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What makes Thermal plastic Polyurethane (TPU) Tacky? 2

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Cabs21

Cabs21

Mechanical
Dec 1, 2011
13
Hello,

I am working on a project that involves sticky/tacky TPU. For my companies first product the level of tackiness was sufficient, but now my project manager wants to make another product using tacky TPU and our current stock is not tacky enough. We have found a similar polymer that exhibits the same properties as our TPU stock but is much tackier.

My question is how do I improve my tackiness of my TPU. I know that TPU can be made non-tacky like in tubing and cell phone cases. I know that TPU can be made very tacky like the toys kids get in vending machines that cling to surfaces and can be washed clean and reused.

I sadly do not know the formula for our stock, and I do not know enough about plastics to figure this solution out on my own.

Any help or direction would be greatly appreciated. Thanks.
 
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Hi Cabs21,

Chemically speaking, I don't know what causes tackiness, however in my experience it is mostly related to the hardness of the TPU.

I had a project to injection mold a soft grade of TPU, and when it comes out of the mold it is warm and incredibly sticky. Even after it cools, it is still rather tacky. Harder TPUs (cell phone cases, tubing) are much easier to work with. I'm told that soft Pebax is also sticky.

So I would specify the softest TPU available, and then use another material as a backing to give you the structure you need.
 
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Tackiness can easily be adjusted in to original formulation of urethane be that either thermoplastic or thermoset. Talk to your urethane suppliers and they will give you a grade that is tackier.
 
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Thanks to shoo650 and dwightdixon for the reply. In my testing and trial and error I have come to the same conclusion that hardness and tackyness are linked.

Dwightdixon, getting in touch with my urethane supplier is touch as I do not deal directly with the supplier. My vendor does but is having trouble getting answers from his supplier about the formula. I am not sure the supplier really knows what they are doing fully.
 
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While hardness is a major aspect it is not the only factor.

If your vendor cannot get the info and obstructs you going direct to get the info, you need a new vendor.

Any decent supplier should be able to supply the data you require re performance of different grades, however they will not disclose their formulations as that is their proprietor knowledge.

Thermoplastic PU covers quite a range of different chemical compositions.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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Thanks patprimmer.

My vendor is not obscuring me and the vendor is our best vendor and supplies more than 60% of our products, so replacing them would be very costly.

The vendor and supplier are both based in china so there is a language barrier for me as I only speak English. Guess I need to brush up on mandarin. Either way, my problem is the supplier cant seem to make what we want because, I dont think, he knows what he is doing exactly.

My project manager thinks that the surface finish of the TPU affects the tackyness or how its manufactured. I think that the surface finish does not affect the tackyness but is a result of how it is manufactured.
 
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First we'd have to define tackiness in order to make any solid conclusions or measurements.

Have you measured the coefficient of friction between the TPU and the surface of interest?

This can be done easily by placing one on the other and tilting until you get slippage. Take the tan of the angle where slip occured and you have the coefficient of friction. You can buy a digital spirit level online or at Sears for $50. I have done this and it works well for most materials and is accurate compared to published values for static COF.

This could be a good tool to get numbers for tackiness to compare. In general soft, rubbery materials have high tack and harder ones low tack. You could for example cool a TPU and tackiness would decrease, especially below the glass transition temperature. Conversely you can increase tack by adding a plasticizer to soften the compound.

Chris DeArmitt
Plastic & Additives Webinars
Training the Fortune 500 since 2003
 
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Demon3,

That test will not work as the point of this TPU is to stick it to a wall and hang weight from it. I macgyvered together a stick on hook from a consumer product called Clingo. I was able to hang 10lbs vertically from the test product for several days and 12 lbs for several hours after that. The surface is drywall with common household latex paint on it. I want to replicate this tacky property for my product. I currently have a tacky TPU but it is not tacky enough to hold 2 lbs for several hours, let alone 10.

I just found out from my project manager that the tacky gel in Clingo's product is not TPU but TPR.
 
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Great, so just add weight until it fails and you have your tackiness measurement.

For the application you described I think a smooth surface for your TPU would be better. Ability to hang there may also be related to the ability for the TPU to wet the surface and create a vacuum. So I think it may be tackiness plus that effect that matter.

All the best,

Chris

Chris DeArmitt
Plastic & Additives Webinars
Training the Fortune 500 since 2003
 
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Chris,

My company already sells a product that works on smooth surfaces at over 20 pounds. I need a product that works on painted drywall and is reusable. That is why I turned to TPU. I needed a product that acted like a permanent adhesive but was not permanent. I know how tacky I want the TPU to be, but getting a sample that is that tacky has been my problem. I dont think my supplier knows what to do to change the tackyness of TPU or TPR.

If I can tell the supplier, you need to make the TPU softer by increasing the cooling time, or changing the fill rate, or putting in an additive for example. Then I can solve my problem.

Thanks for your help so far,
Anthony
 
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Right, so they need to add a plasticizer to make it softer as mentioned.

If they really know what they are doing they need to change the chemistry of the PU composition, more of the softer component and less cross-linking will make it more tacky.

Maybe ask 3M. They make those Command strips that do just what you want.

Chris DeArmitt
Plastic & Additives Webinars
Training the Fortune 500 since 2003
 
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@Demon3

This product would compete with the command strips. Also they are one time use. After you remove them they are trash and a replacement strip must be put in. This product would only need to be washed and reused.
 
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Then I'd analyse the Clingo at a lab and contact someone who knows how to formulate PU.

Chris DeArmitt
Plastic & Additives Webinars
Training the Fortune 500 since 2003
 
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Did that. Currently looking for someone who knows how to formulate PU of if someone can give me a direct answer to my problem.
 
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I'm starting to wonder what you want exactly. You've had solid and specific advise on how to increase the tackiness and more. Surely you don't expect someone here to write you an exact formulation.

Chris DeArmitt
Plastic & Additives Webinars
Training the Fortune 500 since 2003
 
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No. I am not looking for a formulation. I basically wanted to know if there was a simple additive or procedure that could be done to make TPU more tacky. If there is not a simple solution and it is more complex then I will have to figure it out. I talked with an engineer at BASF and he reiterated that hardness and tackyness are inversely proportional to each other in TPUs. Just as you all have said that the harder the TPU the less tacky. He also was able to tell me that adding a wax to the polymer decreases tackyness. I can take this to my supplier and tell them to put as little wax or no wax if possible into the formulation.

That is basically what I am looking for. The supplier does not want to waste a lot of time on my company as we are probably less then 1% of their business. They make cell phone covers for almost every smartphone.

I can not thank you guys enough so far as you have been very helpful to me.
 
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Right and I already said to throw some plasticizer in there. That simple, cheap and increases tackiness.

There are plenty of off the shelf plasticizers for TPU.

Chris DeArmitt
Plastic & Additives Webinars
Training the Fortune 500 since 2003
 
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You are making a very unique pressure sensitive adhesive (PSA). There are teams of formulators all over the world competing to develop products like you describe. Tack is a very complex process and difficult to describe. A plasticizer will soften the polymer and and help surface wetting, which is one component of tack. But a plasticizer would probably destroy the ability to stay attached to the wall with time under load. Tackifier resins usually have no tack themselves but give tack when dissolved in compatible polymers.
Much of this information would be considered trade secrets. Your best bet would be to contact tackifier manufacturers and ask if they have any products that may work. The reusability feature is certainly going to limit your choices. I guess that means that the tack must be temporarily deactivated by water.
 
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I think the traditional temporary tackifier is a bit of spit, which exemplifies the complexity as it neither softens PU nor is it sticky in its own right. In fact it can be also a lubricant.

As I have said several times before, you need to discuss this with at least one major PU supplier. If your local guy is not good enough, you need to move up market or upstream. This is a highly specialised area and any existing knowledge will be proprietary and will certainly not be disclosed here.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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