Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-17
2003-05-20
Harlan, Robert D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S307500, C526S307600, C526S307700, C526S318410, C526S318420, C526S347100, C526S319000, C524S809000, C524S812000, C524S824000
Reexamination Certificate
active
06566472
ABSTRACT:
The present invention relates to binder formulations having a minimum film-forming temperature of less than 10° C. on the basis of an aqueous polymer dispersion.
For reasons of environmental protection and occupational hygiene, modern coating compositions, especially those used in enclosed spaces, such as emulsion paints and dispersion plasters, for example, contain a binder formulation based on an aqueous polymer dispersion. The polymer particles present in the polymer dispersion film on drying to form a polymeric coating which binds any pigment particles and fillers present.
The formation of a uniform and thus stable polymeric coating is only ensured, however, when the coating composition is processed at a temperature which lies above the minimum film-forming temperature of the polymer in the binder formulation.
A low minimum film-forming temperature is ensured in principle when using binders whose polymers have a low glass transition temperature. However, these binders have the disadvantage that the polymer film remains soft and is tacky. This, in turn, has the consequences for the coating of low blocking resistance and high soiling tendency. Alternatively, the minimum film-forming temperature of a polymeric binder may be lowered by processing it with film-forming auxiliaries (coalescants). These are volatile organic compounds, examples being solvents or plasticizers, which when the coating is dried facilitate film formation, initially, and on further drying are emitted to the environment, thereby increasing the surface hardness of the polymer film and reducing its tackiness. This process, however, entails an unwanted burden on the environment. There is therefore an increased need for binders based on aqueous polymer dispersions which ensure uniform film formation without the addition of coalescence auxiliaries and which lead to coatings having high blocking resistance and low soiling tendency.
EP-A-609 756 and EP-612 805 disclose binders based on aqueous polymer dispersions which are suitable for preparing solvent-free dispersions. The binder polymers are multiphase, multistage polymers comprising a hard polymer phase and a soft polymer phase. Polymers of this kind are comparatively difficult to prepare, however.
EP-A-466 409 describes coalescant-free coating compositions comprising as binder a blend of two aqueous polymer dispersions. The polymer of one polymer dispersion has a glass transition temperature above room temperature and the other polymer has a glass transition temperature of below 20° C.
EP-810 274 describes binders for low-emission coating compositions based on aqueous styrene acrylate polymer dispersions having an average film-forming temperature of below 10° C. and containing less than 1% by weight of acidic monomers in copolymerized form. Binders of this kind are particularly suitable for highly pigmented coatings, i.e., for coatings having a pigment volume concentration PVC≧60. The pigment volume concentration PVC, here and below, is 100 times the ratio of the total volume of pigments plus fillers divided by the total volume of pigments, fillers and binder polymers; cf. Ullmanns Enzyklopädie d. Techn. Chem., 4th ed., vol. 15, p. 667. While these binders lead to increased wet abrasion resistance of the coatings at high pigment contents, their surface tack and blocking resistance at lower pigment contents leave something to be desired.
It is an object of the present invention to provide a binder which is based on an aqueous polymer dispersion and both ensures uniform film formation without the addition of coaslescence auxiliaries and leads to coatings of low tack and high blocking resistance.
We have found that this object is achieved by the binder formulations defined below, based on aqueous polymer dispersions, which surprisingly meet these requirements to a particular degree.
Accordingly, the present invention provides binder formulations having a minimum film-forming temperature of below 10° C. and comprising at least one binder polymer P in the form of an aqueous dispersion comprising at least one anionic emulsifier and at least one nonionic emulsifier, the binder polymer P being composed of:
from 20 to 50% by weight of at least one monomer A1, selected from vinylaromatic monomers,
from 0 to 15% by weight of one or more monomers A2, selected from the C
1
-C
4
alkyl esters of methacrylic acid,
from 0 to 30% by weight of one or more monomers A3, selected from acrylonitrile and methacrylonitrile,
from 45 to 70% by weight of at least one monomer B whose homopolymer has a glass transition temperature of below 10° C., selected from the C
1
-C
18
alkyl esters of acrylic acid and the C
5
-C
18
alkyl esters of methacrylic acid,
from 2 to 4% by weight of methacrylic acid as monomer C,
from 0 to 3% by weight of one or more monomers D selected from the amides, C
1
-C
4
hydroxyalkyl esters and C
1
-C
4
alkyl polyalkylene oxide esters of monoethylenically unsaturated C
3
-C
6
monocarboxylic acids,
from 0 to 5% by weight of one or more monomers E other than the monomers A1, A2, A3, B, C and D, the weight fractions of all monomers being based on 100% by weight, the sum of the weight fractions of the monomers A1, A2 and A3 not exceeding 55% by weight, preferably 50% by weight, and the weight fraction of the monomers A2 being at least 5% by weight if the weight fraction of the monomers A3 is below 0.5% by weight. Preferably, the binder formulations of the invention contain the binder polymer P as sole binder.
The minimum film-forming temperature MFT is defined as the temperature below which the polymer in the coating composition no longer forms a coherent polymer film. The minimum film-forming temperature is situated preferably within the range from 10 to 0° C. Valid minimum film-forming temperatures are the values determined in accordance with DIN 53787 (see Ullmanns Enzyklopädie d. Techn. Chem., 4th ed., vol. 19, p. 17). The MFT correlates approximately with the glass transition temperature T
g
of the binder polymer P. It is generally up to 10 K below its glass transition temperature. Accordingly, the binder polymer P generally has a glass transition temperature T
g
of not more than 20° C. and preferably not more than 15° C. In general, the glass transition temperature T
g
of the binder polymer will not be below −10° C., preferably −5° C., in particular 0° C.
The term glass transition temperature as used in this specification means the glass transition temperature (cf. ASTM D 3418-82) determined by the DSC technique (differential scanning calorimetry, 20° C./min, midpoint).
In order to establish the desired T
g
in the preparation of the polymer P, the skilled worker will start from an appropriate monomer mixture. According to Fox (T. G. Fox, Bull. Am. Phys. Soc. (Ser. II) 1, 1956, p. 123 and Ullmanns Enzyklopädie der Techn. Chem., 4th ed., vol. 19. Verlag Chemie, Weinheim (1980), pp. 17-18), the glass transition temperature of copolymers at high molecular masses is given in good approximation by
1
T
g
=
X
1
T
g
1
+
X
2
T
g
2
+
⋯
X
n
T
g
n
where X
1
, X
2
, . . . , X
n
are the mass fractions of the monomers 1, 2, . . . , n and T
g
1
, T
g
2
, . . . , T
g
n
are the glass transition temperatures of the homopolymers composed in each case of only one of the monomers 1, 2, . . . , n, in degrees Kelvin. Sources of tabulated glass transition temperatures of homopolymers are, for example, Ullmann's Encyclopedia of Ind. Chem., 5
th
ed., VCH, Weinheim, Vol. A 21 (1992) p. 169 and J. Brandrup, E. H. Immergut, Polymer Handbook 2
nd
ed, J. Wiley, New York, 1975, pp. 139-192.
Examples of vinylaromatic monomers A1 are styrene, &agr;-methyl-styrene, (C
1
-C
4
)alkyl styrenes such as methylstyrenes and tert-butyl styrene, and methoxystyrenes. The preferred monomer A1 is styrene. Preferably, the binder polymer P of the invention contains the monomers A1 copolymerized in an amount of from 20 to 40% by weight, and in particular from 20 to 35% by weight.
Examples of monomers A2 are methyl methacrylate, ethyl methacrylate, n-propyl
Baumstark Roland
Dersch Rolf
Dobbelaar Johannes
Kirsch Stefan
Melan Michael
BASF - Aktiengesellschaft
Harlan Robert D.
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