Resin molded article

Abstract

Provided is a resin molded article having excellent mechanical strength even if the resin molded article includes a thin portion and has an uneven thickness formed by shaping a foamed resin. This resin molded body (1) is obtained by shaping a foamed resin sheet (10) comprising a core layer (11), a skin layer (12) laminated on one main surface of the core layer (11), and a skin layer (13) laminated on the other main surface. The thinnest wall portion has a thickness of 0.5 mm or more. The thickest wall part has a thickness of 5.0 mm or less. The resin molded body (1) includes a thinnest wall portion (2) having the smallest thickness and a thickest wall portion (3) having the largest thickness. The first ratio (M1 / M2) of the flexural modulus (M1) of the thinnest portion (2) to the flexural modulus (M2) of the thickest portion (3) is 0.7 or more.

Description

Technical Field

[0001] The present disclosure relates to a resin molded body formed by shaping a foamed resin sheet. Background Art

[0002] In recent years, foaming resins have attracted attention because they can improve convenience and reduce carbon dioxide emissions by making the resin molded body lightweight. The molding methods of foaming resins include physical foaming molding and chemical foaming molding. The chemical foaming molding method uses a chemical foaming agent as a foaming agent. Chemical foaming agents have a high environmental load and are not preferred from the perspective of protecting the global environment. On the other hand, the physical foaming molding method uses physical foaming agents such as nitrogen and carbon dioxide as foaming agents. Physical foaming agents have a small environmental load and are therefore preferred from the perspective of protecting the global environment. Among the physical foaming molding methods, as a method for foaming highly heat-resistant engineering plastics and super engineering plastics, there is a method in which the molten resin of the engineering plastics and super engineering plastics is shear-mixed with a high-pressure supercritical fluid to dissolve them.

[0003] Japanese Patent No. 6139038 (Patent Document 1) discloses a method for producing a foamed molded article using a relatively low-pressure physical foaming agent such as nitrogen or carbon dioxide, rather than a high-pressure supercritical fluid. This method enables the formation of fine foam cells in a resin molded article using a relatively simple process using a low-pressure physical foaming agent, without the need for special high-pressure equipment. Patent Document 1 also discloses methods for forming foamed molded articles using injection molding and extrusion molding.

[0004] Injection molding can obtain foaming molded articles of complex shapes. However, the surface layer of the molten resin flows while cooling and solidifying in the mold. At this time, a non-foamed epidermis is formed thinly on the surface layer of the foaming molded article. On the other hand, compared with the injection molding method, the extrusion molding method has fewer restrictions on the size and load of the mold and is suitable for continuously making foaming molded articles of single shape and single thickness. In addition, the sheet-like foaming molded article obtained by the extrusion molding method can be shaped into a foaming molded article of a certain degree of complex shape or a foaming molded article of relatively large size by implementing vacuum forming, etc. However, when the molten resin is discharged from the mold outlet and cooled and solidified, the extrusion molding method is difficult to form an epidermis on the surface layer of the foaming molded article.

[0005] As a method for forming a skin layer of sufficient thickness, Japanese Patent No. 3654697 (Patent Document 2) discloses a method for producing a thermoplastic resin foam sheet. This method allows for the easy formation of a skin layer on the surface of the thermoplastic resin foam sheet through extrusion molding. Japanese Patent Application Laid-Open No. 2000-52370 (Patent Document 3) discloses a method for producing a multilayer laminated molded body. The multilayer laminated molded body is formed by co-extrusion molding, with a core layer and skin layers made of foamed resin. The methods of Patent Documents 2 and 3 use general-purpose plastics such as polypropylene or polystyrene, which have low heat resistance and mechanical strength, as the primary resin material, and the skin layer is not formed for the purpose of enhancing heat resistance and mechanical strength.

[0006] Japanese Patent Gazette No. 7100216 (Patent Document 4) discloses a coextruded sheet that suppresses surface bulging and sheet cracking during thermal shaping, such as vacuum forming, while also achieving excellent lightness and mechanical strength. The coextruded sheet comprises a polycarbonate resin, an engineering plastic with excellent heat resistance and strength. The coextruded sheet comprises a core layer formed of a foamed resin and skin layers laminated on one and the other principal surfaces of the core layer. The coextruded sheet achieves improved mechanical strength and surface smoothness by controlling the density, the ratio of the core and skin layer thicknesses, and the melt volume rate (MVR).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 6139038

[0010] Patent Document 2: Japanese Patent No. 3654697

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2000-52370

[0012] Patent Document 4: Japanese Patent No. 7100216 Summary of the Invention

[0013] However, while the coextruded sheet of Patent Document 4 can achieve excellent mechanical strength and surface smoothness, the shape, for example, thickness, of the resin molded article after vacuum forming is relatively small, and excellent mechanical strength must be maintained even in thin-walled portions where mechanical strength is difficult to achieve. In other words, there is still ample room for research to achieve even greater mechanical strength in resin molded articles formed by vacuum forming a coextruded sheet.

[0014] An object of the present disclosure is to provide a resin molded article having excellent mechanical strength even if the article is a resin molded article having a non-uniform thickness and formed by shaping a foamed resin and including a thin-walled portion.

[0015] To address the above-mentioned issues, the present disclosure adopts the following solution. Specifically, the resin molded article of the present disclosure is formed by shaping a foamed resin sheet comprising a foamed layer, a first non-foamed layer laminated on one principal surface of the foamed layer, and a second non-foamed layer laminated on the other principal surface of the foamed layer. The resin molded article may include a thinnest wall portion having the smallest thickness and a thickest wall portion having the largest thickness. The thinnest wall portion may have a thickness of 0.5 mm or greater. The thickest wall portion may have a thickness of 5.0 mm or less. The first ratio (M1 / M2) of the flexural modulus M1 of the thinnest wall portion to the flexural modulus M2 of the thickest wall portion may be 0.7 or greater.

[0016] According to the resin molded article of the present disclosure, even if the resin molded article includes a thin-walled portion and has an uneven thickness formed by shaping a foamed resin, excellent mechanical strength can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] [ Figure 1 ] Figure 1 It is a perspective view showing a foamed resin sheet.

[0018] [ Figure 2 ] Figure 2 yes Figure 1 An enlarged cross-sectional view of the foamed resin sheet shown.

[0019] [ Figure 3 ] Figure 3 It is a cross-sectional view showing the molding process of the resin molded body according to the present embodiment.

[0020] [ Figure 4 ] Figure 4 It is a cross-sectional view showing the molding process of the resin molded body according to the present embodiment.

[0021] [ Figure 5 ] Figure 5 It is a cross-sectional view showing the molding process of the resin molded body according to the present embodiment.

[0022] [ Figure 6 ] Figure 6 It is a cross-sectional view showing the molding process of the resin molded body according to the present embodiment.

[0023] [ Figure 7 ] Figure 7 It is a cross-sectional view showing a resin molded body according to this embodiment.

[0024] [ Figure 8 ] Figure 8 This is an enlarged cross-sectional view showing a resin molded body according to this embodiment.

[0025] [ Figure 9 ] Figure 9 It is a cross-sectional view showing a resin molded body according to this embodiment.

[0026] [ Figure 10 ] is a three-dimensional diagram showing the mold.

[0027] [ Figure 11 ] is a cross-sectional view showing the molding process of the test body of the embodiment.

[0028] [ Figure 12 ] is a cross-sectional view showing the molding process of a conventional resin molded product.

[0029] [ Figure 13 ] is a cross-sectional view showing the molding process of a conventional resin molded product.

[0030] [ Figure 14 ] is a cross-sectional view showing the molding process of a conventional resin molded product.

[0031] [ Figure 15 ] is a cross-sectional view showing the molding process of a conventional resin molded product.

[0032] [ Figure 16 ] is a cross-sectional view showing the molding process of a conventional resin molded product. DETAILED DESCRIPTION

[0033] As described above, the foamed resin sheet 10 (see FIG. 1 ) is formed by laminating a core layer made of a foamed resin and skin layers made of a non-foamed resin on one main surface and the other main surface of the core layer. Figure 1 and Figure 2 When the resin molded article 1000 is formed by heat forming such as vacuum forming (details will be described later), it is difficult to ensure mechanical strength in the thin-walled portion with a small thickness. The present inventors have investigated the mechanism as follows. Figure 12 As shown, conventionally, when performing vacuum forming of the foamed resin sheet 10, first, the ends of the foamed resin sheet 10 are fixed with a clamp 1001, and both sides of the foamed resin sheet 10 are heated to a temperature above the glass transition temperature of the resin material by a heater 1002. Figure 13 As shown in FIG, the foamed resin sheet 10 becomes molten and deforms in a sagging manner due to its inability to withstand its own weight. That is, the area of ​​the foamed resin sheet 10 increases, and as a result, the thickness of the foamed resin sheet 10 decreases. Figure 14 As shown in FIG. 1 , the bubbles 111 contained in the molten foamed resin sheet 10 are combined or expanded by heating. Figure 15 As shown, the foamed resin sheet 10 deformed in the manner of sagging as described above is vacuum-formed using a mold 1003 and then cooled and solidified. Figure 16 As shown, in conventional resin molded article 1000, the density decreases due to uneven enlargement of bubbles 111, and the flexural modulus of the thin-walled portion is lower than that of foamed resin sheet 10 before vacuum forming. Therefore, it is speculated that it is difficult to ensure mechanical strength in the thin-walled portion. Furthermore, a solid sheet composed solely of non-foamed resin deforms under its own weight when heated. However, the density of the thin-walled portion of the solid sheet does not change, and the flexural modulus of the thin-walled portion, which is a fundamental physical property of the resin itself, does not change.

[0034] The present inventors conducted in-depth research and found that, in a resin molded body obtained by shaping a foamed resin sheet 10 by vacuum forming or the like, if the ratio of the bending elastic modulus of the thinnest wall portion with the smallest thickness to the bending elastic modulus of the thickest wall portion with the largest thickness exceeds a prescribed value, then even a resin molded body with uneven thickness can ensure excellent mechanical strength of the thinnest wall portion, thereby completing the present invention.

[0035] (Composition 1)

[0036] The resin molded article according to an embodiment of the present disclosure is formed by shaping a foamed resin sheet comprising a foam layer, a first non-foamed layer laminated on one principal surface of the foam layer, and a second non-foamed layer laminated on the other principal surface of the foam layer. The resin molded article may include a thinnest wall portion having the smallest thickness and a thickest wall portion having the largest thickness. The thinnest wall portion may have a thickness of 0.5 mm or greater. The thickest wall portion may have a thickness of 5.0 mm or less. The first ratio (M1 / M2) of the flexural modulus M1 of the thinnest wall portion to the flexural modulus M2 of the thickest wall portion may be 0.7 or greater.

[0037] Thus, in the resin molded body 1 having uneven thickness including the thinnest wall portion, density variation relative to the foamed resin sheet before molding can be suppressed, thereby improving the mechanical strength of the resin molded body 1 .

[0038] (Composition 2)

[0039] In the resin molded article of Configuration 1, the first ratio (M1 / M2) may be 2.0 or less.

[0040] (Composition 3)

[0041] In the resin molded article of configuration 1 or 2, the second ratio (t1 / t2) of the thickness t1 of the thinnest wall portion to the thickness t2 of the thickest wall portion can be 0.4 or greater and 0.9 or less. This prevents uneven thickness of the resin molded article 1, suppresses breakage during molding, and reduces breakage and hole formation after molding, while also improving vacuum formability.

[0042] (Composition 4)

[0043] In the resin molded article of any one of configurations 1 to 3, the resin molded article may contain a thermoplastic resin. The density of the resin molded article may be 1.0 g / cm 3 The bending modulus of each of the thinnest wall portion and the thickest wall portion may be 1000 MPa or more. This can suppress a decrease in the bending modulus of the resin molded body 1 formed by thermal shaping such as vacuum forming, and can achieve weight reduction.

[0044] (Composition 5)

[0045] In the resin molded article of any one of Configurations 1 to 4, the resin molded article may contain a polycarbonate resin. This facilitates thermal forming such as vacuum molding and provides a resin molded article 1 having excellent design properties and mechanical strength.

[0046] (Composition 6)

[0047] In the resin molded article according to any one of configurations 1 to 4, the resin molded article may include at least one selected from the group consisting of polycarbonate resin, polypropylene, polyethylene terephthalate, and polystyrene.

[0048] (Composition 7)

[0049] In the resin molded article according to any one of Configurations 1 to 6, the ratio of the first ratio to the second ratio (first ratio / second ratio) may be 4.0 or less.

[0050] (Composition 8)

[0051] In the resin molded article of any one of configurations 1 to 7, the ratio of the first ratio to the second ratio (first ratio / second ratio) may be greater than 1.0. This can reduce strength variations caused by the thicknesses of the thinnest and thickest wall portions, thereby ensuring excellent mechanical strength.

[0052] Below, use Figures 1 to 9 The embodiment of the resin molded article 1 disclosed herein will be described in detail. Identical and corresponding components in the figures are denoted by the same reference numerals, and the same descriptions will not be repeated. Furthermore, to facilitate understanding, the following drawings may be simplified or schematically illustrated, or some components may be omitted.

[0053] First, the material of the resin molded body 1 , that is, the foamed resin sheet 10 before being shaped by vacuum forming or the like, will be described.

[0054] The foamed resin sheet 10 is made of a resin material that can be shaped by vacuum forming or other methods. The foamed resin sheet 10 only needs to have an area and thickness sufficient for shaped by vacuum forming or other methods. However, the foamed resin sheet 10 preferably has a thickness of 1 to 5 mm. This facilitates thermal forming by vacuum forming or other methods. The resin material of the foamed resin sheet 10 is not particularly limited and may be, for example, a thermoplastic resin. Examples of thermoplastic resins include general-purpose plastics such as polyethylene terephthalate (PET), polypropylene, and polystyrene; engineering plastics with heat resistance of 100°C or higher; or super-engineering plastics with heat resistance of 150°C or higher. However, the resin material preferably has a deflection temperature under load of 90°C or higher. This improves formability during thermal forming, such as vacuum forming, and facilitates thermal forming. The resin material may comprise at least one selected from the group consisting of general-purpose plastics, engineering plastics, and super-engineering plastics. An alloy of polycarbonate resin and acrylonitrile-butadiene-styrene copolymer (ABS resin) may also be used. Preferably, the resin material primarily comprises, for example, 50% by weight or more of polycarbonate resin. Polycarbonate resin has excellent heat workability. This facilitates thermal forming such as vacuum forming, particularly thermal forming such as deep drawing as described below, and allows for the production of a resin molded article 1 with excellent design and mechanical strength. In this disclosure, the deflection temperature under load is determined based on ISO 75-B (1.81 MPa load).

[0055] like Figure 1 and Figure 2 As shown, the foamed resin sheet 10 includes a foamed layer (hereinafter referred to as a core layer) 11 , a non-foamed layer (hereinafter referred to as a skin layer) 12 laminated on one main surface of the core layer 11 , and a skin layer 13 laminated on the other main surface of the core layer 11 .

[0056] The core layer 11 is made of foamed resin. The core layer 11 can be formed by physically foaming a molten resin material. Physical foaming agents are, for example, inert gases such as nitrogen, carbon dioxide, air, and argon. It should be noted that the core layer 11 disclosed herein is preferably foamed using physical foaming agents such as nitrogen and carbon dioxide with relatively low pressure, among which nitrogen is more preferred. As a result, the pressure of the physical foaming agent can be set to a relatively low 1~6MPa, and a large number of fine bubbles can be formed. As a result, bulging during high temperature and heating during vacuum forming can be more reliably suppressed. The average bubble diameter of the bubbles can be greater than 0.1mm, can be less than 1.0mm, and is preferably less than 0.3mm. As Figure 2As shown, the core layer 11 has a large number of bubbles 111. The large number of bubbles has a substantially elliptical shape elongated along the extrusion direction in a cross-sectional view cut along the extrusion direction during extrusion molding. Among the large number of bubbles contained in the core layer 11, the bubbles contained near the center of the core layer 11 in the thickness direction have a larger bubble diameter than the bubbles 111 contained near the end portions of the core layer 11 in the thickness direction. The bubble diameter of the large number of bubbles 111 gradually decreases as it moves from the center of the core layer 11 in the thickness direction toward the end portions in the thickness direction.

[0057] like Figure 2As shown, the skin layer 12 is made of a non-foamed resin. That is, the skin layer 12 is not foamed. The skin layer 12 can be extruded from a die outlet in a non-foamed state by a co-extrusion molding method and laminated integrally with the core layer 11. Alternatively, after the core layer 11 is formed, the skin layer 12 can be fixed to one main surface of the core layer 11 by bonding or welding. It should be noted that in the present disclosure, non-foamed means a porosity of less than 5%. In addition, foamed means a porosity of 5% or more. More specifically, the porosity is calculated as follows. First, a portion of the foamed resin sheet 10 is cut out to produce a square sheet of 20 mm × 20 mm when viewed from above. A high-output microfocus X-ray CT system (manufactured by Shimadzu Corporation, model "inspeXio SMX-225CTS") is used to perform a CT scan on the sheet to obtain a CT cross-sectional image cut in the thickness direction along a line passing through the center point of the sheet and the midpoint of a specified side when viewed from above. Detailed measurement conditions included an applied voltage of 160 kV, a pixel size of 0.105 mm / voxel, a pixel count of 512 × 512 × 512, a number of views of 1200, a field of view of 53.5 mm in the XY direction, and a field of view of 48.9 mm in the Z direction. In a cross-sectional view of the foamed resin sheet 10, if the interface between the skin layer 12 and the core layer 11 was clear, the layer with the fewest bubbles visually observed at the clear interface was designated as the skin layer 12, and the layer with the most bubbles was designated as the core layer 11. Furthermore, in the case of a large number of bubbles at the interface between the skin layer 12 and the core layer 11, 15 bubbles close to the surface of the sheet 1 were selected along an imaginary boundary line dividing the cross section of the foamed resin sheet 10 into 16 equal parts in the width direction, and the bubble closest to the surface of the sheet 10 was identified. An imaginary line was drawn through the top of the closest bubble and perpendicular to the thickness direction. The inner side of the imaginary line in the thickness direction was designated as the core layer 11, and the outer side in the thickness direction was designated as the skin layer 12. Next, in the CT cross-sectional image obtained by imaging a cross section of the core layer 11 and skin layer 12, square sections were defined to divide the core layer 11 into 20 equal sections in the thickness direction and the skin layer 12 into 5 equal sections in the thickness direction along the same straight line (thus, the length of one side of each section depends on the thickness of the foamed resin sheet 10). Five columns were extracted, each containing 20 sections arranged along the thickness direction of the core layer 11 and 5 sections arranged along the thickness direction of the skin layer 12. Next, the cells and cell walls were binarized using the image processing software "Image J (manufactured by the National Institutes of Health)." The binarization threshold was determined based on a concentration histogram obtained using the Otsu method. The white portions of the resulting binarized image were then defined as cell walls and the black portions as cells. The cross-sectional area of ​​the closed cells contained in each section of each column was calculated. The cross-sectional area of ​​the closed cells contained in each section was calculated in this manner and divided by the cross-sectional area of ​​each section to calculate the porosity of each section contained in each column.In addition, the extracted 5 columns are respectively located and extracted at the center in the width direction, one end in the width direction, the other end in the width direction, the center between the center in the width direction and one end in the width direction, and the center between the center in the width direction and the other end in the width direction in the cross-sectional images of the core layer 11 and the skin layer 12.

[0058] The skin layer 12 may be made of a thermoplastic resin that can be well bonded to the core layer 11. More specifically, the resin material of the skin layer 12 is particularly preferably the same resin material as that of the core layer 11, but may be different as long as it is a resin that is highly compatible with the resin material of the core layer 11. In addition, in order to strengthen the skin layer 12, the skin layer 12 may be composed of a reinforced resin containing an inorganic filler, or a resin containing additives such as a flame retardant and a foaming nucleating agent, to the extent that the effects of the present disclosure are not impaired. By configuring the skin layer 12, the strength can be efficiently improved, and both lightweighting and strength improvement can be achieved. Examples of inorganic fillers include glass fiber, carbon fiber, aramid fiber, talc, and mica.

[0059] In addition, the skin layer 12 can be colored by applying a coating or pigment, etc., to the extent that the effects of the present disclosure are not impaired. In addition, a decorative film can be provided on the outer side surface of the skin layer 12, that is, the surface opposite to the surface opposite to one main surface of the core layer 11, by bonding or lamination. Thus, after the foamed resin sheet 10 is subjected to heat shaping such as vacuum forming, the design properties of the resin molded body 1 can be improved. In this way, in addition to the three-layer structure consisting of the skin layer 12, the core layer 11, and the skin layer 13, a layer having other functions can be provided on the outer side surface of the skin layer 12 or the skin layer 13. Thus, the foamed resin sheet 10 and the resin molded body 1 can be formed multifunctionally.

[0060] The skin layer 13 is the same as the skin layer 12 except that it is laminated on the other main surface of the core layer 11. Therefore, a specific description of the skin layer 13 is omitted.

[0061] The resin molded body 1 of the present disclosure can be obtained by subjecting the foamed resin sheet 10 to heat forming such as vacuum forming. Figures 3 to 7 , a specific description will be given of a molding method for the resin molded body 1. It should be noted that, here, a molding method using vacuum molding is described, but the molding method for the resin molded body 1 is not particularly limited.

[0062] First, if Figure 3 As shown, first, the foamed resin sheet 10 is fixed by a clamp 101. Figure 4As shown, heating plates 102 made of graphite are arranged above and below the foamed resin sheet 10. The heating plates 102 are preheated to a temperature higher than the glass transition temperature by a high-frequency induction heating device. Graphite has a high thermal conductivity of 2 to 3 times that of copper and is lightweight. In addition, graphite has excellent water repellency and is therefore difficult to adhere to molten resin. Therefore, the heating plates 102 made of graphite are suitable for uniformly limiting the thickness of the foamed resin sheet 10 and heating it. That is, in the molding process of the resin molded body 1 disclosed in the present invention, the foamed resin sheet 10 is preferably heated in such a manner that its thickness becomes uniform over the entire surface. The gap between the upper heating plate 102 and the lower heating plate 102 has a width W of 104% of the thickness of the foamed resin sheet 10. As a result, it is easy to heat the foamed resin sheet 10 in such a manner that the thickness becomes uniform. From the viewpoint of heating the foamed resin sheet 10 in such a manner that the thickness becomes uniform, the width W of the gap is more preferably within 104% of the thickness of the foamed resin sheet 10. In addition, although not particularly shown, the width W of the gap can be adjusted by a spacer disposed between the upper heating plate 102 and the lower heating plate 102 .

[0063] It is presumed that the foamed resin sheet 10 which is restrained and heated so as to have a uniform thickness has the same Figure 2 The foamed resin sheet 10 before heating shown in FIG. has the same bubble structure. That is, the foamed resin sheet 10 after heating becomes a structure in which the bubbles are not unified and the expansion on the surface of the foamed resin sheet 10 is easily suppressed. When the foamed resin sheet 10 heated in this way reaches a temperature higher than the glass transition temperature, it moves to the top of the mold 103. It should be noted that the temperature of the foamed resin sheet 10 is measured by a temperature sensor at the end of the foamed resin sheet 10. Afterwards, as Figure 5 As shown, the upper heating plate 102 and the lower heating plate 102 are removed from the foamed resin sheet 10, and the molten foamed resin sheet 10 is made to adhere to the upper surface of the mold 103, and the space containing the foamed resin sheet 10 is sealed in an airtight manner. Figure 6 As shown in FIG. 1 , the foamed resin sheet 10 is vacuum-formed by suction through the suction holes 104 provided in the mold 103. Afterwards, the molded foamed resin sheet 10 is cooled and solidified and demolded. By trimming the excess parts of the foamed resin sheet 10 thus formed, a foamed resin sheet 10 can be obtained. Figure 7 The resin molded body 1 shown.

[0064] like Figure 8As shown, the bubbles 111 contained in the resin molded body 1 obtained by such a method are flattened in the thickness direction as the resin molded body 1 is thinned during molding, thereby stretching in the vertical direction relative to the thickness and becoming an elliptical disk shape. The density of the resin molded body 1 containing such stretched bubbles becomes higher, and becomes a structure similar to a non-foamed structure. As a result, the resin molded body 1 can suppress the reduction of the bending elastic modulus of the thin-walled part, achieve an improvement in mechanical strength, and also improve the moldability. It should be noted that the resin molded body 1 is not limited to vacuum molding, and can also be thermally shaped by compressed air molding or press molding. As long as the foamed resin sheet 10 can be shaped, the method is not limited. Compressed air molding uses a positive pressure with a pressure difference with atmospheric pressure that is higher than the negative pressure of vacuum. Therefore, by crushing the bubbles that have enlarged due to heating, it is easy to suppress the reduction in strength. Alternatively, press molding can also be used as a method of controlling thickness and strength with a mold while suppressing bubble enlargement. In terms of mold construction and molding process, vacuum molding, pressure molding, or vacuum pressure molding can be performed using a single-sided mold, and therefore is preferred from the perspective of inexpensively producing large parts. Furthermore, mold 103 can be any shape, and can be made of any material, such as metal or wood, as long as it is used in a known shaping method.

[0065] It should be noted that the resin molded article 1 produced by the above-described method, even when it has curvature, is curved, or is relatively small, is thinned during molding. Furthermore, cells collapse and partially expand, resulting in a structure similar to a non-foamed structure, thereby increasing density. Specifically, the resin molded article 1 produced by the above-described method can suppress a decrease in the flexural modulus of the thin-walled portion, thereby achieving improved mechanical strength and enhancing moldability.

[0066] use Figure 9 The resin molded body 1 molded in this manner will be specifically described.

[0067] The resin molded body 1 has a thinnest wall portion 2 with the smallest thickness and a thickest wall portion 3 with the largest thickness. The thinnest wall portion 2 has a thickness of 0.5 mm or more, and the thickest wall portion 3 has a thickness of 5.0 mm or less. If the thickness of the thinnest wall portion 2 is too small, the rigidity of the resin molded body 1 may be reduced. In addition, it may cause problems such as rupture of the foamed resin sheet 10 during vacuum molding. If the thickness of the thickest wall portion 3 is too large, the moldability is reduced and the weight of the resin molded body 1 increases. That is, from the perspective of ensuring the rigidity and moldability of the resin molded body 1 and achieving lightweighting, the thickness of the thinnest wall portion 2 is preferably 1 mm or more, more preferably 1.5 mm or more, and the thickness of the thickest wall portion 3 is preferably 4.5 mm or less, more preferably 4.0 mm or less. The thickness of the thinnest wall portion 2 is preferably 1 mm or more and 4.5 mm or less, more preferably 1.5 mm or more and 4.5 mm or less, and further preferably 1.5 mm or more and 4.0 mm or less.

[0068] The thickness distribution of the resin molded article 1 can be measured using a magnetic thickness gauge, an ultrasonic thickness gauge, or a 3D scanner. This allows the thickness distribution of the resin molded article 1 to be measured without destroying the resin molded article 1. In the present disclosure, the thickness distribution of the resin molded article 1 can be measured using, for example, a 3D scanner-type three-dimensional measuring machine (manufactured by KEYENCE Co., Ltd., model "VL-500"). In the thus measured thickness distribution, the portion with the smallest thickness can be defined as the thinnest wall portion 2, and the portion with the largest thickness can be defined as the thickest wall portion 3.

[0069] The ratio M1 / M2 (hereinafter sometimes referred to as the ratio Y) of the bending modulus M1 of the thinnest wall portion 2 to the bending modulus M2 of the thickest wall portion 3 can be set to 0.7 or greater. This can suppress the reduction in mechanical strength of the thinned resin molded body 1 associated with the density change from the foamed resin sheet 10 before molding, thereby improving the mechanical strength of the resin molded body 1. The ratio Y is preferably set to 1.0 or greater. This can further improve the mechanical strength of the resin molded body 1. It should be noted that the upper limit of the ratio Y is not particularly limited, and for example, it is 2.0 or less. The ratio Y is preferably 0.7 or greater and 2.0 or less, and more preferably 1.0 or greater and 2.0 or less.

[0070] The bending moduli M1 and M2 are values ​​evaluated by a three-point bending test. The three-point bending test is specifically implemented as follows. First, a planar thinnest wall sheet containing the thinnest wall portion 2 and a planar thickest wall sheet containing the thickest wall portion 3 are cut out from the resin molded body 1 using a punching machine. The thinnest wall sheet and the thickest wall sheet are rectangular in shape when viewed from above, with a width of 10 mm and a length of 80 mm, respectively. In the thinnest wall sheet and the thickest wall sheet, the thinnest wall portion 2 and the thickest wall portion 3 are respectively located at the intersection of the diagonals of the rectangular shape when viewed from above. For each of the thinnest wall sheet and the thickest wall sheet, a load is applied to the thinnest wall portion 2 and the thickest wall portion 3 with each point 16 mm from the center of the longitudinal direction toward the two ends of the longitudinal direction as a fulcrum, thereby implementing a three-point bending test. In the present disclosure, the three-point bending test can be implemented, for example, using a precision universal testing machine (manufactured by Shimadzu Corporation, model "AGS-J"). Furthermore, there are cases where the thinnest wall portion 2 or the thickest wall portion 3 is located at an end portion or a stepped portion of the resin molded body 1, making it impossible to perform a three-point bending test. In such cases, the thinnest wall portion 2 and the thickest wall portion 3 can be defined as portions capable of performing a three-point bending test, i.e., portions from which the thinnest wall piece and the thickest wall piece, which are rectangular in plan view, can be cut out, and are defined as portions with the smallest thickness and portions with the largest thickness, respectively.

[0071] In addition, when the thinnest wall portion 2 or the thickest wall portion 3 has a curvature around it, when the thinnest wall piece and the thickest wall piece have curvature, the arc-shaped thinnest wall piece and the thickest wall piece are cut out with a width of 10 mm and an arc length of 80 mm. For example, when the curvature of the arc-shaped thinnest wall piece and the thickest wall piece is 30 mm, -1 In the following cases, the three-point bending test can be performed in the same manner as the above-mentioned planar thinnest wall piece and thickest wall piece. However, if the thinnest wall piece and thickest wall piece are offset during the three-point bending test and cannot be accurately measured, the thinnest wall part 2 and the thickest wall part 3 can be defined as being able to cut out a curvature of 30m. -1 The following are the thinnest and thickest wall parts, as well as the smallest and thickest parts.

[0072] It should be noted that the density of the thinnest wall sheet and the thickest wall sheet can be calculated as follows. First, use a micrometer to measure the width of each of the thinnest wall sheet and the thickest wall sheet, and use a vernier caliper to measure the length. Calculate the volume from these widths, lengths and the above-mentioned average thickness. Regarding the average thickness of each of the thinnest wall sheet and the thickest wall sheet, the thickness of each of the thinnest wall sheet and the thickest wall sheet can be measured at 10 points at equal intervals in the longitudinal direction, and the arithmetic mean of the thickness of these 10 points can be set. In addition, use an electronic balance to measure the weight of each of the thinnest wall sheet and the thickest wall sheet. The density of the thinnest wall sheet and the thickest wall sheet can be calculated by dividing their respective weights by the volume.

[0073] The ratio t1 / t2 (hereinafter sometimes referred to as ratio X) of the thickness t1 of the thinnest wall portion 2 to the thickness t2 of the thickest wall portion 3 can be set to 0.4 or more. This prevents unevenness in the thickness of the resin molded body 1. That is, it is possible to suppress breakage caused by heating during molding when a portion of the resin molded body 1 is extremely thin, or breakage and hole formation after molding. In addition, the ratio X is preferably 0.7 or more. This makes it easy to make the ratio Y 1.0 or more, which can improve the strength of the thinnest wall portion 2. The ratio X only needs to be at least less than 1, for example, it can be set to 0.9 or less. This can improve the moldability during thermal forming such as vacuum molding. The ratio X is preferably 0.7 or more and less than 1, more preferably 0.7 or more and 0.9 or less.

[0074] The thinnest wall portion 2 and the thickest wall portion 3 can each have a flexural modulus of 1000 MPa or greater. This can suppress a decrease in the flexural modulus of the resin constituting the resin molded body 1. From the perspective of ease of molding by thermal forming such as vacuum molding, the flexural modulus of the thinnest wall portion 2 and the thickest wall portion 3 can each be set to 2800 MPa or less. Alternatively, as described above, even when the skin layers 12 and 13 of the foamed resin sheet 10 contain inorganic fillers, the flexural modulus can be set to 3500 MPa or less.

[0075] The resin molded body 1 may have a 3 Thereby, the resin molded body 1 can be made lighter.

[0076] The ratio Y / X (hereinafter sometimes referred to as ratio Z), which is the ratio Y (M1 / M2) to the ratio X (t1 / t2), is preferably greater than 1.0. If ratio Z is 1.0 or less, that is, if ratio X is greater than ratio Y, the strength variation caused by the thickness of the thinnest-walled portion 2 and the thickest-walled portion 3 becomes significant, potentially reducing the strength of the thinnest-walled portion 2. In other words, by considering the balance between ratio Y and ratio X, excellent mechanical strength of the resin molded article 1 can be ensured. The upper limit of ratio Z is not particularly limited, but is preferably 4.0 or less. By setting ratio Z to greater than 1.0 and less than 4.0, ease of molding during thermal forming, such as vacuum forming, can be ensured.

[0077] The resin molded body 1 is formed into various shapes according to the intended use by heat forming such as vacuum forming. The resin molded body 1 can be formed into any shape as long as it can be formed by heat forming such as vacuum forming. For example, the resin molded body 1 can be formed into a box shape, a triangular prism shape, or a cylindrical shape.

[0078] The resin molded body 1 used for specified products and components can reduce the amount of resin used. As a result, the resin molded body 1 of this embodiment can help improve resource utilization efficiency, reduce transportation burdens, reduce energy usage, and reduce CO2 emissions. By providing the resin molded body 1 to society, it can contribute to achieving Goal 7 (access to affordable and clean energy for all), Goal 9 (building a foundation for industrial and technological innovation), and Goal 11 (building sustainable communities) among the 17 goals of the Sustainable Development Goals (SDGs) established by the United Nations. In addition, the resin molded body 1 of this embodiment can be melted and reused, thereby contributing to the achievement of Goal 12 (responsible production, responsible consumption).

[0079] As mentioned above, although embodiment was described, this disclosure is not limited to the said embodiment, Various changes are possible as long as they do not deviate from the summary.

[0080] [Example]

[0081] In Examples 1 to 5 and Comparative Examples 1 and 2, resin molded articles were prepared by molding foamed resin sheets. The flexural modulus was measured by performing the three-point bending test described above on the thinnest and thickest wall portions. It should be noted that the average thickness of the foamed resin sheet in Table 1 below was calculated as follows. The thickness of the foamed resin sheet was measured at 10 points at equal intervals along the width of the cross-section of the foamed resin sheet. The arithmetic mean of the thicknesses at these 10 points was used as the average thickness of the foamed resin sheet.

[0082] [Table 1]

[0083]

[0084] (Example 1)

[0085] In Example 1, a polycarbonate resin (PC) was used as the resin material, and a foamed resin sheet with a width of 200 mm and a length of 400 mm was produced by coextrusion molding. Therefore, the core layer and the skin layer were made of the same resin material. The core layer was foamed using the aforementioned low-pressure physical foaming agent (nitrogen). It should be noted that the polycarbonate resin was Teijin Panlite L-1225Y (density: 1.2 g / cm 3, load deflection temperature: 143°C, flexural modulus 2400 MPa), a small amount of foaming nucleating agent is added for the purpose of increasing melt tension and miniaturizing bubbles. More specifically, first, nitrogen is used to pressurize the molten resin that forms the core layer inside the short-axis screw cylinder (not shown). Then, after the molten resin is discharged from the short-axis screw cylinder, nitrogen is pressurized with a gear pump, and extruded while suppressing foaming. Then, the molten resin for the skin layer, which is adjusted to the same pressure as the core layer resin, is merged in the form of sandwiching the core layer. After forming a laminar flow from the manifold with a hanger-type die, it is extruded from the front end of the die to the foamed resin sheet and solidified with a cooling roller. As a result, an average thickness of 2.5 mm and a density of 0.60 g / cm 3 , a foamed resin sheet with a bending elastic modulus of 1330 MPa.

[0086] Next, the foamed resin sheet thus prepared was heated to 190°C and vacuum-formed using the above-described method to obtain a test piece (resin molded body) of Example 1. It should be noted that the width of the gap between the upper and lower heating plates was adjusted to 104% of the thickness of the foamed resin sheet, and when the temperature of the distal end surface of the foamed resin sheet reached 170°C, the foamed resin sheet was moved to the position directly above the mold. Furthermore, using the Figure 10 The mold 103 shown has a box shape with a width L1 of 100 mm, a length L2 of 200 mm, and a depth L3 of 40 mm.

[0087] For the test body thus obtained, the thinnest and thickest wall portions were determined using the above-described method, and the thickness of each was measured. Furthermore, the density was measured as described above, and the flexural modulus of each of the thinnest and thickest wall portions was measured using the above-described three-point bend test. The three-point bend test was conducted using a desktop precision universal testing machine (Shimadzu Corporation, model "AGS-J") at a test speed of 10 mm / min and a 32 mm distance between support points. The results showed that the flexural modulus M1 of the thinnest wall portion was 1400 MPa, and the flexural modulus M2 of the thickest wall portion was 1800 MPa, both of which were higher than the flexural modulus of the foamed resin sheet before vacuum forming. This is presumably because the bubbles were not coalesced and shattered, resulting in an increased density. Furthermore, the ratio Y was 0.78. Thus, the resin molded body vacuum formed using the above-described method can achieve improved mechanical strength. In Table 1, the densities of the thinnest wall portion and the thickest wall portion refer to the densities of the thinnest wall sheet and the thickest wall sheet described above.

[0088] (Example 2)

[0089] The test piece of Example 2 was produced using the same method as Example 1, except that the mold depth during vacuum forming was set to 60 mm for deep drawing. Deep drawing significantly increases thickness variation, suppressing increases in density. The bending modulus M1 of the thinnest wall portion was 1250 MPa, and the bending modulus M2 of the thickest wall portion was 1300 MPa, which is the same as the bending modulus of the foamed resin sheet. Furthermore, the ratio Y was 0.96, indicating minimal reduction in strength at the thinnest wall portion. Furthermore, the ratio Z was 1.66, sufficiently larger than 1.0, confirming that thickness variation and reduction in mechanical strength were also suppressed during deep drawing.

[0090] (Example 3)

[0091] The test body of Example 3 was formed in the same manner as in Example 1 except that the foamed resin sheet having an average thickness of 2.5 mm was formed into a thickness of 3.0 mm during heating. Specifically, first, Figure 11 As shown, the width W of the gap between the upper heating plate 102 and the lower heating plate 102 is adjusted to 3.0 mm, so that the foamed resin sheet 10 with an average thickness of 2.5 mm is expanded to 3.0 mm by heating, that is, the thickness is uniformly thickened to 0.5 mm. The upper heating plate 102, the lower heating plate 102 and the expanded foamed resin sheet 10 are moved to the top of the mold 103. At this time, it is speculated that Figure 2 Compared to the foamed resin sheet 10 shown in FIG. , the thickness of the foamed resin sheet 10 increases as the bubbles expand. Subsequently, the upper heating plate 102 and the heated lower plate 104 are removed, and vacuum forming is performed. The test piece of Example 3 thus obtained has larger bubbles, and as shown in Table 1, it is possible to suppress the thickness from being thinned.

[0092] In the test body of Example 3, thinning after vacuum forming is suppressed, while there are areas where the density is reduced. In addition, the bending modulus M1 of the thinnest wall portion is 1200 MPa, and the bending modulus M2 of the thickest wall portion is 1100 MPa. The ratio Y is 1.09. That is, the bending modulus M1 of the thinnest wall portion is greater than the bending modulus M2 of the thickest wall portion. It is considered that although the bending moduli M1 and M2 are lower than the bending modulus of the foamed resin sheet, the overall reduction in thickness is suppressed, resulting in excellent rigidity compared to the test body of Example 1. The ratio Z is 1.39, which is greater than 1.0. It can be seen that in Example 3, the molding method of expanding the thickness of the foamed resin sheet during heating is used to suppress changes in the thickness and density of the test body, and as a result, an improvement in mechanical strength is achieved.

[0093] (Example 4)

[0094] The test body of Example 4 was formed by deep drawing in the same manner as in Example 2, except that the average thickness of the foamed resin sheet was set to 3.0 mm. By making the thickness of the foamed resin sheet of Example 4 greater than that of the foamed resin sheet of Example 2, changes in thickness after vacuum forming can be suppressed. In addition, the bending modulus M1 of the thinnest wall portion is 1600 MPa, and the bending modulus M2 of the thickest wall portion is 1100 MPa. In other words, the ratio Y is 1.45, which is greater than 1.0. The ratio Z is 1.73, which is close to 2.0. In other words, it is close to the value of a vacuum-formed product of a non-foamed resin, suggesting that an improvement in mechanical strength can be achieved.

[0095] (Example 5)

[0096] The test body of Example 5 was vacuum formed in the same manner as the test body of Example 1, except that the depth of the box-shaped mold was set to 80 mm. Furthermore, although the thickness changed due to deep drawing, the density of the test body of Example 5 was about the same as that of the test body of Example 1. In addition, the bending modulus M1 of the thinnest wall portion was 1630 MPa, and the bending modulus M2 of the thickest wall portion was 1470 MPa. That is, the ratio Y was 1.11, and the bending modulus of the thinnest wall portion was greater than the bending modulus of the thickest wall portion. The ratio Z was 2.71, which is much higher than 2.0. When the test body of Example 5 was observed in detail, the thinnest wall portion was more similar to the structure of a resin molded product composed of a non-foamed resin, suggesting that an improvement in mechanical strength was achieved.

[0097] Next, the resin material of the test body was changed from the polycarbonate resin of Examples 1 to 5 to polypropylene, polystyrene, or polyethylene terephthalate as general-purpose plastics, or an alloy resin of polycarbonate resin and ABS resin as engineering plastics, and the tests of Examples 6 to 9 were performed.

[0098] (Example 6)

[0099] The test body of Example 6 was produced by the same method as Example 1, except that a polycarbonate resin / ABS resin alloy resin was used as the resin material. Therefore, in the test body of Example 6, the resin material of the core layer and the skin layer was the same. It should be noted that the polycarbonate / ABS alloy resin was Multilon T-2754 (density: 1.11 g / cm 3 ), load deflection temperature: 118°C, flexural modulus: 2200 MPa), a small amount of foaming nucleating agent is added to increase melt tension and miniaturize bubbles. The average thickness of the polycarbonate / ABS foam resin sheet before vacuum forming is 2.5 mm and the density is 0.56 g / cm 3The flexural modulus was 1220 MPa. The flexural modulus M1 of the thinnest wall portion of the vacuum-formed test piece was 1280 MPa, and the flexural modulus of the thickest wall portion was 1650 MPa, both higher than those of the foamed resin sheet before vacuum forming. Furthermore, the ratio Y was 0.78, confirming that even when the resin material was changed to a polycarbonate / ABS alloy resin, thickness changes and reductions in mechanical strength were suppressed.

[0100] (Example 7)

[0101] The test body of Example 7 was produced by the same method as Example 1, except that polypropylene (PP) was used as the resin material. Therefore, in the test body of Example 7, the resin material of the core layer and the skin layer was the same. It should be noted that the polypropylene was Calp 4700G (density: 1.05 g / cm 3 , load deflection temperature: 118°C, flexural modulus: 3200 MPa). Talc is added to increase the strength of the resin. The average thickness of the polypropylene foam resin sheet before vacuum forming is 2.5 mm, and the density is 0.52 g / cm 3 Flexural modulus: 1840 MPa. In the vacuum-formed test piece, the flexural modulus M1 at the thinnest wall was 1940 MPa, and the flexural modulus at the thickest wall was 2490 MPa, both improvements compared to the foamed resin sheet before vacuum forming. Furthermore, the ratio Y was 0.78, confirming that even when the resin material was changed to polypropylene, thickness changes and reductions in mechanical strength were suppressed.

[0102] (Example 8)

[0103] The test body of Example 8 was produced by the same method as Example 1, except that polyethylene terephthalate (PET) was used as the resin material. Therefore, in the test body of Example 8, the resin material of the core layer and the skin layer was the same. It should be noted that the polyethylene terephthalate was polyethylene terephthalate resin SA-1206 (density: 1.41 g / cm 3 , flexural modulus: 2300 MPa). Average thickness of polyethylene terephthalate foam resin sheet before vacuum forming: 2.5 mm, density: 0.7 g / cm 3Flexural modulus: 1280 MPa. In the vacuum-formed test piece, the flexural modulus M1 of the thinnest wall portion was 1350 MPa, and the flexural modulus M2 of the thickest wall portion was 1740 MPa, both improvements compared to the foamed resin sheet before vacuum forming. Furthermore, the ratio Y was 0.78, confirming that even when the resin material was changed to polyethylene terephthalate, thickness changes and reductions in mechanical strength were suppressed.

[0104] (Example 9)

[0105] In Example 9, the same method as in Example 1 was used except that polystyrene (PS) was used as the resin material. Therefore, the core layer and the skin layer had the same resin material. It should be noted that the polystyrene was DIC STYRENE (registered trademark), XC-515 (density: 1.04 g / cm 3 , flexural modulus: 3300 MPa). The average thickness of the polystyrene foam resin sheet before vacuum forming is 2.5 mm, and the density is 0.53 g / cm 3 , flexural modulus: 1830 MPa. In the vacuum-formed test piece, the flexural modulus M1 of the thinnest wall portion was 1930 MPa, and the flexural modulus M2 of the thickest wall portion was 2480 MPa, both improvements compared to the foamed resin sheet before vacuum forming. Furthermore, the ratio Y was 0.78, confirming that even when the resin material was changed to polystyrene, thickness changes and reductions in mechanical strength were suppressed.

[0106] (Comparative Example 1)

[0107] The test body of Comparative Example 1 was formed by the above-mentioned conventional method. Figure 13 As shown, the foamed resin sheet 10 sags due to its own weight when heated, and the bubbles merge and the density decreases after vacuum forming. The thickness of the test body of Comparative Example 1 changes greatly, and the density decreases significantly. In addition, the bending modulus M1 of the thinnest wall portion is 450 MPa, and the bending modulus M2 of the thickest wall portion is 860 MPa. That is, the bending moduli M1 and M2 are significantly lower than the bending modulus of the foamed resin sheet. In addition, the ratio Y is small, at 0.52, and the strength reduction of the thinnest wall portion becomes larger. Furthermore, the ratio Z is 1.00, suggesting that the strength reduction increases with the thickness change after vacuum forming.

[0108] (Comparative Example 2)

[0109] The test body of Comparative Example 2 was vacuum formed in the same manner as in Example 2, except that a deep-drawing mold was used and the thickness of the foamed resin sheet was set to 3.0 mm. It is speculated that the thickness of the foamed resin sheet of the test body of Comparative Example 2 became thicker, and by using a deep-drawing mold, the density and mechanical strength of the thinnest wall portion were further reduced. In addition, the bending modulus M1 of the thinnest wall portion was 350 MPa, and the bending modulus M2 of the thickest wall portion was 860 MPa. That is, the ratio Y was 0.41, which was smaller than that of Comparative Example 1. The ratio Z was 0.74, and the rigidity of the test body was also reduced. Thus, it is suggested that the balance between the mechanical strength and thickness of the test body of Comparative Example 2 deteriorated.

[0110] (Comparative Example 3)

[0111] The test body of Comparative Example 3 was produced using the same method as Comparative Example 1, except that a polycarbonate resin / ABS resin alloy was used as the resin material, as in Example 5. The test body of Comparative Example 3, like Comparative Example 1, exhibited significant thickness variation and reduced density. Furthermore, the bending modulus M1 of the thinnest wall portion was 410 MPa, while the bending modulus M2 of the thickest wall portion was 790 MPa. The ratio Y was 0.52, indicating a significant reduction in strength at the thinnest wall portion. The ratio Z was 0.99, confirming that even when the resin material was changed to polycarbonate / ABS resin, the conventional molding method exhibited a significant reduction in strength associated with thickness variation after vacuum molding.

[0112] (Comparative Example 4)

[0113] The test body of Comparative Example 4 was produced by the same method as Comparative Example 1, except that polypropylene resin was used as the resin material in the same manner as in Example 6. The test body of Comparative Example 4, like Comparative Example 1, showed a large change in thickness and a reduced density. Furthermore, the bending modulus M1 of the thinnest wall portion was 620 MPa, and the bending modulus M2 of the thickest wall portion was 1190 MPa. The ratio Y was 0.52, indicating a significant reduction in strength at the thinnest wall portion. The ratio Z was 0.99, confirming that even when the resin material was changed to polypropylene and talc was added to increase strength, the strength reduction associated with the thickness change after vacuum forming was also significant in conventional molding methods.

[0114] (Comparative Example 5)

[0115] The test body of Comparative Example 5 was produced in the same manner as in Comparative Example 1, except that polyethylene terephthalate resin was used as the resin material, as in Example 7. The test body of Comparative Example 5, like Comparative Example 1, showed a large change in thickness and a decrease in density. Furthermore, the bending modulus M1 of the thinnest wall portion was 430 MPa, and the bending modulus M2 of the thickest wall portion was 830 MPa. The ratio Y was 0.52, indicating a significant decrease in strength in the thinnest wall portion. The ratio Z was 0.99, confirming that even when the resin material was changed to polyethylene terephthalate, the decrease in strength associated with the thickness change after vacuum forming in conventional molding methods also increased.

[0116] (Comparative Example 6)

[0117] The test body of Comparative Example 6 was produced by the same method as Comparative Example 1, except that polystyrene resin was used as the resin material, as in Example 8. The test body of Comparative Example 5, like Comparative Example 1, had a large change in thickness and a reduced density. Furthermore, the bending modulus M1 of the thinnest wall portion was 620 MPa, and the bending modulus M2 of the thickest wall portion was 1180 MPa. The ratio Y was 0.53, indicating a significant reduction in strength at the thinnest wall portion. The ratio Z was 1.00, confirming that even when the resin material was changed to polystyrene resin, the strength reduction associated with the thickness change after vacuum forming was also significant in conventional molding methods.

[0118] Furthermore, as shown in the test results of Examples 6 to 9 and Comparative Examples 3 to 5, similar results were obtained not only when polycarbonate resin was used as the resin material, but also when alloys of polycarbonate resin with ABS resin, an engineering plastic, or general-purpose plastics such as polypropylene, polyethylene terephthalate, and polystyrene were used. Furthermore, similar results were obtained when other resins were used, such as super engineering plastics such as PAR and PPS, and alloys of polycarbonate resin with PAR or PPS.

[0119] The test bodies of Example 1 and Comparative Example 1 were confirmed to deform when a 10 kg weight was placed. In the test body of Comparative Example 1, the vertical wall side of the box-shaped portion, which became the thinnest wall, bent, and the entire test body was destroyed. On the other hand, the test body of Example 1 maintained its original shape. This result confirms that if the ratio Y is 0.7 or above, the resin molded body has high impact strength. In other words, it is believed that the same results can be obtained when using the test bodies of Examples 2 to 5.

[0120] Description of Reference Numerals

[0121] 1 Resin molded body, 2 Thinnest wall portion, 3 Thickest wall portion, 10 Foamed resin sheet, 11 Core layer (foamed layer), 12 Skin layer (non-foamed layer), 13 Skin layer (non-foamed layer), 111 Cells, t1 Thickness of thinnest wall portion, t2 Thickness of thickest wall portion, M1 Bending modulus of thinnest wall portion, M2 Bending modulus of thickest wall portion, X ratio, Y ratio, Z ratio, W Width.

Claims

1. A resin molded article obtained by shaping a foamed resin sheet, the foamed resin sheet comprising a foamed layer, a first non-foamed layer laminated on one principal surface of the foamed layer, and a second non-foamed layer laminated on the other principal surface of the foamed layer. The resin molded body includes a thinnest wall portion with the smallest thickness and a thickest wall portion with the largest thickness. The thinnest wall portion has a thickness of 0.5 mm or more, The thickest wall portion has a thickness of 5.0 mm or less, A first ratio M1 / ​​M2 of the bending elastic modulus M1 of the thinnest wall portion to the bending elastic modulus M2 of the thickest wall portion is 0.7 or more.

2. The resin molded article according to claim 1, wherein The first ratio, M1 / M2, is 2.0 or less.

3. The resin molded article according to claim 1, wherein A second ratio t1 / t2 of the thickness t1 of the thinnest portion to the thickness t2 of the thickest portion is greater than or equal to 0.4 and less than or equal to 0.

9.

4. The resin molded article according to any one of claims 1 to 3, wherein The resin molded body is made of thermoplastic resin and has a density of 1.0 g / cm 3 Hereinafter, the bending modulus of each of the thinnest wall portion and the thickest wall portion is 1000 MPa or more.

5. The resin molded article according to any one of claims 1 to 3, wherein The resin molded body includes a polycarbonate resin.

6. The resin molded article according to any one of claims 1 to 3, wherein The resin molded body includes at least one selected from the group consisting of polycarbonate resin, polypropylene, polyethylene terephthalate, and polystyrene.

7. The resin molded article according to claim 4, wherein The resin molded body includes a polycarbonate resin.

8. The resin molded article according to claim 4, wherein The resin molded body includes at least one selected from the group consisting of polycarbonate resin, polypropylene, polyethylene terephthalate, and polystyrene.

9. The resin molded article according to claim 4, wherein The ratio of the first ratio to the second ratio, ie, first ratio / second ratio, is 4.0 or less.

10. The resin molded article according to claim 9, wherein A ratio of the first ratio to the second ratio, ie, first ratio / second ratio, is greater than 1.0.

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