TW201942284A - Foamed composite sheet, adhesive tape, cushioning material for electronic components, and adhesive tape for electronic components - Google Patents

Abstract

This foamed composite sheet is provided with: a foamed sheet containing at least one type of resin selected from the group consisting of an elastomer resin and a polyolefin resin; and a resin layer stacked on at least one surface of the foamed sheet. This adhesive tape is provided with: the foamed composite sheet; and an adhesive material provided on at least one surface of the foamed composite sheet. This cushioning material for electronic components uses the foamed composite sheet. This adhesive tape for electronic elements is provided with: the cushioning material for electronic components; and an adhesive material provided on at least one surface of the cushioning material for electronic components. According to the present invention, the foamed sheet, the adhesive tape, the cushioning material for electronic components, and the adhesive tape for electronic components can be provided, which have excellent shock absorbing properties and mechanical strength.

Description

Foamed composite sheet, adhesive tape, buffer material for electronic parts, and adhesive tape for electronic parts

The present invention relates to a foamed composite sheet provided with a foamed sheet and a resin layer, an adhesive tape provided with the foamed composite sheet and an adhesive material, a buffer material for electronic components, and an electronic device including the buffer material and adhesive material for electronic components. Adhesive tape for parts.

Conventionally, a porous resin material having a large number of pores inside a layer made of resin has excellent cushioning, heat insulation, water resistance, and moisture resistance. Therefore, packaging materials for articles need to be protected from gas. It can be used in various applications such as parts affected by liquids, sealing materials that seal the peripheral parts of the casing, cushioning materials that cushion vibration and impact, and substrates for adhesive sheets. For example, Patent Document 1 discloses a crosslinked polyolefin resin foam sheet (for example, a crosslinked polyolefin resin foam sheet obtained by foaming a foamable polyolefin resin sheet containing a thermally decomposable foaming agent and crosslinking it). (See Patent Documents 1 and 2).
In recent years, various electronic devices such as mobile phones and personal computers, digital cameras, and compact video cameras have been expected to be accompanied by miniaturization and thinness of products. The resin foam sheets used in these electronic devices are also being used. Thinning.
Prior art literature patent literature

Patent Document 1: International Publication No. 2005/007731 Patent Document 2: Japanese Patent Laid-Open No. 2014-28925

[Problems to be Solved by the Invention]

However, the thinned resin foam sheet generally has low impact absorption properties and low mechanical strength.

For example, a thin resin foam sheet is generally low in impact resistance and impact absorption. Therefore, when it is used in an electronic device, it is difficult to achieve a sufficient function as a buffer material.
In order to improve impact resistance and impact absorption, a resin foam sheet containing an elastomer resin is known. When manufacturing or storing a resin foam sheet, the sheet may be wound on a reel, but especially a resin foam sheet containing an elastomer resin is liable to stick during winding, and when it is rolled out during use And sometimes problems.

Further, if the foamed sheet is thin, mechanical strength such as tensile strength tends to be low. Therefore, for example, when the foamed sheet is used as an adhesive tape, it is likely to be damaged during secondary processing. On the other hand, if the foamed sheet has a reduced foaming ratio in order to increase the mechanical strength, the compressive strength may be increased and the inherent properties of the foamed sheet such as impact absorption may be impaired.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a foamed sheet, an adhesive tape, a buffer material for electronic parts, and an adhesive tape for electronic parts that are excellent in impact absorption and mechanical strength.
Another object of the present invention is to provide a foamed sheet which is excellent in impact resistance and impact absorption while suppressing sticking.
Furthermore, another object of the present invention is to provide a cushioning material for electronic parts having high tensile strength, low compressive strength, and excellent secondary workability, and an adhesive tape for electronic parts using the cushioning material for electronic parts.
[Technical means to solve the problem]

After intensive research, the inventors found that a foamed composite sheet composed of a foamed sheet having excellent impact absorption and a resin layer with excellent mechanical strength would solve the above-mentioned problems, thereby completing the present invention.
That is, the present invention provides one of the following [1] to [20].
[1] A foamed composite sheet comprising:
Foamed sheet: containing at least one resin selected from the group consisting of an elastomer resin and a polyolefin resin; and resin layer: laminated on at least one side of the foamed sheet.
[2] The foamed composite sheet according to the above [1], which has a 25% compressive strength of 1.0 to 700 kPa.
[3] A foamed composite sheet comprising a foamed sheet containing an elastomer resin and a resin layer laminated on at least one side of the foamed sheet, the interlaminar strength of the foamed composite sheet being 0.3 MPa or more, 25% compression The strength is 30 to 700 kPa.
[4] The foamed composite sheet according to the above [3], wherein the elastomer resin is a thermoplastic elastomer resin.
[5] The foamed composite sheet according to the above [3] or [4], wherein the thermoplastic elastomer resin is selected from the group consisting of an olefin-based elastomer resin, a vinyl chloride-based elastomer resin, and a styrene-based elastomer resin At least one of the group.
[6] The foamed composite sheet according to any one of the above [3] to [5], wherein the resin layer is selected from the group consisting of an olefin resin, a vinyl chloride resin, a styrene resin, a polyurethane resin, At least one of a group consisting of a polyester resin, a polyamide resin, and an ionic polymer resin.
[7] The foamed composite sheet according to any one of the above [3] to [6], wherein the thickness of the foamed sheet is 0.05 to 1.5 mm, and the thickness of the resin layer is 0.01 to 0.1 mm.
[8] The foamed composite sheet according to any one of the above [3] to [7], wherein the foamed sheet has an apparent density of 0.1 to 0.8 g / cm ³ .
[9] An adhesive tape comprising the foamed composite sheet according to any one of the above [3] to [8], and an adhesive material provided on at least one side of the foamed composite sheet.
[10] A buffer material for electronic parts, comprising:
Foamed resin layer: has a plurality of cells made of bubbles and contains a polyolefin resin; and a surface resin layer: is provided on at least one side of the foamed resin layer and contains a polyethylene resin.
[11] The buffer material for electronic parts according to the above [10], wherein the thickness of the foamed resin layer is 0.05 to 1.5 mm.
[12] The buffer material for electronic parts according to the above [10] or [11], wherein the thickness of the surface resin layer is 0.005 to 0.5 mm.
[13] The buffer material for electronic parts according to any one of the above [10] to [12], wherein the polyethylene resin is selected from the group consisting of high-density polyethylene (HDPE), linear low-density polyethylene ( LLDPE), high-pressure low-density polyethylene (LDPE), and at least one polyethylene resin in the group consisting of ethylene-based ionic polymers.
[14] The cushioning material for electronic parts according to any one of the above [10] to [13], wherein the ratio of the thickness of the foamed resin layer to the total thickness of the surface resin layer (the thickness of the foamed resin layer) / The total thickness of the surface resin layer) is 1.5 to 300.
[15] The buffer material for an electronic component according to any one of [10] to [14], wherein the tensile strength constant of the surface layer resin layer calculated by the following formula (II) is The tensile strength constant ratio of the tensile strength constant of the foamed resin layer calculated by the formula (I) (the tensile strength constant of the surface resin layer / the tensile strength constant of the foamed resin layer) is multiplied by the following formula (III) The value obtained by the compressive strength constant is 1.5 or more.
Foamed resin layer constant = {tensile strength (MD tensile strength of foamed resin layer (MPa)) × (TD tensile strength of foamed resin layer ^{(MPa))} 1/2} (I)
Surface resin layer constant = {tensile strength (tensile strength in the MD of the surface resin layer (MPa)) × (TD tensile strength of the surface layer of the resin layers ^{(MPa))} 1/2} (II)
Compressive strength constant = 200 / (200 + 25% compressive strength (kPa) of the buffer material for electronic parts) (III)
[16] The buffer material for electronic parts according to any one of the above [10] to [15], wherein a foaming ratio of the foamed resin layer is 1.5 to 30 cm ³ / g.
[17] The buffer material for electronic parts according to any one of the above [10] to [16], wherein the polyolefin resin of the foamed resin layer is an ethylene resin.
[18] The buffer material for electronic parts according to any one of the above [10] to [17], wherein the 25% compressive strength is 1.0 to 100 kPa.
[19] The buffer material for electronic parts according to any one of the above [10] to [18], wherein the foamed resin layer is a foaming composition containing a resin and a thermally decomposable foaming agent. Soaked foam.
[20] An adhesive tape for an electronic component, comprising the buffer material for an electronic component according to any one of the above [10] to [19] and an adhesive material provided on at least one side of the buffer material for an electronic component.
[Effect of the invention]

According to the present invention, it is possible to provide a foamed sheet, an adhesive tape, a buffer material for electronic parts, and an adhesive tape for electronic parts that are excellent in impact absorption and mechanical strength.

In addition, when the foamed sheet contains an elastomer resin and has a 25% compressive strength of 30 to 700 kPa and an interlayer strength of 0.3 MPa or more, according to the present invention, it is possible to provide adhesion suppression, impact resistance, and impact absorption. Excellent foaming composite sheet.

Further, in the present invention, a cushioning material for electronic parts using a foamed composite sheet is used. The foamed sheet is a foamed resin layer having a plurality of cells composed of bubbles and containing a polyolefin resin. In the case of the surface layer resin layer, the present invention further exerts the following effects. In other words, according to the present invention, according to the present invention, it is possible to provide a cushion material for electronic parts with high tensile strength, low compressive strength, and excellent secondary workability, and an adhesive tape for electronic parts using the cushion material for electronic parts. .

Hereinafter, the present invention will be described in detail.
[Foamed composite sheet]
The foamed composite sheet of the present invention includes:
Foamed sheet: containing at least one resin selected from the group consisting of an elastomer resin and a polyolefin resin; and resin layer: laminated on at least one side of the foamed sheet.
Since the foam sheet contains at least one resin selected from the group consisting of an elastomer resin and a polyolefin resin, it has excellent impact absorption properties. On the other hand, the resin layer is excellent in mechanical strength. Since the foamed composite sheet of the present invention includes such a foamed sheet and a resin layer, it is excellent in both impact absorption properties and mechanical strength. In addition, in this specification, a foamed sheet may be called a foamed resin layer.

The 25% compressive strength of the foamed composite sheet of the present invention is preferably 1.0 to 700 kPa. If the 25% compressive strength of the foamed composite sheet of the present invention is 1.0 to 700 kPa, the balance between impact absorption and mechanical strength of the foamed composite sheet will be better.

When the foamed composite sheet of the present invention contains an elastomer resin, the interlaminar strength and 25% compressive strength of the foamed composite sheet are within the prescribed range, thereby suppressing the adhesion and further having superior resistance. Impact and impact absorption. In addition, the foamed composite sheet of the present invention can further have high tensile strength and low tensile strength by using a foamed composite sheet containing a polyolefin resin and a resin layer containing a polyethylene resin layer as a cushioning material for electronic parts. Compressive strength and excellent secondary workability.
Therefore, hereinafter, the foamed composite sheet of the present invention when the foamed sheet contains an elastomer resin is taken as the first embodiment, and the foamed composite is made of a foamed sheet containing a polyolefin resin and a resin layer containing a polyethylene resin layer A case where the sheet is used as a cushioning material for electronic parts will be described as a second embodiment.

[First Embodiment]
[Foamed composite sheet]
The foamed composite sheet according to the first embodiment of the present invention includes a foamed sheet containing an elastomer resin, and a resin layer laminated on at least one side of the foamed sheet. When the foamed sheets containing an elastomer resin are overlapped with each other, sticking tends to occur easily. Therefore, when the sheet is wound on a reel and then unrolled from the reel, defects are likely to occur. On the other hand, since the foamed composite sheet according to the first embodiment of the present invention is provided with a resin layer on at least one side of the foamed sheet containing an elastomer resin, it is possible to avoid direct contact between the foamed sheets when wound on a reel. , And can inhibit adhesion.
The foamed composite sheet according to the first embodiment of the present invention is excellent in impact resistance and impact absorption because interlayer strength and 25% compressive strength are within a predetermined range.

(Interlayer strength)
The interlaminar strength of the foamed composite sheet according to the first embodiment of the present invention is 0.3 MPa or more. If the interlayer strength does not reach 0.3 MPa, the impact resistance of the foamed composite sheet will be deteriorated. The interlayer strength mainly indicates the tensile strength in the thickness direction of the foamed sheet, that is, the difficulty of breaking the foamed sheet when an external force is generated in the tensile direction of the thickness. By setting it to a certain value or more, it becomes impact resistance. Outstanding.
The interlayer strength of the foamed composite sheet is preferably 0.32 MPa or more, and more preferably 0.35 MPa or more. The upper limit of the interlayer strength is not particularly limited, but is usually 5 MPa or less. By setting the interlayer strength of the foamed composite sheet to such a range, the impact resistance becomes more favorable.
The interlayer strength of the foamed composite sheet can be measured by the method described in the examples. In this measurement method, the foamed composite sheet is stretched in the thickness direction and the maximum load when the sheet is broken (peeled) is measured. The damage generated in the interlaminar strength measurement of the foamed composite sheet according to the first embodiment of the present invention is difficult to occur at the interface between the foamed sheet and the resin layer, and is mainly generated inside the foamed sheet. Therefore, the interlayer strength becomes the one which mainly reflects the tensile strength in the thickness direction of the foamed sheet.
The interlayer strength of the foamed composite sheet can be adjusted by adjusting the type of the elastomer resin constituting the foamed sheet, the apparent density of the foamed sheet, and the thickness of the foamed sheet. Furthermore, the interlayer strength of the foamed composite sheet can be adjusted in accordance with the 25% compressive strength described below.

(25% compressive strength)
The 25% compressive strength of the foamed composite sheet according to the first embodiment of the present invention is 30 to 700 kPa. If it is such a range, it will be a thing with favorable impact absorption and excellent softness. In addition, by setting the 25% compressive strength of the foamed composite sheet to such a range, it is easy to adjust the interlayer strength to the above range. The 25% compressive strength is preferably 35 to 200 kPa, and more preferably 40 to 100 kPa.
Hereinafter, the foamed sheet and the resin layer included in the foamed composite sheet according to the first embodiment of the present invention will be described in order.

<Foamed sheet>
In the first embodiment, the foamed sheet contains an elastomer resin. The elastomer resin is not particularly limited, and a thermoplastic elastomer resin is preferred.
Examples of the thermoplastic elastomer resin include an olefin-based elastomer resin, a styrene-based elastomer resin, a vinyl chloride-based elastomer resin, a polyurethane-based elastomer resin, a polyester-based elastomer resin, and a polyamide-based elastomer resin. These can be used alone or in combination of two or more.
Among these, as the thermoplastic elastomer resin, from the viewpoint of improving the impact resistance and impact absorption of the foamed composite sheet, it is preferably selected from the group consisting of an olefin-based elastomer resin, a vinyl chloride-based elastomer resin, and styrene. At least one of the group consisting of a series of elastomer resins, and more preferably an olefin-based elastomer resin.

Examples of the olefin-based elastomer resin include ethylene-α-olefin copolymers such as ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), and ethylene-butene rubber (EBM), and propylene-α. -Olefin copolymer, crystalline olefin-ethylene-butene-crystalline olefin copolymer (CEBC), etc. Among these, CEBC is particularly preferred from the viewpoint of further improving the impact resistance and impact absorption of the foamed composite sheet. The part of the crystalline olefin of CEBC is preferably a crystalline ethylene polymer, and the part of ethylene-butene is preferably an amorphous polymer.
Examples of commercially available products of CEBC include DYNARON manufactured by JSR.

Examples of the vinyl chloride-based elastomer resin include those obtained by adding a plasticizer to polyvinyl chloride having a high degree of polymerization (for example, a degree of polymerization of 2,000 or more), those modified by polyvinyl chloride, and others Blends of resins, etc.

Examples of the styrene-based elastomer resin include a styrene-butadiene-styrene (SBS) block copolymer, a styrene-butadiene-butene-styrene (SBBS) block copolymer, and benzene Ethylene-ethylene-butene-styrene (SEBS) block copolymer, hydrogenated styrene-butene rubber (HSBR), styrene-ethylene-propylene-styrene (SEPS) block copolymer, styrene-isobutylene- Styrene (SIBS) block copolymer, styrene-isoprene-styrene (SIS) block copolymer, etc.

The foamed sheet may contain other resins other than the elastomer resin so long as the effect of the present invention is not hindered. The elastomer resin is preferably 70% by mass or more based on the total amount of the resin component in the foamed sheet. It is preferably 90% by mass or more, and further preferably 100% by mass.
The content of the elastomer resin in the foamed sheet is preferably 70% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and 100% by mass or less.

The apparent density of the foamed sheet is not particularly limited, and from the viewpoint of making impact resistance and impact absorption good, it is preferably 0.1 to 0.8 g / cm ³ , more preferably 0.2 to 0.7 g / cm ³ , and more preferably It is preferably 0.3 to 0.6 g / cm ³ .
The apparent density of the foamed sheet can be measured in accordance with JIS K7222 (2005).

The thickness of the foamed sheet is not particularly limited, but is preferably 0.05 to 1.5 mm, more preferably 0.07 to 1.0 mm, and still more preferably 0.1 to 0.7 mm. By setting the thickness of the foamed sheet to such a range and the thickness of the resin layer described below to be preferably 0.01 to 0.1 mm, more preferably 0.02 to 0.06 mm, the thickness of the foamed composite sheet can be reduced. The foamed composite sheet according to the first embodiment of the present invention is excellent in impact resistance and impact absorption even if the thickness is reduced, so it can be applied to miniaturized electronic equipment.

The thickness of the foamed sheet is preferably thicker than the total thickness of the resin layer. The total thickness of the resin layer relative to the thickness of the foamed sheet (total thickness of the resin layer / thickness of the foamed sheet) is preferably 0.01 to 0.8, more preferably 0.1 to 0.4. By setting it as such a range, it becomes easy to make the interlayer strength and 25% compressive strength into the said range. The total thickness of the resin layer refers to the thickness of the resin layer when the resin layer is provided only on one side of the foamed sheet, and when the resin layer is provided on both sides of the foamed sheet. , Refers to the sum of the thicknesses of the resin layers provided on both sides.

The foamed sheet is preferably produced by foaming a foamable resin composition containing the elastomer resin and a foaming agent. The foaming agent is preferably 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 blowing agent include azomethine, metal azodicarboxylate (such as barium azodicarboxylate), azo compounds such as azobisisobutyronitrile, and N, N'-dinitroso Nitroso compounds such as pentamethylenetetramine, hydrazine dimethylhydrazine, 4,4'-oxybis (benzenesulfonylhydrazine), hydrazine derivatives such as tosylhydrazine, tosylhydrazine urea And other urea compounds.
Examples of the inorganic foaming agent include ammonium carbonate, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and monosodium citrate.
Among these, from the viewpoint of obtaining fine bubbles, and from the viewpoint of economics and safety, an azo compound is preferred, and azomethoxamine is more preferred. These may be used individually by 1 type, and may use 2 or more types together.
The blending amount of the thermally decomposable foaming agent in the foamable resin composition is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, and even more preferably 3 to 100 parts by mass of the elastomer resin. 10 parts by mass.

The foamable resin composition preferably contains a bubble core regulator in addition to the above-mentioned elastomer resin and a thermally decomposable foaming agent. Examples of the bubble core regulator include phenol compounds, nitrogen-containing compounds, thioether compounds, zinc compounds such as zinc oxide and zinc stearate, and organic compounds such as citric acid and urea. Among these, phenol compounds are more preferred. , Nitrogen compounds, thioether compounds, or mixtures of these. The compounding amount of the bubble core adjuster is preferably 0.1 to 8 parts by mass, more preferably 0.2 to 5 parts by mass, and still more preferably 0.3 to 2.5 parts by mass with respect to 100 parts by mass of the elastomer resin.
The foamable resin composition may contain additives, such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and fillers, which are generally used in foams, in addition to the above.

＜ Resin layer ＞
The foamed composite sheet according to the first embodiment of the present invention has a resin layer on at least one side of the foamed sheet. By having a resin layer, the sticking at the time of winding a foamed composite sheet can be suppressed. The resin layer may be provided on one side or both sides of the foamed sheet, but it is preferably provided on both sides from the viewpoint of easier suppression of adhesion.

The type of the resin layer is not particularly limited, but is preferably selected from the group consisting of an olefin resin, a vinyl chloride resin, a styrene resin, a polyurethane resin, a polyester resin, a polyamide resin, and an ionic polymer resin. At least one species in the group. Among these, an olefin-based resin is preferable from the viewpoint of easily suppressing the blocking.
Examples of the olefin-based resin include a polyethylene-based resin and a polypropylene-based resin, and a polyethylene-based resin is preferred.
Examples of the polyethylene resin include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer containing ethylene as a main component, and ethylene as a main component. Ingredients: ethylene-ethyl acrylate copolymers. Among these, high-density polyethylene is preferable because it has a relatively high strength even if it is thinned. The density of the high-density polyethylene is preferably 0.94 g / cm ³ or more, and more preferably 0.942 to 0.970 g / cm ³ .
Examples of the polypropylene-based resin include homopolypropylene, maleic modified polypropylene, chlorinated polypropylene, ethylene-propylene copolymer, butene-propylene copolymer, and the like. The above-mentioned polypropylene-based resins may be used alone, or a plurality of polypropylene-based resins may be used in combination.

As described above, the thickness of the resin layer is preferably 0.01 to 0.1 mm, and more preferably 0.02 to 0.06 mm. Within this range, the thickness of the foamed composite sheet can be reduced, and the 25% compressive strength can be easily adjusted to the above range.
When resin layers are provided on both sides of the foamed sheet, the types and thicknesses of the respective resin layers may be the same or different.

The resin layer may contain additives such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and fillers.

＜ Manufacturing method of foamed composite sheet ＞
The method for producing the foamed composite sheet according to the first embodiment of the present invention is not particularly limited. For example, a foamed sheet and a resin layer may be separately prepared and bonded together, and preferably manufactured by a method including the following steps I to III.
(I) Step (II) of obtaining a multilayer laminated body sheet having a layer composed of a foamable resin composition and a resin layer formed on at least one side of the layer (II) crossing the multilayer laminated body sheet obtained in step (I) Step (III) of obtaining a foamed composite sheet by foaming a layer of a foamed resin composition of a cross-linked multilayer laminate sheet

Each step will be described below.
(Step (I))
The method for obtaining the multilayer laminated body sheet in the step (I) is not particularly limited, and it is preferably performed by coextrusion.

Specific examples of coextrusion are shown below. The resin used to form the resin layer and other optional additives are supplied to the first extruder and melt-kneaded, while the foaming resin containing the elastomer resin, the foaming agent, and the optional additives is composed. The material was supplied to a second extruder and melt-kneaded.
Then, the resin materials supplied from the first and second extruders are merged and extruded into a sheet shape using a T-die or the like, whereby a multilayer laminated body sheet having a two-layer structure can be obtained. In the case of this specific example, a multilayer laminated body sheet including a layer composed of a foamable resin composition and a resin layer formed on one side of the layer can be obtained.

In the case of obtaining a multilayer laminated body sheet having a three-layer structure having a resin layer on both areas of the foamable resin composition, it may be performed in the following manner, for example. While supplying the resin used to form the resin layer and other additives as needed, they are supplied to the first and third extruders and melt-kneaded. On the one hand, they contain elastomer resin, thermal decomposition foaming agent, and other additives. The additive foamable resin composition is supplied to a second extruder and melt-kneaded.
Next, the resin materials supplied from the first to third extruders are combined so that the composition of the second extruder becomes a middle layer, and extruded into a sheet shape using a T-die or the like, thereby obtaining a three-layer structure. Multi-layer laminate.
In the co-extrusion molding, it may be any one of a feed block method and a multi-manifold method, and is preferably a feed block method.

(Step (II))
In step (II), the multilayer laminated body sheet obtained in step (I) is crosslinked. As the crosslinking method, there is also a method in which an organic peroxide is mixed in advance and the multilayer laminated body sheet obtained in step (I) is heated to perform crosslinking, but in the present invention, it is preferable to irradiate the multilayer laminated body sheet Crosslinking is performed by radiation. In addition, examples of the free radiation include an electron beam and a beta ray, and an electron beam is preferred.
The irradiation dose of the free radiation is preferably 30 to 50 kGy, and more preferably 35 to 40 kGy.

(Step (III))
In step (III), the cross-linked multilayer laminate sheet in step (II) is subjected to a foaming treatment to foam a layer composed of a foamable resin composition. The layer composed of the foamable resin composition may be processed so as to foam the foaming agent. However, when the foaming agent is a thermally decomposable foaming agent, the multilayer laminated body sheet is heated. And foam. The heating temperature may be at least the temperature at which the thermally decomposable foaming agent decomposes, and is, for example, about 150 to 320 ° C.
The method of heating the multilayer laminated body sheet is not particularly limited, and examples thereof include a method of heating the multilayer laminated body sheet by hot air, a method of heating by infrared rays, a method of heating by a salt bath, and oil. The method of heating a bath, etc. may be used in combination. In step (III), a foamed composite sheet according to the first embodiment of the present invention can be obtained.

Since the foamed composite sheet according to the first embodiment of the present invention is hard to cause sticking, it may also include a step of winding it on a reel during manufacturing. In addition, the foamed composite sheet according to the first embodiment of the present invention may be stored while being wound on a reel.

The use of the foamed composite sheet according to the first embodiment of the present invention is not particularly limited, and for example, it is preferably used inside an electronic device. Even when the foamed composite sheet according to the first embodiment of the present invention is relatively thin, it has excellent impact resistance and impact absorption. Therefore, it is possible to arrange various portable electronic devices having a small space for the foamed composite sheet. Used internally by the machine. In addition, the foamed composite sheet may be made into a frame shape and used in a portable electronic device.
Examples of portable electronic devices include mobile phones, cameras, game consoles, electronic notebooks, and personal computers. The foamed composite sheet according to the first embodiment of the present invention may be used as an adhesive tape as described below and used inside an electronic device.

[Adhesive tape]
Moreover, a foamed composite sheet can also be used for an adhesive tape which uses a foamed composite sheet as a base material. The adhesive tape is, for example, a foamed composite sheet and an adhesive material provided on at least one side of the foamed composite sheet. The adhesive tape can be bonded to other members via an adhesive material. The adhesive tape may be one provided with adhesive materials on both sides of the foamed composite sheet, or one provided with adhesive materials on one side.

In addition, the adhesive material is only required to have at least an adhesive layer, and it may be a single adhesive layer laminated on the surface of the foamed composite sheet, or it may be two-sided adhesive sheets attached to the surface of the foamed composite sheet. Adhesive layer alone. In addition, the double-sided adhesive sheet includes a base material and adhesive layers provided on both sides of the base material. The double-sided adhesive sheet is used for adhering an adhesive layer to a foamed composite sheet, and adhering another adhesive layer to other components.
The adhesive constituting the adhesive layer is not particularly limited, and examples thereof include an acrylic adhesive, a polyurethane adhesive, and a rubber adhesive. Further, a release sheet such as a release paper may be further bonded to the adhesive material.
The thickness of the adhesive material is preferably 5 to 200 μm, more preferably 7 to 150 μm, and even more preferably 10 to 100 μm.

[Second Embodiment]
[Buffer material for electronic parts]
The buffer material for electronic parts according to the second embodiment of the present invention includes a foamed resin layer and a surface resin layer provided on at least one side of the foamed resin layer. The foamed resin layer is composed of a foam and is provided with a large number of cells composed of air bubbles. The surface resin layer is a non-foamed resin layer having no cells made of bubbles.

As shown in FIG. 2, the cushioning material 20 for electronic parts may include a foamed resin layer 21 and a surface resin layer 22 laminated on only one side thereof, or may include a foamed resin layer 21 and a laminate as shown in FIG. 3. Surface resin layers 22, 22 on both sides. However, as shown in FIG. 2, the cushion material 20 for electronic parts is preferably provided with a surface resin layer 22 only on one side of the foamed resin layer 21.
The surface layer resin layer 22 is preferably laminated directly on the foamed resin layer 21 by coextrusion or the like as described below, but may be laminated on the foamed layer through other layers such as an adhesive layer within a range not hindering the effect of the present invention. Resin layer 21.

Hereinafter, the buffer material for electronic components is demonstrated in more detail.
(thickness)
In the buffer material for electronic parts, the thickness of the foamed resin layer is preferably 0.05 to 1.5 mm. By setting the thickness of the foamed resin layer within the above range, it is easy to make mechanical strength, flexibility, and impact absorption good with good balance. The thickness of the foamed resin layer is more preferably 0.07 to 1.3 mm, and still more preferably 0.1 to 1.0 mm.

In the buffer material for electronic parts, the thickness of the surface resin layer is preferably 0.005 to 0.5 mm. By setting the thickness of the surface resin layer within the above range, it is easy to make the mechanical strength, flexibility, and impact absorption good with good balance. The thickness of the surface resin layer is more preferably 0.01 to 0.3 mm, and further preferably 0.02 to 0.1 mm.

The thickness of the buffer material for electronic parts according to the second embodiment of the present invention is preferably 0.055 to 2.5 mm. When the thickness of the buffer material for electronic parts is 0.055 mm or more, the thickness of the surface resin layer and the foamed resin layer can be suppressed from becoming excessively small, and various functions such as mechanical strength and impact absorption can be made good. In addition, if the thickness of the buffer material for electronic parts is 2.5 mm or less, the buffer material for electronic parts according to the second embodiment of the present invention can be easily applied to various electronic devices that have been thinned, and the resin layer on the surface layer can be suppressed from becoming excessively thick. Impairs the impact absorption and flexibility of the buffer material for electronic parts.
Regarding the thickness of the buffer material for electronic parts, in order to have various properties and be easily used in thin electronic devices, the thickness is preferably 0.08 to 1.9 mm, and more preferably 0.12 to 1.2 mm.

The ratio of the thickness of the foamed resin layer to the total thickness of the surface resin layer (the thickness of the foamed resin layer / the thickness of the surface resin layer) is preferably 1.5 to 300. When the ratio of the thickness of the foamed resin layer to the total thickness of the resin layer of the surface layer is 1.5 to 300, various functions such as mechanical strength and impact absorption of the buffer material for electronic parts can be well balanced. In addition, regarding the total thickness of the surface resin layer, when the surface resin layer is provided only on one side of the foamed resin layer, it means the thickness of one surface resin layer. On the other hand, when a surface resin layer is provided on both sides of the foamed resin layer, the total thickness of the surface resin layer refers to the total thickness of the two surface resin layers.
The ratio of the thickness of the foamed resin layer to the total thickness of the surface resin layer is more preferably 2 to 100, and further preferably 2.5 to 50.

(Foaming ratio)
The foaming ratio of the foamed resin layer is preferably 1.5 to 30 cm ³ / g. By making the expansion ratio of the foamed resin layer 1.5 to 30 cm ³ / g, it is easy to make the flexibility and mechanical strength of the buffer material for electronic parts good, so that the impact absorption of the buffer material for electronic parts is good. The foaming ratio of the foamed resin layer is more preferably 2.0 to 20 cm ³ / g, and even more preferably 2.5 to 15 cm ³ / g.
The foaming magnification is obtained by measuring the apparent density and calculating the inverse number. The apparent density can be measured by the same method as the apparent density of the foamed sheet.

(Average bubble diameter)
The average cell diameter of the MD of the cells in the foamed resin layer is preferably 30 to 350 μm. When the average bubble diameter of the MD of the bubbles in the foamed resin layer is 30 to 350 μm, the flexibility, impact absorption, and the like of the buffer material for electronic parts tend to be good. The average cell diameter of the MD of the cells in the foamed resin layer is more preferably 60 to 300 μm, and even more preferably 100 to 250 μm.
The average cell diameter of the TD of the cells in the foamed resin layer is preferably 30 to 400 μm. When the average bubble diameter of the MD of the bubbles in the foamed resin layer is 30 to 400 μm, the flexibility, impact absorption, and the like of the buffer material for electronic parts tend to be good. The average cell diameter of the TD of the cells in the foamed resin layer is more preferably 60 to 350 μm, and even more preferably 120 to 300 μm.
The average cell diameter of MD and TD of the cells in the foamed resin layer is preferably 30 to 375 μm. When the average bubble diameter of the MD of the bubbles in the foamed resin layer is 30 to 375 μm, the flexibility, impact absorption, and the like of the buffer material for electronic parts tend to be good. The average cell diameter of the TD of the cells in the foamed resin layer is more preferably 60 to 325 μm, and still more preferably 110 to 275 μm.
Furthermore, MD means the machine direction, which is the direction that is consistent with the extrusion direction, etc., and TD means the transverse direction, which is the direction orthogonal to the MD, and is the single side of the multilayer foam sheet. Parallel directions.

(Independent bubble rate)
The foamed resin layer is one having closed cells, and the closed cell ratio is 70% or more. As described above, the bubbles contained in the foamed resin layer are basically closed cells, and it is easy to improve impact absorption properties and the like. The closed cell ratio is preferably 80% or more, and more preferably 90 to 100%. The closed cell ratio can be determined in accordance with ASTM D2856 (1998).

The closed cell ratio can be measured in more detail in the following points.
First, a 5 cm flat square test piece was cut from the foamed resin layer. Then, the thickness of the test piece is measured to calculate the apparent volume V ₁ of the test piece, and the weight W _{1 of the} test piece is measured.
Then, the volume V ₂ occupied by the bubbles is calculated based on the following formula. The density of the matrix resin constituting the test piece is set to ρ (g / cm ³ ).
Volume occupied by bubbles V ₂ = V ₁ －W ₁ ／ ρ
Then, the test piece was immersed in distilled water at 23 ° C to a depth of 100 mm from the water surface, and a pressure of 15 kPa was applied to the test piece for 3 minutes. Thereafter, the pressure was released in water, and after standing for 1 minute, 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 was calculated based on the following formula. ₁ and the independent bubble rate F ₂ .
Continuous bubble rate F ₁ (%) = 100 × (W _2- W ₁ ) / V ₂
Independent bubble rate F ₂ (%) = 100－F ₁

(Degree of cross-linking)
The foamed resin layer and the surface layer resin layer are preferably crosslinked. Specifically, the degree of crosslinking of the foamed resin layer and the surface resin layer is preferably 15 to 60% by mass, and more preferably 20 to 50% by mass. By setting the degree of cross-linking of the foamed resin layer and the surface resin layer within the above range, the mechanical strength, flexibility, impact absorption, and the like of the buffer material for electronic parts can be easily improved. Moreover, foaming in a foamed resin layer can be performed suitably. The method for measuring the degree of crosslinking is as follows.
About 100 mg of test pieces were taken from each of the surface resin layer and the foamed resin layer, and the weight of the test piece A (mg) was accurately weighed. Next, the test piece was immersed in 30 cm ³ of xylene at 120 ° C. and left for 24 hours, and then filtered with a 200-mesh wire mesh to take insoluble components on the wire mesh, vacuum-dried, and accurately weighed. Weight B (mg) of insoluble ingredients. The degree of crosslinking (mass%) was calculated from the obtained value by the following formula.
Crosslinking degree (mass%) = 100 × (B / A)

(25% compressive strength)
The 25% compressive strength of the buffer material for electronic parts is preferably 1.0 to 100 kPa. By setting the 25% compressive strength of the buffer material for electronic parts to 1.0 kPa or more, the mechanical strength of the buffer material for electronic parts becomes good. In addition, by setting the 25% compressive strength of the buffer material for electronic parts to 100 kPa or less, the flexibility, impact absorption, and the like of the buffer material for electronic parts are improved. The 25% compressive strength of the buffer material for electronic parts is more preferably 1.2 to 80 kPa. The 25% compressive strength of the buffer material for electronic parts is measured in accordance with the method of JIS K6767.
Furthermore, from the viewpoints of mechanical strength, flexibility, and impact absorption, the 25% compressive strength of the foamed resin layer is preferably 1.0 to 100 kPa, and more preferably 1.2 to 80 kPa.

(Compression strength constant)
The compressive strength constant of the buffer material for electronic parts is an index indicating how appropriate the 25% compressive strength is when the buffer material for electronic parts is used as the buffer material for electronic parts. The compressive strength constant of the buffer material for electronic parts is calculated by the following formula (III).
Compressive strength constant = 200 / (200 + 25% compressive strength (kPa) of the buffer material for electronic parts) (III)

From the standpoint that flexibility, impact absorption, and the like become better, the compressive strength constant of the buffer material for electronic parts is preferably 0.5 to 0.995, and more preferably 0.6 to 0.994.

(Tensile Strength)
The tensile strength of the buffer material for electronic parts is preferably 5 to 30 MPa on MD and 5 to 25 MPa on TD, more preferably 10 to 25 MPa on MD and 8 to 20 MPa on TD. By setting the tensile strength to these ranges, it is easy to make the mechanical strength of the buffer material for electronic parts good. The tensile strength of the buffer material for electronic parts is measured in accordance with the method of JIS K6767.

(Tensile strength constant ratio)
The tensile strength constant ratio of the buffer material for electronic parts is an index indicating the balance between the tensile strength in the surface resin layer and the tensile strength in the foamed resin layer. The tensile strength constant ratio of the buffer material for electronic parts is the tensile strength constant ratio of the tensile strength constant of the surface resin layer to the tensile strength constant of the foamed resin layer (tensile strength constant of the surface resin layer / stretched of the foamed resin layer) Strength constant). The tensile strength constant of the foamed resin layer can be calculated by the following formula (I). The surface layer resin layer tensile strength constant can be calculated by the following formula (II).
Foamed resin layer constant = {tensile strength (MD tensile strength of foamed resin layer (MPa)) × (TD tensile strength of foamed resin layer ^{(MPa))} 1/2} (I)
Surface resin layer constant = {tensile strength (tensile strength in the MD of the surface resin layer (MPa)) × (TD tensile strength of the surface layer of the resin layers ^{(MPa))} 1/2} (II)
When the cushioning material for electronic parts has no surface resin layer, the tensile strength constant ratio is set to 1.00.

From the viewpoints of secondary workability, mechanical strength, flexibility, and impact absorption, the tensile strength constant of the buffer material for electronic parts is preferably 1 to 50, more preferably 5 to 40, and even more preferably 10 to 30.

Furthermore, from the viewpoint that the flexibility, impact absorption, and the like of the buffer material for electronic parts become good, the tensile strength constant of the foamed resin layer is lower than the tensile strength constant of the surface layer resin layer, and is preferably 0.5 to 10 It is more preferably 1 to 8, and even more preferably 1 to 3.
From the viewpoint of the mechanical strength of the buffer material for electronic parts, the surface layer resin layer tensile strength constant is preferably 10 to 60, more preferably 20 to 55, and even more preferably 25 to 50.

(Tensile strength constant ratio × compressive strength constant)
It is preferred that the tensile strength constant ratio of the surface layer resin layer tensile strength constant calculated by the above formula (II) to the tensile strength constant of the foamed resin layer calculated by the above formula (I) (the surface layer resin layer is stretched) The value obtained by multiplying the strength constant / tensile strength constant of the foamed resin layer by the compressive strength constant calculated by the above formula (III) is 1.5 or more. When the value is 1.5 or more, the mechanical strength, flexibility, impact absorption, and the like of the buffer material for electronic parts are easily improved, and the secondary processability is easily improved.
When the cushioning material for electronic parts has no surface resin layer, the tensile strength constant ratio is set to 1.00.
The value obtained by multiplying the tensile strength constant by the compressive strength constant is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more.

[Resin]
In the second embodiment, the foamed resin layer contains a polyolefin resin. Examples of the polyolefin resin contained in the foamed resin layer include polyethylene resins, polypropylene resins, and ethylene-vinyl acetate copolymers. Among these, polyethylene resins are preferred. The surface resin layer contains a polyethylene resin. Examples of the polyethylene resin contained in the foamed resin layer and the surface resin layer include those obtained by polymerization using polymerization catalysts such as Ziegler Natta catalyst, metallocene catalyst, and chromium catalyst. Polyethylene resin. The resins used for the foamed resin layer and the surface resin layer may be the same as or different from each other. However, from the viewpoint of improving the affinity with the surface resin layer and improving the buildup with the surface resin layer, the foamed resin layer is preferably one containing a polyethylene resin. In addition, since the foamed resin layer and the surface resin layer are uniformly stretched during stretching, from the viewpoint of improving curved surface followability and step followability, the catalyst for polyethylene resin used for manufacturing the foamed resin layer is better. It is the same catalyst as the polyethylene resin used to make the surface resin layer.

Examples of the polyethylene resin contained in the foamed resin layer and the surface resin layer include, for example, high-density polyethylene (HDPE), high-pressure low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and vinyl ions. Polymer, etc. These may be used individually by 1 type, and may use 2 or more types together. Examples of the α, β-unsaturated carboxylic acid used in the vinyl-based ionic polymer include acrylic acid, methacrylic acid, and maleic acid. Examples of the metal ions used in the vinyl-based ionic polymer include Na ⁺ , K ⁺ , Ag ⁺ , Cu ⁺ , Cu ^{2 +} , Ba ^{2 +} , Zn ^{2 +} , and Fe ^{2 +} .
Among these polyethylene resins, the polyethylene resin contained as the foamed resin layer is preferably LLDPE. By including the LLDPE in the foamed resin layer, it is possible to impart high flexibility to the buffer material for electronic parts, and to reduce the thickness of the foamed resin layer.
The LLDPE contained in the foamed resin layer is more preferably copolymerized by copolymerizing ethylene (for example, 75% by mass or more with respect to the total amount of monomers, preferably 90% by mass or more) with a small amount of α-olefin as necessary. The obtained LLDPE.
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, an α-olefin having 4 to 10 carbon atoms is preferred.
The density of the polyethylene resin such as the aforementioned LLDPE is preferably 0.870 to 0.930 g / cm ³ , and more preferably 0.910 to 0.930 g / cm ³ . As the polyethylene resin, various kinds of polyethylene resins may be used, and polyethylene resins outside the above-mentioned density range may be added.

Among the polyethylene resins, the polyethylene resin contained as the surface resin layer is preferably at least one polyethylene resin selected from the group consisting of HDPE and LLDPE. The surface resin layer contains at least one polyethylene resin selected from the group consisting of HDPE and LLDPE, while maintaining high flexibility due to the foamed resin layer, and imparting high tensile strength to the buffer material for electronic parts Strength. From these perspectives, HDPE is more preferred.
The HDPE contained in the surface resin layer is more preferably obtained by copolymerizing ethylene (for example, 90% by mass or more with respect to the total monomer amount, preferably 95% by mass or more) with a small amount of α-olefin as required HDPE.
The α-olefin is preferably an α-olefin having 4 to 6 carbon atoms, and specific examples thereof include 1-butene and 1-hexene.
The density of HDPE is preferably 0.942 g / cm ³ or more, and more preferably 0.942 to 0.959 g / cm ³ . As the polyethylene resin, various kinds of polyethylene resins may be used, and polyethylene resins outside the above-mentioned density range may be added.
The LLDPE contained in the surface resin layer can be the same as the LLDPE contained in the foamed resin layer.

(Metallocene catalyst)
HDPE, LLDPE, and LDPE contained in the foamed resin layer and the surface resin layer are preferably those produced using a metallocene catalyst.
Examples of the metallocene catalyst 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 two or more cyclopentadienyl rings or related substances are present in the form of ligands (ligands) in tetravalent titanium, zirconium, nickel, palladium, hafnium, and platinum. Compounds in transition metals.
The properties of the active sites of such metallocene catalysts are uniform and each active site has the same degree of activity. Polymers synthesized using metallocene catalysts have high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, and the like. Therefore, when a sheet containing a polymer synthesized using metallocene catalysts is crosslinked, it is crosslinked. Will proceed evenly. Since the uniformly crosslinked sheet is uniformly foamed, it is easy to stabilize the physical properties. In addition, since it can be uniformly stretched, the thickness of the foamed resin layer and the surface layer resin layer 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 hydrocarbyl group, a substituted hydrocarbyl 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, and various Cetyl, phenyl, etc. Furthermore, "various" means various isomers containing positive-, second-, third-, and iso-.
In addition, a ligand obtained by polymerizing a cyclic compound as an oligomer may be used.
Furthermore, in addition to π-electron unsaturated compounds, monovalent anionic ligands such as chlorine or bromine or divalent anionic chelate ligands, hydrocarbons, alkoxides, arylamines, and aryl oxides Compounds, amidines, phosphides, aryl phosphides, etc.

Examples of the metallocene catalyst containing a tetravalent transition metal or ligand include cyclopentadienyltris (dimethylfluorenamine) titanium, methylcyclopentadienyltris (dimethylfluorenamine) titanium , Bis (cyclopentadienyl) titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-tertiary butylphosphonium amino zirconium dichloride, and the like.
The metallocene catalyst is used as a catalyst in the polymerization of various olefins by being combined with a specific co-catalyst (auxiliary catalyst). Specific examples of the co-catalyst include methylalumoxane (MAO), a boron-based compound, and the like. Furthermore, the use ratio of the co-catalyst to the metallocene catalyst is preferably 100,000 to 1 million mol times, and more preferably 50 to 5,000 mol times.

(Zigler-Natta catalyst and chromium catalyst)
The HDPE contained in the surface resin layer can also be manufactured using a Ziegler-Natta catalyst or a chromium catalyst.
As the Ziegler-Natta catalyst, for example, a TiCl ₄ supported on a magnesium compound is preferred, and a TiCl ₄ supported on MgCl _{2 is more} preferred.
Examples of the chromium catalyst include a Philips catalyst and a complex chromium catalyst. The Phillips catalyst is obtained by supporting a chromium compound on a carrier of an inorganic oxide and then firing it in the air to oxidize the chromium compound. Examples of the inorganic oxide include silicon dioxide, silicon dioxide-alumina, and silicon dioxide-titanium oxide. Examples of the chromium compound include chromium acetate, tris (acetamidine) chromium, and chromium trioxide. On the other hand, the complex chromium catalyst is obtained by supporting bis (cyclopentadienyl) chromium on silicon dioxide.
For example, HDPE is manufactured by using the above-mentioned catalyst through a slurry polymerization process, a solution polymerization system, or a gas phase polymerization process. HDPE can also be produced by two-stage polymerization to expand the molecular weight distribution.

As the resin contained in each of the foamed resin layer and the surface resin layer, a polyethylene resin may be used alone or in combination with other polyolefin resins. For example, it may be used in combination with other polyolefin resins described below. When using other polyolefin resins in combination, the ratio of other polyolefin resins to polyethylene resin (100 parts by mass) is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and still more preferably 20 parts by mass or less. .

Examples of the ethylene-vinyl acetate copolymer used as another polyolefin resin include an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene.
Examples of the polypropylene resin used as the other polyolefin 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, and 1-heptene. Alkenes, 1-octene, and the like, among these, α-olefins having 6 to 12 carbon atoms are preferred.

The foamed resin layer and the surface resin layer may contain resins other than polyolefin resins. For resins other than polyolefin resins, for example, elastomer resins such as polyamide resins, polycarbonate resins, polyester resins, and hydrogenated styrene-based thermoplastic elastomers (SEBS) can also be used.
In the foamed resin layer, the ratio of the resin other than the polyolefin resin to the total resin is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. On the other hand, in the surface resin layer, the ratio of the resin other than the polyolefin resin to the total resin is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[Foaming agent]
The foamed resin layer in the buffer material for electronic parts according to the second embodiment of the present invention is preferably a foam obtained by foaming a foamable composition containing the resin and a foaming agent. The foamed resin layer obtained by foaming is composed of a foamed body, and the foamed body uses a resin amount or a resin compounded with additives as a matrix resin, and has a large number of cells composed of air bubbles inside.
Examples of the foaming agent include a thermal decomposition foaming agent, and as the thermal decomposition type foaming agent, an organic foaming agent and an inorganic foaming agent can be used. The thermally decomposable foaming agent is generally one having a decomposition temperature higher than the melting temperature of the resin. For example, it is sufficient to use one having a decomposition temperature of 140 to 270 ° C.
The specific organic foaming agent may be the same as the organic foaming agent used in the production of the foamed composite sheet according to the first embodiment of the present invention.
The inorganic foaming agent may be the same as the inorganic foaming agent used in the production of the foamed composite sheet according to the first embodiment of the present invention.
Among these, from the viewpoint of obtaining fine bubbles, and from the viewpoint of economics and safety, an azo compound is preferred, and azomethoxamine is particularly preferred. These thermally decomposable foaming agents can be used individually or in combination of 2 or more types.
The blending amount of the thermally decomposable foaming agent in the foamable composition is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and still more preferably 1 to 10 parts by mass based on 100 parts by mass of the resin. .

[Other additives]
In the foamed resin layer, that is, the foamable composition, it may also be compounded with antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, fillers, decomposition temperature regulators, etc. as required. additive. Among these, an antioxidant and a decomposition temperature adjuster are preferably used.
In addition, the surface resin layer is formed of a resin composition not containing a foaming agent, or may be composed of a simple substance of resin, or an antioxidant, a heat stabilizer, a colorant, a flame retardant, and Various additives such as electrostatic agents, fillers, and decomposition temperature regulators. Among these, an antioxidant is preferably used.

Examples of the antioxidant used for the surface resin layer and the foamed resin layer include phenol-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, and amine-based antioxidants. The content of the antioxidant in each of the surface resin layer and the foamed resin layer is preferably 0.1 to 10 parts by mass, and more preferably 0.2 to 5 parts by mass based on 100 parts by mass of the resin.
Specific examples of the compound for adjusting the decomposition temperature include zinc oxide, zinc stearate, and urea. The content of the decomposition temperature adjuster in each of the surface resin layer and the foamed resin layer is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass based on 100 parts by mass of the resin.

[Manufacturing method of buffer material for electronic parts]
The buffer material for an electronic component according to the second embodiment of the present invention is not particularly limited, and it is produced, for example, by a method including the following steps (1) to (2).
Step (1): A step of obtaining a multilayer sheet by laminating a foamable sheet composed of a foamable composition containing a resin and a thermally decomposable foaming agent with a resin sheet. Step (2): heating the multilayer sheet And the step of foaming the foamable sheet

In step (1), the multilayer sheet is preferably formed by coextrusion. Specifically, a resin, a foaming agent, and other additives as necessary are supplied to the first extruder and melt-kneaded, and a sheet-like foamable composition is extruded from the first extruder (that is, Foamable sheet). At the same time, the resin constituting the surface resin layer and other additives as needed are supplied to the second extruder and melt-kneaded, and a sheet-like resin composition (that is, resin sheet). Then, they are laminated to obtain a multilayer sheet. In the case of a two-area surface resin layer in the foamed resin layer, it is sufficient to prepare two second extruders for extruding the resin composition on the two-area resin sheet in the foamable sheet.
The multilayer sheet may be formed by a method other than co-extrusion. For example, a foamable sheet and a resin sheet previously formed into a sheet shape may be pressed against each other between rolls to form a multilayer sheet.

In step (2), the method for heating the multilayer sheet may include: a method for heating the multilayer sheet by hot air, a method by heating infrared rays, a method of heating by a salt bath, and an oil bath. Heating methods, etc., may be used in combination. The heating temperature may be equal to or higher than the foaming temperature of the thermal decomposition foaming agent, and is preferably 200 to 300 ° C, and more preferably 220 to 280 ° C.

The multilayer sheet can also be extended in step (2) or in the next step. That is, the foamable sheet may be stretched after being foamed to form a multilayer foamed sheet, or may be stretched while the foamable sheet is foamed. In this manufacturing method, it is easy to obtain the average cell diameter and cell thickness in the said range by extending a multilayer foam sheet. Furthermore, when the multilayer foamed sheet is stretched after the foamable sheet is foamed, the multilayer foamed sheet may be continuously cooled without cooling the multilayer foamed sheet while maintaining the molten state during foaming. For stretching, after cooling the multilayer foam sheet, the multilayer foam sheet may be heated again to be in a molten or softened state, and then the multilayer foam sheet may be stretched.
The multilayer foam sheet can be stretched in one of the MD and TD directions, and can also be stretched in both directions, but it is preferably stretched in both directions.
The stretching of the multilayer foamed sheet is preferably performed so that the thickness of the multilayer foamed sheet becomes 0.1 to 0.9 times, and more preferably 0.15 to 0.75 times, and further preferably 0.25 to 0.45 times. By extending the multilayer foam sheet so as to fall within these ranges, the compressive strength and tensile strength of the multilayer foam sheet tend to be good. Moreover, if it is more than a lower limit value, a foamed sheet is prevented from being broken during stretching, or foaming gas escapes from the foamed resin layer during foaming, and the foaming ratio is significantly reduced.
In the stretching, the multilayer foamed sheet may be heated to, for example, 100 to 280 ° C, preferably 150 to 260 ° C.

In this manufacturing method, it is preferable to perform the step (cross-linking step) of cross-linking the multilayer sheet between step (1) and step (2). In the cross-linking step, as a method of cross-linking the multilayer sheet, a method of irradiating the multilayer sheet with free radiation such as an electron beam, α-ray, β-ray, or γ-ray is used. The irradiation amount of the above-mentioned free radiation may be adjusted so that the degree of crosslinking of the obtained multilayer foamed sheet becomes the above-mentioned desired range, and is preferably 1 to 15 Mrad, and more preferably 4 to 13 Mrad.

The manufacturing method of the buffer material for electronic parts is not limited to the above-mentioned method, and may be a method other than the above. For example, instead of irradiating with free radiation, cross-linking may be performed by a method in which an organic peroxide is blended with the foamable composition in advance and the foamable composition is heated to decompose the organic peroxide.

The buffer material for electronic parts is preferably used in an electronic device, for example. The buffer material for electronic parts according to the second embodiment of the present invention is suitable for internal use in thin electronic devices such as various portable electronic devices. Examples of portable electronic devices include a notebook personal computer, a mobile phone, a smartphone, a tablet, and a walkman. The buffer material for an electronic component is arrange | positioned between an electronic component and another component, for example, and absorbs the impact given to an electronic component. As other components, other electronic components, housings of electronic equipment, and other components for supporting electronic components can be cited. The buffer material for electronic parts can be used not only as an impact absorbing material for absorbing impact, but also as a sealing material for filling a gap between components in an electronic device.

[Adhesive tape for electronic parts]
Moreover, the buffer material for electronic components can also be used for the adhesive tape for electronic components which uses the buffer material for electronic components as a base material. The adhesive tape for electronic parts includes, for example, a buffer material for electronic parts and an adhesive material provided on at least one side of the buffer material for electronic parts. The adhesive tape for electronic parts can be bonded to another member via an adhesive material. The adhesive tape for electronic parts may be one provided with adhesive materials on both sides of the buffer material for electronic parts, or one provided with adhesive materials on one side. The adhesive tape for electronic parts can also be used as an impact absorbing material and a sealing material.
The adhesive material is preferably provided on the surface on which the surface resin layer is provided in the buffer material for electronic parts. With this configuration, the buffer material for electronic parts is less likely to be broken during secondary processing.

In addition, the adhesive material is only required to have at least an adhesive layer, and it may be a separate adhesive layer laminated on the surface of the buffer material for electronic parts, or it may be two-sided adhesive sheets attached to the surface of the buffer material for electronic parts. The adhesive layer is preferably a separate body. In addition, the double-sided adhesive sheet includes a base material and adhesive layers provided on both sides of the base material. The double-sided adhesive sheet is used for adhering an adhesive layer to a multilayer foam sheet and adhering another adhesive layer to other components.
The adhesive constituting the adhesive layer is not particularly limited, and examples thereof include an acrylic adhesive, a polyurethane adhesive, and a rubber adhesive. Further, a release sheet such as a release paper may be further bonded to the adhesive material.
The thickness of the adhesive material is preferably 5 to 200 μm, more preferably 7 to 150 μm, and even more preferably 10 to 100 μm.
Examples

The present invention will be described in more detail by 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.

＜ Apparent density and foaming magnification ＞
The apparent density of the foamed sheet and the multilayer foamed sheet are measured in accordance with JIS K7222 (2005), and the reciprocal number is used as the expansion ratio.

<Interlayer Strength>
A schematic diagram of a test apparatus for evaluating the interlayer strength is shown in FIG. 1. After applying a primer ("PPX primer" manufactured by Shi Min Da Hard Co., Ltd.) in a 25 mm square area of the foamed composite sheet 11, a 5 mm diameter adhesive was added dropwise to the center of the coating portion. 12 ("PPX" manufactured by Shi Min Da Da Co., Ltd.). Immediately thereafter, a 25 mm square aluminum jig 13 was placed on the adhesive dropping portion, and the foamed composite sheet and the jig 13 were crimped. Thereafter, the foamed composite sheet was cut along the size of the jig 13. A primer is applied to the side of the cut foamed composite sheet that is not adhered to the jig 13, and an adhesive 12 having a diameter of 5 mm is added dropwise to the center of the coated portion. Immediately thereafter, a 10 mm square aluminum jig 14 was placed on the adhesive dropping portion, and the foamed composite sheet and the jig 14 were crimped. After the adhesive overflowing to the periphery of the jig 14 is wiped, a cut 15 is formed in the foamed composite sheet along the size of the jig 14. This was left at room temperature for 30 minutes, thereby curing the adhesive to prepare a sample for measuring interlayer strength.
Next, a sample for measuring the interlayer strength was mounted on a testing machine provided with a load cell of 1 kN so that the sheet surface of the foamed composite sheet became perpendicular to the tensile direction ("Tensilon Universal Material Testing Machine" manufactured by A & D Corporation) ). One of the jigs was stretched vertically at a speed of 100 mm / min, and only a 1 cm square area of the foamed composite sheet was peeled off. The maximum load at this time was measured and used as the first measurement result. The same operation was repeated three times, and the average value was used as the interlayer strength.

<25% compressive strength>
The 25% compressive strength in the thickness direction of the foamed composite sheet and the multilayer foamed sheet is measured in accordance with JIS K6767. Furthermore, the multilayer foamed sheet can be divided into a foamed sheet and a resin sheet after being immersed in liquid nitrogen for one minute and then cut. Then, the 25% compressive strength of the foamed sheet and the resin sheet can be measured separately.

<Peel strength>
The peel strength of the foamed composite sheet was obtained by superimposing two foamed composite sheets (280 mm in length and 50 mm in width) and pressure-bonding them at a load of 3 Kg and a temperature of 23 ° C for 24 hours. Calculate the strength at the time of peeling at a tensile speed of 300 mm / min.
When two foamed composite sheets are overlapped, the up-down direction of each sheet is overlapped in the same direction. For example, when the foamed composite sheet has a three-layer structure, it is overlapped so that the lower layer of one sheet and the upper layer of the other sheet are in contact.

＜ Comprehensive evaluation ＞
The case where the interlayer strength is 0.3 MPa or more and the peel strength is 0.1 N or less is evaluated as "G (Good)", and the case where the interlayer strength is less than 0.3 MPa or the peel strength exceeds 0.1 N is evaluated as "B (Bad)".

＜ Average bubble diameter ＞
The multilayer foam sheet was cut into 50 mm squares, immersed in liquid nitrogen for 1 minute, then cut along the MD and TD in the thickness direction, using a digital microscope (manufactured by Ens Co., Ltd., product name VHX-900) Take a 200x magnified photo. In the foamed resin layer of the captured image, for all bubbles existing in the cut surface having a length of 2 mm in each of MD and TD, the bubble diameter of MD and the bubble diameter of TD were measured, and the operation was repeated Perform 5 times. Then, the average value of the bubble diameters of MD and TD of all the bubbles was taken as the average bubble diameter of MD and TD.

<Tensile strength>
The multilayer foam sheet is cut into a dumbbell-shaped No. 1 shape as specified in JIS K6251 4.1. This was used as a sample, and the tensile strength of MD and TD was measured using a tensile tester (product name: Tensilon RTF235, manufactured by A & D) at a measurement temperature of 23 ° C in accordance with JIS K6767. Furthermore, the multilayer foamed sheet can be divided into a foamed sheet and a resin sheet after being immersed in liquid nitrogen for one minute and cut. Then, the tensile strength of the foamed sheet and the resin sheet can be measured separately.

<Tensile strength constant ratio × compressive strength constant>
The value obtained by multiplying the tensile strength constant ratio by the compressive strength constant was calculated by the following formulae (I) to (IV). When the resin sheet is not laminated, the tensile strength constant ratio is set to 1.00.
Foamed resin layer constant = {tensile strength (MD tensile strength of foamed resin layer (MPa)) × (TD tensile strength of foamed resin layer ^{(MPa))} 1/2} (I)
Surface resin layer constant = {tensile strength (tensile strength in the MD of the surface resin layer (MPa)) × (TD tensile strength of the surface layer of the resin layers ^{(MPa))} 1/2} (II)
Compressive strength constant = 200 / (200 + 25% compressive strength (kPa) of the buffer material for electronic parts) (III)
Tensile strength constant ratio = surface layer resin layer tensile strength constant / foamed resin layer tensile strength constant (IV)

[Example 1]
100 parts by mass of high-density polyethylene (HDPE) (manufactured by Japan Polyethylene Corporation, trade name HJ360, density 0.951 g / cm ³ ) was put into the first extruder, and melt-kneaded. 100 parts by mass of a crystalline olefin-ethylene-butene-crystalline olefin copolymer (CEBC) (manufactured by JSR, trade name Dynaron 6200P) as a foaming agent was charged into a second extruder. 5.5 parts by mass of azamethoxamine and 1.2 parts by mass of a foaming aid as a bubble core regulator were melt-kneaded to prepare a foamable resin composition. In addition, as a foaming aid, the brand name "SB-1018RG" manufactured by ADEKA Corporation was used. 100 parts by mass of high-density polyethylene (HDPE) (manufactured by Japan Polyethylene Corporation, trade name HJ360, density 0.951 g / cm ³ ) was put into a third extruder, and melt-kneaded.
Next, the resin materials supplied from the first to third extruders are merged and extruded into a sheet shape, thereby obtaining a layer (middle layer) made of a foamable resin composition and forming both sides of the middle layer ( Upper and lower) resin laminates.
Next, the multilayer laminated body sheet was irradiated with an electron beam having an acceleration voltage of 500 kV at 30 kGy on both sides to crosslink it, and then continuously fed to a foaming furnace maintained at 270 ° C by hot air and infrared heaters. It was heated inside for 90 seconds to foam the multilayer laminated body sheet, thereby obtaining a foamed composite sheet having a middle layer as a foamed sheet and an upper layer and a lower layer as a resin layer. The results are shown in Table 1.

[Example 2]
100 parts by mass of high-density polyethylene (HDPE) (manufactured by Japan Polyethylene Corporation, trade name HJ360, density 0.951 g / cm ³ ) was put into the first extruder, and melt-kneaded. 100 parts by mass of a crystalline olefin-ethylene-butene-crystalline olefin copolymer (CEBC) (manufactured by JSR, trade name Dynaron 6200P) as a foaming agent was charged into a second extruder. 5.5 parts by mass of azamethoxamine and 1.2 parts by mass of a foaming aid as a bubble core regulator were mixed and melt-kneaded to prepare a foamable resin composition. In addition, as a foaming aid, the brand name "SB-1018RG" manufactured by ADEKA Corporation was used.
Then, the resin materials supplied from the first and second extruders are merged and extruded into a sheet shape, thereby obtaining a layer (middle layer) composed of a foamable resin composition and one surface formed on the middle layer. (Upper layer) A multilayer laminated body sheet of a layer composed of a resin composition.
Next, the multilayer laminated body sheet was irradiated with an electron beam having an acceleration voltage of 500 kV at 30 kGy on both sides to crosslink it, and then continuously fed to a foaming furnace maintained at 270 ° C by hot air and infrared heaters. It was heated inside for 90 seconds, and the multilayer laminated body sheet was foamed, thereby obtaining a foamed composite sheet having a middle layer as a foamed sheet and an upper layer as a resin layer. The results are shown in Table 1.

[Comparative Example 1]
100 parts by mass of a crystalline olefin-ethylene-butene-crystalline olefin copolymer (CEBC) (manufactured by JSR, trade name Dynaron 6200P) as a foaming agent was charged into a second extruder. 5.5 parts by mass of azamethoxamine and 1.2 parts by mass of a foaming aid as a bubble core regulator were melt-kneaded to prepare a foamable resin composition. In addition, as a foaming aid, the brand name "SB-1018RG" manufactured by ADEKA Corporation was used.
Then, the foamable resin composition was extruded from an extruder to obtain a sheet composed of the foamable resin composition.
Then, the above sheet was irradiated with an electron beam having an acceleration voltage of 500 kV at 30 kGy on both sides to crosslink it, and then continuously fed into a foaming furnace maintained at 270 ° C by hot air and infrared heaters, and heated. The above sheet was foamed for 90 seconds to obtain a foamed sheet. The results are shown in Table 1.

[Comparative Example 2]
100 parts by mass of high-density polyethylene (HDPE) (manufactured by Japan Polyethylene Corporation, trade name HJ360, density 0.951 g / cm ³ ) was put into the first extruder, and melt-kneaded. Into the second extruder, 100 parts by mass of an elastomer resin (product name: Dynaron 6200P, manufactured by JSR Corporation) and 0.1 parts by mass of an antioxidant were charged, and melt-kneaded to prepare a resin composition. 100 parts by mass of high-density polyethylene (HDPE) (manufactured by Japan Polyethylene Corporation, trade name HJ360, density 0.951 g / cm ³ ) was put into a third extruder, and melt-kneaded.
Next, the resin materials supplied from the first to third extruders are merged and extruded into a sheet shape, thereby obtaining a layer (middle layer) composed of a resin composition and forming both sides of the middle layer (upper and lower layers) ) Of a multilayer laminated body sheet of a resin layer.
Next, the multilayer laminated body sheet was irradiated with an electron beam having an acceleration voltage of 500 kV at 30 kGy on both sides to crosslink it, and then continuously fed into a furnace maintained at 270 ° C by hot air and an infrared heater, and Heating was performed for 90 seconds to obtain a composite sheet having a middle layer as a resin sheet and an upper layer and a lower layer as resin layers.

[Comparative Example 3]
100 parts by mass of high-density polyethylene (HDPE) (manufactured by Japan Polyethylene Corporation, trade name HJ360, density 0.951 g / cm ³ ) was put into the first extruder, and melt-kneaded. In a second extruder, 100 parts by mass of CEBC (made by JSR Corporation, trade name Dynaron 6200P) and 0.1 parts by mass of an antioxidant were charged as an elastomer resin, and melt-kneaded to prepare a resin composition.
Then, the resin materials supplied from the first and second extruders are merged and extruded into a sheet shape, thereby obtaining a layer (middle layer) composed of a resin composition and a surface (upper layer) formed on the middle layer. Multilayer resin sheet of the resin layer.
Next, the multilayer laminated body sheet was irradiated with an electron beam having an acceleration voltage of 500 kV at 30 kGy on both sides to crosslink it, and then continuously fed into a furnace maintained at 270 ° C by hot air and an infrared heater, and Heating was performed for 90 seconds to obtain a composite sheet having a middle layer as a resin sheet and an upper layer as a resin layer.

[Comparative Example 4]
100 parts by mass of CEBC (manufactured by JSR, trade name Dynaron 6200P) as an elastomer resin was put into a second extruder, and melt-kneaded to prepare a resin composition.
Then, the resin composition was extruded from an extruder to obtain a sheet.
Next, the above sheet was irradiated with an electron beam having an acceleration voltage of 500 kV at 30 kGy on both sides to crosslink it, and then continuously fed into a furnace maintained at 270 ° C by hot air and infrared heaters and heated for 90 seconds. Clock while getting a single-layer piece.

[Table 1]

According to Table 1, it can be seen that the foamed composite sheet of the first embodiment of the present invention is excellent in impact resistance and impact absorption because the interlayer strength and 25% compressive strength are within the specified ranges, and it is difficult to stick because of its low peel strength. On the other hand, it can be seen that the sheet which does not satisfy the requirements of the first embodiment of the present invention deviates from a predetermined range in interlayer strength or 25% compressive strength, has poor impact resistance, or easily sticks.

[Example 3]
A first extruder and a second extruder were prepared.
A linear low-density polyethylene resin (trade name "KERNEL KF283" manufactured by Japan Polyethylene Corporation, density: 0.921 g / cm ³ ) obtained using a metallocene catalyst was used as the polyolefin for the foamable sheet. As the resin, azomethoxamine was used as a thermally decomposable foaming agent. In addition, zinc oxide (produced by Sakai Chemical Industry Co., Ltd., trade name "OW-212F") was used as a decomposition temperature adjuster, and 2,6-di-third-butyl-p-cresol as a phenol-based antioxidant was used as Antioxidants. 100 parts by mass of a polyolefin resin, 8.0 parts by mass of a thermal decomposition type foaming agent, 1 part by mass of a decomposition temperature adjuster, and 0.5 parts by mass of an antioxidant were supplied to a first extruder and melt-kneaded at 130 ° C to produce a hair Foaming composition.
As the polyethylene resin for the resin sheet, a high-density polyethylene resin (trade name "HD", density: 0.949 g / cm ³ ) obtained by using a metallocene catalyst was used. The polyethylene resin was supplied to a second extruder and melt-kneaded at 130 ° C.
The foamable composition was co-extruded from the first extruder and the polyethylene resin from the second extruder, respectively, and a multilayer sheet was obtained on a single-area layer resin sheet of the foamable sheet.
Next, the surface of the unlaminated resin sheet in the multilayer sheet was irradiated with an electron beam with an acceleration voltage of 500 kV at 4 Mrad to crosslink the multilayer sheet, and the crosslinked multilayer sheet was continuously fed into the sheet by heating with hot air and infrared rays. The device was kept in a foaming furnace at 250 ° C. and heated to foam, thereby obtaining a multilayer foamed sheet of Example 3 in which the resin sheet 1 was laminated on a single area of the foamed sheet 1.

[Example 4]
As the polyethylene resin for the resin sheet, a linear low-density polyethylene resin (trade name "KERNEL KF283", manufactured by Japan Polyethylene Corporation, density: 0.921 g / cm ³ ) obtained using a metallocene catalyst was used. Except for this, the multilayer foamed sheet of Example 4 in which the resin sheet 2 was laminated on a single area of the foamed sheet 1 was obtained by the same method as in Example 3.

[Example 5]
A high-pressure low-density polyethylene resin (made by TAMAPOLY Co., Ltd., trade name "AJ-1", density: 0.924 g / cm ³ ) obtained using a metallocene catalyst was used as the polyethylene resin for the resin sheet. Except for this, the multilayer foamed sheet of Example 5 in which the resin sheet 3 was layered on a single area of the foamed sheet 1 was obtained by the same method as in Example 3.

[Example 6]
As the polyethylene resin for the resin sheet, a vinyl-based ionic polymer (manufactured by TAMAPOLY Corporation, trade name "NC-5"), which is a copolymer of ethylene and methacrylic acid, was used. Except for this, the multilayer foamed sheet of Example 6 in which the resin sheet 4 was layered on a single area of the foamed sheet 1 was obtained by the same method as in Example 3.

[Example 7]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 6.0 parts by mass. Except for this, the multilayer foamed sheet of Example 7 in which the resin sheet 1 was laminated on a single area of the foamed sheet 2 was obtained by the same method as in Example 3.

[Example 8]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 6.0 parts by mass. Other than this, the multilayer foamed sheet of Example 8 in which the resin sheet 2 was laminated on a single area of the foamable sheet 2 was obtained by the same method as in Example 4.

[Example 9]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 6.0 parts by mass. Except for this, the multilayer foamed sheet of Example 9 in which the resin sheet 3 was layered on a single area of the foamed sheet 2 was obtained by the same method as in Example 5.

[Example 10]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 6.0 parts by mass. Other than that, the multilayer foamed sheet of Example 10 in which the resin sheet 4 was laminated on a single area of the foamed sheet 2 was obtained by the same method as in Example 6.

[Example 11]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 4.0 parts by mass. Except for this, the multilayer foamed sheet of Example 11 in which the resin sheet 1 was laminated on a single area of the foamed sheet 3 was obtained by the same method as in Example 3.

[Example 12]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 4.0 parts by mass. Except for this, the multilayer foamed sheet of Example 12 in which the resin sheet 2 was laminated on a single area of the foamed sheet 3 was obtained by the same method as in Example 4.

[Example 13]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 4.0 parts by mass. Except for this, the multilayer foamed sheet of Example 13 in which the resin sheet 3 was laminated on a single area of the foamed sheet 3 was obtained by the same method as in Example 5.

[Example 14]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 4.0 parts by mass. Except for this, the multilayer foamed sheet of Example 14 in which the resin sheet 4 was layered on a single area of the foamed sheet 3 was obtained by the same method as in Example 6.

[Example 15]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 2.0 parts by mass. Other than this, the multilayer foamed sheet of Example 15 in which the resin sheet 1 was laminated on a single area of the foamed sheet 4 was obtained by the same method as in Example 3.

[Example 16]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 2.0 parts by mass. Other than that, the multilayer foamed sheet of Example 16 in which the resin sheet 2 was laminated on a single area of the foamed sheet 4 was obtained by the same method as in Example 4.

[Example 17]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 2.0 parts by mass. Except for this, the multilayer foamed sheet of Example 17 in which the resin sheet 3 was layered on a single area of the foamed sheet 4 was obtained by the same method as in Example 5.

[Example 18]
The blending amount of the thermally decomposable foaming agent was changed from 8.0 parts by mass to 2.0 parts by mass. Except for this, the multilayer foamed sheet of Example 18 in which the resin sheet 4 was layered on a single area of the foamed sheet 4 was obtained by the same method as in Example 6.

[Comparative Example 5]
The resin sheet was not laminated on the foamable sheet, and the thickness of the foamable sheet was adjusted so that the thickness of the foamed sheet became 0.80 mm. Other than that, the foamed sheet of Comparative Example 5 was obtained by the same method as that of Example 3.

[Comparative Example 6]
The resin sheet is not laminated on the foamable sheet, and the thickness of the foamable sheet is adjusted so that the thickness of the foamed sheet becomes 0.80 mm. Other than that, the foamed sheet of Comparative Example 6 was obtained by the same method as that of Example 7.

[Comparative Example 7]
The resin sheet is not laminated on the foamable sheet, and the thickness of the foamable sheet is adjusted so that the thickness of the foamed sheet becomes 0.30 mm. Other than that, the foamed sheet of Comparative Example 7 was obtained by the same method as in Example 11.

[Comparative Example 8]
The resin sheet is not laminated on the foamable sheet, and the thickness of the foamable sheet is adjusted so that the thickness of the foamed sheet becomes 0.20 mm. Other than that, the foamed sheet of Comparative Example 8 was obtained by the same method as in Example 15.

The foamed sheets 1 to 4 and the resin sheets 1 to 4 were evaluated in accordance with the evaluation method described above. Table 2 shows the evaluation results of the foamed sheets 1 to 4, and Table 3 shows the evaluation results of the resin sheets 1 to 4.
The foamed sheets 1 to 4 for evaluation were the same as in Example 3 except that the polyethylene resin was not extruded from the second extruder and the foamable composition was extruded from the first extruder. The multilayer foam sheets of 7, 7, 11 and 15 are manufactured by the same method. The resin sheets 1 to 4 for evaluation were the same as those in Examples 3 to 6 except that the foamable composition was not extruded from the first extruder and the polyethylene resin was extruded from the second extruder. The multi-layer foamed sheet was produced by the same method.

In addition, the multilayer foamed sheets of Examples 3 to 18 and the foamed sheets of Comparative Examples 5 to 8 were evaluated according to the above-mentioned evaluation methods. The evaluation results are shown in Tables 4 to 6.
In addition, in Tables 4 to 6, the secondary processability evaluation refers to an index indicating whether the secondary processability is good when the adhesive tape is made in four levels. In the cases of Examples 3 to 6, the evaluation was performed on the basis of Comparative Example 5. Specifically, in the cases of Examples 3 to 6, when the degree is the same as that of Comparative Example 5, the evaluation is set to "1", and when it is superior to Comparative Example 5 but its degree is small. When the evaluation is set to "2", when it is superior to Comparative Example 5 and its degree is large, the evaluation is set to "3", and when it is more superior to Comparative Example 5 and its degree is greater And set the evaluation to "4". In the cases of Examples 7 to 10, Comparative Example 6 was used as a reference, in the cases of Examples 11 to 14, Based on Comparative Example 7, and in the cases of Examples 15 to 18, Comparative Example 8 was used as reference. The same evaluation. In addition, the adhesive tape used in this evaluation is a single-layered adhesive layer in an area where a multilayer resin sheet is provided with a surface layer resin layer.
The thickness of the foamed sheet in Tables 4 to 6 corresponds to the thickness of the foamed resin layer of the buffer material for electronic parts, and the thickness of the resin sheet corresponds to the thickness of the surface layer resin layer of the buffer material for electronic parts.

[Table 2]

[table 3]

[Table 4]

[table 5]

[TABLE 6]

It is clear from the results of Tables 4 to 6 that the low compressive strength of the foamed sheet can be maintained even if the foamed sheet containing a polyolefin resin has a resin sheet containing a polyethylene resin in at least one area layer. However, the tensile strength of the multilayer foam sheet is higher than that of the foam sheet, and the secondary processability of the multilayer foam sheet is also good.

11‧‧‧foamed composite sheet

12‧‧‧ Adhesive

13‧‧‧Jig

14‧‧‧ aluminum fixture

15‧‧‧ incision

20‧‧‧Multi-layer foam sheet

21‧‧‧ Foamed resin layer

22‧‧‧Surface resin layer

FIG. 1 is a schematic diagram of a test apparatus for evaluating interlayer strength in Examples and Comparative Examples.

FIG. 2 is a schematic cross-sectional view showing a buffer material for an electronic component according to an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a cushion material for an electronic component according to another embodiment of the present invention.

Claims (20)

A foamed composite sheet comprising: Foamed sheet: containing at least one resin selected from the group consisting of an elastomer resin and a polyolefin resin; and Resin layer: laminated on at least one side of the foamed sheet. The foamed composite sheet according to claim 1, whose 25% compressive strength is 1.0 to 700 kPa. The foamed composite sheet according to claim 1 or 2, wherein the foamed sheet contains an elastomer resin, and the foamed composite sheet has a 25% compressive strength of 30 to 700 kPa and an interlayer strength of 0.3 MPa or more. The foamed composite sheet according to claim 3, wherein the elastomer resin is a thermoplastic elastomer resin. The foamed composite sheet according to claim 3 or 4, wherein the thermoplastic elastomer resin is at least 1 selected from the group consisting of an olefin-based elastomer resin, a vinyl chloride-based elastomer resin, and a styrene-based elastomer resin. Species. The foamed composite sheet according to any one of claims 3 to 5, wherein the resin layer is selected from the group consisting of an olefin resin, a vinyl chloride resin, a styrene resin, a polyurethane resin, a polyester resin, and a polymer resin. At least one of the group consisting of a fluorene-based resin and an ionic polymer-based resin. The foamed composite sheet according to any one of claims 3 to 6, wherein the thickness of the foamed sheet is 0.05 to 1.5 mm, and the thickness of the resin layer is 0.01 to 0.1 mm. The foamed composite sheet according to any one of claims 3 to 7, wherein the apparent density of the foamed sheet is 0.1 to 0.8 g / cm ³ . An adhesive tape includes the foamed composite sheet according to any one of claims 3 to 8 and an adhesive material provided on at least one side of the foamed composite sheet. A cushioning material for electronic parts, using the foamed composite sheet according to claim 1 or 2, the foamed sheet is a foamed resin layer having a plurality of cells composed of bubbles and containing a polyolefin resin, and the resin layer It is a surface resin layer containing polyethylene resin. The buffer material for electronic parts according to claim 10, wherein a thickness of the foamed resin layer is 0.05 to 1.5 mm. The buffer material for electronic parts according to claim 10 or 11, wherein the thickness of the surface resin layer is 0.005 to 0.5 mm. The buffer material for electronic parts according to any one of claims 10 to 12, wherein the polyethylene resin is selected from the group consisting of high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and high-pressure method. At least one type of polyethylene resin in the group consisting of density polyethylene (LDPE) and ethylene-based ionic polymer. The buffer material for electronic parts according to any one of claims 10 to 13, wherein the ratio of the thickness of the foamed resin layer to the total thickness of the surface resin layer (the thickness of the foamed resin layer / the thickness of the surface resin layer) Total) is 1.5 to 300. The buffer material for an electronic component according to any one of claims 10 to 14, wherein the surface layer resin layer tensile strength constant calculated by the following formula (II) is calculated with respect to the following formula (I) The tensile strength constant ratio of the tensile strength constant of the foamed resin layer (surface layer resin layer tensile strength constant / foamed resin layer tensile strength constant) multiplied by the compressive strength constant calculated by the following formula (III) value of 1.5 or more, the tensile strength of the foamed resin layer constant = {(MD tensile strength of foamed resin layer (MPa)) × (TD tensile strength of foamed resin layer (MPa))} ^1/2 (I) a resin surface layer constant = {tensile strength (tensile strength in the MD of the surface resin layer (MPa)) × (TD tensile strength of the surface layer of the resin layers ^{(MPa))} 1/2} (II) compressive strength Constant = 200 / (200 + 25% compressive strength (kPa) of buffer material for electronic parts) (III). The buffer material for electronic parts according to any one of claims 10 to 15, wherein a foaming ratio of the foamed resin layer is 1.5 to 30 cm ³ / g. The buffer material for electronic parts according to any one of claims 10 to 16, wherein the polyolefin resin of the foamed resin layer is an ethylene resin. The buffer material for electronic parts according to any one of claims 10 to 17, wherein the 25% compressive strength is 1.0 to 100 kPa. The buffer material for electronic parts according to any one of claims 10 to 18, wherein the foamed resin layer is a foam obtained by foaming a foamable composition containing a resin and a thermally decomposable foaming agent. body. An adhesive tape for electronic parts, comprising the buffer material for electronic parts according to any one of claims 10 to 19 and an adhesive material provided on at least one side of the buffer material for electronic parts.