resin sheet

Abstract

To provide a resin sheet that can improve impact strength. [Solution] The resin sheet 1 includes a core layer 2, a skin layer 3, and a reinforcing skin layer 4. The core layer 2 is made of foamed resin. The skin layer 3 is made of non-foamed resin. The reinforcing skin layer 4 is made of non-foamed resin containing a reinforcing agent 5. As a result, the Young's modulus of the skin layer 3 is greater than that of the core layer 2, and the Young's modulus of the reinforcing skin layer 4 is greater than that of the skin layer 3. Consequently, the Young's moduli of the core layer 2, skin layer 3, and reinforcing skin layer 4 increase in a stepwise manner towards the outward direction in the thickness direction. As a result, stress concentration in each layer can be mitigated when external stress is applied, thereby improving impact strength.

Description

Technical Field

[0001] [[ID=⑤]]The present disclosure relates to a multilayer resin sheet made of a thermoplastic resin. [[ID=⑥]] [[ID=⑦]]

Background Art

[0002] [[ID=⑪]] [[ID=⑫]]In recent years, foamed resins have attracted attention because they can improve convenience by reducing the weight of resin sheets and can reduce carbon dioxide emissions. However, since foamed resins contain a large number of bubbles, they can reduce the strength of resin sheets. Therefore, a resin sheet in which a skin layer made of a non-foamed resin is laminated on a core layer made of a foamed resin has been proposed. [[ID=⑬]] [[ID=⑭]]

[0003] [[ID=⑮]] [[ID=⑯]]International Publication No. 2023 / 0262664 (Patent Document 1) discloses a resin sheet capable of achieving both weight reduction and strength improvement. The resin sheet includes a core layer that is a foamed resin layer and includes a first region and a second region, and a skin layer formed continuously outward in the thickness direction of the core layer. The first region of the core layer has an average porosity of 60% to 95%, the second region has an average porosity smaller than that of the first region, and has an average porosity that gradually decreases from the first region toward the skin layer. The skin layer is a region where the average porosity is less than 5%. The resin sheet aims to achieve both weight reduction and strength improvement by controlling the average porosities of the skin layer, the first region, and the second region of the core layer. [[ID=⑰]] [[ID=⑱]]

Prior Art Documents

Patent Documents

[0004] [[ID=㉕]] [[ID=㉖]] [[ID=㉗]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] [[ID=㊳]] [[ID=㊴]]An object of the present disclosure is to provide a resin sheet capable of improving impact strength. [[ID=㊵]] [[ID=㊶]]

Means for Solving the Problems

[0006] To solve the above problems, this disclosure employs the following solutions. Specifically, the resin sheet according to this disclosure is a resin sheet made of a thermoplastic resin, comprising a core layer made of a foamed resin, a skin layer made of a non-foamed resin and laminated on one main surface of the core layer, and a reinforcing skin layer made of a non-foamed resin containing a reinforcing agent and laminated on the main surface of the skin layer opposite to the core layer. [Effects of the Invention]

[0007] The resin sheet relating to this disclosure can improve impact strength. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is an external perspective view showing the structure of the resin sheet according to the embodiment. [Figure 2] Figure 2 is an enlarged cross-sectional view of the resin sheet shown in Figure 1. [Modes for carrying out the invention]

[0009] As a result of diligent research, the present inventors have obtained the following findings regarding the resin sheet of Patent Document 1. Although the resin sheet of Patent Document 1 has sufficient strength as well as being lightweight, it may break when a large external stress is applied, for example. That is, if the difference in Young's modulus between the core layer and the skin layer of the resin sheet is large, stress due to deformation concentrates at the interface between the core layer and the skin layer, causing the skin layer to break and the resin sheet to break easily. Therefore, by laminating a core layer, a skin layer with a Young's modulus greater than that of the core layer, and a reinforced skin layer with a Young's modulus greater than that of the skin layer, and gradually increasing the Young's modulus from the core layer to the reinforced skin layer, that is, by creating a gradient in the Young's modulus contained in the resin sheet, the stress concentration at the interface between the core layer and the skin layer is mitigated, and the impact strength can be improved. As a result, the breakage of the resin sheet can be suppressed. Based on these findings, the present inventors have completed the resin sheet of this disclosure in order to further improve the strength of multilayer resin sheets such as the resin sheet of Patent Document 1. Note that the Young's modulus of a foamed resin molded article decreases as the porosity of the foamed resin molded article increases. Therefore, in this disclosure, the Young's modulus of the core layer (foamed resin layer) is defined as the Young's modulus of the non-foamed resin multiplied by "100 - porosity of the core layer (%)".

[0010] (Composition 1) The resin sheet according to this embodiment is a resin sheet made of a thermoplastic resin, and includes a core layer made of a foamed resin, a skin layer made of a non-foamed resin and laminated on one main surface of the core layer, and a reinforcing skin layer made of a non-foamed resin containing a reinforcing agent and laminated on the main surface of the skin layer opposite to the core layer.

[0011] The Young's modulus of the non-foamed resin skin layer is greater than that of the foamed resin core layer. The Young's modulus of the reinforced skin layer, which is made of non-foamed resin containing a reinforcing agent, is also greater than that of the non-foamed resin skin layer. By laminating such a core layer, skin layer, and reinforced skin layer, the Young's modulus of each layer increases in a gradual manner from the core layer to the reinforced skin layer. In other words, a Young's modulus gradient can be created along the thickness direction of the resin sheet. This reduces stress concentration at the interfaces of each layer of the resin sheet, thereby improving the impact strength of the resin sheet.

[0012] (Configuration 2) The resin sheet according to configuration 1 may have a core layer with an average porosity of 20% to 80%. This allows for a more effective gradient in the Young's modulus of each layer, thereby further improving the impact strength of the resin sheet. The method for calculating the average porosity will be described later.

[0013] (Composition 3) The resin sheet has a composition of 1 or 2, and the reinforcing agent may be at least one selected from the group consisting of carbon filler, glass filler, and mineral filler. As the mineral filler, talc, mica, calcium carbonate, silica, or clay can be used. This can further improve the strength (rigidity) of the resin sheet. Carbon filler and glass filler tend to contribute to improving the rigidity of the reinforced skin layer, but do not easily improve the impact strength. On the other hand, mineral filler tends to contribute to improving the impact strength of the reinforced skin layer, but does not easily improve the rigidity. Therefore, from the viewpoint of improving both rigidity and impact strength, it is best to add carbon filler, glass filler, and mineral filler to the reinforced skin layer in a balanced manner.

[0014] (Composition 4) A resin sheet comprising any one of configurations 1 to 3, which has undergone a Charpy impact test in the edgewise flat direction in accordance with ISO 179-1 (flatwise and notched) (in other words, ISO 179-1 / 1fU), may have a fracture mode evaluation of "N", "H", or "P" according to JIS K7111-1:2012. This makes it possible to further suppress fracture in the core layer, skin layer, and reinforced skin layer.

[0015] Hereinafter, embodiments of the resin sheet 1 of this disclosure will be specifically described with reference to Figures 1 and 2. In the figures, the same and corresponding components are denoted by the same reference numerals, and the same description will not be repeated. In order to make the explanation easier to understand, the components in the drawings referred to below are shown in a simplified or schematic form, and some components are omitted.

[0016] As shown in Figures 1 and 2, the resin sheet 1 comprises a core layer 2, a skin layer 3 formed on both sides of the core layer 2 in the thickness direction outward, and a reinforcing skin layer 4 formed on both sides of the skin layer in the thickness direction outward. The core layer 2, skin layer 3, and reinforcing skin layer 4 may be molded continuously in the thickness direction, that is, by co-extrusion molding or the like so that no clear interfaces appear between each layer, or each layer of the core layer 2, skin layer 3, and reinforcing skin layer 4 may be molded separately and then fixed to each other.

[0017] The core layer 2 is made of foamed resin. In this disclosure, foamed resin refers to a resin having an average porosity of 5% to 95%. That is, the core layer 2 can also be said to have an average porosity of 5% to 95%. In terms of providing a gradient in the Young's modulus of each layer, the core layer 2, the skin layer 3, and the reinforcing skin layer 4, in order to more effectively provide a gradient in the Young's modulus, the average porosity of the core layer 2 is preferably 20% or more, more preferably 40% or more, preferably 80% or less, and more preferably 60% or less. In other words, the average porosity of the core layer 2 is preferably 20% to 80%, and more preferably 40% to 60%. This makes it possible to suppress the fracture of the resin sheet 1 due to stress concentration at the interface of the core layer 2, the skin layer 3, and the reinforcing skin layer 4 due to deformation, and to further improve the impact strength.

[0018] The resin material of core layer 2 is a thermoplastic resin. The thermoplastic resin may include general-purpose plastics, engineering plastics, or super engineering plastics. Engineering plastics are thermoplastic resins having a deflection temperature of 100°C or higher. Examples of engineering plastics include polycarbonate (PC), modified polyphenylene ether (m-PPE), and syndiotactic polystyrene (SPS). Super engineering plastics are thermoplastic resins having a deflection temperature of 150°C or higher. Examples of super engineering plastics include polyphenylene sulfide (PPS), polysulfone (PSF), polyethersulfone (PES), polyarylate (PAR), polyamide-imide (PAI), thermoplastic polyimide (PI), polyetherimide (PEI), and liquid crystal polymer (LCP). The thermoplastic resin may include at least one selected from the group consisting of general-purpose plastics, engineering plastics, and super engineering plastics.

[0019] The skin layer 3 is made of a non-foamed resin. In the present disclosure, the non-foamed resin refers to a resin having an average porosity of 0% or more and less than 5%. That is, it can be said that the skin layer 3 has an average porosity of 0% or more and less than 5%. The skin layer 3 may be laminated on at least one of the main surfaces of the core layer 2. That is, the skin layer 3 may be laminated on one or both of the main surfaces of the core layer 2. From the viewpoint of improving strength, it is preferable that the skin layer 3 is laminated on both of the main surfaces of the core layer 2. The skin layer 3 may be formed of the same one thermoplastic resin as the core layer 2 or a thermoplastic resin combined with the same plurality of resin materials, or may be formed of one thermoplastic resin different from the core layer 2 or a thermoplastic resin combined with different plurality of resin materials.

[0020] As shown in FIG. 2, the reinforced skin layer 4 is made of a non-foamed resin containing a reinforcing agent 5. That is, it can be said that the reinforced skin layer 4 contains the reinforcing agent 5 and has an average porosity of 0% or more and less than 5%. The reinforced skin layer 4 is laminated on the main surface of the skin layer 3 opposite to the core layer 2. The reinforced skin layer 4 may be formed of the same one thermoplastic resin as the core layer 2 or the skin layer 3 or a thermoplastic resin combined with the same plurality of resin materials, or may be formed of one thermoplastic resin different from the core layer 2 or the skin layer 3 or a thermoplastic resin combined with different plurality of resin materials.

[0021] Further, the reinforced skin layer 4 may be formed in a partial region of the skin layer 3 without being provided separately from the skin layer 3. The skin layer 3 is divided into two along the width direction, the region laminated facing the core layer 2 is used as a skin region made of a non-foamed resin, and the region on the opposite side of the skin region from the core layer 2 may be used as a reinforced region made of a non-foamed resin containing a reinforcing agent 5. That is, in the present disclosure, the reinforced region of the skin layer 3 can be read as the reinforced skin layer 4.

[0022] The reinforcing agent 5 may be at least one selected from the group consisting of a carbon filler, a glass filler, and a mineral filler. As the mineral filler, talc, mica, calcium carbonate, silica, or clay can be used.

[0023] Here, the average porosity (%) of core layer 2, skin layer 3, and reinforced skin layer 4 can be determined from the ratio of the cross-sectional area of ​​foam cells per unit cross-sectional area in resin sheet 1. More specifically, the average porosity is calculated as follows. First, resin sheet 1 is cut in the thickness direction, and the cross-section is photographed at 25x magnification using a scanning electron microscope (Hitachi, Ltd., model number "Miniscope(registered trademark), TM4000Plus2"). In the captured cross-sectional image, resin sheet 1 is divided into 10 equal parts with a width of 1 mm in the thickness direction, and 10 sections arranged in a row along the thickness direction of resin sheet 1 are extracted at three locations: the center and both ends in the width direction of resin sheet 1. Next, closed cells contained in each section are extracted, and the cross-sectional area of ​​these closed cells is calculated using the cell diameter that maximizes the cell size of these closed cells, and assuming that the closed cells are circular. The average value of the cross-sectional area of ​​the closed cells contained in each section is calculated, and the porosity for each section is calculated by dividing this average value by the cross-sectional area of ​​the section. Next, the average value of the porosity of the three sections in the same thickness region in the three columns mentioned above is calculated. This average value of the porosity of the three sections in the same thickness region is called the average porosity. In order to calculate the average porosity in more detail in the thickness direction, the resin sheet 1 may be divided into 11 or more equal parts.

[0024] The Young's modulus of the non-foamed resin skin layer 3 is greater than that of the foamed resin core layer 2. Furthermore, the Young's modulus of the reinforced skin layer 4, which is made of non-foamed resin containing a reinforcing agent, is greater than that of the non-foamed resin skin layer 3. Thus, by laminating the core layer 2, skin layer 3, and reinforced skin layer 4, which have different Young's moduli, the Young's modulus of each layer increases progressively from the core layer 2 to the reinforced skin layer 4. In other words, a Young's modulus gradient can be created along the thickness direction of the resin sheet 1. This reduces stress concentration at the interfaces of each layer in the resin sheet 1, thereby improving the impact strength of the resin sheet 1.

[0025] The impact strength of resin sheet 1 is set at 20 kJ / m², from the viewpoint that it will not easily break when stress is applied to resin sheet 1. 2It is best to keep it above this value. A higher upper limit is preferable, but in the configuration disclosed here, it is 80 kJ / m³. 2 The impact strength of resin sheet 1 can be measured in accordance with ISO 179-1 / 1fU.

[0026] Furthermore, in resin sheet 1 subjected to a Charpy impact test in accordance with ISO 179-1 (flatwise and notched), the failure mode of resin sheet 1 should be one of "N", "H", or "P" based on JIS K7111-1:2012 "Plastics - Determination of Charpy impact properties". The failure modes are defined as follows: "N": non-break The test specimen simply bends on the specimen support stand and does not break. "H": Hinge-break Incomplete fracture occurred when only the thin, hinge-like surface layer with low bending strength remained intact, forming an inseparable test specimen. "P": Partial-break Incomplete failure that does not meet the definition of hinge failure. "C": Complete-break Test specimens that break into two or more fragments In other words, the resin sheet 1 can obtain sufficient impact strength except for complete failure as in "C", and does not easily break when stress is applied to the resin sheet 1.

[0027] As described above, the resin sheet 1 can be manufactured by separately creating the core layer 2, skin layer 3, and reinforcing skin layer 4, and then bonding or welding each layer together using a hot press. In other words, the resin sheet 1 may be manufactured by separately creating the core layer 2, skin layer 3, and reinforcing skin layer 4, and then fixing them together with their main surfaces facing each other. Alternatively, the core layer 2, skin layer 3, and reinforcing skin layer 4 can be integrally formed by co-extrusion molding. In this case, foaming may be performed by a method of dissolving molten resin by shearing and kneading it with a high-pressure supercritical fluid, or foaming may be performed using a physical foaming agent with relatively low pressure, such as an inert gas like nitrogen, carbon dioxide, air, or argon. From the viewpoint of ease of controlling the bubbles formed in the core layer 2, ease of controlling the thickness of the resin sheet 1, and ease of controlling the thickness of the skin layer 3 or reinforcing skin layer 4, it is preferable to manufacture the resin sheet 1 by welding the core layer 2, skin layer 3, and reinforcing skin layer 4 together. On the other hand, as described above, by forming the resin sheet 1 by co-extrusion molding, it is possible to eliminate clear interfaces between the core layer 2, skin layer 3, and reinforcing skin layer 4. As a result, it is possible to suppress fracture of the resin sheet 1 due to stress concentration at the interfaces of the core layer 2, skin layer 3, and reinforcing skin layer 4 due to deformation, and further increase the impact strength. In other words, in co-extrusion molding, the core layer 2 may be integrated with the skin layer 3 and reinforcing skin layer 4 inside the die before or while the core layer 2 is foaming.

[0028] Although embodiments have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the disclosure.

[0029] (Examples) As shown in Table 1 below, test specimens for Examples 1-8 and Comparative Examples 1-2 were prepared in accordance with ISO 179-1 and subjected to Charpy impact tests. Specifically, each test specimen was cut to a width of 10 mm and a length of 80 mm, and Charpy impact tests were performed under flatwise and notched conditions in accordance with ISO 179-1 / 1fU, and the impact strength and fracture mode of each test specimen were evaluated. In Table 1, the "Ratio" is the ratio of the Young's modulus of the reinforced skin layer (referred to as the "reinforcement layer" in Table 1) to the core layer. Also, in Table 1, a higher impact strength value indicates a stronger impact strength of the test specimen. Furthermore, in Table 1, the evaluation of "N", "H", "P", and "C" indicating the fracture mode is based on JIS K7111-1:2012 "Plastics - Determination of Charpy impact properties", as described above. As shown in Table 1, for each test specimen, if the fracture state falls under one of the following categories: "N", "H", "P", or "C", it is indicated with "X", and if it does not fall under any of these categories, it is indicated with "-".

[0030] [Table 1]

[0031] (Comparison of Examples 1-8 and Comparative Examples 1-2) The specimens of Examples 1-8 had a reinforced skin layer and a skin layer, while the specimens of Comparative Examples 1-2 did not have a skin layer. The Charpy impact test results showed that the specimens of Examples 1-8 received a "P" rating, indicating only partial fracture. On the other hand, the specimen of Comparative Example 1 showed partial fracture ("(P)") in some parts, but ultimately suffered complete fracture. The specimen of Comparative Example 2 also suffered complete fracture. Thus, it was confirmed that by providing a reinforced skin layer and gradually increasing the Young's modulus from the core layer towards the reinforced skin layer, stress concentration at the interface between the core layer and the skin layer can be mitigated, thereby improving impact strength.

[0032] (Comparison of Examples 1-8) When comparing Examples 2, 4, 7, and 8, in which the same mineral filler was added to each reinforced skin layer and both the reinforced skin layer and the skin layer had an average porosity of 0%, the impact strength was relatively higher when the average porosity of the core layer was 20-80% (Examples 2 and 4). On the other hand, when the average porosity of the core layer was 90% (Example 7) and 10% (Example 8), the Young's modulus of the core layer was lower compared to Examples 2 and 4. In Example 7, a difference occurred between the Young's modulus of the skin layer and the Young's modulus of the core layer. In Example 8, the difference between the Young's modulus of the skin layer and the Young's modulus of the reinforced skin layer was larger than the difference between the Young's modulus of the skin layer and the Young's modulus of the core layer. In other words, it is thought that the impact strength was slightly reduced in Examples 7 and 8 because it became difficult to create a gradient in Young's modulus. From this, it was confirmed that the impact strength of the test specimen can be improved by setting the average porosity of the core layer to 20-80%. This is thought to be the same for Example 1, in which glass filler was added to the reinforced skin layer, and Example 3, in which carbon filler was added. However, comparing Examples 1 to 8, it is considered that adding mineral fillers is preferable from the standpoint of improving impact strength.

[0033] Furthermore, comparing Example 1 with Example 5, which has an average porosity of 3% in the reinforced skin layer, and Example 6, which has an average porosity of 3% in the skin layer, the impact strength of Examples 5 and 6 was improved compared to Example 1. This is thought to be because the gradation of Young's modulus between layers became gentler in Examples 5 and 6 due to the introduction of a very small amount of air bubbles in the reinforced skin layer or the skin layer. [Explanation of Symbols]

[0034] 1. Resin sheet, 2. Core layer, 3. Skin layer, 4. Reinforcement skin layer, 5. Reinforcement agent

Claims

1. A resin sheet made of thermoplastic resin, A core layer made of foamed resin, A skin layer made of a non-foaming resin, which is laminated on one main surface of the core layer, A resin sheet comprising a non-foaming resin containing a reinforcing agent, and a reinforcing skin layer laminated on the main surface of the skin layer opposite to the core layer.

2. A resin sheet according to claim 1, The core layer is a resin sheet having an average porosity of 20% to 80%.

3. A resin sheet according to claim 1 or 2, The reinforcing agent is at least one selected from the group consisting of carbon filler, glass filler, and mineral filler, in the resin sheet.

4. A resin sheet according to either claim 1 or 2, A resin sheet that has undergone a Charpy impact test in accordance with ISO 179-1 (flatwise and notched), wherein the evaluation of the failure mode according to JIS K7111-1:2012 is one of "N", "H", or "P".

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