This invention relates to a composition for the water-repellent impregnation of porous, mineral building materials and this invention relates more particularly to a composition based on organosilicon compounds containing alkoxy groups which is useful to enhance the water repellency of such building materials.
Organosilanes or organosiloxanes have been used for many years to impregnate porous mineral building materials, in order to protect them against penetration by water. It is particularly important for this hydrophobizing treatment that the active ingredients penetrate deeply into the building material and combine chemically or physically with the building material.
Penetration into the building material is favored by using compounds of the lowest possible molecular weight as active organosilicon ingredients. The depth of penetration can be improved additionally by the concomitant use of organic solvents, which evaporate after the treatment of the building material. High reactivity is attained by using organoalkoxysilanes and/or organoalkoxysiloxanes, which can condense under the influence of moisture and react with the building material as organosilicon compounds. At the same time, the alcohol, which corresponds to the alkoxy group, is split off and evaporated into the atmosphere.
German Patent 3,312,911 discloses such a preparation, which contains organopolysiloxanes of the general formula ##STR2## wherein R.sup.1 is an alkyl or aryl group,
R.sup.2 is an alkyl group with 1 to 4 carbon atoms, PA0 a=0.8 to 1.5 and PA0 b.ltoreq.2. PA0 R.sup.2 is a methyl or ethyl group, PA0 a is 0 to 1.5, PA0 b is 1.0 to 4.0 and PA0 a+b is 2.0 to 4.0. PA0 R.sup.1 is an alkyl group with 3 to 12 carbon atoms and PA0 R.sup.2 is a methyl or ethyl group, PA0 a is 0.8 to 1.2 and PA0 b is 0.2 to 1.2,
This preparation is characterized by a composition consisting of:
a) 1 to 20% by weight of a mixture of organoalkoxysiloxanes of the aforementioned formula, which consists of 25 to 75% by weight of a siloxane, the b value of which is 0.1 to 0.5, and of 75 to 25% by weight of a siloxane, the b value of which is 0.8 to 2.0, wherein a+b are less than or equal to 3,
b) 80 to 99% by weight of a solvent that is not miscible with water and
c) optionally, known condensation catalysts.
The essential characteristic of this preparation is that the impregnation is carried out not with an organoalkoxysiloxane, the molecular weight distribution of which essentially has only a single maximum, but with a mixture of organoalkoxysiloxanes, the characteristic feature of which consists of a different degree of condensation. By these means, high depth of penetration, associated with a high effectiveness, especially on alkaline building materials, and a good, optically visible water beading effect are assured.
German Patent 3,312,911 discloses preparations which have proven their value in practice. Essentially, an improvement in these preparations is possible only with respect to the depth of penetration that is achievable in actual use. This depth of penetration is affected principally by three factors, namely: the solvent used, the porosity of the building material and the care with which this preparation is used. Improvements in impregnating preparations must therefore be measured particularly by the penetration behavior.
As a result of a greater awareness of the environment, the use of organic solvents is increasingly perceived to be disturbing. Therefore, special efforts have been made to develop comparable preparations based on aqueous compositions.
Further developmental work has led to a method, which is the object of German Patent 3,627,060. This patent relates to a method for impregnating mineral building materials, particularly masonry, with aqueous solutions of silanols and/or siloxanols, which are produced at the site of their use by hydrolysis of alkoxysilanes and/or alkoxysiloxanes. As alkoxysilanes and/or alkoxysiloxanes, compounds of the following general formula are selected ##STR3## wherein R.sup.1 is an alkyl group with 1 to 8 carbon atoms, at least 90% of the R.sup.1 groups in the average molecule being alkyl groups with 1 to 4 carbon atoms,
These compounds are hydrolyzed continuously in an amount corresponding to their consumption. The solution obtained is applied on the mineral building material within a period of 3 to 30 minutes after the reactants are mixed.
With this method, a high penetration of the aqueous preparations into the mineral building material is achieved. This penetration is comparable to that achieved when organic solvent containing preparations are used.
However, because of their instability, these solutions must be produced at the place where they are to be used, as required by German Patent 3,627,060.
An aqueous silane emulsion for hydrophobizing ceramic materials is disclosed in published European Patent Application 0 234 024. This emulsion consists essentially of
a) 1 to 40% by weight of a hydrolyzable silane with a molecular weight of up to about 500 and the general formula R.sub.n Si(R').sub.4 -n, wherein R' is an optionally halogenated hydrocarbon group with 1 to 20 carbon atoms, R'is an alkoxy group with 1 to 3 carbon atoms, a halogen, an amino or a carboxyl group, and n is 1 or 2, or the oligomers of these silanes and
b) 0.5 to 50% by weight, based on the silane, of an emulsifier with an HLB value of 4 to 15 and
c) water.
Octyltriethoxysilane is named as an especially preferred silane.
In actual fact, emulsions of such silanes, in which the R group has more than 6 carbon atoms, have an increased stability, since the rate of hydrolysis of these reactive silanes is decreased. However, it is disadvantageous that the hydrolysis of these silanes in the building material is also, necessarily, correspondingly slow and must be catalyzed in a suitable manner. In some building materials, such as fresh concrete, this is possible due to the high alkalinity. This is not possible, however, in neutral or weakly alkaline building materials, such as burned clinker or numerous natural stones. Without such a catalyst, there is no anchoring of the silanes to the surface of the building material. The silanes can evaporate from the surface or be removed mechanically. This leads to a depletion of silane at the surface and thus to a decrease in the hydrophobization. As a consequence, the water beading effect is weak or not present at all. The water absorption capacity in the depleted surface layer is high, so that especially this layer, which is particularly exposed to weathering and mechanical attack, is insufficiently protected. Thus, these preparations can be used only for certain building materials.