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Successfully discharging a print requires that it reach a temperature of about 320 for about 90 seconds or more to give the water in the ink time to evaporate. How much success you have with a flash will probably be determined on how large the image is in comparison to your flash. Cross ventilation in your work area for good air exchange is essential, but it doesn't necessarily need to be a conveyor with a vent. Some steam is going to come out the ends of the dryer. I use Union's Plasticharge, and according to them, you want the ink to heat up evenly, not too hot too quickly, to get the best discharge. A conveyor would be best as it's easier to control the heat. I've got an inexpensive dryer with no vent, and I've had to slow the belt down and reduce the heat to keep the temperature in the zone I want. I've never had to run the shirts through a second time to finish the discharge.
 

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Whenever using discharge inks, always make sure that you are working in a well ventilated environment. While discharge inks and discharge agent are not currently banned in any state or by the feds, I still believe it can be harmful to your health if you are not taking the proper precautions....

  1. Always handle discharge powder carefully. Use as little as possible to receive a good result and always return the lid to the container after mixing into the ink. I also usually wear gloves when handling the product.
  2. Ventilation, ventilation and more ventilation. Do not work with discharge inks in a closed space without having your curing equipment exhausting outside your work area. It may be a good idea to wear a quality respirator in closed environments.
  3. Clean up after yourself. Don't leave dischage inks sitting out and uncovered (like many of us do with plastisol inks). Immediately clean screens, squeegees and spatulas after printing. Definitely wash your hands after handling discharge inks.
  4. Dispose of used ink safely and according to your state and local hazardous waste regulations. A good way to get rid of the old ink after it will no longer discharge is to print it. The ink will still work well on light color garments and you can never have too many samples and extra shirts!
The bottom line on discharge inks is that they are safe to use in most screen printing shops if the printer and shop staff are educated about the process and safety concerns.

I personally wouldn't use a flash cure unit to print discharge inks, but that's just me.
 

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The big problem with flash curing it that most flash units do not have a method to suck the fumes up and out of the building like most of your conveyorized driers do. They are meant to be printed wet on wet then thrown onto the conveyor belt where the ink must reach 320f for enough time to boil off all the water turning into steam and going up the stack setting the ink to make it wash fast. Most rspirators are not adequate to protect you from formaldehyde fumes.
 

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Many folks are currently using Discharge ink as an underprint, lightly flashing the print to dry it enough to lay down plastisol on top, then drying it fully and finishing the discharge on the conveyer. I personally do not like this method since the discharge ink is almost invisible and registering an invisible ink means a LOT of misprints. The finished goods look good if you know what your doing, but i've seen as good a results using all plastisol so not a huge deal. No matter what anyone says discharge ink smells bad in use as its being cured. Even the 24 foot dryer we have with forced air makes little difference. IT STINKS! It will make you feel sick if you work with it for any length of time and so I don't recommend anyone use it on orders larger than say 200 pieces. (30 minutes of print time even done slowly) and then air out your floor.
We run this ink at the end of any day and leave the fans running for a couple of hours to clear the floor before we lock up at night.
 

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Not that I've done it, but I've read from some who use the discharge as an underbase that they set the whole job up with plastisol so they can see what they're doing, then clean the underbase screen and run the job with the discharge.
 

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Many folks are currently using Discharge ink as an underprint, lightly flashing the print to dry it enough to lay down plastisol on top, then drying it fully and finishing the discharge on the conveyer. I personally do not like this method since the discharge ink is almost invisible and registering an invisible ink means a LOT of misprints. The finished goods look good if you know what your doing, but i've seen as good a results using all plastisol so not a huge deal. No matter what anyone says discharge ink smells bad in use as its being cured. Even the 24 foot dryer we have with forced air makes little difference. IT STINKS! It will make you feel sick if you work with it for any length of time and so I don't recommend anyone use it on orders larger than say 200 pieces. (30 minutes of print time even done slowly) and then air out your floor.
We run this ink at the end of any day and leave the fans running for a couple of hours to clear the floor before we lock up at night.

I just wanted to add to this statement..you shouldnt be registering to printed ink on the platen. If you setup your job of with a reg system or to the film, you can register jobs much faster and much more accurate...
 

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LOL yeah trust me We have a 14 color Challenger II, a 10 color Chamelion, and a 6 color Gauntlet we use M&R's Tri-lock registration system very well. We run on average 3-6 designs a day on the Challenger of more than 8 colors with an underprint and more than one colored shirt per design with an average run of 400 pieces so our setup time is as fast as 95% of the better printers out there. Registration systems are only as good as the pre-press and users. So regardless what registration system you use there are always going to be human errors. Underprints that can't be seen untill after they come out of the dryer are not production friendly by anyones criteria. Our quality standards are a little higher than most our misprint/returns rate is less than 1% on average so i'm pretty confidant in my people and I still wouldn't recommend that process compared to the success we get with straight plastisol.
 

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Just wanted to clarify your statement...a long time ago when I got in this business, thats how we were taught...print black, then set everything up to black. What a nightmare....just wanted to let folks know that isnt the way it should be done, and it sounded as if thats what you were suggesting to do. I haven't had a problem printing discharge underbases...once were registered, everything holds tight for production, so it hasnt been an issue at my shop.

There are some great discharge inks out that really work well.
 

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Many of the posts above make reference to formaldehyde fumes. It is my understanding that some of the ink companies are now using an alternative to formaldehyde that has less of an odor and is less corrosive. I would suggest contacting your ink rep and see if they can spec a product that will work with your equipment. It's a lot easier to try different inks than it is to try different equipment. There are also plastisol/discharge hybrid inks you could try.
 

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I've used Union's Plasticharge, and unless you stick your nose in the cup you mix it in, the smell is not particularly strong in the shop. I don't know that I'd use it in a small closed up room, though. After running through the dryer, the shirt does retain a slight sulfur odor, and from what I've read they should be washed before wearing.
 

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We've used three types of discharge inks. All smell bad. On short runs of 50 pieces or less the smell is not so bad that it will run you out of the shop but on orders of 400 by the end of the hour of printing the odor is pervasive enough to warrant clearing out our 5500 foot shop of people overnight. I've felt sick from the smell myself.
 

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Many of the posts above make reference to formaldehyde fumes. It is my understanding that some of the ink companies are now using an alternative to formaldehyde that has less of an odor and is less corrosive.
I'm not sure about that but I do know that the ink formulations are better and that (like with Matsui's discharge) you don't need as much of the discharge agent as you did in the past. For this reason the amount of formaldehyde in the fumes is much lower that in the past.

As far as inks that use non-formaldehyde discharge, I would be cautious of those too. I have heard that many of these non-formaldehyde discharge inks contain chemicals that are just as bad or worse for you than formaldehyde.
 

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CNClark-

Just wanted to clarify your statement...a long time ago when I got in this business, thats how we were taught...print black, then set everything up to black. What a nightmare....just wanted to let folks know that isnt the way it should be done, and it sounded as if thats what you were suggesting to do. I haven't had a problem printing discharge underbases...once were registered, everything holds tight for production, so it hasnt been an issue at my shop.

There are some great discharge inks out that really work well.
This is how we do it. What is the other option. I have a riley hopkin joystick registration press. We generally print the darker color and line the other colors up to those registration marks. I could not think of any other way to do that.

The reason I was reading this thread is because we just started discharge and loved the results. We do not have our dryer vented but we have a vent in our ceiling and open a door to the outside. I am thinking of running a vent tube to our dryer and then up into the attic which has a vent to the outside. We wore respirators with filters and I felt pretty safe.
 

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Good job with taking those precautions tozier9. While discharge inks have not been shown to cause any ill effects to workers in screen printing shops, it is always a good idea to take the necessary precautions.

Good ventilation, careful handling of discharge agent and discharge base, wearing gloves while handling and mixing and sometimes even respirators are highly recommended when printing with these inks. In my opinion, it's better to be safe than sorry!
 
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