DE19828231C2 - Process for the deposition of porous optical layers - Google Patents

Abstract

Process for the deposition of porous optical layers of metal oxides on glasses, ceramics or metals by subjecting the substrate to be coated to a cleaning pretreatment, applying an aqueous metal oxide sol or sol mixture, to which a surfactant mixture has been added, to the substrate to be coated and coating it Substrate is annealed at temperatures from 100 to 550 ° C. The surfactant mixture consists of 15 to 30% by weight of anionic surfactants, 5 to 15% by weight of nonionic surfactants and less than 5% by weight of amphoteric surfactants, which are dissolved in water.

Description

The invention relates to the deposition of porous optical layers from Metal oxides on glasses, ceramics or metals.

It is over for the production of optical layers from liquid precursors Strive for environmental reasons as well as safety-related aspects worth using systems that contain flammable and / or toxic solvents avoid. Previously used processes are based on organometallic Compounds that hydrolyzed on the substrate to be coated and by increasing the temperature in a hard and abrasion-resistant film of a metal oxide are polycondensed. Processes used so far start from alkoxides or acetylacetonates that hydrolyzed with water be settled. The resulting coating solutions contain hence alcohols or other organic solvents. Often become Improvement of flow properties and viscosity additionally added organic solvents.

EP 0 514 973 A2 describes a sol-gel process for the deposition of anti reflective layers on glass that have high scratch resistance and low Have sensitivity to moisture. Alcoholic solutions of alkoxides of the elements silicon, aluminum or titanium become together with water with the addition of small amounts of hydrochloric acid Brought substrate and in for 20 min with a water vapor atmosphere Brought in contact. During this time the substrate will be up from 23 ° C Heated 55 ° C and the resulting layer dried at 150 ° C for 30 min. The added acid catalyzes the hydrolysis of the alkoxide and the Er heating during gel formation leads to better crosslinking of the Gels.

EP 0 597 490 A1 describes a method for forming a silicon dioxide films on a glass substrate as an anti-reflective layer by adding two metal org African silicon compounds with different molecular weights the group of silicon alkylates and silicon acetylacetonates, which is in isopropyl alcohol or 1-butanol are dissolved, applied to the glass substrate and be hydrolyzed at a relative humidity of 40 to 90%.  

By heating to a temperature of 100 ° C, the sol obtained film converted into a gel film and then the coated Heated substrate to 550 ° C.

DE 41 05 235 A1 describes a method for coating an enamelled or glazed surface of a substrate made of glass, ceramic or Metal, in which the surface is first a cleaning pretreatment is then subjected to an aqueous metal oxide sol or a metal oxide sol mixture is applied and then at temperatures between 50 and 250 ° C the coated substrate is annealed and optionally annealed.

The applied metal oxide layers are characterized by a low Porosity, high mechanical and chemical stability, through a high mirror gloss and through a brilliant, on an interference and / or absorption color based color play.

DE 42 33 351 A1 describes the production of metal oxide sols by Electrolysis of metal salt solutions. The metal oxide sols produced are suitable for the production of titanium dioxide layers Ceramic substrates.

DE 43 37 643 C1 describes the production of water-dispersible alumina hydrates with an Al ₂ O ₃ content of 1 to 20%, which are suitable for coating materials such as glass, metal or plastic in order to protect these materials from thermal and / or chemical Protect attack.

EP 0 700 879 A1 describes a scratch-resistant coating made of aluminum oxide on a glass substrate and the process for its manufacture. To one To bring about structural transformation into the stable α phase, this must be done coated glass can be heated to a temperature of over 1000 ° C. The coating is only translucent or transparent described.

These methods have the disadvantage that because of the use of Environmental solvents and organometallic compounds  protection and explosion protection that complicate and make the procedures more expensive.

In addition, the layers obtained have the disadvantage that one for Reflection reduction an interference layer system from at least 2 Layers needed and this reflection reduction only in one be limited wavelength range occurs.

The object of the invention is to provide a method for the deposition of porous To provide metal oxide layers with optical quality on substrates, that carried out without solvents and organometallic compounds can be and that allows the production of layers that already effect the desired reflection reduction as a single layer and the reduction in reflection over the entire transmission range of the Coating material occurs.

This object is achieved according to the invention by a method for the deposition of porous optical layers of metal oxides on glasses, ceramics or metals by

• - The substrate to be coated under a cleaning pretreatment is pulled
• - An aqueous metal oxide sol or sol mixture, which a surfactant mixture is added, is applied to the substrate to be coated and
• - The coated substrate at temperatures of 100 to 550 ° C ge is tempered.

According to this procedure, optically transparent, reflectivity changing layers of metal oxides on glasses, ceramics or Metals with a continuously adjustable refractive index from 1.22 to 2.20 receive.

For example, by applying a porous SiO ₂ layer to a flat glass plate made of soda-lime glass according to Example 1, a reduction in reflection is achieved, which can usually only be achieved with a multilayer interference layer system.

As a starting material for the coating of the substrates mentioned aqueous metal oxide sols are used, which according to the in US 5 378 400 described electrolysis process from aqueous metal salt solutions 0 ° to 15 ° C can be obtained. These brines contain 0.3 to 15% metal oxide. They are highly transparent and contain no stabilizers. To This process uses aluminum oxide, titanium dioxide and zirconium brine oxide, hafnium oxide, niobium oxide, tantalum oxide or from oxides of actinides or lanthanides can be produced.  

Despite the different pH value of the individual brine, they can be used mix and mix in the manner described below Apply th substrates. By mixing brines with different ones Refractive indices can be optical layers with refractive indices between Make 1,22 and 2,2.

Furthermore come aqueous as a starting material for the coating Metal oxide sols in question by hydrolysis of metal salts or metal organic compounds, especially alkoxides, by ion exchange Metal salt solutions, by microemulsion from alkoxides or metal salt solutions or by dialysis or electrodialysis of metal salt solutions be produced by known methods. The particle size of the brine is in the range of 1 to 25 nm.

A microemulsion process is described by D. Burgard, R. Nass and H. Schmidt in Proceedings of the 2nd European Conference on Sol-Gel Technology, North Holland Publisher, Amsterdam 1992, pages 243-255 described. M. Neidle and J. Barab describe in J. Amer. Soc. 39 (1917) on page 71ff the production of brine by dialysis.

Electrodialysis procedures are described by Prajapali, M.N. and Talpade, C.R. in Indian Chem. Manuf. 12 (1), pages 13-21 (1974) and by Frolov, Yu. G. in D. I. Mendeleeva 107 (1979), pages 31ff.

The SiO ₂ sols with particle sizes between 1 and 50 nm used as starting material can be produced from the intermediate product of the process described in US Pat. No. 4,775,520. These are SiO ₂ particles which have been obtained by hydrolytic polycondensation of tetraalkoxysilane in an aqueous-alcoholic-ammoniacal medium. The reaction mixture is subjected to steam distillation to remove the solvent and ammonia and is then suitable as a starting material for the coating of the above-mentioned substrates.

Surprisingly, it was found that a slight addition of certain surfactants, for example a mixture of 15-30% by weight anionic surfactants, 5-15% by weight nonionic surfactants and less  than 5% by weight of amphoteric surfactants leads to porous layers whose Refractive index is 1.30.

The coating solution has a solids content of 0.1 to 20% by weight, preferably 2 to 10% by weight. The concentration depends on the type of Coating process. They are immersion processes or slingshots method applicable. Except for small amounts of detergents or commercially available leveling agents, for example from Byk-Gardiner Chemistry, or complexing agents, for example ethylenediaminetetraacetic acid or citric acid, no further additives are required. The The concentration of detergents and leveling agents is less than 2 wt .-%, the concentrations of complexing agents less than 80% by weight, based on the solids content of the coating solution. Based on the coating solution, the concentration is Complexing agent less than 10 wt .-%.

Glasses, ceramics and metals come into consideration as substrate materials. Metals, however, with the restriction that the wettability is given must be and no reaction with the protons present in the sol occurs.

The substrate surface must be subjected to a pretreatment. This pretreatment consists of cleaning with acetone, ethanol and Water or in an alkaline cleaning, for example with diluted Sodium hydroxide solution, 1N NaOH being preferred. Also commercially available Reini Ambient baths, such as the RBS bath from Roth, are suitable. It is phosphate-free and has a pH of 9.5. Another trade The usual alkaline cleaning bath is "neodisher A8" from the chemical company Factory Dr. Refuses. It consists of 40% sodium carbonate, 25% sodium metasilicate, 20% tetrasodium diphosphate, 10% sodium hydroxide, 3% Sodium polyacrylate and 2% dichloroisocyanurate. The cleaning effect can amplified by using ultrasound.

Before the brine can be incorporated into the coating solution, they are cleaned. A suitable method is pressure filtration, where filters with a pore size of 0.2 to 2 µm can be used.  

Suitable methods for applying the coating solution to the The substrate is immersion, spraying or rotary coating process (spin coating).  

In order to achieve technologically relevant drawing speeds of approx. 10 cm / min to get the sol concentration in the coating solution be dropped off; be discontinued; be deducted; be dismissed. Dilution with 1N HCl is preferred. The Solids concentrations in the dip coating process are the half to 2% by weight to 5% by weight based on the coating solution set.

When using the spin coating process, it is fixed Concentrations of 2 to 20 wt .-% based on the coating solution worked. To do this, the coating solution is applied evenly distributed the substrate and then, for example at 2000 rpm. the excess solution is thrown off.

The applied layers are applied to a temperature in the course of 90 min heated from 100 to 550 ° C and about 5 min at final temperature leave.

In the case of the deposition of titanium dioxide layers, there is a pre drying of the applied layers at 20 to 70 ° C for a period from 0.5 to 10 hours.

The annealed layers have optical quality. The layer thickness can be set to 10 to 300 nm for single coating. The The layer thickness is adjusted by varying the centrifugal or Dive speed and by changing the viscosity and the solid content of the coating solution.

Coated glass plates can be cut without chipping and show abrasion resistance according to the Taber Abraser Test (DIN 52347) such as the metal oxide produced by hydrolysis of alkoxides layers. The layers obtained are stable in the salt spray test (DIN 50021-CASS), compared to 1000 hours aging at 85 ° C and 85% relative humidity and also stable against UV radiation (QUV- B test, DIN 53384-A). Compared to uncoated soda-lime glass was a protective effect for the coated samples in the QUV-B test observed against solarization effects.  

The great advantage of the method is that for the production of Layers do not require organometallic compounds or solvents are such. This means that the required coating systems are not must be explosion proof, which is a significant cost saving is connected.

The following examples are intended to explain the invention in greater detail, without it restrict however.

example 1

Flat glass plates (soda-lime glass) are cleaned with a commercially available cleaning bath (RBS bath from Roth), then with 1N NaOH and then with demineralized water under ultrasound. A neutral SiO ₂ sol with a solids content of 10% by mass (manufacturer: Merck KGaA) is used as the sol. The sol is diluted with 3 parts of demineralized water and then acidified to 2.8 g of dilute sol with 2.8 g of concentrated HCl. For a coating solution for the production of porous layers, 0.7 g of a surfactant mixture is added dropwise to 1000 g of solution. The surfactant mixture consists of 20% sodium dodecylbenzenesulfonate, 10% sodium coconut fatty alcohol ether sulfate (3 ethylene oxide units) and 5% dodecyl polyglycol ether (7 ethylene oxide units), dissolved in water.

Flat glass plates are coated by dipping with a Extraction speed of 90 mm / min. The coating thus obtained conditions are heated to 550 ° C and after a holding time of 15 min in Oven cooled down uncontrolled. The layer thus obtained has a refractive index from 1.30 and is stable with respect to the climate listed in Example 2 Testing.

Example 2

Flat glass plates (soda-lime glass) are made with a commercially available Cleaning bath (RBS bath), then with 1N NaOH and then with de mineralized water cleaned under ultrasound.  

An aqueous ZrO ₂ sol with a solids content of 8.6% by mass ZrO ₂ and a viscosity of 2.25 mm ² / s (manufacturer: Merck KGaA) is filtered through a 0.2 µm filter and after adding 4 drops of the surfactant mixture mentioned in Example 1 was used without further additives for the spin-off coating described below. The coating solution obtained is uniformly distributed on the substrate and the excess portion is spun off at 2000 rpm.

The glass plate covered with the coating solution becomes at room temperature temperature in a convection oven and this within 90 min 500 ° C heated. After a holding time of 5 min at 500 ° C, the be layered glass plate cooled in the oven. The layer thus obtained is full constantly transparent with a layer thickness of approx. 75 nm and shows visually no missing parts. The layer has a refractive index of 2.03 and is stable against weathering tests (85 ° C / 85% relative humidity for 1000 Hours), temperature change test (55 ° C / + 125 ° C according to DIN 40046 sheets 4) L, CASS test (96 h) according to DIN 50021-CASS and QUV-B test (500 h, in Based on DIN 53384-A). The abrasion resistance (according to DIN 52347) of the deposited layer is identical to the abrasion resistance of layer ten, which are produced by hydrolysis of alkoxides.

Claims (3)

1. Process for the deposition of porous optical layers from metal oxides on glasses, ceramics or metals by

• the substrate to be coated is subjected to a cleaning pretreatment,
• - An aqueous metal oxide sol or sol mixture, to which a surfactant mixture is added, is applied to the substrate to be coated and
• - The coated substrate is annealed at temperatures from 100 to 550 ° C.

2. The method according to claim 1, characterized in that the Surfactant mixture of 15 to 30 wt .-% anionic surfactants, 5 to 15% by weight of nonionic surfactants and less than 5% by weight amphoteric surfactants, dissolved in water. 3. The method according to claim 1, characterized in that before Anneal a predrying of the applied layer at 20 to 70 ° C over a period of 0.5 to 10 hours.