vinyl

3/7: Plastisols and plastigels

Plastisol

It sounds like a product or cleaner that dissolves plastic. Nope.

A plastisol is a mixture of PVC (polyvinyl chloride powder) and plasticizer. While it’s not the kind of thing that we can buy at the local grocery store, it’s a pretty common material. Here’s why. Have you ever had one of those t-shirts that are screen-printed with your team name? Or perhaps a tote bag that’s been screen-printed with the name of an event? The ink that they use is plastisol ink. (Here’s a quickie video that shows the basic process.)

Wait. What? The ink on my t-shirt is vinyl? Yes. Plastisols are used as screen-printing ink on fabrics.

Now grab your jewelry pliers. See the handles? Notice how they look like they’re dipped in plastic? They are dipped into a plastisol and then heated to cure. Yes, tool handles are vinyl! Plastisols are liquids poured into metal molds that are then heated to make solid vinyl. In fact, most vinyl products are made from plastisols.

You’re already familiar with plastisols, of course. Liquid clay is a plastisol.

(As an aside, if you’re familiar with Genesis Heat Set Oil Paints, you’ll recognize the entire Genesis system as one of plastisols but made with proper artist’s pigments.)

Plastigel

Plastisols are great, but they’re liquid. Gravity will make them run until they’re heated enough to cure, making them solid. So you can’t free-form a plastisol. It needs to be molded, flowed, or applied onto something. (You’re already familiar with this property by using liquid polymer clay.) You can’t form it into a shape with your fingers. You have to mold, flow, or apply it.

But what if you mix a binder into a plastisol? Something like talc or kaolin (earth clay mineral) or another thickener? It forms a putty called a plastigel. A putty? That sounds familiar!

You’re way ahead of me. Yes, polymer clay is a plastigel. And just as plastisols are cured with heat, you also would cure a plastigel with heat to form a solid plastic. Just like we do with polymer clay.

Plastigels have some interesting properties when it comes to the way they move under pressure. They’re not liquid, but they’re not solid either. Remember that. In my next post, I’ll continue this series to talk about what this means for the way we “move” polymer clay, including conditioning and the dreaded crumbles!

1/7: What is vinyl?

Sure, you know what vinyl is. An old vinyl record. PVC pipes. Barbie and baby dolls. A plastic shower curtain (ew, with that smell). Aquarium tubing. Baby pools. Those cheap swirly balls in the big cage at the grocery store. Garden hoses. Fake leather recliners. Electrical cord coating. Window frames. Plastic tablecloths. Think about those items and how the material feels. That’s vinyl.

But what IS vinyl, actually? It’s a plastic that’s made by mixing PVC powder (polyvinyl chloride) with some pigments, some oils, some heat stabilizers, and in the case of the items above, some plasticizer. The resulting mixture is then heated (cured) to form a solid object.

Plasticizer is a clear, oily liquid (usually) that is added to the vinyl mixture to make the end result more flexible after it’s cured. The more plasticizer in a given mixture, the more flexible the resulting object will be. So you can readily see that a vinyl siding or pipe has very little (or no) plasticizer, a shower curtain would have more, and those super stretchy gelly toys have even more.

You’ve probably realized where I’m going with this. Our beloved polymer clay IS vinyl. And just like all vinyl, it is a mixture of PVC powder, pigments, plasticizer, and “stuff” that makes it behave well. All this time we thought we were dealing with a space-age material or something new and unique. Nope. It’s the same old vinyl that manufacturers have been using forever (okay, since the mid 20th century). It’s just that we get it before it’s cured and get to make it into whatever shapes we want before we bake it. (This is also why it’s so easy for the Chinese companies to make cheap polymer clay…it’s a standard manufacturing material!) It’s also why supplies of polymer clay were disturbed during the pandemic. The raw materials are also used industrially.

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