US3757164A

US3757164A - Neutralizing device

Info

Publication number: US3757164A
Application number: US00055825A
Authority: US
Inventors: L Binkowski
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1970-07-17
Filing date: 1970-07-17
Publication date: 1973-09-04
Anticipated expiration: 1990-09-04
Also published as: JPS4784U; JPS5625000Y2; DE7127878U; AU3131371A

Abstract

An inexpensive and effective neutralizing device for reducing the potential of static electrical charges present on a sheet or web comprised of supple, resilient, conductive filaments of minute diameter attached to a support and means for electrically connecting the filaments to a ground potential. The device may be positioned to make complete and intimate electrical contact with a surface through the extended tips of the filaments to conduct away static electrical charges present thereon without exerting a significant pressure against the contacted surface, or may be positioned to space the tips of the filaments from the web for use as an effective induction neutralizer.

Description

United States Patent 1 m1 3,757,164 Binkowski 1 Sept. 4, 1973 NEUTRALIZING DEVICE Primary ExaminerL. T. Hix t: .Bk k,St.P l,M [75] 0W5 AttorneyAlexander, Sell, Steldt & Delahunt [73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, [57] ABSTRACT An inexpensive and effective neutralizing device for re- 22 Filed; July 17 1970 ducing the potential of static electrical charges present on a sheet or web comprised of supple, resilient, con- [21] Appl' 55,825 ductive filaments of minute diameter attached to a support and means for electrically connecting the fila- 52 us. CI 317/2 1: ments to a ground potential- The device y be P 51 Int. Cl. nosr 3/00 tiehed to make complete and intimate eleetrieel [58] Field of Search 317/2 R teet with a Surface through the extended p of the ments to conduct away static electrical charges present 5 References Cited thereon without exerting a significant pressure against UNITED STATES PATENTS the contacted surface, or may be positioned to space the tips of the filaments from the web for use as an ef- 32:21:36 fective induction neutralizer 2,426,315 8/1947 Marick 317/2 R 8 Claims, 3 Drawing Figures Pmmmw' 5.157.164

I N VEN'TOR. 150.1 BIN/(0116K! NEUTRALIZING DEVICE BACKGROUND OF THE INVENTION This invention relates to an improvement in apparatus for reducing static electrical charges on the surface of an object and in one aspect to an apparatus for reducing static electrical charges on the surface of a moving sheet or web.

Static electrical charges are generated on a dielectric web or sheet material by contact with charged rollers or webs or by frictional contact with stationary guide surfaces necessary to transport it through a handling apparatus. The build-up of these charges can be a severe problem. Such static electrical charges can cause the conveyed material to be attracted to other like material or to portions of the handling apparatus, thus interferring with proper functioning of the apparatus. Additionally, the static electrical charges present on a sheet or web may attract dust, may present a dangerous annoyance to operators, or may present an explosion hazard in an explosive atmosphere. Thus, many types of devices have been used to reduce or remove static electricity on a dielectric web or sheet material.

Included among the devices used are high-voltage and radioactive neutralizers. These devices ionize the air around an adjacent surface to afford a path to ground through the ionized air and the neutralizer to conduct away electrostatic charges on a surface contacted by the ionized air. One disadvantage of these devices is that they are relatively expensive to operate, as they require either a radioactive source which requires occasional replacement, or a high voltage potential which must be generated.

Another type of device used in the induction neutralizer which comprises a multiplicity of pointed conductive metal projections extending from an electrically grounded support which may be spaced from the path of a web or sheet. Static electrical charges on the section of a web or sheet passing the induction neutralizer induce an opposite charge on the projections which charge ionizes the air between the projections and the surface of the web or sheet to afford a path to ground for static electrical charges on the passing web or sheet. With the induction neutralizer, the degree of ionization or the extent to which a charge may be reduced on a sheet or web is dependent upon among other things, the gap between the projections and the surface of the web or sheet, and upon the quantity and sharpness of the conductive projections. Building a highly compact and effective induction neutralizer with a high population of extremely sharp projections is difficult withthe metal projections of the prior art induction neutralizers. Additionally, the relatively inflexible projections of prior art induction neutralizers are difi'icult to space from a web or sheet for the most effective static reduction, as the optimum spacing for the projection varies with the static charge on a surface, which charge may vary along a web, from sheet to sheet, from day to day with humidity conditions, or between various materials being handled.

Contact neutralizers are also used to reduce static electrical charges on a dielectric surface. These devices generally comprise a multiplicity of metal projections on an electrically grounded support which may be positioned transverse to the path of a sheet or web and be spaced so that the projections come into physical contact with successive sections of the surface of a passing sheet or web. These prior art devices also have disadvantages. First, when the contact neutralizer is used on a sheet or web having a delicate surface or coating, the relatively stifi metal projections may scratch or mar the coating or surface. Additionally, the physical size and configuration of the metal projections generally precludes complete and intimate contact between the end of a projection and all points on the surface of a sheet or web moving across the neutralizer unless large numbers of such projections are used as by extending the device along the path of the sheet or web. Also, the contact pressure that results between a passing sheet or web and the relatively stiff metallic projections of prior art contact neutralizers may tend to divert a sheet or web traveling along a path or to slow its speed so that the handling of sheet is not orderly and predictable. Similar difficulties are encountered when metallic grounding rollers are added along the path of a sheet or web, and even when such rolls can be properly incorporated into the design of a device which handles a web or sheets, the cost of manufacturing and mounting such rollers may be relatively high.

SUMMARY OF THE INVENTION I The present invention is a neutralizing device for reducing the potential of, static electrical charges on a sheet or web without danger of marring, scratching, blocking, or diverting a sheet or web. The device comprises a multiplicity of resilient, supple, conductive organic filaments of minute diameter which are supported by a conductive support. The filaments of the device are grounded to provide a conductive path to reduce static electrical charges present on an adjacent surface. The support of the device may be spaced from a surface to provide complete and intimate contact between the extended ends of the filaments and the portion of the surface moved under the device to afford contact neutralization of static electrical charges present thereon. Under these conditions the contact pressure between the filaments and a contacted surface is extremely low, thus substantially eliminating the possibility that the device will slow, divert, or damage a surface moved past the device. Alternatively, the present invention may be positioned in spaced relationship with a surface from which static electrical charges are to be removed. In this position the filaments present a multiplicity'of sharpprojections to allow the device to act as a highly'efficient induction neutralizer for the removal of static electrical charges from a surface moved past the device.

When the device is primarily used as either a contact or an induction neutralizer, a number of the filaments at the edge of the device flex to position their tips in a spaced relationship with the sheet or web apparently to remove by induction a portion of the charge thereon. It is theorized that this self-spacing of some of the filaments accounts for the fact that the present device when used as an induction neutralizer tends to produce consistent static electrical charge reduction from various levels of charge on a sheet or web without varying the spacing of the device from the path of the sheet or web.

The present invention is inexpensive to build and requires no exterior power sources. Additionally, the present invention is not affected by high temperature applications.

The present invention comprises a multiplicity of resilient, supple, electrically conductive carbonaceous filaments of minute diameter, physically attached to a supporting means. At least one end of each filament extends from the supporting means so that the distal ends of said filaments may extend toward a surface to afford a part of an electrical path for reduction of static electrical charges thereon. Means are also provided for electrically connecting the filaments to a ground potential so that the path for grounding static electrical charges may be complete. The filaments comprise thermochemically converted regenerated cellulose fiber starting material which has beenimpregnated with a salt composition and subsequently carbonized to produce a conductive fiber material.

DESCRIPTION OF THE DRAWING The invention will be further described with reference to the accompanying drawing wherein like numbers refer to like parts in the several views and wherein:

FIG. I is a fragmentary perspective view partly in section of one embodiment of a static eliminating device constructed in accordance with the present invention;

FIG. 2 is a fragmentary perspective view of a second embodiment of a static eliminating device constructed in accordance with the present invention; and

FIG. .3 is a perspective view of a pair of trays and of two static eliminating devices according to the present invention positioned relative to a tray on either side of a path for a sheet material passing therebetween into a receiving tray such as that of a collating machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, there is shown a neutralizing device according to the present invention. The device 10 comprises a support means which includes a pair of conductive supporting bars 11. A multiplicity of lengths of contiguously positioned electrically conductive carbonaceous fibers or filaments 12 are positioned between the bars and attached to the bars by the bars being connected by fastening means (not shown) such as bolts or rivets. A shield 14 is placed about the bars and filaments 12 at one end, which shield may bea potting compound 14 molded over the bars 11 and one end of the filaments 12-. The distalends ,of the conductive filaments 12 maybe extended toward a surface and may be brought-into physical contact with the surface to provide electrical contact and'a portion of an electrical path to conduct away static electrical charges cellulose fiber starting material to corresponding black insulative organic fiber material and then carbonizing the latter to provide corresponding conductive fiber material according to U. S. Pat. Nos. 3,235,323 and 3,484,183. These carbonized fibers may contain carbon in proportions ranging from about 70 percent to higher than 99 percent (i.e., to 99+ percent), and can range in electrical conductivity from semiconductors to good conductors (the fiber resistivities ranging in order of magnitude from 10 to 10" ohm-cm.). These fibers are predominantly amorphous and even those of highest carbon content (99+ percent carbon) are not graphitized carbon, and are not graphite" carbon fibers per se, although some degree of polycrystalline graphitic type structure may be present as shown by X-ray diffraction patterns.

While a variety of conductive filaments may be produced according to the processes disclosed in U.S. Pat. Nos. 3,235,323 and 3,484,183, and while any of these filaments may be suitable for use in the static eliminating device of the present invention, one filament which has been utilized and which provides good results is sold commercially by Minnesota Mining and Manufacturing Company, Saint Paul, Minnesota, U.S.A., under the tradename Pluton and designated H-25 Roving. This filament is supplied in a non-twisted strand of about v720 individual filaments, each filament being only about 0.00034 inches in diameter. The strand has a denier of 625, and a breaking strength of over 3 pounds. "Pluton l-I-25 roving has a carbon content of 98.3 percent and the strands have an electrical resistance of 22 ohms per inch'of length.

The device 10 has about 40 lengths of the Pluton strands evenly distributed along each inch of the length of the, bars 11. Thus, the device 10 provides about 28,800 ends of the filaments 12 per inch of length of the bars 11 which will make intimate contact with and conduct static electrical charges away from a contacted surface when the device 10 is used as a contact neutralizer or which will provide sharp points to induce flow of static electricalcharges when the devide 10 is spaced from a surface and used as an induction neutralizer.

The carbonized filaments 12 are supple and resilient and have an inherent quality of elastic recovery which will afford repeated intimate contact with successive segments of surfaces passing the device 10. So long as a filament 12 is not fractured when bent, it will tend to thereon, or maybe spaced from the surface to present a multiplicity of projections'and to afford a portion of a conductive path for an inductive type static eliminator.

Means are also provided which will afford the electrical connection of the conductive filaments 12 to a body at ground potential. The filaments 12 are in electrical contact with each other and with the conductive bars 11, and when the bars 11 are at ground potential such as through a grounding wire 13 attached and electrically connected to one of the bars 11 there is provided a path to ground for electrical charges conducted through or induced to flow to the filaments 12.

The conductive filaments l2 utilized in the present invention are a conductive fiber material produced by a process of thermochemically converting regeneratedstraighten itself, unlike strands of the more conductive metals (i.e., silver and copper) which are extremely ductile and tend to bend permanently undera bending stress. I

The filaments 12 are sized so that each endwillv extend about seven-eighths of an inch beyond thepotting compound 14. At this length, the filaments 12 still have sufficient strength to remain erect regardless of the altitude at which the device 10 is positioned, and yet the filaments 12 are cantilevered for a sufficient length that they offer negligible resistance to a surface deflecting their ends, and may deflect as needed to seek a preferred height above the surface in response to the magnitude of the charge thereon for inductive reduction of the static electrical charges on the surface.

While the potting compound 14 used to bind the bars 11, and filaments 12 together may be of a conductive type, such a compound has not been found necessary for the electrical contact required in the device 10 and thus a non-conductive potting compound such as commercially available RTV Silicone Room temperature curing material has been found satisfactory to assemble the device 10.

Referring now to FIG. 2, there is shown a second embodiment of the static eliminating device according to the present invention generally designated by the numeral 20. The supporting means of the device is a conductive supporting rod 21 around wich are positioned a multiplicity of lengths of the conductive filaments 12. The filaments 12 are attached to the cylindrical bar or rod 21 by the potting compound 14 being placed on the filaments and the rod. A shield, such as a U-shaped conductive exterior shield 23, is then placed about the supporting rod with the flanges thereof extending in the direction of the filaments.

The generally U-shaped metal shield 23 provides a conductive connection between the filaments 12 which serves to protect the filaments l2 and provides a directing means to position the extending ends of the elastic filaments 12 in a row. A pair of edges 25 on the shield 23 are rounded by rolling the edge of the sheet metal back upon itself to prevent cutting of the filaments 12 when they are deflected against one of the edges 25. The shield 22 is formed with a pierced tab 27 at each end of the shield to afford a means to attach the device 20 to a support and to electrically connect the conductive shield 23 to a source of ground potential to complete an electrical path from the filaments 12 to a source of ground potential.

FIG. 3 shows a typical application for a pair of the static eliminating devices 20 which are shown positioned opposing each other on opposite sides of a path for a dieelectric sheet material 30 such as paper at the entrance to a tray 33 for collecting a stack 34 of sheets such as might be used on a collating machine or copying machine (not shown). The devices 20 are electrically connected to the frame of the tray 33 through attachment by the tabs 27 and have the potential of the frame, generally ground potential, and may be positioned with the distal ends of their filaments 12 in contact with each other or extending slightly past each other so that at least the filaments 12 will intersect the path for the sheet 30 and make complete intimate contact to neutralize by conduction static electric charges present on both sides of the sheet 30 passed therebetween. When so positioned the deflection of the supple filaments 12 will not have a noticeable effect on the speed or direction of travel of a passing sheet 30.

The force required to move a sheet or web over the device 10 is so low that it is diffficult to measure. Tests, however, have indicated that a weight of about onesixteenth ounce per inch of brush length is required to deflect the tips of the brush for the passage of a sheet of paper downward between two of the

devices

10 or 20 positioned with their filaments 12 tip to tip and oriented in a horizontal position.

The following is an example of the capabilities of the present invention for neutralization of static electrical charges. in a collator in which sheets are transferred from a copying machine to one of a series of trays at speeds of about 60 inches per second, electrical charges of up to 5000 volts on sheets received from the copying machine were increased under dry atmospheric conditions to up to 50,000 volts in the receiving trays. At this higher voltage, problems existed with proper stacking of sheets and subsequent separation of stacked sheets. The use of a pair of the devices prior to their entry into the trays as shown in FIG. 3 reduced the static electrical charges on the sheets received in the trays to an acceptable level of under 5000 volts under all atmospheric conditions.

Additionally, tests made under conditions of 55 percent relative humidity with two of the static eliminating devices positioned in opposed relationship on opposite sides of a paper web traveling 300 feet per minute and initially charged to 30,000 volts resulted in a reduction of the charge essentially to zero voltage both with the tips of the filaments 12 contacting the paper web, and with the tips spaced one-sixteenth inch from the web. Similar tests made with the static eliminating devices and an acetate web achieved voltage reduction to 2,000 volts.

Having thus described the present invention with reference to two embodiments, it will readily be understood that various modifications can be made in the structural details of the static eliminating devices without departing from the spirit of the invention as defined by the appended claims.

What is claimed is:

1. A device for neutralizing static electrical charges on a surface, said device comprising:

a support means;

a multiplicity of resilient, supple, electrically conductive filaments consisting of over percent carbon and being about 0.00024 inch in diameter, said filaments being positioned continguously on said support means with at least one end of each of said filaments extending in a uniform direction from said support means so that the distal ends of said filaments may extend toward a said surface to aflord reduction of any static electrical charges present on said surface; and

means for attaching said filaments to said support means.

2. A device according to claim 1 wherein said filaments are thermochemically converted regenerated cellulose fiber starting material which has been impregnated with a salt composition and subsequently carbonized to provide conductive fiber material of predominately amorphous carbon.

3. A device according to claim 1 wherein said filaments consist of 98.3 percent carbon.

4. A device according to claim 1 wherein said sup port means comprises at least one bar, and potting compound to attach said filaments to said bar.

5. A machine including at least one device for neutralizing static electrical charges on sheet material, comprising:' v

means for defining a path for said sheetmaterial;

support meanspositioned transverse to and extending across said path;

a multiplicity of electrically conductive, resilient,

supple filaments consisting of over 70 percent carbon and being about 0.00024 inch in diameter, said filaments being positioned contiguously along said support means with at least one end of each of said filaments extending from said support means toward and intersecting said path to afford reduction of static electrical charges present on sheet material moving along said path; and

means for attaching said filaments to said support means.

6. A machine according to claim 5 wherein said filaments are thermochemically converted regenerated ments consist of 98.3 percent carbon.

8. A machine according to claim 5 wherein said support means comprises at least one bar, and potting compound to attach said filaments to said bar.

# I k t mama swans MTENT OFFECE QER'EEEEATE 0F QQRPQEGEWN Patent No. 3,757,1 Dated Sep 973 Inventor(s) Leo J Binkowski It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 8, change "wich" to which line 2 change "shield 22" to shield 23 --.5 and line 33, change "dieelectr'ic" to dielectric Claim 1, line 6, change O. 0002 4 t0 0.0003 1 Claim 5, line 9, change "0.00024" to 0.0003 l Signed and sealed this 15th day of January 197A.

(SEAL) Attest:

EDWARD M. FLETCHER, JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents F OHM PO-105O (10-69) UNETED STATES PATENT GREECE CER'EEFICATE 0F CORRECTWN Patent No. 3,757, Dated September- 1973 Inventor(s) LeO J Binkowski It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 8, change "wich" to which line 2 change "shield 22" to shield 23 and line 33, change "dieelectr'ic" to dielectric Claim 1, line 6, change "0.0002 4 to 0.0003 1 Claim 5, line 9, change "0.00024" to 0.0003 1 Signed and sealed this 15th day of Janu ary lQTLL.

(SEAL) Attest:

EDWARD M. FLETCHER, JR. RENE D. TEGTMEYER Attesting Officer Acting; Commissioner of Patents FQRM PO-1050 (10-69') USCOMPWDC uava p69 4

Claims

1. A device for neutralizing static electrical charges on a surface, said device comprising: a support means; a multiplicity of resilient, supple, electrically conductive filaments consisting of over 70 percent carbon and being about 0.00024 inch in diameter, said filaments being positioned continguously on said support means with at least one end of each of said filaments extending in a uniform direction from said support means so that the distal ends of said filaments may extend toward a said surface to afford reduction of any static electrical charges present on said surface; and means for attaching said filaments to said support means.

4. A device according to claim 1 wherein said support means comprises at least one bar, and potting compound to attach said filaments to said bar.

5. A machine including at least one device for neutralizing static electrical charges on sheet material, comprising: means for defining a path for said sheet material; support means positioned transverse to and extending across said path; a multiplicity of electrically conductive, resilient, supple filaments consisting of over 70 percent carbon and being about 0.00024 inch in diameter, said filaments being positioned contiguously along said support means with at least one end of each of said filaments extending from said support means toward and intersecting said path to afford reduction of static electrical charges present on sheet material moving along said path; and means for attaching said filaments to said support means.

6. A machine according to claim 5 wherein said filaments are thermochemically converted regenerated cellulose fiber starting material which has been impregnated with a salt composition and subsequently carbonized to provide conductive fiber material of predominately amorphous carbon.

7. A machine according to claim 5 wherein said filaments consist of 98.3 percent carbon.