TWI752092B - Polyolefin-based foam sheet, method for producing the same, and adhesive tape - Google Patents

Abstract

The polyolefin-based foamed sheet of the present invention is obtained by foaming a cross-linked foamable composition containing a polyolefin resin, and the average molecular weight between the cross-linking points of the foamable composition is 15,000 to 30,000 . According to the present invention, a foamed sheet having high flexibility and durability can be provided even when the sheet is thinned.

Description

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

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

In electronic devices such as mobile phones, cameras, game consoles, electronic notebooks, personal computers, etc., sealing materials or shock absorbing materials composed of foam sheets, and adhesive tapes based on foam sheets are used. For example, the display device used in the above-mentioned electronic equipment usually 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 the frame portion outside the display panel, a foam sheet is used. Adhesive tape for the substrate.

As a conventional foam sheet used in electronic equipment, a cross-linked polyolefin-based resin obtained by foaming and cross-linking a foamable polyolefin-based resin sheet containing a thermally decomposable foaming agent is known sheet (for example, refer to Patent Document 1).

prior art literature

Patent Literature

Patent Document 1: International Publication No. 2005/007731

However, recently, electronic equipment has been developed in a direction of miniaturization, and on the other hand, various parts have also been developed with high functions, and the space limitation inside the electrical equipment has increased. For example, due to the miniaturization of electronic equipment and the enlargement of the display device, the space of the frame portion outside the display panel becomes narrow. Therefore, for the foamed sheet, not only relatively thick ones are required to have high flexibility and durability, but also high flexibility and durability are required even when they are thinned.

The present invention is made in view of the above circumstances, and its subject 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 foam sheet obtained by foaming a cross-linked foamable composition containing a polyolefin resin, wherein the average molecular weight between cross-linking 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], which has a degree of crosslinking of 20 to 70% by mass.

[5] The polyolefin-based foamed sheet according to any one of the above [1] to [4], which 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.

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

[7] The polyolefin-based foamed 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-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], which is a method for producing a polyolefin-based foamed sheet containing a polyolefin resin and The thermally decomposable foaming agent and the crosslinked foamable composition are heated to foam the above-mentioned 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 board

4: Glass quilt board

5: Support Desk

6: Iron ball

7: Foam sheet

8: Adhesive

9: Jig

10: Adhesive

11: Jig

12: Cut

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

FIG. 2 is an explanatory diagram of a method for measuring interlaminar strength.

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

[Polyolefin-based foam sheet]

The polyolefin-based foamed sheet of the present invention (hereinafter also simply referred to as "foamed sheet") is a foamed sheet obtained by foaming a cross-linked foamable composition containing a polyolefin resin, and is cross-linked. The average molecular weight between the cross-linking points of the foamable 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 more than 30,000, impact resistance, interlaminar strength, and the like decrease, and durability becomes insufficient. In addition, the compressive strength exceeds the desired range, and it becomes difficult to obtain a foamed sheet having suitable flexibility.

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

(polyolefin resin)

The polyolefin resin used for the foamed sheet includes polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer, and the like, and among these, polyethylene resin is preferred.

Examples of polyethylene resins include polyethylene resins polymerized using polymerization catalysts such as Ziegler-Natta compounds, metallocene compounds, and chromium oxide compounds. Polyethylene resin produced by polymerization of metal compound catalyst.

Moreover, as a polyethylene resin, a linear low density polyethylene is preferable. By using the linear low-density polyethylene, the obtained foam sheet obtains high flexibility, and it becomes possible to realize the thinning of the foam sheet. More preferably, the linear low-density polyethylene is obtained by using a polymerization catalyst such as a metallocene compound. Further, 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 monomer amount) and a small amount of α-olefin if necessary. The obtained linear low density polyethylene.

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

The density of polyethylene resin such as the above-mentioned linear low density polyethylene is preferably ^{0.870-0.910 g/cm 3} , more preferably 0.875-0.907 g/cm ³ , and still more preferably ^{0.880-0.905 g/cm 3} . As the polyethylene resin, a variety of polyethylene resins can be used, and polyethylene resins other than the above-mentioned density range may be added.

In the present invention, by crosslinking the polyethylene resin polymerized using the polymerization catalyst of the metallocene compound, especially the linear low density polyethylene, with the following crosslinking degree, it becomes easy to crosslink the resin. The point-to-point average molecular weight is adjusted to the above range.

(two metallocene compounds)

Examples of the dimetallocene compound include compounds such as bis(cyclopentadienyl)metal complexes having a structure in which a transition metal is sandwiched by a π-electron-based unsaturated compound. More specifically, one or two or more cyclopentadienyl rings or their analogs are present in the form of ligands in four such as titanium, zirconium, nickel, palladium, hafnium, and platinum. Compounds of transition metals.

The properties of the active sites of the two metallocene compounds are uniform, and each active site has the same degree of activity. The polymer synthesized using the metallocene compound has high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, etc., so when crosslinking the sheet containing the polymer synthesized using the metallocene compound, The cross-linking will proceed uniformly. Since the uniformly cross-linked sheet is foamed uniformly, the size of the bubble diameter is also likely to be uniform. Moreover, since it can be extended uniformly, the thickness of a foam sheet can be made uniform.

As a ligand, a cyclopentadienyl ring, an indenyl ring, etc. are mentioned, for example. These cyclic compounds may also be substituted with hydrocarbyl, substituted hydrocarbyl, or hydrocarbyl-substituted metalloid groups. As a hydrocarbon group, For example, methyl, ethyl, propyl, butyl, pentyl, hexyl, 2-ethylhexyl, heptyl, octyl, nonyl, decyl, cetyl base, phenyl, etc. In addition, "various" means various isomers including normal, secondary, tertiary, and iso.

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

Furthermore, in addition to π-electron-based unsaturated compounds, monovalent anion ligands such as chlorine or bromine or dianion chelate ligands, hydrocarbons, alkoxides, arylamides, aryl ethers, amides can also be used , arylamide, phosphide, aryl phosphine, etc.

Examples of the dimetallocene compound containing a tetravalent transition metal or a ligand include cyclopentadienyl titanium tris(dimethylamide), methylcyclopentadienyl titanium tris(dimethylamide) ), bis(cyclopentadienyl) titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamide zirconium dichloride, etc.

The dimetallocene compound acts as a catalyst in the polymerization of various olefins by combining with a specific co-catalyst (co-catalyst). As a specific co-catalyst, methylaluminoxane (MAO), a boron type compound, etc. are mentioned. In addition, the use ratio of the co-catalyst to the metallocene compound is preferably 10-1 million mol times, more preferably 50-5,000 mol times.

As an ethylene-vinyl acetate copolymer used as a polyolefin resin, the ethylene-vinyl acetate copolymer containing 50 mass % or more of ethylene is mentioned, for example.

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

Specific examples of the α-olefin constituting the propylene-α-olefin copolymer include: ethylene, 1-butane 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, etc. Among these, α-olefins having 6 to 12 carbon atoms are preferred.

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

In the case of containing other polyolefin resins, the ratio of the other polyolefin resins 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, and further Preferably it is 30 mass % or less. In addition, 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 resins other than the polyolefin resin may be contained as long as the effect of the present invention is not impaired. In the foamed sheet, the ratio of the polyolefin resin to the total resin amount is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more.

As resins other than the polyolefin resin, ethylene-propylene-based thermoplastic elastomers such as styrene-based thermoplastic elastomers and EPDM (ethylene propylene diene monomer, ethylene-propylene-propylene-diene monomers), etc. are mentioned.

(Crosslinking degree)

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

(foaming ratio)

The foaming 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 within the above-mentioned specific range, it becomes possible to improve durability such as impact resistance while securing flexibility at a wide range of foaming ratios.

In addition, with regard to the foamed sheet, by reducing the foaming ratio within the above-mentioned range, the mechanical strength is improved, the durability is further improved, and the cells of the foamed sheet are easily refined or reduced. The following average bubble diameter is smaller. From such a viewpoint, the expansion ratio of the foamed sheet is more preferably 1.3 to 3 cm ³ /g, and more preferably 1.5 to 2.3 cm ³ /g. In addition, in this invention, the density of a foamed sheet was calculated|required based on JISK7222, and the inverse number was made into expansion ratio.

(independent bubble rate)

Regarding the foamed sheet, the cells thereof are preferably closed cells. The fact that the cells are closed cells means that the ratio of closed cells to all the cells (also referred to as closed cell ratio) is 70% or more. The closed cell ratio is preferably 80% or more, more preferably 90% or more.

The closed cell ratio can be determined according to ASTM D2856 (1998). As a commercially available measuring device, dry automatic density meter Accupyc 1330 etc. are mentioned.

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 was calculated according to the following formula. Further, 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 immersed 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 releasing the pressure in water, the test piece was taken out from the water, the water adhering to the surface of the test piece was removed, the weight W _{2 of the test piece was measured, and the open cell ratio F 1} and the closed cell ratio F _{2 were} calculated according to the following formulas.

Open cell ratio 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 foam sheet is preferably 0.02 to 0.8 mm. In the present invention, even within such a relatively wide thickness range, the average molecular weight between crosslinking points is set within a specific range as described above, whereby the flexibility of the foam sheet can be ensured and the resistance can be improved. Durability such as impact resistance. The thickness of the foamed sheet is more preferably 0.08 to 0.50 mm, further preferably 0.10 to 0.40 mm.

字形等，除該等形狀以外，亦可為通常之四方形、圓形等其他任何形狀。 The foamed sheet is not particularly limited, and it can be processed into a thin linear shape, and for example, the width of the foamed sheet can be set to 10 mm or less and used. In addition, for example, it may be 5 mm or less, and further 1 mm or less. When the width of the foam sheet is reduced, it can be suitably used inside a miniaturized electronic device. In addition, even if the foam sheet of the present invention is reduced in width, durability is maintained favorably. The lower limit value 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. In addition, the planar shape of the foam sheet is not particularly limited, and it may be an elongated rectangle, a frame shape, an L-shape,

In addition to these shapes, the font shape and the like may also be any other shape such as a normal square or a circle.

(Mechanical Properties)

The 25% compressive strength of the foamed sheet is preferably 10-2000kPa, more preferably 4000-2000kPa, and still more preferably 800-1500kPa. By making the 25% compressive strength 2000 kPa or less, the foam sheet has shock absorption properties and sealing properties, and can be suitably used as a shock absorber and a sealing material. In addition, by increasing the compressive strength, it becomes easy to make the mechanical strength good. In addition, the 25% compressive strength means the thing obtained by measuring the foamed sheet in accordance with JIS K6767.

Moreover, it is preferable that the result of the impact resistance evaluation of a foam sheet is the range of 25-50 cm. If the impact resistance evaluation result is 25 cm or more, the impact resistance of the foamed sheet becomes sufficient even when the sheet width is narrowed. Furthermore, the interlaminar strength of the foamed sheet is preferably 4.3 MPa or more, and more preferably 4.8 MPa or more. In addition, the values of impact resistance evaluation and interlaminar strength were measured according to the methods of the following examples.

(average bubble diameter)

The average cell diameters of the cell systems MD and TD of the foamed sheet are each preferably 120 μm or less, more preferably 100 μm or less, and more preferably 80 μm or less, and ZD has an average cell diameter of 80 μm or less, preferably 50 μm or less, and more The so-called "microcell" of 40 μm or less is preferable. In the present invention, by thus reducing the bubble diameter, the number of bubble walls per unit length increases. Therefore, even when the width of the foamed sheet is narrowed, for example, it becomes easy to improve impact resistance and the like by the existence of a large number of cell walls in the narrow width. Moreover, in this invention, it becomes easy to form a micropore by making the average molecular weight between crosslinking points into the said range, and making a crosslinking degree and a foaming ratio into the said suitable range.

In addition, from the viewpoint of easy manufacturability, the average cell diameters of MD and TD are each preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 25 μm or more. In addition, the average bubble diameter of ZD is preferably 5 μm or more, more preferably 10 μm or more, and still more preferably 15 μm or more.

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

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

The foamed sheet was cut into a 50 mm square and obtained as a foam sample for measurement. After immersing this in liquid nitrogen for 1 minute, it cut|disconnected in the thickness direction along MD direction, TD direction, and ZD direction with a razor blade, respectively. Using a digital microscope (“VHX-900” manufactured by KEYENCE Co., Ltd.), a 200-fold magnification photograph was taken of the cross-section, and all existing sections of the 2 mm long section in the MD, TD, and ZD directions were taken. The bubble diameter was measured, and this operation was repeated 5 times. Then, the average value of all the bubbles was defined as the average bubble diameter in the MD direction, the TD direction, and the ZD direction.

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

(Thermal Decomposition Foaming Agent)

Preferably, the foamed sheet of the present invention is obtained by foaming a foamable composition containing the above-mentioned 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 organic foaming agents include azo compounds such as azodicarbonamide, metal salts of azodicarboxylate (barium azodicarboxylate, etc.), azobisisobutyronitrile, Nitroso compounds such as nitropentamethylenetetramine (N,N'-dinitrosopentamethylenetetramine), hydrazodicarbonamide, 4,4'-oxybis (benzene sulfohydrazine), toluenesulfonic acid Hydrazine derivatives such as hydrazine, amine urea compounds such as tosylamine carbamide, and the like.

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

Among these, from the viewpoint of obtaining fine bubbles, and from the viewpoint of economy and safety, an azo compound is preferable, and azodimethylamide is particularly preferable. These thermally decomposable foaming agents may be used alone or in combination of two or more.

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 share.

Moreover, it is preferable that a foamable composition contains a cell nucleus adjuster in addition to the said resin and a thermally decomposable foaming agent. Examples of the cell nucleus adjuster include zinc compounds such as zinc oxide and zinc stearate, citric acid, and organic compounds such as urea, and among these, zinc oxide is more preferred. It becomes easy to further reduce a cell diameter by using a cell nucleus adjusting agent in addition to the said foaming agent. The blending amount of the bubble nucleus adjuster 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 optionally contain additives commonly used in foams, such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and fillers.

[Manufacturing method of foam 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. manufacture. More specifically, the manufacturing method thereof includes the following steps (1) to (4).

Step (1): The step of mixing the additives containing the polyolefin resin and the thermally decomposable foaming agent, and forming a sheet-like foamable composition (resin sheet)

Step (2): The step of irradiating the sheet-like foamable composition with ionizing radiation to cross-link the foamable composition

Step (3): Heating the cross-linked foamable composition to make the thermally decomposable foaming agent develop. bubbles, and the steps of forming fine bubbles

Step (4): After forming the micro-bubbles, extend in either or both directions of the MD direction or the TD direction, and extend the micro-bubbles to obtain a foamed sheet

In step (1), the method of forming the resin sheet is not particularly limited. For example, the foamable composition is extruded from the extruder into a sheet by supplying the polyolefin resin and additives to the extruder for melt kneading. , 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 electron beams, α rays, β rays, and γ rays is used. The irradiation amount of the above-mentioned ionizing radiation may be adjusted so that the degree of crosslinking of the obtained foam sheet falls within the above-mentioned desired range, preferably 5-15 Mrad, more preferably 6-13 Mrad.

In step (3), the heating temperature when the foamable composition is heated to foam the thermally decomposable foaming agent is above the foaming temperature of the thermally decomposable foaming agent, preferably 200 to 300°C. ℃, more preferably 220~280℃.

The extension 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, in the case of extending the foam sheet after foaming the resin sheet to obtain the foam sheet, the foam sheet can be continuously extended without cooling the foam sheet and maintaining the molten state at the time of 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 extension ratio of the foam sheet to one or both of the MD direction and the TD direction is preferably 1.1 to 5.0 times, more preferably 1.5 to 4.0 times.

The flexibility and tensile strength of a foam sheet will become favorable easily that a draw ratio is made into the said lower limit or more. On the other hand, if it is below the upper limit value, the foam sheet will be prevented from being broken during stretching When the foaming gas is broken or the foaming gas escapes from the foamed sheet during foaming, the foaming ratio is significantly reduced, the flexibility or tensile strength of the foamed sheet becomes good, and the quality is easy to become uniform.

Moreover, at the time of extending|stretching, what is necessary is just to heat a foam sheet to 100-280 degreeC, for example, Preferably it is 150-260 degreeC.

Moreover, it is preferable to provide the process of rapidly cooling the foam sheet after extending the foam 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, the thickness of the foam sheet can be easily made uniform, and it becomes easy to adjust to a desired cell diameter. The rapid cooling method is not particularly limited, and may be performed by, for example, a method of bringing the foam sheet into contact with a metal roll through which cooling water flows.

However, the present production 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 with ionizing radiation, the foamable composition may be preliminarily blended with an organic peroxide, and the foamable composition may be heated to decompose the organic peroxide, and the like may be used for crosslinking. In addition, step (4), that is, the extension of the foam sheet may be omitted.

The use of the foamed sheet is not particularly limited, but for example, it is preferably used inside an electronic device. Since the foamed sheet of the present invention has high durability even if it is thinned, it is particularly suitable for use in various portable electronic devices in which the space for disposing the foamed sheet is small. As a portable electronic apparatus, a mobile phone, a camera, a game machine, an electronic notepad, a personal computer, etc. are mentioned. The foam sheet can be used as an impact absorbing material and a sealing material inside an electronic device. In addition, it can also be used for adhesive tapes based on foam sheets.

The adhesive tape includes, for example, a foam sheet and an adhesive layer provided on at least one side of the foam sheet, and is preferably a double-sided adhesive tape 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 better It is 7-150 micrometers, More preferably, it is 10-100 micrometers. If the thickness of the adhesive layer is in the range of 5 to 200 μm, the thickness of the structure to be 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, a urethane-based adhesive, a rubber-based adhesive, and the like can be used.

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

The method of forming the adhesive layer on at least one side of the foam sheet is not particularly limited. Examples include: a method of applying an adhesive to at least one side of a foam sheet using a coating machine such as a coater; a method of spraying and applying an adhesive to at least one side of the foam sheet using a sprayer; using a brush to apply an adhesive to the foam sheet A method of applying an adhesive to 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 foam sheet, etc.

Example

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

[test methods]

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

<Average molecular weight between cross-linking points>

The average molecular weight between cross-linking points is obtained by measuring the shear elastic modulus G' of the cross-linked foamable composition, and calculating the average molecular weight between cross-linking points from the following formula based on the classical theory of rubber elasticity.

Mc=2×(1+μ)×ρ×RT/E'

(wherein, Mc: average molecular weight between cross-linking points (g/mol), μ: Poisson ratio (set to 0.5), ρ: density of foamable composition (g/m ³ ), R: Gas constant 8.314J/Kmol, T: temperature at which storage elastic modulus was measured (K), E': storage elastic modulus (Pa); in addition, substitute E'=3G').

(Shear elastic modulus G')

The shear elastic modulus G' is measured using a dynamic viscoelasticity measuring device DVA-200 manufactured by IT Measuring Instruments Co., Ltd., and the temperature is increased at a rate of 5°C/min in the temperature range of 40 to 150°C, while the angular frequency is 1Hz. , under the condition of 1% strain.

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

<Average bubble diameter>

The measurement is carried out according to the above-mentioned method.

<Apparent density and expansion ratio>

About the foamed sheet, the apparent density was measured according to JIS K7222, and the inverse number was set as the expansion ratio.

<Crosslinking degree>

A test piece of about 100 mg was taken from the foamed sheet, and the weight A (mg) of the test piece was accurately weighed. Next, the test piece was ^{immersed in 30 cm 3} of xylene at 120°C for 24 hours, filtered through a wire mesh of 200 meshes, and the insoluble part of the wire mesh was collected, dried in vacuum, and accurately weighed. Weight B (mg) of the dissolved fraction. The degree of crosslinking (mass %) was calculated from the obtained value according to the following formula.

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

<Independent bubble rate>

The measurement is carried out according to the above-mentioned method.

<Shock resistance>

(Preparation of impact resistance evaluation samples)

On both sides of the foam sheets obtained in Examples and Comparative Examples, the adhesive layers obtained by the following methods were laminated, and based on the following points, a double-sided adhesive tape based on the foam sheets was produced.

(The production method of double-sided adhesive tape)

75 parts by mass of butyl acrylate, 22 parts by mass of 2-ethylhexyl acrylate, 3 parts by mass of acrylic acid, 0.2 parts by mass of 2-hydroxyethyl acrylate, and ethyl acetate were added to the reactor equipped with a thermometer, a stirrer, and a cooling pipe. 80 parts by mass, after nitrogen replacement, the reactor was heated and reflux was started. Next, 0.1 part by mass of azobisisobutyronitrile was added to the above-mentioned 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 Corporation as a column, and found to be 600,000.

With respect to 100 parts by mass of the solid content of the acrylic copolymer (z) contained in the solution of the obtained acrylic copolymer (z), 15 parts by mass of polymerized pine ester having a softening point of 135° C., ethyl acetate (no two) were added. Chemical Co., Ltd. product) 125 mass parts, and 2 mass parts of an isocyanate-based crosslinking agent (Dongsuo Co., Ltd. product, Coronate L45) were stirred, and the adhesive (Z) was obtained. In addition, the degree of crosslinking of the acrylic adhesive was 33% by mass.

A release paper with a thickness of 150 μm was prepared, an adhesive (Z) was coated on the release-treated surface of the release paper, and dried at 100° C. for 5 minutes to prepare an acrylic adhesive layer with a thickness of 50 μm. The acrylic adhesive layer is bonded to the surface of the base material composed of the foam sheet. Then, based on the same point, the same acrylic adhesive layer as above is also attached to the opposite surface of the base material. Thereby, the double-sided adhesive tape covered with the release paper of thickness 150 micrometers was obtained.

(Manufacture of impact resistance test device)

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

The impact resistance test apparatus was produced according to the following procedure.

First, the double-sided adhesive tape obtained above was punched so that the outer diameter was 15.0 mm in width, 15.0 mm in length, and the inner diameter was 13.6 mm in width and 13.6 mm in length, and the width of each frame edge was 0.7 mm. Frame-shaped test piece 1 .

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

Next, the "glass-made covering plate 4 covering the size of the hole 2" was attached to the test piece 1 again, and the hole 2 was covered, thereby assembling an impact resistance test apparatus.

After that, the impact resistance testing apparatus was turned upside down, and in the state where the magnesium cover plate 3 was on the upper surface, a pressure of 5 kgf was applied from the magnesium cover plate 3 side for 5 seconds, and the magnesium cover placed on the upper and lower sides was placed. The landing plate 3 was crimped to the test piece, and was left to stand at room temperature for 36 hours.

(Judgment of impact resistance)

As shown in FIG. 1(b), the manufactured impact resistance test apparatus was fixed to the support table 5, and the iron ball 6 with a weight of 50 g was passed through the hole 2 formed in the magnesium covered plate 3 to pass through. The way of hole 2 falls. The height of the falling iron ball was gradually increased gradually, and the height of the falling iron ball when the test piece and the adhered plate were peeled off by the impact applied by the falling of the iron ball was measured, and the impact resistance was evaluated. The case where the height was more than 50 cm was evaluated as "S", the case where the height was 25 cm or more and 50 cm or less was evaluated as "A", and the case where the height was less than 25 cm was evaluated as "B".

<Interlayer Strength>

(Preparation of samples for interlaminar strength measurement)

As shown in Figure 2, a primer (Cemedine) is applied to the area of 25mm square of the foam sheet 7. After "PPX primer" manufactured by Co., Ltd.), Adhesive 8 ("PPX" manufactured by Cemedine Co., Ltd.) was dripped at the center of the coated part with a diameter of 5 mm. Immediately thereafter, a jig 9 made of aluminum with a square of 25 mm was placed on the part where the adhesive was dropped, and the foam sheet 7 and the jig 9 were crimped with the adhesive 8 . Thereafter, the foam sheet is cut along the size of the jig 9 . A primer is applied to the surface of the cut foam sheet 7 that is not attached to the jig 9, and an adhesive agent 10 with a diameter of 5 mm is dropped in the center of the applied portion. Immediately thereafter, a jig 11 made of aluminum with a square of 10 mm was placed on the part where the adhesive was dropped, and the foam sheet 7 and the jig 11 were crimped with the adhesive 10 . After wiping off the adhesive exuded to the periphery of the jig 11 , a cut 12 is cut into the foam sheet along the size of the jig 11 . The adhesive was aged by allowing it to stand at room temperature for 30 minutes, and it was set as a sample for interlayer strength measurement.

(Determination of interlayer strength)

Next, on a testing machine (“Tensilon universal material testing machine” manufactured by A&D Co., Ltd.) equipped with a 1 kN load cell, a sample for interlaminar strength measurement was attached so that the sheet surface of the foam sheet 7 was perpendicular to the tensile direction. The jig 9 was stretched vertically upward at a speed of 100 mm/min, and the interlayer peeling was performed only in the range of 1 cm square of the foam sheet. The maximum load at this time was measured, and it was set as the result of the first measurement. The same operation was repeated three times, and the average value was set as the interlayer strength. The case where the interlaminar strength was 4.8 MPa or more was regarded as "A" which was excellent in the interlaminar strength. In addition, the case where the interlaminar strength was 4.3 MPa or more and less than 4.8 MPa was referred to as "B" with good interlaminar strength. In addition, the case where the interlaminar strength was less than 4.3 MPa was referred to as "C" that the interlaminar strength was insufficient.

<25% compressive strength>

Regarding the foamed sheet, the 25% compressive strength was measured according to JIS K6767.

[Example 1]

Linear low-density polyethylene 100 obtained by using the polymerization catalyst of two metallocene compounds Parts by mass, 2.1 parts by mass of azodimethylamide as a thermally decomposable foaming agent, 1.0 part by mass of zinc oxide as a cell nucleus adjuster, and 0.5 part by mass of antioxidant were supplied to an extruder, and the process was carried out at 130° C. Melt kneading, and extrude into a long resin sheet with a thickness of 290 μm.

In addition, the said linear low density polyethylene used the brand name "Affinity PL1850" (density: 0.902g/cm<^3> ) by Dow Chemical Company. In addition, the brand name "OW-212F" by Sakai Chemical Industry Co., Ltd. was used for the said zinc oxide system.

Next, after irradiating an electron beam 7.4 Mrad with an accelerating voltage of 500 kV on both sides of the above-mentioned long resin sheet to cross-link the resin sheet, the cross-linked resin sheet is continuously fed into a hot air and an infrared heater and kept at 250 °C. It was heated in a foaming furnace at ℃ to make it foamed to obtain a foamed sheet with a thickness of 300 μm.

Then, after the obtained foam sheet was continuously sent out from the foaming furnace, the foam sheet was extended as follows while maintaining the temperature of both surfaces at 200 to 250°C. The foamed sheet is stretched in the TD direction at a stretching ratio of 2.0 times, and the foamed sheet is wound at a winding speed higher than the feeding speed (feeding speed) of the resin sheet to the foaming furnace, thereby making the foamed sheet. The bubble sheet is extended in the MD direction, and is brought into contact with the peripheral surface of the metal roll through which cooling water flows. Thus, the bubbles of the foamed sheet are extended in the TD direction and the MD direction and deformed to obtain a foamed sheet. In addition, the winding speed of the said foamed sheet is adjusted in consideration of the expansion amount to MD direction by foaming of the resin sheet itself. The obtained foam sheet was evaluated according to the above-mentioned evaluation method, and the results are shown in Table 1.

[Example 2]

In place 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., Ltd., trade name "Affinity PL1850", density: 0.902 g/cm ³ ), and ethylene-acetic acid 70 parts by mass of vinyl ester copolymer (manufactured by Tosso Co., Ltd., trade name "Ultrathene 636"). Moreover, the compounding quantity of the azodimethylamide in the foamable composition was made into 1.9 mass parts. These other systems were carried out in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained foam sheet.

[Example 3]

In addition to setting the blending amount of azodimethylamide in the foamable composition to 2.5 parts by mass, the electron beam irradiation dose to be 9.0 Mrad, and the degree of crosslinking to be 57.0 mass % Example 1 was carried out in the same manner. Table 1 shows the evaluation results of the obtained foam sheet.

[Comparative Example 1]

In addition to setting the blending amount of azodimethylamide in the foamable composition to 1.6 parts by mass, the electron beam irradiation dose to be 4.7 Mrad, and the degree of crosslinking to be 16.2 mass %, Example 1 was carried out in the same manner. Table 1 shows the evaluation results of the obtained foam sheet.

[Comparative Example 2]

In place 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 vinyl ester copolymer (manufactured by Tosoh Corporation, trade name "Ultrathene 636"). In addition, the blending amount of the azodimethylamide 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 mass %. Other than these, it carried out similarly to Example 1. Table 1 shows the evaluation results of the obtained foam sheet.

[Comparative Example 3]

The two sides of the foam sheet obtained in Comparative Example 1 were irradiated with an electron beam 7.4 with an accelerating voltage of 500 kV The foam sheet was cross-linked by Mrad, and the degree of cross-linking was 71.0% by mass. Table 1 shows the evaluation results of the obtained foam sheet.

From this, it is considered that Examples 1 and 3 are good in all aspects of 25% compressive strength, interlaminar strength, and impact resistance, and by setting the average molecular weight between cross-linking points in a specific range, they succeeded in maintaining good flexibility. And make durability good. In addition, although the impact resistance of Example 2 was inferior to that of Examples 1 and 3, the interlaminar strength was good, and the flexibility and durability were good. On the other hand, in Comparative Examples 1 and 2, since the average molecular weight between the cross-linking points was large, it was difficult to sufficiently improve the durability. In Comparative Example 3, the average molecular weight between the crosslinking points was small, and it was difficult to sufficiently improve the durability.

Claims (10)

A polyolefin-based foam sheet, which is formed by foaming a cross-linked foamable composition containing a polyolefin resin, and the average molecular weight between the cross-linking points of the foamable composition is 15,000 to 30,000, The average cell diameters of MD and TD of the cells of the polyolefin-based foam sheet are each 80 μm or less. The polyolefin-based foamed sheet according to claim 1, wherein the polyolefin resin is a polyethylene resin. The polyolefin-based foamed sheet of claim 2, wherein the polyolefin resin is a linear low-density polyethylene polymerized using a metallocene compound polymerization catalyst. As in the polyolefin-based foamed sheet of any one of claims 1 to 3, the degree of crosslinking is 20 to 70% by mass. For example, the polyolefin-based foamed sheet of any one of claims 1 to 3 has an impact resistance evaluation result in the range of 25 to 50 cm, and a 25% compressive strength of 10 to 2,000 kPa. The thickness of the polyolefin-based foam sheet according to any one of claims 1 to 3 is 0.02 to 0.8 mm. For example, the polyolefin-based foam sheet of any one of claims 1 to 3 has a foaming ratio of 1.2 to 8 cm ³ /g. The polyolefin-based foam sheet according to any one of claims 1 to 3 is obtained by foaming a foamable composition further containing a thermally decomposable foaming agent. A method for producing a polyolefin-based foamed sheet, which is a method for producing a polyolefin-based foamed sheet according to any one of the first to eighth patent applications, and, In this production method, a crosslinked foamable composition containing a polyolefin resin and a thermally decomposable foaming agent is heated to foam the above-mentioned thermally decomposable foaming agent. An adhesive tape comprising the polyolefin-based foamed sheet of any one of claims 1 to 8, and an adhesive layer provided on at least one side of the polyolefin-based foamed sheet.

Images