KR102876613B1 - double-sided adhesive tape - Google Patents

Abstract

The present invention aims to provide a double-sided adhesive tape having excellent drop impact resistance, which can reduce display unevenness of a display device, and which can easily tear a foam substrate when peeling from an adherend. The present invention is a double-sided adhesive tape having a foam substrate and an adhesive layer laminated on both sides of the foam substrate, wherein the foam substrate has a bubble volume fraction of 40 vol% or more and 75 vol% or less, and a shear breaking strength of 200 N/inch ² or more and 500 N/inch ² or less.

Description

double-sided adhesive tape

The present invention relates to a double-sided adhesive tape.

Adhesive tapes are widely used to secure electronic components. Specifically, adhesive tapes are used to secure the surface cover panels of display devices such as televisions and monitors to the casing. Such adhesive tapes are often placed around the display screen in shapes such as a liquid crystal display.

In recent years, the pursuit of design and functionality has led to a trend toward narrower frame sizes for display devices such as televisions and monitors, leading to rising expectations for bezel-less displays. Conventional display device manufacturing often involved attaching cover panels to the casing by inserting or screwing. However, with display devices with narrower frame sizes, inserting or screwing is becoming more difficult. Consequently, demand for adhesive tape fixation is growing, and adhesive tapes are becoming thinner and narrower.

As an adhesive tape that can be used in such a display device, for example, Patent Documents 1 and 2 describe a shock-absorbing tape in which an acrylic adhesive layer is laminated and integrally formed on at least one side of a substrate layer, and the substrate layer is a crosslinked polyolefin resin foam sheet having a specific degree of crosslinking and an aspect ratio of bubbles.

Japanese Patent Publication No. 2009-242541 Japanese Patent Publication No. 2009-258274

However, display devices such as televisions and monitors are becoming larger, and the weight of fixed components such as cover panels and casings is also increasing. Consequently, adhesive tapes are subjected to significantly greater shear loads than before. This has led to problems, particularly when using thin, narrow adhesive tapes, where impacts such as from drops during transportation can cause interlayer destruction of the substrate or peeling of the adhesive tape.

Furthermore, with the increase in size, display devices are more prone to display unevenness. To reduce display unevenness, adhesive tapes, especially the adhesive tape substrate, must have appropriate flexibility to release stress. Furthermore, as electronic components have recently become more expensive, the ability to rework components in cases such as when a problem occurs during component fixation is required. One method for reworking components is to tear the foam substrate of the adhesive tape with a cutter blade, thereby destroying the layers and separating the components. Even in such cases, the substrate must not be excessively hard and must have appropriate flexibility.

Here, to withstand impacts such as drops during transportation, the substrate's strength needs to be increased. Furthermore, to reduce display unevenness and facilitate tearing, the substrate's flexibility needs to be increased. However, because substrate strength and flexibility are conflicting properties, achieving both is difficult.

The purpose of the present invention is to provide a double-sided adhesive tape having excellent drop impact resistance, capable of reducing display unevenness of a display device, and capable of easily tearing a foam substrate when peeling from an adherend.

The present invention is a double-sided adhesive tape having a foam substrate and an adhesive layer laminated on both sides of the foam substrate, wherein the foam substrate has a bubble volume fraction of 40% by volume or more and 75% by volume or less and a shear breaking strength of 200 N/inch ² or more and 500 N/inch ² or less.

The present invention is described in detail below.

The present inventors have analyzed the cell structure of a foam substrate using an X-ray computed tomography (X-ray CT) device and image analysis software in a double-sided adhesive tape having a foam substrate and adhesive layers laminated on both sides of the foam substrate, and have examined the influence of the cell structure on the performance of the double-sided adhesive tape. As a result, the present inventors have found that by adjusting the cell volume fraction of the foam substrate within a specific range and further adjusting the shear rupture strength of the foam substrate within a specific range, both the strength and flexibility of the foam substrate can be increased. As a result, the present inventors have found that a double-sided adhesive tape having excellent drop impact resistance, being able to reduce display unevenness in a display device, and being able to easily tear the foam substrate when peeling from an adherend can be obtained, and have thus completed the present invention.

The double-sided adhesive tape of the present invention has a foam substrate and adhesive layers laminated on both sides of the foam substrate.

The above foam substrate has appropriate flexibility and can release stress. By including the foam substrate, the stress relaxation properties of the double-sided adhesive tape are improved.

The foam substrate has a lower limit of a bubble volume fraction of 40% by volume and an upper limit of 75% by volume. By adjusting the bubble volume fraction within the above range, both the strength and flexibility of the foam substrate can be increased, thereby achieving both properties simultaneously.

When the bubble volume fraction is 40% by volume or more, the foam substrate can have appropriate flexibility, so that display unevenness of the display device can be reduced, and when the double-sided adhesive tape is peeled from the adherend, the foam substrate can be easily torn. When the bubble volume fraction is 75% by volume or less, the strength of the foam substrate can be suppressed from being excessively reduced, so that the drop impact resistance of the double-sided adhesive tape can be improved. In addition, when the bubble volume fraction is 75% by volume or less, the dustproofing and waterproofing properties of the foam substrate can also be easily secured. The preferable lower limit of the above bubble volume fraction is 42 volume%, the preferable upper limit is 70 volume%, the more preferable lower limit is 46 volume%, the more preferable upper limit is 67 volume%, the further preferable lower limit is 48 volume%, the further preferable upper limit is 63 volume%, the particularly preferable lower limit is 50 volume%, and the particularly preferable upper limit is 60 volume%.

In addition, the bubble volume fraction is calculated by the following equation (1) using an X-ray CT device and image analysis software.

Bubble volume fraction (volume%) = Bubble volume / Volume of foam base material × 100 (1)

In Equation (1), the bubble volume is the sum of the volumes of all bubbles included in the foam substrate of the sample to be measured.

The average and standard deviation of the distribution of the major diameters of the bubbles of the foam substrate are not particularly limited, but the preferred upper limit of the average of the distribution of the major diameters of the bubbles is 55 ㎛, and the preferred upper limit of the standard deviation of the distribution of the major diameters of the bubbles is 30 ㎛.

By adjusting the average and standard deviation of the above-mentioned major diameter distribution to the above-mentioned range and suppressing the bubble size and the bubble size deviation below a certain level, both the strength and flexibility of the foam substrate can be further increased. As a result, the drop impact resistance of the double-sided adhesive tape can be improved, and also, the display unevenness of the display device can be reduced, and the foam substrate can be easily torn when peeling the double-sided adhesive tape from the adherend.

In addition, if the bubbles are excessively large or there is a deviation in the bubble sizes, especially when using a double-sided adhesive tape in a thin and narrow shape, a locally low-strength point will exist in the foam substrate, and when an impact is applied due to a drop during transportation, etc., the interlayer destruction of the foam substrate or peeling of the double-sided adhesive tape will occur starting from the locally low-strength point. By adjusting the average and standard deviation of the major axis distribution within the aforementioned range and suppressing the bubble size and the deviation in the bubble size below a certain level, the locally low-strength point will be suppressed, thereby improving the drop impact resistance of the double-sided adhesive tape.

A more preferable upper limit of the average of the above diameter distribution is 53 ㎛, a more preferable upper limit is 51 ㎛, and an even more preferable upper limit is 49 ㎛. The lower limit of the average of the above diameter distribution is not particularly limited and is determined depending on the cell volume fraction and thickness of the foam base material, but a practical lower limit is 10 ㎛.

A more preferable upper limit of the standard deviation of the above diameter distribution is 28 ㎛, a more preferable upper limit is 27 ㎛, and an even more preferable upper limit is 24 ㎛. The lower limit of the standard deviation of the above diameter distribution is not particularly limited, and is preferable because the smaller it is, the less deviation there is in the bubble size, and the practical lower limit is 5 ㎛.

In addition, the mean and standard deviation of the diameter distribution of the bubbles are obtained by using an X-ray CT device and image analysis software, and the mean and standard deviation are calculated from the obtained diameter distribution.

The expansion ratio of the cells of the above-mentioned foam base material is not particularly limited, but when the above-mentioned foam base material is polyurethane foam, the preferred upper limit of the expansion ratio of the cells is 95% by volume. Generally, polyurethane foams have a foam structure, and the expansion ratio becomes a value close to 100% by volume. Therefore, when the above-mentioned foam base material is polyurethane foam, having a expansion ratio within the above range means that the foam base material has a relatively low expansion ratio and many independent cells among polyurethane foams.

By adjusting the above-mentioned expansion ratio within the above-mentioned range and increasing the number of independent cells, both the strength and flexibility of the polyurethane foam can be further enhanced. As a result, the drop impact resistance of the double-sided adhesive tape can be improved, and also, display unevenness of the display device can be reduced, and the foam substrate can be easily torn when peeling the double-sided adhesive tape from the adherend.

In addition, by adjusting the above-mentioned rate to the above-mentioned range and increasing the number of independent bubbles, the presence of locally particularly low-strength points as described above can be suppressed, thereby improving the drop impact resistance of the double-sided adhesive tape.

A more preferable upper limit of the above-mentioned expansion ratio is 93% by volume, and a more preferable upper limit is 91% by volume. The lower limit of the above-mentioned expansion ratio is not particularly limited, but a general lower limit of the expansion ratio of polyurethane foam is 90% by volume.

In addition, the foaming rate is calculated by the following equation (2) using an X-ray CT device and image analysis software.

Foaming ratio (volume%) = Foaming volume / Foaming volume × 100 (2)

In equation (2), the volume of the communicating bubbles is the sum of the volumes of all communicating bubbles included in the foam substrate of the sample to be measured, and the volume of the bubbles is the sum of the volumes of all bubbles included in the foam substrate of the sample to be measured.

The flatness of the cells of the foam substrate is not particularly limited, but a preferred upper limit is 0.2. By adjusting the flatness within the above range, impact mitigation against drops from all angles can be made more uniform, and the drop impact resistance of the double-sided adhesive tape can be improved.

A more preferable upper limit of the above flatness ratio is 0.18, a more preferable upper limit is 0.16, and an even more preferable upper limit is 0.14. The lower limit of the above flatness ratio is not particularly limited, and as it approaches 0, the bubble becomes closer to a sphere, so that the shock absorption for dropping from all angles becomes more uniform, and thus it is preferable, and the practical lower limit is 0.05.

The aspect ratio of the cells of the foam substrate is not particularly limited, but a preferred upper limit is 1.5. By adjusting the aspect ratio within the above range, impact mitigation against drops from all angles can be made more uniform, and the drop impact resistance of the double-sided adhesive tape can be improved.

The upper limit of the above aspect ratio is more preferable than 1.1, the upper limit is even more preferable than 1.09, and the upper limit is even more preferable than 1.07. The lower limit of the above aspect ratio is not particularly limited, and as it approaches 1, the bubble becomes closer to a circle, and the shock absorption for dropping from all angles becomes more uniform, so it is preferable, and the practical lower limit is 1.01.

In addition, the aspect ratio and flatness of the bubble are calculated by the following equations (3) and (4) using an X-ray CT device and image analysis software.

Aspect ratio = x/y (3)

Flatness = {(x + y)/2 - z} / z (4)

(x = major axis, y = middle axis, z = minor axis, x ≥ y ≥ z)

The above X-ray CT device and the image analysis software are not particularly limited, but analysis using the above X-ray CT device and the image analysis software is performed, more specifically, as follows, for example.

The center of a measurement sample obtained by cutting a foam substrate is imaged using an X-ray CT device (e.g., Yamato Scientific Co., Ltd., “TDM1000H-II (2K)”, resolution approximately 1.5 ㎛/1 pixel), and a rectangular 3D image having a length of 1.5 mm, a width of 1.2 mm, and a height of 0.3 mm is obtained. For the obtained image, noise is removed and binarized using image analysis software (e.g., FEI Co., Ltd., “Avizo9.2.0”), and each value representing the cell structure of the foam substrate (cell volume fraction, average and standard deviation of cell major diameter distribution, cell expansion ratio, cell aspect ratio, cell flatness, etc.) is obtained. As an X-ray source, Mo was used, and the lens (L0270) was used to take pictures under the conditions of binning 2, exposure time 10 seconds, and number of shots 1200.

When analyzing an image, noise is first removed using the Median Filter (Neighborhood value 26) function. Then, binarization is performed using the Interactive Thresholding function. The threshold value is 90 out of 256 gray levels. In the binarized image, whether a bubble is an independent bubble or a connected bubble is determined based on whether or not the continuous portion of the pixel is discontinuous. In addition, when calculating the major diameter, middle diameter, and minor diameter, the bubbles are first divided into each other at the point of contact to obtain the center of gravity of the bubble. Next, a rectangular parallelepiped that has a center of gravity at the same position as the center of gravity and is inscribed in the bubble is set, and the lengths of the three orthogonal sides are designated as the major diameter, middle diameter, and minor diameter, starting from the longer one. In addition, at this time, bubbles with a major diameter of less than 10 ㎛ are excluded.

The method for adjusting each value representing the cell structure of the foam substrate (cell volume fraction, average and standard deviation of cell diameter distribution, cell expansion ratio, cell aspect ratio, cell flatness, etc.) to the above range is not particularly limited.

For example, when the foam base material is polyurethane foam, the types and contents of polyisocyanate and polyol in the urethane resin composition, the conditions for mixing air, nitrogen, etc. into the urethane resin composition, the reaction conditions for heat-curing the urethane resin composition, etc. may be adjusted. Among these, a method of gradually progressing the urethanization reaction by increasing the content of polyisocyanate in the urethane resin composition to increase the fluidity of the resin, thereby generating bubbles of more uniform size and adjusting the bubble structure is preferable.

More specifically, the bubble volume fraction can be adjusted by changing the types and contents of polyisocyanate and polyol in the urethane resin composition, as well as the foaming conditions. Even when the raw materials are the same, the adjustment can be made by changing the conditions when mixing air, nitrogen, etc. into the urethane resin composition, the reaction conditions when heat-curing the urethane resin composition, etc. In addition, the average and standard deviation of the major diameter distribution of the bubbles can be reduced by adjusting the urethane reaction to proceed slowly.

The above foam substrate may have a single-layer structure or a multi-layer structure.

The foam substrate is not particularly limited, and examples thereof include polyurethane foam, polyolefin foam, and acrylic foam. Among these, polyurethane foam is preferred because it has appropriate flexibility and is easy to adjust the cell structure.

As the above polyurethane foam, for example, a polyurethane foam made of a urethane resin composition containing polyisocyanate and polyol can be mentioned. Such a polyurethane foam can be produced by heat-curing the urethane resin composition.

The above polyisocyanate is not particularly limited, and examples thereof include aromatic polyisocyanates or aliphatic polyisocyanates used in general polyurethane foams. Among these, aromatic diisocyanates or aliphatic diisocyanates having two isocyanate groups per molecule are preferred.

Since the polyisocyanate is an aromatic diisocyanate or an aliphatic diisocyanate, the degree of crosslinking of the polyurethane foam is not excessively increased, and the glass transition point (Tg) is relatively low, so that the foam becomes easy to elongate and has high strength and flexibility.

As the above aromatic diisocyanate or aliphatic diisocyanate, specific examples thereof include 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, paraphenylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-xylene diisocyanate, hexamethylene diisocyanate, hydrogenated MDI, isophorone diisocyanate, and the like. In addition, 4,4'-diphenylmethane diisocyanate is also generally called "MDI" or "dinuclear monomeric MDI." Among these, 4,4'-diphenylmethane diisocyanate (MDI) is preferred because it is easy to obtain a polyurethane foam with excellent flexibility. These aromatic diisocyanates or aliphatic diisocyanates may be used alone or in combination of two or more.

The above polyisocyanate may have three or more isocyanate groups per molecule. Examples of such polyisocyanates include polymeric MDI. Furthermore, examples of the above polyisocyanates include urethane prepolymers having isocyanate groups. These polyisocyanates may be used alone, or two or more types may be used in combination.

The above polyol is not particularly limited, and polyols used in general polyurethane foams can be mentioned. Specifically, examples include polyether polyol, polyester polyol, and polyetherester polyol. Furthermore, examples of the above polyol include trifunctional polyether polyol, glycerin, and trimethylolpropane. These polyols may be used alone, or two or more types may be used in combination.

The above polyether polyol is not particularly limited, and examples thereof include polypropylene glycol (PPG). The above polyester polyol is not particularly limited, and a polyester polyol composed of a polyol component and an acid component can be used.

It is preferable that the above polyol contains a short-chain diol.

Since the polyol contains the short-chain diol, the strength of the polyurethane foam increases. Therefore, even when the urethanization reaction is allowed to proceed slowly, for example, by increasing the content of the polyisocyanate in the urethane resin composition to increase the fluidity of the resin and thereby adjust the foam structure by creating more uniformly sized foams, the strength of the polyurethane foam can be prevented from being excessively reduced.

Examples of the short-chain diols include 1,5-pentanediol, 1,6-hexamethylenediol, neopentyl glycol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, neopentyl glycol, and the like. These short-chain diols may be used alone or in combination of two or more. Among them, 1,5-pentanediol or 1,6-hexamethylenediol is preferable because it is easy to obtain a high-strength polyurethane foam. In addition, neopentyl glycol is preferable because it is easy to lower the foaming rate.

The weight average molecular weight of the polyol is not particularly limited, but the preferred lower limit is 500, and the preferred upper limit is 5000. When the weight average molecular weight of the polyol is 500 or more, the polyurethane foam can have appropriate flexibility. When the weight average molecular weight of the polyol is 5000 or less, the strength of the polyurethane foam can be prevented from being excessively reduced. The more preferred lower limit of the weight average molecular weight of the polyol is 700, the more preferred upper limit is 2000, the more preferred lower limit is 800, and the more preferred upper limit is 1500.

In addition, the weight average molecular weight of the polyol can be measured, for example, by preparing a tetrahydrofuran solution of the sample and using a GPC device (e.g., Tosoh Corporation, product name: “HLC-8220,” column: TSKgelSurper HZM-N (4 units)). In the GPC measurement, measurement conditions such as 40°C and a flow rate of 0.5 mL/min can be adopted.

The isocyanate index of the polyisocyanate in the above urethane resin composition is not particularly limited, but the preferred lower limit is 70 and the preferred upper limit is 120.

The isocyanate index is an index relating to the isocyanate equivalent in the reaction between isocyanate and an active hydrogen-containing compound. When the isocyanate index is less than 100, it means that reactive groups such as hydroxyl groups are in excess over isocyanate groups, and when the isocyanate index exceeds 100, it means that isocyanate groups are in excess over reactive groups such as hydroxyl groups.

When the above isocyanate index is 70 or more, crosslinking by the polyisocyanate becomes sufficient, making it easy to adjust the cell structure, so that the polyurethane foam can have an appropriate density, thereby increasing strength and flexibility. When the above isocyanate index is 120 or less, the degree of crosslinking of the polyurethane foam does not become excessively high, and the glass transition point (Tg) becomes relatively low, so that the foam becomes easy to stretch, thereby increasing strength and flexibility.

The content of the polyisocyanate in the urethane resin composition is not particularly limited, but it is preferable to adjust the bubble structure by gradually progressing the urethanization reaction, for example, by increasing the content of the polyisocyanate in the urethane resin composition to increase the fluidity of the resin, thereby generating bubbles of a more uniform size.

The content of the polyisocyanate is preferably a lower limit of 5 wt%, and a higher limit of 30 wt%, relative to 100 wt% of the polyol. When the content of the polyisocyanate is 5 wt% or more, the urethane reaction can proceed more slowly to generate bubbles of a more uniform size, so that the bubble structure can be easily adjusted, and the strength and flexibility of the polyurethane foam are increased. When the content of the polyisocyanate is 30 wt% or less, the degree of crosslinking of the polyurethane foam does not become excessively high, and the glass transition point (Tg) is relatively low, so that the polyurethane foam becomes easy to extensibly expand, and the strength and flexibility are increased. A more preferably lower limit of the content of the polyisocyanate is 15 wt%, and a more preferably upper limit is 25 wt%.

The above urethane resin composition may contain a catalyst, if necessary.

Examples of the catalysts include organotin compounds, organozinc compounds, organonickel compounds, organoiron compounds, metal catalysts, tertiary amine catalysts, and organic acid salts. Among these, organotin compounds are preferred. These catalysts may be used alone or in combination of two or more.

The amount of the catalyst to be added is not particularly limited, but the preferred lower limit is 0.05 parts by weight, the preferred upper limit is 5.0 parts by weight, and the more preferred upper limit is 4.0 parts by weight relative to 100 parts by weight of the polyol.

Examples of the above organotin compounds include stannous octoate, dibutyltin diacetate, dibutyltin dilaurate, etc. Examples of the above organozinc compounds include zinc octylate, etc. Examples of the above organonic nickel compounds include nickel acetylacetate, nickel diacetylacetate, etc. Examples of the above organoiron compounds include iron acetylacetate, etc. Examples of the above metal catalysts include alkoxides and phenoxides of alkali metals such as sodium acetate or alkaline earth metals. Examples of the above tertiary amine catalysts include triethylamine, triethylenediamine, N-methylmorpholinedimethylaminomethylphenol, imidazole, 1,8-diazabicyclo[5.4.0]undecene, etc.

The above urethane resin composition may contain a foaming agent, if necessary.

As the above-mentioned blowing agent, a blowing agent used in general polyurethane foams may be mentioned. Specifically, examples thereof include water, pentane, cyclopentane, hexane, cyclohexane, dichloromethane, carbon dioxide, etc.

The amount of the foaming agent to be added is not particularly limited and may be an appropriate amount. However, when the foaming agent is water, it is usually about 0.1 to 3 parts by weight per 100 parts by weight of the polyol.

The above urethane resin composition may contain a foaming agent, if necessary.

Examples of the above-mentioned foam stabilizers include silicone-based foam stabilizers such as dimethylsiloxane, polyetherdimethylsiloxane, and phenylmethylsiloxane. Among these, polyetherdimethylsiloxane is preferred. Among polyetherdimethylsiloxanes, block copolymers of dimethylpolysiloxane and polyether are more preferred. These foam stabilizers may be used alone or in combination of two or more.

The amount of the above-mentioned stabilizer to be added is not particularly limited, but the preferred lower limit is 0.2 parts by weight, the preferred upper limit is 7 parts by weight, the more preferred lower limit is 0.4 parts by weight, and the more preferred upper limit is 5 parts by weight, relative to 100 parts by weight of the polyol.

The above urethane resin composition may contain, if necessary, additives generally used in the production of polyurethane foam, such as ultraviolet absorbers, antioxidants, organic fillers, inorganic fillers, and colorants.

Examples of methods for producing the above polyurethane foam include a method (mechanical foam method) in which a urethane resin composition (liquid) that has been mechanically mixed with air, nitrogen, or the like to generate bubbles is applied to the surface of a release liner or a resin film, and the applied urethane resin composition is heat-cured to produce a foam. In addition, a method (chemical foaming method) in which a raw material for forming the above polyurethane foam is reacted with the above polyisocyanate to generate gas is also possible. Among these, the mechanical foaming method is preferable. A polyurethane foam obtained by the mechanical foaming method tends to have a high density compared to a polyurethane foam obtained by a chemical foaming method, and further, the cell structure tends to be fine and uniform.

Examples of polyolefin foams include foams made of resins such as polyethylene resins, polypropylene resins, and polybutadiene resins. Among these, polyethylene resins are preferred because they are easy to obtain as flexible polyolefin foams.

The foam substrate has a lower limit of shear rupture strength of 200 N/inch ² and an upper limit of 500 N/inch ² . When the shear rupture strength is 200 N/inch ² or more, the strength of the foam substrate is sufficiently increased, thereby improving the drop impact resistance of the double-sided adhesive tape. When the shear rupture strength is 500 N/inch ² or less, the flexibility of the foam substrate can be prevented from being excessively reduced, thereby reducing display unevenness of the display device, and when peeling the double-sided adhesive tape from the adherend, the foam substrate can be easily torn. The preferred lower limit of the above shear rupture strength is 220 N/inch ² , the preferred upper limit is 470 N/inch ² , the more preferred lower limit is 240 N/inch ² , the more preferred upper limit is 450 N/inch ² , the more preferred lower limit is 270 N/inch ² , the more preferred upper limit is 415 N/inch ² .

Additionally, shear fracture strength can be measured by the following method.

Fig. 1 shows a schematic diagram showing a method for measuring shear breaking strength. First, a test piece (18) of double-sided adhesive tape measuring 25 mm x 25 mm and two SUS plates (19) measuring 125 mm x 50 mm and 2 mm in thickness are laminated as shown in Fig. 1. This laminate is pressed using a press stone under the conditions of 5 kg for 10 seconds, and then left to stand for 24 hours, and a test sample is produced by bonding two SUS plates (19) with the test piece (18) interposed therebetween. After fixing one side of the SUS plate (19) of this test sample, under the condition of 23°C, the upper side of the other side of the SUS plate (19) is pulled at 12.7 mm/min in the direction perpendicular to the stacking direction of the SUS plates (the direction of the arrow in the drawing), and the force (breaking point strength) applied to the test piece (18) when the test piece (18) breaks is measured. In addition, the breaking of the test piece (18) means that the foam base material is destroyed between layers.

The shear rupture strength of the foam substrate can be adjusted by varying the types and contents of polyisocyanate and polyol in the urethane resin composition. Even when the raw materials are the same, the shear rupture strength can be adjusted by setting the cell volume fraction, the average and standard deviation of the cell diameter distribution, etc. within appropriate ranges.

The 25% compressive strength of the above-mentioned foam substrate is not particularly limited, but a preferable lower limit is 0.015 MPa, and a preferable upper limit is 0.08 MPa. When the 25% compressive strength is 0.015 MPa or more, the strength of the foam substrate is sufficiently increased, thereby improving the drop impact resistance of the double-sided adhesive tape. When the 25% compressive strength is 0.08 MPa or less, the flexibility of the foam substrate can be suppressed from being excessively reduced, so that the double-sided adhesive tape can be well pressed, display unevenness of the display device can be reduced, and when the double-sided adhesive tape is peeled from the adherend, the foam substrate can be easily torn. The more preferable lower limit of the above 25% compressive strength is 0.02 MPa, the more preferable upper limit is 0.07 MPa, the more preferable lower limit is 0.025 MPa, the more preferable upper limit is 0.065 MPa, the more preferable lower limit is 0.03 MPa, and the more preferable upper limit is 0.06 MPa.

Additionally, the 25% compressive strength can be obtained by measuring in accordance with JIS K 6254: 2010.

The 25% compressive strength of the above foam substrate can be adjusted by changing the types and contents of polyisocyanate and polyol in the urethane resin composition. Even when the raw materials are the same, the compressive strength can be adjusted by setting the cell volume fraction, the average and standard deviation of the cell diameter distribution, etc. to appropriate ranges.

The glass transition point of the foam substrate is not particularly limited, but a preferred lower limit is -30°C, and a preferred upper limit is 30°C. When the glass transition point of the foam substrate is -30°C or higher, the foam substrate exhibits good low-rebound properties and can relieve stress. When the glass transition point of the foam substrate is 30°C or lower, the foam substrate can have appropriate flexibility, and also becomes a foam that is easy to stretch, thereby increasing strength and flexibility. A more preferred lower limit of the glass transition point of the foam substrate is -25°C, and a more preferred upper limit is 20°C.

In addition, the glass transition point can be obtained using a viscoelasticity measuring device (e.g., Rheometrics Dynamic Analyze RDA-700 manufactured by Rheometrics) under the conditions of a measurement temperature of -30 to 100°C, a heating rate of 3°C/min, and a frequency of 1 Hz.

The thickness of the foam substrate is not particularly limited, but the preferable lower limit is 100 μm, and the preferable upper limit is 1000 μm. When the thickness of the foam substrate is 100 μm or more, the foam substrate can have appropriate flexibility. When the thickness of the foam substrate is 1000 μm or less, the variation in the size of the bubbles can be suppressed, and also, the foam substrate can be suppressed from stretching and breaking due to an impact such as dropping during transportation. The more preferable lower limit of the thickness of the foam substrate is 150 μm, and the more preferable upper limit is 950 μm, the more preferable lower limit is 300 μm, the more preferable upper limit is 750 μm, the more preferable lower limit is 450 μm, and the more preferable upper limit is 700 μm.

Additionally, the thickness of the foam substrate can be measured using a dial thickness gauge (e.g., “ABS Digimatic Indicator” manufactured by Mitutoyo).

The double-sided adhesive tape of the present invention may also have a resin sheet on at least one side of the foam substrate. By using the resin sheet, the foam substrate can be prevented from stretching and breaking during handling, and further, reworkability can be imparted to the double-sided adhesive tape.

The above resin sheet may be laminated on one side of the foam substrate or on both sides.

The resin constituting the above resin sheet is not particularly limited, and examples thereof include polyester resins such as polyethylene terephthalate, acrylic resins, polyethylene resins, polypropylene resins, polyvinyl chloride, epoxy resins, silicone resins, phenol resins, polyimides, polyesters, and polycarbonates. Among these, acrylic resins, polyethylene resins, polypropylene resins, and polyester resins are preferable due to their excellent flexibility. Among polyester resins, polyethylene terephthalate is preferable.

In addition, the resin constituting the above resin sheet may be a thermoplastic resin. The thermoplastic resin is not particularly limited, and examples thereof include styrenic (co)polymers, olefinic (co)polymers, vinyl chloride (co)polymers, polyetherester triblock (co)polymers, polyester (co)polymers, urethane (co)polymers, amide (co)polymers, and acrylic (co)polymers. Among these, from the viewpoint of being able to exhibit strength, elongation, flexibility, and self-adhesiveness as an elastic body, and exhibiting excellent reworkability while further improving the adhesion between the resin sheet and the foam substrate, it is preferable that the thermoplastic resin is an acrylic (co)polymer, a styrenic (co)polymer, or an olefinic (co)polymer. In addition, it is more preferable that it is an acrylic (co)polymer or a styrenic (co)polymer, and it is even more preferable that it is a styrenic (co)polymer.

When the resin constituting the above resin sheet is a thermoplastic resin, the resin sheet preferably has a tensile modulus of 200 MPa or less. By using a flexible resin having a tensile modulus of 200 MPa or less, the flexibility of the entire double-sided adhesive tape is secured, making it easy to wind the double-sided adhesive tape into a roll, thereby significantly improving handling properties.

In addition, the tensile modulus can be measured by a method compliant with JIS K 7161. Specifically, for example, a polymeric gauge punching blade "Tensile No. 1 Dumbbell Shape" is used to punch a resin sheet into a dumbbell shape to produce a test piece. The tensile modulus of the obtained test piece is measured at a tensile speed of 100 mm/min using, for example, an "Autograph AGS-X" manufactured by Shimadzu Corporation. The tensile modulus is calculated from the slope of the tensile strength between 1 and 3% strain.

When the above resin sheets are laminated on both sides of the foam substrate, it is preferable that the resin constituting at least one resin sheet is a thermoplastic resin. That is, the double-sided adhesive tape of the present invention preferably has a resin sheet composed of a thermoplastic resin.

The double-sided adhesive tape of the present invention has a first resin sheet laminated on a first surface of the foam substrate and a second resin sheet laminated on a second surface of the foam substrate, and it is preferable that at least one selected from the group consisting of the first resin sheet and the second resin sheet is a resin sheet composed of a thermoplastic resin.

The thickness of the above resin sheet is not particularly limited, but the preferable lower limit is 10 μm, and the preferable upper limit is 100 μm. When the thickness of the above resin sheet is 10 μm or more, the resin sheet is less likely to break even when stretched. When the thickness of the above resin sheet is 100 μm or less, the decrease in the followability to the adherend can be suppressed. The more preferable lower limit of the thickness of the above resin sheet is 15 μm, and the more preferable upper limit is 80 μm, the more preferable lower limit is 20 μm, the more preferable upper limit is 60 μm, the more preferable lower limit is 25 μm, and the more preferable upper limit is 50 μm.

The above resin sheet may be colored. By coloring the above resin sheet, light-blocking properties can be imparted to the double-sided adhesive tape.

The method for coloring the above resin sheet is not particularly limited, and examples thereof include a method of mixing particles or fine bubbles of carbon black, titanium oxide, etc. into the resin constituting the above resin sheet, a method of applying ink to the surface of the above resin sheet, etc.

The adhesive layers laminated on both sides of the above foam substrate may have the same composition or may have different compositions.

The above-mentioned adhesive layer is not particularly limited, and examples thereof include an adhesive layer made of an acrylic adhesive, a rubber-based adhesive, a urethane adhesive, a silicone-based adhesive, etc. Among these, an adhesive layer made of an acrylic adhesive containing an acrylic copolymer and a tackifier is preferable because the adhesive strength can be easily controlled, it is relatively stable against light, heat, moisture, etc., and it can be applied to various adherends.

The above acrylic copolymer is obtained by copolymerizing a monomer mixture. To obtain the acrylic copolymer by copolymerizing the monomer mixture, the monomer mixture may be radically reacted in the presence of a polymerization initiator. As a method for radically reacting the monomer mixture, i.e., a polymerization method, a conventionally known method may be used, and examples thereof include solution polymerization (boiling point polymerization or isotropic polymerization), emulsion polymerization, suspension polymerization, and bulk polymerization. Examples of the reaction method for radically reacting the monomer mixture include living radical polymerization and free radical polymerization.

The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the above acrylic copolymer (molecular weight distribution, Mw/Mn) is not particularly limited, but a preferable lower limit is 1.05, and a preferable upper limit is 5.0. When the molecular weight distribution (Mw/Mn) is within the above range, the content of low molecular weight components, etc. is reduced, so that the cohesive force of the adhesive layer increases, and the drop impact resistance of the double-sided adhesive tape is improved. A more preferable upper limit of the molecular weight distribution (Mw/Mn) is 3.0, a further preferable upper limit is 2.5, and a particularly preferable upper limit is 2.3. In order to adjust the molecular weight distribution (Mw/Mn) within the above range, polymerization conditions such as the polymerization initiator and polymerization temperature may be adjusted.

In addition, the number average molecular weight (Mn) and the weight average molecular weight (Mw) are molecular weights converted to standard polystyrene by GPC (Gel Permeation Chromatography). For GPC, for example, 2690 Separations Model (manufactured by Waters) can be used. In addition, a GPC device (for example, manufactured by Tosoh Corporation, product name “HLC-8220”, column: TSKgelSurper HZM-N (4 units)) can also be used, tetrahydrofuran can be used as a solvent, and as measurement conditions, for example, 40°C and a flow rate of 0.5 mL/min can be adopted.

When the molecular weight distribution (Mw/Mn) of the above acrylic copolymer is 2.5 or less, the acrylic copolymer preferably contains a structural unit derived from 2-ethylhexyl acrylate.

When the molecular weight distribution (Mw/Mn) of the acrylic copolymer is 2.5 or less, the content of the structural unit derived from 2-ethylhexyl acrylate is not particularly limited, but a preferable lower limit is 80 wt%, and a preferable upper limit is 98 wt%. When the content of the structural unit is 80 wt% or more, the glass transition point of the acrylic copolymer is lowered, the wettability of the adhesive layer to the adherend is increased, and the drop impact resistance of the double-sided adhesive tape is improved. When the content of the structural unit is 98 wt% or less, the cohesive force of the adhesive layer is increased, and the drop impact resistance of the double-sided adhesive tape is improved. A more preferable lower limit of the content of the structural unit is 90 wt%, and a more preferable upper limit is 97 wt%.

When the molecular weight distribution (Mw/Mn) of the above acrylic copolymer is 2.5 or more, the acrylic copolymer preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester having an alkyl group having 4 or fewer carbon atoms.

When the molecular weight distribution (Mw/Mn) of the above acrylic copolymer is 2.5 or more, the (meth)acrylic acid alkyl ester having an alkyl group having 4 or fewer carbon atoms is not particularly limited. Examples of the (meth)acrylic acid alkyl ester having an alkyl group having 4 or fewer carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and the like. Among them, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferable, and these acrylates are more preferable. These (meth)acrylic acid alkyl esters having an alkyl group having 4 or fewer carbon atoms may be used alone, or two or more types may be used in combination.

When the molecular weight distribution (Mw/Mn) of the above acrylic copolymer is 2.5 or more, the content of the structural unit derived from the (meth)acrylic acid alkyl ester having an alkyl group having 4 or less carbon atoms is not particularly limited, but the preferable lower limit is 40 wt%, and the preferable upper limit is 80 wt%. When the content of the above structural unit is 40 wt% or more, the cohesive force of the adhesive layer increases, and the drop impact resistance of the double-sided adhesive tape is improved. When the content of the above structural unit is 80 wt% or less, the wettability of the adhesive layer to the adherend can be suppressed from being excessively reduced, and the drop impact resistance of the double-sided adhesive tape is improved.

Even when the molecular weight distribution (Mw/Mn) of the above acrylic copolymer is 2.5 or more, it is also preferable that the acrylic copolymer contain a structural unit derived from 2-ethylhexyl acrylate.

When the molecular weight distribution (Mw/Mn) of the above acrylic copolymer is 2.5 or more, the content of the structural unit derived from the 2-ethylhexyl acrylate is not particularly limited, but the preferable lower limit is 10 wt%, and the preferable upper limit is 40 wt%. When the content of the above structural unit is 10 wt% or more, the cohesive force of the adhesive layer increases, and the drop impact resistance of the double-sided adhesive tape is improved. When the content of the above structural unit is 40 wt% or less, the cohesive force of the adhesive layer can be suppressed from being excessively lowered, and the drop impact resistance of the double-sided adhesive tape is improved.

The above acrylic copolymer may, if necessary, contain a structural unit derived from another polymerizable monomer capable of copolymerization other than a structural unit derived from the above 2-ethylhexyl acrylate and a structural unit derived from the above (meth)acrylic acid alkyl ester having an alkyl group having 4 or fewer carbon atoms.

Examples of other polymerizable monomers capable of copolymerization include (meth)acrylic acid alkyl esters having an alkyl group having 13 to 18 carbon atoms, functional monomers, etc.

As the (meth)acrylic acid alkyl ester having an alkyl group having 13 to 18 carbon atoms, examples thereof include tridecyl methacrylate, stearyl (meth)acrylate, etc. As the functional monomer, examples thereof include hydroxyalkyl (meth)acrylate, glycerin dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, etc.

These copolymerizable polymerizable monomers may be used alone or in combination of two or more. Among them, functional monomers having polar functional groups such as hydroxyl groups or carboxyl groups are preferred, and functional monomers having hydroxyl groups are more preferred, since forming a crosslinking structure with a crosslinking agent facilitates adjusting the gel fraction of the adhesive layer. In other words, the acrylic copolymer preferably contains hydroxyl groups.

The weight average molecular weight (Mw) of the above acrylic copolymer has a preferable lower limit of 300,000 and a preferable upper limit of 2,000,000. When the weight average molecular weight is 300,000 or more, the adhesive layer has an appropriate hardness, sufficient cohesion, and high adhesive strength. When the weight average molecular weight is 2,000,000 or less, the adhesive strength of the adhesive layer is sufficient. A more preferable lower limit of the weight average molecular weight is 500,000 and a more preferable upper limit is 1,400,000. In order to adjust the weight average molecular weight within the above range, polymerization conditions such as the polymerization initiator and polymerization temperature can be adjusted.

Examples of the polymerization initiator include organic peroxides, azo compounds, etc.

As the organic peroxide, for example, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, etc. can be mentioned.

The above azo compound is not particularly limited as long as it is generally used in radical polymerization. As the above azo compound, for example, 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1-azobis(cyclohexane-1-carbonitrile), 1-[(1-cyano-1-methylethyl)azo]formamide, 4,4'-azobis(4-cyanovaleric acid), dimethyl-2,2'-azobis(2-methylpropionate), dimethyl-1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-Azobis{2-methyl-N-[1,1'-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-Azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-Azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-Azobis(N-butyl-2-methylpropionamide), 2,2'-Azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-Azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride, Examples include 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate, 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, and 2,2'-azobis(2,4,4-trimethylpentane).

In addition, as the polymerization initiator, a polymerization initiator that initiates living radical polymerization is not particularly limited, but an organic tellurium polymerization initiator is preferable.

These polymerization initiators may be used alone or in combination of two or more.

When subjecting the above monomer mixture to a radical reaction, a dispersion stabilizer may be used. Examples of the dispersion stabilizer include polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, ethylcellulose, poly(meth)acrylic acid, poly(meth)acrylic acid ester, polyethylene glycol, etc.

When using a polymerization solvent when subjecting the above monomer mixture to a radical reaction, the polymerization solvent is not particularly limited. As the polymerization solvent, for example, non-polar solvents such as hexane, cyclohexane, octane, toluene, and xylene can be used. In addition, as the polymerization solvent, for example, highly polar solvents such as water, methanol, ethanol, propanol, butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, and N,N-dimethylformamide can be used. These polymerization solvents may be used alone or in combination of two or more. The polymerization temperature is preferably 0 to 110°C from the viewpoint of polymerization rate.

Examples of the above tackifier include rosin-based resins, rosin ester-based resins, hydrogenated rosin-based resins, terpene-based resins, terpene phenol-based resins, coumarone indene-based resins, alicyclic saturated hydrocarbon-based resins, C5-based petroleum resins, C9-based petroleum resins, and C5-C9 copolymerized petroleum resins. These tackifiers may be used alone or in combination of two or more. Among them, rosin-based resins or terpene-based resins are preferable, and rosin-based resins containing hydroxyl groups or terpene-based resins containing hydroxyl groups are more preferable.

The above-mentioned tackifier has a preferable lower limit of softening temperature of 70°C, and a preferable upper limit of softening temperature of 170°C. When the softening temperature is 70°C or higher, the adhesive layer can be prevented from becoming excessively soft, thereby preventing the drop impact resistance of the double-sided adhesive tape from deteriorating. When the softening temperature is 170°C or lower, the wettability of the adhesive layer to the adherend increases, thereby improving the drop impact resistance of the double-sided adhesive tape. A more preferable lower limit of the softening temperature is 120°C.

In addition, the softening temperature is the softening temperature measured by the JIS K 2207 ring and ball method.

The above-mentioned adhesive agent has a preferable lower limit of hydroxyl value of 25 and a preferable upper limit of 160. When the above-mentioned hydroxyl value is within the above-mentioned range, the wettability of the adhesive layer to the adherend is increased, thereby improving the drop impact resistance of the double-sided adhesive tape. A more preferable lower limit of the above-mentioned hydroxyl value is 30 and a more preferable upper limit of the above-mentioned hydroxyl value is 150.

In addition, the hydroxyl value can be measured by JIS K 1557 (phthalic anhydride method).

The content of the tackifier is not particularly limited, but the preferred lower limit is 10 parts by weight, and the preferred upper limit is 60 parts by weight, relative to 100 parts by weight of the acrylic copolymer. When the content of the tackifier is 10 parts by weight or more, the adhesive strength of the adhesive layer increases. When the content of the tackifier is 60 parts by weight or less, the adhesive layer can be prevented from becoming excessively hard, thereby reducing the adhesive strength.

It is preferable that the pressure-sensitive adhesive layer has a crosslinking structure formed between the main chains of the resin (e.g., the acrylic copolymer, the tackifier, etc.) constituting the pressure-sensitive adhesive layer by adding a crosslinking agent. By adjusting the type and amount of the crosslinking agent, it becomes easy to adjust the gel fraction of the pressure-sensitive adhesive layer.

The crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred.

The amount of the crosslinking agent to be added is preferably 0.01 parts by weight, preferably 10 parts by weight, more preferably 0.1 parts by weight, and more preferably 3 parts by weight, based on 100 parts by weight of the acrylic copolymer.

The above-mentioned adhesive layer may contain a silane coupling agent for the purpose of improving adhesive strength. The silane coupling agent is not particularly limited, and examples thereof include epoxy silanes, acrylic silanes, methacrylic silanes, amino silanes, and isocyanate silanes.

The above-mentioned adhesive layer may contain a coloring agent for the purpose of imparting light-blocking properties. The coloring agent is not particularly limited, and examples thereof include carbon black, aniline black, titanium oxide, and the like. Among these, carbon black is preferred due to its relative cheapness and chemical stability.

The gel fraction of the above-mentioned adhesive layer is not particularly limited, but a preferable lower limit is 1 wt%, and a preferable upper limit is 90 wt%. When the gel fraction is 1 wt% or more, the cohesive force of the adhesive layer increases, and the drop impact resistance of the double-sided adhesive tape is improved. When the gel fraction is 90 wt% or less, the wettability of the adhesive layer to the adherend can be suppressed from being excessively reduced, and the drop impact resistance of the double-sided adhesive tape is improved. A more preferable lower limit of the gel fraction is 20 wt%, a more preferable upper limit is 70 wt%, a still more preferable lower limit is 30 wt%, and a still more preferable upper limit is 50 wt%.

Additionally, the gel fraction of the adhesive layer can be measured by the following method.

A test piece is prepared by cutting a double-sided adhesive tape into a flat rectangular shape measuring 50 mm × 100 mm. The test piece is immersed in ethyl acetate at 23°C for 24 hours, then taken out from the ethyl acetate and dried for 1 hour under conditions of 110°C. The weight of the test piece after drying is measured, and the gel fraction is calculated using the following formula (5). In addition, the test piece is not laminated with a release film to protect the adhesive layer.

Gel fraction (wt%) = 100 × (W ₂ -W ₀ )/(W ₁ -W ₀ ) (5)

(W ₀ : weight of the 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 above-mentioned adhesive layer is not particularly limited, but the preferable lower limit of the thickness of the adhesive layer on one side is 20 μm, and the preferable upper limit is 100 μm. When the thickness of the adhesive layer is 20 μm or more, the adhesive strength of the adhesive layer becomes sufficient. When the thickness of the adhesive layer is 100 μm or less, the stress relaxation property of the foam substrate can sufficiently contribute to the stress relaxation property of the double-sided adhesive tape as a whole. The more preferable lower limit of the thickness of the adhesive layer is 25 μm, and the more preferable upper limit is 80 μm, the more preferable lower limit is 30 μm, and the more preferable upper limit is 70 μm, the more preferable lower limit is 35 μm, and the more preferable upper limit is 65 μm.

Additionally, the thickness of the adhesive layer can be measured using a dial thickness gauge (e.g., “ABS Digimatic Indicator” manufactured by Mitutoyo).

The thickness of the double-sided adhesive tape of the present invention is not particularly limited, but the preferable lower limit is 100 μm, and the preferable upper limit is 1200 μm. When the thickness is 100 μm or more, the adhesive strength of the double-sided adhesive tape becomes sufficient, and also the stress relaxation property becomes sufficient. When the thickness is 1200 μm or less, sufficient adhesion and fixation by the double-sided adhesive tape can be realized. The more preferable lower limit of the thickness is 250 μm, the more preferable upper limit is 900 μm, the more preferable lower limit is 350 μm, the more preferable upper limit is 700 μm, the more preferable lower limit is 400 μm, and the more preferable upper limit is 650 μm.

The composition of the double-sided adhesive tape of the present invention is not particularly limited, and the adhesive layer may be laminated on the surface of the foam substrate, or the resin sheet may be laminated between the foam substrate and the adhesive layer.

As a method for manufacturing the double-sided adhesive tape of the present invention, for example, the following methods can be mentioned.

First, a solution of adhesive A is prepared by adding a solvent to an acrylic copolymer, a tackifier, a crosslinking agent, etc. as needed, and this solution of adhesive A is applied to the surface of a foam substrate, and the solvent in the solution is completely dried and removed to form an adhesive layer A. Next, a release film is superimposed on the formed adhesive layer A with its release-treated surface facing the adhesive layer A.

Next, a release film different from the above release film is prepared, a solution of adhesive B is applied to the release-treated surface of this release film, and the solvent in the solution is completely dried and removed, thereby producing a laminated film having an adhesive layer B formed on the surface of the release film. The obtained laminated film is superimposed on the back surface of a foam substrate on which adhesive layer A is formed, with the adhesive layer B facing the back surface of the foam substrate, to produce a laminate. Then, the laminated body is pressed by a rubber roller or the like. As a result, a double-sided adhesive tape having adhesive layers on both sides of the foam substrate and having the surface of the adhesive layer covered with a release film can be obtained.

In addition, two sets of laminated films may be produced using the same method, and these laminated films may be overlapped on each side of a foam substrate with the adhesive layers of the laminated films facing the foam substrate to produce a laminate, and this laminate may be pressed using a rubber roller or the like. In this way, a double-sided adhesive tape having adhesive layers on both sides of a foam substrate and having the surface of the adhesive layer covered with a release film can be obtained.

The double-sided adhesive tape of the present invention has no particular limitations in its use. For example, it is used to secure components in electronic devices. The electronic devices are not particularly limited, and examples thereof include televisions, monitors, portable electronic devices, and automotive electronic devices.

Among them, the double-sided adhesive tape of the present invention is preferably used for fixing components in display devices such as televisions and monitors, especially relatively large display devices, and specifically, for example, it is used for fixing a surface cover panel to a casing in the display device. The double-sided adhesive tape of the present invention has excellent drop impact resistance and can reduce display unevenness of the display device, and therefore is preferably used even when fixing components with a narrow double-sided adhesive tape in a relatively large display device. The double-sided adhesive tape of the present invention may be narrow, and its width is not particularly limited, but a preferable lower limit is 1000 μm, a preferable upper limit is 10000 μm, a more preferable lower limit is 1500 μm, and a more preferable upper limit is 5000 μm. The shape of the double-sided adhesive tape of the present invention for these uses is not particularly limited, but examples thereof include a rectangular shape, a liquid-like shape, a circular shape, an oval shape, and a doughnut shape.

In addition, the double-sided adhesive tape of the present invention may be used for the interior of vehicles, the interior and exterior of home appliances (e.g., TVs, air conditioners, refrigerators, etc.), etc.

According to the present invention, a double-sided adhesive tape can be provided that has excellent drop impact resistance, can reduce display unevenness of a display device, and can easily tear a foam substrate when peeling from an adherend.

Figure 1 is a schematic diagram showing a method for measuring shear fracture strength.
Figure 2 is a schematic diagram showing an interlayer tear test of a double-sided adhesive tape.
Figure 3 is a schematic diagram showing a sample for a tumble test of a double-sided adhesive tape.
Figure 4 shows a schematic diagram showing a surface bending test of a double-sided adhesive tape.

The embodiments of the present invention are described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Manufacture of polyurethane foam 1-1 (PU1-1))

As polyol, 90 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 10 parts by weight of 1,5-pentanediol were used.

To 100 parts by weight of polyol, 0.7 parts by weight of an amine catalyst (Dabco LV33, manufactured by Sankyo Air Products) and 1 part by weight of a foaming agent (SZ5740M, manufactured by Toray/Dow Corning) were added, and the mixture was stirred. Polyisocyanate (dinuclear monomer MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 85. Then, the mixture was mixed with nitrogen gas and stirred to 0.2 g/cm3, thereby obtaining a solution containing fine bubbles. The solution was applied to a PET separator (V-2 manufactured by Nipa) having a thickness of 50 ㎛ using an applicator to a predetermined thickness, and the foaming raw material was reacted to obtain a polyurethane foam.

The shear rupture strength, 25% compressive strength, and thickness of polyurethane foam were measured.

The center of a measurement sample obtained by cutting polyurethane foam was imaged using an X-ray CT device (Yamato Scientific Co., Ltd., "TDM1000H-II (2K)", resolution approximately 1.5 ㎛/1 pixel), and a rectangular 3D image with a length of 1.5 mm, a width of 1.2 mm, and a height of 0.3 mm was obtained. For the obtained image, noise was removed and binarized using image analysis software (FEI Co., Ltd., "Avizo9.2.0"), and the bubble volume fraction, the average and standard deviation of the major diameter distribution of the bubbles, the bubble expansion ratio, the bubble aspect ratio, and the bubble flatness were obtained.

(Manufacture of polyurethane foam 1-2 (PU1-2))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] 90 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000), 5 parts by weight of 1,5-pentanediol, and 5 parts by weight of 1,6-hexamethylenediol were used as polyol.

[2] Polyisocyanate (2-nucleus monomer MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 85.

(Manufacture of polyurethane foam 1-3 (PU1-3))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] 90 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000), 5 parts by weight of 1,5-pentanediol, and 5 parts by weight of neopentyl glycol were used as polyol.

(Manufacture of polyurethane foam 2 (PU2))

A polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1) except for the following points.

[1] 85 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000), 3 parts by weight of 1,6-hexamethylenediol, 3 parts by weight of neopentyl glycol, and 9 parts by weight of ε-caprolactone were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 90.

(Manufacture of polyurethane foam 3-1 (PU3-1))

A polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1) except for the following points.

[1] 91 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 9 parts by weight of ε-caprolactone were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 100.

[3] By adjusting the nitrogen gas being mixed, the thickness of the solution containing fine bubbles was changed (made thinner) when applied onto a PET separator (V-2 manufactured by Nipa) having a thickness of 50 ㎛.

(Manufacture of polyurethane foam 3-2 (PU3-2))

A polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1) except for the following points.

[1] 91 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 9 parts by weight of ε-caprolactone were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 100.

(Manufacture of polyurethane foam 3-3 (PU3-3))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] 91 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 9 parts by weight of ε-caprolactone were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 100.

[3] By adjusting the nitrogen gas being mixed, the thickness of the solution containing fine bubbles was changed (made thicker) when applied onto a PET separator (V-2 manufactured by Nipa) having a thickness of 50 μm.

(Manufacture of polyurethane foam 4 (PU4))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] 90 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000), 5 parts by weight of 1,5-pentanediol, and 5 parts by weight of 1,6-hexamethylenediol were used as polyol.

[2] Polyisocyanate (2-nucleus monomer MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 75.

(Manufacture of polyurethane foam 5 (PU5))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] 90 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 10 parts by weight of 1,6-hexamethylenediol were used as polyol.

[2] Polyisocyanate (2-nucleus monomer MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 95.

(Manufacture of polyurethane foam 6 (PU6))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] 90 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 10 parts by weight of 1,5-pentanediol were used as polyol.

[2] Polyisocyanate (2-nucleus monomer MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 70.

(Manufacture of polyurethane foam 7 (PU7))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] 91 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 9 parts by weight of ε-caprolactone were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 110.

(Manufacture of polyurethane foam 8 (PU8))

A polyurethane foam was obtained in the same manner as the production of polyurethane foam 3-1 (PU3-1) except for the following points.

[1] 91 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000) and 9 parts by weight of ε-caprolactone were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 85.

(Manufacture of polyurethane foam 9 (PU9))

A polyurethane foam was obtained in the same manner as the production of polyurethane foam 8 (PU8) except for the following points.

[1] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 90.

(Manufacture of polyurethane foam 10 (PU10))

Except for the following points, a polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1).

[1] Polyisocyanate (2-nucleus monomer MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 70.

[2] By adjusting the nitrogen gas being mixed, the thickness of the solution containing fine bubbles was changed (made thicker) when applied onto a PET separator (V-2 manufactured by Nipa) having a thickness of 50 μm.

(Manufacture of polyurethane foam 11 (PU11))

A polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1) except for the following points.

[1] 30 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000), 60 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 3100), and 10 parts by weight of 1,5-pentanediol were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 65.

[3] By adjusting the nitrogen gas being mixed, the thickness of the solution containing fine bubbles was changed (made thicker) when applied onto a PET separator (V-2 manufactured by Nipa) having a thickness of 50 μm.

(Manufacture of polyurethane foam 12 (PU12))

A polyurethane foam was obtained in the same manner as the production of polyurethane foam 1-1 (PU1-1) except for the following points.

[1] 20 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 1000), 70 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 3100), and 10 parts by weight of 1,5-pentanediol were used as polyol.

[2] Polyisocyanate (polymeric MDI, manufactured by Tosoh Corporation) was added after adjusting the isocyanate index to 65.

[3] By adjusting the nitrogen gas being mixed, the thickness of the solution containing fine bubbles was changed (made thicker) when applied onto a PET separator (V-2 manufactured by Nipa) having a thickness of 50 μm.

(Polyethylene foam 1 (PE1))

XLIM#15003 (manufactured by Sekisui Chemical Co., Ltd.) was used as polyethylene foam.

(Preparation of adhesive I (radical polymerization))

52 parts by weight of ethyl acetate was placed in a reactor equipped with a thermometer, a stirrer, and a condenser, and after purging with nitrogen, the reactor was heated to initiate reflux. After the ethyl acetate boiled, 0.08 parts by weight of azobisisobutyronitrile as a polymerization initiator was added 30 minutes later. A monomer mixture (60 parts by weight of butyl acrylate (BA), 36.9 parts by weight of 2-ethylhexyl acrylate (2 EHA), 3 parts by weight of acrylic acid (AAc), and 0.1 part by weight of 2-hydroxyethyl acrylate (2 HEA)) was added dropwise evenly and slowly over 1 hour and 30 minutes to allow the reaction. 30 minutes after the end of the dropwise addition, 0.1 parts by weight of azobisisobutyronitrile was added, and the polymerization reaction was further allowed to proceed for 5 hours. ethyl acetate was added into the reactor to dilute the mixture while cooling, thereby obtaining a solution containing an acrylic copolymer.

The weight-average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the obtained acrylic copolymer were determined. Specifically, the obtained acrylic copolymer-containing solution was diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The obtained filtrate was supplied to a gel permeation chromatograph (Waters, 2690 Separations Model), and GPC measurement was performed under the conditions of a sample flow rate of 1 milliliter/min and a column temperature of 40°C, and the polystyrene-equivalent molecular weight of the acrylic copolymer was measured, and the weight-average molecular weight and molecular weight distribution (Mw/Mn) were determined. The weight-average molecular weight was 1 million, and the molecular weight distribution (Mw/Mn) was 2.6. GPCKF-806L (manufactured by Showa Electric Works) was used as the column, and a differential refractometer was used as the detector.

Ethyl acetate was added to 100 parts by weight of the nonvolatile matter of the obtained acrylic copolymer-containing solution, stirred, 5 parts by weight of a crosslinking agent (isocyanate crosslinking agent, Coronate L-55E, manufactured by Tosoh Corporation) and a total of 30 parts by weight of a tackifier were added, stirred, and an adhesive I having a nonvolatile matter of 30 wt% was obtained. As the tackifier, 10 parts by weight of a hydrogenated rosin-based resin (softening point 100°C, hydroxyl value 40 mgKOH/g), 10 parts by weight of a rosin ester-based resin (softening point 150°C, hydroxyl value 40 mgKOH/g), and 10 parts by weight of a terpene phenol-based resin (softening point 150°C, hydroxyl value 40 mgKOH/g) were used.

(Examples 1 to 12, Comparative Examples 1 to 5)

Adhesive I was applied to support layer 1 (resin sheet) and dried at 100°C for 5 minutes to form an adhesive layer 1 having a thickness of 20 μm. One side of a foam substrate was pressed against this adhesive layer 1 to produce a laminate in which the support layer 1 and the foam substrate were laminated with the adhesive layer 1 interposed therebetween. As the support layer 1 (resin sheet), polyethylene terephthalate (PET) (X30, manufactured by Toray Industries, Inc., thickness 50 μm) was used. Next, support layer 2 (resin sheet) was heat-sealed to the other side of the foam substrate to produce a laminate in which the support layer 1, the adhesive layer 1, the foam substrate, and the support layer 2 were laminated in this order. As the support layer 2 (resin sheet), a sheet made of acrylic resin (LA2250, manufactured by Kuraray, 50 μm thick) or urethane block copolymer (TPU) (1198ATR, manufactured by BASF, 20 μm thick) was used.

Next, a release paper having a thickness of 150 ㎛ was prepared, and adhesive I was applied to the release-treated surface of the release paper, and dried at 100°C for 5 minutes to form an adhesive layer 2 having a thickness of 50 ㎛, 55 ㎛, or 60 ㎛. This adhesive layer 2 was bonded to the surface of a support layer 1 (resin sheet) laminated to a foam substrate. Next, in the same manner, an adhesive layer 3 having the same composition as the adhesive layer 2 was bonded to the surface of a support layer 2 (resin sheet) opposite to the foam substrate. Thereafter, curing was performed by heating at 40°C for 48 hours. Thus, a double-sided adhesive tape covered with a release paper was obtained.

Additionally, the tensile modulus of support layer 2 (resin sheet) was 10 MPa and 108 MPa, respectively.

The obtained double-sided adhesive tape was cut into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece, and the test piece was immersed in ethyl acetate at 23°C for 24 hours, then taken out from the ethyl acetate, and dried under conditions of 110°C for 1 hour. The weight of the test piece after drying was measured, and the gel fraction of the adhesive layer was calculated using the following formula (5), and the gel fraction of the adhesive layer was 42 wt%.

Gel fraction (wt%) = 100 × (W ₂ - W ₀ )/(W ₁ - W ₀ ) (5)

(W ₀ : weight of the substrate, W ₁ : weight of the test piece before immersion, W ₂ : weight of the test piece after immersion and drying)

Evaluation

The following evaluations were conducted on the double-sided adhesive tapes obtained in the examples and comparative examples. The results are shown in Tables 1 and 2.

(1) Rework (interlayer tear test)

Fig. 2 shows a schematic diagram showing an interlayer tear test of a double-sided adhesive tape. Fig. 2 (a) is a front view, and Fig. 2 (b) is a side view. A test piece (2) of a double-sided adhesive tape measuring 50 mm × 5 mm and two PC plates (1) measuring 100 mm × 20 mm and 2 mm thick were laminated as shown in Fig. 2. This laminate was pressed using a press stone under the conditions of 5 kg and 10 seconds, and then left for 24 hours, to produce a tear test sample in which two PC plates (1) were bonded together with the test piece (2) interposed therebetween. After fixing one side of the PC board of this tear test sample, a stainless steel wire (3) (0.3φ, "TYWS-03" manufactured by TRUSCO) was hung from below the test piece (2) and pulled at 300 mm/min in the direction of the arrow in Fig. 2. The test force when the interlayer of the test piece (2) was torn by the wire (3) was measured. When the test force was less than 10 N/5 mm, it was indicated by ◎, when it was 10 N/5 mm or more but less than 15 N/5 mm, it was indicated by ○, and when it was 15 N/5 mm or more, it was indicated by ×.

(2) Drop impact (tumble test)

Fig. 3 shows a schematic diagram showing a sample for a tumble test of a double-sided adhesive tape. A test piece (6) of a double-sided adhesive tape, having a long side of 23 mm × a short side of 13.3 mm and a width of 3.2 mm, in the shape of a liquid, was sandwiched between a PMMA plate (5) having a size of 55 mm × 65 mm, a thickness of 10 mm and a weight of 42 g and a SUS plate (4) having a size of 70 mm × 130 mm, a thickness of 2 mm and a weight of 137 g, and laminated as shown in Fig. 3. After pressing this laminate using a press stone under the conditions of 5 kg and 10 seconds, it was left for 24 hours, and a sample for a tumble test was produced by bonding the PMMA plate (5) and the SUS plate (4) together with the test piece (6) therebetween. The tumble test sample was placed in a tumble tester (TDR-1000 A-SC01 manufactured by Shin-Ei Electronic Measuring Instruments Co., Ltd.) and repeatedly subjected to dropping impacts from various angles at a frequency of 10 drops/min. The number of drops until the double-sided adhesive tape broke and the tumble test sample was separated was measured. When the number of drops was 30 or more, it was indicated by ◎, when it was 10 or more but less than 30 times, it was indicated by ○, and when it was less than 10 times, it was indicated by ×.

(3) Display unevenness (surface bending test)

Fig. 4 is a schematic diagram showing a surface bending test of a double-sided adhesive tape. Fig. 4(a) is a top view, and Fig. 4(b) is a cross-sectional view. On a glass plate (10) measuring 256 mm × 182 mm and 4 mm in thickness, a single-sided black shading tape (8) having a width of 15 mm and a thickness of 50 ㎛ was laminated at intervals of 15 mm to create steps. Similarly, on the glass plate (10), a single-sided black shading tape (9) having a width of 15 mm and a thickness of 100 ㎛ was laminated to create steps. From these steps, a test piece (7) of a double-sided adhesive tape having a width of 10 mm was laminated on the four sides of the glass plate (10). A glass plate (12) measuring 256 mm × 182 mm and having a thickness of 1 mm was laminated on a test piece (7), and the glass plate (10) and the glass plate (12) were bonded together with the test piece (7) interposed therebetween. Furthermore, a single-sided black light-shielding tape (13) having a thickness of 100 µm was laminated on the glass plate (12), thereby obtaining a sample for a surface bending test. In accordance with JIS B 0601: 2001, the maximum height Sz of the surface roughness was measured for a measurement area (11) measuring 210 mm × 105 mm in the sample for a surface bending test using a laser microscope (VR-3000 type manufactured by Keyence Co., Ltd.). When the maximum height Sz was less than 120 ㎛, it was indicated as ◎, when it was 120 ㎛ or more but less than 200 ㎛, it was indicated as ○, and when it was 200 ㎛ or more, it was indicated as ×.

Industrial applicability

According to the present invention, a double-sided adhesive tape can be provided that has excellent drop impact resistance, can reduce display unevenness of a display device, and can easily tear a foam substrate when peeling from an adherend.

1: PC version
2: Test piece (double-sided adhesive tape)
3: Wire
4: SUS plate
5: PMMA plate
6: Test piece on liquid surface (double-sided adhesive tape)
7: Test piece (double-sided adhesive tape)
8: Single-sided black shading tape (15 mm wide, 50 μm thick)
9: Single-sided black shading tape (15 mm wide, 100 ㎛ thick)
10: Glass plate
11: Measurement area
12: Glass plate
13: Single-sided black shading tape
18: Test piece (double-sided adhesive tape)
19: SUS plate

Claims (13)

A double-sided adhesive tape having a foam substrate and an adhesive layer laminated on both sides of the foam substrate,
A double-sided adhesive tape characterized in that the foam base material is a polyurethane foam having a bubble volume fraction of 40% by volume or more and 75% by volume or less, a shear rupture strength of 200 N/inch ² or more and 500 N/inch ² or less, and an average major diameter distribution of bubbles of 55 ㎛ or less. In the first paragraph,
A double-sided adhesive tape characterized in that the foam substrate has a 25% compressive strength of 0.015 MPa or more and 0.08 MPa or less. In claim 1 or 2,
A double-sided adhesive tape characterized in that the foam substrate has a standard deviation of the distribution of the major diameters of the bubbles of 30 ㎛ or less. In claim 1 or 2,
A double-sided adhesive tape characterized in that the foam substrate has a flatness of the bubbles of 0.2 or less. In claim 1 or 2,
A double-sided adhesive tape characterized in that the foam substrate has an aspect ratio of bubbles of 1.5 or less. In claim 1 or 2,
A double-sided adhesive tape characterized in that the foam base material has a bubble expansion ratio of 95% by volume or less. In claim 1 or 2,
A double-sided adhesive tape characterized in that the foam substrate has a thickness of 100 ㎛ or more and 1000 ㎛ or less. In claim 1 or 2,
The adhesive layer is made of an acrylic adhesive containing an acrylic copolymer and an adhesive agent, and has a gel fraction of 1 wt% or more and 90 wt% or less,
The above acrylic copolymer contains a hydroxyl group, has a weight average molecular weight of 300,000 to 2,000,000, and a molecular weight distribution (Mw/Mn) of 1.05 to 5.0,
A double-sided adhesive tape characterized in that the above-mentioned adhesive agent is a rosin-based resin containing a hydroxyl group or a terpene-based resin containing a hydroxyl group, and has a softening temperature of 70°C or more and 170°C or less and a hydroxyl value of 25 or more and 160 or less. In claim 1 or 2,
Additionally, a double-sided adhesive tape characterized in that it has a resin sheet on at least one side of a foam substrate, and the thickness of the resin sheet is 10 ㎛ or more and 100 ㎛ or less. In claim 1 or 2,
A double-sided adhesive tape having a first resin sheet laminated on a first surface of a foam substrate and a second resin sheet laminated on a second surface of the foam substrate, wherein at least one selected from the group consisting of the first resin sheet and the second resin sheet is a resin sheet composed of a thermoplastic resin. In claim 1 or 2,
A double-sided adhesive tape characterized in that the thickness of the adhesive layer is 20 ㎛ or more and 100 ㎛ or less. In claim 1 or 2,
A double-sided adhesive tape characterized in that the thickness of the double-sided adhesive tape is 100 ㎛ or more and 1200 ㎛ or less. delete