EP0101280A1

EP0101280A1 - Apparatus and method for applying a liquid to a surface

Info

Publication number: EP0101280A1
Application number: EP83304567A
Authority: EP
Inventors: Allan Willett; Michael Richard Keeling
Original assignee: Willett International Ltd
Current assignee: Willett International Ltd
Priority date: 1982-08-09
Filing date: 1983-08-08
Publication date: 1984-02-22
Also published as: ZA835807B; DK360683D0; AU1766083A; FI832839A0; FI832839A; DK360683A

Abstract

The invention provides apparatus and a method for applying a liquid to a surface. The apparatus comprises a nozzle (1) for directing a continuous stream of drops (5) of uniform size and spacing in a direction to traverse and not impinge on a surface (7) to which the liquid is to be applied, means (8,9) for effecting relative movement between a said stream of drops (5) and a said surface (7) in a direction perpendicular to the direction of travel of the stream of drops, charge electrode means (10) for selectively electrically charging the drops of liquid in said stream, and deflecting means (11 or 11,12) for establishing a steady electric field about the path of travel of said stream of drops for deflecting the electrically charged drops onto said surface.

Description

This invention relates to apparatus for and a method of applying a liquid to a surface.
The present invention has as its object to provide apparatus for and a method of applying a liquid to a surface which is suitable for use with a wide variety of liquids, such as inks and adhesives, which is non-contact in that there need be no contact between the liquid applying means and the surface to which the liquid is to be applied, and which enables a liquid to be accurately applied to selected positions on a surface.
The present invention provides .apparatus for applying a liquid to a surface, the apparatus comprising means for directing a continuous stream of drops of a said liquid in a direction to traverse and not impinge on a surface to which the liquid is to be applied, means for effecting relative movement between a said stream of drops and a said surface in a direction perpendicular to the direction of travel of the stream of drops, means for selectively electrically charging the drops of liquid in said stream, and means for establishing a steady electric field about the path of travel of said stream of drops for deflecting the electrically charged drops onto said surface.
The present invention also provides a method of applying a liquid to a surface, the method comprising directing a continuous stream of drops of a said liquid in a direction to traverse and not impinge on a surface to which the liquid is to be applied, effecting relative movement between the stream of drops and the said surface in a direction perpendicular to the direction of travel of the stream of drops, selectively electrically charging the drops of liquid in said stream, and deflecting the electrically charged drops onto said surface by establishing a steady electric field about the path of travel of the stream of drops.
Preferably the apparatus of the present invention comprises means for forming and directing a moving single stream of uniformly spaced and uniformly sized drops of liquid. Such means may comprise a nozzle for producing a continuous single stream of liquid and means for stimulating the nozzle to cause said stream to break up into drops of uniform size and spacing. The stimulating means may comprise a piezo electric crystal, e.g., may comprise a bimorph or unimorph.
The surface to which the liquid is to be applied may be the surface of an article such as a label or web of paper or other material, and the apparatus may comprise means for transporting such an article or succession of articles along a path which will be traversed by said continuous .stream of drops.
Where the electrically charged drops are to be deposited on a said surface in a straight line then the means for selectively electrically charging the drops of liquid in said stream may be adapted to apply the same charge to the selected drops. Preferably, however, the said means is adapted to place charges on the selected drops which vary according to the position along the path of traverse of a said surface that each drop is required to occupy on the said surface. By varying the charge on the selected drops and coordinating this with the movement of the said surface drops can be deposited on the surface in any selected position to enable the liquid to be applied to the surface in any required pattern or to enable characters or other images to be produced on the surface.
The means for establishing a steady electric field about the path of travel of said stream of drops may comprise opposed deflecting plates arranged on opposite sides of the path of travel of the stream of drops. The path of travel of the surface to which the liquid is to be applied may be between one of said deflector plates and the path of travel of the stream of drops.
The invention will be more particularly described with reference to the accompanying diagrammatic drawings, in which:-

Figure 1 is a diagrammatic view of one embodiment of apparatus according to the present invention,
Figure 2 is a diagrammatic side elevation of another embodiment of apparatus according to the present invention, and
Figure 3 is a diagrammatic side elevation of a further embodiment of apparatus according to the present invention.

Referring to Figure 1 it will be seen that the apparatus illustrated therein comprises a nozzle 1 having an inlet 2 whereby it can be connected to a source of liquid under pressure (not shown) and piezo electric stimulating means 3, e.g., in the form of a bimorph or a unimorph. The nozzle 1 is adapted to produce a single stream 3 of liquid which under the stimulation of the stimulating means 3 breaks up into uniformly spaced and uniformly sized drops 5 which are directed along a path towards a drain or gutter 6 which traverses and is perpendicular to the path of travel of a web 7 extending between a feed roller 8 and a take up roller 9. The apparatus further comprises a charge electrode or electrodes 10 for selectively variably charging the drops 5 and a pair of opposed deflector plates 11 which are arranged on either side of the path of travel of the drops 5 and which are suitably connected into an electric circuit (not shown) for applying either a positive or negative charge thereto so that a steady electric field will be established therebetween. The path of travel of the web 7 is between the lower deflector plate 11 and the path of travel of the stream of drops 5.
When the apparatus in Figure 1 is in use the uncharged drops 5 will pass in a straight line between the deflector plates 11 to the drain or gutter 6 whilst the charged drops 5 will be deflected onto the surface of the web 7 at a selected position across the width thereof depending upon the strength of the charge applied to each individual drop as indicated at 5a and 5b. By selectively varying the charge applied to the selected drops 5 and coordinating this with the speed of travel of the web 7 the selected drops 5 can be deposited at any required selected position on the web 7.
Where the width of the web 7 is such that the path of travel of the drops 6 becomes so long that it becomes difficult to accurately control the placement of the selected drops then a second nozzle 1 and associated charge electrode or electrodes may be located on the opposite side of the web 7 so that each nozzle 1 is adapted to supply drops for depositing oven say, half the width of the web 7.
With the apparatus of the present invention it is the more strongly charged drops which will be deflected onto that part of the web 7 nearest the nozzle 1 and the more weakly charged drops 5 which will be deflected onto that part of the web 7 which is furthest from the nozzle 1. Because those drops which carry the weaker charges have to travel the furthest and because these more weakly charged drops are less affected by the steady electric field between the deflector plates 11, their trajectories tend to be shallower so that they strike the surface of the web 7 at a more acute angle than the more strongly charged drops and accordingly tend to be deposited on the surface as an elliptical rather than a circular spot. Moreover, the further the more weakly charged drops have to travel so the less accurate can become their positioning on the surface 7. These difficulties can be overcome in the manner shown in Figure 2 or Figure 3 wherein like reference numerals have been used to indicate like parts.
In the embodiment of Figure 2 the upper deflector plate 11 has been replaced by a series of upper deflector plates 12 which carry increasingly stronger charges the further they are from the nozzle 1. Thus the strength of the steady electric field between the deflector plates 11 and 12 is of increasing strength the further it is from the nozzle 1 and this serves to steepen the trajectory of the more weakly charged drops as they are deflected towards the surface of the web 7.
A similar effect of a steadily increasing field strength and a more obtuse angle of deposit of the more weakly charged drops onto the surface of the web 7 is obtained with the embodiment of Figure 3 wherein the surface of the web 7 onto which the selected drops 5 are to be deposited and the lower deflector plate 11 progressively converge towards the upper deflector plate 11 and the path of travel of the drops 5 the further they are from the nozzle 1.

Claims

1. Apparatus for applying a liquid to a surface, the apparatus comprising means for directing a continuous stream of drops of a said liquid in a direction to traverse and not impinge on a surface to which the liquid is to be applied, means for effecting relative movement between a said stream of drops and a said surface in a direction perpendicular to the direction of travel of the stream of drops, means for selectively electrically charging the drops of liquid in said stream, and means for establishing a steady electric field about the path of travel of said stream of drops for deflecting the electrically charged drops onto said surface.

2. Apparatus according to claim 1, wherein said means for directing a continuous stream of drops of a said liquid comprises a nozzle for producing a continuous single stream of liquid and means for stimulating the nozzle to cause said stream to breakup into drops of uniform size and spacing.

3. Apparatus according to claim 2, wherein said stimulating means comprises a piezo electric crystal.

4. Apparatus according to claim 1, 2 or 3, comprising means for transporting along a path which will be traversed by said continuous stream of drops at least one article having a said surface to which liquid is to be applied.

5. Apparatus according to any one of the preceding claims, wherein said means for selectively electrically charging the drops of liquid in said stream comprises at least one charge electrode.

6. Apparatus according to claim 5, wherein said at least one charge electrode is adapted to apply the same charge to the selected drops whereby said drops will be deposited on a said surface in a straight line

7. Apparatus according to claim 5, wherein said at least one charge electrode is adapted to place charges on the selected drops which vary according to the position along the path of traverse of a said surface that each drop is required to occupy on the said surface.

8. Apparatus according to claim 7, wherein the variable charging of the selected drops is coordinated with the movement of a said surface relative to said stream of drops to enable any selected drop to be deposited at a selected position on said surface.

9. Apparatus according to any one of the preceding claims, wherein said means for establishing a steady electric field about the path of travel of said stream of drops comprises opposed deflecting plates arranged on opposite sides of the path of travel of the stream of drops.

10. Apparatus according to claim 9, wherein said opposed deflecting plates are parallel.

11. Apparatus according to claim 9 or 10, wherein said opposed deflecting plates comprise at least one series of deflector plates which carry increasingly stronger electrical charges the further they are along the path of said stream of drops from said directing means.

12. Apparatus according to claim 9, wherein said opposed deflecting plates progressively converge the further they are from said directing means.

13. Apparatus according to any one of claims 9 to 12, wherein the path of travel of said surface is between one of said deflecting plates and the path of travel of said stream of drops.

14. Apparatus according to any one of the preceding claims, wherein a drain or gutter is provided towards which said stream of drops is directed and in which the uncharged drops are collected.

15. A method of applying a liquid to a surface, the method comprising directing a continuous stream of drops of a said liquid in a direction to traverse and not impinge on a surface to which the liquid is to be applied, effecting relative movement between the stream of drops and the said surface in a direction perpendicular to the direction of travel of the stream of drops, selectively electrically charging the drops of liquid in said stream, and deflecting the electrically charged drops onto said surface by establishing a steady electric field about the path of travel of the stream of drops.