Pressure-sensitive adhesive sheet and method for peeling pressure-sensitive adhesive sheet

A method for peeling a pressure-sensitive adhesive sheet adhered on an adherend, the method including a water-peel step in which the pressure-sensitive adhesive sheet is peeled from the adherend, in a state where an aqueous liquid exits at an interface between the adherend and the pressure-sensitive adhesive sheet at a front line of peeling the pressure-sensitive adhesive sheet from the adherend, with the aqueous liquid allowed to further enter the interface following a movement of the peel front line,

• wherein
• the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer;
• the pressure-sensitive adhesive layer comprises a layer A forming at least one surface of the pressure-sensitive adhesive layer;
• the layer A is a layer formed from a photocurable pressure-sensitive adhesive composition or a solvent-based pressure-sensitive adhesive composition;
• wherein the layer A further comprises a hydrophilicity enhancer, wherein the hydrophilicity enhancer comprises a surfactant selected from the group consisting of anionic surfactants;
• cationic surfactants;
• and nonionic surfactants having an HLB value of at least 3 and no more than 18;
• and
• the pressure-sensitive adhesive sheet has:
• an adhesive strength N0 of 2.0 N/10 mm or greater, after one day at room temperature following application of the layer A side to a surface of an alkaline glass plate as an adherend fabricated by a float method, the surface of the glass plate has a contact angle of 5° to 10° with distilled water;
• a water-resistant adhesive strength reduction rate of 30% or lower, determined by a first formula (1−(N1/N0))×100 based on its water-resistant adhesive strength N1 (N/10 mm) and the adhesive strength N0 (N/10 mm), wherein N1 is measured after the layer A side is applied to a surface of an alkaline glass plate as an adherend fabricated by a float method with the surface of the glass plate having a contact angle of 5° to 10° with distilled water, and a resultant assembly is stored at room temperature for one day, immersed in water for 30 minutes, taken out from the water and then residual water is wiped off;
• and
• a water-peel adhesive strength reduction rate of 75% or higher, determined by a second formula (1−(N2/N0))×100 based on its water-peel strength N2 (N/10 mm) and an adhesive strength N0 (N/10 mm), wherein N2 is measured according to JIS Z0237:2009 “10.4.1 Method 1:
• 180° Peel Strength to Test Plate” after the layer A side is applied to a surface of an alkaline glass plate as an adherend fabricated by a float method with the surface of the alkaline glass plate having a contact angle of 5° to 10° with distilled water, stored at room temperature for one day, 20 μL of distilled water is dropped onto the adherend and the distilled water is allowed to enter an interfacial edge between the pressure-sensitive adhesive layer and the adherend;
• in particular, measured using a tensile tester at a test temperature of 23° ° C. at a tensile speed of 300 mm/min at a peel angle of 180°, and
• wherein the hydrophilicity enhancer is included in an amount of at least 0.01 part by weight up to 20 parts by weight relative to 100 parts by weight of monomers forming a polymer included in the layer A.

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer,

• wherein
• the pressure-sensitive adhesive layer comprises a layer A forming at least one surface of the pressure-sensitive adhesive layer;
• the layer A is a layer formed from a photocurable pressure-sensitive adhesive composition or a solvent-based pressure-sensitive adhesive composition;
• wherein the layer A further comprises a hydrophilicity enhancer, wherein the hydrophilicity enhancer comprises a surfactant selected from the group consisting of anionic surfactants;
• cationic surfactants;
• and nonionic surfactants selected from the group consisting of polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glyceryl ether, polyoxypropylene glyceryl ether, polyoxyethylene bisphenol A ether, polyoxyethylene fatty acid esters, and polyoxyethylene glyceryl ether fatty acid esters;
• and
• the pressure-sensitive adhesive sheet has:
• an adhesive strength N0 of 2.0 N/10 mm or greater, after one day at room temperature following application of the layer A side to a surface of an alkaline glass plate as an adherend fabricated by a float method, the surface of the glass plate has a contact angle of 5° to 10° with distilled water;
• a water-resistant adhesive strength reduction rate of 30% or lower, determined by a first formula (1−(N1/N0))×100 based on a water-resistant adhesive strength N1 (N/10 mm) and an adhesive strength N0 (N/10 mm), wherein N1 is measured after the layer A side is applied to a surface of an alkaline glass plate as an adherend fabricated by a float method with the surface of the alkaline glass plate having a contact angle of 5° to 10° with distilled water, and a resultant assembly is stored at room temperature for one day, immersed in water for 30 minutes, taken out from the water and then residual water is wiped off;
• and
• a water-peel adhesive strength reduction rate of 75% or higher, determined by a second formula (1−(N2/N0))×100 based on a water-peel strength N2 (N/10 mm) and an adhesive strength N0 (N/10 mm), wherein N2 is measured according to JIS Z0237:2009 “10.4.1 Method 1:
• 180° Peel Strength to Test Plate” after the layer A side is applied to a surface of an alkaline glass plate as an adherend fabricated by a float method with the surface of the alkaline glass plate having a contact angle of 5° to 10° with distilled water, stored at room temperature for one day, 20 μL of distilled water is dropped onto the adherend and the distilled water is allowed to enter an interfacial edge between the pressure-sensitive adhesive layer and the adherend;
• in particular, measured using a tensile tester at a test temperature of 23° C. at a tensile speed of 300 mm/min at a peel angle of 180°, and
• wherein the hydrophilicity enhancer is included in an amount of at least 0.01 part by weight up to 20 parts by weight relative to 100 parts by weight of monomers forming a polymer included in the layer A.