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screen printing => General Screen Printing => Topic started by: Mark @ Hurricane Printing on March 14, 2013, 07:52:02 AM
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I've never been 100% clear on this, and I never had any problems with images washing out. I've always wondered exactly how long plastisol has to remain at its cure point. I see these real little conveyor dryers and think there is no way a shirt can go thru there and reach 330 degress for no longer than a second or two. I have read things where it states that the second plasticol reaches 330 degrees plastisol is cured,,,then I read it has to reach 330 degrees and remain there for 30 seconds or more.
So whats the bottom line on this?
I have an 8ft drier and my heat chamber is about 42 inches long....images hit 330 about half way thru the chamber and max out to about 380-400 right before it exits....from the point it reaches 330 to the time it exits is about 10 to 13 seconds...like I said I never had one problem with an image washing out but it makes me wonder if I can speed up my belt a little bit.
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To the best of my knowledge, the entire in thickness has to reach "320" for a full and proper cure.
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Roger Jennings gave me a tip..it should be under go through the dryer for about a minute.if i remember correctly...which for the small dryers i would have the shirts folded in half so as to fit more on the belt..so if its going in there slow it is baking the plastisol though..this would be good on an underbase print, but on a white tee or something it would probably go through quicker and the ink deposit would reach cure temp..
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it is suppose to get to 320?
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With Brim here - once the whole film thickness reaches 320, the ink has "cross linked"
and is fully cured. Past 350 (temp gun may read higher due to reflection, angle etc.) and starts to re-melt and weaken.
Gaging that temp is a whole other topic. Donut probe embedded in the ink is most accurate, but temp gun I think is most widely used. Wash, wash, wash...
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Thats right we have washers and dryers on site for this as well as for distessed applique. Retention time can vary between our dryers. We have pre-sets for pls and DC but still washtest
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The ink doesn't have to sit at its cure temp for any amount of time. Once it reaches the cure temp, it is cured, period.
The misconception comes from the fact that most people simply measure the surface ink temperature, which could very well be a higher temperature than the ink that is in intimate contact with the garment. It is like cooking a large roast at high temperature. The outside might get done or even burned, but the middle stays raw.
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Roger Jennings gave me a tip..it should be under go through the dryer for about a minute.if i remember correctly...which for the small dryers i would have the shirts folded in half so as to fit more on the belt..so if its going in there slow it is baking the plastisol though..this would be good on an underbase print, but on a white tee or something it would probably go through quicker and the ink deposit would reach cure temp..
Rogers a good man but a minute? No way, if we had to wait a minute on our oven we would print as slow as manuals.
We print at full production speeds on a small electric 54" wide no problem. Wash test all the time for safety, we would do that even if we had a gargantuan oven as well.
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And I'd guess manufacturers build in some "cover my a$$'' latitude as well. I doubt it would be admitted to, but it's there. Wash test is best. Document
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When folks like Roger Jennings or QCM ink state a time like 30 seconds or a minute, I think that they are trying to cover for the folks who may not otherwise get the entire layer uniformly and consistently to cure temp.
I'm almost sure that it is merely insurance.
Though I'm sure that it happens, in my experience, I have rarely seen overcooked ink, but have seen plenty of undercured prints.
And of course, 330 is not the cure temp for all inks.
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We set our dryer up so that the bottom of the ink deposit hits 320 with about 2' left in the heat chamber. We have never had an undercured garment. I do have the luxury of having a donut probe built into our dryer that helped us baseline everything which I know most people don't have that ability, but a $400 donut probe wouldn't be a bad investment for you guys who are way over-curing your garments. Just the electricity or gas savings alone would pay for the probe within the first year.
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I shoot my laser gun up inside the tunnel, keeping the belt slow enough so the ink temp is at around 330 for 10 seconds or so before the temp starts to drop near the exit. Then a stretch test. I also try to keep the ink layer as thin as possible.
The only ink I've ever had trouble with was gold shimmer from Union. The first time I used it I watched temps as usual, did a wash test, and it washed out.
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Ad of course, the tech sheets on metallics and shimmers do warn that the reflective nature of the inks will require an increase in either heat or dwell.
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I think I have to agree with Roger Jennings, unless my donut probe is wrong.
It does take about a minute for the plastisol ink at normal thickness to reach 155 or 160C if you don't want your oven to be too hot. I tried to raise the oven temperature to make it rise quicker, but the ink temperature hits around 170 C towards the end of the tunnel. By the way, I use an infrared oven.
We sometimes heat press wet plastisol, usually we press it for 30sec. Once we pressed it for 10sec for a thin layer of ink.
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I think I have to agree with Roger Jennings, unless my donut probe is wrong.
It does take about a minute for the plastisol ink at normal thickness to reach 155 or 160C if you don't want your oven to be too hot. I tried to raise the oven temperature to make it rise quicker, but the ink temperature hits around 170 C towards the end of the tunnel. By the way, I use an infrared oven.
We sometimes heat press wet plastisol, usually we press it for 30sec. Once we pressed it for 10sec for a thin layer of ink.
Guess that means all the millions of shirts we printed for fifteen years are under cured.
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Roger Jennings gave me a tip..it should be under go through the dryer for about a minute.if i remember correctly...which for the small dryers i would have the shirts folded in half so as to fit more on the belt..so if its going in there slow it is baking the plastisol though..this would be good on an underbase print, but on a white tee or something it would probably go through quicker and the ink deposit would reach cure temp..
Rogers a good man but a minute? No way, if we had to wait a minute on our oven we would print as slow as manuals.
We print at full production speeds on a small electric 54" wide no problem. Wash test all the time for safety, we would do that even if we had a gargantuan oven as well.
This will depend on the size of your dryer. A bigger dryer will let your shirts stay in longer. I've always felt that a dryer shorter than 8 ft. is an invitation to trouble, you have less latitude. Like with a microwave, your food will thank you if you heat it a little slower than full blast... and for those wanting to try out the water based stuff, a larger dryer with convection (gas) is very helpful.
Steve
Steve
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Bottom Line on Plastisol Cure temps and time:
Entire!!!! Ink layer needs to reach 320 degrees, which is the common cure point for plastisol ink. If that takes 2 minutes, it takes two minutes... if it takes 30 seconds, it takes 30 seconds.
Once the resins have fully absorbed the plastisizers in the ink, it is cured. Science is pretty dependable this way. Yes you can get the plastisol to hot.... but it takes a lot of heat to do that and if you are doing that, your shirts are scorching first. Heat stabilizers are added to all inks.
HOWEVER!!!!
The longer plastisol ink is at it's cure temp, the better it's ADHESION is. This really should only be applied (possibly) to athletic garments since they go through a beating during play.
Just something to think about.
Edited for typos lol
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is it possible to over cure plastisol?
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Thanks Colin spot on.
My issue with Rogers statement of one minute is its irresponsible to tell anyone how long any ink in,an oven needs to be period. All ovens are different and all settings are set up different. Everyone's shop has different air flows from one another.
The responsible thing to say is test test test! Find the set up and settings that works for your particular environment and oven. Then document everything and always be diligent and test often.
Steve is correct with a less than eight footer we have to be more than precise on our heat and belt speeds, the latitude is quite small. A tiny adjustment on our belt speed can make a huge difference.
Like I've said before we wash test often, I take strike offs home all the time and rotate them in my washer. Always concerned some day a bad wash will show up but so far our latest oven is rocking.
P.S. if I ran a thirst through my oven for one minute I would have a smoking mess.
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Yes!!!!!! I've did it before on a spot heater, that stuff will bubble up like crazy, and your shirt is just about burn, kinda hard to do but it can happen.
Darryl
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The dryer i used for my manual, yes it was small jennings..so he probably did mean for that particular dryer..
Now i have a Fusion 4 panel and the shirt is in there for like 20-30 seconds, but is twice as long..
but there is different airflow in my shop all the time, if we have a window open or the door open and we always have to check for curing all the time , we dont assume..so we have to adjust...
we dont speed it up to much because we want it in there to get the whole deposit cured..
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I use 19 belt speed for plastisol on tees 12 feet heat sprint 2000
which means about 38 seconds dwell, temp is at 363 on the dryer
if I wasn't using gas I would aim for a longer dwell for sure though
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i just recently bought a vastex d-100 and this lil thing is awesome,, i have it set to take about 1 min 3 seconds for the shirt to go from one end to the other,,it reaches 330-340 no problem...for someone that is just starting out and i was using a flash cure to cure,, this was the best investment i made so far
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Ught oh, sounds like he's hooked. ;D
Don't worry, if you keep at it, you will be amazed at all of the growth and fun new toys you will be buying. Upgrading will seem to never stop.
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Yup that's the fun and bad part of this business. Buying what suits you now, upgrading when you outgrow that to something you need then and then do it all over again. Its a vicious cycle.
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instantaneously once the entire deposit reaches it's cure temp. Plastisol doesn't have to be at a certain temperature for a length of time, just has to reach that temp that it was made to cure at. Most plastisol inks these days cure at a lower temp than 330.
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Alan that is not 100% true. For Example Quick White from Wilflex does require a longer dwell at the curing temp of 320. Just getting there is not enough.
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instantaneously once the entire deposit reaches it's cure temp. Plastisol doesn't have to be at a certain temperature for a length of time, just has to reach that temp that it was made to cure at. Most plastisol inks these days cure at a lower temp than 330.
That blanket statement is kind of like saying all screenprinters are aging, ponytailed, balding, wanna be hippies, who bootleg tye-dyed Deadhead shirts in the parking lot before they get stoned at a GD concert. While it may be true in many instances, ;D there are exceptions.
The plastisol ink guys should chime in here but some of the 'newer' plasticizers require being "held at cure temp" to allow complete conversion to washfast solids.
Ink guys where are you.....
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Alan that is not 100% true. For Example Quick White from Wilflex does require a longer dwell at the curing temp of 320. Just getting there is not enough.
From what I understand about how plastisol inks work, once they reach the "magic" temp, the cure process is finished and there is no need for an extended dwell. The ink goes through 5 stages and the final stage is when the resins completely absorb the plastisizers at the proper temp for that to take place and viola, ink cured. I'm sure there is a given amount of time for that absorption to take place but the absorption process is happening at the same time the ink film is being heated and the final stage and all the plasticizer is absorbed at the right temperature, the cure temp of that specific ink. So I guess it depends on what your definition of dwell is. I'm not suggesting that we find the exact time an ink deposit reaches it's cure temp and then yank it out of the dryer. For example we set our dryer temp and belt speed so that our ink reaches 320 with about 2-3 feet left in the chamber for the shirt to remain under that heat to insure proper cure. Now it could be argued that we are in fact submitting this garment to a "dwell" but again, we're splitting hairs. What Wilflex is saying sounds like the absorption of the plasticizers takes longer and requires a more significant dwell time to insure proper cure, ink has changed chemistry so I'm not really arguing against anything but again, probably a matter of opinion like what "is" really "is".
This is from a Richard Greaves article from years back, so it could be outdated with the new ink requirements: "As plastisol ink is heated, its resin particles simultaneously expand and absorb plasticizer. Full fusion is reached at approximately 320F." And from Union and International Coatings: "Once the entire ink film thickness reaches the proper temperature, the ink is fully cured." Perhaps Wilflex is providing a "cover our ass" with the additional dwell, or the new chemistry of their inks require a longer time at a certain temp for the resins to absorb all the plastisizers...I don't know. Things change, the chemistry of plastisol inks has really changed the last 5 years so perhaps there is something to the need for plastisol inks to dwell at the cure temperature now but I haven't read anything that goes into specifics about the need for a dwell so maybe an expert can chime in and clear up any misinformation.
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instantaneously once the entire deposit reaches it's cure temp. Plastisol doesn't have to be at a certain temperature for a length of time, just has to reach that temp that it was made to cure at. Most plastisol inks these days cure at a lower temp than 330.
That blanket statement is kind of like saying all screenprinters are aging, ponytailed, balding, wanna be hippies, who bootleg tye-dyed Deadhead shirts in the parking lot before they get stoned at a GD concert. While it may be true in many instances, ;D there are exceptions.
The plastisol ink guys should chime in here but some of the 'newer' plasticizers require being "held at cure temp" to allow complete conversion to washfast solids.
Ink guys where are you.....
I guess my use of "instantaneously" was not in the right context, and perhaps my understanding of what I've read from the ink guys is not entirely correct, but when I read what Richard wrote many years ago that's what I took out of it. And again, we all know how the ink manufacturers do like to cover their ass since we know that their recommended cure temps are quite a bit higher than what they actually cure at, so perhaps this new dwell recommendation is a product of that as well. Again, like you Mr. Kitson, I'm awaiting a more clear statement from someone who knows more about it than I.
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instantaneously once the entire deposit reaches it's cure temp. Plastisol doesn't have to be at a certain temperature for a length of time, just has to reach that temp that it was made to cure at. Most plastisol inks these days cure at a lower temp than 330.
That blanket statement is kind of like saying all screenprinters are aging, ponytailed, balding, wanna be hippies, who bootleg tye-dyed Deadhead shirts in the parking lot before they get stoned at a GD concert. While it may be true in many instances, ;D there are exceptions.
The plastisol ink guys should chime in here but some of the 'newer' plasticizers require being "held at cure temp" to allow complete conversion to washfast solids.
Ink guys where are you.....
I believe that, newer plasticizers notwithstanding, the statement may well still be accurate, as it still takes however long that it takes the entire layer of any particular plastisol ink and its particular plastcizers to reach cure temp.
When companies like QCM specified (or recommended) a specific dwell time, it was merely to help ensure cure.
Where's Richard Labov now that I need him? RIP.
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This is a good thread it's almost like which came first the chicken or the egg, but the big question is how long does it take your dryer to cure plastisol in your shop. I can only tell you what it takes in my shop and the results I get, I'm willing to bet two dryers exactly alike will dry different even in the same shop. Then the question ask does not specified a type of dryer being used or how big is the heat chamber, I think all this plays a big roll in the answer, which might be different on whatever equipment you are using, now my answer to the question goes like this, I use an Econo Max dryer (older model) 8 ft with 2 ft heat chamber running at 1000dg which gets the shirt to 340 to 350 degree.... a 35 to 45 second shirt dwell time would be my answer.
Darryl
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We installed a TexAir with 10' of heat a year or two ago. We used to run WB through it and plastisol through a short Vastex, manual printing. We now run all our prints through it- plastisol, WB, DC -on the same settings for WB since the day is a mix of all those inks typically. I can't recall the chamber time off the top of my head but it's very long by comparison.
The Wilflex Epic plasti we print with is absolutely, beyond any shadow of a doubt, a better finished product when cured in this fashion. It is true of all the various Epic inks so far but especially true of the Quick White. They feel great- super soft and pliable with a nice matte finish and adhesion appears to be excellent.
I discovered this one day when I bugged out to see the temp on the heat gun at 340˚F at the back. I thought for sure we were under curing since 360˚ used to be our safety line with the short dryer. Remember, a non-contact pyrometer is reading a cone of air with it's round base on the shirt so this is all relative. Actual donut probe temps are wildly different- 360˚ laser gun ≈ 320˚ on the atkins probe.
Anyways, my printer insists that the shirts are curing fully at this temp. Hmmm...they do pass a stretch test. I skeptically tell her to wait on shipping out this order and wash test. It's perfectly cured and feels way, I mean seriously much, much better than a print that was "zapped" up to cure temp. Our dryer is slowly lifting the entire garment up to temp (forced, hot air knives in the middle help a lot here) and holding it there for a longer time. This allows for a lower surface temp reading and is doing something to that ink film that a shorter, hotter trip is not. I think owners of gas dryers know this feeling perhaps.
Just my experience. I am no longer hearing arguments that "the newer IR panels have a better wavelength" and "you can zap this ink up to cure temp as rapidly as you like, it just has to to hit (insert magic number)" and get the same quality of the finished print. Will it still be "cured" if you rapidly bring the heat up to xxx˚? Sure, but it won't be optimally cured. I'll bet anyone a shiny eisenhower dime that any data out there would confirm this, at least with the the Epic line of inks.
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One thing is for sure, overheating tends to make the surface glossy, so right there is a good argument for slow and steady, but that was not the question.
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My experience with my first gas dryer has been exactly what you've described Zoo. The lower
readings at the back of the dryer are fine because with circulated air and particularly gas heated
circulated air the whole garment is at that temperature, as opposed to straight IR beating down
from above. We run everything except poly/blends at the same temp/speeds, low and slow.
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My thoughts exactly, it's more of an oven than a toaster.