Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-01-08
2002-11-05
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S201000, C524S804000, C524S831000, C524S833000
Reexamination Certificate
active
06476097
ABSTRACT:
The present invention relates to aqueous, essentially solventless pigmented formulations comprising at least one aqueous polymer dispersion.
Pigmented aqueous formulations are in widespread use as coating compositions, sealing compounds and, in particular, emulsion paints for architectural protective or decorative purposes. Such formulations generally comprise as their binder a film-forming polymer in the form of an aqueous polymer dispersion, at least one inorganic pigment and, if desired, one or more inorganic fillers along with customary auxiliaries. When the formulations are dried, the polymer particles in the formulation form a polymer film which binds the nonfilm-forming constituents, viz. the pigments and the inorganic extenders.
For reasons of cost the polymeric binders must be able to bind relatively large amounts of a pigment and/or filler. In polymer-bound pigmented formulations the volume ratio of pigment to binder is characterized by the pigment volume concentration PVC (see Ullmanns Enzyklopädie der technischen Chemie, 4th ed. Vol. 15, p. 667). A poor pigment binding capacity results in low mechanical strength at relatively high PVC, and in particular to low wet abrasion resistance and scuff resistance.
The capacity of a polymer to form a film is an essential determinant of the quality of the coatings obtained when the formulations are dried. In principle, the capacity of a polymer to form a film goes up as the glass transition temperature decreases. A low glass transition temperature, however, has the consequence that the polymer film is soft and thus that the coating becomes tacky, which results in poor blocking resistance and carries with it the risk of soiling. In addition, a coating of a “soft” polymer is easily destroyed under mechanical load. If, conversely, the polymer has too high a glass transition temperature, the uniform formation of a film at common processing temperatures is not ensured, and so such coatings generally lack sufficient mechanical strength unless further measures are taken. Conventional formulations based on aqueous polymer dispersions generally comprise a polymer of relatively high glass transition temperature (relatively hard polymer) and small amounts of organic solvents or plasticizers, known as film-forming auxiliaries (coalescants) in order to reduce the minimum film-forming temperature (MFT), i.e., the temperature above which the polymer in the formulation forms a film, and to ensure that a film of the polymer is formed even at low processing temperatures. Solvents and volatile plasticizers are released when the formulation is dried, which is accompanied by an increase in the surface hardness of the polymer film. However, the release of volatile organic constituents, especially in the case of coating compositions for interior applications as, for example, in the case of emulsion paints, is undesirable. Moreover, coatings based on “hard” polymeric binders are often brittle and lack sufficient flexibility.
WO 98/10001 discloses a process for preparing aqueous polymer dispersions by means of a multistage free-radical aqueous emulsion polymerization in a first stage of which a comparatively soft polymer is prepared, then monomers are added to form a hard polymer, this hard polymer is swollen in the soft polymer, and then polymerization is initiated again. The polymer dispersions described are particularly useful as pressure-sensitive adhesives.
EP-A 609 756 describes solventless emulsion paints whose polymeric binder comprises an aqueous dispersion of a staged polymer whose particles comprise a soft polymer phase with a glass transition temperature in the range from −55 to −5° C. and a harder polymer phase with a glass transition temperature in the range from 0 to +50° C. The mechanical stability of the resultant coatings, however, is unsatisfactory.
EP 612 805 discloses binders for solventless emulsion paints which comprise at least one staged polymer which includes preferably more than 25% by weight of a hard polymer phase having a glass transition temperature in the range from +20 to +160° C. and less than 75% by weight of a soft polymer phase having a glass transition temperature of less than +20° C. and a nonfilm-forming polymer having a glass transition temperature in the range from +20 to +160° C. The pigment content of the emulsion paints described in that document is low.
It is an object of the present invention to provide an essentially solventless pigmented formulation based on an aqueous polymer dispersion which overcomes the disadvantages of the prior art and which even with a relatively high pigment content ensures adequate mechanical stability, especially high wet abrasion resistance.
We have found that this object is achieved, surprisingly, by pigmented aqueous formulations which comprise as their polymeric binder an aqueous dispersion of a polymer A whose particles comprise at least 80% by weight of a water-insoluble polymer 1 having a glass transition temperature in the range from −50 to +40° C. and up to 20% by weight of at least one water-insoluble polymer i having a glass transition temperature of more than 50° C.
The present invention accordingly provides an essentially solventless pigmented aqueous formulation comprising:
i) at least one polymer A in the form of polymer particles in disperse distribution, said particles comprising
from 80 to 99.9% by weight, preferably 85 to 99.9% by weight and, in particular, >90 to 99.9% by weight, based on the overall weight of the polymer A, of a water-insoluble polymer 1 having a glass transition temperature T
g
1 in the range from −50 to +40° C., built up from ethylenically unsaturated monomers M1, and
from 0.1 to 20% by weight, preferably from 0.1 to 15% by weight and, in particular, from 0.1 to <10% by weight, based on the overall weight of the polymer A, of one or more water-insoluble polymers i having a glass transition temperature T
g
i of more than 30° C., preferably more than 50° C., especially more than 70° C., built up from ethylenically unsaturated monomers Mi,
ii) at least one pigment and, if desired, one or more extenders,
said polymer A being obtainable by free-radical aqueous emulsion polymerization of the monomers Mi in the presence of the polymer 1 and it being true for all polymers i that the difference T
g
i−T
g
1 is >10 K.
An essentially solventless formulation generally comprises less than 0.1%, preferably less than 500 ppm and, in particular, less than 100 ppm of volatile organic constituents. Preferably, the formulations of the invention are also free from low molecular mass plasticizers.
The term glass transition temperature as used in this specification means the temperature determined by DSC (differential scanning calorimetry, 20° C./min, midpoint; cf. ASTM D 3418-82).
The glass transition temperature T
g
1 of the polymers 1 (and T
g
i of the polymers i) can also be estimated from the respective monomer composition of the polymer. According to Fox (T. G. Fox, Bull. Am. Phys. Soc. (Ser. II) 1, 123 [1956] and Ullmanns Enzyklopädie der technischen Chemie, 4th edition, Volume 19, Verlag Chemie, Weinheim (1980), p. 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
the glass transition temperatures, in degrees Kelvin, of the homopolymers of the monomers 1, 2, . . . , n. Sources of tabulated glass transition temperatures of homopolymers are, for example, Ullmann's Encyclopedia of Industrial Chemistry, 5
th
ed., VCH, Weinheim, Vol. A 21 (1992) p. 169 and J. Brandrup, E. H. Immergut, Polymer Handbook 2
nd
ed, J. Wiley, N.Y. 1975, pp. 139-192.
The minimum film-forming temperature, i.e., the temperature below which the particles of the polymer A do not form a stable film and therefore do not form a stable co
Dittrich Uwe
Hümmer Wolfgang
Schwartz Manfred
Zhao Cheng-Le
BASF - Aktiengesellschaft
Yoon Tae H.
LandOfFree
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