Why are there Circles on Blu-ray Discs?!

[Vilya]

Originally Posted by Leeon0

Strange that you should say that because to me Viva Elite and "high quality" can no longer appear in the same sentence. The "Elites" are virtually eco thin, they have plenty of residue, and the center hubs are a disaster.

What's more, the appearance of residue can't be correlated with poor quality control. Slip agents are added to the plastic (I assume in the molten state) during the manufacturing process to prevent the plastic sheets from binding. Since the additive is integrated into plastic, the residue appears to perpetually ooze out even after it's cleaned off. The good news is the more you clean it over time the less of it you see reappearing. Denatured alcohol has worked well for me.

I mentioned Viva Elite because they were recommended to me and I have not experienced the issues that you apparently have. Other brands of cases are certainly available.

Blu-ray disc cases are made with a plastic called Polypropylene (PP), specifically polypropylene homopolymer. DVD cases are made with Polystyrene (PS) also known as Plastic #6.

https://omnexus.specialchem.com/sele...ene-pp-plastic

Most plastics "outgas" and at different rates under different conditions.

"Most plastics contain volatile organic compounds (VOCs). These are poisonous, carbon-containing chemicals that are volatile enough to evaporate even at room temperature."

"For example, a shower curtain made with PVC can outgas for a month or longer and high temperature and humidity tend to speed up the process."

New shower curtains often reek!

https://www.directplastics.co.uk/abo...hould-you-care

Improper venting during the injection molding of plastics can exacerbate outgassing.

"Proper venting is essential to molding a defect-free part. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. Trapped gas is one of the most common causes of part burns, and it can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part.

Moreover, trapped gas can cause residue buildup in vented pins, which then necessitates frequent production interruptions to clean the tool. It can even cause corrosion of the tool steel, thereby increasing tool-maintenance costs."

https://www.ptonline.com/articles/ho...ection-molding

"When a Blu-ray case has been wiped clean inside, snapped shut, and tucked away inside a cabinet, none of those contaminants are present. Yet after several months or so, the residue will reappear inside the case. That's evidence of outgassing."

https://forum.blu-ray.com/showpost.p...2&postcount=22

Slip and other agents added to the process can certainly cause problems, too, if not done correctly. All of these are quality control concerns.

I once worked in a factory that did injection molding and those machines were quite persnickety. Defective parts were common if these machines were not meticulously maintained. I worked in a neighboring department where adhesives were mixed; I made different kinds of glue all day. Nasty job that I was happy to leave after just two years.