Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-07
2001-07-17
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S247000, C524S249000, C524S501000, C524S460000, C524S461000, C524S833000
Reexamination Certificate
active
06262159
ABSTRACT:
The present invention relates to a polymer dispersion and to a heat-curable composition comprising it, said dispersion and said composition being suitable as binders for various applications, especially as binders for particulate or fibriform substrates.
To bind wood fibers, textile fibers or natural fibers or to coat wood or mineral substrates it is common to use mixtures of acid-rich solution polymers and low-acid or acid-free emulsion polymers, since using such mixtures it is possible to achieve high mechanical strength and substrate hydrophobicization.
U.S. Pat. No. 5,314,943 describes a low-viscosity fast-curing binder for textile substrates which comprises a mixture of an aqueous emulsion copolymer latex with an aqueous solution copolymer. The aqueous solution copolymer is formed by the copolymerization of an &agr;,&bgr;-ethylenically unsaturated monocarboxylic acid and an &agr;,&bgr;-ethylenically unsaturated dicarboxylic acid. The emulsion copolymer latex includes units of monomers selected from alkenylaromatics, conjugated diolefins, vinyl acetate, and acrylates.
EP-537 910 disclose mixtures of emulsion polymers, synthesized preferably from styrene and n-butyl acrylate, with acid-rich water-soluble polymers, which when used as binders for coating materials are said to lead to coatings having good substrate wetting and high solvent resistance.
EP-257 567 describes a polymer composition obtainable by emulsion polymerization of ethylenically unsaturated monomers, such as olefins, vinylaromatic compounds, &agr;,&bgr;-ethylenically unsaturated carboxylic acids and esters thereof, ethylenically unsaturated dicarboxylic anhydrides or vinyl halides. During the polymerization a water- or alkali-soluble or -dispersible resin having a number-average molecular weight of from about 500 to 20,000 g/mol is added in order to influence the flow properties of the polymer composition. The water- or alkali-soluble or -dispersible resin can have been synthesized, for example, from olefins, vinylaromatic compounds, &agr;,&bgr;-ethylenically unsaturated carboxylic acids and esters thereof or ethylenically unsaturated dicarboxylic anhydrides.
Polymer latices prepared by emulsion polymerization in the presence of water-soluble acid-containing polymers, preferably styrene-acrylic acid copolymers, and natural fatty acids has been discribed. The polymer dispersions obtained are said to exhibit little tendency to foaming and therefore to be suitable as binders for wood primers or water-based printing inks.
U.S. Pat. No. 4,670,505 describes a polyacrylate dispersion prepared by emulsion polymerization in the presence of from 0.05 to 5% by weight of a protective colloid, e.g., polyacrylic acid or its alkali metal salts, and from 0.1 to 5% by weight of a water-soluble amino alcohol having 2 to 36 carbon atoms. The resulting dispersion possesses a low viscosity and good pigment binding capacity and is essentially free from gel specks and stable to shearing. With relatively large amounts of polyacrylic acid the composition is said to exhibit very high viscosity, which opposes its use as a binder for fibrous substrates, for example.
It has been found that the known binder systems provide inadequate wetting of polar fibers, such as wood, flax, jute, sisal, hemp, cotton, glass wool or mineral wool. Furthermore, the shear, electrolyte and freeze-thaw stability of the known binders is capable of improvement.
It is an object of the present invention to provide a polymer dispersion, and heat-curable compositions comprising said dispersion, which for a given solids content exhibit high wetting capacity for polar fibers and a desirably low viscosity at the same time.
We have found that this object is achieved by means of a polymer dispersion comprising in an aqueous medium
a) dispersed particles of a polymer composed of units of ethylenically unsaturated monomers of which more than from 5 to 20% by weight are &agr;,&bgr;-ethylenically unsaturated mono- or dicarboxylic acids;
b) a dissolved polymer containing in copolymerized form from 60 to 100% by weight of at least one &agr;,&bgr;-ethylenically unsaturated mono- or dicarboxylic acid, or salts thereof; and
c) an amine of the formula I
in which
R is an alkyl or alkylene radical having at least 6 carbon atoms or an alkylphenyl radical having at least 6 carbon atoms in the alkyl group;
R′ independently at each occurrence is H or C
1-4
alkyl;
R″ is C
1-4
alkylene;
m, n and o independently of one another are a number ≧0, with the proviso that at least one value of m, n and o is other than 0,
and p is 0 or 1,
the weight ratio, based on solids, of the dispersed particles to dissolved polymer being in the range from 7:1 to 1:7 and the weight ratio of dissolved polymer to amine being in the range from 20:1 to 2:1;
said polymer dispersion being obtainable by emulsion polymerization of said ethylenically unsaturated monomers in the presence of said dissolved polymer and of said amine of the formula I.
The invention further provides a heat-curable composition comprising a polymer dispersion as described above, a polyfunctional alcohol and, optionally, a reaction accelerant.
The polymer dispersion of the invention comprises a comparatively high fraction of acid monomers. The dispersed particles thus contain more than from 5 to 20% by weight of an &agr;,&bgr;-ethylenically unsaturated mono- or dicarboxylic acid. The polymer dispersion further comprises a polymer which is dissolved in the aqueous medium and which contains in copolymerized form from 60 to 100% by weight of &agr;,&bgr;-ethylenically unsaturated mono- or dicarboxylic acids. Surprisingly, the polymer dispersion of the invention has a relatively low viscosity. At a solids content of about 40% by weight, the viscosity of the polymer dispersion of the invention is generally in the range from 10 to 2000 mPas, in particular from 30 to 1000 mPas, as measured using a rotational viscometer in accordance with DIN 53019 at 23° C. and a shear rate of 250 s
−1
.
It has been found that two- or three-dimensional structures, especially in the form of textile sheet materials or shaped parts, that have been produced by impregnating particulate or fibriform substrates with the above-described polymer dispersion and then subjecting the impregnated substrates to heat curing, possess high mechanical strength and also a high level of resistance to water and humidity. Particularly advantageous qualities are obtained if the heat-curable composition of the invention used to impregnate said particulate or fibriform substrates comprises not only the polymer dispersion of the invention but also a polyfunctional alcohol and, optionally, a reaction accelerant.
Polymer dispersions containing less than 5% by weight of &agr;,&bgr;-ethylenically unsaturated carboxylic acid in the dispersed polymer particles lead to binders which effect much poorer wetting of polar fibers. The shaped articles obtained with them exhibit much poorer resistance to water than to humid conditions. The inadequate resistance to water and humid conditions of the dispersions containing less than 5% by weight of polymer particles containing carboxylic acid cannot be substantially improved even by adding polyfunctional alcohols and reaction accelerants.
In preferred polymer dispersions of the invention the weight ratio of dispersed polymer particles to dissolved polymer is in the range from 5:1 to 1:5, in particular in the range from 3:1 to 1:3. The weight ratio of dissolved polymer to amine of the formula I is preferably in the range from 1:10 to 3:1.
The dispersed polymer particles are composed of units of ethylenically unsaturated monomers. They are obtainable by free-radical emulsion polymerization of more than from 5 to 20% by weight, based on the total monomers, of at least one &agr;,&bgr;-ethylenically unsaturated mono- or dicarboxylic acid or anhydrides thereof and from 80 to less than 95% by weight of at least one or more different copolymerizable ethylenically unsaturated monomers (principal monomer).
Suitable acid monomers include:
&agr;
Dreher Stefan
Reck Bernd
Seufert Michael
Türk Johannes
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Szekely Peter
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