Claims
- 1. A method for coating a liquid composition from an applicator to a first surface of a moving plastic web having opposite first and second surfaces, the web being conveyed along a path through an apparatus for coating against a backing roller at a coating point, comprising the steps of:a) wrapping said web about a portion said second surface thereof in a partial wrap around said backing roller of diameter equal to or greater than 10 cm, said backing roller being provided with a conductive, relieved surface, said relieved surface having a pattern that provides venting of entrained air, said pattern having a geometry and depth such that the electrostatic force at said coating point does not vary by more than a factor of about ten, said pattern covering at least 30% or more of the width of the web; b) providing an electrostatic field at said coating point; and c) applying the liquid composition to the first surface at the coating point while maintaining a web speed greater than or equal to 75 meters/minute.
- 2. A method in accordance with claim 1 wherein said electrostatic field has a strength equivalent to that produced by applying a voltage differential of at least about 300 V between said backing roller and said applicator.
- 3. A method in accordance with claim 1 wherein said providing step is carried out with the assistance of a first negatively-charged electrode and a second positively-charged electrode, each being spaced apart from a grounding means, and comprising the step of passing said web between said grounding means and said first and second electrodes to alter electrostatic charges on said first surface of said web.
- 4. A method in accordance with claim 3 wherein said grounding means is a grounded conductive roller.
- 5. A method in accordance with claim 3 wherein said providing step is carried out with the further assistance of first and second DC ionizers of opposite polarity, each being spaced apart from a conductive means, and comprising the step of passing the web between said conductive means and said first and second DC ionizers to alter electrostatic charges on said second surface of said web.
- 6. A method in accordance with claim 5 wherein said electrostatic charge on said web after said electrode and ionizer treatments is substantially zero.
- 7. A method in accordance with claim 5 wherein said conductive means is maintained at a voltage other than zero by a voltage control means electrically connected to said conductive means.
- 8. A method in accordance with claim 7 wherein said voltage control means includes a bipolar high voltage source (±5 kV) and a charge sensor connected to said source.
- 9. A method in accordance with claim 1 wherein said coating applicator is selected from the group consisting of bead coating applicator, curtain coating applicator, extrusion coating applicator, and slide-extrusion coating applicator.
- 10. A method in accordance with claim 1 wherein said coating backing roller is maintained at a voltage other than zero by a voltage control means electrically connected to said roller and wherein said coating applicator is grounded.
- 11. A method in accordance with claim 1 wherein said coating applicator is maintained at a voltage other than zero by a voltage control means electrically connected to said coating applicator and wherein said coating backing roller is grounded.
- 12. A method in accordance with claim 1 wherein said relieved surface composes a plurality of generally uniformly aligned circumferential grooves and ridges, said ridges presenting a generally cylindrical closely axially spaced land area for supporting the web and permitting the web to bridge the grooves, said grooves being vented to ambient atmosphere at the oncoming and off-running sides of the area of web wrap of said roller.
- 13. A method in accordance with claim 1 wherein said relieved surface comprises a branched collection of chambers and troughs in said roller surface with adjacent plateau surfaces presenting a generally cylindrical land area for supporting the web.
- 14. A method for coating a liquid composition from an applicator to a fit surface of a web, the web being conveyed along a path through an apparatus for coating against a backing roller at a coating point, comprising the steps of:a) providing said backing roller with a diameter greater than or equal to 10 cm and a conductive, relieved surface for supporting a second surface of said web; b) fabricating said relieved surface with a pattern that provides venting of entrained air, said pattern having a geometry and depth such that the electrostatic force at said coating point does not vary by more than a factor of about ten, said pattern covering at least 30% or more of the width of the web; c) neutralizing electrostatic charges on said first and second surfaces of said web upstream of said coating point; d) applying an electrostatic force to the composition at the coating point; and e) coating the web at the coating point at a web speed greater than or equal to 75 meters/minute.
- 15. A method in accordance with claim 14 wherein said neutralizing step further comprises the steps of applying and removing negative and positive electrostatic charges.
- 16. A method in accordance with claim 14 wherein said applying step further comprises the step of establishing a voltage differential between said backing roller and said applicator.
- 17. A method in accordance with claim 14 wherein one of said backing roller and said applicator is maintained at electrical ground and the other of said backing roller and said applicator is maintained at a predetermined voltage of either polarity.
- 18. A method for coating a liquid composition from an applicator to a first surface of a moving paper web having opposite first and second surfaces, the web being conveyed along a path through an apparatus for coating against a backing roller at a coating point, comprising the steps of:a) leading said web on said second surface thereof in a partial wrap around said backing roller of diameter equal to or greater than 10 cm, said backing roller being provided with a conductive, relieved surface; b) fabricating said relieved surface with a pattern that provides venting of entrained air, said pattern having a geometry and depth such that the electrostatic force at said coating point does not vary by more than a factor of about ten, said pattern covering at least 30% or more of the width of the web; c) providing an electrostatic field at said coating point with the assistance of a first negatively-charged electrode and a second positively-charged electrode, each being spaced apart from a grounding means, and comprising the step of passing said web between said grounding means and said first and second electrodes to alter electrostatic charges on said first surface of said web, and with the further assistance of first and second DC ionizers of opposite polarity, each being spaced apart from a conductive means, and comprising the step of passing the web between said conductive means and said first and second DC ionizers to alter electrostatic charges on said second surface of said web; and with the further assistance of a power source connected between said backing roller and said coating applicator; and d) coating the web at the coating point at a web speed greater than or equal to 75 meters/minute.
- 19. A method in accordance with claim 18 wherein said electrostatic field has a strength equivalent to that produced by applying a voltage differential of at least about 300 V between said backing roller and said applicator.
DESCRIPTION
This application is a continuation in part of U.S. patent application Ser. No. 09/185,045 filed Nov. 3, 1998 now abandoned.
US Referenced Citations (6)
Foreign Referenced Citations (1)
Number |
Date |
Country |
530 752 |
Oct 1993 |
EP |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
09/185045 |
Nov 1998 |
US |
Child |
09/396098 |
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US |