Production method for two-layer molded sheets

Abstract

The present invention aims to provide a method for producing a two-layer molded body that stabilizes the appearance quality, reduces the amount of additives in the skin layer, and contributes to the reuse of waste materials. [Solution] The present invention provides a method for producing a two-layer molded body, characterized in that the ratio of the thickness of the core layer to the thickness of the two layers is 50 to 60% by mass, the mass ratio of waste material from the two layers used to form the two-layer molded body is 40 to 50% by mass, and the waste material is reused as core material.

Description

Technical Field

[0001] The present invention relates to a method for producing a two-layer plate body.

Background Art

[0002] Conventionally, a two-layer plate having a recycled layer (core layer) using waste materials of resin extrudates and a surface layer (skin layer) made of unused resin has been known (for example, see Patent Document 1). Specifically, in this two-layer plate, based on the color difference [ΔE] between the crushed resin kneaded product of the dark-colored waste material that is the raw material of the core layer and the unused resin that is the raw material of the skin layer, the thickness of the skin layer is adjusted so that the color of the lower core layer does not affect the color of the upper skin layer. According to such a two-layer plate, it is possible to stabilize the appearance quality of the color tone of the two-layer plate without performing color selection of the waste materials that are the raw materials of the core layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional two-layer plate (for example, see Patent Document 1), instead of adjusting the thickness of the skin layer so that the color of the lower core layer does not affect the color of the upper skin layer, for example, adding a light-scattering agent such as titanium oxide to the skin layer can be considered. According to such a two-layer plate, the light-scattering agent can more reliably conceal the color of the core layer compared to the conventional case. However, adding a light-scattering agent to the skin layer increases the manufacturing cost of the two-layer plate. Also, adding a light-scattering agent to the skin layer increases impurities from the perspective of recent circular economy.

[0005] The object of the present invention is to provide a method for producing a two-layer molded body that stabilizes the appearance quality, reduces the amount of additives in the skin layer, and contributes to the reuse of resource waste materials such as scraps and runners generated during the manufacturing process. [Means for solving the problem]

[0006] The present invention, which solves the aforementioned problems, provides a method for producing a two-layer molded body, comprising the steps of: preparing a two-layer body in which a skin layer containing a skin material as a base material and a core layer having a color difference of a certain degree or more from the skin material and using the same type of core material as the skin material are in close contact with each other; molding the two-layer body to produce a two-layer molded body; and reusing the resource waste material of the two-layer body generated during the molding of the two-layer molded body as material for another two-layer body separate from the two-layer body, wherein the ratio of the thickness of the core layer to the thickness of the two-layer body is 50-60%, and the mass ratio of waste material of the two-layer body to the total two-layer body used in molding the two-layer molded body is 40-50%, and the waste material is reused as core material.

[0007] Furthermore, according to the above production method, a two-layer molded sheet can be obtained, which comprises a skin layer formed by including a light scattering agent that causes Mie scattering in a skin material, and a core layer that adheres closely to the skin layer, has a color difference of a certain degree or more with respect to the skin material, and uses a core material containing recycled material, wherein the amount of the light scattering agent added to the skin layer is 2% by mass or more and 4% by mass or less, and the thickness of the skin layer is set such that the color difference between the skin layer and the core layer on the skin layer side is a certain degree or less.

[0008] Furthermore, the design method for such a two-layer molded body is a design method for a two-layer molded body having a skin layer formed by the above production method and containing a light scattering agent that causes Mie scattering in the skin material, and a core layer that adheres closely to the skin layer, has a color difference of a certain amount or more with respect to the skin material, and uses a core material that contains recycled material, the method comprising a step of selecting the light scattering agent, and a step of selecting the addition rate of the light scattering agent to the skin layer based on the relationship between the light transmittance of the skin layer shown by the following formula (2) and the thickness of the skin layer.

[0009]

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[0010] (However, in equation (2), I(t) is the transmitted light intensity of the skin layer, Io is the incident light intensity in the skin layer, ρ is the number density of particles of the light scattering agent, and σ is the scattering cross-section in Mie scattering.) [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a method for producing a two-layer molded body that stabilizes the appearance quality, reduces the amount of additives to the skin layer, and contributes to the reuse of waste materials. [Brief explanation of the drawing]

[0012] [Figure 1A] This is a schematic cross-sectional view of a two-layer plate, which is a production material for a two-layer plate molded article according to an embodiment of the present invention. [Figure 1B] This is a magnified view of section IB in Figure 1A. [Figure 2] This is a process diagram of a production method for a two-layer plate molded article according to an embodiment of the present invention. [Figure 3A] Figure 2 is an explanatory diagram of the vacuum forming process. [Figure 3B] Figure 2 is an explanatory diagram of the vacuum forming process. [Figure 3C] Figure 2 is an explanatory diagram of the vacuum forming process. [Figure 4]It is a process diagram of a design method for a two-layer plate formed body according to an embodiment of the present invention. [Figure 5] It is an explanatory diagram of the process for determining the light transmittance of the skin layer shown in FIG. 4. [Figure 6] It is a graph showing the relationship between the light transmittance of the skin layer used in an example of the present invention and the addition rate (mass fraction) of titanium oxide (light scattering agent) in the skin layer. [Figure 7] It is a table showing the relationship between the thickness of the skin layer used in an example of the present invention and the amount of titanium contained in the skin layer.

Mode for Carrying Out the Invention

[0013] Hereinafter, a mode (embodiment) for carrying out the production method of the two-layer plate formed body of the present invention will be described in detail with appropriate reference to the drawings. Here, before explaining the production method of the two-layer plate formed body, the two-layer plate which is the production material of the two-layer plate formed body of the present embodiment will be explained.

[0014] <Two-Layer Plate> FIG. 1A is a schematic cross-sectional view of a two-layer plate 1 which is a production material of a two-layer plate formed body 10 (see FIG. 3) according to the present embodiment. FIG. 1B is a partially enlarged view of the IB portion of FIG. 1A. As shown in FIG. 1A, the two-layer plate 1 is formed of resin. For example, by co-extrusion T-die molding, it is configured to have a core layer C (recycled material corresponding to milky white) and a skin layer S (white virgin material) in close contact with the core layer C. In this example, a two-layer plate (laminated plate) is taken as an example, but for example, a multi-layer plate such as sandwich molding may also be used. Further, the formed body (plate member) may be formed from a sheet shape composed of a roll member. Also, not limited to injection molding, a multi-layer plate may be formed by thermal welding, ultrasonic welding, or with an intervening adhesive member.

[0015] The core layer C is formed of a core material, and the skin layer S is formed of a skin material. The resins of the core material and the skin material are each composed of the same type of resin. In this embodiment, the resin is assumed to be acrylonitrile butadiene styrene resin (ABS resin), but it is not limited to this, and other thermoplastic resins such as polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET) can also be used.

[0016] The core material is composed of the resource waste material L (see Figure 3C) of the two-layer molded body 10 (see Figure 3) described later. The resource waste material L may include not only runners from normal production but also crushed resin from waste materials such as defective products, and is not particularly limited. The utilization rate Ri[%] of resource waste material L (see Figure 3C) in the core material is set to satisfy the following inequality (1) in terms of mass, thereby ensuring that no resource waste material is left over during plastic product molding, and thus being resource-recyclingly efficient. 100≧Ri>66 (1) Furthermore, for example, by co-extrusion T-die molding, the core material of the two-layer plate 1 in this embodiment can include recycled materials (resource waste material L, etc.) in a range of 39% or less by mass. As shown in Figure 1B, it is preferable to set the thickness T2 of the core layer C, which is made of such a core material, to 50-60% of the thickness T1 of the two-layer plate 1 (a thickness ratio of 50-60%). The skin material is composed of unused resin (virgin material) containing a predetermined amount of light scattering agent. The core layer C and skin layer S, which consist of such a core material and skin material, will be explained in detail later, along with the design method for the two-layer molded body 10 described below.

[0017] <Production method for two-layer molded sheets> The two-layer molded body of this embodiment can be used, for example, as plastic parts in industrial equipment and household appliances (refrigerators, air conditioners, water heaters, cooking appliances, washing machines, vacuum cleaners, blowers, video equipment, lighting equipment, etc.). Here, we will explain using a refrigerator as an example. A characteristic of materials for refrigerators is that the created two-layer board is finished into interior parts by vacuum forming. Because the interior parts of refrigerators have a complex structure and the parts themselves are large, injection molding is not suitable, and vacuum forming must be chosen. However, due to the manufacturing method of vacuum forming, a grip portion is always generated, and this portion becomes resource waste. In these interior parts, the total amount of resource waste, including the grip portion and holes for wiring, reaches 40-50% of the product. Therefore, the challenge arises of effectively utilizing this resource waste. In this embodiment, we envision an inner box 10a (see Figure 3C) that constitutes the insulated box of a refrigerator, with the aim of solving the aforementioned problems. This two-layer molded body (inner box) will be described together with the vacuum forming apparatus A (see Figures 3A to 3C) described later, which forms the two-layer molded body 10 (see Figure 3C). Figure 2 is a process diagram of the production method (hereinafter simply referred to as "production method") for the two-layer plate molded body 10 (see Figure 3C) according to this embodiment. As shown in Figure 2, the production method of this embodiment includes a step of preparing a two-layer plate 1 (see Figure 1A) (see step S101) and a vacuum forming step of the two-layer plate molded body 10 (see Figure 3C) (see step S102). In step S101, a two-layer plate 1 (Figure 1A) designed according to the design method for the two-layer plate molded body 10 described later is prepared.

[0018] In step S101, a two-layer plate 1 (Figure 1A) is formed using a vacuum forming apparatus. Figures 3A to 3C are explanatory diagrams of the vacuum forming process shown in Figure 2. As shown in Figure 3A, the vacuum forming apparatus A mainly consists of a clamping mechanism CL, a heater H, and a mold M.

[0019] In this vacuum forming process (see step S102 in Figure 2), the two-layer plate 1 is attached to the vacuum forming apparatus A. Specifically, both edges of the two-layer plate 1 are held and supported by the clamping mechanism CL of the vacuum forming apparatus A. Next, the two-layer plate 1 is heated by the heater H. This causes the two-layer plate 1 to become plasticized.

[0020] As shown in Figure 3B, the mold M is pressed against the plasticized two-layer plate 1. The mold M is hollow and has an outer shape that mimics the inner box 10a (see Figure 3C) that makes up the insulation box of a refrigerator. The plasticized two-layer plate 1 undergoes plastic deformation to conform to the mold M. At the same time, the hollow portion of the mold M is evacuated, causing the two-layer plate 1 to adhere tightly to the outside of the mold M. Then, as shown in Figure 3C, after the two-layer plate 1 is cooled and hardened, it is removed from the mold M and trimmed at a predetermined position to obtain a two-layer plate molded body 10 (inner box 10a).

[0021] <Two-layer plate molded body> As shown in Figure 3C, the inner box 10a, which is a two-layer molded body 10, has a U-shape in cross-section. The two-layer plate 1 remaining on the clamp mechanism CL side forms resource waste material L. Furthermore, of the two-layer plates 1 used in the molding of the two-layer plate molded body 10 (inner box 10a), the mass ratio of waste material L of the two-layer plates 1 is preferably 40 to 50%.

[0022] The inner box 10a, together with the outer box (not shown), forms a U-shaped hollow box. Vacuum insulation material or on-site foamed insulation material is placed in the hollow part of the box to constitute the insulated box of the refrigerator. A skin layer S (see Figure 1A) is formed on the inside of the inner box 10a. A core layer C (see Figure 1A) is formed on the outside of the inner box 10a. Incidentally, the inner box (skin layer S) is the part that the user sees. In this embodiment, the core layer C (see Figure 1A) is assumed to be white or milky white (cream colored).

[0023] Furthermore, the core layer C (see Figure 1A) reuses resource waste material (not shown) generated in the production process of another two-layer molded body (not shown), separate from this two-layer molded body 10 (inner box 10a), and the core layer C of this two-layer molded body 10 contains more than 66% by mass of resource waste material (not shown) generated in the production process of the other two-layer molded body (not shown). Furthermore, the titanium dioxide content of the skin layer S (see Figure 1A) is 8.3 g / m² in terms of metallic titanium per unit area of ​​the skin layer S. 2 It is desirable that the amount is greater than or equal to 4% by mass or less. By using this titanium dioxide content, the presence of sufficient titanium dioxide in the skin layer S allows the skin layer S to effectively conceal the color of the core layer C.

[0024] <Design method for two-layer molded bodies> Next, a design method for a two-layer molded body according to this embodiment will be described. Figure 4 is a process diagram of the design method (hereinafter simply referred to as "design method") for the two-layer molded body 10 (see Figure 3C) according to this embodiment. As shown in Figure 4, the design method of this embodiment includes a step of selecting the color tone of the core material that forms the core layer C (see Figure 1A) (see step S201), a step of selecting a light scattering agent (see step S202), a step of selecting the addition rate of the light scattering agent (see step S203), a step of determining the light transmittance of the skin layer S (see Figure 1A) (see step S204), and a step of determining the thickness of the skin layer S (see Figure 1A) (see step S205).

[0025] In the core material color selection process (see step S201), the producer of the two-layer molded body 10 (see Figure 3C) selects the color tone of the core material based on the content of resource waste material L (see Figure 3C) that is included in the core material in an amount exceeding 66% by mass of the core layer C (see Figure 1A), and other recycled materials that can be included in the core material. When resource waste material L or recycled materials are included in the core material, the color tone of the core layer C (see Figure 1A) changes. At this time, when the color difference ΔE between the color tone of the core material and the color tone of the skin material that will be used as the raw material for the skin layer S is ΔE > 1.6, which is clearly visible to the human eye, the specifications of the skin layer S (see Figure 1A) are considered, as will be explained in detail later. Incidentally, in this embodiment, when titanium dioxide is used as a light scattering agent, for example, the color tone of the core material is selected to be white or milky white (approximately equivalent to the same color).

[0026] In the light scattering agent selection process (see step S202), a light scattering agent that induces Mie scattering is selected. Mie scattering is a phenomenon in which light is scattered by spherical particles that are at least the size of the wavelength of light. Mie scattering has little wavelength dependence of scattering intensity and appears white. Examples of such light scattering agents include, but are not limited to, titanium dioxide, zinc oxide, aluminum oxide, aluminum hydroxide, zirconium oxide, boron nitride, and barium sulfate. Among these, titanium dioxide is preferred.

[0027] In the step of selecting the light scattering agent addition rate (see step S203), the addition rate of the light scattering agent to the skin layer S (see Figure 1A) is selected based on the relationship between the light transmittance of the skin layer S (see Figure 1A) shown by the following formula (2) and the thickness of the skin layer S (see Figure 1A).

[0028]

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[0029]

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[0030] Then, in the process of selecting the light scattering agent addition rate (see step S203), the addition rate [%] of the light scattering agent is selected from the range of a graph of each skin layer thickness, with the light transmittance of the skin layer S (see Figure 1A), which is obtained by equation (2), on the vertical axis of Figure 6, and the addition rate of the light scattering agent in the skin layer S (see Figure 1A) on the horizontal axis of the same figure. The method for selecting this light scattering agent addition rate [%] will be explained in detail based on the examples described later.

[0031] In the light transmittance determination step (see step S204), the light transmittance of the skin layer S (see Figure 1A) is determined. Figure 5 is an explanatory diagram of the process for determining the light transmittance of the skin layer shown in Figure 4 (see step S204). In this light transmittance determination process, as shown in Figure 5, first, a core material Cm whose color tone has been selected in the core material color tone selection process (see step S201) is prepared. Next, in this light transmittance determination process, the core material Cm from which the color tone has been selected is combined Multiple skin materials S1 (e.g., white), skin material S2 (e.g., range from white to milky white) A skin material S3 (for example, milky white) is prepared. These skin materials S1 to S3 differ in the amount of light scattering agent they contain, as indicated by the intensity of the shading in Figure 5. Furthermore, the skin materials S1 to S3 differ from each other in terms of their thicknesses Ta, Tb, and Tc. Next, in this light transmittance determination process, two-layer plates 1A to 1C are prepared, in which skin materials S1 to S3 are combined with a core material Cm. The color tone of the skin layer in these two-layer boards 1A to 1C is thought to be easily influenced by the color tone of the core material Cm that lies beneath the skin layer. Furthermore, even though the two-layer plates 1A to 1C have a core layer made of the same core material Cm, the color tones of the skin layers differ visually from each other, even if they are roughly equivalent in color (e.g., white to milky white), depending on the amount of light scattering agent added to the skin materials S1 to S3 and the thicknesses Ta, Tb, and Tc. In this light transmittance determination process, a sensory test was performed to evaluate whether the core layer (core material Cm) of the two-layer plates 1A to 1C could be seen through the skin layer (skin material S1 to S3) of the two-layer plates 1A to 1C when the two-layer plates 1A to 1C were visually observed. Then, by selecting a two-layer plate from two-layer plates 1A to 1C in which the core layer (core material Cm) is not visible, the upper limit of the light transmittance that can be allowed in the skin layer is determined. Furthermore, as mentioned above, this light transmittance corresponds to the degree of transparency of the skin layer due to the influence of the core layer, i.e., the color difference ΔE between the core layer and the skin layer. And, for laminates of approximately the same color, this color difference ΔE is preferably 1.6 or less. Incidentally, when using resource waste material L (see Figure 3C) of approximately the same color (white or milky white) as the core material in this embodiment in the predetermined amount described above, the light transmittance of the skin layer should preferably be 20% or less. In this example, three skin materials S1 to S3 are prepared for testing, but the number of skin materials can be increased or decreased as needed.

[0032] In the process of determining the thickness of the skin layer S (see Figure 1A) (see step S205), the lower limit Ts of the required thickness for the skin layer (= thickness T1 of the two-layer plate 1 - thickness T2 of the core layer C) is determined. The lower limit Ts of this thickness is determined from equation (2) based on the light scattering agent addition rate in the skin layer S (see Figure 1A) determined in the light scattering agent addition rate selection step (see step S203) and the light transmittance of the skin layer S (see Figure 1A) determined in the light transmittance determination step (see step S204).

[0033] In other words, the design method for the two-layer molded body 10 (see Figure 3C) according to this embodiment includes a step of determining the light transmittance of the skin layer S (see Figure 1A) such that the color difference (laminates of approximately the same color) between the skin layer of the two-layer plates 1A to 1C (see Figure 5), which are made by combining skin materials S1 to S3 (see Figure 5) with a core material Cm (see Figure 5) of which has been selected for its color tone, and the core material Cm (see Figure 5) is 1.6 or less, and a step of determining the thickness of the skin layer S (see Figure 1A) based on the light transmittance of the selected skin layer S (see Figure 1A) and the addition rate of the light scattering agent to the selected skin layer S (see Figure 1A).

[0034] <Effects> Next, the effects and benefits of this embodiment will be described. In general, recycled resin materials (resource waste materials L) can be produced in roughly the same color tone by sorting them by color tone at the waste material stage.

[0035] Conventionally, two-layer plates are known that have a recycled layer (core layer) made from waste resin extruded material and a surface layer (skin layer) made from unused resin (see, for example, Patent Document 1). In these two-layer plates, the thickness of the skin layer is adjusted based on the color difference [ΔE] between the crushed resin mixture of waste material with a color other than the same color that serves as the raw material for the core layer and the unused resin that serves as the raw material for the skin layer, so that the color of the lower core layer does not affect the color of the upper skin layer.

[0036] In such a two-layer plate (see, for example, Patent Document 1), it is also conceivable to add a light scattering agent to the skin layer to conceal the color of the core layer. However, adding light scattering agents to the skin layer increases the manufacturing cost of two-layer plates. Furthermore, from the perspective of a circular economy, which is increasingly required to reduce resource loss, adding light scattering agents to the skin layer increases impurities.

[0037] In contrast, the production method for a two-layer molded body of this embodiment includes the steps of: preparing a two-layer plate 1 in which a skin layer S containing a skin material as a base material and a core layer C using a core material of the same type (approximately the same color) as the skin material, with a color difference ΔE of a certain level or higher, are in close contact with each other; molding the two-layer plate 1 to produce a two-layer molded body 10; and reusing the resource loss material L of the two-layer plate 1 generated during the molding of the two-layer molded body 10 as material for another two-layer plate 1 separate from the two-layer plate 1. The ratio of the thickness T2 of the core layer C to the thickness T1 of the two-layer plate 1 is set to 50-60%, and the mass ratio of the loss material L of the two-layer plate 1 is set to 40-50% of all the two-layer plates 1 used in the molding of the two-layer molded body 10. Based on these conditions, the loss material is reused as core material. In this embodiment, "a certain color difference ΔE" means a well-known standard value used to judge the identity of the contrasting color tones. Incidentally, in this embodiment, "a constant color difference ΔE" means, for example, using the aforementioned ΔE of 1.6 as a reference, but the color difference ΔE is not limited to this.

[0038] This method for producing a two-layer molded body 10 helps to stabilize the appearance quality, reduce the amount of additives in the skin layer S, and facilitate the reuse of waste materials L.

[0039] Furthermore, in this production method, the process of forming a two-layer plate 1 to produce a two-layer plate molded body 10 includes a vacuum forming process for the two-layer plate 1, the skin layer S contains titanium oxide, and the titanium oxide content of the skin layer S is, for example, 8.3 g / m² in terms of metallic titanium per unit area of ​​the skin layer S. 2Preferably, the above and 4% by mass or less, and at least the core layer C in the two-layer molded body 10 is white or milky white (approximately the same color), and the core layer C in another two-layer molded body 10 obtained by molding another two-layer plate 1 is an example of a laminated plate in which resource loss material L is contained in more than 66% by mass, at least in this embodiment.

[0040] This method of producing two-layer molded sheets allows for more reliable stabilization of appearance quality for materials of roughly the same color, while also reducing the amount of additives in the skin layer S and contributing to the reuse of waste materials L.

[0041] Furthermore, the two-layer molded body 10 of this embodiment is produced by the above production method and comprises a skin layer S formed by including a light scattering agent that causes Mie scattering in the skin material, and a core layer C that adheres closely to the skin layer S, has a color difference ΔE with respect to the skin material of a certain level or more, and uses a core material containing resource loss material L. The amount of light scattering agent added to the skin layer S is 2% by mass or more and 4% by mass or less, and the thickness of the skin layer S is set so that the color difference ΔE between the skin layer S and the core layer C on the skin layer S side is 1.6 or less. This results in a visually identical color tone.

[0042] Furthermore, the design method for the two-layer molded body 10 of this embodiment is a design method for a two-layer molded body 10 having a skin layer S produced by the above production method and formed by including a light scattering agent that causes Mie scattering in the skin material, and a core layer C that adheres closely to the skin layer S, has a color difference ΔE with respect to the skin material of a certain level or more, and uses a core material that includes recycled material, and comprises a step of selecting a light scattering agent and a step of selecting the addition rate of the light scattering agent to the skin layer S based on the relationship between the light transmittance of the skin layer S shown by the following formula (2) and the thickness of the skin layer S.

[0043] Furthermore, in this design method, the optimal light scattering agent addition rate can be selected from the range of a graph of each skin layer thickness, where the light transmittance of the skin layer S set based on equation (2) is the vertical axis of Figure 6, and the addition rate of the light scattering agent to the skin layer S is the horizontal axis of Figure 6. [Examples]

[0044] Next, specific examples of the production method for a two-layer molded body, the two-layer molded body, and the design method thereof according to the present invention will be described. (Reuse of waste materials) The two-layer molded body produced by the production method of this embodiment is obtained by vacuum forming a two-layer plate in which a core layer containing recycled material and a skin layer are tightly adhered together. ABS resin was used for the core and skin layers. Titanium dioxide was used as the light scattering agent. The surface (skin layer) of the two-layer board was made of unused ABS resin (virgin material of roughly the same color (white)). The back surface (core layer of roughly the same color (milky white or white)) of the two-layer board was composed of resource waste material and recycled material. Virgin material can also be optionally used for the core layer. Incidentally, the lower limit Ts of the skin layer thickness in this embodiment was evaluated at 40% of the thickness t of the two-layer molded body (Ts = 0.4t).

[0045] (Reduction of additives in the skin layer) Figure 6 is a graph showing the relationship between the light transmittance of the skin layer used in this embodiment and the thickness of each skin layer, with the vertical axis representing the light transmittance and the horizontal axis representing the addition rate (mass fraction) of titanium dioxide (light scattering agent) in the skin layer. Figure 6 is a graph obtained based on the above equation (2). Figure 7 is a table showing the relationship between the thickness of the skin layer used in this embodiment and the amount of titanium contained in the skin layer.

[0046] In this embodiment, where titanium dioxide is used as a light scattering agent, as shown in Figure 6, regardless of the thickness of the skin layer, the decrease in the light transmittance of the skin layer relative to the mass fraction of titanium dioxide slows down as the mass fraction of titanium dioxide in the skin layer increases to about 3% by mass. Therefore, in this embodiment, the titanium dioxide addition rate (mass fraction of titanium dioxide) in the skin layer was selected from within the range where the curves showing the thickness of each skin layer (100 μm to 500 μm) as shown in Figure 6 correspond to a mass fraction of titanium dioxide in the skin layer of 2% to 5%.

[0047] In other words, the titanium dioxide addition rate to the skin layer is set to approximately 2% to 4% by mass, preferably 3% to 4% by mass, based on the equivalent value of metallic titanium at skin layer thicknesses (200 μm, 300 μm, and 400 μm), as shown by the shading in Figure 7. Figure 7 also shows the corresponding titanium dioxide addition amounts (equivalent value of metallic titanium). However, the selection range for titanium dioxide in the skin layer can also be within the range of 3 ± 0.5 mass% (2.5 mass% to 3.5 mass%).

[0048] (Lower limit of skin layer thickness Ts) The lower limit Ts of the skin layer thickness is preferably determined to be within 20% of the light transmittance of the skin layer, based on the amount of titanium oxide in the skin layer and the light transmittance of the skin layer (the 20% shown in Figure 6 represents a boundary line that has been evaluated as a good value for the light transmittance of the skin layer where the color difference between the skin layer and the core material (a laminate with approximately the same color) is 1.6 or less), as shown in the graph in Figure 6. In this embodiment, the lower limit Ts of the skin layer thickness is set to about 3-4 mass%, as shown by the shading in Figure 7. According to the production method for a two-layer molded body, the two-layer molded body, and the design method thereof of this embodiment, it is possible to stabilize the appearance quality while reducing the amount of additives to the skin layer and contributing to the reuse of waste materials.

[0049] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and can be implemented in various forms. [Explanation of Symbols]

[0050] 1 double layer board 10 Two-layer board molded body C Core Layer L Loss material S Skin layer

Claims

1. A skin layer containing a skin material as the base material, A step of preparing a two-layer plate in which a core layer made of the same type of core material as the skin material is in close contact with the skin material, wherein the color difference ΔE with respect to the skin material is above a certain level, A process for producing a two-layer molded body by forming the aforementioned two-layer plate, A process for reusing the waste material from the two-layer plate generated during the molding of the two-layer plate molded body as material for another two-layer plate separate from the aforementioned two-layer plate, It has, The ratio of the thickness of the core layer to the thickness of the two-layer plate is set to 50-60%. A method for producing a two-layer molded body, characterized in that, of the two layers used in the molding of the two-layer molded body, the mass ratio of resource waste material of the two layers is set to 40 to 50%, and the resource waste material is reused as core material.

2. The process of forming the two-layer plate to produce a two-layer plate molded body includes a vacuum forming process for the two-layer plate, The aforementioned skin layer contains titanium dioxide, The titanium oxide content of the skin layer is 8.3 g / m² in terms of metallic titanium per unit area of ​​the skin layer. ２ The above and 4% by mass or less, At least the core layer in the two-layer molded body is of substantially the same color, A method for producing a two-layer molded body according to claim 1, wherein the core layer in another two-layer molded body obtained by molding the other two-layer plate includes reusing at least the resource waste material as the core material.

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