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...
Reexamination Certificate
2000-01-24
2002-06-04
Wu, David W. (Department: 1713)
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...
C524S458000, C524S460000, C524S599000, C524S612000, C526S073000, C526S080000, C526S319000, C526S320000, C526S346000
Reexamination Certificate
active
06399691
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to new aqueous copolymers, a process for their preparation and their use in coating compositions.
2. Description of the Prior Art
It is known from a large number of publications and patents to employ dispersions based on copolymers in water-dilutable paints and coating compositions.
For example, EP-A 225,612 and DE-A 3,543,361 describe polymer dispersions which dry by physical means and are prepared by a two-stage polymerization process, wherein one of the two stages use monomers containing carboxyl groups. Ammonia is employed as a neutralizing agent to achieve a good resistance of the coatings to water. The addition of other neutralizing agents impairs the resistance of the films to water. Monomers containing hydroxyl groups are not used since these can adversely influence the resistance to water.
EP-A 363,723, DE-A 4,009,858, DE-A 4,009,931, EP-A 521,919, DE 4,009,932 and EP 365,775 each describe processes for the preparation of multi-layered coatings, in which a base layer is first applied, a polymer film is formed therefrom, a top layer is then applied and the base layer and top layer are subsequently stoved together. Copolymer dispersions obtained by a two-stage preparation process are employed for the base or top layer, optionally in combination with aminoplast resins. By using these specific copolymer dispersions, higher layer thicknesses and good optical properties of the films are possible. A disadvantage of all these dispersions is the high content of carboxyl-functional monomers in he hydrophilic copolymer portion.
JP-A 80/82 166 describes polyacrylate dispersions which are prepared in two stages and contain carboxyl groups in both stages. This leads to dispersions with relatively low solids contents and coatings having reduced resistance to water.
U.S. Pat. No. 4,151,143 describes polyacrylate dispersions, which are prepared in two stages, wherein the 1st stage is prepared in an organic solution and is then dispersed, and an emulsion polymerization is carried out in the presence of the 1st stage. Products of high molecular weights, unfavorable film formation and overall different properties to conventional secondary dispersions result from this.
EP-A 557,844 describes aqueous two-component polyurethane coating compositions containing emulsion copolymers, which are essentially free from carboxylate groups and stabilized by external emulsifiers, and hydrophilic polyisocyanates. Because of the high molecular weights of the polymers and the remaining hydrophilicity in the case of external emulsifiers, such coating systems still have deficiencies in resistance to water, wetting of pigments and optical properties of the films for some applications.
EP-A 358,979 describes aqueous two-component polyurethane reactive systems, which have good properties. However, improvements in the solids content, in the resistance to water and in the processing time or application reliability are desirable for some applications.
DE-A 4,439,669, DE-A 4,322,242 and JP-A 4,001,245 describe aqueous two-component polyurethane reactive systems based on copolymers, which can be prepared in two stages and from specific monomers. The specific monomers are said to result in improved properties, but the products are considerably more expensive, so that the possibilities of economical use are limited.
In addition to the disadvantages already listed for the polymer dispersions of the prior art, many of these dispersions have a lack of storage stability with regard to viscosity, i.e. the viscosity of the binder dispersion decreases significantly during storage. A remedy can be provided by significantly increasing the acid number of the binder; however, this increases the hydrophilicity of films produced therefrom in an undesirable manner and thus impairs the resistance properties of the coating.
An object of the present invention is to provide a binder dispersion having good storage stability, which has an acid number, based on solids, of <30 mg KOH/g. In addition to good storage stability for the binder, it is also an object of the present invention to provide coating compositions and resulting coatings which possess a high solids content, a high reactivity coupled with a good pot life, good resistance to solvents, water and environmental influences and very good optical properties (gloss) and mechanical properties (hardness, flexibility). It is an additional object of the present invention for the coating compositions to be employed in as many fields of application as possible, which requires good compatibility with as many commercially available crosslinking agents as possible. It is a final object of the present invention to avoid the use of time- and cost-intensive processes, such as distillation steps, in the preparation process.
Surprisingly, these objects may be achieved with the aqueous coating compositions of the present invention, which are described in detail hereinafter. The compositions contain selected copolymers P which have a specific uniform molecular weight distribution and are prepared by a multi-stage process.
SUMMARY OF THE INVENTION
The present invention relates to a hydroxy-functional copolymer P, which is present as a dispersion and/or solution in water, has an acid number, based on solids, of <30 mg KOH/g, and is obtained by successively carrying out process steps A-D:
A) Initially introducing a hydrophobic polymer containing hydroxyl groups into a reaction vessel,
B) introducing an initiator component into that vessel,
C) subsequently polymerizing a hydrophobic monomer mixture containing hydroxyl groups in that vessel and
D) subsequently polymerizing a hydrophilic monomer mixture containing hydroxyl and acid groups in that vessel.
In a preferred embodiment of the present invention, the process is carried out as follows:
A): initially introducing
A1) 0 to 40 wt. %, based on the solids content of copolymer P, of a hydroxy-functional hydrophobic copolymer having an acid number, based on solids, of <10 mg KOH/g, which is not sufficient for dispersing or dissolving copolymer A1) in water, an OH content, based on solids, of 0.5 to 7 wt. %, a number average molecular weight of 1,500 to 20,000 and a content of organic solvents of 0 to 60 wt. %, based on the weight of A1, and
A2) 0 to 15 wt. %, based on the solids content of copolymer P, of additional organic solvents,
into a reaction vessel and heating the reaction mixture to the polymerization temperature before, during or after step A,
B): metering in 5 to 40 wt. %, based on the weight of B1+C2+D2, of a free-radical initiator B1, optionally dissolved in an organic solvent,
C): simultaneously metering in 40 to 80 wt. %, based on the solids content of copolymer P, of a hydrophobic monomer mixture C1 which is substantially free from carboxyl groups and contains
c1) 30 to 90 wt. % of (meth)acrylic acid esters with C
1
to C
18
-hydrocarbon radicals in the alcohol portion, vinylaromatics and/or vinyl esters,
c2) 10 to 60 wt. % of hydroxy-functional monomers and
c3) 0 to 2 wt. % of monomers containing acid groups, wherein the percentages of c1+c2+c3 add up to 100% and a free-radical initiator C2 in an amount of 25 to 90 wt. %, based on the weight of B1+C2+D2, optionally dissolved in an organic solvent,
D): simultaneously metering in 5 to 50 wt. %, based on the solids content of copolymer P, of a hydrophilic monomer mixture D1 containing
d1) 10 to 70 wt. % of (meth)acrylic acid esters with C
1
to C
18
-hydrocarbon radicals in the alcohol portion, vinylaromatics and/or vinyl esters,
d2) 10 to 70 wt. % of hydroxy-functional monomers and
d3) 5 to 30 wt. % of acid-functional monomers,
wherein the percentages of d1+d2+d3 adding up to 100%, and a free-radical initiator D2 in an amount of 5 to 40 wt. %, based on the weight of B1+C2+D2, optionally dissolved in an organic solvent,
wherein the total amount of B1+C2+D2, based on the solids content of copolymer P, is 0.8 to 5.0 wt. %.
The present invention
Bachmann Rolf
Blum Harald
Hovestadt Wieland
Melchiors Martin
Noble Karl-Ludwig
Bayer Aktiengesellschaft
Cheung William K
Gil Joseph C.
Roy Thomas W.
Wu David W.
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