Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-04-19
2002-04-23
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S081000, C522S083000, C522S084000, C522S086000, C524S845000
Reexamination Certificate
active
06376570
ABSTRACT:
The present invention relates to aqueous, essentially solvent-free, pigmented coating compositions which comprise at least one dispersion of a film-forming polymer P.
Pigmented aqueous coating compositions generally include a film-forming polymer in the form of an aqueous polymer dispersion as a binder for the pigment particles and any fillers that may be present. When the coating dries, the polymer particles present in the polymer dispersion form a polymer film which binds the pigment particles and the fillers. The development of a uniform polymer film is only ensured when the coating composition is processed at temperatures above the minimum film-forming temperature (MFT; the temperature above which the polymer in the coating composition forms a polymer film). A low minimum film-forming temperature can be obtained in principle by using a polymeric binder having a low glass transition temperature. Polymeric binders having a low glass transition temperature, however, have the disadvantage that the polymer film is soft and tacky. This has the consequence, in turn, of low blocking resistance and a high soiling tendency of the coating. Conventional coating compositions therefore generally include a polymer having a relatively high glass transition temperature and a film-forming auxiliary which lowers the film formation temperature of the polymer. The film-forming auxiliaries (coalescants) are generally volatile organic compounds, such as solvents or plasticizers, which initially facilitate film formation when the coating is drying. On further drying, the film-forming auxiliaries are emitted to the ambient atmosphere, as a result of which the surface hardness of the polymer film is increased and its tackiness is reduced. The emission of such volatile substances to the ambient atmosphere, however, represents a severe environmental burden. It is therefore desirable to avoid film-forming auxiliaries and other volatile constituent in pigmented aqueous coating compositions.
U.S. Pat. Nos. 5,530,056 and 5,610,225 disclose binders for solvent-free aqueous coating compositions which comprise in copolymerized form special esters of acrylic acid or methacrylic acid with polyethylene glycols (PEG monomers). PEG monomers are comparatively expensive and their effect is not always satisfactory.
EP-A-327 006 describes aqueous addition-polymer dispersions which comprise small amounts of silane monomers in copolymerized form. Polymer dispersions of this kind are likewise suitable as binders for low-solvent coating compositions. Even a low level of incorporation of silane monomers, however, increases considerably the costs of preparing the binder polymers.
EP-A-609 756 and EP-612 805 disclose binders for solvent-free emulsion paints which comprise as binder polymers multistage addition polymers comprising a hard polymer and a soft polymer.
DE 196 21 574 describes the use of copolymers of vinylaromatic monomers with alkyl acrylates as binders in coating compositions containing pigments or fillers. coatings based on the binders described therein have high wet abrasion resistance especially when the binder polymer contains less than 1% by weight of acidic monomers in copolymerized form. The resultant coatings possess only average weathering stability, especially on prolonged exposure to UV radiation.
U.S. Pat. No. 3,320,198 discloses that the soiling tendency of coatings comprising a polyacrylate as polymeric binder can be reduced by adding benzophenone in an amount of more than 0.3% by weight, preferably from 0.5 to 3% by weight, based on the polymeric binder. The emulsion paints it describes, however, contain relatively large amounts of organic solvents. DE 38 27 975 likewise discloses coating compositions containing photoinitiators. The examples, however, describe only pigment-free coating compositions of at least 0.4% by weight of photoinitiator, based on the polymeric binder.
EP-A-599 676 describes latex paint binders comprising aqueous polymer dispersions which comprise polymerizable derivatives of benzophenone in copolymerized form. The use of special monomers of this kind likewise increases the costs of the binder to a considerable extent.
It is an object of the present invention to provide aqueous pigmented coating compositions which result in coatings having good wet abrasion resistance and a low soiling tendency and being essentially free from volatile organic compounds such as plasticizers and solvents. The binder polymer should be preparable without complex preparation processes and without the use of costly, special monomers. The coatings, furthermore, should be particularly stable with respect to exposure to UV radiation, i.e., on prolonged weathering.
We have found that this object is achieved and that pigmented coating compositions which are essentially free from volatile organic compounds and whose binder polymer is composed essentially of esters of acrylic acid and/or of methacrylic acid lead to coatings having a low soiling tendency and good weathering stability if the coating composition includes a small amount, but less than 0.3% by weight, based on the polymer, of a nonpolymerizable photoinitiator.
The present invention accordingly provides aqueous pigmented coating compositions having a pigment volume concentration of at least 10 which are essentially free from volatile organic compounds and comprise:
(i) at least one aqueous room temperature film forming polymer dispersion of at least one polymer P which is composed of
from 80 to 99.95% by weight of at least one monomer A selected from the esters of acrylic acid with C
2
-C
20
alkanols or C
5
-C
10
cycloalkanols and the esters of methacrylic acid with C
1
-C
20
alkanols or C
5
-C
10
cycloalkanols,
from 0.05 to 10% by weight of at least one monomer B selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids and their salts, and
from 0 to 20% by weight of one or more monomers C which are different than the monomers A and A,
(ii) at least one inorganic pigment and, if desired, organic or inorganic fillers,
(iii) from 0.05 to <0.3% by weight, based on the polymer P, of at least one nonpolymerizable photoinitiator,
(iv) water, and customary auxiliaries.
The coating compositions of the invention generally contain less than 0.5%, preferably less than 0.1%, in particular less than 500 ppm and, especially, less than 300 ppm of volatile organic compounds. These include organic solvents, plasticizers (organic liquids having a boiling point above 250° C.) and—deriving from their preparation—unpolymerized monomers (known as residual monomers). The volatile organic compounds present in the coating compositions of the invention preferably do not include additions such as solvents or plasticizers but exclusively contain volatile organic impurities deriving from their preparation, such as residual monomers and conversion products thereof. The residual monomer content of the coating compositions of the invention is advantageously below 300 ppm and in particular below 200 ppm.
The pigment volume concentration (pvc) is defined as 100 times the quotient of the total volume of fillers and pigments present in the coating composition divided by the total volume of fillers, pigments and binder polymer, in this case polymer P.
In order to be assured of uniform film formation without the addition of film-forming auxiliaries it is necessary for the minimum film-forming temperature (MFT) of the dispersion of the polymer P to be below its processing temperature. The difference between processing temperature and minimum film-forming temperature is preferably at least 5 K and in particular at least 10 K. The minimum film-forming temperature of the aqueous dispersion of the polymer P will be preferably below 10° C. and in particular below 5° C. The minimum film-forming temperatures considered are the values determined in accordance with DIN 53787 (see Ullmanns Enzyklopädie der Technischen Chemie, 4th Ed. Vol. 19, VCH Weinheim 1980, p. 17). In accordance with the inven
Dittrich Uwe
Franzmann Gernot
Schwartz Manfred
Zhao Cheng-Le
BASF - Aktiengesellschaft
Berman Susan W.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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