CA1144418A - Erosion process for generation of offset masters - Google Patents
Erosion process for generation of offset mastersInfo
- Publication number
- CA1144418A CA1144418A CA000362742A CA362742A CA1144418A CA 1144418 A CA1144418 A CA 1144418A CA 000362742 A CA000362742 A CA 000362742A CA 362742 A CA362742 A CA 362742A CA 1144418 A CA1144418 A CA 1144418A
- Authority
- CA
- Canada
- Prior art keywords
- film
- printing plate
- aluminum
- conducting
- printing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 28
- 230000008569 process Effects 0.000 title claims abstract description 24
- 230000003628 erosive effect Effects 0.000 title abstract description 27
- 238000007639 printing Methods 0.000 claims abstract description 71
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 52
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 52
- 239000000758 substrate Substances 0.000 claims abstract description 25
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims abstract description 22
- 230000002209 hydrophobic effect Effects 0.000 claims abstract description 9
- 229920000728 polyester Polymers 0.000 claims abstract description 8
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 5
- QDOXWKRWXJOMAK-UHFFFAOYSA-N dichromium trioxide Chemical compound O=[Cr]O[Cr]=O QDOXWKRWXJOMAK-UHFFFAOYSA-N 0.000 claims description 5
- 230000004044 response Effects 0.000 claims description 4
- 239000004642 Polyimide Substances 0.000 claims description 2
- 229920001721 polyimide Polymers 0.000 claims description 2
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 2
- 229910052721 tungsten Inorganic materials 0.000 claims description 2
- 239000010937 tungsten Substances 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 14
- 239000003989 dielectric material Substances 0.000 abstract description 3
- 230000001681 protective effect Effects 0.000 abstract description 2
- 235000010210 aluminium Nutrition 0.000 description 47
- 239000010408 film Substances 0.000 description 44
- 229940024548 aluminum oxide Drugs 0.000 description 16
- 239000010410 layer Substances 0.000 description 11
- 229910052751 metal Inorganic materials 0.000 description 10
- 239000002184 metal Substances 0.000 description 10
- 238000003384 imaging method Methods 0.000 description 9
- 238000006748 scratching Methods 0.000 description 8
- 230000002393 scratching effect Effects 0.000 description 8
- 238000005566 electron beam evaporation Methods 0.000 description 7
- 239000000126 substance Substances 0.000 description 7
- 230000015556 catabolic process Effects 0.000 description 6
- 229920002799 BoPET Polymers 0.000 description 5
- 239000005041 Mylar™ Substances 0.000 description 5
- 238000000151 deposition Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 240000007594 Oryza sativa Species 0.000 description 2
- 239000003990 capacitor Substances 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 238000001017 electron-beam sputter deposition Methods 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 229920002120 photoresistant polymer Polymers 0.000 description 2
- 239000011241 protective layer Substances 0.000 description 2
- 101100536354 Drosophila melanogaster tant gene Proteins 0.000 description 1
- 101100459301 Mus musculus Myl4 gene Proteins 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical compound [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 description 1
- 238000007743 anodising Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000012822 chemical development Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000004519 grease Substances 0.000 description 1
- 229910000449 hafnium oxide Inorganic materials 0.000 description 1
- WIHZLLGSGQNAGK-UHFFFAOYSA-N hafnium(4+);oxygen(2-) Chemical compound [O-2].[O-2].[Hf+4] WIHZLLGSGQNAGK-UHFFFAOYSA-N 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000005660 hydrophilic surface Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920003223 poly(pyromellitimide-1,4-diphenyl ether) Polymers 0.000 description 1
- -1 polyethylene terephthalate Polymers 0.000 description 1
- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
- B41N3/00—Preparing for use and conserving printing surfaces
- B41N3/03—Chemical or electrical pretreatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
- B41C1/00—Forme preparation
- B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
- B41C1/1008—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by removal or destruction of lithographic material on the lithographic support, e.g. by laser or spark ablation; by the use of materials rendered soluble or insoluble by heat exposure, e.g. by heat produced from a light to heat transforming system; by on-the-press exposure or on-the-press development, e.g. by the fountain of photolithographic materials
- B41C1/1033—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by removal or destruction of lithographic material on the lithographic support, e.g. by laser or spark ablation; by the use of materials rendered soluble or insoluble by heat exposure, e.g. by heat produced from a light to heat transforming system; by on-the-press exposure or on-the-press development, e.g. by the fountain of photolithographic materials by laser or spark ablation
Abstract
abstract An improved lithographic printing plate includes a sub-strate layer of a nonconducting, hydrophobic polyester, an intermediate film of conducting, hydrophilic material such as aluminum and a top protective film of relatively hard hydrophilic dielectric material, such as aluminum oxide. .A printing image is formed in the lithographic printing plate by an electroerosion process wherein ero-sion electrodes are pulsed with voltage to break down the dielectric in areas adjacent to the erosion electrodes and to evaporate or otherwise remove corresponding por-tions of the conducting film, thereby creating holes that extend through the dielectric and conducting films and that expose portions of the surface of the underlying hydrophobic substrate.
Description
EROSION PROC~:S!~ ~OR CENE~TION OF OFFSET MASTF'RS
_ _ _ _ .
Description Technical Field The invention relates to lithographic printing plates and, more particularly, to a printing plate having a protective dielectric film that improves the wear charac-terlstics of the plate and that enhances the electro-erosion of an adjacent conducting layer of the plate.
Background Art Lithographic prin-ting plates are employed to print a par-ticular image iJl ink on sheets of a recording medium, for example paper. The lithographic printing process is de-pendent upon the in~iscibility of grease and water and, more particularly, upon the tendency of one substance to re~ain a greasy, image-forming material and a complemen-tary substance to retain an aqueous dampening fluid.
A lithographic printIng plate or o~fset master typically includes an imaging area comprised of oleophilic or hy-drophobic material and a non-image area comprised of oleophobic or hydrophilic material. A greasy material is applied to the hydrophobic image area of the plate and the entire surface of the plate ls then moistened with an aqueous solution. The image area will tend to repel the water and the non-image area wiIl tend to retain the water and, thus, upon a subsequent applica-tion of greasy in~, the image portion retains the ink whereas the moistened non-image area repels it. The ink on the image area may then be transferred to the surface of a material on which the image is reproduced, for example paper or cloth, through an intermediary of~-set or blanket c~linder. The printing plate may be used in the above-described printing process to print many sheets of paper or cloth be~ore chemical or physical YOg7~-036 wear of the imaging or non-imaging area of the plate re-sults in an unacceptable degradation in the clarity of the printed image.
In order to extend ~he print llfetime of a lithographic -5 printing plate, it is necessary to utilize imaging and non-imaging materials that are resi~tant to chemical and physical wear. In the U.S~ Patent to Chu, "Process of Electrolyically Anodizing a Mechanically Grained Aluminum Base and Artic1e Made Thereby", No. 3,831,516, issued Jun~
24, 1375, a more durable lithographic printing plate is disclosed. The printing plate includes an aluminum base plate to which is anodized a layer of aluminum oxide, The layer oE aluminum oxide covers the entire surface of the aluminum plate and thereby provides a hydrophilic sur-face that is resistant to abraslon, wear and erosion. Alayer of photoresist is applied over the aluminum oxide and is etched by a wet chemical deveIopment process to provide a hydrophobic printing surface.
Although the lithographic printing plate of Chu has an incr~ased resistance to wear and corroslon at its hydrophilic non-image surface, the plate is still sub-ject to wear at its photoresist, hydropho~ic prlnting surface. Also, the printing plate of Chu must be con-struc~ed by the relatively complicated, time-consuming and expensive process of photographic exposure ~nd we-t chemical development.
A relatively simple znd cost~efficient electroerosion process has been developed to form image and non-image ar~as on printing plates from digitally coded informa-tion, thereby a~oiding the time consuming photographicprocess of Chu, In ~nown electroerosion processes, a printing plate is provided with a nonconductin~ hydro-phobic substrate, for example a polyester material sold under the trademark MYLAR that is covered, for example by an 800 angstrom film of a hydrophilic material such as aluminum. An image is formed ln the plate by electri-cally eroding a plurality of holes in the aluminum filmand thereby expos-ing the surface o~ the MYLAR substrate at each hole. The lmage that is to be printed is, of CQUrse~ - formed by the pattern of thé holes in the aluminum.
A hole is formecl in the aluminum layer by moving an ero-cion electrode adjc~cent to a point on the surface of the aluminum layer and applying a voltage pulse to the elec-trode so that a spot on the aluminum is rapidly heated and a correspondillg portion of the aluminum is evaporated or otherwise removed from the substrate. Thereafter, the erosion electrode is moved to the next prlnting position and the electrical erosion process is repeated. In prac-tice, a line of erosion electrodes is scanned across the aluminum surface of a printing plate and particular elec-trodes in the line of electrodes are energized to form holes in accordance with digitally coded image informa-tion.
A disadvantage of lcnown electroerosion printing processes is that the metallized plastic printing plates have a relatively short print lifetime. The lifetime is limited both by the relati~e softness and low resistance to abra-sion and corrosion of aluminwn, or other common litho-: graphic metals suited to the electroerosion process, and by the small thickness of these metals that can be eroded electricall~. Accordingiy, typical lithographic plates having an alumin~n film of less than 800 angstromsma~ be expected to produce a few hundred prints before physical wear of the aluminum surface causes non-printing regions of the plate to ink and to print.
Yo978-036 The print life of lithographic plates may be increased somewhat by using a thicker metal film. ~owever, with a thicker film, more electrical power must be applied to the printina electrodes to form a hole that extends S to the substrate. ~s a practical matter, the aluminum film of prior art plates has not exceeded 1000 angstroms, due both to limitations in the amount of power that may be applied by a printing electrode,~and the fact that the high thermal conductivity of the metal films results in spot welding of the electrode to the substrate.
A further disadvan~age of electroerosion systems is that the surface of the metal film of a plate is often bur-nished or scra~ched by the printing electrodes as the electrodes move over the surface of the plate. The burnishing or scratching is particularly damaging if the printing electrodes are pressed against the sur-face of the metal with excessive force. If the metal is scratched, the normally non-printlng metal surface of the plate will produce an objectionable gray or lined background for a printed image.
Accordingly, it is an object of the invention to provide a lithographic printing plate upon which an image may be formed by the electroerosion process in an energy~
efficient manner.
A further object of the invention is to provide such a printing plate that is resistant to burnishing or scratch-ing and to chemical or physical wear and that has a cor-respondingly extended print lifetime.
Another object of the invention is to provide a method for producing a lithoara~hic printing plate that has in-crease~l ~urability and that is suitable for en~roY-effi-cient ima~in~ by an electroerosion process.
YO~78-036 .
~3~ 4~
These and other objects of the invention will become ap-parent from a revie~ of the detailed specification which follows and a consideration of the accompanying drawing.
Disclosure of the Invention 5- In order to achieve the objects of the invention and to overcome the probiems of the prior~art, the lithographic printing plate, according to the invention, includes a substrate of nonconductive hydrophobic material, for ex-ample a polyester such as is sold under the trademark MYLAR and a first film of conducting hydrophilic material, for example aluminum.
A second film of hydrophilic, dielectric material, for example aluminum o~ide (A12O3) is provided to protect the aluminum film from scratching or burnishing and to extend the print life of the printing plate. The di-electric also enhances the erosion of spots of aluminum in response to voltage pulses.
The lithographic printing plate of the invention i5 made by depositing a l.~yer of aluminum over the hydrophobic substrate by appropriate means, such as electron beam evaporation, sputtering or resistance evaporation. The protective layer of aluminum oxide may be applied by known thin film techniques, such as electron beam eva-poration, sputtering or anod~zing.
.
5a 1 The oxide coating functions as a capacitor, storlng energy until capacitive breakdown occurs. The release of the stored energy coupled with the normal erosion process, which is operative after breakdown, permits removal of additional metal at reduced voltages.
Brief Description of the Drawing The drawing illustrates a perspective view in partial section, not to scale, of a lithographic printing pla-te in accordance with the invention and associated electro-erosion imaging apparatus~
Best Mode for Carrying out the Invention The remaining por-tion of this specification will describe preferred embodiments of the invention when read in con-junction with the att:ached drawing in which like reference --h-characters ident;fy identical apparatus.
The drawing illustrates a perspective view in partial sec-tion of a lithoaraphic printing plate 1 in accordance with the invention alld all associated electroerosion printing appara~us. The printi~ plate has been drawn out of scale in order to facilitate an understanding of the invention.
The lithographic printing plate of the invention has a nonconducting, hy~rophobic substrate 2 made of, for exam-ple, a polyethylene terephthalate such as is sold under the trademark MYL~R or a polyimide such as is sold under the trademark KAPTON. A first film 3 of conducting hydro-philic material rnade of, for example, aluminum is formed on the substrate 2 by electron beam evaporation. Elec-tron beam evaporation techniques are well-known to the art and, therefore, it will be understood by those skilled in the art how such techniques may be employed to deposit a layer of aluminum on the substrate.
In a preferred embodiment of the invention, the aluminum film 3 is evaporated on the substrate 2 ~o a depth of ap-proximately 2000 angstroms, a thickness substantially inexcess of the t~pical thickness o~ 1000 angstroms or less for correspondin~t conductive films of prior art litho-graphic printing plates. However, as a practical matter, the aluminum film may have a thickness at least within the ranye of 1000 to 3000 angstroms, without departing from the invention.
A second film 5 of relatively hard, hydrcphilic dielec-tric material, fcr example aluminum oxide (A1203) is dis-posed over the aluminum film 3. The aluminum o~ide f~lm may be applied b~ s~uttering, electron beam evaporation or anodizin~ techniques that are well-known to the art. In the preferred e~odiment of the invention, a~proximately 50C an~stroms o. aluminum oxide is deposited over the film 3 of aluminum by elec-tron beam evaporation. Since the alu~inum oxide is a relatively hard material and, in particular, is much harder than the aluminum, the plate constructed in accordance with the invention has a sub-stantially increctsed durability and toughness and is, therefore, more resistant to physical or chemical wear.
As shown in the drawing, a printing image is formed in the lithographic printing plate 1 by moving a plurality of electrodes 7 over the plate and energizing particular elec-trodes to form corresponding holes 8 in the aluminum and the alurninum oxicle so that the underlying surface of the polyester substrate is exposed at each hole. In operation, a broad area electrode 9 is placed in conductive contact with the aluminum film 3 of the printing plate, for exam-ple by pressing the electrode 9 against an area of the printing plate at which the aluminum oxide has been re-moved and the aluminum has been exposed. A control ap-paratus 11 then operates a scanning mechanism to scan the erosion electrodes 7 across the aIuminum oxide surface of the printing plate ~nd to energize particular erosion electrodes 7 with voltage pulses, for example of from 10-100 volts and 1 rn~ec to 1 ~sec duration, in accordance with a digital image pattern that is stored in the control apparatus. The control apparatus is not a part of the present invention and, therefore, is not disclosed in de-tail. However, electroerosion scanners are kno~n to the 25 art and are commercially available.
When the control apparatus 11 energizes a particular erosion electrode 7 with a voltage pulse, the energy of the electrical pulse is passed to an area of the aluminurn oxide film that is i~ttediately adjacent to 30 the electrode. Lhe voltage pulse is sufficiently large to break down the aluminum oxide and to cause a heating current I to flo~Y from the printing electrode 7 to the broad area electrode ~, through the aluminum film. The concentrated current in the area of the aluminum film YOg78-Q36 adjacent to the point of application of the voltage pulse causes a hole to be evaporated in the aluminum. In ex-perimental tests, an eroSiQn pulse of 50 volts and 200 microseconds duration was sufficient to erode a hole extending to the MYLA~ substrate in a printing plate having a 2000 angstrom film of aluminum and associated S00 angstrom fi lm of aluminum oxide, in accordance with the invention. However, when a pulse of the same magni-tude was applied to a prior art printing plate having only a MYLAR substrate and an aluminum film, only approxi-mately 800 angstroms of aluminum was eroded.
It is theorized that the greater penetration for the printing plate of the invention is due to the fact that the dielectric layer of aluminum oxide acts as a capaci-tor that initially stores energy as a voltage pulse isapplied and that releases the stored energy when the dielectric film breaks down. The release of the stored energy apparently adds to the heat that is normally pro-duced by the erosion current I and, therefore, more alumi-num is evaporatecl.
A capacitive breakdown scheme has been employed in theU.S. Patent to Reis, "Electrosensitive Recording", No.
3,299,433, issued January 17, 1957, to heat a surface recording medium that changes color in response to ap-plied heat. However, the capacitive breakdown that isdisclosed in the Reis patent is not directed to an electroerosion process-wherein a hole is formed in a dielectric film and an underlying aluminum film.
It has also been e~perimentally determined that a prior art nrjnting plate having a polyester substrate, such as MYLAR and an 800 angstrom aluminum layer is subject to scratching and burnishing on the exposed aluminum film when the erosion electrodes 7 contact the plate with pressures re~-lired by the electroerosion process while scanning the plate. Thus, the contact pressure of the erosion electrodes must be closely monitored in prior art electroerosion systems in order to avoid such undesirable burnishing or scratching. However, a prin-S ting plate constructed in accordance with the invention,having a 2000 angstrom aluminum film and an associated 500 angstrom aluminum oxide film, is resistant to scratching and burnislling, with onl~ moderate attention being given to the contact pressure of the erosion elec-trodes. In addition, the above prior art printing platewas able to print no more ~han 500 copies before signi-ficant image degradation occurred due to wearing of the imaging surfaces of the plate, while the above plate con-structed in accordance with the invention was used to lS print 10,000 copies, with, apparently, no signs of wear.
It should be understood that, since the printing plate of the invention is not subject to scratching and burnishing by the erosion electrodes 7, only routine attention need be given to electrode pressure during the process of forming an image on the plate. However, prior art plates are subject to objectionable scratching and buxnishing by tllc ~rosion electrodes and, therefore, during the imaging process, particular care must be taken to avoid excessive pressure of the erosion electrodes.
Accordingly, the lithographic printing plate of the in-vention is less difficult to produce than prior art printing plates, since less care need be taken in the imaging process. In addition, the hard layer of aluminum oxide on the printing plate provides an extended opera-tional lifetime that is many times greater than hashe~etofore been achieved. ~oreover, the dielectric film increases tlle energy efficiency of the erosion pro-cess and, therefore, substantially thic~er layers of metal may be eroded, thereby extending the print l-ifetime Y~978-036 of the printing plate even further.
Although aluminum and aluminum oxide were employed to respectively form the first conducting film and second protective layer for a preferred em~odiment of the in-vention, other materials may be employed without de-parting from the spirit of the invention. For example, tungsten may be used in place of aluminun and hafnium oxide (E3fO2) or Schott glass may be used in place of the aluminum oxide.
An improved lithographic printing plate may also be made in accordance with the invention by depositing an aluminum film over a polyester substrate in the above-described manner and then depositing a chrome film over the aluminum film and an aluminum oxide (A1203) film or chrome oxide (Cr203) film over the chrome film. For such an embodiment of the invention, the combined chrome and aluminum films behave in much the same fashion as the aluminum film of the embodiment oE the drawing.
It should be appreciated that means other than electron beam evaporation may be employed to deposit a conducting film on a polyester substrate, for example some conductors may be deposited by electroless deposition or sputtering.
It should also be appreciated that the dielectric film of the invention may be used in conjunction with an alu-minum layer of typical thickness f for example 800 ang-stroms, and the voltage and/or duration of the erosion pulses of the. erosion electrodes may then be reduced, to conserve energy in the process of making the printing plate. Moreover, it should be und~rs~ood that the cited examples of erosion electrode voltage and pulse duration and of the thickness of the aluminum and alu-minum oxide films are not intended to limit the scope YOg78-036 of the invention. Other magnitudes of electrode pulses and thicknesses of cQnducting and dielectric film may be used without departing from the spirit of the inven-tion.
It has been observed in this regard that variatlon of the pulse voltage and duxation affects a predictable modification of the size and shape 'of the eroded hole.
Increasing the pulse voltage produces an overall enlarge-ment of the hole in the direction of relative travel or the erosion electrode. Moreover, the size of the hole tends to follow, subject to the above-mentioned influ-ences, the cross-sectional size of the erosion electrode.
It is thus apparent that control of the size o the ero-ded hole, and consequently of the resolution of the eroded image, is provided by the specification of the erosion electrode dimensions, the pulse voltage and the pulse duration. The capability of producing "half-tone"
images, in which varying shades of grey are produced by varying spot size rather than by varying spot density, is thus seen ta reside in the above-described process.
The invention may be embodied in other specific forms without departing from its spirit or essential charac-teristics. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the claims rather than by the foregoing description, -~ and all changes which come within the meaning and range of the equivalents of the claims are therefore intended to be embraced therein.
_ _ _ _ .
Description Technical Field The invention relates to lithographic printing plates and, more particularly, to a printing plate having a protective dielectric film that improves the wear charac-terlstics of the plate and that enhances the electro-erosion of an adjacent conducting layer of the plate.
Background Art Lithographic prin-ting plates are employed to print a par-ticular image iJl ink on sheets of a recording medium, for example paper. The lithographic printing process is de-pendent upon the in~iscibility of grease and water and, more particularly, upon the tendency of one substance to re~ain a greasy, image-forming material and a complemen-tary substance to retain an aqueous dampening fluid.
A lithographic printIng plate or o~fset master typically includes an imaging area comprised of oleophilic or hy-drophobic material and a non-image area comprised of oleophobic or hydrophilic material. A greasy material is applied to the hydrophobic image area of the plate and the entire surface of the plate ls then moistened with an aqueous solution. The image area will tend to repel the water and the non-image area wiIl tend to retain the water and, thus, upon a subsequent applica-tion of greasy in~, the image portion retains the ink whereas the moistened non-image area repels it. The ink on the image area may then be transferred to the surface of a material on which the image is reproduced, for example paper or cloth, through an intermediary of~-set or blanket c~linder. The printing plate may be used in the above-described printing process to print many sheets of paper or cloth be~ore chemical or physical YOg7~-036 wear of the imaging or non-imaging area of the plate re-sults in an unacceptable degradation in the clarity of the printed image.
In order to extend ~he print llfetime of a lithographic -5 printing plate, it is necessary to utilize imaging and non-imaging materials that are resi~tant to chemical and physical wear. In the U.S~ Patent to Chu, "Process of Electrolyically Anodizing a Mechanically Grained Aluminum Base and Artic1e Made Thereby", No. 3,831,516, issued Jun~
24, 1375, a more durable lithographic printing plate is disclosed. The printing plate includes an aluminum base plate to which is anodized a layer of aluminum oxide, The layer oE aluminum oxide covers the entire surface of the aluminum plate and thereby provides a hydrophilic sur-face that is resistant to abraslon, wear and erosion. Alayer of photoresist is applied over the aluminum oxide and is etched by a wet chemical deveIopment process to provide a hydrophobic printing surface.
Although the lithographic printing plate of Chu has an incr~ased resistance to wear and corroslon at its hydrophilic non-image surface, the plate is still sub-ject to wear at its photoresist, hydropho~ic prlnting surface. Also, the printing plate of Chu must be con-struc~ed by the relatively complicated, time-consuming and expensive process of photographic exposure ~nd we-t chemical development.
A relatively simple znd cost~efficient electroerosion process has been developed to form image and non-image ar~as on printing plates from digitally coded informa-tion, thereby a~oiding the time consuming photographicprocess of Chu, In ~nown electroerosion processes, a printing plate is provided with a nonconductin~ hydro-phobic substrate, for example a polyester material sold under the trademark MYLAR that is covered, for example by an 800 angstrom film of a hydrophilic material such as aluminum. An image is formed ln the plate by electri-cally eroding a plurality of holes in the aluminum filmand thereby expos-ing the surface o~ the MYLAR substrate at each hole. The lmage that is to be printed is, of CQUrse~ - formed by the pattern of thé holes in the aluminum.
A hole is formecl in the aluminum layer by moving an ero-cion electrode adjc~cent to a point on the surface of the aluminum layer and applying a voltage pulse to the elec-trode so that a spot on the aluminum is rapidly heated and a correspondillg portion of the aluminum is evaporated or otherwise removed from the substrate. Thereafter, the erosion electrode is moved to the next prlnting position and the electrical erosion process is repeated. In prac-tice, a line of erosion electrodes is scanned across the aluminum surface of a printing plate and particular elec-trodes in the line of electrodes are energized to form holes in accordance with digitally coded image informa-tion.
A disadvantage of lcnown electroerosion printing processes is that the metallized plastic printing plates have a relatively short print lifetime. The lifetime is limited both by the relati~e softness and low resistance to abra-sion and corrosion of aluminwn, or other common litho-: graphic metals suited to the electroerosion process, and by the small thickness of these metals that can be eroded electricall~. Accordingiy, typical lithographic plates having an alumin~n film of less than 800 angstromsma~ be expected to produce a few hundred prints before physical wear of the aluminum surface causes non-printing regions of the plate to ink and to print.
Yo978-036 The print life of lithographic plates may be increased somewhat by using a thicker metal film. ~owever, with a thicker film, more electrical power must be applied to the printina electrodes to form a hole that extends S to the substrate. ~s a practical matter, the aluminum film of prior art plates has not exceeded 1000 angstroms, due both to limitations in the amount of power that may be applied by a printing electrode,~and the fact that the high thermal conductivity of the metal films results in spot welding of the electrode to the substrate.
A further disadvan~age of electroerosion systems is that the surface of the metal film of a plate is often bur-nished or scra~ched by the printing electrodes as the electrodes move over the surface of the plate. The burnishing or scratching is particularly damaging if the printing electrodes are pressed against the sur-face of the metal with excessive force. If the metal is scratched, the normally non-printlng metal surface of the plate will produce an objectionable gray or lined background for a printed image.
Accordingly, it is an object of the invention to provide a lithographic printing plate upon which an image may be formed by the electroerosion process in an energy~
efficient manner.
A further object of the invention is to provide such a printing plate that is resistant to burnishing or scratch-ing and to chemical or physical wear and that has a cor-respondingly extended print lifetime.
Another object of the invention is to provide a method for producing a lithoara~hic printing plate that has in-crease~l ~urability and that is suitable for en~roY-effi-cient ima~in~ by an electroerosion process.
YO~78-036 .
~3~ 4~
These and other objects of the invention will become ap-parent from a revie~ of the detailed specification which follows and a consideration of the accompanying drawing.
Disclosure of the Invention 5- In order to achieve the objects of the invention and to overcome the probiems of the prior~art, the lithographic printing plate, according to the invention, includes a substrate of nonconductive hydrophobic material, for ex-ample a polyester such as is sold under the trademark MYLAR and a first film of conducting hydrophilic material, for example aluminum.
A second film of hydrophilic, dielectric material, for example aluminum o~ide (A12O3) is provided to protect the aluminum film from scratching or burnishing and to extend the print life of the printing plate. The di-electric also enhances the erosion of spots of aluminum in response to voltage pulses.
The lithographic printing plate of the invention i5 made by depositing a l.~yer of aluminum over the hydrophobic substrate by appropriate means, such as electron beam evaporation, sputtering or resistance evaporation. The protective layer of aluminum oxide may be applied by known thin film techniques, such as electron beam eva-poration, sputtering or anod~zing.
.
5a 1 The oxide coating functions as a capacitor, storlng energy until capacitive breakdown occurs. The release of the stored energy coupled with the normal erosion process, which is operative after breakdown, permits removal of additional metal at reduced voltages.
Brief Description of the Drawing The drawing illustrates a perspective view in partial section, not to scale, of a lithographic printing pla-te in accordance with the invention and associated electro-erosion imaging apparatus~
Best Mode for Carrying out the Invention The remaining por-tion of this specification will describe preferred embodiments of the invention when read in con-junction with the att:ached drawing in which like reference --h-characters ident;fy identical apparatus.
The drawing illustrates a perspective view in partial sec-tion of a lithoaraphic printing plate 1 in accordance with the invention alld all associated electroerosion printing appara~us. The printi~ plate has been drawn out of scale in order to facilitate an understanding of the invention.
The lithographic printing plate of the invention has a nonconducting, hy~rophobic substrate 2 made of, for exam-ple, a polyethylene terephthalate such as is sold under the trademark MYL~R or a polyimide such as is sold under the trademark KAPTON. A first film 3 of conducting hydro-philic material rnade of, for example, aluminum is formed on the substrate 2 by electron beam evaporation. Elec-tron beam evaporation techniques are well-known to the art and, therefore, it will be understood by those skilled in the art how such techniques may be employed to deposit a layer of aluminum on the substrate.
In a preferred embodiment of the invention, the aluminum film 3 is evaporated on the substrate 2 ~o a depth of ap-proximately 2000 angstroms, a thickness substantially inexcess of the t~pical thickness o~ 1000 angstroms or less for correspondin~t conductive films of prior art litho-graphic printing plates. However, as a practical matter, the aluminum film may have a thickness at least within the ranye of 1000 to 3000 angstroms, without departing from the invention.
A second film 5 of relatively hard, hydrcphilic dielec-tric material, fcr example aluminum oxide (A1203) is dis-posed over the aluminum film 3. The aluminum o~ide f~lm may be applied b~ s~uttering, electron beam evaporation or anodizin~ techniques that are well-known to the art. In the preferred e~odiment of the invention, a~proximately 50C an~stroms o. aluminum oxide is deposited over the film 3 of aluminum by elec-tron beam evaporation. Since the alu~inum oxide is a relatively hard material and, in particular, is much harder than the aluminum, the plate constructed in accordance with the invention has a sub-stantially increctsed durability and toughness and is, therefore, more resistant to physical or chemical wear.
As shown in the drawing, a printing image is formed in the lithographic printing plate 1 by moving a plurality of electrodes 7 over the plate and energizing particular elec-trodes to form corresponding holes 8 in the aluminum and the alurninum oxicle so that the underlying surface of the polyester substrate is exposed at each hole. In operation, a broad area electrode 9 is placed in conductive contact with the aluminum film 3 of the printing plate, for exam-ple by pressing the electrode 9 against an area of the printing plate at which the aluminum oxide has been re-moved and the aluminum has been exposed. A control ap-paratus 11 then operates a scanning mechanism to scan the erosion electrodes 7 across the aIuminum oxide surface of the printing plate ~nd to energize particular erosion electrodes 7 with voltage pulses, for example of from 10-100 volts and 1 rn~ec to 1 ~sec duration, in accordance with a digital image pattern that is stored in the control apparatus. The control apparatus is not a part of the present invention and, therefore, is not disclosed in de-tail. However, electroerosion scanners are kno~n to the 25 art and are commercially available.
When the control apparatus 11 energizes a particular erosion electrode 7 with a voltage pulse, the energy of the electrical pulse is passed to an area of the aluminurn oxide film that is i~ttediately adjacent to 30 the electrode. Lhe voltage pulse is sufficiently large to break down the aluminum oxide and to cause a heating current I to flo~Y from the printing electrode 7 to the broad area electrode ~, through the aluminum film. The concentrated current in the area of the aluminum film YOg78-Q36 adjacent to the point of application of the voltage pulse causes a hole to be evaporated in the aluminum. In ex-perimental tests, an eroSiQn pulse of 50 volts and 200 microseconds duration was sufficient to erode a hole extending to the MYLA~ substrate in a printing plate having a 2000 angstrom film of aluminum and associated S00 angstrom fi lm of aluminum oxide, in accordance with the invention. However, when a pulse of the same magni-tude was applied to a prior art printing plate having only a MYLAR substrate and an aluminum film, only approxi-mately 800 angstroms of aluminum was eroded.
It is theorized that the greater penetration for the printing plate of the invention is due to the fact that the dielectric layer of aluminum oxide acts as a capaci-tor that initially stores energy as a voltage pulse isapplied and that releases the stored energy when the dielectric film breaks down. The release of the stored energy apparently adds to the heat that is normally pro-duced by the erosion current I and, therefore, more alumi-num is evaporatecl.
A capacitive breakdown scheme has been employed in theU.S. Patent to Reis, "Electrosensitive Recording", No.
3,299,433, issued January 17, 1957, to heat a surface recording medium that changes color in response to ap-plied heat. However, the capacitive breakdown that isdisclosed in the Reis patent is not directed to an electroerosion process-wherein a hole is formed in a dielectric film and an underlying aluminum film.
It has also been e~perimentally determined that a prior art nrjnting plate having a polyester substrate, such as MYLAR and an 800 angstrom aluminum layer is subject to scratching and burnishing on the exposed aluminum film when the erosion electrodes 7 contact the plate with pressures re~-lired by the electroerosion process while scanning the plate. Thus, the contact pressure of the erosion electrodes must be closely monitored in prior art electroerosion systems in order to avoid such undesirable burnishing or scratching. However, a prin-S ting plate constructed in accordance with the invention,having a 2000 angstrom aluminum film and an associated 500 angstrom aluminum oxide film, is resistant to scratching and burnislling, with onl~ moderate attention being given to the contact pressure of the erosion elec-trodes. In addition, the above prior art printing platewas able to print no more ~han 500 copies before signi-ficant image degradation occurred due to wearing of the imaging surfaces of the plate, while the above plate con-structed in accordance with the invention was used to lS print 10,000 copies, with, apparently, no signs of wear.
It should be understood that, since the printing plate of the invention is not subject to scratching and burnishing by the erosion electrodes 7, only routine attention need be given to electrode pressure during the process of forming an image on the plate. However, prior art plates are subject to objectionable scratching and buxnishing by tllc ~rosion electrodes and, therefore, during the imaging process, particular care must be taken to avoid excessive pressure of the erosion electrodes.
Accordingly, the lithographic printing plate of the in-vention is less difficult to produce than prior art printing plates, since less care need be taken in the imaging process. In addition, the hard layer of aluminum oxide on the printing plate provides an extended opera-tional lifetime that is many times greater than hashe~etofore been achieved. ~oreover, the dielectric film increases tlle energy efficiency of the erosion pro-cess and, therefore, substantially thic~er layers of metal may be eroded, thereby extending the print l-ifetime Y~978-036 of the printing plate even further.
Although aluminum and aluminum oxide were employed to respectively form the first conducting film and second protective layer for a preferred em~odiment of the in-vention, other materials may be employed without de-parting from the spirit of the invention. For example, tungsten may be used in place of aluminun and hafnium oxide (E3fO2) or Schott glass may be used in place of the aluminum oxide.
An improved lithographic printing plate may also be made in accordance with the invention by depositing an aluminum film over a polyester substrate in the above-described manner and then depositing a chrome film over the aluminum film and an aluminum oxide (A1203) film or chrome oxide (Cr203) film over the chrome film. For such an embodiment of the invention, the combined chrome and aluminum films behave in much the same fashion as the aluminum film of the embodiment oE the drawing.
It should be appreciated that means other than electron beam evaporation may be employed to deposit a conducting film on a polyester substrate, for example some conductors may be deposited by electroless deposition or sputtering.
It should also be appreciated that the dielectric film of the invention may be used in conjunction with an alu-minum layer of typical thickness f for example 800 ang-stroms, and the voltage and/or duration of the erosion pulses of the. erosion electrodes may then be reduced, to conserve energy in the process of making the printing plate. Moreover, it should be und~rs~ood that the cited examples of erosion electrode voltage and pulse duration and of the thickness of the aluminum and alu-minum oxide films are not intended to limit the scope YOg78-036 of the invention. Other magnitudes of electrode pulses and thicknesses of cQnducting and dielectric film may be used without departing from the spirit of the inven-tion.
It has been observed in this regard that variatlon of the pulse voltage and duxation affects a predictable modification of the size and shape 'of the eroded hole.
Increasing the pulse voltage produces an overall enlarge-ment of the hole in the direction of relative travel or the erosion electrode. Moreover, the size of the hole tends to follow, subject to the above-mentioned influ-ences, the cross-sectional size of the erosion electrode.
It is thus apparent that control of the size o the ero-ded hole, and consequently of the resolution of the eroded image, is provided by the specification of the erosion electrode dimensions, the pulse voltage and the pulse duration. The capability of producing "half-tone"
images, in which varying shades of grey are produced by varying spot size rather than by varying spot density, is thus seen ta reside in the above-described process.
The invention may be embodied in other specific forms without departing from its spirit or essential charac-teristics. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the claims rather than by the foregoing description, -~ and all changes which come within the meaning and range of the equivalents of the claims are therefore intended to be embraced therein.
Claims (12)
1. A lithographic printing plate for use in an electroerosion process comprising:
an electrically nonconducting hydrophobic substrate;
an electrically conducting hydrophilic film having a thickness of from 1000 to 3000 angstroms disposed on said substrate; and a dielectric hydrophilic film having a thickness of from 100 to 800 angstroms disposed on a printing portion of said conducting film for protecting said printing portion of the conducting film and breaking down in response to at least one electrical pulse of a particular voltage and duration.
an electrically nonconducting hydrophobic substrate;
an electrically conducting hydrophilic film having a thickness of from 1000 to 3000 angstroms disposed on said substrate; and a dielectric hydrophilic film having a thickness of from 100 to 800 angstroms disposed on a printing portion of said conducting film for protecting said printing portion of the conducting film and breaking down in response to at least one electrical pulse of a particular voltage and duration.
2. The printing plate of claim 1 wherein said nonconducting substrate is made of a polyester.
3. The printing plate of claim 1 wherein said nonconducting substrate is made of a polyimide.
4. The printing plate of claim 1 wherein said dielectric film and said electrically conducting film are hydrophilic.
5. The printing plate of claim 1 wherein said conducting film is made of aluminum.
6. The printing plate of claim 1 wherein said conducting film is made of tungsten.
7. The printing plate of claim 1 wherein said dielectric film is made of aluminum oxide A1203.
8. The printing plate of claim 1 wherein said conducting film includes a lower layer of aluminum and an upper layer of chrome and said dielectric film is made of chrome oxide Cr203 .
9. The printing plate of claim 1 wherein said conducting film includes a lower layer of aluminum and an upper layer of chrome and said dielectric film is made of aluminum oxide A1203.
10. The printing plate of claim 1 wherein the dielectric film has a hardness in excess of the hardness of said conducting film.
11. The printing plate of claim 1 wherein said particular voltage is from 10 to 100 and said particular duration is from 1 microsecond to 1 millisecond.
12. A lithoqraphic printing plate having a relatively thick conducting film for producing a relatively large number of copies, for use in an electroerosion process with printing voltage pulses of magnitude of from 10 to 100 volts and duration of from 1 microsecond to 1 millisecond,comprising:
an electrically non-conducting hydrophobic substrate;
an electrically conducting hydrophilic film of aluminum having a thickness of from 1000 -to 3000 angstroms disposed on said substrate; and a dielectric hydrophilic film of aluminum oxide having a thickness of from 100 to 800 angstroms disposed on a printing portion of said conducting film for protecting said printing portion of the conducting film and for breaking down in response to said printing voltage pulses of from 10 to 100 volts, and of duration of from 1 microsecond to 1 millisecond.
an electrically non-conducting hydrophobic substrate;
an electrically conducting hydrophilic film of aluminum having a thickness of from 1000 -to 3000 angstroms disposed on said substrate; and a dielectric hydrophilic film of aluminum oxide having a thickness of from 100 to 800 angstroms disposed on a printing portion of said conducting film for protecting said printing portion of the conducting film and for breaking down in response to said printing voltage pulses of from 10 to 100 volts, and of duration of from 1 microsecond to 1 millisecond.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US10396579A | 1979-12-17 | 1979-12-17 | |
| US103,965 | 1979-12-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1144418A true CA1144418A (en) | 1983-04-12 |
Family
ID=22297957
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000362742A Expired CA1144418A (en) | 1979-12-17 | 1980-10-20 | Erosion process for generation of offset masters |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0030642A3 (en) |
| JP (1) | JPS5693590A (en) |
| CA (1) | CA1144418A (en) |
| IT (1) | IT1149864B (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0088139B1 (en) * | 1982-03-09 | 1987-01-07 | Ibm Deutschland Gmbh | Lithographic printing plate and method for producing the same |
| EP0101266A3 (en) * | 1982-08-09 | 1985-04-03 | Milliken Research Corporation | Printing method and apparatus |
| JPS59114543A (en) * | 1982-12-15 | 1984-07-02 | ロネオ・アルカテル・リミテツド | Opaque recording sheet and manufacture of offset lithographic plate using same |
| EP0164461A1 (en) * | 1984-06-06 | 1985-12-18 | Roneo Alcatel Limited | IMprovements in or relating to electro-sensitive materials |
| DE3416867A1 (en) * | 1984-05-08 | 1985-11-14 | Hoechst Ag, 6230 Frankfurt | ONE-STEP ELECTROCHEMICAL IMAGING METHOD FOR REPRODUCTION LAYERS |
| GB2200323B (en) * | 1986-12-16 | 1991-05-01 | Tetra Pak Ab | Offset printing |
| DE3717652A1 (en) * | 1987-05-26 | 1988-12-08 | Hoechst Ag | ONE-STEP ELECTROCHEMICAL IMAGING METHOD FOR REPRODUCTION LAYERS |
| DE3717653A1 (en) * | 1987-05-26 | 1988-12-08 | Hoechst Ag | METHOD FOR SELECTIVE ADDITIVE CORRECTION OF MISTAKES IN COPY LAYERS |
| DE69313835T2 (en) * | 1993-06-11 | 1998-04-02 | Agfa Gevaert Nv | Heat recording process and process for the production of printing plates therewith |
| US5674416A (en) * | 1995-08-28 | 1997-10-07 | Aluminum Company Of America | Arc treatment of metal surfaces |
| US5783364A (en) * | 1996-08-20 | 1998-07-21 | Presstek, Inc. | Thin-film imaging recording constructions incorporating metallic inorganic layers and optical interference structures |
| GB2320461A (en) * | 1996-12-18 | 1998-06-24 | British Aerospace | Application of stop-off material,particularly for use in diffusion bonding and superplastic forming |
| US6107001A (en) * | 1997-05-05 | 2000-08-22 | Presstek, Inc. | Method and apparatus for non-ablative, heat-activated lithographic imaging |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE849609C (en) * | 1950-11-06 | 1952-09-15 | Bosch Gmbh Robert | Tape-shaped recording medium for recording measuring instruments |
| DE2111274C3 (en) * | 1971-03-09 | 1975-12-11 | Robert Bosch Gmbh, 7000 Stuttgart | Recording media with a metallic covering for recording devices |
| DE2204509C3 (en) * | 1972-02-01 | 1981-12-03 | Robert Bosch Gmbh, 7000 Stuttgart | Data carriers for recorders |
| JPS5550794B2 (en) * | 1973-09-26 | 1980-12-19 | ||
| JPS5059112A (en) * | 1973-09-26 | 1975-05-22 | ||
| GB1480081A (en) * | 1973-09-18 | 1977-07-20 | Ricoh Kk | Methods of producing printing masters by spark-recording |
| GB1451378A (en) * | 1973-12-13 | 1976-09-29 | Vickers Ltd | Lithographic printing blanks and their inscription |
| JPS518574A (en) * | 1974-07-10 | 1976-01-23 | Matsushita Electric Ind Co Ltd | Insatsuhaisenbanno seizohoho |
-
1980
- 1980-10-20 CA CA000362742A patent/CA1144418A/en not_active Expired
- 1980-11-20 EP EP80107228A patent/EP0030642A3/en not_active Withdrawn
- 1980-12-03 IT IT26395/80A patent/IT1149864B/en active
- 1980-12-05 JP JP17106880A patent/JPS5693590A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| IT1149864B (en) | 1986-12-10 |
| EP0030642A2 (en) | 1981-06-24 |
| JPS5693590A (en) | 1981-07-29 |
| EP0030642A3 (en) | 1982-05-26 |
| JPS6151558B2 (en) | 1986-11-10 |
| IT8026395A0 (en) | 1980-12-03 |
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