Ensuring High-Quality Screen Printing

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. In order to have a quality control program, we have to examine where things can go wrong and be able to test and document results once standards are established.

There are a number of “tests” that should be conducted constantly in order to ensure that the garments you deliver are to the customer’s satisfaction and to the standards the company requires. In order to have an effective quality-control program, it is necessary to establish the various tests to be performed and know how to judge the results of the tests and the number of times per day that these tests need to be performed. All results of the tests need to be documented on proper forms and filed for review in case of a problem.

Prior to conducting any tests comes the inspection of garments. This should be done as they are removed from their packages. Recording the results is generally not done unless the garments are expensive or there is an excessive quantity of seconds. It may not feasible to inspect each garment at this time, so as they are being put on press, they should also be inspected as much as possible. It is possible that some flaws will fall through the cracks, but that’s to be expected. The important thing is to catch these flawed garments prior to shipping, if possible.

At the start of a production run, the first thing to do is obtain the form to be filled out over the course of the run. Before using this form in actual production, however, you need to run two tests.

First, print a shirt, but do not fully cure the ink by keeping the garment temperature below 250°F. That done, run all of the tests listed on the form.

Next, take the same garment and run it through the dryer several times until it is scorched. Run the tests again and compare the results. You will now have the results of a print with ink that is definitely not cured and one that definitely is. Hang these examples on the wall so they can be used for comparison by others. Note: the last three tests are for poly/cotton shirts. Again, these tests need to be run before the shirts are printed.

After that, tests should be conducted at the following times: first thing in the morning; just after the first break; just after the second break. Long jobs run on automatic presses should be tested on an hourly basis.

The following is an outline of the testing information to be entered and the procedures to be used for the tests:

1. Temperature Setting of Dryer: This will probably not be changed often.

2. Belt Speed: This will be changed often to allow either more or less heat to be absorbed by the shirt. Slower speeds = higher temperatures; faster speeds = lower temperatures.

3. Relative Humidity: This is very important for use in the future. Eventually there will be a history of documented settings to be able to adjust the dryers quickly as the relative humidity changes so curing the ink is not a problem.

4. Thermo Probe: Use an Atkins probe and record the time the probe reading was above 305°F and the maximum temperature reached. The temperature should be 305 or above for 10 seconds or longer. A fresh shirt should be used each time this test is conducted. The same shirt can be retested after two days. Shirts that are used prior to that period of time may give a higher temperature reading than a shirt that hasn’t been put through the dryer, since the moisture content has been removed.

5. Crock Test: The test sample should be placed on the Crock meter with the long dimension in the direction of the rub. Attach a clean crock cloth to the Crock meter and run 10 cycles. Evaluate against the AATCC Chromatic Transference Scale (0-5 where 0 is total fail and 5 is no crock). Pass is normally 3.5 or better. If you don’t have a crock meter, take a piece of light-colored fabric and rub it over the print and check to see if any color rubs off. Some might, but an excessive amount is not a good sign. Do not rub too much. One or two medium pressure rubs will do. This test is not conclusive by itself.

6. Stretch Test: For a standard plastisol ink to pass the stretch test, it should be able to stretch about 25 percent without cracking. Make a mark 4-inch-wide on the folding tables and another mark at 5 inches. Hold the print to the 4-inch mark and stretch it to the 5-inch mark. Examine for cracking. This test is for shirts printed through a coarse mesh. Jobs printed through a fine mesh will be very difficult to check for cracking. Shirts printed with athletic plastisol or spandex ink will stretch 25 percent even if they are not fully cured. This test is not conclusive by itself.

7. Cellosolve Acetate Test: Open a shirt to the inside and find an area that has some of the printed colors on the front of it. Use a dropper to put a few drops of cellosolve acetate behind the print on the inside of the shirt. Take a piece of clean white fabric and squeeze it to the printed area on the outside of the shirt where the cellosolve acetate has been applied. Hold with pressure for two minutes. Remove the piece of fabric and inspect for any staining. If there are no stains, the ink is probably cured. Some ink colors are not very stable and do stain slightly even though they are cured, especially red.

If a print fails any of these tests, all the shirts that have been put through the dryer since the last passed test need to be put through again. If you’re doing a long run job, it may be desirable to do tests on an hourly basis so the number of shirts that would have to be put through the dryer in case of a problem will be minimal.

There are many tests that companies perform to check if the ink on a garment is cured (fused) properly. Most of these are quick tests that are not completely reliable but are good for quick results. The best test and most reliable is a wash test. Unfortunately, wash tests take a lot of time, but if the job is big enough or the client is important enough, then doing a wash test is the most reliable way to check the ink and make sure it is fully cured.

Continuity between prints is an issue when printing certain types of designs, especially four-color process since contamination is an issue and changes the colors of a design. There isn’t a specific test to perform in order to control this but there are ways of setting up, so the prints are viewed and inspected on a regular basis.

There should be an inspection station at the back of the dryer. The inspection station should include a table with a controlled light above it. One suggestion is a GE Kelvin 50 bulb, which is supposed to simulate daylight. There should also be a rail across the station so a sample or control-printed garment can hang from it. A roll of colored tape can be used to make out where there is a pin hole or some kind of misprint or damage to a garment. Measuring tape to check the placement of a print is also useful.

For runs where colors can shift easily, such as a four-color process, the following can be done to see if the colors are shifting: buy a piece of cork or Gray Wall that is about 18 inches high and about 10 feet long and mount it to a wall. Take the approved print, fold it in half the long way and mount it at the extreme left or right of the cork or Gray Wall.

During the run, take a garment every 50 to 75 prints, fold it the long way and see how it matches up to the control-approved print. If it matches, continue printing. If the colors are starting to drift away too much, either add fresh ink to what is in the screen or remove the ink in the screen and add fresh ink. If this is done on a regular basis, it is unlikely that the colors will drift too far apart. If too many garments are printed before inspection, it is very possible the ink will have to be changed.

The most important thing about a quality control system or quality assurance system is that it gets used for every job, every day no matter who the client is, even if it’s an in-house job. Quality is king if you want to land high quality clients.

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