The instant invention relates to an improved electrode useful for modifying a substrate using corona or plasma treatment or coating a substrate using plasma enhanced chemical vapor deposition under atmospheric or near atmospheric pressure conditions.
Numerous prior art electrode configurations have been developed for atmospheric or near atmospheric pressure operation. The prior art configurations can be classified into two major types. The first type is intended to be used with a ground electrode positioned on the other side of the substrate from the working electrode. Examples of the first type of electrode are disclosed in WO 2006/049794 and WO 2006/049865. The second type uses a ground electrode position of the same side of the substrate as the working electrode. Examples of the second type of electrode are discussed in WO02/23960, U.S. Pat. No. 6,441,553 and U.S. Pat. No. 7,067,405.
The quality and coating uniformity provided by prior art electrodes is primarily a function of two factors: (a) the gas flow velocity from the electrode onto the substrate to be coated; and (b) the uniformity of the gas flow velocity across the substrate to be coated (as discussed, for example, in USPAP 20050093458). A higher gas flow velocity produces a better quality coating. However, a lower gas flow velocity produces a more uniform coating. Thus, there remains a need for an atmospheric pressure plasma coating electrode that provides both a high gas flow velocity and a uniform gas flow velocity.
The instant invention is a solution to the above-mentioned problems. The electrode of the instant invention provides both a high gas flow velocity and a uniform gas flow velocity. More specifically, the instant invention is an improved electrode useful for modifying a substrate using corona discharge or dielectric barrier discharge or glow discharge plasma treatment or coating a substrate using plasma enhanced chemical vapor deposition under atmospheric or near atmospheric pressure conditions, the electrode comprising a body defining a cavity therein, the body having at least one inlet passageway therethrough in gaseous communication with the cavity so that a gas mixture can be flowed into the cavity by way of the at least one inlet passageway, the electrode having at least one outlet passageway therethrough in gaseous communication with the cavity so that a gas that is flowed into the cavity can flow out of the cavity by way of the at least one outlet passageway, the at least one outlet passageway being a slot, wherein the improvement comprises a porous body positioned in and sealed to the wall of the cavity adjacent to the outlet passageway so that a gas that is flowed into the cavity will pass through the porous body before flowing through the outlet passageway.
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Examples of suitable working gases include organosilicon compounds such as silanes, siloxanes, and silazanes generated from the headspace of a contained volatile liquid 52 of such material and carried by a carrier gas 49 from the headspace and merged with balance gas 53 to form the mixture of gases 16. Examples of silanes include dimethoxydimethylsilane, methyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane, diethoxydimethylsilane, methyltriethoxysilane, triethoxyvinylsilane, tetraethoxysilane, dimethoxymethylphenylsilane, phenyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacrylpropyltrimethoxysilane, diethoxymethylphenylsilane, tris(2-methoxyethoxy)vinylsilane, phenyltriethoxysilane, and dimethoxydiphenylilane. Examples of siloxanes include tetramethyldisiloxane, hexamethyldisiloxane, octamethyltrisiloxane, and tetraethylorthosilicate. Examples of silazanes include hexamethylsilazanes and tetramethylsilazanes. Siloxanes are preferred working gases, with tetramethyldisiloxane being especially preferred.
The working gas is preferably diluted with a carrier gas 49 such as air or nitrogen before being merged with the balance gas. The v/v concentration of the working gas in the carrier gas is related to the vapor pressure of the working gas, and is preferably not less than 1%, more preferably not less than 5%, and most preferably not less than 10%; and preferably not greater than 50%, more preferably not greater than 30%, and most preferably not greater than 20%.
Examples of suitable balance gases include air, oxygen, nitrogen, helium, and argon, as well as combinations thereof. The flow rate of the balance gas is sufficiently high to drive the plasma polymerizing working gas to the substrate to form a contiguous film, as opposed to a powder. Preferably the flow rate of the balance gas is such that the velocity of the balance gas passing through the slot of at least 1000 feet per minute, more preferably at least 2000 feet per minute, and even more preferably more than 4000 feet per minute (such as 10000 feet per minute or even 20000 feet per minute or more. Control of the relative flow rates of the balance gas and the working gas also contributes to the quality of the coating formed on the substrate. Preferably, the flow rates are adjusted such that v/v ratio of balance gas to working gas is at least 0.002%, more preferably at least 0.02%, and most preferably at least 0.2%; and preferably not greater than 10%, more preferably not greater than 6%, and most preferably not greater than 1%. The actual numeral values for gas injection speed, concentrations, and compositions depends, of course, on the type of coating that is being put down on the substrate as is well understood in the art.
Although it is possible to carry out the process of the present invention by applying a vacuum or partial vacuum in, for example and without limitation thereto, the corona discharge region, (i.e, the region where the corona discharge is formed) the process is preferably carried out so that the corona discharge region is not subject to any vacuum or partial vacuum, that is, carried out at atmospheric or near pressure.
The substrate to be coated or treated by the electrodes of the instant invention is not limited. Examples of substrates include, polyolefins such as polyethylene and polypropylene, polystyrenes, polycarbonates, and polyesters such as polyethylene terephthalate and polybutylene terephthalate.
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The porous body used in the instant invention is preferably formed of sintered granules of a solid material such as sintered glass or metal (and especially, sintered granules of stainless steel, available, for example, from SSI-Sintered Specialties, Janesville Wis.). The permeability of the porous body is preferably in the range of from 3×106 m2 to 3×1010 m2. The permeability of the porous body is more preferably in the range of from 3×107 m2 to 3×109 m2. The permeability of the porous body is most preferably in the range of from 1×108 m2 to 6×108 m2 when the slot height is in the range of from 4-8 mm and when the thickness of the porous body is in the range of from 1.5 to 3 mm.
In conclusion, it should be readily apparent that although the invention has been described above in relation with its preferred embodiments, it should be understood that the instant invention is not limited thereby but is intended to cover all alternatives, modifications and equivalents that are included within the scope of the invention as defined by the following claims.
This application claims benefit of U.S. Provisional Application No. 60/848,940, filed Oct. 3, 2006.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2007/021039 | 9/27/2007 | WO | 00 | 3/18/2009 |
Number | Date | Country | |
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60848940 | Oct 2006 | US |