Process of coating a mineral molding with an aqueous...

Coating processes – Miscellaneous

Reexamination Certificate

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C427S133000, C427S393600, C524S156000, C524S558000, C524S560000, C524S563000, C524S577000

Reexamination Certificate

active

06472024

ABSTRACT:

The present invention relates to aqueous preparations which comprise, as film-forming constituent, at least one polymer P which is present in dispersed form in the aqueous phase of the preparation. The present invention also relates to the use of these preparations for coating mineral moldings.
For the purposes of the present invention, mineral moldings are moldings comprising a mineral binder and mineral aggregates. The preparations made from the mineral binder and aggregates can be molded when moist, and solidify in the course of time in air or else under water, if desired with exposure to elevated temperatures, to give the desired stone-like mineral molding. Mineral binders are well known. They are finely divided inorganic materials, such as lime, gypsum, clay and/or cement. Mineral aggregates are generally granular or fibrous, naturally occurring or synthetic rock materials (gravel, sand, mineral fibers) with grain sizes or fiber lengths which are matched to the particular application in a manner known per se. In particular cases the mineral moldings also comprise metals or organic additives. Color pigments are also frequently added for coloration.
Examples of mineral moldings to be coated according to the present invention are concrete pipes, e.g. for wastewater, concrete roofing tiles (cf. for example DE-A 39 01 073), curbstones, steps, floor slabs, plinth tiles and fiber-filled concrete panels, i.e. slab-like mineral moldings which have been filled with inorganic or organic fibers, e.g. polyester fibers or nylon fibers.
A disadvantage of mineral moldings is that they lose strength on exposure to weathering (in particular exposure to water) since the cationic constituents, such as Ca
2+
, are dissolved out in the course of time. Another disadvantageous property of mineral moldings is the occurrence of efflorescence phenomena. These are probably attributable to the fact that the mineral binders comprise higher-valency cations such as Ca
2+
in an alkaline environment. Reaction with the carbon dioxide from the air can therefore cause unsightly white lime markings, which have low solubility in water, to appear on the surface of the mineral moldings. Efflorescence can appear either as early as during the hardening of freshly prepared mineral moldings or else on exposure to weathering of mineral moldings which have already hardened.
To overcome the abovementioned disadvantageous properties mineral moldings are frequently given a coating. Nowadays this is usually done using aqueous coating systems whose film-forming constituent is an aqueous polymer dispersion. Conventional film-forming constituents include styrene-acrylate copolymers, homo- and copolymers of vinyl acetate, pure acrylates and the like. The coating gives the mineral moldings a glossy appearance which is desirable for many applications, in particular for concrete roofing tiles.
EP-A-469 295 and DE-A-195 14 266 have provided improvements in which the risk of efflorescence on mineral moldings is effectively removed using coating compositions based on styrene-acrylate dispersions and, respectively, pure acrylate dispersions. For this EP-A-469 295 recommends the use of a specific anionic emulsifier and DE-A-195 14 266 recommends the use of polymers which contain specific comonomers with sulfonate groups.
Prior art coatings all have the disadvantage of comparatively high water absorption. This water absorption carries with it a risk that low-molecular-weight constituents of the coating, for example emulsifiers required to stabilize the polymer particles in the coating compositions, can be washed out during prolonged weathering. This washing-out can be seen, for example, in increased white discoloration on the surface, or in embrittlement of the coating. Another consequence of this water absorption, due to the associated swelling of the polymer, is a reduction in the mechanical stability of the coating and an increase in surface slip, undesirable particularly for reasons of safety in concrete roofing tiles. A further risk with pigment-containing coatings is that the water absorption of the coating causes undesirable changes in perceived color.
It is an object of the present invention to provide coating compositions which are intended for use with mineral moldings and which give coatings having low water absorption and undergoing no disadvantageous changes in their strength and optical appearance even after prolonged exposure to moisture.
We have found that this object is achieved by preparations of film-forming polymers P which give coatings with low water absorption if the emulsifiers present in the preparations are salts of sulfuric acid monoesterified with ethoxylated C
10
-C
20
alkanols.
The present invention therefore provides aqueous preparations comprising:
i. as film-forming constituent at least one polymer P which is composed of ethylenically unsaturated monomers M and which is present in dispersed form in the aqueous phase of the preparation and which has a glass transition temperature T
G
in the range from −25 to +80° C., and
ii. at least one anionic emulsifier selected from the class consisting of the salts of formula I
Alk-[O-Et]
n
—OSO
2
O—M
+
  (I)
 where
Alk is linear or branched, saturated alkyl having from 10 to 18 carbon atoms,
Et is 1,2-ethylene,
n is an integer from >20 to 40, and
M
+
is a monovalent cation or a cation equivalent,
or mixtures of these salts, if desired with other anionic emulsifiers.
The invention further relates to the use of preparations of this type for coating mineral moldings.
Preferred salts of formula I are those where Alk is linear or branched alkyl having from 12 to 16 carbon atoms. n in formula I is preferably a number in the range from 25 to 40. In the case of mixtures of salts of formula I the average value of n is within the range given.
M
+
in formula I is preferably a cation or a cation equivalent of a metal of the 1st or 2nd main group of the Periodic Table. M
+
is in particular Na
+
, K
+
, ½ Ca
2+
or an ammonium ion (NH
4
+
), and particularly a sodium cation. The novel preparations frequently use mixtures of salts of formula I.
A specific embodiment of the present invention relates to preparations which comprise a mixture of salts of formula I, where Alk is linear or branched alkyl having from 12 to 14 carbon atoms and the average value of n is 30. In this case M
+
is in particular a sodium cation.
Salts of formula I are known and commercially available, for example as DISPONIL® FES 77 (manufacturer: Henkel KGaA) or can be prepared in a manner similar to that for known salts of formula I.
Besides the salts of formula I the novel preparations may also comprise other anionic emulsifiers. However, the salts of formula I generally make up at least 30% by weight, preferably at least 50% by weight and in particular at least 60% by weight, of the total amount of anionic emulsifiers in the preparation. For low water absorption it is particularly advantageous if the salts of formula I make up at least 80% by weight of the anionic emulsifiers and in particular are the sole anionic emulsifiers.
The total amount of anionic emulsifiers is generally from 0.1 to 5% by weight, preferably from 0.2 to 4% by weight and in particular from 0.5 to 3% by weight, based on the polymer P in the aqueous dispersion.
Examples of suitable other anionic emulsifiers are selected from the class consisting of the salts, in particular the alkali metal and ammonium salts, of alkyl sulfates (alkyl: C
8
-C
12
), of sulfuric acid monoesterified with ethoxylated alkylphenols (EO number: from 3 to 50, alkyl: C
4
-C
9
), of alkylsulfonic acids (alkyl: C
12
-C
18
) and of alkylarylsulfonic acids (alkyl: C
9
-C
18
).
Another embodiment of the present invention relates to aqueous preparations whose anionic emulsifiers comprise, in addition to the salt of formula I, at least one other anionic emulsifier selected from the class consisting of the salts of formula II
where R
1
and R
2
, independently

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