TW201817787A - Polyolefin foam sheet, production method therefor, and adhesive tape - Google Patents

Abstract

A polyolefin foam sheet according to the present invention contains a polyolefin resin, and is obtained by causing a cross-linked foamable composition to foam, wherein the average molecular weight between crosslinks of the foamable composition is 15,000-30,000. The present invention can provide a foam sheet which has high flexibility and high durability even when the sheet has a reduced thickness.

Description

   Polyolefin-based foamed sheet, manufacturing method thereof and adhesive tape   

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

For electronic devices such as mobile phones, cameras, game consoles, electronic notebooks, and personal computers, a sealing material or an impact absorbing material composed of a foamed sheet, and an adhesive tape based on the foamed sheet are used. For example, a display device used in the above-mentioned electronic equipment generally has a structure in which a protective panel is provided on a display panel such as an LCD. In order to attach the protective panel to a frame portion on the outside of the display panel, a foam sheet is used. Adhesive tape for substrate.

As a conventional foamed sheet used in an electronic device, a crosslinked polyolefin resin obtained by foaming and crosslinking a foamable polyolefin resin sheet containing a thermally decomposable foaming agent is known. Sheet (see, for example, Patent Document 1).

Prior art literature

Patent literature

Patent Document 1: International Publication No. 2005/007731

However, in recent years, electronic devices have been developed toward miniaturization, and on the other hand, various parts have been developed to be highly functional, and the space limitation inside electrical devices has increased. For example, the frame portion on the outside of the display panel is narrowed due to the miniaturization of electronic devices and the enlargement of display devices. Therefore, for a foamed sheet, not only a relatively thick one is required to have high softness and durability, but also a high softness and durability is required even when thinned.

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

The present invention provides the following [1] to [10].

[1] A polyolefin-based foamed sheet obtained by foaming a crosslinked foamable composition containing a polyolefin resin, and the average molecular weight between the crosslinking points of the foamable composition is 15,000 ~ 30000.

[2] The polyolefin-based foamed sheet according to the above [1], wherein the polyolefin resin is a polyethylene resin.

[3] The polyolefin-based foamed sheet according to the above [2], wherein the polyolefin resin is a linear low-density polyethylene polymerized by a polymerization catalyst of a metallocene compound.

[4] The polyolefin-based foamed sheet according to any one of the above [1] to [3], wherein the degree of crosslinking is 20 to 70% by mass.

[5] The polyolefin-based foamed sheet according to any one of the above [1] to [4], wherein the impact resistance evaluation result is in a range of 25 to 50 cm, and the 25% compressive strength is 10 to 2,000 kPa.

[6] The polyolefin-based foamed sheet according to any one of the above [1] to [5], which has a thickness of 0.02 to 0.8 mm.

[7] The polyolefin-based foamed sheet according to any one of the above [1] to [6], which has a foaming ratio of 1.2 to 8 cm ³ / g.

[8] The polyolefin-based foamed sheet according to any one of the above [1] to [7], which is obtained by foaming a foamable composition further containing a thermally decomposable foaming agent.

[9] A method for producing a polyolefin-based foamed sheet, which is the method for producing a polyolefin-based foamed sheet according to any one of the above [1] to [8], and further comprising a method of containing a polyolefin resin and The thermally decomposable foaming agent and the crosslinked foamable composition are heated to foam the thermally decomposable foaming agent.

[10] An adhesive tape comprising the polyolefin-based foamed sheet according to any one of the above [1] to [8], and an adhesive layer provided on at least one surface of the polyolefin-based foamed sheet.

According to the present invention, a foamed sheet having high flexibility and durability can be provided even when the sheet is thinned.

1‧‧‧test piece

2‧‧‧ hole

3‧‧‧ Magnesium quilt

4‧‧‧ glass quilt

5‧‧‧ support desk

6‧‧‧ iron ball

7‧‧‧ foamed sheet

8‧‧‧ Adhesive

9‧‧‧ jig

10‧‧‧ Adhesive

11‧‧‧Jig

12‧‧‧ incision

Figure 1 is a schematic diagram of an impact resistance test apparatus.

Fig. 2 is an explanatory diagram of a method for measuring interlayer strength.

Hereinafter, the present invention will be described in detail using embodiments.

[Polyolefin foam sheet]

The polyolefin-based foamed sheet (hereinafter also simply referred to as "foamed sheet") of the present invention is a foamed sheet obtained by foaming a polyolefin resin-containing and cross-linked foamable composition, and is cross-linked. The average molecular weight between the crosslinking points of the foamable composition is 15,000 to 30,000.

In the present invention, when the average molecular weight between the crosslinking points is less than 15,000 or exceeds 30,000, impact resistance, interlayer strength, and the like are reduced, and durability is insufficient. In addition, the compressive strength exceeds a desired range, and it becomes difficult to obtain a foamed sheet having suitable flexibility.

In addition, from the viewpoint of improving durability and flexibility, the average molecular weight between the crosslinking points is preferably 20,000 to 29,000, and more preferably 23,000 to 29,000.

(Polyolefin resin)

Examples of the polyolefin resin used in the foamed sheet include polyethylene resins, polypropylene resins, and ethylene-vinyl acetate copolymers. Among these, polyethylene resins are preferred.

Examples of the polyethylene resin include polyethylene resins polymerized by using a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, and a chromium oxide compound, and it is preferable to use a polyethylene resin A polyethylene resin polymerized by a polymerization catalyst of a metal compound.

The polyethylene resin is preferably a linear low-density polyethylene. By using a linear low-density polyethylene, the obtained foamed sheet has high flexibility, and it becomes possible to reduce the thickness of the foamed sheet. The linear low-density polyethylene is more preferably obtained by using a polymerization catalyst such as a metallocene compound. The linear low-density polyethylene is more preferably 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 a small amount of α-olefin as necessary. The obtained linear low-density polyethylene.

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

The polyethylene resin, such as the linear low-density polyethylene described above, preferably has a density of 0.870 to 0.910 g / cm ³ , more preferably 0.875 to 0.907 g / cm ³ , and still more preferably 0.880 to 0.905 g / cm ³ . As the polyethylene resin, various kinds of polyethylene resins can be used, and polyethylene resins outside the above-mentioned density range may be added.

In the present invention, a polyethylene resin, especially a linear low-density polyethylene, which is polymerized by using a polymerization catalyst of a metallocene compound, is crosslinked at the following degree of crosslinking, thereby making it easy to crosslink. The average molecular weight between points was adjusted to the above range.

(Dimetallocene compound)

Examples of the metallocene compound include compounds such as a bis (cyclopentadienyl) metal complex having a structure in which a transition metal is sandwiched by an π-electron unsaturated compound. More specifically, one or more cyclopentadienyl rings or the like are present in the form of ligands in titanium, zirconium, nickel, palladium, hafnium, and platinum. Valence transition metal compounds.

The properties of the active points of the metallocene compound are uniform, and each active point has the same degree of activity. Polymers synthesized using a metallocene compound have high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, and the like. Therefore, when cross-linking a sheet containing a polymer synthesized using a metallocene compound, Cross-linking takes place uniformly. Since the uniformly crosslinked sheet foams uniformly, the size of the bubble diameter also tends to become uniform. In addition, since the stretching can be performed uniformly, the thickness of the foamed sheet can be made uniform.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may also be substituted with a hydrocarbon group, a substituted hydrocarbon group, or a hydrocarbon-substituted metalloid group. Examples of the hydrocarbon group include methyl, ethyl, various propyl, various butyl, various pentyl, various hexyl, 2-ethylhexyl, various heptyl, various octyl, various nonyl, various decyl, Various cetyl, phenyl, etc. In addition, the "various" means various isomers including positive, second, third, and different.

Alternatively, a cyclic compound may be polymerized to form an oligomer as a ligand.

Furthermore, in addition to π-electron unsaturated compounds, monovalent anion ligands or divalent anion chelate ligands such as chlorine or bromine, hydrocarbons, alkoxides, aramide, aryl ether, and amine , Aramide, phosphide, aryl phosphide, etc.

Examples of the divalent metallocene compound containing a tetravalent transition metal or a ligand include cyclopentadienyl titanium tris (dimethylfluorenamine), methyl cyclopentadienyl titanium tris (dimethylfluorenamine) ), Bis (cyclopentadienyl) titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylphosphoniumamine zirconium dichloride, and the like.

The metallocene compound is used as a catalyst in the polymerization of various olefins in combination with a specific co-catalyst (promoter). Specific examples of the co-catalyst include methylalumoxane (MAO), a boron-based compound, and the like. In addition, the use ratio of the co-catalyst relative to the metallocene compound is preferably 100,000 to 1 million mol times, and more preferably 50 to 5,000 mol times.

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.

Examples of the polypropylene resin include polypropylene, and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. These may be used 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, α-olefins having 6 to 12 carbon atoms are preferred.

When the polyolefin resin contained in the foamed sheet uses the above-mentioned linear low-density polyethylene, the above-mentioned linear low-density polyethylene can be used alone or in combination with other polyolefin resins. These other polyolefin resins are used in combination.

When other polyolefin resins are contained, the proportion of other polyolefin resins relative to the total amount of linear low-density polyethylene and other polyolefin resins is preferably 75% by mass or less, more preferably 50% by mass or less, It is preferably 30% by mass or less. The other polyolefin resin is preferably an ethylene-vinyl acetate copolymer.

In addition, as the resin contained in the foamable composition, a polyolefin resin may be used alone, and as long as the effect of the present invention is not impaired, a resin other than a polyolefin resin may be contained. In the foamed sheet, the ratio of the polyolefin resin to the total resin is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

Examples of resins other than polyolefin resins include styrene-based thermoplastic elastomers and ethylene-propylene-based thermoplastic elastomers such as EPDM (ethylene propylene diene monomer).

(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 in such a range, it becomes easy to obtain a foamed sheet having an average molecular weight between the crosslinking points in the above range. From this viewpoint, the degree of crosslinking is more preferably 30 to 65% by mass, and even more preferably 35 to 60% by mass.

(Foaming ratio)

The expansion ratio of the foamed sheet is preferably 1.2 to 8 cm ³ / g. In the present invention, by setting the average molecular weight between the crosslinking points to the specific range described above, it becomes possible to improve durability such as impact resistance while ensuring flexibility at a wide range of expansion ratios.

In addition, by reducing the foaming ratio to the above range, the foamed sheet has improved mechanical strength and further improved durability, and it is easy to miniaturize or reduce bubbles in the foamed sheet. Lower the average bubble diameter below. From such a viewpoint, the expansion ratio of the foamed sheet is more preferably 1.3 to 3 cm ³ / g, and even more preferably 1.5 to 2.3 cm ³ / g. In the present invention, the density of the foamed sheet is obtained in accordance with JIS K7222, and its inverse number is set as the expansion ratio.

(Independent bubble rate)

Regarding the foamed sheet, the bubbles are preferably closed cells. The term “bubbles as closed cells” means that the ratio of closed cells to all cells (also referred to as the closed cell ratio) becomes 70% or more. The closed cell ratio is preferably 80% or more, and more preferably 90% or more.

The closed cell ratio can be determined in accordance with ASTM D2856 (1998). As a commercially available measuring instrument, a dry automatic density meter Accupyc 1330 and the like can be cited.

More specifically, the closed cell ratio is measured based on the following points. From the foamed sheet, a test piece having a flat square shape with a side length of 5 cm and a certain thickness was cut out. The thickness of the test piece was measured, the apparent volume V _{1 of the} test piece was calculated, and the weight W _{1 of the} test piece was measured. Next, the apparent volume V ₂ occupied by the bubbles is calculated according to the following formula. The density of the resin constituting the test piece was set to 1 g / cm ³ .

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

Next, the test piece was sunk from the water surface to a depth of 100 mm in distilled water at 23 ° C., and a pressure of 15 kPa was applied to the test piece for 3 minutes. After the pressure was released in water, the test piece was taken out of the water, the moisture attached to the surface of the test piece was removed, and the weight W ₂ of the test piece was measured, and the continuous cell ratio F ₁ and the closed cell ratio F _{2 were} calculated according to the following formula.

Continuous bubble rate F ₁ (%) = 100 × (W ₂ -W ₁ ) / V ₂

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

(Size of foam sheet)

The thickness of the foamed sheet is preferably 0.02 to 0.8 mm. In the present invention, even in such a relatively wide thickness range, as described above, the average molecular weight between the crosslinking points is set to a specific range, thereby making it possible to ensure the flexibility of the foamed sheet and improve the resistance. Durability such as impact. The thickness of the foamed sheet is more preferably 0.08 to 0.50 mm, and still more preferably 0.10 to 0.40 mm.

The foamed sheet is not particularly limited, and can be processed into a thin line shape. For example, the foamed sheet can be used with a width of 10 mm or less. In addition, it may be, for example, 5 mm or less, and further 1 mm or less. If the width of the foamed sheet is reduced, it can be suitably used inside a miniaturized electronic device. In addition, the foamed sheet of the present invention maintains durability well even if the width is reduced. The lower limit value of the width of the foamed sheet is not particularly limited, and may be, for example, 0.1 mm or more and 0.2 mm or more. In addition, the planar shape of the foamed sheet is not particularly limited, and it may be set to a slender rectangle, a frame shape, an L shape, In addition to these shapes, the shape can also be any other shapes, such as square, round, etc.

(Mechanical characteristics)

The 25% compressive strength of the foamed sheet is preferably 10 to 2000 kPa, more preferably 4000 to 2000 kPa, and even more preferably 800 to 1500 kPa. By setting the 25% compressive strength to 2000 kPa or less, the foamed sheet has impact absorption and sealing properties, and can be suitably used as a buffer absorbent material and a sealing material. In addition, by increasing the compressive strength, it becomes easy to improve the mechanical strength. In addition, 25% compressive strength refers to those obtained by measuring a foamed sheet in accordance with JIS K6767.

In addition, it is preferable that the foamed sheet has an impact resistance evaluation result in a range of 25 to 50 cm. When the impact resistance evaluation result is 25 cm or more, even when the sheet width is narrowed, the impact resistance of the foamed sheet becomes sufficient. Further, the interlayer strength of the foamed sheet is preferably 4.3 MPa or more, and more preferably 4.8 MPa or more. The values of impact resistance evaluation and interlayer strength were measured in accordance with the methods of the following examples.

(Average bubble diameter)

The average bubble diameter of the foamed MD and TD of the foamed sheet is preferably 120 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less, and the average cell diameter of ZD is 80 μm or less, preferably 50 m or less, more It is preferably a so-called "microcell" having a diameter of 40 µm or less. In the present invention, by reducing the bubble diameter in this way, the number of bubble walls per unit length will increase. Therefore, even when the foamed sheet has a narrow width, for example, when a large number of cell walls exist in the narrow width, it becomes easy to improve the impact resistance and the like. In addition, in the present invention, by setting the average molecular weight between the crosslinking points to the above-mentioned range, and setting the degree of crosslinking and the expansion ratio to the appropriate ranges described above, it becomes easy to form micropores.

From the viewpoint of ease of manufacturability, the average cell diameters of MD and TD are each preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more. The average cell diameter of ZD is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more.

In addition, the ratio of the average bubble diameter of the MD to the average bubble diameter of the ZD (hereinafter also referred to as "MD / ZD") is preferably 1 to 8, and the average bubble diameter of the TD to the average bubble diameter of the ZD The ratio (hereinafter also referred to as "TD / ZD") is 1 to 8. Furthermore, it is more preferable that the MD / ZD is 2 to 7 and the TD / ZD is 2 to 7.

The average bubble diameter is measured based on the following points.

A foamed sheet was cut into 50 mm squares and the obtained specimen was prepared as a foam sample for measurement. After immersing it in liquid nitrogen for 1 minute, it was cut in the thickness direction along a MD direction, a TD direction, and a ZD direction with a razor blade, respectively. A digital microscope ("VHX-900" manufactured by Keyence Corporation) was used to take a magnification of 200 times on the cross section, and all of the cut surfaces of the 2 mm sections in the MD direction, TD direction, and ZD direction were present. The bubble diameter was measured, and this operation was repeated 5 times. Then, the average value of all the bubbles was set as the average bubble diameter of MD direction, TD direction, and ZD direction.

In addition, the MD direction means the machine direction, which is consistent with the extrusion direction, etc., and the TD direction means the transverse direction, which is orthogonal to the MD direction, and is a sheet-like foam (foamed sheet). A direction parallel to the surface of the sheet. The ZD direction is a thickness direction of the foam, and is a direction perpendicular to both the MD direction and the TD direction.

(Thermal decomposition type foaming agent)

The foamed sheet of the present invention is preferably formed by foaming a foamable composition containing the resin and a thermally decomposable foaming agent.

As the thermally decomposable foaming agent, an organic foaming agent and an inorganic foaming agent can be used. Examples of the organic foaming agent include azo compounds such as azomethamine, metal salts of azodicarboxylic acid (such as barium azodicarboxylate), and azobisisobutyronitrile; Nitroso compounds such as nitropentamethylenetetramine (N, N'-dinitrosopentamethylenetetramine), hydrazodicarbonamide, 4,4'-oxybis (benzenesulfonylhydrazine), tosylsulfonium Hydrazine derivatives such as hydrazine, amine urea compounds such as tosyl sulfonamide, and the like.

Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium boron hydride, and anhydrous monosodium citrate.

Among these, from the viewpoint of obtaining fine bubbles, and from the viewpoint of economy and safety, an azo compound is preferred, and azomethoxamine is particularly preferred. These thermal decomposition type foaming agents can be used alone or in combination of two or more kinds.

The blending amount of the thermally decomposable 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 parts by mass relative to 100 parts by mass of the resin. Serving.

In addition, the foamable composition preferably contains a bubble core regulator in addition to the resin and the thermally decomposable foaming agent. Examples of the bubble core regulator include zinc compounds such as zinc oxide and zinc stearate; organic compounds such as citric acid and urea; and among these, zinc oxide is more preferred. By using a bubble core regulator in addition to the above-mentioned foaming agent, it becomes easy to further reduce the bubble diameter. The blending amount of the bubble nucleating agent 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.

In addition to the above, the foamable composition may contain additives, such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and fillers, which are generally used in foams, as necessary.

[Manufacturing method of foamed sheet]

The manufacturing method of the foamed sheet is not particularly limited. For example, by heating a crosslinked foamable composition containing a polyolefin resin and a thermally decomposable foaming agent, the thermally decomposable foaming agent is foamed. Manufacturing. The manufacturing method more specifically includes the following steps (1) to (4).

Step (1): A step of mixing an additive containing a polyolefin resin and a thermally decomposable foaming agent and forming a sheet-like foamable composition (resin sheet)

Step (2): Irradiating the sheet-like foamable composition with ionizing radiation to crosslink the foamable composition

Step (3): heating the cross-linked foamable composition to foam the thermally decomposable foaming agent to form fine bubbles

Step (4): After forming microbubbles, the microbubbles are stretched in one or both of the MD direction or the TD direction, and the microbubbles are extended to obtain a foamed sheet.

In step (1), the method of forming the resin sheet is not particularly limited. For example, a polyolefin resin and an additive are supplied to an extruder for melt-kneading, and the foamable composition is extruded from the extruder into a sheet shape , And the resin sheet can be formed.

In step (2), as a method of crosslinking the foamable composition, a method of irradiating the resin sheet with ionizing radiation such as an electron beam, an α ray, a β ray, or a γ ray is used. The irradiation amount of the ionizing radiation may be adjusted in such a manner that the degree of crosslinking of the obtained foamed sheet becomes the above-mentioned required range, preferably 5 to 15 Mrad, and more preferably 6 to 13 Mrad.

In step (3), the heating temperature when the foamable composition is heated to foam the thermally decomposable foaming agent may be equal to or higher than the foaming temperature of the thermally decomposable foaming agent, and preferably 200 to 300. ℃, more preferably 220 ~ 280 ℃.

The stretching of the foamed sheet in step (4) may be performed after foaming the resin sheet to obtain a foamed sheet, or may be performed while foaming the resin sheet. In addition, when the resin sheet is foamed to obtain a foamed sheet and the foamed sheet is stretched, the foamed sheet can be continuously stretched without cooling the foamed sheet and maintaining the molten state during foaming. After cooling the foamed sheet, the foamed sheet may be heated again to extend the foamed sheet in a molten or softened state.

In step (4), the stretching ratio of the foamed sheet in one or both of the MD direction and the TD direction is preferably 1.1 to 5.0 times, and more preferably 1.5 to 4.0 times.

When the stretching ratio is set to the above lower limit value or more, the flexibility and tensile strength of the foamed sheet tend to be good. On the other hand, if it is less than the upper limit value, it will prevent the foamed sheet from breaking during stretching, or the foaming gas will escape from the foamed sheet during foaming, resulting in a significant decrease in the expansion ratio. The softness or tensile strength of the sheet becomes good, and the quality tends to become uniform.

In addition, at the time of stretching, the foamed sheet may be heated to, for example, 100 to 280 ° C, preferably 150 to 260 ° C.

In addition, it is preferable to provide a step of rapidly cooling the foamed sheet after extending the foamed sheet in one or both of the MD direction and the TD direction. Thereby, shrinkage or expansion of the expanded foam sheet can be suppressed, it becomes easy to make the thickness of the foam sheet uniform, and it becomes easy to adjust to a desired bubble diameter. The quenching method is not particularly limited, and may be performed by, for example, a method in which a foamed sheet is brought into contact with a metal roller through which cooling water flows.

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

The use of the foamed sheet is not particularly limited, and it is preferably used inside an electronic device, for example. Since the foamed sheet of the present invention has high durability even if thinned, it is particularly suitable for internal use in various portable electronic devices with a small space for arranging the foamed sheet. Examples of portable electronic devices include mobile phones, cameras, game consoles, electronic notebooks, and personal computers. The foam sheet can be used as an impact absorbing material and a sealing material in an electronic device. In addition, it can also be used for adhesive tapes based on foamed sheets.

The adhesive tape is, for example, a double-sided adhesive tape provided with a foam sheet and an adhesive layer provided on at least one side of the foam sheet, and provided with an adhesive layer on both sides.

The thickness of the adhesive layer constituting the adhesive tape is preferably 5 to 200 μm. The thickness of the adhesive layer is more preferably 7 to 150 m, and further preferably 10 to 100 m. If the thickness of the adhesive layer is in the range of 5 to 200 μm, the thickness of the structure fixed using the adhesive tape can be reduced.

The adhesive used for the adhesive layer is not particularly limited, and for example, an acrylic adhesive, an amine ester adhesive, a rubber adhesive, or the like can be used.

In addition, a release sheet such as a release paper may be further laminated on the adhesive layer.

The method for forming an adhesive layer on at least one side of the foamed sheet is not particularly limited. For example, a method of applying an adhesive to at least one side of the foamed sheet using a coater such as a coater; a method of spraying and applying an adhesive to at least one side of the foamed sheet using a sprayer; and using a brush to foam A method of coating an adhesive on at least one side of a sheet; a method of transferring an adhesive layer formed on a release sheet to at least one side of a foamed sheet, and the like.

Examples

Hereinafter, the present invention will be described in more detail through examples, but the present invention is not limited to these examples.

[test methods]

The measurement method and evaluation method of each physical property are as follows.

<Average molecular weight between crosslinking points>

The average molecular weight between cross-linking points is determined by measuring the shear elastic modulus G ′ for the cross-linked foamable composition, and the average molecular weight between cross-linking points is determined based on the following formula based on classical rubber elasticity theory.

Mc = 2 × (1 + μ) × ρ × RT / E '

(Where, Mc: average molecular weight between cross-linking points (g / mol), μ: Poisson ratio (set to 0.5), ρ: density (g / m ³ ) of foamable composition, R: Gas constant 8.314 J / Kmol, T: Temperature (K) when measuring storage modulus, E ': Storage modulus (Pa); In addition, substitute E' = 3G ').

(Shear modulus of elasticity G ')

The shear modulus G 'is a dynamic viscoelasticity measuring device DVA-200 manufactured by IT Measurement Machinery Co., Ltd., and is heated at a temperature of 5 ° C / minute in a temperature range of 40 to 150 ° C, while the angular frequency is 1 Hz. Measured under the condition of 1% strain.

The density (g / m ³ ) of the foamable composition was measured using a high-precision model hydrometer SD-200L manufactured by M & K Corporation.

<Average bubble diameter>

The measurement was performed according to the method described above.

<Apparent density and expansion ratio>

The apparent density of the foamed sheet was measured in accordance with JIS K7222, and its inverse number was set as the expansion ratio.

<Crosslinking degree>

About 100 mg of the test piece was taken from the foamed tablet, and the weight A (mg) of the test piece was accurately weighed. Next, after immersing the test piece in 30 cm ³ of xylene at 120 ° C. for 24 hours, it was filtered by a 200-mesh metal wire mesh, and the insoluble part on the metal wire mesh was vacuum dried and accurately weighed. The weight of the dissolved part B (mg). The degree of crosslinking (mass%) was calculated from the obtained value according to the following formula.

Degree of cross-linking (% by mass) = 100 × (B / A)

<Independent bubble rate>

The measurement was performed according to the method described above.

<Impact resistance>

(Preparation of impact resistance evaluation samples)

On both sides of the foamed sheets obtained in the examples and comparative examples, an adhesive layer obtained by the following method was laminated, and a double-sided adhesive tape based on the foamed sheet was produced based on the following points.

(Making 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 ethyl acetate were added to a reactor equipped with a thermometer, a stirrer, and a cooling tube. After 80 parts by mass of nitrogen was replaced, the reactor was heated and reflux was started. Then, 0.1 part by mass of azobisisobutyronitrile was added to the reactor as a polymerization initiator. This was refluxed for 5 hours to obtain a solution of the 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 Co., Ltd., and it was 600,000.

With respect to 100 parts by mass of the solid content of the acrylic copolymer (z) contained in the obtained solution of the acrylic copolymer (z), 15 parts by mass of polymerized turpentine having a softening point of 135 ° C. and ethyl acetate (Fuji 125 parts by mass of Chemical Pharmaceutical Co., Ltd., 2 parts by mass of isocyanate-based cross-linking agent (manufactured by Tosoh Corporation, Coronate L45), and stirred to obtain an adhesive (Z). The degree of crosslinking of the acrylic pressure-sensitive adhesive was 33% by mass.

A release paper having a thickness of 150 μm was prepared, and an adhesive (Z) was applied to the release-treated surface of the release paper, followed by drying at 100 ° C. for 5 minutes to prepare an acrylic adhesive layer having a thickness of 50 μm. This acrylic adhesive layer was bonded to the surface of a base material composed of a foamed sheet. Then, based on the same points, the same acrylic adhesive layer as above was also adhered on the opposite surface of the substrate. Thereby, a double-sided adhesive tape covered with a release paper having a thickness of 150 μm was obtained.

(Manufacture of impact resistance test equipment)

FIG. 1 shows a schematic diagram of an impact resistance test apparatus.

The impact resistance test apparatus was produced by the following procedure.

First, the double-sided adhesive tape obtained above was punched out so that the outer diameter became 15.0 mm in width, the length was 15.0 mm, and the inner diameter was 13.6 mm in length and 13.6 mm in length, and a square with a width of 0.7 mm was produced. Frame-shaped test piece 1.

Next, as shown in FIG. 1 (a), a magnesium-coated sheet 3 having a square hole 2 provided in the center is prepared, and a test piece from which the release paper has been peeled off 1 is attached to the entire outer peripheral side of the hole 2 and attached to it. The upper surface of the cladding plate 3 is made of magnesium.

Next, "the glass-coated plate 4 covering the size of the said hole 2" was affixed again to 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 was turned upside down, and a pressure of 5 kgf was applied from the side of the magnesium plate 3 for 5 seconds with the magnesium plate 3 as the upper surface. The plate 3 was crimped to the test piece, 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 device is fixed to a support table 5 so that an iron ball 6 having a weight of 50 g and having a size formed in the hole 2 of the magnesium plate 3 is passed through. Hole 2 way down. Increasing the height of the dropped iron ball slowly and gradually, and measuring the height of the dropped iron ball when the test piece and the plate to be peeled off due to the impact applied by the dropping of the iron ball, and evaluated the impact resistance. The case where the height is more than 50 cm is evaluated as "S", the case where the height is 25 cm or more and 50 cm or less is evaluated as "A", and the case where the height is less than 25 cm is evaluated as "B".

<Interlayer Strength>

(Production of samples for measuring interlayer strength)

As shown in Fig. 2, after applying a primer ("PPX primer" manufactured by Cemedine Co., Ltd.) within a 25 mm square of the foamed sheet 7, an amount of 5 mm in diameter was added dropwise to the center of the coating portion. Adhesive 8 ("PPX" manufactured by Cemedine Co., Ltd.). Immediately after that, a 25 mm square aluminum jig 9 was placed on the dripping part of the adhesive, and the foamed sheet 7 and the jig 9 were crimped with the adhesive 8. Thereafter, the foamed sheet was cut along the size of the jig 9. A primer is applied to the surface of the cut foamed sheet 7 that is not adhered to the jig 9, and an adhesive 10 having a diameter of 5 mm is added dropwise to the center of the coated portion. Immediately thereafter, a 10 mm square aluminum jig 11 was placed on the adhesive dropping portion, and the foamed sheet 7 and the jig 11 were crimped with the adhesive 10. After wiping off the adhesive exuding to the periphery of the jig 11, the foam sheet is cut into the incision 12 along the size of the jig 11. This was left to stand at room temperature for 30 minutes, and then the adhesive was aged to prepare a sample for measuring interlayer strength.

(Judgment of Interlayer Strength)

Next, a sample for measuring interlayer strength was mounted on a testing machine ("Tensilon Universal Material Testing Machine" manufactured by A & D Co., Ltd.) provided with a 1kN load cell so that the surface of the foamed sheet 7 was perpendicular to the direction of stretching. The jig 9 was stretched vertically at a speed of 100 mm / minute, and the interlayer peeling was performed only within a 1 cm square range of the foam sheet. The maximum load at this time was measured, and it was set as the 1st measurement result. The same operation was repeated three times, and the average value was set as the interlayer strength. A case where the interlayer strength is 4.8 MPa or more is referred to as "A" having excellent interlayer strength. In addition, the case where the interlayer strength is 4.3 MPa or more and less than 4.8 MPa is referred to as "B" where the interlayer strength is good. In addition, the case where the interlayer strength is not more than 4.3 MPa is referred to as "C" where the interlayer strength is insufficient.

<25% compressive strength>

The foamed sheet was measured for 25% compressive strength in accordance with JIS K6767.

[Example 1]

100 parts by mass of linear low-density polyethylene obtained using a polymerization catalyst of a metallocene compound, 2.1 parts by mass of azomethoxamine as a thermally decomposable foaming agent, and zinc oxide as a bubble core regulator 1.0 part by mass and 0.5 part by mass of an antioxidant were supplied to an extruder, melt-kneaded at 130 ° C., and extruded into a long resin sheet having a thickness of 290 μm.

In addition, as the linear low-density polyethylene, a trade name “Affinity PL1850” (density: 0.902 g / cm ³ ) manufactured by Dow Chemical Co. was used. In addition, the said zinc oxide uses the brand name "OW-212F" manufactured by Hori Chemical Industry Co., Ltd.

Next, the resin sheet was cross-linked by irradiating the two sides of the long resin sheet with an electron beam of 7.4 Mrad at an acceleration voltage of 500 kV, and then the cross-linked resin sheet was continuously fed into a hot air and infrared heater and maintained at 250. The foaming furnace at a temperature of ℃ was heated and foamed to obtain a foamed sheet having a thickness of 300 μm.

Then, after the obtained foamed sheet was continuously sent out from the foaming furnace, the foamed sheet was extended in the following manner while maintaining the temperature of both sides of the foamed sheet at 200 to 250 ° C. The foamed sheet is stretched in its TD direction at an extension ratio of 2.0 times, and the foamed sheet is wound at a winding speed higher than the feeding speed (feed speed) of the resin sheet to the foaming furnace, thereby making the foam sheet The blister sheet extends in the MD direction and is brought into contact with the peripheral surface of a metal roller through which cooling water flows. In this way, the bubbles of the foamed sheet are extended in the TD direction and the MD direction to deform the foamed sheet to obtain a foamed sheet. In addition, the winding speed of the foamed sheet is adjusted in consideration of the expansion amount of the resin sheet itself in the MD direction due to foaming. The obtained foamed sheet was evaluated according to the above-mentioned evaluation method, and the results are shown in Table 1.

[Example 2]

Instead of the resin of Example 1, the composition of the resin was 30 parts by mass of linear low-density polyethylene (manufactured by Dow Chemical, trade name "Affinity PL1850", density: 0.902 g / cm ³ ), and ethylene-acetic acid. 70 parts by mass of a vinyl ester copolymer (manufactured by Tosho Corporation, trade name "Ultrathene 636"). In addition, the blending amount of azomethoxamine in the foamable composition was 1.9 parts by mass. The rest is implemented in the same manner as in Example 1. The evaluation results of the obtained foamed sheets are shown in Table 1.

[Example 3]

The blending amount of azomethoxamine in the foamable composition is 2.5 parts by mass, the electron beam irradiation amount is 9.0 Mrad, and the degree of crosslinking is 57.0% by mass. Example 1 was carried out in the same manner. The evaluation results of the obtained foamed sheets are shown in Table 1.

[Comparative Example 1]

The blending amount of azomethoxamine in the foamable composition is 1.6 parts by mass, the electron beam irradiation amount is 4.7 Mrad, and the degree of cross-linking is 16.2 mass%. Example 1 was carried out in the same manner. The evaluation results of the obtained foamed sheets are shown in Table 1.

[Comparative Example 2]

Instead of the resin of Example 1, the composition of the resin was 30 parts by mass of linear low-density polyethylene (manufactured by Dow Chemical Co., trade name "Affinity PL1850", density: 0.902 g / cm ³ ), and ethylene-acetic acid. 70 parts by mass of a vinyl ester copolymer (manufactured by Tosoh Corporation, trade name "Ultrathene 636"). In addition, the blending amount of azomethoxamine in the foamable composition was 1.5 parts by mass, the irradiation amount of the electron beam was 4.7 Mrad, and the degree of crosslinking was 19.2% by mass. Other than that, it implemented similarly to Example 1. The evaluation results of the obtained foamed sheets are shown in Table 1.

[Comparative Example 3]

Both sides of the foamed sheet obtained in Comparative Example 1 were irradiated with an electron beam at an acceleration voltage of 500 kV at 7.4 Mrad to crosslink the foamed sheet, and the degree of crosslinking was set to 71.0% by mass. The evaluation results of the obtained foamed sheets are shown in Table 1.

From this, it can be considered that Examples 1 and 3 are good in all aspects of 25% compressive strength, interlayer strength, and impact resistance. By setting the average molecular weight between the crosslinking points to a specific range, the softness was successfully maintained, And make the durability good. In addition, although the impact resistance of Example 2 was inferior to that of Examples 1 and 3, the interlayer strength was good, and the flexibility and durability were good. In contrast, Comparative Examples 1 and 2 have a large average molecular weight between the crosslinking points, and thus it is difficult to sufficiently improve the durability. Comparative Example 3 had a small average molecular weight between crosslinking points, and it was difficult to sufficiently improve durability.

Claims (10)

    A polyolefin foam sheet is obtained by foaming a crosslinked foamable composition containing a polyolefin resin, and the average molecular weight between the crosslinking points of the foamable composition is 15,000 to 30,000.         For example, the polyolefin-based foamed sheet according to item 1 of the application, wherein the polyolefin resin is a polyethylene resin.         For example, the polyolefin-based foamed sheet according to item 2 of the patent application range, wherein the polyolefin resin is a linear low-density polyethylene polymerized by using a polymerization catalyst of a metallocene compound.         For example, the polyolefin-based foamed sheet according to any of claims 1 to 3 has a crosslinking degree of 20 to 70% by mass.         For example, the polyolefin-based foamed sheet according to any of claims 1 to 4 has an impact resistance evaluation result in a range of 25 to 50 cm and a 25% compressive strength of 10 to 2,000 kPa.         For example, the polyolefin-based foamed sheet according to any of claims 1 to 5 has a thickness of 0.02 to 0.8 mm.     For example, the polyolefin-based foamed sheet according to any of claims 1 to 6, has a foaming ratio of 1.2 to 8 cm ³ / g.     For example, the polyolefin-based foamed sheet according to any of claims 1 to 7 is obtained by foaming a foamable composition further containing a thermally decomposable foaming agent.         A method for manufacturing a polyolefin-based foamed sheet, which is a method for manufacturing a polyolefin-based foamed sheet according to any one of claims 1 to 8, and the method for manufacturing a polyolefin-containing foam The foaming composition and the crosslinked foamable composition are heated to foam the thermally decomposable foaming agent.         An adhesive tape includes a polyolefin-based foamed sheet according to any one of claims 1 to 8 and an adhesive layer provided on at least one side of the polyolefin-based foamed sheet.