Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-07-30
2001-09-11
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S272000, C524S457000, C524S458000, C524S461000, C524S529000, C524S533000, C524S764000, C525S244000, C525S267000, C526S931000, C428S343000, C428S35500R
Reexamination Certificate
active
06288148
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the technical field of aqueous acrylic emulsions with excellent adhesion, particularly to the technical field for bonding materials having unsmooth surfaces, i.e. polymer foams such as urethane foams, polyolefin foams, rubber foams; fibrous materials such as paper, cloth, non-woven fabric; or materials roughened on their surfaces by embossing, abrasion, chemical treatment or the like to each other or to other materials.
PRIOR ART
Solvent-type acrylic adhesives obtained by solution polymerization are used by suitably changing their composition, molecular weight, molecular weight distribution or the like to well balance their adhesive characteristics for the intended use. However, the use of solvents has recently posed environmental problems, which prompted attempts to replace solvent-based adhesives by aqueous ones, but acrylic emulsions prepared by emulsion polymerization with the composition unchanged often show poor water resistance or lowered adhesion. It has been known that this is because the surfactants used are localized on the surface or emulsion particles are wholly not fused to each other during drying to hinder homogenization.
A known effective solution to this problem is to add a tackifier into acrylic emulsions. However, some special techniques are required to add an oily resin tackifier into aqueous acrylic emulsions. Such previously known techniques include:
1) absorbing a tackifier dissolved in a solvent to acrylic emulsion particles, and
2) mechanically dispersing a tackifier into emulsion and then mixing it with an acrylic emulsion.
However, the first technique 1) has the problem that the resulting acrylic emulsion is less stable and includes the solvent. The second technique 2) has the problem that the surfactant used for emulsifying the tackifier is excessively included or the effect of adding a tackifier can not be sufficiently produced because the tackifier is hardly homogenized with acrylic resins during drying.
In order to solve these problems, JPA No. 23641/79 proposes an acrylic emulsion obtained by emulsion polymerization of acrylic monomers in which a tackifier has been dissolved. JPB No. 30351/90 proposes a process for more stably preparing such an acrylic emulsion. Furthermore, JPA No. 80482/90 describes that tackifiers can efficiently be incorporated into particles by emulsion polymerization of acrylic monomers in which the tackifiers have been dissolved in the presence of a seed polymer.
These disclosures suggest that tackifier particles are divided as finely as acrylic emulsions to allow them to be readily homogenized with acrylic resins. However, the existence of tackifiers during emulsion polymerization has the serious problem of lowering the molecular weight of the acrylic polymer and thus extremely lowering its cohesive force because they generally act as potent chain transfer agents. Therefore, all of the above disclosures rely on positively enhancing the crosslinking density with a crosslinkable monomer or abundantly including a relatively cohesive monomer to prevent lowering of cohesive force.
However, such procedures impose a considerable limitation on balancing characteristics of adhesives. Namely, an enhanced crosslinking density or an abundant cohesive element impairs wettability and therefore adhesion. Particularly, it has the disadvantage of impairing adhesion to polyolefin materials or rough surfaces, especially to polymer foams.
JPA No. 178402/92 points out this problem and proposes that a seed polymer having a high swell for solvents should be preliminarily prepared and subsequently an acrylic monomer containing a tackifier dissolved therein should be polymerized in emulsion to facilitate absorption of the tackifier into particles of the seed during polymerization and thus to obtain a good holding power without increasing the crosslinking density.
However, in this disclosure, 65% or more of the acrylic monomer is consumed to preliminarily polymerize a seed polymer and uses a multifunctional monomer and a chain transfer agent in combination for crosslinking so that the entire system finally has a high crosslinking density. Thus, this solution would not provide a polymer with tackifier having a sufficiently low crosslinking density, therefore having a good wettability enough to sufficiently give adhesion to polyolefin materials or rough surfaces, particularly polymer foams.
The present invention was made to overcome the above disadvantages of the prior art and aims to improve adhesion and holding power of acrylic emulsions, adhesive compositions using said acrylic emulsions and adhesive tapes using them.
DISCLOSURE OF THE INVENTION
In order to solve the above problems, the invention as defined in claim
1
provides an acrylic emulsion obtained by preparing at least two acrylic monomer dispersions containing a tackifier dissolved at different proportions in an acrylic monomer, carrying out a polymerization reaction of one acrylic monomer dispersion and then adding the other acrylic monomer dispersion to further proceed the polymerization reaction.
The invention as defined in claim
2
provides an acrylic emulsion according to claim
1
wherein the proportion of the tackifier contained in said one acrylic monomer dispersion is lower than the proportion of the tackifier contained in said other acrylic monomer dispersion.
The invention as defined in claim
3
provides an acrylic emulsion according to claim
1
wherein the tackifier in said one acrylic monomer dispersion is based on a xylene resin contained at a weight proportion of 6% or less on the basis of the weight of the acrylic monomer in said one acrylic monomer dispersion.
The invention as defined in claim
4
provides an acrylic emulsion according to claim
3
wherein each of said acrylic monomer dispersions is an aqueous emulsion dispersion.
The invention as defined in claim
5
provides an acrylic emulsion according to claim
4
wherein the acrylic monomer in said acrylic monomer dispersions does not contain any multifunctional monomer.
The invention as defined in claim
6
provides an acrylic emulsion according to claim
1
wherein the tackifier in said one acrylic monomer dispersion is based on a rosin ester resin contained at a weight proportion of 3% or less on the basis of the total weight of said one acrylic monomer dispersion.
The invention as defined in claim
7
provides an acrylic emulsion according to claim
6
wherein each of said acrylic monomer dispersions is an aqueous emulsion dispersion.
The invention as defined in claim
8
provides an acrylic emulsion according to claim
7
wherein the acrylic monomer in said acrylic monomer dispersions does not contain any multifunctional monomer.
The invention as defined in claim
9
provides an adhesive tape comprising an adhesive layer consisting of an adhesive composition containing an acrylic emulsion according to any one of claims
1
to
8
formed on at least one face of a substrate.
The invention as defined in claim
10
provides a process for preparing an acrylic emulsion, comprising preparing at least two acrylic monomer dispersions containing a tackifier dissolved at different proportions in an acrylic monomer, carrying out a polymerization reaction of one acrylic monomer dispersion and then adding the other acrylic monomer dispersion to further proceed the polymerization reaction.
The invention as defined in claim
11
provides a process for preparing an acrylic emulsion according to claim
10
wherein the proportion of the tackifier contained in said one acrylic monomer dispersion is lower than the proportion of the tackifier contained in said other acrylic monomer dispersion.
The invention as defined in claim
12
provides a process for preparing an acrylic emulsion according to claim
10
using a xylene resin as a major component of the tackifier in said one acrylic monomer dispersion, wherein said tackifier is contained at a proportion of 6% or less on the basis of the weight of the acrylic monomer.
The invention as defined in claim
13
provides a
Samukawa Hiroshi
Shibata Kazuki
Egwim Kelechi
Oliff & Berridg,e PLC
Sony Chemicals Corp.
Wu David W.
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