Injection molding a part so it needs no paint, currently painting
Injection molding a part so it needs no paint, currently painting
(OP)
Hi I am new to the forumn and am a product engineer with about 3 years exp.
I am currently haveing a part molded for me that is quite big, it is a case to a medical instrument. It is currently made of ABS+PC (Hybrid S570 or similar) w/ chem. foaming agent (Hydrocerol or sim.). This material is OK, it just looks like white chocolate and the parts needs to be pantone cool gray 1 U.
Here are my questions:
1. How would I spec out a material that can be shot in this color.
2. Is it possible to add dye to the current material?
3. Paint hides sink and mold flow lines, the bare part currently has a lot of these. This would rule out using this material correct?
This is a good start if anyone can help. Thanks so much for any assistance.
-Dennis
I am currently haveing a part molded for me that is quite big, it is a case to a medical instrument. It is currently made of ABS+PC (Hybrid S570 or similar) w/ chem. foaming agent (Hydrocerol or sim.). This material is OK, it just looks like white chocolate and the parts needs to be pantone cool gray 1 U.
Here are my questions:
1. How would I spec out a material that can be shot in this color.
2. Is it possible to add dye to the current material?
3. Paint hides sink and mold flow lines, the bare part currently has a lot of these. This would rule out using this material correct?
This is a good start if anyone can help. Thanks so much for any assistance.
-Dennis






RE: Injection molding a part so it needs no paint, currently painting
You have one supplier now who is not delivering what you wish to have. Contact them and see what they can do. Then look for other suppliers. Your question above appears to be very well written as an initial question. Send it to prospective suppliers.
With a little work you will find someone that can guide you though the whole processes, including helping you write specifications.
Tom
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
Good engineering starts with a Grainger Catalog.
RE: Injection molding a part so it needs no paint, currently painting
I think the essence of the technique was that the mold cavity was coated with a release agent, then painted, possibly with a dry film, and then whatever resin you wanted to use was shot inside the paint. ... and magically adhered to the paint without substantially distorting it.
ISTR photos of stuff like lawn tractor engine covers provided as examples. Hint: They were painted in that specific bright green that clashes with everything other than bright yellow.
I have no idea if the process is actually in use now.
Mike Halloran
Pembroke Pines, FL, USA
RE: Injection molding a part so it needs no paint, currently painting
RE: Injection molding a part so it needs no paint, currently painting
Another alternative is to have the colour matched and pigment supplied in the form of a master batch, although with ABS or ABS blends this can have some variation from batch to batch due to variations in the base colour of the ABS. It depends on just how fussy you or more importantly your customers are about aesthetics.
Also be aware that a Pantone chip has a different surface texture and reflection. This can have a significant influence on the appearance of a colour. Colour is a very subjective thing and the appearance of the same colour can vary a lot with circumstances. For instance, a glass of beer. The beer and the froth are the same liquid and therefore the same colour, but they look very different. I mention this because you are foaming your part, presumably to reduce weight and/or control sinks.
The more glossy your surface the more obvious sinks will be. A foamed moulding will exaggerate the appearance of flow lines.
Paint will mostly cover flow lines, but not so much sinks.
If you have tried to discuss this with your moulder and he has not provided a significant amount of the info above, maybe you need a new moulder, or you at least need to push him for information.
Regards
Pat
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RE: Injection molding a part so it needs no paint, currently painting
In a bit of conclusion, it doesn't sound like color matching is a different type of problem than any other material selection problem. I thought these materials would be a different class of plastic. Not sure why I thought that since many other parts I make are a specific color and are not painted.
I will post updated as the issue advances. This would save my company a huge amount of money.
RE: Injection molding a part so it needs no paint, currently painting
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Injection molding a part so it needs no paint, currently painting
I sort of don't see this happening in the my current mold for the part. I may be adding a touch screen to the instrument in the future, so I may be developing a new mold, in that case, I will without a doubt, engineer in texture and the use of no paint.
RE: Injection molding a part so it needs no paint, currently painting
Regards
Pat
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RE: Injection molding a part so it needs no paint, currently painting
RE: Injection molding a part so it needs no paint, currently painting
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: Injection molding a part so it needs no paint, currently painting
RE: Injection molding a part so it needs no paint, currently painting
RE: Injection molding a part so it needs no paint, currently painting
The more things you need to control, the higher the price goes. One of the things that scares me about this project is how high the price may end up going.
RE: Injection molding a part so it needs no paint, currently painting
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Injection molding a part so it needs no paint, currently painting
PC/ABS is particularly sensitive to shear during moulding.
A longer screw in general should be easier on the material so long as the residence time is similar. More important is screw profile or compression ratio. PC/ABS does not like high compression screws, particularly ones designed for nylon or for PP and high speed packaging applications. It also does not like to much back pressure. It particularly does not like small gates.
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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RE: Injection molding a part so it needs no paint, currently painting