WO2019066077A1

WO2019066077A1 - Double-sided adhesive tape

Info

Publication number: WO2019066077A1
Application number: PCT/JP2018/036595
Authority: WO
Inventors: 健人永井; 秀明矢野; 慶人菱沼; 上田　雄大; 健一郎高須
Original assignee: 積水化学工業株式会社
Priority date: 2017-09-29
Filing date: 2018-09-28
Publication date: 2019-04-04
Also published as: KR20200060384A; CN111148808A; JP7193229B2; JP2019065153A; KR102625608B1

Abstract

This double-sided adhesive tape is obtained by providing both surfaces of a polyolefin resin foam sheet, which is obtained by foaming an expandable composition that contains a polyolefin resin, with adhesive layers. With respect to this double-sided adhesive tape, the average foam cell diameter of the polyolefin resin foam sheet is from 25 to 150 μm; and at least one of the adhesive layers has an adhesive force of from 1.1 to 23 N/25 mm at 25°C as determined in accordance with JIS Z0237 (2009). Consequently, the present invention is able to provide a double-sided adhesive tape which has excellent reworkability, and which exhibits good waterproof properties even after reworking.

Description

Double-sided adhesive tape

The present invention relates to a double-sided pressure-sensitive adhesive tape having a polyolefin resin foam sheet.

Conventionally, porous resin materials in which a large number of holes are formed in the resin layer are excellent in, for example, buffer property, heat insulation property, waterproofness and moisture resistance, and therefore protection from the packing material of articles, gas or liquid is required. It is used for various applications, such as a sealing material which seals peripheral parts, such as parts, a shock absorbing material which absorbs vibration and impact, and a base material of an adhesive sheet. As a specific polyolefin resin foam sheet, Patent Document 1 discloses a crosslinked polyolefin resin foam sheet obtained by foaming and crosslinking a foamable polyolefin resin sheet containing a thermal decomposition type foaming agent (patent Reference 1).

WO 2005/007731

By the way, in recent years, high waterproof performance is required in small communication devices such as smart phones and wearable terminals. Therefore, a gasket material composed of a double-sided pressure-sensitive adhesive tape having a flexible foam as a base material is disposed in the gap generated between the display panel and the housing or in the vicinity of the opening such as the SIM card slot. Such a gasket material is required to have a strong adhesion to the portion to be adhered from the viewpoint of water blocking, while the attachment position can be finely corrected when the gasket material is attached to a product. And removability (hereinafter, also referred to as "reworkability") must be excellent. Specifically, when fine correction is required after attaching the gasket material to the adherend part, it is required to peel off the gasket material and maintain excellent waterproofness even after reattachment. There is.
However, the gasket material for water blocking constructed of the double-sided pressure-sensitive adhesive tape conventionally used is inferior in reworkability, and the waterproofness after rework may be lowered.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a double-sided pressure-sensitive adhesive tape which is excellent in reworkability and exhibits good waterproofness even after rework.

As a result of intensive investigations by the present inventors, it is possible to adjust the average cell diameter of the polyolefin resin foamed sheet to a specific range and adjust the adhesion of at least one of the pressure-sensitive adhesive layers to a specific range. It has been found that the nature is improved, and the present invention has been completed. That is, the present invention is as follows.

[1] A double-sided pressure-sensitive adhesive tape in which an adhesive layer is provided on both sides of a polyolefin resin foam sheet obtained by foaming a foamable composition containing a polyolefin resin, wherein the average cell diameter of the polyolefin resin foam sheet is 25 to A double-sided pressure-sensitive adhesive tape which is 150 μm and has a 90 ° peel adhesive strength at 25 ° C. of 1.1 to 23 N / 25 mm measured at 25 ° C. according to JIS Z0237-2009 for at least one of the pressure-sensitive adhesive layers.
[2] The double-sided pressure-sensitive adhesive tape according to [1], wherein the thickness of the polyolefin resin foam sheet is 1.5 mm or less.
[3] The double-sided pressure-sensitive adhesive tape as described in [1] or [2] above, wherein the 25% compressive strength of the polyolefin resin foamed sheet is 10 to 1,000 kPa.
[4] The double-sided pressure-sensitive adhesive tape according to any one of the above [1] to [3], wherein the amount of the polyethylene resin is 30% by mass or more based on the total amount of the resin contained in the foamable composition.
[5] The double-sided pressure-sensitive adhesive tape according to any one of the above [1] to [4], wherein at least one of the pressure-sensitive adhesive layers is composed of an acrylic pressure-sensitive adhesive.
[6] The pressure-sensitive adhesive layer provided on one side of the polyolefin resin foam sheet has a 90 degree peel adhesive strength weaker than the pressure-sensitive adhesive layer provided on the other side, of [1] to [5] The double-sided pressure-sensitive adhesive tape according to any one of the items.
[7] The double-sided pressure-sensitive adhesive tape according to any one of the above [1] to [6], wherein the expansion ratio of the foamed polyolefin resin sheet is 1.2 to 15 cm ³ / g.
[8] The double-sided pressure-sensitive adhesive tape according to any one of the above [1] to [7], wherein the polyolefin resin is a linear low density polyethylene polymerized with a polymerization catalyst of a metallocene compound.
[9] A method for producing the double-sided pressure-sensitive adhesive tape according to any one of the above [1] to [8],
A sheet-like foamable composition containing a resin and a thermal decomposition-type foaming agent is crosslinked and heated to foam the thermal decomposition-type foaming agent, and at least one of TD direction and MD direction at a draw ratio of 1.1 times or more The manufacturing method of the double-sided adhesive tape which manufactures the said polyolefin resin foamed sheet by extending | stretching to one side.

According to the present invention, it is possible to provide a double-sided pressure-sensitive adhesive tape which is excellent in reworkability and shows good waterproofness even after rework.

Hereinafter, the present invention will be described in detail using embodiments.
[Double-sided adhesive tape]
The double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention is obtained by providing a pressure-sensitive adhesive layer on both sides of a polyolefin resin foam sheet obtained by foaming a foamable composition containing a polyolefin resin. The double-sided pressure-sensitive adhesive tape has an average cell diameter of 25 to 150 μm of the polyolefin resin foam sheet, and 90 ° peel adhesion at 25 ° C. measured according to JIS Z0237-2009 for at least one of the pressure-sensitive adhesive layers. It is 1.1 to 23 N / 25 mm.
In the present invention, since the average cell diameter of the polyolefin resin foam sheet is within the above range, the fine tearing occurs even when a large force is applied to the double-sided pressure-sensitive adhesive tape when the attachment position is finely corrected (that is, during rework). It can be peeled off cleanly without breaking. In addition, since at least one of the pressure-sensitive adhesive layers has a specific adhesive force, it can be peeled off well during rework while being waterproof, and can maintain sufficient adhesion to the adhered part even after rework. Because it can be maintained waterproof.

<Average bubble diameter>
The average cell diameter of the polyolefin resin foamed sheet (hereinafter, also simply referred to as “foamed sheet”) used in the present invention is 25 to 150 μm. When the average cell diameter of the foamed sheet exceeds 150 μm, when a large force is applied to the double-sided pressure-sensitive adhesive tape at the time of rework, breakage occurs around the cell having a large cell diameter as a starting point. That is, when a large number of cells having a large cell diameter are present in the foam sheet, many parts having a low density in the foam sheet are present, and thus tears and the like are more likely to occur than the parts. Furthermore, when it exfoliates, expansion tends to occur in a foaming sheet and it becomes the tendency for 90 degree peel exfoliation power to become high.
Therefore, from the viewpoint of improving the reworkability, the average cell diameter of the foam sheet is preferably 140 μm or less, more preferably 130 μm or less, still more preferably 120 μm or less, still more preferably 110 μm or less, still more preferably 100 μm or less More preferably, it is 95 μm or less. The lower limit value of the average cell diameter is not particularly limited, but a foamed sheet containing many small cell diameters is preferably at least 30 μm, more preferably at least 40 μm, still more preferably at least 50 μm, still more preferably. Is 55 μm or more.
Bubbles of such an average bubble diameter are generally called fine bubbles. In the present invention, by setting the average cell diameter to 150 μm or less, the strength and flexibility of the foam sheet can be maintained.
In addition, the average bubble diameter in this invention points out the average bubble diameter computed from the average bubble diameter of MD direction measured by the below-mentioned method, and the average bubble diameter of TD direction.

The average bubble diameter refers to one measured in the following manner.
What cut the foamed sheet into 50 mm squares was prepared as a foam sample for measurement. This was immersed in liquid nitrogen for 1 minute, and then cut in the thickness direction along the MD and TD directions with a razor blade. This cross section is taken a 200x magnification with a digital microscope ("VHX-900" manufactured by KEYENCE CORPORATION), and all bubbles present in the cut surface for 2 mm in length in the MD direction and TD direction respectively The bubble diameter was measured, and the operation was repeated five times. And the average value of all bubbles was made into the average bubble diameter of MD direction and TD direction.
In addition, MD direction means Machine direction and is a direction coincident with extrusion direction etc., and TD direction means Transverse direction and is a direction orthogonal to MD direction, and is a sheet-like foam (foam sheet In the direction parallel to the sheet surface.

<Adhesiveness of adhesive layer>
In the present invention, at least one of the pressure-sensitive adhesive layers has a 90 ° peel adhesive strength at 25 ° C. measured according to JIS Z 0237-2009 of 1.1 to 23 N / 25 mm. When the adhesive strength is less than 1.1 N / 25 mm, a gap is formed between the double-sided adhesive tape and the adhered portion, and the waterproofness is reduced. On the other hand, if the adhesive strength exceeds 23 N / 25 mm, the double-sided pressure-sensitive adhesive tape adheres firmly to the adhered portion, so even when the average cell diameter of the foam sheet is adjusted within the above range, it breaks during rework. A thousand cuts will occur. From such a point of view, the adhesive strength is preferably 1.5 to 22 N / 25 mm, more preferably 2.5 to 21 N / 25 mm, still more preferably 3 to 20 N / 25 mm.

In the present invention, the pressure-sensitive adhesive layer provided on one surface of the polyolefin-based resin foam sheet may satisfy the pressure-sensitive adhesive force, and both pressure-sensitive adhesive layers may satisfy the pressure-sensitive adhesive force. However, from the viewpoint of reworkability, it is preferable that the pressure-sensitive adhesive layer provided on one of the surfaces satisfies the adhesive strength.
In addition, in the double-sided pressure-sensitive adhesive tape of the present invention, the pressure-sensitive adhesive layer provided on one side of the polyolefin resin foam sheet has a 90 degree peel adhesive strength weaker than the pressure-sensitive adhesive layer provided on the other side. Is preferred. Thereby, when it is going to peel off the double-sided pressure-sensitive adhesive tape at the time of rework, it becomes easy to peel off from the pressure-sensitive adhesive layer having weak adhesive force, so it becomes easy to prevent tearing or breaking of the double-sided pressure-sensitive adhesive tape. That is, in the double-sided pressure-sensitive adhesive tape of the present invention, one side of the polyolefin resin foam sheet is a weak pressure-sensitive adhesive layer having relatively weak adhesion, and the other side is strongly adhesive than the weak pressure-sensitive adhesive layer. It is preferable to have two pressure-sensitive adhesive layers which are agent layers, and it is preferable that at least the weak pressure-sensitive adhesive layer satisfies the adhesive strength.

[Weak adhesive layer]
In the case of providing the weak pressure-sensitive adhesive layer and the strong pressure-sensitive adhesive layer on the double-sided pressure-sensitive adhesive tape, the 90 degree peel adhesive strength at 25 ° C. measured according to JIS Z0237-2009 for the weak pressure-sensitive adhesive layer is preferably 1.5 to 22 N / 25 mm, still more preferably 2.5 to 18 N / 25 mm, still more preferably 3 to 12 N / 25 mm, still more preferably 4 to 8 N / 25 mm, still more preferably 4.5 to 7 N / 25 mm. When the weak pressure-sensitive adhesive layer is in the above-mentioned range, it is possible to prevent tearing or breaking at the time of rework.
The adhesion of the weak pressure-sensitive adhesive layer is, for example, the type of monomer, the type of crosslinking agent, the amount of crosslinking agent, the type of tackifying resin, the amount of tackifying resin, etc. in the production process if it is an acrylic adhesive. Can be adjusted by changing.

The thickness of the weak pressure-sensitive adhesive layer is preferably 5 to 100 μm. If the thickness of the weak pressure-sensitive adhesive layer is less than 5 μm, the adhesion between the double-sided pressure-sensitive adhesive tape and the member becomes insufficient and the waterproofness is reduced. On the other hand, when the thickness of the weak pressure-sensitive adhesive layer is larger than 100 μm, the double-sided pressure-sensitive adhesive tape becomes thick, which makes it difficult to use the inside of a small electronic device. From such a viewpoint, the thickness of the weak pressure-sensitive adhesive layer is more preferably 8 to 80 μm, further preferably 10 to 50 μm, and still more preferably 10 to 40 μm.

[Strong adhesive layer]
In the case of providing a weak pressure-sensitive adhesive layer and a strong pressure-sensitive adhesive layer on a double-sided pressure-sensitive adhesive tape, the 90 degree peel adhesive strength at 25 ° C. measured according to JIS Z0237-2009 for the strong pressure-sensitive adhesive layer is higher than that of the weak pressure-sensitive adhesive layer The adhesive force is not particularly limited, but preferably 25 N / 25 mm or more, more preferably 26 N / 25 mm or more, still more preferably 27 N / 25 mm or more. When the adhesion of the strong pressure-sensitive adhesive layer is the above lower limit value, the adherend part and the double-sided pressure-sensitive adhesive tape are in close contact with each other, whereby the waterproofness is improved. On the other hand, 50 N / 25 mm or less is preferable, as for the upper limit of the adhesive force of a strong adhesive layer, 45 N / 25 mm or less is more preferable, and 40 N / 25 mm or less is still more preferable. If the adhesive strength of the strong pressure-sensitive adhesive layer is the above upper limit value, reworkability can be secured.
The adhesive force of the strong pressure-sensitive adhesive layer is also, for example, the type of monomer, the type of crosslinking agent, the amount of crosslinking agent, the type of tackifying resin, the amount of tackifying resin in the production process if it is an acrylic adhesive. It can be adjusted by changing etc.

The thickness of the strong pressure-sensitive adhesive layer is preferably 5 to 100 μm. If the thickness of the strong pressure-sensitive adhesive layer is less than 5 μm, the adhesion between the double-sided pressure-sensitive adhesive tape and the member becomes insufficient and the waterproofness is lowered. On the other hand, if the thickness of the strong pressure-sensitive adhesive layer is more than 100 μm, the double-sided pressure-sensitive adhesive tape becomes thick, which makes it difficult to use the inside of a small electronic device. From such a viewpoint, the thickness of the pressure-sensitive adhesive layer is more preferably 8 to 80 μm, further preferably 10 to 50 μm, and still more preferably 15 to 40 μm.

[Difference in adhesion between weak adhesive layer and strong adhesive layer]
The difference in adhesion between the weak pressure-sensitive adhesive layer and the strong pressure-sensitive adhesive layer (difference in adhesion at 25 ° C. measured in accordance with JIS Z 0237-2009) is preferably 3 to 40 N / 25 mm. If the difference in adhesive strength is within the above range, it is possible to obtain a double-sided adhesive tape having excellent reworkability while maintaining excellent waterproofness. From such a viewpoint, more preferably 6 to 35 N / 25 mm, still more preferably 10 to 32 N / 25 mm, still more preferably 14 to 28 N / 25 mm, still more preferably 18 to 25 N / 25 mm.

<Expansion ratio>
The expansion ratio of the foam sheet is preferably 1.2 to 15 cm ³ / g. By setting the foaming ratio within the above range, the average cell diameter and the compressive strength can be easily adjusted within the above range. In addition, by setting the expansion ratio to 1.2 cm ³ / g or more, the flexibility becomes good, and the impact absorbability and the sealability of the foam sheet tend to be good. On the other hand, by setting it as 15 cm < ³ > / g or less, mechanical strength becomes high and it becomes easy to improve impact resistance etc.
From this viewpoint, the expansion ratio, ³ ~ 14cm 3 / g, more preferably, 5 more preferably ~ 13cm ³ / g, more preferably more that 5 ~ 12cm ³ / g, further more is 6 ~ 11cm ³ / g preferable. In the present invention, the density of the foam sheet is determined in accordance with JIS K7222, and the reciprocal thereof is defined as the expansion ratio.

<25% compressive strength>
The 25% compressive strength of the foam sheet is preferably 10 to 1,000 kPa. When the 25% compressive strength is within the above range, the foamed sheet becomes flexible, so that the foamed sheet is difficult to tear during rework. Furthermore, since it becomes possible to stick without gaps between members, waterproofness can be secured. From such a viewpoint, the 25% compressive strength of the foam sheet is more preferably 20 to 500 kPa, still more preferably 30 to 250 kPa, still more preferably 40 to 150 kPa, and still more preferably 40 to 100 kPa.
In addition, 25% compressive strength means what measured the foamed sheet based on JISK6767.

<Crosslinking degree>
The degree of crosslinking of the foam sheet is preferably 30% by mass or more. If the degree of crosslinking is less than 30% by mass, it is difficult to adjust the average cell diameter to the above range, and as a result, the reworkability is deteriorated. By setting the content to 30% by mass or more, the bubbles of the resin sheet can be easily miniaturized, and the variation in the size of the bubbles can be reduced, and the rework property and the mechanical strength can be improved. From such a viewpoint, the degree of crosslinking of the foam sheet is more preferably 35 to 65% by mass, further preferably 40 to 60% by mass, and still more preferably 42 to 55% by mass. By setting the content to the upper limit value or less, it becomes easy to foam the foam appropriately, and it becomes easy to increase the foaming ratio. By increasing the expansion ratio of the foamed sheet, it becomes easy to increase the flexibility and to make the compressive strength an appropriate value.

<Closed cell rate>
The foam sheet preferably has closed cells. Having a closed cell means that the ratio of the closed cell to all the cells (referred to as the “closed cell rate”) is 70% or more. When the foam sheet used in the present invention has closed cells, waterproofness can be easily secured. The closed cell rate is preferably 75% or more, more preferably 90% or more.
The closed cell rate can be determined in accordance with ASTM D2856 (1998). In a commercially available measuring device, a dry automatic densimeter Accupyc 1330 and the like can be mentioned.

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

<Dimension of foam sheet>
The thickness of the foam sheet is preferably 1.5 mm or less. When the thickness is 1.5 mm or less, thinning can be achieved, and the device can be suitably used for miniaturized electronic devices. From such a viewpoint, the thickness is preferably 1 mm or less, more preferably 0.9 mm or less, and further preferably 0.8 mm or less. The lower limit of the thickness is not particularly limited, but is preferably 0.1 mm or more, more preferably 0.15 mm or more, in view of the relationship with the average cell diameter. When the thickness is 0.1 mm or more, it is easy to ensure waterproofness, impact resistance and flexibility of the foam sheet.

The foam sheet preferably has a narrow width, and specifically, it is preferably processed into a thin line. For example, the width of the foam sheet may be 5 mm or less, preferably 3 mm or less, more preferably 1 mm or less. Since the foam sheet used in the present invention is excellent in waterproofness, for example, excellent waterproofness can be obtained even when the width is 1 mm, and it can be suitably used inside a miniaturized electronic device. .
The lower limit of the width of the foam sheet is not particularly limited, but may be, for example, 0.1 mm or more, or 0.2 mm or more. The planar shape of the foam sheet is not particularly limited, but it may be an elongated rectangular shape, a frame shape, an L shape, a U shape, or the like. However, other than these shapes, it may be any other shape such as a regular square or a circle.

<Polyolefin resin>
Although various resins may be used as the resin used for the foam sheet, it is preferable to use a polyolefin resin among them. By using a polyolefin resin, it becomes easy to adjust the average cell diameter within the above range while securing appropriate flexibility of the foam sheet.
Examples of the polyolefin resin include polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer, etc. Among these, polyethylene resin and ethylene-vinyl acetate copolymer are preferable.

[Polyethylene resin]
The polyethylene resin may, for example, be a polyethylene resin polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound or a chromium oxide compound, and preferably a polyethylene resin polymerized with a polymerization catalyst of a metallocene compound.

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

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

As a ligand, a cyclopentadienyl ring, an indenyl ring, etc. can be mentioned, for example. These cyclic compounds may be substituted by a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group. As a hydrocarbon group, for example, methyl group, ethyl group, various propyl groups, various butyl groups, various amyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups And various cetyl groups, phenyl groups and the like. "Various" means various isomers including n-, sec-, tert- and iso-.
Also, a polymer obtained by polymerizing a cyclic compound as an oligomer may be used as a ligand.
Furthermore, in addition to unsaturated compounds of π electron system, monovalent anion ligands or divalent anion chelate ligands such as chlorine and bromine, hydrocarbons, alkoxides, arylamides, aryloxides, aryloxides, amides, arylamides, phosphides, aryls Phosphide or the like may be used.

Examples of metallocene compounds containing tetravalent transition metals and ligands include cyclopentadienyl titanium tris (dimethylamide), methyl cyclopentadienyl titanium tris (dimethyl amide), bis (cyclopentadienyl) titanium dichloride, dimethyl And silyl tetramethyl cyclopentadienyl-t-butylamido zirconium dichloride and the like.
The metallocene compound acts as a catalyst in the polymerization of various olefins in combination with a specific co-catalyst (co-catalyst). Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron compounds. The use ratio of the cocatalyst to the metallocene compound is preferably 10 to 1,000,000 moles, and more preferably 50 to 5,000 moles.
As the polyolefin resin contained in the foam sheet, when using the above-mentioned linear low density polyethylene, the above linear low density polyethylene may be used alone, but may be used in combination with other polyolefin resin For example, it may be used in combination with other polyolefin resins described below. When it contains other polyolefin resin, 40 mass parts or less are preferable, and, as for the ratio of the other polyolefin resin with respect to linear low density polyethylene (100 mass parts), 30 mass parts or less are more preferable.

[Polypropylene resin]
Examples of polypropylene resins include polypropylene and propylene-α-olefin copolymers containing 50% by mass or more of propylene. One of these may be used alone, or two or more may be used in combination.
Specific examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1- An octene etc. can be mentioned, Among these, a C6-C12 alpha-olefin is preferable.

[Ethylene-vinyl acetate copolymer]
The ethylene-vinyl acetate copolymer used as the polyolefin resin is, for example, ethylene-acetic acid containing preferably 6 to 40% by mass, more preferably 12 to 35% by mass, still more preferably 20 to 33% by mass of vinyl acetate. A vinyl copolymer is mentioned.
In the present invention, for example, two or more types having different molecular weights, amounts of vinyl acetate as copolymer components, melting points and the like can be used in combination.
The ethylene-vinyl acetate copolymer used in the present invention may contain ethylene alcohol and vinyl acetate, as well as vinyl alcohol produced by hydrolyzing a part of vinyl acetate.
As such ethylene-vinyl acetate copolymer, for example, “Ultrasen” manufactured by Tosoh Corp., “Evaflex” manufactured by DuPont-Polychemicals Co., Ltd., “UBE polyethylene” manufactured by Ube Industries, Ltd., Asahi Kasei Chemicals Co., Ltd. Company-made "Suntech" etc. are mentioned.

[Content of each resin]
When using polyethylene resin as polyolefin resin, 30 mass% or more is preferable, 50 mass% or more is more preferable, 60 mass% or more is still more preferable, 70 mass% or more is still more preferable, as for the quantity of polyethylene resin with respect to resin whole quantity. It may consist essentially of polyethylene resin. Waterproofness and rework property improve that content of a polyethylene resin is 30 mass% or more.

Moreover, when using ethylene-vinyl acetate copolymer as polyolefin resin, 20 mass% or more is preferable, and, as for the quantity of ethylene-vinyl acetate copolymer with respect to resin whole quantity, 40 mass% or more is more preferable, 60 mass% or more More preferably, it may consist essentially of ethylene-vinyl acetate copolymer. Waterproofness and rework property improve that content of a polyethylene resin is 20 mass% or more.

Furthermore, when the foam sheet contains a polyolefin resin as a resin, the resin contained in the foam sheet may be a polyolefin resin alone, but may contain a resin other than the polyolefin resin. When the foamed sheet contains a resin other than the polyolefin resin, the proportion of the polyolefin resin to the total amount of the resin is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more.
Moreover, as resins other than polyolefin resin used for a foam sheet, various elastomers, such as a styrene-type thermoplastic elastomer, ethylene propylene-type thermoplastic elastomers, such as EPDM, a rubber component, etc. are mentioned.

(Pyrolytic foam)
The foamed sheet of the present invention is preferably formed by foaming a foamable composition containing the above-mentioned resin and a thermal decomposition-type foaming agent. Moreover, as a thermal decomposition type foaming agent, it is preferable to use that whose particle size is less than 15 micrometers. In the present invention, those having a particle size of less than 15 μm can be used, and adjustment of the degree of crosslinking to a specific range enables adjustment to the range of the average cell diameter, as a result, double-sided adhesive tape Reworkability can be improved. From such a viewpoint, the particle size of the thermal decomposition-type foaming agent is preferably 2 to 14 μm, and more preferably 5 to 13 μm.
The particle size of the thermal decomposition type foaming agent is a value measured by a laser diffraction method, and means a particle size (D50) corresponding to a cumulative frequency of 50%.

As a thermal decomposition type foaming agent, an organic foaming agent and an inorganic foaming agent can be used. As an organic foaming agent, azo compounds such as azodicarbonamide, metal salts of azodicarboxylate (such as barium azodicarboxylate), azobisisobutyronitrile and the like, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine, and hydra Examples thereof include hydrazine derivatives such as zodicarbonamide, 4,4′-oxybis (benzenesulfonyl hydrazide), toluene sulfonyl hydrazide, and semicarbazide compounds such as toluene sulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate and the like.
Among these, an azo compound is preferable, and azodicarbonamide is more preferable, from the viewpoint of obtaining fine bubbles and from the viewpoint of economy and safety. One of these may be used alone, or two or more may be used in combination.
The blending amount of the thermal decomposition type foaming agent in the foamable composition is preferably 1 to 20 parts by mass, more preferably 2 to 18 parts by mass, and still more preferably 4 to 15 parts by mass with respect to 100 parts by mass of the resin.

In addition to the resin and the thermal decomposition type foaming agent, the foamable composition preferably contains a cell nucleus modifier. Examples of the cell nucleus modifier include zinc compounds such as zinc oxide and zinc stearate, citric acid, organic compounds of urea and the like, and among these, zinc oxide is more preferable. By using the cell nucleus adjusting agent in addition to the above-described small particle size foaming agent, it becomes easy to reduce the variation of the average cell diameter and the cell diameter. The amount of the cell nucleus modifier 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 resin. It is.
The foamable composition optionally contains, in addition to the above, additives generally used for foams such as an antioxidant, a heat stabilizer, a colorant, a flame retardant, an antistatic agent, and a filler. It may be done.

[Production method of foam sheet used for double-sided adhesive tape]
The method for producing the foam sheet used for the double-sided pressure-sensitive adhesive tape is not particularly limited. For example, the foamable composition containing a resin and a thermal decomposition-type foaming agent is crosslinked, heated to foam the thermal decomposition-type foaming agent, and stretched. It manufactures by extending | stretching to at least one of TD direction and MD direction by 1.1 times or more of magnification. More specifically, the production method includes the following steps (1) to (4).
Step (1): A step of mixing a resin and an additive containing a thermal decomposition-type foaming agent to form a sheet-like foamable composition (resin sheet) Step (2): Sheet-like foamable composition Step (3): Crosslinking the foamable composition by irradiation with ionizing radiation (3): Heating the crosslinked foamable composition to foam a thermal decomposition-type foaming agent to obtain a foam sheet (4) : Stretching a foamed sheet in either or both of the MD direction and the TD direction at a draw ratio of 1.1 times or more

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

Stretching of the foamed sheet in the step (4) may be performed in both the MD and TD directions, or may be performed in only one direction, but is preferably performed in both directions. In addition, stretching of the foam sheet may be performed after the resin sheet is foamed to obtain the foam sheet, or may be performed while the resin sheet is foamed. When the foamed sheet is stretched after the resin sheet is foamed to obtain the foamed sheet, the foamed sheet may be continuously stretched without cooling the foamed sheet while maintaining the molten state at the time of foaming. After the foamed sheet is cooled, the foamed sheet may be heated again to be in a melted or softened state, and then the foamed sheet may be stretched. The foamed sheet can be easily made thin by stretching.
In the step (4), the draw ratio of the foam sheet in one or both of the MD direction and the TD direction is preferably 1.2 to 4.0 times, more preferably 1.5 to 3.3 times. Among them, it is particularly preferable to set the draw ratio to both in these ranges. By setting it as this range, it becomes easy to make 25% compressive strength into a desired range.
Moreover, when a draw ratio is made more than the said lower limit, the softness | flexibility and tensile strength of a foam sheet will become favorable easily. On the other hand, if the upper limit value is used or lower, the foam sheet is broken during stretching, or the foam gas is removed from the foam sheet during foam to prevent the expansion ratio from being significantly reduced, and the flexibility and tensile strength of the foam sheet are prevented. And the quality is likely to be uniform.
In addition, the foamed sheet may be heated to, for example, 100 to 280 ° C., preferably 150 to 260 ° C. during stretching.
The foamed sheet obtained as described above may be cut into a desired shape by cutting using a known method such as punching.

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

<Pressure-sensitive adhesive layer>
The pressure-sensitive adhesive layer in the double-sided pressure-sensitive adhesive tape of the present invention has adhesive strength satisfying the above-mentioned range, and has adequate adhesion to the adhered portion, so that waterproofness of the double-sided pressure-sensitive adhesive tape can be secured. In addition to being able to peel off cleanly at the time of rework, since it is possible to maintain sufficient adhesion with the part to be adhered after rework, waterproofness can be maintained.

[Adhesive agent]
There is no restriction | limiting in particular as an adhesive used for an adhesive layer, For example, an acrylic adhesive, a urethane adhesive, a rubber adhesive etc. can be used, From a rework property and a waterproof viewpoint, an acrylic type Adhesives are preferred.
In the present invention, both sides of the double-sided pressure-sensitive adhesive tape may be constituted by the same pressure-sensitive adhesive layer, or may be constituted by different pressure-sensitive adhesive layers, but from the viewpoint of production cost It is preferable to comprise in an agent layer. Specifically, at least one pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape is preferably made of an acrylic pressure-sensitive adhesive, and both sides are preferably made of an acrylic pressure-sensitive adhesive.

(Acrylic adhesive)
Hereinafter, one embodiment of the acrylic pressure sensitive adhesive used for an adhesive layer is described in more detail. The acrylic pressure-sensitive adhesive is a pressure-sensitive adhesive containing an acrylic polymer obtained by polymerizing a polymerizable monomer containing a (meth) acrylic acid alkyl ester type monomer (A).
In the present specification, the term "(meth) acrylic acid alkyl ester" refers to a concept including both acrylic acid alkyl ester and methacrylic acid alkyl ester, and other similar terms are also the same. . In addition, the term "polymerizable monomer" is not only a compound having no repeating unit but is a compound copolymerizable with a (meth) acrylic acid alkyl ester type monomer (A), the other monomers described later are repeating units themselves. It also refers to the concept that can be included.

・ (Meth) acrylic acid alkyl ester monomer (A)
The (meth) acrylic acid alkyl ester monomer (A) is an ester of (meth) acrylic acid and an aliphatic alcohol, and the carbon number of the alkyl group of the aliphatic alcohol is preferably 2 to 14, and more preferably Alkyl esters derived from aliphatic alcohols, which are 4 to 10, are preferred. When the carbon number of the alkyl group is within this range, it becomes easy to adjust the peel adhesion to the above-mentioned range.

Specific (meth) acrylic acid alkyl ester monomers (A) are, for example, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl ( Meta) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) Acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate and the like
Among these, n-butyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate and n-octyl (meth) acrylate are preferable, n-butyl (meth) acrylate, More preferred is 2-ethylhexyl (meth) acrylate or a combination thereof.
The (meth) acrylic acid alkyl ester-based monomer may be used alone or in combination of two or more.

The structural unit derived from the (meth) acrylic acid alkyl ester-based monomer (A) constitutes the main component in the pressure-sensitive adhesive, and the content thereof is preferably 30% by mass or more in general based on the total amount of the pressure-sensitive adhesive. Is 40% by weight or more, more preferably 45% by weight or more. As described above, when the content of the (meth) acrylic acid alkyl ester-based monomer (A) is increased, it is possible to provide the adhesive with desired adhesion.
The content of the structural unit derived from the (meth) acrylic acid alkyl ester-based monomer (A) in the pressure-sensitive adhesive is substantially the same as the content of the (meth) acrylic acid alkyl ester-based monomer (A) in the pressure-sensitive adhesive composition described later. Because they are the same, they can be replaced and represented. The same applies to components other than the component (A) described below.

· Polar group-containing vinyl monomer (B)
The polymerizable monomer preferably contains a polar group-containing vinyl monomer (B) in addition to the (meth) acrylic acid alkyl ester type monomer (A). The polar group-containing vinyl monomer (B) is one having a polar group and a vinyl group. By using the polar group-containing monomer (B) in the pressure-sensitive adhesive layer, it becomes easy to adjust the peel adhesive strength and the like of the pressure-sensitive adhesive layer.

As the polar group-containing vinyl monomer (B), for example, (meth) acrylic acid, and carboxylic acids containing a vinyl group such as itaconic acid, and anhydrides thereof; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (Meth) acrylates, 4-hydroxybutyl (meth) acrylates, caprolactone modified (meth) acrylates, polyoxyethylene (meth) acrylates, and vinyl monomers having a hydroxyl group such as polyoxypropylene (meth) acrylates; (meth) acrylonitriles; N-vinyl pyrrolidone, N-vinyl caprolactam, N-vinyl lauryl lactam, (meth) acryloyl morpholine, (meth) acrylamide, dimethyl (meth) acrylamide, N- methylol (meth) acrylamide, N- butoxymethyl ( Data) acrylamide, and nitrogen-containing vinyl monomers such as dimethylaminomethyl (meth) acrylate.
Among these, (meth) acrylic acid and carboxylic acids containing a vinyl group such as itaconic acid and the like, and anhydrides thereof are preferable, (meth) acrylic acid is more preferable, and acrylic acid is still more preferable. These polar group-containing vinyl monomers (B) may be used alone or in combination of two or more.

When the polar group-containing vinyl monomer (B) is used, the content of the structural unit derived from the polar group-containing vinyl monomer (B) in the adhesive is 100% of the structural unit derived from the (meth) acrylic acid alkyl ester-based monomer (A) The amount is preferably 1 to 15 parts by mass, more preferably 2 to 12 parts by mass, and still more preferably 3 to 10 parts by mass with respect to the mass parts. By setting the content of the polar group-containing vinyl monomer (B) in such a range, it becomes easy to adjust the Tg, cohesion, adhesion and the like of the pressure-sensitive adhesive layer to an appropriate range.

-Other monomer The polymerizable monomer may contain other monomers other than (A) and (B) described above. Examples of other monomers include styrene monomers, polyfunctional monomers, and carboxylic acid vinyl esters such as vinyl acetate. Examples of the styrene-based monomer include styrene, α-methylstyrene, o-methylstyrene, and p-methylstyrene.
Moreover, as a polyfunctional monomer, the monomer which has two or more vinyl groups is mentioned, Preferably the polyfunctional (meth) acrylate which has two or more (meth) acryloyl groups is mentioned. Use of a polyfunctional monomer makes it possible to form a network structure in the acrylic polymer.
Specific examples of multifunctional monomers include hexanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, ethoxylated bisphenol A di (meth) acrylate, tris (2-hydroxyethyl) Isocyanurate triacrylate, ethoxylated trimethylolpropane triacrylate, proxyed trimethylolpropane triacrylate, proxyed glyceryl triacrylate, neopentyl glycol adipate diacrylate and the like can be mentioned.
When other monomers are used, in the pressure-sensitive adhesive, the content of the structural unit derived from the other monomer is 0. 0 to 100 parts by mass of the structural unit derived from the (meth) acrylic acid alkyl ester monomer (A) 5. The amount is 5 to 15 parts by mass, more preferably 1 to 7 parts by mass, and still more preferably 1 to 5 parts by mass.
The weight average molecular weight of the acrylic polymer measured by the GPC method is not particularly limited, and is, for example, 200,000 to 1,000,000, preferably 400,000 to 900,000.

[Tackifying resin]
The acrylic pressure-sensitive adhesive may contain a tackifying resin from the viewpoint of improving the adhesive strength. The tackifier resin is preferably a tackifier resin having low polymerization inhibition such as hydrogenated terpene resin, hydrogenated rosin, disproportionated rosin resin, rosin ester polymer, petroleum resin and the like. Among them, rosin-based ones are preferable because a tackifying resin having many double bonds inhibits the polymerization reaction, and among these, rosin ester-based polymers are preferable.

The softening point of the tackifying resin may be about 95 ° C. or higher from the viewpoint of improving the cohesion and adhesion of the pressure-sensitive adhesive, but preferably contains 120 ° C. or higher, for example, 95 ° C. or higher and 120 ° C. Less than one and less than 120 ° C and less than 150 ° C may be used in combination. The softening point may be measured by the ring and ball method defined in JIS K 2207.
The content of the tackifying resin in the acrylic pressure-sensitive adhesive is preferably 2 to 40 parts by mass, more preferably 4 to 35 parts by mass, still more preferably 5 to 25 parts by mass with respect to 100 parts by mass of the acrylic polymer. is there.
When the weak pressure-sensitive adhesive layer is provided on one side of the double-sided pressure-sensitive adhesive tape and the strong pressure-sensitive adhesive layer is provided on the other side, the adhesion may be adjusted by the amount of tackifying resin. Specifically, the content of the tackifying resin in the strong pressure-sensitive adhesive layer may be larger than the content of the tackifying resin in the weak pressure-sensitive adhesive layer. The difference in the content of the tackifier resin in the strong pressure-sensitive adhesive layer and the weak pressure-sensitive adhesive layer is preferably 1 part by mass or more, more preferably 3 parts by mass or more. Moreover, the upper limit of the difference in content is not particularly limited, and is, for example, 10 parts by mass. In addition, content here means content with respect to 100 mass parts of acrylic polymers in each layer.

[Crosslinking agent]
When the resin constituting the acrylic pressure-sensitive adhesive has a hydroxyl group or a carboxy group, a crosslink structure may be formed between the main chains by using a crosslinking agent from the viewpoint of improving the adhesiveness.
As a crosslinking agent, an isocyanate type crosslinking agent, an epoxy-type crosslinking agent, an aziridine type crosslinking agent, a metal chelate type crosslinking agent etc. are mentioned, for example. Among these, isocyanate crosslinking agents and epoxy crosslinking agents are preferable.

As an isocyanate type crosslinking agent, a polyisocyanate compound is mentioned, for example. Specific examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. Etc. Further, these biuret bodies, isocyanurate bodies, and also adduct bodies which are reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, castor oil and the like can be mentioned.
These may be used singly or in combination of two or more.

Examples of epoxy crosslinking agents include bisphenol A epoxy compounds, bisphenol F epoxy compounds, 1,3-bis (N, N-diglycidylaminomethyl) toluene, N, N, N ′, N′-tetraglycidyl -4,4-Diaminodiphenylmethane, N, N, N ', N'-tetraglycidyl m-xylenediamine, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, 1,6-diglycidyl n-hexane Etc.

When the weak pressure-sensitive adhesive layer is provided on one side of the double-sided pressure-sensitive adhesive tape and the strong pressure-sensitive adhesive layer is provided on the other side, their adhesion may be adjusted by the amount of the crosslinking agent.
The compounding amount of the crosslinking agent to the pressure-sensitive adhesive in the case of producing the weak pressure-sensitive adhesive layer is adjusted from the viewpoint of adjusting the adhesion of the weak pressure-sensitive adhesive layer to 100 parts by mass of the acrylic polymer. The amount is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 7 parts by mass or less, more preferably 5 parts by mass or less.
On the other hand, the blending amount of the crosslinking agent in the case of producing the strong pressure-sensitive adhesive layer is preferably adjusted to satisfy the range of the adhesive strength of the strong pressure-sensitive adhesive layer with respect to 100 parts by mass of the acrylic polymer. It is 0.5 parts by mass or more, more preferably 0.7 parts by mass or more, and preferably 6 parts by mass or less, more preferably 4 parts by mass or less.
The blending amount of the crosslinking agent in the strong pressure-sensitive adhesive layer is preferably smaller than the blending amount of the crosslinking agent in the weak pressure-sensitive adhesive layer. In addition, a compounding quantity as used herein means the compounding quantity with respect to 100 mass parts of acrylic polymers in each layer in an adhesive.

[Other ingredients]
The acrylic pressure-sensitive adhesive used in the present invention contains various additives conventionally used in pressure-sensitive adhesives such as plasticizers, softeners, pigments, dyes, photopolymerization initiators and flame retardants, in addition to the components described above. You may

(Rubber pressure sensitive adhesive)
Next, the rubber-based pressure-sensitive adhesive used for the pressure-sensitive adhesive will be described. The rubber-based pressure-sensitive adhesive contains a rubber component and a tackifying resin, and as the rubber component, it is preferable to use a styrene-isoprene block copolymer. The styrene-isoprene block copolymer preferably has a diblock ratio of 25 to 70% by mass, more preferably 30 to 65% by mass, and still more preferably 45 to 60% by mass. Here, the diblock is a diblock composed of styrene and isoprene. The styrene-isoprene block copolymer exhibits sufficient adhesion when the diblock ratio is 25% or more, and the shear strength is easily increased by setting the diblock ratio to 70% by mass or less. The styrene-isoprene block copolymer also contains, in addition to the diblock, one having three or more blocks such as styrene, isoprene and a triblock consisting of a styrene block.

The amount of styrene in the styrene-isoprene block copolymer is not particularly limited, but is preferably 14 to 24% by mass, and more preferably 15 to 18% by mass. When the amount of styrene is 14% by mass or more, the adhesive becomes highly cohesive, and it becomes easy to increase the shear strength. When the content is 24% by mass or less, the cohesion force has an appropriate size, and the cohesion force is easily expressed.
Although the molecular weight of the styrene-isoprene block copolymer is not particularly limited, it is preferably 100,000 to 400,000 by mass average molecular weight, and more preferably 150,000 to 250,000. In addition, the mass mean molecular weight here means what is measured as polystyrene conversion molecular weight by GPC (gel permeation chromatography) method.

Although various tackifying resins can be used as the tackifying resin used for the rubber-based pressure-sensitive adhesive, a petroleum-based resin, a terpene resin, and a coumarone resin are preferably used. The tackifier resin may be used alone or in combination of two or more. However, the petroleum resin and at least one selected from terpene resin and coumarone resin may be used in combination. preferable. It becomes easy to make peel adhesive force favorable by the combination of such tackifying resin.
Examples of petroleum resins include aliphatic petroleum resins (C5 petroleum resins), alicyclic petroleum resins, aromatic petroleum resins and the like, and from the viewpoint of compatibility with styrene-isoprene block copolymers, fatty resins Preferred are petroleum-based petroleum resins. In addition, it is preferable to use a petroleum resin having a softening point of about 90 to 120 ° C.
As the terpene resin, one having a softening point of about 80 to 120 ° C. can be used, but one having a softening point of less than 100 ° C. is preferable from the viewpoint of securing the adhesive strength. Further, as the coumarone resin, one having a softening point of preferably 110 to 130 ° C., more preferably 115 to 125 ° C. is used in order to secure cohesion.

The tackifying resin is preferably 60 to 250 parts by mass, more preferably 100 to 200 parts by mass, and still more preferably 110 to 180 parts by mass with respect to 100 parts by mass of the rubber component. By making the compounding quantity of tackifying resin into the said range, it becomes possible to make a cohesion force favorable and to provide moderate peel adhesive force.
When a petroleum resin and at least one selected from terpene resin and coumarone resin are used in combination, the petroleum resin is preferably 50 to 200 parts by mass, and 60 to 150 parts by mass with respect to 100 parts by mass of the rubber component. The parts by mass are preferable, and 60 to 110 parts by mass are more preferable. On the other hand, the terpene resin is preferably 10 to 70 parts by mass, more preferably 20 to 60 parts by mass, and still more preferably 30 to 50 parts by mass with respect to 100 parts by mass of the rubber component. Further, the coumarone resin is preferably 10 to 60 parts by mass, more preferably 15 to 50 parts by mass, and still more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the rubber component.
The rubber-based pressure-sensitive adhesive may contain the above-described fine particles similarly to the acrylic pressure-sensitive adhesive, and the rubber-based pressure-sensitive adhesive may contain, as necessary, a softener, an antioxidant, a filler and the like. It is also good.

(Urethane-based adhesive)
The above-described urethane-based pressure-sensitive adhesive is not particularly limited, and examples thereof include a urethane resin obtained by reacting at least a polyol and a polyisocyanate compound. As said polyol, a polyether polyol, polyester polyol, polycarbonate polyol, polycaprolactone polyol etc. are mentioned, for example. As said polyisocyanate compound, diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate etc. are mentioned, for example. These urethane-based pressure-sensitive adhesives may be used alone or in combination of two or more.
Further, as the urethane-based pressure-sensitive adhesive, a urethane resin obtained by reacting a polyurethane polyol and a polyfunctional isocyanate-based curing agent may be used. As the polyurethane polyol, one obtained by reacting the above-described polyol and a polyisocyanate compound, or one obtained by reacting a polyol, a polyisocyanate compound and a chain extender such as diamine is mentioned. The polyfunctional isocyanate-based curing agent may be a compound having two or more isocyanate groups, and the above-mentioned isocyanate compound can be used.
The urethane-based pressure-sensitive adhesive may contain the above-described fine particles in addition to the urethane resin, and the urethane-based pressure-sensitive adhesive may, if necessary, be a tackifying resin, a softener, an antioxidant, a filler, etc. You may contain.

[Method of producing pressure-sensitive adhesive layer]
The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer heats and refluxes the pressure-sensitive adhesive composition containing the polymerizable monomer described above and the polymerization initiator when using an acrylic pressure-sensitive adhesive, and then crosslinks the polymer. It can be obtained by It is also possible to obtain by polymerizing the polymerizable monomer by irradiating the pressure-sensitive adhesive composition containing the above-mentioned polymerizable monomer with light.
The pressure-sensitive adhesive composition may optionally contain at least one of the above-mentioned tackifying resin, fine particles, and other components.

The method for forming the pressure-sensitive adhesive layer on both sides of the foam sheet is not particularly limited, but, for example, a method of applying the pressure-sensitive adhesive using a coater such as a coater, a method of spraying and applying the pressure-sensitive adhesive using a spray, The method of apply | coating an adhesive using a brush, the method of transcribe | transferring the adhesive layer formed on the peeling sheet to a foam sheet, etc. are mentioned.

<Application of double-sided adhesive tape>
Although the use of a double-sided adhesive tape is not specifically limited, Since it is excellent in waterproofness, it is preferable to use it, for example as a sealing material inside electronic devices. Further, since the double-sided pressure-sensitive adhesive tape of the present invention has durability, it can be suitably used particularly in various portable electronic devices in which a space for arranging a foam sheet is small. Examples of the electronic device include a liquid crystal display, an organic EL display, a mobile phone, a camera, a game device, an electronic notebook, a personal computer and the like.

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

[Measuring method]
The measuring method and evaluation method of each physical property are as follows.
<Apparent density and expansion ratio>
The apparent density of the foam sheet was measured in accordance with JIS K7222, and the reciprocal thereof was taken as the foaming ratio.

<Average bubble diameter>
The average cell diameter of the foam sheet was measured by the method described in the specification.

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

<Crosslinking degree>
A test piece of about 100 mg is taken from the foam sheet, and the weight A (mg) of the test piece is precisely weighed. Next, the test piece is immersed in 30 cm ³ of xylene at 120 ° C. and left for 24 hours, and then filtered through a 200 mesh wire mesh to collect insolubles on the wire net, vacuum-dried, and the weight of the insoluble portion Carefully weigh B (mg). The degree of crosslinking (% by mass) was calculated from the obtained value by the following equation.
Degree of crosslinking (mass%) = (B / A) × 100

<Closed cell rate>
The closed cell rate of the foam sheet was measured by the method described in the specification.

<90 degree peel adhesion of adhesive layer>
The adhesive strength of the pressure-sensitive adhesive layer conforms to the 90 ° peeling method of JIS Z 0237, and specifically, the peeling of the peelable substrate at 25 ° C. at a speed of 300 mm / min. Peel strength was measured.

<1 mm width waterproofness>
The waterproofness evaluation is based on IPX7 standard (JIS C 0920 and IEC 60529), and the test sample prepared by the following method under the conditions of temperature 23 ° C. and relative humidity 50% is immersed in water depth 1 m, visual confirmation of water immersion It did by doing.
In addition, this waterproofness evaluation was performed after curing for 6 hours on condition of temperature 23 degreeC and 50% of relative humidity after producing a test sample.
The evaluation criteria are "S" when there was no water immersion for 24 hours inside the frame shape after sinking in 1 m of water, "A" when there was no water immersion for 6 hours, and "B" when there was no water immersion for 30 minutes The case where there was no water immersion for 5 minutes was evaluated as “C”, and the case where water immersion immediately started after being submerged was evaluated as “D”.

(Preparation of test sample)
The double-sided tape was punched into a frame shape having an outer periphery of 60 mm long × 40 mm wide, an inner periphery of 58 mm long × 38 mm wide, and a width of 1.0 mm. In addition, at the time of punching, all corners were rounded with R 5 mm.
Next, the obtained frame-shaped sealing material was sandwiched between two 100 mm square acrylic plates having a thickness of 10 mm, and a load of 5 kg was applied for 10 seconds to be crimped.
Then, this test sample was submerged in 1 m of water by the above-mentioned method, and it was visually confirmed whether water was submerged inside the frame shape.

<Reworkability evaluation test>
A sample was prepared in the same manner as the 1 mm width waterproofing test, and the peelability was evaluated when two acrylic plates were peeled off by hand after aging for 6 hours under conditions of temperature 23 ° C. and relative humidity 50%. . The weak pressure-sensitive adhesive layer was neatly removed, and the frame shape was not broken and was reusable, "S", although the weak pressure-sensitive adhesive layer was finely removed, the one showing slight deformation was "A", Although only the weak pressure-sensitive adhesive layer was peeled off, those with a weak pressure-sensitive adhesive remaining on the acrylic plate were evaluated as "B", those with the foam sheet torn were evaluated as "C", and those with no peeling were evaluated as "D".

[resin]
The resins used in this example are shown below.
Resin A (LLDPE): Linear low density polyethylene resin (manufactured by Dow Chemical Co., trade name "Affinity PL 1850", density 0.902 g / cm ³ )
Resin B (EVA): ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, trade name "Ultrasen 636")
Resin C (St-based elastomer): Styrene-ethylene-butylene-styrene block copolymer (manufactured by JSR Corporation, trade name "Dynalon 8600P")

[Production of adhesive layer]
<Production of weak adhesive layer (1)>
55 parts by mass of butyl acrylate, 40 parts by mass of 2-ethylhexyl acrylate and 5 parts by mass of acrylic acid were charged into a reactor equipped with a thermometer, a stirrer and a cooling tube, and 80 parts by mass of ethyl acetate was further added, followed by nitrogen substitution. The reactor was then heated to begin refluxing. Subsequently, 0.1 parts by mass of azobisisobutyronitrile as a polymerization initiator was added to the reactor, and the solution was refluxed at 70 ° C. for 5 hours to obtain a solution of an acrylic copolymer.
It was 600,000 when the weight average molecular weight was measured by GPC method using "2690 Separations Model" made from Water as a column about the obtained acrylic copolymer.
1 part by mass of an isocyanate-based crosslinking agent and 5 parts by mass of a rosin ester-based modified polymer were mixed in a solution of the obtained acrylic copolymer (100 parts by mass), and a pressure-sensitive adhesive was obtained by stirring.

<Production of weak adhesive layer (2)>
A weak pressure-sensitive adhesive layer (2) was produced in the same manner as the weak pressure-sensitive adhesive layer (1) except that the composition was changed to the composition described in Table 1. The weak pressure-sensitive adhesive layer (2) was used in Example 5 and Comparative Example 6.

<Method for producing strong pressure-sensitive adhesive layer>
A strong pressure-sensitive adhesive layer was produced in the same manner as the weak pressure-sensitive adhesive layer (1) except that the composition was changed to the composition described in Table 1.

Example 1
(Production of foam sheet)
100 parts by mass of resin A, 11 parts by mass of azodicarbonamide as a thermal decomposition-type foaming agent, and 0.5 parts by mass of zinc oxide as a cell nucleus regulator (trade name "OW-212F" manufactured by Sakai Chemical Industry Co., Ltd.) And 1.0 part by mass of an antioxidant were supplied to an extruder and melt-kneaded at 130 ° C., and extruded into a long resin sheet having a thickness of 300 μm.
Next, 7 Mrad of electron beam with an accelerating voltage of 500 kV is irradiated on both sides of the above long resin sheet for 7 Mrad to crosslink the resin sheet, and then the crosslinked resin sheet is held in a foaming furnace maintained at 250 ° C. by hot air and infrared heater. The solution was continuously fed into the flask, heated and foamed to obtain a sheet-like foam having a thickness of 600 μm.
Subsequently, the obtained foam sheet was continuously sent out from the foaming furnace. Then, while maintaining the temperature of the foam sheet on both sides at 200 to 250 ° C., the foam sheet is stretched at a draw ratio of 2.5 times in the TD direction, and the foam sheet is fed into the foaming furnace. The foamed sheet was stretched 2.0 times also in the MD direction by winding the foamed sheet at a winding speed higher than the speed (feed rate). Thus, a foam sheet (thickness: 500 μm) of Example 1 was obtained. In addition, the winding speed of the said foam sheet was adjusted in consideration of the expansion part to MD direction by foaming of resin sheet itself. The resulting foam sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

(Manufacture of double-sided adhesive tape)
Prepare a release paper with a thickness of 150 μm, apply an adhesive that forms a weak adhesive layer on the release-treated surface of the release paper, and dry at 100 ° C. for 5 minutes to form a weak adhesive layer with a thickness of 250 μm. And bonded to the surface of the base made of a foamed sheet. Then, in the same manner, a strong pressure-sensitive adhesive layer was attached to the opposite surface of the substrate. Thus, a double-sided pressure-sensitive adhesive tape in which both sides were covered with a 150 μm-thick release paper was obtained.

[Examples 2 to 11 and Comparative Examples 1 to 7]
A foamed sheet and a double-sided pressure-sensitive adhesive tape were obtained in the same manner as in Example 1 except that the resin, the additive, the thickness of the foam sheet, and the weak pressure-sensitive adhesive layer were changed as shown in Tables 2 and 3 below. The draw ratio of MD and TD was adjusted in the range of 1.5 to 3.5. The resulting foam sheet was evaluated according to the above evaluation method, and the results are shown in Tables 2 and 3.

ADVANTAGE OF THE INVENTION According to this invention, the double-sided adhesive tape which is excellent in rework property, and shows favorable waterproofness even after rework can be provided.

Claims

A double-sided pressure-sensitive adhesive tape provided with an adhesive layer on both sides of a polyolefin resin foam sheet obtained by foaming a foamable composition containing a polyolefin resin, wherein the average cell diameter of the polyolefin resin foam sheet is 25 to 150 μm A double-sided pressure-sensitive adhesive tape having a 90 ° peel adhesive strength at 25 ° C. of 1.1 to 23 N / 25 mm as measured at least one of the pressure-sensitive adhesive layers according to JIS Z0237-2009.
The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the foamed polyolefin-based resin sheet has a thickness of 1.5 mm or less.
The double-sided pressure-sensitive adhesive tape according to claim 1 or 2, wherein the 25% compressive strength of the polyolefin resin foam sheet is 10 to 1,000 kPa.
The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 3, wherein the amount of the polyethylene resin relative to the total amount of the resin contained in the foamable composition is 30% by mass or more.
The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 4, wherein at least one of the pressure-sensitive adhesive layers is composed of an acrylic pressure-sensitive adhesive.
The pressure-sensitive adhesive layer provided on one side of the polyolefin-based resin foam sheet has a 90 degree peel adhesive strength weaker than the pressure-sensitive adhesive layer provided on the other side. Double-sided adhesive tape.
The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 6, wherein the expansion ratio of the polyolefin resin foam sheet is 1.2 to 15 cm 3 / g.
The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 7, wherein the polyolefin resin is a linear low density polyethylene polymerized with a polymerization catalyst of a metallocene compound.
A method for producing the double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 8,
A sheet-like foamable composition containing a resin and a thermal decomposition-type foaming agent is crosslinked and heated to foam the thermal decomposition-type foaming agent, and at least one of TD direction and MD direction at a draw ratio of 1.1 times or more The manufacturing method of the double-sided adhesive tape which manufactures the said polyolefin resin foamed sheet by extending | stretching to one side.