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...
Patent
1997-05-09
1999-08-17
Reddick, Judy M.
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...
523201, 524521, 524522, 526201, 526203, C08F 216
Patent
active
059394820
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a two-stage method of preparing aqueous, autocrosslinking copolymer dispersions based on acrylate copolymers which have acetoacetyl groups and carboxyl groups and which are neutralized with polyamines which act as a crosslinking component, and to their use as binders for storage-stable one-component coating materials and, in combination with low molecular mass polyisocyanates, as binders for two-component coating materials which crosslink at room temperature or at elevated temperature.
2. Description of Related Art
EP 0555774 A1 discloses a one-stage method of preparing such copolymer dispersions. The products, however, have a disadvantage. Firstly, a high proportion of acetoacetyl groups is required in order to achieve a sufficient crosslinking density of the coating films; secondly, this high proportion of appropriate monomers brings about the formation, during the copolymerization, of bits and coagulum which can be removed again only at great length and using complex apparatus.
SUMMARY OF THE INVENTION
It has surprisingly now been found that films of aqueous copolymer dispersions with small proportions of acetoacetyl groups also have a high crosslinking density if the emulsion copolymerization takes place by a two-stage method in which monomers having in each case acetoacetyl or carboxyl groups are employed only in the first stage.
The invention relates accordingly to a method of preparing aqueous, autocrosslinking copolymer dispersions whose monomer composition is
(Aa) from 3 to 35% by weight, preferably from 8 to 15% by weight, of (meth)acrylate monomers containing acetoacetyl groups,
A(b) from 1 to 20% by weight, preferably from 3 to 16% by weight, of .alpha.,.beta.-ethylenically unsaturated carboxylic acids, preferably (meth)acrylic acid,
A(c) from 11 to 96% by weight, preferably from 30 to 70% by weight, of (meth)acrylic alkyl esters and, if desired, diesters of maleic or fumaric acid, and
A(d) from 0 to 40% by weight, preferably from 0 to 25% by weight, of other free-radically polymerizable monomers, such as vinyl aromatic compounds, vinyl esters, hydroxyalkyl (meth)acrylates and (meth)acrylamide, 100, and the dispersions being neutralized with polyamines which act as a crosslinking component, which method is characterized in that
A) a two-stage free-radical emulsion polymerization is carried out, with the proviso that in the first stage from 60 to 90% by weight of a mixture of the monomers (Aa) to (Ad) and in the second stage from 10 to 40% by weight of a mixture of the monomers (Ac) and (Ad) are copolymerized, the sum of the percentages again necessarily being 100 and the condition holding that the acrylate copolymers (A) contain acetoacetyl groups in an amount of from 0.2 to 1.7 mol/kg, preferably from 0.4 to 0.8 mol/kg, and carboxyl groups in an amount of from 0.15 to 1.6 mol/kg, preferably from 0.4 to 0.75 mol/kg, and that the carboxyl groups are present in an amount of from 50 to 95 mol-%, preferably from 80 to 90 mol-%, relative to the acetoacetyl groups,
B) the carboxyl groups of the copolymer dispersions (A) are reacted with polyamines which contain at least two primary amino groups in the molecule, in a proportion of from 50 to 100 mol-%, preferably from 90 to 100 mol-%, relative to the total primary amino groups, with salts being formed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention additionally relates to the copolymer dispersions prepared in accordance with the invention and to their use as binders for storage-stable one-component coating materials and, in combination with low molecular mass polyisocyanates, as binders for two-component coating materials which crosslink at room temperature or at elevated temperature.
The primary polyamines serve as neutralizing agents for stabilizing the aqueous copolymer dispersions and, finally, as a crosslinking component during film formation.
In accordance with the invention the copolymer dispersions are prepared by the method of a two-stage free-r
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patent: 5055506 (1991-10-01), Knutson
patent: 5116895 (1992-05-01), Knutson
patent: 5308890 (1994-05-01), Snyder
patent: 5369163 (1994-11-01), Chiou et al.
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Awad Rami-Raimund
Gossak Kurt
Gsoell Hannelore
Hirschmann Bernhard
Kriessmann Ingo
Reddick Judy M.
Vianova Resins Aktiengesellschaft
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