Strange resin sought 4

[Theophilus]

I'm looking for a sort of thermoset, such as unfilled polyester casting resin. At least that's what I think it is.

A client of mine is getting some parts machined from what I believe is a pre-cast resin in rod form (from a vendor in England, I believe). This seems to be because of the nature of the appearance and water resistance of the part.

I need a nice opaque white part, able to put a polished finish on it. I've looked at the thermoplastics available and cannot seem to find quite the right look/feel. (Tried Delrin--nice white, but somewhat translucent.) Normally, injection molded high-volume production stuff is my niche, but this part cannot be feasibly molded while retaining the aesthetic characteristics I need (very thick sections--over 1" in areas--with thin sections in other areas, bad undercuts to be machined in, etc.)

This part will work as part of a premium-line bathing accessory, so it will get plenty of soap and hot water over time. It doesn't need to be terribly accurate (+/-0.015" tolerance is fine) when machined, but needs to be able to sustain decent drops onto the floor without damage.

Can anyone recommend a resin that may work for this machining process, even if somewhat complicated?

One more thing--if it's a cast thermoset, we can cast the rods ourselves, but cannot use the material if there is a significant risk of air bubbles within the rod to be machined.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe trumps reason.

 

[HDS]

Thanks for responding with your results It greatly increases the value of this thread. Most people fail to close the loop on this board.

 

[Theophilus]

Update:
I just picked up some machined samples today from our machinist--the rod was extruded Tenite (Butyrate, Eastman) from another vendor. It machined great, and the machinist may be able to obtain a perfect (for our standards) finish right on the lathe without any post-process vapor polishing. The first trial is looking promising.

Thanks again! More to follow as things progress, but it looks like we're on the right track with this very versatile material.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Demon3]

Thanks for the update, great to hear how things are working out!


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Pud]

Hi Jeff/All,

Just goes to show - all these fancy new materials and one of the original plastics did the job!!

We will be talking caesin or Bakelite next!!

btw - if you eventually go for injection moulding, one of the CA's (not sure if it's the butyrate or propionate, or even both!), smells like dog s**t when molten!! You might like to warn your moulder if you go that route...

Perhaps when in production and confidentiality no longer applies you could post a photo/rendered drg. of the part - be interested to see it.

Cheers

Harry

 

[Theophilus]

Thanks again, will do!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Demon3]

Yes, the cellulosics are temperature sensitive and so not so easy to injection mold. Long residence time will burn the cellulose acetate proprionate and I assume the other cellulosics too. Also you need a certain screw type in your injection molding machine, not a standard PE/PP screw. Eastman can help with all the details. Don't worry though, it can be done even for large parts, you just need to be aware of the conditions needed.


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[patprimmer]

Cellulose Butyrate smells like rancid butter as both contain butyric acid.

Propionate is very transparent and easier to mould with no unpleasant side effects. It was traditionally used for spectacle frames and tooth brushes.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Demon3]

I once did some experiments with a series of carboxylic acids, C2, C3, C4, C5, etc up to C12 and C18. We surface treated fillers with them.

The very short chain ones like formic acid smell sharp like vinegar. The long ones smell fresh like soap. But as Pat said C4 and those next to it smell hideous. Was a week before the smell left the lab.


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Theophilus]

We've encountered a bit of a roadblock. One of the post-processes we intend to do with this part is a dye sublimation process (image transfer) that uses heat (325F) to sublimate and transfer the dye to the part. However, at that temperature, we're seeing the delivery mechanism for the dye stick to the part--because the surface of the part is melting.

So this is a deal-killer with this resin (for now).

Can anyone think of a way around this? I love this material, but the low melting point is certainly a problem with this post-process surface treatment. Is there perhaps a sister material with an increased melting point? A filler or other additive?

Thanks,



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Demon3]

Best to ask Eastman who make the materials. It's
well known that the surface softens when heated. Normally they have that as a selling point because a lightly scratched surface can be fixed by heat treatment where the scratch heals.

The material we had from them was available with differing amounts of plasticiser. You should check with them what grades they have. One with less plasticiser should resist the heat a bit better.

Adding filler could help a bit, for example fine silica to maintain transparency but that may change the feels (haptic) of the part.

What happens when you put the parts in a fridge or freezer before the dye sublimation? That way perhaps you can stick with the material as-is and avoid too much surface heating!


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Theophilus]

Thanks! I've contacted Eastman, but my contact was out of the office last week.

From what I saw on their materials pages, the melting point with similar plasticizer levels were all near 219F--still far too low.

Decreasing the part temperature is a great idea--I don't know if the part surface itself has to be warm for the dye transfer, but I can find out.

Thanks!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

If you want to use the sublistatic dyeing process, polyester will work a lot better. The process was developed for polyester fibres which are thermoplastic PET. 2 pot polyester casting resins are thermoset PET and will have a similar dye affinity.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Theophilus]

Thanks, Pat. I've looked into PET (thermoplastic) and have difficulties with the white color and opacity. Ironically, however, I think our existing material is a polyester thermoset (such as a casting resin), and it does pick up the dye transfer fairly well. However, it has a lack-luster finish, so it gets tumbled in a pellet/wax treatment to gain gloss (as best we can tell).

I like the Tenite we found because it machines so beautifully and we have so many other options available for color, etc. Just seems the dye transfer isn't working very well.

Eastman is now checking into some alternatives, so I should have word back from them by mid-week.

Thanks!

Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

You can dye cellulosics, just not reliably by the sublistatic process.

Dyes that work for acetate rayon should work. They tend to be the same basic class as used for polyester (being dispersed dyes) but of a lower molecular weight so they can absorb into the polymer or fibre at lower temperatures.

The sublistatic process works by evaporating the dye, then allowing it to condense onto the substrate, so evaporating temp vs substrate melting point is critical.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[HDS]

There are dye sublimation processes modified for plastics. KOLORFUSION INTERNATIONAL is an example in the US but there are others.

 

[Theophilus]

Eastman ended up falling through for an alternative resin that would work for our needs. So we're now giving POM a more serious look, since it works great for the dye sublimation.

My client was already working with Kolorfusion--that's interesting you mentioned them. I read an article a while back that discussed this whole process that listed several others as well:

http://urltea.com/ja8

I think our difficulties will be in finding a good adhesive/solvent for the POM material and getting that perfect opaque look from the resin. I'm concerned about that, but we're working on some samples to see what we can get.

Thanks!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Pud]

Jeff,

Colour/pigmentation will not be a problem - talk to your local masterbatch folk.

Bonding POM - serious stuff. Solvents very toxic/noxious etc. Suggest you look at mechanical fixings. POM v. good for snap fits etc.

Good luck.

Cheers

Harry

 

[Theophilus]

Thanks, Harry. I've got some housings I think I'll need to bond together--small stuff where I cannot mold undercut prongs and cosmetic so I cannot use shut-offs. I don't think a friction fit will work well enough either.

Maybe I need to bark up another tree in materials--something else that I can find a solvent/adhesive for that works with dye sublimation and delivers great molded and machined results. (Any ideas?)

Thanks again,



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

POM is almost impossible to bond by methods other than welding.

Having said that, if anyone can bond it, 3M can.

DuPont and Ticona also probably have some data.

Cellulosics can be dyed by selected dispersed. Low molecular weight dispersed dyes might work by the sublistatic method, but you would need to make your own sublistatic dye impregnated paper. This might not be viable due to scale or available resources for project.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Theophilus]

I'm considering this Rynite PET as a possibility (sorry--looks like we're going all the way round to where we started--ug), but I've not yet seen the material "in person" to see if it will work aesthetically for my client.

From the article I posted earlier, I see this chart:

http://www.appliancedesign.com/AM/Home/Images/Fig-1-DuPont_large.jpg

Since the ability to do the dye sublimation is critical with these parts, this looks like a new "anchor" from which to decide materials. I'm also attempting to see if we can approach the other dye options you mentioned, Pat. We'll see how it shakes out.

Thanks again for the great input!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.