US3043217A - Electrostatic printing apparatus - Google Patents

Description

Filed Dec. 21, 1960 July 10, 1962 WALKUP 3,043,217

ELECTROSTATIC PRINTING APPARATUS 3 Sheets-Sheet l INVENTOR. LEWIS E. WALKUP BY M m A Z TORNE r July 10, 1962 L. E. WALKUP 3,043,217

ELECTROSTATIC PRINTING APPARATUS Filed Dec. 21, 1960 3 Sheets$heet 2 IN V EN TOR.

LEWIS E.WALKUP BY Q m A 7' TORNEY July 10, 1962 E. WALKUP ELECTROSTATIC PRINTING APPARATUS 3 Sheets-Sheet 3 Filed Dec. 21, 1960 INVENTOR. LEWIS E. WALKUP ATTORNEY This invention relates to improvements in xerographic printing and more particularly to improved method and apparatus for electrostatic printing of multiple image sizes.

In Schatfert patent US. 2,576,047 there is disclosed electrostatic printing, commonly referred to as xeroprinting, in which an image or images of an electrostically charged permanent insulating pattern is developed with a granulated powder by electrostatic deposition, and the developed image transferred to a transfer material. In general, xeroprinting is used to produce a relatively large number of copies of a single image and employs a printing plate that consists of a permanent image, in the form of an electrically insulating or non-conductive pattern in conjunction with metal or other conductive material, The conductor, usually as a backing plate, is suitably grounded and may be either rigid or flexible and mounted to be continually advanced past the appropriate stations for developing and transferring.

Since documentary and other images vary in size, any printing plate as a minimum should have sufiicient length to contain the pattern and should preferably be an exact multiple of an individual image length. Printing apparatus of the prior art are limited to a fixed standard size of printing plate, the size of which is determined by experience to be economically optimum for the size of image reproduction most frequently encountered. This obviously restricts the use of the apparatus in that plates of longer than standard size cannot be accommodated, whereas a standard size plate is required for an image consuming less than, and even substantially less than, the entire plate length.

The plate image is developed and transferred to a transfer material on which the developed image is permanently aflixed, and which for the purpose of this invention is a continuous web, preferably of paper. The transfor material is advanced at identically the same rate as the printing plate and contacts the plate at a transfer station to be described below.

In the process of xeroprinting, as in any continuous printing operation with a large reproduction volume, considerable length and a correspondingly large volume of transfer material is consumed. Since it is well known in the printing art that the cost of paper represents a substantial portion of the manufacturing cost of printed copy, frequently running approximately fifty percent thereof, it is most desirable to keep paper cost to a minimum by minimizing waste. Since waste is comprised of unused portions of transfer material, it should be apparent that in the instance of a plate having considerably more length than the image thereon, there will occur, with a continuously advancing paper web, a considerable waste thereof comprised of extensive lengths of blank areas between the printed portions thereon. The blank areas, except for borders required for the printed image, constitute Waste that is substantially proportional to the non-image length of the printing plate.

Whereas waste is a high cost factor, at the same time, the cost of printing apparatus is very substantial and it is regarded as economically undesirable to have available a difierent size printing apparatus for each size of printing plate. In conventional printing presses, for example, utilizing rigid plates, close operating tolerances and very Bfiifilli. Patented July 10, ISEZ heavy printing pressures limit feasibility of more than one size plate.

From the foregoing it should be apparent that in commercially competitive situations, printing apparatus able to accommodate only a fixed size plate is a decided disadvantage.

Accordingly, -it is the principal object of the invention to provide improved apparatus and methods for elw trostatic printing of multiple image sizes.

It is a further object of the invention to provide improved xerographic printing machines whereby a machine is adapted to accommodate selective lengths of flexible printing plates.

These and additional objects of the invention are attained according to the present invention as illustrated in one embodiment comprised of a plurality of rollers several of which define a path of travel past main operating positions of the printing apparatus. Plates of diflierent lengths are threaded over a selective number of rollers as is required to take-up slack created by the individual plate length.

Several embodiments of the invention are illustrated in the following drawings in which:

FIG, 1 is an isometric view of an electrostatic printer incorporating the apparatus of the invention;

FIG. 2 is a schematic side elevation, partly in section, of an electrostatic printer incorporating the apparatus of the invention;

FIG. 3 is an isometric view of one embodiment of the plate support of the invention; t

FIG. 4 is a sectional view taken substantially on line 4-4 of FIG. 3;

FIG. 5 is an isometric view of a second embodiment of the invention; and

FIG. 6 is a schematic illustration of a third embodiment of the invention.

Illustrated in FIGS. 1 and 2, is apparatus according of one embodiment of the invention including a printing plate support ltiillustrated in the form of a drum or cylinder. The drum is suitably mounted on a shaft 11 supported and arranged to rotate in a frame 12 mounted on a base 13. The shaft 11 and drum 10 are driven counterclockwise from an electric motor 14 through a belt 15 connected to pulleys 16 and 17 connected respectively to shaft 11 and the motor shaft 24 and are selected with the appropriate ratio of pitch diameters to turn the drum at the desired rate of rotation. Condnctor 18 suitably grounds the drum.

Frame 12 includes a journaled support 19 held to the frame by means of a pair of thumb locks 23. By loosening the thumb locks and swinging them outwardly, support 19 can be withdrawn from shaft 11, as shown dashed, whereby one end of the drum is rendered accessible for the purpose of installing thereover an endless printing plate to be described.

Spaced from the plate support 10 is the plate support generally designated 20, that includes a plurality of roller cylinders 21 and which is to be described below.

Adapted to be mounted over both plate supports, in the manner to be described, is a printing element or plate 22 that, for the purpose of this invention, may comprise a flexible material formed as an endless belt by seaming or the like. The printing plate may be made by any of several difierent methods as, for example, writing or tracing the desired design or subject on a metal plate with an insulating or non-conducting lacquer or paint and other methods known in the art. The electrically conductive backing or support lies against a support therefor, and the image layer continuously receives successive electrostatic charges from the transfer operation to be described:

As the plate advances, the electrostatic-ally charged image passes-through a developing station 26 in which a two-component developing material 27, which may be of the type disclosed in Walkup patent U.S. 2,618,551

is cascaded over the drum surface. In the developing apparatus as'disclosed in FIGS. 1 and '2,' developing material is elevated from sump 29 by conveyor 30 which is driven by suitable'drive means" from motor 31, and then is released onto chute 32 wherefrom it cascades down over the :plate surface. Toner component 33, of the developer, and consumed in developing, isstored in dispenser 34 and is rel eased'in amounts controlled by gate 35. 1

As an alternative to cascade developing apparatus. 28, other forms of developing apparatus known in theiart could be substituted therefor,' as for example, a form of brush development disclosed in French Patent 2,120,534,

. magnetic brush development disclosed in Young patent U.S. 2,786,441, liquid development disclosed in British Patent 755,486 or others achieving the appropriate result asaforesaidg 1 After development, the powder image'passes through an image transfer station 42 atfwhich the powder image is transferred to a web 'of traveling transfer material 43, for example, as disclosed in Schaffert patent U.S. 2,576,- 047.

The transfer material towhich the powder image is transferred may be of any convenient type, such as paper, which is: obtained from a supply roll 45, fed 'over guide rolls 46 and 47, being directed into surface contact with the plate in the immediate vicinity of transfer corona generating device 44. After transfer, the transfer material is separated from the plate surface and, as described in the above cited Schaifert patent, recharges the plate image for indefinite operation 'of successive cycles. Thereafter, the transfer material is guided through afusing apparatus, generally designated 48, which may be of a solvent ivapor' type such as disclosed inlCarlson patent U.S. 2,776,907, and wherein the'powder image is passed through a chamber of 'solvent vapor which permanently affixes the image tothe transfer material. Thereaften'the transfer material may be fed over a further system of guide and tensioning 'rolls and onto a take-up roll .52 mounted forrotationin bearing blocks 53 and '54 anddriven by motor 14 through belt 55, throughidler' gears 56 and 57 and slipclutch 58 that controls the'paper'tak'e-up rate at the'same lineal rate as the advancing rate of the'printing plate. v 7 Whereas other forms of fusing may be employed,

vapor fusing is presently preferred. However, other fus ing apparatus,"such as those utilizing heat, as disclosed in Crumrine et al. patent U.S. 2,852,6"l, may be em! ployedinthe alternative.

' By apparatus thus far described copyis produced from a printingplate comprisedof a permanent insulatin g layer on'a conductive backing, the image layer of which is electrostatically charged 'by charge retention from the transfer operationf j However, in the alternae tive or in addition thereto, acharging apparatus (not shown) may be employed to apply charge to the insulating image layer.

As the plate advances the'charged image is developed with an oppositely charged devel oping material thatis deposited on the image layer to form a Xerographic powder'image. The powder image is'th'en electrostatically transferred to a transfer material to which itmay be affixed by a suitable fusing device, whereby the powder image iscaused permanently to adhere to the transfer materiaL' I 7 v V Referring to-FIGS. 1, 3 and 4 there isjdisclosed a length of printing plate can be accommodated in a'printing machine. The plate support includes a frame sup port 80 adapted to be pivotally mounted on'frame 13 bymeans of brackets 81 and 82 through which there 4 the perimeter of journal support 19. In the side walls of the frame there are a plurality of slots 84 that are aligned in opposite side walls and open at the bottom. Each pair of opposite slots is intended to accommodate the support for a cylindrical roller 21 whereby each roller may be moved to change its spacing relative to plate support drum 10.

Each roller, which may be of steel or have a peripheral rubber coating or the like for increased traction, is supported on a pair of; bearings 85 having their inner race' mounted on a stationary shaft 89 that extends outward of slots 84. To support the roller at any desired height within the Slots there is provided a' clamp support cornprising an outer plate 90 and an inner plate 91held together and drawn tight to the frame by means of bolts 7 92. On each side of outer plate 90 is a shaft-supporting boss, one of which contains a set-screw 93 seated in a flat of shaft 89 whereby lateral and rotational movement thereof is prevented.

For the purpose of illustration, three rollers are indicated although any reasonable number may be provided.

To install a printing plate the frame is preferably tilted backward about rod 83 and as many rollers as are required to take-up slack of the printing plate are removed from the frame through the bottom opening of their respective slots. An endless printing plate is first inserted over the end of drum 10, rendered accessible by remov- H V in'g journal support 19 as aforesaid, and is then slipped over the rollers, after which the frame is brought forward and the rollers raised within the slots until the printing plate is adequately taut, at which timebolts 92, are tightened to secure the roller position. The various plate travel paths through plate support 20 are noted in FIG.

' 2 whereinfor the longest path the plate is indicated in solid outline, and alternative paths are indicated'in dashed lines.

Referring to FIG. 5, another embodiment of the invention is illustrated wherein a frame 96 is adapted for mounting on a printing apparatus at a fixed spacing relative to a drum 10, as shown inf-1G. 1. As in FIG. 3, any feasible number of cylinder rollers '21 are included which are supported on a pair of bearings 97,'each having its inner race secured to a stationary shaft 98 cantilevered from pivoted bracket 99. A set-screw 101 secures the shaft within the bracket. V f V Each bracket 99 is supported on a pin 102 extending horizontally through a channel section of the name and secured against lateral movement a set-screw 103 ex tending into. a peripheral recess (not shown) 'of the pin. 7 Each bracket is continually urged to its uppermost position by means of a tensioned spring 104 secured to the bracket at one end, and at the other end mounted on a i stationary pm 105 extending from and secured to the frame; By this means, any number of rollers as are required to take-up slack in the printing Plate can be manually depressed toward the plate support 10 of the printing apparatus by pivoting bracket 99 downward in the direction indicated by the arrows and the printing plate slipped over the unsupported end of the depressed roller or rollers. Releasing the rollers permits spring 104 to urge the rollers upward until the plate'slack is taken up and the plate is retained taut on the rollers over which it is to move.

7 plate support unit 20 of the invention whereby variable Each of the plate supports illustrated in FIGS; 3 and 5 is completely flexible to accommodate, incombination with the plate support 10., a wide range of plate lengths. It is contemplated that drum 10 will have a smaller pe riphery than the maximum length of plate to be utilized and that at least one roller of apparatus 20 will always be required to take-up slack and maintain the plate under tension or reasonably taut. Obviously, in existing machines, replacement of the plate support therein with. one of smaller size would be optional.

In FIG. 6, a third embodiment of the invention is schematically illustrated. The embodiment thereof comprises a plurality of rollers, several of which define a path of travel past main operating positions. An electrostatic printing plate 22, of the aforementioned type is supported for movement on rollers 107, 108 and 159 and on additional rollers 21 of plate support unit 20 as are required to take up slack for an individual plate length. As in the previous embodiments, a motor herein designated 113, is operative to move web 43 and plate 22 at identical rates. As the plate advances, it moves past developing station 26 at which developing material descends from hopper 114 thereover into a suitable receiving bin 115 from which the developing material is returned to the hopper by a suitable conveying means designated 116. A suitable toner dispenser 117 may also be provided.

Electrostatic transfer of the powder image formed in developing is effected at transfer station 42 by means of corona generating device 44.

Three rollers 21 are illustrated and as above are typical as to the number of rollers that may be required, although any feasible number of rollers may be supported in an adjustable manner, similarly as described and illustrated in FIGS. 3, 4 and 5. The apparatus may be suitably adapted for an assembly mounting specifically as required.

Since documentary and other images to be reproduced vary in size, a printing plate bearing the image pattern must have sufficient length to accommodate the entire pattern or repeated patterns and preferably should have a minimum of excess length thereover. It should be apparent therefore that there are no real limits to which the length of plate can extend.

Whereas the invention is directed primarily for use in conjunction with electrostatic printers of the xeroprinting type, it is not the intention to restrict the invention thereto but it is intended also to encompass printing by means of xerography, for example, as disclosed in Carlson Patent 2,297,691 and related art.

Since many changes could be made in the above construction and many apparently widely diflerent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a xeroprinting apparatus in which images are reproduced from an endless flexible printing plate containing an image pattern comprised of configured insulating material on a conductive support, wherein the said apparatus includes a rotatable first support means adapted to advance a printing plate into operative relation past a plurality of treating stations, said treating stations including a charging station at which the printing plate receives an electrostatic charge that is retained by the insulating material thereon, a developing station at which electroscopic marking particles are presented to the charged insulating material on the plate to effect its development, and a transfer station at which developer on the insulating material is transferred to a moving support Web arriving at said transfer station in face-to-face relation with the developed pattern on said plate; the improvement comprising a second support means adapted in cooperation with said first support means to receive and support endless, flexible printing plates of at least two different dimensional lengths, said second support means comprising:

(a) a stationary frame disposed spaced from said first support means, said frame having two parallel opposite walls spaced apart at least the width of a printing plate to be supported;

(b) a plurality of aligned elongated slots defined in said opposite walls of said frame, each of said slots being arranged with one end opening into the edge of said walls;

(c) a plurality of cylindrical rollers each adapted to support a portion of printing plate to be advanced thereover;

(a!) mounting means to mount each of said rollers for rotation in oppositely aligned of said slots and removable through the open ends thereof; and,

(e) securement means adapted to secure each roller relatively in its slot at a position at which said rollers collectively support a printing plate in a taut relation to the portion of printing plate on said first support means.

2. In a xeroprinting apparatus in which images are reproduced from an endless flexible printing plate containing an image pattern comprised of configured insulating material on a conductive support, wherein the said apparatus includes a rotatable first support means adapted to advance a printing plate into operative relation past a plurality of treating stations, said treating stations including a charging station at which the printing plate receives an electrostatic charge that is retained by the insulating material thereon, adeveloping station at which electroscopic' marking particles are presented to the charged insulating material 011 the plate to effect its development, and a transfer station at which developer on the insulating material is transferred to a moving support web arriving at said transfer station in face-to-face relation with the developed pattern on saidplate; the improvement comprising a second support means adapted in cooperation with said first support means to receive and support endless, flexible printing plates of at least two different dimensional lengths, said second support means comprising:

(a) a stationary support frame disposed spaced from said first support means;

(b) a plurality of rotatable cylindrical rollers each adapted to support a portion of printing plate to be advanced thereover;

(c) a plurality of roller support means pivotally mounted on said frame and each adapted to support one of said rollers cantilevered from one end in position for rotation with the opposite end accessible for mounting a printing plate thereover; and,

(d) depressible resilient means connected between the frame and each of said support means to urge said rollers therein to a position tending away from said first support means whereby said rollers collectively support a printing plate continuously in a taut relation to a portion of said printing plate on said first support means.

References Cited in the file of this patent UNITED STATES PATENTS Meyer Nov. 10, 1925

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