Gravure Printing Surface Treatment (1)

I. Preface Gravure is promising for its advantages such as good printing quality, high print-resistance, and long-term imprints. The method of gravure platemaking has been carbon paper, direct screening, electronic engraving, laser engraving and gravure conversion. Although different methods, but with the application of surface treatment process. The continuous improvement and innovation of the surface treatment process will inevitably make up for the shortcomings of the gravure plate production cycle, increase the resistance to printing force, reduce the cost, and provide a strong guarantee for the wide application of the gravure plate.
Second, the surface treatment process plate-making applications 1. Electrodepositing a copper layer of the plate making process Before the copper layer is made, the base roll is deposited with a preplating layer, and the method is not limited. For example, dark nickel plating, cyanide copper plating, and Ballard treatment as required. The quality of the plated copper layer must meet the following requirements: The purity of copper is high and the grains are fine; the surface of the plated layer should be smooth without dents, no stripes, etc.; the coating has sufficient hardness and toughness. For this reason, the mature copper plating methods such as sulfuric acid, copper plating, bismuth borate, and cyanide plating can be selected. According to the consideration of cost and ease of solution management, the sulphate copper plating process is accepted by most organizations. At present, the advanced high-speed acid copper electroplating method has a cathodic current density in the range of 13-20 A/dm2. The hardness of the obtained copper layer is Vickers (210±10) HV, which can meet the requirements of electric engraving. . Of course, it is also applicable to the plate-making process except for laser engraving because they only need Brinell hardness of 60-90 HB. Anodes used in high-speed electroplating consume relatively fast. Based on the requirement of increasing the actual surface area of ​​the anode to prevent anode passivation, the anode is preferably spherical. Copper anodes do not dissolve well, and copper powders easily affect the quality of the copper layer. However, copper anodes containing 0.1% of phosphorus, due to the presence of Cu3P (non-stoichiometric components), are uniformly dissolved and have higher dissolution rates under the same conditions. Sulfuric acid concentration, impurity iron ion, and chloride ion content have a great influence on the quality of the copper layer, and the solution management should be given special attention.
In recent years, the sulfate electroforming copper method, which is one of electrodeposition processes, has been paid attention to and improved by the technicians because of its advantages of quick deposition speed and low cost. Electroforming is the process of electrodeposition on a mandrel and then separating to make or reproduce metal products. The main difference between electroforming and electroplating lies in the different process methods and implementation requirements. The replating of copper by the drum of the barrier layer (Ballard process) is actually the same as that defined by electroforming. Sulfate electroforming copper electrolyte general process:
Copper sulfate 150～300g/l
Sulfuric acid 40～110g/l
Temperature 20°C～50°C
Cathode current density 10 ~ 30A/dm2
The appropriate amount of additive anode and cathode current efficiency is close to 100%.
Electrodeposition of copper to achieve considerable speed and quality requirements, additives are essential. The choice must be specific to the process specification and must not be taken care of.
The copper layer obtained by the process and other reasons may inevitably cause blisters, short scratches and other defects. The remedial measures afterwards include: filling with glue and copper powder; soldering iron solder spot welding or tin-mercury soldering; use a 5-15V rectifying power source to repair the simplest form of the brush plating process. Practice has proved that brush copper plating repair method is the most convenient and reliable. The operation method is as follows: clean the correction area, use the drum as the cathode, lead a wire from the rectifier cathode, and wrap the bare part with cotton, and immerse the plating solution as an anode and wipe lightly back and forth on the area to be corrected until the copper is completely plated. Adjustment of the voltage to prevent scorching of the coating causes the binding force between the brush plating layer and the copper plate making layer to be weak and the work is abandoned. Finally, sanding with water can be used.
2 Hard chrome plating Hard chrome plating has a high hardness and a high degree of wear resistance and chemical stability. To improve the resistance to printing, the hardness of the chromium layer is mainly increased. If the number of imprints reaches 500,000 impressions, the hardness of chromium needs to be 750-950 HV. Although the quality of ordinary hard chromium plating process is stable, the low deposition rate of chromium can not meet the fierce market competition. (To be continued)