How To Anneal PC - Lexan HP1R?? 1

[jtrex]

I was wondering if anyone could let me know the best way to easily anneal Lexan HP1R or even knew its Tg? I found some sites saying heat to 250F for an hour but that was for Polycarbonates in general. Any help appreciated, thanks!

 

[Demon3]

All data on Lexan HP1R

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=PGE8NA156

Table of Tg for thermoplastics

http://www.azom.com/details.asp?ArticleID=83

According to that Tg of polycarbonet is 150°C so anneal somewhat below that.

And now for a question. Why are you using polycarbonate and not some other polymer? Why do you need to anneal it? Polycarbonate has a lot of stresses built in after moulding, some other transparent polymers don't. As an example MABS has much better flow and much lower stress than PC (as measured under polarised light). Also PC has poor ESCR. Yet another thing most people don't know is that the exceptionally good impact resistance of PC is only true for thin parts (3mm or less).

 

[plastx]

For LEXAN HP1R use 140 - 145C (about 290F) and depending on the thickness up to 4 hours in the oven. A good rule of thumb is 2 hours for 2mm thick and add 30 minutes for every 0.5mm after that. You should even slowly cool the parts at a controlled rate for the best results.

There are processimg methods to help reduce stress in PC before making the finished part. You don't say how your parts are processed but in general hotter molds or dies will help. Typically HP1 is an injection molding material.

D3 brings up some good points about clear materials. If you are using an HP grade of LEXAN than you must be making medical type parts so changing may be an issue. Also PC does have a critical thickness as D3 mentions however I found it to be about 4.5mm where it becomes brittle. That's 4.5mm for average flow (around 12 MFR) and as the flow goes up the critical thickness drops. HP1 runs about 25 MFR. You can see this if you look at "bullet-proof glass" using PC. Look at the thick panel and you will see layers of 4mm sheets stacked together to make the panel.

Mike

 

[Demon3]

If you need a medical grade tranparent plastic without internal stresses then you could try Terlux MABS, that's the only one I am aware of.

 

[jtrex]

Yes, we need it for medical grade. It is also for a disposable part and therefore the relatively cheap cost of the Lexan is desirable. I will check out Terlux MABS though. Thanks alot for both your help, much appreciated!

JT

 

[Pud]

There's also Styrolux (BASF) and K Resin (Philips), both of which have USP approved grades. There's probably others too. It's cheaper than MABS too.

Cannot autoclave it (same as Terlux), but can be radiation sterilized. Don't think can be ETO'd either.


Rgds

Harry

 

[Demon3]

MABS (e.g. Terlux) is cost competitive with polycarbonate and has some advantages as well. As always it depends on the balance of properties you need. MABS has much better flow than PC, better chemical resistance but lower impact resistance. Pud is right, Styrolux (a type of SBS) is a candidate with lower cost but lacks some of the properties of MABS.

 

[TechQA]

I having a problem on crack lines on a radio comestic part. It's small and thin, but the cracks cannot be found after compounding and moulding. Market claims were filed. Is this due to internal stress, i'm using Iupilon S3000R PC.

 

[TechQA]

I'm having problems with crack lines on my part for a radio comestic part. I cannot detect any defects after colour compounding and injection moulding. Suspect it's due to internal stress. Any ideas ? faced many market claims for that. Material is Iupilon S3000R PC.

 

[patprimmer]

It is normally best to start a new thread with a new topic.

PC is very prone to solvent stress cracking. This can be triggered by many factors. Much more info is needed if the answers are to be more than generalised guesses. Many factors have for and against aspects.

General suggestions.

Increase in molecular weight, decrease in melt flow index, increase in melt viscosity (call it what you like) increases stress crack resistance, but also increases risk of inducing residual stress.

Adding a mould release decreases solvent stress crack resistance, but might help reduce residual stress.

Any additive, including colours can effect the physical properties and moulding characteristics. PC is especially sensitive to this.

Many very common solvents can stress crack polycarbonate. Sometimes these are in the form of impurities in commercial grades of products, but not in the AR grade, so they don't show up in lab tests if AR grade rather than commercial grade reagents are used.

PC is especially susceptible to even traces of aromatic hydrocarbons and chlorinated hydrocarbons. You might find these in lubricants, fuels, candle wax, cleaning reagents, cosmetics, food, insect repellents, paints, adhesives etc.



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 would suggest that you make the part of MABS (transparent ABS) instead of PC. One tradename is Terlux from BASF. You can find data on MABS and PC at

http://www.matweb.com

for free. The MABS is transparent, has good mechanical properties, the same price per part as PC and is less dense. Most importantly it has good resistance to environmental stress cracking and low built-in stresses after moulding. It's an amorphous polymer so you can use it in your existing mold. You can also find a lot of information at

http://www.specialchem.com