JP7295623B2 - Polyolefin resin foam sheet and adhesive tape using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyolefin resin foam sheet and an adhesive tape using the same.

2. Description of the Related Art Conventionally, in electronic devices such as mobile phones, cameras, game machines, electronic notebooks, tablet terminals, and notebook personal computers, sealing materials or shock absorbing materials made of foam sheets have been used. These sealing materials or shock absorbing materials are sometimes used in the form of adhesive tapes or the like using a foam sheet as a base material. For example, the display device in the electronic device generally has a structure in which a protective panel is installed on a display panel such as an LCD. A sheet-based adhesive tape is used.
As a foam sheet used inside electronic devices, a crosslinked polyolefin resin foam sheet obtained by foaming and crosslinking an expandable polyolefin resin sheet containing a thermally decomposable foaming agent is known (for example, Patent Document 1 reference).

WO 2005/007731

By the way, while electronic devices are being miniaturized, they may be exposed to high temperatures, such as being left behind in a vehicle parked under the scorching sun. Also, when electronic equipment is mounted in a vehicle, the electronic equipment may be exposed to high temperatures. Polyolefin-based resin foam sheets have problems such as adhesion to peripheral members when exposed to high temperatures. For this reason, foam sheets used inside electronic devices are required to have higher thermal stability than ever before.

Accordingly, an object of the present invention is to provide a polyolefin resin foamed sheet having high thermal stability and an adhesive tape using the same.

As a result of intensive studies, the inventors have found that the above problems can be solved by including a polypropylene resin in the resin composition used for producing a polyolefin resin foamed sheet, and have completed the present invention below. That is, the present invention provides the following [1] to [10].
[1] A resin composition containing a polyolefin resin is foamed, and the polyolefin resin is 50 to 90 parts by mass or more of a polypropylene resin and 10 to 50 parts by mass of the polyolefin resin with respect to 100 parts by mass of the polyolefin resin. A polyolefin resin foam sheet having a thickness of 0.1 to 1.5 mm and containing at least one polyolefin polymer material selected from the group consisting of polyethylene resins and polyolefin rubbers.
[2] The polyolefin resin foam sheet according to [1] above, which has a 25% compressive strength of 40 to 350 kPa.
[3] The polyolefin resin foam sheet according to [1] or [2] above, which has a degree of cross-linking of 30 to 59% by mass.
[4] The polyolefin resin foam sheet according to any one of [1] to [3] above, which has an average pore size of 90 to 250 μm in the MD direction and the TD direction.
[5] The polyolefin resin foam sheet according to any one of [1] to [4] above, wherein the polypropylene resin is an ethylene-propylene random copolymer.
[6] The polyolefin resin foam sheet according to any one of [1] to [5] above, wherein the polyolefin rubber comprises an ethylene-α-olefin copolymer rubber.
[7] The polyolefin resin foam sheet according to any one of [1] to [6] above, wherein the polyethylene resin is a linear low density polyethylene resin (LLDPE).
[8] The polyolefin resin foam sheet according to any one of [1] to [7] above, which is used for electronic devices.
[9] The polyolefin-based resin foam sheet according to the above [8], which is used for in-vehicle electronic equipment.
[10] An adhesive tape comprising the polyolefin resin foam sheet according to any one of the above [1] to [9] and an adhesive layer provided on at least one surface of the polyolefin resin foam sheet.

ADVANTAGE OF THE INVENTION According to this invention, the polyolefin-type resin foam sheet|seat which has high thermal stability, and an adhesive tape using the same can be provided.

The polyolefin-based resin foamed sheet of the present invention is obtained by foaming a resin composition containing a polyolefin-based resin. The polyolefin resin is selected from the group consisting of 50 to 90 parts by mass or more of a polypropylene resin and 10 to 50 parts by mass of a polyethylene resin and a polyolefin rubber with respect to 100 parts by mass of the polyolefin resin. and at least one kind of polyolefin polymer material, and has a thickness of 0.1 to 1.5 mm.
The polyolefin resin foamed sheet of the present invention will be described in detail below.

[Polyolefin resin foam sheet]
The polyolefin-based resin foamed sheet of the present invention is preferably obtained by foaming a resin composition containing a polyolefin-based resin (hereinafter also referred to as "resin composition (a)"). is crosslinked and foamed.

[Polyolefin resin]
The polyolefin-based resin contained in the resin composition (a) includes a polypropylene-based resin and at least one polyolefin-based polymer material selected from the group consisting of polyethylene-based resins and polyolefin-based rubbers. The polyolefin-based resin preferably includes a polypropylene-based resin and a polyolefin-based rubber.

The polypropylene-based resin contained in the polyolefin-based resin is not particularly limited, and examples thereof include copolymers of propylene and other olefins. The copolymer of propylene and other olefins may be a block copolymer, a random copolymer, or a random block copolymer, but is preferably a random copolymer (random polypropylene).
In copolymers of propylene and other olefins, other olefins to be copolymerized with propylene include, for example, ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1- Examples include α-olefins such as octene, 1-nonene and 1-decene, among which ethylene is particularly preferred. That is, an ethylene-propylene random copolymer is preferable as the polypropylene resin.
In addition, the copolymer of propylene and other olefins usually contains 90 to 99.5% by weight of propylene and 0.5 to 10% by weight of α-olefin other than propylene, and 95 to 99% by weight of propylene. %, and α-olefin other than propylene is preferably 1 to 5% by mass.

The polypropylene resin preferably has a melt flow rate (hereinafter also referred to as "MFR") of 0.4 to 4.0 g/10 minutes, more preferably 0.5 to 2.5 g/10 minutes. preferable. By using a polypropylene resin having the above MFR, the moldability when processing the resin composition (a) into a polyolefin resin foam sheet and the moldability when secondary processing the polyolefin resin foam sheet are improved. easier to make better.
The above polypropylene-based resins may be used alone or in combination of two or more.
The MFR is a value measured under conditions of a temperature of 230° C. and a load of 2.16 kgf based on JIS K7210.

The content of the polypropylene resin in the polyolefin resin is 50 to 90 parts by mass, preferably 55 to 85 parts by mass, more preferably 57 to 83 parts by mass, based on 100 parts by mass of the polyolefin resin. , more preferably 60 to 80 parts by mass. If the content of the polypropylene-based resin is less than 50 parts by mass, the polyolefin-based resin foamed sheet will have poor thermal stability. As a result, problems such as adhesion of the polyolefin resin foamed sheet to peripheral members occur. If the content of the polypropylene resin is more than 90 parts by mass, the flexibility of the polyolefin resin foam sheet may be insufficient for using the polyolefin resin foam sheet as a sealing material or a shock absorbing material.

Linear low-density polyethylene is preferable as the polyethylene-based resin contained in the polyolefin-based resin. By using linear low-density polyethylene, it becomes possible to impart flexibility to the foamed sheet and to reduce the thickness of the resin foamed sheet. This linear low-density polyethylene is more preferably obtained using a polymerization catalyst such as a metallocene compound. In addition, linear low-density polyethylene is obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more with respect to the total amount of monomers) and a small amount of α-olefin if necessary. Linear low-density polyethylene is more preferred.
Specific examples of α-olefins include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Of these, α-olefins having 4 to 10 carbon atoms are preferred.
The density of the polyethylene resin, for example, the linear low-density polyethylene described above is preferably 0.870 to 0.930 g/cm ³ , more preferably 0.875 to 0.920 g/cm ³ , and more preferably 0.880 to 0.910 g/cm 3 . /cm ³ is more preferred. A plurality of polyethylene resins can be used as the polyethylene resin, and a polyethylene resin having a density other than the density range described above may be added.

Examples of metallocene compounds include compounds such as bis(cyclopentadienyl) metal complexes having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum have one or more cyclopentadienyl rings or analogues thereof as ligands. can be mentioned.
Such a metallocene compound has uniform properties of active sites and each active site has the same degree of activity. Polymers synthesized using metallocene compounds have high uniformity in terms of molecular weight, molecular weight distribution, composition, and composition distribution. proceed to A uniformly crosslinked sheet is uniformly foamed, and thus, as described above, it is easy to reduce the variation in cell diameter. Moreover, since it can be drawn uniformly, it becomes easy to make the thickness of the foam sheet uniform. Furthermore, the flexibility of the foam sheet can be enhanced.

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

Examples of metallocene compounds containing tetravalent transition metals and ligands include cyclopentadienyltitanium tris(dimethylamide), methylcyclopentadienyltitanium tris(dimethylamide), bis(cyclopentadienyl)titanium dichloride, dimethyl and silyltetramethylcyclopentadienyl-t-butylamide zirconium dichloride.
A metallocene compound, in combination with a specific co-catalyst (co-catalyst), exhibits its action as a catalyst in the polymerization of various olefins. Specific co-catalysts include methylaluminoxane (MAO), boron-based compounds, and the like. The ratio of the cocatalyst used to the metallocene compound is preferably 100,000 to 1,000,000 mol times, more preferably 50 to 5,000 mol times.

As the polyolefin rubber contained in the polyolefin resin, an amorphous or low-crystalline rubber-like substance obtained by substantially randomly copolymerizing two or more olefin monomers is preferable, and moldability and flexibility are well balanced. From the viewpoint of improvement, those containing ethylene-α-olefin copolymer rubber are more preferable.
Examples of α-olefins used in ethylene-α-olefin copolymer rubber include propylene, 1-butene, 2-methylpropylene, 3-methyl-1-butene, 1-pentene, 1-hexene, 4-methyl- One or more α-olefins having 3 to 15 carbon atoms, preferably 3 to 10 carbon atoms such as 1-pentene and 1-octene can be used. Among these, propylene and 1-butene are preferred, and propylene is more preferred.
Moreover, a polyethylene-type resin may be used individually by 1 type, and may use 2 or more types together.

The ethylene-α-olefin copolymer rubber may have other monomer units in addition to ethylene units and α-olefin units.
Monomers forming the other monomer units include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and the like. Conjugated dienes having 4 to 8 carbon atoms; dicyclopentadiene, 5-ethylidene-2-norbornene, 1,4-hexadiene, 1,5-dicyclooctadiene, 7-methyl-1,6-octadiene, 5-vinyl- non-conjugated dienes having 5 to 15 carbon atoms such as 2-norbornene; vinyl ester compounds such as vinyl acetate; unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate and ethyl methacrylate; Examples include unsaturated carboxylic acids such as acrylic acid and methacrylic acid. These monomers can be used alone or in combination of two or more. Among these, non-conjugated dienes having 5 to 15 carbon atoms are preferred, and 5-ethylidene-2-norbornene, 1,4-hexadiene, and dicyclopentadiene (DCPD) are more preferred from the viewpoint of availability.

The ethylene unit content of the ethylene-α-olefin copolymer rubber is usually 30 to 85% by mass, preferably 40 to 80% by mass, more preferably 45 to 75% by mass. The content of 15, preferably 3 to 10 α-olefin units is usually 10 to 60% by weight, preferably 15 to 50% by weight, and the content of other monomeric units such as non-conjugated dienes is Usually 0 to 20% by weight, preferably 1 to 10% by weight.

Ethylene-α-olefin copolymer rubber having a Mooney viscosity (ML ₁₊₄ , 100° C.) of 15 to 85 is used. By setting the Mooney viscosity within the above range, it is possible to improve flexibility and moldability in a well-balanced manner. Further, the Mooney viscosity of the olefin rubber is more preferably 25-75, more preferably 30-70, in order to improve flexibility and moldability. The Mooney viscosity (ML ₁₊₄ , 100° C.) can be measured according to JIS K6300-1.

As the polyolefin rubber, an olefin thermoplastic elastomer (TPO) can also be used. Thermoplastic olefin elastomers (TPO) generally have polyolefins such as polyethylene and polypropylene as hard segments, and rubber components such as EPM and EPDM as soft segments. Any of blend type, dynamic cross-linking type and polymerization type can be used for the olefinic thermoplastic elastomer (TPO).
The thermoplastic olefinic elastomer (TPO) preferably has an MFR of 0.4 to 3.0 g/10 minutes, more preferably 0.6 to 2.0 g/10 minutes. By using the olefinic thermoplastic elastomer having the above MFR, it becomes easier to improve moldability when processing the resin composition (a) into a foam. The MFR of the olefinic thermoplastic elastomer (TPO) is a value measured under conditions of a temperature of 230° C. and a load of 2.16 kgf based on JIS K7210.

Preferred specific examples of polyolefin rubber include ethylene-propylene copolymer rubber (EPR), ethylene-propylene-diene copolymer rubber (EPDM) and olefinic thermoplastic elastomer (TPO), but EPDM alone Alternatively, combination use of EPDM and TPO is preferred. Examples of EPDM include ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber and ethylene-propylene-dicyclopentadiene copolymer rubber. Among these, ethylene-propylene-dicyclopentadiene copolymer rubber is preferred.

Olefin rubbers can be used alone or in combination of two or more.

The content of at least one polyolefin polymer material selected from the group consisting of polyethylene resin and polyolefin rubber in the polyolefin resin is 10 to 50 parts by mass with respect to 100 parts by mass of the polyolefin resin, It is preferably 15 to 45 parts by mass, more preferably 17 to 43 parts by mass, still more preferably 20 to 40 parts by mass. When the content of the polyolefin polymer material is less than 10 parts by mass, the flexibility of the polyolefin resin foam sheet is insufficient for using the polyolefin resin foam sheet as a sealing material or a shock absorbing material. There is When the content of the polyolefin polymer material is more than 90 parts by mass, the thermal stability of the polyolefin resin foam sheet may deteriorate.

[Other ingredients]
The polyolefin-based resin may be composed only of a polypropylene-based resin and at least one polyolefin-based compound selected from polyethylene-based resins and polyolefin-based rubbers. However, the polyolefin-based resin may contain other resin components as long as the object of the present invention is not impaired.
Examples of such resin components include ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-(meth)alkyl acrylate copolymers, and modified copolymers obtained by copolymerizing these with maleic anhydride. etc.

From the viewpoint of improving the thermal stability and mechanical strength of the polyolefin resin foamed sheet and ensuring flexibility and moldability, the content of the olefin resin in the resin composition (a) is preferably 80 to 99. % by mass, more preferably 83 to 98% by mass.

<Additive>
The resin composition (a) usually contains a foaming agent as an additive in addition to the olefinic resin. Moreover, the resin composition (a) preferably contains one or both of a cross-linking aid and an antioxidant.

(foaming agent)
Methods for foaming the resin composition (a) include a chemical foaming method and a physical foaming method. The chemical foaming method is a method of forming bubbles by gas generated by thermal decomposition of a compound added to the resin composition (a), and the physical foaming method is a method in which a low boiling point liquid (foaming agent) is added to the resin composition ( After impregnation with a), the foaming agent is volatilized to form cells. The foaming method is not particularly limited, but a chemical foaming method is preferred from the viewpoint of obtaining a uniform closed-cell foam sheet.
As the foaming agent, a thermal decomposition type foaming agent is used, and for example, an organic or inorganic chemical foaming agent having a decomposition temperature of about 160 to 270° C. can be used.
Organic foaming agents include azodicarbonamide, azodicarboxylic acid metal salts (barium azodicarboxylate, etc.), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, Hydrazodicarbonamide, 4,4'-oxybis(benzenesulfonylhydrazide), hydrazine derivatives such as toluenesulfonylhydrazide, semicarbazide compounds such as toluenesulfonylsemicarbazide, and the like.

Examples of inorganic foaming agents include ammonium acid, sodium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride, and anhydrous monosoda citric acid.
Among these, azo compounds and nitroso compounds are preferred from the viewpoint of obtaining fine air bubbles and from the viewpoints of economy and safety, and azodicarbonamide, azobisisobutyronitrile, and N,N'-dinitrosopentamethylene. Tetramine is more preferred, and azodicarbonamide is particularly preferred.
A foaming agent can be used individually or in combination of 2 or more types.
The amount of the thermally decomposable foaming agent added is preferably 1 to 25 parts by mass, more preferably 1.5 to 15 parts by mass based on 100 parts by mass of the resin component, from the viewpoint of properly foaming the foamed sheet without bursting the cells. More preferably 2 to 12 parts by mass.

(crosslinking aid)
A polyfunctional monomer can be used as a cross-linking aid. For example, trifunctional (meth)acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; Compounds having three functional groups in one molecule; 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, neopentyl glycol dimethacrylate and other bifunctional ( compounds having two functional groups in one molecule, such as meth)acrylate compounds and divinylbenzene; diallyl phthalate, diallyl terephthalate, diallyl isophthalate, ethylvinylbenzene, lauryl methacrylate, stearyl methacrylate, and the like. Among these, trifunctional (meth)acrylate compounds are more preferred.
A crosslinking aid can be used individually or in combination of 2 or more.
By adding the cross-linking aid to the resin composition (a), it becomes possible to cross-link the resin composition (a) with a small ionizing radiation dose. Therefore, it is possible to prevent the resin molecules from being cut and degraded due to irradiation with ionizing radiation.
The content of the cross-linking aid is 0.2 to 20 parts by mass with respect to 100 parts by mass of the polyolefin resin from the viewpoint of ease of adjustment and control of the degree of cross-linking when foaming the resin composition (a). Preferably, 0.5 to 15 parts by mass is more preferable.

(Antioxidant)
Examples of antioxidants include phenol antioxidants, sulfur antioxidants, phosphorus antioxidants, amine antioxidants, and the like. Among these, phenolic antioxidants and sulfuric antioxidants are preferred, and it is more preferred to use a combination of phenolic antioxidants and sulfuric antioxidants.
Phenolic antioxidants include 2,6-di-tert-butyl-p-cresol, n-octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2-tert- Butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate ] methane and the like.
Examples of sulfur-based antioxidants include dilauryl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate, and pentaerythrityl tetrakis(3-laurylthiopropionate).
These antioxidants can be used alone or in combination of two or more.
The content of the antioxidant is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, per 100 parts by mass of the polyolefin resin.
In addition, the resin composition (a) may optionally include zinc oxide, zinc stearate, decomposition temperature adjusters such as urea, flame retardants, metal damage inhibitors, antistatic agents, stabilizers, fillers, pigments, and the like. may contain additives other than the above.
Furthermore, the resin composition (a) may contain a resin other than the polyolefin-based resin within a range that does not impair the effects of the present invention.

[Polyolefin resin foam sheet]
As described above, the polyolefin resin foamed sheet of the present invention (hereinafter also simply referred to as "foamed sheet") is obtained by foaming the resin composition (a) described above.
(thickness)
The thickness of the foam sheet is 0.1-1.5 mm, preferably 0.15-1.3 mm, more preferably 0.2-1.0 mm. When the thickness of the foamed sheet is less than 0.1 mm, the foamed sheet tends to thermally shrink. In addition, when the foam sheet is used for electronic equipment or in-vehicle electronics, sufficient sealing performance or sufficient impact absorption cannot be ensured. If the thickness of the foam sheet is more than 1.5 mm, the foam sheet may not be suitable for use in electronic equipment or in-vehicle electronic equipment.

(25% compressive strength)
The 25% compressive strength of the foam sheet is determined from the viewpoint of ensuring the mechanical strength of the foam sheet and from the viewpoint of ensuring flexibility and step conformability (performance that can be closely attached to the uneven surface inside the device without gaps). , preferably 40 to 350 kPa. Further, from the viewpoint of further ensuring thermal stability, the 25% compressive strength of the foam sheet is more preferably 80 to 350 kPa, still more preferably 80 to 330 kPa, still more preferably 80 to 320 kPa, More preferably 80 to 150 kPa, more preferably 80 to 140 kPa, still more preferably 85 to 135 kPa, and particularly preferably 90 to 130 kPa.
The 25% compressive strength is measured according to JIS K6767.

(Average pore diameter)
The average cell diameter in the MD direction and the TD direction in the foam sheet is preferably 90 to 250 μm, more preferably 100 to 200 μm, and even more preferably 105 from the viewpoint of improving the flexibility and conformability of the foam sheet. ˜155 μm.
In the present invention, "MD" means "Machine Direction" and means a direction that coincides with the extrusion direction of the foam sheet. Moreover, "TD" means "Transverse Direction" and means a direction orthogonal to MD and parallel to the foam sheet.
In addition, the average bubble diameter can be measured according to the method of Examples described later.

(Degree of cross-linking)
The degree of crosslinking (% by mass) of the entire foam sheet is preferably 30% or more, more preferably 36% or more, and still more preferably 38%, from the viewpoint of improving flexibility, mechanical strength, and moldability in a well-balanced manner. % or more, particularly preferably 40% or more, preferably 62% or less, more preferably 60% or less, and still more preferably 59% or less.
Moreover, the degree of cross-linking can be measured by the method described in Examples below.

(density)
The density (apparent density) of the foamed sheet is preferably 0.05 g/cm 3 or more, more preferably 0.05 g/cm ³ or more, from the viewpoint of improving thermal stability and improving flexibility and mechanical strength in a well-balanced manner. 08 g/cm ³ or more, more preferably 0.1 g/cm ³ or more, and preferably 0.4 g/cm ³ or less, more preferably 0.3 g/cm ³ or less, still more preferably 0.2 g / cm ³ or less.

Since the foamed sheet of the present invention has flexibility and excellent thermal stability, it is suitable for use in electronic devices, particularly in vehicle-mounted electronic devices. In addition, since the foam sheet of the present invention is excellent in flexibility and step conformability, it is suitable for use as a sealing material or a cushioning material for electronic devices, especially in-vehicle electronic devices. It is particularly suitable for device applications.
In recent years, as electronic devices have become smaller and more sophisticated, various parts have become more sophisticated, limiting the space available inside electronic devices. be. For example, the width of the frame portion outside the display panel has become narrower due to the miniaturization of electronic devices and the increase in size of display devices, and the width of the foam sheet provided in the frame portion has also become narrower. The width is, for example, 10 mm or less, preferably 5 mm or less, more preferably 1 mm or less. As described above, the foamed sheet of the present invention is excellent in flexibility and conformability to unevenness, and is therefore particularly suitable for use in a narrow portion such as a frame portion on the outer side of a display panel.

<Method for manufacturing foam sheet>
The foamed sheet can be produced, for example, by melting and kneading the resin composition (a) and molding it into a desired shape, and then irradiating the resin composition (a) with ionizing radiation to heat and foam the resin composition (a).
Specifically, a manufacturing method having the following steps 1 to 3 is more preferable.
Step 1: Step of obtaining a sheet-like resin composition (a) after melt-kneading each component constituting the resin composition (a) Step 2: The resin composition (a) obtained in Step 1 has ionizing properties Step of irradiating with radiation to crosslink Step 3: Step of heating the resin composition (a) crosslinked in Step 2 to a temperature equal to or higher than the decomposition temperature of the thermally decomposable foaming agent to foam to obtain a foamed sheet Step 4: A step of stretching the foam sheet in either or both of the MD direction and the TD direction. As described above, "MD" means "machine direction" and is the direction that matches the extrusion direction of the foam sheet. means Moreover, "TD" means "Transverse Direction" and means a direction orthogonal to MD and parallel to the foam sheet.

In step 1, each component constituting the resin composition (a) is supplied to a kneading device and melt-kneaded at a temperature lower than the decomposition temperature of the thermally decomposable foaming agent, and then the melt-kneaded resin composition (a ) is preferably formed into a sheet by the kneading device used in the melt-kneading.
Examples of the kneading device used here include general-purpose kneading devices such as injection molding machines, extruders (single-screw extruders, twin-screw extruders, etc.), Banbury mixers, and rolls. An extruder is preferred, and an injection molding machine can be used for production with good productivity.
The resin temperature inside the injection molding machine or extruder is preferably 120 to 220°C, more preferably 140 to 200°C, still more preferably 150 to 195°C.

In step 2, the sheet-shaped resin composition (a) is irradiated with ionizing radiation.
Examples of ionizing radiation include electron beams, α-rays, β-rays, γ-rays, and X-rays. Among these, an electron beam is preferable from the viewpoint of productivity and uniform irradiation.
The ionizing radiation may be applied to only one surface of the resin composition (a) molded into a sheet, or may be applied to both surfaces.
The accelerating voltage of the ionizing radiation depends on the thickness of the foamable resin composition to be irradiated, but for example, when the thickness is 0.05 to 3 mm, it is preferably 400 to 1200 kV, more preferably 500 to 1100 kV. More preferably, it is 600 to 1000 kV.
The irradiation dose of ionizing radiation may be an amount that can obtain the desired degree of cross-linking without causing surface roughness or cracking, taking into consideration the thickness of the foamable resin composition to be irradiated. .1 to 10 Mrad is preferred, 0.2 to 5 Mrad is more preferred, and 0.3 to 3 Mrad is more preferred.

In step 3, after the resin composition (a) is crosslinked by irradiation with ionizing radiation as described above, the resin composition (a) is heated to a temperature higher than the decomposition temperature of the foaming agent and foamed to obtain a foamed sheet. be able to.
Here, the temperature for heating and foaming the resin composition (a) depends on the decomposition temperature of the thermal decomposition type foaming agent used as the foaming agent, but is usually 140 to 300°C, preferably 150 to 280°C, more preferably 160°C. ~260°C.

In step 4, the foam sheet is stretched in one or both of the MD direction and the TD direction. The stretching of the foamed sheet in step 4 may be performed after foaming the resin sheet to obtain the foamed sheet, or may be performed while foaming the resin sheet. In addition, when stretching the foamed sheet after foaming the resin sheet to obtain the foamed sheet, the foamed sheet may be stretched while maintaining the molten state at the time of foaming without cooling the foamed sheet. After cooling the foam sheet, the foam sheet may be heated again to be in a molten or softened state and then stretched. By stretching the foam sheet, it becomes easier to make it thinner.
In step 4, the stretch ratio of the foamed sheet in one or both of the MD and TD directions is preferably 1.1 to 5.0 times, more preferably 1.5 to 4.0 times.
When the draw ratio is equal to or higher than the above lower limit, the foam sheet tends to have good flexibility and tensile strength. On the other hand, when it is below the upper limit, it is possible to prevent the foam sheet from breaking during stretching, and the expansion ratio from being significantly reduced due to the escape of foaming gas from the foam sheet during foaming, and the flexibility and tensile strength of the foam sheet. becomes better, and it becomes easier to make the quality uniform.
The foam sheet may be heated to, for example, 100 to 280.degree. C., preferably 150 to 260.degree. C. during stretching.

However, the present manufacturing method is not limited to the above, and a foamed sheet may be obtained by a method other than the above. For example, instead of irradiating ionizing radiation, cross-linking may be performed by adding an organic peroxide to the foamable composition in advance and heating the foamable composition to decompose the organic peroxide. good. Moreover, the step 4, that is, the stretching of the foam sheet may be omitted.

The foam sheet of the present invention preferably has a closed-cell structure, but may have a closed-cell structure containing open cells.

[Adhesive tape]
The pressure-sensitive adhesive tape of the present invention is a pressure-sensitive adhesive tape using the above-described foamed sheet as a base material, and specifically includes a foamed sheet and an adhesive layer provided on at least one surface of the foamed sheet.
The thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive tape is preferably 5-200 μm, more preferably 7-150 μm, even more preferably 10-100 μm.
The pressure-sensitive adhesive tape of the present invention preferably has pressure-sensitive adhesive layers on both sides of the foamed sheet. That is, the pressure-sensitive adhesive tape of the present invention can be used as both a single-sided tape and a double-sided tape, depending on the application.

The adhesive constituting the adhesive layer is not particularly limited, and examples thereof include acrylic adhesives, urethane-based adhesives, rubber-based adhesives, silicone-based adhesives, and the like.
The method of applying an adhesive to the foam sheet and laminating the adhesive layer on the foam sheet includes, for example, a method of applying an adhesive to at least one surface of the foam sheet using a coating machine such as a coater, Examples include a method of spraying and applying the adhesive to at least one surface of the foam sheet, and a method of applying the adhesive to one surface of the foam sheet using a brush.

Since the adhesive tape of the present invention uses a foamed sheet having excellent thermal stability as a base material, it is suitable for use in electronic devices, particularly in vehicle-mounted electronic devices. Moreover, since the pressure-sensitive adhesive tape of the present invention is excellent in flexibility and conformability to irregularities, it is suitable for use as a sealing material or a cushioning material for electronic devices, particularly electronic devices mounted on vehicles. The adhesive tape of the present invention is particularly suitable for use in image display devices, particularly in-vehicle image display devices.
Further, as described above, the foamed sheet of the present invention is particularly suitable for use in a narrow portion such as a frame portion on the outside of the display panel. It is particularly suitable for narrow part applications such as parts.

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
In addition, the measuring method of each physical property and the evaluation method of a foam sheet are as follows.

(1) Thickness of foam sheet The thickness of the foam sheet was measured using a dial gauge.
(2) Density and expansion ratio of foamed sheet The density (apparent density) of the foamed sheet was measured according to JISK7222.
In addition, the reciprocal of the density of the foamed sheet was taken as the foaming ratio.
(3) Degree of Crosslinking A test piece of about 100 mg is sampled from the foamed sheet, and the mass A (mg) of the test piece is precisely weighed. Next, this test piece is immersed in 30 cm ³ of xylene at 120° C. and allowed to stand for 24 hours. After that, it is filtered through a 200-mesh wire mesh, the insoluble matter on the wire mesh is collected, dried in a vacuum, and the mass B (mg) of the insoluble matter is accurately weighed. From the obtained values, the degree of cross-linking (% by mass) was calculated according to the following formula.
Crosslinking degree (mass%) = 100 x (B/A)
(4) MD and TD Average Pore Size A foam sheet was cut into 50 mm squares and prepared as a foam sample for measurement. After immersing this in liquid nitrogen for 1 minute, it was cut in the thickness direction along the MD direction and the TD direction with a razor blade. A digital microscope ("VHX-900" manufactured by KEYENCE CORPORATION) was used to take a photograph of this cross section at a magnification of 200 times, and all closed cells present on the cut surface with a length of 2 mm in each of the MD direction and the TD direction The bubble diameter was measured for , and the operation was repeated 5 times. Then, the average value of all the bubbles was taken as the average bubble diameter in the MD and TD directions.
(5) 25% Compressive Strength The 25% compressive strength of the foam sheet was measured according to JIS K6767.
(6) Adhesion resistance after curing at 95°C for 100 hours A foamed sheet was cut into a width of 25 mm and a length of 300 mm, adhered to a glass plate, compressed by 33% with a stainless steel plate, and left at 95°C for 100 hours. bottom. After 100 hours, the compression was released and the peel adhesion in the 90° direction was measured.
Then, the adhesion resistance after curing at 95° C. for 100 hours was evaluated according to the following criteria.
A (good adhesion resistance): Adhesive strength = 0.9 N/25 mm or less B (no adhesion resistance): Adhesive strength = greater than 0.9 N/25 mm Note that if the thermal stability of the foam sheet is low, the glass of the foam sheet Adhesion to the plate increases, and adhesion resistance decreases.
(7) Comprehensive Evaluation of Foamed Sheets Foamed sheets with extremely excellent flexibility and excellent thermal stability (anti-adhesion) were evaluated as "good" (good). In addition, foamed sheets with moderately excellent flexibility and excellent thermal stability were evaluated as "Δ" (acceptable). Furthermore, a foam sheet with poor thermal stability was evaluated as "x" (improper).

Foamed sheets of Examples 1 to 10 and Comparative Examples 1 to 5 were produced as follows.
(Example 1)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Corporation, trade name "Novatec EG7F" 60 parts by mass, and ethylene-propylene-diene copolymer (manufactured by Sumitomo Chemical Co., Ltd., product name "ESPRENE 301") Further, 20 parts by mass of a linear low-density polyethylene resin (trade name “Affinity PL1850” manufactured by Dow Chemical Co., Ltd.) and 3 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent were supplied to the extruder. , 3.0 parts by mass of trimethylolpropane trimethacrylate as a cross-linking aid and 0.5 parts by mass of an antioxidant were supplied to the extruder, and melted and kneaded at 130 ° C. to form a long shape having a thickness of 250 µm. Extruded into resin sheet.
Next, both surfaces of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet. Then, the crosslinked resin sheet is continuously fed into a foaming furnace maintained at 250° C. with hot air and an infrared heater to heat and foam, and while foaming, the MD stretch ratio is 3.0 times, and the TD is stretched. It was stretched at a magnification of 2.5 times. Thus, a foamed sheet of Example 1 was produced.

(Example 2)
A foamed sheet of Example 2 was produced in the same manner as the foamed sheet of Example 1, except that the amount of the thermally decomposable foaming agent was changed to 5 parts by mass and the thickness of the resin sheet was changed to 300 μm.

(Example 3)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Corporation, trade name "Novatec EG7F" 60 parts by mass, and ethylene-propylene-diene copolymer (manufactured by Sumitomo Chemical Co., Ltd., product name "ESPRENE 301") Further, 20 parts by mass of a linear low-density polyethylene resin (trade name “Affinity PL1850” manufactured by Dow Chemical Co., Ltd.) and 7 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent were supplied to the extruder. , 3.0 parts by mass of trimethylolpropane trimethacrylate as a cross-linking aid and 0.5 parts by mass of an antioxidant were supplied to the extruder, and melted and kneaded at 130 ° C. to form a long shape having a thickness of 350 µm. Extruded into resin sheet.
Next, both sides of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was foamed at 250° C. with hot air and an infrared heater. It was continuously fed into a furnace and heated to foam. Thus, a foamed sheet of Example 3 was produced.

(Example 4)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Corporation, trade name "Novatec EG7F" 60 parts by mass, and ethylene-propylene-diene copolymer (manufactured by Sumitomo Chemical Co., Ltd., product name "ESPRENE 301") Further, 7 parts by mass of azodicarbonamide as a pyrolytic foaming agent, 3.0 parts by mass of trimethylolpropane trimethacrylate as a cross-linking aid, and 0.5 parts by mass of an antioxidant were supplied to the extruder. The parts were supplied to an extruder, melt-kneaded at 130° C., and extruded into a long resin sheet having a thickness of 350 μm.
Next, both sides of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was foamed at 250° C. with hot air and an infrared heater. It was continuously fed into a furnace and heated to foam. Thus, a foamed sheet of Example 4 was produced.

(Example 5)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Co., Ltd., trade name "Novatec EG7F" 60 parts by mass, and ethylene-propylene-diene copolymer (manufactured by Sumitomo Chemical, product name "ESPRENE 301") 20 parts by mass Further, 20 parts by mass of an olefinic thermoplastic elastomer (manufactured by SunAllomer Co., Ltd., product name "Cataloy Q200F"), 3 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent, and 3.0 parts by mass of trimethylolpropane trimethacrylate and 0.5 parts by mass of an antioxidant were supplied to an extruder, melt-kneaded at 130° C., and extruded into a long resin sheet having a thickness of 250 μm. .
Next, both sides of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was heated to 250° C. in a foaming furnace with hot air and an infrared heater. The material was continuously fed and heated to foam, and was stretched at a MD draw ratio of 3.0 times and a TD draw ratio of 2.5 times while foaming. Thus, a foamed sheet of Example 5 was produced.

(Example 6)
A foamed sheet of Example 6 was produced in the same manner as the foamed sheet of Example 5, except that the amount of the thermally decomposable foaming agent was changed to 5 parts by mass and the thickness of the resin sheet was changed to 300 μm.

(Example 7)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Co., Ltd., product name "Novatec EG7F" 80 parts by mass, and ethylene-propylene-diene copolymer (manufactured by Sumitomo Chemical, product name "ESPRENE 301") 20 parts by mass Further, 3.5 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent, 3.0 parts by mass of trimethylolpropane trimethacrylate as a cross-linking aid, and 0.5 parts by mass of an antioxidant. was supplied to an extruder, melt-kneaded at 130° C., and extruded into a long resin sheet having a thickness of 250 μm.
Next, both sides of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was heated to 250° C. in a foaming furnace with hot air and an infrared heater. The material was continuously fed and heated to foam, and was stretched at a MD draw ratio of 3.0 times and a TD draw ratio of 2.5 times while foaming. Thus, a foamed sheet of Example 7 was produced.

(Example 8)
A foamed sheet of Example 8 was produced in the same manner as in Example 5, except that the amount of the thermal decomposition type foaming agent was changed to 6 parts by mass and the thickness of the resin sheet was changed to 300 μm.

(Example 9)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Co., Ltd., trade name "Novatec EG7F" 60 parts by mass, linear low-density polyethylene resin (manufactured by Dow Chemical Co., trade name "Affinity PL1850" 40 parts by mass) In addition, 3 parts by mass of azodicarbonamide as a thermally decomposable foaming agent, 3.0 parts by mass of trimethylolpropane trimethacrylate as a cross-linking aid, and 0.5 parts by mass of an antioxidant were extruded. Then, it was melt-kneaded at 130° C. and extruded into a long resin sheet having a thickness of 250 μm.
Next, both sides of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was heated to 250° C. in a foaming furnace with hot air and an infrared heater. The material was continuously fed and heated to foam, and was stretched at a MD draw ratio of 3.0 times and a TD draw ratio of 2.5 times while foaming. Thus, a foamed sheet of Example 9 was produced.

(Example 10)
A foamed sheet of Example 10 was produced in the same manner as the foamed sheet of Example 9, except that the amount of the thermal decomposition type foaming agent was changed to 5 parts by mass and the thickness of the resin sheet was changed to 300 μm.

(Comparative example 1)
Linear low-density polyethylene resin (manufactured by Dow Chemical Company, trade name "Affinity PL1850" 100 parts by mass, 2.5 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent, and 0.5 parts by mass of antioxidant The mixture was supplied to an extruder, melt-kneaded at 130° C., and extruded into a long resin sheet having a thickness of 270 μm.
Next, both sides of the long resin sheet were irradiated with 4 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was continuously heated to 250°C by hot air and an infrared heater in a foaming furnace. While foaming, it was stretched at a MD draw ratio of 3.0 and a TD draw ratio of 2.5. Thus, a foamed sheet of Comparative Example 1 was produced.

(Comparative example 2)
A foamed sheet of Comparative Example 2 was produced in the same manner as the foamed sheet of Comparative Example 1, except that the amount of the thermal decomposition type foaming agent was changed to 3 parts by mass and the thickness of the resin sheet was changed to 340 μm.

(Comparative Example 3)
Linear low-density polyethylene resin (manufactured by Dow Chemical Company, trade name "Affinity PL1850" 100 parts by mass, 7 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent, and 0.5 parts by mass of an antioxidant are extruded. and melt-kneaded at 130° C., and extruded into a long resin sheet having a thickness of 450 μm.
Next, both sides of the long resin sheet were irradiated with 7 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was continuously heated to 250°C by hot air and an infrared heater in a foaming furnace. and heated to foam. Thus, a foamed sheet of Comparative Example 3 was produced.

(Comparative Example 4)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Co., Ltd., trade name "Novatec EG7F" 30 parts by mass, linear low-density polyethylene resin (manufactured by Dow Chemical Co., trade name "Affinity PL1850" 70 parts by mass) Further, 5 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent, 3.0 parts by mass of trimethylolpropane trimethacrylate as a cross-linking aid, and 0.5 parts by mass of an antioxidant were extruded. Then, it was melt-kneaded at 130° C. and extruded into a long resin sheet having a thickness of 370 μm.
Next, both sides of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was heated to 250° C. in a foaming furnace with hot air and an infrared heater. The material was continuously fed and heated to foam, and was stretched at a MD draw ratio of 3.0 times and a TD draw ratio of 2.5 times while foaming. Thus, a foamed sheet of Comparative Example 4 was produced.

(Comparative Example 5)
Ethylene-polypropylene random copolymer resin (manufactured by Japan Polypropylene Corporation, trade name "Novatec EG7F" 20 parts by mass, and ethylene-propylene-diene copolymer (manufactured by Sumitomo Chemical Co., Ltd., product name "ESPRENE 301") Further, 60 parts by mass of a linear low-density polyethylene resin (trade name “Affinity PL1850” manufactured by Dow Chemical Co., Ltd.) and 5 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent were supplied to the extruder. , 3.0 parts by mass of trimethylolpropane trimethacrylate as a cross-linking aid and 0.5 parts by mass of an antioxidant were supplied to an extruder, and melt-kneaded at 130°C to form a long resin having a thickness of 370 µm. Extruded into sheets.
Next, both sides of the long resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was heated to 250° C. in a foaming furnace with hot air and an infrared heater. The material was continuously fed and heated to foam, and was stretched at a MD draw ratio of 3.0 times and a TD draw ratio of 2.5 times while foaming. Thus, a foamed sheet of Comparative Example 5 was produced.

Tables 1 to 3 show the composition of the resin composition used to prepare the foamed sheets of Examples 1 to 10 and Comparative Examples 1 to 5, and the physical properties and evaluation results of the foamed sheets of Examples 1 to 10 and Comparative Examples 1 to 5. shown.

The resin components and additives shown in Tables 1 to 3 are as follows.
Random PP: ethylene-propylene random copolymer, manufactured by Japan Polypropylene Corporation, trade name: Novatec EG7F, MFR: 1.3 g/10 min, ethylene content: 3% by mass
EPDM: ethylene-propylene-diene copolymer, manufactured by Sumitomo Chemical Co., Ltd., product name: Esprene 301, Mooney viscosity (ML ₁₊₄ , 100° C.)=55, ethylene content: 62% by mass, DCPD content: 3% by mass %
TPO: olefin-based thermoplastic elastomer, product name of SunAllomer Co., Ltd., product name: Catalloy Q200F, MFR: 0.8 g/10 min LLDPE: linear low-density polyethylene, manufactured by Dow Chemical Company, product name: Affinity PL1850, density : 0.902g/ ^cm3
Blowing agent: Azodicarbonamide Cross-linking aid: Trimethylolpropane trimethacrylate Antioxidant: Dilauryl thiodipropionate

As described above, the foam sheets of Examples 1 to 10 were all evaluated for adhesion resistance after curing at 95° C. for 100 hours, and the foam sheets of Examples 1 to 10 had excellent thermal stability. I found out. Furthermore, the 25% compression strength of the foam sheets of Examples 1 to 10 is in the range of 80 to 350 kPa, and the foam sheets of Examples 1 to 10 have appropriate flexibility for electronic device applications. have understood. In particular, the 25% compressive strength of the foamed sheets of Examples 1-6 was 150 kPa or less, and the flexibility of the foamed sheets of Examples 1-6 was very excellent.
On the other hand, all of the foamed sheets of Comparative Examples 1 to 5 were rated as B for adhesion resistance after curing at 95° C. for 100 hours, and the thermal stability of the foamed sheets of Comparative Examples 1 to 5 was poor.

Claims (8)

A resin composition containing a polyolefin resin is foamed, and the polyolefin resin is 50 to 90 parts by mass of a polypropylene resin and 10 to 50 parts by mass of a polyethylene resin in 100 parts by mass of the polyolefin resin. and at least one polyolefin polymer material selected from the group consisting of resins and polyolefin rubbers,
The thickness is 0.1 to 1.5 mm,
25% compressive strength is 40 to 350 kPa,
The average pore diameter in the MD direction and the TD direction is 90 to 250 μm,
The content of the polyolefin rubber is 10 to 50 parts by mass with respect to 100 parts by mass of the polyolefin resin,
A polyolefin resin foam sheet having a closed cell structure . The polyolefin resin foam sheet according to claim 1, having a degree of cross-linking of 30 to 59% by mass. The polyolefin resin foam sheet according to claim 1 or 2, wherein the polypropylene resin is an ethylene-propylene random copolymer. The polyolefin resin foam sheet according to any one of claims 1 to 3, wherein the polyolefin rubber contains an ethylene-α-olefin copolymer rubber. The polyolefin resin foam sheet according to any one of claims 1 to 4, wherein the polyethylene resin is a linear low density polyethylene resin (LLDPE). The polyolefin resin foam sheet according to any one of claims 1 to 5, which is used for electronic equipment. The polyolefin-based resin foam sheet according to claim 6, which is used for in-vehicle electronic equipment. An adhesive tape comprising the polyolefin resin foam sheet according to any one of claims 1 to 7 and an adhesive layer provided on at least one surface of the polyolefin resin foam sheet.