Coated composite-resin molded object

Abstract

This coated composite-resin molded object comprises a composite-resin molded object comprising a main-component resin and a fibrous filler and a coating film formed on a surface of the composite-resin molded object. The coating film has a hydrophilic diol structure, and the fibrous filler is exposed on the surface of the composite-resin molded object, the coated composite-resin molded object having an air layer at the boundary between the fibrous filler exposed on the surface of the composite-resin molded object and the composite-resin molded object.

Description

Composite resin molded painted body

[0001] The present disclosure relates to a coated composite resin molded body in which a coating film is applied to the surface of a composite resin molded body, and which can improve adhesion between the composite resin molded body and the coating film.

[0002] So-called "general-purpose plastics," such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), are not only very inexpensive, but also easy to mold and are a fraction of the weight of metals or ceramics. For this reason, general-purpose plastics are often used as materials for a variety of everyday items, such as bags, various types of packaging, various types of containers, and sheets, as well as industrial parts, such as automobile parts and electrical parts, and as materials for daily necessities and miscellaneous goods.

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

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

[0005] Therefore, there is a demand for significant improvements in the material properties (mechanical strength, etc.) of general-purpose plastics. A known technique for strengthening general-purpose plastics is to disperse fibrous fillers such as natural fibers, glass fibers, and carbon fibers in the resin of the general-purpose plastic to improve the mechanical strength of the general-purpose plastic. Another known technique is to disperse particulate fillers such as inorganic powders such as talc and silica, and cellulose-based powders such as pulp powder, waste paper powder, and wood chips in the resin of the general-purpose plastic to improve the mechanical strength of the general-purpose plastic. Among these, organic fibrous fillers such as cellulose are attracting attention as reinforcing fibers because they are inexpensive and environmentally friendly when disposed of.

[0006] When fiber-reinforced resins are used as exterior components for various industrial products, including automobiles and other mechanical products, as well as electrical, electronic, and information products, they are often painted or covered with a film to prevent deterioration due to moisture absorption by the fibers and to smooth out surface irregularities caused by the fibers. To use fiber-reinforced resins as exterior components, strong adhesion is required for the paint or film applied to the fiber-reinforced resin surface.

[0007] Studies are being conducted to improve the appearance of molded articles, and in Patent Document 1, in order to improve appearance, a chlorinated polyolefin resin and a hydroxyl group-containing vinyl copolymer are added to a base coat, and the material and composition of the base coat layer are adjusted to increase adhesion to the molded article.

[0008] Japanese Patent Application Laid-Open No. 2000-518

[0009] However, in Patent Document 1, a base coat is used to improve adhesion to the polyolefin molded body, but the base coat has low rigidity, which reduces the rigidity of the entire molded body including the base coat. Furthermore, applying a base coat increases the number of materials and processes, resulting in increased costs. Furthermore, when painting on resins such as polyolefins, oil-based paints are used to ensure appearance, but water-based paints are preferable from the perspective of VOC emissions. However, applying water-based paints to resins has the problem of poor surface properties due to repellency and other factors.

[0010] The present disclosure aims to solve the above-mentioned conventional problems and to provide a composite resin molded coated body that has high appearance and strong adhesion without a base coat or primer layer, even when a water-based paint is applied to the resin.

[0011] In order to achieve the above-mentioned object, the composite resin molded coated body of the present disclosure is a composite resin molded coated body including a composite resin molded body containing a main resin and a fibrous filler, and a coating film formed on the surface of the composite resin molded body, wherein the coating film has a hydrophilic diol structure, the fibrous filler is exposed on the surface of the composite resin molded body, and an air layer is present at the boundary between the fibrous filler exposed on the surface of the composite resin molded body and the composite resin molded body.

[0012] The coated composite resin molded body according to the present disclosure can achieve high appearance and strong adhesion.

[0013] 1 is a schematic cross-sectional view showing the cross-sectional structure of a composite resin molded, coated body according to embodiment 1. (a) is a schematic cross-sectional view showing the cross-sectional structure of the interface between the coating film of the composite resin molded, coated body according to embodiment 1 and the composite resin molded body, and (b) is a schematic view showing that hardening of the coating film 3 occurs from the interface. (b) is an electron microscope image showing the defibrated state of the end of a fibrous filler according to embodiment 1. (c) is a flow diagram of a method for producing a composite resin composition and a method for producing a composite resin molded, coated body according to embodiment 1. (d) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (e) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (f) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (g) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (h ...i) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (ii) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (iii) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (iv) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (v) is a flow diagram of a method for producing a composite resin composition and a composite resin molded, coated body according to embodiment 1. (vi) is a flow

[0014] The composite resin molded coated body of the first aspect is a composite resin molded coated body comprising a composite resin molded body containing a main resin and a fibrous filler, and a coating film formed on the surface of the composite resin molded body, wherein the coating film has a hydrophilic diol structure, the fibrous filler is exposed on the surface of the composite resin molded body, and an air layer is present at the boundary between the fibrous filler exposed on the surface of the composite resin molded body and the composite resin molded body.

[0015] In the composite resin molded coated body of the second aspect, when the volume of the air layer is defined as the volume recessed from a virtual surface extending from the surface of the composite resin molded body in the first aspect, the volume of the air layer may be 1% or more and 50% or less of the volume of the adjacent fibrous filler.

[0016] The composite resin molded coated body of the third aspect is the above-mentioned first or second aspect, in which the content of the fibrous filler is in the range of 5 to 85 weight %, the fibrous filler has a hydroxyl group, and the adhesion between the fibrous filler and the coating film may be stronger than the adhesion between the surface of the composite resin molded body and the coating film.

[0017] A fourth aspect of the coated composite resin molded article is any one of the first to third aspects, wherein the fibrous filler may be partially exposed from the surface of the composite resin molded article.

[0018] The coated composite resin molded body according to the fifth aspect is any one of the first to fourth aspects, in which the fibrous filler in the composite resin molded body may be defibrated only at the ends of the fibrous filler.

[0019] In a composite resin molded coated body according to a sixth aspect, the fibrous filler may be a fiber made of a natural fiber containing cellulose.

[0020] A seventh aspect of the coated composite resin molded body is any one of the first to sixth aspects, wherein the resin is an olefin resin.

[0021] Hereinafter, a composite resin molded coated body according to an embodiment will be described with reference to the drawings. In the following description, the same components are designated by the same reference numerals and the description will be omitted where appropriate.

[0022] (Embodiment 1) Fig. 1 is a schematic cross-sectional view showing the cross-sectional structure of a composite resin molded coated body 10 according to embodiment 1.

[0023] The coated composite resin molded body 10 according to the first embodiment of the present disclosure includes a composite resin molded body 5 containing a base resin 1 and a fibrous filler 2, and a coating film 3 formed on the surface of the composite resin molded body 5. The composite resin molded body 5, which serves as a substrate, is made of a melt-kneaded mixture containing a base resin, a fibrous filler, and a dispersant. As shown in the schematic cross-sectional view of FIG. 1 , the composite resin molded body has the fibrous filler 2 dispersed in the base resin 1. The coating film 3 has a hydrophilic diol structure. The fibrous filler 2 is exposed on the surface of the composite resin molded body 5, and an air layer 4 is present at the boundary between the fibrous filler 2 exposed on the surface of the composite resin molded body 5 and the composite resin molded body 5. The coating film 3 is formed by an applied coating film.

[0024] This composite resin molded painted body can achieve high appearance and strong adhesion.

[0025] If the volume of the air layer 4 is defined as the volume recessed from an imaginary surface 6, which is an extension of the surface of the composite resin molded body 5, the volume of the air layer 4 may be 1% to 50% of the volume of the adjacent fibrous filler 2. The imaginary surface 6 substantially coincides with the lower surface of the coating film 3. Therefore, the air layer 4 means the space between the recessed surface of the composite resin molded body 5 and the lower surface of the coating film 3.

[0026] The components that make up this composite resin coated molded body 10 will be described below.

[0027] <Composite Resin Molded Article> The composite resin molded article 5 is a molded article of a composite resin composition containing a main resin 1, a fibrous filler 2, and a dispersant as an optional element.

[0028] <Main Resin> In the present embodiment 1, the main resin 1 is preferably a thermoplastic resin to ensure good moldability. Examples of thermoplastic resins include olefin resins (including cyclic olefin resins) such as polyethylene and polypropylene, 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 (2,6-xylenol polymers, etc.), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), lignin resins, modified lignin resins, silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubber or elastomer (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubbers, urethane rubbers, silicone rubbers, etc.), and engineering plastics. The resin may be derived from petroleum, plants, or microorganisms. The resin may also be a recycled resin obtained by reprocessing a resin that has already been molded. Recycling methods include material recycling and chemical recycling. The resins may be used alone or in combination. They may also be decomposable by microorganisms, water, heat, etc. The base resin 1 is not limited to the above materials as long as it has thermoplastic properties.

[0029] Among these thermoplastic resins, the main resin 1 is preferably an olefin-based resin or a polyamide-based resin, which has a relatively low melting point. Olefin-based resins include homopolymers of olefin-based monomers, copolymers of olefin-based monomers, and copolymers of olefin-based monomers with other copolymerizable monomers. Examples of olefin-based monomers 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-based monomers may be used alone or in combination. Of the above olefin-based monomers, linear olefins such as ethylene and propylene are preferred. Other copolymerizable monomers include, for example, 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)acrylate; unsaturated dicarboxylic acids or anhydrides thereof such as maleic acid, fumaric acid, and maleic anhydride; vinyl esters of carboxylic acids (e.g., vinyl acetate and vinyl propionate); cyclic olefins such as norbornene and cyclopentadiene; and dienes such as butadiene and isoprene. These copolymerizable monomers may be used alone or in combination. 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), polypropylene, ethylene-propylene copolymers, and terpolymers such as ethylene-propylene-butene-1. Examples of polyamide resins, which are polymers formed by bonding a large number of monomers together through amide bonds, include nylon (polyamide) 6, nylon 11, nylon 12, nylon 66, nylon 610, nylon 612, nylon 1010, nylon 1012, and nylon 6T.

[0030] <Additives> Next, additives will be described. The composite resin molded body in the first embodiment may contain additives for purposes such as improving the adhesion between the fibrous filler 2 and the base resin 1 or the dispersibility of the fibrous filler 2 in the base resin 1. Examples of additives include various titanate-based coupling agents, silane coupling agents, unsaturated carboxylic acids, modified polyolefins grafted with maleic acid, maleic anhydride, or their anhydrides, fatty acids, fatty acid metal salts, and fatty acid esters. The silane coupling agents are preferably unsaturated hydrocarbon-based or epoxy-based. The surface of the additive may be modified by treating it with a thermosetting or thermoplastic polymer component. The additive in the present embodiment is preferably a polymer grafted with a hydrophilic group such as maleic anhydride, as described above. It is even more preferable that the additive polymer be a resin with the same molecular structure as the base resin 1. The additive is appropriately selected depending on the combination of the base resin 1 and the fibrous filler 2, and may not be added if the combination does not require an additive.

[0031] <Fibrous Filler> Next, the fibrous filler 2 will be described. Fibrous fillers also include particulate fillers that have approximately the same diameter and fiber length. The particulate filler is basically made of the same material as the fibrous filler 2, and differs only in filler length and aspect ratio. Therefore, the following description will describe the fibrous filler 2 in detail. The fibrous filler 2 (hereinafter sometimes simply referred to as "fiber") contained in the composite resin molding of this embodiment is used primarily for the purposes of improving mechanical properties and improving dimensional stability by reducing the linear expansion coefficient in resin moldings molded using the composite resin molding. For this purpose, the fibrous filler 2 preferably has a higher elastic modulus than the base resin 1. Specific examples include carbon fiber, carbon nanotubes, pulp, cellulose, cellulose nanofiber, lignocellulose, lignocellulose nanofiber, basic magnesium sulfate fiber (magnesium oxysulfate fiber), potassium titanate fiber, aluminum borate fiber, calcium silicate fiber, calcium carbonate fiber, silicon carbide fiber, wollastonite, xonotlite, various metal fibers, natural fibers such as cotton, silk, wool, and hemp, recycled fibers such as jute fiber, rayon, and cupra, semi-synthetic fibers such as acetate and promix, synthetic fibers such as polyester, polyacrylonitrile, polyamide, aramid, and polyolefin, and modified fibers chemically modified on the surface and ends of these fibers. Needle-shaped fillers are also acceptable, and include wood flour and bark from cedar, cypress, bamboo, reed, and the like, as well as powders of coffee, barley, tea leaves, and the like. Furthermore, among these, carbons and celluloses are particularly preferred from the viewpoints of availability, high elastic modulus, and environmental friendliness. Furthermore, from the viewpoint of a recycling-oriented society, natural fibers such as celluloses and wood flour, natural materials, and waste materials obtained from them are preferred.

[0032] The shapes of fibrous fillers and particulate fillers will be described. In the case of natural fibers and natural materials, the starting materials for the fibrous fillers and particulate fillers are the same, and the particulate fillers are formed into particles by being finely ground. The symbol L represents the length of the fibrous filler or particulate filler (hereinafter sometimes referred to as "fiber length"), and the symbol d represents the width of the fibrous filler or particulate filler (hereinafter sometimes referred to as "fiber diameter"). For fibrous fillers and particulate fillers, the more fibers with a large aspect ratio (L / d), i.e., the more fibrous filler, the higher the elastic modulus. The aspect ratio of the fibrous filler is preferably 10 or more. However, if there are many fibers with a large aspect ratio, the fibers become more entangled, resulting in poor flowability and moldability. On the other hand, if there are many fibers with a small aspect ratio, i.e., if there are many particulate fillers, the flowability is improved, there are fewer fiber aggregates, and the appearance is also good. The aspect ratio of the particulate filler is preferably 2 or less. However, if there are many fibers with a small aspect ratio, the elastic modulus decreases. The aspect ratio (L / d) is calculated using the fiber length L excluding the defibrated portion at the end.

[0033] From the viewpoint of mechanical properties, a large number of bonding interfaces between the fiber and the resin leads to an improvement in the modulus of elasticity, so a high specific surface area of ​​the fiber, i.e., a small fiber diameter d, is preferable. Figure 3 is an electron microscope image showing the defibrated state of the end of a fibrous filler. To achieve the two objectives of a small aspect ratio and a large specific surface area, it is most preferable that at least one end, preferably both ends, in the fiber length direction within a single fiber are partially defibrated, as shown in Figure 3.

[0034] From the viewpoint of appearance, it is also preferable to include fibrous fillers having a structure in which the ends in the fiber length direction are partially defibrated within a single fiber, as shown in Figure 3. By defibrating only the ends and by using faster cooling conditions than usual during injection molding of the composite resin molded body, the defibrated end parts of the fibrous filler are more likely to enter the molded body, and the central undefibrated part of the fibrous filler is more likely to be exposed, and this structure increases the wettability of the paint during painting.

[0035] Figure 2(a) is a schematic cross-sectional view showing the cross-sectional structure of the interface between the paint film 3 and the composite resin molded body 5 of the composite resin molded painted body 10 of embodiment 1, and (b) is a schematic view showing that hardening of the paint film 3 occurs from the interface.

[0036] The resin shrinks slightly, and as shown in Figure 2(a), an air layer 4 can be formed at the boundary between the fibrous filler 2 exposed on the surface of the composite resin molded body and the composite resin molded body 5. In the case of a coating film that undergoes a curing reaction due to oxygen or the like, shrinkage typically occurs when the coating film 3 dries after application. This shrinkage near the interface causes the bond between the coating film 3 and the composite resin molded body 5 serving as the substrate to separate, resulting in a deterioration in adhesive strength. In contrast, in the composite resin molded body 10 according to embodiment 1, the presence of the air layer 4 at the interface between the coating film 3 and the composite resin molded body 5 as described above allows the coating film to harden from the interface, as shown in Figure 2(b), with hardened portions 7a and 7b spreading inward from the interface. This makes it less likely for shrinkage to occur near the interface, preventing the bond between the coating film 3 and the composite resin molded body 5 serving as the substrate from separating, preventing a deterioration in adhesive strength, and improving appearance.

[0037] Furthermore, when the shrinkage rate of the base resin 1 is high, the fibers hardly shrink, resulting in a large volume of the air layer 4. The air layer 4 can also be enlarged by foam molding the composite resin molded body 5, which serves as the base material. However, a large air layer can result in uneven coating, such as voids in the coating film. The air layer is defined as the area recessed from the surface of the composite resin molded body, and the volume of the air layer per area is preferably 1% to 50% of the volume of the adjacent fibrous filler. Furthermore, to expose the fibrous filler on the surface, the weight concentration of the fibrous filler is preferably 5% by weight or more. Because excessively high concentrations generate heat during molding, a weight concentration of 85% by weight or less is preferred from the viewpoint of molding, and more preferably 15% to 70% by weight.

[0038] As described above, the exposed central undefibrated portion of the fibrous filler improves the appearance of the coating film that accompanies the curing reaction, but because the fibrous filler contains hydroxyl groups, the adhesion between the fibrous filler and the coating film is stronger than the adhesion between the surface of the composite resin molding and the coating film, which makes it even more difficult for the bond points to come loose, prevents deterioration of the adhesive strength, and improves the appearance.

[0039] Next, the characteristics of the fibrous filler 2 will be described. The types of the base resin 1 and the fibrous filler 2 are as described above. However, if the fibrous filler 2 is too soft relative to the base resin 1, i.e., has a low elastic modulus, the composite resin composition will have a low overall elastic modulus, resulting in reduced strength. On the other hand, if the fibrous filler 2 is too hard relative to the base resin 1, i.e., has a high elastic modulus, shock waves generated upon impact will not propagate but will be absorbed at the interface between the base resin 1 and the fibrous filler 2, making cracks and crazes more likely to occur near the interface, resulting in reduced impact strength. Therefore, in the relationship between the elastic moduli of the base resin 1 and the fibrous filler 2, it is preferable that the elastic modulus of the fibrous filler 2 be higher, and that the difference between them be as small as possible. The optimal relationship is calculated from simulation results, and it is preferable that the difference in elastic modulus between the base resin 1 and the fibrous filler 2 be within 20 GPa.

[0040] These fibrous fillers 2 are almost all hydrophilic, except for petroleum-derived artificial fibers. In particular, the above-mentioned cellulose fibers have many hydroxyl groups in their molecules and are hydrophilic. When these hydrophilic fillers are combined with resin, they are generally hydrophobized because the resin is hydrophobic. However, in order to improve the appearance, it is preferable not to hydrophobize them in advance. By not hydrophobizing them in advance, the hydrophilic groups of the fibers are more likely to remain, and the presence of these fibers near the surface of the molded article improves the appearance.

[0041] As described above, these fibrous fillers 2 may be partially surface-treated with various titanate coupling agents, silane coupling agents, unsaturated carboxylic acids, maleic acid, maleic anhydride, or modified polyolefins grafted with maleic anhydride, fatty acids, fatty acid metal salts, fatty acid esters, etc., for the purpose of improving adhesion to the base resin 1 or dispersibility in the composite resin composition. Alternatively, they may be partially surface-treated with a thermosetting or thermoplastic polymer component. The above treatment methods allow for control of the exposed portions of the fibers. By pre-surface-treating the fiber surface, only the outer surface of the fiber is rendered hydrophobic. Although the fibers are defibrated in the composite resin, the inside of the defibrated fibers remains hydrophilic. Therefore, in the final molded product, the defibrated ends of the fibers in the molded product are more hydrophilic, and the defibrated ends are exposed on the surface of the molded product. On the other hand, if the fibers are not hydrophobized in advance and a compatibilizer such as maleic anhydride is added to the resin and kneaded, the resin with hydrophilic groups will enter the defibrated portion, and the defibrated end portions will blend with the resin in the same way as the center portion, and the center portion can be exposed by accelerating the cooling during molding. In this disclosure, it has been confirmed that exposing the center portion of the fiber makes it easier to create an air layer, so a method of adding a compatibilizer to the resin without hydrophobizing the fibers in advance was adopted.

[0042] Furthermore, by using fibers that have not been pre-hydrophobized, the amount of hydroxyl groups present on the surface of the molded body is greater than that of the base resin. This results in a lower contact angle of the molded body with the paint used for painting than with a base resin that does not contain fibers, making it easier for the paint to penetrate. By inducing a curing reaction from the penetrated area, the bond points are more resistant to separation, adhesion strength is not impaired, and appearance is improved.

[0043] <Paint film> As shown in Fig. 1 , the paint film 3 is provided on the surface of the composite resin molded body 5, and together with the composite resin molded body 5, constitutes a composite resin molded coated body 10. The paint film 3 is formed by paint applied to the surface of the composite resin molded body 5.

[0044] The following describes the paint used to form the coating film on the surface of the composite resin molded product. For example, paints with a diol structure, such as lacquer, urethane, or thinner-solvent urethane, are preferred. Furthermore, the viscosity range of the paint is preferably 0.01 to 1000 Pa·s. The coating method used was a common method, such as a comma coater, dip coater, die coater, or applicator.

[0045] <Method for manufacturing a composite resin molded, coated body> Next, a method for manufacturing a composite resin molded, coated body will be described. Fig. 4 is a flow diagram of the method for manufacturing a composite resin composition and the method for manufacturing a composite resin molded, coated body according to the first embodiment.

[0046] (1) First, a base resin, a fibrous filler, and, if necessary, additives are placed in a melt-kneading processing device and melt-kneaded within the device. This melts the base resin, and the fibrous filler and additives are dispersed into the molten base resin. At the same time, the shearing action of the device promotes defibration of agglomerates of the fibrous filler, allowing the fibrous filler to be finely dispersed within the base resin.

[0047] Conventionally, fibrous fillers have been used in which the fibers have been defibrated in advance through pretreatment such as wet dispersion. However, when fibrous fillers are defibrated in advance in the solvent used in wet dispersion, they are more easily defibrated than when defibrated in a molten base resin, making it difficult to defibrate only the ends, and the entire fibrous filler ends up in a defibrated state. In addition, adding pretreatment increases the number of processes, which reduces productivity, which is an issue.

[0048] In contrast, in the method for producing a composite resin composition according to the first embodiment, a pretreatment by wet dispersion for the purpose of defibrating or modifying the fibrous filler is not performed, and instead, the fibrous filler is melt-kneaded together with a base resin, a dispersant, etc. (all-dry method). In this method, by not performing a wet dispersion treatment of the fibrous filler, it is possible to partially defibrate only the ends of the fibrous filler as described above, and the number of steps is reduced, thereby improving productivity.

[0049] To produce the fiber of the present invention by an all-dry method, it is preferable to apply high shear stress during kneading, and specific kneading methods include a single-screw kneader, a twin-screw kneader, a roll kneader, a Banbury mixer, etc. From the viewpoint of easy application of high shear and high mass productivity, a continuous twin-screw kneader and a continuous roll kneader are particularly preferable. Kneading methods other than those mentioned above may also be used as long as they are capable of applying high shear stress.

[0050] (2) The composite resin composition extruded from the melt kneading device is cut into pellets using a pelletizer or the like. Pelletization methods include in-air hot cutting, underwater hot cutting, and strand cutting, which are carried out immediately after the resin is melted, as well as crushing and cutting methods in which a molded body or sheet is formed first.

[0051] (3) Next, the pellets are injection molded to produce an injection-molded article as a composite resin molding. As described above, by cooling at a rate faster than usual during injection molding, the central undefibrated portion of the fibrous filler becomes more easily exposed, thereby making it possible to obtain an injection-molded article with improved appearance and adhesion to a paint film.

[0052] Hereinafter, examples and comparative examples of the experiments conducted by the inventors will be described.

[0053] Example 1 A pulp-dispersed polypropylene composite resin coated molded body was produced by the following production method.

[0054] Polypropylene (manufactured by Prime Polymer Co., Ltd., product name: J108M) as the base resin, cotton-like softwood pulp (manufactured by Mitsubishi Paper Mills, product name: NBKP Celgar) as the fibrous filler, and maleic anhydride (manufactured by Sanyo Chemical Industries, Ltd., product name: Umex) as the dispersant were weighed out in a weight ratio of 42:55:3 and dry-blended. The mixture was then melt-kneaded and dispersed in a twin-screw kneader (KRC Kneader, manufactured by Kurimoto Iron Works Co., Ltd.). The shear force can be changed by changing the screw configuration and shape of the twin-screw kneader; in Example 1, a medium shear type was used. The molten resin was hot-cut to produce pulp-dispersed polypropylene pellets.

[0055] The pulp-dispersed polypropylene pellets were used to prepare composite resin molded specimens using an injection molding machine (180AD, manufactured by Japan Steel Works, Ltd.). The specimen preparation conditions were a resin temperature of 190°C, a mold temperature of 20°C, an injection speed of 90 mm / s, and a holding pressure of 100 MPa. The mold temperature was lower than usual to increase the cooling rate. The pellets were fed into the molding machine's screw via a hopper. The penetration rate during this process was measured by the amount of pellet loss per hour, which was confirmed to be consistent. The specimen shape was varied depending on the evaluation items described below. Size 1 dumbbells were prepared for elastic modulus measurements, and 60 mm square, 1.2 mm thick flat plates were prepared for appearance testing. The resulting pulp-dispersed polypropylene composite resin molded specimens were evaluated using the following methods.

[0056] (Presence or absence of fiber exposure, exposure ratio, and in-plane uniformity of exposed portion) The obtained pulp-dispersed polypropylene composite resin molding was observed by X-ray CT to check the form of fibers exposed on the surface and the air layers present near the fibers. The recessed areas on the surface of the composite resin molding were defined as air layer areas, and the volume of the air layer per area observed by X-ray CT was found to be approximately 20 to 40% of the volume of the adjacent fibers.

[0057] (Length ratio of defibrated fiber portion) The obtained composite resin molding was immersed in xylene solvent to dissolve the polypropylene, and the shape of the remaining pulp fibers was observed using an SEM. Defibrated portions were observed at the ends in the fiber length direction, and the defibrated portions accounted for approximately 20 to 30% of the total fiber length.

[0058] X-ray CT measurement was carried out on the composite resin molding, which revealed the distribution of fibers in the depth direction. Measurement of several representative fibers revealed that there were exposed fiber areas on the surface, with many exposed fibers in the center.

[0059] (Elastic Modulus of Composite Resin Molded Article) A tensile test was carried out using the obtained No. 1 dumbbell-shaped test piece.

[0060] The modulus of elasticity of the test piece was 3.5 GPa.

[0061] (Coating of Coating Film) The fiber composite resin molded body obtained as described above was used as a substrate, and its surface was coated. For the coating, lacquer was used, which is an environmentally friendly water-based solvent, contains a diol structure with two or more hydroxyl groups, such as urushiol or laccol, and hardens in the presence of oxygen in the air. Furthermore, lacquer is 100% plant-derived and environmentally friendly.

[0062] (Paint Adhesion and Appearance) The composite resin molded article obtained was painted, and the paint adhesion was evaluated by a cross-cut peel test (JIS K 5600).

[0063] The resulting coated composite resin molded article was free from peeling.

[0064] The appearance was also judged visually: a uniform surface was rated as ◎, a surface with slight irregularities of several tens of microns due to partial fiber exposure, etc. was rated as ○, a surface with irregularities of several millimeters or more due to air layer depressions, etc. was rated as ×, and intermediate irregularities of several hundred microns were rated as △.

[0065] The coated composite resin molded article obtained in Example 1 had a uniform surface and was evaluated as excellent.

[0066] In Example 2, the paint was changed from lacquer to urethane, and the other material conditions and process conditions were the same as in Example 1 to produce pulp-dispersed polypropylene pellets and a composite resin-molded coated body. Evaluations were also performed in the same manner as in Example 1.

[0067] In Example 3, the concentration of the fibrous filler was changed to 70% by weight, and the other material conditions and process conditions were the same as in Example 1 to produce pulp-dispersed polypropylene pellets and a composite resin molded coated body. Evaluations similar to those in Example 1 were also carried out.

[0068] In Example 4, the concentration of the fibrous filler was changed to 15% by weight, and the other material conditions and process conditions were the same as in Example 1 to produce pulp-dispersed polypropylene pellets and a composite resin molded coated body. Evaluations similar to those in Example 1 were also carried out.

[0069] In Example 5, the base resin was changed from polypropylene to biopolyethylene (BioPE_SHA7260 manufactured by Braskem), and the other material and process conditions were the same as in Example 1 to produce pulp-dispersed resin pellets and a composite resin molded coated body. Evaluations similar to those in Example 1 were also carried out.

[0070] In Example 6, the base resin was changed from polypropylene to polyamide (UBE NYLON 1013B manufactured by Ube Industries, Ltd.), and the other material conditions and process conditions were the same as in Example 1 to produce pulp-dispersed resin pellets and a composite resin molded coated body. Evaluations similar to those in Example 1 were also carried out.

[0071] In Example 7, pulp-dispersed polypropylene pellets and a composite resin molding were prepared under the same material and process conditions as in Example 1. After that, a small amount of the resin on the surface was removed by etching with a solvent to increase the volume of the air layer in the composite resin molding, and then painting was carried out.

[0072] In Comparative Example 1, pulp-dispersed polypropylene pellets and a molded body were produced under the same material and process conditions as in Example 1. The surface of the composite resin molded body was then mirror-polished to remove air gaps, and then painted. Evaluations similar to those in Example 1 were also carried out.

[0073] Comparative Example 2 In Example 8, a urethane polymer was used as the paint, which did not undergo a curing reaction, but instead underwent only a drying reaction of the solvent NMP (N-methyl-2-pyrrolidone), and coating was carried out. Evaluations were also carried out in the same manner as in Example 1.

[0074] In Example 8, pulp-dispersed polypropylene pellets and a composite resin molding were prepared under the same material and process conditions as in Example 2, and coating was performed using thinner as the solvent for the urethane coating. Evaluations were also performed in the same manner as in Example 1.

[0075] In Example 9, the conveying screw was changed to one that was almost free from shear stress, and the other material conditions and process conditions were the same as in Example 1 to produce pulp-dispersed polypropylene pellets and a composite resin molded coated body. Evaluations similar to those in Example 1 were also carried out.

[0076] FIG. 5 is Table 1 showing the measurement results for Examples 1 to 9 and Comparative Examples 1 and 2.

[0077] As is clear from Table 1 in Figure 5, in Example 2, in which the paint was changed to urethane, the elastic modulus was slightly lower, but due to the water solvent, air curing, and diol structure, the results were almost the same as in Example 1. In Example 3, in which the filler concentration was increased to 70 wt%, the resin viscosity increased during kneading, resulting in more defibrated areas, a decrease in the amount of fiber exposed on the surface, and a slight deterioration in appearance. Conversely, in Example 4, in which the filler concentration was reduced to 15%, the viscosity of the resin during kneading decreased, resulting in fewer defibrated areas and a slight decrease in the volume of the air layer. As a result, the adhesion of the paint film was slightly worsened and the appearance also deteriorated. In Examples 5 and 6, in which the resin type was changed, the elastic modulus of the molded body changed slightly due to the change in resin type, but otherwise the results were almost the same as in Example 1. In Examples 2 to 6, similar to Example 1, there were no problems with the modulus of elasticity and appearance, and it was confirmed that paint adhesion and appearance could be improved if the following conditions were met: filler concentration of 15 to 70% by weight, proportion of defibrated areas of 5 to 50%, fibers were exposed on the surface of the molded body, the volume of the air layer near the exposed fibers was in the range of 50% or less of the fiber volume, the base resin was a thermoplastic resin, and the paint was a water-based paint with a diol structure.

[0078] In Example 7, in which the volume of the air layer in the molded body was increased before painting, the paint became uneven due to the depressions in the air layer, resulting in poor surface properties and somewhat poor appearance.

[0079] In Comparative Example 1, where painting was carried out after the air layer volume was reduced to 1% or less, the paint contracted in the in-plane direction when hardening, causing peeling at the adhesion points of the paint film and resulting in poor paint adhesion. As a result, approximately 50% peeling was observed in the adhesion evaluation using a cross-cut peeling test, resulting in poor appearance.

[0080] In Comparative Example 2, where a polymer paint was used as the paint, there was no curing reaction and the paint did not have a diol structure that is compatible with cellulose, so the paint adhesion was poor, the paint contracted in the in-plane direction when cured, and the adhesion points of the paint film peeled off, resulting in poor paint adhesion.As a result, in an adhesion evaluation using a cross-cut test, about 50% peeled off, resulting in poor appearance.

[0081] In Example 8, where paint was applied using thinner as the solvent, not only was it unfriendly to the environment, but the solvent was incompatible with cellulose, causing problems such as repellency during painting, resulting in somewhat poor appearance. The repellency also resulted in poor paint adhesion.

[0082] In Example 9, in which the conveying screw was changed to one that was not subject to shear and the fibers were not defibrated much in the molten resin, the length ratio of the defibrated portion was 0 to 4%. This resulted in a low specific surface area of ​​the fibers in the molded body and a reduced elastic modulus of 2.7 GPa. In addition, the entire fiber was exposed to the surface, which repelled paint during painting, resulting in somewhat poor appearance.

[0083] From the above evaluation, it was found that by producing a composite resin molded body using a resin material in which only the ends of the fibers are defibrated, the fibers are exposed on the surface, there is an air layer near the fibers, and a high elastic modulus can be achieved. Furthermore, it was found that by using a paint that involves a curing reaction, uses water as a solvent, and has a diol structure, it is possible to provide a composite resin molded coated body that has good adhesion, good appearance, and a high elastic modulus without using a primer layer.

[0084] The coated composite resin molded article according to the present disclosure can provide a molded article with superior mechanical strength compared to conventional general-purpose resins. The coated composite resin molded article according to the present disclosure can improve the properties of the base resin, and can therefore be used as a substitute for engineering plastics or metal materials. This can significantly reduce the manufacturing costs of various industrial products or household items made of engineering plastics or metals. Furthermore, it can be used in everyday items, home appliance housings, building materials, and automotive components.

[0085] REFERENCE SIGNS LIST 1 base resin 2 fibrous filler 3 coating film 4 air space 5 composite resin molded body 6 virtual surface (interface) (underside of coating film) 7a, 7b hardened portion 10 composite resin molded coated body

Claims

1. A composite resin molded coated body comprising: a composite resin molded body containing a base resin and a fibrous filler; and a coating film formed on the surface of the composite resin molded body, wherein the coating film has a hydrophilic diol structure, the fibrous filler is exposed on the surface of the composite resin molded body, and an air layer is present at the boundary between the composite resin molded body and the fibrous filler exposed on the surface of the composite resin molded body.

2. A composite resin molded coated body as described in claim 1, wherein, when the volume of the air layer is defined as the volume recessed from a virtual surface extending from the surface of the composite resin molded body, the volume of the air layer is 1% or more and 50% or less of the volume of the adjacent fibrous filler.

3. A composite resin molded coated body as described in claim 1, wherein the content of the fibrous filler in the composite resin molded body is in the range of 5 to 85 weight percent, the fibrous filler has a hydroxyl group, and the adhesion between the fibrous filler and the paint film is stronger than the adhesion between the surface of the composite resin molded body and the paint film.

4. A composite resin molded coated body as described in claim 1, wherein the fibrous filler is partially exposed from the surface of the composite resin molded body.

5. A composite resin molded coated body as described in claim 1, wherein the fibrous filler in the composite resin molded body is defibrated only at the ends of the fibrous filler.

6. The composite resin molded coated body according to claim 1, wherein the fibrous filler is a fiber made of natural fibers such as cellulose.

7. The composite resin molded coated body according to claim 1, wherein the base resin is an olefin resin.

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