Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-07-23
2001-04-03
Wilson, Donald R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S522000, C524S523000, C524S458000, C525S301000, C525S309000
Reexamination Certificate
active
06211288
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a highly water resistant tackifier resin and a process for producing the tackifier resin.
BACKGROUND OF THE INVENTION
Adhesive technology is advancing day by day. Advanced adhesives include an acrylic emulsion adhesive. This acrylic emulsion adhesive is an adhesive in which an acrylic copolymer as a tack component is dispersed in particulate form in water. No organic solvent is used in the acrylic emulsion adhesive, so that the working environment is free from organic solvent pollution and is also free from the danger of inflammation. Therefore, the acrylic emulsion adhesive is being widely used.
This acrylic emulsion adhesive is commonly produced by dispersing an acrylic monomer in water with the use of an emulsifier and polymerizing the acrylic monomer. A tackifying component is generally added to the acrylic emulsion adhesive in order to improve the adhesion performance thereof. For example, a polymerized rosin ester, a terpene resin or a petroleum resin is used as the tackifying component. It is extremely difficult to disperse such a tackifying component in water, so a very large amount of emulsifier is needed to uniformly disperse the tackifying component in water. The emulsifier is a surfactant, and, the higher the emulsifier content, the lower the water resistance of the obtained acrylic emulsion adhesive. On the other hand, when the amount of added emulsifier is decreased for ensuring water resistance, uniform dispersion of the tackifying component becomes difficult, so that a new problem arises in that the adhesion properties are different between parts where the tackifying component is present and parts where the tackifying component is absent.
In this situation, there have been proposed processes in which a tackifier resin is present in the reaction system of emulsion polymerization of an acrylic monomer for producing an acrylic polymer in place of the conventional addition of the tackifying component after the production of the acrylic polymer.
For example, Japanese Patent Laid-open Publication No. 59(1984)-58069 discloses an invention of a strongly adherent emulsion-type pressure sensitive adhesive comprising a mixture of:
100 parts by weight, in terms of solid contents, of an tackifier resin emulsion (A) obtained by conducting a water-based emulsion polymerization of a resin solution consisting of 100 parts by weight of a tackifier resin dissolved in 30 to 150 parts by weight of an &agr;, &bgr;-monoolefin monomer; and
20 to 1000 parts by weight, in terms of solid contents, of an &agr;, &bgr;-monoolefin polymer emulsion (B) which contains no tackifier resin and exhibits a polymer second transition temperature of not higher than 10° C.
As is apparent from the Examples described in the above publication, the tackifier resin emulsion (A) is produced by dispersing an alkyl acrylate such as butyl acrylate and acrylic acid as acrylic monomers and a tackifier resin in water with the use of an anionic surfactant and a nonionic surfactant and performing a polymerization. The &agr;, &bgr;-monoolefin polymer emulsion (B) is produced in the presence of an anionic surfactant and a nonionic surfactant in the same manner except that no tackifier resin is used. The obtained tackifier resin emulsion (A) and &agr;-monoolefin polymer emulsion (B) are blended together to thereby obtain the strongly adherent emulsion-type pressure sensitive adhesive. Therefore, this strongly adherent emulsion-type pressure sensitive adhesive contains a relatively large amount of surfactant which has been used as the emulsifier. Thus, in the polymerization of the above acrylic monomer together with the tackifier resin in the presence of a catalyst, the use of a relatively large amount of emulsifier is inevitable for stable emulsification of the acrylate monomer containing the acrylic acid monomer.
The strongly adherent emulsion-type pressure sensitive adhesive described in the above publication is directly used as a pressure sensitive adhesive or an adhesive, so that the used emulsifier still remains in the strongly adherent emulsion-type pressure sensitive adhesive.
OBJECT OF THE INVENTION
The inventors have noted that in order to uniformly disperse the tackifying component, which has commonly been blended for improving the performance of the adhesive, in the emulsion-type pressure sensitive adhesive, the use of a very large amount of emulsifier has been needed.
It is therefore an object of the present invention to provide a tackifier resin in which the content of emulsifier is reduced and, despite the reduction of the use of the emulsifier content, the tackifying component is uniformly dispersed.
It is another object of the present invention to provide a tackifier resin which has excellent water resistance.
It is a further object of the present invention to provide a process for producing a tackifier resin either with the use of a small amount of emulsifier or without the use thereof.
SUMMARY OF THE INVENTION
In one aspect of the present invention, there is provided a highly water resistant tackifier resin which comprises an acrylic (co)polymer incorporating therein at least part of a tackifying component as a raw material on or around seed particles of 0.05 to 15 &mgr;m in average particle size having polar groups on their surfaces.
This highly water resistant tackifier resin can be produced by a process which comprises the steps of:
dispersing a tackifying component as a raw material, an oil-soluble peroxide or oil-soluble azo initiator and an acrylic monomer in an aqueous medium in which seed particles of 0.05 to 15 &mgr;m in average particle size having polar groups on their surfaces are dispersed; and
polymerizing the acrylic monomer while at least part of the tackifying component is incorporated in the acrylic (co)polymer on or around the surfaces of the seed particles so that the seed particles grow.
According to the present invention, by virtue of the use of seed particles of specified average particle size having polar groups on their surfaces as the starting material, the seed particles, tackifying component as a raw material and monomer component can be uniformly dispersed in the aqueous medium with the use of such a small amount of emulsifier that the water resistance is not influenced. When the thus obtained aqueous dispersion is subjected to polymerization in the presence of a specified polymerization initiator, the acrylic monomer is (co)polymerized while the tackifying component as the raw material is incorporated in the acrylic (co)polymer on or around the seed particles, so that the seed particles grow. The grown seed particles still have polar groups on their surfaces, so that they are stably dispersed in the aqueous medium.
The amount of emulsifier contained in the thus obtained tackifier resin of the present invention is very small. Therefore, an adhesive prepared by blending this tackifier resin with an acrylic polymer emulsion exhibits excellent water resistance despite the fact that it is an emulsion.
DETAILED DESCRIPTION OF THE INVENTION
The highly water resistant tackifier resin of the present invention along with the process therefor will be described in detail below.
The highly water resistant tackifier resin of the present invention can be produced by a process which comprises the steps of:
dispersing a tackifying component as a raw material, an oil-soluble peroxide or oil-soluble azo initiator and an acrylic monomer in an aqueous medium in which seed particles of 0.05 to 15 &mgr;m in average particle size having polar groups on their surfaces are dispersed; and
polymerizing the acrylic monomer while at least part of the tackifying component is incorporated in the acrylic (co)polymer on or around the surfaces of the seed particles so that the seed particles grow.
Examples of the seed particles having polar groups on their surfaces for use in the present invention include:
seed particles of a copolymer obtained by polymerizing a (meth)acrylic ester and a monomer which can be copolymerized with the (meth)acrylic ester
Soken Chemical & Engineering Co., Ltd.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
Wilson Donald R.
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