I’m looking for any wisdom related to molding or painting molded thermoplastic parts for a gloss-white effect.
Concerns being:
Wear & tear: scratches etc. (is white better/worse for allowing? Hiding?)
Durability against cleaning solvants
Strength (I’ve heard it can be brittle–Apple has had problems with hairlines)
Any examples of gloss white products that take wear-and-tear would be appreciated!
I dont know (obviously) what you are making, but one way to make something gloss white and really durable is to use a clear glossy plastic, like lexan, and paint the inside…
There are special paints that are flexible and bond permanently to lexan.
You might take a look at kitchen electrics. Almost every product comes in a white version. I can’t name the exact plastic used, but they generally have some give or flex, unlike the more brittle Apple stuff (3G iPhone)
Yeah, I’ve had really good luck with this as well. acrylic and that krylon plastic work well together too. watch for the static though, it makes the paint get a wierd texture, but once you flip it around you can’t tell.
another key thing is to polish the tool and then chrome plate it - that produces the best gloss surfaces.
Is it for a Medical Device? (The solvents thing tends to be a big medical specific criteria)
Have your molds chromed before you go into production. It should always be the last step. Also, when you’re designing watch your draft angles, even with chroming, any walls perpendiclar to your parting line can get scuffed when the mold splits.
White is by far the best color for hiding scratches, scuffs and fingerprints on a high gloss surface.
The rest of your questions regarding materials really depends on the application.
We run some high gloss parts where there is a major requirement for scratch/scuff resistance and impact performance.
During development we looked at a few different materials. We experimented with Lexans that have good scratch resistance (approx. 2H) but they are very brittle and tended to shatter.
In the end we picked a tougher plastic and used an anti scratch coating to satisfy the mechanical and aesthetic requirements. A more expensive route perhaps but it will depend on your specific requirments and what punishment you expect the product to receive.
If you want to paint the part, I know a molder in Montreal that makes parts for Bombardier (Ski-Doo, Sea-Doo, etc). Obviously, they know how to make painted plastic parts that are very durable. However, I don’t think they make many white parts.
Here’s the contact:
Les Produits de Plastique Age
www.plastic-age.com
tel: 514.251.9550
For the parts they were doing, they would mold the part in PP (I think), in the closest match to the paint they could manage. Then they have a supplier that paints the parts, but has a very durable flexible paint. The quality control is very good.
I have that Sony radio. Great finish in ABS. Still glossy after 4-5 years now. Kitchen appliances are pretty high gloss too and typically just shot with PP
I haven’t had a project call for such a finish, but I have been waiting for the opportunity. I’d use a clear plastic (acrylic lexan etc) that meets your chemical and mechanical requirements and then paint it inside out. The intent is to give a translucent layer kinda like what show cars have with the extra layers of clear coat.
One of our issues is one large part (about 2x2’), which R&D would prefer to manufacture using structural foam molding for tooling savings. Problem is that structural foam needs to be painted, and painting to a quality white gloss is difficult.
So let me modify the question: how can we achieve a high gloss white on a large affordably molded part?
I think the answer is that we can’t and we may want to choose an entirely different method, such as baked enamel on metal (as in your typical washer/dryer), and just hope we can get the color close to the adjacent IM parts.
From what I understand the issues with cracking in high gloss white parts is due in large part to the UV stabilizers, not sure what advances have been made here recently, but would be curious to know.
Color matching Enamels to IM parts is never fun, I would either A) ensure you are locked in on color standards for the other parts and work with a good supplier or good CMF consultant that can give the people doing the enamel a quality target using the correct substrate and enamel or B) establish the Color standard for the Enamel first then work with the supplier or a good CMF consultant to create material specific color targets for the remaining materials. If you need a good CMF consultant PM me.
I assume structural foam is a self skinning poly urethane RIM process, which also involves tooling. Your durability for solvents will be determined by adhesion of paint to part (chemical bond) and the paint properties itself.
I agree with IDiot on color matching enamel to IM parts - very different material properties cause color qualities to change at different rates under different light sources. But white could have a wider tolerence.
Have you considered thermo-forming (vacuum forming)? Considering the size of the part you could match IM part material (ABS?) and you should be able to maintain the high gloss qualities of your starting sheet stock in your final part. Tooling should be inexpensive, but may not work if you are looking at a very high production rate.
We use a Sherwin-Williams Polane 2.8T+ paint on our structural foam parts. It’s fairly glossy and very durable, I’m sure they have a clearcoat to put over it too. Polytech out of chicago does a really good job on the molding and have a good relationship with a painter. They can hit the surface of the part with bondo to fill voids before it gets sent off to paint. The problem with any structural foam part (or RIM) is that you have to paint it and that paint will eventually scratch. I would recommend a base plastic of the structural foam that is a similar color to the paint. Or a nicely contrasting color if you want to highlight the damage. Stay away from RIM though, Rim parts warp just sitting on the shelf and isn’t as strong as structural foam, tooling is about the same and we got much better pricing on structural foam parts.
I agree with 51 though, look into thermoforming. You can thermoform plastic up to 1/2" thick (or thicker at some specialty places) which for a 2’x2’ part you would be able to drive a car over without a problem. Screw bosses can be glued in or inserts can be sonic welded. Tooling is dirt cheap. The only thing is undercuts can be a problem. Some venders can get you an undercut on the one side of the part by thinning out the plastic in that area, like for a reveal line.
2x2 isn’t outside the realm of possibility for injection molding, a simple aluminum open-and-close tool run in a mudbox could be cheaper than the structural foam tool. I’d talk it over with a supplier.
good luck with your project.
Excellent! I will definitely consider IM with an aluminum tool.
…What’s a mudbox?
MUD = Master Unit Die
Basically, a standardized base and inserts for a mold. Quick and cheap. Google will be more in depth than me.
Okay, here’s a new one!
Engineering is saying that Matte finishes are easier to color-match from unit-to-unit than Gloss finishes. They have not provided any data that supports this argument.
I would think the opposite: gloss would allow more non-conformity between parts because so much of what you’re looking at is actually the environment reflected into the part.
Thoughts? Experiences?
For large parts using fiber, matts, or structural foam I believe the process you are looking for is in-mold coating. There are a couple methods such as liquid injection, or spray. If used, you’ll need to consider the process in the part design, but it’s pretty accommodating for those molding processes.
http://www.omnova.com/products/chemicals/inMold.aspx
IMD using film would be cost prohibitive for such large parts, it can give you the high gloss surface “painted behind clear substrate” look on smaller parts. It’s a little more involved on the development side, but perfectly doable on cell phone size parts.