Resin sheet and resin molded body

Abstract

The invention provides a resin sheet and a resin molded body, which can use a thermoplastic resin with a high load deflection temperature and has both light weight and strength. The resin sheet (1) comprises a thermoplastic resin, and is provided with a core layer (2) which is a foamed resin layer, and a surface layer (3) which is continuously formed on the outside in the thickness direction of the core layer (2). The core layer (2) includes a region (A1) and a region (A2) positioned between the region (A1) and the two surface layers (3). The average porosity of the region (A2) is smaller than that of the region (A1) by less than 50%. The thermoplastic resin has a load deflection temperature of 90 DEG C or more. The resin sheet has a thickness of 1-40 mm. The surface layer has a thickness of 5-50% of the thickness of the resin sheet. Thus, in a thermoplastic resin having a deflection temperature under load of 90 DEG C or more, the thickness of the resin sheet and the thickness of the surface layer are appropriately set, whereby both lightweight properties and strength can be achieved.

Description

[0001] This invention patent application is a divisional application of the invention patent application with national application number 202211223399.0 (international application number PCT / JP2021 / 037500) entitled "resin sheet and resin molded body". Technical Field

[0002] This disclosure relates to resin sheets made of engineering plastics and super engineering plastics as resin materials, and resin molded articles made of resin sheets. Background Technology

[0003] In recent years, foamed resins have attracted attention due to their ability to reduce carbon dioxide emissions by making resin molded parts lighter. Foaming molding methods for foamed resins include physical foaming molding and chemical foaming molding. Chemical foaming molding has a high environmental impact and a significant environmental effect. Therefore, research has been conducted on physical foaming molding using physical foaming agents such as nitrogen or carbon dioxide. For physical foaming molding, a method for foaming high-heat-resistant engineering plastics and super-engineering plastics involves shearing and mixing molten resin of engineering plastics and super-engineering plastics with high-pressure supercritical fluid to dissolve them.

[0004] Japanese Patent No. 6139038 (Patent Document 1) discloses a method for manufacturing foamed molded articles using physical foaming agents such as nitrogen or carbon dioxide at low pressure without requiring supercritical fluids. According to this method, fine foamed units can be formed in resin molded articles using low-pressure physical foaming agents with a relatively simple process without the use of special high-pressure equipment.

[0005] Furthermore, methods for molding foamed resins include injection molding, which can produce resin molded bodies with complex shapes, and extrusion molding, which can continuously produce resin molded bodies with a single shape. In injection molding, when molding foamed resin, the surface layer of molten resin flows while cooling and solidifying within the mold, thus forming a non-foamed surface layer on the surface of the resin molded body. On the other hand, compared to injection molding, extrusion molding has fewer restrictions on mold size and load, making it suitable for producing resin molded bodies of a single thickness. Additionally, after obtaining a sheet-shaped resin molded body through extrusion molding, it is possible to obtain a relatively complex and large resin molded body through vacuum forming or similar methods. However, in extrusion molding, the molten resin foams and expands as it exits the mold (model), and then cools and solidifies; however, it is difficult to form a surface layer on the surface of the resin molded body.

[0006] Japanese Patent No. 3654697 (Patent Document 2) discloses a method for manufacturing a thermoplastic resin foam sheet that can easily form a surface layer on the surface of a thermoplastic resin foam sheet by extrusion molding. Furthermore, Japanese Unexamined Patent Application Publication No. 2000-52370 (Patent Document 3) discloses a method for manufacturing a multilayer laminated body having a foam layer and a surface layer by co-extrusion molding. In the method for manufacturing the thermoplastic resin foam sheet of Patent Document 2 and the method for manufacturing the multilayer laminated body of Patent Document 3, general-purpose plastics with relatively low heat resistance and strength, such as polypropylene or polystyrene, are used as the main resin material, rather than engineering plastics or super engineering plastics with excellent heat resistance and strength. Moreover, the manufacturing methods of Patent Documents 2 and 3 aim at the ease or stability of manufacturing the foamed body, rather than at improving heat resistance and strength.

[0007] Japanese Patent No. 3568655 (Patent Document 4) discloses a polycarbonate resin extruded foam laminated sheet formed by laminating multiple polycarbonate resin extruded foam sheets. However, the polycarbonate resin extruded foam laminated sheet in Patent Document 4 is a relatively thick polycarbonate resin foam sheet formed by cutting and laminating polycarbonate resin extruded foam sheets, and is not a surface layer for controlling the surface layer.

[0008] Japanese Patent Application Publication No. 06-79816 (Patent Document 5) discloses a multilayer high molecular weight polycarbonate resin foam in which the weight-average molecular weight of the surface layer is more than 1.15 times higher than that of the other layers. The multilayer high molecular weight polycarbonate resin foam in Patent Document 5 suppresses the reduction in surface layer strength by lowering the foaming density of the high molecular weight polycarbonate resin foam, but does not precisely control the mechanical strength of the surface layer or the mechanical properties of the foam sheet.

[0009] Japanese Patent Application Publication No. 2020-138402 (Patent Document 6) discloses a laminated foamed sheet with a foamed layer thickness of 0.1 to 3.0 mm and a non-foamed layer thickness of 0.05 to 0.5 mm. However, the resin material of the laminated foamed sheet is a polyolefin resin, a polystyrene resin, a polyester resin, or a general-purpose plastic with relatively low heat resistance and mechanical strength, rather than an engineering plastic or a super engineering plastic with excellent heat resistance and mechanical strength.

[0010] Japanese Patent Application Publication No. 2014-172381 (Patent Document 7) discloses a foamed resin board with a foaming ratio of 1.15 to 6 times, a thickness of 1 to 30 mm, and a non-foamed layer thickness of 0.15 to 1 mm. This results in a foamed resin board with high hardness and excellent smoothness. However, the foamed resin board is not intended to suppress the reduction in heat resistance and impact strength.

[0011] Japanese Patent Application Publication No. 08-072628 (Patent Document 8) discloses a substrate for molding automotive interior materials, which is composed of laminated foamed resin sheets that exhibit excellent thermal dimensional stability and shape retention due to their independent, flattened bubble morphology. The automotive interior material molding substrate of Patent Document 8 improves the thermal dimensional stability and shape retention after heat forming by making the bubble morphology flattened, rather than suppressing the reduction in the mechanical strength of the substrate itself. Generally, foamed molded articles tend to have reduced impact strength due to the decrease in density. Therefore, foamed molded articles in the transportation industry and the like require lightweight and impact resistance. That is, even with resins like polycarbonate, which have excellent impact resistance, the evaluation of the impact strength of the substrate itself is important when manufacturing foamed articles. Patent Document 8 is characterized by its processability, rather than suppressing the reduction in impact strength through the effects of sheet thickness, density, and cell diameter.

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: Japanese Patent No. 6139038

[0015] Patent Document 2: Japanese Patent No. 3654697

[0016] Patent Document 3: Japanese Patent Application Publication No. 2000-52370

[0017] Patent Document 4: Japanese Patent No. 3568655

[0018] Patent Document 5: Japanese Patent Application Publication No. 06-79816

[0019] Patent Document 6: Japanese Patent Application Publication No. 2020-138402

[0020] Patent Document 7: Japanese Patent Application Publication No. 2014-172381

[0021] Patent Document 8: Japanese Patent Application Publication No. 08-072628 Summary of the Invention

[0022] The problem that the invention aims to solve

[0023] The subject of this disclosure is to provide a resin sheet and resin molded body that can use a thermoplastic resin with high heat resistance while taking into account lightweight and mechanical strength.

[0024] Solution for solving the problem

[0025] To address the aforementioned issues, this disclosure provides the following solution: The resin sheet of this disclosure can be composed of a thermoplastic resin. The resin sheet can have a core layer as a foamed resin layer and surface layers continuously formed outward in the thickness direction of the core layer. The core layer can include a first region and a second region positioned between the first region and the two surface layers. The second region has a smaller average porosity than the first region, and the thermoplastic resin can have a load flexural temperature of 90°C or higher. The resin sheet can have a thickness of 1 to 40 mm.

[0026] Invention Effects

[0027] According to the resin sheet and resin molded body disclosed herein, a thermoplastic resin with high heat resistance can be used, which balances lightweight and strength. Attached Figure Description

[0028] Figure 1 This is a perspective view showing the structure of the resin sheet according to the embodiment.

[0029] Figure 2 yes Figure 1 An enlarged cross-sectional view of the resin sheet shown.

[0030] In the picture:

[0031] 1—Resin sheet, 2—Core layer, 3—Surface layer, t1—Thickness, t2—Thickness, A1—Area, A2—Area, C—Center in the thickness direction. Detailed Implementation

[0032] The resin sheet of the present disclosure can be made of thermoplastic resin. The resin sheet can have a core layer as a foamed resin layer and a surface layer continuously formed outward in the thickness direction of the core layer. The core layer can include a first region and a second region positioned between the first region and the two surface layers. The second region has an average porosity less than 50% smaller than that of the first region, and the thermoplastic resin can have a load flexural temperature of 90°C or higher. The resin sheet can have a thickness of 1 to 40 mm. The surface layer can have a thickness of 5 to 50% of the thickness of the resin sheet. This resin sheet can more effectively improve strength. Furthermore, details regarding the calculation method of the average porosity, etc., will be described later.

[0033] Thus, by appropriately setting the thickness of the resin sheet, the thickness of the surface layer, and the average porosity of the core layer in thermoplastic resins with a load flexural temperature above 90°C, it is possible to use thermoplastic resins with high heat resistance that balance lightweight and strength.

[0034] Resin sheets can reduce the average porosity from the center of the core layer towards the surface of the resin sheet. This gradual reduction in porosity from the center of the core layer towards the surface prevents stress concentration at the interface between the core and surface layers when external forces are applied to the resin sheet. Consequently, the impact strength of the resin sheet can be improved.

[0035] The first region can have an average porosity of 50% to 95%. The second region can have a smaller average porosity than the first region. More preferably, the porosity gradually decreases from the first region toward the surface layer. This allows for a more effective increase in strength.

[0036] The first region can have an average porosity of 65% to 90%. More preferably, the porosity decreases from the first region toward the surface layer. This allows for a more effective increase in strength.

[0037] Resin sheets can have a flexural modulus of elasticity of over 1.5 GPa and a g / cm³. 3 The following density. The surface layer can have a flexural modulus that is more than 1.5 times that of the core layer. This allows for a more effective balance between lightweight and strength.

[0038] Resin sheets can have a load flexural temperature above 150°C, a flexural modulus above 3 GPa, and a strength of 1.3 g / cm³. 3 The following density allows for a more effective balance between lightweight and strength.

[0039] The surface layer can be made of a reinforced resin containing inorganic fillers. This allows for efficient improvement in strength, achieving both lightweighting and increased strength.

[0040] Thermoplastic resins may contain at least one component selected from the group consisting of polycarbonate, modified polyphenylene ether, syndiotactic polystyrene, polyphenylene sulfide, polysulfone, polyethersulfone, polyarylate, polyamide-imide, thermoplastic polyimide, polyether-imide, and liquid crystal polymer.

[0041] The resin molded body of the embodiments of this disclosure can be a resin molded body formed by heating and shaping any of the above-mentioned resin sheets.

[0042] The following uses Figure 1 and Figure 2 Embodiments of the resin sheet 1 of the present invention will be described in detail. Furthermore, identical or equivalent structures in the figures will not be described repeatedly using the same symbols. Additionally, to facilitate understanding, the structures are shown in a simplified or schematic manner in the accompanying drawings, or some structural components are omitted.

[0043] like Figure 1 and Figure 2 As shown, the resin sheet 1 includes a core layer 2 and two surface layers 3 formed on both sides of the core layer 2 outside its thickness direction. That is, the surface layers 3 are continuously formed outside the thickness direction of the core layer 2. Here, "continuous outside the thickness direction of the core layer 2" means that the interface is not clearly defined as if the core layer 2 and the surface layers 3 were made separately and then fixed together, but rather the core layer 2 and the surface layers 3 are integrally formed using a co-extrusion molding method, so that no clear interface is exhibited.

[0044] The core layer 2 is composed of a foamed resin layer. The resin material of the core layer 2 is a thermoplastic resin. The thermoplastic resin used in this disclosure has a load flexural temperature of 90°C or higher. Here, the load flexural temperature is defined according to a load of 1.81 MPa, ISO 075-2B.

[0045] The thermoplastic resin used in the core layer 2 of this disclosure can include engineering plastics and super engineering plastics. Engineering plastics are thermoplastic resins having a load flexural temperature of 100°C or higher. Examples of engineering plastics used in the core layer 2 of this disclosure include polycarbonate (PC), modified polyphenylene ether (m-PPE), and syndiotactic polystyrene (SPS). Super engineering plastics are thermoplastic resins having a load flexural temperature of 150°C or higher. Examples of super engineering plastics used in the core layer 2 of this disclosure include polyphenylene sulfide (PPS), polysulfone (PSF), polyethersulfone (PES), polyarylate (PAR), polyamide-imide (PAI), thermoplastic polyimide (PI), polyether-imide (PEI), and liquid crystal polymer (LCP). The thermoplastic resin used in the core layer 2 of this disclosure can include at least one selected from the group consisting of these engineering plastics and super engineering plastics.

[0046] If the foaming ratio of the core layer 2 is relatively large, weight reduction can be achieved, but strength will be reduced. If the foaming ratio (specific gravity reduction rate) is relatively small, strength can be improved, but weight reduction cannot be achieved. Therefore, from the viewpoint of achieving both weight reduction and strength improvement, the foaming ratio (specific gravity reduction rate) of the core layer 2 can be 1.2 times (17%) or more, preferably 5 times (80%) or less, and from the viewpoint of suppressing the reduction of processability such as breakage during vacuum forming and other heat forming processes, it is more preferably 3 times (67%) or less.

[0047] The surface layer 3 is laminated on at least one of the main surfaces of the core layer 2. That is, the surface layer 3 is laminated on one or both of the core layers 2. From the viewpoint of improving strength, it is more preferable that the surface layer 3 is laminated on both of the main surfaces of the core layer 2. The resin material of the surface layer 3 is a thermoplastic resin having a load flexural temperature of 90°C or higher. The thermoplastic resin used in the surface layer 3 may include at least one selected from the group consisting of engineering plastics and super engineering plastics used in the core layer 2. The surface layer 3 may be formed from a single thermoplastic resin identical to that of the core layer 2 or from a combination of multiple identical resin materials, or it may be formed from a single thermoplastic resin different from that of the core layer 2 or from a combination of multiple different resin materials.

[0048] The resin sheet 1 is constructed with an inclined structure in which the average porosity (%) decreases from the center C in the thickness direction toward the surface of the resin sheet 1. In other words, the diameter of the bubbles formed in the resin sheet 1 decreases from the center in the thickness direction toward the surface. The average porosity can be calculated based on the ratio of the cross-sectional area of ​​the foaming units per unit cross-sectional area of ​​the resin sheet 1. Details of the calculation method for the average porosity will be described later.

[0049] Core layer 2 is composed of foamed resin. Core layer 2 is a region with an average porosity of 5% to 95%. For example... Figure 2 As shown, when the total thickness of the core layer 2 is set to 100%, the core layer 2 has a region A1 located from the center C in the thickness direction of the core layer 2 toward the surface layer 3 within a range of 0% to less than 40%, and a region A2 located between region A1 and the surface layer 3. Furthermore, in Figure 2In the diagram, dashed lines represent the boundaries of each layer or region, and two dashed lines represent the center line of the thickness direction center C. Region A1 has an average porosity of 50% to 95%. By making region A1 range from the center C along the thickness direction to 40% relative to the total thickness of the resin sheet 1, large bubbles are less likely to form near the surface of the resin sheet 1 during thermoforming such as vacuum forming, thus reducing the deterioration of processability such as expansion and breakage of the resin sheet 1 surface. Region A2 has a smaller average porosity than region A1, and the average porosity decreases from region A1 toward the surface layer 3. By reducing the average porosity of region A2, i.e., thickening the walls between bubbles (hereinafter also referred to as bubble walls), the reduction in impact strength caused by foaming can be suppressed. In addition, by making the average porosity of region A1 greater than that of region A2, a lightweight effect can be ensured. When the average porosity of region A1 is less than 50%, there is a concern that the foaming ratio of the core layer 2 may be less than 1.2 times. Therefore, in order to form a core layer 2 with a foaming ratio of 1.3 to 3 times that is preferred for achieving lightweighting, it is preferable to set the average porosity to 50% or more. In the case of applications such as impact-resistant materials, a thin sheet with a large total thickness is preferred, and therefore, it is more preferable to set the average porosity of region A1 to 65% or more. When the average porosity of region A1 is 96% or more, although a sufficient lightweighting effect can be expected, the bubble walls become extremely thin, and there is a possibility of the sheet breaking upon impact. Therefore, the average porosity of region A1 is preferably set to 95% or less, and more preferably, from the viewpoint of suppressing the breakage of bubble walls due to the stretching of the sheet during thermal forming such as vacuum forming, it is preferable to set it to 90% or less. As an example, when the average porosity of region A1 is 80%, the average porosity of region A2 decreases towards the surface layer 3 from an average porosity of less than 80%, which is smaller than that of region A1. That is, region A1, within a thickness direction from the center C of the thickness direction toward the surface layer 3, has a predetermined average porosity determined in the range of 50% to 95%, preferably 65% ​​to 90%, where the porosity is 0% or more and less than 40%. Region A2, within the range between region A1 and the surface layer 3, may have a smaller average porosity than the aforementioned predetermined average porosity, or may have an average porosity that decreases toward the surface layer 3. However, if the average porosity of region A2 is 50% or more, the impact resistance of the resin sheet 1 decreases. Therefore, the average porosity of region A2 is preferably less than 50%. The surface layer 3 is composed of a non-foamed resin. That is, the surface layer 3 refers to the region having an average porosity of 0% or more and less than 5% among three zoning areas located in any extracted region of the same thickness.

[0050] More specifically, the average porosity was calculated as follows. First, a portion of the resin sheet 1 was cut out to create a square sheet measuring 20mm × 20mm from top view. Using a high-output miniature X-ray CT system (Shimadzu Corporation, model "inspeXio SMX-225CTS"), the sheet was CT-scanned to obtain a CT cross-sectional image cut along a line passing through the center point of the sheet and the midpoint of a predetermined side from top view, in the thickness direction. Detailed measurement conditions were: 160kV applied, pixel size 0.105mm / voxel, pixel count 512 × 512 × 512, viewpoint count 1200, field of view 53.5mm in the XY direction, and field of view 48.9mm in the Z direction. In the cross-section of the resin sheet 1, bubbles close to the surface of the resin sheet 1 were selected from among 15 abundant bubbles along imaginary boundary lines when the cross-section of the resin sheet 1 was divided into 16 equal parts in the width direction. The bubble closest to the surface of the resin sheet 1 among these bubbles was then identified. An imaginary line is drawn passing through the upper end of the nearest bubble and orthogonal to the thickness direction. The layer inside the imaginary line in the thickness direction is designated as core layer 2, and the layer outside the thickness direction is designated as surface layer 3. The thickness t2 of surface layer 3 is measured. Next, in a CT cross-sectional image obtained by photographing the core layer 2, square regions are defined by dividing core layer 2 into 20 equal parts in the thickness direction (therefore, the length of one side of each region depends on the thickness of the resin sheet 1). Five columns are extracted from these 20 regions arranged along the thickness direction of core layer 2. Thus, each column passes through regions A1 and A2 along the thickness direction of core layer 2. Next, the bubble and bubble wall are binarized using image processing software "Image J" (made by the National Institutes of Health). The threshold for binarization is determined based on the concentration histogram obtained using the Otsu method. Then, the white portion of the resulting binarized image is designated as the bubble wall, and the black portion as the bubble, and the cross-sectional area of ​​the individual bubbles contained in each region of each column is calculated. The cross-sectional area of ​​each individual bubble contained in each zone is calculated and divided by the cross-sectional area of ​​each zone to calculate the porosity of each zone contained in each column. Finally, the average porosity of all zones contained in region A1 and the average porosity of all zones contained in region A2 are calculated. This average porosity of the zones contained in regions A1 and A2 is called the average porosity. Furthermore, to calculate the average porosity in more detail along the thickness direction, the core layer 2 can be divided into 21 or more equal parts. Additionally, zones containing the boundary between regions A1 and A2 are excluded from the calculation of the average porosity. Furthermore, the five extracted columns are located in the cross-sectional image of the core layer 2 at the center in the width direction, the end of one side in the width direction, the end of the other side in the width direction, the center between the center in the width direction and the end of one side in the width direction, and the center between the center in the width direction and the end of the other side in the width direction, respectively.

[0051] like Figure 1 As shown, the resin sheet 1 has a thickness t1 of 1 to 40 mm. The surface layer 3 has a thickness t2 that is 5 to 50% of the thickness t1 of the resin sheet 1. As described above, the surface layer 3 can be laminated on one or both sides of the main surface of the core layer 2. When the surface layer 3 is laminated on both sides of the main surface of the core layer 2, the thickness t2 of the surface layer 3 is the sum of the thickness of one surface layer 3 and the thickness of the other surface layer 3.

[0052] When the thickness t1 of the resin sheet 1 is 1 to 5 mm, that is, when the thickness t1 is small, the strength improvement effect is greater even if the thickness t2 of the surface layer 3 is relatively small. If the thickness t2 of the surface layer 3 is relatively large, the weight reduction effect is easily reduced. Therefore, when the thickness t1 of the resin sheet 1 is 1 mm or more and less than 5 mm, the thickness t2 of the surface layer 3 is 5% or more of the thickness t1 of the resin sheet 1. Considering high rigidity, impact strength, and suppression of breakage and peeling during thermal forming such as vacuum forming, it is preferably 10% or more and less than 50%. Considering the weight reduction effect, it is preferably less than 40%. When the thickness is less than 5 mm, it can be processed into any shape through post-processing such as vacuum forming, so it is expected to be applied to lightweight structural components, panel components, etc. In addition, when the thickness t1 of the resin sheet 1 is 5 mm or more, that is, when the thickness t1 is large, compared with the case of a small thickness t1, it is difficult to achieve a strength improvement if the thickness of the surface layer 3 is relatively small. Therefore, when the resin sheet 1 has a thickness t1 of 5~40mm, the surface layer thickness t2 needs to be relatively thick, at least 10%. Furthermore, from the perspective of achieving lightweighting, it can be less than 50%, and further considering lightweighting, it can be less than 40%. Such a thick sheet will also have higher thermal insulation properties, making it difficult to shape through post-processing such as vacuum forming. However, the sheet has very high rigidity, thus enabling its application in building materials, plywood, etc.

[0053] As described above, by appropriately setting the thickness of the resin sheet 1 and the thickness of the surface layer 3, and appropriately setting the average porosity of the core layer 2, it is possible to use a thermoplastic resin with high heat resistance while taking into account both lightweight and strength.

[0054] When the resin sheet 1 is made of engineering plastic, the resin sheet 1 has a flexural modulus of elasticity of 1.5 GPa or higher and a g / cm³ of 1.0 g / cm³. 3 The following density. In this disclosure, the flexural modulus is defined as the value evaluated by a three-point bending test (ISO 178). When the resin sheet 1 is made of engineering plastic, the reduction in density (lightweighting) and the increase in strength are achieved by the lightweighting brought about by the foamed core layer 2 and the increase in strength brought about by the non-foamed surface layer 3.

[0055] When the resin sheet 1 is made of super engineering plastic, the resin sheet 1 has a flexural modulus of more than 3 GPa and a strength of 1.3 g / cm³. 3 The density is as follows. Superior engineering plastics are generally harder than other thermoplastic resins (such as general-purpose plastics), and therefore difficult to stretch. Therefore, if the foaming ratio of superior engineering plastics is increased during foaming molding, bubble breakage occurs, significantly reducing mechanical strength. Therefore, when the resin sheet 1 is made of superior engineering plastic, the foaming ratio of the core layer 2 is preferably 1.2 to 2 times.

[0056] The surface layer 3 can also be formed using a thermoplastic resin whose flexural modulus is more than 1.5 times that of the core layer 2. The surface layer 3 can be made of any thermoplastic resin that can bond well with the core layer 2. Furthermore, to strengthen the surface layer 3, it can be composed of a reinforcing resin containing inorganic fillers. Through these surface layer 3 configurations, strength can be efficiently improved, and both lightweighting and strength enhancement can be achieved. Inorganic fillers include, for example, glass fiber, carbon fiber, aramid fiber, talc, and mica. In this disclosure, the mechanical properties of the thermoplastic resin of the surface layer 3 can be evaluated by mechanically separating the core layer 2 and the surface layer 3 and then remelting them to form a test specimen. The mechanical properties of the core layer 2 can be determined by mechanically peeling off the surface layer 3.

[0057] Regarding the resin sheet 1, the core layer 2 and the surface layer 3 can be fabricated separately by hot-melt bonding. That is, the resin sheet 1 can also be fabricated separately by core layer 2 and surface layer 3, and then fixed with their main surfaces facing each other. Alternatively, the core layer 2 and surface layer 3 can be integrally formed by co-extrusion molding. In this case, foaming can be achieved by shearing and mixing the molten resin with a high-pressure supercritical fluid to dissolve it, or foaming can be achieved using a low-pressure physical foaming agent, such as nitrogen, carbon dioxide, air, or an inert gas like argon. Furthermore, from the viewpoint of ease of controlling the bubbles formed in the core layer 2, and ease of controlling the thickness t1 of the resin sheet 1 and the thickness t2 of the surface layer 3, it is preferable to manufacture the resin sheet 1 by fusion bonding the core layer 2 and the surface layer 3. On the other hand, by forming the resin sheet 1 using co-extrusion molding as described above, a distinct interface can be eliminated between the core layer 2 and the surface layer 3, and a region A2 with reduced average porosity can be formed between region A1 and the surface layer 3. As a result, the resin sheet 1 can improve impact strength. That is, in the co-extrusion molding method, it is preferable to integrate the core layer 2 and the surface layer 3 inside the mold before or during the foaming of the core layer 2.

[0058] The resin sheet 1 manufactured in this way can be thermoformed into a desired shape. Thermoforming, as referred to here, generally means pressing a heated and softened plastic sheet into a desired mold to form it. Even in thermoforming, vacuum forming is preferred, where air is expelled from the gap between the mold and the resin sheet 1, and atmospheric pressure is used to press the resin sheet 1 tightly against the mold to form it. Furthermore, as another example, air-forming using compressed air at pressures greater than atmospheric pressure, and vacuum-air-forming using both vacuum forming and air-forming, can be cited. Further, as another example, two-sided vacuum forming can be cited, where the resin sheet 1 is placed in a space larger than its thickness, located between a mold having a concave shape and a mold having a convex shape, and then vacuum-drawn from both sides of the mold. The thermoforming method is not particularly limited; for example, plug forming, mating mold forming, and plunger-assisted forming methods can be exemplified. Furthermore, the formed shape is not particularly limited. By performing thermoforming, it can be used for the following applications. For example, resin molded bodies formed by heating and shaping such resin sheets 1 are wide products and parts such as billboards or automotive exterior materials requiring high strength; heat-resistant products and parts such as batteries or trays for heating components used in manufacturing processes involving heating; or products and parts requiring lightweight. Resin sheets 1 contain thermoplastic resin, and are therefore suitable as materials for molding these resin molded bodies.

[0059] Products and components made from resin sheet 1 can reduce resin usage. As a result, resin sheet 1 of this embodiment can contribute to improved resource utilization efficiency, reduced transportation burden, reduced energy consumption, and reduced CO2 emissions. By providing resin sheet 1 to society, it is possible to help achieve Goal 7 (Affordable Clean Energy), Goal 9 (Industry, Innovation and Infrastructure), and Goal 11 (Sustainable Cities and Communities) of the 17 Sustainable Development Goals (SDGs) set by the United Nations. In addition, since resin sheet 1 of this embodiment can be melted and reused, it can help achieve Goal 12 (Responsible Consumption and Production).

[0060] The implementation methods have been described above, but this disclosure is not limited to the above implementation methods, and various modifications can be made without departing from its spirit.

[0061] (Example)

[0062] As shown in Table 1 below, various resin sheets were prepared as test specimens, and the specific flexural modulus of each specimen was calculated to confirm their lightweight and strength. In Table 1, test specimens 1-4, 11, 12, 17, 21, and 27 are comparative examples, while the other test specimens are exemplary examples. Furthermore, test specimens comprising both a core layer and a surface layer (except for test specimen 27) were prepared by using the same main resin material as the core layer for the surface layer and producing resin sheets via co-extrusion molding. The core layer was prepared by using a known physical foaming agent under high pressure through screw shearing and mixing via foam extrusion molding. The preparation method of test specimen 27 will be described later. The polycarbonate resin used here is Teijin PANLITE L-1250Y, with a strength of 1.2 g / cm³. 3 The density, flexural temperature under load of 143°C, and flexural modulus of elasticity of 2.2~2.3 GPa are given. Under these conditions, the specific flexural modulus of elasticity (the value obtained by dividing the flexural modulus of elasticity by the density) of the resin sheet is 1.83 GPa. It can be said that the higher the specific flexural modulus of elasticity, the lighter the material and the higher its rigidity. In addition, the "Surface Layer Thickness Ratio (%)" in Table 1 is the ratio of the surface layer thickness t2 to the resin sheet thickness t1.

[0063] [Table 1]

[0064]

[0065] The cross-sections of the test pieces obtained by cutting each test body along the thickness direction were calculated using the method described above to determine the surface layer and the core layer. The average porosity of regions A1 and A2 of the core layer is shown in Table 1.

[0066] The prepared test specimens were subjected to a three-point bending test based on ISO 178, and the flexural modulus and specific flexural modulus were calculated, as shown in Table 1.

[0067] Charpy impact test (according to ISO 179-1) was conducted on each test piece under undamaged conditions, with a flat-wound vertical test and a 4J oscillator used to evaluate for any damage. For each test piece, 10 sample test pieces were evaluated. The probability of complete failure, pivot failure, or partial failure was 0%, designated as "A"; 1% to less than 30%, designated as "B"; 31% to less than 50%, designated as "C"; and 51% to 100%, designated as "D," as shown in Table 1.

[0068] First, Test 1 is a thin resin sheet consisting only of a core layer made of foamed resin. That is, Test 1 does not have a surface layer. Test 1 was prepared as follows: polycarbonate resin was melted in a screw cylinder at 270°C to form molten resin. Nitrogen gas, used as a physical foaming agent, was mixed into the molten resin at a ratio of 0.3% using a known high-pressure device. The mold outlet temperature was set to 215°C, and the sheet was extruded at a thickness of 2 mm at a push-out speed of 0.7 m / min. The foaming ratio of Test 1 was 2 times (50% reduction in specific gravity). Furthermore, the density of Test 1 was 0.6 g / cm³. 3 The flexural modulus is 1 GPa. Based on these properties, the specific flexural modulus is calculated to be 1.66 GPa·g / cm³. 3 .

[0069] Test piece 2 is also a resin sheet with only a core layer. That is, test piece 2 does not have a surface layer. Test piece 2 was prepared as follows: polycarbonate resin was melted in a screw cylinder at 270°C to form molten resin. Isopentane, as a physical foaming agent, was mixed with this molten resin using a known high-pressure device at a ratio of 0.53 mol / kg resin. The mold outlet temperature was set to 215°C, and the sheet was extruded at a thickness of 2 mm at a push-out speed of 0.7 m / min. The foaming ratio of test piece 1 was 6 times (specific gravity reduction rate of 84%). Furthermore, the density of test piece 2 was 0.2 g / cm³. 3 The flexural modulus is 0.7 GPa. Based on these properties, the specific flexural modulus is calculated to be 3.5 GPa·g / cm. 3 .

[0070] Next, test specimens 4-12 were prepared. Test specimens 4-12 are resin sheets with a surface layer made of the same polycarbonate resin formed on a core layer made of polycarbonate resin. These resin sheets were co-extruded to form the surface layer on both sides outside the thickness direction of the core layer. The foamed core layer, formed by the main extruder and the auxiliary extruder, was formed as described above. For the surface layer resin in the auxiliary extruder, polycarbonate resin was fed into the screw cylinder of the auxiliary extruder, heated and mixed at 270°C, and the mold outlet temperature was set to 215°C, extruded on both sides of the core layer. At this time, the thickness of the surface layer was adjusted to an arbitrary thickness, similar to that of the main extruder, by adjusting the outlet opening, becoming the thickness listed in Table 1. Furthermore, the average porosity was adjusted by increasing or decreasing the temperature of the single tube from the screw cylinder to the mold. Specifically, to increase the average porosity of region A1 of the core layer, the temperature of the single tube was adjusted in the upward direction; to decrease the average porosity of region A1, the temperature of the single tube was adjusted in the downward direction.

[0071] Compared to test specimen 1, test specimen 2 has a lower density. Therefore, the specific flexural modulus of test specimen 2 is significantly higher than that of test specimen 1. Thus, test specimen 2 achieves substantial weight reduction compared to test specimen 1. However, like test specimen 1, it shows a "D" in the Charpy impact test and its flexural modulus is lower than that of test specimen 1. This indicates that in resin sheets made of polycarbonate resin, if weight reduction is achieved solely by increasing the foaming ratio, the impact resistance of the resin sheet itself deteriorates.

[0072] Test specimen 4 has a surface layer thickness ratio of 4%, which is less than 5%. Compared with test specimen 1, test specimen 4 does not show an improvement in flexural modulus and also shows a "C" result in the Charpy impact test.

[0073] Test pieces 5-10 have a surface layer thickness ratio of 5% or more. Therefore, the flexural modulus of test pieces 5-10 is higher than that of test piece 1. Furthermore, when the surface layer thickness ratio (%) is 5% or more, the specific flexural modulus of test pieces 5-10 is higher than that of test piece 1. According to the Charpy impact test results of test piece 6, when the surface layer thickness ratio is 10% or more, the probability of fragment failure in the Charpy impact test is 0%, i.e., an evaluation of "A", indicating superior impact resistance. Excellent impact resistance is also obtained in test pieces 7 and 8. According to the Charpy impact test results of test pieces 9 and 10, when the average porosity in the core layer region A1 is 64% or less, an evaluation of "B" is shown, indicating slightly better impact resistance. Here, if we compare test piece 9 and test body 10, when the surface layer thickness ratio is 50%, the specific flexural modulus of test bodies 9 and 10 are approximately the same, and the effects of lightweighting and strength improvement are saturated.

[0074] Among test specimens 4-10, the highest specific flexural modulus was 2.09 GPa for specimen 9. For specimen 7, it was 0.85 g / cm³. 3 The density of the core layer is increased, and the flexural modulus is increased compared to test specimen 1. On the other hand, according to test specimen 11, the average porosity of region A2 in the core layer exceeds 50%, meaning that the proportion of resin near the surface layer decreases, resulting in poorer impact resistance. Furthermore, according to the test results of test specimen 12, the average porosity of regions A1 and A2 in the core layer is high, which reduces the stress mitigation effect at the interface between the surface layer and the core layer, resulting in a significant decrease in the structure's impact resistance. Therefore, based on the flexural modulus and Charpy impact test results of test specimens 4-11, if the surface layer thickness ratio is 5-50% and the average porosity of region A2 is less than 50%, both lightweight and increased strength can be achieved. Furthermore, it is known that if the average porosity of region A1 is 65% or more, even better impact resistance can be obtained.

[0075] In addition, in test subjects 5-10, the flexural modulus of the resin sheet was above 1.5 GPa, and the density of the resin sheet was 1.0 g / cm³. 3 Furthermore, the flexural modulus of the surface layer is more than 1.5 times that of the core layer. Therefore, compared with the solid thin plate consisting of a surface layer without a core layer, i.e., test piece 3, test pieces 5-10 can further improve the specific flexural modulus.

[0076] Next, test specimens 13-16 were fabricated. In the fabrication of test specimens 13-16, the extruder conditions were the same as for test specimens 4-12, but the temperature of the single tube of the auxiliary extruder was appropriately adjusted to regulate their respective average porosity. As shown in Table 1, in test specimens 13-16, the thicknesses of the surface layers stacked on the outer side of the core layer in the thickness direction were 0.1 mm (test specimen 13), 0.2 mm (test specimen 14), 0.3 mm (test specimen 15), and 0.5 mm (test specimen 16), respectively. That is, the sum of the thicknesses (thickness t2) of the two surface layers formed on the outer side of the core layer in the thickness direction were 0.2 mm (test specimen 13), 0.4 mm (test specimen 14), 0.6 mm (test specimen 15), and 1.0 mm (test specimen 16). The surface layers of test specimens 13-16 differed from those of test specimens 4-12, using polycarbonate resin (Teijin PANLITE G-3330M, density: 1.44 g / cm³) with added glass filler. 3 It is made using the following parameters: load flexural temperature: 138℃, flexural modulus of elasticity: 3.8GPa.

[0077] Based on the test results of test subjects 13-16, if a surface layer with a high flexural modulus is formed in the core layer with a surface layer thickness ratio of 5% or more, the rigidity can be effectively improved, resulting in a higher specific flexural modulus than that of test subject 3, which is a solid thin plate. Based on the test results of test subject 16, by setting the surface layer thickness ratio to 33.3%, a density of 1 g / cm³ can be achieved. 3 Compared to test specimen 3, the flexural modulus and specific flexural modulus are improved. Furthermore, the specific flexural modulus of test specimen 16 is more than 60% higher than that of test specimen 3. Thus, it can be seen that both lightweight and improved strength are achieved in test specimens 13-16.

[0078] Next, test subjects 18-20 were prepared. Test subjects 18-20 were prepared using PPS resin (DIC Z230, density: 1.53 g / cm³). 3The core layer was subjected to a flexural temperature of 260℃ (1.8MPa load) and a flexural modulus of 10GPa. Resin sheets with surface layers formed on both outer sides of the core layer in the thickness direction were produced by co-extrusion molding. The core layer thickness was 2.0mm, and the foaming ratio was 1.5 times (33% reduction in specific gravity). Although not shown in Table 1, the physical properties of the core layer monomer for test samples 18-20 were: density: 1.0g / cm³. 3 Flexural modulus: 0.6 GPa. The calculated specific flexural modulus of the core layer monomer is 6 GPa, lower than the 6.54 GPa of test specimen 17, which is a solid thin plate. The thicknesses of the surface layers formed on the outer side of the core layer in the thickness direction are 0.2 mm (test specimen 18), 0.3 mm (test specimen 19), and 0.5 mm (test specimen 20), respectively. That is, the sum of the thicknesses (thickness t2) of the two surface layers formed on the outer side of the core layer in the thickness direction is 0.4 mm (test specimen 18), 0.6 mm (test specimen 19), and 1.0 mm (test specimen 20). Based on the test results of test specimens 18-20, compared with test specimen 17, weight reduction and improved specific flexural stiffness can be achieved.

[0079] Next, test specimens 21-26 were fabricated. The core layer of test specimens 21-26 is a polycarbonate foam resin layer with a thickness of 24 mm. Even with such a relatively thick core layer, if the surface layer is formed at a ratio of 5% or more to the surface layer thickness, rigidity can be effectively improved, resulting in a higher specific flexural modulus than test specimen 3. Thus, in the resin sheet range of 1-40 mm in thickness, by forming a surface layer on the outside of the core layer in a ratio of 5% to 50% of the resin sheet thickness, the specific flexural modulus can be further improved than that of test specimen 1. Furthermore, when the surface layer thickness ratio exceeds 10%, the specific flexural modulus is significantly improved, resulting in a lighter and more rigid resin sheet.

[0080] Furthermore, strength tests were conducted using test bodies 1, 8, and 27. Specifically, the strength test involved dropping a 1 kg iron ball freely from a height of 1 m above the surface of each test body to confirm the presence of cracks in each test body. Test body 27 has the same layered structure as test body 8, but is manufactured by bonding the core layer and surface layer using methyl ethyl ketone (MEK) organic solvent. That is, in the cross-section of test body 27, there is a clear interface between the surface layer and the core layer. On the other hand, as described above, test body 8 is manufactured by co-extrusion molding, and the core layer and surface layer are formed by reducing the average porosity from the center of the resin sheet in the thickness direction toward the surface of the resin sheet. When the cross-section in the thickness direction of test body 8 was checked, with the total thickness of the core layer set to 100%, the average porosity from the center of the core layer in the thickness direction toward both surface layers was 72% within a range of 0% to less than 20% (region A1), and the average porosity of the surface layer was 2%. Furthermore, in region A2, located between the core layer and the surface layer, the average porosity decreases from 72% to 23% from region A1 toward the surface layer, exhibiting the aforementioned inclined structure. As described above, the test specimen 1 is formed solely from the core layer.

[0081] For these test objects 1, 8 and 27, after the iron ball was dropped freely from a height of 1m, test object 1 was completely destroyed, while test objects 8 and 27 did not develop cracks and were not destroyed.

[0082] Next, for test objects 8 and 27, the iron ball was dropped freely from a height of 1.25m. Test object 27 developed cracks in a portion but was not completely destroyed. Test object 8, however, did not develop cracks and was not destroyed. This is believed to be because in test object 8, the core layer and surface layer are integrally formed, causing the average porosity to decrease from the center towards the surface in the thickness direction, thereby avoiding stress concentration from external forces.

Claims

1. A co-extruded resin sheet, comprising a thermoplastic resin, characterized in that, have: As the core layer of the foamed resin layer; and A surface layer continuously formed outward in the thickness direction of the core layer. The core layer includes a first region and a second region located between the first region and the two surface layers. The first region has an average porosity of 50%-95%. The second region has an average porosity of less than 50% and is smaller than that of the first region. The thermoplastic resin has a load flexural temperature above 90°C. The resin sheet has a thickness of 1-40 mm. The average porosity of the second region gradually decreases continuously from the center of the core layer in the thickness direction toward the surface of the resin sheet. The surface layer has a thickness of 5 to 50% of the thickness of the resin sheet.

2. The resin sheet according to claim 1, characterized in that, The first region has an average porosity of 65% to 90%.

3. The resin sheet according to claim 1, characterized in that, The surface layer is composed of a reinforced resin containing inorganic fillers.

4. The resin sheet according to any one of claims 1 to 3, characterized in that, The surface layer has a flexural modulus that is more than 1.5 times that of the core layer.

5. The resin sheet according to any one of claims 1 to 3, characterized in that, The resin sheet has a load flexural temperature of 150°C or higher, a flexural modulus of elasticity of 3 GPa or higher, and a density of 1.3 g / cm³ or lower.

6. The resin sheet according to any one of claims 1 to 3, characterized in that, The thermoplastic resin comprises at least one selected from the group consisting of polycarbonate, modified polyphenylene ether, syndiotactic polystyrene, polyphenylene sulfide, polysulfone, polyethersulfone, polyarylate, polyamide-imide, thermoplastic polyimide, polyether-imide, and liquid crystal polymer.

7. The resin sheet according to any one of claims 1 to 3, characterized in that, The average porosity is calculated based on the ratio of the cross-sectional area of ​​the foaming units per unit cross-sectional area in the resin sheet.

8. A resin molded article, characterized in that, The resin sheet according to any one of claims 1 to 7 is formed by heating and shaping.

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