JPWO2018181486A1 - Resin foam sheet, method for producing resin foam sheet, and adhesive tape - Google Patents

Abstract

A resin foam sheet, wherein a breaking compression parameter represented by the formula A: strength at break in the MD direction (MPa) × strength at break in the TD direction (MPa) / 25% compression strength (kPa) × 1000 is 700 or more and 1500 or more. Less than 35% by mass and a degree of crosslinking is 35% by mass or more.

Description

  The present invention relates to a resin foam sheet, a method for producing a resin foam sheet, and an adhesive tape.

2. Description of the Related Art Conventionally, in electronic devices such as a mobile phone, a camera, a game device, an electronic organizer, a tablet terminal, and a notebook personal computer, a sealing material or a shock absorbing material made of a foam sheet is used. These sealing materials or shock-absorbing materials are sometimes used as pressure-sensitive adhesive tapes based on foamed sheets. For example, the display device in the electronic device generally has a structure in which a protection panel is provided on a display panel such as an LCD. In order to attach the protection panel to a frame portion on the outside of the display panel, foaming is performed. An adhesive tape based on a sheet is used.
As a foamed sheet used inside an electronic device, a crosslinked polyolefin-based resin foamed sheet obtained by foaming and crosslinking a foamable polyolefin-based resin sheet containing a pyrolytic foaming agent is known (for example, Patent Document 1). reference).

International Publication No. 2005/007731

By the way, in recent years, as electronic devices have been reduced in size, the functions of various components have also been advanced, and not only the space inside the electronic devices has been restricted, but also the internal structure of the devices has been complicated. It is assumed that as the internal structure becomes more complicated, the number of housings having various steps, large and small, will increase. At this time, if there is a gap between the tape and the housing, the waterproofness is lost, and the tape is easily peeled from the starting point.
Therefore, when a tape is attached to an electronic device or the like, a step followability is required from the viewpoint of waterproofness and adhesive strength. At the same time, from the viewpoint of reusing parts, reworkability is required, in which the tape can be easily peeled without breaking.

  The present invention has been made in view of the above circumstances, and provides good adhesiveness following a step, and provides a resin foam sheet having good reworkability and an adhesive tape including the resin foam sheet. Make it an issue.

  As a result of intensive studies, the inventors have found that a resin foam sheet satisfying a specific parameter (breaking compression parameter) consisting of a breaking strength in the MD direction, a breaking strength in the TD direction, and a 25% compressive strength follows the step. The present invention was found to exhibit good adhesiveness and good reworkability, and completed the present invention. That is, the present invention is as follows.

[1] A resin foamed sheet, wherein the breaking compression parameter represented by the following formula A is 700 or more and less than 1500 and the degree of crosslinking is 35% by mass or more.
Formula A: strength at break in MD (MPa) × strength at break in TD (MPa) / 25% compressive strength (kPa) × 1000
[2] The resin foam sheet according to [1], wherein the average cell diameter in each of the MD direction and the TD direction is 100 µm or less.
[3] The resin foam sheet according to [1] or [2], which has a thickness of 0.01 to 0.3 mm.
[4] The resin foam sheet according to any one of [1] to [3], wherein the strength at break in the MD direction is 7 to 30 MPa, and the strength at break in the TD direction is 10 to 25 MPa.
[5] The resin foam sheet according to any one of [1] to [4], wherein the 25% compressive strength is 130 to 500 kPa.
[6] The resin foam sheet according to any one of [1] to [5], wherein the foaming ratio is 1.2 to ⁴ cm ³ / g.
[7] The resin foam sheet according to any one of [1] to [6], wherein the resin foam sheet contains a polyolefin resin.
[8] The resin foam sheet according to [7], wherein the polyolefin resin is a polyethylene resin.
[9] The resin foam sheet according to [7] or [8], wherein the polyolefin resin is a linear low-density polyethylene polymerized with a metallocene compound polymerization catalyst.
[10] The method for producing a foamed resin sheet according to any one of [1] to [9], wherein the foamable composition containing a resin and a pyrolyzable foaming agent is cross-linked and heated to obtain the heat. A method for producing a resin foam sheet, comprising foaming a decomposable foaming agent and stretching in a TD direction and / or an MD direction at a stretching ratio of 1.1 or more.
[11] An adhesive tape comprising the foamed resin sheet according to any one of [1] to [9], and an adhesive layer provided on at least one surface of the foamed resin sheet.

  According to the present invention, it is possible to provide a resin foam sheet exhibiting good adhesiveness following a step and having good reworkability, and an adhesive tape provided with the resin foam sheet.

It is explanatory drawing explaining the outline of a push test.

Hereinafter, the present invention will be described in detail using embodiments.
[Resin foam sheet]
The resin foam sheet according to the embodiment of the present invention has a breaking compression parameter represented by the following formula A of 700 or more and less than 1500, and a degree of crosslinking of 35% by mass or more.
Formula A: strength at break in MD (MPa) × strength at break in TD (MPa) / 25% compressive strength (kPa) × 1000
Here, the unit of the breaking point strength in Formula A is MPa, and the unit of the 25% compressive strength is kPa.
That is, when the breaking point strength in the MD direction and the breaking point strength in the TD direction are each 12 MPa and the 25% compressive strength is 147 kPa, the above formula A is calculated as follows.
Formula A: 12 × 12/147 × 1000 = 980

The step followability is required to be soft in the surface direction and the thickness direction of the sheet. Further, the reworkability is required to be hard to be stretched and to be hard to be cut in a direction horizontal to the surface of the sheet. From these viewpoints, in the present invention, the ratio of the product of the breaking strength in the MD direction and the breaking strength in the TD direction and the ratio of the 25% compressive strength (= formula A) is within a predetermined range, so that the step following step is achieved. Compatibility and reworkability.
Therefore, if the breaking compression parameter is out of the range of 700 or more and less than 1500, at least one of the step followability and the reworkability is inferior. The breaking compression parameter is preferably from 740 to 1400, more preferably from 750 to 1380, even more preferably from 750 to 1200, and even more preferably from 800 to 1,000.
In order to set the breaking compression parameter in the above range, for example, the stretching ratio at the time of producing the resin foam sheet may be increased. Alternatively, the degree of crosslinking may be increased, or a resin having high mechanical strength may be used. Further, it can be adjusted by appropriately setting the average cell diameter, the expansion ratio, and the like within the ranges described below.

Here, the breaking point strength in the MD direction is preferably from 7 to 30 MPa, and more preferably from 10 to 25 MPa. The breaking point strength in the TD direction is preferably from 7 to 30 MPa, and more preferably from 10 to 20 MPa. When the breaking point strength in the MD direction and the TD direction is 7 to 30 MPa, when peeling a tape that has been finely punched in both directions such as a frame, the tape can be easily peeled without breaking even if pulled in either direction. .
Further, the MD elongation until breaking is preferably from 100 to 600%, more preferably from 120 to 500%. The TD elongation is preferably from 100 to 600%, more preferably from 120 to 300%. When the elongation percentage in the MD direction and the TD direction is 600% or less, when the tape is peeled off by pulling its end, the tape is hardly stretched and can be easily peeled off.

Further, the 25% compressive strength is preferably from 130 to 500 kPa, and more preferably from 140 to 500 kPa. When the compressive strength is 130 to 500 kPa, it can be stuck to an adherend having a step without gaps, and the waterproofness can be secured.
In addition, 25% compressive strength means what measured the resin foam sheet according to JISK6767.

  The degree of crosslinking of the foamed sheet according to the present invention is 35% by mass or more. If the degree of crosslinking is less than 35% by mass, at least one of the step followability and the reworkability will be inferior. When the content is 35% by mass or more, the bubbles of the resin sheet are easily made finer, and the variation in the size of each bubble is easily reduced, so that the mechanical strength can be improved. The crosslinking degree is preferably from 40 to 65% by mass, more preferably from 43 to 60% by mass. When the content is not more than these upper limits, the foam can be easily foamed appropriately, and the expansion ratio can be easily increased. By increasing the expansion ratio of the foamed sheet, the flexibility is easily increased, and the compression strength is easily adjusted to an appropriate value.

<Average bubble diameter>
The foamed sheet has an average cell diameter in the MD and TD directions of preferably 100 μm or less, more preferably 90 μm or less, and even more preferably 70 μm or less. Bubbles having such an average bubble diameter are generally called fine bubbles. If the 25% compressive strength is small, the interlayer strength may be reduced and the tape strength may be impaired. However, the strength can be compensated for when the average bubble diameter is 100 μm or less. Further, since the foamed sheet has fine cells, even when the sheet width is narrowed, many closed cells exist between the narrowed widths. Therefore, even when the width is reduced, appropriate compressive strength and rupture strength can be secured.

  The average cell diameter of MD and TD is preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 30 μm or more from the viewpoint of ease of production.

  In addition, it is preferable that the air bubbles spread flat along the surface direction of the resin foam sheet. That is, the ratio of the average cell diameter of MD to the average cell diameter of ZD of the cells (MD / ZD) and the ratio of the average cell diameter of TD to the average cell diameter of ZD (TD / ZD) are all greater than 1. Preferably, and further preferably, all are 2-7.

The average bubble diameter refers to a value measured in the following manner.
A resin foam sheet cut into a square of 50 mm was prepared as a foam sample for measurement. This was immersed in liquid nitrogen for 1 minute, and then cut in the thickness direction along the MD and TD directions with a razor blade. Using a digital microscope (“VHX-900” manufactured by KEYENCE CORPORATION), this cross section was photographed at a magnification of 200 times, and all of the sections existing on the cut surface of 2 mm length in the MD, TD and ZD directions were taken. The bubble diameter of the bubble was measured, and the operation was repeated five times. The average value of all the bubbles was defined as the average bubble diameter in the MD, TD, and ZD directions.
Note that the MD direction means Machine direction, which is a direction coinciding with the extrusion direction and the like, and the TD direction means Transverse direction, which is a direction orthogonal to the MD direction and parallel to the sheet surface of the resin foam sheet. Direction. The ZD direction is the thickness direction of the foam, and is a direction perpendicular to both the MD direction and the TD direction.

<Closed cell rate>
The resin foam sheet of the present invention preferably has closed cells. Having closed cells means that the ratio of closed cells to all cells (referred to as “closed cell rate”) is 70% or more. The closed cell rate is preferably at least 75%, more preferably at least 90%.
The closed cell rate can be determined in accordance with ASTM D2856 (1998). A commercially available measuring instrument includes a dry automatic densimeter Acupic 1330.

The closed cell ratio is measured more specifically as follows. From the foamed sheet, a test piece having a square shape with a side of 5 cm and a constant thickness is cut out. The thickness of the test piece was measured, to measure the weight W ₁ of the specimen to calculate the apparent volume V ₁ of the test piece. Then calculated based on the apparent volume V ₂ occupied by the bubbles in the following formula. The density of the resin constituting the test piece is 1 g / cm ³ .
Apparent volume occupied by bubbles V ₂ = V ₁ −W ₁
Subsequently, the test piece is immersed in distilled water at 23 ° C. to a depth of 100 mm from the water surface, and a pressure of 15 kPa is applied to the test piece for 3 minutes. Thereafter, the test piece is taken out of the water to remove water adhering to the surface of the test piece, the weight W _{2 of the} test piece is measured, and the open cell rate F ₁ and the closed cell rate F ₂ are calculated based on the following equation. I do.
Open cell rate F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂
Closed cell rate F ₂ (%) = 100−F ₁

<Dimensions of resin foam sheet>
The thickness of the resin foam sheet is preferably from 0.01 to 0.3 mm. When the thickness is 0.01 m or more, it is easy to secure impact resistance and flexibility of the resin foam sheet. When the thickness is 0.3 mm or less, the thickness can be reduced, and the electronic device can be suitably used for miniaturized electronic devices. From these viewpoints, the thickness of the resin foam sheet is more preferably from 0.03 to 0.25 mm, and still more preferably from 0.05 to 0.2 mm.
The resin foam sheet preferably has a narrow width, and specifically, a sheet processed into a fine line is preferable. For example, the foamed sheet may be used with a width of 5 mm or less, preferably 3 mm or less, more preferably 1 mm or less. When the width of the resin foam sheet is reduced, it can be suitably used inside a miniaturized electronic device.
The lower limit of the width of the resin foam sheet is not particularly limited, but may be, for example, 0.1 mm or more, or may be 0.2 mm or more. The planar shape of the foam sheet is not particularly limited, but may be an elongated rectangular shape, a frame shape, an L shape, a U shape, or the like. However, other than these shapes, any other shapes such as a normal square and a circle may be used.

<Expansion ratio>
The expansion ratio of the resin foam sheet is preferably from 1.2 to ⁴ cm ³ / g. By setting the expansion ratio within these ranges, the compression strength can be easily adjusted within the above range. When the expansion ratio is 1.2 cm ³ / g or more, the compressive strength and flexibility are improved, and the impact absorption and sealing properties of the foam sheet are easily improved. On the other hand, by setting it to 4 cm ³ / g or less, mechanical strength is increased, and impact resistance and the like are easily improved.
In view of the foregoing, expansion ratio is more preferably 1.3~3.5cm ³ / g, more preferably 1.5~3.0cm ³ / g. In the present invention, the density of the resin foam sheet is determined according to JIS K7222, and the reciprocal thereof is defined as the expansion ratio.

<Polyolefin resin>
As the resin used for the resin foam sheet, various resins may be used, and among them, a polyolefin resin is preferably used. By using a polyolefin resin, it is possible to reduce the average cell diameter while securing appropriate flexibility of the resin foam sheet.
Examples of the polyolefin resin include a polyethylene resin, a polypropylene resin, an ethylene-vinyl acetate copolymer and the like, and among these, a polyethylene resin is preferable.
Examples of the polyethylene resin include a polyethylene resin polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, and a chromium oxide compound. Preferably, a polyethylene resin polymerized with a metallocene compound polymerization catalyst is used.

As the polyethylene resin, a linear low-density polyethylene is preferable. By using the linear low-density polyethylene, flexibility is given to the foamed sheet, and the resin foamed sheet can be made thinner. This linear low-density polyethylene is more preferably obtained using a polymerization catalyst such as a metallocene compound. The linear low-density polyethylene is obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more with respect to the total amount of monomers) and a small amount of α-olefin as required. The resulting linear low density polyethylene is more preferred.
Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene and the like. Among them, α-olefins having 4 to 10 carbon atoms are preferred.
Polyethylene resin, for example the density of the linear low density polyethylene as described above is preferably 0.870~0.910g / cm ^3, more preferably 0.875~0.907g / cm ^3, 0.880~0.905g / Cm ³ is more preferred. As the polyethylene resin, a plurality of polyethylene resins can be used, and a polyethylene resin having a density other than the above-described range may be added.

(Metallocene compound)
Examples of the metallocene compound include compounds such as a bis (cyclopentadienyl) metal complex having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, and platinum has one or more cyclopentadienyl rings or analogs thereof as a ligand (ligand). Can be mentioned.
Such metallocene compounds have uniform active site properties, and each active site has the same activity. Since the polymer synthesized using the metallocene compound has high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, etc., when the sheet containing the polymer synthesized using the metallocene compound is cross-linked, the cross-linking is uniform. Proceed to As a result, since the sheet can be stretched uniformly, it is easy to make the thickness uniform even when the foamed sheet is thinned.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted by a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group. Examples of the hydrocarbon group include a methyl group, an ethyl group, various propyl groups, various butyl groups, various amyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. , Various cetyl groups, phenyl groups and the like. In addition, "various" means various isomers including n-, sec-, tert-, and iso-.
Further, a compound obtained by polymerizing a cyclic compound as an oligomer may be used as a ligand.
Further, besides the π-electron unsaturated compounds, monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, aryls Phosphides and the like may be used.

Examples of the metallocene compound containing a tetravalent transition metal or a ligand include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethyl And silyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride.
The metallocene compound, when combined with a specific co-catalyst (co-catalyst), exhibits a function as a catalyst when polymerizing various olefins. Specific co-catalysts include methylaluminoxane (MAO), boron compounds and the like. The use ratio of the cocatalyst to the metallocene compound is preferably 100,000 to 1,000,000 times, more preferably 50 to 5,000 times.
Polyolefin resin contained in the resin foam sheet, when using the linear low-density polyethylene described above, the linear low-density polyethylene may be used alone, but may be used in combination with other polyolefin resin For example, it may be used in combination with another polyolefin resin described below. When containing another polyolefin resin, the ratio of the other polyolefin resin to the linear low-density polyethylene (100% by mass) is preferably 40% by mass or less, more preferably 30% by mass or less, and further preferably 20% by mass or less. preferable.

The ethylene-vinyl acetate copolymer used as the polyolefin resin includes, for example, an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene.
Examples of the polypropylene resin include polypropylene and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. These may be used alone or in combination of two or more.
As the α-olefin constituting the propylene-α-olefin copolymer, specifically, ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1- Octene and the like can be mentioned, and among these, α-olefins having 6 to 12 carbon atoms are preferable.

When the resin foam sheet uses a polyolefin resin as the resin, the resin contained in the resin foam sheet may use the polyolefin resin alone, but may include a resin other than the polyolefin resin. In the foamed sheet, the ratio of the polyolefin resin to the total amount of the resin is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.
Examples of the resin other than the polyolefin resin used for the resin foam sheet include various elastomers such as a styrene-based thermoplastic elastomer, an ethylene-propylene-based thermoplastic elastomer such as EPDM, and a rubber component.

(Pyrogenic foaming agent)
The resin foam sheet of the present invention is preferably formed by foaming a foamable composition containing the above resin and a pyrolytic foaming agent. As the thermal decomposition type foaming agent, an organic foaming agent and an inorganic foaming agent can be used. Examples of the organic blowing agent include azo compounds such as azodicarbonamide, metal salts of azodicarboxylic acid (such as barium azodicarboxylate), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine, Examples thereof include hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium carbonate, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, anhydrous monocitrate, and the like.
Among these, azo compounds are preferred, and azodicarbonamide is particularly preferred, from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety. These pyrolytic foaming agents can be used alone or in combination of two or more.
The amount of the pyrolytic foaming agent in the foamable composition is preferably 1 to 10 parts by mass, more preferably 1.5 to 8 parts by mass, and still more preferably 2 to 6 parts by mass with respect to 100 parts by mass of the resin. It is.

Further, the foamable composition preferably contains a cell nucleus modifier in addition to the resin and the pyrolytic foaming agent. Examples of the cell nucleus adjusting agent include zinc compounds such as zinc oxide and zinc stearate, and organic compounds of citric acid and urea. Of these, zinc oxide is more preferable. By using a cell nucleus adjusting agent in addition to the above-described foaming agent having a small particle diameter, the average cell diameter and the variation in the cell diameter can be easily reduced. The compounding amount of the cell nucleating agent is preferably 0.4 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, and still more preferably 0.8 to 2.5 parts by mass with respect to 100 parts by mass of the resin. It is.
The foamable composition contains, if necessary, additives generally used for foams such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, fillers, etc., in addition to the above. It may be.

[Method of manufacturing resin foam sheet]
The method for producing the resin foam sheet is not particularly limited. For example, a foamable composition containing a resin and a pyrolytic foaming agent is crosslinked and heated to foam the pyrolytic foaming agent. It is manufactured by stretching in at least one of the TD direction and the MD direction by a factor of two or more. More specifically, the manufacturing method includes the following steps (1) to (4).
Step (1): mixing a resin and an additive containing a pyrolytic foaming agent to form a sheet-like foamable composition (resin sheet) Step (2): forming a sheet-like foamable composition Step (3) of irradiating ionizing radiation to crosslink the foamable composition: Step (4) of heating the crosslinked foamable composition to foam the pyrolytic foaming agent to obtain a foamed sheet : A step of stretching the foamed sheet in one or both of the MD direction and the TD direction at a stretching ratio of 1.1 or more.

In the step (1), a method for forming a resin sheet is not particularly limited. For example, a resin and an additive are supplied to an extruder and melt-kneaded, and the foamable composition is extruded from the extruder into a sheet. The resin sheet may be formed by the following method.
As a method for crosslinking the foamable composition in the step (2), a method of irradiating the resin sheet with ionizing radiation such as an electron beam, α-ray, β-ray, and γ-ray is used. The irradiation amount of the ionizing radiation may be adjusted so that the degree of crosslinking of the obtained foamed sheet falls within the above-described desired range, but is preferably 5 to 15 Mrad, and more preferably 6 to 13 Mrad.
In the step (3), the heating temperature when the foamable composition is heated to foam the thermal decomposition type foaming agent may be at least the foaming temperature of the thermal decomposition type foaming agent, but is preferably 200 to 300 ° C, Preferably it is 220-280 degreeC.

The stretching of the foam sheet in the step (4) may be performed in both the MD and TD directions, or may be performed only in one direction, but is preferably performed in both directions. The stretching of the foamed sheet may be performed after foaming the resin sheet to obtain a foamed sheet, or may be performed while foaming the resin sheet. When the foamed sheet is stretched after foaming the resin sheet to obtain the foamed sheet, the foamed sheet may be continuously stretched while maintaining the molten state at the time of foaming without cooling the foamed sheet. After cooling the foamed sheet, the foamed sheet may be stretched after the foamed sheet is heated again to be in a molten or softened state. The foamed sheet can be easily made thin by stretching.
In the step (4), the stretching ratio of the foamed sheet in one or both of the MD direction and the TD direction is preferably 1.2 to 4.0 times, and more preferably 1.5 to 3.3 times. Above all, it is particularly preferred that the stretching ratio for both is within these ranges. By setting such a range, the breaking compression parameter can be easily set to a desired range.
When the draw ratio is equal to or more than the lower limit, the flexibility and tensile strength of the foamed sheet tend to be improved. On the other hand, when the value is not more than the upper limit, the foamed sheet is prevented from being broken during stretching, and the foaming gas is prevented from being released from the foamed sheet during foaming and the expansion ratio is significantly reduced, and the flexibility and tensile strength of the foamed sheet are prevented. And the quality is easy to be uniform.
Further, the foamed sheet may be heated at the time of stretching, for example, to 100 to 280 ° C, preferably 150 to 260 ° C.
The foamed sheet obtained as described above may be cut into a desired shape by a known method such as punching.

  However, the present production method is not limited to the above, and a foamed sheet may be obtained by a method other than the above. For example, instead of irradiating with ionizing radiation, an organic peroxide may be previously blended in the foamable composition, and the foaming composition may be heated and crosslinked by a method of decomposing the organic peroxide. Good.

The use of the foam sheet is not particularly limited, but is preferably used, for example, inside an electronic device. Since the foamed sheet of the present invention has good reworkability even if it is thin, it can be suitably used inside various portable electronic devices in which the space for disposing the foamed sheet is small. Examples of the portable electronic device include a mobile phone, a camera, a game device, an electronic organizer, a tablet terminal, a notebook personal computer, and the like. The foam sheet can be used as an impact absorbing material and a sealing material inside the electronic device.
Moreover, you may use for the adhesive tape which uses a foamed sheet as a base material. By using the foamed sheet of the present invention having good step followability and good reworkability as the base material of the pressure-sensitive adhesive tape, poor adhesion and the like are less likely to occur.

[Adhesive tape]
The pressure-sensitive adhesive tape includes, for example, the resin foam sheet according to the present invention, and a pressure-sensitive adhesive layer provided on at least one surface of the resin foam sheet. Tape is preferred.
The thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive tape is preferably from 5 to 200 μm. The thickness of the pressure-sensitive adhesive layer is more preferably 7 to 150 μm, and still more preferably 10 to 100 μm. When the thickness of the pressure-sensitive adhesive layer is in the range of 5 to 200 μm, the thickness of the structure fixed using the pressure-sensitive adhesive tape can be reduced.
The pressure-sensitive adhesive used for the pressure-sensitive adhesive layer is not particularly limited, and for example, an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, or the like can be used.
Further, a release sheet such as release paper may be further laminated on the pressure-sensitive adhesive layer.
The method for forming the pressure-sensitive adhesive layer on at least one surface of the foamed sheet is not particularly limited. For example, a method of applying a pressure-sensitive adhesive on at least one surface of the foamed sheet using a coating machine such as a coater may be used. Also, a method of spraying and applying an adhesive by using a spray on at least one surface of a resin foam sheet, a method of applying an adhesive by using a brush on at least one surface of a foam sheet, and foaming an adhesive layer formed on a release sheet A method of transferring the image onto at least one surface of the sheet may be used.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Measuring method]
The measuring method and evaluation method of each physical property are as follows.
<Apparent density and expansion ratio>
The apparent density of the resin foam sheet was measured in accordance with JIS K7222, and the reciprocal thereof was defined as the expansion ratio.
<Degree of crosslinking>
About 100 mg of a test piece is collected from the resin foam sheet, and the weight A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in 30 cm ³ of xylene at 120 ° C. and allowed to stand for 24 hours, then filtered through a 200-mesh wire gauze to collect the insoluble matter on the wire gauze, vacuum-dried, and weighed the insoluble matter. Weigh B (mg) precisely. From the obtained values, the degree of crosslinking (% by mass) was calculated by the following equation.
Degree of crosslinking (% by mass) = 100 × (B / A)

<Average cell diameter, closed cell rate>
The average cell diameter and closed cell ratio were measured by the methods described in the specification.

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

<Strength at break and elongation>
The resin foam sheet was cut into a dumbbell-shaped No. 1 shape specified in JIS K6251 4.1. Using this as a sample, the breaking point strength in the MD and TD directions and the elongation at that time were measured at a measurement temperature of 23 ° C. according to JIS K6767.
<Parameter>
The breaking compression parameters in the MD direction and the TD direction of the resin foam sheet (MPa) and the 25% compressive strength (kPa) and the breaking compression parameter were obtained from the formula A.

<PUSH adhesive strength evaluation test>
(Production of double-sided adhesive tape)
A pressure-sensitive adhesive layer obtained by the following method was laminated on both sides of the resin foam sheet, and a double-sided pressure-sensitive adhesive tape having a resin foam sheet as a base material was produced in the following manner.

In a reactor equipped with a thermometer, a stirrer, and a condenser, 75 parts by mass of butyl acrylate, 22 parts by mass of 2-ethylhexyl acrylate, 3 parts by mass of acrylic acid, 0.2 parts by mass of 2-hydroxyethyl acrylate, and 80 parts by mass of ethyl acetate Was added, and the atmosphere was replaced with nitrogen. Then, the reactor was heated to start refluxing. Subsequently, 0.1 parts by mass of azobisisobutyronitrile was added as a polymerization initiator into the reactor. The mixture was refluxed for 5 hours to obtain a solution of the acrylic copolymer (z). The weight-average molecular weight of the obtained acrylic copolymer (z) measured by GPC using "2690 Separations Model" manufactured by Water as a column was 600,000.
15 parts by mass of a polymerized rosin ester having a softening point of 135 ° C. and ethyl acetate (Fuji Chemical Co., Ltd.) were added to 100 parts by mass of the solid content of the acrylic copolymer (z) contained in the obtained solution of the acrylic copolymer (z). 125 parts by mass of Yakuhin Chemical Co., Ltd. and 2 parts by mass of an isocyanate-based crosslinking agent (Coronate L45, manufactured by Tosoh Corporation) were added and stirred to obtain a pressure-sensitive adhesive (Z). The degree of crosslinking of the acrylic pressure-sensitive adhesive was 33% by mass.
A release paper having a thickness of 150 μm was prepared, an adhesive (Z) was applied to the release treated surface of the release paper, and dried at 100 ° C. for 5 minutes to form an acrylic pressure-sensitive adhesive layer having a thickness of 50 μm. . This acrylic pressure-sensitive adhesive layer was bonded to the surface of a substrate made of a foamed sheet. Next, in the same manner, the same acrylic pressure-sensitive adhesive layer was bonded to the opposite surface of the substrate. Thus, a double-sided pressure-sensitive adhesive tape having both sides covered with a release paper having a thickness of 150 μm was obtained.

(Production of test equipment)
(1) Test apparatus A: PC / Glass
FIG. 1 shows a schematic diagram of a push test of a double-sided adhesive tape. The obtained double-sided pressure-sensitive adhesive tape was punched into an outer diameter of 46 mm, a length of 61 mm, an inner diameter of 44 mm, and a length of 59 mm to prepare a frame-shaped test piece 1 having a width of 1 mm. Then, as shown in FIG. 1 (a), the test piece 1 obtained by peeling the release paper from a polycarbonate plate 3 having a thickness of 2 mm and a square hole having a width of 38 mm and a length of 50 mm in the center portion is substantially square in the center. Paste so that it is located in. Thereafter, a glass plate 5 having a width of 55 mm, a length of 65 mm, and a thickness of 2 mm was attached from the upper surface of the test piece 1 so that the test piece 1 was located substantially at the center, and a test apparatus A was assembled.
Thereafter, a pressure of 30 kgf was applied for 10 seconds at 70 ° C. from the side of the glass plate 5 positioned on the upper surface of the test apparatus A, and the glass plate and the polycarbonate plate positioned above and below were heat-pressed and allowed to stand at room temperature for 24 hours. .

(2) Test apparatus B: SUS / Glass
A test apparatus B was assembled in the same manner as the test apparatus A, except that the polycarbonate plate 3 was a stainless plate (SUS304, thickness: 2 mm). Thereafter, in the same manner as in the case of the test apparatus A, it was heated and pressed and left at room temperature for 24 hours.

(Push test)
As shown in FIG. 1 (b), the test device A or the test device B was turned upside down (with the glass plate 5 facing downward) and fixed to a support table, and the lower surface of the lower surface was set at a speed of 10 mm / min from the opening side. The glass plate 5 was pushed down, and the load (N) when the glass plate 5 was peeled was measured. The measurement was performed at 23 ° C.
If the PUSH adhesive strength in PC / Glass is 70 to 90N, and if the PUSH adhesive strength in SUS / Glass is 150 to 190N, it can be said that the ease of sticking due to softness is good. Properties can be improved.

<Rework evaluation test>
First, a pressure-sensitive adhesive tape having an acrylic pressure-sensitive adhesive layer provided on one surface of a resin foam sheet was prepared in the same manner as in the “PUSH pressure-sensitive adhesive strength evaluation test”. Under an environment of room temperature 23 ° C. and relative humidity 50%, an adhesive tape cut into a size of 2 mm × 100 mm was attached to a stainless steel plate and left for 24 hours. Thereafter, the adhesive tape was peeled off, and the peeled state was subjected to a sensory evaluation. When it was peeled in the same state as before the attachment, it was evaluated as "A" as good reworkability, and when the sheet was torn or stretched and the glue remained on the stainless steel plate, it was evaluated as "B" as poor reworkability.

[Polyolefin resin]
The polyolefin resin used in this example is shown below.
Resin A: linear low-density polyethylene resin (Dow Chemical Co., Ltd. under the trade name "Affinity PL1850", density 0.902g / ^cm 3)
Resin B: a linear low density polyethylene resin (Dow Chemical Co., Ltd. under the trade name "Affinity KC8852", density 0.875g / ^cm 3)
Resin C: a hydrogenated styrene-isoprene-butadiene block copolymer resin (Kuraray's trade name "Hybrar 7311", density 0.890 g / ^cm 3)

[Example 1]
100 parts by mass of resin A, 5 parts by mass of azodicarbonamide having a particle size of 13 μm as a pyrolytic foaming agent, and zinc oxide (trade name “OW-212F”, manufactured by Sakai Chemical Industry Co., Ltd.) 0.0 parts by mass and 0.5 parts by mass of an antioxidant (acid protection) were supplied to an extruder, melt-kneaded at 130 ° C., and extruded into a long resin sheet having a thickness of 300 μm.
Next, the resin sheet was cross-linked by irradiating 7 Mrad of an electron beam with an accelerating voltage of 500 kV to both surfaces of the long resin sheet, and then the cross-linked resin sheet was heated in a foaming furnace maintained at 250 ° C. by hot air and an infrared heater. , And foamed by heating to obtain a foamed sheet having a thickness of 500 µm.
Next, after continuously feeding the obtained foamed sheet from the foaming furnace, the foamed sheet is moved in the TD direction by 2.5 mm in a state where the temperature of both sides of the foamed sheet is maintained at 200 to 250 ° C. The foamed sheet is stretched at twice the draw ratio, and the foamed sheet is wound at a winding speed higher than a feeding speed (supply speed) of the foamed sheet to the foaming furnace. Thus, the foamed sheet was stretched 2.0 times in the MD direction to obtain a resin foamed sheet (thickness: 0.1 mm). The winding speed of the resin foam sheet was adjusted in consideration of the amount of expansion in the MD direction due to foaming of the resin sheet itself. The obtained resin foam sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

[Examples 2 to 6 and Comparative Examples 1 to 5]
A resin foam sheet was obtained in the same manner as in Example 1, except that the thickness of the resin, the additive, and the resin foam sheet were changed as shown in Tables 1 and 2 below. The stretching ratio of MD and TD was adjusted within the range of 1.5 to 3.5. The obtained resin foam sheet was evaluated according to the above evaluation method, and the results are shown in Tables 1 and 2.

1 Test piece 3 Polycarbonate plate 5 Glass plate

Claims (11)

A resin foam sheet, wherein a breaking compression parameter represented by the following formula A is 700 or more and less than 1500 and a degree of crosslinking is 35% by mass or more.
Formula A: strength at break in MD (MPa) × strength at break in TD (MPa) / 25% compressive strength (kPa) × 1000   The resin foam sheet according to claim 1, wherein the average cell diameter in each of the MD direction and the TD direction is 100 µm or less.   The resin foam sheet according to claim 1, wherein the thickness is 0.01 to 0.3 mm.   The resin foam sheet according to any one of claims 1 to 3, wherein the breaking point strength in the MD direction is 7 to 30 MPa, and the breaking point strength in the TD direction is 10 to 25 MPa.   The resin foam sheet according to any one of claims 1 to 4, wherein the 25% compressive strength is 130 to 500 kPa. The resin foam sheet according to any one of claims 1 to 5, wherein an expansion ratio is 1.2 to ⁴ cm3 / g.   The resin foam sheet according to any one of claims 1 to 6, wherein the resin foam sheet includes a polyolefin resin.   The resin foam sheet according to claim 7, wherein the polyolefin resin is a polyethylene resin.   The resin foam sheet according to claim 7 or 8, wherein the polyolefin resin is a linear low-density polyethylene polymerized with a metallocene compound polymerization catalyst. It is a manufacturing method of the resin foam sheet according to any one of claims 1 to 9,
A foamable composition containing a resin and a thermal decomposition type foaming agent is cross-linked and heated to foam the thermal decomposition type foaming agent, and stretched in at least one of the TD direction and the MD direction at a stretching ratio of 1.1 or more. To manufacture a resin foam sheet.   An adhesive tape comprising the resin foam sheet according to any one of claims 1 to 9 and an adhesive layer provided on at least one surface of the resin foam sheet.

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