JPS5989787A - Chromium plated steel sheet for lithographic printing - Google Patents

Abstract

PURPOSE:To improve the hydrophilic property, water retentivity, rust resistance and printing resistance of the titled steel sheet and to reduce the cost by forming a metallic Cr layer on the roughened surface of a steel sheet and a Cr oxide hydrate layer on the metallic Cr layer and by providing specified surface roughness. CONSTITUTION:The surface of a steel sheet is roughened by mechanical polishing, chemical polishing, electropolishing or other method, and a metallic Cr layer is formed on the roughened surface by electroplating by 70-200mg/m<2>. A Cr oxide hydrate layer is formed on the metallic Cr layer by electrolytic chromating by 8-60mg/m<2> when expressed in terms of Cr. The surface roughness is then regulated to 0.3-2.0mum Ra and 100-800PPI at 0.5mum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a chromium-plated steel sheet having an upper layer of metallic chromium and a lower layer of chromium water-conserving oxide on the rough surface of the steel sheet. This invention relates to a chromium-plated steel plate for planographic printing that has printing durability equivalent to that of planographic printing.

The lithographic plate-making process consists of plate surface pretreatment → photosensitive liquid application → baking →
It consists of development → plate surface post-processing, and the 28th plate (a plate that has been pre-treated and given photosensitivity) is one in which the plate surface is pre-treated and then coated with a photosensitive liquid by a photosensitive material manufacturer. The purpose of surface pretreatment is to improve the adhesion of the photosensitive film, strengthen the printing durability of the image area of the printing plate, and improve the water retention of the non-image area. Lithographic printing is a printing method that takes advantage of the difference in hydrophilicity between printed areas and non-printed areas, and the materials used are galvanized steel plates or aluminum plates, but aluminum is less hydrophilic than zinc. Because it is low in oiliness and highly hydrophilic, sharp lines can be obtained, and the effect can be further improved by anodizing.

At present, aluminum is mainly used as the material for the lithographic CF2 plate. However, due to recent resource conservation, energy conservation, and the rapid rise in the price of non-ferrous metals,
There is an increasing demand for lower prices by guaranteeing surface properties equivalent to those of aluminum.

The present invention is intended to meet such demands, and is intended to provide a ROM-plated steel plate, which is cheaper than aluminum, as a printing plate material. As a printing plate material, in order to obtain sharp lines without printing stains, the non-print areas must be highly hydrophilic, and the dampening water supplied to the non-print areas must retain water to maintain hydrophilicity. You need to be good at sex. In addition, a material with excellent rust resistance is required, which does not cause rust due to dampening water during printing, and does not cause rust during storage before and after plate making, and before and after printing.

On the other hand, if the adhesion between the photosensitive agent in the image area and the holding steel plate material is poor, the printing durability will be reduced. In conventional chrome-plated steel sheets,
The chromium hydrated oxide layer itself on the surface of the steel sheet is highly hydrophilic;
Because it is very active, it is easily contaminated in the air and becomes water repellent over time after production, making it difficult to maintain hydrophilicity.

Therefore, it is necessary to perform a hydrophilic treatment to remove surface contamination before plate making, and since water repellency remains after normal degreasing treatment, a treatment such as permiston polishing must be performed. However,
Such treatment will scrape off the chromate layer on the surface, reducing rust resistance. Furthermore, since the surface of conventional chromium-plated steel sheets is smooth, they have poor adhesion to photosensitizers and water retention of dampening water, resulting in poor printing durability. On the other hand, aluminum plates have excellent hydrophilicity, water retention, rust resistance, and printing durability, but apart from the high material cost, they require pre-plate-making treatment such as anodizing after roughening. I need.

In the present invention, after roughening the steel plate surface by mechanical polishing, chemical polishing, or electrolytic polishing, the steel plate surface is roughened by 70%
A metal chromium layer of ~200%'/m', with a further chromium content of 8~6oη/r1? The present invention provides a chromium-plated steel sheet for lithographic printing, which forms a chromium hydrated oxide layer with a surface roughness of 0.3-2, O11mR&, and a PPI of 100-800 at 0.5pm. This makes it possible to overcome the above-mentioned drawbacks of the prior art.

Hereinafter, the chromium-plated steel plate for lithographic printing of the present invention will be explained in detail.

The chromium-plated steel sheet of the present invention is obtained by roughening the surface of the plated original plate in advance by mechanical polishing, chemical polishing, electrolytic polishing, etc., and then forming a metallic chromium layer on the steel sheet surface and a chromium water-conserving oxide layer thereon. So, the metal chromium layer is 70-20
0■/17? is suitable.

The amount of metallic chromium is 70η/lr? If it is less than 20 (I + r / ffIF), the rust resistance will deteriorate, and if it exceeds 20 (I + r / ffIF), it will be disadvantageous in terms of economic efficiency. 8~60my/rF
? is suitable. If the amount of chromium in the film is less than 8η/i, the hydrophilicity and rust resistance will be poor, and if it exceeds 60η/i, the surface color tone will be poor and correction during plate making will be difficult.

On the other hand, the surface roughness of the steel plate is preferably such that after chromium plating and electrolytic chromic acid treatment, Ra is 0.3 to 2.0 pm and PPI at o, 5 pm is 100 to 800. Ra less than 0.3μm or PPI force 3100
If it is less than 1, the hydrophilicity, water retention, and adhesion between the photosensitive agent and the supporting steel plate are insufficient, and the image area may flow during development, making it impossible to make a plate, or even if it is possible to make a plate, it may become smeared during printing. The printing durability is poor, and the printed areas tend to peel off. Ra is 2
．． If the PPI exceeds 0 μm or PPI 800, the tone reproducibility of the printed matter will be poor compared to the original number when used as a printing plate, and it will also tend to cause mark 811 unevenness, making it impossible to print beautifully. The chromium-plated steel plate for lithographic printing of the invention will be explained with reference to Examples and Comparative Examples.

[Examples 1 to 5] A cold-rolled steel plate with a thickness of 0.22 m was subjected to alkaline electrolytic degreasing treatment (caustic soda 50f/4, 80°C, 5A/, 1ni'', 30
seconds), and then treated under the pretreatment conditions (surface roughening treatment conditions) shown in Table 1. After treatment, rinse thoroughly with water and remove CrO31.
80f/l, H2SO40,6f/Ls NazSI
F46 f/L chrome plating solution, temperature 50℃, current density 30k/1Ltr? Electrolysis is carried out for 2 to 3 seconds at CrO350t/L, HzsO40,5t/
L electrolytic chromic acid treatment solution at a temperature of 40℃ and a current density of 5A/
dd for 2 to 3 seconds to obtain a chromium-plated steel sheet. A photosensitive layer consisting of a diazo resin and a binder was formed on this steel plate to a thickness of 3 μm, imagewise exposed, the exposed portion was removed with an aqueous alkali solution, developed, and rubberized with an aqueous gum arabic solution.

The following various tests were conducted using the planographic plate thus obtained. The test results are shown in Table 1 together with the test results of the comparative examples shown below. The planographic material obtained as described above has a metallic chromium content of 70 to 200πgen? , chromium hydrated oxide film amount 8~60■/7r? , surface roughness Ra 0
．． PPI at 3-2.0 pm, 0.5 pm
was 100 to 800, and it was found that the printability was excellent because it had excellent rust resistance, as well as hydrophilicity, water retention, and adhesion.

<Hydrophilicity> Evaluation was performed by conducting a water wetness test on the test piece before plate making.

○...Water-repellent area ratio 0% Δ...Water-repellent area ratio less than 10% ×...Water-repellent area ratio 10 inches or more <Rust resistance> Rust resistance is determined by dampening water immersion test at the time of printing The rust resistance was evaluated. In the dampening water immersion test, half of the test piece was immersed in dampening water, and the rusting state after 2 days of immersion was evaluated.

○...Rust rate 0% Δ...Rust rate less than 10% ×...Rust rate io* or more <Printing durability> Offset printing was performed using the obtained planographic material, and 50,000 sheets were printed. The printing durability was evaluated. The evaluation method is as follows.

○... Beautiful printing △... There is some dirt on the printing surface, uneven printing ×...
Staining of the printed surface and peeling of the printed area (Measurement of surface roughness) The surface roughness was measured by Ra and PPI at 0.5 μm using a stylus roughness meter.

[Comparative Examples 1 to 4] After treatment under the pretreatment (surface roughening treatment) conditions shown in Table 1, the same chromium plating solution as in the example was used at 50°C and 30 A/dj.
1? , chromium plating treatment was carried out under the conditions of 1 to 4 seconds, and then the same electrolytic chromic acid treatment solution as in the example was used at 40°C for 5 seconds.
A chromium-plated steel plate was prepared by electrolytic chromic acid treatment under the conditions of 0 to 3 seconds at 0 to 3 seconds.The obtained steel plate was subjected to the same tests as in the Examples, and the results are shown in Table 1.

From the results shown in Table 1, the amount of metallic chromium is 570 my
/n? Less than 8 rny/rr of chromium hydrated oxide film
? If it is less than le, the corrosion resistance is poor and the surface roughness le
When a is less than 0.30 μm or more than 2.0 μm, and when the PPI at 0.5 μm is less than 100 or more than 800, the printability is poor (G).

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Claims (1)

[Claims] 70 to 200 f on the steel plate surface that has been roughened in advance
fV/lr? The metal chromium layer and the chromium amount on top of it are 8~60f/rr? A chromium-plated steel plate for lithographic printing, characterized in that it has a chromium hydrated oxide layer of .