On 29/04/2014 09:23 AM, scott wrote:
>> Interesting. I was under the impression that UV-resistent coatings are
>> just overly-optimistic marketing, and in reality none of these coatings
>> actually work.
>
> One of the first image results from google gave this:
>
> http://www.alpineastro.com/filters/uv_ir_cut_specs.htm
>
> That's a pretty sharp fall-off below 400 nm. Whether it works or not is
> unquestionable, what is usually up for debate is whether it's actually
> useful on a camera. On skin, eyes or paint of course it works and is
> useful.

That's a pretty sharp cuttoff. OTOH, from this scale you can't tell 
whether the filter still passes, say, 1% of the UV. 1% UV is presumably 
still easily enough to utterly destroy whatever is underneith. (E.g., a 
plastic coated in this stuff will get ruined in a few months rather than 
a few days.)

I am not a professional chemist, but as I understand it, UV just 
destroys absolutely everything it touches, and it's very hard to make it 
not do this.

> Then there are all the things the consumer doesn't even notice. Like
> plastics that are easier to mould (more complicated shapes are possible
> to be made faster with finer details), possible to process in thinner
> films, flame retardants that are environmentally friendly, stronger and
> stiffer plastics that enable things to be made with less plastic for the
> same performance etc.

So... essentially you're saying the only real change is that plastic is 
cheaper now?

And to think I was under the impression that plastic only exists in the 
*first* place because it's cheaper...

> The software we use here for simulating the moulding of a plastic part
> (to make sure it will fill correctly and not leave any sink marks, weld
> lines etc) has a built-in database of plastic materials to choose from.
> There are over 10000 of them, and there are plenty not in the list. They
> have all been developed for a specific reason, and most of them recently
> (not 30 years ago).

I knew there were at least 6 main plastic types. But 10,000? Really? I 
can imagine you could have 10,000 different compounds, with different 
additives in them to adjust how springy or brittle they are, etc. But 
10,000 fundamentally different molecules? Really?



Actually, I just thought of something. One thing we didn't have when I 
was a kid: oven bags. As in, plastic bags that you cook things inside. I 
still can't quite wrap my mind around how this works; most plastics melt 
if you pour boiling water on them, never mind heating them to *hundreds* 
of degrees...

(Also, if this plastic as such a high melting point, how do you mould it 
in the first place??)

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