Zero Shrinkage, Self Levelling Resin??

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#1

Hello all, new member here. I am looking for information on a composite with the following properties (if it exists that is):

. zero shrinkage
. self levelling
. smooth surface

Would appreciate any information on which resins meet the above criteria. I have discovered that zero shrinkage resins and self levelling resins are available, both with a smooth surface, but is there anything available that does all three??

My potential app for such a resin would be in spin casting of telescope mirrors where a very smooth surface is mandatory at both the macro and micro levels. In such a system the liquid resin would be rotated in a mold to form a parabola at the surface (which is where the self-levelling comes in) and, very importantly, that parabolic surface would have to be accurately maintained as the resin cures, ideally within at least +/- 100 nanometres (which is where the zero shrinkage comes in).

It’s a very tough requirement and I don’t know if it is possible but I would like to try it if it appears that some particular composite material might fill the bill.

Any assistance provided would be much appreciated…

#2

What we call “zero shrinkage” in fact still has a shrink rate of some 0,1-1%

Also, a factor that can play a role, is heat stability. I presume you would like to vacuum down a layer of metal on the surface. I have no idea on the heat requirements that this takes, and the heat requirements during use.

Still, I feel that an epoxy resin could be used. I recommend contacting for instance MAS Epoxy in the USA.

#3

Thank you Herman. A shrinkage of 0.1% sounds like too much for an optically flat surface but I’m just guessing here. I have however found this web page that refers to a study claiming “zero” shrinkage:

http://link.springer.com/article/10.1007%2FBF01105666#page-1

Abstract

Epoxy resin copolymer with zero shrinkage can be obtained by copolymerizing epoxy resin E51 with the expanding monomer of 3,9-di(5-norbornene-2,2)-1,5,7,11 -tetraoxaspiro[5,5]undecane (NSOC). The volume changes of an epoxy resin copolymerized with various amounts of NSOC during cure was measured with a dilatometer. The epoxy copolymer giving zero shrinkage was an epoxy resin with a E51:NSOC ratio equivalent to 5.88∶1. This epoxy resin copolymer with zero shrinkage has been used as an adhesive to join the optical parts of a large optical telescope.

Sounds encouraging but I’m not sure I want to spring for $40 to find out exactly what they mean by “zero”.

As far as deposition of a reflective surface, there are essentially two ways of doing that, one being chemical precipitation of silver (no heat involved) and the other being aluminum vapour deposition under vacuum (the Al gets locally vapourized but I don’t believe the mirror substrate warms to any extent as the amount of Al deposited is very small). I suppose that any outgassing from the resin might present a problem though as a pretty hard vacuum is required for the process to work.

Thank you for the reference to MAS - I will contact them…

#4

Zero shrinkage basically leaves you with epoxies.

This epoxy flowcoat is specifically meant for coating engine rooms since it hard, durable, glossy and easy to keep clean.

http://www.atlcomposites.com.au/files2/products.epoxy.coatings/trez_r1300_flowcoat.pdf

#5

Thanks for the replies to my query. I posted a response to herman a couple of days ago and got a message saying the post had to be approved by the moderator. Don’t know what happened after that as it has not shown up here. Anyhow, will see if this post makes the cut.

#6

Indeed did not see it. Probably still in the moderation queue

#7

OK, that post was added immediately so will try herman’s reply again.

As for “zero” shrinkage, I have discovered the following article reference that claims zero shrinkage although I have not sprung for the $40 to download the article to see just what they mean by “zero”. It appears however they have formulated a combination of an expoxy that shrinks with one that expands so, in the proper ratio, the two cancel each other out. So it appears it is possible but the article was dated 1989 and I don’t know if anything similar is currently commercially available.

http://link.springer.com/article/10.1007%2FBF01105666#page-1

As to a reflective surface, the mirror would be coated in a similar fashion to glass mirrors, either by vacuum deposition of aluminum or precipitation of silver via chemical reaction i.e. no heating of the mirror in either case.

#8

OK, just re-posted a reply to herman and same message resulted. Maybe it depends on the message length.

Or, maybe because it had an embedded URL…

#9

You mean a private message? If all else fails, you can mail to herman at hmtf dot nl

#10

Nope, just a “Quick Reply” message. If my posts don’t show up I will email you.