Optical pressure-sensitive adhesive sheet

Abstract

Provided is an optical pressure-sensitive adhesive sheet having satisfactory colorlessness / transparency, excels in whitening resistance, high-temperature bonding reliability, bump absorptivity, and in workability. The sheet includes a plastic film substrate and, on at least one side thereof, an acrylic pressure-sensitive adhesive layer and has a moisture content of 0.65 percent by weight or more after storage in an environment of 60° C. and 95% RH for 120 hours. The plastic film substrate has a total light transmittance of 88% or more, an internal haze of 1.5% or less, a b* value of −0.5 to 0.5, and a thickness of 12 to 75 μm, the acrylic pressure-sensitive adhesive layer contains an acrylic polymer and has a storage shear modulus at 23° C. of 0.8×105 to 5.0×105 Pa, and the acrylic polymer is formed from, as an essential monomer component, a monomer forming a homopolymer with a glass transition temperature of −10° C. or higher.

Description

TECHNICAL FIELD[0001]The present invention relates to optical pressure-sensitive adhesive sheets which are used typically for the lamination of optical members (optical elements) and for the production of optical products.BACKGROUND ART[0002]Liquid crystal displays (LCDs) and other display devices, as well as touch panels and other input devices to be used in combination with the display devices have been recently widely employed in various areas. Transparent pressure-sensitive adhesive sheets (pressure-sensitive adhesive tapes) are used for the lamination of optical members typically in the production of such display devices and input devices. For example, transparent pressure-sensitive adhesive sheets are used for the lamination of touch panels with various display devices or optical members (e.g., protective plates) and for the lamination of constitutional members of touch panels with each other (see, for example, Patent Literature (PTL) 1, PTL 2, PTL 3, and PTL 4).[0003]Pressure...

AI Technical Summary

Benefits of technology

[0020]The optical pressure-sensitive adhesive sheet according to the present invention, as having the configuration, exhibits excellent tackiness and blistering / separation resistance at high temperatures and thus excels in high-temperature bonding reliability. The optical pressure-sensitive adhesive sheet according to the present invention has satisfactory colorlessness / transparency in an ordinary state, also has superior whitening resistance, and thereby does not adversely affect the appearances of optical members and optical products obtained by the use of the sheet. Particularly when the optical products (optical members) are display devices (display members), the sheet does not lower the visibility of displays of them. Even when applied typically to optical members having bumps or steps, the sheet can fill in (conform) such bumps, does not cause bubbles in the bump regions, and thus excels also in bump absorptivity. Even when subjected typically to blanking, the sheet does not suffer from problems such as dust deposition on an end face (cut surface), adhesive stringing, and adhesive deficiency, and thereby excels in workability. The optical pressure-sensitive adhesive sheet according to the present invention, when used, contributes to better productivity of optical products (optical members).

Problems solved by technology

However, a pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive, when exposed to high temperatures, has an insufficient adhesive strength and suffers from blistering and separation, thus being inferior in high-temperature bonding reliability.

Specifically, under present circumstances, a pressure-sensitive adhesive sheet having both whitening resistance and high-temperature bonding reliability at certain level has not yet been obtained.

However, when the sheet is subjected to blanking, the pressure-sensitive adhesive layer is often squeezed-out from the cut surface, and the squeezed pressure-sensitive adhesive layer adheres to an end face of a separator (release liner) to cause “adhesive stringing” (adhesive webbing) and “adhesive deficiency” and / or is contaminated by dust (dust deposition), thus being inferior in workability.

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