The invention relates to an early-rain-resistant sealing composition based on aqueous polymer dispersions and to a process for its preparation. c ml Sealing compositions based on aqueous acrylate polymer dispersions are known for various fields of applications. Their disadvantage lies in their lack of resistance to being washed out under the action of moisture immediately after use, for example in a sealing joint

The objective of the present invention is to provide sealing 0 compositions based on aqueous acrylate polymer dispersions and which have distinctly better values in respect of their resistance to early rain.

This objective is achieved by the addition of certain polysaccharides polyvinyl alcohols to standard formulations of sealing compositions based on aqueous acrylate polymer dispersions. 5 The invention therefore relates to an early-rain-resistant sealing composition based on aqueous acrylate polymer dispersions, characterized in that it contains from about 0.1 to 6 % by weight, preferably about 0.2 to 2 % by weight of a polysaccharide which is water-soluble or highly swellable in water and which is preferably selected from the group comprising pectin, 0 algin, carrageenan, agar, gum arabic, tragacanth, karaya gum, ghatti gum, carob bean flour, guar gum, tara gum and derivatives thereof. The derivatives of these plant-based polysaccharides are preferably alkyl, aralkyl, hydroxyalkyl and or carboxy-alkyl ethers of the said polysaccharides. Guar gum and derivatives thereof, such as hydroxypropyl-guar, carboxylmethyl- 5 guar and or carboxymethylhydroxypropyl-guar, are particularly preferred.

The sealing composition of the invention contains an aqueous dispersion of a polyalkyl (meth)acrylate and or of an alkyl (meth)acrylate copolymer as aqueous acrylate polymer dispersion. The aqueous dispersions used are preferably those which are obtained by polymerisation, specifically 0 by emulsion polymerisation, of alkyl (meth)-acrylates and/or by copolymerisation of alkyl (meth)-acrylates and/or by copolymerisation of alkyl (meth)-acrylates with themselves and/or with copolymerisable comonomers, such as, preferably, (meth)acrylic acid, (meth)acrylamide, styrene, itaconic acid, acrylonitrile and or citraconic acid, the alkyl groups of the alkyl (meth)acrylates preferably having 1 to 6 carbon atoms. Aqueous dispersions of polybutyl acrylate, polyethylhexyl acrylate or alkyl (meth)-

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acrylate/styrene copolymers are particularly preferred according to the invention. The acrylate (co)polymer dispersion is preferably mixed with the other constituents at a pH value in the range of about 7 to 9, preferably a pH value of 8, the pH being adjusted to this value, if necessary, using dilute sodium hydroxide solution or ammonia solution for example. This aqueous acrylate (co)potymer dispersion preferably has a solid content of about 40 to 70 % by weight, preferably of about 45 to 65 % by weight

The early-rain-resistant composition according to the invention preferably has a total water content of about 9 to 50 % by weight preferably about 10 to 30 % by weight and most preferably about 12 to 20 % by weight It can optionally contain further conventional additives, such as plasticisers, fillers, pigments, additives to adjust the rheological properties, dispersion auxiliaries, biocides, preservatives and anti-ageing agents, wetting agents, anti-foams and/or skin formation-retardants. These further additives are commercially available products which are known to those skilled in the art in the field of sealing compositions, in particular for building purposes.

The plasticisers preferably contained in the sealing composition according to the inventioa which is resistant to early-rain, are propylene glycol alkylphenyl ethers, ethylene glycol phenyl ether, chlorinated paraffins, polyisobutylenes, phthalic acid esters and/ or sulphonic acid esters.

Fillers which the sealing composition can contain are, for example, chalk, barium sulphate, quartz, talc, kaolin, calcium sulphate and/ or calcium silicate. Pigments which the sealing composition can contain are, preferably, titanium dioxide, zinc sulphide, zinc oxide and/or organic or inorganic coloured pigments.

The additives which the sealing composition according to the invention can contain in order to adjust the rheological properties are, for example, highly disperse silica, bentonites, polyacryiates and/or cellulose ethers.

A preferred sealing composition according to the inventioa which is resistant to early raia contains - about 25 to 90, preferably about 25 to 40 % by weight of the aqueous acrylate (co)polymer dispersioa

- 0 to about 20 % by weight preferably about 4 to 10 % by weight of plasticiser,

- 0 to about 60 % by weight preferably about 50 to 60 % by weight of fillers, and - 0 to about 10 % by weight preferably about 4 to 6 % by weight of at least one of the further additives, the sum of the constituents being 100 % by weight

The invention also relates to a process for the preparation of the above-described early-rain resistant sealing compositioa which process is characterised in that the aqueous acrylate (copolymer) dispersioa the pH value of which has been adjusted, if necessary, to a value in the range of about 7 to 9, e.g. by adding eg. sodium hydroxide and/or ammonium hydroxide, is initially introduced into a vessel and the liquid organic components, for example the plasticisers, are then added. If pigments are used, they are preferably suspended and added in a portion of the plasticiser. The fillers are then added, and mixed ia in portions. The polysaccharide is added together with the last portion of filler, having been mixed intimately with the fillers before the additioa After the last additioa the mixture is preferably further stirred for some time, after which a vacuum is advantageously applied in order to degas the compositions.

The process according to the invention is preferably carried out in a stirred vessel at a low speed of rotation and using high shear forces, for example in a planetary mixer. Advantageously, the equipment used should provide a possibility for degassing the compositions after the mixing operation by applying vacuum.

It has been found that the sealing composition according to the invention has a surprisingly high resistance to early raia which was tested with the aid of the following test method :

The sealing composition is coated in a thickness of 5 mm on a test piece and sprinkled with water using a commercially available spray head. For this test the test pieces are inclined at an angle of 45° to the direction of fall of the water. Spraying is carried out under the following conditions : Distance from spray head to centre of the test piece : 60 cm. Water throughput : 22 litres/5 minutes. Spraying time : 5 minutes.

Surface area of the test piece : 25 x 100 mm.

The resistance to early rain is tested 10 minutes after the sealing composition is applied. The assessment was carried out by weighing the test pieces before and after spraying and by determining the percentage of the material leached out

In the following examples, which serve for further explanation of the inventioa all amounts are by weight except if otherwise indicated. Examples 1 to 3 and Comparison Example

An aqueous polybutyl acrylate dispersion which has a solids content of 62 % and has been adjusted to a pH of 8 whith a 10 % strength aqueous sodium hydroxide solution is initially introduced into a laboratory planetary mixer. A fatty alcohol ethoxylate, as an emulsifier, and sodium polyacrylate, as a dispersing agent are then stirred in successively, while stirring at a medium speed The titanium dioxide, which is a surface-treated rutile pigment having a Tiθ ₂ content of 93 %, is dispersed beforehand in the plasticiser 1, a polypropylene glycol alkylphenyl ether, with the aid of a dissolver. This mixture and the plasticiser 2, e. ethylene glycol monophenyl ether, are also stirred ia Naturally occuring chalk coated with stearate and having an average particle diameter of 5 μm, is then introduced in two to three portions, the mixture being stirred for 2 to 3 minutes after each additioa The silicic acid in the form of highly disperse, amorphous, hydrophobic silicon dioxide having a BET surface area of 90 m ² /g is added together with the chalk. In Example 1 to 3 according to the inventioa carboxymethylhydroxypropyl-guar, as a polysaccharide, is then added together with the last portion of chalk. Thereafter, the mixture is further stirred for another 20 minutes, after which, finally, a vacuum is applied for 5 minutes, while stirring, in order to degas the compositions.

The amounts of the constituents are shown in the following table, to ether with the results of the determination of the resistance to earl rain :