Cellulose fiber composite resin composition, molded object of cellulose fiber composite resin, and production methods therefor

Abstract

A cellulose fiber composite resin composition comprising: a main-component resin; cellulose fibers; a low-molecular-weight resin; and a crosslinking agent capable of forming two or more kinds of crosslinked structures selected from among one between molecules of the main-component resin, one between molecules of the low-molecular-weight resin, and one between a molecule of the main-component resin and a molecule of the low-molecular-weight resin.

Description

Cellulose fiber composite resin composition, cellulose fiber composite resin molded body, and method for producing the same

[0001] The present disclosure relates to a cellulose fiber composite resin composition, a molded article, and a manufacturing method.

[0002] So-called "general-purpose plastics" such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) are relatively inexpensive, lightweight (a fraction of the weight of metals or ceramics), and easy to process, such as molding. For these reasons, general-purpose plastics are used as materials for a variety of everyday items such as bags, various types of packaging, various types of containers, and sheets, as well as industrial parts such as automobile parts and electrical parts, and for daily necessities and miscellaneous goods.

[0003] However, general-purpose plastics have drawbacks such as insufficient mechanical strength, and therefore do not have sufficient properties required for materials used in various industrial products, including mechanical products such as automobiles, and electrical, electronic, and information products, and the range of their application is currently limited.

[0004] On the other hand, so-called "engineering plastics" such as polyacetal (POM), polyamide (PA), polycarbonate (PC), and fluororesin have excellent mechanical properties and are used in various industrial products, including mechanical products such as automobiles, and electrical, electronic, and information products. However, engineering plastics have problems such as being expensive, difficulty in monomer recycling, and a large environmental impact.

[0005] Therefore, there is a demand for significant improvements in the material properties (mechanical strength, etc.) of general-purpose plastics. A known method for improving the material properties of general-purpose plastics is to produce composite resins by blending two or more types of resins or additives such as fillers. In particular, fibrous fillers such as natural fibers, glass fibers, and carbon fibers are used to improve mechanical strength. Among these, organic fibrous fillers such as cellulose have recently attracted attention as reinforcing fibers because they are inexpensive and environmentally friendly when disposed of.

[0006] Increasing the amount of fibrous filler added improves the mechanical strength of the composite resin, but significantly reduces its fluidity. This reduced fluidity leads to poor filling during molding, poor appearance, and poor moldability. Patent Document 1 uses a low-molecular-weight wax to coat the surface of a cellulose-based powder, improving moldability.

[0007] Patent No. 3167020

[0008] However, the composite resin described in Patent Document 1 uses a low molecular weight wax, and since low molecular weight wax has low strength as a single substance, there is a problem in that the strength of the entire composite resin is reduced.

[0009] The present disclosure is intended to solve the above-mentioned conventional problems, and has an object to provide a cellulose fiber composite resin composition that has good flowability during molding and high strength after molding.

[0010] The cellulose fiber composite resin composition according to the present disclosure includes a main resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent capable of forming crosslinked structures between two or more of the main resin, the low molecular weight resin, and the main resin and the low molecular weight resin.

[0011] The cellulose fiber composite resin composition according to the present disclosure contains a low-molecular-weight resin, which provides high fluidity during molding. On the other hand, after molding, the crosslinking agent contained therein allows for the formation of crosslinked structures in the base resin and / or the low-molecular-weight resin by irradiation, resulting in the production of a high-strength cellulose fiber composite resin molding.

[0012] 1 is a schematic diagram showing the structure of a cellulose fiber composite resin composition according to Embodiment 1. FIG. 2 is a diagram showing conditions and measurement results in Examples 1 to 4 and Comparative Example 1.

[0013] Hereinafter, a cellulose fiber composite resin composition and a cellulose fiber composite resin molded article according to embodiments will be described with reference to the accompanying drawings. In the following description, the same components are denoted by the same reference numerals, and the description will be omitted where appropriate.

[0014] The cellulose fiber composite resin composition according to the first aspect includes a main resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent capable of forming crosslinked structures between two or more of the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin.

[0015] In the cellulose fiber composite resin composition according to the second aspect, the low molecular weight resin may have the same basic structure as the main resin in the first aspect.

[0016] The cellulose fiber composite resin composition according to the third aspect may be the cellulose fiber composite resin composition according to the first or second aspect, wherein the content of the cellulose fibers in the entire cellulose fiber composite resin composition is 10% by mass or more and 90% by mass or less.

[0017] A cellulose fiber composite resin composition according to a fourth aspect is any one of the first to third aspects, wherein the cellulose fibers have an average particle size of 10 μm or more and 500 μm or less.

[0018] A cellulose fiber composite resin composition according to a fifth aspect is any one of the first to fourth aspects, wherein the low molecular weight resin has a weight average molecular weight of 1,000 or more and 50,000 or less.

[0019] The cellulose fiber composite resin composition according to the sixth aspect may be any one of the first to fifth aspects, wherein the ratio of the number of cellulose fibers whose extension direction is bent by 90° or more midway relative to the longitudinal direction is 1% or more and 30% or less.

[0020] The cellulose fiber composite resin composition according to the seventh aspect may be any of the first to fifth aspects, in which the low molecular weight resin is 0.5% by mass or more and 20% by mass or less relative to 100% by mass of the total amount of the base resin, cellulose fiber, low molecular weight resin, and crosslinking agent.

[0021] The method for producing a cellulose fiber composite resin composition according to the eighth aspect includes a mixing step of adhering a powdered or liquid low molecular weight resin having a lower molecular weight than the main resin to cellulose fibers, and a step of kneading the main resin, cellulose fibers, the low molecular weight resin, and a crosslinking agent capable of forming crosslinked structures between two or more of the main resin, the low molecular weight resin, and the main resin and the low molecular weight resin to form a cellulose fiber composite resin composition.

[0022] The cellulose fiber composite resin molding of the ninth aspect is a cellulose fiber composite resin molding made of a cellulose fiber composite resin composition containing a main resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent, and has a crosslinked structure caused by the crosslinking agent in two or more of the following: between the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin.

[0023] A cellulose fiber composite resin molded article according to a tenth aspect may be the cellulose fiber composite resin molded article of the ninth aspect, wherein the gel fraction of the cellulose fiber composite resin molded article is 10% or more.

[0024] The method for producing a cellulose fiber composite resin molded body according to the eleventh aspect includes the steps of kneading a base resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent to obtain a cellulose fiber composite resin composition, molding the cellulose fiber composite resin composition to obtain a molded body, and irradiating the molded body with radiation to form crosslinked structures by the crosslinking agent in two or more of the following: between the base resin, between the low molecular weight resin, and between the base resin and the low molecular weight resin.

[0025] A twelfth aspect of the present invention relates to a method for producing a cellulose fiber composite resin molded article according to the eleventh aspect, wherein the low molecular weight resin has the same basic structure as the main resin.

[0026] The method for producing a cellulose fiber composite resin molding according to the thirteenth aspect is the eleventh or twelfth aspect, wherein the cellulose fiber content in the entire cellulose fiber composite resin molding may be 10% by mass or more and 90% by mass or less.

[0027] A fourteenth aspect of the method for producing a cellulose fiber composite resin molding according to any one of the eleventh to thirteenth aspects is such that the cellulose fibers have an average particle size of 10 μm or more and 500 μm or less.

[0028] The method for producing a cellulose fiber composite resin molding according to a fifteenth aspect is any one of the eleventh to fourteenth aspects, wherein the low molecular weight resin may have a weight average molecular weight of 1,000 or more and 50,000 or less.

[0029] The method for producing a cellulose fiber composite resin molding according to the 16th aspect may be such that, in any of the 11th to 15th aspects, the ratio of the number of cellulose fibers whose extension direction is bent by 90° or more halfway relative to the longitudinal direction is 1% or more and 30% or less.

[0030] The method for producing a cellulose fiber composite resin molding according to the seventeenth aspect may be any of the eleventh to sixteenth aspects, in which the low molecular weight resin is 0.5% by mass or more and 20% by mass or less relative to a total amount of 100% by mass of the main resin, cellulose fiber, low molecular weight resin, and crosslinking agent.

[0031] The method for producing a cellulose fiber composite resin molding according to the eighteenth aspect may further include a mixing step of adhering a powdered or liquid low molecular weight resin to the cellulose fibers in any of the eleventh to seventeenth aspects.

[0032] A nineteenth aspect of the method for producing a composite resin molded article is any one of the eleventh to eighteenth aspects, wherein the cellulose fiber composite resin molded article may have a gel fraction of 10% or more.

[0033] Hereinafter, a cellulose fiber composite resin composition and a cellulose fiber composite resin molded article according to embodiments will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals, and the description will be omitted as appropriate.

[0034] First Embodiment Cellulose Fiber Composite Resin Composition FIG. 1 is a schematic diagram showing the configuration of a cellulose fiber composite resin composition 10 according to a first embodiment.

[0035] The composite resin 10 according to the first embodiment includes a main resin 1, cellulose fibers 2, a low-molecular-weight resin 3, and a crosslinking agent 4. As shown in Fig. 1 , the cellulose fiber composite resin composition 10 has cellulose fibers 2, a low-molecular-weight resin 3, and a crosslinking agent 4 dispersed in a matrix of the main resin 1, and the low-molecular-weight resin 3 is present around the cellulose fibers 2. The crosslinking agent is capable of forming crosslinked structures between two or more of the main resins, between the low-molecular-weight resins, and between the main resin and the low-molecular-weight resin.

[0036] This cellulose fiber composite resin composition 10 has high fluidity during molding because it contains the low molecular weight resin 3. On the other hand, after molding, because it contains the crosslinking agent 4, a crosslinked structure can be formed in the main resin 1 and / or the low molecular weight resin 3 by irradiation with radiation, and a cellulose fiber composite resin molded product with high strength and heat resistance and reduced bleed-out can be obtained.

[0037] The cellulose fiber composite resin composition 10 may be a fluid or solid, and may be in the form of, for example, a block, a rectangle, or a pellet for storage or distribution.

[0038] The components constituting the cellulose fiber composite resin composition 10 will be described below.

[0039] <Main Resin> The main resin 1 in the first embodiment is preferably a thermoplastic resin to ensure good moldability. Examples of thermoplastic resins include olefin-based resins (including cyclic olefin-based resins), styrene-based resins, (meth)acrylic resins, organic acid vinyl ester-based resins or derivatives thereof, vinyl ether-based resins, halogen composite resins, polycarbonate-based resins, polyester-based resins, polyamide-based resins, thermoplastic polyurethane resins, polysulfone-based resins (polyethersulfone, polysulfone, etc.), polyphenylene ether-based resins (2,6-xylenol polymers, etc.), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubber or elastomer (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubbers, urethane rubbers, silicone rubbers, etc.). The above resins may be used alone or in combination. The resins are not limited to the above materials as long as they have thermoplastic properties.

[0040] Of these thermoplastic resins, the main resin 1 is preferably a resin that can form a crosslinked structure upon irradiation with radiation or that can form a crosslinked structure upon irradiation with the addition of a crosslinking agent. Radiation includes electron beams and gamma rays, and electron beam irradiation is primarily used in the present application. Examples of resins that can form a crosslinked structure upon irradiation with radiation or with the addition of a crosslinking agent include olefin resins, polyamide resins, and polylactic acid resins. The above resins may be used alone or in combination of two or more. The resin is not limited to the above materials, as long as it is a resin that can form a crosslinked structure upon irradiation with the addition of a crosslinking agent.

[0041] <Cellulose Fibers> Examples of the cellulose fibers 2 in the first embodiment include cellulose fibers, lignocellulose fibers, etc. Raw materials for cellulose fibers and lignocellulose fibers include natural materials such as wood (coniferous trees and broad-leaved trees), cotton linters, kenaf, Manila hemp (abaca), sisal hemp, jute, sabai grass, esparto grass, bagasse, rice straw, wheat straw, reeds, and bamboo.

[0042] The content of cellulose fiber 2 is preferably 10% by mass or more and 90% by mass or less. When it is 90% by mass or less, the cellulose fiber content is suppressed, allowing the cellulose fiber composite resin composition to flow and be molded. When it is 10% by mass or more, the effect of forming a crosslinked structure with low energy due to the presence of cellulose fiber can be fully exerted. Therefore, the content of cellulose fiber is preferably 10% by mass or more and 90% by mass or less, more preferably 30% by mass or more and 90% by mass or less, and even more preferably 50% by mass or more and 90% by mass or less.

[0043] The average particle size of the cellulose fibers 2 is preferably 10 μm or more and 500 μm or less, and more preferably 20 μm or more and 400 μm or less. When the average particle size of the cellulose fibers is 500 μm or less, the cellulose fibers are less likely to come into contact with each other and form aggregates. When the average particle size of the cellulose fibers is 10 μm or more, the surface area of ​​the cellulose fibers can be reduced, thereby improving the fluidity of the cellulose fiber composite resin composition. Therefore, the average particle size of the cellulose fibers is preferably 10 μm or more and 500 μm or less, and more preferably 20 μm or more and 400 μm or less.

[0044] Among the cellulose fibers, the ratio of the number of cellulose fibers whose extension direction is bent by 90° or more with respect to the longitudinal direction is preferably 1% or more and 30% or less. When the ratio of the number of cellulose fibers whose extension direction is bent by 90° or more is 30% or less, the bent cellulose fibers are less likely to come into contact with each other and become entangled, making it difficult to form aggregates. When the ratio of the number of cellulose fibers whose extension direction is bent by 90° or more is 1% or more, the presence of bent cellulose fibers allows for the formation of a crosslinked structure of the resin and entanglement of the cellulose fibers. Therefore, the ratio of cellulose fibers whose extension direction is bent by 90° or more is preferably within the above range.

[0045] <Low Molecular Resin> The low molecular resin 3 in the first embodiment is preferably a thermoplastic resin because it must be melted during kneading. Examples of thermoplastic resins include olefin resins (including cyclic olefin resins), styrene resins, (meth)acrylic resins, organic acid vinyl ester resins or derivatives thereof, vinyl ether resins, halogen composite resins, polycarbonate resins, polyester resins, polyamide resins, thermoplastic polyurethane resins, polysulfone resins (polyethersulfone, polysulfone, etc.), polyphenylene ether resins (2,6-xylenol polymers, etc.), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubber or elastomer (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubbers, urethane rubbers, silicone rubbers, etc.), and waxes. The above resins may be used alone or in combination. The resin is not limited to the above materials as long as it has thermoplastic properties.

[0046] Of these thermoplastic resins, the low-molecular-weight resin 3 is preferably a resin that can form a crosslinked structure upon irradiation with radiation or that can form a crosslinked structure upon irradiation with the addition of a crosslinking agent. Radiation includes electron beams and gamma rays, and electron beam irradiation is primarily used in the present application. Examples of resins that can form a crosslinked structure upon irradiation with radiation or with the addition of a crosslinking agent include olefin resins, polyamide resins, and polylactic acid resins. The above resins may be used alone or in combination of two or more. The resin is not limited to the above materials, as long as it is a resin that can form a crosslinked structure upon irradiation with the addition of a crosslinking agent.

[0047] The low-molecular-weight resin 3 may have a lower molecular weight than the base resin and the same basic structure as the base resin. If the base resin and the low-molecular-weight resin have different structures, crosslinking structures are likely to be preferentially formed between base resins or between low-molecular-weight resins when crosslinked during radiation exposure. If crosslinking structures are preferentially formed between base resins, low-molecular-weight resins are less likely to form crosslinked structures, making it difficult to suppress a decrease in strength and heat resistance. Furthermore, if crosslinking structures are preferentially formed between low-molecular-weight resins, because they are low-molecular-weight resins, the promotion of polymerization due to crosslinking is slower, making it difficult to suppress a decrease in strength and heat resistance. Therefore, it is preferable that the low-molecular-weight resin have the same basic structure as the base resin. This allows a crosslinking structure to be formed between the base resin and the low-molecular-weight resin.

[0048] The phrase "having the same basic structure" means having a portion composed of common monomer units, i.e., the base resin and the low-molecular-weight resin have a portion with the same repeating molecular structure.

[0049] The low molecular weight resin is preferably 0.5% by mass or more and 20% by mass or less relative to the total amount (100% by mass) of the base resin, cellulose fiber, low molecular weight resin, and crosslinking agent. When the low molecular weight resin is 0.5% by mass or more, the amount of low molecular weight resin is sufficient to improve the fluidity of the composite resin, making it possible to mold it and enabling molding under conditions that are not high temperatures. When the low molecular weight resin is 20% by mass or less, the amount of low molecular weight resin is not too high, making it possible to suppress a decrease in the strength of the cellulose fiber composite resin composition. Therefore, the low molecular weight resin is preferably 0.5% by mass or more and 20% by mass or less relative to the total amount (100% by mass) of the base resin, cellulose fiber, low molecular weight resin, and crosslinking agent.

[0050] The molecular weight of the low molecular weight resin 3 is preferably 1,000 or more and 50,000 or less, and more preferably 3,000 or more and 30,000 or less. When the molecular weight is 1,000 or more, the strength of the resin alone is sufficient, so that a decrease in the strength of the entire cellulose fiber composite resin composition can be suppressed. When the molecular weight is 50,000 or less, the viscosity of the low molecular weight resin alone does not become too high, so that the fluidity of the cellulose fiber composite resin can be improved. Therefore, the molecular weight of the low molecular weight resin 3 is preferably within the above range.

[0051] The "molecular weight" mentioned above refers to the "weight average molecular weight." The weight average molecular weight was measured using gel permeation chromatography (GPC). Note that the mobile phase for GPC has different liquid components that can dissolve different resins, so an appropriate material is selected for each resin. For example, σ-dichlorobenzene can be used as the mobile phase for polyolefins.

[0052] The cellulose fiber composite resin composition 10 contains a low molecular weight resin, which increases the fluidity of the cellulose fiber composite resin composition even when it contains cellulose fibers. On the other hand, the crosslinking agent contained in the cellulose fiber composite resin composition allows a crosslinked structure to be formed by irradiating the molded product with radiation after molding, thereby improving the strength and heat resistance of the composition even when it contains a low molecular weight resin. Therefore, the cellulose fiber composite resin composition 10 preferably contains at least a base resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent.

[0053] <Crosslinking Agent> The crosslinking agent 4 in the first embodiment is preferably a multifunctional crosslinking agent having two or more reactive groups in the molecule. Adding a crosslinking agent makes it easier for the crosslinking reaction to occur uniformly. Examples of multifunctional crosslinking agents include triacyl isocyanurate (TAIC), triallyl cyanurate (TAC), and divinylbenzene (DVB). Note that the crosslinking agent is not limited to the above materials as long as it is multifunctional. For example, modified cellulose fibers may also be used.

[0054] <Additives> The cellulose fiber composite resin composition may contain various additives in addition to the various materials described above. For example, when producing the cellulose fiber composite resin composition, maleic anhydride polypropylene (dispersant) may be added in addition to polypropylene (main resin), pulverized pulp (cellulose fiber), low molecular weight polypropylene (low molecular weight resin), and triacyl isocyanurate (crosslinking agent).

[0055] The average particle size can be measured by, for example, sieving (JIS K 0069:1992), laser diffraction / scattering (JIS Z 8825:2013), dynamic light scattering (JIS Z 8828:2013), and other methods. In the sieving method, particles are sieved using multiple sieves with different mesh sizes, and the particle size distribution is measured from the weight of the particles remaining on each sieve. In the laser diffraction / scattering method, particles in a liquid or gas are irradiated with a laser beam, and the particle size is measured based on the fact that the intensity pattern of the scattered light scattered by the particles depends on the particle size. In the laser diffraction / scattering method, the particle size is measured as the spherical equivalent diameter. In the dynamic light scattering method, particle size is measured based on the Brownian motion of particles suspended in a liquid. In other words, the phase shift between the scattered light due to Brownian motion and the incident light is observed, and the particle size is calculated from the observed phase shift.

[0056] The average particle size is, for example, the median diameter D where the cumulative frequency in the obtained particle size distribution is 50%. ５０ The average particle size may be determined by the median diameter D ５０ is shown using

[0057] <Method for Producing Cellulose Fiber Composite Resin Composition> The method for producing a cellulose fiber composite resin composition includes a step (kneading step) of kneading a base resin, cellulose fibers, a low-molecular-weight resin, and a crosslinking agent to form a cellulose fiber composite resin composition. The crosslinking agent is capable of forming crosslinked structures between two or more of the base resins, the low-molecular-weight resins, and the base resin and the low-molecular-weight resin. Furthermore, the method for producing a cellulose fiber composite resin composition may include a mixing step for adhering a powder or liquid low-molecular-weight resin to the cellulose fibers 2. By adhering a powder or liquid low-molecular-weight resin to the surfaces of the cellulose fibers prior to the kneading step, direct contact between the cellulose fibers is reduced, thereby suppressing aggregation of the cellulose fibers. Furthermore, adhering the low-molecular-weight resin to the surfaces of the cellulose fibers reduces flow resistance due to the cellulose fibers, improving fluidity. Note that when the low-molecular-weight resin is used in the form of resin pellets, their size is significantly larger than that of the cellulose fibers. Therefore, even if the low-molecular-weight resin in the resin pellets is mixed with the cellulose fibers, the individual components separate, making it impossible to adhere the resin to the cellulose fibers. Therefore, powder or liquid low molecular weight resin 3 may be used. Furthermore, a mixing step of cellulose fibers and powder or liquid low molecular weight resin may be carried out before the kneading step.

[0058] Examples of kneading devices used in the kneading step of the method for producing a cellulose fiber composite resin composition include single-screw kneaders, twin-screw kneaders, roll kneaders, kneaders, Banbury mixers, and combinations thereof. Continuous twin-screw kneaders and continuous roll kneaders are preferred because they are easy to apply high shear and are suitable for mass production. Other kneading methods may also be used as long as they can apply high shear stress. Furthermore, because cellulose fibers are prone to thermal degradation, it is preferable to knead them at as low a temperature as possible.

[0059] <Cellulose fiber composite resin molding> The cellulose fiber composite resin molding according to the first embodiment is a cellulose fiber composite resin molding made of a cellulose fiber composite resin composition containing a base resin, cellulose fibers, a low-molecular-weight resin, and a crosslinking agent. This cellulose fiber composite resin molding has a crosslinked structure formed by the crosslinking agent in at least two of the following locations: between the base resin components, between the low-molecular-weight resin components, and between the base resin component and the low-molecular-weight resin component.

[0060] Furthermore, the gel fraction of the cellulose fiber composite resin molding is preferably 10% or more, more preferably 30% or more, and even more preferably 50% or more. The gel fraction is an index that can estimate the degree of crosslinking of the main resin and the low molecular weight resin. When the gel fraction is 10% or more, the low molecular weight resin can form a crosslinked structure, thereby improving the strength of the composite resin. Therefore, the gel fraction of the cellulose fiber composite resin molding is preferably 10% or more.

[0061] This cellulose fiber composite resin molding has excellent mechanical strength due to the crosslinked structure estimated by the gel fraction.

[0062] <Method for Producing Cellulose Fiber Composite Resin Molded Article> A method for producing a cellulose fiber composite resin molded article according to the first embodiment is, for example, as follows.

[0063] (1) First, a base resin, cellulose fibers, a low-molecular-weight resin, and a crosslinking agent are kneaded to obtain a cellulose fiber composite resin composition (kneading step).

[0064] The kneading step is substantially the same as the kneading step in the method for producing a cellulose fiber composite resin composition. Examples of kneading devices used in the kneading step include single-screw kneaders, twin-screw kneaders, roll kneaders, kneaders, Banbury mixers, and combinations thereof. Continuous twin-screw kneaders and continuous roll kneaders are preferred because they are easy to apply high shear stress and are suitable for mass production. Other kneading methods may also be used as long as they can apply high shear stress. Furthermore, because cellulose fibers are susceptible to thermal degradation, it is preferable to knead them at as low a temperature as possible.

[0065] The composite resin composition extruded from the kneading device is cut into pellets using a pelletizer or the like. Pelletization methods include, for example, air hot cutting, underwater hot cutting, and strand cutting, which are performed immediately after the resin is melted. Alternatively, a crushing method may be used in which a molded body or sheet is molded and then crushed and cut.

[0066] (2) Next, the obtained cellulose fiber composite resin composition is molded to obtain a molded body.

[0067] The molded article is produced by molding the pellets, using molding methods such as injection molding, extrusion molding, compression molding, and blow molding.

[0068] (3) Next, the molded body is irradiated with radiation to obtain a cellulose fiber composite resin molded body in which crosslinked structures are formed between two or more of the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin.

[0069] By irradiating the molded body with radiation, crosslinked structures are formed between two or more of the base resins, between the low molecular weight resins, and between the base resin and the low molecular weight resin. Examples of devices used for radiation irradiation include electron beam irradiation devices. Other devices may also be used as long as they can irradiate relatively low-energy radiation of 300 kGy or less in order to suppress damage to the material from radiation.

[0070] In this manner, a cellulose fiber composite resin molded article is obtained.

[0071] In a method for producing a cellulose fiber composite resin molded article, the inclusion of a low-molecular-weight resin in the step of obtaining a cellulose fiber composite resin composition can improve the fluidity of the composite resin and make it easier to mold. Furthermore, the inclusion of a crosslinking agent can uniformly form crosslinked structures between the base resin and the low-molecular-weight resin upon irradiation. Therefore, the method for producing a cellulose fiber composite resin molded article preferably includes the steps of kneading the base resin, cellulose fibers, the low-molecular-weight resin, and the crosslinking agent to obtain a cellulose fiber composite resin composition, and irradiating the molded article obtained from the cellulose fiber composite resin composition with radiation to obtain a cellulose fiber composite resin molded article in which crosslinked structures are formed between the base resin, the low-molecular-weight resin, and between the base resin and the low-molecular-weight resin or ....

[0072] Hereinafter, each example and each comparative example carried out by the inventors will be described.

[0073] (Examples 1 to 4, Comparative Example 1) FIG. 2 is a diagram showing the conditions and measurement results for Examples 1 to 4 and Comparative Example 1.

[0074] A cellulose fiber composite resin composition and a cellulose fiber composite resin molded article were produced by the following manufacturing method. As described above, a single-screw kneader, a twin-screw kneader, a roll kneader, a kneader, a Banbury mixer, or a combination thereof can be used as the kneading device, but a twin-screw kneader was used in the examples.

[0075] Polypropylene (manufactured by Japan Polypropylene Corporation, product name: BC03C) was used as the base resin, ground pulp as the cellulose fiber, low-molecular-weight polyolefin (manufactured by Mitsui Chemicals, Inc., product name: Hiwax) as the low-molecular-weight resin, and triallyl isocyanate (manufactured by Mitsubishi Chemical Corporation) as the crosslinking agent, all weighed out to a mass ratio of 38:55:5:2. The base resin, ground pulp, low-molecular-weight resin, and crosslinking agent were mixed and fed separately into the kneader. Hardwood pulp (manufactured by Mitsubishi Paper Mills, product name: Mitsubishi Kitakami LBKP) was used as the starting material for ground pulp. This pulp was ground in a grinder to obtain ground pulp. The size of the cellulose fibers was adjusted during the grinding process. As for the grinding method, dry grinding is preferred because wet grinding requires a drying process after grinding and can cause aggregation during drying.

[0076] The mixture was melted, kneaded, and dispersed in a twin-screw kneader (KRC Kneader manufactured by Kurimoto Iron Works Co., Ltd.). The shear force can be changed by changing the screw configuration of the twin-screw kneader, and a low-shear type was used in Example 1. The cellulose fiber composite resin composition discharged from the twin-screw kneader was hot-cut to produce cellulose fiber composite resin pellets made of the cellulose fiber composite resin composition.

[0077] The cellulose fiber composite resin pellets were used to prepare composite resin molded specimens using an injection molding machine (180AD manufactured by Japan Steel Works, Ltd.). The conditions for preparing dumbbell specimens were a resin temperature of 200°C, a mold temperature of 40°C, an injection speed of 60 mm / s, and a holding pressure of 100 MPa. The pellets were fed into the screw of the molding machine via a hopper, and the penetration rate during this process was measured by the amount of pellet loss per hour, which was confirmed to be consistent. The shape of the specimen was changed depending on the evaluation items described below, and size 1 dumbbell specimens were prepared for elastic modulus measurement.

[0078] The prepared test piece of the cellulose fiber composite resin composition was irradiated with an electron beam using an electron beam irradiation device. The electron beam irradiation conditions were adjusted to irradiate with an energy of 30 kGy at an acceleration voltage of 4.6 MV and a current of 20 mA. In this way, a test piece of a cellulose fiber composite resin molding was obtained.

[0079] The test pieces of the obtained cellulose fiber composite resin moldings were evaluated by the following methods.

[0080] [Evaluation Items of Composite Resin Molded Article] (Strength of Composite Resin Molded Article) A three-point bending test was carried out using the obtained No. 1 dumbbell-shaped test piece. The modulus of elasticity of the test piece was 52 MPa.

[0081] (Evaluation of bending degree of cellulose fibers in composite resin molding) A portion was cut out from the obtained No. 1 dumbbell-shaped test piece and observed under SEM. The ratio of the number of cellulose fibers in the resin whose extension direction was bent at an angle of 90° or more with respect to the longitudinal direction was 14%.

[0082] (Gel Fraction) A portion was cut out from the obtained No. 1 dumbbell-shaped test piece, and the gel fraction, which is an index of the degree of crosslinking, was evaluated. Referring to JIS K6796, the cut test piece was weighed, wrapped in a wire mesh, and immersed in a flask containing a solvent for approximately 8 hours. The test piece was then removed, dried, and weighed, and the gel fraction was calculated from the mass ratio before and after immersion. The denominator of the mass ratio was the mass excluding the mass of cellulose fibers and other components other than the base resin and low-molecular-weight resin. The gel fraction of the test piece was 53%.

[0083] In Example 2, maleic anhydride-modified polypropylene (trade name: Umex, manufactured by Sanyo Chemical Industries, Ltd.) was used as the dispersant, and the mass ratio of base resin: cellulose fiber: low molecular weight resin: crosslinking agent: dispersant was changed to 36:55:5:2:2. Other conditions were the same as in Example 1, and cellulose fiber composite resin pellets and a molded product were produced. Evaluations similar to those in Example 1 were also carried out.

[0084] In Example 3, the amount of cellulose fiber added was reduced compared to Example 1, and the mass ratio of base resin:cellulose fiber:low molecular weight resin:crosslinking agent was changed to 54:40:2. Other material conditions and process conditions were the same as in Example 1, and cellulose fiber composite resin pellets and molded articles were produced. Evaluations similar to those in Example 1 were also carried out.

[0085] Example 4 In Example 4, the amount of low-molecular-weight resin added was increased compared to Example 1, and the mass ratio of base resin:cellulose fiber:dispersant:low-molecular-weight resin:crosslinking agent was changed to 33:55:10:2. Other material conditions and process conditions were the same as in Example 1, and cellulose fiber composite resin pellets and molded articles were produced. Evaluations similar to those in Example 1 were also carried out.

[0086] Comparative Example 1 In Comparative Example 1, no crosslinking agent was added, and the mass ratio of base resin: ground pulp: dispersant: crosslinking agent was changed to 40:55:5:0. Other material conditions and process conditions were the same as in Example 1, and composite resin pellets and molded bodies were produced. Evaluations similar to those in Example 1 were also performed.

[0087] The measurement results for each of Examples 1 to 4 and Comparative Example 1 are shown in the table of FIG.

[0088] In Example 2, in which a dispersant was used, the compatibility between the cellulose fiber and the resin was improved compared to Example 1, and the strength was 78 MPa.

[0089] In Example 3, in which the amount of cellulose fiber added was reduced, the cellulose fiber concentration was lower than in Example 1, so the reinforcing effect of the cellulose fiber was reduced and the effect of promoting crosslinking by low-energy radiation irradiation was also reduced, resulting in a strength of 42 MPa.

[0090] In Example 4, in which the amount of low-molecular-weight resin added was increased, the fluidity was further improved compared to Example 1. On the other hand, the crosslinking effect suppressed the decrease in strength due to the increase in the amount of low-molecular-weight resin added, so the strength was 47 MPa.

[0091] In Comparative Example 1, in which no crosslinking agent was used, crosslinking did not proceed due to the absence of the crosslinking agent, and the strength was 33 MPa.

[0092] From the above evaluation, it was found that the addition of a crosslinking agent promoted crosslinking, suppressed the decrease in strength caused by the addition of a low molecular weight resin, and enabled the strength of the cellulose fiber composite resin molding to be at the required level.

[0093] As described above, the cellulose fiber composite resin composition containing the base resin, cellulose fiber, low-molecular-weight resin, and crosslinking agent provides high fluidity during molding. Furthermore, by irradiating the composition after molding with radiation to form crosslinked structures in two or more of the base resin, the low-molecular-weight resin, and the base resin and the low-molecular-weight resin, the mechanical strength of the resulting cellulose fiber composite resin molding is increased.

[0094] The cellulose fiber composite resin composition according to the present disclosure has high fluidity during molding, and after molding, it is possible to provide a molded article having superior mechanical strength and heat resistance compared to conventional general-purpose resins. The cellulose fiber composite resin molded article obtained by using the cellulose fiber composite resin composition according to the present disclosure can be used for home appliance housings, building materials, exterior automotive components, and other applications that require excellent mechanical strength and heat resistance.

[0095] REFERENCE SIGNS LIST 1 base resin 2 cellulose fiber 3 low molecular weight resin 4 crosslinking agent 10 cellulose fiber composite resin composition

Claims

1. A cellulose fiber composite resin composition comprising: a base resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent capable of forming crosslinked structures between two or more of the base resin, between the low molecular weight resins, and between the base resin and the low molecular weight resin.

2. The cellulose fiber composite resin composition according to claim 1, wherein the low molecular weight resin has the same basic structure as the main resin.

3. A cellulose fiber composite resin composition as described in claim 1, wherein the cellulose fiber is present in an amount of 10 mass% or more and 90 mass% or less in the entire cellulose fiber composite resin composition.

4. The cellulose fiber composite resin composition according to claim 1, wherein the cellulose fibers have an average particle size of 10 μm or more and 500 μm or less.

5. The cellulose fiber composite resin composition according to claim 1, wherein the low molecular weight resin has a weight average molecular weight of 1,000 or more and 50,000 or less.

6. A cellulose fiber composite resin composition as described in claim 1, wherein the ratio of the number of cellulose fibers whose extension direction is bent by 90° or more halfway relative to the longitudinal direction is 1% or more and 30% or less.

7. A cellulose fiber composite resin composition as described in claim 1, wherein the low molecular weight resin is 0.5 mass% or more and 20 mass% or less relative to a total amount of 100 mass% of the base resin, the cellulose fiber, the low molecular weight resin, and the crosslinking agent.

8. A method for producing a cellulose fiber composite resin composition, comprising: a mixing step of adhering a powdered or liquid low molecular weight resin having a lower molecular weight than a main resin to cellulose fibers; and a step of kneading the main resin, the cellulose fibers, the low molecular weight resin, and a crosslinking agent capable of forming crosslinked structures between the main resin, between the low molecular weight resin, and between the main resin and the low molecular weight resin to form a cellulose fiber composite resin composition.

9. A cellulose fiber composite resin molding comprising a cellulose fiber composite resin composition containing a base resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent, wherein the cellulose fiber composite resin molding has a crosslinked structure formed by the crosslinking agent in at least two of the following: between the base resins, between the low molecular weight resins, and between the base resin and the low molecular weight resin.

10. The cellulose fiber composite resin molding according to claim 9, wherein the gel fraction of the cellulose fiber composite resin molding is 10% or more.

11. A method for producing a cellulose fiber composite resin molding, comprising the steps of: kneading a base resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent to obtain a cellulose fiber composite resin composition; molding the cellulose fiber composite resin composition to obtain a molded body; and irradiating the molded body with radiation to form crosslinked structures by the crosslinking agent in two or more of the following: between the base resin, between the low molecular weight resin, and between the base resin and the low molecular weight resin.

12. The method for producing a cellulose fiber composite resin molding according to claim 11, wherein the low molecular weight resin has the same basic structure as the main resin.

13. A method for producing a cellulose fiber composite resin molding as described in claim 11, wherein the cellulose fiber content in the entire cellulose fiber composite resin molding is 10 mass% or more and 90 mass% or less.

14. A method for producing a cellulose fiber composite resin molding as described in claim 11, wherein the cellulose fibers have an average particle size of 10 μm or more and 500 μm or less.

15. A method for producing a cellulose fiber composite resin molding as described in claim 11, wherein the low molecular weight resin has a weight average molecular weight of 1,000 or more and 50,000 or less.

16. A method for producing a cellulose fiber composite resin molding as described in claim 11, wherein the ratio of the number of cellulose fibers whose extension direction is bent by 90° or more with respect to the longitudinal direction is 1% or more and 30% or less.

17. A method for producing a cellulose fiber composite resin molding as described in claim 11, wherein the low molecular weight resin is 0.5 mass% or more and 20 mass% or less relative to a total amount of 100 mass% of the base resin, the cellulose fiber, the low molecular weight resin, and the crosslinking agent.

18. The method for producing a cellulose fiber composite resin molding according to claim 11, further comprising a mixing step of adhering a powder or liquid low molecular weight resin to the cellulose fibers.

19. The method for producing a cellulose fiber composite resin molding according to claim 11, wherein the cellulose fiber composite resin molding has a gel fraction of 10% or more.

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