This is a National Phase of Application No. PCT/JP2017/043901 filed Dec. 7, 2017, which claims the benefit of Japanese Application No. 2016-239867 filed Dec. 9, 2016. The disclosure of each of the prior applications is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

This description relates to pressure-sensitive adhesive composition and to a use therefor.

BACKGROUND ART

Pressure-sensitive adhesive compositions are worked into various forms including films, tapes and labels for example, and used in a wide range of applications. They are also applied to a range of substances including glass and plastic in various flat panel displays (FPDs) such as liquid crystal displays (LCDs) and plasma display panels (PDPs).

For example, pressure-sensitive adhesives used in display applications are required to be highly durable and heat resistant in order to prevent lifting and peeling from the adherend under high-temperature, high-humidity conditions.

From the standpoint of heat resistance and the like, pressure-sensitive adhesive compositions containing high-molecular-weight acrylic polymers and low-molecular-weight acrylic polymers have been disclosed (Patent Literature 1 and 2). In addition to other properties, these pressure-sensitive adhesive compositions achieve resistance to lifting and peeling under high-temperature, high-humidity conditions (60° C., 90% RH) and high-temperature conditions (80° C.) through a combination of acrylic polymers with different molecular weights.

It has also been disclosed (Patent Literature 3) that lifting and peeling after high-humidity load (60° C., 95% RH and 85° C., 85% RH) can be prevented with a pressure-sensitive adhesive composition containing a specific vinyl polymer and acrylic pressure-sensitive adhesive polymer even when the adherend is a plastic plate.

CITATION LIST

Patent Literature 1: Japanese Patent Application Publication No. 2012-41453Patent Literature 2: Japanese Patent Application Publication No. 2011-232470Patent Literature 3: Japanese Patent Application Publication No. 2014-88549

SUMMARY OF INVENTION

Technical Problem

However, greater and greater heat resistance (durability) is being demanded in recent years. In the case of automotive touch panels for example, resistance to temperatures around 100° C. may be required. In the case of displays having curvature for design purposes and the like, heat resistance under high-temperature conditions exceeding 100° C. is required when the display is worked by bending it at a high temperature.

From the standpoint of the handling and reworking properties, moreover, there is demand for pressure-sensitive adhesives that have low tackiness but strong adhesion under heat and pressure when a display is subject to pressure-sensitive adhesive sheet processing for example.

The pressure-sensitive adhesive compositions described in Patent Literature 1 and 2 cannot adequately prevent lifting and peeling due to outgassing from the plastic plate under high-temperature, high-humidity conditions. Moreover, even the pressure-sensitive adhesive composition described in Patent Literature 3 has not been durable under severe conditions near 100° C.

The present description provides a pressure-sensitive adhesive composition with even greater heat resistance, along with a use therefor.

Solution to Technical Problem

The inventors succeeded in further improving heat resistance by combining an acrylic pressure-sensitive adhesive polymer as a base polymer component with a specific vinyl polymer as a tackifying component. We also discovered that a specific combination has low tackiness as well as strong adhesive force under heat and pressure. The present description provides the following means.

(1) A pressure-sensitive adhesive composition, including: a vinyl polymer (A) and an acrylic pressure-sensitive adhesive polymer (B), wherein

the vinyl polymer (A) has a glass transition temperature (Tg) of 60° C. to 200° C. and a number-average molecular weight of 500 to 10,000, and is contained in an amount of 0.5 mass parts to 60 mass parts per 100 mass parts of the acrylic pressure-sensitive adhesive polymer (B), and

when the pressure-sensitive adhesive composition is coated on a separator and dried to obtain a pressure-sensitive adhesive layer, a first Tg, which is a glass transition temperature of the pressure-sensitive adhesive layer as a whole, is −80° C. to 10° C., and

a second Tg, which is a glass transition temperature calculated from the surface layer part based on X-ray photoelectron spectroscopy of the pressure-sensitive adhesive layer, is at least 40° C., and is at least 30° C. higher than the first Tg.

(2) The pressure-sensitive adhesive composition according to (1), wherein the first Tg is −30° C. to 5° C., and the second Tg is 50° C. to 180° C.

(3) The pressure-sensitive adhesive composition according to (2), wherein the first Tg is −25° C. to 1° C., and the second Tg is 70° C. to 180° C.

(4) The pressure-sensitive adhesive composition according to any one of (1) to (3), wherein the glass transition temperature of the acrylic pressure-sensitive adhesive polymer (B) is −80° C. to 10° C.

(5) The pressure-sensitive adhesive composition according to (4), wherein the glass transition temperature of the acrylic pressure-sensitive adhesive polymer (B) is −30° C. to 10° C.

(6) The pressure-sensitive adhesive composition according to any one of (1) to (5), wherein at least one kind of compound selected from the group consisting of the (meth)acrylic acid alkoxyalkyl esters having C2-4alkoxyalkyl groups and the (meth)acrylic acid alkyl esters having C1-3alkyl groups is contained in the amount of 10 mass % to 99 mass % of the total monomer units constituting the acrylic pressure-sensitive adhesive polymer (B).

(7) The pressure-sensitive adhesive composition according to any one of (1) to (6), wherein a (meth)acrylic acid alkyl ester having a C1-3alkyl group is contained in the amount of 10 mass % to 80 mass % of the total monomer units constituting the acrylic pressure-sensitive adhesive polymer (B).

(8) The pressure-sensitive adhesive composition according to any one of (1) to (7), wherein a peeling strength of a pressure-sensitive adhesive sheet, the pressure-sensitive adhesive sheet including a 50 μm-thick pressure-sensitive adhesive layer of the pressure-sensitive adhesive composition and a 100 μm-thick polyethylene terephthalate film substrate on which the pressure-sensitive adhesive layer is attached, to a glass plate at 100° C. is at least 5.0 N/25 mm.

(9) The pressure-sensitive adhesive composition according to any one of (1) to (8), wherein the vinyl polymer (A) is contained in the amount of 10 mass parts to 60 mass parts per 100 mass parts of the acrylic pressure-sensitive adhesive polymer (B).

(10) A pressure-sensitive adhesive product provided with a pressure-sensitive adhesive layer, wherein

the pressure-sensitive adhesive layer contains a pressure-sensitive adhesive composition including a vinyl polymer (A) and an acrylic pressure-sensitive adhesive polymer (B), and

the vinyl polymer (A) has a glass transition temperature (Tg) of 60° C. to 200° C. and a number-average molecular weight of 500 to 10,000, and is contained in the amount of 0.5 mass parts to 60 mass parts per 100 mass parts of the acrylic pressure-sensitive adhesive polymer (B), and

when the pressure-sensitive adhesive composition is coated on a separator and dried to obtain a pressure-sensitive adhesive layer, a first Tg, which is a glass transition temperature of the pressure-sensitive adhesive layer as a whole, is −80° C. to 10° C., and

a second Tg, which is a glass transition temperature calculated from the surface layer part based on X-ray photoelectron spectroscopy of the pressure-sensitive adhesive layer, is at least 40° C., and is at least 30° C. higher than the first Tg.

(11) The pressure-sensitive adhesive product according to (10), which is a pressure-sensitive adhesive sheet or pressure-sensitive adhesive tape including the pressure-sensitive adhesive layer on one or both sides of a substrate.

