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Originally Posted by TeddyRocky |  | | | | | | | | | I have a black body 1600 BF1 model flash dryer I am using to cure my prints. The dryer itself gets about 550-600 degrees F. About 1.5 inches away from the shirt, the shirt reaches approx. 325 degrees F in 12 seconds. Plastisol is being used, and I made sample squares and washed them last night. One set of white colored shirt, and one set of charcoal colored shirt with black ink. All the ink stayed on all sample squares, and I did a stretch test, and some of the non shiny looking prints split when pulled with the shirt fibers (which should be normal i think) and goes back together. Some of the shiny looking ones (purposely cured for a 40-50 seconds to rule out some time variables) they dont crack no matter what, but look bad. Which one is considered properly cured? | |  | |  | |
Hello, cured is cured is the best answer. The stretch test is an 'old wives tale' that has been around long enough to be taken as fact by a great number of people, but in fact is completely without fact. Let me explain with the question: "What does the stretch test prove?" If the plastisol ink is cured and the resin has been converted to a pliable layer of ink will it break apart when stretched? Sure! If the plastisol ink is cured on the surface only and the ink on the bottom is not cured, will the ink break apart when stretched? Sure! If the ink is not cured at all, will the ink break apart when stretched? Sure! If the ink is actually overcured, will it break apart when stretched? Sure!!!! f you use the stretch test you will never have a cured shirt! This is not a test, but an exercise in failure.
Now, there will be a dozen responses to the by every Tom, Dick and Harry finding fault with the premise and arguing that they have been stretching shirts for a dozen years and they know for a fact that the stretch test works because they have never had a shirt returned. So, what does that prove? That the customers didn't bring the shirt back! Nothing else!
The truth is that the only way to be sure that ink is cured all the way through is to actually test the temperature that the ink reaches while being heated. The only instrument that I know of that will do this is the Atkins Donut Probe.
The Temperature strips (used to measure the heat of engine blocks) are only accurate on the surface of the ink.
The Ray Gun (used by air conditioning repairpersons) is a total waste as it cannot measure the highest temperature of the ink inside the heating chamber and it can only measure the ambient air 'around' in the ink. Actually the gun measures in a conical shape from the nose of the gun and at 8-inches it measures a full 12-inches across. If you really wanted to measure the ink you would have pretty much have to hold it to the surface of the ink and then you'd only be getting the surface temperature.
Most ink companies build their plastisol inks to cure in what is frequently referred to "300-350°F" range. This cure range can vary up and down depending on the color of the ink, the thickness of the ink, the ambient moisture or relative humidity of the substrate and many other variables.
There are generally three temperature levels in a plastisol's curing cycle - gel, fusion and remelt. The actual temperature of each can be obtained from the ink manufacturers. Keep in mind that these temperatures are arrived at in the ink manufacturers ‘lab oven’ and can vary widely around the world. What happens in New Jersey, stays in New Jersey and cannot be easily repeated in Tempe, Arizona in the heat of the summer there. You can, though, use the manufacturers temperatures to draw some conclusions that will work in your shop.
The three curing stages are never the same from one ink to another or from color to color. Some inks will have a high gel temperature and a low fusion temperature, while another will have a low gel and a high fusion temperature. Most plastisol inks used for direct printing will have a wide variance between the gel stage and the fusion stage. This is needed so that the inks can be gelled with a flash unit and then later brought to fusion, when needed.
The gel stage, used when printing an underbase or in some cases to preserve the detail in one color before printing the next color, must happen at a very low temperature and very quickly. When an ink is gelled it simply means that the resin has absorbed quite a bit of the plasticizer making the ink less tacky so that the next color can be printed on top and bond to the surface of the gelled ink. Remember, though that plastisol ink cannot stick to plastisol ink that has been cured, so you can’t gel the ink past the gel stage of about 180-degrees Fahrenheit. In other words a chemical bond cannot happen once the ink is cured and thus the upper layer of ink may wash away during laundering.
Plastisol ink fuses as soon as it reaches the given temperature where the resin absorbs the total of all plasticizers. The ink temperature then begins to drop and as it cools the result is a soft and pliable layer of plastic resins. If the ink is allowed to overcure, then the plasticizers are ‘burned off’ and the resin will become a fairly stiff and very dry layer of ink. This overcured ink can sometimes be brushed away from the shirt and will certainly wash away in the laundry. If the upper surface of the ink is cured but the cure did not reach to the bottom of the ink layer, the uncured ink will wash away in the laundry and carry away the ‘cured’ ink on the surface with it as the top layer is not actually adhered to anything.
Another ‘old wife’s tale’ is that curing takes place in a certain amount of time and temperature. The ink manufacturer will almost always give a cure in temperature only, because they have no idea if you are using a 12-inch curing tunnel or one that is 12-feet long. No ink manufacturer can give you a time and no dryer manufacturer can give you a temperature as neither knows the other’s equipment.
The basis of this time and temperature came from the fact that the conveyor dryer with Infrared units is in a constant state of heating and cooling. If you place a shirt in the dryer just as it has reached the highest temperature then the heat is lowering and the shirt may evacuate the dryer after the heat has lowered past the cure temperature.
If you place a shirt in the dryer just as the lowest temperature has been reached and the heat is on the rise, the shirt may evacuate the dryer before the heat reaches the point that will cure the ink.
To keep the shirt in the dryer for the prescribed time, most dryer manufacturers will tell you that the ink will be cured at 320 degrees and for 2 minutes to assure that you slow the dryer down so that the dryer reaches the highest and lowest points while the shirt is still in the tunnel.
Now, to address the flash you are using. Regardless of what any manufacturer states about their flash unit it is not a flash dryer or flash cure unit. These are two different things. Flash means to gel the ink and cure means that the resin has fully absorbed the plasticizers.
The flash unit actually can cure ink, but in a very haphazard manner. Given the way in which the moisture from the substrate is released in an upward manner and then held in the heat of the flash unit, it actually works more as a very small sauna. The temperature in the middle of the flash unit will be very hot and very moist while the heat around the edges will be cooler and dry.
Now, add any movement of the air in the room and woosh – all that heat is gone and that shirt is not ‘cured’ the same as the previous one. Timing is everything and most flash units are completely manual in that the printer usually counts ‘one thousand one, one thousand two, one thousand.. ‘ well you get the point. Not exactly accurate.
And guess what? Most printers believe that if a flash unit situated about 1.5 inches above a shirt for 12 second will cure a shirt at 8:30 a.m then they can safely use that temperature and time all day long, day in and day out, week and month after month. No! It ain’t gonna happen that way!!! As the day progresses and the moisture level changes, so will the cure change. As the flash unit ages it becomes weaker and weaker and the cure will take longer and longer, but is anyone measuring? Oh no!
There are a dozen other reasons why a flash unit shouldn’t be used to cure ink, but hopefully I have given enough reason to raise some question in your mind and make you want to investigate a conveyor dryer. Grant it is nothing more an a conveyor with a couple of flash units mounted in it, but it is a very good way to cure ink and even cook pizzas in a crunch.