KR20180132631A - Crosslinked polyolefin resin foam sheet and manufacturing method thereof - Google Patents

Abstract

A crosslinked polyolefin resin foam sheet in which a closed cell is formed, wherein a degree of strain hardening (? Max) determined from the uniaxial extensional viscosity at a deformation rate of 0.2 to 1.0 [l / s] And the slope m of the linear region of the shear viscosity? ⁺ And the elongation time t [s] satisfies 0.7? M? 1.0 at the temperature at the time of foaming, and the average cell diameter in the MD and TD directions is 120 탆 or less, based on the total weight of the crosslinked polyolefin resin foam sheet.

Description

Crosslinked polyolefin resin foam sheet and manufacturing method thereof

The present invention relates to a crosslinked polyolefin resin foam sheet and a method for producing the same.

A screen of a small electronic device (such as a cellular phone, a camera, a game, or an electronic notebook) has a structure in which a display portion protective panel is provided on a display portion (e.g., LTD) of a box body, An adhesive tape is used.

For example, Patent Document 1 discloses a pressure-sensitive adhesive tape which is preferably applied to small-sized electronic apparatuses, and includes a crosslinked polyolefin-based resin film having a thickness of 0.05 to 2 mm, which is obtained by foaming and crosslinking a foamable polyolefin- An adhesive tape using a resin foam sheet is disclosed.

International Publication No. 2005/007731

However, in recent years, the frame portion outside the screen tends to be narrowed in order to increase the screen size and the design of the small electronic apparatus, and the tape width of the adhesive tape used in this frame portion tends to become narrow.

However, in the conventional pressure-sensitive adhesive tapes using a crosslinked polyolefin-based resin foam sheet, for example, when the width of the tape is reduced to 0.7 mm or less, sufficient strength sufficient to withstand impacts such as dropping And there is a drawback that the sheet as a base material constituting the tape tends to be broken.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a pressure-sensitive adhesive tape having sufficient strength to withstand an impact such as dropping, And to provide a crosslinked polyolefin-based resin foam sheet capable of realizing a tape.

The inventors of the present invention have conducted intensive studies in order to achieve the above object, and as a result, have found that the object can be achieved by a crosslinked polyolefin resin foam sheet having a strain hardening degree and a shear viscosity in respective specific ranges. The present invention has been accomplished based on this finding.

That is, the present invention provides the following [1] to [7].

[1] A crosslinked polyolefin resin foam sheet in which a closed cell is formed, wherein a degree of strain hardening (? Max) determined from the uniaxial stretching viscosity at a deformation rate of 0.2 to 1.0 [ And the slope m of the linear region of the shear viscosity? ⁺ And the time t [s] satisfies a relationship of 0.7? M? 1.0 at a temperature at the time of foam formation, and the average cell diameter Is 120 [micro] m or less.

[2] The crosslinked polyolefin resin foam sheet of [1], wherein the average cell diameter of ZD is 80 μm or less.

[3] A crosslinked polyolefin resin foam sheet of [1] or [2], wherein the interlaminar strength is 4.3 MPa or more and the 25% compression strength is 400 to 2000 kPa.

[4] The crosslinked polyolefin resin foam sheet according to any one of [1] to [3], wherein the thickness of the crosslinked polyolefin resin foam sheet is 0.10 mm to 0.20 mm.

[5] The crosslinked polyolefin resin foam sheet of any one of [1] to [4], wherein the polyolefin resin comprises linear low-density polyethylene obtained from a polymerization catalyst of a metallocene compound.

[6] A process for producing a polyolefin resin sheet, comprising the steps of: feeding an additive including a polyolefin resin and a thermally decomposable foaming agent to an extruder, melt kneading the same, and extruding the extrudate into a sheet form from an extruder; A step of crosslinking the polyolefin resin sheet at a degree of crosslinking of 5 mass% or more; and a step of heating the crosslinked polyolefin resin sheet to foam the thermally decomposable foaming agent to form microcells.

[7] The method for producing a crosslinked polyolefin resin foam sheet of [6], which comprises a step of stretching the microcels in one or both directions of the MD direction or the TD direction after the formation of the microcels, and stretching the microcels.

According to the present invention, there is provided a crosslinked polyolefin-based resin foam sheet capable of realizing, for example, an adhesive tape having sufficient strength to withstand an impact such as dropping even when the width of the tape is reduced to 0.7 mm or less can do.

1 is a schematic view of an impact resistance testing apparatus.
2 is an explanatory diagram of a method for measuring interlaminar strength.

[Crosslinked polyolefin resin foam sheet]

The crosslinked polyolefin resin foam sheet according to the present invention is a crosslinked polyolefin resin foam sheet obtained by subjecting a polyolefin resin processed into a sheet form to a crosslinking treatment and a foaming treatment and has a deformation rate of 0.2 to 1.0 [ s] of the linear region of the shear viscosity? ⁺ and the time t [s] at the temperature at the time of foaming is 0.1 or more and less than 0.5, and the strain hardening degree (? max) , 0.7? M? 1.0.

<Independent bubble>

The closed cell of the crosslinked polyolefin resin foam sheet preferably has an average cell diameter of MD and TD of 120 占 퐉 or less, preferably 100 占 퐉 or less, more preferably 80 占 퐉 or less, an average cell diameter of ZD of 80 占 퐉 or less, Called &quot; microcell &quot;, which is 50 m or less, and more preferably 40 m or less. The lower limit value of the average cell diameter is not particularly limited, but the average cell diameter of MD and TD is, for example, 5 占 퐉 or more, preferably 20 占 퐉 or more. The average cell diameter of ZD is, for example, 5 占 퐉 or more, and preferably 10 占 퐉 or more.

The bubble diameter is measured by the measuring method described later in the Examples.

In the present invention, the bubbles are independent bubbles means that the ratio of the independent bubbles to the total bubbles (referred to as the closed cell ratio) is 70% or more, preferably 75% or more, more preferably 90% or more.

The closed cell ratio can be obtained according to JIS K7138 (2006) or ASTM D2856 (1998). Examples of commercially available measuring instruments include a dry type auto density meter, such as AccuPeak 1330.

The closed cell ratio is measured, for example, in the following manner. From the crosslinked polyolefin resin foam sheet, a specimen having a flat square shape with a side of 5 cm and a certain thickness is cut out. 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. Then, the apparent volume V ₂ occupied by the bubbles is calculated based on the following equation. The density of the resin constituting the test piece is 1 g / cm ³ .

Apparent volume occupied by air bubbles V ₂ = V ₁ -W ₁

Subsequently, the test piece was immersed in distilled water at 23 DEG C at a depth of 100 mm from the water surface, and a pressure of 15 kPa was applied to the test piece over 3 minutes. After releasing the pressure in water, the test piece was taken out from the water to remove water adhering to the surface of the test piece, and the weight W ₂ of the test piece was measured. The open cell ratio F ₁ and the closed cell ratio F ₂ .

Open cell ratio F ₁ (%) = 100 x (W ₂ -W ₁ ) / V ₂

The closed cell ratio F ₂ (%) = 100-F ₁

<Cross-linking>

The crosslinking degree of the crosslinked polyolefin resin foam sheet is preferably from 5 to 80% by mass, and more preferably from 15 to 75% by mass. The crosslinking degree is more preferably 35 to 70% by mass. By setting the crosslinking degree to 5 mass% or more, the following strain hardening degree and shear viscosity can be realized. On the other hand, when the degree of crosslinking is less than 5% by mass, the degree of strain hardening becomes large and the elongation viscosity becomes small, so that the growth of bubbles during foaming is promoted, and the impact resistance is lowered when the foaming agent is used narrowly. From this viewpoint, the degree of crosslinking is preferably within the above-mentioned range.

The degree of crosslinking is measured by the measuring method described later in the Examples.

It is also possible to control the extensional viscosity by adding an ultra-molecular weight polymer to the resin.

<Deformation hardening degree and shear viscosity>

The degree of strain hardening (? Max) determined from the uniaxial extensional viscosity at a deformation rate of 0.2 to 1.0 [l / s] at a temperature at the time of foaming is 0.1 or more and less than 0.5 and is 0.1 to 100 [ The slope m of the linear region of the shear viscosity? ⁺ And the elongation time t [s] satisfies the relationship of 0.7? M? 1.0. By setting the strain hardening degree and m in this range, it is possible to realize a crosslinked polyolefin resin foam sheet having excellent impact resistance and interlaminar strength and having sufficient mechanical strength.

In addition, the elongation viscosity can be divided into a region that slowly increases without depending on the strain rate, and a region that sharply increases depending on the strain rate. The gently increasing region is called the linear region and the elongational viscosity is equal to three times the shear viscosity. The phenomenon that is abruptly increased is called strain hardening, and the degree of strain hardening is represented by the degree of strain hardening.

The re-wave of the crosslinked polyolefin resin foam sheet is a phenomenon which occurs when a stress is concentrated on a specific portion when an impact is applied, and from that point as a starting point. When the tape width is narrowed to 0.7 mm or less as described in the Background Art, the risk of re-waveing increases because the force applied per unit area of the tape becomes large at the time of drop impact or the like, By making m as high as the above range, the growth of bubbles at the time of foaming can be suppressed, and the strain hardening degree can be suppressed to be as low as in the above range, so that bubble growth can be stopped gently. Accordingly, the risk of re-wave due to the narrowing of the width of the tape width is reduced, and the above effect is realized.

The degree of strain hardening is measured by the measuring method described later in Examples and the shear viscosity is obtained by the method described later in the Examples.

&Lt; Thickness of crosslinked polyolefin resin foam sheet >

The thickness of the crosslinked polyolefin resin foam sheet is preferably 50 to 300 占 퐉, more preferably 70 to 150 占 퐉.

When the thickness is 50 mu m or more, the mechanical strength and flexibility of the crosslinked polyolefin resin foam sheet can be easily secured. When the thickness is set to 300 탆 or less, it is possible to form a thin film, which can be suitably used for miniaturized electronic equipment.

<Expansion ratio>

In the present invention, the expansion ratio of the crosslinked polyolefin resin foam sheet is 1.3 to 2.3 cm ³ / g. When the expansion ratio is less than 1.3 cm ³ / g, the flexibility is lowered and the impact absorbability and the like are deteriorated, so that the crosslinked polyolefin resin foam sheet may not be able to sufficiently exhibit its function as a sealing material and an impact material. On the other hand, if it is larger than 2.3 cm ³ / g, there is a possibility that the mechanical strength of the crosslinked polyolefin resin foam sheet can not be improved. In order to improve the impact absorbability and the mechanical strength of the crosslinked polyolefin resin foam sheet, the expansion ratio is more preferably 1.5 to 2.0 cm &lt; ³ &gt; / g. Further, in the present invention, the density of the foam sheet is determined in accordance with JIS K7222, and the inverse number thereof is defined as the expansion ratio.

<25% Compressive Strength>

The 25% compression strength of the crosslinked polyolefin resin foam sheet is preferably 400 to 2000 kPa, more preferably 600 to 1800 kPa. By setting the 25% compression strength to 2000 kPa or less, the crosslinked polyolefin resin foam sheet is allowed to have shock absorbing performance and can be used as a buffer material or a sealing material. The 25% compression strength refers to a value obtained by measuring a crosslinked polyolefin resin foam sheet in accordance with JIS K6767.

<Mechanical strength>

When the crosslinked polyolefin resin foam sheet has a mechanical strength of an interlaminar strength of 4.3 MPa or more and a 25% compression strength of 400 to 2000 kPa, even when the width of the tape is reduced to, for example, 0.7 mm or less, It is possible to have characteristics that can withstand. The interlaminar strength and the 25% compressive strength were measured by the measuring method described later in the Examples.

[Polyolefin Resin]

Examples of the polyolefin resin used for forming the above-described crosslinked polyolefin resin foam sheet include a polyethylene resin polymerized with a polymerization catalyst such as a chitin / Natta compound, a metallocene compound, and a chromium oxide compound, A polyethylene resin polymerized with a polymerization catalyst of a metallocene compound is used. As the polyethylene-based resin used for forming the crosslinked polyolefin resin foam sheet of the present invention, a linear low-density polyethylene obtained by copolymerizing ethylene and a small amount of -olefin, if necessary, by using a polymerization catalyst such as a metallocene compound is preferable Do. By using the linear low-density polyethylene, high flexibility can be obtained in the obtained crosslinked polyolefin resin foam sheet, and the crosslinked polyolefin resin foam sheet can be made thin.

Specific examples of the? -olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Of these,? -Olefins having 4 to 10 carbon atoms are preferred.

The density of polyethylene-based resin is, in terms of high flexibility is obtained in the produced cross-linked polyolefin resin foam sheet, 0.870 ~ 0.910g / cm ³ is preferable, and more preferable is ^{0.875 ~ 0.907g / cm 3, 0.880} ~ 0.905g / cm &lt; ³ &gt; is more preferable. As the polyethylene-based resin, a plurality of polyethylene-based resins may be used, or a polyethylene-based resin other than the above-mentioned density range may be added.

By using the straight-chain low-density polyethylene as described above, the degree of strain hardening and m can be easily made to fall within the above range.

&Lt; Metallocene compound >

Examples of the metallocene compound preferable in the present invention include compounds such as a bis (cyclopentadienyl) metal complex having a structure in which a transition metal is sandwiched by an π-electron system unsaturated compound. More specifically, there may be mentioned a compound in which one or more cyclopentadienyl rings or their analogues exist as a ligand (ligand) in a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium and platinum.

In such a metallocene compound, the properties of the active sites are uniform and each active site has the same activity. The polymer synthesized by using the metallocene compound has high uniformity such as molecular weight, molecular weight distribution, composition, composition distribution, etc. Therefore, when a sheet containing a polymer synthesized using a metallocene compound is crosslinked, . The uniformly crosslinked sheet can be stretched uniformly, so that the thickness of the crosslinked polyolefin resin foam sheet can be made uniform.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted by 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 cetyl groups, phenyl groups, and the like. The term &quot; various &quot; means various isomers including n-, sec-, tert-, and iso-.

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

In addition to the π-electron system unsaturated compound, monovalent anion ligands such as chlorine or bromine, or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, arylphosphides May be used.

Examples of the metallocene compound containing a tetravalent transition metal or ligand include cyclopentadienyl titanium tris (dimethyl amide), methyl cyclopentadienyl titanium tris (dimethyl amide), bis (cyclopentadienyl) titanium Dichloride, dimethylsilyltetramethylcyclopentadienyl-t-butylamide zirconium dichloride, and the like.

The metallocene compound exerts its action as a catalyst in the polymerization of various olefins by combining with a specific cocatalyst (cocatalyst). Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron-based compounds. The ratio of the cocatalyst to the metallocene compound is preferably 10 to 100,000 moles, more preferably 50 to 5,000 moles.

<Chigler · Natta compound>

The chigler · Natta compound is a triethylaluminum-titanium tetrachloride solid composite comprising a titanium trichloride composition obtained by reducing titanium tetrachloride with an organoaluminum compound and further treating with various electron donors and electron acceptors, A method of combining an aromatic carboxylic acid ester with a compound (see JP-A-56-100806, JP-A-56-120712, JP-A-58-104907) A method of a supported catalyst in which titanium tetrachloride is brought into contact with various electron donors (Japanese Patent Application Laid-Open No. 57-63310, Japanese Patent Application Laid-Open No. 63-43915, Japanese Patent Application Laid-Open No. 63-83116) And the like.

&Lt; Other polyolefin resins >

When the linear low density polyethylene described above is used as the polyolefin resin constituting the polyolefin resin sheet, the above linear low density polyethylene may be used singly or may contain other polyolefin resins.

Other polyolefin resins include, for example, other polyethylene-based resins such as ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene, and polypropylene-based resins. These may be used singly or in combination of two or more.

Examples of the polypropylene-based resin include polypropylene and a propylene-? -Olefin copolymer containing 50% by mass or more of propylene. These may be used singly or in combination of two or more.

Specific examples of the? -Olefin constituting the propylene-? -Olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, Of these,? -Olefins having 6 to 12 carbon atoms are preferable. When other polyolefin resins are contained, the proportion of other polyolefin resins relative to the linear low density polyethylene is preferably 40 mass% or less, more preferably 30 mass% or less, and most preferably 20 mass% or less.

[Method for producing crosslinked polyolefin resin foam sheet]

The production method of the crosslinked polyolefin resin foam sheet is not particularly limited and can be produced, for example, by a production method including the following steps (1) to (4).

Step (1)

A process for producing a polyolefin resin sheet by feeding an additive including a polyolefin resin and a thermally decomposable foaming agent to an extruder, melting and kneading the mixture, and extruding the extrudate into a sheet form

Step (2)

A step of irradiating the polyolefin resin sheet with electrolytic radiation to crosslink the foamable polyolefin resin sheet at a degree of crosslinking of 5% by mass or more

Step (3)

A step of heating the crosslinked polyolefin resin sheet to foam the thermally decomposable foaming agent to form a microcell

Step (4)

A step of stretching the microcels in either or both directions of the MD or TD direction after the formation of the microcels to obtain a crosslinked polyolefin resin foam sheet

The crosslinked polyolefin resin foam sheet can be produced by the method described in WO2005 / 007731, in addition to this method.

The thermally decomposable foaming agent is not particularly limited and includes, for example, azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, p-toluenesulfonylsemicarbazide, and the like. Of these, azodicarbonamide is preferable. The thermally decomposable foaming agent may be used alone or in combination of two or more.

The addition amount of the thermally decomposable foaming agent in the foamable polyolefin resin composition is preferably from 1 to 8 parts by mass, more preferably from 2 to 6 parts by mass, per 100 parts by mass of the polyolefin resin. When the addition amount of the thermally decomposable foaming agent is within this range, the foamability of the foamable polyolefin resin sheet is improved, and a crosslinked polyolefin resin foam sheet having a desired expansion ratio can be obtained. When the amount is 2 parts by mass or more, it becomes possible to set the thickness of the average cell wall to the same range as the objective while increasing the bubble size and increasing the average cell diameter.

The foaming method is not limited to the above, and physical foaming with butane gas or the like may be used.

The foamable polyolefin resin composition may optionally contain additives such as an antioxidant such as 2,6-di-t-butyl-p-cresol, a foaming aid such as zinc oxide, a bubble nucleus modifier, a heat stabilizer, a colorant, a flame retardant, Or the like may be added within a range that does not impair the physical properties of the crosslinked polyolefin resin foam sheet. For example, the size of the bubble diameter can be adjusted by the bubble nucleus adjusting material.

As a method of crosslinking the foamable polyolefin resin composition, a method of irradiating the foamable polyolefin resin sheet with ionizing radiation such as electron beam,? -Ray,? -Ray or? -Ray is used.

The irradiation dose of the ionizing radiation may be adjusted within a range of, for example, 2 to 75 Mrad, preferably 15 to 75 Mrad, and more preferably 30 to 70 Mrad so that the degree of crosslinking can be adjusted to 5 to 80 mass%. In some cases, it may be 2 to 15 Mrad or 3 to 12 Mrad.

The stretching of the foam sheet may be performed after foaming the foamable polyolefin resin sheet to obtain a foam sheet, or may be performed while foaming the foamable polyolefin resin sheet. When the foamed sheet is stretched after foaming the foamable polyolefin resin sheet to obtain a foamed sheet, the foamed sheet may be stretched continuously without cooling the foamed sheet while maintaining the molten state at the time of foaming, After cooling, the foam sheet may be stretched again after heating the foam sheet to melt or soften the foam sheet.

In the step (4), the stretching magnification of the crosslinked polyolefin resin foam sheet in the MD direction is preferably 1.1 to 2.0 times, more preferably 1.2 to 1.8 times.

When the stretching magnification of the crosslinked polyolefin resin foam sheet in the MD direction is set to the lower limit value or more, flexibility and tensile strength of the crosslinked polyolefin resin foam sheet tend to be improved. On the other hand, when it is not more than the upper limit, it is prevented that the foam sheet breaks during stretching, the foaming gas leaks from the foaming sheet during foaming, and the foaming magnification is remarkably lowered, and the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet become good , And it becomes easy to make the quality uniform.

[Adhesive tape]

By using a crosslinked polyolefin resin foam sheet according to the present invention as a substrate, a pressure-sensitive adhesive layer is provided on at least one surface of the crosslinked polyolefin resin foam sheet to obtain an adhesive tape.

The thickness of the pressure-sensitive adhesive layer constituting the adhesive tape is preferably 5 to 200 占 퐉. The thickness of the pressure-sensitive adhesive layer is more preferably 7 to 150 占 퐉, and still more preferably 10 to 100 占 퐉. When the thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive tape is in the range of 5 to 200 占 퐉, the thickness of the constituent fixed by using the pressure-sensitive adhesive tape can be reduced.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer which is laminated and integrated on one surface or both surfaces of the crosslinked polyolefin resin foam sheet is not particularly limited and, for example, acrylic pressure-sensitive adhesives, urethane pressure-sensitive adhesives, and rubber pressure-sensitive adhesives can be used.

Examples of the method for applying the pressure-sensitive adhesive on at least one side of the crosslinked polyolefin resin foam sheet to laminate and integrate the pressure-sensitive adhesive layer include a method of applying a pressure-sensitive adhesive on at least one side of a crosslinked polyolefin resin foam sheet using a coater such as a coater, A method of spraying and applying a pressure-sensitive adhesive on at least one surface of a resin foam sheet by spraying, a method of applying a pressure-sensitive adhesive on at least one surface of a crosslinked polyolefin resin foam sheet using a brush, and the like.

Example

The present invention will be described in more detail by way of examples, but the present invention is by no means limited by these examples.

[How to measure]

The measurement method of each property in the present specification is as follows.

<Expansion ratio>

The density of the crosslinked polyolefin resin foam sheet was measured in accordance with JIS K7222, and the inverse number was determined as the expansion ratio.

<Density>

Three sheets of 10 × 10 cm measurement samples were cut out from the crosslinked polyolefin resin foam sheet in the width direction, and the thickness and weight of each sample were measured. The arithmetic mean value of the density calculated from the weight and volume of each sample was defined as the density.

<25% Compressive Strength>

The crosslinked polyolefin resin foam sheet was measured in accordance with JIS K6767.

<Cross-linking>

About 100 mg of the test piece is taken from the crosslinked polyolefin resin foam sheet, and the weight A (mg) of the test piece is precisely weighed. Subsequently, this test piece was immersed in 30 cm ³ of xylene at 120 ° C. and left for 24 hours. Then, the test piece was filtered with a 200-mesh wire net to collect insoluble fractions on the wire net and vacuum dried to obtain the weight B Weigh. From the obtained values, degree of crosslinking (mass%) was calculated by the following formula.

Crosslinking degree (mass%) = 100 x (B / A)

<Average Bubble Diameter and Maximum Bubble Diameter>

The average cell diameter refers to a value measured in the following manner.

A foaming sheet for measurement was cut in 50 mm square and prepared as a foam sample for measurement. This was immersed in liquid nitrogen for 1 minute and then cut in the thickness direction along the MD direction, the TD direction and the ZD direction with a razor blade. This cross-section was photographed at a magnification of 200 times using a digital microscope (VHX-900, manufactured by Keyens Co., Ltd.), and the cross section was observed at a cut surface of 2 mm in length in the MD direction, the TD direction and the ZD direction The bubble diameter was measured for all the closed bubbles, and the operation was repeated five times. The average value of all the bubbles was defined as the average bubble diameter in the MD direction, the TD direction, and the ZD direction.

In addition, the length of the largest bubble among the measured bubble diameters was defined as the maximum bubble diameter.

<Deformation hardening degree and shear viscosity>

(Method of preparing measurement sample)

A polyolefin resin sheet having a thickness of 290 탆 was formed in the same manner as in Example 1, except that the thermally decomposable foaming agent was excluded. Subsequently, the obtained polyolefin resin sheet was divided and irradiated with electron beams of 4.7 Mrad, 7.4 Mrad, and 10.1 Mrad, respectively, to obtain measurement samples.

(Measurement of uniaxial elongational viscosity)

For the measurement, a viscoelasticity measuring device ARES (Rheometrics Scientific F. E) was used.

The sample was cut into a sheet having a thickness of 290 탆 in a width of 1 cm and a length of 3 cm.

The uniaxial extensional viscosity was measured at a temperature of 250 DEG C and a deformation rate of 0.3, 0.5, 1.0 (1 / s).

(Measurement of Shear Viscosity)

For the measurement, a viscoelasticity measuring device ARES (Rheometrics Scientific F. E) was used.

The sample was measured by cutting a 290 탆 thick sheet into a circle having a diameter of 8 mm and setting it on a parallel disc plate having a diameter of 8 mm.

The dynamic viscoelasticity measurement was performed under the conditions of a temperature of 250 DEG C, a deformation amount of 1%, and an angular frequency omega = 0.1 to 100 (rad / s).

(Calculation of slope m of shear viscosity)

The slope m of the shear viscosity is given by the following equation.

[Equation 1]

Here, η ⁺ is the shear viscosity and t is the time calculated using t = 1 / ω using the angular frequency ω.

(Calculation of strain hardening degree)

The strain hardening degree λmax is expressed by the following equation.

&Quot; (2) &quot;

Here, η _E is extensional viscosity, 3η ⁺ is the shear viscosity η ⁺ (t) obtained by the method described in storage elastic modulus, and for the following literature (1) for example from a loss elastic modulus obtained by measuring the shear viscosity of the non-linear region , And? Is the deformation amount.

, Masuda, Takahashi, Ono, Japanese Journal of Riolology, vol16, p117, (1988) (1)

<Impact resistance>

(Adjustment of impact resistance evaluation sample)

On both sides of the crosslinked polyolefin resin foam sheet obtained in Examples and Comparative Examples, a pressure-sensitive adhesive sheet obtained by the following method was laminated to prepare a double-sided pressure-sensitive adhesive tape based on a crosslinked polyolefin resin foam sheet.

(Production Method of Double-Sided Adhesive Tape)

75 parts by mass of butyl acrylate, 22 parts by mass of 2-ethylhexyl acrylate, 3 parts by mass of acrylic acid, 0.2 parts by mass of 2-hydroxyethyl acrylate, and 80 parts by mass of ethyl acetate were added to a reactor equipped with a thermometer, After nitrogen substitution, the reactor was heated to initiate reflux. Subsequently, 0.1 part by mass of azobisisobutyronitrile as a polymerization initiator was added to the reactor. And refluxed for 5 hours to obtain a solution of the acrylic copolymer (z). With respect to the obtained acrylic copolymer (z), the weight average molecular weight of the obtained acrylic copolymer (z) was measured by GPC method using "2690 Separations Model" manufactured by Water as a column.

15 parts by mass of polymerized rosin ester having a softening point of 135 占 폚, 125 parts by mass of ethyl acetate (manufactured by Fuji Chemical Co., Ltd.), 100 parts by mass of acrylic copolymer (z) And 2 parts by mass of an isocyanate-based crosslinking agent (Coronate L45, manufactured by Toso Co., Ltd.) were added and stirred to obtain a pressure-sensitive adhesive (Z). The acrylic pressure-sensitive adhesive had a degree of crosslinking of 33 mass%.

A releasing paper having a thickness of 150 占 퐉 was prepared and a releasing treated surface of the releasing paper was coated with a pressure-sensitive adhesive (Z) and dried at 100 占 폚 for 5 minutes to form an acrylic pressure-sensitive adhesive layer having a thickness of 50 占 퐉. This acryl pressure-sensitive adhesive layer was stuck to the surface of the base material of the crosslinked polyolefin resin foam sheet. Then, in the same manner, the same acrylic pressure-sensitive adhesive layer as above was applied to the opposite surface of the substrate made of the polyolefin foam. Thus, a double-faced pressure-sensitive adhesive tape covered with a release paper having a thickness of 150 mu m was obtained.

(Production of Impact Tester)

1 is a schematic view of an impact resistance testing apparatus.

The impact resistance testing apparatus was produced in the following order.

First, the double-faced pressure-sensitive adhesive tape obtained above was punched to have an outer diameter of 15.0 mm in width, 15.0 mm in length, 14.3 mm in inner diameter and 14.3 mm in length, and a frame-shaped test piece 1 having a width of 0.7 mm .

Subsequently, as shown in Fig. 1A, a test piece 1 having a release surface peeled off is prepared by preparing a magnesium-plated plate 3 provided with a square hole 2 at the center, On the outer circumferential side of the hole 2, as shown in Fig.

Subsequently, a glass adhered plate 4 of a size to cover the hole 2 was overlaid on the test piece 1, and the hole 2 was covered to assemble the impact resistance testing device.

Thereafter, the impact resistance testing apparatus was vertically inverted to apply a pressure of 5 kgf for 5 seconds from the side of the magnesium-made plate 3 in the state of the upper surface of the magnesium-containing plate 3 as an upper surface, The plate (3) and the test piece were pressed and allowed to stand at room temperature for 36 hours.

(Determination of impact resistance)

As shown in Fig. 1 (b), the produced impact resistance testing apparatus was fixed to a support base 5, and a steel ball having a weight of 50 g which was passed through the hole 2 formed in the magnesium- (6) was dropped through the hole (2). The height at which the steel ball is dropped is gradually increased and the height at which the steel ball is dropped when the test piece and the adherend are peeled off by the impact applied by dropping the steel ball is measured and the result of "impact resistance [cm] . The case where the impact resistance was not less than 23 cm was defined as &quot; passing: &quot;, and the case where the impact resistance was less than 23 cm was designated as &quot;

<Interlaminar Strength>

(Preparation of Sample for Interlayer Strength Measurement)

As shown in Fig. 2, a primer ("PPX primer" manufactured by Cemedine Co., Ltd.) was applied to a range of 25 mm in length and breadth of the foam sheet 7 and then an adhesive 8 &Quot; PPX &quot;, manufactured by Cemeta Inc.). Immediately thereafter, a jig 9 made of aluminum having a width of 25 mm was placed on the adhesive drop portion, and the foam sheet 7 and the jig 9 were then pressed. Thereafter, the foam sheet was cut according to the size of the jig 9. A primer was applied to the surface of the cut foam sheet 7 on which the jig 9 was not adhered, and an adhesive agent 10 having a diameter of 5 mm was dropped to the center of the application portion. Immediately thereafter, a jig 11 made of aluminum having a width of 10 mm was placed on the adhesive drop portion, and the foam sheet 7 and the jig 11 were pressed. After the adhesive agent that has been released to the periphery of the jig 11 is wiped off, the slit 12 is inserted into the foam sheet along the size of the jig 11. [ This was allowed to stand at room temperature for 30 minutes to cure the adhesive to obtain a sample for measuring the interlaminar strength.

(Determination of interlaminar strength)

Subsequently, a sample for measuring the interlaminar strength was placed on a tester (A &amp; D &amp; D &amp; tic &amp; Tencilon Universal Material Testing Machine Co., Ltd.) equipped with a 1 kN load cell so that the sheet surface of the foam sheet was perpendicular to the tensile direction. The jig 9 was pulled in the vertical direction at a speed of 100 mm / minute, and only the width of 1 cm of the foam sheet was delaminated. The maximum load at this time was measured, and the first measurement result was obtained. The same operation was repeated three times, and the average value was used as the interlaminar strength. The case where the interlaminar strength was 4.3 MPa or more was defined as &quot; Pass: &quot;, and the case where the interlaminar strength was less than 4.3 MPa was designated as &quot;

[Example 1]

Straight chain obtained by the polymerization catalysts of the metallocene compounds low-density polyethylene resin (Dow Chemical Co., trade name "Affinity PL1850", density: 0.902g / cm ³⁾ azodicarbonyl reubon amide as 100 parts by weight, the heat decomposable blowing agent 2.1 parts by mass (manufactured by Otsuka Chemical Co., Ltd., trade name &quot; SO-G3 &quot;), 0.5 part by mass of an antioxidant and 1.0 part by mass of a foam nucleating agent was supplied to an extruder, followed by melt kneading at 130 DEG C And extruded into a long polyolefin resin sheet having a thickness of 290 mu m.

Subsequently, the foamed polyolefin resin sheet was crosslinked (cross-linking degree: 41.4%) by irradiating an electron beam having an acceleration voltage of 500 kV at 7.4 Mrad on both sides of the elongated polyolefin resin sheet, and then the foamed polyolefin resin sheet was heat- ° C, and heated to obtain a foam sheet having a thickness of 300 탆.

Subsequently, the obtained foam sheet was continuously fed from a foaming furnace, and then the foam sheet was stretched at a stretching ratio of 1.5 times in the TD direction in a state where the temperature of both sides of the foam sheet was kept at 200 to 250 ° C Together, the foam sheet was stretched in the MD direction by winding the foam sheet at a winding speed faster than the feeding speed (feeding speed) of the foamable polyolefin resin sheet to the foaming furnace to stretch the foams of the foam sheet in the TD and MD directions To obtain a crosslinked polyolefin resin foam sheet. The winding speed of the foam sheet was adjusted while taking into account the expansion of the foamable polyolefin resin sheet itself in the MD direction due to foaming. The resulting crosslinked polyolefin resin foam sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

[Example 2]

Except that the irradiation dose of the electron beam was set to 10.1 Mrad and the degree of crosslinking was set to 69.1%, the same procedure as in Example 1 was carried out. The evaluation results of the obtained crosslinked polyolefin resin foam sheet are shown in Table 1.

[Comparative Example 1]

The procedure of Example 1 was repeated except that the blending amount of azodicarbonamide in the expandable polyolefin resin composition was changed to 1.6 parts by mass, the electron beam irradiation amount was set to 4.7 Mrad, and the degree of crosslinking was changed to 16.2%. The evaluation results of the obtained crosslinked polyolefin resin foam sheet are shown in Table 1.

As shown in Table 1, the strain hardening degree (? Max) determined from the uniaxial extensional viscosity at a strain rate of 0.2 to 1.0 [l / s] is 0.1 or more and less than 0.5, and the shear viscosity? ⁺ And the elongation time t [ Examples 1 and 2, in which the linear region slope m satisfies the relationship of 0.7? m? 1.0, has a higher degree of strain hardening (? max) and a lower impact resistance than the Comparative Example 1 in which m is out of the above- .

1 specimen
2 holes
3 Magnesium coated plate
4 Glass plate
5 support
6 iron ore
7 foam sheet
8 Adhesive
9 jig
10 Adhesive
11 jig
12 slits

Claims (7)

A crosslinked polyolefin resin foam sheet having formed therein a closed cell,
The strain hardening degree (? Max) determined from the uniaxial extensional viscosity at a deformation rate of 0.2 to 1.0 [l / s] at a temperature at the time of foaming is 0.1 or more and less than 0.5,
The slope m of the linear region between the shear viscosity? ⁺ And the elongation time t [s] satisfies the relationship of 0.7? M? 1.0 and the average cell diameter in the MD and TD directions is 120 占 퐉 or less , A crosslinked polyolefin resin foam sheet. The method according to claim 1,
Wherein the average cell diameter of ZD is 80 占 퐉 or less. 3. The method according to claim 1 or 2,
An interlaminar strength of 4.3 MPa or more, and a 25% compression strength of 400 to 2000 kPa. 4. The method according to any one of claims 1 to 3,
Wherein the crosslinked polyolefin resin foam sheet has a thickness of 0.10 mm to 0.20 mm. 5. The method according to any one of claims 1 to 4,
Wherein the polyolefin resin comprises a linear low density polyethylene obtained from a polymerization catalyst of a metallocene compound. A step of supplying an additive including a polyolefin resin and a thermally decomposable foaming agent to an extruder, melting and kneading the mixture, and extruding the extrudate into a sheet form to produce a polyolefin resin sheet,
Irradiating the polyolefin resin sheet with electrolytic radiation to crosslink the foamable polyolefin resin sheet at a degree of crosslinking of 5 mass% or more,
A method for producing a crosslinked polyolefin resin foam sheet, which comprises heating a crosslinked polyolefin resin sheet to foam a thermally decomposable foaming agent to form microcells. The method according to claim 6,
A step of stretching the microcels in either one or both directions of the MD direction or the TD direction after the formation of the microcels, thereby stretching the microcels.

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