Composite resin molded article and method for producing same

Abstract

The composite resin molded body has a base resin, a plurality of natural fibers dispersed in the base resin, and a microorganism and / or an enzyme supported on the plurality of natural fibers, and at least a part of the surface of the natural fibers is coated with a coating resin. The amount of the coating resin located in the center of the composite resin molded body is small, and at least one of the plurality of natural fibers has a portion exposed on the surface of the composite resin molded body.

Description

Technical Field

[0001] The present invention relates to a composite resin molded body having high mechanical strength and a regulated biodegradation rate in a humid environment, and a method for producing the same. Background Art

[0002] So-called "general-purpose plastics" such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) are not only very cheap, but also easy to shape, and are lightweight, weighing only a fraction of metals or ceramics. Therefore, general-purpose plastics are widely used as materials for a wide variety of daily necessities such as bags, various packages, various containers, and sheets, as well as for industrial parts such as automobile parts and electrical parts, home appliances, construction products, and daily necessities and sundry goods.

[0003] Under such circumstances, the amount of plastic waste after use is gradually increasing. Since it is a material with difficult decomposition characteristics, it accumulates in the natural environment, causing environmental damage, pollution and other public nuisance problems. In recent years, as one of the countermeasures to solve these many problems, biodegradable plastics that decompose into water and carbon dioxide in the natural environment have been proposed, and it is expected to replace general-purpose plastics that use petroleum-based raw materials and expand their use.

[0004] However, biodegradable plastics have disadvantages such as insufficient mechanical strength compared to general-purpose plastics. Therefore, the reality is that biodegradable plastics do not have sufficient properties required for materials used in various industrial products such as mechanical products such as automobiles and electrical, electronic, and information products, and their application range is limited.

[0005] On the other hand, the environment has a great influence on the biodegradation rate of discarded biodegradable plastics. In an environment with few microorganisms such as the ocean, it takes a long time to completely decompose, and the biodegradability characteristic cannot be fully utilized. In order to solve this problem, various methods have been proposed to accelerate the decomposition of discarded biodegradable plastics.

[0006] In order to solve this problem, the decomposition inside the biodegradable plastic should be promoted, and therefore, a molded product is disclosed in which a decomposition-promoting layer containing polyvinyl alcohol or starch mixed with microorganisms is coated on the surface of the biodegradable plastic (for example, see Patent Document 1). In addition, a method for manufacturing a molded body is disclosed in which microorganisms having enzyme activity to decompose the same material are added to the biodegradable plastic during melt kneading or molding, or a molded body is coated on the surface of the molded body before the surface of the molded plastic is solidified and then pressurized (for example, see Patent Document 2).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2006-137917

[0010] Patent Document 2: Japanese Patent Application Publication No. 2013-209587 Summary of the invention

[0011] A composite resin molded body according to one embodiment of the present invention comprises a main resin, a plurality of natural fibers dispersed in the main resin, and microorganisms and / or enzymes carried on the plurality of natural fibers, at least a portion of the surfaces of the plurality of natural fibers are covered with a coating resin, the amount of the coating resin located at the center of the composite resin molded body is small relative to the surface of the composite resin molded body, and at least one of the plurality of natural fibers has a portion exposed on the surface of the composite resin molded body.

[0012] A method for manufacturing a composite resin molded body according to one embodiment of the present invention comprises: a step of preparing microorganisms and / or enzymes, natural fibers, a water-soluble coating resin and a main resin; a step of loading microorganisms and / or enzymes on natural fibers; a step of melt-kneading the main resin, wherein the natural fibers are melt-kneaded together with the main resin, and the natural fibers are opened from the ends in the fiber length direction to obtain a composite resin composition having an enlarged surface area of ​​the opened portion at the ends; a step of molding the composite resin composition to obtain a composite resin molded body; and a step of coating and impregnating the surface of the composite resin molded body with a coating resin and then drying it to obtain a composite resin molded body in which the amount of coating resin located at the center of the composite resin molded body relative to the surface of the composite resin molded body is small and at least a portion of the surface of the natural fibers is coated with the coating resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic cross-sectional view of the composite resin molded body according to the first embodiment.

[0014] Figure 2 This is a schematic cross-sectional view of natural fibers contained in the composite resin molded body according to the first embodiment.

[0015] Figure 3 This is a schematic diagram of natural fibers having a fiber-opening portion contained in the composite resin molded body of the first embodiment.

[0016] Figure 4 This is a flowchart of the manufacturing process of the composite resin molded body according to the first embodiment.

[0017] Figure 5 This is a table showing the structures and measurement results of composite resin molded bodies of Examples 1 and 2 and Comparative Examples 1 to 3 in Embodiment 1. DETAILED DESCRIPTION

[0018] In the method described in Patent Document 1, it is necessary to perform treatments such as roughening the surface of the molded body or providing permeable holes before applying the decomposition accelerating layer, which is not only complicated but also disadvantageous in terms of cost.

[0019] On the other hand, in the method described in Patent Document 2, since microorganisms having enzyme activity for decomposing biodegradable plastics are uniformly present inside the molded body or are present in large quantities on the surface of the molded body, the biodegradation rate is uniform or slows down from the surface of the molded body toward the center of the molded body, resulting in the problem that it takes time to complete the decomposition.

[0020] An object of the present invention is to solve the above-mentioned problems and to provide a composite resin molded body which maintains mechanical strength during use and promotes biodegradation in a humid environment such as the ocean or soil after disposal, and a method for producing the same.

[0021] The first mode of the composite resin molded body comprises a main resin, a plurality of natural fibers dispersed in the main resin, and microorganisms and / or enzymes carried on the plurality of natural fibers, at least a portion of the surfaces of the plurality of natural fibers are covered with a coating resin, the amount of the coating resin located at the center of the composite resin molded body is small relative to the surface of the composite resin molded body, and at least one of the plurality of natural fibers has a portion exposed on the surface of the composite resin molded body.

[0022] A composite resin molded article according to a second aspect may be the composite resin molded article according to the first aspect, wherein the amount of the coating resin decreases from the surface of the composite resin molded article toward the center of the composite resin molded article.

[0023] In the composite resin molded article of the third aspect, in the first or second aspect, the moisture content of the natural fiber may be 5% or more according to the method specified in JIS L0105:2020.

[0024] The composite resin molded body of the fourth embodiment may be any one of the first to third embodiments, wherein the main resin is a biodegradable resin selected from any one of polyhydroxyalkanoic acid, polylactic acid, polybutylene succinate, polybutylene adipate terephthalate, polycaprolactone, polyamide, and modified starch.

[0025] In a fifth aspect of the composite resin molded product according to any one of the first to fourth aspects, the coating resin may be a water-soluble resin such as polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, or starch-based resin.

[0026] A composite resin molded article according to a sixth aspect may be any one of the first to fifth aspects, wherein the natural fiber carries a microorganism and / or an enzyme on the fiber surface.

[0027] In a seventh aspect of the composite resin molded product according to any one of the first to sixth aspects, the natural fibers may be cellulose.

[0028] The composite resin molded product according to an eighth aspect may be any one of the first to seventh aspects, wherein the natural fibers have fiber-opening portions at the ends in the fiber length direction.

[0029] A composite resin molded product according to a ninth aspect may be any one of the first to eighth aspects, wherein the content of the natural fiber is 10% by mass or more and 99% by mass or less, when the composite resin molded product is taken as 100% by mass.

[0030] The method for manufacturing a composite resin molded body of the tenth embodiment includes: a step of preparing microorganisms and / or enzymes, natural fibers, a water-soluble coating resin and a main resin; a step of loading the above-mentioned microorganisms and / or enzymes on the above-mentioned natural fibers; a step of melt-kneading the main resin, wherein the above-mentioned natural fibers are melt-kneaded together with the above-mentioned main resin, and the natural fibers are opened from the ends of the above-mentioned natural fibers in the fiber length direction to obtain a composite resin composition with an enlarged surface area of ​​the opened portion at the end; a step of molding the composite resin composition to obtain a composite resin molded body; and a step of coating and impregnating the surface of the above-mentioned composite resin molded body with a coating resin and then drying it to obtain a composite resin molded body in which the amount of coating resin located at the center of the composite resin molded body relative to the surface of the above-mentioned composite resin molded body is small, and at least a portion of the surface of the natural fiber is coated with the coating resin.

[0031] The composite resin molded article according to one embodiment of the present invention can realize a composite resin molded article that achieves a high elastic modulus compared to a single resin and also controls the biodegradation rate in a high-humidity environment.

[0032] Hereinafter, a composite resin molded body and a method for producing the same according to an embodiment of the present invention will be described with reference to the drawings. In the following description, the same reference numerals are used for the same components, and the description thereof will be appropriately omitted.

[0033] (Implementation Method 1)

[0034] <Composite resin molded body>

[0035] Figure 1 This is a schematic cross-sectional view of the composite resin molded body 10 according to the first embodiment. Figure 2 This is a schematic cross-sectional view of the natural fiber 2 included in the composite resin molded body according to the first embodiment.

[0036] The composite resin molded body 10 of the first embodiment is composed of a melt-kneaded product of a main resin 1 and a natural fiber 2 carrying a microorganism and / or an enzyme 4 and coated with a coating resin 3. Figure 1 and Figure 2As shown in the schematic cross-sectional view of , the composite resin molded body 10 has natural fibers 2 carrying microorganisms and / or enzymes 4, which are coated with a coating resin 3, dispersed in a main resin 1. In addition, the coating resin 3 is impregnated into the interior of the composite resin molded body 10, and the amount of the coating resin 3 coating the natural fibers 2 located at the center 10b of the composite resin molded body 10 is small relative to the amount of the coating resin 3 coating the natural fibers 2 located at the surface 10a of the composite resin molded body 10, or the amount of the coating resin 3 coating the natural fibers 2 decreases from the surface 10a of the composite resin molded body 10 toward the center 10b of the composite resin molded body 10.

[0037] also, Figure 3 Schematic diagram showing a natural fiber 2 having a fiber-opening portion 6 included in a composite resin molded body according to Embodiment 1. Figure 3 As shown, by having the fiber-spreading part 6 at the end of the natural fiber 2, the specific surface area of ​​the fiber-spreading part 6 increases, and the contact points between the natural fibers 2 increase. Thus, water can be absorbed into the composite resin molded body 10 through the contact points between the natural fibers 2 in a humid environment.

[0038] According to the composite resin molded body 10, since at least one natural fiber 2 is exposed on the surface 10a of the composite resin molded body 10, the natural fibers 2 have contact points with each other, so that high elastic modulus is achieved and high water absorption is also achieved. In a humid environment, if the coated resin 3 is dissolved due to water absorption of the natural fiber 2, the microorganisms and / or enzymes 4 carried on the natural fiber 2 are released, and the decomposition of the main resin 1 is promoted. At this time, since the amount of the coating resin 3 coating the natural fiber 2 located at the center 10b of the composite resin molded body 10 is small relative to the amount of the coating resin 3 coating the natural fiber 2 located at the surface 10a of the composite resin molded body 10, or the amount of the coating resin 3 coating the natural fiber 2 decreases from the surface 10a of the composite resin molded body 10 toward the center 10b of the composite resin molded body 10, if the coating resin 3 located at the surface 10a of the composite resin molded body 10 is dissolved, the microorganisms and / or enzymes 4 carried on the natural fiber 2 are released, and the decomposition of the main component resin 1 located at the surface 10a of the composite resin molded body 10 is promoted. Thereafter, since the coating resin 3 decreases toward the center 10b of the composite resin molded body 10, the dissolution is unnecessary, and the microorganisms and / or enzymes 4 carried on the natural fiber 2 can be easily released, and the decomposition of the main component resin 1 is accelerated. Therefore, it is possible to realize a composite resin molded body 10 that maintains high rigidity during use and has excellent biodegradability in a humid environment such as the ocean and soil after disposal.

[0039] Hereinafter, each member constituting the composite resin molded body will be described.

[0040] <Main resin>

[0041] In the present embodiment 1, the main resin 1 is preferably a biodegradable plastic comprising any one of polyhydroxy acids such as polylactic acid, polyglycolic acid, and polycaprolactone, polyhydroxyalkanoates (polyhydroxyalkanoates: PHA) such as polyhydroxybutyrate and polyhydroxyvalerate, polyester resins such as polyalkylene dicarboxylates, polybutylene adipate terephthalate, polyethylene succinate, and polybutylene succinate, polyamides, and modified starches. In addition, in order to ensure good formability, a thermoplastic resin is preferably used, and the above resins can be used alone or in combination of two or more. It should be noted that the main resin 1 is not limited to the above materials as long as it is biodegradable.

[0042] In the present embodiment 1, the so-called "biodegradable plastic" refers to "a resin that has the same function as existing petroleum-derived resins when used, and is ultimately decomposed into water and carbon dioxide by microorganisms in the soil and ocean in nature after use". Specifically, there can be cited polyhydroxyalkanoates such as polyhydroxybutyrate and polyhydroxyvalerate, polyhydroxy acids such as polylactic acid, polyglycolic acid, and polycaprolactone, polyester resins such as polyalkylene dicarboxylates such as polybutylene adipate terephthalate, polyethylene succinate, and polybutylene succinate, and modified starch. As a polyester resin, in addition to homopolymers of polyester monomers, copolymers of polyester monomers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and copolymers of polyester monomers and other copolymerizable monomers are also included. These polyester resins can be used alone or in combination of two or more.

[0043] <Natural Fiber>

[0044] Next, the natural fiber 2 is described. The first main purpose of adding the natural fiber 2 (hereinafter sometimes referred to as "fiber") contained in the composite resin molded body 10 of the present embodiment 1 is that when the composite resin molded body 10 is discarded after use, it will not burden the environment, and the coating resin 3 is dissolved by absorbing water in the soil or the ocean, so that it comes into contact with water. In order to achieve this purpose, the natural fiber 2 preferably has high water absorption, and the moisture content of the natural fiber 2 is preferably 5% or more according to the method specified in JIS L0105:2020. Specifically, pulp, cellulose, cellulose nanofiber, wood cellulose, wood cellulose nanofiber, cotton, silk or hemp is preferred.

[0045] The second purpose of adding natural fiber 2 is to improve mechanical strength and improve dimensional stability by the reduction of linear expansion coefficient. In order to achieve this purpose, natural fiber 2 preferably has a high elastic modulus compared with main agent resin 1. Specifically, pulp, cellulose, cellulose nanofiber, lignocellulose, lignocellulose nanofiber, cotton, silk, wool or hemp can be cited. In addition, among them, from the viewpoint of availability, high elastic modulus and low linear expansion coefficient, cellulose is particularly preferred. It should be noted that natural fiber 2 is not limited to the above-mentioned material as long as it can improve mechanical strength and has water absorption.

[0046] Regarding the content of the natural fiber 2 carrying the microorganism and / or enzyme 4 in the composite resin molded body 10, when the composite resin molded body 10 is set to 100 volume %, it is preferably 10 volume % or more and 99 volume % or less. If the content of the natural fiber 2 carrying the microorganism and / or enzyme 4 is less than 10 volume %, it is not easy for the natural fibers 2 to have contact points with each other inside the composite resin molded body 10, and it does not have sufficient water absorption. On the other hand, if the content of the natural fiber 2 carrying the microorganism and / or enzyme 4 is greater than 99 volume %, the proportion of the main resin 1 becomes smaller, so the effect of bonding the natural fibers 2 to each other disappears, and the formability becomes poor.

[0047] The morphology of the natural fibers 2 dispersed in the composite resin molded body 10 is described. In order to improve the water absorbency of the composite resin molded body 10, it is preferred that the natural fibers 2 are exposed on the surface of the composite resin molded body 10. When the natural fibers 2 are exposed on the surface of the composite resin molded body 10, water is absorbed from the exposed portion, and the capillary phenomenon of the natural fibers 2 is used to absorb the water into the composite resin molded body 10. The smaller the specific surface area of ​​the natural fibers 2 exposed on the surface of the composite resin molded body 10, the higher the water absorbency. This is because, when the specific surface area of ​​the natural fibers 2 exposed on the surface is large, the hydrophobicity is improved due to the effect of fine concave-convex. In addition, by Figure 3 As shown, the natural fiber 2 has an open fiber portion 6 at the end thereof. The specific surface area of ​​the open fiber portion 6 is increased, and the contact points between the natural fibers 2 are increased, so that the water absorption rate can be increased through the contact points of the natural fibers 2 in a humid environment.

[0048] The central portion of the natural fiber 2 that has a small specific surface area and has not been opened is less entangled with the main resin 1 and is easily exposed on the surface of the molded body depending on the molding conditions. On the contrary, the front end portion of the natural fiber 2 that has been opened is more entangled with the main resin 1 and enters the interior together with the main resin 1. As a result, a composite resin molded body 10 can be obtained in which the central portion of the natural fiber 2, excluding the two end portions, is exposed on the surface.

[0049] The leading end spread portion is preferably 5% or more and 50% or less of the fiber length L of the entire natural fiber 2. If the spread portion is less than 5% of the entire fiber length L, the specific surface area is small, so that the elastic modulus is not improved. If it is greater than 50%, the spread portion with a large aspect ratio is exposed on the surface of the molded article, and the water absorption is deteriorated.

[0050] Next, the characteristics of the natural fiber 2 are described. As described above, the types of the main resin 1 and the natural fiber 2 are too soft relative to the main resin 1, that is, the elastic modulus of the natural fiber 2 is small, then the elastic modulus of the composite resin molded body 10 as a whole becomes smaller, and the strength is reduced. On the other hand, if the natural fiber 2 is too hard relative to the main resin 1, that is, the elastic modulus of the natural fiber 2 is large, the shock wave generated during the impact is not propagated, but is absorbed at the interface between the main resin 1 and the natural fiber 2, so it is easy to produce cracks and cracks near the interface, and the impact strength is reduced. Therefore, with regard to the relationship between the elastic modulus of the main resin 1 and the elastic modulus of the natural fiber 2, it is preferred that the elastic modulus of the natural fiber 2 is higher than the elastic modulus of the main resin 1, and the difference is preferably as small as possible. The best relationship can be calculated based on the simulation results, and the difference in elastic modulus between the main resin 1 and the natural fiber 2 is preferably within 20GPa.

[0051] In addition, these natural fibers 2 are sometimes surface-treated for the purpose of improving adhesion to the main resin 1 or dispersibility in the composite resin molded body 10. However, if the water absorption of the natural fibers 2 is impaired by the surface treatment, it is preferably not surface-treated in advance.

[0052] <Additives>

[0053] Additives may be used as necessary for the purpose of improving the affinity between the main resin 1 and the natural fiber 2. It should be noted that any additive that is commonly used may be used.

[0054] <Coating resin>

[0055] Next, the coating resin 3 is described. The coating resin 3 in the present embodiment 1 is used in the composite resin molded body 10 for the purpose of protecting the microorganisms and / or enzymes 4 carried on the natural fiber 2 and preventing contact with the main resin 1. After the composite resin molded body 10 is discarded, in order to promote biodegradation in a humid environment, it is necessary to dissolve the coating resin 3 and release the microorganisms and / or enzymes 4 carried on the natural fiber 2. Therefore, a water-soluble resin that is soluble in water at a temperature of 20°C is preferred. Specifically, polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, and modified starches can be cited. The above-mentioned resins can be used alone or in combination of two or more. It should be noted that the coating resin 3 is not limited to the above-mentioned materials as long as it is water-soluble. In addition, as a water-resistant treatment, a reaction that connects water-soluble resins to each other and changes physical and chemical properties can also be carried out. For example, a crosslinking agent can be added according to the type of water-soluble resin, or a heat treatment or radiation irradiation can be performed as a post-treatment. The crosslinking agent preferably includes at least one selected from isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and metal chelate crosslinking agents, but is not limited thereto as long as it is a crosslinking agent that is resistant to water.

[0056] The existence state of the coating resin 3 in the composite resin molded body 10 is described. By controlling the content of the coating resin 3 in the composite resin molded body 10, the release of the microorganisms and / or enzymes 4 supported on the natural fiber 2 can be slowed down, and the decomposition rate can be controlled. Therefore, for example, if the content of the coating resin 3 in the composite resin molded body 10 is as high as 50% by mass or more, the release of the microorganisms and / or enzymes 4 supported on the natural fiber 2 slows down, and the speed at which the decomposition starts decreases. On the contrary, if it is less than 50% by mass, the release of the microorganisms and / or enzymes 4 supported on the natural fiber 2 speeds up, and the speed at which the decomposition starts increases.

[0057] <Microorganisms and / or enzymes>

[0058] Next, the microorganism and / or enzyme 4 will be described. The microorganism and / or enzyme 4 contained in the composite resin molded body of the present embodiment 1 is used for the purpose of accelerating the decomposition of the composite resin molded body 10 in a humid environment. The microorganism and / or enzyme 4 in the present embodiment varies depending on the main resin 1. Specifically, there can be cited microorganisms of the genus Amycolatopsis as a polylactic acid degrader (Japanese: degrader) and polybutylene succinate degrader, microorganisms of the genus Streptomyces as a poly-3-hydroxybutyric acid degrader, microorganisms of the genus Pseudomonas, such as Pseudomonas sutcheri, microorganisms of the genus Alcaligenes, and Alcaligenes arguably, and microorganisms of the genus Pseudomonas as a degrader of polyethers such as polyethylene glycol, such as Pseudomonas stutzeri, Pseudomonas aeruginosa, Pseudomonas vesicularis, microorganisms of the genus Alcaligenes, microorganisms of the genus Acinetobacter, and microorganisms of the genus Xanthomonas.

[0059] As the enzyme in the present embodiment 1, for example, various enzymes extracted from the above-mentioned microorganisms can be cited. Specifically, as the enzyme for decomposing polylactic acid, proteinase K, polyvinyl alcohol dehydrogenase, polyvinyl alcohol oxidase, secondary alcohol oxidase, etc. can be cited, as the enzyme for decomposing poly (3-hydroxybutyric acid), PHB depolymerase can be cited, as the enzyme for decomposing polyurethane, cholesterol esterase, CHITO PEARL cholesterol esterase, urease, etc. can be cited. The above-mentioned microorganisms and / or enzymes can be used alone or in combination of two or more. It should be noted that the enzyme is not limited to the above-mentioned materials as long as it has decomposability to the main resin 1.

[0060] <Method for producing composite resin molded body>

[0061] Next, a method for producing the composite resin molded body 10 according to the first embodiment will be described. Figure 4 This is a flowchart illustrating the production process of the composite resin molded body 10 according to the first embodiment.

[0062] (1) Microorganisms and / or enzymes 4 are preliminarily supported on the surface of natural fibers 2. Methods for supporting microorganisms and / or enzymes 4 include physical adsorption based on dry mixing, impregnation of natural fibers with a dispersion solvent, crosslinking, embedding, etc. The supporting method is not limited to the above method as long as it can maintain the microorganisms and / or enzymes 4 on the surface of natural fibers 2.

[0063] (2) After dry mixing the main resin 1 and the natural fiber 2 carrying the microorganism and / or enzyme 4, the main resin 1 and the natural fiber 2 carrying the microorganism and / or enzyme 4 are placed in a melt kneading treatment device and melt kneaded in the device. Thus, the shearing action of the device can promote the fiber opening of the agglomerated mass of the natural fiber 2, so that the natural fiber 2 carrying the microorganism and / or enzyme 4 is finely dispersed in the main resin 1. By adjusting the shearing conditions at this time, it is also possible to Figure 3The ends of the natural fibers 2 are opened as shown to obtain opened portions. It is to be noted that, for example, if the material temperature is 180°C and the conditions are about 5 minutes as in Example 1 described later, it is considered that the microorganisms and / or enzymes 4 will not be thermally damaged by the melted main resin 1.

[0064] In the past, when fibers are compounded with resins, fibers that have been previously opened by pretreatment such as wet dispersion are used. However, if natural fibers are opened in the solvent used in wet dispersion, the fibers swell due to the solvent. Therefore, in order to allow the natural fibers to fully absorb water and swell in composite resin molding materials and composite components, it is necessary to dry the solvent in the natural fibers before mixing with the main resin. In addition, since opening based on wet dispersion is easier than opening in molten main resin, it is not easy to open only the ends, but the natural fibers are opened as a whole. In addition, there is a problem of increasing the number of steps and deteriorating productivity due to the addition of pretreatment.

[0065] In contrast, in the manufacturing process of the composite resin molded body 10 of the present embodiment 1, a pretreatment based on wet dispersion for the purpose of fiber opening of the natural fiber 2 is not performed, but a melt kneading treatment (complete dry process) is performed together with the main resin 1. In this process, the natural fiber 2 is not subjected to a wet dispersion treatment, thereby suppressing the swelling of the natural fiber 2 in the manufacturing process and improving the water absorption rate of the natural fiber 2 in the composite resin molded body 10. By drying the natural fiber 2 in advance or during kneading, the water absorption rate in a humid environment in the composite resin molded body 10 can be further improved. In addition, since the natural fiber 2 has a fiber opening portion, the natural fibers 2 have a large number of contact points with each other inside the composite resin molded body 10 and are entangled, thereby increasing the water absorption rate of the composite resin molded body 10 through the contact points between the fibers.

[0066] If the natural fiber 2 of the present embodiment is to be made by fully dry process, it is preferred to apply high shear stress during mixing. As specific mixing method, single screw mixer, twin screw mixer, roll mixer, Banbury mixer and their combination etc. can be enumerated. From the viewpoint that it is easy to apply high shear, mass production is also high, particularly preferably continuous twin screw mixer, continuous roll mixer. As long as it is a method that can apply high shear stress, it can also be the mixing method beyond the above.

[0067] (3) By subjecting the composite resin composition extruded from the melt-kneading device to injection molding, an injection-molded product as the composite resin molded body 10 can be produced.

[0068] (4) Applying the water dispersion of the water-soluble coating resin 3 to the surface of the composite resin molded body 10. Specific coating methods include die coater, screen printing, pad printing, inkjet, spray coating, dip coating, and combinations thereof. Any coating method other than the above may be used as long as it is a method that can apply the water dispersion of the coating resin 3 to the three-dimensional shape of the composite resin molded body 10. By this coating treatment, the coating resin 3 can be impregnated from the surface 10a of the composite resin molded body 10. At this time, at least one natural fiber 2 is exposed on the surface 10a of the composite resin molded body 10. Since the natural fibers 2 have contact points with each other, the coating resin 3 can be impregnated into the interior of the composite resin molded body 10. Thereafter, a drying treatment is performed, thereby achieving a composite resin molded body 10 impregnated with the coating resin 3 as follows: the amount of coating resin 3 of the coated natural fibers 2 located at the center 10b of the composite resin molded body 10 is less than the amount of coating resin 3 of the coated natural fibers 2 located at the surface 10a of the composite resin molded body 10, or the amount of coating resin 3 of the coated natural fibers 2 decreases from the surface 10a of the composite resin molded body 10 toward the center 10b of the composite resin molded body 10.

[0069] Embodiment 1 is described in more detail below with reference to examples. Embodiment 1 is not limited to the following examples, and may be implemented with appropriate modifications within the scope of the above and below-described gist, all of which are included in the technical scope of Embodiment 1.

[0070] (Example 1)

[0071] In Example 1, a composite resin molded body using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (hereinafter abbreviated as PHBV) as a main component resin was produced by the following production method.

[0072] (1) Conifer pulp (trade name: NBKP Celgar, manufactured by Mitsubishi Paper Corp.) was used as a starting material of natural fibers, and PHB depolymerase extracted from a culture solution of a microorganism of the genus Streptomyces was used as a PHBV degrading enzyme.

[0073] (2) Conifer pulp and PHB depolymerase were dry-mixed at a mass ratio of 90:10 and pulverized using a roll mill to obtain an enzyme-supported cellulose filler.

[0074] (3) Then, the enzyme-loaded cellulose filler and PHBV (trade name: Y1000P, manufactured by TianAn Biopolymer) as the main resin were weighed to a mass ratio of 90:10 and dry-mixed. Thereafter, melt-mixed was performed using a twin-screw mixer (KRC kneader manufactured by Kurimoto Iron Works). The screw was set to a medium shear type. The melt-mixed conditions were set to a material temperature of 180°C and a rotation speed of 50 min. -1 The composite resin composition discharged from the twin-screw kneader was hot-cut to produce composite resin pellets having a mass ratio of main agent resin, natural fiber, and enzyme of 10:81:9.

[0075] (4) Thereafter, a composite resin molded body in the shape of a test piece was produced using an injection molding machine (180AD manufactured by Nippon Steel Works). The test piece production conditions were set to a main resin temperature of 180°C, a mold temperature of 50°C, an injection speed of 100 mm / s, and a holding pressure of 100 Pa. At this time, the total heating time for the above-mentioned melt kneading and injection molding was set to within 5 minutes. The shape of the test piece was changed according to the evaluation items described below.

[0076] (5) Regarding the coating resin, a polyvinyl alcohol resin (PVA217 manufactured by Kuraray Co., Ltd.) was used as a water-soluble resin and dissolved in pure water using a homogenizer so as to have a weight solid content of 5%, thereby preparing a water-soluble resin solution. The water-soluble resin solution was added to a glass container corresponding to the shape of the test piece together with the test piece and kept in an immersed state for 1 hour. Thereafter, the test piece was taken out and subjected to a natural drying treatment for 24 hours to prepare a composite resin molded body impregnated with the coating resin. According to the weight change before and after the impregnation with the coating resin, when the composite resin molded body is set to 100% by mass, the content of the coating resin is about 15% by mass.

[0077] (Evaluation of water absorption of fibers)

[0078] The water absorption of the fiber is evaluated by measuring the moisture content of the fiber according to the method specified in JIS L0105:2020. Specifically, the weight of the fiber dried at 80°C for 24 hours is measured, and then the weight of the fiber maintained at a temperature of 20°C and a humidity of 65% for 24 hours is measured. Fibers with a moisture content of less than 5% are rated as "bad", and fibers with a moisture content of more than 5% are rated as "good". In the composite resin molded body of Example 1, the moisture content of conifer pulp is 6.5%, which is evaluated as "good".

[0079] (Fiber end opening)

[0080] The obtained composite resin molded body was immersed in chloroform and pure water to dissolve PHBV and PVA, and the shape of the remaining cellulose fibers was observed by SEM. In the composite resin molded body of Example 1, the ends of the fibers were in a state of being opened.

[0081] (Evaluation of Elastic Modulus of Composite Resin Molded Article)

[0082] The obtained dumbbell-shaped test piece of JIS K7139 type A12 size was used to perform a three-point bending test. Here, as a method for evaluating the elastic modulus, a test piece with a value less than 200 MPa is regarded as "poor", and a test piece with a value of 200 MPa or more is regarded as "good". In the composite resin molded body of Example 1, the elastic modulus of the same test piece was 598 MPa, which was evaluated as "good".

[0083] (Evaluation of Biodegradability of Composite Resin Molded Articles)

[0084] A biodegradation test was conducted using a rod-shaped test piece made from the obtained cellulose composite resin molded body. 50 g of a composting plant source (YK-11 manufactured by Yawata Bussan) was placed in a plastic container, and a rod-shaped test piece with a height of 20 mm, a width of 10 mm, and a thickness of 3 mm, the weight of which was previously measured, was buried in the plant source. The temperature was maintained at 58°C and the humidity was 50%, and the weight reduction after 1 month and 2 months was evaluated. As a method for evaluating the biodegradability, a test piece with a weight reduction of 50% or more after 2 months was rated as "good", and a test piece with a weight reduction of less than 50% was rated as "poor". The biodegradability of the same test piece after 1 month was 22%, and the biodegradability after 2 months was 55%, which was evaluated as "good".

[0085] (Example 2)

[0086] In Example 2, the mass ratio of the main resin, natural fiber, and enzyme was changed to 60:31:9, and the other material conditions and process conditions were the same as those in Example 1 to produce a composite resin molded body. The same evaluation as in Example 1 was also performed.

[0087] (Comparative Example 1)

[0088] In Comparative Example 1, instead of applying, impregnating, and drying the coating resin to the composite resin molded body later, the coating resin was compounded simultaneously when the main resin and the enzyme-supported cellulose filler were melt-kneaded. Except for the change in this process, the other material conditions and process conditions were the same as those in Example 1 to produce a composite resin molded body. The same evaluation as in Example 1 was also performed. The content of the coating resin relative to the composite resin molded body was adjusted to 15% by mass, which was the same as in Example 1.

[0089] (Comparative Example 2)

[0090] In Comparative Example 2, natural fiber was not used, the volume ratio of the main resin to the enzyme was changed to 91:9, and the other material conditions and process conditions were the same as those of Example 1 to produce a composite resin molded body.

[0091] (Comparative Example 3)

[0092] In Comparative Example 3, PET fibers with a fiber diameter of 20 μm and a fiber length of 100 μm were used instead of conifer pulp to produce enzyme-supported PET fibers. The other material conditions and process conditions were the same as those in Example 1 to produce a composite resin molded body. The same evaluation as in Example 1 was also performed.

[0093] The structures and measurement results of the composite resin molded bodies of Examples 1 and 2 and Comparative Examples 1 to 3 are shown in FIG. Figure 5 middle.

[0094] from Figure 5 It is clearly seen that in Examples 1 and 2, which are composite resin molded bodies in which the enzyme carried on the natural fiber is protected by the coating resin, the elastic modulus is as high as 200 MPa or more, and Example 1, which has a large proportion of natural fibers, shows a higher elastic modulus than Example 2. The biodegradation rate after 1 month is not significantly different from that of the comparative example, but the biodegradation rate after 2 months is greatly promoted. This is the result of the following reasons, that is, the amount of coating resin of the natural fiber coated at the center of the composite resin molded body is small relative to the amount of coating resin of the natural fiber coated at the surface of the composite resin molded body, or the amount of coating resin of the natural fiber coated decreases from the surface of the composite resin molded body toward the center of the composite resin molded body, so if the coating resin at the surface of the composite resin molded body is dissolved, the microorganisms and / or enzymes carried on the natural fiber are released, and the decomposition of the main agent resin at the surface of the composite resin molded body is promoted. Thereafter, since the coating resin decreases toward the center of the composite resin molded body, the microorganisms and / or enzymes supported on the natural fibers can be easily released without dissolving the coating resin, thereby accelerating the decomposition of the main resin.

[0095] Comparative Example 1, in which the coating resin is uniformly present in the composite resin molded body, has a high elastic modulus of 200 MPa or more, and the biodegradation rate after 1 month is equivalent to that of Examples 1 and 2. However, the biodegradation rate after 2 months is as low as 50% or less, and is evaluated as "poor". This is the result of the following reasons, that is, since the coating resin needs to be dissolved toward the center of the composite resin molded body, it is difficult for the microorganisms and / or enzymes supported on the natural fibers to be released, and the decomposition of the main resin is slowed down.

[0096] The elastic modulus of Comparative Example 2 produced without using natural fibers was reduced and was evaluated as "poor". In addition, since the coating resin aqueous solution was not impregnated into the composite resin molded body by the natural fibers, the coating resin existed only on the surface of the composite resin molded body, and since the natural fibers were not used to absorb water into the composite resin molded body, the coating resin was not dissolved, and the microorganisms and / or enzymes carried on the natural fibers were difficult to be released, the decomposition of the main resin was slow, and the biodegradation rate was as low as 50% or less, which was evaluated as "poor".

[0097] Although Comparative Example 3, which was made by using PET fiber instead of coniferous pulp, had an elastic modulus evaluation of ○ due to the reinforcement effect of PET fiber, the moisture content of PET fiber was low and it had no water absorption. Therefore, as in Comparative Example 2, the coating resin existed only on the surface of the composite resin molded body, and the natural fiber was not used to absorb water into the interior of the composite resin molded body, so the coating resin could not be dissolved, the microorganisms and / or enzymes carried on the natural fiber were difficult to be released, the decomposition of the main resin was slow, and the biodegradation rate was as low as below 50%, which was evaluated as "poor".

[0098] Based on the above evaluation results, it is confirmed that if there are microorganisms and / or enzymes carried on multiple natural fibers, at least a portion of the surfaces of the multiple natural fibers are covered with a covering resin, the amount of covering resin of the covered natural fibers located at the center of the composite resin formed body is small relative to the amount of covering resin of the covered natural fibers located on the surface of the composite resin formed body, or the amount of covering resin of the covered natural fibers decreases from the surface of the composite resin formed body toward the center of the composite resin formed body, at least one of the multiple natural fibers has a portion exposed on the surface of the composite resin formed body, and the water absorption rate of the natural fibers is high, then a composite resin with high elastic modulus, high durability, and high biodegradability can be obtained.

[0099] It should be noted that the present invention includes a case where any of the various embodiments and / or examples described above are appropriately combined to exert the effects of each embodiment and / or example.

[0100] Industrial Applicability

[0101] According to the composite resin molded body of the present invention, it is possible to provide a molded body that can control the mechanical strength and biodegradation rate compared to existing biodegradable plastics. According to the present invention, since the characteristics of the main resin can be improved, it can be used as a substitute for general-purpose plastics derived from petroleum. Therefore, the environmental burden of various industrial products or daily necessities made of general-purpose plastics derived from petroleum can be greatly reduced. In addition, it can be used in packaging materials, daily necessities, home appliance housings, building materials, etc.

[0102] Description of Reference Numerals

[0103] 1 main resin, 2 natural fiber, 3 coating resin, 4 microorganism and / or enzyme, 6 fiber opening part, 10 composite resin molded body, 10a surface of composite resin molded body, 10b center of composite resin molded body.

Claims

1. A composite resin molded body comprising a main resin, a plurality of natural fibers dispersed in the main resin, and a microorganism and / or an enzyme supported on the plurality of natural fibers, At least a portion of the surfaces of the plurality of natural fibers are coated with a coating resin, and an amount of the coating resin located at the center of the composite resin molded body is smaller than that at the surface of the composite resin molded body. At least one of the plurality of natural fibers has a portion exposed on the surface of the composite resin molded body.

2. The composite resin molded article according to claim 1, wherein The amount of the coating resin decreases from the surface of the composite resin molded body toward the center of the composite resin molded body.

3. The composite resin molded article according to claim 1, wherein The moisture content of the natural fiber is 5% or more according to the method specified in JIS L0105:2020.

4. The composite resin molded article according to claim 1, wherein The main resin is a biodegradable resin selected from polyhydroxyalkanoic acid, polylactic acid, polybutylene succinate, polybutylene adipate terephthalate, polycaprolactone, polyamide, and modified starch.

5. The composite resin molded article according to claim 1, wherein The coating resin is a water-soluble resin such as polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, starch-based resin, etc.

6. The composite resin molded article according to claim 1, wherein The natural fibers in the composite resin molded body carry the microorganisms and / or enzymes on the fiber surfaces.

7. The composite resin molded article according to claim 1, wherein The natural fibers are cellulose.

8. The composite resin molded article according to claim 1, wherein The natural fibers have open fiber portions at ends in the fiber length direction.

9. The composite resin molded article according to claim 1, wherein The content of the natural fiber supporting the microorganism and / or enzyme is 10% by mass or more and 99% by mass or less, based on 100% by mass of the composite resin molded body.

10. A method for producing a composite resin molded body, The manufacturing method comprises: The steps of preparing microorganisms and / or enzymes, natural fibers, water-soluble coating resins and main resins; A step of supporting the microorganism and / or enzyme on the natural fiber; A main resin melt kneading step, wherein the natural fibers are melt kneaded together with the main resin, and the natural fibers are opened from the ends in the fiber length direction to obtain a composite resin composition having an enlarged surface area of ​​the opened portions at the ends; The step of molding the composite resin composition to obtain a composite resin molded body; as well as The step of coating and impregnating the surface of the composite resin molded body with a coating resin and then drying it to obtain the composite resin molded body in which the amount of the coating resin located at the center of the composite resin molded body relative to the surface of the composite resin molded body is small and at least a portion of the surface of the natural fiber is coated with the coating resin.

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