Real Talk: Ink Curing
We manufacture plastisol ink. We are doing it. It's messy. Come to Louisville and check it out. This is happening. Having said this, why are we not the first phone call you make in regards to testing your dryer temperature? Oh, you called the dryer manufacturer? Bad idea. These guys are more interested in how many prints an hour their dryer can produce. Their testing methods are clearly biased towards a fast dryer belt speed and higher temperature. This makes them look good when you are producing 800 or 1000 prints an hour (I picture an equipment salesperson flexing his muscles as he brags of production capabilities). Hey, we like some of these guys but this is how they sell equipment. Fast and hot is not a curing strategy we can get behind. Too much can go wrong.
Again, we manufacture ink. Our motivation is to keep the ink on your fabric. Vibrant prints. Consistent prints. No fabric damage. Our motivation of keeping our ink looking good should tell you that listening to us about curing will keep YOUR best interest in mind. We don't want our ink washing out. Under/over curing can lead to dye migration. We don't want that either. We want you making fantastic prints you can post to our Facebook page with a smiley face emoji or a thumbs up.
Let's get into it. How are you testing your dryer? Whatever you do, don't say the thermostat on the dryer. This is an important number but not for judging the ink temperature. Are you using Thermolabels (paper thermometer), heat probe, infrared gun, something else, or nothing at all? Scratch the something else and nothing at all from your wish list. Nope. Can't do that. How about the infrared gun? This is a sticky situation and I can already feel the eye roll coming. You can't use this to measure ink curing. You can't. I know you want to. I know it's convenient. You can't. The infrared gun will only measure the surface temperature of the ink. When an ink is not cured, it is always where the fabric meets the ink. This part of the ink deposit is still "gummy" for lack of a better word. It is not fully fused. It isn't cured at the bottom. The infrared gun can't see this. I was once told this was similar to a PC vs. Mac conversation. I was against the gun out of my own snotty preference. Nope. I was against the gun out of necessity. It can't help you unless you are looking for hot/cold spots on a heat press or checking a dryer element to see if it is working. I am not questioning its accuracy, only its ability to measure where it matters. Moving on. The heat probe is accurate only when the cross wires are placed in the ink. This creates a few problems. First, it ruins the print. Those wire marks aren't coming out. Second, it can be hard with thin ink deposits to keep the wires in the ink. Finally, it is known to be inaccurate when testing dryers without forced air. Most electric dryers do not have forced air.
This conversation just lead us to Thermolabels. These paper thermometers are not perfect. However, they are the best option to ensure your ink is cured properly. This is reality. This beautiful, low tech device has been saving screen printers from bad decisions for years. The #5 package measures from 290ºF to 330ºF. This is perfect for regular plastisol ink which is most often cured at 320ºF. The #4 package is available for our low temperature inks measuring from 240ºF to 280ºF. Side note: if you aren't using our low temperature inks...you want to. Call me.
So, how do you use these wonderful little devices? First, my suggestion is always to test each and every fabric you are going to print when you are going to print them. Place a Thermolabel next to the first and last print of the order. Take these Thermolabels and attach them to the work order. This is accountability at its finest. This will save you thousands of dollars and prevent angry customers. Just do it. OK, this is important...make sure when you are attaching the Thermolabel to the fabric, you push it down firmly. Rub it if you have to. Thermolabels often get a bad name when the 310ºF indicator has not turned black but 320ºF indicator has. This is why I like to attach it when it is still on the platen. This gives you a hard, flat surface to work with. The 310ºF indicator didn't turn black as it was not fully attached to the fabric. It's not a bad label, it simply did not get the opportunity to read accurately. Another important note, the temperature has not been reached until the entire 320ºF square is black. Black around the edges is meaningless, please disregard these.
Now that you know how we test for ink curing, you need to know how to set up your conveyor dryer. Gas dryers are the most consistent. This is always our preference as electric dryers are prone to hot/cold spots. This can really be a drag, especially when you are running a fast belt speed. Regardless of your dryer type, they will be set up the same way. Let's get your belt speed correct. Don't worry about the temperature yet. Get a hold of a stop watch or a smart phone with a timer. Place something on the belt and start timing the moment it enters the chamber and stop the moment it exits. The size of your dryer combined with your production requirements will largely determine your belt speed. We would like to see the print in the heating chamber for a minute if you have a short dryer belt. A minute and a half is ideal for a longer dryer belt. We know many printers with smaller dryers don't want to hear this but it really is the way it should be. However, if you simply cannot do this, please keep the print in the dryer for an absolute minimum of 30 seconds. This is risky as ink curing is a time and temperature event. Thanks to the inconsistent nature of electric dryers, if there is temperature fluctuation, there is no chance the ink will be cured. Very small margin of error.
Now that you have the belt speed set up, you need a temperature. I really can't tell you what temperature your dryer needs to be. So many factors! I can tell you a few things I have seen. Gas dryers are often in the 350ºF to 375ºF range. Electric dryers could be anywhere. 400ºF...800ºF...1100ºF...I have no idea. It depends. This is why Thermolabels. You need them. Get yourself a starting point, let the dryer heat up, and test with a Thermolabel attached to a cotton shirt. Important note, we are sticking with cotton for the moment. You don't need a printed shirt, only a shirt and Thermolabel. Also, don't change shirt colors. Don't change shirt sizes. Keep it consistent. This matters, especially with electric dryers.
Do you have it now? I am looking for a slow belt speed, a cotton t-shirt with zero heat-related damage, and a Thermolabel with 320ºF indicator that is completely black. If so, you aren't finished. Grab a thick cotton hoodie. Attach your Thermolabel. Place it on the belt. Now you may be upset. Those of you with a gas dryer and a long dwell time in the heating chamber probably feel pretty good. Those of you with an electric dryer hate me. It's not my fault. Be nice. The Thermolabel is indicating a far lower temperature. This is reality. Yes, the hoodie was heavier than the cotton t-shirt. This means it takes longer to heat up. This is why you will be attaching a Thermolabel to each and every order. First and last print. You can predict some of these temperature fluctuations but not all. A thin 100% polyester tee will go the opposite direction. You will heat up quicker and possibly damage the fabric. Again, printing with our low temperature inks yet? Call me. What you will want to do now is slightly slow the belt speed for the heavy cotton hoodie. Slightly speed up the dryer belt for the thin polyester tee. I said slightly. Remember the time minimums I discussed earlier? Try to stay above these.
OK, you now have a road map for curing ink properly. You have Thermolabels. You have accountability on every order you will print. Now for the fun part! I get to tell you what is going to happen if you don't listen to me. Predicting the future is my favorite!
- Fast dryer belt speed: You are begging for a problem. A faster dryer belt means you need a hotter chamber temperature. So many problems. Think about this...the faster the belt is moving, the quicker the print will either into a box or be stacked onto a table. In both situations you have ink risks. The ink is really hot with no cool down time. It may stick to itself or another print. Ruined! Also, if plastisol ink heats up too quickly it can get bubbles or little holes in the ink. This looks terrible. Add fabric problems such as ghosting, shrinking, scorching, fabric discoloration, and melting to the already fatal ink problems, just don't do it. Have you heard of our low temperature inks? Call me.
- Using an infrared gun: Your ink is under-cured. That's the deal. Promise. Your gun measures 320ºF. Your Thermolabel is not turning black. None of the indicators are black. Does this mean the Thermolabel is broken? Expired? They never worked? Nope. 320ºF is the surface temperature. That is all. For those who want to make the argument that they can use the infrared gun to measure the surface temperature of the ink to the same surface temperature of the ink when a Thermolabel was indicating 320ºF...how thick is that ink? What color is that ink? Just don't.
- Using a heat probe: This is not a horrible option but you are left with lines in your print and calibrating every year. Time consuming. Messy. I love me some Thermolabels.
- Not testing your dryer at all: Why did you even read this? You are living on the edge.
- Using Thermolabels...but not often: Your dryer may look like your most trustworthy friend, but it is not. This is your dryer. Test it. Each fabric heats up differently. Test it.
Hopefully after reading this you are timing your dryer belt speed, adjusting temperature, and including accountability into your process. If you have any questions or problems, be sure to call me at 800-942-4447.
Director of Product Development