Resin foam

Abstract

Provided is a resin foam which is thin and has excellent impact resistance.　A resin foam according to the present invention has an apparent density of 0.02 g / cm3-0.30 g / cm3, a 25% compression load of 90 kPa or less, an elastic strain energy of 10 kPa or more upon compression, and a bubble structure. In one embodiment, the resin foam has an average bubble diameter of 10-200 μm. In one embodiment, the resin foam has a bubble fraction of 30% or more. In one embodiment, the resin foam has a coefficient of variation of bubble diameter of 0.5 or less.

Description

[Technical Field]

[0001] The present invention relates to a resin foam. [Background technology]

[0002] Cushioning materials are widely used to protect the screens and circuit boards of electronic devices. In recent years, with the trend toward thinner electronic devices, there has been a demand for narrower clearances where cushioning materials are placed. Furthermore, flexible electronic devices using organic electroluminescence (EL) panels are being investigated. Such electronic devices are subject to loads that are different from those of conventional rigid LCD panels.

[0003] Examples of cushioning materials include materials with a foam structure, and a method for obtaining a foam with a fine cell structure has been proposed in which an inert gas is dissolved in a polymer under high pressure, and then the pressure is suddenly reduced to form a foam structure (Reference 1). Attempts have also been made to improve the impact absorption properties of foam materials (References 2 and 3). However, no thin foam material has been obtained that achieves the high level of impact resistance required not only for devices used with conventional rigid displays, but also for devices used with flexible displays and devices in which the flexible displays are bent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-322168 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-186504 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-034299 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a resin foam that is thin but has excellent impact absorption properties. [Means for solving the problem]

[0006] The resin foam of the present invention has an apparent density of 0.02 g / cm 3 ~0.30g / cm 3 The 25% compression load is 90 kPa or less, the elastic strain energy during compression is 10 kPa or more, and the material has a cellular structure. 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 cellular content of 30% or more. 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 an unfoamed bending stress of 5 MPa or more. In one embodiment, the resin foam further contains a filler. In one embodiment, the filler is inorganic. In one embodiment, the filler is organic. In one embodiment, the resin foam contains a polyolefin-based resin. In one embodiment, the polyolefin-based resin is a mixture of a polyolefin other than the polyolefin-based elastomer and a polyolefin-based elastomer. In one embodiment, the resin foam has a heat-fusible layer on one or both sides. According to another aspect of the present invention, there is provided a foam material having a resin foam layer and a pressure-sensitive adhesive layer disposed on at least one side of the resin foam layer, the resin foam layer being the resin foam described above. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a resin foam that is thin but has excellent impact absorption properties. The resin foam of the present invention exhibits excellent impact absorption properties even when combined with a flexible sheet. [Brief explanation of the drawings]

[0008]

Figure 1

[0009] A. Resin foam The resin foam of the present invention has an apparent density of 0.02 g / cm 3 ~0.30g / cm 3 The resin foam of the present invention has a cellular structure (cell structure). Examples of the cellular structure (cell structure) include a closed-cell structure, an open-cell structure, and a semi-open, semi-closed cell structure (a cell structure in which a closed-cell structure and an open-cell structure are mixed). The cell structure of the resin foam is preferably an open-cell structure or a semi-open, semi-closed cell structure, and more preferably a semi-open, semi-closed cell structure. The resin foam of the present invention can be obtained by foaming a resin composition. The resin composition is a composition containing at least the resin that constitutes the resin foam.

[0010] As described above, the apparent density of the resin foam of the present invention is 0.02 g / cm 3 ~0.30g / cm 3 Within this range, a resin foam excellent in flexibility and stress dispersibility can be obtained. The apparent density of the resin foam of the present invention is preferably 0.03 g / cm. 3 ~0.28g / cm 3 and more preferably 0.04 g / cm 3 ~0.25g / cm 3 and particularly preferably 0.05 g / cm 3 ~0.20g / cm 3 and most preferably 0.07 g / cm3 ~0.15g / cm 3 Within this range, the above-mentioned effects become significant. The method for measuring the apparent density will be described later.

[0011] As described above, the 25% compression load of the resin foam of the present invention is 90 kPa or less. A resin foam with a 25% compression load within this range can reduce the load on the component to which it is applied. More specifically, when the resin foam is applied to a location with narrow clearance by being slightly compressed, the resin foam of the present invention can reduce the stress on other components. For example, when the resin foam is applied to a display component, the stress on the display component can be alleviated and dispersed, which is useful from the perspectives of reducing color unevenness and protecting the component. The 25% compression load of the resin foam of the present invention is preferably 80 kPa or less, more preferably 75 kPa or less, and even more preferably 55 kPa or less. Within this range, the above-mentioned effects are prominent. Furthermore, the 25% compression load of the resin foam of the present invention is preferably as low as possible, and the lower limit is, for example, 10 kPa, preferably 5 kPa, more preferably 1 kPa, and particularly preferably 0.1 kPa. The method for measuring the 25% compression load will be described later.

[0012] As described above, the resin foam of the present invention has an elastic strain energy during compression of 10 kPa or more. The "elastic strain energy during compression" refers to the total amount of compression repulsion force when the resin foam is compressed by 10%. Specifically, the "elastic strain energy during compression" is determined from a compression ss curve, with the x-axis representing the compression rate (%) and the y-axis representing the compression repulsion force (kPa), measured in a compression test in accordance with JIS K 6767 (test temperature: 23°C, sample size: 10 mm × 10 mm, compression speed: 10 mm / min). The "elastic strain energy during compression" is the area of the region defined by the ss curve and the x-axis in the range of compression rate from 0% to 10%. Resin foams having an elastic strain energy during compression within the above range can have excellent impact absorption properties. More specifically, resin foams having an elastic strain energy within the above range consume a large amount of energy to deform when subjected to an impact, and are therefore able to absorb even strong impacts well. The elastic strain energy of the resin foam of the present invention when compressed is preferably 20 kPa or more, more preferably 28 kPa or more, even more preferably 35 kPa or more, even more preferably 50 kPa or more, still more preferably 80 kPa or more, particularly preferably 100 kPa or more, and most preferably 150 kPa or more. Within such a range, the above-mentioned effects become significant. The upper limit of the elastic strain energy of the resin foam of the present invention when compressed is, for example, 500 kPa (preferably 800 kPa).

[0013] In the present invention, by setting the apparent density, 25% compression load, and elastic strain energy during compression within the above ranges, a resin foam excellent in flexibility, stress dispersibility, and impact resistance can be obtained. Furthermore, a resin foam satisfying all of the above properties exhibits excellent impact resistance even in a thin layer, and also exhibits excellent impact resistance when combined with a flexible member (e.g., an organic EL panel, a resin substrate).

[0014] The thickness of the resin foam of the present invention is preferably 30 μm to 5000 μm, more preferably 35 μm to 4000 μm, even more preferably 40 μm to 3000 μm, even more preferably 45 μm to 2000 μm, even more preferably 50 μm to 1000 μm, and particularly preferably 55 μm to 500 μm. As described above, the resin foam of the present invention exhibits excellent impact resistance despite being a thin layer. Furthermore, when the thickness of the resin foam is within the above range, a fine and uniform cell structure can be formed, which is advantageous in that excellent impact absorption can be achieved.

[0015] The elongation at break of the resin foam of the present invention at 25°C is preferably 120% or less, more preferably 110% or less, even more preferably 100% or less, and particularly preferably 90% or less. Within these ranges, a resin foam with excellent flexibility and stress dispersibility can be obtained. A small elongation at break reduces the deformation of the cell walls of the resin foam when a load is applied to the resin foam. For example, when a filler is added, slippage is more likely to occur at the interface between the resin constituting the resin foam and the filler, thereby enabling the load to be more easily absorbed. On the other hand, if the elongation at break is too large, the cell walls of the resin foam may deform more, making it difficult to absorb the load. The elongation at break can be measured in accordance with JIS K 6767.

[0016] The resin foam has an average cell diameter (average cell size) of preferably 10 μm to 200 μm, more preferably 15 μm to 180 μm, even more preferably 20 μm to 150 μm, particularly preferably 23 μm to 120 μm, particularly preferably 25 μm to 100 μm, and most preferably 30 μm to 80 μm. Within these ranges, a resin foam having excellent flexibility and stress dispersibility can be obtained. Furthermore, a resin foam having excellent compression recovery and resistance to repeated impacts can be obtained. The method for measuring the average cell size will be described later.

[0017] The aspect ratio of the cells in the resin foam is preferably 1.5 or more. Within this range, a resin foam with excellent thickness recovery property can be obtained. The aspect ratio of the cells constituting the resin foam is preferably 2.0 or more, more preferably 2.5 or more. Within this range, the above-mentioned effects become significant. Furthermore, the upper limit of the aspect ratio of the cells constituting the resin foam is preferably 8, more preferably 6, and even more preferably 5. Within this range, a resin foam with excellent impact absorption property can be obtained.

[0018] In this specification, the "aspect ratio of the cells in the resin foam" refers to the ratio of the cell size to the cell size of a given area (3 mm2) in the cross section of the resin foam at a randomly selected point. 2 The specific method for determining the "aspect ratio of cells in a resin foam" is as follows. The resin foam was cut with a razor blade in the TD (direction perpendicular to the flow direction) and in the direction perpendicular to the main surface of the resin foam (thickness direction), and cut into pieces of a specified area (3 mm 2 ) area is observed at a magnification of 100x. The length of one bubble in the thickness direction and the length of the TD are measured. · Similar measurements are performed on all bubbles present within a specified area. The aspect ratio of the bubbles is calculated by dividing the TD length by the thickness length. The same calculation is performed for all bubbles, and the average value is taken as the "aspect ratio of the bubbles in the resin foam."

[0019] The coefficient of variation of the cell diameter of the resin foam of the present invention is preferably 0.5 or less, more preferably 0.48 or less, even more preferably 0.45 or less, particularly preferably 0.43 or less, and most preferably less than 0.4. Within these ranges, deformation due to impact becomes uniform, localized stress loads are prevented, and a resin foam having excellent stress dispersibility and particularly excellent impact resistance can be obtained. The smaller the coefficient of variation, the more preferable it is, and the lower limit thereof is, for example, 0.2 (preferably 0.15, more preferably 0.1, and even more preferably 0.01). The method for measuring the coefficient of variation of the cell diameter will be described later.

[0020] The resin foam of the present invention preferably has a cellular content (cell content) of 30% or more, more preferably 50% or more, and even more preferably 80% or more. Within this range, a resin foam with low resilience stress upon compression can be obtained. When the resin foam is slightly compressed and applied to a location with a narrow clearance, such a resin foam can reduce the stress applied to other components. For example, when the resin foam is applied to a display component, it can alleviate and distribute the stress applied to the display component, which is useful from the perspectives of reducing color unevenness and protecting the component. The upper limit of the cellular content is, for example, 99% or less. A method for measuring the cellular content will be described later.

[0021] The thickness of the cell walls of the resin foam of the present invention 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 2.8 μm. Within these ranges, a resin foam with superior flexibility and stress dispersion can be obtained. If the cell wall thickness is too thin, the resin foam may easily deform under load, and a sufficient stress dispersion effect may not be obtained. If the cell wall thickness is too thick, the resin foam may be difficult to deform under load, and when used in a gap in a device, its ability to conform to steps may be poor. A method for measuring the cell wall thickness will be described later.

[0022] When the resin foam of the present invention has a semi-open, semi-closed cell structure, the proportion of closed cell structures therein is preferably 40% or less, more preferably 30% or less. In this specification, the closed cell fraction of a resin foam is determined, for example, by submerging a measurement object in water at a temperature of 23°C and a humidity of 50%, measuring the mass, and then thoroughly drying the object in an oven at 80°C and measuring the mass again. Since open cells can retain moisture, the mass of the open cells is measured and determined.

[0023] The non-foaming bending stress of the resin foam of the present invention is preferably 5 MPa or more, more preferably greater than 5 MPa, more preferably 7 MPa or more, and even more preferably 10 MPa or more. Within this range, a large amount of energy is required to deform the cell walls of the resin foam, resulting in a resin foam with excellent impact absorption. The resin foam of the present invention moderately reduces the flexibility, which has traditionally been considered important in cushioning materials, and balances it with other properties, thereby enabling improved impact resistance (shock absorption). The resin foam of the present invention, which exhibits impact absorption properties through this unique mechanism, is particularly useful in configurations in which impact propagates within a narrow range (configurations in which impact is less likely to spread in the planar direction), and is particularly useful, for example, when applied to flexible components (e.g., components made of resin). The upper limit of the non-foaming bending stress is preferably 20 MPa, more preferably 15 MPa. Within this range, a resin foam with excellent flexibility and stress dispersibility can be obtained. "Non-foamed bending stress" refers to the bending stress of a resin molded product a that has been returned to a bubble-free, non-foamed state (bulk) by hot-pressing a resin foam. The density of the resin molded product a can be made equal to the density of a resin molded product b that has been formed from a resin composition described below before foaming. The bending stress of the resin molded product a (non-foamed bending stress of the resin foam) can be made equal to that of the resin molded product b. The method for measuring the bending stress will be described later.

[0024] The thickness recovery rate of the resin foam is preferably 65% or more, more preferably 70% or more, and even more preferably 75% or more. The thickness recovery rate of the foam layer is defined by the following formula. This thickness recovery rate of the foam layer is a recovery rate measured by applying a load to a foam sheet over a certain area to compress it, and is different from the so-called dent recovery rate, which is measured by applying a load locally to dent only a part of it. Thickness recovery rate (%) = {(thickness 0.5 seconds after releasing the compression state) / (initial thickness)} × 100 Initial thickness: The thickness of the resin foam before applying a load. Thickness 0.5 seconds after releasing the compression: 1000g / cm for resin foam 2 The thickness of the resin foam is measured 0.5 seconds after the load is applied and maintained for 120 seconds, and then the compression is released.

[0025] The resin foam of the present invention may have any suitable shape depending on the purpose, and a typical example of such a shape is a sheet.

[0026] The resin foam of the present invention may have a heat-meltable layer on one or both sides thereof. A resin foam having a heat-meltable layer can be obtained, for example, by rolling a resin foam (or a precursor of a resin foam) using a pair of heated rolls heated to a temperature equal to or higher than the melting temperature of the resin composition constituting the resin foam.

[0027] The resin foam of the present invention can be formed by any appropriate method as long as the effects of the present invention are not impaired. A representative example of such a method is a method of foaming a resin composition containing a resin material (polymer).

[0028] A-1. Resin composition The resin foam of the present invention can typically be obtained by foaming a resin composition containing any appropriate resin material (polymer).

[0029] Examples of the polymer include acrylic resins, silicone resins, urethane resins, polyolefin resins, ester resins, rubber resins, etc. The polymers may be used alone or in combination of two or more.

[0030] The content of the polymer 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, relative to 100 parts by weight of the resin composition. Within such ranges, a resin foam having excellent flexibility and stress dispersibility can be obtained.

[0031] In one embodiment, a polyolefin resin is used as the polymer.

[0032] 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 polymer.

[0033] The polyolefin resin is preferably at least one selected from the group consisting of polyolefins and polyolefin elastomers, and more preferably a combination of polyolefins and polyolefin elastomers. The polyolefins and polyolefin elastomers may each be used alone or in combination of two or more. In this specification, the term "polyolefin" does not include "polyolefin elastomers."

[0034] When polyolefin and polyolefin elastomer are used in combination as the polyolefin resin, the weight ratio of polyolefin to polyolefin elastomer (polyolefin / polyolefin elastomer) is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 90 / 10, still more preferably 20 / 80 to 80 / 20, and particularly preferably 30 / 70 to 70 / 30. Within such a range, the effects of the present invention become remarkable.

[0035] Any appropriate polyolefin may be used as the polyolefin as long as it does not impair the effects of the present invention. Examples of such polyolefins include linear polyolefins and branched (branched) polyolefins. In one embodiment, a branched polyolefin is used as the polyolefin-based resin. In this embodiment, only a branched polyolefin may be used as the polyolefin, or a branched polyolefin and a linear polyolefin may be used in combination. By using a branched polyolefin, a resin foam having a small average cell diameter and excellent impact resistance can be obtained. The content of the branched polyolefin is preferably 30 to 100 parts by weight, more preferably 80 to 120 parts by weight, relative to 100 parts by weight of the polyolefin.

[0036] Examples of the polyolefin include polymers containing structural units derived from α-olefins. The polyolefin may be composed solely of structural units derived from α-olefins, or may be composed of structural units derived from α-olefins and structural units derived from monomers other than α-olefins. When the polyolefin is a copolymer, any appropriate copolymerization form may be adopted. Examples include random copolymers and block copolymers.

[0037] The α-olefin that can constitute the polyolefin is preferably, for example, an α-olefin 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.). Only one type of α-olefin may be used, or two or more types may be used.

[0038] 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, vinyl alcohol, etc. The monomers other than α-olefins may be of one type only, or of two or more types.

[0039] Specific examples of polyolefins include 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 an α-olefin other than ethylene, copolymers of propylene and an α-olefin other than propylene, copolymers of ethylene, propylene and an α-olefin other than ethylene and propylene, and copolymers of propylene and an ethylenically unsaturated monomer.

[0040] In one embodiment, a polypropylene-based polymer having a structural unit derived from propylene is used as the polyolefin. Examples of the polypropylene-based polymer include polypropylene (propylene homopolymer), a copolymer of ethylene and propylene, and a copolymer of propylene and an α-olefin other than propylene, and polypropylene (propylene homopolymer) is preferred. One type of polypropylene-based polymer may be used alone, or two or more types may be used in combination.

[0041] The melt flow rate (MFR) of the polyolefin at a temperature of 230°C is preferably 0.2 g / 10 min to 10 g / 10 min, more preferably 0.25 g / 10 min to 5 g / 10 min, even more preferably 0.3 g / 10 min to 3 g / 10 min, and particularly preferably 0.35 g / 10 min to 1.5 g / 10 min, in order to further exhibit the effects of the present invention. In this specification, the melt flow rate (MFR) refers to the MFR measured at a temperature of 230°C and a load of 2.16 kgf in accordance with ISO1133 (JIS-K-7210).

[0042] In one embodiment, two or more polyolefins having different melt flow rates (MFR) at 230°C within the above range are used in combination. In this case, a polyolefin having a melt flow rate (MFR) at 230°C of preferably 0.2 g / 10 min or more and less than 0.7 g / 10 min (more preferably 0.2 g / 10 min to 0.65 g / 10 min) can be used in combination with a polyolefin having a melt flow rate (MFR) at 230°C of preferably 0.7 g / 10 min to 10 g / 10 min (more preferably 0.7 g / 10 min to 5 g / 10 min, even more preferably 0.7 g / 10 min to 3 g / 10 min, particularly preferably 0.7 g / 10 min to 1.5 g / 10 min, and most preferably 0.7 g / 10 min to 1.3 g / 10 min). This allows for the production of a resin foam having a small average cell diameter and excellent impact resistance.

[0043] When two or more polyolefins having different melt flow rates (MFR) at a temperature of 230°C within the above range are used in combination, for example, a polyolefin having a melt flow rate (MFR) at a temperature of 230°C of preferably 0.2 g / 10 min or more but less than 0.7 g / 10 min (more preferably 0.2 g / 10 min to 0.65 g / 10 min) and a polyolefin having a melt flow rate (MFR) at a temperature of 230°C of preferably 0.7 g / 10 min to 10 g / 10 min (more preferably 0.7 g / 10 min to 10 g / 10 min) are used in combination. The weight ratio of the polyolefin (usually 0.10 min to 5 g / 10 min, more preferably 0.7 g / 10 min to 3 g / 10 min, particularly preferably 0.7 g / 10 min to 1.5 g / 10 min, and most preferably 0.7 g / 10 min to 1.3 g / 10 min) to the polyolefin is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 90 / 10, still more preferably 20 / 80 to 80 / 20, particularly preferably 30 / 70 to 70 / 30, and most preferably 40 / 60 to 60 / 40.

[0044] As the polyolefin, commercially available products may be used, such as "E110G" (manufactured by Prime Polymer Co., Ltd.), "EA9" (manufactured by Japan Polypropylene Corporation), "EA9FT" (manufactured by Japan Polypropylene Corporation), "E-185G" (manufactured by Prime Polymer Co., Ltd.), "WB140HMS" (manufactured by Borealis), and "WB135HMS" (manufactured by Borealis).

[0045] Any suitable polyolefin elastomer may 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 (TPOs) such as ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-vinyl acetate copolymers, polybutene, polyisobutylene, chlorinated polyethylene, elastomers in which a polyolefin component and a rubber component are physically dispersed, and elastomers in which a polyolefin component and a rubber component are microphase-separated; dynamically crosslinked thermoplastic olefin elastomers (TPVs) which are multiphase polymers obtained by dynamically heat-treating a mixture containing a matrix-forming resin component A (olefin resin component A) and a domain-forming rubber component B in the presence of a crosslinking agent, and which have a sea-island structure in which crosslinked rubber particles are finely dispersed as domains (island phases) in the matrix (sea phase) of resin component A; and the like.

[0046] The polyolefin-based elastomer preferably contains a rubber component, and examples of such rubber components include those described in JP-A-08-302111, JP-A-2010-241934, JP-A-2008-024882, JP-A-2000-007858, JP-A-2006-052277, JP-A-2012-072306, JP-A-2012-057068, JP-A-2010-241897, JP-A-2009-067969, and JP-A-03 / 002654.

[0047] Specific examples of elastomers having a microphase-separated structure of a polyolefin component and an olefinic rubber component include elastomers made of polypropylene resin (PP) and ethylene-propylene rubber (EPM), elastomers made of polypropylene resin (PP) and ethylene-propylene-diene rubber (EPDM), etc. The weight ratio of the polyolefin component to the olefinic rubber component (polyolefin component / olefinic rubber) is preferably 90 / 10 to 10 / 90, and more preferably 80 / 20 to 20 / 80.

[0048] Dynamically crosslinked thermoplastic olefin elastomers (TPV) generally have a higher elastic modulus and a smaller compression set than non-crosslinked thermoplastic olefin elastomers (TPO), which results in good recovery properties and allows them to exhibit excellent recovery properties when foamed.

[0049] As mentioned above, dynamically crosslinked thermoplastic olefin-based elastomers (TPVs) are obtained by dynamically heat-treating a mixture containing a resin component A (olefin-based resin component A) that forms the matrix and a rubber component B that forms the domains in the presence of a crosslinking agent. These TPVs are multiphase polymers with a sea-island structure in which crosslinked rubber particles are finely dispersed as domains (island phases) in the resin component A that forms the matrix (sea phase).

[0050] Examples of dynamically crosslinked thermoplastic olefin-based elastomers (TPVs) include those described in JP 2000-007858 A, JP 2006-052277 A, JP 2012-072306 A, JP 2012-057068 A, JP 2010-241897 A, JP 2009-067969 A, and JP 03 / 002654 A.

[0051] As the dynamically crosslinked thermoplastic olefin-based elastomer (TPV), commercially available products may be used, such as "Zeotherm" (manufactured by Nippon Zeon Co., Ltd.), "Thermorun" (manufactured by Mitsubishi Chemical Corporation), and "Sarlink 3245D" (manufactured by Toyobo Co., Ltd.).

[0052] The melt flow rate (MFR) of the polyolefin elastomer at a temperature of 230°C is preferably 2 g / 10 min to 15 g / 10 min, more preferably 3 g / 10 min to 10 g / 10 min, even more preferably 3.5 g / 10 min to 9 g / 10 min, particularly preferably 4 g / 10 min to 8 g / 10 min, and most preferably 4.5 g / 10 min to 7.5 g / 10 min.

[0053] 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.

[0054] The JIS A hardness of the polyolefin elastomer 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°. The JIS A hardness is measured in accordance with ISO7619 (JIS K6253).

[0055] In one embodiment, the resin foam (i.e., the resin composition) may further contain a filler. By incorporating a filler, a resin foam can be formed that requires a large amount of energy to deform the cell walls, and the resin foam exhibits excellent impact absorption properties. Furthermore, by incorporating a filler, a fine and uniform cell structure can be formed, which is advantageous in that excellent impact absorption properties can be exhibited. One type of filler may be used alone, or two or more types may be used in combination.

[0056] The content of the 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. If the content is within this range, the above-mentioned effects become significant.

[0057] In one embodiment, the filler is an inorganic substance. Examples of materials constituting 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, and graphite.

[0058] In one embodiment, the filler is an organic substance. Examples of materials constituting the organic filler include polymethyl methacrylate (PMMA), polyimide, polyamideimide, polyetheretherketone, polyetherimide, and polyesterimide.

[0059] A flame retardant may be used as the filler. Examples of the flame retardant include bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, and antimony-based flame retardants. From the viewpoint of safety, a non-halogen, non-antimony-based flame retardant is preferably used.

[0060] 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.

[0061] The filler may be subjected to any suitable surface treatment, such as silane coupling treatment or stearic acid treatment.

[0062] The bulk density of the filler is preferably 0.8 g / cm 3 or less, more preferably 0.6 g / cm 3 More preferably, it is 0.4 g / cm or less. 3 or less, and particularly preferably 0.3 g / cm 3 Within this range, the filler can be incorporated with good dispersibility, and the effect of adding the filler can be fully exhibited even with a low filler content. A resin foam with a low filler content is advantageous in that it is highly foamed, flexible, and has excellent stress dispersibility and appearance. The lower limit of the bulk density of the filler is, for example, 0.01 g / cm. 3 and preferably 0.05 g / cm 3 and more preferably 0.1 g / cm3 is.

[0063] The number-average particle size (primary particle size) 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 incorporated with good dispersibility and a uniform cell structure can be formed. As a result, a resin foam with excellent stress dispersion and appearance can be obtained. The lower limit of the number-average particle size of the filler is, for example, 0.1 μm. The number-average particle size of the filler can be measured using a particle size distribution analyzer (Micrtrac II, Microtrac Bell Co., Ltd.) using a suspension prepared by mixing 1 g of filler with 100 g of water as a sample.

[0064] The specific surface area of the filler is preferably 2 m 2 / g or more, and more preferably 4m 2 / g or more, more preferably 6m 2 / g or more. Within this range, the filler can be incorporated with good dispersibility and a uniform cell 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 m 2 The specific surface area of a filler can be measured by the BET method, that is, by adsorbing molecules with known adsorption areas onto the surface of the filler at low temperatures using liquid nitrogen, and measuring the amount of adsorption.

[0065] The resin composition may contain any appropriate other components as long as the effects of the present invention are not impaired. Such other components may be present in a single type or in two or more types. Examples of such other components include rubber, resins other than the polymers blended as the resin material, softeners, aliphatic compounds, antioxidants, 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, foam nucleating agents, 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 dispersing aids.

[0066] A-2. Formation of resin foam The resin foam of the present invention is typically obtained by foaming a resin composition. The foaming method (cell formation method) can be a method typically used in foam molding, such as a physical method or a chemical method. That is, the resin foam of the present invention may typically be a foam formed by foaming using a physical method (physical foam) or a foam formed by foaming using a chemical method (chemical foam). Physical methods generally involve dispersing a gas component such as air or nitrogen in a polymer solution and mechanically mixing the resulting mixture to form cells (mechanical foam). Chemical methods generally involve forming cells using gas generated by thermal decomposition of a blowing agent added to a polymer base, thereby obtaining a foam.

[0067] The resin composition to be subjected to foam molding may be prepared, for example, by mixing the constituent components using any suitable melt-kneading device, 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.

[0068] <First embodiment of forming a resin foam of the present invention> In one embodiment 1 of forming a resin foam of the present invention, for example, a resin foam is formed through a step (Step A) of mechanically foaming an emulsion resin composition (an emulsion containing a resin material (polymer), etc.). Examples of foaming devices include high-speed shear devices, vibration devices, and pressurized gas discharge devices. Among these foaming devices, high-speed shear devices are preferred from the viewpoints of miniaturizing the cell diameter and producing a large volume of foam. This one embodiment 1 of forming a resin foam of the present invention can be applied to formation from any resin composition.

[0069] From the viewpoint of film-forming properties, the solids concentration of the emulsion is preferably high, and is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more.

[0070] The bubbles generated by mechanical stirring are gases trapped in the emulsion. Any suitable gas can be used 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.

[0071] The resin foam of the present invention can be obtained by applying the foamed emulsion resin composition (bubble-containing emulsion resin composition) to a substrate and drying it (Step B). Examples of the substrate include a release-treated plastic film (e.g., a release-treated polyethylene terephthalate film) and a plastic film (e.g., a polyethylene terephthalate film).

[0072] Any appropriate method can be used as the coating method and drying method in step B as long as the effects of the present invention are not impaired. Step B preferably includes a preliminary drying step B1 in which the bubble-containing emulsion resin composition applied to the substrate is dried at 50°C or higher and lower than 125°C, and a main drying step B2 in which the composition is further dried at 125°C or higher and 200°C or lower.

[0073] By providing the preliminary drying step B1 and the main drying step B2, it is possible to prevent bubbles from coalescing and bursting due to a sudden rise in temperature. In particular, in a foamed sheet having a small thickness, bubbles are likely to coalesce and burst due to a sudden rise in temperature, so providing the preliminary drying step B1 is significant. The temperature in the preliminary drying step B1 is preferably 50°C to 100°C. The time period for the preliminary drying step B1 is preferably 0.5 to 30 minutes, more preferably 1 to 15 minutes. The temperature in the main drying step B2 is preferably 130°C to 180°C or less, more preferably 130°C to 160°C. The time period for the main drying step B2 is preferably 0.5 to 30 minutes, more preferably 1 to 15 minutes.

[0074] <Embodiment 2 for forming resin foam of the present invention> In a second embodiment of the present invention, a resin foam is formed by foaming a resin composition with a foaming agent. The foaming agent may be one typically used in foam molding, and from the viewpoints of environmental protection and low contamination of the foamed object, it is preferable to use a high-pressure inert gas.

[0075] Any suitable inert gas can be used as the inert gas as long as it is inert to the resin composition and can be impregnated with the resin composition. Examples of such inert gases include carbon dioxide, nitrogen gas, and air. These gases may be used in combination. Among these, carbon dioxide is preferred from the viewpoints of a large amount of impregnation into the resin material (polymer) and a fast impregnation rate.

[0076] The inert gas is preferably in a supercritical state. That is, it is particularly preferable to use carbon dioxide in a supercritical state. In a supercritical state, the solubility of the inert gas in the resin composition is further increased, allowing for high concentrations of the inert gas to be mixed in. In addition, the inert gas becomes highly concentrated during a sudden pressure drop, resulting in the generation of more bubble nuclei. The density of the bubbles formed by the growth of the bubble nuclei is greater than in other states even if the porosity is the same, allowing for the production of finer bubbles. The critical temperature of carbon dioxide is 31°C, and the critical pressure is 7.4 MPa.

[0077] Examples of methods for forming a foam by impregnating a resin composition with a high-pressure inert gas include a gas impregnation step in which a resin composition containing a resin material (polymer) is impregnated with an inert gas under high pressure, a decompression step in which the pressure is reduced to foam the resin material (polymer), and a heating step in which bubbles are grown by heating, if necessary. In this case, a pre-formed unfoamed molded body may be impregnated with the inert gas, or a molten resin composition may be impregnated with the inert gas under pressure and then molded under reduced pressure. These steps may be performed using either a batch process or a continuous process. That is, a batch process may be used in which the resin composition is pre-formed into an appropriate shape, such as a sheet, to form an unfoamed resin molded body, and then the unfoamed resin molded body is impregnated with a high-pressure gas and foamed by releasing the pressure. Alternatively, a continuous process may be used in which the resin composition is kneaded with a high-pressure gas under pressure, molded, and then the pressure is released simultaneously, thereby simultaneously molding and foaming.

[0078] An example of producing a foam using the 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, the resin composition is uniformly mixed using a kneader equipped with blades such as a roller, cam, kneader, or Banbury type mixer, and then pressed to a predetermined thickness using a hot plate press or the like to produce an unfoamed resin molded body. The unfoamed resin molded body thus obtained is placed in a high-pressure container and a high-pressure inert gas (such as carbon dioxide in a supercritical state) is injected to impregnate the unfoamed resin molded body with the inert gas. Once the inert gas has sufficiently impregnated the unfoamed resin molded body, 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 or, in some cases, may be grown by heating. Heating methods that are well known or commonly used include a water bath, oil bath, heated roll, hot air oven, far infrared rays, near infrared rays, and microwaves. After the bubbles have grown in this way, the product is rapidly cooled with cold water or the like to fix the shape, thereby obtaining a foam. The unfoamed resin molded product to be foamed is not limited to a sheet-like product, and various shapes can be used depending on the application. The unfoamed resin molded product to be foamed can also be produced by other molding methods such as extrusion molding, press molding, and injection molding.

[0079] An example of continuous foam production is shown below. For example, a resin composition is kneaded using an extruder such as a single-screw extruder or a twin-screw extruder while a high-pressure gas (particularly an inert gas, or even carbon dioxide) is injected (introduced) into the resin composition to sufficiently impregnate the resin composition with the high-pressure gas in a kneading / impregnation step. The resin composition is then extruded through a die or the like at the tip of the extruder to release the pressure (usually to atmospheric pressure), and foaming and foaming are simultaneously performed in a molding / decompression step. Furthermore, continuous foam molding may optionally include a heating step in which cells are grown by heating. After the cells have grown in this manner, the cells may be rapidly cooled with cold water or the like to fix the shape, if necessary. The high-pressure gas may be introduced continuously or discontinuously. Furthermore, the kneading / impregnation step and the molding / decompression step may be performed using, for example, an extruder or an injection molding machine. Heating methods for growing cell nuclei include any appropriate method, such as a water bath, an oil bath, a heated roll, a hot air oven, far infrared rays, near infrared rays, or microwaves. The foam may have any suitable shape, such as a sheet, a prism, a cylinder, or an irregular shape.

[0080] 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 product.

[0081] The pressure when impregnating the resin composition with an inert gas can be appropriately selected taking into consideration operability and other factors. Such a pressure is, for example, preferably 6 MPa or higher (e.g., 6 MPa to 100 MPa), 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 in order to maintain the supercritical state of carbon dioxide. If the pressure is lower than 6 MPa, significant bubble growth during foaming occurs, resulting in excessively large bubble diameters, making it impossible to obtain a desirable average cell diameter (average cell diameter). This is because, at low pressures, the amount of gas impregnated is relatively small compared to high pressures, which reduces the rate of bubble nucleation and the number of formed cell nuclei. Consequently, the amount of gas per bubble increases, resulting in extremely large bubble diameters. Furthermore, at pressures lower than 6 MPa, even small changes in the impregnation pressure significantly affect the bubble diameter and cell density, making it difficult to control the bubble diameter and cell density.

[0082] The temperature in the gas impregnation step varies depending on the type of inert gas used and the types of components in the resin composition, and can be selected from a wide range. When operability and other factors are taken into consideration, the temperature is preferably 10°C to 350°C. When an unfoamed molded body is impregnated with an inert gas, the impregnation temperature is preferably 10°C to 250°C, and more preferably 40°C to 230°C, in a batch process. When the gas-impregnated molten polymer is extruded to simultaneously foam and mold, the impregnation temperature is preferably 60°C to 350°C in a continuous process. When carbon dioxide is used as the inert gas, the temperature during impregnation is preferably 32°C or higher, and more preferably 40°C or higher, in order to maintain a supercritical state.

[0083] In the depressurizing step, the depressurizing speed is preferably 5 MPa / sec to 300 MPa / sec in order to obtain uniform fine bubbles.

[0084] The heating temperature in the heating step is preferably 40°C to 250°C, and more preferably 60°C to 250°C.

[0085] B. Foam material 1 is a schematic cross-sectional view of a foam member according to one embodiment of the present invention. The foam member 100 has a resin foam layer 10 and a pressure-sensitive adhesive layer 20 disposed on at least one side of the resin foam layer 10. The resin foam layer 10 is composed of the above-mentioned resin foam.

[0086] The thickness of the pressure-sensitive adhesive layer is preferably 5 μm to 300 μm, more preferably 6 μm to 200 μm, further preferably 7 μm to 100 μm, and particularly preferably 8 μm to 50 μm. When the thickness of the pressure-sensitive adhesive layer is within the above range, the foam material of the present invention can exhibit excellent impact absorption properties.

[0087] The pressure-sensitive adhesive layer may be a layer made of any appropriate pressure-sensitive adhesive. Examples of pressure-sensitive adhesives constituting the pressure-sensitive adhesive layer include rubber-based pressure-sensitive adhesives (synthetic rubber-based pressure-sensitive adhesives, natural rubber-based pressure-sensitive adhesives, etc.), urethane-based pressure-sensitive adhesives, acrylic urethane-based pressure-sensitive adhesives, acrylic-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, polyester-based pressure-sensitive adhesives, polyamide-based pressure-sensitive adhesives, epoxy-based pressure-sensitive adhesives, vinyl alkyl ether-based pressure-sensitive adhesives, fluorine-based pressure-sensitive adhesives, and rubber-based pressure-sensitive adhesives. The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is preferably at least one selected from acrylic-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, and rubber-based pressure-sensitive adhesives. One or more types of such pressure-sensitive adhesives may be used. The pressure-sensitive adhesive layer may be a single layer or two or more layers.

[0088] Pressure-sensitive adhesives can be classified by adhesive form, for example, emulsion-type pressure-sensitive adhesives, solvent-type pressure-sensitive adhesives, ultraviolet-crosslinking (UV-crosslinking) pressure-sensitive adhesives, electron-beam-crosslinking (EB-crosslinking) pressure-sensitive adhesives, hot-melt pressure-sensitive adhesives, etc. Only one type of such pressure-sensitive adhesive may be used, or two or more types may be used.

[0089] The water vapor permeability of the adhesive layer is preferably 50 (g / (m 2 24 hours)) or less, and more preferably 30 (g / (m 2 24 hours)) or less, and more preferably 20 (g / (m 2 24 hours)) or less, and particularly preferably 10 (g / (m2 When the water vapor permeability of the pressure-sensitive adhesive layer is within the above range, the foamed sheet of the present invention can stabilize its impact absorption properties without being affected by moisture. The water vapor permeability can be measured, for example, by a method in accordance with JIS Z 0208 under test conditions of 40°C and a relative humidity of 92%.

[0090] The adhesive constituting the adhesive layer may contain any appropriate other components as long as the effects of the present invention are not impaired. Examples of other components include other polymer components, softeners, antioxidants, curing agents, plasticizers, fillers, antioxidants, thermal polymerization initiators, photopolymerization initiators, UV absorbers, light stabilizers, colorants (pigments, dyes, etc.), solvents (organic solvents), surfactants (e.g., ionic surfactants, silicone surfactants, fluorine-based surfactants, etc.), crosslinking agents (e.g., polyisocyanate-based crosslinking agents, silicone-based crosslinking agents, epoxy-based crosslinking agents, alkyl-etherified melamine-based crosslinking agents, etc.). The thermal polymerization initiator or photopolymerization initiator may be included in the material for forming the polymer component.

[0091] The foam material of the present invention can be produced by any appropriate method, such as a method of laminating a resin foam layer and a pressure-sensitive adhesive layer, or a method of laminating a pressure-sensitive adhesive layer-forming material and a resin foam layer, and then forming a pressure-sensitive adhesive layer by a curing reaction or the like. [Example]

[0092] The present invention will be specifically described below using examples, but the present invention is not limited to these examples. The test and evaluation methods used in the examples are as follows. The term "parts" means "parts by weight" unless otherwise specified, and the term "%" means "% by weight" unless otherwise specified.

[0093] <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 prepare a test piece, and the dimensions of the test piece were measured with a vernier caliper. Next, the weight of the test piece was measured with an electronic balance. Then, the apparent density was calculated using the following formula. Apparent density (g / cm 3 ) = weight of test piece / volume of test piece

[0094] (2) 25% compression load The measurement was carried out in accordance with the method for measuring the compression hardness of foams described in JIS K 6767. Specifically, the resin foams obtained in the examples and comparative examples were cut into test pieces of 30 mm × 30 mm in size, and the stress (N) when compressed at a compression rate of 10 mm / min until the compression ratio reached 25% was measured per unit area (1 cm). 2 ) per unit, 25% compressive load ( kPa ) was decided.

[0095] (3) Average bubble diameter (average cell diameter) and coefficient of variation of bubble diameter (cell diameter) The resin foam was cut with 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 enlarged images of the foam's bubbles. The image was analyzed using the instrument's analysis software to determine the number-average bubble diameter (average cell diameter) (μm). The number of bubbles in the captured enlarged image was approximately 400. The standard deviation was calculated from all 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)

[0096] (4) Bubble rate (cell rate) Measurements were carried out in an environment with a temperature of 23°C and humidity of 50%. The resin foams obtained in the Examples and Comparative Examples were punched out using a 100 mm x 100 mm punching die (two processing blades (product name "NCA07"), 0.5 mm thick, cutting edge angle 45°, manufactured by Nakayama Corporation)), and the dimensions of the punched samples were measured. The thickness was also measured using a 1 / 100 dial gauge with a measuring probe diameter (φ) of 20 mm. From these values, the volume of the resin foams obtained in the Examples and Comparative Examples was calculated. Next, the weight of the resin foams obtained in the Examples and Comparative Examples was measured using a top-loading balance with a minimum scale of 0.01 g or more. From these values, the void content (cell content) of the resin foams obtained in the Examples and Comparative Examples was calculated.

[0097] (5) Thickness of the cell wall The resin foam was cut with 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 an enlarged image of the bubble portion of the resin foam. The image was analyzed using the instrument's analysis software to determine the thickness (μm) of the bubble walls (cell walls). The number of bubbles in the captured enlarged image was approximately 400.

[0098] (6) Non-foam bending stress The resin foam was pressed using a vacuum press molding machine (IVM-70: Iwaki Kogyosha) at a temperature of (melting point + 70°C) and a pressure of 15 MPa for 5 minutes to obtain a non-foamed resin molded body a. Resin molded body a was cut into a sample with a width of 20 mm and a length of 150 mm. This sample was placed on a three-point bending jig with a support distance of 100 mm, and an indentation test (manufactured by Shimadzu Corporation, product name "AG-Xplus") was performed at an indentation speed of 5 mm / min in an environment of 23°C x 50% RH. The load (g) when the sample was indented 5 mm was taken as the non-foaming bending stress.

[0099] (7) Elastic strain energy Based on the compression test section of JIS K 6767, the compressibility (%) and compression repulsion (kPa) of the resin foam were measured, and the area enclosed by the x-axis and the compression SS curve, with the x-axis representing the compressibility and the y-axis representing the compression repulsion, where the compression ratio was 0% to 10% was calculated as the elastic strain energy.

[0100] (8) Impact absorption measurement method A test specimen was formed by placing a resin foam, double-sided tape (product number: No. 5603W, manufactured by Nitto Denko), and a PET film (product number: Diafoil MRF75, manufactured by Mitsubishi Plastics) in that order on top of an impact force sensor. A 66g iron ball was dropped onto the test specimen from a height of 50cm above the PET film to measure the impact force F1. In addition, the impact force F0 of the blank was measured by dropping an iron ball directly onto the impact force sensor as described above. The impact absorption (%) was calculated from F1 and F0 using the formula (F0-F1) / F0×100.

[0101] (9) Thickness recovery rate Resin foam, 1000g / cm 2 The load was applied and maintained for 120 seconds, the compression was released, and the thickness of the resin foam 0.5 seconds after release (thickness 0.5 seconds after release of compressed state) was measured. The thickness recovery rate was calculated from the "thickness 0.5 seconds after release of compressed state" and the thickness of the resin foam before application of the load (initial thickness) using the following formula. Thickness recovery rate (%) = {(thickness 0.5 seconds after releasing the compression state) / (initial thickness)} × 100

[0102] (10) Aspect ratio of bubbles A digital microscope (product name "VHX-2000", manufactured by Keyence Corporation) was used as a measuring instrument to measure the aspect ratio of the cells in the resin foams obtained in the examples and comparative examples by the following method. The resin foam is cut with a razor blade in the TD (direction perpendicular to the flow direction) and in the direction perpendicular to the main surface of the resin foam (thickness direction), and the cut surface is measured with a microscope (for example, Keyence VHX-2000) to obtain a predetermined area (3 mm 2 ) area was observed at a magnification of 100 times, and the length in the thickness direction and the length along the transverse direction of one bubble were measured. The same measurement was performed on all bubbles present within a given area. The aspect ratio of the bubbles is calculated by dividing the TD length by the thickness length. The same calculation was performed for all bubbles, and the average value was used as the "aspect ratio of the bubbles in the resin foam."

[0103] Example 1 65 parts by weight of polypropylene (melt flow rate (MFR) (230°C): 0.40 g / 10 min), 35 parts by weight of polyolefin elastomer (melt flow rate (MFR): 6 g / 10 min, JIS A hardness: 79°), 80 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a twin-screw mixer manufactured by Japan Steel Works (JSW) at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) under 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 being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and then extruded through a die to obtain a sheet-like resin foam a having a thickness of 1.8 mm. Furthermore, the resin foam a was passed through the gap between a pair of rolls (the gap between the rolls) of which one roll was heated to 200°C, to obtain a resin foam A having a thickness of 0.1 mm. The gap between the rolls was set so that a resin foam A having a thickness of 0.1 mm was obtained. The obtained resin foam A was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0104] Example 2 65 parts by weight of polypropylene (melt flow rate (MFR) (230°C): 0.40 g / 10 min), 35 parts by weight of polyolefin elastomer (melt flow rate (MFR): 6 g / 10 min, JIS A hardness: 79°), 80 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a twin-screw mixer manufactured by Japan Steel Works (JSW) at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a single-screw extruder manufactured by Japan Steel Works, 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 3.5 parts by weight per 100 parts by weight of resin. After being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and then extruded through a die to obtain a sheet-like resin foam b having a thickness of 1.8 mm. Furthermore, the resin foam b was passed through the gap between a pair of rolls (the gap between the rolls) of which one roll was heated to 200°C, to obtain a resin foam C having a thickness of 0.1 mm. The gap between the rolls was set so as to obtain a resin foam B having a thickness of 0.1 mm. The obtained resin foam B was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0105] Example 3 65 parts by weight of polypropylene (melt flow rate (MFR) (230°C): 0.40 g / 10 min), 35 parts by weight of polyolefin elastomer (melt flow rate (MFR): 6 g / 10 min, JIS A hardness: 79°), 120 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a twin-screw mixer manufactured by Japan Steel Works (JSW) at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) under an atmosphere of 220°C. Carbon dioxide gas was injected at a ratio of 3.0 parts by weight per 100 parts by weight of resin. After being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and then extruded through a die to obtain a sheet-like resin foam c having a thickness of 1.8 mm. Furthermore, the resin foam c was passed through the gap between a pair of rolls (the gap between the rolls) of which one roll was heated to 200°C, to obtain a resin foam C having a thickness of 0.1 mm. The gap between the rolls was set so that a resin foam C having a thickness of 0.1 mm was obtained. The obtained resin foam C was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0106] Example 4 Apparent density is 0.3g / cm 3 and the 25% compressive load is 50 kPa Resin foam D having an elastic strain energy of 26 kPa and containing polyethylene as a main component was prepared. This resin foam D was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0107] Example 5 60 parts by weight of polypropylene (melt flow rate (MFR) (230°C): 0.40 g / 10 min), 40 parts by weight of polyolefin elastomer (melt flow rate (MFR): 6 g / 10 min, JIS A hardness: 79°), 120 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a twin-screw mixer manufactured by Japan Steel Works (JSW) at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) under an atmosphere of 220°C. Carbon dioxide gas was injected at a ratio of 3.5 parts by weight per 100 parts by weight of resin. After being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and then extruded through a die to obtain a sheet-like resin foam e having a thickness of 0.6 mm. Furthermore, the resin foam e was passed through the gap between a pair of rolls (the gap between the rolls) in which one roll was heated to 200°C, to obtain a resin foam E having a thickness of 0.1 mm. The gap between the rolls was set so that a resin foam E having a thickness of 0.1 mm was obtained. The obtained resin foam E was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0108] Example 6 60 parts by weight of polypropylene (melt flow rate (MFR) (230°C): 0.40 g / 10 min), 40 parts by weight of polyolefin elastomer (melt flow rate (MFR): 6 g / 10 min, JIS A hardness: 79°), 120 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a twin-screw mixer manufactured by Japan Steel Works (JSW) at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) under an atmosphere of 220°C. Carbon dioxide gas was injected at a ratio of 4.0 parts by weight per 100 parts by weight of resin. After being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and then extruded through a die to obtain a sheet-like resin foam j with a thickness of 0.5 mm. Furthermore, the resin foam j was passed through the gap between a pair of rolls (the gap between the rolls) in which one roll was heated to 200°C, to obtain a resin foam J having a thickness of 0.1 mm. The gap between the rolls was set so that a resin foam J having a thickness of 0.1 mm was obtained. The obtained resin foam J was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0109] Comparative Example 1 16.5 parts by weight of polypropylene (melt flow rate (MFR) at 230°C: 0.40 g / 10 min), 16.5 parts by weight of polypropylene (melt flow rate (MFR) at 230°C: 1.1 g / 10 min), 67 parts by weight of polyolefin elastomer (melt flow rate (MFR) at 6 g / 10 min, JIS A hardness: 79°), 40 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a Japan Steel Works (JSW) twin-screw mixer at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a Japan Steel Works (JSW) single-screw extruder and carbon dioxide gas was injected at 13 MPa (12 MPa after injection) under a 220°C atmosphere. Carbon dioxide gas was injected at a ratio of 3 parts by weight per 100 parts by weight of the resin. After the resin was fully saturated with carbon dioxide gas, it was cooled to a temperature suitable for foaming and then extruded through a die to obtain a sheet-like resin foam f with a thickness of 1.8 mm. Furthermore, the resin foam f was passed through the gap between a pair of rolls (the gap between the rolls) in which one roll was heated to 200°C, to obtain a resin foam F having a thickness of 0.1 mm. The gap between the rolls was set so that a resin foam F having a thickness of 0.1 mm was obtained. The obtained resin foam F was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0110] Comparative Example 2 45 parts by weight of polypropylene (melt flow rate (MFR) (230°C): 0.40 g / 10 min), 55 parts by weight of polyolefin elastomer (melt flow rate (MFR): 6 g / 10 min, JIS A hardness: 79°), 10 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a Japan Steel Works (JSW) twin-screw mixer at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a Japan Steel Works (JSW) single-screw extruder 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 5.5 parts by weight per 100 parts by weight of resin. After being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and then extruded through a die to obtain a sheet-like resin foam (g) having a thickness of 2.2 mm. Furthermore, the resin foam g was passed through the gap between a pair of rolls (the gap between the rolls) of which one roll was heated to 200°C, to obtain a resin foam G having a thickness of 0.1 mm. The gap between the rolls was set so that a resin foam G having a thickness of 0.1 mm was obtained. The obtained resin foam G was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0111] Comparative Example 3 65 parts by weight of polypropylene (melt flow rate (MFR) (230°C): 0.40 g / 10 min), 35 parts by weight of polyolefin elastomer (melt flow rate (MFR): 6 g / 10 min, JIS A hardness: 79°), 80 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a twin-screw mixer manufactured by Japan Steel Works (JSW) at 200°C, extruded into strands, cooled with water, and formed into pellets. The pellets were then placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) under 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 being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming and then extruded through a die to obtain a 1.8 mm thick sheet-like resin foam (h). Resin foam (h) was then thinned to a thickness of 0.1 mm using a slicer to obtain resin foam (H). The obtained resin foam (H) was subjected to the above evaluations (1) to (10). The results are shown in Table 1.

[0112] Comparative Example 4 100 parts by weight of an acrylic emulsion solution (solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45:48:7)), 2 parts by weight of a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33%), 2 parts by weight of a carboxybetaine-type amphoteric surfactant ("Amogen CB-H", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 4 parts by weight of an oxazoline-based crosslinking agent ("Epocross WS-500", manufactured by Nippon Shokubai Co., Ltd., solid content 39%), and 1 part by weight of carbon black ("NAF-5091", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) were stirred and mixed in a Disper ("Robomix", manufactured by Primix Corporation) to generate foam. This foaming composition was applied to a release-treated PET (polyethylene terephthalate) film (thickness: 38 μm, product name "MRF#38" manufactured by Mitsubishi Plastics, Inc.) and dried at 70°C for 4.5 minutes and then at 140°C for 4.5 minutes to obtain Resin Foam I (thickness: 0.1 mm). The obtained Resin Foam I was subjected to the above-mentioned evaluations (1) to (10). The results are shown in Table 1.

[0113] [Table 1] [Industrial Applicability]

[0114] The resin foam of the present invention can be suitably used, for example, as a cushioning material for electronic devices. [Explanation of symbols]

[0115] 100 Foam material 10 Resin foam layer 20 adhesive layer

Claims

1. Apparent density is 0.02 g / cm ３ ~0.30 g / cm ３ and The 25% compressive load is 40 kPa to 90 kPa, The elastic strain energy upon compression is 26 kPa or more, The thickness is 30 μm to 500 μm, The thickness recovery rate is 65% or more. It has a cellular structure, Contains polyolefin resin, The polyolefin-based resin is a mixture of a polyolefin other than the polyolefin-based elastomer and a polyolefin-based elastomer. Resin foam.

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

3. The resin foam according to claim 1 or 2, having a foaming rate of 30% or more.

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

5. The resin foam according to claim 1 , wherein the non-foaming bending stress is 5 MPa or more.

6. The resin foam according to claim 1 , further comprising a filler.

7. The resin foam according to claim 6 , wherein the filler is an inorganic substance.

8. The resin foam according to claim 6 or 7, wherein the filler is an organic substance.

9. The resin foam according to claim 1 , which has a heat-fusible layer on one or both sides.

10. a resin foam layer and a pressure-sensitive adhesive layer disposed on at least one side of the resin foam layer; The resin foam layer is the resin foam according to any one of claims 1 to 9. Foam material.

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