Cellulose-based resin molded product and its manufacturing method, and injection molding die

Abstract

To provide a molded product which is obtained by injection molding using a composite resin material containing cellulose particles in the resin material, and which has improved appearance and surface texture.SOLUTION: A molded product is an injection-molded product of a resin material containing cellulose-based particles, the molded product has an uneven shape on a surface, a pitch of the uneven shape is in a range from an average particle size of the cellulose-based particles to 5 times or less of the average particle size, and a depth of the uneven shape is in a range from 0.3 times or more of the average particle size to 3 times or less of the average particle size of the cellulose-based particles.SELECTED DRAWING: Figure 2-A

Description

[Technical field]

[0001] The present disclosure relates to a molded article produced by injection molding a resin material containing a cellulose-based filler and a method for producing the same. The present disclosure also relates to an injection molding die for injection molding a resin material containing a cellulose-based filler. [Background technology]

[0002] Conventionally, molded products produced by injection molding of resin materials have been widely used for automobile parts, home appliance parts, and other daily necessities because of the high degree of freedom in the shape of the parts that can be obtained.

[0003] Among the materials used as fillers dispersed in resin materials, cellulose particles, a type of natural fiber, are highly available and can be produced from wood, etc., which is expected to reduce costs. They also have the advantage of being easy to dispose of after disposal and suitable for recycling, resulting in a small environmental impact.

[0004] When using cellulose-based particles as a filler, in order to obtain sufficient strength, it is necessary to carry out a defibration process in which the fibers are finely untangled from raw materials such as wood pulp, and a dispersion process in a resin material. In this dispersion process, there is a problem that the cellulose-based particles have hydrophilic groups and are therefore difficult to disperse in hydrophobic resin materials.

[0005] Therefore, in Patent Document 1, it is said that the cellulose-based particles can be well dispersed by blending a specific dispersant into the resin material and the cellulose-based particles. The dispersant contains a dispersant having a hydroxyl value of 30 mgKOH / g or more, and preferably has a concentration of 2 to 10 mass %. With this configuration, it is said that the cellulose-based particles are well dispersed in the resin material, and a molded product can be obtained. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-87199 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the conventional molded articles have a problem in that when the surface of the molded article is smoothed, the area on the exterior surface through which the cellulose particles are visible is reduced, resulting in a poor appearance and texture.

[0008] The present disclosure is devised to solve the above-mentioned problems of the conventional art, and aims to provide a molded product having an improved appearance surface texture, which is obtained by injection molding a composite resin material containing cellulose-based particles as a resin material. [Means for solving the problem]

[0009] In order to achieve the above-mentioned objective, the molded article of the present disclosure is a molded article made of an injection-molded resin material containing cellulose-based particles, and the molded article has an uneven surface, the pitch of the uneven surface is equal to or greater than the average particle diameter of the cellulose-based particles and equal to or less than 5 times the average particle diameter, and the depth of the uneven surface is equal to or greater than 0.3 times the average particle diameter and equal to or less than 3 times the average particle diameter. Effect of the Invention

[0010] As described above, according to the molded article of the present disclosure, the cellulose-based particles remain on the exterior surface, making it possible to improve the texture of the exterior surface of the molded article, as compared to the case of the conventional molded article. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a state in which cellulose-based particles are distributed in a resin material in a partial cross-section of a molded product of Reference Example 1. [Figure 2-A] FIG. 2 is a schematic cross-sectional view showing a partial cross-section of the molded article according to the first embodiment, in which cellulose-based particles are distributed in a resin material along the uneven surface shape. [Figure 2-B] FIG. 2 is a schematic cross-sectional view showing a state in which cellulose-based particles cannot be distributed along the uneven surface shape when the pitch of the uneven surface shape on a molded article is less than the average particle size of the cellulose-based particles. [Diagram 3] 11 is a schematic cross-sectional view of a partial cross section of a molded product according to embodiment 2, showing a state in which an angle θ1 of the bottom of the protrusions on the front side in the flow direction of the uneven surface shape is larger than an angle θ2 of the bottom of the rear side. [Figure 4] 1 is a schematic cross-sectional view of a part of a molded product according to Reference Example 2, showing a state in which the angle θ1 of the bottom of the protrusions on the front side in the flow direction of the uneven surface shape is smaller than the angle θ2 of the bottom of the rear side. [Diagram 5] 10 is a partial cross-sectional view of a first modified example of a molded product according to a second embodiment, showing that the surface of the uneven shape has a second finer uneven shape. FIG. [Figure 6] 10 is a schematic cross-sectional view showing an example of a method for forming a second concave-convex shape on the surface of a die for injection molding by electric discharge machining. FIG. [Figure 7] 1 is a schematic cross-sectional view showing the cross-sectional structures of cellulose particles having aspect ratios (ratio of particle diameter:particle length) of 1 and 3 used in Modification 2 of the molded article according to Embodiment 2. FIG. [Figure 8A] FIG. 8 is a schematic cross-sectional view showing the state of resistance in the flow direction when cellulose particles having different aspect ratios of FIG. 7 are used in Modification 2 of the molded article according to Embodiment 2. [Figure 8B] FIG. 11 is a schematic cross-sectional view showing a state in which a cellulose-based particle is caught on a convex portion of the uneven shape in Variation 2 of the molded article according to Embodiment 2. [Figure 9a] 11 is a schematic cross-sectional view showing a step of clamping a mold cavity and a mold core of an injection mold in a manufacturing method for a molded product according to embodiment 2. FIG. [Figure 9b] FIG. 11 is a schematic cross-sectional view showing a step of injecting a resin material containing cellulose-based particles into a cavity in a manufacturing method for a molded product according to a second embodiment. [Figure 9c]10 is a schematic cross-sectional view showing a step of opening the mold cavity and the mold core to remove the molded article in the manufacturing method of the molded article according to the second embodiment. FIG. [Figure 10] 1 is an example of a photograph showing the appearance of the obtained molded product. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The molded article of the first embodiment is a molded article made of an injection-molded resin material containing cellulose-based particles, and the molded article has an uneven surface, the pitch of the uneven surface is in the range of not less than the average particle diameter of the cellulose-based particles and not more than 5 times the average particle diameter, and the depth of the uneven surface is not less than 0.3 times the average particle diameter of the cellulose-based particles and not more than 3 times the average particle diameter.

[0013] The molded article according to the second aspect is the molded article according to the first aspect above, wherein the curvature of the curve of the convex parts of the uneven shape on the surface of the molded article is equal to or greater than the radius of the average particle size of the cellulose particles and is equal to or less than twice the radius of the average particle size, and the curve of the convex parts of the uneven shape may have a wavy shape that follows the shape of the cellulose particles.

[0014] The molded product of the third aspect is the molded product of the first or second aspect above, wherein the uneven shape of the surface of the molded product may be such that, in a cross section including the flow direction of the resin material during injection molding and the normal direction to the surface, the angle between the front edge of the convex parts of the uneven shape in the flow direction and the flow direction is larger than the angle between the rear edge of the convex parts in the flow direction and the flow direction.

[0015] The molded article according to a fourth aspect may be any one of the first to third aspects, in which the aspect ratio of the particle length to the particle diameter (particle length:particle diameter) of the cellulose-based particles is 1:1 to 5:1.

[0016] A molded article according to a fifth aspect is any one of the first to fourth aspects, wherein the cellulose-based particles are at least one selected from the group consisting of bamboo, cypress, and wood flour.

[0017] The molded article according to the sixth aspect is any one of the first to fifth aspects above, wherein the molded article has a second fine uneven surface having a pitch shorter than the pitch of the uneven surface and a depth shallower than the depth of the uneven surface.

[0018] The injection molding die of the seventh aspect is an injection molding die used for injection molding using a resin material containing cellulose-based particles, and the surface that comes into contact with the resin material containing cellulose-based particles before hardening and is transferred to the surface of a molded product made of the hardened resin material has an uneven shape, the pitch of the uneven shape is in the range of not less than the average particle size of the cellulose-based particles and not more than 5 times the average particle size, and the depth of the uneven shape is not less than 0.3 times the average particle size of the cellulose-based particles and not more than 3 times the average particle size.

[0019] The injection molding die of the eighth aspect is the same as that of the seventh aspect, and the uneven shape may be such that, in a cross section including the flow direction of the resin material during injection molding and the normal direction to the surface, the angle between the front edge of the concave part of the uneven shape in the flow direction and the flow direction is larger than the angle between the rear edge of the concave part in the flow direction and the flow direction.

[0020] The injection molding die according to a ninth aspect is the injection molding die according to the seventh or eighth aspect above, and may have a fine second concave-convex shape on the surface having a pitch shorter than the pitch of the concave-convex shape and a depth shallower than the depth.

[0021] The method for producing a molded body according to the tenth aspect includes the steps of clamping the mold cavity and mold core of an injection molding mold according to any one of the seventh to ninth aspects, injecting a resin material containing cellulose-based particles into a cavity defined between the mold cavity and the mold core while the mold cavity and the mold core are clamped, and opening the mold cavity and the mold core after the resin material has hardened, and removing the molded product.

[0022] Hereinafter, a molded article and a manufacturing method thereof according to an embodiment of the present disclosure, an injection mold used for injection molding of the molded article and a manufacturing method thereof will be described with reference to the drawings. Note that the present disclosure is not limited to the embodiment.

[0023] (Embodiment 1) <Molded products> FIG. 1 is a schematic cross-sectional view showing a state in which cellulose particles 2 are distributed in a resin material 3 in a partial cross-section of a molded article 50 of Reference Example 1. FIG. 2-A is a conceptual diagram showing that cellulose particles 2 are distributed in a resin material 3 along a surface irregularity 11 in a partial cross-section of a molded article 1 according to embodiment 1. FIG. 2-B is a schematic cross-sectional view showing a state in which cellulose particles cannot be distributed along the surface irregularity when the pitch of the surface irregularity of a molded article is less than the average particle size of the cellulose particles. Note that each figure is a conceptual diagram, and the size of the cellulose particles 2 may differ from the actual scale.

[0024] The molded article 1 according to the first embodiment is made of an injection-molded product of a resin material 3 containing cellulose-based particles 2. The molded article 1 has an uneven surface 11. The pitch 12 of the uneven surface 11 is in a range of not less than the average particle diameter of the cellulose-based particles 2 and not more than twice the average particle diameter. The depth 13 of the uneven surface 11 is not less than the average particle diameter of the cellulose-based particles 2 and not more than 1.5 times the average particle diameter.

[0025] The molded product 50 of Reference Example 1 shown in Figure 1 has a smooth appearance, and only a portion of the cellulose-based particles dispersed as a filler in the resin material 3 is visible on the exterior surface, so the texture provided by the cellulose-based particles is not fully obtained. On the other hand, in the molded product 1 according to the embodiment 1 shown in FIG. 2-A, when the uneven shape 11 on the external surface is compared with the shape of the cellulose-based particle 2, the pitch 12 of the uneven shape 11 is in a range of not less than the average particle diameter of the cellulose-based particle 2 but not more than 5 times the average particle diameter. The pitch 12 of the uneven shape 11 is preferably in a range of not less than the average particle diameter but not more than 3 times the average particle diameter. More preferably, the pitch 12 is in a range of not less than the average particle diameter but not more than 2 times the average particle diameter. The depth 13 of the uneven shape 11 is not less than 0.3 times the average particle diameter of the cellulose-based particle 2 but not more than 3 times the average particle diameter. The depth 13 of the uneven shape 11 is preferably not less than 0.5 times the average particle diameter but not more than 2 times the average particle diameter. More preferably, the pitch 12 is not less than the average particle diameter but not more than 1.5 times the average particle diameter. Since the uneven shape 11 on the surface and the shape of the cellulose-based particle 2 are similar in this way, the range visible on the external surface of the cellulose-based particle 2 is wider than that shown in FIG. 1. As a result, the area in which the cellulose particles 2 are visible on the exterior surface of the molded article 1 is increased compared to the molded article of Reference Example 1, and it is believed that the texture (material feel) of the exterior surface is improved.

[0026] It is desirable that the size relationship between the uneven shape 11 of the molded article 1 and the cellulose-based particles 2 exactly match, but this is difficult in manufacturing. Thus, the pitch 12 of the uneven shape 11 on the surface of the molded article 1 is equal to or greater than the average particle size of the cellulose-based particles 2 and equal to or less than twice the average particle size, and the depth is equal to or greater than the average particle size and equal to or less than 1.5 times the average particle size. The curvature of the uneven shape 11 of the molded article 1 is preferably equal to or greater than the radius of the average particle size of the cellulose-based particles 2 and equal to or less than twice the radius of the average particle size, and is preferably a wavy shape that follows the shape of the cellulose-based particles 2. If the pitch 12 of the uneven shape 11 is outside the above range, the area where the cellulose-based particles 2 are visible on the external surface will decrease, as shown in FIG. 2-B, for example, and the texture (feel of material) of the external surface will be deteriorated.

[0027] The components constituting this molded article 1 will be described below.

[0028] <Cellulose-based particles> The size of the cellulose-based particles 2 is an average particle size represented by D50 in particle size distribution measurement of about 300 μm, and the particle size distribution is, for example, 100 to 500 μm. The amount of the cellulose-based particles added is preferably 15 to 70% by weight out of 100% by weight of the total of the resin material and the cellulose-based particles.

[0029] The cellulose-based particles 2 include, for example, pulp, cellulose, cellulose nanofiber, lignocellulose, lignocellulose nanofiber, bamboo, cypress, wood flour, and other plant-derived grains and particles, and may also be used in combination with fibers.

[0030] <Resin materials> Moreover, the resin material 3 is preferably a thermoplastic resin in order to ensure good moldability. Examples of the thermoplastic resin include olefin resins (including cyclic olefin resins), styrene resins, (meth)acrylic resins, organic acid vinyl ester resins or derivatives thereof, vinyl ether resins, halogen-containing resins, polycarbonate resins, polyester resins, polyamide resins, thermoplastic polyurethane resins, polysulfone resins (polyethersulfone, polysulfone, etc.), polyphenylene ether resins (polymers of 2,6-xylenol, etc.), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubber or elastomers (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubbers, urethane rubbers, silicone rubbers, etc.). The above resins can be used alone or in combination of two or more kinds. The resin material 3 is not limited to the above materials as long as it has thermoplasticity. Among these thermoplastic resins, an olefin-based resin having a relatively low melting point is preferable as the resin material 3. Olefin-based resins include homopolymers of olefin-based monomers, copolymers of olefin-based monomers, and copolymers of olefin-based monomers and other copolymerizable monomers.

[0031] Examples of the olefin monomer include linear olefins (α-C2-20 olefins such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 4-methyl-1-pentene, and 1-octene), and cyclic olefins. These olefin monomers can be used alone or in combination of two or more. Among the above olefin monomers, linear olefins such as ethylene and propylene are preferred.

[0032] Examples of other copolymerizable monomers include fatty acid vinyl esters such as vinyl acetate and vinyl propionate; (meth)acrylic monomers such as (meth)acrylic acid, alkyl (meth)acrylates, and glycidyl (meth)acrylates; unsaturated dicarboxylic acids or anhydrides thereof such as maleic acid, fumaric acid, and maleic anhydride; vinyl esters of carboxylic acids (e.g., vinyl acetate, vinyl propionate, etc.); cyclic olefins such as norbornene and cyclopentadiene; and dienes such as butadiene and isoprene. These copolymerizable monomers can be used alone or in combination of two or more.

[0033] Specific examples of olefin resins include copolymers of linear olefins (particularly α-C2-4 olefins) such as polyethylene (low density, medium density, high density, or linear low density polyethylene, etc.), polypropylene, ethylene-propylene copolymers, and terpolymers such as ethylene-propylene-butene-1.

[0034] <Injection mold> Next, an injection mold used for injection molding using a resin material containing cellulose-based particles according to the first embodiment will be described. This injection mold has a surface that comes into contact with the resin material containing cellulose-based particles before hardening and is transferred to the surface of a molded product made of the hardened resin material, and has an uneven shape. The pitch of the uneven shape is in the range of not less than the average particle diameter of the cellulose-based particles but not more than twice the average particle diameter, and the depth of the uneven shape is not less than the average particle diameter of the cellulose-based particles but not more than 1.5 times the average particle diameter.

[0035] By having the above-mentioned uneven shape on the surface of the injection molding die, the uneven shape corresponding to the above-mentioned uneven shape is transferred to the surface of the molded article to be injection molded. As a result of the transfer, the concaves in the injection molding die become convex parts in the molded article. The pitch 12 of the uneven shape 11 is in a range of not less than the average particle diameter of the cellulose-based particles 2 but not more than twice the average particle diameter. In addition, the depth 13 of the uneven shape 11 is not less than the average particle diameter of the cellulose-based particles 2 but not more than 1.5 times the average particle diameter. Since the uneven shape 11 on the surface and the shape of the cellulose-based particles 2 are similar in this way, the range in which the cellulose-based particles 2 are visible on the external surface is wider than that in FIG. 1. As a result, it is considered that the range in which the cellulose-based particles 2 are visible on the external surface of the molded article 1 is greater than that in the case of the molded article of the reference example, and the texture (feel of material) of the external surface is improved.

[0036] <Manufacturing method for injection mold> The injection mold is manufactured as follows. (1) The size of the cellulose particles 2 to be used in injection molding is measured in advance using a particle size distribution meter. The median value of D50 in the obtained particle size distribution is regarded as the average particle size of the cellulose particles. (2) A CAD system is used to create an uneven shape including a corrugated shape of the mold surface that conforms to the shape of the cellulose-based particles 2 within the above-described range. Based on this CAD data, a design drawing of the mold surface, including the uneven shape, is created. The structure and parting of the mold are determined, and once the design drawing is complete, programming required for processing is performed. Once the design drawing and programming are complete, the mold is manufactured according to the following procedure. (3) The first step in manufacturing a mold is rough machining. Rough machining involves drilling large holes or making cuts in the block of metal to remove distortion. Rough machining is also performed at the same time. Rough machining is the process of removing unnecessary parts of the metal to reduce the load during finish machining. Specifically, this refers to the process of cutting the metal to a size slightly larger than the finishing dimensions or drilling holes slightly smaller than the finishing dimensions. (4) After rough cutting, machining is performed. Machining refers to the process of cutting out the outline of the mold using a machine tool (machining center). It can handle simple machining as well as complex machining. Although machining centers can handle complex machining, they cannot perform all types of machining. (5) After machining, we perform machining of the fine details that cannot be handled by a machining center. Specifically, we perform electrical discharge machining and wire cutting. Electric discharge machining is the process of machining edges and threads using an electrical discharge machine that can perform high-voltage discharges. Wire cutting is the process of machining ejector pin holes, core pin holes, etc. using wire and electrical energy. Through these processes, we machine the fine details of the mold. (6) Once the shape of the mold is complete, finishing processing is carried out. Once the polishing work is complete, the parts are gathered and the mold is assembled to obtain the injection molding mold. In this injection molding die, the surface that comes into contact with the resin material containing the cellulose-based particles before curing and is transferred to the surface of a molded article made of the cured resin material has an uneven shape. The pitch of the uneven shape is in the range of not less than the average particle size of the cellulose-based particles and not more than twice the average particle size, and the depth of the uneven shape is not less than the average particle size of the cellulose-based particles and not more than 1.5 times the average particle size.

[0037] <Method of manufacturing molded products> Next, a method for producing the molded product 1 according to the first embodiment will be described. The molded article 1 according to the first embodiment can be manufactured by the following steps. (1) The mold cavity and the mold core of the injection molding mold are clamped together. The injection molding mold has an uneven surface, and the uneven surface has the above-mentioned numerical range. (2) With the mold cavity and the mold core clamped together, a resin material containing cellulose-based particles is injected into the cavity defined between the mold cavity and the mold core. (3) After the resin material has hardened, the mold cavity and the mold core are opened and the molded product is removed. This makes it possible to obtain a molded product having an uneven surface.

[0038] (Embodiment 2) FIG. 3 is a schematic cross-sectional view of a portion of a molded product 1a according to embodiment 2, showing a state in which an angle θ1 of the front side of the bottom of the protrusions of the uneven surface shape 11 in the flow direction is larger than an angle θ2 of the rear side of the bottom. In FIG. 3, the molded product 1a is formed of a resin material 3 in which cellulose-based particles 2 are distributed, and the surface of the molded product 1 has an uneven shape 11. In this molded product, an angle θ1 of the front side of the convex part of the uneven shape is different from an angle θ2 of the rear side of the convex part with respect to the flow direction of the resin material 3, and the angle θ1 of the front side of the convex part is larger than the angle θ2 of the rear side of the convex part. This makes it easier for the cellulose-based particles 2 to be caught on the convex part as the resin material 3 flows. The angle of the bottom of the convex part of the uneven shape is, for example, 30° to 45° for the bottom angle θ2 on the rear side (inlet side) of the flow direction corresponding to the inlet side, and 60° to 90° for the bottom angle θ1 on the front side of the flow direction corresponding to the outlet side. This makes it easier for the cellulose-based particles to be caught in the flow direction.

[0039] (Reference example 2) FIG. 4 is a schematic cross-sectional view of a part of a molded product 50a according to Reference Example 2, showing a state in which an angle θ1 of the front side of the protrusions of the uneven surface in the flow direction is smaller than an angle θ2 of the rear side of the protrusions. In Fig. 4, a molded article 50a is formed of a resin material 3 in which cellulose-based particles 2 are distributed, and the surface of the molded article 50a has an uneven shape. In the molded article according to Reference Example 2, the angle θ1 of the bottom of the protrusions on the front side in the flow direction is smaller than the angle θ2 of the bottom of the rear side. Therefore, compared to the case of Fig. 3, the cellulose-based particles 2 are less likely to get caught on the protrusions in the flow direction.

[0040] (Variation 1) FIG. 5 is a partial cross-sectional view of modified example 1b of molded product according to embodiment 2, showing that surface unevenness 11 has a second fine unevenness 21 on its surface. As shown in Fig. 5, the molded article 1b is formed of a resin material 3 having cellulose-based particles 2 distributed therein, and has a finer second uneven shape (Ra 10 µm to 50 µm) 21 on the surface of the uneven shape 11 of the molded article 1b. The second uneven shape has, for example, a pitch shorter than the pitch of the uneven shape and a depth shallower than the depth. The fine second uneven shape 21 added to the surface in this way increases the surface area, thereby quickly cooling the skin layer of the resin material that comes into contact with the surface of the injection mold during injection molding, and can play a role in fixing the cellulose-based particles 2 dispersed in the resin material. It is desirable to take care so that the fine unevenness in FIG. 5 does not result in an undercut shape.

[0041] Regarding the resin material 3, in order to prevent carbonization and deterioration of the cellulose-based particles 2, among the resin materials 3 described above, polypropylene (PP), polyethylene (PE), acrylonitrile styrene (AS), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC), polyacetal (POM), and acrylic (PMMA), which have a melting point of 220°C or less, are preferable.

[0042] The second fine uneven shape can be provided on the surface of a molded product in addition to the uneven shape by, for example, injection molding using an injection molding die having a second uneven shape that can be transferred to the surface. The second uneven shape on the surface of the injection molding die can be provided on the surface of the injection molding die by, for example, electric discharge machining as shown in FIG.

[0043] (Variation 2) Fig. 7 is a schematic cross-sectional view showing the cross-sectional structure of cellulose particles having aspect ratios (ratio of particle length to particle diameter) of 1 and 3 used in Modification 2 of the molded article according to Embodiment 2. Fig. 8A is a schematic cross-sectional view showing the state of resistance in the flow direction when cellulose particles having different aspect ratios of Fig. 7 are used in Modification 2 of the molded article according to Embodiment 2. Fig. 8B is a schematic cross-sectional view showing a state in which the cellulose particles are caught on convex portions of the uneven shape in Modification 2 of the molded article according to Embodiment 2. As shown in Fig. 7, the aspect ratio of the cellulose-based particles 2 (which may be expressed as the ratio of particle length:particle diameter, the numerical value of the ratio, or "particle length:particle diameter") may be changed. The aspect ratio may be in the range of 1:1 to 3:1. If the aspect ratio is 3 or more, it becomes difficult for the cellulose-based particles 2 to match the uneven shape of the external surface, and the amount of cellulose-based particles 2 visible on the outside may decrease, resulting in a deterioration in the external texture. On the other hand, the cellulose-based particle has an elliptical shape with a large aspect ratio, and thus has less resistance in the flow direction, and when the cellulose-based particle gets caught on a convex portion of the uneven shape, it experiences less resistance than when the aspect ratio is 1, and the cellulose-based particle 2 is less likely to escape from the uneven shape, as shown in Figures 8A and 8B. Therefore, the aspect ratio of the cellulose-based particle is more preferably 1.5 to 3.

[0044] <Method of manufacturing molded products> Next, a method for producing a molded product according to the second embodiment will be described with reference to Figs. 9a to 9c. (1) A mold cavity 101 having an uneven surface 104 is clamped to a mold core 102 (FIG. 9a). By clamping the mold cavity 101 to the mold core 102, a sprue 103 for injecting resin is formed. (2) With the mold cavity 101 and the mold core 102 clamped together, molten cellulose-based filler composite resin 105 is injected from a sprue 103 into the cavity defined between the mold cavity 101 and the mold core 102 (FIG. 9b). The cavity is completely filled with the molten resin, and an injection-molded body is obtained. (3) The mold cavity 101 and the mold core 102 are opened, and the runner 106 and the molded product 107 are removed in a separated state (FIG. 9c). In this manner, a molded product having a concave-convex shape transferred to its surface can be obtained. During molding by this injection molding, the molding may be performed while controlling the temperature by providing a heater or a temperature control circuit in the mold cavity and / or the mold core for controlling the mold temperature.

[0045] (Example) FIG. 10 is an example of a photograph showing the appearance of the obtained molded product. The resin molded part 5 is a resin molded part with a smooth surface obtained using a smooth-surface injection mold. The surface roughness Ra of this resin molded part 5 is 1 to 5 μm. In the resin molded part 5, the cellulose particles as the filler are only partially visible on the exterior surface, and a sufficient texture cannot be obtained. Resin molded part 6 is a resin molded part having an uneven surface according to this embodiment, obtained using an injection molding die having an uneven surface. With this resin molded part 6, the area in which cellulose particles 2 are visible on the exterior surface of molded article 1 is increased compared to resin molded part 5, improving the texture (feel of material) of the exterior surface. [Industrial Applicability]

[0046] The molded article according to the present disclosure has cellulose particles as a filler, and the uneven surface shape keeps the cellulose particles on the surface, which makes it possible to improve the texture (material feel) of the external surface. Therefore, it is useful as a structural molded article for automobile parts, home appliance parts, and other daily necessities. In addition, the uneven surface shape of the injection molding die according to the present disclosure makes it possible to easily manufacture molded articles having the above characteristics. [Explanation of symbols]

[0047] 1, 1a, 1b Molded products 2. Cellulosic particles 3. Resin materials 4 Double-sided tape 5. Resin molded parts 6 Plastic molding parts 11 Uneven shape 12 Pitch 13 Depth d 21 Second uneven shape 50, 50a molded product 101 Mold Cavity 102 Mold Core 103 sprue 104 Uneven shape 105 Cellulosic filler composite resin 106 Runner 107 Molded products

Claims

1. A molded article made of an injection-molded body of a resin material containing cellulose-based particles, the molded article has an uneven surface, and the pitch of the uneven surface is equal to or greater than the average particle diameter of the cellulose-based particles and is equal to or less than 5 times the average particle diameter; a depth of the uneven shape is 0.3 times or more and 3 times or less of the average particle size of the cellulose-based particles; Molded products.

2. 2. The molded product according to claim 1, wherein the curvature of the curve of the convex portion of the uneven shape on the surface of the molded product is equal to or greater than the radius of the average particle diameter of the cellulose-based particles and is equal to or less than twice the radius of the average particle diameter, and the curve of the convex portion of the uneven shape has a wavy shape that follows the shape of the cellulose-based particles.

3. 2. The molded product according to claim 1, wherein the uneven shape of the surface of the molded product is such that, in a cross section including the flow direction of the resin material during injection molding and the normal direction to the surface, the angle between the front edge of the convex portion of the uneven shape in the flow direction and the flow direction is greater than the angle between the rear edge of the convex portion in the flow direction and the flow direction.

4. The molded article according to claim 1, wherein the aspect ratio of the particle length to the particle diameter (particle length:particle diameter) of the cellulose-based particles is 1:1 to 5:

1.

5. The molded article according to claim 1 , wherein the cellulose-based particles are at least one selected from the group consisting of bamboo, cypress, and wood flour.

6. The molded product according to claim 1 , wherein the molded product has a second minute uneven shape on the surface, the second minute uneven shape having a pitch shorter than the pitch of the uneven shape and a depth shallower than the depth of the uneven shape.

7. An injection molding die used for injection molding using a resin material containing cellulose-based particles, the surface which comes into contact with the resin material containing cellulose-based particles before hardening and which is transferred to a surface of a molded article constituted by the hardened resin material has an uneven shape, the pitch of the uneven shape being in a range of not less than an average particle diameter of the cellulose-based particles and not more than 5 times the average particle diameter, a depth of the uneven shape is 0.3 times or more and 3 times or less than the average particle size of the cellulose-based particles.

8. 8. The injection molding die according to claim 7, wherein in a cross section including the flow direction of the resin material during injection molding and the normal direction to the surface, an angle between a front edge of a concave portion of the uneven shape in the flow direction and the flow direction is larger than an angle between a rear edge of the concave portion in the flow direction and the flow direction.

9. The injection mold according to claim 7 , wherein the injection mold has a second minute uneven shape on a surface thereof, the second minute uneven shape having a pitch shorter than the pitch of the uneven shape and a depth shallower than the depth of the uneven shape.

10. clamping a mold cavity and a mold core of the injection mold according to any one of claims 7 to 9; a step of injecting a resin material containing cellulose-based particles into a cavity defined between the mold cavity and the mold core while the mold cavity and the mold core are clamped together; After the resin material has hardened, opening the mold cavity and the mold core to remove the molded product; A method for producing a molded article, comprising:

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