Resin foam body and foam member

Abstract

Provided is a resin foam body that has excellent punching processability and suppresses dust production.　A resin foam body according to the embodiments of the present invention comprises a foam layer that has a bubble structure. The apparent density of the foam layer is at least 0.06 g / cm3, and the arithmetic average surface roughness Ra of the resin foam body is no more than 50 μm.

Description

Resin foam and foamed material

[0001] The present invention relates to a resin foam and a foam member.

[0002] Foams are often used as cushioning materials for protecting the screens, circuit boards, electronic components, and the like of electronic devices. In recent years, with the trend toward thinner electronic devices, there has been a demand for narrower clearances in areas where cushioning materials are placed. Furthermore, as electronic devices become smaller and more multifunctional, the electronic components used also tend to become smaller, which may result in a demand for smaller cushioning materials (foams).

[0003] Usually, to obtain a foam of a desired shape, a foam raw material is punched. In the punching process, a foam having a desired shape is obtained by applying high pressure to the foam using a mold. Foams to be used in places with narrow clearances are required to have excellent punching processability, in other words, to have small thickness changes due to punching.

[0004] Furthermore, in recent years, dust generation from foams during processing, partly due to the increasing complexity of processing shapes, has become a problem in some cases, and therefore foams that are excellent in punching processability and low dust generation are desired.

[0005] JP 2017-186504 A JP 2015-034299 A

[0006] An object of the present invention is to provide a resin foam that is excellent in punching processability and suppresses dust generation.

[0007] [1] A resin foam according to an embodiment of the present invention is a resin foam including a foam layer having a cell structure, wherein the apparent density of the foam layer is 0.06 g / cm ３or more, and the resin foam has an arithmetic mean surface roughness Ra of 50 μm or less. [2] In the resin foam according to [1] above, the foam layer may have an open cell ratio of 90% or less. [3] In the resin foam according to [1] or [2] above, the foam layer may have an average cell diameter of 300 μm or less. [4] In the resin foam according to any one of [1] to [3] above, the foam layer may have a coefficient of variation of cell diameter of 0.6 or less. [5] In the resin foam according to any one of [1] to [4] above, the resin foam may have a density of 1000 g / cm ２ The thickness recovery rate after maintaining a load of 0.02 mm or more for 120 seconds may be 80% or more. [6] The resin foam according to any one of [1] to [5] above may further include a surface layer on at least one side of the foam layer. [7] In the resin foam according to [6] above, the surface layer may have a single-layer thickness of 0.02 mm or more. [8] In the resin foam according to [6] or [7] above, the total thickness of the surface layer may be 5% or more of the thickness of the resin foam. [9] In the resin foam according to any one of [6] to [8] above, the ratio of the single-layer thickness of the surface layer to the foam layer thickness (thickness of foam layer / single-layer thickness of surface layer) may be 5 to 55.

[10] In the resin foam according to any one of [6] to [9] above, the surface layer may be a heat-fusible layer.

[11] In the resin foam according to any one of [1] to

[10] above, the foam layer may contain a polyolefin-based resin.

[12] In the resin foam according to the above item

[11] , the polyolefin resin may be a mixture of a polyolefin other than the polyolefin elastomer and a polyolefin elastomer.

[13] A foam material according to an embodiment of the present invention comprises the resin foam according to any one of the above items [1] to

[12] and a pressure-sensitive adhesive layer disposed on at least one side of the resin foam.

[0008] According to the present invention, it is possible to provide a foam that has excellent punching processability, exhibits little change in thickness before and after punching, and suppresses dust generation during punching and other processes.

[0009] 1 is a schematic cross-sectional view of a resin foam according to one embodiment of the present invention; 2 is a schematic cross-sectional view of a foam member according to one embodiment of the present invention;

[0010] A. Resin Foam A resin foam according to an embodiment of the present invention has an arithmetic mean surface roughness Ra of 50 μm or less on at least one surface. The resin foam includes a foam layer. The foam layer has a cell structure. Examples of the 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). Preferably, the cell structure of the resin foam is a semi-open, semi-closed cell structure. Typically, the resin foam of the present invention is obtained by foaming a resin composition. The resin composition is a composition containing at least the resin that constitutes the resin foam.

[0011] 1 is a schematic cross-sectional view of a resin foam according to one embodiment of the present invention. Resin foam 100 according to the embodiment of the present invention includes a foam layer 10 and a surface layer 20 formed on at least one surface of the foam layer. In one embodiment, the surface layer may be, for example, a heat-melting layer formed by heat-melting the foam layer.

[0012] The apparent density of the foam layer is 0.06 g / cm ３ Within this range, a resin foam having excellent punching processability, flexibility, and stress dispersibility can be obtained. Furthermore, a resin foam having reduced dust generation during punching can be obtained. The apparent density of the foam layer is preferably 0.065 g / cm. ３ More preferably, 0.07 g / cm ３ More preferably, it is 0.075 g / cm ３ More preferably, it is 0.08 g / cm ３ Within this range, the above-mentioned effects are remarkable. The apparent density of the foamed layer is preferably 0.4 g / cm. ３ or less, more preferably 0.2 g / cm ３ or less, more preferably 0.1 g / cm ３The foaming property can be judged by the apparent density. The method for measuring the apparent density will be described later.

[0013] In one embodiment, the resin foam has a tensile strength of 0.5 MPa or more. Within this range, a resin foam can be obtained that exhibits excellent shape retention during punching. Furthermore, a resin foam that suppresses dust generation during punching can be obtained. The tensile strength of the resin foam is preferably 0.7 MPa or more, more preferably 1.0 MPa or more, even more preferably 1.2 MPa or more, and particularly preferably 1.3 MPa or more. Within this range, the above-described effects become significant. Furthermore, the tensile strength of the resin foam is preferably 6 MPa or less, more preferably 3 MPa or less. The tensile strength can be measured by subjecting a dumbbell-shaped No. 1 sample defined in JIS K6251 4.1 to a tensile test in accordance with JIS K6767 (measurement temperature: 23°C, chuck distance: 10 mm, tensile speed: 500 mm / min).

[0014] In one embodiment, the 50% compression load of the resin foam is 20 N / cm ２ Within this range, a resin foam having favorable flexibility and excellent punching processability can be obtained. The 50% compression load of the resin foam is preferably 15 N / cm or less. ２ More preferably, 12 N / cm or less. ２ and more preferably 10 N / cm or less. ２ More preferably, it is 8 N / cm or less. ２ and particularly preferably 5 N / cm ２ and most preferably 3 N / cm ２ Within this range, the above-mentioned effects are significant. The lower limit of the 50% compressive 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 compression rate of 50% per unit area (1 cm ２ ) converted into

[0015] As described above, the resin foam has an arithmetic mean surface roughness Ra of at least one surface of 50 μm or less. Within this range, a resin foam with reduced dust generation can be obtained. The arithmetic mean surface roughness Ra of the resin foam is preferably 40 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, particularly preferably 10 μm or less, and most preferably 7 μm or less. Within this range, the above-mentioned effects become more pronounced. Furthermore, the lower limit of the arithmetic mean surface roughness Ra of the surface layer is, for example, 1 μm. The arithmetic mean surface roughness Ra of the resin foam can be adjusted by the composition of the resin constituting the resin foam and the surface layer formation conditions (temperature, etc.) described below. The arithmetic mean surface roughness Ra can be measured in accordance with JIS B 0601 (1994).

[0016] In an embodiment of the present invention, by setting the apparent density of the foam layer within the above range (preferably, further setting the tensile strength and / or 50% compression load of the resin foam within the above range), a resin foam having favorable flexibility and excellent punchability can be obtained. More specifically, the resin foam exhibits favorable behavior, such as minimal change in shape (e.g., thickness) when punched, and recovers its thickness quickly even when temporarily reduced by punching, resulting in excellent punchability. The resin foam is also advantageous in that it exhibits the above-described excellent punchability even when configured to be thick. By using the above configuration and further setting the arithmetic mean surface roughness Ra of the resin foam within the above range, dust generation can be suppressed. An embodiment of the present invention is particularly advantageous in that dust generation is suppressed even in a thick resin foam. For example, the resin foam according to an embodiment of the present invention can prevent dust generation due to breakage of the resin foam when the resin foam is temporarily fixed to an adhesive sheet and then peeled off. Examples of the adhesive sheet include carrier sheets used for storing and transporting resin foams, foam members described below, and the like.

[0017] In one embodiment, the surface layer has an arithmetic mean surface roughness Ra of 50 μm or less. Forming the surface layer facilitates adjustment of the arithmetic mean surface roughness Ra of the resin foam, and also significantly reduces dust generation. The arithmetic mean surface roughness Ra of the surface layer is preferably 40 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, particularly preferably 10 μm or less, and most preferably 7 μm or less. The lower limit of the arithmetic mean surface roughness Ra of the surface layer is, for example, 1 μm.

[0018] In one embodiment, the resin foam described above can be formed by using a resin having a die swell ratio of 1.4 or less at a melting point (the melting point of the resin constituting the resin foam) + 20°C as the resin constituting the resin foam (foam layer). That is, in one embodiment, the die swell ratio of the resin forming the resin foam (foam layer) at a melting point + 20°C before foaming is 1.4 or less. Using a resin with a die swell ratio within the above range prevents shrinkage during resin foam formation, allowing for the formation of a thick resin foam (foam layer), which may contain small bubbles. The die swell ratio of the resin forming the resin foam (foam layer) at a melting point + 20°C before foaming is preferably 1.2 or less, more preferably 1.1 or less. The lower limit of the die swell ratio of the 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 a 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 resin (after foaming) is, for example, 1.05 (preferably 1.02, more preferably 1.01). In this specification, the die swell ratio refers to the value obtained by dividing the diameter of the resin extruded from a die in a molten state by the diameter of the die. The die swell ratio is calculated by extruding a resin molten at a 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, measuring the diameter of the resulting string-like molded product, and then calculating the ratio using the formula: molded product diameter (mm) / die diameter (mm). 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) is measured using a differential scanning calorimeter (for example, product name "Q-2000" manufactured by TA Instruments) under the conditions of a sample weight of 3 mg and a heating rate of 10°C / min. When two or more peaks are present, the peak top temperature on the higher side is taken as the melting point.

[0019] In one embodiment, the resin foam (foam layer) described above can be formed by using a resin having a shear viscosity of 3000 Pa·s or less at a melting point (the melting point of the resin constituting the resin foam) + 20°C. That is, in one embodiment, the shear viscosity of the resin forming the resin foam (foam layer) at a melting point + 20°C before foaming is 3000 Pa·s or less. Using a resin with a shear viscosity within the above range allows the gas used to form the cell structure during resin foam formation to be favorably dispersed, resulting in a foam layer with small cell sizes. The shear viscosity of the resin forming the resin foam (foam layer) at a melting point + 20°C 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 resin (before foaming) is, for example, 500 Pa·s (preferably 700 Pa·s, more preferably 1000 Pa·s). The shear viscosity of the resin constituting the resin foam (i.e., the resin after foaming) at a melting point of +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 resin (after foaming) is, for example, 500 Pa·s (preferably 700 Pa·s, more preferably 1000 Pa·s). Herein, the shear viscosity can be measured by extruding a resin molten at a melting point of +20°C using a die having a length of 10 mm and a diameter of 1 mm at a shear rate of 20 mm / s.

[0020] The thickness of the resin foam is preferably 70 μm or more, more preferably 100 μm or more, more preferably 200 μm or more, even more preferably 300 μm or more, and particularly preferably 400 μm or more. The thickness of the resin foam is preferably 8000 μm or less, more preferably 4000 μm or less, even more preferably 3000 μm or less, and particularly preferably 2000 μm or less. A thickness within this range is advantageous in that excellent punching processability and impact absorption properties can be achieved.

[0021] The thickness of the foam layer is preferably 50 μm or more, more preferably 100 μm or more, even more preferably 150 μm or more, even more preferably 200 μm or more, and particularly preferably 250 μm or more. The thickness of the foam layer is preferably 7500 μm or less, more preferably 3500 μm or less, and even more preferably 1000 μm or less. A thickness within this range is advantageous in that a fine and uniform cell structure can be formed, and excellent punching processability and impact absorption properties can be achieved.

[0022] The cell density of the foam layer is preferably 30 cells / mm ２ More preferably, 50 pieces / mm ２ More preferably, 70 pieces / mm ２ More preferably, 80 pieces / mm ２ More preferably, 90 pieces / mm ２ More preferably, 100 pieces / mm ２ More preferably, it is 110 pieces / mm ２ That is all. Within this range, the above-mentioned effects become more pronounced. Furthermore, the higher the cell density, the easier it is to store energy when compressed, and a resin foam with excellent compression recovery can be obtained. Such a resin foam has excellent punching processability. Furthermore, the cell density of the foam layer is preferably 400 cells / mm ２ More preferably, 200 pieces / mm ２ More preferably, it is 150 pieces / mm or less. ２ and particularly preferably 130 pieces / mm２ The cell number density of the foam layer is the cell number density in a cross section of the foam layer observed in a randomly selected cross section, and can be determined by image analysis of the cross section of the foam layer.

[0023] The average bubble diameter (average cell diameter) in the foam layer is preferably 300 μm or less, more preferably 250 μm or less, more preferably 200 μm or less, more preferably 180 μm or less, even more preferably 150 μm or less, even more preferably 100 μm or less, and particularly preferably 80 μm or less. Furthermore, the average bubble diameter (average cell diameter) is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more. Within these ranges, a resin foam having excellent flexibility and stress dispersibility can be obtained. Furthermore, a resin foam having excellent compression recovery, punching processability, and resistance to repeated impacts can be obtained. The method for measuring the average bubble diameter will be described later.

[0024] The coefficient of variation of the cell diameter in the foam layer is preferably 0.6 or less, more preferably 0.55 or less, more preferably 0.50 or less, more preferably 0.45 or less, more preferably 0.40 or less, more preferably 0.30 or less, even more preferably 0.25 or less, and particularly preferably 0.20 or less. Within these ranges, a resin foam can be obtained that exhibits minimal variation in cell deformation when subjected to compressive force, such as by punching. Such a resin foam can produce a processed product (cut product) with excellent thickness accuracy, for example, when punched. Furthermore, when the coefficient of variation of the cell diameter is within the above range, deformation due to impact is uniform, localized stress load is prevented, and a resin foam with excellent stress dispersibility and particularly excellent impact resistance can be obtained. The smaller the coefficient of variation, the more preferable it is, with the lower limit being, for example, 0.15 (preferably 0.1, more preferably 0.01). A method for measuring the coefficient of variation of the cell diameter will be described later.

[0025] The foam layer 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 having appropriate flexibility can be obtained. Such a resin foam has excellent punching processability and prevents the occurrence of residual cuts when punched. The upper limit of the cellular content is, for example, 99% or less. The method for measuring the cellular content will be described later.

[0026] The thickness of the cell walls of the foam layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. The thickness of the cell walls of the foam layer is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. Within these ranges, a resin foam having appropriate strength can be obtained. Such a resin foam has excellent punching processability and prevents tearing, dust generation, and residual cutting during punching. Furthermore, a cell wall thickness within the above range can provide a resin foam with superior flexibility and stress dispersion. The cell wall thickness can be measured by capturing an enlarged image of the cell portion of the resin foam and analyzing the image using the instrument's analysis software.

[0027] When the foam layer has a semi-open, semi-closed cell structure, the proportion of closed cell structures therein is preferably greater than 10% by volume, more preferably greater than 40% by volume. In this specification, the proportion of closed cell structures in the foam layer 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 thereafter, and then thoroughly drying the object in an oven at 80°C, followed by measuring the mass again. Furthermore, since open cells can retain moisture, the mass of the open cells is measured and determined.

[0028] The open cell ratio of the foam layer is preferably 90% by volume or less, more preferably 70% by volume or less, and even more preferably 60% by volume or less. Within such a range, a resin foam with reduced dust generation can be obtained. Furthermore, a resin foam with excellent punching processability can be obtained. Furthermore, the open cell ratio of the foam layer is preferably 10% by volume or more, and more preferably 20% by volume or more.

[0029] The impact absorption of the 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. Impact absorption is measured as follows: A test specimen was formed by placing the 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 this order on an impact force sensor. A 66 g iron ball was dropped onto the test specimen from a height of 50 cm above the PET film to measure the impact force F1. Furthermore, the iron ball was dropped directly onto the impact force sensor as described above to measure the impact force F0 of the blank. Impact absorption (%) was calculated from F1 and F0 using the formula (F0 - F1) / F0 x 100.

[0030] The resin foam is applied with 1000 g / cm ２ The thickness recovery rate after maintaining the applied load for 120 seconds is preferably 80% or more, more preferably 85% or more, more preferably 87% or more, even more preferably 90% or more, even more preferably 92% or more, and particularly preferably 95% or more. Within such a range, excellent punching processability is achieved. The higher the thickness recovery rate, the better, but the upper limit is, for example, 99% (preferably 100%). The method for measuring the thickness recovery rate will be described later.

[0031] The thickness recovery rate after processing of the resin foam is preferably 80% or more, more preferably 85% or more, more preferably 87% or more, even more preferably 90% or more, even more preferably 92% or more, and particularly preferably 95% or more. Within such a range, excellent punching processability is achieved. The higher the thickness recovery rate after processing of the resin foam, the more preferable it is, and the upper limit is, for example, 99%. In this specification, the thickness recovery rate after processing of the resin foam is the thickness recovery rate calculated from the thickness of the end and center of the punched piece when the resin foam is punched into a 10 mm square piece by the formula [100 × (1 - (center thickness - end thickness) / center thickness)].

[0032] The resin foam may have any suitable shape depending on the purpose, and a typical example of such a shape is a sheet.

[0033] As described above, in one embodiment, the surface layer may be a heat-melting layer formed by heat-melting the foam layer. A resin foam having a heat-melting layer can be obtained, for example, by rolling the foam layer (or a precursor of the foam layer (foam structure)) 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.

[0034] The single layer thickness of the surface layer is preferably 0.015 mm or more, more preferably 0.02 mm or more, more preferably 0.022 mm or more, and even more preferably 0.025 mm or more. Within this range, a resin foam with particularly suppressed dust generation can be obtained. Furthermore, the single layer thickness of the surface layer is preferably 5 mm or less, more preferably 2 mm or less, even more preferably 1 mm or less, even more preferably 0.5 mm or less, and even more preferably 0.2 mm or less. Within this range, a resin foam with excellent impact absorption can be obtained.

[0035] When the surface layer is formed on both sides of the foam layer, the total thickness of the surface layer is preferably 0.03 mm or more, more preferably 0.04 mm or more, more preferably 0.045 mm or more, and even more preferably 0.05 mm or more. Within this range, a resin foam with particularly suppressed dust generation can be obtained. Furthermore, the total thickness of the surface layer is preferably 10 mm or less, more preferably 4 mm or less, even more preferably 2 mm or less, even more preferably 1 mm or less, and even more preferably 0.4 mm or less. Within this range, a resin foam with excellent impact absorption can be obtained.

[0036] The ratio of the single layer thickness of the surface layer to the foam layer thickness (thickness of foam layer / single layer thickness of surface layer) is preferably 55 or less, more preferably 50 or less, even more preferably 45 or less, and even more preferably 40 or less. Within this range, a resin foam having excellent impact absorption and excellent punching processability can be obtained. The ratio of the single layer thickness of the surface layer to the foam layer thickness (thickness of foam layer / single layer thickness of surface layer) is preferably 5 or more, more preferably 8 or more, even more preferably 10 or more, even more preferably 12 or more, even more preferably 15 or more, even more preferably 20 or more, even more preferably 22 or more, even more preferably 25 or more, and even more preferably 30 or more. Within this range, a resin foam having particularly suppressed dust generation can be obtained.

[0037] The total thickness of the surface layer is preferably 5% or more, more preferably 8% or more, and even more preferably 9% or more, relative to the thickness of the resin foam. Within this range, a resin foam in which dust generation is particularly suppressed can be obtained. The total thickness of the surface layer is preferably 85% or less, more preferably 80% or less, even more preferably 70% or less, even more preferably 50% or less, even more preferably 30% or less, and even more preferably 20% or less, relative to the thickness of the resin foam. Within this range, a resin foam with excellent impact absorption properties and excellent punching processability can be obtained.

[0038] The average bubble diameter (average cell diameter) in the surface layer is preferably 80 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less.

[0039] The ratio of the average cell diameter (average cell diameter) of the foam layer to the average cell diameter (average cell diameter) of the surface layer (average cell diameter of foam layer / average cell diameter of surface layer) is preferably 1.1 or more, more preferably 1.3 or more, even more preferably 1.5 or more, even more preferably 1.8 or more, even more preferably 2 or more, and even more preferably 2.5 or more. Within this range, a resin foam with particularly suppressed dust generation can be obtained. The ratio of the average cell diameter (average cell diameter) of the foam layer to the average cell diameter (average cell diameter) of the surface layer (average cell diameter of foam layer / average cell diameter of surface layer) is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Within this range, a resin foam with particularly suppressed dust generation can be obtained. In addition, generally, the smaller the cell diameter of the foam layer, the more suppressed dust generation. However, if the cell diameter of the foam layer is too small, the cell wall thickness will be thin, and the interlayer strength of the foam layer will be weakened, which may make it difficult to suppress dust generation. From this viewpoint, it is also preferable that the size of the cell diameter is within the above-mentioned preferred range, and that the ratio of the cell diameter in the foamed layer to the cell diameter in the surface layer is within the above-mentioned specific range.

[0040] The cellular content of the surface layer is preferably 30% or less, more preferably 20% or less, even more preferably 10% or less, particularly preferably 5% or less, and most preferably 0%. Within such a range, a resin foam with particularly suppressed dust generation can be obtained.

[0041] The ratio of the cellular content of the surface layer to the cellular content of the foamed layer (cellular content of the surface layer / cellular content of the foamed layer) is preferably 0.1 or less, more preferably 0.08 or less, and even more preferably 0.05 or less. Within this range, a resin foam with particularly suppressed dust generation can be obtained.

[0042] The ratio of the foam content of the foam layer to the foam content of the surface layer (foam content of foam layer / foam content of surface layer) is preferably 1.5 or more, more preferably 2.0 or more, more preferably 5 or more, more preferably 7 or more, even more preferably 10 or more, even more preferably 12.5 or more, even more preferably 15 or more, and even more preferably 20 or more. Within this range, a resin foam with particularly suppressed dust generation can be obtained. The ratio of the foam content of the foam layer to the foam content of the surface layer (foam content of foam layer / foam content of surface layer) is preferably 50 or less, more preferably 45 or less, and even more preferably 40 or less. Within this range, a resin foam with particularly suppressed dust generation can be obtained.

[0043] The resin foam can be formed by any suitable 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).

[0044] A-1. Resin Composition The foam layer can typically be obtained by foaming a resin composition. The resin composition contains any appropriate resin material (polymer).

[0045] 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.

[0046] 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, relative to 100 parts by weight of the resin composition. Within such ranges, a resin foam having superior flexibility and stress dispersibility can be obtained.

[0047] In one embodiment, a polyolefin resin is used as the polymer.

[0048] 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.

[0049] 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."

[0050] When a polyolefin and a polyolefin elastomer are used in combination as the polyolefin resin, the weight ratio of the polyolefin to the polyolefin elastomer (polyolefin / polyolefin 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 the polyolefin to the polyolefin elastomer (polyolefin / polyolefin elastomer) is preferably 25 / 75 to 75 / 25, more preferably 35 / 65 to 65 / 35. Within this range, a resin foam can be obtained that has excellent compression recovery, is suppressed in shape change (particularly thickness change) before and after punching, has appropriate strength, and is excellent in punching processability.

[0051] 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 50 to 80 parts by weight, per 100 parts by weight of the polyolefin.

[0052] 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.

[0053] Examples of α-olefins that can constitute polyolefins include 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.). Only one type of α-olefin may be used, or two or more types may be used.

[0054] Examples of the monomer other than α-olefin constituting the polyolefin include ethylenically unsaturated monomers such as vinyl acetate, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, vinyl alcohol, etc. The monomer other than α-olefin may be one type only, or two or more types may be used.

[0055] 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.

[0056] 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.

[0057] 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 further exhibit the effects of the present invention. Note that, 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 (21.2 N) in accordance with 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.

[0058] 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 these ranges, 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 these ranges, 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).

[0059] As the polyolefin, commercially available products may be used, for example, "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).

[0060] Any appropriate polyolefin elastomer may be used as the polyolefin elastomer 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; and dynamically crosslinked thermoplastic olefin elastomers (TPVs) 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 which have a sea-island structure in which crosslinked rubber particles are finely dispersed as domains (island phases) in the resin component A that forms a matrix (sea phase).

[0061] The polyolefin-based elastomer preferably contains a rubber component. 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.

[0062] 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.

[0063] Dynamically crosslinked thermoplastic olefin elastomers (TPVs) generally have a higher elastic modulus and a smaller compression set than non-crosslinked thermoplastic olefin elastomers (TPOs), which results in good recovery properties and allows the formation of resin foams with excellent recovery properties.

[0064] As described above, a dynamically crosslinked thermoplastic olefin-based elastomer (TPV) is obtained by dynamically heat-treating a mixture containing a resin component A (olefin-based resin component A) that forms a matrix and a rubber component B that forms domains in the presence of a crosslinking agent, and is a multiphase polymer having 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).

[0065] Examples of dynamically crosslinked thermoplastic olefin-based elastomers (TPVs) include those described in 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.

[0066] As the dynamically crosslinked thermoplastic olefin-based elastomer (TPV), commercially available products may be used, such as "Zeotherm" (manufactured by Zeon Corporation), "Thermorun" (manufactured by Mitsubishi Chemical Corporation), and "Sarlink 3245D" (manufactured by Toyobo Co., Ltd.).

[0067] 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 constituting the foamed layer are controlled by the melt flow rate of the polyolefin elastomer.

[0068] In one embodiment, two or more polyolefin elastomers having different melt flow rates (MFR) 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 of preferably 1.5 g / 10 min or more and less than 8 g / 10 min (more preferably 2 g / 10 min to 5 g / 10 min) can be used in combination with a polyolefin elastomer (high MFR polyolefin elastomer) having a melt flow rate (MFR) at 230°C of preferably 8 g / 10 min to 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). In this way, the melt tension of the polyolefin elastomer can be preferably adjusted, resulting in remarkable effects of the present invention.

[0069] 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 such a range, the melt tension of the polyolefin elastomer can be suitably adjusted, resulting in remarkable effects of the present invention.

[0070] The melt tension (at 190°C at break) of the polyolefin elastomer is preferably less than 10 cN, more preferably 5 cN to 9.5 cN. In one embodiment, the die swelling ratio and shear viscosity of the polyolefin elastomer constituting the foam layer are controlled by the melt tension of the polyolefin elastomer.

[0071] 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 ISO 7619 (JIS K6253).

[0072] In one embodiment, the foam layer (i.e., the resin composition) may further contain a filler. By incorporating a filler, a foam layer can be formed that requires a large amount of energy to deform the cell walls, and the foam layer exhibits excellent impact absorption. Furthermore, by incorporating a filler, a fine and uniform cell structure can be formed, which is advantageous in that excellent impact absorption can be achieved. Only one type of filler may be used alone, or two or more types may be used in combination.

[0073] 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 foam layer. Within such a range, the above-mentioned effects become significant.

[0074] 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.

[0075] In one embodiment, the filler is an organic substance. Examples of materials constituting the organic filler include polymethyl methacrylate (PMMA), polyimide, polyamide-imide, polyether ether ketone, polyether-imide, and polyester-imide.

[0076] 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.

[0077] 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.

[0078] The filler may be subjected to any suitable surface treatment, such as silane coupling treatment or stearic acid treatment.

[0079] 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 contained with good dispersibility, and the effect of adding the filler can be fully exerted even with a low filler content. A foamed layer with a low filler content is advantageous in that it is highly foamed, flexible, and has excellent stress dispersion 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 / cm ３ is.

[0080] 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 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 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 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.

[0081] The specific surface area of ​​the filler is preferably 2 m ２ / g or more, more preferably 4m ２ / g or more, and 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 ​​the 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.

[0082] The resin composition may contain any appropriate other component 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.

[0083] A-2. Formation of Resin Foam The resin foam of the present invention is typically obtained by foaming a resin composition. Furthermore, a resin foam having a surface layer can be obtained by forming a surface layer on a foam layer (or a precursor of the foam layer (foam structure)) obtained by foaming a resin composition using any appropriate method. 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 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 into a polymer solution and mechanically mixing to form bubbles (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.

[0084] 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 non-open-type Banbury mixer, a single-screw extruder, a twin-screw extruder, a continuous kneader, or a pressure kneader.

[0085] <Embodiment 1 for Forming a Resin Foam (Foam Layer)> One embodiment 1 for forming a resin foam (foam layer) includes, for example, a form in which a resin foam (foam layer) is formed through a step (step A) of mechanically foaming an emulsion resin composition (an emulsion containing a resin material (polymer) or the like). 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 viewpoint of reducing the bubble diameter and producing a large volume. This embodiment 1 for forming a resin foam (foam layer) can be applied to formation from any resin composition.

[0086] From the viewpoint of film-forming properties, the solids concentration of the emulsion is preferably high, and the solids 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.

[0087] 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.

[0088] The foamed emulsion resin composition (bubble-containing emulsion resin composition) is applied to a substrate and dried (Step B), thereby obtaining a resin foam (foam layer). 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).

[0089] 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 bubble-containing emulsion resin composition is further dried at 125°C or higher and 200°C or lower.

[0090] By providing the preliminary drying step B1 and the main drying step B2, it is possible to prevent bubble coalescence and bubble burst due to a sudden rise in temperature. The preliminary drying step B1 is particularly significant in a foamed sheet with a small thickness, since a sudden rise in temperature can cause bubbles to coalesce and burst. The temperature in the preliminary drying step B1 is preferably 50°C to 100°C. The duration of 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 duration of the main drying step B2 is preferably 0.5 to 30 minutes, more preferably 1 to 15 minutes.

[0091]

[0033] <Embodiment 2 for Forming a Resin Foam (Foam Layer)> In one embodiment 2 for forming a resin foam (foam layer), a foam is formed by foaming a resin composition with a foaming agent. As the foaming agent, a foam that is commonly used in foam molding can be used, and from the viewpoints of environmental protection and low contamination of the foamed object, it is preferable to use a high-pressure inert gas.

[0092] 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. 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.

[0093] 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 increased generation of 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, so that fine bubbles can be obtained. The critical temperature of carbon dioxide is 31°C and the critical pressure is 7.4 MPa.

[0094] 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.

[0095] 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 kneaded using a kneader equipped with blades such as a roller, cam, kneader, or Banbury type, 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 can be used include known and conventional methods such as 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.

[0096] 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 injecting (introducing) a high-pressure gas (particularly an inert gas, or even carbon dioxide) 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.

[0097] 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 (foam layer).

[0098] The pressure when impregnating the resin composition with an inert gas can be appropriately selected taking into consideration operability, etc. Such a pressure is, for example, preferably 6 MPa or more (e.g., 6 MPa to 100 MPa), more preferably 8 MPa or more (e.g., 8 MPa to 50 MPa). When using carbon dioxide in a supercritical state, the pressure is preferably 7.4 MPa or more 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, the bubble diameter becomes too large, and a desirable average cell diameter (average cell diameter) may not be obtained. This is because, at low pressures, the amount of gas impregnated is relatively small compared to high pressures, the rate of bubble nucleation decreases, and the number of bubble nuclei formed decreases. Consequently, the amount of gas per bubble increases, resulting in an extremely large bubble diameter. Furthermore, in pressure regions lower than 6 MPa, even a small change in impregnation pressure significantly changes the bubble diameter and cell density, making it difficult to control the bubble diameter and cell density.

[0099] 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.

[0100] In the depressurizing step, the depressurizing speed is preferably 5 MPa / sec to 300 MPa / sec in order to obtain uniform fine bubbles.

[0101] The heating temperature in the heating step is preferably 40°C to 250°C, more preferably 60°C to 250°C.

[0102] In one embodiment, after obtaining a foamed structure through a predetermined process (e.g., after obtaining a foamed layer by the method of <Embodiment 1> or <Embodiment 2>), the foamed structure is rolled to obtain a resin foam having a surface layer. The foamed structure may be thinned before roll rolling. By undergoing such a process, a resin foam having an appropriately adjusted aspect ratio can be obtained. Furthermore, a resin foam having a small thickness (e.g., 0.2 mm or less) can be obtained. Furthermore, the surface layer (thermally fusible layer) can also be formed by the roll rolling.

[0103] The foam structure can be thinned using any appropriate slicer. The thickness of the foam structure after thinning is preferably 0.18 mm to 1 mm, more preferably 0.2 mm to 0.8 mm, and even more preferably 0.3 mm to 0.7 mm.

[0104] Preferably, the roll used in the rolling is a heated roll. The temperature of the roll is preferably 150° C. to 250° C., more preferably 160° C. to 230° C. If the temperature is within this range, a resin foam having a preferable surface layer formed thereon can be obtained.

[0105] The rolling ratio of the foamed 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 such a range, a resin foam having a preferable surface layer formed thereon can be obtained.

[0106] B. Foam Member Fig. 2 is a schematic cross-sectional view of a foam member according to one embodiment. Foam member 200 includes resin foam 100 and a pressure-sensitive adhesive layer 110 disposed on at least one side of resin foam 100.

[0107] The thickness of the pressure-sensitive adhesive layer is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 7 μm or more, and particularly preferably 8 μm or more. The thickness of the pressure-sensitive adhesive layer is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and most preferably 50 μm or less. 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.

[0108] 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. Only one type of such pressure-sensitive adhesive may be used, or two or more types may be used. The pressure-sensitive adhesive layer may be a single layer, or two or more layers.

[0109] 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.

[0110] The water vapor permeability of the pressure-sensitive 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 / (m ２When the water vapor permeability of the pressure-sensitive adhesive layer is within the above range, the foam sheet can stabilize its impact absorption properties without being affected by moisture. The water vapor permeability can be measured, for example, according to JIS Z 0208 under test conditions of 40°C and a relative humidity of 92%.

[0111] 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.

[0112] The foam material can be produced by any appropriate method, such as a method of laminating a resin foam and a pressure-sensitive adhesive layer, or a method of laminating a material for forming a pressure-sensitive adhesive layer and a resin foam and then forming a pressure-sensitive adhesive layer by a curing reaction or the like.

[0113] 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.

[0114] <Evaluation Method> (1) Apparent Density The density (apparent density) of the foam layer was calculated as follows. The foam layer of 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 (g / cm) was calculated using the following formula. ３ ) = weight of test piece / volume of test piece

[0115] (2) 50% Compression Load: This was measured in accordance with the method for measuring the compression hardness of resin 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 x 30 mm in size, and the stress (N) when compressed to a compression rate of 50% at a compression rate of 10 mm / min was measured per unit area (1 cm). ２ ) and converted to a 50% compression load (N / cm ２ )

[0116] (3) Average bubble diameter (average cell diameter) and coefficient of variation of bubble diameter (cell diameter) A 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 (trade name "VHX-500", manufactured by Keyence Corporation) was used as a measuring instrument to capture an image of the cross section of the resin foam. The image was analyzed using the instrument's analysis software to determine the number-average bubble diameter (average cell diameter) (μm) of the foam layer and surface layer. 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)

[0117] (4) Porosity (cell ratio) 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 observed using a digital microscope (product name "VHX-500", manufactured by Keyence Corporation) as a measuring instrument. The image was binarized using image processing software (WinROOF, manufactured by Mitani Shoji Co., Ltd.), and the porosity (porosity area ratio) of the foam layer and the surface layer was calculated using the following formula. The number of porosity in the imported enlarged image was about 400. Porosity (porosity area ratio) (%) = porosity area / total area

[0118] (5) Open Cell Ratio The foam layer was submerged in water at a temperature of 23°C and a humidity of 50%, and then the weight was measured. After that, the foam layer was thoroughly dried in an oven at 80°C, and the weight was measured again. The volume of the open cells was calculated from the water content obtained by the weight measurement, and further, the volume ratio of the open cells to the volume of the foam layer (open cell ratio) was calculated.

[0119] (6) Post-Processing Recovery Rate of Resin Foam (Punching Processability) A resin foam was punched in the MD (flow direction) and TD (direction perpendicular to the flow direction) using a mold (two processing blades (trade name "NCA07", thickness 0.7 mm, cutting edge angle 43°, spacing between the two processing blades 10 mm, manufactured by Nakayama Corporation)) to a size of 10 mm x 10 mm, and the cross section in the MD and TD directions where the thickness change was greater was observed with a microscope (trade name "VHX-2000", manufactured by Keyence Corporation), and the thicknesses of the end and center were measured from the image. Using the measured thickness, the post-processing thickness recovery rate was calculated using the following formula. The higher the thickness recovery rate, the smaller the shape change due to punching and the more excellent the punching processability. Post-Processing Thickness Recovery Rate (%) = 100 x (1 - (Center Thickness - End Thickness) / Center Thickness)

[0120] (7) Thickness recovery rate (instantaneous recovery rate) 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 the release (thickness 0.5 seconds after the compressed state was released) was measured. The thickness recovery rate (instantaneous recovery rate) was calculated from the "thickness 0.5 seconds after the compressed state 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 the compressed state was released) / (initial thickness)} × 100

[0121] (8) Carrier Tape Pickup Property After storing a resin foam (width: 10 mm x length: 120 mm) for 24 hours or more under an atmosphere of temperature: 23 ± 2 ° C. and humidity: 50 ± 5 RH% (pretreatment conditions conforming to JIS Z 0237), it was fixed to a silicone-treated release paper using a double-sided adhesive tape (trade name "No. 5603" manufactured by Nitto Denko Corporation, double-sided adhesive tape with substrate, substrate: PET substrate) with a width: 10 mm x length: 120 mm, and pressed with a 2 kg roller once back and forth so that the opposite side of the foam was in contact with the adhesive layer surface of a low-adhesion carrier tape (trade name "3164S" manufactured by Kern Co., Ltd.). The sample was then left for 24 hours to prepare a measurement sample. If the carrier tape of the measurement sample could be lifted by hand, the pickup property was evaluated as "pass" (○); if the carrier tape peeled off and could not be lifted, the pickup property was evaluated as "fail" (×).

[0122] (9) Carrier Tape Processability After storing a resin foam (width: 10 mm x length: 120 mm) for 24 hours or more under an atmosphere of temperature: 23 ± 2 ° C. and humidity: 50 ± 5 RH% (pretreatment conditions conforming to JIS Z 0237), it was fixed to a SUS plate using a double-sided adhesive tape (product name "No. 5603" manufactured by Nitto Denko Corporation) with a width of 10 mm x length of 120 mm, and pressed with a 2 kg roller once back and forth so that the opposite side of the resin foam was in contact with the adhesive layer surface of a weak adhesive carrier tape (product name "3165S" manufactured by Kern Co., Ltd.). The tape was then left for 24 hours to prepare a measurement sample. The carrier tape was quickly peeled off by hand, and the state of peeling was visually confirmed to evaluate whether or not surface damage had occurred on the foam. In Table 1, cases where there was no surface damage to the resin foam were marked as "pass" (○), and cases where there was surface damage to the resin foam were marked as "fail" (×). In addition, cases where there was no surface damage to the resin foam in the above evaluation and the evaluation was "○", and there was no damage to the foam layer of the resin foam when measured in the same manner as above using a strong adhesive carrier tape (product name "3166S", manufactured by Kern Co., Ltd.), were marked as "pass" (◎).

[0123] (10) Arithmetic Mean Surface Roughness Ra The arithmetic mean roughness Ra of the resin foam was measured in accordance with JIS B 0601 (1994). The measurement conditions were as follows: Measuring device: Confocal laser microscope (Model: LEXT OLS5000, manufactured by Olympus Corporation) Settings: High precision setting Objective lens: 10x magnification Evaluation length: 1279 μm Filter: Gaussian filter Cutoff: λc = 80.000 μm, λs = none, λf = none

[0124] (11) Tensile Strength The resin foam was cut into a dumbbell shape No. 1 as specified in JIS K6251 4.1. Using this as a sample, the tensile strength in the TD direction was measured at a measurement temperature of 23°C in accordance with JIS K6767.

[0125] Example 1 Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230°C, load 21.2 N), density: 0.90 g / cm ３35 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 43 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of magnesium hydroxide (trade name "KISUMA" Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and formed into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of resin. After sufficient saturation with carbon dioxide gas and cooling to a temperature suitable for foaming, a sheet-like foam structure a was obtained. The foam structure a was then thinned using a slicer to obtain a foam structure a1 having a thickness of 1.0 mm. Furthermore, the foamed structure a1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 210°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would have the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0126] [Example 2] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３35 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 45 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 15 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 15 parts by weight of magnesium hydroxide (trade name "KISUMA" Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and molded into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of the resin. After sufficient saturation with carbon dioxide gas and cooling to a temperature suitable for foaming, a sheet-like foam structure b was obtained. The foam structure b was then thinned using a slicer to obtain a foam structure b1 having a thickness of 1.0 mm. Furthermore, the foamed structure b1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 210°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would be the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0127] [Example 3] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３45 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 35 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 15 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 15 parts by weight of magnesium hydroxide (trade name "KISUMA" Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and molded into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of the resin. After sufficient saturation with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and a sheet-like foam structure c was obtained. The foam structure c was then thinned using a slicer to obtain a foam structure c1 with a thickness of 1.0 mm. Furthermore, the foamed structure c1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 220°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would be the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0128] [Example 4] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３45 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 40 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 10 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 10 parts by weight of magnesium hydroxide (trade name "KISUMA" Ten parts by weight of "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 kneaded at 200°C using a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and molded into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of the resin. After sufficient saturation with carbon dioxide gas and cooling to a temperature suitable for foaming, a sheet-like foam structure d was obtained. The foam structure d was then thinned using a slicer to obtain a foam structure d1 having a thickness of 1.0 mm. Furthermore, the foamed structure d1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 220°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would have the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0129] [Example 5] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３40 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 38 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of magnesium hydroxide (trade name "KISUMA Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and molded into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of resin. After sufficient saturation with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and a sheet-like foamed structure e was obtained. The foamed structure e was then thinned using a slicer to obtain a foamed structure e1 having a thickness of 1.0 mm. Furthermore, the foamed structure e1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 230°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would be the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0130] Example 6 A foamed structure e1 having a thickness of 1.0 mm was obtained in the same manner as in Example 5, except that carbon dioxide gas was injected at a ratio of 4.6 parts by weight per 100 parts by weight of the resin. Furthermore, the foamed structure e1 was passed through the gap between a pair of rolls heated to 230°C (the gap between the rolls) to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer was the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0131] [Example 7] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３ 40 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 38 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of magnesium hydroxide (trade name "KISUMA Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and formed into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 3.8 parts by weight per 100 parts by weight of resin. After sufficient saturation with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and a sheet-like foamed structure f was obtained. The foamed structure f was then thinned using a slicer to obtain a foamed structure f1 having a thickness of 1.0 mm. Furthermore, the foamed structure f1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 230°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would be the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0132] [Example 8] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３45 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 40 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 10 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 10 parts by weight of magnesium hydroxide (trade name "KISUMA" Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and formed into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of the resin. After sufficient saturation with carbon dioxide gas and cooling to a temperature suitable for foaming, a sheet-like foam structure g was obtained. The foam structure g was then thinned using a slicer to obtain a foam structure g1 having a thickness of 1.0 mm. Furthermore, the foamed structure g1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 210°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would have the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0133] [Example 9] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３45 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 35 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 15 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 15 parts by weight of magnesium hydroxide (trade name "KISUMA" Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and formed into pellets. The pellets were 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 4.2 parts by weight per 100 parts by weight of resin. After sufficient saturation with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and a sheet-like foam structure h was obtained. The foam structure h was then thinned using a slicer to obtain a foam structure h1 with a thickness of 1.0 mm. Furthermore, the foamed structure h1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 220°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would be the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0134] [Comparative Example 1] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３40 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 39 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of magnesium hydroxide (trade name "KISUMA Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and molded into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.5 parts by weight per 100 parts by weight of resin. After sufficient saturation with carbon dioxide gas and cooling to a temperature suitable for foaming, a sheet-like foam structure g was obtained. The foam structure g was then thinned using a slicer to obtain a foam structure g1 with a thickness of 0.8 mm. Furthermore, the foamed structure g1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 230°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would have the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0135] [Comparative Example 2] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３40 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 39 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of magnesium hydroxide (trade name "KISUMA Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and formed into pellets. The pellets were 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 4.4 parts by weight per 100 parts by weight of resin. After sufficient saturation with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming, and a sheet-like foam structure h was obtained. The foam structure h was then thinned using a slicer to obtain a foam structure h1 with a thickness of 0.7 mm. Furthermore, the foamed structure h1 was passed through the gap between a pair of rolls (the gap between the rolls) heated to 230°C to obtain a resin foam having a thickness of 0.6 mm. The gap between the rolls was set so that the thickness of the surface layer would be the value shown in Table 1. In this way, a resin foam consisting of a surface layer / foam layer / surface layer was obtained.

[0136] [Comparative Example 3] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３40 parts by weight of ethylene content: 0% by weight, propylene content: 100% by weight, weight average molecular weight: 64,500, molecular weight distribution: 8.43), 39 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "9020NS", MFR: 14 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of polyolefin elastomer (manufactured by Mitsui Chemicals, Inc., trade name "4010NA", MFR: 5 g / 10 min (230°C, load 21.2 N)), 17 parts by weight of magnesium hydroxide (trade name "KISUMA Ten parts by weight of "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 kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into a strand, cooled with water, and formed into pellets. The pellets were 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. The carbon dioxide gas was injected at a ratio of 4.4 parts by weight per 100 parts by weight of the resin. After sufficient saturation with carbon dioxide gas and cooling to a temperature suitable for foaming, a sheet-like foam structure i was obtained. The foam structure i was then thinned using a slicer to obtain a foam structure (foam layer) i1 with a thickness of 0.6 mm.

[0137]

[0138] The resin foam of the present invention can be suitably used, for example, as a cushioning material for electronic devices.

[0139] REFERENCE SIGNS LIST 10 foam layer 20 surface layer 100 resin foam 110 pressure-sensitive adhesive layer 200 foam member

Claims

1. A resin foam having a foamed layer having a cell structure, wherein the apparent density of the foamed layer is 0.06 g / cm ３ or more, and the resin foam has an arithmetic mean surface roughness Ra of 50 μm or less.

2. The resin foam according to claim 1, wherein the foam layer has an open cell rate of 90% or less.

3. The resin foam according to claim 1, wherein the average cell diameter in the foam layer is 300 μm or less.

4. The resin foam according to claim 1, wherein the coefficient of variation of bubble diameter in the foam layer is 0.6 or less.

5. The resin foam is applied with a load of 1000 g / cm ２ The resin foam according to claim 1, having a thickness recovery rate of 80% or more after maintaining a load of 1.0 mm for 120 seconds.

6. The resin foam according to claim 1, further comprising a surface layer on at least one side of the foam layer.

7. The resin foam according to claim 6, wherein the surface layer has a single layer thickness of 0.02 mm or more.

8. The resin foam according to claim 6, wherein the total thickness of the surface layer is 5% or more of the thickness of the resin foam.

9. The resin foam according to claim 6, wherein a ratio of the single layer thickness of the surface layer to the foam layer thickness (thickness of foam layer / single layer thickness of surface layer) is 5 to 55.

10. The resin foam according to claim 6, wherein the surface layer is a heat-fusible layer.

11. The resin foam according to claim 1, wherein the foam layer comprises a polyolefin-based resin.

12. The resin foam according to claim 11, wherein the polyolefin-based resin is a mixture of a polyolefin other than a polyolefin-based elastomer and a polyolefin-based elastomer.

13. A foam member comprising the resin foam according to claim 1 and a pressure-sensitive adhesive layer disposed on at least one side of the resin foam.

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