very low CTE moldable plastic looking for lower melt temp suggestions

[rmetzger]

We currently are using a Sabic ULTEM 2410, 40% glass material for a project but would like to find something of a similar CTE but with a lower melting temperature. Ideally something with a similar water absorption (as this part is continuously submerged in fresh and salt water) and with similar flow characteristics.

Water Absorption 0.130 %
Melt Flow 5.20 g/10 min
CTE, linear, Parallel to Flow 14.4 µm/m-°C

Max operating temp of our product is 80C

Any ideas?

 

[Demon3]

The CTE should mainly depend on the glass fiber content so you should be able to find something else that gives that CTE but at lower melting temperature.

Semi-crystalline polymers should have lower CTE than amorphous.

Water uptake depends on polarity so low polarity polymers like polyolefins and styrenics and good whereas nylons have high polarity and take up lots of water.

Based on what you've said I'd look into syndiotactic polystyrene. It has amazing flow and really low water uptake. Contact Tom Fiola at Idemitsu (the product is called Xarec).

Also search

http://www.matweb.com

for free to find materials with the CTE you want.

Chris DeArmitt - PhD FRSC CChem
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[patprimmer]

It sounds like you are really looking for maximum dimensional stability and you really mean minimal dimensional change from water absorption. To specify an approximate number for water absorption rather than a maximum number unnecessarily limits your choice.

Also, unless this is a student homework question, I suspect there are many other requirements that have not been mentioned as Ultem is an expensive high end product and many cheaper materials are good for low expansion and 80 deg C continuous use.

Without further information I would also look at polycarbonate and modified PPO and maybe even a high heat ABS.

MFI is not that good an indicator of maximum flow length. Flow length to wall thickness ratio data is much more useful.

Regards
Pat
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[rmetzger]

We are looking for high dimensional stability as well as maintaining a mechanical bond to a substrate that has an extremely low CTE. The product deals with a fairly wide temperature range in its typical use and the substrate needs to remain mechanically bonded to the the overmold (in our current case - 40% glass filled ultem). The current mechanical stability is fine but we are melting the solder off the electrical connection with our substrate during overmolding - hence the requirements for a low CTE. Compounding this is the fact that our product lives underwater for months at a time and our substrate effectively does not absorb water so any dimensional change due to water absorption works against our mechanical bonding as well.

In order of mechanical importance;

Low CTE (variation in expansion / contraction is typically the highest failure mode in products like this one)

Lower molding temperature (this is causing manufacturing issues thus preventing the product from being made consistently)

Low water absorption (this is also a source of failure but much less than a high CTE variation

typically we've found that a well selected low CTE material will have good dimensional stability within our range so selecting a high glass material (or other filled plastics to limit dimensional changes with temperature) takes care of the dimensional stability side of the problem. Of course we need to bond with our substrate as well but that's a chemistry problem that we can take care of.

 

[Pud]

LCP's can have the same low CTE as steel:

http://tools.ticona.com/tools/mcbasei/product-tools.php?sPolymer=LCP&sProduct=VECTRA

Melt temp maybe too high at 280C, but heat of fusion very low (hence very rapid cycling ability)

H

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