Today I will be posting my first Technical Tips. As my I have written dozens of technical articles on my blog but this new concept is designed to provide short and quick technical informations on screen printing technology.
Since it’s my first post, so I requested my GURU Michel Caza to kick start by posting one short technical tips.
Yesterday evening I requested him to send me few technical articles & tips so that I shall keep you posting one by one.
He was quite helpful to send me one quick article on Screen Making but there are many more to come from us and also from many other technocrats of this industry.
This is just a beginning, you will see many in-depth articles, tips, videos, visual to learn every day with many new innovative ideas.
Q – The small dots and fine lines printed disappear on the screen after stencilling?
Dots and lines too fine on the film
Respect the indications about the maximum possible fineness to reproduce
Dots and lines not black enough on the film
This can happen with films made by inkjet, not dark enough.
The sharpness, resolution, edge definition of the film must be perfect.
Colour of the screen mesh
Always use yellow mesh, avoid white mesh, to prevent light dispersion in the thread
Too coarse fabric or/and too large thread diameter
This prevent to print fine lines or dot : use S or T, thread diameter of 27 to 31 microns
in 120 to 165 thread/cm, plain wave (PW) if possible
Improper emulsion sensibility for fine lines definition and resolution
Choose a good emulsion, diazo (SBQ) or better, diazo polymer (wide latitude when exposing) with high amount of solid content.
Too many emulsion coats
As it must be exposed more, this causes the closing of the fines lines and dots.
Over exposure of the screen
Even with a correct coating of emulsion (1 coat, 1 + 1, or 2 + 1 maximum), respect the indication given by the Exposure Calculator.
Handling of screen under Improper light.
When the emulsion is dry, before and after exposure and beginning of developing with water, it is sensible to the light and can then be hardened, partially or totally. Then use yellow light in stencil room. When wetted on both sides of the screen , the white light can be used.
Poor contact in the exposing unit
To prevent any dispersion of the UV light during the exposure the contact between film and screen must be perfect. Check your vacuum pump or the rubber carpet quality which must be clean and without holes. Use a thread to the screen frame to permit a better drainage of the air.
Use of “UV tubes” light
I do not advise this because the UV light is not punctual enough and the dispersed light is not able to stencil properly line and dots under 100 microns. For fine lines, use a metal halide lamp.
No “light integrator”
Take care of exposure “time” which can drastically change during the day with the variations of supplied electricity. Use a light integrator which automatically measure and supplies the exact “amount of light” needed
Poor development of the screen.
If some emulsion remains in the finest lines or dot that should be totally open, those will be closed and of course impossible to print.
All the best from;
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