layer. It is presumed that the protective effect of the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhered to the surface of the reaction product layer on the surface of the cellulose-based material (A) prevents the cellulose-based material (A) from aggregating and allows it to be highly dispersed in the thermoplastic resin (C). Thereafter, when the melt-kneading is continued and the water is removed, it is presumed that a reaction product layer of the polyamines (D) and the carboxylic acids (E) and a polyvinyl acetate polymer composition layer containing polyvinyl alcohol are formed on the surface of the cellulosic material (A) by the reaction product layer and the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhering to the surface, as shown in Figure 1C. This polyvinyl acetate polymer composition layer is further firmly adhered to the surface of the cellulosic material (A) via the layer consisting of the reaction product of the polyamines (D) and the carboxylic acids (E), and therefore it is presumed that the mechanical strength of the molded article made from the resin composition of the present invention is further improved.

[0024] According to the present invention, it is possible to obtain a molded article having excellent mechanical strength, which is made from a resin composition containing a cellulose-based material and a thermoplastic resin.

[0025] FIG. 1 is a schematic diagram showing an example of the state of a cellulose-based material (A) and a polyvinyl acetate polymer composition layer in a resin composition of the present invention. FIG. 2 is a schematic diagram showing an example of the state of a cellulose-based material (A), a polyvinyl acetate polymer composition layer, and a polyamine (D) layer in a resin composition of the present invention. FIG. 3 is a schematic diagram showing an example of the state of a cellulose-based material (A), a polyvinyl acetate polymer composition layer, polyamines (D), and carboxylic acids (E) in a resin composition of the present invention. FIG. 4 is a fluorescent micrograph of a pellet-shaped resin composition obtained in Example 1. FIG. 5 is a fluorescent micrograph of a pellet-shaped resin composition obtained in Example 2. FIG. 6 is a fluorescent micrograph of a pellet-shaped resin composition obtained in Example 3. FIG. 7 is a fluorescent micrograph of a pellet-shaped resin composition obtained in Example 4. FIG. 8 is a fluorescent micrograph of a pellet-shaped resin composition obtained in Comparative Example 1. FIG. 9 is a schematic diagram showing an example of the state of a cellulose-based material (A) and an ethylene-vinyl acetate copolymer emulsion in a conventional resin composition.

[0026] The present invention will be described in detail below based on preferred embodiments thereof.

[0027] [Resin Composition] First, the resin composition of the present invention will be described. The resin composition of the present invention is a melt-kneaded mixture of a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant, and a thermoplastic resin (C). Molded articles made from this resin composition have excellent mechanical strength.

[0028] In the resin composition of the present invention, it is preferable that the mixture (α) further contains a polyamine (D), i.e., the mixture contains the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamine (D). A molded article made of the resin composition, which is a melt-kneaded mixture of the mixture (α) and the thermoplastic resin (C), has even better mechanical strength.

[0029] Furthermore, in the resin composition of the present invention, it is more preferable that the mixture (α) further contains polyamines (D) and carboxylic acids (E), i.e., the mixture contains the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), the polyamines (D), and the carboxylic acids (E). A molded article made of a resin composition that is a melt-kneaded product of the mixture (α) and the thermoplastic resin (C) has particularly excellent mechanical strength.

[0030] The resin composition of the present invention is also preferably a mixture (α) further containing a polyamine (D), i.e., a melt-kneaded mixture of the mixture (α) containing the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamine (D) with a melt-kneaded mixture (β) containing the thermoplastic resin (C) and the carboxylic acid (E). Molded articles made from this resin composition also have excellent mechanical strength.

[0031] Each component used in the present invention will be described below.

[0032] (A) Cellulose-based material The cellulose-based material (A) used in the present invention is not particularly limited as long as it can be used in fiber-reinforced plastics, and examples thereof include cellulose-based fibers such as pulp (plant fiber) and cellulose-based powders such as wood flour. Furthermore, such cellulose-based material (A) may be pulverized (microfine cellulose-based material) or not pulverized (non-microfiberized cellulose-based material). However, from the viewpoint of increasing the strength of the molded article made from the resin composition of the present invention, a microfiber cellulose-based material is preferred. Such a microfiber cellulose-based material may be a non-microfiberized cellulose-based material that has been microfiberized in advance, or a non-microfiberized cellulose-based material that has been microfiberized during the production of the resin composition of the present invention.

[0033] Examples of the fine cellulose-based material include cellulose-based fibers that have been finely divided (defibrated) (fine cellulose-based fibers) and finely divided cellulose-based powders (fine cellulose-based powders), and examples of the non-fine cellulose-based material include cellulose-based fibers that have not been finely divided (defibrated) (non-fine cellulose-based fibers) and cellulose-based powders that have not been finely divided (non-fine cellulose-based powders).

[0034] Examples of the non-micronized cellulose fibers include natural cellulose fibers such as pulp that has not been micronized (defibrated). The average fiber diameter of such non-micronized cellulose fibers is not particularly limited, but is generally 50 to 60 μm. Examples of the micronized cellulose fibers include micronized (defibrated) pulp. From the viewpoint of increasing the strength of molded articles made from the resin composition of the present invention, the average fiber diameter of such micronized cellulose fibers is preferably 1 nm to 10 μm, more preferably 1 nm to 1 μm, and even more preferably 1 nm to 500 nm. From the viewpoint of increasing the strength of molded articles made from the resin composition of the present invention, the micronized cellulose fibers are preferably non-micronized cellulose fibers that have been microfibrillated (MF-converted) (MF-converted cellulose fibers). Furthermore, in the MF-converted cellulose fibers, not all of the non-micronized cellulose fibers need to be uniformly MF-converted. For example, cellulose-based fibers in which the surface of a thick portion (e.g., a portion with a diameter of about 5 μm) of a non-micronized cellulose-based fiber has been MF-processed to a diameter of about 10 nm (partially MF-processed cellulose-based fiber) can also be suitably used as the cellulose-based material (A) in the present invention.

[0035] Examples of the non-micronized cellulose powder include unmicronized wood flour. The average particle size of such non-micronized cellulose powder is not particularly limited, but is generally 300 to 500 μm. Examples of the micronized cellulose powder include micronized wood flour. From the viewpoint of increasing the strength of molded articles made from the resin composition of the present invention, the average particle size of such micronized cellulose powder is preferably 1 nm to 100 μm, more preferably 1 nm to 10 μm, and even more preferably 1 nm to 1 μm. Furthermore, from the viewpoint of increasing the strength of molded articles made from the resin composition of the present invention, the micronized cellulose powder is preferably a microfibrillated (MF) non-micronized cellulose powder (MF cellulose powder). Furthermore, in the MF cellulose powder, not all of the non-micronized cellulose powder needs to be uniformly MF-treated. For example, a cellulose powder in which only a portion of the surface of a non-micronized cellulose powder has been MF-treated (partially MF cellulose powder) can also be suitably used as the cellulose material (A) in the present invention.

[0036] The pulp is not particularly limited as long as it can be used in fiber-reinforced plastics, and may be wood pulp or non-wood pulp. Such pulp may be pulp that has been pulverized (defibrated) or not, but pulp that has been pulverized (defibrated) is preferred from the viewpoint of increasing the strength of a molded article made from the resin composition of the present invention. Furthermore, the pulp that has been pulverized (defibrated) may be pulp that has been pulverized (defibrated) in advance, or pulp that has not been pulverized (defibrated) may be pulp that has been pulverized (defibrated) during the production of the resin composition of the present invention.

[0037] Examples of the wood pulp include those derived from conifers (N-wood) and broad-leaved trees (L-wood). Examples of the non-wood pulp include those derived from seed fibers, bast fibers, leaf vein fibers (vascular fibers), fruit fibers, and stem fibers (lignocellulosic fibers). Seed fibers include cotton, kapok, and ash. Bast fibers include ramie, flax, jute, hemp, paper mulberry, mitsumata, gampi, kenaf, and mulberry. Vein fibers include sisal, Manila hemp, pineapple, New Zealand hemp, Sansevieria hemp, banana, and agave hemp. Fruit fibers include coconut coir and oil palm coir. Examples of stem fibers include sugarcane bagasse, bamboo, rice straw, wheat straw, reeds, palm, napier grass (elephant grass), switchgrass, miscanthus, and erianthus.

[0038] The pulp may be a chemical pulp (CP) or a mechanical pulp (MP). Examples of chemical pulp include kraft pulp (KP), sulfide pulp (SP), and alkaline pulp (AP). Examples of mechanical pulp include groundwood pulp (GP), refiner ground pulp (RGP), thermo-mechanical pulp (TMP), and chemi-thermo-mechanical pulp (CTMP). Furthermore, the pulp may be bleached with chemicals or the like (BP: Bleached Pulp) or unbleached (UP: Unbleached Pulp).

[0039] Specific examples of the wood pulp include softwood bleached chemical pulp (NBCP) such as softwood bleached kraft pulp (NBKP), softwood unbleached chemical pulp (NUCP) such as softwood unbleached kraft pulp (NUKP), hardwood bleached chemical pulp (LBCP) such as hardwood bleached kraft pulp (LBKP), and hardwood unbleached chemical pulp (LUCP) such as hardwood unbleached kraft pulp (LUKP), but are not limited to these.

[0040] Furthermore, the pulp may be dry pulp or never-dry pulp. The never-dry pulp is pulp that has never been dried and remains wet, and is not particularly limited, but examples include unbleached pulp (for example, never-dry pulp in NUCP such as NUKP or LUCP such as LUKP) obtained by boiling raw material chips with chemicals to break down the fibers of the chips in a manufacturing process of the pulp, washing the broken down fibers to remove lignin and foreign matter, and further decomposing the remaining lignin with oxygen, and further bleached pulp (for example, never-dry pulp in NBCP such as NBKP or LBCP such as LBKP) that has been bleached with chemicals or the like.

[0041] The cellulosic material (A) used in the present invention may be either a lignin-containing material (lignocellulosic material) or a lignin-free material. Examples of the lignocellulosic material include fine lignocellulosic fibers, non-refined lignocellulosic fibers, fine lignocellulosic powder, and non-refined lignocellulosic powder.

[0042] Furthermore, the cellulose-based material (A) used in the present invention may be chemically modified (chemically modified cellulose-based material) or may not be chemically modified. Here, chemical modification means that the hydroxyl groups of the sugar chains and / or lignin constituting the surface of the cellulose-based material are esterified with a carboxylic acid, half-esterified (monoesterified with a carboxylic acid anhydride), or etherified with an alkyl group which may have a substituent.

[0043] Examples of the chemically modified cellulose-based material include chemically modified microfibrillated cellulose-based fibers, chemically modified non-microfibrillated cellulose-based fibers, chemically modified microfibrillated cellulose-based powders, and chemically modified non-microfibrillated cellulose-based powders. Among these, those in which the hydroxyl groups of the sugar chains and / or lignin constituting the surface of the cellulose-based material are esterified with an aliphatic carboxylic acid or an alkyl or alkenyl succinic anhydride are preferred. Note that these chemically modified cellulose-based materials may contain lignin (chemically modified lignocellulose-based materials) or may not contain lignin.

[0044] Furthermore, from the viewpoint of ease of handling of the chemical modification, the chemically modified cellulose material is preferably in the form of a fiber, specifically, chemically modified microfibrillated cellulose fibers or chemically modified non-microfibrillated cellulose fibers are preferred, with chemically modified microfibrillated cellulose fibers being more preferred, and microfibrillated cellulose fibers in which the hydroxyl groups of the sugar chains and / or lignin constituting the surface thereof are esterified with an aliphatic carboxylic acid or an alkyl or alkenyl succinic anhydride are even more preferred. Note that the chemically modified microfibrillated cellulose fibers and the chemically modified non-microfibrillated cellulose fibers may contain lignin (chemically modified microfibrillated lignocellulose fibers and chemically modified non-microfibrillated lignocellulose fibers) or may not contain lignin.

[0045] In the present invention, these cellulose-based materials (A) may be used alone or in combination of two or more.

[0046] (B) Polyvinyl acetate polymer emulsion The polyvinyl acetate polymer emulsion (B) used in the present invention is a polyvinyl acetate polymer, i.e., an emulsion of a vinyl acetate homopolymer, containing polyvinyl alcohol as a dispersant. By using such a polyvinyl acetate polymer emulsion (B), it is possible to highly disperse the cellulose-based material (A) in the thermoplastic resin (C). Furthermore, by using the polyvinyl acetate polymer emulsion (B) when preparing a mixture (α) containing the cellulose-based material (A), polyamines (D), and carboxylic acids (E), it is possible to uniformly mix the cellulose-based material (A), polyamines (D), and carboxylic acids (E) without using a solvent for dissolving the carboxylic acids (E) (e.g., a solvent having both hydrophilic and hydrophobic groups, such as tripropylene glycol).

[0047] There are no particular limitations on the polyvinyl acetate polymer emulsion (B) used, and for example, vinyl acetate resin emulsion adhesives commercially available as wood glues can be used.

[0048] (C) Thermoplastic Resin The thermoplastic resin (C) used in the present invention is not particularly limited, and examples thereof include polyolefins, polyamides, aliphatic polyesters, aromatic polyesters, polyacetals, polycarbonates, polystyrenes, acrylonitrile-butadiene-styrene copolymers (ABS resins), polycarbonate-ABS alloys (PC-ABS alloys), cellulose-based resins, polylactic acid (PLA), polyhydroxybutyrate (PHBT), polyhydroxyhexanoate (PHAT), copolymers of polyhydroxybutyrate and polyhydroxyhexanoate (PHBH), polybutylene succinate (PBS), modified polyphenylene ether (m-PPE), and polyvinyl chloride.

[0049] Among these thermoplastic resins, polyolefin, polyamide, aliphatic polyester, aromatic polyester, polyacetal, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer (ABS resin), polycarbonate-ABS alloy (PC-ABS alloy), cellulose-based resin, polylactic acid (PLA), polyhydroxybutyrate (PHBT), polyhydroxyhexanoate (PHAT), copolymer of polyhydroxybutyrate and polyhydroxyhexanoate (PHBH), polybutylene succinate (PBS), and modified polyphenylene ether ( m-PPE) is preferred, and from the viewpoints of environmental conservation, thermal stability, strength properties, and weight reduction of molded articles, biomass-derived polyethylene, biomass-derived polypropylene, a copolymer of biomass-derived ethylene and biomass-derived propylene, a copolymer of at least one of biomass-derived ethylene and biomass-derived propylene with a petrochemical-derived olefin, polylactic acid (PLA), polyhydroxybutyrate (PHBT), polyhydroxyhexanoate (PHAT), a copolymer of polyhydroxybutyrate and polyhydroxyhexanoate (PHBH), and polybutylene succinate (PBS) are more preferred.

[0050] In the present invention, these thermoplastic resins (C) may be used alone or in combination of two or more.

[0051] (D) Polyamines Examples of the polyamines (D) used in the present invention include aliphatic polyamines and aromatic polyamines.

[0052] Examples of the aliphatic polyamine include polyethyleneimine (sometimes called "polyaziridine"), poly(trimethyleneimine) [repeating unit: -NHCH ２ CH ２ CH ２ -], poly(aminomethylethylene) [repeating unit: -CH ２ CH (CH ２ NH ２ )-)], poly(aminoethylene) [repeating unit: —CH ２ CH(NH２ )-)], and poly(meth)acrylic acid amino alkylene amide (a polymer in which a carboxylic acid of polyacrylic acid or polymethacrylic acid forms an amide bond with one amino group of an alkylenediamine), among which polyethyleneimine is preferred.

[0053] The polyethyleneimine may be linear (containing all secondary amino groups), branched (containing primary, secondary, and tertiary amino groups), or completely branched dendrimer-like, but branched polyethyleneimine is preferred. As the branched polyethyleneimine, for example, one commercially available under the trade name Epomin® can be used. The number-average molecular weight (Mn) of the polyethyleneimine is preferably 300 to 100,000, and more preferably 300 to 70,000.

[0054] As the aromatic polyamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl 1,3-bis(4-aminophenoxy)benzene, resorcinol bis(4-aminophenyl)ether (CAS number: 2479-46-1), 1,4-bis(4-aminophenoxy)benzene (CAS number: 3491-12-1), 4,4'-bis(4-aminophenoxy)biphenyl (CAS number: 13080-85-8), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (CAS number: 13080-86-9), bis(4-aminophenyl)sulfone (CAS number: 80-08-0), and 2,2'-dimethylbiphenyl-4,4'-diamine (CAS number: 84-67-3) are preferred.

[0055] In the present invention, these polyamines (D) may be used alone or in combination of two or more.

[0056] (E) Carboxylic Acids The carboxylic acids (E) used in the present invention are not particularly limited as long as they are capable of imparting hydrophobicity to the cellulosic material (A), and examples thereof include carboxylic acids having a hydrophobic group, and the hydrophobic group may be a hydrophobic hydrocarbon group. Further, examples of the carboxylic acids include polycarboxylic acids such as monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, and tetracarboxylic acids, and acid anhydrides thereof.

[0057] The carboxylic acid (E) may be a compound represented by the following formula (1): R—(COOH) ｎ (1) (wherein R represents a hydrophobic group, and n represents the number of carboxyl groups in one molecule and is an integer of 1 or 2 or more).

[0058] In the formula (1), R is a hydrophobic group (e.g., a hydrophobic hydrocarbon group), and examples thereof include an alkyl group, an alkenyl group, an alicyclic hydrocarbon group, an oxyalkyl group having an alicyclic hydrocarbon group bonded thereto, and a phenoxyalkyl group. An alkyl group or an alicyclic hydrocarbon group may be bonded to the phenyl group of the phenoxyalkyl group. The alkyl group (including the alkyl group bonded to the phenyl group of the phenoxyalkyl group) and the alkenyl group may have a branched chain. Furthermore, a plurality of the alicyclic hydrocarbon groups (including the alicyclic hydrocarbon groups bonded to the oxyalkyl group and the alicyclic hydrocarbon groups bonded to the phenyl group of the phenoxyalkyl group) may be crosslinked or condensed.

[0059] From the viewpoint of further improving the mechanical strength of the molded article, the alkyl group which may have a branched chain is preferably an alkyl group having 1 to 17 carbon atoms (e.g., methyl group, ethyl group, isobutyl group, t-butyl group, n-undecyl group, n-tridecyl group, n-pentadecyl group, n-heptadecyl group), more preferably an alkyl group having 1 to 12 carbon atoms (e.g., methyl group, ethyl group, isobutyl group, t-butyl group, n-undecyl group), and even more preferably an alkyl group having 1 to 5 carbon atoms (e.g., methyl group, ethyl group, isobutyl group, t-butyl group).

[0060] Furthermore, from the viewpoint of further improving the mechanical strength of the molded body, the alkenyl group which may have a branched chain is preferably an alkenyl group having 2 to 17 carbon atoms, more preferably an alkenyl group having 2 to 12 carbon atoms, and even more preferably an alkenyl group having 2 to 5 carbon atoms.

[0061] Examples of the alicyclic hydrocarbon group, a plurality of which may be crosslinked or condensed, include an adamantyl group, a cyclohexyl group, and a 4-(t-butyl)cyclohexyl group, and from the viewpoint of further improving the mechanical strength of the molded article, an adamantyl group is preferred.

[0062] Examples of the oxyalkyl group having an alicyclic hydrocarbon group bonded thereto include a bornyloxymethyl group, an isobornyloxymethyl group, and a menthyloxymethyl group.

[0063] Examples of the phenoxyalkyl group which may have an alkyl group or an alicyclic hydrocarbon group bonded thereto include a phenoxymethyl group, a 4-(t-butyl)phenoxymethyl group, a 4-(1,1,3,3-tetramethyl)butylphenoxymethyl group, an adamantylphenoxymethyl group, a bornylphenoxymethyl group, a bornylphenoxypentyl group, and a menthylphenoxymethyl group. From the viewpoint of further improving the mechanical strength of a molded article, the 4-(t-butyl)phenoxymethyl group, the 4-(1,1,3,3-tetramethyl)butylphenoxymethyl group, an adamantylphenoxymethyl group, a bornylphenoxymethyl group, and a menthylphenoxymethyl group are preferred.

[0064] Examples of the monocarboxylic acid used in the present invention include aliphatic monocarboxylic acids such as propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, nonanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, acrylic acid, oleic acid, linoleic acid, and linolenic acid; and aromatic monocarboxylic acids such as benzoic acid and salicylic acid.

[0065] Examples of the polycarboxylic acid used in the present invention include an aliphatic polycarboxylic acid having 2 to 3 carboxy groups in the molecule, and an aromatic polycarboxylic acid having 2 to 4 (preferably 3 to 4) carboxy groups in the molecule.

[0066] Examples of the aliphatic polycarboxylic acid include aliphatic polycarboxylic acids having a linear hydrocarbon group having 1 to 10 carbon atoms, and specific examples thereof include malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, eicosanedioic acid, itaconic acid, fumaric acid, and maleic acid.

[0067] The aliphatic polycarboxylic acid also includes an aliphatic polycarboxylic acid having a branched hydrocarbon group. Examples of such aliphatic polycarboxylic acids having a branched hydrocarbon group include alkylsuccinic acid, alkenylsuccinic acid, alkyldodecanedioic acid, and alkenyldodecanedioic acid. The number of carbon atoms in the alkyl group that is a branched chain of the alkylsuccinic acid and the alkenyl group that is a branched chain of the alkenylsuccinic acid are preferably 4 to 17.

[0068] Specific examples of alkylsuccinic acids include octyl succinic acid, dodecyl succinic acid, tridecenyl succinic acid, tetrahexadecyl succinic acid, hexadecyl succinic acid, and octadecyl succinic acid. Specific examples of alkenyl succinic acids include pentenyl succinic acid, hexenyl succinic acid, octenyl succinic acid, decenyl succinic acid, undecenyl succinic acid, dodecenyl succinic acid, tridecenyl succinic acid, tetradecenyl succinic acid, hexadecenyl succinic acid, octadecenyl succinic acid, and iso-octadecenyl succinic acid.

[0069] Examples of the aromatic polycarboxylic acid include phthalic acid (1,2-benzenedicarboxylic acid), isophthalic acid (1,3-benzenedicarboxylic acid), terephthalic acid (1,4-benzenedicarboxylic acid), pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), trimellitic acid (1,2,4-benzenetricarboxylic acid), and trimesic acid (1,3,5-benzenetricarboxylic acid).

[0070] In the present invention, rosin acids can also be used as the carboxylic acid (E). Examples of the rosin acids include rosin acids such as abietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid, and dehydroabietic acid, as well as derivatives of these rosin acids. Examples of the rosin acid derivatives include condensates of the rosin acid, acrylic acid-modified rosin acid, fumaric acid-modified rosin acid, maleic anhydride-modified rosin acid, phenolized rosin acid, and rosin acid-modified phenolic resins. Among these rosin acids, from the viewpoint of further improving the mechanical strength of the molded article, rosin acid, maleic anhydride-modified rosin acid, and rosin acid-modified phenolic resins are preferred, with abietic acid, dehydroabietic acid, maleic anhydride-modified abietic acid, and abietic acid-modified phenolic resins being more preferred.

[0071] In the present invention, these carboxylic acids (E) may be used alone or in combination of two or more.

[0072] (F) Acid Anhydride-Modified Polyolefins The resin composition of the present invention may contain an acid anhydride-modified polyolefin (F). Examples of such acid anhydride-modified polyolefins (F) include maleic anhydride-modified polyolefins (i.e., those in which maleic anhydride is grafted into the polyolefin molecule and / or to the molecular terminal, and copolymers of maleic anhydride and olefin) and their hydrolysates (i.e., those in which the acid anhydride group in the maleic anhydride-modified polyolefin is hydrolyzed). The use of such acid anhydride-modified polyolefins (F) makes it possible to more highly disperse the cellulose-based material (A) in the thermoplastic resin (C), and to obtain molded articles with even better mechanical strength.

[0073] Examples of the maleic anhydride-modified polyolefin and hydrolysates thereof include those obtained by modifying a polymer and / or copolymer of an alkene having 2 to 6 carbon atoms with maleic anhydride, a copolymer of maleic anhydride and an alkene having 2 to 6 carbon atoms, and those obtained by hydrolyzing the acid anhydride groups thereof. Among these, those obtained by modifying a polymer and / or copolymer of an alkene having 2 to 6 carbon atoms with maleic anhydride, and those obtained by hydrolyzing the acid anhydride groups thereof are preferred. Specific examples include maleic anhydride-modified polyethylene (abbreviation: MAPE), maleic anhydride-modified polypropylene (abbreviation: MAPP), maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified polybutene, maleic anhydride-modified polypentene, maleic anhydride-modified polyhexene, and those obtained by hydrolyzing the acid anhydride groups thereof. MAPE, MAPP, and hydrolysates thereof are more preferred.

[0074] The average molecular weight (MW) of the maleic anhydride-modified polyolefin (particularly, maleic anhydride-modified polypropylene) is preferably 9,000 to 100,000, more preferably 9,000 to 70,000, and even more preferably 9,000 to 50,000. Furthermore, maleic anhydride-modified polypropylene having an average molecular weight (MW) of 9,000 to 70,000 (preferably 9,000 to 50,000), which is obtained by grafting maleic anhydride onto polypropylene fragments obtained by thermally decomposing polypropylene having a high average molecular weight, can also be used as the acid anhydride-modified polyolefin.

[0075] The acid load (acid value) of the maleic anhydride-modified polyolefin (particularly, maleic anhydride-modified polypropylene) is preferably 1.4 to 120 mgKOH / g, more preferably 3.5 to 60 mgKOH / g.

[0076] In the present invention, these acid anhydride-modified polyolefins (F) may be used alone or in combination of two or more.

[0077] (Resin Composition) The resin composition of the present invention is a melt-kneaded mixture of a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant, and a thermoplastic resin (C). By using such a resin composition, a molded article having excellent mechanical strength can be obtained.

[0078] In the resin composition of the present invention, the content of the cellulose-based material (A) is preferably 0.1 to 79.9% by mass, more preferably 0.5 to 49.5% by mass, and even more preferably 1 to 20% by mass, based on the total mass of the resulting resin composition. If the content of the cellulose-based material (A) is less than the lower limit, it tends to be difficult to obtain a molded product excellent in mechanical strength, coefficient of linear expansion (CTE), heat resistance (e.g., heat distortion temperature), etc., while if the content exceeds the upper limit, the molded product tends to have a reduced surface smoothness, a reduced transparency, a reduced flowability of the molten resin composition, distortion of the molded product, poor adhesion, etc.

[0079] The content of the polyvinyl acetate polymer emulsion (B) is preferably 0.1 to 15% by mass, more preferably 0.5 to 12% by mass, and even more preferably 1 to 10% by mass, in terms of polyvinyl acetate polymer relative to the total amount of the resulting resin composition. If the content of the polyvinyl acetate polymer emulsion (B) is less than the lower limit, the cellulose-based material (A) is not sufficiently hydrophobic, the cellulose-based material (A) cannot be highly dispersed in the thermoplastic resin (C), and it tends to be difficult to obtain a molded product with excellent mechanical strength. On the other hand, if the content exceeds the upper limit, the excess polyvinyl acetate polymer emulsion (B) loosens the interface or overflows into the thermoplastic resin (C), which tends to reduce the physical properties of the resin composition and the molded product.

[0080] The content of the thermoplastic resin (C) is preferably 20 to 99.8% by mass, more preferably 50 to 99% by mass, and even more preferably 70 to 98% by mass, based on the total mass of the resulting resin composition. If the content of the thermoplastic resin (C) is less than the lower limit, molding defects and breakage or damage during use due to reduced impact resistance tend to occur, while if the content exceeds the upper limit, the amount of the cellulose-based material (A) becomes relatively small, making it difficult to obtain a molded product having excellent physical properties such as mechanical strength.

[0081] Furthermore, in the resin composition of the present invention, it is preferable that the mixture (α) further contains polyamines (D). By using such a resin composition, a molded article with even better mechanical strength can be obtained. In this case, the content of the polyamines (D) is preferably 0.1 to 70 parts by mass, more preferably 0.1 to 50 parts by mass, and even more preferably 0.1 to 30 parts by mass, per 100 parts by mass of the cellulose-based material (A). If the proportion of the polyamines (D) is less than the lower limit, the cellulose-based material (A) is not sufficiently hydrophobic, and the cellulose-based material (A) cannot be highly dispersed in the thermoplastic resin (C), which tends to make it difficult to obtain a molded article with excellent mechanical strength. On the other hand, if the proportion exceeds the upper limit, it tends to be necessary to recover the excess polyamines.

[0082] Furthermore, in the resin composition of the present invention, it is more preferable that the mixture (α) further contains polyamines (D) and carboxylic acids (E). The resin composition of the present invention is also more preferably a melt-kneaded mixture of the mixture (α) further containing polyamines (D) and a melt-kneaded mixture (β) containing a thermoplastic resin (C) and carboxylic acids (E). By using these resin compositions, molded articles with particularly excellent mechanical strength can be obtained. In this case, the ratio of the acid value of the carboxylic acids (E) to the amine value of the polyamines (D) (acid value / amine value) is preferably 0.01 to 2.0, more preferably 0.1 to 1.0 (equivalents). If the ratio (acid value / amine value) is below the lower limit, the cellulose-based material (A) is not sufficiently hydrophobic, and the cellulose-based material (A) cannot be highly dispersed in the thermoplastic resin (C), making it difficult to obtain molded articles with excellent mechanical strength. On the other hand, if the ratio exceeds the upper limit, metal corrosion and other problems associated with the acidity of the excess carboxylic acids tend to occur.

[0083] Furthermore, when the resin composition of the present invention contains an acid anhydride-modified polyolefin (F), the ratio of the sum of the acid values ​​of the carboxylic acids (E) and the acid anhydride-modified polyolefin (F) to the amine value of the polyamine (D) (total amine value of acid values) is preferably 0.01 to 2.0, more preferably 0.1 to 1.0 (equivalents).

[0084] (Additives) In the present invention, a filler (G) and / or a compatibilizer (H) can be used as an additive, which improves the dispersibility of the cellulose-based material (A) in the thermoplastic resin (C).

[0085] (G) Filler Examples of the filler (G) include talc, clay, zeolite, aluminum oxide, calcium carbonate, titanium oxide, silica, magnesium oxide, and mica, and among these, talc, clay, zeolite, and calcium carbonate are preferred. These fillers (G) may be used alone or in combination of two or more. By including such a filler (G), the cellulose-based material (A) in the resin composition is easily defibrated during melt-kneading, thereby improving the dispersibility of the cellulose-based material (A).

[0086] When the resin composition of the present invention contains the filler (G), the content thereof is preferably 1 to 40 parts by mass, more preferably 2 to 20 parts by mass, and even more preferably 5 to 10 parts by mass, relative to 100 parts by mass of the thermoplastic resin (C).

[0087] (H) Compatibilizer The compatibilizer (H) is not particularly limited as long as it has affinity for both the cellulose-based material (A) and the thermoplastic resin (C) and improves the dispersibility of the cellulose-based material (A) in the thermoplastic resin (C), and examples thereof include modified polyolefins (excluding those corresponding to the acid anhydride-modified polyolefins (F)), graft products of polyolefins with other polymers (excluding those corresponding to the acid anhydride-modified polyolefins (F)), and graft products of acrylic polymer chains having affinity for polyolefins with acrylic polymer chains having affinity for celluloses. These compatibilizers (H) may be used alone or in combination of two or more.

[0088] Examples of the grafted product of polyolefin and other polymers include copolymers of polyolefin such as polyethylene, polypropylene, polybutene, and polyvinyl acetate (PVAc), poly(meth)acrylic acid, or poly(meth)acrylate.

[0089] Examples of the grafted product of an acrylic polymer chain having an affinity for polyolefins and an acrylic polymer chain having an affinity for celluloses include a block copolymer having a resin affinity segment and a cellulose affinity segment, as described in Japanese Patent No. 6234037.

[0090] When the resin composition of the present invention contains the compatibilizer (H), the content thereof is preferably 1 to 20 parts by mass, more preferably 2 to 10 parts by mass, and even more preferably 5 to 10 parts by mass, per 100 parts by mass of the thermoplastic resin (C).

[0091] (Other Additives) Furthermore, the resin composition of the present invention may contain various additives such as antioxidants, surfactants, plasticizers, antistatic agents, ultraviolet absorbers, colorants, and deodorizers, as long as the effects of the present invention are not impaired.

[0092] [Method for Producing Resin Composition] Next, a method for producing the resin composition of the present invention will be described. The method for producing the resin composition of the present invention is a method (Method 1) comprising a step of mixing the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B) to prepare a mixture (α) [mixture (α) preparation step], and a step of melt-kneading the mixture (α) with the thermoplastic resin (C) [melt-kneading step]. This method makes it possible to highly disperse the cellulose-based material (A) in the thermoplastic resin (C), and further to perform pulverization (e.g., defibration) of the cellulose-based material (A) as necessary, thereby obtaining a resin composition capable of forming a molded article having excellent mechanical strength.

[0093] In the step of preparing the mixture (α), it is preferable to further mix a polyamine (D) with the mixture (α) (Method 2), and it is more preferable to further mix a carboxylic acid (E) with the mixture (α) containing the polyamine (D) (Method 3).

[0094] In addition, in the method for producing the resin composition of the present invention, it is also more preferable that in the mixture (α) preparation step, polyamines (D) are further mixed into the mixture (α), and the thermoplastic resin (C) and carboxylic acids (E) are melt-kneaded to prepare a melt-kneaded product (β) [melt-kneaded product (β) preparation step], and the mixture (α) and the melt-kneaded product (β) are melt-kneaded [melt-kneading step] (Method 4).

[0095] That is, the above methods 1 to 4 can be summarized as follows.

[0096] (Method 1) A method comprising: a step of preparing a mixture (α) by mixing the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B) (mixture (α) preparation step); and a step of melt-kneading the mixture (α) with the thermoplastic resin (C) (melt-kneading step).

[0097] (Method 2) A method comprising: a step of preparing a mixture (α) by mixing the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamines (D) (mixture (α) preparation step); and a step of melt-kneading the mixture (α) with the thermoplastic resin (C) (melt-kneading step).

[0098] (Method 3) A method comprising: a step of preparing a mixture (α) by mixing the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), the polyamines (D), and the carboxylic acids (E) (mixture (α) preparation step); and a step of melt-kneading the mixture (α) with the thermoplastic resin (C) (melt-kneading step).

[0099] (Method 4) A method comprising: a step of mixing the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamines (D) to prepare a mixture (α) [mixture (α) preparation step]; a step of melt-kneading the thermoplastic resin (C) and the carboxylic acids (E) to prepare a melt-kneaded product (β) [melt-kneaded product (β) preparation step]; and a step of melt-kneading the mixture (α) and the thermoplastic resin (C) [melt-kneading step].

[0100] In the method for producing a resin composition of the present invention, the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), the thermoplastic resin (C), the polyamines (D), and the carboxylic acids (E) described above for the resin composition of the present invention can be used. The blending amounts of each component may be appropriately set so that the content of each component in the resulting resin composition falls within a predetermined range.

[0101] (Solvent) In the method for producing a resin composition of the present invention, by using the polyvinyl acetate polymer emulsion (B), the cellulose-based material (A), the polyamines (D), and the carboxylic acids (E) can be uniformly mixed without using a solvent for dissolving the carboxylic acids (E) (for example, a solvent having both a hydrophilic group and a hydrophobic group, such as tripropylene glycol). This prevents the adhesion of dirt to the production line (particularly the exhaust line) during melt-kneading, and contamination due to solvents containing residual solvents or unreacted components in the resin composition, and also reduces VOC emissions. However, a solvent having both a hydrophilic group and a hydrophobic group, such as tripropylene glycol, may be used as long as it prevents the adhesion of dirt to the production line (particularly the exhaust line) during melt-kneading, and contamination due to solvents containing residual solvents or unreacted components in the resin composition, and also reduces VOC emissions.

[0102] [Mixture (α) Preparation Step] In the mixture (α) preparation step, the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B) are mixed to prepare the mixture (α). The mixture (α) contains the cellulose-based material (A) having the polyvinyl acetate polymer emulsion (B) (preferably a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) attached to its surface. This polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) forms a polyvinyl alcohol-containing polyvinyl acetate polymer composition layer in the melt-kneading step described below, thereby imparting hydrophobicity to the surface of the cellulose-based material (A). The cellulose-based material (A) with its surface imparted with hydrophobicity is highly dispersed in the thermoplastic resin (C), and the resulting molded article made of the resin composition has excellent mechanical strength.

[0103] In the step of preparing the mixture (α), it is preferable to further mix the polyamines (D). As a result, the polyvinyl acetate polymer emulsion (B) (preferably a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the cellulose-based material (A) via the polyamines (D). This polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) forms a polyvinyl alcohol-containing polyvinyl acetate polymer composition layer in the melt-kneading step described below, and the polyvinyl acetate polymer composition layer firmly adheres to the surface of the cellulose-based material (A) via the polyamines (D) layer, thereby obtaining a resin composition capable of forming a molded product with even greater mechanical strength. Examples of a method for further mixing the polyamines (D) include a method in which the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamines (D) are simultaneously mixed; a method in which the cellulose-based material (A) and the polyamines (D) are mixed together, and then the polyvinyl acetate polymer emulsion (B) is further mixed therewith; and a method in which the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B) are mixed together, and then the polyamines (D) are further mixed therewith.

[0104] Furthermore, when the polyamines (D) are further mixed in the mixture (α) preparation step, it is more preferable to further mix the carboxylic acids (E) in the mixture (α) preparation step and melt-knead this mixture (α) (containing the polyamines (D) and the carboxylic acids (E)) with the thermoplastic resin (C). Also, as described below, it is more preferable to melt-knead the thermoplastic resin (C) and the carboxylic acids (E) to prepare a melt-kneaded product (β), and then melt-knead this melt-kneaded product (β) with the mixture (α) (containing the polyamines (D)). As a result, the polyvinyl acetate polymer emulsion (B) (preferably a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the cellulose-based material (A) via the reaction product of the polyamines (D) and the carboxylic acids (E). In the melt-kneading step described below, this polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) forms a polyvinyl acetate polymer composition layer containing polyvinyl alcohol, and the polyvinyl acetate polymer composition layer adheres more firmly to the surface of the cellulosic material (A) via the polyamine (D) layer, thereby obtaining a resin composition that can be used to form molded articles with particularly excellent mechanical strength.

[0105] In the step of preparing the mixture (α), examples of a method for further mixing the polyamines (D) and the carboxylic acids (E) include a method of simultaneously mixing the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), the polyamines (D), and the carboxylic acids (E); a method of mixing the cellulose-based material (A), the polyamines (D), and the carboxylic acids (E), and then mixing the polyvinyl acetate polymer emulsion (B); a method of mixing the cellulose-based material (A) and the polyamines (D), and then mixing the carboxylic acids (E), and then mixing the polyvinyl acetate polymer emulsion (B); a method of mixing the cellulose-based material (A) and the polyamines (E), and then mixing the carboxylic acids (E), and then mixing the polyvinyl acetate polymer emulsion (B); and a method of mixing the cellulose-based material (A) and the carboxylic acids (E), and then mixing the polyamines (D), and then mixing the polyvinyl acetate polymer emulsion (B).

[0106] When a non-micronized cellulose-based material such as pulp or wood flour is used as the raw material cellulose-based material (A), in the mixture (α) preparation step, the cellulose-based material (A) in the mixture prepared in the mixture preparation step may be subjected to a micronization treatment (e.g., a defibration treatment) as necessary.

[0107] The acid anhydride-modified polyolefins (F), the filler (G), the compatibilizer (H), and other additives may be mixed in the mixture (α) preparation step. In the method for producing a resin composition of the present invention, the acid anhydride-modified polyolefins (F), the filler (G), the compatibilizer (H), and other additives may be the same as those described for the resin composition of the present invention.

[0108] The method for mixing the components in the mixture (α) preparation step is not particularly limited, and examples thereof include stirring with a stirring device such as a planetary mixer and kneading with a kneading device such as an extruder. Among these mixing methods, when kneading is performed with a kneading device such as an extruder, the mixture preparation step and the melt-kneading step can be carried out continuously. Furthermore, when a non-micronized cellulosic material (pulp (particularly, never-dry pulp), wood, etc.) is used as the raw material cellulosic material (A), the cellulosic material (A) can be micronized (defibrated) by kneading with a kneading device such as an extruder.

[0109] [Melt-kneaded product (β) preparation step] When the polyamines (D) are further mixed in the mixture (α) preparation step, it is also preferable to melt-knead the thermoplastic resin (C) and the carboxylic acids (E) to prepare the melt-kneaded product (β). As a result, the polyvinyl acetate polymer emulsion (B) (preferably, a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the cellulose-based material (A) via the reaction product of the polyamines (D) and the carboxylic acids (E). This polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) forms a polyvinyl alcohol-containing polyvinyl acetate polymer composition layer in the melt-kneading step described below, and the polyvinyl acetate polymer composition layer further adheres firmly to the surface of the cellulose-based material (A) via the polyamines (D) layer, resulting in a resin composition capable of forming a molded product with particularly excellent mechanical strength.

[0110] The method for melt-kneading each component in the step of preparing the melt-kneaded product (β) is not particularly limited, and examples thereof include melt-kneading using a kneading device such as an extruder. The temperature during melt-kneading is preferably in the range of the softening point of the thermoplastic resin (C) to the melting point + 20°C, more preferably in the range of the melting point of the thermoplastic resin (C) to the melting point + 10°C.

[0111] [Melt-Kneading Step] The melt-kneading step is a step of melt-kneading the mixture (α) and the thermoplastic resin (C). Specifically, the melt-kneading step is a step of melt-kneading the mixture (α) of the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B) with the thermoplastic resin (C); a step of melt-kneading the mixture (α) of the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamines (D) with the thermoplastic resin (C); or a step of melt-kneading the mixture (α) of the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), the polyamines (D), and the carboxylic acids (E) with the thermoplastic resin (C).

[0112] In the resin composition (melt-kneaded product) obtained by these steps, the polyvinyl acetate polymer emulsion (B) (preferably a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface (preferably via a layer of the polyamines (D), more preferably via a layer of the reaction product of the polyamines (D) and the carboxylic acids (E)), and the hydrophobic cellulose-based material (A) is highly dispersed in the thermoplastic resin (C). By further continuing the melt-kneading, the polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer) adhered to the surface of the cellulose-based material (A) forms a polyvinyl acetate polymer composition layer containing polyvinyl alcohol, thereby imparting hydrophobicity to the surface of the cellulose-based material (A). The cellulose-based material (A) whose surface has been imparted hydrophobicity is highly dispersed in the thermoplastic resin (C), resulting in a molded article made from the resin composition having excellent mechanical strength. Furthermore, from the viewpoint of obtaining a resin composition in which the polyvinyl acetate polymer composition layer adheres more firmly to the surface of the cellulose-based material (A) and which is capable of forming a molded article having even greater mechanical strength, it is preferable that the polyvinyl acetate polymer composition layer adheres to the surface of the cellulose-based material (A) via the polyamine (D) layer, and it is more preferable that the polyvinyl acetate polymer composition layer adheres to the surface of the cellulose-based material (A) via a reaction product layer of the polyamine (D) and the carboxylic acid (E).

[0113] In addition, in this melt-kneading step, the mixture (α) of the cellulose-based material (A), the polyvinyl acetate polymer emulsion (B), and the polyamines (D) may be melt-kneaded with the melt-kneaded mixture (β) of the thermoplastic resin (C) and the carboxylic acids (E). As a result, the polyamines (D) and the carboxylic acids (E) react with each other, and the polyvinyl acetate polymer emulsion (B) (preferably, a granular polyvinyl acetate polymer whose surface is protected with polyvinyl alcohol) adheres to the surface of the cellulose-based material (A) via the reaction product. By further continuing the melt-kneading of this polyvinyl acetate polymer emulsion (B) (the granular polyvinyl acetate polymer), a polyvinyl alcohol-containing polyvinyl acetate polymer composition layer is formed, and the polyvinyl acetate polymer composition layer adheres more firmly to the surface of the cellulose-based material (A) via the reaction product layer, resulting in a molded article made of the resulting resin composition having particularly excellent mechanical strength.

[0114] The method for melt-kneading each component in such a melt-kneading step is not particularly limited, but examples thereof include kneading using a kneading device such as an extruder. At this time, the melt-kneading is performed while removing water contained in the mixture (α) or after removing the water. The temperature during melt-kneading is preferably a temperature within the range of the softening point of the thermoplastic resin (C) to the melting point + 20°C, more preferably a temperature within the range of the melting point of the thermoplastic resin (C) to the melting point + 10°C.

[0115] The acid anhydride-modified polyolefins (F), the filler (G), the compatibilizer (H), and other additives may be mixed in this melt-kneading step. In the method for producing a resin composition of the present invention, the acid anhydride-modified polyolefins (F), the filler (G), the compatibilizer (H), and other additives may be those described above for the resin composition of the present invention.

[0116] [Molded Article] Next, the molded article of the present invention will be described. The molded article of the present invention is made from the resin composition of the present invention. As described above, in the resin composition of the present invention, the cellulose-based material (A) is highly dispersed in the thermoplastic resin (C), and therefore the molded article of the present invention made from this resin composition has excellent mechanical strength.

[0117] The method for producing such a molded article of the present invention is not particularly limited, and it can be produced, for example, by molding the resin composition of the present invention in pellet or powder form into a desired shape by various known molding methods such as compression molding, injection molding, extrusion molding, blow molding, and foam molding.

[0118] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0119] Example 1 First, a polyvinyl acetate polymer emulsion containing polyvinyl alcohol as a dispersant (Vinyl Acetate Resin Emulsion Wood Adhesive for Woodworking 605, manufactured by Cemedine Co., Ltd., water content: 56-60%, polyvinyl acetate polymer content: 40-44%) was added to MF cellulose fiber (Daicel Miraize Co., Ltd., "Cerish KY110N," water content: 85%) so that the blending amount in the resin composition would be the blending amount shown in Table 1, and the mixture was stirred and mixed for 1 hour using a planetary mixer to prepare mixture (α). The amount of polyvinyl acetate polymer emulsion added was determined so that the blending amount of polyvinyl acetate polymer would be the blending amount shown in Table 1.

[0120] Next, polypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation, melt index: 40) was mixed with the resulting mixture (α) in an amount ¼ of the blending amount in the resin composition (blend amount shown in Table 1). Furthermore, 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the resulting mixture. The resulting mixture was then quantitatively charged into an extruder (L / D = 45) and melt-kneaded while removing water by drying to produce a pellet-shaped masterbatch.

[0121] Thereafter, the remaining amount of polypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation, melt index: 40) was added to the obtained masterbatch, and further, 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the obtained mixture. Thereafter, the obtained mixture was quantitatively charged into an extruder (L / D=45) and melt-kneaded to produce a pellet-shaped resin composition.

[0122] Example 2 First, polyethyleneimine (number average molecular weight 1800) dissolved in water, polyvinyl acetate polymer emulsion containing polyvinyl alcohol as a dispersant (Vinyl Acetate Resin Emulsion Wood Adhesive for Woodworking 605, manufactured by Cemedine Co., Ltd., water content: 56-60%, polyvinyl acetate polymer content: 40-44%), and calcium carbonate (Viscoexcel-30, manufactured by Shiraishi Kogyo Co., Ltd.) were added to MF cellulose fiber (Cerish KY110N, manufactured by Daicel Miraizu Co., Ltd., water content: 85%) so that the blending amounts in the resin composition were as shown in Table 1. A mixture (α) was prepared in the same manner as in Example 1.

[0123] Furthermore, dehydroabietic acid powder was powder-mixed with polypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation, melt index: 40) in an amount ¼ of the amount in the resin composition (the amount shown in Table 1) so that the amount in the resin composition was the amount shown in Table 1. Further, 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added to 100 parts by mass of the resulting mixture, and the resulting mixture was melt-kneaded to prepare a melt-kneaded product (β).

[0124] Next, the mixture (α) and the melt-kneaded product (β) were mixed, and further, 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added relative to 100 parts by mass of the solid content of the obtained mixture. Thereafter, the obtained mixture was quantitatively charged into an extruder (L / D=45), and melt-kneaded while removing water by drying, to prepare a pellet-shaped master batch.

[0125] Thereafter, the remaining amount of polypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation, melt index: 40) was added to the obtained masterbatch, and further, 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the obtained mixture. Thereafter, the obtained mixture was quantitatively charged into an extruder (L / D=45) and melt-kneaded to produce a pellet-shaped resin composition.

[0126] (Example 3) Polyethyleneimine (number average molecular weight 1800) and acetic acid were added to water and mixed to prepare an ammonium carboxylate solution so that the blending amounts in the resin composition were as shown in Table 1. To this ammonium carboxylate solution, MF cellulose fiber (Daicel Miraize Co., Ltd. "Cerish KY110N", water content: 85%), polyvinyl acetate polymer emulsion containing polyvinyl alcohol as a dispersant (Cemedine Co., Ltd. "Vinyl acetate resin emulsion wood adhesive for woodworking 605", water content: 56 to 60%, polyvinyl acetate polymer content: 40 to 44%), and calcium carbonate (Shiraishi Kogyo Co., Ltd. "Viscoexcel-30") were added to prepare a mixture (α), and further, the blending amount of polypropylene was changed to the blending amount shown in Table 1. A pellet-shaped resin composition was prepared in the same manner as in Example 1.

[0127] Example 4 Polyethyleneimine (number average molecular weight 1800) dissolved in water was added to MF cellulose fiber (Daicel Miraizu Co., Ltd.'s "Cerish KY110N", water content: 85%) so that the blending amount in the resin composition was the blending amount shown in Table 1, and further, a polyvinyl acetate polymer emulsion containing polyvinyl alcohol as a dispersant (Cemedine Co., Ltd.'s "Vinyl Acetate Resin Emulsion Wood Adhesive for Woodworking 605", water content: 56 to 60%, polyvinyl acetate polymer content: 40 to 44%) was added to prepare a mixture (α), and further, a pellet-shaped resin composition was prepared in the same manner as in Example 1, except that the blending amount of polypropylene was changed to the blending amount shown in Table 1.

[0128] Comparative Example 1 A mixture was prepared by adding an ethylene-vinyl acetate copolymer emulsion (Aica Kogyo Co., Ltd.'s "Vinyl copolymer resin emulsion adhesive AE-1000", water content: 44%, ethylene-vinyl acetate copolymer resin content: 56%) and calcium carbonate (Shiraishi Kogyo Co., Ltd.'s "Viscoexcel-30") to MF cellulose fiber (Daicel Miraize Co., Ltd.'s "Cerish KY110N", water content: 85%) so that the blending amounts in the resin composition were as shown in Table 1, and further, a pellet-shaped resin composition was prepared in the same manner as in Example 1, except that the blending amount of polypropylene was changed to the blending amount shown in Table 1.

[0129] <Fluorescence Microscope Observation> The pellet-shaped resin compositions obtained in Examples 1 to 4 and Comparative Example 1 were observed using a fluorescence microscope. FIGS. 2A to 2D are fluorescence microscope photographs of the pellet-shaped resin compositions obtained in Examples 1 to 4, respectively, and FIG. 3 is a fluorescence microscope photograph of the pellet-shaped resin composition obtained in Comparative Example 1. It was confirmed that the cellulose-based material (A) was more highly dispersed in the molded articles (Examples 1 to 4, FIGS. 2A to 2D) made from the resin composition of the present invention, which was a melt-kneaded mixture of a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) with a thermoplastic resin (C), than in the molded article (Comparative Example 1, FIG. 3) made from the resin composition, which was a melt-kneaded mixture of a mixture containing a cellulose-based material (A) and an ethylene-vinyl acetate copolymer emulsion with a thermoplastic resin (C).

[0130] <Bending Test> A bending test was conducted in accordance with JIS K7171 for the pellet-shaped resin compositions obtained in Examples 1 to 4 and Comparative Example 1. Specifically, first, rectangular test pieces (10 mm x 80 mm x 4 mm) were prepared using an injection molding machine using the pellet-shaped resin compositions obtained in Examples 1 to 4 and Comparative Example 1. Next, the obtained test pieces were left to stand for two days in an atmosphere at a temperature of 23°C and a relative humidity of 50%, and then a bending test was conducted using a universal testing machine under conditions of a support distance of 64 mm and a test speed of 10 mm / min, and the flexural modulus and flexural strength were measured. The results are shown in Table 1.

[0131]

[0132] As shown in Table 1, it was confirmed that the molded articles (Examples 1 to 4) made from the resin composition of the present invention, which is a melt-kneaded mixture of a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) with a thermoplastic resin (C), have superior flexural modulus and flexural strength compared to the molded article (Comparative Example 1) made from a resin composition, which is a melt-kneaded mixture of a mixture containing a cellulose-based material (A) and an ethylene-vinyl acetate copolymer emulsion with a thermoplastic resin (C).

[0133] Although the reason why the molded articles made from the resin compositions obtained in Examples 1 to 4 had superior flexural modulus and flexural strength compared to the molded article made from the resin composition obtained in Comparative Example 1 is not entirely clear, the present inventors speculate as follows. Specifically, it is speculated that, in the resin composition obtained in Example 1, a polyvinyl acetate polymer composition layer containing polyvinyl alcohol is formed on the surface of the cellulose-based material (A), as shown in FIG. 1A . Furthermore, in the resin compositions obtained in Examples 2 and 3, it is speculated that a polyvinyl acetate polymer composition layer containing polyvinyl alcohol is formed on the surface of the cellulose-based material (A), via a reaction product layer of polyamines (D) and carboxylic acids (E), as shown in FIG. 1C . Furthermore, in the resin composition obtained in Example 4, it is speculated that a polyvinyl acetate polymer composition layer containing polyvinyl alcohol is formed on the surface of the cellulose-based material (A), via a polyamine (D) layer, as shown in FIG. 1B . Since polyvinyl acetate polymers (homopolymers of vinyl acetate) have hydrophobic methyl groups in their side chains, a polyvinyl acetate polymer composition layer is formed on the surface of the cellulosic material (A), thereby imparting hydrophobicity to the surface of the cellulosic material (A). As a result, in the resin compositions obtained in Examples 1 to 4, the affinity between polypropylene and the surface of the cellulosic material (A) is increased, and the cellulosic material (A) is highly dispersed in the polypropylene, so that the molded articles are presumably excellent in flexural modulus and flexural strength.

[0134] On the other hand, in the resin composition obtained in Comparative Example 1, it is presumed that an ethylene-vinyl acetate copolymer composition layer was formed on the surface of the cellulose-based material (A), as shown in Figure 4. Since the ethylene-vinyl acetate copolymer has a lower proportion of structural units having hydrophobic methyl groups in the side chains than a polyvinyl acetate polymer (a homopolymer of vinyl acetate), it is presumed that the surface of the cellulose-based material (A) was not sufficiently hydrophobic, and that the resin composition obtained in Comparative Example 1 had lower dispersibility of the cellulose-based material (A) in polypropylene than the resin compositions obtained in Examples 1 to 4, resulting in lower flexural modulus and flexural strength of the molded article.

[0135] Furthermore, it was found that when polyamines (D) were added to the mixture (α) (Examples 2 to 4), the flexural modulus was improved compared to when no polyamines (D) were added (Example 1). Furthermore, when polyamines (D) were added to the mixture (α) and carboxylic acids (E) were added to the thermoplastic resin (C) (Example 2), or when polyamines (D) and carboxylic acids (E) were added to the mixture (α) (Example 3), the flexural modulus was improved compared to when polyamines (D) were added but no carboxylic acids (E) were added (Example 4). Furthermore, it was found that when acetic acid was added as the carboxylic acid (E) (Example 3), the flexural modulus was improved compared to when dehydroabietic acid was added (Example 2).

[0136] Furthermore, it was found that when polyamines (D) were added to the mixture (α) and dehydroabietic acid was added as carboxylic acids (E) to the thermoplastic resin (C) (Example 2), or when polyamines (D) were added to the mixture (α) without adding carboxylic acids (E) (Example 4), the bending strength was improved compared to when polyamines (D) and carboxylic acids (E) were not added to the mixture (α) (Example 1).

[0137] (Example 5) First, a polyvinyl acetate polymer emulsion containing polyvinyl alcohol as a dispersant ("Vinyl Acetate Resin Emulsion Wood Adhesive for Woodworking 605" manufactured by Cemedine Co., Ltd., water content: 56-60%, polyvinyl acetate polymer content: 40-44%) was added to undried softwood bleached kraft pulp (NBKP, moisture content: 50%) so that the blending amount in the resin composition was the blending amount shown in Table 2, and the mixture was stirred and mixed for 20 minutes using a kneader to prepare a mixture (α). Further, a pellet-shaped resin composition was produced in the same manner as in Example 1, except that the blending amount of polypropylene was changed to the blending amount shown in Table 2.

[0138] Comparative Example 2 First, maleic anhydride-modified polypropylene (MAPP, "UMEX 1001" manufactured by Sanyo Chemical Industries, Ltd.) was added to undried bleached softwood kraft pulp (NBKP, moisture content: 50%) so that the blending amount in the resin composition was the blending amount shown in Table 2, and the mixture was stirred and mixed for 20 minutes using a Henschel mixer to prepare a mixture. Further, a pellet-shaped resin composition was produced in the same manner as in Example 5, except that the blending amount of polypropylene was changed to the blending amount shown in Table 2.

[0139] Comparative Example 3 First, undried bleached softwood kraft pulp (NBKP, moisture content: 50%) was mixed in an amount corresponding to the blending amount in the resin composition shown in Table 2 with polypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation, melt index: 40) in an amount ¼ of the blending amount in the resin composition (blend amount shown in Table 2), and a pellet-shaped master batch was prepared in the same manner as in Example 5, except that 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the resulting mixture.

[0140] Thereafter, the remaining amount of polypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation, melt index: 40) was added to the obtained masterbatch, and a pellet-shaped resin composition was prepared in the same manner as in Example 5, except that 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was further added per 100 parts by mass of the obtained mixture.

[0141] Comparative Example 4 Only polypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation, melt index: 40) was subjected to each physical property test.

[0142] Example 6 First, a mixture (α) was prepared in the same manner as in Example 5, except that a polyvinyl acetate polymer emulsion containing polyvinyl alcohol as a dispersant ("Vinyl Acetate Resin Emulsion Wood Adhesive for Woodworking 605" manufactured by Cemedine Co., Ltd., water content: 56 to 60%, polyvinyl acetate polymer content: 40 to 44%) was added to undried bleached softwood kraft pulp (NBKP, moisture content: 50%) so that the blending amounts in the resin composition were as shown in Table 2.

[0143] Next, the obtained mixture (α) was mixed with impact-resistant polypropylene (Novatec BC6DRF manufactured by Japan Polypropylene Corporation, melt index: 2.5) in an amount of ¼ of the blending amount in the resin composition (blend amount shown in Table 2), and further, 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the obtained mixture, and a pellet-shaped masterbatch was prepared in the same manner as in Example 5.

[0144] Thereafter, the remaining amount of impact-resistant polypropylene (Novatec BC6DRF manufactured by Japan Polypropylene Corporation, melt index: 2.5) was added to the obtained masterbatch, and a pellet-shaped resin composition was prepared in the same manner as in Example 5, except that 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the obtained mixture.

[0145] Comparative Example 5 First, maleic anhydride-modified polypropylene (MAPP, "UMEX 1001" manufactured by Sanyo Chemical Industries, Ltd.) was added to undried bleached softwood kraft pulp (NBKP, moisture content: 50%) so that the blending amount in the resin composition was the blending amount shown in Table 2, and the mixture was stirred and mixed for 20 minutes using a Henschel mixer to prepare a mixture. Further, a pellet-shaped resin composition was prepared in the same manner as in Example 6, except that the blending amount of polypropylene was changed to the blending amount shown in Table 2.

[0146] Comparative Example 6 First, impact-resistant polypropylene (Novatec BC6DRF manufactured by Japan Polypropylene Corporation, melt index: 2.5) was mixed with undried softwood bleached kraft pulp (NBKP, moisture content: 50%) in an amount corresponding to the blending amount in the resin composition shown in Table 2, in an amount ¼ of the blending amount in the resin composition (blend amount shown in Table 2). Further, 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the resulting mixture. A pellet-shaped masterbatch was prepared in the same manner as in Example 6.

[0147] Thereafter, the remaining amount of impact-resistant polypropylene (Novatec BC6DRF manufactured by Japan Polypropylene Corporation, melt index: 2.5) was added to the obtained masterbatch, and a pellet-shaped resin composition was prepared in the same manner as in Example 6, except that 0.1 parts by mass of a phenolic antioxidant (Irganox 1010 manufactured by BASF) was added per 100 parts by mass of the obtained mixture.

[0148] Comparative Example 7 Only impact-resistant polypropylene (Novatec BC6DRF manufactured by Japan Polypropylene Corporation, melt index: 2.5) was subjected to each physical property test.

[0149] <Bending Test> A bending test was carried out in accordance with JIS K7171 for the pellet-shaped resin compositions obtained in Examples 5 to 6, Comparative Examples 2 to 3, and Comparative Examples 5 to 6, and the polypropylenes of Comparative Examples 4 and 7. Specifically, rectangular test pieces were prepared for the pellet-shaped resin compositions obtained in Examples 5 to 6, Comparative Examples 2 to 3, and Comparative Examples 5 to 6, and the polypropylenes of Comparative Examples 4 and 7, and a bending test was carried out to measure the flexural modulus and flexural strength in the same manner as in Examples 1 to 4 and Comparative Example 1. The results are shown in Table 2.

[0150] <Charpy Impact Test> A Charpy impact test was performed in accordance with JIS K7111-1 on the pellet-shaped resin compositions obtained in Examples 5-6, Comparative Examples 2-3, and Comparative Examples 5-6, and the polypropylenes of Comparative Examples 4 and 7. Specifically, rectangular test specimens (10 mm x 80 mm x 4 mm) were first prepared using an injection molding machine from the pellet-shaped resin compositions obtained in Examples 5-6, Comparative Examples 2-3, and Comparative Examples 5-6, and the polypropylenes of Comparative Examples 4 and 7. Next, the obtained test specimens were mounted in a Charpy impact tester, and a Charpy impact test was performed under the condition of a hammer weight of 2 J to measure the Charpy impact strength. The results are shown in Table 2.

[0151]

[0152] As shown in Table 2, the molded articles (Examples 5-6) made from the resin composition of the present invention, which is a melt-kneaded mixture of a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) and a thermoplastic resin (C), were confirmed to have superior flexural modulus, flexural strength, and Charpy impact strength compared to the molded articles (Comparative Examples 2-5) made from a resin composition, which is a melt-kneaded mixture of a mixture containing a cellulose-based material (A) and an acid anhydride-modified polyolefin (F) (acting as a dispersant) and a thermoplastic resin (C). From these results, it was confirmed that even when a non-micronized cellulose-based material (A) was used, a molded article with excellent mechanical strength could be obtained by blending a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant.

[0153] Furthermore, the molded article made of the resin composition obtained in Example 5 was superior in flexural modulus, flexural strength, and Charpy impact strength, despite the fact that the blending amount of the cellulose-based material (A) was smaller than those made of the resin compositions obtained in Comparative Examples 2 and 3. This is thought to be because the cellulose-based material (A) was more highly dispersed in the resin composition obtained in Example 5 than in the resin compositions obtained in Comparative Examples 2 and 3.

[0154] As described above, according to the present invention, it is possible to obtain a molded article having excellent mechanical strength, which is made from a resin composition containing a cellulose-based material and a thermoplastic resin.

[0155] Therefore, it is possible to produce automotive exterior and interior panels, electrical equipment housings, building materials, etc. using a resin composition of the present invention in smaller amounts than conventional resin compositions containing a cellulose-based material and a thermoplastic resin, and the present invention is useful for reducing greenhouse gas emissions. Furthermore, by using the resin composition of the present invention, various molded articles can be produced at low cost. Furthermore, the molded articles of the present invention can be used not only in the field of conventional fiber-reinforced plastics, but also in fields requiring even higher mechanical strength (e.g., bending strength).

Claims

1. A resin composition which is a melt-kneaded mixture of a mixture (α) containing a cellulose-based material (A) and a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant, and a thermoplastic resin (C).

2. The resin composition according to claim 1, wherein the mixture (α) further contains polyamines (D).

3. The resin composition according to claim 2, wherein the mixture (α) further contains a carboxylic acid (E).

4. The resin composition according to claim 2, which is a melt-kneaded product of the mixture (α) and a melt-kneaded product (β) containing the thermoplastic resin (C) and a carboxylic acid (E).

5. The resin composition according to claim 1, wherein the content of the polyvinyl acetate polymer emulsion (B) in the resin composition is 0.1 to 15 mass % calculated as polyvinyl acetate polymer.

6. A molded article made of the resin composition according to any one of claims 1 to 5.

7. A method for producing a resin composition, comprising: a step of preparing a mixture (α) by mixing a cellulose-based material (A) with a polyvinyl acetate polymer emulsion (B) containing polyvinyl alcohol as a dispersant; and a step of melt-kneading the mixture (α) with a thermoplastic resin (C).

8. The method for producing a resin composition according to claim 7, further comprising mixing the mixture (α) with a polyamine (D).

9. The method for producing a resin composition according to claim 8, further comprising mixing the mixture (α) with a carboxylic acid (E).

10. A method for producing a resin composition according to claim 8, further comprising the step of melt-kneading the thermoplastic resin (C) and a carboxylic acid (E) to prepare a melt-kneaded product (β), and melt-kneading the mixture (α) and the melt-kneaded product (β).

11. A method for producing a resin composition according to claim 7, wherein the cellulose-based material (A) and the polyvinyl acetate polymer emulsion (B) are mixed together so that the content of the polyvinyl acetate polymer emulsion (B) in the resulting resin composition is 0.1 to 15 mass % in terms of polyvinyl acetate polymer.