Aqueous self-crosslinking copolymer dispersions, a process...

Details Aqueous self-crosslinking copolymer dispersions, a process... Aqueous self-crosslinking copolymer dispersions, a process...

1999-10-15

2003-02-04

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...

C524S458000, C524S512000, C524S522000, C524S523000, C524S542000, C524S592000, C524S598000, C525S376000, C525S902000

Reexamination Certificate

active

06515042

ABSTRACT:

RELATED APPLICATIONS
This application claims priority to Austrian application No. A1739/98, filed Oct. 19, 1998, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to aqueous self-crosslinking copolymer dispersions having a core-shell structure, at least some of the monomers forming the copolymer in the core having carbonyl groups and carboxyl groups as well as free-radically polymerizable olefinically unsaturated groups, and comprising dicarboxylic dihydrazides or bishydrazine compounds. The invention additionally relates to a two-stage process for preparing these aqueous self-crosslinking copolymer dispersions and to their use as binders for storage-stable one-component coating materials which crosslink at room temperature or at elevated temperature.
2. Description of the Related Art
EP-A 0 649 865 discloses self-crosslinking carbonyl-containing polyurethane-vinyl hybrid dispersions which crosslink by way of hydrazine compounds but do not have a core-shell structure.
EP-A 0 555 774 discloses copolymer dispersions formed by copolymerizing monomers having carbonyl groups and carboxyl groups. These dispersions also do not have a core-shell structure, as they are prepared in a single-stage polymerization with no change in the composition of the monomer mixture. The binders prepared with these dispersions are crosslinked by reaction with the polyamines employed as neutralizing agents. With these products, first a high proportion of carbonyl groups is required to achieve sufficient crosslinking density of the coating films and second this high proportion of corresponding monomers results, during the copolymerization, in the formation of gel specks and coagulum whose removal can only be accomplished at great expense in terms of time and apparatus. In addition, the polyamine employed as crosslinking component leads to severe yellowing of the coating film and so to problems in numerous applications.
AT-B 402 504 describes self-crosslinking aqueous polymer dispersions which are prepared in a two-stage process. In this process, the composition of the monomer mixture for the second stage of the polymerization differs from that of the first stage. These copolymer dispersions have small fractions of carbonyl groups and permit high crosslinking densities without forming the coagulum or gel specks that are difficult to remove. However, the polyamines employed as crosslinking component likewise occasion severe yellowing of the resulting coating films.
European Patent Application EP-A 0 795 568 describes aqueous polymer dispersions having a core-shell structure in the core of which at least 50% of the monomers which are employed are those whose homopolymers have a glass temperature of below 0° C. while the proportion of such monomers employed in the shell is less than 45%. Difunctional acid hydrazides can also be added to the dispersion. Where such hydrazides are added in the examples, the monomer mixture for the shell of the polymer particles also includes a monomer that contains ketone groups. In this case, the monomer composition is selected in accordance with the desired minimum film-forming temperatures.
In AT-B 403 478, the dispersions known from AT-B 402 504 are combined with polyfunctional isocyanates of low molar mass to form two-component binders. Although it is possible in this way to provide coating materials which have a reduced tendency to yellow and an improved resistance to water, chemicals and light exposure, there are disadvantages associated with these coating materials. These include the complex preparation of the coating material, the limited pot life, prolonged drying time, and relatively low film hardness.
OBJECT OF THE INVENTION
It has surprisingly now been found that aqueous copolymer dispersions prepared in accordance with AT-B 402 504 by a two-stage process in which monomers having in each case carbonyl and carboxyl groups are employed only in the first stage (which leads to the core of the particles) can be crosslinked, following neutralization of the carboxyl groups by adding small amounts of ammonia, amines or aqueous alkalis, with polyfunctional hydrazides and lead to binders having a sufficient pot life which can be processed to give coating materials having high film hardness, good resistance to mechanical and chemical exposure, rapid drying, and little or no tendency to yellow.
SUMMARY OF THE INVENTION
The invention accordingly provides aqueous self-crosslinking copolymer dispersions ABC obtainable by free-radically initiated copolymerization in the first stage of a monomer mixture A comprising mass fractions in the mixture of
A1 from about 2 to about 55%, preferably from about 4 to about 45% and, with particular preference, from about 6 to about 40% of olefinically unsaturated monomers having in each case at least one carbonyl group per molecule,
A2 from about 0.5 to about 20%, preferably from about 1 to about 15% and, with particular preference, from about 3 to about 12% of &agr;,&bgr;-olefinically unsaturated carboxylic acids or monoesters of &agr;,&bgr;-olefinically unsaturated dicarboxylic acids with linear, branched or cyclic alcohols having 1 to 15 carbon atoms,
A3 from about 20 to about 70%, preferably from about 22 to about 60% and, with particular preference, from about 24 to about 50% of olefinically unsaturated monomers selected from vinylaromatic compounds, n-butyl methacrylate and also alkyl esters of &agr;,&bgr;-olefinically unsaturated carboxylic acids or dialkyl esters of &agr;,&bgr;-olefinically unsaturated dicarboxylic acids, the alkyl groups being selected from linear and branched alkyl groups having up to 3 carbon atoms in the alkyl radical and cyclic and polycyclic alkyl groups having 5 to 15 carbon atoms in the alkyl group,
A4 from about 10 to about 60%, preferably from about 15 to about 50% and, with particular preference, from about 20 to about 45% of esters selected from alkyl esters of &agr;,&bgr;-olefinically unsaturated carboxylic acids or dialkyl esters of &agr;,&bgr;-olefinically unsaturated dicarboxylic acids, the alkyl groups being selected from linear and branched alkyl groups having more than 3 carbon atoms in the alkyl radical, with the exception of n-butyl methacrylate, and
A5 from 0 to about 25%, preferably from about 2 to about 20% and, with particular preference, from about 5 to about 15% of other free-radically polymerizable monomers selected from vinyl esters of aliphatic saturated carboxylic acids having 2 to 18 carbon atoms, hydroxyalkyl esters, nitrites and amides of &agr;,&bgr;-unsaturated carboxylic acids,
the sum of the mass fractions of components A1 to A5 necessarily being 100%, and by subsequent addition of a second monomer mixture B and further free-radically initiated polymerization of this monomer mixture in the second stage, the mixture B comprising mass fractions of
B1 from about 30 to about 90%, preferably from about 40 to about 80% and, with particular preference, from about 50 to about 75% of olefinically unsaturated monomers selected from vinylaromatic compounds, n-butyl methacrylate and also alkyl esters of &agr;,&bgr;-olefinically unsaturated carboxylic acids or dialkyl esters of &agr;,&bgr;-olefinically unsaturated dicarboxylic acids, the alkyl groups being selected from linear and branched alkyl groups having up to 3 carbon atoms in the alkyl radical and cyclic and polycyclic alkyl groups having 5 to 15 carbon atoms in the alkyl group,
B2 from about 10 to about 60%, preferably from about 20 to about 50% and, with particular preference, from about 25 to about 40% of esters selected from alkyl esters of &agr;,&bgr;-olefinically unsaturated carboxylic acids or dialkyl esters of &agr;,&bgr;-olefinically unsaturated dicarboxylic acids, the alkyl groups being selected from linear and branched alkyl groups having more than 3 carbon atoms in the alkyl radical, with the exception of n-butyl methacrylate, and
B3 from 0 to about 40%, preferably from about 5 to about 30% and, with particular preference, from about 10 to about 25% of other free-radic

Affiliated with

Also associated with

Rating

Aqueous self-crosslinking copolymer dispersions, a process... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Aqueous self-crosslinking copolymer dispersions, a process..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous self-crosslinking copolymer dispersions, a process... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3169076