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
2000-06-21
2003-05-06
Chu, John S. (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
C430S306000
Reexamination Certificate
active
06558870
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a water-washable photosensitive flexo plate superior in image reproducibility.
BACKGROUND OF THE INVENTION
The flexo printing has been conventionally employed in a broad range of use, because it is advantageous in terms of environmental hygiene, it only requires a simple printer and it achieves high productivity, due to the use of water-based ink and alcohol-based ink having low viscosity. When compared to relief printing, lithographic printing, gravure printing and the like, wherein oil-based ink is used, however, the flexo printing shows poor image reproducibility. Therefore, an improvement in the image reproducibility is required for the flexo printing.
A printing plate to be used for the flexo printing is made from a material having rubber elasticity and is characteristically thick, for example, 1 mm-7 mm.
When the printing plate comes into contact with a printing material for the transfer of ink thereon during printing, therefore, the printing plate deforms and the printed images may be enlarged as compared to the original images: the occurrence of so-called dot-gain.
In addition, since a flexo printing plate is thicker than a relief printing plate or a lithographic printing plate, for which oil-based ink is used, the light necessary for forming images cannot permeate sufficiently through to the inside of the plate. This results in poor image reproducibility.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a plate that can make a flexo printing plate superior in image reproducibility and in printability with smaller dot-gain in the flexo printing.
According to the present invention, there has now been provided a photosensitive flexo printing plate having high image reproducibility as achieved by making the dynamic hardness of a surface different from that of an inside of the printing plate, by making the hardness of a dot part different from that of a solid part, or by other means.
To be specific, the present invention provides a water-washable photosensitive flexo plate capable of reproducing images of a level as defined by the halftone resolution of 1% to 95% at 200 lines/inch, a minimum isolated dot having a diameter of 100 &mgr;m, and by a minimum isolated line having a width of 30 &mgr;m.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will become clear by the following description.
The water-washable photosensitive flexo plate of the present invention characteristically reproduces images of the level as defined by a halftone resolution of 1% to 95% at 200 lines/inch, a minimum isolated dot having a diameter of 100 &mgr;m, and by a minimum isolated line having a width of 30 &mgr;m.
Preferably, the water-washable photosensitive flexo plate of the present invention has at least a support base and a photosensitive resin layer, the photosensitive resin layer comprising an ethylenically unsaturated compound and having a sea-island type phase structure consisting of an island component and a sea component, wherein the ethylenically unsaturated compound is contained in a greater amount in the sea component than in the island component.
More preferably, the above-mentioned ethylenically unsaturated compound has a molecular weight of not more than 500.
The photosensitive flexo printing plate having the image reproducibility of the present invention can be obtained by (1) setting the ratio (A)/(B) of the dynamic hardness (A) of the surface of a water-washable photosensitive flexo printing plate and the dynamic hardness (B) of the inside of the printing plate to not less than 1.1; (2) setting, in a water-washable photosensitive flexo printing plate, the ratio (C)/(D) of the dynamic hardness (C) of the surface of dots having a density (proportion of the area occupied by dots per unit area) of not more than 50% and the dynamic hardness (D) of the surface of the solid part having a density of 100% to not less than 1.1; (3) decreasing scattering of light at a wavelength necessary for forming images; or by other method.
The water-washable photosensitive flexo plate of the present invention preferably consists of at least a support base and a photosensitive resin layer. The support base usable for the plate of the present invention is not particularly limited, and is exemplified by a polyester film, preferably a polyethylene terephthalate film. The support base has a thickness of preferably 10 &mgr;m-500 &mgr;m, more preferably 50 &mgr;m -400 &mgr;m. The photosensitive resin layer usable for the plate of the present invention can be made from a photosensitive resin composition. The photosensitive resin layer has a thickness of preferably 50 &mgr;m-20000 &mgr;m, more preferably 100 &mgr;m-1000 &mgr;m.
By the water-washable photosensitive flexo printing plate of the present invention is meant the above-mentioned flexo plate after exposure and development to remove non-imaged parts.
In the above-mentioned (1), the dynamic hardness of the surface of the printing plate is that measured for the part of from the outermost surface of the printing plate to the depth of 0-10 &mgr;m, and the dynamic hardness of the inside of the printing plate is that measured for the part having a depth of not less than 11 &mgr;m from the outermost surface of the printing plate. In the above-mentioned (2), the dynamic hardness of the surface of dots having a density of not more than 50% is that measured for the part of from the outermost surface of the dots having a density of not more than 50% to the depth of 0-10 &mgr;m, and the dynamic hardness of the surface of the solid part having a density of 100% is that measured for the part of from the outermost surface of the solid part having a density of 100% to the depth of 0-10 &mgr;m. The dynamic hardness is measured using the dynamic ultra-microhardness tester DUH201 (SHIMADZU CORPORATION) that provides information of strength of the surface of a specimen, as described in SHIMADZU REVIEW, Vol. 50. No. 3 (1993. 12) 321.
In the above-mentioned (1), when the ratio (A)/(B) of the dynamic hardness (A) of the surface of a water-washable photosensitive flexo printing plate and the dynamic hardness (B) of the inside of the printing plate is not less than 1.1, the surface of the printing plate has a higher hardness than in the inside, and does not permit deformation because the difference in the hardness produces a cushioning effect. Consequently, ink is transferred to a printing material, faithfully reproducing the shape of the printing plate and minimizing the dot-gain peculiar to the flexo printing, while providing a sharp print. The preferable range of the above-mentioned ratio (A)/(B) is 1.1-50.0, more preferably 1.1-30.0. When this ratio (A)/(B) of the dynamic hardness is less than 1.1, the aforementioned cushioning effect becomes void, and the surface of a printing plate deforms during printing to produce large dot-gain, unpreferably impairing sharp details of printed images.
In the above-mentioned (1), the ratio (A)/(B) of the dynamic hardness (A) of the surface of a water-washable photosensitive flexo printing plate and the dynamic hardness (B) of the inside of the printing plate can be set to not less than 1.1 by, for example, but not limited to, changing the crosslinking density of a photosensitive resin composition constituting the photosensitive resin layer, between the surface and the inside of the printing plate.
One method of changing the crosslinking density of the surface and the inside of a printing plate comprises employing a phase structure, which shows the distribution state of a photosensitive resin composition, of a sea-island type phase separation structure consisting of a sea component and an island component, and utilizing a difference in the solubility of crosslinkable components in the respective sea and island components, thereby creating a difference in the hardness.
In the above-mentioned (2), when the ratio (C)/(D) of the dynamic hardness (C) of the surface of the dots and the dynamic hardness (D) of the surface of the s
Kawahara Keizo
Okazaki Yasuyuki
Satomi Hiroshi
Wada Tohru
Chu John S.
Toyo Boseki Kabushiki Kaisha
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