JP6791705B2 - Resin foam sheet, method of manufacturing resin foam sheet, and resin foam sheet with support - Google Patents

Description

The present invention relates to a resin foam sheet, a method for producing a resin foam sheet, and a resin foam sheet with a support.

Conventionally, a porous resin material in which a large number of holes are formed inside a resin layer is excellent in cushioning property, heat insulating property, waterproof property, and moisture proof property, and therefore needs to be protected from packing materials, gases or liquids of articles. It is used in various applications such as a sealing material for sealing parts, a peripheral portion of a housing, a cushioning material for cushioning vibration and impact, and a base material for an adhesive sheet. For example, Patent Document 1 discloses a crosslinked polyolefin-based resin foamed sheet obtained by foaming and cross-linking a foamable polyolefin-based resin sheet containing a pyrolytic foaming agent (see, for example, Patent Document 1).

International Publication No. 2005/007731

By the way, in recent years, in various electronic devices such as mobile phones, personal computers and other IT devices, digital cameras and small video cameras, the resin foam sheets used inside these electronic devices have become smaller and thinner. , It is desired to have flexibility.
However, a highly flexible resin foam sheet has low mechanical strength and is likely to be stretched, torn, wrinkled, etc. during processing, transportation, etc., and is therefore difficult to handle alone. In order to prevent this, it is preferable that the resin foam sheet is processed in a state where the support for reinforcing the mechanical strength is bonded with a weak force.
The support needs to be attached to the resin foam sheet with an adhesive force that effectively functions as a reinforcing material during processing, but on the other hand, after processing, the resin foam sheet can be easily attached without damaging it. Must be able to peel off. However, since the resin foam sheet has a high adhesion to the support, it may be difficult to peel off the support after processing. Therefore, the resin foam sheet is required to reduce the adhesion to other members such as a support.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a resin foam sheet having reduced adhesion to other members such as a support.

That is, the present invention provides the following [1] to [12].
[1] A resin foam sheet having closed cells, wherein the surface roughness of at least one surface of the resin foam sheet is 12.0 μm or less at the maximum height Rz and 2.0 μm or less at the arithmetic mean roughness Ra. Resin foam sheet that is.
[2] The resin foam sheet according to the above [1], which contains a polyolefin resin.
[3] The resin foam sheet according to the above [2], wherein the polyolefin resin is a polyethylene resin.
[4] The resin foam sheet according to the above [3], wherein the polyolefin resin is a linear low-density polyethylene polymerized with a polymerization catalyst of a metallocene compound.
[5] The resin foam sheet has an average cell diameter (DL) of 120 μm or less on the major axis and a standard deviation (σL) of the cell diameter on the major axis of 60 μm or less, as described above [1] to [4]. ] The resin foam sheet according to any one of.
[6] The resin foam sheet according to any one of [1] to [5] above, wherein the degree of cross-linking is 30% by mass or more.
[7] The resin foam sheet according to any one of the above [1] to [6], wherein the foaming ratio is 1.2 to 10.0 cm ³ / g.
[8] The resin foam sheet according to any one of the above [1] to [7], wherein the thickness of the resin foam sheet is 0.05 to 0.5 mm.
[9] The resin foam sheet according to any one of the above [1] to [8], wherein the 25% compression strength of the resin foam sheet is 10 to 2000 kPa.
[10] The method for producing a resin foam sheet according to any one of the above [1] to [9].
A method for producing a resin foam sheet in which a foamable composition containing a resin and a pyrolysis foaming agent is heated to foam the pyrolysis foaming agent.
[11] The resin foam sheet and the support according to any one of the above [1] to [9] are provided, and the support is arranged on at least one surface of the resin foam sheet. A resin foam sheet with a support having a surface roughness of at least one surface of 12.0 μm or less at a maximum height Rz and 2.0 μm or less at an arithmetic mean roughness Ra.
[12] The resin foam sheet with a support according to the above [11], wherein the support is a polyolefin film.

According to the present invention, it is possible to provide a resin foam sheet having reduced adhesion to other members such as a support.

Hereinafter, the present invention will be described in detail using embodiments.
[Resin foam sheet]
The resin foam sheet according to the present invention is a resin foam sheet having closed cells, and the surface roughness of at least one surface of the resin foam sheet is 12.0 μm or less at a maximum height Rz and an arithmetic mean roughness. Ra is 2.0 μm or less.
As described above, the resin foam sheet of the present invention has a reduced surface roughness to reduce the adhesion to other members such as a support. Specifically, the resin foam sheet of the present invention and the support bonded to the resin foam sheet are formed by adjusting the surface roughness of the surface to which the support or the like is bonded to a specific value or less as described above. It is presumed that the anchor effect generated between the resin and the like is reduced, thereby reducing the adhesion to the support and the like.

On the other hand, when the maximum height Rz exceeds 12.0 μm or the arithmetic mean roughness Ra exceeds 2.0 μm, the adhesion to the support or the like becomes high, and the support while maintaining the performance of the resin foam sheet. Etc. become difficult to peel off.
The maximum height Rz of at least one surface of the resin foam sheet is 1.0 μm or more from the viewpoint of imparting adhesion to the extent that the support or the like effectively functions as a reinforcing material, and the support or the like is used as the reinforcing material. From the viewpoint of enabling effective functioning and easy peeling after processing, 2.0 to 11.5 μm is preferable, and 3.0 to 11.0 μm is more preferable.
Further, the arithmetic mean roughness Ra of at least one of the surfaces is 0.1 μm or more from the viewpoint of imparting adhesion to the extent that the support or the like effectively functions as a reinforcing material, and the support or the like is used as the reinforcing material. From the viewpoint of making it function effectively and allowing it to be easily peeled off after processing, 0.5 to 1.9 μm is preferable.
The maximum height Rz and the arithmetic mean roughness Ra in the present specification are values based on JIS B0601 (2001) and can be obtained by the method described in the examples.

The resin foam sheet according to the present invention preferably has an average cell diameter (DL) of 120 μm or less on the major axis and a standard deviation (σL) of the cell diameter on the major axis of 60 μm or less. By making the bubbles fine as described above and reducing the standard deviation of the bubble diameter, it is possible to suppress the occurrence of irregularities on the surface of the resin foam sheet and reduce the surface roughness.

The average cell diameter (DL) on the major axis is 30 μm or more, but from the viewpoint of ease of production and the above, 35 to 100 μm is more preferable, and 40 to 80 μm is further preferable.
The standard deviation (σL) of the bubble diameter on the long axis is preferably 45 μm or less, more preferably 35 μm or less, from the viewpoint of improving durability. The lower the standard deviation (σL) on the long axis, the better, but it is usually 5 μm or more, and practically 10 μm or more.

The bubbles in the resin foam sheet have an average cell diameter (DS) on the minor axis equal to or less than the average cell diameter (DL) on the major axis, and an average cell diameter (DM) on the middle axis on the minor axis. The average cell diameter (DS) or more and the average cell diameter (DL) or less on the long axis.
In the present specification, the long axis of the bubble means the maximum length on each side when the bubble is regarded as a close rectangular parallelepiped, the middle axis means the second maximum length, and the short axis means the third maximum length. Further, in the following, the average cell diameters on the major axis, the minor axis, and the middle axis are also simply referred to as the average cell diameter (DL), the average cell diameter (DM), and the average cell diameter (DS), respectively.

The average value of the ratio of the length of the major axis to the length of the minor axis of the bubble (hereinafter, also referred to as “average aspect ratio D (L / S)”) is preferably 1.1 to 20. The average value of the ratio of the length of the middle axis to the length of the minor axis of the bubble (hereinafter, also referred to as “average aspect ratio D (M / S)”) is preferably 1.05 to 15. Further, it is more preferable that the average aspect ratio D (L / S) is 1.5 to 10 and the average aspect ratio D (M / S) is 1.5 to 10, and the average aspect ratio D (L / S). It is more preferable that S) is 2.0 to 8.0 and the average aspect ratio D (M / S) is 2.0 to 8.0.
In the resin foam sheet, the minor axis is usually an axis that is parallel to the thickness direction of the sheet or is inclined at a small angle from the thickness direction. Therefore, each bubble has a disk shape that spreads along the surface direction of the sheet when the average aspect ratio D (L / S) and the average aspect ratio D (M / S) are within the above ranges. Here, the disk shape is not limited to a circular shape in a plan view, and may be an elliptical shape or a shape further modified from a circular or elliptical shape.

The standard deviation (σM) of the bubble diameter on the central axis is not particularly limited, but is preferably smaller than the standard deviation (σL) of the bubble diameter on the long axis. The standard deviation (σS) of the bubble diameter on the short axis is not particularly limited, but is preferably smaller than any of the standard deviation (σL) and the standard deviation (σM) of the bubble diameter on the major axis and the middle axis, respectively.
The average cell diameter (DL), average cell diameter (DM), average cell diameter (DS), standard deviation (σL), standard deviation (σM), and standard deviation (σS) are as shown in Examples described later. In addition, it is calculated from the bubble diameter measured in the three-dimensional image taken by X-ray CT. The average aspect is similar.
Further, the coefficient of variation (VL) on the major axis obtained by dividing the standard deviation (σL) by the average cell diameter (DL) is preferably less than 1. When the coefficient of variation (VL) is less than 1, it becomes possible to further reduce the variation in the bubble diameter on the long axis. The coefficient of variation (VL) is preferably 0.7 or less, more preferably 0.55 or less, from the viewpoint of reducing variation in bubble diameter on the long axis.
Further, the coefficient of variation (VM) on the central axis obtained by dividing the standard deviation (σM) by the average cell diameter (DM) and the coefficient of variation (VS) on the short axis obtained by dividing the standard deviation (σS) by the average cell diameter (DS), respectively. Also, it is preferably less than 1, more preferably 0.7 or less, and even more preferably 0.55 or less.
The lower the coefficient of variation (VL) is, the more the variation in the bubble diameter can be suppressed, but it is usually 0.1 or more, and practically 0.2 or more. The same applies to the coefficient of variation (VM) and (VS).

(Closed cell ratio)
In the resin foam sheet, the bubbles are closed cells as described above. The fact that the cells are closed cells means that the ratio of the closed cells to the total cells (referred to as the closed cell ratio) is 70% or more. The closed cell ratio is preferably 75% or more, more preferably 90% or more.
The closed cell ratio can be determined according to ASTM D2856 (1998). Examples of commercially available measuring instruments include the dry automatic densitometer Accupic 1330.

The closed cell ratio is more specifically measured as follows. A test piece having a square shape with a side of 5 cm and a constant thickness is cut out from the resin foam sheet. The thickness of the test piece was measured, to measure the weight W ₁ of the specimen to calculate the apparent volume V ₁ of the test piece. Next, the apparent volume V ₂ occupied by the bubbles is calculated based on the following formula. The density of the resin constituting the test piece is 1 g / cm ³ .
Apparent volume occupied by bubbles V ₂ = V ₁ −W ₁
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 for 3 minutes. After releasing the pressure in water, the test piece is taken out of the water to remove the water adhering to the surface of the test piece, the weight W _{2 of the} test piece is measured, and the open cell ratio F ₁ and the closed cell ratio are based on the following formulas. Calculate F ₂ .
Continuous bubble ratio F ₁ (%) = 100 × (W _2- W ₁ ) / V ₂
Closed cell ratio F ₂ (%) = 100-F ₁

(Crosslink degree)
The resin foam sheet is preferably crosslinked, and the degree of crosslinking is preferably 30% by mass or more. By setting the degree of cross-linking to 30% by mass or more, the average bubble diameter and the standard deviation of the bubbles of the resin foam sheet can be reduced, and the surface roughness can be easily reduced. From these viewpoints, the degree of cross-linking is more preferably 35 to 70% by mass, further preferably 38 to 60% by mass. By setting the degree of cross-linking to these upper limit values or less, it becomes easy to appropriately foam the foam. The degree of cross-linking can be measured by the method described in Examples.

(Dimensions of resin foam sheet)
The thickness of the resin foam sheet is preferably 0.05 to 0.5 mm. When the thickness is 0.05 mm or more, it becomes easy to secure the mechanical strength of the resin foam sheet. Further, when the thickness is 0.5 mm or less, the sheet can be made thin, and it can be suitably used for a miniaturized electronic device. From these viewpoints, the thickness of the resin foam sheet is more preferably 0.06 to 0.4 mm, further preferably 0.08 to 0.35 mm.

(Expansion magnification)
The foaming ratio of the resin foam sheet is preferably 1.2 to 10.0 cm ³ / g. By setting the foaming ratio to 1.2 cm ³ / g or more, the compression strength and flexibility are improved, and the impact absorption and sealing property of the resin foam sheet are likely to be improved. On the other hand, when the thickness is 10.0 cm ³ / g or less, the mechanical strength is increased and the durability is more easily improved. In addition, the average cell diameter and the standard deviation of the cell diameter are reduced, and the surface roughness can be easily reduced. In view of the foregoing, expansion ratio is more preferably 1.3~9.0cm ³ / g, more preferably 1.5~8.5cm ³ / g. In the present invention, the density of the foamed sheet is determined according to JIS K7222, and the reciprocal of the density is defined as the foaming ratio.

(Compression strength)
The 25% compressive strength of the resin foam sheet is preferably 10 to 2000 kPa, more preferably 40 to 1500 kPa. By setting the 25% compression strength to 2000 kPa or less, the resin foam sheet is imparted with shock absorption and sealing properties, and can be suitably used as a buffer absorbing material and a sealing material. Further, when it is set to 10 kPa or more, it becomes easy to improve the mechanical strength. The 25% compression strength refers to a resin foam sheet measured in accordance with JIS K6767.

[Polyolefin resin]
As the resin used for the resin foam sheet, various resins may be used, and among them, polyolefin resin is preferably used. By using the polyolefin resin, it is possible to reduce the surface roughness while ensuring the flexibility of the resin foam sheet.
Examples of the polyolefin resin include polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer and the like, and among these, polyethylene resin is preferable.
Examples of the polyethylene resin include polyethylene resins polymerized with a polymerization catalyst such as a Cheegler-Natta compound, a metallocene compound, and a chromium oxide compound, and preferably, a polyethylene resin polymerized with a polymerization catalyst of a metallocene compound is used.

Further, as the polyethylene resin, linear low density polyethylene is preferable. By using the linear low-density polyethylene, high flexibility can be obtained in the obtained resin foamed sheet, and the thickness of the resin foamed sheet can be thinned. The linear low-density polyethylene is more preferably obtained by using a polymerization catalyst such as a metallocene compound. Further, the linear low-density polyethylene can be 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, if necessary, a small amount of α-olefin. The linear low density polyethylene to be obtained is more preferable.
Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene and the like. Among these, α-olefins having 4 to 10 carbon atoms are preferable.
Polyethylene resin, for example the density of the linear low density polyethylene as described above is preferably 0.870~0.910g / cm ^3, more preferably 0.875~0.907g / cm ^3, 0.880~0.905g / Cm ³ is more preferred. As the polyethylene resin, a plurality of polyethylene resins may be used, and polyethylene resins other than the above-mentioned 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, one or more cyclopentadienyl rings or their analogs are present as ligands in tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum. Compounds can be mentioned.
In such a metallocene compound, the properties of active sites are uniform, 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. Therefore, when a sheet containing a polymer synthesized using a metallocene compound is crosslinked, the cross-linking is uniform. Proceed to. Since the uniformly crosslinked sheet is uniformly foamed, it is easy to reduce the standard deviation as described above. Moreover, since it can be stretched uniformly, the thickness of the resin foam sheet can be made uniform.

Examples of the ligand include a cyclopentadienyl ring, an indenyl ring and the like. 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 methyl group, ethyl group, various propyl group, various butyl group, various amyl group, various hexyl group, 2-ethylhexyl group, various heptyl group, various octyl group, various nonyl group and various decyl group. , Various cetyl groups, phenyl groups and the like. In addition, "various" means various isomers including n-, sec-, tert-, and iso-.
Further, a product obtained by polymerizing a cyclic compound as an oligomer may be used as a ligand.
Furthermore, 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, and aryls. You may use phosphide or the like.

Examples of the metallocene compound containing a tetravalent transition metal, a ligand, etc. include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), and bis (cyclopentadienyl) titanium dichloride. Examples thereof include dimethylsilyltetramethylcyclopentadienyl-t-butylamide zirconium dichloride.
The metallocene compound exerts an action as a catalyst in the polymerization of various olefins by combining with a specific co-catalyst (co-catalyst). Specific examples of the co-catalyst include methylaluminoxane (MAO) and boron-based compounds. The ratio of the cocatalyst used to the metallocene compound is preferably 10 to 1 million mol times, more preferably 50 to 5,000 mol times.
When the above-mentioned linear low-density polyethylene is used as the polyolefin resin contained in the resin foam sheet, the above-mentioned linear low-density polyethylene may be used alone or in combination with other polyolefin resins. Often, for example, it may be used in combination with other polyolefin resins described below. When the other polyolefin resin is contained, the ratio of the other polyolefin resin to the linear low-density polyethylene (100% by mass) is preferably 40% by mass or less, more preferably 30% by mass or less, and further preferably 20% by mass or less. preferable.

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 polypropylene and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. One of these may be used alone, or two or more thereof may be used in combination.
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-hexene, and 1-. Octene and the like can be mentioned. Of these, α-olefins having 6 to 12 carbon atoms are preferable.

When a polyolefin resin is used as the resin, the polyolefin resin may be used alone, or may contain a resin other than the polyolefin resin. In the resin foam sheet, the ratio of the polyolefin resin to the total amount of the resin is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more.
Examples of the resin other than the polyolefin resin used for the resin foam sheet include various elastomers such as styrene-based thermoplastic elastomer and EPDM.

(Pyrolytic foaming agent)
The resin foam sheet of the present invention is preferably formed by foaming a foamable composition containing the above resin and a thermally decomposable foaming agent. Further, as the pyrolysis type foaming agent, it is preferable to use one having a particle size of less than 15 μm. By using a resin having a particle size of less than 15 μm, the degree of cross-linking can be increased as described above, and the bubble diameter and standard deviation of the resin foam sheet can be reduced, and the surface roughness can be easily reduced. .. The particle size of the pyrolysis foaming agent is preferably 2 to 14 μm, more preferably 5 to 13 μm.
The particle size of the pyrolysis foaming agent is a value measured by a laser diffraction method and means a particle size (D50) corresponding to a cumulative frequency of 50%.

As the pyrolytic foaming agent, an organic foaming agent and an inorganic foaming agent can be used. Examples of the organic foaming agent include azodicarboxylic amides, azodicarboxylic acid metal salts (such as barium azodicarboxylic acid), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine, and hydrazine. Examples thereof include zodicarboxylic amides, hydrazine derivatives such as 4,4'-oxybis (benzenesulfonyl hydrazide) and toluenesulfonyl hydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium boron hydride, monosoda anhydrous citrate and the like.
Among these, an azo compound is preferable, and an azodicarbonamide is more preferable, from the viewpoint of obtaining fine bubbles, economy, and safety. One of these may be used alone, or two or more thereof may be used in combination.
The blending amount of the thermally decomposable foaming agent in the effervescent composition is preferably 1 to 10 parts by mass, more preferably 1 to 8 parts by mass, still more preferably 1.5 to 7 parts by mass with respect to 100 parts by mass of the resin. ..

Further, the effervescent composition preferably contains a bubble nucleation adjusting agent in addition to the above resin and a pyrolysis type effervescent agent. Examples of the bubble nucleating agent include zinc compounds such as zinc oxide and zinc stearate, and organic compounds of citric acid and urea, and among these, zinc oxide is preferable. By using a bubble nucleating agent in addition to the above-mentioned small particle size foaming agent, it becomes easier to reduce the bubble diameter and standard deviation. The blending amount of the bubble nucleating agent is preferably 0.4 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, still more preferably 0.8 to 2.5 parts by mass with respect to 100 parts by mass of the resin. ..
The effervescent composition contains, if necessary, additives generally used for foams such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and fillers, in addition to the above. You may be doing it.

[Manufacturing method of resin foam sheet]
The method for producing the resin foam sheet is not particularly limited, but for example, it is produced by heating a foamable composition containing a resin and a pyrolysis foaming agent and foaming the pyrolysis foaming agent. More specifically, the manufacturing method includes the following steps (1) to (4).
Step (1): Mixing a resin and an additive containing a pyrolysis type foaming agent to form a sheet-like foamable composition (resin sheet) Step (2): Forming a sheet-like foamable composition Steps of irradiating ionizing radiation to crosslink the effervescent composition (3): Steps of heating the crosslinked effervescent composition to foam a pyrolytic foaming agent to form fine bubbles (4). ): A step of forming fine bubbles and then stretching in either one or both of the MD direction and the TD direction to stretch the fine bubbles to obtain a resin foam sheet.

In the step (1), the method for molding the resin sheet is not particularly limited, but for example, the resin and the additive are supplied to the extruder, melt-kneaded, and the foamable composition is extruded into a sheet from the extruder. The resin sheet may be molded according to the above.
As a method of cross-linking the foamable composition in the step (2), a method of irradiating the resin sheet with ionizing radiation such as electron beam, α ray, β ray, and γ ray is used. The irradiation amount of the ionizing radiation may be adjusted so that the degree of cross-linking of the obtained foamed sheet is within the above-mentioned desired range, but 5 to 15 Mrad is preferable, and 6 to 13 Mrad is more preferable.
In the step (3), the heating temperature at which the foamable composition is heated to foam the pyrolysis-type foaming agent may be equal to or higher than the foaming temperature of the pyrolysis-type foaming agent, but is preferably 200 to 300 ° C., 220. ~ 280 ° C. is more preferable.

The stretching of the resin foam sheet in the step (4) may be performed after the resin sheet is foamed to obtain the resin foam sheet, or may be performed while foaming the resin sheet. When the resin foamed sheet is stretched after the resin foamed sheet is foamed to obtain the resin foamed sheet, the resin foamed sheet is continuously stretched while maintaining the molten state at the time of foaming without cooling the resin foamed sheet. Alternatively, after cooling the resin foam sheet, the resin foam sheet may be heated again to be in a molten or softened state, and then the resin foam sheet may be stretched.
In the step (4), the draw ratio of the resin foam sheet in one or both of the MD direction and the TD direction is preferably 1.1 to 5.0 times, more preferably 1.5 to 4.0 times.
When the draw ratio is at least the above lower limit value, the flexibility and tensile strength of the resin foam sheet tend to be improved. On the other hand, when it is set to the upper limit or less, it is prevented that the foamed sheet is broken during stretching, or the foamed gas is released from the foamed sheet during stretching and the foaming ratio is significantly lowered, and the flexibility and tension of the resin foamed sheet are prevented. The strength becomes good, and it becomes easy to make the quality uniform.
Further, the resin foam sheet may be heated to, for example, 100 to 280 ° C., preferably 150 to 260 ° C. during stretching.

However, the present production method is not limited to the above, and a resin foam sheet may be obtained by a method other than the above. For example, instead of irradiating with ionizing radiation, the effervescent composition may be preliminarily blended with an organic peroxide, and the effervescent composition may be heated to decompose the organic peroxide for cross-linking. Good.

From the viewpoint of reinforcing the mechanical strength, the resin foam sheet is preferably a resin foam sheet with a support in which supports are bonded together and the support is arranged on at least one surface. At this time, the surface to which the supports are attached is a surface having a surface roughness of 12.0 μm or less at the maximum height Rz and 2.0 μm or less at the arithmetic mean roughness Ra.
Examples of the support include a fiber base material, an organic film, a metal film, and the like. Among these, an organic film is preferable from the viewpoint of handleability and versatility.
Examples of the organic film include polyester films such as polyethylene terephthalate (PET) film, polybutylene terephthalate (PBT) film, and polyethylene naphthalate (PEN) film; polyethylene (PE) film, biaxially stretched polypropylene (OPP) film, and none. Polyolefin films such as stretched polypropylene (CPP) films; polyimide films, polycarbonate films, polyvinyl acetate films and the like can be mentioned. Among these, a polyolefin film is preferable, and a biaxially stretched polypropylene (OPP) film is more preferable from the viewpoint of handleability and versatility.

The thickness of the support is not particularly limited, but is preferably 10 to 500 μm, more preferably 12 to 200 μm, and even more preferably 15 to 100 μm from the viewpoint of handleability.

The adhesion strength between the resin foam sheet and the support is 0 to 0.2 N from the viewpoint of making the support function effectively as a reinforcing material during processing and allowing the support to be easily peeled off after processing. / Mm is preferable, 0.01 to 0.15 N / mm is more preferable, and 0.01 to 0.12 N / mm is further preferable.
The adhesion strength described above can be measured by the method described in Examples.

The support may be attached to the resin foam sheet obtained in the above steps (1) to (4). It is preferable that the resin foam sheet and the support are bonded under pressure. Pressurization can be performed using, for example, a roll press, a flat plate press, or the like. The crimping pressure at the time of pressurization may be appropriately determined according to the material of the support and the like, and can be, for example, in the range of 0.4 to 0.6 MPa.

When the resin foam sheet of the present invention has a support, the support is usually peeled off after processing or the like.
The use of the resin foam sheet is not particularly limited, but it is preferably used inside an electronic device, for example. Since the resin foam sheet of the present invention is thin but has excellent handleability, it can be suitably used inside various portable electronic devices in which a space for arranging the resin foam sheet is small. Examples of portable electronic devices include mobile phones, cameras, game devices, electronic organizers, personal computers and the like. The resin foam sheet can be used as a shock absorber and a sealing material inside an electronic device. Further, it may be used for an adhesive tape using a resin foam sheet as a base material.

The adhesive tape includes, for example, a resin foam sheet and an adhesive layer provided on at least one surface of the resin foam sheet, and a double-sided adhesive tape having adhesive layers on both sides is preferable.
The thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive tape is preferably 5 to 200 μm, more preferably 7 to 150 μm, and even more preferably 10 to 100 μm. When the thickness of the pressure-sensitive adhesive layer is in the range of 5 to 200 μm, the thickness of the structure fixed by using the pressure-sensitive adhesive tape can be reduced.
The pressure-sensitive adhesive used for the pressure-sensitive adhesive layer is not particularly limited, and for example, an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, or the like can be used.
Further, a release sheet such as a paper pattern may be further attached on the pressure-sensitive adhesive layer.
The method of forming the adhesive layer on at least one surface of the resin foam sheet is not particularly limited. For example, a method of applying an adhesive to at least one surface of the resin foam sheet using a coating machine such as a coater, a method of applying an adhesive to the resin foam sheet. A method of spraying and applying an adhesive to at least one surface using a spray, a method of applying an adhesive to at least one surface of a resin foam sheet using a brush, and a method of applying an adhesive layer formed on a release sheet to at least one surface of the resin foam sheet. Examples thereof include a method of transferring to.

The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[Measuring method]
The measurement method and evaluation method of each physical property are as follows.
<Maximum height Rz, arithmetic mean roughness Ra>
A laser microscope "VK-X100" manufactured by KEYENCE CORPORATION was used to photograph the surface of the resin foam sheet at a magnification of 10 times, and then analysis was performed using the attached analysis application. A measurement line having a length of 1 mm was set at an arbitrary position on the photographed screen, and the line roughness curve of that portion was measured. Next, the obtained curve was analyzed under the conditions shown below, and the maximum height Rz and the arithmetic mean roughness Ra of the arbitrary position were calculated. Further, the same measurement was performed at any three points of the resin foam sheet, and the average values were taken as the maximum height Rz of the resin foam sheet and the arithmetic mean roughness Ra.
<Analysis conditions>
・ Light intensity smoothing: None ・ Height smoothing: ± 12 simple average ・ Tilt correction: None ・ Cutoff by phase compensation type reduction filter: λs25μm, no λc

<Average cell diameter and standard deviation>
The average cell diameter and standard deviation were measured according to the following method.
(Shooting 3D images)
The resin foam sheet was cut into about 5 mm square and imaged using an X-ray CT device (TDM1000H-II (2K) manufactured by Yamato Scientific Co., Ltd.) (tube voltage 40 kV, tube current 0.087 mA) to obtain a continuous tomographic image. ..
(Analysis of 3D image)
The obtained tomographic image was image-processed using Aviso9 (manufactured by FEI). First, in the central part of the image, a region having a size of containing about 1000 bubbles was set as a measurement region, and the outer image was erased. The size of the region was 0.4 mm × about 0.45 mm in Example 1 and about 3 mm × about 4.5 mm in Comparative Example 1. In the thickness direction, the sample thickness was used as the measurement region as it was. Then, after removing noise with a median filter, binarization was performed to distinguish between the resin part and the bubble part. A three-dimensional image was obtained by performing surface rendering on the image data from which only the bubble portion was extracted. Bubbles on the boundary between the measurement area and the outside were deleted. Labeling was performed on the bubbles in the remaining measurement region, and the maximum length, the second maximum length, and the third maximum length of each bubble on each side of the close rectangular parallelepiped were calculated as the lengths of the major axis, the middle axis, and the minor axis of the bubbles, respectively. .. Among the measured bubbles, the average values of the major axis, the middle axis, and the minor axis of the bubbles having a major axis length of 30 μm or more are defined as the average cell diameter (DL), the average cell diameter (DM), and the average cell diameter (DS), respectively. did. However, if the number of measurement data used for calculating each average bubble diameter is less than 100, it is assumed that there are not enough bubbles to be measured and there is no measurement data.

In addition, the standard deviations (σL, σM, σS) were calculated from the individual measurement data used for calculating the average cell diameter (DL), average cell diameter (DM), and average cell diameter (DS). The following general formula was used to calculate the standard deviation. Note that σ is the standard deviation, χ is the measurement data, and n is the number of measurements.

Further, the ratio of (length of major axis / length of minor axis) in each bubble whose average cell diameter was measured was calculated, and the average value was taken as the average aspect ratio D (L / S). Similarly, the average value of the ratios (length of the central axis / length of the minor axis) was defined as the average aspect ratio D (M / S).

<Apparent density and foaming ratio>
The apparent density of the resin foam sheet was measured in accordance with JIS K7222, and the reciprocal of the density was taken as the foam magnification.

<Crosslink degree>
About 100 mg of a test piece is collected from the resin foam sheet, 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 left for 24 hours, 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 values, the degree of cross-linking (mass%) was calculated by the following formula.
Degree of cross-linking (mass%) = 100 x (B / A)

<Closed cell ratio>
The measurement was performed according to the method described in the specification.

<25% compression strength>
The 25% compression strength of the resin foam sheet was measured according to JIS K6767.

<Adhesion to the support>
An OPP film having a thickness of 20 μm was attached to one surface of the resin foam sheet with a force of 0.5 MPa to obtain a resin foam sheet with a support. At this time, the surface on which the OPP film was attached was the surface on which the maximum height Rz and the arithmetic mean roughness Ra were measured. The resin foam sheet with a support was cut to a length of 25 mm × 250 mm, and then the foam surface was bonded to a SUS plate using double-sided tape to prepare a measurement sample.
The SUS plate was fixed so that the length direction of the resin foam sheet coincided with the vertical direction, and the measurement sample was set in a tensile tester (“Tencilon Universal Material Tester” manufactured by A & D Co., Ltd.). Then, the OPP film was pulled vertically upward at a peeling angle of 180 ° and a speed of 300 mm / min, and the load when the resin foam sheet and the OPP film were peeled off was measured, and the measured value was used as the adhesion force to the support.

[Example 1]
Linear low density polyethylene resin (LLDPE) (manufactured by Dow Chemical Co., Ltd., trade name "Affinity PL1850", density: 0.902 g / cm ³ ) obtained by a polymerization catalyst of a metallocene compound, 100 parts by mass, and pyrolysis type foaming 2.1 parts by mass of azodicarboxylic amide having a particle size of 13 μm as an agent, 1.0 part by mass of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., trade name “OW-212F”) as a bubble nucleating agent, and 0 antioxidant. .5 parts by mass was supplied to an extruder, melt-kneaded at 130 ° C., and extruded into a long resin sheet having a thickness of 290 μm.
Next, after the resin sheet was crosslinked by irradiating both sides of the long resin sheet with an electron beam having an accelerating voltage of 500 kV by 7.4 Mrad, the crosslinked resin sheet was held at 250 ° C. by hot air and an infrared heater for foaming. It was continuously fed into the furnace and heated to foam to obtain a foamed sheet having a thickness of 300 μm.
Next, after the obtained foam sheet was continuously sent out from the foam furnace, the foam sheet was kept at a temperature of 200 to 250 ° C. on both sides of the foam sheet, and the foam sheet was 2.00 in the TD direction. The foamed sheet is stretched in the MD direction by stretching at a double stretching ratio and winding the foamed sheet at a winding speed faster than the feeding speed (supply speed) of the resin sheet to the foaming furnace to stretch the foamed sheet. The bubbles were stretched in the TD direction and the MD direction and deformed to obtain a resin foam sheet. The winding speed of the resin foam sheet was adjusted in consideration of the expansion amount in the MD direction due to the foaming of the resin sheet itself. The obtained resin foam sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

[Example 2]
The same procedure as in Example 1 was carried out except that the degree of cross-linking of the effervescent composition was 44% by mass and the stretching ratio in the TD direction was 2.5 times. The evaluation results of the obtained resin foam sheet are shown in Table 1.

[Example 3]
Except that the blending amount of the foaming agent (azodicarbonamide) in the effervescent composition was 3.6 parts by mass, the degree of cross-linking was 46% by mass, and the draw ratio in the TD direction was 2.5 times. It was carried out in the same manner as in Example 1. The evaluation results of the obtained resin foam sheet are shown in Table 1.

[Example 4]
The same procedure as in Example 1 was carried out except that the blending amount of the foaming agent (azodicarbonamide) in the effervescent composition was 6.0 parts by mass and the degree of cross-linking was 52% by mass. The evaluation results of the obtained resin foam sheet are shown in Table 1.

[Example 5]
The same procedure as in Example 1 was carried out except that the blending amount of the foaming agent (azodicarbonamide) in the effervescent composition was 6.4 parts by mass and the degree of cross-linking was 51% by mass. The evaluation results of the obtained resin foam sheet are shown in Table 1.

[Comparative Example 1]
The amount of the foaming agent (azodicarbonamide) blended in the effervescent composition was 1.3 parts by mass, the electron beam irradiation amount was 4.7 Mrad, the degree of cross-linking was 26% by mass, and the drawing in the TD direction. The procedure was carried out in the same manner as in Example 1 except that the magnification was set to 1.8 times. The evaluation results of the obtained resin foam sheet are shown in Table 1.

[Comparative Example 2]
Comparison except that the blending amount of the foaming agent (azodicarbonamide) in the effervescent composition was 6.0 parts by mass, the degree of cross-linking was 24% by mass, and the draw ratio in the TD direction was 1.5 times. It was carried out in the same manner as in Example 1. The evaluation results of the obtained resin foam sheet are shown in Table 1.

[Comparative Example 3]
Except that the blending amount of the foaming agent (azodicarbonamide) in the effervescent composition was 5.8 parts by mass, the degree of cross-linking was 26% by mass, and the stretching ratio in the TD direction was 2.5 times. It was carried out in the same manner as in Comparative Example 1. The evaluation results of the obtained resin foam sheet are shown in Table 1.

[Comparative Example 4]
Except that the blending amount of the foaming agent (azodicarbonamide) in the effervescent composition was 2.5 parts by mass, the degree of cross-linking was 29% by mass, and the draw ratio in the TD direction was 1.5 times. It was carried out in the same manner as in Comparative Example 1. The evaluation results of the obtained resin foam sheet are shown in Table 1.

As described above, in Examples 1 to 5, the resin foam sheet has reduced adhesion to the support by setting the maximum height Rz to 12.0 μm or less and the arithmetic mean roughness Ra to 2.0 μm or less. was gotten. On the other hand, in Comparative Examples 1 to 4, the resin used was the same as that in Example 1, but the maximum height Rz and the arithmetic mean roughness Ra were large, so that the reduction in adhesion to the support was insufficient. It was.

Next, Table 2 shows physical property values and the like representing the bubble shape of the resin foam sheets obtained in Example 1 and Comparative Example 1.

From Table 2, it can be seen that the resin foamed sheet of Example 1 having a small maximum height Rz and arithmetic mean roughness Ra has an average cell diameter and standard deviation smaller than that of the resin foamed sheet of Comparative Example 1. That is, it is suggested that the resin foam sheet of the present invention has uniform and sufficiently finely divided bubbles, whereby the surface roughness can be reduced.

Claims (10)

A resin foam sheet having closed cells, wherein the surface roughness of at least one surface of the resin foam sheet is 12.0 μm or less at the maximum height Rz and 2.0 μm or less at the arithmetic mean roughness Ra. A foamed sheet and a support are provided, and the support is arranged on at least one surface of the resin foamed sheet, and the surface roughness of the at least one surface is 12.0 μm at a maximum height Rz. A resin foam sheet with a support having the following and an arithmetic average roughness Ra of 2.0 μm or less . The resin foam sheet with a support according to claim 1, wherein the resin foam sheet contains a polyolefin resin. The resin foam sheet with a support according to claim 2, wherein the polyolefin resin is a polyethylene resin. The resin foam sheet with a support according to claim 3, wherein the polyolefin resin is a linear low-density polyethylene polymerized with a polymerization catalyst of a metallocene compound. The resin foam sheet has an average cell diameter (DL) of 120 μm or less on the major axis and a standard deviation (σL) of the cell diameter on the major axis of 60 μm or less, any one of claims 1 to 4. The resin foam sheet with a support described in. The resin foam sheet with a support according to any one of claims 1 to 5, wherein the degree of cross-linking is 30% by mass or more. The resin foam sheet with a support according to any one of claims 1 to 6, wherein the foaming ratio is 1.2 to 10.0 cm ³ / g. The resin foam sheet with a support according to any one of claims 1 to 7, wherein the thickness of the resin foam sheet is 0.05 to 0.5 mm. The resin foam sheet with a support according to any one of claims 1 to 8, wherein the 25% compression strength of the resin foam sheet is 10 to 2000 kPa. The resin foam sheet with a support according to any one of claims 1 to 9 , wherein the support is a polyolefin film.