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

Abstract

A cellulose fiber composite resin composition includes a base resin, cellulose fibers, a low-molecular-weight resin, and a crosslinking agent capable of forming a crosslinking structure at two or more sites between the base resin, between the low-molecular-weight resins, and between the base resin and the low-molecular-weight resin.

Description

Technical Field

[0001] This disclosure relates to cellulose fiber composite resin compositions, molded articles, and manufacturing methods. Background Technology

[0002] Polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), known as "general-purpose plastics," are relatively inexpensive. Compared to metals or ceramics, they are a fraction of the weight, making them lightweight and easy to process, such as molding. Therefore, general-purpose plastics are used as materials for a wide variety of everyday items, including bags, various packaging materials, containers, and sheets. They are also used in industrial components such as automotive and electrical parts, as well as in daily necessities and general merchandise.

[0003] However, general-purpose plastics have drawbacks such as insufficient mechanical strength. Therefore, the current situation is that general-purpose plastics do not possess sufficient properties required for materials used in mechanical products such as automobiles, as well as various industrial products, primarily electrical / electronic / information products, thus limiting their application scope.

[0004] On the other hand, so-called "engineering plastics" such as polyacetal (POM), polyamide (PA), polycarbonate (PC), and fluoropolymers have excellent mechanical properties and are used in mechanical products such as automobiles, as well as various industrial products, primarily electrical / electronic / information products. However, they also have drawbacks such as high cost, difficulty in monomer recycling, and significant environmental impact.

[0005] Therefore, there is a desire to significantly improve the material properties (mechanical strength, etc.) of general-purpose plastics. As a method for improving the material properties of general-purpose plastics, techniques for manufacturing composite resins by blending two or more resins or fillers and other additives are known. In particular, for the purpose of improving mechanical strength, natural fibers, glass fibers, carbon fibers, etc., are used as fibrous fillers. Among these, organic fibrous fillers such as cellulose have gained attention in recent years as reinforcing fibers due to their low cost and environmentally friendly nature when disposed of.

[0006] Increasing the amount of fibrous filler improves the mechanical strength of the composite resin, but on the other hand, it significantly reduces its fluidity. This reduced fluidity leads to poor filling and poor appearance during molding, resulting in poor formability. Patent Document 1 improves formability by coating the surface of cellulose-based powder with a low-molecular-weight wax.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 3167020 Summary of the Invention

[0008] However, the composite resin described in Patent Document 1 uses low-molecular-weight wax. Due to the low strength of the elemental wax, the overall strength of the composite resin is reduced.

[0009] This disclosure addresses the aforementioned problems and aims to provide a cellulose fiber composite resin composition that exhibits good flowability during molding and high strength after molding.

[0010] The cellulose fiber composite resin composition disclosed herein comprises a main resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent capable of forming a crosslinking structure at two or more locations between the aforementioned main resins, between the aforementioned low molecular weight resins, and between the aforementioned main resins and the aforementioned low molecular weight resins.

[0011] According to the cellulose fiber composite resin composition disclosed herein, the fluidity during molding is increased due to the inclusion of a low molecular weight resin. On the other hand, after molding, since a crosslinking agent is included, a crosslinked structure can be formed in the main resin and / or the low molecular weight resin by radiation irradiation, thereby obtaining a cellulose fiber composite resin molded article with high strength. Attached Figure Description

[0012] Figure 1 This is a schematic diagram showing the structure of the cellulose fiber composite resin composition of Embodiment 1.

[0013] Figure 2 The figure shows the conditions and measurement results in Examples 1-4 and Comparative Example 1. Detailed Implementation

[0014] Hereinafter, the cellulose fiber composite resin composition and the cellulose fiber composite resin molded article of the embodiments will be described with reference to the accompanying drawings. It should be noted that in the following description, the same components will be labeled with the same reference numerals, and descriptions will be omitted where appropriate.

[0015] The cellulose fiber composite resin composition of the first method comprises a main resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent capable of forming a crosslinking structure at two or more locations between the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin.

[0016] The second method of the cellulose fiber composite resin composition may be in which, in the first method described above, the low molecular weight resin has the same basic structure as the main agent resin.

[0017] The cellulose fiber composite resin composition of the third method may be wherein, in the first or second method described above, the content of cellulose fiber in the total cellulose fiber composite resin composition is 10% by mass or more and 90% by mass or less.

[0018] The cellulose fiber composite resin composition of the fourth method may be such that, in any of the methods of the first to the third method described above, the average particle size of the cellulose fibers is 10 μm or more and 500 μm or less.

[0019] The cellulose fiber composite resin composition of the fifth method may be such that, in any of the methods 1 to 4 above, the weight average molecular weight of the low molecular weight resin is 1,000 or more and 50,000 or less.

[0020] The cellulose fiber composite resin composition of the sixth method may be such that, in any of the methods 1 to 5 above, the ratio of the number of cellulose fibers that bend at more than 90° relative to the length direction of extension is more than 1% and less than 30%.

[0021] The cellulose fiber composite resin composition of the seventh method may be, in any of the methods 1 to 5 above, wherein, relative to 100% by mass of the total mass of the main resin, cellulose fiber, low molecular weight resin and crosslinking agent, the low molecular weight resin is 0.5% by mass or more and 20% by mass or less.

[0022] The method for manufacturing the cellulose fiber composite resin composition of the eighth method includes the following steps: a mixing step in which a low molecular weight resin, which is a powder or liquid and has a lower molecular weight than the main resin, is attached to cellulose fibers; and a step in which the main resin, cellulose fibers, low molecular weight resin, and a crosslinking agent capable of forming crosslinking structures at two or more locations between the main resin, between the low molecular weight resin, and between the main resin and the low molecular weight resin, are mixed to form the cellulose fiber composite resin composition.

[0023] The cellulose fiber composite resin molded body of the ninth embodiment is a cellulose fiber composite resin molded body formed from a cellulose fiber composite resin composition comprising a main resin, cellulose fibers, low molecular weight resin and a crosslinking agent, having a crosslinking structure based on the crosslinking agent at two or more locations between the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin.

[0024] The cellulose fiber composite resin molded body of the 10th method may be, in the above-mentioned 9th method, have a gelation rate of 10% or more.

[0025] The method for manufacturing a cellulose fiber composite resin molded article according to the 11th method includes the following steps: a step of mixing a main resin, cellulose fibers, low molecular weight resin and a crosslinking agent to obtain a cellulose fiber composite resin composition; a step of molding the cellulose fiber composite resin composition to obtain a molded article; and a step of irradiating the molded article with radiation to form a crosslinking structure based on the crosslinking agent at two or more locations between the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin.

[0026] The method for manufacturing the cellulose fiber composite resin molded article of the 12th method may be that, in the 11th method above, the low molecular weight resin has the same basic structure as the main agent resin.

[0027] The method for manufacturing the cellulose fiber composite resin molded article of the 13th method may be that, in the 11th or 12th method described above, the content of cellulose fiber in the whole cellulose fiber composite resin molded article is 10% by mass or more and 90% by mass or less.

[0028] The method for manufacturing the cellulose fiber composite resin molded article of the 14th method may be such that, in any of the methods 11 to 13 above, the average particle size of the cellulose fibers is 10 μm or more and 500 μm or less.

[0029] The method for manufacturing the cellulose fiber composite resin molded article of the 15th method may be that, in any of the methods 11 to 14 above, the weight average molecular weight of the low molecular weight resin is 1,000 or more and 50,000 or less.

[0030] The method for manufacturing the cellulose fiber composite resin molded article of the 16th method may be such that, in any of the methods 11 to 15 above, the ratio of the number of cellulose fibers that bend at more than 90° relative to the length direction of extension is more than 1% and less than 30%.

[0031] The method for manufacturing the cellulose fiber composite resin molded article of the 17th method may be that, in any of the methods 11 to 16 above, the low molecular weight resin is 0.5% to 20% by mass or more, relative to 100% by mass of the total mass of the main resin, cellulose fiber, low molecular weight resin and crosslinking agent.

[0032] The method for manufacturing the cellulose fiber composite resin molded article of the 18th method may include, in any of the methods 11 to 17 above, a mixing step of attaching a powdered or liquid low molecular weight resin to the cellulose fibers.

[0033] The method for manufacturing the composite resin molded article of the 19th method may be such that, in any of the methods 11 to 18 above, the gelation rate of the aforementioned cellulose fiber composite resin molded article is 10% or more.

[0034] Hereinafter, the cellulose fiber composite resin composition and the cellulose fiber composite resin molded article of the embodiments will be described with reference to the accompanying drawings. It should be noted that in the following description, the same components will be labeled with the same reference numerals, and descriptions will be omitted where appropriate.

[0035] (Implementation Method 1)

[0036] <Cellulose Fiber Composite Resin Composition>

[0037] Figure 1 This is a schematic diagram showing the structure of the cellulose fiber composite resin composition 10 according to Embodiment 1.

[0038] The composite resin 10 of Embodiment 1 comprises a main resin 1, cellulose fibers 2, a low molecular weight resin 3, and a crosslinking agent 4. The cellulose fiber composite resin composition 10 is as follows... Figure 1 As shown, cellulose fibers 2, low molecular weight resin 3, and crosslinking agent 4 are dispersed in the matrix of main agent resin 1, with low molecular weight resin 3 present around the cellulose fibers 2. The crosslinking agent is a substance capable of forming crosslinked structures at two or more points: between the main agent resins, between the low molecular weight resins, and between the main agent resin and the low molecular weight resin.

[0039] The cellulose fiber composite resin composition 10 has increased fluidity during molding because it contains low molecular weight resin 3. On the other hand, after molding, because it contains crosslinking agent 4, crosslinking structures can be formed in the main resin 1 and / or low molecular weight resin 3 by radiation irradiation, resulting in a cellulose fiber composite resin molded body with high strength, high heat resistance, and suppressed exudation.

[0040] It should be noted that the cellulose fiber composite resin composition 10 can be a fluid or a solid, and furthermore, for preservation and distribution, it can also be made into block, rectangular, or granular shapes, for example.

[0041] The components constituting the cellulose fiber composite resin composition 10 will be described below.

[0042] <Main Agent Resin>

[0043] As the main resin 1 in Embodiment 1, a thermoplastic resin is preferred to ensure good formability. Examples of thermoplastic resins include olefin resins (including cyclic olefin resins), styrene resins, (meth)acrylic resins, vinyl ester resins or their derivatives, vinyl ether resins, halogenated composite resins, polycarbonate resins, polyester resins, polyamide resins, thermoplastic polyurethane resins, polysulfone resins (polyethersulfone, polysulfone, etc.), polyphenylene ether resins (polymers of 2,6-xylenol, etc.), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubbers or elastomers (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubbers, polyurethane rubbers, silicone rubbers, etc.). The above resins can be used alone or in combination of two or more. It should be noted that the resin is not limited to the materials mentioned above as long as it is thermoplastic.

[0044] In these thermoplastic resins, the main resin 1 is preferably a resin capable of forming a cross-linked structure upon irradiation, or a resin capable of forming a cross-linked structure upon irradiation with the addition of a cross-linking agent. It should be noted that radiation includes electron beams and gamma rays, etc., and electron beam irradiation is mainly used in this application. Examples of resins capable of forming a cross-linked structure upon irradiation or upon irradiation with the addition of a cross-linking agent include olefin resins, polyamide resins, and polylactic acid resins. The above-mentioned resins can be used alone or in combination of two or more. It should be noted that any resin capable of forming a cross-linked structure upon irradiation with the addition of a cross-linking agent is acceptable, and the resin is not limited to the materials mentioned above.

[0045] Cellulose fibers

[0046] As the cellulose fiber 2 in Embodiment 1, examples include cellulose fiber and lignocellulose fiber. Examples include cellulose fiber, wood (coniferous trees, broad-leaved trees) that are raw materials for lignocellulose fiber, cotton linters, kenaf, abaca (Manila hemp), sisal, jute, Sabai grass, fine-stemmed needle grass, bagasse, rice straw, wheat straw, reeds, bamboo, and other natural materials.

[0047] 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 form. When it is 10% by mass or more, the low-energy cross-linking structure formation effect brought about by the presence of cellulose fibers can be fully utilized. 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.

[0048] The average particle size of the cellulose fibers 2 is preferably 10 μm or more and 500 μm or less, 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 are less likely to form aggregates. When it is 10 μm or more, the surface area of ​​the cellulose fibers can be suppressed, thus improving the flowability of the cellulose fiber composite resin composition. Therefore, the aforementioned average particle size of the cellulose fibers is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 400 μm or less.

[0049] In cellulose fibers, the ratio of the number of cellulose fibers that bend at 90° or more midway along their length direction is preferably 1% or more and 30% or less. When the ratio of cellulose fibers that bend at 90° or more midway along their length direction is 30% or less, the bent cellulose fibers are less likely to come into contact and entangle, thus making it difficult to form aggregates. When the ratio of cellulose fibers that bend at 90° or more midway along their length direction is 1% or more, the presence of bent cellulose fibers allows for the formation of resin crosslinking structures and entanglement of cellulose fibers. Therefore, the ratio of cellulose fibers that bend at 90° or more midway along their length direction is preferably within the above-mentioned range.

[0050] Low molecular weight resin

[0051] As for the low molecular weight resin 3 in Embodiment 1, since it needs to be melted during mixing, a thermoplastic resin is preferred. Examples of thermoplastic resins include olefin resins (including cyclic olefin resins), styrene resins, (meth)acrylic resins, vinyl ester resins or their derivatives, vinyl ether resins, halogenated composite resins, polycarbonate resins, polyester resins, polyamide resins, thermoplastic polyurethane resins, polysulfone resins (polyethersulfone, polysulfone, etc.), polyphenylene ether resins (polymers of 2,6-xylenol, etc.), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubbers or elastomers (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubber, polyurethane rubber, silicone rubber, etc.), waxes, etc. The above resins can be used alone or in combination of two or more. It should be noted that the resin only needs to be thermoplastic and is not limited to the materials mentioned above.

[0052] Among these thermoplastic resins, the low-molecular-weight resin 3 is preferably a resin capable of forming a cross-linked structure upon irradiation with radiation, or a resin capable of forming a cross-linked structure upon irradiation with the addition of a cross-linking agent. It should be noted that radiation includes electron beams and gamma rays, etc., and electron beam irradiation is mainly used in this application. Examples of resins capable of forming a cross-linked structure upon irradiation with radiation or with the addition of a cross-linking agent include olefin resins, polyamide resins, and polylactic acid resins. The above-mentioned resins can be used alone or in combination of two or more. It should be noted that any resin capable of forming a cross-linked structure upon irradiation with the addition of a cross-linking agent is acceptable, and the resin is not limited to the materials mentioned above.

[0053] The low-molecular-weight resin 3 has a lower molecular weight than the main resin and can have the same basic structure as the main resin. When the main resin and the low-molecular-weight resin have different structures, cross-linking structures are more likely to form between the main resins or between the low-molecular-weight resins during radiation irradiation. When cross-linking structures are preferentially formed between the main resins, it is difficult for the low-molecular-weight resin to form cross-linking structures, making it difficult to suppress the decrease in strength and heat resistance. Furthermore, when cross-linking structures are preferentially formed between low-molecular-weight resins, the promotion of polymerization due to cross-linking is slowed down, making it difficult to suppress the decrease in strength and heat resistance. Therefore, the low-molecular-weight resin preferably has the same basic structure as the main resin. This allows for the formation of cross-linking structures between the main resin and the low-molecular-weight resin.

[0054] It should be noted that "having the same basic structure" refers to having parts composed of common monomer units. That is, it means that the main resin and the low molecular weight resin have the same repeating molecular structure.

[0055] Of the total mass of the main resin, cellulose fiber, and crosslinking agent, the low molecular weight resin is preferably 0.5% by mass or more and 20% by mass or less. When the low molecular weight resin is 0.5% by mass or more, the amount is sufficient, thus improving the flowability of the composite resin, allowing for molding, and enabling molding under non-high temperature conditions. When the low molecular weight resin is 20% by mass or less, the amount is not excessive, thus suppressing the reduction in strength of the cellulose fiber composite resin composition. Therefore, of the total mass of the main resin, cellulose fiber, and crosslinking agent, the low molecular weight resin is preferably 0.5% by mass or more and 20% by mass or less.

[0056] The molecular weight of the low molecular weight resin 3 is preferably 1000 or more and 50000 or less, more preferably 3000 or more and 30000 or less. When the molecular weight is 1000 or more, the strength of the resin element is sufficient, thus suppressing the reduction in the overall strength of the cellulose fiber composite resin composition. When the molecular weight is 50000 or less, the viscosity of the low molecular weight resin element does not increase excessively, improving the flowability of the cellulose fiber composite resin. Therefore, the molecular weight of the low molecular weight resin 3 is preferably within the above-mentioned range.

[0057] The "molecular weight" mentioned above refers to "weight-average molecular weight." Weight-average molecular weight is determined using gel permeation chromatography (GPC). It should be noted that the mobile phase used in GPC varies depending on the resin, and therefore an appropriate material must be selected for each resin. For example, σ-dichlorobenzene can be used as the mobile phase for polyolefins.

[0058] The cellulose fiber composite resin composition 10, by containing a low-molecular-weight resin, improves the flowability of the cellulose fiber composite resin composition even when containing cellulose fibers. On the other hand, due to the presence of a crosslinking agent, a crosslinked structure can be formed after molding by irradiating the molded body with radiation, thereby improving strength and heat resistance even when containing a low-molecular-weight resin. Therefore, the cellulose fiber composite resin composition 10 is preferably formed from at least a main resin, cellulose fibers, a low-molecular-weight resin, and a crosslinking agent.

[0059] Crosslinking agent

[0060] As the crosslinking agent 4 in Embodiment 1, a multifunctional crosslinking agent having two or more reactive groups in its molecule is preferred. By adding a crosslinking agent, the crosslinking reaction becomes easier to occur uniformly. Examples of multifunctional crosslinking agents include triacyl isocyanurate (TAIC), triallyl cyanurate (TAC), and divinylbenzene (DVB). It should be noted that the crosslinking agent is not limited to any of the above materials, as long as it is multifunctional. For example, modified cellulose fibers can be used.

[0061] <Additives>

[0062] Cellulose fiber composite resin compositions may contain various additives in addition to the above-mentioned materials. For example, when making cellulose fiber composite resin compositions, maleic anhydride polypropylene (dispersant) may be added to polypropylene (main resin), pulverized pulp (cellulose fiber), low molecular weight polypropylene (low molecular weight resin), and triacyl isocyanurate (crosslinking agent).

[0063] It should be noted that the average particle size can be determined by methods such as sieving (JIS K 0069:1992), laser diffraction-scattering (JIS Z8825:2013), and dynamic light scattering (JIS Z8828:2013). Sieving involves using multiple sieves with different mesh sizes to sieve the particles, and the particle size distribution is determined based on the weight of the residue on each sieve. Laser diffraction-scattering involves irradiating particles in a liquid or gas with a laser beam, and determining the particle size by utilizing the fact that the intensity spectrum of the scattered light depends on the particle size. It should be noted that in laser diffraction-scattering, the diameter is measured as the equivalent sphere diameter. Dynamic light scattering determines the particle size by utilizing the Brownian motion of particles suspended in a liquid. That is, the phase deviation between the scattered light and the incident light caused by Brownian motion is observed, and the particle size is calculated based on the observed phase deviation.

[0064] Furthermore, as the average particle size, for example, the median particle size D, which accumulates to 50% of the frequencies in the resulting particle size distribution, can be used. 50 The average particle size mentioned above uses the median particle size D. 50 express.

[0065] <Method for manufacturing cellulose fiber composite resin composition>

[0066] The method for manufacturing a cellulose fiber composite resin composition includes a step (mixing step) of mixing a main resin, cellulose fibers, a low-molecular-weight resin, and a crosslinking agent to form a cellulose fiber composite resin composition. The crosslinking agent is a substance capable of forming crosslinked structures at two or more locations between the main resins, between the low-molecular-weight resins, and between the main resin and the low-molecular-weight resin. Furthermore, the method for manufacturing the cellulose fiber composite resin composition may include a mixing step of attaching powdered or liquid low-molecular-weight resin to the surface of the cellulose fibers 2. By attaching powdered or liquid low-molecular-weight resin to the surface of the cellulose fibers before the aforementioned mixing step, direct contact between the cellulose fibers becomes less likely, thus suppressing the aggregation of the cellulose fibers. Furthermore, by attaching the low-molecular-weight resin to the surface of the cellulose fibers, the flow resistance caused by the cellulose fibers can be suppressed, improving flowability. It should be noted that, as a form, the low-molecular-weight resin, when using resin granules, is significantly larger in size than the cellulose fibers. Therefore, even when mixing the low-molecular-weight resin granules with the cellulose fibers, it will separate into individual components, making it impossible to attach to the cellulose fibers. Therefore, the low-molecular-weight resin 3 can be a powdered or liquid substance. Furthermore, a mixing process of cellulose fibers with powder or liquid low-molecular-weight resins can also be carried out before the mixing process.

[0067] Examples of mixing apparatus used in the mixing process of the method for manufacturing cellulose fiber composite resin compositions include single-screw mixers, twin-screw mixers, roller mixers, kneaders, Banbury mixers, and combinations thereof. From the perspective of ease of applying high shear and high production capacity, continuous twin-screw mixers and continuous roller mixers are preferred. Any method capable of applying high shear stress is acceptable, and mixing methods other than those mentioned above are also acceptable. Furthermore, since cellulose fibers are prone to heat-induced degradation, it is preferable to perform mixing at the lowest possible temperature.

[0068] <Cellulose Fiber Composite Resin Molded Body>

[0069] The cellulose fiber composite resin molded body of Embodiment 1 is a cellulose fiber composite resin molded body formed from a cellulose fiber composite resin composition comprising a main resin, cellulose fibers, low molecular weight resin, and a crosslinking agent. This cellulose fiber composite resin molded body has a crosslinking structure based on the crosslinking agent at two or more locations: between the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin.

[0070] Furthermore, the gel rate of the cellulose fiber composite resin molded article is preferably 10% or more, more preferably 30% or more, and even more preferably 50% or more. The gel rate is an indicator that can estimate the degree of cross-linking structure of the main resin and the low-molecular-weight resin. When the gel rate is 10% or more, the low-molecular-weight resin can form a cross-linked structure, thus improving the strength of the composite resin. Therefore, the gel rate of the cellulose fiber composite resin molded article is preferably 10% or more.

[0071] This cellulose fiber composite resin molded body has excellent mechanical strength due to its cross-linked structure estimated based on the above-mentioned gelation rate.

[0072] <Manufacturing Method of Cellulose Fiber Composite Resin Molded Articles>

[0073] The method for manufacturing the cellulose fiber composite resin molded body of Embodiment 1 is as follows, for example.

[0074] (1) First, the main resin, cellulose fiber, low molecular weight resin and crosslinking agent are mixed to obtain a cellulose fiber composite resin composition (mixing process).

[0075] The above-described mixing process is essentially the same as the mixing process described in the method for manufacturing cellulose fiber composite resin compositions. Therefore, examples of mixing apparatus used in the mixing process include single-screw mixers, twin-screw mixers, roller mixers, kneaders, Banbury mixers, and combinations thereof. From the perspective of ease of applying high shear and high production capacity, continuous twin-screw mixers and continuous roller mixers are preferred. Any method capable of applying high shear stress is acceptable, and mixing methods other than those described above are also permissible. Furthermore, since cellulose fibers are prone to heat-induced degradation, it is preferable to perform mixing at the lowest possible temperature.

[0076] The composite resin composition extruded from the mixing unit is granulated into granules through a cutting process such as a granulator. Granulation methods include those performed immediately after the resin melts, such as aerial thermal cutting, underwater thermal cutting, and wire cutting. Alternatively, there are pulverization methods that involve first forming the molded body or sheet and then crushing and cutting it.

[0077] (2) Next, the obtained cellulose fiber composite resin composition is shaped to obtain a shaped body.

[0078] Molded bodies are made by shaping granules. Molding methods include injection molding, extrusion molding, compression molding, and blow molding.

[0079] (3) Next, the molded body is irradiated with radiation to obtain a cellulose fiber composite resin molded body with cross-linked structures formed at two or more locations between the main resin, between the low molecular weight resin, and between the main resin and the low molecular weight resin.

[0080] The molded article is subjected to radiation irradiation, resulting in the formation of cross-linked structures at two or more locations: between the main resins, between the low-molecular-weight resins, and between the main resin and the low-molecular-weight resins. Examples of devices used for radiation irradiation include electron beam irradiation devices. To suppress radiation damage to the material, any device capable of irradiating with low-energy radiation below 300 kGy is acceptable; other than those mentioned above are also permissible.

[0081] From the above, the cellulose fiber composite resin molded body can be obtained.

[0082] In the method for manufacturing a cellulose fiber composite resin molded article, in the step of obtaining the cellulose fiber composite resin composition, the inclusion of a low-molecular-weight resin improves the flowability of the composite resin, enabling molding. Furthermore, when a crosslinking agent is included, a crosslinking structure can be uniformly formed between the main resin and the low-molecular-weight resin during radiation irradiation. Therefore, the method for manufacturing a cellulose fiber composite resin molded article preferably includes the following steps: a step of mixing the main resin, cellulose fibers, low-molecular-weight resin, and crosslinking agent to obtain a cellulose fiber composite resin composition; and a step of irradiating the molded article obtained by molding the cellulose fiber composite resin composition with radiation to obtain a cellulose fiber composite resin molded article in which crosslinking structures are formed at two or more locations between the main resins, between the low-molecular-weight resins, and between the main resin and the low-molecular-weight resins.

[0083] The following describes the various embodiments and comparative examples performed by the inventors.

[0084] (Examples 1-4, Comparative Example 1)

[0085] Figure 2 The figure shows the conditions and measurement results of Examples 1-4 and Comparative Example 1.

[0086] Cellulose fiber composite resin compositions and cellulose fiber composite resin molded articles are manufactured by the following manufacturing method. As mentioned above, the mixing apparatus can be a single-screw mixer, a twin-screw mixer, a roll mixer, a kneader, a Banbury mixer, and combinations thereof, etc., and a twin-screw mixer is used in the examples.

[0087] Polypropylene (trade name: BC03C, manufactured by Nippon Polypropylene Co., Ltd.) as the main resin, pulverized pulp as cellulose fiber, low molecular weight polyolefin (trade name: Hi-Wax, manufactured by Mitsui Chemicals Co., Ltd.) as the low molecular weight resin, and triallyl isocyanate (manufactured by Mitsubishi Chemical Co., Ltd.) as the crosslinking agent are weighed in a mass ratio of 38:55:5:2. The main resin, pulverized pulp, low molecular weight resin, and crosslinking agent mixture are fed separately into a mixer. Hardwood pulp (trade name: Mitsubishi Kitakami LBKP, manufactured by Mitsubishi Paper Co., Ltd.) is used as the starting material for the pulverized pulp. This pulp is pulverized using a pulverizer to obtain pulverized pulp. The size of the cellulose fibers, etc., is adjusted through the pulverization process. As a pulverization method, in the case of wet pulverization, a drying process is required after pulverization; however, since aggregation occurs during drying, dry pulverization is preferred.

[0088] The mixture was melt-blended and dispersed using a twin-screw extruder (KRC kneader manufactured by Kurimoto Iron Works Co., Ltd.). By changing the screw configuration of the twin-screw extruder, the shear force could be altered; in Example 1, a low-shear type specification was used. The cellulose fiber composite resin composition discharged from the twin-screw extruder was thermally cut to produce cellulose fiber composite resin granules formed from the cellulose fiber composite resin composition.

[0089] Using the prepared cellulose fiber composite resin granules, test pieces of composite resin molded bodies were fabricated using an injection molding machine (180AD manufactured by Nippon Steel Corporation). The conditions for fabricating the dumbbell test pieces were set as follows: resin temperature 200°C, mold temperature 40°C, injection speed 60 mm / s, and holding pressure 100 MPa. The granules were held by the screw of the molding machine via a hopper, and the invasiveness was measured by the amount of granules reduced per unit time, which was then confirmed to be constant. The shape of the test pieces was modified according to the evaluation items described below, and dumbbell test pieces of size 1 were fabricated for measuring the elastic modulus.

[0090] The test specimens of the prepared cellulose fiber composite resin composition were irradiated with an electron beam irradiation device. The irradiation conditions were adjusted to irradiate an electron beam with an energy of 30 kGy at an accelerating voltage of 4.6 MV and a current of 20 mA. This yielded test specimens of the cellulose fiber composite resin molded body.

[0091] The experimental pieces of the obtained cellulose fiber composite resin molded articles were evaluated using the following methods.

[0092] [Evaluation Items for Composite Resin Molded Articles]

[0093] (Strength of composite resin molded articles)

[0094] A three-point bending test was conducted using the obtained dumbbell-shaped test piece (No. 1). The elastic modulus of this test piece was 52 MPa.

[0095] (Evaluation of the tortuosity of cellulose fibers in composite resin molded articles)

[0096] A portion was cut from the obtained dumbbell-shaped test piece (No. 1) and observed using SEM. The proportion of cellulose fibers in the resin that were bent at an angle of more than 90° relative to their length direction was 14%.

[0097] (Gel ratio)

[0098] A portion was cut from the obtained dumbbell-shaped test piece (No. 1) to evaluate the gel rate, an indicator of the degree of crosslinking. Referring to JIS K6796, the cut test piece was weighed, wrapped in a metal mesh, and immersed in a flask containing solvent for approximately 8 hours. Then, the test piece was removed, dried, and weighed. The gel rate was calculated based on the mass ratio before and after immersion. It should be noted that the denominator of the mass ratio is the mass of cellulose fibers, excluding the main resin and low-molecular-weight resin. The gel rate of this test piece was 53%.

[0099] (Example 2)

[0100] In Example 2, maleic anhydride-modified polypropylene (trade name: UMEX, manufactured by Sanyo Chemical Industries, Ltd.) was used as a dispersant, and the mass ratio of main resin: cellulose fiber: low molecular weight resin: crosslinking agent: dispersant was changed to 36:55:5:2:2. Cellulose fiber composite resin granules and molded articles were prepared under the same conditions as in Example 1. The same evaluation was performed as in Example 1.

[0101] (Example 3)

[0102] Compared to Example 1, Example 3 reduced the amount of cellulose fiber added and changed the mass ratio of main resin: cellulose fiber: low molecular weight resin: crosslinking agent to 54:40:2. All other material and process conditions were the same as in Example 1 to prepare the cellulose fiber composite resin granules and molded articles. The evaluation was also conducted in the same manner as in Example 1.

[0103] (Example 4)

[0104] Compared to Example 1, Example 4 increased the amount of low molecular weight resin added, and changed the mass ratio of main resin: cellulose fiber: dispersant: low molecular weight resin: crosslinking agent to 33:55:10:2. All other material and process conditions were the same as in Example 1 to prepare the cellulose fiber composite resin granules and molded articles. The evaluation was also conducted in the same manner as in Example 1.

[0105] (Comparative Example 1)

[0106] Comparative Example 1, without the addition of a crosslinking agent, changed the mass ratio of main resin: pulverized pulp: dispersant: crosslinking agent to 40:55:5:0. The composite resin granules and molded articles were prepared in the same manner as in Example 1, except for other material and process conditions. The same evaluation was performed as in Example 1.

[0107] The measurement results of Examples 1-4 and Comparative Example 1 are shown below. Figure 2 The table.

[0108] Compared to Example 1, Example 2, which used a dispersant, showed improved compatibility between the cellulose fibers and the resin, resulting in a strength of 78 MPa.

[0109] Compared to Example 1, Example 3, which reduced the amount of cellulose fiber added, had a lower concentration of cellulose fiber, thus reducing the reinforcing effect from the cellulose fiber and the crosslinking promotion effect from low-energy radiation irradiation, resulting in a strength of 42 MPa.

[0110] In Example 4, with an increased amount of low molecular weight resin, the flowability was further improved compared to Example 1. Furthermore, due to the crosslinking effect, the strength reduction caused by the increased amount of low molecular weight resin was suppressed, resulting in a strength of 47 MPa.

[0111] Comparative Example 1, which did not use a crosslinking agent, did not have crosslinking progress due to the absence of a crosslinking agent, and its strength was 33 MPa.

[0112] Based on the above evaluation, by adding a crosslinking agent to promote crosslinking, the strength reduction caused by the addition of low molecular weight resin can be suppressed, and the strength of the cellulose fiber composite resin molded body can reach the required level.

[0113] As described above, the cellulose fiber composite resin composition, by comprising a main resin, cellulose fibers, low molecular weight resin, and a crosslinking agent, achieves high fluidity during molding. Furthermore, by subjecting the molded product to radiation irradiation, crosslinking structures are formed at two or more locations between the main resins, between the low molecular weight resins, and between the main resin and the low molecular weight resin, thereby increasing the mechanical strength of the resulting cellulose fiber composite resin molded body.

[0114] Industrial availability

[0115] The cellulose fiber composite resin composition disclosed herein exhibits high fluidity during molding and provides molded articles with superior mechanical strength and heat resistance compared to existing general-purpose resins. Cellulose fiber composite resin molded articles obtained using the cellulose fiber composite resin composition disclosed herein can be used in applications requiring excellent mechanical strength and heat resistance, such as the housings of household appliances, building materials, and exterior parts of automotive components.

[0116] Symbol Explanation 1. Main agent resin 2. Cellulose fibers 3. Low molecular weight resin 4. Crosslinking agent 10 Cellulose Fiber Composite Resin Composition

Claims

1. A cellulose fiber composite resin composition comprising: Main components: resin, cellulose fiber, low molecular weight resin, and A crosslinking agent capable of forming crosslinking structures at two or more locations between the main resins, between the low molecular weight resins, and between the main 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. The cellulose fiber composite resin composition according to claim 1, wherein, The content of the cellulose fiber in the cellulose fiber composite resin composition is more than 10% by mass and less than 90% by mass.

4. The cellulose fiber composite resin composition according to claim 1, wherein, The average particle size of the cellulose fibers is greater than 10 μm and less than 500 μm.

5. The cellulose fiber composite resin composition according to claim 1, wherein, The weight-average molecular weight of the low molecular weight resin is above 1000 and below 50000.

6. The cellulose fiber composite resin composition according to claim 1, wherein, The proportion of the number of cellulose fibers that bend more than 90° relative to their length direction is more than 1% and less than 30%.

7. The cellulose fiber composite resin composition according to claim 1, wherein, The low molecular weight resin is 0.5% to 20% by mass relative to 100% by mass of the total mass of the main resin, the cellulose fiber, the low molecular weight resin, and the crosslinking agent.

8. A method for manufacturing a cellulose fiber composite resin composition, comprising the following steps: A mixing process in which a low molecular weight resin, either powder or liquid, lower in molecular weight than the main resin, adheres to cellulose fibers; and The process of mixing the main resin, the cellulose fiber, the low molecular weight resin, and a crosslinking agent capable of forming crosslinking structures at two or more locations 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 molded article, said cellulose fiber composite resin molded article being formed from a cellulose fiber composite resin composition comprising a main resin, cellulose fibers, a low molecular weight resin, and a crosslinking agent. It has a cross-linking structure based on the cross-linking agent at two or more locations between the main agent resin, between the low molecular weight resin, and between the main agent resin and the low molecular weight resin.

10. The cellulose fiber composite resin molded article according to claim 9, wherein, The gelation rate of the cellulose fiber composite resin molded body is above 10%.

11. A method for manufacturing a cellulose fiber composite resin molded article, comprising the following steps: The process of mixing the main resin, cellulose fiber, low molecular weight resin and crosslinking agent to obtain a cellulose fiber composite resin composition. The process of molding the cellulose fiber composite resin composition to obtain a molded article; and The process of irradiating the molded body with radiation to form a cross-linked structure based on the cross-linking agent at two or more locations between the main resin, between the low molecular weight resin, and between the main resin and the low molecular weight resin.

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

13. The method for manufacturing the cellulose fiber composite resin molded article according to claim 11, wherein, The content of cellulose fiber in the cellulose fiber composite resin molded body is more than 10% by mass and less than 90% by mass.

14. The method for manufacturing the cellulose fiber composite resin molded article according to claim 11, wherein, The average particle size of the cellulose fibers is greater than 10 μm and less than 500 μm.

15. The method for manufacturing a cellulose fiber composite resin molded article according to claim 11, wherein, The weight-average molecular weight of the low molecular weight resin is above 1000 and below 50000.

16. The method for manufacturing a cellulose fiber composite resin molded article according to claim 11, wherein, The proportion of the number of cellulose fibers that are bent at more than 90° relative to their length extension direction is more than 1% and less than 30%.

17. The method for manufacturing a cellulose fiber composite resin molded article according to claim 11, wherein, The low molecular weight resin is 0.5% to 20% by mass relative to 100% by mass of the total mass of the main resin, the cellulose fiber, the low molecular weight resin, and the crosslinking agent.

18. The method for manufacturing a cellulose fiber composite resin molded article according to claim 11, further comprising a mixing step of attaching a powdered or liquid low-molecular-weight resin to the cellulose fibers.

19. The method for manufacturing a cellulose fiber composite resin molded article according to claim 11, wherein, The gelation rate of the cellulose fiber composite resin molded body is above 10%.

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