Thermoplastic resin composite material and molded article formed from same

Abstract

The present invention addresses the problem of providing a thermoplastic resin composite material that contains cellulose fibers and has high moldability and mechanical strength. Said problem is solved by a thermoplastic resin composite material containing cellulose fibers and thermoplastic resin, the content of the cellulose fibers being 30-70 mass%, the content of the thermoplastic resin being 20-70 mass%, the load-dependent characteristics thereof being 7-32 (g / 10 min / kgf).

Description

Thermoplastic resin composite material and molded article made therefrom

[0001] The present invention relates to a thermoplastic resin composite material and a molded article made therefrom.

[0002] Since cellulose fibers are natural polymers, they have a low environmental impact and excellent properties such as a high elastic modulus, high strength, and low coefficient of linear expansion. Further, they are lightweight compared to glass fibers, carbon fibers, inorganic fillers, and the like. Therefore, research and development of resin compositions containing cellulose fibers and molded articles made therefrom have been advanced.

[0003] For example, Patent Document 1 describes a composite having cellulose and a coating provided on part or all of the cellulose surface, the coating containing a fluorene compound having a plurality of hydroxyl groups. And it is described that such a composite can provide a composite capable of improving the strength of a resin composition without performing chemical modification of the cellulose surface.

[0004] Japanese Unexamined Patent Application Publication No. 2019 - 178266

[0005] A resin composition containing cellulose fibers preferably has high moldability and mechanical strength.

[0006] The present invention provides a thermoplastic resin composite material containing cellulose fibers and having high moldability and mechanical strength, and a molded article made therefrom.

[0007] The inventors diligently studied to solve the above problems and completed the present invention. The present invention is as follows (1) to (9): (1) A thermoplastic resin composite material comprising cellulose fibers and a thermoplastic resin, wherein the cellulose fiber content is 30 to 70% by mass, the thermoplastic resin content is 20 to 70% by mass, and the load-dependent properties are 7 to 32 (g / 10min / kgf). (2) The thermoplastic resin composite material according to (1) above, wherein the average weight molecular weight of the thermoplastic resin is 200,000 g / mol or less. (3) The thermoplastic resin composite material according to (1) or (2) above, further containing 15% by mass or less of a compatibilizer. (4) The thermoplastic resin composite material according to (3) above, wherein the compatibilizer is an acid-modified polyolefin resin modified with an unsaturated dicarboxylic acid and / or its acid anhydride. (5) The thermoplastic resin composite material according to any one of (1) to (4) above, wherein the thermoplastic resin is a polyolefin. (6) The thermoplastic resin composite material according to any one of (1) to (5) above, wherein the thermoplastic resin is a polypropylene-polyethylene copolymer. (7) The thermoplastic resin composite material according to (6) above, wherein the thermoplastic resin is a random copolymer. (8) The thermoplastic resin composite material according to any one of (1) to (7) above, wherein the water retention rate of the cellulose fibers is 5 to 20% by mass. (9) A molded article made from the thermoplastic resin composite material according to any one of (1) to (8) above.

[0008] According to the present invention, it is possible to provide a thermoplastic resin composite material containing cellulose fibers and having high moldability and mechanical strength, as well as a molded product made therefrom.

[0009] The present invention will now be described. The present invention is a thermoplastic resin composite material comprising cellulose fibers and a thermoplastic resin, wherein the cellulose fiber content is 30 to 70% by mass, the thermoplastic resin content is 20 to 70% by mass, and the load-dependent properties are 7 to 32 (g / 10min / kgf). Such a thermoplastic resin composite material will also be referred to as "the composite material of the present invention" below.

[0010] Conventionally, when molding thermoplastic resin composites with a high cellulose fiber content, it was sometimes difficult to obtain molded articles with the desired shape. This tendency was particularly strong for molded articles with complex shapes or shapes containing intricate details. In contrast, the composite material of the present invention has high moldability, making it possible to obtain molded articles with the desired shape with a high yield. For example, using the composite material of the present invention, even if the molded article has a complex shape or a shape containing intricate details, it can be obtained by applying, for example, injection molding.

[0011] The inventors believe that the main reason for the high moldability and mechanical strength of the composite material of the present invention lies in obtaining it by a specific manufacturing method described later. In other words, the inventors believe that the composite material of the present invention, manufactured by the specific manufacturing method described later, has high moldability and mechanical strength because of its special structure. Furthermore, the inventors believe that the composite material of the present invention, having such a special structure, has a load-dependent characteristic of 7 to 32 (g / 10min / kgf).

[0012] Furthermore, the inventors have found that the composite material of the present invention obtained by the specific manufacturing method described later has a lower molecular weight of the thermoplastic resin it contains compared to conventional products. In other words, the inventors believe that the lower molecular weight of the thermoplastic resin constituting 20 to 70% by mass of the composite material of the present invention compared to conventional products contributes to the improved moldability and mechanical strength of the composite material of the present invention.

[0013] The composite material of the present invention will be described in detail below.

[0014] <Cellulose Fibers> The cellulose fibers contained in the composite material of the present invention will now be described. In the composite material of the present invention, the cellulose fiber content is 30 to 70% by mass, preferably 40 to 70% by mass, more preferably 45 to 65% by mass, and particularly preferably 50 to 60% by mass. When the cellulose fiber content in the composite material of the present invention is 30% by mass or more, molding is possible without applying high pressure to the thermoplastic resin during molding. In other words, the composite material of the present invention has excellent moldability. When the cellulose fiber content in the composite material of the present invention is 70% by mass or less, when the composite material of the present invention is loaded into a mold and molded, the composite material of the present invention is less likely to leak from the gaps in the mold, less likely to generate burrs, and has excellent moldability. Despite the high cellulose fiber content, the composite material of the present invention has high moldability. Therefore, molded bodies of the desired shape can be obtained with a high yield. For example, using the composite material of the present invention, even if the molded body has a complex shape or a shape that includes fine details, it can be obtained, for example, by injection molding.

[0015] In the composite material of the present invention, the cellulose fibers are not particularly limited and may be, for example, conventionally known cellulose fibers, and more specifically, they may be crushed pulp (pulp-derived).

[0016] Pulps can be categorized into wood pulp and non-wood pulp. Wood pulps include MP, CP, GP, RGP, CGP, SP, AP, KP, SCP, etc., which are made from coniferous trees such as fir and pine, and broad-leaved trees such as eucalyptus and poplar. These can be unbleached or bleached pulp. Non-wood pulps include natural fibers, specifically cotton; straw; bamboo; esparto; bagasse; linter; kenaf; hemp pulps such as Manila hemp, flax, hemp, and jute; ganpi; etc. In addition to natural fibers, recycled paper pulp, made from recycled paper and scraps, can be considered a non-wood pulp.

[0017] The pulp is preferably derived from coniferous trees, broad-leaved trees, cotton, or hemp, and more preferably from coniferous and broad-leaved trees. Using cellulose fibers derived from these pulps results in superior fluidity during melting, making it possible to obtain thermoplastic resin composites with superior moldability and excellent mechanical properties such as strength and elastic modulus. Furthermore, pulp derived from coniferous trees is preferred because it contains less lignin, hemicellulose, etc., which are sources of odor and color, and these can be removed relatively easily, resulting in a simpler manufacturing process.

[0018] Pulp may be mechanical pulp, chemical pulp, or other types of pulp.

[0019] Pulp can be used alone or in combination with other pulps.

[0020] The cellulose fibers preferably have an average fiber diameter of 1 to 50 μm, more preferably 1 to 40 μm, and even more preferably 1 to 30 μm. In this case, the composite material of the present invention has superior fluidity during melting, resulting in excellent moldability, and a molded product with excellent mechanical properties such as strength and elastic modulus can be obtained.

[0021] Furthermore, it is preferable that all cellulose fibers contained in the composite material of the present invention have a fiber diameter of 1 to 50 μm, more preferably 1 to 40 μm, and most preferably 1 to 30 μm. Note that if, when the fiber diameter of the cellulose fibers contained in the composite material of the present invention is measured by the method described later, no cellulose fibers of any other fiber diameter are detected, then all cellulose fibers contained in the composite material of the present invention are considered to have that fiber diameter.

[0022] The cellulose fibers preferably have an average fiber length of 10 to 400 μm, more preferably 10 to 300 μm, and even more preferably 10 to 200 μm. In this case, the composite material of the present invention has superior fluidity during melting, resulting in excellent moldability, and a molded product with excellent mechanical properties such as strength and elastic modulus can be obtained.

[0023] Furthermore, it is preferable that all cellulose fibers contained in the composite material of the present invention have a fiber length of 10 to 400 μm, more preferably 10 to 300 μm, and even more preferably 10 to 200 μm. Note that when the fiber length of the cellulose fibers contained in the composite material of the present invention is measured by the method described below, if no cellulose fibers of other fiber diameters are detected, then all cellulose fibers contained in the composite material of the present invention are considered to have that fiber length.

[0024] This document describes a method for measuring the average fiber diameter and average fiber length of cellulose fibers. First, the composite material of the present invention is imaged using an X-ray CT analyzer, and the fiber diameter and fiber length of all cellulose fibers in the obtained image are measured. Then, the obtained fiber diameter and fiber length values ​​are simply averaged to obtain the average fiber diameter and average fiber length. The X-ray CT analyzer is used under the following observation conditions: Analyzer: Rigaku high-resolution 3DX X-ray microscope nano3DX Measurement conditions: X-ray source Cu (40kV, 30mA) Analysis software: Dragonfly Object Research Systems Image size: 347.7 × 763.2 μm Thickness: 654 μm

[0025] The fiber diameter and fiber length of the cellulose fibers can be adjusted not only by appropriately selecting the fiber diameter and fiber length of the cellulose fibers used as raw materials, but also by changing the rotation speed of the mixing means when mixing the cellulose fibers and thermoplastic resin, the load applied by the screw pattern, or the blending ratio of the cellulose fibers, as described later.

[0026] It is preferable that the cellulose fibers have a water retention rate of 5 to 20% by mass. When the water retention rate of the cellulose fibers is 5% by mass or higher, the cellulose fibers loosen well, and aggregation of the cellulose fibers is less likely to occur, resulting in a composite material with superior moldability in the present invention. When the water retention rate of the cellulose fibers is 20% by mass or lower, foaming due to water evaporation is less likely to occur during kneading of the raw materials, and the temperature rise during kneading is smoother, resulting in superior production efficiency.

[0027] The water retention rate of cellulose fibers is calculated using the following formula: Water retention rate (%) = (Mass of cellulose fibers (g) - Mass of cellulose fibers when dry (g)) / Mass of cellulose fibers (g) × 100 Here, the mass of cellulose fibers when dry is the value obtained after keeping the cellulose fibers in a constant temperature bath at 120°C for 5 hours.

[0028] <Thermoplastic Resin> The thermoplastic resin contained in the composite material of the present invention will now be described. The thermoplastic resin content in the composite material of the present invention is 20 to 70% by mass, preferably 20 to 60% by mass, more preferably 25 to 55% by mass, and particularly preferably 30 to 50% by mass.

[0029] The thermoplastic resin included in the composite material of the present invention is not particularly limited and may be, for example, a conventionally known thermoplastic resin. Examples include polyethylene resin, polypropylene resin, vinyl chloride resin, methacrylic resin, polystyrene resin, ABS resin, polycarbonate resin, polyacetal resin, polyamide resin, polysulfone resin, modified PPO resin, and polyester resin. From the viewpoint of obtaining the composite material of the present invention which has excellent flowability when melted and thus superior moldability, and which can produce molded products with excellent mechanical properties such as strength and elastic modulus, polyethylene resin and / or polypropylene resin are preferred, polypropylene-polyethylene copolymer is more preferred, and polypropylene resin is even more preferred. When a polypropylene-polyethylene copolymer is used as the thermoplastic resin, the composite material of the present invention has high impact strength and superior mechanical strength.

[0030] The thermoplastic resin is preferably a random copolymer. When the thermoplastic resin is a random copolymer, the composite material of the present invention has high impact strength and superior mechanical strength.

[0031] In the composite material of the present invention, the thermoplastic resin may be of one type or may contain multiple types of thermoplastic resins.

[0032] The thermoplastic resin contained in the composite material of the present invention preferably has an average weight molecular weight of 200,000 g / mol or less, more preferably 150,000 g / mol or less, and even more preferably 100,000 g / mol or less. In this case, the composite material of the present invention has high fluidity and excellent moldability when molded. As described above, the composite material of the present invention obtained by a specific manufacturing method has a lower molecular weight of the thermoplastic resin it contains compared to conventional products. That is, the inventors believe that the lower molecular weight of the thermoplastic resin constituting 20 to 70% by mass of the composite material of the present invention compared to conventional products contributes to the improved moldability and mechanical strength of the composite material of the present invention.

[0033] The average weight molecular weight of the thermoplastic resin contained in the composite material of the present invention shall be the value obtained by the following measurement. The average weight molecular weight of the thermoplastic resin shall be measured using an HCL-8321GPC / HT type high-temperature gel permeation chromatograph (Tosoh). The sample shall be weighed to a value of 20 mg of thermoplastic resin (PP) component, 20 mL of mobile phase for GPC measurement shall be added, and the sample shall be shaken at 145°C to dissolve it. The solution shall be thermally filtered through a 0.5 μm P TFE membrane filter to separate cellulose fibers, etc., and the filtrate shall be used for GPC measurement. The conditions for the high-temperature gel permeation chromatograph shall be set as follows. Temperature: 140°C; Mobile phase: o-dichlorobenzene (containing 0.025 wt% BHT); Flow rate: 1.0 mL / min; Injection volume: 0.4 mL; Detector: Differential refractometer (RI); Column calibration: Monodisperse PS (TSKgel standard polystyrene: Tosoh); Molecular weight calibration: Relative calibration method (PS conversion); Analysis software: Empower3 (Waters Japan)

[0034] The composite material of the present invention preferably contains 70% by mass or more of cellulose fibers and thermoplastic resin in total, more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more.

[0035] <Compatibilizer> The composite material of the present invention preferably contains a compatibilizer. The compatibilizer content in the composite material of the present invention is preferably 15% by mass or less, more preferably 1 to 10% by mass, and even more preferably 2 to 8% by mass.

[0036] When the composite material of the present invention contains a compatible additive, it exhibits superior fluidity during melting, resulting in superior moldability and allowing for the production of molded products with excellent mechanical properties such as strength and elastic modulus. Furthermore, when kneading cellulose fibers with thermoplastic resin, the cellulose fibers disperse easily within the thermoplastic resin, thus simplifying the manufacturing process.

[0037] The compatibilizer plays the role of dispersing relatively hydrophilic cellulose fibers within a relatively hydrophobic thermosetting resin. Therefore, the compatibilizer is preferably a block copolymer having nonpolar segments and polar segments.

[0038] The nonpolar segment is preferably an olefin-based segment. The olefin-based segment is a segment obtained by polymerization of an olefin monomer or copolymerization of an olefin monomer and a styrene monomer. Examples of olefin monomers include ethylene, propylene, methylpentene, butadiene, and norbornene derivatives. Only one type of olefin monomer may be used, or two or more types may be used.

[0039] The polar segment is preferably an ester-based segment or a styrene-based segment. The ester-based segment is a segment formed by the condensation polymerization of an alcohol-based monomer and an acid-based monomer.

[0040] Examples of alcohol-based monomers include α,ω-alkylenediols (C2-C12) such as ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, and 1,12-dodecanediol; polyalkylene glycols such as diethylene glycol, triethylene glycol, and dipropylene glycol; aliphatic dihydric alcohols such as 1,2-propanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol; glycerin, 1,1,1-tris(4-hydroxyphenyl)ethane, trimethylolethane, trimethylolpropane; monosaccharides, disaccharides, ring-opened sugars, and modified sugars. Polyhydric alcohols, bisphenols such as 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-phenyl-4-hydroxyphenyl)propane, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl ether, and bis(4-hydroxyphenyl)diphenylmethane, as well as bisphenols whose hydroxyl groups have been modified with alkylene glycols such as polyethylene glycol and polypropylene glycol, and bisphenols whose aromatic rings have been hydrogenated, are used.

[0041] Examples of acidic monomers include saturated aliphatic carboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and octyl succinic acid; unsaturated aliphatic carboxylic acids such as maleic acid, fumaric acid, and maleic anhydride; cyclic aliphatic carboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 2,3-bicyclo[2,2,1]dicarboxylic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, 1,2,4-cyclohexanetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid anhydride, 1,2,4-butanetricarboxylic acid, 1,2,4-butanetricarboxylic acid anhydride, 2,5,7-naphthalentricarboxylic acid, 1,2,4-naphthalentricarboxylic acid, and 1,2,4-naphthalentricarboxylic acid anhydride; and polycarboxylic acids with a valency of three or more. Here, the carboxylic acid may be an acid halide, ester, or acid anhydride. Among these, maleic anhydride-modified polypropylene, which has been successfully modified while maintaining a high molecular weight, exhibits improved adhesion to fillers and, due to molecular-level entanglement, can enhance the strength of polyolefin-based composite materials.

[0042] Styrene-based segments are segments formed by the polymerization of styrene monomers or copolymerization of styrene monomers and acrylic monomers.

[0043] Examples of styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylsterene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, and 3,4-dichlorostyrene.

[0044] Examples of acrylic monomers include n-butyl methacrylate, isobutyl methacrylate, ethyl acrylate, n-butyl acrylate, methyl methacrylate, glycidyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, diethylaminopropyl acrylate, 2-ethylhexyl acrylate, butyl acrylate-N-(ethoxymethyl)acrylamide, ethylene glycol methacrylate, 4-hexafluorobutyl methacrylate, and the like. These acrylic monomers can be used alone or in combination of two or more. Note that these monomers may be modified ones.

[0045] Other monomers may be polymerized in the compatibilizer. Examples of other monomers include vinyl monomers. For example, as vinyl ester monomers, there are vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; as vinyl ether monomers, there are vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether; as vinyl ketone monomers, there are vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone; as diene monomers, there are diene monomers such as isoprene, 2-chlorobutadiene, and the like.

[0046] The compatibilizer is preferably an acid-modified polyolefin resin modified with an unsaturated dicarboxylic acid, an acid-modified polyolefin resin modified with an acid anhydride of an unsaturated dicarboxylic acid, or a resin mixture containing both of them. Such a compatibilizer not only has good compatibility with the thermoplastic resin, but also the carboxylic acid of the compatibilizer binds to the OH group of the cellulose fiber, thus improving the affinity (adhesion) between the thermoplastic resin and the cellulose fiber.

[0047] The compatibilizer is preferably selected according to the combination of the cellulose fiber and the thermoplastic resin.

[0048] The composite material of the present invention comprises the cellulose fibers and thermoplastic resin described above, and may further contain a compatibilizer. It may also contain other components (hereinafter referred to as "other components"). Examples of other components include organic components. The organic components may be anionic or nonionic surfactants and mixtures thereof that are soluble in water and water-soluble alcohols such as ethanol and methanol. Specifically, examples include stearic acid, oleic acid, glycerin, and compounds thereof. Stearic acid is the most abundant saturated fatty acid in animal and vegetable fats and is widely distributed in nature as a component of oils and fats. Specifically, stearic acid includes stearic acid, stearic acid amide, stearic acid ester, aluminum stearate, magnesium stearate, sodium stearate, calcium stearate, barium stearate, PEG stearate, PEG-glyceryl stearate, PG stearate, ascorbyl stearate, isocetyl stearate, glycol stearate, glyceride stearate, glyceryl stearate, cholesteryl stearate, diethanolamide stearate, and diethylaminoethyl stearate. Examples include amides, ethyl stearate, vinyl stearate, sucrose stearate, sorbitan stearate, sodium stearate, batyl stearate, butyl stearate, cetyl stearate, methyl stearate, hexyldecyl stearate, stearyl stearate, glycerol distearate, isohexadecyl stearate, glycerol monostearate, 12-hydroxystearic acid, 2-ethylhexyl stearate, glycerol monoisostearate, and N,N'-ethylenebisstearate amide.Specifically, examples of oleic acid include oleic acid, oleic anhydride, ethyl oleate, oleic acid esters, butyl oleate, methyl oleate, oleyl oleate, sodium oleate, glycidyl oleate, copper(II) oleate, cholesteryl oleate, glycerol dioleate, glyceryl monooleate, butyl oleate ester, propyl oleate ester, dibutylammonium oleate, potassium oleate, ethyl oleate ester, N,N-diethanololeamide, N,N-diethanololeamide, 4-methylumbelliferyl oleate, trimethylolpropane trioleate, sodium sulfosuccinimidyloleate, N,N'-ethylenebisoleamide, and 5-bromo-4-chloro-3-indoxyl oleate.Specifically, glycerin includes glycerin, diglycerin, PPG-9 diglyceryl, PPG-14 polyglyceryl-2 ether, diglycerin monocaprylate, POP(9) polyglyceryl ether, POP(14) polyglyceryl ether, POP(24) polyglyceryl ether, POE(13) polyglyceryl ether, POE(20) polyglyceryl ether, POE(30) polyglyceryl ether, POE(40) polyglyceryl ether, polyglycerin, glycerin fatty acid ester, polyglyceryl monoisostearate, polyglyceryl diisostearate, polyglyceryl monolaurate, decaglyceryl monomyristate, polyglyceryl monooleate, polyglyceryl monostearate, polyglyceryl distearate, polyglyceryl condensed ricinoleate, diglyceryl tetraisostearate, polyglyceryl pentaisostearate, adipic acid, diethylene glycol, ethylhexyl glycerin, octoxyglycerin, ozonized glycerin, cyclohexyl glycerin, thioglycerin, bisdioleoyl glycerophosphoglycerin 2Na, hexyl glycerin, polyglycerol-4, polyglycerol-6, polyglycerol-10, polyglycerol-20, polyglycerol fatty acid ester, diglycerol fatty acid ester, polyoxyethylene polyglyceryl ether, glycerin fatty acid ester, monoglyceride, acetylated monoglyceride, organic acid monoglyceride, medium-chain fatty acid monoglyceride, polyglycerol fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, etc.

[0049] The content of other components that the composite material of the present invention may contain is preferably 10% by mass or less, more preferably 5% by mass or less. The content of other components can be determined as the remainder after measuring the cellulose fiber, thermoplastic resin, and compatibilizer contained in the composite material of the present invention as described above.

[0050] The inventors believe that the composite material of the present invention, manufactured by a specific manufacturing method described later, has a special structure, and as a result, its load-dependent properties are 7 to 32 (g / 10 min / kgf). When the load-dependent properties are 7 g / 10 min / kgf or higher, molding is possible without applying high pressure to the thermoplastic resin during molding. In other words, the composite material of the present invention has excellent moldability. When the load-dependent properties are 32 g / 10 min / kgf or lower, when the composite material of the present invention is loaded into a mold and molded, the composite material of the present invention is less likely to leak from the gaps in the mold, less likely to generate burrs, and has excellent moldability.

[0051] Here, the load-dependent characteristic is a value obtained by the following formula: Load-dependent characteristic = (MFR value at 10 kgf - MFR value at 2.16 kgf) / (10 kgf - 2.16 kgf) The MFR is measured using the method described in JIS K7210-1:2014 "Plastics - Method for determining melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastic plastics - Part 1: Standard test methods". Here, the temperature is fixed at 190°C and the load is varied during measurement.

[0052] <Manufacturing Method> The composite material of the present invention is manufactured by the manufacturing method described below (hereinafter also referred to as "the manufacturing method of the present invention"). The inventors believe that the composite material of the present invention obtained by the manufacturing method of the present invention has high moldability and mechanical strength due to its special structure.

[0053] The present invention provides a manufacturing method for obtaining a composite material of the present invention by kneading cellulose fibers and / or pulp fragments with a thermoplastic resin. The kneading is such that, assuming that only the thermoplastic resin is used for kneading, the average weight molecular weight of the thermoplastic resin before kneading is A (g / mol) and the average weight molecular weight of the thermoplastic resin after kneading is B (g / mol), then B / A is 0.28 to 0.68. This kneading method is applied to the kneading of cellulose fibers and / or pulp fragments with a thermoplastic resin to obtain the composite material of the present invention. Here, pulp fragments refer to those obtained by crushing (including disintegrating; the same applies hereinafter) pulp, which is the raw material for cellulose fibers.

[0054] The manufacturing method of the present invention described above involves spraying water onto pulp, crushing it to form pulp fragments, contacting them with a molten compatibilizer to adhere the compatibilizer to the pulp fragments, and then kneading these together with a thermoplastic resin to obtain the composite material of the present invention. Preferably, the kneading is such that, if only the thermoplastic resin is used for kneading, the average weight molecular weight of the thermoplastic resin before kneading is A (g / mol) and the average weight molecular weight of the thermoplastic resin after kneading is B (g / mol), then B / A is 0.28 to 0.68. The manufacturing method of the present invention is preferably applied to the kneading of pulp fragments, a compatibilizer, and a thermoplastic resin to obtain the composite material of the present invention.

[0055] In the manufacturing method of the present invention, the average gravimetric molecular weights A and B of the thermoplastic resin before and after kneading were measured using an HCL-8321GPC / HT type high-temperature gel permeation chromatograph (Tosoh). The sample was weighed to a thermoplastic resin (PP) component of 20 mg, 20 mL of mobile phase for GPC measurement was added, and the sample was shaken at 145°C to dissolve it. The solution was thermally filtered through a 0.5 μm P TFE membrane filter, and the filtrate was used for GPC measurement. The conditions for the high-temperature gel permeation chromatograph were set as follows. Temperature: 140°C; Mobile phase: o-dichlorobenzene (containing 0.025 wt% BHT); Flow rate: 1.0 mL / min; Injection volume: 0.4 mL; Detector: Differential refractometer (RI); Column calibration: Monodisperse PS (TSKgel standard polystyrene: Tosoh); Molecular weight calibration: Relative calibration method (PS conversion); Analysis software: Empower3 (Waters Japan)

[0056] The manufacturing method of the present invention described above may specifically be the following manufacturing method X. In other words, the manufacturing method X described below may correspond to the manufacturing method of the present invention.

[0057] In manufacturing method X, it is preferable to crush (including disintegration; the same applies hereinafter) the pulp to obtain pulp fragments. These pulp fragments then become cellulose fibers. In other words, the cellulose fiber content in the resulting composite material of the present invention is equal to the amount of pulp added.

[0058] The method for crushing pulp into pulp fragments is not particularly limited. Examples include crushing methods using grinders such as hammer mills, cutter mills, or jet mills, and methods using mixers such as Henschel mixers, super mixers, or ribbon mixers.

[0059] It is preferable to spray water onto the pulp before grinding, or to grind the pulp while spraying water onto it. This is because spraying water makes the pulp easier to break down.

[0060] The size of the pulp fragments obtained by crushing the pulp is not particularly limited. To facilitate mixing and shorten the kneading time, it is preferable that the longest diameter of the pulp fragments be 10 to 50 mm.

[0061] In manufacturing method X, it is preferable to knead a thermoplastic resin with pulp fragments and / or cellulose fibers obtained by crushing pulp fragments. In addition to the thermoplastic resin and pulp fragments and / or cellulose fibers, a compatibilizer and other components may also be kneaded together.

[0062] Alternatively, pulp may be fed into a crusher or mixer as described above to break it into pulp fragments, then a compatibilizer may be added, the compatibilizer may be melted, the pulp fragments and compatibilizer may be mixed, and then a thermoplastic resin may be added and kneaded. If the compatibilizer is added before the thermoplastic resin is added and the compatibilizer is melted and kneaded with the pulp fragments, the melted compatibilizer will adhere to the cellulose fibers formed from the loosened pulp fragments. As a result, the moldability and mechanical strength of the composite material obtained by the manufacturing method of the present invention tend to be increased.

[0063] Next, the cellulose fibers (or cellulose fibers with a compatibilizer) and the thermoplastic resin are mixed at a temperature above the melting point of the thermoplastic resin, specifically at a mixing temperature 10 to 50°C higher than the melting point of the thermoplastic resin. Let this mixing time be Y1. Subsequently, the mixture is mixed at a mixing temperature 50 to 80°C lower than the melting point of the thermoplastic resin. Let this mixing time be Y2. Subsequently, the mixture is mixed at a mixing temperature of 30°C or lower. Let this mixing time be Y3.

[0064] The ratio of the above-mentioned mixing times Y1, Y2, and Y3 (Y1:Y2:Y3) is preferably 35-40:50-55:5-15. In this case, the composite material of the present invention has superior fluidity during melting, resulting in better moldability.

[0065] Here, the melting point of the thermoplastic resin is determined by using a differential thermogravimetric thermometer (TG-DSC, manufactured by Hitachi High-Tech Science Corporation) and identifying the endothermic peak. The specific measurement conditions were as follows: First, a sample with a thickness of 0.2 mm was molded; Step 1: The temperature was raised to 240°C at a rate of 30°C / min and held for 10 minutes; Step 2: The temperature was lowered to 30°C at a rate of 10°C / min; Step 3: The temperature was raised to 240°C at a rate of 10°C / min. The endothermic peak at the third step was taken as the melting point.

[0066] The mixing temperature is the value obtained by measuring the temperature of the discharge port of the mixing equipment (mixer) using a temperature sensor.

[0067] The mixing method is not particularly limited, and examples include methods using a twin-screw extruder, a Banbury mixer, or a pressure roller.

[0068] When performing such an operation, namely kneading at a temperature above the melting point of the thermoplastic resin, followed by kneading at a temperature 50 to 80°C below the melting point of the thermoplastic resin, and then kneading at a temperature of 30°C or lower, using only thermoplastic resin, the ratio B / A tends to be between 0.28 and 0.68, where A (g / mol) is the average weight molecular weight of the thermoplastic resin before kneading and B (g / mol) is the average weight molecular weight of the thermoplastic resin after kneading.

[0069] Such a manufacturing method X may correspond to the manufacturing method of the present invention.

[0070] The composite material of the present invention obtained by the manufacturing method of the present invention may be further granulated. The shape of the granulated body (pellets) obtained by granulation is not particularly limited. For example, it may be particulate, cylindrical, polygonal prismatic, etc.

[0071] One granulation method involves extruding the composite material of the present invention from a die using an extruder and cutting it into pellets with a rotating blade under air cooling. The cutting length of the pellets can be changed by adjusting the rotation speed of the rotating blade.

[0072] The composite material of the present invention, which is in the form of a granulated body (pellet), can be molded using a mold such as an injection mold.

[0073] Examples of molded products made from the composite material of the present invention include molded parts for vehicles, equipment, and devices having fine or complex structures, industrial materials such as containers, pallets, plastic cores, and building materials, as well as daily necessities and general merchandise.

[0074] The present invention will be described below using examples, but the present invention is not limited to these examples.

[0075] In each of the examples and comparative examples, the pulp, thermoplastic resin, and compatibilizer shown in Tables 1 and 2 below were prepared. Since all the pulp consists of cellulose fibers, the pulp content shown in Tables 1 and 2 is equal to the cellulose fiber content in the composite material of the present invention.

[0076] The details of each raw material shown in Tables 1 and 2 are as follows: (Pulp) ・Pulp 1: Average fiber length: 180 μm, Average fiber diameter: 25 μm, Water retention: 12% by mass ・Pulp 2: Average fiber length: 180 μm, Average fiber diameter: 25 μm, Water retention: 2% by mass ・Pulp 3: Average fiber length: 180 μm, Average fiber diameter: 25 μm, Water retention: 8% by mass ・Pulp 4: Average fiber length: 180 μm, Average fiber diameter: 25 μm, Water retention: 17% by mass Here, the water retention of pulp is the same as that of cellulose fibers. The water retention of pulp can be determined in the same way as the water retention of cellulose fibers.

[0077] (Thermoplastic Resins) ・Thermoplastic Resin 1: Polypropylene-polyethylene copolymer (Molecular weight: 68,000 g / mol, random copolymer) ・Thermoplastic Resin 2: Polypropylene-polyethylene copolymer (Molecular weight: 160,000 g / mol, random copolymer) ・Thermoplastic Resin 3: Polypropylene-polyethylene copolymer (Molecular weight: 230,000 g / mol, random copolymer) ・Thermoplastic Resin 4: Polypropylene-polyethylene copolymer (Molecular weight: 62,000 g / mol, block copolymer) ・Thermoplastic Resin 5: Polypropylene (Molecular weight: 80,000 g / mol)

[0078] (Compatibilizers) • Compatibilizer 1: Maleic anhydride-modified polypropylene • Compatibilizer 2: Silane-modified polypropylene

[0079] In each of the examples and comparative examples, the pulp, thermoplastic resin, and compatibilizer described above were prepared in the proportions (mass%) shown in Tables 1 and 2 described later, and thermoplastic resin composite materials were obtained by the methods described below.

[0080] First, a predetermined amount of pulp (any of pulp types 1-5) was sprayed with water, and then it was put into a Henschel mixer. The pulp was then crushed into small pieces.

[0081] Next, a predetermined amount of compatibilizer (compatibility agent 1 or 2) was added to the Henschel mixer, and the pulp pieces and compatibilizer were kneaded together, with the temperature inside the Henschel mixer set to the temperature at which the compatibilizer melts. The compatibilizer was then thoroughly applied to the pulp pieces.

[0082] Next, a predetermined amount of thermoplastic resin (any of thermoplastic resins 1 to 5) was fed into a twin-screw extruder. Then, the thermoplastic resin was added to a mixture of pulp fragments and a compatibilizer, and these were kneaded. First, the temperature inside the twin-screw extruder was adjusted to be 10 to 50°C higher than the melting point of the thermoplastic resin, and kneading was performed. Let this kneading time be y1. Next, the temperature inside the twin-screw extruder was adjusted to be 50 to 80°C lower than the melting point of the thermoplastic resin, and kneading was performed. Let this kneading time be y2. Next, kneading was performed with the temperature inside the twin-screw extruder below 30°C. Let this kneading time be y3. The ratio of the above kneading times y1, y2, and y3 (y1:y2:y3) satisfied 35-40:50-55:5-15.

[0083] If such mixing is performed using only thermoplastic resin, and the average weight molecular weight of the thermoplastic resin before mixing is A (g / mol), and the average weight molecular weight of the thermoplastic resin after mixing is B (g / mol), then B / A will be between 0.28 and 0.68.

[0084] By this method, thermoplastic resin composites were obtained in each of the examples and comparative examples. However, in Comparative Example 5, although the mixing of the thermoplastic resin with the mixture of pulp fragments and compatibilizer was carried out at a temperature above the melting point of the thermoplastic resin, subsequent mixing was not carried out at a temperature 50 to 80°C below the melting point of the thermoplastic resin, nor at a temperature below 30°C. In this case, the above B / A is not within the range of 0.28 to 0.68. Also, in Comparative Example 6, after the above mixing, it was further mixed at a temperature above the melting point of the thermoplastic resin, then at a temperature 50 to 80°C below the melting point, and then at a temperature below 30°C. In this case, the above B / A is not within the range of 0.28 to 0.68.

[0085] The thermoplastic resin composite materials obtained in each of the examples and comparative examples were subjected to the following measurements and evaluations.

[0086] <Load-dependent properties> The load-dependent properties of each thermoplastic resin composite obtained in the examples and comparative examples were measured using the method described above. The results are shown in Tables 1 and 2.

[0087] <Evaluation of Moldability> For each thermoplastic resin composite material obtained in the examples and comparative examples, dumbbell test specimens (Type A1) for bending tests were prepared using an injection molding machine (J80ADS, manufactured by Japan Steel Works, Ltd.). The molding conditions for the test specimens were kept constant at a mold temperature of 25°C, an injection speed of 30 mm / s, and a holding pressure of 35 MPa. Molding was then performed using three cylinder temperature settings: less than 175°C, 175°C to less than 185°C, and 185°C to less than 195°C. The results were evaluated as follows: ・If molding was possible even when the cylinder temperature setting was less than 175°C, the molding was very good (A). ・If molding was possible when the cylinder temperature setting was between 175°C and less than 185°C, the molding was good (B). ・If molding was possible when the cylinder temperature setting was between 185°C and less than 195°C, molding was possible (C). - If the injection pressure exceeds the limit value regardless of the cylinder temperature setting, molding is not possible, or if burrs cannot be removed due to overfilling, molding is not possible (F).

[0088] <Evaluation of Mechanical Strength> The dumbbell test specimens prepared for the moldability evaluation as described above were subjected to flexural modulus measurement in accordance with ISO 178 using an Instron type material testing machine (Shimadzu Corporation: Autograph AG25 TA). The following evaluations were made: - If the flexural modulus is 5000 MPa or higher... A - If the flexural modulus is 4000 MPa or higher and less than 5000 MPa... B - If the flexural modulus is 3000 MPa or higher and less than 4000 MPa... C - If the flexural modulus is less than 3000 MPa... F

[0089] <Overall Evaluation> Based on the results of the above evaluations of moldability and mechanical strength, the overall evaluation was made as follows: • If both are A... A rating • If either is B... B rating • If either is C... C rating • If either is F... F rating

[0090]

[0091]

[0092] This application claims priority based on Japanese Patent Application No. 2024-172971, filed on 2 October 2024, and incorporates all of its disclosures herein.

Claims

1. A thermoplastic resin composite material comprising cellulose fibers and a thermoplastic resin, wherein the cellulose fiber content is 30 to 70% by mass, the thermoplastic resin content is 20 to 70% by mass, and the load-dependent properties are 7 to 32 (g / 10min / kgf).

2. The thermoplastic resin composite material according to claim 1, wherein the average weight molecular weight of the thermoplastic resin is 200,000 g / mol or less.

3. The thermoplastic resin composite material according to claim 1 or 2, further containing 15% by mass or less of a compatibilizer.

4. The thermoplastic resin composite material according to claim 3, wherein the compatibilizer is an acid-modified polyolefin resin modified with an unsaturated dicarboxylic acid and / or its acid anhydride.

5. The thermoplastic resin composite material according to claim 1 or 2, wherein the thermoplastic resin is a polyolefin.

6. The thermoplastic resin composite material according to claim 1 or 2, wherein the thermoplastic resin is a polypropylene-polyethylene copolymer.

7. The thermoplastic resin composite material according to claim 6, wherein the thermoplastic resin is a random copolymer.

8. The thermoplastic resin composite material according to claim 1 or 2, wherein the water retention rate of the cellulose fibers is 5 to 20% by mass.

9. A molded article made of the thermoplastic resin composite material according to claim 1 or 2.

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