DE19534764A1 - Sol-gel mfr of thin, crack-free silica films - Google Patents

Abstract

Prodn. of thin silica film comprises hydrolysing and condensing a compsn. comprising 40-100 wt.% one or more silanes of formula Rx-Si-A4-x (I), 0-50 wt.% colloidal silica and/or 0-10 wt.% organic binder, processing the resulting viscous sol to a gel film, and heat treating the gel film. In (I), A = a hydrolytically cleavable substit.; R = a hydrolytically non-cleavable substit.; and x is such that at least 70% of (I) has x = 1 or more.

Description

The invention relates to thin, crack-free, preferably trans Parente and colorless SiO₂ films, a process for their Manufactured according to the sol-gel process and their use e.g. B. as membranes, filters, components of laminates or Backing materials with incorporated functional additive fabrics.

Glass foils are usually drawn or extruded sions process made from the melt. This ver driving are from the thermal properties of the glass (Softening point, crystallization rate etc.) dependent and therefore on certain glass compositions limited. Another limitation is with regard to the minimum thickness of the glass films that can be produced, which makes it So far it was not possible to use silica glass films with a thickness below about 250 µm by melting and subsequent To produce molding processes.

It is known that by sol-gel techniques the Verdich processing temperature of glassy and / or ceramic work substances can be significantly reduced. The production of SiO₂ films after the sol-gel process failed, however previously problems with the transfer of the mostly watery alcoholic precursors (brine) in the xerogel body Solvent withdrawal or addition of a gelling agent. When drying brines on substrates, Ka pillar forces and due to the different drying speed at the top or bottom slightly Formation of cracks. In addition, the gel films loosen due to the preferred solvent evaporation at the When drying, remove the surface from the surface and roll a. There was therefore no known method according to the trans Parente, crack-free SiO₂ films with larger dimensions  Pouring and gelling SiO₂ sols on a base can be produced.

Surprisingly, it has now been found that thin SiO₂- Foils very simple and in practically any dimensions (Length and width) can be produced in a sol-gel process are.

The invention relates to a method for producing thin SiO₂ films, which is characterized in that

• a) 40 to 100% by mass of one or more silanes of the general formula (I) R _x -Si-A _4-x (I) in which the radicals A are identical or different and are hydrolytically removable substituents, the radicals R are identical or different are and represent hydrolytically non-removable substituents and x has the value 1, 2 or 3, wherein at least 70% by mass of the silanes x is 1; optionally in the presence of
• b) 0 to 50, preferably 0 to 25% by mass of colloidal SiO₂ and / or
• c) 0 to 10% by mass of an organic binder

hydrolyzed and condensed, the viscous sol obtained processed a gel sheet and the gel sheet heat-treated.

The invention further relates to this way adjustable SiO₂ films and SiO₂ films with a thickness of 2.5 to 250 µm and an area of at least 25 cm² preferably at least 50 cm², particularly preferably at least 100 cm².  

The SiO₂ films according to the invention are thin, crack-free, before preferably transparent and colorless, are characterized by high Flexibility and minimal shrinkage.

Details of the sol-gel process are available from C.J. Brinker, G.W. Scherer: "Sol-Gel Science - The Physics and Chemistry of Sol-Gel Processing, "Academic Press, Boston, San Diego, New York, Sydney (1990) and in DE 19 41 191, DE 37 19 339, DE 41 17 041 and DE 42 17 432 are described.

There are also specific examples of those in the invention usable silanes and their hydroly residues A that can be split off table and hydrolytically not split off bare residues R. Preferred examples of the residues A are alkoxy, amine, halogen, hydride and carboxylate groups and groups forming Si-polyol complexes, the are derived from glycol, glycerin or pyrocatechol. Specific examples of the radicals R are alkyl, cyclo alkyl, aryl, alkaryl and arylalkyl radicals, the given if can be substituted. The index x has a value of 1, 2 or 3, preferably 1.

The SiO₂ film according to the invention can, for. B. from pure Methyltriethoxysilane (MTEOS) or from mixtures of MTEOS and tetraethoxysilane (TEOS). A special The preferred system comprises 90% MTEOS and 10 substance% TEOS.

To improve manageability and other mechani shear properties of the thin SiO₂ films is preferred colloidal SiO₂ as an additional starting material turns. Its use also increases density and that Pore volume of the foils. The colloidal SiO₂ can, for. B. in Form of silica sols or nanoscale, dispersible Powders are available. An alcoholic pebble is preferred sol with particle sizes of approx. 10 nm.  

An organic bandage can be used as a further contingent component agents are applied, which thereafter ther mix can be removed from the gel film. Suitable bindemite tel are z. B. polyvinyl alcohol, polyvinyl acetate, starch, Polyethylene glycol and gum arabic.

The hydrolysis and condensation is carried out under sol-gel conditions gene preferably in an alcoholic solvent (e.g. Methanol or ethanol) under basic catalysis (e.g. with Ammonia) until a viscous sol is formed. Around a favorable sol particle morphology and sol viscosity adjust, subject the hydrolyzate / condensate preferably a targeted aging step in which the Reaction mixture for several hours to several days Temperatures of 40 to 120 ° C is heated. Especially be Preference is given to heating to 80 ° C for about 4 days. Here a sol with a viscosity of preferably 5 is formed up to 100 Pa · s, particularly preferably 20 to 25 Pa · s.

The sol can then become one in different ways Gel film can be processed, for example by pouring and gelling on a substrate or in a mold, film pull, blowing techniques or squeezing out of a slot nozzle se, the gelation by evaporation of the solvent and / or addition of gelling agents (HCl or NH₃-Bega solution). Casting or are particularly preferred Doctor blade on a non-stick pad, e.g. B. made of poly styrene, polyethylene or teflon and evaporating the solution by means of. The sol can also gel continuously e.g. B. on a roller or a conveyor belt.

In the particularly preferred system of 90% by mass MTEOS and 10% by mass TEOS surprisingly became found that this with basic catalysis and a tem temperature of 80 ° C even after a period of 100 h or condensed only marginally. This contradicts the  conventional experience, according to which the presence of basi catalysts accelerate the condensation reaction. In contrast, the system according to the invention is practically full constantly hydrolyzed, but not condensed, so that no gelation takes place. As a result, the one pour the sol into a mold, evaporate the solvent can without gelling. Only when the Lö is almost completely evaporated, one sets Gelation to form a gel sheet.

The gel sheet obtained is then dried, preferably at temperatures from room temperature to 100 ° C below normal pressure or reduced pressure. Particularly preferred dry Conditions are 3 h at 20 to 30 ° C, followed by 15 h at 50 ° C.

The gel body obtained can optionally be different Pretreatments are subjected. For example, a Shaping through mechanical or chemical processing take place, e.g. B. drilling, cutting, dissolving, etching, structure (embossing, ion bombardment), folding or bending.

To improve the mechanical properties, the Gel film if necessary in functional (reactive) solution introduced or treated with agents, e.g. B. with Water, alcohols, amines, Si compounds (e.g. TEOS), or treated with reactive gases, e.g. B. with HCl or NH₃.

If necessary, the gel film can also be pretreated done by corona or plasma generators.

Finally, the gel film is heat-treated in the Temperature range from 100 to 1400 ° C, below 200 ° C annealing takes place in the range from 200 to 700 ° C the organic components are burned out and above  700 ° C thermal compression (sintering) takes place.

The heat treatment can be carried out by e.g. B. by heating, loading radiate with infrared, laser or flash light radiation (Rapid Thermal Annealing). Here are heating up speeds of preferably 40 to 50 ° C / h applied.

The heat treatment can be in different gas atmospheres be performed, e.g. B. in air, oxygen, nitrogen, Ammonia, chlorine, carbon tetrachloride or equivalent the gas mixtures.

Thermal compression in air is preferred for thinner SiO₂ foils with a thickness of up to 50 µm. At 1000 ° C, thin transparent glass foils are formed. Sintering in nitrogen at 1000 to 1250 ° C results black glass foils with enclosed coals fabric particles that have high strength and z. B. as Substrates or for laminates are suitable. By sintering in Surprisingly, ammonia can also use thicker glass foils of excellent transparency.

The SiO₂ films according to the invention show no tendency to Cracking, unwanted detachment or curling. Further it was surprisingly found that the used organic components without any cracking can be removed thermally, so that colorless-transparent annuity glass films can be produced, the dimensions of which le diglich limited by the size of the pad.

The SiO₂ film according to the invention are suitable for the various Most applications, e.g. B. as membranes, filters, inventory parts of laminates or substrates with incorporated functional additives such as magnetic particles cels, carbon, metal colloids, dyes (also pho tochrome) and pigments. Other areas of application are  optical and electronic components as well as multilayer mate materials for bulletproof glazing.

The following examples illustrate the invention without it restrict.

example 1

A mixture of 0.92 mole MTEOS, 0.08 mole TEOS and 0.25 Moles of colloidal SiO₂ (MA-ST from Nissan Chemicals; 30% in Methanol) is diluted with 4.5 mol of absolute ethanol and with 4 moles of ammonia water (0.34 g of 25% ammonia solution in 72 g Water) hydrolyzed with a magnetic stirrer. The stirrer is continued for a further 3 minutes. Through 4 days Aging the reaction mixture at 80 ° C in a closed NEN container becomes a viscous sol with a viscosity of Get 20-25 Pa · s.

The sol is poured directly onto flat polystyrene molds or doctored, drawing speeds from 5 to 20 mm / s can be applied. The polystyrene is then covered shape and keep them in an oven at temperatures of 15 h 40 to 65 ° C. During this time, the viscous sol and it gel a gel and tear-free and warp-free gel film can be removed be the 3 h at 20-30 ° C and then 15 h at 50 ° C is dried.

The gel films produced in this way can be independent gig of their thickness in air at temperatures up to 400 ° C are sintered, producing transparent glass foils. Gel films with a thickness of less than 50 µm can be cracked formation in air up to 1000 ° C to transparent glass foils be sintered.  

When sintering thicker foils in nitrogen in the area from 400 to 1250 ° C mechanically and thermally bile black glass foils, which are then heated show no visible change at 1300 ° C. The thermo mechanical properties correspond approximately to those of pure pebble glass.

When sintered in an ammonia atmosphere at temperatures up to 1000 ° C are crack-free even with thicker gel foils Obtain glass films of excellent transparency. In the Ammonia sintered SiO₂ films have better chemical and thermal stability and higher breaking strength, micro-hard te and high temperature resistance than pure pebbles glasses.

Example 2

To produce photochromic glass films, a 1 × 10 ^-3 molar solution of a photochromic spiropyran dye in methanol is prepared and 1 ml of this solution is added dropwise to 10 ml of the sol prepared as in Example 1, which has a solids content of almost 30% by mass. Further processing is carried out as in Example 1.

Example 3

For the production of magnetic glass foils, 2.5 ml with a suspension of nanoscale maghemite particles a primary particle size of 10 nm and a solid content of 6% by mass to that produced in Example 1 dripped ten sol. Further processing takes place as in Example 1, being transparent in air during sintering red-brown colored magnetic glass foils can be obtained.

Claims (9)

1. A process for producing thin SiO₂ films, characterized in that

• a) 40 to 100% by mass of one or more silanes of the general formula (I) R _x -Si-A _4-x (I) in which the radicals A are identical or different and are hydrolytically removable substituents, the radicals R are identical or different are and represent hydrolytically non-removable substituents and x has the value 1, 2 or 3, where at least 70% by mass of the silanes x is 1; optionally in the presence of
• b) 0 to 50% by mass of colloidal SiO₂ and / or
• c) 0 to 10% by mass of an organic binder

hydrolyzed and condensed, the viscous obtained Sol processed into a gel sheet and the gel sheet heat treated. 2. The method according to claim 1, characterized in that to hydrolysis and condensation in the presence of acidic or basic, preferably basic con performs condensation catalysts. 3. The method according to claim 1 or 2, characterized net that the hydrolyzate / condensate by several hours aging up to several days at temperatures of 40 transferred to a viscous sol up to 120 ° C.   4. The method according to any one of claims 1 to 3, characterized characterized that the sol on a non-haf trending base into a gel film. 5. The method according to any one of claims 1 to 4, characterized characterized in that the gel film is dried and at Temperatures up to 1400 ° C heat treated. 6. Thin SiO₂ films, can be produced by the method one of claims 1 to 5. 7. Thin SiO₂ films with a thickness of 2.5 to 250 microns and an area of at least 25 cm². 8. Use of the SiO₂ films according to claim 6 or 7 as Membranes, filters, components of laminates or Carrier materials with incorporated functional Additives.