How to Clean Pad Printing Plates? Three Tips to Get It Right.

【Abstract】Pad printing plates play a dominant role in pad printing technology. The 100% ink cup pad printing machines and 16% ink cup pad printing machines use thick steel plates of about 10mm in thickness; some ink cup pad printers use thinner steel plates with thicknesses of 0.25mm and 0.5mm. Whether thin or thick, the plate-making technology is the same. The surface of the pad printing plate must be smooth and bright, So, how to clean pad printing plates effectively? Three simple steps will help you handle it easily.  While following the "clean immediately after use" principle, it is also essential to clean and maintain it regularly and take appropriate protective measures based on the usage intervals. The protection measures can be summarized as "Clean, Dry, Maintain." What issues might arise in practice?

1. How to Clean the Pad Printing Plate?

Pad printing plates are particularly sensitive to water and can easily rust when exposed to moisture. When cleaning the pad printing plate, the "clean immediately after use" principle should be followed. If the ink has completely dried on the plate, the cleaning difficulty increases significantly.

• First, at the end of each workday, clean the ink off the plate with a washing solution, repeating the process if necessary.

• Second, when cleaning the plate, avoid soaking it in the solvent for an extended period.

• Third, after cleaning the plate, use a blow dryer to dry the surface completely. Then, apply a thin layer of oil or rust inhibitor to the plate, just like applying cream to your skin. If the plate will be used the next day, it can be disassembled; however, if it will not be used for a long time, it should be disassembled, coated with oil or rust inhibitor, and then wrapped in a plastic bag to preserve its condition.

2. How to Protect the Pad Printing Plate?

When using the pad printing plate, if pinholes appear, it could be due to inadequate cleaning where residual ink remains on the plate or a humid environment causing moisture damage. If pinholes become severe, the plate is essentially "retired" and can no longer be used. Therefore, proper protection is crucial. The method is summarized in seven words: "Clean, Dry, Maintain."

• Clean: Clean immediately after use, ensuring thorough cleaning.

• Dry: After cleaning, use a blow dryer to ensure the plate is completely dry.

• Maintain: Once dry, apply a layer of oil or rust inhibitor. If the plate will not be used for a long time, seal it in a PE plastic bag and lay it flat. (Do not store the plate upright or at an angle to avoid unnecessary risks. A pad printing plate, especially a thick one, can be heavy. Handle with care to avoid damage.)

In addition to these protection steps, use a hygrometer to monitor the environment’s humidity. If the humidity is too high, especially during the "wet" season in areas like Guangdong, the plate is more likely to rust.

3. Frequently Asked Questions (FAQ) About Pad Printing Plates:

3.1）Some customers report that their pad printing plates rust overnight after the machine is stopped?

Yes, this is a common occurrence, so regular maintenance is essential. It’s important to develop good maintenance habits. Again, the key is "Clean, Dry, Maintain."

3.2） Does rust inhibitor oil affect the quality of the pad printing plate?

No, it doesn’t affect the quality of the plate itself, but it can impact the printing quality. Therefore, before use, be sure to wash off the rust inhibitor oil with a cleaning solution.

3.3） What printing defects can be caused by the pad printing plate?

Common defects include pinholes and other quality issues, which are mainly due to improper cleaning.

3.4）What is the process for making a pad printing plate?

Here’s a brief summary:

3.4.1. Create the film based on the printing content.

3.4.2. Apply photosensitive emulsion to the steel plate.

3.4.3. Attach the film to the plate.

3.4.4. Expose the plate in an exposure unit.

3.4.5. Etch the plate.

3.4.6. Final product.

Details are as follows:

• Clean the Plate (Washing): Thoroughly remove any oil or dust from the plate. If not cleaned properly, defects will occur.

• Photosensitive Emulsion Coating: Use a coating machine to apply a uniform layer of photosensitive emulsion to the plate. Place the plate with the emulsion side down in a clean darkroom. If you lack a coating machine, you can coat it manually. The emulsion needs to dry for about 12 hours at room temperature or 15 minutes at 150°C in an oven (room temperature drying is recommended).

• Film Attachment: Attach the film to the appropriate position on the plate and fix it with transparent tape, ensuring there are no bubbles or wrinkles.

• Exposure Process: Place the coated plate tightly against the glass of the exposure unit (we will not go into detailed operation here). Exposure time for normal patterns is about 40 seconds, while halftone exposure is 8–10 seconds. Accurate exposure time ensures a clear transfer of the pattern onto the plate.

• Development: Wash the plate with developer for 20-40 seconds and then rinse with water. If development is insufficient, repeat the washing process until the pattern is clearly visible. Finally, dry the plate using a blow dryer. This step removes the unexposed photosensitive emulsion and reveals the design.

• Filling Holes: After drying, cover any unetched areas with tape, and fill in the sand holes. Be sure to avoid dust contamination during this process, as dust is the main cause of sand holes.

• Etching: Use an etching solution to etch the plate for approximately 1.8 minutes. Adjust the etching time according to the temperature and line thickness. Once etching is complete, wash off the solution with water. If the etching is not deep enough, re-etch for a short time, but do not exceed 0.5mm in depth to ensure the plate’s strength and longevity.

• Final Cleaning: Wash the plate with wash-off solution to remove any remaining photosensitive emulsion, completing the production of the pad printing plate.

3.5）If the pad printing plate has rust, can it still be used? 

It is not recommended to continue using a rusty plate.

3.6）Can the plate be etched without development? 

No. Development is an essential step in the manufacturing process and cannot be skipped.