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  • 1.  Acrylic Paint - Brainstorm

    Posted 19-11-2024 17:17

    Hi Brains Trust,

    I'm looking for someone who can help with the below enquiry from a member of the public who has turned to the RACI for advice. Obviously I am not the one with the answers, but I am hoping there may be a community member that may be able to help this nice guy out!

    _ _ _

    "I'm trying to create my own acrylic paint for tabletop miniature models to sell, and I've run into some issues with my formula. The consistency seems fine initially, but when I paint it onto surfaces, one colour (brown oxide) separates almost like silicone, and other colours dry with a gritty texture. I'm using a glass muller and a sanded glass chopping board, and I follow this process: I grind the pigment using PPG (Polypropylene Glycol), then add small amounts of Hydrocryl 1361, mix it with a bar mixer, and strain it through a paint bag. I'm wondering if the issue could be related to pigment dispersion or stabilisation, or if I'm not grinding the pigment long enough or finely enough. Could the grit be from insufficient mixing, grinding, or straining? Should I consider using a magnetic stirrer, longer mixing times, or different straining methods (e.g., coffee filter paper)? Any advice on how to fix these issues and achieve a smooth finish for miniatures would be greatly appreciated, as I'm trying to make a return on this business as soon as possible"

    Also- Bonus points for anyone who knows anywhere in Australia he can put his pigment through a bead mill.

    _ _ _

    Any help I can pass on would be appreciated!

    Many thanks!

    Sian



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    Sian Pilling
    Events & Awards
    The Royal Australian Chemical Institute
    Email: events2@raci.org.au
    Phone: (03) 9328 2033
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  • 2.  RE: Acrylic Paint - Brainstorm

    Posted 21-11-2024 23:13

    Firstly, I'm presuming that your contact has tried to find commercial sources of paints without success, and has turned to formulating his own. I don't have any direct experience, but I'm willing to kick off some discussion (and suffer some corrections) if it helps to move things along.

    1. The separation of the brown oxide pigment. Is this a particle size problem, or is it caused by a hydrophobic or hydrophilic incompatibility with the substrate, where the pigment is clumping? Does the pigment require some sort of surface treatment (e.g., silanes) prior to mixing with the materials used in the substrate?
    2. Size reduction and separation. I can't help with location of a bead mill, but I'd certainly suggest that this is the right way to go to achieve the low or sub-micron size range that your contact is looking for. Perhaps researchers in the ceramics field might be able to help out here. maybe you could contact distributors of such mills (e. g., Retsch) who might point you in the right direction of some customers who might be able to help out. These mills seem to produce materials of uniform size, which is what your contact might want. 

      I do have some experience in the separation of naturally fine minerals from coarser particles, but this may not be of much interest to your contact because it's a fairly lengthy process requiring some knowledge of surface chemistry. There was a project by Comalco (Rio Tinto subsidiary) back in the 1980s to find a use for the millions of tonnes of bauxite fines (red brown colour) washed yearly from Weipa bauxite pisolites in the beneficiation process. These fines had a particle size averaging around 200 nm from recollection. To separate from larger particles, the fines were first dispersed (with a polyacrylate I think), and the coarser particles allowed to settle out. The quite stable supernatant suspension was then spray dried for further experimentation. The spray dried particles were spheroids with a diameter around 20um.

    This is a bit of an aside to your contact's problem, but it does touch on the problem of fine particles clumping on formulation. I'm a bike rider, and I wanted to make a dry lubricant for my bike chain. A popular method is to bathe the clean chain in a melted mixture of wax and teflon powder in a rice cooker. That's not possible where we live. I wanted a product where I could drop the mixture onto each link and melt it in with a hot air gun. Teflon powder is available on eBay and has a particle size around 1.5 um. My idea was to dissolve the wax in a petroleum solvent (mineral turps), then mix in the teflon. The teflon clumped, and did not disperse. I then found that it dispersed nicely in 2-propanol before mixing it with the wax-turps solution. It works perfectly. Perhaps the 2-propanol helps discharge the static charge on the very fine teflon particles. 



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    Tom Smith
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  • 3.  RE: Acrylic Paint - Brainstorm

    Posted 22-11-2024 18:44

    The original querent said they were using PPG as a grinding aid and mixing in the resulting pigment grind with a small amount of Hydrocryl 1361 - which I can't find a listing for, but I'm going to assume is an aqueous acrylic emulsion being used as the primary binder.

    The characteristics of the binder (MFFT, Tg) may be part of the issue - and they don't mention the use of a coalescing agent and/or suspension aid so it's possible that uneven drying is seeing separation of the pigment in an uneven manner.

    Paints are a lot more than just colour and binder - maybe direct them to the Surface Coating Association of Australia (SCAA). I think they have some on-line resources for the budding paint formulator.



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    Bruce Heath
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  • 4.  RE: Acrylic Paint - Brainstorm

    Posted 23-11-2024 08:34

    I have used a small roller mill for dispersing and grinding pigments. The mill is from National Geographic and is designed for rolling and polishing gemstones at a hobby level. Using a glass jar with marbles and making sure the slurry of pigments in liquid is the right viscosity gives surprisingly good results.



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    Barry Hunt
    Senior Formulation Scientist
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  • 5.  RE: Acrylic Paint - Brainstorm

    Posted 19-12-2024 19:41

    A huge thanks to @Thomas (Tom) Smith @Bruce Heath and @Barry Hunt + all those via email for collaborating and providing information and guidance to our paint enthusiast!

    Shane Burns from Mini Man Studio was very grateful for everyone's insight and now follows us on RACI socials, give him a follow back to see how he goes!

    A great example of wonderful RACI spirit! 



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    Sian Pilling
    Events & Awards
    The Royal Australian Chemical Institute
    Email: events2@raci.org.au
    Phone: (03) 9328 2033
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  • 6.  RE: Acrylic Paint - Brainstorm

    Posted 08-01-2025 22:59

    Hello Sian,

    Maybe I am a bit late to the conversation, but plastic compounding companies such as https://www.welvic.com/ or https://rbmplastics.com.au/ have mills to grind colours into the plastic resin before extrusion. They might have the mill that your member needs, or know somebody that does. 

    Kind Regards



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    Dennis Planner
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