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
2000-01-15
2001-03-06
Michl, Paul R. (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...
Reexamination Certificate
active
06197871
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to thickeners based on carboxyl- and carboxamido-containing addition polymers, to their use in coating compositions, adhesives and hydraulically setting binders, and to processes for their preparation.
2) Background Art
In addition to polyurethane thickeners and celluloses, carboxyl- and carboxamido-containing aqueous copolymer dispersions are widely employed as thickeners. They develop their thickening action only in an alkaline medium following neutralization of the carboxyl groups. In order to achieve a good thickening effect, high molecular weights are required in these polymers. A disadvantage of these products is that they possess very high viscosities in neutralized form but in acidic form are not stable on storage. In order to avoid these disadvantages, the following procedures are known.
In EP-A 529 206 (U.S. Pat. No. 5,545,688) polyacrylamide is prepared by inverse emulsion polymerization. This technique can be transferred to carboxylate-containing polymers, and in DE-A 3520507 (U.S. Pat. No. 4,681,912) a water-in-oil microemulsion comprising an aqueous acrylamide/acrylic acid solution, an organic solvent and a nonionic surfactant is polymerized. A disadvantage of this method, however, is that large amounts of organic solvent must be used in order to ensure the phase inversion and must then be separated off again subsequently, which is complex. These organic solvents, such as Isopar®M and toluene, moreover, are nowadays unacceptable on environmental grounds.
According to EP-A 736 547 (CA-A 2173297) the problems set out above can be avoided by preparing conventional emulsion polymers from water-soluble and water-insoluble monomers, but again in the presence of organic solvents which must subsequently be separated off by distillation. A further disadvantage is that in order to obtain stable dispersions use is made in addition of surfactant monomers which act as associatively thickening groups.
EP-A 450 437 (U.S. Pat. No. 5,231,145) describes copolymers based on alkyl acrylates and/or alkyl methacrylates, prepared with polyvinyl alcohol as protective colloid, for use as sizes. The products, however, are unsuitable for use as thickeners since they show no increase in viscosity on neutralization.
The object of EP-A 627 450 was to prepare thickeners based on (meth)acrylate-(meth)acrylic acid copolymers which are present in acidic form as a stable dispersion and exhibit no WeiBenberg effect, without using the toxic compound ethyl acrylate. Said object was achieved by means of polyvinyl alcohol-stabilized, (meth)acrylate-based copolymer dispersions which are described as being suitable thickeners for aqueous dispersions, especially emulsion paints. The thickening effect, however, is not sufficient to provide the required stability in hydraulically setting compositions.
Thickeners obtainable commercially include those based on acrylamide-acrylic acid copolymers prepared by the technique of precipitation polymerization. A disadvantage of such a thickener is that, in the acidic state in which the product is obtained, its storage stability is unsatisfactory, and without stirring the product rapidly forms a sediment and an agglomerating product cake which can no longer be stirred up or disrupted. For this reason the product is converted at an early stage into the neutralized form, in which it is indeed storage-stable but has a very high viscosity (10,000 mPas at 7% solids content) and can therefore be prepared only in very highly diluted form, and hence uneconomically.
The object was therefore to provide storage-stable, water-soluble polymers of low viscosity which can be employed as thickeners.
SUMMARY OF THE INVENTION
The invention provides thickeners based on carboxyl- and carboxamido-containing addition polymers obtainable by free-radical emulsion or suspension polymerization of
a) from 30 to 70% by weight of carboxyl-containing, ethylenically unsaturated monomers,
b) from 10 to 70% by weight of carboxamido-containing, ethylenically unsaturated monomers and
c) from 0.1 to 30% by weight of further ethylenically unsaturated monomers
in the presence of at least 5% by weight of one or more water-soluble protective colloids from the group consisting of polyvinyl alcohols, polyvinyl pyrrolidones and (meth)acrylate-(meth)acrylic acid copolymers, the percentages by weight being based in each case on the overall weight of the comonomers.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable carboxyl-containing monomers a) are ethylenically unsaturated mono- and dicarboxylic acids, preferably acrylic, methacrylic, maleic, itaconic, fumaric and crotonic acid. Particular preference is given to acrylic and methacrylic acids.
Suitable carboxamido-containing monomers b) are the amides of the acids referred to under a), preferably the monoamides and diamides of acrylic, methacrylic, maleic, itaconic, fumaric and crotonic acid. Particular preference is given to acrylamide and methacrylamide.
Monomers suitable as further ethylenically unsaturated monomers are hydrophobic monomers, examples being vinyl esters, (meth)acrylates and vinylaromatic compounds. Preference is given to the methacrylates and acrylates of C
1
to C
12
alcohols, with particular preference n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate and 2-ethylhexyl acrylate.
Preferably, from 30 to 60% by weight of carboxyl-containing monomers a) and from 30 to 60% by weight of carboxamido-containing monomers b) are copolymerized and the proportion of hydrophobic comonomer c) is restricted to the necessary minimum, preferably from 5 to 20% by weight.
As protective colloids it is preferred to employ partially hydrolyzed polyvinyl alcohols having a Höppler viscosity (DIN 53015, Höppler method, 4% strength aqueous solution) of from 3 to 28 mPas and a hydrolysis number of from 70 to 200. Particular preference is given to the use of partially hydrolyzed polyvinyl alcohols having a Höppler viscosity of from 3 to 15 mPas and a hydrolysis number of from 100 to 150. The partially hydrolyzed polyvinyl alcohols may be employed alone or in a mixture with other water-soluble protective colloids. By water-soluble here is meant that under normal conditions more than 10 g of the substance can be dissolved in a liter of water. The protective colloids are preferably employed in an amount of from 10 to 80% by weight.
The thickeners are prepared by the technique of emulsion or suspension polymerization in the aqueous phase, preferably at temperatures of from 30 to 60° C. Polymerization is initiated by the customary initiators, oil-soluble initiators for suspension polymerization and at least partially water-soluble initiators for emulsion polymerization.
Preference is given to preparation by the emulsion polymerization technique. Initiation takes place by means of the customary, at least partially water-soluble free-radical initiators, which are preferably employed in amounts of from 0.01 to 3.0% by weight, based on the overall weight of the monomers. Examples of these initiators are sodium persulfate, hydrogen peroxide, t-butyl peroxide, t-butyl hydroperoxide; potassium peroxodiphosphate, azobisisobutyronitrile. If desired, said free-radical initiators can also be combined in a known manner with from 0.01 to 6.0% by weight of reducing agents, based on the overall weight of the monomers. For example, alkali metal formaldehyde-sulfoxylates and ascorbic acid are suitable. In the case of redox initiation, one or both redox catalyst components are preferably metered in the course of polymerization.
As dispersants it is possible if desired to employ anionic or nonionic emulsifiers in addition to the protective colloid component. Preferably, no emulsifiers are employed. The pH range desired for polymerization, which is generally between 2.0 and 10, preferably between 2 and 3, can be established in a known manner by means of acids, bases and customary buffer salts, such as alkali metal phosphates or alkali metal carbonates. To adjust the molecular weight it is possible in
Braunsperger Robert
Weitzel Hans-Peter
Burgess, Ryan & Wayne
Michl Paul R.
Moran William R.
Wacker-Chemie GmbH
Wayne Milton J.
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