Transfer sheet and method for manufacturing molded article

Abstract

[Problem] The present invention addresses the problem of providing: a transfer sheet that is not prone to peeling defects by adjusting the peeling force of the mold release layer of the transfer sheet; a molded article obtained using this transfer sheet. [Solution] In the present invention, a molded article 10 has a flat plate shape, and includes: an injection molded body 11; an adhesive layer 54 formed on the injection molded body 11; and a peel-off layer 53 that is formed on the adhesive layer 54 on the surface on which the injection molded body 11 is not formed. The molded article 10 is configured so that the adhesive layer 54 and the peel-off layer 53 are transferred onto the injection molded body 11 by in-mold molding using a transfer sheet 50. The mold 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.

Description

Transfer sheet and method for manufacturing molded product

[0001] The present invention relates to a method for manufacturing a transfer sheet and a molded product, and more particularly to a method for manufacturing a transfer sheet and a molded product using a transfer sheet that is less likely to cause peeling defects.

[0002] Conventionally, molded products have been produced by in-mold molding, in which a transfer sheet is transferred to an injection-molded body within an injection mold. Such molded products are used for automobile interiors, electrical appliance exteriors, display cover panels, and the like. For example, Patent Document 1 describes a molding method that reduces the occurrence of foil burrs during in-mold molding using a transfer sheet. In Patent Document 1, a product portion and a dummy portion are formed by injection molding with a gap therebetween, and the resins of the product portion and the dummy portion are configured so that they are not connected to each other. While foil burrs tend to occur at the boundary between the transfer area and the non-transfer area, the product portion and the dummy portion 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 portion, making it less likely that foil burrs will occur.

[0003] Patent No. 2020-163585

[0004] In the conventional manufacturing method of a molded product as described above, a step of cutting out the dummy portion from the product portion after molding is required, which can reduce productivity.

[0005] This invention has been made to solve the above-mentioned problems, and aims to provide a transfer sheet that is less likely to have peeling problems by adjusting the peeling force of the release layer of the transfer sheet, and a molded product using such a transfer sheet.

[0006] In order to achieve the above object, a first invention is a transfer sheet comprising a base sheet, a release layer formed on the base sheet, and a peeling 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 releasability of the thermosetting resin and the adhesiveness of the thermoplastic resin, resulting in a transfer sheet that is less likely to produce burrs and leaves no peeling marks.

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

[0009] When configured in this manner, 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 this transfer sheet is used for injection molding, the product has excellent crack resistance and impact resistance, and uneven product characteristics are suppressed.

[0010] A third invention is the transfer sheet of the second invention, wherein the ratio of the urethane resin to the xylene resin is 20:1 to 5:2.

[0011] In this configuration, when the xylene resin is used in a ratio of urethane resin:xylene resin of more than 20:1, the adhesiveness is good and foil burrs are unlikely to occur. Also, when the xylene resin is used in a ratio of less than 5:2, the flexibility is good and cracks are unlikely to occur.

[0012] A fourth invention is the transfer sheet according to the second or third invention, wherein 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 is less likely to change depending on the temperature, making it easier to stabilize moldability.

[0014] A fifth invention is a transfer sheet according to the second or third invention, wherein the release layer further contains 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 releasability derived from the high molecular weight melamine resin, and making it difficult for peeling marks to remain.

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

[0017] By configuring it in this way, the transfer sheet can be highly effective in suppressing foil burrs and peeling marks.

[0018] A seventh invention is a method for manufacturing a molded product, comprising the steps of: preparing a transfer sheet comprising a base sheet, a release layer formed on the base sheet, and a peel 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 a cavity surface of a first mold of an injection molding mold having a first mold and a second mold that forms a cavity between the first mold and a second mold by clamping the injection molding mold; clamping the injection molding mold; injecting molten resin into the cavity to form an injection molded product, and simultaneously transferring the release layer to the surface of the injection molded product; and opening the injection molding mold, peeling the base sheet of the transfer sheet together with the release layer from the molded product, and removing the injection molded product.

[0019] With this configuration, the release layer has a good balance between the releasability of the thermosetting resin and the adhesiveness of the thermoplastic resin, resulting in a molded product that is less likely to produce burrs and leaves no peeling marks.

[0020] According to the present invention, it is possible to obtain a transfer sheet that is less prone to peeling defects and a molded product using the transfer sheet.

[0021] Fig. 1 is a schematic cross-sectional view of a molded product according to a first embodiment of the present invention. Fig. 2 is a schematic cross-sectional view of a transfer sheet according to a first embodiment of the present invention. Fig. 3 is a schematic cross-sectional view illustrating a manufacturing process of a molded product according to a first embodiment of the present invention. Fig. 4 is a schematic cross-sectional view of a molded product according to a second embodiment of the present invention. Fig. 5 is a schematic cross-sectional view of a transfer sheet according to a second embodiment of the present invention.

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

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

[0024] 2, the transfer sheet 50 includes a base sheet 51, a release layer 52 formed on the base sheet 51, a peeling layer 53 formed on the release layer 52, and an adhesive layer 54 formed on the peeling layer 53. The molded product 10 is used for, for example, a cover panel for a display, an interior of an automobile, or an exterior of an electrical appliance.

[0025] The injection-molded body 11 may be made of, for example, a general-purpose resin such as polystyrene resin, polyolefin resin, ABS resin, AS resin, or AN resin; a general-purpose engineering resin such as polycarbonate resin, acrylic resin, or thermoplastic polyurethane; or a super-engineering resin such as polyimide resin or liquid crystal polyester resin. Composite resins containing reinforcing materials such as glass fiber or inorganic filler may also be used. The thickness of the molded resin body 11 is not particularly limited and is selected to match the thickness of the housing of the product to be manufactured.

[0026] The base sheet 51 supports the release layer 52, peel layer 53, and adhesive layer 54. Examples of the base sheet 51 include thermoplastic resins 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, and ABS resin, as well as 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, the base sheet 51 has a thickness that is excellent in handleability, and if the thickness is 200 μm or less, the base sheet 51 has appropriate rigidity and therefore good flexibility.

[0027] The release layer 52 is a layer that is peeled off together with the base 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, the release layer 52 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, the layer can be stably applied to the base sheet, and good releasability can be obtained. If the thickness is 0.5 μm or less, unevenness in the thickness of the release layer is less likely to occur, and releasability is more likely to be stable.

[0028] The thermosetting resin is a material that can mainly impart releasability to the release layer 52, and examples of suitable thermosetting resins include melamine resin, urea resin, epoxy resin, and urethane resin. Melamine resin is particularly preferred, as it has good releasability when used in the transfer sheet 50. Examples of suitable melamine resins include butyl group-type melamine, ethyl group-type melamine, methyl group-type melamine, imino group-type melamine, mixed imino group-ethyl group-type melamine, butyrol group-type melamine, ethylol group-type melamine, and methylol group-type melamine.

[0029] An acid catalyst may be used in combination with the thermosetting resin. When forming the release layer 52 on the base sheet 51, for example, various materials including a thermosetting resin are diluted with an organic solvent, applied to the base sheet 51, and then dried and cured. The use of an acid catalyst in this process promotes the polymerization of the low-molecular-weight material that becomes a thermosetting resin after polymerization, which is contained in the material diluted with the organic solvent along with the thermosetting resin, thereby achieving good release properties derived from the high-molecular-weight thermosetting resin. Furthermore, when a melamine resin is used as the thermosetting resin, it is preferable to use p-toluenesulfonic acid as the acid catalyst. The use of p-toluenesulfonic acid as the acid catalyst promotes the polymerization of the low-molecular-weight melamine particularly efficiently.

[0030] The thermoplastic resin is a resin that mainly imparts adhesiveness to the release layer 52, and for example, a urethane resin or an acrylic resin can be used as the base resin, and a xylene resin, petroleum resin, terpene resin, rosin, or the like can be used as the tackifier. One or more of these materials may be used.

[0031] It is more preferable to use a melamine resin as the thermosetting resin and a mixture of a urethane resin and a xylene resin as the thermoplastic resin as the material for the release layer 52. Melamine resin has good releasability when used in the transfer sheet 50. Urethane resin has high flexibility as well as adhesiveness, and therefore has excellent crack resistance and impact resistance when injection molding is performed using the transfer sheet 50. Xylene resin not only provides adhesion but also acts as a compatibilizer for the melamine resin and the urethane resin, making it easier to form the release layer 52 into a uniform film and suppressing unevenness in product characteristics.

[0032] Examples of urethane resins include urethane resins obtained by polymerizing a polyol resin and an isocyanate. Examples of polyol resins that can be used include polyester polyols and polyether polyols, which are commonly used in adhesive applications. Examples of isocyanates that can be used include 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. The glass transition temperature of the urethane resin is preferably −80° C. to 0° C., 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 is unlikely to change with temperature, so that moldability is likely to be stable. As the xylene resin, for example, an unmodified xylene resin crosslinked with a methylene bond or an ether bond 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 releasability of the thermosetting resin and the adhesiveness of the thermoplastic resin, resulting in a transfer sheet that is less likely to produce burrs and leaves no peeling marks.

[0034] When a mixture of urethane resin and xylene resin is used as the thermoplastic resin, the ratio of urethane resin to xylene resin is preferably 20:1 to 5:2. When the xylene resin is more than 20:1 (urethane resin:xylene resin), good adhesiveness is exhibited, making foil burrs less likely to occur. When the xylene resin is less than 5:2 (urethane resin:xylene resin), the good flexibility inherent in the urethane resin is fully obtained, making cracks less likely to occur during molding.

[0035] The release layer 53 is a layer that becomes the outermost surface of the molded article 10 by being peeled off at the interface between the release layer 52 and the release layer 53 during in-mold molding. The release layer 53 may function as a layer having hard coating properties and chemical resistance to protect the molded article 10. Examples of materials that can be used for the release layer 53 include thermoplastic resins such as acrylic resins, polystyrene resins, polyamide resins, chlorinated polyolefin resins, chlorinated ethylene-vinyl acetate copolymer resins, cyclized rubbers, and coumarone-indene resins. The release layer 53 may also be formed using a photocurable resin such as an ultraviolet-curable resin, a radiation-curable resin such as an electron beam-curable resin, or a thermosetting resin. Examples of such resins include urethane acrylate resins, cyanoacrylate resins, epoxy acrylate resins, polyester acrylate resins, and resins obtained by adding additives such as isocyanates to these resins.

[0036] The adhesive layer 54 is a layer for adhering the transfer sheet 50 and the injection-molded body 11. For example, an acrylic resin, a urethane resin, a polyester resin, a polyvinyl acetate resin, a vinyl chloride resin, or a 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, an outline of a method for manufacturing the molded product 10 according to the first embodiment of the present invention will be described with reference to the drawings.

[0038] Referring to FIG. 3( a), a transfer sheet 50 is prepared. The transfer sheet 50 includes a base sheet 51, a release layer 52 formed on the base sheet 51, a peeling layer 53 formed on the release layer 52, and an adhesive layer 54 formed on the peeling layer 53. The transfer sheet 50 is placed in an injection molding die 80. The injection molding die 80 is composed of a first die 81 and a second die 82. The first die 81 has a cavity surface 83 formed therein that corresponds to the shape of the molded product 10, and the second die 82 has an injection port 84 formed therein for injecting molten resin. Furthermore, by clamping the first die 81 and the second die 82 together, a space is formed between the first die 81 and the second die 82. This space is called a cavity 87. In the process of placing the transfer sheet 50 in the injection molding die 80, the transfer sheet 50 passes over a guide roller 85 from above the first die 81, is placed between the first die 81 and the second die 82 so that the base sheet 51 faces the cavity surface 83 of the first die 81, and passes under the guide roller 86. Next, referring to FIG. 3( b), a suction mechanism (not shown) applies suction from the first die 81 side, thereby three-dimensionally molding the transfer sheet 50 along the shape of the cavity surface 83 of the first die 81. Next, referring to FIG. 3( c), the first die 81 and the second die 82 are clamped together. Next, molten resin is injected from the injection port 84 of the second die 82 to form the injection-molded body 11, and simultaneously, the adhesive layer 54 of the transfer sheet 50 is fixed to the surface of the injection-molded body 11 facing the first die 81. Next, referring to Figure 3 (d), the injection molding die 80 is opened, and the portion of the transfer sheet 50 that is adhered to the injection molded body 11 is released at the interface between the release layer 52 and the peeling layer 53, and the molded article 10 in which the adhesive layer 54 and the peeling layer 53 are adhered to the injection molded body 11 is removed, thereby producing the molded article 10.

[0039] The transfer sheet 50 used in the above manufacturing method is configured so that the release layer 52 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. If the ratio of the thermosetting resin to the thermoplastic resin is within the above range, the balance between the releasability derived from the thermosetting resin of the release layer 52 and the adhesiveness derived from the thermoplastic resin is good, and when the base sheet 51 and the release layer 52 are peeled off after injection molding or transfer, burrs are unlikely to occur and peeling marks are unlikely to remain.

[0040] Next, the effects and advantages of using a thermosetting resin and a thermoplastic resin in a ratio of 2:1 to 6:1 for the release layer 52 will be described. Melamine resin was used as the thermosetting resin, and a mixture of urethane resin and xylene resin was used as the thermoplastic resin. Furthermore, p-toluenesulfonic acid was used as a catalyst together with the melamine resin. Referring to Tables 1 and 2, transfer sheets 50 were created using the release layers 52 of Examples 1 to 10 and Comparative Examples 1 to 5, and an investigation was conducted into whether foil burrs or peeling marks would occur during insert molding using the transfer sheets 50. The amounts of melamine resin, urethane resin, xylene resin, and catalyst in Tables 1 and 2 represent their respective weight ratios. Furthermore, 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 listed in terms of solid content after the release layer 52 is applied to the base sheet 51 and dried. Although melamine resin, which is the most preferred thermosetting resin, and a mixture of urethane resin and xylene resin, which are the most preferred thermoplastic resins, were used, other materials can also be used. Furthermore, in the examples and comparative examples shown in Table 1, acrylic resin A was primarily 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 primarily used for the release layer, and the thickness of the release layer was 5 μm.

[0041] In Tables 1 and 2, a mark of ◎ for foil burr resistance indicates a very high foil burr suppression effect. A mark of ○ for foil burr resistance indicates a high foil burr suppression effect. A mark of × for foil burr resistance indicates that foil burrs have occurred at a level that significantly impacts production yield. A mark of ◎ for peel mark resistance indicates a very high peel mark suppression effect. A mark of ○ for peel mark resistance indicates a high peel mark suppression effect. A mark of × for peel mark resistance indicates that peel marks have occurred. In Examples 1 to 10, both foil burr resistance and peel mark resistance were marked ◎ or ○, indicating that the ratio of thermosetting resin to thermoplastic resin was 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. The term "foil burrs" refers to a layer transferred to a transfer area of ​​a molded product, remaining as a burr in a non-transfer area. The term "peeling marks" refers to a portion of the release layer 53 remaining on the base sheet when the base sheet 51 is peeled off together with the release layer 52, resulting in a transfer defect remaining on the molded product 10. From the above, it was found that the thermosetting resin / thermoplastic resin ratio shown in Examples 1 to 10 is optimal when it is 2.00 to 6.00, i.e., when the thermosetting resin / thermoplastic resin ratio is in the range of 2:1 to 6:1. Furthermore, Experimental Examples 3 to 5, 8, and 9 revealed 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 effects of suppressing foil burrs and peeling marks are extremely high, and this range is more preferable.

[0042]

[0043]

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

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

[0046] The molded product 20 is produced by in-mold molding using a transfer sheet 60, in which an adhesive layer 64, a decorative layer 65, and a release layer 63 are transferred onto an 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 peeling layer 63 formed on the release layer 62, a decorative layer 65 formed on the peeling 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 article 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 gravure ink solvents 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 article 20. Note that decoration is not limited to the application of imparting color to the molded article, and may also include imparting functions. Examples of imparting functions include anti-reflection and anti-glare functions.

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

[0050] Although the molded articles according to the above embodiments are flat plate-shaped, they may have any shape that can be formed by injection molding, including three-dimensional shapes.

[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 as long as the molded product is decorated with the decorative layer, it may be formed only on a portion of the molded product, for example, on only the outer periphery of the molded product.

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

[0053] Furthermore, in the manufacturing methods of molded products according to each of the above embodiments, an injection molding die having an injection port in the second mold is used, but as long as molten resin can be injected from the injection port into the cavity of the injection molding die, the injection port may be located in either the first mold or the second mold.

[0054] REFERENCE SIGNS LIST 10 Molded article 11 Injection molded article 20 Molded article 21 Injection molded article 50 Transfer sheet 51 Base sheet 52 Release layer 53 Peel layer 54 Adhesive layer 60 Transfer sheet 61 Base sheet 62 Release layer 63 Peel layer 64 Adhesive layer 80 Injection molding die 81 First die 82 Second die 83 Cavity surface 87 Cavity

Claims

1. A transfer sheet comprising: a base sheet; a release layer formed on said base sheet; and a peeling layer formed on said release layer, said release layer containing a thermosetting resin and a thermoplastic resin, and a ratio of said thermosetting resin to said thermoplastic resin is 2:1 to 6:

1.

2. The transfer sheet according to claim 1, wherein the thermosetting resin is a melamine resin, and the thermoplastic resin is a mixture of a urethane resin and a xylene resin.

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

2.

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

5. The transfer sheet according to claim 2 or 3, wherein the release layer further contains p-toluenesulfonic acid as a catalyst.

6. The transfer sheet according to claim 2 or 3, wherein the release layer has a thickness of 0.16 μm to 0.22 μm.

7. A method for manufacturing a molded product, comprising the steps of: preparing a transfer sheet comprising a base sheet, a release layer formed on the base sheet, and a peeling layer formed on the release layer, the release layer containing a thermosetting resin and a thermoplastic resin, the ratio of the thermosetting resin to the thermoplastic resin being 2:1 to 6:1; placing the transfer sheet on a cavity surface of a first mold of an injection molding die having a first mold and a second mold which forms a cavity between the first mold and a second mold by clamping the first mold; clamping the injection molding die; injecting molten resin into the cavity to mold an injection molded product, and at the same time transferring the peeling layer to a surface of the injection molded product; opening the injection molding die, peeling the base sheet of the transfer sheet together with the release layer from the molded product, and removing the injection molded product.

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