Unpainted resin molded product with a two-layer structure

Abstract

The present invention provides a means for achieving both impact resistance and rigidity in an unpainted resin molded product having a two-layer structure comprising a thermoplastic resin layer and a filler-containing layer containing a thermoplastic resin and a filler. [Solution] The present invention relates to an unpainted resin molded product having a two-layer structure comprising a thermoplastic resin layer containing a thermoplastic resin and a filler-containing layer disposed on top of the thermoplastic resin layer, wherein the ratio of the thickness of the filler-containing layer to the combined thickness of the thermoplastic resin layer and the filler-containing layer is in the range of 0.167 to 0.333.

Description

Technical Field

[0001] The present invention relates to an unpainted resin molded product having a two-layer structure, which is characterized by achieving both impact resistance and rigidity.

Background Art

[0002] Conventionally, in various molded products, for example, parts used in automobiles and the like, painting has been performed on the surface of the parts for the purpose of protecting the molded product, imparting desirable functions and aesthetics.

[0003] On the other hand, in recent years, considering the reduction of carbon dioxide during the production of parts of products such as automobiles and recyclability in the market, unpainted, that is, unpainted resin parts are increasing in the market. And in unpainted resin (adhesive resin) parts, in order to exhibit a high-luminance appearance, it has been carried out to incorporate an inorganic or metal filler into the resin.

[0004] In the method of incorporating an inorganic or metal filler into a resin, it is known that the filler improves the rigidity of the resin, but on the other hand, it reduces the impact resistance. Therefore, high-luminance adhesive resin parts molded by injection molding have ensured impact resistance by increasing their thickness (sarcastically) or restricting the structure of the parts. However, thickening has problems in that the mass increases and the rigidity of the parts becomes excessive, and restricting the structure has a problem in that the design freedom decreases.

[0005] Japanese Patent Application Laid-Open No. 2003-103705 (Patent Document 1) discloses a resin laminate that can be electrostatically painted and is excellent in impact resistance, heat resistance, and rigidity. The resin laminate disclosed in Patent Document 1 is produced by laminating a layer (A) in which a conductive filler is added to a thermoplastic resin and a layer (B) in which no filler or only a small amount of filler is added to the thermoplastic resin. In Patent Document 1, from the viewpoints of impact resistance and moldability of the laminate, it is disclosed that the ratio of the thickness of the layer (A) to the total thickness of the laminate is from 0.01 to 0.3.

[0006] Japanese Patent Publication No. 4-153036 (Patent Document 2) discloses a resin molded product for vehicles, characterized in that the inner layer is made of a propylene molding material and the outer layer is made of a polypropylene molding material mixed with an inorganic filler.

[0007] Japanese Utility Model Publication No. 60-114730 (Patent Document 3) discloses a surface-processed plastic sheet characterized by coating a base sheet made of a plastic sheet to which additives have been added with a surface layer containing a binder resin, solvent, dispersant, filler, etc., without stretching the base sheet.

[0008] Japanese Patent Publication No. 2024-022209 (Patent Document 4) discloses a resin composition that contains post-consumer recycled materials while exhibiting excellent properties that enable horizontal recycling into resin sheets or resin containers, and a resin sheet or resin container using this resin composition.

[0009] Japanese Patent Publication No. 2001-038852 (Patent Document 5) discloses a molded article made of a thermoplastic resin that has excellent rigidity and impact resistance without the use of fillers or glass fibers, and a method for manufacturing the same. According to Patent Document 5, by using a specific laminate (α) with excellent rigidity and impact resistance in the part of a thermoplastic resin molded article where rigidity or impact resistance is required, a molded article with excellent rigidity and impact resistance can be obtained even with a complex shape. Furthermore, by arranging the laminate (α) in the outermost layer on one or both sides, a molded article with excellent design and surface hardness can be obtained. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2003-103705 [Patent Document 2] Japanese Patent Application Publication No. 4-153036 [Patent Document 3] Japanese Utility Model Publication No. 60-114730 [Patent Document 4] Japanese Patent Publication No. 2024-022209 [Patent Document 5] Japanese Patent Publication No. 2001-038852 [Overview of the project] [Problems that the invention aims to solve]

[0011] The resin laminate described in Patent Document 1 has a coating applied to the resin, and does not relate to a material-bonded resin. Therefore, the thickness ratio of 0.01 to 0.3 disclosed in Patent Document 1 is a numerical range in which rigidity and impact resistance can be achieved when a coating is applied. Since the rigidity of a coated resin is improved by the annealing effect due to the heat during coating, the rigidity may be insufficient in this numerical range for a material-bonded resin that is not coated, and the conditions under which rigidity and impact resistance can be achieved in a material-bonded resin are unknown.

[0012] Furthermore, polypropylene molding materials mixed with inorganic fillers have the problem of becoming heavier. According to the technology in Patent Document 2, the outer layer can have sufficient heat resistance and rigidity by mixing in inorganic fillers, while the weight of the inner layer can be reduced by mixing in a foaming agent or the like into the polypropylene molding material. Patent Document 2 discloses the reduction of the weight of the inner layer, but it does not show the conditions under which rigidity and impact resistance can be achieved simultaneously, such as the ratio of the outer layer to the inner layer.

[0013] Although Patent Document 3 discloses a plastic sheet in which a filler layer or the like is superimposed on a plastic sheet, this plastic sheet is intended to provide offset printability and resistance to repeated use, and does not disclose any means for achieving both impact resistance and rigidity in the resin.

[0014] Regarding Patent Document 4, in resin compositions using post-consumer recycled materials alone, the DuPont impact strength is low, at only 1.9 J / mm or 2.2 J / mm, and while cascade recycling is possible, horizontal recycling cannot be achieved. When post-consumer recycled materials are laminated with unused propylene-based polymer materials by heat pressing or the like, a resin sheet exhibiting high DuPont impact strength can be formed. When the post-consumer recycled material content is set to 5 to 50% by mass, the DuPont impact strength of the resin sheet is dramatically improved while maintaining strength.

[0015] Thus, Patent Document 4 discloses a component (resin container) that achieves both impact resistance and strength by laminating materials with low and high impact resistance. However, in Patent Document 4, as the post-consumer content with low impact resistance increases, the DuPont impact decreases uniformly in a parabolic shape, and there is no characteristic relationship. Therefore, in Patent Document 4, the only difference in properties between post-consumer recycled materials and unused propylene-based polymer materials is impact resistance, and no characteristic relationship is shown even when they are composited.

[0016] While the embodiments in Patent Document 5 disclose examples of ensuring impact resistance and ensuring rigidity, there is no disclosure of how to create a component that achieves both impact resistance and rigidity simultaneously.

[0017] Thus, none of the prior art documents disclose the optimal conditions for achieving both impact resistance and rigidity in unpainted resin-coated products. Therefore, the object of the present invention is to provide a means for achieving both impact resistance and rigidity in an unpainted resin molded product having a two-layer structure comprising a thermoplastic resin layer and a filler-containing layer containing a thermoplastic resin and a filler. [Means for solving the problem]

[0018] As a result of intensive research by the present inventors to solve the above problems, in an unpainted resin molded product having a two-layer structure including a thermoplastic resin layer and a filler-containing layer in which a filler is added to the thermoplastic resin layer to exhibit a high-luminance appearance, it has been found that impact resistance and rigidity can be achieved simultaneously by setting the ratio of the thickness of the filler-containing layer within the range of 0.167 to 0.333 in the combined thickness of the thermoplastic resin layer and the filler-containing layer.

[0019] That is, the present invention includes the following inventions. (Embodiment 1) An unpainted resin molded product having a two-layer structure including a thermoplastic resin layer containing a thermoplastic resin and a filler-containing layer disposed on the upper layer of the thermoplastic resin layer and containing a thermoplastic resin and a filler, wherein the ratio of the thickness of the filler-containing layer in the combined thickness of the thermoplastic resin layer and the filler-containing layer is within the range of 0.167 to 0.333. (Embodiment 2) The unpainted resin molded product according to Embodiment 1, wherein the thermoplastic resin is a resin selected from the group consisting of a polypropylene resin, a polyamide resin, an acrylic resin, and a polyethylene resin. (Embodiment 3) The unpainted resin molded product according to Embodiment 2, wherein the thermoplastic resin is a polypropylene resin. (Embodiment 4) The unpainted resin molded product according to any one of Embodiments 1 to 3, wherein the filler is made of at least one material selected from the group consisting of aluminum flakes, mica, pearl, glass fiber, and carbon fiber. (Embodiment 5) The unpainted resin molded product according to Embodiment 4, wherein the filler is aluminum flakes. (Embodiment 6) A method for manufacturing an unpainted resin molded product having a two-layer structure in which a thermoplastic resin layer containing a thermoplastic resin and a filler-containing layer containing a thermoplastic resin and a filler are laminated, including a molding step of disposing the filler-containing layer on the upper layer of the thermoplastic resin layer and performing molding. The method wherein the ratio of the thickness of the filler-containing layer in the combined thickness of the thermoplastic resin layer and the filler-containing layer is within the range of 0.167 to 0.333. (Embodiment 7) The method according to Embodiment 6, wherein the molding step is performed by two-color molding or press molding.

Advantages of the Invention

[0020] According to the present invention, in an unpainted resin molded article, by disposing a filler-containing layer in which a filler is contained in a thermoplastic resin at a specific range of thickness on the upper layer of the thermoplastic resin layer, it has become possible to achieve both impact resistance and rigidity. Further, by containing a high-brightness filler having the property of reflecting light in the filler-containing layer, a high-brightness appearance can also be imparted to the unpainted resin molded article.

Brief Description of the Drawings

[0021] [Figure 1] It is a schematic diagram showing an outline of the configuration of the unpainted resin molded article of the present invention. [Figure 2] It is a schematic diagram of the configuration of an unpainted resin molded article in which the ratio of the resin layer (thermoplastic resin layer) and the high-brightness layer (filler-containing layer) prepared in Test 1 is variously changed (from Level A to G), and the thickness (mm) of the resin layer and the high-brightness layer. [Figure 3] It is a schematic diagram showing an outline of the tensile modulus of elasticity test of Test 2. [Figure 4] It is a schematic diagram showing an outline of the impact resistance test of Test 3. [Figure 5] It is a diagram showing the results of measuring the impact resistance (left vertical axis, 〇) and the rigidity (right vertical axis, □) in a flat plate of an unpainted resin molded article in which the ratio of the high-brightness layer is variously changed.

Modes for Carrying Out the Invention

[0022] The present invention will be described in more detail.

[0023] (1) Unpainted resin molded product of the present invention The unpainted resin molded product of the present invention has a two-layer structure comprising a thermoplastic resin layer containing a thermoplastic resin and a filler-containing layer disposed on top of the thermoplastic resin layer, characterized in that the ratio of the thickness of the filler-containing layer to the combined thickness of the thermoplastic resin layer and the filler-containing layer is in the range of 0.167 to 0.333.

[0024] In this specification, "unpainted resin" refers to resin that has not undergone any coating treatment. In this specification, "unpainted resin" may also be referred to as "coated resin."

[0025] In this specification, "unpainted resin molded product" means a resin molded product manufactured without painting.

[0026] In this specification, an unpainted resin molded product manufactured for use as a component of a product is referred to as an "unpainted resin part."

[0027] In this specification, "thermoplastic resin layer" refers to a resin layer containing thermoplastic resin that serves as the base material for a resin molded product. In this specification, "thermoplastic resin layer" may also be simply referred to as "resin layer."

[0028] In this specification, "filler-containing layer" refers to a layer of resin to which a filler has been added to the base resin. In this specification, "filler-containing layer" may also be simply referred to as "filler layer."

[0029] By using a high-brightness filler in the filler-containing layer, a high-brightness appearance can also be imparted to the unpainted resin molded product of the present invention. In this specification, when such a filler is included, the filler-containing layer may be referred to as the "high-brightness layer" or "high-brightness resin layer."

[0030] Furthermore, it is possible to apply a design to the surface of the filler layer. In this specification, the surface of the filler-containing layer to which a design has been applied is referred to as the "designed surface".

[0031] As mentioned in the section on prior art, there is a growing trend to use unpainted resin parts in automobiles and other vehicles, as these parts offer advantages in reducing carbon dioxide emissions and being easily recyclable in the market.

[0032] The present invention provides a material-bonded resin part in which a high-gloss filler layer is placed only on the design surface, and the other layers consist of resin layers without filler, achieved by methods such as two-color molding or press molding with laminated resin. With this configuration, the present invention provides a material-bonded resin material that achieves both impact resistance and rigidity, and furthermore, has a high-gloss appearance.

[0033] High-brightness filler layers have high rigidity due to the presence of fillers. In resin molded products consisting of two layers—a resin layer and a filler layer—rigidity increases as the proportion of the high-brightness resin layer in the total thickness of the resin molded product increases. In the case of painted resin molded products, rigidity increases due to the annealing effect caused by the heat during painting. However, unpainted resin molded products do not benefit from this effect because they are not painted. Therefore, it is necessary to provide unpainted resin molded products with a high-brightness layer of appropriate thickness to achieve rigidity equivalent to that of painted resin parts. On the other hand, mixing fillers into the resin reduces its impact resistance.

[0034] The inventors have found conditions for achieving both impact resistance and rigidity in unpainted resin molded products. Specifically, by examining the relationship between the ratio of the thickness of the resin layer and the filler layer in a resin plate with varying thickness ratios, and the relationship between impact resistance and rigidity, it was found that for rigidity, the proportion of the high-brightness layer in the resin plate must be 0.167 or higher, and for impact resistance, the proportion of the high-brightness layer in the resin plate must be 0.333 or lower. Therefore, in the unpainted resin molded product of the present invention, impact resistance and rigidity are achieved when the ratio of the thickness of the filler-containing layer to the combined thickness of the thermoplastic resin layer and the filler-containing layer is in the range of 0.167 to 0.333. The ratio of the thickness of the high-brightness layer can be appropriately selected depending on whether impact resistance or rigidity is to be prioritized.

[0035] The type of thermoplastic resin is not limited, but suitable examples of thermoplastic resins include polypropylene resin, polyamide resin, acrylic resin, and polyethylene resin. Polypropylene is particularly preferred as the thermoplastic resin used in the present invention.

[0036] The type of filler is not limited, but suitable examples of fillers include aluminum flakes, mica, pearl, glass fiber, and carbon fiber. Because these fillers have light-reflecting properties, they can impart a high-brightness appearance to the filler layer and further enhance its metallic design. The most preferred filler used in this invention is aluminum flakes.

[0037] In the filler-containing layer, the filler content can be, for example, in the range of 0.6 to 10% by mass, more preferably 1% by mass, relative to the total mass of the filler content, but is not limited to this range. If it is below the lower limit, the rigidity of the unpainted resin molded product of the present invention may decrease. Also, if it exceeds the upper limit, the impact resistance of the unpainted resin molded product of the present invention may decrease. Therefore, by keeping the filler content in the filler-containing layer within the range exemplified above, the unpainted resin molded product of the present invention can achieve both impact resistance and rigidity.

[0038] In this invention, the rigidity of the unpainted resin molded product can be determined, for example, by a static tensile test. Furthermore, the impact resistance of the unpainted resin molded product can be determined, for example, by a puncture test.

[0039] (2) Method for manufacturing unpainted resin molded articles of the present invention Another aspect of the present invention is a method for manufacturing an unpainted resin molded article as described in (1) above. The method of the present invention is a method for manufacturing an unpainted resin molded article having a two-layer structure in which a thermoplastic resin layer containing a thermoplastic resin and a filler-containing layer containing a thermoplastic resin and a filler are laminated, and is characterized in that the ratio of the thickness of the filler-containing layer to the combined thickness of the thermoplastic resin layer and the filler-containing layer is in the range of 0.167 to 0.333.

[0040] An unpainted resin molded product containing a thermoplastic resin layer and a filler-containing layer is as described in (1) above.

[0041] The present invention relates to a method for producing an unpainted resin molded product, which includes a molding step in which a filler-containing layer is placed on top of a thermoplastic resin layer and then molded. Suitable molding methods in the present invention include, but are not limited to, two-color molding and press molding.

[0042] Two-color molding is a type of injection molding in which a heated and molten material (such as a thermoplastic resin) is extruded into a mold and solidified by cooling. It refers to a molding method that combines and integrates two different resins or materials.

[0043] Press forming is a type of plastic deformation process that utilizes the plastic deformation of a workpiece. It involves heating and softening the workpiece, then applying pressure with a processing machine to shape the material into the form of a mold.

[0044] For example, by placing a filler-containing layer on top of a thermoplastic resin layer and performing two-color molding or press molding, the unpainted resin molded product described in (1) above can be manufactured.

[0045] The temperature range during press molding can be, for example, 155°C to 170°C, more preferably 160°C to 165°C, but is not limited to this range.

[0046] For the reasons stated in (1) above, in the method of the present invention, the ratio of the thickness of the filler-containing layer to the combined thickness of the thermoplastic resin layer and the filler-containing layer is in the range of 0.167 to 0.333. In the method of the present invention, the unpainted resin molded product described in (1) above can be efficiently manufactured. [Examples]

[0047] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0048] (Test 1) Flat sheets of unpainted resin molded products were fabricated by varying the ratio of the thickness of the thermoplastic resin layer (resin layer) to the thickness of the high-brightness layer (filler-containing layer) as described below.

[0049] Specifically, a flat plate was manufactured by press molding, in which a high-brightness layer, made by adding aluminum flakes as a filler to polypropylene resin, was placed on top of a resin layer made of polypropylene resin. The ratio of aluminum flakes in the polypropylene resin in the high-brightness layer was 1% by mass. The thickness of the flat plate was 3 mm.

[0050] The conditions under which the flat plate was manufactured by press forming are as follows: Specifically, flat plates were produced by press molding under conditions of a resin temperature of 160-165°C during pressing.

[0051] Flat plates were fabricated so that the ratio of the thickness (mm) of the resin layer to the high-brightness resin layer fell into seven levels, A through G, as shown below (Figures 1 and 2). Level A has a resin layer thickness of 3 mm and a high-brightness resin layer thickness of 0 mm. Level B has a resin layer thickness of 2.5 mm and a high-brightness resin layer thickness of 0.5 mm. Level C has a resin layer thickness of 2 mm and a high-brightness resin layer thickness of 1 mm. Level D has a resin layer thickness of 1.5 mm, and the high-brightness resin layer thickness is 1.5 mm. Level E has a resin layer thickness of 1 mm, and a high-brightness resin layer thickness of 2 mm. Level F has a resin layer thickness of 0.5 mm, and a high-brightness resin layer thickness of 2.5 mm. Level G has a resin layer thickness of 0 mm, and a high-brightness resin layer thickness of 3 mm.

[0052] (Exam 2) The tensile modulus (stiffness) of flat, unpainted resin molded products of levels A to G, prepared in Test 1, was evaluated. The tensile modulus was measured according to the method specified in ISO 527. Figure 3 shows a schematic diagram of Test 2.

[0053] The results of the tensile modulus measurements are shown in Table 1.

[0054] [Table 1]

[0055] The tensile modulus (MPa) is the experimental data of the tensile modulus actually obtained in this test. The Δ modulus is the difference obtained by subtracting the value of the minimum tensile modulus (level A) from the tensile modulus of each level. The normalization is the percentage of the Δ modulus of each level, with the value of the Δ modulus of the level showing the maximum tensile modulus (level G) being set to 100%.

[0056] Table 1 shows that as the proportion of the high-brightness layer thickness increases, the tensile modulus increases, making the plate less susceptible to deformation from external forces. In other words, the high-brightness layer containing the filler has high rigidity, and the rigidity increases as the proportion of the high-brightness layer in the plate thickness increases.

[0057] (Exam 3) The impact resistance of flat plates of unpainted resin molded products of levels A to G, prepared in Test 1, was evaluated. The impact was applied to the high-gloss layer on top of the resin layer, with a surface impact from above. Impact resistance was measured using a HydroShot HITS-PX puncture impact tester at a test temperature of 23°C. Figure 4 shows a schematic diagram of Test 3.

[0058] The results of the impact resistance measurements are shown in Table 2.

[0059] [Table 2]

[0060] Impact resistance (N·mm) is the experimental data of impact resistance actually obtained in this test. Δ Impact resistance is the difference obtained by subtracting the minimum impact resistance value (level G) from the impact resistance value of each level. Normalization is the percentage of Δ Impact resistance for each level, with the Δ modulus value of the level showing the maximum Δ Impact resistance (level A) set to 100%. Table 2 shows that the impact resistance decreases as the proportion of the high-brightness layer thickness increases.

[0061] (Consideration) Figure 5 shows a plot of the relationship between the proportion of the high-brightness layer in the plate thickness (horizontal axis), impact resistance (left vertical axis, ○), and rigidity (right vertical axis, □). As shown in Figure 5, the high-brightness layer has high rigidity because it contains fillers, and the rigidity increases as the proportion of the high-brightness layer in the plate thickness increases.

[0062] As mentioned earlier, painted resin parts gain increased rigidity (modulus of elasticity) due to the annealing effect caused by the heat generated during painting. However, unpainted resin parts also require the same level of rigidity as painted parts. In a separate experiment, when a polypropylene resin plate similar to that in the above example was painted, the measured tensile modulus of elasticity was 1850 MPa, indicating that the rigidity improved by approximately 3% due to the heat generated during painting.

[0063] Therefore, for material-bonded resin parts, the same rigidity of approximately 1850 MPa as for painted resin parts was used as an evaluation index. Thus, the range in which appropriate rigidity is achieved was defined as 16.8 or higher in the standardized numerical value. Therefore, in terms of rigidity, the proportion of the high-brightness layer in the plate thickness must be 0.167 or higher.

[0064] On the other hand, as shown in Figure 5 (and Table 2), impact resistance decreases as the proportion of the high-brightness layer in the plate thickness increases. Furthermore, when the proportion of the high-brightness layer in the plate thickness exceeds 0.333, the relationship with the proportion of the high-brightness layer is no longer a uniform decrease.

[0065] When the thickness of the high-brightness layer is thin, the force applied by the impact is in the compressive direction, allowing it to withstand the impact. On the other hand, if the proportion of the high-brightness layer in the total thickness exceeds 0.333, tensile force is applied to the high-brightness layer soon after the impact, causing cracks to form in the resin plate, and these cracks propagate and grow. Therefore, in terms of impact resistance, the proportion of the high-brightness layer in the total thickness needs to be 0.333 or less.

[0066] From the above, in unpainted resin parts, the range in which both impact resistance and rigidity are achieved is when the proportion of the high-gloss layer in the plate thickness is between 0.167 and 0.333. The present invention provides conditions that enable both impact resistance and rigidity to be achieved in unpainted resin molded products.

[0067] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. In addition, it is possible to add, delete, and / or replace some of the configurations in each embodiment with other configurations.

Claims

1. An unpainted resin molded product having a two-layer structure comprising a thermoplastic resin layer containing a thermoplastic resin and a filler-containing layer disposed on top of the thermoplastic resin layer, The unpainted resin molded product wherein the ratio of the thickness of the filler-containing layer to the combined thickness of the thermoplastic resin layer and the filler-containing layer is in the range of 0.167 to 0.

333.

2. The unpainted resin molded article according to claim 1, wherein the thermoplastic resin is a resin selected from the group consisting of polypropylene resin, polyamide resin, acrylic resin, and polyethylene resin.

3. The unpainted resin molded article according to claim 2, wherein the thermoplastic resin is polypropylene resin.

4. The unpainted resin molded article according to claim 1 or claim 2, wherein the filler consists of at least one material selected from the group consisting of aluminum flakes, mica, pearl, glass fiber, and carbon fiber.

5. The unpainted resin molded article according to claim 4, wherein the filler is aluminum flakes.

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