Printing – Planographic – Lithographic printing plates
Reexamination Certificate
2001-06-15
2003-05-20
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic printing plates
Reexamination Certificate
active
06564712
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a material for producing a lithographic plate (also referred to as a “printing plate” hereinafter) by the hot-melt transfer recording method utilizing a hot-melt transfer recording medium (ink ribbon).
Recently, there have been proposed plate making methods in which image signals from computers are directly output on a printing plate material by using a digital outputting machine equipped with a thermal head or infrared semiconductor laser, without outputting the image signals onto a photographic paper or lithographic film. As one of such direct plate making methods, a plate making method based on the hot-melt transfer recording method utilizing a hot-melt transfer recording medium (ink ribbon) is disclosed in Japanese Patent Laid-open Publication (Kokai) No. 10-16420.
In the hot-melt transfer using an ink ribbon, if the transfer and fixation of the ink layer are not sufficient, problems occur due to insufficient printing durability of the printing plate, such as white omissions in solid image portions and omission of small dots or fine lines, when a lithographic plate material is used for plate making and then printing with that plate. Therefore, it is desirable that lithographic plate materials have good transfer and fixation of the ink from the ink layer of ink ribbon. However, surfaces of lithographic plate materials are generally made to have a certain degree of unevenness in order to impart water retention, and such unevenness may be a cause for the degradation of ink transfer of the ink layer of an ink ribbon. Moreover, when there is used a material having a surface preliminarily subjected to a hydrophilization treatment to eliminate the necessity of desensitization after plate making (referred to as a material of “non-etch type” hereinafter), the fixation of ink from the ink ribbon is reduced, and there remains the aforementioned problem of poor printing performance.
On the other hand, ink ribbons with a very thin ink layer have come to be used as ink ribbons in the hot-melt transfer recording method in order to attain printing with high resolution. And it is believed that, also in the plate making method utilizing the hot-melt transfer recording, printed matter of high resolution can be obtained by using such an ink ribbon having a very thin ink layer.
However, if such an ink ribbon having an extremely thin ink layer is used for the transfer onto a lithographic plate material having an uneven surface, as described above, the problem of poorer transfer results, that is, protrusions penetrate the ink layer, thus causing white omissions in solid image portions of the printed matter. Further, the protrusions in the non-image portions scrape the ink layer surface to cause scumming of the printed matter, and hence good printed images cannot be obtained.
In particular, the above-mentioned problem observed in image portions is particularly serious in the non-etch type material which includes a thermosetting water-soluble resin as a binder of the image-receptive layer. It is considered that this is because the uneven surface of the thermosetting water-soluble resin is scarcely flattened by heat and pressure of a thermal head used for the transfer of ink layer, although an uneven surface of a thermoplastic resin material may be flattened to a certain extent by heat and pressure.
Therefore, an object of the present invention is to provide a lithographic plate material that shows good ink layer transfer and excellent ink layer fixation and hence enables production of a printing plate having excellent printing durability even if an ink ribbon having a very thin ink layer is used. Another object of the present invention is to provide a lithographic plate material that shows excellent water retention, does not require desensitization treatment after plate making, and shows excellent fixation of the ink of the ink layer.
SUMMARY OF THE INVENTION
In order to achieve the aforementioned objects, the inventors of the present invention studied the surface conditions of lithographic plate materials. As a result, they found that, while the water retention showed correlation with arithmetical mean deviation Ra, which is a generally used parameter for surface roughness, and good water retention could be obtained in a certain range of arithmetical mean deviation Ra, depending on the material constituting the image-receptive layer, the mean surface roughness Ra was not necessarily reflected in quality of the transfer of ink from the ink ribbon, but it showed correlation with 10-point height of irregularities Rz, and good transfer and fixation could be obtained and water retention could also be secured within a certain range of 10-point height of irregularities Rz.
Specifically, the lithographic plate material of the present invention is a lithographic plate material having an image-receptive layer for hot-melt transfer recording formed on a support, the image-receptive layer having water retention or capable of being imparted with water retention, wherein the image-receptive layer has surface roughness (JIS-B0601-1994) of 0.15 &mgr;m or more in terms of arithmetical mean deviation Ra and 1.00-3.00 &mgr;m in terms of 10-point height of irregularities Rz.
In the lithographic plate material of the present invention, the image-receptive layer may contain a hydrophilic polymer binder and a surface roughening agent having an average particle diameter of 1.5-2.5 &mgr;m. Further, in the lithographic plate material of the present invention, the hydrophilic polymer binder may be a crosslinked hydrophilic polymer compound.
In the lithographic plate material of the present invention, the surface roughness of the image-receptive layer, in particular, the 10-point height of irregularities Rz, is selected to be within a specific range. This makes it possible to secure water retention for the surface, and to provide excellent transfer and fixation of the hot-melt transfer recording medium (ink ribbon). Thus, there can be obtained a printing plate showing excellent printing durability. In particular, it shows excellent transfer of ink from the ink layer of ink ribbon even when the ink layer is of a small thickness, and therefore it can provide a lithographic plate that provides printed images of high resolution.
PREFERRED EMBODIMENT OF THE INVENTION
The lithographic plate material of the present invention has a structure comprising a support and an image-receptive layer formed on the support, which enables hot-melt transfer recording utilizing an ink ribbon.
The support may be a plastic film composed of a resin such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyethylene terephthalate, waterproof paper having such a plastic film laminated thereon or waterproof paper coated with such a resin.
A polyethylene terephthalate film is particularly preferred in view of its mechanical strength, dimensional stability, resistance to chemicals and water resistance. The support may be a film made of a resin mixed with a light-shielding pigment such as carbon black and titanium oxide in order to impart light-shielding. While the thickness of the support it not particularly limited, it is generally 50 &mgr;m to 300 &mgr;m.
In order to improve adhesion to the image-receptive layer, the support may be subjected to a plasma treatment, corona discharge treatment or far ultraviolet ray exposure. As a technique to give easy adhesion between the support and the image-receptive layer, an undercoat layer may be provided.
The undercoat layer is preferably composed of a resin showing good adhesion to both the support and the image-receptive layer. Therefore, the resin of the undercoat layer may differ depending on the nature of the resins used for the support and the image-receptive layer. Examples thereof include polymers and copolymers of vinyl acetate, vinyl chloride, styrene, butadiene, acrylic esters, methacrylic esters, ethylene, acrylonitrile and so forth, water-insoluble polymers such as polyester resins, polyurethane resins, alkyd resins and epo
Katsuoka Toshimichi
Nouda Junichi
Sato Hironori
Funk Stephen R.
Kimoto & Co., Ltd.
Lorusso, Loud & Kelly
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