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US-20260124643-A1 - Plasma induced crystallization and densification of amorphous coatings

US20260124643A1US 20260124643 A1US20260124643 A1US 20260124643A1US-20260124643-A1

Abstract

A method for coating a substrate and a respectively coated substrate. The created coating is characterized by a crystalline and dense structure which is particularly suitable for applying further layers of coatings onto it. The method uses a plasma for curing the applied solution instead of a thermal curing and is, hence, faster, less energy consuming, and applicable to more temperature sensitive substrates.

Inventors

  • Stefanie STUCKENHOLZ
  • Fang Tong XIE
  • Yakup GOENUELLUE
  • Stephanie Mangold
  • Sonja Mareike Breunig
  • Eveline Rudigier-Voigt

Assignees

  • SCHOTT AG
  • SCHOTT GLASS TECHNOLOGIES (SUZHOU) CO. LTD.

Dates

Publication Date
20260507
Application Date
20221011

Claims (20)

  1. 1 - 26 . (canceled)
  2. 27 : A method for coating a substrate comprising the steps of: a) providing a substrate, b) applying a coating solution on a surface of the substrate, c) thermally drying the coating solution to form an amorphous coating, and d) treating the amorphous coating with a plasma treatment to form an at least partially crystalized coating.
  3. 28 : The method as recited in claim 27 wherein the coating solution is a sol-gel based coating solution and is applied in a sol-gel-process.
  4. 29 : The method as recited in claim 27 wherein a maximum treatment temperature does not exceed 400° C.
  5. 30 : The method as recited in claim 27 wherein during an entirety of the method, the coating is exposed to a maximum temperature of at most 150° C. to 400° C. for a duration of at most 0.1 min to 90 min.
  6. 31 : The method as recited in claim 27 wherein the treating the amorphous coating with the plasma treatment according to step d) forms a crystalized coating having a degree of reflection of 0.05 to 0.3 when determined according to ISO 15368:2001 under an angle of 6° in a range of 250 nm to 850 nm on a coating having a thickness of 100 nm-120 nm.
  7. 32 : The method as recited in claim 27 wherein the treating the amorphous coating with the plasma treatment according to step d) forms a crystalized coating having a porosity of less than 20% when determined as a ratio between an inter-crystallite area and a total examined area in a scanning electron microscope image.
  8. 33 : The method as recited in claim 27 further comprising one or more repetitions of steps b) to d) to form one or more further layer of further crystalized coating on the crystalized coating.
  9. 34 : The method as recited in claim 27 wherein the substrate includes glass, polymers, metals, or alloys or combinations thereof.
  10. 35 : The method as recited in claim 27 wherein the coating solution includes a metal or a metal oxide.
  11. 36 : The method as recited in claim 35 wherein a precursor is decomposed by the action of the plasma treatment into the metal or metal oxide and organic components transferred into a gas phase.
  12. 37 : The method as recited in claim 27 wherein the coating includes a metal or a metal oxide.
  13. 38 : The method as recited in claim 27 wherein step d) forms a crystalized coating having an average crystallite size of less than 40 nm when determined on a coating having a thickness of 80 nm-120 nm via image processing an SEM image.
  14. 39 : The method as recited in claim 27 wherein the plasma treatment includes creating a radio frequency plasma or a microwave plasma.
  15. 40 : The method as recited in claim 27 wherein plasma of the plasma treatment is created in an atmosphere of oxygen, argon, nitrogen, air, or hydrogen either at ambient pressure or at reduced pressure.
  16. 41 : The method as recited in claim 27 wherein a time of the plasma treatment is from 0.1 s to 120 min.
  17. 42 : The method as recited in claim 27 wherein during the plasma treatment the substrate temperature does not exceed 400° C.
  18. 43 : The method as recited in claim 27 wherein a plasma of the plasma treatment is generated via a radio frequency plasma generator with a capacitive electrode arrangement or a pulsed magnetron microwave generator.
  19. 44 : The method as recited in claim 27 wherein a generator for generation of plasma of the plasma treatment is operated at a power of 0.2 kW-10 kW.
  20. 45 : The method as recited in claim 27 wherein a morphology of the amorphous coating is modified regarding a state of crystallization or a state of modification or density or surface roughness.

Description

The present invention relates to a method for coating a substrate and a respectively coated substrate. The created coating is characterized by a crystalline and dense structure which is particularly suitable for applying further layers of coatings thereon. BACKGROUND Many substrates are provided with a coating in order to achieve a certain desired effect or enhancement of properties. Depending on the application, the coatings have a thickness in the range from several nanometers up to some millimeters. For example, for optic lenses and ophthalmic lenses typically several layers of coatings in the range from nanometers to micrometers are applied for providing the glass or polymer with UV filter, anti-reflective, and anti-scratch properties as well as chemical resistivity. For the application of coatings of such a thickness, in general a sol-gel-process is used. A solution of the coating medium or a precursor of the same is prepared in a first step and then spread by different techniques onto the substrate for the creation of a thin liquid film. Finally, the solvent is evaporated from the film to obtain the coating. SUMMARY OF THE INVENTION Since these coatings on substrates are often amorphous after this initial coating step, usually a curing in form of a thermal annealing step is applied as a further step to crystallize, densify, and/or modify the coating. The thermal annealing leads to different film modifications, depending on the applied temperature program. The evaporation of the solvent in the initial coating step is done by heating the substrate only to moderate temperatures-if heating at all-whereas the curing step requires much higher temperatures. The coating is always applied on a substrate with certain restrictions regarding the maximum temperature that can be applied in a thermal annealing step. In many cases, the temperature required by common coating substances is too high for temperature sensitive substrates such as polymers. Moreover, the curing step is often also quite time and energy consuming. Conventional annealing of sol-gel coatings usually takes place at high temperatures of several hundred degrees Celsius for durations of up to several hours. A typical example of a coating on glass lenses made of soda lime glass is a UV protection layer consisting of ZnO. In a standard sol-gel-coating process on a soda lime glass, the ZnO coating is applied via dip coating (v=30 cm/min), dried in a first step for 6 min at 145° C., and annealed in a second step for 60 min at 500° C. The second heating step is intended to bring the coating from an amorphous state into a crystalline state and to burn off any organic binder in the system. The goal is to achieve a dense and crystalline ZnO film on the soda lime glass. However, the second heating step leads in the case of ZnO coatings on glass only to a binder burn off and to a crystallization of the ZnO, but results in a highly porous film. Such a highly porous film is not—or at most very limited—suitable for the application of further layers of coatings. Additionally, the high temperatures put a lot of thermal stress on the substrate. A crystallization of the coating system of ZnO on a polymeric substrate is, due to the temperature restrictions of the substrate, not feasible with thermal annealing. This example of the ZnO coating is illustrative for the problems faced with sol-gel-coatings of different kinds of coating materials on diverse substrates. While the curing times and temperatures may vary, the basic problems of high temperatures, long annealing times, high energy consumption, insufficient crystallinity, and insufficient density are persistent. Moreover, these problems described by means of the example of a sol-gel-process and particularly a ZnO coating likewise affect other coating processes using liquid solutions and requiring a thermal annealing step for curing the initially created amorphous layer. An object underlying the present invention is to provide an improved coating process which does not or at least to a lesser extent suffer the problems of the prior art. In particular, a coating process should be provided which results in a coating suitable for applying further layers onto it. The present invention can be used in the field of coatings, in particular sol-gel-coatings, on substrates (e.g. glass, polymers, metals or other materials) that comprise an annealing step with the goal of densification, crystallization or other morphological changes of the coating, particularly for the purpose of making the coating suitable as a base layer for further layers. The method uses a plasma for curing the applied solution instead of a thermal curing and is, hence, faster, less energy consuming, and applicable to more temperature sensitive substrates. The inventors have discovered that the thermal annealing step to modify the morphology (state of crystallization/modification and/or density and surface roughness) and resulting film properties (e.g. U