CA2128911C - Lithographic printing members having secondary ablation layers for use with laser-discharge imaging apparatus - Google Patents
Lithographic printing members having secondary ablation layers for use with laser-discharge imaging apparatusInfo
- Publication number
- CA2128911C CA2128911C CA002128911A CA2128911A CA2128911C CA 2128911 C CA2128911 C CA 2128911C CA 002128911 A CA002128911 A CA 002128911A CA 2128911 A CA2128911 A CA 2128911A CA 2128911 C CA2128911 C CA 2128911C
- Authority
- CA
- Canada
- Prior art keywords
- layer
- substrate
- plate
- laser
- ink
- 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 - Fee Related
Links
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
- B41N1/00—Printing plates or foils; Materials therefor
- B41N1/003—Printing plates or foils; Materials therefor with ink abhesive means or abhesive forming means, such as abhesive siloxane or fluoro compounds, e.g. for dry lithographic printing
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- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41P—INDEXING SCHEME RELATING TO PRINTING, LINING MACHINES, TYPEWRITERS, AND TO STAMPS
- B41P2227/00—Mounting or handling printing plates; Forming printing surfaces in situ
- B41P2227/70—Forming the printing surface directly on the form cylinder
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
- Y10S430/145—Infrared
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
- Y10S430/146—Laser beam
Abstract
Lithographic printing plates suitable for imaging by means of laser devices. Laser output ablates one or more plate layers, resulting in an imagewise pattern of features on the plate. The image features exhibit an affinity for ink or an ink-abhesive fluid that differs from that of unexposed areas.
The plates also include a secondary ablation layer that ablates only partially, and in a controlled fashion, as a result of destruction of overlying layers.
The plates also include a secondary ablation layer that ablates only partially, and in a controlled fashion, as a result of destruction of overlying layers.
Description
LITHOGRAPHIC PRINTING MEMBERS HAVING
SECONDARY ABLATION LAYERS FOR USE
WITH LASER-DISCHARGE IMAGING APPARATUS
BACKGROUND OF THE INVENTION
A. Fleld of the Invention The present invention relates to digital printing apparatus and methods, and more particularly to lithographic printing plate constructions that may be imaged on- or off-press using digitally controlled laser output.
B. Description of the Related Art Traditional techniques of introducing a printedimage onto a recording material include letterpress printlng, gravure printing and offset lithography, All of these printing methods require a plate, usually loaded onto a plate cylinder of a rotary press for efficlency, to transfer ink in the pattern of the .lmage. In letterpress printing, the image pattern is represented on the plate in the form of raised areas that accept ink and transfer it onto the recordlng medium by impression. Gravure printing cylinders, in contrast, contain series of wells or indentation that accept ink for deposlt onto the recording medium; excess ink must be removed from the cylinder by a doctor blade or similar device prior to contact between the cylinder and the recording medium.
In the case of offset lithography, the image is s present on a plate or mat as a pattern of ink-accepting ~oleophilic) and ink-repellent (oleophobic) surface areas. In a dry printing system, the plate is slmply lnked and the lmage transferred onto a recordlng materlal; the plate first makes contact with a compliant lntermedlate surface called a blanket cylinder whlch, in turn, applies the image to the paper or other recording medlum. In typlcal sheet-fed press systems, the recording medlum is plnned to an lmpresslon cylinder, which brings lt lnto contact with the blanket cylinder.
In a wet lithographic system, the non-image areas are hydrophllic, and the necessary lnk-repellency ls provlded by an lnitial application of a dampening (or "fountain") solution to the plate prior to inking. The ink-repellent fountain solutlon prevents ink from adhering to the non-image areas, but does not affect the oleophlllc character of the image areas.
If a press is to prlnt in more than one color, a separate printing plate corresponding to each color is required, each such plate usually being made photographically as described below. In addition to preparlng the appropriate plates for the different colors, the operator must mount the plates properly on the plate cylinders of the press, and coordlnate the positlons of the cylinders so that the color components printed by the different cyllnders will be ln register on the printed copies. Each set of cylinders associated with a particular color on a press is usually referred to as a printing station.
2128~1 1 - 2a -In most conventional presses, the prlnting statlons are arranged in a straight or "ln-line" configuration, Each such statlon typically includes an impression cylinder, a blanket cylinder, a plate cylinder and the necessary ink (and, in wet systems, dampenlng) assemblles. The recordlng material is transferred among the print stations sequentially, each station applying a dlfferent ink color to the material to produce a composite multi-color image. Another-configuration, descrlbed in U.S. Patent No. 4,936,211 (co-owned with the present applicatlon, relles on a central impression cylinder that carries a sheet of recordlng materlal past each prlnt statlon, eliminating the need for mechanical transfer of the medium to each print station.
CA 02128911 1998-0~-13 Wlth elther type of press, the recordlng medlum can be supplled to the prlnt statlons ln the form of cut sheets or a contlnuous "web" of materlal. The number of prlnt statlons on a press depends on the type of document to be prlnted. For mass copylng of text or slmple monochrome llne-art, a slngle prlnt statlon may suffice. To achleve full tonal rendltlon of more complex monochrome lmages, lt ls customary to employ a "duotone" approach, ln whlch two statlons apply dlfferent densltles of the same color or shade. Full-color presses apply lnk accordlng to a selected color model, the most common belng based on cyan, magenta, yellow and black (the "CMYK"
model). Accordlngly, the CMYK model requlres a mlnlmum of four prlnt stations; more may be requlred lf a partlcular color ls to be emphaslzed. The press may contaln another station to apply spot lacquer to varlous portlons of the prlnted document, and may also feature one or more "perfectlng" assemblles that lnvert the recordlng medlum to obtaln two-slded prlntlng.
The plates for an offset press are usually produced photographlcally. To prepare a wet plate uslng a typlcal negatlve-worklng subtractlve process, the orlglnal document ls photographed to produce a photographlc negatlve. Thls negatlve ls placed on an alumlnum plate havlng a water-receptlve oxlde surface coated wlth a photopolymer. Upon exposure to llght or other radlatlon through the negatlve, the areas of the coatlng that recelved radlatlon (correspondlng to the dark or prlnted areas of the orlglnal) cure to a durable CA 02128911 1998-0~-13 - 3a -oleophilic state. The plate ls then subiected to a developing process that removes the uncured areas of the coatlng (l.e., those which dld not recelve radiatlon, correspondlng to the non-lmage or background areas of the orlginal), exposing the hydrophlllc surface of the alumlnum plate.
A slmllar photographlc process is used to create dry plates, which typically include an oleophobic (e.g., sillcone) surface layer coated onto a photosensitive layer, which ls itself coated onto a substrate of suitable stabillty (e.g., an aluminum sheet). Upon exposure to actinic radlatlon, the photosensltlve layer cures to a state that destroys lts bonding to the surface layer. After exposure, a treatment is applled to deactivate the photoresponse of the photosensltlve layer ln unexposed areas and to further improve anchorage of the surface layer to these areas. Immerslon of the exposed plate in developer results ln dissolution and removal of the surface layer at those portions of the plate surface that have received radiation, thereby exposing the ink-receptive, cured photosensitive layer.
Photographic plate maklng processes tend to be tlme consuming and require facilities and equipment adequate to support the necessary chemistry. To circumvent these shortcomings, practltioners have developed a number of electronic alternatives to plate imaging, some of which can be utilized on-press. With these systems, digitally controlled devices alter the ink-receptivity of blank plates in a pattern representative of the image to be printed. Such imaging devices lnclude sources of electromagnetic-radiation pulses, produced by one or more laser or non-laser sources, that create chemical changes on plate blanks (thereby eliminating the need for a photographic negative); ink-~et equipment that directly deposits ink-repellent or ink-accepting spots on plate blanks; and spark-dlscharge equipment, ln which an electrode in contact with or spaced close to a plate blank produces electrlcal sparks to physlcally alter the topology of the plate blank, thereby producing "dots" which collectively form a desired image (see e.g., U.S. Patent No. 4,911,075, co-owned with the present application.
Because of the ready availability of laser equipment ~.
212~ql 1 and their amenability to digital control, significant effort has been devoted to the development of laser-based imaging systems. Early examples utilized lasers to etch away material from a plate blank to form an intaglio or letterpress pattern.
See,e.g., U.S. Patent Nos. 3,506,779; 4,347,785. This approach was later extended to production of lithographic plates, e.g., by removal of a hydrophilic surface to reveal an oleophilic underlayer. See, e.g., U.S. Patent No. 4,054,094.
The systems generally require high-power lasers, which are expensive and slow.
A second approach to laser imaging involves the use of laser-ablation-transfer materials. See e.g., U.S. Patent Nos. 3,945,318; 3,962,513; 3,964,389; 4,395,946; 5,156,938 and 5,171,650. With these systems, a polymer sheet tranparent to the radiation emitted by the laser is coated with a transferable material. During operation the transfer side of this construction is brought into contact with an acceptor sheet, and the transfer material is selectively irradiated through the transparent layer. Irradiation causes the transfer material to adhere preferentially to the acceptor sheet. The transfer and acceptor materials exhibit different affinities for fountain solution and/or ink, so that removal of the transparent layer together wlth unlrradlated transfer material leaves a suitably imaged, finished plate. Typically, the transfer material ls oleophllic and the acceptor material hydrophilic. Plates produced with transfer-type systems tend to exhiblt short useful llfetlmes due to the llmited amount of ~' ~, . i 2128~1 1 - 5a -material that can effectively be transferred. In addition, because the transfer process involves melting and resolidlflcation of material, lmage quality tends to be vislbly poorer than that obtalnable with other methods.
Flnally, lasers can be used to expose a photosensltlve blank for tradltlonal chemlcal processlng. See e.a., U.S. Patent Nos. 3,506,779; 4,020,762. In an alternatlve to this approach, a laser has been employed to selectlvely remove, ln an lmagewlse pattern, an opaque coating that overlies a photosensitive plate blank. The plate is then exposed to a source of radiation, with the unremoved material acting as a mask that prevents radiation from reaching underlylng portlons of the plate. See e.g., U.S. Patent No.
4,132,168. Elther of these lmaglng techniques requlres the cumbersome chemical processing associated with traditlonal, non-dlgltal plate making.
Corresponding Canadian Patent application Serial No.
Z,100,517 filed on July 14, 1993 and commonly owned, with the present application discloses a variety of plate-blank constructions, enabling production of "wet" plates that utlllze fountaln solution during prlnting of "dry" plates to which ink ls applied directly. In partlcular, the '517 appllcation descrlbes a flrst embodlment that includes a first layer and a CA 02128911 1998-0~-13 substrate underlying the first layer, the substrate being characterized by efficlent absorptlon of lnfrared ("IR") radlatlon, and the first layer and substrate having different affinities for lnk (in a dry-plate construction) or a fluid that repels ink (in a wet-plate constructlon). Laser radiation is absorbed by the substrate, and ablates the substrate surface in contact with the first layer; thls action disrupts the anchorage of the substrate to the overlying first layer, whlch is then easlly removed at the polnts of exposure.
The result of removal ls an lmage spot whose afflnlty for the ink or ink-repellent fluid differs from that of the unexposed flrst layer. The '517 appllcation also discloses a varlation of this embodiment in which the first layer, rather than the substrate, absorbs IR radiation. In thls case the substrate serves a support functlon and provldes contrastlng afflnity characteristlcs.
In a second embodlment dlsclosed ln the '517 application, the flrst, topmost layer ls chosen for lts affinlty for (or repulslon of) ink or an lnk-repellent fluid.
Underlying the flrst layer ls a second layer, whlch absorbs IR
radlation. A strong, stable substrate underlles the second layer, and ls characterlzed by an afflnlty for (or repulslon of) ink or an lnk-repellent fluid opposite to that of the flrst layer. Exposure of the plate to a laser pulse ablates the absorblng second layer, weakenlng the topmost layer as CA 02128911 1998-0~-13 well. As a result of ablation of the second layer, the weakened surface layer ls no longer anchored to an underlylng layer, and ls easlly removed.
Flnally, the '517 appllcation descrlbes varlatlon of the foregolng embodlments by addition, beneath the absorbing layer, of an additional layer that reflects IR radiation.
This additional layer reflects any radiation that penetrates the absorbing layer back through that layer, so that the effectlve flux through the absorblng layer ls slgnlficantly increased.
All of these constructions, while useful and effective generally require removal of the dlsrupted -- but still remaining -- topmost layer (and any debris remaining from destruction of the absorptive second layer) in a post-imaging cleaning step. Depending on the materials chosen for the substrate and topmost layers, imaging exposure can fuse these two layers, rendering the latter especially resistant to removal. Furthermore, in some constructions, debrls from one or more ablated layers can condense or otherwise deposit on the topmost unablated layer (e.g., the substrate), resulting in the need for strenuous cleaning that can prove both tlme-consumlng and cumbersome. Flnally, we have also ln some lnstances observed charrlng of the topmost unablated layer, an effect that can degrade prlnting performance by roughening this layer and thereby lnterferlng wlth lts lnteractlon with CA 02128911 1998-0~-13 - 7a -prlnting fluids (an effect also observed when post-imaging cleaning falls to remove a sufflcient proportion of the accumulated debris) DESCRIPTION OF THE INVENTION
A. Brlef Summary of the Invention The present inventlon enables rapid, efflclent production of lithographlc prlnting plates using laser equlpment, and the approach contemplated herein may be applied to any of a variety of laser sources that emlt in various regions of the electromagnetic spectrum. The problems of debrls buildup and/or charring, common to numerous laser-imaging processes, are ameliorated by introduction of a secondary ablation layer into the plate constructions. As used herein, the term "plate" refers to any type of printing member or surface capable of recording an image defined by regions exhibiting differential affinitles for lnk and/or fountain solution; suitable configurations include the traditional planar or curved lithographic plates that are mounted on the plate cylinder of a prlnting press, but can also include cylinders (e.g., the roll surface of a plate cylinder), an endless belt, or other arrangement.
All constructions of the present invention utillze materials that enhance the ablative efficiency of the laser beam. Substances that do not heat rapldly or absorb 21289~ ~
significant amounts of radiation will not ablate unless they are irradiated for relatively long lntervals and/or receive high-power pulses.
In particular, the printlng media of the present invention are based on a cooperative construction that includes a "secondary" ablation layer. This layer ablates, or decomposes into gases and volatile fragments, in response to heat generated by ablation of one or more overlying layers, If transmltted dlrectly to the plate substrate, the heat might char that layer. The secondary ablation layer preferably does not interact with the laser radiation and, to facilitate reverse-side imaging as described in co-pending Canadian Patent application Serlal No. 2,100,413 filed on July 14, l9g3 and commonly owned with the present application, is desirably transparent (or substantially so) to such radiation.
In a typical construction, a radiation-absorbing layer underlies a surface coating chosen for its interaction with ink and/or fountain solution, The secondary ablation layer is located beneath the absorbing layer, and may be anchored to a substrate having superior mechanical properties.
It may be preferable in some lnstances to introduce an additional layer between the secondary ablation layer and the substrate to enhance adhes~on therebetween, as more fully described below.
Alternatlvely, the basic plate construction can consist of a substrate that supports a radiation-absorptive layer (which performs the functions of the surface and ~7~, .
21289~ ~
absorbing layers in the constructions discussed above), the two layers differing in their affinities for ink and/or fountain solution. In this case, the secondary ablation layer is located between the substrate, and the radiation-absorptive layer.
The secondary ablation layer should ablate "cleanly"--that is, exhibit sufflcient thermal instability as to decompose rapidly and uniformly upon application of heat, evolving primarily gaseous decomposition products. Preferred materials undergo substantially complete thermal decomposition !or pyrolysis) with limited melting or formation of solid decomposition products, and are typically based on chemical structures that readily undergo, upon exposure to sufficient thermal energy, eliminations (e.g. Decarboxylations) and rearrangements producing volatlle products.
The secondary ablation layer is applied at a thickness sufficient to ablate only partially in response to the heat produced by ablation of the one or more overlying layers. Accordingly, the plates of the present invention are properly viewed as cooperative constructions tailored for a particular imaging system, in that the proper thickness of the secondary ablation layer is determined by the degree of absorbance exhibited by the overlying absorbing layer and the ablative responsiveness of the layer to imaging radiation.
For example, ablation of a radiation-absorbing layer can reflect an exothermic process (e.g., exothermic oxidation), resulting in the production of more energy than is delivered ~ 1 2;~
- 9a -by the laser.
Our preferred material are based on polymethylmethacrylate (PMMA), which may be doped wlth radlatlon-absorblng chromophores as descrlbed below, although numerous other polymerlc materlals havlng the foregolng characterlstlcs provlde acceptable performance.
Because they ablate cleanly, secondary ablatlon layers avoid the uneven topologies assoclated with charring of the plate substrate; indeed, the secondary ablation layer performs a protective function that shields the substrate from the thermal effects of lmaglng radlatlon; this function proves partlcularly useful ln conjunction wlth metal substrate.
Furthermore, the rapid decomposltlon of the secondary ablatlon layer evolves a gaseous plume or cloud that discourages accumulation of partlculate remnants of overlylng layers. One can even ellminate the need for post-lmaglng cleanlng of the flnlshed plate by uslng secondary ablation layers of sufficient thlckness (and/or relatlve unresponsiveness to thermal stress) to permlt the use of hlgh-power imaglng lasers whose output is strong enough to fully remove all overlying layers.
In summary, the present lnvention provides, a lithographlc prlntlng member dlrectly lmageable by laser discharge, the member comprising: a. a topmost first layer;
and b. a second layer underlylng the flrst layer, the second layer being characterised by ablative absorption of laser radlatlon; c. a third layer underlying the second layer, the ~ ,' 2l 28q~ ~
- 9b -third layer: i. being substantially transparent to the laser radiation; ii. being ablated only partially in response to ablation of the second layer; and iii. differing from the first layer in its affinity for at least one printlng liquid selected from the group consisting of ink and a fluid that repels ink.
B. Brief Description of the Drawings The foregoing discussion will be understood more readily from the following detailed description of the invention, when taken in conjunction with the accompanying drawings, in which:
s ' CA 02128911 1998-0~-13 FIG. 1 ls an enlarged sectional view of a llthographlc plate havlng a top layer, a radlatlon-absorptive layer, and a secondary ablation layer mounted to a substrate by means of an adheslon-promoting layer;
FIG. 2 ls an enlarged sectlonal vlew of a llthographlc plate having a top layer, a radiation-absorptive composite lncluding TiO and aluminlum layers, and a secondary ablatlon layer mounted to a substrate by means of an adhesion-promoting layer;
FIG. 3 is an enlarged sectional view of a lithographic plate having a top layer that absorbs laser radiation and a secondary ablation layer mounted to a substrate by means of an adheslon-promoting layer; and FIG. 4 is an enlarged sectional vlew of a lithographic plate having a top layer and a secondary ablation layer.
C. Detailed Description of the Preferred Embodiments 1. Imaqinq APparatus Imaging apparatus suitable for use in con~unction wlth the present prlntlng members lncludes at least one laser devlce that emlts ln the reglon of maximum plate responslveness, l.e., whose l~mhAal,,ax closely approxlmates the wavelength reglon where the plate absorbs most strongly.
Speclflcatlons for lasers that emlt ln the near-IR reglon are fully descrlbed ln the '431 appllcation; lasers emitting in CA 02128911 1998-0~-13 other reglons of the electromagnetlc spectrum are well-known to those skllled in the art.
Sultable lmaglng configuratlons are also set forth in detall ln the '517 appllcation. ~riefly, laser output can be provided directly to the plate surface via lenses or other beam-guiding components, or transmitted to the surface of a blank printlng plate from a remotely sited laser using a fiber-optlc cable. A controller and associated posltlonlng hardware malntalns the beam output at a preclse orlentatlon with respect to the plate surface, scans the output over the surface, and activates the laser at posltions ad~acent selected points or areas of the plate. The controller responds to incoming image signals corresponding to the original document or picture being copied onto the plate to produce a precise negatlve or posltive image of that orlglnal.
The lmage slgnals are stored as a bitmap data file on a computer. Such files may be generated by a raster image processor (RIP) or other suitable means. For example, a RIP
can accept input data in page-description language, which defines all of the features required to be transferred onto the printing plate, or as a combination of page-descriptlon language and one or more image data files. The bitmaps are constructed to define the hue of the color as well as screen frequencies and angles.
The imaging apparatus can operate on its own, functioning solely as a platemaker, or can be incorporated directly into a llthographic printing press. In the latter CA 02128911 1998-0~-13 case, prlnting may commence immedlately after application of the lmage to a blank plate, thereby reducing press set-up tlme conslderably. The imaging apparatus can be configured as a flatbed recorder or as a drum recorder, wlth the llthographlc plate blank mounted to the interior or exterior cylindrical surface of the drum. Obviously, the exterior drum design is more appropriate to use in situ, on a lithographic press, in which case the print cylinder itself constitutes the drum component of the recorder or plotter.
In the drum configuration, the requisite relative motion between the laser beam and the plate is achieved by rotating the drum (and the plate mounted thereon) about its axis and moving the beam parallel to the rotation axis, thereby scanning the plate circumferentially so the image 'grows" in the axial directlon. Alternatively, the beam can move parallel to the drum axis and, after each pass across the plate, lncrement angularly so that the image on the plate "grows" clrcumferentially. In both cases, after a complete scan by the beam, an lmage correspondlng (posltively or negatively) to the beam, an image corresponding (positively or negatively) to the original document or picture will have been applied to the surface of the plate.
In the flatbed configuration, the beam is drawn across either axls of the plate, and is indexed along the other axls after each pass. Of course, the requlslte relatlve CA 02128911 1998-0~-13 - 12a -motlon between the beam and the plate may be produced by movement of the plate rather than (or in addltion to) movement of the beam.
Regardless of the manner ln which the beam ls scanned, lt ls generally preferable (for on-press appllcatlons) to employ a plurallty of lasers and gulde their outputs to a slngle wrltlng array. The wrltlng array ls then lndexed, after completlon of each pass across or along the plate, a dlstance determlned by the number of beams emanatlng from the array, and by the deslred resolution (l.e, the number of lmage polnts per unlt length). Off-press appllcatlons, whlch can be deslgned to accommodate very rapld plate movement (e.g., through use of hlgh-speed motors) and thereby utlllze hlgh laser pulse rates, can frequently utlllze a slngle laser as an lmaglng source.
SECONDARY ABLATION LAYERS FOR USE
WITH LASER-DISCHARGE IMAGING APPARATUS
BACKGROUND OF THE INVENTION
A. Fleld of the Invention The present invention relates to digital printing apparatus and methods, and more particularly to lithographic printing plate constructions that may be imaged on- or off-press using digitally controlled laser output.
B. Description of the Related Art Traditional techniques of introducing a printedimage onto a recording material include letterpress printlng, gravure printing and offset lithography, All of these printing methods require a plate, usually loaded onto a plate cylinder of a rotary press for efficlency, to transfer ink in the pattern of the .lmage. In letterpress printing, the image pattern is represented on the plate in the form of raised areas that accept ink and transfer it onto the recordlng medium by impression. Gravure printing cylinders, in contrast, contain series of wells or indentation that accept ink for deposlt onto the recording medium; excess ink must be removed from the cylinder by a doctor blade or similar device prior to contact between the cylinder and the recording medium.
In the case of offset lithography, the image is s present on a plate or mat as a pattern of ink-accepting ~oleophilic) and ink-repellent (oleophobic) surface areas. In a dry printing system, the plate is slmply lnked and the lmage transferred onto a recordlng materlal; the plate first makes contact with a compliant lntermedlate surface called a blanket cylinder whlch, in turn, applies the image to the paper or other recording medlum. In typlcal sheet-fed press systems, the recording medlum is plnned to an lmpresslon cylinder, which brings lt lnto contact with the blanket cylinder.
In a wet lithographic system, the non-image areas are hydrophllic, and the necessary lnk-repellency ls provlded by an lnitial application of a dampening (or "fountain") solution to the plate prior to inking. The ink-repellent fountain solutlon prevents ink from adhering to the non-image areas, but does not affect the oleophlllc character of the image areas.
If a press is to prlnt in more than one color, a separate printing plate corresponding to each color is required, each such plate usually being made photographically as described below. In addition to preparlng the appropriate plates for the different colors, the operator must mount the plates properly on the plate cylinders of the press, and coordlnate the positlons of the cylinders so that the color components printed by the different cyllnders will be ln register on the printed copies. Each set of cylinders associated with a particular color on a press is usually referred to as a printing station.
2128~1 1 - 2a -In most conventional presses, the prlnting statlons are arranged in a straight or "ln-line" configuration, Each such statlon typically includes an impression cylinder, a blanket cylinder, a plate cylinder and the necessary ink (and, in wet systems, dampenlng) assemblles. The recordlng material is transferred among the print stations sequentially, each station applying a dlfferent ink color to the material to produce a composite multi-color image. Another-configuration, descrlbed in U.S. Patent No. 4,936,211 (co-owned with the present applicatlon, relles on a central impression cylinder that carries a sheet of recordlng materlal past each prlnt statlon, eliminating the need for mechanical transfer of the medium to each print station.
CA 02128911 1998-0~-13 Wlth elther type of press, the recordlng medlum can be supplled to the prlnt statlons ln the form of cut sheets or a contlnuous "web" of materlal. The number of prlnt statlons on a press depends on the type of document to be prlnted. For mass copylng of text or slmple monochrome llne-art, a slngle prlnt statlon may suffice. To achleve full tonal rendltlon of more complex monochrome lmages, lt ls customary to employ a "duotone" approach, ln whlch two statlons apply dlfferent densltles of the same color or shade. Full-color presses apply lnk accordlng to a selected color model, the most common belng based on cyan, magenta, yellow and black (the "CMYK"
model). Accordlngly, the CMYK model requlres a mlnlmum of four prlnt stations; more may be requlred lf a partlcular color ls to be emphaslzed. The press may contaln another station to apply spot lacquer to varlous portlons of the prlnted document, and may also feature one or more "perfectlng" assemblles that lnvert the recordlng medlum to obtaln two-slded prlntlng.
The plates for an offset press are usually produced photographlcally. To prepare a wet plate uslng a typlcal negatlve-worklng subtractlve process, the orlglnal document ls photographed to produce a photographlc negatlve. Thls negatlve ls placed on an alumlnum plate havlng a water-receptlve oxlde surface coated wlth a photopolymer. Upon exposure to llght or other radlatlon through the negatlve, the areas of the coatlng that recelved radlatlon (correspondlng to the dark or prlnted areas of the orlglnal) cure to a durable CA 02128911 1998-0~-13 - 3a -oleophilic state. The plate ls then subiected to a developing process that removes the uncured areas of the coatlng (l.e., those which dld not recelve radiatlon, correspondlng to the non-lmage or background areas of the orlginal), exposing the hydrophlllc surface of the alumlnum plate.
A slmllar photographlc process is used to create dry plates, which typically include an oleophobic (e.g., sillcone) surface layer coated onto a photosensitive layer, which ls itself coated onto a substrate of suitable stabillty (e.g., an aluminum sheet). Upon exposure to actinic radlatlon, the photosensltlve layer cures to a state that destroys lts bonding to the surface layer. After exposure, a treatment is applled to deactivate the photoresponse of the photosensltlve layer ln unexposed areas and to further improve anchorage of the surface layer to these areas. Immerslon of the exposed plate in developer results ln dissolution and removal of the surface layer at those portions of the plate surface that have received radiation, thereby exposing the ink-receptive, cured photosensitive layer.
Photographic plate maklng processes tend to be tlme consuming and require facilities and equipment adequate to support the necessary chemistry. To circumvent these shortcomings, practltioners have developed a number of electronic alternatives to plate imaging, some of which can be utilized on-press. With these systems, digitally controlled devices alter the ink-receptivity of blank plates in a pattern representative of the image to be printed. Such imaging devices lnclude sources of electromagnetic-radiation pulses, produced by one or more laser or non-laser sources, that create chemical changes on plate blanks (thereby eliminating the need for a photographic negative); ink-~et equipment that directly deposits ink-repellent or ink-accepting spots on plate blanks; and spark-dlscharge equipment, ln which an electrode in contact with or spaced close to a plate blank produces electrlcal sparks to physlcally alter the topology of the plate blank, thereby producing "dots" which collectively form a desired image (see e.g., U.S. Patent No. 4,911,075, co-owned with the present application.
Because of the ready availability of laser equipment ~.
212~ql 1 and their amenability to digital control, significant effort has been devoted to the development of laser-based imaging systems. Early examples utilized lasers to etch away material from a plate blank to form an intaglio or letterpress pattern.
See,e.g., U.S. Patent Nos. 3,506,779; 4,347,785. This approach was later extended to production of lithographic plates, e.g., by removal of a hydrophilic surface to reveal an oleophilic underlayer. See, e.g., U.S. Patent No. 4,054,094.
The systems generally require high-power lasers, which are expensive and slow.
A second approach to laser imaging involves the use of laser-ablation-transfer materials. See e.g., U.S. Patent Nos. 3,945,318; 3,962,513; 3,964,389; 4,395,946; 5,156,938 and 5,171,650. With these systems, a polymer sheet tranparent to the radiation emitted by the laser is coated with a transferable material. During operation the transfer side of this construction is brought into contact with an acceptor sheet, and the transfer material is selectively irradiated through the transparent layer. Irradiation causes the transfer material to adhere preferentially to the acceptor sheet. The transfer and acceptor materials exhibit different affinities for fountain solution and/or ink, so that removal of the transparent layer together wlth unlrradlated transfer material leaves a suitably imaged, finished plate. Typically, the transfer material ls oleophllic and the acceptor material hydrophilic. Plates produced with transfer-type systems tend to exhiblt short useful llfetlmes due to the llmited amount of ~' ~, . i 2128~1 1 - 5a -material that can effectively be transferred. In addition, because the transfer process involves melting and resolidlflcation of material, lmage quality tends to be vislbly poorer than that obtalnable with other methods.
Flnally, lasers can be used to expose a photosensltlve blank for tradltlonal chemlcal processlng. See e.a., U.S. Patent Nos. 3,506,779; 4,020,762. In an alternatlve to this approach, a laser has been employed to selectlvely remove, ln an lmagewlse pattern, an opaque coating that overlies a photosensitive plate blank. The plate is then exposed to a source of radiation, with the unremoved material acting as a mask that prevents radiation from reaching underlylng portlons of the plate. See e.g., U.S. Patent No.
4,132,168. Elther of these lmaglng techniques requlres the cumbersome chemical processing associated with traditlonal, non-dlgltal plate making.
Corresponding Canadian Patent application Serial No.
Z,100,517 filed on July 14, 1993 and commonly owned, with the present application discloses a variety of plate-blank constructions, enabling production of "wet" plates that utlllze fountaln solution during prlnting of "dry" plates to which ink ls applied directly. In partlcular, the '517 appllcation descrlbes a flrst embodlment that includes a first layer and a CA 02128911 1998-0~-13 substrate underlying the first layer, the substrate being characterized by efficlent absorptlon of lnfrared ("IR") radlatlon, and the first layer and substrate having different affinities for lnk (in a dry-plate construction) or a fluid that repels ink (in a wet-plate constructlon). Laser radiation is absorbed by the substrate, and ablates the substrate surface in contact with the first layer; thls action disrupts the anchorage of the substrate to the overlying first layer, whlch is then easlly removed at the polnts of exposure.
The result of removal ls an lmage spot whose afflnlty for the ink or ink-repellent fluid differs from that of the unexposed flrst layer. The '517 appllcation also discloses a varlation of this embodiment in which the first layer, rather than the substrate, absorbs IR radiation. In thls case the substrate serves a support functlon and provldes contrastlng afflnity characteristlcs.
In a second embodlment dlsclosed ln the '517 application, the flrst, topmost layer ls chosen for lts affinlty for (or repulslon of) ink or an lnk-repellent fluid.
Underlying the flrst layer ls a second layer, whlch absorbs IR
radlation. A strong, stable substrate underlles the second layer, and ls characterlzed by an afflnlty for (or repulslon of) ink or an lnk-repellent fluid opposite to that of the flrst layer. Exposure of the plate to a laser pulse ablates the absorblng second layer, weakenlng the topmost layer as CA 02128911 1998-0~-13 well. As a result of ablation of the second layer, the weakened surface layer ls no longer anchored to an underlylng layer, and ls easlly removed.
Flnally, the '517 appllcation descrlbes varlatlon of the foregolng embodlments by addition, beneath the absorbing layer, of an additional layer that reflects IR radiation.
This additional layer reflects any radiation that penetrates the absorbing layer back through that layer, so that the effectlve flux through the absorblng layer ls slgnlficantly increased.
All of these constructions, while useful and effective generally require removal of the dlsrupted -- but still remaining -- topmost layer (and any debris remaining from destruction of the absorptive second layer) in a post-imaging cleaning step. Depending on the materials chosen for the substrate and topmost layers, imaging exposure can fuse these two layers, rendering the latter especially resistant to removal. Furthermore, in some constructions, debrls from one or more ablated layers can condense or otherwise deposit on the topmost unablated layer (e.g., the substrate), resulting in the need for strenuous cleaning that can prove both tlme-consumlng and cumbersome. Flnally, we have also ln some lnstances observed charrlng of the topmost unablated layer, an effect that can degrade prlnting performance by roughening this layer and thereby lnterferlng wlth lts lnteractlon with CA 02128911 1998-0~-13 - 7a -prlnting fluids (an effect also observed when post-imaging cleaning falls to remove a sufflcient proportion of the accumulated debris) DESCRIPTION OF THE INVENTION
A. Brlef Summary of the Invention The present inventlon enables rapid, efflclent production of lithographlc prlnting plates using laser equlpment, and the approach contemplated herein may be applied to any of a variety of laser sources that emlt in various regions of the electromagnetic spectrum. The problems of debrls buildup and/or charring, common to numerous laser-imaging processes, are ameliorated by introduction of a secondary ablation layer into the plate constructions. As used herein, the term "plate" refers to any type of printing member or surface capable of recording an image defined by regions exhibiting differential affinitles for lnk and/or fountain solution; suitable configurations include the traditional planar or curved lithographic plates that are mounted on the plate cylinder of a prlnting press, but can also include cylinders (e.g., the roll surface of a plate cylinder), an endless belt, or other arrangement.
All constructions of the present invention utillze materials that enhance the ablative efficiency of the laser beam. Substances that do not heat rapldly or absorb 21289~ ~
significant amounts of radiation will not ablate unless they are irradiated for relatively long lntervals and/or receive high-power pulses.
In particular, the printlng media of the present invention are based on a cooperative construction that includes a "secondary" ablation layer. This layer ablates, or decomposes into gases and volatile fragments, in response to heat generated by ablation of one or more overlying layers, If transmltted dlrectly to the plate substrate, the heat might char that layer. The secondary ablation layer preferably does not interact with the laser radiation and, to facilitate reverse-side imaging as described in co-pending Canadian Patent application Serlal No. 2,100,413 filed on July 14, l9g3 and commonly owned with the present application, is desirably transparent (or substantially so) to such radiation.
In a typical construction, a radiation-absorbing layer underlies a surface coating chosen for its interaction with ink and/or fountain solution, The secondary ablation layer is located beneath the absorbing layer, and may be anchored to a substrate having superior mechanical properties.
It may be preferable in some lnstances to introduce an additional layer between the secondary ablation layer and the substrate to enhance adhes~on therebetween, as more fully described below.
Alternatlvely, the basic plate construction can consist of a substrate that supports a radiation-absorptive layer (which performs the functions of the surface and ~7~, .
21289~ ~
absorbing layers in the constructions discussed above), the two layers differing in their affinities for ink and/or fountain solution. In this case, the secondary ablation layer is located between the substrate, and the radiation-absorptive layer.
The secondary ablation layer should ablate "cleanly"--that is, exhibit sufflcient thermal instability as to decompose rapidly and uniformly upon application of heat, evolving primarily gaseous decomposition products. Preferred materials undergo substantially complete thermal decomposition !or pyrolysis) with limited melting or formation of solid decomposition products, and are typically based on chemical structures that readily undergo, upon exposure to sufficient thermal energy, eliminations (e.g. Decarboxylations) and rearrangements producing volatlle products.
The secondary ablation layer is applied at a thickness sufficient to ablate only partially in response to the heat produced by ablation of the one or more overlying layers. Accordingly, the plates of the present invention are properly viewed as cooperative constructions tailored for a particular imaging system, in that the proper thickness of the secondary ablation layer is determined by the degree of absorbance exhibited by the overlying absorbing layer and the ablative responsiveness of the layer to imaging radiation.
For example, ablation of a radiation-absorbing layer can reflect an exothermic process (e.g., exothermic oxidation), resulting in the production of more energy than is delivered ~ 1 2;~
- 9a -by the laser.
Our preferred material are based on polymethylmethacrylate (PMMA), which may be doped wlth radlatlon-absorblng chromophores as descrlbed below, although numerous other polymerlc materlals havlng the foregolng characterlstlcs provlde acceptable performance.
Because they ablate cleanly, secondary ablatlon layers avoid the uneven topologies assoclated with charring of the plate substrate; indeed, the secondary ablation layer performs a protective function that shields the substrate from the thermal effects of lmaglng radlatlon; this function proves partlcularly useful ln conjunction wlth metal substrate.
Furthermore, the rapid decomposltlon of the secondary ablatlon layer evolves a gaseous plume or cloud that discourages accumulation of partlculate remnants of overlylng layers. One can even ellminate the need for post-lmaglng cleanlng of the flnlshed plate by uslng secondary ablation layers of sufficient thlckness (and/or relatlve unresponsiveness to thermal stress) to permlt the use of hlgh-power imaglng lasers whose output is strong enough to fully remove all overlying layers.
In summary, the present lnvention provides, a lithographlc prlntlng member dlrectly lmageable by laser discharge, the member comprising: a. a topmost first layer;
and b. a second layer underlylng the flrst layer, the second layer being characterised by ablative absorption of laser radlatlon; c. a third layer underlying the second layer, the ~ ,' 2l 28q~ ~
- 9b -third layer: i. being substantially transparent to the laser radiation; ii. being ablated only partially in response to ablation of the second layer; and iii. differing from the first layer in its affinity for at least one printlng liquid selected from the group consisting of ink and a fluid that repels ink.
B. Brief Description of the Drawings The foregoing discussion will be understood more readily from the following detailed description of the invention, when taken in conjunction with the accompanying drawings, in which:
s ' CA 02128911 1998-0~-13 FIG. 1 ls an enlarged sectional view of a llthographlc plate havlng a top layer, a radlatlon-absorptive layer, and a secondary ablation layer mounted to a substrate by means of an adheslon-promoting layer;
FIG. 2 ls an enlarged sectlonal vlew of a llthographlc plate having a top layer, a radiation-absorptive composite lncluding TiO and aluminlum layers, and a secondary ablatlon layer mounted to a substrate by means of an adhesion-promoting layer;
FIG. 3 is an enlarged sectional view of a lithographic plate having a top layer that absorbs laser radiation and a secondary ablation layer mounted to a substrate by means of an adheslon-promoting layer; and FIG. 4 is an enlarged sectional vlew of a lithographic plate having a top layer and a secondary ablation layer.
C. Detailed Description of the Preferred Embodiments 1. Imaqinq APparatus Imaging apparatus suitable for use in con~unction wlth the present prlntlng members lncludes at least one laser devlce that emlts ln the reglon of maximum plate responslveness, l.e., whose l~mhAal,,ax closely approxlmates the wavelength reglon where the plate absorbs most strongly.
Speclflcatlons for lasers that emlt ln the near-IR reglon are fully descrlbed ln the '431 appllcation; lasers emitting in CA 02128911 1998-0~-13 other reglons of the electromagnetlc spectrum are well-known to those skllled in the art.
Sultable lmaglng configuratlons are also set forth in detall ln the '517 appllcation. ~riefly, laser output can be provided directly to the plate surface via lenses or other beam-guiding components, or transmitted to the surface of a blank printlng plate from a remotely sited laser using a fiber-optlc cable. A controller and associated posltlonlng hardware malntalns the beam output at a preclse orlentatlon with respect to the plate surface, scans the output over the surface, and activates the laser at posltions ad~acent selected points or areas of the plate. The controller responds to incoming image signals corresponding to the original document or picture being copied onto the plate to produce a precise negatlve or posltive image of that orlglnal.
The lmage slgnals are stored as a bitmap data file on a computer. Such files may be generated by a raster image processor (RIP) or other suitable means. For example, a RIP
can accept input data in page-description language, which defines all of the features required to be transferred onto the printing plate, or as a combination of page-descriptlon language and one or more image data files. The bitmaps are constructed to define the hue of the color as well as screen frequencies and angles.
The imaging apparatus can operate on its own, functioning solely as a platemaker, or can be incorporated directly into a llthographic printing press. In the latter CA 02128911 1998-0~-13 case, prlnting may commence immedlately after application of the lmage to a blank plate, thereby reducing press set-up tlme conslderably. The imaging apparatus can be configured as a flatbed recorder or as a drum recorder, wlth the llthographlc plate blank mounted to the interior or exterior cylindrical surface of the drum. Obviously, the exterior drum design is more appropriate to use in situ, on a lithographic press, in which case the print cylinder itself constitutes the drum component of the recorder or plotter.
In the drum configuration, the requisite relative motion between the laser beam and the plate is achieved by rotating the drum (and the plate mounted thereon) about its axis and moving the beam parallel to the rotation axis, thereby scanning the plate circumferentially so the image 'grows" in the axial directlon. Alternatively, the beam can move parallel to the drum axis and, after each pass across the plate, lncrement angularly so that the image on the plate "grows" clrcumferentially. In both cases, after a complete scan by the beam, an lmage correspondlng (posltively or negatively) to the beam, an image corresponding (positively or negatively) to the original document or picture will have been applied to the surface of the plate.
In the flatbed configuration, the beam is drawn across either axls of the plate, and is indexed along the other axls after each pass. Of course, the requlslte relatlve CA 02128911 1998-0~-13 - 12a -motlon between the beam and the plate may be produced by movement of the plate rather than (or in addltion to) movement of the beam.
Regardless of the manner ln which the beam ls scanned, lt ls generally preferable (for on-press appllcatlons) to employ a plurallty of lasers and gulde their outputs to a slngle wrltlng array. The wrltlng array ls then lndexed, after completlon of each pass across or along the plate, a dlstance determlned by the number of beams emanatlng from the array, and by the deslred resolution (l.e, the number of lmage polnts per unlt length). Off-press appllcatlons, whlch can be deslgned to accommodate very rapld plate movement (e.g., through use of hlgh-speed motors) and thereby utlllze hlgh laser pulse rates, can frequently utlllze a slngle laser as an lmaglng source.
2. LlthoqraPhlc Prlntlnq Plates Refer flrst to FIG. 1, whlch lllustrates a representatlve embodlment of a llthographlc plate ln accordance wlth the present lnvention. The plate lllustrated ln FIG. l lncludes a surface layer 100, a layer 102 capable of absorblng lmaglng radlatlon, a secondary ablatlon layer 104, and a substrate 106. Secondary ablatlon layer 104 may be adhered to substrate 106 by means of an adheslon-promotlng layer 108. These layers wlll now be descrlbed ln detall.
a. Surface layer 100 Layers 100 and 104 exhlblt opposlte afflnltles for CA 02l289ll l998-05-l3 - 12b -ink or an ink-repellent fluid. In one version of this plate, surface layer 100 ls a slllcone polymer that repels lnk, whlle secondary ablatlon layer 104 iS oleophillc polyester. In a 2t2891 ~
second wet plate version, surface layer 100 is a hydrophilic material, while secondary ablation layer 104 is both oleophilic and hydrophobic.
Examples of suitable materials for surface layer 100 are set forth below. In general, silicone materials of the type described in U.S. Patent No. 5,212,048 provide advantageous performance for dry plates; materials based on polyvinyl alcohol (e.g., the Airvol 125 material supplied by Air products, Allentown, PA and as described in the '431 application~ provide a satisfactory surface material for wet plates.
As a specific example, the following silicone coatlng provides advantageous performance in a positive-working dry plate construction Components Parts PS-445 22.56 PC-072 .70 VM&P Naphtha 76.70 Syl-Off 7367 .04 (these components are descrlbed ln greater detail, and thelr sources indicated, in U.S. Patent No 5,188,032 and U.S. Patent No, 5,212,048 and U.S. Patent No. 5,310,869; these documents describe numerous other silicone formulations useful as the material of an oleophobic layer 100.) 2 l ~89 1 1 b. Radiation-Absorptive LaYer 102 Layer 102 absorbs energy from incident imaging radiation and, in response fully ablates. It can consist of a polymeric system that intrinsically absorbs in the laser's region of maximum power output, or a polymeric coating into which radiation-absorbing components have been dispersed or dissolved.
For example, we have found that many of the surface layers described in U.S. Patent Nos. 5,109,771, 5,165,345 and 5,249,525 (all commonly owned with the present application which contain filler particles that assist the spark-imaging process, can also serve as an IR-absorbing surface layer. In fact, the only filler pigments totally unsuitable as IR
absorbers are those whose surface morphologles result in highly reflective surfaces. Thus, white particles such as TiO2 and ZnO, and off-white compounds such as SnO2. owe their light shadings to efficient reflection of incident light, and prove unsuitable for use.
Among the particles suitable as IR absorbers, direct correlation does not exist between performance in the present environment and the degree of usefulness as a spark-discharge plate filler. Indeed, a number of compounds of limited advantage to spark-dlscharge lmaglng absorb IR radlat~on quite well. Semiconductive compounds appear to exhibit, as a class, the best performance characteristics for the present invention. Without being bound to any particular theory or mechanism, we believe that electrons energetically located in B
- 14a -and ad~acent to conducting bands are readily promoted lnto and within the band by absorblng IR radlation, a mechanism in agreement with the known tendency of semiconductors to exhlblt lncreased conductlvlty upon heatlng due to thermal promotion of electrons lnto conductlng bands.
Currently, lt appears that metal borides, carbides, nltrldes, carbonltrldes, bronze-structured oxldes, and oxldes structurally related to the bronze famlly but lacking the A
component ~e.g., W02 g)perform best.
Black plgment, such as carbon black, absorb adequately over substantlally all of the vlslble region, and can be utillzed ln coniunctlon wlth vlslble-spectrum lasers.
~ ,?
CA 02128911 1998-0~-13 As an example, a nitrocellulose layer contalning carbon black as an absorblng plgment ls produced from the following base composltlon:
comPonent Parts Nltrocellulose 14 Cymel 303 2 2-Butanone (methyl ethyl ketone)236 The nltrocellulose utlllzed ls the 30% lsopropanol wet 5-6 Sec RS Nltrocellulose supplled by Aqualon Co., Wllmlngton, DE.
Cymel 303 ls hexamethoxymethylmelamlne, supplled by Amerlcan Cyanamld Corp.
Equal parts of carbon black (speclflcally, the Vulcan XC-72 conductlve carbon black plgment supplled by the Speclal ~lacks Dlvlslon of Cabot Corp., Waltham, MA) and NaCure 2530, an amlne-blocked p-toluenesulfonlc acld solutlon ln an lsopropanol/methanol blend whlch ls supplled by Klng Industrles, Norwalk, CT, are comblned wlth the base nltrocellulose composltlon ln proportlons of 4:4:252. The resultlng composltlon may be applled to a polyester substrate uslng a wlre-wound rod. In partlcular, after drylng to remove the volatlle solvent(s) and curlng (1 mln at 300 ~F ln a lab convectlon oven performed both functlons), the coatlng ls preferably deposlted at 1 g/m2.
Alternatlvely, organlc chromophores can be used in lleu of plgments. Such materlals are deslrably soluble or easily dlspersed in the materlal whlch, when cured, functlons CA 02128911 1998-0~-13 - 15a -as layer 100. IR-absorptlve dyes include a variety of phthalocyanine and naphthalocyanlne compounds, while chromophores that absorb ln the ultravlolet region include benzoin, pyrene, benzophenone, acridine, 4-aminobenzoylhydrazide, 2-(2'-hydroxy-3',5'-diisopentylphenyl) benzotriazole, rhodamine 6G, tetraphenylporphyrin hematoporphyrin, ethylcarbazole, and poly(N-vinylcarbazole).
Generally, suitable chromophores can 2~,'c~o1 1 be found to accommodate imaglng using vlrtually any practicable type of laser. See, e.g., U.S. Patent Nos.
5,156,938 and 5,171,650. The chromophores concentrate laser energy wlthln the absorblng layer and cause its destructlon, dlsruptlng and posslbly consuming the surface layer as well, and intentlonally damaglng the secondary ablatlon layer.
Absorblng layer 102 can also be a composite of more than one layer. For example, FIG. 2 illustrates an alternatlve embodlment whereln absorbing layer 102 has been replaced with a bilayer construction conslsting of a thin layer 112 of TiO, preferably having a thickness of 25-700 A, which resides atop a thln layer 114 of alumlnum preferably havlng a thickness of approximately 500 ~. These layers are anchored to a secondary ablatlon layer 104. Thls embodlment can be straightforwardly manufactured by coatlng the secondary ablation layer onto a substrate, electron-beam evaporating an aluminum layer thereon, electron-beam evaporating the TiO
layer onto the aluminum layer, and coating the surface layer onto the applied TiO layer. It is also possible to substitute, other metals such as chromlum, nlckel, zinc, copper, or titanium for aluminum, although aluminum is preferred for ease of ablatlon and favourable envlronmental and toxlcity characteristics.
Conversely, the functlon of absorblng layer 102 can be merged wlth that of surface layer 100 as shown in FIG.3.
The illustrated embodiment includes a surface layer 115 containing a chromophore or a disperson of pigments that ~ :? ~
- 16a -absorb radlation in the spectral reglon of the lmaglng laser.
Pigments that absorb in the near-IR region are discussed above, while IR-absorbing slllcone compositions sultable for use in the present context as surface layer 100 for dry-plate constructions are descrlbed ln U.S. Pat-ent No. 5,210,869.
c. Secondary Ablation Layer 104 As stated above, the secondary ablatlon layer undergoes rapld and uniform thermal degradation. Polymerlc materlals ~-~ 64421-562 , ,, CA 02128911 1998-0~-13 that exhiblt llmlted thermal stablllty, partlcularly those transparent to lmaglng radlatlon (or at least able to transmlt such radlatlon with mlnlmal scattering, refractlon and attenuatlon), are preferred. Useful polymers lnclude (but are not llmlted to) materlals based on PMMA, polycarbonates, polyesters, polyurethanes, polystyrenes, styrene/acrylonltrlle polymers, celluloslc ethers and esters, polyacetals, and comblnatlons (e.g., copolymers or terpolymers) of the foregoing.
The secondary ablatlon layer is applied to a thickness adequate to avold complete ablatlon ln response to the thermal flux orlglnatlng ln the ablatlon of absorblng layer 102. Useful thlcknesses range from a mlnlmum of 1 mlcron, wlth upper llmlts dlctated prlmarlly by economlcs (e.g., 30 mlcrons or more); a typlcal worklng range ls 4-10 mlcrons. The followlng formulatlons can be utllized on polyester fllm or alumlnum substrates:
Example 3 4 5 6 7 Component Parts 2-Butanone 65 65 70 81.5 Normal Propyl Acetate 20 20 Acrylold B-44 10 10 Doresco AC2-79A - - 25 Carglll 72-7289 - - - 13.5 Cymel 303 4 4 4 4 Cycat 4040 10% H3P04 Soln. - 2 Deft 03-X-85 A - - - - 50 Deft 03-X-85 B - - - - 50 CA 02l289ll l998-0~-l3 Acrylold B-44 ls an acryllc resln supplled by Rohm & Haas, Phlladelphla, PA. Doresco AC2-79A ls a 40%-solids acryllc resin solution in toluene, and is supplied by Dock Reslns Corp., Llnden, NJ. Carglll 72-7289 ls a 75%-solids polyester resln solution ln propylene glycol monopropyl ether supplled by Carglll Inc., Carpentersvllle, IL. Cycat 4040 is a 40%-sollds paratoluene sulfonlc acld solutlon ln lsopropanol supplled by Amerlcan cyanamld Co., Wayne, NJ. Deft 03-X-35 A
ls a 65% polyester resin solutlon supplled by Deft, Inc., Irvlne, CA, and the 03-X-35 B product ls a 50% allphatlc lsocyanate resln solutlon. The solvent of the phosphorlc acld solutlon ls 2-butanone.
The composltion of Example 3 ls well-sulted to use on polyester substrates. Example 4 lncludes a phosphorlc acld solutlon, whlch promotes adheslon of the secondary ablatlon layer to an alumlnum substrate. The coatlngs of Examples 5 and 6 can be used elther on polyester or metal substrates, whlle that of Example 7 ls best sulted to alumlnum substrates.
d. Substrate 106 and Adheslon-Promotlng Layer 108 Substrate 106 ls preferably mechanlcally strong, durable and flexlble, and may be a polymer fllm, or a paper or metal sheet. Polyester fllms (ln a preferred embodlment, the MYLAR product sold by E.I. duPont de Nemours Co., Wllmlngton, DE, or, alternatlvely, the MELINEX product sold by ICI Fllms, Wllmlngton, DE) furnlsh useful examples. A preferred polyester-fllm thlckness ls 0.007 lnch, but thlnner and thlcker verslons can be used effectively. Alumlnum ls a CA 02l289ll l998-0~-l3 preferred metal substrate. Paper substrates are typlcally "saturated" wlth polymerlcs to lmpart water resistance, dlmenslonal stablllty and strength.
For addltlonal strength, lt ls posslble to utlllze the approach descrlbed ln the '032 patent. As dlscussed ln that patent, a metal sheet can be lamlnated elther to the substrate materlals descrlbed above, or lnstead can be utlllzed dlrectly as a substrate and lamlnated to secondary ablatlon layer 104. Sultable metals, lamlnatlng procedures and preferred dlmenslons and operatlng condltlons are all descrlbed ln the '032 patent, and can be stralghtforwardly applled to the present context wlthout undue experlmentatlon.
For example, ln the case of alumlnum substrates, sllanes or lndustrlal protelns (such as the photographlc gelatlns used ln many conventlonal llthographlc dry plates) serve well to promote adheslon to polymerlc secondary ablatlon layers.
Adheslon-promotlng layers can also be used ln connectlon wlth polyester or other fllm substrates to enhance bondlng to secondary ablatlon layer 104. For example, the CRONAR polyester fllms marketed by duPont employ polyvlnylldene chlorlde layers overcoated wlth a gelatln that enhances adheslon.
Flnally, lf secondary ablatlon layer 104 exhlblts adequate mechanlcal propertles, lt can be employed ln sufflclent thlckness to ltself serve as a substrate, resultlng ln the constructlon shown ln FIG. 4.
CA 02128911 1998-0~-13 The secondary ablation layers of Examples 3-7 are each coated onto a polyester or metal substrate. The absorblng-layer formulation of Example 2 ls then coated over the secondary-ablatlon layers. Speclflcally, followlng additlon of the carbon black and dlsperslon thereof ln the base composltlon, the blocked PTSA catalyst ls added, and the resultlng mlxtures applled to the secondary ablatlon layer uslng a wlre-wound rod. After drylng to remove the volatlle solvent(s) and curlng (1 mln at 300 ~F ln a lab convection oven performed both functlons), the coatlngs are deposlted at 1 g/m2. To thls bllayer constructlon is applled the slllcone coatlng of Example 1 uslng a wlre-wound rod. The coatlng ls drled and cured to produce a unlform deposltlon of 2 g/m2.
Exposure of the foregolng constructlons to the output of an lmaglng laser at surface layer 100 weakens or ablates that layer, ablates absorblng layer 102, and partlally ablates layer 104 ln the reglon of exposure. Alternatlvely, the constructlons can be imaged from the reverse slde, l.e., through substrate 106. So long as all layers below absorblng layer 102 are transparent to laser radlatlon, the beam will contlnue to perform the functlons of ablatlng absorblng layer 102 and weakenlng or ablatlng surface layer 100, whlle destructlon of layer 102 wlll produce the approprlate controlled damage to layer 104.
Although thls "reverse lmaglng" approach does not requlre slgnlficant additlonal laser power (energy losses CA 02128911 1998-0~-13 - 20a -through substantially transparent layers are mlnimal), it does affect the manner ln whlch the laser beam ls focused for imaging. Ordlnarlly, wlth surface layer 100 ad~acent the laser output, lts beam ls focused onto the plane of surface layer 100. In the reverse-imaglng case, by contrast, the beam must pro~ect through all layers underlylng absorblng layer 102. Therefore, not only must the beam be focused on the surface of an lnner layer (l.e., absorblng layer 102~ rather than the outer surface of the constructlon, but that focus must also accommodate refractlon of the beam caused by its transmlssion through the intervening layers.
Because the plate layer that faces the laser output remains lntact durlng reverse imaging, thls approach prevents debrls generated by ablation from accumulatlng ln the reglon between the plate and the laser output. Another advantage of reverse lmaglng ls ellmlnatlon of the requlrement that surface layer 100 efflclently transmlt laser radlatlon. Surface layer 100 can, ln fact, be completely opaque to such radlatlon so long as lt remalns vulnerable to degradatlon and subsequent removal.
It will therefore be seen that we have developed a highly versatile imaglng system and a varlety of plates for use therewlth. The terms and expresslons employed hereln are used as terms of descrlptlon and not of limitatlon, and there ls no lntentlon, in the use of such terms and expresslons, of excluding any equivalents of the features shown and descrlbed ~ CA 02128911 1998-05-13 - 20b -or portions thereof, but it ls recognized that various modificatlons are possible withln the scope of the inventlon clalmed.
a. Surface layer 100 Layers 100 and 104 exhlblt opposlte afflnltles for CA 02l289ll l998-05-l3 - 12b -ink or an ink-repellent fluid. In one version of this plate, surface layer 100 ls a slllcone polymer that repels lnk, whlle secondary ablatlon layer 104 iS oleophillc polyester. In a 2t2891 ~
second wet plate version, surface layer 100 is a hydrophilic material, while secondary ablation layer 104 is both oleophilic and hydrophobic.
Examples of suitable materials for surface layer 100 are set forth below. In general, silicone materials of the type described in U.S. Patent No. 5,212,048 provide advantageous performance for dry plates; materials based on polyvinyl alcohol (e.g., the Airvol 125 material supplied by Air products, Allentown, PA and as described in the '431 application~ provide a satisfactory surface material for wet plates.
As a specific example, the following silicone coatlng provides advantageous performance in a positive-working dry plate construction Components Parts PS-445 22.56 PC-072 .70 VM&P Naphtha 76.70 Syl-Off 7367 .04 (these components are descrlbed ln greater detail, and thelr sources indicated, in U.S. Patent No 5,188,032 and U.S. Patent No, 5,212,048 and U.S. Patent No. 5,310,869; these documents describe numerous other silicone formulations useful as the material of an oleophobic layer 100.) 2 l ~89 1 1 b. Radiation-Absorptive LaYer 102 Layer 102 absorbs energy from incident imaging radiation and, in response fully ablates. It can consist of a polymeric system that intrinsically absorbs in the laser's region of maximum power output, or a polymeric coating into which radiation-absorbing components have been dispersed or dissolved.
For example, we have found that many of the surface layers described in U.S. Patent Nos. 5,109,771, 5,165,345 and 5,249,525 (all commonly owned with the present application which contain filler particles that assist the spark-imaging process, can also serve as an IR-absorbing surface layer. In fact, the only filler pigments totally unsuitable as IR
absorbers are those whose surface morphologles result in highly reflective surfaces. Thus, white particles such as TiO2 and ZnO, and off-white compounds such as SnO2. owe their light shadings to efficient reflection of incident light, and prove unsuitable for use.
Among the particles suitable as IR absorbers, direct correlation does not exist between performance in the present environment and the degree of usefulness as a spark-discharge plate filler. Indeed, a number of compounds of limited advantage to spark-dlscharge lmaglng absorb IR radlat~on quite well. Semiconductive compounds appear to exhibit, as a class, the best performance characteristics for the present invention. Without being bound to any particular theory or mechanism, we believe that electrons energetically located in B
- 14a -and ad~acent to conducting bands are readily promoted lnto and within the band by absorblng IR radlation, a mechanism in agreement with the known tendency of semiconductors to exhlblt lncreased conductlvlty upon heatlng due to thermal promotion of electrons lnto conductlng bands.
Currently, lt appears that metal borides, carbides, nltrldes, carbonltrldes, bronze-structured oxldes, and oxldes structurally related to the bronze famlly but lacking the A
component ~e.g., W02 g)perform best.
Black plgment, such as carbon black, absorb adequately over substantlally all of the vlslble region, and can be utillzed ln coniunctlon wlth vlslble-spectrum lasers.
~ ,?
CA 02128911 1998-0~-13 As an example, a nitrocellulose layer contalning carbon black as an absorblng plgment ls produced from the following base composltlon:
comPonent Parts Nltrocellulose 14 Cymel 303 2 2-Butanone (methyl ethyl ketone)236 The nltrocellulose utlllzed ls the 30% lsopropanol wet 5-6 Sec RS Nltrocellulose supplled by Aqualon Co., Wllmlngton, DE.
Cymel 303 ls hexamethoxymethylmelamlne, supplled by Amerlcan Cyanamld Corp.
Equal parts of carbon black (speclflcally, the Vulcan XC-72 conductlve carbon black plgment supplled by the Speclal ~lacks Dlvlslon of Cabot Corp., Waltham, MA) and NaCure 2530, an amlne-blocked p-toluenesulfonlc acld solutlon ln an lsopropanol/methanol blend whlch ls supplled by Klng Industrles, Norwalk, CT, are comblned wlth the base nltrocellulose composltlon ln proportlons of 4:4:252. The resultlng composltlon may be applled to a polyester substrate uslng a wlre-wound rod. In partlcular, after drylng to remove the volatlle solvent(s) and curlng (1 mln at 300 ~F ln a lab convectlon oven performed both functlons), the coatlng ls preferably deposlted at 1 g/m2.
Alternatlvely, organlc chromophores can be used in lleu of plgments. Such materlals are deslrably soluble or easily dlspersed in the materlal whlch, when cured, functlons CA 02128911 1998-0~-13 - 15a -as layer 100. IR-absorptlve dyes include a variety of phthalocyanine and naphthalocyanlne compounds, while chromophores that absorb ln the ultravlolet region include benzoin, pyrene, benzophenone, acridine, 4-aminobenzoylhydrazide, 2-(2'-hydroxy-3',5'-diisopentylphenyl) benzotriazole, rhodamine 6G, tetraphenylporphyrin hematoporphyrin, ethylcarbazole, and poly(N-vinylcarbazole).
Generally, suitable chromophores can 2~,'c~o1 1 be found to accommodate imaglng using vlrtually any practicable type of laser. See, e.g., U.S. Patent Nos.
5,156,938 and 5,171,650. The chromophores concentrate laser energy wlthln the absorblng layer and cause its destructlon, dlsruptlng and posslbly consuming the surface layer as well, and intentlonally damaglng the secondary ablatlon layer.
Absorblng layer 102 can also be a composite of more than one layer. For example, FIG. 2 illustrates an alternatlve embodlment whereln absorbing layer 102 has been replaced with a bilayer construction conslsting of a thin layer 112 of TiO, preferably having a thickness of 25-700 A, which resides atop a thln layer 114 of alumlnum preferably havlng a thickness of approximately 500 ~. These layers are anchored to a secondary ablatlon layer 104. Thls embodlment can be straightforwardly manufactured by coatlng the secondary ablation layer onto a substrate, electron-beam evaporating an aluminum layer thereon, electron-beam evaporating the TiO
layer onto the aluminum layer, and coating the surface layer onto the applied TiO layer. It is also possible to substitute, other metals such as chromlum, nlckel, zinc, copper, or titanium for aluminum, although aluminum is preferred for ease of ablatlon and favourable envlronmental and toxlcity characteristics.
Conversely, the functlon of absorblng layer 102 can be merged wlth that of surface layer 100 as shown in FIG.3.
The illustrated embodiment includes a surface layer 115 containing a chromophore or a disperson of pigments that ~ :? ~
- 16a -absorb radlation in the spectral reglon of the lmaglng laser.
Pigments that absorb in the near-IR region are discussed above, while IR-absorbing slllcone compositions sultable for use in the present context as surface layer 100 for dry-plate constructions are descrlbed ln U.S. Pat-ent No. 5,210,869.
c. Secondary Ablation Layer 104 As stated above, the secondary ablatlon layer undergoes rapld and uniform thermal degradation. Polymerlc materlals ~-~ 64421-562 , ,, CA 02128911 1998-0~-13 that exhiblt llmlted thermal stablllty, partlcularly those transparent to lmaglng radlatlon (or at least able to transmlt such radlatlon with mlnlmal scattering, refractlon and attenuatlon), are preferred. Useful polymers lnclude (but are not llmlted to) materlals based on PMMA, polycarbonates, polyesters, polyurethanes, polystyrenes, styrene/acrylonltrlle polymers, celluloslc ethers and esters, polyacetals, and comblnatlons (e.g., copolymers or terpolymers) of the foregoing.
The secondary ablatlon layer is applied to a thickness adequate to avold complete ablatlon ln response to the thermal flux orlglnatlng ln the ablatlon of absorblng layer 102. Useful thlcknesses range from a mlnlmum of 1 mlcron, wlth upper llmlts dlctated prlmarlly by economlcs (e.g., 30 mlcrons or more); a typlcal worklng range ls 4-10 mlcrons. The followlng formulatlons can be utllized on polyester fllm or alumlnum substrates:
Example 3 4 5 6 7 Component Parts 2-Butanone 65 65 70 81.5 Normal Propyl Acetate 20 20 Acrylold B-44 10 10 Doresco AC2-79A - - 25 Carglll 72-7289 - - - 13.5 Cymel 303 4 4 4 4 Cycat 4040 10% H3P04 Soln. - 2 Deft 03-X-85 A - - - - 50 Deft 03-X-85 B - - - - 50 CA 02l289ll l998-0~-l3 Acrylold B-44 ls an acryllc resln supplled by Rohm & Haas, Phlladelphla, PA. Doresco AC2-79A ls a 40%-solids acryllc resin solution in toluene, and is supplied by Dock Reslns Corp., Llnden, NJ. Carglll 72-7289 ls a 75%-solids polyester resln solution ln propylene glycol monopropyl ether supplled by Carglll Inc., Carpentersvllle, IL. Cycat 4040 is a 40%-sollds paratoluene sulfonlc acld solutlon ln lsopropanol supplled by Amerlcan cyanamld Co., Wayne, NJ. Deft 03-X-35 A
ls a 65% polyester resin solutlon supplled by Deft, Inc., Irvlne, CA, and the 03-X-35 B product ls a 50% allphatlc lsocyanate resln solutlon. The solvent of the phosphorlc acld solutlon ls 2-butanone.
The composltion of Example 3 ls well-sulted to use on polyester substrates. Example 4 lncludes a phosphorlc acld solutlon, whlch promotes adheslon of the secondary ablatlon layer to an alumlnum substrate. The coatlngs of Examples 5 and 6 can be used elther on polyester or metal substrates, whlle that of Example 7 ls best sulted to alumlnum substrates.
d. Substrate 106 and Adheslon-Promotlng Layer 108 Substrate 106 ls preferably mechanlcally strong, durable and flexlble, and may be a polymer fllm, or a paper or metal sheet. Polyester fllms (ln a preferred embodlment, the MYLAR product sold by E.I. duPont de Nemours Co., Wllmlngton, DE, or, alternatlvely, the MELINEX product sold by ICI Fllms, Wllmlngton, DE) furnlsh useful examples. A preferred polyester-fllm thlckness ls 0.007 lnch, but thlnner and thlcker verslons can be used effectively. Alumlnum ls a CA 02l289ll l998-0~-l3 preferred metal substrate. Paper substrates are typlcally "saturated" wlth polymerlcs to lmpart water resistance, dlmenslonal stablllty and strength.
For addltlonal strength, lt ls posslble to utlllze the approach descrlbed ln the '032 patent. As dlscussed ln that patent, a metal sheet can be lamlnated elther to the substrate materlals descrlbed above, or lnstead can be utlllzed dlrectly as a substrate and lamlnated to secondary ablatlon layer 104. Sultable metals, lamlnatlng procedures and preferred dlmenslons and operatlng condltlons are all descrlbed ln the '032 patent, and can be stralghtforwardly applled to the present context wlthout undue experlmentatlon.
For example, ln the case of alumlnum substrates, sllanes or lndustrlal protelns (such as the photographlc gelatlns used ln many conventlonal llthographlc dry plates) serve well to promote adheslon to polymerlc secondary ablatlon layers.
Adheslon-promotlng layers can also be used ln connectlon wlth polyester or other fllm substrates to enhance bondlng to secondary ablatlon layer 104. For example, the CRONAR polyester fllms marketed by duPont employ polyvlnylldene chlorlde layers overcoated wlth a gelatln that enhances adheslon.
Flnally, lf secondary ablatlon layer 104 exhlblts adequate mechanlcal propertles, lt can be employed ln sufflclent thlckness to ltself serve as a substrate, resultlng ln the constructlon shown ln FIG. 4.
CA 02128911 1998-0~-13 The secondary ablation layers of Examples 3-7 are each coated onto a polyester or metal substrate. The absorblng-layer formulation of Example 2 ls then coated over the secondary-ablatlon layers. Speclflcally, followlng additlon of the carbon black and dlsperslon thereof ln the base composltlon, the blocked PTSA catalyst ls added, and the resultlng mlxtures applled to the secondary ablatlon layer uslng a wlre-wound rod. After drylng to remove the volatlle solvent(s) and curlng (1 mln at 300 ~F ln a lab convection oven performed both functlons), the coatlngs are deposlted at 1 g/m2. To thls bllayer constructlon is applled the slllcone coatlng of Example 1 uslng a wlre-wound rod. The coatlng ls drled and cured to produce a unlform deposltlon of 2 g/m2.
Exposure of the foregolng constructlons to the output of an lmaglng laser at surface layer 100 weakens or ablates that layer, ablates absorblng layer 102, and partlally ablates layer 104 ln the reglon of exposure. Alternatlvely, the constructlons can be imaged from the reverse slde, l.e., through substrate 106. So long as all layers below absorblng layer 102 are transparent to laser radlatlon, the beam will contlnue to perform the functlons of ablatlng absorblng layer 102 and weakenlng or ablatlng surface layer 100, whlle destructlon of layer 102 wlll produce the approprlate controlled damage to layer 104.
Although thls "reverse lmaglng" approach does not requlre slgnlficant additlonal laser power (energy losses CA 02128911 1998-0~-13 - 20a -through substantially transparent layers are mlnimal), it does affect the manner ln whlch the laser beam ls focused for imaging. Ordlnarlly, wlth surface layer 100 ad~acent the laser output, lts beam ls focused onto the plane of surface layer 100. In the reverse-imaglng case, by contrast, the beam must pro~ect through all layers underlylng absorblng layer 102. Therefore, not only must the beam be focused on the surface of an lnner layer (l.e., absorblng layer 102~ rather than the outer surface of the constructlon, but that focus must also accommodate refractlon of the beam caused by its transmlssion through the intervening layers.
Because the plate layer that faces the laser output remains lntact durlng reverse imaging, thls approach prevents debrls generated by ablation from accumulatlng ln the reglon between the plate and the laser output. Another advantage of reverse lmaglng ls ellmlnatlon of the requlrement that surface layer 100 efflclently transmlt laser radlatlon. Surface layer 100 can, ln fact, be completely opaque to such radlatlon so long as lt remalns vulnerable to degradatlon and subsequent removal.
It will therefore be seen that we have developed a highly versatile imaglng system and a varlety of plates for use therewlth. The terms and expresslons employed hereln are used as terms of descrlptlon and not of limitatlon, and there ls no lntentlon, in the use of such terms and expresslons, of excluding any equivalents of the features shown and descrlbed ~ CA 02128911 1998-05-13 - 20b -or portions thereof, but it ls recognized that various modificatlons are possible withln the scope of the inventlon clalmed.
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A lithographic printing member directly imageable by laser discharge, the member comprising:
a. a topmost first layer; and b. a second layer underlying the first layer, the second layer being characterized by ablative absorption of laser radiation;
c. a third layer underlying the second layer, the third layer:
i. being substantially transparent to the laser radiation;
ii. being ablated only partially in response to ablation of the second layer; and iii. differing from the first layer in its affinity for at least one printing liquid selected from the group consisting of ink and a fluid that repels ink.
a. a topmost first layer; and b. a second layer underlying the first layer, the second layer being characterized by ablative absorption of laser radiation;
c. a third layer underlying the second layer, the third layer:
i. being substantially transparent to the laser radiation;
ii. being ablated only partially in response to ablation of the second layer; and iii. differing from the first layer in its affinity for at least one printing liquid selected from the group consisting of ink and a fluid that repels ink.
2. The member of claim 1 further comprising a mechanically strong, durable and flexible substrate underlying the third layer.
3. The member of claim 2 further comprising and adhesion-promoting layer located between the substrate and the third layer.
4. The member of claim 1 wherein the first layer is oleophobic.
5. The member of claim 4 wherein the first layer is a coating comprising silicone.
6. The member of claim 5 wherein the first layer includes a dispersion of particles that absorb laser radiation.
7. The member of claim 5 wherein the first layer includes a dye that absorbs laser radiation.
8. The member of claim 1 wherein the first layer is wettable by fountain solution.
g. The member of claim 8 wherein the first layer is a polyvinyl alcohol chemical species.
10. The member of claim 2 wherein the substrate is polyester.
11. The member of claim 2 wherein the substrate is metal.
12. The member of claim 11 wherein the metal is aluminum.
13. The member of claim 2 wherein the third layer is selected from the group consisting of polymethylmethacrylate, polycarbonates, polyesters, polyurethanes, polystyrenes, styrene/acrylonitrile polymer, cellulosic ethers and esters, polyacetals, and combinations thereof.
14. The member of claim 11 wherein the third layer is a polymethylmethacrylate chemical species.
15. The member of claim 1 wherein the third layer is at least 3 but no more than than 6 microns thick.
16. The member of claim 1 wherein the second layer is a composite including TiO and aluminum layers.
17. The member of claim 3 wherein the substrate is polyester, and the substrate and the adhesion-promoting layer together represent a print- or coatability-treated polyester film.
- 22a -
- 22a -
18. The member of claim 3 wherein the substrate is metal and the adhesion-promoting layer is a silane or an industrial protein.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/125,319 | 1993-09-22 | ||
| US08/125,319 US5353705A (en) | 1992-07-20 | 1993-09-22 | Lithographic printing members having secondary ablation layers for use with laser-discharge imaging apparatus |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2128911A1 CA2128911A1 (en) | 1995-03-23 |
| CA2128911C true CA2128911C (en) | 1998-09-22 |
Family
ID=22419182
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002128911A Expired - Fee Related CA2128911C (en) | 1993-09-22 | 1994-07-27 | Lithographic printing members having secondary ablation layers for use with laser-discharge imaging apparatus |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5353705A (en) |
| EP (1) | EP0644047B1 (en) |
| JP (1) | JP2828405B2 (en) |
| AT (1) | ATE177683T1 (en) |
| AU (1) | AU673441B2 (en) |
| CA (1) | CA2128911C (en) |
| DE (1) | DE69417129T2 (en) |
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- 1994-07-29 AU AU68783/94A patent/AU673441B2/en not_active Ceased
- 1994-08-03 AT AT94305766T patent/ATE177683T1/en not_active IP Right Cessation
- 1994-08-03 DE DE69417129T patent/DE69417129T2/en not_active Expired - Lifetime
- 1994-08-03 EP EP94305766A patent/EP0644047B1/en not_active Expired - Lifetime
- 1994-09-22 JP JP6228358A patent/JP2828405B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| AU6878394A (en) | 1995-04-06 |
| EP0644047A2 (en) | 1995-03-22 |
| EP0644047A3 (en) | 1995-11-15 |
| ATE177683T1 (en) | 1999-04-15 |
| DE69417129D1 (en) | 1999-04-22 |
| DE69417129T2 (en) | 1999-10-21 |
| JPH07164773A (en) | 1995-06-27 |
| JP2828405B2 (en) | 1998-11-25 |
| AU673441B2 (en) | 1996-11-07 |
| US5353705A (en) | 1994-10-11 |
| CA2128911A1 (en) | 1995-03-23 |
| EP0644047B1 (en) | 1999-03-17 |
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