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> What people forget is the covering is really designed to protect the data layer not the surface. Right. But that this started explicitly about calling the po

> What people forget is the covering is really designed to protect the data layer not the surface. Right. But that this started explicitly about calling the polycarbonate -- that clear layer -- as scratch resistant. And this is just flat out wrong: "Polycarbonate is a durable material. Although it has high impact-resistance, it has low scratch-resistance." https://en.wikipedia.org/wiki/Polycarbonate#Properties_and_processing https://en.wikipedia.org/wiki/Polycarbonate#Properties_and_p... I agree that it serves its purpose of protecting the data layer of the CD. But again, CDs and their readers were designed in a way that typical surface scratches and other imperfections would not inhibit reading. And so polycarbonate was an acceptable choice. The same approach applies to eye glass lenses; a scratch on a lens is typically not in focus and therefore has little to no effect on vision. So, TL;DR: Polycarbonate the material is not scratch resistant. CDs are scratch resistant, but that is due to their optical design and in spite of the polycarbonate.

Retric 9y ago
I don't directly disagree with what your saying, my point is there is more than one type of scratch resistance. Because not all scratches are created equal. If you look at say :https://omnexus.specialchem.com/polymer-properties/properties/hardness-shore-d https://omnexus.specialchem.com/polymer-properties/propertie... You find it's good relative to other plastics at preventing penetration which is also why it's good at preventing deep scratches. So, yes if you want a crystal clear optical element then it's not scratch resistant and look for something high on the Mos scale. But, if you want a coating that protects from deeper scratches it's quite good. In that context it's good material to protect CD's from scratches that matter. Which again is why I find the word resistance tricky because it's always resistant in some context.
- jdmichal 9y ago
  Ah, I understand your point now. Thanks for clarifying for me.

Retric 9y ago

I don't directly disagree with what your saying, my point is there is more than one type of scratch resistance. Because not all scratches are created equal. If you look at say :https://omnexus.specialchem.com/polymer-properties/properties/hardness-shore-d https://omnexus.specialchem.com/polymer-properties/propertie... You find it's good relative to other plastics at preventing penetration which is also why it's good at preventing deep scratches. So, yes if you want a crystal clear optical element then it's not scratch resistant and look for something high on the Mos scale. But, if you want a coating that protects from deeper scratches it's quite good. In that context it's good material to protect CD's from scratches that matter. Which again is why I find the word resistance tricky because it's always resistant in some context.

jdmichal 9y ago
Ah, I understand your point now. Thanks for clarifying for me.