IL131425A - Erasable printing member, method for its manufacture and printing apparatus using said printing member - Google Patents

Abstract

Method of manufacturing a planographic/lithographic printing member (10), which comprises the following steps: (a) uniformly electrostatically charging a dielectric or insulated substrate; (b) developing the electrostatic charge pattern with dry development material (20); (c) fusing said particles to define an image; (d) removing the non-fused particles from said substrate, leaving thereon the image defined by the fused particles. 2254 י" ד באלול התשס" ד - August 31, 2004

Description

ο^τππ Ρ7Π3 ωππωππ Πϋ3τπ ii?nm ,ms"7 πυτω ,πρ^η^ lmn ΙΓΕΠΤ. p7n ERASABLE PRINTING MEMBER, METHOD FOR ITS MANUFACTURE AND PRINTING APPARATUS USING SAID PRINTING MEMBER 8526/99 PATENT APPLICATION FOR: ERASABLE PRINTING MEMBER. METHOD FOR ITS MANUFACTURE AND PRINTING APPARATUS USING SAID PRINTING MEMBER Field of the Invention This invention relates to lithographic printing members, plates and/or cylinders, more particularly to reusable lithographic printing members, to a method for manufacturing such printing members and to their use in printing process and apparatus.

Background of the Invention Lithography or offset printing is currently the dominant printing technology. The printing is typically performed by a printing form/plate that has a specially prepared/treated surface, some areas of which are capable of accepting lithographic ink, whereas other areas, when moistened with water or dampening solution, will not accept the ink. For a positive printing plate the areas, which accept ink, form the printing image areas and the water accepting (ink-repelling) areas form the background areas. For a negative working plate, the situation is inverse.

The specially prepared/treated surface typically presents an anodized aluminum surface coated by a thin layer of ink-receptive photopolymer, that hardens when exposed to an image wise radiation. In a subsequent process stage, called development, the non-exposed areas are washed out, exposing the water-accepting anodized aluminum surface. This process 8526/99 -2- results in a plate that provides excellent image quality and sustains long mechanical wear and tear typical for long print runs.

Use of this type of printing plate implies use of water on the printing press. The complicated relationship between the amount of water and the amount of ink requires significant skills on behalf of the press operator. Developments of so-called dry or waterless printing plates allows simplifying of the press operation, but has introduced a number of other problems.

Another disadvantage of these printing plates is that processing requires the use of chemicals and/or solvents. The plates are typically sensitive to UV radiation, and a scarcity of sources of UV radiation complicates their exposure by digital exposure means, such as plate setters. To overcome this obstacle, development of IR sensitive offset printing plates, where a large variety of radiation sources exists, was undertaken and such plates have been recently commercialized by a number of companies.

Further efforts to reduce or eliminate plate processing resulted in so-called ablation-type plates, disclosed in U.S.P. 5,339,737, and so-called phase change plates, disclosed in U.S.P. 5,839,369, 5,839,370, 5,855,173, 5,836,249 and others. The appearance of processless and waterless plates has led to the development of printing presses with on-press plate imaging. Such presses are available from a number of vendors, such as Karat Digital Press, Heidelberg Druckmaschinen AG, Heidelberg, Germany, and others. USP 5,339,737 discloses such a press. It is clear 8526/99 that the need to have the plates prepared ahead of time at a special production facility hampers further development of both computer-to-plate systems and on-press imaging.

Efforts to enable in situ preparation have been disclosed in USP 4,718,340, USP 5,339,737, and others. They typically teach the coating of a cylinder by a fluid that, when dried, has certain hydrophilic or oleophilic properties, and may be selectively removed or its properties altered to form an image-wise pattern that represents the printing master. Although progressive, these solutions require bulky fluid coating equipment, and make the process much more suitable for use with on-press imaging solutions than with computer-to-plate devices (most of them being suitable for only one type of printing, wet or waterless).

The purpose of the present invention is to offer an easy, operative printing member manufacturing method, suitable for both computer-to-plate and on-press imaging.

Summary of the Invention The method of manufacturing a planographic/lithographic printing member according to the invention comprises the following steps: a - uniformly electrostatically charging a dielectric or insulated substrate; b - developing the electrostatic charge pattern with dry development material p article s ; c - fusing said dry particles to define an image; 8526/99 -4- d - moving the non-fused particles from said dielectric or insulated substrate, leaving thereon the image defined by the fused particles.

The development material is generally an electrophotographic toner, such as E230 commercially available from Fuji-Xerox Co, Ltd., Tokyo, Japan, although practically any electrophotographic toner may be used for this purpose. Both dry and liquid toners may be used in carrying out the invention: accordingly, the term "toners", whenever used in this specification and claims, must be construed to include both dry and liquid toners. The development material, therefore, will be called hereinafter "toner", but this denomination must not be construed as a limitation. The development material, as applied, must have a charge of opposite charge to that with which the substrate has been charged.

The resulting printing member can be used in a printing apparatus carrying out a printing process, said apparatus and process being also part of the invention.

The fused toner particles defining the image can be removed from the printing member, after its use in printing, leaving a clean substrate, which can be treated once again by the aforesaid steps to produce a new and different planographic/lithographic printing member.

The reusable printing member, obtained by the aforesaid process, is also an object of this invention. 8526/99 The invention also comprises as apparatus for manufacturing a planographic/lithographic printing member, which comprises: I - a support for an dielectric or insulated substrate; II — a charging device for uniformly electrostatically charging said substrate; III - means for applying to the charged substrate dry development material particles whereby to develop the electrostatic charge pattern; IV — a radiation source for selectively applying sufficient energy to said development material to fuse development material particles; V- scanning means for imparting to said radiation source a scanning motion whereby selectively to fuse said particles to define a predetermined image; VI - a device for removing the non-fused particles from said substrate, leaving thereon said image.

The printing process in which a printing member according to the invention is used, is also a part of this invention.

Brief Description of the Drawings In the drawings: - Fig. 1 schematically illustrates the manufacture of a printing plate according to an embodiment of the invention; - Fig. 2 schematically illustrates the manufacture of a printing plate according to another embodiment of the invention; - Fig. 3 schematically illustrates the manufacture of a printing drum according to another embodiment of the invention; 8526/99 -6- - Fig. 4 schematically illustrates an on-press embodiment of a plate manufacturing apparatus according to the invention; - Fig. 5 illustrates a flexographic plate manufacturing apparatus according to an embodiment of the invention; and - Figs. 6A, 6B, 6C and 6D are detailed illustrations of consecutive steps of the flexographic plate manufacturing process by an apparatus according to an embodiment of the invention.

Detailed Description of Preferred Embodiments According to the invention, a printing member comprises a plate or a cylinder that has a dielectric or insulating surface with predefined properties with respect to water, hydrophilic or hydrophobic and printing ink, oleophilic or oleophobic. A typical example of such a surface may be anodized aluminum similar to the substrate of the regular presensitized photopolymer offset plates. Anodized aluminum is a strong dielectric. The dielectric surface is evenly charged by a source of charge to a potential that insures attraction and certain retention of toner particles to its surface. The even potential field created is developed by a material bearing the opposite charge sign and having surface properties different from those of the dielectric substrate, i.e., if the substrate is hydrophilic, the development material should have oleophihc/hpophilic properties. As a result of the presence of opposite charges, the development material or toner uniformly covers the dielectric surface. The development material is held onto the surface by electrostatic forces generated by the charges of both the dielectric surface and development material. While this is not critical, it may be desirable to control the thickness of the toner layer. A 8526/99 -7- toner metering device may be provided, and such devices are known in the art and need not be described.

At the next stage, the development material is selectively set attached/fused to the dielectric surface according to a predetermined pattern that defines the image to be printed. The development material attachment/fusion may be performed by melting said material according to said predetermined pattern by means of a scanning radiation beam. A scanning radiation beam, generally a laser beam, of proper power may provide the energy required for melting said material. Following this stage of the process, the charge remaining on the substrate is neutralized; then, the remaining and unmelted development material is cleaned off the plate and the plate is ready for printing. The removed/cleaned material is recycled and returned to the toner cartridge for reuse, eliminating waste of materials.

Fig. 1 is a schematic representation of one of the embodiments of a printing plate manufacturing apparatus, generally indicated at 10, constructed in accordance with the principles of the present invention. The plate manufacturing apparatus 10 comprises a plate 12 that is positioned on a moving table (not shown). Plate 12 is made of aluminium and has one of its sides anodized similar to the regular presensitized photopolymer offset plates. Anodized aluminum is a dielectric, and a typical printing plate has a layer a few micron thick of anodized aluminum with strong hydrophilic properties. Thicker layers of up to 30-35 micron may be manufactured in case of need. 8526/99 -8- For the purpose of plate preparation, the plate moves in the direction indicated by arrow 14. In the course of its movement, the plate passes under the charging device 16, which may be a corotron or a scorotron. The dielectric surface (the anodized aluminium layer) is evenly charged by the charging device 16 to a potential that ensures attraction and certain retention of the development material. There are no stringent requirements to the uniformity of the potential relief created by the deposited charge, since it does not bear a latent image. The purpose of the charge is to facilitate the process of development material deposition on the plate surface. The charge decay in such a configuration is primarily defined by surface resistance which is relatively high for anodized aluminum. The charge is therefore maintained for more than a few minutes. This is sufficient time for all subsequent stages of the process. It will be understood that, while in this an other embodiments of the invention, it is the substrate that moves, only its relative motion with respect to the other apparatus components is important, and therefore said relative motion could be obtained by moving said other components or both them and the substrate.

The uniform potential field created is developed by a material bearing an opposite charge sign and having surface properties different from those of the dielectric substrate, i.e., if the substrate is hydrophilic, the development material should have oleophihc/lipophilic properties. In this particular example, the development material is a simple electrophotographic toner, which is oleophilic. The use of a simple 8526/99 -9- electrophotographic toner for the purpose of printing plate creation is disclosed in a number of patents, such as USP 5,213,920, 5,213,030, and others, and a number of commercial products using such a toner are available on the market. A regular magnetic brush device 18 performs the development of the electrostatic field. Other development devices may also be used. Following the development of the electrostatic field, the development material/toner 20 uniformly covers the dielectric surface of the plate 12. The development material is held onto the surface by the electrostatic forces generated by the charges of both the dielectric surface and the development material.

At the next stage of the process, the development material is attached/fused to the dielectric surface selectively according to a predetermined pattern defining the image to be printed. The word SCITEX, referenced by numeral 22 in Fig. 1, schematically shows an image formed by development material fused to plate 12. A scanning laser beam 24 of proper power performs the selective toner melting/fusing operation. The scanning of the laser beam is conveniently performed by an oscillating mirror 26. Other scanning means, such as polygon or prism, msiy also be used.

Following the above stage of the process, the remaining unmelted development material/toner 20 is cleaned off the plate and the plate is ready for use. The cleaning may be accomplished by a regular doctor Blade type arrangement, a magnetic brush-like' cleaning device 28, or a vacuum cleaner-type device. Dotted line 30 indicates an imaginary 8526/99 131425/2 -10- cleaned image area on plate 12, and the word SCITEX, referenced by numeral 32, schematically shows development material/toner fused to the plate and formin the printing image.

Fig. 2 is a schematic representation of an embodiment of a plate manufacturing apparatus constructed according to another embodiment of the invention. It is the same as that of Fig. 1, except that an AC corona 34 is placed before the cleanin device 28* The AC corona neutralizes the remains of the plate charge and facilitates the removal from the plate of unfused toner.

Although the above example refer to flat bed plate manufacturing apparatus, other plate manufacturing apparatus structures can optionally be used. Figure 3 is a schematic representation of an embodiment of a plate manufacturing apparatus, constructed in accordance with the principles of the present invention, and implemented as an external drum device.

In this particular example of plate manufacturing, the printing member, in this case a plate substrate 50, is mounted on a rotating drum 52. The drum with the plate rotates in the direction indicated by arrow 54. In the course of its rotation, the plate passes under the charging device 56, which may be a corotron or a scprotron. The dielectric surface is uniformly charged by the" device' 56. The created uniform electrostatic field and the respective potential are developed by regular electrophotographic toner with the help of a regular developing magnetic 8526/99 -11- brush device 58. Following the development of the electrostatic field, the toner (not shown) uniformly covers the dielectric surface of the plate 50. At the next stage, the development toner field is selectively attached/fused to the dielectric surface in a pattern defining an image. The word SCITEX, referenced by numeral 60, schematically indicates development material fused to the plate. To speed up the process, a number of scanning laser beams 62 of proper power are used. The scanning head 64, that emits the multiple laser beams, moves in the direction orthogonal to drum rotation, as indicated by arrow 66.

Following this stage, the remaining unfused development material/toner is cleaned off the plate and the plate is ready for use. The cleaning may be accomplished by a regular doctor Blade type arrangement, a magnetic brush-like cleaning device 68, or a vacuum cleaner-type device. Dotted line 70 indicates an imaginary cleaned image area on the plate, and the word SCITEX, referenced by numeral 72, schematically shows the toner fused to the plate, that forms the printing image. The plate prepared in such a way may be mounted on the press and used for printing. Upon completion of the printing process the fused development material may be removed from the plate and the substrate used once again to produce another plate Fig. 4 is a schematic representation of an on-press embodiment of a plate manufacturing apparatus", constructed in accordance with the principles of the present invention. The press, generally indicated at 100, comprises a printing/plate cylinder 102, made of a ceramic such as zirconia. The 8526/99 -12- plate manufacturing process is similar to the one described earlier, and only the stages of a full printing cycle will be described here.

At the beginning of a printing cycle, the printing cyhnder 102 rotates in the direction indicated by the arrow 104. In the course of its rotation, the cylinder 102 passes under the charging device 106, which evenly charges its dielectric surface. Regular electrophotographic toner, with the help of a regular magnetic brush developing device 108, develops the even electrostatic field created on cyhnder 102. Thereafter, the toner deposited on said cylinder is selectively attached/fused to the cyhnder surface by a multibeam scanning laser exposure head 110 to form a pattern defining an image. A cleaning device 112 cleans the remaining unmelted development material/toner off the cylinder, which is then ready for printing. At this stage, the charging device 106, developing device 108, multibeam scanning laser exposure head 110 and the cleaning device 112 may be distanced from the drum 102, and the printing process is commenced. A similar process may be applied to the plate manufacturing method and apparatus described hereinbefore.

For printing, a conventional water delivery system 114, shown only schematically, and a conventional inking system 116, shown only schematically, are activated, and the blanket cylinder 118, viz. the rubber cyhnder to which the image is offset, is brought into contact with the cyhnder 102. Numeral 120 designates the impression cylinder, and the paper is indicated by numeral 122. The rotating speed of the cylinder is adjusted to meet the printing requirements. 8526/99 -13- Upon completion of the run, a cleaning system 124 for removal of the fused toner is actuated, and the cylinder is cleaned and prepared for the next printing cycle. The fused toner cleaning system 124 may consist of a brush wetted in an appropriate solvent. Alternatively, a hot transfer system in which the toner is melted and wicked by a paper or cloth, may be used.

Fig. 5 is an illustration of a flexographic plate manufacturing apparatus constructed in accordance with the principles of the present invention.

Flexographic plates consist of a relatively thick sheet of polymer material to which UV radiation is selectively applied to define an image. The imaged areas polymerize, and a regular etching process etches the non-polymerized background or unexposed areas. Recently, the flexographic plates have been manufactured coated with a typically black mask that is ablated to define an image. The areas where the mask has been removed are exposed to UV radiation, and the subsequent processes proceed in a conventional way. Such a technique is problematic and costly, since, in order to enable easy ablation, the mask should be thin (about 1 micron). A thin mask, however, does not provide sufficient blocking density to prevent exposure of the background areas to UV radiation. The cost of producing such a plate is also more than five times the cost of a conventional plate. 8526/99 -14- In the method of plate preparation of this invention, a conventional flexographic plate 150 is placed on a conductive plate/table support 152 that moves in the direction indicated by arrow 154. In the course of its movement, the plate passes under a charging device 156. The dielectric surface of the plate is evenly charged by the device 156 to a potential that ensures attraction and certain retention of the development material.

The uniform electrostatic field and the thus created potential is developed by an opaque material bearing an opposite charge sign. Regular black electrophotographic toner is adequate for these purposes. A regular magnetic brush device 158 performs the development of the potential field. Other potential relief field development devices may also be used.

Following the development of the potential field, the development material/toner 160 uniformly covers the dielectric surface of the plate 150. The development material is held onto the surface by the electrostatic forces generated by the charges of both the dielectric surface and the development material.

At the next stage, the development material is selectively attached/fused to the dielectric surface to form a pattern defining an image. A scanning laser beam 162 of proper power may perform the selective toner melting/fusing process. The scanning of the laser beam is performed by the scanning means described above. Fused and attached areas of the development material/toner 164 are shown in black in the drawing. 8526/99 -15- Following this stage, the remaining unmelted development material/toner 160 is cleaned off the plate 150. A regular doctor Blade type arrangement, a magnetic brush-like cleaning device 166, or a vacuum cleaner-type device may accomplish the cleaning. As the plate 150 continues to move in the direction indicated by the arrow 154, it is exposed to a source of UV radiation 170. Alternatively, it may be removed from the support 152 for off-line UV exposure and a subsequent etching process. It is clear that the last two stages, not shown in the illustration, may be combined in one apparatus with the previous stages. Following the etching, the plate is ready for use.

Figs. 6A, 6B, 6C and 6D schematically indicate the process in more detail, and Fig. 6D shows the plate structure after etching. There is no need to remove the melted toner 164 from the plate: the toner is oleophilic, and attracts printing ink to it.

While embodiments of the invention have been described for the purpose of illustration, it will be apparent that the invention may be carried out by persons skilled in the art with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims. 8526/99 -16-

Claims (34)

1. Method of manufacturing a planographic/lithographic printing remember, which comprises the following steps: a — uniformly electrostatically charging a dielectric or insulated substrate,*^ b - developing the electrostatic charge pattern with dry development material; <

2. Method according to claim 1, wherein the development material is a toner.

3. Method according to claim 1, wherein the charged substrate and the development material have opposite charge signs.

4. Method according to claim 1, wherein the substrate and the development material have opposite surface properties.

5. Method according to claim 1, wherein the substrate is evenly charged to a potential that insures attraction and certain retention of development material particles to its surface. 8526/99 -17-

6. Method according to claim 1, wherein the substrate is a dielectric with hydrophilic properties

7. Method according to claim 1, wherein the substrate has a layer of anodized aluminum.

8. Method according to claim 1, wherein the development material particles are fused by an image wise scanning radiation beam delivering the required energy.

9. Method according to claim 8, wherein the scanning radiation beam is a laser beam.

10. Method according to claim 2, wherein the toner is an oleophilic electrophotographic toner.

11. Method according to claim 9, wherein the laser beam is scanned by an oscillating mirror.

12. Method according to claim 9, wherein the laser beam is scanned by a polygon.

13. Method according to claim 9, wherein the laser beam is scanned by a rotating prism. 8526/99 -18-

14. Method according to claim 1, wherein the removal of the unfused particles is carried out by means chosen from among doctor Blade type arrangements, magnetic brush-like cleaning device, or vacuum cleaner-type devices.

15. Method according to claim 1, further comprising neutralizing the remains of the substrate charge before removal from the substrate of unfused development material

16. Method according to claim 1, further comprising removing the fused development material after using the printing member, and preparing a new printing member by the steps defined in claim 1.

17. Method according to claim 1, wherein the substrate is supported in plane configuration.

18. Method according to claim 1, wherein the substrate is supported in cylindrical configuration.

19. Method according to claim 1, which comprises, after removing the non-fused particles of development material from the substrate, submitting the substrate carrying the fused particles to UV irradiation and subsequently etching it, to remove substrate material from the areas not covered by said fused particles. c 8526/99 -19-

20. Method of manufacturing a planographic/lithographic printing member, comprising a substrate of dielectric substance and fused particles of toner defining an image to be printed.

21. Reusable printing plate, prepared by a method according to any of claims 1 to 19.

22. Apparatus for manufacturing a planographic/lithographic printing member, which comprises: I — a support for an dielectric or insulated substrate; II - a charging device for uniformly electrostatically charging said substrate; III - means for applying to the charged substrate dry development material particles whereby to develop the electrostatic charge pattern; IV - a radiation source for selectively applying sufficient energy to said development material to fuse development material particles; V- scanning means for imparting to said radiation source a scanning motion whereby selectively to fuse said particles to define a predetermined image; VI - a device for removing the non-fused particles from said substrate, leaving thereon said image.

23. Apparatus according to claim 22, further comprising means for discharging the substrate "after fusing the development material particles. 8526/99 -20-

24. Apparatus according to claim 22, wherein the radiation source is a generator of a laser beam.

25. Apparatus according to claim 22, wherein the scanning means comprises an oscillating mirror.

26. Apparatus according to claim 22, wherein the substrate support is a flat plate which has a plane relative motion with respect to the charging device, the means for applying the development material particles and the device for removing the non-fused particles.

27. Apparatus according to claim 22, wherein the substrate support is a drum which has a rotary relative motion with respect to the charging device, the means for applying the development material particles and the device for removing the non-fused particles.

28. Apparatus according to claim 22, integrated with a printer in an on-press printing plate manufacturing apparatus.

29. Apparatus according to claim 22, for manufacturing a planographic/hthographic printing member, which comprises a movable support for a substrate, a charging device, a device for applying electrophotographic toner to the substrate, a scanning laser beam for fusing said toner to define" an image, a device for cleaning off the unfused toner, and a source of UV radiation, said support having a linear motion 8526/99 -21- with respect to said other components, and further comprising a source of UV radiation and means for carrying out an etching process,

30. Printing process, comprising defining the image to be printed in a planographic/lithographic printing member according to any of claims 1 to 19.

31. Method of manufacturing a planographic/Hthographic printing member, substantially as described and illustrated.

32. Reusable printing plate, substantially as described and illustrated.

33. Apparatus for manufacturing a planographic/lithographic printing member, substantially as described and illustrated.

34. Printing process, substantially as described and illustrated. LUZZATTO & LUZZATTO