Resin composition, resin molded body, and method for producing resin pellets

Abstract

Disclosed is a method for producing a resin composition, the method including a step for kneading plant fibers, a polyolefin resin, and at least one of a first cyclic compound, a second cyclic compound, a third cyclic compound, and a fourth cyclic compound so as to obtain a resin composition.

Description

Resin composition, resin molded body, and method for producing resin pellets

[0001] The present invention relates to a resin composition containing plant fibers and a polyolefin resin, a resin molded product, and a method for producing resin pellets.

[0002] Conventionally, in order to ensure the strength of a resin composition, a method has been adopted in which plant fibers or inorganic materials such as calcium carbonate, talc, or glass fibers are blended as a filler into a base synthetic resin (polyolefin resin). In particular, plant fibers have a lower specific gravity than inorganic materials, and are therefore used as fillers as a way to improve the strength of a resin composition while reducing its weight.

[0003] However, when the temperature of plant fibers, which are composed of components such as lignin and hemicellulose, rises to a high temperature (approximately 200°C), the lignin and hemicellulose undergo thermal decomposition, generating corrosive gases such as carboxylic acids. Therefore, when a resin composition containing plant fibers and a synthetic resin is injection molded at a high temperature, there is a risk of corrosion of the mold used for injection molding.

[0004] For example, Patent Document 1 discloses a method for producing a resin composition for molding material containing plant fibers, a thermoplastic resin, and a compound reactive with a carboxy group.

[0005] Patent No. 6986655

[0006] However, when the molecular weight of the carboxylic acid is small and the compound that reacts with the carboxylic acid is a chain carbodiimide, there is a problem in that isocyanate gas is generated.

[0007] The present invention has been made in consideration of the above points, and aims to provide a resin composition, a resin molded product, and a method for producing resin pellets that suppress corrosion of a mold during injection molding and prevent the generation of isocyanate gas.

[0008] The method for producing a resin composition of the present invention includes a step of kneading plant fibers, a polyolefin resin, and at least one of a first cyclic compound, a second cyclic compound, a third cyclic compound, and a fourth cyclic compound to obtain a resin composition, wherein the first cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide in which a first nitrogen and a second nitrogen are bonded by a bonding group, and two or more first subcyclic structures fused to a portion of the main cyclic structure, the second cyclic compound is a cyclic compound having the main cyclic structure and two or more second subcyclic structures extending as substituents from the main cyclic structure, and the third cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure fused to a portion of the main cyclic structure, and second subcyclic structures extending as substituents from each of the first subcyclic structures, The fourth cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure fused to a portion of the main cyclic structure, and a second subcyclic structure fused to a portion of the first subcyclic structure.

[0009] FIG. 1 is a diagram showing a manufacturing process for a resin composition and a resin molded body according to a first embodiment of the present invention. FIG. 2 is a diagram showing a reaction process between a corrosive gas and a cyclic compound. FIG. 3 is a diagram showing a manufacturing process for a resin composition and a resin molded body according to a first modified example of the first embodiment of the present invention. FIG. 4 is a diagram showing a manufacturing process for resin pellets according to a second modified example of the first embodiment of the present invention. FIG. 5 is a table summarizing the results of comparison between examples and comparative examples of a resin composition of the present invention.

[0010] [First Embodiment] A first embodiment of the present invention will be described. As shown in FIG. 1 , in the method for producing a resin composition according to the first embodiment, a plant fiber 10, a polyolefin resin 11, and a cyclic compound 20 having a carbodiimide group are kneaded in a twin-screw mixer 40 at a screw rotation speed of 250 rpm and a cylinder temperature of 200°C, for example, to obtain a resin composition 30. Next, the resin composition 30 is injected into a molding machine 41 and injection-molded at a high temperature to obtain a resin molded body 31. The screw rotation speed and cylinder temperature of the twin-screw mixer can be changed as appropriate. Furthermore, the device used for kneading is not limited to a twin-screw mixer.

[0011] Plant fibers 10 are natural fibers extracted from plants, and their main components are cellulose, hemicellulose, and lignin, which are structural components of plant cell walls. As shown in Figure 2, hemicellulose and lignin are thermally decomposed at high temperatures (approximately 200°C) to generate carboxylic acid, a corrosive gas 10A.

[0012] The carboxylic acid generated from the plant fiber 10 reacts with the cyclic compound 20. In other words, the carboxylic acid is masked by the cyclic compound 20. This prevents the carboxylic acid from reacting with a mold (e.g., iron) used in injection molding, thereby preventing the mold from corroding. The reaction mechanism between the carboxylic acid and the cyclic compound 20 is shown below.

[0013] Furthermore, the use of the cyclic compound 20 can prevent the generation of isocyanate gas due to the above-mentioned reaction mechanism. In other words, by incorporating the cyclic compound 20 into the plant fibers 10 and the polyolefin resin 11 and kneading them, it is possible to prevent the generation of isocyanate gas while suppressing corrosion of the mold due to carboxylic acid generated from the plant fibers 10.

[0014] It should be noted that isocyanate gas is generated, for example, when the molecular weight of the carboxylic acid generated from the plant fiber is small and the compound that reacts with the carboxylic acid is a chain carbodiimide.

[0015] Furthermore, by using cyclic compound 20, the above-mentioned reaction mechanism is followed, and therefore fogging caused by isocyanate gas from the resin composition can be prevented. Here, fogging caused by isocyanate gas refers to the volatilization of isocyanate gas from the resin composition due to an increase in the temperature of the resin composition.

[0016] Examples of the plant fibers 10 used in the resin composition of the present invention include wood flour, wood fibers such as paper, cellulose fibers, cellulose nanofibers, plant-derived biomass materials, cellulose extracted from plants or separately synthesized, hemicellulose, and lignin. Examples of wood flour that can be used include wood flour derived from softwoods, hardwoods, rice straw, rice husks, wheat straw, bamboo, pine, cedar, cypress, kenaf, pulp, sisal hemp, Manila hemp, jute hemp, coconut, corn, reed, palm, and papyrus.

[0017] It is preferable to use wood flour derived from coniferous trees as the plant fibers 10. When comparing coniferous trees and broad-leaved trees, the amount of cellulose is the same, but coniferous trees have a higher amount of lignin and a lower amount of hemicellulose than broad-leaved trees. The thermal decomposition temperature of hemicellulose is 180 to 300°C, and the thermal decomposition temperature of lignin is 280 to 550°C. Therefore, coniferous trees, which have a relatively lower amount of hemicellulose and a higher amount of lignin, have high heat resistance. Therefore, by using wood flour derived from coniferous trees as the plant fibers 10, the heat resistance of the resin composition 30 can be improved.

[0018] The blending amount of plant fiber 10 is preferably 10% by weight (wt%) to 85% by weight, and more preferably 30% by weight to 70% by weight, relative to the total amount of resin composition 30. Since it is difficult to ensure sufficient strength when the blending amount of plant fiber is low, the blending amount of plant fiber is preferably 10% by weight or more, and more preferably 30% by weight or more. Furthermore, the strength increases as the blending amount of plant fiber increases, but on the other hand, the fluidity of the resin composition decreases, making it difficult to sufficiently knead. Therefore, the blending amount of plant fiber is preferably 85% by weight or less, and more preferably 70% by weight or less. Furthermore, the decreased fluidity of the resin composition makes it difficult to ensure sufficient moldability.

[0019] The polyolefin resin 11 may be polypropylene (PP), polyethylene (PE), or the like.

[0020] The blending amount of polyolefin resin 11 is preferably 15% by weight to 90% by weight, and more preferably 30% by weight to 70% by weight, relative to the total amount of resin composition 30. If the blending amount of polyolefin resin is low, the fluidity of the resin composition decreases and it becomes difficult to sufficiently knead it, so the blending amount of polyolefin resin is preferably 15% by weight or more, and more preferably 30% by weight or more. Furthermore, if the blending amount of polyolefin resin is high, it becomes difficult to ensure sufficient strength, so the blending amount of polyolefin resin is preferably 90% by weight or less, and more preferably 70% by weight or less. Furthermore, since polyolefin resins are made from fossil fuels such as petroleum, reducing the blending amount of polyolefin resin is also useful from the perspective of preserving environmental resources.

[0021] The cyclic compound 20 is any one of the following first, second, third and fourth cyclic compounds.

[0022] The first cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide to which the first nitrogen and the second nitrogen are bonded via a bonding group, and two or more first subcyclic structures fused to a portion of the main cyclic structure. The main cyclic structure refers to a structure with the minimum number of bonds forming a cyclic carbodiimide. The first cyclic compound may have multiple main cyclic structures. The bonding group refers to a carbon atom constituting the carbodiimide group. The first nitrogen and the second nitrogen refer to the nitrogen atoms bonded to the carbon atom that is the bonding group, respectively.

[0023] As the first cyclic compound, for example, the following compounds (1) to (26) can be used. Note that, because of ease of synthesis and inexpensive raw materials, it is preferable to use the following compound (1) as the first cyclic compound.

[0024] The second cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide to which the first and second nitrogen atoms are bonded via a bonding group, and two or more second subcyclic structures extending from the main cyclic structure as substituents. The main cyclic structure refers to the structure with the minimum number of bonds that form a cyclic carbodiimide. The bonding group refers to the carbon atoms that constitute the carbodiimide group. The first nitrogen atom and the second nitrogen atom refer to the nitrogen atoms bonded to the carbon atoms that are the bonding groups, respectively.

[0025] As the second cyclic compound, for example, the following compounds (27) to (30) can be used.

[0026] The third cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide to which a first nitrogen and a second nitrogen are bonded via a bonding group, a first subcyclic structure fused to a portion of the main cyclic structure, and a second subcyclic structure extending from the first subcyclic structure as a substituent. The main cyclic structure refers to the structure with the minimum number of bonds that form a cyclic carbodiimide. The bonding group refers to the carbon atom that constitutes the carbodiimide group. The first nitrogen and the second nitrogen refer to the nitrogen atom bonded to the carbon atom that is the bonding group, respectively.

[0027] As the third cyclic compound, for example, the following compounds (31) to (32) can be used.

[0028] The fourth cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide in which the first nitrogen and the second nitrogen are bonded by a bonding group, a first subcyclic structure fused to a portion of the main cyclic structure, and a second subcyclic structure fused to a portion of the first subcyclic structure.

[0029] As the quaternary cyclic compound, for example, the following compounds (33) to (35) can be used.

[0030] Alternatively, the fourth cyclic compound may be a cyclic compound having a main cyclic structure containing a carbodiimide in which the first nitrogen and the second nitrogen are bonded via a bonding group, a first subcyclic structure fused to a portion of the main cyclic structure, a second subcyclic structure fused to a portion of the first subcyclic structure, and a third subcyclic structure fused to a portion of the second subcyclic structure, as shown in compound (36) below.

[0031] The blending amount of the cyclic compound 20 is preferably 0.05% to 5.00% by weight relative to the plant fiber 10. If the blending amount of the cyclic compound is less than 0.05% by weight, the blending amount of the cyclic compound is insufficient relative to the corrosive gas 10A, and much of the corrosive gas 10A remains unreacted. As a result, corrosion of the mold used during molding is not sufficiently suppressed.

[0032] It is preferable to set the blending amount of cyclic compound 20 to 0.5% by weight or more and to use wood flour derived from coniferous trees as the plant fibers 10. By setting the blending amount of cyclic compound 20 to 0.5% by weight or more and to use wood flour derived from coniferous trees as the plant fibers 10, corrosion resistance can be further improved.

[0033] The uses of the resin molded article 31 produced from the resin composition 30 of the present invention are not particularly limited, and it can be used for automobile exterior and interior parts, lighting equipment, imaging equipment such as cameras and sensors, fixtures, everyday items such as stationery, etc. In particular, the resin molded article 31 produced from the resin composition 30 of the present invention is useful for use as a component of equipment having a heat source with a temperature of 300°C or less, such as a housing or bracket of a vehicle lamp, because it prevents fogging caused by isocyanate gas at high temperatures.

[0034] The first embodiment will be described in more detail below with reference to modified examples. It should be noted that the present invention is not limited to these modified examples. [Modification 1 of First Embodiment] Modification 1 of the method for producing a resin composition of the first embodiment will be described. As shown in FIG. 3 , in Modification 1 of the method for producing a resin composition of the present embodiment, a polyolefin resin 12 containing plant fibers and a cyclic compound 20 are kneaded in a twin-screw mixer 40 at a screw rotation speed of 250 rpm and a cylinder temperature of 200° C., for example, to obtain a resin composition 30. The resin composition 30 is injected into a molding machine 41 and subjected to a molding process in which the resin composition is injection-molded at high temperature to form a resin molded body 31.

[0035] [Modification 2 of First Embodiment] A description will be given of Modification 2 of the resin composition manufacturing method of the first embodiment. As shown in Fig. 4, in Modification 2 of the resin composition manufacturing method of this embodiment, a polyolefin resin 12 containing plant fibers and a cyclic compound 20 are kneaded in a twin-screw mixer 40 at a screw rotation speed of 250 rpm and a cylinder temperature of 200°C, for example, to obtain pellet-shaped resin pellets 32. [Second Embodiment]

[0036] A second embodiment of the present invention will be described below, and the description of the same components as those in the first embodiment of the present invention will be omitted as appropriate.

[0037] As shown in Figure 5, in the second embodiment of the resin composition manufacturing method, plant fiber 10, polyolefin resin 11, cyclic compound 20, and polyamine 50 containing at least one of a primary amine and a secondary amine are kneaded in a twin-screw mixer 40 at a screw rotation speed of 250 rpm and a cylinder temperature of 200°C to obtain a resin composition 30. The resin composition 30 is then injected into a molding machine 41 and injection-molded at high temperature to obtain a resin molded body 31. In other words, the second embodiment of the resin composition manufacturing method differs from the first embodiment in that a polyamine is contained. Note that a polyoxazoline may be contained instead of the polyamine, or both a polyamine and a polyoxazoline may be contained.

[0038] Polyamine or polyoxazoline reacts with carboxylic acids and aldehydes, which are corrosive gases 10A generated when the plant fibers 10 are thermally decomposed. Therefore, by including polyamine or polyoxazoline, corrosion of the mold can be further suppressed.

[0039] For example, a carboxylic acid can react with a primary amine and / or a secondary amine to form a carboxylic acid amide. As an example, the reaction mechanism between a carboxylic acid and a primary amine is shown below.

[0040] For example, an aldehyde may react with a primary amine and / or a secondary amine to form an imine. As an example, the reaction mechanism between an aldehyde and a primary amine is shown below.

[0041] The corrosive gas 10A generated from hemicellulose or lignin contains a large proportion of long-chain fatty acids. The long-chain fatty acids reacted with polyamine or polyoxazoline are oriented in the flow direction during injection molding. Because most of the long-chain fatty acids are hydrophobic hydrocarbon groups, the resin composition exerts a wax effect on its surface, resulting in high releasability from hydrophobic molds.

[0042] Examples of polyamine 50 that can be used include aliphatic amines such as polyallylamine, polyethyleneimine, polyvinylamine, polypropyleneimine, polybutyleneimine, and polyisopropyleneimine, as well as aromatic amines having an alkyl group such as p-hexylaniline and 2-hexyl-5-aminothiophene. If the boiling point of the polyamine is low, there is a concern that it may evaporate when kneaded with plant fibers 10 and polyolefin resin 11. Therefore, it is preferable to use an aliphatic amine or aromatic amine with a boiling point or decomposition temperature of 250°C or higher.

[0043] The weight-average molecular weight (Mw) of the polyamine 50 and polyoxazoline is preferably 300 to 100,000, more preferably 10,000 to 100,000, and even more preferably 10,000 to 70,000. If the weight-average molecular weight of the polyamine and polyoxazoline is less than 300, the polyamine will volatilize due to the heat generated when kneading with the plant fiber 10 and the polyolefin resin 11. As a result, the wax effect on the surface of the resin composition is not achieved, and mold releasability is reduced. Furthermore, if the weight-average molecular weight is low, the polyamine is highly toxic, requiring careful handling. This reduces workability during production. If the weight-average molecular weight of the polyamine and polyoxazoline is greater than 100,000, the viscosity of the resin composition increases, making it difficult to knead sufficiently. As a result, the reaction between the primary amine and / or secondary amine and the corrosive gas is insufficient, leaving much of the corrosive gas unreacted. Therefore, the corrosion of the mold used during injection molding is insufficiently suppressed. Furthermore, when the weight-average molecular weight of the polyamine and polyoxazoline is greater than 100,000, the proportion of tertiary amine per unit mass increases, and the proportion of primary amine and / or secondary amine that reacts with the corrosive gas 10A decreases. Therefore, the corrosion of the mold used during injection molding is insufficiently suppressed.

[0044] The amount of polyamine 50 or polyoxazoline blended is preferably 0.05% to 3.00% by weight relative to the plant fiber 10. By blending the amount of polyamine or polyoxazoline at 0.05% by weight or more, mold corrosion can be further suppressed. Furthermore, if the amount of polyamine or polyoxazoline blended is greater than 3.00% by weight, the amount of polyamine may be excessive relative to the corrosive gas 10A generated from the plant fiber 10. The excess polyamine or polyoxazoline reacts with the hydrophobic components of the resin composition, which exhibit hydrophobic mold releasability, thereby reducing the mold releasability of the resin composition.

[0045] The second embodiment will be described in more detail below with reference to modified examples. It should be noted that the present invention is not limited to these modified examples. [Modification 1 of Second Embodiment] Modification 1 of the method for producing a resin composition of the second embodiment will be described. In Modification 1 of the method for producing a resin composition of the present embodiment, a polyolefin resin 12 containing plant fibers, a cyclic compound 20, and a polyamine 50 containing at least one of a primary amine and a secondary amine are kneaded in a twin-screw mixer 40 at a screw rotation speed of 250 rpm and a cylinder temperature of 200°C to obtain a resin composition 30. The resin composition 30 is injected into a molding machine 41 and injection-molded at high temperature to obtain a resin molded body 31.

[0046] [Variation 2 of Second Embodiment] The following describes Variation 2 of the method for producing a resin composition of the second embodiment. In Variation 2 of the method for producing a resin composition of the present embodiment, polyolefin resin 12 containing plant fibers, cyclic compound 20, and polyamine 50 having at least one of a primary amine and a secondary amine are kneaded in a twin-screw mixer 40 at a screw rotation speed of 250 rpm and a cylinder temperature of 200°C, for example, to obtain resin pellets 32.

[0047] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0048] Example 1: A resin material A-1 (manufactured by I-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The following cyclic compound B-1 was used as the carbodiimide, in an amount of 0.10% relative to the wood flour.

[0049] These materials were kneaded in a twin-screw kneader (manufactured by Technovel Co., Ltd., KZW25TW-60MG-NH(-600)) at, for example, a screw rotation speed of 250 rpm and a cylinder temperature of 200 ° C. to obtain a resin composition. Next, the obtained resin composition was dried for 2 hours in a hot air dryer at 100 ° C. Next, the dried resin composition was injection molded in an injection molding machine (manufactured by The Japan Steel Works, Ltd., J100ADS-100U) equipped with an ISO physical property test piece mold under the following conditions: cylinder temperature 300 ° C., mold temperature 80 ° C., injection pressure 50 MPa (gauge pressure), injection speed 200 mm / sec, injection time / cooling time = 20 sec / 20 sec. A rectangular test piece (resin molded body) of Example 1 having a length of 80.0 mm, a width of 10.0 mm, and a thickness of 4.0 mm was obtained.

[0050] Example 2: Resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, the same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 5.00% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 2 were obtained by the same method as in Example 1.

[0051] Example 3: Resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, the following cyclic compound B-2 was used as the carbodiimide, in an amount of 0.10% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 3 were obtained by the same method as in Example 1.

[0052] Example 4: A resin material A-1 (manufactured by I-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, the same cyclic compound B-2 as in Example 3 was used as the carbodiimide, in an amount of 5.00% relative to the wood flour. Using these materials, a strip-shaped test piece for Example 4 was obtained by the same method as in Example 1.

[0053] Example 5: Resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, the following cyclic compound B-3 was used as the carbodiimide, in an amount of 0.10% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 5 were obtained by the same method as in Example 1.

[0054] Example 6: A resin material A-1 (manufactured by I-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-3 as in Example 5 was used as the carbodiimide, in an amount of 5.00% relative to the wood flour. Using these materials, a strip-shaped test piece for Example 6 was obtained by the same method as in Example 1.

[0055] Example 7: Resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, the following cyclic compound B-4 was used as the carbodiimide, in an amount of 0.10% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 7 were obtained by the same method as in Example 1.

[0056] Example 8: Resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, the same cyclic compound B-4 as in Example 7 was used as the carbodiimide, in an amount of 5.00% relative to the wood flour. Using these materials, a strip-shaped test piece for Example 8 was obtained by the same method as in Example 1.

[0057] Example 9: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.05% based on the wood flour. Using these materials, strip-shaped test specimens for Example 9 were obtained using the same method as in Example 1.

[0058] Example 10: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 3.00% based on the wood flour. Using these materials, a strip-shaped test specimen for Example 10 was obtained using the same method as in Example 1.

[0059] Example 11: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.05% based on the wood flour. Using these materials, strip-shaped test specimens for Example 11 were obtained using the same method as in Example 1.

[0060] Example 12: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 3.00% based on the wood flour. Using these materials, strip-shaped test specimens for Example 12 were obtained using the same method as in Example 1.

[0061] Example 13: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyethyleneimine C-2 (product name: Epomin®, product number: P-1000, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyamine, in an amount of 0.05% based on the wood flour. Using these materials, strip-shaped test specimens for Example 13 were obtained using the same method as in Example 1.

[0062] Example 14: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyethyleneimine C-2 (product name: Epomin®, product number: P-1000, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyamine, in an amount of 3.00% based on the wood flour. Using these materials, strip-shaped test specimens for Example 14 were obtained using the same method as in Example 1.

[0063] Example 15: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% based on the wood flour. Furthermore, polyethyleneimine C-2 (product name: Epomin®, product number: P-1000, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyamine, in an amount of 0.05% based on the wood flour. Using these materials, a strip-shaped test specimen for Example 13 was obtained using the same method as in Example 1.

[0064] Example 16: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% based on the wood flour. Furthermore, polyethyleneimine C-2 (product name: Epomin®, product number: P-1000, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyamine, in an amount of 3.00% based on the wood flour. Using these materials, strip-shaped test specimens for Example 16 were obtained using the same method as in Example 1.

[0065] Example 17: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyoxazoline C-3 (product name: EPOCROS®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 0.50% based on the wood flour. Using these materials, strip-shaped test specimens for Example 17 were obtained using the same method as in Example 1.

[0066] Example 18: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyoxazoline C-3 (product name: EPOCROS®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 3.00% based on the wood flour. Using these materials, strip-shaped test specimens for Example 18 were obtained using the same method as in Example 1.

[0067] Example 19: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% relative to the wood flour. Furthermore, polyoxazoline C-3 (product name: EPOCROS®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 0.05% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 19 were obtained using the same method as in Example 1.

[0068] Example 20: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% relative to the wood flour. Furthermore, polyoxazoline C-3 (product name: EPOCROS®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 3.00% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 20 were obtained using the same method as in Example 1.

[0069] Example 21: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyoxazoline C-4 (product name: EPOCROS®, product number: WS-500, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyoxazoline, in an amount of 0.50% based on the wood flour. Using these materials, strip-shaped test specimens for Example 21 were obtained using the same method as in Example 1.

[0070] Example 22: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyoxazoline C-4 (product name: EPOCROS®, product number: WS-500, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyoxazoline, in an amount of 3.00% based on the wood flour. Using these materials, strip-shaped test specimens for Example 22 were obtained using the same method as in Example 1.

[0071] Example 23: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% relative to the wood flour. Furthermore, polyoxazoline C-4 (product name: EPOCROS®, product number: WS-500, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyoxazoline, in an amount of 0.05% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 23 were obtained using the same method as in Example 1.

[0072] Example 24: A resin material A-1 (manufactured by i-Compology Co., Ltd.) consisting of 55% broadleaf wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% relative to the wood flour. Furthermore, polyoxazoline C-4 (product name: EPOCROS®, product number: WS-500, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 70,000 was used as the polyoxazoline, in an amount of 3.00% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 24 were obtained using the same method as in Example 1.

[0073] Example 25: Resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.05% based on the wood flour. Using these materials, strip-shaped test specimens for Example 25 were obtained using the same method as in Example 1.

[0074] Example 26: Resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 3.00% based on the wood flour. Using these materials, strip-shaped test specimens for Example 26 were obtained using the same method as in Example 1.

[0075] Example 27: Resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.05% based on the wood flour. Using these materials, strip-shaped test specimens for Example 27 were obtained using the same method as in Example 1.

[0076] Example 28: Resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% relative to the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 3.00% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 28 were obtained using the same method as in Example 1.

[0077] Example 29: Resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.50% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.50% based on the wood flour. Using these materials, strip-shaped test specimens for Example 29 were obtained using the same method as in Example 1.

[0078] Example 30: Resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.50% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 1.50% based on the wood flour. Using these materials, strip-shaped test specimens for Example 30 were obtained using the same method as in Example 1.

[0079] Example 31: A resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 1.50% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.50% based on the wood flour. Using these materials, a strip-shaped test specimen for Example 31 was obtained using the same method as in Example 1.

[0080] Example 32: Resin material A-2 (manufactured by i-Compology Co., Ltd.) consisting of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 1.50% based on the wood flour. Furthermore, polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 1.50% based on the wood flour. Using these materials, strip-shaped test specimens for Example 32 were obtained using the same method as in Example 1.

[0081] Example 33: A resin material A-2 (manufactured by i-Compology Co., Ltd.) composed of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% relative to the wood flour. Furthermore, polyethyleneimine C-1 (trade name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.025% relative to the wood flour. Polyoxazoline C-3 (trade name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 0.025% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 33 were obtained using the same method as in Example 1.

[0082] Example 34: The plant fiber-blended polyolefin resin used was resin material A-2 (manufactured by i-Compology Co., Ltd.), consisting of 55% coniferous wood flour and 45% polypropylene (PP). The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.05% relative to the wood flour. The polyamine used was polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000, in an amount of 1.50% relative to the wood flour. The polyoxazoline used was polyoxazoline C-3 (product name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000, in an amount of 1.50% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 34 were obtained using the same method as in Example 1.

[0083] Example 35: A resin material A-2 (manufactured by i-Compology Co., Ltd.) composed of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% relative to the wood flour. Furthermore, polyethyleneimine C-1 (trade name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.025% relative to the wood flour. Polyoxazoline C-3 (trade name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 0.025% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 35 were obtained using the same method as in Example 1.

[0084] Example 36: A resin material A-2 (manufactured by i-Compology Co., Ltd.) composed of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 3.00% relative to the wood flour. Furthermore, polyethyleneimine C-1 (trade name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 1.50% relative to the wood flour. Polyoxazoline C-3 (trade name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 1.50% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 36 were obtained using the same method as in Example 1.

[0085] Example 37: The plant fiber-blended polyolefin resin used was resin material A-2 (manufactured by i-Compology Co., Ltd.), consisting of 55% coniferous wood flour and 45% polypropylene (PP). The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.50% relative to the wood flour. The polyamine used was polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000, in an amount of 0.025% relative to the wood flour. The polyoxazoline used was polyoxazoline C-3 (product name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000, in an amount of 0.025% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 37 were obtained using the same method as in Example 1.

[0086] Example 38: The plant fiber-blended polyolefin resin used was resin material A-2 (manufactured by i-Compology Co., Ltd.), consisting of 55% coniferous wood flour and 45% polypropylene (PP). The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 0.50% relative to the wood flour. The polyamine used was polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000, in an amount of 0.75% relative to the wood flour. The polyoxazoline used was polyoxazoline C-3 (product name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000, in an amount of 0.75% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 38 were obtained using the same method as in Example 1.

[0087] Example 39: The plant fiber-blended polyolefin resin used was resin material A-2 (manufactured by i-Compology Co., Ltd.), consisting of 55% coniferous wood flour and 45% polypropylene (PP). The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 1.50% relative to the wood flour. The polyamine used was polyethyleneimine C-1 (product name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000, in an amount of 0.025% relative to the wood flour. The polyoxazoline used was polyoxazoline C-3 (product name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000, in an amount of 0.025% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 39 were obtained using the same method as in Example 1.

[0088] Example 40: A resin material A-2 (manufactured by i-Compology Co., Ltd.) composed of 55% coniferous wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. The same cyclic compound B-1 as in Example 1 was used as the carbodiimide, in an amount of 1.50% relative to the wood flour. Furthermore, polyethyleneimine C-1 (trade name: Epomin®, product number: SP-200, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 10,000 was used as the polyamine, in an amount of 0.75% relative to the wood flour. Polyoxazoline C-3 (trade name: Epocross®, product number: WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a weight-average molecular weight of 40,000 was used as the polyoxazoline, in an amount of 0.75% relative to the wood flour. Using these materials, strip-shaped test specimens for Example 40 were obtained using the same method as in Example 1.

[0089] Comparative Example 1: A resin material A-1 (manufactured by I-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, N,N'-dicyclohexylcarbodiimide B-5 was used as the carbodiimide, in an amount of 0.10% based on the wood flour. Using these materials, a strip-shaped test piece for Comparative Example 1 was obtained by the same method as in Example 1.

[0090] Comparative Example 2: Resin material A-1 (manufactured by I-Compology Co., Ltd.) consisting of 55% hardwood-derived wood flour and 45% polypropylene (PP) was used as the plant fiber-blended polyolefin resin. Furthermore, N,N'-dicyclohexylcarbodiimide B-5 was used as the carbodiimide, in an amount of 5.00% based on the wood flour. Using these materials, strip-shaped test pieces for Comparative Example 2 were obtained by the same method as in Example 1.

[0091] (Evaluation of Isocyanate Gas Generation Amount) The test pieces of Examples 1 to 40 and Comparative Examples 1 and 2 were analyzed using pyrolysis GC / MS. The GC / MS used was a GC-MS-QP2020 NX manufactured by Shimadzu Corporation, the pretreatment device was an EGA / PY-3030D manufactured by Frontier Labs, and the column was a UA +5 manufactured by Frontier Labs. The amount of isocyanate gas generated was evaluated on a five-point scale (A to E) based on the amount of isocyanate gas detected by pyrolysis GC / MS. The evaluation was as follows: A if no isocyanate gas was detected; B if less than 20 ppm of isocyanate gas was detected; C if 20 ppm or more but less than 50 ppm of isocyanate gas was detected; D if 50 ppm or more but less than 100 ppm of isocyanate gas was detected; and E if 100 ppm or more of isocyanate gas was detected. FIG. 6 shows the evaluation results of the amount of isocyanate gas generated in Examples 1 to 40 and Comparative Examples 1 and 2.

[0092] (Evaluation of releasability) The contact area between the test piece and the mold after the ejection step of injection molding in the preparation process of the test pieces of Examples 1 to 40 and Comparative Examples 1 and 2 was visually confirmed, and the releasability was evaluated on a 5-point scale of A to E. The evaluation was as follows: A when 100% of the surface of the test piece was separated from the mold; B when 70% or more but less than 100% of the surface of the test piece was separated from the mold; C when 50% or more but less than 70% of the surface of the test piece was separated from the mold; D when 20% or more but less than 50% of the surface of the test piece was separated from the mold; and E when less than 20% of the surface of the test piece was separated from the mold. Figure 6 shows a summary of the evaluation results of the releasability of Examples 1 to 40 and Comparative Examples 1 and 2.

[0093] (Evaluation of Corrosion) Test pieces of Examples 1 to 40 and Comparative Examples 1 and 2 were each produced in a series of 100 pieces. The condition of the mold surface was checked after each test piece was produced, and the corrosivity was evaluated on a 5-point scale (A to E) based on the number of test pieces produced until the mold surface was contaminated. Here, "contaminated mold surface" refers to the occurrence of rust on the mold surface. The evaluation was rated as follows: A if no mold surface contamination was observed when 100 test pieces were produced; B if mold surface contamination was observed when 31 to 99 test pieces were produced; C if mold surface contamination was observed when 11 to 30 test pieces were produced; D if mold surface contamination was observed when 2 to 10 test pieces were produced; and E if mold surface contamination was observed when one test piece was produced. Figure 6 shows the evaluation results of corrosivity for Examples 1 to 40 and Comparative Examples 1 and 2.

[0094] (Evaluation of Heat Resistance) The deflection temperatures under load of the test pieces of Examples 1 to 40 and Comparative Examples 1 and 2 were measured in accordance with ISO-75 at a load of 0.45 MPa and a heating rate of 2°C / min. The measurements were performed three times for each test piece, and the heat resistance was evaluated on a five-point scale of A to E based on the average of the measurements. When the deflection temperature under load was 140°C or higher, it was rated as A; when the deflection temperature under load was 130°C or higher but lower than 140°C, it was rated as B; when the deflection temperature under load was 120°C or higher but lower than 130°C, it was rated as C; when the deflection temperature under load was 100°C or higher but lower than 120°C, it was rated as D; and when the deflection temperature under load was lower than 100°C, it was rated as E. The evaluation results of heat resistance of Examples 1 to 40 and Comparative Examples 1 and 2 are summarized in FIG. 6.

[0095] As is clear from Figure 6, Examples 1 to 40, which are resin compositions obtained by kneading plant fibers, a polyolefin resin, and at least one of a first cyclic compound, a second cyclic compound, a third cyclic compound, and a fourth cyclic compound, are able to suppress corrosion of the mold during injection molding and prevent the generation of isocyanate gas.

[0096] From the results of Examples 9 to 40, it is clear that when polyamine or polyoxazoline is contained, better corrosion resistance can be ensured, since no mold surface contamination was confirmed in the corrosion evaluation when at least 30 test pieces were produced. Furthermore, the evaluations of mold releasability and heat resistance were also rated B or A, so it is clear that better mold releasability and heat resistance can be ensured by containing polyamine or polyoxazoline.

[0097] From the results of Examples 25 to 40, it is clear that when wood flour derived from coniferous trees is used as the plant fiber and polyethyleneimine having a weight-average molecular weight of 10,000 is used as the polyamine, the deflection temperature under load is 140°C or higher in the heat resistance evaluation, and therefore better heat resistance can be ensured.

[0098] In contrast, Comparative Examples 1 and 2, which are resin compositions obtained by kneading plant fibers, a polyolefin resin, and N,N'-dicyclohexylcarbodiimide, a carbodiimide in which a first nitrogen and a second nitrogen are bonded by a bonding group and an unsubstituted aromatic is bonded to each of the first and second nitrogens, fail to suppress the generation of isocyanate gas. Furthermore, in the evaluation of mold releasability, less than 20% of the test specimen's surface was separated from the mold, indicating insufficient mold releasability during injection molding.

[0099] As described above, the resin composition, resin molded article, and method for producing resin pellets of the present invention can suppress corrosion of the mold during injection molding and also suppress the generation of isocyanate gas.

[0100] REFERENCE SIGNS LIST 10 Plant fiber 10A Corrosive gas 11 Polyolefin resin 12 Polyolefin resin blended with plant fiber 20 Cyclic compound 30 Resin composition 31 Resin molded body 32 Resin pellet 40 Twin-screw mixer 41 Molding machine 50 Polyamine

Claims

1. A method for producing a resin composition, comprising the steps of kneading plant fibers, a polyolefin resin, and at least one of a first cyclic compound, a second cyclic compound, a third cyclic compound, and a fourth cyclic compound to obtain a resin composition, wherein the first cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide to which a first nitrogen and a second nitrogen are bonded by a bonding group, and two or more first subcyclic structures condensed to a portion of the main cyclic structure, the second cyclic compound is a cyclic compound having the main cyclic structure and two or more second subcyclic structures extending from the main cyclic structure as substituents, and the third cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure condensed to a portion of the main cyclic structure, and second subcyclic structures extending from each of the first subcyclic structures as substituents, The fourth cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure condensed to a portion of the main cyclic structure, and the second subcyclic structure condensed to a portion of the first subcyclic structure.

2. A method for producing a resin composition according to claim 1, comprising the step of kneading the plant fibers, the polyolefin resin, at least one of the first cyclic compound, the second cyclic compound, the third cyclic compound and the fourth cyclic compound, a polyamine having at least one of a primary amine and a secondary amine, and at least one of a polyoxazoline to obtain a resin composition.

3. A method for producing a resin composition according to claim 1 or 2, wherein the plant fiber is wood flour derived from a coniferous tree.

4. A method for producing a resin molded product, comprising the steps of: kneading plant fibers, a polyolefin resin, and at least one of a first cyclic compound, a second cyclic compound, a third cyclic compound, and a fourth cyclic compound to obtain a resin composition; and molding the resin composition into a component of a device having a heat source having a temperature of 300°C or less, wherein the first cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide to which a first nitrogen and a second nitrogen are bonded by a bonding group, and two or more first subcyclic structures condensed to a portion of the main cyclic structure, the second cyclic compound is a cyclic compound having the main cyclic structure and two or more second subcyclic structures extending from the main cyclic structure as substituents, and the third cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure condensed to a portion of the main cyclic structure, and second subcyclic structures extending from each of the first subcyclic structures as substituents, The fourth cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure condensed to a portion of the main cyclic structure, and the second subcyclic structure condensed to a portion of the first subcyclic structure.

5. The method for producing a resin molded article according to claim 4, wherein the component is a housing or a bracket of a vehicle lamp.

6. A method for producing resin pellets, comprising the steps of kneading plant fibers, a polyolefin resin, and at least one of a first cyclic compound, a second cyclic compound, a third cyclic compound, and a fourth cyclic compound to obtain a resin composition, and molding the resin composition into pellets, wherein the first cyclic compound is a cyclic compound having a main cyclic structure containing a carbodiimide to which a first nitrogen and a second nitrogen are bonded by a bonding group, and two or more first subcyclic structures condensed to a portion of the main cyclic structure, the second cyclic compound is a cyclic compound having the main cyclic structure and two or more second subcyclic structures extending from the main cyclic structure as substituents, and the third cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure condensed to a portion of the main cyclic structure, and second subcyclic structures extending from each of the first subcyclic structures as substituents, The fourth cyclic compound is a cyclic compound having the main cyclic structure, the first subcyclic structure condensed to a portion of the main cyclic structure, and the second subcyclic structure condensed to a portion of the first subcyclic structure.

7. A method for producing resin pellets as described in claim 6, comprising a step of kneading the plant fibers, the polyolefin resin, at least one of the first cyclic compound, the second cyclic compound, the third cyclic compound and the fourth cyclic compound, a polyamine having at least one of a primary amine and a secondary amine, and at least one of a polyoxazoline to obtain a resin composition.

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