Good dental instrument plastic

[cssmythe3]

Hey guys, I'm working with plastics after many years of being a sheetmetal / machining guy, so I'm looking for some validitaion on my material selection now that I'm designing a plastic housing for a medical instrument.

Requirements:
-good impact resistance
-good chemical resistance (alchohols and amonia)
-does NOT need heat / autoclave resistance
-good mold flow (housing has thin walls)
-Medical: USP Class III (classs VI a bonus)

I'm using a very small volume of material so $/lb not a big deal.

I've got the short list down to:
-Bayer's Makrolon PC
-GE's Ultem PEI
-GE's Valox PBT/PC (pretty bad impact though...)
-EMS-Grivory's Grilamd Nylon 12

Anything not on the list that really should be? Any bad experiences with any of the materials on the list?

Thanks in advance...

-Chuck Smith,
NY, NY

 

[Demon3]

I would suggest that you go to

http://www.matweb.com

where you can put in the values you want for impact, modulus etc and it will give you the plastics that match. Even better it's free.

You certainly are considering some relatively expensive polymers. I would add MABS (transparent ABS) to the list due to good chemical resistance (used for electric toothbrushes and cosmetics packaging) and quite good impact resistance. You could check out PET, PETG and CAP (cellulose acetate proprionate from Eastman, gives a special feel to the hand). Also look at RTP's site for chemical resistance data for many plastics

http://www.rtpcompany.com/info/guide/resistance.htm

Also look at

http://www.omnexus.com/

where they also have a plastics selection guide plus area specialised in transparent plastics.

Lastly good luck!

 

[patprimmer]

Polypropylene, ABS and nylon 6 are notable by their absence.

To give good advice much more data is required, like.

Sensitivity to warping.
Required flex mod.
Dimensional stability.
Food contact.
A full list of chemicals that might contact (note, spectacle frames in polycarbonate often fail from chemical contact with things like personal insect repelant or toothpaste).
Is the design notched.
Resistance to sink marks.
Does it need further finishing, like painting or printing.
How will it be assembled.
Exposure to UV light.

PP, ABS or Nylon are hard to beat for housings, depending on what qualities are important

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]

Very good point Pat. Somehow I looked at his preliminary choices and assumed he needed transparency. Now that you mention it that wasn't specified so PP and ABS are naturals.

 

[Pud]

You do not mention is it is to be sterilized? i.e ETO, Gamma, etc. This will narrow your selection down somewhat.

I think the best bet is to find out what is available that has USP approval. This will again reduce the options.

From your list of requirements, I would have a look at K Resin (Philips) or Styrolux (BASF) - both used extensively for medical parts and have USP approvals (Class VI I think - check their websites). OK for gamma sterilizing, although a bit of blue tint will improve the after colour. It's ok with alcohol - not sure about ammonia (Demon3 where are you??)

Its also the easiest to process (no drying, low temp), and is not too expensive.

Cheers

Harry

 

[MIHIR142]

Chuck,

I have used Grilamid TR( transparent nylon)Which is transparent nylon with low mositure absorbtion. and also it has good clarity( even at higher thicknesses) and also a great chemical resistance.

I know they grilamid TR is USP class VI.

 

[craigmj]

Take PC off your list. Bad chemical resistance to hydroxides and not good for thin walls. Excellent for impact thou.

Triax is good (nylon/ABS blend), but low modulus.
I have used Grivery with sucess, but dim stability might be an issue. Could add a filler to help, but you open a whole new can of worms when you do that.

As Patprimmer says, really depends on what you are trying to do.

If you want real advice please expand on your specific needs.
Cheers,
Craig

 

[cssmythe3]

Thanks guys, that's given me plenty to chew on, I appreciate the help and you're all a great resource.

That's pretty funny about the transparency thing, because I actually need it to be opaque. I have yet to run down all of the above suggestions.

My initial list has been destroyed:

-Makrolon PC - SUSCEPTIBLE TO AMONIUM COMPOUND ATTACK
-GE's Ultem PEI - TOO BRITTLE
-GE's Valox PBT/PC - TOO BRITTLE
-EMS-Grivory's Grilamd Nylon 12 - LACK OF BIOCOMPATIBILITY

My current front runner is:

Solvay's Radel-R 5100

Answers to questions:

> Sensitivity to warping.
> Dimensional stability.
I have very little clearance inside the housing so warpage and dimensional stability is important.

> Required flex mod.
> Is the design notched.
Doesn't carry a load, so not a big deal. Might be some failry sharp notches in a tongue/groove interface.

> Food contact.
Early versions of this product were certified to FDA 21CFR177, but we're moving to a more stringent (I think) USP Class VI. Technically, we only need USP Class III, but all the resin manufacturers only seem to list things as VI.

> A full list of chemicals that might contact
Ehtanol, isopropyl alchohol, and quaternary ammonium compounds are 99% of what I'm up against.

> Resistance to sink marks.
We're stippling the outside surface, so sink marks shouldn't be too critical

> Does it need further finishing
Simple pad printing and / or laser marking.

> How will it be assembled.
Hopefully ultrasonic welding, if not, a tongue/groove with epoxy.

> Exposure to UV light.
It will only be used indoors, _possibly_ exposed to germicidal UV lamps by an end user who doesn't follow instructions (pesky end users).

Thanks again for all your help gentlemen!

-Chuck

 

[Demon3]

Firstly, excellent post on your requirements. If you want to 3D print a prototype then I know that Stratasys can print in the thermopolastic you selected (polyphenylsulfone)

http://www.stratasys.com/

What about polysulfone and polyethersulfone? Will they work too?


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