US3418930A

US3418930A - Electrostatic screen printing using a toner repelling screen

Info

Publication number: US3418930A
Application number: US496516A
Authority: US
Inventors: Kenneth W Rarey; Jr John B Kennedy
Original assignee: Continental Can Co Inc
Current assignee: Continental Can Co Inc
Priority date: 1965-10-15
Filing date: 1965-10-15
Publication date: 1968-12-31
Anticipated expiration: 1985-12-31

Description

Dec. 31, 1968 K. W. RAREY ETAL 3,418,930

ELECTROSTATIC SCREEN PRINTING USING A TONER REPELLING SCREEN Filed Oct. 15, 1965 Sheet of 2 MAGNH'UDE 26 I162 CONTROL. 3% 40 H \GH 44 Hvv. "Eg $UPPLY 48 5 E48 go 32 A 2 o i H 3U P PLY 2 INVENTORS 26 KENNETH u). RAREY EN HM BKENNEDQJr.

ATTORNEYS Dec. 31, 968 K. w. RAREY ETAL ELECTROSTATIC SCREEN PRINTING USING A TONER REPELLING SCREEN Sheet Filed Oct. 15, 1965 INVENTORS KENNETH m. RAIZEY uouu BKEMHEDYAI. m VJQ, M3, M

"IIIIIIIIIIIIIIIIIAI ATTORNEYS United States Patent 3,418,930 ELECTROSTATIC SCREEN PRINTING USING A TONER REPELLING SCREEN Kenneth W. Rarey, South Holland, and John B. Kennedy,

Jr., Chicago, Ill., assignors to Continental Can Compani, Inc., New York, N.Y., a corporafion of New Yor Filed Oct. 15, 1965, Ser. No. 496,516 Claims. (Cl. 101-114) ABSTRACT OF THE DISCLOSURE The disclosure relates to electrostatic screen printing wherein a toner-repelling screen is maintained at a potential which is like that induced upon the toner, and the toner is carried toward the toner-repelling screen by conductive carrier particles. Upon impact of the carrier particles and toner with the screen, the toner is dislodged from the carrier particles and is either repelled from the screen toward the substrate or repelled from the screen toward a base electrode.

This invention relates to methods and apparatus for coating a substrate and more specifically to the deposition of printing material upon a substrate through the forces exerted by electrical potentials. If potentials yielding printing material repulsion forces and/ or attraction forces are selectively applied to the elements of the invention, the printing material is concentrated upon desired areas (such as a substrate) and its deposition upon undesired elements is eliminated or substantially reduced.

Briefly, a developer mixture including carrier particles having toner adhering thereto by triboelectric forces is caused to be accelerated toward a screen, which may have selected open and closed portions for defining a pattern. Certain of the toner will be dislodged from the carrier particles with the toner continuing through the open areas of the screen while the carrier particles are halted at the screen. Electric fields are provided for accelerating the carrier particles and the toner and for urging the dislodged toner to deposit upon the substrate. A salient feature of the invention relates to the potentials applied to the various elements of the process and apparatus.

The art of electrostatic printing is rapidly developing and has achieved a high degree of success. However, numerous problems remain and the present invention relates to the solution of one of the problems. It is known to employ an electrostatic field to effect movement of particles for deposit in a pattern upon a substrate, the pattern being previously determined by causing the particles to be arranged upon the surface in a predetermined configuration and then accelerating the particles therefrom to the substrate. That is, it is known to employ a selectively charged substrate so that some areas thereof attract and retain particles while others do not. Further, it is known to bring the particles to a charged pattern screen of conductive material whereby the particles are charged and are then attracted toward a substrate which, if of conductive material, is polarized oppositely to the charged particles and, if the substrate is of a non-conductive material, is positioned in front of a back electrode which is charged oppositely to the particles. In previous efforts, it was believed that if a potential was maintained upon the patterned screen or screen-stencil, the potential must be one so as to attract the toner particles. However, this procedure introduced additional maintenance problem in that the toner would build up on the pattern screen or screen-stencil so that periodic cleaning of the screen was necessary. This problem is overcome by causing the patterned screen or screen-stencil to be of like potential to the toner so that repulsion exists between the toner and the patterned screen or screen-stencil. In this manner, the aforementioned build-up of the toner on the patterned screen is eliminated or at least substantially and materially reduced.

As taught by the present invention, a mixture of coarse conductive carrier particles and fine non-conductive toner particles is prepared, wherein one or more toner particles adhere to each carrier particle to form a developer mixture, the adhesion occurring by triboelectric effects when the carrier particles are mixed with the toner. A base electrode is electrically charged and such developer mixture in contact therewith has the conductive carrier particles charged therefrom so that a repulsion effect is established to cause the developer mixture to be repelled from the base electrode. A pattern or stencil is presented in the path of the developer mixture and a screen in such path serves mechanically to prevent the passage of the coarse carrier particles therefrom while allowing the fine toner particles to continue onward to form a deposit upon the substrate in accordance with the pattern or stencil.

When the substrate is of conductive material, it is charged oppositely to the toner particles for controlling the paths thereof from the screen to the substrate. When the substrate is of a non-conductive nature, a backing or back electrode bearing a predetermined potential is placed at the rear of the substrate and on :a side opposite to the side of the substrate facing the screen and base electrode.

The use of the words toner or toner particles is employed herein to designate particles smaller than the mesh of the screen, capable of adhesion to the carrier particles by a force less than that developed upon impact of the carrier particles against the screen, and capable of forming a pattern effect on the substrate. In usual practice, the toner particles are of a different color than the substrate surface which is to be printed. Toner may be negatively charged or positively charged. Toner particles are charged triboelectrically by mixing them with carrier particles. The polarity of charge the toner particles acquire is dependent upon the properties of both the toner and carrier material. Preferably, toners are used which when mixed with iron or nickel carrier particles, exhibit a negative charge. Negatively charged toner particles are preferably of non-conductive materials and commercially available types are manufactured by the Xerox Corporation. The non-conductive toner particles comprise essentially pigmented or dyed particles of, for instance, a mix ture of n-butyl methacrylate (41%) and polystyrene (59%) with an average particle size of about 17 microns. Toner capable of assuming a charge which is positive with respect to a reference is commercially available from Interchemical Printing Inks and is designated XRL 8969.

Many distinct advantages arise from the use of conductive carriers and non-conductive toners. Non-conductive toners can be made from material of low melting temperature. Thus, the materials can generally be fused to print objects more readily than other toners.

A further important advantage in using a carrier with the toner in an electrostatic printing apparatus is to promote ease of handling and distribution of the toner. Whereas toner particles alone are difficult to handle and stick to everything they touch including each other, toner and carrier flow readily and may be easily distributed uniformly over extended areas. The toner in a developer mixture normally contributes from about one to about four percent of the total mass so that the ability of the mix ture to flow is due to the presence of the carrier.

Further advantages are evident. The toner particles may acquire considerably greater velocities by this method than if they were accelerated without a conductive carrier.

The large conductive carrier experiences conductive charging because of contact with the base electrode and can attain relatively large terminal velocities. The small toner particle passes through the apertures in a stencil, or other type of screen, with this high velocity so that the toner particle can travel a great distance to an object to be printed. In addition, the time to travel the given distance can be substantially reduced which results in more rapid printing speeds. Further, unlike conductive toner particles, a non-conductive toner is useful for printing on conductive surfaces. A conductive particle would surrender its charge and be easily displaced from such a surface.

Accelerating the toner particles prior to introduction through the stencil, or other type screen, also insures that the velocity vector associated with the toner particles is properly oriented, i.e., perpendicular to the screen stencil at time of passage through the stencil. This insures that minimal dispersion of the pattern will occur during transport. These two characteristics, high magnitude and proper orientation of the velocity vector at the time of introduction through the screen, are unique with methods and apparatus exemplified by the present invention.

Accordingly, it is the principal object of the present invention to improve printing and coating processes and apparatus of the type employing electrical phenomenon.

It is a further object of the present invention to improve electrostatic printing and coating processes of the type wherein non-conductive toner is propelled through a pattern defining screen to be deposited upon a substrate in accordance with the defined screen.

It is a further object of the present invention to provide a means for eliminating or substantially reducing certain maintenance procedures previously associated with electrostatic screen process printing and coating.

It is a further object of the present invention to provide a means for eliminating or substantially reducing electrical shock hazards previously associated with electrostatic screen process printing and coating devices employing high electrical potentials.

It is a still further object of the present invention to provide a means for more efiiciently utilizing the electrical potentials established on the potential bearing elements of electrostatic screen process printing and coating apparatus.

In the present invention, toner and carrier particles become triboelectrically charged when mixed with the result that the smaller toner particles adhere to the larger carrier particles. The carrier particles have a diameter several times that or" the toner so that the toner forms a particulate coating on the carrier particles due to their electrical attraction. In one embodiment of the invention, tone-r capable of assuming a negative charge is employed along with iron filings, as the carrier particles, which become positively charged. When this developer mixture is employed to print or coat a substrate, the carrier particles are also charged by contact with a base electrode and a screen. This charging is superimposed upon that due to triboelectric etlects. The carrier particles acquire sufi'icient charge that the electric field causes them to be repulsed by the base electrode and attracted to the screen. At the screen, the carrier particles lose their charge and are then repelled away from the screen and attracted to the base electrode. Thus, the carrier particles, transporting the toner, oscillate back and forth between the base electrode and the screen. These oscillations occur as long as a sufficient potential difference is maintained between the screen and the base electrode, regardless of the electrical polarities associated with these components or with the toner. The carrier particles carry toner particles that are eventually dislodged by collisions with the screen, the base electrode, or other carrier particles.

In previous work, it appeared that the screen had to be maintained at a polarity, relative to the base electrode, which was opposite to the charge carried by the toner.

Subsequent work as shown by the present invention discloses that this is not true and that many advantages occur if the screen can always repel free toner, i.e., the screen is maintained at a polarity which is like the charge carried by the toner.

For example, the screen may be maintained at a negative potential, the base electrode at a positive potential and the toner negatively charged which is like the negative potential of the screen. In addition, if a back electrode is used, which would be the case for non-conductive substrate, the back electrode should be maintained at a positive polarity. With this arrangement, an electric field is maintained on opposite sides of the screen and oriented in opposite directions. Using the conventional means of describing such fields, it is stated that the electric field intensity vector is directed away from both the base electrode and the back electrode and toward the screen. An isolated negatively charged toner particle would thus experience electrical forces which would tend to move it to- Ward the base electrode or the back electrode depending upon which side of the screen it was located.

Consider a substrate to be coated or printed upon in the following manner: First, the base electrode is uniformly coated with a toner-carrier developer mixture. Next, a voltage is applied, observing the polarities set forth, and of sufiicient magnitude to produce vigorous oscillation of the carrier particles. When the voltage is first applied, the carrier particles become positively charged. These particles along wih the toner adhering thereto are carried upwardly by the electric field until they strike the screen. The much smaller toner particles, which had formed a discontinuous coating on the carrier particles are dislodged at this impact. Some of the toner passes through the open apertures of the screen, experience an electric force due to the potential diflerence between the screen and the back electrode, and are directed onto the object to be printed. However, the remaining toner is blocked by the screen, 'by the closed apertures in the screen, or by the carrier particles. This toner experiences an electric force due to the potential ditference between the screen and the base electrode and is accelerated back to the base electrode.

A number of advantages accrue to this method of operation in that the screen does not accumulate toner while printing or coating is occurring. Toner either is deposited upon the substrate, the carrier, or the base electrode, the base electrode being relatively easy to maintain in a clean condition. In addition, the base and back electrodes may be operated at ground potential, with only the screen, which is mechanically shielded by the base and back electrodes, at a high potential relative to ground. This arrangement provides a convenient safety feature in that the potentials employed may range upwards of hundred thousand volts. Also, the toner particle falls through the same potential diiference twice, effectively doubling the applied voltage. First, it is carried from ground to the screen potential because it is attached to the carrier particle which is oppositely charged. When the carrier particle is suddently stopped by the screen, the toner particles that pass on through the screen presumably do so at high velocity and, ideally, essentially that velocity of the carrier particle just before impact. The toner now falls from the screen potential back to ground with a further increase in velocity. The toner particle, in effect, can fall through the same potential difference twice, and end up at the initial potential with an increase in velocity. In etTect, the particle has changed polarity midway in its fall. Actually, the polarity of the toner has remained the same but it was carried part way by an oppositely charged carrier particle.

The invention both as to its organization and method of operation together with further objects and advantages thereof will best be understood 'by reference to the following specification taken in conjunction with the ac companying drawings in which:

FIGURE 1 is a diagrammatical view illustrating a single developer particle which is comprised of a larger carrier particle and a plurality of small toner particles, a plurality of the carrier particle-toner being known as the developer mixture;

FIGURE 2 is a diagrammatical view illustrating the relative potentials maintained on the electrodes and the screen, a means for varying those potentials and switch means for disconnecting the potentials;

FIGURE 3 is a diagrammatic view of the invention and illustrating a carrier particle with tOner being accelerated toward the screen, toner after being dislodged and being attracted to the base electrode, and the carrier particle, now oppositely charged being accelerated back to the base electrode;

FIGURE 4 is a diagrammatic view of one embodiment of the invention and illustrating the coating or printing upon a non-conductive substrate;

FIGURE 5 is a diagrammatic view of another embodiment and illustrating the screen-stencil combination and printing upon a non-conductive substrate;

FIGURE 6 is a diagrammatic view of another embodiment of the invention and illustrating the printing upon a conductive substrate;

FIGURE 7 is a diagrammatic view of another embodiment of the invention and illustrating the grounding of the screen electrode and the base and back electrodes being maintained at a positive potential relative thereto;

FIGURE 8 is a diagrammatic view of another embodiment of the invention and showing the base and back electrodes being at ground potential while the screen is maintained at a negative potential relative thereto;

FIGURE 9 is a perspective view of a stencil-screen combination which may be employed in the practice of the invention;

FIGURE 10 is a diagrammatic side elevational view of another form of the invention and illustrating more a practical application thereof;

FIGURE 11 is a sectional view taken along the line 1111 of the FIGURE 10;

FIGURE 12 is a diagrammatic view illustrating the potentials applied to the electrodes and the screen when employing toner capable of assuming a positive electrostatic charge; and,

FIGURE 13 is a diagrammatic view, similar to the FIGURE 1, but illustrating a single developer particle which is comprised of a negatively charged carrier particle having a plurality of positively charged toner particles adhering thereto.

With reference to the FIGURE 1, one particle of the developer mixture is generally indicated by the numeral 20 which is comprised of a large carrier particle 22 and a plurality of toner particles 24 adhering thereto. The carrier particles 22 are formed of a conductive material such as charcoal, metal shot made of various materials such as steel, aluminum, copper or, preferably, small granular iron filings of a range from around 25 to 1000 microns. It will be apparent from the following description that the lower limit of particle size is determined by the apertures in the screen utilized in the present invention since the screen must not pass the carrier particles. The toner particles 24 are preferably of non-conductive material and are commercially available through the Xerox Corporation. The composition of the toner has been previously set forth. It is apparent that the carrier particles 22 are much larger than the toner particles 24 and as illustrated in the FIGURE 1, a number of toner particles 24 can adhere to a single carrier particle 22 because of well-known triboelectric forces.

A generalized embodiment of the invention is shown in the FIGURE 2 wherein a base electrode 26 is in spatial relationship with a back electrode 28, a conductive screen 30 being positioned therebetween. A high voltage supply 32, which may be of the order of 100,000 volts, is controlled by a magnitude control 33 and has its positive output conductor coupled through a resistor 34 to a switch 36 which, When closed, applies the positive potential to the base electrode 26. Similarly, the positive conductor of the high voltage supply 32 is coupled through a resistor 38 to a switch 40 and when the switch 40 is closed, the positive supply is connected to the back electrode 28. The negative output from the high voltage supply 32 is connected through a resistor 42 to a switch 44 and when the switch 44 is closed, the negative potential is applied to the screen 30.

To summarize the showing in the FIGURE 2, the screen 30 is maintained at a potential which is negative with respect to the base electrode 26 and the back electrode 28. It will be understood that a referencing point such as grounding of certain of the electrodes, can be established and these embodiments are shown in later figures. Further, the

resistors

34, 38, and 42 are not necessary but are inserted to act as current limiters in the event of arc-over.

The FIGURE 3 is a view illustrating one carrier-toner of the developer mixture 20 being accelerated from the base electrode 26 and another returning to the electrode 26. Positioned immediately above the screen 30 is a stencil 46 hearing a plurality of apertures 48, the apertures 48 defining the pattern to be impressed upon the back electrode 28, the back electrode 28 in this case being a conductive substrate upon which the coating or printing is to be deposited. It will be understood that the screen 30- stencil 46 could be combined as shown in a later figure and not of the dual construction as set forth.

With the potentials applied as shown in the FIGURE 3, an electric field E is established between the base electrode 26 and the screen 30 and employing the conventional manner of illustrating such electric fields, the field would be directed in the direction as indicated by the arrow, i.e., toward the screen 30. Also, an electric field E is established between the back electrode 28 or substrate to be printed upon and the screen 30 and also oriented toward the screen 30 as indicated by the arrow. After toner 24 is caused to adhere to the carrier particles 22 through triboelectric forces such as mixing or agitating the toner 24 and carrier particles 22 together, the developer mixture is flowed onto in any suitable manner the base electrode 26. When the positive potential is applied as shown in the FIGURE 3, the carrier particle 22 becomes positively charged and is accelerated away from the base electrode 26. The carrier particles 22 carrying the toner 24 will strike the screen 30 and if the position of the toner 24 is substantially in line with one of the apertures 48, then that toner will be released from the carrier particles 22 and advanced through the screen 30 and aperture 48 of the stencil 46. Immediately, the released toner 24 above the screen 30 experience an electric force to urge them against the back electrode 28, to be deposited upon the electrode 28 in a pattern according to the position of the apertures 48 of the stencil 46.

Upon striking the screen 30, the carrier particle 22 now takes on the potential of the screen 30 (negative in the embodiment set forth in the FIGURE 3) and is immediately repelled by the screen 30 back toward the base electrode 26. Some of the toner 24 may become dislodged from the carrier particle 22 or may stay attached to the particle 22 through the triboelectric force still present. In actual practice, it will be understood that a great quantity of developer mixture is supplied through the area above the base electrode 26 so that a cloud is formed and sufficient toner is passed through the screen 30 and apertures 48 of the stencil 46 so as to accomplish the coating or printing operation in a minimum of time.

As shown in the FIGURE 4, the embodiment illustrates the printing upon a non-conductive substrate and the positioning of the stencil between the base electrode 26 and the screen 30. The stencil is identified as 50 and bears a plurality of apertures 48 through which the toner 24 may pass. A non-conductive substrate 52 such as paper, plastic, etc., is positioned between the screen 30 and the back electrode 28 and will receive the toner 24 as determined by the apertures 48 of the stencil 50. As set forth earlier, in the event that the substrate to be printed upon is of a conductive nature, then the substrate may be made the electrode, such as the electrode 28 of the FIGURE 3. As the cloud of developer mixture oscillates between the base electrode 26 an dthe screen 30-stencii 50, the toner particles 24 may be released and advanced through the screen 30-stencil 50 and to the substrate 52 or blocked and returned to the base electrode 26, with or without a carrier particle 22, to attach themselves to other carrier particles 22 in the event that they may have become dislodged from their earlier carrier particle. Thus, there are no net forces tending to retain the toner at or near the screen 30 so that the build-up of toner on the screen 30 is inhibited.

The embodiment shown in the FIGURE is similar to the embodiment of the FIGURE 4 except that the screen 30-stencil 46 of the FIGURE 3 has been substituted for the screen 30-stencil 50. In this embodiment, it will be noted that the stencil 46 is positioned between the sceen 30 and the substrate 52, which is the preferred embodiment or manner of deploying the stencil 46.

The FIGURE 6 illustrates the manner of printing on a conductive substrate which is similar to the showing of the FIGURE 3 except for the connections of the high voltage supply 32. Since the substrate or back electrode 28 of the FIGURE 6 is conductive, it may be made the electrode for establishing the electric field E and the substrate 52 will receive the coating or printing of toner as defined by the apertures 48 of the stencil 46.

In the FIGURE 7, the screen 30 has been placed at ground potential as shown by the conductor 54 so that the base electrode 26 and the back electrode 28 are now the prescribed volts above ground. In certain environment, it may be determined that the screen 30 be maintained at ground potential.

Alternatively, in the FIGURE 8, the conductors of the power supply 32 coupled to the base electrode 26 and the back electrode 28 is grounded by a conductor 56 so that the screen 30 is now maintained at the prescribed volts below ground. The embodiment of the FIGURE 8 introduces a safety feature in that the outside electrodes, those

electrodes

26 and 28 which may be or come in contact with an operator, are maintained at the harmless ground potential whereas the inner electrode or screen 30 bears a high negative charge and the screen 30 may be effectively insulated and maintained away from an operator.

The FIGURE 9 illustrates a stencil-screen combination 58 which may be of a conductive material and wherein the pattern or characters A, B and C have been formed. If the stencil-screen 58 is employed, then it would replace the screen 30-stencil 46 of the earlier figures. In the earlier figures, the stencil 46 is of a normally nonconducting material. If the stencil-screen 58 of the FIG- URE 9 is utilized, then any suitable pattern or indicia may be formed thereon and in the specific stencil-screen 58 illustrated, images of the first three alphabetical characters would be transferred to either the back electrode 28 or the substrate 52.

In the FIGURE 10, a practical embodiment of the invention is illustrated wherein a funnel-shaped receiver 60 would be filled with carrier particles 22 and toner 24 and allowed to mix together and drop upon an inclined base electrode 26'. Upon the mixing or agitation of the carrier particles 22 with the toner 24, the developer mixture would be formed due to the triboelectric forces as previously set forth. The inclined base electrode 26' is maintained in its position as shown by a stand 62 which, for convenience, may be of an insulating material since a positive potential is applied to the electrode 26' by the high voltage power supply 32. A negative potential is applied by the power supply 32 to the inclined screen 30 while a potential identical to the potential upon the base electrode 26' is applied to an inclined back electrode 28'. A substrate 52' is positioned between the inclined stencil 46 and for convenience, means (not shown) may be employed to advance the substrate 52' with respect to the back electrode 28. A pattern or image will be formed upon the substrate 52' in accordance with the apertures 48 of the stencil 46 by the oscillating developer mixture 20 which carries the toner 24 through the screen 30' and apertures 48. A tray 64 is provided to receive the carrier particles 22 and/or toner 24 as they emerge from the lowemost portion of the back electrode 26.

The FIGURE 11 is a sectional view taken along the line 1111 of the FIGURE 10 and is of primary interest in that it discloses a plurality of non-conducting or insulating spacers 66 which are employed to maintain the base electrode 26, screen 30-stenci1 46', and substrate 52-back electrode 28' in spatial relationship. It will be understood that rollers could be substituted for the upper spacers 66 so that the substrate 52 could be rolled or conveniently advanced past the printing station of the FIGURES 10 and 11.

In the event that toner which adheres to a carrier through triboelectric forces wherein the toner takes on a positive charge, is employed, then the embodiment shown in FIGURE 12 would be suitable for causing coating or printing upon the substrate 52. The apparatus of the FIGURE 12 is substantially identical to the apparatus of the FIGURE 8 except that the screen is maintained at a potential which is positive with respect to ground. Such positively charged toner is shown in the FIGURE 13 and identified as positive developer mixture 68. The apparatus of the FIGURE 12 would operate in a manner similar to the foregoing figures, i.e., oscillation of the developer mixture 68 would occur between the base electrode 26 and the screen 30 and certain of the toner particles would be dislodged so as to advance through the apertures 48 of the stencil 46 and be deposited upon the substrate 52. Since the polarity of the

electrodes

26, 28 and the screen 30 have been reversed, the electric field would now be oriented in a direction opposite to that shown in the FIGURE 3.

Accordingly, the present invention has described and illustrated a method and apparatus which has overcome a number of problems inherent with electrostatic printing devices heretofore known. In the present invention, the center or screen electrode does not accumulate toner while printing is occurring since the electric fields are so oriented that the toner either ends up on the substrate, the carrier particle, or back at the base electrode. In addition, the base and back electrodes may be operated at ground potential with only the screen, which is mechanically shielded by the two electrodes, at a high potential relative to ground. This provides a convenient safety feature. Also, the toner particle falls through the same potential difference twice, effectively doubling the applied voltage. In effect, the particle has changed polarity midway in its fall. Actually, the polarity of the toner has remained the same but it was carried half way to its target by an oppositely charged carrier particle.

After the toner has been deposited upon the substrate or electrode in the desired pattern, it will be readily understood that the toner may be fixed in any suitable manner such as by heating, solvent action, etc. In addition, positively charged as well as negatively charged toner may be employed in the practice of the invention although the greater emphasis has been on the illustration of the toner which takes on a negative charge when mixed or agitated with a particular carrier particle.

Thus, the present invention may be embodied in other specific form-s without departing from the spirit and the essential characteristics of the invention. The present embodiment is, therefore, to be considered in all respects as illustrative and the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are, therefore, intended to be embraced therein.

What is claimed is:

1. Apparatus for coating a substrate comprising a base electrode in spaced relation to the substrate, means defining a pattern to be coated upon the substrate and positioned between the substrate and said base electrode, carrier particles having toner of a predetermined electric charge adhering thereto by triboelectric forces, means for accelerating said particles toward said means defining a pattern, and means for establishing an electric field between the substrate and the means defining a pattern, the predetermined electric charge of the toner being of like polarity to the polarity induced upon the means defining a pattern by said means for establishing an electric field and of unlike polarity to said base electrode.

2. Apparatus for coating a substrate comprising a base electrode in spaced relation to the substrate, a screen positioned between said base and the substrate, a stencil for defining a pattern to be coated upon the substrate and positioned between said screen and the substrate, carrier particles having toner of a predetermined electric charge adhering thereto by triboelectric forces, means for accelerating said particles from said base electrode through said screen to the substrate, and means for establishing an electric field between the substrate and said screen, the predetermined electric charge of the toner being of like polarity to the polarity induced upon the screen by said means for establishing an electric field and of unlike polarity to said base electrode.

3. Apparatus for coating a substrate comprising a base electrode and a back electrode in spaced relation so as to permit the positioning of the substrate therebetween, means defining a pattern to be coated upon a substrate and positioned between the substrate and said base electrode, carrier particles having toner of a predetermined electric charge adhering thereto by triboelectric forces, means for accelerating said particles from said base electrode toward said means defining a pattern, and means for establishing an electric field between said back electrode and the means defining a pattern so as to induce to be deposited upon the substrate as determined by said means defining a pattern, the predetermined electric charge of the toner being of like polarity to the polarity induced upon the :means defining a pattern by said means for establishing an electric field and of unlike polarity to said base and back electrodes.

4. Apparatus for coating a substrate comprising a base electrode in spaced relation to the substrate, means defining a pattern to be coated upon the substrate and positioned between the substrate and said base electrode, carrier particles having toner of a predetermined electric charge adhering thereto by triboelectric forces, means for establishing a first electric field between said base electrode and said means defining a pattern and directed toward said means defining a pattern so as to accelerate said particles toward said means defining a pattern, and means for establishing a second electric field between the substrate and the means defining a pattern and directed toward the means defining a pattern so as to induce toner to deposit upon the substrate, the predetermined electric charge of the toner being of like polarity to the polarity induced upon the means defining a pattern by said means for establishing an electric field and of unlike polarity to said base electrode.

5. Apparatus for coating a substrate comprising a base electrode in spaced relation to a back electrode and permitting the positioning of a substrate therebetween, a screen electrode positioned between the substrate and said base electrode, carrier particles having toner of a predetermined electric charge adhering thereto by triboelectric forces, a power supply, means for coupling said power supply to said screen electrode and said base electrode for causing acceleration of said particles away from said base electrode toward said screen electrode,

and means for coupling said power supply to said screen electrode and said back electrode for establishing an electric field between said screen electrode and base electrode and directed away from said back electrode so as to induce toner to be deposited upon the substrate, the predetermined electric charge of the toner being of like polarity to the polarity of the screen and of unlike polarity to said base electrode and back electrode.

6. The combination as defined in claim 5 including a stencil for defining a pattern to be coated upon the substrate and positioned between the substrate and said screen electrode.

7. The combination as defined in claim 5 including a stencil for defining a pattern to be coated upon the substrate and positioned between said screen electrode and said base electrode.

8. Apparatus for coating a substrate comprising a base electrode in spaced relation to the substrate, a screen positioned between said base electrode and the substrate, carrier particles having negatively charged toner adhering thereto by triboelectric forces, means for providing a positive electrical potential on said base electrode and the substrate and means for providing a negative electrical potential on said screen, the potentials so provided establishing a first electrical field between said screen and said base electrode and oriented toward said screen so as to propel the positively charged carrier particles supporting the negatively charged toner toward said screen and a second electrical field between said substrate and said screen and oriented toward said screen so as to urge the toner toward the substrate to be deposited thereon, the carrier particles being sufficiently large enough to be precluded from passage through said screen so as to oscillate between said screen and said base electrode.

9. The combination as defined in claim 8 including individual means coupled to each of said base electrode, screen, and substrate for varying the magnitude of the potential applied thereto.

10. A method for coating a substrate comprising the steps of positioning a base electrode and a substrate in spatial relationship, providing a screen between the base electrode and the substrate, supporting carrier particles retaining negatively charged toner thereon upon said base electrode, and applying a first electric field oriented toward said screen and a second electric field also oriented toward said screen but on the opposite side thereof so as to propel said particles toward said screen and to dislodge the toner for deposition upon the substrate.

11. A method for coating a substrate comprising the steps of positioning a base electrode and a back electrode in spaced relation, positioning a substrate to receive the coating between the electrodes, providing a screen between the base electrode and the substrate, supporting carrier particles retaining negatively charged toner thereon upon the base electrode, and applying a first electric field oriented toward said screen so as to propel said particles toward said screen and to dislodge the toner and a second electric field also oriented toward said screen but on the opposite side thereof for urging the dislodged toner to deposit upon the substrate.

12. The method as defined in claim 11 including the step of positioning a stencil for defining the pattern to be coated upon the substrate between the substrate and said screen.

13. The method as defined in claim 11 including the step of positioning a stencil defining the pattern to be coated upon the substrate between said base electrode and said screen.

14. A method for coating a substrate comprising the steps of positioning a base electrode and a back electrode in spatial relationship, inserting a substrate therebetween for receiving the coating, providing a screen defining a pattern to be coated upon the substrate between the substrate and the base electrode, supporting carrier particles retaining negatively charged toner thereon upon said base electrode, placing the base electrode and the back electrode at ground potential, and applying a potential to the screen which is negative with respect to the base and back electrodes so as to produce a first electric field oriented from the base electrode toward the screen so as to propel the particles toward the screen for dislodging the toner for passage therethrough and a second electric field directed from the back electrode toward said screen for urging the dislodged toner from the screen to the substrate to be deposited thereon according to the defined pattern.

15. Apparatus for coating a substrate comprising a base electrode disposed in spaced relation from a back electrode, stencil-screen means disposed in spaced relation between said base electrode and said back electrode with the space between said stencil-screen means and said back electrode being sufficiently large enough to accommodate said substrate therebetween, power means for establishing a potential difference between said base electrode and said stencil-screen means and between said stencil-screen means and said back electrode with the polarity of said stencil-screen means being opposite from the polarity of said base electrode and said back electrode, means for maintaining said base electrode and said back electrode at ground potential, carrier particles and toner triboelectrically adhering thereto with the polarity of the toner being of the same polarity as the stencil-screen means, means for depositing said carrier particles and toner on said base electrode whereby the electric field created by the potential difference between the stencil-screen means and said base electrode propels said carrier particles and toner toward said stencil-screen means, said carrier particles oscillating between said stencil-screen means and said base electrode and being inhibited from passage through said stencil-screen means while permitting the propulsion of the toner therethrough, and the toner being repelled from said stencilscreen means because of their like polarity.

References Cited UNITED STATES PATENTS 2,940,864 6/1960 Watson. 3,081,698 3/1963 Childress et al. 3,285,167 11/1966 Childress et al.

ROBERT E. PULFREY, Primary Examiner.

EDGAR S. BURR, Assistant Examiner.