Quality control is an essential part of growing any manufacturing business and maintaining customer satisfaction and loyalty. Screen printing has its challenges, but that’s what separates the good from the excellent.FULL STORY
Screen Printing: Process + Techniques
Screen Preparation and Reclamation for Apparel DecoratorsIn the second of a series of excerpts from his book, The Screen Printers Handbook and Survival Guide, veteran T-shirt and apparel decorator Charlie Taublieb discusses screen construction and maintenance
Screen making is an area that I focus on heavily, since the quality of the print will be very influenced by, if not dictated by the quality of the screen. Many shops make the same mistakes, and the most obvious one is how they dried their screens. The following is a step-by-step of what I would do to make a screen from the beginning:
1) Stretch a screen to a specific tension (all my shops used retensionable screens). To make life easier, I prefer working to one tension range for each of the mesh counts and staying there. The following are the tensions I like to see maintained in newton centimeters (N/cm—a unit of torque):
A. Up to 230 mesh (or 90cm) 35 N/cm
B. Above 230 mesh (or 90cm) 20-23 N/cm
The mesh counts above are based on standard “T” or “M” thread diameters and not special “thin” diameters or super tension meshes. The lower your mesh tension, the lower the mesh count needs to be in order to get a decent print. There really isn’t a substitute for high tension.
2) Record the tension on the bottom of the mesh using a Sharpie and draw a fat line after it. It is important to document the number of times a screen has been retensioned, and this is an easy way of following it. This information will be used in selecting screens for a job, since it is very important to use screens that all have been retensioned the same number of times to not lose registration during printing. New mesh loses tension much faster than an old screen that has been retensioned many times. If using rigid frames, new screens will allow for a crisper image than old ones, since their tension will be higher than the old ones. In either case, having screens of a similar age, number of times used, reclaimed and retensioned will make for a better-looking print.
3) Wet the screen. It would be best if your shop has two sinks, one for degreasing and washout, and a second for reclaiming to help prevent contamination problems that can arise from the “splash back” of chemicals. This is usually where “fisheyes” come from. If you only have one sink, make sure it is washed down completely before going on.
4) Abrade the screen if it is new or if the screen has been used for five or more reclaimings and has not been abraded. Abrading scratches the surface of the mesh and allows the emulsion to bite on to it for better adhesion. Abraders come as a powder or paste. There are some degreasers that have an abrader in them as well. If using the latter, an abrader by itself is not necessary. The brush used for abrading a screen should only be used for that purpose, as should the brushes for each of the other steps in this process.
5) Rinse the screen and apply the degreaser, working it in with its brush. Degrease both sides.
6) Dry the screen. One of the best ways is to vacuum off the water and then put the screen in a drying cabinet. The quicker a screen is dried, the less chance there is of dust settling onto it and creating problems. Never use compressed air to dry a degreased screen. Compressed air is dirtier than the screen was before it was degreased due to the oils and other containments in the compressor.
7) Coat the screen on the substrate side first (the side that faces down and touches the garment), then coat the inside of the screen. Only apply the amount of emulsion necessary. Do not apply the emulsion with the screen on the floor. Use a screen holder (or build one) that will hold the screen so you can use two hands for coating. Scraping off excess emulsion wastes time and creates lots of little bubbles in the scoop coater, which can cause streaks and weak spots on the next screen. Coat screens until you notice a fair number of bubbles in the scoop coater. Empty the emulsion into a clean empty container. This emulsion will be usable again once the bubbles have burst. There should be a second empty container to put the emulsion into from the first container so there will be no bubbles present when starting the coating process.
8) Dry the screen in a drying cabinet with the substrate side facing down. The reason we do our last coat on the inside of the screen and face the outside down when drying the screen is to create a smooth surface on the inside for the squeegee to glide over and not get caught on the edge of the emulsion or drag on it. The drying cabinet should maintain a temperature of 95°F if using pure polymer emulsion or 105°F if using a diazo or dual exposing emulsion. At those temperatures, a screen should be dry in 10-15 minutes. Put a thermometer into your drying cabinet to check the temperature. Be aware that setting the thermometer to a particular temperature doesn’t mean the inside of the drying cabinet is actually reaching that temperature. Do not use fans to dry your screens. They throw dust at the wet screen and create problems.
9) Once the screen is dry, it is time to expose it. If the screen was dried and put into storage, check the relative humidity before exposing the screen. The ideal relative humidity is about 40 percent. Having a hygrometer in the screen storage area is necessary for this reason. If the relative humidity is above 50 percent, put the screen back into the drying cabinet for a few minutes (3-5 minutes) prior to exposing it. Emulsion pulls moisture from the air and can re-wet a screen. A “wet” screen takes longer to expose properly than a dry one. Many screen breakdown problems are a result of screens being underexposed because of the moisture in them. When conducting exposure tests using a calculator, make sure you are using dry screens. Touching a screen to see if it is dry will not give you that information. Screens coming out of a drying cabinet or screens stored in an area where the relative humidity is less than 50 percent should be used.
10) After the screen has been exposed, wet it and let it stand for a few seconds before washing it. This allows the emulsion to soften in the areas that are supposed to wash out. Using a 1,000-PSI washer from about three feet away, wash the screen. If the exposure was correct, the emulsion will not break down. If the emulsion does break down, this is a better place to find out the screen wasn’t made correctly than on the press.
11) Dry the screen. A vacuum with a special nozzle is my favorite way of doing this, but compressed air works and so does putting the screen in a drying cabinet after blotting off the excess water. Just make sure the image area is free of water so there is no scumming, i.e., a shiny clear film forming in the image area from the unexposed emulsion settling there, that will dry in and not let the ink through it. If this happens, use a damp cloth to open the area up again.
12) Block out and tape up the screen. You’re ready to print!
13) When you’re done printing with the screen, remove and clean all ink.
14) Put the screen in the reclaiming sink and wet it.
15) Apply ink degradent and work it in with a brush, then apply and work in the reclaimer.
16) Blast with a 1,000-PSI washer or higher.
17) Haze Remover could be used at this point. However, I recommend you only use haze remover about every five reclaimings, if at all. (I don’t like haze removers because they are very caustic, and most employees don’t want to wear the correct protective gear when using them). If haze remover was used, spray the screen down with a mixture of 50 percent white vinegar and 50 percent water to neutralize the alkaline in it. Haze Remover is responsible for breaking mesh by slowly eating away at it. That is why sometimes a screen breaks even when it is not being used.
After that, re-tension the screen, document the tension on the screen per step 2. That done, continue on to step 3 to start prepping the screen for use all over again.
Veteran decorator and screen-printing guru Charlie Taublieb is both the principal of Taublieb Consulting and a regular Impressions Expo conference program presenter. His new book, The Screen Printers Handbook & Survival Guide, is available either digitally or in the form of a spiral-bound book at taubliebconsulting.com. To see Part 1 of Impressions’ three-part series of excerpts, click here.
Mesh Counts and Their Uses
There are a lot of mesh counts and thread diameters available for printing textiles. Some companies do not have enough of a selection. Others have too many different meshes available. Mesh counts refer to the number of threads of mesh crossing per square inch. A 110 mesh, for example, has 110 threads crossing per square inch. The higher the mesh count, the finer the threads and the smaller the holes in the screen.
Almost all mesh comes with two or more thread diameters. As textile printers, we generally work with “T” or “M” mesh, which is the medium thickness. There are also those who work with “S” mesh, a thin strand that allows for a greater deposit of ink, especially 150/48 for white underlays. However, the mesh is very delicate and needs to be stretched to around 20-22 newton centimeters (N/cm—a unit of torque).
Among the meshes and threads I list below, the first three meshes are the ones I recommend for day-to-day use. All three should be stretched to around 35 N/cm. For these and all other meshes, I’ve included what to use them for.
110 mesh/80-micron thread: Underlay for fleece, water base and discharge ink, adhesive for foil. This is for cotton and poly/cotton garments. Use when working with polyester inks on 100 percent polyester. Good for printing an adhesive for foil.
156 mesh/64-micron thread: Underlay for tee shirts, water base and discharge ink, light and medium-colored shirts where you want strong color. This is for cotton and poly/cotton garments. Will hold 45 LPI half-tones. Use when working with polyester inks on 100 percent polyester. Good for foil when needing fine detail.
230 mesh/48-micron thread: Printing on top of the underlay, light colored garments. Will hold fine detail. Simulated process printing. This is for cotton and poly/cotton garments. Will hold 45 LPI – 55 LPI halftones.
86 mesh/100-micron thread: Use for heavy ink deposits for athletic printing. Good for printing an adhesive for foil. Tension to 35 N/cm or higher.
305 mesh/34-micron thread: Use for very fine detail on light colored tees. Use when printing four-color process with 45 LPI – 65 LPI halftones. This is for cotton and poly/cotton garments. Tension to 22 N/cm but no higher.
330 mesh/34-micron thread: Used for very fine detail on light colored T-shirts when working with 65 LPI halftones and higher especially four-color process. Tension to 22 N/cm but no higher.
80 mesh/70-micron S thread: Use for thick capillary film for printing with high density inks. Tension to 35 N/cm or higher.
60 mesh/120-micron thread: Used for a small flake glitter and Crystalina. Tension to 35 N/cm or higher.
40 mesh/200-micron thread: Used for large flake glitter. Tension to 35 N/cm or higher.
Note: in all cases, depending on the specific manufacturer, mesh counts may be slightly higher or lower than the ones listed.
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