Foams and articles

Abstract

To provide a foam that is not slippery even with load applied on it.SOLUTION: A foam 1 is prepared by crosslinking a composition containing polyethylene, an ethylene vinyl acetate copolymer, and an olefinic elastomer. When the total of the polyethylene, the ethylene vinyl acetate copolymer, and the olefinic elastomer is 100 pts.mass, the olefinic elastomer is more than 0 pt.mass to less than 50 pts.mass.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to foams. [Background technology]

[0002] Patent Document 1 discloses a closed-cell resin foam. Patent Document 1 shows an example of a closed-cell resin foam whose surface has a static friction coefficient against a SUS plate measured according to JIS K7125 of 0.35 to 0.63. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-053186 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional foams do not have a sufficient coefficient of static friction, and there was concern that they would slip when a load was applied. The present disclosure aims to provide a foam that is non-slip even when a load is applied. The present disclosure can be realized in the following aspects. [Means for solving the problem]

[0005] [1] Polyethylene, Ethylene vinyl acetate copolymer (hereinafter referred to as EVA), A foam obtained by crosslinking a composition containing an olefin-based elastomer, A foam in which the olefin-based elastomer is contained in an amount of more than 0 parts by mass and less than 50 parts by mass when the total amount of the polyethylene, the EVA, and the olefin-based elastomer is taken as 100 parts by mass. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a foam that is not slippery even when a load is applied. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating a method for measuring the static friction coefficient of a foam. [Figure 2] 1 is a photograph (magnification: 30 times) showing a cross section of the foam of Example 1. [Figure 3] 1 is a photograph (magnification: 30 times) showing a cross section of the foam of Comparative Example 2. [Figure 4] 1 is a photograph (magnification: 30 times) showing the surface of the foam of Example 1. [Figure 5] 1 is a photograph (magnification: 30 times) showing the surface of the foam of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] Here, a preferred example of the present disclosure will be described. [2] The foam according to [1], wherein the crosslinking is performed by electron beam irradiation.

[0009] [3] The foam according to [1] or [2], having a static friction coefficient measured in accordance with JIS K7125 of 1.4 or more in an atmosphere at a temperature of 23°C and a relative humidity of 50%.

[0010] The present disclosure will be described in detail below. In this specification, when a numerical range is indicated using "to" it is intended to include both the lower limit and the upper limit unless otherwise specified. For example, the expression "10 to 20" includes both the lower limit "10" and the upper limit "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

[0011] 1. Foam 1 The foam 1 of this embodiment is a foam obtained by crosslinking a composition containing polyethylene, EVA (ethylene-vinyl acetate copolymer), and an olefin-based elastomer. The amount of the olefin-based elastomer is more than 0 parts by mass and less than 50 parts by mass, where the total amount of the polyethylene, EVA, and olefin-based elastomer is 100 parts by mass.

[0012] (1) Foam 1 raw material (1.1) Polyethylene Examples of polyethylene include low density polyethylene, linear low density polyethylene, linear very low density polyethylene, medium density polyethylene, high density polyethylene, and copolymers containing ethylene as a main component. Examples of copolymers containing ethylene as a main component include copolymers of ethylene and one or more comonomers selected from α-olefins having 3 to 10 carbon atoms, vinyl esters, unsaturated carboxylic acid esters, conjugated dienes, and non-conjugated dienes. Examples of α-olefins having 3 to 10 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. Examples of vinyl esters include vinyl acetate and vinyl propionate. Examples of unsaturated carboxylic acid esters include methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. Among these, low-density polyethylene is preferred from the viewpoint of crosslinking of molecular chains and melt tension at high temperatures during foaming. The density of the low-density polyethylene in the non-foamed state is preferably 0.910 g / cm. 3 More than 0.940g / cm 3 or less, more preferably 0.915 g / cm 3 More than 0.935g / cm 3 More preferably, it is 0.920 g / cm or less. 3 More than 0.930g / cm 3 The following is the result. The melt flow rate (MFR) of the polyethylene is not particularly limited. From the viewpoint of moldability, the MFR of the polyethylene is preferably 0.1 g to 20 g / 10 min, more preferably 0.3 g to 10 g / 10 min, and even more preferably 0.5 g to 5.0 g / 10 min, as measured at 190°C under a load of 2.16 kg in accordance with ASTM D 1238.

[0013] The polyethylene content is more than 0 parts by mass, preferably 5 parts by mass to 50 parts by mass, based on 100 parts by mass of the total of polyethylene, EVA, and olefin-based elastomer. A polyethylene content of at least the above value is preferred in that poor foaming is less likely to occur. A polyethylene content of no more than the above value is preferred in that a desired high static friction coefficient can be obtained.

[0014] (1.2) EVA EVA is flexible and has excellent elongation. By using EVA for the foam 1, defects such as warping, cracks, and pinholes are suppressed. The vinyl acetate content in the EVA is not particularly limited. From the viewpoint of appropriately softening the foam 1 and suppressing defects such as warping, cracking, and pinholes, the vinyl acetate content is preferably 5% by mass or more, more preferably 10% by mass or more, based on 100% by mass of the EVA. On the other hand, the vinyl acetate content is preferably 40% by mass or less, more preferably 30% by mass or less. Vinyl acetate is more easily crosslinked than ethylene. When the vinyl acetate content is equal to or less than the above value, the degree of crosslinking of the foam 1 can be prevented from becoming excessively high. Therefore, poor foaming, such as cracking or unevenness of the foam 1 caused by expanding a highly crosslinked (hard) material, can be prevented. From these viewpoints, the vinyl acetate content is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less. The vinyl acetate content is based on JIS K 6924-1.

[0015] The melt flow rate (MFR) of the EVA is not particularly limited. From the viewpoint of moldability, the MFR of the EVA is preferably 0.1 g to 20 g / 10 min, more preferably 0.3 g to 10 g / 10 min, and even more preferably 0.5 g to 5.0 g / 10 min, as measured at 190°C under a load of 2.16 kg in accordance with ASTM D 1238.

[0016] The EVA content is more than 0 parts by mass, preferably 35 to 80 parts by mass, based on 100 parts by mass of the total of polyethylene, EVA, and olefin-based elastomer. An EVA content of at least the above value is preferred in that a desired high static friction coefficient can be obtained. An EVA content of at most the above value is preferred in that poor foaming is less likely to occur. The blend ratio of polyethylene to EVA (polyethylene / EVA) is preferably 1 / 99 to 90 / 10 by mass, more preferably 5 / 95 to 70 / 30, and even more preferably 10 / 90 to 45 / 55.

[0017] (1.3) Olefin-based elastomers The olefin-based elastomer is not particularly limited in the type of olefin that serves as a constituent monomer, and may be any of those that are commonly used as olefin-based elastomers. Examples of olefin-based elastomers include copolymers having structural units derived from at least one selected from the group consisting of ethylene and propylene, and structural units derived from at least one selected from α-olefins, butadiene, hydrogenated butadiene, isoprene, hydrogenated isoprene, and isobutene. Among these, ethylene-α-olefin copolymers are preferred.

[0018] The ethylene-α-olefin copolymer is a copolymer having structural units derived from ethylene and structural units derived from at least one α-olefin selected from α-olefins having 4 to 10 carbon atoms. The ethylene-α-olefin copolymer may be any of a random copolymer, a block copolymer, and a graft copolymer.

[0019] Specific examples of the α-olefin having 4 to 10 carbon atoms used in the ethylene-α-olefin copolymer include 1-octene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-decene, and α-olefins having a cyclic structure, with 1-octene and 1-butene being preferred.

[0020] The content of structural units derived from at least one α-olefin selected from α-olefins having 4 to 10 carbon atoms contained in the ethylene-α-olefin copolymer is preferably 10% by mass or more and 70% by mass or less, more preferably 20% by mass or more and 55% by mass or less, and even more preferably 25% by mass or more and 45% by mass or less (the total mass of the ethylene-α-olefin copolymer is taken as 100% by mass).

[0021] Specific examples of the ethylene-α-olefin copolymer include ethylene-1-octene copolymer, ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-decene copolymer, ethylene-(3-methyl-1-butene) copolymer, and copolymers of ethylene and an α-olefin having a cyclic structure.

[0022] An example of the ethylene-α-olefin copolymer is ENGAGE (trademark) manufactured by Dow Chemical Japan.

[0023] The melt flow rate (MFR) of the olefin-based elastomer is not particularly limited. From the viewpoint of moldability, the melt flow rate (MFR) of the olefin-based elastomer is preferably 0.1 g to 20 g / 10 min, more preferably 0.3 g to 10 g / 10 min, and even more preferably 0.5 g to 5.0 g / 10 min, as measured at 190°C under a load of 2.16 kg in accordance with ASTM D 1238.

[0024] The content of the olefin-based elastomer is more than 0 part by mass, preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 13 parts by mass or more, when the total of the polyethylene, EVA, and olefin-based elastomer is 100 parts by mass. If the content of the olefin-based elastomer is equal to or more than the above value, it is preferable in that a desired high static friction coefficient can be obtained. The content of the olefin-based elastomer is less than 50 parts by mass, preferably 45 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, based on 100 parts by mass of the total of polyethylene, EVA, and olefin-based elastomer. If the content of the olefin-based elastomer is less than the above value, it is preferable from the viewpoint of foam moldability (reduction of cracks, etc.) and blocking resistance. From these viewpoints, the content of the above-mentioned olefin-based elastomer is more than 0 parts by mass and less than 50 parts by mass, preferably 5 parts by mass or more and 45 parts by mass or less, more preferably 10 parts by mass or more and 40 parts by mass or less, and even more preferably 13 parts by mass or more and 30 parts by mass or less.

[0025] (1.4) Other ingredients The composition may contain, as necessary, a foaming agent, a filler (such as calcium carbonate), a crosslinking agent, an antioxidant, a foaming aid, a crosslinking aid, a pigment, a plasticizer, a function-imparting agent (for example, a flame retardant), and the like.

[0026] The foaming agent is preferably a thermal decomposition type that decomposes upon heating to generate gas, and is not particularly limited. For example, one or more of azodicarbonamide (ADCA), 2,2'-azobisisobutyronitrile, diazoaminobenzene, benzenesulfonylhydrazide, benzene-1,3-sulfonylhydrazide, diphenyloxide-4,4'-disulfonylhydrazide, 4,4'-oxybisbenzenesulfonylhydrazide, paratoluenesulfonylhydrazide, N,N'-dinitrosopentamethylenetetramine, N,N'-dinitroso-N,N'-dimethylphthalamide, terephthalazide, pt-butylbenzazide, sodium bicarbonate, ammonium bicarbonate, etc. are used. Azodicarbonamide and 4,4'-oxybisbenzenesulfonylhydrazide are particularly preferred.

[0027] The crosslinking agent is preferably used for chemical crosslinking, and examples of the crosslinking agent include organic peroxides such as dicumyl peroxide, 2,5-dimethyl-2,5-bis-tert-butylperoxyhexane, and 1,3-bis-tert-peroxy-isopropylbenzene.

[0028] The composition may also contain polymers other than the above-mentioned polymers, such as modifiers (hereinafter also referred to as other polymers), to the extent that the effects of the present disclosure are not significantly impaired. In such cases, the content of the other polymers is preferably 10 parts by mass or less, more preferably 1 part by mass or less, per 100 parts by mass of the total of polyethylene, EVA, and olefin-based elastomer.

[0029] (2) Structure of Foam 1 (2.1) Crosslinked structure The foam 1 is obtained by crosslinking a composition. Examples of crosslinking include electron beam crosslinking, chemical crosslinking, and silane crosslinking. Among these, the crosslinking of the foam 1 is preferably performed by electron beam irradiation. Typically, foam 1 crosslinked by electron beam crosslinking tends to have finer cells than foams crosslinked by chemical crosslinking. Therefore, when the crosslinking of the foam 1 is performed by electron beam irradiation, the contact area with the contact object can be secured, and the anti-slip properties can be improved. When the crosslinking of the foam 1 is performed by electron beam irradiation, the surface of the foam 1 that comes into contact with the object to be contacted is preferably the surface irradiated with the electron beam in the electron beam crosslinking. When the foam 1 is in a sheet form, it is preferable that both surfaces of the sheet are irradiated with the electron beam in the electron beam crosslinking. By irradiating the electron beam at an acceleration voltage corresponding to the thickness of the sheet, a crosslinked structure can be formed on the surface layer of the sheet-like foam 1 or on the entire sheet.

[0030] The gel fraction of the foam 1 is not particularly limited. The gel fraction of the foam 1 is preferably 10% to 98%, more preferably 15% to 95%. If the gel fraction is equal to or higher than the lower limit of the above range, the cells are less likely to break, which is preferable. If the degree of crosslinking is equal to or lower than the upper limit of the above range, the foam 1 is less likely to crack or break. The gel fraction, which indicates the degree of crosslinking of the foam 1, can be measured in accordance with JIS K 6796 / ISO-15875-2:2003 (measured after refluxing with xylene for 8 hours and drying).

[0031] (2.2) Coefficient of static friction From the viewpoint of improving anti-slip properties, the static friction coefficient of the foam 1 is preferably 1.4 or more, more preferably 1.8 or more, and even more preferably 2.2 or more. From the viewpoint of ease of production and ease of handling as a product, the static friction coefficient of the foam 1 is preferably 15.0 or less, more preferably 9.0 or less, and even more preferably 3.0 or less. More specifically, if the static friction coefficient of the foam 1 is the above-mentioned value or less, it is easy to handle when rewinding as a product or when processing into a desired thickness, size, or shape. From these viewpoints, the static friction coefficient of the foam 1 is preferably 1.4 or more and 15.0 or less, more preferably 1.8 or more and 9.0 or less, and even more preferably 2.2 or more and 3.0 or less. The static friction coefficient can be measured in accordance with JIS K7125 at a test speed of 100 mm / min, at a temperature of 23°C, and in an atmosphere with a relative humidity of 50%. The static friction coefficient is measured on the surface of the foam 1 that comes into contact with the object. The static friction coefficient is calculated as the average value of three measurements taken for one sample.

[0032] The reason why the foam 1 of this embodiment has a high static friction coefficient is not clear, but is presumed to be as follows: However, the present disclosure should not be construed as being limited in any way by this presumed reason. First, a polyethylene foam obtained by crosslinking a composition that does not contain an olefin elastomer, unlike the present embodiment, will be described. Such polyethylene foams generally have a static friction coefficient of approximately 0.3 to 1.2. The polyethylene foam composition contains polyethylene as the main resin, and may also contain EVA as a part of the composition to adjust hardness. Even when the composition contains EVA, no significant improvement in the static friction coefficient has been observed. FIG. 2 is a photograph showing a cross section of a foam according to an embodiment of the present invention (Example 1, described later). FIG. 3 is a photograph showing a cross section of a cross-linked polyethylene foam not containing an olefin-based elastomer (Comparative Example 2, described later). FIG. 4 is a photograph showing the surface of the foam according to Example 1. FIG. 5 is a photograph showing the surface of the foam according to Comparative Example 2. All photographs are images observed with an optical microscope at 30x magnification. The foam according to Comparative Example 2 has fine irregularities in the cell membrane visible behind the cell openings, as in the cell within the frame indicated by C2 in FIG. 3, and scattered areas where light reflected by the irregularities appears white. This suggests that the cell membrane is brittle and easily torn, i.e., has weak strength. On the other hand, the foam according to Example 1 has smooth cell membranes visible behind the cell openings, as in the cell within the frame indicated by C1 in FIG. 2, and the white areas where light appears to be reflected are less fine than those of Comparative Example 2. This suggests that the cell membrane is stronger and more resistant to tearing than Comparative Example 2. Furthermore, although not shown, when the cross sections of the foam of Example 1 and the foam of Comparative Example 2 were observed with an optical microscope at 100x magnification, it was observed that the cross section of the cell membrane of Example 1 was thicker than the cross section of the cell membrane of Comparative Example 2. It is presumed that the foam 1 of this embodiment has a smooth and tear-resistant cell membrane, thereby ensuring a sufficient contact area with the contact object. Furthermore, it is presumed that the foam 1 of this embodiment has a thick cell membrane and high resilience. It is presumed that a configuration with high resilience of the cell membrane makes it easier to maintain contact between the surface of the foam 1 and the contact object, even when a load is applied to the foam 1. In this way, it is presumed that the contact area between the foam 1 and the contact object is suitably ensured in this embodiment, resulting in a configuration with a high static friction coefficient.

[0033] (2.3) Apparent density and expansion ratio The apparent density of foam 1 is 30 kg / m 3 More than 150kg / m 3 It is preferable that the saturation is 50 kg / m or less. 3 More than 120kg / m 3 More preferably, it is 60 kg / m or less. 3 More than 100kg / m 3The density of the foam 1 can be measured in accordance with JIS K 6767. The expansion ratio of the foam 1 is preferably 5 times or more and 50 times or less. When the expansion ratio of the foam 1 is 20 times or less, the foam 1 can be suitably obtained by one-stage block foaming. The expansion ratio of the foam 1 increases as the density of the foam 1 decreases. The expansion ratio of the foam 1 can be calculated based on the apparent density of the foam 1.

[0034] (2.4) Rebound Resilience The impact resilience of the foam 1 is preferably 30% or more and 90% or less, and more preferably 40% or more and 80% or less. The density of the foam 1 can be measured in accordance with JIS K6400-3.

[0035] (2.5) Cell Structure The foam 1 preferably has a closed-cell structure. The average cell diameter of the foam 1 is not particularly limited. From the viewpoints of shape stability during foaming and increasing the contact area with the object to be contacted, the average cell diameter is preferably 200 μm or more and 1200 μm or less, more preferably 400 μm or more and 1000 μm or less, and more preferably 600 μm or more and 800 μm or less. When the method for producing the foam 1 is "(3) Block foaming by chemical crosslinking" described below, the average cell diameter is preferably 100 μm or more and 500 μm or less.

[0036] The average cell diameter is measured according to the following method. First, a scanning electron microscope (SEM, Keyence Corporation, VHXD-500) is used to take a photograph of the cross section of Foam 1. Then, the image processing software Image-Pro PLUS (Media Cybernetics, 6.3 version) is used to measure the diameter of each cell. More specifically, the SEM image is read, and the contrast is adjusted to recognize the cells by contrast. Next, the cell shape is read using image processing (recognizing the shape as it is, not a perfect circle). Next, "Diameter (average)" is selected as the measurement item. Next, the diameter passing through the center of gravity of the object is measured in 2-degree increments, and the average value is used to calculate the diameter of each cell. The cell diameters of all cells appearing within a certain area of the cross section of Foam 1 are calculated, and the average is calculated by averaging the number of cells to obtain the average cell diameter.

[0037] (2.6) Shape of foam 1 The shape of the foam 1 is not particularly limited, but it is preferably a sheet. The thickness of the sheet-like foam 1 is preferably 0.5 mm to 20 mm, more preferably 0.8 mm to 18 mm, and even more preferably 1 mm to 16 mm. When the foam 1 is in a sheet form, it is suitable as a base material, cushioning material, sealing material, etc. for products that require anti-slip properties. In addition, the foam 1 exhibits anti-slip properties simply by being placed on a surface without any special treatment, so it is also suitable as a yoga mat, rug, flooring material, etc. The foam 1 may be formed into a sheet by continuously foaming a kneaded sheet obtained by extrusion molding, or may be formed into a sheet by slicing a block of the foam 1.

[0038] The foam 1 is preferably formed into a sheet by continuously foaming a kneaded sheet obtained by extrusion molding. The foam 1 has a high static friction coefficient but is not sticky. Therefore, even when the foam 1 is wound into a roll, problems such as blocking are unlikely to occur, making it suitable for foaming into a sheet. Furthermore, foam 1 formed into a sheet by extrusion molding and heating is less likely to have cell openings on the surface that comes into contact with the object, compared to foam formed by slicing a block of foam, which ensures a sufficient contact area between foam 1 and the object, improving anti-slip properties.

[0039] 2. Effects of the Foam 1 of the Present Embodiment The foam 1 of this embodiment has a high static friction coefficient and is not slippery even when a load is applied. Therefore, it can be used in a variety of applications. Specifically, conventional cross-linked polyethylene foams have an insufficient static friction coefficient, which raises concerns about slippage when a load is applied. This limits their applications. Furthermore, conventional cross-linked polyethylene foams require a separate process, such as applying a pressure-sensitive adhesive or adhesive, to impart non-slip properties. On the other hand, the foam 1 of this embodiment has a high static friction coefficient of its own, and therefore has non-slip properties even without applying a pressure-sensitive adhesive or adhesive. Therefore, it can be used in a variety of applications that require non-slip properties. When the crosslinking of the foam 1 is performed by electron beam irradiation, the cells tend to be finer than when chemically crosslinked, and the anti-slip properties can be improved. If the static friction coefficient measured in accordance with JIS K7125 is 1.4 or more in an atmosphere at a temperature of 23°C and a relative humidity of 50%, the friction coefficient is extremely high and the anti-slip properties are good.

[0040] 3. Method for producing foam 1 The foaming method used in the manufacturing method of the foam 1 is not particularly limited. Examples of foaming methods include long foaming by chemical crosslinking or electron beam crosslinking, and block foaming by chemical crosslinking. Among these, long foaming by electron beam crosslinking is preferred. In this disclosure, "long foaming" refers to foaming a sheet-like base plate while feeding it in one direction to obtain a foam that is long in one direction. The manufacturing methods using long foaming by electron beam crosslinking, long foaming by chemical crosslinking, and block foaming by chemical crosslinking will be described below in order. (1) Manufacturing method using long foaming by electron beam crosslinking The manufacturing method using long-length foaming by electron beam crosslinking includes, for example, the following steps A to C. Step A: A step of feeding polyethylene, EVA, and an olefin-based elastomer, as well as other additives that are blended as necessary, into an extruder, melt-kneading the mixture, and then extruding the mixture from the extruder to obtain a composition in a predetermined shape, such as a sheet. Step B: A step of crosslinking the composition obtained in step A by irradiating it with an electron beam. Step C: A step of foaming the composition crosslinked in Step B to obtain Foam 1.

[0041] In step B, the composition obtained in step A is irradiated with an electron beam to crosslink it. When the foam 1 is in a sheet form, the electron beam can be irradiated at least once from both the front and back sides of the sheet-like base plate. The electron beam irradiation dose may be any dose that can achieve the desired degree of crosslinking, but is preferably 0.1 Mrad to 10 Mrad, and more preferably 1.0 Mrad to 4.0 Mrad. The acceleration voltage is adjusted according to the thickness of the sheet before foaming. Since the progress of crosslinking by electron beam irradiation is affected by the composition, the irradiation dose is usually adjusted while measuring the gel fraction (degree of crosslinking).

[0042] In this production method, it is preferable to blend a thermally decomposable foaming agent as the foaming agent. When a thermally decomposable foaming agent is blended, in step C, the sheet-shaped base plate is placed in a heating furnace and foamed to obtain foam 1. The heating temperature when foaming the composition is preferably equal to or higher than the decomposition temperature of the thermally decomposable foaming agent.

[0043] (2) Manufacturing method using long foamed sheet by chemical crosslinking The manufacturing method using long foaming by chemical crosslinking includes, for example, the following steps D and E. Step D: A step of feeding polyethylene, EVA, and an olefin-based elastomer, as well as other additives that are blended as necessary, into an extruder, melt-kneading the mixture, and then extruding the mixture from the extruder to obtain a composition in a predetermined shape, such as a sheet. Step E: A step of heating the composition obtained in Step D to crosslink and foam it.

[0044] In this production method, it is preferable to blend an organic peroxide as a crosslinking agent and a thermally decomposable foaming agent as a foaming agent into the composition. When an organic peroxide and a thermally decomposable foaming agent are blended, in step E, the sheet-shaped base plate is placed in a heating furnace to crosslink and foam, thereby obtaining foam 1. The heating temperature during crosslinking and foaming of the composition is preferably equal to or higher than the decomposition temperature of the organic peroxide and the thermally decomposable foaming agent.

[0045] (3) Manufacturing method using block foaming by chemical crosslinking The manufacturing method using block foaming by chemical crosslinking includes, for example, the following steps F to H. Step F: A step of filling a foaming mold with a composition obtained by kneading polyethylene, EVA, and an olefin-based elastomer, as well as other additives that may be blended as needed. Step G: A step of crosslinking and foaming the composition in the foaming mold to obtain a block-shaped foam. Step H: A step of slicing the block foam to obtain a sheet-like foam 1

[0046] In this production method, it is preferable to blend an organic peroxide as a crosslinking agent and a thermally decomposable foaming agent as a foaming agent into the composition. When an organic peroxide and a thermally decomposable foaming agent are blended, in step G, the composition is heated and pressurized to decompose the crosslinking agent and the foaming agent, and then the foaming mold is opened to foam, thereby obtaining a block-shaped foam (one-stage foaming). [Example]

[0047] The present invention will be explained in more detail below with reference to examples.

[0048] 1. Foam Preparation Foams of the examples and comparative examples were produced using the blending ratios shown in Table 1. Details of the main raw materials are shown below in Table 1. In Table 1, the blending ratios represent blending ratios (parts by mass) when the total amount of polymers including polyethylene, EVA, and olefin-based elastomer is 100 parts by mass. (1) Raw materials Polyethylene 1: Low density polyethylene MFR (190℃, 2.16kg, ASTM D 1238): 3.0g / 10min Density: 0.921g / cm 3 (ASTM D 1505) Polyethylene 2: Low-density polyethylene composition containing ADCA masterbatch and azodicarbonamide (Table 1 shows the blending ratio converted into the amount of low-density polyethylene) EVA1: MFR (190℃, 2.16kg, ASTM D 1238): 1.8g / 10min Ethylene / vinyl acetate = 81 wt% (mass%) / 19 wt% (mass%) Density: 0.940g / cm 3 (ASTM D 1505) EVA2: MFR (190℃, 2.16kg, JIS K 6924-1): 2.8g / 10 minutes Ethylene / vinyl acetate = 75 wt% (mass%) / 25 wt% (mass%) Density: 0.948g / cm 3 (JIS K 6924-2) Olefin elastomer: ENGAGE™ 8180 (Dow Chemical Company), ethylene / 1-octene triolefin elastomer MFR (190℃, 2.16kg, ASTM D 1238): 0.5g / 10min Foaming agent: Azodicarbonamide Crosslinking agent: dicumyl peroxide (DCP)

[0049] (2) Preparation of foams in examples and comparative examples Specifically, each foam was prepared as follows. (2.1) Example 1 A composition was obtained by blending the polymers in the blending ratios shown in Table 1 and adding a foaming agent. The amount of foaming agent added was adjusted to achieve a target foaming ratio of 13 times. The crosslinking and foaming of the composition was carried out according to the method described in "(1) Manufacturing method using long-length foaming by electron beam crosslinking" in the embodiment. The composition was formed into a sheet, which was then crosslinked and foamed to obtain a sheet-like foam with a thickness of 4 mm. The average cell diameter of this foam was 620 μm. (2.2) Example 2 The polymers were blended in the blending ratios shown in Table 1, and a foaming agent and crosslinking agent were added to obtain a composition. The foaming agent was contained in an ADCA masterbatch of polyethylene 2, and the amount added was adjusted to achieve a target foaming ratio of 11. The amount of crosslinking agent added was 0.6 parts by mass per 100 parts by mass of the total polymers. The crosslinking and foaming of the composition was carried out by the method described in "(3) Manufacturing method using block foaming by chemical crosslinking" in the embodiment. The block foam obtained by crosslinking and foaming the composition was sliced to obtain a sheet-like foam with a thickness of 4 mm. The average cell diameter of this foam was 240 μm. (2.3) Comparative Examples 1 and 2 Compositions were obtained by blending polymers in the blending ratios shown in Table 1 and adding a blowing agent. The amount of blowing agent added in Comparative Example 1 was adjusted to achieve a target expansion ratio of 15 times. The amount of blowing agent added in Comparative Example 2 was adjusted to achieve a target expansion ratio of 30 times. The crosslinking and foaming of the composition was carried out by the method described in "(1) Manufacturing method using long foaming by electron beam crosslinking" in the embodiment. The composition was formed into a sheet, and then crosslinked and foamed to obtain a sheet-like foam with a thickness of 4 mm. The average cell diameter of the foam of Comparative Example 1 was 650 μm. The average cell diameter of the foam of Comparative Example 2 was 680 μm.

[0050] In the "Crosslinked Structure" column of Table 1, "EB" indicates crosslinking by electron beam, and "PO" indicates crosslinking by chemical crosslinking. The gel fraction of the foam of Example 1 measured in accordance with JIS K 6796 / ISO-15875-2:2003 (measured after refluxing with xylene for 8 hours and then drying) was 27%.

[0051] 2. Evaluation Method (1) Foaming and appearance The foaming property and appearance were evaluated according to the following criteria. Good: Good foaming properties and appearance. Poor: Poor foaming and appearance. (2) Apparent density Apparent density (kg / m 3 ) was measured in accordance with JIS-K 6767.

[0052] (3) Expansion Ratio The density of the unfoamed resin composition was set to a predetermined density, and the density of the foamed product was calculated from the formula (density of unfoamed resin composition / density of foamed product).

[0053] (4) Coefficient of static friction The static friction coefficient was measured in accordance with JIS K7125 at a test speed of 100 mm / min, at a temperature of 23°C, and in an atmosphere with a relative humidity of 50%. The static friction coefficient was measured on one side of the sheet-like foam. No spring was used. Figure 1 shows a schematic diagram of the test. The test apparatus is equipped with a sample stage 2, a glass plate 3, a sliding piece 4, a pulley 5, and a load cell 6.

[0054] (5) Anti-slip The evaluation of anti-slip properties was based on the following criteria, taking into consideration how easily the surface slips when a load is applied by pressing a product switch or the like with the hand when the surface is used as a base material for the product. A: The static friction coefficient is 2.2 or more and 3.0 or less. B: The static friction coefficient is 1.8 or more and less than 2.2, or more than 3.0 and 9.0 or less. C: The static friction coefficient is 1.4 or more and less than 1.8, or more than 9.0 and 15.0 or less. D: The static friction coefficient is 1.0 or more and less than 1.4. E: The static friction coefficient is less than 1.0 or more than 15.0.

[0055] (6) Rebound elasticity The impact resilience (%) was measured in accordance with JIS K6400-3. The measurement was carried out by laminating foams to a thickness of 24 mm or more without using any adhesive.

[0056] [Table 1]

[0057] [Table 2]

[0058] 3.Results The results are shown in Table 1. Both the Examples and Comparative Examples had good foaming properties. It was confirmed that Examples 1 and 2 had apparent densities and expansion ratios that made them suitable for use as foams in a variety of applications. It was confirmed that Examples 1 and 2 had higher impact resilience than Comparative Example 1.

[0059] Examples 1 and 2 are foams obtained by crosslinking a composition containing more than 0 parts by mass and less than 50 parts by mass of an olefin-based elastomer. Examples 1 and 2 had a high static friction coefficient and were rated A or C in terms of anti-slip properties. Comparative Examples 1 and 2 are foams obtained by crosslinking compositions that do not contain an olefin-based elastomer. Comparative Examples 1 and 2 had low static friction coefficients regardless of the expansion ratio, and the anti-slip properties were rated D or E. These results show that Examples 1 and 2, in which compositions containing a predetermined amount of olefin-based elastomer were crosslinked, have better anti-slip properties than Comparative Examples 1 and 2, in which compositions containing no olefin-based elastomer were crosslinked.

[0060] Comparing Example 1 and Example 2, Example 1, which has a crosslinked structure formed by electron beam crosslinking, has better anti-slip properties than Example 2, which has a crosslinked structure formed by chemical crosslinking. This suggests that crosslinking by electron beam crosslinking can suitably improve anti-slip properties.

[0061] Examples 3 to 7 satisfy the following requirements (a) and (b): Examples 3 to 7 that satisfy requirements (a) and (b) have a high static friction coefficient and are rated A, B, or C for anti-slip properties. Requirement (a): The foam is a crosslinked composition containing polyethylene, ethylene vinyl acetate copolymer, and an olefin elastomer. Requirement (b): The content of the olefin-based elastomer is more than 0 parts by mass and less than 50 parts by mass. Comparative Examples 3 and 4 do not satisfy requirement (b). Comparative Example 5 does not satisfy requirement (a). Comparative Example 3 could not be evaluated for anti-slip properties due to poor molding, and Comparative Examples 4 and 5 were evaluated as D for anti-slip properties. These results show that Examples 3 to 7, which satisfy requirements (a) and (b), have better anti-slip properties than Comparative Examples 3 to 5, which do not satisfy requirements (a) or (b).

[0062] 4. Effects of the Example According to the above-described embodiments, a foam that is not slippery even when a load is applied can be provided.

[0063] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible. [Explanation of symbols]

[0064] 1...Foam

Claims

1. Polyethylene and ethylene vinyl acetate copolymer; A foam obtained by crosslinking a composition containing an olefin-based elastomer, the polyethylene is at least one selected from low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, medium-density polyethylene, and high-density polyethylene; The olefin-based elastomer is A copolymer having, as structural units having 2 or 3 carbon atoms, a structural unit derived from one of ethylene and propylene and a structural unit derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, butadiene, hydrogenated butadiene, isoprene, hydrogenated isoprene, and isobutene; or A copolymer having structural units derived from at least one selected from the group consisting of ethylene and propylene, and structural units derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, hydrogenated butadiene, hydrogenated isoprene, and isobutene, the amount of the olefin-based elastomer is more than 0 part by mass and less than 50 parts by mass, relative to 100 parts by mass of the total amount of the polyethylene, the ethylene-vinyl acetate copolymer, and the olefin-based elastomer; The foam has an apparent density of 30 kg / m 3 or more and 102 kg / m 3 or less.

2. Polyethylene and ethylene vinyl acetate copolymer; and a foam obtained by crosslinking a composition containing an olefin-based elastomer by electron beam irradiation, The olefin-based elastomer is A copolymer having, as structural units having 2 or 3 carbon atoms, a structural unit derived from one of ethylene and propylene and a structural unit derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, butadiene, hydrogenated butadiene, isoprene, hydrogenated isoprene, and isobutene; or A copolymer having structural units derived from at least one selected from the group consisting of ethylene and propylene, and structural units derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, hydrogenated butadiene, hydrogenated isoprene, and isobutene, A foam in which the olefin-based elastomer is present in an amount of more than 0 parts by mass and less than 50 parts by mass when the total amount of the polyethylene, the ethylene-vinyl acetate copolymer, and the olefin-based elastomer is taken as 100 parts by mass.

3. Polyethylene and ethylene vinyl acetate copolymer; A foam obtained by crosslinking a composition containing an olefin-based elastomer, the polyethylene is at least one selected from low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, medium-density polyethylene, and high-density polyethylene; The olefin-based elastomer is A copolymer having, as structural units having 2 or 3 carbon atoms, a structural unit derived from one of ethylene and propylene and a structural unit derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, butadiene, hydrogenated butadiene, isoprene, hydrogenated isoprene, and isobutene; or A copolymer having structural units derived from at least one selected from the group consisting of ethylene and propylene, and structural units derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, hydrogenated butadiene, hydrogenated isoprene, and isobutene, a foam in which, when the total amount of the polyethylene, the ethylene-vinyl acetate copolymer, and the olefin-based elastomer is 100 parts by mass, the olefin-based elastomer is more than 0 parts by mass and less than 50 parts by mass, and the polyethylene is 20.8 parts by mass or more and 63.9 parts by mass or less.

4. Polyethylene and ethylene vinyl acetate copolymer; A foam obtained by crosslinking a composition containing an olefin-based elastomer, the polyethylene is at least one selected from low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, medium-density polyethylene, and high-density polyethylene; The olefin-based elastomer is A copolymer having, as structural units having 2 or 3 carbon atoms, a structural unit derived from one of ethylene and propylene and a structural unit derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, butadiene, hydrogenated butadiene, isoprene, hydrogenated isoprene, and isobutene; or A copolymer having structural units derived from at least one selected from the group consisting of ethylene and propylene, and structural units derived from at least one selected from an α-olefin having 4 to 10 carbon atoms, hydrogenated butadiene, hydrogenated isoprene, and isobutene, a foam in which, when the total amount of the polyethylene, the ethylene-vinyl acetate copolymer, and the olefin-based elastomer is 100 parts by mass, the amount of the olefin-based elastomer is more than 0 parts by mass and less than 50 parts by mass, and the amount of the ethylene-vinyl acetate copolymer is 63.1 parts by mass or less.

5. An article comprising the foam according to any one of claims 1 to 4, which is placed on a surface for use.

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