JP2013053177A - Crosslinked polyolefin resin foamed sheet, pressure-sensitive adhesive tape, and sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crosslinked polyolefin resin foamed sheet that can sufficiently exert functions of sealability, cushioning performance, impact resistance or the like even if the planar dimension of a mounting blank portion is small, and to provide a pressure-sensitive adhesive tape and a sealing material that use the crosslinked polyolefin resin foamed sheet.SOLUTION: The crosslinked polyolefin resin foamed sheet comprises crosslinking and foaming a polyolefin resin sheet, wherein the polyolefin resin sheet includes at least one of a low density polyethylene resin (A) and a high density polyethylene resin (B) obtained by using an organometallic complex as a polymerization catalyst. The crosslinked polyolefin resin foamed sheet is characterized in that the degree of crosslinking is 15-50 mass%, and the expansion ratio is 1.5-2.3 cm/g.

Description

  The present invention relates to a crosslinked polyolefin resin foam sheet that can sufficiently exhibit functions such as sealing properties, buffering properties, and impact resistance, and an adhesive tape and a seal material using the crosslinked polyolefin resin foam sheet.

Conventionally, a porous resin material in which a large number of pores are formed inside a resin layer has excellent buffering properties, heat insulating properties, waterproof properties, and moisture proof properties, and therefore needs to be protected from packing materials, gas, or liquid of articles. It is used in various applications such as a sealing material that seals the peripheral part of parts and housings, a buffer material that cushions vibrations and shocks, and a base material for adhesive sheets.
As such a porous resin material, Patent Document 1 proposes a porous resin material formed by adding an inorganic filler to a polyolefin resin, processing it into a sheet shape, and further stretching and making it porous. ing. Since such a porous sheet has a large number of holes, flexibility and mechanical strength are improved as compared with a sheet not provided with holes. However, the porous sheet is not sufficiently flexible because it is difficult to increase the density of the holes. Furthermore, since the porous sheet is not subjected to a crosslinking treatment, the porous sheet cannot be stretched at a temperature higher than the melting point of the polyolefin resin, and the porous sheet is distorted during the stretching process. And the porous sheet contracts during use.

  Patent Document 2 discloses that a porous resin material having further increased flexibility and mechanical strength is processed into a sheet by adding a foaming agent to an ultra-high-density polyethylene resin having a predetermined density. A cross-linked polyolefin resin foam sheet in which bubbles are formed by foaming has been proposed. However, the crosslinked ethylene resin foam does not have sufficient flexibility and heat resistance. In addition, it is conceivable to increase the expansion ratio of the crosslinked ethylene resin foam to improve flexibility. However, if the expansion ratio is increased, the thickness of the foam increases, so that the demand for a thin film thickness cannot be met. There was a problem.

  In recent years, electronic devices have been remarkably miniaturized. For example, in a small electronic device having a display screen such as a mobile phone, the ratio of the screen size occupying the main surface of the casing tends to be as large as possible. The width of the margin part, which is the attachment part, has been designed to be about 2 mm or less.

JP-A-63-251436 JP-A 64-001740

  The present invention relates to a cross-linked polyolefin resin foam sheet capable of sufficiently exhibiting functions such as sealing properties, shock-absorbing properties, impact resistance, etc., even if the mounting blank portion has a small planar size, and an adhesive tape using this cross-linked polyolefin resin foam sheet And it aims at providing a sealing material.

As a result of intensive studies to solve the above problems, the present inventors have found that the problems can be solved by the following invention. That is, the gist of the present invention is the following [1] to [3].
[1] A crosslinked polyolefin resin foamed sheet obtained by crosslinking and foaming a polyolefin resin sheet, wherein the polyolefin resin sheet is obtained by using an organometallic complex as a polymerization catalyst, and a low density polyethylene resin (A) and It contains at least one kind of high-density polyethylene resin (B), and the crosslinked polyolefin resin foam sheet has a crosslinking degree of 15 to 50% by mass and an expansion ratio of 1.5 to 2.3 cm ³ /. A cross-linked polyolefin resin foam sheet characterized by being g.
[2] An adhesive tape provided with an adhesive layer on at least one surface of the crosslinked polyolefin resin foamed sheet, wherein the thickness of the crosslinked polyolefin resin foamed sheet is 50 to 300 μm.
[3] A sealing material that is slit or punched so that the width of the adhesive tape is 2 mm or less.

  According to the present invention, a crosslinked polyolefin resin foamed sheet having high tensile strength, excellent interlayer strength, and capable of being thinned, and an adhesive tape and a sealing material using the crosslinked polyolefin resin foamed sheet are provided. Can be provided.

FIG. 1 is a schematic view showing an MD direction, a CD direction, and a ZD direction of a crosslinked polyolefin resin foamed sheet.

[Crosslinked polyolefin resin foam sheet]
The crosslinked polyolefin resin foamed sheet of the present invention is a crosslinked polyolefin resin foamed sheet obtained by crosslinking and foaming a polyolefin resin sheet, and the polyolefin resin sheet is obtained by using an organometallic complex as a polymerization catalyst. It contains at least one of a polyethylene-based resin (A) and a high-density polyethylene-based resin (B). The crosslinked polyolefin resin foamed sheet has a crosslinking degree of 15 to 50% by mass and an expansion ratio of 1. 5 to 2.3 cm ³ / g.

<Polyolefin resin sheet>
As described above, the polyolefin resin sheet in the present invention contains at least one of a low density polyethylene resin (A) and a high density polyethylene resin (B) obtained using an organometallic complex as a polymerization catalyst. Therefore, functions such as sealing properties, buffering properties and impact resistance can be sufficiently exhibited.

The low density polyethylene resin (A) is preferably a linear low density polyethylene obtained by copolymerizing ethylene and a small amount of α-olefin using an organometallic complex described later. This linear low density polyethylene is preferable from the viewpoint of reducing the thickness of the final product.
Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Then, a C4-C10 alpha olefin is preferable.

The density of the low-density polyethylene resin (A) is preferably 0.870 to 0.910 g / cm ³ , more preferably 0.875 to 0.907 g / cm ³ from the viewpoint of the flexibility of the foam obtained. 0.880 to 0.905 g / cm ³ is more preferable.

  Moreover, as said high density polyethylene-type resin (B), the high density polyethylene obtained by copolymerizing ethylene and a small amount of alpha olefin using the below-mentioned organometallic complex is preferable. As the α-olefin, the aforementioned α-olefin can be used.

The density of the high density polyethylene resin (B), from the viewpoint of improving the tensile strength of the resulting foam, preferably 0.915~0.965g / cm ^3, is 0.920~0.963g / cm ³ More preferred is 0.922 to 0.960 g / cm ³ .
In the present invention, the low density polyethylene resin (A) and the high density polyethylene resin (B) may be produced using the same organometallic complex, or may be produced using different organometallic complexes. Also good.

  In the case where the low-density polyethylene resin (A) and the high-density polyethylene resin (B) are used in combination, the low-density polyethylene resin relative to the total of the low-density polyethylene resin (A) and the high-density polyethylene resin (B). The ratio of (A) is preferably 80% by mass or less, more preferably 20 to 75% by mass, and more preferably 30 to 70% by mass, from the viewpoint of both providing flexibility and improving tensile strength of the foam obtained. Further preferred.

≪Organic metal complex≫
In the present invention, an organometallic complex is used as a polymerization catalyst. Examples of the organometallic complex include metallocene compounds, organoaluminum-titanium trichloride composites, organoaluminum-titanium tetrachloride composites, and chromium oxide compounds. Among these, metallocene compounds are preferably used. .

(Metallocene compound)
Suitable metallocene compounds in the present invention 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 their analogs as ligands (ligands). Can be mentioned.
Such metallocene compounds have uniform active site properties and each active site has the same activity. Therefore, since the polymer synthesized using the metallocene compound has high uniformity such as molecular weight, molecular weight distribution, composition, composition distribution, etc., crosslinking of the sheet containing this polymer proceeds uniformly. Since the uniformly cross-linked sheet can be uniformly stretched, the thickness of the cross-linked polyolefin resin foam sheet can be made uniform.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These rings may be substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group. Examples of the hydrocarbon group include a methyl group, an 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. Groups, various cetyl groups, phenyl groups and the like. The “various” means various isomers including n-, sec-, tert-, and iso-.
Moreover, what polymerized the said ring as an oligomer may be used as a ligand.
In addition to the π-electron unsaturated compounds, monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, An aryl phosphide or the like may be used.

  Examples of the metallocene compound containing a tetravalent transition metal or a ligand include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), and bis (cyclopentadienyl) titanium dichloride. And dimethylsilyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride.

  The said metallocene compound exhibits the effect | action as a catalyst in the case of superposition | polymerization of various olefins by combining with a specific cocatalyst (promoter). Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron compounds. In addition, the usage-amount of the cocatalyst with respect to a metallocene compound has preferable 10-1 million mol times, and 50-5,000 mol times is more preferable.

≪Polymerization method and polymerization conditions≫
The polymerization method of the low density polyethylene resin (A) and the high density polyethylene resin (B) is not particularly limited, and includes a solution polymerization method, a bulk polymerization method with substantially no medium, and a gas phase polymerization method. Can be mentioned. For example, the low density polyethylene-based resin (A) can be produced by using oxygen or peroxide in the air as an initiator and setting the pressure to 1000 to 4000 atm and high temperature and high pressure of 100 to 350 ° C. by radical polymerization. it can. In addition, the high-density polyethylene resin (B) can be produced by injecting ethylene into the solvent at a pressure of about several atmospheres using an aliphatic hydrocarbon as a solvent in the presence of a Ziegler-Natta catalyst and polymerizing for about 60 to 100 hours. .

≪Other polyolefin resin≫
As described above, the polyolefin resin constituting the polyolefin resin sheet may contain at least one of the low-density polyethylene resin (A) or the high-density polyethylene resin (B), and may contain other polyolefin resins. Good.
Examples of the other polyolefin resins include polyethylene resins and polypropylene resins. Examples of the polyethylene resin include an ethylene-α-olefin copolymer containing 50% by mass or more of ethylene and an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene. These may be used alone or in combination of two or more.
Examples of the α-olefin constituting the ethylene-α-olefin copolymer include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Among these, α-olefins having 4 to 10 carbon atoms are preferable.

Examples of the polypropylene resin include polypropylene and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. These may be used alone or in combination of two or more.
Examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene and the like. Among these, α-olefins having 6 to 12 carbon atoms are preferable.

  When the other polyolefin resin is contained, the ratio of the other polyolefin resin to the total of the low density polyethylene resin (A), the high density polyethylene resin (B) and the other polyolefin resin is preferably 40% by mass or less. 1-30 mass% is more preferable, and 1-20 mass% is still more preferable.

<Crosslinked polyolefin resin foam sheet>
The crosslinked polyolefin resin foamed sheet in the present invention has a crosslinking degree of 15 to 50% by mass and an expansion ratio of 1.5 to 2.3 cm ³ / g.

≪Crosslinking degree≫
In the present invention, the degree of cross-linking of the cross-linked polyolefin resin foam sheet is 15 to 50% by mass. When the degree of cross-linking is less than 15% by mass, bubbles in the vicinity of the surface of the foamed sheet are broken when the foamed sheet is stretched to cause surface roughness, and the appearance design of the resulting cross-linked polyolefin resin foamed sheet is reduced. To do. On the other hand, when the degree of crosslinking exceeds 50% by mass, the melt viscosity of the expandable polyolefin resin composition becomes too large, and it becomes difficult to foam when the foamable polyolefin resin composition is heated and foamed, and the desired expansion ratio is adjusted. It becomes difficult to do. From such a viewpoint, the degree of crosslinking is more preferably 20 to 40% by mass, and further preferably 25 to 35% by mass.

The degree of crosslinking of the crosslinked polyolefin resin foam sheet in the present invention refers to that measured by the following method. That is, a test piece of about 100 mg is taken from the crosslinked polyolefin resin foamed sheet, and the weight A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in 30 cm ³ of xylene at 120 ° C. and allowed to stand for 24 hours, and then filtered through a 200-mesh wire mesh to collect the insoluble matter on the wire mesh, vacuum dried, and the weight of the insoluble matter. Weigh B (mg) precisely. From the obtained value, the degree of crosslinking (mass%) is calculated by the following formula.
Crosslinking degree (% by mass) = 100 × (B / A)

≪Foaming ratio≫
The expansion ratio of the crosslinked polyolefin resin foamed sheet is 1.5 to 2.3 cm ³ / g. When the expansion ratio is less than 1.5 cm ³ / g, flexibility is significantly reduced when a crosslinked polyolefin resin foam sheet having a thickness of 50 to 300 μm is used as an adhesive tape. On the other hand, when it exceeds 2.3 cm ³ / g, when a 50 to 300 μm crosslinked polyolefin resin foam sheet is used as an adhesive tape, sufficient material strength cannot be maintained. This expansion ratio is more preferably 1.6~2.3cm ³ / g, more preferably 1.7~2.2cm ³ / g.
The expansion ratio is measured according to JIS K7222.

≪Tensile strength≫
The tensile strength at 23 ° C. in the MD direction or the CD direction in the cross-linked polyolefin resin foamed sheet is preferably 5 to 30 MPa from the viewpoint of material strength and ease of cutting when used as a base material for an adhesive tape, 7-25 MPa is more preferable, and 9-20 MPa is still more preferable.
In addition, in this specification, the tensile strength in MD direction or CD direction of a crosslinked polyolefin resin foam sheet is the value measured based on JISK6767 at 23 degreeC.
Further, the MD direction in the present invention refers to the extrusion direction of the crosslinked polyolefin resin foamed sheet 1 as shown in FIG. 1, and the CD direction is orthogonal to the MD direction and on the surface of the crosslinked polyolefin resin foamed sheet 1. The direction along the width (width direction) is referred to, and the ZD direction refers to a direction orthogonal to the surface of the crosslinked polyolefin resin foam sheet 1.

≪25% compressive strength≫
The 25% compressive strength of the crosslinked polyolefin resin foamed sheet based on JIS K6767 is preferably 180 to 550 kPa, more preferably 200 to 550 kPa, and even more preferably 220 to 500 kPa. If the 25% compressive strength is within the above range, impact absorbing performance can be obtained. When the pressure is 180 kPa or more, a reduction in thickness due to pressing when winding the crosslinked polyolefin resin foamed sheet can be suppressed. When the pressure is 550 kPa or less, it is possible to obtain unevenness followability when used as a sealing material.

≪Average bubble diameter and aspect ratio≫
In the crosslinked polyolefin resin foam sheet of the present invention, the average cell diameters in the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet are each preferably 130 μm or less.
The aspect ratio A of the bubbles (average bubble diameter in the MD direction / average bubble diameter in the CD direction) is preferably 0.25 to 2, and the aspect ratio B of the bubbles (average bubble diameter in the CD direction / foamed sheet) The average cell diameter in the thickness direction (ZD) is preferably 2-18.

  If the average cell diameter in the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet is within the above range, sufficient sealing properties can be obtained when this crosslinked polyolefin resin foam sheet is used as a sealing material. Can do. From such a viewpoint, the average cell diameter in the MD direction and the CD direction is more preferably 50 to 125 μm, and still more preferably 60 to 120 μm.

  If the aspect ratio A of the bubbles (average bubble diameter in the MD direction / average bubble diameter in the CD direction) is within the above range, the thickness, flexibility and tensile strength of the crosslinked polyolefin resin foam sheet may vary. The flexibility of the crosslinked polyolefin resin foamed sheet may decrease. From such a viewpoint, the aspect ratio A is more preferably 0.25 to 1.2. More preferably, it is 0.5-1.15, More preferably, it is 0.6-1.1.

When the aspect ratio B of the bubbles (average cell diameter in the CD direction / average cell diameter in the ZD direction) is within the above range, the flexibility of the crosslinked polyolefin resin foamed sheet decreases, and the thickness of the crosslinked polyolefin resin foamed sheet, Variations in flexibility and tensile strength may occur. From such a viewpoint, the aspect ratio B is more preferably 2.5 to 15.
The average bubble diameter in the MD direction, the average bubble diameter in the ZD direction, and the average bubble diameter in the CD direction can be measured by the method described in WO2005 / 007731.

≪Independent bubble≫
In the present invention, the bubbles are preferably closed cells from the viewpoint of improving the water-stopping property. The closed cell means that the ratio of closed cells to all bubbles (referred to as closed cell rate) is 65% or more.
The closed cell ratio is measured in the following manner. A test piece having a flat square shape with a side of 5 cm and a constant thickness is cut out from the crosslinked polyolefin resin foam sheet. The thickness of the test piece is measured, the apparent volume V ₁ of the test piece is calculated, and the weight W _{1 of the} test piece is measured. Next, the apparent volume V ₂ occupied by the bubbles is calculated based on the following formula. The density of the resin constituting the test piece is 1 g / cm ³ .
Apparent volume occupied by bubbles V ₂ = V ₁ −W ₁
Subsequently, the test piece is submerged in distilled water at 23 ° C. to a depth of 100 mm from the water surface, and a pressure of 15 kPa is applied to the test piece over 3 minutes. Thereafter, the test piece is taken out of the water to remove water adhering to the surface of the test piece, the weight W _{2 of the} test piece is measured, and the open cell rate F ₁ and the closed cell rate F ₂ are calculated based on the following equations. To do.
Open cell ratio F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂
Closed cell ratio F ₂ (%) = 100−F ₁

≪Thickness of crosslinked polyolefin resin foam sheet≫
The thickness of the crosslinked polyolefin resin foamed sheet is preferably 50 to 300 μm, and more preferably 70 to 150 μm.
When the thickness of the crosslinked polyolefin resin foamed sheet is within the above range, the flexibility and the tensile strength are improved, and the texture, mechanical strength, and the like of the resulting adhesive tape are improved.

≪Heat dimensional change rate≫
The dimensional change rate in the MD direction at 90 ° C. of the crosslinked polyolefin resin foamed sheet is preferably −10% or more, more preferably −10 to 5%, and still more preferably −2.0 to 2.0%. When the heating dimensional change rate is within the above range, when the cross-linked polyolefin resin foam sheet is used as the base material of the pressure-sensitive adhesive tape, a problem that the pressure-sensitive adhesive tape contracts or expands and is displaced from the sticking position is prevented. .
In addition, the heating dimensional change rate in the MD direction at 90 ° C. of the crosslinked polyolefin resin foamed sheet is a value measured according to JIS K6767 except that the measurement temperature is 90 ° C.

≪Number of bubbles in 1mm width≫
The number of bubbles within 1 mm width is preferably 5 to 20, more preferably 6 to 20, and still more preferably 8 to 20 from the viewpoint of improving the sealing performance. The number of bubbles in a 1 mm width of 5 to 20 corresponds to an average bubble diameter in the 1 mm width direction of approximately 50 to 200 μm.

<Method for producing crosslinked polyolefin resin foam sheet>
There is no restriction | limiting in particular about the manufacturing method of a crosslinked polyolefin resin foam sheet, For example, it can manufacture with the manufacturing method containing the process of the following processes (1)-(3).
Process (1)
The process which manufactures a foamable polyolefin resin sheet by supplying a polyethylene-type resin (A) polyethylene-type resin (B) and a thermal decomposition-type foaming agent to an extruder, melt-kneading, and extruding in a sheet form from an extruder.
Step (2)
A step of irradiating the foamable polyolefin resin sheet with ionizing radiation to crosslink the foamable polyolefin resin sheet to a crosslinking degree of 15 to 50% by mass.
Process (3)
The foamed polyolefin resin sheet that has been cross-linked is heated and foamed, and the resulting foamed sheet is stretched in one or both of the MD direction and the CD direction while maintaining the molten state during foaming. A step of producing a crosslinked polyolefin resin foam sheet having the above-mentioned characteristics by stretching the bubbles.
About the manufacturing method of the said crosslinked polyolefin resin foam sheet, it can manufacture by the method of WO2005 / 007731 other than said method.

  The pyrolytic foaming agent that can be used in the production method is not particularly limited, and examples thereof include azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide, and the like. Of these, azodicarbonamide is preferred. In addition, a thermal decomposition type foaming agent may be used individually by 1 type, and may use 2 or more types together.

  1-12 mass parts is preferable with respect to 100 mass parts of polyolefin resins, and, as for the addition amount of the thermal decomposition type foaming agent in a foamable polyolefin resin composition, 1-8 mass parts is more preferable. When the amount of the pyrolytic foaming agent is within the above range, the foamability of the foamable polyolefin resin sheet is improved, and a crosslinked polyolefin resin foam sheet having a desired foaming ratio can be obtained, as well as tensile strength and compression. Recovery is improved.

  In the foamable polyolefin resin composition, if necessary, an antioxidant such as 2,6-di-t-butyl-p-cresol, a foaming aid such as zinc oxide, a cell core modifier, a heat stabilizer, Colorants, flame retardants, antistatic agents, fillers, and the like may be added within a range that does not impair the physical properties of the crosslinked polyolefin resin foam sheet.

Examples of the method for crosslinking the expandable polyolefin resin sheet include a method of irradiating the expandable polyolefin resin sheet with ionizing radiation such as electron beam, α ray, β ray, γ ray, and the like. A method of blending a peroxide and heating the obtained expandable polyolefin resin sheet to decompose the organic peroxide can be used. These methods may be used in combination.
The amount of ionizing radiation used to irradiate the expandable polyolefin resin sheet with ionizing radiation can be adjusted and adjusted so that the degree of crosslinking is 15 to 50% by mass. For example, it is preferably 5 to 10 Mrad.

  Examples of the organic peroxide that can be used in the production method include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy). And cyclohexane. These may be used alone or in combination of two or more.

  0.01-5 mass parts is preferable with respect to 100 mass parts of polyolefin resin, and, as for the addition amount of an organic peroxide, 0.1-3 mass parts is more preferable. When the added amount of the organic peroxide is within the above range, the crosslinking of the foamable polyolefin resin sheet is likely to proceed, and the amount of decomposition residue of the organic peroxide is suppressed in the obtained crosslinked polyolefin resin foamed sheet. be able to.

  The method for foaming the foamable polyolefin resin sheet is not particularly limited, and examples include a method of heating with hot air, a method of heating with infrared rays, a method using a salt bath, a method using an oil bath, a method using induction heating, and the like. These may be used in combination.

  The use of the thus obtained crosslinked polyolefin resin foam sheet is not particularly limited. For example, it is used as an adhesive tape described later, or used as a sealing material for waterproofing and dustproofing IT products by punching into a predetermined shape. It is done.

[Adhesive tape]
The pressure-sensitive adhesive tape of the present invention is characterized in that a pressure-sensitive adhesive layer is provided on at least one surface of the crosslinked polyolefin resin foamed sheet of the present invention, and the thickness of the crosslinked polyolefin resin foamed sheet is 50 to 300 μm. And
When the thickness of the crosslinked polyolefin resin foamed sheet is within the above range, flexibility, tensile strength, and the like are improved, and the resulting adhesive tape has excellent texture and mechanical strength. From such a viewpoint, the thickness of the crosslinked polyolefin resin foamed sheet is more preferably 100 to 200 μm.
It is preferable that the thickness of the cross-linked polyolefin resin foam sheet is small in that the parts are fixed in a narrow space. Specifically, 50-100 micrometers is preferable and 50-80 micrometers is more preferable.

  There is no restriction | limiting in particular as an adhesive which comprises the adhesive layer laminated | stacked and integrated on the one or both surfaces of a crosslinked polyolefin resin foam sheet, For example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, etc. are used. be able to.

  As a method of applying a pressure-sensitive adhesive to at least one surface of the crosslinked polyolefin resin foam sheet and laminating and integrating the pressure-sensitive adhesive layer, for example, the pressure-sensitive adhesive is applied to at least one surface of the cross-linked polyolefin resin foam sheet using a coater or the like. Examples thereof include a method of applying, a method of spraying and applying a pressure-sensitive adhesive using at least one surface of a cross-linked polyolefin resin foam sheet, a method of applying a pressure-sensitive adhesive using a brush on at least one surface of the cross-linked polyolefin resin foam sheet, and the like.

The pressure-sensitive adhesive tape of the present invention can be used as a pressure-sensitive adhesive tape for known applications, and can be used as a pressure-sensitive adhesive tape for absorbing unevenness on an uneven surface, or can be used in an electronic device body such as a mobile phone or video camera. Can be used to fix the electronic components to be used. Since the crosslinked polyolefin resin foamed sheet of the present invention maintains excellent flexibility and tensile strength even when processed thinly, it can be suitably used for electronic devices that are remarkably miniaturized.
The adhesive tape of the present invention is preferably thin in terms of fixing components in a narrow space, the thickness of the crosslinked polyolefin resin foam sheet is preferably 50 to 100 μm, and the thickness of the adhesive layer is 5 to 80 μm. Is preferred. The thickness of the pressure-sensitive adhesive layer is more preferably 7 to 70 μm, and further preferably 10 to 50 μm.

[Sealant]
The pressure-sensitive adhesive tape using the crosslinked polyolefin resin foam sheet of the present invention prevents an impact from being applied to an electronic component housed in an electronic device body such as a portable phone or a video camera, and prevents dust or dirt in the electronic device body. It can be used as a sealing material that prevents moisture and the like from entering.
The sealing material is formed by subjecting the pressure-sensitive adhesive tape of the present invention to slit processing or punching processing so as to have a planar dimension of a predetermined attachment blank portion.
Since the pressure-sensitive adhesive tape using the crosslinked polyolefin resin foamed sheet of the present invention has flexibility and tensile strength, it has good workability when slitting or punching, and has good shape stability after processing. For this reason, the width can be processed to 2 mm or less, and further to 1 mm or less.
Since the sealing material using the crosslinked polyolefin resin foam sheet of the present invention is easy to process when the width is 2 mm or less, the display screen panel of a small electronic device having a display screen such as a portable telephone or the like. Applicable to mounting part. Thereby, the ratio of the screen size to the main surface of the housing | casing of a small electronic device can be formed as large as possible.
Moreover, even if the sealing material using the crosslinked polyolefin resin foam sheet of the present invention has a width of 2 mm or less, it can sufficiently exhibit functions such as sealing properties, buffer properties, and impact resistance.

Examples The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
[Example 1]
Linear low density polyethylene resin (A) obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (manufactured by Dow Chemical, trade name “Affinity PL1850”, density: 0.902 g / cm ³ ) 100 A foamable polyolefin resin composition composed of parts by mass, 2 parts by mass of azodicarbonamide, 0.3 parts by mass of 2,6-di-t-butyl-p-cresol and 1 part by mass of zinc oxide is supplied to an extruder. The mixture was melt-kneaded at 130 ° C. and extruded into a long foamable polyolefin resin sheet having a width of 200 mm and a thickness of 310 μm.

Next, the foamed polyolefin resin sheet was crosslinked by irradiating an electron beam with an acceleration voltage of 800 kV for 6 Mrad on both sides of the long foamed polyolefin resin sheet, and then the foamed polyolefin resin sheet was heated with hot air and an infrared heater. The mixture was continuously fed into a foaming furnace maintained at 0 ° C. and heated to cause foaming so that the expansion ratio was 2.2 cm ³ / g. The thickness of the obtained foam was 0.35 mm.

  Next, after continuously feeding the obtained foamed sheet from the foaming furnace, the foamed sheet is stretched in the CD direction while maintaining the foamed sheet at a temperature of 200 to 250 ° C. The foamed sheet is stretched in the MD direction by winding the foamed sheet at a winding speed faster than the feeding speed (feeding speed) of the foamable polyolefin resin sheet to the foaming furnace, and the bubbles in the foamed sheet are expanded in the CD direction. Stretched and deformed in the MD direction to obtain a crosslinked polyolefin resin foamed sheet. The winding speed of the foamed sheet was adjusted in consideration of the expansion in the MD direction due to foaming of the foamable polyolefin resin sheet itself. The obtained crosslinked polyolefin resin foam sheet was evaluated by the following method. The results are shown in Table 1.

[Example 2]
A crosslinked polyolefin resin foamed sheet was produced in the same manner as in Example 1 except that the electron beam irradiation amount was 6.9 Mrad and the expansion ratio was 1.9 cm ³ / g, and evaluated by the following method. The results are shown in Table 1.
[Example 3]
A crosslinked polyolefin resin foam sheet was produced in the same manner as in Example 2 except that the electron beam irradiation amount was 7.8 Mrad, and evaluated by the following method. The results are shown in Table 1.

[Example 4]
Other than using 100 parts by mass of the high-density polyethylene resin (B) (trade name “HY540” manufactured by Nippon Polyethylene Co., Ltd., density: 0.960 g / cm ³ ) instead of the linear low-density polyethylene. Produced a crosslinked polyolefin resin foam sheet by the same method as in Example 1, and evaluated by the following method. The results are shown in Table 1.
[Example 5]
Linear low-density polyethylene resin (A) (manufactured by Dow Chemical, trade name “affinity PL1850”, density: 0.902 g / cm ³ ) 70 parts by mass, high-density polyethylene resin (B) (manufactured by Nippon Polyethylene Co., Ltd.) The product name “HY540”, density: 0.960 g / cm ³ ) was used in the same manner as in Example 1 except that 30 parts by mass and the electron beam irradiation amount was 6.4 Mrad. Sheets were produced and evaluated by the following methods. The results are shown in Table 1.

[Comparative Example 1]
A crosslinked polyolefin resin foam sheet was produced in the same manner as in Example 1 except that the electron beam irradiation amount was 4.6 Mrad, and the foaming ratio was 2.5 cm ³ / g, and evaluation was performed by the following method. The results are shown in Table 1.

[Measuring method]
<Degree of crosslinking>
The degree of crosslinking was measured according to the method described above.
<Tensile strength>
A cross-linked polyolefin resin foam sheet cut into a dumbbell-shaped No. 1 defined in JIS K 6251 4.1 was used as a sample, and the tensile strength was measured at 23 ° C. in accordance with JIS K6767.
In addition, length means the production direction in extrusion and foaming, and horizontal means the direction orthogonal to the production direction in extrusion and foaming.
<25% compressive strength>
The 25% compressive strength was measured according to JIS K6767.

  As is apparent from Table 1, according to the present invention, there is provided a crosslinked polyolefin resin foamed sheet that can sufficiently exhibit functions such as sealing properties, buffering properties, and impact resistance even when the planar size of the attachment blank portion is small. be able to.

Claims (5)

A crosslinked polyolefin resin foamed sheet obtained by crosslinking and foaming a polyolefin resin sheet, the polyolefin resin sheet obtained by using an organometallic complex as a polymerization catalyst, and a low density polyethylene resin (A) and a high density polyethylene The cross-linked polyolefin resin foam sheet has a degree of cross-linking of 15 to 50% by mass and a foaming ratio of 1.5 to 2.3 cm ³ / g. A cross-linked polyolefin resin foam sheet.   The ratio of the low density polyethylene resin (A) to the total of the low density polyethylene resin (A) and the high density polyethylene resin (B) is 80% by mass or less. . The density of the low density polyethylene resin (A) is 0.870 to 0.910 g / cm ³ , and the density of the high density polyethylene resin (B) is 0.915 to 0.965 g / cm ^3. Item 3. The crosslinked polyolefin resin foam sheet according to Item 1 or 2.   It is the adhesive tape which provided the adhesive layer in the at least one surface of the crosslinked polyolefin resin foam sheet in any one of Claims 1-3, Comprising: The thickness of this crosslinked polyolefin resin foam sheet is 50-300 micrometers tape.   The sealing material which gave the slit process or the punching process with respect to the adhesive tape of Claim 4 so that a width | variety might be 2 mm or less.

Images