Composite resin molded coated body

Abstract

The composite resin molded and coated body comprises 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, the coating film having a hydrophilic diol structure, and the fibrous filler being exposed out of the surface of the composite resin molded body. And an air layer is provided at the boundary between the composite resin molded body and the fibrous filler that exposes the surface of the composite resin molded body.

Description

Technical Field

[0001] This disclosure relates to a composite resin molded coated body obtained by coating a coating film onto the surface of a composite resin molded body, and to a composite resin molded coated body that can improve the adhesion between the composite resin molded body and the coating film. Background Technology

[0002] Polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), among other so-called "general-purpose plastics," are not only very inexpensive but also easy to mold. Compared to metals or ceramics, they are lightweight, weighing only a fraction of their weight. Therefore, general-purpose plastics are widely used as materials for a wide variety of everyday products, such as bags, various packaging materials, containers, and sheets. Furthermore, they are fully utilized as materials for industrial components, including automotive and electrical parts, as well as for daily necessities and general merchandise.

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

[0004] On the other hand, so-called "engineering plastics," such as polycarbonate, fluoropolymers, and acrylic resins, possess excellent mechanical properties and are used in automotive and other mechanical products, as well as various industrial products, primarily electrical / electronic / information products. However, engineering plastics suffer from drawbacks such as high cost, difficulty in monomer recycling, and significant environmental impact.

[0005] Therefore, it is desirable to significantly improve the material properties (mechanical strength, etc.) of general-purpose plastics. For the purpose of reinforcing general-purpose plastics, the following techniques are known: dispersing natural fibers, glass fibers, carbon fibers, etc., as fibrous fillers into the resin of a general-purpose plastic to improve its mechanical strength. Furthermore, techniques are also known to improve the mechanical strength of a general-purpose plastic by dispersing inorganic powders such as talc and silica, pulp powders, waste paper powders, and cellulose-based powders such as wood chips, as particulate fillers, into the resin of a 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 using fiber-reinforced resins as exterior components for automotive and other mechanical products, as well as various industrial products, primarily electrical / electronic / information products, coatings and film bonding are sometimes applied to prevent deterioration caused by fiber moisture absorption and to achieve a uniform surface finish, addressing any unevenness caused by the fibers. For effective use of fiber-reinforced resins as exterior components, strong adhesion is required for coatings and films applied to the resin surface.

[0007] Research is being conducted to improve the appearance of the molded body. In Patent Document 1, chlorinated polyolefin resin and hydroxyl-containing vinyl copolymer are added to the primer to improve the appearance, and the material and composition of the primer layer are adjusted to improve the adhesion to the molded body.

[0008] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2000-518 Summary of the Invention

[0009] However, in Patent Document 1, a primer is used to improve adhesion to the polyolefin molded body. However, due to the primer's weak rigidity, the overall rigidity of the molded body containing the primer is reduced. Furthermore, applying a primer increases the amount of material, the number of processes, and costs. Additionally, while oil-based coatings are used to ensure appearance when coating resins such as polyolefins, water-based coatings are preferred from a VOC emission perspective. However, applying water-based coatings to resins can lead to poor surface properties due to repulsion.

[0010] This disclosure addresses the aforementioned problems and aims to provide a composite resin molded coating that exhibits high appearance and strong adhesion even when water-based coatings are applied to resin without a primer or undercoat.

[0011] To achieve the above objectives, the composite resin molded coating of this disclosure includes a composite resin molded body containing a main resin and fibrous filler, and a coating film formed on the surface of the composite resin molded body. 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 formed 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 composite resin molded coating disclosed herein can achieve high appearance and strong adhesion. Attached Figure Description

[0013] Figure 1 This is a schematic cross-sectional view showing the cross-sectional structure of the composite resin molded coating body according to Embodiment 1.

[0014] Figure 2 (a) is a schematic cross-sectional view showing the interface structure between the coating film and the composite resin molded coating of Embodiment 1. Figure 2 (b) is a schematic diagram showing the curing of the coating film 3 occurring from the interface.

[0015] Figure 3This is an electron microscope image showing the defiberized state of the end of the fibrous filler of Embodiment 1.

[0016] Figure 4 This is a flowchart of the method for manufacturing the composite resin composition according to Embodiment 1 and the method for manufacturing the composite resin molded coating.

[0017] Figure 5 Table 1 shows the measurement results of each of Examples 1 to 6 and each of Comparative Examples 1 to 5. Detailed Implementation

[0018] The first type of composite resin molded coating includes a composite resin molded body containing a main resin and fibrous filler, and a coating film formed on the surface of the composite resin molded body. 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.

[0019] The composite resin molded coating body of the second method can be, in the first method described above, when the volume of the imaginary surface recess obtained by extending the surface of the composite resin molded body is used as the volume of the air layer, the volume of the air layer is more than 1% and less than 50% of the volume of the adjacent fibrous filler.

[0020] The composite resin molded coating body of the third method may be, in the first or second method above, wherein the content of fibrous filler is in the range of 5 to 85% by weight, the fibrous filler has hydroxyl groups, and the adhesion between the fibrous filler and the coating film is stronger than the adhesion between the surface of the composite resin molded body and the coating film.

[0021] The fourth type of composite resin molded coating body may be in any of the first to third types described above, where fibrous filler is partially exposed from the surface of the composite resin mold body.

[0022] The fifth type of composite resin molded coating body can be in any of the first to fourth types above, wherein only the ends of the fibrous filler in the composite resin molded body are defibered.

[0023] The composite resin molded coating of the sixth method may be wherein the aforementioned fibrous filler is a fiber formed from natural fibers containing cellulose.

[0024] The composite resin molded coating of the seventh method may be an olefin resin, in any of the methods 1 to 6 above.

[0025] Hereinafter, the composite resin molded coating body according to the embodiment will be described with reference to the accompanying drawings. It should be noted that in the following description, the same reference numerals are used for the same components, and descriptions are omitted where appropriate.

[0026] (Implementation Method 1)

[0027] Figure 1 This is a schematic cross-sectional view showing the cross-sectional structure of the composite resin molded coating body 10 according to Embodiment 1.

[0028] The composite resin molded coating body 10 of Embodiment 1 of this disclosure includes a composite resin molded body 5 containing a main 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, as a substrate, is formed from a melt-mixed compound containing a main resin, a fibrous filler, and a dispersant. The composite resin molded body is as follows... Figure 1 As shown in the schematic cross-sectional view, fibrous filler 2 is dispersed in the main resin 1. The coating film 3 has a hydrophilic diol structure. Furthermore, 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 the applied coating film.

[0029] The composite resin molded coating can achieve high appearance and strong adhesion.

[0030] When the volume of the recessed portion of the imaginary surface 6 obtained by extending the surface of the composite resin molded body 5 is taken as the volume of the air layer 4, the volume of the air layer 4 can be more than 1% and less than 50% of the volume of the adjacent fibrous filler 2. It should be noted that the imaginary surface 6 is substantially consistent with the lower surface of the coating film 3. Therefore, the air layer 4 refers to the space between the recessed surface of the composite resin molded body 5 and the lower surface of the coating film 3.

[0031] The components constituting the composite resin molded coating body 10 will be described below.

[0032] <Composite Resin Molded Body>

[0033] 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.

[0034] <Main Agent Resin>

[0035] In this embodiment 1, to ensure good formability, the main resin 1 is preferably a thermoplastic resin. Examples of thermoplastic resins include, for instance, olefin resins such as polyethylene and polypropylene (including cyclic olefin resins), styrene resins, (meth)acrylic resins, vinyl ester resins or their derivatives, 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.), lignin resins, modified lignin resins, silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubbers or elastomers (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubber, polyurethane rubber, silicone rubber, etc.), and engineering plastics. These resins can be derived from petroleum, plants, or microorganisms. Furthermore, the aforementioned resin can be a recycled resin obtained by reprocessing previously molded resin. Recycling methods include material recycling, chemical recycling, etc. The aforementioned resin can be used alone or in combination of two or more. Additionally, it can possess decomposability based on microorganisms, water, heat, etc. It should be noted that the main resin 1 only needs to be thermoplastic and is not limited to the aforementioned materials.

[0036] Among these thermoplastic resins, the main resin 1 is preferably an olefin resin or a polyamide resin with a lower melting point. As an olefin resin, in addition to homopolymers of olefin monomers, it also includes copolymers of olefin monomers and copolymers of olefin monomers with other comonomers. Examples of olefin monomers include chain olefins (such as α-C2-20 olefins like 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 aforementioned olefin monomers, chain olefins such as ethylene and propylene are preferred. Other comonomers include, for example, vinyl acetate, vinyl propionate, and other vinyl esters of fatty acids; (meth)acrylic acid, (meth)acrylate, glycidyl methacrylate, and other (meth)acrylic acid monomers; maleic acid, fumaric acid, maleic anhydride, and other unsaturated dicarboxylic acids or their anhydrides; vinyl esters of carboxylic acids (e.g., vinyl acetate, vinyl propionate); cyclic olefins such as norbornene and cyclopentadiene; and dienes such as butadiene and isoprene. These comonomers can be used alone or in combination of two or more. Specific examples of olefin-based resins include copolymers of chain olefins (especially 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. Polyamide resins, which are polymers formed by combining multiple monomers using amide bonds, include Nylon (polyamide) 6, Nylon 11, Nylon 12, Nylon 66, Nylon 610, Nylon 612, Nylon 1010, Nylon 1012, and Nylon 6T.

[0037] <Additives>

[0038] Next, the additives will be explained. The composite resin molded body in Embodiment 1 may contain additives to improve the adhesion between the fibrous filler 2 and the main resin 1, or the dispersibility of the fibrous filler 2 in the main resin 1. Examples of additives include various titanate coupling agents, silane coupling agents, unsaturated carboxylic acids, maleic acid, maleic anhydride, or modified polyolefins grafted with their anhydrides, fatty acids, fatty acid metal salts, fatty acid esters, etc. The silane coupling agents are preferably unsaturated hydrocarbon or epoxy-based substances. It is also acceptable to modify the surface of the additives by treating them with thermosetting or thermoplastic polymer components. As described above, the additives in this embodiment are preferably polymers grafted with hydrophilic groups such as maleic anhydride, and the polymers of the additives are further preferably resins having the same molecular structure as the main resin 1. The additives are appropriately selected based on the combination of the main resin 1 and the fibrous filler 2; in cases where no additive is required, no additives may be added.

[0039] <Fibrous packing>

[0040] Next, the fibrous filler 2 will be described. Fibrous fillers also include particulate fillers with essentially the same diameter and fiber length. The particulate fillers are essentially the same material as the fibrous filler 2, differing only in filler length and aspect ratio. Therefore, the fibrous filler 2 will be described in detail below. The fibrous filler 2 (hereinafter sometimes simply referred to as "fiber") included in the composite resin molded body of this embodiment is used primarily for improving mechanical properties and reducing the coefficient of linear expansion, thereby improving dimensional stability, in resin molded bodies formed using the composite resin molded body. For this purpose, the fibrous filler 2 preferably has a higher elastic modulus than the main resin 1. Specifically, examples include carbon fiber, carbon nanotubes, pulp, cellulose, cellulose nanofibers, lignocellulose, lignocellulose nanofibers, basic magnesium sulfate fiber (magnesium oxysulfate fiber), potassium titanate fiber, aluminum borate fiber, calcium silicate fiber, calcium carbonate fiber, silicon carbide fiber, wollastonite, hard calcium silicate, various metal fibers, natural fibers such as cotton, silk, wool or hemp, jute fiber, regenerated fibers such as rayon or cuprammonium fiber, acetate, semi-synthetic fibers such as Promix, synthetic fibers such as polyester, polyacrylonitrile, polyamide, aramid, polyolefin, etc., and modified fibers obtained by further chemically modifying their surfaces and ends. It may not be fibrous but needle-like, and may be powder from wood flour, bark, coffee, wheat, tea, etc., obtained from cedar, cypress, bamboo, reeds, etc. Furthermore, among these, carbon-based and cellulose-based materials are particularly preferred from the perspectives of availability, high modulus of elasticity, and environmental friendliness. Moreover, from the perspective of a circular society, cellulose-based materials, natural fibers such as wood flour, natural materials, and the waste generated from them are preferred.

[0041] The shapes of fibrous and particulate fillers are described. When using natural fibers or natural materials, the starting materials for both fibrous and particulate fillers are the same; the particulate filler is formed by further pulverizing. The symbol L represents the length of the fibrous or particulate filler (hereinafter sometimes referred to as "fiber length"), and the symbol d represents the width of the fibrous or particulate filler (hereinafter sometimes referred to as "fiber diameter"). Regarding fibrous and particulate fillers, a higher aspect ratio (L / d) with more fibers, i.e., more fibrous filler, results in a higher elastic modulus. The aspect ratio for fibrous fillers is preferably 10 or more. However, a higher aspect ratio with more fibers leads to more fiber entanglement, resulting in poorer flowability and formability. On the other hand, a lower aspect ratio with more fibers, i.e., more particulate filler, results in better flowability, fewer fiber aggregates, and better appearance. The aspect ratio for particulate fillers is preferably 2 or less. However, a lower aspect ratio with more fibers results in a lower elastic modulus. It should be noted that the above aspect ratio (L / d) is calculated using the fiber length L after deducting the unwinding portion at the end.

[0042] From the perspective of mechanical properties, since a larger number of interfaces between fibers and resins will lead to an increase in elastic modulus, it is preferable to have fibers with a high specific surface area, i.e., a small fiber diameter d. Figure 3 This is an electron microscope image showing the defibrilated state of the ends of the fibrous filler. To achieve both a low aspect ratio and a large specific surface area, the optimal choice is as follows... Figure 3 The structure shown is a defiber structure that occurs locally at at least one end, preferably two ends, along the length of a single fiber.

[0043] From an aesthetic point of view, it is also preferable to include, for example Figure 3 The diagram shows a fibrous filler with a structure in which defibering occurs locally at the end of a single fiber along its length. By defibering only at the ends and by advancing the cooling conditions during injection molding of the composite resin molded body compared to normal, the defibered portion at the ends of the fibrous filler can easily enter the molded body, while the undefibered portion in the center of the fibrous filler becomes easily exposed. This structure increases the wettability of the coating during application.

[0044] Figure 2 (a) is a schematic cross-sectional view showing the interface structure between the coating film 3 and the composite resin molded body 5 of the composite resin molded coating body 10 according to Embodiment 1. Figure 2 (b) is a schematic diagram showing the curing of the coating film 3 occurring from the interface.

[0045] The resin shrinks slightly, such as Figure 2As shown in (a), an air layer 4 can be present at the boundary between the fibrous filler 2 and the composite resin molded body 5, where the surface of the composite resin molded body is exposed. In the case of a coating film that undergoes a curing reaction due to oxygen, shrinkage usually occurs during drying after coating. Due to shrinkage near the interface, the bonding point between the coating film 3 and the composite resin molded body 5, which serves as the substrate, detaches, resulting in poor adhesion. On the other hand, in the composite resin molded coating body 10 of Embodiment 1, by having an air layer 4 at the interface between the coating film 3 and the composite resin molded body 5 as described above, thus... Figure 2 As shown in (b), curing is performed from the interface of the coating film. The cured portions 7a and 7b expand inward from the interface, so shrinkage near the interface is less likely to occur. The bonding point between the coating film 3 and the composite resin molded body 5 as the substrate will not fall off, the adhesion will not deteriorate, and the appearance will be improved.

[0046] Furthermore, regarding the air layer 4, since the shrinkage rate of the main resin 1 is high while the fibers hardly shrink, the volume of the air layer 4 increases. Additionally, the air layer 4 can also be increased by foaming the composite resin molded body 5, which serves as the substrate. However, a large air layer can create voids in the coating film, leading to uneven coating. As a definition of the air layer, the area recessed from the surface of the composite resin molded body is considered the air layer area. Preferably, the volume of the air layer in one area is 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. Excessive concentration will generate heat during molding; therefore, from a molding perspective, 85% by weight or less is preferred, and more preferably 15% by weight or more and 70% by weight or less.

[0047] As described above, the exposed central undisintegrated portion of the fibrous filler improves the appearance of the coating film accompanying the curing reaction. Furthermore, the presence of hydroxyl groups in the fibrous filler enhances the adhesion between the fibrous filler and the coating film compared to the adhesion between the surface of the composite resin molded body and the coating film, making the bonding points less prone to detachment, maintaining adhesion strength, and improving appearance.

[0048] Next, the characteristics of the fibrous filler 2 will be explained. Regarding the types of the main resin 1 and the fibrous filler 2, as described above, if the fibrous filler 2 is too soft relative to the main resin 1, i.e., has a low elastic modulus, the overall elastic modulus of the composite resin composition decreases, resulting in reduced strength. On the other hand, if the fibrous filler 2 is too hard relative to the main resin 1, i.e., has a high elastic modulus, the shock wave generated during impact cannot propagate and is absorbed at the interface between the main resin 1 and the fibrous filler 2. Therefore, it becomes easier for cracks and streaks to form near this interface, resulting in reduced impact resistance. Therefore, the relationship between the elastic moduli of the main resin 1 and the fibrous filler 2 is preferably such that the elastic modulus of the fibrous filler 2 is higher and the difference is as small as possible. Regarding the optimal relationship, calculations based on simulation results show that the difference in elastic modulus between the main resin 1 and the fibrous filler 2 is preferably within 20 GPa.

[0049] These fibrous fillers 2, except for petroleum-derived artificial fibers, are almost entirely hydrophilic. In particular, the aforementioned cellulose fibers have a large number of hydroxyl groups within their molecules, making them hydrophilic. When these hydrophilic fillers are compounded with resin, the resin is generally hydrophobic, and therefore the fillers are typically hydrophobized. However, for the purpose of improving appearance, it is preferable not to pre-hydrophobize them. By not pre-hydrophobizing, the hydrophilic groups of the fibers are more likely to remain, and the presence of these fibers near the surface of the molded body improves the appearance.

[0050] As described above, these fibrous fillers 2, for purposes such as improving adhesion to the main resin 1 or dispersibility in the composite resin composition, can be materials that have undergone partial surface treatment using various titanate coupling agents, silane coupling agents, unsaturated carboxylic acids, maleic acid, maleic anhydride, or modified polyolefins grafted with their anhydrides, fatty acids, fatty acid metal salts, fatty acid esters, etc. Alternatively, materials that have undergone partial surface treatment using thermosetting or thermoplastic polymer components are also acceptable. Through the above treatment method, the exposed portion of the fibers can be controlled. By pre-treating the fiber surface, the hydrophobic portion is only the outer surface of the fiber. Although the fibers will defibril in the composite resin, since the inner side of the defibriled fiber is hydrophilic, in the final molded body, the hydrophilicity of the defibriled ends of the fibers increases, and the defibriled ends are exposed on the surface of the molded body. On the other hand, when a compatibilizer such as maleic anhydride is added to the resin for compounding without pre-hydrophobicating the fibers, the resin with hydrophilic groups enters the defiberization section. The end defiberization section also has the same affinity for the resin as the central section. By accelerating cooling during molding, the central section can be exposed. This disclosure has found that it is easier to form an air layer if the central section of the fiber is exposed. Therefore, it adopts the method of adding a compatibilizer to the resin without pre-hydrophobicating the fibers.

[0051] Furthermore, by using fibers that have not been pre-hydrophobicated, the amount of hydroxyl groups present on the surface of the molded body is greater than that of the base resin. As a result, the contact angle of the molded body relative to the paint used in coating becomes lower than that of the fiber-free base resin, allowing the paint to penetrate more easily. By initiating a curing reaction from the penetration point, the bond joints are less likely to detach, adhesion strength is not compromised, and the appearance is improved.

[0052] <Coating Film>

[0053] Coating film 3 Figure 1 As shown, the coating film 3 is disposed on the surface of the composite resin molded body 5 and together with the composite resin molded body 5 constitutes the composite resin molded coating body 10. The coating film 3 is formed by coating material applied to the surface of the composite resin molded body 5.

[0054] The coating material used to form a coating film on the surface of the composite resin molded body is described. As the coating material, preferably, it is a lacquer, a urethane, or a urethane with a diol structure, such as a lacquer or a urethane with a diluent solvent. Furthermore, the viscosity range of the coating material is preferably within 0.01 to 1000 Pa·s. Conventional coating methods such as comma-type coating machines, dip coating machines, die-casting machines, and coating machines are used.

[0055] <Manufacturing Method of Composite Resin Molded Coated Body>

[0056] Next, the manufacturing method of the composite resin molded coating body will be described. Figure 4 This is a flowchart of the method for manufacturing the composite resin composition of Embodiment 1 and the method for manufacturing the composite resin molded coating.

[0057] (1) First, the main resin, fibrous filler, and additives as needed are added to the melt-blending treatment device, and melt-blending is carried out in the device. As a result, the main resin melts, and the fibrous filler and additives are dispersed in the molten main resin. In addition, the shearing action of the device promotes the defibering of the aggregates of fibrous filler, so that the fibrous filler is finely dispersed in the main resin.

[0058] To date, materials that have undergone pre-treatment to defibril the fibers, such as wet dispersion, have been used as fibrous fillers. However, when defibrilating fibrous fillers in the solvent used in wet dispersion, it is easier to defibril them than to defibril them in the molten main resin. Therefore, it is difficult to defibril only at the ends, resulting in the entire fibrous filler being defibriled. Furthermore, adding pre-treatment increases the number of steps and reduces productivity.

[0059] In contrast, the method for manufacturing the composite resin composition in Embodiment 1 does not involve defibrillation of the fibrous filler or pretreatment based on wet dispersion for modification purposes. Instead, it involves melt mixing with the main resin, dispersant, etc. (a completely dry process). By avoiding wet dispersion of the fibrous filler, this process allows the fibrous filler to be defibrillated only locally at its ends, as described above. Furthermore, it involves fewer steps, thus improving productivity.

[0060] To produce the fibers of the present invention using a completely dry process, it is preferable to apply high shear stress during mixing. Specific mixing methods include single-screw mixers, twin-screw mixers, roll mixers, and Banbury mixers. From the perspective of easy application of high shear stress and high yield, continuous twin-screw mixers and continuous roll mixers are particularly preferred. Any method capable of applying high shear stress is acceptable, and mixing methods other than those mentioned above are also acceptable.

[0061] (2) The composite resin composition extruded from the melt mixing device is cut into granules by a granulator or the like. As a method of granulation, there are methods that are carried out immediately after the resin is melted, such as air thermal cutting, underwater thermal cutting, wire cutting, etc., or there are crushing methods that are carried out by first forming the molded body or sheet and then crushing and cutting it.

[0062] (3) Next, by injection molding the granules, an injection-molded article as a composite resin molded body can be produced. As described above, during injection molding, by cooling at a faster rate than usual, the central undisintegrated portion of the fibrous filler becomes easier to expose, thereby obtaining an injection-molded article with improved appearance and adhesion to the coating film.

[0063] The following describes the various embodiments and comparative examples in the experiments conducted by the inventors.

[0064] (Example 1)

[0065] The following manufacturing method is used to manufacture pulp-dispersed polypropylene composite resin molded coatings.

[0066] Polypropylene (trade name: J108M, manufactured by Priman Polymers Co., Ltd.), used as the main resin, cotton-like softwood pulp (trade name: NBKP Celgar, manufactured by Mitsubishi Paper Co., Ltd.), used as the fibrous filler, and maleic anhydride (trade name: UMEX, manufactured by Sanyo Chemical Industries, Ltd.), used as the dispersant, were weighed and dry-mixed in a weight ratio of 42:55:3. Then, the mixture was melt-mixed and dispersed using a twin-screw extruder (KRC kneader manufactured by Kurimoto Iron Works Co., Ltd.). By changing the screw configuration and shape of the twin-screw extruder, the shear force could be altered; in Example 1, a medium-shear type was used. The resin melt was thermally cut to produce pulp-dispersed polypropylene granules.

[0067] Using the prepared pulp-dispersed polypropylene granules, test specimens of composite resin molded articles were fabricated using an injection molding machine (180AD manufactured by Nippon Steel Corporation). The fabrication conditions for the test specimens were set as follows: resin temperature 190°C, mold temperature 20°C, injection speed 90 mm / s, and holding pressure 100 MPa. Cooling was accelerated by lowering the mold temperature than usual. The granules were held in place by the screw of the molding machine via a hopper, and the invasiveness was measured by the amount of granules reduced per unit time, which was then confirmed to be constant. The shape of the test specimens was modified according to the evaluation items described below: a size 1 dumbbell was fabricated for measuring the elastic modulus, and a 60 mm square, 1.2 mm thick plate was fabricated for the appearance test. The obtained pulp-dispersed polypropylene composite resin molded article test specimens were evaluated using the following methods.

[0068] (Whether fibers are exposed, the proportion of exposed fibers, and the in-plane uniformity of exposed fibers)

[0069] For the obtained pulp-dispersed polypropylene composite resin molded body, the fiber morphology on the exposed surface and the air layer present near the fibers were observed by X-ray CT. The area where the surface of the composite resin molded body is recessed is defined as the air layer area. The volume of the air layer in a single area observed by X-ray CT is approximately 20-40% of the volume of the adjacent fiber.

[0070] (Length ratio of the fiber unwinding section)

[0071] The resulting composite resin molded body was impregnated with xylene solvent to dissolve the polypropylene. The shape of the remaining pulp fibers was observed using SEM. Defibrilation sites were observed at the ends of the fibers along their length, accounting for approximately 20-30% of the total fiber length.

[0072] X-ray CT analysis was performed on the composite resin molded body. This revealed the fiber distribution along the depth direction. Several representative fibers were measured, and the results showed exposed fiber portions on the surface, with a large number of fibers exposed in the central region.

[0073] (Elastic modulus of composite resin molded body)

[0074] Tensile tests were conducted using the obtained dumbbell-shaped test piece (No. 1).

[0075] The elastic modulus of the test piece is 3.5 GPa.

[0076] (Coating of the coating film)

[0077] The fiber composite resin molded body obtained as described above is used as a substrate, and its surface is coated. In the coating process, water is used as the solvent, which is environmentally friendly. Raw lacquer, which has a diol structure with two or more hydroxyl groups, such as urushiol and laccol, and is cured using oxygen in the air, is used as the coating material. Furthermore, raw lacquer is 100% plant-based and is also nature-friendly.

[0078] (Coating adhesion, appearance)

[0079] The resulting composite resin molded body was coated, and the coating adhesion was evaluated by the checkerboard peel test (JIS K 5600).

[0080] The resulting composite resin molded coating did not peel off.

[0081] In addition, appearance is judged based on its appearance. A coating with a uniform surface is rated ◎; a coating with a small amount of unevenness at the tens of μm level due to factors such as exposed fibers is rated 〇; a coating with unevenness at the several mm level or more due to factors such as air gaps is rated ×; and unevenness at the hundreds of μm level in the middle is rated △.

[0082] The composite resin molded coating obtained in Example 1 has a uniform surface and is rated as ◎.

[0083] (Example 2)

[0084] In Example 2, the coating was changed from lacquer to urethane. All other material and process conditions were the same as in Example 1 for preparing pulp-dispersed polypropylene granules and composite resin molded coatings. The evaluation was also conducted in the same manner as in Example 1.

[0085] (Example 3)

[0086] In Example 3, the concentration of the fibrous filler was changed to 70% by weight. All other material and process conditions were the same as in Example 1 to prepare the pulp-dispersed polypropylene granules and the composite resin molded coating. The evaluation was also conducted in the same manner as in Example 1.

[0087] (Example 4)

[0088] In Example 4, the concentration of the fibrous filler was changed to 15% by weight. All other material and process conditions were the same as in Example 1 to prepare the pulp-dispersed polypropylene granules and the composite resin molded coating. The evaluation was also conducted in the same manner as in Example 1.

[0089] (Example 5)

[0090] In Example 5, the main resin was changed from polypropylene to bio-polyethylene (Braskem BioPE_SHA7260). All other material and process conditions were the same as in Example 1 for preparing the pulp-dispersed resin granules and the composite resin molded coating. The evaluation was also conducted in the same manner as in Example 1.

[0091] (Example 6)

[0092] In Example 6, the main resin was changed from polypropylene to polyamide (UBENYLON 1013B manufactured by Ube Industries, Ltd.). All other material and process conditions were the same as in Example 1 to prepare the pulp-dispersed resin granules and the composite resin molded coating. The evaluation was also conducted in the same manner as in Example 1.

[0093] (Example 7)

[0094] In Example 7, pulp-dispersed polypropylene granules and composite resin molded articles were prepared under the same material and process conditions as in Example 1. Then, only a small amount of resin was removed from the surface by solvent-based etching to increase the volume of the air layer in the composite resin molded article before coating. The evaluation was conducted in the same manner as in Example 1.

[0095] (Comparative Example 1)

[0096] In Comparative Example 1, pulp-dispersed polypropylene granules and molded articles were prepared under the same material and process conditions as in Example 1. The surface of the composite resin molded article was then mirror-polished to remove air layers, and a coating was applied. The evaluation was conducted in the same manner as in Example 1.

[0097] (Comparative Example 2)

[0098] In Comparative Example 2, regarding the coating, a polyurethane-based polymer with no curing reaction and only a drying reaction of NMP (N-methyl-2-pyrrolidone) as a solvent was used as the coating and applied. The same evaluation as in Example 1 was performed.

[0099] (Example 8)

[0100] In Example 8, pulp-dispersed polypropylene granules and composite resin molded articles were prepared under the same material and process conditions as in Example 2. A diluent was used as the solvent for the urethane coating. The evaluation was conducted in the same manner as in Example 1.

[0101] (Example 9)

[0102] In Example 9, a conveying screw with almost no shear was used, while the other material and process conditions were the same as in Example 1 to produce the pulp-dispersed polypropylene granules and the composite resin molded coating. The evaluation was also conducted in the same manner as in Example 1.

[0103] Figure 5 Table 1 shows the measurement results of each of Examples 1 to 9 and Comparative Examples 1 to 2.

[0104] Depend on Figure 5 As shown in Table 1, in Example 2, where the coating was changed to urethane, the elastic modulus decreased slightly, but due to the water-based solvent, air curing, and the presence of a diol structure, the results were almost identical to those of Example 1. In Example 3, where the filler concentration was increased to 70% by weight, the resin thickening during mixing resulted in more defibrillation sites, reduced exposed fiber content, and slightly worse appearance. Conversely, in Example 4, where the filler concentration was reduced to 15%, the resin viscosity during mixing decreased, resulting in fewer defibrillation sites and a slightly reduced air layer volume. Consequently, the adhesion of the coating film and its appearance deteriorated slightly. In Examples 5 and 6, where 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 identical to those of Example 1. The elastic modulus and appearance of Examples 2 to 6 were the same as those of Example 1, and there were no problems. It was confirmed that if the following conditions are met: filler concentration of 15-70% by weight, fiber defiber ratio of 5-50%, fiber exposure on the surface of the molded body, air volume near the exposed fiber falling below 50% of the fiber volume, base resin of thermoplastic resin, and coating with water-based diol structure, the coating's adhesion and appearance can be improved.

[0105] In Example 7, where the volume of the air layer of the molded body was increased before coating, the paint became uneven due to the pits in the air layer, resulting in poor surface properties and slightly poor appearance.

[0106] In Comparative Example 1, where the air layer volume was reduced to less than 1% before coating, the coating contracted inwards during curing, causing peeling at the adhesion points of the coating film, resulting in poor coating adhesion. Consequently, approximately 50% of the adhesion was peeled off in the checkerboard peel test, resulting in poor appearance.

[0107] In Comparative Example 2, which uses a polymer coating, the coating lacks a curing reaction and also does not possess a diol structure with good affinity for cellulose. Therefore, the coating adhesion is poor. During curing, the coating shrinks inwards, causing peeling at the adhesion points, resulting in poor coating adhesion. Consequently, approximately 50% of the coating peels off in the checkerboard test-based adhesion evaluation, leading to poor appearance.

[0108] In Example 8, where a solvent was used to apply the coating, the environmental impact was poor, and the solvent was not compatible with cellulose, resulting in rejection and other adverse effects during coating, leading to slightly poorer appearance. Due to this rejection, the coating adhesion was also poor.

[0109] In Example 9, where the conveying screw was modified to not apply shear and the fibers were essentially not defiberized in the molten resin, the length ratio of the defiberized portion was 0-4%. As a result, the specific surface area of ​​the fibers in the molded article was low, and the elastic modulus decreased to 2.7 GPa. Furthermore, the fibers were entirely exposed on the surface, causing the paint to be repelled during coating, resulting in slightly poorer appearance.

[0110] Based on the above evaluation, it can be seen that by using a resin material in which only the fiber ends are defibrinated to create a composite resin molded body, the fibers are exposed on the surface with an air layer nearby, and a high elastic modulus can be achieved. It can also be seen that by using a coating material with a curing reaction and water as the solvent, which has a diol structure, even without a base coat, a composite resin molded coated body with good adhesion, good appearance, and a high elastic modulus can be provided.

[0111] Industrial availability

[0112] The composite resin molded coating disclosed herein provides molded articles with superior mechanical strength compared to existing general-purpose resins. By utilizing the composite resin molded coating of this disclosure, the properties of the main resin can be improved, thus allowing it to be used as a substitute for engineering plastics or metal materials. Therefore, the manufacturing costs of various industrial products or consumer goods made of engineering plastics or metals can be significantly reduced. Furthermore, it can be used in daily necessities, household appliance housings, building materials, and automotive components.

[0113] Symbol Explanation 1. Main agent resin 2. Fibrous packing 3. Coating film 4. Air layer 5 Composite Resin Molded Body 6. Imaginary surface (interface) (the lower surface of the coating film) 7a and 7b Curing sections 10 Composite Resin Molded Coated Body

Claims

1. A composite resin molded coated body comprising: a composite resin molded body containing a main agent resin and a fibrous filler, and a coating film formed on a surface of the composite resin molded body, the coating film has a hydrophilic diol structure, the fibrous filler exposes a surface of the composite resin molded body, and a boundary between the fibrous filler exposing the surface of the composite resin molded body and the composite resin molded body has an air layer.

2. The composite resin molded coated body according to claim 1, wherein, A volume of a portion of a virtual surface obtained by extending the surface of the composite resin molded body and recessing the portion is taken as a volume of the air layer, and the volume of the air layer is 1% or more and 50% or less of a volume of the fibrous filler adjacent thereto.

3. The composite resin molded coating body according to claim 1, wherein a content of the fibrous filler in the composite resin molded body is in a range of 5 to 85% by weight, the fibrous filler has a hydroxyl group, a cohesive force of the fibrous filler to the coating film is stronger than a cohesive force of the surface of the composite resin molded body to the coating film.

4. The composite resin molded coating body according to claim 1, wherein the fibrous filler is partially exposed from the surface of the composite resin molded body.

5. The composite resin molded coating body according to claim 1, wherein only an end portion of the fibrous filler is exposed in the fibrous filler in the composite resin molded body.

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

7. The composite resin molded coating body according to claim 1, wherein the main agent resin is an olefin resin.

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