Home > Links, Technical Tips > Technical Tips by Bhargav Mistry, DMI – #3

Technical Tips by Bhargav Mistry, DMI – #3

In my previous blog post I had mentioned about Humidity control and I would like to further elaborate on this subject.

Controlling Humidity is very important and essential in screen making department. Few companies do have Air-Conditioned in their screen making department but that only will not help. Split/ceiling mount or wall mount units are all comfort AC’s and do not have humidity control system.

If you want to achieve high quality screens and repetition accuracy then controlling Temperature and Humidity becomes very crucial.

In DMI many times we keep screens till max. 15/20 day unexposed. Obviously under control environment and in total dark condition to prevent from light and to avoid hardening of screens.

To achieve longer shelf life from pre-coated screens do not allow screens to get expose to any kind of light including yellow light of your screen making room.

Once the coating is over and the screen is removed from the screen dryer. Keep those screens inside cupboards to avoid lights.

The main reason we could keep our pre-coated screens in perfect condition till 15/20 days is due to controlled temperature and humidity.

Alway try to keep humidity as low as possible at DMI we maintain between 50% to 55% RH and temperature 23℃ to 24℃
Humidifier_WhiteWestingHouseIf you are thinking about investment and running cost. Believe me its negligible compare to quality.

Currently in DMI we use centralised air-condition plant with inbuilt humidity control system.

But previously in DMI we were using White-Westinghouse Model WDE550. This machine consumes approx. 20 units in 24 hours which costs us max. ₹140/- per day which is very negligible.

It’s worth spending because the quality of screen will improves drastically. Plus you will always get repetition accuracy.

Especially when you use Inkjet films it will help a lot because I have observed people complaining of ink transferring on emulsion after exposing and there after the films can no longer be used.

The main reason for this is humidity or improper time given for emulsion to dry. The use of Screen Dryer is very much essential to achieve proper drying of liquid emulsions.

Investing on a humidity control system is very much essential in screen making department.

These kind of humidifier are available online on Amazon and Flipkart. The one which we use WDE550 cover approx. 550 sq. ft. easily (5500 Cubic Ft.).

“It’s vital that the amount of remaining moisture in the emulsion coat in the screen – when totally dry after coating (before exposing ), and also when dry after development (before printing) – remains under 4%. If it must resist to printing, especially in the part of India and Asia or in any other country when the humidity of external or internal air is above 70%. There are tools available in market which can measure internal emulsion humidity.” Says Michel Caza.

Below I have mentioned few important points if your screen making department has proper yellow lights, no windows to prevent outside lights, plus controlled temperature and humidity.

  1. Repetition accuracy
  2. Image Sharpness
  3. Reduce stencil breakdown during printing
  4. Increases quantity of prints
  5. Avoid inkjet films black ink transfer on emulsion after exposing
  6. Reuse inkjet films
  7. Reduces tackiness
  8. Increases pre-coated screens storage life
  9. Avoid pinhole problems
  10. Reuse screens after short print runs

So if you want to improve your screens, improve your screen making department first.

In my next post I shall highlight the importance each department and process.

Till then good bye.

Bhargav Mistry

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