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January 24, 2023

Screen printing exposure unit

A screen printing exposure device is a machine used to create screens for screen printing. It uses ultraviolet (UV) light to expose a photosensitive emulsion that has been applied to a mesh screen. The emulsion hardens when exposed to UV light, creating a stencil that can be used to print designs on T-shirts, posters and other materials.

Different Screen Printer Exposure Units from new to old models

This depends on the amount of UV radiation emitted by the exposure unit. The emulsion-coated screen printing mesh reacts only to UV radiation. The black positive film blocks the UV radiation, and where no UV radiation hits the emulsion, it is washed out. This is how we transferred the film to the screen.

Explore the possibilities of our exposure units!

The different types of screen printing exposure equipment are UV curing systems, vacuum exposure machines, light tables and yes it is also possible to develop screens with the sun.
As mentioned, UV curing systems use ultraviolet light to instantly cure the emulsion on the screen, so it is very important to also get max uv on our emulsion. Here we introduce different systems.
Vacuum exposure machines use a vacuum to expose a screen with a positive film. The light source used here is ultraviolet light, usually with a very powerful metal halide lamp, or the new LED light bars.


1) Screen printer exposure DIY Version

A very simple Screen Printing Exposure Unit with a normal bulb

Firstly, you can take a powerful lamp, turn the screen upside down with its coating on, fix the film on top and shine the light on the whole thing from above. This is the simplest and probably the most primitive way of exposing your screen.

The result is that the light source emits very little UV. This means that screens developed with this type of illumination are difficult to develop. The light diffusion is not the same everywhere and mostly the film is exposed sideways (underexposed), e.g. fine lines can hardly be developed with this. Also forget CMYK or even index separation, the light source is simply too weak for that.
But as I said, for full color it is possible, and if you only need it as a hobby, it is doable.


2) Table Version Screen Printer Exposure DIY

A old Screen Printing Exposure Unit With neon tubes

The second DIY variant are the self-made light boxes, where the light source is usually underlaid with several neon tubes or LED strips. the whole thing is covered with a glass, so you fix the film to the glass. put the coated frame over it, put a black cardboard exactly the inside frame size and weigh the whole thing down so that it lies flat.

This way is better than the first version. Because here the film is pressed somehow, so that the film has direct contact with the coated screen, so to speak. and the light source is stronger. This is how I had coated my first frames myself, but again, for full color prints feasible, but high quality is not to be expected and for CMYK and other fine color operations, not suitable.

3) Direct Sun Screen Printing Exposure

The sun, it is a first-class source of UV!

The sun as a Screen Printing Exposure Unit direct sunlight DIY version 3
Hold your screen directly in the sun for best results

The procedure is as follows. In your darkroom, flip the coated screen as in DIY version 1, fix the film to it and cover the whole thing with a glass pane that matches the size of the screen frame. It is advisable to fill the inside of the frame with a rigid foam that fits exactly to the inside of the frame. Now cover the whole thing with a light-proof cloth. Take it out into the sun. Hold the prepared frame in the sun and remove the cloth. And that is how you expose with one of the best UV sources we have. BUT how long should you expose? How strong is the sun at the moment? Are there clouds in the way? Unfortunately, it depends on so many things to get a constant exposure every time.

As you can see, there are many variables in this method that we cannot estimate at the time of exposure.
I’ll never forget developing a CMYK separation this way once, and it was top notch.

But seriously, we got lucky and the frames held up until the end of production. Because imagine if the frame had had to be replaced during production. It would have been almost impossible to get the exposure time and UV strength as accurate as the first frame, and we would never have gotten the same printed image again.
Bottom line: yes, you can develop screen printing frames in the sun, but you don’t have durability.

For the hobby screen printer, this may not matter, as this method is also cheap. But if we go to professional screen printing. Then this is a clear NO GO!

Please note

Please note that I only wanted to offer you these possibilities, as a hobby moderately feasible. but if you wanted to operate professional screen printing, I can only advise you against the first three possibilities.
You always have to keep in mind that we want UV radiation. Neon lamps aren’t very UV intensive, and even with LEDs, you have to be careful about how much they emit. The sun of course emits a lot of UV, but unfortunately, it is hard to do consistency here because you are weather and season dependent.

4) Screen Printer exposure unit as Table with a vacuum unit

A classic Screen Printing Exposure Unit with Vacuum unit
Sreen Printer Exposure unit with vacuum and timer

Screen printing exposure unit as a table with a vacuum unit.
This is the most commonly used method, an exposure table with a vacuum unit.
Classic screen printing exposure unit with vacuum unit
Screen printing exposure unit with vacuum and timer
The setup is also a bit similar to DIY version 2. We have a box where the light source is located,
Glass over the light source, the film and on top of it the frame. Instead of weighing the whole thing down with a weight, we usually put a neoprene sheet over the whole thing, attached to a frame that is lowered onto the glass to make an airtight seal. If you turn on the vacuum pump, the air escapes, and now the glass, film and screen are really tight against each other. Now absolutely no light can penetrate through the sides of the film. This vacuum table uses as light source mostly a metal halide lamp or the newer special UV LED’s.

Exposure Timer

Moreover, most vacuum exposure tables also have a built-in timer. Where you can set how long the exposure should be. So you have a consistency that always remains the same. But even here, it is crucial which light source used. But since it is already about more professional Screen printing exposure unit. Is there at least a metal halide unit used or now also special LEDs or even special neon lamps, with a high UV radiation.


5) Metal Halide Units with a stand

A older Screen Printing Exposure Unit with metal halide unit stand
Exposure, Metal Halide Units with a stand

We also have metal halide units that stand on themselves in front of a large, rotating glass frame, which in turn has a vacuum mat attached to the back of it, so that when the vacuum is turned on, the neopreane mat, frame, and film are pressed against the glass.

Die Halogen-Metalldampflampe beleuchtet aus größerer Entfernung. Der Abstand spielt hier eine wichtige Rolle, denn wenn die Lichtquelle zu nahe ist, ist dies nicht vorteilhaft. Ein gewisser Abstand muss eingehalten werden, damit das Licht gerade auf das Glas trifft.


6) The future of exposure in screen printing

The future in exposure in screen printing are the combined versions of DTS (direct to screen) or also called CTS (computer to screen) with an exposure unit incl. or as a metal halide unit from the side.

A new Screen Printing Exposure Unit CTS model with Metal Halid
DTS with metal halide units separate
A direkt to screen printer including a Screen Printing Exposure Unit With LED lights
DTS Unit with inbuild LED exposure unit.

Today, the trend is towards DTS (Digital to Screen) or CTS (Computer to Screen), where the film is printed directly onto the mesh of the frame.
The usual film no longer exists. So again, some variables are eliminated, which is great. Because we want to minimise the variables we have in screen printing.

Some advantages of the CTS exposure units

  • Foils cannot be damaged because they are not present.
  • Printing is done directly on the screen coating, no vacuum is needed anymore.
  • No storage space required for the films
  • No dirty glass that can lead to pinholes in the screen
  • No film output device required
  • Faster than the old process
  • Less variables

These combo versions that print the film and expose it immediately are in the same device. The prices for such devices are very high, but if you are an advanced screen printer, you should include this in your next budget.

In addition, with each of these exposure devices, you should check over time that the UV content does not decrease. This is because, with many light sources, the UV content decreases over time. This means that your exposure time will change.

Is this UV light dangerous for us screen printers?

At this point I should mention that this UV (ultraviolet) is not so dangerous, because we work with it here only a few minutes.
There is no need to go near the machine with gloves and sunglasses. I have seen this myself during a consultation in Madagascar.
However, I don’t keep my eyes open all the time in the solarium either, just like you don’t look directly into the bright sun, so you should avoid direct eye contact, especially with the free-standing exposure units.


ScreenPrint Exposure Unit Summary

The DIY versions shown here are more or less for hobby screen printers. The homemade exposure table could be used for a small print shop on a budget. Just make sure that your light source has a maximum light intensity in the UV range.
The vacuum exposure table is the most common version used in screen printers, and it’s great to be able to control the variables. As a suitable timer is included, the exposure time is reduced. The price depends mainly on the UV power and, of course, the size of the screen they can accommodate. The professional screen printer should definitely keep up with the times. The high price of the CTS should be quickly recouped, it is practical and reduces many variables in screen printing. of course, one should make the calculation, from how many screen frames per day, the whole thing is profitable.

More on Screen Printing Equipment

More than 30 Years in the Screen Printing Business. Living in Mauritius Island in the Indian Ocean, Nationality : German, Married, two children.

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