Incremental printing of symbolic information – Thermal marking apparatus or processes – Multicolor
Reexamination Certificate
1998-05-07
2001-03-20
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Multicolor
Reexamination Certificate
active
06204874
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to printing and mo re specifically to platemaking and color proofing, which are pre-press steps in printing.
BACKGOUND OF THE INVENTION
As the printing industry is moving to Computer-to-Plate systems, new methods of digital color proofing are needed to replace the traditional film based proofing. Computer-to-Plate, or CTP, refers to directly imaging printing plates. Color proofers are used to generate a composite color image representative of the output of a color printing press. A common type of color proofers is the thermal transfer type, wherein a dye or pigment is transferred from a donor sheet to a receiver sheet by heating the dye or pigment. The heating can be accomplished by resistive type electrical heaters or by a focused beam of a laser, typically an infra-red laser. This type of system performs “thermal” or “heatmode” imaging. In operation, the receiver sheet, which can be paper or an intermediate receiver, is held on a rotating drum while four or more donor sheets of different colors are placed, one at a time, over the receiver sheet and the color transferred from the donor sheets to selected areas of the receiver sheet. This is followed by applying a protective coating on the receiver sheet or lamination of the intermediate receiver to paper stock. The most well known system of this type is the KODAK APPROVAL™ system, manufactured by Kodak Co. (Rochester, N.Y.).
In order to automate the of creating a proof process prior art proofers use primarily two methods, shown in
FIG. 1-
a
and
FIG. 1-
b.
For small format proofers, such as dye sublimation proofers, the four donor sheets are coated on a common substrate supplied in roll form. A typical appearance of such a composite donor roll is shown in
FIG. 1-
a,
where the Cyan, Yellow, Magenta and Black pages appear in sequence throughout the roll. For larger formats each donor is supplied on an individual roll, as shown in
FIG. 1-
b.
To load the donors from the rolls onto a drum, feed rollers (item
14
in
FIG. 1-
b
) and a cutter (item
13
in
FIG. 1-
b
) are used. There are disadvantages in these two prior art systems, the main one being the difficulty of using special colors, other than the standard Red, Green, Blue or Cyan, Yellow, Magenta, Black. From time to time the need arises to add a special color (such as gold or silver) to a single proof. The roll feed system eliminates the flexibility of a sheet fed system to quickly change the colors or sizes of the donor sheets. A second disadvantage of roll fed system is the lower manufacturing yield of the donors, as a single defective sheet in the roll will cause the complete roll to be scrapped instead of simply scrapping the defective sheet. Another disadvantage of the system shown in
FIG. 1-
b
is the large space taken by the donor rolls. A further disadvantage of the system of
FIG. 1
b
is that the system is dedicated for proofing, requiring a separate machine for plate exposure. In theory it would have been possible to generate proofs and plates on a single prior art thermal unit, however, the required manual loading of each sheet separately made the process unproductive, as each proof would have required at least
10
steps (one receiver and at least four donors, each one having to be loaded and unloaded).
Another type of prior art system is disclosed in European Patent Application EP0402079 and uses electrophotographic recording to produce proofs and plates from the same units. Electrographic plates were not successful due to poor resolution and short life, while the color toners required for the electrophotographic proofs were difficult to change for special colors. Other colors, such as metallic tones, are not possible using this process as the toner has to be an electrical insulator. A different approach, by Optronics (Chelmsford, Mass.) uses an imager with color lasers to make plates and uses photographic paper for proofs. This system has not been not successful as the photographic film requires complex processing and does not allow any special colors (since colors have to be built into the photographic paper emulsion).
SUMMARY OF THE INVENTION
It is an object of this invention to provide a single device capable of automatically loading printing plates and proofing sheets onto the same drum and using a single laser head to expose both. This generates the best match between the plate and the proof, and consequently the best match between the printed material and the proof. A second object of this invention to have the flexibility of sheet fed system with the automation previously only available in roll fed proofers, particularly the flexibility of changing proof size and adding special colors. A third object is to build a compact, low cost proofs. A further object is to lower cost of proofer and proofing materials by the inherent yield advantages of cut sheet. Still a further object is to provide a system which does not require any chemical processing for plates or proofing.
The invention combines a Computer-to-Plate system using a thermal imaging head with a thermal proofer. The invention uses a color proofer of conventional design, the innovation involving to combining both units into a single machine and automating the loading process of proofs using a sheet feeding tray. In this tray the materials are stacked in the same order the proofer is using them: a receiver sheet followed by four different donor sheets, this sequence being repeated many times. As in prior art, the donor sheets are larger than the receiver sheet, to allow the vacuum around the receiver sheet to hold the donor sheets. Means of loading the sheets onto the drum are provided, preferably a hinged tray, in order to bring the sheets into contact with the drum, allowing the drum to grip a sheet from the tray using the vacuum holes in the drum. The discarded donor sheets are unloaded into a second tray. The sequencing of the sheets in the tray can be done by pre-packing them by the supplier in the correct sequence or by the user of the color proofer. This allows the easy addition of customized colors and replacement of sheets with different colors. The printing plate can be loaded in the same tray as the proofing materials or have a separate loading means.
REFERENCES:
patent: 5276464 (1994-01-01), Kerr et al.
patent: 5280307 (1994-01-01), Parsons
patent: 5341159 (1994-08-01), Kerr
patent: 5436695 (1995-07-01), Lucking et al.
patent: 5699099 (1997-12-01), Garand et al.
patent: 5734408 (1998-03-01), Rombult et al.
patent: 5734409 (1998-03-01), Rombult et al.
patent: 5852464 (1998-12-01), Hebert et al.
patent: 0 402 079 A2 (1990-06-01), None
Creo Products Inc.
Oyen Wiggs Green & Mutala
Tran Huan
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