Pressure-sensitive adhesive sheet

Abstract

Provided is a PSA sheet that can be used on a metal adherend because it has anti-metal-corrosive properties and can also maintain good removability while preventing or inhibiting adherend surface contamination even when prolongedly adhered to the adherend. A PSA sheet having a PSA layer is provided. The PSA layer comprises at least 95% base polymer by weight and has a chloride ion amount of less than 300 μg per gram of pressure-sensitive adhesive layer, determined by hot water extraction.

Description

TECHNICAL FIELD[0001]The present invention relates to a pressure-sensitive adhesive sheet.[0002]The present application claims priority to Japanese Patent Applications No. 2018-246231, No. 2018-246232 each filed on Dec. 27, 2018 and No. 2019-118312 filed on Jun. 26, 2019; the entire content thereof is incorporated herein by reference.BACKGROUND ART[0003]In general, pressure-sensitive adhesive (PSA) exists as a soft solid (a viscoelastic material) in a room temperature range and has a property to adhere easily to an adherend with some pressure applied. For such a property, in processing and transporting various articles, PSA has been widely used as PSA sheets for various purposes, including surface protective sheets to prevent damage (scratches, contamination, corrosion, etc.) of their surfaces. For instance, a PSA sheet having a PSA layer on one face of a substrate is preferably used as a surface protective sheet to protect metal plate surface. Conventional art documents disclosing ...

AI Technical Summary

Benefits of technology

[0008]By using the PSA comprising at least 95% base polymer by weight, the PSA sheet can maintain good removability while preventing or inhibiting contamination of adherend surface even when adhered to the adherend for a long period.

[0010]In summary, according to the embodiment, even when adhered to a metal adherend for a long period, it can maintain good removability while preventing or inhibiting adherend surface contamination and can also prevent metal corrosion in the adherend.

[0012]In some preferable embodiments, the FSA layer includes 3% rust inhibitor by weight or less. The PSA layer in this embodiment is free of a rust inhibitor or includes up to the prescribed level of rust inhibitor. While rust inhibitor is an effective additive for preventing corrosion, an increase in its usage tends to result in compromised aged removability. By limiting the use of rust inhibitor to or below the prescribed level, the increase in aged adhesive strength can be reduced to preferably maintain good removability. It is also significant to limit the rust inhibitor usage in view of highly inhibiting contamination of adherend surface. For instance, when the adherend surface is subjected to a process such as coating after removal of the PSA sheet adhered for a certain time period, defects (coating defects, etc.) due to adherend contamination can be avoided in the process.

[0017]In an application adhered to a metal plate, even when adhered to the metal plate for a long period, the PSA sheet disclosed herein can maintain good removability while preventing or inhibiting contamination of adherend surface and can also prevent corrosion of the metal plate. Thus, it is preferably used for protecting metal plates. After the protection period by the PSA sheet ends, the metal plate (e.g. an aluminum plate) can be subjected to surface coating, etc. Accordingly, it is desirable that adherend contamination is highly inhibited as it may badly affect the coating, etc. By applying the art disclosed herein for metal plate protection, after the protection by the PSA sheet ends, the metal plate may still be free of defects (coating defects, etc.) even in post-processes such as coating. The PSA sheet disclosed herein is particularly preferably used for protecting aluminum plates.

Problems solved by technology

However, when used in an embodiment involving prolonged protection by the PSA sheet, the adhesive strength may increase due to changes in temperature, etc., and the intended removability may not be maintained.

As a solution, an adhesive strength adjuster may be added to reduce the increase in aged adhesive strength; however, the adhesive strength adjuster may contaminate the adherend surface.

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