Radiation imagery chemistry: process – composition – or product th – Stripping process or element – Element
Utility Patent
1997-12-07
2001-01-02
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Stripping process or element
Element
C430S293000
Utility Patent
active
06168899
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a photopolymerized material utilized in a process for preparing images, particularly color proofs, whereby a layer having imagewise tacky and nontacky areas is toned, and the toner adhering to the tacky areas is transferred first onto a temporary support and therefrom to an image receptor. The process utilizing such materials enables the preparation of multiple images and color proofs.
BACKGROUND OF THE INVENTION
Halftone color separations are used in reprography as copy masters for preparing offset or relief printing plates. Before the printing plates are exposed, the color separations are checked in color proofing processes to determine whether the ultimate printing result will be a tonally accurate reproduction of the original. According to general standard specifications, for example, high quality offset printing requires a resolution of 2%-98% dots, even 1%-99% dots on modem printing machines, for a 60 lines/cm screen. It is especially difficult to achieve satisfactory resolution of the small 2% dots in the highlights and 98% dots in the shadows. For good tonal reproduction, it is especially important that dots of the same size be sharply delineated over the entire area and reproduced uniformly, that is, without size variations.
A considerable proportion of these color proofs is supplied by proofing presses, essentially small offset printing presses for the smallest runs. U.S. Pat. No. 5,380,620 discloses a process that uses special, photosensitive, aqueous-developable materials and can be used for color proofing processes. These materials have areas, formed by special auxiliary layers, that accept or repel printing inks, analogous to dry offset plates. Washoff processes have the important disadvantage that waste water containing chemicals must be disposed of, and additional developing processors must be used. U.S. Pat. No. 5,380,620 does mention briefly a material that can be used without aqueous development. However, these offset materials must use very special, fluorine-containing, diazo compounds to make areas that accept or repel printing inks. Tonable photopolymerizable materials are not disclosed.
These are known in other color proofing processes using photosensitive recording materials in which differences in the tackiness of exposed and unexposed areas of the photosensitive layer are used to make the image. German Patent 12 10 321 (UK Patent 945,807), U.S. Pat. Nos. 3,620,726, 3,582,327, 3,649,268, 4,356,253, 4,948,704 and 4,243,741 disclose a reproduction process, wherein a tacky, photopolymerizable, recording material, comprises a support and a photopolymerizable layer containing at least one addition-polymerizable monomer, and a photopolymerization initiator. This recording material is hardened by imagewise exposure, whereupon the exposed image areas lose their tackiness. The latent image is made visible by the application of suitable toners that adhere only to the unexposed tacky areas and can be removed from the exposed nontacky areas. This process yields positive, optionally color images of the original similar in appearance to images produced by the use of printing inks.
The toners, comprising predominantly finely divided powders, can be applied by being dusted on the imagewise exposed surface. According to another embodiment, the toner can also be loosely bonded on a special support and transferred by bringing this support into contact with the imagewise exposed layer. Such transfer layers are significantly more advantageous, because handling is considerably simpler, cleaner, and more friendly to the environment. Color proofing processes using pigmented transfer layers are disclosed in German Patent 12 05 117, 29 49 462, U.S. Pat. Nos. 4,806,451, 4,902,363, 4,939,029, 5,126,226, 5,210,001, 5,090,774, and German Patent 41 20 793, and in U.S. Pat. No. 4,935,331.
However, the cited photographic color proofing processes have the disadvantage that the preparation of multiple copies of the color separations is time-consuming and costly. New photosensitive material must be exposed imagewise and toned to obtain each copy, and multiple photosensitive materials must be processed for polychromatic images. Another disadvantage is that the finished color proofs contain photopolymerized and unphotopolymerized material, which can lead to alterations in colors and changes in dot growth.
U.S. Pat. No. 3,060,025 and EP-C 0 034 816 disclose the preparation of multiple copies of a color separation by transfer of an imagewise color layer onto a receptor. However, these processes also have disadvantages. U.S. Pat. No. 3,060,025 does indeed mention the possibility of making multiple copies by the use of only one photosensitive material, but the final image also contains photosensitive starting material. The process of EP-C 0 034 816 uses toners that become tacky when heated and retain this tackiness a while after cooling, so that a portion of the toner layer can be transferred repeatedly. However, polychromatic images are difficult to prepare this way, because the preceding toner layer is partially transferred back when a new color is applied. Partial transfer of toner layers also alters colors. As contact exposure of the photosensitive material is not possible, because specular images would usually be obtained, the quality required for color proofs cannot be achieved with this process. This problem can be circumvented by the use of temporary supports, as described in U.S. Pat. No. 5,240,810, but the final proof contains additional adhesive layers that affect image quality.
The complex shear moduli of known photopolymerizable layers utilized in proofing applications, for example CROMALIN® 4BX and CROMALIN® 8BX, are outside the range described below.
The problem involved in the invention is to make available multiple, right-reading copies of a color separation or a polychromatic image without using time-consuming and costly processes, while avoiding the indicated disadvantages of known processes, and maintaining constant from the first to the last copy the color locus and resolution required for the color proof.
This problem is solved by providing a photopolymeric layer, a pigmented toning element and a temporary support which are utilized in a process for preparing multiple copies of images.
SUMMARY OF THE INVENTION
The invention provides a photopolymerizable layer, especially for use in color proofing processes, containing at least one polymeric binder, at least one ethylenically unsaturated, photopolymerizable monomer, and at least one photoinitiator, the layer having a thickness of ≧10 &mgr;m, wherein the photopolymerizable layer has a complex shear modulus of 170-700 kPa at 25° C., measured in each case at 10 Hz and tau 9750 Pa.
The invention also relates to a pigmented element, for toning a photopolymerizable layer comprising at least one plasticizing component consisting essentially of a support and a pigmented transfer layer, wherein the pigmented transfer layer comprises at least one polymeric component selected from the group consisting of a polymeric binder, a plastizied polymeric binder and mixtures thereof, and wherein the polymeric component is compatible with the at least one plasticizing component of the photopolymerizable layer.
The invention further relates to a temporary support useful in color proofing processes which use a photopolymerizable layer comprising at least one plasticizing component and a pigmented element comprising a pigmented layer on a support, comprising
a flexible, dimensionally stable base layer and;
an adhesive layer comprising a 2-5 &mgr;m thick coating containing at least one thermoplastic polymer, wherein the coating is compatible with the at least one plasticizing component of the photopolymerizable layer and the pigmented layer, and wherein the coating has a softening temperature of +25 to 130° C.
DETAILED DESCRIPTION OF THE INVENTION
The photopolymerizable layer of the invention and its use in processes for preparing images make it possible to prepare right-reading color proof
Bode Udo Dietrich
Convers Ronald John
Grossa Mario
Kalo Steven Max
Kudva Ashok Kamalaksha
Ashton Rosemary
Baxter Janet
E. I. Du Pont de Nemours and Company
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