Radiation imagery chemistry: process – composition – or product th – Imaged product – Including resin or synthetic polymer
Reexamination Certificate
2000-10-16
2002-09-17
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Including resin or synthetic polymer
C430S175000, C430S302000
Reexamination Certificate
active
06451491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved colorant dispersions and to photosensitive compositions using such dispersions. More particularly to lithographic compositions which are aqueous developable, negative acting, and have improved image contrast.
2. Description of the Prior Art
It is known in the art to produce photosensitive compositions suitable for the production of printing plates and color proofing films. Lithographic printing plates generally are composed of an aluminum containing substrate which may or may not have been treated with a variety of processes recognized in the art including anodization, graining and hydrophilization. The prepared substrate may then be applied with a photosensitive coating comprising a photosensitizer, binding resins, colorants, acid stabilizers, surfactants and other art recognized components. Common photosensitizers include diazo compounds, including polymeric diazonium condensates salts and photopolymerizable compositions. Sensitizers, binders and printing plates employing aromatic diazonium compounds are described in U.S. Pat. Nos. 3,175,906; 3,046,118; 2,063,631; 2,667,415; 3,867,147 and 3,679,419 which are incorporated herein by reference.
In order to be useful, such photosensitive compositions must have a series of properties including good image contrast, developability with aqueous alkaline solutions, no redeposit of developed particles back onto image areas and good cleanout of nonimage areas by development. It must also have good printing runs, photosensitivity, ink receptivity, and oleophilicity of its a binding resins. U.S. Pat. No. 3,867,147 discloses photosensitive materials comprising a mixture of condensation products of diazonium salts and polymeric binders including polyvinyl acetals, such as polyvinyl formal or polyvinyl butyrals to produce printing plates. These photosensitive compositions have high photosensitivity and good oleophilicity and print runs but can only be properly processed by developers containing a large amount of volatile organic solvents. U.S. Pat. No. 4,387,151 discloses printing plates prepared from photosensitive mixtures of condensation products of diazonium salts and polymeric binders. These can be developed with aqueous, alkaline solutions without organic solvents, however, lithographic printing plates made from these compositions produce light hardened layers having unsatisfactory ink receptivity. Photosensitive compositions with polyvinyl acetal polymers are known from U.S. Pat. No. 4,413,091 and 4,085,079, however, these photosensitive elements must also be developed with developers which contain organic solvents. It is desirable to develop printing plates without the use of organic solvents since vapors and waste waters originating from these developers are disadvantageous. U.S. Pat. No. 4,631,245, which is incorporated herein by reference, teaches an anhydride modified polyvinyl acetal polymer which is most useful as a binder for photosensitive composition layers. They can be developed with neutral or weakly alkaline, aqueous solutions and produce printing plates with a high print run performance and good ink receptivity. These photosensitive mixtures yield image areas with good oleophilic properties, resistance to abrasion during printing and etching resistance. Unfortunately, these compositions only permit a relatively small amount of pigment to be incorporated into a pigment dispersion which is subsequently used to produce photographic elements. Hence the contrast between the developed image and the background substrate is exceedingly low. This is a disadvantage to the printer when trying to view the image. The present invention improves on the foregoing method of preparing pigment dispersions and photographic compositions used to produce photographic elements by using a solvent composition which allows a much higher pigment loading. Photographic elements thereby produced have a much greater image to substrate contrast and an image which is much easier to view. It has been found that the use of propylene lycol methyl ether (PGME) butyrolactone (BLO), tetrahydrofuran (THF), methyl cellosolve (MC) i.e., ethylene glycol monomethyl ether and methyl cellosolve acetate (MCA) produce stable pigment dispersions and photosensitive coating which allow the formation of a stable photosensitive coating with a high pigment loading.
The present invention provides a negative working photosensitive composition which is suitable for use in the production of photographic elements such as lithographic printing plates, and which has the aforesaid advantages of good photographic elements and additionally has an improved contrast between the image and the background substrate. The photosensitive composition can still be developed by means of practically solvent-free, neutral or alkaline aqueous solutions, and yields printing plates producing large print runs and having a good ink receptivity.
SUMMARY OF THE INVENTION
The invention provides a colorant dispersion which comprises in admixture
(a) at least one pigment;
(b) a solvent composition which comprises at least one of a C
1
-C
8
aliphatic alcohol, a mono- or di-C
1
-C
8
alkylene glycol C
1
-C
8
alkyl ether, or a cyclic ketone; and
(c) at least one aqueous alkaline soluble or swellable polymeric compound which is the reaction product of a hydroxy containing polymer and an anhydride in the presence of a catalytic amount of a tertiary amine catalyst;
wherein the pigment and the polymeric compound are present in a weight ratio of from about 0.75:1.25 to about 1.25:0.75 and wherein the solvent composition is present in an amount sufficient to form a uniform, stable dispersion.
The invention also provides a negative working photosensitive composition which comprises an admixture of at least one light sensitive component diazonium compound or photopolymerizable composition, in an amount sufficient to form a uniform photosensitive composition; at least one aqueous alkaline soluble or swellable polymeric binder compound which is the reaction product of a hydroxy containing polymer and an anhydride in the presence of a catalytic amount of a tertiary amine catalyst, which binder is present in an amount sufficient to bind the photosensitive composition in a uniform admixture; and the above dispersion in an amount sufficient to uniformly color the photosensitive composition.
The invention further provides an imagewise exposed and developed photographic element having high contrast between image and removed non-image areas which comprises
(a) a substrate;
(b) a photographic image on the substrate, which image has been produced by coating and drying a photosensitive composition on the substrate, imagewise exposing the photosensitive composition to actinic radiation and removing the non-image areas of the photosensitive composition to thereby uncover portions of the substrate underlying the non-image areas while not removing the image areas; wherein the substrate under the removed non-image areas has a Hunter stimulus lightness value L ranging from about 35 to about 80, the image areas have an L value of from about 20 to about 60 and the difference between the L value for the substrate under the removed non-image areas and the L value for the image areas is at least about 15.
The invention also provides a method of producing an imagewise exposed and developed photographic element having high contrast between image and removed non-image areas which comprises
i) forming the above colorant dispersion
ii) forming a negative working photosensitive composition which comprises an admixture of at least one light sensitive component diazonium compound or photopolymerizable composition, in an amount sufficient to form a uniform photosensitive composition; at least one aqueous alkaline soluble or swellable polymeric binder compound which is the reaction product of a hydroxy containing polymer and an anhydride in the presence of a catalytic amount of a tertiary amine catalyst, which binder is present in an amount sufficient
Dhillon Major S.
Sprintschnik Gerhard
Wanat Stanley F.
Agfa Corporation
Chu John S.
Roberts Richard S.
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