US 3228326 A
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Description (OCR text may contain errors)
Jan. 11, 1966 c. o. CHILDRESS SPACER CONTACT FOR ELECITROSTATIC PRINTING Filed March 18, 1963 28 IIHII ll S 5 P D M w 0 f m L C INVENTOR.
United States Patent 3,228,326 SPACER CONTACT FOR ELECTRGSTATTC PRINTTNG Clyde 0. Chiidress, Pain Alto, Caiifi, assignor to Eiectrostatic Printing Corporation of America, San Francisco,
Calif., a corporation of California Fiied Mar. I8, 1963, Ser. No. 265,7ti4 4 Ciairns. (Cl. MEL-1T4) This invention relates to electrostatic printing and more particularly to improvements therein.
An electrostatic printing system has been developed by this invention wherein an electric field is established between an electroscopic powder image forming member and a powder image receiving member. The powder image forming member may comprise a conductive screen having apertures therein arranged in the desired powder image pattern. Electroscopic powder is forced through the apertures of the screen into the electric field and is carried thereby to the image receiving member. The image on the image receiving member is thereafter fixed as by heat or by spray with a fixative or by treatment with a fixing vapor.
One of the features of this electrostatic printing system is that it can print on irregularly shaped objects and that the conductive screen need not contact the object on which printing is to occur. As a result, the electrostatic printing mechanism finds application in printing on a great many diverse materials amongst which, by way of example, is fruit, where other types of printing bruise the skin. It will be appreciated that materials such as apple's, avocados, etc., do not have a uniform size, therefore when it is desired to print on these materials on a production line basis, a problem is presented in positioning the image forming electrode at a substantially uniform distance from the object to be printed on. This is desirable for a number of reasons amongst which are, to obtain a uniform printing size, and also because there is an optimal distance which is dependent upon potentials employed, the screen and the powders used for achieving the sharpest printing.
Provision must also be made for applying a potential to the fruit, or object being printed upon, it is sufficiently conductive to establish an electric field with the powder image forming electrode which will cause the powder image to be applied thereto. Apples, or avocados are indeed quite conductive for this purpose.
An object of the present invention is the provision of an arrangement for properly spacing an irregularly shaped object from a powder image forming member in an electrostatic printing system.
Another object of the present invention is the provision of an arrangement for properly spacing an irregularly shaped object from a powder image forming electrode in an electrostatic printing system and also connecting that object to the electric field forming potential source.
Yet another object of the present invention is the provision of a simple and useful arrangement for affording proper spacing and electrical connection of a series of non-uniform objects in an electrostatic printing system.
These and other objects of the invention are achieved by providing a conductive screen which has apertures therethrough only in regions defining the pattern of the desired powder image. The conductive screen is attached to a thin sheet of insulating material which has an opening therethrough slightly larger than the region of the screen through which the powder image transfer is to occur. The opposite side of the thin insulating sheet has a conductive coating. The screen and the conductive coating are connected to an electric field establishing source of potential. Means are provided to bring the object upon which the printing is to occur in contact with Patented Jan. 11, 1966 the conductive side of the insulating sheet. As a result, it serves to establish an electric field therebetwcen and the screen. Electroscopic powder particles are urged through the screen at this time and are carried to the surface of the image receiving object. The screen is then withdrawn and the image is then fixed on the object.
The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and. advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:
FIGURE 1 illustrates how the embodiment of the invention is used in continuous printing on apples, by way of example,
FIGURE 2 illustrates the embodiment of the invention,
FIGURE 3 is a cross sectional view of the embodiment of the invention, and
FIGURE 4 illustrates a cross sectional view of another arrangement for the embodiment of the invention.
Referring now to FIGURE 1, there may be seen a plurality of apples 10, 12, 14, 16, which are moving from left to right on a conveyor line 18. These are shown to illustrate the utility of the invention in printing on a regularly sized and shaped object.
The apples move on a conveyor line 18 from left to right. Conveyor line 18 has the apples regularly spaced therealong. The conveyor moves upwardly underneath the printing location and carries the apples in contact with an electrostatic printing arrangement which includes an embodiment of this invention. This comprises an electrostatic printing assembly 20, which includes a container 22, which is supported, as by springs 24, 26, from a rotating overhead support 28. As each apple moves upward on the conveyor 18, it engages one of these containers which moves therewith for a short distance and then the apple moves downwardly to be disengaged therefrom as it is carried along by the conveyor belt. The details of the mechanization for effectuating the various movement are not shown herein, since they do not constiute a part of this invention. However, they are well known in the conveyor art.
As shown in FIGURES 2 and 3 the base of the container 20 comprises the embodiment of this invention which is a powder image forming electrode which is a conductive screen 30, having apertures 32 therethrough, which are arranged in the pattern desired for the powder image. The screen is adhered to a sheet of insulating material 34. The sheet of insulating material has an opening which is slightly larger than the area through which printing is to occur. On the opposite face of the screen there is deposited a conductive material 36, such as copper, which need not cover the entire surface, but only enough of it to insure a good contact with the fruit or other conductive object which is brought in contact therewith. A source of field establishing potential 38, is connected between the conductive layer 36, and the conductive screen 30.
The container 20 will include electroscopic powder and any suitable means, such as a rotating brush, not shown, for urging powder through the apertures of the screen as a powder image into an electric field. The powder image is carried through the space established by the spacer 34, to be deposited on the conductive object, such as the apple 12. The fixing of the powder image on the apple is done by any suitable arrangement such as a fixing spray or by exposing the area to a vapor which fixes the powder particles to the surface of the apple. The containers 20 are supported and weighted in a manner so that when the apple is brought in contact therewith, very little weight rests upon the apple. In an embodiment of the invention which was built, the insulating sheet 34 consisted of a inch copper clad circuit board with an opening slightly larger than the area to be printed. The under surface of the copper clad circuit board from the electrical connection whereby the field establishing potential 38 may be applied thereto for transferring a powder image from the conductive screen thereto.
While the arrangement for the spacer contact shown in FIGURE 2 is flat, this is not to be construed as a limitation, since, as shown in FIGURE 4, the configuration may be curved if desired, to fit to the contours of the object on which electrostatic printing is to take place. Furthermore, the spacer insulator may serve as a holder or cup, for conveying the object on which the powder image is to be formed. That is, the cup may be brought up to pick up the object and carry it a short distance while the powder image deposition takes place. The cup may then be removed from contact with the object which proceeds to an image fixing station.
The embodiment of the invention insures an exact spacing between the conductive object on which the powder image transfer is to occur and the conductive screen. Not only does this insure uniformity in the quality of the printing which occurs, but also this assures that the best results are obtained at all times.
1. In an electrostatic powder image transfer system of the type where it is desired to transfer a powder image by means of an electric field from an image forming electrode to a conductive object, an improved means for spacing said conductive object from said image forming electrode and for connecting electric field establishing potential thereto comprising an insulating spacer having an opening therethrough sufiiciently large not to obstruct the transfer of said powder image from said image forming electrode to said conductive object, and conductive material on one side of said spacer, said spacer being interposed between said conductive object and said powder image forming electrode and having the conductive material covered side thereof in contact with said conductive object and the opposite side thereof in contact with said image forming electrode a source of electric field establishing potential, and means for connecting said source of electric field establishing potential between said image forming electrode and said conductive material.
2. In an electrostatic printing system for printing on a conductive object the combination of a conductive screen having all of its surface masked except for an apertured region thereof having the shape of a desired image, an insulating sheet attached to one side of said conductive screen and having an opening therethrough exposing the apertured region of said conductive screen, conductive material on the side of said insulating sheet which is not attached to said conductive screen, a conductive object positioned in contact with said conductive material at said opening through said insulating sheet, a source of electric potential, and means for applying an electric potential from said source between said conductive screen and said conductive material for establishing an electric field between said conductive screen and said conductive object when said conductive object is in contact with said conductive material.
3. In an electrostatic printing system of the type wherein a powder image is transferred by means of an electric field to a conductive powder image receiving object, the improvement comprising a screen powder image forming electrode having apertures therethrough in the shape of said desired powder image, an insulating layer having a predetermined thickness, said insulating layer being positioned adjacent to and covering one side of said image forming electrode and having an opening extending therethrough, said opening having an area sufiiciently larger than the apertures of said screen forming the powder image to enable the transfer of the powder image therethrough, a conductive coating on said insulating layer on the surface opposite to the surface adjacent said powder image forming electrode, a powder image receiving object in contact with said conductive coating, and means including said conductive coating for establishing an electric field between said screen and said powder image receiving object.
4. In an electrostatic printing system of the type wherein an electric field establishing potential is applied between a conductive screen and a conductive object to establish an electric field therebetween for transferring a powder image to said conductive object, said powder image being formed by applying electroscopic powder particles to the apertures of the conductive screen which apertures are arranged to form said powder particles into a powder image, said powder particles being smaller than said screen apertures to pass therethrough, the improvement in said system comprising a spacer separating said conductive object and said screen, said spacer comprising insulating means adjacent one side of said screen and having an opening therethrough with an area sufiiciently larger than said powder image for permitting the transfer of the powder image through said opening to said conductive object, and a conductive layer on the side of said insulating means opposite to the side adjacent said screen for contacting said conductive object, and means for connecting said source of electric field establish-ing potential between said screen and said conductive layer.
References Cited by the Examiner UNITED STATES PATENTS 1,906,094 4/1933 Powell l0141 2,787,556 4/ 1957 Haas. 2,817,598 12/ 1957 Hayford. 2,910,351 10/1959 Szpak et a1. 10l426 3,081,698 3/1963 Childress et al.
ROBERT E. PULFREY, Primary Examiner.
WILLIAM B. PENN, Examiner.
PAUL R. WOODS, Assistant Examiner.