JPS5926479B2 - Positive photosensitive lithographic printing plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positive photosensitive lithographic printing plate having a photosensitive layer coated on an aluminum support. A lithographic printing plate is obtained and effective.

This invention relates to a highly sensitive positive photosensitive lithographic printing plate. Lithographic printing is a printing method that takes advantage of the essentially immiscible nature of water and oil.

The printing plate surface has areas that accept water and repel oil-based ink; The former is the non-image area, and the latter is the image area, as opposed to the area that repels and receives the oil-based ink. Aluminum supports used in lithographic printing plates are required to have excellent hydrophilicity, storage stability, and adhesion. For this reason, the surface of aluminum is roughened (grained) by adding fine irregularities to the surface by mechanical, chemical, or electrochemical methods. However, in this case, increasing the depth of the grain improves water retention, but if the depth is increased beyond a certain level, the sensitivity decreases and a residual film tends to remain, which may result in "staining" during printing. Until now, no patents have been found that describe a method for solving this problem. An object of the present invention is to improve the above-mentioned conventional drawbacks, to produce a lithographic printing plate with good water retention, and to obtain a Hong-type photosensitive lithographic printing plate with high effective sensitivity.

In order to achieve the above object, the inventors of the present invention conducted intensive studies and determined that the centerline average surface roughness of the grains (hereinafter abbreviated as Ha) was 0.6.
It has been discovered that a positive-working photosensitive lithographic printing plate, in which a positive-working photosensitive layer is coated on a white aluminum support with a μ~1.2μ and a surface reflectance of 50% or more, is suitable for this purpose. .

In the present invention, an aluminum plate or an aluminum alloy plate containing aluminum as a main component and containing zinc, magnesium, iron, etc. is used. Methods for imparting grain with the above-mentioned surface roughness to the surface of such an aluminum plate include mechanical methods such as ball polishing and brushing polishing, chemical methods, and electrical methods. Methods such as chemical methods and combinations thereof may be used. Among these methods, the surface of the aluminum plate is electrochemically corroded using hydrochloric acid, nitric acid, or an electrolytic solution based on these, which can deepen the grain to a certain extent and also create a uniform grain. Electrolytic surface processing methods are advantageous. This method is suitable not only for treating aluminum sheets, but also for continuously treating aluminum rolls, and has been attracting attention in recent years. This electrolytic assembling treatment method uses hydrochloric acid, nitric acid, or an electrolytic solution mainly composed of these, and uses an appropriate electrolytic plate such as a graphite plate as a counter electrode in an electrolytic cell to electrolytically process an aluminum plate by alternating current electrolysis. I'm going. According to this method, the depth of the grains can be controlled by controlling the electrolytic conditions. The grained aluminum plate is further anodized if necessary.

As a method for anodic oxidation, a well-known method using an electrolytic solution of sulfuric acid, oxalic acid, phosphoric acid, or an appropriate mixture of these has been used. However, if the roughness of the grain is less than 0.6 μm, the water retention property is insufficient, and when the amount of ink is increased on a lithographic printing machine, some of the shadows are easily tangled and are easily smudged.

When the roughness of the grain is set to Ha=0.6μ or more, water retention improves, but the sensitivity of the photosensitive printing plate decreases.

When the roughness of the grain is Ha: 1.2μ or more, residual film tends to occur, and even if the water retention property is improved, the photosensitive film remains, making it easy to stain. Further, there were problems such as a large decrease in sensitivity and a decrease in ink adhesion to the image area. However, it was confirmed that by increasing the surface reflectance of the aluminum support, even if the grain roughness was increased to 0.6 μm or more, the effective sensitivity in terms of tone reproduction of halftone dots did not decrease.

That is, an aluminum plate is grained using a method such as an electrolytic surface roughening treatment, and the depth of the grain is set to Ha: 0.6μ to 1.

2μ, and the reflectance of the support before coating the photosensitive layer is 50
% or more, it was found that a lithographic printing plate with good water retention and a positive working photosensitive lithographic printing plate with high effective sensitivity could be obtained.

As a method of whitening the support (increasing the reflectance), after graining, etching is performed with a basic or acidic aluminum etching solution, as described in Japanese Patent Publication No. 51-33444. There are a method of etching with a basic or acidic aluminum etching solution before anodizing, and an electrolytic treatment method as described in Japanese Patent Publication No. 51-6571.

An o-quinonediazide type photosensitive material is often used as the positive photosensitive layer coated on the aluminum support prepared as described above.

It is already known that the photosensitive material contains the following structural unit as a photosensitive group in its molecule and is decomposed by an active light source to form an alkali-soluble group. C.O. S'1iSLieb
igsAnna1enderChemieVol.55665
(1944)] The positive-working photosensitive lithographic printing plate is o-
A quinonediazide type photosensitive material is applied alone or mixed with an alkali-soluble resin to a support such as Dojo.

When this photosensitive planographic printing plate is exposed to actinic light through a transparent positive image, the O-quinonediazide type photosensitive material in the exposed area decomposes and becomes soluble in an aqueous alkaline solution.If treated with a developer consisting of an aqueous alkaline solution, This part is easily removed and gives a positive image. Positive-working photosensitive lithographic printing plates are often used for color printing.

Color printed matter is required to have well-opened halftone dots in the middle to dark areas and good reproducibility in illumination areas. If the depth Δ of the grain is greater than 0.6μ Ha2, the sensitivity will decrease, and unless the exposure amount is increased, the tone reproducibility Δ will not be as good as that of conventional products.

In order to increase the exposure amount, it is not preferable to increase the exposure time from the viewpoint of workability. The present invention has solved this problem by increasing the reflectance of such a support with deep grain roughness. Next, the present invention will be explained in more detail based on examples.
Example 1 Purity 99.

After degreasing and washing a 5% aluminum plate with an aqueous sodium hydroxide solution, the surface was electrolytically roughened using a hydrochloric acid electrolyte with a concentration of 1% by weight at a temperature of 20°C and a current density of 17A/Dnl2 by changing the electrolysis time and using a sine wave or alternating waveform current. oxidation treatment was performed.

The aluminum plate was treated with 30% sulfuric acid at 80° C. for different times. Next, this plate was subjected to a direct current anodizing treatment using 15% sulfuric acid as an electrolytic bath, and then washed with water and dried. The centerline surface roughness Ha of this plate was measured using a surface roughness meter SURFCOM (needle diameter 5 μm). A Ha value of 0.5 to 1.25 μm was obtained.

Also, the reflection density was measured using a Maghes reflection densitometer, but it was D-0.
26 to 0.4 (39 in reflectance.

9% to 54.

5%) was obtained.

This product includes 1 part by weight of naphthoquinone-1,2-diazide-5-sulfonic acid ester of polyhydroxyphenyl obtained by polycondensation of acetone and pyrogallol as described in Japanese Patent Publication No. 43-28403, and novolac type phenol formaldehyde. A photosensitive solution was prepared by dissolving the resin in 2 parts by weight of 2-methoxyethyl acetate and 20 parts by weight of methyl ethyl ketone and coating. This material is dried, printed using a PS light manufactured by Fuji Photo Film Co., Ltd., through film charts with different halftone dot areas, and clay scale manufactured by Fuji Photo Film Co., Ltd., with varying exposure amounts, and then developed using the usual method. did. This plate was coated with PI ink manufactured by Fuji Photo Film Co., Ltd., and the number of clay scale clear steps and halftone dot area were measured. The halftone dot area was measured using a Viewback halftone dot area meter. The printing plates treated in this manner were printed on art paper using an Idelberg KORD printing machine, the ink-water balance was varied, and the degree of staining on the printed matter was observed. Further, staining of the blanket under normal conditions was also observed, and the results shown in Table 1 were obtained. From this result, H
If a = 0.6μ to 1.2μ, there is less dirt and the ink water balance is wide (good water retention), and if the surface reflectance is 50 (:!) or more, it will be possible to print points without increasing the exposure amount. It shows a tendency to slip, indicating that the effective sensitivity is high.

Claims (1)

[Claims] 1. In a photosensitive lithographic printing plate having a photosensitive layer formed on an aluminum support, the surface of the support has a grain with a centerline average surface roughness (Ha) of 0.6 to 1.2μ. A positive-working photosensitive lithographic printing plate having a surface reflectance of 50% or more.