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
1999-04-30
2002-07-16
Baxter, Janet (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
C430S273100, C430S281100, C430S192000, C430S075000, C430S286100
Reexamination Certificate
active
06420087
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of positive working lithographic plates.
BACKGROUND OF THE INVENTION
Positive working lithographic plates are very widely manufactured and probably account for over half of all lithographic plates. The photosensitive compositions used are comparatively simple and easy to manufacture, typically comprising an o-quinonediazide light sensitive component and a phenolic resin. Their processing after image-wise exposure is also simple. However, if the processing is not carried out according to the manufacturers instructions, such as the use of developing solutions which are stronger than that recommended or if temperature of the developing solution is too hot, there is a tendency for the developing solution to remove not only the exposed areas of the plate but also to attack the image areas in the non-exposed areas of the plate. This attack on the printing image areas produces a poor image and in many cases renders the plate unusable. The use of strong developing solutions exacerbates the problem of image attack, as does developing times over 30 seconds as are often used in the processing of direct positive plates.
Common formulation means for decreasing attack by strong developers or through the use of conditions leading to over development, such as using phenolic resins with reduced alkali solubility, would normally lead to a reduction in plate sensitivity for the same plate under less aggressive development conditions. Accordingly methods to increase plate sensitivities, such as the use of speed enhancers, often result in reduced resistance to developer attack
SUMMARY OF THE INVENTION
We have discovered a positive working lithographic plate precursor and methods of producing said precursor which exhibit a reduced tendency to developer attack of the image obtained after image-wise exposure under aggressive development whilst significantly reducing any accompanying loss of sensitivity in less aggressive developers and development conditions.
Therefore according to the present invention there is provided a positive working lithographic plate precursor comprising a support having a hydrophilic surface and a coating thereon comprising a positive working photosensitive composition and an aryl alkyl polysiloxane.
According to a further aspect of the invention there is provided a positive working lithographic plate precursor comprising a support having a hydrophilic surface and a coating thereon comprising a positive working, photosensitive composition and an aryl alkyl polysiloxane at least part of which aryl alkyl polysiloxane is present as a thin layer at the uppermost surface of the plate precursor.
According to a further aspect of the present invention there is provided a method of preparing a positive working lithographic plate precursor of the present invention comprising coating on a support having a hydrophilic surface a coating comprising in admixture a positive working photosensitive composition and an aryl alkyl polysiloxane.
DETAILED DESCRIPTION OF THE INVENTION
A preferred aryl alkyl polysiloxane useful in the present invention is a phenyl methyl polysiloxane.
Suitably the aryl alkyl polysiloxane constitutes at least 0.3%, preferably at least 1%, preferably up to 50%, more preferably up to 10% by weight of the dry coating. Thus a preferred weight range for the aryl alkyl polysiloxane may be expressed as 1-10% of the total dry coating weight.
The preferred positive working photosensitive compositions of the present invention are those comprising an o-napthoquinone diazide as the light sensitive component. Most preferably these are present either as sulphonic acid esters or as carboxylic acid esters.
Examples of particularly preferred o-quinone diazide compounds are disclosed in a variety of publications such as U.S. Pat. Nos. 2,766,118; 2,767,092, 2,772,972; 2,859,112; 2,907,665; 3,046,110; 3,046,111; 3,046,115; 3,046,118; 3,046,119; 3,046,120; 3,046,121; 3,046,122, 3,046,123; 3,061,430; 3,102,809, 3,106,465; 3,635,709 and 3,647,443 and these compounds may preferably be used in the invention. Among these, particularly preferred are o-naphthoquinonediazidosulfonates or o-naphthoquinonediazido carboxylates of aromatic hydroxyl compounds; o-naphthoquinonediazidosulfonic acid amides or o-naphthoquinonediazido-carboxylic acid amides of aromatic amine compounds, for instance, esters of benzoquinone-1,2-diazidosulfonic acid or naphthoquinone-1,2-diazidosulfonic acid with polyhydroxyphenyl (hereinafter the term “ester” also include partial esters); esters of naphthoquinone-1,2-diazido-4-sulfonic acid or naphthoquinone-1,2-diazido-5-sulfonic acid with pyrogallo/acetone, resins; esters of benzoquinone-1,2- diazidosulfonic acid or naphthoquinone-1,2-diazidosulfonic acid with novolak type phenol/formaldehyde resins or novalak type cresol/formaldehyde resins; amides of poly(p-aminostyrene) and naphthoquinone-1,2-diazido4-sulfonic acid or naphthoquinone-1,2- diazido-5-sulfonic acid; esters of poly(p-hydroxystyrene) and naphthoquinone-1,2- diazido-5-sulfonic acid; esters of polyethylene glycol with naphthoquinone-1,2-diazido-4-sulfonic acid or naphthoquinone-1, 2-diazido 5-sulfonic acid: amides of polymeric amines with naphthoquinone-1,2-diazido-4-sulfonic.
The preferred binder for the photosensitive composition is an alkali soluble resin. Particularly useful as the alkali soluble resins are the condensation products from the interaction between phenol, C-alkyl substituted phenols (such as cresols and p-tert-butyl-phenol), diphenols (such as bisphenol-A) and aldehydes (such as formaldehyde). Particularly useful in this invention are novolak resins, resole resins and novolak/resole resin mixtures.
The most preferred photosensitive composition comprises o-napthoquinonediazide sulphonyl esters of a phenolic resin.
Suitably the photosensitive composition constitutes at least 50%, preferably at least 90%, preferably up to 99.7%, more preferably up to 99% by weight of the dry coating. Thus a preferred weight range for the photosensitive composition may be expressed as 90-99% of the total dry coating weight.
Suitable solvents for the coating solutions are, for example, the known glycol derivatives (such as 2-ethoxy ethanol and 1-methoxy-propan-2-ol) and ketones (such as butanone) in common use for the manufacture of such photosensitive coatings.
The wet coated composition is dried at elevated temperatures to remove coating solvents. If drying temperature or drying time is too low then residual solvents can adversely effect the resulting developer resistance of the coating. If drying, is too severe then unwanted reactions can occur in the drying film. Preferably the coated compositions are dried between 100° C. for 210 seconds and 130° C. for 90 seconds.
According to a further preferred embodiment there is provided a method of preparing a positive working lithographic plate precursor according to the present invention comprising coating on a support having a hydrophilic surface a positive working photosensitive composition and applying an additional composition comprising an aryl alkyl polysiloxane on said photosensitive layer.
Suitably the aryl alkyl polysiloxane is laid down to a dry film weight of at least 0.02 gm
−2
, preferably at least 0.05 gm
−2
, preferably up to 0.6 gm
−2
, more preferably up to 0.4 gm
−2
. Thus a preferred weight range for the aryl alkyl polysiloxane may be expressed as 0.05-0.4 gm
−2
dry film weight.
The aryl alkyl polysiloxane composition can be applied to the photosensitive layer by various means such as spraying. Suitably the composition is coated onto the photosensitive layer.
Whilst the applicants do not wish to be limited by any theoretical explanation of how their invention operates, it is believed that the presence of at least part of the aryl alkyl polysiloxane at the uppermost surface of the precursor is a key factor. It is believed that during the first method of the present invention at least part of the aryl alkyl polysiloxane separates out of the coating and depo
Bennett Peter A. R.
Hearson John A.
Smith Carole-Anne
Baxter Janet
Clarke Yvette M.
Kodak Polychrome Graphics LLC
Ratner & Prestia
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