Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-08-03
2002-04-23
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S049700
Reexamination Certificate
active
06376144
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a photoconductive composition useful for the preparation of printing plates. In particular, the invention relates to a composition comprising an organic photoconductor, a charge carrier generating material, and polymeric binders, to a printing plate precursor comprising the photoconductive composition, and to a method for imaging the printing plate precursor.
BACKGROUND OF THE INVENTION
Printing plate precursors, especially lithographic printing plate precursors, can be obtained by applying a photosensitive coating to a substrate. The precursor is imagewise exposed to radiation, such as ultraviolet light or infrared radiation, and developed with an alkaline developer in order to obtain an imaged printing plate. Depending on whether the exposed areas are removed from or remain on the plate during developing, such plates are called positive-working plates and negative-working plates, respectively. The different solubility of exposed and unexposed areas in the developer is due to a photoreaction of the photosensitive layer during exposure to ultraviolet or infrared radiation.
Besides such kinds of printing plate precursors, there exist also electrophotographic systems. The process for imaging such plates includes the following steps:(1) corona charging, (2) imagewise exposure to radiation and thereby discharging of the exposed parts, (3) applying a dry or liquid toner thereto, (4) fixing the toner by heating and (5) removing the non-image areas by a stripper. Photoconductive materials for such electrophotographic printing plate systems are well known in the art. They are also used for the production of printed circuits.
Electrophotographic plates must meet the following general requirements:
(1) The charging of the plate should be high.
(2) The dark decay should be as low as possible.
(3) The photodecay of the charged plate should be high.
(4) There should be a fast developability and—if any—only a low change of developability after thermal treatment for toner fixing.
(5) The adhesion of the toner should be high.
(6) Only a low amount of sludge should be formed in the developing machines.
Whether these requirements are met and to which extent mainly depends on the polymeric binder used in the photoconductive layer. Therefore, research in this field has concentrated on the development of suitable binders.
Elsaesser, U.S. Pat. No. 5,744,272, discloses a photoconductive composition for lithographic printing plates that comprises an organic photoconductor, a sensitizer and a binder. The binder comprises a mixture of (a) a copolymer comprising units composed of a first vinyl aromatic compound (e.g., styrene) and units composed of maleic anhydride and/or a maleic partial ester, and (b) a copolymer comprising units composed of a second vinyl aromatic compound (e.g. styrene) and units of (meth)acrylic acid. Electrophotographic plates obtained from such a composition, however, show an insufficient developer capacity.
The photoconductive compositions disclosed in EP-A-0 420 002 [Mueller-Hess, U.S. Pat. No. 5,126,504] comprise a graft polymer with polyurethane being the graft basis to which vinyl alcohol units are grafted; the hydroxyl groups of the vinyl alcohol are carboxylated by maleic acid anhydride. Although such a recording material shows good properties there is the disadvantage that the synthesis of the binder is very complex and, therefore, is relatively expensive to manufacture.
EP-A-0 324 180 [Lind, U.S. Pat. No. 4,933,248] provides a photoconductive composition comprising an organic photoconductor, a sensitizer and an optionally substituted polyvinyl phenol resin as binder. Besides homopolymers, copolymers of vinylphenols and other vinyl compounds such as styrene or acrylic acid esters can be used. In addition to the vinyl phenol binder, additional binders can be used that may, for instance, be selected from copolymers of styrene and maleic acid anhydride and their partial esters, polyvinylacetates, polyacrylates, and the like. However, the developability in aqueous developers (“strippers”) of a printing form obtained from such a composition is insufficient. The developer has to be strong alkaline, which makes it very sensitive to carbon dioxide from the air.
Another electrophotographic recording material is disclosed in EP-B- 0 089 603. The photoconductive layer thereof comprises, besides a photoconductor, a sensitizer and optional other additives, a polymeric binder which is the reaction product of a sulfonyl isocyanate and a hydroxyl containing polymer like a vinyl alcohol copolymer (e.g. polyvinyl butyral), a polyester and a cellulose ester. Like the material of EP-A-0 324 180, this material shows an insufficient developability and requires a strong alkaline developer.
Therefore, a need exits for a photoconductive composition useful for the preparation of printing plates and printed circuits, which produces electrophotographic recording materials meeting requirements (1) to (6), but which does not require an expensive binder, has sufficient developability, and does not require a strong alkaline developer.
SUMMARY OF THE INVENTION
In one embodiment the invention is a photoconductive composition comprising:
(1) at least one organic photoconductor;
(2) at least one charge carrier generating material; and
(3) a binder comprising:
(a) at least one copolmyer comprising an aromatic vinyl monomer and maleic acid anhydride ring opened by a first aliphatic alcohol, and
(b) at least one copolymer comprising the following monomers:
(i) CH
2
═CH—(CH
2
)
n
—OR, in which n is 0 or 1, and R is selected from the group consisting of hydrogen, aliphatic groups having 1 to about 10 carbon atoms, and —COR′ in which R′ is an aliphatic group having 1 to about 10 carbon atoms, and
(ii) maleic acid anhydride ring opened by a second aliphatic alcohol.
In one embodiment, copolymer (b) additionally comprises monomer (iii): CH
2
═CH—R″, in which R″ is a substituted or unsubstituted aromatic residue comprising from about 6 to about 20 ring atoms, the ring atoms selected from the group consisting of carbon, oxygen, nitrogen, and sulfur, in which not more than 3 ring atoms are selected from the group consisting of oxygen, nitrogen and sulfur.
In another embodiment, the invention is an electrophotographic recording element that comprises a substrate and a photoconductive layer comprising the photoconductive composition. In still another embodiment, the invention is a method for forming an image, typically an imaged and developed printing plate, using the electrophotographic recording element.
DETAILED DESCRIPTION OF THE INVENTION
When used in this application, the term “alkyl” includes straight chain, branched and cyclic alkyl groups unless defined otherwise; the same applies to alkyl moieties of alkoxy groups.
The photoconductive composition comprises at least one organic photoconductor. Suitable organic photoconductors are, for example, compounds based on aromatic rings or aromatic heterocycles, which may have one or more substituents, preferably basic amino groups. Such photoconductors are described, for example, in Neugebauer, U.S. Pat. No. 3,189,447; Sus, U.S. Pat. No. 3,257,203; DE-A-29 49 826 [CA 1,146,794]; and EP-A-0 125 481 [Lind, U.S. Pat. No. 4,528,256]. More preferably, the organic photoconductors are derived from oxadiazoles or oxazoles, triphenylamines, triphenylmethans, more highly condensed aromatic hydrocarbons such as anthracene, benzofused heterocycles, pyrazolines, hydrazones, imidazoles or triazoles. Most preferred are oxadiazoles, oxazoles, aromatic hydrazones, pyrazolines and triarylamines. The photoconductors may be used individually or as mixtures. The proportion of organic photoconductor is preferably about 14 to about 75% by weight, based on the total weight of the nonvolatile constituents of the photoconductive composition, more preferably about 25 to about 50% by weight.
A further essential component is the charge carrier generating material (also called a
Kodak Polychrome Graphics LLC
Ratner & Prestia
Rodee Christopher
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