Images not printing correctly on thinner items

[paul 44]

I've been doing a ton of coasters recently without any issues at all, print perfectly every time when printing 2 coasters at 60 seconds each at the same time.

When I do thinner items such as a tea towel or sublimatable card and printed using high pressure and recommended temps, i get parts where the ink hasn't transferred completely.
So...my thinking is this, it can't be a cold spot on the plate as this would show up on the coasters, pressure is quite high on the thinner items so i'm thinking whether this just needs a longer press time as the pressing area is larger, a towel for example will cover the entire platen, sublimation card is A4 size, both showed areas right in the middle where the image hasn't transferred properly, when cutting the card down into smaller strips they print fine in the middle of the plate?

Is this just a case of longer pressing, all of the mentioned above are printed for 60-70 seconds

[webtrekker]

I don't do towels, but I sublimate polyester tote bags with full A4 designs at 190 deg C for 60 secs, medium pressure, and never have any fading problems.

[pisquee]

What press have you got?
Do you have an infra red (non contact) thermometer to measure the platen?
Could be your platen isn't as hot as it says it is across the platen, or the platen isn't as flat as it could be

[socialgiraffe]

I would say that it is either your platen that is slightly curved or more likely your rubber base is worn.

In order to try and circumnavigate this try placing something like a teflon pillow underneath your item, this well help in creating better pressure between the heat platen and your substrate and smooth out any "defects" in the base.

If this works then go back to the supplier of the heat press and purchase a new base rubber. Base rubber does, over time wear down, and eventually you will get the cold spots as described, even though the platen is consistent.

[paul 44]

What press have you got?
Do you have an infra red (non contact) thermometer to measure the platen?
Could be your platen isn't as hot as it says it is across the platen, or the platen isn't as flat as it could be

HI,
This is a chinese press, served me well to be fair so i'm one of the lucky ones.
I have a thermo but the plate has teflon cover attached so is not really accurate when measuring the temp of the plate due to the teflon hanging down slightly (1/2 inch maybe) so the result is inaccurate

I have 2 plates, one is newer than the one on the machine, both same results which is weird

[paul 44]

I would say that it is either your platen that is slightly curved or more likely your rubber base is worn.

In order to try and circumnavigate this try placing something like a teflon pillow underneath your item, this well help in creating better pressure between the heat platen and your substrate and smooth out any "defects" in the base.

If this works then go back to the supplier of the heat press and purchase a new base rubber. Base rubber does, over time wear down, and eventually you will get the cold spots as described, even though the platen is consistent.

Hi Sg, thanks for reply!

I will look into that, I just find it strange that when I cut the items eg sublimatable card, into smaller strips, they print no problem in the middle of the press, it's always when I print larger, flatter items that this happens, but when i cut these flat items into sections they print fine.
Would I be right in thinking that as this is a larger flat item eg A4, I just need to up the time for the pressing when I sublimate as the heat is being drawn out the heat plate and just needs a little longer?

Coasters print fine (2 at a time) at 60 secs at 190c, obviously the contact area is more solid so I might whack the pressure up on the press for the softer larger items in order to get that more solid contact and as you suggested use a pillow beneath, hopefully that solve the issue and maybe up the press time by 5-10 seconds?

[socialgiraffe]

If it is what I think it is then upping the pressure should do the trick and as suggested, try a teflon pillow (or something similar) underneath. I don't think upping the time or temperature will solve the issue if it is what I think it is as you will end up burning the outer parts while the middle prints perfect.

Cutting into strips make sense to me in terms of it printing correctly as it is not "warping or twisting" so contact with the upper platen is consistent.

[paul 44]

If it is what I think it is then upping the pressure should do the trick and as suggested, try a teflon pillow (or something similar) underneath. I don't think upping the time or temperature will solve the issue if it is what I think it is as you will end up burning the outer parts while the middle prints perfect.

Cutting into strips make sense to me in terms of it printing correctly as it is not "warping or twisting" so contact with the upper platen is consistent.

Many thanks for your help on this, appreciated!

I'm thinking of taking off the teflon sheet which is on the heat plate as I can see a few wrinkles bang in the middle, this may be an issue, if creased then this will inhibit heat transfer to the item.
When pressing I always use grease proof paper also (on top of the substrate) to help stop any ink transferring to the plate itself.

I've just checked both plates, they both have creases in the teflon fabric on the heat plate

Make sense to you SG if i did this?

[socialgiraffe]

Yes, I would remove both covers if they are creased. Don’t worry, you will not damage either platens by doing a couple of presses without the covers and you can always wipe the platen clean after use (keep the press on and just wipe it with a dry cloth).

What you are ultimately try to do is make sure your item is sandwiched between the top and bottom platens without any creases, bumps, kinks or slight curves.

If you imagine trying to heat press a ball using a flat heating plate you get the idea of what I think could be the problem (obviously convex instead of concave though).

Even the slightest of curves could have an effect hence why upping the pressure and using something underneath should help.


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[paul 44]

well ive stripped a teflon sheet off one of the plates, did a heat check on the plate with the IR thermometer, reading is half what it should be 170f on thermo 356f on heat press but coasters are printing fine, i think thermo is goosed as 170f is only 76 Celsius, i couldn't touch the plate, too hot...new thermo i think!