Selecting suitable polymer for Outdoor Call point? 1

[maestro0]

Hello all,

I do some design work for a company in the UK and I have little experience when it comes to material selection.

They have asked me to specify a polymer for a project just finished, specifically an outdoor call point.

Its an injection moulded plastic enclosure, 2mm wall thickness, 5 year product life, and being that its an outdoor product~ UV stability is important, and I suppose general resistance to the elements!(product is most popular in the middle east, exposed to hot temps and lots of sun!).

I don't really know where to start, any suggestions would be great!

 

[Pud]

We use this for chimney caps, and used to use it for microwave antenna covers.

http://www.ineos-nova.com/Products/PerformanceProducts/styrosun.htm

You will no doubt get many other suggestions (there are many suitable materials) but this is probably the most cost-effective at sub £2 per kilo. It also does not require any pre-drying prior to moulding.

Harry

http://www.tynevalleyplastics.co.uk

 

[Demon3]

Harry's suggestion looks good, especially as he's recommending it based on real world experience. I did a Google search and found that Styrosun is a type of HIPS with UV stable impact modifier.

I have a nice diagram of this but will try to explain in text.

Here is a run-down of the styrenic options

1. Polystyrene - Stiff, cheap, poor chemical resistance and poor impact resistance.

2. HIPS - Polystyrene with non uv-stable impact modifier (polybutadiene) to give impact resistance. Some loss of moldulus and strength. Still poor chemical resistance.

3. SBS - Polystyrene copolymerised with butadiene. Normally these are elastomers but with low butadiene content you get a polystyrene like material with somewhat improved impact resistance.

4. Styrosun - Same as HIPS but with some added cost and using a UV resistant impact modifier (probably polybutylacrylate)

If you need better chemical resistance then you copolymerize the styrene with acrylonitrile to make SAN. The higher the acrylonitrile content, the better the chemical resistance.

1. SAN - Good stiffness and strengt and poor impact resistance like polystyrene. Improved chemical resistance at but some added cost compared to PS.

2. ABS - SAN with non UV stable impact modifier (polybutadiene). Can be UV stabilized but will still degrade after prolonged sunlight exposure. Some loss of modulus and stength compared to SAN. Decent chemical resistance.

3. ASA - SAN with UV stable impact modifier (polybutylacrylate). This has properties like ABS but costs much more. It is used where color and impact properties must be retained after years outdoors. Some grades have higher acrylonitrile content than ABS and hence slightly better chemical resistance.

4. MABS - Modified ABS to match the refractive index of the impact modifier and that of the matrix polymer. Mechanical properties like ABS only MABS is transparent. The impact modifier is polybutadiene based so it cannot be used outdoors. Like ASA, MABS is a specialty and cost significantly more than ABS.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

 

[GilPolymers]

Excellent post... I was wondering if you could upload this diagram, if would fit perfectly on my notes.
Thanks
Cheers,
Gil

 

[Demon3]

Hi Gil,

The diagram includes PS, SAN, HIPS, ABS, ASA and MABS. I did not know about Harry's Styrosun at that time. If I get a moment I will try to add that and upload it. No promises though, I'm swamped at work.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

 

[patprimmer]

maestro0

All the above are excellent advice, but from your post, it is difficult to gauge the overall balance of properties required apart from good UV resistance unless one knows what a call point is. I must admit I have no idea what it is and therefore do not know what it has to endure apart from relatively high UV exposure.

Also s you say the project is just finished, have moulds been made and therefore material mould shrinkage is fixed.

Just on the UV quality I would recommend acrylic. If it has to be tough, I would recommend UV stabilised PP or reclaimed PET from beverage bottles, but they each have their own problems. eg PET s strong, cheap and very good to UV but is a @#$$ to mould and requires some very special equipment. PP shrinks and warps lot, acrylicis brittle

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[Pud]

Styrosun impact modifier is EPDM.

Btw: ASA = sh*t to masterbatch. Requires compounded colours - min order etc, etc.

You all missed UV stabilised PC. Doh!

Maestro:

If you would like a sample of a moulded part in Styrosun, just ask.

Without seeing the part design, 2mm seems awfully thin...? Your flow length if injection moulded won't be much more than 300mm - much less in ASA or PC. Thermoforming no problem, obviously.

Ok all, I give in! Where's the diagram?

Harry

http://www.tynevalleyplastics.co.uk

 

[Demon3]

Hi Harry,

Thanks for illuminating me on the impact modifier in Styrosun, could not find that anywhere on the net.

You mentioned using polymers for microwave antenna caps. Some years ago, we looked at making mobile phone housings out of some polymers and found that some types of impact modifier absorb a large amount of signal. We were amazed as the shell is so thin. I believe polar impact modifiers like polybutylacrlate are worst, polybutadiene and EPDM should be fine.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

 

[Pud]

Chris: Took me some time to extract EPDM from rep too!

Thin phone shells are made on multi cavity tooling with small diameter screw assemblies to get the speed/pressure required. Pretty well packaging moulding type kit. Not for the general trade moulder. I think they are usually PC/ABS.

PS is pretty well transparent to microwaves, although Ericsson used to use PC. Butadiene rubber is I believe a good absorber too (not desirable). We used to make a different thickness for each frequency (Iirc, between 2-3 GHz)

H

http://www.tynevalleyplastics.co.uk

 

[Demon3]

If we're throwing in interesting tidbits then I should make a comment on ASA regarding what you said Harry.

The rubber in ASA scatters light twice as much as the rubber in ABS does (because the difference in refractive index betwee the rubber and matrix is more for ASA than for ABS). The result is that ASA needs twice the pigment to get to a given color as compared to ABS. It also means that you can't achieve the most intense colors.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

 

[patprimmer]

Pud

I deliberately left PC of the list, mainly due to price and the fact that it is one of my least favourite materials due to it's extremes of good and bad properties, however I as probably being influenced by my prejudice.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[Demon3]

You are not alone Pat. Using a polymer that can spontaneously explode when exposed to one drop of solvent gives me the shivers.

In my list of styrenic polymers I forgot to add polystyrene-co-maleic anhydride. An interesting polymer for blends as it is miscible with some SAN types and PMMA.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

 

[patprimmer]

Ah yes SMA. One of the forgotten polymers.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[Demon3]

Forgotten indeed and it should not be as mealeated polymers make great coupling agents. Look at the use of maleated PP.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

 

[patprimmer]

Of topic , but from memory, may tie layers are mealeated polymers.

My memories of it involve a container load of Dylark imported into Aus for use in a new product. It was an Egg Centre and somehow knew how to accurately boil one or more eggs of any size.

They made a few prototype mouldings and tested them in the lab for hydrolysis resistance which was claimed to be excellent and lab tests on the actual moulding using distilled water confirmed this. They then ordered the FCL to launch he product.

In the meantime, one of the engineers took home a "sample" and used tap water nd actually put an egg in it to prepare his breakfast.It solvent stress cracked on the first use. PANIC PANIC. What to use for launch. What to do with about 15 tonnes of Dylark?

Although I was not involved it taught me to ALWAYS test under a variety of adverse real world conditions before committing. That philosophy has cost me sales at times, but I have never been sued.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[Pud]

So where is the op? Was his query answered?

Harry

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

He logged on once only, 1 1/2 days ago and has not returned yet.

I know it got of topic, but I learned a bit from this thread and had some fun.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[btrueblood]

"I learned a bit from this thread "

Me too, as usual. Demon3's star well deserved.

 

[maestro0]

Such a great response! I didn't expect to receive much of a reply what a great community you have here!

Thanks to all, esp demon your advice is priceless.

I have en-listed the help of a local polymer manufacturer as I now realise I'm in well over my head when it comes to this even with a little push in the right direction from you guys! I'll let you know what we decide upon.

PS. pat>> a call point is the terminal you set off a fire alarm system at. google call point images will show you quickly.