Multi-layer coating method

In a method for coating substrates, providing a plurality of serially connected chambers capable of being evacuated, and having sealing ducts therebetween utilizing the first and last chambers in the series as entrance and exit chambers respectively, utilizing certain of the serially connected chambers as coating chambers, evacuating said coating chambers down to at least below a predetermined vacuum, evacuating the remaining chambers in the series on the opposite ends of the serially connected coating chambers so that at least the chambers closest to the coating chambers have a pressure which is below that of the pressure in the coating chambers to thereby positively control the composition of the gases in the coating chambers during the coating operation, closing off the entrance chamber and the exit chamber so that they are out of communication with the other chambers in the series, providing in an ambient atmosphere a plurality of substrates to be coated, continuously advancing one of said plurality of substrates from the ambient atmosphere into the entrance chamber, closing off the entrance chamber from the ambient atmosphere, evacuating the entrance chamber, opening the entrance chamber so it is in communication with the other chambers in the series, rapidly advancing said substrate from the entrance chamber into the remaining chambers, closing the entrance chamber so it is out of communication with the other chambers in the series as soon as said substrate has been moved out of the entrance chamber, continuously advancing the substrate through the remaining chambers preceding the coating chambers and then into the coating chambers at a rate which is less than the rate it is advanced out of the entrance chamber, positioning said substrate in the coating chambers as it is being advanced so it lies in a generally horizontal plane with the surface to be coated facing downwardly, depositing on said substrate while it is being advanced in said coating chambers on the downwardly facing surface successive layers of coating materials with only one layer of one material being deposited in each coating chamber, continuously advancing the substrate through the chambers following the coating chambers and preceding the exit chamber, closing the exit chamber so it is out of communication with the ambient atmosphere, opening the exit chamber so that it is in communication with the chambers following the coating chambers, rapidly advancing said substrate into the exit chamber at a rate greater than the rate of advance in the chambers following the coating chambers, closing the exit chamber so that it is out of communication with the chambers following the coating chambers as soon as said substrate has been advanced into the exit chamber, opening the exit chamber to the ambient atmosphere, advancing said substrate from the exit chamber into the ambient atmosphere and moving the remaining substrates of the plurality of substrates through the same series of steps while at least at all times maintaining a spaced apart relationship between the substrates as they are being coated.