CN108431105B

CN108431105B - Polyolefin resin foam sheet and adhesive tape

Info

Publication number: CN108431105B
Application number: CN201780005106.2A
Authority: CN
Inventors: 永井麻美; 松木繁季
Original assignee: Sekisui Chemical Co Ltd
Current assignee: Sekisui Chemical Co Ltd
Priority date: 2016-03-30
Filing date: 2017-03-30
Publication date: 2021-06-29
Anticipated expiration: 2037-03-30
Also published as: CN110790972A; KR20180127337A; JP2019178341A; JPWO2017170941A1; KR102078236B1; JP6665336B2; JP6550131B2; JP6665340B2; CN113308041A; CN110746678B; CN108431105A; WO2017170941A1; JP2019218563A; CN110746678A

Abstract

The present invention provides a polyolefin resin foamed sheet obtained by foaming a polyolefin resin composition containing a polyolefin resin and a pigment, wherein the polyolefin resin composition has a 25% compressive stress of 80 to 1400kPa, a pigment content of 0.60 to 10.00 parts by mass per 100 parts by mass of the resin, and a density of 0.10 to 0.60g/cm³The gel content is 25 to 60 mass%.

Description

Polyolefin resin foam sheet and adhesive tape

Technical Field

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

Background

A foam sheet in which a large number of cells are formed inside a resin layer has excellent impact cushioning properties, and therefore, is widely used as an impact absorbing material for various electronic devices. In a display device used for, for example, a mobile phone, a notebook computer, an electronic book, or the like, the impact absorbing material is disposed between a glass plate constituting a surface of the device and an image display member. As a foam sheet used for such applications, patent document 1 discloses an adhesive tape having a polyolefin resin as a base material.

Documents of the prior art

Patent document

Patent document 1 International publication No. 2013/099755

Disclosure of Invention

Problems to be solved by the invention

The foam sheet and the sealing material used for such applications are required to be thin and narrow in width due to the downsizing of the device, but when used at a position close to a light emitting portion such as a backlight of a display device, there is a problem that the light passes through the thin portion of the foam sheet and the sealing material and leaks to the outside of the device.

As a method for solving this problem, there are conceivable a method of reducing the expansion ratio of the foamed sheet and a method of increasing the thickness of the foamed sheet, but when these methods are employed, the flexibility of the foamed sheet is lost, and there is a problem that it cannot be used in a small electronic device.

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a polyolefin resin foam sheet having excellent light-shielding properties and also excellent flexibility, and an adhesive tape using the polyolefin resin foam sheet.

Means for solving the problems

The technical idea of the invention is the following [ 1 ] to [ 2 ].

【1】 A polyolefin resin foamed sheet obtained by foaming a polyolefin resin composition containing a polyolefin resin and a pigment, wherein the polyolefin resin composition has a 25% compressive stress of 80 to 1400kPa, a pigment content of 0.60 to 10.00 parts by mass per 100 parts by mass of the resin, and a density of 0.10 to 0.60g/cm³The gel content is 25 to 60 mass%.

【2】 An adhesive tape comprising a polyolefin resin foam sheet as described in [ 1 ] above and a pressure-sensitive adhesive layer provided on at least one surface of the polyolefin resin foam sheet.

Effects of the invention

The present invention can provide a polyolefin resin foam sheet having excellent light-shielding properties and excellent flexibility, and an adhesive tape using the polyolefin resin foam sheet.

Detailed Description

[ polyolefin resin foam sheet ]

The polyolefin resin foamed sheet (hereinafter also referred to as "foamed sheet") of the present invention is a polyolefin resin foamed sheet obtained by foaming a polyolefin resin composition containing a polyolefin resin and a pigment, and has a 25% compressive stress of 80 to 1400kPa, a pigment content of 0.60 to 10.00 parts by mass per 100 parts by mass of the resin, and a density of 0.10 to 0.60g/cm³The gel content is 25 to 60 mass%.

< 25% compressive stress >

The foamed sheet of the present invention has a 25% compressive stress of 80kPa or more, preferably 90kPa or more, more preferably 100kPa or more, and 1400kPa or less, preferably 1200kPa or less, more preferably 1000kPa or less, further preferably 900kPa or less, further preferably 800kPa or less, further preferably 700kPa or less, further preferably 600kPa or less, further preferably 550kPa or less. When the 25% compressive stress is not less than the lower limit, the impact absorbability is improved, and when the compressive stress is not more than the upper limit, the flexibility of the foamed sheet is improved, the followability to an adherend after the production of the adhesive tape becomes good, and water and air are less likely to enter the electronic device.

The 25% compressive stress can be measured by the method described in examples described later.

< pigment >

The pigment that can be used in the present invention is not particularly limited, and organic pigments and inorganic pigments can be used.

Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoxazolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

Examples of the inorganic pigment include carbon black, metal oxides, metal sulfides, and metal chlorides. These pigments may be used alone or in combination of 2 or more.

Amount of pigment

The amount of the pigment is 0.60 parts by mass or more, preferably 0.70 parts by mass or more, more preferably 0.80 parts by mass or more, further preferably 0.90 parts by mass or more, and further preferably 1.00 parts by mass or more per 100 parts by mass of the polyolefin resin from the viewpoint of improving the light-shielding property of the foam sheet, and is 10.00 parts by mass or less, preferably 5.00 parts by mass or less, more preferably 3.00 parts by mass or less, and further preferably 1.50 parts by mass or less from the viewpoint of preventing a decrease in flexibility of the foam sheet.

< Density >

The density of the foam sheet in the present invention is 0.10g/cm from the viewpoint of improving the light-shielding property of the foam sheet³Above, preferably 0.15g/cm³Above, more preferably 0.20g/cm³Above, more preferably 0.25g/cm³Above, more preferably 0.30g/cm³Above, more preferably 0.35g/cm³Above, and from the viewpoint of preventing the reduction of flexibility of the foamed sheet, 0.60g/cm³Less than, preferably 0.55g/cm³Less than, more preferably 0.50g/cm³Less than, and more preferably 0.45g/cm³Less, more preferably 0.40g/cm³The following.

< expansion ratio >

The expansion ratio of the foam sheet of the present invention can be defined as the reciprocal of the density of the foam sheet, and is preferably 1.5cm³A concentration of 1.6cm or more³A concentration of 1.7cm or more³A value of at least g, more preferably 1.8cm³A concentration of 10.0cm or more³A concentration of 8.0cm or less³A concentration of 7.0cm or less³A value of not more than g, more preferably 6.0cm³A value of not more than g, more preferably 5.5cm³A value of not more than g, more preferably 5.0cm³The ratio of the carbon atoms to the carbon atoms is less than g. When the expansion ratio is within the above range, the light-shielding property of the foam sheet can be improved, and the impact absorbability and the step following property of the foam sheet can be easily ensured.

< gel ratio >

The foaming sheet of the present invention has a gel fraction after crosslinking of 25 mass% or more, preferably 30 mass% or more, more preferably 35 mass% or more, and 60 mass% or less, preferably 55 mass% or less, more preferably 53 mass% or less, from the viewpoint of reducing the average cell diameter (also referred to as the average cell diameter) in the ZD direction. When the gel ratio is not less than the lower limit, sufficient crosslinking can be formed, and by foaming the resulting foam, a foamed sheet having a small average cell diameter can be obtained. When the gel fraction is not more than the upper limit, the flexibility of the foamed sheet can be easily ensured.

The gel fraction can be measured by the method described in examples below.

< average bubble diameter >

The average cell diameter in the MD direction in the foam sheet of the present invention is preferably 10 μm or more, more preferably 20 μm or more, further preferably 25 μm or more, further preferably 30 μm or more, further preferably 32 μm or more, and is preferably 150 μm or less, more preferably 140 μm or less, further preferably 135 μm or less, further preferably 130 μm or less, further preferably 125 μm or less, further preferably 120 μm or less, further preferably 115 μm or less, from the viewpoint of improving the light-shielding property, flexibility and step following property of the foam sheet. When the average cell diameter in the MD direction is equal to or greater than the lower limit, flexibility and level difference following properties are improved. When the average cell in the MD direction is equal to or less than the upper limit value, the light-shielding property of the foam sheet is improved.

The average cell diameter in the TD direction in the foam sheet of the present invention is preferably 10 μm or more, more preferably 20 μm or more, further preferably 25 μm or more, further preferably 30 μm or more, further preferably 35 μm or more, further preferably 38 μm or more, and preferably 250 μm or less, more preferably 210 μm or less, further preferably 170 μm or less, further preferably 130 μm or less, further preferably 125 μm or less, further preferably 120 μm or less, further preferably 115 μm or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet. When the average cell diameter in the MD direction is equal to or greater than the lower limit, flexibility and level difference following properties are improved. When the average cell in the MD direction is equal to or less than the upper limit value, the light-shielding property of the foam sheet is improved.

The average cell diameter in the ZD direction in the foam sheet of the present invention is preferably 5 μm or more, more preferably 7 μm or more, further preferably 9 μm or more, more preferably 11 μm or more, more preferably 13 μm or more, more preferably 15 μm or more, and preferably 60 μm or less, more preferably 55 μm or less, further preferably 50 μm or less, more preferably 45 μm or less, and more preferably 40 μm or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet. When the average bubble diameter in the ZD direction is equal to or greater than the lower limit value, flexibility and step following properties are improved. When the average bubble in the ZD direction is equal to or less than the upper limit value, the light-shielding properties of the foam sheet are improved.

< maximum bubble diameter >

The maximum cell diameter in the MD direction in the foam sheet of the present invention is preferably 30 μm or more, more preferably 40 μm or more, even more preferably 50 μm or more, and is preferably 400 μm or less, more preferably 350 μm or less, even more preferably 300 μm or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet. When the maximum cell diameter in the MD direction is not less than the lower limit, flexibility and level difference following property are improved. When the maximum cells in the MD direction are equal to or less than the upper limit value, the light-shielding property of the foam sheet is improved.

The maximum cell diameter in the TD direction in the foam sheet of the present invention is preferably 80 μm or more, more preferably 90 μm or more, even more preferably 100 μm or more, and is preferably 500 μm or less, more preferably 450 μm or less, even more preferably 400 μm or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet. When the maximum cell diameter in the TD direction is equal to or greater than the lower limit value, flexibility and level difference following properties are improved. When the maximum bubble in the TD direction is equal to or less than the upper limit value, the light-shielding property of the foam sheet is improved.

The maximum bubble diameter in the ZD direction in the foam sheet of the present invention is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 30 μm or more, and is preferably 150 μm or less, more preferably 140 μm or less, even more preferably 130 μm or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet. When the maximum bubble diameter in the ZD direction is equal to or greater than the lower limit value, flexibility and step following properties are improved. When the maximum bubble in the ZD direction is equal to or less than the upper limit value, the light-shielding properties of the foam sheet are improved.

In the present invention, "MD" means a Machine Direction (Machine Direction) and is a Direction corresponding to an extrusion Direction of the polyolefin resin foam sheet or the like. Further, "TD" refers to a Transverse Direction (Transverse Direction), which is a Direction perpendicular to the MD and parallel to the foam sheet. Further, "ZD" refers to the Thickness Direction (Thickness Direction) and is a Direction perpendicular to both MD and TD.

The average cell diameter can be measured by the method of the examples described later.

< thickness >

The thickness of the foam sheet of the present invention is preferably 0.020mm or more, more preferably 0.030mm or more, further preferably 0.040mm or more, further preferably 0.050mm or more, and further preferably 0.38mm or less, more preferably 0.35mm or less, further preferably 0.32mm or less, further preferably 0.30mm or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet. When the thickness of the foam sheet is not less than the lower limit, the light-shielding property and strength of the foam sheet can be improved. When the thickness of the foamed sheet is not more than the above upper limit, the foamed sheet can be used in a thin electronic device, and flexibility and level difference following property can be further improved.

Average number of air bubbles < 0.5mm >)

The average number of cells per 0.5mm in the MD direction of the foam sheet of the present invention is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, and is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less, and even more preferably 15 or less, and even more preferably 13 or less, and even more preferably 11 or less, and even more preferably 9 or less, and even more preferably 8 or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet.

The average number of cells per 0.5mm in the TD direction of the foam sheet of the present invention is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, and is preferably 18 or less, more preferably 16 or less, and even more preferably 14 or less, and even more preferably 12 or less, even more preferably 10 or less, and even more preferably 8 or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet.

The average number of bubbles per 0.5mm in the ZD direction of the foam sheet of the present invention is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, and is preferably 13 or less, more preferably 11 or less, and even more preferably 9 or less, and even more preferably 8 or less, and even more preferably 6 or less, from the viewpoint of improving the light-shielding property, flexibility, and step following property of the foam sheet.

When the average number of cells per 0.5mm of the foam sheet is not less than the lower limit, the light-shielding property of the foam sheet can be improved. When the average number of bubbles per 0.5mm is not more than the upper limit, the resin composition can be used in a thin electronic device, and flexibility and step following property can be further improved.

The average number of bubbles per 0.5mm can be measured by the method of the example described later.

< independent bubble rate >

The foamed sheet of the present invention preferably has the cells as independent cells. When the air bubbles are independent air bubbles, the amount of deformation of the air bubbles upon receiving an impact can be suppressed, and the amount of deformation of the foamed sheet against the impact can be suppressed, resulting in further improvement in the impact absorbability.

The independent bubble percentage is preferably 70 to 100%, more preferably 80 to 100%, and even more preferably 90 to 100% in order to further improve the impact absorbability.

When the independent bubbles are in the above range, the movement of air in the foamed sheet is restricted, and heat conduction due to convection of air can be suppressed, thereby improving heat insulation.

Further, the independent bubble rate was measured in accordance with ASTM D2856 (1998).

[ polyolefin resin ]

Examples of the polyolefin resin used for forming the foamed sheet include a polyethylene resin, a polypropylene resin, and a mixture thereof.

< polyethylene resin >

The polyethylene resin may be an ethylene homopolymer or a polyethylene resin obtained by copolymerizing ethylene and, if necessary, a small amount of α -olefin (for example, 30% by mass or less, preferably 10% by mass or less of the total monomers), and particularly linear low-density polyethylene is preferable.

Specific examples of the α -olefin constituting the polyethylene resin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Among them, an α -olefin having 4 to 10 carbon atoms is preferable.

Further, as the polyethylene resin, an ethylene-vinyl acetate copolymer is preferable. The ethylene-vinyl acetate copolymer is usually a copolymer containing 50% by mass or more of ethylene units.

The polyethylene resin preferably has a low density in order to improve flexibility and impact absorption resistance of the foamed sheet. The density of the polyethylene resin is particularly preferably 0.920g/cm³Less, more preferably 0.880 to 0.915g/cm³More preferably 0.885 to 0.910g/cm³。

Further, the density was measured in accordance with ASTM D792.

< Polypropylene resin >

Examples of the polypropylene resin include a propylene homopolymer, a propylene-ethylene copolymer containing 50 mass% or more of a propylene unit, and a propylene- α -olefin copolymer. One kind of them may be used alone, or 2 or more kinds may be used in combination.

Specific examples of the α -olefin constituting the propylene- α -olefin copolymer include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene, and among these, α -olefins having 6 to 12 carbon atoms are preferable.

The polyolefin-based resin in the present invention is preferably a polyethylene-based resin, a polypropylene-based resin, or a mixture thereof obtained by polymerization using a metallocene compound, a ziegler natta compound, a chromium oxide compound, or the like as a catalyst, from the viewpoint of improving flexibility and impact absorption, and among the polyethylene-based resins, linear low-density polyethylene is more preferable.

When a polyethylene resin, an ethylene-vinyl acetate copolymer, or a mixture thereof obtained by using a metallocene compound as a catalyst is used, the content thereof is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, and further preferably 100% by mass of the entire polyolefin resin.

< metallocene Compound >

Preferable examples of the metallocene compound include compounds such as bis (cyclopentadienyl) metal complexes having a structure in which a transition metal is sandwiched between pi-electron-based unsaturated compounds. More specifically, there may be mentioned compounds in which 1 or 2 or more cyclopentadiene rings or the like are present as ligands in a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, platinum, or the like.

The metallocene compound has uniform properties of active sites, and each active site has the same activity degree. Since the polymer synthesized using the metallocene compound has high uniformity in molecular weight, molecular weight distribution, composition distribution, and the like, when a sheet containing the polymer synthesized using the metallocene compound is crosslinked, the crosslinking can be uniformly performed. Since the uniformly crosslinked sheet is easily stretched uniformly, the thickness of the crosslinked polyolefin resin foamed sheet can be easily made uniform.

Examples of the ligand include a cyclopentadiene ring and an indene ring. These cyclic compounds may be substituted with hydrocarbyl, substituted hydrocarbyl or hydrocarbon-substituted metalloid radicals. Examples of the hydrocarbon group include methyl, ethyl, various propyl groups, various butyl groups, various pentyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various hexadecyl groups, and phenyl groups. The term "various" means various isomers including normal, secondary, tertiary and iso isomers.

Further, an oligomer obtained by polymerizing a cyclic compound may be used as a ligand.

Further, in addition to the pi-electron-based unsaturated compound, monovalent anion ligands such as chlorine and bromine, divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides (phosphides), arylphosphides, and the like can be used.

Examples of the metallocene compound containing a tetravalent transition metal and a ligand include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, and dimethylsilyl tetramethylcyclopentadienyl-tert-butylamido zirconium dichloride.

By using a metallocene compound in combination with a specific cocatalyst (cocatalyst), the catalyst can function when polymerizing various olefins. Specific examples of the cocatalyst include Methylaluminoxane (MAO) and boron compounds. The ratio of the cocatalyst to the metallocene compound is preferably 10 to 100 ten thousand mol times, and more preferably 50 to 5,000 mol times.

< Ziegler-Natta compound >

The ziegler natta compound is a triethylaluminium-titanium tetrachloride solid complex, preferably produced by the following process: a method of using a combination of a titanium trichloride composition obtained by reducing titanium tetrachloride with an organoaluminum compound and further treating the titanium trichloride composition with various electron donors and electron acceptors (see Japanese patent application laid-open Nos. 56-100806, 56-120712 and 58-104907), and a method of using a supported catalyst in which a magnesium halide is brought into contact with titanium tetrachloride and various electron donors (see Japanese patent application laid-open Nos. 57-63310, 63-43915 and 63-83116).

< other component which may be contained in the polyolefin-based resin >

As the polyolefin-based resin, a resin other than the above-mentioned polyolefin-based resin may be used in combination.

Further, the polyolefin resin may be mixed with various additives described later and other optional components.

The total amount of the resin and the rubber other than the polyolefin resin is smaller than the content of the polyolefin resin, and is usually about 50 parts by mass or less, preferably about 30 parts by mass or less, based on 100 parts by mass of the polyolefin resin.

[ Process for producing foam sheet ]

The foamed sheet of the present invention can be produced by foaming the polyolefin resin composition by a conventional method. The method for producing the foamed sheet of the present invention is not particularly limited, and the foamed sheet can be produced by crosslinking a polyolefin resin composition and then foaming the crosslinked polyolefin resin composition.

Specifically, the foamed sheet of the present invention can be produced by a method having, for example, the following steps (1) to (3).

Step (1): a step of supplying the polyolefin resin, the pigment, the thermal decomposition type foaming agent and other additives to an extruder, melting and kneading the mixture, and extruding the mixture into a sheet shape by using the extruder to obtain a sheet-shaped polyolefin resin composition;

step (2): a step of crosslinking the sheet-like polyolefin resin composition;

step (3): and a step of heating the crosslinked sheet-like polyolefin resin composition to foam the thermal decomposition type foaming agent.

Further, as a method for producing a crosslinked polyolefin resin foamed sheet, in addition to this method, the foamed sheet can be produced by the method described in international publication No. 2005/007731.

The thermal decomposition type foaming agent is not particularly limited, and examples thereof include azodicarbonamide, N' -dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide, and the like. Among these compounds azodicarbonamide is preferred. The thermal decomposition type foaming agent can be used alone, or 2 or more kinds of them can be used in combination.

The content of the thermal decomposition type foaming agent in the polyolefin resin composition is preferably 1 to 12 parts by mass, more preferably 1 to 8 parts by mass, per 100 parts by mass of the polyolefin resin. When the content of the thermal decomposition type foaming agent is within the above range, a polyolefin resin foamed sheet having a desired expansion ratio with improved foamability of the polyolefin resin composition can be easily obtained, and tensile strength and compression recovery properties can be improved.

Examples of the other additives used in the step (1) include a decomposition temperature regulator, a crosslinking assistant, and an antioxidant.

The decomposition temperature adjusting agent is added to lower the decomposition temperature of the thermal decomposition type foaming agent or to increase the decomposition rate, and specific compounds include zinc oxide, zinc stearate, urea, and the like. The decomposition temperature adjusting agent is used for adjusting the surface state of the foamed sheet, and is added in an amount of, for example, 0.01 to 5 parts by mass per 100 parts by mass of the polyolefin resin.

As crosslinking assistants, polyfunctional monomers can be used. By adding the crosslinking assistant to the polyolefin resin, the amount of ionizing radiation irradiated in step (2) can be reduced, and the resin molecules can be prevented from being cut or deteriorated by irradiation with ionizing radiation.

Specific examples of the crosslinking assistant include compounds having 3 functional groups in 1 molecule, such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl trimellitate, triallyl 1,2, 4-benzenetrimethacrylate, triallyl isocyanurate, and the like, compounds having 2 functional groups in 1 molecule, such as 1, 6-hexanediol dimethacrylate, 1, 9-nonanediol dimethacrylate, 1, 10-decanediol dimethacrylate, divinylbenzene, and the like, diallyl phthalate, diallyl terephthalate, diallyl isophthalate, ethylvinylbenzene, neopentyl glycol dimethacrylate, lauryl methacrylate, stearyl methacrylate, and the like.

These crosslinking assistants may be used alone or in combination of 2 or more.

The amount of the crosslinking aid added is preferably 0.2 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and still more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the polyolefin resin. When the amount is 0.2 parts by mass or more, a desired gel fraction of the foam sheet can be stably obtained, and when the amount is 10 parts by mass or less, the gel fraction of the foam sheet can be easily controlled.

Examples of the antioxidant include phenol antioxidants such as 2, 6-di-tert-butyl-p-cresol.

The method of foaming the polyolefin resin composition is not particularly limited, and examples thereof include a method of heating the polyolefin resin composition with hot air, a method of heating with infrared rays, a method of heating with a salt bath, a method of heating with an oil bath, and the like, and these methods can be used in combination.

The foaming of the polyolefin resin composition is not limited to the case of using a thermal decomposition type foaming agent, and physical foaming using butane gas or the like may be used.

Examples of the method of crosslinking the polyolefin resin composition include a method of mixing an organic peroxide in advance with the polyolefin resin composition and heating the polyolefin resin composition to decompose the organic peroxide.

Examples of the organic peroxide used for crosslinking include 1, 1-bis (t-butylperoxy) 3,3, 5-trimethylcyclohexane and 1, 1-bis (t-butylperoxy) cyclohexane. These compounds may be used alone in 1 kind, or in combination of 2 or more kinds. The amount of the organic peroxide added is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the polyolefin resin. When the amount of the organic peroxide added is within the above range, crosslinking of the polyolefin resin composition is facilitated, and the amount of decomposition residue of the organic peroxide in the resulting crosslinked polyolefin resin foamed sheet can be suppressed.

Further, as a method for crosslinking the polyolefin resin composition, there is a method of irradiating the polyolefin resin composition with ionizing radiation such as electron beam, α ray, β ray, γ ray, and the like.

The dose of the ionizing radiation is preferably 5 to 200kGy, more preferably 30 to 120kGy, so that the gel ratio is 25 to 60% by mass.

The method of crosslinking the polyolefin resin composition may be used in combination, but from the viewpoint of uniform crosslinking, a method of irradiating with ionizing radiation is preferred.

The polyolefin resin foamed sheet of the present invention is preferably stretched in one or both of the MD direction and the TD direction. When stretching is performed in one or both of the MD direction and the TD direction, the average cell diameter in the ZD direction becomes smaller, and the distance of the thermally conductive resin portion becomes longer, so that heat is not easily transmitted, and the heat insulation property is improved.

The stretching may be performed after the polyolefin resin composition is foamed to obtain a foamed sheet, or may be performed while the polyolefin resin composition is foamed. Further, it is preferable that the foamed sheet is stretched while keeping the molten state during foaming without cooling the foamed sheet when the foamed sheet is foamed after foaming the polyolefin resin composition to obtain a foamed sheet, but the foamed sheet may be stretched after cooling the foamed sheet and heating the foamed sheet again to melt or soften the foamed sheet.

The stretching ratio of the foamed sheet in the MD direction is preferably 1.1 to 3.2 times, and more preferably 1.3 to 3.0 times. When the MD stretch ratio of the foam sheet is equal to or higher than the lower limit value, the foam sheet tends to have good flexibility and tensile strength. On the other hand, if the amount is equal to or less than the upper limit, the foam sheet can be prevented from being broken during stretching or from escaping from the foam gas in the foam sheet during foaming, the expansion ratio is reduced, the flexibility and tensile strength of the foam sheet are improved, and the quality is easily made uniform. The stretch ratio in the TD direction of the foamed sheet is preferably 1.3 to 3.8 times, and more preferably 1.5 to 3.5 times.

[ adhesive tape ]

The adhesive tape of the present invention is obtained by using the foamed sheet of the present invention as a base material and providing a pressure-sensitive adhesive layer on one or both surfaces of the foamed sheet. The thickness of the tape is usually 0.03 to 2.0mm, preferably 0.05 to 1.0 mm.

The thickness of the pressure-sensitive adhesive layer constituting the adhesive tape is preferably 5 to 200 μm, more preferably 7 to 150 μm, and still more preferably 10 to 100 μm. When the thickness of the pressure-sensitive adhesive layer constituting the tape is 5 to 200 μm, the thickness of the tape can be reduced, and the electronic device itself using the tape can be miniaturized and reduced in thickness.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer provided on one or both sides of the foam sheet is not particularly limited, and for example, an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, or the like can be used.

Examples of the method of applying a pressure-sensitive adhesive to a foamed sheet and laminating a pressure-sensitive adhesive layer on the foamed sheet include a method of applying a pressure-sensitive adhesive to at least one surface of a foamed sheet using a coater (e.g., a coater), a method of spray-applying a pressure-sensitive adhesive to at least one surface of a foamed sheet by spraying, and a method of applying a pressure-sensitive adhesive to one surface of a foamed sheet using a brush.

The adhesive tape using the foam sheet of the present invention can be used as an impact absorbing material for preventing an electronic component provided in an electronic device body such as a cellular phone or a video camera from receiving an impact, and a sealing material for preventing dust, moisture, or the like from entering the electronic device body.

Examples

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

[ measurement method ]

The measurement methods of the physical properties in the present specification are as follows.

< thickness >

Measured according to JIS K6767.

< Density and expansion ratio >

The densities of the foamed sheets obtained in examples and comparative examples were measured in accordance with JIS K7222, and the reciprocal thereof was defined as the expansion ratio.

< independent bubble rate >

The independent bubble rate was measured according to ASTM D2856 (1998).

< gel ratio >

About 50mg of test pieces were taken from the foamed sheets obtained in examples and comparative examples, and the weight A (mg) of the test pieces was accurately weighed. Next, the test piece was immersed in 30ml of xylene at 105 ℃ and left for 24 hours, and then filtered through a 200-mesh wire gauze to collect insoluble matter on the wire gauze, dried in vacuum, and the weight B (mg) of the insoluble matter was accurately weighed. From the obtained values, the gel fraction (% by mass) was calculated from the following equation.

Gel ratio (% by mass) (B/a) × 100

< 25% compressive stress >

The 25% compressive stress was measured in accordance with JIS K6767 for the polyolefin resin foamed sheet. In the present invention, the 25% compressive stress is preferably small from the viewpoint of improving flexibility and step following property.

< average bubble diameter in MD, TD and ZD directions, and maximum bubble diameter >

The foamed sheets obtained in each of examples and comparative examples were cut into 50mm square pieces as foam samples for measurement, immersed in liquid nitrogen for 1 minute, and then cut with razor blades in the MD direction, TD direction, and ZD direction as thickness directions. Then, a magnified photograph of the cross section at 200 times was taken using a digital microscope (product name VHX-900, manufactured by キーエンス K.) and the cell diameters were measured for all the independent cells present in the cross section having a length of 2mm in both the MD direction and the TD direction, and this operation was repeated 5 times. On the other hand, for the ZD direction, the bubble diameter of the independent bubbles present in a square of 2mm × 2mm was measured, and this operation was repeated 5 times. Then, the average value of all the cells in each direction was defined as the average cell diameter in the MD direction, TD direction and ZD direction, and the largest cell diameter among the measured cell diameters was defined as the maximum cell diameter.

Average number of air bubbles < 0.5mm >)

The average number of cells in the MD direction and the TD direction was calculated by measuring the average cell diameter by the above method, and dividing the punching width at the time of actual use by the average cell diameter to calculate the average number of cells per 0.5 mm.

Average number of cells per 0.5mm (0.5 mm)/average cell diameter (μm) × 1000

The average number of cells per 0.5mm in the ZD direction was calculated by dividing the thickness of the foamed sheet by the average cell diameter in the ZD direction.

Average number of air bubbles (number) in ZD direction ═ thickness (mm)/average bubble diameter (μm) × 1000

< full light transmittance >

The total light transmittance was measured by a haze meter (NDH 2000, manufactured by Nippon Denshoku industries Co., Ltd.). The total light transmittance was measured in each direction of ZD, MD, and TD of the foamed sheet.

In the MD and TD directions, after punching to a width of 0.5mm and a length of 25mm, the layers were laminated to a thickness of 5mm or more, and both ends of 25mm were fixed so as not to cause a gap, and the width direction of 0.5mm was measured.

< evaluation >

The case where the total light transmittance in the ZD direction is 1% or less is referred to as "pass: g ", the case other than this case is referred to as" fail: and B'.

Example 1

A polyolefin resin was prepared by blending a linear low-density polyethylene ("Exact 3027" manufactured by エクソンケミカル Co., Ltd., density: 0.900 g/cm)³)100 parts by mass of a pigment (AP-09979, manufactured by Daihai chemical Co., Ltd.), 1.13 parts by mass of an azodicarbonamide as a thermal decomposition type foaming agent, 2.1 parts by mass of zinc oxide as a decomposition temperature adjusting agent, and 0.5 part by mass of 2, 6-di-t-butyl-p-cresol as an antioxidant were fed to an extruder, melt-kneaded at 130 ℃ and then the polyolefin resin composition was extruded into a long sheet having a thickness of about 0.3 mm.

Subsequently, the polyolefin resin composition in a long sheet form was crosslinked by irradiating both surfaces with an electron beam of 70kGy having an acceleration voltage of 500kV, and then continuously fed into a foaming furnace maintained at 250 ℃ by a hot air and infrared heater to be heated and foamed, and the resulting foamed sheet was stretched while being foamed to a MD stretch ratio of 1.3 times and a TD stretch ratio of 2.0 times, thereby obtaining a foamed sheet having a thickness of 0.14 mm. Table 1 shows the evaluation results of the obtained foamed sheet.

Examples 2 to 8, and comparative examples 1 to 8

The same procedure as in example 1 was repeated, except that the compounding of the polyolefin resin composition was changed as shown in tables 1 and 2, the amount of the yarn during crosslinking was adjusted to the gel ratio in tables 1 and 2, and the stretching ratios in MD and TD were adjusted to 1.2 to 4.0 times.

TABLE 1

TABLE 2

As is clear from the results of the above examples, the present invention can provide a polyolefin resin foam sheet having excellent light-shielding properties and also excellent flexibility, and an adhesive tape using the polyolefin resin foam sheet. In contrast, in comparative examples 1 and 2, the gel fraction was outside the predetermined range, the cell diameter was large, and the light-shielding property was insufficient. In comparative examples 3 and 4, the 25% compressive stress was out of the predetermined range, and the blending amount of the pigments in comparative examples 6 to 8 was out of the predetermined range, so that the light-shielding property was insufficient. In comparative example 5, the density was high, the 25% compressive stress was also high, and the flexibility was insufficient.

Claims

1. A polyolefin resin foamed sheet is obtained by foaming a polyolefin resin composition containing a polyolefin resin and a pigment, and has a 25% compressive stress of 80 to 1400kPa and a density of 0.15 to 0.60g/cm³The gel fraction is 25 to 60 mass%, the total light transmittance in the ZD direction is 1% or less, the independent bubble rate is 95 to 100%, and the pigment is carbon black.

2. The foamed polyolefin resin sheet according to claim 1, wherein the amount of the pigment is 0.60 to 10.00 parts by mass per 100 parts by mass of the resin.

3. The polyolefin resin foam sheet according to claim 1 or 2, wherein the average number of cells per 0.5mm in the MD direction is 2 to 20.

4. The expanded polyolefin-based resin sheet according to claim 1 or 2, wherein the average cell diameter in the MD of the expanded polyolefin-based resin sheet is 150 μm or less.

5. The expanded polyolefin-based resin sheet according to claim 1 or 2, wherein the average cell diameter in the TD direction of the expanded polyolefin-based resin sheet is 250 μm or less.

6. The expanded polyolefin-based resin sheet according to claim 1 or 2, wherein the average bubble diameter in the ZD direction of the expanded polyolefin-based resin sheet is 60 μm or less.

7. An adhesive tape comprising the polyolefin resin foam sheet according to any one of claims 1 to 6 and a pressure-sensitive adhesive layer provided on at least one surface of the polyolefin resin foam sheet.