Electrostatic spray apparatus and method

Claim 3

The method of claim 1 wherein said charge-removing step includes conducting electrical charge from the exterior surface of said conduit by electrically connecting said exterior conduit surface at a point proximate said spray device to a potential source having a potential substantially lower than the coating charging potential.

Claim 4

The method of claim 1 wherein said charge-removing step includes conducting electrical charge from the exterior surface of said conduit by electrically connecting said exterior conduit surface at a point proximate the coating supply to a potential source having a potential substantially lower than the coating charging potential.

Claim 5

The method of claim 1 wherein said charge-removing step includes conducting electrical charge from the exterior surface of said conduit by electrically connecting said exterior conduit surface at a first point proximate said spray device and at a second point proximate said coating supply to a potential substantially lower than the coating charging potential.

Claim 6

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a source of high voltage unidirectional electrical current, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, an electrically conductive element electrically connected to said high voltage source and located to electrically charge said coating material prior to coating said object, and a coating conduit interconnecting said spraying device and said coating supply having a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. an inner zone surrounding said bore, said inner zone including material which is substantially chemically inert and impermeable to said coating material, b. an outer zone of electrically conductive material surrounding said inner zone, said outer zone being electrically connected to a source of electrical potential substantially lower than said potential of said high voltage source, and c. an intermediate zone between said inner and outer zones, said intermediate zone including dielectric Material, said inner and intermediate zones having dielectric constants and radial thicknesses selected to avoid dielectric breakdown therein when subjected to the potential difference existing between 1) the interface of said transported coating and inner zone and 2) said outer zone, said inner and intermediate zones having resistivities collectively permitting electrical current leakage from said transported coating in said bore to said outer zone in an amount which, if allowed to accumulate, would electrically charge said outer zone to a measurable level and produce unsafe operator electrical shock and/or explosive atmosphere ignition hazards.

Claim 7

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a source of high voltage unidirectional electrical current, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, an electrically conductive element electrically connected to said high voltage source and located to electrically charge said coating material prior to coating said object, and a coating conduit interconnecting said spraying device and said coating supply having a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. an inner zone surrounding said bore, said inner zone including material which is substantially chemically inert and impermeable to said coating material, b. an outer zone of electrically conductive material surrounding said inner zone, said outer zone being electrically connected to a source of electrical potential substantially lower than said potential of said high voltage source, and c. an intermediate zone between said inner and outer zones, said intermediate zone including dielectric Material, said inner and intermediate zones having dielectric constants and radial thicknesses selected to avoid dielectric breakdown therein when subjected to the potential difference existing between 1) the interface of said transported coating and inner zone and 2) said outer zone, said inner and intermediate zones having resistivities collectively permitting electrical current leakage from said transported coating in said bore to said outer zone in an amount which, if allowed to accumulate, would electrically charge said outer zone to a measurable level and produce unsafe operator electrical shock and/or explosive atmosphere ignition hazards.

Claim 8

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a source of high voltage unidirectional electrical current, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, an electrically conductive element electrically connected to said high voltage source and located to electrically charge said coating material prior to coating said object, and a coating conduit interconnecting said spraying device and said coating supply having a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. a first zone surrounding said bore, said first zone including electrically conductive material connected to a source of electrical potential substantially lower than said potential of said high voltage source, and b. a second zone between said bore and said first zone, said second zone including material which is substantially chemically inert and impermeable to said coating material, said second zone including dielectric material constructed to avoid dielectric breakdown therein when subjected to the potential difference existing between 1) said transported coating and 2) said first zone, said second zone having a resistivity permitting electrical current leakage therethrough from said transported coating in said bore to said first zone in an amount which would, if allowed to accumulate, electrically charge said second zone to a measurable level and produce unsafe operator electrical shock and/or explosive atmosphere ignition hazards.

Claim 9

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a source of high voltage unidirectional electrical current, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, an electrically conductive element electrically connected to said high voltage source and located to electrically charge said coating material prior to coating said object, and a coating conduit interconnecting said spraying device and said coating supply having a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. a first zone surrounding said bore, said first zone including electrically conductive material connected to a source of electrical potential substantially lower than said potential of said high voltage source, and b. a second zone between said bore and said first zone, said second zone including material which is substantially chemically inert and impermeable to said coating material, said second zone including dielectric material constructed to avoid dielectric breakdown therein when subjected to the potential difference existing between 1) said transported coating and 2) said first zone, said second zone having a resistivity permitting electrical current leakage therethrough from said transported coating in said bore to said first zone in an amount which would, if allowed to accumulate, electrically charge said second zone to a measurable level and produce unsafe operator electrical shock and/or explosive atmosphere ignition hazards.

Claim 10

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, coating charging apparatus for electrically charging said coating material prior to coating said object, and a coating conduit interconnecting said spraying device and said coating supply, said conduit including a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. a first zone surrounding said bore in electrical contact with said transported coating, said first zone including dielectric material for avoiding dielectric breakdown of said first zone when contacted by electrically charged coating material transported in said bore, and b. a second zone surrounding said first zone, said second zone including electrically conductive material connected to an electrical potential source of lower potential than the potential of said transported coating for preventing accumulation of electrical charge radially interiorly of said second zone occasioned by electrical current conduction radially through said first zone.

Claim 11

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, coating charging apparatus for electrically charging said coating material prior to coating said object, and a coating conduit interconnecting said spraying device and said coating supply, said conduit including a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. a first zone surrounding said bore in electrical contact with said transported coating, said first zone including dielectric material for avoiding dielectric breakdown of said first zone when contacted by electrically charged coating material transported in said bore, and b. a second zone surrounding said first zone, said second zone including electrically conductive material connected to an electrical potential source of lower potential than the potential of said transported coating for preventing accumulation of electrical charge radially interiorly of said second zone occasioned by electrical current conduction radially through said first zone.

Claim 12

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, coating charging apparatus for electrically charging said coating material prior to coating said object, and a coating conduit inteconnecting said spraying device and said coating supply, said conduit including a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. a dielectric wall surrounding said bore and having a zone in contact with the coating which is substantially chemically inert and impermeable to said coating, said dielectric wall withstanding electrical breakdown when subjected to the coating charging potential, said dielectric wall permitting only an insubstantial electrical current flow in a radial dirction, and b. charge conduction means for removing charge from said wall occasioned by said radial electrical current conduction.

Claim 13

An electrostatic spray coating system comprising: a supply of at least moderately electrically conductive coating material, a coating spraying device located remote from said coating supply for spraying coating material onto an object to be coated, said object being maintained at an electrical potential different from said high voltage source, coating charging apparatus for electrically charging said coating material prior to coating said object, and a coating conduit inteconnecting said spraying device and said coating supply, said conduit including a bore through which coating material is transported from said coating supply to said spray device, said conduit including a. a dielectric wall surrounding said bore and having a zone in contact with the coating which is substantially chemically inert and impermeable to said coating, said dielectric wall withstanding electrical breakdown when subjected to the coating charging potential, said dielectric wall permitting only an insubstantial electrical current flow in a radial dirction, and b. charge conduction means for removing charge from said wall occasioned by said radial electrical current conduction.

Claim 14

An electrostatic coating spray system comprising: a coating spray device, an antenna fixed relative to said spray device, a source of high voltage unidirectional current, said source electrically connected to said antenna to electrostatically charge coating material prior to deposition thereof on an object to be coated, a source of moderately conductive coating material, a hollow coating conduit interconnecting said coating source and said spray device for transporting coating material to said spray device, said conduit having a dielectric wall with a zone in contact with the coating which is substantially chemically inert and impermeable to said coating, said wall constructed to withstand dielectric breakdown when subjected to an electrical potential by electrically charged coating material in said conduit, and charge removal means electrically connected to the exterior surface of the said dielectric wall for removing therefrom electrical charge which has been conducted radially through said wall from electrically charged coating material in said conduit.

Claim 15

An electrostatic coating spray system comprising: a coating spray device, an antenna fixed relative to said spray device, a source of high voltage unidirectional current, said source electrically connected to said antenna to electrostatically charge coating material prior to deposition thereof on an object to be coated, a source of moderately conductive coating material, a hollow coating conduit interconnecting said coating source and said spray device for transporting coating material to said spray device, said conduit having a dielectric wall with a zone in contact with the coating which is substantially chemically inert and impermeable to said coating, said wall constructed to withstand dielectric breakdown when subjected to an electrical potential by electrically charged coating material in said conduit, and charge removal means electrically connected to the exterior surface of the said dielectric wall for removing therefrom electrical charge which has been conducted radially through said wall from electrically charged coating material in said conduit.

Claim 16

An electrostatic coating spray system of claim 9 wherein said dielectric wall has an electrical resistance sufficiently low to permit electrical current to flow therethrough from said charged coating in said conduit in an amount which would, if allowed to accumulate, electrically charge said exterior surface of said dielectric wall to a measurable level and produce unsafe operator electrical shock and/or explosive atmosphere ignition hazards.