Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2000-04-25
2002-10-08
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S270100, C430S348000, C430S944000, C430S945000, C430S964000
Reexamination Certificate
active
06461795
ABSTRACT:
The present specification relates to methods of manufacturing lithographic printing form precursors. The invention relates further to such lithographic printing form precursors per se, and to their use.
The art of lithographic printing is based on the immiscibility of ink, generally an oily formulation, and water, wherein in the traditional method the ink is preferentially retained by the image or pattern area and the water or fountain solution is preferentially retained by the non-image or non-pattern area. When a suitably prepared surface is moistened with water and an ink is then applied, the background or non-image area retains the water whilst the image area accepts ink and repels the water. The ink on the image area is then transferred to the surface of a material upon which the image is to be reproduced, such as paper, cloth and the like. Commonly the ink is transferred to an intermediate material called the blanket which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
New types of “waterless” lithographic printing employ only an oily ink material and preferentially ink-accepting image areas and ink-repelling non-image areas on the printing form.
A generally used type of lithographic printing form precursor (by which we mean a coated printing form prior to exposure and development) has a radiation sensitive coating applied to an aluminium substrate. Negative working lithographic printing form precursors have a radiation sensitive coating which when imagewise exposed to radiation of a suitable wavelength hardens in the exposed areas. On development the non-exposed areas of the coated composition are removed leaving the image. On the other hand positive working lithographic printing form precursors have a radiation sensitive coating, which after imagewise exposure to radiation of a suitable wavelength becomes more soluble in the exposed areas than in the non-exposed areas, in a developer. In both cases only the image area on the printing form itself is ink-receptive.
The differentiation between image and non-image areas is made in the exposure process where a film is applied to the printing form precursor with a vacuum to ensure good contact. The printing form precursor is then exposed to a radiation source; conventionally this has been a UV radiation source. In the case where a positive form precursor is used, the area of the film that corresponds to the image in the printing form precursor is opaque so that no light will strike the printing form precursor, whereas the area on the film that corresponds to the non-image area is clear and permits the transmission of light to the coating which becomes more soluble and is removed on development.
Most positive working systems rely on the inhibition of the inherent solubility of phenolic resins, in suitable developers. Traditionally this has been achieved through the use of diazide moieties, especially naphthoquinone diazide (NQD) moieties, to provide compositions which only following exposure to UV radiation are soluble in the developer.
As demands on the performance of UV sensitive positive working coatings have increased so NQD technology has become limiting. In addition, digital and laser imaging technology is making new demands on coatings for lithographic printing.
It is known from GB 1245924 that the solubility of phenolic resins in lithographic developers may be increased by the application of heat. The heat may be delivered by infra-red radiation, assisted by radiation absorbing components such as carbon black or Milori Blue (C.I. Pigment Blue 27). However the developer resistance of the non-exposed areas to commercial developers is low, and the solubility differential is low compared to the commercial UV sensitive compositions containing NQD moieties.
We have devised new positive working heat sensitive systems comprising phenolic resins, to meet the new demands. Our new systems and methods are the subject of our patent applications PCT/GB97/01117, GB 9700877.5 (taken forward as PCT/GB98/00132), GB 9714169.1 (taken forward as PCT/GB98/01953, MY PI 9803095 and ZA 98/5913), GB 9714172.5 (taken forward as PCT/GB98/01957, MY PI 9803069 and ZA 98/5912), and GB 9722862.1, all unpublished at the priority date of this application. We have observed that. in our new systems there may be an alteration in their sensitivity over time, after the heat sensitive composition has been applied to a substrate and dried, such effect being the result of reduced developer solubility of the unexposed compositions with time prior to exposure. Thus when we mention “sensitivity” in this specification we are considering this in the context of the entire process of exposure and development. We are not referring to the matter of how the areas of the composition which are exposed react to that exposure. Sometimes this “sensitivity” is called “operating speed” in the art.
We have devised a process which improves the new systems mentioned above, such that a consistent and stable material can be supplied to an end user. The invention may also be applied to other compositions containing phenolic resins, for example those of GB 1245924 mentioned above, as well as those of U.S. Pat. Nos. 5,491,046, 5,466,557, 5,372,915, 5,372,907 and U.S. Pat. No. 4,708,925, described hereinafter.
In accordance with a first aspect of the invention there is provided a method of manufacturing a printing form precursor which comprises a coating on a substrate, the coating comprising a positive working composition which comprises a phenolic resin, wherein the method of manufacturing comprises the application of the composition in a solvent to the substrate, the drying of the composition, and the subsequent heat treatment of the coated substrate.
Preferably the composition of the precursor manufactured by the method of the invention is heat sensitive, such that its solubility in a developer increases in heated areas during patternwise exposure. Suitably it may be patternwise exposed by direct heat, or by charged particle radiation or electromagnetic radiation, in each case converted to heat by the coating. In the latter case the electromagnetic radiation to which the coating is sensitive is preferably of wavelength exceeding 450 nm (i.e. entirely or predominantly above 450 nm), preferably exceeding 500 nm, more preferably exceeding 600 nm. In patternwise exposing the precursor the use of electromagnetic radiation is preferred.
A said preferred, heat sensitive, composition preferably includes a modifying means for modifying the properties of the composition. Such a modifying means is preferably arranged to alter the developer solubility of the composition compared to when said modifying means is not present in a said composition. Said modifying means may be covalently bonded to said phenolic resin or may be a compound which is not covalently bonded to said phenolic resin.
Said modifying means may be selected from:
functional groups Q, as described in any statement hereinafter with regard to what is referred to as the “'169 invention”;
diazide moieties;
nitrogen containing compounds wherein at least one nitrogen atom is either quaternized, incorporated in a heterocyclic ring or quaternized and incorporated in a heterocyclic ring, as described in any statement hereinafter with regard to what is referred to as the “'117 invention”;
latent Bronsted acids, onium salts or acid generating compounds as described in any statement hereinafter with regard to further compositions.
Said heat sensitive composition preferably passes tests 1 to 5 described hereinafter with respect to the '117 invention wherein a reference in the tests to an “active polymer” should be substituted with a reference to said phenolic resin, described above in the absence of said modifying means; and a reference to a “reversible insolubiliser compound” should be substituted with a reference to said modifying means.
As indicated above the invention can be applied to compositions containing diazide moieties. We have discovered that compositions contai
Kitson Anthony Paul
McCullough Christopher David
Monk Alan Stanley
Parsons Gareth Rhodri
Ray Kevin Barry
Baker & Botts LLP
Baxter Janet
Gilmore Barbara
Kodak Polychrome Graphics LLC
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