Gravure Printing Surface Treatment (2)

Chromium hardness is closely related to temperature, current density, chromic anhydride, and sulfuric acid content. Adding the right amount of additives to hard chrome plating baths is common. It has been reported that the addition of a low-chromium bath containing a rare earth addition penalty increases the current efficiency of high-chromium baths from 60% to 15% of high chromium to 20% to 31%; the deposition rate increases by 600% to 110%; and the hardness increases. 30% to 60% for wear-resistant hard chrome plating. The chromium hardness obtained from chromium plating waves containing organic additives may be higher than normal. Chromium added Liu summed up into 4 categories:
1) Inorganic anionic additives (eg SO42-, F-, etc.)
2) Organic anionic additives (eg carboxylic acids, sulfonic acids, etc.)
3) Rare earth cationic ion additives (such as La3+, Pr3+, etc.)
4) Non-rare earth cations from additives (eg Sr2+Mg2+, etc.)
Research on the addition of rare earths in China is quite active, and some have gone out of the laboratory and applied to production practices. It plays a major role in solving the deficiencies of chrome plating. However, the stability and reliability of quality have also been exposed in trial production. Some manufacturers have weak technical strength, and the plating caused by additives is difficult to interpret with them. Therefore, when selecting additives, we must take the principle of advancement, stability, and economy. Conditions can visit the relevant application manufacturers to understand. There are several domestic plants that produce non-rare earth additives.
Chromium anhydride is expensive and toxic. It is a type of environmental control chemicals. It is particularly important to strengthen solution management. The impurities that affect the chromium layer quality are mainly copper ions and nitrogen ions. The source of copper is mainly the copper dissolution on the surface of the hangers and rollers. If copper exceeds the standard (>8g/l), the chromium layer in the middle of the drum will be black, making the product unusable. Excessive chlorine will make the drum grey. The method for removing impurities in the hard chrome plating bath includes electrolysis and ion exchange using DJ001 macroporous resin in a countercurrent manner. French patent FR 2607489A (1988.6.3) provides a method for recovering chromic anhydride from waste liquor. But for most plate manufacturers, it is always a headache for the scrapping of the chromium solution.
2. The chromium-reporting gravure plate must be checked before it leaves the factory. If there is a quality problem, the drum is usually treated as chromium-removal. Therefore, the chromium removal process, especially the speed of chromium removal, has attracted increasing attention. At present, there are two kinds of de-chroming solutions, one is a hydrochloric acid solution with a volume ratio of 1:1; the other is a sodium hydroxide electrolytic solution with a concentration of 80 g/1, and the current density is 10 to 13 A/dm2. For a 4.5V process. The latter is an improvement of the former. However, the rate of chromium removal of the two is relatively invasive, such as 0.01mm thick chromium layer, the two will take 20 ~ 25min before retiring clean. A desorption process with dilute sulfuric acid and additive has emerged in foreign countries. The desorption time is only 4 min and there is no over-corrosion to meet the need of high efficiency, but the additive is more expensive. Based on the principle of electrochemistry, the author developed an additive that is equivalent to its function. The Hull cell test showed that the hard chrome layer with a thickness of 0.01 mm was removed within 2 to 4 minutes and the copper plate was bright. The LD-D4 digital display depth meter was used to measure the net value of the test piece. There is no change before and after chromium.
3. The surface-modified laser-engraved engraving substrate is a specially formulated epoxy layer. If the number of prints is more than 500,000, the hard-edged plate will be hard-chrome plated. Since the epoxy resin is non-metal and the electroless plating of the hard chromium process is still in the research stage, only the surface modification can hard chromium plating. Electroless copper plating or electroless silver plating is a relatively mature process and the solution composition is simple. Easy to operate. The coating can be used as a conductive layer to meet the current requirements for hard chromium plating.
3. Conclusion Gravure printing is a systematic project. When involved in several disciplines, the surface treatment technology is more complex and has the most potential for development. How to take advantage of new achievements in surface treatment is an important issue before us. (Finish)