Printing – Planographic – Lithographic printing plates
Reexamination Certificate
1999-03-15
2001-02-27
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic printing plates
C101S467000
Reexamination Certificate
active
06192799
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat mode imaging element for preparing a lithographic printing plate. More specifically the invention is related to a heat mode imaging element for preparing a lithographic printing plate whereof the difference in the penetrability to, or solubilization by, aqueous developer between the exposed and non-exposed areas of the top layer is increased.
BACKGROUND OF THE INVENTION
Lithography is the process of printing from specially prepared surfaces, some areas of which are capable of accepting lithographic ink, whereas other areas, when moistened with water, will not accept the ink. The areas which accept ink form the printing image areas and the ink-rejecting areas form the background areas.
In the art of photolithography, a photographic material is made imagewise receptive to oily or greasy inks in the photo-exposed (negative-working) or in the non-exposed areas (positive-working) on a hydrophilic background.
In the production of common lithographic printing plates, also called surface litho plates or planographic printing plates, a support that has affinity to water or obtains such affinity by chemical treatment is coated with a thin layer of a photosensitive composition. Coatings for that purpose include light-sensitive polymer layers containing diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely used.
Upon imagewise exposure of the light-sensitive layer the exposed image areas become insoluble and the unexposed areas remain soluble. The plate is then developed with a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.
Alternatively, printing plates are known that include a photosensitive coating that upon image-wise exposure is rendered soluble at the exposed areas. Subsequent development then removes the exposed areas. A typical example of such photosensitive coating is a quinone-diazide based coating.
Typically, the above described photographic materials from which the printing plates are made are camera-exposed through a photographic film that contains the image that is to be reproduced in a lithographic printing process. Such method of working is cumbersome and labor intensive. However, on the other hand, the printing plates thus obtained are of superior lithographic quality.
Attempts have thus been made to eliminate the need for a photographic film in the above process and in particular to obtain a printing plate directly from computer data representing the image to be reproduced. However the photosensitive coating is not sensitive enough to be directly exposed with a laser. Therefore it has been proposed to coat a silver halide layer on top of the photosensitive coating. The silver halide may then directly be exposed by means of a laser under the control of a computer. Subsequently, the silver halide layer is developed leaving a silver image on top of the photosensitive coating. That silver image then serves as a mask in an overall exposure of the photosensitive coating. After the overall exposure the silver image is removed and the photosensitive coating is developed. Such method is disclosed in for example JP-A-60-61 752 but has the disadvantage that a complex development and associated developing liquids are needed.
GB-1 492 070 discloses a method wherein a metal layer or a layer containing carbon black is provided on a photosensitive coating. This metal layer is then ablated by means of a laser so that an image mask on the photosensitive layer is obtained. The photosensitive layer is then overall exposed by UV-light through the image mask. After removal of the image mask, the photosensitive layer is developed to obtain a printing plate. This method however still has the disadvantage that the image mask has to be removed prior to development of the photosensitive layer by cumbersome processing.
Furthermore methods are known for making printing plates involving the use of imaging elements that are heat-sensitive rather than photosensitive. A particular disadvantage of photosensitive imaging elements such as described above for making a printing plate is that they have to be shielded from the light. Furthermore they have a problem of sensitivity in view of the storage stability and they show a lower resolution. The trend towards heat mode printing plate precursors is clearly seen on the market.
For example, Research Disclosure no. 33303 of January 1992 discloses a heat mode imaging element comprising on a support a cross-linked hydrophilic layer containing thermoplastic polymer particles and an infrared absorbing pigment such as e.g. carbon black. By image-wise exposure to an infrared laser, the thermoplastic polymer particles are image-wise coagulated thereby rendering the surface of the imaging element at these areas ink-acceptant without any further development. A disadvantage of this method is that the printing plate obtained is easily damaged since the non-printing areas may become ink accepting when some pressure is applied thereto. Moreover, under critical conditions, the lithographic performance of such a printing plate may be poor and accordingly such printing plate has little lithographic printing latitude.
U.S. Pat. No. 4,708,925 discloses imaging elements including a photosensitive composition comprising an alkali-soluble novolac resin and an onium-salt. This composition may optionally contain an IR-sensitizer. After image-wise exposing said imaging element to UV-visible- or IR-radiation followed by a development step with an aqueous alkali liquid there is obtained a positive or negative working printing plate. The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.
EP-A-625 728 discloses an imaging element comprising a layer which is sensitive to UV- and IR-irradiation and which may be positive or negative working. This layer comprises a resole resin, a novolac resin, a latent Bronsted acid and an IR-absorbing substance. The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.
U.S. Pat. No. 5,340,699 is almost identical with EP-A-625 728 but discloses the method for obtaining a negative working IR-laser recording imaging element. The IR-sensitive layer comprises a resole resin, a novolac resin, a latent Bronsted acid and an IR-absorbing substance. The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.
GB-A-1 208 415 discloses a method of recording information comprising information-wise heating a recording material comprising a support bearing, with or without an interlayer a heat-sensitive recording layer constituted so that such information-wise heating creates a record of the information in terms of a difference in the water permeabilities of different areas of the recording layer, treating the recording material with an aqueous liquid which penetrates through the water-permeable or more water-permeable areas of the recording layer and is constituted so as to effect a permanent physical and/or chemical change of at least the surface portions of the underlying support or inter-layer in the corresponding areas, and removing the whole of the recording layer to expose said information-wise changed support or interlayer.
JP-A-01-46739 discloses a method for preventing the line-like unequalities generated by foam by dissolving a photosensitive composition containing at least a photosensitive material, fluorine surfactant and defoaming agent into a coating solvent, then coating the solution on a base and drying the coating.
JP-A-02-29750 discloses a method for obtaining a photosensitive composition suitable for a positive photosensitive printing plate by using o-naphthoquinonediazide sulphonic acid, an alkali-soluble resin, and a non-ionic surfactant such as polyoxyethylene naphthol.
EP-A-0527 369 discloses a light sensitive recording material comprising a support and a positive working light
Damme Marc Van
Hauquier Guido
Vermeersch Joan
Verschueren Eric
Agfa-Gevaert N.V.
Breiner & Breiner
Funk Stephen R.
LandOfFree
Heat mode sensitive imaging element for making positive... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat mode sensitive imaging element for making positive..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat mode sensitive imaging element for making positive... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593086