Claims
- 1. An electrodynamic coating process comprising the steps of:
- (a) providing a substrate to be coated;
- (b) supplying charged particles of a given polarity charge in the vicinity of said substrate and thereby effecting coating of said substrate by said charged particles; and
- (c) applying in the vicinity of the coated side of said coated substrate and at a time when the supplying step (b) has been completed a postcharge of a polarity the same as said given polarity so as to effect an increase in the electrostatic forces holding said particles to said substrate.
- 2. A process as recited in claim 1 wherein said substrate provided in step (a) is a continuous web and step (a) includes conveying said substrate along a predetermined path which includes at least a coating position and a post-charging position both independent of one another.
- 3. A process as recited in claim 1 including after step (a) precharging the substrate with a polarity opposite to said given polarity so as to effect a higher deposition rate and more uniform coating during step (b).
- 4. A process as recited in claim 3 wherein said substrate provided in step (a) is a continuous web and step (a) includes conveying said substrate along a predetermined path which includes a precharging position, a coating position, and a postcharging position all independent of each other.
- 5. A process as recited in claim 1 wherein said postcharging includes the step of providing a groundplane electrode on the uncoated side of the web.
- 6. A process as recited in claim 1 wherein step (b) takes place with said substrate in a coating position by providing at said coating position:
- a fluidizing reservoir means for receiving said particles and for fluidizing said particles so as to provide fluidized particles for coating;
- charging bed means disposed adjacent to said fluidizing reservoir means for receiving said fluidized particles provided for coating, and disposed adjacent to said coating position for charging said fluidized particles so as to cause electrostatic attraction of said fluidized particles to said substrate;
- recharging means disposed between said charging bed means and said coating position for recharging said fluidized particles attracted to said substrate prior to coating of said substrate; and
- porous wall means between said fluidizing reservoir means and said charging bed means for containing said fluidized particles within said fluidizing reservoir means, and for providing passage of said fluidized particles from said fluidizing reservoir means and to said charging bed means, whereby said particles may be fed at a high feed rate without harmful effect on the operation of said charging bed means.
- 7. A process as recited in claim 6 wherein the providing of said recharging means includes providing a control grid located in such a position relative to said coating position that the particle-to-air ratio of said position of said control grid is 6-10 times lower than the bulk density of fed particles.
- 8. A process as recited in claim 6 wherein the providing of said charging bed means includes providing a charging plate and an array of corona pins mounted thereon, and the providing of said recharging means includes providing a control grid.
- 9. A process as recited in claim 6 wherein the providing of said charging bed means further includes providing first source means connected to said array of corona pins for providing a plate-pin voltage thereto, and the providing of said recharging means further includes providing second source means connected to said control grid for providing a control grid voltage thereto.
- 10. A process as recited in claim 9 wherein the providing of said first and second source means includes providing variable voltage sources adjustable to provide such values of said plate-pin voltage and control grid voltage, respectively, that said control grid voltage is lower in absolute value than said plate-pin voltage.
- 11. A process as recited in claim 9 wherein the providing of said first and second source means includes providing variable voltage sources adjustable to provide such levels and polarities of said plate-pin voltage and said control grid voltage, respectively, that said fluidized particles attracted to said substrate form a particle cloud statically suspended between said charging plate and said control grid.
- 12. A process as recited in claim 6 wherein the providing of said recharging means includes providing a control grid which has a geometrical design so as to cause said fluidized particles attracted to said substrate to form a particle cloud which is intensified according to said geometrical design, and said substrate is coated with varying intensities in various areas.
- 13. A process as recited in claim 6 wherein the providing of said recharging means includes providing further means for introducing ionized gas at a position relative to said coating position such that the particle-to-air ratio at said position is lower than the bulk density of fed particles.
Parent Case Info
This is a continuation, of Ser. No. 863,215 filed Dec. 22, 1977, abandoned, which, in turn, is a division of prior application Ser. No. 789,625 filed Apr. 21, 1977, now U.S. Pat. No. 4,086,872, which, in turn, is a division of Ser. No. 676,513 filed Apr. 13, 1976, now U.S. Pat. No. 4,088,093.
US Referenced Citations (4)
Divisions (2)
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Number |
Date |
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Parent |
789625 |
Apr 1977 |
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Parent |
676513 |
Apr 1976 |
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Continuations (1)
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863215 |
Feb 1977 |
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