Easily cleanable coating

A process for making a product with a long-lasting easily cleanable surface is described. By said process, there is applied to the surface a mixture comprising a hydrolyzable, network-forming gel and a hydrophobic substance. The gel is preferably formed from SiO 2 , Al 2 O 3 , Fe 2 O 3 , In 2 O 3 , SnO 2 , ZrO 2 , B 2 O 3 and/or TiO 2 , and the hydrophobic substance is preferably chemically linked with the gel network.

EXAMPLE 1 
 Preparation of a Hydrophobically Modified SiO 2 Dipping Solution 88.6 mL of methyl silicate, 80 mL of distilled water and 10 mL of glacial acetic acid were stirred into 240 mL of ethanol. The resulting solution was allowed to stand 72 hours. It was then diluted with 1580 mL of ethanol, and the hydrolysis was stopped with 2 mL of 37% hydrochloric acid solution. Then, 8.6 mL of tridecafluorooctyltriethoxysilane (supplied under the tradename Dynasylan F 8261 by DEGUSSA-HÜLS, Frankfurt, Germany) was added with stirring. The coating was applied according to the invention in a single dipping step and allowed to dry for 5 min at room temperature. It was then baked at 250° C. for a maximum of 30 min, which caused the silica gel to harden. 
 EXAMPLE 2 
 Preparation and Testing of a Coating of the Invention A clean 2-mm-thick 10×20 cm panel of borosilicate glass was immersed at room temperature in the SiO 2 dipping solution described hereinabove in Example 1 and was then withdrawn from the solution at a rate of 20 cm/minute. The coating film thus applied was allowed to dry for 5 min at room temperature and was then baked for 20 min in an oven at 250° C. (Table 1 , coating 1 ) or at 300° C. (Table 1 , coating 2 ). After the baking, the coating of the invention was about 120 nm thick. The hydrophobing process was evaluated by determining the contact angle with water. This was done with a model G 10 contact angle meter supplied by KRÜSS, Hamburg &lsqb;Germany&rsqb;. By this method, freshly cleaned glass surfaces show a contact angle of &lE;20°, coated glass surfaces one of about 60° and surfaces freshly rendered hydrophobic one of &gE;100°. Immediately after the preparation according to the invention, a value of 110° was measured at room temperature in this manner. Thereafter, a Schrubb test was performed as follows. A piece of felt having an contact surface of about 3 cm 2 and moistened with water was moved on the test specimen back and forth while subjecting it to a total load of m&equals;1 kg. Here, a rubbing cycle corresponds to one to and fro movement. After 500 rubbing cycles by the Schrubb test, the contact angle was still 102°, after 1000 cycles it was 103° and after 2000 cycles it was still 100°, within an accuracy of ±3°. 
 EXAMPLE 3 
 Comparative Example 
 Hydrophobing by Use of a Fluoroalkylsilane A glass surface was rendered hydrophobic in accordance with the prior art by applying tridecafluoro-octyltriethoxysilane (F 8262, supplied by DEGUSSA-HÜLS). The fluoroalkylsilane was applied to the entire surface with a textile cloth and fixed for 20 min at 200° or 250° C. Determination of the contact angle with water showed immediately after preparation a value of 108°. After 500 rubbing cycles by the Schrubb test (see above), the contact angle was 81°, after 1000 cycles it was 68° and after 2000 cycles it was still 67°. Similar values were also obtained for identically tested hydrophobic glass surfaces from different manufacturers. 
 EXAMPLE 4 
 Comparative Example 
 Hydrophobing by Use of a Silicone Oil By applying hydromethylpolysiloxane (Fluid 1107, supplied by DOW CORNING), a glass surface was rendered hydrophobic in accordance with the prior art. The silicone oil was applied to the entire surface with a textile cloth and fixed at 180° C. for 20 minutes. Determination of the contact angle with water showed immediately after preparation a value of 102°. After 500 rubbing cycles by the Schrubb test (see above), the contact angle was 87°, after 1000 cycles it was 71° and after 2000 cycles it was still 51°. Similar values were also obtained for identically tested hydrophobic glass surfaces from different manufacturers. 
 EXAMPLE 5 
 Comparative Example 
 Performance of Commercially Available Hydrophobic Glass Surfaces Four different commercially available hydrophobic glasses from different manufacturers were subjected to a rubbing or Schrubb test as described in Example 2 . The test results are summarized in Table 1 . 1 TABLE 1 Contact Angle with Water in Degrees on Different Hydrophobic Glass Surfaces After n Rubbing Cycles Preparation/Origin n &equals; 0 n &equals; 500 n &equals; 1000 n &equals; 2000 Coating 1, according to 114 106 102 101 invention, Example 2 (250° C.) Coating 2, according to 110 102 103 100 invention, Example 2 (300° C.) Example 3 (Comp. Example 108 81 68 67 according to prior art, coated with fluoroalkyl- silane) Example 4 (Comp. Example 102 87 71 51 according to prior art, coated with silicone oil) Commercially available 90-99 54-89 50-71 — hydrophobic glass sur- faces as per Example 5