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 buffer layer 4. The core layer 2 is made of foamed resin. The skin layer 3 is made of non-foamed resin. The buffer layer 4 is made of foamed resin containing a reinforcing agent 5 and is positioned between the core layer 2 and the skin layer 3. The average porosity of the buffer layer 4 is less than or equal to the average porosity of the core layer 2. As a result, the Young's modulus of the skin layer 3 is greater than that of the buffer layer 4, and the Young's modulus of the buffer layer 4 is greater than that of the core layer 2. That is, the Young's moduli of the core layer 2, the skin layer 3, and the buffer layer 4 increase in steps toward the outward direction in the thickness direction. As a result, stress concentration in each layer is mitigated when external stress is applied, and impact strength can be improved.

Description

Technical Field

[0001] The present disclosure relates to a multilayer resin sheet made of a thermoplastic resin.

Background Art

[0002] 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 air 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.

[0003] WO 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%, and the second region has an average porosity smaller than that of the first region and gradually decreasing from the first region toward the skin layer. The skin layer is a region having an average porosity of less than 5%. The resin sheet aims to achieve both weight reduction and strength improvement by controlling the average porosity of the skin layer, the first region, and the second region of the core layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present disclosure is to provide a resin sheet capable of improving impact strength.

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, and includes a core layer made of a foamed resin, a skin layer made of a non-foamed resin, and a buffer layer made of a foamed resin containing a reinforcing agent, positioned between the core layer and the skin layer. The average porosity of the buffer layer is less than or equal to the average porosity of 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. [Figure 3] Figure 3 is an enlarged cross-sectional view of a resin sheet containing a reinforcing agent in the skin layer. [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, the resin sheet 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 placing a buffer layer between the core layer and the skin layer, which has a Young's modulus greater than that of the core layer and a Young's modulus less than that of the skin layer, and gradually increasing the Young's modulus from the core layer to the 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 alleviated, and the impact strength can be improved. 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 a buffer layer made of a foamed resin containing a reinforcing agent, positioned between the core layer and the skin layer. The average porosity of the buffer layer is less than or equal to the average porosity of the core layer.

[0011] The Young's modulus of the non-foamed resin skin layer is greater than that of the buffer layer made of foamed resin containing a reinforcing agent. The Young's modulus of the buffer layer is greater than that of the foamed resin core layer. By laminating the core layer, skin layer, and buffer layer in this manner, the Young's modulus of each layer increases in a gradual manner from the core layer to the 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 of composition 1 may contain a reinforcing agent in the skin layer. This makes it possible to more reliably create a gradient in the Young's modulus of each layer, alleviate stress concentration at the interfaces of each layer of the resin sheet, and improve the impact strength of the resin sheet.

[0013] (Composition 3) The resin sheet has one or two components, and the core layer may have an average porosity of 20% to 80%. The ratio of the average porosity A of the core layer to the average porosity B of the buffer layer (B / A) may be less than 1.0. 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.

[0014] (Composition 4) The resin sheet is composed of one of the three components, and the reinforcing agent contained in the buffer layer or skin layer 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 buffer layer or skin layer, but do not easily improve impact strength. On the other hand, mineral filler tends to contribute to improving the impact strength of the buffer layer and skin layer, but does not easily improve 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 buffer layer or skin layer in a balanced manner.

[0015] (Composition 5) A resin sheet comprising any one of the configurations 1 to 4, 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 buffer layer.

[0016] Hereinafter, embodiments of the resin sheet 1 of this disclosure will be specifically described with reference to Figures 1 to 3. 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.

[0017] As shown in FIGS. 1 and 2, the resin sheet 1 includes a core layer 2, buffer layers 4 formed on both outer sides of the core layer 2 in the thickness direction, and skin layers 3 formed on both outer sides of the buffer layers 4 in the thickness direction. The core layer 2, the skin layer 3, and the buffer layer 4 may be continuously formed with each other in the thickness direction, that is, formed by a coextrusion molding method or the like so that no clear interface appears between the layers. Alternatively, after each of the core layer 2, the skin layer 3, and the buffer layer 4 is separately molded, the layers may be fixed to each other.

[0018] The core layer 2 is made of a foamed resin. In the present disclosure, the foamed resin refers to a resin having an average porosity of 5% to 95%. That is, it can also be said that the core layer 2 has an average porosity of 5 to 95%. From the viewpoint of providing a gradient in the Young's modulus in each of the core layer 2, the skin layer 3, and the buffer 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%. Also, the average porosity of the buffer layer 4 is preferably not more than the average porosity of the core layer 2. The ratio (B / A) of the average porosity A of the core layer 2 to the average porosity B of the buffer layer 4 can be less than 1.0. Thereby, it is possible to suppress the breakage of the resin sheet 1 due to stress concentration at the interfaces of the skin layer 3, the buffer layer 4, and the core layer 2 caused by deformation, and to further improve the impact strength.

[0019] The resin material of the core layer 2 is a thermoplastic resin. The thermoplastic resin can include general-purpose plastics, engineering plastics, or super engineering plastics. Engineering plastics are thermoplastic resins having a heat deflection temperature of 100 °C or higher. Engineering plastics are, for example, polycarbonate (PC), modified polyphenylene ether (m-PPE), syndiotactic polystyrene (SPS), and the like. Super engineering plastics are thermoplastic resins having a heat deflection temperature of 150 °C or higher. Super engineering plastics are, for example, polyphenylene sulfide (PPS), polysulfone (PSF), polyethersulfone (PES), polyarylate (PAR), polyamideimide (PAI), thermoplastic polyimide (PI), polyetherimide (PEI), liquid crystal polymer (LCP), and the like. The thermoplastic resin can include at least one selected from the group consisting of general-purpose plastics, engineering plastics, and super engineering plastics.

[0020] 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 also 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 thermoplastic resin as the core layer 2 or a thermoplastic resin combined with the same plurality of resin materials, or may be formed of a thermoplastic resin different from the core layer 2 or a thermoplastic resin combined with different plurality of resin materials.

[0021] As shown in FIG. 3, the skin layer 3 may contain a reinforcing agent 5. The reinforcing agent 5 will be described later.

[0022] As shown in Figure 2, the buffer layer 4 is made of a foamed resin containing a reinforcing agent 5. In other words, the buffer layer 4 contains the reinforcing agent 5 and also has an average porosity of 5% to 95%. The buffer layer 4 is positioned between the core layer 2 and the skin layer 3. The buffer layer 4 may be formed from the same thermoplastic resin as the core layer 2 or skin layer 3, or from a thermoplastic resin made from the same combination of multiple resin materials, or from a different thermoplastic resin than the core layer 2 or skin layer 3, or from a combination of different resin materials.

[0023] Furthermore, the buffer layer 4 may not be provided separately from the core layer 2, but may be formed in a part of the core layer 2. As shown in Figure 2, a configuration corresponding to the case where the buffer layer 4 is provided on both main surfaces of the core layer 2 may be to divide the core layer 2 into three parts along the width direction, with one buffer region made of foamed resin containing a reinforcing agent being laminated opposite one skin layer 3, the other buffer region made of foamed resin containing a reinforcing agent being laminated opposite the other skin layer 3, and the region located between the two buffer regions being the core region made of foamed resin. Although not specifically shown, a configuration corresponding to the case where the buffer layer 4 is provided on one main surface of the core layer 2 may be to divide the core layer 2 into two parts along the width direction, with one buffer region made of foamed resin containing a reinforcing agent being laminated opposite the skin layer 3, and the other region being the core region. In other words, in this disclosure, the buffer region of the core layer 2 can be read as the buffer layer 4.

[0024] The reinforcing agent 5 may be at least one selected from the group consisting of carbon fillers, glass fillers, and mineral fillers. As the mineral filler, talc, mica, calcium carbonate, silica, or clay can be used.

[0025] Here, the average porosity (%) of the core layer 2, skin layer 3, and buffer layer 4 can be determined from the ratio of the cross-sectional area of ​​foam cells per unit cross-sectional area in the resin sheet 1. More specifically, the average porosity is calculated as follows. First, the 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, the 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 the resin sheet 1 are extracted at three locations: the center and both ends in the width direction of the resin sheet 1. Next, the 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.

[0026] The Young's modulus of the non-foamed resin skin layer 3 is greater than that of the buffer layer 4 made of foamed resin containing the reinforcing agent 5. Furthermore, the Young's modulus of the buffer layer 4 is greater than that of the foamed resin core layer 2. In this way, by laminating the core layer 2, skin layer 3, and buffer layer 4, which have different Young's moduli, the Young's modulus of each layer increases in a gradual manner from the core layer 2 to the skin layer 3. 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 of the resin sheet 1 and improves the impact strength of the resin sheet 1.

[0027] Furthermore, as described above, when the skin layer 3 contains the reinforcing agent 5 (see Figure 3), the Young's modulus of the skin layer 3 becomes even larger, making it possible to more reliably create a gradient in the Young's modulus of each layer. This makes it possible to more effectively alleviate stress concentration at the interfaces of each layer of the resin sheet 1 and improve the impact strength of the resin sheet 1.

[0028] 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. 2 It is best to keep it above this value. A higher upper limit is preferable, but in the configuration disclosed here, it is 60 kJ / m³. 2 The impact strength of resin sheet 1 can be measured in accordance with ISO 179-1 / 1fU.

[0029] 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.

[0030] As described above, the resin sheet 1 can be manufactured by separately creating the core layer 2, skin layer 3, and buffer 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 buffer layer 4, and then fixing them together with their main surfaces facing each other. Alternatively, the core layer 2, skin layer 3, and buffer 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 buffer layer 4, it is preferable to manufacture the resin sheet 1 by welding the core layer 2, skin layer 3, and buffer layer 4 together. On the other hand, as described above, by molding the resin sheet 1 by co-extrusion molding, it is possible to eliminate clear interfaces between the core layer 2, skin layer 3, and buffer layer 4. As a result, it is possible to suppress fracture of the resin sheet 1 due to stress concentration at the interfaces between the skin layer 3, buffer layer 4, and core layer 2 due to deformation, and further increase impact strength. In other words, in co-extrusion molding, the core layer 2 may be integrated with the skin layer 3 and buffer layer 4 inside the die before or while the core layer 2 is foaming.

[0031] 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.

[0032] (Examples) As shown in Table 1 below, test specimens for Examples 1-8 and Comparative Examples 1-4 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 a Charpy impact test was 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, "Ratio X" is the ratio of the average porosity in the buffer layer and the core layer, and "Ratio Y" is the ratio of the Young's modulus in the buffer layer and 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, an "X" indicates that the fracture state falls under one of the following categories: "N", "H", "P", or "C", and a "-" indicates that it does not fall under any of these categories. In addition, each test specimen contains filler in the skin layer, and for test specimens marked "Yes" in the "Presence or Absence of Buffer Layer" section of Table 1, the buffer layer also contains filler.

[0033] [Table 1]

[0034] (Comparison of Examples 1-7 and Comparative Examples 1-3) The specimens of Examples 1-7 had a buffer layer, while the specimens of Comparative Examples 1 and 2 did not. Comparative Example 3 had a buffer layer, but the average porosity of the buffer layer was greater than that of the core layer. The Charpy impact test results showed that the specimens of Examples 1-7 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 specimens of Comparative Examples 2 and 3 also suffered complete fracture. Thus, it was confirmed that by providing a buffer layer and gradually increasing the Young's modulus from the core layer to the skin layer, fracture due to stress concentration at the interface of each layer can be suppressed, thereby improving impact strength. The impact strength of Comparative Examples 2 and 3 was greater than that of Examples 6 and 7. This is due to the type of reinforcing agent added to the skin layer or buffer layer; when talc or mica is added, as in Examples 2 and 3, the impact strength tends to be higher. However, in Comparative Examples 2 and 3, it is believed that complete fracture "C" occurred because a gradient in Young's modulus could not be established.

[0035] (Comparison of Examples 1-7) Comparing Examples 1, 4, 6, and 7, which used the same glass filler, Examples 1 and 4, with an average porosity of 20-80% in the core layer, showed relatively higher impact strength values ​​of 20 kJ / m². 2 This value was exceeded. On the other hand, in Example 6, where the average porosity of the core layer was 90%, and in Example 7, where the average porosity of the core layer was 10%, the impact strength values ​​were relatively small. 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%. [Explanation of Symbols]

[0036] 1. Resin sheet, 2. Core layer, 3. Skin layer, 4. Buffer 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 non-foaming resin, It consists of a foamed resin containing a reinforcing agent and includes a buffer layer positioned between the core layer and the skin layer, A resin sheet having an average porosity smaller than that of the core layer.

2. A resin sheet according to claim 1, The aforementioned skin layer is a resin sheet containing a reinforcing agent.

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

4. A resin sheet according to claim 1, The reinforcing agent contained in the buffer layer is at least one selected from the group consisting of carbon filler, glass filler, and mineral filler, in a resin sheet.

5. A resin sheet according to any one of claims 1 to 3, 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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