JP7724131B2 - Foams and articles - Google Patents

Description

This disclosure relates to foams.

Patent Document 1 discloses a closed-cell resin foam. Patent Document 1 gives an example of a closed-cell resin foam whose surface has a static friction coefficient against a stainless steel plate, measured according to JIS K7125, of 0.35 to 0.63.

JP 2018-053186 A

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.

[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 more than 0 parts by mass and less than 50 parts by mass when the total of the polyethylene, the EVA, and the olefin-based elastomer is 100 parts by mass.

This disclosure makes it possible to provide a foam that is non-slip even when a load is applied.

FIG. 1 is a diagram illustrating a method for measuring the static friction coefficient of a foam. 1 is a photograph (magnification: 30 times) showing a cross section of the foam of Example 1. 1 is a photograph (magnification: 30 times) showing a cross section of the foam of Comparative Example 2. 1 is a photograph (magnification: 30 times) showing the surface of the foam of Example 1. 1 is a photograph (magnification: 30 times) showing the surface of the foam of Comparative Example 2.

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.

[3] The foam described in [1] or [2], which has 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%.

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

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.

(1) Raw Materials of Foam 1 (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 the 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 viewpoints of crosslinking of molecular chains and melt tension at high temperatures during foaming. The density of the non-foamed low-density polyethylene is preferably 0.910 g/ ^cm3 or more and 0.940 g/ ^cm3 or less, more preferably 0.915 g/ ^cm3 or more and 0.935 g/ ^cm3 or less, and even more preferably 0.920 g/ ^cm3 or more and 0.930 g/cm3 or ^less .
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.

The polyethylene content is greater than 0 parts by mass, preferably 5 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 less than the above value is preferred in that the desired high static friction coefficient can be achieved.

(1.2) EVA
EVA is flexible and has excellent elongation, and 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, and 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, and 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 suppressed. From these viewpoints, the vinyl acetate content is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less. The vinyl acetate content is determined in accordance with JIS K 6924-1.

The melt flow rate (MFR) of the EVA is not particularly limited. From the standpoint of moldability, the MFR of the EVA, as measured at 190°C under a load of 2.16 kg in accordance with ASTM D 1238, 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.

The content of EVA is more than 0 parts by mass, preferably 35 parts by mass 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 not more than 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.

(1.3) Olefin-Based Elastomer The olefin-based elastomer is not particularly limited in terms of the type of olefin that serves as a constituent monomer, and may be any of those 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.

Ethylene-α-olefin copolymers are copolymers 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. Ethylene-α-olefin copolymers may be random copolymers, block copolymers, or graft copolymers.

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

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).

Specific examples of ethylene-α-olefin copolymers include ethylene-1-octene copolymers, ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-1-decene copolymers, ethylene-(3-methyl-1-butene) copolymers, and copolymers of ethylene and α-olefins having a cyclic structure.

An example of an ethylene-α-olefin copolymer is ENGAGE (trademark) manufactured by Dow Chemical Japan, Ltd.

The melt flow rate (MFR) of the olefin-based elastomer is not particularly limited. From the standpoint of moldability, the melt flow rate (MFR) of the olefin-based elastomer, as measured at 190°C under a load of 2.16 kg in accordance with ASTM D 1238, 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.

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. An olefin-based elastomer content of the above value or more 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 the polyethylene, EVA, and olefin-based elastomer. An olefin-based elastomer content of not more than the above value is preferable from the viewpoint of foam moldability (reduction of cracks, etc.) and blocking resistance.
From these viewpoints, the content of the 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.

(1.4) Other Components 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.

The foaming agent is preferably a thermally decomposable agent that decomposes upon heating to generate gas, but is not particularly limited. Examples include 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, p-t-butylbenzazide, sodium bicarbonate, and ammonium bicarbonate. Azodicarbonamide and 4,4'-oxybisbenzenesulfonylhydrazide are particularly preferred.

Crosslinking agents are preferably used for chemical crosslinking. Examples of crosslinking agents include organic peroxides such as dicumyl peroxide, 2,5-dimethyl-2,5-bis-tertiarybutylperoxyhexane, and 1,3-bis-tertiaryperoxy-isopropylbenzene.

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, and more preferably 1 part by mass or less, per 100 parts by mass of the total of polyethylene, EVA, and olefin-based elastomer.

(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 the surfaces 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 in the surface layer portion of the sheet-like foam 1 or in the entire sheet.

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 indicating the degree of crosslinking of the foam 1 can be measured in accordance with JIS K 6796/ISO-15875-2:2003 (measured by refluxing in xylene for 8 hours, then drying).

(2.2) Static Friction Coefficient 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 any 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 of 50% relative humidity. The static friction coefficient is measured on the surface of the foam 1 that comes into contact with an object. The static friction coefficient is calculated as the average value of three measurements per sample.

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 below). 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 below). 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. Therefore, it is presumed 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. Therefore, it is presumed 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 the 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.

(2.3) Apparent Density and Expansion Ratio The apparent density of the foam 1 is preferably 30 kg/m ^{or more} and 150 kg/m ^{or less} , more preferably 50 kg/m ^{or more} and 120 kg/m ^or less, and even more preferably 60 kg/m or ^more and 100 kg/m ^{or less} . The density of the foam 1 can be measured in accordance with JIS K 6767.
The expansion ratio of the foam 1 is preferably 5 to 50 times. 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.

(2.4) Rebound Resilience The rebound 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.

(2.5) Cell Structure The foam 1 preferably has a closed-cell structure.
There are no particular limitations on the average cell diameter of the foam 1. From the viewpoints of shape stability during foaming and an increase in the contact area with an 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 even 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.

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 the foam 1. Then, using image processing software Image-Pro PLUS (Media Cybernetics, ver. 6.3), each cell diameter is measured. 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 (the shape is recognized as 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 each cell diameter. The cell diameters of all cells appearing in a certain area of the cross section of the foam 1 are calculated, and the average is calculated by averaging the number of cells to determine the average cell diameter.

(2.6) Shape of Foam 1 The shape of the foam 1 is not particularly limited, but 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. Furthermore, since the foam 1 exhibits anti-slip properties simply by being placed on a surface without any special treatment, 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.

The foam 1 is preferably formed into a sheet by continuously foaming a kneaded sheet obtained by extrusion molding. The foam 1 has a large static friction coefficient but is not sticky. Therefore, problems such as blocking are unlikely to occur even when the foam 1 is wound into a roll, 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.

2. Effects of the Foam 1 of the Present Embodiment The foam 1 of the present embodiment has a high static friction coefficient and is not slippery even when a load is applied. This makes it applicable to a variety of applications. Specifically, conventional cross-linked polyethylene foams have an insufficient static friction coefficient, and there is a concern that they may slip 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 the present 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. This makes it applicable to a variety of applications requiring non-slip properties.
When the crosslinking of the foam 1 is performed by electron beam irradiation, the cells tend to be finer than when the foam is chemically crosslinked, and the anti-slip properties can be improved.
When 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.

3. Method for Producing Foam 1 The foaming method used in the production of 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-Length 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, an olefin-based elastomer, and other additives 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 irradiating the composition obtained in Step A with an electron beam to crosslink the composition. Step C: A step of foaming the composition crosslinked in Step B to obtain Foam 1.

In step B, the composition obtained in step A is irradiated with an electron beam to crosslink it. When the foam 1 is in 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 can be any amount 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 due to electron beam irradiation is affected by the composition, the irradiation dose is usually adjusted while measuring the gel fraction (degree of crosslinking).

In this manufacturing 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.

(2) Manufacturing Method Using Long Length Foaming by Chemical Crosslinking The manufacturing method using long length 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 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.

In this manufacturing 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 when crosslinking and foaming the composition is preferably equal to or higher than the decomposition temperature of the organic peroxide and the thermally decomposable foaming agent.

(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 kneaded with polyethylene, EVA, and an olefin-based elastomer, as well as other additives if necessary; 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-shaped foam to obtain a sheet-shaped foam 1.

In this manufacturing 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 foaming agent, and then the foaming mold is opened to foam, yielding a block-shaped foam (single-stage foaming).

The following provides a more detailed explanation using examples.

1. Preparation of Foams Foams of the Examples and Comparative Examples were prepared according to 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 the polymers including polyethylene, EVA, and olefin-based elastomer is taken as 100 parts by mass.
(1) Raw Materials Polyethylene 1: Low-density polyethylene MFR (190°C, 2.16 kg, ASTM D 1238): 3.0 g/10 min Density: 0.921 g/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°C, 2.16 kg, ASTM D 1238): 1.8 g/10 min Ethylene/vinyl acetate = 81 wt% (mass%)/19 wt% (mass%)
Density: 0.940g/ ^cm3 (ASTM D 1505)
・EVA2:
MFR (190°C, 2.16 kg, JIS K 6924-1): 2.8 g/10 min Ethylene/vinyl acetate = 75 wt% (mass%)/25 wt% (mass%)
Density: 0.948g/ ^cm3 (JIS K 6924-2)
Olefin elastomer: ENGAGE™ 8180 (Dow Chemical Company), ethylene/1-octene olefin elastomer MFR (190°C, 2.16 kg, ASTM D 1238): 0.5 g/10 min Foaming agent: azodicarbonamide Crosslinking agent: dicumyl peroxide (DCP)

(2) Preparation of Foams in Examples and Comparative Examples Each foam was prepared specifically 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 composition was crosslinked and foamed by 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
A composition was obtained by blending the polymers in the blending ratios shown in Table 1, and adding a foaming agent and a crosslinking agent. The foaming agent was contained in the 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) Production 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 Example 1 and Comparative Example 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 were carried out by 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, 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.

In the column "Crosslinked Structure" in Table 1, "EB" represents crosslinking by electron beam, and "PO" represents 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%.

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

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

(4) Static Friction Coefficient 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 of 50% relative humidity. 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 includes a sample stage 2, a glass plate 3, a slider 4, a pulley 5, and a load cell 6.

(5) Anti-slip property The evaluation of anti-slip property was based on the following criteria, taking into consideration how easily the product slips when a load is applied by pressing a product switch or the like with a hand when the product is used as a base material.
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.

(6) Rebound Resilience Rebound resilience (%) was measured in accordance with JIS K6400-3 by laminating foams to a thickness of 24 mm or more without using any adhesive.

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 were 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.

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 for anti-slip properties.
The foams of Comparative Examples 1 and 2 were obtained by crosslinking compositions containing no olefin-based elastomer. The coefficients of static friction of Comparative Examples 1 and 2 were low 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.

Comparing Example 1 and Example 2, Example 1, which has a crosslinked structure formed by electron beam crosslinking, had 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 effectively improve anti-slip properties.

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-based elastomer.
Requirement (b): 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 molding defects, 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).

4. Effects of the Examples According to the above examples, it is possible to provide a foam that is not slippery even when a load is applied.

This disclosure is not limited to the embodiments detailed above, and various modifications and variations are possible.

1...Foam

Claims (5)

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