Pressure-sensitive materials with small amounts of styrene

Details Pressure-sensitive materials with small amounts of styrene Pressure-sensitive materials with small amounts of styrene

1999-02-09

2001-04-10

Warzel, Mark L. (Department: 1714)

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...

C524S272000, C524S560000, C524S561000, C524S562000, C526S317100, C526S324000, C526S329700, C428S522000

Reexamination Certificate

active

06214925

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a polymer composed of
from 50 to 99.98% by weight of a C
1
-C
12
alkyl (meth)acrylate a),
from 0.02 to 1.8% by weight of a vinyl-aromatic compound b),
from 0 to 10% by weight of an ethylenically unsaturated acid or an ethylenically unsaturated acid anhydride c), and
from 0 to 40% by weight of other monomers d), the percentages by weight being based on the polymer.
Furthermore, the invention relates to the use of the polymers or their aqueous dispersions.
2. Description of the Background
Pressure-sensitive adhesives (PSAs) form a permanent tacky film which at room temperature, even under slight pressure, sticks to a very wide variety of surfaces. Pressure-sensitive adhesives are used to produce self-adhesive products such as self-adhesive labels, tapes and films. Products of this kind are very simple to use and make it possible to work rapidly when bonding. In contrast to contact adhesive compositions, no ventilation times are necessary. Moreover, there is no “open time” within which the adhesive bond must be implemented. The quality of a self-adhesive article depends essentially on whether the internal strength (cohesion) and the sticking of the adhesive film on the surface that is to be bonded (adhesion) are set properly in relation to one another in accordance with the utility.
In the case of pressure-sensitive adhesives for labels, in particular, the level of cohesion must be sufficient for no stringing and no emergence of glue at the edges to occur in the course of stamping and cutting, since otherwise the cutting tools become soiled and the cut faces sticky. At the same time, the adhesion should be at a high level in order to obtain good sticking on the substrate that is to be bonded.
In general it is impossible to optimize adhesion and cohesion independently of one another. There is a desire for measures which either lift the level of both properties or, at least, maintain one property unchanged while improving the other.
Adhesives, including pressure-sensitive adhesives, based on polymers which can contain styrene are already known from DE-A-3 013 812, U.S. Pat. No. 5,416,134 and EP-A-625 557. The polymers prepared or used in the examples of these disclosures, however, contain at least 4% by weight styrene. Copolymers of this kind still do not have the desired level of adhesion and cohesion or the desired ratio of adhesion to cohesion.
SUMMARY OF THE INVENTION
It is an object of the present invention, therefore, to provide polymers of improved adhesion and/or cohesion.
We have found that this object is achieved by the polymers defined above and their use as pressure-sensitive adhesives.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel polymer preferably contains at least 0.05% by weight of a vinyl-aromatic compound and preferably not more than 1.5% by weight, in particular not more than 1.0% by weight, particularly preferably not more than 0.5% by weight, of the vinyl-aromatic compound.
Preferred polymers are composed of
from 50 to 99.98%
by weight of a C
1
-C
12
alkyl (meth)acrylate a)
from 0.02 to 1.5%
by weight of a vinyl-aromatic compound b)
from 0 to 10% by
weight of an ethylenically unsaturated acid c)
from 0 to 40% by
weight of other monomers d) which are different from a) to c)
Particularly preferred polymers are composed of
from 60 to 99.95
% by weight of
a)
from 0.05 to 1
% by weight of
b)
from 0 to 5
% by weight of
c)
from 0 to 35
% by weight of
d)
Especially preferred polymers are composed of
from 80 to 99.8
% by weight of
a)
from 0.2 to 1
% by weight of
b)
from 0 to 2
% by weight of
c)
from 0 to 18
% by weight of
d)
In one particular embodiment the content of monomers c) is at least 0.1% by weight, the maximum content of components a) lowering accordingly.
Particularly suitable C
1
-C
12
alkyl (meth)acrylates are methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl acrylate and isooctyl acrylate.
In one particularly preferred embodiment the monomers a) necessarily include C
1
-C
2
-alkyl (meth)acrylate (monomers a
1)
) in addition to C
3
-C
12
-alkyl (meth)acrylates (monomers a
2)
).
In particular, from 5 to 50% by weight, preferably from 10 to 40% by weight, particularly preferably from 10 to 20% by weight, of the overall amount of monomers a) are monomers a
1
), i.e. methyl (meth)acrylate or ethyl (meth)acrylate, preferably methyl acrylate.
Preferred vinyl-aromatic compounds are those having up to 20 carbon atoms. Suitable examples are vinyltoluene and &agr;- and &bgr;-methyl-styrene. Styrene is particularly preferred.
Examples of ethylenically unsaturated acids or anhydrides c) are maleic acid, fumaric acid, itaconic acid and, preferably, acrylic acid and/or methacrylic acid, (meth)acrylic anhydride or maleic anhydride.
Other monomers which may be mentioned are, in particular, alkyl (meth)acrylates having more than 12 carbon atoms in the alkyl radical, hydroxyl-containing monomers, especially C
1
-C
10
-hydroxy-alkyl (meth)acrylates, vinyl esters of C
1
-C
20
carboxylic acids, examples being vinyl acetate, vinyl propionate and vinyl ethers, preferably of C
1
-C
4
alcohols, for example vinyl methyl ether or vinyl isobutyl ether, and C
2
-C
8
hydrocarbons having one or two ethylenically unsaturated groups, for example ethylene, butadienes or isoprene, and monomers containing nitrile groups, for example (meth)acrylonitrile.
The monomers can be polymerized preferably by free-radical means or, where possible, anionically. As customary polymerization methods, both free-radical and anionic polymerization are familiar to the skilled worker.
Free-radical polymerization can be carried out, for example, in solution, such as in an organic solvent (solution polymerization), in aqueous dispersion (emulsion polymerization, suspension polymerization) or in bulk, i.e. essentially in the absence of water or organic solvents (bulk polymerization).
The novel polymer is preferably prepared by emulsion polymerization.
The emulsion polymerization is carried out using ionic and/or nonionic emulsifiers and/or protective colloids and/or stabilizers as surface-active compounds.
A detailed description of suitable protective colloids is given in Houben-Weyl, Methoden der organischen Chemie, volume XIV/1, Makromolekulare Stoffe, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 411-420. Suitable emulsifiers include anionic, cationic and nonionic emulsifiers. As accompanying surface-active substances it is preferred to use exclusively emulsifiers, whose molecular weights—unlike those of the protective colloids—are usually below 2,000 g/mol. Where mixtures of surface-active substances are used the individual components must of course be mutually compatible, which in case of doubt can be checked using a few preliminary experiments. Anionic and nonionic emulsifiers are preferably used as surface-active substances. Examples of customary accompanying emulsifiers are ethoxylated fatty alcohols (EO degree: 3 to 50, alkyl radical: C
8
to C
36
), ethoxylated mono-, di- and tri-alkylphenols (EO degree: 3 to 50, alkyl radical: C
4
to C
9
), alkali metal salts of dialkyl esters of sulfosuccinic acid, and alkali metal salts and ammonium salts of alkyl sulfates (alkyl radical: C
8
to C
12
), of ethoxylated alkanols (EO degree: 4 to 30, alkyl radical: C
12
to C
18
), of ethoxylated alkylphenols (EO degree: 3 to 50, alkyl radical: C
4
to C9), of alkylsulfonic acids (alkyl radical: C
12
to C
18
) and of alkylarylsulfonic acids (alkyl radical: C
9
to C
18
).
Other suitable emulsifiers are compounds of the formula II
in which R
5
and R
6
are hydrogen or C
4
-C
14
-alkyl but are not both hydrogen, and X and Y can be alkali metal ions and/or ammonium ions. R
5
and R
6
are preferably linear or branched alkyls having 6 to 18 carbons, or hydrogen, and in particular have 6, 12 or 16 carbons, and are not both simultaneously hydrogen. X and Y are preferably sodium, potassium or ammonium ions, sodium being particular

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