How are acrylic protractors printed? 1

[Clifford44]

I have a design for a measuring device that I may want to have manufactured that is similar to a clear acrylic protractor. The protractors I've handled have slightly raised print or paint on one side that doesn't scratch off easily. What process creates this result? Here is a picture of what I'm referring to.
Thanks!

Link

 

[Compositepro]

It is probably screen printed, but I've seen plastic rulers where the marks are part of the mold and then the raised areas are inked. How do you know it is acrylic?

 

[Clifford44]

I see. I just assumed they were acrylic. Maybe not. What other possibilities are there for inexpensive firm clear plastic tools like that?

The protractor I'm holding now has no raised areas, just the paint that you can sort of feel by running a fingernail over it. That's what I'm going for.

 

[MikeHalloran]

Acrylic, which I think is more formally known as polymethylmethacrylate, is an old traditional material for aircraft canopies and for transparent tools like navigation slide rules and such. It has a characteristic odor that appears when it is drilled or sawed. ... okay, all plastics have their own odor. I think PMMA is continuous cast from solvent solution, on a large chrome plated wheel. ... or once was; there are probably other ways to get it into useful form now.

I have a protractor almost exactly like the one in the photo. Mine is at least 55 years old. The blue cast suggests polycarbonate, which is often blued slightly to offset a normal yellow cast, but I don't think PC was common that long ago, so I'm guessing a polystyrene alloy.

Polystyrene is cheap, clear and colorless, but brittle. You may remember it from the transparencies in plastic model kits. Nowadays, except for plastic models, you'll probably find styrene alloyed with acrylonitrile (vinyl cyanide) as SAN, or acrylonitrile and butadiene as ABS, or a thousand other things sold under a million names. ... well, almost.

Polysulfone is a little more yellow than polycarbonate, less subject to environmental stress cracking, more temperature resistant, similarly tough and similarly priced.

You might want to visit your local plastic sheet seller to buy a few sheets of various thicknesses and compositions, to get a feel for how stiff you want your product and how difficult it will be to fabricate it from sheet.

I'm guessing your protractor was screen printed (in two steps, one for each color), which requires some care to get good registration. Your screen printer may not like it, but you can specify epoxy ink for durability. Start with whatever ink the printer suggests, and test a few samples yourself.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

If you want 'military grade', go with PMMA, get it CNC-engraved, and the engraving filled with paint/ink. There used to be people/companies who specialized in that sort of stuff. I don't know if/where they survive.



Mike Halloran
Pembroke Pines, FL, USA

 

[Clifford44]

Wow. Thanks for the detailed reply, Mike! And thanks to both of you for such quick replies.

 

[Clifford44]

I forgot to ask if there is a process that makes clear plastics anti-glare.

 

[MikeHalloran]

If you're molding the part, you can specify a matte finish on the mold, which will transfer to the surface of the part. Clear-ish grades of ABS may not need a roughened mold surface.

If you're working with sheet, you can wet sand the surface before screening.

You may be able to cover the finished part with a clear semigloss spray, but do some testing to make sure the overcoat doesn't dissolve the screened image or attack the plastic.




Mike Halloran
Pembroke Pines, FL, USA

 

[Clifford44]

Great! Thanks again, Mike!

 

[Compositepro]

If the item is made from sheet material it may be PET (Mylar).

 

[Pud]

I used to work for a company that made "scholastic equipment".

Cheapo plastic rules, set squares, protractors etc, were made from crystal styrene (transparent) or HIPS (not transparent) which were silk screen printed with a UV-cured ink ( <1 second to cure).

Rules classed as "shatterproof" (rather than unbreakable) were made from K Resin*

Cheers

H

*K Resin is a trade name for styrene butadiene co-polymer (SBC) - other equivalents are available.

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[Clifford44]

Wow. I didn't realize there were so many options for transparent firm plastic parts. I just read about UV-cured ink and saw a quick demonstration of it on YouTube. It looks like a great option for me. Thanks for pointing it out, Pud.

 

[itsmoked]

If you're actually going to have a mold made you can go with the classic raised lines and numbers, then a paint roller is passed across the molded product. The paint only lays down on the raised parts making them stand out rather dramatically and lends the tool the ability to still work even if the paint wears off - unlike a simply painted flat surface.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Clifford44]

Yes, Keith. That sounds like an interesting option too. Thanks!