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Optical Media and Temperature

December 12, 2011

It is common knowledge that heat is bad for discs, but most people do not understand the foundations behind this or exactly how much heat is bad. I”m going to get into a little more detail than you might find absolutely necessary on this topic, but it should be interesting.

Obviously there is a point at which the polycarbonate substrate of a disc begins to melt. The lower boundary of this temperature is called the glass point and it is where the material softens, quite a bit before it turns to a liquid. For polycarbonate the glass point is 150C. Clearly, you do not want to approach this temperature as the disc will distort.

Understand is that write-once discs use organic dye to hold the data written to them. This dye starts out fairly transparent and when exposed to heat from a laser in the act of writing to the disc the dye becomes less transparent where the laser heats the dye up. How hot does the laser make the dye? Good question, and I do not have this information, but I believe it is in the range of 100-150C. Keep in mind that this temperature is reached in the dye for only a very brief time.

Overall however, the dye is sensitive to heat above 120F or 48.8C. This seems to apply pretty universally to all manufacturers – the discs are rated for storage up to, but not exceeding 120F. Above 120F, even for fairly short periods of time, can result in overall darkening of the dye, reducing the contrast ratio and decreasing readability of the disc.

What this means is that storing discs above 120F even for short periods of time is bad for readability. Leaving a disc in a hot car in the summer where the temperatures can exceed 140F or 60C will certainly have an effect and turn the disc from perfectly readable into something more marginally readable.

Rewritable discs are less susceptable to high temperatures, but the alloy used is going to be affected by temperatures above 140F.

The organic dyes today are far less susceptable to UV than in the 1990s but it is still not a good idea to leave them out in the sun where they may get hot.

If you find yourself with a disc that is not readable because of exposure to heat, it may be possible to read the disc with a better-than-average drive. Contact InfinaDyne for assistance and we can likely point you in the right direction.

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