Specifying Opacity Of Parts 2

[EngMark]

I have two pigmented semi-transparent parts which will be made from different resins by different suppliers. They both need to be visually similar in color and degree of semi-transparency (opacity?). One would be polypropylene 1mm thick and the other would be silicone rubber having three different thicknesses, but at the 1mm thickness should match the appearance of the polypropylene part. The tone of the color (purple) should be easy to specify through a chart such as Pantone (is this standard amongst resin suppliers or is there a better system to use for color specification?). The degree of color saturation or degree of transparency is what I'm struggling to characterize in my drawing for these parts. Is there a standard method for specifying this to suppliers?

Thanks,

Mark

 

[patprimmer]

%age transmission and Haze factor are two typically specified properties in transparent plastics.

The actual terminology used is

Transparent. This means you can see clearly through it like water clear. It is expressed as %age transmission being high and haze low.

Translucent. This still transmits a lot of light but scatters the light like a frosted glass light bulb where all the light comes through but is scattered so you don't clearly see the filament glowing. It is expressed by relatively high transmission and high haze factor.

Opaque means zero transmission.

Opacity means degree of non transmission.

A transparent tint is like coloured or stained glass. Sun glasses are a grey or brown tint. Tint is a somewhat ambiguous term as it also has other meanings, like a small change in colour.

You need to match the hue, the %age transmission and the haze factor to be close. Surface reflection will also cause illusions.

Colour is quite subjective and is impossible to fully define subjectively.

An example. Many years ago I had to match a colour for a wide contrasting stripe across the chest and a thinner stripe the same colour in approximate line across the arm.

When the same yarn was used to kit both stripes it appeared to mismatch. We had to deliberate mismatch so as to appear to match. ie we had to offset for the illusion.

Regards
Pat
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[Demon3]

There's a good chance the parts won't look the same even when you've matched the opacity.

I'd try adding a white pigment like a trace of TiO2 to the silicone to make it cloudy like the PP. Or get transparent PP, which is made using an additive that makes the PP crystals so small that they no longer scatter visible light. The leader is Milliken who sell such additives. Ask your PP supplier, they'll know, the additives are known as clarifying agents or clarifiers.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry