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What Additive Makes an Acrylic Medium Dry Tacky?ApproveRejectUn-ApproveSubscribeUn-Unsubscribe

Question asked 2016-12-14 23:46:43 ... Most recent comment 2016-12-15 00:03:00
I mostly use GAC 700 and Specialty Polymers BH61 because I like their clarity when dry.  They both have very high solids content.  While they seem similar in many regards they are very different in their tackiness when dry.  GAC 700 is very tacky and BH61 is very hard.  I notice GAC 700 will be flexible soon after it is dry but BH61 will take weeks to become flexible.  After they are fully cured both can be bent completely over without breaking.  I wonder if the "gumminess" of GAC 700 occurs because it is made to be flexible sooner and if this occurs by an additive that creates the stickiness of the final film and what that additive might be?   I have tried propylene glycol but I don't think that is it.   Also I notice that BH61 will sometimes form fine cracks (not fissures) in certain drying conditions and I wonder if this is related to the tackiness?
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Moderator Answer (Sands, Sarah)

[2016-12-15 07:54:19]

Hi -

Ulysses Jackson, one our formulators in the Lab and a member of our R&D Department, provided this information which should help explain things a little more:

"The Tg of the binder in GAC 700 is higher than the listed Tg of  http://www.specpoly.com/product/raycryl-61/ - or rather 16°C vs 11°C for the H61 .  Could not find BH61 but believe B stands for binder 

What possibly may be occurring is that we have some slower evaporating coalescing agents in our formulated product  that would not be present in a neat resin. This would explain the sense of tackiness. Over time this would reduce as they are volatile all be it slow. "

​Hope that helps and if you need additional information or further explanation about the above, just ask.

Sarah Sands
Senior Technical Specialist
Golden Artist Colors


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User Comment

[2016-12-15 10:04:34]
Note that Sarah's reply indicates "slower evaporating coalescing agents" in acrylics. Water isn't the only component that leaves the film as it dries. Coalescents moderate the rate at which film integrity is achieved, after water has evaporated. Coalescents like propylene glycol are also in retarders which keep acrylics wet longer. Excessive use of retarders can also induce tackiness. Matthew Kinsey, Utrecht Art Supplies
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Moderator Answer (Kristin deGhetaldi)

[2016-12-15 10:56:14]
I would also like to add that this BH61 acrylic polymer is a product that is designed to suit "exterior industrial" purposes. Industrial products are not necessarily any better-suited for art purposes....in fact they may even cause problems in the future. For a bit of a perspective on this I refer you to number 13 in our "Myths, FAQs, and Common Misconceptions" document which you can download from our Resources section.
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User Comment

[2016-12-23 15:50:50]
Thanks Ulysses and others. That was good info and much appreciated. Yes BH61 is the same as Raycryl 61. I wonder what other coalescing agents are commonly used to formulate acrylic mediums for artists? I have used propylene glycol and Texanol from Eastman coatings. Perhaps "Benzoflex 9-88 plasticizer" from Eastman would stop the cracking when drying pools of BH61 in uneven temperatures? Some of these additives are carried by Kremer and Guerra in NY and are available to artists to try out. Golden has also been very kind to sell me their thickeners. The reason why some artists use BH61 or Raycryl 61 is it was recommended (by Ray the now deceased owner) as a non-yellowing, non-brittle polymer for painters. I believe Dan Smith used it in some of their acrylics as well. I have used it for about 20 years now. Now I often use GAC 700 in combination with BH61 because it is clearer than adding GAC 200 to reduce the tackiness of pure GAC 700 (as recommended by Golden).
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