Resin foams and foamed components

Abstract

The present invention provides a resin foam which is excellent in terms of both low dielectric properties and punchability.　A resin foam according to the present invention has a cell structure; the apparent density of this resin foam is less than 0.4 g / cm3; and the thickness recovery rate after maintaining the resin foam under a load of 1000 g / cm2 for 120 seconds is 80% or more. In one embodiment of the present invention, the resin foam has a cell number density of 30 / mm2 or more. In one embodiment of the present invention, the resin foam has an average cell diameter of 10 to 200 μm.

Description

[Technical Field]

[0001] This invention relates to resin foams and foamed components. [Background technology]

[0002] Foam is widely used as a cushioning material to protect screens, circuit boards, and electronic components in electronic devices. In recent years, with the trend towards thinner electronic devices, there has been a need to reduce the clearance in the areas where cushioning materials are placed. Furthermore, with the miniaturization and multi-functionality of electronic devices, the electronic components used are also tending to become smaller, sometimes requiring even smaller cushioning materials (foam). In addition, to prevent communication interference in communication equipment and electrical malfunctions in electronic devices, the above-mentioned cushioning materials (foam) may require low dielectric properties.

[0003] Typically, to obtain a foam material of a desired shape, the foam material is punched out. In punching, a die is used to apply high pressure to the foam material to obtain a foam material with the desired shape. In conventional foam materials, the thickness reduced by punching may not fully recover after the process, resulting in a change in thickness. This phenomenon is particularly problematic when applied to areas with narrow clearances, and especially when punching out narrow shapes (e.g., 1 mm wide), such as picture frames.

[0004] Patent Document 1 discloses a resin foam with excellent shock absorption properties. However, this document does not disclose or suggest anything about processability (punching processability) during punching. Patent Document 2 also discloses a thin-layer resin foam with excellent shock absorption properties. However, this document does not disclose recovery or crushing after punching. Furthermore, a resin foam that achieves both low dielectric properties and punching processability has not yet been realized. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-186504 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-034299 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-69493 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] An object of the present invention is to provide a resin foam excellent in both low dielectric properties and punching processability. [Means for Solving the Problems]

[0007] The resin foam of the present invention is a resin foam having a cell structure, and the apparent density of the resin foam is less than 0.4 g / cm 3 and the thickness recovery rate after maintaining a load of 1000 g / cm 2 for 120 seconds is 80% or more. In one embodiment, the resin foam has a cell number density of 30 cells / mm 2 or more. In one embodiment, the resin foam has an average cell diameter of 10 μm to 200 μm. In one embodiment, the resin foam has a coefficient of variation of cell diameter of 0.5 or less. In one embodiment, the resin foam has a porosity of 30% or more. In one embodiment, the resin foam has a tensile elastic modulus at 25°C of 1.5 MPa or more. In one embodiment, the resin foam has a 50% compression load of 20 N / cm 2 or less. In one embodiment, the resin foam contains a polyolefin-based resin. In one embodiment, the polyolefin resin is a mixture of a polyolefin other than a polyolefin elastomer and a polyolefin elastomer. In one embodiment, the resin foam has a heat-melt layer on one or both sides. According to another aspect of the present invention, a foamed member is provided. This foamed member has a resin foam layer and an adhesive layer disposed on at least one side of the resin foam layer, wherein the resin foam layer is the resin foam described above. [Effects of the Invention]

[0008] According to the present invention, even after die-cutting, the change in thickness before and after the process is minimal, and a resin foam with excellent die-cutting processability can be provided. The resin foam of the present invention is also excellent in that it has low dielectric properties. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of a foamed member according to one embodiment of the present invention. [Modes for carrying out the invention]

[0010] A. Resin foam The resin foam of the present invention has a cellular structure. Examples of cellular structures include closed-cell structures, open-cell structures, and semi-open-cell structures (a cellular structure in which closed-cell and open-cell structures are mixed). Preferably, the cellular structure of the resin foam is a semi-open-cell structure. Typically, the resin foam of the present invention is obtained by foaming a resin composition. The resin composition is a composition that contains at least the resin constituting the resin foam.

[0011] The apparent density of the resin foam is 0.4 g / cm³. 3 It is less than 1000 g / cm³ of the above resin foam. 2The thickness recovery rate (hereinafter also referred to as the instantaneous recovery rate) after maintaining for 120 seconds under the applied load is 80% or more. According to the present invention, by having appropriate voids, being excellent in low dielectric properties, and setting the instantaneous recovery rate within a specific range, a resin foam excellent in punching processability can be obtained without inhibiting the low dielectric properties. More specifically, when the above resin foam is punched, the shape change such as the thickness change is small, and even when the thickness is temporarily reduced by punching, it shows a favorable behavior of recovering in a short time, and is excellent in punching property.

[0012] The apparent density of the resin foam is preferably 3 not more than 0.4 g / cm 3 ³, more preferably 0.01 g / cm 3 ³ to 0.3 g / cm 3 ³, more preferably 0.02 g / cm 3 ³ to 0.2 g / cm 3 ³, still more preferably 0.03 g / cm 3 ³ to 0.1 g / cm 3 ³, particularly preferably 0.03 g / cm 3 ³ to 0.05 g / cm

[0013] When the above resin foam is maintained for 120 seconds under the applied load of 1000 g / cm 2 ³, the thickness recovery rate (hereinafter also referred to as the instantaneous recovery rate) is preferably 80% or more, more preferably 85% or more, still more preferably 87% or more, and particularly preferably 90% or more. Within such a range, the above effects become remarkable. Although the higher the thickness recovery rate, the more preferable it is, the upper limit thereof is, for example, 99% (preferably 100%). The measurement method of the thickness recovery rate will be described later.

[0014] In one embodiment, the resin foam described above can be formed by using a resin as the resin constituting the resin foam, which has a die swell ratio of 1.4 or less at its melting point (the melting point of the resin constituting the resin foam) + 20°C. That is, in one embodiment, the die swell ratio of the resin forming the resin foam at its melting point + 20°C before foaming is 1.4 or less. By using a resin with a die swell ratio within the above range, shrinkage during resin foam formation is prevented, and a thick resin foam can be formed, which may contain small bubbles. The die swell ratio of the resin forming the resin foam at its melting point + 20°C before foaming is preferably 1.2 or less, and more preferably 1.1 or less. The lower limit of the die swell ratio of the above resin (before foaming) is, for example, 1.05 (preferably 1.02, more preferably 1.01). Furthermore, the die swell ratio of the resin constituting the resin foam (i.e., the resin after foaming) at its melting point + 20°C is preferably 1.4 or less, more preferably 1.2 or less, and even more preferably 1.1 or less. The lower limit of the die swell ratio of the above resin (after foaming) is, for example, 1.05 (preferably 1.02, more preferably 1.01). In this specification, the die swell ratio means the value obtained by dividing the diameter of the extruded resin by the diameter of the die when the molten resin is extruded from the die. The die swell ratio is calculated by measuring the diameter of the molded product (mm) / die diameter (mm) after extruding a resin molten at its melting point + 20°C using a die with a length of 10 mm and a diameter of 1 mmφ at a shear rate of 20 mm / s, and measuring the diameter of the resulting string-like molded product. The melting point of the resin is measured by the peak top temperature of the endothermic peak obtained by differential scanning calorimetry (DSC) measurement. Differential scanning calorimetry (DSC) measurements are performed using a differential scanning calorimeter (e.g., product name "Q-2000," TA Instruments) with a sample weight of 3 mg and a heating rate of 10 °C / min. If there are two or more peaks, the peak top temperature of the higher-temperature peak is taken as the melting point.

[0015] In one embodiment, the resin foam described above can be formed by using a resin whose shear viscosity at the melting point (the melting point of the resin constituting the resin foam) + 20°C is 3000 Pa·s or less. That is, in one embodiment, the shear viscosity at the melting point + 20°C of the resin forming the resin foam before foaming is 3000 Pa·s or less. If a resin with a shear viscosity in the above range is used, the gas used to form the bubble structure during resin foam formation can be preferably dispersed, and as a result, a resin foam with small bubble size can be obtained. The shear viscosity at the melting point + 20°C of the resin forming the resin foam before foaming is preferably 2500 Pa·s or less, more preferably 2100 Pa·s or less, even more preferably 2000 Pa·s or less, and particularly preferably 1900 Pa·s or less. The lower limit of the shear viscosity of the above resin (before foaming) is, for example, 500 Pa·s (preferably 700 Pa·s, more preferably 1000 Pa·s). Furthermore, the shear viscosity of the resin constituting the resin foam (i.e., the resin after foaming) at its melting point + 20°C is preferably 3000 Pa·s or less, more preferably 2500 Pa·s or less, even more preferably 2100 Pa·s or less, particularly preferably 2000 Pa·s or less, and most preferably 1900 Pa·s or less. The lower limit of the shear viscosity of the above resin (after foaming) is, for example, 500 Pa·s (preferably 700 Pa·s, more preferably 1000 Pa·s). In this specification, the shear viscosity can be measured by extruding the resin, which is molten at its melting point + 20°C, using a die with a length of 10 mm and a diameter of 1 mmφ at a shear rate of 20 mm / s.

[0016] The thickness of the above resin foam is preferably 100 μm to 8000 μm, more preferably 200 μm to 5000 μm, even more preferably 300 μm to 4000 μm, even more preferably 400 μm to 3000 μm, and even more preferably 500 μm to 2000 μm. Within this range, a fine and uniform cellular structure can be formed, which is advantageous in that it can exhibit excellent die-cutting processability and shock absorption.

[0017] The average cell diameter of the resin foam described above is preferably 10 μm to 200 μm, more preferably 20 μm to 180 μm, even more preferably 40 μm to 150 μm, and particularly preferably 40 μm to 80 μm. Within this range, a resin foam with superior flexibility and stress distribution can be obtained. Furthermore, a resin foam with excellent compression recovery, punching processability, and resistance to repeated impacts can be obtained. In one embodiment, the average cell diameter of the resin foam is 90 μm or less (preferably 80 μm or less). Within this range, a resin foam with low dielectric constant and excellent punching processability can be obtained. The method for measuring the average cell diameter will be described later.

[0018] The coefficient of variation of the cell diameter (bubble diameter) of the above-mentioned resin foam is preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.3 or less, even more preferably 0.25 or less, and particularly preferably 0.2 or less. Within this range, when compressive force is applied by punching or the like, the variation in bubble deformation is reduced. With such a resin foam, for example, when punched, it is possible to obtain processed products (cut products) with excellent thickness accuracy. Furthermore, if the coefficient of variation of the cell diameter is within the above range, deformation due to impact becomes uniform, localized stress loading is prevented, and a resin foam with excellent stress distribution and particularly excellent impact resistance can be obtained. The smaller the coefficient of variation, the better, but the lower limit is, for example, 0.15 (preferably 0.1, more preferably 0.01). The method for measuring the coefficient of variation of the cell diameter will be described later.

[0019] The cell content (bubble rate) of the above-mentioned resin foam is preferably 30% or more, more preferably 50% or more, and even more preferably 80% or more. Within this range, a resin foam with appropriate flexibility can be obtained. Such a resin foam has excellent die-cutting properties, and the occurrence of uncut pieces during die-cutting is prevented. The upper limit of the cell content is, for example, 99% or less. The method for measuring the cell content will be described later.

[0020] The thickness of the cell walls of the resin foam described above is preferably 0.1 μm to 10 μm, more preferably 0.3 μm to 8 μm, even more preferably 0.5 μm to 5 μm, particularly preferably 0.7 μm to 4 μm, and most preferably 1 μm to 3 μm. Within this range, a resin foam with appropriate strength can be obtained. Such a resin foam has excellent die-cutting properties, preventing tearing, dust generation, and uncut parts during die-cutting. Furthermore, if the thickness of the cell walls is within the above range, a resin foam with superior flexibility and stress distribution can be obtained. In one embodiment, the thickness of the cell walls of the resin foam described above is 5 μm or less. Within this range, the above effects become particularly pronounced. The thickness of the cell walls can be measured by capturing an enlarged image of the cell portion of the resin foam and performing image analysis using the analysis software of the measuring instrument.

[0021] When the cell structure of the above-mentioned resin foam is a semi-continuous semi-closed cell structure, the proportion of closed-cell structures is preferably 40% or less, and more preferably 30% or less. In this specification, the proportion of closed-cell structures in the resin foam is determined, for example, by immersing the object to be measured in water under conditions of 23°C and 50% humidity, measuring the mass thereafter, then thoroughly drying it in an 80°C oven, and then measuring the mass again. In addition, since open-cell structures can retain moisture, the mass portion of the moisture retained is measured as open-cells to determine the proportion of open-cells. The proportion of open-cells in the above-mentioned resin foam is preferably higher than 60%, and more preferably higher than 70%. Within this range, a resin foam with a low dielectric constant can be obtained. The proportion of open-cells is also determined by immersing the object to be measured in water under conditions of 23°C and 50% humidity, measuring the mass thereafter, then thoroughly drying it in an 80°C oven, and then measuring the mass again.

[0022] The number density of bubbles in the above resin foam is preferably 30 bubbles / mm². 2 The above is more preferable, 50 pieces / mm 2 The above is preferable to 65 pieces / mm 2 The above is preferable to 80 pieces / mm 2The above is preferable to 90 pieces / mm 2 The above is true, and more preferably 100 pieces / mm 2 The above is the most preferred, with a particularly favorable value of 110 pieces / mm 2 That concludes the explanation. Within this range, it is possible to obtain a resin foam that is preferably flexible, has a low dielectric constant, and excellent die-cutting properties. Furthermore, the higher the number density of bubbles, the easier it is to store energy when compressed, resulting in a resin foam with excellent compression recovery. The upper limit of the number density of bubbles in the resin foam is preferably 400 bubbles / mm². 2 More preferably 200 pieces / mm 2 And more preferably, 150 pieces / mm 2 The number density of bubbles in a resin foam is the number density of bubbles observed in a randomly selected cross-section of the resin foam, and can be determined by image analysis of the cross-section of the resin foam.

[0023] The 50% compression load of the above resin foam is preferably 20 N / cm². 2 The following is more more than 10 N / cm 2 The following is more preferably 8 N / cm 2 The following is more preferably 5 N / cm 2 The following is particularly preferred: 3 N / cm 2 The following applies. Within this range, a resin foam with desirable flexibility and excellent die-cutting properties can be obtained. The lower limit of the 50% compression load of the resin foam is, for example, 0.5 N / cm. 2 The 50% compression load of a resin foam is the stress (N) when compressed to a compressibility of 50% per unit area (1 cm²). 2 This is the price per unit.

[0024] The tensile modulus of the above resin foam at 25°C is preferably 1.5 MPa or higher, more preferably 1.6 MPa to 2.5 MPa, and more preferably 1.8 MPa to 2.0 MPa. Within this range, the foam has the required strength and can maintain its shape even after punching. The above tensile modulus is determined by fixing a sample (size: 10 mm x 80 mm) with a chuck distance of 40 mm and performing a tensile test at a tensile speed of 500 mm / min to obtain a tensile strain-tensile strength curve, and then determining the slope of the line connecting the origin of this curve and the tensile strength at a tensile strain of 10%.

[0025] The relative permittivity of the above resin foam is preferably 3 or less, more preferably 2 or less, even more preferably 1.5 or less, and particularly preferably 1.2 or less. According to the present invention, a resin foam with a low relative permittivity suitable for communication equipment, electronic equipment, etc., can be obtained. The lower limit of the relative permittivity of the resin foam is, for example, 1.01. The method for measuring the relative permittivity will be described later.

[0026] The impact absorption of the above resin foam is preferably 20% or more, more preferably 27% or more, even more preferably 30% or more, particularly preferably 35% or more, and most preferably 40% or more. The impact absorption is measured as follows. A test specimen was formed by arranging resin foam, double-sided tape (product number: No. 5603W, manufactured by Nitto Denko), and PET film (product number: Diafoil MRF75, manufactured by Mitsubishi Plastics) in that order on an impact force sensor. A 66g steel ball was dropped onto the test specimen from a height of 50cm above the PET film, and the impact force F1 was measured. Furthermore, the impact force F0 of the blank is measured by dropping the steel ball directly onto the impact force sensor as described above. The impact absorption (%) is calculated from F1 and F0 using the formula (F0-F1) / F0×100.

[0027] The shape of the resin foam described above can be any appropriate shape depending on the purpose. A typical example of such a shape is a sheet.

[0028] The above-mentioned resin foam may have a heat-melt layer on one or both sides. A resin foam having a heat-melt layer can be obtained, for example, by rolling the resin foam (or a precursor (foamed structure) of the resin foam) using a pair of heated rolls heated to a temperature above the melting temperature of the resin composition constituting the resin foam.

[0029] The above-mentioned resin foam can be formed by any suitable method, as long as it does not impair the effects of the present invention. Typical such methods include foaming a resin composition containing a resin material (polymer).

[0030] A-1. Resin composition The resin foam of the present invention can typically be obtained by foaming a resin composition. The resin composition comprises any suitable resin material (polymer). In one embodiment, a non-crosslinked resin composition is used. The non-crosslinked resin composition is suitably used in the resin foam formation method described later.

[0031] Examples of the polymers mentioned above include acrylic resins, silicone resins, urethane resins, polyolefin resins, ester resins, and rubber resins. These polymers may be used individually or in combination of two or more types.

[0032] The polymer content is preferably 30 to 95 parts by weight, more preferably 35 to 90 parts by weight, even more preferably 40 to 80 parts by weight, and particularly preferably 40 to 60 parts by weight, per 100 parts by weight of the resin composition. Within this range, a resin foam with superior flexibility and stress dispersion can be obtained.

[0033] In one embodiment, a polyolefin resin is used as the polymer. Using such a resin, a resin foam with a preferably adjusted dielectric constant can be obtained.

[0034] The content of the polyolefin resin is preferably 50 to 100 parts by weight, more preferably 70 to 100 parts by weight, even more preferably 90 to 100 parts by weight, particularly preferably 95 to 100 parts by weight, and most preferably 100 parts by weight, relative to 100 parts by weight of the above polymer.

[0035] Preferably, the polyolefin resin is at least one selected from the group consisting of polyolefins and polyolefin-based elastomers, and more preferably, polyolefins and polyolefin-based elastomers are used in combination. Polyolefins and polyolefin-based elastomers may be used individually or in combination of two or more. In this specification, the term "polyolefin" does not include "polyolefin-based elastomers."

[0036] When polyolefin and polyolefin-based elastomer are used in combination as the polyolefin-based resin, the weight ratio of polyolefin to polyolefin-based elastomer (polyolefin / polyolefin-based elastomer) is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 90 / 10, even more preferably 20 / 80 to 80 / 20, and particularly preferably 30 / 70 to 70 / 30. In one embodiment, the weight ratio of polyolefin to polyolefin-based elastomer (polyolefin / polyolefin-based elastomer) is preferably 25 / 75 to 75 / 25, and more preferably 35 / 65 to 65 / 35. Within this range, a resin foam can be obtained that has excellent compression recovery, suppresses shape changes (especially thickness changes) before and after die-cutting, has appropriate strength, and has excellent die-cutting processability.

[0037] As the polyolefin, any suitable polyolefin can be used as long as it does not impair the effects of the present invention. Examples of such polyolefins include linear polyolefins and branched (having branched) polyolefins. In one embodiment, a branched polyolefin is used as the polyolefin resin. In this embodiment, only a branched polyolefin may be used as the polyolefin, or a combination of a branched polyolefin and a linear polyolefin may be used. By using a branched polyolefin, a resin foam with a small average bubble diameter and excellent impact resistance can be obtained. The content ratio of the branched polyolefin is preferably 30 to 100 parts by weight, and more preferably 50 to 80 parts by weight, per 100 parts by weight of polyolefin.

[0038] Examples of the polyolefins mentioned above include polymers containing structural units derived from α-olefins. The polyolefin may consist solely of structural units derived from α-olefins, or it may consist of structural units derived from α-olefins and structural units derived from monomers other than α-olefins. When the polyolefin is a copolymer, any suitable copolymerization form can be adopted. Examples include random copolymers and block copolymers.

[0039] As α-olefins that can constitute polyolefins, for example, α-olefins having 2 to 8 carbon atoms (preferably 2 to 6, more preferably 2 to 4) (e.g., ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, etc.) are preferred. There may be only one α-olefin or two or more α-olefins.

[0040] Examples of monomers other than α-olefins that constitute polyolefins include ethylenically unsaturated monomers such as vinyl acetate, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, and vinyl alcohol. There may be only one monomer other than α-olefin, or there may be two or more monomers.

[0041] Examples of polyolefins include, for example, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene (propylene homopolymer), copolymers of ethylene and propylene, copolymers of ethylene and α-olefins other than ethylene, copolymers of propylene and α-olefins other than propylene, copolymers of ethylene, propylene, and α-olefins other than ethylene and propylene, and copolymers of propylene and ethylenically unsaturated monomers.

[0042] In one embodiment, a polypropylene polymer having propylene-derived structural units is used as the polyolefin. Examples of polypropylene polymers include polypropylene (propylene homopolymer), copolymers of ethylene and propylene, and copolymers of propylene and α-olefins other than propylene, with polypropylene (propylene homopolymer) being preferred. The polypropylene polymer may be used alone or in combination of two or more types.

[0043] The melt flow rate (MFR) of the polyolefin at a temperature of 230°C is preferably 0.25 g / 10 min to 10 g / 10 min, more preferably 0.3 g / 10 min to 6 g / 10 min, even more preferably 0.35 g / 10 min to 5 g / 10 min, particularly preferably 0.35 g / 10 min to 1 g / 10 min, and most preferably 0.35 g / 10 min to 0.6 g / 10 min, in order to better exhibit the effects of the present invention. In this specification, the above melt flow rate (MFR) refers to the MFR measured at a temperature of 230°C and a load of 2.16 kgf (21.2 N) based on ISO 1133 (JIS-K-7210). In one embodiment, the die swell ratio and shear viscosity of the resin are controlled by the melt flow rate of the polyolefin constituting the resin foam.

[0044] The weight-average molecular weight of the polyolefin is preferably 50,000 to 120,000, more preferably 55,000 to 110,000, and even more preferably 60,000 to 100,000. Within this range, the die swell ratio and shear viscosity of the resin can be favorably adjusted. Furthermore, the molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the polyolefin is preferably 7 to 10, more preferably 6 to 9. Within this range, the die swell ratio and shear viscosity of the resin can be favorably adjusted. The weight-average molecular weight and number-average molecular weight can be determined by gel permeation chromatography (solvent: tetrahydrofuran, polystyrene equivalent).

[0045] As for the polyolefin, commercially available products may be used, such as "E110G" (manufactured by Prime Polymer Co., Ltd.), "EA9" (manufactured by Nippon Polypropylene Co., Ltd.), "EA9FT" (manufactured by Nippon Polypropylene Co., Ltd.), "E-185G" (manufactured by Prime Polymer Co., Ltd.), "WB140HMS" (manufactured by Borealis), and "WB135HMS" (manufactured by Borealis).

[0046] As the polyolefin elastomer, any suitable polyolefin elastomer can be used as long as it does not impair the effects of the present invention. Examples of such polyolefin elastomers include so-called non-crosslinked thermoplastic olefin elastomers (TPO), such as ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-vinyl acetate copolymer, polybutene, polyisobutylene, chlorinated polyethylene, elastomers in which polyolefin components and rubber components are physically dispersed, and elastomers having a structure in which polyolefin components and rubber components are microphase separated; and dynamically crosslinked thermoplastic olefin elastomers (TPV), which are multiphase polymers obtained by dynamically heat-treating a mixture containing a resin component A (olefin resin component A) that forms a matrix and a rubber component B that forms domains in the presence of a crosslinking agent, and having a sea-island structure in which crosslinked rubber particles are finely dispersed as domains (island phases) in the resin component A which is the matrix (sea phase).

[0047] The polyolefin elastomer preferably contains a rubber component. Examples of such rubber components are those described in Japanese Patent Publication No. 08-302111, Japanese Patent Publication No. 2010-241934, Japanese Patent Publication No. 2008-024882, Japanese Patent Publication No. 2000-007858, Japanese Patent Publication No. 2006-052277, Japanese Patent Publication No. 2012-072306, Japanese Patent Publication No. 2012-057068, Japanese Patent Publication No. 2010-241897, Japanese Patent Publication No. 2009-067969, and Japanese Patent Publication No. 03 / 002654.

[0048] Elastomers having a structure in which the polyolefin component and the olefin-based rubber component are microphase separated include, specifically, elastomers composed of polypropylene resin (PP) and ethylene-propylene rubber (EPM), and elastomers composed of polypropylene resin (PP) and ethylene-propylene-diene rubber (EPDM). The weight ratio of the polyolefin component to the olefin-based rubber component (polyolefin component / olefin-based rubber) is preferably 90 / 10 to 10 / 90, and more preferably 80 / 20 to 20 / 80.

[0049] Dynamically crosslinked thermoplastic olefin elastomers (TPVs) generally have a higher elastic modulus and lower compression set than non-crosslinked thermoplastic olefin elastomers (TPOs). This results in good recovery properties, and when used in resin foams, they can exhibit excellent resilience.

[0050] Dynamically crosslinked thermoplastic olefin elastomers (TPVs), as described above, are obtained by dynamically heat-treating a mixture containing a resin component A (olefin resin component A) that forms the matrix and a rubber component B that forms the domains, in the presence of a crosslinking agent. They are multiphase polymers having a sea-island structure in which crosslinked rubber particles are finely dispersed as domains (island phases) in the resin component A, which is the matrix (sea phase).

[0051] Examples of dynamically crosslinked thermoplastic olefin elastomers (TPVs) include those described in Japanese Patent Publication No. 2000-007858, Japanese Patent Publication No. 2006-052277, Japanese Patent Publication No. 2012-072306, Japanese Patent Publication No. 2012-057068, Japanese Patent Publication No. 2010-241897, Japanese Patent Publication No. 2009-067969, and Table 03 / 002654, etc.

[0052] As the dynamically crosslinked thermoplastic olefin elastomer (TPV), commercially available products may be used, such as "Zeotherm" (manufactured by Nippon Zeon Co., Ltd.), "Thermoran" (manufactured by Mitsubishi Chemical Corporation), and "Sarlink 3245D" (manufactured by Toyobo Co., Ltd.).

[0053] The melt flow rate (MFR) of the polyolefin elastomer at a temperature of 230°C is preferably 1.5 g / 10 min to 25 g / 10 min, more preferably 2 g / 10 min to 20 g / 10 min, and even more preferably 2 g / 10 min to 15 g / 10 min. In one embodiment, the die swell ratio and shear viscosity of the resin are controlled by the melt flow rate of the polyolefin elastomer constituting the resin foam.

[0054] In one embodiment, two or more polyolefin elastomers having different melt flow rates (MFRs) at 230°C within the above range are used in combination. In this case, a polyolefin elastomer (low-MFR polyolefin elastomer) having a melt flow rate (MFR) at 230°C preferably between 1.5 g / 10 min and less than 8 g / 10 min (more preferably 2 g / 10 min to 5 g / 10 min) and a polyolefin elastomer (high-MFR polyolefin elastomer) having a melt flow rate (MFR) at 230°C preferably between 8 g / 10 min and 25 g / 10 min (more preferably 9 g / 10 min to 20 g / 10 min, and even more preferably 10 g / 10 min to 20 g / 10 min) can be used in combination. In this way, the melt tension of the polyolefin elastomer is preferably adjusted, and as a result, the effects of the present invention become more pronounced.

[0055] The blending ratio of the low-MFR polyolefin elastomer to the high-MFR polyolefin elastomer (low-MFR polyolefin elastomer / high-MFR polyolefin elastomer; weight ratio) is preferably 1.5 to 5, more preferably 1.8 to 3.5, and particularly preferably 2 to 3. Within this range, the melt tension of the polyolefin elastomer is nicely adjusted, and as a result, the effects of the present invention become remarkable.

[0056] The melt tension (at 190°C, at break) of the polyolefin elastomer is preferably less than 10 cN, and more preferably 5 cN to 9.5 cN. In one embodiment, the die swell ratio and shear viscosity of the resin are controlled by the melt tension of the polyolefin elastomer constituting the resin foam.

[0057] The JIS A hardness of polyolefin elastomers is preferably 30° to 95°, more preferably 35° to 90°, even more preferably 40° to 88°, particularly preferably 45° to 85°, and most preferably 50° to 83°. Note that JIS A hardness is measured according to ISO 7619 (JIS K6253).

[0058] In one embodiment, the resin foam (i.e., the resin composition) may further contain a filler. By including a filler, it is possible to form a resin foam that requires a large amount of energy to deform the cell walls, and this resin foam exhibits excellent shock absorption. Furthermore, including a filler is advantageous because it allows for the formation of a fine and uniform cell structure, which can also result in excellent shock absorption. The filler may be used alone or in combination of two or more types.

[0059] The content ratio of the above-mentioned filler is preferably 10 to 150 parts by weight, more preferably 30 to 130 parts by weight, and even more preferably 50 to 100 parts by weight, relative to 100 parts by weight of the polymer constituting the resin foam. Within this range, the above-mentioned effect becomes significant.

[0060] In one embodiment, the filler is inorganic. Examples of materials that constitute the inorganic filler include aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate whiskers, silicon nitride, boron nitride, crystalline silica, amorphous silica, metals (e.g., gold, silver, copper, aluminum, nickel), carbon, graphite, and the like.

[0061] In one embodiment, the filler is an organic material. Examples of materials that constitute the organic filler include polymethyl methacrylate (PMMA), polyimide, polyamideimide, polyether ether ketone, polyetherimide, polyesterimide, and the like.

[0062] A flame retardant may be used as the filler material. Examples of flame retardants include bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, and antimony-based flame retardants. Preferably, from the viewpoint of safety, a non-halogen-non-antimony flame retardant is used.

[0063] Examples of non-halogen-non-antimony flame retardants include compounds containing aluminum, magnesium, calcium, nickel, cobalt, tin, zinc, copper, iron, titanium, boron, etc. Examples of such compounds (inorganic compounds) include hydrated metal compounds such as aluminum hydroxide, magnesium hydroxide, magnesium oxide-nickel oxide hydrate, and magnesium oxide-zinc oxide hydrate.

[0064] The above-mentioned filler may be subjected to any appropriate surface treatment. Examples of surface treatments include silane coupling treatment and stearic acid treatment.

[0065] The bulk density of the above-mentioned filler is preferably 0.8 g / cm³. 3 The following, and more preferably 0.6 g / cm³ 3 The following, and more preferably 0.4 g / cm³ 3 The following, and particularly preferably 0.3 g / cm³ 3 The following applies. Within this range, the filler can be incorporated with good dispersibility, and the effect of adding the filler can be fully realized even with a low filler content. Resin foams with a low filler content are advantageous in that they are highly foamed, flexible, and have excellent stress distribution and appearance. The lower limit of the bulk density of the filler is, for example, 0.01 g / cm³. 3 The concentration is preferably 0.05 g / cm³. 3 More preferably 0.1 g / cm³ 3 That is the case.

[0066] The number-average particle diameter (primary particle diameter) of the filler is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. Within this range, the filler can be contained with good dispersibility and a uniform cellular structure can be formed. As a result, a resin foam with excellent stress dispersibility and appearance can be obtained. The lower limit of the number-average particle diameter of the filler is, for example, 0.1 μm. The number-average particle diameter of the filler can be measured using a particle size analyzer (Micrtrac II, Microtrac-Bell Co., Ltd.) with a suspension prepared by mixing 1 g of filler with 100 g of water at 25°C as a sample.

[0067] The specific surface area of ​​the above-mentioned filler is preferably 2 m². 2 / g or more, more preferably 4m 2 / g or more, and more preferably 6m 2 The value is 1 / g or more. Within this range, the filler can be incorporated with good dispersibility and a uniform cellular structure can be formed. As a result, a resin foam with excellent stress dispersion and appearance can be obtained. The upper limit of the specific surface area of ​​the filler is, for example, 20 m². 2 The value is / g. The specific surface area of ​​the filler can be measured by the BET method, that is, by adsorbing molecules with a known adsorption area onto the filler surface under low temperature conditions using liquid nitrogen, and then measuring the amount of adsorption.

[0068] The resin composition may contain any other suitable components, as long as they do not impair the effects of the present invention. Such other components may be one or more. Examples of such other components include rubber, resins other than polymers blended as resin materials, softeners, aliphatic compounds, anti-aging agents, antioxidants, light stabilizers, weathering agents, UV absorbers, dispersants, plasticizers, carbon, antistatic agents, surfactants, crosslinking agents, thickeners, rust inhibitors, silicone compounds, tension modifiers, shrinkage inhibitors, flow modifiers, gelling agents, curing agents, reinforcing agents, foaming agents, foaming nucleators, colorants (pigments, dyes, etc.), pH adjusters, solvents (organic solvents), thermal polymerization initiators, photopolymerization initiators, lubricants, crystal nucleating agents, crystallization accelerators, vulcanizing agents, surface treatment agents, and dispersion aids. In one embodiment, a resin composition that does not contain a crosslinking agent is used.

[0069] A-2. Formation of resin foam The resin foam of the present invention is typically obtained by foaming a resin composition. Methods commonly used in foam molding, such as physical or chemical methods, can be employed for foaming (methods for forming bubbles). That is, the resin foam may typically be a foam formed by a physical method (physical foam) or a foam formed by a chemical method (chemical foam). The physical method generally involves dispersing gaseous components such as air or nitrogen in a polymer solution and forming bubbles through mechanical mixing (mechanical foam). The chemical method generally involves forming cells with gas produced by the thermal decomposition of a foaming agent added to a polymer base, thereby obtaining the foam.

[0070] The resin composition to be subjected to foam molding may be prepared, for example, by mixing its constituent components using any suitable melt-kneading apparatus, such as an open-type mixing roll, a closed-type Banbury mixer, a single-screw extruder, a twin-screw extruder, a continuous kneader, or a pressure kneader.

[0071] <Embodiment 1 for forming a resin foam> One embodiment 1 for forming a resin foam is a method in which a resin foam is formed by mechanically foaming an emulsion resin composition (an emulsion containing a resin material (polymer), etc.) through a step (step A). ​​Examples of foaming devices include high-speed shear type devices, vibration type devices, and pressurized gas discharge type devices. Among these foaming devices, a high-speed shear type device is preferred from the viewpoint of miniaturizing the bubble diameter and producing large volumes. This embodiment 1 for forming a resin foam is applicable to formation from any resin composition.

[0072] A higher solid content concentration in the emulsion is preferable from the viewpoint of film-forming properties. The solid content concentration of the emulsion is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more.

[0073] The bubbles generated by mechanical stirring are formed when gas is incorporated into the emulsion. Any suitable gas can be used as the gas, as long as it is inert to the emulsion and does not impair the effects of the present invention. Examples of such gases include air, nitrogen, and carbon dioxide.

[0074] The foamed emulsion resin composition (bubble-containing emulsion resin composition) foamed by the above method can be applied to a substrate and dried in a step (step B) to obtain the foamed resin of the present invention. Examples of substrates include peel-treated plastic films (such as peel-treated polyethylene terephthalate films) and plastic films (such as polyethylene terephthalate films).

[0075] In step B, any suitable coating method and drying method can be adopted as long as they do not impair the effects of the present invention. Preferably, step B includes a pre-drying step B1 in which the bubble-containing emulsion resin composition applied to the substrate is dried at 50°C or higher and less than 125°C, and a main drying step B2 in which it is then dried further at 125°C or higher and 200°C or lower.

[0076] By providing a pre-drying step B1 and a main drying step B2, it is possible to prevent the coalescence and bursting of bubbles due to a rapid rise in temperature. In particular, with thin foam sheets, bubbles coalesce and burst due to a rapid rise in temperature, so providing a pre-drying step B1 is highly significant. The temperature in the pre-drying step B1 is preferably 50°C to 100°C. The duration of the pre-drying step B1 is preferably 0.5 minutes to 30 minutes, and more preferably 1 minute to 15 minutes. The temperature in the main drying step B2 is preferably 130°C to 180°C or lower, and more preferably 130°C to 160°C. The duration of the main drying step B2 is preferably 0.5 minutes to 30 minutes, and more preferably 1 minute to 15 minutes.

[0077] <Embodiment 2 for forming a resin foam> One embodiment 2 for forming a resin foam is a method in which a resin composition is foamed with a foaming agent to form a foam. As the foaming agent, one that is normally used in foam molding can be used, and from the viewpoint of environmental protection and low contamination of the foamed material, it is preferable to use a high-pressure inert gas.

[0078] Any suitable inert gas can be used as the inert gas, as long as it is inert to the resin composition and can impregnate it. Examples of such inert gases include carbon dioxide, nitrogen gas, and air. These gases may be used in mixtures. Of these, carbon dioxide is preferred from the viewpoint of impregnating the resin material (polymer) in large quantities and having a fast impregnation rate.

[0079] The inert gas is preferably in a supercritical state. In particular, it is especially preferable to use supercritical carbon dioxide. In a supercritical state, the solubility of the inert gas in the resin composition is increased, allowing for high concentrations of inert gas to be incorporated. Furthermore, because the concentration of the inert gas becomes high during a rapid pressure drop, more bubble nuclei are generated. The density of the bubbles formed by the growth of these nuclei is higher than in other states, even if the porosity is the same, thus enabling the production of fine bubbles. The critical temperature of carbon dioxide is 31°C and the critical pressure is 7.4 MPa.

[0080] Methods for forming a foam by impregnating a resin composition with a high-pressure inert gas include, for example, a gas impregnation step in which an inert gas is impregnated under high pressure into a resin composition containing a resin material (polymer), a depressurization step in which the pressure is reduced after the gas impregnation step to foam the resin material (polymer), and a heating step in which bubbles are grown by heating as needed. In this case, a pre-molded unfoamed molded body may be impregnated with the inert gas, or a molten resin composition may be impregnated with an inert gas under pressure and then molded under depressurization. These steps may be carried out in either a batch or continuous manner. That is, the resin composition may be pre-molded into an appropriate shape such as a sheet to form an unfoamed resin molded body, and then this unfoamed resin molded body may be impregnated with a high-pressure gas and foamed by releasing the pressure in a batch manner, or the resin composition may be kneaded with a high-pressure gas under pressure, molded and foamed simultaneously by releasing the pressure in a continuous manner.

[0081] An example of manufacturing foam using a batch method is shown below. For example, a resin sheet for foam molding is produced by extruding a resin composition using an extruder such as a single-screw extruder or a twin-screw extruder. Alternatively, an unfoamed resin molded body is produced by uniformly kneading a resin composition using a kneader equipped with blades such as rollers, cams, kneaders, or Banbarri types, and then pressing it to a predetermined thickness using a hot plate press or the like. The resulting unfoamed resin molded body is placed in a high-pressure vessel, and high-pressure inert gas (such as supercritical carbon dioxide) is injected to impregnate the unfoamed resin molded body with the inert gas. Once sufficient impregnation with the inert gas has occurred, the pressure is released (usually to atmospheric pressure) to generate bubble nuclei in the resin. The bubble nuclei may be allowed to grow at room temperature, but in some cases they may be grown by heating. As for heating methods, known and conventional methods such as water baths, oil baths, hot rolls, hot air ovens, far-infrared radiation, near-infrared radiation, and microwaves can be used. After growing bubbles in this manner, the foam can be obtained by rapidly cooling it with cold water or the like to fix its shape. The unfoamed resin molded body used for foaming is not limited to a sheet; various shapes can be used depending on the application. Furthermore, the unfoamed resin molded body can be manufactured using other molding methods such as injection molding, in addition to extrusion molding and press molding.

[0082] An example of a continuous foam manufacturing method is shown below. For example, a kneading and impregnation step is performed in which a resin composition is kneaded using an extruder such as a single-screw extruder or twin-screw extruder while a high-pressure gas (especially an inert gas, and even carbon dioxide) is injected (introduced) to sufficiently impregnate the resin composition with the high-pressure gas. A molding and depressurization step is performed in which the pressure is released (usually to atmospheric pressure) by pushing the resin composition through a die provided at the tip of the extruder, and molding and foaming are performed simultaneously. In addition, when foam molding is performed in a continuous method, a heating step may be provided as needed to grow bubbles by heating. After growing bubbles in this way, the shape may be fixed by rapidly cooling with cold water or the like as needed. Furthermore, the introduction of high-pressure gas may be performed continuously or discontinuously. Furthermore, in the kneading and impregnation step and the molding and depressurization step, for example, an extruder or injection molding machine may be used. Any appropriate method for heating when growing bubble nuclei can be a water bath, oil bath, hot roll, hot air oven, far-infrared radiation, near-infrared radiation, microwaves, etc. Any suitable shape can be adopted for the foam. Examples of such shapes include sheet-like, prismatic, cylindrical, and irregularly shaped forms.

[0083] The amount of gas mixed when foam molding the resin composition is preferably 2% to 10% by weight, more preferably 2.5% to 8% by weight, and even more preferably 3% to 6% by weight, relative to the total amount of the resin composition, in order to obtain a highly foamed resin foam.

[0084] The pressure used when impregnating the resin composition with an inert gas can be appropriately selected considering ease of operation and other factors. Such a pressure is preferably 6 MPa or higher (e.g., 6 MPa to 100 MPa), and more preferably 8 MPa or higher (e.g., 8 MPa to 50 MPa). When using supercritical carbon dioxide, the pressure is preferably 7.4 MPa or higher from the viewpoint of maintaining the supercritical state of carbon dioxide. If the pressure is lower than 6 MPa, bubble growth during foaming is significant, and the bubble diameter may become too large, making it impossible to obtain a desirable average cell diameter (average bubble diameter). This is because at lower pressures, the amount of gas impregnated is relatively less compared to high pressures, the bubble nucleation rate decreases, and the number of bubble nuclei formed decreases, so the amount of gas per bubble increases, and the bubble diameter becomes extremely large. In addition, in the pressure range below 6 MPa, even a slight change in impregnation pressure can greatly change the bubble diameter and bubble density, making it difficult to control the bubble diameter and bubble density.

[0085] The temperature during the gas impregnation process varies depending on the type of inert gas used and the components in the resin composition, and can be selected within a wide range. Considering ease of operation, the temperature is preferably 10°C to 350°C. When impregnating an unfoamed molded body with an inert gas, the impregnation temperature in a batch process is preferably 10°C to 250°C, and more preferably 40°C to 230°C. Furthermore, when extruding a gas-impregnated molten polymer to simultaneously perform foaming and molding, the impregnation temperature in a continuous process is preferably 60°C to 350°C. When carbon dioxide is used as the inert gas, the impregnation temperature is preferably 32°C or higher, and more preferably 40°C or higher, in order to maintain a supercritical state.

[0086] In the depressurization process, the depressurization rate is preferably 5 MPa / sec to 300 MPa / sec in order to obtain uniform fine bubbles.

[0087] The heating temperature in the heating process is preferably 40°C to 250°C, and more preferably 60°C to 250°C.

[0088] In one embodiment, after obtaining a foamed structure through a predetermined process (for example, after obtaining a resin foam by the method of <Embodiment 1> or <Embodiment 2>), the foamed structure is thinned, and then roll-rolled to obtain a resin foam. By going through such a process, a resin foam with an appropriately adjusted aspect ratio can be obtained. Furthermore, a resin foam with a thin thickness (for example, 0.2 mm or less) can be obtained. The above-mentioned roll-rolling may also form the above-mentioned heat-melted layer.

[0089] The foam structure can be thinned using any suitable slicer. The thickness of the foam structure after thinning is preferably 0.01 mm to 3 mm, more preferably 0.05 mm to 2 mm, even more preferably 0.1 mm to 1 mm, and particularly preferably 0.1 mm to 0.5 mm.

[0090] Preferably, the rolls used in the roll rolling process are heated rolls. The temperature of the rolls is preferably 150°C to 250°C, and more preferably 160°C to 230°C.

[0091] The rolling ratio of the foam structure (thickness after rolling / thickness before rolling × 100) is preferably 80% or less, more preferably 10% to 80%, even more preferably 20% to 75%, and particularly preferably 30% to 75%. Within this range, a resin foam with an appropriately adjusted aspect ratio can be obtained.

[0092] B. Foamed materials Figure 1 is a schematic cross-sectional view of a foamed member according to one embodiment. The foamed member 100 has a resin foam layer 10 and an adhesive layer 20 disposed on at least one side of the resin foam layer 10. The resin foam layer 10 is made of the resin foam described above.

[0093] The thickness of the adhesive layer is preferably 5 μm to 300 μm, more preferably 6 μm to 200 μm, even more preferably 7 μm to 100 μm, and particularly preferably 8 μm to 50 μm. By having the thickness of the adhesive layer within the above range, the foamed member of the present invention can exhibit excellent shock absorption.

[0094] The adhesive layer can be made of any suitable adhesive. Examples of adhesives that make up the adhesive layer include rubber-based adhesives (synthetic rubber-based adhesives, natural rubber-based adhesives, etc.), urethane-based adhesives, acrylic urethane-based adhesives, acrylic-based adhesives, silicone-based adhesives, polyester-based adhesives, polyamide-based adhesives, epoxy-based adhesives, vinyl alkyl ether-based adhesives, fluorine-based adhesives, and rubber-based adhesives. Preferably, the adhesive that makes up the adhesive layer is at least one selected from acrylic-based adhesives, silicone-based adhesives, and rubber-based adhesives. There may be only one such adhesive or two or more such adhesives. The adhesive layer may be one layer or two or more layers.

[0095] Adhesives can be classified by their adhesive form into, for example, emulsion-type adhesives, solvent-type adhesives, ultraviolet-crosslinked (UV-crosslinked) adhesives, electron-beam-crosslinked (EB-crosslinked) adhesives, and hot-melt adhesives. There may be only one type of such adhesive, or two or more types.

[0096] The water vapor permeability of the adhesive layer is preferably 50 g / m². 2 • 24 hours)) or less, more preferably 30 (g / (m³) 2 • 24 hours)) or less, and more preferably 20 (g / (m³) 2 • 24 hours)) or less, and particularly preferably 10 (g / (m³) 2 The water vapor permeability of the adhesive layer is less than or equal to 24 hours. If the water vapor permeability of the adhesive layer is within the above range, the foamed sheet can stabilize its shock absorption without being affected by moisture. The water vapor permeability can be measured, for example, by a method conforming to JIS Z 0208, under test conditions of 40°C and 92% relative humidity.

[0097] The adhesive constituting the adhesive layer may contain any other suitable components as long as they do not impair the effects of the present invention. Examples of other components include other polymer components, softeners, antioxidants, curing agents, plasticizers, fillers, antioxidants, thermal polymerization initiators, photopolymerization initiators, ultraviolet absorbers, light stabilizers, colorants (such as pigments and dyes), solvents (organic solvents), surfactants (e.g., ionic surfactants, silicone-based surfactants, fluorinated surfactants, etc.), and crosslinking agents (e.g., polyisocyanate-based crosslinking agents, silicone-based crosslinking agents, epoxy-based crosslinking agents, alkyl ether-based melamine-based crosslinking agents, etc.). Note that thermal polymerization initiators and photopolymerization initiators may be included in the materials for forming the polymer components.

[0098] The foamed material described above can be manufactured by any suitable method. Examples of such methods include laminating a resin foam layer and an adhesive layer, or laminating an adhesive layer forming material and a resin foam layer, and then forming the adhesive layer by a curing reaction or the like. [Examples]

[0099] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way to these examples. The test and evaluation methods in the examples are as follows. When "parts" is written, it means "parts by weight" unless otherwise specified, and when "%" is written, it means "percent by weight" unless otherwise specified.

[0100] <Evaluation Method> (1) Apparent density The density (apparent density) of the resin foam was calculated as follows. The resin foam obtained in the examples and comparative examples was punched out to a size of 20 mm x 20 mm to make test specimens, and the dimensions of the test specimens were measured with calipers. Next, the weight of the test specimens was measured with an electronic balance. Then, the density was calculated using the following formula. Apparent density (g / cm³) 3 ) = Weight of test specimen / Volume of test specimen

[0101] (2) 50% compression load The compression hardness of resin foam was measured according to the method for measuring compression hardness of resin foam described in JIS K 6767. Specifically, the resin foam obtained in the examples and comparative examples was cut into 30 mm x 30 mm size test pieces, and the stress (N) was measured per unit area (1 cm²) when compressed at a compression speed of 10 mm / min until the compression ratio reached 50%. 2 Converted to a unit per inch, 50% compressive load (N / cm²) 2 )

[0102] (3) Average bubble diameter (average cell diameter), coefficient of variation of bubble diameter (cell diameter) The resin foam was cut using a razor blade in the TD direction (perpendicular to the flow direction) and perpendicular to the main surface of the resin foam (thickness direction). A digital microscope (product name "VHX-500", manufactured by Keyence Corporation) was used as a measuring instrument to capture images of the cut surface of the resin foam. The number-mean bubble diameter (average cell diameter) (μm) was determined by image analysis using the analysis software of the same instrument. The number of bubbles in the magnified image captured was approximately 400. The standard deviation was calculated from all the cell diameter data, and the coefficient of variation was calculated using the following formula. Coefficient of variation = Standard deviation / Average bubble diameter (Average cell diameter)

[0103] (4) Bubble rate (cell rate) Measurements were performed under conditions of 23°C and 50% humidity. The resin foam obtained in the examples and comparative examples was punched out using a 100mm x 100mm punching die (processing blade (product name "NCA07", thickness 0.7mm, cutting edge angle 43°, manufactured by Nakayama Co., Ltd.)), and the dimensions of the punched samples were measured. The thickness was also measured using a 1 / 100 dial gauge with a measuring terminal diameter (φ) of 20mm. From these values, the volume of the resin foam obtained in the examples and comparative examples was calculated. Next, the weight of the resin foam obtained in the examples and comparative examples was measured using a balance scale with a minimum scale of 0.01g or more. From these values, the bubble rate (cell rate) of the resin foam obtained in the examples and comparative examples was calculated.

[0104] (5) Number of bubbles The resin foam was cut using a razor blade in the TD direction (perpendicular to the flow direction) and perpendicular to the main surface of the resin foam (thickness direction). A digital microscope (product name "VHX-500", manufactured by Keyence Corporation) was used as the measuring instrument to capture images of the cross-section of the resin foam, and the image was analyzed using the instrument's analysis software to determine the area per unit area [mm²]. 2 The number of bubbles per unit was measured.

[0105] (6) Thickness recovery rate (instantaneous recovery rate) 1000 g / cm³ of resin foam 2 The load was applied and maintained for 120 seconds, then the compression was released. The thickness of the resin foam 0.5 seconds after the release (thickness 0.5 seconds after the compression was released) was measured. The thickness recovery rate (instantaneous recovery rate) was calculated from the "thickness 0.5 seconds after the compression was released" and the thickness of the resin foam before the load was applied (initial thickness) using the following formula. Thickness recovery rate (%) = {(Thickness 0.5 seconds after decompression) / (Initial thickness)} × 100

[0106] (7) Relative permittivity The relative permittivity was measured using an E4980A Precision LCR meter (Agilent Technologies) under conditions of 23°C and 50% humidity. The measurement was performed using the parallel plate capacitor method (based on JIS C 2138) with a compressibility of 0%.

[0107] (8) Tensile modulus The tensile modulus was determined by performing a tensile test at an ambient temperature of 25°C using a tensile testing machine (RTG-1201, manufactured by Tansui Co., Ltd.). A sample (size: 10mm x 80mm) was fixed with a chuck distance of 40mm and the tensile speed was 500mm / min. A curve consisting of tensile strain and tensile strength was obtained. The tensile modulus was determined from the slope of the line connecting the origin of this curve and the tensile strength at 10% tensile strain.

[0108] (9) Die-cutting capability (10mm x 10mm) A resin foam was punched out to a size of 10mm x 10mm using a mold (two cutting blades (product name "NCA07", thickness 0.7mm, cutting edge angle 43°, distance between the two cutting blades 10mm, manufactured by Nakayama Co., Ltd.)) in the MD direction (flow direction) and the TD direction (direction perpendicular to the flow direction). The cross-section with the greater thickness change between the MD and TD directions was observed with a microscope (product name "VHX-2000", manufactured by Keyence Corporation). The thickness recovery rate after processing was measured using the thickness of the edge measured from the image and the thickness before punching, using the following formula. A larger thickness recovery rate indicates less shape change due to punching and superior punching processability. Thickness recovery rate after processing (%) = 100 × (1 - (thickness before punching - thickness at the edge) / thickness before punching)

[0109] (10) Punching processability (1 mm width) A resin foam was punched out using a mold (two cutting blades (product name "NCA07", thickness 0.7 mm, cutting edge angle 43°, distance between the two cutting blades 1 mm, manufactured by Nakayama Co., Ltd.)) in the MD direction (flow direction) with a distance of 1 mm between the two cutting blades and a length of 50 mm, perpendicular to the main surface of the resin foam (thickness direction). The cross-section was observed with a microscope (product name "VHX-2000", manufactured by Keyence Corporation). The thickness recovery rate after processing was measured using the thickness of the edges measured from the image and the thickness before punching, using the following formula. A larger thickness recovery rate indicates less shape change due to punching and superior punching processability. Thickness recovery rate after processing (%) = 100 × (1 - (thickness before punching - thickness at the edge) / thickness before punching)

[0110] (11) Dicewell ratio Using an extensional viscometer (product name "RH-7", Malvern Corporation) as the measuring instrument, the sample (resin constituting the resin foam (size: 5 mm square)) was placed in a cylinder at a temperature 20°C higher than the melting point of the resin constituting the resin foam, and melted over 7 minutes. The molten material was then extruded at a shear rate of 20 mm / s through a die 10 mm long with a diameter of 1 mmφ. The diameter of the resulting string-like molded product was measured using a digital caliper (product name "CD67-s PM", Mitutoyo Corporation), and the die swell ratio was calculated using the following formula. The die swell ratio of the resin was measured both before and after foaming. Note that for Comparative Example 2, it was not possible to measure the die swell ratio for the foam composed of a cross-linked material. Die swell ratio = Diameter of molded part (mm) / Die bore (mm)

[0111] (12) Shear viscosity Using an extensional viscometer (product name "RH-7", Malvern Corporation) as the measuring instrument, a sample (resin constituting the foam (size: 5mm square)) was placed in a cylinder at a temperature 20°C higher than the melting point of the resin constituting the foam, and melted over 7 minutes. The molten material was then extruded at a shear rate of 20 mm / s through a die 10 mm long with a diameter of 1 mm, and the shear viscosity was measured. The shear viscosity of the resin was measured both before and after foaming. Note that in Comparative Example 2, it was not possible to measure the shear viscosity of the foam composed of a cross-linked material.

[0112] [Example 1] Polypropylene (propylene homopolymer, MFR: 0.4g / 10min (230℃, load 21.2N), density: 0.90g / cm³) 330 parts by weight of (ethylene content: 0% by weight, propylene content: 100% by weight, weight-average molecular weight: 64500, molecular weight distribution: 8.43), 46 parts by weight of polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°), 19 parts by weight of polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°), 10 parts by weight of magnesium hydroxide (product name "KISUMA 5P", manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (product name "Asahi #35", manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at a temperature of 200°C in a twin-screw kneader manufactured by Japan Steel Works, Ltd. (JSW), then extruded into strands, water-cooled, and molded into pellets. These pellets were fed into a single-screw extruder manufactured by Japan Steel Works, Ltd., and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere of 220°C. The carbon dioxide gas was injected at a ratio of 4.8 parts by weight per 100 parts by weight of resin. After the carbon dioxide gas was sufficiently saturated, the material was cooled to a temperature suitable for foaming, and then extruded from the die to obtain a sheet-like resin foam a. Furthermore, a thin film was obtained using a slicer to obtain a resin foam A with a thickness of 1.0 mm. The obtained resin foam A was subjected to the above evaluation. The results are shown in Table 1.

[0113] [Example 2] Polypropylene (propylene homopolymer, MFR: 0.4g / 10min (230℃, load 21.2N), density: 0.90g / cm³) 335 parts by weight of ethylene (0% by weight, propylene (100% by weight)), 42 parts by weight of polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°), 18 parts by weight of polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°), 10 parts by weight of magnesium hydroxide (product name "KISUMA 5P", manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (product name "Asahi #35", manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at a temperature of 200°C in a twin-screw mixer manufactured by Japan Steel Works, Ltd., then extruded into strands, water-cooled and formed into pellets. These pellets were fed into a single-screw extruder manufactured by Japan Steel Works, Ltd., and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere of 220°C. Carbon dioxide gas was injected at a ratio of 4.8 parts by weight per 100 parts by weight of resin. After the carbon dioxide gas was sufficiently saturated, the mixture was cooled to a temperature suitable for foaming, and then extruded from the die to obtain a sheet-like resin foam b. Furthermore, a thin film was created using a slicer to obtain resin foam B with a thickness of 1.0 mm. The obtained resin foam B was subjected to the above evaluation. The results are shown in Table 1.

[0114] [Example 3] Resin foam c was obtained in the same manner as in Example 2, except that the amount of carbon dioxide gas injected was 4.5 parts by weight per 100 parts by weight of resin. Furthermore, a thin film was created using a slicer to obtain a resin foam C with a thickness of 1.0 mm. The obtained resin foam C was subjected to the above evaluation. The results are shown in Table 1.

[0115] [Example 4] A resin foam d was obtained in the same manner as in Example 2, except that the amount of carbon dioxide gas injected was 4.2 parts by weight per 100 parts by weight of resin. Furthermore, a thin film was obtained using a slicer to obtain a resin foam D with a thickness of 1.0 mm. The obtained resin foam D was subjected to the above evaluation. The results are shown in Table 1.

[0116] [Example 5] Polypropylene (propylene homopolymer, MFR: 0.4g / 10min (230℃, load 21.2N), density: 0.90g / cm³) 3 40 parts by weight of ethylene (0% by weight, propylene (100% by weight)), 39 parts by weight of polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°), 16 parts by weight of polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°), 10 parts by weight of magnesium hydroxide (product name "KISUMA 5P", manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (product name "Asahi #35", manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at a temperature of 200°C in a twin-screw mixer manufactured by Japan Steel Works, Ltd., then extruded into strands, water-cooled and formed into pellets. These pellets were fed into a single-screw extruder manufactured by Japan Steel Works, Ltd., and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere of 220°C. Carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of resin. After the carbon dioxide gas was sufficiently saturated, the mixture was cooled to a temperature suitable for foaming, and then extruded from the die to obtain a sheet-like resin foam e. Furthermore, a thin film was obtained using a slicer to obtain a resin foam E with a thickness of 1.0 mm. The obtained resin foam E was subjected to the above evaluation. The results are shown in Table 1.

[0117] [Example 6] Polypropylene (propylene homopolymer, MFR: 0.5g / 10min (230℃, load 21.2N), density: 0.90g / cm³) 340 parts by weight of (ethylene content: 0% by weight, propylene content: 100% by weight, weight-average molecular weight: 54500, molecular weight distribution: 9.83), 39 parts by weight of polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°), 16 parts by weight of polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°), 10 parts by weight of magnesium hydroxide (product name "KISUMA 5P", manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (product name "Asahi #35", manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at a temperature of 200°C in a twin-screw kneader manufactured by Japan Steel Works, Ltd. (JSW), then extruded into strands, water-cooled, and molded into pellets. These pellets were fed into a single-screw extruder manufactured by Japan Steel Works, Ltd., and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) under an atmosphere of 220°C. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of resin. After the carbon dioxide gas was sufficiently saturated, the material was cooled to a temperature suitable for foaming, and then extruded from the die to obtain a sheet-like resin foam f. Furthermore, a thin film was created using a slicer to obtain a resin foam F with a thickness of 1.0 mm. The obtained resin foam F was subjected to the above evaluation. The results are shown in Table 1.

[0118] [Example 7] Resin foam e was obtained in the same manner as in Example 2, except that the amount of carbon dioxide gas injected was 4.2 parts by weight per 100 parts by weight of resin. Furthermore, the resin foam was thinned using a slicer to obtain a resin foam with a thickness of 0.3 mm. Then, the resin foam was passed through the gap between two rolls in a pair of rolls, one of which was heated to 230°C, to obtain a resin foam E with a thickness of 0.20 mm. The gap between the rolls was set to obtain a resin foam E with a thickness of 0.20 mm. The obtained resin foam E was subjected to the above evaluation. The results are shown in Table 1.

[0119] [Comparative Example 1] Polypropylene (propylene homopolymer, MFR: 0.4g / 10min (230℃, load 21.2N), density: 0.90g / cm³) 3 65 parts by weight of (ethylene content: 0% by weight, propylene content: 100% by weight, weight-average molecular weight: 108,000, molecular weight distribution: 4.93), 35 parts by weight of polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°), 5 parts by weight of magnesium hydroxide (product name "KISUMA 5P", manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (product name "Asahi #35", manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at a temperature of 200°C in a twin-screw kneader manufactured by Japan Steel Works, Ltd., then extruded into strands, water-cooled and molded into pellets. These pellets were fed into a single-screw extruder manufactured by Japan Steel Works, Ltd., and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) under an atmosphere of 220°C. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of resin. After sufficiently saturating the area with carbon dioxide gas, the material was cooled to a temperature suitable for foaming, and then extruded from the die to obtain a sheet-like resin foam f. Furthermore, a thin film was created using a slicer to obtain a resin foam F with a thickness of 1.0 mm. The obtained resin foam F was subjected to the above evaluation. The results are shown in Table 1.

[0120] [Comparative Example 2] Polyurethane-based resin foam (apparent density: 0.7 g / cm³) 3 A resin foam was prepared. The resin foam was subjected to the above evaluation. The results are shown in Table 1.

[0121] [Table 1]

[0122] As is clear from Table 1, the resin foam of the present invention has low dielectric properties and excellent die-cutting processability by setting the apparent density and instantaneous recovery rate within a specific range. [Industrial applicability]

[0123] The resin foam of the present invention can be suitably used, for example, as a cushioning material for electronic devices. [Explanation of symbols]

[0124] 100 Foamed material 10. Resin foam layer (resin foam) 20 Adhesive layer

Claims

1. A resin foam having a cellular structure, The apparent density of the resin foam is 0.4 g / cm³. ３ It is less than, 1000 g / cm³ of the resin foam ２ The thickness recovery rate after maintaining the applied load for 120 seconds is 85% or more. The resin foam contains a polyolefin resin, The polyolefin resin is a mixture of a polyolefin other than a polyolefin elastomer and a polyolefin elastomer. Resin foam.

2. The number density of bubbles is 30 / mm ２ The resin foam according to claim 1.

3. The resin foam according to claim 1, wherein the average bubble diameter is 10 μm to 200 μm.

4. The resin foam according to claim 1, wherein the coefficient of variation of the bubble diameter is 0.5 or less.

5. The resin foam according to claim 1, wherein the bubble rate is 30% or more.

6. The resin foam according to claim 1, wherein the tensile modulus at 25°C is 1.5 MPa or more.

7. A 50% compression load is 20 N / cm ２ The resin foam according to claim 1, which is as follows:

8. The resin foam according to claim 1, having a heat-melting layer on one or both sides.

9. It has a resin foam layer and an adhesive layer disposed on at least one side of the resin foam layer, The resin foam layer is the resin foam described in claim 1. Foamed material.

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