GB1574570A

GB1574570A - Plate making attachment for graphic art cameras

Info

Publication number: GB1574570A
Application number: GB25476/78A
Authority: GB
Original assignee: Coulter Systems Corp
Current assignee: Coulter Systems Corp
Priority date: 1977-06-01
Filing date: 1978-05-31
Publication date: 1980-09-10
Also published as: IT1104701B; DE2823896A1; JPS5439132A; CA1133572A; FR2393350A1; BE867658A; CH622627A5; NL7805921A; IT7849621A0

Abstract

The accessory includes an endless belt (20) of electrophotographic film which is charged by a corona source (44) exposed, rotated until facing a station (38) where liquid toner is applied to the resulting latent image under polarisation conditions. A reserve of sheet material (34), such as paper, aluminium, plastic, or other flexible substrate, is included and a detached sheet or part of a continuous reserve roller is brought into the restriction which a pressure roller (40), interacting with the endless belt (20), constitutes, transferring the image provided with toner and bringing it to a fixing station (42) and subsequently causing the completed plate to appear. This plate can be used in an offset printing press. <IMAGE>

Description

(54) PLATE MAKING ATTACHMENT FOR GRAPHIC ART CAMERAS (71) We, COULTER SYSTEMS COR- PORATION, organised and existing under the laws of the State of Illinois, of 35 Wiggins Avenue, Bedford, Massachusetts 017330, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The field of this invention is the art of making offset printing plates for use in printing through the use of electrophotographic techniques.

Offset plates are made photographically by complex methods requiring the use of silver halide film, photoresists, and the processing of the images to achieve their incorporation onto plates that can be used in printing presses. In recent years electrostatic techniques have also been used to make such plates but their quality is so inferior to the quality of photographically made plates that not much of this type of technique is used.

The invention herein revolves around a type of electrophotographic film that is capable of being imaged with quality and grey scale as good as if not better than that achieved by photographic techniques and with resolution that is better. The film comprises an inorganic coating of microcrystalline material that is bonded onto la polyester substrate with an intervening ohmic layer to aid of charging. The material which is used comprises a coating of radio frequency sputtered cadmium sulfide that is from about 2000 Angstroms to about 2 microns thick upon a layer of about 300 to 500 Angstroms thick of indium tin axide which in turn is bonded to a sheet of stable polyester plastic about .005 inch thick. One such film is described in U.S. Patent No.

4,025,339, issued May 24, 1977.

Because of the fact that the film can be exposed at high speed and transferred immediately to a carrier such as paper, alu- minum, plastic and the like, the entire process can be carried on inside of a cartridge that takes the place of the usual photographic film cartridge that is used with graphic arts cameras. This is convenient and eliminates considerable processing since the complete plate emerges from the device, can be immersed in a suitable bath which renders the toned and untoned parts of the image ink receptive and ink repellant, respectively, and then utilized in an offset printing press.

An atachment for the back of a graphic arts camera comprising means for mounting the attachment to the camera and means interior of the attachment for supporting and rotating an endless belt of electrophotographic material for charging, exposure, toning and transfer to a carrier. The carrier comprises sheeting carried in the attachment and fed to the belt, means for pressing the carrier against the belt after the image has been toned to transfer the image to the carrier and means for dispensing the toned carrier from the attachment. The attachment may include means for moving the carrier past a fixing station prior to being dispensed.

Accordingly, a first object of the invention is to provide an attachment adapted for use with a graphic art camera that has structure for projecting a light image to an image plane at the rear of the camera and exposing such plane to such image for reproducing purposes, said attachment including a rotatable endless belt including at least a portion of an electrophotographic film, a first planar reach of the belt disposed generally at a first plane and having a second planar reach and means for controlled rotation of the belt and positioning said film portion thereof to occupy the reaches, means associated with said first reach for charging the film, means to stop and accurately locate the film portion at said first reach at the first plane and hold the same securely for exposure but capable of releasing the film belt to permit its subsequent rotation, toner supply and dispensing means for applying toner to the second reach of the film belt, transfer means for bringing a carrier material into close proximity with said film portion to transfer a toned image to said carrier material, and means for leading the carrier material out of the attachment.

A second object of the invention is to provide a method for reproducing an image onto a carrier material from an electrophotographic film portion of an endless belt including, rotating said belt through a series of locations, charging said film portion at a first location, positioning said film portion at a second location, stopping said film portion at said second location, securing said film portion in an exposure plane in said second location, releasing said film portion, toning said film portion at a third location, and transferring an image from said film portion to a carrire material at a fourth location.

The preferred embodiments of this invention will now be described, by way of example, with reference to the drawings accompanying this specification in which: Figure 1 is a block diagram showing how the attachment of the invention is connected to the back of a graphic arts camera, and Figure 2 is a diagram of the attachment showing the basic parts and construction thereof.

Offset printing plates are made by a technique which requires that the image to be incorporated into the plate be photographed.

The cameras which are used are specialized for the purpose and commence the process by extosing silver halide film contained in cartridges that are secured to the back of the camera at the image plane thereof.

Figure 1 illustrates such a camera at 10 with a lens system that can partially be seen at 12 and having the normal cartridge replaced by the attachment of the invention as shown at 14. The completed plate as dispensed from the attachment 16 is shown at 18.

On its interior, the attachment 16 is shown to contain an endless electrophotographic film belt 20 with drive and/or mounting rollers at 22 and 24. A drive roller 26 may be utilized in addition to the mounting rollers, The bottom reach 28 of the belt 20 is shown facing the optical system of the camera, represented by the lens 30, so that when the camera is used to image copy, the image will be projected onto the outer surface of the belt on the bottom thereof. The attachment also contains a toner and bias belt 32, a supply of plate material at 34 mounted on a suitable support 36, toner supply and dispensing means at 38, a pressure roller 40 and an optional fixing station at 42.Various guide and drive rollers, controls, electrical connections and the like are required but not shown since, as will be explained, when the invention is described these will become apparent to those skilled in this art.

There is a corona voltage source and a corona wire mounting at 44 which may be fixed or oscillating to provide an even distribution of charge when the attachment is in operation.

When it is desired to use the camera 10 and the attachment 16, the camera is focussed on the copy, the copy is suitably illuminated and the cycle of operation is started by any suitable switch. The sequence of operation is readily programmed by switching and logic circuits that are readily constructed and incorporated into the atattachment The first thing that happens is that the belt 20 is driven in a generally clockwise direction by the drive roller 26 or other drive means for a period of time that is required to carry a portion of the length thereof past the corona device 44 and onto the bottom of the belt to form the reach 28 along substantially the entire length thereof.

The corona device 44 has in the meantime been energized and it charges the photoconductive coating of the film forming the belt 20. The direction of movement is shown by the arrows.

Ireally the charge of the belt 20 is controlled by suitably controlling the corona voltage and/or the speed of the belt 20. The surface voltage may be measured by an electrostatic voltmeter and related to the amount of exposure that is to be made.

Once the charged length of the film of the belt 20 has been positioned to form the reach 28, the belt is stopped in its movement and rigidly held at the specific location with respect to the focal plane of the camera 10 by means of a platen 46. The platen 46 may be pressed against the film or may be provided with vacuum means.

Suitable means to operate the platen are provided and are not shown. The vacuum platen 46 sucks the film reach 28 flatly against itself and holds it there until the exposure has been made. This, like the other functions of the attachment 16 can be worked into an automatic program or can be performed in a sequence manually by the operator.

With the belt fixed, the camera shutter is now operated to expose the film reach 28 to the projected light image of the copy being reproduced. It is understood that the entire attachment 16 is in darkness.

After exposure the belt is released from the platen 46 by applying air pressure thereto and the belt drive operated by the roller 26 to move the belt 20 in the same clockwise direction for a period of time which will carry the now-exposed bottom section up and onto the top of the belt at the reach 48. Here the belt stops moving once more.

Now the toning and bias belt 32 is started up and rotates in a clockwise direction also, shown by the arrows. This movement is relatively rapid in order to dispense toner particles in a liquid form ontao the upper reach 48 of the belt 20. Suitable dams and absorbant confining members are provided to prevent the toner from running off the edges and ends of the areas which it is desired to tone. Toner is dispensed from a supply which is shown at 38. The belt 32 is formed of conductive material such as metal and a bias of about 2-20 volts d.c. plus is established between the two belts in the gap between them by a bias circuit 33, the film belt 20 being positive relative the toning belt.After a period of time has elapsed when there has been sufficient adherence of the toner particles, there is a voltage applied to the two belts across the gap of the order of negative 200 volts d.c. on the toner belt relative to the film belt 20 so that there is a sweeping of the uncommitted toner particles from the toned image.

The gap between the belts is of the order of capillary dimensions to enable the handling of the liquid toner. The belt 32 is squeegeed dry by a suitable doctor blade 50 located at the left end thereof as viewed in Figure 2.

After the image on the belt 20 has been toned, that is, developed, the belt commences to move again, this time carrying the image to the right and into the nip between the rollers 24 and 40. In the meantime the plate material 34 which can be metal, paper or plastic, has been led through the feed rollers 52 also to the nip as indicated at 54 and is being pressed against or brought into close proximity with the surface of the belt 20 as the belt rotates. The toned image which is still moist is transferred to the plate material and emerges at the right as shown at 56. Suitable guide and confining means ensure this movement.

There will preferably be a transfer voltage of approximately negative 400 volts d.c.

applied to the transfer roller 40 to move the toner image onto the carrier material.

After the transferred carrier material emeges from the transfer means at 56 the image may be ejected or may pass over a fixing station of heat lamps or the like at 42 where the toner is fused to the carrier. This completes the making of the plate which emerges at 18 from the attachment 16. The only thing left to be done to it is to render the toned image ink receptive and the untoined portion ink repellant. This is a technique which has been achieved by applying suitable chromate compounds or the like thereto, but this is not considered a part of this invention.

The plate material 34 is preferably in the form of a continuous strip and means are in such case provided to cut off the portion which has been processed as it emerges at 18. Such cutoff means are indicated generally by the block 58.

The belt 20 may also be an endless webb containing only a portion of film substantially equal to the reach 28. The fixing of the toner may be done outside of the attachment. The corona device 44 may be energized after the belt is stopped in the reach 28 and the device 44 may be moved past the stopped film to apply the charge.

WHAT WE CLAIM IS:- 1. An attachment for use with a graphic art camera that has structure for projecting a light image to an image plane at the rear of the camera and exposing such plane to such image for reproducing purposes, said attachment including a rotatable endless belt including at least a portion of an electrophotographic film, a first planar reach of the belt disposed generally at a first plane and having a second planar reach and means for controlled rotation of the belt and positioning said film portion thereof to occupy the reaches, means associated with said first reach for charging the film, means to stop and accurately locate the film portion at said first reach at the first plane and hold the same securely for exposure but capable of releasing the film belt to permit its subsequent rotation, toner supply and dispensing means for applying toner to the second reach of the film belt, transfer means for bringing a carrier material into close proximity with said film portion to transfer a toned image to said carrier material, and means for leading the carrier material out of the attachment.

2. The attachment as claimed in claim 1 in which the toner dispensing means in dude a second belt having a top reach and a bottom reach, the toner supply being arranged to apply toner to the top reach of the second belt, the bottom reach of the second belt being juxtaposed to the second reach of the film belt and adapted to move parallel but in opposite direction relative thereto, the toner adapted to be carried from the top reach of the second belt around to the bottom reach thereof and thereafter dropped onto the upwardly facing film portion of the belt to tone a latent image carried thereon.

3. The attachment as claimed in claims 1 or 2 in which the toner is in liquid form.

4. The attachment as claimed in claims 2 or 3 in which means are provided electrically to bias the belts relative to one another across the space between belts to assist in the toning operation.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. will carry the now-exposed bottom section up and onto the top of the belt at the reach 48. Here the belt stops moving once more. Now the toning and bias belt 32 is started up and rotates in a clockwise direction also, shown by the arrows. This movement is relatively rapid in order to dispense toner particles in a liquid form ontao the upper reach 48 of the belt 20. Suitable dams and absorbant confining members are provided to prevent the toner from running off the edges and ends of the areas which it is desired to tone. Toner is dispensed from a supply which is shown at 38. The belt 32 is formed of conductive material such as metal and a bias of about 2-20 volts d.c. plus is established between the two belts in the gap between them by a bias circuit 33, the film belt 20 being positive relative the toning belt.After a period of time has elapsed when there has been sufficient adherence of the toner particles, there is a voltage applied to the two belts across the gap of the order of negative 200 volts d.c. on the toner belt relative to the film belt 20 so that there is a sweeping of the uncommitted toner particles from the toned image. The gap between the belts is of the order of capillary dimensions to enable the handling of the liquid toner. The belt 32 is squeegeed dry by a suitable doctor blade 50 located at the left end thereof as viewed in Figure 2. After the image on the belt 20 has been toned, that is, developed, the belt commences to move again, this time carrying the image to the right and into the nip between the rollers 24 and 40. In the meantime the plate material 34 which can be metal, paper or plastic, has been led through the feed rollers 52 also to the nip as indicated at 54 and is being pressed against or brought into close proximity with the surface of the belt 20 as the belt rotates. The toned image which is still moist is transferred to the plate material and emerges at the right as shown at 56. Suitable guide and confining means ensure this movement. There will preferably be a transfer voltage of approximately negative 400 volts d.c. applied to the transfer roller 40 to move the toner image onto the carrier material. After the transferred carrier material emeges from the transfer means at 56 the image may be ejected or may pass over a fixing station of heat lamps or the like at 42 where the toner is fused to the carrier. This completes the making of the plate which emerges at 18 from the attachment 16. The only thing left to be done to it is to render the toned image ink receptive and the untoined portion ink repellant. This is a technique which has been achieved by applying suitable chromate compounds or the like thereto, but this is not considered a part of this invention. The plate material 34 is preferably in the form of a continuous strip and means are in such case provided to cut off the portion which has been processed as it emerges at 18. Such cutoff means are indicated generally by the block 58. The belt 20 may also be an endless webb containing only a portion of film substantially equal to the reach 28. The fixing of the toner may be done outside of the attachment. The corona device 44 may be energized after the belt is stopped in the reach 28 and the device 44 may be moved past the stopped film to apply the charge. WHAT WE CLAIM IS:-

1. An attachment for use with a graphic art camera that has structure for projecting a light image to an image plane at the rear of the camera and exposing such plane to such image for reproducing purposes, said attachment including a rotatable endless belt including at least a portion of an electrophotographic film, a first planar reach of the belt disposed generally at a first plane and having a second planar reach and means for controlled rotation of the belt and positioning said film portion thereof to occupy the reaches, means associated with said first reach for charging the film, means to stop and accurately locate the film portion at said first reach at the first plane and hold the same securely for exposure but capable of releasing the film belt to permit its subsequent rotation, toner supply and dispensing means for applying toner to the second reach of the film belt, transfer means for bringing a carrier material into close proximity with said film portion to transfer a toned image to said carrier material, and means for leading the carrier material out of the attachment.

5. The attachment as claimed in claim

4 in which said bias means include structure for applying a low voltage bias at the beginning of a toning period and a higher bias at the end of such period.

6. The attachment as claimed in any one of claims 1 to 5 in which said means to locate and hold the belt comprise a platen located parallel to the first reach and having a bottom planar portion at the first plane.

7. The attachment as claimed in claim 6 in which the platen includes vacuum means to draw said film portton flat against said bottom planar portion.

8. The attachment as claimed in any one of claims 1 to 7 in which means are provided to remove toner from the second belt as it rotates and prior to entry thereof to its top reach.

9. The attachment as claimed in any one of claims 1 to 8 in which the transfer means include transfer roll means engaged against the film surface and providing a nip between itself and the film surface, a supply of said carrier material, and means for leading said carrier material into the nip as said film portion is rotated by the roll means.

10. The attachment as claimed in any one of claims 1 to 9 in which means are provided for fixing a transferred image on said carrier material before it is led out of the attachment.

11. The attachment as claimed in any one of claims 1 to 10 in which means are provided electrically to bias said carrier material relative to said film portion.

12. A method for reproducing an image onto a carrier material from an electrophotographic film portion of an endless belt comprising, rotating said belt through a series of locations, charging said film portion at a first location, positioning said film portion at a second location, stopping said film portion at said second location, securing said film portion in an exposure plane in said second location, releasing said film portion, toning said film portion at a third location, and transferring an image from said film portion to a carrier material at a fourth location.

13. A method of reproducing as claimed in claim 12 in which said toning includes, forming a planar reach in said third location, stopping said film portion in said planar reach, and applying toner to the top of a second belt rotating with a bottom reach substantially parallel to and spaced from said planar reach to dispense said toner onto said film portion.

14. A method of reproducing as claimed in claim 13 in which said toning includes, electrically biasing the belts relative to one another.

15. A method of reproducing as claimed in claim 14 in which said toning includes, applying a low voltage bias between the belts for a first period of time, and applying a second higher voltage bias between the belts following said first period of time.

16. A method of reproducing as claimed in any one of claims 13 to 15 in which said toning includes, removing said toner from said second belt before it rotates from its bottom reach.

17. A method of reproducing as claimed in any one of claims 12 to 16 in which said securing includes, applying a negative pressure to one side of said film portion across the exposure plane to draw said film portion against the exposure plane.

18. A method of reproducing as claimed in any one of claims 12 to 17 in which said transferring includes, rolling said carrier material against said film portion as it rotates past said fourth location.

19. A method of reproducing as claimed in any one of claims 12 to 18 including fixing said image onto said carrier material at a fifth location.

20. A method of reproducing as claimed in any one of claims 12 to 19 in which said transferring includes, electrically biasing said carrier material relative to said film portion.

21. An attachment for use with a graphic art camera substantially as hereinbefore described with reference to the accompanying drawngs.

22. A method for reproducing an image substantially as hereinbefore described with reference to the accompanying drawings.

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