Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-07-28
2002-12-31
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S270100, C430S944000, C430S910000, C430S964000
Reexamination Certificate
active
06500600
ABSTRACT:
This application is based on European Patent Application No. 99830489.3 filed on Jul. 30, 1999, the content of which is incorporated hereinto by reference.
FIELD OF INVENTION
The present invention relates to a composition sensitive to IR radiation and to heat, and a lithographic plate coated with this composition.
In particular, it relates to a composition sensitive to IR radiation and to heat which is useful for the production of a lithographic plate of the positive type.
It also relates to a composition sensitive to laser radiation which is useful for the production of a lithographic plate of the positive type.
BACKGROUND OF INVENTION
As is well-known, the technique of printing by means of lithographic plates is based on differential partition between fatty substances and water. The fatty substance or ink is retained preferentially by the image area and the water is preferentially retained by the non-image area. When the surface of a lithographic plate, suitably prepared, is moistened with water and then sprinkled with ink, the non-image area retains the water and repels the ink, while the image area accepts the ink and repels the water. Then, the ink on the image area is transferred onto the surface of a material on which it is desired to reproduce the image, such as, for example, paper, textile and the like.
In general, the lithographic plates used in printing processes are formed from an aluminium support covered with a composition sensitive to light (photosensitive). When such a composition becomes soluble in an alkaline developing bath through the action of heat or of radiation of appropriate wavelength, the printing process is termed “positive”. Conversely, when the portion exposed to heat or to radiation of appropriate wavelength becomes insoluble in an alkaline developing bath, the printing process is termed “negative”. In both cases, the remaining, image area is lipophilic and hence accepts the ink, while the non-image area is hydrophilic and accepts the water.
The recent developments in the field of lithographic plates have been directed towards the search for compositions sensitive to laser light, preferably in the near IR. In particular, to laser light controlled by software, in such a way as directly to transfer the image created by computer onto the surface of the plate. This technique has the advantage of eliminating the photographic films, with consequent reduction in the pollution due to the chemical substances used for the preparation and production of these and elimination of all the problems that arise in the transfer of the image onto the plate via photographic films.
In the first place, a composition sensitive to radiation emitted by a laser could impart greater reliability to the system.
Secondly, it would be possible to work under ambient illumination, thus eliminating the automatic loading systems or the darkrooms.
With the aim of attaining this objective, in recent years many compositions comprising a polymeric binder and a solubility inhibitor have been investigated. Such a solubility inhibitor has the ability to render the polymeric binder insoluble in a suitable alkaline developing bath as long as it has not been exposed to a sufficient quantity of heat and of then rendering it soluble in the said developing bath after such exposure to heat. Besides the aforesaid components, many of the compositions described until now also comprise a so-called IR absorber, usually consisting of a compound capable of absorbing IR radiation and of transforming part of the radiation absorbed into heat, giving it up to the immediately surrounding environment.
OBJECTS OF INVENTION
The present invention aims to provide a composition sensitive to heat and a lithographic plate of the positive type coated with the said composition wherein the solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof.
The present invention also aims to provide a composition sensitive to IR radiation and a lithographic plate of the positive type coated with the said composition wherein the solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof.
The present invention also aims to provide a composition sensitive to laser radiation and a lithographic plate of the positive type coated with the said composition wherein the solubility inhibitor is a hydroxylated acrylic polymer, a hydroxylated acrylic copolymer or a derivative thereof.
Definitions
The term “lithographic plate” means a support covered with a coating which, after being suitably exposed and developed, is used, as a planographic matrix, in printing processes wherein there is differeritial partition between fatty substances and water.
Typical examples of support materials are constituted by plates of aluminium, zinc, copper, polyester and paper covered with a polymer. Preferably, the support is a sheet of grained aluminium, oxidized and suitably treated to receive the photosensitive composition.
The term “positive type” means that the portion of the photosensitive coating exposed to the radiation or to heat becomes soluble in such a way that it can be removed during the process of development of the plate. Typically, the development process is performed in alkalis having a conductivity pf from 75 to 110 mS.
The term “polymeric binder” means a polymer soluble in alkali, such as for example a novolac resin, a resol resin, a vinylphenolic resin, derivatives thereof or mixtures thereof.
Typically, a novolac resin is a polycondensation product obtained by reaction in an acidic environment between formaldehyde and phenol and/or m-cresol and/or symmetrical xylenol in a molecular ratio of less than 1 (for example formaldehyde:phenol=1:2). Optionally, the thus obtained compound is variously modified such as, for example, by reaction with amides.
Typical examples of commercial novolac resins are the products LB 6564 (mean ponderal molecular weight=6000-10,000) and LB 744 (mean ponderal molecular weight=8000-13,000) from the firm Bakelite (Germany), R 7100 (mean ponderal molecular weight=8000-10,000) from the firm Rohner, and PN 320 (mean ponderal molecular weight=3000-5000) and PN 430 (mean ponderal molecular weight=5000-9500) from the firm Clariant; 010/129/2 (mean ponderal molecular weight=8700-9700), 010/129/1 (mean ponderal molecular weight=2200-32 00), and 010/127/1 (mean ponderal molecular weight=800-1800), 76/159 (mean ponderal molecular weight=2900-3900), 76/160 (mean ponderal molecular weight=2200-3200), 76/190 (mean ponderal molecular weight=7500-8500) from the firm Rohner.
The term “heat-sensitive composition” means a composition which includes a polymeric binder and has the property of being insoluble in an alkaline developing bath as long as it has not been exposed to a sufficient quantity of heat and of then being soluble in the said bath after such exposure to heat.
The term “solubility inhibitor” means a compound capable of rendering a heat-sensitive composition that contains it insoluble in a suitable alkaline developing bath as long as the said composition has not been exposed to a sufficient quantity of heat and/or laser radiation and of then rendering it soluble in the said developing bath after such exposure to heat and/or laser radiation.
The term “hydroxyl number” means the number of milligrams of KOH equivalent to the hydroxyl content of 1 gram of the compound under test. The determination is made by acetylating the compound under test with acetic anhydride in pyridine, hydrolysing with water the excess acetic anhydride that has not reacted and titrating the free acetic acid with KOH (phenolphthalein indicator).
The term “acidity number” means the number of milligrams of KOH necessary to neutralize the free acid present in 1 gram of the compound under test.
The term “IR absorber” means a compound capable of absorbing IR radiation and of transforming part of the absorbed radiation into heat and giving it up to the immediately
Bernardini Roberto
Bolli Angelo
Tiefenthaler Domenico
Hamilton Cynthia
Lastra S.p.A.
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