KR102062297B1 - Crosslinked Polyolefin Resin Foam Sheet and Manufacturing Method Thereof - Google Patents

Abstract

A crosslinked polyolefin resin foam sheet having an independent bubble, wherein the strain hardening degree (λ max) determined from the uniaxial extensional viscosity at a strain rate of 0.2 to 1.0 [1 / s] at a temperature at the time of foam formation is 0.1 or more and less than 0.5 At the temperature at the time of foam formation, the inclination m of the linear region of the shear viscosity η ⁺ and the elongation time t [s] satisfies the relationship of 0.7 ≦ m ≦ 1.0, and the average bubble diameter in the MD direction and the TD direction is 120 Crosslinked polyolefin resin foam sheet which is micrometer or less.

Description

Crosslinked Polyolefin Resin Foam Sheet and Manufacturing Method Thereof

This invention relates to a crosslinked polyolefin resin foam sheet and its manufacturing method.

The screen of small electronic devices (mobile phones, cameras, games, electronic notebooks, etc.) has a structure in which a display unit protection panel is provided on the display unit (LTD, etc.) of the box body. In order to stick together, the adhesive tape is used.

As adhesive tape which application to a small electronic device is preferable, For example, patent document 1 has the thickness of 0.05-2 mm crosslinked polyolefin system obtained by foaming and crosslinking the foamable polyolefin resin sheet containing a thermal decomposition type foaming agent. An adhesive tape using a resin foam sheet is disclosed.

International Publication 2005/007731

By the way, in recent years, the frame part outside the screen tends to be narrow for the screen size of a small electronic device and the design improvement, and the tape width of the adhesive tape used for this frame part also tends to become narrow.

However, in the adhesive tape using the conventional crosslinked polyolefin resin foam sheet, when the tape width is processed to 0.7 mm or less, for example, the adhesive tape has sufficient strength to withstand impacts such as drops. There was a drawback that the sheet, which is the base material constituting the tape, could not be broken easily.

This invention is made | formed in view of the above situation, The subject of this invention is adhesiveness which has sufficient intensity | strength which can endure impacts, such as a fall, even when the width | variety processing is performed to tape width to 0.7 mm or less, for example. It is to provide a crosslinked polyolefin resin foam sheet which can realize a tape.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to achieve the said objective, the present inventors discovered that the objective can be achieved by the crosslinked polyolefin resin foam sheet whose strain hardening degree and shear viscosity are respectively a specific range. The present invention has been completed based on these findings.

That is, this invention provides the following [1]-[7].

[1] A crosslinked polyolefin resin foam sheet having independent bubbles formed therein, wherein a strain hardening degree (λ max) obtained from a uniaxial extensional viscosity at a strain rate of 0.2 to 1.0 [1 / s] is 0.1 at a temperature at the time of foam formation. The slope m of the linear region of the shear viscosity η ⁺ and the time t [s] satisfies the relationship of 0.7 ≦ m ≦ 1.0 at the temperature at the time of foam formation, which is less than 0.5, and the average bubble diameter in the MD direction and the TD direction The crosslinked polyolefin resin foam sheet which is 120 micrometers or less.

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

[3] The crosslinked polyolefin resin foam sheet according to [1] or [2], wherein the interlayer strength is 4.3 MPa or more and 25% compressive strength is 400 to 2000 kPa.

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

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

[6] a step of producing a polyolefin resin sheet by supplying an additive containing a polyolefin resin and a thermal decomposition foaming agent to an extruder to melt kneading and extruding the sheet into a sheet shape, and irradiating ionizing radiation to the polyolefin resin sheet The manufacturing method of crosslinked polyolefin resin foam sheet which has the process of crosslinking a polyolefin resin sheet with a crosslinking degree of 5 mass% or more, and the process of heating a crosslinked polyolefin resin sheet, foaming a thermal decomposition type foaming agent, and forming a microcell.

[7] The method for producing a crosslinked polyolefin resin foam sheet according to [6], having a step of stretching the microcell by stretching in one or both directions of the MD direction or the TD direction after forming the microcell.

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

1 is a schematic diagram of an impact resistance test apparatus.
2 is an explanatory diagram of a method for measuring interlayer strength.

[Crosslinked Polyolefin Resin Foam Sheet]

The crosslinked polyolefin resin foam sheet according to the present invention is a crosslinked polyolefin resin foam sheet in which a crosslinking treatment and a foaming treatment are performed on a polyolefin resin processed into a sheet shape, and has a strain rate of 0.2 to 1.0 [1 /] at a temperature at the time of foam formation. The strain hardening degree ((lambda) max) calculated | required from uniaxial elongation viscosity in s] is 0.1 or more and less than 0.5, and in the temperature at the time of foam formation, the slope m of the linear region of shear viscosity (eta) ⁺ and time t [s] is , 0.7 ≦ m ≦ 1.0 is satisfied.

<Independent bubble>

As for the independent bubble of crosslinked polyolefin resin foam sheet, the average bubble diameter of MD and TD is 120 micrometers or less, Preferably it is 100 micrometers or less, More preferably, it is 80 micrometers or less, The average bubble diameter of ZD is 80 micrometers or less, Preferably 50 micrometers or less, More preferably, it is what is called a "microcell" of 40 micrometers or less. In addition, although the lower limit of the average bubble diameter is not specifically limited, The average bubble diameter of MD and TD is 5 micrometers or more, Preferably it is 20 micrometers or more. In addition, the average bubble diameter of ZD is 5 micrometers or more, Preferably it is 10 micrometers or more.

In addition, bubble diameter is measured by the measuring method mentioned later in an Example column.

In the present invention, that the bubble is an independent bubble means that the ratio of the independent bubble to the total bubble (called an independent bubble rate) is 70% or more, preferably 75% or more, and more preferably 90% or more.

The independent bubble ratio can be calculated | required based on JISK7138 (2006) and ASTM D2856 (1998). In the commercially available measuring instrument, a dry automatic density meter accucu 1330 etc. are mentioned.

The independent bubble ratio is measured by the following method, for example. From the crosslinked polyolefin resin foam sheet, one side is a 5 cm planar square shape, and the test piece of constant 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. Subsequently, the apparent volume V ₂ occupied by the bubble is calculated based on the following formula. In addition, the density of resin which comprises the test piece shall be 1 g / cm <^3> .

The apparent volume occupied by the bubbles V ₂ = V ₁ -W ₁

Subsequently, the test piece is submerged in a depth of 100 mm from the surface of the water in distilled water at 23 ° C., and a pressure of 15 kPa is applied to the test piece over 3 minutes. After releasing the pressure in water, the test piece was taken out of the water to remove moisture adhering to the surface of the test piece, the weight W ₂ of the test piece was measured, and the continuous bubble rate F ₁ and the independent bubble rate F ₂ were determined according to the following equation. Calculate.

Continuous Bubble Rate F ₁ (%) = 100 × (W ₂ -W ₁ ) / V ₂

Independent bubble ratio F ₂ (%) = 100-F ₁

<Bridge>

It is preferable that it is 5-80 mass%, and, as for the crosslinking degree of crosslinked polyolefin resin foam sheet, it is more preferable that it is 15-75 mass%. Moreover, as for crosslinking degree, it is more preferable that it is 35-70 mass%. By setting the crosslinking degree to 5% by mass or more, the following strain hardening degree and shear viscosity can be realized. On the other hand, when crosslinking degree is less than 5 mass%, strain hardening degree becomes large, elongation viscosity becomes small, bubble growth at the time of foaming is accelerated | stimulated, and impact resistance falls when used narrowly. In view of this, the degree of crosslinking is preferably within the above range.

In addition, a crosslinking degree is measured by the measuring method mentioned later in an Example column.

In addition, it is also possible to control the elongational viscosity by adding the ultra-molecular weight polymer to the resin.

<Strain Hardness and Shear Viscosity>

At the temperature at the time of foam formation, the strain hardening degree ((lambda) max) calculated | required from uniaxial elongation viscosity in strain rate 0.2-1.0 [1 / s] is 0.1 or more and less than 0.5, and in time 0.1-100 [s]. The shear viscosity η ⁺ and the slope m of the linear region of the elongation time t [s] satisfy a relationship of 0.7 ≦ m ≦ 1.0. By setting the strain hardening degree and m in this range, the crosslinked polyolefin resin foam sheet having excellent impact resistance and interlaminar strength and having sufficient mechanical strength can be realized.

In addition, the elongational viscosity can be divided into a region that gradually increases without depending on the strain rate and a region that rapidly increases depending on the strain rate. The slowly increasing region is called a linear region and the extensional viscosity is equal to three times the shear viscosity. The rapidly increasing phenomenon is called strain hardening, and the degree is shown by strain hardening.

The rewave of the crosslinked polyolefin resin foam sheet is a phenomenon in which stress is concentrated in a specific portion when an impact is applied and occurs from that point. When the tape width is narrowed down to 0.7 mm or less as described in the Background Art section, the force applied per unit area of the tape increases at the time of impact of dropping, so the risk of breaking is increased. By increasing m as in the above range, the growth of bubbles at the time of foaming is suppressed, and the growth of bubbles is suppressed as low as the above range. This reduces the risk of re-wave due to narrowing the tape width and realizes the above effects.

In addition, strain hardening degree is measured by the measuring method mentioned later in an Example column, and shear viscosity is calculated | required by the method mentioned later in an Example column.

<Thickness of crosslinked polyolefin resin foam sheet>

It is preferable that it is 50-300 micrometers, and, as for the thickness of crosslinked polyolefin resin foam sheet, it is more preferable that it is 70-150 micrometers.

When thickness is 50 micrometers or more, securing mechanical strength and flexibility of a crosslinked polyolefin resin foam sheet becomes easy. Moreover, when thickness is 300 micrometers or less, thin film becomes possible and can be used suitably for a miniaturized electronic device.

<Foam ratio>

In the present invention, the expansion ratio of the crosslinked polyolefin resin foam sheet is 1.3 to 2.3 cm ³ / g. If the foaming ratio is less than 1.3 cm ³ / g, the flexibility decreases, the shock absorbency and the like deteriorate, and the crosslinked polyolefin resin foam sheet may not be able to sufficiently exhibit the functions as the sealing material and the impact material. On the other hand, when larger than 2.3 cm <^3> / g, there exists a possibility that the mechanical strength of a crosslinked polyolefin resin foam sheet may not become favorable. In order to improve the shock absorbency and mechanical strength of a crosslinked polyolefin resin foam sheet, 1.5-2.0 cm <^3> / g of foaming ratio is more preferable. In addition, in this invention, the density of foam seat | seet is calculated | required according to JISK7222, and the reciprocal is made into foaming ratio.

<25% compressive strength>

It is preferable that it is 400-2000 kPa, and, as for 25% compressive strength of crosslinked polyolefin resin foam sheet, 600-1800 kPa is more preferable. By setting the 25% compressive strength to 2000 kPa or less, the crosslinked polyolefin resin foam sheet has a shock absorbing performance and can be used as a cushioning material or a sealing material. In addition, 25% compressive strength says what measured the crosslinked polyolefin resin foam sheet based on JISK6767.

<Mechanical strength>

When the crosslinked polyolefin resin foam sheet has a mechanical strength of interlaminar strength of 4.3 MPa or more and 25% compressive strength of 400 to 2000 kPa, even when the width of the tape is narrowed down to, for example, 0.7 mm or less, impact such as dropping may occur. It can be equipped with the property which can endure. In addition, interlayer strength and 25% compressive strength are respectively measured by the measuring method mentioned later in an Example column.

[Polyolefin resin]

As polyolefin resin used for formation of the above-mentioned crosslinked polyolefin resin foam sheet, polyethylene-type resin superposed | polymerized by polymerization catalysts, such as a Ziegler-Natta compound, a metallocene compound, and a chromium oxide compound, is mentioned, Preferably, Polyethylene resin polymerized as a polymerization catalyst of a metallocene compound is used. As polyethylene-type resin used for formation of the crosslinked polyolefin resin foam sheet of this invention, linear low-density polyethylene obtained by copolymerizing ethylene and a small amount of alpha-olefins as needed using polymerization catalysts, such as a metallocene compound, is preferable. Do. By using linear low-density polyethylene, while high flexibility is obtained for the crosslinked polyolefin resin foam sheet obtained, the crosslinked polyolefin resin foam sheet can be thinned.

Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Especially, the C4-10 alpha-olefin is preferable.

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 ³ is more preferred. As polyethylene-type resin, some polyethylene-type resin can also be used and polyethylene-type resin other than the said density range may be added.

By using the linear low density polyethylene as mentioned above, it becomes easy to carry out strain hardening degree and m in the said range.

<Metallocene compound>

As a preferable metallocene compound in this invention, compounds, such as the bis (cyclopentadienyl) metal complex which has a structure which interposed the transition metal by (pi) electron type unsaturated compound, are mentioned. More specifically, the compound in which 1 or 2 or more cyclopentadienyl ring or its analog exists in tetravalent transition metals, such as titanium, zirconium, nickel, palladium, hafnium, and platinum, as a ligand (ligand) is mentioned.

Such a metallocene compound has the property of an active point uniform, and each active point has the same activity. Since the polymer synthesize | combined using the metallocene compound has high uniformity of molecular weight, molecular weight distribution, a composition, a composition distribution, etc., when it crosslinks the sheet | seat containing the polymer synthesize | combined using a metallocene compound, it bridge | crosslinks. Proceeds uniformly. Since the uniformly crosslinked sheet can be stretched uniformly, the thickness of the crosslinked polyolefin resin foam sheet can be made uniform.

As a ligand, a cyclopentadienyl ring, an indenyl ring, etc. are mentioned, for example. 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 methyl group, 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, various decyl groups, Various cetyl group, a phenyl group, etc. are mentioned. In addition, "various" means various isomers containing n-, sec-, tert-, and iso-.

Moreover, you may use what superposed | polymerized the cyclic compound as an oligomer as a ligand.

In addition to π-electron unsaturated compounds, monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, phosphides, and arylphosphides may be used. do.

As a metallocene compound containing a tetravalent transition metal and a ligand, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium Dichloride, dimethyl silyl tetramethyl cyclopentadienyl t-butylamide zirconium dichloride, etc. are mentioned.

By combining with a specific cocatalyst (cocatalyst), a metallocene compound exhibits an effect | action as a catalyst at the time of superposition | polymerization of various olefins. As a specific cocatalyst, methyl aluminoxane (MAO), a boron type compound, etc. are mentioned. Moreover, as for the use ratio of the cocatalyst with respect to a metallocene compound, 10-1 million mole times are preferable, and 50-5,000 mole times are more preferable.

<Ziegler-Natta compound>

The Ziegler-Natta compound is a triethylaluminum tetrachloride solid composite, a titanium trichloride composition obtained by reducing titanium tetrachloride with an organoaluminum compound, and further treated with various electron donors and electron acceptors, and organoaluminum To a compound and an aromatic carboxylic acid ester (see Japanese Patent Application Laid-Open No. 56-100806, Japanese Patent Application Laid-Open No. 56-120712, and Japanese Patent Application Laid-open No. 58-104907), and magnesium halide Method of supported catalyst for contacting titanium tetrachloride and various electron donors (see Japanese Patent Application Laid-Open No. 57-63310, Japanese Patent Application Laid-Open No. 63-43915, Japanese Patent Application Laid-Open No. 63-83116) It is preferable that it is made by the like.

<Other polyolefin resin>

When the above-mentioned linear low density polyethylene is used, the polyolefin resin which comprises a polyolefin resin sheet may use said linear low density polyethylene independently, but may contain other polyolefin resin.

As another polyolefin resin, other polyethylene resins, such as ethylene-vinyl acetate copolymer containing 50 mass% or more of ethylene, polypropylene resin, etc. are mentioned, for example. These may be used individually by 1 type and may use 2 or more types together.

As polypropylene resin, the propylene-alpha-olefin copolymer etc. which contain 50 mass% or more of polypropylene and propylene are mentioned, for example. These may be used individually by 1 type and may use 2 or more types together.

Specific 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, C6-C12 alpha-olefin is preferable. When it contains another polyolefin resin, 40 mass% or less is preferable, as for the ratio of the other polyolefin resin with respect to linear low density polyethylene, 30 mass% or less is more preferable, and its 20 mass% or less is more preferable.

[Manufacturing method of crosslinked polyolefin resin foam sheet]

There is no restriction | limiting in particular in the manufacturing method of crosslinked polyolefin resin foam sheet, For example, it can manufacture by the manufacturing method containing the following process (1)-(4).

Process (1)

A process for producing a polyolefin resin sheet by supplying an additive containing a polyolefin resin and a thermal decomposition foaming agent to an extruder to melt kneading, and extruding the sheet into a sheet shape from the extruder.

Process (2)

Irradiating the polyolefin resin sheet with ionizing radiation to crosslink the expandable polyolefin resin sheet with a crosslinking degree of 5% by mass or more

Process (3)

The process of heating a crosslinked polyolefin resin sheet, foaming a thermal decomposition foaming agent, and forming a microcell

Process (4)

After formation of a microcell, the process of extending | stretching in any one or both directions of a MD direction or a TD direction, extending | stretching a microcell, and obtaining a crosslinked polyolefin resin foam sheet

Moreover, as a manufacturing method of a crosslinked polyolefin resin foam sheet, it can manufacture by the method of WO2005 / 007731 other than this method.

There is no restriction | limiting in particular as a thermal decomposition type foaming agent, For example, azodicarbonamide, N, N'- dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide etc. are mentioned. Among these, azodicarbonamide is preferable. In addition, a thermal decomposition type foaming agent may be used individually by 1 type, and may use 2 or more types together.

1-8 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, 2-6 mass parts is more preferable. If the addition amount of a thermal decomposition type foaming agent is in this range, the foamability of a foamable polyolefin resin sheet improves, and the crosslinked polyolefin resin foam sheet which has a desired foaming ratio can be obtained. Moreover, by setting it as 2 mass parts or more, a bubble becomes large and it becomes possible to set the thickness of an average cell wall in the same range as the objective, increasing an average bubble diameter.

In addition, as a foaming method, it is not limited to the above, You may use physical foaming by butane gas etc ..

In the foamable polyolefin resin composition, an antioxidant such as 2,6-di-t-butyl-p-cresol, a foaming aid such as zinc oxide, a bubble nucleus regulator, a heat stabilizer, a colorant, a flame retardant, an antistatic agent, a filler Etc. may be added in the range which does not impair the physical property of a crosslinked polyolefin resin foam sheet. For example, the size of bubble diameter can be adjusted with a bubble core adjustment material.

As a method of crosslinking a foamable polyolefin resin composition, the method of irradiating ionizing radiation, such as an electron beam, (alpha) rays, (beta) rays, (gamma) rays, is used for a foamable polyolefin resin sheet.

What is necessary is just to adjust within the range of 2-75 Mrad, for example, so that the irradiation amount of the said ionizing radiation can adjust the crosslinking degree to 5-80 mass%, It is preferable that it is 15-75 Mrad, and it is more preferable that it is 30-70 Mrad. In addition, depending on the case, 2-15 Mrad may be sufficient and 3-12 Mrad may be sufficient.

Stretching of a foam sheet may be performed after foaming a foamable polyolefin resin sheet, and obtaining a foam sheet, and you may carry out foaming a foamable polyolefin resin sheet. In addition, after foaming a foamable polyolefin resin sheet and obtaining a foamed sheet, when extending | stretching a foamed sheet, you may extend | stretch a foamed sheet continuously, maintaining the molten state at the time of foaming without cooling a foamed sheet, After cooling, the foam sheet may be stretched again after heating the foam sheet to a molten or softened state.

In process (4), 1.1-2.0 times are preferable and, as for the draw ratio in MD direction of a crosslinked polyolefin resin foam sheet, 1.2-1.8 times are more preferable.

When the draw ratio in MD direction of a crosslinked polyolefin resin foam sheet is more than the said lower limit, the flexibility and tensile strength of a crosslinked polyolefin resin foam sheet will become easy to become favorable. On the other hand, when it is below an upper limit, foam seat | seet is broken during extending | stretching, foaming gas leaks out from foam seat | seat during foaming, and foaming magnification is prevented from falling remarkably, and the flexibility and tensile strength of crosslinked polyolefin resin foam sheet become favorable. The quality is also easy to be uniform.

[Adhesive tape]

Using the crosslinked polyolefin resin foam sheet which concerns on this invention as a base material, an adhesive layer can be provided in at least one surface of a crosslinked polyolefin resin foam sheet, and an adhesive tape can be obtained.

It is preferable that the thickness of the adhesive layer which comprises an adhesive tape is 5-200 micrometers. The thickness of an adhesive layer becomes like this. More preferably, it is 7-150 micrometers, More preferably, it is 10-100 micrometers. When the thickness of the adhesive layer which comprises an adhesive tape is a range of 5-200 micrometers, the thickness of the structure fixed using the adhesive tape can be made thin.

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

As a method of apply | coating an adhesive to at least one surface of a crosslinked polyolefin resin foam sheet, and laminating | solidizing an adhesive layer, for example, the method of apply | coating an adhesive using at least one surface of a crosslinked polyolefin resin foam sheet using a coating machine, such as a coater, and a crosslinked polyolefin The method of spraying and apply | coating an adhesive to at least one surface of a resin foam sheet using a spray, The method of apply | coating an adhesive using at least one surface of a crosslinked polyolefin resin foam sheet using a brush, etc. are mentioned.

Example

Although this invention is demonstrated in detail to an Example, this invention is not limited at all by these examples.

[How to measure]

The measuring method of each physical property in this specification is as follows.

<Foam ratio>

About the crosslinked polyolefin resin foam sheet, density was measured based on JISK7222, and the reciprocal was made into foaming ratio.

<Density>

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

<25% compressive strength>

It measured based on JISK6767 about crosslinked polyolefin resin foam sheet.

<Bridge>

About 100 mg of test piece is extract | collected from a crosslinked polyolefin resin foam sheet, and the weight A (mg) of a test piece is weighed precisely. Subsequently, the test piece was immersed in xylene 30 cm ³ at 120 ° C. and left to stand for 24 hours. After filtering with a 200 mesh wire mesh, the insoluble fraction on the wire mesh was collected and vacuum dried to precisely weigh the weight B (mg) of the insoluble fraction. To be weighed. From the obtained value, the crosslinking degree (mass%) was computed by the following formula.

Degree of crosslinking (mass%) = 100 × (B / A)

<Average bubble diameter, and maximum bubble diameter>

An average bubble diameter says what was measured with the following method.

What cut the foam seat | seet for measurement in 50 mm square was prepared as the foam sample for a measurement. After soaking this in liquid nitrogen for 1 minute, it cut | disconnected in the thickness direction with the razor blade along the MD direction, TD direction, and ZD direction, respectively. This section is taken using a digital microscope (VHX-900 manufactured by Keyence Co., Ltd.) to take an enlarged picture of 200 times, and exists on a cut surface of length 2mm in each of the MD direction, the TD direction, and the ZD direction. Bubble diameters were measured for all independent bubbles, and the operation was repeated five times. And the average value of all the bubbles was made into the average bubble diameter of MD direction, TD direction, and ZD direction.

In addition, the largest bubble diameter was made into the largest bubble length among the measured bubble diameters.

<Strain Hardness and Shear Viscosity>

(How to make a measurement sample)

A polyolefin resin sheet having a thickness of 290 μm was molded in the same manner as in Example 1 except that the thermal decomposition foaming agent was excluded. Next, the obtained polyolefin resin sheet was divided | segmented, the electron beam of 4.7 Mrad, 7.4 Mrad, and 10.1 Mrad was irradiated, respectively, and the measurement sample was obtained.

(Measurement of Uniaxial Elongation Viscosity)

The viscoelasticity measuring instrument ARES (made by Rheomatic Scientific F, E company) was used for the measurement.

The sample cut the sheet | seat of thickness 290 micrometers into width 1cm, length 3cm.

Uniaxial extensional viscosity was measured by the static deformation of the temperature of 250 degreeC, strain rate 0.3, 0.5, and 1.0 (1 / s).

(Measurement of Shear Viscosity)

The viscoelasticity measuring instrument ARES (made by Rheomatic Scientific F, E company) was used for the measurement.

The sample cut | disconnected the sheet | seat of 290 micrometers thickness in circular shape of diameter 8mm, and measured by setting on the parallel disk plate of diameter 8mm.

Dynamic viscoelasticity measurement was performed on conditions of the temperature of 250 degreeC, 1% of deformation amount, and each frequency (omega) = 0.1-100 (rad / s).

(Calculation of the slope m of the shear viscosity)

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

[Equation 1]

Here, η ⁺ is the shear viscosity, and t is the time calculated as t = 1 / ω using the respective frequencies ω.

(Calculation of Strain Hardness)

Strain hardening degree (lambda) max is represented by a following formula.

[Equation 2]

Here, η _E is the elongational viscosity in the nonlinear region, and 3η ⁺ is the shear viscosity η ⁺ (t) determined from the storage modulus and loss modulus obtained by the shear viscosity measurement, for example, by the method described in the following document (1). The elongational viscosity, ε, of the linearity calculated from is the amount of deformation.

Lee, Masuda, Takahashi, Ono, Japan Society of Rheology, vol16, p117, (1988) (1)

<Impact resistance>

(Adjustment of impact resistance sample)

The adhesive sheet obtained by the following method was laminated | stacked on both surfaces of the crosslinked polyolefin resin foam sheet obtained by the Example and the comparative example, and the double-sided adhesive tape of a crosslinked polyolefin resin foam sheet base material was created.

(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 in a reactor equipped with a thermometer, a stirrer and a cooling tube After addition and nitrogen replacement, the reactor was heated to reflux. Subsequently, 0.1 mass part of azobisisobutyronitrile was added to the said reactor as a polymerization initiator. It was refluxed for 5 hours, and the solution of acrylic copolymer (z) was obtained. About the obtained acrylic copolymer (z), it was 600,000 when the weight average molecular weight was measured by GPC method using "2690 Separations Model" made by Water Corporation as a column.

15 mass parts of polymerization rosin ester of softening point 135 degreeC, 125 mass parts of ethyl acetate (made by Fuji Chemicals Co., Ltd.) with respect to 100 mass parts of solid content of the acrylic copolymer (z) contained in the solution of the obtained acrylic copolymer (z), 2 mass parts of isocyanate type crosslinking agents (The Toso Corporation make, Coronate L45) were added, and the adhesive (Z) was obtained by stirring. In addition, the crosslinking degree of the acrylic adhesive was 33 mass%.

A release adhesive paper having a thickness of 150 μm was prepared, an adhesive (Z) was applied to the release treatment surface of the release paper, and dried at 100 ° C. for 5 minutes to form an acrylic adhesive layer having a thickness of 50 μm. This acrylic adhesive layer was bonded to the surface of a crosslinked polyolefin resin foam sheet base material. Subsequently, in the same manner, the same acrylic pressure-sensitive adhesive layer was bonded to the surface of the substrate made of the polyolefin foam. This obtained the double-sided adhesive tape covered with the release paper of thickness 150micrometer.

(Production of impact resistance test apparatus)

The schematic diagram of the impact resistance test apparatus is shown in FIG.

The impact resistance test apparatus was produced in the following procedures.

First, the double-sided adhesive tape obtained above was punched out such that the outer diameter was 15.0 mm wide, 15.0 mm long, and the inner diameter was 14.3 mm wide and 14.3 mm long, and the frame-shaped test piece 1 having a width of 0.7 mm was formed. Made.

Subsequently, as shown to Fig.1 (a), the magnesium to-be-adhered plate 3 which provided the square hole 2 in the center was prepared, and the test piece 1 which peeled off the release paper was made into the magnesium-attached plate 3 ), And adhered over the entire circumference of the outer circumferential side of the hole 2.

Next, the glass adhesion plate 4 of the size which coat | covers the said hole 2 was piled up on the test piece 1, and the said hole 2 was covered and the impact resistance test apparatus was assembled.

Thereafter, the impact resistance test apparatus is vertically inverted, and in a state where the magnesium deposition plate 3 is placed on the upper surface, a pressure of 5 kgf is applied for 5 seconds from the magnesium deposition plate 3 side, and the magnesium deposition is placed up and down. The board 3 and the test piece were crimped and left to stand at room temperature for 36 hours.

(Judgment of impact resistance)

As shown in Fig. 1 (b), the manufactured impact resistance test apparatus is fixed to the support table 5, and a steel ball having a weight of 50 g having a size passing through the hole 2 formed in the magnesium plate 3 The ball 6 was dropped to pass through the hole 2. The height of dropping the steel balls was gradually increased, and the height of dropping the steel balls when the test piece and the adherend were peeled off by the impact applied by the dropping of the steel balls was measured, and the result of "impact resistance [cm] at 0.7 mm width '' was measured. Got. The case where impact resistance was 23 cm or more was made into "pass: (circle)", and the case of less than 23 cm was made into "failed: x."

<Interlayer Strength>

(Production of Sample for Interlayer Strength Measurement)

As shown in FIG. 2, after apply | coating a primer ("PPX primer" by Semedane Co., Ltd.) to the 25-mm-width range of the foam sheet 7, the adhesive agent 8 for diameter 5mm in the center of an application part ( "PPX" made by Semedin Corporation was dropped. Immediately thereafter, a 25 mm aluminum jig 9 was placed in the adhesive dropping portion, and the foam sheet 7 and the jig 9 were crimped. Thereafter, the foam sheet was cut according to the size of the jig 9. The primer was apply | coated to the surface in which the jig 9 of the cut foam sheet 7 was not adhere | attached, and the adhesive 10 for diameter 5mm was dripped at the center of the application | coating part. Immediately thereafter, a 10 mm aluminum jig 11 was placed on the adhesive dropping portion, and the foam sheet 7 and the jig 11 were crimped. After wiping the adhesive protruding around the jig 11, the slit 12 was placed in the foam sheet along the size of the jig 11. The adhesive was cured by leaving this to stand at room temperature for 30 minutes to obtain a sample for measuring the interlaminar strength.

(Determination of interlayer strength)

Subsequently, the sample for interlayer strength measurement was attached to the tester provided with the 1 kN load cell (A & D Co., Ltd. "Tensilon Universal Testing Machine") so that the sheet surface of the foam sheet was perpendicular to the tensile direction. The jig 9 was pulled in the vertical upward direction at a speed of 100 mm / min, and only the range of 1 cm in length and width of the foam sheet was exfoliated. The maximum load at this time was measured and set as the first measurement result. The same operation was repeated three times, and the average value was made into interlayer strength. The case where interlaminar strength was 4.3 Mpa or more was made into "pass: o", and the case of less than 4.3 Mpa was made into "failed: x."

Example 1

100 parts by mass of linear low density polyethylene resin (manufactured by Dow Chemical Company, trade name "Affinity PL1850", Density: 0.902 g / cm ³ ) obtained by a polymerization catalyst of a metallocene compound, and azodicarbonamide as a thermal decomposition foaming agent The foamed polyolefin resin composition composed of 2.1 parts by mass (Otsuka Chemical Co., Ltd., trade name "SO-G3"), 0.5 parts by mass of antioxidant and 1.0 parts by mass of the bubble core modifier was fed to an extruder and melt-kneaded at 130 ° C. It extruded into the elongate polyolefin resin sheet of 290 micrometers.

Subsequently, after irradiating 7.4 Mrad of the electron beam of an acceleration voltage of 500 kV to both surfaces of the said elongate polyolefin resin sheet, the foamed polyolefin resin sheet was crosslinked (crosslinking degree of 41.4%), and then the foamed polyolefin resin sheet was heated by hot air and an infrared heater. It was continuously sent to a foaming furnace held at 0 ° C. and heated to obtain a foam sheet having a thickness of 300 μm.

Subsequently, after the obtained foam sheet was continuously sent out from the foam furnace, the foam sheet was stretched at a draw ratio of 1.5 times in the TD direction while maintaining the foam sheet at a temperature of 200 to 250 ° C. on both sides thereof. At the same time, the foam sheet is stretched in the MD direction by winding the foam sheet at a winding speed faster than the sending speed (feeding speed) of the foamed polyolefin resin sheet to the foam furnace, and the bubbles of the foam sheet are stretched and deformed in the TD direction and the MD direction. A crosslinked polyolefin resin foam sheet was obtained. In addition, the winding speed of the said foam seat | seet was adjusted, taking into account the expansion content to MD direction by foaming of foamable polyolefin resin sheet itself. The obtained crosslinked polyolefin resin foam sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

Example 2

It carried out similarly to Example 1 except having an electron beam irradiation amount of 10.1 Mrad and a crosslinking degree of 69.1%. Table 1 shows the evaluation results of the obtained crosslinked polyolefin resin foam sheet.

Comparative Example 1

It carried out similarly to Example 1 except having set the compounding quantity of the azodicarbonamide in foamable polyolefin resin composition to 1.6 mass parts, the electron beam irradiation amount to 4.7 Mrad, and the crosslinking degree to 16.2%. Table 1 shows the evaluation results of the obtained crosslinked polyolefin resin foam sheet.

As shown in Table 1, the strain hardening degree ((lambda) max) calculated | required from uniaxial elongation viscosity in strain rate 0.2-1.0 [1 / s] is 0.1 or more and less than 0.5, and shear viscosity (eta) ⁺ and elongation time t [ Examples 1 and 2 in which the slope m of the linear region of s] satisfies the relationship of 0.7 ≦ m ≦ 1.0 have a higher impact resistance and interlaminar strength than Comparative Example 1 in which the strain hardening degree (λ max) and m are outside the above ranges. Was found to be excellent.

1 test piece
2 holes
3 magnesium plate
4 glass mounting plate
5 support
6 iron ball
7 foam sheet
8 glue
9 jig
10 glue
11 jig
12 slits

Claims (7)

A crosslinked polyolefin resin foam sheet having independent bubbles formed thereon,
At the temperature at the time of foam formation, the strain hardening degree ((lambda) max) calculated | required from uniaxial elongation viscosity in strain rate 0.2-1.0 [1 / s] is 0.1 or more and less than 0.5,
At the temperature at the time of foam formation, the slope m of the linear region between the shear viscosity η ⁺ and the elongation time t [s] satisfies the relationship of 0.7 ≦ m ≦ 1.0, and the average bubble diameter in the MD direction and the TD direction is 120 μm or less And a crosslinking degree of 41.4 mass% or more and 80 mass% or less. The method of claim 1,
Crosslinked polyolefin resin foam sheet whose average bubble diameter of ZD is 80 micrometers or less. The method according to claim 1 or 2,
The crosslinked polyolefin resin foam sheet having an interlaminar strength of 4.3 MPa or more and 25% compressive strength of 400 to 2000 kPa. The method according to claim 1 or 2,
Crosslinked polyolefin resin foam sheet whose thickness of crosslinked polyolefin resin foam sheet is 0.10 mm-0.20 mm. The method according to claim 1 or 2,
Crosslinked polyolefin resin foam sheet in which the said polyolefin resin is equipped with linear low density polyethylene obtained from the polymerization catalyst of a metallocene compound. A process of producing a polyolefin resin sheet by supplying an additive containing a polyolefin resin and a thermal decomposition type blowing agent to an extruder to melt kneading and extruding the sheet into a sheet shape from the extruder;
Irradiating the polyolefin resin sheet with ionizing radiation to crosslink the expandable polyolefin resin sheet with a crosslinking degree of 5% by mass to 80% by mass, and
The manufacturing method of a crosslinked polyolefin resin foam sheet which has the process of heating a crosslinked polyolefin resin sheet, foaming a thermal decomposition type foaming agent, and forming a microcell. The method of claim 6,
A method for producing a crosslinked polyolefin resin foam sheet, which has a step of stretching the microcell by stretching in any one or both directions of the MD direction or the TD direction after forming the microcell.

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