Chapter 16
Introduction To Ink; Water Based & Plastisol Screen Printing Inks
For screen printing shirts at home, we can say there are two common types of inks used. There are air dry textile inks and plastisol textile inks. For printing posters and paper type flat work, you would use poster ink which is also an air-dry ink. Either of the two textile inks may be used for screen printing shirts but the poster ink is used only for flat work and graphics printed on porous or glossy paper materials. The screen printing process for printing shirts and flat work will be very similar. It is the same process in general but there will be differences in materials used, beginning with the ink.
The air-dry inks are made for many different applications and in general will be the most popular for hobby and home applications. These include inks like Speedball, Jantexinks and Permaset. These are manufacturers of poster and textile inks often referred to as water-based inks. Some of these may be 100% water-based. However, many inks considered to be water-based are often a combination of solvents including but not limited to water. Many air-dry inks may need to be heat set or do not really air dry per say, but cure in a way. To make things easier, from here on we will refer to the air-dry inks as water-based. Most textile water-based inks will need to be heat set to become wash safe. Amex is an Italian water-based ink with excellent professional print results.
VIDEO: Introduction To Screen Printing Inks
With that in mind it is important to note that different inks will call for different emulsions. Some emulsions will break down when using water-based inks. This makes it necessary to use a water-resistant emulsion. And the story is the same for plastisol inks. They may cause premature stencil break down on emulsions made for water-based inks. This sounds all very complicated but it is not. If you are printing very small print runs at home, you most likely will never experience stencil break down due to incorrect ink to emulsion usage. But it is important to know these things if you wish to begin printing any quantity of product in a commercial application.
As stated earlier, certain water-based inks may also contain other solvents and/or do not "dry" by evaporation alone. Ultimately all air-dry inks, even solvent based inks, fall into two categories; non oxidizers and oxidizers. Non oxidizers dry only by the evaporation of the solvents. There is not any chemical process involved. The solvents act as a carrier only. Oxidizing ink, often found in industrial printing, may contain common solvents that evaporate but they also contain chemicals which dry by the process of oxidation much like rusting. Now they do not really rust but they dry by reacting with oxygen to harden the ink. Non oxidizing inks are most popular today as they are easier to work with. Textile and poster inks will be non-oxidizing but textile inks may require heat setting for permanency. This can be done with an iron or a heat press.
Plastisol inks are limited to textiles. Manufactures of these inks include Excalibur, Wilflex, Union, and Rutland. Most plastisol inks may be used at home when screen printing tee shirts. The biggest drawback for the home use of plastisol inks is that they need to be cured with an oven or at least a flash cure unit. Plastisol inks will never dry even when exposed to air until they are cured with heat. Plastisol ink has to reach a temperature of 320 to 330 degrees Fahrenheit so that it will cure and be dry to the touch. However, this ink is often considered to be easier to work with just because it will not dry in the screen during printing. Plastisol ink is also known to have excellent color, coverage, and durability.
There are different ways of curing plastisol inks. This is traditionally the problem for most home-based screen printers. The machine of choice to have, is a belt dryer. The shirt is simply pulled off the pallet and placed on a moving belt which carries it into the oven chamber where the ink reaches proper curing temperature. This is the easiest, most consistent method to cure large quantities of screen printed shirts. But it costs money and it requires space. Many home printers choose to use a flash cure unit to cure their plastisol printed shirts. This can be done on press or after the shirt has been pulled off the pallet. Yet other residential printers use space heaters, heat guns, blow dryers and more to cure plastisol inks. Many of these "garage boy" techniques may work at home but they are not well suited for high volume commercial work.
Most water-based inks will be thinner in comparison to plastisol inks and may require the use of a different mesh count for optimum results depending on your application. Many people recommend using an open mesh for water-based inks to prevent drying in the screen but others prefer to use high mesh counts due to the ease of which you can print water-based inks with them. Using an open mesh with a thinner ink will make flooding of the design a problem. Ink drying in the screen can often be solved by using a retarder or by back flooding the screen with ink in between prints.
Choosing which ink to use at home will ultimately depend on your application, economic limitations, space restrictions and/or your end goals. Many people choose to use water-based ink for printing shirts because they have an ecofriendly reputation. But there are plastisol inks that are manufactured today which are much more environmentally safe than you would think and comply with many government regulations regarding children.
The Benefits & Challenges Of Water Based Inks
If you go to any retail mall these days you will find a huge variety of screen printed garments with a diverse array of specialty effects. There are many different modern specialty printing techniques that are used a great deal but two factors in many popular screen printed logo wear lines is the soft feel of the print and oversized, all over prints. These trends are not too difficult to print even for beginners in screen printing textiles. If you are used to plastisol inks, then you just must learn how to work with an entirely new kind of ink.
Water-based inks are perfect for the soft hand feel that many consumers want today. It is true that you can print “soft hand” prints with plastisol inks, but that will tend to limit you to halftones or lighter colored garments. And there is only so soft a plastisol print can feel when there are considerable layers of multi colored ink built up. And the way plastisol ink tends to sit on top of the fabrics knit also makes it a challenge to print over seams, pockets, collars or stitching of any kind. It can produce unsightly build up on uneven surfaces. But water-based inks are excellent for this purpose because of their tendency to be absorbed into the fabric.
Water-based inks come in many different brands and they can be manufactured for any number of printing applications. In actual production, water-based inks will present entirely different issues than when working with plastisol inks. These problems can be related to artwork, garments, ink brands or additives and your printing application. Before you begin to promote or sell water-based screen printing, it is very important to make sure you fully understand the process. Working with water-based inks is much more labor intensive because of the speed, coordination, tools, supplies and extra skills or experience required. If you can learn how to print water-based inks properly and efficiently, they can often command higher prices than those of standard plastisol screen printing.
Although there are some opaque water-based inks made to be printed on dark garments such as black, they tend to be thick and stiff due to the amount of ink required for good coverage. Standard water-based inks will not show up on dark garments. To keep that “soft hand” feel to the print on black shirts, discharge water-based inks are required. This printing process also needs another totally separate set of skills, experiences, tools, supplies, choreography, and speed. When printing discharge water-based inks, it is necessary to add an activator to release the dye from the fabric of the shirt. If discharge printing is to work properly, you must have the experience to know the right drying times and use the right brand of garments. Even the screens must be created specifically for this type of printing. You would really have to make sure to have the correct set of tools and the right equipment for water-based discharge printing. And even when you can manage to work all the details out to a science, color matching can still be a difficult problem to solve.
Water-based printing will demand a different set of screens and even your art can be designed accordingly. Artwork creation, especially for halftones, will be a whole new animal due to the way the ink is absorbed into the garment fabric. Obviously, this in turn requires screens and mesh counts. Making very small and detailed artwork with tiny stencil openings can promote ink drying on press. Therefore, artwork for water-based work is done specifically for it. Distressed and textured prints or loose, hand sketched art, blends well with any irregularities in printing due to ink flow issues. Just as it is with standard plastisol screen printing, your artwork can make or break you.
VIDEO Using Water Based Inks With A Forced Air Flash Cure & Standard Infrared Dryer
Remember to use an emulsion that is designed for water-based inks and solvents. A special additive can be used with some emulsions to protect the stencil from water-based discharge inks. You can reclaim any screens used for water-based printing the usual way but make sure to clean the screen of any ink immediately after use. If you do not, the water-based ink can clog the mesh permanently. Also keep in mind these inks are much thinner than plastisol inks and will not need as much squeegee pressure when printing.
And one last note: if you plan on doing any large volume commercial printing with water-based inks, you should seriously consider a decent size belt dryer. The larger oven chamber will facilitate the curing process and ensure consistency throughout your print run. Just because water-based inks are said to "air dry" they most often need to be heat set to properly cure in commercial applications.
How To Keep Water Based Textile Inks Flowing On Press
When we talk about screen printing tee shirts there are generally 2 types of inks we use for textiles. Plastisol and water-based. Discharge inks seem to fall into the same category as water-based inks even though they work a little differently in being heat activated. Plastisol inks are “cured” with heat while water-based inks are “heat set.” The fact that water-based inks dry by evaporation makes them a little harder to learn how to screen print with. Textile water-based inks dry by evaporation and they need to be heat set for the pigments to be wash safe in the laundry. But because water-based inks dry when exposed to air, they can dry in the screen while you are working. This can make it difficult to keep the ink from drying in the mesh during printing. While there are many ways to help prevent the ink from drying, there are a few basic things we can do to help keep the ink flowing through the stencil on press.
The first thing you can do to keep the ink printing on press is use a retarder. Many manufacturers that produce water-based inks also make an additive known as a “retarder.” This additive will slow down the drying time of the air-dry ink. It is probably a good idea to call the manufacturer or dealer for your water-based ink and ask if they have a retarder you can keep on hand. An additive like this can be very helpful in slowing the drying time down so you can keep printing without issues. It may also thin the ink out some. It is important to note that some air-dry water-based textile inks may be formulated to have a slower drying time. It pays to do some research on the ink before you stock it for use. Always follow the manufacturer’s directions for mixing and printing.
Another very important procedure you can use on press to keep the stencil wet and printing well is back flooding. This is a very simple way of keeping the ink left in the stencil wet between prints and it is easy to forget to do. Back flooding is when you follow up a print by flooding ink back into the stencil with the squeegee so we can pull the shirt off the press, load new shirts, print other colors or what have you. Between printing each screen, we make sure the stencil mesh is completely flooded and filled with ink. You will want to keep enough ink on the screen to back flood the stencil with a nice thick coat of ink.
Thinner inks should run less when spread out as well so this can also help control the ink on the screen when it is in the up position. Be careful not to use too much pressure on the back flood. You do not want to extrude the ink through the stencil. You simply want to cover it with the ink. It should naturally fill in the mesh without much pressure from the squeegee. The thinner the ink is, the less pressure you may need to do the back flood.
VIDEO: Back Flooding Water-based Inks
Some water-based textile inks can also be kept wet by using a spray bottle with water on press to mist the screen between prints. Here we fill a simple spray bottle with cold tap water and set the bottle nozzle to a fine mist. Then we spray the open stencil with the misted water between prints. You would not back flood the screen in this case. With this technique, the water keeps the ink left in the stencil wet and flowing. Water-based inks that are truly water soluble will work well with this method. If the ink can be cleaned up with only water, then this method may work well for you. It may also work for other inks that need a solvent for cleanup but I would suggest some testing before an actual production run.
It is also important to note that relative humidity can also affect the speed at which the air-dry water-based inks dry on screen. Obviously if your relative humidity is very low like 20% or lower, you can experience very fast drying times with water-based inks. This is due to the low humidity in the air where you may be working. A higher relative humidity will create an environment where the ink takes a little longer to dry by evaporation since we would have much more moisture in the air. It could be helpful to use a humidifier in the print shop where you are using water-based inks. However, high humidity can affect the drying time as well as the heat setting time since we will see much higher moisture content in the garments in the room with a humidifier. Keep in mind that while high humidity may slow down the drying time of the water-based ink on screen, it may also slow down the drying of the ink on the shirt and add time to your heat setting process as well.
VIDEO: Printing Water Based Ink Live At ISS Long Beach
The very last tip I will share with you is simple. Work as fast as you possibly can. When printing air dry water-based inks, you will want to start working and never stop until you have finished. This means you do not want to ink up until you are ready to print and once you do, you will need to print until the job is complete. Then you must clean up immediately since the ink will dry while you do anything else. This is very important because most often when air dry water-based textile inks dry in screen or on the squeegee and/or other tools, it ruins them permanently. Usually, it is very difficult to remove dry water-based inks from squeegees or ink scoops. If the ink dries in the stencil, it will most likely not be able to be removed thus destroying the screen mesh and rendering the screen useless. Sometimes we can use a haze remover to soften up the dried ink making it possible to reclaim with a pressure washer. But you will want to avoid that scenario with proper procedure as described here.
Since we want to work with speed and accuracy when printing water-based textile inks, you may want to consider a forced air belt dryer. If you are just starting out with a single station press and you are working with a forced air flash cure unit only, you will want to print fast and lay the shirts out to dry by evaporation before heat setting them with the flash cure unit. That way you can keep printing the entire run and then follow up with the heat setting. Remember to clean up before you spend time heat setting any shirts. Or better yet use a forced air belt dryer so you can pull the shirts off the press and put them straight into the belt dryer. With a rotary press we can use the forced air flash cure on press for multi-color printing and then run the shirts through the forced air belt dryer for the final heat setting of the pigments in the water-based textile inks. That would be the most ideal situation.
VIDEO: Black Water Based Ink ISS Show Freebies Print Run
One last note; be sure not to have any drafts blowing down on your screen with water-based inks. That means you will want to be sure there are no heating or cooling vents blowing down onto the screen. Fans, open windows, or any other source of blowing air can speed up the drying times of any air-dry ink. Working in a closed environment with no drafts or blowing air will help reduce premature drying issues.
It is always a good idea to contact your dealer or manufacturer for specific directions for usage of your water-based textile ink. These tips may be helpful to many with a variety of air-dry inks including but not limited to air dry solvent or poster inks. But the maker of the ink may have specific tips or technical information to share with you that will make working with the ink much easier. Combine these tips with any information about the ink from the dealer or the manufacturer and you should have a more productive printing run with air dry water-based inks.
Tips And Advice For Working With Plastisol Screen Printing Inks:
1) Plastisol inks are thixotropic therefore the more you mix and/or stir them, the thinner and creamier they will get. Working the ink on screen will also make it thinner as you print such as is the case with automatic presses.
2) The ambient room temperature can affect the thickness of plastisol ink. The colder it is the thicker it will be. Therefore, it is wise to store inks, especially high opacity inks, at room temperature between 74 and 84 degrees F.
3) Adding reducers, soft hand base or thinners to high opacity inks will change their ink flow characteristics and reduce the opacity. Since these inks are formulated to be opaque it is illogical to add anything to the more expensive high opacity plastisol inks.
4) If you notice a clear, watery solution sitting on the top of your plastisol ink in the bucket then you need to mix it very well. The clear liquid is the plasticizer and that is what rubberizes the ink. The plastisol ink will not print or bond to the fabric properly unless mixed thoroughly so there is no clear liquids visibly present sitting on top of the ink.
5) Keep the plastisol ink containers tightly closed when not in use. Long periods of exposure to air will not only invite dust and debris but it may also thicken the ink up over time.
6) Plastisol inks begin to gel at about 175 to 250 degrees F so it is important to make sure plastisol inks do not get over heated for any reason. Semi gelled plastisol inks will not print well and may present bonding issues.
7) If your screen printing supplies dealer sells you an ink additive to solve a problem you are complaining about you should seriously consider changing suppliers. At Catspit Productions we do not sell you secondary products to fix and compensate for a product that fails to meet up to your expectations. We either replace it or take it back with a full refund.
8) Plastisol inks cure at 330 degrees F. This can take up to 1 minute or longer depending on how much ink is printed on the garment. Be sure to do cure tests to see that the ink is fully cured otherwise it will washout during repeated washings in the laundry.
9) When printing plastisol inks on polyester garments, you may need to use a polyester white ink under base to prevent dye migration. That is when the dye in the shirt seeps into the plastisol ink and discolors it. This can happen with 50/50 poly cotton shirts and 100% polyester.
10) High humidity in the shop area when curing plastisol inks can be a problem. Either use a dehumidifier or run the garments through the belt dryer immediately prior to printing. Heavy 100% cotton fleece garments can hold a lot of moister and need time to dry out.
Controlling Dye Migration With Plastisol Inks
Dye migration is also known as bleeding or dye sublimation. This is a process that occurs mostly between standard plastisol inks and synthetic fibers like polyester. It is most notable with white inks on shirt colors like red, navy, maroon and even dark greens. It may appear immediately when the shirts exit the oven, when they are left to sit overnight and even two weeks later. There are two common causes of dye migration.
The real cause of dye migration is simply the fact that the dyes in the polyester fabric sublimates or turns gaseous when heated to about 330 degrees Fahrenheit during the curing of the plastisol ink. Then the dye, in gaseous form, seeps into the ink layer thus tinting it the color of the shirt. This is inherent in the dyeing process of polyester and is unavoidable but not impossible to deal with. When screen printing polyester or polyester blend garments precautions must be taken to prevent this bleeding from happening. This is what we will call the "first" cause; over curing.
Overheating your printed polyester garments during curing is inadvisable. It is important to monitor the oven temperature to ensure consistent results. This includes flash curing. Be careful not to overheat the shirt when flash curing on press. Cure all your polyester garments under 320 degrees Fahrenheit. It is also possible to use a catalyst like Nylobond to reduce curing temperatures of plastisol inks. Lower curing temperatures are the best defense against color bleed. Thicker layers of ink will inhibit dye migration but it will also require longer heating times and temperatures.
It is best to use an ink specifically designed to be low bleed or one that is made for polyester materials. White ink is the absolute worst for bleeding problems. But do not be surprised to see other inks discolor after being printed on navy or black. You could also use an under base to prevent bleeding and some ink manufacturers offer under base inks specifically for this application.
The "second" cause is basically the same problem prompted by different factors. The simple fact of the matter is that sometimes the dyeing process for the polyester garments, which is a sublimated one, is of substandard quality and the dye will tend to migrate easily from the fabric into the ink layer. This is a problem that can only be addressed at the factory where the fabric is being dyed. Good luck. Using higher quality products may help to avoid this factor.
Another part of the second cause is re-dyed shirts. This is also something that starts at the factory. Let us say Fruit of the Loom makes more yellow shirts one spring season for some reason and then they experience larger orders for shirts like black or navy and even maroon. Can you guess what they do? That is right, a re-dye job. Any re-dyed garments will have a tendency for the dyes to bleed into the ink layer. This goes for 100% cotton shirts as well as polyester or polyester blends. Printing white ink on a 100% cotton tee shirt that has been re-dyed may also result in color bleeding into the ink layer. Using a good quality, low bleed, high opacity white ink for all your darker colored 100% cotton shirts is recommended.
It is important to ensure the quality of your polyester garments before printing them. And there is a simple way of doing that in addition to buying a well-known name brand garment. Take a clean piece of white cotton tee shirt fabric and tightly wrap it around your index finger. Then rub an area of the polyester fabric a few times with your finger. If there is a very slight color transfer, it should be alright. If there is a very significant color transfer, then I would be very cautious about printing those shirts. This test may also be repeated with the cotton fabric damp if you are unable to get readable results dry.
Finally, there are high quality garments like Under Armour® that just have a bad problem with standard plastisol inks and bleeding. They also tend to crack or flake with standard plastisol inks as well. If you are approached with an Under Armour® print job, be wary and contact your ink manufacturer for the correct ink to use. It is always a good idea to consult your ink supplier to ensure proper ink usages in your print shop.
VIDEO: Polyester Shirts: Controlling Dye Migration With White Ink