Spraying apparatus

• US 4,801,086 A
• Filed: 05/31/1988
• Issued: 01/31/1989
• Est. Priority Date: 02/19/1985
• Status: Expired due to Term

• Current Assignee: Battelle Memorial Institute
• Original Assignee: Imperial Chemical Industries PLC (Nouryon BV)
• Inventors: Noakes, Timothy J.
• Primary Examiner(s): Kashnikow, Andres
• Assistant Examiner(s): Forman, Michael J.
• Application Number:
  US07/201,330
• Time in Patent Office: 245 Days
• Field of Search: 239/3, 239/8, 239/690, 239/696, 239/704, 239/706, 239/707, 239/708, 239/419.3, 239/422, 239/424, 239/549, 239/568, 239/555
• US Class Current: 239/3
• CPC Class Codes: B05B 5/0255 spraying and depositing by electrostatic forces only

Abstract

An apparatus and process for the electrostatic spraying of a mixture of a plurality of liquids, suitably liquids which react together rapidly to form a solid, liquids which are physically imcompatible, or liquids, such as paints, to provide novel optical effects. The apparatus includes a sprayhead formed with a plurality of channels which communicate with a common outlet means. The liquids are supplied to respective channels and meet at the outlet means. There they are subjected to an electrical field which causes a mixture of the liquids to be drawn from the sprayhead in the form of one or more filaments, the or each filament constaining a mixture of liquids in the proportions equal or substantially equal to the proportions in which the liquids were supplied to the sprayhead.

Claims

1. An apparatus for the electrostatic spraying of a mixture of a plurality of liquids, the apparatus comprising a sprayhead formed with a plurality of channels, each channel having a separate inlet connectable to a supply of liquid separate from supplies to other of said channels, and each channel communicating with a common outlet means, the channels being so arranged that each of the said liquids flows through a respective one of the channels and the said liquids meet at said common outlet means only outside the channels, and means for subjecting liquids emerging from the outlet means to an electrical field sufficiently high for a mixture of liquids to be drawn from the sprayhead in the form of at least one filament, the said at least one filament containing a mixture of liquids in proportions substantially equal to the proportions in which they were supplied to the apparatus.

2. An apparatus as claimed in claim 1, wherein the sprayhead comprises a series of mutually spaced plates, and each channel is formed by the space between a pair of adjacent plates and the outlet means comprise an outlet edge of each of the plates.

3. An apparatus as claimed in claim 2, wherein the sprayhead comprises a central plate and two outer plates, a channel is formed between each outer plate and the central plate, and the outlet means comprises an outlet edge of each of the plates, the outlet edge of the central plate being located downstream of the outlet edges of respective outer plates.

4. An apparatus as claimed in claim 3, wherein an angle which is included between opposed sides of the central plate at the outlet edge thereof is smaller than the included angle between outer sides of respective outer plates.

5. An apparatus as claimed in claim 4, wherein the said angle between opposed sides of the central plate is between 10°

and 60°

, and the angle between outer sides of respective outer plates is between 80° and

150°

.

6. An apparatus as claimed in claim 1, wherein the sprayhead comprises a series of coaxially arranged, generally tubular elements, and each channel is formed by a space of generally annular section between two adjacent elements and the outlet means comprise axially outer edges of respective elements.

7. An apparatus as claimed in claim 6, wherein the sprayhead comprises radially inner, intermediate and outer guide elements, and the outlet means comprises axially outer edges of respective elements, the axially outer edge of the intermediate element being located downstream of the axially outer edges of the inner and outer elements.

8. An apparatus as claimed in claim 7, wherein an angle which, in an axial section of the sprayhead, is included between opposed sides of the intermediate element at the axially outer edge thereof is smaller than the angle between a radially outer side of the outer element and a radially inner side of the inner element.

9. An apparatus as claimed in claim 8, wherein the said angle between opposed sides of the intermediate element is between 10°

and 60°

, and the said angle between the radially outer side of the outer element and the radially inner side of the inner element is between 80° and

150°

.

10. An apparatus as claimed in claim 1, wherein the sprayhead comprises a body having a generally conical tip, and each channel extends through the body to an outlet at the tip of a the body and the outlet means comprise the outlets of respective channels.

11. An apparatus as claimed in claim 1, wherein the outlet means comprise a surface of at least semi-conducting material, and the means for subjecting the liquids to an electrical field comprise means for applying an electrical potential to the said surface.

12. An apparatus as claimed in claim 1, wherein the outlet means is formed of non-conducting material, and an electrode is arranged a short distance upstream of the outlet means and at a location such that the electrode is contacted, in use, by at least one of the liquids, the means for subjecting the liquids to an electrical field comprising means for applying an electrical potential to the said electrode.

13. An apparatus as claimed in claim 1, wherein an electrode is mounted adjacent the sprayhead, and the means for subjecting liquids emerging from the outlet means to an electric field comprise means for causing a first potential to be applied to the liquids and means for maintaining the electrode at a second potential, the difference between the first and second potentials being sufficient to cause formation of said at least one filament.

14. An apparatus as claimed in claim 13, wherein, for spraying a target at zero potential, the first potential is 1 to 20 KV and the second potential is at or near earth potential.

15. An apparatus as claimed in claim 13, wherein, for spraying a target at zero potential, the first potential is 25 to 50 KV and the second potential is 10 to 40 KV.

16. An apparatus as claimed in claim 13, wherein the electrode comprises a core of at least semi-conducting material sheathed in a material of dielectric strength and volume resistivity sufficiently high to prevent sparking between the electrode and the sprayhead and of volume resistivity sufficiently low to allow charge collected on the surface of the sheathing material to be conducted through that material to the at least semi-conducting core.

17. An apparatus as claimed in claim 16, wherein the volume resistivity of the sheathing material is between 5×

10¹¹ and 5×

10¹³ ohm. cms., the dielectric strength of the sheathing material is greater than 15 KV/mm. and the thickness of the sheathing material is 0.75 to 5.0 mms.

18. An apparatus as claimed in claim 16, wherein the thickness of the sheathing material is 1.5 to 3 mms.

19. An apparatus as claimed in claim 16, wherein the specific resistance of the sheathing material is between 5×

10¹⁰ and 5×

10¹².

20. An apparatus as claimed in claim 1, comprising means for supplying a plurality of liquids to the sprayhead such that said at least one filament becomes unstable and breaks up into charged droplets a short distance away from the outlet means.

21. An apparatus as claimed in claim 20, wherein means are provided for causing a stream of gas to flow through the region of the high electrical field, the direction and velocity of the stream of gas being such that charged droplets of liquid are removed from the said region, thereby to reduce a build-up in space charge which affects the magnitude of the electrical field.

22. An apparatus as claimed in claim 21, wherein the velocity of the stream of gas is approximately equal to or greater than the velocity of the droplets in the absence of the stream of gas.

23. An apparatus as claimed in claim 1, comprising means for supplying a plurality of liquids to the sprayhead such that the mixture of liquids remains in the form of at least one filament until striking a target.

24. A process for the electrostatic spraying of a plurality of different liquids comprising supplying each of the different liquids to respective channels in a sprayhead, each channel communicating with an outlet means at which the liquids flowing through respective channels meet, and subjecting liquids emerging from the outlet means to an electrical field sufficiently high for a mixture of liquids to be drawn from the sprayhead in the form of at least one filament containing a mixture of liquids in proportions equal to the proportions in which they were supplied.

25. An apparatus for the electrostatic spraying of a mixture of a plurality of liquids, the apparatus comprising a sprayhead formed with a plurality of channels, each channel having an inlet and each channel communicating with an outlet means, means for supplying the said liquids to respective inlets of the channels, whereby the liquids flow through respective channels and meet at the outlet means, and means for subjecting liquids emerging from the outlet means to an electrical field sufficiently high for a mixture of liquids to be drawn from the sprayhead in the form of at least one filament, said at least one filament containing a mixture of liquids in proportions substantially equal to the proportions in which they were supplied to the apparatus.

26. Apparatus for electrostatically spraying in plurality of different liquids in the form of a mixture of the different liquids, said apparatus comprising a sprayhead having a plurality of discrete flow channels, each channel having an inlet end for receiving a respective different liquid from a supply thereof and each channel having an outlet end communicating with a common outlet means for merging liquids flowing from said outlet ends of said channels, and means for subjecting liquids at said outlet means to an electrical field sufficiently high for a mixture of liquids from different channels to be drawn from the outlet means in the form of at least one filament which contains different liquids in proportions substantially equal to the proportions in which they were supplied to said inlet ends of said channels.