Methods and apparatus for vacuum thin film deposition
View Patent ↗The present invention provides a polymer coating method. In the method, in a vacuum chamber, a low temperature monomer evaporation chamber is used to heat a liquid monomer and a cooled substrate at a temperature lower than the liquid monomer reservoir or vapor. The liquid monomer is allowed to condense on the cooled substrate surface where it is polymerized by a radiation source. The process depends on the vapor pressure difference between liquid in the monomer source and liquid condensed on the surface of the cooled substrate. The film thickness is dependent on the temperature difference between the monomer reservoir and the substrate, and the time that is required to move the coated substrate from the evaporation chamber to the cure station. The method is suitable for forming very thin, uniform, pinhole-free, polymer coatings from a variety of monomers, having at least two olefinic groups per molecule, on a variety of substrates.
1. A method of forming a polymer coating on a surface of a substrate in a vacuum chamber evacuated to a pressure of less than about 10 −2 Torr, wherein the method comprises:
(a) providing in the vacuum chamber an evaporation chamber, wherein the evaporation chamber comprises a reservoir of a liquid monomer, wherein the monomer has two or more olefinic groups per molecule and a vapor pressure in the range of 10 −6 to 10 −1 Torr at standard temperature and pressure, and wherein the reservoir of liquid monomer is heated at a temperature below that at which thermal polymerization of liquid monomer is initiated, thereby forming a vapor of the monomer;
(b) allowing the vapor formed by heating the reservoir of liquid monomer to flow to the surface of the substrate, the surface at a temperature below the temperature of the liquid monomer reservoir or vapor;
(c) condensing the vapor on the surface of the substrate to deposit a monomer layer on the surface of the substrate; and
(d) polymerizing the monomer layer formed in step (c) to form the polymer coating on the surface of the substrate.
2. The method of claim 1 , wherein step (a) further comprises forming the vapor in a heated evaporation chamber, the heated evaporation chamber comprising parallel sides and a gated aperture, the gated aperture adjustable to provide a cross-sectional area from 0 to 30% of the surface area of the reservoir of liquid monomer in the heated evaporation chamber.
3. The method of claim 1 , wherein step (a) further comprises heating the liquid monomer to a temperature of less than about 80° C. to form the vapor.
4. The method of claim 1 , wherein the surface of the substrate is at a temperature of less than about 30° C.
5. The method of claim 1 , wherein the surface of the substrate is at a temperature of less than about 20° C.
6. The method of claim 1 , wherein the substrate is a web.
7. The method of claim 1 , wherein the polymerization is induced by a radiation source.
8. The method of claim 7 , wherein the radiation source comprising one or more of the group consisting of e-beam and ultraviolet radiation.
9. The method of claim 1 , wherein the vapor pressure of the liquid monomer is from about 10 −2 to about 10 −4 Torr at standard temperature and pressure.
10. The method of claim 1 , wherein the molecular weight of the monomer is from about 150 to 800.
11. The method of claim 1 , wherein the liquid monomer comprises one or more of the group consisting of glycol acrylates, polyglycol acrylates, and polyol polyacrylates.
12. The method of claim 1 , wherein the liquid monomer is selected from the group consisting of hexanediol diacrylate, trimethylolpropane triacrylate, and tripropyleneglycol diacrylate.
13. The method of claim 1 , wherein the coating formed in step (d) is from about 0.005 μm to about 10 μm in thickness.
14. The method of claim 1 , wherein the coating formed in step (d) is from about 0.01 μm to about 1 μm in thickness.
15. The method of claim 7 , wherein the substrate is a web moving past the radiation source.
16. The method of claim 1 wherein evaporation is not carried out with a flash evaporation process.
17. A method of forming a two-part coating on a substrate in a vacuum chamber:
(a) sputtering a first layer onto the substrate;
(b) forming a second layer by:
(i) exposing the substrate to a vapor of monomer, wherein the vapor is formed by heating a reservoir of liquid monomer in an evaporation chamber, wherein the evaporation chamber is positioned in the vacuum chamber, at a temperature below that at which thermal polymerization of the monomer is initiated, wherein the liquid monomer has two or more olefinic groups per molecule, and a vapor pressure in the range of 10 −6 to 10 −1 Torr at standard temperature and pressure;
(ii) allowing the vapor formed by heating the reservoir of liquid monomer to flow to the surface of the substrate, the surface at a temperature below the temperature of the liquid monomer reservoir or vapor;
(iii) condensing the vapor on the surface of the substrate to deposit a monomer layer on the surface of the substrate; and
(iv) polymerizing the monomer layer formed in step (c) to form the polymer coating on the surface of the substrate.
18. The method of claim 17 wherein steps (b) is performed prior to step (a).
19. The method of claim 17 wherein the first layer is a metal or metal oxide layer.