Specification of Electroplating Process - Chrome Plating Process (4)

3. Experience Introduction Some plate-making companies have summed up an experience in production. After chromium plating and unloading, high-temperature dehydrogenation (H2) method is used, ie 100°C boiling water is used to burn the plate cylinder. The principle is that after the chrome plating, there will be residual hydrogen ions, which can be washed away by high temperature, so that the chrome layer is brighter and smoother, and the blue and white is green, the effect is very satisfactory. If the rinse is not clean, residual hydrogen ions can corrode chromium, which is also a factor that causes chromium to be removed.

4. Precautions There will be chromium liquid on the loading and unloading live support. If the scrubbing is not clean, it will easily adhere to the plated roller. Therefore, it must be cleaned.

(7) Chromium quality standards

1. The surface of the drum is smooth and free from defects such as dechrome, copper, spots and scratches. The chrome layer should be free of burrs, pits, bumps and smooth rims.
2. The thickness of one side of the chromium layer is 10~5μm, and the chromium layer is too thin, which affects the protective performance of the chromium layer; the chromium layer is too thick, which affects the small dot transfer performance due to the tip effect.
3. Chromium hardness: CY/T9~94 is defined as HV800 to HV1000, and production practice has proved that the best is 850HV. Too low a hardness will affect the printing plate's resistance to printing force. Too high a level will cause the "knife" phenomenon in printing. Chromium hardness and printing plate resistance.

4. The hardness of the chromium layer should be uniform.

(8) Electroplating

When I was at a platemaking company, I heard a German expert suggested that after grinding and before electric carving, a special treatment method is adopted: the surface of the copper layer is processed, the conventional mirror requirements are exceeded, and no light is required. Even not Polishing, consciously treating the surface as a "sss" shape, giving it a certain degree of roughness. This not only enhances the bond between copper and chromium, but also enhances the durability of the chromium, making it possible to reduce the wear of the blade considerably. .

According to this view, the company used the back of the 1000# fine sandpaper before the carving to grind the surface of the drum to make the copper surface have a certain roughness, and then carry out engraving and chrome plating. After the printing experiment, the resistance to the printing force was improved and the chromium was removed. The phenomenon has decreased. In addition, in the process of making eroded plates, chromium has never been removed by long-term sanding of the surface. Of course, they also used long-term high-temperature hydrogen removal after chrome plating, that is, the method of boiling hot water to achieve the above effect. This subject needs further study and experimentation.

It is worth noting that the copper surface is treated to have a certain degree of roughness. If it is not well-controlled, it will hang ink when printed.

(9) Chromium removal replating process

After the completion of gravure cylinder production, the chromium layer does not meet the quality standards, or the printing plate wears (but does not harm the copper layer) and the plate cylinder can not continue to use the fault occurs. This requires the chromium replating, common retreat There are the following three plating methods.

1. Sodium hydroxide method

Prepare a sodium hydroxide electrolytic solution with a concentration of 80 g/L. Immerse the plate cylinder in the solution. Rotate the roller slowly and apply electricity. The current density is 10 to 13 A/dm2 and the voltage is 4 to 5 V. It usually takes 30 minutes to remove the chromium layer.

2. Hydrochloric acid method

(1) Warm up the volumetric hydrochloric acid solution with a volume ratio of 1:1 with steam or electric current, and then put it into the plate cylinder. After leaching for more than 10 minutes, the chromium layer can be removed. Speed ​​is the advantage of this method.
(2) Simple method: First, turn the drum with boiling water for 5 minutes, then convert the boiling water and hydrochloric acid into 2 kg of each solution, and then slowly roll the drum to remove chromium.

3. Dilute sulfuric acid and additives

A desorption process with dilute sulfuric acid and additives has emerged in foreign countries. The desorption time is only 4 minutes, and there is no over-corrosion to meet the needs of high-efficiency production, but the additives are more expensive. Mr. Zeng Xianxiong of Nanhai City, Guangdong, China, has developed an additive that is functionally equivalent to the electrochemical principle. Hull cell experiments show that the hard chrome layer with a thickness of 0.01 mm can be removed in 2 to 4 minutes and the copper layer is bright. The TLD-D4 digital display depth meter is used to measure the hardness of the test piece. There is no change before and after chromium removal, it is worth promoting.

Source "Printing Technology"