TWI891908B - Double-sided adhesive tape - Google Patents

Abstract

The present invention aims to provide a double-sided adhesive tape having high gradient tracking properties on both adhesive surfaces, high holding power against shear and tilt loads, and excellent workability on at least one adhesive surface. Furthermore, the double-sided adhesive tape comprises a foam substrate and adhesive layers laminated on both surfaces of the foam substrate. The foam substrate comprises 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. At least one of the adhesive layers has a storage modulus of 11,000 Pa or greater at 180°C.

Description

Double-sided adhesive tape

The present invention relates to a double-sided adhesive tape having high step-following properties on both adhesive surfaces and exhibiting high holding force against shear and tilt loads. At least one adhesive surface has excellent workability, and further, excellent operability during attachment.

Adhesive tape is widely used to secure electronic components. Specifically, in display devices like televisions and monitors, adhesive tape is used to secure the cover panel to the housing. This adhesive tape is placed around the display screen in a shape such as a frame.

In recent years, the pursuit of design and functionality has led to a trend toward narrower bezels on display devices such as televisions and monitors, and expectations for borderless displays have also grown. In previous display manufacturing processes, covers were sometimes secured to the housing by inserting or screwing. However, these methods are becoming increasingly difficult with narrower bezels. Consequently, the demand for adhesive tape for securing these features has grown, and these tapes are becoming increasingly thinner and narrower.

As adhesive tapes that can be used in such display devices, for example, Patent Documents 1 and 2 disclose shock-absorbing tapes 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 with a specific degree of crosslinking and cell aspect ratio. Because the foam base material has appropriate flexibility and can mitigate stress, using a foam base material as the base material for the adhesive tape offers advantages such as improved step tracking, enhanced shock resistance, and reduced display unevenness in the display device. Prior Art Patent Document

Patent Document 1: Japanese Patent Application Publication No. 2009-242541 Patent Document 2: Japanese Patent Application Publication No. 2009-258274

[The problem that the invention aims to solve]

However, as display devices such as televisions and monitors become larger, the weight of the fixed components, such as covers and housings, has also increased. Consequently, adhesive tapes, especially those that have become thinner and narrower, are subject to significantly greater loads than before. In particular, they are subject to very large loads in the shear direction, requiring the tape to have a high holding force against shear loads. Furthermore, applications such as wall-mounted televisions are increasingly seeing displays tilted forward, for example, by 20 to 45 degrees relative to the vertical, requiring the tape to have a high holding force against tilted loads.

Furthermore, electronic components have become increasingly expensive in recent years, leading to a need for reworkability in situations such as when fixing a component. One method for rework involves using a cutting blade to tear the foam backing of the adhesive tape, breaking the interlayer structure to remove the component, and then peeling off any remaining adhesive tape. In this case, the adhesive tape must exhibit excellent reworkability, allowing it to be peeled off without leaving residue (e.g., residual foam backing from a fracture) on the component.

The present invention aims to provide a double-sided adhesive tape having high gradient tracking properties on both adhesive surfaces, exhibiting high holding power against shear and tilt loads, and having excellent workability on at least one adhesive surface. Furthermore, the tape also exhibits excellent operability during application. [Technical Solution]

The double-sided adhesive tape of the present invention comprises a foam substrate and adhesive layers laminated on both sides of the foam substrate. The foam substrate comprises 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. At least one of the adhesive layers has a storage modulus of 11,000 Pa or greater at 180°C. The present invention is described in detail below.

To improve the holding power against shear and tilt loads and enhance the workability of at least one adhesive surface, the inventors of this invention have developed a double-sided adhesive tape comprising a foam substrate and adhesive layers laminated on both sides of the foam substrate. The invention utilizes a multilayer substrate reinforced with a laminated resin layer on at least one side of the foam resin layer as the foam substrate. However, if the resin layer on one or both sides is too hard, the gradient tracking ability of the laminated side with the resin layer is reduced, making it prone to delamination. In recent years, there have been increasing cases where the adhesive tape partially overlaps with the polarizing plate in the display device, or partially overlaps with the guide formed on the casing to display the attachment point of the adhesive tape. Even if a thin and narrow adhesive tape is used, it is required to fully follow the steps of such polarizing plates, guides, etc. On the other hand, when both sides of the resin layer are made too soft to improve step followability (for example, when a styrene-acrylic block copolymer is used for the resin layer on both sides), the problem of insufficient holding power against shear load and tilt load may arise, and the adhesive tape may stretch during application, resulting in poor operability.

To address these issues, the inventors have developed a method in which the resin layer stacked on the foamed resin layer (the central foamed resin layer) also uses a foamed resin layer (the outermost layer), and the foaming ratio of the outermost layer is adjusted to be lower than that of the central foamed resin layer. The inventors have discovered that by using this multi-layer substrate as the foam substrate, it is possible to achieve both adhesive surfaces' step-following properties, as well as shear and tilt load retention, and reworkability on at least one adhesive surface, while also achieving excellent workability. The inventors further discovered that by adjusting the storage modulus of at least one adhesive layer at 180°C to a specific range, the holding force against shear loads and tilt loads can be further improved, thereby completing the present invention.

The double-sided adhesive tape of the present invention comprises a foam substrate and adhesive layers laminated on both sides of the foam substrate. The foam substrate improves the tape's gradient tracking properties and exhibits excellent stress-relieving properties.

The foam substrate comprises 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, deformation stress in the first foamed resin layer caused by shear loads or oblique loads is mitigated, making it less likely to be transmitted to the adhesive layer, thereby suppressing delamination of the adhesive layer. Furthermore, by laminating the second foamed resin layer onto the first foamed resin layer, the double-sided adhesive tape of the present invention can be peeled and removed during rework without leaving residue (e.g., a portion of the first foamed resin layer remaining due to a break) on the adherend on the side laminated with the second foamed resin layer, thereby exhibiting excellent reworkability. Furthermore, when an excessively hard resin layer is laminated on the first foamed resin layer, the step-adjustability of the side with the resin layer laminated thereon is reduced. In contrast, in the double-sided adhesive tape of the present invention, the step-adjustability of both adhesive surfaces can be suppressed by laminating the second foamed resin layer on the first foamed resin layer. On the other hand, when excessively soft resin layers are laminated on both sides of the first foamed resin layer to improve gradient tracking (for example, when a styrene-acrylic block copolymer is used as the resin layer on both sides), sufficient holding power against shear and tilt loads may be insufficient, resulting in poor workability during application. In contrast, the double-sided adhesive tape of the present invention, by laminating the second foamed resin layer on the first foamed resin layer, exhibits high holding power against shear and tilt loads, resulting in excellent workability during application.

The foam substrate may have the second foam resin layer on only one side of the first foam resin layer, or may have the second foam resin layer on both sides of the first foam resin layer. In particular, having the second foam resin layer on both sides of the first foam resin layer is preferred, as it further improves the double-sided adhesive tape's holding power against shear and tilt loads and provides excellent workability on both adhesive surfaces. In this case, the resin composition, physical properties, and thickness of the second foam resin layers on both sides may be the same or different. Adhesive tapes are typically provided in a rolled form and are drawn from the roll for use. Furthermore, if an overly hard resin layer is laminated on both sides of the first foamed resin layer, wrinkles or bends may occur when the core diameter exceeds a certain size. In contrast, the double-sided adhesive tape of the present invention, by laminating the second foamed resin layer on the first foamed resin layer, maintains the overall flexibility of the tape even when the second foamed resin layer is laminated on both sides. This makes it easier to roll the tape, significantly improving its usability and preventing wrinkles or bends during rolling.

In addition to the first foaming resin layer and the second foaming resin layer, the foam substrate may have other layers such as an adhesive layer. However, from the perspective of preventing the complication of the manufacturing process, it is preferred that there is no other layer between the first foaming resin layer and the second foaming resin layer.

Figure 3 is a cross-sectional view schematically illustrating an example of a double-sided adhesive tape according to the present invention. The double-sided adhesive tape 7 shown in Figure 3 comprises a foam substrate 8 and adhesive layers 91 and 92 laminated on both sides of the foam substrate 8. The foam substrate 8 comprises a first foam resin layer 10 and second foam resin layers 11 and 12 laminated on both sides of the first foam resin layer 10. Furthermore, in the double-sided adhesive tape shown in Figure 3, the second foam resin layers are laminated on both sides of the first foam resin layer, but the present invention is not limited to this embodiment.

The first foamed resin layer may have either a continuous or independent cell structure, but preferably has an independent cell structure. Having an independent cell structure increases the strength of the first foamed resin layer, thereby suppressing deformation and interlayer damage when subjected to shear and tilt loads, further enhancing the double-sided adhesive tape's ability to retain shear and tilt loads.

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 may include, for example, a polyurethane foamed resin layer, a polyolefin foamed resin layer, a rubber foamed resin layer, or an acrylic foamed resin layer. Of these, polyurethane foamed resin layers or polyolefin foamed resin layers are preferred, with polyolefin foamed resin layers being more preferred, due to their excellent stress-relieving properties and strength.

The polyurethane foam resin layer is not particularly limited. For example, a polyurethane foam resin layer composed of an urethane resin composition containing polyisocyanate and polyol can be exemplified. Such a polyurethane foam resin layer can be produced by heating the urethane resin composition to harden it.

The polyolefin foamed resin layer is not particularly limited. Examples include those composed of resins such as polyethylene resins, polypropylene resins, and polybutadiene resins. Polyolefin foamed resins are particularly preferred, as they provide a soft and flexible polyolefin foamed resin layer. The polyethylene resin is not particularly limited. Examples include those polymerized using polymerization catalysts such as Ziegler-Natta compounds, metallocene compounds, and chromium oxide compounds. Furthermore, to enhance the softness of the first foamed resin layer, the polyethylene resin is preferably linear low-density polyethylene. The linear low-density polyethylene is preferably a linear low-density polyethylene copolymerized with ethylene and, if necessary, a small amount of an α-olefin. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. α-olefins having 4 to 10 carbon atoms are preferred.

The expansion ratio of the first foamed resin layer is not particularly limited, as long as it is higher than that of the second foamed resin layer. When the first foamed resin layer is a polyolefin foamed resin layer, the expansion ratio of the first foamed resin layer preferably has a lower limit of 5 ^cm³ /g and an upper limit of 30 ^cm³ /g. A foaming ratio of 5 ^cm³ /g or greater provides the first foamed resin layer with adequate flexibility, further improving the gradient conformability and stress relaxation properties of the two adhesive surfaces of the double-sided adhesive tape. If the expansion ratio is 30 ^cm³ /g or less, the strength of the first foamed resin layer is sufficiently increased, further enhancing the double-sided adhesive tape's ability to hold shear and tilt loads. The lower limit of the expansion ratio is preferably 8 ^cm³ /g, the upper limit is more preferably 25 ^cm³ /g, the lower limit is more preferably 10 ^cm³ /g, the upper limit is more preferably 20 ^cm³ /g, and the upper limit is more preferably 18 ^cm³ /g. Furthermore, the expansion ratio can be calculated according to JIS K 7222 (when polyethylene is used). Furthermore, the expansion ratio can be calculated as the inverse of the apparent density.

The thickness of the first foamed resin layer is not particularly limited, with a preferred lower limit of 100 μm and an upper limit of 2000 μm. A thickness of 100 μm or greater provides the first foamed resin layer with adequate flexibility, further improving the gradient-following and stress-relieving properties of the double-sided adhesive tape's two adhesive surfaces. A thickness of 2000 μm or less suppresses deformation of the first foamed resin layer under shear and tilt loads, further enhancing the tape's ability to withstand these loads. The lower limit of the aforementioned thickness is more preferably 300 μm, the upper limit is more preferably 1500 μm, the lower limit is even more preferably 500 μm, and the upper limit is even more preferably 1000 μm. Alternatively, the thickness of the foamed resin layer can be measured using a needle-disc thickness gauge (e.g., the "ABS Digimatic Indicator" manufactured by Mitutoyo Corporation of Japan).

The second foamed resin layer is not particularly limited as long as it has a lower expansion ratio than the first foamed resin layer. It may have the same cell structure, layer structure, resin composition, and physical properties as the first foamed resin layer, or it may have a different cell structure, layer structure, resin composition, and physical properties from the first foamed resin layer. The second foamed resin layer may have either a continuous cell structure or an independent cell structure, but preferably has an independent cell structure. The independent cell structure increases the strength of the second foamed resin layer. Therefore, during rework, the double-sided adhesive tape can be peeled off with less residue (e.g., portions of the first foamed resin layer remaining due to fracture) on the adherend layered with the second foamed resin layer, resulting in superior 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 may include, for example, a polyurethane foamed resin layer, a polyolefin foamed resin layer, a rubber foamed resin layer, or an acrylic foamed resin layer. Of these, polyurethane foamed resin layers or polyolefin foamed resin layers are preferred, with polyolefin foamed resin layers being more preferred, due to their excellent stress-relieving properties and strength. The polyurethane foamed resin layer is not particularly limited and may be the same as the polyurethane foamed resin layer in the first foamed resin layer. The polyolefin foamed resin layer is not particularly limited and may be the same as the polyolefin foamed resin layer in the first foamed resin layer.

The expansion ratio of the second foamed resin layer is not particularly limited, provided it is lower than that of the first foamed resin layer. A preferred lower limit is 1.1 ^cm³ /g, and a preferred upper limit is 7 ^cm³ /g. If the expansion ratio is 1.1 ^cm³ /g or higher, the second foamed resin layer will possess suitable flexibility, further improving the gradient conformability and stress relief properties of the double-sided adhesive tape's two adhesive surfaces. If the expansion ratio is 7 ^cm³ /g or lower, the second foamed resin layer will have sufficient strength, further enhancing the tape's ability to hold shear and tilt loads, and further improving ease of application. The lower limit of the expansion ratio is more preferably 1.3 cm ³ /g, the upper limit is more preferably 5 cm ³ /g, the lower limit is further preferably 1.4 cm ³ /g, the upper limit is further preferably 2 cm ³ /g, the lower limit is further preferably 1.5 cm ³ /g, and the upper limit is further preferably 1.9 cm ³ /g.

The thickness of the second foamed resin layer is not particularly limited, but the lower limit is preferably 5 μm and the upper limit is preferably 100 μm. A thickness of 5 μm or greater further enhances the double-sided adhesive tape's holding power against shear and tilt loads. A thickness of 100 μm or less further enhances the tape's gradient tracking and stress relief properties on both adhesive surfaces. The lower limit of the thickness is more preferably 10 μm, the upper limit is more preferably 80 μm, the lower limit is further preferably 30 μm, and the upper limit is further preferably 60 μm.

The 25% compressive strength of the foam substrate (the entire foam substrate) is not particularly limited, but the lower limit is preferably 1 kPa and the upper limit is preferably 200 kPa. If the 25% compressive strength is 1 kPa or greater, the strength of the foam substrate is sufficiently increased, further improving the double-sided adhesive tape's ability to hold shear and tilt loads. If the 25% compressive strength is 200 kPa or less, the foam substrate has appropriate flexibility, further improving the gradient tracking and stress relaxation properties of the two adhesive surfaces of the double-sided adhesive tape. The lower limit of the 25% compressive strength is more preferably 10 kPa, the upper limit is more preferably 100 kPa, the lower limit is further preferably 20 kPa, and the upper limit is further preferably 40 kPa. The 25% compressive strength of the foam substrate (the entire foam substrate) can be adjusted to fall within the above range by, for example, adjusting the expansion ratio of the first foamed resin layer. Also, the 25% compressive strength can be determined by measuring in accordance with JIS K 6254:2016 using, for example, the "Automatic Stereograph AGS-X" manufactured by Shimadzu Corporation, using the following method. The foam substrate is cut into 20 mm x 20 mm pieces and stacked to form a sample approximately 5 mm x 20 mm x 20 mm thick. The sample was compressed at a speed of 10 mm/min in the compression direction, and the pressure (N) at 25% compression was determined. The 25% compression strength was calculated from the obtained pressure using the following formula (2). Furthermore, when the thickness of the sample was set to 100 and the sample was compressed by 25% (the thickness of the sample became 75), it was defined as 25% compression. Compression strength (kPa) = Pressure (N) / 0.4   (2)

The thickness of the foam substrate (the entire foam substrate) is not particularly limited, but the lower limit is preferably 105 μm and the upper limit is preferably 2100 μm. Within this range, the double-sided adhesive tape further improves its holding power against shear and oblique loads, and further enhances the gradient tracking and stress relief properties of the two adhesive surfaces. The lower limit of the thickness is more preferably 310 μm, the upper limit is more preferably 1580 μm, the lower limit is further preferably 530 μm, and the upper limit is further preferably 1060 μm.

In the foam substrate, the ratio of the thickness of the first foamed resin layer to the thickness of the second foamed resin layer (the value of the thickness of the first foamed resin layer / the thickness of the second foamed resin layer) is not particularly limited, but the lower limit is preferably 1.0 and the upper limit is preferably 400. When the thickness ratio is within the above range, the double-sided adhesive tape further improves its holding power against shear loads and oblique loads, and the step-adjusting properties and stress relief properties of the two adhesive surfaces are also further improved. The lower limit of the thickness ratio is more preferably 3, the upper limit is more preferably 150, the lower limit is further preferably 5, and the upper limit is further preferably 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 the lower limit is preferably 1.3, and the upper limit is preferably 100. When the expansion ratio ratio is within this range, the double-sided adhesive tape further improves its holding power against shear loads and oblique loads, and the step-adjusting properties and stress relief properties of the two adhesive surfaces are also further improved. The lower limit of the expansion ratio ratio is more preferably 3, the upper limit is more preferably 50, the lower limit is further preferably 8, and the upper limit is further preferably 20.

The method for producing the foam substrate is not particularly limited. The first and second foam resin layers may be produced separately and then pressed together or bonded together via an adhesive layer. However, a preferred method is to extrude the foam composition forming the first and second foam resin layers in multiple layers. This multi-layer extrusion method allows the first and second foam resin layers to be stacked without the use of an adhesive layer, which is preferred from the perspective of reducing the complexity of the production process.

The method for performing the multi-layer extrusion is not particularly limited. For example, the foamable composition forming the first foamable resin layer and the foamable composition forming the second foamable resin layer are first extruded separately, and then the separately extruded foamable compositions are combined in a molten state in layers within a mold to obtain a laminated sheet composed of multiple foamable compositions. The foamable composition forming the first foamable resin layer and the foamable composition forming the second foamable resin layer are, for example, compositions containing a polyethylene resin and a thermally decomposable foaming agent as described above. The expansion ratio of the resulting foamed resin layer can be adjusted by varying the type and amount of the thermally decomposable foaming agent. Next, at least one surface of the resulting laminate sheet is irradiated with ionizing radiation to crosslink the polyethylene resin. By varying the degree of crosslinking of the polyethylene resin, the expansion ratio of the resulting foamed resin layer can be adjusted. Furthermore, the crosslinked laminate sheet is foamed by heating, etc., thereby obtaining a foam substrate having the first foamed resin layer and the second foamed resin layer. The crosslinked laminate sheet, which is foamed by heating, etc., can be stretched during and/or after foaming.

The adhesive layer is deposited on both sides of the foam substrate. Furthermore, the resin composition, physical properties, thickness, etc. of the adhesive layers on both sides may be the same or different.

The lower limit of the storage modulus at 180°C of at least one of the adhesive layers is 11,000 Pa. Furthermore, in this case, the storage modulus at 180°C of both sides of the adhesive layer may be within this range, or only one side may be within this range. If the storage modulus at 180°C is 11,000 Pa or greater, the bulk strength of the adhesive layer is increased, which can prevent the adhesive layer from peeling when subjected to shear or oblique loads. The lower limit of the storage modulus at 180°C is preferably 13,000 Pa, more preferably 15,000 Pa, and even more preferably 20,000 Pa. The upper limit of the storage modulus at 180°C is not particularly limited, but is preferably 50,000 Pa. If the storage modulus at 180°C is 50,000 Pa or less, interfacial delamination due to a lack of wettability at the interface of the adhesive layer under shear or oblique loads can be suppressed. The upper limit of the storage modulus at 180°C is more preferably 40,000 Pa, and even more preferably 32,000 Pa. The storage modulus of the adhesive layer at 180°C can be adjusted to within the above range by, for example, 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 adhesive layer, adjusting the type and amount of the crosslinker and adhesion-imparting resin contained in the adhesive layer, and adjusting the gel fraction of the adhesive layer. Furthermore, the storage modulus at 180°C can be determined using a viscoelasticity measuring instrument (e.g., the "Rheometrics Dynamic Analyzer RDA-700" manufactured by Rheometrics) under the conditions of a measurement temperature of -40°C to 200°C, a heating rate of 3°C/minute, and a frequency of 10 Hz.

The adhesive layer is not particularly limited, and examples thereof include acrylic adhesives, rubber adhesives, urethane adhesives, and silicone adhesives. However, at least one of the adhesive layers is preferably an acrylic adhesive, given its relative stability to light, heat, and moisture, and its ability to adhere to a variety of adherends (with low adherend selectivity). Specifically, at least one of the adhesive layers preferably contains an acrylic copolymer. In this case, the adhesive layer may contain the acrylic copolymer on both sides or only on one side.

To enhance initial tack and improve low-temperature adhesion, the acrylic copolymer is preferably obtained by copolymerizing a monomer mixture containing butyl acrylate and/or 2-ethylhexyl acrylate. More preferably, the acrylic copolymer is obtained by copolymerizing a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate. The butyl acrylate content in the total monomer mixture is preferably 30% by weight at the lower limit and 80% by weight at the upper limit. By maintaining the butyl acrylate content within this range, both high adhesion and tack can be achieved. The 2-ethylhexyl acrylate content in the total monomer mixture is preferably 10% by weight at the lower limit and 100% by weight at the upper limit, more preferably 30% by weight at the lower limit, more preferably 80% by weight at the upper limit, further preferably 50% by weight at the lower limit, and further preferably 60% by weight at the upper limit. By keeping the 2-ethylhexyl acrylate content within this range, high adhesion can be achieved.

The monomer mixture may optionally contain other copolymerizable monomers in addition to butyl acrylate and 2-ethylhexyl acrylate. Examples of such other copolymerizable monomers include alkyl (meth)acrylates having an alkyl group with 1-3 carbon atoms, alkyl (meth)acrylates having an alkyl group with 13-18 carbon atoms, and functional monomers. Examples of such alkyl (meth)acrylates having an alkyl group with 1-3 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate. Examples of such alkyl (meth)acrylates having an alkyl group with 13-18 carbon atoms include tridecyl methacrylate and stearyl (meth)acrylate. Examples of the functional monomers include hydroxyalkyl (meth)acrylates, glycerol dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, and fumaric acid. Among these, hydroxyalkyl (meth)acrylates and glycerol dimethacrylate are preferred from the perspective of improving the storage modulus and bulk strength of the adhesive layer at 180°C. In other words, the acrylic copolymer preferably contains structural units derived from hydroxyl-containing monomers. The hydroxyalkyl (meth)acrylate is not particularly limited; more specifically, examples include 2-hydroxyethyl (meth)acrylate.

To copolymerize the monomer mixture to obtain the acrylic copolymer, the monomer mixture may be subjected to a free radical reaction in the presence of a polymerization initiator. The free radical reaction of the monomer mixture, i.e., the polymerization method, may be a conventionally known method, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, or bulk polymerization.

The lower limit of the weight-average molecular weight (Mw) of the acrylic copolymer is preferably 500,000. When the weight-average molecular weight of the acrylic copolymer is 500,000 or greater, the storage modulus and bulk strength of the adhesive layer at 180°C are increased, thereby suppressing delamination of the adhesive layer under shear or oblique loads. The lower limit of the weight-average molecular weight is more preferably 600,000, more preferably 800,000, and even more preferably 1,000,000. The upper limit of the weight-average molecular weight of the acrylic copolymer is not particularly limited, but is preferably 2,000,000. When the weight-average molecular weight of the acrylic copolymer is 2,000,000 or less, delamination of the adhesive layer under shear or oblique loads due to a lack of wettability at the interface can be suppressed. The upper limit of the weight-average molecular weight of the acrylic copolymer is more preferably 1.9 million, further preferably 1.8 million, and even more preferably 1.75 million. The weight-average molecular weight (Mw) refers to the weight-average molecular weight in terms of standard polystyrene as measured by GPC (Gel Permeation Chromatography).

The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic copolymer (Mw/Mn) preferably has a lower limit of 1.05 and an upper limit of 5.0. When Mw/Mn is 5.0 or less, the proportion of low-molecular-weight components is suppressed, increasing the storage modulus and bulk strength of the adhesive layer at 180°C, thereby suppressing delamination of the adhesive layer under shear or oblique loads. The upper limit of Mw/Mn is more preferably 4.5, more preferably 4, and even more preferably 3.5.

From the perspective of ensuring that at least one of the adhesive layers exhibits high adhesion, it is preferred that the adhesive layer contain a tackifying resin. Furthermore, in this case, the adhesive layer may contain the tackifying resin on both sides or only on one side. Examples of the tackifying resins include rosin resins, rosin ester resins, hydrogenated rosin resins, terpene resins, terpene phenol resins, benzofuran-indene resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, C9 petroleum resins, and C5-C9 copolymer petroleum resins. These tackifying resins may be used alone or in combination. Among them, rosin-based resins or terpene-based resins are preferred, and hydroxyl-containing rosin-based resins or terpene-based resins are more preferred.

The softening temperature of the adhesion-imparting resin is preferably 70°C (lower limit) and 170°C (upper limit). A softening temperature of 70°C or higher prevents the adhesive layer from becoming excessively soft and reducing its holding power against shear and tilt loads. A softening temperature of 170°C or lower prevents interfacial delamination under shear or tilt loads due to a lack of wettability at the adhesive layer interface. The lower limit of the softening temperature is more preferably 120°C. The softening temperature is the softening temperature measured by the JIS K2207 global method.

The lower limit of the hydroxyl value of the adhesion-imparting resin is preferably 25. By setting the hydroxyl value above this value, interfacial delamination of the adhesive layer due to poor interaction under shear or oblique loads can be suppressed. The lower limit of the hydroxyl value is more preferably 30. The upper limit of the hydroxyl value is not particularly limited. The hydroxyl value can be measured according to JIS K1557 (phthalic anhydride method).

The content of the tackifier resin is not particularly limited, but the lower limit is preferably 10 parts by weight and the upper limit is preferably 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 greater, the adhesive strength of the adhesive layer is enhanced. If the content of the tackifier resin is 40 parts by weight or less, the adhesive layer can be prevented from becoming too hard and thus reducing its adhesive strength.

At least one of the adhesive layers preferably includes a crosslinking agent, forming a crosslinked structure between the main chains of the resin comprising the adhesive layer (e.g., the acrylic copolymer, the adhesion-imparting resin, etc.). Furthermore, in this case, the crosslinking agent may be added to both sides of the adhesive layer, or only to one side. By adjusting the type and amount of the crosslinking agent, the storage modulus and gel fraction of the adhesive layer at 180°C can be easily adjusted. The crosslinking agent is not particularly limited, and examples thereof include isocyanate crosslinkers, aziridine crosslinkers, epoxy crosslinkers, and metal chelate crosslinkers. Isocyanate-based crosslinking agents are preferred. The lower limit of the amount of the crosslinking agent added relative to 100 parts by weight of the acrylic copolymer is preferably 0.01 parts by weight, and the upper limit is preferably 10 parts by weight. The lower limit is more preferably 0.1 parts by weight, and the upper limit is more preferably 3 parts by weight.

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

To impart light-shielding properties, the adhesive layer may contain a coloring material. The coloring material is not particularly limited, and examples thereof include carbon black, aniline black, and titanium oxide. Carbon black is particularly preferred due to its relative low cost and chemical stability.

The adhesive layer may contain inorganic particles, conductive particles, antioxidants, foaming agents, organic fillers, inorganic fillers and other previously known particles and additives as needed.

The lower limit of the gel fraction of at least one of the adhesive layers is preferably 15% by weight. Furthermore, in this case, the gel fraction of both sides of the adhesive layer may be within this range, or only one side may be within this range. If the gel fraction is 15% by weight or greater, the storage modulus and bulk strength of the adhesive layer at 180°C increase, thereby suppressing peeling of the adhesive layer due to shear or oblique loads. The lower limit of the gel fraction is more preferably 30% by weight, and the lower limit is further preferably 40% by weight. There is no particular upper limit to the gel fraction, but the upper limit is preferably 80% by weight. If the gel fraction is 80% by weight or less, it is possible to suppress peeling of the adhesive layer when subjected to a shear load or an oblique load due to the lack of wettability at the interface of the adhesive layer. The upper limit of the gel fraction is preferably 75% by weight, the upper limit is further preferably 70% by weight, and the upper limit is further preferably 65% by weight. Furthermore, the gel fraction of the adhesive layer can be measured by the following method. A double-sided adhesive tape is cut into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece. After the test piece is immersed in ethyl acetate at 23°C for 24 hours, it is taken out of ethyl acetate and dried at 110°C for 1 hour. The weight of the dried test piece is measured, and the gel fraction is calculated using the following formula (1). Furthermore, the test piece used was not coated with a release film for protecting the adhesive layer. Gel fraction (weight %) = 100 × (W ₂ - _{W 0} ) / (W ₁ - _{W 0} ) (1) (W ₀ : weight of the foam substrate; W ₁ : weight of the test piece before immersion; W ₂ : weight of the test piece after immersion and drying)

The thickness of the adhesive layer is not particularly limited. The lower limit of the thickness of the adhesive layer on one side is preferably 20 μm, and the upper limit is preferably 100 μm. If the thickness of the adhesive layer is 20 μm or greater, the adhesive layer will have sufficient adhesion. If the thickness of the adhesive layer is 100 μm or less, the stress-relieving properties of the foam substrate will fully contribute to the stress-relieving properties of the double-sided adhesive tape as a whole. The lower limit of the thickness of the adhesive layer is more preferably 25 μm, the upper limit is more preferably 80 μm, the lower limit is further preferably 30 μm, the upper limit is further preferably 70 μm, the lower limit is further preferably 35 μm, and the upper limit is further preferably 65 μm. Alternatively, you can use a needle-plate thickness gauge (e.g., the "ABS Digimatic Indicator" manufactured by Mitutoyo Corporation of Japan) to measure the thickness of the adhesive layer.

The double-sided adhesive tape of the present invention may contain other layers in addition to the foam substrate and the adhesive layer as needed.

The double-sided adhesive tape of the present invention preferably has a lower limit of strength of 1.5 N when stretched 5 mm from the initial gripping distance during a tensile test. A strength of 1.5 N or greater further enhances the tape's ability to hold shear and tilt loads, and also improves ease of application. The lower limit of this strength is more preferably 1.7 N, and even more preferably 2.2 N. The strength can be adjusted to within this range by, for example, adjusting the expansion ratio of the second foamed resin layer to an appropriate range to increase the strength of the second foamed resin layer. Furthermore, the strength when stretched 5 mm from the initial gripping distance during a tensile test can be measured according to JIS K 7161. Specifically, a double-sided adhesive tape is punched into a matte-bell shape using a punching blade such as the "Stretching Type 3 Dumbbell" manufactured by Kobunsu Keiki Co., Ltd. to produce a test piece. The resulting test piece is then stretched at a rate of 50 mm/min at 25°C and a relative humidity of 50% using a gauge such as the "Autograph AGS-X" manufactured by Shimadzu Corporation. The initial gripper distance is set to 60 mm, and the strength is measured at a 5 mm elongation (at a gripper distance of 65 mm).

The 25% compressive strength of the double-sided adhesive tape of the present invention is not particularly limited, but the lower limit is preferably 20 kPa, and the upper limit is preferably 70 kPa. If the 25% compressive strength is 20 kPa or greater, the double-sided adhesive tape's holding power against shear loads and tilt loads is further improved. If the 25% compressive strength is 70 kPa or less, the tape's gradient tracking and stress relaxation properties are further improved between the two adhesive surfaces. The lower limit of the 25% compressive strength is more preferably 25 kPa, further preferably 27 kPa, and even more preferably 30 kPa. The upper limit of the 25% compressive strength is more preferably 65 kPa, further preferably 60 kPa, and even more preferably 40 kPa. The 25% compressive strength of the double-sided adhesive tape of the present invention can be measured in accordance with JIS K 6254:2016, similar to the 25% compressive strength of the foam substrate.

In the double-sided adhesive tape of the present invention, a sample sliced from the first foamed resin layer preferably has a tensile strength at break of 2 N or greater in a 23°C tensile test. A tensile strength of 2 N or greater allows the double-sided adhesive tape to exhibit superior workability at room temperature. The tensile strength at break is more preferably 3 N or greater, and even more preferably 4 N or greater. The upper limit of the tensile strength at break is not particularly limited; however, from the perspectives of gradient tracking and stress relaxation, the upper limit is preferably 20 N, and even more preferably 15 N.

In the double-sided adhesive tape of the present invention, the tensile elongation at break of a sample sliced from the first foamed resin layer in a 23°C tensile test is preferably 30 mm or greater. A tensile elongation at break of 30 mm or greater allows the double-sided adhesive tape to exhibit superior workability at room temperature. The tensile elongation at break is more preferably 50 mm or greater, and even more preferably 70 mm or greater. The upper limit of the tensile elongation at break is not particularly limited; however, from the perspective of demonstrating holding power against shear loads and tilt loads, the upper limit is preferably 200 mm.

The following method was used to perform a 23°C tensile test on samples obtained by slicing the first foamed resin layer. Double-sided adhesive tape was cut into matte #3 slices (5 mm center width). The first foamed resin layer (center portion) was sliced using a feather blade. This yielded a sample consisting of "adhesive layer/second foamed resin layer/first foamed resin layer (approximately half the thickness)." Tensile testing was performed on each sample using a Shimadzu Autograph AGS-X at a temperature of 23°C, a gripper distance of 45 mm, and a tensile speed of 100 mm/min. The tensile strength at break was determined as the strength at break, and the elongation at break was determined as the elongation at break.

In the double-sided adhesive tape of the present invention, a sample sliced from the first foamed resin layer preferably exhibits a tensile strength at break of 1 N or greater in a tensile test at 80°C. A tensile strength of 1 N or greater allows the double-sided adhesive tape to exhibit superior workability at high temperatures. The tensile strength at break is more preferably 1.5 N or greater. The upper limit of the tensile strength at break is not particularly limited; however, from the perspectives of gradient tracking and stress relaxation, the upper limit is preferably 10 N.

In the double-sided adhesive tape of the present invention, the reduction in tensile strength at break of a sample sliced from the first foamed resin layer in an 80°C tensile test is preferably 70% or less. A reduction in tensile strength at break of 70% or less allows the double-sided adhesive tape to exhibit superior workability at high temperatures. The reduction in tensile strength at break is more preferably 60% or less. The lower limit of the reduction in tensile strength at break is not particularly limited; a lower value is preferred, with a practical lower limit being approximately 10%.

The 80°C tensile test method for samples sliced from the first foamed resin layer is as follows. The double-sided adhesive tape was cut into 5 mm strips, and the first foamed resin layer (center portion) was sliced with a feather blade. This yielded a sample consisting of "adhesive layer/second foamed resin layer/first foamed resin layer (approximately half the thickness)." Tensile tests were conducted on each sample using a Shimadzu Autograph AGS-X at 80°C, a gripper gap of 10 mm, and a tensile speed of 100 mm/min. After the sample was set at a gripper gap of 10 mm, it was placed in an 80°C environment for 5 minutes before the measurement began. The strength at which the sample breaks is taken as the tensile fracture strength. Furthermore, the tensile fracture strength reduction rate is calculated as 1 - (tensile fracture strength at 80°C / tensile fracture strength at 23°C).

The thickness of the double-sided adhesive tape of the present invention is not particularly limited, and the lower limit is preferably 100 μm, and the upper limit is preferably 3000 μm. If the thickness is 100 μm or more, the double-sided adhesive tape has sufficient adhesion and also has sufficient stress relief. If the thickness is 3000 μm or less, the double-sided adhesive tape can be fully used for connection and fixation, and its two adhesive surfaces also have sufficient step tracking properties. The lower limit of the thickness is more preferably 250 μm, the upper limit is more preferably 1600 μm, the lower limit is further preferably 350 μm, the upper limit is further preferably 1500 μm, the lower limit is further preferably 500 μm, and the upper limit is further preferably 1300 μm.

The following method can be used to produce the double-sided adhesive tape of the present invention. First, a solvent is added to an acrylic copolymer, an adhesive imparting agent, a crosslinking agent, etc. to prepare an adhesive A solution. This adhesive A solution is applied to the release-treated surface of a release film and dried to remove the solvent, thereby forming an adhesive layer. The adhesive layer is then applied to the surface of a foam substrate using pressure using a rubber roller or the like. Similarly, the adhesive layer is applied to the other side of the foam substrate, resulting in a double-sided adhesive tape having adhesive layers on both sides of the foam substrate and a release film covering the adhesive layer surface.

The double-sided adhesive tape of the present invention has no particular application limitations. For example, it can be used to secure components in electronic devices. Examples of such electronic devices include televisions, monitors, portable electronic devices, and in-vehicle electronic devices. The double-sided adhesive tape of the present invention is particularly suitable for securing components in display devices such as televisions and monitors, particularly those in relatively large display devices. Specifically, it can be used to secure the surface cover of such display devices to the housing. Because the double-sided adhesive tape of the present invention exhibits high holding force against shear and tilt loads, it is also suitable for securing components in relatively large display devices using a narrow double-sided adhesive tape. The double-sided adhesive tape of the present invention can have a narrow width, and its width is not particularly limited. The lower limit is preferably 0.5 mm, the upper limit is preferably 20 mm, the lower limit is more preferably 1 mm, and the upper limit is more preferably 5 mm. In these applications, the shape of the double-sided adhesive tape of the present invention is not particularly limited, and can be rectangular, frame-shaped, circular, elliptical, or ring-shaped. Furthermore, the double-sided adhesive tape of the present invention can also be used for vehicle interior components and interior and exterior components of home appliances (e.g., televisions, monitors, air conditioners, refrigerators, etc.). [Effects of the Invention]

According to the present invention, a double-sided adhesive tape can be provided, wherein both adhesive surfaces have high step tracking properties, can exhibit high holding force against shear loads and tilt loads, at least one adhesive surface has excellent workability, and further, also has excellent operability during attachment.

The following examples will be given to further illustrate the 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, stirrer, and cooling tube, 159 parts by weight of ethyl acetate, 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 added as solvents. After nitrogen purge, the reactor was placed in a water bath set at 60°C, heated, and refluxed. 30 minutes after the start of reflux, 0.050 parts by weight of azobisisobutyronitrile was added as a polymerization initiator and the reaction was allowed to proceed for 6 hours. Ethyl acetate was then added to the reactor for dilution while cooling the reaction to obtain a solution of Acrylic Copolymer A. The resulting solution of acrylic copolymer A was diluted 50-fold with tetrahydrofuran (THF) and filtered through a filter (material: polytetrafluoroethylene; pore size: 0.2 μm). The filtrate was fed to a gel permeation chromatography (GPC) instrument (Waters, 2690 Separations Model) for GPC analysis at a sample flow rate of 1 ml/min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of acrylic copolymer A was measured to determine the weight-average molecular weight (Mw). The weight-average molecular weight (Mw) was 1.4 million. A GPC KF-806L (Showa Denko K.K.) column was used, 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 for 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 resulting Acrylic Copolymer B was 800,000.

(Preparation of Acrylic Copolymer C) A solution of Acrylic Copolymer C was obtained in the same manner as for Preparation of Acrylic Copolymer A, except that the polymerization initiator was replaced with 0.04 parts by weight of azobisisobutyronitrile. The weight-average molecular weight of the resulting Acrylic Copolymer C was 1.6 million.

(Preparation of Acrylic Copolymer D) A solution of Acrylic Copolymer D was obtained in the same manner as for Acrylic Copolymer A, except that the amount of acrylic acid added was changed to 3 parts by weight. The weight-average molecular weight of the resulting Acrylic Copolymer D was 1.4 million.

(Preparation of Acrylic Copolymer E) In a reactor equipped with a thermometer, stirrer, and cooling tube, 50 parts by weight of ethyl acetate was added as a solvent. After nitrogen substitution, the reactor was heated and refluxed. After boiling the ethyl acetate for 30 minutes, 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 uniformly and slowly added dropwise over 1 hour and 30 minutes to allow the reaction to proceed. 30 minutes after the addition was complete, 0.15 parts by weight of azobisisobutyronitrile was added, and the polymerization reaction was allowed to proceed for another 5 hours. Ethyl acetate was added to the reactor for dilution and cooling to obtain 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) Styrene-acrylic block copolymer A having the properties and composition shown in Table 1 was prepared.

[Table 1] Styrene-acrylic block copolymer A Weight average molecular weight k (Mw) Hard segment ratio (weight %) Weight average molecular weight k of hard chain segment (Mw) Weight average molecular weight k of the soft chain segment (Mw) Triblock ratio (wt%) Phase separation structure Gel fraction (weight %) Hard segment composition (weight %) Soft chain composition (weight %) Styrene (St) Acrylic acid (Aac) Hydroxyethyl acrylate (HEA) Butyl acrylate (BA) Methyl acrylate (MA) 338 20 68 270 70 spherical 65 84 13 3 50 50

(Example 1) (1) A foam substrate is prepared by using 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-tert-butyl-p-cresol as an antioxidant as a foaming composition for forming the first foaming resin layer (center foaming resin layer). The second foaming resin layer (outermost layer) was formed using a foaming composition consisting of 100 parts by weight of a polyethylene resin (UBE Polyethylene F420), 1.1 parts by weight of azodicarbonamide as a thermally decomposable foaming agent, 1 part by weight of zinc oxide as a decomposition temperature regulator, and 0.5 parts by weight of 2,6-di-tert-butyl-p-cresol as an antioxidant. UBE Polyethylene F420 refers to "UBE Polyethylene F420" manufactured by Ube Maruzen Polyethylene Co., Ltd. (density: 0.920 g/ ^cm³ ). The foamable composition forming the first foaming resin layer (center foaming resin layer) and the foamable composition forming the second foaming resin layer (outermost layer) are fed to an extruder for multi-layer extrusion molding and melt-kneaded at 130°C. After melt-kneading, a long sheet of foam raw material with a thickness of approximately 1.0 mm is extruded. The sheet has layers of the foamable composition forming the second foaming resin layer (outermost layer) on both sides of the layer of the foamable composition forming the first foaming resin layer (center foaming resin layer). Next, both sides of the long foam sheet were irradiated with an electron beam at an accelerating voltage of 500 kV at a 4.0 Mrad to crosslink the long foam sheet. The crosslinked foam sheet was then continuously fed into a foaming furnace maintained at 250°C using hot air and infrared heaters, where it was heated and foamed. The foam was then stretched at a stretch ratio of 3.5 times in the MD and 3.5 times in the TD. This produced a foam substrate comprising a first foam resin layer (center foam resin layer) with second foam resin layers (outermost layer)-1 and (outermost layer)-2 laminated on either side. The thickness of each foaming resin layer and its expansion ratio according to JIS K 7222, as well as the thickness of the foam substrate and its 25% compressive strength according to JIS K 6254:2016, were measured. The results are shown in Table 2.

(2) Preparation 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 (PENSEL D-135 manufactured by Arakawa Chemical Industries, Ltd., softening point 135°C, hydroxyl value 45) and 15 parts by weight of terpene phenol resin (YS POLYSTER G150 manufactured by Yasuhara Chemicals, softening point 150°C, hydroxyl value 135) were added. Furthermore, 30 parts by weight of ethyl acetate (manufactured by Fuji Chemical Co., Ltd.) and 1.3 parts by weight of an isocyanate crosslinking agent (manufactured by Japan Polyurethane Co., Ltd., trade name "Coronate L45") were added as solid content, and the mixture was stirred to obtain an adhesive solution. Prepare a 75 μm thick release film. Apply an adhesive solution to the release-treated surface of the film and dry at 110°C for 5 minutes to form a 50 μm thick adhesive layer. This adhesive layer is then applied to the surface of the foam substrate obtained above. Next, apply the same adhesive layer to the other surface of the foam substrate after removing the PET separator. Then, heat at 40°C for 48 hours to cure. This results in a double-sided adhesive tape covered with a release film.

(3) Determination of gel fraction: Cut the double-sided adhesive tape into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece. After soaking the test piece in ethyl acetate at 23°C for 24 hours, remove it from ethyl acetate and dry it at 110°C for 1 hour. Measure the weight of the dried test piece and calculate the gel fraction using the following formula (1). In addition, the test piece does not contain a release film for protecting the adhesive layer. Gel fraction (weight %) = 100 × (W ₂ - W ₀ ) / (W ₁ - _{W 0} ) (1) (W ₀ : weight of the foam substrate; W ₁ : weight of the test piece before soaking; W ₂ : weight of the test piece after soaking and drying)

(4) Determination of the storage modulus at 180°C Using a viscoelasticity tester (Rheometrics Dynamic Analyzer RDA-700, manufactured by Rheometrics), the storage modulus of the adhesive layer at 180°C was determined under the following conditions: a temperature range of -40°C to 200°C, a heating rate of 3°C/min, and a frequency of 10 Hz.

(5) Determination of the strength at 5 mm elongation from the initial gripping distance (tensile test) According to JIS K 7161, the strength at 5 mm elongation from the initial gripping distance was measured as follows. Using a punching blade "Stretching No. 3 Dumbbell" manufactured by Kobunsu Keiki Co., Ltd., the double-sided adhesive tape was punched into a dumbbell shape to prepare a test piece. Using "Autograph AGS-X" manufactured by Shimadzu Corporation, the obtained test piece was stretched at a tensile speed of 50 mm/min at 25°C and a relative humidity of 50%. At this time, the initial gripping distance was set to 60 mm, and the strength at 5 mm elongation (gripping distance of 65 mm) was read.

(6) Determination of 25% compressive strength The 25% compressive strength of the double-sided adhesive tape was also determined in accordance with JIS K 6254:2016 in the same manner as for the determination of the 25% compressive strength of the foam substrate.

(7) 23℃ tensile test The double-sided adhesive tape was cut into the size of Dumbbell No. 3 (center width 5 mm), and the first foam resin layer (center part) was sliced with a feather blade. In this way, the samples were divided into adhesive layer/second foam resin layer (outermost layer)-1/first foam resin layer (about half the thickness) (referred to as "second foam resin layer (outermost layer)-1 side sample") and first foam resin layer (about half the thickness)/second foam resin layer (outermost layer)-2/adhesive layer sample (referred to as "second foam resin layer (outermost layer)-2 side sample"). Tensile tests were conducted on each sample using a Shimadzu Autograph AGS-X at a temperature of 23°C, a gripper distance of 45 mm, and a tensile speed of 100 mm/min. The tensile strength at fracture was determined as the strength, and the elongation at fracture was determined as the elongation.

(8) 80℃ tensile test The double-sided adhesive tape was cut into 5 mm strips and the first foamed resin layer (center part) was sliced with a feather blade. In this way, the samples were divided into adhesive layer/second foamed resin layer (outermost layer)-1/first foamed resin layer (about half the thickness) (referred to as "second foamed resin layer (outermost layer)-1 side sample") and first foamed resin layer (about half the thickness)/second foamed resin layer (outermost layer)-2/adhesive layer sample (referred to as "second foamed resin layer (outermost layer)-2 side sample"). Tensile tests were conducted on each sample using a Shimadzu Autograph AGS-X at 80°C, a gripper distance of 10 mm, and a tensile speed of 100 mm/min. The sample was placed at a gripper distance of 10 mm and then placed in an 80°C environment for 5 minutes before measurement. The tensile strength at break was determined as the strength at break. Furthermore, the tensile strength reduction rate was calculated as 1 - (tensile strength at break at 80°C / tensile strength at break at 23°C).

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

(Examples 7-10) Double-sided adhesive tapes were obtained in the same manner as in Example 1, except that the adhesive layer was modified as shown in Table 2. Furthermore, in Example 6, acrylic copolymer B was used, and the crosslinking agent was used at a level of 1.9 parts by weight based on the solid content. In Example 7, acrylic copolymer C was used, and the crosslinking agent was used at a level of 1.1 parts by weight based on the solid content. In Examples 8 and 9, acrylic copolymer D was used, but the crosslinking agent was used at a level of 1.4 parts by weight based on the solid content in Example 8 and 1.1 parts by weight based on the solid content in Example 9, thereby varying the gel fraction.

(Comparative Example 1) In "(1) Preparation of Foam Base Material", the foaming composition for forming the second foaming resin layer (outermost layer) was not used, and only the foaming composition for forming the first foaming resin layer (center foaming resin layer) was used. A polyethylene terephthalate (PET) sheet and a styrene-acrylic acid copolymer sheet were laminated on both sides of the obtained first foaming resin layer (center foaming resin layer), respectively. A double-sided adhesive tape was obtained in the same manner as in Example 1 except that

Specifically, in "(1) Preparation of the foam substrate", first, only the first foaming resin layer (center foaming resin layer) is formed. Then, an adhesive solution containing acrylic copolymer A is applied to the surface of a polyethylene terephthalate (PET) sheet (manufactured by Toray Industries, Ltd., X30) having a thickness of 50 μm, and dried at 110°C for 5 minutes to form an adhesive layer having a thickness of 20 μm. The first foaming resin layer (center foaming resin layer) obtained is laminated on the adhesive layer to obtain a laminate consisting of polyethylene terephthalate (PET) sheet/adhesive layer/first foaming resin layer (center foaming resin layer). Furthermore, a crosslinking agent (5 parts by weight per 100 parts by weight) was added to an ethyl acetate solution of styrene-acrylic block copolymer A. The solution was then coated onto a 50 μm thick polyethylene terephthalate (PET) sheet that had been subjected to a release treatment. The resulting film was dried to obtain a 40 μm thick uncrosslinked resin film. The crosslinking agent used was "Coronate L45," manufactured by Japan Polyurethane Co., Ltd. A non-crosslinked resin film was laminated on the first foamed resin layer (center foamed resin layer) side of a laminate composed of a polyethylene terephthalate (PET) sheet/adhesive layer/first foamed resin layer (center foamed resin layer), thereby obtaining a laminate composed of a polyethylene terephthalate (PET) sheet/adhesive layer/first foamed resin layer (center foamed resin layer)/non-crosslinked resin film. Next, the uncrosslinked resin film was heated at 40°C for 48 hours to thermally crosslink it, thereby obtaining a foam substrate composed of a polyethylene terephthalate (PET) sheet/adhesive layer/first foaming resin layer (center foaming resin layer)/styrene-acrylic copolymer sheet.

(Comparative Example 2) In "(1) Preparation of Foam Base Material", a double-sided adhesive tape was obtained in the same manner as in Example 1 except that the foaming composition for forming the second foaming resin layer (outermost layer) was not used, and only the foaming composition for forming the first foaming resin layer (center foaming resin layer) was used. Styrene-acrylic copolymer sheets were laminated on both sides of the obtained first foaming resin layer (center foaming resin layer).

Specifically, in "(1) Preparation of the foam substrate", first, only the first foaming resin layer (center foaming resin layer) is formed. Then, 5 parts by weight of a crosslinking agent is mixed with 100 parts by weight of the styrene-acrylic acid block copolymer A in an ethyl acetate solution, and the mixture is coated on a 50 μm thick polyethylene terephthalate (PET) sheet with a surface release treatment, and dried to obtain a 40 μm thick uncrosslinked resin film. As a crosslinking agent, "Coronate L45" manufactured by Japan Polyurethane Co., Ltd. is used. An uncrosslinked resin film is laminated onto the first foamed resin layer (center foamed resin layer) to obtain a laminate consisting of uncrosslinked resin film/first foamed resin layer (center foamed resin layer). Next, the uncrosslinked resin film is thermally crosslinked by heating at 40°C for 48 hours, thereby obtaining a laminate consisting of styrene-acrylic copolymer sheet/first foamed resin layer (center foamed resin layer). Furthermore, an uncrosslinked resin film prepared in the same manner was laminated onto the first foamed resin layer (center foamed resin layer) side of a laminate consisting of a styrene-acrylic copolymer sheet/first foamed resin layer (center foamed resin layer), resulting in a laminate consisting of a styrene-acrylic copolymer sheet/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, resulting in a foam substrate consisting of a styrene-acrylic copolymer sheet/first foamed resin layer (center foamed resin layer)/styrene-acrylic copolymer sheet.

(Comparative Example 3) In "(1) Preparation of Foam Base Material", a double-sided adhesive tape was obtained in the same manner as in Example 1 except that the foaming composition for forming the second foaming resin layer (outermost layer) was not used, and only the foaming composition for forming the first foaming resin layer (center foaming resin layer) was used. Polyethylene (PE) sheets were laminated on both sides of the obtained first foaming resin layer (center foaming resin layer).

Specifically, in "(1) Preparation of the Foam Base Material," first, only the first foaming resin layer (center foaming resin layer) is formed. A release film having a thickness of 75 μm is prepared, and an adhesive solution containing acrylic copolymer A is applied to the release-treated surface of the release film, followed by drying at 110°C for 5 minutes to form an adhesive layer having a thickness of 6 μm. Next, the adhesive layer is bonded to the surface of a low-density polyethylene (PE) sheet having a thickness of 40 μm, thereby obtaining a laminate consisting of an adhesive layer/low-density polyethylene (PE) sheet. The adhesive layer release film is peeled off from the laminate consisting of an adhesive layer/low-density polyethylene (PE) sheet, and the laminate is then laminated to the first foamed resin layer (center foamed resin layer). Next, the adhesive layer/low-density polyethylene (PE) sheet is laminated to the other surface of the first foamed resin layer (center foamed resin layer) in the same manner. The laminate is then heated at 40°C for 48 hours to cure. This results in a foam substrate consisting of polyethylene (PE) sheet/adhesive layer/first foamed resin layer (center foamed resin layer)/adhesive layer/polyethylene (PE) sheet.

(Comparative Example 4) In "(1) Preparation of Foam Base Material", a double-sided adhesive tape was obtained in the same manner as in Example 2 except that the foaming composition for forming the second foaming resin layer (outermost layer) was not used, and only the foaming composition for forming the first foaming resin layer (center foaming resin layer) was used. A polyethylene terephthalate (PET) sheet was layered on one area of the obtained first foaming resin layer (center foaming resin layer).

Specifically, in "(1) Preparation of a foam substrate", first, only the first foaming resin layer (center foaming resin layer) is formed. Then, an adhesive solution containing acrylic copolymer A is applied to the surface of a polyethylene terephthalate (PET) sheet (manufactured by Toray Industries, Ltd., X30) having a thickness of 50 μm, and dried at 110°C for 5 minutes to form an adhesive layer having a thickness of 20 μm. The first foaming resin layer (center foaming resin layer) obtained is laminated on the adhesive layer to obtain a foam substrate consisting of polyethylene terephthalate (PET) sheet/adhesive layer/first foaming resin layer (center foaming resin layer).

(Comparative Example 5) In "(1) Preparation of Foam Base Material", a double-sided adhesive tape was obtained in the same manner as in Example 2 except that the foaming composition for forming the second foaming resin layer (outermost layer) was not used and only the foaming composition for forming the first foaming resin layer (center foaming resin layer) was used.

(Comparative Examples 6-8) Double-sided adhesive tapes were obtained in the same manner as in Example 1, except that the adhesive layer was modified as shown in Table 3. Furthermore, in Comparative Example 6, acrylic copolymer E was used, but the amount of crosslinking agent was adjusted to 2.5 parts by weight based on the solid content, thereby varying the gel fraction. Similar to Examples 8 and 9, in Comparative Example 7, acrylic copolymer D was used, but the amount of crosslinking agent was adjusted to 0.7 parts by weight based on the solid content, thereby varying the gel fraction.

(Comparative Example 9) In "(1) Preparation of Foam Base Material", the foaming composition for forming the second foaming resin layer (outermost layer) was not used, and only the foaming composition for forming the first foaming resin layer (center foaming resin layer) was used. Acrylic copolymer sheets were laminated on both sides of the obtained first foaming resin layer (center foaming resin layer), and a double-sided adhesive tape was obtained in the same manner as in Example 1 except that the acrylic copolymer sheets were laminated on both sides of the obtained first foaming resin layer (center foaming resin layer).

Specifically, in "(1) Preparation of the foam substrate", first, only the first foaming resin layer (center foaming resin layer) is formed. Next, 100 parts by weight of ethyl acetate is added to 45 parts by weight of LA2270 manufactured by Kuraray Co., Ltd. and stirred to obtain a solution. The obtained solution is 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 resin film with a thickness of 40 μm. The exposed surface of the resin film is bonded to one side of the first foaming resin layer (center foaming resin layer). A 40 μm thick resin film was again prepared using the same procedure as above. The exposed surface of the resin film was bonded to the other side of the first foaming resin layer (center foaming 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 tracking performance A single-sided adhesive tape (125 mm × 20 mm, 300 μm thick) was attached to a glass plate (125 mm × 50 mm, 1.5 mm thick) to create a step height of 300 μm. A double-sided adhesive tape was cut into 25 mm × 50 mm pieces, and one side was lined with a 23 μm thick polyethylene terephthalate (PET) sheet. The other side of the double-sided adhesive tape was attached to the stepped surface of the glass plate, and a 2 kg rubber roller was moved back and forth once from the side of the glass plate to perform press bonding. The distance of air penetrating the stepped portion was measured and evaluated according to the following criteria. A: Air penetration distance less than 700 μm B: Air penetration distance 700 μm or more and less than 800 μm C: Air penetration distance 800 μm or more and less than 900 μm D: Air penetration distance 900 μm or more and less than 1000 μm E: Air penetration distance 1000 μm or more

(2) Evaluation of holding power (2-1) 45° tilt holding power test Figure 1 is a schematic diagram showing the 45° tilt holding power test of a double-sided adhesive tape. The obtained double-sided adhesive tape 18 was cut into 25 mm × 25 mm pieces. The adhesive layer on the second side of the second foamed resin layer (outermost layer) was attached to a glass plate 17. A 2 kg rubber roller was moved back and forth once on the double-sided adhesive tape 18 at a speed of 300 mm/min. Next, the adhesive layer on the -1 side of the second foam resin layer (outermost layer) of double-sided adhesive tape 18 was attached to a SUS plate 16. A 5 kg weight was applied from the side of the SUS plate 16 for 10 seconds. The plate was then placed in an environment at 23°C and 50% relative humidity for 24 hours to create a test sample. For this test sample, a 1 kg weight 15 was attached to the center of the SUS plate 16 at 60°C and 90% relative humidity to apply a load to the double-sided adhesive tape 18 and the plate 16. The plate was tilted at 45°. The time it took for the weight 15 to fall (fall time) was measured and evaluated according to the following criteria. ○: The falling time is 250 hours or more △: The falling time is 50 hours or more but less than 250 hours ×: The falling time is less than 50 hours

(2-2) Shear Holding Strength Test Figure 2 is a schematic diagram illustrating the shear holding strength test of a double-sided adhesive tape. Figure 2(a) is a front view, and Figure 2(b) is a side view. As shown in Figures 2(a) and (b), the adhesive layer on the second side (outermost layer) of the second foamed resin layer of the double-sided adhesive tape 3 is lined with a PET film (#50) 4. The adhesive layer on the first side (outermost layer) of the second foamed resin layer of the double-sided adhesive tape 3 is attached to SUS plates 1 and 2, producing a test sample with a 25 mm × 25 mm attachment area between the SUS plates 1 and the double-sided adhesive tape 3. The test sample was prepared as follows. First, prepare SUS plate 1 (2 mm × 50 mm × 70 mm thick, SUS304 steel plate specified in JIS-G-4305, surface evenly polished with 360 grit sandpaper) and SUS plate 2 (1 mm × 30 mm × 50 mm thick, unpolished). Wash SUS plates 1 and 2 with ethanol and allow them to dry thoroughly. Cut double-sided adhesive tape 3 into a 25 mm wide × 140 mm long sheet. Peel off the release film from one side and attach PET film (#50) 4 to the exposed adhesive layer. Next, peel off the release film from the other side and attach the exposed adhesive layer's edge to SUS plate 1, preventing air bubbles from forming. Press-bond the tape using a 2 kg rubber roller moving back and forth at a speed of 10 mm/second. At this point, the double-sided adhesive tape 3 is attached to the SUS plate 1 so that it overlaps by 30 mm. The end of the adhesive layer opposite the end attached to the SUS plate 1 is then attached to the SUS plate 2. A 2 kg rubber roller is used to reciprocate once at a speed of 10 mm/second for pressure bonding. The double-sided adhesive tape 3 is positioned to cover both the front and back surfaces of the SUS plate 2. Through holes 5 are then formed in the double-sided adhesive tape 3 and the SUS plate 2. The double-sided adhesive tape 3 is then cut so that the area between the SUS plate 1 and the double-sided adhesive tape 3 is 25 mm x 25 mm. After placing the test sample prepared as described above in a constant temperature chamber at 50°C and 80% RH for 24 hours, a 2 kg weight 6 was attached to the through-hole 5 in the same environment. Displacement after 200 hours was measured and evaluated according to the following criteria. The shear holding strength of the adhesive layer on the second side of the second foam resin layer (outermost layer) of the double-sided adhesive tape 3 was also evaluated in the same manner. ○: Displacement less than 2 mm after 200 hours △: Displacement of 2 mm or more but less than 10 mm after 200 hours X: Displacement of 10 mm or more after 200 hours

(3) Evaluation of 23°C and 80°C Reworkability Double-sided adhesive tape was cut into 5 mm × 100 mm pieces and one side was attached to a glass plate. The other side of the double-sided adhesive tape was also attached to the glass plate to produce a glass plate/double-sided adhesive tape/glass plate laminate. The laminate was pressed together with a 5 kg weight for 10 seconds. The first foamed resin layer (center portion) of the laminate was sliced with a feather blade. This resulted in samples consisting of glass plate/adhesive layer/second foamed resin layer (outermost layer)-1/first foamed resin layer (approximately half the thickness) (referred to as "second foamed resin layer (outermost layer)-1 sample") and first foamed resin layer (approximately half the thickness)/second foamed resin layer (outermost layer)-2/adhesive layer/glass plate (referred to as "second foamed resin layer (outermost layer)-2 sample"). To evaluate reworkability at 23°C, each sample was stored at 23°C for four days, and then the double-sided adhesive tape was manually and quickly peeled off the glass plate. To evaluate reworkability at 80°C, each sample was placed at 80°C for one day, then removed and immediately and quickly peeled from the glass plate with the double-sided adhesive tape. ◎: No adhesive residue, the double-sided adhesive tape was not broken, and the glass plate was reworkable. ○: Adhesive residue was present, but the double-sided adhesive tape was not broken, and the glass plate was reworkable. ×: The double-sided adhesive tape was broken, and the glass plate could not be reworked.

Based on the evaluation results of the samples on the second foamed resin layer (outermost layer) -1 side and the samples on the second foamed resin layer (outermost layer) -2 side, comprehensive evaluations of heavy-duty properties were conducted for both 23°C and 80°C, respectively, according to the following standards. ◎: The evaluation results for 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 for 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 0. △: At least one of the evaluation results for 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 0. ×: The evaluation results for the sample on the second foamed resin layer (outermost layer) - side 1 and the sample on the second foamed resin layer (outermost layer) - side 2 were both ×.

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

(5) Evaluation of the presence of bends The obtained double-sided adhesive tape was cut into a size of 100 mm × 300 mm and wound around a paper core with a diameter of 3 inches with the second foam resin layer (outermost layer) -2 side as the inner side to obtain a roll. After pulling the double-sided adhesive tape out of the obtained roll, visually observe and evaluate according to the following criteria. ○: No bends were observed. ×: Bending was observed.

[Table 2] Unit Embodiment 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Foam substrate First foam resin layer (center foam resin layer) Resin type - PE PE PE PE PE PE PE PE PE PE PE PE PE PE thickness μm 680 800 800 800 680 680 680 680 680 680 800 740 170 1600 Foaming ratio cm ³ /g 15 8 30 15 15 15 15 15 15 15 8 20 6 20 2nd foam resin layer (outermost layer) -1 Resin type - PE PE PE PE PE PE PE PE PE PE without PE PE PE thickness μm 50 50 50 50 50 50 50 50 50 50 25 25 25 Foaming ratio cm ³ /g 1.7 1.7 1.7 5 1.3 1.5 1.7 1.7 1.7 1.7 1.7 1.7 1.7 Second foam resin layer (outermost layer) -2 Resin type - PE PE PE PE PE PE PE PE PE PE PE PE PE PE thickness μm 50 50 50 50 50 50 50 50 50 50 50 25 25 25 Foaming ratio cm ³ /g 1.7 1.7 1.7 5 1.3 1.5 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 Adhesive layer thickness μm - - - - - - - - - - - - - - Thickness of foam substrate μm 780 900 900 900 780 780 780 780 780 780 850 790 220 1650 25% compressive strength of foam substrate kPa 33 61 28 31 35 34 32 33 33 33 33 33 33 33 Adhesive layer Types of acrylic copolymers - A A A A A A B C D D A A A A Weight average molecular weight of acrylic copolymer ten thousand 140 140 140 140 140 140 80 160 140 140 140 140 140 140 thickness μm 50 50 50 50 50 50 50 50 50 50 50 50 50 50 Gel fraction weight% 50% 50% 50% 50% 50% 50% 50% 50% 50% 20% 50% 50% 50% 50% Storage modulus at 180℃ Pa 29250 29250 29250 29250 29250 29250 13910 31390 27630 14510 29250 29250 29250 29250 Thickness of double-sided adhesive tape μm 880 1000 1000 1000 880 880 880 880 880 880 950 890 320 1750 Strength when the gripper is extended by 5 mm from the initial gripping distance N 2.44 3.15 2.44 1.55 4.00 4.00 2.54 2.50 2.48 2.44 2.82 1.82 1.52 2.11 25% compression strength kPa 39 60 28 36 38 37 39 39 39 39 62 28 30 27 Second foam resin layer (outermost layer) - sample on side 1 Tensile breaking strength (23℃) N 8.3 9.2 4.0 3.8 10.5 9.7 9.0 9.5 9.3 9.1 Unable to determine 5.2 4.8 5.9 Tensile elongation at break (23°C) mm 118 168 151 146 182 170 158 162 157 168 Unable to determine 78 86 92 Tensile breaking strength (80℃) N 3.5 4.8 2.0 1.6 4.7 4.7 4.8 5.2 4.9 4.7 Unable to determine 2.6 2.1 2.6 Tensile breaking strength reduction rate - 58% 48% 50% 58% 55% 52% 47% 45% 47% 48% - 50% 56% 56% Second foam resin layer (outermost layer) - sample on side 2 Tensile breaking strength (23℃) N 8.3 9.2 4.0 3.8 10.5 9.7 9.0 9.5 9.3 9.1 9.2 5.2 4.8 5.9 Tensile elongation at break (23°C) mm 118 168 151 146 182 170 158 162 157 168 168 78 86 92 Tensile breaking strength (80℃) N 3.5 4.8 2.0 1.6 4.7 4.7 4.8 5.2 4.9 4.7 4.8 2.6 2.1 2.6 Tensile breaking strength reduction rate - 58% 48% 50% 58% 55% 52% 47% 45% 47% 48% 48% 50% 56% 56% [Table 3] Unit Comparative example 1 2 3 4 5 6 7 8 9 Foam substrate First foam resin layer (center foam resin layer) Resin type - PE PE PE PE PE PE PE PE PE thickness μm 680 680 680 800 800 680 680 600 680 Foaming ratio cm ³ /g 15 15 15 8 8 15 15 1.7 15 2nd foam resin layer (outermost layer) -1 Resin type - Styrene acrylic (non-foamed) Styrene acrylic (non-foamed) PE (non-foamed) without without PE PE PE Acrylic (non-foamed) thickness μm 40 40 40 50 50 100 40 Foaming ratio cm ³ /g - - - 1.7 1.7 15 - Second foam resin layer (outermost layer) -2 Resin type - PET (non-foamed) Styrene acrylic (non-foamed) PE (non-foamed) PET (non-foamed) without PE PE PE Acrylic (non-foamed) thickness μm 50 40 40 50 50 50 100 40 Foaming ratio cm ³ /g - - - - 1.7 1.7 15 - Adhesive layer thickness μm 20 - 12 20 - - - - 20 Thickness of foam substrate μm 790 760 772 870 800 780 780 780 780 25% compressive strength of foam substrate kPa 40 37 25 60 58 33 33 100＜ 40 Adhesive layer Types of acrylic copolymers - A A A A A E D A A Weight average molecular weight of acrylic copolymer ten thousand 140 140 140 140 140 40 140 140 140 thickness μm 50 50 50 50 50 50 50 50 50 Gel fraction weight% 50% 50% 50% 50% 50% 50% 10% 50% 50% Storage modulus at 180℃ Pa 29250 29250 29250 29250 29250 10820 10280 29250 29250 Thickness of double-sided adhesive tape μm 870 860 860 950 900 880 880 900 860 Strength when the gripper is extended by 5 mm from the initial gripping distance N 33.20 1.30 4.26 33.06 2.64 2.43 2.51 12.30 1.10 25% compression strength kPa 44 42 44 63 59 40 39 100＜ 41 Second foam resin layer (outermost layer) - sample on side 1 Tensile breaking strength (23℃) N 6.4 6.8 6.2 Unable to determine Unable to determine 8.3 8.3 Unable to determine 3.3 Tensile elongation at break (23°C) mm 46 45 133 Unable to determine Unable to determine 118 118 Unable to determine 135.4 Tensile breaking strength (80℃) N 0.9 1.1 3.3 Unable to determine Unable to determine 3.5 3.5 Unable to determine 0.5 Tensile breaking strength reduction rate - 85% 84% 47% - - 57% 58% - 85% Second foam resin layer (outermost layer) - sample on side 2 Tensile breaking strength (23℃) N 47.9 6.8 6.2 6.2 Unable to determine 8.3 8.3 Unable to determine 3.3 Tensile elongation at break (23°C) mm 27 45 133 133 Unable to determine 118 118 Unable to determine 135.4 Tensile breaking strength (80℃) N 46.5 1.1 3.3 3.3 Unable to determine 3.5 3.5 Unable to determine 0.5 Tensile breaking strength reduction rate - 3% 84% 47% 47% - 57% 58% - 85%

[Table 4] Unit Embodiment 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Reviews class following 2nd foam resin layer (outermost layer) -1 μm 720 744 705 745 851 809 718 714 713 727 662 620 719 601 determination B B B B C C B B B B A A B A 2nd foam resin layer (outermost layer) -2 μm 716 766 694 763 877 806 714 721 716 725 766 632 692 688 determination B B A B C C B B B B B A A A Retention 45° tilt holding force hr 500↑ 500↑ 500↑ 500↑ 500↑ 500↑ 100 500↑ 500↑ 200 200 500↑ 500↑ 500↑ determination ○ ○ ○ ○ ○ ○ △ ○ ○ △ △ ○ ○ ○ 2 kg shear holding force (displacement after 200 hours) 2nd foam resin layer (outermost layer) -1 mm Below 1 Below 1 Below 1 Below 1 Below 1 Below 1 2.5 Below 1 Below 1 2.5 Below 1 Below 1 Below 1 Below 1 determination ○ ○ ○ ○ ○ ○ △ ○ ○ △ ○ ○ ○ ○ Second foam resin layer (outermost layer) -2 mm Below 1 Below 1 Below 1 Below 1 Below 1 Below 1 2.5 Below 1 Below 1 2.5 Below 1 Below 1 Below 1 Below 1 determination ○ ○ ○ ○ ○ ○ △ ○ ○ △ ○ ○ ○ ○ 23℃ Heavy duty Second foam resin layer (outermost layer) - sample on side 1 result ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ × ◎ ◎ ◎ Second foam resin layer (outermost layer) - sample on side 2 result ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Comprehensive evaluation determination ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ◎ ◎ ◎ 80℃ heavy duty Second foam resin layer (outermost layer) - sample on side 1 result ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ × ◎ ◎ ◎ Second foam resin layer (outermost layer) - sample on side 2 result ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Comprehensive evaluation determination ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ◎ ◎ ◎ Operability Elongation when a 3 mm width is stretched at 1 N for 10 seconds mm 4.02 3.07 7.925 6.23 1.93 2.05 1.93 4.3 4.52 3.99 3.78 5.11 7.63 2.53 determination ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Whether there is any bend determination ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

[Table 5] Unit Comparative example 1 2 3 4 5 6 7 8 9 Reviews class following 2nd foam resin layer (outermost layer) -1 μm 653 587 929 650 631 720 722 1162 562 determination A A D A A B B E A 2nd foam resin layer (outermost layer) -2 μm 1615 643 965 1703 640 714 718 1263 582 determination E A D E A B B E A Retention 45° tilt holding force hr 500↑ 24↓ 500↑ 240 24↓ 24↓ 24↓ 24↓ 24↓ determination ○ × ○ △ × × × × × 2 kg shear holding force (displacement after 200 hours) 2nd foam resin layer (outermost layer) -1 mm 2.5 2.5 Below 1 Below 1 Below 1 25 25 25 3 determination △ △ ○ ○ ○ × × × △ 2nd foam resin layer (outermost layer) -2 mm Below 1 2.5 Below 1 Below 1 Below 1 25 25 25 3 determination ○ △ ○ ○ ○ × × × △ 23℃ Heavy duty Second foam resin layer (outermost layer) - sample on side 1 result ○ ○ ◎ × × ◎ ◎ × ○ Second foam resin layer (outermost layer) - sample on side 2 result ○ ○ ◎ ○ × ◎ ◎ × ○ Comprehensive evaluation determination ○ ○ ◎ △ × ◎ ◎ × ○ 80℃ heavy duty Second foam resin layer (outermost layer) - sample on side 1 result × × ◎ × × ◎ ◎ × × Second foam resin layer (outermost layer) - sample on side 2 result ○ ○ ◎ ○ × ◎ ◎ × ○ Comprehensive evaluation determination △ △ ◎ △ × ◎ ◎ × △ Operability Elongation when a 3 mm width is stretched at 1 N for 10 seconds mm 0.135 15.95 1.705 0.155 3.565 4.55 4.01 0.81 17.62 determination ○ × ○ ○ ○ ○ ○ ○ × Whether there is any bend determination ○ ○ × ○ ○ ○ ○ ○ ○ [Industrial Availability]

According to the present invention, a double-sided adhesive tape can be provided, wherein the two adhesive surfaces have high step tracking properties and can exhibit high holding force against shear loads and tilt loads. At least one adhesive surface has excellent workability, and further, the workability during attachment is also excellent.

1, 2: SUS board 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 foaming resin layer 11, 12: Second foaming resin layer 15: Weight (1 kg) 16: SUS board 17: Glass board 18: Double-sided adhesive tape

Figure 1 is a schematic diagram showing a 45° tilt holding strength test for a double-sided adhesive tape. Figure 2 is a schematic diagram showing a shear holding strength test for a double-sided adhesive tape. Figure 3 is a schematic cross-sectional view of an example of the double-sided adhesive tape of the present invention.

7: Double-sided adhesive tape

8: Foam substrate

10: 1st foam resin layer

11,12: Second foam resin layer

91,92: Adhesive layer

Claims (12)

A double-sided adhesive tape comprising a foam substrate and adhesive layers laminated on both sides of the foam substrate. The double-sided adhesive tape is characterized in that the foam substrate comprises 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; at least one of the adhesive layers has a storage modulus of 11,000 Pa or greater at 180°C; and at least one of the adhesive layers has a gel fraction of 65% by weight or less. The double-sided adhesive tape of claim 1, wherein the foam substrate has no other layer between the first foamed resin layer and the second foamed resin layer. The double-sided adhesive tape of claim 1 or 2, wherein, in a tensile test, the strength of the double-sided adhesive tape when extended 5 mm from an initial gripping clamp distance is 1.5 N or greater. The double-sided adhesive tape of claim 1 or 2, wherein the 25% compressive strength of the foam substrate is 200 kPa or less. The double-sided adhesive tape of claim 1 or 2, wherein a sample obtained by slicing the first foamed resin layer has a tensile strength at break of 2 N or greater when subjected to a tensile test at 23°C, and a sample obtained by slicing the first foamed resin layer has a tensile strength at break of 1 N or greater when subjected to a tensile test at 80°C, and the reduction rate of the tensile strength at break is 70% or less. The double-sided adhesive tape of claim 1 or 2, wherein a sample obtained by slicing the first foamed resin layer exhibits a tensile elongation at break of 30 mm or greater when subjected to a tensile test at 23°C. The double-sided adhesive tape of claim 1 or 2, wherein the first foamed resin layer is a polyolefin foamed resin layer and has a foaming ratio of 5 cm ³ /g to 30 cm ³ /g. The double-sided adhesive tape of claim 1 or 2, wherein the foam substrate has the second foam resin layer on both sides of the first foam resin layer. The double-sided adhesive tape of claim 1 or 2, wherein at least one of the adhesive layers contains an acrylic copolymer having a weight average molecular weight of 500,000 or greater and a gel fraction of 15% by weight or greater. The double-sided adhesive tape of claim 1 or 2, wherein the second foamed resin layer is a polyolefin foamed resin layer. For double-sided adhesive tapes as specified in claim 1 or 2, the width shall be less than 20 mm. The double-sided adhesive tape of claim 1 or 2, wherein the thickness is not less than 100 μm and not more than 3000 μm.