WO2018062444A1

WO2018062444A1 - Closed cell resin foam and method for manufacturing same

Info

Publication number: WO2018062444A1
Application number: PCT/JP2017/035362
Authority: WO
Inventors: 宮崎　健次
Original assignee: 積水化学工業株式会社
Priority date: 2016-09-30
Filing date: 2017-09-28
Publication date: 2018-04-05
Also published as: KR102125912B1; CN108713037B; JP2018053186A; CN108713037A; JP6625032B2; KR20190055778A; CN112341690A

Abstract

This closed cell resin foam has closed cells, and the static friction coefficient of the surface of the closed cell resin against a SUS plate is 0.30-0.70 as measured in accordance with JIS K7125.

Description

Closed cell resin foam and method for producing the same

The present invention relates to a closed cell resin foam, and more particularly to a closed cell resin foam used as a sealing material such as a waterproof seal material.

In portable devices such as notebook personal computers, mobile phones, smartphones, tablets, and portable music devices, a waterproof seal material may be used around the electrical components to prevent the electrical components from being flooded. A closed cell foam is used as the waterproof sealing material because it has both excellent flexibility and sealing properties. It is known that the closed cell foam is obtained, for example, by foaming a polyolefin resin blended with a foaming agent, as disclosed in Patent Document 1.

JP 2013-53179 A

The closed cell foam may have fine irregularities on the surface due to foaming of the foaming agent, and the smoothness may be impaired by the fine irregularities. When the foam with impaired smoothness is used as a waterproof sealing material, the adhesive strength with the peripheral parts becomes low, and furthermore, a groove-like space is generated between the peripheral parts and the space is a water passage. As a result, waterproofness is reduced.
This invention is made | formed in view of the above situation, and makes it a subject to provide the closed cell foam from which sealing properties, such as waterproofness, become favorable.

As a result of intensive studies, the present inventor has found that the above problem can be solved by setting the friction coefficient of the foam surface to a predetermined range, and has completed the following present invention. The present invention provides the following [1] to [9].
[1] A closed cell resin foam having closed cells and having a static friction coefficient of 0.30 to 0.70 against the SUS plate measured by JIS K7125 on the surface.
[2] The closed cell resin foam according to [1], wherein the resin constituting the closed cell foam includes a polyolefin resin.
[3] The closed cell resin foam according to [2], wherein the polyolefin resin is a polyethylene resin.
[4] The closed-cell resin foam according to any one of [1] to [3], wherein the expansion ratio is 1.8 to 20 times.
[5] The closed cell resin foam according to any one of [1] to [4], wherein the average cell diameter is 30 to 350 μm in MD, 30 to 400 μm in TD, and 10 to 150 μm in ZD.
[6] The ratio of the average bubble diameter in MD to the average bubble diameter in ZD is 1.5 to 8, and the ratio of average bubble diameter in TD to the average bubble diameter in ZD is 1.5 to 9. ] The closed cell resin foam according to any one of [5] to [5].
[7] The closed cell resin foam according to any one of the above [1] to [6], wherein the closed cell resin foam is crosslinked, and the degree of crosslinking is 15 to 60% by mass.
[8] The closed-cell resin foam according to any one of [1] to [7], wherein the thickness is 0.02 to 1 mm.
[9] A method for producing a closed cell resin foam as described in any one of [1] to [8] above, wherein a foamable composition containing a resin and a thermally decomposable foaming agent is foamed and foamed. A method for producing a closed cell resin foam, wherein an intermediate is obtained, and the foamed intermediate is stretched so that unevenness caused by foaming on the surface of the foamed intermediate is smoothed.

In the present invention, it is possible to provide a closed cell resin foam having good sealing properties such as waterproofness.

Hereinafter, it explains in detail, referring to an embodiment of the present invention.
[Closed-cell resin foam]
The closed cell resin foam of the present invention (hereinafter also referred to as a foam) has closed cells and has a static friction coefficient of 0.30 to 0.70 with respect to the SUS plate measured by JIS K7125 on the surface. is there.
In the closed cell resin foam, when the static friction coefficient is less than 0.30, the smoothness of the surface of the foam is not good, and the sealing properties such as waterproofness cannot be made good. Moreover, when larger than 0.70, it will become difficult to manufacture a foam with various resin, such as polyolefin resin. In order to make it possible to easily produce a foam while improving the static friction coefficient, the static friction coefficient is preferably 0.35 to 0.65, and more preferably 0.40 to 0.65.

The foam of the present invention has closed cells, and the closed cell rate is 70% or more. Accordingly, the air bubbles contained in the foam are almost closed and the sealing properties such as waterproofness are improved. The closed cell ratio of the foam is preferably 80% or more, more preferably 90 to 100%, from the viewpoint of ensuring various sealing properties such as high waterproof sealing properties even when the foam is thin. The closed cell ratio can be determined according to ASTM D2856 (1998).

The closed cell ratio can be measured in more detail as follows.
First, a flat square test piece having a side of 5 cm is cut out from the foam. Then, the thickness of the test piece is measured to calculate the apparent volume V ₁ of the test piece, and the weight W _{1 of the} test piece is measured.
Next, the volume V ₂ occupied by the bubbles is calculated based on the following formula. The density of the resin constituting the test piece is ρ (g / cm ³ ).
Volume occupied by bubbles V ₂ = V ₁ −W ₁ / ρ
Subsequently, the test piece is submerged in distilled water at 23 ° C. to a depth of 100 mm from the water surface, and a pressure of 15 kPa is applied to the test piece over 3 minutes. Then, after releasing from pressurization in water and allowing to stand for 1 minute, the test piece is taken out of the water, the water adhering to the surface of the test piece is removed, and the weight W _{2 of the} test piece is measured. The open cell rate F ₁ and the closed cell rate F ₂ are calculated.
Open cell ratio F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂
Closed cell ratio F ₂ (%) = 100−F ₁

The foam should just have the static friction coefficient in the above-mentioned range at least one surface. The foam is preferably in the form of a sheet (foamed sheet), and at least one surface may have a static friction coefficient within the above range, but it is preferable that both surfaces have a static friction coefficient within the above range.
The foam preferably has a thickness of 0.02 to 1 mm, more preferably 0.05 to 0.8 mm, and still more preferably 0.08 to 0.7 mm. When the foam is made thin in this way, it can be suitably used in various electronic devices, for example, portable devices with many space constraints.

(Average bubble diameter)
The average cell diameter of the foam is preferably 30 to 350 μm in MD, 30 to 400 μm in TD, and 10 to 150 μm in ZD. The average cell diameter of the bubbles in the foam is more preferably 60 to 300 μm in MD, 60 to 300 μm in TD, and 15 to 70 μm in ZD.
The ratio of the average bubble diameter of MD to the average bubble diameter of bubbles (hereinafter also referred to as “MD / ZD”) is 1.5 to 8, and the average bubble diameter of TD with respect to the average bubble diameter of ZD The ratio (hereinafter also referred to as “TD / ZD”) is preferably 1.5 to 9. More preferably, MD / ZD is 2 to 7, and TD / ZD is 2 to 7.
When the ratio of the average cell diameter and the average cell diameter is in the above range, the foam has good flexibility and can be suitably used as a waterproof sealing material.
In addition, MD means Machine direction and is a direction that coincides with the extrusion direction and the like, and TD means Transverse direction and is a direction orthogonal to MD. In a sheet-like foam (foamed sheet), The direction is parallel to the sheet surface. ZD is the thickness direction of the foam, and is the direction perpendicular to both MD and TD.

(Foaming ratio)
The expansion ratio of the foam is preferably 1.8 to 20 times, and more preferably 2.5 to 15 times. By setting the expansion ratio within the above-mentioned range, the foam is suitable for flexibility, mechanical strength and the like of the foam, and it is easy to improve the sealing property of the foam. Moreover, it becomes easy to make a foam surface smooth by the manufacturing method mentioned later.
In addition, the expansion ratio of the foam is the specific volume (unit: cc / g) of the foam before foaming (foamable composition) and after foaming (foam), and the specific volume after foaming / foaming. It is calculated by the previous specific volume.

(Apparent density)
The apparent density of the foam is preferably 0.05 to 0.5 g / cm ³ , and more preferably 0.08 to 0.30 g / cm ³ . When the foam has an apparent density within the above range, the foam has a suitable flexibility, mechanical strength, and the like, and the sealing property of the foam is easily improved. The apparent density of the foam is measured according to JIS K7222.

(25% compressive strength)
The 25% compressive strength of the foam is preferably 10 to 2000 kPa. By setting the pressure to 10 kPa or more, the mechanical strength is improved, and by setting the pressure to 2000 kPa or less, the flexibility of the foam is improved. The 25% compressive strength is more preferably 30 to 200 kPa from the viewpoints of improving mechanical strength and flexibility in a balanced manner and improving sealing properties such as waterproofness. The 25% compressive strength of the foam is measured according to the method of JIS K6767.

(Crosslinking degree)
The foam is usually cross-linked. The degree of crosslinking of the foam is preferably 15 to 60% by mass. By setting the degree of crosslinking to 15% by mass or more, when the foam is stretched, it is possible to prevent bubbles in the vicinity of the surface of the foam from breaking and causing surface roughness. Further, when the degree of crosslinking is 60% by mass or less, the resin material can be easily adjusted to a desired expansion ratio at the time of heat foaming. From such a viewpoint, the degree of crosslinking is more preferably 20 to 50% by mass.

(Polyolefin resin)
As the resin constituting the foam, a resin or rubber conventionally used for the foam can be used, but a polyolefin resin is preferable. Examples of the polyolefin resin include a polyethylene resin, a polypropylene resin, and an ethylene-vinyl acetate copolymer. Among these, a polyethylene resin is preferable. By using a polyolefin resin, particularly a polyethylene resin, it becomes easy to adjust the static friction coefficient of the foam within the above range. Moreover, it becomes easy to adjust various physical properties such as compressive strength within the above range, and can be suitably used as a waterproof sealing material.
Examples of the polyethylene resin include a polyethylene resin polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, and a chromium oxide compound. Preferably, a polyethylene resin polymerized with a polymerization catalyst of a metallocene compound is used.

The polyethylene resin is preferably linear low density polyethylene. The linear low density polyethylene is more preferably obtained by using a polymerization catalyst of a metallocene compound. By using linear low-density polyethylene obtained by using a polymerization catalyst of a metallocene compound, it is possible to impart high flexibility and mechanical strength to the foam, and it is possible to reduce the thickness, which is excellent as a waterproof sealing material. Become.
The linear low density polyethylene is obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more with respect to the total amount of monomers) and a small amount of α-olefin as required. A chain low density polyethylene is more preferred.
Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Of these, α-olefins having 4 to 10 carbon atoms are preferred.
Polyethylene resin, for example the density of the above-mentioned linear low density polyethylene is preferably 0.870 ~ 0.910g / cm ^3, more preferably ^{0.875 ~ 0.907g / cm 3, 0.880} ~ 0.905g / Cm ³ is more preferable. As the polyethylene resin, a plurality of polyethylene resins can be used, and a polyethylene resin outside the above-described density range may be added.

(Metallocene compound)
Examples of the metallocene compound include compounds such as a bis (cyclopentadienyl) metal complex having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum have one or more cyclopentadienyl rings or their analogs as ligands (ligands). Can be mentioned.
Metallocene compounds have uniform active site properties and each active site has the same activity. A polymer synthesized using a metallocene compound has high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, etc., so when a sheet containing a polymer synthesized using a metallocene compound is crosslinked, the crosslinking is uniform. Proceed to. Therefore, since it can extend | stretch uniformly, the thickness of a foam can be made uniform and sealing properties, such as waterproofness, become favorable.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group. Examples of the hydrocarbon group include a methyl group, an ethyl group, various propyl groups, various butyl groups, various amyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. , Various cetyl groups, phenyl groups and the like. The “various” means various isomers including n-, sec-, tert-, and iso-.
Moreover, what polymerized the cyclic compound as an oligomer may be used as a ligand.
In addition to π-electron unsaturated compounds, monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, aryls Phosphide or the like may be used.

Examples of metallocene compounds containing tetravalent transition metals and ligands include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethyl And silyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride.
The metallocene compound exhibits an action as a catalyst in the polymerization of various olefins by combining with a specific cocatalyst (co-catalyst). Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron compounds. The proportion of the cocatalyst used with respect to the metallocene compound is preferably 100,000 to 1,000,000 mole times, more preferably 50 to 5,000 mole times.

Examples of the ethylene-vinyl acetate copolymer used as the polyolefin resin include an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene.
Examples of the polypropylene resin include homopolypropylene and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. These may be used alone or in combination of two or more.
Specific examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1- Among these, α-olefins having 6 to 12 carbon atoms are preferable.

When the above-mentioned linear low density polyethylene is used as the polyolefin resin contained in the foam, the above linear low density polyethylene may be used alone, or may be used in combination with other polyolefin resins. For example, you may use together with other polyolefin resin mentioned above.
When other polyolefin resin is contained, the ratio of the linear low density polyethylene to the total amount of the linear low density polyethylene and the other polyolefin resin is preferably 50% by mass or more, more preferably 70% by mass or more, More preferably, it is 90 mass% or more. The other polyolefin resin is preferably an ethylene-vinyl acetate copolymer.

Moreover, as resin which comprises a foam, although polyolefin resin may be used independently, unless the effect of this invention is impaired, resin other than polyolefin resin may be included. In the foam, the ratio of the polyolefin resin to the total amount of the resin is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more.
Examples of the resin other than the polyolefin resin used in the foam include rubber components other than polyolefin resins such as ethylene propylene diene rubber (EPDM), hydrogenated styrene thermoplastic elastomer (SEBS), and olefin elastomer, and resin components.

(Pyrolytic foaming agent)
The foam of the present invention is preferably obtained by foaming a foamable composition containing a pyrolytic foaming agent in addition to the above resin. As the thermally decomposable foaming agent, for example, one having a decomposition temperature higher than the melting temperature of the resin is used. For example, an organic or inorganic chemical foaming agent having a decomposition temperature of 140 to 270 ° C. is used.
Organic foaming agents include azodicarbonamide, azodicarboxylic acid metal salts (such as barium azodicarboxylate), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N′-dinitrosopentamethylenetetramine, And hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate, and the like.
Among these, azo compounds and nitroso compounds are preferable from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety, and azodicarbonamide, azobisisobutyronitrile, N, N′-dinitrosopentamethylene. Tetramine is more preferred, and azodicarbonamide is still more preferred.
These pyrolytic foaming agents are used alone or in combination of two or more.
The amount of the pyrolytic foaming agent added is preferably 1 to 10 parts by weight, more preferably 1.5 to 5 parts by weight, and more preferably 1.5 to 3 parts by weight with respect to 100 parts by weight of the resin (for example, polyolefin resin). Further preferred.

(Other additives)
In addition to the above, the foamable composition contains additives generally used for foams such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, fillers, etc. You may do it.

The foam of the present invention may be used for any application, but is preferably used as a sealing material for waterproofing, dustproofing, etc., and more preferably used as a waterproof sealing material. For example, the sealing material is used by pressing at least one surface against another member. As described above, the foam of the present invention has a smooth surface and is in close contact with other members. Therefore, when used as a sealing material, the foam can exhibit high sealing performance. Moreover, it is preferable to use a foam for portable electronic devices, such as an electronic device, specifically a notebook personal computer, a mobile phone, a smart phone, a tablet, a portable music device.

When the foam of the present invention is in the form of a sheet, it may be a pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer on one or both sides. Further, when the foam is used as a sealing material, it is adhered to an adherend with an adhesive layer or a double-sided adhesive tape on one surface, and the other surface is another member such as a glass plate or an acrylic plate. It may be used by being pressed against.
The pressure-sensitive adhesive layer has a thickness of 5 to 200 μm, more preferably 7 to 150 μm. There is no restriction | limiting in particular as an adhesive which comprises an adhesive layer, For example, an acrylic adhesive, a urethane type adhesive, a rubber-type adhesive, etc. are used.

[Method for producing foam]
The foam of the present invention is obtained by, for example, foaming a foamable composition containing a resin and a thermally decomposable foaming agent to obtain a foamed intermediate, and the unevenness on the surface of the foamed intermediate resulting from foaming is smoothed. Thus, it is obtained by extending the foamed intermediate. More specifically, the manufacturing method includes the following steps.
Step (1): Step of mixing an additive such as a resin and a thermally decomposable foaming agent to form a foamable composition into a resin sheet Step (2): Crosslinking the foamable composition obtained in Step (1) Step (3): Step of heating the cross-linked foamable composition and foaming the pyrolyzable foaming agent to obtain a foamed intermediate Step (4): of the surface of the foamed intermediate resulting from foaming The step of stretching the foamed intermediate so that the unevenness is smoothed

In the step (1), the method for forming the resin sheet is not particularly limited. For example, the resin and the additive are supplied to an extruder, and melt-kneaded at a temperature lower than the decomposition temperature of the pyrolytic foaming agent. What is necessary is just to shape | mold a resin sheet by extruding a foamable composition from a machine in a sheet form.
Examples of the method of crosslinking the foamable composition in the step (2) include a method of irradiating the resin sheet with ionizing radiation. Further, an organic peroxide or a sulfur-based compound such as sulfur is blended in advance with the foamable composition, and the foamable composition is heated to decompose the organic peroxide or vulcanize with the sulfur-based compound. Crosslinking may be performed by a method or the like. In these, it is preferable to perform bridge | crosslinking by ionizing radiation.
Examples of the ionizing radiation include α-rays, β-rays, γ-rays, and electron beams, and electron beams are more preferable. The amount of ionizing radiation applied to the resin sheet is preferably 1 to 10 Mrad, more preferably 1.5 to 8 Mrad.

In step (3), the crosslinked foamable composition is heated to a temperature equal to or higher than the decomposition temperature of the thermally decomposable foaming agent to foam. In the step (3), the heating temperature when the foamable composition is heated to foam the pyrolytic foaming agent is usually 140 to 300 ° C, preferably 160 to 260 ° C. The method for foaming the resin sheet is not particularly limited, and examples thereof include a method of heating with hot air, a method of heating with infrared rays, a method using a salt bath, a method using an oil bath, and the like. Good.
Further, the foamable composition may be stretched while being foamed in the step (3). In this case, for example, the film may be stretched in MD or TD, but is preferably stretched in a direction orthogonal to the direction of stretching in the step (4). For example, when extending to TD in a process (4), it is good to extend to MD.
In addition, in this manufacturing method, it becomes easy to adjust the ratio of an average bubble diameter and an average bubble diameter to the above-mentioned desired range by extending | stretching in process (3) and process (4) mentioned later.

Next, in step (4), the foamed intermediate is stretched so that the irregularities on the surface of the foamed intermediate caused by foaming are smoothed. In the step (4), the foamed intermediate is preferably stretched in one direction, specifically, preferably stretched to TD or MD, more preferably stretched to TD. In addition, when extending | stretching to TD, it is good to extend to TD, for example, sending a sheet-like intermediate foam to MD.

In order to smooth the foam surface when the foam intermediate is stretched, the tensile elastic modulus at the time of stretching may be adjusted to be within a predetermined range. When the tensile elastic modulus at the time of stretching falls within a predetermined range so that the foamed intermediate body is stretched in a somewhat softened state, it is estimated that the unevenness due to foaming on the foam surface is thereby reduced or lost. The Moreover, it is not stretched more than necessary, and the foamed intermediate is prevented from breaking.
Further, as will be described later, the tensile elastic modulus required for smoothing the foam surface varies depending on the foaming ratio of the foam, and decreases as the foaming ratio of the foam increases. This is probably because the higher the expansion ratio, the higher the flexibility of the foamed intermediate, so that the surface is smoothed with a small tensile force, and the required tensile elastic modulus decreases accordingly.

Specifically, when the resin constituting the foam contains a polyolefin resin and the foamed intermediate is stretched in one direction, the foamed intermediate is pulled so as to have a tensile elastic modulus shown in Table 1 below. That's fine. Table 1 shows that when the foaming ratio of the foam is the value on the left side, the foam intermediate may be stretched so as to have the right tensile elastic modulus. By pulling the foamed intermediate with the tensile modulus shown below, the surface of the foam is smoothed, the static friction coefficient can be increased, and the foamed intermediate is also prevented from breaking.

Here, the tensile modulus is tensile stress / strain, but generally decreases as the temperature increases. Therefore, the tensile modulus is adjusted by appropriately adjusting the temperature of the intermediate foam during stretching. Is possible. Further, the foamed intermediate body may be pulled to increase the strain and exceed the yield point at the time of stretching, but when the yield point is exceeded, the tensile stress decreases. Therefore, the tensile elastic modulus may vary depending on the amount of strain (that is, elongation). Accordingly, at the time of stretching, the temperature and the elongation rate may be adjusted so that the tensile elastic modulus is in the range shown in Table 1 above.
Specifically, the temperature of the intermediate foam during stretching is not particularly limited, but is, for example, 80 to 150 ° C., preferably 90 to 130 ° C. The intermediate foam may be pulled so that the elongation percentage is, for example, 30 to 300%, preferably 40 to 250%. In addition, elongation rate is a ratio with respect to the length of the original intermediate | middle foam of elongation amount (distortion).
In addition, the tensile elasticity modulus at the time of extending | stretching can be confirmed by pulling a foaming intermediate body using a tensile tester on the same strain (elongation rate) and temperature conditions.
According to the above production method, for example, a foam having a high static friction coefficient can be provided without polishing the surface or cutting the foam.

Examples The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Various physical properties and evaluation methods are as follows.
<Apparent density>
It measured according to the method of JISK7222.
<Foaming ratio>
The specific volume (unit: cc / g) of the foamable composition and the foam was measured and calculated by the specific volume of the foam / the specific volume of the foamable composition.
<Degree of crosslinking>
A test piece of about 100 mg is taken from the foam, and the weight A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in 30 cm ³ of xylene at 120 ° C. and allowed to stand for 24 hours, and then filtered through a 200-mesh wire mesh to collect the insoluble matter on the wire mesh, vacuum dried, and the weight of the insoluble matter. Weigh B (mg) precisely. From the obtained value, the degree of crosslinking (mass%) is calculated by the following formula.
Crosslinking degree (% by mass) = 100 × (B / A)
<Compressive strength>
It measured according to the method of JIS K6767.
<Closed cell ratio>
The closed cell ratio of the foam is measured by the method described in the specification.
<Average bubble diameter>
The foam is cut into a 50mm square, immersed in liquid nitrogen for 1 minute, then cut in the thickness direction along each of MD and TD, and using a digital microscope (product name VHX-900, manufactured by Keyence Corporation). I took a 200x magnified photo. In the enlarged photograph, the bubble diameters of MD and ZD and the bubble diameters of TD and ZD and the bubble diameters of TD and ZD were measured for all the bubbles present on the cut surface corresponding to a length of 2 mm in each of MD and TD, and the operation was repeated five times. The average value of the bubble diameters of all the bubbles MD and TD is taken as the average bubble diameter of the MD and TD, and the average value of the bubble diameters of all ZDs measured by the above operation is taken as the average bubble diameter of the ZD. It was.
<Static friction coefficient>
In accordance with the method specified in JIS K 7125, a foam is placed on a SUS plate (SUS304), a bottom surface is placed on a felt slip plate, and a 200 g weight is placed thereon, and then parallel to the contact interface. The foam was pulled in the direction and the coefficient of static friction when the foam started to move was measured.
<Tensile modulus>
By pulling the intermediate foam using a tensile tester (product name: Tensilon RTF series, manufactured by Yamato Scientific Co., Ltd.) under the conditions at the time of stretching in each Example and Comparative Example, the tensile elastic modulus at the time of stretching was It was measured. The tensile modulus was measured according to JIS K6767.
<Waterproof test>
A sample for waterproof evaluation was prepared using the foams of the examples and comparative examples. The sample for waterproof evaluation is obtained by sandwiching the foams of the respective examples and comparative examples between two acrylic plates each having a thickness of 10 mm and a vertical and horizontal dimension of 100 mm, and compressed by 30% of the original thickness. The foam has a frame shape in which the outer shape is 60 mm in length and 40 mm in width, and the center of the foam is 58 mm in length and 38 mm in width. Of the two acrylic plates, a hole having a diameter of 8 mm is formed at the center of one acrylic plate, and water pressure can be applied from there. Also, the double-sided pressure-sensitive adhesive tape (thickness 0.048 mm, manufactured by TESA, “tesa4972”) cut into a frame shape of the same shape as the foam is pasted on one side of the foam, and the other side with the double-sided pressure-sensitive adhesive tape It was made to stick on the acrylic board.
After filling the center of the frame-shaped foam with water, water pressure was applied from the hole with a diameter of 8 mm, and the waterproof property was evaluated according to JISC0920 IPX5. “A” indicates that water leakage does not occur even after 3 minutes from the application of water pressure, “A” indicates that water resistance is excellent, and “B” indicates that water leakage does not leak for more than 3 minutes for less than 3 minutes. A case where water leakage occurred in less than 1 minute was evaluated as “C” because the waterproofness was insufficient.

[Example 1]
Linear low-density polyethylene obtained by using a metallocene compound [manufactured by Exxon Chemical Co., Ltd., trade name. EXACT3027] 100 parts by mass, 5 parts by mass of azodicarbonamide as a pyrolytic foaming agent, 0.02 parts by mass of 2,6-di-t-butyl-p-cresol, 0.2 parts by mass of zinc oxide, Was supplied to an extruder and melt-kneaded at 135 ° C., and then extruded as a resin sheet having a thickness of about 0.6 mm.
Next, the resin sheet was cross-linked by irradiating an electron beam with an acceleration voltage of 500 kV on both surfaces thereof for 5 Mrad, and then continuously fed into a foaming furnace maintained at 210 ° C. by hot air and an infrared heater, and the resin sheet was MD. The foamed intermediate was obtained by foaming by heating while being stretched. Thereafter, the foamed intermediate is fed to MD and heated to 110 ° C., and stretched to TD so that the tensile modulus is 1.3 MPa with an elongation of 90%, thereby obtaining a foam sheet having a thickness of 0.5 mm. It was. Table 1 shows the evaluation results of the obtained foamed sheet.

[Example 2]
It implemented like Example 1 except having changed the elongation rate at the time of extending | stretching a foam intermediate body into 40%, and setting it as the tensile elasticity modulus 1.3MPa.
[Example 3]
Example 1 except that the pyrolytic foaming agent was changed to 2.5 parts by mass, the elongation when the foam intermediate was stretched was changed to 60%, and the tensile modulus was 2.1 MPa. It carried out similarly.
[Example 4]
The pyrolytic foaming agent was changed to 2.5 parts by mass, the electron beam was changed to 8 Mrad, the elongation when the foam intermediate was stretched was changed to 60%, and the tensile modulus was 2.5 MPa. Except for this, the same procedure as in Example 1 was performed.

[Comparative Example 1]
The foamed intermediate was stretched at 75 ° C. with an elongation of 90%, and the same procedure as in Example 1 was performed except that the tensile modulus was 4.2 MPa.
[Comparative Example 2]
The foamed intermediate was stretched at 155 ° C. at an elongation of 90%, and the same procedure as in Example 1 was performed except that the tensile modulus was 0.3 MPa.

* The foamed sheets of the examples and comparative examples had the same coefficient of static friction on both sides.

In each of the above examples, the foam intermediate was stretched so as to have a predetermined tensile elastic modulus after foaming, the surface of the foam was smoothed, and the static friction coefficient became a high value of 0.3 or more. The property could be improved. On the other hand, in each comparative example, the foam intermediate was not stretched so as to have a predetermined tensile modulus after foaming, so the surface of the foam was not sufficiently smoothed, and the static friction coefficient was low, less than 0.3. Value. For this reason, the waterproof property could not be improved.

Claims

A closed cell resin foam having closed cells and having a static friction coefficient of 0.30 to 0.70 against a SUS plate measured by JIS K7125 on the surface.
The closed cell resin foam according to claim 1, wherein the resin constituting the closed cell foam contains a polyolefin resin.
The closed cell resin foam according to claim 2, wherein the polyolefin resin is a polyethylene resin.
The closed-cell resin foam according to any one of claims 1 to 3, wherein the expansion ratio is 1.8 to 20 times.
The closed cell resin foam according to any one of claims 1 to 4, wherein the average cell diameter is 30 to 350 µm in MD, 30 to 400 µm in TD, and 10 to 150 µm in ZD.
The ratio of the average bubble diameter in MD to the average bubble diameter in ZD is 1.5 to 8, and the ratio of average bubble diameter in TD to the average bubble diameter in ZD is 1.5 to 9. The closed cell resin foam according to any one of the preceding claims.
The closed-cell resin foam according to any one of claims 1 to 6, wherein the closed-cell resin foam is crosslinked and has a degree of crosslinking of 15 to 60% by mass.
The closed-cell resin foam according to any one of claims 1 to 7, which has a thickness of 0.02 to 1 mm.
A method for producing a closed-cell resin foam according to any one of claims 1 to 8, wherein a foamable composition containing a resin and a pyrolytic foaming agent is foamed to obtain a foamed intermediate, A process for producing a closed-cell resin foam, the foamed intermediate being stretched so that unevenness caused by foaming on the surface of the foamed intermediate is smoothed.