JP7681004B2 - Double-sided adhesive tape - Google Patents

Description

The present invention relates to a double-sided adhesive tape that has high conformability to uneven surfaces on both adhesive surfaces, can exhibit high holding power against shear loads and tilt loads, has excellent reworkability on at least one of the adhesive surfaces, and also has excellent handling properties when applied.

Adhesive tapes are widely used to secure electronic components. Specifically, for example, adhesive tapes are used to secure the front cover panels of display devices such as televisions and monitors to their housings. Such adhesive tapes are used in a shape such as a picture frame and are placed around the periphery of the display screen.

In recent years, the pursuit of design and functionality has led to increasingly narrower framed display devices such as televisions and monitors, and expectations for bezel-less display devices are also growing. In conventional display device manufacturing, cover panels were sometimes fixed to the housing by fitting or screwing, but as fitting or screwing is difficult for display devices with narrower framed displays, there is an increasing demand for fixing with adhesive tape, and adhesive tapes are also becoming thinner and narrower.

As an example of an adhesive tape that can be used in such a display device, Patent Documents 1 and 2 describe an impact absorbing tape in which an acrylic adhesive layer is integrally laminated on at least one surface of a base layer, and the base layer is a cross-linked polyolefin resin foam sheet having a specific degree of cross-linking and aspect ratio of bubbles.
Since a foam substrate has appropriate flexibility and can relieve stress, using a foam substrate as the substrate for an adhesive tape has advantages such as improved conformability to unevenness, improved impact resistance, and reduced display unevenness on a display device.

JP 2009-242541 A JP 2009-258274 A

However, display devices such as televisions and monitors are becoming larger, and the weight of the fixed members such as cover panels and housings is also increasing. For this reason, adhesive tapes, especially those that have become thinner and narrower, are subjected to much larger loads than before. In particular, very large loads are applied in the shear direction, and high holding power against shear loads is required. In addition, in applications such as wall-mounted televisions, display devices are increasingly being installed in a state tilted forward, for example, by about 20 to 45 degrees from the vertical direction, and high holding power against tilt loads is also required.

Furthermore, in recent years, electronic components have tended to become more expensive, and so there is a demand for components to be reworkable, for example, when a defect occurs during component fixation. One method for reworking components is to tear the foam base material of the adhesive tape with, for example, a cutter blade, causing interlayer destruction to remove the component, and then peeling off the part of the adhesive tape remaining on the component. In such cases, the adhesive tape is required to have excellent reworkability that allows it to be peeled off and removed without leaving any residue on the component (for example, the part of the foam base material that remains after breaking off).

The present invention aims to provide a double-sided adhesive tape that has high conformability to uneven surfaces on both adhesive surfaces, can exhibit high holding power against shear loads and tilt loads, has excellent reworkability on at least one of the adhesive surfaces, and also has excellent handling properties when applied.

The present invention is a double-sided adhesive tape having a foam substrate and adhesive layers laminated on both sides of the foam substrate, wherein the foam substrate has a first foamed resin layer and a second foamed resin layer laminated on at least one side of the first foamed resin layer and having a lower expansion ratio than the first foamed resin layer, and at least one of the adhesive layers has a storage modulus at 180°C of 11,000 Pa or more.
The present invention will be described in detail below.

The inventors considered using a multilayer substrate as the foam substrate, in which at least one side of a foamed resin layer is reinforced with a resin layer, in order to increase the holding strength against shear loads and tilt loads and to improve the reworkability of at least one adhesive surface in a double-sided adhesive tape having a foam substrate and adhesive layers laminated on both sides of the foam substrate.
However, for example, if the resin layer on one or both sides is too hard, the step-following ability of the side on which the resin layer is laminated is reduced, and peeling is likely to occur. In recent years, adhesive tapes have increasingly been overlapped partially with polarizing plates in display devices or partially with guides formed on housings to indicate the location where the adhesive tape is to be applied, and adhesive tapes are required to sufficiently follow the steps of such polarizing plates, guides, etc. even when used thin and narrow. On the other hand, if the resin layers on both sides are made too soft in an attempt to improve step-following ability (for example, when a styrene-acrylic block copolymer is used for the resin layers on both sides), the holding force against shear load and tilt load is not sufficient, and the adhesive tape stretches when applied, resulting in problems such as poor handling properties.

In response to these problems, the present inventors have considered using a foamed resin layer (outermost layer) as a resin layer laminated to a foamed resin layer (central foamed resin layer) and adjusting the foaming ratio of the outermost layer to be lower than that of the central foamed resin layer. The present inventors have found that by using such a multi-layer substrate as a foam substrate, it is possible to achieve both step-following ability of both adhesive surfaces, holding power against shear load and tilt load, and reworkability of at least one adhesive surface, and also to obtain excellent handleability. The present inventors have further found that by adjusting the storage modulus at 180°C of at least one of the adhesive layers to a specific range, the holding power against shear load and tilt load can be further increased, and have completed the present invention.

The double-sided adhesive tape of the present invention has a foam substrate and adhesive layers laminated on both sides of the foam substrate. By having the foam substrate, the double-sided adhesive tape of the present invention has high conformability to uneven surfaces and can also exhibit excellent stress relaxation properties.

The foam base material has a first foamed resin layer and a second foamed resin layer laminated on at least one surface of the first foamed resin layer and having a lower expansion ratio than the first foamed resin layer.
By laminating the second foamed resin layer on the first foamed resin layer, the deformation stress of the first foamed resin layer caused by the application of a shear load or an inclined load can be alleviated and made difficult to be transmitted to the pressure-sensitive adhesive layer, and peeling of the pressure-sensitive adhesive layer can be suppressed. In addition, by laminating the second foamed resin layer on the first foamed resin layer, the double-sided pressure-sensitive adhesive tape of the present invention can be peeled and removed during rework without leaving any residue (for example, a part of the first foamed resin layer that remains after breaking) on the adherend on the side where the second foamed resin layer is laminated, and can exhibit excellent reworkability.
Furthermore, when a resin layer that is too hard is laminated on the first foamed resin layer, the step conformability of the side on which the resin layer is laminated decreases, whereas in the double-sided pressure-sensitive adhesive tape of the present invention, the second foamed resin layer is laminated on the first foamed resin layer, thereby suppressing the decrease in step conformability of both adhesive surfaces. On the other hand, when a resin layer that is too soft is laminated on both sides of the first foamed resin layer in an attempt to improve step conformability (for example, when a styrene-acrylic block copolymer is used for the resin layers on both sides), the holding force against shear load and tilt load is not sufficiently obtained, and the handling property during application is also poor. In contrast, the double-sided pressure-sensitive adhesive tape of the present invention, having the second foamed resin layer laminated on the first foamed resin layer, can exhibit high holding force against shear load and tilt load, and is also excellent in handling property during application.

The foam base material may have the second foamed resin layer on only one side of the first foamed resin layer, or may have the second foamed resin layer on both sides of the first foamed resin layer. In particular, it is preferable to have the second foamed resin layer on both sides of the first foamed resin layer, since the holding power of the double-sided adhesive tape against shear load and tilt load is further improved and excellent reworkability can be exhibited on both adhesive sides. In this case, the resin composition, physical properties, thickness, etc. of the second foamed resin layers on both sides may be the same or different.
In addition, the adhesive tape is usually provided in a state of being wound into a roll, and is used by being pulled out from the roll. If too hard resin layers are laminated on both sides of the first foamed resin layer, wrinkles and folds will occur during winding when the diameter of the core becomes a certain size or larger. In contrast, in the double-sided adhesive tape of the present invention, the second foamed resin layer is laminated on the first foamed resin layer, so that the flexibility of the entire double-sided adhesive tape can be ensured even when the second foamed resin layers are laminated on both sides. This makes it easy to wind the double-sided adhesive tape into a roll, significantly improves handling, and can suppress the occurrence of wrinkles and folds during winding.

The foam base material may have other layers, such as an adhesive layer, in addition to the first foamed resin layer and the second foamed resin layer, but from the viewpoint of preventing the manufacturing process from becoming complicated, it is preferable that no other layers are present between the first foamed resin layer and the second foamed resin layer.

Figure 3 shows a cross-sectional view that illustrates a schematic example of a double-sided adhesive tape of the present invention. The double-sided adhesive tape 7 shown in Figure 3 has a foam substrate 8 and adhesive layers 91, 92 laminated on both sides of the foam substrate 8. The foam substrate 8 has a first foamed resin layer 10 and second foamed resin layers 11, 12 laminated on both sides of the first foamed resin layer 10. Note that in the double-sided adhesive tape shown in Figure 3, the second foamed resin layer is laminated on both sides of the first foamed resin layer, but the present invention is not limited to this embodiment.

The first foamed resin layer may have an open cell structure or a closed cell structure, but preferably has a closed cell structure. The closed cell structure increases the strength of the first foamed resin layer, suppressing deformation and interlayer destruction of the first foamed resin layer when a shear load and a tilt load are applied, and further improves the holding power of the double-sided adhesive tape against a shear load and a tilt load.

The first foamed resin layer may have a single-layer structure or a multi-layer structure.
The first foamed resin layer is not particularly limited, and examples thereof include a polyurethane foamed resin layer, a polyolefin foamed resin layer, a rubber-based foamed resin layer, an acrylic foamed resin layer, etc. Among these, a polyurethane foamed resin layer or a polyolefin foamed resin layer is preferred, and a polyolefin foamed resin layer is more preferred, because they can exhibit excellent stress relaxation properties and strength.

The polyurethane foam resin layer is not particularly limited, and may be, for example, a polyurethane foam resin layer made of a urethane resin composition containing polyisocyanate and polyol. Such a polyurethane foam resin layer can be produced by heat curing the urethane resin composition.

The polyolefin foamed resin layer is not particularly limited, and examples thereof include foamed resin layers made of resins such as polyethylene-based resins, polypropylene-based resins, polybutadiene-based resins, etc. Among these, a foamed resin layer made of a polyethylene-based resin is preferred because a flexible polyolefin foamed resin layer is easily obtained.
The polyethylene resin is not particularly limited, and examples thereof include polyethylene resins polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, or a chromium oxide compound. In addition, the polyethylene resin is preferably a linear low-density polyethylene, since the flexibility of the first foamed resin layer is increased. The linear low-density polyethylene is preferably a linear low-density polyethylene obtained by copolymerizing ethylene and, if necessary, a small amount of an α-olefin, and examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Among these, an α-olefin having 4 to 10 carbon atoms is preferable.

The expansion ratio of the first foamed resin layer is not particularly limited as long as it is higher than the expansion ratio of the second foamed resin layer.
When the first foamed resin layer is a polyolefin foamed resin layer, the preferred lower limit of the expansion ratio of the first foamed resin layer is 5 cm ³ /g, and the preferred upper limit is 30 cm ³ /g. If the expansion ratio is 5 cm ³ /g or more, the first foamed resin layer can have appropriate flexibility, and the step followability and stress relaxation properties of both adhesive surfaces of the double-sided adhesive tape are further improved. If the expansion ratio is 30 cm ³ /g or less, the strength of the first foamed resin layer is sufficiently high, and the holding power of the double-sided adhesive tape against shear load and tilt load is further improved. The more preferred lower limit of the expansion ratio is 8 cm ³ /g, and the more preferred upper limit is 25 cm ³ /g, and even more preferred lower limit is 10 cm ³ /g, and even more preferred upper limit is 20 cm ³ /g, and even more preferred upper limit is 18 cm ³ /g.
The expansion ratio can be determined in accordance with JIS K 7222 (when polyethylene is used) and can be determined as the reciprocal of the apparent density.

The thickness of the first foamed resin layer is not particularly limited, but the preferred lower limit is 100 μm, and the preferred upper limit is 2000 μm. If the thickness is 100 μm or more, the first foamed resin layer can have appropriate flexibility, and the step-following ability and stress relaxation ability of both adhesive surfaces of the double-sided adhesive tape are further improved. If the thickness is 2000 μm or less, the deformation of the first foamed resin layer when a shear load and a tilt load are applied can be suppressed, and the holding power of the double-sided adhesive tape against a shear load and a tilt load is further improved. The more preferred lower limit of the thickness is 300 μm, the more preferred upper limit is 1500 μm, the even more preferred lower limit is 500 μm, and the even more preferred upper limit is 1000 μm.
The thickness of the foamed resin layer can be measured using a dial thickness meter (for example, "ABS Digimatic Indicator" manufactured by Mitutoyo Corporation).

The second foamed resin layer is not particularly limited as long as it is a foamed resin layer having a lower expansion ratio than the first foamed resin layer, and may be a foamed resin layer having the same bubble structure, layer structure, resin composition, physical properties, etc. as the first foamed resin layer, or may be a foamed resin layer having a different bubble structure, layer structure, resin composition, physical properties, etc. from the first foamed resin layer.
The second foamed resin layer may have an open cell structure or a closed cell structure, but preferably has a closed cell structure. The closed cell structure increases the strength of the second foamed resin layer, so that the double-sided pressure-sensitive adhesive tape can be peeled off and removed without leaving any residue (e.g., a part of the first foamed resin layer that is broken and remains) on the adherend on the side where the second foamed resin layer is laminated during rework, and can exhibit better reworkability.

The second foamed resin layer may have a single-layer structure or a multi-layer structure.
The second foamed resin layer is not particularly limited, and examples thereof include a polyurethane foamed resin layer, a polyolefin foamed resin layer, a rubber-based foamed resin layer, an acrylic foamed resin layer, etc. Among these, a polyurethane foamed resin layer or a polyolefin foamed resin layer is preferred, and a polyolefin foamed resin layer is more preferred, because they can exhibit excellent stress relaxation properties and strength.
The polyurethane foam layer is not particularly limited and may be the same as the polyurethane foam layer in the first foam layer. The polyolefin foam layer is also not particularly limited and may be the same as the polyolefin foam layer in the first foam layer.

The expansion ratio of the second foamed resin layer is not particularly limited as long as it is lower than that of the first foamed resin layer, but the preferred lower limit is 1.1 ^cm3 /g and the preferred upper limit is 7 ^cm3 /g. If the expansion ratio is 1.1 ^cm3 /g or more, the second foamed resin layer can have appropriate flexibility, and the step-following ability and stress relaxation ability of both adhesive surfaces of the double-sided pressure-sensitive adhesive tape are further improved. If the expansion ratio is 7 ^cm3 /g or less, the strength of the second foamed resin layer is sufficiently high, the holding power of the double-sided pressure-sensitive adhesive tape against shear load and tilt load is further improved, and the handling property during application is also further improved. The expansion ratio is more preferably 1.3 cm ³ /g in lower limit and 5 cm ³ /g in upper limit, still more preferably 1.4 cm ³ /g in lower limit and 2 cm ³ /g in upper limit, still more preferably 1.5 cm ³ /g in lower limit and 1.9 cm ³ /g in upper limit.

The thickness of the second foamed resin layer is not particularly limited, but a preferred lower limit is 5 μm and a preferred upper limit is 100 μm. If the thickness is 5 μm or more, the holding power of the double-sided adhesive tape against shear load and tilt load is further improved. If the thickness is 100 μm or less, the step-following ability and stress relaxation ability of both adhesive surfaces of the double-sided adhesive tape are further improved. A more preferred lower limit of the thickness is 10 μm and a more preferred upper limit is 80 μm, an even more preferred lower limit is 30 μm and an even more preferred upper limit is 60 μm.

The 25% compressive strength of the foam substrate (whole foam substrate) is not particularly limited, but the preferred lower limit is 1 kPa, and the preferred upper limit is 200 kPa. If the 25% compressive strength is 1 kPa or more, the strength of the foam substrate is sufficiently high, and the holding power of the double-sided adhesive tape against shear load and tilt load is further improved. If the 25% compressive strength is 200 kPa or less, the foam substrate can have appropriate flexibility, and the step-following ability and stress relaxation ability of both adhesive surfaces of the double-sided adhesive tape are further improved. The more preferred lower limit of the 25% compressive strength is 10 kPa, the more preferred upper limit is 100 kPa, the even more preferred lower limit is 20 kPa, and the even more preferred upper limit is 40 kPa.
The 25% compressive strength of the foam base material (the entire foam base material) can be adjusted within the above range, for example, by adjusting the expansion ratio of the first foamed resin layer.
The 25% compressive strength can be measured in accordance with JIS K 6254:2016 using, for example, Shimadzu Corporation's "Autograph AGS-X" as follows.
The foam substrate is cut to 20 mm x 20 mm, and these are stacked to prepare a sample with a thickness of about 5 mm x 20 mm x 20 mm. The sample is crushed in the compression direction at a speed of 10 mm/min, and the pressure (N) at the time of 25% compression is confirmed. From the obtained pressure, the 25% compression strength is calculated using the following formula (2). Note that when the thickness of the sample is 100, the sample is considered to be compressed by 25% (when the thickness of the sample becomes 75).
Compressive strength (kPa) = pressure (N) / 0.4 (2)

The thickness of the foam substrate (the entire foam substrate) is not particularly limited, but a preferred lower limit is 105 μm and a preferred upper limit is 2100 μm. If the thickness is within the above range, the holding power of the double-sided adhesive tape against shear load and tilt load is further improved, and the step-following ability and stress relaxation ability of both adhesive surfaces are also further improved. A more preferred lower limit of the thickness is 310 μm, a more preferred upper limit is 1580 μm, an even more preferred lower limit is 530 μm, and an even more preferred upper limit is 1060 μm.

In the foam base material, the ratio of the thickness of the first foamed resin layer to the thickness of the second foamed resin layer (value of thickness of the first foamed resin layer/thickness of the second foamed resin layer) is not particularly limited, but a preferred lower limit is 1.0 and a preferred upper limit is 400. If the thickness ratio is within the above range, the holding power of the double-sided adhesive tape against shear load and tilt load is further improved, and the step-following ability and stress relaxation ability of both adhesive surfaces are also further improved. A more preferred lower limit of the thickness ratio is 3, a more preferred upper limit is 150, an even more preferred lower limit is 5, and an even more preferred upper limit is 40.

In the foam substrate, the ratio of the expansion ratio of the first foamed resin layer to the expansion ratio of the second foamed resin layer (expansion ratio of the first foamed resin layer/expansion ratio of the second foamed resin layer) is not particularly limited, but a preferred lower limit is 1.3 and a preferred upper limit is 100. If the expansion ratio is within the above range, the holding power of the double-sided adhesive tape against shear load and tilt load is further improved, and the step-following ability and stress relaxation ability of both adhesive surfaces are also further improved. A more preferred lower limit of the expansion ratio is 3, a more preferred upper limit is 50, an even more preferred lower limit is 8, and an even more preferred upper limit is 20.

The method for producing the foam base material is not particularly limited, and may be a method in which the first foamed resin layer and the second foamed resin layer are produced, respectively, and then pressed together or bonded together via an adhesive layer or the like, but a method in which a multi-layer extrusion is performed using a foamable composition forming the first foamed resin layer and a foamable composition forming the second foamed resin layer is preferred. The multi-layer extrusion method allows the first foamed resin layer and the second foamed resin layer to be laminated without an adhesive layer or the like, and is preferred from the viewpoint of preventing the manufacturing process from becoming complicated.

The method of performing the multi-layer extrusion is not particularly limited, but for example, first, the foamable composition forming the first foamed resin layer and the foamable composition forming the second foamed resin layer are extruded separately, and the separately extruded foamable compositions are merged in a layered form in a die in a molten state to obtain a laminated sheet in which layers made of a plurality of foamable compositions are laminated. The foamable composition forming the first foamed resin layer and the foamable composition forming the second foamed resin layer are, for example, compositions containing a polyethylene resin and a thermally decomposable foaming agent as described above. The expansion ratio of the obtained foamed resin layer can be adjusted by changing the type and amount of the thermally decomposable foaming agent.
Next, at least one surface of the obtained laminate sheet is irradiated with ionizing radiation to crosslink the polyethylene resin. By changing the degree of crosslinking of the polyethylene resin, the expansion ratio of the obtained foamed resin layer can be adjusted.
Furthermore, the crosslinked laminate sheet can be expanded by heating or the like to obtain a foam base material having the first foamed resin layer and the second foamed resin layer. The crosslinked laminate sheet may be stretched when and/or after being expanded by heating or the like.

The pressure-sensitive adhesive layer is laminated on both sides of the foam substrate. The resin composition, physical properties, thickness, etc. of the pressure-sensitive adhesive layer on both sides may be the same or different.

At least one of the pressure-sensitive adhesive layers has a lower limit of the storage modulus at 180 ° C. of 11000 Pa. In this case, the pressure-sensitive adhesive layer may have a storage modulus at 180 ° C. of both sides within this range, or may have a storage modulus at 180 ° C. of only one side within this range. If the storage modulus at 180 ° C. is 11000 Pa or more, the bulk strength of the pressure-sensitive adhesive layer is increased, and the pressure-sensitive adhesive layer can be prevented from peeling off when a shear load or an oblique load is applied. The preferred lower limit of the storage modulus at 180 ° C. is 13000 Pa, more preferably 15000 Pa, and even more preferably 20000 Pa.
The upper limit of the storage modulus at 180° C. is not particularly limited, but the preferred upper limit is 50000 Pa. If the storage modulus at 180° C. is 50000 Pa or less, the interface of the pressure-sensitive adhesive layer has poor wettability, so that it is possible to suppress interfacial peeling when a shear load or tilt load is applied. The more preferred upper limit of the storage modulus at 180° C. is 40000 Pa, and the even more preferred upper limit is 32000 Pa.
The storage modulus at 180°C of the pressure-sensitive adhesive layer can be adjusted to within the above range, for example, by adjusting the composition, weight average molecular weight, molecular weight distribution (weight average molecular weight/number average molecular weight) of the acrylic copolymer contained in the pressure-sensitive adhesive layer, adjusting the type and amount of the crosslinking agent and tackifier resin contained in the pressure-sensitive adhesive layer, adjusting the gel fraction of the pressure-sensitive adhesive layer, etc.
The storage modulus at 180° C. can be determined using a viscoelasticity measuring device (for example, Rheometrics Dynamic Analyzer RDA-700 manufactured by Rheometrics Corporation) under conditions of a measurement temperature of −40 to 200° C., a heating rate of 3° C./min, and a frequency of 10 Hz.

The pressure-sensitive adhesive layer is not particularly limited, and examples thereof include an acrylic pressure-sensitive adhesive layer, a rubber-based pressure-sensitive adhesive layer, a urethane pressure-sensitive adhesive layer, a silicone-based pressure-sensitive adhesive layer, and the like. Among these, it is preferable that at least one of the pressure-sensitive adhesive layers is an acrylic pressure-sensitive adhesive layer, since it is relatively stable against light, heat, moisture, and the like, and can adhere to various adherends (it has low adherend selectivity). In other words, it is preferable that at least one of the pressure-sensitive adhesive layers contains an acrylic copolymer. In this case, both sides of the pressure-sensitive adhesive layer may contain an acrylic copolymer, or only one side may contain an acrylic copolymer.

From the viewpoint of improving initial tackiness and thus easiness of application at low temperatures, the acrylic copolymer is preferably obtained by copolymerizing a monomer mixture containing butyl acrylate and/or 2-ethylhexyl acrylate, and more preferably, the acrylic copolymer is obtained by copolymerizing a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate.
The preferred lower limit of the content of the butyl acrylate in the total monomer mixture is 30% by weight, and the preferred upper limit is 80% by weight. By setting the content of the butyl acrylate within this range, it is possible to achieve both high adhesive strength and tackiness.
The preferred lower limit of the content of the 2-ethylhexyl acrylate in the total monomer mixture is 10% by weight, and the preferred upper limit is 100% by weight, and the more preferred lower limit is 30% by weight, and the more preferred upper limit is 80% by weight, and the even more preferred lower limit is 50% by weight, and the even more preferred upper limit is 60% by weight. By keeping the content of the 2-ethylhexyl acrylate within this range, high adhesive strength can be exhibited.

The monomer mixture may contain other copolymerizable polymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate as necessary. Examples of the other copolymerizable polymerizable monomers include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 3 carbon atoms, (meth)acrylic acid alkyl esters having an alkyl group with 13 to 18 carbon atoms, and functional monomers.
Examples of the (meth)acrylic acid alkyl esters having an alkyl group with 1 to 3 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, etc. Examples of the (meth)acrylic acid alkyl esters having an alkyl group with 13 to 18 carbon atoms include tridecyl methacrylate, stearyl (meth)acrylate, etc. Examples of the functional monomers include hydroxyalkyl (meth)acrylate, glycerin dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, etc.
Among these, from the viewpoint of increasing the storage modulus and bulk strength of the pressure-sensitive adhesive layer at 180° C., hydroxyl-containing monomers such as hydroxyalkyl (meth)acrylate and glycerin dimethacrylate are preferred. That is, the acrylic copolymer preferably has a structural unit derived from a hydroxyl-containing monomer. The hydroxyalkyl (meth)acrylate is not particularly limited, and more specific examples include 2-hydroxyethyl (meth)acrylate.

To obtain the acrylic copolymer by copolymerizing the monomer mixture, the monomer mixture may be subjected to a radical reaction in the presence of a polymerization initiator. As a method for radically reacting the monomer mixture, i.e., a polymerization method, a conventionally known method may be used, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc.

The weight average molecular weight (Mw) of the acrylic copolymer is preferably 500,000 at the lower limit. If the weight average molecular weight of the acrylic copolymer is 500,000 or more, the storage modulus and bulk strength of the pressure-sensitive adhesive layer at 180°C are increased, and the peeling of the pressure-sensitive adhesive layer when a shear load or an inclined load is applied can be suppressed. The weight average molecular weight is more preferably 600,000 at the lower limit, more preferably 800,000 at the lower limit, and even more preferably 1,000,000 at the lower limit.
The upper limit of the weight-average molecular weight of the acrylic copolymer is not particularly limited, but the preferred upper limit is 2 million.If the weight-average molecular weight of the acrylic copolymer is 2 million or less, the wettability of the interface of the pressure-sensitive adhesive layer is poor, so that it can suppress the interface peeling when a shear load or an inclined load is applied.The more preferred upper limit of the weight-average molecular weight of the acrylic copolymer is 1.9 million, the more preferred upper limit is 1.8 million, and the even more preferred upper limit is 1.75 million.
The weight average molecular weight (Mw) is a weight average molecular weight calculated based on standard polystyrene by gel permeation chromatography (GPC).

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic copolymer has a preferred lower limit of 1.05 and a preferred upper limit of 5.0. When Mw/Mn is 5.0 or less, the proportion of low molecular weight components is suppressed, the storage modulus and bulk strength of the pressure-sensitive adhesive layer at 180°C are increased, and peeling of the pressure-sensitive adhesive layer when a shear load or an oblique load is applied can be suppressed. A more preferred upper limit of Mw/Mn is 4.5, an even more preferred upper limit is 4, and an even more preferred upper limit is 3.5.

From the viewpoint of exerting high adhesive strength, at least one of the pressure-sensitive adhesive layers preferably contains a tackifier resin. In this case, both surfaces of the pressure-sensitive adhesive layer may contain a tackifier resin, or only one surface of the pressure-sensitive adhesive layer may contain a tackifier resin.
Examples of the tackifier resin include rosin resins, rosin ester resins, hydrogenated rosin resins, terpene resins, terpene phenol resins, coumarone-indene resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, C9 petroleum resins, C5-C9 copolymer petroleum resins, etc. These tackifier resins may be used alone or in combination of two or more. Among them, rosin resins or terpene resins are preferred, and rosin resins or terpene resins having a hydroxyl group are more preferred.

The tackifier resin has a softening temperature of preferably 70° C. at the lower limit and 170° C. at the upper limit. If the softening temperature is 70° C. or higher, the pressure-sensitive adhesive layer can be prevented from becoming too soft, which can prevent the holding power against shear load and tilt load from decreasing. If the softening temperature is 170° C. or lower, the pressure-sensitive adhesive layer can be prevented from having poor interface wettability when a shear load or tilt load is applied, which can prevent interfacial peeling. The more preferred lower limit of the softening temperature is 120° C.
The softening temperature is a softening temperature measured by the ring and ball method according to JIS K2207.

The tackifier resin preferably has a lower limit of a hydroxyl value of 25. When the hydroxyl value is equal to or greater than the above value, the adhesive layer has poor interaction with the interface, and therefore, when a shear load or an inclined load is applied, interfacial peeling can be suppressed. The more preferred lower limit of the hydroxyl value is 30. The upper limit of the hydroxyl value is not particularly limited.
The hydroxyl value can be measured in accordance with JIS K1557 (phthalic anhydride method).

The content of the tackifier resin is not particularly limited, but a preferred lower limit is 10 parts by weight and a preferred upper limit is 40 parts by weight relative to 100 parts by weight of the acrylic copolymer. If the content of the tackifier resin is 10 parts by weight or more, the adhesive strength of the adhesive layer is increased. If the content of the tackifier resin is 40 parts by weight or less, it is possible to prevent the adhesive layer from becoming too hard and losing its adhesive strength.

At least one of the pressure-sensitive adhesive layers is preferably formed with a crosslinking structure between the main chains of the resins (e.g., the acrylic copolymer, the tackifier resin, etc.) constituting the pressure-sensitive adhesive layer by adding a crosslinking agent. In this case, the crosslinking agent may be added to both sides of the pressure-sensitive adhesive layer, or may be added to only one side. By adjusting the type and amount of the crosslinking agent, it becomes easier to adjust the storage modulus and gel fraction at 180°C of the pressure-sensitive adhesive layer.
The crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-type crosslinking agents, etc. Among these, isocyanate-based crosslinking agents are preferred.
The amount of the crosslinking agent added is preferably 0.01 parts by weight at the lower limit and 10 parts by weight at the upper limit, more preferably 0.1 parts by weight at the lower limit and 3 parts by weight at the upper limit, per 100 parts by weight of the acrylic copolymer.

The pressure-sensitive adhesive layer may contain a silane coupling agent to improve adhesion. The silane coupling agent is not particularly limited, and examples thereof include epoxy silanes, acrylic silanes, methacrylic silanes, amino silanes, and isocyanate silanes.

The adhesive layer may contain a coloring material to impart light-blocking properties. The coloring material is not particularly limited, and examples include carbon black, aniline black, titanium oxide, etc. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable.

The adhesive layer may contain conventionally known fine particles and additives such as inorganic fine particles, conductive fine particles, antioxidants, foaming agents, organic fillers, and inorganic fillers, as necessary.

At least one of the pressure-sensitive adhesive layers has a preferred lower limit of gel fraction of 15% by weight. In this case, the pressure-sensitive adhesive layer may have a gel fraction on both sides within this range, or may have a gel fraction on only one side within this range. If the gel fraction is 15% by weight or more, the storage modulus and bulk strength of the pressure-sensitive adhesive layer at 180°C are increased, and the peeling of the pressure-sensitive adhesive layer when a shear load or an inclined load is applied can be suppressed. The more preferred lower limit of the gel fraction is 30% by weight, and the even more preferred lower limit is 40% by weight.
The upper limit of the gel fraction is not particularly limited, but the preferred upper limit is 80% by weight. If the gel fraction is 80% by weight or less, the wettability of the interface of the pressure-sensitive adhesive layer is poor, so that it is possible to suppress interfacial peeling when a shear load or tilt load is applied. The more preferred upper limit of the gel fraction is 75% by weight, the even more preferred upper limit is 70% by weight, and the even more preferred upper limit is 65% by weight.
The gel fraction of the pressure-sensitive adhesive layer can be measured by the following method.
The double-sided adhesive tape is cut into a flat rectangular shape of 50 mm x 100 mm to prepare a test piece. The test piece is immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The weight of the test piece after drying is measured, and the gel fraction is calculated using the following formula (1). Note that no release film for protecting the adhesive layer is laminated on the test piece.
Gel fraction (wt%)=100×(W ₂ −W ₀ )/(W ₁ −W ₀ ) (1)
(W ₀ : weight of foam substrate, W ₁ : weight of test piece before immersion, W ₂ : weight of test piece after immersion and drying)

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the preferred lower limit of the thickness of the pressure-sensitive adhesive layer on one side is 20 μm, and the preferred upper limit is 100 μm. If the thickness of the pressure-sensitive adhesive layer is 20 μm or more, the adhesive strength of the pressure-sensitive adhesive layer is sufficient. If the thickness of the pressure-sensitive adhesive layer is 100 μm or less, the stress relaxation property of the foam substrate can sufficiently contribute to the stress relaxation property of the double-sided pressure-sensitive adhesive tape as a whole. The more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 25 μm, and the more preferred upper limit is 80 μm, and the even more preferred lower limit is 30 μm, and the even more preferred upper limit is 70 μm, and the even more preferred lower limit is 35 μm, and the even more preferred upper limit is 65 μm.
The thickness of the pressure-sensitive adhesive layer can be measured using a dial thickness meter (for example, "ABS Digimatic Indicator" manufactured by Mitutoyo Corporation).

The double-sided adhesive tape of the present invention may, if necessary, have layers other than the foam substrate and the adhesive layer.

The double-sided adhesive tape of the present invention has a preferred lower limit of strength when stretched 5 mm from the initial gripping jig distance in a tensile test of 1.5 N. If the strength is 1.5 N or more, the double-sided adhesive tape has improved holding power against shear load and tilt load, and handleability during application is also improved. A more preferred lower limit of the strength is 1.7 N, and an even more preferred lower limit is 2.2 N.
The strength can be adjusted within the above range, for example, by adjusting the expansion ratio of the second foamed resin layer within an appropriate range to increase the strength of the second foamed resin layer.
In addition, the strength when stretched 5 mm from the initial gripping jig distance in the tensile test can be measured by a method conforming to JIS K 7161. Specifically, for example, a double-sided adhesive tape is punched into a dumbbell shape using a punching blade "Tension No. 3 Dumbbell Shape" manufactured by Kobunshi Keiki Co., Ltd., etc. to prepare a test piece. The obtained test piece is pulled at a pulling speed of 50 mm/min using, for example, an "Autograph AGS-X" manufactured by Shimadzu Corporation, at 25°C and a relative humidity of 50%. At this time, the initial gripping jig distance is set to 60 mm, and the strength when stretched 5 mm from this distance (grip jig distance 65 mm) is read.

The 25% compressive strength of the double-sided adhesive tape of the present invention is not particularly limited, but the preferred lower limit is 20 kPa, and the preferred upper limit is 70 kPa. If the 25% compressive strength is 20 kPa or more, the holding power of the double-sided adhesive tape against shear load and tilt load is further improved. If the 25% compressive strength is 70 kPa or less, the step-following ability and stress relaxation ability of both adhesive surfaces of the double-sided adhesive tape are further improved. The more preferred lower limit of the 25% compressive strength is 25 kPa, the even more preferred lower limit is 27 kPa, and the particularly preferred lower limit is 30 kPa. The more preferred upper limit of the 25% compressive strength is 65 kPa, the even more preferred upper limit is 60 kPa, and the particularly preferred upper limit is 40 kPa.
The 25% compressive strength of the double-sided pressure-sensitive adhesive tape of the present invention can be measured in accordance with JIS K 6254:2016, similarly to the 25% compressive strength of the foam substrate.

The double-sided pressure-sensitive adhesive tape of the present invention preferably has a tensile breaking strength of 2N or more when a tensile test is performed at 23°C on a sample sliced from the first foamed resin layer. If the tensile breaking strength is 2N or more, the double-sided pressure-sensitive adhesive tape can exhibit better reworkability at room temperature. The tensile breaking strength is more preferably 3N or more, and even more preferably 4N or more.
The upper limit of the tensile breaking strength is not particularly limited, but from the viewpoint of conformability to unevenness and stress relaxation, the upper limit is preferably 20N, and more preferably 15N.

The double-sided pressure-sensitive adhesive tape of the present invention preferably has a tensile breaking elongation of 30 mm or more when a tensile test is performed at 23° C. on a sample sliced from the first foamed resin layer. If the tensile breaking elongation is 30 mm or more, the double-sided pressure-sensitive adhesive tape can exhibit better reworkability at room temperature. The tensile breaking elongation is more preferably 50 mm or more, and even more preferably 70 mm or more.
The upper limit of the tensile elongation at break is not particularly limited, but from the viewpoint of exerting a holding force against a shear load and an oblique load, a preferable upper limit is 200 mm.

The method for carrying out a tensile test at 23° C. on the sample sliced from the first foamed resin layer is as follows.
The double-sided adhesive tape is cut into a size of a dumbbell No. 3 (5 mm in width at the center), and the first foamed resin layer (center portion) is sliced with a feather blade to obtain a sample of adhesive layer/second foamed resin layer/first foamed resin layer (about half the thickness).
A tensile test is carried out on each sample using an Autograph AGS-X manufactured by Shimadzu Corporation at a tensile speed of 100 mm/min, a temperature of 23° C., and a gripping jig distance of 45 mm. The strength at which the sample breaks is the tensile breaking strength, and the elongation at which the sample breaks is the tensile breaking elongation.

The double-sided pressure-sensitive adhesive tape of the present invention preferably has a tensile breaking strength of 1 N or more when a sample sliced from the first foamed resin layer is subjected to a tensile test at 80° C. If the tensile breaking strength is 1 N or more, the double-sided pressure-sensitive adhesive tape can exhibit superior reworkability at high temperatures. The tensile breaking strength is more preferably 1.5 N or more.
The upper limit of the tensile breaking strength is not particularly limited, but from the viewpoint of conformability to unevenness and stress relaxation, a preferable upper limit is 10 N.

The double-sided pressure-sensitive adhesive tape of the present invention preferably has a tensile break strength reduction rate of 70% or less when a sample sliced from the first foamed resin layer is subjected to a tensile test at 80° C. If the tensile break strength reduction rate is 70% or less, the double-sided pressure-sensitive adhesive tape can exhibit superior reworkability at high temperatures. The tensile break strength reduction rate is more preferably 60% or less.
The lower limit of the tensile breaking strength reduction rate is not particularly limited, but the lower limit is preferably lower, and the substantial lower limit is about 10%.

The method for carrying out a tensile test at 80° C. on the sample sliced from the first foamed resin layer is as follows.
The double-sided adhesive tape is cut into a rectangular shape of 5 mm, and the first foamed resin layer (center portion) is sliced with a feather blade to obtain a sample of adhesive layer/second foamed resin layer/first foamed resin layer (about half the thickness).
Using Shimadzu Corporation's "Autograph AGS-X," a tensile test is performed on each sample at a tensile speed of 100 mm/min, a temperature of 80°C, and a gripping jig distance of 10 mm. After setting the sample at a gripping jig distance of 10 mm, the sample is left in an 80°C environment for 5 minutes before starting the measurement. The strength at which the sample breaks is taken as the tensile breaking strength. The value of 1 - (tensile breaking strength at 80°C/tensile breaking strength at 23°C) is calculated as the tensile breaking strength reduction rate.

The thickness of the double-sided adhesive tape of the present invention is not particularly limited, but a preferred lower limit is 100 μm and a preferred upper limit is 3000 μm. If the thickness is 100 μm or more, the adhesive strength of the double-sided adhesive tape will be sufficient, and the stress relaxation properties will also be sufficient. If the thickness is 3000 μm or less, sufficient adhesion and fixation by the double-sided adhesive tape can be achieved, and the step-following properties of both adhesive surfaces will also be sufficient. A more preferred lower limit of the thickness is 250 μm, a more preferred upper limit is 1600 μm, an even more preferred lower limit is 350 μm, an even more preferred upper limit is 1500 μm, an even more preferred lower limit is 500 μm, and an even more preferred upper limit is 1300 μm.

The double-sided pressure-sensitive adhesive tape of the present invention can be produced, for example, by the following method.
First, a solvent is added to an acrylic copolymer, a tackifier, a crosslinking agent, etc. to prepare a solution of adhesive A. This solution of adhesive A is applied to the release-treated surface of a release film, and the solvent in the solution is dried and removed to form an adhesive layer. This adhesive layer is pressed and laminated to the surface of the foam substrate by a rubber roller or the like. In the same manner, an adhesive layer is also laminated to the other side of the foam substrate, and a double-sided adhesive tape having adhesive layers on both sides of the foam substrate and the surface of the adhesive layer covered with a release film can be obtained.

The double-sided pressure-sensitive adhesive tape of the present invention can be used for, for example, fixing components in electronic devices. The electronic devices are not particularly limited, and examples thereof include televisions, monitors, portable electronic devices, and in-vehicle electronic devices.
In particular, the double-sided adhesive tape of the present invention is preferably used for fixing components in display devices such as televisions and monitors, particularly in relatively large display devices, and is specifically used, for example, for fixing the cover panel on the surface of the display device to the housing. The double-sided adhesive tape of the present invention can exhibit high holding power against shear loads and tilt loads, so it is preferably used even when components are fixed by a narrow double-sided adhesive tape in a relatively large display device. The double-sided adhesive tape of the present invention may be narrow, and the width is not particularly limited, but a preferred lower limit is 0.5 mm, a preferred upper limit is 20 mm, a more preferred lower limit is 1 mm, and a more preferred upper limit is 5 mm. The shape of the double-sided adhesive tape of the present invention in these applications is not particularly limited, but examples thereof include rectangular, frame-shaped, circular, elliptical, and donut-shaped shapes.
The double-sided pressure-sensitive adhesive tape of the present invention may also be used for vehicle interiors, and the interior and exterior of home appliances (for example, TVs, monitors, air conditioners, refrigerators, etc.).

According to the present invention, it is possible to provide a double-sided adhesive tape that has high conformability to unevenness on both adhesive surfaces, exhibits high holding power against shear loads and tilt loads, has excellent reworkability on at least one of the adhesive surfaces, and further has excellent handling properties when applied.

FIG. 2 is a schematic diagram showing a 45° inclination holding power test of a double-sided adhesive tape. FIG. 2 is a schematic diagram showing a shear holding strength test of a double-sided adhesive tape. 1 is a cross-sectional view illustrating a schematic diagram of an example of a double-sided pressure-sensitive adhesive tape of the present invention.

The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

(Preparation of Acrylic Copolymer A)
In a reactor equipped with a thermometer, a stirrer, and a cooling tube, 159 parts by weight of ethyl acetate as a solvent, 75 parts by weight of butyl acrylate (BA), 25 parts by weight of 2-ethylhexyl acrylate (2EHA), 0.1 parts by weight of 2-hydroxyethyl acrylate (HEA), and 5 parts by weight of acrylic acid (AAc) were placed. After nitrogen replacement, the reactor was placed in a water bath set at 60°C, and the reactor was heated to start reflux. 30 minutes after the start of reflux, 0.050 parts by weight of azobisisobutyronitrile was added as a polymerization initiator to the reactor, and the reaction was allowed to proceed for 6 hours. Thereafter, ethyl acetate was added to the reactor to dilute it while cooling, thereby obtaining a solution of acrylic copolymer A.
The obtained solution of acrylic copolymer A was diluted 50 times with tetrahydrofuran (THF) and the obtained diluted solution was filtered with a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The obtained filtrate was supplied to a gel permeation chromatograph (Waters, 2690 Separations Model) and GPC measurement was performed under conditions of a sample flow rate of 1 milliliter/min and a column temperature of 40° C., and the polystyrene-equivalent molecular weight of acrylic copolymer A was measured to obtain the weight average molecular weight (Mw). The weight average molecular weight (Mw) was 1.4 million. A GPC KF-806L (Showa Denko KK) was used as the column, and a differential refractometer was used as the detector.

(Preparation of Acrylic Copolymer B)
A solution of acrylic copolymer B was obtained in the same manner as in the preparation of acrylic copolymer A, except that the solvent was changed to 100 parts by weight of ethyl acetate and 50 parts by weight of toluene, and the polymerization initiator was changed to 0.14 parts by weight of azobisisobutyronitrile. The weight average molecular weight of the obtained acrylic copolymer B was 800,000.

(Preparation of Acrylic Copolymer C)
A solution of acrylic copolymer C was obtained in the same manner as in the preparation of acrylic copolymer A, except that the polymerization initiator was changed to 0.04 parts by weight of azobisisobutyronitrile. The weight average molecular weight of the obtained acrylic copolymer C was 1,600,000.

(Preparation of Acrylic Copolymer D)
A solution of acrylic copolymer D was obtained in the same manner as in the preparation of acrylic copolymer A, except that the amount of acrylic acid was changed to 3 parts by weight. The weight average molecular weight of the obtained acrylic copolymer D was 1,400,000.

(Preparation of Acrylic Copolymer E)
50 parts by weight of ethyl acetate was placed in a reactor equipped with a thermometer, a stirrer, and a cooling tube as a solvent, and the reactor was heated to start refluxing. 30 minutes after the ethyl acetate boiled, 0.20 parts by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 75 parts by weight of butyl acrylate, 25 parts by weight of 2-ethylhexyl acrylate, 0.1 parts by weight of 2-hydroxyethyl acrylate, and 3 parts by weight of acrylic acid was added dropwise evenly and gradually over 1 hour and 30 minutes to react. 30 minutes after the end of the dropwise addition, 0.15 parts by weight of azobisisobutyronitrile was added, and the polymerization reaction was continued for another 5 hours. Ethyl acetate was added to the reactor to dilute it and cool it, thereby obtaining a solution of acrylic copolymer E. The weight average molecular weight of the obtained acrylic copolymer E was 400,000.

(Styrene-Acrylic Block Copolymer A)
A styrene-acrylic block copolymer A having the physical properties and composition shown in Table 1 was prepared.

Example 1
(1) Preparation of Foam Base Material As the foamable composition for forming the first foamed resin layer (central foamed resin layer), a composition consisting of 100 parts by weight of a polyethylene resin (UBE polyethylene F420), 8.5 parts by weight of azodicarbonamide as a thermal decomposition type foaming agent, 1 part by weight of zinc oxide as a decomposition temperature regulator, and 0.5 parts by weight of 2,6-di-t-butyl-p-cresol as an antioxidant was used.
As the foamable composition for forming the second foamed resin layer (outermost layer), a composition consisting of 100 parts by weight of a polyethylene resin (UBE polyethylene F420), 1.1 parts by weight of azodicarbonamide as a thermal decomposition type foaming agent, 1 part by weight of zinc oxide as a decomposition temperature regulator, and 0.5 parts by weight of 2,6-di-t-butyl-p-cresol as an antioxidant was used.
The UBE polyethylene F420 is "UBE polyethylene F420" (density: 0.920 g/cm ³ ) manufactured by Ube Maruzen Polyethylene Co., Ltd.
The foamable composition forming the first foamed resin layer (central foamed resin layer) and the foamable composition forming the second foamed resin layer (outermost layer) were fed to an extruder for multi-layer extrusion molding and melt-kneaded at 130° C. After melt-kneading, a long sheet-like foam raw material having a thickness of about 1.0 mm was extruded, in which a layer made of the foamable composition forming the second foamed resin layer (outermost layer) was laminated on both sides of the layer made of the foamable composition forming the first foamed resin layer (central foamed resin layer).
Next, the long sheet-like foam raw material was crosslinked by irradiating both sides with an electron beam of 500 kV at an acceleration voltage of 4.0 Mrad. The crosslinked foam raw material was continuously sent into a foaming furnace maintained at 250 ° C. by hot air and an infrared heater to be heated and foamed, and stretched at a MD stretch ratio of 3.5 times and a TD stretch ratio of 3.5 times. As a result, a foam base material was obtained in which a second foamed resin layer (outermost layer)-1 and a second foamed resin layer (outermost layer)-2 were laminated on both sides of the first foamed resin layer (central foamed resin layer). The thickness of each foamed resin layer and the expansion ratio in accordance with JIS K 7222, as well as the thickness of the foam base material and the 25% compression strength in accordance with JIS K 6254:2016 were measured. The measurement results are shown in Table 2.

(2) Production of double-sided adhesive tape To 100 parts by weight of the solid content of acrylic copolymer A, 15 parts by weight of polymerized rosin ester resin (Arakawa Chemical Industries, Ltd., Pencel D-135, softening point 135°C, hydroxyl value 45) and 15 parts by weight of terpene phenol resin (Yasuhara Chemical, Ltd., YS Polystar G150, softening point 150°C, hydroxyl value 135) were added. Furthermore, 30 parts by weight of ethyl acetate (Fuji Chemical Industries, Ltd.) and 1.3 parts by weight of solid content of an isocyanate-based crosslinking agent (Nippon Polyurethane Co., Ltd., product name "Coronate L45") were added and stirred to obtain an adhesive solution.
A release film with a thickness of 75 μm was prepared, and a pressure-sensitive adhesive solution was applied to the release-treated surface of the release film, and the solution was dried at 110° C. for 5 minutes to form a pressure-sensitive adhesive layer with a thickness of 50 μm. This pressure-sensitive adhesive layer was attached to the surface of the foam substrate obtained above. Next, in the same manner, the same pressure-sensitive adhesive layer was attached to the opposite surface of the foam substrate after peeling off the PET separator. Then, the film was cured by heating at 40° C. for 48 hours. This resulted in a double-sided pressure-sensitive adhesive tape covered with a release film.

(3) Measurement of gel fraction The double-sided adhesive tape was cut into a flat rectangular shape of 50 mm x 100 mm to prepare a test piece. The test piece was immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (1). Note that no release film for protecting the adhesive layer was laminated on the test piece.
Gel fraction (wt%)=100×(W ₂ −W ₀ )/(W ₁ −W ₀ ) (1)
(W ₀ : weight of foam substrate, W ₁ : weight of test piece before immersion, W ₂ : weight of test piece after immersion and drying)

(4) Measurement of storage modulus at 180° C. The storage modulus of the pressure-sensitive adhesive layer at 180° C. was determined using a viscoelasticity measuring device (Rheometrics Dynamic Analyzer RDA-700 manufactured by Rheometrics Corporation) under conditions of a measurement temperature of −40 to 200° C., a heating rate of 3° C./min, and a frequency of 10 Hz.

(5) Measurement of strength when stretched 5 mm from the initial gripping jig distance (tensile test)
In accordance with JIS K 7161, the strength was measured when the specimen was elongated by 5 mm from the initial distance between the gripping jigs as described below.
A double-sided adhesive tape was punched into a dumbbell shape using a punching blade "Tension No. 3 Dumbbell Shape" manufactured by Kobunshi Keiki Co., Ltd. The obtained test piece was pulled at a pulling speed of 50 mm/min using an "Autograph AGS-X" manufactured by Shimadzu Corporation at 25°C and a relative humidity of 50%. At this time, the initial gripping jig distance was set to 60 mm, and the strength was read when the sample was stretched by 5 mm from this distance (gripping jig distance 65 mm).

(6) Measurement of 25% Compressive Strength The 25% compressive strength of the double-sided adhesive tape was also measured in accordance with JIS K 6254:2016, in the same manner as the 25% compressive strength of the foam substrate.

(7) 23°C tensile test The double-sided adhesive tape was cut into a size of a dumbbell No. 3 (5 mm in width at the center), and the first foamed resin layer (center portion) was sliced with a feather blade. This resulted in separation into a sample of adhesive layer/second foamed resin layer (outermost layer)-1/first foamed resin layer (about half the thickness) (referred to as the "sample on the second foamed resin layer (outermost layer)-1 side") and a sample of first foamed resin layer (about half the thickness)/second foamed resin layer (outermost layer)-2/adhesive layer (referred to as the "sample on the second foamed resin layer (outermost layer)-2 side").
A tensile test was performed on each sample using an Autograph AGS-X manufactured by Shimadzu Corporation at a tensile speed of 100 mm/min, a temperature of 23° C., and a gripping jig distance of 45 mm. The strength at which the sample broke was taken as the tensile breaking strength, and the elongation at which the sample broke was taken as the tensile breaking elongation.

(8) 80°C tensile test The double-sided adhesive tape was cut into a rectangular shape of 5 mm, and the first foamed resin layer (center part) was sliced with a feather blade, thereby dividing it into a sample of adhesive layer/second foamed resin layer (outermost layer)-1/first foamed resin layer (about half thickness) (referred to as the "sample on the second foamed resin layer (outermost layer)-1 side") and a sample of first foamed resin layer (about half thickness)/second foamed resin layer (outermost layer)-2/adhesive layer (referred to as the "sample on the second foamed resin layer (outermost layer)-2 side").
Using Shimadzu Corporation's "Autograph AGS-X," a tensile test was performed on each sample at a tensile speed of 100 mm/min, a temperature of 80°C, and a gripping jig distance of 10 mm. The sample was set with a gripping jig distance of 10 mm, and then left in an 80°C environment for 5 minutes before starting the measurement. The strength at which the sample broke was taken as the tensile breaking strength. The value of 1 - (tensile breaking strength at 80°C/tensile breaking strength at 23°C) was calculated as the tensile breaking strength reduction rate.

(Examples 2 to 6, 11 to 14)
Double-sided pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the foam substrate was changed as shown in Table 2. The thickness of the foamed resin layer was adjusted by adjusting the thickness during multi-layer extrusion and the stretch ratios in MD and TD, and the expansion ratio of the foamed resin layer was adjusted by adjusting the amount of the thermally decomposable foaming agent.

(Examples 7 to 10)
Double-sided pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive layer was changed as shown in Table 2. In Example 6, acrylic copolymer B was used, and the amount of crosslinking agent was 1.9 parts by weight of solid content. In Example 7, acrylic copolymer C was used, and the amount of crosslinking agent was 1.1 parts by weight of solid content. In both Examples 8 and 9, acrylic copolymer D was used, but the amount of crosslinking agent was changed to 1.4 parts by weight of solid content in Example 8 and 1.1 parts by weight of solid content in Example 9, thereby changing the gel fraction.

(Comparative Example 1)
In "(1) Preparation of foam substrate", no foamable composition was used to form the second foamed resin layer (outermost layer), and only the foamable composition to form the first foamed resin layer (central foamed resin layer) was used. A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that a polyethylene terephthalate (PET) sheet and a styrene-acrylic copolymer sheet were laminated on both sides of the obtained first foamed resin layer (central foamed resin layer).

Specifically, in "(1) Preparation of foam substrate", first, only the first foamed resin layer (central foamed resin layer) was formed. Next, a pressure-sensitive adhesive solution containing acrylic copolymer A was applied to the surface of a 50 μm-thick polyethylene terephthalate (PET) sheet (Toray Industries, X30), and dried at 110° C. for 5 minutes to form a 20 μm-thick pressure-sensitive adhesive layer. The obtained first foamed resin layer (central foamed resin layer) was laminated on the pressure-sensitive adhesive layer to obtain a laminate consisting of a polyethylene terephthalate (PET) sheet/pressure-sensitive adhesive layer/first foamed resin layer (central foamed resin layer).
Furthermore, 5 parts by weight of a crosslinking agent was mixed with 100 parts by weight of styrene-acrylic block copolymer A in an ethyl acetate solution, and the mixture was applied to a 50 μm-thick polyethylene terephthalate (PET) sheet with a release treatment on the surface, and dried to obtain an uncrosslinked resin film with a thickness of 40 μm. The crosslinking agent used was "Coronate L45" manufactured by Nippon Polyurethane Co., Ltd. The uncrosslinked resin film was laminated on the first foamed resin layer (center foamed resin layer) side of a laminate consisting of a polyethylene terephthalate (PET) sheet/adhesive layer/first foamed resin layer (center foamed resin layer) to obtain a laminate consisting of a polyethylene terephthalate (PET) sheet/adhesive layer/first foamed resin layer (center foamed resin layer)/uncrosslinked resin film. Next, the uncrosslinked resin film was thermally crosslinked by heating at 40°C for 48 hours, thereby obtaining a foam substrate consisting of a polyethylene terephthalate (PET) sheet/adhesive layer/first foamed resin layer (central foamed resin layer)/styrene-acrylic copolymer sheet.

(Comparative Example 2)
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that in "(1) Preparation of foam substrate", no foamable composition for forming the second foamed resin layer (outermost layer) was used, and only the foamable composition for forming the first foamed resin layer (central foamed resin layer) was used, and styrene-acrylic copolymer sheets were laminated on both sides of the obtained first foamed resin layer (central foamed resin layer).

Specifically, in "(1) Preparation of foam substrate", first, only the first foamed resin layer (central foamed resin layer) was formed. Next, 5 parts by weight of a crosslinking agent was mixed with 100 parts by weight of styrene-acrylic block copolymer A in an ethyl acetate solution of styrene-acrylic block copolymer A, and the mixture was applied to a 50 μm-thick polyethylene terephthalate (PET) sheet whose surface had been subjected to a release treatment, and then dried to obtain an uncrosslinked resin film having a thickness of 40 μm. As the crosslinking agent, "Coronate L45" (trade name, manufactured by Nippon Polyurethane Co., Ltd.) was used.
An uncrosslinked resin film was laminated on the first foamed resin layer (central foamed resin layer) to obtain a laminate consisting of the uncrosslinked resin film/first foamed resin layer (central foamed resin layer).Then, the uncrosslinked resin film was thermally crosslinked by heating at 40°C for 48 hours to obtain a laminate consisting of the styrene-acrylic copolymer sheet/first foamed resin layer (central foamed resin layer).
Further, the uncrosslinked resin film prepared in the same manner was laminated on the first foamed resin layer (central foamed resin layer) side of the laminate consisting of a styrene-acrylic copolymer sheet/first foamed resin layer (central foamed resin layer) to obtain a laminate consisting of a styrene-acrylic copolymer sheet/first foamed resin layer (central foamed resin layer)/uncrosslinked resin film. The uncrosslinked resin film was then thermally crosslinked by heating at 40° C. for 48 hours to obtain a foam base material consisting of a styrene-acrylic copolymer sheet/first foamed resin layer (central foamed resin layer)/styrene-acrylic copolymer sheet.

(Comparative Example 3)
A double-sided adhesive tape was obtained in the same manner as in Example 1, except that in "(1) Preparation of foam substrate", no foamable composition for forming the second foamed resin layer (outermost layer) was used, and only the foamable composition for forming the first foamed resin layer (central foamed resin layer) was used, and polyethylene (PE) sheets were laminated on both sides of the obtained first foamed resin layer (central foamed resin layer).

Specifically, in "(1) Preparation of foam substrate", first, only the first foamed resin layer (central foamed resin layer) was formed. A release film with a thickness of 75 μm was prepared, and an adhesive solution containing acrylic copolymer A was applied to the release-treated surface of this release film, and dried at 110° C. for 5 minutes to form an adhesive layer with a thickness of 6 μm. This adhesive layer was then bonded to the surface of a low-density polyethylene (PE) sheet with a thickness of 40 μm to obtain a laminate consisting of an adhesive layer/low-density polyethylene (PE) sheet. The release film of the adhesive layer in the laminate consisting of an adhesive layer/low-density polyethylene (PE) sheet was peeled off, and the first foamed resin layer (central foamed resin layer) was bonded thereto. Next, in the same manner, an adhesive layer/low-density polyethylene (PE) sheet was also bonded to the opposite surface of the first foamed resin layer (central foamed resin layer). After that, the product was cured by heating at 40° C. for 48 hours. A foam substrate consisting of a polyethylene (PE) sheet/adhesive layer/first foamed resin layer (central foamed resin layer)/adhesive layer/polyethylene (PE) sheet was obtained.

(Comparative Example 4)
A double-sided adhesive tape was obtained in the same manner as in Example 2, except that in "(1) Preparation of foam substrate", no foamable composition for forming the second foamed resin layer (outermost layer) was used, and only the foamable composition for forming the first foamed resin layer (central foamed resin layer) was used, and a polyethylene terephthalate (PET) sheet was laminated on one side of the obtained first foamed resin layer (central foamed resin layer).

Specifically, in "(1) Preparation of foam substrate", first, only the first foamed resin layer (central foamed resin layer) was formed. Next, an adhesive solution containing acrylic copolymer A was applied to the surface of a 50 μm-thick polyethylene terephthalate (PET) sheet (Toray Industries, Inc., X30) and dried at 110° C. for 5 minutes to form an adhesive layer with a thickness of 20 μm. The obtained first foamed resin layer (central foamed resin layer) was laminated on the adhesive layer to obtain a foam substrate consisting of a polyethylene terephthalate (PET) sheet/adhesive layer/first foamed resin layer (central foamed resin layer).

(Comparative Example 5)
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 2, except that in "(1) Preparation of foam substrate", no foamable composition for forming the second foamed resin layer (outermost layer) was used, and only the foamable composition for forming the first foamed resin layer (central foamed resin layer).

(Comparative Examples 6 to 8)
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive layer was changed as shown in Table 3. In Comparative Example 6, acrylic copolymer E was used, but the amount of crosslinking agent was set to 2.5 parts by weight of solid content to change the gel fraction. In Comparative Example 7, acrylic copolymer D was used as in Examples 8 and 9, but the amount of crosslinking agent was set to 0.7 parts by weight of solid content to change the gel fraction.

(Comparative Example 9)
In "(1) Preparation of foam substrate", no foamable composition was used to form the second foamed resin layer (outermost layer), and only the foamable composition to form the first foamed resin layer (central foamed resin layer) was used. A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that an acrylic copolymer sheet was laminated on each side of the obtained first foamed resin layer (central foamed resin layer).

Specifically, in "(1) Preparation of foam substrate", first, only the first foamed resin layer (central foamed resin layer) was formed. Next, 100 parts by weight of ethyl acetate was added to 45 parts by weight of LA2270 manufactured by Kuraray Co., Ltd., and stirred to obtain a solution. The obtained solution was applied to a 50 μm-thick polyethylene terephthalate (PET) sheet with a release treatment on the surface, and dried at 110°C for 5 minutes to obtain a 40 μm-thick resin film. The exposed surface of the resin film was attached to one side of the first foamed resin layer (central foamed resin layer). A 40 μm-thick resin film was prepared again by the same operation as above, and the exposed surface of the resin film was attached to the opposite side of the first foamed resin layer (central foamed resin layer) to obtain a foam substrate.

<Evaluation>
The double-sided adhesive tapes obtained in the Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 4 and 5.

(1) Evaluation of step conformability A single-sided adhesive tape (125 mm x 20 mm, thickness 300 μm) was attached to a glass plate (125 mm x 50 mm, thickness 1.5 mm) to create a step of 300 μm in height. The double-sided adhesive tape was cut into a size of 25 mm x 50 mm, and one side was backed with a polyethylene terephthalate (PET) sheet of 23 μm in thickness. The other side of the double-sided adhesive tape was attached to the surface of the glass plate where the step was created, and a 2 kg rubber roller was moved back and forth once from the glass plate side to press it. The air entrapment distance from the step portion was measured and evaluated according to the following criteria.
A: Air entrapment distance is less than 700 μm B: Air entrapment distance is 700 μm or more and less than 800 μm C: Air entrapment distance is 800 μm or more and less than 900 μm D: Air entrapment distance is 900 μm or more and less than 1000 μm E: Air entrapment distance is 1000 μm or more

(2) Evaluation of Holding Power (2-1) Holding Power Test at 45° Incline FIG. 1 shows a schematic diagram illustrating a holding power test at a 45° inclination of a double-sided pressure-sensitive adhesive tape.
The obtained double-sided adhesive tape 18 was cut into a size of 25 mm x 25 mm, the adhesive layer on the second foamed resin layer (outermost layer)-2 side was attached to a glass plate 17, and a 2 kg rubber roller was reciprocated once at a speed of 300 mm/min on the double-sided adhesive tape 18. Next, the adhesive layer on the second foamed resin layer (outermost layer)-1 side of the double-sided adhesive tape 18 was attached to a SUS plate 16, and pressure was applied from the SUS plate 16 side with a 5 kg weight for 10 seconds to bond them together, and then the resulting product was left in an environment of 23°C and a relative humidity of 50% for 24 hours to prepare a test sample.
This test sample was placed at 60°C and a relative humidity of 90%, and a 1 kg weight 15 was attached to the center of a SUS plate 16 so that a load was applied to the double-sided adhesive tape 18 and the SUS plate 16. The weight 15 was then held at an angle of 45°, and the time it took for the weight 15 to fall (fall time) was measured and evaluated according to the following criteria.
◯: Fall time is 250 hours or more △: Fall time is 50 hours or more and less than 250 hours ×: Fall time is less than 50 hours

(2-2) Shear Holding Strength Test A schematic diagram showing a shear holding strength test of a double-sided pressure-sensitive adhesive tape is shown in Figure 2. Figure 2(a) is a front view, and Figure 2(b) is a side view.
2(a) and (b), the adhesive layer on the second foamed resin layer (outermost layer)-2 side of the double-sided adhesive tape 3 was backed with a PET film (#50) 4. The adhesive layer on the second foamed resin layer (outermost layer)-1 side of the double-sided adhesive tape 3 was attached to a SUS plate 1 and a SUS plate 2 to prepare a test sample with an attachment area of 25 mm x 25 mm between the SUS plate 1 and the double-sided adhesive tape 3. The test sample was prepared as follows.
First, a SUS plate 1 (thickness 2 mm x 50 mm x 70 mm, the surface of a SUS304 steel plate specified in JIS-G-4305 was uniformly polished with water-resistant abrasive paper No. 360) and a SUS plate 2 (thickness 1 mm x 30 mm x 50 mm, unpolished) were prepared. The SUS plate 1 and the SUS plate 2 were washed with ethanol and then thoroughly dried. The double-sided adhesive tape 3 was cut to a width of 25 mm x length of 140 mm, the release film on one side was peeled off, and a PET film (#50) 4 was attached to the exposed adhesive layer. Next, the release film on the other side was peeled off, and the end of the exposed adhesive layer was attached to the SUS plate 1 so as not to trap air bubbles, and a 2 kg rubber roller was reciprocated once at a speed of 10 mm/sec to pressure-bond the two plates. At this time, the SUS plate 1 and the double-sided adhesive tape 3 were attached so that the overlap was 30 mm. Furthermore, the end of the adhesive layer opposite to the end attached to the SUS plate 1 was attached to the SUS plate 2, and a 2 kg rubber roller was moved back and forth once at a speed of 10 mm/sec to pressure-bond the adhesive. At this time, the double-sided adhesive tape 3 was arranged so as to cover the front and back surfaces of the SUS plate 2. After that, a through hole 5 was provided in the double-sided adhesive tape 3 together with the SUS plate 2, and the double-sided adhesive tape 3 was cut so that the attachment area between the SUS plate 1 and the double-sided adhesive tape 3 was 25 mm x 25 mm.
The test sample prepared as described above was left in a thermostatic chamber at 50°C and 80% RH for 24 hours, and then a 2 kg weight 6 was attached to the through hole 5 in the same environment, and the displacement after 200 hours was measured and evaluated according to the following criteria. The shear holding strength of the pressure-sensitive adhesive layer on the second foamed resin layer (outermost layer)-2 side of the double-sided pressure-sensitive adhesive tape 3 was also evaluated in the same manner.
◯: Misalignment after 200 hours is less than 2 mm △: Misalignment after 200 hours is 2 mm or more and less than 10 mm ×: Misalignment after 200 hours is 10 mm or more

(3) Evaluation of reworkability at 23°C and reworkability at 80°C The double-sided adhesive tape was cut into a size of 5 mm x 100 mm, and one side was attached to a glass plate. The other side of the double-sided adhesive tape was also attached to a glass plate to prepare a laminate of glass plate/double-sided adhesive tape/glass plate, and pressure-bonded with a weight of 5 kg for 10 seconds. The first foamed resin layer (center part) of the obtained laminate was sliced with a feather blade. This resulted in a sample of glass plate/adhesive layer/second foamed resin layer (outermost layer)-1/first foamed resin layer (about half the thickness) (referred to as the "sample on the second foamed resin layer (outermost layer)-1 side") and a sample of first foamed resin layer (about half the thickness)/second foamed resin layer (outermost layer)-2/adhesive layer/glass plate (referred to as the "sample on the second foamed resin layer (outermost layer)-2 side").
In the evaluation of the 23° C. reworkability, each sample was left to stand at 23° C. for 4 days, and then the double-sided adhesive tape portion was peeled off the glass plate by hand at high speed.
In the evaluation of 80° C. reworkability, each sample was left at 80° C. for one day, and immediately after being taken out, the double-sided adhesive tape portion was peeled off the glass plate by hand at high speed.
◎: No adhesive residue, no breakage of the double-sided adhesive tape, and the glass plate can be reworked. ○: Some adhesive residue remains, but the double-sided adhesive tape does not break, and the glass plate can be reworked. ×: The double-sided adhesive tape breaks, and the glass plate cannot be reworked.

From the evaluation results of the sample on the second foamed resin layer (outermost layer)-1 side and the sample on the second foamed resin layer (outermost layer)-2 side, a comprehensive evaluation of the reworkability was performed for each of the 23°C reworkability and the 80°C reworkability according to the following criteria.
◎: The evaluation results of the sample on the second foamed resin layer (outermost layer)-1 side and the sample on the second foamed resin layer (outermost layer)-2 side were both ◎. ◯: At least one of the evaluation results of the sample on the second foamed resin layer (outermost layer)-1 side and the sample on the second foamed resin layer (outermost layer)-2 side was ◎ or both were ◯. △: At least one of the evaluation results of the sample on the second foamed resin layer (outermost layer)-1 side and the sample on the second foamed resin layer (outermost layer)-2 side was ◯. ×: The evaluation results of the sample on the second foamed resin layer (outermost layer)-1 side and the sample on the second foamed resin layer (outermost layer)-2 side were both ×.

(4) Evaluation of handling properties The obtained double-sided adhesive tape was cut into a size of 3 mm wide x 10 mm long, and the double-sided adhesive tape was pulled at 1 N for 10 seconds at 25°C and 50% relative humidity using an Autograph AGS-X (manufactured by Shimadzu Corporation), and the elongation (mm) was measured. Evaluation was made according to the following criteria. The initial load change was set to 1 N/sec.
A: The elongation was less than 10 mm.
×: Elongation was 10 mm or more.

(5) Evaluation of the Presence or Absence of Folding The obtained double-sided pressure-sensitive adhesive tape was cut into a size of 100 mm × 300 mm, and wound around a paper core having a diameter of 3 inches with the second foamed resin layer (outermost layer)-2 side facing inward to obtain a roll-shaped product.
The double-sided adhesive tape was pulled out from the obtained roll, and then visually observed and evaluated according to the following criteria.
A: No breaks were observed.
×: Bending was observed.

According to the present invention, it is possible to provide a double-sided adhesive tape that has high conformability to unevenness on both adhesive surfaces, exhibits high holding power against shear loads and tilt loads, has excellent reworkability on at least one of the adhesive surfaces, and further has excellent handling properties when applied.

1, 2 SUS plate 3 Test piece (double-sided adhesive tape)
4 PET film (#50)
5 Through hole 6 Weight (3 kg)
7 Double-sided adhesive tape 8 Foam substrate 91, 92 Adhesive layer 10 First foamed resin layer 11, 12 Second foamed resin layer 15 Weight (1 kg)
16 SUS plate 17 Glass plate 18 Double-sided adhesive tape

Claims (11)

A double-sided pressure-sensitive adhesive tape having a foam substrate and pressure-sensitive adhesive layers laminated on both sides of the foam substrate,
The foam base material has a first foamed resin layer and a second foamed resin layer laminated on at least one surface of the first foamed resin layer and having an expansion ratio lower than that of the first foamed resin layer,
At least one of the pressure-sensitive adhesive layers has a storage modulus of 11,000 Pa or more at 180° C.,
The double-sided adhesive tape has a tensile breaking strength of 2 N or more when a tensile test is performed at 23° C. on a sample sliced from the first foamed resin layer, and has a tensile breaking strength of 1 N or more when a tensile test is performed at 80° C. on a sample sliced from the first foamed resin layer, and a tensile breaking strength reduction rate of 70% or less.
A double-sided adhesive tape characterized by: A double-sided pressure-sensitive adhesive tape having a foam substrate and pressure-sensitive adhesive layers laminated on both sides of the foam substrate,
The foam base material has a first foamed resin layer and a second foamed resin layer laminated on at least one surface of the first foamed resin layer and having an expansion ratio lower than that of the first foamed resin layer,
At least one of the pressure-sensitive adhesive layers has a storage modulus of 11,000 Pa or more at 180° C.,
The double-sided adhesive tape has a tensile breaking elongation of 30 mm or more when a tensile test is carried out at 23° C. on a sample sliced from the first foamed resin layer.
A double-sided adhesive tape characterized by: 3. The double-sided pressure-sensitive adhesive tape according to claim 1 , wherein the foam substrate does not have any other layer between the first foamed resin layer and the second foamed resin layer. 4. The double-sided adhesive tape according to claim 1, wherein the strength of the double-sided adhesive tape when stretched 5 mm from the initial gripping jig distance in a tensile test is 1.5 N or more. 5. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the foam substrate has a 25% compressive strength of 200 kPa or less. 6. The double-sided pressure-sensitive adhesive tape according to claim 1, 2, 3, 4 or 5 , wherein the first foamed resin layer is a polyolefin foamed resin layer and has an expansion ratio of 5 cm ³ /g or more and 30 cm ³ /g or less. 7. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the foam substrate has the second foamed resin layer on both sides of the first foamed resin layer. 8. The double-sided pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5 , 6 or 7, wherein at least one of the pressure-sensitive adhesive layers contains an acrylic copolymer having a weight-average molecular weight of 500,000 or more and a gel fraction of 15% by weight or more. 9. The double-sided adhesive tape according to claim 1, wherein the second foamed resin layer is a polyolefin foamed resin layer. 10. The double-sided adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9 , wherein the double-sided adhesive tape has a width of 20 mm or less. 11. The double-sided adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 , wherein the double-sided adhesive tape has a thickness of 100 μm or more and 3000 μm or less.

Images