JP5899027B2 - Cross-linked polyolefin resin foam sheet, adhesive tape and sealing material - Google Patents

Description

  The present invention relates to a crosslinked polyolefin resin foam sheet having excellent flexibility and heat resistance, an adhesive tape using the crosslinked polyolefin resin foam sheet, and a sealing material.

Conventionally, a crosslinked polyolefin resin foamed sheet has been used in various applications such as a base material for an adhesive tape, a base material for a patch, and a sealing material for electronic devices. Therefore, in these applications, the thickness is thin and flexibility is required.
As such a cross-linked polyolefin resin foam sheet, in Patent Document 1, an inorganic filler is added to a polyolefin resin to form a sheet, and the sheet is stretched to make it porous, thereby providing flexibility and mechanical strength. Improved porous sheets have been proposed.

  However, the porous sheet is not sufficiently flexible because it is difficult to increase the expansion ratio, and further, the porous sheet is not subjected to a crosslinking treatment. There was a problem that the stretching treatment above the melting point of the polyolefin resin constituting the sheet could not be performed, the porous sheet was distorted during the stretching treatment, and the porous sheet contracted during use. .

In addition, as a cross-linked polyolefin resin foamed sheet, Patent Document 2 discloses a cross-linked product obtained by foaming a sheet-like material irradiated with an electron beam of 1 Mrad or less, comprising an ultra-high density polyethylene resin having a predetermined density and a foaming agent. Ethylene-based resin foams have been proposed.
However, the above-mentioned crosslinked ethylene resin foam does not have sufficient flexibility and heat resistance. In addition, it is conceivable to improve the flexibility by increasing the expansion ratio of the crosslinked ethylene resin foam. However, when the expansion ratio is increased, only a thick foam can be obtained.

Japanese Patent Publication No. 7-64942 Japanese Patent Publication No. 6-76505

  The present invention provides a cross-linked polyolefin resin foam sheet that can be thinned while maintaining excellent flexibility and heat resistance, an adhesive tape using the cross-linked polyolefin resin foam sheet, and a sealing material. It is for the purpose.

[1] A crosslinked polyolefin resin foamed sheet obtained by crosslinking and foaming a polyolefin resin sheet obtained by extrusion molding, wherein the polyolefin resin sheet uses a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. A crosslinked polyolefin resin foamed sheet containing 40% by mass or more of the obtained polyethylene resin, wherein the crosslinked polyolefin resin foamed sheet satisfies the following conditions (a) to (e): .
<Conditions>
(A) Crosslinking degree is 5 to 60% by mass
(B) The average cell diameter in the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet is 180 μm or less, respectively. (C) Aspect ratio A (average cell diameter in the MD direction / average cell diameter in the CD direction) ) Is 0.2
5-2
(D) Aspect ratio B of bubbles (average cell diameter in CD direction / average cell diameter in thickness direction of foamed sheet (ZD)) is 2 to 18
(E) The expansion ratio of the foamed sheet is 12 cm ³ / g or less. [2] An adhesive tape provided with an adhesive layer on at least one surface of the crosslinked polyolefin resin foamed sheet, An adhesive tape having a thickness of 0.05 to 2 mm.
[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, there are provided a cross-linked polyolefin resin foam sheet that can be thinned while maintaining excellent flexibility and heat resistance, an adhesive tape using the cross-linked polyolefin resin foam sheet, and a sealing material. can do.

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

[Crosslinked polyolefin resin foam sheet]
The crosslinked polyolefin resin foam sheet of the present invention is obtained by extruding a polyolefin resin containing 40% by mass or more of a polyethylene resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. A polyolefin resin sheet is crosslinked and foamed, and the crosslinked polyolefin resin foam sheet satisfies a specific condition.
In this specification, “a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst” may be referred to as a “metallocene polymerized polyethylene resin”.

<Polyolefin resin sheet>
As described above, the polyolefin resin sheet in the present invention is a sheet obtained by extruding a polyolefin resin containing 40% by mass or more of a metallocene polymerized polyethylene resin.
When the content of the metallocene polymerized polyethylene resin in the polyolefin resin sheet is less than 40% by mass, the adhesiveness increases, and the aspect ratio of the bubbles to be described later cannot be within a predetermined range. The mechanical strength and flexibility of the polyolefin resin foam sheet are lowered. That is, when the polyolefin resin sheet is stretched, the bubbles in the foamed sheet are stretched in the stretching direction so that the cell walls are close to each other, and the adhesiveness is similar to that of an ethylene-vinyl acetate copolymer. When a high polyolefin resin is used as a main component, the cell walls are closely integrated with each other, so that it is difficult to obtain a specific bubble aspect ratio. From such a viewpoint, the content of the metallocene polymerized polyethylene resin is more preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 100% by mass.
The content of the metallocene polymerized polyethylene resin of 100% by mass means that only the metallocene polymerized polyethylene resin is used as the polyolefin resin.

As the metallocene polymerized polyethylene resin, linear low density polyethylene obtained by copolymerizing ethylene and a small amount of α-olefin using a metallocene compound described later is preferable.
Examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene.

≪Metalocene compound≫
In the present invention, a metallocene compound containing a tetravalent transition metal is used as a polymerization catalyst.
Examples of the metallocene compound include compounds such as a bis (cyclopentadienyl) metal complex 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 compounds containing tetravalent transition metals and ligands include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), and bis (cyclopentadienyl) titanium dichloride. Dimethylsilyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-t-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium Chloride, methylphenylsilyltetramethylcyclopentadienyl-t-butylamidohafnium dichloride, indenyltitanium tris (dimethylamide), indenyltitanium Tris (diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

  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 metallocene polymerized polyethylene resin is not particularly limited, and examples thereof include a solution polymerization method, a bulk polymerization method substantially free of a medium, and a gas phase polymerization method. The polymerization temperature is preferably −100 ° C. to 300 ° C., and the polymerization pressure is preferably normal pressure to 100 kg / cm ² .

≪Other polyethylene resin≫
As described above, the polyolefin resin constituting the polyolefin resin sheet may contain other polyolefin resin as long as it contains 40% by mass or more of the metallocene polymerized polyethylene resin.
Examples of polyolefin resins other than metallocene polymerized polyethylene resins include polyethylene resins and polypropylene resins.
Examples of the polyethylene resin include linear low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-α-olefin copolymer containing 50% by mass or more of ethylene, and 50% by mass of ethylene. The ethylene-vinyl acetate copolymer etc. which are contained above are mentioned. 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. Can be mentioned.

  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. Can be mentioned.

<Crosslinked polyolefin resin foam sheet>
The crosslinked polyolefin resin foam sheet in the present invention satisfies the following conditions (a) to (e).
<Conditions>
(A) Crosslinking degree is 5 to 60% by mass
(B) The average cell diameter in the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet is 180 μm or less, respectively. (C) Aspect ratio A (average cell diameter in the MD direction / average cell diameter in the CD direction) ) Is 0.2
5-2
(D) Aspect ratio B of bubbles (average cell diameter in CD direction / average cell diameter in thickness direction of foamed sheet (ZD)) is 2 to 18
(E) The foaming ratio of the foamed sheet is 12 cm ³ / g or less. 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 MD. The direction (width direction) perpendicular to the direction and along the surface of the crosslinked polyolefin resin foamed sheet 1 is referred to, and the ZD direction refers to the direction orthogonal to the surface of the crosslinked polyolefin resin foamed sheet 1.
Hereinafter, each condition will be described in detail.

<< Condition (a): Degree of crosslinking >>
In the present invention, the degree of cross-linking of the cross-linked polyolefin resin foam sheet is 5 to 60% by mass. When the degree of crosslinking is less than 5% by mass, bubbles in the vicinity of the surface of the foamed sheet break up when the foamed sheet is stretched, resulting in surface roughness, and the appearance of the resulting crosslinked polyolefin resin foamed sheet has a good design. descend. On the other hand, if the degree of crosslinking exceeds 60% by mass, the melt viscosity of the expandable polyolefin resin composition becomes too large, and it becomes difficult to foam when the expandable polyolefin resin composition is heated and foamed, and the desired expansion ratio It becomes difficult to adjust to. From such a viewpoint, the degree of crosslinking is more preferably 10 to 40% by mass.

The degree of cross-linking of the cross-linked polyolefin resin foam sheet in the present invention refers to that measured by the following method. That is, about 100 mg of a test piece is collected from the crosslinked polyolefin resin foam 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)

<< Conditions (b) to (d): Average bubble diameter and aspect ratio >>
The cross-linked polyolefin resin foam sheet of the present invention has an average cell diameter of 180 μm or less in each of the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet (Condition b), and the aspect ratio A (MD The average bubble diameter in the direction / average bubble diameter in the CD direction) is 0.25 to 2 (condition c), and the aspect ratio B of the bubbles (average bubble diameter in the CD direction / thickness direction of the foamed sheet (ZD)) Of the average bubble diameter) is 2 to 18 (condition d).

  When the average cell diameter in the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet exceeds 180 μm, sufficient sealing properties can be obtained when this crosslinked polyolefin resin foam sheet is used as a sealing material. I can't. From such a viewpoint, the average bubble diameter in the MD direction and the CD direction is preferably 40 to 160 μm, more preferably 50 to 130 μm, still 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 less than 0.25, the expansion ratio is lowered and the flexibility is lowered, or the cross-linked polyolefin resin foam sheet is used. Variations in thickness, flexibility and tensile strength can occur. On the other hand, when the aspect ratio A exceeds 2, the flexibility of the crosslinked polyolefin resin foam sheet is lowered. From such a viewpoint, the aspect ratio A is more preferably 0.25 to 0.60.

  When the aspect ratio B of the bubbles (average bubble diameter in the CD direction / average bubble diameter in the ZD direction) is less than 2, the flexibility of the cross-linked polyolefin resin foam sheet is lowered, and when the aspect ratio B exceeds 18, the expansion ratio May decrease and the flexibility may decrease, or the thickness, flexibility and tensile strength of the crosslinked polyolefin resin foam sheet may vary. From such a viewpoint, the aspect ratio B is more preferably 2.5 to 15.

≪Measuring method of average bubble diameter in MD direction≫
The average cell diameter in the MD direction of the crosslinked polyolefin resin foam sheet is measured by the following method. That is, the cross-linked polyolefin resin foam sheet is cut over the entire length in a plane parallel to the ZD direction at the center in the CD direction, and the cut surface is enlarged 60 times using a scanning electron microscope (SEM). Take a photo so that the entire length fits. Next, a straight line having a length of 15 cm (actual length of 2500 μm before magnification) on the photograph is drawn at the center in the ZD direction so as to be parallel to the surface of the crosslinked polyolefin resin foam sheet. The number of bubbles located on this straight line is counted visually, and the average bubble diameter in the MD direction of the bubbles is calculated based on the following formula.
Average bubble diameter in the MD direction (μm) = 2500 (μm) / number of bubbles (pieces)

≪Measurement method of average bubble diameter in ZD direction≫
The average cell diameter in the ZD direction of the crosslinked polyolefin resin foam sheet is measured by the following method. That is, photography is performed by the same method as that used for calculating the average bubble diameter in the MD direction. In the photograph taken, three straight lines are drawn in the direction orthogonal to the surface of the crosslinked polyolefin resin foam sheet (ZD) so as to divide the MD direction of the cut surface into four parts over the entire length of the foam sheet. Next, the length of each straight line was measured and the number of bubbles located on each straight line was visually counted, and the average bubble diameter in the ZD direction of the bubbles was calculated for each straight line based on the following formula, and the arithmetic mean of these Is the average cell diameter in the ZD direction.
Average bubble diameter in ZD direction (μm) = length of straight line on photograph (μm) / (60 × number of bubbles (pieces))

≪Measurement method of average bubble size in CD direction≫
The average cell diameter in the CD direction of the crosslinked polyolefin resin foam sheet is measured by the following method. That is, the cross-linked polyolefin resin foam sheet is cut over the entire length in the thickness direction on a plane parallel to the CD direction and parallel to the direction (ZD) perpendicular to the surface of the cross-linked polyolefin resin foam sheet. Next, the cut surface is magnified 60 times using a scanning electron microscope (SEM), and a photograph is taken so that the total length in the thickness direction of the cross-linked polyolefin resin foam sheet is accommodated. Then, based on the photographed image, the average bubble diameter in the CD direction is calculated in the same manner as when the average bubble diameter in the MD direction is measured.

In the above-described method of measuring the average bubble diameter, when counting the number of bubbles located on a straight line, the bubble diameter is determined based only on the bubble cross section appearing on the photograph. That is, even if the bubbles seem to be completely separated from each other by the cell walls on the cut surface of the crosslinked polyolefin resin foam sheet, the bubbles communicate with each other at a portion other than the cut surface of the crosslinked polyolefin resin foam sheet. However, in the present invention, the cross-linked polyolefin resin foam sheet is not considered whether or not it is in communication with each other in the portion other than the cut surface, and based only on the cross section of the bubble film shown on the photograph. The bubble form is judged, and one void portion completely surrounded by the bubble film cross section appearing on the photograph is judged as one bubble.
Positioning on a straight line means that the straight line completely penetrates the bubble at any part of the bubble, and at both ends of the straight line, the straight line does not completely penetrate the bubble and the end of the straight line When the part was in a state of being located in the bubble, the bubble was counted as 0.5.

  When photographing the cut surface of the cross-linked polyolefin resin foam sheet, coloring the cross-section of the cross-linked polyolefin resin foam sheet facilitates the discrimination of air bubbles and enlarges the 2500 μm scale together to take a photo. This makes it easier to specify the straight line length on the photograph.

In the present invention, the expansion ratio of the crosslinked polyolefin resin foam sheet is 12 cm ³ / g or less. When the expansion ratio exceeds 12 cm ³ / g, for example, the material strength when a crosslinked polyolefin resin foam sheet having a thickness of 2 mm or less is used as an adhesive tape is lowered. From this point of view, the expansion ratio is more preferably 1.2~12cm ³ / g, more preferably 1.3~10cm ³ / g.

≪25% compressive strength≫
The 25% compressive strength of the crosslinked polyolefin-based resin foam sheet in accordance with JIS K6767 is preferably 15 to 200 kPa, more preferably 20 to 120 kPa, and still more preferably 22 to 65 kPa. If the 25% compressive strength is within the above range, it is possible to suppress a decrease in the feel of the crosslinked polyolefin resin foam sheet and a decrease in impact absorption performance, and also due to pressing when winding the crosslinked polyolefin resin foam sheet. A decrease in thickness can be suppressed.

≪Tensile strength≫
The tensile strength at 23 ° C. in at least one direction of the MD direction or the CD direction in the crosslinked polyolefin-based resin foamed sheet is 5 × 10 ² from the viewpoint of material strength and ease of cutting when used as a base material for an adhesive tape. 8 × 10 ⁶ kPa is preferable, 8 × 10 ² to 8 × 10 ⁴ kPa is more preferable, and 1 × 10 ³ to 8 × 10 ³ kPa is more preferable.
In addition, in this specification, the tensile strength in MD direction or CD direction of a crosslinked polyolefin-type resin foam sheet is the value measured based on JISK6767 at 23 degreeC.

≪Heat dimensional change rate≫
The dimensional change rate in the MD direction at 90 ° C. of the crosslinked polyolefin-based resin foam 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, the problem that the pressure-sensitive adhesive tape contracts or expands and is displaced from the sticking position is prevented. The
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 in a 1 mm width can be measured by the method described in Examples described later, and the higher this value, the better the sealing performance. Therefore, the number of bubbles in 1 mm width in the present invention is preferably 5 to 20, more preferably 6 to 20, and still more preferably 8 to 20.

≪Method for producing crosslinked polyolefin resin foam sheet≫
There is no restriction | limiting in particular about the manufacturing method of the crosslinked polyolefin-type resin foam sheet of this invention, For example, it can manufacture by the method of the following (1)-(4).

Manufacturing method (1)
The production method (1) includes the following steps (1-1) to (1-3).
A polyolefin resin containing 40% by mass or more of a metallocene polymerized polyethylene resin and a thermally decomposable foaming agent are supplied to an extruder, melt kneaded, and extruded into a sheet form from the extruder to produce a foamable polyolefin resin sheet. Step (1-1) to perform,
Irradiating this foamable polyolefin resin sheet with ionizing radiation to crosslink the foamable polyolefin resin sheet to a crosslinking degree of 5 to 60% by mass;
The foamed polyolefin resin sheet that has been crosslinked is heated and foamed, and the resulting foamed sheet is stretched and expanded in either the MD direction or the CD direction, or both while maintaining the molten state during foaming. A step (1-3) of stretching a bubble of the sheet to produce a crosslinked polyolefin resin foam sheet having the above-mentioned characteristics.

Manufacturing method (2)
The production method (2) includes the following steps (2-1) to (2-3).
A polyolefin resin containing 40% by mass or more of a metallocene polymerized polyethylene resin, a thermally decomposable foaming agent, and an organic peroxide are supplied to an extruder, melt-kneaded, and extruded into a sheet form from the extruder to expand the polyolefin. A process (2-1) for producing a resin sheet,
Heating the foamable polyolefin resin sheet to decompose the organic peroxide, and foaming the foamable polyolefin resin sheet while crosslinking the foamable polyolefin resin sheet to a crosslinking degree of 5 to 60% by mass;
The obtained foamed sheet is stretched in the MD direction or the CD direction while maintaining the melted state at the time of foaming, and the foamed sheet is stretched to stretch the foamed sheet. The manufacturing method which has a process (2-3) which manufactures a resin foam sheet.

Manufacturing method (3)
The production method (3) includes the following steps (3-1) to (3-5).
A polyolefin resin containing 40% by mass or more of a metallocene polymerized polyethylene resin and a thermally decomposable foaming agent are supplied to an extruder, melt kneaded, and extruded into a sheet form from the extruder to produce a foamable polyolefin resin sheet. Step (3-1) to perform,
Irradiating the foamable polyolefin resin sheet with ionizing radiation to crosslink the foamable polyolefin resin sheet to a crosslinking degree of 5 to 60% by mass (3-2);
A step (3-3) of producing a foamed sheet by heating and foaming the cross-linked foamable polyolefin resin sheet and then cooling the foamed resin sheet;
Step (3-4) of heating this foamed sheet again to a molten or softened state;
Step of producing a crosslinked polyolefin resin foamed sheet having the above-mentioned characteristics by stretching the foamed sheet in one or both of the MD direction and the CD direction to stretch the bubbles of the foamed sheet (3-5 ).

Manufacturing method (4)
The production method (4) includes the following steps (4-1) to (4-3).
A polyolefin resin containing 40% by mass or more of a metallocene polymerized polyethylene resin, a thermally decomposable foaming agent, and an organic peroxide are supplied to an extruder, melt-kneaded, and extruded into a sheet form from the extruder to expand the polyolefin. A step (4-1) of producing a resin sheet,
The foamable polyolefin resin sheet is heated to decompose the organic peroxide, and the foamable polyolefin resin sheet is foamed while being crosslinked to a crosslinking degree of 5 to 60% by mass, and then cooled to produce a foam sheet. Step (4-2);
Step (4-3) of heating this foamed sheet again to a molten or softened state,
Step of producing a crosslinked polyolefin resin foamed sheet having the above-mentioned characteristics by stretching the foamed sheet toward one or both of the MD direction and the CD direction to stretch the bubbles of the foamed sheet (4-4) And the like.

  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 resin, 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, and the tensile strength can be obtained. In addition, the compression recoverability is improved.

  For 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 Further, a colorant, a flame retardant, an antistatic agent, a filler, 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. In addition, an organic peroxide is blended in advance, and the resulting foamable polyolefin resin sheet is heated to decompose the organic peroxide. These methods may be used in combination.

  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). Cyclohexane, 2,2-bis (t-butylperoxy) octane, n-butyl-4,4-bis (t-butylperoxy) valerate, di-t-butyl peroxide, t-butylcumyl peroxide, dic Milperoxide, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2 , 5-Di (t-butylperoxy) hexyne-3, benzoyl peroxide, cumylperoxyneodecanate, t-butylperoxybenzoate , 2,5-dimethyl-2,5-di (benzoyl peroxy) hexane, t- butyl peroxy isopropyl carbonate, t- butyl peroxy allyl carbonate. 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 expandable polyolefin resin sheet is likely to proceed, and the amount of the decomposition residue of the organic peroxide is reduced in the obtained crosslinked polyolefin resin foam sheet. Can be suppressed.

  The method for foaming the foamable polyolefin resin sheet is not particularly limited, and examples thereof 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, and the like. May be.

  The stretching of the foamed sheet may be performed after the foamable polyolefin resin sheet is foamed to obtain a foamed sheet, or may be performed while foaming the foamable polyolefin resin sheet. In addition, after foaming a foamable polyolefin resin sheet to obtain a foamed sheet, when the foamed sheet is stretched, the foamed sheet is continuously stretched while the foamed sheet is maintained in a molten state without being cooled. Alternatively, after cooling the foamed sheet, the foamed sheet may be heated again to be melted or softened and then stretched.

The molten state of the foamed sheet refers to a state in which the double-sided temperature of the foamed sheet is heated above the melting point of the polyolefin resin constituting the foamed sheet. In addition, melting | fusing point (degreeC) of polyolefin resin means the temperature of the maximum peak among the endothermic peaks accompanying the melting | dissolving of a crystal | crystallization acquired when calorimetric analysis is performed by differential scanning calorimetry (DSC).
The softened state of the foamed sheet refers to a state where the foamed sheet is heated to a temperature at which the double-sided temperature T (° C.) satisfies the following formula. The softening point (° C.) of the polyolefin-based resin is a vicat softing point measured in accordance with ASTM D1525.
Softening point of polyolefin resin−10 ° C. ≦ T ≦ Softening point of polyolefin resin + 10 ° C.

  By stretching the foamed sheet, it is possible to produce a crosslinked polyolefin resin foamed sheet in which the foam sheet has an aspect ratio within a predetermined range by stretching and deforming the foamed cells in a predetermined direction.

  In the extending | stretching direction of a foam sheet, it extends | stretches toward MD direction or CD direction of a elongate foamable polyolefin resin sheet, or toward MD direction and CD direction. When the expandable polyolefin resin sheet is stretched in the MD direction and the CD direction, the foam sheet may be stretched simultaneously in the MD direction and the CD direction, or may be stretched separately one by one. .

  As a method of stretching the foam sheet in the MD direction, for example, the long foam sheet is cooled after foaming rather than the speed (supply speed) at which the long foamable polyolefin resin sheet is supplied to the foaming process. The method of drawing the foamed sheet in the MD direction by increasing the winding speed (winding speed) while the speed at which the foamed sheet is taken up (feeding speed) than the speed at which the obtained foamed sheet is supplied to the stretching process (feeding speed) Examples thereof include a method of stretching the foam sheet in the MD direction by increasing the winding speed.

In the former method, the foamable polyolefin resin sheet expands in the MD direction by its own foaming. Therefore, when the foamed sheet is stretched in the MD direction, the MD direction due to foaming of the foamable polyolefin resin sheet. The sheet supply speed and the winding speed can be adjusted so that the foamed sheet is stretched in the MD direction more than the expansion amount in consideration of the expansion amount.
In addition, as a method of extending the foam sheet in the CD direction, foaming is performed by gripping both ends of the foam sheet in the CD direction by a pair of gripping members and gradually moving the pair of gripping members in directions away from each other. A method of stretching the sheet in the CD direction is preferable. In addition, since the expandable polyolefin resin sheet expands in the CD direction by its own foaming, when the expanded sheet is stretched in the CD direction, the expansion in the CD direction due to the expansion of the expandable polyolefin resin sheet is reduced. In consideration, it is necessary to adjust so that the foam sheet is stretched in the CD direction more than the expansion.

  Here, if the draw ratio in the MD direction of the cross-linked polyolefin resin foam sheet is small, the flexibility and tensile strength of the cross-linked polyolefin resin foam sheet may decrease, while if large, the foam sheet is cut during the stretch. Or foaming gas escapes from the foaming sheet being foamed, and the foaming ratio is remarkably reduced, and the flexibility and tensile strength of the crosslinked polyolefin resin foamed sheet may be lowered or the quality may be uneven. 1 to 2.0 times is preferable, and 1.2 to 1.5 times is more preferable.

In addition, the draw ratio in MD direction of a crosslinked polyolefin resin foam sheet is calculated in the following manner. That is, while obtaining the third root F of the expansion ratio of the crosslinked polyolefin resin foam sheet, the ratio (winding speed / supply speed) V between the winding speed and the supply speed is determined, and the crosslinked polyolefin resin foam is calculated based on the following formula. The draw ratio in the MD direction of the sheet can be calculated. However, the expansion ratio of the cross-linked polyolefin resin foam sheet is obtained by dividing the specific gravity of the expandable polyolefin resin sheet by the specific gravity of the cross-linked polyolefin resin foam sheet.
Stretch ratio (times) in MD direction of foam sheet = V / F

In addition, if the stretch ratio in the CD direction of the crosslinked polyolefin resin foam sheet is small, the flexibility and tensile strength of the cross-linked polyolefin resin foam sheet may be reduced. On the other hand, if the stretch ratio is large, the foam sheet is cut during stretching. Or the foaming gas escapes from the foaming sheet being foamed, the expansion ratio of the resulting crosslinked polyolefin resin foam sheet is significantly reduced, and the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet are reduced. Since it may become nonuniform, 1.2 to 4.5 times are preferable and 1.5 to 3.5 times are more preferable.
In addition, the draw ratio in the CD direction of the crosslinked polyolefin resin foam sheet is the CD of the crosslinked polyolefin resin foam sheet obtained by heating and foaming the expandable polyolefin resin sheet without stretching it in the MD direction and the CD direction. The length in the direction is W ₁ , while the length in the CD direction of the crosslinked polyolefin resin foam sheet stretched in the CD direction is W ₂ and can be calculated based on the following formula.
Stretch ratio (times) in CD direction of foam sheet = W ₂ / W ₁

  The use of the cross-linked polyolefin resin foam sheet thus obtained is not particularly limited. For example, it can be used as an adhesive tape described later, or can be used for medical purposes by applying a drug to one surface of the cross-linked polyolefin resin foam sheet. Used as a patch.

[Adhesive tape]
The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer on at least one surface of the cross-linked polyolefin resin foam sheet of the present invention, and the thickness of the cross-linked polyolefin resin foam sheet is 0.05 to 2 mm. It is characterized by being.
When the thickness of the crosslinked polyolefin resin foamed sheet is less than 0.05 mm, flexibility, tensile strength, and the like are lowered, and texture and mechanical strength of the resulting adhesive tape are lowered. On the other hand, if the thickness exceeds 2 mm, the improvement of the performance of the adhesive tape cannot be expected and the production efficiency is lowered. From such a viewpoint, the thickness of the crosslinked polyolefin resin foam sheet is more preferably 0.1 to 0.8 mm.

  The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer laminated and integrated on one or both sides of the crosslinked polyolefin-based resin foam sheet is not particularly limited. For example, an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, etc. Can be used.

  As a method of applying an adhesive to at least one surface of the cross-linked polyolefin resin foamed sheet and laminating and integrating the pressure-sensitive adhesive layer, for example, an adhesive using a coater or the like is applied to at least one surface of the cross-linked polyolefin resin foamed sheet. A method of applying an adhesive, a method of spraying and applying an adhesive using a spray on at least one surface of a crosslinked polyolefin resin foam sheet, a method of applying an adhesive using a brush on at least one surface of a crosslinked polyolefin resin foam sheet, etc. Is mentioned.

  The pressure-sensitive adhesive tape of the present invention is used as a pressure-sensitive adhesive tape for absorbing irregularities on a concavo-convex surface, and prevents an impact from being applied to an electronic component incorporated in an electronic device body such as a mobile phone or a video camera. It can be used as a sealing material for electronic equipment for preventing dust and the like from entering the equipment body. Since the crosslinked polyolefin resin foam sheet of the present invention maintains excellent flexibility and heat resistance even if it is processed thinly, it can be suitably used for electronic devices that are remarkably miniaturized.

[Sealant]
The sealing material of the present invention is obtained by subjecting the adhesive tape of the present invention to slit processing or punching processing so that the width is 2 mm or less.
When the width is 2 mm or less, it is possible to reduce the width of the frame of a screen such as a small personal computer or a mobile phone, which is preferable. When this width exceeds 2 mm, it is necessary to design the width of the outer frame of the image display panel using the width, so that the screen size is restricted.

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
[Examples 1 to 3]
Linear low-density polyethylene obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (trade name “EXACT3027” manufactured by Exxon Chemical Co., Ltd., density: 0.900 g / cm ³ , melting point: 98 ° C. , Softening point: 85 ° C.) Expandable polyolefin resin composition comprising 100 parts by mass, 2 parts by mass of azodicarbonamide, 0.3 part by mass of 2,6-di-t-butyl-p-cresol and 1 part by mass of zinc oxide The product was supplied to an extruder, melted and kneaded at 130 ° C., and extruded into a long foamable polyolefin resin sheet having a width of 200 mm and a thickness of 0.3 mm.

  Next, after irradiating 7 Mrad of an electron beam with an acceleration voltage of 800 kV on both sides of the long foamable polyolefin resin sheet to crosslink the foamable polyolefin resin sheet, the foamable polyolefin resin sheet is heated with hot air and infrared rays. It was continuously fed into a foaming furnace maintained at 250 ° C. by a heater, and heated and foamed.

  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 higher 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. And it extended | stretched and deformed to MD direction, and the crosslinked polyolefin-type resin foam sheet which has the width | variety shown in Table 1, the thickness, the crosslinking degree, and an expansion ratio was obtained. 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.

[Comparative Examples 1-3]
Using 5 parts by mass of azodicarbonamide, irradiating both surfaces of the foamable polyolefin resin sheet with an acceleration voltage of 800 kV and 5 Mrad, and setting the thickness of the foamable polyolefin resin sheet to 0.8 mm A crosslinked polyolefin resin foamed sheet having the physical properties shown in Table 1 was obtained in the same manner as in the Examples except for the above. The obtained crosslinked polyolefin resin foam sheet was evaluated by the following method. The results are shown in Table 1.

[Evaluation method]
≪Tensile strength≫
A cross-linked polyolefin resin foam sheet cut to 1 mm width was used as a sample, and the tensile strength was measured at a measurement temperature of 23 ° C. according to JIS K6767.
≪Number of bubbles in 1mm width≫
The number of bubbles within 1 mm width of the crosslinked polyolefin resin foam sheet was measured as follows. That is, the cross-linked polyolefin resin foam sheet was cut along a plane including the CD direction and the MD direction (a plane perpendicular to the ZD direction) so that the thickness direction of the sheet was equally divided into two. Next, the cut surface of the cross-linked polyolefin resin foam sheet was magnified 60 times using a scanning electron microscope (SEM) and photographed. In the obtained photograph, straight lines Lcd and Lmd are drawn so that the actual length of the foamed sheet is 1 mm in the direction corresponding to the CD direction and MD direction of the crosslinked polyolefin resin foamed sheet. Next, the number of bubbles on Lcd and Lmd was visually counted, respectively, and Ncd and Nmd were obtained, respectively, and the average value was the number of bubbles of 1 mm width (number).

≪25% compressive strength≫
The 25% compressive strength was measured according to JIS K6767.
≪Heat dimensional change rate≫
The heating dimensional change rate was measured at a measurement temperature of 90 ° C. according to JIS K6767.

≪Crosslinking degree≫
The degree of crosslinking of the crosslinked polyolefin resin foam sheet was measured as follows.
About 100 mg of a test piece was taken from the crosslinked polyolefin resin foamed sheet, and the weight A (mg) of the test piece was 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 (% by mass) was calculated by the following formula.
Crosslinking degree (% by mass) = 100 × (B / A)

  As is apparent from Table 1, according to the present invention, it is possible to provide a crosslinked polyolefin resin foam sheet that is excellent in flexibility and heat resistance and can be thinned.

Claims (5)

A cross-linked polyolefin resin foam sheet obtained by cross-linking and foaming a polyolefin resin sheet obtained by extrusion molding, wherein the polyolefin resin sheet is obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. A cross-linked polyolefin resin foam sheet comprising 40% by mass or more of a polyethylene resin, wherein the cross-linked polyolefin resin foam sheet satisfies the following conditions (a) to ( f ).
<Conditions>
(A) Crosslinking degree is 5 to 60% by mass
(B) The average cell diameter in the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet is 180 μm or less, respectively. (C) Aspect ratio A (average cell diameter in the MD direction / average cell diameter in the CD direction) ) Is 0.2
5-2
(D) Aspect ratio B of bubbles (average cell diameter in CD direction / average cell diameter in thickness direction of foamed sheet (ZD)) is 2 to 18
(E) The foaming ratio of the foamed sheet is 12 cm ³ / g or less.
(F) The number of bubbles in 1 mm width in the MD direction and CD direction of the foam sheet is 8 to 20   2. The crosslinked polyolefin resin foam sheet according to claim 1, wherein the average cell diameter in the extrusion direction (MD) of the foam sheet and the width direction (CD) of the foam sheet under the condition (b) is 130 μm or less, respectively. The 25% compressive strength in accordance with JIS K6767 is 15 to ²⁰⁰ kPa, and the tensile strength in at least one direction in the MD direction or CD direction measured in accordance with JIS K6767 is 5 × 10 ² kPa or more, and JIS K6767 The cross-linked polyolefin-based resin foamed sheet according to claim 1 or 2, wherein a heating dimensional change rate in the MD direction at 90 ° C measured in accordance with the above is -10% or more.   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 0.05- Adhesive tape that is 2 mm.   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.

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