Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-01-07
2002-04-09
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550AC, C525S190000
Reexamination Certificate
active
06368707
ABSTRACT:
TECHNICAL FIELD
This invention relates to an adhesive sheet. More particularly, it relates to a heat-sensitive adhesive sheet which has non-adhesive properties or has very low adhesive properties at ordinary temperature, but exhibits adhesive properties upon heating and also exhibits adhesive properties by applying pressure.
BACKGROUND ART
In general, adhesive sheets with release papers (mold-release papers) covered on the adhesive surface thereof are subjected to storage, distribution, marketing, etc. Further, wind-up type products such as adhesive tapes use substrates having a back surface having been subjected to a release treatment, so as to be capable of re-winding the tape when using the same. Since release papers become unnecessary after adhering adhesive tapes onto adherends, release paper-free adhesive sheets are demanded from the reasons of resource saving and cost reduction. Furthermore, if substrates, the back surface of which being not subjected to release treatment, can be used in adhesive tapes, it is possible to simplify the production steps of the adhesive tape substrates and also decrease the production cost.
Known examples of release paper-free adhesive sheets include heat-sensitive adhesive sheets coated with delayed-tack type adhesives (JP-B-62-21835 and JP-A-6-10084; the term “JP-A” as used herein means an “unexamined published Japanese patent application”, and the term “JP-B” as used herein means an “examined Japanese patent publication”). Those publications disclose delayed-tack type adhesives comprising thermoplastic resins such as ethylene/vinyl acetate copolymers having mixed therewith solid plasticizers such as dicyclohexyl phthalate. Those publications also describe that the adhesives have non-adhesive properties at ordinary temperature but exhibit adhesive force due to that the plasticizers melt by heating.
However, these conventional delayed-tack type adhesives containing solid plasticizers have various problems as mentioned in (i) to (iv) below, and are applicable only to limited and specific purposes of use at the present stage.
(i) After crystallization of a solid plasticizer proceeds, adhesive force is lost. Therefore, once an adhesive sheet is peeled off from an adherend, such an adhesive tape cannot again be adhered thereto.
(ii) The heating temperature for exhibiting adhesive properties depends on the melting point of a solid plasticizer, which makes it impossible to arbitrarily set the heating temperature.
(iii) After the crystallization proceeds, the adhesive becomes hard, and loses its flexibility. Therefore, if the adhesive tape is adhered to an adherend, and then the adherend is bent or vibration is applied to the adherend, there is a fear that the adhesive layer cannot follow the adherend and, as a result, peels off therefrom.
(iv) Where the substrate used in the adhesive sheet is made of woodfree paper, etc., the plasticizer tends to ooze out onto the sheet surface when the adhesive sheet is heated.
Therefore, an object of the present invention is to provide a heat-sensitive adhesive sheet which has non-adhesive properties or has very low adhesive properties at ordinary temperature and, therefore, can be handled as marketed products as such even if release treatment to the adhesive layer (for example, a release paper or release treatment of the back surface of a substrate) is not always conducted, and on the other hand, can exhibit adhesive properties when heating or when applying pressure, thereby being effectively used as adhesive sheets or adhesive tapes.
Another object of the present invention is to provide a heat-sensitive adhesive sheet having excellent qualities and free from the above-mentioned problems (i) to (iv) in the conventional delayed-tack type adhesives.
DISCLOSURE OF THE INVENTION
The present inventors have conducted extensive studies to solve the above-mentioned problems. As a result, they have found that if a heat-sensitive adhesive sheet is formed by mixing an aqueous emulsion containing a specific alkyl (meth)acrylate-based polymer with a copolymer having carboxyl groups neutralized with a specific base to obtain a polymer composition and forming an adhesive layer comprising this polymer composition on a substrate, such an adhesive does not show adhesive properties at all or does not substantially show adhesive properties at ordinary temperature but exhibits adhesive properties when heating or when applying pressure, and thus can effectively be used as an adhesive sheet.
Further, the present inventors have found that in the adhesive sheet thus obtained, the adhesive properties once exhibited are not lost and good adhering state is maintained even if the adhesive sheet is adhered on a substrate and time passes; the adhesive layer does not become hard even after the passage of time; and components in the adhesive layer do not ooze out onto the substrate even by heating. The present invention has been completed based on those findings.
Accordingly, the present invention provides a heat-sensitive adhesive sheet or a heat-sensitive adhesive tape, comprising a substrate having formed thereon an adhesive layer comprising a polymer composition (C) which comprises the following aqueous emulsion (A) and copolymer (B), wherein an adhesive force determined by the 180° peeling test method as specified in JIS Z 0237 at a temperature of 25° C. is 10 g/25 mm or less:
Aqueous emulsion (A): An aqueous emulsion containing an alkyl (meth)acrylate-based polymer (a) having a glass transition temperature of −10° C. or below, which is obtained by emulsion-polymerizing radically polymerizable monomers containing as the main component an alkyl (meth)acrylate; and
Copolymer (B): A water-soluble or water-dispersible copolymer (B) having a glass transition temperature of 20° C. or above, which is a copolymer obtained by copolymerizing an &agr;,&bgr;-ethylenically unsaturated carboxylic acid with other radically polymerizable monomers, wherein a part or the entire amount of carboxyl groups in the copolymer is neutralized with a base having a boiling point of 110° C. or below.
Further, the present invention is a heat-sensitive adhesive sheet, characterized in that it is a heat-sensitive adhesive sheet having on a substrate an adhesive layer comprising a polymer composition emulsion (C) obtained by emulsion polymerizing a radically polymerizable monomer comprising as a main component, an alkyl (meth)acrylate forming an alkyl (meth)acrylate-based polymer (a) having a glass transition temperature of −10° C. or less, in an aqueous medium in the presence of a water-soluble or water-dispersible copolymer (B) having a glass transition temperature of 20° C. or more, which is a copolymer having an acid value of 30-260 mgKOH/g obtained by copolymerizing an &agr;,&bgr;-ethylenically unsaturated carboxylic acid with other radically polymerizable monomers, wherein a part or the entire amount of carboxyl groups in the copolymer is neutralized with a base having a boiling point of 110° C. or less; and that an adhesive force determined by the 180° peeling test method as specified in JIS Z 0237 at a temperature of 25° C. is 10 g/25 mm or less
The heat-sensitive adhesive sheet of the present invention as described above can be used without subjecting any release treatment to the adhesive layer (that is, without using a release paper or without subjecting release treatment to the back surface of the substrate). Further, the sheet can also be used in the state that the release treatment has been applied, if desired.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in detail below.
The term “heat-sensitive adhesive sheet” as used herein means one having an adhesive layer comprising a polymer composition which comprises the above-mentioned aqueous emulsion (A) and copolymer (B), formed on a substrate. The substrate in such a heat-sensitive adhesive sheet is not particularly limited in shape, size, form, material, etc., and any one may be used. Accordingly, the “heat-sensitive adhesive sheet” of the present invention me
Kamiya Daisuke
Maeda Keiji
Ota Hiroyuki
Bagwell Melanie D.
Seidleck James J.
Sughrue & Mion, PLLC
Toagosei Co. Ltd.
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