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Black is first, red is printed on top of the black. Finished print is at the bottom.
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Any printer with an automatic press that isn’t printing some of the special effect inks that are available are missing out on one of the most lucrative areas of garment printing. It is also one of the most difficult because it requires you to understand everything about how to produce a quality print. The artwork, screen mesh and stencil, squeegee selection, inks and printing procedures need to be correct in order to have a successful finished product. Because of this, many printers don’t use special effect inks which opens up some opportunities such as having less competition and therefore able to make more money. Many of the products used will require increasing charges since costs will also increase, but with less competition, that usually isn’t a problem.
The special effect inks and procedures that will be covered in this article are the basic ones, high density inks and gels. Once you understand how to use these, the ability to use some of the unusual bases and printing techniques will present themselves.
Let’s start with the artwork. Most of the artwork will be done in a vector program like Illustrator or Corel. We would not be able to do a very good job in a raster program such as Photoshop because of the size of the halftone dots we would need to use to get some of the inks through the screens.
One color work is not difficult, but also not very exciting most of the time. In designing a multicolor piece, keep in mind that the difference between a standard in and high density ids the high density has a dimension. The base color of a multicolor high density print needs to incorporate all the high density colors that will follow giving them a surface that is on the same level. Each color need to incorporate the following colors into it. The art department dictates color order and that order usually cannot be changed.
Once you’re done with the designed and separations, it time for the screen making. I like to us a mesh count of 80-83 depending on the mesh manufacturer, with a 70 micron thread. Most 86 mesh being used is 100 microns thick and only has a 44% open area. The 70 micron thread has almost a 60% open area and allows the inks and gels to pass through with less pressure. Because of the thinner thread, the tension should be about 30 N/cm. Much more and the mesh will rip.
There are wet emulsions that can be used for coating the screens, but I’m a fan of capillary film because it’s easier to use and far better for repeatability. In order to apply the capillary film, it is important to follow procedures. Capillary film come in thicknesses from 100-1000 microns. Most of the prints will require 200-400 microns for the effects we want. Different effects may require different thicknesses. Using the thick capillary film requires attaching it to the screen using emulsion and not water as is used for standard capillary film. Each manufacturer has a specific emulsion they recommend for attaching their capillary film. The capillary films are expensive and requires additional charges to you clients just to cover your additional costs.
(Set by step procedures for applying capillary film-Article #3)
Once the capillary film has been adhered to the screen, it has to dry. In a heated drying cabinet it could take several hours. Without heat, it’s best to let the screen dry overnight. You’ll know if it’s dry or not when you go to remove the backing sheet. If it doesn’t want to release, it’s still wet.
Each manufacturer has a range of exposure times based of the strength of the exposure unit used. Although it is possible to use other than metal halide exposure units, it is not recommended. A 5K metal halide exposure unit will require approximately 90 seconds per 100 microns of film to expose at about 40” from the glass to the lamp. Weaker lights will require more time and testing should be done.
If you have a dip tank, put your screen in for several minutes prior to washing. If not, wet both sides of the screen but only wash the side with the capillary film on it using a 1000 PSI washer from about 12 inches away.
Once the screen is dry, touched up and ready for printing, we need to select the squeegee. I like to use a 65/90/65 triple durometer squeegee that is sharp and straight for most high density inks and the stiffer gels. Squeegees used on an automatic should be sharpened about once a week to stay sharp. New squeegees should be sharpened to be straight. For the softer gels, I like to use a 60 durometer squeegee so it doesn’t scoop out the ink instead of putting down. If too hard a squeegee is used with a soft gel to cover a large open space, the fibers of the garment will show through the print.
Make sure you stir your inks before putting them into the screens. If the inks are stiff, it will be difficult to print with them and get them to clear the screens. When the inks are stirred, they will be soft and print easily.
The difference between an ink and a gel is inks are not supposed to melt and shine, although they will if they are given too much heat. Gels are made to melt, although if kept at a lower temperature, they could have a matt finish and can look like ink. Different gels melt at different temperatures.
Setting up the press for high density is not much different that setting it up for standard inks with a few exceptions. You will need higher off contact that with standard inks. The amount should be enough so the screen is not touching the print after the print stroke. On multicolor high density jobs, the first two colors may have the same amount of off contact, but the third color will probably require more. Since we need to lay down a large amount of ink, you will need to set your squeegee at a big angle. I like to use 250-30 degrees. The flood and print strokes should be medium speed with the print stroke continuing for 3”-4” past the image to give the screen time to peel away from the design. The pressure should be just enough so the ink clears out of the screen. Flashing the high density inks and gels is not a problem. They may even flash faster than some of the standard plastisol inks you use. You will need to flash between each high density color and a cool down station is recommended if you have enough heads.
One of the important items to record when printing high density is your dryer settings. Because some of the gels melt at a low temperature and others require a high temperature, recording the belt speed, thermostat setting, internal temperature and exit temperature will make it easier to repeat the job. Since the thicknesses of the prints are much greater than standard plastisol prints, they will require more time and temperature in the dryer. Some of the gels may require temperatures as high as 380 degrees. Check with the ink companies to find out what temperature range is required to fuse the particular inks and gels you’re using.
In the future, I will write some articles addressing different looks techniques and products to achieve a variety of effects. In the meantime, enjoy experimenting.
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