Method for manufacturing thermosetting resin molded article

Abstract

Provided is a method for manufacturing a thermosetting resin molded article, said method having a high work efficiency and not being affected by the hardness of the thermosetting resin molded article. This method for manufacturing a thermosetting resin molded article has: a step in which a thermoplastic elastomer solution resulting from dissolving a thermoplastic elastomer in a solvent is applied at least to a region of a mold surface, said region forming a design surface; a step in which the mold is dried to form a thermoplastic elastomer film; and a step in which a thermosetting resin composition is injected into a cavity of the mold and the thermosetting resin composition is heated and cured, thereby obtaining a thermosetting resin molded article having the thermoplastic elastomer film provided on the surface thereof, wherein the temperature of the mold is 20-100°C. A thermosetting resin molded article is manufactured according to this method.

Description

Method for manufacturing a thermosetting resin molded product

[0001] The present invention relates to a method for manufacturing a thermosetting resin molded product. More specifically, it relates to a method for manufacturing a thermosetting resin molded product that enables the formation of a plating film by plating on the surface of the thermosetting resin molded product or the formation of a coating film by coating.

[0002] As methods for applying a paint to the surface of a thermosetting resin molded product, an in-mold coat that performs molding and coating of the molded product simultaneously and an after-coat that applies a paint to the surface of the manufactured molded product are known. The in-mold coat is proposed, for example, in Patent Document 1. The after-coat requires degreasing and sanding, applies a primer coating to the surface of the manufactured molded product, and further applies a resin paint (main coating) to the surface of the primer coating.

[0003] On the other hand, when forming a plating film on the surface of a thermosetting resin molded product, it is common to manufacture the product by vacuum molding an ABS resin sheet of the plating grade type on the surface of this molded product and then perform plating using a plating line for ABS resin.

[0004] By the way, there was a problem that the corners of the molded product became rounded in vacuum molding. Specifically, in the case of vacuum molding, the molding die is inexpensive and the molding die can be manufactured in a short time. However, there is a drawback that an R shape due to the plate thickness of the ABS resin sheet is formed and the corners of the molded product become rounded, and the quality of the molded product is unsatisfactory.

[0005] As a way to solve such problems, a method for manufacturing a thermosetting resin molded product is known, comprising the steps of: applying a thermoplastic resin solution obtained by dissolving a styrene-based resin in a solvent to at least a region of the mold surface that forms a design surface; drying the mold to form a thermoplastic resin film; and injecting a thermosetting resin composition into the cavity of the mold and heating and curing the thermosetting resin composition to obtain a thermosetting resin molded product having the thermoplastic resin film on its surface (for example, Patent Document 2). Another method for manufacturing a thermosetting resin molded product is known, comprising the steps of: applying a conductive thermoplastic resin liquid obtained by dissolving and dispersing a styrene-based resin and a carbon material in a solvent to at least a region of the mold surface that forms a design surface; drying the mold to form a conductive thermoplastic resin film; and injecting a thermosetting resin composition into the cavity of the mold and heating and curing the thermosetting resin composition to obtain a thermosetting resin molded product having the conductive thermoplastic resin film on its surface (for example, Patent Document 3).

[0006] Japanese Patent Publication No. 2010-23269, Japanese Patent Publication No. 2015-116754, Japanese Patent Publication No. 2015-116755

[0007] However, the manufacturing methods described in Patent Documents 2 and 3 did not take into account the production of soft thermosetting resin molded products with low hardness, and cracks sometimes occurred on the surface of the thermosetting resin molded products. In recent years, there has been a demand for a manufacturing method that can handle thermosetting resin molded products with a wide range of hardness. Furthermore, when using a thermoplastic resin solution in which styrene resin is dissolved, as in Patent Documents 2 and 3, increasing the styrene resin concentration in the thermoplastic resin solution increases the stringiness of the thermoplastic resin solution, so the concentration must be kept relatively low. This necessitates multiple applications to form a thermoplastic resin film of the desired thickness, which reduces work efficiency.

[0008] Therefore, the present invention aims to provide a method for manufacturing thermosetting resin molded articles that is highly efficient and independent of the hardness of the thermosetting resin composition being manufactured.

[0009] The present invention relates to a method for manufacturing a thermosetting resin molded product, comprising the steps of: applying a thermoplastic elastomer solution, obtained by dissolving a thermoplastic elastomer in a solvent, to at least a region of the surface of a mold that forms a design surface; drying the mold to form a thermoplastic elastomer film; and injecting a thermosetting resin composition into the cavity of the mold and heating and curing the thermosetting resin composition to obtain a thermosetting resin molded product having the thermoplastic elastomer film on its surface, wherein the temperature of the mold is 20 to 100°C.

[0010] According to the present invention, it is possible to provide a method for manufacturing thermosetting resin molded products that is highly efficient and independent of the hardness of the thermosetting resin molded product. In particular, it is possible to provide a manufacturing method suitable for producing thermosetting resin molded products with low hardness.

[0011] This is a cross-sectional view of the mold before it is closed. This is a cross-sectional view of the mold after it has been closed and the soft urethane resin composition has been injected.

[0012] In this invention, a thermosetting resin molded product is obtained by injecting a thermosetting resin composition into the cavity of a mold and heating and curing the thermosetting resin composition. Examples of injection-molded liquid thermosetting resin compositions include urethane resin compositions such as flexible urethane resin compositions and rigid urethane resin compositions, epoxy resin compositions, polyester resin compositions, and phenolic resin compositions. In this specification, a method for producing a urethane resin molded product using a flexible urethane resin composition will be specifically described as an example.

[0013] Figure 1 is a cross-sectional view showing the mold before cladding, and Figure 2 is a cross-sectional view showing the state after the mold has been cladded and a liquid soft urethane resin composition has been injected into the cavity. In Figures 1 and 2, the mold 1 consists of a male mold (upper mold) 2 having a convex portion 3 on its lower surface and a female mold (lower mold) 4 having a concave portion 5 on its upper surface. The male mold 2 and female mold 4 may be made of metal such as aluminum, or of synthetic resin.

[0014] As shown in Figures 1 and 2, it is preferable that the surface of the mold 1 is covered with a composite plating film 6. That is, it is preferable that the composite plating is applied in advance to at least the area of ​​the surface of the mold 1 that forms the design surface. This improves the flow of the thermosetting resin composition when it is injected into the cavity of the mold, making it less likely for scratches to occur on the surface of the resulting thermosetting resin molded product and facilitating mold release of the thermosetting resin molded product. The area on which the composite plating film 6 is formed may be only the area of ​​the surface of the mold 1 that forms the design surface, or it may be the entire cavity forming surface, or it may be the entire surface of the mold 1 as shown in Figures 1 and 2. The thickness of the composite plating film 6 formed on the surface of the mold 1 is preferably 5 to 20 μm. However, the mold does not have to be coated with composite plating.

[0015] As a composite plating, electroless nickel-PTFE composite plating is preferred. Electroless nickel-PTFE composite plating is what is commonly known as Teflon® plating, and forms a film in which PTFE (polytetrafluoroethylene) fine particles are uniformly dispersed and co-deposited within an electroless nickel film. PTFE is a fluororesin (fluorocarbon resin) composed only of fluorine atoms and carbon atoms, and is chemically stable with excellent heat resistance and chemical resistance. Furthermore, since the matrix firmly holds each individual PTFE fine particle, and the matrix is ​​metallic, the adhesion between the substrate and the PTFE plating is strong. The PTFE content in the plating solution is preferably 25 to 40% by volume.

[0016] Next, a method for manufacturing a urethane resin molded product using this mold 1 will be described. First, after cleaning the mold 1 as necessary, a thermoplastic elastomer solution, obtained by dissolving a thermoplastic elastomer in a solvent, is applied to at least the area on the surface of the mold 1 that forms the design surface. Then, the mold 1 is dried to form a thermoplastic elastomer film (not shown). The area on which the thermoplastic elastomer solution is applied to form the thermoplastic elastomer film may be only the area on the surface of the mold 1 that forms the design surface, the entire cavity forming surface, or the entire surface of the mold 1. The thickness of the thermoplastic elastomer film formed on the surface of the mold 1 is preferably 10 to 100 μm, and more preferably 20 to 60 μm.

[0017] Examples of thermoplastic elastomers include (meth)acrylic elastomers, thermoplastic polyurethanes, vinyl chloride thermoplastic elastomers, polystyrene thermoplastic elastomers, and polyamide elastomers. Among these, acrylic elastomers are particularly preferred when considering solubility in solvents, applicability, and the strength of the film formed, and acrylic block copolymers are more preferred. Examples of acrylic block copolymers include methacrylate alkyl ester / acrylate alkyl ester block copolymers such as a block copolymer of methyl methacrylate (MMA) and butyl acrylate (nBA), and a block copolymer of methyl methacrylate (MMA) and butyl acrylate (nBA) / 2-ethylhexyl acrylate (2EHA). Among these, a block copolymer of methyl methacrylate (MMA) and butyl acrylate (nBA) is preferred.

[0018] The tensile strength of the thermoplastic elastomer, measured in accordance with ISO 37, is preferably 9 to 25 MPa, more preferably 10 to 22 MPa, and even more preferably 11 to 20 MPa. This more effectively prevents cracking on the surface of the thermosetting resin molded product when manufacturing a soft thermosetting resin molded product with low hardness, and allows for the more suitable manufacture of a soft thermosetting resin molded product. Furthermore, the tensile elongation of the thermoplastic elastomer, measured in accordance with ISO 37, is preferably 90 to 200%, more preferably 100 to 180%, and even more preferably 110 to 170%. This more effectively suppresses cracking on the surface of the thermosetting resin molded product when manufacturing a soft thermosetting resin molded product with low hardness, and also more effectively suppresses stickiness on the surface of the thermosetting resin molded product. Furthermore, the 100% modulus of the thermoplastic elastomer, measured in accordance with ISO 37, is preferably 5 to 25 MPa, more preferably 6 to 22 MPa, and even more preferably 7 to 20 MPa. This makes it possible to more effectively prevent cracks from occurring on the surface of thermosetting resin molded products when manufacturing soft thermosetting resin molded products with low hardness, and to manufacture soft thermosetting resin molded products more favorably.

[0019] Furthermore, the hardness of the thermoplastic elastomer, as measured in accordance with ISO 7619-1 (Type A), is preferably 66 to 110, more preferably 68 to 105, and even more preferably 70 to 100. This makes it possible to more effectively suppress the occurrence of cracks on the surface of thermosetting resin molded products when manufacturing soft thermosetting resin molded products with low hardness, and to more effectively suppress the occurrence of stickiness on the surface of thermosetting resin molded products.

[0020] As a solvent, ketones such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and acetone are preferred because they dry easily. It is more preferable to use a combination of two or more of these, and even more preferable to use a combination of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK). The thermoplastic elastomer solution can be prepared, for example, by dissolving a powdered or pelletized thermoplastic elastomer in a mixed solvent of MEK and MIBK. Furthermore, the viscosity of the thermoplastic elastomer solution can be adjusted with toluene (thinner) or the like. The concentration of the thermoplastic elastomer solution is preferably 10 to 30% by mass, more preferably 12 to 25% by mass, and even more preferably 14 to 25% by mass. This allows for more efficient formation of the thermoplastic elastomer film. Even at such relatively high concentrations, stringiness does not occur, so the number of times the thermoplastic elastomer solution is applied can be reduced when forming a film of the desired thickness, thereby improving work efficiency.

[0021] The thermoplastic elastomer solution may also contain a thermoplastic resin in addition to the thermoplastic elastomer. As the thermoplastic resin, it is preferable to use styrene-based resins such as polystyrene, styrene-acrylonitrile copolymer resin (SAN resin), acrylonitrile-butadiene-styrene copolymer resin (ABS resin), and acrylonitrile-ethylene-styrene copolymer resin (AES resin) because they are easily soluble in the solvent. Among these, it is more preferable to use ABS resin, and even more preferable to use a plating-grade type ABS resin. For example, by including ABS resin as the thermoplastic resin, the resulting urethane resin molded product can be plated using a decorative plating line. In this case, a thermoplastic elastomer solution can be used in which 15 to 30% by mass (20% by mass as an example) of thermoplastic elastomer and 5 to 14% by mass (12% by mass as an example) of ABS resin are dissolved in MEK.

[0022] After forming a thermoplastic elastomer film on the surface of the mold 1, the mold 1 is closed, and a liquid thermosetting resin composition, a flexible urethane resin composition 7, is injected into the cavity S formed between the male mold 2 and the female mold 4, and then heat-cured. In this way, a urethane resin molded product with a thermoplastic elastomer film on its surface can be obtained. Heating can be performed, for example, by continuously heating the male mold 2 and the female mold 4 using a heating means (not shown). The temperature of the mold 1 is preferably 20 to 100°C, and can be maintained at, for example, about 75°C. The injected flexible urethane resin composition 7 hardens through a urethane reaction, but the reaction time can be shortened and the heat resistance increased by hardening through a urethane-urea reaction. The hardness of the cured product of the thermosetting resin composition (flexible urethane resin composition), as measured in accordance with JIS K 6253, is preferably 90 or less, more preferably 10 to 70, and even more preferably 15 to 60. Even with soft urethane resin compositions that have relatively low hardness in their cured form, the manufacturing method of the present invention can suppress the occurrence of cracks and other defects on the surface of the manufactured urethane resin molded product.

[0023] Subsequently, the mold 1 is opened, and the urethane resin molded product is removed from the mold 1. At this time, the thermoplastic elastomer film formed on the surface of the mold 1 easily separates from the mold 1, allowing the urethane resin molded product to be easily removed. After that, deburring is performed as needed.

[0024] The resulting urethane resin molded product can be painted or otherwise treated. Furthermore, by forming a thermoplastic elastomer film using a mixture of thermoplastic elastomer and ABS resin as the thermoplastic elastomer solution, the resulting urethane resin molded product can be plated. In particular, when using a plating-grade type ABS resin, direct electroless plating becomes possible. As for the plating method, the methods described in Patent Documents 2 and 3 can be used.

[0025] Furthermore, as mentioned above, the thermoplastic elastomer film formed on the surface of the mold 1 easily separates from the mold 1, eliminating the need to apply a release agent to the surface of the mold 1. Of course, a release agent can be applied to the surface of the mold 1, but if no release agent is applied, the surface of the resulting urethane resin molded product can be painted or plated without degreasing, sanding with sandpaper, or correcting any resulting pinholes.

[0026] In other words, a urethane resin molded product with a thermoplastic elastomer coating on its surface can be painted as is after deburring as necessary. Alternatively, the urethane resin molded product can be electroless plated as is after deburring as necessary, or electrolytic plated on its surface. Therefore, the number of processes is reduced, significantly shortening the molding time, and the working environment is improved because no powder is generated by sanding. As a result, work efficiency is increased.

[0027] Furthermore, according to the manufacturing method described above, even with a flexible urethane resin composition (a flexible thermosetting composition), the occurrence of cracks and other defects on the surface of the thermosetting resin molded product can be suppressed, and the thermosetting resin molded product can be manufactured regardless of the hardness of the thermosetting resin composition being manufactured. In addition, since the concentration of the thermoplastic elastomer solution can be increased, the number of times the thermoplastic elastomer solution is applied when forming the thermoplastic elastomer film can be reduced, resulting in high work efficiency.

[0028] <Example 1> First, an acrylic elastomer solution (thermoplastic elastomer solution) was prepared by dissolving an acrylic elastomer (manufactured by Kuraray Co., Ltd., product name: Clarity® LA2270, tensile strength (ISO37): 12 MPa, tensile elongation (ISO37): 149%, 100% modulus (ISO37): 9 MPa, hardness (ISO7619-1 (Type A)): 71) in a mixed solvent of MEK and MIBK (50:50 volume) to a concentration of 20% by mass. Next, the acrylic elastomer solution was sprayed onto the surfaces of the upper mold (convex part) and lower mold (concave part) of a mold set to 50°C (measured temperature) using a spray gun to achieve a dry film thickness of 30 μm, and then dried. After that, the upper and lower molds of the mold were closed, and a flexible urethane resin composition was injected into the formed cavity, and the flexible urethane resin composition was heat-cured. Subsequently, the upper and lower molds were opened to remove the urethane resin molded product, and the burrs were removed. The soft urethane resin composition used had a hardness of 40, as measured according to JIS K 6253 standards for its cured product.

[0029] <Example 2> First, an acrylic elastomer solution was prepared by dissolving an acrylic elastomer (manufactured by Kuraray Co., Ltd., trade name: Clarity® LA4285, tensile strength (ISO37): 19 MPa, tensile elongation (ISO37): 140%, 100% modulus (ISO37): 19 MPa, hardness (ISO7619-1 (Type A)): 95) in a mixed solvent of MEK and MIBK (50:50 volume) to a concentration of 20% by mass. Next, the acrylic elastomer solution was sprayed onto the surfaces of the upper mold (convex part) and lower mold (concave part) of a mold set to 50°C (measured temperature) using a spray gun to achieve a dry film thickness of 30 μm, and then dried. After that, the upper and lower molds of the mold were closed, and a flexible urethane resin composition was injected into the formed cavity and the flexible urethane resin composition was heat-cured. After that, the upper and lower molds of the mold were opened, the urethane resin molded product was removed, and the burrs were removed. Furthermore, the flexible urethane resin composition used had a hardness of 40, as measured according to JIS K 6253 standards for its cured product.

[0030] <Example 3> First, an acrylic elastomer solution was prepared by dissolving an acrylic elastomer (manufactured by Kuraray Co., Ltd., product name: Clarity® LA2250, tensile strength (ISO37): 9 MPa, tensile elongation (ISO37): 380%, 100% modulus (ISO37): 3.7 MPa) in a mixed solvent of MEK and MIBK (50:50 volume) to a concentration of 20% by mass. Next, the acrylic elastomer solution was sprayed onto the surfaces of the upper mold (convex part) and lower mold (concave part) of the mold, which were set to 50°C (measured temperature), using a spray gun to achieve a dry film thickness of 30 μm, and then dried. After that, the upper and lower molds of the mold were closed, and a flexible urethane resin composition was injected into the formed cavity and the flexible urethane resin composition was heat-cured. After that, the upper and lower molds of the mold were opened, the urethane resin molded product was removed, and the burrs were removed. Furthermore, the flexible urethane resin composition used had a hardness of 40, as measured according to JIS K 6253 standards for its cured product.

[0031] <Comparative Example 1> First, a plating-grade ABS resin (manufactured by Nippon A&L Co., Ltd., for plating, product name: Clarastic® AP-8A) was dissolved in MEK, and then diluted with slow-drying thinner (manufactured by Daishin Chemical Co., Ltd.) to prepare an ABS resin solution with a concentration of 12% by mass. Next, the ABS resin solution was sprayed onto the surfaces of the upper mold (convex part) and lower mold (concave part) of a mold set to 65°C (actual temperature) using a spray gun to achieve a dry film thickness of 50 μm, and then dried. After that, the upper and lower molds of the mold were closed, and a soft urethane resin composition similar to that in Example 1 was injected into the formed cavity, and the soft urethane resin composition was heat-cured. After that, the upper and lower molds of the mold were opened, the urethane resin molded product was removed, and the burrs were removed. When the formed urethane resin molded product was observed, cracks were confirmed on the surface.

[0032] <Comparative Example 2> First, a general-grade ABS resin (manufactured by Nippon A&L Co., Ltd., ABS powder, product name: Clarastic® K-2540A) was dissolved in MEK, and then diluted with slow-drying thinner (manufactured by Daishin Chemical Co., Ltd.) to prepare an ABS resin solution with a concentration of 12% by mass. Next, the ABS resin solution was sprayed onto the surfaces of the upper mold (convex part) and lower mold (concave part) of the mold, which were set to 65°C (measured temperature), using a spray gun to achieve a dry film thickness of 25 μm, and then dried. After that, the upper and lower molds of the mold were closed, and a soft urethane resin composition similar to that in Example 1 was injected into the formed cavity, and the soft urethane resin composition was heat-cured. After that, the upper and lower molds of the mold were opened, the urethane resin molded product was removed, and the burrs were removed.

[0033] <Evaluation> The surface of the urethane resin molded products obtained in each example and comparative example was examined to check for cracks and stickiness. The results are shown in Table 1.

[0034]

[0035] As can be seen from Table 1, no cracks were observed on the surface of the urethane resin molded products in the examples. Furthermore, no stickiness was observed in the urethane resin molded products of Examples 1 and 2. In addition, when the urethane resin molded products obtained in each example were painted without any pretreatment, a uniform paint film was formed.

[0036] Embodiments of the present invention have been described above, but various alternatives, modifications, or variations are possible for those skilled in the art based on the above description, and the present invention encompasses the aforementioned various alternatives, modifications, or variations without departing from its spirit. Furthermore, this specification encompasses at least the following inventions: [1] A method for manufacturing a thermosetting resin molded article, comprising the steps of: applying a thermoplastic elastomer solution, obtained by dissolving a thermoplastic elastomer in a solvent, to at least a region of the surface of a mold that forms a design surface; drying the mold to form a thermoplastic elastomer film; and injecting a thermosetting resin composition into the cavity of the mold and heating and curing the thermosetting resin composition to obtain a thermosetting resin molded article having the thermoplastic elastomer film on its surface. [2] The method for manufacturing a thermosetting resin molded article according to [1], wherein the thermoplastic elastomer is an acrylic elastomer. [3] The method for manufacturing a thermosetting resin molded article according to [1] or [2], wherein the tensile strength of the thermoplastic elastomer, as measured in accordance with ISO 37, is 10 to 25 MPa. [4] The method for manufacturing a thermosetting resin molded article according to any one of [1] to [3], wherein the tensile elongation of the thermoplastic elastomer, as measured in accordance with ISO 37, is 90 to 200%. [5] The method for manufacturing a thermosetting resin molded article according to any one of [1] to [4], wherein the concentration of the thermoplastic elastomer solution is 10 to 30% by mass. [6] The method for manufacturing a thermosetting resin molded article according to any one of [1] to [5], wherein the hardness of the cured product of the thermosetting resin composition, as measured in accordance with JIS K 6253, is 90 or less. [7] The method for manufacturing a thermosetting resin molded article according to [6], wherein the thermosetting resin composition is a soft urethane resin composition. [8] The method for manufacturing a thermosetting resin molded article according to any one of [1] to [7], wherein the temperature of the mold is 20 to 100°C.

[0037] 1. Molding mold 2. Male mold (upper mold) 3. Protrusion 4. Female mold (lower mold) 5. Recess 6. Composite plating film 7. Soft urethane resin composition S. Cavity

Claims

1. A method for manufacturing a thermosetting resin molded product, comprising the steps of: applying a thermoplastic elastomer solution, obtained by dissolving a thermoplastic elastomer in a solvent, to at least a region of the surface of a mold that forms a design surface; drying the mold to form a thermoplastic elastomer film; and injecting a thermosetting resin composition into the cavity of the mold and heating and curing the thermosetting resin composition to obtain a thermosetting resin molded product having the thermoplastic elastomer film on its surface, wherein the temperature of the mold is 20 to 100°C.

2. The method for producing a thermosetting resin molded article according to claim 1, wherein the thermoplastic elastomer is an acrylic elastomer.

3. The method for manufacturing a thermosetting resin molded article according to claim 1, wherein the tensile strength of the thermoplastic elastomer, as measured in accordance with ISO 37, is 10 to 25 MPa.

4. The method for manufacturing a thermosetting resin molded article according to claim 1, wherein the tensile elongation of the thermoplastic elastomer, measured in accordance with ISO 37, is 90 to 200%.

5. The method for producing a thermosetting resin molded article according to claim 1, wherein the concentration of the thermoplastic elastomer solution is 10 to 30% by mass.

6. The method for producing a thermosetting resin molded article according to claim 1, wherein the hardness of the cured product of the thermosetting resin composition, as measured in accordance with JIS K 6253, is 90 or less.

7. The method for producing a thermosetting resin molded article according to claim 6, wherein the thermosetting resin composition is a flexible urethane resin composition.

Images