Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-04-21
2002-05-21
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S375000, C524S378000, C524S503000, C524S557000
Reexamination Certificate
active
06391957
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a release coating composition used for a pressure sensitive adhesive tape or contact sheet, and to a pressure sensitive adhesive tape or contact sheet. More particularly, it relates to an aqueous emulsion type release coating composition used for a pressure sensitive adhesive tape or contact sheet, which has a base such as a thermoplastic plastic film. The invention further relates to a pressure sensitive adhesive tape or contact sheet.
(2) Description of the Related Art
A pressure sensitive adhesive tape or contact sheet has an adhesive layer formed on a major surface thereof and is protected by a cover sheet. When the pressure sensitive adhesive tape or contact sheet is used, the cover sheet is peeled therefrom. A surface of the cover sheet, which is placed in contact with the adhesive layer, is coated with a release coating composition for easy peeling of the cover sheet from the adhesive layer.
As examples of the release coating composition, there can be mentioned a silicone release coating composition and a non-silicone release coating composition. The silicone release coating composition includes an addition type silicone or a condensation type silicone. The silicone release coating composition exhibits excellent releasability, residual adhesion and heat resistance, but is expensive, and must be heat-cured at a high temperature and thus is difficult or even impossible to apply to a plastic film, especially a thermoplastic film.
The non-silicone release coating composition comprises, for example, a long chain alkyl pendant type polymer. The non-silicone release coating composition generally has releasability and other characteristics, which are inferior to those of the silicone release coating composition. But, a non-silicone release coating composition comprising a long chain alkyl pendant type polymer, as described in, for example, Japanese Examined Patent Publication No. 60-30355, exhibits releasability which is acceptable to a satisfying extent, and thus is widely used. Further, this non-silicone release coating composition is advantageous in that there is no need of using a special catalyst nor curing at a high temperature. Releasability can be obtained merely by coating a base film with a solution of the release coating composition in a solvent, followed by drying, and therefore, the release coating composition can advantageously be applied to a base film having a poor heat resistance such as a thermoplastic film. However, the long chain pendant type polymer is insoluble in water and must be used as a solution in an organic solvent.
However, in recent years, a deep interest is felt on problem of safety and environment, and thus, an aqueous release coating composition is eagerly desired. Proposals of an aqueous emulsion type release coating composition as an aqueous release coating composition have been made. For example, in Japanese Unexamined Patent Publication (hereinafter abbreviated to “JP-A”) No. H3-86,778, an aqueous release coating composition comprising an aqueous emulsion of a long chain alkyl pendant type polymer, which is a product produced by reaction of polyvinyl alcohol or a modified product thereof with an alkyl isocyanate, is proposed. In JP-A H8-176,372, an aqueous release coating composition comprising an aqueous dispersion of (i) a product produced by reaction of a saponified vinyl acetate copolymer having a specific polymerization degree and saponification degree with a long chain alkyl compound having a functional group capable of reacting with hydroxyl groups of the saponified vinyl acetate copolymer, and (ii) an acid-modified olefin copolymer with a specific acid value.
The heretofore proposed aqueous emulsion type release coating compositions have poor storage stability, i.e., when the coating compositions are allowed to stand for a long period, the long chain alkyl pendant-type polymer contained as an effective ingredient is readily precipitated or coagulated. Further, the aqueous emulsion type release coating compositions have releasability and residual adhesion, which are inferior to those of non-aqueous release coating compositions containing an organic solvent.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an emulsion-type release coating composition exhibiting high and balanced releasability and residual adhesion, and having good storage stability.
Another object of the present invention is to provide a pressure sensitive adhesive tape or contact sheet exhibiting high and balanced releasability and residual adhesion.
In accordance with the present invention, there is provided an aqueous emulsion-type release coating composition comprising (i) a product produced by reaction of an ethylene-vinyl alcohol copolymer represented by the following formula (1):
wherein the total of n, m and m′ is an integer of 300 to 3,000, the ratio of n/(n+m+m′) is in the range of 0.1 to 0.9, and the ratio of m/(m+m′) is in the range of 0.9 to 1.0, with a C
8-30
alkyl isocyanate (said product is hereinafter referred to as “modified Et-VAl copolymer” when appropriate), and (ii) a surface active agent which is a combination of a nonionic surface active agent having a hydrophilic-lyophilic balance (HLB) of not larger than 12, with an ionic surface active agent.
In accordance with the present invention, there is further provided a pressure sensitive adhesive tape or contact sheet, having a laminate structure composed of superposed base films or a wound base film, each of which has a layer of a pressure sensitive adhesive formed on one surface thereof, and a layer of a release coating composition formed on the other surface thereof so that the release coating composition layer is in direct contact with the pressure sensitive adhesive layer formed on one surface of the adjacent base film; said release coating composition being the above-mentioned aqueous emulsion type release coating composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The aqueous emulsion-type release coating composition of the present invention is characterized as containing a combination of a nonionic surface active agent having a low HLB, i.e., a HLB of not larger than 12, (hereinafter abbreviated to “low-HLB surfactant” when appropriate) and an ionic surface active agent (hereinafter abbreviated to “high-HLB surfactant” when appropriate).
In general, in order to prepare an aqueous polymer emulsion by emulsifying the polymer with a surface active agent, a surface active agent having a HLB falling between that of water and that of the polymer is used as an emulsifier. However, the modified Et-VAl copolymer used in the present invention has an extremely hydrophobic polymer, and therefore, a surface active agent used for the preparation of an aqueous emulsion of the modified Et-VAl copolymer must be appropriately chosen. If a surface active agent having a high HLB is used, it has poor affinity for and compatibility with the modified Et-VAl copolymer, and thus, the modified Et-VAl copolymer is difficult to emulsify. In contrast, a surface active agent having a low HLB is used, it has good affinity for and compatibility with the modified Et-VAl copolymer, but the surface active agent is too hydrophilic to emulsify the modified Et-VAl copolymer.
A nonionic surface active agent having a HLB not larger than 12, i.e., a low-HLB surfactant, used in the present invention exhibits a high affinity for the modified Et-VAl copolymer. An ionic surface active agent, i.e., a high-HLB surfactant, used in the present invention exhibits a high affinity for water as ionic surface active agents generally do. The high-HLB surfactant and the low-HLB surfactant are compatible with each other. Therefore, the modified Et-VAl copolymer can be easily emulsified with a combination of the two surfactants. The thus-prepared aqueous emulsion of the modified Et-VAl copolymer is of an oil-in-water (O/W) type.
The nonionic surface active agent having a HLB of not larger than 12 pre
Kanemoto Kouji
Nishikawa Sadahiko
Ipposha Oil Industries Co., Ltd.
Nixon & Vanderhye
Reddick Judy M.
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