Copper plating process for gravure printing plates: standard grinding and polishing process

To achieve the best smoothness, the plate cylinder must undergo fine grinding and polishing. Therefore, standardizing the grinding and polishing process is very important.

(1) The standard grinding process should be based on the equipment conditions of the company. For example:

(a) Some large plate-making companies with high product grades use the Swiss-made MDC polishmaster lathe grinding machine. The processed plate cylinders have particularly precise concentricity, with geometric accuracy errors of less than 0.005mm; the surface finish of the plate cylinders reaches a mirror-like brightness; and they fully meet printing suitability. To obtain high-quality plate cylinders, four standardized process flows should be established based on the condition of the lathe grinding machine.

① New lathe grinding machine: cylinder copper layer → lathe grinding processing → electro-engraving.

② Lathe grinding machine used for a few years: cylinder copper layer → lathe grinding processing → polishing → electro-engraving.

③ Lathe grinding machine used for several more years: cylinder copper layer → lathe grinding processing → 3000# fine grinding → polishing → electro-engraving.

④ Old lathe grinding machine: cylinder copper layer → 800# rough grinding → 3000# fine grinding → polishing → electro-engraving.

(b) Some plate-making companies have many electro-engraving machines and higher product grades, using MDC lathe polishing machines for lathe grinding and polishing → electro-engraving, which is particularly fast.

(d) Some plate-making companies have more electro-engraving machines but lower product grades. To reduce equipment investment, the standardized process flow is: cylinder copper layer → external cylindrical grinding machine → 800# rough grinding → 3000# fine grinding → polishing → electro-engraving.

(e) Some plate-making companies, in order to achieve good grinding quality, standardize the process as follows:320# grinding wheelfor rough grinding, leaving a grinding amount of 0.03mm, then switch to800# grinding wheelto grind off 0.02mm, then switch to2000# grinding wheel, and finally switch to3000# grinding wheel for fine grinding, grinding three passes. The downside of this process is that the grinding time is relatively long. Additionally, some plate-making companies have summarized an experience, which is to pay attention to a technical detail, such as usingslowing down the grinding stone speed, reducing the grinding stone pressure, and increasing the plate cylinder rotation speed during the last two passes of grinding to reduce surface residues from the 800# grinding wheel and increase surface smoothness, which has a good effect.800# grinding wheel(f) Standardized rough grinding

① Rough grinding with 800# grinding wheel should be done for two passes.

② During rough grinding,

the grinding wheelmust not vibrate, and fine grinding must be carried out afterward.(g) Standardized fine grinding

① Grinding precision is very important, and the key is the selection of the 3000# grinding wheel,

it is recommended to use the yellow 3000# grinding wheel from Maituo Company.② During fine grinding, it is essential to be careful and serious to prevent defects such as grinding marks, cross lines, and burrs, and to avoid injection marks.

(8)

The grinding stone speed should be an integer multiple of the plate roller speed, and the moving speed should be 0.8-1.5mm/revolution, adjusting suitable parameters based on the quality of the grinding machine and the size of the plate roller. (ConsultMaituoCompany for technical support)(h) Standardized increment for plate cylinders: Based on the printing color sequence and the different substrates, the standardized parameters are as follows:

① The increment for small diameter plate cylinders is 0.02mm;

② The increment for plate cylinders used for printing paper is 0.02mm;

③ The increment for plate cylinders used for printing OPP film, PE film, and other films is 0.03 to 0.05mm. Ensure that there is no reverse increment to guarantee precise printing registration.

(2) The standardized polishing process is carried out using a polishing machine.

(a) When not polishing, the current is around 10A.

(b) The selection of polishing paste is the most important; most companies use oil-based polishing paste primarily made of silicon carbide, which has proven to be very effective in actual production.

(c) During polishing, the polishing paste must be applied evenly, with uniform pressure, and the polishing force should not be too great.

(d) Polish for one pass, paying special attention to ensuring both ends are polished bright; after polishing, electronic engraving can be performed.