JP7225665B2 - Polyolefin resin cross-linked foam sheet, method for producing polyolefin resin cross-linked foam sheet, and adhesive tape - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyolefin resin crosslinked foam sheet, a method for producing a polyolefin resin crosslinked foam sheet, and an adhesive tape.

Polyolefin-based resin crosslinked foams generally have excellent flexibility, shock-absorbing properties, and heat-insulating properties. Therefore, a polyolefin resin crosslinked foam sheet formed by molding a polyolefin resin crosslinked foam into a sheet has been widely used as a shock absorbing material or a waterproof/dustproof member in electronic and electrical equipment. (See Patent Document 1, for example).

WO2016/052557

As one of the general modes when the polyolefin resin cross-linked foam sheet is incorporated into electronic/electric devices as described above, a mode in which an adhesive is adhered to the surface of the polyolefin resin cross-linked foam sheet and used as an adhesive tape. It has been known. Therefore, polyolefin-based resin crosslinked foam sheets that are incorporated in electronic and electrical devices are required to have excellent adhesiveness to pressure-sensitive adhesives.

Further, in recent years, electronic and electric devices used in the field of information technology have been miniaturized and their display areas have been enlarged. Along with this, there is a demand for further reduction in the thickness of foamed sheets incorporated in electronic and electrical equipment. The inventors of the present application have found that slicing of the crosslinked foamed polyolefin resin sheet in the direction perpendicular to the thickness direction is useful for thinning the crosslinked foamed polyolefin resin sheet. However, due to the characteristics of polyolefin resin cross-linked foamed sheets with high flexibility and shock-absorbing properties, it may be difficult for the blade used for slicing to properly enter the direction perpendicular to the thickness direction of the foamed sheet. had a problem. Therefore, in the polyolefin-based resin crosslinked foamed sheet, it is desired to improve the adhesiveness to the adhesive and the slicing workability.

The present invention can be implemented as the following modes.

(1) According to one aspect of the present invention, a polyolefin-based resin crosslinked foam sheet is provided. This polyolefin resin crosslinked foam sheet contains 0.05 parts by mass or more and 0.5 parts by mass or less of a lubricant and 0.005 parts by mass or more and 0.05 parts by mass or less of silicon dioxide with respect to 100 parts by mass of the polyolefin resin. and, characterized in that at least one of the two surfaces of the polyolefin-based resin crosslinked foamed sheet has open cell cross sections.
(2) The polyolefin-based resin cross-linked foamed sheet according to (1), wherein the polyolefin-based resin is an ethylene-based copolymer.
(3) The polyolefin resin crosslinked foam sheet according to (1) or (2), wherein the lubricant is a fatty acid amide.
(4) The polyolefin resin crosslinked foam sheet according to any one of (1) to (3), wherein the polyolefin resin crosslinked foam sheet has a gel fraction of 35% or more.
(5) The polyolefin resin crosslinked foam sheet according to any one of (1) to (4) 4, wherein the polyolefin resin has an average cell diameter of 400 μm or less on the surface where the cell cross section opens. Crosslinked foam sheet.
(6) The polyolefin resin crosslinked foamed sheet according to any one of (1) to (5), wherein the surface roughness Ra of the surface where the cell cross section opens is 1 μm or more and 5 μm or less. Polyolefin resin cross-linked foam sheet.
(7) The polyolefin resin crosslinked foam sheet according to any one of (1) to (6), wherein the polyolefin resin crosslinked foam sheet has a thickness of 0.1 mm or more and 0.5 mm or less. A polyolefin resin crosslinked foam sheet having a density of 0.10 g/cm ³ or more and 0.50 g/cm ³ or less.
(8) A method for producing a polyolefin resin crosslinked foamed sheet according to any one of (1) to (7), comprising foaming a polyolefin resin containing a polyolefin resin, a lubricant and silicon dioxide. to prepare a crosslinked foamed sheet, slice the crosslinked foamed sheet in a direction perpendicular to the thickness direction of the crosslinked foamed sheet, and open the cell cross section on the sliced surface formed by slicing polyolefin resin crosslinked A method for manufacturing a foam sheet.
(9) In the method for producing a polyolefin resin crosslinked foam sheet according to (8), the polyolefin resin comprises slicing the crosslinked foam sheet, heating the sliced surface, and compressing and stretching the crosslinked foam sheet. A method for producing a crosslinked foam sheet.
(10) A pressure-sensitive adhesive tape, comprising: the polyolefin resin crosslinked foam sheet according to any one of (1) to (7); A pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive provided.
(11) The adhesive tape according to (10), wherein the adhesive is an acrylic adhesive.
(12) The adhesive tape according to (10) or (11), which is used for adhesively fixing a component constituting an electronic/electrical device to a main body constituting the electronic/electrical device. .

ADVANTAGE OF THE INVENTION According to this invention, it is a polyolefin resin crosslinked foam sheet. WHEREIN: The adhesiveness with an adhesive and the slicing processability can be improved.

A. Composition of polyolefin resin crosslinked foam sheet:
Hereinafter, embodiments of the present invention will be described in detail. A polyolefin-based resin crosslinked foam sheet according to an embodiment of the present invention includes a polyolefin-based resin, a lubricant, and silicon dioxide.

(A-1) Polyolefin resin:
The polyolefin-based resin contained in the polyolefin-based resin crosslinked foam sheet according to the embodiment of the present invention is not particularly limited. polyethylene-based resin can be exemplified. In addition, the definition of the density described above is that "ultra-low density" is less than 0.910 g/cm ³ , "low density" is 0.910 g/cm ³ or more and 0.940 g/cm ³ or less, and " “High density” means greater than 0.940 g/cm ³ and less than or equal to 0.965 g/cm ³ .

Moreover, when using polyethylene-type resin as polyolefin-type resin, an ethylene-type copolymer other than homopolyethylene can be used. Ethylene-based copolymers refer to copolymers and multi-component copolymers of ethylene and other monomers. Examples of ethylene copolymers include ethylene and α-olefins having 4 or more carbon atoms (e.g., 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, etc.), ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and the like obtained by polymerization.

In the ethylene-vinyl acetate copolymer, the vinyl acetate content is preferably 4.5% by mass or more, more preferably 10% by mass or more. Also, the vinyl acetate content is preferably 50% by mass or less, more preferably 35% by mass or less. Furthermore, the melting point of the ethylene-vinyl acetate copolymer is preferably 50°C or higher, more preferably 60°C or higher. Also, the melting point of the ethylene-vinyl acetate copolymer is preferably 110° C. or less, more preferably 100° C. or less. Here, there is a general correlation between the content of vinyl acetate and the melting point, and the higher the content of vinyl acetate, the lower the melting point of the ethylene-vinyl acetate copolymer. For example, when the vinyl acetate content is about 4.5 to 10% by mass, the melting point is about 110 to 100°C, and when the vinyl acetate content is about 10 to 35% by mass, the melting point is about 100 to 60°C. When the vinyl acetate content is about 35-50% by mass, the melting point is about 60-50°C. By reducing the content of vinyl acetate to 50% by mass or less and suppressing the lowering of the melting point of the ethylene-vinyl acetate copolymer, problems such as "swelling" in the production process of polyolefin resin crosslinked foam sheets, that is, resin input It is possible to suppress the occurrence of problems such as coalescence of resins. In addition, by making the content of vinyl acetate 4.5% by mass or more to suppress the increase in the melting point of the ethylene-vinyl acetate copolymer, polyolefin containing foaming agents etc. It is possible to suppress the inconvenience of decomposition of the foaming agent due to heat generated by shearing during melt-kneading of the resin composition. Furthermore, by setting the content of vinyl acetate to 4.5% by mass or more, it is possible to increase the flexibility and elongation of the resulting polyolefin-based resin crosslinked foamed sheet. The melt mass flow rate (MFR) of such ethylene-vinyl acetate copolymer based on JIS K6760 is not particularly limited, but is preferably 1 g/10 min or more and 25 g/10 min or less. By setting the MFR value to 1 g/10 minutes or more, it is possible to suppress the inconvenience of decomposition of the blowing agent due to heat generated by shearing during melt-kneading. Further, by setting the MFR value to 25 g/10 minutes or less, the viscosity of the polyolefin-based resin composition during melt-kneading can be suppressed, and melt-kneading can be easily performed without trouble.

In the ethylene-ethyl acrylate copolymer, the content of ethyl acrylate is preferably 2% by mass or more, more preferably 4% by mass or more. By setting the ethyl acrylate content to 2% by mass or more, it is possible to increase the flexibility and elongation of the obtained polyolefin-based resin crosslinked foamed sheet. The content of ethyl acrylate is preferably 30% by mass or less, more preferably 20% by mass or less. By setting the content of ethyl acrylate to 30% by mass or less, it is possible to prevent the obtained polyolefin-based resin crosslinked foam sheet from becoming excessively flexible. As a result, when the long polyolefin resin cross-linked foamed sheet is wound into a roll, it is possible to prevent the sheets from sticking to each other over time, thereby eliminating the inconvenience that the polyolefin resin cross-linked foamed sheet becomes difficult to remove from the roll. can be suppressed.

Further, the polyolefin resins include polypropylene resins represented by homopolypropylene, ethylene-propylene random copolymers, ethylene-propylene block copolymers, and the like.

The polyolefin resin contained in the polyolefin resin crosslinked foam sheet according to the embodiment of the present invention is more preferably low density polyethylene, linear low density polyethylene, ultra-low density polyethylene, ethylene-α-olefin copolymer, ethylene-acetic acid. A vinyl copolymer or an ethylene-ethyl acrylate copolymer may be used. More preferably, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer may be used. It is particularly preferable to use an ethylene copolymer as the polyolefin resin because a polyolefin resin crosslinked foam sheet having excellent flexibility and followability can be obtained. The polyolefin-based resin contained in the polyolefin-based resin cross-linked foamed sheet according to the embodiment of the present invention may be a single resin among the above-described polyolefin-based resins, or may be a mixture of a plurality of types of resins. .

(A-2) Lubricant and silicon dioxide:
The polyolefin-based resin cross-linked foamed sheet according to the embodiment of the present invention contains a predetermined amount of lubricant and silicon dioxide for improving adhesion and slicing processability. The "adhesiveness" of the polyolefin resin cross-linked foam sheet indicates the performance assuming that the polyolefin resin cross-linked foam sheet is provided with an adhesive layer and used as an adhesive tape. Adhesion can be evaluated by the peel strength between the polyolefin resin crosslinked foam sheet and the pressure-sensitive adhesive layer. The “slicing workability” of the polyolefin resin crosslinked foam sheet indicates the ability to satisfactorily slice the polyolefin resin crosslinked foam sheet. The slicing process is a process of slicing the polyolefin resin crosslinked foam sheet in a direction perpendicular to the thickness direction to make the polyolefin resin crosslinked foam sheet thinner.

As the lubricant contained in the polyolefin resin crosslinked foamed sheet according to the embodiment of the present invention, a known lubricant used for foam molding can be used. For example, fatty acid amides; fatty acid carboxylic acids such as stearic acid, behenic acid and 12-hydroxystearic acid and their derivatives; hydrocarbons such as liquid paraffin, paraffin wax, microwax and polyethylene wax; butyl stearate, monoglyceride stearate, penta fatty acid esters such as erythritol tetrastearate, hydrogenated castor oil and stearyl stearate; higher alcohols such as stearyl alcohol; metal soaps such as calcium stearate, zinc stearate, magnesium stearate and lead stearate. The lubricity exhibited by lubricants is classified into external lubricity, which provides lubricity on the contact surface between the resin and the processing machine, and internal lubricity, which improves the lubricity between the resins. The lubricant according to the embodiment of the present invention desirably exhibits excellent external lubricity from the viewpoint of improving the slicing processability of the polyolefin resin crosslinked foamed sheet. Fatty acid amides are preferably used as lubricants because they exhibit excellent external lubricity and are readily available.

Examples of fatty acid amides include hydroxy fatty acid amide, stearic acid amide, oleic acid amide, erucic acid amide, methylenebisstearic acid amide, ethylenebisstearic acid amide, ethylenebisstearic acid amide and the like.

The hydroxy fatty acid amide is not particularly limited, and can be appropriately selected from various compounds and used. Among them, those in which the number of carbon atoms in the hydroxy fatty acid portion is in the range of 8 or more and 22 or less are preferable, and those in which the number of carbon atoms is 18 are particularly preferable from the viewpoint of easy availability and effects to be obtained. Specific examples of hydroxy fatty acid amides include hydroxystearic acid amide, ricinoleic acid amide, ethylenebishydroxystearic acid amide, hexamethylenebishydroxystearic acid amide and the like. Hydroxy fatty acid amides contain hydroxyl groups, and are compounds that are remarkably adsorbed to metals by the hydroxyl groups. Therefore, by using a hydroxy fatty acid amide as a lubricant, the effect of reducing the dynamic friction coefficient between the polyolefin resin crosslinked foam sheet and the metal, improving the slipperiness, and improving the slicing workability can be particularly enhanced.

As the lubricant contained in the polyolefin-based resin cross-linked foamed sheet of the present embodiment, a single substance among the lubricants described above may be used, or a plurality of kinds of substances may be mixed and used.

The content of the lubricant in the polyolefin-based resin cross-linked foamed sheet is preferably 0.05 parts by mass or more, more preferably 0.06 parts by mass or more, relative to 100 parts by mass of the polyolefin-based resin. Also, the content of the lubricant is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, with respect to 100 parts by mass of the polyolefin resin. The content of silicon dioxide in the polyolefin resin crosslinked foam sheet is preferably 0.005 parts by mass or more, more preferably 0.006 parts by mass or more, relative to 100 parts by mass of the polyolefin resin. The content of silicon dioxide is preferably 0.05 parts by mass or less, more preferably 0.04 parts by mass or less, relative to 100 parts by mass of the polyolefin resin. In order to achieve the desired adhesiveness and slicing processability in the polyolefin resin crosslinked foamed sheet, it is desirable to blend both a lubricant and silicon dioxide and to satisfy the above range for each content. If the content of each of the lubricant and silicon dioxide is less than the above range, the effect of improving the adhesiveness and slicing processability of the polyolefin resin crosslinked foamed sheet will be insufficient. When the content of each of the lubricant and silicon dioxide is higher than the above range, the surface of the polyolefin resin crosslinked foamed sheet (for example, the sliced surface formed by slicing) contains more lubricant and silicon dioxide. Due to this, adhesion may be reduced. Furthermore, if the content of each of the lubricant and silicon dioxide is more than the above ranges, the appearance of the polyolefin resin crosslinked foamed sheet may be impaired. Specifically, if the content of the lubricant and silicon dioxide is high, in the process of manufacturing the polyolefin resin crosslinked foam sheet, when the polyolefin resin is formed into a sheet by extrusion molding, the sheet-like polyolefin resin discharged from the die Additives such as lubricants tend to bleed out from the resin. As a result, the bleed-out lubricant or the like is transferred to a polishing roll or the like used for conveying the sheet during production and adheres to the polyolefin resin sheet, impairing the appearance of the obtained polyolefin resin crosslinked foam sheet.

(A-3) Other components:
The polyolefin resin crosslinked foam sheet of the present embodiment may further contain other components as long as the influence on the properties of the polyolefin resin crosslinked foam sheet is within an allowable range. For example, it may contain a thermoplastic resin other than the polyolefin resin. Examples of thermoplastic resins other than polyolefin resins that do not contain halogen include polystyrene; acrylic resins such as polymethyl methacrylate and styrene-acrylic acid copolymers; styrene-butadiene copolymers; ethylene. polyvinyl acetate; polyvinyl alcohol; polyvinyl acetal; polyvinyl pyrrolidone; petroleum resin; cellulose; polyethylene; saturated alkyl polyester resins; aromatic polyester resins such as polyethylene terephthalate, polybutylene terephthalate and polyarytate; polyamide resins; polyacetal resins; polycarbonate resins; Examples thereof include copolymers having a nitrogen vinyl monomer. The halogen-free thermoplastic resin other than the polyolefin resin may further include an elastomer such as isoprene rubber, styrene-butadiene rubber, butyl rubber, dimethylsilicone rubber, and ethylene-propylene rubber. Examples of halogen-containing thermoplastic resins other than polyolefin resins include polyvinyl chloride, polyvinylidene chloride, polyvinylidene chloride trifluoride, polyvinylidene fluoride, fluorocarbon resins, perfluorocarbon resins, and solvents. Examples include soluble perfluorocarbon resins. The polyolefin-based resin crosslinked foam sheet of the present embodiment may contain one type of resin among the resins described above as a thermoplastic resin other than the polyolefin-based resin, or may contain a plurality of types of resin. may be The type of resin to be contained and the content of the resin to be contained may be appropriately set according to the desired physical properties of the polyolefin resin crosslinked foamed sheet.

Other components contained in the polyolefin resin crosslinked foam sheet of the present embodiment include various additives such as cell nucleus modifiers, antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and inorganic fillers. At least one of them may be used.

It is important that the polyolefin-based resin crosslinked foam sheet of the present embodiment contains a polyolefin-based resin as a main component. Here, the main component means the largest component in terms of mass in the polyolefin resin crosslinked foam sheet. More preferably, the polyolefin resin should be 50% by mass or more and 100% by mass or less in 100% by mass of all components of the polyolefin resin crosslinked foamed sheet. Thermoplastic resins other than the above-described polyolefin resins and other additives may be added in an amount of 0% by mass or more and 50% by mass or less in 100% by mass of all components of the polyolefin resin crosslinked foam sheet. The contents of the lubricant, silicon dioxide, and other additives in the polyolefin resin crosslinked foam sheet can be determined by gas chromatography mass spectrometry and elemental analysis of the polyolefin resin crosslinked foam sheet. The thermoplastic resin content in the polyolefin-based resin crosslinked foam sheet can be determined by measurement using a Fourier transform infrared spectrophotometer (FT-IR).

(A-4) Characteristics of polyolefin resin crosslinked foamed sheet:
The polyolefin-based resin crosslinked foamed sheet of the present embodiment has open cell cross sections on at least one of the two surfaces perpendicular to the thickness direction. The average bubble diameter on the surface where the cross section of the bubbles opens is preferably 400 μm or less, more preferably 380 μm or less, and even more preferably 350 μm or less. By making the average cell diameter on the surface where the cell cross section opens smaller, for example, 400 μm or less, the deterioration of the surface smoothness of the polyolefin resin crosslinked foam sheet is suppressed, and the deterioration of the adhesiveness with the pressure-sensitive adhesive described above. can be suppressed. It is considered that the suppression of such a decrease in adhesiveness is an effect obtained because a larger contact area with the pressure-sensitive adhesive can be ensured by suppressing a decrease in the smoothness of the surface of the polyolefin resin crosslinked foam sheet. In addition, the average bubble diameter on the surface where the cross section of the bubble opens is preferably 250 μm or more, more preferably 270 μm or more. To suppress an increase in the density of the polyolefin resin crosslinked foam sheet and secure the flexibility of the polyolefin resin crosslinked foam sheet by increasing the average cell diameter on the surface where the cell cross section opens, for example, 250 μm or more. becomes easier. The average cell diameter on the surface where the cell cross section opens is, for example, the gel fraction described later in the polyolefin resin crosslinked foam sheet, the type and amount of the foaming agent added to the polyethylene resin when producing the polyolefin resin crosslinked foam sheet, It can be adjusted by the temperature, time, etc. in the foaming step described later.

In the polyolefin-based resin cross-linked foamed sheet of the present embodiment, the surface roughness Ra of the surface where the cell cross section opens is preferably 1 μm or more, more preferably 2 μm or more. Blocking of the resin sheet is suppressed during and after the production of the polyolefin resin crosslinked foam sheet by increasing the surface roughness Ra of the surface where the cell cross section opens, for example, 1 μm or more. can be done. Blocking refers to a phenomenon in which stacked resin sheets adhere to each other and become difficult to separate. Further, the surface roughness Ra of the surface where the bubble cross section opens is preferably 5 μm or less, more preferably 4 μm or more. By making the value of the surface roughness Ra of the surface where the cell cross section opens smaller, for example, 5 μm or less, the deterioration of the smoothness of the surface of the polyolefin resin crosslinked foam sheet is suppressed, and as described above, the pressure sensitive adhesive It is possible to suppress the decrease in adhesion with. The surface roughness Ra of the surface where the cell cross section opens is, for example, the gel fraction described later in the polyolefin resin crosslinked foam sheet, and the type and amount of the foaming agent added to the polyethylene resin when manufacturing the polyolefin resin crosslinked foam sheet. , the temperature and time in the foaming step described later can be adjusted.

The gel fraction of the polyolefin-based resin crosslinked foamed sheet of the present embodiment is not particularly limited, but is preferably 35% or more, more preferably 36% or more. By increasing the gel fraction, for example, to 35% or more, it is possible to prevent the cells from becoming too large in the polyolefin-based resin crosslinked foamed sheet. As a result, the average cell diameter of the cross-section of the cells opened on the surface of the polyolefin resin crosslinked foam sheet is suppressed, and the surface smoothness of the polyolefin resin crosslinked foam sheet is deteriorated, and the adhesiveness with the above-mentioned adhesive is reduced. deterioration can be suppressed. Further, the gel fraction of the polyolefin resin crosslinked foamed sheet of the present embodiment is preferably 60% or less, more preferably 50% or less. By making the gel fraction smaller, for example, 60% or less, it becomes easier to control the foaming state of the sheet when producing the polyolefin resin crosslinked foamed sheet, and the cell cross section in the polyolefin resin crosslinked foamed sheet can be easily controlled. It becomes easy to adjust the average cell diameter, density, thickness, etc. of the polymer to a desired range. Furthermore, deterioration of flexibility of the polyolefin-based resin crosslinked foam sheet can be suppressed.

The gel fraction is a value that serves as an indicator of the degree of cross-linking in the polyethylene-based resin that constitutes the polyolefin-based resin cross-linked foam sheet. Specifically, the gel fraction is obtained by immersing a resin sample in a solvent and expressing the ratio of the dry mass (insoluble mass) of the resin sample after immersion to the mass of the resin sample before immersion, expressed as a percentage. value. In this embodiment, tetralin is used as the solvent for immersing the resin sample, and the immersion time is 3 hours. For example, when producing a polyolefin resin crosslinked foam sheet, when the polyolefin resin is crosslinked by irradiating the polyolefin resin with ionizing radiation, the gel fraction is determined by the irradiation dose for crosslinking (polyolefin resin can be adjusted by the absorbed dose absorbed by

The thickness of the polyolefin-based resin crosslinked foamed sheet of the present embodiment is preferably 0.1 mm or more, and may be 0.15 mm or more. By increasing the thickness of the polyolefin-based resin cross-linked foamed sheet to, for example, 0.1 mm or more, it becomes easy to ensure the impact absorption and cushioning properties of the polyolefin-based resin cross-linked foamed sheet. The thickness of the polyolefin-based resin crosslinked foam sheet is preferably 0.5 mm or less, and may be 0.4 mm or less. If the thickness of the polyolefin resin cross-linked foam sheet is made thinner, for example, 0.5 mm or less, the polyolefin resin cross-linked foam sheet can be used to fix the parts of electronic and electrical equipment to the device body. , making electronic and electrical equipment thinner. For example, in the process of producing a polyolefin resin crosslinked foam sheet, when a polyethylene resin is formed into a sheet by extrusion molding, the thickness of the polyolefin resin crosslinked foam sheet can be adjusted by the shape of the die of the extruder. . Furthermore, in the manufacturing process of the polyolefin resin crosslinked foamed sheet, when the above-mentioned slicing process of slicing the polyolefin resin crosslinked foamed sheet in the direction perpendicular to the thickness direction is performed, the thickness of the polyolefin resin crosslinked foamed sheet is , can be adjusted by the arrangement of the slicing blades attached to the slicing device (clearance above and below the blades in the device).

The density of the polyolefin resin crosslinked foamed sheet of the present embodiment is preferably 0.10 g/cm ³ or more, more preferably 0.20 g/cm ³ or more. By increasing the density of the polyolefin resin crosslinked foam sheet, for example, 0.10 g/cm ³ or more, the strength and impact absorption of the polyolefin resin crosslinked foam sheet can be secured, or wrinkles can be generated during processing. is easier to suppress. Further, the density of the polyolefin resin crosslinked foamed sheet of the present embodiment is preferably 0.50 g/cm ³ or less, more preferably 0.40 g/cm ³ or less. By lowering the density of the polyolefin resin crosslinked foam sheet, for example, to 0.50 g/cm ³ or less, it is possible to prevent the polyolefin resin crosslinked foam sheet from becoming too hard and easily ensure cushioning properties. Become. The density of the polyolefin resin crosslinked foam sheet is determined by, for example, the gel fraction of the polyolefin resin crosslinked foam sheet, the type and amount of the foaming agent added to the polyethylene resin when producing the polyolefin resin crosslinked foam sheet, and the foaming process described later. can be adjusted by the temperature, time, etc. The density of the polyolefin-based resin crosslinked foamed sheet of the present embodiment is the density of the foam as a whole including the cells formed inside.

It is preferable that the polyolefin-based resin crosslinked foam sheet of the present embodiment has a closed cell structure. The term "closed-cell structure" as used herein refers to a structure in which there are no holes or the like for communication between the cells in the resin portion existing between the cells, and gas does not flow between the adjacent cells. On the other hand, the open-cell structure refers to a structure in which adjacent cells communicate with each other through pores, and gas flows between the cells. By having a closed-cell structure, it is possible to enhance the cushioning properties of the polyolefin-based resin cross-linked foamed sheet, and at the same time, it is possible to obtain the effect that the polyolefin-based resin cross-linked foamed sheet can be more easily molded. In the polyolefin-based resin crosslinked foamed sheet of the present embodiment, the closed cell ratio is preferably at least 90% or more.

The closed cell content in the foam sheet refers to a value measured as follows. That is, samples cut into 25 mm squares are superimposed to a thickness of about 5 cm to prepare a sample piece, and the actual volume V of this sample piece is measured by a micromeritex dry automatic density meter (manufactured by Shimadzu Corporation, Accupic II (V1. 0)). At this time, the sample pieces are stacked so as to minimize the gap between the stacked samples to a thickness of about 5 cm. Also, the apparent volume V0 of the sample piece is calculated from the outer shape of the sample piece. From the obtained value, the closed cell ratio (%) is calculated by the following formula.
Closed cell rate (%) = [1-(V0-V)/V0] x 100

The surface of the polyolefin resin crosslinked foam sheet of the present embodiment may be subjected to a known surface treatment. For example, chemical or physical surface treatments such as undercoating, corona discharge treatment, and plasma treatment may be applied. More specifically, conventional surface treatments such as corona discharge treatment, chromic acid treatment, ozone exposure, flame exposure, high-voltage shock exposure, ionizing radiation treatment, etc. are performed in order to enhance the adhesion to the acrylic pressure-sensitive adhesive layer. It may be subjected to oxidation treatment or the like by a chemical or physical method, or may be subjected to coating treatment or the like using an undercoat agent or a release agent. Corona discharge treatment is desirable from the viewpoint of not changing the surface smoothness of the polyolefin resin crosslinked foamed sheet.

B. Method for producing polyolefin resin crosslinked foamed sheet:
The method for producing the polyolefin resin crosslinked foam sheet of the present embodiment is not particularly limited. and a step of slicing the crosslinked foamed sheet in a direction perpendicular to its thickness direction to open the cross section of cells on the slice surface formed by slicing (hereinafter also referred to as a slicing step). , is preferred. Furthermore, after slicing the crosslinked foam sheet, the crosslinked foam sheet may be heated and further compressed and stretched (hereinafter also referred to as a heating/compressing/stretching process). As the method for producing the polyolefin-based resin crosslinked foamed sheet of the present embodiment, it is preferable to employ a mode in which a long resin sheet is continuously conveyed by a roll-to-roll system and subjected to each step.

(B-1) Crosslinked foam sheet forming step:
The step of forming a crosslinked foamed sheet from a resin composition obtained by blending a lubricant and silicon dioxide with a polyolefin resin includes a step of forming a crosslinked foamed sheet into a sheet, and a step of forming the resin composition into a sheet. and a foaming step of foaming the polyolefin crosslinked resin. In this embodiment, preferably, the sheeting process, the cross-linking process, and the foaming process are performed in this order. However, in the step of forming the crosslinked foamed sheet, it is also possible to change the order of each step or perform a plurality of steps simultaneously.

The sheeting step can be carried out, for example, by melt-kneading a polyolefin-based resin composition containing a polyolefin-based resin, a lubricant, silicon dioxide, and a thermally decomposable foaming agent, and then extruding. Specifically, for example, a predetermined amount of the polyolefin resin composition is mixed with a thermally decomposable foaming agent using a kneading device such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader mixer, or a mixing roll. It is uniformly melted and kneaded below the decomposition temperature and formed into a sheet. In order to remove volatile components generated during processing, the kneading apparatus may be provided with a degassing facility such as a vacuum vent, if necessary. The (L/D) ratio, which is the length-to-diameter ratio in the extruder, is also not particularly limited. The above polyolefin-based resin composition may further contain additives as other components described above.

Since the lubricant and silicon dioxide hardly decompose during the manufacturing process, the content of the lubricant and silicon dioxide in the polyolefin resin crosslinked foamed sheet of the present embodiment described above is the same as the lubricant and silicon dioxide in the polyolefin resin composition. It matches the amount of silicon compounded. The form of raw materials for these lubricant and silicon dioxide is not particularly limited, and for example, they may be prepared in the form of powder or resin-containing pellets and supplied to the kneading apparatus described above. In addition, it may be prepared as a compound containing other additives, if necessary. The lubricant and silicon dioxide may be added to the polyolefin-based resin during melt-kneading of the polyolefin-based resin, or may be added to the polyolefin-based resin before melt-kneading.

The thermal decomposition type foaming agent is not particularly limited as long as it has a decomposition temperature higher than the melting temperature of the resin composition containing the polyolefin resin, which is the raw material of the polyolefin resin crosslinked foam sheet of the present embodiment. Azodicarbonamide is preferred. In addition, hydrazodicarbonamide, azodicarboxylic acid barium salt, dinitrosopentaethylenetetramine, nitrosoguanidine, p,p'-oxybisbenzenesulfonyl, which is a blowing agent having a decomposition temperature equal to or higher than that of azodicarbonamide Semicarbazide, trihydrazine symmetric triazine, bisbenzenesulfonyl hydrazide, barium azodicarboxylate, azobisisobutyronitrile, toluenesulfonyl hydrazide, etc. may be used. These thermal decomposition type foaming agents may be used alone or in combination of two or more. The amount of the thermally decomposable foaming agent to be blended may be about 2 to 40 parts by mass with respect to 100 parts by mass of the total amount of the resin components, and the blending amount may be set according to the desired expansion ratio. Here, "100 parts by mass of the total amount of resin components" means 100 parts by mass of the total amount of all resins such as polyolefin resins and other thermoplastic resins. In this case, when additives and the like to be added to the polyolefin resin composition are prepared as pellets mixed with resin in advance, "100 parts by mass of the total amount of resin components" is the amount of resin in the pellet containing the additive. including.

The cross-linking step is carried out, for example, by irradiating the resin sheet obtained by the sheet forming step with a predetermined dose of ionizing radiation to cross-link the polyolefin resin. Electron beams, X-rays, β-rays, γ-rays, etc. are used as ionizing radiation. The absorption dose absorbed by the resin sheet may be, for example, 1 kGy or more and 300 kGy or less, and may be appropriately set according to the desired gel fraction. The cross-linking step may be performed by cross-linking by peroxide or silane cross-linking instead of cross-linking by irradiation of ionizing radiation.

In the foaming step, for example, the resin sheet after the cross-linking step is heated to a temperature higher than the decomposition temperature of the thermal decomposition foaming agent and higher than the melting point of the polyolefin resin composition, for example, a temperature range of 190°C or higher and 290°C or lower. is carried out by heating at Heating of the resin sheet in the foaming step can be performed using, for example, hot air, infrared rays, a metal bath, an oil bath, a salt bath, or the like. The time of the foaming step is adjusted by the length of the portion where the heat medium such as hot air is arranged in the conveying path of the resin sheet to be crosslinked, the conveying speed when the resin sheet is conveyed while being in contact with the heat medium, and the like. be able to. Through such a foaming process, a crosslinked foamed sheet made of the polyolefin resin composition is formed. In the foaming step, by heating with hot air or the like as described above, a crosslinked foamed sheet having a surface on which almost no cells are opened (hereinafter referred to as a skin surface) is obtained as the sheet surface.

(B-2) Slicing step:
In the slicing step, as described above, the crosslinked foam sheet is sliced in a direction perpendicular to its thickness direction (ZD direction: Thickness Direction), and the cell cross section is opened on the sliced surface formed by slicing. It is a process. The direction perpendicular to the thickness direction of the crosslinked foam sheet refers to a direction parallel to the MD-TD plane defined by the MD direction (Machine Direction) and the TD direction (Transverse Direction) of the crosslinked foam sheet. When dividing the crosslinked and foamed sheet obtained in the crosslinked and foamed sheet forming step into two, the crosslinked and foamed sheet after splitting has a skin surface on one side and a sliced surface in which the cell cross section is opened on the other side. have The number of divisions in the slicing step may be three or more. By performing such a slicing step, a sliced surface can be formed on at least one surface of the crosslinked foam sheet, and the crosslinked foam sheet can be made thinner. Therefore, by adopting the slicing process when producing the polyolefin resin crosslinked foam sheet, the production efficiency of producing a relatively thin polyolefin resin crosslinked foam sheet can be increased. When one surface of the crosslinked foam sheet is used as a skin surface and the other surface is used as a slice surface, different functions are imparted to the front and back surfaces of the polyolefin resin crosslinked foam sheet of the present embodiment. becomes possible.

The equipment used for slicing the crosslinked foam sheet in the slicing step may be any equipment capable of slicing industrial soft materials and rubber sheets. The slicing step can be performed, for example, by using a slicer (splitting machine) having a blade that rotates in the width direction (TD direction) of the crosslinked foamed sheet while sandwiching the crosslinked foamed sheet between a pair of upper and lower nip rolls. As a slicer used in the slicing step, for example, "NP-120" manufactured by Nippi Machine Co., Ltd. can be used.

(B-3) Heating/compression/stretching step:
After the slicing step, a heating/compressing/stretching step of heating the crosslinked foam sheet and further compressing and stretching may be performed. However, these steps are not essential. Alternatively, for example, only the step of heating the crosslinked foam sheet may be performed.

In the step of heating the crosslinked foam sheet, at least one surface of the crosslinked foam sheet surfaces may be heated, and at least the sliced surfaces are preferably heated. For example, in an apparatus for producing a polyolefin resin crosslinked foamed sheet by a roll-to-roll method, an electric heater is provided downstream of the apparatus for performing the slicing step, and the sliced surface of the crosslinked foamed sheet is opposed to the heater. The crosslinked foam sheet may be continuously conveyed. The heating temperature may be a temperature at which the polyolefin resin constituting the crosslinked foam sheet softens, and may be a temperature equal to or lower than the melting point of the polyolefin resin. By heating the crosslinked foam sheet to soften the surface of the sliced surface in this way, the value of the surface roughness Ra of the sliced surface and the average cell diameter of the cross section of cells opened on the sliced surface are made smaller, The surface smoothness of the polyolefin resin crosslinked foam sheet can be enhanced. Thereby, the adhesiveness with the adhesive on the slice surface can be enhanced. However, the slicing step and the heating/compressing/stretching step may not be carried out continuously, but may be carried out independently.

The step of compressing and stretching the crosslinked foam sheet is a step of compressing the crosslinked foam sheet in the thickness direction (ZD direction) and applying a force to stretch the crosslinked foam sheet. Compression can be performed, for example, by sandwiching the crosslinked foam sheet between a pair of nip rolls. While compressing and holding down the crosslinked foam sheet in this manner, the crosslinked foam sheet can be stretched by applying a stretching force from the downstream side of the resin flow. At this time, since the heating is performed prior to the compressing and stretching steps, the crosslinked foamed sheet is softened and can be easily stretched to a desired extent. A thinner polyolefin-based resin crosslinked foam sheet can be obtained by carrying out the steps of compression and stretching. The stretching of the crosslinked foam sheet may be performed in multiple directions instead of in one direction. For example, it may be stretched only in the MD direction, which is the flow direction of the resin, or it may be stretched by applying a tensile force not only in the MD direction but also in the TD direction, which is the width direction of the crosslinked foam sheet. When the crosslinked foamed sheet is compressed as described above, the density of the obtained polyolefin resin crosslinked foamed sheet can be adjusted depending on the degree of compression. For example, by reducing the gap between the pair of nip rolls and increasing the degree of compression, the density of the polyolefin resin crosslinked foam sheet can be increased.

(B-4) Other manufacturing methods:
The production method of the polyolefin-based resin crosslinked foamed sheet of the present embodiment is not limited to the production method described above, and conventionally known different methods can be employed. An example is shown below. First, a polyolefin resin, a chemical cross-linking agent, a lubricant, silicon dioxide, and talc as a cell nucleating agent are mixed to prepare a resin composition, and then pellets are produced using an extruder. Next, the pellets are supplied to the first extruder of two-stage tandem extruders arranged in parallel and melt-kneaded. Then, from the middle of the first extruder, supercritical carbon dioxide gas (carbon dioxide) is injected as a foaming agent, and the molten resin composition and carbon dioxide are uniformly mixed and kneaded, and the foaming agent is included. A molten resin composition is continuously fed to a second extruder. In the second extruder, the molten resin composition is melt-kneaded and cooled to a resin temperature suitable for foaming. A cylindrical foam is obtained. A foam sheet may be obtained by incising this cylindrical foam with a cutter.

As described above, when a foamed sheet is produced by physical foaming, depending on the production conditions, the resulting foamed sheet may not have a skin surface and the cell cross section may be open on the surface. Even with such a polyolefin-based resin crosslinked foam sheet, the above-described effect of enhancing the adhesiveness with the pressure-sensitive adhesive can be obtained by setting the blending amounts of the lubricant and silicon dioxide to the polyolefin-based resin within the above-described range. be done. Further, the foamed sheet thus obtained may be further thinned by subjecting it to the slicing step described above. Even with such a configuration, the slicing workability is improved by setting the blending amounts of the lubricant and the silicon dioxide to the polyolefin resin within the ranges described above, so that the slicing process can be performed satisfactorily. Alternatively, the foamed sheet produced by the physical foaming may be further subjected to the heating/compressing/stretching steps described above.

C. Adhesive tape:
The polyolefin-based resin crosslinked foam sheet of the present embodiment can be suitably used for producing an adhesive tape. In order to produce an adhesive tape, an adhesive layer is laminated on the skin surface of the polyolefin resin cross-linked foamed sheet of the present embodiment, the surface where the cell cross section is open, or both the skin surface and the surface where the cell cross section is open. do it. When the surface on which the pressure-sensitive adhesive layer is laminated is the surface on which the cell cross section opens, the values of the average cell diameter and the surface roughness Ra on the surface on which the cell cross section opens are within the ranges described above. Adhesiveness with an adhesive can be improved.

As the adhesive contained in the adhesive layer, commonly used known adhesives can be used. Examples include acrylic adhesives, rubber adhesives (natural rubber adhesives, synthetic rubber adhesives, etc.), silicone adhesives, polyester adhesives, urethane adhesives, polyamide adhesives, and epoxy adhesives. , vinyl alkyl ether-based adhesives, fluorine-based adhesives, and the like. Further, the adhesive may be any type of adhesive such as an emulsion adhesive, a solvent adhesive, a hot melt adhesive, an oligomer adhesive, and a solid adhesive. As the adhesive, a single adhesive among the adhesives described above may be used, or two or more of them may be used in combination. Among them, it is preferable to use an acrylic pressure-sensitive adhesive as the pressure-sensitive adhesive from the viewpoint of preventing contamination of the adherend. That is, the pressure-sensitive adhesive tape of the present embodiment preferably has a pressure-sensitive adhesive layer containing an acrylic pressure-sensitive adhesive on the polyolefin resin cross-linked foamed sheet of the present embodiment.

Although the thickness of the pressure-sensitive adhesive layer is not particularly limited, it is preferably 5 μm or more, more preferably 7 μm or more. This makes it easier to obtain sufficient adhesion in the adhesive tape. Moreover, the thickness of the adhesive layer is preferably 200 μm or less, more preferably 150 μm or less. As a result, it becomes easy to reduce the thickness of the adhesive tape as a whole, and it becomes easy to reduce the size and thickness of the electronic/electric device in which the adhesive tape is used. The pressure-sensitive adhesive layer may be a single layer, or may be a laminate in which a plurality of layers having different types of pressure-sensitive adhesive are laminated.

The adhesive tape using the polyolefin-based resin crosslinked foam sheet of the present embodiment is used to adhere and fix parts constituting electronic/electrical equipment, such as mobile phones and video cameras, to main bodies constituting electronic/electrical equipment. can be used for In addition, the adhesive tape of the present embodiment is a shock absorbing material that prevents impacts from being applied to the electronic parts that are installed inside the body of the electronic/electrical equipment, and prevents dust, moisture, etc. from entering the body of the electronic/electrical equipment. It can be suitably used as a sealing material for preventing

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples. Polyolefin resin crosslinked foam sheets (hereinafter also referred to as resin foam sheets) of a plurality of types of examples and comparative examples described later were produced, and physical properties and the like were measured and performance and the like were evaluated. First, the method of measurement and evaluation will be explained.

(Thickness measurement)
The thickness of the resin foam sheet was measured according to ISO 1923 (1981) "Methods for measuring linear dimensions of foamed plastics and rubber". Specifically, the resin foam sheet was placed on a flat table, and a dial gauge with a circular probe having an area of 10 ^cm2 was brought into contact with the surface of the resin foam sheet at a constant pressure of 10 g/10 ^cm2 . bottom.

(Density measurement)
The density of the foamed resin sheet was measured and calculated according to JIS K6767 (1999) "Foamed plastics-Polyethylene-Test method". Specifically, the thickness and mass of a 10 cm square test piece (resin foam sheet) were measured, and the density was determined by the following formula.
Density (g/cm ³ ) = mass of test piece (g)/[test piece area 100 (cm ² ) x thickness of test piece (cm)]

(Measurement of gel fraction)
The gel fraction of the foamed resin sheet was measured as follows. 100 mg of a resin foam sheet cut into a square of about 0.5 mm was weighed with an accuracy of 0.1 mg. The weighed foamed resin sheet was immersed in 200 mL of tetralin at 140° C. for 3 hours, then naturally filtered through a 100-mesh stainless steel wire mesh, and the undissolved matter on the wire mesh was dried in a hot air oven at 120° C. for 1 hour. Next, the dried insoluble matter was cooled in a desiccator containing silica gel for 30 minutes, the mass of this insoluble matter was accurately weighed, and the gel fraction of the foam was calculated as a percentage according to the following formula.
Gel fraction (%) = [mass of insoluble matter (mg)/mass of weighed resin foam sheet (mg)] x 100

(Measurement of average bubble diameter)
For the average cell diameter, the average cell diameter in each of the MD direction and the TD direction is obtained on the surface where the cell cross section of the resin foam sheet opens, and then the average cell diameter in the MD direction and the average cell diameter in the TD direction are averaged. was obtained by A method for measuring the average bubble diameter in the MD direction will be described below.

The surface of the foamed resin sheet on which the cell cross section is open was photographed with a scanning electron microscope ("S-3000N" manufactured by Hitachi High-Technologies Corporation) at a magnification of 65 times. Next, the photographed image is printed on A4 paper, the number of bubbles on an arbitrary line segment (length 60 mm) parallel to the MD direction is counted, and the average chord length (t) of the bubbles is calculated by the following formula. bottom.
Average chord length t (mm) = 60 (mm)/number of bubbles

However, as far as possible, the above arbitrary line segments were made to pass through the bubbles instead of passing through the points of contact between adjacent bubbles. When the line segment passed through a contact point between bubbles, the number of bubbles on the line segment was counted as 2 at the point where the contact point was passed. The measurement was performed by drawing six line segments per measurement direction (MD direction). The magnification of the photographed image was obtained by measuring the scale bar on the image to 1/100 mm with a "Digimatic Caliper" manufactured by Mitutoyo Co., Ltd. and using the following formula.
Image magnification = Measured length of scale bar on image (mm)/Display value of scale bar (mm)

Then, the bubble diameter (d) in the MD direction was calculated by the following formula.
d (mm) = t (mm) / [0.616 x image magnification]

Also in the TD direction, the bubble diameter (d) was calculated in the same manner as in the MD direction, and the arithmetic average value of the bubble diameters (d) in the MD and TD directions was taken as the average bubble diameter.

(Measurement of surface roughness Ra)
The surface roughness Ra of the resin foam sheet was measured according to the surface roughness measurement method of JIS B0601-2001 on the surface of the resin foam sheet where the cell cross section is open. Specifically, using a surface roughness measuring machine SE-2300 manufactured by Kosaka Laboratory Co., Ltd., the measurement was performed by setting the measurement length to 30 mm, the measurement speed to 0.5 mm/s, and the cutoff value to 2.5 mm.

(Evaluation of slicing workability)
The slicing processability was evaluated for each resin foam sheet. Each resin foam sheet is manufactured through a slicing process as described later. Here, the slicing processability was evaluated based on the shape of each foamed resin sheet finally obtained through slicing, not on the sheet immediately after slicing. The evaluation results are shown below. In the following criteria, "the sliced surface is smooth" means that the surface roughness Ra is 7 μm or less, and "the sliced surface has unevenness" means that the surface roughness Ra exceeds 7 μm. point to In addition, "cutting defect occurred" means that fold-shaped deformation occurred at the width direction end of the resin foam sheet, and "no cutting defect" means the width direction end of the resin foam sheet. , it shows that the above deformation did not occur. The presence or absence of such deformation could be clearly determined by visual inspection.
A: The sliced surface is smooth, and there is no cutting defect at the end in the width direction.
B: The sliced surface was smooth, but defective cutting occurred at the edges in the width direction.
C: Unevenness was found on the sliced surface, and cut defects occurred at the edges in the width direction.

(Evaluation of adhesiveness)
In order to evaluate the adhesiveness of the resin foam sheet, a commercially available double-sided adhesive tape (manufactured by Sumitomo 3M, product number "KRE -19”) were laminated together. Then, the adhesiveness between the foamed resin sheet and the adhesive was evaluated by measuring the peel strength. Adhesiveness was measured in part according to JIS Z0237:2009 "Adhesive tape/adhesive sheet test method". Specifically, after bonding the resin foam sheet and the adhesive layer together, the sheet having the adhesive layer was cut into a width of 19 mm and a length of 150 mm, and a rubber roller having a mass of 2 kg was reciprocated once on the cut sheet. The foamed resin sheet and the pressure-sensitive adhesive layer were pressure-bonded with each other and allowed to stand for 30 minutes under conditions of a temperature of 23° C. and a humidity of 50% to obtain a test piece. Using such a test piece, a 180-degree peel test was performed between the resin foam sheet and the pressure-sensitive adhesive layer using a Tensilon universal tester UCT-500 manufactured by Orientec to measure the peel strength. The evaluation results are shown below.
A: The peel strength is 5N or more.
B: The peel strength is 3N or more and less than 5N.
C: The peel strength is less than 3N.

(comprehensive evaluation)
Comprehensive evaluation was performed based on the evaluation result of slicing workability and the evaluation result of adhesiveness. The evaluation results are shown below.
A: Both the evaluation result of slicing workability and the evaluation result of adhesiveness are "A"
B: Other than the above "A", neither the evaluation result of the slicing workability nor the evaluation result of the adhesiveness is "C".
C: At least one of the evaluation result of the slicing workability and the evaluation result of the adhesiveness is "C".

Examples 1 to 12 and Comparative Examples 1 to 14 are described below. The composition, processing method, physical properties, and evaluation results of each sample are summarized in Tables 1 to 4. Table 1 shows Examples 1-8, Table 2 shows Examples 9-12, Table 3 shows Comparative Examples 1-9, and Table 4 shows Comparative Examples 10-14. In addition, in Table 1-4, "heating/compression/stretching step" is simply described as "stretching step" with respect to the processing method.

[Example 1]
As the polyolefin resin, ethylene-vinyl acetate copolymer (density: 0.936 g/cm ³ , MFR: 1.5 g/10 min, vinyl acetate content: 15% by mass, "Ultrasen 630" manufactured by Tosoh Corporation. EVA ) was used, and hydroxy fatty acid amide was used as a lubricant. 0.06 parts by mass of a lubricant and 0.006 parts by mass of silicon dioxide were added to 100 parts by mass of the polyolefin resin. Furthermore, with respect to 100 parts by mass of polyolefin resin, 5.4 parts by mass of pellets containing azodicarbonamide as a foaming agent ("Panthrene H7330" manufactured by Eiwa Kasei Kogyo Co., Ltd.), a heat stabilizer ("Irganox" manufactured by BASF Japan Co., Ltd. 1010") 0.11 parts by mass and 1.7 parts by mass of carbon black as a pigment were blended. These materials are mixed in a Henschel mixer, put into an extruder with a screw diameter of 60 mm, melted and kneaded while the temperature inside the cylinder is adjusted to 160 ° C., and then extruded to a thickness of 0. A polyolefin resin sheet of 0.65 mm was produced.

The polyolefin resin sheet thus obtained was irradiated with electron beams of a predetermined absorption dose from both sides at an acceleration voltage of 800 kV to obtain a crosslinked sheet, and then the crosslinked sheet was placed in a salt bath set at 235°C. It was floated on top and heated with an infrared heater from above to foam. After that, the resulting foamed sheet was cooled with water at 50°C, and the surface of the foamed sheet was washed with water and dried. A long roll of foam with faces was obtained. The obtained long roll of foam was sliced in a direction perpendicular to the thickness direction by a splitting machine (slicing step). As a result, a long rolled foam having a thickness of 0.55 mm, one surface being a skin surface and the cell cross section being open on the slice surface, which is the other surface, was obtained. The sliced surface of the sliced long roll foam is heated at 150 ° C. to 180 ° C. with an infrared heater (heating step), and while compressing the foam in the thickness direction using nip rolls with a gap of 0.1 mm, MD It was stretched 140% in the direction (compression/stretching step). As a result, a polyolefin resin crosslinked foam sheet was obtained. The obtained polyolefin-based resin crosslinked foamed sheet was evaluated according to the evaluation method described above.

[Example 2-8]
The same procedure as in Example 1 was performed except that the composition of the polyolefin resin, hydroxy fatty acid amide, silicon dioxide, foaming agent, heat stabilizer, and pigment, and the stretching ratio in the MD direction were as shown in Table 1. was made.

[Example 9]
As polyolefin resin, ethylene-ethyl acrylate copolymer (density: 0.930 g/cm ³ , MFR: 6.0 g/10 min, ethyl acrylate content: 15% by mass, "Elvaloy AC2615" manufactured by DuPont). It was produced in the same manner as in Example 1, except that EEA) was used.

[Example 10]
It was produced in the same manner as in Example 9, except that the contents of hydroxy fatty acid amide and silicon dioxide were as shown in Table 2.

[Example 11]
It was produced in the same manner as in Example 6, except that the irradiation dose in the cross-linking step was changed.

[Example 12]
It was produced in the same manner as in Example 6, except that the surface to be heated in the heating step was a skin surface.

[Comparative Example 1-9]
The same procedure as in Example 1 was performed except that the composition of the polyolefin resin, hydroxy fatty acid amide, silicon dioxide, foaming agent, heat stabilizer, and pigment, and the stretching ratio in the MD direction were as shown in Table 1. was made.

[Comparative Examples 10-14]
As the polyolefin resin, the same ethylene-ethyl acrylate copolymer as in Examples 9 and 10 was used, and the composition of the polyolefin resin, hydroxy fatty acid amide, silicon dioxide, foaming agent, heat stabilizer, and pigment, and It was produced in the same manner as in Example 1, except that the stretching ratio in the MD direction was performed as shown in Table 1.

As shown in Table 1-4, in the polyolefin resin cross-linked foamed sheet with open cell cross sections on at least one side, 0.05 parts by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin and 0.005 parts by mass or more and 0.05 parts by mass or less of silicon dioxide exhibit excellent slicing workability and adhesiveness. Further, from the comparison results between Example 6 and Example 11, by setting the gel fraction to 35% or more, the average bubble diameter of the surface where the bubble cross section opens is 400 μm or less, and the surface roughness Ra is 5 μm. It was confirmed that the following becomes easier, and the slicing workability and adhesiveness are improved. In addition, from the comparison results between Example 6 and Example 12, by setting the surface to be heated in the heating/compressing/stretching process to the surface where the bubble cross section opens, the surface roughness Ra of the surface where the bubble cross section opens It was confirmed that the value can be easily adjusted to 5 μm or less, and the adhesiveness is improved.

Claims (10)

A polyolefin resin crosslinked foam sheet,
0.05 parts by mass or more and 0.5 parts by mass or less of a lubricant and 0.005 parts by mass or more and 0.05 parts by mass or less of silicon dioxide with respect to 100 parts by mass of a polyolefin resin,
At least one of the two surfaces of the polyolefin-based resin crosslinked foamed sheet has an open cell cross section, and the average cell diameter of the surface where the cell cross section is open is 400 μm or less, and the gel fraction is 35% or more. A polyolefin resin crosslinked foam sheet characterized by: The polyolefin resin crosslinked foam sheet according to claim 1,
A polyolefin-based resin crosslinked foam sheet, wherein the polyolefin-based resin is an ethylene-based copolymer. The polyolefin resin crosslinked foam sheet according to claim 1 or claim 2,
A polyolefin-based resin crosslinked foam sheet, wherein the lubricant is a fatty acid amide. The polyolefin resin crosslinked foam sheet according to any one of claims 1 to 3 ,
A polyolefin-based resin crosslinked foam sheet, wherein the surface roughness Ra of the surface where the cell cross section is open is 1 μm or more and 5 μm or less. The polyolefin resin crosslinked foam sheet according to any one of claims 1 to 4 ,
The polyolefin resin crosslinked foam sheet has a thickness of 0.1 mm or more and 0.5 mm or less,
A polyolefin resin crosslinked foam sheet having a density of 0.10 g/cm ³ or more and 0.50 g/cm ³ or less. A method for producing the polyolefin resin crosslinked foam sheet according to any one of claims 1 to 5 ,
A polyolefin crosslinked resin containing a polyolefin resin, a lubricant and silicon dioxide is foamed to produce a crosslinked foamed sheet,
Slicing the crosslinked foam sheet in a direction perpendicular to the thickness direction of the crosslinked foam sheet,
A method for producing a polyolefin-based resin cross-linked foamed sheet, comprising opening cross-sections of cells on a sliced surface formed by slicing. A method for producing a polyolefin resin crosslinked foam sheet according to claim 6 ,
A method for producing a polyolefin resin crosslinked foamed sheet, comprising: slicing the crosslinked foamed sheet, heating the sliced surface, and compressing and stretching the crosslinked foamed sheet. Adhesive tape,
The polyolefin resin crosslinked foam sheet according to any one of claims 1 to 7 ;
a pressure-sensitive adhesive layer containing a pressure-sensitive adhesive provided on the surface of the polyolefin resin cross-linked foamed sheet where the cell cross section is open;
Adhesive tape with The adhesive tape according to claim 8 ,
The pressure-sensitive adhesive tape, wherein the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive. The adhesive tape according to claim 8 or 9 ,
An adhesive tape used for adhering and fixing a part that constitutes an electronic/electrical device to a main body portion that constitutes the electronic/electrical device.