JP7791304B2 - Transparent adhesive sheet and transparent adhesive sheet with release agent - Google Patents

Description

The present invention relates to a transparent adhesive sheet and a transparent adhesive sheet with release materials on both sides.

Transparent adhesives are used as a means of joining components in various devices, such as liquid crystal display devices. Such transparent adhesives are described, for example, in Patent Documents 1 to 3 listed below.

JP 2015-140408 A Special table 2016-505690 publication JP 2017-66294 A

In devices equipped with optical sensors, the optical sensors are often incorporated with their sensing surfaces facing or abutting a transparent cover member such as glass. In such devices equipped with optical sensors, when a transparent liquid adhesive is used as a means of bonding between the transparent cover member and the optical sensor, it may not be possible to bond the optical sensor to the transparent cover member with good orientation accuracy. This is because the thickness of the liquid adhesive can be uneven when applied or supplied to the transparent cover member or the optical sensor, and the adhesive can also overflow from between the cover member and the optical sensor, which are the objects to be bonded, during the bonding process. Poor orientation accuracy when bonding or attaching an optical sensor can result in reduced yields in the manufacture of devices incorporating the optical sensor.

On the other hand, conventional sheet-type adhesives, when used as a means of joining a transparent cover member and an optical sensor, may not be able to achieve a transparency sufficient to ensure the effective detection sensitivity of the optical sensor within the device while ensuring bonding reliability.

The present invention was conceived in light of the above circumstances, and its purpose is to provide a transparent adhesive sheet and a transparent adhesive sheet with a release material that can be used as a bonding material between the detection surface of an optical sensor and a transparent cover member, and that is suitable for manufacturing optical sensor-equipped devices with high yield and ensuring sensor detection sensitivity.

According to a first aspect of the present invention, a transparent adhesive sheet is provided. This transparent adhesive sheet is a thermosetting adhesive material, and when heat-cured by heating at 150°C for 1 hour, it has a transmittance (light transmittance) of 85% or more in the wavelength range of 450 to 1200 nm.

This transparent adhesive sheet can be manufactured with a highly uniform thickness and can supply adhesive material between objects to be joined in the form of a sheet that is resistant to fluidity (an adhesive material that is resistant to fluidity is less likely to spill out from between the objects during the joining process). Therefore, this transparent adhesive sheet makes it possible to join the objects to be joined, an optical sensor and a transparent cover member, with an adhesive layer that is more uniform in thickness than when using a liquid adhesive. The ability to join an optical sensor and a transparent cover member with an adhesive layer that is more uniform in thickness is advantageous for joining the optical sensor to the transparent cover member with high positional accuracy, and ultimately for manufacturing devices incorporating the optical sensor with high yield.

In addition, as described above, this transparent adhesive sheet has a transmittance of 85% or more in the wavelength range of 450 to 1200 nm when thermally cured by heating at 150°C for 1 hour. This transmittance is preferably 87% or more, and more preferably 90% or more. The transparent adhesive sheet exhibits such light transmittance across the visible light to near-infrared wavelength range after thermal curing, making it suitable for use as a bonding material between the detection surface of an optical sensor and a transparent cover member, ensuring the effective detection sensitivity of the optical sensor within the device.

As described above, this transparent adhesive sheet is suitable for use as a bonding material between the detection surface of an optical sensor and a transparent cover member, enabling high-yield manufacturing of devices equipped with optical sensors while also ensuring sensor detection sensitivity.

When the transparent adhesive sheet is heat-cured by heating at 150°C for 1 hour, the ratio (first ratio) of the transmittance at a wavelength of 450 nm after undergoing a moisture absorption test under conditions (first conditions) of 30°C, 70% relative humidity, and 200 hours to the transmittance at a wavelength of 450 nm before the test is preferably 0.9 or more, more preferably 0.92 or more, and even more preferably 0.94 or more. A configuration in which the decrease in transmittance of the transparent adhesive sheet due to the moisture absorption test under the first conditions is this small is advantageous for ensuring the above-mentioned sensor detection sensitivity. Furthermore, the first ratio is, for example, 1 or less.

When this transparent adhesive sheet is heat-cured by heating at 150°C for 1 hour, the ratio (second ratio) of the transmittance at a wavelength of 450 nm after a heating test at 260°C for 5 minutes (second conditions) to the transmittance at a wavelength of 450 nm before the heating test is preferably 0.9 or more, more preferably 0.92 or more, and more preferably 0.94 or more. A configuration in which the decrease in transmittance of the transparent adhesive sheet due to the heating test under the second conditions is this small is advantageous for ensuring the above-mentioned sensor detection sensitivity. Furthermore, the second ratio is, for example, 1 or less.

The viscosity of this transparent adhesive sheet or the adhesive composition that forms it at 120°C is preferably 1 to 30 kPa·s, more preferably 3 to 30 kPa·s, more preferably 4 to 27 kPa·s, and more preferably 5 to 25 kPa·s. This configuration is suitable for ensuring good wettability of this transparent adhesive sheet to the object to be joined.

The storage modulus of this transparent adhesive sheet at 250°C in a heat-cured state after heating at 150°C for 1 hour is preferably 0.5 to 50 MPa, more preferably 0.6 to 45 MPa, and even more preferably 0.7 to 40 MPa. This configuration is suitable for ensuring the post-curing bonding strength of the transparent adhesive sheet between objects to be joined, and is therefore suitable for ensuring the bonding reliability between objects joined by this transparent adhesive sheet.

When this transparent adhesive sheet is in a heat-cured state after heating at 150°C for 1 hour, its weight loss at 300°C, as measured by thermogravimetry under conditions of a nitrogen atmosphere, a heating rate of 10°C/min, and a temperature range of 23 to 300°C, is preferably 1.5% or less, and more preferably 1.2% or less. This configuration is suitable for ensuring the heat resistance of this transparent adhesive sheet, and therefore is suitable for ensuring the bonding reliability of objects bonded with this transparent adhesive sheet.

This transparent adhesive sheet exhibits a peel adhesion strength of preferably 1 N/10 mm or more, and more preferably 1.5 N/10 mm or more, against a flat glass surface in a peel test conducted at 23°C, a peel angle of 180°, and a peel speed of 30 mm/min. This configuration is advantageous for ensuring the adhesive strength of this transparent adhesive sheet to the object to be joined.

The ratio (third ratio) of the glass shear adhesive strength of the transparent adhesive sheet after undergoing a moisture absorption test at 40°C, 95% relative humidity, and 120 hours (third conditions) in the glass-adhered state to the glass shear adhesive strength when the transparent adhesive sheet is heated at 150°C for 1 hour and then adhered to a flat glass surface (glass-adhered state) is preferably 0.6 or more, more preferably 0.7 or more, and more preferably 0.75 or more. Such a small decrease in the glass shear adhesive strength of the transparent adhesive sheet after undergoing a moisture absorption test under the third conditions is advantageous for ensuring the bonding reliability of objects bonded with the transparent adhesive sheet. The third ratio is, for example, 1.5 or less.

When this transparent adhesive sheet is cured by heating at 150°C for 1 hour, its refractive index at a wavelength of 633 nm is preferably 1.4 to 1.5, and more preferably 1.42 to 1.48. This configuration is suitable for ensuring the above-mentioned sensor detection sensitivity.

The transparent adhesive sheet preferably contains an acrylic resin. This acrylic resin preferably has a nitrile group and preferably an epoxy group. The proportion of the acrylic resin in the organic components contained in the transparent adhesive sheet is preferably 95% by mass or more, more preferably 97% by mass or more. Furthermore, the transparent adhesive sheet preferably does not contain, or is substantially free of, epoxy resin and/or phenol resin. These configurations are suitable for achieving a high degree of transparency in the transparent adhesive sheet.

When the transparent adhesive sheet contains an acrylic resin such as a nitrile group-containing acrylic resin, the average molecular weight of the acrylic resin is preferably 400,000 or less, and more preferably 350,000 or less. This configuration is suitable for achieving the above-mentioned preferred configuration regarding the viscosity of the transparent adhesive sheet.

The transparent adhesive sheet preferably contains a filler with an average particle size of 5 to 100 nm. The filler content in the transparent adhesive sheet is preferably 5 to 45% by mass, more preferably 6 to 40% by mass, and even more preferably 7 to 35% by mass. These configurations are suitable for ensuring the heat resistance of the transparent adhesive sheet, and therefore are suitable for ensuring the bonding reliability of objects bonded with the transparent adhesive sheet. These configurations also contribute to ensuring the transparency of the transparent adhesive sheet.

The present transparent adhesive sheet preferably contains a phosphorus-based antioxidant. The content of the phosphorus-based antioxidant in the present transparent adhesive sheet is preferably 0.1 to 2 mass %, more preferably 0.3 to 1.5 mass %. These configurations are suitable for preventing and suppressing oxidation of the components contained in the present transparent adhesive sheet, and therefore are suitable for preventing and suppressing a decrease in transparency due to such oxidation.

The transparent adhesive sheet preferably contains an imidazole-based curing agent. The content of the imidazole-based curing agent in the transparent adhesive sheet is preferably 0.1 to 2 mass %, more preferably 0.2 to 1.5 mass %. This configuration is suitable for achieving both the curability and storage stability of the transparent adhesive sheet.

According to a second aspect of the present invention, a transparent adhesive sheet with a release material is provided. This transparent adhesive sheet with a release material has a laminated structure including a first release material, a second release material, and the transparent adhesive sheet according to the first aspect described above between these release materials. The transparent adhesive sheet according to the first aspect of the present invention may thus be accompanied by a release material.

In this transparent adhesive sheet with a release liner, the first release liner preferably has a thickness of 38 μm or more, and the second release liner preferably has a thickness of 25 μm or more. The ratio of the thickness of the first release liner to the thickness of the second release liner is preferably 0.2 to 1.8, more preferably 0.22 to 1.6, and even more preferably 0.3 to 1.55. This configuration is preferable from the perspective of ease of handling this transparent adhesive sheet with a release liner. Specifically, this configuration is suitable for preventing or suppressing the occurrence of wrinkles or folds in the transparent adhesive sheet when the first release liner is peeled off from the transparent adhesive sheet (which has the second release liner on the side opposite the first release liner).

In this transparent adhesive sheet with a release liner, the first release liner exhibits a first peel adhesion strength of preferably 0.01 N/100 mm or greater, more preferably 0.015 N/100 mm or greater, in a peel test at 100°C, a peel angle of 180°, and a peel speed of 300 mm/min, and the second release liner exhibits a second peel adhesion strength of preferably 0.04 N/100 mm or greater, in a peel test at 100°C, a peel angle of 180°, and a peel speed of 300 mm/min, in a peel test. The ratio of the first peel adhesion strength to the second peel adhesion strength is preferably 0.01 to 0.75, more preferably 0.02 to 0.7. These configurations are preferred from the standpoint of achieving a balance between sufficient adhesion of each release liner to the transparent adhesive sheet (which are often peeled separately from the transparent adhesive sheet in different stages) and adequate releasability of both release liner materials from the transparent adhesive sheet when handling this transparent adhesive sheet with a release liner.

In this transparent adhesive sheet with a release material, the second release material is preferably a dicing tape having a laminated structure including a substrate and an adhesive layer, and the transparent adhesive sheet is releasably adhered to the adhesive layer of the dicing tape. In this way, the transparent adhesive sheet according to the first aspect of the present invention may be configured as a transparent adhesive sheet with a dicing tape.

The adhesive layer of the dicing tape preferably contains an acrylic resin having a 2-ethylhexyl group. The thickness of this adhesive layer is preferably 5 to 40 μm, and more preferably 10 to 30 μm. This configuration is suitable for achieving high adhesion between the dicing tape adhesive layer and the transparent adhesive sheet.

A third aspect of the present invention provides a bonding method. In this bonding method, the transparent adhesive sheet according to the first aspect of the present invention is used to bond a glass member to another member. In this way, the transparent adhesive sheet according to the first aspect of the present invention and the transparent adhesive sheet with release material according to the second aspect of the present invention may be used to bond a glass member to another member.

According to a fourth aspect of the present invention, another bonding method is provided. In this bonding method, the transparent adhesive sheet according to the first aspect of the present invention is used to bond a transparent resin member having a transmittance of 80% or more at a wavelength of 500 nm to another member. In this way, the transparent adhesive sheet according to the first aspect of the present invention and the transparent adhesive sheet with release material according to the second aspect of the present invention may be used to bond the transparent resin member to another member.

According to a fifth aspect of the present invention, another bonding method is provided. This bonding method includes the steps of: laminating the transparent adhesive sheet according to the first aspect of the present invention to a component; singulating the component together with the transparent adhesive sheet to obtain component pieces with the transparent adhesive sheet attached; and bonding the component pieces with the transparent adhesive sheet attached to another component via the transparent adhesive sheet. This bonding method makes it possible to efficiently obtain component pieces (one of the components to be bonded) with the transparent adhesive sheet attached. Therefore, this bonding method is suitable for improving the efficiency of the work and process of bonding components to be bonded.

1 is a cross-sectional view of a transparent adhesive sheet with a release material according to one embodiment of the present invention. 1 is a cross-sectional view showing bonding between members by a transparent adhesive sheet according to one embodiment of the present invention. 1 is a cross-sectional view of a transparent adhesive sheet with a release material according to one embodiment of the present invention. 4 shows some steps in a bonding method in which the transparent adhesive sheet with a release material shown in FIG. 3 is used. 4 shows some steps in a bonding method in which the transparent adhesive sheet with a release material shown in FIG. 3 is used. 4 shows some steps in a bonding method in which the transparent adhesive sheet with a release material shown in FIG. 3 is used. 4 shows some steps in a bonding method in which the transparent adhesive sheet with a release material shown in FIG. 3 is used.

Figure 1 is a cross-sectional schematic diagram of a transparent adhesive sheet X1 with a release material according to one embodiment of the present invention. The transparent adhesive sheet X1 with a release material has a laminated structure including a transparent adhesive sheet 10 according to one embodiment of the present invention and release liners R1 and R2, which are release materials.

The transparent adhesive sheet 10 is a thermosetting, transparent sheet-like adhesive that can be used, for example, as an adhesive for bonding the detection surface of an optical sensor to a transparent cover member during the manufacturing process of a device equipped with an optical sensor. The transparent adhesive sheet 10 may have a composition (first composition) containing a thermosetting resin and a thermoplastic resin as resin components, or a composition (second composition) containing a thermoplastic resin as a resin component that has a thermosetting functional group that can react with a curing agent to form a bond. When the transparent adhesive sheet 10 has the second composition, the transparent adhesive sheet 10 does not need to further contain a thermosetting resin.

When the transparent adhesive sheet 10 has the first composition, examples of the thermosetting resin include epoxy resin, phenolic resin, amino resin, unsaturated polyester resin, polyurethane resin, silicone resin, and thermosetting polyimide resin. The transparent adhesive sheet 10 may contain one type of thermosetting resin, or two or more types of thermosetting resins.

Examples of the epoxy resins include bifunctional and polyfunctional epoxy resins such as bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, brominated bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol AF epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, fluorene epoxy resin, phenol novolac epoxy resin, orthocresol novolac epoxy resin, trishydroxyphenylmethane epoxy resin, and tetraphenylolethane epoxy resin. Epoxy resins also include hydantoin epoxy resin, trisglycidyl isocyanurate epoxy resin, and glycidylamine epoxy resin. The transparent adhesive sheet 10 may contain one type of epoxy resin or two or more types of epoxy resins.

When the transparent adhesive sheet 10 has the first composition, the content of the thermosetting resin in the transparent adhesive sheet 10 is preferably 1 to 80% by mass, and more preferably 1 to 50% by mass, from the viewpoint of allowing the transparent adhesive sheet 10 to properly function as a thermosetting adhesive.

When an epoxy resin is used as the thermosetting resin in the transparent adhesive sheet 10, phenolic resin and imidazole-based curing agents are preferred as curing agents for imparting thermosetting properties to the epoxy resin.

Examples of phenolic resins that can act as curing agents for epoxy resins include novolac-type phenolic resins, resol-type phenolic resins, and polyoxystyrenes such as polyparaoxystyrene. Examples of novolac-type phenolic resins include phenol novolac resins, phenol aralkyl resins, cresol novolac resins, tert-butylphenol novolac resins, and nonylphenol novolac resins. The transparent adhesive sheet 10 may contain one type of phenolic resin, or two or more types of phenolic resins.

Examples of the imidazole-based curing agents include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-methyl-4-ethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2 Examples of imidazole-based curing agents include 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. When the transparent adhesive sheet 10 contains an imidazole-based curing agent, the content of the imidazole-based curing agent in the transparent adhesive sheet is preferably 0.1 to 2 mass%, more preferably 0.2 to 1.5 mass%.

The thermoplastic resin in the transparent adhesive sheet 10 functions as a binder, for example. When the transparent adhesive sheet 10 has the first composition, examples of the thermoplastic resin in the transparent adhesive sheet 10 include acrylic resin, natural rubber, butyl rubber, isoprene rubber, chloroprene rubber, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, polybutadiene resin, polycarbonate resin, thermoplastic polyimide resin, polyamide resin such as 6-nylon and 6,6-nylon, phenoxy resin, saturated polyester resin such as polyethylene terephthalate and polybutylene terephthalate, polyamide-imide resin, and fluororesin. The transparent adhesive sheet 10 may contain one type of thermoplastic resin or two or more types of thermoplastic resin. Acrylic resin is preferred as the thermoplastic resin in the transparent adhesive sheet 10 because it has low ionic impurities and high heat resistance.

When the transparent adhesive sheet 10 contains an acrylic resin as a thermoplastic resin, the acrylic polymer that constitutes the acrylic resin preferably contains the largest amount of monomer units derived from (meth)acrylic acid esters by mass. "(Meth)acrylic" refers to "acrylic" and/or "methacrylic."

(Meth)acrylic acid esters that form the monomer units of the acrylic polymers described above, i.e., (meth)acrylic acid esters that are constituent monomers of acrylic polymers, include, for example, (meth)acrylic acid alkyl esters, (meth)acrylic acid cycloalkyl esters, and (meth)acrylic acid aryl esters. Examples of (meth)acrylic acid alkyl esters include the methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, isobutyl ester, s-butyl ester, t-butyl ester, pentyl ester, isopentyl ester, hexyl ester, heptyl ester, octyl ester, 2-ethylhexyl ester, isooctyl ester, nonyl ester, decyl ester, isodecyl ester, undecyl ester, dodecyl ester, tridecyl ester, tetradecyl ester, hexadecyl ester, octadecyl ester, and eicosyl ester of (meth)acrylic acid. Examples of (meth)acrylic acid cycloalkyl esters include the cyclopentyl ester and cyclohexyl ester of (meth)acrylic acid. Examples of (meth)acrylic acid aryl esters include phenyl (meth)acrylate and benzyl (meth)acrylate. A single type of (meth)acrylic acid ester may be used as a constituent monomer of an acrylic polymer, or two or more types of (meth)acrylic acid esters may be used. Furthermore, acrylic polymers for acrylic resins can be obtained by polymerizing the raw material monomers used to form them. Polymerization techniques include, for example, solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization.

The acrylic polymer may contain one or more other monomers copolymerizable with (meth)acrylic acid esters as constituent monomers, for example, to improve its cohesive strength or heat resistance. Examples of such monomers include carboxyl group-containing monomers, acid anhydride monomers, hydroxyl group-containing monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, acrylamide, and acrylonitrile. Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of acid anhydride monomers include maleic anhydride and itaconic anhydride. Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and 4-hydroxymethylcyclohexylmethyl (meth)acrylate. Examples of sulfonic acid group-containing monomers include styrene sulfonic acid, allyl sulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, and (meth)acryloyloxynaphthalenesulfonic acid. Examples of phosphate group-containing monomers include 2-hydroxyethyl acryloyl phosphate. From the viewpoint of realizing high cohesive strength in the transparent adhesive sheet 10, when an acrylic resin is contained in the transparent adhesive sheet 10, the acrylic polymer constituting the acrylic resin is a nitrile group-containing acrylic polymer. The nitrile group-containing acrylic polymer is, for example, an acrylic polymer containing acrylonitrile as a constituent monomer, and examples of such acrylic polymers include copolymers of ethyl acrylate, butyl acrylate, and acrylonitrile.

When the transparent adhesive sheet 10 has the first composition, the content of the thermoplastic resin in the transparent adhesive sheet 10 is preferably 30 to 95% by mass, and more preferably 35 to 90% by mass, from the viewpoint of properly exhibiting the binder function of the thermoplastic adhesive.

When the transparent adhesive sheet 10 has the second composition, the thermoplastic resin containing a thermosetting functional group in the transparent adhesive sheet 10 can be, for example, an acrylic resin containing a thermosetting functional group. The acrylic polymer forming the acrylic backbone of this acrylic resin containing a thermosetting functional group preferably contains, by mass, the largest amount of monomer units derived from a (meth)acrylic acid ester. Examples of such (meth)acrylic acid esters include the (meth)acrylic acid esters described above as constituent monomers of the acrylic polymer described above when the transparent adhesive sheet 10 has the first composition. The acrylic polymer forming the acrylic backbone of the thermosetting functional group-containing acrylic resin may contain, as constituent monomers, one or more other monomers copolymerizable with a (meth)acrylic acid ester, for example, to improve the cohesive strength or heat resistance of the acrylic resin. Examples of such other constituent monomers include carboxyl group-containing monomers, acid anhydride monomers, hydroxyl group-containing monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, acrylamide, and acrylonitrile. Specifically, the above-mentioned copolymerizable other constituent monomers can be used as the constituent monomers of the acrylic polymer described above when the transparent adhesive sheet 10 has the first composition. From the perspective of achieving high cohesive strength in the transparent adhesive sheet 10, the acrylic polymer that forms the acrylic skeleton of the acrylic resin with thermosetting functional groups in the transparent adhesive sheet 10 is a nitrile group-containing acrylic polymer. The nitrile group-containing acrylic polymer is, for example, an acrylic polymer that contains acrylonitrile as a constituent monomer. Examples of such acrylic polymers include copolymers of ethyl acrylate, butyl acrylate, and acrylonitrile.

Examples of thermosetting functional groups for forming a thermoplastic resin having a thermosetting functional group include an epoxy group, a carboxy group, a hydroxy group, and an isocyanate group, with an epoxy group being preferred. The thermoplastic resin having a thermosetting functional group is preferably a thermoplastic resin having an epoxy group. When the transparent adhesive sheet 10 contains an epoxy group-containing thermoplastic resin, the transparent adhesive sheet 10 preferably contains an imidazole-based curing agent as a curing agent. Specific examples of imidazole-based curing agents are as described above. Furthermore, when the transparent adhesive sheet 10 contains an imidazole-based curing agent, the content of the imidazole-based curing agent in the transparent adhesive sheet is preferably 0.1 to 2% by mass, more preferably 0.2 to 1.5% by mass.

When the transparent adhesive sheet 10 has the second composition, the content of the thermosetting functional group-containing acrylic resin, such as the nitrile group-containing acrylic resin, in the transparent adhesive sheet 10 is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 80% by mass or more, more preferably 95% by mass or more, and more preferably 97% by mass or more. Furthermore, when the transparent adhesive sheet 10 has the second composition, the transparent adhesive sheet 10 does not need to further contain a thermosetting resin, and preferably does not contain or substantially does not contain an epoxy resin and/or a phenol resin.

When the transparent adhesive sheet 10 has the first composition, the average molecular weight of the thermoplastic resin, such as an acrylic resin, contained in the transparent adhesive sheet 10, and when the transparent adhesive sheet 10 has the second composition, the average molecular weight of the thermoplastic resin with a thermosetting functional group contained in the transparent adhesive sheet 10, is preferably 450,000 or less, and more preferably 400,000 or less. Such a configuration is suitable for achieving the above-mentioned preferred configuration regarding the viscosity of the transparent adhesive sheet.

The transparent adhesive sheet 10 may contain a filler. Adding a filler to the transparent adhesive sheet 10 is preferable for adjusting the sheet's physical properties, such as its elastic modulus, viscosity, breaking strength, and breaking elongation. Examples of fillers include inorganic and organic fillers. Examples of inorganic filler materials include aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate whiskers, boron nitride, crystalline silica, and amorphous silica. Examples of inorganic filler materials include elemental metals such as aluminum, gold, silver, copper, and nickel, as well as alloys, amorphous carbon, and graphite. Examples of organic filler materials include polymethyl methacrylate (PMMA), polyimide, polyamideimide, polyetheretherketone, polyetherimide, and polyesterimide. The transparent adhesive sheet 10 may contain one type of filler or two or more types of fillers. The filler may also have various shapes, such as spherical, needle-like, or flake-like.

When the transparent adhesive sheet 10 contains a filler, the average particle size of the filler is preferably 5 to 100 nm, more preferably 5 to 60 nm. The average particle size of the filler can be determined, for example, using a photometric particle size distribution analyzer (product name "LA-910", manufactured by Horiba, Ltd.). When the transparent adhesive sheet 10 contains a filler, the filler content is preferably 5 to 45 mass%, more preferably 6 to 40 mass%, and more preferably 7 to 35 mass%. These configurations are suitable for ensuring the heat resistance of the transparent adhesive sheet 10, and therefore are suitable for ensuring the reliability of the bond between objects bonded by the transparent adhesive sheet 10. These configurations also contribute to ensuring the transparency of the transparent adhesive sheet 10.

The transparent adhesive sheet 10 may contain an antioxidant. Examples of antioxidants include phosphorus-based antioxidants, phenol-based antioxidants, and thioether-based antioxidants. The transparent adhesive sheet 10 preferably contains a phosphorus-based antioxidant. Examples of phosphorus-based antioxidants include 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and 2,2'-methylenebis(4,6-di-tert-butylphenyl)2-ethylhexylphosphite. When the transparent adhesive sheet 10 contains an antioxidant such as a phosphorus-based antioxidant, the content of the antioxidant in the transparent adhesive sheet 10 is preferably 0.1 to 2 mass%, and more preferably 0.3 to 1.5 mass%.

The transparent adhesive sheet 10 may contain one or more other components as needed. Examples of such other components include a flame retardant, a silane coupling agent, and an ion trapping agent.

The thickness of the transparent adhesive sheet 10 is preferably 5 μm or more, more preferably 10 μm or more, and more preferably 20 μm or more. The thickness of the transparent adhesive sheet 10 is preferably 150 μm or less, more preferably 140 μm or less, more preferably 130 μm or less, and more preferably 120 μm or less.

When the transparent adhesive sheet 10 is thermally cured by heating at 150°C for 1 hour, its transmittance in the wavelength range of 450 to 1200 nm is 85% or more, preferably 87% or more, and more preferably 90% or more.

When the transparent adhesive sheet 10 is in a heat-cured state after being heated at 150°C for 1 hour, the ratio (first ratio) of the transmittance at a wavelength of 450 nm after undergoing a moisture absorption test under conditions (first conditions) of 30°C, 70% relative humidity, and 200 hours to the transmittance at a wavelength of 450 nm before the test is preferably 0.9 or more, more preferably 0.92 or more, and even more preferably 0.94 or more. The first ratio is, for example, 1 or less.

When the transparent adhesive sheet 10 is in a heat-cured state after being heated at 150°C for 1 hour, the ratio (second ratio) of the transmittance at a wavelength of 450 nm after a heating test at 260°C for 5 minutes (second conditions) to the transmittance at a wavelength of 450 nm before the heating test is preferably 0.9 or more, more preferably 0.92 or more, and more preferably 0.94 or more. The second ratio is, for example, 1 or less.

The viscosity of the transparent adhesive sheet 10 or the adhesive composition that forms it at 120°C is preferably 1 to 30 kPa·s, more preferably 3 to 30 kPa·s, more preferably 4 to 27 kPa·s, and more preferably 5 to 25 kPa·s.

The transparent adhesive sheet 10 preferably has a storage modulus at 250°C in a heat-cured state after heating at 150°C for 1 hour of 0.5 to 50 MPa, more preferably 0.6 to 45 MPa, and even more preferably 0.7 to 40 MPa.

When the transparent adhesive sheet 10 is in a heat-cured state after heating at 150°C for 1 hour, the weight loss at 300°C measured by thermogravimetry under conditions of a nitrogen atmosphere, a temperature increase rate of 10°C/min, and a temperature increase range of 23 to 300°C is preferably 1.5% or less, and more preferably 1.2% or less.

The transparent adhesive sheet 10 exhibits a peel adhesion strength of 1 N/10 mm or more, preferably 1.5 N/10 mm or more, against a flat glass surface in a peel test conducted at 23°C, a peel angle of 180°, and a peel speed of 30 mm/min.

The ratio (third ratio) of the glass shear adhesive strength of the transparent adhesive sheet 10 after undergoing a moisture absorption test at 40°C, 95% relative humidity, and 120 hours (third conditions) in the glass-adhered state to the glass shear adhesive strength in the state (glass-adhered state) after heating at 150°C for 1 hour, is preferably 0.6 or more, more preferably 0.7 or more, and even more preferably 0.75 or more. The third ratio is, for example, 1.5 or less, and may be 1 or less.

The refractive index of the transparent adhesive sheet 10 at a wavelength of 633 nm when it is heat-cured by heating at 150°C for 1 hour is preferably 1.4 to 1.5, and more preferably 1.42 to 1.48.

The release liners R1 and R2 in the release-attached transparent adhesive sheet X1 are elements that cover and protect the surface of the transparent adhesive sheet 10, and are peeled off from the sheet when the transparent adhesive sheet 10 is used. The release liners R1 and R2 can be made of a resin film or paper material whose surface, which will come into close contact with the transparent adhesive sheet 10, has been subjected to, for example, corona treatment and subsequent release treatment.

Resin materials for the resin film used in the release liner include, for example, polyolefins and polyesters. Examples of polyolefins include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, very low-density polyethylene, random copolymer polypropylene, block copolymer polypropylene, homopolypropylene, polybutene, polymethylpentene, ethylene-vinyl acetate copolymer (EVA), ionomer resin, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester copolymer, ethylene-butene copolymer, and ethylene-hexene copolymer. Examples of polyesters include polyethylene terephthalate (PET), polyethylene naphthalate, and polybutylene terephthalate (PBT). The resin film used in the release liner may be a non-oriented film, a uniaxially oriented film, or a biaxially oriented film. Release liners R1 and R2 may each be composed of one type of material or two or more types of materials. Release liners R1 and R2 may have a single-layer structure or a multi-layer structure. Furthermore, examples of release treatment agents used in the above-mentioned release treatment include silicone-based release treatment agents, long-chain alkyl-based release treatment agents, fluorine-based release treatment agents, and molybdenum sulfide release treatment agents.

In the release-backed transparent adhesive sheet X1, the thickness _T1 of the release liner R1 (first release liner) is preferably 38 μm or more, and the thickness _T2 of the release liner R2 (second release liner) is preferably 25 μm or more. The ratio ( _T1 / _T2 ) of the thickness _{T1 of} the release liner R1 to the thickness T2 of the release liner R2 is preferably 0.2 to 1.8, more preferably 0.22 to 1.6, and even more preferably 0.3 to 1.55. This configuration is preferable from the viewpoint of ease of handling the release-backed transparent adhesive sheet X1. Specifically, this configuration is suitable for preventing or suppressing the occurrence of wrinkles or folds in the transparent adhesive sheet 10 when the release liner R1 is peeled from the transparent adhesive sheet 10 (which has release liner R2 on the side opposite to release liner R1).

In the release-attached transparent adhesive sheet X1, the release liner R1 (first release liner) exhibits a first peel adhesion strength of preferably 0.01 N/100 mm or greater, more preferably 0.015 N/100 mm or greater, to the transparent adhesive sheet 10 in a peel test at 100°C, a peel angle of 180°, and a peel speed of 300 mm/min. The release liner R2 (second release liner) exhibits a second peel adhesion strength of preferably 0.04 N/100 mm or greater to the transparent adhesive sheet 10 in a peel test at 100°C, a peel angle of 180°, and a peel speed of 300 mm/min. The ratio of the first peel adhesion strength to the second peel adhesion strength is preferably 0.01 to 0.75, more preferably 0.02 to 0.7. These configurations are preferable from the viewpoint of balancing sufficient adhesion of release liners R1, R2 (which are often peeled separately from transparent adhesive sheet 10 at different stages) to transparent adhesive sheet 10 when handling release-attached transparent adhesive sheet X1, and appropriate releasability of release liners R1, R2 from transparent adhesive sheet 10. If the adhesion is insufficient, release liners R1, R2 may unexpectedly peel off from transparent adhesive sheet 10 during handling. Furthermore, if appropriate releasability is not ensured between transparent adhesive sheet 10 and release liners R1, R2, poor release or a so-called tearful separation may occur when each release liner is peeled off from transparent adhesive sheet 10.

The transparent adhesive sheet X1 with a release liner having the above-described configuration can be produced, for example, as follows. First, an adhesive composition for forming the transparent adhesive sheet 10 is prepared, and then the composition is applied to a long release liner R1 to form a long adhesive composition layer. Examples of methods for applying the adhesive composition include roll coating, screen coating, and gravure coating. The adhesive composition layer is then dried on the release liner R1 to form an adhesive layer. Next, a long, predetermined separator (first separator) is laminated on and along the adhesive layer. Next, transparent adhesive sheets 10 of a predetermined shape are formed on the release liner R1 by a punching process in which a processing blade is inserted from the side of the first separator to the release liner R1. Each transparent adhesive sheet 10 has a shape and size corresponding to the intended adhesive supply location on the object to be joined, and is arranged in a row along the extension direction of the long release liner R1. Next, while leaving the formed transparent adhesive sheet 10 on the release liner R1, the first separator and the adhesive layer material between the transparent adhesive sheets 10 are removed from the release liner R1. Next, another long separator (second separator) is laminated on the multiple transparent adhesive sheets 10 so as to cover the multiple transparent adhesive sheets 10 spaced apart on the long release liner R1. Next, the second separator is punched to form a release liner R2 of a predetermined shape, and the second separator material between the release liners R2 is removed. For example, a release-compatible transparent adhesive sheet X1 can be produced in the above manner. In the release-compatible transparent adhesive sheet X1, a single long transparent adhesive sheet 10, which will be cut into small pieces as needed, may be placed between a pair of long release liners R1 and R2. The release-compatible transparent adhesive sheet X1 may also be wound around a core to form a roll.

Figure 2 shows the state in which the detection surface 1a of the optical sensor 1 and the transparent cover member 2 are bonded together by a heat-cured transparent adhesive sheet 10 or an adhesive layer 11 derived therefrom. The optical sensor is, for example, an optical fingerprint authentication sensor. The transparent cover member 2 is, for example, a glass or transparent resin member with a transmittance of 80% or more at a wavelength of 500 nm. With the uncured transparent adhesive sheet 10 of a predetermined size interposed between the optical sensor 1 and the transparent cover member 2, which are the objects to be bonded, the transparent adhesive sheet 10 is heat-cured to bond the detection surface 1a of the optical sensor 1 and the transparent cover member 2.

The transparent adhesive sheet 10 described above can be manufactured with a highly uniform thickness and can supply adhesive material between objects to be joined in the form of a sheet that is resistant to fluidity (an adhesive material that is resistant to fluidity is less likely to spill out from between the objects during the joining process). Therefore, the transparent adhesive sheet 10 makes it possible to join the objects to be joined, the optical sensor 1 and the transparent cover member 2, with an adhesive layer 11 that is more uniform in thickness than when using a liquid adhesive. The ability to join the optical sensor 1 and the transparent cover member 2 with an adhesive layer 11 that is resistant to fluidity is advantageous for joining the optical sensor 1 to the transparent cover member 2 with high positional accuracy, and ultimately for manufacturing devices incorporating the optical sensor 1 with high yield.

In addition, as described above, the transparent adhesive sheet 10, when thermally cured by heating at 150°C for one hour, has a transmittance of 85% or more, preferably 87% or more, and more preferably 90% or more in the wavelength range of 450 to 1200 nm. The transparent adhesive sheet 10 exhibits such light transmittance across the visible light to near-infrared wavelength range after thermal curing, making it suitable for use as a bonding material between the detection surface 1a of the optical sensor 1 and the transparent cover member 2 to ensure the effective detection sensitivity of the optical sensor 1 within the device.

As described above, the transparent adhesive sheet 10 is suitable as a bonding material between the detection surface 1a of the optical sensor 1 and the transparent cover member 2, allowing for high-yield manufacturing of optical sensor-equipped devices while also ensuring sensor detection sensitivity.

As described above, when the transparent adhesive sheet 10 is heat-cured by heating at 150°C for 1 hour, the ratio (first ratio) of the transmittance at a wavelength of 450 nm after undergoing a moisture absorption test under conditions (first conditions) of 30°C, 70% relative humidity, and 200 hours to the transmittance at a wavelength of 450 nm before the test is preferably 0.9 or greater, more preferably 0.92 or greater, and more preferably 0.94 or greater. This small decrease in transmittance of the transparent adhesive sheet 10 after undergoing a moisture absorption test under the first conditions is suitable for use as a bonding material between the detection surface 1a of the optical sensor 1 and the transparent cover member 2, ensuring the effective detection sensitivity of the optical sensor 1 within the device.

As described above, when the transparent adhesive sheet 10 is in a heat-cured state after being heated at 150°C for 1 hour, the ratio (second ratio) of the transmittance at a wavelength of 450 nm after the heating test at 260°C for 5 minutes (second conditions) to the transmittance at a wavelength of 450 nm before the heating test is preferably 0.9 or greater, more preferably 0.92 or greater, and even more preferably 0.94 or greater. A configuration in which the decrease in transmittance of the transparent adhesive sheet 10 due to the heating test under the second conditions is this small is advantageous for ensuring the above-mentioned sensor detection sensitivity.

As described above, the viscosity of the transparent adhesive sheet 10 or the adhesive composition that forms it at 120°C is preferably 1 to 30 kPa·s, more preferably 3 to 30 kPa·s, more preferably 4 to 27 kPa·s, and more preferably 5 to 25 kPa·s. This configuration is suitable for ensuring good wettability of the transparent adhesive sheet 10 to objects to be joined, such as the optical sensor 1 and transparent cover member 2.

As described above, the transparent adhesive sheet 10 preferably has a storage modulus at 250°C in a heat-cured state after heating at 150°C for one hour of 0.5 to 50 MPa, more preferably 0.6 to 45 MPa, and even more preferably 0.7 to 40 MPa. This configuration is suitable for ensuring the post-curing bonding strength of the transparent adhesive sheet 10 between objects to be joined, such as between the optical sensor 1 and the transparent cover member 2, and is therefore suitable for ensuring the reliability of the bond between objects joined by the transparent adhesive sheet 10.

As described above, when the transparent adhesive sheet 10 is in a heat-cured state after heating at 150°C for one hour, the weight loss at 300°C measured by thermogravimetry under conditions of a nitrogen atmosphere, a temperature rise rate of 10°C/min, and a temperature rise range of 23 to 300°C is preferably 1.5% or less, and more preferably 1.2% or less. This configuration is suitable for ensuring the heat resistance of the transparent adhesive sheet 10, and therefore is suitable for ensuring the bonding reliability of objects such as the optical sensor 1 and transparent cover member 2 that are bonded by the transparent adhesive sheet 10.

As described above, the transparent adhesive sheet 10 exhibits a peel adhesion strength of 1 N/10 mm or more, preferably 1.5 N/10 mm or more, to a flat glass surface in a peel test conducted at 23°C, a peel angle of 180°, and a peel speed of 30 mm/min. This configuration is suitable for ensuring the adhesive strength of the transparent adhesive sheet 10 to objects to be joined, such as the optical sensor 1 and transparent cover member 2.

As described above, the transparent adhesive sheet 10 has a glass shear adhesive strength after undergoing a moisture absorption test at 40°C, 95% relative humidity, and 120 hours (third conditions) in the glass-bonded state, relative to the glass shear adhesive strength when heated at 150°C for one hour and then bonded to a flat glass surface (glass-bonded state). This ratio (third ratio) is preferably 0.6 or greater, more preferably 0.7 or greater, and more preferably 0.75 or greater. Having such a small reduction in the glass shear adhesive strength of the transparent adhesive sheet 10 after undergoing a moisture absorption test under the third conditions is advantageous for ensuring the bonding reliability of objects such as the optical sensor 1 and transparent cover member 2 bonded by the transparent adhesive sheet 10.

As mentioned above, the transparent adhesive sheet 10 preferably has a refractive index at a wavelength of 633 nm when heat-cured by heating at 150°C for one hour of 1.4 to 1.5, and more preferably 1.42 to 1.48. This configuration is suitable for ensuring the above-mentioned sensor detection sensitivity.

As described above, the transparent adhesive sheet 10 preferably contains an acrylic resin, and this acrylic resin preferably has a nitrile group and preferably has an epoxy group. The proportion of the acrylic resin in the organic components contained in the transparent adhesive sheet 10 is preferably 95% by mass or more, more preferably 97% by mass or more. Furthermore, the transparent adhesive sheet 10 preferably does not contain, or is substantially free of, epoxy resin and/or phenol resin. These configurations are suitable for achieving the high degree of transparency described above in the transparent adhesive sheet 10.

When the transparent adhesive sheet 10 contains an acrylic resin such as a nitrile group-containing acrylic resin, the average molecular weight of the acrylic resin is preferably 450,000 or less, and more preferably 400,000 or less, as described above. This configuration is suitable for achieving the above-mentioned preferred configuration regarding the viscosity of the transparent adhesive sheet 10.

As described above, the transparent adhesive sheet 10 preferably contains filler with an average particle size of 5 to 100 nm. As described above, the filler content in the transparent adhesive sheet 10 is preferably 5 to 40 mass %, more preferably 7 to 35 mass %. These configurations are suitable for ensuring the heat resistance of the transparent adhesive sheet 10, and are therefore suitable for ensuring the bonding reliability of objects such as the optical sensor 1 and transparent cover member 2 bonded by the transparent adhesive sheet 10. Furthermore, these configurations also contribute to ensuring the transparency of the transparent adhesive sheet 10 as described above.

As described above, the transparent adhesive sheet 10 preferably contains a phosphorus-based antioxidant. As described above, the content of the phosphorus-based antioxidant in the transparent adhesive sheet 10 is preferably 0.1 to 2 mass %, and more preferably 0.3 to 1.5 mass %. This configuration is suitable for preventing and suppressing oxidation of the components contained in the transparent adhesive sheet 10, and therefore is suitable for preventing and suppressing a decrease in transparency due to such oxidation.

As described above, the transparent adhesive sheet 10 preferably contains an imidazole-based curing agent. As described above, the content of the imidazole-based curing agent in the transparent adhesive sheet 10 is preferably 0.1 to 2 mass %, more preferably 0.2 to 1.5 mass %. This configuration is suitable for achieving both the curability and storage stability of the transparent adhesive sheet 10.

Figure 3 is a cross-sectional schematic diagram of a release-material-attached transparent adhesive sheet X2 according to one embodiment of the present invention. The release-material-attached transparent adhesive sheet X2 has a laminated structure including a transparent adhesive sheet 10 according to one embodiment of the present invention, a release liner R1 as one release material (second release material), and a dicing tape 20 as the other release material (second release material). With regard to the laminated structure, the release-material-attached transparent adhesive sheet X2 differs from the release-material-attached transparent adhesive sheet X1 described above in that it includes a dicing tape 20 instead of a release liner R2 as the second release material.

The dicing tape 20 has a laminated structure including a substrate 21 and an adhesive layer 22. The adhesive layer 22 has an adhesive surface 22a on the transparent adhesive sheet 10 side. The transparent adhesive sheet 10 is releasably adhered to the adhesive layer 22 or its adhesive surface 22a of the dicing tape 20. Such a transparent adhesive sheet X2 with a release material can be used, for example, to obtain an optical sensor with a transparent adhesive layer during the manufacturing process of a device equipped with an optical sensor. The dicing tape 20 and transparent adhesive sheet 10 have a disk shape large enough to accommodate attachment of workpieces incorporating multiple optical sensors, and in this embodiment, are arranged concentrically. In other respects, such as the constituent materials of the transparent adhesive sheet 10, the transparent adhesive sheet X2 with a release material is the same as the transparent adhesive sheet X1 with a release material.

The substrate 21 of the dicing tape 20 in the transparent adhesive sheet X2 with a release liner is an element that functions as a support in the dicing tape 20 or the transparent adhesive sheet X2 with a release liner. The substrate 21 is, for example, a plastic substrate, and a plastic film is preferably used as the plastic substrate. Examples of materials constituting the plastic substrate include polyolefin, polyester, polyurethane, polycarbonate, polyether ether ketone, polyimide, polyetherimide, polyamide, wholly aromatic polyamide, polyvinyl chloride, polyvinylidene chloride, polyphenyl sulfide, aramid, fluororesin, cellulose-based resin, and silicone resin. Examples of polyolefins include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, very low-density polyethylene, random copolymer polypropylene, block copolymer polypropylene, homopolypropylene, polybutene, polymethylpentene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester copolymer, ethylene-butene copolymer, and ethylene-hexene copolymer. Examples of polyesters include polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. The substrate 21 may be made of one type of material, or two or more types of materials. The substrate 21 may have a single-layer structure or a multi-layer structure. If the adhesive layer 22 on the substrate 21 is UV-curable, the substrate 21 is preferably UV-transparent.

The surface of the substrate 21 facing the adhesive layer 22 may be subjected to a physical treatment, chemical treatment, or primer treatment to enhance adhesion to the adhesive layer 22. Examples of physical treatments include corona treatment, plasma treatment, sand matting, ozone exposure, flame exposure, high-voltage shock exposure, and ionizing radiation treatment. Examples of chemical treatments include chromate treatment.

The thickness of the substrate 21 is preferably 40 μm or more, more preferably 50 μm or more, from the viewpoint of ensuring the strength necessary for the substrate 21 to function as a support for the dicing tape 20 or the transparent adhesive sheet X2 with a release material. Furthermore, from the viewpoint of achieving adequate flexibility in the dicing tape 20 or the transparent adhesive sheet X2 with a release material, the thickness of the substrate 21 is preferably 200 μm or less, more preferably 180 μm or less.

The adhesive layer 22 of the dicing tape 20 contains an adhesive. This adhesive may be an adhesive whose adhesive strength can be intentionally reduced by external action during use of the release-attached transparent adhesive sheet X2 (a reduced-adhesion adhesive), or an adhesive whose adhesive strength is hardly or not reduced at all by external action during use of the release-attached transparent adhesive sheet X2 (a non-reduced-adhesion adhesive). Whether a reduced-adhesion adhesive or a non-reduced-adhesion adhesive is used as the adhesive in the adhesive layer 22 can be selected appropriately depending on the usage mode of the release-attached transparent adhesive sheet X2. When a reduced-adhesion adhesive is used as the adhesive in the adhesive layer 22, it is possible to selectively use the adhesive layer 22 in a state where it exhibits relatively high adhesive strength or a state where it exhibits relatively low adhesive strength during use of the release-attached transparent adhesive sheet X2.

Examples of the reduced-tack adhesive include adhesives that can be cured by radiation exposure during use of the release-material-attached transparent adhesive sheet X2 (radiation-curable adhesives) and heat-foaming adhesives. The adhesive layer 22 of this embodiment may use one type of reduced-tack adhesive, or two or more types of reduced-tack adhesives. The entire adhesive layer 22 may be formed from a reduced-tack adhesive, or only a portion of the adhesive layer 22 may be formed from a reduced-tack adhesive. For example, when the adhesive layer 22 has a single-layer structure, the entire adhesive layer 22 may be formed from a reduced-tack adhesive, or a specific portion of the adhesive layer 22 may be formed from a reduced-tack adhesive and other portions from a non-reduced-tack adhesive. When the adhesive layer 22 has a multilayer structure, all layers of the multilayer structure may be formed from a reduced-tack adhesive, or only a portion of the multilayer structure may be formed from a reduced-tack adhesive.

Examples of radiation-curable adhesives for the adhesive layer 22 include adhesives that cure when exposed to electron beams, ultraviolet rays, alpha rays, beta rays, gamma rays, or X-rays, and adhesives that cure when exposed to ultraviolet rays (ultraviolet-curable adhesives) are particularly suitable.

Examples of radiation-curable adhesives for the adhesive layer 22 include additive-type radiation-curable adhesives containing a base polymer, such as an acrylic polymer, which is an acrylic adhesive, and a radiation-polymerizable monomer component or oligomer component having a functional group such as a radiation-polymerizable carbon-carbon double bond.

The acrylic polymer serving as the base polymer of the radiation-curable adhesive preferably contains, by mass, the largest proportion of monomer units derived from (meth)acrylic esters. Examples of (meth)acrylic esters that constitute the monomer units of the acrylic polymer, i.e., (meth)acrylic esters that are the constituent monomers of the acrylic polymer, include (meth)acrylic acid alkyl esters, (meth)acrylic acid cycloalkyl esters, and (meth)acrylic acid aryl esters. More specifically, examples of such (meth)acrylic esters include the (meth)acrylic esters described above as the constituent monomers of the acrylic polymer that constitute the acrylic resin for the transparent adhesive sheet 10. A single type of (meth)acrylic ester may be used as the constituent monomer of the acrylic polymer, or two or more types of (meth)acrylic esters may be used. A preferred constituent monomer of the acrylic polymer is 2-ethylhexyl acrylate. In other words, the acrylic polymer that constitutes the acrylic adhesive in the adhesive layer 22 preferably contains a 2-ethylhexyl group. This configuration is suitable for achieving high adhesion between the adhesive layer 22 of the dicing tape 20 and the transparent adhesive sheet 10. Furthermore, in order to properly exhibit basic properties such as adhesion due to the (meth)acrylic acid ester in the adhesive layer 22, the proportion of the (meth)acrylic acid ester in all constituent monomers of the acrylic polymer is preferably 40% by mass or more, and more preferably 60% by mass or more.

The acrylic polymer may contain one or more other monomers copolymerizable with (meth)acrylic acid esters as constituent monomers, for example to improve its cohesive strength or heat resistance. Examples of such other monomers include carboxyl group-containing monomers, acid anhydride monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, acrylamide, and acrylonitrile. More specifically, such other monomers include the copolymerizable other constituent monomers listed above as constituent monomers of the acrylic polymer used to form the acrylic resin for the transparent adhesive sheet 10.

The acrylic polymer used as the acrylic adhesive for the adhesive layer 22 may contain a monomer unit derived from a polyfunctional monomer copolymerizable with a monomer component such as a (meth)acrylic acid ester to form a crosslinked structure within the polymer backbone. Examples of such polyfunctional monomers include hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyglycidyl (meth)acrylate, polyester (meth)acrylate, and urethane (meth)acrylate. "(Meth)acrylate" refers to "acrylate" and/or "methacrylate." One type of polyfunctional monomer may be used as the constituent monomer of the acrylic polymer, or two or more types of polyfunctional monomers may be used. In order to properly exhibit basic properties such as adhesiveness due to the (meth)acrylic acid ester in the adhesive layer 22, the proportion of polyfunctional monomers in all the constituent monomers of the acrylic polymer is preferably 40% by mass or less, and preferably 30% by mass or less.

Acrylic polymers can be obtained by polymerizing the raw material monomers used to form them. Examples of polymerization techniques include solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. From the perspective of high cleanliness in processes such as semiconductor device manufacturing where dicing tape 20 or transparent adhesive sheet X2 with release liner is used, it is preferable that the pressure-sensitive adhesive layer 22 of dicing tape 20 or transparent adhesive sheet X2 with release liner contain as few low-molecular-weight components as possible. The number-average molecular weight of the acrylic polymer is preferably 100,000 or more, and more preferably 200,000 to 3,000,000.

The adhesive layer 22 or the adhesive that forms it may contain, for example, an external crosslinking agent to increase the number average molecular weight of the base polymer, such as an acrylic polymer. Examples of external crosslinking agents that react with the base polymer, such as an acrylic polymer, to form a crosslinked structure include polyisocyanate compounds, epoxy compounds, polyol compounds, aziridine compounds, and melamine-based crosslinking agents. The content of the external crosslinking agent in the adhesive layer 22 or the adhesive that forms it is preferably 5 parts by weight or less, more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the base polymer.

Examples of the radiation-polymerizable monomer component used to form the radiation-curable adhesive include urethane (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of the radiation-polymerizable oligomer component used to form the radiation-curable adhesive include various oligomers, such as urethane-based, polyether-based, polyester-based, polycarbonate-based, and polybutadiene-based oligomers, with those with a molecular weight of approximately 100 to 30,000 being appropriate. The total content of radiation-polymerizable monomer and oligomer components in the radiation-curable adhesive is determined within a range that appropriately reduces the adhesive strength of the adhesive layer 22 formed, and is preferably 5 to 500 parts by weight, and more preferably 40 to 150 parts by weight, per 100 parts by weight of the base polymer, such as an acrylic polymer. Furthermore, additive-type radiation-curable adhesives such as those disclosed in JP-A-60-196956 may also be used.

Examples of radiation-curable adhesives for the adhesive layer 22 include inherent radiation-curable adhesives containing a base polymer having functional groups such as radiation-polymerizable carbon-carbon double bonds on the polymer side chain, in the polymer main chain, or at the end of the polymer main chain. Such inherent radiation-curable adhesives are suitable for suppressing unintended changes in adhesive properties over time due to the migration of low-molecular-weight components within the adhesive layer 22 that is formed.

The base polymer contained in the intrinsic radiation-curable adhesive preferably has an acrylic polymer as its basic skeleton. The acrylic polymers described above as the base polymer contained in the additive-type radiation-curable adhesive can be used as the acrylic polymer forming such a basic skeleton. One method for introducing a radiation-polymerizable carbon-carbon double bond into an acrylic polymer is to copolymerize raw material monomers including a monomer having a specific functional group (first functional group) to obtain an acrylic polymer, and then subject the acrylic polymer to a condensation reaction or addition reaction with a compound having a radiation-polymerizable carbon-carbon double bond and a specific functional group (second functional group) that can react with and bond to the first functional group while maintaining the radiation polymerizability of the carbon-carbon double bond.

Examples of combinations of first and second functional groups include a carboxy group and an epoxy group, an epoxy group and a carboxy group, a carboxy group and an aziridyl group, an aziridyl group and a carboxy group, a hydroxy group and an isocyanate group, and an isocyanate group and a hydroxy group. Of these combinations, from the perspective of ease of reaction tracking, a combination of a hydroxy group and an isocyanate group, or a combination of an isocyanate group and a hydroxy group, is preferred. Furthermore, since producing a polymer containing a highly reactive isocyanate group is technically difficult, from the perspective of ease of production or availability of the acrylic polymer, it is more preferred that the first functional group on the acrylic polymer be a hydroxy group and the second functional group be an isocyanate group. Examples of isocyanate compounds that contain both a radiation-polymerizable carbon-carbon double bond and an isocyanate group as a second functional group, i.e., radiation-polymerizable unsaturated functional group-containing isocyanate compounds, include methacryloyl isocyanate, 2-methacryloyloxyethyl isocyanate (MOI), and m-isopropenyl-α,α-dimethylbenzyl isocyanate.

The radiation-curable adhesive for the adhesive layer 22 preferably contains a photopolymerization initiator. Examples of photopolymerization initiators include α-ketol compounds, acetophenone compounds, benzoin ether compounds, ketal compounds, aromatic sulfonyl chloride compounds, photoactive oxime compounds, benzophenone compounds, thioxanthone compounds, camphorquinone, halogenated ketones, acylphosphinoxides, and acylphosphonates. The content of the photopolymerization initiator in the radiation-curable adhesive in the adhesive layer 22 is, for example, 0.05 to 20 parts by weight per 100 parts by weight of the base polymer, such as an acrylic polymer.

The non-reducing adhesive in the adhesive layer 22 can be, for example, a pressure-sensitive adhesive. Examples of pressure-sensitive adhesives that can be used include acrylic adhesives with an acrylic polymer as the base polymer and rubber-based adhesives. When the adhesive layer 22 contains an acrylic adhesive as the pressure-sensitive adhesive, the acrylic polymer that serves as the base polymer of the acrylic adhesive preferably contains a monomer unit derived from a (meth)acrylic acid ester as the majority monomer unit by mass. Examples of such acrylic polymers include the acrylic polymers described above in relation to radiation-curable adhesives.

In the adhesive layer 22 of this embodiment, one type of non-reduced adhesive may be used, or two or more types of non-reduced adhesive may be used. The entire adhesive layer 22 may be formed from a non-reduced adhesive, or only a portion of the adhesive layer 22 may be formed from a non-reduced adhesive. For example, when the adhesive layer 22 has a single-layer structure, the entire adhesive layer 22 may be formed from a non-reduced adhesive, or a specific portion of the adhesive layer 22 may be formed from a non-reduced adhesive and other portions may be formed from a reduced-adhesion adhesive. When the adhesive layer 22 has a laminated structure, all layers of the laminated structure may be formed from a non-reduced adhesive, or only a portion of the laminated structure may be formed from a non-reduced adhesive.

In addition to the components described above, the adhesive layer 22 or the adhesive used to form it may contain a crosslinking accelerator, tackifier, antioxidant, colorant, etc. Colorants include pigments and dyes. The colorant may also be a compound that changes color when exposed to radiation. Examples of such compounds include leuco dyes.

The thickness of the adhesive layer 22 is preferably 5 to 40 μm, and more preferably 10 to 30 μm. This configuration is suitable for achieving high adhesion between the adhesive layer 22 of the dicing tape 20 and the transparent adhesive sheet 10.

The transparent adhesive sheet X2 with release material having the above-described configuration can be produced, for example, by laminating a transparent adhesive sheet 10 to the adhesive layer 22 side of a dicing tape 20, and then providing a release liner R1 on the dicing tape 20 so as to cover the transparent adhesive sheet 10 and the surrounding surface of the adhesive layer 22.

In the release-backed transparent adhesive sheet X2, the thickness _T1 of the release liner R1 (first release material) is preferably 38 μm or more, and the thickness _T2 of the dicing tape 20 (second release material) is preferably 25 μm or more. The ratio ( _T1 / _T2 ) of the thickness _T1 of the release liner R1 to the thickness _T2 of the dicing tape 20 is preferably 0.2 to 1.8, more preferably 0.22 to 1.6, and even more preferably 0.3 to 1.55. This configuration is preferable from the viewpoint of ease of handling the release-backed transparent adhesive sheet X2. Specifically, this configuration is suitable for preventing or suppressing the occurrence of wrinkles or folds in the transparent adhesive sheet 10 when the release liner R1 is peeled from the transparent adhesive sheet 10 (which has the dicing tape 20 on the side opposite the release liner R1).

In the transparent adhesive sheet X2 with a release liner, the release liner R1 (first release liner) exhibits a first peel adhesion strength of preferably 0.01 N/100 mm or greater, more preferably 0.015 N/100 mm or greater, to the transparent adhesive sheet 10 in a peel test at 100°C, a peel angle of 180°, and a peel speed of 300 mm/min. The dicing tape 20 (second release liner) exhibits a second peel adhesion strength of preferably 0.04 N/100 mm or greater to the transparent adhesive sheet 10 in a peel test at 100°C, a peel angle of 180°, and a peel speed of 300 mm/min. The ratio of the first peel adhesion strength to the second peel adhesion strength is preferably 0.01 to 0.75, more preferably 0.02 to 0.7. These configurations are preferable from the viewpoint of achieving a balance between sufficient adhesion of the release liner R1 and dicing tape 20 (which are often peeled off separately from the transparent adhesive sheet 10 at different stages) to the transparent adhesive sheet 10 when handling the release-attached transparent adhesive sheet X2, and appropriate releasability of the release liner R1 and dicing tape 20 from the transparent adhesive sheet 10.

Figures 4 to 7 show a bonding method using a transparent adhesive sheet X2 with a release material. This bonding method includes the following lamination process, singulation process, temporary fixing process, and bonding process.

In the lamination process, the release liner R1 is peeled off from the transparent adhesive sheet X2 with a release material to expose the transparent adhesive sheet 10, and then the workpiece W is laminated onto the transparent adhesive sheet 10 as shown in Figure 4. The workpiece W has a first surface Wa, which is the side that will be laminated to the transparent adhesive sheet 10, and a second surface Wb on the opposite side. The workpiece W has multiple optical sensors built into it, each with a detection surface on the first surface Wa side.

In the singulation process, the workpiece W on the transparent adhesive sheet 10 is cut using a dicing blade provided in a dicing machine, and the workpiece W is singulated as shown in Figure 5 (in Figure 5, the cut locations are schematically represented by thick lines). Specifically, in this process, the workpiece W is singulated into optical sensors 1, and at the same time, the transparent adhesive sheet 10 is cut into small pieces. This results in an optical sensor 1 with the transparent adhesive sheet 10 or the adhesive layer 11 derived from it on the sensing surface 1a side, i.e., an optical sensor 1 with adhesive layer 11.

When the adhesive layer 22 of the dicing tape 20 contains a radiation-curable adhesive, after the above-described dicing step, the adhesive layer 22 may be irradiated with radiation such as ultraviolet light from the side of the substrate 21 to reduce the adhesive strength of the adhesive layer 22. The irradiation dose is, for example, 50 to 500 mJ/ ^cm2 .

In the temporary fixing process, the optical sensor 1 with the adhesive layer 11 is picked up from the dicing tape 20, and then, as shown in Figure 6, the optical sensor 1 with the adhesive layer 11 is pressed against the transparent cover member 2 via the adhesive layer 11 side to temporarily fix it.

In the bonding process, as shown in Figure 7, the adhesive layer 11 interposed between the temporarily fixed optical sensor 1 and transparent cover member 2 is thermally cured to bond the detection surface 1a of the optical sensor 1 to the transparent cover member 2.

In this way, the optical sensor 1 and the transparent cover member 2 can be bonded using the transparent adhesive sheet X2 with release material.

Like the transparent adhesive sheet X1 with a release material, the transparent adhesive sheet X2 with a release material also includes a transparent adhesive sheet 10. As described above with respect to the embodiment of the transparent adhesive sheet X1 with a release material, the transparent adhesive sheet 10 is used as a bonding material between the detection surface 1a of the optical sensor 1 and the transparent cover member 2, making it suitable for manufacturing optical sensor-equipped devices with high yields and ensuring sensor detection sensitivity. In addition, the above-described bonding method using the transparent adhesive sheet X2 with a release material can efficiently obtain component pieces bearing the transparent adhesive sheet 10 or the adhesive layer 11 derived therefrom (in this embodiment, the optical sensor 1 with the adhesive layer 11). Therefore, this bonding method is suitable for improving the efficiency of the work and process of bonding objects to be bonded.

Example 1
An adhesive composition with a solids concentration of 20% by mass was prepared by adding and mixing 90 parts by mass of acrylic resin _A1 (trade name "Teisan Resin SG-80H", weight average molecular weight of 350,000, glass transition temperature Tg of 11°C, manufactured by Nagase ChemteX Corporation), 7 parts by mass of inorganic filler (trade name "YA010C", spherical silica particles, average particle size of 10 nm, manufactured by Admatechs Co., Ltd.), 0.27 parts by mass of curing agent (trade name "Curesol 2MZ", imidazole-based curing agent, Shikoku Chemicals Corporation), and 0.27 parts by mass of antioxidant (trade name "Adekastab PEP-8", phosphorus-based antioxidant, manufactured by ADEKA Corporation) to methyl ethyl ketone. Next, an adhesive composition was applied using an applicator to the silicone release-treated surface of a polyethylene terephthalate (PET) film (trade name "Diafoil MRF", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) serving as a first release material. This adhesive composition layer was then heated and dried at 130°C for 2 minutes to produce a 20 μm thick transparent adhesive sheet on the PET film. The silicone release-treated surface of a PET film (trade name "Diafoil MRA", thickness 25 μm, manufactured by Mitsubishi Chemical Corporation) serving as a second release material, also having a silicone release-treated surface, was then attached to the transparent adhesive sheet at a temperature of 60°C. In this manner, the transparent adhesive sheet with release material of Example 1 was produced, having a laminated structure of a 38 μm thick PET film (first release material), a 25 μm thick PET film (second release material), and a 20 μm thick transparent adhesive sheet between them.

Example 2
<Preparation of dicing tape>
In a reaction vessel equipped with a condenser, a nitrogen inlet tube, a thermometer, and a stirrer, a mixture containing 120 parts by mass of 2-ethylhexyl acrylate, 17 parts by mass of 2-hydroxyethyl acrylate, 0.4 parts by mass of benzoyl peroxide as a polymerization initiator, and 80 parts by mass of toluene as a polymerization solvent was stirred at 60°C for 10 hours under a nitrogen atmosphere (polymerization reaction). This resulted in a polymer solution containing acrylic polymer _P1 . Next, a mixture containing this polymer solution containing acrylic polymer _P1 , 2-methacryloyloxyethyl isocyanate (MOI), and dibutyltin dilaurate as an addition reaction catalyst was stirred at 50°C for 60 hours under an air atmosphere (addition reaction). In this reaction solution, the blending amount of MOI was 1.4 parts by mass per 100 parts by mass of acrylic polymer _P1 , and the blending amount of dibutyltin dilaurate was 0.1 parts by mass per 100 parts by mass of acrylic polymer _P1 . This addition reaction yielded a polymer solution containing an acrylic polymer _P2 having a methacryloyl group in its side chain. Next, 1.1 parts by mass of a polyisocyanate compound (trade name "Coronate L _" , manufactured by Tosoh Corporation) and 3 parts by mass of a photopolymerization initiator (trade name "Irgacure 184", manufactured by BASF) were added to the polymer solution and mixed per 100 parts by mass of the acrylic polymer P2. Toluene was then added to dilute the mixture so that the viscosity of the mixture at room temperature was 500 mPa·s, yielding a pressure-sensitive adhesive composition. Next, the pressure-sensitive adhesive composition was applied using an applicator to the silicone release-treated surface of a PET film (38 μm thick) having a silicone release-treated surface to form a pressure-sensitive adhesive composition layer. This composition layer was then heated and dried at 120°C for 2 minutes to form a 30 μm-thick pressure-sensitive adhesive layer on the PET film. Next, a laminator was used to attach an ethylene-vinyl acetate copolymer (EVA) substrate (trade name "Fanclea NRB#80", thickness 80 μm, manufactured by Gunze Ltd.) to the exposed surface of the adhesive layer at room temperature. In this way, a dicing tape was produced.

<Preparation of transparent adhesive sheet with release material>
An adhesive composition with a solids concentration of 20% by mass was prepared by adding and mixing 90 parts by mass of acrylic resin _A1 (trade name "Teisan Resin SG-80H", weight average molecular weight of 350,000, glass transition temperature Tg of 11°C, manufactured by Nagase ChemteX Corporation), 65 parts by mass of inorganic filler (trade name "MEK-ST-ZL", spherical silica particles, particle diameter of 70 to 100 nm, manufactured by Nissan Chemical Industries, Ltd.), 0.9 parts by mass of curing agent (trade name "Curesol 2MZ", imidazole-based curing agent, manufactured by Shikoku Chemical Industries Co., Ltd.), and 0.9 parts by mass of antioxidant (trade name "Adekastab PEP-8", phosphorus-based antioxidant, manufactured by ADEKA Corporation) to methyl ethyl ketone. Next, an adhesive composition was applied using an applicator to the silicone release-treated surface of a PET film (product name "Diafoil MRA", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) serving as a first release material. This adhesive composition layer was then heated and dried at 130°C for 2 minutes to produce a 20 μm-thick transparent adhesive sheet on the PET film. The transparent adhesive sheet with a release material of Example 2 was then produced in the same manner as the transparent adhesive sheet with a release material of Example 1, except that the 25 μm-thick PET film described above was replaced with the dicing tape used as the second release material. Specifically, the PET film was peeled from the dicing tape produced as described above, and the adhesive layer side of the dicing tape was then attached to a 20 μm-thick transparent adhesive sheet on the PET film (first release material) at a temperature of 60°C. In this manner, a transparent adhesive sheet with release material of Example 2 was produced, which had a laminated structure of a 38 μm thick PET film (first release material), a 110 μm thick dicing tape (second release material), and a 20 μm thick transparent adhesive sheet between them.

Example 3
An adhesive composition with a solids concentration of 20% by mass was prepared by adding and mixing 93 parts by mass of an acrylic resin solution (trade name "PARACRON EG-2201M", solids concentration of 60% by mass, weight average molecular weight of 100,000, glass transition temperature Tg of -40°C, manufactured by Negami Chemical Industrial Co., Ltd.), 41 parts by mass of inorganic filler (trade name "YA010C", spherical silica particles, average particle diameter of 10 nm, manufactured by Admatechs Co., Ltd.), 0.4 parts by mass of a curing agent (trade name "Curesol 2MZ", imidazole-based curing agent, manufactured by Shikoku Chemicals Corporation), and 0.5 parts by mass of an antioxidant (trade name "ADK STAB PEP-8", phosphorus-based antioxidant, manufactured by ADEKA Corporation) to methyl ethyl ketone. Next, an adhesive composition was applied using an applicator to the silicone release-treated surface of a PET film (trade name "Diafoil MRA", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) serving as a first release material, which had a silicone release-treated surface, to form an adhesive composition layer. This composition layer was then heated and dried at 130°C for 2 minutes to produce a 20 μm-thick transparent adhesive sheet on the PET film. The silicone release-treated surface of a PET film (trade name "Diafoil MRF", thickness 25 μm, manufactured by Mitsubishi Chemical Corporation) serving as a second release material, which also had a silicone release-treated surface, was then attached to the transparent adhesive sheet at a temperature of 60°C. In this way, a transparent adhesive sheet with a release material of Example 3 was produced, which had a laminated structure of a 38 μm-thick PET film (first release material), a 25 μm-thick PET film (second release material), and a 20 μm-thick transparent adhesive sheet between them.

Comparative Example 1
An adhesive composition with a solids concentration of 20% by mass was prepared by adding and mixing 90 parts by mass of acrylic resin _A2 (trade name "Teisan Resin WS-023 EK30", weight average molecular weight 500,000, glass transition temperature Tg -10°C, manufactured by Nagase ChemteX Corporation), 3 parts by mass of phenolic resin (trade name "MEH-7851H", manufactured by Meiwa Kasei Co., Ltd.), 52 parts by mass of epoxy resin (trade name "KI-3000", manufactured by Tohto Kasei Co., Ltd.), and 60 parts by mass of inorganic filler (trade name "SO-25R", silica particles, average particle size 500 nm, manufactured by Admatechs Co., Ltd.) to methyl ethyl ketone. Next, an adhesive composition was applied using an applicator to the silicone release-treated surface of a polyethylene terephthalate (PET) film (trade name "Cerapeel WZ", 20 μm thick, manufactured by Toray Advanced Film Co., Ltd.) serving as a first release material. This adhesive composition layer was then heated and dried at 130°C for 2 minutes to produce a 20 μm thick transparent adhesive sheet on the PET film. The silicone release-treated surface of a PET film (trade name "Diafoil MRF", 25 μm thick, manufactured by Mitsubishi Chemical Corporation) serving as a second release material was then attached to the transparent adhesive sheet at a temperature of 60°C. In this manner, a transparent adhesive sheet with a release material of Comparative Example 1 was produced, having a laminated structure of a 20 μm thick PET film (first release material), a 25 μm thick PET film (second release material), and a 20 μm thick transparent adhesive sheet between them.

<Transmittance measurement>
The transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1 were examined for transmittance before heat curing, transmittance in a heat-cured state, transmittance after a predetermined moisture absorption test in a heat-cured state, and transmittance after a predetermined heating test in a heat-cured state. Each heat curing of the transparent adhesive sheet was performed under heating conditions of 150°C for 1 hour. For the moisture absorption test, the heat-cured transparent adhesive sheet was placed in an environment of 30°C and 70% relative humidity for 200 hours. For the heating test, the heat-cured transparent adhesive sheet was placed under heating conditions of 260°C for 5 minutes. For each transmittance measurement, a sample piece cut from the transparent adhesive sheet (20 μm thick) was measured for total light transmittance spectrum in the wavelength range of 300 to 1300 nm using a UV-Vis-NIR spectrophotometer (product name "V-670DS", manufactured by JASCO Corporation) and an integrating sphere unit. The minimum transmittance in the wavelength range of 450 to 1200 nm for the heat-cured transparent adhesive sheet is transmittance _T1 (%), the transmittance at 450 nm for the heat-cured transparent adhesive sheet is transmittance _T2 (%), the transmittance at 450 nm for the heat-cured transparent adhesive sheet after undergoing the moisture absorption test is transmittance _T3 (%), and the transmittance at 450 nm for the heat-cured transparent adhesive sheet after undergoing the heating test is transmittance _T4 (%), all of which are listed in Table 1. Table 1 also lists the values of _T3 / _T2 and _T4 / _T2 .

<Viscosity measurement>
The viscosity of the transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1 was measured using a dynamic viscoelasticity measuring device (product name "HAAKE MARS III", manufactured by Thermo Fisher Scientific). The sample pieces used for the measurement were prepared by forming a laminate in which multiple transparent adhesive sheets were stacked to a thickness of 200 μm, and then cutting the laminate into a disk shape with a diameter of 8 mm. In this measurement, the measurement temperature range was 80°C to 180°C, the heating rate was 5°C/min, and the frequency was 1 Hz.

Storage modulus
The storage modulus of the transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1 was measured by dynamic viscoelasticity measurement using a dynamic viscoelasticity measuring device (trade name "RSA-III", manufactured by TA Instruments). The sample pieces used for the dynamic viscoelasticity measurement were prepared by forming a laminate of multiple transparent adhesive sheets to a thickness of 200 μm, cutting a 10 mm wide x 40 mm long sample from the laminate, and then heat-curing the sample by heating at 150°C for 1 hour. In this measurement, the initial chuck distance between the sample piece-holding chucks was 22.5 mm, the measurement mode was tension mode, the measurement temperature range was -30°C to 250°C, the frequency was 1 Hz, the dynamic strain was 0.005%, and the heating rate was 10°C/min. The storage modulus (MPa) at 250°C obtained is shown in Table 1.

[Weight reduction rate]
The weight loss rate at 300°C was investigated for the transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1. A sample of approximately 10 mg was cut out from the transparent adhesive sheet, and the weight loss of this sample during the heating process was measured using a differential thermal/thermogravimetric simultaneous analyzer (product name "Thermo plus TG8120", manufactured by Rigaku Corporation). This measurement was performed in a nitrogen atmosphere, raising the temperature from the reference weight temperature of 23°C to 300°C at a heating rate of 10°C/min. The weight loss rate (%) of the sample from 23°C (reference weight) to 300°C is shown in Table 1.

[Adhesion to glass]
The adhesive strength of the transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1 to a flat glass surface was examined. First, a backing tape (product name "BT-315", manufactured by Nitto Denko Corporation) was attached to one side of the transparent adhesive sheet, and then a sample piece (10 mm wide x 150 mm long) was cut from the backing tape-attached transparent adhesive sheet. Next, a glass plate was placed on a hot plate set at 60°C, and after confirming that its surface temperature was 60°C, the surface of the glass plate (flat glass surface) was bonded to the exposed surface of the transparent adhesive sheet on the sample piece. This bonding was performed by rolling a 2 kg hand roller back and forth once. After this bonding, the sheet was left to stand on the hot plate for 2 minutes, and then left to stand at room temperature for 20 minutes. Then, a peel test was performed using a tensile tester (product name "Autograph AGS-J", manufactured by Shimadzu Corporation) to peel the sample piece from the glass plate under conditions of 23°C, a peel angle of 180°, and a peel speed of 300 mm/min, and the 180° peel adhesive strength (N/10 mm) of the transparent adhesive sheet from the flat glass surface at 23°C was measured. The results are shown in Table 1.

[Shear adhesive strength to glass]
The shear adhesive strength of the transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1 to a flat glass surface was examined. The transparent adhesive sheets of Examples 1 and 3 and Comparative Example 1 were bonded to dicing tape to form transparent adhesive sheets with dicing tape. The transparent adhesive sheet with release liner of Example 2 was obtained by peeling off the first release material to form a transparent adhesive sheet with dicing tape. Each transparent adhesive sheet with dicing tape was then used as follows: First, a silicon wafer (500 μm thick) was bonded to the transparent adhesive sheet with dicing tape. For bonding, a laminator was used, with a bonding speed of 10 mm/sec, a temperature of 60°C, and a pressure of 0.15 MPa. Next, the silicon wafer on the transparent adhesive sheet with dicing tape was singulated into chips (5 mm x 5 mm) using a dicing device (trade name "DFD6361", manufactured by Disco Corporation). This resulted in chips with an adhesive layer derived from the transparent adhesive sheet. The chip with the adhesive layer was pressure-bonded to a glass plate via the adhesive layer side (temporary fixation). In this temporary fixation, the pressure-bonding temperature was 120°C, the pressure-bonding load was 0.1 MPa, and the pressure-bonding time was 2 seconds. Next, the adhesive layer interposed between the glass plate and the chip was thermally cured by heating at 150°C for 1 hour, and the glass plate and the chip were bonded by the adhesive layer. In this manner, a sample for measuring shear adhesive strength to glass was prepared. The shear adhesive strength F ₁ (MPa) of the sample was measured using a bonding strength tester (trade name "Dage4000", manufactured by Nordson). Furthermore, the sample prepared as described above underwent a moisture absorption test under conditions of 40°C, 95% relative humidity, and 120 hours, and then the shear adhesive strength F ₂ (MPa) was measured using a bonding strength tester (trade name "Dage4000", manufactured by Nordson). In each measurement, the measurement temperature was 23° C., the shear rate was 30 mm/min, and the maximum stress value obtained was taken as the shear adhesive strength (MPa). These results and the F ₂ /F ₁ value are shown in Table 1.

<Refractive index measurement>
The refractive index at 633 nm after thermal curing was measured for the transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1. The transparent adhesive sheets were thermally cured at 150°C for 1 hour. The refractive index was measured using a refractive index measuring device (product name "Prism Coupler Model 2010/M", manufactured by Metricon). The measurement results are shown in Table 1.

[Peel adhesive strength of release material]
The peel adhesion strength of the first release material to the transparent adhesive sheet was examined for the release-attached transparent adhesive sheets of Examples 1 to 3 and Comparative Example 1. Specifically, the second release material was first peeled from the release-attached transparent adhesive sheet, and then a backing tape (product name "BT-315", manufactured by Nitto Denko Corporation) was attached to the exposed transparent adhesive sheet. A sample piece (100 mm wide x 60 mm long) was cut from the backing tape-attached transparent adhesive sheet. A peel test was then conducted using a tensile tester (product name "Autograph AGS-J", manufactured by Shimadzu Corporation) to peel the first release material from the transparent adhesive sheet at 23°C, a peel angle of 180°, and a peel speed of 300 mm/min, and the 180° peel adhesion strength (N/100 mm) of the first release material to the transparent adhesive sheet at 23°C was measured. After peeling the first release material from the release-attached transparent adhesive sheet, a backing tape (product name "BT-315", manufactured by Nitto Denko Corporation) was attached to the exposed transparent adhesive sheet, and a sample piece (100 mm wide x 60 mm long) was cut from the backing tape-attached transparent adhesive sheet. A peel test was then conducted using a tensile tester (product name "Autograph AGS-J", manufactured by Shimadzu Corporation) to peel the second release material from the transparent adhesive sheet at 23°C, a peel angle of 180°, and a peel rate of 300 mm/min, and the 180° peel adhesion strength (N/100 mm) of the second release material to the transparent adhesive sheet at 23°C was measured. The peel adhesion strength _P1 of the first release material, the peel adhesion strength _P2 of the second release material, and the _P1 / _P2 values are listed in Table 1.

[Peel test]
A peel test was conducted on the release-lined transparent adhesive sheets of Examples 1 to 3 and Comparative Example 1 as follows. The release-lined transparent adhesive sheets used in the peel test measured 10 cm x 10 cm. A 10 mm-wide backing tape (product name "BT-315", manufactured by Nitto Denko Corporation) was attached to one corner of the exposed surface of the first release material of the release-lined transparent adhesive sheet, with an attachment area of 12.5 ^mm² . The backing tape was then pulled at an angle of 180° between the first release material and the transparent adhesive sheet to peel the first release material from the transparent adhesive sheet. During the peeling process, a test was evaluated as "good" if the first release material could be peeled from the transparent adhesive sheet without peeling between the transparent adhesive sheet and the second release material, and a test was evaluated as "poor" if peeling occurred between the transparent adhesive sheet and the second release material. The evaluation results are shown in Table 1.

[Heat test after moisture absorption]
The transparent adhesive sheets with release liner of Examples 1 to 3 and Comparative Example 1 were subjected to a post-moisture absorption heating test as follows. First, a transparent adhesive sheet was attached to the 9.5 mm square flat surface of a 9.5 mm square silicon mirror chip to prepare a chip with an adhesive layer. The temperature during attachment was 60°C. Next, the chip with the adhesive layer was pressed against a glass plate via the adhesive layer side (temporary fixation). During this temporary fixation, the pressing temperature was 120°C, the pressing load was 0.1 MPa, and the pressing time was 2 seconds. Next, the adhesive layer interposed between the glass plate and the chip was thermally cured at 150°C, a pressure of 0.7 MPa, and heating for 1 hour, bonding the glass plate and the chip via the adhesive layer. In this way, nine bonded samples were prepared for each transparent adhesive sheet. Next, the bonded samples were subjected to a moisture absorption treatment at a temperature of 30°C, a humidity of 60% RH, and a time of 72 hours. Next, the bonded samples were passed through an IR reflow oven set to maintain a temperature of 260°C or higher for 10 seconds. The bonded samples were then examined for the presence of peeling at the interface between the transparent adhesive sheet and the glass plate. The nine bonded samples were evaluated as "good" if no peeling occurred at the interface between the transparent adhesive sheet and the glass plate, and as "poor" if peeling occurred at the interface between the transparent adhesive sheet and the glass plate in at least one of the nine bonded samples. The evaluation results are shown in Table 1.

To summarize the above, the configuration of the present invention and its variations are listed below as an appendix.

(Appendix 1)
A transparent adhesive sheet that is thermosetting and has a transmittance in the wavelength range of 450 to 1200 nm of 85% or more, preferably 87% or more, and more preferably 90% or more, in a heat-cured state by heating at 150°C for 1 hour.
(Appendix 2)
Attachment 1: The transparent adhesive sheet according to claim 1, wherein in the heat-cured state, the ratio of the transmittance at a wavelength of 450 nm after undergoing a moisture absorption test under conditions of 30°C, 70% relative humidity, and 200 hours to the transmittance at a wavelength of 450 nm before undergoing the moisture absorption test is 0.9 or more, preferably 0.92 or more, and more preferably 0.94 or more.
(Appendix 3)
3. The transparent adhesive sheet according to claim 1, wherein in the heat-cured state, the ratio of the transmittance at a wavelength of 450 nm after the heating test at 260°C for 5 minutes to the transmittance at a wavelength of 450 nm before the heating test is 0.9 or more, preferably 0.92 or more, and more preferably 0.94 or more.
(Appendix 4)
Appendices 1 to 3. The transparent adhesive sheet according to any one of Appendices 1 to 3, having a viscosity at 120°C of 1 to 30 kPa·s, preferably 3 to 30 kPa·s, more preferably 4 to 27 kPa·s, and more preferably 5 to 25 kPa·s.
(Appendix 5)
5. The transparent adhesive sheet according to any one of claims 1 to 4, wherein the storage modulus at 250°C in the heat-cured state is 0.5 to 50 MPa, preferably 0.6 to 45 MPa, and more preferably 0.7 to 40 MPa.
(Appendix 6)
6. The transparent adhesive sheet according to any one of Appendices 1 to 5, wherein in the heat-cured state, the weight loss rate at 300°C is 1.5% or less, preferably 1.2% or less, as measured by thermogravimetry under conditions of a nitrogen atmosphere, a temperature rise rate of 10°C/min, and a temperature rise range of 23 to 300°C.
(Appendix 7)
7. A transparent adhesive sheet according to any one of Appendices 1 to 6, which exhibits a peel adhesive strength of 1 N/10 mm or more, preferably 1.5 N/10 mm or more, against a flat glass surface in a peel test under conditions of 23°C, a peel angle of 180°, and a peel rate of 30 mm/min.
(Appendix 8)
8. The transparent adhesive sheet according to any one of Appendices 1 to 7, wherein the ratio of the glass shear adhesive strength after a moisture absorption test under conditions of 40°C, a relative humidity of 95%, and 120 hours to the glass shear adhesive strength before the test, when heated at 150°C for 1 hour and then adhered to a flat glass surface, is 0.6 or more, preferably 0.7 or more, and more preferably 0.75 or more.
(Appendix 9)
The transparent adhesive sheet according to any one of claims 1 to 8, wherein the refractive index at a wavelength of 633 nm in the heat-cured state is 1.4 to 1.5, preferably 1.42 to 1.48.
(Appendix 10)
10. The transparent adhesive sheet according to any one of claims 1 to 9, comprising an acrylic resin.
(Appendix 11)
11. The transparent adhesive sheet according to claim 10, wherein the acrylic resin has a nitrile group.
(Appendix 12)
12. The transparent adhesive sheet according to claim 10 or 11, wherein the acrylic resin has an epoxy group.
(Appendix 13)
13. The transparent adhesive sheet according to any one of claims 10 to 12, wherein the average molecular weight of the acrylic resin is 400,000 or less, preferably 350,000 or less.
(Appendix 14)
14. The transparent adhesive sheet according to any one of claims 10 to 13, wherein the proportion of the acrylic resin in the organic components contained is 95% by mass or more, and preferably 97% by mass or more.
(Appendix 15)
15. A transparent adhesive sheet according to any one of claims 1 to 14, which does not contain or substantially does not contain an epoxy resin and/or a phenolic resin.
(Appendix 16)
16. The transparent adhesive sheet according to any one of claims 1 to 15, containing a filler having an average particle size of 5 to 100 nm.
(Appendix 17)
17. The transparent adhesive sheet according to claim 16, wherein the filler content is 5 to 45% by mass, preferably 6 to 40% by mass, and more preferably 7 to 35% by mass.
(Appendix 18)
18. The transparent adhesive sheet according to any one of claims 1 to 17, containing a phosphorus-based antioxidant.
(Appendix 19)
19. The transparent adhesive sheet according to claim 18, wherein the content of the phosphorus-based antioxidant is 0.1 to 2% by mass, preferably 0.3 to 1.5% by mass.
(Appendix 20)
20. The transparent adhesive sheet according to any one of claims 1 to 19, containing an imidazole-based curing agent.
(Appendix 21)
21. The transparent adhesive sheet according to claim 20, wherein the content of the imidazole-based curing agent is 0.1 to 2% by mass, preferably 0.2 to 1.5% by mass.
(Appendix 22)
A transparent adhesive sheet with a release material, having a laminated structure including a first release material, a second release material, and a transparent adhesive sheet described in any one of Appendices 1 to 21 between these release materials.
(Appendix 23)
the first release material has a thickness of 38 μm or more;
the second release material has a thickness of 25 μm or more;
23. The transparent adhesive sheet with a release material according to claim 22, wherein the ratio of the thickness of the first release material to the thickness of the second release material is 0.2 to 1.8, preferably 0.22 to 1.55, and more preferably 0.3 to 1.6.
(Appendix 24)
the first release material exhibits a first peel adhesive strength of 0.01 N/100 mm or more, preferably 0.015 N/100 mm or more, in a peel test with respect to the transparent adhesive sheet under conditions of 100°C, a peel angle of 180°, and a peel speed of 300 mm/min;
24. The transparent adhesive sheet with release liner described in Appendix 22 or 23, wherein the second release liner exhibits a second peel adhesion strength of 0.04 N/100 mm or more when used with the transparent adhesive sheet in a peel test at 100°C, a peel angle of 180°, and a peel speed of 300 mm/min.
(Appendix 25)
25. The transparent adhesive sheet with a release material according to claim 24, wherein the ratio of the first peel adhesive strength to the second peel adhesive strength is 0.01 to 0.75, preferably 0.02 to 0.7.
(Appendix 26)
the second release material is a dicing tape having a laminated structure including a base material and a pressure-sensitive adhesive layer,
26. A transparent adhesive sheet with a release material according to any one of claims 22 to 25, wherein the transparent adhesive sheet is releasably adhered to the pressure-sensitive adhesive layer of the dicing tape.
(Appendix 27)
27. The transparent adhesive sheet with a release material according to claim 26, wherein the pressure-sensitive adhesive layer contains an acrylic resin having a 2-ethylhexyl group.
(Appendix 28)
28. The transparent adhesive sheet with a release material according to claim 26 or 27, wherein the thickness of the pressure-sensitive adhesive layer is 5 to 40 μm, preferably 10 to 30 μm.
(Appendix 29)
A bonding method for bonding a glass member to another member using the transparent adhesive sheet according to any one of claims 1 to 21.
(Appendix 30)
A bonding method using the transparent adhesive sheet according to any one of appendices 1 to 21 to bond a transparent resin member having a transmittance of 80% or more at a wavelength of 500 nm to another member.
(Appendix 31)
A step of attaching the transparent adhesive sheet according to any one of Supplementary Notes 1 to 21 to a member;
A step of dividing the component together with the transparent adhesive sheet to obtain component pieces with the transparent adhesive sheet attached;
and a step of bonding the small piece of component with the transparent adhesive sheet to another component via the transparent adhesive sheet.

REFERENCE SIGNS LIST 1 Optical sensor 1a Detection surface 2 Transparent cover members X1, X2 Transparent adhesive sheet with release material 10 Transparent adhesive sheet 11 Adhesive layers R1, R2 Release liner 20 Dicing tape 21 Substrate 22 Pressure-sensitive adhesive layer W Work

Claims (14)

It has thermosetting properties, and when heat-cured by heating at 150°C for 1 hour, it has a minimum transmittance of 85% or more in the wavelength range of 450 to 1200 nm,
A transparent adhesive sheet containing an acrylic resin, wherein the proportion of the acrylic resin in the organic components is 97 mass % or more. The transparent adhesive sheet according to claim 1, wherein in the heat-cured state, the ratio of the transmittance at a wavelength of 450 nm after undergoing a moisture absorption test under conditions of 30°C, 70% relative humidity, and 200 hours to the transmittance at a wavelength of 450 nm before the test is 0.9 or greater. The transparent adhesive sheet according to claim 1 or 2, wherein in the heat-cured state, the ratio of the transmittance at a wavelength of 450 nm after undergoing a heating test at 260°C for 5 minutes to the transmittance at a wavelength of 450 nm before the heating test is 0.9 or greater. The transparent adhesive sheet according to any one of claims 1 to 3, having a viscosity at 120°C of 1 to 30 kPa·s. The transparent adhesive sheet according to any one of claims 1 to 4, wherein the storage modulus at 250°C in the heat-cured state is 0.5 to 50 MPa. A transparent adhesive sheet according to any one of claims 1 to 5, wherein in the heat-cured state, the weight loss at 300°C is 1.5% or less when measured by thermogravimetry under conditions of a nitrogen atmosphere, a temperature rise rate of 10°C/min, and a temperature rise range of 23 to 300°C. A transparent adhesive sheet according to any one of claims 1 to 6, which exhibits a peel adhesive strength of 1 N/10 mm or more against a flat glass surface in a peel test under conditions of 23°C, a peel angle of 180°, and a peel speed of 30 mm/min. The transparent adhesive sheet according to any one of claims 1 to 7, wherein the ratio of the glass shear adhesive strength after a moisture absorption test under conditions of 40°C, 95% relative humidity, and 120 hours, when heated at 150°C for 1 hour and then adhered to a flat glass surface, to the glass shear adhesive strength before the test, is 0.6 or greater. The transparent adhesive sheet according to any one of claims 1 to 8, wherein the refractive index at a wavelength of 633 nm in the heat-cured state is 1.4 to 1.5. A transparent adhesive sheet with a release material, having a laminated structure including a first release material, a second release material, and a transparent adhesive sheet according to any one of claims 1 to 9 between the release materials. the first release material has a thickness of 38 μm or more;
the second release material has a thickness of 25 μm or more;
11. The transparent adhesive sheet with a release material according to claim 10, wherein the ratio of the thickness of the first release material to the thickness of the second release material is 0.2 to 1.8. the first release material exhibits a first peel adhesive strength of 0.01 N/100 mm or more in a peel test with respect to the transparent adhesive sheet under conditions of 100°C, a peel angle of 180°, and a peel speed of 300 mm/min;
12. The transparent adhesive sheet with a release liner according to claim 10 or 11, wherein the second release liner exhibits a second peel adhesion strength of 0.04 N/100 mm or more relative to the transparent adhesive sheet in a peel test under conditions of 100°C, a peel angle of 180°, and a peel speed of 300 mm/min. The transparent adhesive sheet with release material according to claim 12, wherein the ratio of the first peel adhesive strength to the second peel adhesive strength is 0.01 to 0.75. the second release material is a dicing tape having a laminated structure including a base material and a pressure-sensitive adhesive layer,
The transparent adhesive sheet with a release material according to claim 10 , wherein the transparent adhesive sheet is releasably adhered to the pressure-sensitive adhesive layer of the dicing tape.