JPWO2018062514A1 - Polyolefin-based foam sheet, method for producing the same and adhesive tape - Google Patents

Abstract

The polyolefin foam sheet of the present invention is a polyolefin foam sheet containing a polyolefin resin and having a crosslinked foamable composition foamed, and the average molecular weight between crosslinking points in the foamable composition is 15,000 to 30,000. It is. According to the present invention, it is possible to provide a foamed sheet having high flexibility and durability even when the sheet is thinned.

Description

  The present invention relates to a polyolefin foam sheet, a method for producing the same, and a pressure-sensitive adhesive tape having the polyolefin foam sheet.

In electronic devices such as mobile phones, cameras, game machines, electronic notebooks, personal computers and the like, a sealing material or an impact absorbing material made of a foam sheet, and further, an adhesive tape using a foam sheet as a substrate is used. For example, the display device used in the electronic device described above generally has a structure in which a protective panel is installed on a display panel such as an LCD, but the protective panel is bonded to a frame portion outside the display panel. For this purpose, an adhesive tape based on a foamed sheet is used.
Conventionally, as a foam sheet used inside an electronic device, a crosslinked polyolefin resin foam sheet obtained by foaming and crosslinking a foamable polyolefin resin sheet containing a thermal decomposition-type foaming agent is known (for example, a patent) Reference 1).

International Publication No. 2005/007731

  By the way, recently, while the miniaturization of electronic devices is progressing, the functionalization of various parts is also advancing, and the restriction of the space inside the electrical devices is becoming larger. For example, in the frame portion on the outer side of the display panel, the space is narrowed due to the miniaturization of electronic devices and the enlargement of display devices. Therefore, foam sheets are required not only to be relatively thick but also to have high flexibility and durability even when thinned.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a foamed sheet having high flexibility and durability even when the sheet is made thin.

The present invention provides the following [1] to [10].
[1] A polyolefin foam sheet comprising a polyolefin resin and having a crosslinked foamable composition foamed, the polyolefin foam sheet having an average molecular weight between crosslinking points in the foamable composition of 15,000 to 30,000. .
[2] The polyolefin foam sheet according to the above [1], wherein the polyolefin resin is a polyethylene resin.
[3] The polyolefin foam sheet according to the above [2], wherein the polyolefin resin is a linear low density polyethylene polymerized with a polymerization catalyst of a metallocene compound.
[4] The polyolefin foam sheet according to any one of the above [1] to [3], which has a crosslinking degree of 20 to 70% by mass.
[5] The polyolefin foam according to any one of the above [1] to [4], wherein the impact resistance evaluation result is in the range of 25 to 50 cm and the 25% compressive strength is 10 to 2,000 kPa. Sheet.
[6] The polyolefin foam sheet according to any one of the above [1] to [5], having a thickness of 0.02 to 0.8 mm.
[7] The polyolefin foam sheet according to any one of the above [1] to [6], which has an expansion ratio of 1.2 to 8 cm ³ / g.
[8] The polyolefin foam sheet according to any one of the above [1] to [7], which is formed by foaming a foamable composition further containing a thermal decomposition-type foaming agent.
[9] A method for producing a polyolefin foam sheet according to any one of the above [1] to [8], which is a foamable composition containing a polyolefin resin and a thermal decomposition-type foaming agent, and being crosslinked. The manufacturing method of the polyolefin-type foam sheet which heats and foams the said thermal decomposition type foaming agent.
[10] A pressure-sensitive adhesive tape comprising the polyolefin foam sheet according to any one of the above [1] to [8] and a pressure-sensitive adhesive layer provided on at least one surface of the polyolefin foam sheet.

  According to the present invention, it is possible to provide a foamed sheet having high flexibility and durability even when the sheet is thinned.

It is a schematic diagram of an impact resistance test device. It is explanatory drawing of the interlayer strength measurement method.

Hereinafter, the present invention will be described in detail using embodiments.
[Polyolefin foam sheet]
The polyolefin foam sheet according to the present invention (hereinafter, also simply referred to as "foam sheet") is a foam sheet formed by foaming a crosslinked foamable composition containing a polyolefin resin, wherein the crosslinked foamability is achieved. The average molecular weight between crosslinking points in the composition is 15,000 to 30,000.
In the present invention, when the average molecular weight between crosslinking points is less than 15,000 or exceeds 30,000, the impact resistance, the interlayer strength, etc. decrease and the durability becomes insufficient. In addition, it is difficult to obtain a foamed sheet having suitable flexibility without the compressive strength falling within the desired range.
Moreover, from a viewpoint of making durability and pliability excellent, 20000-29000 are preferable and, as for the average molecular weight between crosslinking points, 23 000-29000 are more preferable.

(Polyolefin resin)
Examples of the polyolefin resin used for the foam sheet include polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer and the like, and among these, polyethylene resin is preferable.
The polyethylene resin may, for example, be a polyethylene resin polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound or a chromium oxide compound, and preferably a polyethylene resin polymerized with a polymerization catalyst of a metallocene compound.

Moreover, as a polyethylene resin, linear low density polyethylene is preferable. By using linear low density polyethylene, high flexibility can be obtained in the resulting foam sheet, and thinning of the foam sheet becomes possible. The linear low density polyethylene is more preferably one obtained by using a polymerization catalyst such as a metallocene compound. In addition, linear low density polyethylene is obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more with respect to the total amount of monomers) and, if necessary, a small amount of α-olefin. Linear low density polyethylene is more preferred.
Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Especially, a C4-C10 alpha-olefin is preferable.
Polyethylene resin, for example the density of the linear low density polyethylene as described above is preferably 0.870~0.910g / cm ^3, more preferably 0.875~0.907g / cm ^3, 0.880~0.905g / Cm ³ is more preferred. As a polyethylene resin, a plurality of polyethylene resins can also be used, and polyethylene resins other than the above-described density range may be added.
In the present invention, by crosslinking the polyethylene resin polymerized with the polymerization catalyst of the metallocene compound, particularly linear low density polyethylene, at a crosslinking degree described later, it becomes easy to adjust the average molecular weight between crosslinking points to the above-mentioned range.

(Metallocene compounds)
As a metallocene compound, compounds, such as a bis (cyclopentadienyl) metal complex which has a structure which pinched | interposed the transition metal between the π electron system unsaturated compounds, can be mentioned. More specifically, one or more cyclopentadienyl rings or their analogs exist as ligands (ligands) in tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum. Compounds can be mentioned.
The metallocene compound is uniform in the nature of the active site, and each active site has the same activity. A polymer synthesized using a metallocene compound has high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, etc. Therefore, when a sheet containing a polymer synthesized using a metallocene compound is crosslinked, the crosslinking becomes uniform. Proceed to Since the uniformly crosslinked sheet is uniformly foamed, the size of the cell diameter can be easily made uniform. Moreover, since it can extend | stretch uniformly, the thickness of a foam sheet can be made uniform.

As a ligand, a cyclopentadienyl ring, an indenyl ring, etc. can be mentioned, for example. These cyclic compounds may be substituted by a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group. As a hydrocarbon group, for example, 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 And various cetyl groups, phenyl groups and the like. "Various" means various isomers including n-, sec-, tert- and iso-.
Also, a polymer obtained by polymerizing a cyclic compound as an oligomer may be used as a ligand.
Furthermore, in addition to unsaturated compounds of π electron system, monovalent anion ligands or divalent anion chelate ligands such as chlorine and bromine, hydrocarbons, alkoxides, arylamides, aryloxides, aryloxides, amides, arylamides, phosphides, aryls Phosphide or the like may be used.

Examples of metallocene compounds containing tetravalent transition metals and ligands include cyclopentadienyl titanium tris (dimethylamide), methyl cyclopentadienyl titanium tris (dimethyl amide), bis (cyclopentadienyl) titanium dichloride, dimethyl And silyl tetramethyl cyclopentadienyl-t-butylamido zirconium dichloride and the like.
The metallocene compound acts as a catalyst in the polymerization of various olefins in combination with a specific co-catalyst (co-catalyst). Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron compounds. The molar ratio of the cocatalyst to the metallocene compound is preferably 10 to 1,000,000 mol, and more preferably 50 to 5,000 mol.

Examples of the ethylene-vinyl acetate copolymer used as the polyolefin resin include an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene.
Moreover, as a polypropylene resin, the propylene-alpha-olefin copolymer etc. which contain 50 mass% or more of polypropylene and propylene etc. are mentioned, for example. One of these may be used alone, or two or more may be used in combination.
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- An octene etc. can be mentioned, Among these, a C6-C12 alpha-olefin is preferable.

As the polyolefin resin contained in the foam sheet, when using the above-mentioned linear low density polyethylene, the above linear low density polyethylene may be used alone, but may be used in combination with other polyolefin resin For example, it may be used in combination with the other polyolefin resins described above.
When other polyolefin resin is contained, the ratio of the other polyolefin resin to the total amount of the linear low density polyethylene and the other polyolefin resin is preferably 75% by mass or less, and 50% by mass or less Is more preferable, and 30% by mass or less is more preferable. Moreover, it is preferable that another polyolefin resin is ethylene-vinyl acetate copolymer.

Moreover, as resin contained in a foamable composition, although you may use polyolefin resin independently, as long as the effect of this invention is not impaired, you may include resin other than polyolefin resin. In the foamed sheet, the proportion of the polyolefin resin to the total amount of the resin is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more.
Examples of resins other than polyolefin resins include styrene thermoplastic elastomers, ethylene propylene thermoplastic elastomers such as EPDM, and the like.

(Crosslinking degree)
The foamed sheet is crosslinked, and the degree of crosslinking is preferably 20 to 70% by mass. By setting the degree of crosslinking within such a range, it becomes easy to obtain a foam sheet having an average molecular weight between cross-linking points within the above-mentioned range. Moreover, from such a viewpoint, the degree of crosslinking is more preferably 30 to 65% by mass, and still more preferably 35 to 60% by mass.

(Expansion ratio)
The expansion ratio of the foam sheet is preferably 1.2 to 8 cm ³ / g. In the present invention, by setting the average molecular weight between crosslinking points within the above-described predetermined range, it is possible to improve durability such as impact resistance while securing flexibility in a wide range of expansion ratio.
In addition, by lowering the expansion ratio even within the above-described range, the foam sheet has high mechanical strength and is more likely to improve the durability, and it is easy to make the foam of the foam finer and the average cell diameter described later It becomes easy to make it smaller. From such a viewpoint, the expansion ratio of the foam sheet is more preferably 1.3 to ³ cm ³ / g, further preferably 1.5 to 2.3 cm ³ / g. In the present invention, the density of the foam sheet is determined in accordance with JIS K7222, and the reciprocal thereof is defined as the expansion ratio.

(Closed cell rate)
In the foam sheet, the cells are preferably closed cells. The cell being a closed cell means that the ratio of the closed cell to all the cells (referred to as the closed cell ratio) is 70% or more. The closed cell rate is preferably 80% or more, more preferably 90% or more.
The closed cell rate can be determined in accordance with ASTM D2856 (1998). In a commercially available measuring device, a dry automatic densimeter Accupyc 1330 etc. may be mentioned.

The closed cell rate is more specifically measured in the following manner. From the foam sheet, a flat square with a side of 5 cm and a test piece of constant thickness are cut out. The thickness of the test piece was measured, to measure the weight W ₁ of the specimen to calculate the apparent volume V ₁ of the test piece. Next, the apparent volume V ₂ occupied by the air bubbles is calculated based on the following equation. In addition, the density of the resin which comprises the test piece shall be 1 g / cm < ³ >.
Apparent volume occupied by air bubbles V ₂ = V ₁ -W ₁
Subsequently, the test piece is immersed in distilled water at 23 ° C. to a depth of 100 mm from the water surface, and a pressure of 15 kPa is applied to the test piece for 3 minutes. After releasing the pressure in water, the test piece is taken out of the water to remove water adhering to the surface of the test piece, and the weight W _{2 of the} test piece is measured, and the open cell ratio F ₁ and the closed cell ratio are to calculate the F _2.
Open cell ratio F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂
Closed cell rate F ₂ (%) = 100-F ₁

(Dimensions of foam sheet)
The thickness of the foam sheet is preferably 0.02 to 0.8 mm. In the present invention, even in such a relatively wide thickness range, by setting the average molecular weight between crosslinking points within the predetermined range as described above, durability such as impact resistance is ensured while securing the flexibility of the foamed sheet. It becomes possible to improve the The thickness of the foam sheet is more preferably 0.08 to 0.50 mm, further preferably 0.10 to 0.40 mm.
The foamed sheet is not particularly limited, but may be processed into a thin line, for example, the foamed sheet may have a width of 10 mm or less. For example, 5 mm or less, and also 1 mm or less may be sufficient. By narrowing the width of the foam sheet, it can be suitably used inside a miniaturized electronic device. In addition, the foamed sheet of the present invention maintains good durability even when the width is narrowed. The lower limit of the width of the foam sheet is not particularly limited, but may be, for example, 0.1 mm or more, or 0.2 mm or more. The planar shape of the foam sheet is not particularly limited, but may be an elongated rectangular shape, a frame shape, an L-shape, a U-shape, etc. Other than these shapes, other regular square, circular etc. It may have any shape.

(Mechanical properties)
The 25% compressive strength of the foam sheet is preferably 10 to 2000 kPa, more preferably 4000 to 2000 kPa, and still more preferably 800 to 1500 kPa. By setting the 25% compressive strength to 2000 kPa or less, the foam sheet is provided with impact absorption and sealability, and can be suitably used as a shock absorbing material and a sealing material. In addition, the mechanical strength can be easily improved by increasing the compressive strength. In addition, 25% compressive strength means what measured the foamed sheet based on JISK6767.
Moreover, it is preferable that a foamed sheet has an impact resistance evaluation result in the range of 25 to 50 cm. When the impact resistance evaluation result is 25 cm or more, the impact resistance of the foam sheet is sufficient even when the sheet width is narrowed. Furthermore, the foamed sheet preferably has an interlayer strength of 4.3 MPa or more, and more preferably 4.8 MPa or more. In addition, the value of impact resistance evaluation and interlayer strength is measured according to the method of the Example mentioned later.

(Average bubble diameter)
The foam of the foam sheet has an average cell diameter of MD and TD of preferably 120 μm or less, more preferably 100 μm or less, still more preferably 80 μm or less, and an average cell diameter of ZD of 80 μm or less, preferably 50 m or less, more preferably 40 μm It is the following so-called "microcell". In the present invention, by thus reducing the cell diameter, the number of cell walls per unit length increases. Therefore, even when the width of the foam sheet is narrowed, for example, a large number of cell walls are present in the narrow width, and the impact resistance and the like can be easily enhanced. In the present invention, microcells can be easily formed by setting the average molecular weight between crosslinking points in the above-described range and setting the degree of crosslinking and the expansion ratio in the above-described suitable ranges.
The average cell diameter of each of MD and TD is preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 25 μm or more from the viewpoint of ease of production. Further, the average cell diameter of ZD is preferably 5 μm or more, more preferably 10 m or more, and still more preferably 15 μm or more.
In addition, the ratio of the average bubble diameter of MD to the average bubble diameter of ZD of the bubbles (hereinafter also referred to as "MD / ZD") is 1 to 8, and the ratio of the average bubble diameter of TD to the average bubble diameter of ZD ( Hereinafter, it is preferable that "TD / ZD" is 1 to 8. More preferably, MD / ZD is 2 to 7 and TD / ZD is 2 to 7.

The average bubble diameter refers to one measured in the following manner.
What cut the foamed sheet into 50 mm squares was 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, TD and ZD directions with a razor blade. This cross section is taken a 200x magnification with a digital microscope ("VHX-900" manufactured by KEYENCE CORPORATION), and all existing on the cut surface for 2 mm in the MD, TD and ZD directions The bubble diameter was measured for air bubbles, and the operation was repeated five times. And the average value of all bubbles was made into the average bubble diameter of MD direction, TD direction, and ZD direction.
In addition, MD direction means Machine direction and is a direction coincident with extrusion direction etc., and TD direction means Transverse direction and is a direction orthogonal to MD direction, and is a sheet-like foam (foam sheet In the direction parallel to the sheet surface. Further, the ZD direction is the thickness direction of the foam, and is a direction perpendicular to both the MD direction and the TD direction.

(Pyrolytic foam)
The foam sheet of the present invention is preferably formed by foaming a foamable composition containing a thermal decomposition-type foaming agent in addition to the above-mentioned resin.
As a thermal decomposition type foaming agent, an organic foaming agent and an inorganic foaming agent can be used. As an organic foaming agent, azo compounds such as azodicarbonamide, metal salts of azodicarboxylate (such as barium azodicarboxylate), azobisisobutyronitrile and the like, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine, Examples include hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide), toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of inorganic foaming agents include ammonium acid, sodium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate and the like.
Among these, an azo compound is preferable, and azodicarbonamide is particularly preferable, from the viewpoint of obtaining fine bubbles, and from the viewpoint of economy and safety. These thermally decomposable blowing agents can be used alone or in combination of two or more.
The compounding amount of the thermal decomposition-type foaming agent in the foamable composition is preferably 1 to 10 parts by mass, more preferably 1 to 7 parts by mass, and still more preferably 1.5 to 3.5, with respect to 100 parts by mass of the resin. It is a mass part.

In addition to the resin and the thermal decomposition type foaming agent, the foamable composition preferably contains a cell nucleus modifier. Examples of the cell nucleus modifier include zinc compounds such as zinc oxide and zinc stearate, citric acid, organic compounds of urea and the like, and among these, zinc oxide is more preferable. The use of the cell nucleus modifier in addition to the above-mentioned foaming agent makes it easier to reduce the cell diameter. The compounding amount of the cell nucleus modifier is preferably 0.4 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, and still more preferably 0.8 to 2.5 parts by mass with respect to 100 parts by mass of the resin. It is.
The foamable composition optionally contains, in addition to the above, additives generally used for foams such as an antioxidant, a heat stabilizer, a colorant, a flame retardant, an antistatic agent, and a filler. It may be done.

[Production method of foam sheet]
The method for producing the foam sheet is not particularly limited, but, for example, it is produced by heating a crosslinkable foamable composition containing a polyolefin resin and a thermal decomposition-type foaming agent and foaming the thermal decomposition-type foaming agent. . More specifically, the manufacturing method includes the following steps (1) to (4).
Step (1): A step of mixing a polyolefin resin and an additive containing a thermal decomposition-type foaming agent to form a sheet-like foamable composition (resin sheet) Step (2): Sheet-like foamable composition Step (3): Crosslinking the foamable composition by irradiating the ionizing radiation to the foamable composition Step (3): A step of heating the crosslinked foamable composition to foam the thermal decomposition-type foaming agent to form fine cells ( 4): After forming the microbubbles, stretching in the direction of either or both of the MD direction and the TD direction to stretch the microbubbles to obtain a foamed sheet

Although the method to shape | mold a resin sheet is not specifically limited in process (1), For example, a polyolefin resin and an additive are supplied to an extruder, and it melt-kneades, and extrudes a foamable composition into a sheet form from an extruder. Thus, the resin sheet may be formed.
As a method of crosslinking the foamable composition in the step (2), a method of irradiating the resin sheet with ionizing radiation such as an electron beam, an alpha ray, a beta ray, and a gamma ray is used. The irradiation dose of the ionizing radiation may be adjusted so that the degree of crosslinking of the resulting foam sheet falls within the above-described desired range, but is preferably 5 to 15 Mrad, and more preferably 6 to 13 Mrad.
In the step (3), the heating temperature when heating the foamable composition to foam the thermal decomposition-type foaming agent may be at least the foaming temperature of the thermal decomposition-type foaming agent, preferably 200 to 300 ° C., Preferably it is 220-280 degreeC.

Stretching of the foamed sheet in the step (4) may be performed after the resin sheet is foamed to obtain the foamed sheet, or may be performed while the resin sheet is foamed. When the foamed sheet is stretched after the resin sheet is foamed to obtain the foamed sheet, the foamed sheet may be continuously stretched without cooling the foamed sheet while maintaining the molten state at the time of foaming. After the foamed sheet is cooled, the foamed sheet may be heated again to be in a melted or softened state, and then the foamed sheet may be stretched.
In the step (4), the draw ratio of the foam sheet in one or both of the MD direction and the TD direction is preferably 1.1 to 5.0, and more preferably 1.5 to 4.0.
When the draw ratio is at least the above lower limit, the flexibility and the tensile strength of the foam sheet are likely to be good. On the other hand, if the upper limit value is used or lower, the foam sheet is broken during stretching, or the foam gas is removed from the foam sheet during foam to prevent the expansion ratio from being significantly reduced, and the flexibility and tensile strength of the foam sheet are prevented. And the quality is likely to be uniform.
In addition, the foamed sheet may be heated to, for example, 100 to 280 ° C., preferably 150 to 260 ° C. at the time of stretching.
Further, it is preferable to provide a step of quenching the foamed sheet after the foamed sheet is stretched in one or both of the MD direction and the TD direction. As a result, shrinkage and expansion of the foamed sheet after stretching can be suppressed, and the thickness of the foamed sheet can be easily made uniform, and it can be easily adjusted to a desired cell diameter. Although the method of quenching is not particularly limited, for example, it may be performed by a method of contacting the foam sheet with a metal roll through which cooling water is passed.

  However, the present manufacturing method is not limited to the above, and a foam sheet may be obtained by a method other than the above. For example, instead of irradiating ionizing radiation, crosslinking may be carried out by a method in which an organic peroxide is blended in advance with the foamable composition and the foamable composition is heated to decompose the organic peroxide. Good. In addition, step (4), that is, stretching of the foam sheet may be omitted.

  Although the use of a foam sheet is not specifically limited, For example, it is preferable to use inside electronic devices. Since the foamed sheet of the present invention has high durability even if it is thin, it can be suitably used particularly in various portable electronic devices in which the space for arranging the foamed sheet is small. The portable electronic device includes a mobile phone, a camera, a game device, an electronic notebook, a personal computer and the like. The foamed sheet can be used as an impact absorbing material and a sealing material inside the electronic device. Moreover, you may use for the adhesive tape which makes a foam sheet a base material.

The pressure-sensitive adhesive tape includes, for example, a foam sheet and a pressure-sensitive adhesive layer provided on at least one surface of the foam sheet, but a double-sided pressure-sensitive adhesive tape provided with a pressure-sensitive adhesive layer on both sides is preferable.
It is preferable that the thickness of the adhesive layer which comprises an adhesive tape is 5-200 micrometers. The thickness of the pressure-sensitive adhesive layer is more preferably 7 to 150 μm, still more preferably 10 to 100 μm. When the thickness of the pressure-sensitive adhesive layer is in the range of 5 to 200 μm, the thickness of the structure fixed using the pressure-sensitive adhesive tape can be reduced.
There is no restriction | limiting in particular as an adhesive used for an adhesive layer, For example, an acrylic adhesive, a urethane adhesive, a rubber adhesive etc. can be used.
In addition, a release sheet such as release paper may be further bonded on the pressure-sensitive adhesive layer.
The method for forming the pressure-sensitive adhesive layer on at least one surface of the foam sheet is not particularly limited. For example, a method of applying an adhesive to at least one surface of a foam sheet using a coating machine such as a coater, a method of spraying and applying an adhesive to at least one surface of a foam sheet using a spray, brushing at least one surface of a foam sheet And a method of transferring the pressure-sensitive adhesive layer formed on the release sheet to at least one surface of the foam sheet.

  The present invention will be described in more detail by way of examples, but the present invention is not limited by these examples.

[Measuring method]
The measuring method and evaluation method of each physical property are as follows.
<Average molecular weight between crosslinking points>
The inter-crosslink point average molecular weight was obtained by measuring the shear modulus G ′ of the crosslinkable foamable composition, and determining the inter-crosslink point average molecular weight based on the following equation according to the classical rubber elasticity theory.
Mc = 2 × (1 + μ) × ρ × RT / E ′
(However, Mc: average molecular weight between crosslinking points (g / mol), μ: Poisson's ratio (0.5), ρ: density of the foamable composition (g / m ³ ), R: gas constant 8.314 J / Kmol, T: temperature (K) at the time of storage elastic modulus measurement, E ': storage elastic modulus (Pa), and E' = 3 G 'is substituted).
(Shear modulus G ')
The shear elastic modulus G ′ is measured using a dynamic viscoelasticity measuring apparatus DVA-200 manufactured by Aty Measurement Instruments Co., Ltd., while raising the temperature range up to 40 to 150 ° C. at a rate of 5 ° C./min, the angular frequency 1 Hz The strain amount was measured under the condition of 1%.
In addition, the density (g / m ³ ) of the foamable composition was measured by a high accuracy model hydrometer SD-200L manufactured by M and K Co., Ltd.

<Average bubble diameter>
It measured according to the method mentioned above.
<Apparent density and expansion ratio>
The apparent density of the foam sheet was measured in accordance with JIS K7222, and the reciprocal thereof was taken as the foaming ratio.
<Crosslinking degree>
A test piece of about 100 mg is taken from the foam sheet, and the weight A (mg) of the test piece is precisely weighed. Next, the test piece is immersed in 30 cm ³ of xylene at 120 ° C. and left for 24 hours, and then filtered through a 200 mesh wire mesh to collect insolubles on the wire net, vacuum-dried, and the weight of the insoluble portion Carefully weigh B (mg). The degree of crosslinking (% by mass) was calculated from the obtained value by the following equation.
Degree of crosslinking (% by mass) = 100 × (B / A)
<Closed cell rate>
It measured according to the method mentioned above.

<Impact resistance>
(Adjustment of impact resistance evaluation sample)
The adhesive layer obtained by the following method was laminated | stacked on both surfaces of the foam sheet obtained by the Example and the comparative example, and the double-sided adhesive tape which uses a foam sheet as a base material was produced in the following ways.
(Production method of double-sided adhesive tape)
In a reactor equipped with a thermometer, a stirrer and a condenser, 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 The reaction vessel was heated to start refluxing. Subsequently, 0.1 parts by mass of azobisisobutyronitrile as a polymerization initiator was added into the reactor. Refluxing for 5 hours gave a solution of acrylic copolymer (z). The weight average molecular weight of the obtained acrylic copolymer (z) was measured by GPC using “2690 Separations Model” manufactured by Water as a column, and was 600,000.
15 parts by mass of polymerized rosin ester having a softening point of 135 ° C., based on 100 parts by mass of the solid content of the acrylic copolymer (z) contained in the obtained solution of the acrylic copolymer (z), ethyl acetate A pressure-sensitive adhesive (Z) was obtained by adding 125 parts by mass of Chemical Co., Ltd., and 2 parts by mass of an isocyanate crosslinking agent (Coronato L45, manufactured by Tosoh Corporation) and stirring. In addition, the crosslinking degree of the acrylic adhesive was 33 mass%.
A release paper having a thickness of 150 μm was prepared, an adhesive (Z) was applied to the release-treated 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 pressure-sensitive adhesive layer was bonded to the surface of a base material made of a foamed sheet. Then, in the same manner, the same acrylic adhesive layer as described above was bonded to the opposite surface of the substrate. Thus, a double-sided pressure-sensitive adhesive tape covered with a 150 μm-thick release paper was obtained.

(Production of impact resistance test equipment)
FIG. 1 shows a schematic view of an impact resistance test device.
The impact resistance test device was produced in the following procedure.
First, the double-sided pressure-sensitive adhesive tape obtained above is punched so that the outer diameter is 15.0 mm in width, 15.0 mm in length, and 13.6 mm in inner diameter and 13.6 mm in length. A square frame test piece 1 of 7 mm was produced.
Next, as shown in FIG. 1 (a), a magnesium coated plate 3 provided with a square hole 2 at the center is prepared, and the test piece 1 from which the release paper is peeled off is the upper surface of the magnesium coated plate 3 Then, the entire outer periphery of the hole 2 was attached.
Then, a glass-made adhesion plate 4 of a size to cover the holes 2 was stacked on the test piece 1 and attached, and the holes 2 were covered to assemble an impact resistance test device.
Thereafter, the impact resistance test apparatus is turned upside down, and a pressure of 5 kgf is applied for 5 seconds from the side of the magnesium deposition plate 3 in a state where the magnesium deposition plate 3 is on the top surface, The mounting plate 3 and the test piece were pressure-bonded and left at room temperature for 36 hours.

(Judgement of impact resistance)
As shown in FIG. 1 (b), the manufactured impact resistance test device is fixed to the support base 5, and an iron ball of 50 g in weight passing through the hole 2 formed in the magnesium-made adherend 3 6 was dropped to pass through hole 2. Gradually raise the height to drop the iron ball, measure the height to which the iron ball was dropped when the test piece and the adherend plate were peeled off by the impact applied by the drop of the iron ball, and evaluate the impact resistance did. The case where the height is larger than 50 cm is evaluated as "S", the case of 25 cm or more and 50 cm or less as "A", and the case less than 25 cm as "B".

<Interlayer strength>
(Preparation of sample for interlayer strength measurement)
As shown in FIG. 2, after applying a primer ("PPX primer" manufactured by Cemedine Co., Ltd.) to the 25 mm square range of foam sheet 7, adhesive 8 (diameter: 5 mm in diameter) is applied to the center of the coated part ") Was dropped. Immediately thereafter, an aluminum jig 9 of 25 mm square was placed on the adhesive dropping portion, and the foam sheet 7 and the jig 9 were pressure-bonded with the adhesive 8. Thereafter, the foam sheet was cut along the size of the jig 9. The primer was applied to the surface of the cut foam sheet 7 to which the jig 9 was not adhered, and the adhesive 10 having a diameter of 5 mm was dropped at the center of the applied portion. Immediately thereafter, an aluminum jig 11 of 10 mm square was placed on the adhesive dropping portion, and the foam sheet 7 and the jig 11 were pressure-bonded with the adhesive 10. After wiping off the adhesive sticking out around the jig 11, a cut 12 was made in the foam sheet along the size of the jig 11. The adhesive was cured by leaving it to stand at room temperature for 30 minutes, and used as a sample for interlayer strength measurement.
(Determination of interlayer strength)
Subsequently, the interlaminar strength was measured on a tester equipped with a 1 kN load cell ("Analy &Dey's Tensilon Universal Material Tester") so that the sheet surface of the foam sheet 7 was perpendicular to the tensile direction. Attached the sample. The jig 9 was pulled vertically upward at a speed of 100 mm / min to delaminate only the 1 cm square area of the foam sheet. The maximum load at this time was measured and taken as the first measurement result. The same operation was repeated three times, and the average value was taken as the interlayer strength. When the interlaminar strength is 4.8 MPa or more, the interlaminar strength is considered as “A”. Further, when the interlayer strength is 4.3 MPa or more and less than 4.8 MPa, "B" is determined as the interlayer strength is good. Moreover, when the interlayer strength was less than 4.3 MPa, it was considered as "C" because the interlayer strength was insufficient.

<25% compressive strength>
The 25% compressive strength of the foamed sheet was measured according to JIS K6767.

Example 1
100 parts by mass of linear low density polyethylene obtained by a polymerization catalyst of a metallocene compound, 2.1 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent, and 1.0 parts by mass of zinc oxide as a cell nucleus modifier 0.5 parts by mass of an antioxidant was supplied to an extruder, and the mixture was melt-kneaded at 130 ° C., and extruded into a long resin sheet having a thickness of 290 μm.
In addition, as said linear low density polyethylene, the brand name "affinity PL1850" (density: 0.902 g / cm < ³ >) made from Dow Chemical Co., Ltd. was used. Moreover, as said zinc oxide, the brand name "OW-212F" by Sakai Chemical Industry Co., Ltd. was used.
Next, an electron beam with an accelerating voltage of 500 kV is applied at 7.4 Mrad to both surfaces of the above long resin sheet to crosslink the resin sheet, and then the crosslinked resin sheet is kept at 250 ° C. by hot air and an infrared heater. The mixture was continuously fed into a furnace, heated and foamed to obtain a foamed sheet having a thickness of 300 μm.
Next, the obtained foam sheet was continuously fed from the foaming furnace, and the foam sheet was stretched as follows while maintaining the temperature of both sides thereof at 200 to 250 ° C. The foamed sheet is stretched at a draw ratio of 2.0 times in the TD direction, and the foamed sheet is wound by winding the foamed sheet at a winding speed faster than the feeding speed (feed rate) of the resin sheet into the foaming furnace. It was made to extend in the MD direction and was brought into contact with the circumferential surface of the metal roll through which the cooling water was passed. Thus, the cells of the foam sheet were stretched and deformed in the TD direction and the MD direction to obtain a foam sheet. In addition, the winding speed of the said foam sheet was adjusted in consideration of the expansion part to MD direction by foaming of resin sheet itself. The resulting foam sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

Example 2
30 parts by mass of linear low density polyethylene (manufactured by Dow Chemical Co., trade name "Affinity PL 1850", density: 0.902 g / cm ³ ) instead of the resin of Example 1 and ethylene-vinyl acetate 70 parts by mass of a copolymer (manufactured by Tosoh Corp., trade name "Ultrasen 636"). Further, the blending amount of azodicarbonamide in the foamable composition was 1.9 parts by mass. Other than these, it implemented similarly to Example 1. The evaluation results of the obtained foam sheet are shown in Table 1.

[Example 3]
The compounding amount of the azodicarbonamide in the foamable composition is 2.5 parts by mass, the electron beam irradiation amount is 9.0 Mrad, and the crosslinking degree is 57.0 mass%, except for the same points as in Example 1 Implemented. The evaluation results of the obtained foam sheet are shown in Table 1.

Comparative Example 1
The compounding amount of the azodicarbonamide in the foamable composition is 1.6 parts by mass, the electron beam irradiation amount is 4.7 Mrad, and the cross-linking degree is 16.2 mass%, except for the following points. Implemented. The evaluation results of the obtained foam sheet are shown in Table 1.

Comparative Example 2
30 parts by mass of linear low density polyethylene (manufactured by Dow Chemical Co., trade name "Affinity PL 1850", density: 0.902 g / cm ³ ) instead of the resin of Example 1 and ethylene-vinyl acetate 70 parts by mass of a copolymer (manufactured by Tosoh Corp., trade name "Ultrasen 636"). Further, the blending amount of azodicarbonamide in the foamable composition is 1.5 parts by mass, the irradiation amount of electron beam is 4.7 Mrad, and the degree of crosslinking is 19.2 mass%. Other than these, it implemented similarly to Example 1. The evaluation results of the obtained foam sheet are shown in Table 1.

Comparative Example 3
An electron beam with an accelerating voltage of 500 kV was applied at 7.4 Mrad to both surfaces of the foam sheet obtained in Comparative Example 1 to crosslink the foam sheet, and the degree of crosslinking was 71.0% by mass. The evaluation results of the obtained foam sheet are shown in Table 1.

  As described above, in Examples 1 and 3, all of 25% compressive strength, interlayer strength, and impact resistance are good, and by setting the average molecular weight between crosslinking points within a predetermined range, flexibility is achieved. It can be understood that the durability was able to be improved while maintaining good condition. Moreover, in Example 2, compared with Examples 1 and 3, although the impact resistance was inferior, interlayer strength was favorable and the softness | flexibility and durability were favorable. On the other hand, in Comparative Examples 1 and 2, it was difficult to sufficiently improve the durability because the average molecular weight between crosslinking points was large. In Comparative Example 3, the average molecular weight between crosslinking points was small, and it was difficult to sufficiently improve the durability.

Reference Signs List 1 test specimen 2 hole 3 magnesium adhesion plate 4 glass adhesion plate 5 support 6 iron ball 7 foam sheet 8 adhesive 9 jig 10 adhesive 11 jig 12 incision

Claims (10)

  A polyolefin foam sheet comprising a polyolefin resin and having a crosslinked foamable composition foamed therein, wherein the foamable composition has an average molecular weight between crosslink points of 15,000 to 30,000.   The polyolefin foam sheet according to claim 1, wherein the polyolefin resin is a polyethylene resin.   The polyolefin foam sheet according to claim 2, wherein the polyolefin resin is a linear low density polyethylene polymerized with a polymerization catalyst of a metallocene compound.   The polyolefin foam sheet according to any one of claims 1 to 3, which has a crosslinking degree of 20 to 70% by mass.   The polyolefin foam sheet according to any one of claims 1 to 4, wherein the impact resistance evaluation result is in the range of 25 to 50 cm and the 25% compressive strength is 10 to 2,000 kPa.   The polyolefin foam sheet according to any one of claims 1 to 5, which has a thickness of 0.02 to 0.8 mm. Expansion ratio is 1.2~8cm ³ / g, a polyolefin foamed sheet according to any one of claims 1-6.   The polyolefin foam sheet according to any one of claims 1 to 7, which is obtained by foaming a foamable composition further comprising a thermal decomposition-type foaming agent. It is a manufacturing method of the polyolefin-type foam sheet of any one of Claims 1-8, Comprising:
A method for producing a polyolefin-based foam sheet, comprising heating a crosslinkable foamable composition containing a polyolefin resin and a thermal decomposition-type foam agent to foam the thermal decomposition-type foam agent.   The adhesive tape provided with the polyolefin-type foam sheet of any one of Claims 1-8, and the adhesive layer provided in the surface of at least any one of the said polyolefin-type foam sheet.

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