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
2002-02-12
2003-12-16
Ashton, Rosemary (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, C430S325000, C430S914000, C430S915000, C430S916000, C430S926000, C430S947000, C522S025000, C522S029000, C522S114000
Reexamination Certificate
active
06664025
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to initiator systems for photosensitive compositions. In particular, this invention relates to a visible radiation sensitive composition comprising a cyanopyridone sensitizer.
BACKGROUND OF THE INVENTION
The use of photoinitiator systems to initiate photopolymerization is well known. When irradiated by actinic radiation, the photoinitiator system generates free radicals, which initiate polymerization of the monomer or monomers. The photoinitiator system may be a single compound that absorbs actinic radiation and forms the initiating radicals or it may consist of several different materials that undergo a complex series of reactions to produce radicals. Components that absorb actinic radiation and increase the efficiency of photoinitiation are known as sensitizers. Components that do not absorb actinic radiation but increase the efficiency of the photoinitiation are known as coinitiators.
Many of the well-known photoinitiator systems limit the applicability of photopolymerizable photosensitive compositions because they are activated only by ultraviolet radiation. The availability of reliable, relatively inexpensive visible lasers, which can be controlled by computer to expose the photopolymer system directly, eliminating the intermediate photomask, has made it desirable to develop photoinitiator systems that can be activated by visible radiation. From an economical point of view, it is also important that the photoinitiator system have high sensitivity to visible radiation so that low-intensity lasers, which are less expensive and more reliable than high-intensity lasers, can be used.
A large number of photoinitiator systems that are activated by visible radiation have been developed. Photoreducible dyes combined with various coinitiators have been widely studied, a useful discussion of which can be found in “Dye Sensitized Photopolymerization” by D. F. Eaton in
Adv. in Photochemistry
, Vol. 13, D. H. Volman, G. S. Hammond, and K. Gollinick, Eds., Wiley-Interscience, New York, 1986, pp. 427-487. However, many dye-sensitized systems undergo dark reactions and are not shelf stable.
Baumann, U.S. Pat. No. 6,051,366, discloses a visible radiation sensitive composition that comprises a binder, one or more polymerizable monomers, one or more dyes having an absorption range in the emission range of the radiation source, a metallocene, and an onium compound. The composition can be exposed by visible lasers and is especially suited for recording materials such as printing plates.
Despite the advances that have been made in visible sensitive photoinitiator systems, there is a continuing need for improved systems that have dark stability, low toxicity, efficient absorption, reasonable cost, and high photospeed.
SUMMARY OF THE INVENTION
In one aspect, the invention is a photosensitive composition. The composition comprises:
at least one ethylenically unsaturated monomer capable of free radical initiated addition polymerization; and
a photoinitiator system comprising a coinitiator and a sensitizer;
in which:
the photoinitiator system is present in an amount sufficient to initiate polymerization of the at least one monomer on exposure to actinic radiation;
the sensitizer has an absorption maximum in the range of 400 nm to 700 nm; and
the sensitizer is a cyanopyridone derivative selected from the group consisting of compounds of Formula I, Formula II, Formula III, Formula IV, and Formula V.
Preferably, the photosensitive composition additionally comprises a binder. Preferably, the coinitiator is a metallocene, more preferably a metallocene that comprises four aromatic ligands and titanium or zirconium as the metal atom. More preferably, the coinitiator comprises the metallocene and an onium salt.
In another aspect, the invention is an imageable element comprising a layer comprising the photosensitive composition and a support. In another aspect, the invention is a method for forming an image useful as a lithographic printing plate by exposing the imageable element with actinic radiation and developing the exposed imageable element. In another aspect, the invention is a lithographic printing plate prepared by exposing the imageable element with actinic radiation and developing the exposed imageable element.
The imageable elements exhibit high photospeed when they are exposed with visible radiation whose wavelength is greater than 400 nm (i.e. 400 nm to 700 nm), high capacity to resolve details (high resolution), and good shelf life. Lithographic printing plates formed from these elements have high durability on press.
DETAILED DESCRIPTION OF THE INVENTION
Unless the context indicates otherwise, in the specification and claims, the terms “monomer,” “binder,” “coinitiator,” “metallocene,” “onium compound,” “sensitizer,” “cyanopyridone derivative,” “coating solvent,” and similar terms also refer to mixtures of such materials. Unless otherwise indicated, percentages are expressed in percentage by weight (wt %).
Photosensitive Compositions
Negative working, photopolymerizable photosensitive compositions comprise at least one ethylenically unsaturated, free radical polymerizable monomer; at least one photoinitiator system; and, optionally and typically, at least one binder. Other ingredients that are conventional components of photopolymerizable photosensitive compositions may also be present. These compositions are generally described, for example, in “Photopolymers: Radiation Curable Imaging Systems,” by B. M. Monroe, in
Radiation Curing: Science and Technology
, S. P. Pappas, Ed., Plenum, New York, 1992, pp. 399-440, and “Polymer Imaging” by A. B. Cohen and P. Walker, in
Imaging Processes and Material
, J. M. Sturge, et al., Eds., Van Nostrand Reinhold, New York, 1989, pp. 226-262.
Photoinitiator System
The composition comprises a photoinitiator system that comprises a coinitiator and a sensitizer. The sensitizer absorbs actinic radiation and causes the system to produce free radicals, which initiate polymerization of the polymerizable monomer.
The sensitizer is a cyanopyridone derivative that has an absorption maximum in the range of 400 nm to 700 nm and has a structure represented by Formula I, Formula II, Formula III, Formula IV, or Formula V:
in which:
R
1
and R
2
are each independently hydrogen, or a substituted or unsubstituted alkyl, aryl or aralkyl group;
X is S or N(R
3
);
Y is O, S, Se, N(R
3
), or C(R
4
)(R
5
),
R
3
, R
4
, and R
5
are each independently a substituted or unsubstituted alkyl, aryl or aralkyl group;
R
6
, R
7
, R
8
, and R
9
are each independently hydrogen, a substituted or unsubstituted saturated or unsaturated alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aralkyl group;
R
10
, R
11
, R
12
, and R
13
are each independently hydrogen, a substituted or unsubstituted saturated or unsaturated alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aralkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted oxy group, or R
10
and R
11
, R
11
, and R
12
, or R
12
and R
13
are joined to form a 5- or 6-membered substituted or unsubstituted ring;
R
14
, R
15
, R
16
, and R
17
are each independently hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, halogen, carbalkoxy, a substituted or unsubstituted amino group, a substituted or unsubstituted oxy group, or R
14
and R
15
, or R
16
and R
17
are joined to form a 5- or 6-membered substituted or unsubstituted ring;
R
18
and R
19
are each independently hydrogen, or a substituted or unsubstituted saturated or unsaturated alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aralkyl group, or R
18
and R
15
and/or R
19
and R
16
are joined to form a 5- or 6-membered substituted or unsubstituted ring, and
Het is a 5- or 6-membered substituted or unsubstituted heterocyclic ring residue.
Where substitution is possible, any of the aliphatic, ar
Baumann Harald
Flugel Michael
Ashton Rosemary
Kodak Polychrome Graphics LLC
RatnerPrestia
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