Method for producing an aqueous composition comprising a condensate based on silicon compounds for producing antireflective coatings

Abstract

A method for producing an aqueous composition comprising a condensate based on silicon compounds, involving the steps of i) introducing at least one polymeric rheology control agent into water; ii) adding at least one acidic catalyst; iii) adding at least one silicon compound of general formula (I) RnSiX4-n in which the radicals X are the same or different and stand for hydrolysable groups or hydroxyl groups, the radicals R are the same or different and stand for non-hydrolysable groups, and n is 0, 1, 2, or 3; and iv) performing a hydrolysis reaction of at least part of the silicon compounds of general formula (I) added in step iii). The present invention further relates to a composition that can be obtained by means of the method according to the invention.

Claims

1. A method for producing an aqueous composition comprising a condensate based on silicon compounds, comprising the following steps: i) introducing at least one polymeric rheology control agent into water; ii) adding at least one acidic catalyst; iii) adding at least one silicon compound of formula (I):
R.sub.nSiX.sub.4-n(I), in which the residues X are the same or different and stand for hydrolyzable groups or hydroxyl groups, the residues R are the same or different and stand for non-hydrolyzable groups, and n is 0, 1, 2 or 3; and iv) performing a hydrolysis reaction of at least a portion of the silicon compounds of formula (I) added in step iii), wherein steps i), ii), iii) and iv) are carried out in the sequence i), ii), iii) and iv), wherein organic compounds having a molecular weight of no more than 400 g/mol are present in the composition at a proportion of no more than 10 wt % based on the total weight of the composition, wherein the composition is free of organic solvents, wherein the quantity of silicon compounds of the general formula (I) is in the range of 0.1 wt % to 5 wt % based on the mixture obtained in step (iii), and wherein the mixture obtained in step (iii) comprises 70 wt % to 99.79 wt % water and polymeric rheology control agent.

2. The method according to claim 1, characterized in that the rheology control agent has a molecular weight M.sub.w within the range of 1000 to 2000000 g/mol.

3. The method according to claim 1, characterized in that 0.1 wt % to 40 wt % rheology control agent based on the weight of the mixture obtained in step i) is used to produce the composition in step i).

4. The method according to claim 1, characterized in that the rheology control agent is a polyacrylamide, a cellulose or a cellulose derivative.

5. The method according to claim 1, characterized in that at least one silicon compound of the formula SiX.sub.4 is used, in which the residues X are the same or different and stand for hydrolyzable groups or hydroxyl groups.

6. The method according to claim 1, characterized in that the proportion of the silicon compound according to the formula SiX.sub.4 is within the range of 80 wt % to 100 wt %, based on the total quantity of silicon compounds of formula (I).

7. The method according to claim 1, characterized in that after step iv) has been performed, a surface active substance is added to the composition.

8. The method according to claim 1, characterized in that the at least one silicon compound of formula (I) is selected from the group consisting of SiCl.sub.4, HSiCl.sub.3, Si(OCH.sub.3).sub.4, Si(OOCCH.sub.3).sub.4, Si(OC.sub.2H.sub.5).sub.4 and Si(OC.sub.3H.sub.7).sub.4, tetraalkoxysilanes, Si(OCH.sub.3).sub.4, Si(OC.sub.3H.sub.7).sub.4, and combinations thereof.

9. The method according to claim 1, characterized in that no more than 80 wt % of the at least one silicon compound of formula (I) comprises one selected from the group consisting of Cl.sub.3SiCH.sub.3, Si(CH.sub.3)(OC.sub.2H.sub.5).sub.3, Cl.sub.3Si(C.sub.2H.sub.5), Si(C.sub.2H.sub.5)(OC.sub.2H.sub.5).sub.3, Si(OC.sub.2H.sub.5).sub.3(CH.sub.2CHCH.sub.2), Si(OOCCH.sub.3).sub.3(CH.sub.2CHCH.sub.2), Cl.sub.3Si(CHCH.sub.2), Si(CHCH.sub.2)(OC.sub.2H.sub.5).sub.3, Si(CHCH.sub.2)(OC.sub.2H.sub.4OCH.sub.3).sub.3, Si(CHCH.sub.2)(OOCCH.sub.3).sub.3, and combinations thereof.

10. The method according to claim 9, characterized in that no more than 20 wt % of the at least one silicon compound of formula (I) comprises at least one selected from the group consisting of (C.sub.6H.sub.5).sub.3SiOH, Si(CH.sub.3).sub.3(OC.sub.2H.sub.5), Si(CH.sub.2CH.sub.3).sub.3(OC.sub.2H.sub.5), and combinations thereof.

11. The method according to claim 1, characterized in that no more than 20 wt % of the at least one silicon compound of formula (I) comprises at least one selected from the group consisting of Cl.sub.2Si(CH.sub.3).sub.2, Si(CH.sub.3).sub.2(OC.sub.2H.sub.5).sub.2, Si(C.sub.2H.sub.5).sub.2(OC.sub.2H.sub.5).sub.2, Cl.sub.2Si(CHCH.sub.2)(CH.sub.3), Si(CH.sub.3).sub.2(OCH.sub.3).sub.2, Cl.sub.2Si(C.sub.6H.sub.5).sub.2, Si(C.sub.6H.sub.5).sub.2(OC.sub.2H.sub.5).sub.2, and combinations thereof.

12. The method according to claim 1, wherein the step iv) is performed without the presence of a surface active substance.

Description

EXAMPLE 1

(1) Production of a coating composition comprising a polycondensate from tetraethoxysilane (TEOS).

(2) 1.25 g hydroxypropyl cellulose (Nisso M, available from Nisso Chemical Europe GmbH, viscosity of an aqueous solution with 2 wt/% Nisso M is approximately 150 to 400 mPa*s, measured at 20 C., molecular weight is approximately 620000 g/mol) was added to 46.766 g water and stirred for 30 minutes at 30 C. to obtain a clear solution, to which 0.25 g HNO.sub.3 was added in a second step, 1.734 g tetraethoxysilane was stirred into the resulting mixture, and after 18 hours at 30 C. a clear composition was obtained, which was applied to a glass substrate. The coating composition had a viscosity of 1.5 Pa*s at a shear rate of 0.2 s-1. Following application, the coating was dried for 10 minutes at 120 C. and baked for 5 minutes at 600 C. The result was an antireflective coating giving a dark blue reflection with slight spotting.

EXAMPLE 2

(3) Example 1 was essentially repeated, however 0.1 wt/% of a surface active substance (polyether modified siloxane Byk 348, available from Byk Chemicals Japan) was added after the hydrolysis step.

(4) An antireflective coating giving a dark blue reflection was obtained, which had fewer optical defects than the layer of Example 1.

EXAMPLE 3

(5) Example 1 was essentially repeated, however 0.1 wt/% of a surface active substance (Byk 348, available from Byk Chemicals Japan) was added prior to the hydrolysis step.

(6) An antireflective coating giving a dark blue reflection was obtained, which had considerably more optical defects than the layer of Example 1, with clearly visible spots developing.

COMPARATIVE EXAMPLE 1

(7) Three drops TEOS were added to 10 ml water, wherein the silicon compound could not be dispersed in the water by stirring. The addition of 2 drops HNO3 led to the formation of opaque white floccules, with no development of a useful composition being observed.

EXAMPLE 4

(8) 2.2 g hydroxypropyl cellulose (Klucel L, available from Hercules, molecular weight approximately 95000 g/mol) was added to 95.5 g water that contained 0.263 g 50% H.sub.2SO.sub.4, and this was stirred for 60 minutes at 30 C. to obtain a clear solution. 1.363 g tetraethoxysilane was stirred into the resulting mixture which was hydrolyzed for 60 minutes. 0.661 g Koestrosol 3550 was stirred into the resulting mixture. The resulting composition was applied to sheet glass by screen printing (mesh 100T), producing a smooth layer. Following application, the coating was baked at 690 C. The result was an antireflective layer giving a blue to violet reflection.