JP7100968B2 - Polyolefin resin foam sheet and adhesive tape using it - Google Patents

Description

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

Polyolefin-based resin foams are generally excellent in flexibility, light weight, shock absorption and heat insulating properties, and are widely used as laminates with skin materials, heat insulating materials, cushioning materials and the like. Further, since the polyolefin-based resin foam has excellent flexibility, excellent shock absorption, and excellent heat insulating properties, application to adhesive tapes used in electronic devices has been attempted. For the polyolefin-based foam used in electronic devices, for example, a polyethylene-based resin is used (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2017-660403

Since some electronic devices generate a large amount of heat, when the polyolefin-based resin foam is used for the adhesive tape used in the electronic device, the polyolefin-based resin foam preferably has excellent heat resistance. In particular, when a polyolefin-based resin foam is used for an adhesive tape used in an in-vehicle electronic device, the polyolefin-based resin foam has even better heat resistance because the electronic device is exposed to a high temperature environment in the vehicle. Is preferable. The adhesive tape using a polyolefin-based resin foam described in Patent Document 1 is excellent not only in flexibility, shock absorption and heat insulation, but also in heat resistance. However, an adhesive tape having even better heat resistance is desired.
Therefore, an object of the present invention is to provide a polyolefin-based resin foam sheet having excellent heat resistance, an adhesive tape using the same, and a sealing material for an electronic device using the same.

The present invention has been made based on the finding that the above problems can be solved by using a foamed sheet having a specific heat shrinkage rate.
That is, the present invention provides the following [1] to [13].
[1] A polyolefin-based resin foam sheet having a thickness of 0.05 to 3 mm and having a shrinkage rate in the plane direction of 5% or less when cured at a temperature of 120 ° C. for 1 hour.
[2] The thermoplastic resin composition containing a polyolefin resin is foamed, and the polyolefin resin contains 50 parts by mass or more of a polypropylene resin with respect to 100 parts by mass of the polyolefin resin. [1] The polyolefin-based resin foam sheet described in 1.
[3] The polyolefin-based resin foamed sheet according to the above [2], wherein the polypropylene-based resin is an ethylene-propylene random copolymer.
[4] The thermoplastic resin composition further contains an azodicarboxylic amide and at least one basic magnesium selected from the group consisting of magnesium oxide and magnesium hydroxide, and the base in the thermoplastic resin composition. The polyolefin-based resin foamed sheet according to the above [2] or [3], wherein the content of the magnesium (B) is 0.03 to 1.0 part by mass with respect to 100 parts by mass of the polyolefin-based resin.
[5] The polyolefin-based resin foamed sheet according to any one of the above [2] to [4], wherein the polyolefin-based resin further contains a polyethylene-based resin.
[6] The polyolefin-based resin foamed sheet according to the above [5], wherein the polyethylene-based resin is a linear low-density polyethylene-based resin (LLDPE).
[7] The polyolefin-based resin foam sheet according to any one of the above [2] to [6], wherein the polyolefin-based resin further contains a polyolefin-based rubber.
[8] The polyolefin-based resin foam sheet according to the above [7], wherein the polyolefin-based rubber is an ethylene-α-olefin-based copolymer rubber.
[9] The polyolefin-based resin foamed sheet according to any one of the above [1] to [8], which has a density of 0.065 / cm ³ or more.
[10] The polyolefin-based resin foamed sheet according to any one of the above [1] to [9], which has a 25% compressive strength of 30 to 600 kPa.
[11] The polyolefin-based resin foam sheet according to any one of the above [1] to [10] used in electronic devices.
[12] The polyolefin-based resin foam sheet according to the above [11] used in an in-vehicle electronic device.
[13] An adhesive tape comprising the polyolefin-based resin foamed sheet according to any one of the above [1] to [12] and an adhesive layer provided on at least one surface of the polyolefin-based resin foamed sheet.

According to the present invention, it is possible to provide a polyolefin-based resin foam sheet having excellent heat resistance and an adhesive tape using the same.

The polyolefin-based resin foam sheet of the present invention is characterized in that it has a thickness of 0.05 to 3 mm and has a shrinkage rate in the plane direction of 5% or less when cured at a temperature of 120 ° C. for 1 hour.
Hereinafter, the polyolefin-based resin foam sheet of the present invention will be described in detail.

[Polyolefin resin foam sheet]
The polyolefin-based resin foam sheet of the present invention is preferably formed by foaming a thermoplastic resin composition containing a polyolefin-based resin (hereinafter, also referred to as “resin composition (a)”). Further, the polyolefin-based resin foam sheet of the present invention may be obtained by cross-linking and foaming a thermoplastic resin composition containing a polyolefin-based resin (hereinafter, also referred to as "resin composition (a)"). More preferred.

[Polyolefin-based resin]
The polyolefin-based resin is not particularly limited as long as it contains a polypropylene-based resin. The polypropylene-based resin is not particularly limited, and examples thereof include a copolymer of propylene and another olefin. The copolymer of propylene and other olefins may be a block copolymer, a random copolymer, or a random block copolymer, but a random copolymer (random polypropylene) is preferable.
In the copolymer of propylene and other olefins, other olefins that are copolymerized with propylene include, for example, ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-. Examples thereof include α-olefins such as octene, 1-nonene and 1-decene, and among these, ethylene is particularly preferable. That is, the polypropylene resin is preferably an ethylene-propylene random copolymer.
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-olefins other than propylene, but 95 to 99% by weight of propylene. %, The α-olefin other than propylene is preferably 1 to 5% by mass.

The polypropylene-based resin preferably has a melt flow rate (hereinafter, also referred to as “MFR”) of 0.4 to 4.0 g / 10 minutes, and more preferably 0.5 to 2.5 g / 10 minutes. preferable. By using the polypropylene-based resin having the above-mentioned MFR, the moldability when the resin composition (a) is processed into the polyolefin-based resin foamed sheet and the moldability when the polyolefin-based resin foamed sheet is secondarily processed can be improved. It will be easier to improve.
The above polypropylene-based resin can be used alone or in combination of two or more.
The MFR is a value measured based on JIS K7210 under the conditions of a temperature of 230 ° C. and a load of 2.16 kgf.

The content of the polypropylene-based resin in the polyolefin-based resin is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and further preferably 55 parts by mass or more with respect to 100 parts by mass of the polyolefin-based resin. It is more preferably 60 parts by mass or more, preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and further preferably 75 parts by mass or less.
As described above, when the polyolefin-based resin contains 40 parts by mass or more of the polypropylene-based resin, the polyolefin-based resin foamed sheet can have high mechanical strength and excellent heat resistance. Further, as described above, the polypropylene-based resin is preferably random polypropylene.

From the viewpoint of obtaining a foamed sheet having excellent heat resistance and flexibility, the polyolefin-based resin preferably further contains at least one polyolefin-based compound selected from a polyethylene-based resin and a polyolefin-based rubber.

Examples of the polyethylene-based resin include low-density polyethylene-based resin, medium-density polyethylene-based resin, high-density polyethylene-based resin, and linear low-density polyethylene-based resin. Among these, linear low-density polyethylene-based resin is used. Resin (LLDPE) is preferred.
The linear low-density polyethylene-based resin is polyethylene having a density of 0.910 g / cm ³ or more and less than 0.950 g / cm ³ , preferably having a density of 0.910 to 0.930 g / cm ³ . Since the foam contains a low-density linear low-density polyethylene-based resin, the workability when processing the resin composition into a foam and the moldability when molding the foam into a molded body are improved. It tends to be good. The density of the resin is measured according to JIS K7112.
The linear low-density polyethylene is usually composed of ethylene as a main component (80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more of the total monomer), and is a copolymer of ethylene and a small amount of α-olefin. It is a polymer. Here, examples of the α-olefin include those having 3 to 12 carbon atoms, preferably 4 to 10 carbon atoms, and specifically, 1-butene, 1-pentene, 1-hexene, and 4-methyl-1. -Pentene, 1-heptene, 1-octene and the like. In the copolymer, these α-olefins can be used alone or in combination of two or more.
Further, the polyethylene-based resin may be used alone or in combination of two or more.

As the polyolefin-based rubber, an amorphous or low-crystalline rubber-like substance obtained by substantially randomly copolymerizing two or more kinds of olefin-based monomers is preferable, and ethylene is used from the viewpoint of improving moldability and flexibility in a well-balanced manner. -Α-Olefin copolymer rubber is more preferable.
The α-olefins used in the ethylene-α-olefin copolymer rubber include propylene, 1-butene, 2-methylpropylene, 3-methyl-1-butene, 1-pentene, 1-hexene and 4-methyl-. Examples thereof include one or more α-olefins having 3 to 15 carbon atoms, preferably 3 to 10 carbon atoms such as 1-pentene and 1-octene. Among these, propylene and 1-butene are preferable, and propylene is more preferable.

The ethylene-α-olefin copolymer rubber may have other monomer units in addition to the ethylene unit and the α-olefin unit.
Examples of the monomer forming the other monomer unit include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and the like. Conjugate diene with 4-8 carbon atoms; dicyclopentadiene, 5-ethylidene-2-norbornene, 1,4-hexadiene, 1,5-dicyclooctadiene, 7-methyl-1,6-octadien, 5-vinyl- Non-conjugated diene having 5 to 15 carbon atoms such as 2-norbornene; vinyl ester compound such as vinyl acetate; unsaturated carboxylic acid ester such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate; Examples thereof 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 diene having 5 to 15 carbon atoms is preferable, and 5-ethylidene-2-norbornene, 1,4-hexadiene, and dicyclopentadiene (DCPD) are more preferable 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, and has 3 to 3 to 75 carbon atoms such as propylene. 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 diene is. It is usually 0 to 20% by weight, preferably 1 to 10% by weight.

Further, as the polyolefin-based rubber, an olefin-based thermoplastic elastomer (TPO) can also be used. The olefin-based thermoplastic elastomer (TPO) generally has a polyolefin such as polyethylene or polypropylene as a hard segment and a rubber component such as EPM or EPDM as a soft segment. As the olefin-based thermoplastic elastomer (TPO), any of a blend type, a dynamic cross-linking type, and a polymerization type can be used.

Preferable specific examples of the polyolefin-based rubber include ethylene-propylene copolymer rubber (EPR) and ethylene-propylene-diene copolymer rubber (EPDM), with EPDM being preferred. Examples of EPDM include ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber and ethylene-propylene-dicyclopentadiene copolymer rubber, and among these, ethylene-propylene-dicyclopentadiene copolymer rubber. Is preferable.

As the polyolefin-based rubber, one 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 becomes possible to improve flexibility and moldability in a well-balanced manner. Further, in order to improve the flexibility and moldability, the Mooney viscosity of the olefin rubber is more preferably 25 to 75, and further preferably 30 to 70. The Mooney viscosity (ML _{1 + 4} , 100 ° C.) can be measured according to JIS K6300-1.
The olefin rubber can be used alone or in combination of two or more.

The content of at least one polyolefin compound selected from the polyethylene resin and the polyolefin rubber in the polyolefin resin is preferably 10 parts by mass or more, more preferably 20 parts by mass with respect to 100 parts by mass of the polyolefin resin. It is more than parts by mass, more preferably 25 parts by mass or more, and preferably 60 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 45 parts by mass or less, still more preferably. It is 40 parts by mass or less.
As described above, when the polyolefin-based resin contains 10 parts by mass or more of the above-mentioned polyolefin-based compound, the polyolefin-based resin foamed sheet can have good flexibility.

[Other ingredients]
The polyolefin-based resin may be composed of only a polypropylene-based resin or at least one polyolefin-based compound selected from the polypropylene-based resin and the polyethylene-based resin and the polyolefin-based rubber, but the object of the present invention is impaired. As long as it does not, it may contain resin components other than those.
Examples of the resin component include an ethylene-vinyl acetate copolymer, an ethylene-acrylic acid copolymer, an ethylene- (meth) alkyl acrylate copolymer, or a modified copolymer obtained by copolymerizing these with maleic anhydride. And so on.

From the viewpoint of improving the heat resistance and mechanical strength of the polyolefin-based resin foam sheet and ensuring flexibility and moldability, the content of the olefin-based resin in the resin composition (a) is preferably 80 to 99 mass. %, More preferably 83 to 98% by mass.

<Additives>
The resin composition (a) usually contains a foaming agent as an additive in addition to the olefin resin. Further, the resin composition (a) may further contain at least one basic magnesium selected from the group consisting of magnesium oxide and magnesium hydroxide. Further, the resin composition (a) preferably contains one or both of a cross-linking aid and an antioxidant.

(Effervescent agent)
As a method for foaming the resin composition (a), there are a chemical foaming method and a physical foaming method. The chemical foaming method is a method of forming bubbles by the gas generated by the thermal decomposition of the compound added to the resin composition (a), and the physical foaming method is a method of forming a low boiling point liquid (foaming agent) into a resin composition (foaming agent). This is a method in which a) is impregnated and then the foaming agent is volatilized to form a cell. The foaming method is not particularly limited, but a chemical foaming method is preferable from the viewpoint of obtaining a uniform closed cell foaming 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.
Examples of the organic foaming agent include azodicarbonamides, azodicarboxylic acid metal salts (azodicarboxylic acid barium and the like), azo compounds such as azobisisobutyronitrile, and nitroso compounds such as N, N'-dinitrosopentamethylenetetramine. Examples thereof include hydrazodicarbonamides, 4,4'-oxybis (benzenesulfonyl hydrazide), hydrazine derivatives such as toluenesulfonyl hydrazide, and semi-carbazide compounds such as toluenesulfonyl semicarbazide.

Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium boron hydride, anhydrous monosoda citrate and the like.
Among these, azo compounds and nitroso compounds are preferable from the viewpoint of obtaining fine bubbles, and from the viewpoint of economy and safety, azodicarbonamide, azobisisobutyronitrile, N, N'-dinitrosopentamethylene. Tetramine is more preferred, and azodicarbonamide is particularly preferred.
The foaming agent can be used alone or in combination of two or more.
The amount of the heat-decomposable foaming agent added is preferably 1 to 25 parts by mass, preferably 1.5 to 15 parts by mass with respect to 100 parts by mass of the resin component, from the viewpoint of appropriately foaming the foam sheet without bursting bubbles. More preferably, 2 to 10 parts by mass is further preferable.

(Basic magnesium)
The basic magnesium is preferably at least one selected from the group consisting of magnesium oxide and magnesium hydroxide. The resin composition (a) may contain only one of magnesium oxide and magnesium hydroxide, or may contain both.
When the foaming agent, particularly azodicarbonamide, is decomposed by heating, a part of it becomes a sublimate and fogging occurs. However, since the resin composition (a) contains basic magnesium, the occurrence of fogging due to such a sublimated product is prevented. Therefore, in the present invention, when azodicarbonamide is used as the foaming agent, it is particularly preferable that the resin composition (a) contains basic magnesium.

The content of basic magnesium in the resin composition (a) is preferably 0.03 to 1.0 part by mass, and more preferably 0.04 to 0.8 part by mass with respect to 100 parts by mass of the polyolefin resin. Parts, more preferably 0.05 to 0.7 parts by mass.

(Crosslinking aid)
As the cross-linking aid, a polyfunctional monomer can be used. For example, trifunctional (meth) acrylate compounds such as trimethylolpropanetrimethacrylate and trimethylolpropanetriacrylate; trimellitic acid triallyl ester, 1,2,4-benzenetricarboxylic acid triallyl ester, triallyl isocyanurate and the like. Compounds having 3 functional groups in one molecule; bifunctional (1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, neopentylglycoldimethacrylate, etc.) Meta) Compounds having two functional groups in one molecule such as acrylate compounds and divinylbenzene; examples thereof include diallyl phthalate, diallyl terephthalate, diallyl isophthalate, ethyl vinylbenzene, lauryl methacrylate and stearyl methacrylate. Of these, trifunctional (meth) acrylate compounds are more preferred.
The cross-linking aid can be used alone or in combination of two 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 amount of ionizing radiation. Therefore, it is possible to prevent cutting and deterioration of each resin molecule 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 easy adjustment and control of the degree of cross-linking when foaming the resin composition (a). It is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 15 parts by mass.

(Antioxidant)
Examples of the antioxidant include a phenol-based antioxidant, a sulfur-based antioxidant, a phosphorus-based antioxidant, an amine-based antioxidant, and the like. Among these, phenol-based antioxidants and sulfur-based antioxidants are preferable, and it is more preferable to use a phenol-based antioxidant and a sulfur-based antioxidant in combination.
Examples of the phenolic antioxidant include 2,6-di-tert-butyl-p-cresol, n-octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and 2-tert-. Butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenylacrylate, tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate ] Methyl and the like can be mentioned.
Examples of the sulfur-based antioxidant include dilaurylthiodipropionate, dimyristylthiodipropionate, disstearylthiodipropionate, and pentaerythrityltetrakis (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 with respect to 100 parts by mass of the polyolefin resin.
Further, the resin composition (a) may be a decomposition temperature adjusting agent for zinc oxide, zinc stearate, urea and the like, a flame retardant, a metal damage inhibitor, an antistatic agent, a stabilizer, a filler, a pigment and the like, if necessary. Additives other than the above may be contained.
Further, the resin composition (a) may contain a resin other than the polyolefin-based resin as long as the effect of the present invention is not impaired.

[Polyolefin resin foam sheet]
As described above, the polyolefin-based resin foamed sheet of the present invention (hereinafter, also simply referred to as “foamed sheet”) is formed by foaming the above-mentioned resin composition (a).
(density)
The density (apparent density) of the foamed sheet is preferably 0.065 / cm ³ or more, more preferably 0.08, from the viewpoint of improving heat resistance and improving flexibility and mechanical strength in a well-balanced manner. / Cm ³ or more, more preferably 0.1 / cm ³ or more, and preferably 0.7 g / cm ³ or less, more preferably 0.5 g / cm ³ or less, still more preferably 0.4 g / It is less than cm ³ .

(Crosslink degree)
The degree of cross-linking (mass%) of the entire foamed sheet is preferably 30% or more, more preferably 35% or more, still more preferably 40% or more, from the viewpoint of improving flexibility, mechanical strength, and moldability in a well-balanced manner. And, preferably 65% or less, more preferably 60% or less, still more preferably 55% or less.
The degree of cross-linking can be measured by the method described in Examples described later.

(thickness)
The thickness of the foam sheet is 0.05 to 3 mm. If the thickness of the foam sheet is less than 0.05 mm, the foam sheet tends to shrink due to heat. In addition, sufficient sealing properties cannot be ensured when applied to electronic devices and the like. If the thickness of the foam sheet is larger than 3 mm, the foam sheet may not be suitable for use in electronic devices or in-vehicle electronic devices. The thickness of the foamed sheet is preferably 0.1 mm or more, more preferably 0.3 mm or more, and preferably 2 mm or less, more preferably 1.5 mm or less, still more preferably 1.0 mm or less.

(Shrinkage rate in the plane direction when cured at a temperature of 120 ° C. for 1 hour)
The shrinkage rate in the plane direction when the foamed sheet is cured at a temperature of 120 ° C. for 1 hour is 5% or less. If the shrinkage rate in the plane direction when the foam sheet is cured at a temperature of 120 ° C. for 1 hour is larger than 5%, it is suitable for use in electronic devices that generate a large amount of heat or in a high temperature environment inside a vehicle. In some cases, a foamed sheet having sufficient heat resistance cannot be obtained. The shrinkage rate in the plane direction when the foamed sheet is cured at a temperature of 120 ° C. for 1 hour is preferably 4.5% or less, more preferably 3% or less. The lower limit of the range of the shrinkage rate in the plane direction when the foamed sheet is cured at a temperature of 120 ° C. for 1 hour is not particularly limited, but is, for example, 0.1%.
In addition, in accordance with JIS K 6767, when the dimensional change of the foamed sheet at 120 ° C. was measured, the heat shrinkage rate (%) was calculated, and the value was cured at the temperature of 120 ° C. of the foamed sheet for 1 hour. The shrinkage rate in the plane direction of.

(25% compressive strength)
The 25% compressive strength of the foamed sheet is preferably 30 kPa or more, more preferably 35 kPa or more, still more preferably 40 kPa or more, from the viewpoint of ensuring the mechanical strength and heat resistance of the foamed sheet. Further, the 25% compressive strength of the foamed sheet is preferably 600 kPa or less, more preferably 550 kPa or less, preferably 500 kPa or less for straw, and further preferably 480 kPa or less from the viewpoint of ensuring the flexibility of the foamed sheet.
The 25% compressive strength is measured according to JIS K6767.

Since the foamed sheet of the present invention has excellent heat resistance, it is suitable for applications in electronic devices, particularly in-vehicle electronic devices. In particular, it is suitable for applications in image display devices such as head-up display devices and liquid crystal display devices, and further suitable for applications in in-vehicle image display devices. Further, the foamed sheet of the present invention is further excellent in antifogging property. If the foam sheet has poor antifogging properties, the window portion for projecting or displaying an image may become cloudy, making it impossible to project or display a clear image.

<Manufacturing method of foam sheet>
The foamed sheet can be produced, for example, by melt-kneading the resin composition (a), forming it into a desired shape, and then irradiating it with ionizing radiation to heat-foam the resin composition (a).
Specifically, a production method having the following steps 1 to 3 is more preferable.
Step 1: After melt-kneading each component constituting the resin composition (a), a sheet-shaped resin composition (a) is obtained. Step 2: The resin composition (a) obtained in step 1 is ionizable. Step 3: Step of cross-linking by irradiating with radiation Step 3: A step of heating the resin composition (a) cross-linked in step 2 to a temperature higher than the decomposition temperature of the heat-decomposable foaming agent and foaming the resin composition (a) to obtain a foamed sheet.

In step 1, each component constituting the resin composition (a) is supplied to a kneading device, melt-kneaded at a temperature lower than the decomposition temperature of the heat-decomposable foaming agent, and then melt-kneaded (a). ) Is preferably formed into a sheet by the kneading device used in the melt kneading.
Examples of the kneading device used here include an injection molding machine, an extruder (single-screw extruder, twin-screw extruder, etc.), a Banbury mixer, a general-purpose kneading device such as a roll, and the like. An extruder is preferable, and if an injection molding machine is used, it can be manufactured with high productivity.
The resin temperature inside the injection molding machine or extruder is preferably 120 to 220 ° C, more preferably 140 to 200 ° C, and even more preferably 150 to 195 ° C.

In step 2, the resin composition (a) formed into a sheet is irradiated with ionizing radiation.
Examples of the ionizing radiation include electron beam, α ray, β ray, γ ray, X-ray and the like. Among these, an electron beam is preferable from the viewpoint of productivity and uniform irradiation.
Irradiation of ionizing radiation may be performed on only one side of the resin composition (a) formed into a sheet, or on both sides.
The acceleration 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, preferably 500 to 1100 kV. It is more preferable, and it is more preferable that it is 600 to 1000 kV.
The irradiation dose of the ionizing radiation may be an amount that can obtain a desired degree of cross-linking without causing surface roughness or cracks in consideration of the thickness of the foamable resin composition to be irradiated, etc., but is usually used. 0.1 to 10 Mrad is preferable, 0.2 to 5 Mrad is more preferable, and 0.3 to 3 Mrad is more preferable.

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. After foaming the resin composition (a), or while foaming the resin composition (a), the resin composition (a) may be stretched in either one or both of the MD direction and the CD direction.
Here, the temperature at which the resin composition (a) is heated and foamed depends on the decomposition temperature of the thermally decomposable foaming agent used as the foaming agent, but is usually 140 to 300 ° C, preferably 150 to 280 ° C, more preferably 160. It is about 260 ° C.
The foamed sheet of the present invention preferably has a closed cell structure, but may have a closed cell structure including open cells.

[Adhesive tape]
The adhesive tape of the present invention is an adhesive tape using the above-mentioned 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 to 200 μm, more preferably 7 to 150 μm, still more preferably 10 to 100 μm.
The adhesive tape of the present invention preferably has adhesive layers on both sides of the foamed sheet. That is, the adhesive tape of the present invention is preferably a double-sided tape.
Further, since the adhesive tape of the present invention can seal the gap even if there is a step in the gap, the electronic device used to prevent dust and moisture from entering the inside of the electronic device from the outside. It can be suitably used as a sealing material for vehicles, and in particular, it can be suitably used as a sealing material for in-vehicle electronic devices.

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

Since the adhesive tape of the present invention uses a foamed sheet having excellent heat resistance as a base material, it is suitable for applications in electronic devices, particularly in-vehicle electronic devices. Further, the adhesive tape of the present invention is suitable for use in image display devices such as head-up display devices and liquid crystal display devices, and is more suitable for use in in-vehicle image display devices. Since the adhesive sheet of the present invention uses a foamed sheet having excellent anti-fogging properties as a base material, it has excellent anti-fogging properties. If the adhesive tape has poor antifogging properties, the window portion for projecting or displaying an image may become cloudy, making it impossible to project or display a clear image.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.
The method for measuring each physical property and the method for evaluating the foamed sheet are as follows.

(1) Degree of cross-linking A test piece of about 100 mg is collected from the foamed sheet, and the mass A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in xylene 30 cm ³ at 120 ° C. and left for 24 hours, then filtered through a 200 mesh wire mesh to collect the insoluble matter on the wire mesh, vacuum dried, and the mass of the insoluble matter. Weigh B (mg) precisely. From the obtained values, the degree of cross-linking (mass%) was calculated by the following formula.
Degree of cross-linking (% by mass) = 100 x (B / A)
(2) Density of foamed sheet The density of foamed sheet (apparent density) was measured according to JIS K 7222.
(3) Thickness of foam sheet The thickness of the foam sheet was measured using a dial gauge.
(4) 25% compressive strength The 25% compressive strength of the foamed sheet was measured according to JIS K6767.
(5) Anti-fogging (ISO)
The anti-fogging property of the foamed sheet was measured by measuring the haze after curing the foamed sheet at 100 ° C. for 20 hours using an equipment compliant with ISO6452. The haze was measured using NDH-300A manufactured by Nippon Denshoku Kogyo Co., Ltd.
(6) Heat shrinkage (120 ° C x 1 hr)
In accordance with JIS K 6767, the dimensional change of the foamed sheet at 120 ° C. was measured, the heat shrinkage rate (%) was calculated, and the value was cured at the temperature of 120 ° C. of the foamed sheet for 1 hour. The contraction rate in the direction was used.
(7) Comprehensive evaluation of foamed sheet The foamed sheet having excellent heat resistance and anti-fogging property was evaluated as "○" (good). In addition, a foamed sheet having excellent heat resistance but poor anti-fogging property was evaluated as "Δ" (possible). Further, the foamed sheet having poor heat resistance was evaluated as "x" (impossible).

Examples 1 to 14 and Comparative Examples 1 to 7.
Each of the resin components and additives shown in Tables 1 to 3 is put into a single-screw extruder in each number of copies shown in Tables 1 to 3, melt-kneaded at a resin temperature of 180 ° C., extruded, and predetermined. A sheet-shaped resin composition having a thickness was obtained. The resin composition was crosslinked by irradiating both sides of the sheet-shaped resin composition with an electron beam. Then, the crosslinked resin composition was heated in a hot air oven at 250 ° C. for 5 minutes and foamed by the heating to obtain a foamed sheet having a predetermined thickness. Tables 1 to 3 show the physical properties of the foamed sheet and the evaluation results.

Details of the resin components and additives shown in Tables 1 to 3 are as follows.
Random PP: Ethylene-propylene random copolymer, manufactured by Nippon Polypro Co., Ltd., Product name: Novatec EG7F, MFR: 1.3 g / 10 minutes, Ethylene content: 3% by mass
LLDPE: Linear low density polyethylene, manufactured by Dow Chemical Co., Ltd., product name: 2036P, MFR: 2.5 g / 10 minutes EPDM: ethylene-propylene-diene copolymer, manufactured by Sumitomo Chemical Co., Ltd., product name: Esplen 301, Mooney viscosity (ML _{1 + 4} , 100 ° C) = 55, ethylene content: 62% by mass, DCPD content: 3% by mass
Crosslinking aid: Trimethylolpropane Trimethacrylate Antioxidant 1: 2,6-di-tert-butyl-p-cresol Antioxidant 2: Dilaurylthiodipropionate

As described above, the heat shrinkage of the foamed sheets of Examples 1 to 14 was 5% or less, and it was found that the foamed sheets of Examples 1 to 14 had excellent heat resistance. Further, the foam sheets of Examples 1 to 12 were also excellent in antifogging property.
On the other hand, the foam sheets of Comparative Examples 1 to 7 had poor heat resistance and anti-fogging property.

Claims (10)

It has a thickness of 0.3 to 1.5 mm and has a thickness of 0.3 to 1.5 mm.
The shrinkage rate in the plane direction when cured at a temperature of 120 ° C. for 1 hour is 3% or less.
The thermoplastic resin composition containing the polyolefin resin is foamed, and the polyolefin resin contains 50 parts by mass or more of the polypropylene resin with respect to 100 parts by mass of the polyolefin resin.
The polypropylene-based resin is an ethylene-propylene random copolymer, and is
The proportion of propylene in the ethylene-propylene random copolymer is 95 to 99% by mass, and the proportion of ethylene is 1 to 5% by mass.
The degree of cross-linking is 40% or more ,
A polyolefin-based resin foam sheet having a 25% compressive strength of 140 to 600 kPa . The thermoplastic resin composition further comprises an azodicarbonamide and at least one basic magnesium selected from the group consisting of magnesium oxide and magnesium hydroxide.
The polyolefin-based resin foam sheet according to claim 1, wherein the content of the basic magnesium in the thermoplastic resin composition is 0.03 to 1.0 part by mass with respect to 100 parts by mass of the polyolefin-based resin. The polyolefin-based resin foam sheet according to claim 1 or 2, wherein the polyolefin-based resin further contains a polyethylene-based resin. The polyolefin-based resin foam sheet according to claim 3, wherein the polyethylene-based resin is a linear low-density polyethylene-based resin (LLDPE). The polyolefin-based resin foam sheet according to any one of claims 1 to 4, wherein the polyolefin-based resin further contains a polyolefin-based rubber. The polyolefin-based resin foam sheet according to claim 5, wherein the polyolefin-based rubber is an ethylene-α-olefin-based copolymer rubber. The polyolefin-based resin foam sheet according to any one of claims 1 to 6, which has a density of 0.065 / cm ³ or more. The polyolefin-based resin foam sheet according to any one of claims 1 to 7 , which is used for electronic devices. The polyolefin-based resin foam sheet according to claim 8 , which is used for an in-vehicle electronic device. An adhesive tape comprising the polyolefin-based resin foamed sheet according to any one of claims 1 to 9 and an adhesive layer provided on at least one surface of the polyolefin-based resin foamed sheet.