Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-28
2004-03-23
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S066000, C525S103000, C525S127000, C525S145000, C525S148000, C525S178000, C524S379000, C524S504000, C524S520000, C524S522000, C524S523000, C524S564000
Reexamination Certificate
active
06710127
ABSTRACT:
RELATED APPLICATION
This application claims priority under 35 USC 119 from German Application No. 100 48 258.9, filed Sep. 29, 2000, which application is incorporated herein by reference.
The invention relates to levelling agents for surface coatings having a weight-average molecular weight of from 5000 to 100,000 which are suitable for giving coating compositions, such as paints, a uniform surface. The invention further relates to the use of the levelling agents of the invention for coating formulations and to coating formulations comprising the levelling agents of the invention.
Paint surfaces are normally not entirely smooth but instead have a more or less structured surface referred to as waviness or else as orange peel. These surfaces may be finely structured, with a short wave, or coarsely structured, with a long wave. In the majority of cases, this waviness is unwanted. The structure depends on the nature and composition of the coating compositions; for example, on whether these coating compositions comprise solvents or else are solvent-free, as in the case of powder coating materials. In the case of powder coating materials it is absolutely necessary to add levelling agents, since without these levelling agents it is impossible to achieve a surface which is in any way smooth.
It is known that poly(meth)acrylates and polysiloxanes may be used as levelling promoters for coatings. In the case of the polysiloxanes the compounds concerned generally comprise polydimethylsiloxanes, polymethylalkylsiloxanes, or else polyether- or polyester-modified polydimethyl- or polymethylalkylsiloxanes.
In the case of the poly(meth)acrylates, preference is given to the use of polymers or copolymers of alkyl acrylates having an alkyl radical chain length of C
2
-C
8
, such as ethyl acrylate, 2-ethylhexyl acrylate or n-butyl acrylate, for example. The products used possess in some cases molecular weights of up to 100,000.
These poly(meth)acrylate (co)polymers used as levelling promoters may be used as such or as solutions in organic solvents, or else as powders applied to silica, for example. This is normally the case particularly when they are used in powder coating materials. The amounts of such products that are used are usually from 0.1 to 2% by weight, based on the coating formulations.
The action of all these products is based on surface activity at the liquid/gas interface: owing to a certain incompatibility with the actual binder of the coating system, these products adopt an orientation to the interface. This incompatibility may be increased by raising the molecular weight of these polymers. A disadvantage then, however, is that owing to this incompatibility there may be a certain haze of the coating and the viscosity of the levelling agent becomes so high that handling for the user becomes very difficult if not impossible.
The existing polymers provide only an inadequate solution to the levelling problem in the case of coatings, and there is an urgent need for new levelling promoters which make it possible to produce absolutely smooth coating films, which is of utmost importance in the case of powder coatings in particular.
Surprisingly it has been found that this objective can be achieved by adding branched polymers comprising a free-radically or ionically polymerized base molecule into which monoethylenically unsaturated macromonomeric units have been incorporated by copolymerization as levelling agents to the surface coatings.
The copolymerization of these monomers, which are very different in their molecular weight, produces highly branched polymers which despite a high overall molecular weight have a much smaller base molecule chain length, owing to the macromolecular side chains. Furthermore, block structures with different compatibilities can be obtained by appropriately selecting the monomers for the base molecule and the monomers of the macromonomer; this cannot be done by free-radical copolymerization of low molecular weight monomers.
The invention accordingly provides levelling agents of the type specified at the outset which are characterized in that the levelling agent is a branched polymer comprising a free-radically or ionically polymerized base molecule into which macromonomeric units containing at one end a monomeric unit which has an ethylenically unsaturated bond and possessing a weight-average molecular weight of from 1000 to 30,000 have been incorporated by free-radical or ionic copolymerization, the weight fraction of the macromonomeric units, based on the total weight of the branched polymer, being from 1 to 60% by weight.
Advantageous embodiments of the levelling agent of the invention are evident from the dependent claims.
Graft copolymers with a comb-like structure, comprising a main chain and copolymerized macromonomer side chains, are known per se. They are used, for example, as pigment dispersants and in that case contain groups in the molecule that have affinity for the pigment. By way of example, amine-functional polymers having a macromonomer component are described in EP-A-732 346. The requirements imposed on dispersants, however, are entirely different to those imposed on levelling agents. It was therefore not obvious to use graft copolymers with a comb-like structure as levelling agents.
In order to prepare the levelling agents of the invention, monoethylenically unsaturated monomers are copolymerized with monoethylenically unsaturated macromonomers having molecular weights (MW) of from 1000 to 30,000, preferably from 5000 to 10,000, by known processes, preferably free-radically or ionically.
Preferred free-radically or ionically polymerized monomeric units of the base molecule are selected from the group consisting of alkenes and arylalkenes having from 2 to 30 carbon atoms, alkyl acrylates and alkyl methacrylates of straight-chain, branched or cyclo-aliphatic alcohols having from 1 to 22 carbon atoms, aralkyl acrylates and aralkyl methacrylates of aralkyl alcohols having from 8 to 18 carbon atoms, acrylamides and methacrylamides of straight-chain, branched or cycloaliphatic amines having from 1 to 22 carbon atoms, aminoalkyl acrylates and aminoalkyl methacrylates of straight-chain, branched or cycloaliphatic amino alcohols having from 2 to 8 carbon atoms, maleates, itaconates and fumarates of straight-chain, branched or cycloaliphatic alcohols having from 1 to 22 carbon atoms, and vinyl esters, vinyl ethers and vinyl ketones having from 3 to 20 carbon atoms.
As monomeric units of the base molecule it is also possible to use monomeric units containing polyethylene glycol, in order to allow the branched polymers of the invention to be soluble in water or emulsifiable in water. Examples of polyethylene glycol-containing monomeric units that can be used include polyethylene glycol monoacrylates or polyethylene glycol monomethacrylates having from 5 to 80 carbon atoms.
It is also possible to use monomeric units containing functional groups, in order to allow later incorporation into the respective polymeric matrix or the binder. Examples of monomeric units with functional groups that can be used include acrylic acid, methacrylic acid, and hydroxyalkyl acrylates or hydroxyalkyl methacrylates of straight-chain, branched or cycloaliphatic diols having from 2 to 36 carbon atoms. In order to permit crosslinking of the hydroxy-functional levelling agents of the invention with, for example, acrylic melamine-formaldehyde resins, it is also possible to react some or all of these hydroxyl groups with isocyanates to give secondary carbamate groups, so that during the crosslinking of the system as a whole the levelling agent is left with sufficient time to orient itself at the interface, to develop its action there, and, after a certain delay, to react with the melamine-formaldehyde resin.
In order greatly to reduce the surface tension of the branched polymers of the invention, it is advantageous to copolymerize small amounts of monomeric units having perfluoroalkyl groups. As monomeric units of perfluoroalkyl groups it is possible, for example, to use perfluor
Bubat Alfred
Frank Albert
Haubennestel Karlheinz
Asinovsky Olga
BYK- Chemie GmbH
Seidleck James J.
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