Radiation-sensitive mixtures comprising IR-absorbing cyanine...

Details Radiation-sensitive mixtures comprising IR-absorbing cyanine... Radiation-sensitive mixtures comprising IR-absorbing cyanine...

1999-07-29

2002-12-10

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

C430S270100, C430S273100, C430S278100, C430S270200, C430S281100, C430S905000, C430S302000, C430S944000, C430S926000

Reexamination Certificate

active

06492093

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to positive-working, radiation-sensitive mixtures which contain an organic, polymeric binder which is insoluble in water but soluble in aqueous alkaline solution and an IR-absorbing dye or pigment. It also relates to recording materials comprising a substrate and a layer of a mixture as described above, as well as to processes for the production of lithographic printing plates. Radiation-sensitive layers of the present invention have photosensitivity in the IR range so that recording materials prepared therewith are suitable, for example, for direct image production by the computer-to-plate (CTP) method.
2. Description of the Related Art
The use of dyes and pigments as IR absorbers in radiation-sensitive mixtures is generally known in the art. For example, the recording material according to WO 96/20429 comprises a layer containing IR-absorbing carbon black pigments, 1,2-naphthoquinone-2-diazidosulfonic esters or -carboxylic esters and a phenolic resin. 1,2-naphthoquinone-2-diazidosulfonic acid or -carboxylic acid can also be esterified directly with the hydroxyl groups of the phenol resin. The layer is first exposed uniformly to UV radiation and then imagewise to IR laser beams. As a result of the action of the IR radiation, specific parts of the layer rendered soluble by the UV radiation become insoluble again. This is therefore a negative-working system. The processing of the material is thus relatively complicated.
EP-A 0 784 233 also describes a negative-working mixture which contains a) novolak and/or polyvinylphenol, b) amino compounds for curing the component a), c) a cyanine and/or polymethine dye which absorbs in the near IR range and d) photochemical acid formers.
The non-prior-published patent application DE 197 39 302 describes a positive-working, IR-sensitive mixture which comprises a binder which is insoluble in water but soluble or at least swellable in aqueous alkali and carbon black particles dispersed therein, the carbon black particles being the radiation-sensitive component important for imagewise differentiation.
WO 97/39894 describes layers which contain dissolution-inhibiting additives. Such additives reduce the solubility of the unexposed parts of the layer on development in aqueous alkaline solutions. The additives are, in particular cationic compounds, especially dyes and cationic IR absorbers, such as quinolinecyanine dyes, benzothiazolecyanine dyes or merocyanines, in addition to various pigments. However, if these layers are heated to 50 to 100° C. for from 5 to 20 seconds, the additives lose their dissolution inhibiting activity.
The positive-working mixture disclosed in EP-A 0 823 327 contains, as IR absorbers, cyanine, polymethine, squarylium, croconium, pyrylium or thiopyrylium dyes. Most of these dyes are cationic and have an inhibiting effect. Moreover, many of them are halogen-containing. Under unfavorable conditions, particularly upon IR irradiation or during baking, environmentally harmful decomposition products can form therefrom. Some dyes containing betaine groups and an anionic dye (compound S-9 on page 7) are also disclosed. After drying of the layer, however, due to its large number of sulfonated groups, the presence of this anionic dye generally causes crystallization or precipitation of components of the layer, leading to substantially poorer properties of the IR-sensitive layer and resulting in a poor appearance of the layer.
The disadvantage of the layer compositions known from the art is that the increase in solubility which is achieved by post-bake is reversible after storage at room temperature. If a printing plate is not further processed immediately after heating (for example, by using a heating oven), the development properties change, which may lead to reproduction problems in the processing of the recording materials. As already mentioned, environmentally harmful decomposition products may even form under unfavorable conditions as a result of halogen-containing cationic additives.
SUMMARY OF THE INVENTION
It was one object of the present invention to provide radiation-sensitive mixtures of the type described at the outset which contain neither diazonium compounds nor heat-curable or acid-curable amino compounds nor any silver halide compounds. Apart from an imagewise exposure and development, it is desirable that mixtures of the present invention generally require no additional operation, such as post-bake or postexposure, which was also an object of the present invention.
These and other objects can be achieved by a positive-working, radiation-sensitive mixture which contains an organic polymeric binder which is insoluble in water but soluble or at least swellable in aqueous alkaline solution and at least one IR-absorbing cyanine dye having a betaine structure or having a betaine structure and containing an anion, the cyanine dye having the formula (I)
wherein
R
1
to R
8
independently of one another, comprise a hydrogen or halogen atom, a sulfonate, carboxylate, phosphonate, hydroxyl, (C
1
-C
4
)alkoxy, nitro, amino, (C
1
-C
4
)alkylamino, di-(C
1
-C
4
)alkylamino group or a (C
6
-C
10
)aryl group, which in turn may be substituted by one or more halogen atoms and/or one or more sulfonate, carboxylate, phosphonate, hydroxyl, (C
1
-C
4
)alkoxy, nitro, amino, (C
1
-C
4
)alkylamino and/or di(C
1
-C
4
)alkylamino groups,
R
9
and R
10
independently of one another, comprise a straight-chain or branched (C
1
-C
6
)alkyl, a (C
7
-C
6
)aralkyl or a (C
6
-C
10
)aryl group, each of which in turn may be substituted by one or more halogen atoms and/or one or more sulfonate, carboxylate, phosphonate, hydroxyl, (C
1
-C
4
)alkoxy, nitro, amino, (C
1
-C
4
)alkylamino and/or di(C
1
-C
4
)alkylamino groups,
R
11
and R
12
independently of one another, comprise (C
1
-C
4
)alkyl or (C
6
-C
10
)aryl groups, which in turn may be substituted,
Z
1
and Z
2
independently of one another, comprise a sulfur atom, a di(C
3
-C
4
)alkylmethylene group or an ethene-1,2-diyl group and
A comprises a carbon atom or a chain having conjugated double bonds which results in the formation of a delocalized &pgr;-electron system between the quaternary nitrogen atom of the 3H-indolium, quinolinium or benzothiazolium radical and the enolate oxygen atom of the pyrimidine-2,4,6-trione radical.
Additional objects, features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects, features and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
A chain having the conjugated double bonds is in general 3 to 15 carbon atoms long. A delocalized relectron system in some embodiments usually also extends between the two bicyclic ring systems. Preferred dyes include those having a symmetrical structure, i.e. those in which the (partly) aromatic radicals in the formula (I) are substituted in the same way and in which n=m. They are also generally easier to synthesize.
The (C
1
-C
4
)alkoxy group is preferably a methoxy or ethoxy group, while the (C
7
-C
16
)aralkyl group is preferably a benzyl group. The halogen atoms are generally chlorine, bromine or iodine atoms. R
11
and R
12
are preferably methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, phenyl or naphth-1-yl or naphth-2-yl groups. The two radicals R
11
and R
12
are particularly preferably identical and are also particularly preferably being methyl groups.
The compounds of the formula (I) are referred to as “having a betaine structure” because, in addition to the quaternary nitrogen atom of the 3H-indolium, quinolinium or benzothiazolium ring, they contain the pyrimidine-2,4,6-trione-enolate group shown in the formula. Carboxylate, sulfonate and/or phosphonate groups may also be present, so that the compounds as a

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