Common resin for pacifiers? 8

[Theophilus]

Here's another project in which I need to work with resins with which I'm not familiar. I'm working on a pacifier design in which the nipple will be formed with a sort of silicone, but I'll also have some molded hard plastic parts. I think I can find the silicone grade (although help on this would be great), but I'm wondering what to use for the harder structural parts. These need to be bonded to one another (hard piece to hard piece) with solvent or adhesive and will need to withstand high temperatures (boiling in water, dishwasher heat, etc.).

Any ideas which direction to move? I'll need something that's food-grade (minimally) and don't know what sorts of restrictions of which to be aware regarding solvents/adhesives for the rigid structural members.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

I would use polypropylene and friction weld it. If not possible, polycarbonate will work for a while until the boiling water destroys it.

Noryl or PPO might also work.

Regards

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[Theophilus]

Thanks, Pat. I have a few samples of existing pacifier products and am wondering what the harder of the plastics is--it seems to be available in bright colors (nice for this application) and quite hard (almost like acrylic, certainly much harder than PP or even PC) as well as structurally rigid.

One design has two plastic parts sandwiching a flexible silicone nipple between them. I haven't broken this apart yet, but it appears to be adhered together (instead of solvent-bonded).

Since I commonly design plastic widgets, I'm familiar with ABS, PP, PE, certain nylons, styrene, and PC--generally the less expensive resins great for cranking out cheap products for sale to the masses. The stuff I'm seeing in these pacifiers have me stumped--not something I've used before (almost like a hard version of PC).



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

Maybe it is acrylic, but from your description, more likely polysulphone or polyarylate or Polyetheramide. These would seem excessive for the application though.

Regards

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

 

[Theophilus]

I'm familiar with none of those, so I'll check them out and see what I can find (probably expensive, eh?).

Thanks!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

Very expensive.

Regards

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[Pud]

I would have thought SAN (Styrene AcryloNitrile) would be a good choice - it is used a lot for dishwasher safe containers/drinking "glasses" etc.

It is stiff, easily bonded due to the styrene content, about the same price as ABS, transparent so it takes colours well and it is easy to mould!!

It is used sometimes for blood contact parts so USP grades will be available. I would guess all the commonly used grades wil be FDA approved.

A Google will give you a squillion manufacturers and their data sheets........

Cheers

Harry

 

[Theophilus]

Polysuphone was looking good, but expensive. I'll check out SAN and see what I can find.

Thanks!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Pud]

Jeff,

SAN is great for widgets!

Customers have never heard of it, even though they have a cupboard full of it!

Great for the "sell" to customers (the old adage: bull***t baffles brains - everytime!)

I'm sure you'll use it often!!

Cheers


Harry

PS At least it's better than one RFQ we had: material= "Black Plastic"- and I kid you not!

 

[Theophilus]

After a quick look, I'm impressed with SAN. Might need to incorporate it much more often in my widget designing. (I use ABS quite often already--this looks similar, but with a styrene base.)



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[CoryPad]

SAN is ABS without the butadiene elastomer phase.

Regards,

Cory

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

 

[patprimmer]

SAN is an obvious choice.

It is not a resin I have ever had much to do with, so it slipped my mind.

It is hard, probably tough enough, easy to mould, reasonable price, nice glossy surface, food contact, clear base colour and can be solvent welded.

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.

 

[Theophilus]

Awesome--thanks so much for the quick feedback. I can hardly believe I've not used this stuff before. I can think of projects for which this would have been nice.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Pud]

Other useful widget materials if you need toughness as well as clarity are SBC's (Styrene Block Copolymer), trade names Styrolux by BASF, K Resin by Chevron Philips and others).

Tough as ABS, (No Break on un-notched impact testing), about the same or less cost, no pre drying required, easy moulding, etc.

Much used for medical stuff (USP) and by inference, FDA too.

The only drawback is the relatively low softening (Vicat) temp of around 65 Deg C. Can be mixed with crystal PS to make it a bit stiffer/cheaper, although at some ratios can get slightly cloudy depending on processing conditions. No problem if colouring though.

Cheers

Harry

 

[Theophilus]

Thanks, Harry, I've not used SBCs either. Looks like it's about time to get some samples to start getting a "feel" for their uses.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Pud]

Jeff,

One of our UK suppliers has some neat comparison tables - click on the icons (as it says)! and dowload the .pdf files.

http://www.distrupol.com/

As they are distributors for many manufacturers there is a good range of products compared - I guess most of the products or direct equivalents will be sold in the US too.

Disclaimer:
There may be others too (but I have not seen one quite so neat). I have no commercial interest with the company apart from they supply to my company.

Cheers

Harry

 

[Theophilus]

Nice! Thanks!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Demon3]

I fully agree that SAN is a good choice, cheap, quite chemical resistant and dishwasheable. Just make sure to get the dishwasher safe grade, most of them are not.

You can think of SAN as polystyrene that's modified to be chemically more resistant. In fact the chemical resistance increases in proportion to the amount of acrylonitrile (AN) in the copolymer. In addition to the chemical resistance, the AN adds some yield strength compared to PS. In natural form it can have a yellow tinge, especially the grades with high AN and therefore good chemical resistance. Normal SAN has about 25% AN, as you get to 30% and over it becomes way more yellow. This is easily compensated using some blue dye, the manufacturer will know how to do that.

If you need SAN with higher heat distortion temperature / Vicat there are grades available for that too. They use a third monomer to achieve it. Some manufacturers use alphamethylstyrene where the extra methyl stiffens the backbone at high temperatures. Other manufacturers use N-phenyl maleimide instead, the effect is the same.

Hope that helps!


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Demon3]

The SBC idea was not a bad one but I would avoid them as anything with butadiene in it will become brittle and yellow over time due to heat.


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Theophilus]

Good to know--thanks for the further insight!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.