Coating processes – Coating remains adhesive or is intended to be made adhesive – Pressure sensitive adhesive
Reexamination Certificate
1999-12-07
2002-08-13
Dawson, Robert (Department: 1712)
Coating processes
Coating remains adhesive or is intended to be made adhesive
Pressure sensitive adhesive
C428S413000, C428S500000, C428S523000, C525S094000, C526S093000, C526S320000, C526S145000, C526S146000, C526S147000
Reexamination Certificate
active
06432475
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pressure-sensitive adhesive composition comprising a crosslinked polymer obtained by crosslinking a block copolymer comprising at least two of a styrene-based polymer block A and an acrylic polymer block B block-bonded each other and a process for the preparation thereof. The present invention also relates to pressure-sensitive adhesive sheets of the pressure-sensitive adhesive composition in the form of sheet, tape or the like.
BACKGROUND OF THE INVENTION
In recent years, pressure-sensitive adhesives such as solvent type pressure-sensitive, emulsion type pressure-sensitive adhesive and hot-melt type pressure-sensitive adhesive have been used for materials which are required to be easily adhered by simply pressing, such as packaging pressure-sensitive adhesive tapes, masking pressure-sensitive adhesive tapes for coating, sanitary pressure-sensitive adhesive tape, paper diaper fixing tape and pressure-sensitive adhesive label.
As the solvent type pressure-sensitive adhesives there have been known acrylic and rubber-based pressure-sensitive adhesives. In recent years, it has been required that the amount of pressure-sensitive adhesives to be used be minimized from the standpoint of drying efficiency, energy saving and working atmosphere. If the amount of the solvent to be used in the polymerization is reduced to meet this demand, a safety problem occurs due to difficulty in controlling the resulting polymerization heat. Further, the emulsion type pressure-sensitive adhesives are disadvantageous in that since they comprise polymer particles dispersed in water, the water content needs to be finally removed during the formation of the pressure-sensitive adhesive layer, resulting in the deterioration of drying efficiency and energy saving.
The hot-melt type pressure-sensitive adhesives are superior to the solvent type or emulsion type pressure-sensitive adhesives with respect to safety or economy. For example, hot-melt type pressure-sensitive adhesives mainly comprising styrene-isoprene block copolymer have been known. In general, however, this type of pressure-sensitive adhesives exhibits a poor light resistance and thus are disadvantageous in that the resulting products exhibit deterioration in properties with the lapse of time. In an attempt to overcome these difficulties and hence obtain pressure-sensitive adhesives free from these difficulties, acrylic polymer components, which are normally known to exhibit a good light resistance, are introduced instead of the isoprene-based polymer components, which cause the deterioration of the light resistance of the resulting products.
A random copolymer of acrylic monomer with styrene-based monomer can be easily synthesized. There are examples of an pressure-sensitive adhesive mainly comprising such a random copolymer. However, no products exhibiting satisfactory pressure-sensitive adhesive properties have been obtained. On the other hand, block copolymers of styrene-based polymer component and acrylic polymer component cannot be easily obtained by any of radical polymerization method, anionic polymerization method and cationic polymerization method. There are no examples of a pressure-sensitive adhesive mainly comprising such a block copolymer.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a pressure-sensitive adhesive composition which comprises as an pressure-sensitive adhesive a block copolymer of a styrene-based polymer component and an acrylic polymer component that has been easily produced free from safety problems in the absence of solvent or in the presence of a small amount of a solvent to satisfy the desired pressure-sensitive adhesive properties in addition to the inherent characteristics due to the introduction of acrylic polymer component, i.e., enhancing the light resistance, without causing economic problems as in the conventional emulsion type pressure-sensitive adhesives, i.e., problems in drying efficiency and energy saving due to removal of water content.
Another object of the present invention is to provide a process for the preparation the pressure sensitive adhesive composition.
Still another object of the present invention is to provide pressure-sensitive adhesive sheets comprising the pressure-sensitive adhesive composition.
As a result of extensive studies on the above-described problems, it has been found that a living radical polymerization of a styrene-based monomer with an acrylic monomer in the presence of a specific activating agent and a polymerization initiator makes it easy to produce an A-B type or B-A type block copolymer or three-block or higher copolymers of styrene-based polymer block A and acrylic polymer block B, no appropriate synthesis methods of which having been known, in the absence of a solvent or in the presence of a small amount of a solvent without causing any problems in controlling the resulting polymerization heat. It has also been found that the use of a crosslinked polymer obtained by crosslinking the copolymer as a main component of a pressure-sensitive adhesive makes it possible to obtain a pressure-sensitive adhesive composition which sufficiently satisfies the desired pressure-sensitive adhesive properties, particularly well-balanced pressure-sensitive adhesive force and cohesive force and excellent heat resistance, in addition to the effect of enhancing the light resistance characteristic to the acrylic polymer block B without causing any economic problems as: in the conventional emulsion type pressure-sensitive adhesives. The present invention has been completed based on those findings.
The present invention provides a pressure-sensitive adhesive composition comprising a crosslinked polymer obtained by crosslinking a block copolymer comprising at least two of a styrene-based polymer block A and an acrylic polymer block B having a structural unit represented by the general formula (1): —[CH
2
—C(R
1
)COOR
2
]— wherein R
1
represents a hydrogen atom or methyl group, and R
2
represents a C
2-14
alkyl group), block-bonded each other.
The present invention also provides pressure-sensitive adhesive sheets comprising a layer of the pressure-sensitive adhesive composition having the above structure provided on a support.
The present invention further provides a process for the preparation of the pressure-sensitive adhesive composition, which comprises subjecting a styrene-based monomer and an acrylic monomer represented by the general formula (1A): CH
2
═C(R
1
)COOR
2
wherein R
1
represents a hydrogen atom or methyl group, and R
2
represents a C
2-14
alkyl group, optionally together with a monomer having an epoxy group in its molecule and/or a monomer having a hydroxyl group in its molecule, to a living radical polymerization in an appropriate order of monomers using a polymerization initiator in the presence of a transition metal and its ligand to produce a block copolymer comprising at least two of a styrene-based polymer block A and an acrylic polymer block B, block-bonded to each other, and then subjecting said block copolymer to crosslinking to produce a crosslinked polymer.
DETAILED DESCRIPTION OF THE INVENTION
Details of the living radical polymerization method are described in various literature references, e.g., (1) Patten et al., “Radical Polymerization Yielding Polymers with Mw/Mn ~1.05 by Homogeneous Atom Transfer Radical Polymerization”, Polymer Preprinted, pp. 575-576, No. 37 (March 1996), (2) Matyjasewski et al., “Controlled/Living Radical Polymerization. Halogen Atom Transfer Radical Polymerization Promotedbya Cu(I)/Cu(II) Redox Process”, Macromolecules 1995, 28, 7901-7910, Oct. 15, 1995, (3) PCT/US96/03302 to Matyjasewski et al., International Publication No. W096/30421, Oct. 3, 1996, (4) M. Sawamoto et al., “Ruthenium-mediated Living Radical Polymerization of Methyl Methacrylate”, Macromolecules, 1996, 29, 1070.
The present inventors paid their attention to the living radical polymerization method. As a result, it was found that the living radica
Doi Tomoko
Kamifuji Fumiko
Moroishi Yutaka
Okada Ken'ichi
Yamamoto Michiharu
Dawson Robert
Feely Michael J
Nitto Denko Corporation
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