Material for Instrument Window

[scrubbs]

We are currently working with a customer on an instrument cluster assembly. Their design calls for a flat piece of plastic as the window in the front. What materials are generally used for this?

Options we are exploring:
1)polycarbonate with anti-scratch coating on the outside with anti-fog coating on the inside
Pro: impact resistant
Cons: yellows over time, scratches somewhat easily

2)acrylic with anti-anti scratch on the outside and anti-fog on the inside
Pros: Scratch Resistant, does not weather
Cons: so far difficult to find someone that can anti-fog coat,

What are the pros and cons of either option? Is an anti fog coating needed(or used in industry) for a totally sealed unit? I have talked to suppliers and a lot are saying it is tough to get an anti fog coating to adhere to acrylic.

 

[patprimmer]

As far as I know acrylic is always used unless there is a potential head impact situation. This is for reasons of optical clarity, scratch resistance, resistance to some very commonly used personal care chemicals and resistance to UV light and cost.

I never saw a requirement for anti fog.

With the heat generated from the instruments, I never saw fog as an issue.

Regards

eng-tips, by professional engineers for professional engineers
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[scrubbs]

yeah, it seems our customer is more accustomed to glass and is new to using a plastic material for this.

I am not sure about the anti-fog either, as its a sealed unit with a large PCB in it so it should generate a lot of heat.

I have not yet found a supplier that can coat acrylic sheets in an anti-fog coating, something about it won't adhere properly. I have talked to people that anti-fog molded components, but they said you have to match the right acrylic resin to the anti-fog coating in order to get proper adhesion.

Is there anywhere else i can find information on what is normally used for this sort of thing?

 

[CoryPad]

Extra con for polycarbonate: low chemical resistance

I don't think yellowing would be that much of a problem as long as you work with the material supplier on an appropriate grade.

Extra con for acrylic: low fracture toughness




Regards,

Cory

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[scrubbs]

does anyone have any other thoughts on this?

still unable to find a supplier that can supply acrylic with an anti fog coating. The customer is currently using a polycarbonate with an anti-fog coating(or so they say...) on the inside, and that is why they asked for it.

And yes, from those who i have talked to already, it seems PC options would not really weather with the new grades and coatings available.