A Great Screen Saves Money

Screen Frame

The screen is one of the most important pieces of equipment a shop owns. The screen determines profitability and quality more that most people realize.

Do you wipe the bottoms of screens while printing? Are ink deposits heavier than you would like? Do you have problems keeping colors butt registered while printing? These and other problems normally come from low tension screens.

Loose Mesh
When mesh in the frame is not tight it moves from the friction of the squeegee being drawn down the screen. Ink that has passed though the screen is smeared, perhaps slightly, across the bottom of the screen and on the garment. You might notice under the screen a build up of ink around the outer edges of images. Prints are not as sharp and clean as they were when first printing.

Soft Mesh
When mesh is soft the mesh forms a wave in front of the squeegee that is moving down the screen. Pushing that wave requires more effort and can produce carpel tunnel syndrome. Ink is being pushed through the screen and rolled on to the garment rather than being placed on the garment by an up-down motion in off-contact printing. The rolling action deposits more ink on the garment than the up-down motion.

The lateral movement and rolling action of a wave translates into images being printed in the area where you want the image, but not exactly on the same spot print after print. This is most noticeable when trying to butt register colors.
If printing true process or simulated process, careful inspection of dots will reveal dot gain. You might not see the dot gain with the naked eye, but you will probably see colors or shades you did not intend. Certainly the resolution and depth of color will be lost.

What should you do?
When screen printers recognize they have such problems they typically try to tighten the screen in the press. They might tighten up the registration gate. Those are not the problem. The problem is the mesh is shifting within the frame. The only solution is tight mesh in the frame.

Ask almost any screen printer, do you prefer screens with tight mesh or loose mesh, and the answer is always the same. Ask whether they noticed a new screen is not as tight after printing a hundred or more garments, and again the answer is almost always yes.

When mesh is stretched the first time to its maximum it will lose 25% of the tension within 2 hours. After the 2 hours the mesh can be tensioned again recovering the lost tension and raising the tension. Mesh that is glued to a frame never recovers. Stretched screens received from the supplier have already lost significant tension, but are considered by many screen printers as those “tight” screens.

Then, 4 hours after the 1st re-tensioning the mesh will have lost another 15%, and after the 2nd re-tensioning another 5% by the next day. Coarse mesh counts like 110 mesh (43 in metric) hold tension much better than say 305 mesh (120 in metric), because the thread diameter is so much larger. I typically tension and re-tension new 305 mesh 6 times over at least 3 days before coating with emulsion and printing the first time.

Procedure
After each job the stencil (emulsion) and ink should be removed, in that order, and then the mesh tensioned again before coating the screen with emulsion for another job. After about 500 prints and increasing the tension several times after the first print run the mesh finally becomes dimensionally stable. Stable mesh is referred to as “work hardened.” That means the tension at the end of a print run is the same or very close to the tension at the beginning.

Until a shop gets to work hardened status print one and print 300 probably do not look or feel the same. Non-critical work should be printed with new screens, and work hardened screens saved for the most critical work. Such quality can only be achieved with retensionable frames like the Newman frames. These frames are aluminum tubes that can be rotated with the mesh locked in the tube to raise the quality standards of the print shop.

The pay off from switching to frames like Newman is jobs can be set up and printed faster. The work of wiping the bottoms of screens is eliminated. No longer does the person have to be so careful printing to compensate for what the screen might do. Ink deposits are determined by the stencil thickness alone and will be thinner, softer prints.

Some frame options
You can prove the benefits described in this article by getting one frame which you stretch and tension several times yourself. This single small investment will probably be the greatest improvement you can make to your printing operations.

Aluminum frames have another advantage. The frame will not warp from being processed through water. Quality printing requires that the screen be absolutely flat. We know that the amount of ink deposited during the print stroke changes with the off-contact distance. A greater off-contact distance allows the mesh to open more and deposit more ink. The off-contact distance, and ink deposit, are not uniform with warped screens.

Emulsion or Capillary film
Once a shop has very tight mesh from re-tensioning, capillary film rather than liquid emulsion offers important benefits. Capillary film is fundamentally different from liquid emulsion. Liquid emulsion is embedded in the mesh. Capillary film is applied with plain water to the print side of the mesh forming a two-ply structure.

Ink passes around the threads of the mesh and fills a void created by the stencil, substrate and mesh. The thickness of the ink film is determined by the thickness of the capillary film. A high mesh count is used with a thin capillary film. A thin capillary film deposits a thinner ink deposit and produces a softer feel to the print.

When printing white ink on a dark fabric like black a more coarse mesh allows more ink to pass through the screen. The capillary film must be thicker to bridge over the holes of the mesh. A thin capillary film on coarse mesh will break down during printing. With a thicker capillary film on the coarse mesh the thicker deposit of ink offers greater opacity on dark garments.

The image formed by the tight mesh in the frame and capillary film produces an image that more accurately mirrors the image that was on the film positive. There isn’t the dot gain or image expansion experienced with soft screens. The edges of the printed image are formed by capillary film rather than being influenced by the threads of the mesh.

The combination of re-tensioned mesh and capillary film allows printing a thickness of ink that is opaque after one print stroke. The cost of flash curing and printing a second time is avoided. This is a dramatic cost savings. Most printers typically report they manually print 100-120 shirts per hour when they print one color dark ink on a light colored shirt. When they print a light colored ink on a dark garment they have to flash cure and print a second time. The flash cure and second print cause production to drop to about 35 shirts per hour. So the production difference is 300-400%.

White ink printed on dark garments with one print stroke will have a softer feel and be more comfortable to wear. Most consumers want images they can see, but not feel. A great screen is a critical part of producing what consumers want.

The combination of very tight mesh and capillary film also creates the opportunity to print 3-dimensional images using 3-D ink. The 3-dimensional effect can be used two ways.

3-d effect
First, many fabrics are textured. Golf shirts can be woven many ways like pique. A 600 denier polyester tote bag has a coarse texture. 3-D ink printed through a very tight screen and capillary film will fill the voids of the fabric, produce sharp edges to the image, and leave an opaque coating of ink on the fabric.

For example, I print 3-D ink using a 110 mesh and 100 micron capillary film on golf shirts. The image is opaque, soft, flexible, and not raised above the fabric. Inks which are not 3-D will follow the line of the texture of the fabric and appear to be saw-tooth.

Second, inks can be printed in the third dimension by using a thick capillary film. Images that are 200 and 300 microns thick are clearly noticeable as being 3 dimensional images.

Layer upon layer of thick ink can be printed to create images in tiers. The screen must be tight in a re-tensionable frame and capillary film must be used to produce ink deposits of uniform thickness. Unusual effects can be created. A thick deposit of ink printed on pique covers the texture and presents an image raised above the fabric surface. Flash cured 3-D inks do not expand with heat. 3-D inks are not puff inks. Then, for example, large half tone dots can be printed on top of a basketball to create the bumps on a real basketball.

Such unusual images are immediately noticed by the public, and command higher selling prices. Printing on textured material like golf shirts, tote bags, and seams of caps are ways to increase sales and profits. Without that great screen, such opportunities are beyond your reach.

For comments and questions, contact the author at roger@screenprintingbiz.com.