Material selection question

[CalculatorDave]

Howdy all,

I'm trying to select a plastic, but am having a heck of a time. Here are the required properties:

1. Weldable ultrasonically
2. Low moisture absorption (< .03% )
3. UV stable
4. LIght in color
5. SErvice temperature up to 80 deg. C
6. Injection moldable

I have looked at UHMW (not UV resistant except in dark colors), PP (won't take the heat), and PS (terrible weather resistance). These all have low moisture absorption, but fail in the areas mentioned. Any suggestions?

David

 

[patprimmer]

Why low moisture absorbtion. Unless it changes an important property it shouldn't matter as such.

That would open up the posibilities of PBT, PET, PC, and ASA

Although the all absorb some moisture, it has negligable effect in dimensions and dimensional stability

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CalculatorDave]

Low moisture absorption is important to this application because it operates outdoors, and any dimension change due to moisture absorption will place unacceptable stress onto the adjacent adhesive bond. Unfortunately, the adhesive bond design cannot be changed.

 

[patprimmer]

I think you are off in left field a bit Dave.

The plastics I have listed above will not change dimension enough from water absobtion to stress any joints, although the polyesters listed are virtually unglueable, as is PE and PP.

I would be looking seriously at Polycarbonate, or maybe high heat Acrylic.

PC is much tougher and has somewhat better heat deflection temperature, but Acrylic (PMM) has much better UV resistance.

Both are easy to glue, and both absorb a little moisture, but don't change dimensions enough to be a bother.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CalculatorDave]

Thank you for your input to this question. Any other feedback from other people out there? I really do have to have less than .03% moisture absorptivity in this plastic.

David

 

[gambro]

If a moisure uptake of max 0.03% is really that important, I suggest you try TOPAS, a hard (ultrasonic weldable), transparent, high temperature resistant, injection moldable cyclic olefine material manufactured by TICONA. I don't know too much on the UV-stability issue, so I suggest you contact TICONA directly.

 

[buut]

try FEP film,regards,
Ernst

 

[thx4thehelp]

3M(and I am sure others) has a new adhesive for PP that works very well. It is a 2 part epoxy. I have used used it in a couple of under the hood applications that were subject to stress in all three axis. This particular part has been in use for over three years without a single failure due to the adhesive. The part was not suited to ultrasonic or spin welding technics due to some geometry problems with the main body of the part.

Sincerely,

Jay Rogers
American Tool & Engineering, Inc.

Visit our website at:

http://www.atemold.com

 

[patprimmer]

3M certainly do offer a range of adhesives and adhesive tapes that perform well beyond the traditional boundaries for sticking to low surface energy plastics.

On thinking about the <.03% moisture requirement, the stress from the &quot;swelling due to moisture&quot; will be so insignificant compared to the stress from thermal expansion differences, that it really is not worth considering. The closest analogy I can think of is that it is like trying to measure to the nearest micron with a wooden rule.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[shoobaka1]

In the same line as the TOPAS (coc). TPX might be an option as well. (pmp)

 

[patprimmer]

TPX is lousy to UV and as difficult to stick as PP.

It will take the heat. It is very expensive.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mrglynn]

Good suggestions and comments so far. Here is another. Solvay has a PPA (Polyphthalamide) semi-crystalline resin called Amodel that is injection moldable. With respect to the moisture absorption issue, I agree with many of the other posts that it is probably not as significant as you think. I am assuming this is why you (and others) are not looking at PA's (Nylons) although there are a number of low moisture grades available. Back to Amodel, its moisture absorption is about half of nylon. But you really need to look at the data charts to appreciate the numbers. Amodel bonds well and looks good. Excellent heat and impact.
Mike Glynn
763-428-6180

 

[nbucska]

Often you can design around any mechanical disadvantage --
there is no optimal material just good enough.

Engineering is the science of possible. You have to design
by finding compromisses between cost and material properties
etc.


<nbucska@pcperipherals.com>

 

[eliassen]

Fortron, from Ticona, is a PPS, with 0,03 % moisture
absorption limit. Colour might be a problem, there are limited choises for colour, but it should work with your other demands.

Eliassen