US 3396308 A
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Description (OCR text may contain errors)
Aug. 6, 1968 T. c. WHITMORE WEB TREATING DEVICE Filed July 2. 1965 THOMAS c. WH/TMORE INVENTOR. BY flZku/M ATTORNEY 8 AGENT United States Patent ice 3,396,308 WEB TREATING DEVICE Thomas Clement Whitmore, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed July 2, 1965, Ser. No. 469,157 3 Claims. (Cl. 317-4) ABSTRACT OF THE DISCLOSURE A device for generating a flow of ionized gas which is provided with an opening through which the gas is directed toward a surface of a sheet of dielectric material for altering the electrostatic condition thereof. The device is grounded through a resistor connected to electrically conductive portions adjacent the opening for directionally increasing the flow of ionized gas through the opening.
The present invention relates to apparatus for treating the surface of a web and more particularly to apparatus for generating a flow of ionized gas that is directed toward and against the surface of a dielectric web for altering or changing the electrostatic charge on the web and for removing particulate matter.
A flow of ionized air can be applied to a web by an air nozzle, but such a device is satisfactory only for a narrow web or one of a very limited width because the ionized air directed toward and against the web is not uniformly concentrated; that is, the highest concentration of such ionized air is directly under the nozzle and decreases toward the outer edge of the air flow. Another method of discharging the electrostatic charge on a web is to blow charged or ionized air at the edge or edges of the web so that the air flows across the web surfaces. Since the charge in such a system decays very rapidly, the system is limited in its use to a very narrow web.
One object of the present invention is to provide a small compact unit which can be conveniently attached to apparatus adjacent a dielectric web for generating a flow of ionized gas that can then be directed toward and against a surface of the web for altering any electrostatic charge thereon.
Another object of the invention is to provide an apparatus which generates and directs a substantially uniform flow of ionized gas toward and against a moving dielectric web for generating a flow of ionized gas that can then be directed toward and against a surface of the web for altering any electrostatic charge thereon.
Another object of the invention is to provide an apparatus which generates and directs a substantially uniform flow of ionized gas toward and against a moving dielectric web for altering or changing the electrostatic charge on the web and for removing particulate matter from the web.
The aforementioned objects of the invention are attained by a device having corona discharge means arranged within a housing having an opening that is of suflicient length so that it extends across and beyond the side edges of a moving web. A flow of ionized gas is directed through the opening toward and against the web across its entire width, thereby uniformly altering or changing the electrostatic charge on the web and which, depending on the particular application, can also be used to remove any particulate matter that has accumulated on the web. Preferably, such a device is arranged on each side of the web and can be used With either an AC or DC source of potential depending on the type of material to be treated. While the device is described hereinafter as being used for removing or substantially altering electrostatic charges on a web of photographic material, it
Patented Aug. 6, 1968 can also be used with any web or sheet of dielectric material to alter the charge, that is, to change the charge from a negative one to a positive one, or vice versa, to change the charge on the web, that is, increase or decrease the charge whether it is a negative or a positive one, or to place a negative or a positive charge on an uncharged web. The term alter or altering as used in this specification and in the claims is intended to include any one of the aforementioned conditions.
The term corona discharge device or means as used in this specification and in the claims is intended to define a self-sustaining electrical discharge device for generating positive and/or negative ions in accordance with the applied voltage; that is, with alternating current applied to the corona discharge device, positive ions will be generated on the positive half of the cycle, whereas negative ions will be generated on the negative half, and with direct current, positive or negative ions will be generated in accordance with the direction of current flow.
Still other objects and advantages of the present invention will be readily apparent to those skilled in the art from the following description with respect to the drawing in which like characters denote like parts and wherein:
FIG. 1 is a perspective view showing one arrangement of a pair of devices incorporating the invention in which said devices are arranged on opposite sides of and adjacent to a moving web, one of the devices having an end plate removed to show the arrangement of the corona discharge means within the housing;
FIG. 2 is a vertical, sectional view through one of the devices showing one embodiment of the invention and a simplified circuit for generating a corona discharge;
FIG. 3 is a vertical sectional view through one of the devices showing another embodiment of the invention; and
FIG. 4 is a vertical sectional view through another form of the device disclosed in FIGS. 13 and showing still another embodiment of the invention.
With reference to FIGS. 1-3, the device 10 comprises an elongated hollow housing 11 which provides a substantially enclosed chamber 12 when each of the ends is covered by an end plate 13. The housing has a cross section, substantially as shown in FIGS. 2 and 3, with tapered sides 14 that terminate in a pair of lips 15 that form a narrow, elongate-d slot 16. The housing 11 can be made of metal (FIG. 2) or, preferably, of a high dielectric material (FIG. 3). The length of the housing 11 is such that the slot 16 extends across and beyond the edges 18 of a moving dielectric web W. An opening 17 is provided in one or both of end plates 13 for receiving suitable connector means 19 to which a source of air or a suitable gas, under pressure is connected.
If the housing 1.1 is made of an electrical conducting material, a strip 20 of a dielectric material is secured to the sides 14 on the inner surfaces thereof, adjacent slot 16, as shown in FIG. 2. Such insulation within the chamber 12 is necessary in order that sufficient voltage can be applied to a corona discharge device 21 positioned within chamber 12 so that a desired ionized field is generated without arcing across to the sides 14 of the housing 11, and at the same time reducing the possibility of arc breakdown of the corona in the immediate vicinity of the slot 16. The thickness of the dielectric strip 20 should be sufficient to prevent such electrical breakdown in the anticipated operating voltage range. The strips 20 therefore serve to make the chamber 12 electrically safe, thereby removing any shock hazard to operating personnel. Such strips can be of poly(tetrafluoroethylene) tape, electrical tape, rubber tape, polyethylene terephthlate tape,
or an insulating lacquer can be used in place of the strips 20.
The corona discharge device 21 comprises a rod 22 which extends the length of the housing 1.1 and supports a plurality of needle-like electrodes 23 that are arranged and fixed in spaced relation along rod 22 with the ends 24 in close proximity to the slot 16. The rod 22 is adjustably mounted in a slot 25 in each of end plates 13 to permit the ends 24 of the electrodes 23 to be properly positioned relative to slot 16. The electrodes 23 can also be adjustably mounted in rod 22 to position each electrode individually relative to slot 16.
A voltage source 28, which can be either an AC or DC source, is connected by line 29 to rod 22 and to ground via line 30. The lips are connected through a fixed or variable resistor 31 to ground, or can be connected directly to ground. When the lips 15 are connected directly to ground, an increased ion flow is obtained. However, the ion flow can be further increased and, at the same time, the device can be made more safe electrically, if the lips 15 are connected to ground through the resistor 31, thereby reducing the corona current and increasing the ion current. When the housing 11 is made of a dielectric material, see FIG. 3, suitable conducting strips 32 are connected directly to ground or through resistor 31 in the same manner as lips .15. Optionally, the end plates 13 can be connected to ground in the same manner.
The means for moving the ions generated by the corona discharge means 21 into contact with a surface of web W is a stream of gas that is expelled from chamber 12 through the slot 16 toward and against the web W. Since the lips 15, or the strips 32, are grounded, the ion flow toward the web W is increased by the increase in electric field. The gas that is introduced into the chamber 12 via opening 17 can be air, nitrogen or one of the noble gases. Chemically active gases can also be used in this device to improve treatment of the web.
Depending on the dielectric material to be treated, a device 10 can be arranged normal to or at an angle to a surface of the material. As disclosed in FIG. 1, the devices 10 are preferably arranged at an angle to the surfaces of a moving web W to provide a uniform flow of the ionized gas onto the surface of the web for altering any electrostatic charge and for removing any particulate matter. The distance between the surface of the web and the lips of its respective device 10 will vary in accordance with the material that is to be treated. This distance is dependent on the air pressure used, the ion output of the corona device, and the speed and type of web being treated.
The minimum electrical voltage that is required to generate a corona discharge is dependent on the distance between the electrodes 23 as well as the shape of the electrodes. In addition, other factors which affect the minimum voltage to produce a corona discharge are the type of gas that is used, including its chemical composition, temperature, pressure, velocity and humidity, and the dielectric material used for the housing 1.1 or the strips as well as the shape of the slot 16.
The operation of the device 10, as described thus far, can best be understood from an actual example of one of its uses. In a photographic contact printer or an enlarger printer in which prints are made from a positive or negative film, or of each image on a roll of positive or negative film, it is desirable that any electrostatic charge that is present on the film be removed or substantially altered prior to entry of the film into the printing station. This reduces the possibility of the film attracting or picking up any ambient dust, etc., prior to printing due to any electrostatic charge. It is also desirable that any charge on the film be removed prior to printing to reduce the possibility of adherence of the film to the photographic paper or the film gate, thereby facilitating the positioning of one relative to the other in the printing station.
For such an operation, a device 10 is arranged on each side of web W with the slots 16 adjacent its respective surface of the web. The devices 10 are angularly disposed so that the flow of ionized air emitted by slots 16 is directed toward and against the surfaces of web W as shown in FIG. 1, thereby also serving to remove any particulate matter on the surfaces of the web. Although the source 28 applied to device 10 can be a v., AC, 60 cycle source, such a source of potential will produce a corona discharge that is less than satisfactory for some applications. A higher voltage applied to device 10 produces a more satisfactory corona discharge for treating a web to alter its electrostatic charge. As is known, if the voltage frequency is increased, the breakdown voltage of the corona decreases and, under some conditions, this can result in an increase of the ion current. In the present example, it was found that very satisfactory results are obtained when a 60 cycle AC potential of 3,600 volts is used as a source 28, and air under pressure of approximately ten p.s.i.g. is introduced into chamber 12. With such a voltage applied to electrodes 23 and the lips .15 or strips 32 connected to ground, a current of approximately 30 microamperes is obtained, when measured between the lips 15 or strip 32 and ground. As the air moves past the electrodes 23 toward slot 16, it is ionized by the corona and is directed by slot 16 toward and against the surface W, the ion current measured in the air between lips 15, or strips 32, and the surface of web W is approximately 3 1()- amperes. Since an AC source is used, the air is alternately ionized with a positive and a negative charge. The web, if already charged, self-selects the polarity and number of ions required to alter this charge on the web.
It has been found that when the ground connection is made in close proximity to the end of electrodes 23 that the ion current is increased and the corona current is decreased so that an increased flow of ions is obtained, as compared to merely connecting any part of the housing 11 to ground; that is, when the housing is made of a conducting material. For this reason, the housing 11 is preferably made of a dielectric material with conducting strips 32, as shown in FIG. 3.
As in the above example, the flow of ions can be increased by reducing the total corona current and increasing the ion current so that the efficiency of the device is improved toward substantially 100 percent, the efficiency being measured as the ratio of ion current to total corona current. This can be accomplished when the lips 15, or strips 32, are connected to ground through the resistor 31. With a 3,600 volt, 60 cycle, AC source of potential, air under pressure of 10 p.s.i.g. and a resistor 31 of megohms connecting lips 15 or strips 32 to ground, it has been found that less than one microampere of total corona current is present between lips 15, or strips 32, and ground, and the air (ion) current measures approximately .42 10- amperes. An increased flow of ions due to the ground connection through resistor 31 at lips 15 or strips 23 is therefore obtained.
In FIG. 4 another embodiment of the invention is disclosed in which a device 35 comprises a housing 36 having a chamber 37 in which a corona discharge device 38 is arranged and into which a supply of air under pressure is introduced via opening 17'. In this embodiment, the end 39 of the housing that is positioned adjacent the moving web W is enclosed with a plate 40 having a plurality of openings 41 that are aligned with electrodes 42 which, in turn, are suspended from a rod 43 in the same manner as described above. As in the embodiment described above with respect to FIGS. 2 and 3, the rod 43 is connected to a suitable AC source of potential 45 via line 46. The plate 40 is an electrical conducting material which is connected directly, .or through a resistor 44, to ground. Results comparable to those obtained with the device 10 shown in FIGS. 2 and 3 can be obtained by the device shown in FIG. 4, provided the location of openings 41 relative to each other is such that they provide a uniformly concentrated flow of ionized air across the web.
It will be recognized by those skilled in the art that the devices and 35 can be used with a suitable AC or DC source of potential. Also, the present invention can be supplemented by means for measuring the amount and polarity of any electrostatic charge on a web prior to its being moved between a pair of devices 10, as shown in FIG. 1, in order that the voltage, air velocity, etc. can be varied to provide the required ionized flow of air to alter or change the electrostatic charge on the web.
The invention has been described in detail with particular reference to preferred embodiments therof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. Apparatus for generating a flow of ionized gas that is directed toward a dielectric material for altering the electrostatic condition thereof, said apparatus comprising:
a housing having a chamber connected to a source of pressurized gas, said chamber including a pair of opposed converging walls which form at least one opening that can be arranged in close proximity to a surface of said material for directing a uniform flow of said gas onto said surface, each of said walls having an electrically conductive portion extending inwardly from and adjacent said opening and an electrically insulating portion contiguous to and coextensive with said electrically conductive portion; and
corona discharge means comprising at least one needle mounted within said chamber between said electrically conductive portions with one end of said needle connected to a source of potential and the other end arranged between and in close proximity to the electrically conductive portions of said walls for generating an ionized zone between said opening and the surface of said material;
the electrically conductive portion of said walls being electrically grounded through a resistor for directionally increasing the flow of ionized gas through said opening.
2. Apparatus for generating a flow of ionized gas that is directed toward a dielectric material for altering the electrostatic condition thereof, said apparatus comprising:
an electrically conductive housing having a chamber connected to a source of pressurized gas, said chamber including a pair of opposed converging walls which form an elongated slot that can be arranged in close proximity to a surface of said material for directing a uniform flow of said gas onto said surface;
a strip of dielectric material secured to the inner surface of each of said walls in spaced, generally parallel relation to said slot for electrically insulating at least a portion of each of said walls; and
5 corona discharge means comprising a plurality of needles arranged in spaced, parallel alignment within said chamber and between said strips, the one end of said needles being connected to a source of potential and the other end of said needles being arranged in close proximity to the electrically conductive por- 10 tion of said walls adjacent said slot, for generating an ionized zone between said slot and the surface of said material;
the electrically conductive portion of said walls adjacent said slot being electrically grounded through a resistor for directionally increasing the flow of ionized gas through said slot.
3. Apparatus for generating a flow of ionized gas that is directed toward a dielectric material for altering the electrostatic condition thereof, said apparatus comprising:
a dielectric housing having a chamber connected to a source of pressurized gas, said chamber including a pair of opposed converging walls which form an elongated slot that can be arranged in close proximity to a surface of said material for directing a uniform flow of gas onto said surface;
a strip of electrically conductive material secured to the inner surface of each of said walls adjacent said slot; and
corona discharge means comprising a plurality of needles arranged in spaced, parallel alignment within said chamber, the one end of said needles being connected to a source of potential and the other end of said needles being arranged between and in close proximity to said strips, for generating an ionized zone between said slot and the surface of said material;
said strips being electrically grounded through a resistor for directionally increasing the How of ionized gas through said slot.
References Cited UNITED STATES PATENTS FOREIGN PATENTS 9/1932 Germany. 3/1957 England.
LEE T. HIX, Primary Examiner.
J. A. SILVERMAN, Assistant Examiner.