Claims
- 1. A lithographic plate that is transformable so as to change the affinity of said plate for ink, said plate being a layered structure including an ink-receptive substrate, a conductive layer and an ink-repellent coating, said coating containing a dispersion of particles consisting essentially of at least one crystalline metal oxide compound.
- 2. The plate of claim 1 wherein said crystalline metal oxide compound contains at least two metal ions or atoms of different oxidation states.
- 3. The plate of claim 2 wherein said at least two metal ions or atoms are the same metal.
- 4. The plate of claim 2 wherein said at least two metal ions or atoms are different metals.
- 5. The plate of claim 2 Wherein said oxidation states are +2 and +3.
- 6. The plate of claim 1 wherein said crystalline metal oxide compound contains at least two metal ions or atoms of the same oxidation state.
- 7. The plate of claim 3 wherein said at least one crystalline metal oxide compound comprises at least one member of the group consisting of Fe.sub.3 O.sub.4, gamma Fe.sub.2 O.sub.3, Co.sub.3 O.sub.4, Mn.sub.3 O.sub.4, CrO.sub.2, ZnO, MnO.sub.2, MoO.sub.2, NbO.sub.2, SnO.sub.2, CuO, Cu.sub.2 O, TiO, Ti.sub.2 O.sub.3, V.sub.2 O.sub.3, VO.sub.2, WO.sub.2 and WO.sub.3.
- 8. The plate of claim 3 wherein said crystalline metal oxide compound comprises Fe.sub.3 O.sub.4.
- 9. The plate of claim 3 wherein said crystalline metal oxide compound comprises gamma Fe2O.sub.3.
- 10. The plate of claim 3 wherein said crystalline metal oxide compound comprises Co.sub.3 O.sub.4.
- 11. The plate of claim 3 wherein said crystalline metal oxide compound comprises Mn.sub.3 O.sub.4.
- 12. The plate of claim 3 wherein said crystalline metal oxide compound comprises CrO.sub.2.
- 13. The plate of claim 3 wherein said crystalline metal oxide compound comprises ZnO.
- 14. The plate of claim 3 wherein said crystalline metal oxide compound comprises MnO.sub.2.
- 15. The plate of claim 3 wherein said crystalline metal oxide compound comprises MoO.sub.2.
- 16. The plate of claim 3 wherein said crystalline metal oxide compound comprises NbO.sub.2.
- 17. The plate of claim 3 wherein said crystalline metal oxide compound comprises SnO.sub.2.
- 18. The plate of claim 3 wherein said crystalline metal oxide comprises Cu.sub.2 O.
- 19. The plate of claim 3 wherein said crystalline metal oxide comprises CuO.
- 20. The plate of claim 3 wherein said crystalline metal oxide compound comprises TiO.
- 21. The plate of claim 3 wherein said crystalline metal oxide compound comprises Ti.sub.2 O.sub.3.
- 22. The plate of claim 3 wherein said crystalline metal oxide compound comprises V.sub.2 O.sub.3.
- 23. The plate of claim 3 wherein said crystalline metal oxide compound comprises VO.sub.2.
- 24. The plate of claim 3 wherein said crystalline metal oxide compound comprises WO.sub.2.
- 25. The plate of claim 3 wherein said crystalline metal oxide compound comprises WO.sub.3.
- 26. The plate of claim 4 wherein said at least one crystalline metal oxide compound comprises at least one member of the group consisting of CoCr.sub.2 O.sub.4, CuCr.sub.2 O.sub.4, MnCr.sub.2 O.sub.4, NiCr.sub.2 O.sub.4, LaCrO.sub.3, Fe,Mn(Fe,Mn).sub.2 O.sub.4, Fe,Mn(Fe,Mn).sub.2 O.sub.4 :CuO, Cu(Fe,Cr).sub.2 O.sub.4, CuFe.sub.2 O.sub.4, CuCr.sub.2 O.sub.4, CoFe.sub.2 O.sub.4, NiFe.sub.2 O.sub.4, MgFe.sub.2 O.sub.4 and MnFe.sub.2 O.sub.4.
- 27. The plate of claim 4 wherein said crystalline metal oxide compound comprises CoCr.sub.2 O.sub.4.
- 28. The plate of claim 4 wherein said crystalline metal oxide compound comprises MnCr.sub.2 O.sub.4.
- 29. The plate of claim 4 wherein said crystalline metal oxide compound comprises NiCr.sub.2 O.sub.4.
- 30. The plate of claim 4 wherein said crystalline metal oxide compound comprises LaCrO.sub.3.
- 31. The plate of claim 4 wherein said crystalline metal oxide compound comprises Fe,Mn(Fe,Mn).sub.2 O.sub.4.
- 32. The plate of claim 4 wherein said crystalline metal oxide compound comprises Fe,Mn(Fe,Mn).sub.2 O.sub.4 :CuO.
- 33. The plate of claim 4 wherein said crystalline metal oxide compound comprises Cu(Fe,Cr).sub.2 O.sub.4.
- 34. The plate of claim 4 wherein said crystalline metal oxide compound comprises CuFe.sub.2 O.sub.4.
- 35. The plate of claim 4 wherein said crystalline metal oxide compound comprises CuCr.sub.2 O.sub.4.
- 36. The plate of claim 4 wherein said crystalline metal oxide compound comprises CoFe.sub.2 O.sub.4.
- 37. The plate of claim 4 wherein said crystalline metal oxide compound comprises NiFe.sub.2 O.sub.4.
- 38. The plate of claim 4 wherein said crystalline metal oxide compound comprises MgFe.sub.2 O.sub.4.
- 39. The plate of claim 4 wherein said crystalline metal oxide compound comprises MnFe.sub.2 O.sub.4.
- 40. The plate of claim 1 wherein said crystalline metal oxide compound is a high-temperature superconductor or related precursor.
- 41. The plate of claim 40 wherein said at least one crystalline metal oxide compound comprises at least one member of the group consisting of Ba.sub.2 CuO.sub.3, Ba.sub.2 Ca.sub.3 Cu.sub.4 O.sub.9, Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8+x, La.sub.2 CuO.sub.4 and YB a.sub.2 Cu.sub.3 O.sub.7-x, wherein x ranges from 0.1 to 0.5.
- 42. The plate of claim 40 wherein said crystalline metal oxide compound comprises B a.sub.2 CuO.sub.3.
- 43. The plate of claim 40 wherein said crystalline metal oxide compound comprises B a.sub.2 Ca.sub.3 Cu.sub.4 O.sub.9.
- 44. The plate of claim 40 wherein said crystalline metal oxide compound comprises Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8+x, wherein x ranges from 0.1 to 0.5.
- 45. The plate of claim 40 wherein said crystalline metal oxide compound comprises La.sub.2 CuO.sub.4.
- 46. The plate of claim 40 wherein said crystalline metal oxide compound comprises YB a.sub.2 Cu3O7-x wherein x ranges from 0.1 to 0.5.
- 47. The plate of claim 1 wherein the lattice of said crystalline metal oxide compound contains a physical feature extending across a crystal grain, which feature provides a low-energy pathway for electron migration.
- 48. The plate of claim 1 wherein the lattice of said crystalline metal oxide compound contains metal and oxygen atoms or ions placed such that metal d orbital and oxygen p or .pi..sub.p orbital overlap occurs.
- 49. The plate of claim 1 wherein the potential energy of the lattice of said crystalline metal oxide compound is not appreciably elevated by delocalization of one or more d-orbital electrons from the metal atom or ion into a conduction band.
- 50. A method of imaging a lithographic plate having a printing surface and including a surface layer containing selective filler material, a thin metal layer and a substrate, comprising the steps of:
- a. mounting the plate to the plate cylinder of a lithographic press having at least one plate cylinder, a corresponding number of blanket cylinders and an impression cylinder;
- b. exposing the surface layer to spark discharges between the plate and an electrode spaced close to the printing surface produced in response to picture signals representing an image, the spark discharges producing sufficient heat to remove the surface layer and the thin metal layer from the substrate at the points thereof exposed to the spark discharges;
- c. moving the electrode and the plate relatively to effect a scan of the printing surface;
- d. controlling the spark discharges to the plate in accordance with picture signals so that they occur at selected times in the scan; and
- e. causing straight-line travel of the spark discharges as they emerge from the electrode.
- 51. An apparatus for producing a lithographic plate comprising:
- a. a lithographic plate blank having a printing surface and including a surface layer, a thin metal layer and a substrate;
- b. a lithographic press having at least one plate cylinder to which the plate blank is mounted, a corresponding number of blanket cylinders and an impression cylinder;
- c. an electrode spaced close to the printing surface for producing spark discharges in response to picture signals representing an image, the spark discharges creating sufficient heat to remove the thin metal layer from the substrate at the points thereof exposed to the spark discharges;
- d. means for moving the electrode and the plate blank relatively to effect a scan of the printing surface; and
- e. means for controlling the spark discharges to the plate blank in accordance with picture signals so that they occur at selected times in the scan,
- wherein the surface layer promotes straight-line travel of the spark as it emerges from the electrode.
RELATED APPLICATION Aug. 19, 1988
This application is a continuation-in-part of Ser. No. 07/234,475 filed 8/19/88, now U.S. Pat. No. 4,911,075.
This invention relates to offset lithography relates more specifically to improved lithography plates and method and apparatus for imaging these plates.
There are a variety of known ways to print hard copy in black and white and in color. The traditional techniques include letterpress printing, rotogravure printing and offset printing. These conventional printing processes produce high quality copies. However, when only a limited number of copies are required, the copies are relatively expensive. In the case of letterpress and gravure printing, the major expense results from the fact that the image has to be cut or etched into the plate using expensive photographic masking and chemical etching techniques. Plates are also required in offset lithography. However, the plates are in the form of mats or films which are relatively inexpensive to make. The image is present on the plate or mat as hydrophilic and hydrophobic (and ink-receptive) surface areas. In wet lithography, water and then ink are applied to the surface of the plate. Water tends to adhere to the hydrophilic or water-receptive areas of the plate creating a thin film of water there which does not accept ink. The ink does adhere to the hydrophobic areas of the plate and those inked areas, usually corresponding to the printed areas of the original document, are transferred to a relatively soft blanket cylinder and, from there, to the paper or other recording medium brought into contact with the surface of the blanket cylinder by an impression cylinder.
Most conventional offset plates are also produced photographically. In a typical negative-working, subtractive process, the original document is photographed to produce a photographic negative. The negative is placed on an aluminum plate having a water-receptive oxide surface that is coated with a photopolymer. Upon being exposed to light through the negative, the areas of the coating that received light (corresponding to the dark or printed areas of the original) cure to a durable oleophilic or ink-receptive state. The plate is then subjected to a developing process which removes the noncured areas of the coating that did not receive light (corresponding to the light or background areas of the original). The resultant plate now carries a positive or direct image of the original document.
If a press is to print in more than one color, a separate printing plate corresponding to each color is required, each of which is usually made photographically as aforesaid. In addition to preparing the appropriate plates for the different colors, the plates must be mounted properly on the print cylinders in the press and the angular positions of the cylinders coordinated so that the color components printed by the different cylinders will be in register on the printed copies.
The development of lasers has simplified the production of lithographic plates to some extent. Instead of applying the original image photographically to the photoresist-coated printing plate as above an original document or picture is scanned line-by-line by an optical scanner which develops strings of picture signals, one for each color. These signals are then used to control a laser plotter that writes on and thus exposes the photoresist coating on the lithographic plate to cure the coating in those areas which receive lights. That plate is then developed in the usual way by removing the unexposed areas of the coating to create a direct image on the plate for that color. Thus, it is still necessary to chemically etch each plate in order to create an image on that plate.
There have been some attempts to use more powerful lasers to write images on lithographic plates by volatilizing the surface coating so as to avoid the need for subsequent developing. However, the use of such lasers for this purpose has not been entirely satisfactory because the coating on the plate must be compatible with the particular laser which limits the choice of coating materials. Also, the pulsing frequencies of some lasers used for this purpose are so low that the time required to produce a halftone image on the plate is unacceptably long.
There have also been some attempts to use scanning E-beam apparatus to etch away the surface coatings on plates used for printing. However, such machines are very expensive. In addition, they require the workpiece, i.e. the plate, be maintained in a complete vacuum, making such apparatus impractical for day-to-day use in a printing facility.
An image has also been applied to a lithographic plate by electro-erosion. The type of plate suitable for imaging in this fashion and disclosed in U.S. Pat. No. 4,596,733, has an oleophilic plastic substrate, e.g. Mylar brand plastic film, having a thin coating of aluminum metal with an overcoating containing conductive graphite which acts as a lubricant and protects the aluminum coating against scratching. A stylus electrode in contact with the graphite containing surface coating is caused to move across the surface of the plate and is pulsed in accordance with incoming picture signals. The resultant current flow between the electrode and the thin metal coating is by design large enough to erode away the thin metal coating and the overlying conductive graphite containing surface coating thereby exposing the underlying ink receptive plastic substrate on the areas of the plate corresponding to the printed portions of the original document. This method of making lithographic plates is disadvantaged in that the described electro-erosion process only works on plates whose conductive surface coatings are very thin and the stylus electrode which contacts the surface of the plate sometimes scratches the plate. This degrades the image being written onto the plate because the scratches constitute inadvertent or unwanted image areas on the plate which print unwanted marks on the copies.
Finally, we are aware of a press system, only recently developed, which images a lithographic plate while the plate is actually mounted on the print cylinder in the press. The cylindrical surface of the plate, treated to render it either oleophilic or hydrophilic, is written on by an ink jetter arranged to scan over the surface of the plate. The ink jetter is controlled so as to deposit on the plate surface a thermoplastic image-forming resin or material which has a desired affinity for the printing ink being used to print the copies. For example, the image-forming material may be attractive to the printing ink so that the ink adheres to the plate in the areas thereof where the image-forming material is present and phobic to the "wash" used in the press to prevent inking of the background areas of the image on the plate.
While that prior system may be satisfactory for some applications, it is not always possible to provide thermoplastic image-forming material that is suitable for jetting and also has the desired affinity (philic or phobic) for all of the inks commonly used for making lithographic copies. Also, ink jet printers are generally unable to produce small enough ink dots to allow the production of smooth continuous tones on the printed copies, i.e. the resolution is not high enough.
Thus, although there have been all the aforesaid efforts to improve different aspects of lithographic plate production and offset printing, these efforts have not reached full fruition primarily because of the limited number of different plate constructions available and the limited number of different techniques for practically and economically imaging those known plates. Accordingly, it would be highly desirable if new and different lithographic plates became available which could be imaged by writing apparatus able to respond to incoming digital data so as to apply a positive or negative image directly to the plate in such a way as to avoid the need of subsequent processing of the plate to develop or fix that image.
Accordingly, the present invention aims to provide various lithographic plate constructions which can be imaged or written on to form a positive or negative image therein.
Another object is to provide such plates which can be used in a wet or dry press with a variety of different printing inks.
Another object is to provide low cost lithographic plates which can be imaged electrically.
A further object is to provide an improved method for imaging lithographic printing plates.
Another object of the invention is to provide a method of imaging lithographic plates which can be practiced while the plate is mounted in a press.
Still another object of the invention is to provide a method for writing both positive and negative or background images on lithographic plates.
Still another object of the invention is to provide such a method which can be used to apply images to a variety of different kinds of lithographic plates.
A further object of the invention is to provide a method of producing on lithographic plates half tone images with variable dot sizes.
A further object of the invention is to provide improved apparatus for imaging lithographic plates.
Another object of the invention is to provide apparatus of this type which applies the images to the plates efficiently and with a minimum consumption of power.
Still another object of the invention is to provide such apparatus which lends itself to control by incoming digital data representing an original document or picture.
Other objects will, in part, be obvious and will, in part, appear hereinafter. The invention accordingly comprises an article of manufacture possessing the features and properties exemplified in the constructions described herein and the several steps and the relation of one or more of such steps with respect to the others and the apparatus embodying the features of construction, combination of elements and the arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
In accordance with the present invention, images are applied to a lithographic printing plate by altering the plate surface characteristics at selected points or areas of the plate using a non-contacting writing head which scans over the surface of the plate and is controlled by incoming picture signals corresponding to the original document or picture being copied. The writing head utilizes a precisely positioned high voltage spark discharge electrode to create on the surface of the plate an intense-heat spark zone as well as a corona zone in a circular region surrounding the spark zone. In response to the incoming picture signals and ancillary data keyed in by the operator such as dot size, screen angle, screen mesh, etc. and merged with the picture signals, high voltage pulses having precisely controlled voltage and current profiles are applied to the electrode to produce precisely positioned and defined spark/corona discharges to the plate which etch, erode or otherwise transform selected points or areas of the plate surface to render them either receptive or non-receptive to the printing ink that will be applied to the plate to make the printed copies.
Lithographic plates are made ink receptive or oleophilic initially by providing them with surface areas consisting of unoxidized metals or plastic materials to which oil and rubber based inks adhere readily. On the other hand, plates are made water receptive or hydrophilic initially in one of three ways. One plate embodiment is provided with a plated metal surface, e.g. of chrome, whose topography or character is such that it is wetted by surface tension. A second plate has a surface consisting of a metal oxide, e.g. aluminum oxide, which hydrates with water. The third plate construction is provided with a polar plastic surface which is also roughened to render it hydrophilic. As will be seen later, certain ones of these plate embodiments are suitable for wet printing, others are better suited for dry printing. Also, different ones of these plate constructions are preferred for direct writing; others are preferred for indirect or background writing.
The present apparatus can write images on all of these different lithographic plates having either ink receptive or water receptive surfaces. In other words, if the plate surface is hydrophilic initially, our apparatus will write a positive or direct image on the plate by rendering oleophilic the points or areas of the plate surface corresponding to the printed portion of the original document. On the other hand, if the plate surface is oleophilic initially, the apparatus will apply a background or negative image to the plate surface by rendering hydrophilic or oleophobic the points or areas of that surface corresponding to the background or non-printed portion of the original document. Direct or positive writing is usually preferred since the amount of plate surface area that has to be written on or converted is less because most documents have less printed areas than non-printed areas.
The plate imaging apparatus incorporating our invention is preferably implemented as a scanner or plotter whose writing head consists of one or more spark discharge electrodes. The electrode (or electrodes) is positioned over the working surface of the lithographic plate and moved relative to the plate so as to collectively scan the plate surface. Each electrode is controlled by an incoming stream of picture signals which is an electronic representation of an original document or picture. The signals can originate from any suitable source such as an optical scanner, a disk or tape reader, a computer, etc. These signals are formatted so that the apparatus' spark discharge electrode or electrodes write a positive or negative image onto the surface of the lithographic plate that corresponds to the original document.
If the lithographic plates being imaged by our apparatus are flat, then the spark discharge electrode or electrodes may be incorporated into a flat bed scanner or plotter. Usually, however, such plates are designed to be mounted to a print cylinder. Accordingly, for most applications, the spark discharge writing head is incorporated into a so-called drum scanner or plotter With the lithographic plate being mounted to the cylindrical surface of the drum. Actually, as we shall see, our invention can be practiced on a lithographic plate already mounted in a press to apply an image to that plate in situ. In this application, then, the print cylinder itself constitutes the drum component of the scanner or plotter.
To achieve the requisite relative motion between the spark discharge writing head and the cylindrical plate, the plate can be rotated about its axis and the head moved parallel to the rotation axis so that the plate is scanned circumferentially with the image on the plate "growing" in the axial direction. Alternatively, the writing head can move parallel to the drum axis and after each pass of the head, the drum can be incremented angularly so that the image on the plate grows circumferentially. In both cases, after a complete scan by the head, an image corresponding to the original document or picture will have been applied to the surface of the printing plate.
As each electrode traverses the plate, it is supported on a cushion of air so that it is maintained at a very small fixed distance above the plate surface and cannot scratch that surface. In response to the incoming picture signals, which usually represent a half tone or screened image, each electrode is pulsed or not pulsed at selected points in the scan depending upon whether, according to the incoming data, the electrode is to write or not write at these locations. Each time the electrode is pulsed, a high voltage spark
discharge occurs between the electrode tip and the particular point on the plate opposite the tip. The heat from that spark discharge and the accompanying corona field surrounding the spark etches or otherwise transforms the surface of the plate in a controllable fashion to produce an image-forming spot or dot on the plate surface which is precisely defined in terms of shape and depth of penetration into the plate.
Preferably the tip of each electrode is pointed to obtain close control over the definition of the spot on the plate that is affected by the spark discharge from that electrode. Indeed, the pulse duration, current or voltage controlling the discharge may be varied to produce a variable dot on the plate. Also, the polarity of the voltage applied to the electrode may be made positive or negative depending upon the nature of the plate surface to be affected by the writing, i.e. depending upon whether ions need to be pulled from or repelled to the surface of the plate at each image point in order to transform the surface at that point to distinguish it imagewise from the remainder of the plate surface, e.g. to render it oleophilic in the case of direct writing on a plate whose surface is hydrophilic. In this way, image spots can be written onto the plate surface that have diameters in the order of 0.005 inch all the way down to 0.0001 inch.
After a complete scan of the plate, then, the apparatus will have applied a complete screened image to the plate in the form of a multiplicity of surface spots or dots which are different in their affinity for ink from the portions of the plate surface not exposed to the spark discharges from the scanning electrode.
Thus, using our method and apparatus, high quality images can be applied to our special lithographic plates which have a variety of different plate surfaces suitable for either dry or wet offset printing. In all cases, the image is applied to the plate relatively quickly and efficiently and in a precisely controlled manner so that the image on the plate is an accurate representation of the printing on the original document. Actually using our technique, a lithographic plate can be imaged while it is mounted in its press thereby reducing set up time considerably. An even greater reduction in set up time results if the invention is practiced on plates mounted in a multi-color press because correct color registration between the plates on the various print cylinders can be accomplished electronically rather than manually by controlling the timings of the input data applied to the electrodes that control the writing of the images on the corresponding plates. As a consequence of the forgoing combination of features, our method and apparatus for applying images to lithographic plates and the plates themselves should receive wide acceptance in the printing industry.
US Referenced Citations (22)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 64-30786 |
Apr 1989 |
JPX |
Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
234475 |
Aug 1988 |
|
Patent Grant
5109771
