Method for manufacturing transfer sheets and molded articles

Abstract

To provide a transfer sheet which is less susceptible to peeling defects by adjusting a peeling force of a release layer of the transfer sheet, and a molded product using the transfer sheet.SOLUTION: A molded product 10 is a flat plate, and has an injection molded body 11 and an adhesive layer 54 formed on the injection molded body 11, and a release layer 53 formed on a surface of the adhesive layer 54 on which the injection molded body 11 is not formed. The molded product 10 is formed by transferring the adhesive layer 54 and the release layer 53 onto the injection molded body 11 by in-mold molding using a transfer sheet 50. The release layer contains a thermosetting resin and a thermoplastic resin, and a ratio of the thermosetting resin to the thermoplastic resin is 2:1 to 6:1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a method for manufacturing a transfer sheet and a molded product, and particularly to a method for manufacturing a transfer sheet and a molded product using a transfer sheet with low peeling failure.

Background Art

[0002] Conventionally, molded products have been manufactured by in-mold molding in which a transfer sheet is transferred to an injection molded body in an injection mold. Such molded products are used for automotive interiors, exteriors of electrical appliances, cover panels of displays, etc. For example, Patent Document 1 describes a molding method in which foil burrs are unlikely to occur during in-mold molding using a transfer sheet. In Patent Document 1, a dummy part is formed by injection molding with a gap between the product parts, and the product parts and the dummy part are configured such that the respective resins are not connected to each other. Foil burrs are likely to occur at the boundary between the transfer area and the non-transfer area, but the product parts and the dummy part are connected by the transfer layer of the transfer sheet, and there is no boundary between the transfer area and the non-transfer area around the product parts, so foil burrs are unlikely to occur.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional method for manufacturing a molded product as described above, a step of cutting off the dummy part from the product part after molding is required, so the productivity may decrease.

[0005] This invention has been made to solve the above problems, and an object thereof is to provide a transfer sheet with low peeling failure and a molded product using the transfer sheet by adjusting the peeling force of the release layer of the transfer sheet. [Means for solving the problem]

[0006] To achieve the above objective, the first invention is a transfer sheet comprising a base sheet, a release layer formed on the base sheet, and a release layer formed on the release layer, wherein the release layer contains a thermosetting resin and a thermoplastic resin, and the ratio of the thermosetting resin to the thermoplastic resin is 2:1 to 6:1.

[0007] With this configuration, the release layer has a good balance between the release properties of the thermosetting resin and the tackiness of the thermoplastic resin, resulting in a transfer sheet that is less prone to foil sticking and leaves minimal residue.

[0008] The second invention is a transfer sheet in which, in the first invention, the thermosetting resin is melamine resin and the thermoplastic resin is a mixture of urethane resin and xylene resin.

[0009] With this configuration, the urethane resin has high flexibility, and the xylene resin acts as a compatibilizer between the melamine resin and the urethane resin, resulting in a uniform release layer. Therefore, when injection molding is performed using this transfer sheet, it exhibits excellent crack resistance and impact resistance, and inconsistencies in product characteristics are suppressed.

[0010] The third invention is a transfer sheet in which, in the second invention, the ratio of urethane resin to xylene resin is 20:1 to 5:2.

[0011] With this configuration, if the xylene resin is more abundant than 20:1 (urethane resin:xylene resin), it exhibits good adhesion, making foil burrs less likely to occur. Conversely, if the xylene resin is less abundant than 5:2 (urethane resin:xylene resin), it exhibits good flexibility, making cracks less likely to occur.

[0012] The fourth invention is a transfer sheet in which, in the second or third invention, the urethane resin has a glass transition temperature of -80°C to 0°C.

[0013] With this configuration, the glass transition temperature of the urethane resin is sufficiently lower than room temperature, and the peel strength does not change easily with temperature, thus making it easier to maintain stable moldability.

[0014] The fifth invention is a transfer sheet in which, in the second or third invention, the release layer further comprises p-toluenesulfonic acid as a catalyst.

[0015] With this configuration, the polymerization of low-molecular-weight melamine is promoted by p-toluenesulfonic acid, resulting in good release properties derived from the high-molecular-weight melamine resin, and making it less likely for peeling marks to remain.

[0016] The sixth invention is a transfer sheet in which, in the second or third invention, the release layer has a thickness of 0.16 μm to 0.22 μm.

[0017] This configuration results in a transfer sheet with extremely high effectiveness in suppressing foil burrs and peeling marks.

[0018] The seventh invention is a method for manufacturing a molded article, comprising the steps of: preparing a transfer sheet comprising a base sheet, a release layer formed on the base sheet, and a release layer formed on the release layer, wherein the release layer contains a thermosetting resin and a thermoplastic resin, and the ratio of the thermosetting resin to the thermoplastic resin is 2:1 to 6:1; placing the transfer sheet on the cavity surface of the first mold of an injection molding die having a first mold and a second mold that forms a cavity between itself and the first mold by clamping; clamping the injection molding die; injecting molten resin into the cavity to form an injection molded article and simultaneously transferring the release layer to the surface of the injection molded article; and opening the injection molding die, peeling the base sheet of the transfer sheet together with the release layer from the molded article, and removing the injection molded article.

[0019] With this configuration, the release layer has a good balance between the release properties of the thermosetting resin and the tackiness of the thermoplastic resin, resulting in a molded product that is less prone to foil burrs and leaves minimal residue after removal. [Effects of the Invention]

[0020] According to the present invention, a transfer sheet in which peeling failure hardly occurs and a molded article using the transfer sheet can be obtained.

Brief Description of the Drawings

[0021] [Figure 1] It is a schematic cross-sectional view of a molded article according to the first embodiment of the present invention. [Figure 2] It is a schematic cross-sectional view of a transfer sheet according to the first embodiment of the present invention. [Figure 3] It is a schematic cross-sectional view for explaining the manufacturing process of a molded article according to the first embodiment of the present invention. [Figure 4] It is a schematic cross-sectional view of a molded article according to the second embodiment of the present invention. [Figure 5] It is a schematic cross-sectional view of a transfer sheet according to the second embodiment of the present invention.

Modes for Carrying Out the Invention

[0022] The molded article 10 according to the first embodiment of the present invention will be described with reference to the drawings.

[0023] Referring to FIG. 1, the molded article 10 according to the first embodiment of the present invention is in a flat plate shape, an injection molded body 11 is formed, an adhesive layer 54 is formed on the injection molded body 11, and a release layer 53 is formed on the surface of the injection molded body 11 where the adhesive layer 54 is not formed. The molded article 10 is formed by in-mold molding using the transfer sheet 50, and the adhesive layer 54 and the release layer 53 are transferred onto the injection molded body 11.

[0024] Referring to FIG. 2, the transfer sheet 50 includes a base sheet 51, a release layer 52 formed on the base sheet 51, a release layer 53 formed on the release layer 52, and an adhesive layer 54 formed on the release layer 53. The molded article 10 is applied to, for example, a cover panel of a display, an in-vehicle interior, or an exterior of an electric appliance.

[0025] The injection-molded body 11 can be, for example, general-purpose resins such as polystyrene resin, polyolefin resin, ABS resin, AS resin, AN resin, general-purpose engineering resins such as polycarbonate resin, acrylic resin, thermoplastic polyurethane, or super engineering resins such as polyimide resin or liquid crystal polyester resin. Composite resins with added reinforcing materials such as glass fibers or inorganic fillers can also be used. The thickness of the molded resin body 11 is not particularly limited and is selected according to the thickness of the housing of the product being manufactured.

[0026] The base sheet 51 supports the release layer 52, the release layer 53, and the adhesive layer 54. For example, it can be a thermoplastic resin such as polypropylene resin, polyethylene resin, polyamide resin, acrylic resin, olefin resin, epoxy resin, polyimide resin, thermoplastic polyurethane, silicone resin, polyester resin, vinyl chloride resin, polycarbonate resin, ABS resin, or laminates thereof. The thickness of the base sheet 40 is preferably, for example, 12 μm to 200 μm. If the thickness of the base sheet 51 is 12 μm or more, it has a thickness that is easy to handle, and if the thickness is 200 μm or less, it has appropriate rigidity and good flexibility.

[0027] The release layer 52 is a layer that is peeled off together with the substrate sheet 51 during in-mold transfer. The release layer 52 contains both a thermosetting resin and a thermoplastic resin. In addition to the thermosetting resin and the thermoplastic resin, it may also contain additives such as stabilizers and catalysts. The thickness of the release layer 52 is preferably, for example, 0.1 μm to 0.5 μm. If the thickness is 0.1 μm or more, it can be stably coated onto the substrate sheet and good release properties can be obtained. If the thickness is 0.5 μm or less, thickness unevenness of the release layer is less likely to occur and the release properties tend to be more stable.

[0028] Thermosetting resins are materials that primarily impart release properties to the release layer 52, and examples include melamine resin, urea resin, epoxy resin, and urethane resin. Melamine resin is particularly preferred, as it exhibits good release properties when used in the transfer sheet 50. Examples of melamine resins that can be used include butyl-based melamine, ethyl-based melamine, methyl-based melamine, imino-based melamine, imino-based ethyl-based mixed melamine, butyrol-based melamine, ethylol-based melamine, and methylol-based melamine.

[0029] An acid catalyst may be used in combination with the thermosetting resin. When forming the release layer 52 on the substrate sheet 51, for example, various materials including the thermosetting resin are diluted with an organic solvent, coated onto the substrate sheet 51, and dried and cured. By using an acid catalyst in combination at this time, the polymerization of low-molecular-weight materials that become thermosetting resins after polymerization, which are contained together with the thermosetting resin in the material diluted with the organic solvent, is promoted, and good release properties derived from the high-molecular-weight thermosetting resin are obtained. Furthermore, when melamine resin is used as the thermosetting resin, it is preferable to use p-toluenesulfonic acid as the acid catalyst. By using p-toluenesulfonic acid as the acid catalyst, the polymerization of low-molecular-weight melamine is promoted particularly efficiently.

[0030] The thermoplastic resin is a resin that primarily imparts tackiness to the release layer 52. For example, urethane resin, acrylic resin, xylene resin, petroleum resin, terpene resin, rosin, etc., can be used as the base resin, and xylene resin, petroleum resin, terpene resin, rosin, etc., can be used as the tackifier. Alternatively, one or more of these materials may be used.

[0031] It is even more preferable to use melamine resin as the thermosetting resin and a mixture of urethane resin and xylene resin as the thermoplastic resin for the release layer 52. Melamine resin has good release properties when used in the transfer sheet 50. Urethane resin has high flexibility as well as adhesiveness, so when injection molding is performed using the transfer sheet 50, it has excellent crack resistance and impact resistance. In addition to providing tackiness, xylene resin acts as a compatibilizer between the melamine resin and the urethane resin, so it plays a role in making it easier to form a uniform film of the release layer 52 and suppressing inconsistencies in product properties.

[0032] Examples of urethane resins include those obtained by polymerizing a polyol resin and an isocyanate. As polyol resins, for example, polyester polyols and polyether polyols, which are commonly used in adhesive applications, can be used. As isocyanates, for example, diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, biphenylmethane diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, dimethoxybiphenylene diisocyanate, naphthalene diisocyanate, dimethylbiphenylene diisocyanate, diphenylene diisocyanate, diisocyanate diphenyl ether, xylylene diisocyanate, diisocyanate methylcyclohexane, diisocyanate dicyclohexane, diisocyanate cyclohexylmethane, and isophorone diisocyanate can be used. The glass transition temperature of the urethane resin is preferably -80°C to 0°C, and more preferably -60°C to -30°C. If the glass transition temperature of the urethane resin is within this range, it is sufficiently lower than room temperature, and the peel strength does not change easily with temperature, so the moldability tends to be stable. For example, an unmodified xylene resin crosslinked with methylene bonds or ether bonds can be used.

[0033] The release layer 52 is formed with a ratio of thermosetting resin to thermoplastic resin of 2:1 to 6:1. This configuration provides a good balance between the release properties of the thermosetting resin and the tackiness of the thermoplastic resin, resulting in a transfer sheet that is less prone to foil burrs and leaves minimal residue.

[0034] When using a mixture of urethane resin and xylene resin as the thermoplastic resin, the ratio of urethane resin to xylene resin is preferably 20:1 to 5:2. If the amount of xylene resin is greater than 20:1, good tackiness is achieved, making foil burrs less likely to occur. Also, if the amount of xylene resin is less than 5:2, sufficient good flexibility derived from the urethane resin is obtained, making cracks less likely to occur during molding.

[0035] The release layer 53 is the outermost layer of the molded product 10, which is peeled off at the interface between the mold release layer 52 and the release layer 53 during in-mold molding. The release layer 53 may also function as a layer with hard coating properties and chemical resistance to protect the molded product 10. For example, thermoplastic resins such as acrylic resins, polystyrene resins, polyamide resins, chlorinated polyolefin resins, chlorinated ethylene-vinyl acetate copolymer resins, cyclized rubber, and coumarone indene resin can be used as the material for the release layer 53. It can also be formed by including any of the following: photocurable resins such as UV-curable resins, radiation-curable resins such as electron beam-curable resins, or thermosetting resins. Examples of such resins include urethane acrylate resins, cyanoacrylate resins, epoxy acrylate resins, polyester acrylate resins, and resins to which additives such as isocyanates have been added.

[0036] The adhesive layer 54 is a layer for adhering the transfer sheet 50 and the injection molded body 11 to a tight bond. For example, acrylic resin, urethane resin, polyester resin, polyvinyl acetate resin, vinyl chloride resin, or vinyl chloride-vinyl acetate copolymer can be used. The thickness of the adhesive layer 54 can be, for example, 2 to 20 μm.

[0037] Next, the general method for manufacturing the molded article 10 according to the first embodiment of this invention will be described with reference to the figures.

[0038] Refer to Figure 3(a) and prepare the transfer sheet 50. The transfer sheet 50 comprises a base sheet 51, a release layer 52 formed on the base sheet 51, a release layer 53 formed on the release layer 52, and an adhesive layer 54 formed on the release layer 53. Place this transfer sheet 50 in the injection molding die 80. The injection molding die 80 consists of a first mold 81 and a second mold 82. The first mold 81 has a cavity surface 83 corresponding to the shape of the molded product 10, and the second mold 82 has an injection port 84 for injecting molten resin. Furthermore, by clamping the first mold 81 and the second mold 82 together, a space is formed between the first mold 81 and the second mold 82. This space is called a cavity 87. In the step of placing the transfer sheet 50 in the injection molding die 80, the transfer sheet 50 is positioned between the first mold 81 and the second mold 82, passing over the guide roller 85 from above the first mold 81, with the base sheet 51 facing the cavity surface 83 of the first mold 81, and passing over the guide roller 86 below the first mold 81. Next, referring to Figure 3(b), the transfer sheet 50 is molded three-dimensionally along the shape of the cavity surface 83 of the first mold 81 by suction from the first mold 81 side using a suction mechanism (not shown). Next, referring to Figure 3(c), the first mold 81 and the second mold 82 are clamped together. Then, molten resin is injected from the injection port 84 of the second mold 82 to form the injection molded body 11, and at the same time, the adhesive layer 54 of the transfer sheet 50 is fixed to the surface of the injection molded body 11 on the first mold 81 side. Next, referring to Figure 3(d), the injection molding die 80 is opened, and the molded product 10, with the adhesive layer 54 and release layer 53 fixed to the injection molded body 11, is removed by releasing the transfer sheet 50 in the portion fixed to the injection molded body 11 at the interface between the release layer 52 and the release layer 53, thereby manufacturing the molded product 10.

[0039] The transfer sheet 50 used in the above manufacturing method is configured to contain a thermosetting resin and a thermoplastic resin in the release layer 52, with the ratio of thermosetting resin to thermoplastic resin being 2:1 to 6:1. If the ratio of thermosetting resin to thermoplastic resin is within the above range, the release properties derived from the thermosetting resin in the release layer 52 are well balanced, making it less likely for foil burrs to form and less likely for peeling marks to remain when peeling the base sheet 51 and the release layer 52 after injection molding or transfer.

[0040] Next, the effects of using a thermosetting resin and a thermoplastic resin in a ratio of 2:1 to 6:1 in the release layer 52 will be explained. Melamine resin was used as the thermosetting resin, and a mixture of urethane resin and xylene resin was used as the thermoplastic resin. In addition, p-toluenesulfonic acid was used as a catalyst together with the melamine resin. Referring to Tables 1 and 2, transfer sheets 50 were prepared using the release layers 52 of Examples 1 to 10 and Comparative Examples 1 to 5, and it was investigated whether foil burrs or peeling marks occurred when insert molding was performed using the transfer sheets 50. The amounts of melamine resin, urethane resin, xylene resin, and catalyst in Tables 1 and 2 represent the weight ratios of each. The ratio of thermosetting resin to thermoplastic resin, the amount of melamine resin, the amount of urethane resin, the amount of xylene resin, and the film thickness of the release layer 52 are described as the solid content after the release layer 52 has been coated onto the substrate sheet 51 and dried. In addition, while melamine resin was used as the most preferred thermosetting resin and a mixture of urethane resin and xylene resin was used as the most preferred thermoplastic resin, the materials are not limited to these and other materials can also be used. Furthermore, in the examples and comparative examples shown in Table 1, acrylic resin A was mainly used for the release layer, and the thickness of the release layer was 3 μm. In the examples and comparative examples shown in Table 2, acrylic resin B, which is different from acrylic resin A, was mainly used for the release layer, and the thickness of the release layer was 5 μm.

[0041] In Tables 1 and 2, a ◎ for foil burr resistance indicates a very high foil burr suppression effect. A ○ for foil burr resistance indicates a high foil burr suppression effect. A × for foil burr resistance indicates foil burr is occurring at a level that significantly impacts production yield. A ◎ for peel mark resistance indicates a very high peel mark suppression effect. A ○ for peel mark resistance indicates a high peel mark suppression effect. A × for peel mark resistance indicates peel marks are occurring. In Examples 1 to 10, both foil burr resistance and peel mark resistance were ◎ or ○, indicating that the ratio of thermosetting resin to thermoplastic resin is within the optimal range. On the other hand, in Comparative Examples 1 and 4, the thermosetting resin / thermoplastic resin ratio was 7.85, but foil burrs occurred after insert molding. In Comparative Examples 2, 3, and 5, the thermosetting resin / thermoplastic resin ratio was 1.01, but peel marks were observed after insert molding. Furthermore, foil burrs refer to the residue left as burrs in the non-transfer areas of a molded product from the layer that is transferred to the transfer area. Delamination marks refer to the residue left on the molded product 10 when a portion of the release layer 53 remains on the base sheet side when the base sheet 51 is peeled off together with the release layer 52. From the above, it was found that the optimal thermosetting resin / thermoplastic resin ratio, as shown in Examples 1 to 10, is 2.00 to 6.00, i.e., a ratio of thermosetting resin to thermoplastic resin within the range of 2:1 to 6:1. Furthermore, from Experimental Examples 3 to 5 and Experimental Examples 8 and 9, it was found that when the thermosetting resin / thermoplastic resin ratio is in the range of 2.00 to 6.00 and the release layer film thickness is 0.16 μm to 0.22 μm, the effect of suppressing foil burrs and peeling marks is very high, making it a more preferable range.

[0042] [Table 1]

[0043] [Table 2]

[0044] Next, the molded article 20 according to the second embodiment of this invention will be described, focusing on the differences from the molded article 10 according to the first embodiment.

[0045] Referring to Figure 4, the molded product 20 is the same as the injection-molded body 21 in that an adhesive layer 64 and a release layer 63 are formed on it, but it differs from the molded product 10 according to the first embodiment in that it has an additional decorative layer 65 between the adhesive layer 64 and the release layer 63.

[0046] The molded product 20 is formed by in-mold molding using a transfer sheet 60, which transfers an adhesive layer 64, a decorative layer 65, and a release layer 63 onto the injection-molded body 21.

[0047] Referring to Figure 5, the transfer sheet 60 comprises a base sheet 61, a release layer 62 formed on the base sheet 51, a release layer 63 formed on the release layer 62, a decorative layer 65 formed on the release layer 63, and an adhesive layer 64 formed on the decorative layer 65.

[0048] The decorative layer 65 is a layer for decorating the molded product 20. The decorative layer 65 is formed, for example, by gravure ink. The gravure ink contains a binder resin, a solvent, and a colorant. Examples of binder resins include vinyl chloride vinyl acetate copolymer resin, acrylic resin, polyester resin, and polyurethane resin. The solvent is used to dissolve the resin and is selected according to the resin. Examples of solvents for gravure inks include toluene, methyl ethyl ketone, ethyl acetate, and isopropyl alcohol. The decorative layer 65 is formed, for example, on the entire surface of the molded product 20. It should be noted that decoration is not limited to adding color to the molded product, but may also include adding functionality. Examples of functionality include anti-reflective and anti-glare functions.

[0049] The materials for the other layers and the manufacturing method for the molded article 20 are the same as those for the molded article 10 according to the first embodiment.

[0050] In addition, although the molded products according to the above embodiments are flat plates, they can be any shape that can be formed by injection molding, and may even be three-dimensional.

[0051] Furthermore, in the molded product according to the second embodiment described above, the decorative layer is formed on the entire surface of the molded product, but it is sufficient that the molded product is decorated by the decorative layer, and it may be formed only on the molded product, for example, only on the outer periphery of the molded product.

[0052] Furthermore, although the molded articles according to the above embodiments have been described in which the release layer is the outermost surface, the outermost surface of the molded article is not limited to the release layer, and other layers may be provided. For example, after manufacturing a molded article in which the release layer is the outermost surface by insert molding, other layers can be formed on top of the release layer. Examples of other layers include a hard coat layer.

[0053] Furthermore, although the manufacturing methods for molded articles according to the above embodiments use an injection molding die having an injection port in the second mold, it is sufficient that molten resin can be injected from the injection port into the cavity of the injection molding die, and the injection port may be located in either the first mold or the second mold. [Explanation of symbols]

[0054] 10 Molded products 11 Injection molded body 20 Molded products 21 Injection molded body 50 Transfer Sheets 51 Base Sheet 52 Release layer 53 Exfoliation layer 54 Adhesive layer 60 Transfer Sheets 61 Base Sheet 62 Release layer 63 Exfoliation layer 64 Adhesive layer 80 Injection molding dies 81 First mold 82. Second mold 83 Cavity surface 87 Cavity

Claims

1. Base sheet and A release layer formed on the substrate sheet, The system comprises a release layer formed on the aforementioned release layer, The release layer comprises a thermosetting resin and a thermoplastic resin. The weight ratio of the thermosetting resin to the thermoplastic resin is 2:1 to 6:

1. The thermosetting resin is a melamine resin. The aforementioned thermoplastic resin is a transfer sheet which is a mixture of urethane resin and xylene resin.

2. The transfer sheet according to claim 1, wherein the weight ratio of the urethane resin to the xylene resin is 20:1 to 5:

2.

3. The transfer sheet according to claim 1 or claim 2, wherein the urethane resin has a glass transition temperature of -80°C to 0°C.

4. The transfer sheet according to claim 1 or claim 2, wherein the release layer further comprises p-toluenesulfonic acid as a catalyst.

5. The transfer sheet according to claim 1 or claim 2, wherein the release layer has a thickness of 0.16 μm to 0.22 μm.

6. A step of preparing a transfer sheet comprising a base sheet, a release layer formed on the base sheet, and a release layer formed on the release layer, wherein the release layer contains a thermosetting resin and a thermoplastic resin, the weight ratio of the thermosetting resin to the thermoplastic resin is 2:1 to 6:1, the thermosetting resin is melamine resin, and the thermoplastic resin is a mixture of urethane resin and xylene resin, A step of placing the transfer sheet on the cavity surface of the first mold of an injection molding die having a first mold and a second mold that forms a cavity between itself and the first mold by clamping, The process of clamping the injection molding die, The process involves injecting molten resin into the cavity to form an injection-molded body, and simultaneously transferring the release layer to the surface of the injection-molded body. A method for manufacturing a molded product, comprising the steps of opening the injection molding die, peeling off the release layer and the release layer of the transfer sheet, and removing the injection molded product.

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