Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – To produce printing surface
Reexamination Certificate
2000-01-28
2001-05-29
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
To produce printing surface
C430S302000
Reexamination Certificate
active
06238831
ABSTRACT:
The invention relates to photosensitive coating compositions, processes for the preparation of a printing plate using these coating compositions, and printing plates prepared in this way. In particular, the invention relates to printing plates with high print run stability, the photosensitive layer of which contains homogeneously distributed polymer particles.
In recent times, the requirements with regard to the print run stability of offset printing plates have increased. For the improvement of the mechanical properties of offset plates, basically two methods have been discussed.
One of them relates to the improvement of the properties of the binders or the photosensitive composition (U.S. Pat. No. 4,102,686). This method often entails high costs due to the complexity of the synthesis regarding the preparation of such custom high-performance binders.
The other, less expensive method is the introduction of polymer particles into the photosensitive layer. The mechanical resistance of such particle-containing layers is often superior to that of layers with modified binders. Apart from the increase of the mechanical resistance of the layer, there are further advantages: From the literature it is known that the chemical resistance can be increased while the exhausting times in the copying frame and the adhesiveness can be reduced. So far, various methods have been employed for introducing the polymer particles into the layer.
Commercially available micronized particles which are difficult to dissolve in common organic solvents (for example polyethylene, polytetrafluoroethylene, cross-linked polymethylmethacrylate or polyamide) are dispersed and added to the coating solution. This entails the disadvantage that these polymer particles first have to be dispersed which constitutes an additional process step. In some areas, the particles are often distributed rather inhomogeneously after the coating has been completed. Furthermore, in particles consisting of nonpolar polymers the adhesion to the layer is reduced. The retention time of the coating solution prepared is limited as well since these dispersions tend to form sediments or agglomerates. Furthermore, the particle dispersions cause problems in the filtering of the coating solution since the pore size of the filter cannot be smaller than the particle diameter. Starting solutions which have not been sufficiently filtered often lead to coating defects.
Another method is to prepare dispersions or emulsions of polymers by emulsion/dispersion polymerization, for example in copolymers of acrylates, styrene derivatives and other monomers, or by precipitation reaction of polymers which dissolve in common organic solvents, for example acrylonitrile butadiene styrenes (ABS) which are then added to the coating solution (U.S. Pat. No. 4,233,390, EP-A-0 709 399, U.S. Pat. No. 5,616,449, EP-A-0 632 328, EP-B-0 509 523).
Thus, due to the higher polarity of the polymer particles, an improved adhesion of the particles to the layer is achieved, but the above-mentioned disadvantages such as poor filterability, locally inhomogeneous distribution in the layer, and short stability of the batch remain.
Another process describes, with regard to positive working printing plates, the use of specifically developed polymers which are soluble in alkaline developers and organic media and which form a homogenous solution with the coating composition. By way of complicated drying apparatuses difficult to operate with regard to the process control, a separation of the binders intended for the positive plates and the polymers during drying is achieved (EP-A-0 766 140). This coating solution can be filtered since a “real” solution is present. A disadvantage of this method is that the particles are preferably formed in the upper part of the photosensitive layer, with the lower part of the layer not being protected from mechanical abrasion. Furthermore, both the drying apparatus and the polymers which form the particles, have to be specifically adapted to this purpose of use, which constitutes a high cost factor. A further disadvantage of this method is that the resulting polymer particles, which are soluble in the developer, can partly be extracted from the layer by the developing step and that the remaining cavities rather destabilize the image areas.
In spite of the intensive research in the field of offset printing plates with high print run stability, the present solution approaches still call for improvements, particularly with respect to easier producibility and less expensive materials.
Therefore, it is the object of the invention to provide coating solutions which provide printing plates, particularly offset printing plates, with high print run stability without having to accept the above-mentioned disadvantages. Additionally, the printing plate is supposed to be developable by means of conventional developers and has to exhibit high resolutions. Furthermore, the ink acceptance of the printing plate is supposed to be fast and good. Moreover, a sufficient resistance to the common purification chemicals such as benzine-based rubber blanket detergents, plate detergents etc. should be provided.
This object is solved by a coating solution, comprising
a) a positive or negative working, or electrophotographically working photosensitive composition,
b) a thermoplastic polymer which is soluble in organic media but insoluble in alkaline media,
c) a solvent component A which dissolves both the photosensitive composition and the thermoplastic polymer, and optionally
d) a solvent component B which dissolves the photosensitive composition but not the thermoplastic polymer and which is less volatile than component A,
with a) and b) being homogeneously dissolved in the mixture of c) and d).
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patent: 5700619 (1997-12-01), Baumann et al.
patent: 6060217 (2000-05-01), Nguyen et al.
patent: 9524851 (1997-01-01), None
patent: 0766140 (1997-04-01), None
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patent: WO9911458 (1999-03-01), None
Hauck Gerhard
Jarek Mathias
Kesselman Jerome
Pappas Socrates Peter
Baker & Botts L.L.P.
Goodrow John
Kodak Polychrome Graphics LLC
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