Stock material or miscellaneous articles – Layer or component removable to expose adhesive – Release layer
Reexamination Certificate
2002-08-13
2003-12-09
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Layer or component removable to expose adhesive
Release layer
C427S208400, C427S505000, C427S516000, C428S040100, C428S041300, C428S004000, C428S041700, C428S352000, C428S354000
Reexamination Certificate
active
06660354
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a release material, a release material article using the same, and a process for producing the release material article.
BACKGROUND OF THE INVENTION
Pressure-sensitive adhesive tapes and pressure-sensitive adhesive sheets are usually obtained by providing a pressure-sensitive adhesive on the surface of a substrate. In the case of tapes, the article is typically stored in a roll form. On the back surface of the substrate, a release material is usually coated so as to protect the adhesive surface and facilitate unwinding upon use. In some cases, another substrate having a release material coated thereon is used to cover and, thereby, protect the adhesive surface.
In general, release materials are roughly classified into those materials containing silicone (“silicone-type release material”) and those materials not containing silicone (“non-silicone type release material”). Silicone-type release material can provide a release strength over a wide range, from relatively low (e.g., 0.1 N/25 mm or less) to relatively high (e.g., 10 N/25 mm or more). However, silicone-type release material may readily transfer to an adhesive surface due to insufficient anchoring to the substrate, for example, a plastic substrate. The transferred silicone-type release material may give rise to contamination. For examples, in the electronics industry, this may be undesirable.
Non-silicone type release material is further classified into those materials containing fluorine (“fluorine-type release material”) and those materials containing a long chain alkyl group (“long chain alkyl group-type release material”). Fluorine-type release materials are generally relatively expensive and the types of solvent that can be used for diluting and coating fluorine-type release materials are typically limited to fluorine-type solvents due to solubility issues. Therefore, practical use of fluorine-type release materials is limited. Long chain alkyl group-type release materials typically consist of a copolymer of an acrylic ester, vinyl ether, and acrylamide derivative or the like and these are disclosed, for example, in Japanese Examined Patent Publication (Kokoku) Nos. 44-9599, 40-8903 and 43-21855. More specifically, Japanese Examined Patent Publication (Kokoku) No. 44-9599 discloses a release material consisting of a copolymer of octadecyl methacrylate and acrylonitrile. Japanese Examined Patent Publication (Kokoku) No. 40-8903 discloses a release material consisting of a copolymer of octadecyl vinyl ether and acrylonitrile. Also, Japanese Patent Publication (Kokoku) No. 43-21855 discloses a release material consisting of a copolymer of octadecyl acrylamide and acrylic acid.
However, these release materials are poor in anchoring to certain substrates, such as polyester. Furthermore, these release materials usually contain a group having high affinity for a pressure-sensitive adhesive, such as carboxyl group, nitrile group, amide group, or hydroxyl group. Such a group may drive the release material to readily transfer to the interface with, or into, an adjacent pressure-sensitive adhesive, or vice versa. As a result, the release material tends to be difficult to release from the pressure-sensitive adhesive or the adhesive properties, such as adhesive strength, of the pressure-sensitive adhesive tend to be decreased. These tendencies are generally more pronounced when the release material is heated to higher temperatures.
Japanese Unexamined Patent Publication (Kokai) No. 63-202685 discloses an acrylic release material obtained by crosslinking an acrylic copolymer of an acrylic ester and an acrylic compound having a functional group with a crosslinking agent. According to this publication, a crosslinking agent such as isocyanate is used for a crosslinking treatment. Crosslinking reactions involving isocyanates tend to proceed gradually and, thus, an undesirably high amount of time may be necessary for the desired performance, such as releasing strength, to be obtained in such materials. Furthermore, the above-described acrylic copolymer contains a polar group such as carboxyl group, hydroxyl group, or amide group, which may provide a higher release strength as compared with release strengths of silicone-type release materials. In addition, when an acrylic copolymer is crosslinked using an isocyanate, it tends to be difficult to release the release material from an acrylic pressure-sensitive adhesive. This tendency is generally more pronounced at a higher temperature.
Japanese Unexamined Patent Publication (Kokai) No. 11-152459 discloses a non-silicone type release material consisting of an acrylic copolymer that does not contain a polar group. This release material is obtained by polymerizing a release material forming composition containing (a) an organic compound having two or more (meth)acryloyl groups and having a number average molecular weight of 600 or more and (b) an alkyl (meth)acrylate under the irradiation of an active energy ray, such as ultraviolet ray or electron beam, while forming crosslinks through the (meth)acryloyl group, and curing the polymer. The release material of this publication contains no polar groups and even when exposed to high temperatures, the release strength is presumed to not significantly increase. However, organic compounds having two or more (meth)acryloyl groups do not effectively decrease the release strength. Although the monomer unit of alkyl (meth)acrylate, which is contained in the copolymer after curing, has a tendency for decreasing the release strength of the release material, the monomer of alkyl (meth)acrylate contained in the release material forming composition is not completely polymerized, even under irradiation of an active energy ray, and partially remains as an unreacted monomer. This may impair the stability of a residual adhesion strength of a pressure-sensitive adhesive after removal of the release material.
On the other hand, Japanese Unexamined Patent Publication (Kokai) Nos. 55-65281, 55-80479, 55-152775 and 55-155079 disclose a method for producing a pressure-sensitive adhesive tape or sheet where the release layer is a release material consisting of a polyolefin-based elastomer or a release material consisting of a mixture of a polyolefin-based elastomer and polyethylene and the adhesive layer is a pressure-sensitive adhesive mainly comprising a polyacrylic ester. The polyolefin-based elastomer used in these publications is one having a shear storage modulus according to a JIS K7213 test of 2.0×10
7
Pa or less and a surface wetting property such that the equilibrium contact angle to a standard solution having a surface tension of 50 mN/m for use in the JIS K6768 test is 55° or more at a temperature of 20±1° C. and a relative humidity of 65±5%. The release material disclosed in these publications is formed by extrusion molding and the release material obtained is not subjected to any treatment. The untreated release material has a problem in that the adhesion between this release material and a substrate supporting the release material is low. Furthermore, the release strength of the release material from the pressure-sensitive adhesive is relatively high and in particular, when exposed to a high temperature, the release strength is increased and the release material obtained disadvantageously fails in having a sufficiently low release strength.
SUMMARY OF THE INVENTION
The present invention provides a release material that is enhanced in its anchoring to a substrate, relatively low in its release strength from a pressure-sensitive adhesive (even after the exposure to a high temperature), and capable of allowing the pressure-sensitive adhesive to hold a stable residual adhesion strength. Also disclosed are release material articles using the same and a process for producing the article.
Specifically, the present invention provides a release material formed by irradiating a release material precursor having a shear storage modulus (hereinafter sometimes referred to as a “storage
Shinohara Masaru
Suwa Toshihiro
Toma Tetsuya
Yasui Yutaka
3M Innovative Properties Company
Ahmad Nasser
Lambert Nancy M.
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