Cellulose fiber reinforced resin molding and method for producing the same

Abstract

A cellulose-fiber-reinforced molded resin object obtained by molding a cellulose-fiber-reinforced resin composite comprising a polypropylene resin, an alkoxysilane-modified polypropylene resin, and cellulose fibers; and a method for producing the molded resin object.

Description

[Technical Field]

[0001] The present invention relates to a cellulose fiber reinforced resin molding and a method for producing the same. [Background technology]

[0002] Cellulose fiber is an almost inexhaustible natural resource found in all plants. Because it is lightweight yet strong, its use in automobile parts and structural materials in combination with resins is being considered. However, in order to put cellulose fiber-reinforced resins into practical use, it is necessary to sufficiently increase the integration between the highly hydrophilic cellulose fibers and the highly hydrophobic resin, such as polyolefin resin, and there are limitations to improving the strengthening (reinforcing) effect of cellulose fibers on the resin.

[0003] In order to enhance the reinforcing effect of cellulose fibers, it has been proposed in recent years to add a compatibilizer such as maleic anhydride-modified polyolefin to improve the adhesion at the interface between the cellulose fibers and the hydrophobic resin. For example, Patent Document 1 proposes obtaining a fiber-reinforced resin by using a polyolefin modified with an unsaturated compound containing a carboxyl group or a carboxyl derivative group in addition to a polyolefin resin and plant fibers. Furthermore, Patent Document 3 proposes obtaining a fiber-reinforced resin by using a modified polypropylene resin grafted with an unsaturated carboxylic acid or its anhydride or derivative in addition to a polypropylene resin and cellulose fibers. Furthermore, Patent Document 4 proposes obtaining a fiber-reinforced resin by using an epoxy-modified polyolefin resin in addition to a polyolefin resin and cellulose fibers. Patent Document 5 proposes obtaining a fiber-reinforced resin using a mixture or reaction composition of a cellulosic material, a silane-containing polymer, and a thermoplastic resin, and proposes using a copolymer of an α-olefin and an ethylenically unsaturated silane as the silane-containing polymer. Furthermore, Patent Document 6 proposes obtaining a fiber-reinforced resin by kneading a composite of a synthetic polymer obtained by graft-polymerizing an alkoxysilane monomer with natural plant fibers with the synthetic polymer.

[0004] On the other hand, Patent Document 2 proposes that when cellulose fibers and resin are combined, the cellulose fibers are surface-treated with a silane coupling agent before use. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-283475 [Patent Document 2] Patent No. 5322470 [Patent Document 3] Patent No. 5578854 [Patent Document 4] Patent No. 6052167 [Patent Document 5] Patent No. 5128955 [Patent Document 6] International Publication No. 2008 / 053817 Summary of the Invention [Problem to be solved by the invention]

[0006] Lightweight and high strength are required for automobile parts, structural materials, etc. Furthermore, many of these are intended for outdoor use or use in harsh environments, and therefore durability is required to maintain the desired high strength even when exposed to high temperature, high humidity conditions, and rain for a long period of time. The present inventors have studied the cellulose fiber-reinforced resins described in the above patent documents and have found that there is room for improvement in mechanical strength and long-term durability under high temperature and high humidity conditions.

[0007] An object of the present invention is to provide a cellulose fiber reinforced resin molding that has excellent mechanical strength and can maintain sufficiently high mechanical strength even when exposed to harsh conditions of high temperature and high humidity for a long period of time, and a method for producing the same. [Means for solving the problem]

[0008] The present inventors have investigated solutions to the above technical problems for cellulose fiber-reinforced resin moldings containing cellulose fibers and polypropylene resin from the perspective of the compatibilizer used, and have found that by using an alkoxysilane-modified polypropylene resin as a compatibilizer, the mechanical strength of the resulting cellulose fiber-reinforced resin molding can be effectively increased, and further, that this molding is less likely to deteriorate in mechanical strength even when exposed to a high-temperature, high-humidity environment for a long period of time.The present invention was completed after further investigation based on these findings.

[0009] That is, the above-mentioned problems of the present invention have been solved by the following means. [1] A cellulose fiber reinforced resin molded article obtained by molding a cellulose fiber reinforced resin composite containing polypropylene resin, alkoxysilane-modified polypropylene resin, and cellulose fibers. [2] The cellulose fiber reinforced resin molding according to [1], wherein the alkoxysilane-modified polypropylene resin is a graft-modified polypropylene resin with a silane coupling agent having an ethylenically unsaturated group-containing group and an alkoxysilyl group. [3] The cellulose fiber reinforced resin molding according to [2], wherein the silane coupling agent is vinyltrimethoxysilane. [4] The cellulose fiber reinforced resin molding according to [2], wherein the silane coupling agent is a (trimethoxysilyl)alkyl (meth)acrylate. [5] The cellulose fiber reinforced resin molding according to [4], wherein the alkoxysilane modified polypropylene resin is a graft modified polypropylene resin with the silane coupling agent and a reaction aid having a vinyl group. [6] The cellulose fiber reinforced resin molded article according to [5], wherein the Q value of the reaction aid having a vinyl group is 0.010 to 5.00. [7] 6. The cellulose fiber reinforced resin molded article according to claim 5, wherein the Q value of the reaction aid having a vinyl group is 0.54 to 5.00. [8] The cellulose fiber reinforced resin molded article according to any one of [5] to [7], wherein the reaction aid having a vinyl group is at least one of a styrene compound and a (meth)acrylic acid ester compound. [9] The cellulose fiber reinforced resin molded article according to any one of [5] to [8], wherein the reaction aid having a vinyl group is a styrene compound.

[10] The cellulose fiber reinforced resin molded body according to any one of [1] to [9], wherein the content of the alkoxysilane-modified polypropylene resin in the cellulose fiber reinforced resin molded body is 0.1 to 20 mass %.

[11] A method for producing a cellulose fiber reinforced resin molding according to any one of [1] to [9], comprising the following steps (a) and (b): (a) A step of mixing a polypropylene resin and a silane coupling agent in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide, and subjecting the polypropylene resin to a grafting reaction with the silane coupling agent to prepare an alkoxysilane-modified polypropylene resin. (b) melt-mixing the alkoxysilane-modified polypropylene resin, cellulose fibers, and polypropylene resin such that the proportion of the alkoxysilane-modified polypropylene resin in the total amount of the alkoxysilane-modified polypropylene resin, the cellulose fibers, and the polypropylene resin is 0.1 to 20% by mass;

[12] The method for producing a cellulose fiber reinforced resin molding according to

[11] , wherein the alkoxysilane-modified polypropylene resin is prepared in the presence of a reaction aid having a vinyl group.

[13] The method for producing a cellulose fiber reinforced resin molding according to

[12] , wherein the alkoxysilane-modified polypropylene resin is prepared in the presence of a styrene compound.

[0010] In the description of the present invention, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit. [Effects of the Invention]

[0011] The cellulose fiber reinforced resin molding of the present invention exhibits excellent tensile strength and can achieve sufficiently high mechanical strength even when exposed to a high-temperature, high-humidity environment for a long period of time, resulting in excellent long-term reliability. The method for producing a cellulose fiber reinforced resin molding of the present invention is a method suitable for producing the cellulose fiber reinforced resin molding. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Resin molded body] The cellulose fiber reinforced resin molding of the present invention (hereinafter also referred to as "resin molding of the present invention") is a resin molding obtained by molding a cellulose fiber reinforced resin composite containing a polypropylene resin, an alkoxysilane-modified polypropylene resin, and cellulose fibers. The shape of the resin molding can be set depending on its application. The cellulose fiber-reinforced resin composite constituting the resin molded article of the present invention contains at least a portion of a condensate of an alkoxysilane-modified polypropylene resin and cellulose fibers. More specifically, the cellulose fiber-reinforced resin composition constituting the resin molded article of the present invention contains a condensate formed by a dealcoholization condensation reaction between an alkoxysilyl group of an alkoxysilane-modified polypropylene resin and a hydroxyl group of a cellulose fiber, and / or a condensate formed by dehydration condensation between a silanol group generated by hydrolysis of an alkoxysilyl group of an alkoxysilane-modified polypropylene resin and a hydroxyl group of a cellulose fiber. This sufficiently enhances the adhesion at the interface between the alkoxysilane-modified polypropylene resin and the cellulose fibers, thereby enhancing the dispersibility of the cellulose fibers in the resin molded article and effectively utilizing the reinforcing effect of the cellulose fibers. Furthermore, the cellulose fiber-reinforced resin composite constituting the resin molded article of the present invention may contain a condensate formed by a dealcoholization / dehydration condensation reaction between an alkoxysilyl group and a silanol group. In this case, a network can be formed via the reaction points between the alkoxysilane-modified polypropylene resin and the cellulose fibers. The cellulose fiber-reinforced resin composite constituting the resin molded article of the present invention may contain an alkoxysilane-modified polypropylene resin that has not undergone a dealcoholization / dehydration condensation reaction, or cellulose fibers that have not undergone a dealcoholization / dehydration condensation reaction. Furthermore, the alkoxysilyl group / silanol group and the cellulose fibers may be bonded by hydrogen bonding or the like in addition to the dealcoholization / dehydration condensation reaction. The components of the cellulose fiber reinforced resin composite that constitutes the resin molded article of the present invention and the materials used in preparing the resin molded article will be described below.

[0013] (polypropylene resin) The polypropylene resin (hereinafter also referred to as polypropylene resin A) in the cellulose fiber reinforced resin composite constituting the resin molded article of the present invention can be any polypropylene resin conventionally used for automobile parts, structural materials, etc., without any particular limitation. In the present invention, polypropylene resin A may be referred to as the base resin.

[0014] Polypropylene includes not only propylene homopolymers but also ethylene-propylene copolymers (random copolymers and block copolymers).

[0015] (Alkoxysilane modified polypropylene resin) The alkoxysilane-modified polypropylene resin acts as a compatibilizer between the base resin and the cellulose fibers. The alkoxysilane-modified polypropylene resin is not particularly limited as long as it is a polypropylene resin having an alkoxysilyl group in its main chain or at its terminal. The alkoxysilane-modified polypropylene resin may be one prepared by modifying a polypropylene resin with a silane coupling agent (alkoxysilane compound) having an alkoxysilyl group. That is, the alkoxysilane-modified polypropylene resin can be one obtained by grafting a polypropylene resin with a silane coupling agent having an alkoxysilyl group. The alkoxysilane-modified polypropylene resin is preferably a graft-modified product of a polypropylene resin with a silane coupling agent having an ethylenically unsaturated group and an alkoxysilyl group, as described below. The alkoxysilane-modified polypropylene resin can be synthesized by a conventional method, and commercially available products may also be used.

[0016] The polypropylene resin before modification used in preparing the alkoxysilane-modified polypropylene resin preferably has a site capable of undergoing grafting reaction with a silane coupling agent (described later) and a site capable of undergoing grafting reaction in the presence of an organic peroxide. Such a site capable of grafting reaction is not particularly limited, but examples thereof include an unsaturated bond site in the carbon chain and a carbon atom having a hydrogen atom. The polypropylene resin A described above can be used as the polypropylene resin raw material used in preparing the alkoxysilane-modified polypropylene resin.

[0017] The silane coupling agent used in preparing the alkoxysilane-modified polypropylene resin is preferably an alkoxysilane compound having a functional group for grafting. Examples of silane coupling agents that can be used include those having a site (group or atom) capable of undergoing a grafting reaction with a polypropylene resin in the presence of radicals generated by decomposition of an organic peroxide, and an alkoxysilyl group. Examples of sites capable of undergoing a grafting reaction with a polypropylene resin include groups containing an ethylenically unsaturated group. Examples of groups containing an ethylenically unsaturated group include, but are not limited to, vinyl groups, allyl groups, (meth)acryloyloxy groups, (meth)acryloyloxyalkylene groups, and p-styryl groups. The alkoxysilyl group may be in the form of a trialkoxysilyl group, a dialkoxysilyl group, or a monoalkoxysilyl group, and a trialkoxysilane compound is preferably used. The alkoxy group of the alkoxysilyl group preferably has 1 to 6 carbon atoms, more preferably a methoxy group or an ethoxy group. The silane coupling agent is preferably one having a group containing an ethylenically unsaturated group and an alkoxysilyl group. One type of silane coupling agent may be used, or two or more types may be used. Specific examples of the silane coupling agent include vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, vinyldimethoxyethoxysilane, vinyldimethoxybutoxysilane, vinyldiethoxybutoxysilane, allyltrimethoxysilane, allyltriethoxysilane, vinyltriacetoxysilane, and trimethoxy(4-vinylphenyl)silane; and (meth)acrylic silane compounds such as 3-(trimethoxysilyl)propyl (meth)acrylate, 3-(methyldimethoxysilyl)propyl (meth)acrylate, 3-(methyldiethoxysilyl)propyl (meth)acrylate, 3-(triethoxysilyl)propyl (meth)acrylate, and 3-(methoxydimethylsilyl)propyl (meth)acrylate. Among these, vinyltrimethoxysilane or (trimethoxysilyl)alkyl(meth)acrylate is particularly preferred, and at least one of (trimethoxysilyl)alkyl(meth)acrylate and vinyltrimethoxysilane can be used. The alkyl group of the (trimethoxysilyl)alkyl(meth)acrylate preferably has 1 to 10 carbon atoms, more preferably 1 to 6, and even more preferably 2 to 4, with propyl being particularly preferred. From the viewpoint of increasing tensile strength, it is preferred to use 3-(trimethoxysilyl)propyl methacrylate.

[0018] The organic peroxide used in preparing the alkoxysilane-modified polypropylene resin can be a compound that generates radicals upon thermal decomposition. These radicals abstract hydrogen atoms from the polypropylene resin or the silane coupling agent, causing a radical reaction (grafting reaction, addition reaction) between the silane coupling agent and the polypropylene resin, resulting in the alkoxysilane-modified polypropylene resin. As the organic peroxide, a wide variety of organic peroxides commonly used in radical polymerization reactions can be used. For example, benzoyl peroxide, dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, or 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexyne-3 is preferred. One or more organic peroxides may be used. The decomposition temperature of the organic peroxide is preferably 80 to 195°C, and particularly preferably 125 to 180°C. In the present invention, the decomposition temperature of the organic peroxide means the temperature (one-minute half-life temperature) at which, when a single-component organic peroxide is heated, it decomposes into two or more compounds within one minute at a certain temperature or temperature range, reducing the concentration (mass) by half. Specifically, this can be determined by thermal analysis such as DSC.

[0019] In preparing the alkoxysilane-modified polypropylene resin, the grafting ratio of the silane coupling agent to the polypropylene resin is not particularly limited as long as it is within a range that does not impair the effects of the present invention. The grafting ratio of the silane coupling agent in the alkoxysilane-modified polypropylene resin is, for example, preferably 0.1 to 20 mass%, more preferably 1 to 5 mass%, and particularly preferably 2 to 5 mass%. The grafting ratio refers to the number of parts (%) of the graft structure relative to 100 parts by mass (100%) of polypropylene. The grafting rate can be set within a predetermined range depending on the type or content of the organic peroxide, the type and amount of the polypropylene resin and silane coupling agent used as raw materials, and the like. The grafting rate can be determined by removing unreacted monomer components by heating and dissolving an alkoxysilane-modified polypropylene resin in hot xylene, dropping it into acetone, and reprecipitating it. FT-IR analysis of the purified alkoxysilane-modified polypropylene resin thus reprecipitated can then be performed. The grafting rate can be calculated in terms of mass % from the intensity ratio of the peak derived from the polypropylene and the peak derived from the graft structure. In FT-IR, the peak derived from the alkoxysilyl group is at 1100 cm -1 A peak due to the Si-O asymmetric stretching vibration is observed around 803 cm -1 A peak due to Si-O bending vibration is observed around 1193 cm -1 Peaks due to Si-C stretching vibrations can be detected.

[0020] From the viewpoint of the type of silane coupling agent used in the preparation, preferred embodiments of the alkoxysilane-modified polypropylene resin can be divided into an embodiment (first embodiment) of an alkoxysilane-modified polypropylene resin prepared using a vinylsilane compound and an embodiment (second embodiment) of an alkoxysilane-modified polypropylene resin prepared using a (meth)acrylic silane compound.

[0021] The alkoxysilane-modified polypropylene resin may further have a vinyl group-containing reaction aid grafted onto its main chain. This form can be used for both the alkoxysilane-modified polypropylene resin of the first embodiment and the alkoxysilane-modified polypropylene resin of the second embodiment, but is preferred for the alkoxysilane-modified polypropylene resin of the second embodiment. The reaction aid having a vinyl group is not particularly limited as long as it has a vinyl group and a substituent that has the effect of stabilizing the resonance of radicals (excluding those corresponding to the above-mentioned silane coupling agent). Here, the compound does not include a form having a main chain with a repeating unit in its structure. The Q value of the vinyl group-containing reaction aid is not particularly limited and can be 0.010 or greater, preferably 0.49 to 5.00, more preferably 0.54 to 5.00, more preferably 0.54 to 4.38, more preferably 0.8 to 4.38, and even more preferably 0.96 to 4.38. Here, the Q value refers to a parameter related to the resonance effect of monomers in a radical copolymerization reaction of two types of monomers. In the present invention, the specific Q value of each reaction aid is based on the Qe value described in the "Plastics Materials Dictionary" (https: / / www.plastics-material.com / qe%e5%80%a4 / ) and other literature. For the significance of the Q value in radical polymerization reactions, see Takayuki Otsu, "Monomer Structure and Reactivity: Empirical Parameters and Radical Polymerization Reactivity," Organic Synthetic Chemistry, Vol. 28, No. 12, pp. 1183-1196, 1970. This document describes that conjugated monomers with large Q values ​​have high reactivity as monomers but low radical reactivity, and that non-conjugated monomers with small Q values ​​have low reactivity as monomers but high radical reactivity. It also describes that the Q value can be calculated from the reaction rate constant of the propagation reaction in a radical copolymerization reaction with styrene, with styrene as the reference (1.0). The Q value of compounds for which Q values ​​are not listed in documents such as the "Plastic Materials Dictionary" can be calculated by referring to the method described in this document. Specific examples of reaction aids having a vinyl group are listed below along with their Q values. For some reaction aids, the Q value is not listed. Specific examples of reaction aids having a vinyl group that can be used include styrene compounds, vinylpyridine compounds, acrylonitrile (Q value: 0.48), (meth)acrylic acid ester compounds, (meth)acrylamide compounds, and fatty acid vinyl esters. Examples of styrene compounds include styrene (Q value: 1.00), 2-methylstyrene, 3-methylstyrene (Q value: 1.57), 4-methylstyrene (Q value: 1.10), and α-methylstyrene (Q value: 0.97). Examples of vinylpyridine compounds include 4-vinylpyridine (Q value: 2.47). Examples of the (meth)acrylic acid ester compound include glycidyl methacrylate (Q value: 0.96) and 2-hydroxypropyl methacrylate (Q value: 4.38). Examples of fatty acid vinyl esters include vinyl laurate (Q value: 0.011). From the viewpoint of increasing the mechanical strength, the reaction aid having a vinyl group is preferably a reaction aid having a Q value of 0.54 to 5.00. From the viewpoint of increasing the mechanical strength, the reaction aid having a vinyl group is preferably a styrene compound or a (meth)acrylic acid ester compound.

[0022] The grafting rate of the vinyl group-containing reaction aid in the alkoxysilane-modified polypropylene resin is preferably 0.1 to 20% by mass, more preferably 1 to 5% by mass. The grafting rate of the vinyl group-containing reaction aid can be calculated in terms of mass% by dissolving the alkoxysilane-modified polypropylene resin in hot xylene, adding the resultant alkoxysilane-modified polypropylene resin dropwise into acetone and reprecipitating the resultant to remove unreacted monomer components, and then measuring the FT-IR.

[0023] In alkoxysilane-modified polypropylene resins in which a reaction aid having a vinyl group is present during the grafting reaction, it is thought that the resin is stabilized and the grafting reaction of the silane coupling agent is made more efficient. Although the reason for this is unclear, one possible reason is that when these reaction aids are grafted onto the polypropylene resin during the preparation of the alkoxysilane-modified polypropylene resin, they resonantly stabilize the polymer radicals generated in the polypropylene resin, suppressing chain scission of the polypropylene, which is a side reaction of the grafting reaction, and also increase the efficiency of introducing the silane coupling agent through the copolymerization reaction with the (meth)acrylsilane compound.

[0024] (cellulose fiber) The origin of the cellulose fibers used in the present invention is not particularly limited, and examples include cellulose fibers obtained from raw materials such as wood, bamboo, hemp, jute, kenaf, agricultural waste (e.g., straw from wheat or rice, stalks from corn or cotton, sugarcane), cloth, recycled pulp, and waste paper. Pulp is also used as a raw material for paper and is primarily composed of tracheids extracted from plants. Chemically, its primary component is a polysaccharide, and the primary component is cellulose. Wood-derived cellulose fibers are particularly preferred as the cellulose fibers used in the present invention. The cellulose fibers can be obtained by any manufacturing method without any particular limitations. Examples include cellulose fibers obtained by mechanical processing, which involves pulverization using physical forces, chemical processing such as the kraft pulp method, sulfide pulp method, and alkali pulp method, or a combination of these processes. In the chemical processing, chemicals such as caustic soda are used to remove lignin, hemicellulose, and the like from plant raw materials such as wood, thereby extracting near-pure cellulose fibers. Cellulose fibers obtained in this manner are also called pulp fibers.

[0025] The cellulose fibers used in the present invention are preferably those prepared by chemical treatment, and more preferably those prepared by the kraft pulp method, from the viewpoint of improving mechanical properties. The cellulose fibers contained in the resin molded product of the present invention may be of one type or two or more types.

[0026] The cross-sectional diameter of the cellulose fibers used in the present invention is preferably 1 to 30 μm, more preferably 1 to 25 μm, and even more preferably 5 to 20 μm, and the length (fiber length) is preferably 10 to 2200 μm, and more preferably 50 to 1000 μm.

[0027] The diameter of the cellulose fibers contained in the resin molded product of the present invention can be measured using a scanning electron microscope (SEM) or a fiber analyzer. The fiber length of the cellulose fibers can also be measured by SEM observation. In measuring the fiber length by SEM observation, the resin components in the resin molded product of the present invention are eluted with hot xylene, and the residue is placed on a stage, and the residue is subjected to a treatment such as vapor deposition, followed by SEM observation, whereby the fiber length can be measured.

[0028] (Content of each ingredient) The content of polypropylene resin A in the resin molded product of the present invention is preferably 30 to 99 mass%, more preferably 50 to 99 mass%, even more preferably 60 to 99 mass%, and still more preferably 70 to 95 mass%. The content of the alkoxysilane-modified polypropylene resin in the resin molded product is preferably 0.1 to 20% by mass, more preferably 0.5 to 20% by mass, even more preferably 1 to 20% by mass, even more preferably 1 to 10% by mass, and even more preferably 1 to 5% by mass. The content of the alkoxysilane-modified polypropylene resin in the resin molded product refers to the total amount of the alkoxysilane-modified polypropylene resin that has formed a dehydration condensation product with cellulose fibers and the alkoxysilane-modified polypropylene resin that has not formed a dehydration condensation product with cellulose fibers. While this depends on the content of other components, increasing the content of the alkoxysilane-modified polypropylene resin tends to increase the initial mechanical strength, but tends to decrease durability under high temperature and high humidity. The content of cellulose fibers in the resin molded product of the present invention is preferably 0.9 to 50% by mass, more preferably 1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 5 to 30% by mass. Although it depends on the contents of other components, increasing the content of cellulose fibers tends to increase the initial mechanical strength, but on the other hand, tends to decrease the durability under high temperature and high humidity conditions. From the viewpoint of increasing the initial tensile strength, it is also preferable that the contents of the respective components in the resin molded product of the present invention be as follows. That is, the content of polypropylene resin A is preferably 25 to 95% by mass, preferably 30 to 90% by mass, or even preferably 30 to 87% by mass. The content of alkoxysilane-modified polypropylene resin is preferably 2 to 25% by mass, or even preferably 3 to 20% by mass. The content of cellulose fiber is preferably 1 to 60% by mass, or even preferably 3 to 50% by mass, or even preferably 5 to 50% by mass, or even preferably 7 to 50% by mass, or even preferably 8 to 50% by mass. The ratio (mass ratio) of the content of cellulose fiber to the content of alkoxysilane-modified polypropylene resin is preferably [content of cellulose fiber] / [alkoxysilane-modified polypropylene resin]=0.1 to 20, more preferably [content of cellulose fiber] / [alkoxysilane-modified polypropylene resin]=1 to 10, and even more preferably [content of cellulose fiber] / [alkoxysilane-modified polypropylene resin]=2 to 8.

[0029] (Other ingredients) The resin molded article of the present invention may be composed of the above-mentioned polypropylene resin A, alkoxysilane-modified polypropylene resin, and cellulose fibers, and may also contain the following components within the range that does not impair the effects of the present invention. For example, an elastomer such as an ethylene-α-olefin copolymer may be added to improve the physical properties of the resin molded article. Furthermore, the resin molded product of the present invention may contain, as appropriate, antioxidants, light stabilizers, radical scavengers, ultraviolet absorbers, colorants (dyes, organic pigments, inorganic pigments), fillers, lubricants, plasticizers, processing aids such as acrylic processing aids, foaming agents, lubricants such as paraffin wax, surface treatment agents, crystal nucleating agents, mold release agents, hydrolysis inhibitors, antiblocking agents, antistatic agents, antifogging agents, antifogging agents, ion trapping agents, flame retardants, flame retardant aids, and the like, within a range that does not impair the above-mentioned purpose. Furthermore, when the resin molded article of the present invention is produced by a preferred method for producing the resin molded article of the present invention, which will be described later, the resin molded article of the present invention may or may not contain a hydrophilic compound such as water or maleic anhydride.

[0030] (Method for determining whether or not cellulose fiber is contained) The presence or absence of cellulose fibers in the resin molded article of the present invention can be confirmed as follows. The cellulose in cellulose fibers is known to have various crystal structures, such as type I and type II. Natural cellulose has type Iα (triclinic) and type Iβ (monoclinic) crystal structures, and plant-derived cellulose generally contains a large amount of type Iβ crystals. In wide-angle X-ray diffraction measurement, the resin molded article of the present invention has a scattering vector s of 3.86±0.1 nm -1 This diffraction peak is derived from the (004) plane of the Iβ type crystal of cellulose. That is, in the resin molded product of the present invention, at least a part of the cellulose in the cellulose fiber has a crystalline structure, and at least a part of that is Iβ type crystal. There is no particular restriction on the crystal structure other than the Iβ type crystal that occupies the crystalline structure of cellulose. Hereinafter, cellulose fiber will be referred to as "a cellulose fiber having a scattering vector s of 3.86±0.1 nm" -1 A component having a diffraction peak at a position corresponding to the diffraction peak is sometimes referred to as a "component having a diffraction peak at a position corresponding to the diffraction peak." The presence of cellulose fibers can be confirmed by various methods. For example, it can be confirmed by observing the diffraction peaks derived from cellulose crystals in cellulose fibers using X-rays. Care must be taken because the diffraction peak position varies depending on the wavelength of the X-rays used, but when CuKα rays (λ = 0.15418 nm) are used, the scattering vector s is 3.86 nm. -1A diffraction peak originating from the (004) plane of cellulose Iβ crystals can be observed near (2θ = 34.6°). In order to capture the diffraction from the (004) plane, the sample must be rotated by θ before the X-rays are incident. In other words, when using CuKα radiation, the sample stage must be rotated θ = 17.3°. Other diffraction peaks originating from cellulose crystals can be observed inside the (004) plane, but their diffraction positions overlap with those of the diffraction peaks originating from polypropylene, making it difficult to determine whether they are distinct diffraction peaks. For this reason, in this specification, the presence or absence of cellulose fibers is determined using the diffraction peak from the (004) plane of cellulose Iβ crystals.

[0031] [Method for producing resin molded body] The resin molded article of the present invention can be obtained by melt-mixing at least polypropylene resin A, an alkoxysilane-modified polypropylene resin, and cellulose fibers, and molding the resulting molten mixture (cellulose fiber-reinforced resin composite). That is, the method for producing a resin molded article of the present invention includes the steps of melt-mixing polypropylene resin A, an alkoxysilane-modified polypropylene resin, and cellulose fibers, and molding the mixture. By melt-mixing, the alkoxysilyl groups of the alkoxysilane-modified polypropylene resin undergo a dealcoholization condensation reaction with the hydroxyl groups of the cellulose fibers, and / or the silanol groups generated by hydrolysis of the alkoxysilyl groups of the alkoxysilane-modified polypropylene resin undergo dehydration condensation with the hydroxyl groups of the cellulose fibers. These condensation reactions enhance the adhesion (integrity) between the alkoxysilane-modified polypropylene resin and the cellulose fibers, effectively improving the dispersibility of the cellulose fibers in the polypropylene resin A and the reinforcing effect of the cellulose fibers. In order to efficiently enhance the reinforcing effect of the cellulose fibers, a catalyst that promotes the condensation may be used.

[0032] The amounts of polypropylene resin A, alkoxysilane-modified polypropylene resin, and cellulose fiber blended during melt mixing are set to be the amounts that will result in the contents in the resin molded product described above. The melt-mixing temperature is not particularly limited as long as it is equal to or higher than the melting point of the resin, and can be, for example, 160 to 230°C, and more preferably 170 to 210°C. The melt mixing temperature is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower, from the viewpoint of reducing thermal decomposition of the cellulose fibers. When the melt-mixing step is carried out at a high temperature, an antioxidant or the like may be added to the melt-mixing step in order to suppress thermal degradation or oxidative degradation, for example. The melt-mixing time is not particularly limited and can be set appropriately. The apparatus used for the melt mixing is not particularly limited as long as it is capable of melt mixing at or above the melting point of the resin components. Examples include a blender, kneader, mixing roll, Banbury mixer, and single-screw or twin-screw extruder, with a twin-screw extruder being preferred. From the viewpoint of ease of handling in the subsequent molding step, it is preferable to process the obtained molten mixture into pellets (hereinafter, the obtained pellets may also be simply referred to as "pellets"). The conditions for pelletization are not particularly limited, and the pelletization can be carried out by a conventional method. For example, the molten mixture can be cooled with water and then processed into pellets using a strand cutter or the like. Prior to melt-mixing, the components may be dry-blended (pre-mixed). The dry-blending method is not particularly limited and can be carried out according to a conventional method.

[0033] To improve the dispersion of cellulose in the base resin during the melt mixing, the alkoxysilane-modified polypropylene resin and cellulose fibers may be premixed at a temperature below the melting point of the alkoxysilane-modified polypropylene resin before melt kneading, or may be melt mixed in the presence of a cellulose dispersion aid. When melt mixing is performed in the presence of a cellulose dispersion aid, the cellulose dispersion aid can be added to a mixing device (e.g., an extruder) and recovered through a vent. Water and maleic anhydride are preferred as cellulose dispersion aids, and water is more preferred because it is easy to separate and recover, has low environmental impact, and even if it remains, it has little adverse effect on cellulose.

[0034] The method for molding the molten mixture is not particularly limited as long as it can be molded into a desired shape. For example, a method of melt compression molding the molten mixture, a method of injection molding, etc. may be mentioned. The molten mixture may be processed into pellets and then molded into a desired shape. In the present invention, it is preferable to obtain a molded article by processing the molten mixture into pellets and then injection molding it. Molding can be carried out simultaneously with or consecutively to melt mixing. That is, an embodiment in which the components are melt mixed during melt molding, such as injection molding, or immediately before that can be used. For example, a series of steps can be employed in which the components are melt mixed in a molding device, then injected, and molded into a desired shape.

[0035] In the above injection molding, the injection temperature is not particularly limited as long as it is equal to or higher than the melting point of the polypropylene resin. For example, when polypropylene resin is used, the injection temperature can be 160 to 230°C, and preferably 170 to 210°C. The injection temperature is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower, from the viewpoint of reducing thermal decomposition of the cellulose fibers. The conditions for the injection molding, such as the injection speed, mold temperature, pressure holding, and pressure holding time, can be adjusted appropriately depending on the purpose.

[0036] In the melt compression molding, the melt compression temperature is not particularly limited as long as it is equal to or higher than the melting point of the polypropylene resin. For example, when a polypropylene resin is used, the temperature can be 160 to 230°C, preferably 170 to 210°C. The melt compression temperature is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower, from the viewpoint of reducing thermal decomposition of the cellulose fibers. The conditions for the melt compression molding, such as preheating time, pressurizing time, and pressure, can be adjusted appropriately depending on the purpose. The apparatus used for the melt compression molding is not particularly limited and may be, for example, a press. Alternatively, sheeting using an extruder for sheet molding may also be used. The shape of the sheet is not particularly limited, but can be processed into, for example, a dumbbell shape. Furthermore, the width, length, thickness, etc. can be appropriately adjusted to facilitate the aforementioned stretching. For example, the thickness of the sheet is preferably 2 mm or less, more preferably 1 mm or less.

[0037] The alkoxysilane-modified polypropylene resin can be prepared by grafting a silane coupling agent onto a polypropylene resin in the presence of radicals generated by decomposition of an organic peroxide. That is, the polypropylene resin and the silane coupling agent are melt-mixed in the presence of the organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide. The raw materials used in this preparation (polypropylene resin, silane coupling agent, and organic peroxide) are as described above. The temperature at which the above components are melted and mixed is equal to or higher than the decomposition temperature of the organic peroxide, preferably a temperature between [the decomposition temperature of the organic peroxide + 25°C] and [the decomposition temperature of the organic peroxide + 110°C]. At this mixing temperature, the above components melt, the organic peroxide decomposes to generate radicals, and the required grafting reaction proceeds sufficiently. Depending on the raw materials used, the melt-mixing temperature can be 160 to 300°C, 170 to 250°C, or 180 to 210°C. Other conditions, such as the mixing time, can be appropriately set in consideration of efficiency and purpose. The kneading device used for mixing may be a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, or various kneaders. In preparing the alkoxysilane-modified polypropylene resin, the amount of the silane coupling agent mixed per 100 parts by mass of the raw material polypropylene resin is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, and even more preferably 2 to 6 parts by mass. In preparing the alkoxysilane-modified polypropylene resin, the amount of organic peroxide added relative to 100 parts by mass of the raw material polypropylene resin is preferably 0.001 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, even more preferably 0.05 to 5 parts by mass, still more preferably 0.05 to 3 parts by mass, and also preferably 0.1 to 2 parts by mass.

[0038] When a (meth)acrylic silane compound is used as the silane coupling agent, the preparation of the alkoxysilane-modified polypropylene resin can also be carried out in the presence of a reaction aid having a vinyl group. Preparation in the presence of a reaction aid having a vinyl group can improve the reaction efficiency of the (meth)acrylic silane compound. Specifically, the reaction aid having a vinyl group is added when the polypropylene resin and the (meth)acrylic silane compound are melt-mixed in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide. In preparing the alkoxysilane-modified polypropylene resin, the amount of the reaction aid having a vinyl group added per 100 parts by mass of the raw polypropylene resin is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, even more preferably 1 to 7 parts by mass, and particularly preferably 1.5 to 5 parts by mass.

[0039] The preparation of the alkoxysilane-modified polypropylene resin can also be carried out simultaneously with melt-mixing of the polypropylene resin A with the cellulose fibers. That is, the polypropylene resin A can be molded while undergoing a dealcoholization / dehydration condensation reaction with the cellulose fibers while being partially modified with the alkoxysilane, to obtain the resin molded article of the present invention.

[0040] In the production method of the present invention, subsequent to the preparation of the alkoxysilane-modified polypropylene resin, the polypropylene resin A and cellulose fibers can be melt-mixed. A preferred embodiment of the production method of the present invention is as follows. A method for producing a cellulose fiber reinforced resin molded body containing polypropylene resin, alkoxysilane-modified polypropylene resin, and cellulose fibers, comprising the following steps (a) and (b): (a) A step of mixing a polypropylene resin and a silane coupling agent in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide, and subjecting the polypropylene resin to a grafting reaction with the silane coupling agent to prepare an alkoxysilane-modified polypropylene resin. (b) A step of melt-mixing the alkoxysilane-modified polypropylene resin, cellulose fibers, and polypropylene resin such that the proportion of the alkoxysilane-modified polypropylene resin in the total amount of the alkoxysilane-modified polypropylene resin, the cellulose fibers, and the polypropylene resin is 0.1 to 20 mass%. When a (meth)acrylic silane compound is used as the silane coupling agent (second embodiment), the preparation of the alkoxysilane-modified polypropylene resin is preferably carried out in the presence of a reaction aid having a vinyl group, as described above, and more preferably in the presence of a styrene compound.

[0041] [Application] The resin molded article of the present invention can be used as the following products, parts, and / or members that require mechanical strength and long-term durability: transportation equipment (automobiles, motorcycles, trains, aircraft, etc.), structural members for robot arms, amusement robot parts, prosthetic limb members, home appliance materials, office automation equipment housings, information processing equipment, mobile terminals, building materials, greenhouse films, drainage facilities, toiletry product materials, various tanks, containers, sheets, packaging materials, toys, stationery, food containers, bobbins, tubes, furniture materials (wall materials, handrails, etc.), shoes, and sporting goods.

[0042] Examples of materials for transportation equipment include vehicle materials, such as trims such as dashboard trim, door trim, and pillar trim, interior parts such as meter panels, meter housings, glove boxes, package trays, roof headlinings, consoles, instrument panels, armrests, seats, seat backs, trunk lids, trunk lid lowers, door inner panels, pillars, spare tire covers, door handles, light housings, and back trays, bumpers, hoods, spoilers, radiator grills, fenders, fender liners, rocker panels, side steps, door outer panels, side doors, These include exterior parts such as back doors, roofs, roof carriers, wheel caps / covers, door mirror covers, under covers, as well as battery cases, engine covers, fuel tanks, fuel tubes, fuel filler boxes, air intake ducts, air cleaner housings, air conditioner housings, coolant reserve tanks, radiator reserve tanks, window washer tanks, intake manifolds, rotating parts such as fans and pulleys, parts such as wire harness protectors, connection boxes or connectors, and integrally molded parts such as front end modules and front end panels. [Example]

[0043] The present invention will be described in more detail based on examples, but the present invention is not limited to these examples except as defined in the present invention. In the following examples and comparative examples, "parts" means "parts by mass" unless otherwise specified.

[0044] -Materials used- The materials used are listed below. <Cellulose fiber> ARBOCEL B400 (product name), manufactured by RETTENMAIER <Polypropylene resin> J106MG (product name), manufactured by Prime Polymer Co., Ltd. <Resin modifying monomer> 3-(trimethoxysilyl)propyl methacrylate, manufactured by Tokyo Chemical Industry Co., Ltd. Vinyltrimethoxysilane, manufactured by Tokyo Chemical Industry Co., Ltd. Glycidyl methacrylate, manufactured by Tokyo Chemical Industry Co., Ltd. <Reaction aids containing vinyl groups> Styrene, manufactured by Junsei Chemical Co., Ltd. Vinyl laurate, manufactured by Tokyo Chemical Industry Co., Ltd. Acrylonitrile, manufactured by Tokyo Chemical Industry Co., Ltd. Glycidyl methacrylate, manufactured by Tokyo Chemical Industry Co., Ltd. α-Methylstyrene, manufactured by Tokyo Chemical Industry Co., Ltd. 2-Hydroxypropyl methacrylate, manufactured by Tokyo Chemical Industry Co., Ltd. <Organic peroxide> Dicumyl peroxide: Percumyl D (trade name), manufactured by Nippon Oil & Fats Co., Ltd., 1-minute half-life temperature 175.2°C <Maleic anhydride modified polypropylene resin> Maleic anhydride modified PP (MAH-PP): Rikeaid MG250P (product name), manufactured by Riken Vitamin Co., Ltd.

[0045] The resin molded bodies of Examples 1 to 11, which were prepared using a graft-modified polypropylene resin with a silane coupling agent as the alkoxysilane-modified polypropylene resin, the resin molded bodies of Comparative Examples 1, 2, and 5, which were prepared using a modified material other than this graft-modified material, and the resin molded bodies of Comparative Examples 3, 4, and 6 to 8, which were prepared without using any modified material, are described below.

[0046] Example 1 -Preparation of modified resin- An alkoxysilane-modified polypropylene resin (modified resin) was prepared as follows using polypropylene resin (PP) as the base resin, 3-(trimethoxysilyl)propyl methacrylate as the silane coupling agent, and styrene as the reaction aid. Polypropylene resin was charged into a co-rotating twin-screw extruder (trade name: KZW15TW-45MG-NH, manufactured by Technovel Co., Ltd.) with a screw diameter of 15 mm and an L / D ratio of 45. A mixed solution of 3-(trimethoxysilyl)propyl methacrylate (SiMA), styrene, and dicumyl peroxide was added dropwise via a syringe through a liquid addition vent located midway through the barrel to maintain a constant ratio, and the mixture was extruded into strands at a strand die temperature of 190 °C. The mixture was adjusted so that 5 parts by weight of 3-(trimethoxysilyl)propyl methacrylate (SiMA), 3.75 parts by weight of styrene, and 0.2 parts by weight of dicumyl peroxide were mixed per 100 parts by weight of polypropylene resin. After cooling and cutting, pellets of 3-(trimethoxysilyl)propyl methacrylate-modified polypropylene resin (SiMA-PP) were obtained.

[0047] - Melt mixing and molding - 79 parts by weight of polypropylene resin, 1 part by weight of SiMA-PP, and 20 parts by weight of cellulose fiber were added and dry-blended. The mixture was then fed into a 15 mm twin-screw extruder (product name: KZW15TW-45MG-NH, Technovel Co., Ltd.). The mixture was melt-mixed at 170 °C in the twin-screw extruder and discharged from an extrusion die (strand die) set at 190 °C. The molten mixture was water-cooled and then processed into pellets using a strand cutter. The pellets were thoroughly dried and then fed into an injection molding machine (product name: ROBOSHOT α-S30iA, Fanuc Corporation) to obtain JIS No. 5 dumbbell test pieces (resin molded articles).

[0048] <Example 2> A resin molded article was obtained in the same manner as in Example 1, except that the amount of SiMA-PP added was changed to 3 parts by mass and the amount of polypropylene resin was changed to 77 parts by mass.

[0049] Example 3 A resin molded article was obtained in the same manner as in Example 1, except that the amount of SiMA-PP added was changed to 5 parts by mass and the amount of polypropylene resin was changed to 75 parts by mass.

[0050] Example 4 A resin molded body was obtained in the same manner as in Example 1, except that the amount of SiMA-PP added was changed to 5 parts by mass, the amount of cellulose fiber was changed to 1 part by mass, and the amount of polypropylene resin was changed to 94 parts by mass.

[0051] <Example 5> A resin molded body was obtained in the same manner as in Example 1, except that the amount of SiMA-PP added was changed to 5 parts by mass, the amount of cellulose fiber was changed to 5 parts by mass, and the amount of polypropylene resin was changed to 90 parts by mass.

[0052] Example 6 A resin molded body was obtained in the same manner as in Example 1, except that the amount of SiMA-PP added was changed to 5 parts by mass, the amount of cellulose fiber was changed to 10 parts by mass, and the amount of polypropylene resin was changed to 85 parts by mass.

[0053] Example 7 A resin molded body was obtained in the same manner as in Example 1, except that the amount of SiMA-PP added was changed to 7 parts by mass, the amount of cellulose fiber was changed to 30 parts by mass, and the amount of polypropylene resin was changed to 63 parts by mass.

[0054] Example 8 A resin molded body was obtained in the same manner as in Example 1, except that the amount of SiMA-PP was changed to 15 parts by mass, the amount of cellulose fiber was changed to 40 parts by mass, and the amount of polypropylene resin was changed to 45 parts by mass.

[0055] Example 9 A resin molded body was obtained in the same manner as in Example 1, except that the amount of SiMA-PP was changed to 20 parts by mass, the amount of cellulose fiber was changed to 50 parts by mass, and the amount of polypropylene resin was changed to 30 parts by mass.

[0056] Example 10 In Example 1, the silane coupling agent used in "Preparation of modified resin" was changed to vinyltrimethoxysilane (VTMS), and further, polypropylene resin modified with vinyltrimethoxysilane (VTMS-PP) was obtained without adding styrene, and a resin molded body was obtained in the same manner as in Example 1, except that 5 parts by mass of VTMS-PP was used as the modified resin and the amount of polypropylene resin was changed to 75 parts by mass.

[0057] Example 11 A resin molded article was obtained in the same manner as in Example 3, except that in "preparation of modified resin", modified SiMA-PP without adding styrene was used.

[0058] <Comparative Example 1> A resin molded article was obtained in the same manner as in Example 1, except that the SiMA-PP used in the "melt mixing and molding" step was changed to maleic anhydride-modified polypropylene PP (MAH-PP).

[0059] <Comparative Example 2> In Example 1, the silane coupling agent used in "Preparation of modified resin" was changed to glycidyl methacrylate (GMA), and polypropylene resin modified with glycidyl methacrylate (GMA-PP) was obtained without adding styrene. A resin molded body was obtained in the same manner as in Example 1, except that 5 parts by mass of GMA-PP was used as the modified resin and the amount of polypropylene resin was changed to 75 parts by mass.

[0060] <Comparative Example 3> A resin molded body was obtained in the same manner as in Example 1, except that in the "melt mixing and molding" step, no modified resin was added, and the amounts of polypropylene resin and cellulose fiber were changed to 80 parts by mass and 20 parts by mass, respectively.

[0061] <Comparative Example 4> An aqueous dispersion containing 20% ​​by mass of cellulose fiber and 1% by mass of SiMA was prepared and stirred at room temperature for 2 hours. The aqueous dispersion was filtered, and the cellulose fiber remaining as a filter cake was filtered twice with water to wash away unreacted silane coupling agent. The cellulose fiber recovered after washing was dried overnight at 120°C in a thermostatic chamber. In this way, cellulose fiber surface-treated with a silane coupling agent was obtained. In Example 1, a resin molded body was obtained in the same manner as in Example 1, except that no modified resin was added in the "melt mixing and molding" step, the amount of polypropylene resin was changed to 80 parts by mass, and the 20 parts by mass of cellulose fiber was changed to 20 parts by mass of cellulose fiber surface-treated with the above-mentioned silane coupling agent.

[0062] <Comparative Example 5> In Example 1, the base resin used in "Preparation of modified resin" was changed to high-density polyethylene resin (HDPE), the silane coupling agent was changed to vinyltrimethoxysilane (VTMS), a high-density polyethylene resin modified with vinyltrimethoxysilane without adding styrene (VTMS-HDPE) was obtained, 5 parts by mass of VTMS-HDPE was used as the modified resin, and 79 parts by mass of polypropylene resin was changed to 75 parts by mass of HDPE. A resin molded body was obtained in the same manner as in Example 1.

[0063] <Comparative Example 6> In Example 1, the base resin used in "Preparation of Modified Resin" was changed to high-density polyethylene resin (HDPE), the silane coupling agent was changed to vinyltrimethoxysilane (VTMS), and a molten mixture of vinyltrimethoxysilane and high-density polyethylene resin (VTMS / HDPE) was obtained without adding styrene and dicumyl peroxide. This molten mixture was used in place of the modified resin in an amount of 5 parts by mass, and 79 parts by mass of polypropylene resin was replaced with 75 parts by mass of HDPE. In this molten mixture, graft polymerization of VTMS to HDPE via the ethylenically unsaturated groups did not occur, and therefore, no alkoxysilane-modified polyethylene resin was produced. VTMS interacts with cellulose fibers and polyethylene resin via its functional groups.

[0064] <Comparative Example 7> In Example 1, the silane coupling agent used in the "Preparation of Modified Resin" was changed to vinyltrimethoxysilane (VTMS), and a molten mixture of vinyltrimethoxysilane and polypropylene resin (VTMS / PP) was obtained without adding styrene and dicumyl peroxide (peroxide). A resin molded article was obtained in the same manner as in Example 1, except that 5 parts by mass of this molten mixture was used instead of the modified resin, and the amount of polypropylene resin was changed to 75 parts by mass. In the molten mixture, graft polymerization of VTMS to the polypropylene resin via the ethylenically unsaturated groups did not occur, and therefore, no alkoxysilane-modified polypropylene resin was produced. VTMS interacts with the cellulose fiber and polypropylene resin via its functional groups.

[0065] <Comparative Example 8> A resin molded product was obtained in the same manner as in Comparative Example 5, except that no modified resin was added, and the amounts of high-density polyethylene resin and cellulose fibers were changed to 80 parts by mass and 20 parts by mass, respectively.

[0066] The obtained dumbbell test pieces (resin molded articles) were subjected to the following tests, and the results are shown in Table 1.

[0067] [Tensile strength test] As an index of mechanical strength, tensile strength was evaluated. The dumbbell test pieces obtained above were subjected to a tensile test using an autograph precision universal testing machine (Shimadzu Corporation) based on JIS standard K7161 to measure the tensile strength (MPa). The test conditions were room temperature (25°C), a gauge length of 60 mm, and a tensile speed of 50 mm / min.

[0068] [Durability test] As an index of durability under high temperature and humidity, the change in tensile strength before and after the moist heat treatment was evaluated. This test is based on the moisture and water resistance test method for automobile parts described in JIS standard D0203. The dumbbell test specimens obtained above were placed in a thermo-hygrostat (product name: PSL-2J, manufactured by ESPEC Co., Ltd.) and left to stand for 1000 hours at a temperature of 85°C and a relative humidity of 95%. The dumbbell test specimens were removed from the thermo-hygrostat and dried at 100°C for 24 hours, and then left to stand for 7 days at a temperature of 25°C and a relative humidity of 50%. In this way, moist heat-treated dumbbell test specimens were obtained. The dumbbell test pieces after the moist heat treatment were subjected to a tensile test in accordance with the above-mentioned tensile strength test. The tensile strength before exposure to an environment of 85°C and 95% relative humidity (before moist heat treatment) was σ 0h , the tensile strength of the heat-moisture treated product is σ 1000h The ratio of the tensile strength of the dumbbell test piece after heat-moisture treatment to the tensile strength of the dumbbell test piece before heat-moisture treatment (σ 1000h / σ 0h , tensile strength ratio) was calculated. Tensile strength ratio σ before and after moist heat treatment 1000h / σ 0h A tensile strength ratio of 1 means that the tensile strength before the moist heat treatment (initial value) is maintained even after the moist heat treatment. Furthermore, a decrease of 0.1 in the tensile strength ratio means that the tensile strength decreases by 10% after the moist heat treatment. Here, the deterioration in the accelerated aging test of 1000 hours of moist heat treatment corresponds to deterioration over a usage period equivalent to 7 years in an actual environment, in accordance with the 10°C half-life rule. For long-lasting components with a long design life (e.g., 10 years or more), such as automobile parts, a decrease of more than 10% in the designed mechanical strength during usage is sometimes deemed to indicate poor long-term reliability. Therefore, from the perspective of application to long-lasting components, a tensile strength ratio of 0.9 or higher is preferable.

[0069] Each dumbbell specimen was also evaluated for appearance quality (before and after the moist heat treatment) as a desirable characteristic.

[0070] [Appearance observation] The overall appearance of the dumbbell test piece obtained above (before the moist heat treatment) was visually observed and evaluated according to the following criteria. A: No spots with a maximum diameter of 3 mm or more were observed in plan view. B: In plan view, 1 to 3 spots with a maximum diameter of 3 mm or more were observed. C: Four or more spots with a maximum diameter of 3 mm or more were observed in plan view, and / or the surface became sticky due to eluted material. The "maximum diameter" means the longest distance on a straight line passing through the interior of a speck from one point on the periphery of the speck to another point in a plan view.

[0071] [Appearance observation after moist heat treatment] The overall appearance of the dumbbell test piece after the above-mentioned moist heat treatment was visually observed and evaluated according to the following criteria. A: No spots with a maximum diameter of 3 mm or more were observed in plan view. B: In plan view, 1 to 3 spots with a maximum diameter of 3 mm or more were observed. C: Four or more spots with a maximum diameter of 3 mm or more were observed in plan view, and / or the surface became sticky due to eluted material.

[0072] [Table 1-1]

[0073] [Table 1-2]

[0074] As is clear from the results shown in Table 1, the resin moldings of the comparative examples that do not satisfy the composition prescribed in the present invention are unable to achieve both high initial tensile strength and durability.

[0075] The resin molding containing the maleic anhydride-modified polypropylene resin shown in Comparative Example 1 had a higher initial tensile strength than the resin molding containing no modified PP shown in Comparative Example 3, but σ 1000h / σ 0hThe tensile strength of the cellulose fiber reinforced resin was below 0.90, and after the moist heat treatment, four or more spots with a maximum diameter of more than 3 mm and stickiness due to eluted materials were observed, resulting in poor appearance. As in Comparative Example 1, the cellulose fiber reinforced resin to which the maleic anhydride-modified resin was added is thought to have excellent initial tensile strength because the succinic anhydride groups derived from the maleic anhydride-modified resin form ester bonds with the hydroxyl groups of the cellulose fiber. On the other hand, the moist heat treatment is thought to have caused the ester bonds between the cellulose fiber and the maleic anhydride-modified resin to be cleaved by hydrolysis, or the succinic anhydride groups of the maleic anhydride-modified resin to generate acid, which accelerated the deterioration of the cellulose fiber and resulted in poor durability.

[0076] The resin molding of Comparative Example 2 had high durability, but its initial tensile strength was about the same as that of Comparative Example 3, and the reinforcing effect of the cellulose fibers was not sufficiently obtained. It is thought that the cellulose fiber reinforced resin to which polypropylene resin modified with glycidyl methacrylate (also called epoxy-modified polypropylene resin) was added, as in Comparative Example 2, had insufficient interfacial adhesion between the epoxy groups derived from the epoxy-modified polypropylene resin and the cellulose fibers.

[0077] The resin molded article of Comparative Example 3 did not obtain a sufficient reinforcing effect of the cellulose fibers, which is thought to be due to poor interfacial adhesion between the cellulose fibers and the polypropylene resin.

[0078] The resin molded body of Comparative Example 4 uses cellulose fibers whose surface has been modified with a silane coupling agent with reference to Patent Document 2, but the initial tensile strength is about the same as that of Comparative Example 3, and the reinforcing effect of the cellulose fibers is not fully achieved. When the cellulose fibers are surface-modified with a silane coupling agent, as in Comparative Example 4, the polypropylene resin does not have functional groups that contribute to the adhesion between the cellulose fibers and the polypropylene resin. For this reason, the silane coupling agent only acts as a dispersant for the cellulose fibers, and it is thought that there are limitations to improving the adhesion at the interface between the cellulose fibers and the polypropylene resin.

[0079] The resin moldings of Comparative Examples 5 and 6 used VTMS-HDPE or VTMS / HDPE as the silane-containing polymer with reference to Patent Document 5, but the initial tensile strength was similar to that of Comparative Example 8, which did not contain VTMS-HDPE or VTMS / HDPE, and the reinforcing effect of the cellulose fibers was not fully achieved.

[0080] The resin molding of Comparative Example 7 has a composition in which no peroxide was added when the alkoxysilane-modified polypropylene resin was prepared, and the initial tensile strength is similar to that of Comparative Example 3. When the silane coupling agent is not grafted to the polypropylene, as in Comparative Example 7, the interface between the polypropylene and the cellulose fiber does not adhere sufficiently, and the reinforcing effect of the cellulose fiber is not sufficiently obtained.

[0081] In contrast, the resin molded article satisfying the requirements of the present invention has a higher initial tensile strength than Comparative Example 3, and maintains this high tensile strength at a high level even after 1000 hours of wet heat treatment (σ 1000h / σ 0h It can be seen that the initial tensile strength is 0.90 or more. Thus, the resin molded article of the present invention exhibits an initial tensile strength suitable for use in automobile parts and structural members, and can maintain that tensile strength for a long period of time even under high temperature and high humidity conditions. The reason why the resin molded article of the present invention exhibits the above-mentioned excellent effects is thought to be that the use of an alkoxysilane-modified polypropylene resin as a compatibilizer not only brings out the reinforcing effect of the cellulose fiber, but also suppresses deterioration of the cellulose fiber, thereby maintaining the reinforcing effect.

[0082] Next, Examples 13 to 18 show examples in which the silane coupling agent used in preparing the alkoxysilane-modified polypropylene resin is (trimethoxysilyl)alkyl (meth)acrylate, and the type of reaction aid having a vinyl group used in combination is changed. Example 12 is an example in which a reaction aid having a vinyl group is not used.

[0083] Example 12 In Example 1, a resin molded body was obtained in the same manner as in Example 1, except that in the "Preparation of modified resin" step, modified SiMA-PP without adding styrene was used, the amount of SiMA-PP was changed to 10 parts by mass, and the amount of polypropylene resin was changed to 70 parts by mass.

[0084] Example 13 A resin molded article was obtained in the same manner as in Example 1, except that in "Preparation of modified resin" in Example 1, SiMA-PP modified by changing styrene to 8.15 parts by mass of vinyl laurate was used, the amount of SiMA-PP was changed to 10 parts by mass, and the amount of polypropylene resin was changed to 70 parts by mass. The Q value of vinyl laurate was 0.011, and the amount added was equimolar to that of styrene in Example 1.

[0085] Example 14 A resin molded article was obtained in the same manner as in Example 1, except that in "Preparation of modified resin" in Example 1, SiMA-PP modified by changing styrene to 1.91 parts by mass of acrylonitrile was used, the amount of SiMA-PP was changed to 10 parts by mass, and the amount of polypropylene resin was changed to 70 parts by mass. The Q value of acrylonitrile was 0.48, and the amount added was equimolar to that of styrene in Example 1.

[0086] Example 15 A resin molded article was obtained in the same manner as in Example 1, except that in "Preparation of modified resin" in Example 1, SiMA-PP modified by changing styrene to 5.13 parts by mass of glycidyl methacrylate was used, the amount of SiMA-PP was changed to 10 parts by mass, and the amount of polypropylene resin was changed to 70 parts by mass. The Q value of glycidyl methacrylate was 0.96, and the amount added was equimolar to that of styrene in Example 1.

[0087] Example 16 A resin molded article was obtained in the same manner as in Example 1, except that in "Preparation of modified resin" in Example 1, SiMA-PP modified by changing styrene to 4.25 parts by mass of α-methylstyrene was used, the amount of SiMA-PP was changed to 10 parts by mass, and the amount of polypropylene resin was changed to 70 parts by mass. The Q value of α-methylstyrene was 0.97, and the amount added was equimolar to that of styrene in Example 1.

[0088] Example 17 A resin molded body was obtained in the same manner as in Example 1, except that the amount of SiMA-PP was changed to 10 parts by mass and the amount of polypropylene resin was changed to 70 parts by mass in Example 1. The Q value of styrene was 1.00.

[0089] Example 18 A resin molded article was obtained in the same manner as in Example 1, except that in "Preparation of modified resin" in Example 1, SiMA-PP modified by changing styrene to 5.19 parts by mass of 2-hydroxypropyl methacrylate was used, the amount of SiMA-PP was changed to 10 parts by mass, and the amount of polypropylene resin was changed to 70 parts by mass. The Q value of 2-hydroxypropyl methacrylate was 4.38, and the amount added was equimolar to that of styrene in Example 1.

[0090] The obtained dumbbell test pieces (resin molded articles) were subjected to the above-mentioned [tensile strength test], [durability test], [appearance observation], and [appearance observation after moist heat treatment]. The results are shown in Table 2.

[0091] [Table 2]

[0092] The resin molded articles of Examples 12 to 18, which satisfy the requirements of the present invention, have a high initial tensile strength compared to Comparative Example 3, and maintain this high tensile strength at a high level even after 1000 hours of wet heat treatment (σ 1000h / σ 0h It can be seen that the correlation coefficient is 0.90 or higher. The resin molded articles of Examples 13 and 14 used a vinyl-containing reaction aid during the preparation of the alkoxysilane-modified polypropylene resin. However, their initial tensile strength was comparable to that of the resin molded article of Example 12, which did not use a vinyl-containing reaction aid. The Q value of the reaction aid used in Examples 13 and 14 was less than 0.54, the median between the Q value of propylene (0.009) and the Q value of 3-(trimethoxysilyl)propyl methacrylate (1.08). However, when the Q value of the reaction aid is less than 0.54, it is believed that the reaction aid is less likely to radicalize, making it easier for the SiMA monomer to graft onto the polypropylene resin without the aid of the reaction aid. Therefore, the grafting rate of the SiMA monomer was not improved compared to when the reaction aid was not used, and the improvement in the reinforcing effect of the cellulose fiber was thought to be limited. On the other hand, in the resin moldings of Examples 15 to 18, a reaction aid having a vinyl group was used during the preparation of the alkoxysilane-modified polypropylene resin. In these cases, the initial tensile strength was improved compared to the resin molding of Example 12, which did not use a reaction aid having a vinyl group. The reaction aids used in Examples 15 to 18 had Q values ​​of 0.54 to 5.00 or less, which is thought to facilitate grafting of the reaction aid to the polypropylene resin. Therefore, it is thought that the reaction aid grafted to the polypropylene resin polymerized with the SiMA monomer, increasing the grafting rate of the SiMA monomer and thereby more effectively utilizing the reinforcing effect of the cellulose fiber.

[0093] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0094] This application claims priority based on Japanese Patent Application No. 2020-119781, filed on July 13, 2020, the contents of which are incorporated herein by reference as part of the present specification.

Claims

1. A cellulose fiber reinforced resin molded body obtained by molding a cellulose fiber reinforced resin composite containing a polypropylene resin, an alkoxysilane-modified polypropylene resin, and a cellulose fiber, The cellulose fiber reinforced resin molded body is a polypropylene resin graft-modified with a (trimethoxysilyl)alkyl (meth)acrylate in which the alkyl group has 1 to 10 carbon atoms and a reaction aid having a vinyl group (however, the reaction aid is not a silane coupling agent having an alkoxysilyl group).

2. The cellulose fiber reinforced resin molded body according to claim 1, wherein the Q value of the reaction aid having a vinyl group is 0.010 to 5.

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3. The cellulose fiber reinforced resin molded body according to claim 1, wherein the Q value of the reaction aid having a vinyl group is 0.54 to 5.

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4. The cellulose fiber reinforced resin molding according to any one of claims 1 to 3, wherein the reaction aid having a vinyl group is at least one of a styrene compound and a (meth)acrylic acid ester compound.

5. The cellulose fiber reinforced resin molded body according to any one of claims 1 to 4, wherein the reaction aid having a vinyl group is a styrene compound.

6. The cellulose fiber reinforced resin molded body according to any one of claims 1 to 5, wherein the content of the alkoxysilane-modified polypropylene resin in the cellulose fiber reinforced resin molded body is 0.1 to 20 mass%.

7. The method for producing a cellulose fiber reinforced resin molded body according to any one of claims 1 to 5, comprising the following steps (a) and (b): (a) A step of mixing a polypropylene resin and a (trimethoxysilyl)alkyl (meth)acrylate in which the alkyl group has 1 to 10 carbon atoms in the presence of an organic peroxide and a reaction aid having a vinyl group (provided that the reaction aid is not a silane coupling agent having an alkoxysilyl group) at a temperature equal to or higher than the decomposition temperature of the organic peroxide, and grafting the (trimethoxysilyl)alkyl (meth)acrylate and the reaction aid having a vinyl group onto the polypropylene resin to prepare an alkoxysilane-modified polypropylene resin. (b) A step of melt-mixing the alkoxysilane-modified polypropylene resin, cellulose fibers, and polypropylene resin such that the ratio of the alkoxysilane-modified polypropylene resin to the total amount of the alkoxysilane-modified polypropylene resin, the cellulose fibers, and the polypropylene resin is 0.1 to 20 mass%.

8. The method for producing a cellulose fiber reinforced resin molded body according to claim 7, wherein the reaction aid having a vinyl group contains a styrene compound.

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