I think the answer here depends on whether or not you have actually been penalized and why the site is dropping out of the SERPS.  Do you have a warning in WMT?  If not, then you're probably not penalized.

It's unlikely to be Penguin because Penguin did not refresh lately.  Similarly, Panda did not refresh on the days you mentioned.  So, it's not likely a penalty but rather some type of site structure issue.

Is there duplicate content between the subdomain and the root?  If so, then Google will choose one as the owner and not show the other prominently.  Any issues with robots.txt?  Are the canonicals set correctly?  Any chance of accidental noindexing?

You have some significant duplicate content issues with www.ides.com.  There is not a lot of text on your home page and what is there is duplicated in many places across the web.

Your second level pages are all just links.  I would noindex, follow these.

I looked at two inner pages:

http://plastics.ides.com/generics/6/alphamethylstyrene-ams - extremely thin content

Here is a Google search for text I copied from the styrene-acrylonitrile page.  There are 247 pages that use this opening sentence.

My guess is that this is indeed a Panda issue.  But please know that I've only just taken a quick look so I can't say for sure.  What doesn't make sense is that your traffic drops don't happen on Panda dates which really should be the case if it was Panda.

Panda definitely can affect just one part of a site (such as a root and not a subdomain).  I would work on making these pages completely unique and also noindexing the thin pages.