Somebody just made reference to some 'tips' in a book on waterbase printing. You might find this useful, it's not everything you need to know, but it will get you closer.
Using Waterbase Inks Successfully
By Andy MacDougall
For the fine art or poster printer, waterbase (WB) screen printing inks provide a solution to long standing problems when working with solvent-based ink systems in small studios or classroom situations. These include smelly VOC (volatile organic compounds) laden air, cleanup with thinners or other nasty stuff, and working in a toxic environment. In general, WB inks give off very little smell, clean up with water, are brighter than traditional solvent based, and print with most of the same characteristics as satin poster or any of the traditional oil based products that have been in use for decades. With all these good points, it makes sense to make the switch.
Unfortunately, many first time users of WB inks experience problems which lead them to the mistaken conclusion WB is difficult to use. Rapid drying in, hard to clean screens, stencil breakdown, and distorted paper are common complaints. All of these difficulties in the printing process are blamed on the ink, when in fact it is mostly the methodology of the printer that is the culprit. All it takes to enjoy success and problem free printing with WB ink systems are some slight changes to stencil making, make-ready, and the printing and cleanup processes.
None of this is new, just different.
None of this is hard, but it requires more attention to the technology of screenprinting.
If all you want to do is pull a squeegee, then go stand on a street corner and wait for the cars to stop. If you want to print waterbased inks, then follow these simple rules.
Depending on the application and the inks, monofilament screen meshes of 200-300 threads per inch, properly tensioned, will give the best results on paper. It is critical that new meshes be put through a haze/degrease cycle, along with an initial roughening with micro grit. After screens are in use, always perform a thorough stencil & haze remover/degrease cycle with pressure washer before recoating. A simple test is to run water over the screen. If it sheets, itís good. If it beads up, you need to degrease it better. Ensure the mesh is completely dry before applying emulsion.
WB inks require a water resistant stencil. Most capillary, indirect film, and pure photopolymer (SBQ) stencils do not provide this. Use direct diazo-based emulsion that is rated for use with waterbased inks. Some manufacturers provide a liquid that can be put on a screen after exposure to increase its water resistance over a long production run. There are a few key points to producing a good water resistant stencil.
1. The emulsion must be completely dried, with the humidity in the screen drying area below 50% relative humidity for 3 hours. This can be done using heat, or better, with a dehumidifier. Once the stencil has cured for the 3 hours, its water resistance locks in.
2. It is very important that the exposure be complete - if the screen is underexposed, the top surface of the stencil will not harden properly, and come loose during the print run, causing blocking in as it mixes with the ink, or going soft and pin holing or delaminating during printing. Run your hand over the squeegee side after washout. If it is sticky or still gives off an emulsion film, it is underexposed. If the surface is hard with no emulsion residue but the image is closed in, itís overexposed. If it is hard and the image looks like your film, itís perfect.
3. After washout, place the screen in direct sunlight, or re-expose. This will ensure all the stencil has hardened.
Obviously, a water soluble block out wonít work. You can use emulsion for this, but ensure it is coated on thin, completely dried, and then re-exposed to UV light. In my experience, this does not provide a long term block out. I use a lacquer block for long runs. There are other water resistant block outs now available from suppliers.
Use a good quality clear packing tape to cover gutters or to make dams to control the ink. Seal the tape to the stencil by running the back of a fingernail along the edge. This helps stop the ink from working its way underneath. Run two strips of tape where the squeegee ends travel on the stencil. This becomes a wear point on long runs, the tape will protect the stencil from breakdown. On the bottomside of the stencil, run tape along the point where the paper edge contacts the screen, this will protect the stencil from developing pinholes, cracks, and ink leaks over a long run.
Mixing The Ink
With TW inks, I add Ďprocess clearí to the ink. This acts as both an extender and a retarder. I then thin with water to a desired consistency. This consistency is much thinner than regular solvent inks. Inks that are too thick will dry in easier, and be harder to print.
Most of the WB inks are acrylic based, and they have a tendency to accumulate dried bits of ink on the sides of containers which wonít rewet. Use a plastic strainer or a piece of old mesh on any mixes or old ink before the print run, or you will be picking ink flakes out of the screen mesh during the run.
Starting The Run
TW inks come with a screen cleaner (SO-34). Take this and prepare two mixtures. One is mixed 50% with water, the other is 20%. Put them in two spray bottles, mark the mix on the side, and get a few medium soft sponges. Apparently, 409 or Fantastic cleaner will do the same thing - no amonia.
Once you are ready to start, spray some 20% on the sponge, and cover the entire print surface with an even coating. This acts as a lube, and stops the ink from freezing in the dry screen when you pull your first print.
When you start to print, it will be runny - quickly pull prints on clean scrap newsprint and watch the print to make sure all detail is printing. The print will quickly clean up, and the color density will return to normal. Once this happens, feed in your good paper. Adjust your register at this point, always remember to keep the printing going - if you stop to admire your work too long, it will dry in.
During The Print Run
If you experience detail drying in, spray the 20% solution over the entire print area, let sit for a moment, then print off on scrap paper. You may have to gently rub a dried in area with the sponge.
If you notice a buildup of ink on the surface of the stencil, flood with a thick coating. When you print, notice that the dried ink layer is rewet and removed with a thick flood.
If either of these problems persist, thin the ink a bit. Do the thick flood every 20 prints or as needed. Be aware it may cause an edge bleed on your image, use scrap stock.
Dust spots are best removed after a print stroke but before the flood, this way you can see the offending cruddy and pick it off with a fingernail - avoid rubbing with a finger as the oils will affect the next few prints.
Every 40 or 50 prints, scrape the ink from the squeegee and remix with your fresh to keep the ink from drying and clumping. Continue to add fresh ink during the run, and thin as necessary.
When you reach the end of the print run, scrape all ink towards the center, and then pull a thick flood. Your final print can go on a scrap sheet. If your flood was good and thick, and you scraped all your excess ink into the center, when you pull your last print you will have very little ink left on the screen, and it should all be in a puddle at one end. If you taped out properly, this puddle can be on top of tape, making clean-up easy.
1. Take your 50% solution and thoroughly soak a sponge and cover all open stencil areas with a good dose of liquid. This will stop ink from drying in while you clean up the excess ink.
2. Remove the squeegee and scrape into the ink container, then spray the blade with the 50% and take to the sink. Let it sit.
3. Next, quickly scrape up the excess ink with an ink knife. Remove the tape, being careful not to splatter any ink residue.
4. Once all the ink is gone, spray with the 50% if you are going to clean the screen at the table. If not, remove the screen and take it to the washout sink, then spray.
It is important the screen is soaked with the cleaner before rinsing with water, because of the reaction some water has with the ink - it freezes in. The 50% solution makes it all come clean easily when rubbed with the sponge. Spray the squeegee and the ink knife too, then rinse all completely with water.
It is important to clean all the ink from the screen mesh and the tools while it is wet. Hard WB ink is almost impossible to remove once it dries.
Now you can go admire your print....but itís all wavy you say...
Flattening Your Stock
Waterbase inks have a tendency to puff up and soften the rigidity of a sheet of paper. After all, a big flood of essentially water would do that to just about anything. There are two ways of dealing with it:
1. The first is to prepare a flood screen the same size as the image, mix a batch of clear with a bit of white, and precoat your whole addition. When it dries, unrack and carefully stack the entire addition, with a board and weights placed on top to flatten the paper. When you run the rest of the print, the flooded area will accept the new inks and allow them to retain better color density, as it will stop the paper from absorbing ink. If you continue to unrack and stack during the run, the paper flattens.
2. Option two is to skip the pre-flood, but do the unrack-and-stack with board and weight after each color run. The results are the same, a nice flat sheet. Iíve seen much wavier papers printed with solvent inks, and they will never go flat, because of the uneven surface tension.
Happy printing. Readers comments are always welcome, either on the Q&A section of Squeegeeville.com, or by emailing firstname.lastname@example.org
Copyright 2003 MacDougall Screen Printing Ltd. All rights reserved. Reproduction of this article is forbidden without the express written consent of the author.