Double-sided adhesive sheets, laminates, and methods for manufacturing laminates

Abstract

This invention provides a double-sided adhesive sheet that, when optical components constituting a display device equipped with a touch panel include metal conductive parts, suppresses ion migration of the metal conductive parts and suppresses resistance changes caused by humid and hot environments and ultraviolet light when the optical components are bonded together. A double-sided adhesive sheet, a laminate, and a method for manufacturing the laminate are also provided. The double-sided adhesive sheet is used to bond a first substrate and a second substrate, both constituting optical components of a display device equipped with a touch panel. In the double-sided adhesive sheet, at least one of the first substrate and the second substrate has a conductive part, has a sulfur content of 50 mg / kg or less, a spectral transmittance of 30% or less at a wavelength of 380 nm, a water vapor transmittance of 400 g / m² / 24h or less, or a water absorption rate of 1.0% or less.

Description

Technical Field

[0001] This invention relates to a double-sided adhesive sheet, a laminate, and a method for manufacturing the laminate. Prior Technology

[0002] Liquid crystal displays (LCDs) and other display devices, as well as touch panels and other input devices, are widely used in various fields. Touch panels can be resistive or capacitive, but capacitive touch panels are the most common. In the manufacture of these display devices equipped with touch panels, transparent adhesive sheets are used for bonding optical components and for bonding the display device to the input device.

[0003] In small display devices with touch panels, such as smartphones, metal oxides such as indium tin oxide (ITO) are mostly used in the mesh electrode sensors (transparent conductive films) located on the screen, from the perspective of transparency. In recent years, in display devices with touch panels and large screens of 10 inches or more, such as personal computers (PCs), ITO has insufficient conductivity, reduced sensitivity, and may cause malfunctions. Therefore, electrode sensors with conductive parts of metals such as silver or copper are used.

[0004] When the optical components constituting a display device equipped with a touch panel include a metal conductive part, problems sometimes arise if the previously used transparent adhesive sheet is used.

[0005] For example, when a mesh electrode sensor with a wiring width of several μm is made into a metal conductive part, the following problem sometimes occurs: corrosion alone will cause the resistance value to increase and the sensor sensitivity to decrease.

[0006] Furthermore, while metal is sometimes used for the wiring leading out of the screen's bezel, with the trend towards narrower bezels in touch panels and the wiring spacing being set to around 10 μm, the following problem sometimes arises: metal ion migration. If ion migration occurs, at the positive electrode, the electrode dissolves and the wire breaks; or at the negative electrode, dendrites form due to the deposition of positive electrode components, resulting in a short circuit. In particular, ion migration is overwhelmingly more likely to occur on the positive electrode side than on the negative electrode side. When evaluating ion migration, it is preferable to use parallel wiring compared to series wiring, and especially preferable to evaluate the anode side.

[0007] In contrast, adhesive sheets that can effectively prevent / suppress ion migration are known. For example, Patent Document 1 describes an adhesive composition that forms an adhesive for bonding a first display body structural member having a step difference on at least the bonding side surface to a second display body structural member, wherein the first display body structural member and / or the second display body structural member have electrodes on at least the bonding side surface, and the adhesive composition contains a (meth)acrylate polymer (A), a silane coupling agent having mercapto groups (B), and an active energy line curing component (C).

[0008] On the other hand, regarding a method for preventing ITO corrosion as a metal oxide, Patent Document 2 describes an adhesive composition for bonding conductive films, which contains an acrylic polymer (A) and a crosslinking agent (B). The acrylic polymer (A) is an acrylic polymer that is substantially free of acidic groups and has a weight average molecular weight of 50,000 or more but less than 400,000, obtained by copolymerizing monomers containing 50% or more of alkyl methacrylate (a-1), 0.5% to 10% of a hydroxyl-containing monomer (a-2), and 0.1% to 5% of a nitrogen-containing monomer (a-3). The homopolymer of the alkyl methacrylate (a-1) with a weight average molecular weight of 500,000 has a water vapor transmission rate of less than 500 g / m²·day at 40°C and 90% RH, as determined by the cup method.

[0009] Furthermore, Patent Document 3 describes a conductive sheet comprising: a support body; and a conductive portion disposed on the support body and containing conductive fine wires containing metallic silver and gelatin. In this conductive sheet, the conductive fine wires on the support body are substantially free of gelatin, and the volume ratio (A / B) of the metallic silver in the conductive fine wires to the volume of gelatin is 0.3 to 10.0. Furthermore, Patent Document 3 also describes a touch panel comprising: a conductive sheet with the aforementioned structure; and a transparent adhesive layer disposed on the conductive portion side of the conductive sheet. In this touch panel, the adhesive contained in the transparent adhesive layer has an acid value of 100 mg KOH / g or less, and a water absorption rate of 1.0% or less. [Existing Technical Documents] [Patent Literature]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2017-014379

[0011] [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-047296

[0012] [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-209332 Summary of the Invention Problems to be Solved by the Invention

[0013] In Patent Document 1, it is described that ion migration can be suppressed by using a mercapto group-containing silane coupling agent. However, the inventors of the present invention conducted research and found that sometimes the suppression of ion migration becomes insufficient due to the composition of the adhesive composition such as the type or blending ratio of the (meth)acrylate polymer. Furthermore, as a new problem when a sulfur component is contained in the adhesive sheet, such as when using a chain transfer agent or a silane coupling agent having a mercapto group (thiol group), the inventors found that the resistance value increases due to the corrosion of the metal conductive part, and particularly found that significant resistance value changes are caused by a humid heat environment or ultraviolet rays.

[0014] In Patent Document 2, regarding the method for preventing ITO corrosion, only attention was paid to preventing corrosion caused by acid by using an adhesive substantially free of acid components, and only attention was paid to the relationship between the water vapor transmission rate and the wet heat stability.

[0015] In Patent Document 3, no research was conducted on suppressing the resistance value change caused by corrosion, and particularly no suggestion was made regarding the resistance value change caused by the corrosion of the metal conductive part due to a humid heat environment and ultraviolet rays. In addition, Patent Document 3 describes the use of a migration inhibitor such as an organic mercapto compound to stabilize the metal silver in the conductive part, and no suggestion was made regarding suppressing the sulfur content.

[0016] The problem to be solved by the present invention is to provide a double-sided adhesive sheet that can suppress ion migration of the metal conductive part and can suppress the resistance value change caused by a humid heat environment and ultraviolet rays when the optical members constituting a display device equipped with a touch panel are bonded to each other. Means for Solving the Problems

[0017] The specific structure and preferred structure of the present invention are as described below.

[0018] [1] A double-sided adhesive sheet is used to bond a first substrate and a second substrate, both of which are optical components constituting a display device equipped with a touch panel, wherein at least one of the first substrate and the second substrate has a metal conductive part, the sulfur content is less than 50 mg / kg, the spectral transmittance at a wavelength of 380 nm is less than 30%, the water vapor transmittance is less than 400 g / m2 / 24h, or the water absorption rate is less than 1.0%.

[0019] [2] As described in [1], the double-sided adhesive sheet, wherein the first substrate is a touch panel and the second substrate is an image display device or a cover material.

[0020] [3] As described in [1] or [2], the double-sided adhesive sheet has a total light transmittance of 90% to 100%, a haze value of less than 1%, and a chromaticity b* of -1 to 1 as specified by the International Commission on Illumination (CIE) 1976 L*a*b* color system.

[0021] [4] The double-sided adhesive sheet as described in any one of [1] to [3], wherein the double-sided adhesive sheet has an adhesive layer with a gel content of 40% to 90%.

[0022] [5] The double-sided adhesive sheet as described in any one of [1] to [4], wherein the double-sided adhesive sheet has an adhesive layer comprising a base polymer containing 70% to 98% by mass of units derived from (meth)acrylates having a branch chain having 8 to 18 carbon atoms, and 1% to 20% by mass of units derived from (meth)acrylates containing hydroxyl groups.

[0023] [6] A laminate includes: a double-sided adhesive sheet as described in any one of [1] to [5]; and a first adhesive body and a second adhesive body disposed on both surfaces of the double-sided adhesive sheet and both constituting optical components of a display device equipped with a touch panel, wherein at least one of the first adhesive body and the second adhesive body has a metal conductive portion.

[0024] [7] As described in [6], the first substrate is a touch panel, the second substrate is an image display device or a cover material, and at least one of the touch panel and the image display device or the cover material includes a transparent conductive film having a mesh conductive portion and lead wires connected to the mesh conductive portion.

[0025] [8] The laminate according to [6] or [7], wherein the conductive portion contains silver or copper.

[0026] [9] A method for manufacturing a laminate, comprising the steps of: applying pressure in a state where one surface of each of a first adherend and a second adherend, which are both optical members constituting a display device equipped with a touch panel, is in contact with the double-sided adhesive sheet according to any one of [1] to [5], and at least one of the first adherend and the second adherend has a metal conductive portion. Advantages of the Invention

[0027] According to the present invention, there can be provided a double-sided adhesive sheet which, when optical members are bonded to each other in a case where an optical member constituting a display device equipped with a touch panel includes a metal conductive portion, can suppress ion migration of the metal conductive portion and can suppress changes in the resistance value caused by a humid and hot environment and ultraviolet rays. Brief Explanation of Drawings

[0028] FIG. 1 is a schematic view showing an example of a cross-sectional structure of the double-sided adhesive sheet of the present invention.

[0029] FIG. 2 is a cross-sectional view showing an example of a cross-sectional structure of the laminate of the present invention.

[0030] FIG. 3 is a schematic view showing the structure of a conductive thin film for evaluation including silver wiring.

[0031] FIG. 4 is a schematic view showing the structure of a sample for evaluation of ion migration suppression.

[0032] FIG. 5 is a schematic view showing the circuit structure used in the evaluation of ion migration suppression.

[0033] FIG. 6 is a schematic view showing the structure of a conductive thin film for evaluation of resistance value including silver wiring.

[0034] FIG. 7 is a schematic view showing the structure of a sample for evaluation of resistance value. Embodiments

[0035] Hereinafter, the present invention will be described in detail. The description of the structural elements described below is sometimes based on representative embodiments or specific examples, but the present invention is not limited to such embodiments.

[0036] [Double-sided adhesive sheet]

[0037] The double-sided adhesive sheet of this embodiment is used to bond a first substrate and a second substrate, both of which are optical components constituting a display device equipped with a touch panel. In the double-sided adhesive sheet, at least one of the first substrate and the second substrate has a metallic conductive part, the sulfur content is less than 50 mg / kg, the spectral transmittance at a wavelength of 380 nm is less than 30%, the water vapor transmittance is less than 400 g / m2 / 24h, or the water absorption rate is less than 1.0%.

[0038] The double-sided adhesive sheet of this embodiment, by means of the structure described above, when the optical components constituting the display device equipped with the touch panel include metal conductive parts, can suppress ion migration of the metal conductive parts and suppress changes in resistance value caused by humid and hot environments and ultraviolet rays when the optical components are bonded together.

[0039] In this embodiment, by setting the sulfur content of the adhesive sheet to a specific range or below, and consequently setting the spectral transmittance at a wavelength of 380 nm to a specific range or below, and setting the water vapor transmittance or water absorption rate to a specific range or below, ion migration in the conductive metal portion can be suppressed, and changes in resistance caused by humid and hot environments and ultraviolet light can be suppressed. Previously, in the field of adhesive sheets, methods are known to suppress ion migration using silane coupling agents having thiol groups (sulfur-containing groups) (Japanese Patent Application Laid-Open No. 2017-014378, Japanese Patent Application Laid-Open No. 2020-114914, Japanese Patent No. 6170202, etc., excluding Patent Document 1) or to suppress corrosion by forming a cross-linked structure using sulfur-containing organic salts (Japanese Patent Application Laid-Open No. 2021-504750). In contrast, this embodiment, which sets the sulfur content to a specific range or below, solves the aforementioned problem based on a completely different perspective in the field of adhesive sheets.

[0040] The preferred form of the double-sided adhesive sheet of this embodiment will be described below.

[0041] Characteristics of Double-Sided Adhesive Sheets

[0042] (Water vapor transmission rate)

[0043] In the first embodiment of the present invention, the water vapor transmission rate of the double-sided adhesive sheet is 400 g / m² / 24h or less. Preferably, the water vapor transmission rate of the double-sided adhesive sheet is 300 g / m² / 24h or less, more preferably 200 g / m² / 24h or less. From the viewpoint of easily suppressing migration when the double-sided adhesive sheet is used in an optical component including a metal conductive portion, the water vapor transmission rate is preferably within the aforementioned range. Preferably, only the water vapor transmission rate of the adhesive layer, described later, is within the aforementioned range.

[0044] (Water absorption rate)

[0045] In the second embodiment of the present invention, the water absorption rate of the double-sided adhesive sheet is 1.0% or less. Preferably, the water absorption rate of the double-sided adhesive sheet is 0.7% or less, more preferably 0.6% or less. From the viewpoint of easily suppressing migration when the double-sided adhesive sheet is used in an optical component including a metal conductive portion, the water absorption rate is preferably within the aforementioned range. Preferably, only the water absorption rate of the adhesive layer described later is within the aforementioned range.

[0046] (Sulfur content)

[0047] The sulfur content of the double-sided adhesive sheet in this embodiment is 50 mg / kg or less. Preferably, the sulfur content of the double-sided adhesive sheet is 40 mg / kg or less, more preferably 30 mg / kg or less. Preferably, the sulfur content of the double-sided adhesive sheet is 0 mg / kg, i.e., preferably below the detection limit. From the viewpoint that it is easy to suppress resistance changes caused by humid and hot environments when using the double-sided adhesive sheet in optical components including metal conductive parts, the sulfur content is preferably within the aforementioned range. Previously, the increase in resistance of conductive parts of metals such as silver was not a major concern; however, as a problem, the inventors have found that when using the double-sided adhesive sheet to bond optical components having conductive parts of metals such as copper or silver, resistance changes caused by humid and hot conditions are easily generated. Preferably, only the sulfur content of the adhesive layer described later is within the aforementioned range.

[0048] There are no particular limitations on the method of setting the sulfur content of the double-sided adhesive sheet to below the aforementioned range. For example, when using a chain transfer agent in the synthesis of the base polymer, one can use a chain transfer agent other than a sulfur-based one, or use an additive that does not contain sulfur, or reduce the content of additives containing sulfur. Specifically, when using a chain transfer agent in the polymerization of the base polymer, one can use a chain transfer agent that does not contain thiols, such as 2,4-diphenyl-4-methyl-1-pentene, or use a silane coupling agent other than a mercapto-based one as an additive, or reduce the content of mercapto-based silane coupling agents, etc.

[0049] (380nm transmittance)

[0050] The double-sided adhesive sheet of this embodiment has a spectral transmittance of 30% or less at a wavelength of 380 nm. Preferably, the spectral transmittance of the double-sided adhesive sheet at a wavelength of 380 nm is 25% or less, more preferably 20% or less. From the viewpoint that it is easy to suppress changes in resistance caused by ultraviolet (UV) treatment when using the double-sided adhesive sheet in optical components including metal conductive parts, the spectral transmittance is preferably within the aforementioned range. Previously, changes in resistance caused by UV light were not a concern, but as a problem, the inventors have found that when using the double-sided adhesive sheet to bond optical components having conductive parts of metals such as copper or silver, changes in resistance are easily caused by UV light. Preferably, only the spectral transmittance of the adhesive layer described later is within the aforementioned range.

[0051] The spectral transmittance of the double-sided adhesive film at a wavelength of 380nm is preferably above 0%, and from the perspective of chromaticity b* value, it is even better to be above 10%.

[0052] (chromaticity b* value)

[0053] In the double-sided adhesive sheet of this embodiment, the chromaticity b* value specified by the CIE 1976 L*a*b* color system at 23°C and 50% relative humidity is preferably -1 to 1, more preferably greater than -1 but less than 1, and more preferably greater than -0.5 but less than 0.5. If the b* value is within the range described above, the required transparency or color reproduction of the image display device when using the double-sided adhesive sheet in optical components can be satisfied.

[0054] (Total light transmittance)

[0055] In the double-sided adhesive sheet, the total light transmittance (measured according to Japanese Industrial Standards (JIS) K 7361-1:1997) under an environment of 23°C and 50% relative humidity can be set to 80%. The total light transmittance of the double-sided adhesive sheet in this embodiment is preferably 90% to 100%. If the total light transmittance is within the aforementioned range, the transparency is high, making it suitable for optical applications.

[0056] (Haze value)

[0057] In the double-sided adhesive sheet, the haze value in an environment of 23°C and 50% relative humidity can be set to 0% or more and 2% or less. The haze value of the double-sided adhesive sheet in this embodiment is preferably 0% or more and less than 1%. If the haze value is within the aforementioned range, the required transparency for using the double-sided adhesive sheet in optical components can be met, making it suitable for optical applications.

[0058] <Structure of Double-Sided Adhesive Sheets>

[0059] The double-sided adhesive sheet of this embodiment may include an adhesive layer and other layers, but preferably only an adhesive layer. Examples of other layers include a support, a release liner, etc.

[0060] Figure 1 is a cross-sectional view showing an example of the structure of a double-sided adhesive sheet with release tabs. The double-sided adhesive sheet 1 shown in Figure 1 has release tabs (12a, 12b) on both surfaces of the adhesive layer 11. Furthermore, the double-sided adhesive sheet of Figure 1 is a carrier-free single-layer adhesive sheet, and it is a double-sided adhesive sheet.

[0061] <Support>

[0062] Examples of supporting materials include: plastic films such as polystyrene, styrene-acrylic acid copolymer, acrylic resin, polyethylene terephthalate, polycarbonate, polyetheretherketone, and triacetyl cellulose; and optical films such as anti-reflective films and electromagnetic wave shielding films.

[0063] <Peeling tablets>

[0064] The double-sided adhesive sheet in this embodiment preferably has an adhesive layer, and the surface of the adhesive layer is preferably covered by a release liner. That is, this embodiment can be a double-sided adhesive sheet with a release liner.

[0065] Examples of release sheets include: release laminates having a release sheet substrate and a release agent layer disposed on one side of the release sheet substrate, or polyolefin films such as polyethylene films or polypropylene films as low polarity substrates.

[0066] Paper or polymer films can be used as the release liner substrate in release laminates. As the release agent constituting the release agent layer, for example, commonly used addition-type or condensation-type silicone-based release agents or compounds containing long-chain alkyl groups can be used. In particular, highly reactive addition-type silicone-based release agents are preferred.

[0067] Specifically, examples of silicone-based stripping agents include BY24-4527 and SD-7220 manufactured by Toray Dow Corning Silicone, Ltd., and KS-3600, KS-774, and X62-2600 manufactured by Shin-Etsu Chemical Co., Ltd. Furthermore, it is preferable that the silicone-based stripping agent contains an organosilicon compound, i.e., a silicone resin, having SiO2 units and (CH3)3SiO1 / 2 units or CH2=CH(CH3)SiO1 / 2 units. Specific examples of silicone resins include BY24-843, SD-7292, and SHR-1404 manufactured by Toray Dow Corning Silicone, Ltd., and KS-3800 and X92-183 manufactured by Shin-Etsu Chemical Co., Ltd.

[0068] In the release tab 12 shown in Figure 1, it is preferable that the release tab 12a and the release tab 12b have different peelability for easier peeling. That is, if the peelability of one is different from that of the other, it is easier to peel off the release tab 12 with higher peelability first. In this case, the peelability of the release tab 12a and the release tab 12b as release tabs can be adjusted according to the bonding method or bonding sequence.

[0069] <Adhesive layer>

[0070] The double-sided adhesive sheet in this embodiment preferably includes an adhesive layer.

[0071] The thickness of the adhesive layer can be appropriately set according to the application and is not particularly limited. Generally, the thickness of the adhesive layer is preferably in the range of 10 μm to 500 μm, more preferably 20 μm to 450 μm, further preferably 30 μm to 450 μm, especially preferably 40 μm to 400 μm, even more preferably 40 μm to 350 μm, and most preferably 40 μm to 300 μm. By setting the thickness of the adhesive layer within the aforementioned range, sufficient conformability to uneven surfaces can be ensured, thereby improving durability. In addition, by setting the thickness of the adhesive layer within the aforementioned range, it is easy to manufacture double-sided adhesive sheets.

[0072] (Gel fraction)

[0073] The gel content of the adhesive layer is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more. Furthermore, the gel content of the adhesive layer is preferably 90% by mass or less. From the viewpoint of easily reducing water vapor transmission rate or water absorption rate, it is preferable to set the gel content to the lower limit or above. By setting the gel content to the upper limit or below, the adhesive strength can be improved.

[0074] The composition of the adhesive layer is not particularly limited, but it preferably includes a base polymer (A). The adhesive layer preferably includes a crosslinking agent (B), a silane coupling agent (C), and an ultraviolet absorber (D) as any additives, and more preferably includes a solvent (E).

[0075] (Base polymer (A))

[0076] The base polymer (A) is not particularly limited, but it is preferably composed of units derived from (meth)acrylates. The base polymer (A) is preferably transparent to a degree that does not reduce the visibility of the display device. Furthermore, in this specification, "unit" refers to a repeating unit (monolithic unit) constituting the polymer.

[0077] The base polymer (A) preferably contains units (a1) derived from non-crosslinked (meth)acrylate and units (a2) derived from (meth)acrylate monomers having crosslinking functional groups.

[0078] Preferably, at least one of the units (a1) derived from non-crosslinked (meth)acrylates and the units (a2) derived from (meth)acrylate monomers having crosslinking functional groups is a unit derived from methacrylates. For example, if the unit (a1) derived from non-crosslinked (meth)acrylates is a unit derived from non-crosslinked acrylates, then the unit (a2) derived from (meth)acrylate monomers having crosslinking functional groups is preferably a unit derived from methacrylate monomers having crosslinking functional groups.

[0079] Alternatively, if the unit (a2) derived from the (meth)acrylate monomer having a crosslinking functional group is a unit derived from the acrylic monomer, the unit (a1) derived from the non-crosslinking (meth)acrylate is preferably 50% or more of the unit derived from the non-crosslinking methacrylate.

[0080] -Units derived from non-crosslinked (meth)acrylates (a1)-

[0081] The unit (a1) derived from a non-crosslinked (meth)acrylate is preferably a unit derived from a (meth)acrylate with a branched chain having 8 to 18 carbon atoms. Examples of such alkyl (meth)acrylates include 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and isononyl (meth)acrylate. These can be used individually or in combination of two or more. Among these, 2-ethylhexyl (meth)acrylate is preferably used as the non-crosslinked (meth)acrylate unit (a1). Here, if the unit (a2) derived from a (meth)acrylate monomer having a crosslinking functional group is a unit derived from an acrylic monomer, the unit (a1) derived from a non-crosslinked (meth)acrylate is preferably a unit derived from a non-crosslinked methacrylate. In this case, the unit (a1) derived from the non-crosslinked (meth)acrylate is preferably a unit derived from the methacrylate having a branched chain having 8 to 18 carbon atoms, and more preferably 2-ethylhexyl methacrylate (2EHMA).

[0082] The branched alkyl group of the unit (a1) derived from non-crosslinked (meth)acrylate has a carbon number of 8 to 18, preferably 8 or more and 10 or less. By setting the carbon number of the branched alkyl group within the aforementioned range, the degree of polymerization of the base polymer (A) can be easily controlled, thereby obtaining an adhesive composition with excellent processability.

[0083] Relative to the total mass of the base polymer (A), the content of units (a1) derived from non-crosslinked (meth)acrylates in the base polymer (A) is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more. Furthermore, the content of units (a1) is preferably 95% by mass or less, more preferably 90% by mass or less. From the viewpoint of controlling water vapor transmission rate or hygroscopicity, the content of units (a1) is preferably at or above the lower limit of the aforementioned range, and from the viewpoint of controlling adhesive properties, it is preferably at or below the upper limit of the aforementioned range.

[0084] -Derived from unit (a2) of (meth)acrylic acid monomer with crosslinking functional group-

[0085] Examples of units (a2) derived from (meth)acrylic acid monomers with crosslinking functional groups include: monomer units containing hydroxyl groups, monomer units containing amino groups, monomer units containing glycidyl groups, and monomer units containing carboxyl groups. These monomer units may be one type or more than two types.

[0086] The hydroxyl-containing monomer unit is a repeating unit derived from a hydroxyl-containing monomer. Examples of hydroxyl-containing monomers include: hydroxyethyl methacrylate, 4-hydroxybutyl methacrylate, 2-hydroxypropyl methacrylate, and other hydroxyl-containing (meth)acrylates; (meth)acrylate mono(diethylene glycol) and other (meth)acrylates [(mono, di, or poly)alkylene glycol]; (meth)acrylate monocaprolactone and other (meth)acrylate lactones. Here, when the unit (a1) derived from a non-crosslinked (meth)acrylate is a unit derived from a non-crosslinked acrylate, the unit (a2) derived from a (meth)acrylate monomer having a crosslinking functional group is preferably a unit derived from a methacrylate monomer having a crosslinking functional group. In this case, the hydroxyl-containing monomer is preferably a hydroxyl-containing methacrylate, methacrylate [(mono, di, or poly)alkylene glycol], methacrylate lactone, more preferably a hydroxyl-containing methacrylate, and especially preferably 2-hydroxyethyl methacrylate (2HEMA).

[0087] Examples of amine-containing monomer units include repeating units derived from amine-containing monomers such as (meth)acrylamide and allylamine.

[0088] Monomer units containing glycidyl groups can be exemplified by repeating units derived from glycidyl acrylate and other monomer units containing glycidyl groups.

[0089] Monomeric units containing carboxyl groups include acrylic acid and methacrylic acid.

[0090] Relative to the total mass of the base polymer (A), the content of unit (a2) (preferably a hydroxyl-containing (meth)acrylate ester) derived from a (meth)acrylate monomer having crosslinking functional groups in the base polymer (A) is preferably 1.0% by mass or more, more preferably 5.0% by mass or more, and particularly preferably 10.0% by mass or more. Furthermore, the content of unit (a2) is preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. From the viewpoint of suppressing the increase in resistivity under humid and hot conditions or controlling the gel fraction, the content of unit (a2) is preferably at or above the lower limit of the aforementioned range, and from the viewpoint of controlling water vapor transmission rate or hygroscopicity, it is preferably at or below the upper limit of the aforementioned range. In the unit (a2) derived from a (meth)acrylate monomer having crosslinking functional groups, from the viewpoint of suppressing the increase of resistivity under humid and hot conditions or controlling the gel fraction, the content of hydroxyl-containing (meth)acrylate is preferably above the lower limit of the range, and from the viewpoint of controlling water vapor permeability or hygroscopicity, it is preferably below the upper limit of the range.

[0091] -Other single-volume units-

[0092] The base polymer (A) may, as needed, have other monomeric units besides units (a1) derived from non-crosslinked (meth)acrylates and monomeric (a2) units having crosslinking functional groups. Examples of other monomeric units include (meth)acrylate units with 4 or fewer carbon atoms or 10 or more carbon atoms. Specifically, examples include: methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, etc. Furthermore, other (meth)acrylate units may include (meth)acrylate units having a straight-chain alkyl group with 5 or more carbon atoms and 9 or fewer. Specifically, examples include: n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, etc. Furthermore, other (meth)acrylate units may include: cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and other (meth)acrylate units with cyclic groups, or (meth)acrylonitrile, vinyl acetate, styrene, vinyl chloride, vinylpyrrolidone, vinylpyridine, etc. The content of other monomeric units in the base polymer (A) is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

[0093] - Properties of the base polymer (A) -

[0094] The weight-average molecular weight (WMB) of the base polymer (A) is preferably 100,000 or more and 2,000,000 or less, more preferably 300,000 or more and 1,500,000 or less. By setting the WMB within this range, the semi-cured state of the adhesive sheet can be maintained, and sufficient conformability to uneven surfaces can be ensured. Furthermore, the WMB of the base polymer (A) is the value before crosslinking with the crosslinking agent. The WMB is determined by gel permeation chromatography (GPC) and the value is obtained based on polystyrene. Commercially available base polymers (A) can be used, or those synthesized by known methods can be used.

[0095] -Content of base polymer (A)-

[0096] The content of the base polymer (A) relative to the total mass of the adhesive composition is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. Furthermore, the content of the base polymer (A) is preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.

[0097] (Cross-linking agent (B))

[0098] Crosslinking agent (B) is a crosslinking agent that reacts with the base polymer (A) by heat. As the crosslinking agent (B), it can be appropriately selected from known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and butylated melamine compounds, taking into account their reactivity with the crosslinking functional groups of the base polymer (A). For example, in the case where a hydroxyl group is included as a crosslinking functional group, an isocyanate compound can be used based on the reactivity of the hydroxyl group. From the viewpoint of facilitating the crosslinking of units (a2) derived from (meth)acrylate monomers having crosslinking functional groups, isocyanate compounds and epoxy compounds are preferred.

[0099] Examples of isocyanate compounds include: toluene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, etc.

[0100] Examples of epoxy compounds include: ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, tetraglycidyl dimethyl diamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, trimethylolpropane polyglycidyl ether, dipropylene glycol polyglycidyl ether, polypropylene glycol polyglycidyl ether, sorbitol polyglycidyl ether, etc.

[0101] Commercially available products can be used as crosslinking agents (B) such as isocyanate compounds. Examples of commercially available products include Takenate D-110N (an isocyanate compound manufactured by Mitsui Chemicals Co., Ltd.).

[0102] As a crosslinking agent (B), one can be used alone, or two or more can be used together. The content of the crosslinking agent (B) in the adhesive composition can be appropriately selected according to the desired adhesion properties, etc., and there is no particular limitation. It can be set to 0.01 parts by mass or more and 5 parts by mass or less, and 0.10 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the base polymer (A).

[0103] In addition, relative to the total mass of the adhesive composition, the content of crosslinking agent (B) can be set to 0.01% by mass or more and 5.0% by mass or less, and can be set to 0.02% by mass or more and 2.0% by mass or less.

[0104] (Silane coupling agent (C))

[0105] As silane coupling agents, silane coupling agents containing reactive functional groups can be used, for example: mercapto-based silane coupling agents, (meth)acrylic acid-based silane coupling agents, isocyanate-based silane coupling agents, epoxy-based silane coupling agents, amino-based silane coupling agents, etc. As mercapto-based silane coupling agents, mercaptoalkoxy silane compounds (e.g., mercapto-substituted alkoxy oligomers, etc.) can be listed, but the content should be noted as described later. As other silane coupling agents containing reactive functional groups, those described in Japanese Patent Application Publication No. 2020-114914

[0094] to

[0096] can be listed, which is incorporated herein by reference.

[0106] Among these, from the viewpoint of reducing the sulfur content of the double-sided adhesive sheet, (meth)acrylic acid-based silane coupling agents, isocyanate-based silane coupling agents, epoxy-based silane coupling agents, and amino-based silane coupling agents are preferred, with epoxy-based silane coupling agents being even more preferred.

[0107] Commercially available products can be used as silane coupling agents. Examples of commercially available products include epoxy-based silane coupling agents (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) and mercapto-based silane coupling agents (X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd.).

[0108] When a silane coupling agent is included in the double-sided adhesive sheet, the content of the silane coupling agent is preferably set to 1 part by weight or less, and more preferably 0.5 parts by weight or less, relative to 100 parts by weight of the base polymer (A). From the viewpoint of reducing the sulfur content of the double-sided adhesive sheet, the content of the mercapto-based silane coupling agent is preferably set to 0.06 parts by weight or less, and more preferably 0.04 parts by weight or less, relative to 100 parts by weight of the base polymer (A).

[0109] (UV absorber (D))

[0110] The ultraviolet absorber can be selected from those with the maximum absorption wavelength in the ultraviolet region. Preferably, it is an ultraviolet absorber with the maximum absorption wavelength at or above 350 nm. Examples of ultraviolet absorbers with the maximum absorption wavelength at or above 350 nm include benzotriazole-based ultraviolet absorbers and benzotriazine-based ultraviolet absorbers. Additionally, compounds represented by the following general formula (1) or general formula (2) can be used as ultraviolet absorbers.

[0111] [Chemistry 1] General Formula (1)

[0112] In the above formula, R1 represents a hydrogen atom, a halogen atom, an alkoxy group with 1 to 4 carbon atoms, a nitro group, or a cyano group; R2 represents a hydrogen atom or an alkyl group with 1 to 8 carbon atoms; and R3 represents an alkyl-based structure.

[0113]

[0114] In the above formula, R4, R5, and R6 are hydrogen atoms, hydroxyl groups, alkyl groups, or halogen atoms, and R4, R5, and R6 are not all hydrogen atoms. Furthermore, the term "alkyl group" refers to a concept that includes substituted or unsubstituted alkyl groups, or substituted or unsubstituted alkoxy groups, etc., with alkyl as the main substituent.

[0115] The ultraviolet absorber preferably contains at least one compound that is oily or liquid at 23°C. Particularly preferred ultraviolet absorbers are those that improve compatibility by introducing a large molecular weight alkyl group into the aromatic ring of the basic skeleton and exhibit an oily or liquid state at 23°C. Here, "exhibiting an oily or liquid state at 23°C" means that the ultraviolet absorber is fluid even without a diluent.

[0116] Commercially available products can be used as ultraviolet absorbers. Examples of commercially available products include triazine-based ultraviolet absorbers (Tinuvin 477) and benzotriazole-based ultraviolet absorbers (Tinuvin 384-2, Tinuvin PS) manufactured by BASF Corporation of Japan.

[0117] Relative to 100 parts by weight of the base polymer (A), the content of the ultraviolet absorber is preferably 0.1 parts by weight to 8.0 parts by weight, more preferably 0.5 parts by weight to 4.0 parts by weight, and particularly preferably 1.0 parts by weight to 3.0 parts by weight. The ultraviolet absorber may be used alone or in combination with two or more types; when two or more types are used together, the total mass is preferably within the range described above.

[0118] (solvent(E))

[0119] The adhesive composition may also contain more solvent (E). Solvent (E) is used to improve the coating adaptability of the adhesive composition.

[0120] Examples of solvents (E) include: hydrocarbons such as hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane; halogenated hydrocarbons such as dichloromethane, trichloroethane, trichloroethylene, tetrachloroethylene, and dichloropropane; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and diacetone alcohol; ethers such as diethyl ether, diisopropyl ether, dioxane, and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, and ethyl butyrate; and polyols and their derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate.

[0121] Solvent (E) may be used alone or in combination with two or more. The content of solvent (E) in the adhesive composition is not particularly limited, but may be set to 25 parts by mass or more and 500 parts by mass or more and 30 parts by mass or more and 400 parts by mass relative to 100 parts by mass of the base polymer (A).

[0122] In addition, relative to the total mass of the adhesive composition, the solvent (E) content can be set to 10% by mass or more and 90% by mass or less, and can be set to 20% by mass or more and 80% by mass or less.

[0123] (Other ingredients)

[0124] The adhesive composition may also contain other components besides those described, without impairing the effects of the present invention. Other components may be selected from those known as additives for adhesives, such as plasticizers, monomers, polymerization initiators, antioxidants, metal corrosion inhibitors, adhesion promoters, hindered amine compounds, and light stabilizers, as needed.

[0125] Nonfunctional acrylic polymers can be used as plasticizers.

[0126] Examples of antioxidants include: phenolic antioxidants, amine antioxidants, lactone antioxidants, phosphorus antioxidants, and sulfur antioxidants. These antioxidants can be used alone or in combination of two or more.

[0127] Benzotriazole resins can be listed as metal corrosion inhibitors.

[0128] Examples of adhesives include: rosin-based resins, terpene-based resins, terpene phenol-based resins, coumarone-indene-based resins, styrene-based resins, xylene-based resins, phenolic resins, petroleum resins, and methacrylic resins.

[0129] <Manufacturing Method of Double-Sided Adhesive Sheets>

[0130] The manufacturing method of the double-sided adhesive sheet in this embodiment is not particularly limited.

[0131] The manufacturing steps of the double-sided adhesive sheet in this embodiment preferably include a step of applying an adhesive composition to the release sheet to form a coating film.

[0132] The following describes a representative step of forming a coating by applying an adhesive composition to a release sheet.

[0133] A semi-cured material (adhesive sheet) is formed by reacting the base polymer (A) and crosslinking agent (B) with a heated coating. To achieve a semi-cured state of the adhesive composition, an aging treatment can be performed: after coating, the solvent is removed, and then the adhesive sheet is left to stand at a certain temperature for a specific period of time. For example, the aging treatment can be performed by standing at 23°C for 7 days.

[0134] The application of the adhesive composition forming the adhesive sheet can be carried out using known coating apparatus. Examples of such coating apparatus include: scraper coaters, air knife coaters, roller coaters, bar coaters, gravure coaters, micro-gravure coaters, bar-scraper coaters, lip coaters, die coaters, curtain coaters, etc.

[0135] In addition, the coating can be heated using known heating devices such as heating furnaces and infrared lamps.

[0136] (How to use adhesive tape)

[0137] In the method of using the double-sided adhesive sheet of this embodiment, the release liner on the lightly peeling side of the adhesive sheet is peeled off, and the adhesive layer is brought into contact with the surface of the first substrate for bonding. Then, the release liner on the heavily peeling side is peeled off, and the adhesive layer on the side opposite to the first substrate is brought into contact with the second substrate. When the adhesive sheet is a semi-cured adhesive sheet with post-curing properties, the adhesive layer can be completely cured by irradiating an active energy line in this state.

[0138] [Laminated body]

[0139] The laminate of this embodiment includes: the double-sided adhesive sheet; and a first adhesive body and a second adhesive body, which are disposed on both surfaces of the double-sided adhesive sheet and are both optical components constituting a display device equipped with a touch panel. In the laminate, at least one of the first adhesive body and the second adhesive body has a metal conductive portion.

[0140] The first and second substrates are preferably optical components that constitute an image display device, namely, an image display device having a liquid crystal module with a cover material mounted on it. In this embodiment, the laminate is preferably an optical component that constitutes an image display device, namely, an image display device having a liquid crystal module with a cover material mounted on it. The cover material is a component disposed on the side of the touch panel opposite to the image display device. Examples of cover materials include cover glass or a cover lens made of resin.

[0141] The laminate of this embodiment is preferably obtained by the following steps: contacting the adhesive layer of the double-sided adhesive sheet with the surface of the substrate, and then using an autoclave or similar device to pressurize, heat, and degas the material to improve adhesion. In the laminate of this embodiment, the adhesive layer may not be completely hardened after contacting the surface of the substrate.

[0142] Figure 2 is a cross-sectional view showing an example of the structure of a laminate 20 formed by attaching the double-sided adhesive sheet 21 of this embodiment to the first substrate 22 and the second substrate 24. As shown in Figure 2, the first substrate 22 and the second substrate 24 may have conductive portions (27a, 27b, 27c, 27d) that form a stepped portion. In Figure 2, the first substrate 22 has conductive portions (27a, 27b), and the second substrate 24 has conductive portions (27c, 27d). Furthermore, the thickness of the conductive portions (27a, 27b, 27c, 27d) is typically 5 μm or more and 60 μm or less. As described above, the double-sided adhesive sheet 21 of this embodiment can also be attached to a component having a stepped portion, preferably one that follows the unevenness or concavity created by the stepped portion.

[0143] In this embodiment, the first and second adhesives are disposed on both surfaces of the double-sided adhesive sheet and are both optical components constituting a display device equipped with a touch panel. Furthermore, at least one of the first and second adhesives has a conductive metal portion.

[0144] As optical components, examples include various structural components found in optical products such as touch panels or image display devices. Examples of structural components for touch panels include: metal films with a mesh metal film or metal windings on a transparent resin film; metal glass with a mesh metal film or metal windings on the surface of a glass plate; ITO films with an ITO film on a transparent resin film; ITO glass with an ITO film on the surface of a glass plate; transparent conductive films formed by coating conductive polymers onto these transparent resin films; hard-coated films; and fingerprint-resistant films. Examples of structural components for image display devices include anti-reflective films, alignment films, polarizing films, phase difference films, and brightness-enhancing films used in liquid crystal display devices.

[0145] Materials used in these components include: glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cyclic olefin polymers, triacetin cellulose, polyimide, acetylated cellulose, etc.

[0146] In the case of the double-sided adhesive sheet in this embodiment, it can be used for bonding two adhered objects. In this case, the double-sided adhesive sheet of this embodiment can be used for bonding metal films to each other, bonding metal films to metallic glass, bonding metal films to ITO films, bonding ITO films to metallic glass, bonding the metal film of the touch panel to the liquid crystal panel, bonding the cover material to the metal film, etc. The double-sided adhesive sheet of this embodiment is preferably used for bonding the cover material to the metal film, and more preferably for bonding the cover material to the metal film of the touch panel.

[0147] In this embodiment, the first substrate is preferably a touch panel, and the second substrate is preferably an image display device or a cover material (preferably a cover glass). Furthermore, it is more preferable that at least one of the touch panel, the image display device, or the cover material includes a transparent conductive film having a mesh conductive portion and lead-out wiring connected to the mesh conductive portion. Particularly preferred is that the cover material includes a transparent conductive film having a mesh conductive portion and lead-out wiring connected to the mesh conductive portion.

[0148] In this embodiment, the conductive metal portion preferably comprises copper, silver, iron, tin, zinc, nickel, molybdenum, chromium, tungsten, lead, and alloys containing two or more metals selected from these metals; more preferably, it comprises copper, copper alloys, silver, and silver alloys; and most preferably, it comprises silver or silver alloys. As the conductive portion containing silver, it is preferably manufactured from a material containing silver halide. The double-sided adhesive sheet of this embodiment is most suitable for use as an adhesive for conductive fine wires containing silver, as described in Japanese Patent Application Publication Nos. 2014-209332

[0006] to

[0160] , which are manufactured by exposing and developing a photosensitive material containing silver halide. As a silver alloy, alloys made by adding palladium and copper to silver are preferably examples. Unoxidized metals have a higher tendency to ionize than metal oxides such as ITO; even in this case, the double-sided adhesive sheet of this embodiment can suppress ion migration. As a result, when the double-sided adhesive sheet of this embodiment comes into contact with the miniaturized and narrow-pitched electrodes or wiring, it can also prevent the electrodes or wiring from breaking or short-circuiting.

[0149] [Manufacturing method of laminated bodies]

[0150] The manufacturing method of the laminate in this embodiment includes the following steps: heating and pressurizing at least one of the following steps while the double-sided adhesive sheet of this embodiment is in contact with one surface of each of the first substrate and the second substrate, which are both optical components constituting a display device equipped with a touch panel, wherein at least one of the first substrate and the second substrate has a metal conductive portion.

[0151] There are no particular limitations on the step of applying pressure while the double-sided adhesive sheet of this embodiment is in contact with one surface of each of the first and second substrates. Preferably, degassing is performed by applying pressure, or the degassing step is performed before or after the pressure step. Furthermore, it is preferable to perform the pressure step simultaneously with heating, or the heating step is performed before or after the pressure step. For example, it is preferable to include the following steps: by contacting the double-sided adhesive sheet with the surfaces of the first and / or second substrates, and in this state, applying pressure, heating, and degassing using an autoclave or the like, or in this state, applying pressure and vacuum degassing to improve adhesion. [Example]

[0152] The features of the present invention will be described more specifically below with examples and comparative examples. The materials, amounts, proportions, processing contents, and processing procedures shown in the following examples may be appropriately modified without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as limited by the specific examples shown below.

[0153] [Synthesis example]

[0154] Synthesis of Crosslinked (Meth)acrylic Acid Copolymer A-1

[0155] A monomer mixture of 2-ethylhexyl methacrylate (2EHMA) and 2-hydroxyethyl acrylate (2HEA) in a mass ratio of 85:15 was polymerized in ethyl acetate as the polymerization solvent at 60°C in the presence of azobisisobutyronitrile (AIBN). This yielded a solution (a-1) of a crosslinked (meth)acrylic acid copolymer (A-1) with a solids content of 50% by mass and a weight average molecular weight of 450,000.

[0156] Synthesis of Crosslinked (Meth)acrylic Acid Copolymer A-2

[0157] A monomer mixture of 2-ethylhexyl acrylate (2EHA) and 2-hydroxyethyl methacrylate (2HEMA) in a mass ratio of 85:15 was polymerized in ethyl acetate as the polymerization solvent at 60°C in the presence of azobisisobutyronitrile (AIBN). This yielded a solution (a-2) of a crosslinked (meth)acrylic acid copolymer (A-2) with a solids content of 50% by mass and a weight average molecular weight of 480,000.

[0158] Synthesis of Crosslinked (Meth)acrylic Acid Copolymer A-3

[0159] A monomer mixture of 2-ethylhexyl methacrylate (2EHMA) and 2-hydroxyethyl acrylate (2HEA) in a mass ratio of 95:5 was polymerized in ethyl acetate as the polymerization solvent at 60°C in the presence of azobisisobutyronitrile (AIBN). This yielded a solution (a-3) of a crosslinked (meth)acrylic acid copolymer (A-3) with a solids content of 50% by mass and a weight average molecular weight of 440,000.

[0160] Synthesis of Crosslinked (Meth)acrylic Acid Copolymer A-4

[0161] A monomer mixture of 2-ethylhexyl acrylate (2EHA) and 2-hydroxyethyl methacrylate (2HEMA) in a mass ratio of 95:5 was polymerized in ethyl acetate as the polymerization solvent at 60°C in the presence of azobisisobutyronitrile (AIBN). This yielded a solution (a-4) of a crosslinked (meth)acrylic acid copolymer (A-4) with a solids content of 50% by mass and a weight average molecular weight of 460,000.

[0162] Synthesis of Crosslinked (Meth)acrylic Acid Copolymer A-5

[0163] A monomer mixture of 2-ethylhexyl methacrylate (2EHMA) and 2-hydroxyethyl acrylate (2HEA) in a mass ratio of 70:30 was polymerized in ethyl acetate as the polymerization solvent at 60°C in the presence of azobisisobutyronitrile (AIBN). This yielded a solution (a-5) of a crosslinked (meth)acrylic acid copolymer (A-5) with a solids content of 50% by mass and a weight average molecular weight of 450,000.

[0164] Synthesis of Crosslinked (Meth)acrylic Acid Copolymer A-6

[0165] A monomer mixture consisting of butyl acrylate (BA) and 2-hydroxyethyl acrylate (2HEA) in a mass ratio of 85:15 was polymerized in ethyl acetate as the polymerization solvent at 60°C in the presence of azobisisobutyronitrile (AIBN). This yielded a solution (a-6) of a crosslinked (meth)acrylic acid copolymer (A-6) with a solids content of 50% by mass and a weight average molecular weight of 500,000.

[0166] <Weight Average Molecular Weight>

[0167] The weight-average molecular weights of the crosslinked (meth)acrylic acid copolymer (A) and methyl methacrylate polymer (B) were determined using the following method and gel permeation chromatography (GPC). The GPC determination conditions are as described below.

[0168] ‧Solvent: Tetrahydrofuran

[0169] • Pipeline: Shodex KF801, KF803L, KF800L, KF800D (using four connectors manufactured by Showa Denko Co., Ltd.)

[0170] • Column temperature: 40℃

[0171] • Sample concentration: 0.5% by mass

[0172] • Detector: RI-2031plus (manufactured by JASCO)

[0173] • Pump: RI-2080plus (manufactured by JASCO)

[0174] • Flow rate: 0.8 ml / min

[0175] • Injection volume: 10μl

[0176] • Calibration curves: Calibration curves were obtained using 10 samples based on standard polystyrene (Shodex standard polystyrene manufactured by Showa Denko Co., Ltd.) with a value of Mw=1320~2,500,000.

[0177] [Example 1]

[0178] <Preparation of Adhesive Composition>

[0179] An adhesive composition was prepared by adding 0.1 parts by mass of an isocyanate compound (D-110N, manufactured by Mitsui Chemicals Co., Ltd.) as a crosslinking agent, 0.02 parts by mass of an epoxy silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 1.2 parts by mass of an ultraviolet absorber (Tinuvin 384-2, manufactured by BASF) to ethyl acetate at a concentration of 45% by mass and stirring.

[0180] <Making of Double-Sided Adhesive Sheets>

[0181] The adhesive composition prepared as described above was uniformly applied to the surface of a polyethylene terephthalate film (first release sheet, manufactured by Prince Aveta (F-Tex), 50RL-07(2)) having a release agent layer of 50 μm thickness after being treated with a silicone-based release agent, using a dressing applicator to form a coating film. The coating film was dried at 80°C for 3 minutes using an air-circulating constant temperature oven, thereby forming an adhesive layer (double-sided adhesive sheet of Example 1) on the surface of the first release sheet.

[0182] <Preparation of Adhesive Sheets with Release Sheets>

[0183] Subsequently, a second release sheet (manufactured by F-Tex, 38RL-07(L)) with a thickness of 38 μm and a different peel force than the first release sheet was bonded to the surface of the adhesive layer, and cured for 14 days at 23°C and 50% relative humidity. This resulted in an adhesive sheet with a release sheet structure consisting of an adhesive layer (adhesive sheet) sandwiched between a pair of release sheets with different peel forces: a first release sheet / adhesive layer / second release sheet.

[0184] [Example 2]

[0185] The solution (a-1) of acrylic copolymer (A-1) was changed to a solution (a-2) of acrylic copolymer (A-2), otherwise an adhesive sheet with a release sheet was obtained by the same procedure as in Example 1.

[0186] [Example 3]

[0187] The solution (a-1) of acrylic copolymer (A-1) was changed to a solution (a-3) of acrylic copolymer (A-3), and the epoxy silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) was changed to a mercapto silane coupling agent (X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd.). Otherwise, the adhesive sheet with release sheet was obtained by the same procedure as in Example 1.

[0188] [Example 4]

[0189] The solution (a-3) of acrylic copolymer (A-3) was changed to a solution (a-4) of acrylic copolymer (A-4), otherwise an adhesive sheet with a release sheet was obtained by the same procedure as in Example 3.

[0190] [Example 5]

[0191] The solution (a-1) of acrylic copolymer (A-1) was changed to a solution (a-5) of acrylic copolymer (A-5), and otherwise, an adhesive sheet with a release liner was obtained by the same procedure as in Example 1.

[0192] [Example 6]

[0193] The amount of the isocyanate compound (D-110N, manufactured by Mitsui Chemicals Co., Ltd.) used as a crosslinking agent was changed from 0.1 parts by weight to 0.04 parts by weight. Otherwise, the adhesive sheet with a release sheet was obtained by the same procedure as in Example 1.

[0194] [Comparative Example 1]

[0195] The amount of mercapto-based silane coupling agent (X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd.) added was changed from 0.02 parts by weight to 0.04 parts by weight. Otherwise, the adhesive sheet with release sheet was obtained by the same procedure as in Example 3.

[0196] [Comparative Example 2]

[0197] Except for the absence of 1.2 parts by weight of UV absorber (Tinuvin 384-2, manufactured by BASF), an adhesive sheet with a release liner was obtained by the same procedure as in Example 1.

[0198] [Comparative Example 3]

[0199] The solution (a-1) of acrylic copolymer (A-1) was changed to a solution (a-6) of acrylic copolymer (A-6), otherwise an adhesive sheet with a release liner was obtained by the same procedure as in Example 1.

[0200] [Characteristics of double-sided adhesive sheets]

[0201] The characteristics of the double-sided adhesive sheets obtained in each embodiment and comparative example were measured by the following procedure. The results are recorded in Table 1 below.

[0202] <Water vapor transmission rate>

[0203] The separator on the lightly peeled side of the adhesive sheet with a thickness of 50 μm, prepared in the examples and comparative examples, was peeled off and attached to a nonwoven sheet (manufactured by Nepi Wipe or Nepia) using a hand roller. Then, the adhesive surfaces of the double-sided adhesive sheet, on which the lightly peeled side of the adhesive sheet with a thickness of 50 μm prepared in the examples and comparative examples had been peeled off again, were attached to the adhesive surface of the heavily peeled side of the adhesive sheet with a nonwoven sheet liner, creating a sample sheet with an adhesive layer thickness of 100 μm, consisting of a nonwoven sheet / adhesive layer (100 μm) / heavily peeled separator. Next, on a glass bottle containing 50 ml of distilled water with an opening diameter of 2.5 cm, the diaphragm on the peeling side of the sample sheet was peeled off, exposing the adhesive side to the bottle side. The sample sheet was then used to cover the bottle opening and capped. Next, sealing tape was used to secure the sample sheet covering the bottle opening, ensuring it did not stick to the opening and completely sealing the glass bottle. The bottle was then placed in an oven set at 40°C and 20%RH (in other words, without water contacting the sample) for 24 hours without tilting. The weight reduction of water was determined by measuring the weight before and after the treatment, and the water vapor transmission rate (g / m² / 24h) was calculated.

[0204] <Water Absorption Rate>

[0205] Only the adhesive layers of the 50 μm thick double-sided adhesive sheets prepared in the examples and comparative examples were overlapped, and the adhesive layers with a thickness of approximately 5 mm were cut into 5 cm × 5 cm squares to prepare samples for water absorption evaluation. These samples were then placed in pre-weighed glass petri dishes and treated in a drying oven at 105°C for 5 hours. After removal from the drying oven, the samples, along with the petri dishes, were quickly weighed, and the weight of the pre-weighed petri dishes was subtracted to determine the absolute dry weight of the water absorption evaluation samples. Next, the evaluation samples, along with the petri dishes, were placed in a constant temperature and humidity chamber at 85°C and 95% RH for 24 hours. After removal (while water droplets remained on the evaluation samples or petri dishes), they were quickly weighed, and the weight of the petri dishes was subtracted, similar to when determining the absolute dry weight, to determine the weight of the water absorption evaluation samples after water absorption. The water absorption rate was calculated using the following formula 1.

[0206] (Water absorption rate) = (Weight of the sample used for evaluating water absorption rate after water absorption) / (Weight of the sample used for evaluating water absorption rate after absolute drying) × 100… Equation 1

[0207] <Sulfur content>

[0208] The 50 μm thick adhesive sheets with release liner prepared in the examples and comparative examples were cut into three pieces of 5 cm × 5 cm. Then, the lightly peeled and heavily peeled diaphragms of each adhesive sheet with release liner were peeled off, leaving only the adhesive layer. After weighing, the pieces were placed in a decomposition container, and 5 ml of nitric acid and 0.2 ml of hydrogen peroxide were added. Pressure acid decomposition was performed using a microwave decomposition system (MARS5, CEM Corporation). After decomposition, as measurement data, the decomposition solutions of the three pieces at each level were mixed and quantified to 20 ml. The sulfur content was quantified using an inductively coupled plasma (ICP) luminescence spectrophotometer (CIROS120, Rigaku Corporation), and converted to the sulfur content (mg) per kg of double-sided adhesive sheet.

[0209] <380nm transmittance>

[0210] The 50 μm thick adhesive sheet with release liner prepared in the examples and comparative examples was cut into 50 mm × 50 mm pieces. The diaphragm on the lightly peeled side was peeled off and attached to a glass slide (Matsunami Glass Co., Ltd., S9112) using a manual roller to prevent air from entering. Then, the diaphragm on the heavily peeled side was peeled off to prepare an evaluation sample of the glass / adhesive layer structure. The spectrophotometer transmittance of the evaluation sample at a wavelength of 380 nm was measured using a self-recording spectrophotometer (model: UV-3100PC, Shimadzu Corporation).

[0211] <Gel fraction>

[0212] The 50 μm adhesive strips with release diaphragms prepared in the examples and comparative examples were cut into 10 cm × 10 cm pieces. Then, the lightly peeled diaphragm and the heavily peeled diaphragm of each adhesive strip with release diaphragm were peeled off, and only 0.1 g of the adhesive layer (double-sided adhesive strip) was weighed and transferred to a sample vial. 30 ml of ethyl acetate was added, and the mixture was heated to 40 °C while shaking for 24 hours. Subsequently, the contents of the sample vial were separated by filtering with a 150-mesh stainless steel mesh. The residue on the mesh was dried at 100 °C for 3 hours, and the dried mass (g) was measured. The gel fraction was calculated based on the obtained dried mass using Equation 2 below.

[0213] Gel fraction (mass %) = (dry weight / weight of double-sided adhesive sheet) × 100… Equation 2

[0214] [Review of Double-Sided Adhesive Sheets]

[0215] The evaluation of the adhesive sheets with release tabs obtained in each embodiment and comparative example was performed by the following procedure. The results obtained, excluding total light transmittance and haze value, are recorded in Table 1 below.

[0216] <Ion migration inhibition>

[0217] (Evaluation of the fabrication of conductive thin films)

[0218] On a 100μm thick PET film (Cosmoshine A4360 manufactured by Toyobo Co., Ltd.) that has undergone easy bonding treatment, a pattern was printed using silver paste (RAFS059 manufactured by Toyo Chemical Co., Ltd.) via screen printing, as shown in Figure 3, with two straight and parallel lines including the lead-out wiring section. Subsequently, the silver paste was hardened by heat treatment at 135°C for 30 minutes, thereby obtaining an evaluation conductive film including silver wiring as shown in Figure 3. The width of the two wirings is 40μm, and the distance between the wirings is 15μm.

[0219] (Preparation of the evaluation sample)

[0220] The diaphragm on the lightly peeled side of the adhesive sheet with release tab prepared in the examples and comparative examples was peeled off. The adhesive side was then attached to a 100 μm PET film (Cosmoshine A4360 manufactured by Toyobo Co., Ltd.) using a manual roller to obtain a laminated film with a structure of PET film / adhesive layer / heavily peeled-off diaphragm. Subsequently, the heavily peeled-off diaphragm was peeled off from this laminated film and attached to the wiring of the prepared evaluation conductive film as shown in Figure 4. After autoclaving at 30°C and 0.5 MPa for 30 minutes, the sample was placed at 23°C and 50% relative humidity (RH) for 24 hours to prepare an evaluation sample.

[0221] (Evaluation of ion migration inhibition effect)

[0222] A circuit structure with wiring (parallel wiring) as shown in Figure 5 was formed on the evaluation sample. Ion migration tests were conducted by applying a 15V direct current (DC) voltage and treating the sample at 85°C and 95%RH for 240 hours. The wiring between the adhesive layers (double-sided adhesive sheets) of the evaluation sample treated as described above was observed using an optical microscope, and the ion migration suppression effect was evaluated based on the evaluation criteria shown below. Furthermore, no floating, peeling, or bubbles occurred in any of the samples from the embodiments and comparative examples.

[0223] A: No dendrite formation or yellow (or orange) discoloration is observed in the wiring.

[0224] B: A slight yellow (or orange) oozing discoloration was observed in the wiring.

[0225] C: Dendrite formation or yellow (or orange) exudate-like discoloration is observed between the wiring.

[0226] <Resistance value increases>

[0227] (Fabrication of conductive thin films for evaluating resistance values)

[0228] On a 100μm thick PET film (Cosmoshine A4360 manufactured by Toyobo Co., Ltd.) that has undergone easy bonding treatment, a mesh pattern with measuring electrodes (four corners) at both ends, as shown in Figure 6, was printed using silver paste (RAFS059 manufactured by Toyo Chemical Co., Ltd.). Subsequently, a heat treatment at 135°C for 30 minutes was performed to harden the silver paste, thereby obtaining a conductive film for evaluating resistance values, including silver wiring, as shown in Figure 6. The mesh pattern spacing was 500μm, and the line width was 15μm.

[0229] (Preparation of samples for resistance evaluation)

[0230] The diaphragm on the lightly peeled side of the adhesive sheet with release tab prepared in the examples and comparative examples was peeled off. The adhesive side was then attached to a 100 μm PET film (Cosmoshine A4360 manufactured by Toyobo Co., Ltd.) using a manual roller to obtain a laminated film with a structure of PET film / adhesive layer / heavily peeled side diaphragm. Subsequently, the heavily peeled side diaphragm was peeled off from this laminated film and attached to the wiring of the conductive film for resistance evaluation prepared as shown in Figure 7. After autoclaving at 30°C and 0.5 MPa for 30 minutes, the sample was placed at 23°C and 50% RH for 24 hours to prepare a resistance evaluation sample.

[0231] (The resistance value increases when treated at 85℃ and 95%)

[0232] The initial resistance value between the measuring electrodes at both ends of the conductive portion of the resistance evaluation sample was measured using a testing instrument. Subsequently, after treatment at 85°C and 95%RH for 240 hours, the resistance value between the electrodes was measured again using the testing instrument. The average resistance value before and after treatment (n=3) was used as described above, and the rate of increase in resistance value was calculated using Equation 3 below. The increase in resistance value was evaluated based on the evaluation criteria shown below. Furthermore, no floating, peeling, or bubbles occurred in the resistance evaluation samples of any of the embodiments and comparative examples.

[0233] (Resistance increase rate) = (Resistance value after 85℃ and 95% treatment) / (Initial resistance value) ... Equation 3

[0234] A: The rate of increase in resistance is less than 1.0.

[0235] B: The rate of increase in resistance is greater than 1.0 but less than 1.05.

[0236] C: The rate of increase in resistance is greater than 1.05.

[0237] (The resistance increases during UV treatment)

[0238] Instead of treating at 85°C and 95%RH for 100 hours, a Xenon Super Weather meter (Suga Testing Machine Co., Ltd. Super Xenon Weather meter SX75) was used with 70W / m² and a black panel temperature of 65°C for 100 hours. Otherwise, the resistance increase was performed in the same manner as for "resistance increase during 85°C and 95%RH treatment," and the resistance increase rate was calculated using Equation 4 below. The resistance increase was evaluated based on the evaluation criteria shown below. Furthermore, no floating, peeling, or bubbles occurred in the resistance evaluation samples of any of the embodiments and comparative examples.

[0239] (Resistance increase rate) = (Resistance after UV treatment) / (Initial resistance) ... Equation 4

[0240] A: The rate of increase in resistance is less than 1.0.

[0241] B: The rate of increase in resistance is greater than 1.0 but less than 1.05.

[0242] C: The rate of increase in resistance is greater than 1.05.

[0243] <Color value b*>

[0244] The same procedure was performed as for the evaluation sample prepared in the "380nm transmittance" measurement. An evaluation sample with a glass / adhesive layer structure was prepared, and the b* in the CIE1976 L*a*b* color system was measured according to JIS Z8781-4:2013.

[0245] Total light transmittance and haze value

[0246] Similar to the evaluation sample prepared for the "380nm transmittance" measurement, an evaluation sample with a glass / adhesive layer structure was prepared, and the total light transmittance of the obtained sample was measured according to JIS K 7361-1. Additionally, the haze value of the obtained sample was measured according to JIS K 7136. These measurements were performed three times, and the average value was taken as the measured value. An integrating sphere light transmittance measuring apparatus (Nippon Denshoku Kogyo Co., Ltd., NDH-5000) was used in the measurements.

[0247] As a result, the total light transmittance of the double-sided adhesive sheets prepared in the examples and comparative examples was 90%~100% in an environment of 23°C and 50% relative humidity, and the haze value was less than 1% in an environment of 23°C and 50% relative humidity.

[0248] [Table 1]

[0249] As can be seen from Table 1, when the optical components constituting a display device equipped with a touch panel include metal conductive parts, the double-sided adhesive sheet of the present invention can suppress ion migration of the metal conductive parts and suppress resistance changes caused by humid and hot environments and ultraviolet rays when the optical components are bonded together.

[0250] In Comparative Example 1, the sulfur content of the double-sided adhesive sheet exceeded the range specified in this invention, and the resistance value changed significantly due to the humid and hot environment and ultraviolet radiation.

[0251] In Comparative Example 2, the spectral transmittance of the double-sided adhesive sheet at a wavelength of 380 nm exceeds the range specified in this invention, and the resistance value changes significantly due to ultraviolet treatment.

[0252] In Comparative Example 3, the water vapor transmittance and water absorption rate of the double-sided adhesive sheet exceeded the range specified in this invention, resulting in significant ion migration in the conductive parts when the optical components were bonded together.

[0253] 1: Double-sided adhesive film with release liner

[0254] 11: Double-sided adhesive sheet (adhesive layer)

[0255] 12a, 12b: Peeling sheets

[0256] 20: Laminated body

[0257] 21: Double-sided adhesive sheet (adhesive layer)

[0258] 22: The first body to be attached

[0259] 24: The second body to be attached

[0260] 27a, 27b, 27c, 27d: Conductive parts

Claims

1. A double-sided adhesive sheet for bonding a first substrate and a second substrate, both of which constitute optical components of a display device equipped with a touch panel, wherein at least one of the first substrate and the second substrate has a metallic conductive portion, the double-sided adhesive sheet has an adhesive layer, the adhesive layer comprising a base polymer containing 70% to 98% by mass of units derived from (meth)acrylates having branched chains having 8 to 18 carbon atoms, and 1% to 20% by mass of units derived from (meth)acrylates containing hydroxyl groups, the sulfur content of the adhesive layer being less than 50 mg / kg, the spectral transmittance of the adhesive layer at a wavelength of 380 nm being less than 30%, the water vapor transmittance of the adhesive layer being less than 400 g / m² / 24h, or the water absorption rate being less than 1.0%.

2. The double-sided adhesive sheet as described in claim 1, wherein, The first substrate is a touch panel, and the second substrate is an image display device or a cover material.

3. The double-sided adhesive sheet as described in claim 1, wherein, The total light transmittance is 90% to 100%, the haze value is less than 1%, and the chromaticity b* is -1 to 1 as specified by the International Commission on Illumination 1976 L*a*b* color system.

4. The double-sided adhesive sheet as described in claim 1, wherein, The double-sided adhesive sheet has an adhesive layer, and the gel content of the adhesive layer is 40% to 90%.

5. A laminate, comprising: Double-sided adhesive sheet as described in any one of claims 1 to 4; The first adhesive and the second adhesive are disposed on both surfaces of the double-sided adhesive sheet and are both optical components constituting a display device equipped with a touch panel. In the laminate, at least one of the first adhesive and the second adhesive has a metal conductive portion.

6. The laminate as described in claim 5, wherein, The first substrate is a touch panel, and the second substrate is an image display device or a cover material. At least one of the touch panel, the image display device, or the cover material includes a transparent conductive film, namely a transparent conductive film having a mesh conductive portion and lead wires connected to the mesh conductive portion.

7. The laminate as described in claim 5, wherein, The conductive part contains silver or copper.

8. A method for manufacturing a laminate, comprising the step of applying pressure while a double-sided adhesive sheet as described in any one of claims 1 to 4 is in contact with one surface of each of a first adhesive body and a second adhesive body, both of which are optical components constituting a display device equipped with a touch panel, wherein at least one of the first adhesive body and the second adhesive body has a metal conductive portion.