Resin composition, method for producing same, and molded body

Abstract

A resin composition according to the present invention contains a cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and ethylene-propylene copolymers.

Description

Resin composition, its manufacturing method, and molded article

[0001] The present invention relates to a resin composition containing a cellulose-based material, a method for producing the same, and a molded article of 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 view of the problems associated with the above-described conventional techniques, and aims to provide a resin composition that contains a cellulose-based substance and at least one thermoplastic resin selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer, and that is capable of forming a molded article having excellent mechanical strength; a method for producing the same; and a molded article of the resin composition.

[0007] As a result of extensive research conducted by the present inventors to achieve the above-mentioned object, they discovered that although two-component systems of a cellulose-based material and polyvinyl acetate, and two-component systems of polyvinyl acetate and polyethylene, polypropylene, or ethylene-propylene copolymer are difficult to melt-knead uniformly, three-component systems of a cellulose-based material, polyvinyl acetate, and the above-mentioned thermoplastic resin can be melt-kneaded uniformly, and further, that molded articles made from the resulting melt-kneaded product (resin composition) have excellent mechanical strength, which led to the completion of the present invention.

[0008] That is, the present invention provides the following aspects. [1] A resin composition that is a melt-kneaded product containing a cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer. [2] The resin composition according to [1], wherein the content of the polyvinyl acetate (B) is 1 to 40 mass%. [3] A molded product obtained by molding the resin composition according to [1] or [2]. [4] A method for producing a resin composition, comprising simultaneously melt-kneading the cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer. [5] A method for producing a resin composition according to [4], comprising simultaneously melt-kneading the cellulose-based material (A), the polyvinyl acetate (B), and a portion of the thermoplastic resin (C) to prepare a masterbatch, and then melt-kneading the masterbatch with the remainder of the thermoplastic resin (C).

[0009] According to the present invention, it is possible to obtain a molded article having excellent mechanical strength by molding a resin composition containing a cellulose-based material and at least one thermoplastic resin selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer.

[0010] 1 is an optical microscope photograph of the resin composition obtained in Example 1. FIG. 2 is an optical microscope photograph of the resin composition obtained in Example 2. FIG. 3 is an optical microscope photograph of the resin composition obtained in Example 3. FIG. 4 is an optical microscope photograph of the resin composition obtained in Example 5. FIG. 5 is an optical microscope photograph of the resin composition obtained in Comparative Example 1. FIG. 6 is an optical microscope photograph of the resin composition obtained in Comparative Example 2. FIG. 7 is a fluorescent microscope photograph of the resin composition obtained in Example 1. FIG. 8 is a fluorescent microscope photograph of the resin composition obtained in Example 2. FIG. 9 is a fluorescent microscope photograph of the resin composition obtained in Example 3. FIG. 10 is a fluorescent microscope photograph of the resin composition obtained in Example 1. FIG. 11 is a fluorescent microscope photograph of the resin composition obtained in Comparative Example 2. FIG. 12 is a graph showing the results (stress-strain curves) of bending tests of molded articles of the resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 and 2, and a molded article made of only polypropylene in Comparative Example 3. 1 is a graph showing the results (stress-strain curves) of bending tests of molded articles from the resin compositions obtained in Example 6 and Comparative Examples 4 and 5, and of a molded article made of only polypropylene in Comparative Example 6. FIG. 2 is a graph showing the results (stress-strain curves) of bending tests of molded articles from the resin compositions obtained in Example 7 and Comparative Examples 7 to 8, and of a molded article made of only polypropylene in Comparative Example 9. FIG. 3 is a graph showing the results (stress-strain curves) of bending tests of molded articles from the resin compositions obtained in Example 8 and Comparative Examples 10 and 11, and of a molded article made of only polyethylene in Comparative Example 12.

[0011] The present invention will be described in detail below based on preferred embodiments thereof.

[0012] [Resin Composition] First, the resin composition of the present invention will be described. The resin composition of the present invention is a melt-kneaded product containing a cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer. A molded article of this resin composition has excellent mechanical strength.

[0013] Each component used in the present invention will be described below.

[0014] (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). Furthermore, the microfiber cellulose-based material may be a non-microfiberized cellulose-based material that has been previously microfiberized.

[0015] 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).

[0016] 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. The average fiber diameter of such micronized cellulose fibers is not particularly limited, but is generally 1 nm to 10 μm. The micronized cellulose fibers may also be those obtained by micronizing the non-micronized cellulose fibers in advance (e.g., microfibrillated (MF) (MF cellulose fibers)). Furthermore, in the MF cellulose fibers, not all of the non-micronized cellulose fibers may be uniformly MF-treated. For example, the surface of a thick portion of a non-micronized cellulose fiber (e.g., a portion with a diameter of about 5 μm) may be MF-treated to a diameter of about 10 nm (partially MF cellulose fibers).

[0017] An example of the non-micronized cellulose powder is unmicronized wood flour. The average particle size of such a non-micronized cellulose powder is not particularly limited, but is generally 300 to 500 μm. An example of the micronized cellulose powder is micronized wood flour. The average particle size of such a micronized cellulose powder is not particularly limited, but is generally 1 nm to 100 μm. The non-micronized cellulose powder may be one that has been micronized in advance (for example, one that has been microfibrillated (MF) (MF cellulose powder)). Furthermore, in the MF cellulose powder, not all of the non-micronized cellulose powder may be uniformly MF. For example, a cellulose powder in which only a portion of the surface of the non-micronized cellulose powder has been MF (partially MF cellulose powder) may be used.

[0018] 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 pulverized (defibrated) or not pulverized (defibrated). Furthermore, pulp that has been pulverized (defibrated) may be pulverized (defibrated) in advance.

[0019] 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.

[0020] 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).

[0021] 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.

[0022] 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.

[0023] 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.

[0024] Furthermore, the cellulose-based material (A) used in the present invention may be either chemically modified (chemically modified cellulose-based material) or unmodified. That is, in the present invention, a resin composition capable of forming a molded article having excellent mechanical strength can be obtained not only when a chemically modified cellulose-based material (A) is used, but also when a chemically unmodified cellulose-based material is used. 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.

[0025] Examples of the chemically modified cellulose-based material include chemically modified cellulose-based fibers and chemically modified cellulose-based powders, and 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.

[0026] From the viewpoint of ease of chemical modification, the chemically modified cellulose material is preferably a chemically modified cellulose fiber, and more preferably a cellulose fiber in which the hydroxyl groups of the sugar chains and / or lignin constituting the surface of the cellulose fiber are esterified with an aliphatic carboxylic acid or an alkyl or alkenyl succinic anhydride. The chemically modified cellulose fiber may contain lignin (lignocellulose fiber) or may not contain lignin.

[0027] In the present invention, these cellulose-based materials (A) may be used alone or in combination of two or more.

[0028] (B) Polyvinyl Acetate The polyvinyl acetate (B) used in the present invention is a homopolymer of vinyl acetate and is a non-emulsion. By blending polyvinyl acetate (B) with a melt-kneaded product containing the cellulose-based material (A) and the thermoplastic resin (C) described below, it becomes possible to highly disperse the cellulose-based material (A) in the thermoplastic resin (C), thereby obtaining a molded product with excellent mechanical strength. There are no particular restrictions on the molecular weight of polyvinyl acetate (B), but from the viewpoints of the burden on the manufacturing equipment, such as melt viscosity during heating, and ease of dispersion, it is preferably 500 to 500,000, more preferably 50,000 to 150,000.

[0029] (C) Thermoplastic Resin The thermoplastic resin (C) used in the present invention is at least one selected from the group consisting of polyethylene, polypropylene, and ethylene-propylene copolymer. The polyethylene, polypropylene, and ethylene-propylene copolymer may be petrochemically-derived polyethylene, petrochemically-derived polypropylene, or petrochemically-derived ethylene-propylene copolymer. However, from the viewpoints of environmental conservation, thermal stability, strength properties, and lightweight molded articles, biomass-derived polyethylene, biomass-derived polypropylene, a copolymer of biomass-derived ethylene and biomass-derived propylene, or a copolymer of at least one of biomass-derived ethylene and biomass-derived propylene and at least one of petrochemically-derived ethylene and petrochemically-derived propylene is preferred. The molecular weight of the thermoplastic resin (C) is not particularly limited, but from the viewpoints of mechanical strength, heat resistance, and moldability, a molecular weight of 40,000 to 800,000 is preferred.

[0030] (Resin Composition) The resin composition of the present invention is a melt-kneaded product containing a cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer. By using such a resin composition, a molded article having excellent mechanical strength can be obtained.

[0031] In the resin composition of the present invention, the content of the cellulose-based material (A) is preferably 1 to 90% by mass, more preferably 2 to 50% by mass, and even more preferably 3 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.

[0032] The content of the polyvinyl acetate (B) is preferably 1 to 40% by mass, more preferably 2 to 25% by mass, and even more preferably 3 to 15% by mass, based on the total mass of the resulting resin composition. If the content of the polyvinyl acetate (B) is less than the lower limit, 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 of the polyvinyl acetate (B) is more than the upper limit, the excess polyvinyl acetate (B) loosens the interface or overflows into the thermoplastic resin (C), and the physical properties of the resin composition and the molded product thereof tend to be reduced.

[0033] The content of the thermoplastic resin (C) is preferably 5 to 98% by mass, more preferably 40 to 96% by mass, and even more preferably 70 to 94% 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.

[0034] Furthermore, the resin composition of the present invention may contain various additives such as polyvinyl alcohol, antioxidants, surfactants, plasticizers, antistatic agents, ultraviolet absorbers, colorants, deodorizers, etc., to the extent that the effects of the present invention are not impaired. These additives may be added directly to the resin composition containing the cellulose-based material (A), polyvinyl acetate (B), and thermoplastic resin (C), or may be added in the form of a solution obtained by dissolving them in a solvent or the like.

[0035] [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 for simultaneously melt-kneading a cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer. By simultaneously melt-kneading at least three components, namely the cellulose-based material (A), the polyvinyl acetate (B), and the thermoplastic resin (C), the cellulose-based material (A) can be highly dispersed in the thermoplastic resin (C), resulting in a resin composition capable of forming a molded article with excellent mechanical strength. Furthermore, because there is no need to use a solvent (e.g., tripropylene glycol (TPG)) for highly dispersing the cellulose-based material (A) in the thermoplastic resin (C), a moderate bonding effect is exhibited between the cellulose-based material (A) and the thermoplastic resin (C), which tends to improve the mechanical strength of the molded article.

[0036] In the method for producing a resin composition of the present invention, the entire amount of the cellulose-based material (A), the entire amount of the polyvinyl acetate (B), and the entire amount of the thermoplastic resin (C) to be blended into the resulting resin composition may be melt-kneaded simultaneously (Method 1), or the entire amount of the cellulose-based material (A), the entire amount of the polyvinyl acetate (B), and a portion of the thermoplastic resin (C) may be melt-kneaded simultaneously to prepare a masterbatch, and then this masterbatch and the remaining amount of the thermoplastic resin (C) may be melt-kneaded (Method 2).

[0037] In the method for producing a resin composition of the present invention, the cellulose-based material (A), the polyvinyl acetate (B), and the thermoplastic resin (C) 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.

[0038] (Method 1) In the method 1, first, the total amount of the cellulose-based material (A), the total amount of the polyvinyl acetate (B), the total amount of the thermoplastic resin (C), and, if necessary, the total amount of the various additives to be blended in the resulting resin composition are mixed to prepare a mixture (α). There are no particular limitations on the mixing method used to prepare the mixture (α), and examples include stirring using a stirring device such as a planetary mixer and kneading using a kneading device such as an extruder. Among these mixing methods, when kneading using a kneading device such as an extruder, it is possible to continuously prepare the mixture (α) and the melt-kneading described below.

[0039] Next, the mixture (α) prepared in this manner is melt-kneaded to obtain the resin composition (melt-kneaded product) of the present invention. In this resin composition, the cellulose-based material (A) is highly dispersed in the thermoplastic resin (C), and by molding this resin composition, a molded product with excellent mechanical strength can be obtained. The method for melt-kneading the mixture (α) is not particularly limited, and examples thereof include kneading using a kneading device such as an extruder. At this time, the mixture (α) is melt-kneaded while or after removing water contained in the mixture (α). The temperature during melt-kneading is preferably in the range of from the softening point of the thermoplastic resin (C) to the melting point + 20°C, and more preferably in the range of from the melting point of the thermoplastic resin (C) to the melting point + 10°C.

[0040] (Method 2) In the method 2, first, the entire amount of the cellulose-based material (A), the entire amount of the polyvinyl acetate (B), a portion of the thermoplastic resin (C), and, if necessary, the entire amount or a portion of the various additives to be blended in the resulting resin composition are mixed to prepare a mixture (β).

[0041] The amount of the portion of the thermoplastic resin (C) is not particularly limited as long as the cellulose-based material (A) is highly dispersed in the thermoplastic resin (C) in the resulting masterbatch. However, from the viewpoint of the dispersibility of the cellulose-based material (A) in the thermoplastic resin (C), the amount is preferably 1 / 6 to 1 / 1.5, and more preferably 1 / 4 to 1 / 2, of the total amount of the thermoplastic resin (C) blended in the resulting resin composition.

[0042] The mixing method for preparing the mixture (β) 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 with a kneading device such as an extruder is performed, it becomes possible to continuously carry out the preparation of the mixture (β) and the melt-kneading described below.

[0043] Next, the mixture (β) prepared in this manner is melt-kneaded to obtain a masterbatch (melt-kneaded product). In this masterbatch, the cellulose-based material (A) is highly dispersed in the thermoplastic resin (C). The method for melt-kneading the mixture (β) is not particularly limited, and examples thereof include kneading using a kneading device such as an extruder. At this time, the mixture (β) is melt-kneaded while or after removing water contained in the mixture (β). 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, and more preferably in the range of the melting point of the thermoplastic resin (C) to the melting point + 10°C.

[0044] Next, the masterbatch thus prepared is mixed with the remaining amount of the thermoplastic resin (C) to prepare a mixture (γ). The mixing method for preparing the mixture (γ) 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 with a kneading device such as an extruder, it is possible to continuously prepare the mixture (γ) and the melt-kneading described below.

[0045] Next, the mixture (γ) prepared in this manner is melt-kneaded to obtain the resin composition (melt-kneaded product) of the present invention. In this resin composition, the cellulose-based material (A) is highly dispersed in the thermoplastic resin (C), and by molding this resin composition, a molded product with excellent mechanical strength can be obtained. The method for melt-kneading the mixture (γ) is not particularly limited, and examples thereof include kneading using a kneading device such as an extruder. In this case, the mixture (γ) is melt-kneaded while or after removing water contained in the mixture (γ). The temperature during melt-kneading is preferably in the range of from the softening point of the thermoplastic resin (C) to the melting point + 20°C, and more preferably in the range of from the melting point of the thermoplastic resin (C) to the melting point + 10°C.

[0046] [Molded Article] Next, the molded article of the present invention will be described. The molded article of the present invention is obtained by molding 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 obtained by molding this resin composition has excellent mechanical strength.

[0047] 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.

[0048] 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.

[0049] Example 1 First, 30 parts by mass of MF cellulose fiber (Daicel Miraize Co., Ltd., "Cerish KY110N", solid content: 15% by mass, moisture content: 85%), 30 parts by mass of powdered polyvinyl acetate (Wacker, molecular weight: 70,000), and 40 parts by mass of homopolypropylene (Japan Polypropylene Corporation, "Novatec MA04A") were blended and mixed using a planetary mixer. The resulting mixture was quantitatively charged into an extruder (L / D = 45) set at 170°C, and melt-kneaded while removing moisture by drying to prepare a pellet-shaped masterbatch (solid content: 100% by mass).

[0050] Next, 100 parts by mass of this pellet-shaped masterbatch was mixed with 200 parts by mass of homopolypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation), and the resulting mixture was quantitatively charged into an extruder (L / D = 45) set at 180°C and melt-kneaded to obtain a pellet-shaped resin composition. The contents of each component in this resin composition are shown in Table 1.

[0051] (Example 2) A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 1, except that the amount of powdered polyvinyl acetate was changed to 15 parts by mass and the amount of homopolypropylene was changed to 55 parts by mass. A pellet-shaped resin composition was obtained in the same manner as in Example 1, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 1.

[0052] (Example 3) A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 1, except that the amount of powdered polyvinyl acetate was changed to 7.5 parts by mass and the amount of homopolypropylene was changed to 62.5 parts by mass. A pellet-shaped resin composition was obtained in the same manner as in Example 1, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 1.

[0053] Example 4 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 1, except that the amount of homopolypropylene was changed to 38.5 parts by mass and 1.5 parts by mass of a PVA aqueous solution (partially saponified, PVA molecular weight: 44,000) calculated as polyvinyl alcohol (PVA) was further blended. A pellet-shaped resin composition was obtained in the same manner as in Example 1, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 1.

[0054] Example 5 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 1, except that the amount of powdered polyvinyl acetate was changed to 15 parts by mass, the amount of homopolypropylene was changed to 53.5 parts by mass, and 1.5 parts by mass of a PVA aqueous solution (partially saponified, PVA molecular weight: 44,000) calculated as polyvinyl alcohol (PVA) was further blended. A pellet-shaped resin composition was obtained in the same manner as in Example 1, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 1.

[0055] Comparative Example 1 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 1, except that the amount of homopolypropylene was changed to 68.5 parts by mass and powdered polyvinyl acetate was not mixed. A pellet-shaped resin composition was obtained in the same manner as in Example 1, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 1.

[0056] (Comparative Example 2) First, 30 parts by mass of MF cellulose fiber (Daicel Miraize Co., Ltd. "Cerish KY110N", solid content: 15% by mass, moisture content: 85%) was added to 50 parts by mass of tripropylene glycol (TPG), and 70 parts by mass of homopolypropylene (Japan Polypropylene Corporation "Novatec MA04A") was further blended and mixed using a planetary mixer. The resulting mixture was quantitatively charged into an extruder (L / D = 45) set at 170 ° C., melt-kneaded while removing moisture by drying, and a pellet-shaped masterbatch was prepared. This pellet-shaped masterbatch was immersed in hot water at 80 ° C. for 12 hours to remove the TPG and wash, and then dried at 110 ° C. for 12 hours. The solid content was determined to be 20.6% by mass.

[0057] Next, 100 parts by mass of the pellet-shaped masterbatch and 200 parts by mass of homopolypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation) were mixed in terms of solid content, and the resulting mixture was quantitatively charged into an extruder (L / D = 45) set at 180°C and melt-kneaded to obtain a pellet-shaped resin composition. The contents of each component in this resin composition are shown in Table 1.

[0058] Comparative Example 3 Only homopolypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation) was used.

[0059] <Optical Microscopy and Fluorescence Microscopy> The pellet-shaped resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 2 were observed using an optical microscope and a fluorescence microscope. FIGS. 1 to 7 are optical microscope photographs of the pellet-shaped resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 2, respectively, and FIGS. 8 to 14 are fluorescence microscope photographs of the pellet-shaped resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 2, respectively. The resin compositions of the present invention (Examples 1 to 5, FIGS. 1 to 5 and 8 to 12), which are melt-kneaded mixtures containing a cellulose-based material (A), polyvinyl acetate (B), and a thermoplastic resin (C), exhibited a higher dispersion of the cellulose-based material (A) than the resin compositions not containing polyvinyl acetate (B) (Comparative Example 1, FIGS. 6 and 13). It was confirmed that the dispersibility of the cellulose-based material (A) was comparable to that obtained when the cellulose-based material (A) was dispersed using TPG (Comparative Example 2, FIGS. 7 and 14). It was also found that the dispersibility of the cellulose-based material (A) tended to increase with increasing polyvinyl acetate (B) content.

[0060] <Bending Test> A bending test was conducted in accordance with JIS K7171 for the pellet-shaped resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 and 2, and the polypropylene of Comparative Example 3. Specifically, first, rectangular test specimens (10 mm x 80 mm x 4 mm) were prepared using an injection molding machine from the pellet-shaped resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 and 2, and the polypropylene of Comparative Example 3. Next, the obtained test specimens were left to stand in an atmosphere of 23°C and 50% relative humidity for two days, 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 a stress-strain curve was obtained. The results are shown in Figure 15. The flexural modulus and flexural strength were determined from the obtained stress-strain curve. These results are shown in Table 1.

[0061]

[0062] As shown in Table 1, the molded articles of the resin compositions of the present invention (Examples 1 to 5), which are melt-kneaded products containing a cellulose-based material (A), polyvinyl acetate (B), and polypropylene as the thermoplastic resin (C), were found to have superior flexural modulus and flexural strength compared to a molded article of a resin composition not containing polyvinyl acetate (B) (Comparative Example 1), a molded article of a resin composition in which the cellulose-based material (A) was dispersed using TPG (Comparative Example 2), and a molded article of polypropylene alone (Comparative Example 3). It was also found that the flexural modulus and flexural strength increased with increasing polyvinyl acetate (B) content.

[0063] The reason why the molded articles of the resin compositions obtained in Examples 1 to 5 had superior flexural modulus and flexural strength compared to the molded article of polypropylene alone (Comparative Example 3) and the molded article of the resin composition not containing polyvinyl acetate (B) (Comparative Example 1) is not entirely clear, but the present inventors speculate as follows. That is, in the molded article of the resin composition not containing polyvinyl acetate (B) (Comparative Example 1), as shown in FIGS. 6 and 13, the cellulose-based material (A) aggregated in the resin composition, and this aggregated material played a role similar to a filler, which is thought to have improved the flexural modulus and flexural strength compared to the molded article of polypropylene alone (Comparative Example 3). Furthermore, as shown in FIGS. 1 to 5 and 8 to 12, the molded articles of the resin compositions of the present invention (Examples 1 to 5) have improved flexural modulus and flexural strength compared to the molded article of the resin composition not containing polyvinyl acetate (B) (Comparative Example 1).

[0064] Furthermore, the reason why the molded articles of the resin compositions obtained in Examples 1 to 5 had superior flexural modulus and flexural strength compared to the molded article of the resin composition in which the cellulose-based material (A) was dispersed using TPG (Comparative Example 2) is not entirely clear, but the present inventors speculate as follows: That is, in the molded article of the resin composition in which the cellulose-based material (A) was dispersed using TPG (Comparative Example 2), as shown in Figures 7 and 14, although the cellulose-based material (A) was highly dispersed in the resin composition, the adhesion effect between the cellulose-based material (A) and the thermoplastic resin (C) was insufficient, so that the cellulose-based material (A) slipped when stress was applied during the bending test, and the flexural modulus and flexural strength were not improved compared to the molded articles of the resin compositions of the present invention (Examples 1 to 5) and the molded article of the resin composition not containing polyvinyl acetate (B) (Comparative Example 1).

[0065] Example 6 First, 50 parts by mass of non-defibrated softwood bleached kraft pulp (non-defibrated NBKP, solids: 85% by mass, moisture content: 15%), 10 parts by mass of powdered polyvinyl acetate (manufactured by WACKER, molecular weight: 70,000), and 40 parts by mass of homopolypropylene ("Novatec MA04A" manufactured by Japan Polypropylene Corporation) were blended and mixed using a Henschel mixer. The resulting mixture was quantitatively charged into an extruder (L / D = 45) set at 170°C, and melt-kneaded while removing moisture by drying to prepare a pellet-shaped masterbatch (solids content: 100% by mass).

[0066] Next, 100 parts by mass of this pellet-shaped masterbatch was mixed with 100 parts by mass of homopolypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation), and the resulting mixture was quantitatively charged into an extruder (L / D = 45) set at 180°C and melt-kneaded to obtain a pellet-shaped resin composition. The contents of each component in this resin composition are shown in Table 2.

[0067] Comparative Example 4 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 6, except that 10 parts by mass of maleic anhydride-modified polypropylene ("Kayabrid 002PP-W" manufactured by Nissei Sangyo Co., Ltd., molecular weight: 70,000) was used instead of powdered polyvinyl acetate. A pellet-shaped resin composition was prepared in the same manner as in Example 6, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 2.

[0068] Comparative Example 5 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 6, except that the amount of homopolypropylene was changed to 50 parts by mass and no powdered polyvinyl acetate was added. A pellet-shaped resin composition was prepared in the same manner as in Example 6, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 2.

[0069] Comparative Example 6 Only homopolypropylene (Novatec MA04A manufactured by Japan Polypropylene Corporation) was used.

[0070] Example 7 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 6, except that 40 parts by mass of block polypropylene (Novatec BC6DRF, manufactured by Japan Polypropylene Corporation) was used instead of the homopolypropylene. Next, a pellet-shaped resin composition was prepared in the same manner as in Example 6, except that 100 parts by mass of this pellet-shaped masterbatch and 100 parts by mass of block polypropylene (Novatec BC6DRF, manufactured by Japan Polypropylene Corporation) were mixed. The contents of each component in this resin composition are shown in Table 2.

[0071] Comparative Example 7 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 7, except that 10 parts by mass of maleic anhydride-modified polypropylene ("Kayabrid 002PP-W" manufactured by Nissei Sangyo Co., Ltd., molecular weight: 70,000) was used instead of powdered polyvinyl acetate. A pellet-shaped resin composition was prepared in the same manner as in Example 7, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 2.

[0072] Comparative Example 8 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 7, except that the amount of block polypropylene was changed to 50 parts by mass and no powdered polyvinyl acetate was added. A pellet-shaped resin composition was prepared in the same manner as in Example 7, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 2.

[0073] Comparative Example 9 Only block polypropylene (Novatec BC6DRF manufactured by Japan Polypropylene Corporation) was used.

[0074] Example 8 A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 6, except that 40 parts by mass of low-density polyethylene ("Sumikathene F200-0" manufactured by Sumitomo Chemical Co., Ltd.) was used instead of the homopolypropylene. Next, a pellet-shaped resin composition was prepared in the same manner as in Example 6, except that 100 parts by mass of this pellet-shaped masterbatch and 100 parts by mass of low-density polyethylene ("Sumikathene F200-0" manufactured by Sumitomo Chemical Co., Ltd.) were mixed. The content of each component in this resin composition is shown in Table 3.

[0075] (Comparative Example 10) A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 8, except that 10 parts by mass of maleic anhydride-modified polypropylene ("Kayabrid 002PP-W" manufactured by Nissei Sangyo Co., Ltd., molecular weight: 70,000) was used instead of powdered polyvinyl acetate. A pellet-shaped resin composition was prepared in the same manner as in Example 8, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 3.

[0076] (Comparative Example 11) A pellet-shaped masterbatch (solid content: 100% by mass) was prepared in the same manner as in Example 8, except that the amount of low-density polyethylene was changed to 50 parts by mass and powdered polyvinyl acetate was not blended. A pellet-shaped resin composition was prepared in the same manner as in Example 8, except that 100 parts by mass of this pellet-shaped masterbatch was used. The contents of each component in this resin composition are shown in Table 3.

[0077] Comparative Example 12 Only low-density polyethylene ("Sumikathene F200-0" manufactured by Sumitomo Chemical Co., Ltd.) was used.

[0078] <Bending Test> A bending test was performed in accordance with JIS K7171 on the pellet-shaped resin compositions obtained in Examples 6 to 8, Comparative Examples 4 to 5, Comparative Examples 7 to 8, and Comparative Examples 10 to 11, the polypropylenes of Comparative Examples 6 and 9, and the polyethylene of Comparative Example 12. Specifically, rectangular test specimens were prepared for the pellet-shaped resin compositions obtained in Examples 6 to 8, Comparative Examples 4 to 5, Comparative Examples 7 to 8, and Comparative Examples 10 to 11, the polypropylenes of Comparative Examples 6 and 9, and the polyethylene of Comparative Example 12, in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 3, and bending tests were performed to determine stress-strain curves. The results are shown in Figures 16 to 18. The flexural modulus and flexural strength were determined from the obtained stress-strain curves. These results are shown in Tables 2 and 3.

[0079] <Charpy Impact Test> Charpy impact tests were performed in accordance with JIS K7111-1 on the pellet-shaped resin compositions obtained in Examples 6 to 8, Comparative Examples 4 to 5, Comparative Examples 7 to 8, and Comparative Examples 10 to 11, the polypropylenes of Comparative Examples 6 and 9, and the polyethylene of Comparative Example 12. 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 6 to 8, Comparative Examples 4 to 5, Comparative Examples 7 to 8, and Comparative Examples 10 to 11, the polypropylenes of Comparative Examples 6 and 9, and the polyethylene of Comparative Example 12. Next, the obtained test specimens were mounted in a Charpy impact tester, and a Charpy impact test was performed under a hammer weight of 2 J to measure the Charpy impact strength. The results are shown in Tables 2 and 3.

[0080]

[0081] As shown in Table 2, the molded body of the resin composition of the present invention, which is a melt-kneaded product containing a cellulose-based material (A), polyvinyl acetate (B), and a thermoplastic resin (C), was confirmed to have superior flexural modulus and flexural strength, as well as superior Charpy impact strength, when non-defibrated NBKP was used as the cellulose-based material (A) (Example 6), as well as when MF cellulose fiber was used (Examples 1 to 5), compared to the molded body of the resin composition not containing polyvinyl acetate (B) (Comparative Example 5) and the molded body of only thermoplastic resin (C) (Comparative Example 6).

[0082] Furthermore, as shown in Table 2, it was confirmed that the molded articles of the resin composition of the present invention (Examples 6 and 7), which is a melt-kneaded product containing non-fibrillated NBKP as the cellulose-based material (A), polyvinyl acetate (B), and polypropylene as the thermoplastic resin (C), have superior flexural modulus, flexural strength, and Charpy impact strength compared to molded articles of the resin composition not containing polyvinyl acetate (B) (Comparative Examples 5 and 8) when compared with molded articles containing the same polypropylene.

[0083] From the above results, it was confirmed that in a molded body of a resin composition containing a cellulose-based material (A) and a thermoplastic resin (C), when polypropylene is used as the thermoplastic resin (C), the mechanical strength is improved by blending polyvinyl acetate (B) compared to when polyvinyl acetate (B) is not blended.

[0084] On the other hand, when compared with molded articles containing the same polypropylene, the molded articles of the resin compositions (Comparative Examples 4 and 7) in which maleic anhydride-modified polypropylene was blended instead of polyvinyl acetate (B) were inferior in flexural modulus and Charpy impact strength to the molded articles of the resin compositions (Comparative Examples 5 and 8) that did not contain polyvinyl acetate (B) and maleic anhydride-modified polypropylene.

[0085] Furthermore, it was also confirmed that the molded articles of the resin compositions of the present invention containing polyvinyl acetate (B) (Examples 6 and 7) were superior in flexural modulus and Charpy impact strength to the molded articles of the resin compositions containing maleic anhydride-modified polypropylene instead of polyvinyl acetate (B) (Comparative Examples 4 and 7) when compared with molded articles containing the same polypropylene.

[0086]

[0087] As shown in Table 3, it was confirmed that a molded article of the resin composition of the present invention (Example 8), which is a melt-kneaded product containing non-fibrillated NBKP as the cellulose-based material (A), polyvinyl acetate (B), and polyethylene as the thermoplastic resin (C), had superior flexural modulus, flexural strength, and Charpy impact strength compared to a molded article of a resin composition (Comparative Example 11) that did not contain polyvinyl acetate (B). From these results, it was confirmed that when polyethylene was used as the thermoplastic resin (C) in a molded article of a resin composition containing a cellulose-based material (A) and a thermoplastic resin (C), the incorporation of polyvinyl acetate (B) improved the mechanical strength compared to when polyvinyl acetate (B) was not incorporated.

[0088] On the other hand, the molded article of the resin composition (Comparative Example 10) in which maleic anhydride-modified polypropylene was blended instead of polyvinyl acetate (B) was inferior in flexural modulus and Charpy impact strength to the molded article of the resin composition (Comparative Example 11) in which polyvinyl acetate (B) and maleic anhydride-modified polypropylene were not included.

[0089] It was also confirmed that the molded article of the resin composition of the present invention containing polyvinyl acetate (B) (Example 8) was superior in flexural modulus, flexural strength, and Charpy impact strength to the molded article of the resin composition containing maleic anhydride-modified polypropylene instead of polyvinyl acetate (B) (Comparative Example 10).

[0090] 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 at least one thermoplastic resin selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer.

[0091] Therefore, the resin composition of the present invention can be used in smaller amounts than conventional resin compositions containing a cellulose-based material and at least one thermoplastic resin selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer to produce automotive exterior panels, interior panels, housings for electrical equipment, building materials, and the like, making the present invention 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 in fields requiring even higher mechanical strength (e.g., bending strength) in addition to the fields of conventional fiber-reinforced plastics.

Claims

1. A resin composition which is a melt-kneaded mixture containing a cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and ethylene-propylene copolymer.

2. The resin composition according to claim 1, wherein the content of the polyvinyl acetate (B) is 1 to 40% by mass.

3. A molded article obtained by molding the resin composition according to claim 1 or 2.

4. A method for producing a resin composition, comprising simultaneously melt-kneading a cellulose-based material (A), polyvinyl acetate (B), and at least one thermoplastic resin (C) selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer.

5. A method for producing a resin composition according to claim 4, wherein the cellulose-based material (A), the polyvinyl acetate (B), and a portion of the thermoplastic resin (C) are simultaneously melt-kneaded to prepare a masterbatch, and then the masterbatch and the remainder of the thermoplastic resin (C) are melt-kneaded.

Images