refurbishing plastic (polycarbonate) and preventing scratches

[hydrive]

Hi I have been trying to find a good method to refurbish plastic (specifically the plastic housing on a cell phones). I have many plastic pieces to refurbish (several hundred). I am resorting to refurbishing them myself because every time I order them from a supplier the parts end up being aftermarket. I have a supplier that can deliver true OEM parts however they all have minor scratch marks on them. All plastics I am working with are for the same model phone, which is the Motorola V265.

Basically the plastic is black with silver paint on each side. The black plastic is not painted at all. Most of the plastics I have are only scuffed, I can not feel the marking with my fingernail if I run my nail over it. I have tried many methods and the one thing that seems to work is by sandblasting (with baking soda for the abrasive). That brings up a new problem however, the finish turns very dull in appearance, almost looks like its covered in a powder (even after washing it off). See photos below, the one on the left is the OEM battery cover with a minor scuff. The one on the right looked similar to the one on the left (just the scuff was in another location) then the cover was sandblasted with baking soda, removing all the scuff marks.

http://img.photobucket.com/albums/v229/mds33200/V265blasted.jpg

I found one cleaning product that works pretty good in giving the plastic its shine back, the product is called "countertop magic". However it dullens over time and also if you scratch the plastic against your fingernail even very lightly, it shows up as a scuff mark. Prior to the sandblasting if you scrape your fingernail over the plastic, a new scuff mark did not show. That means the sandblasting removed some protective coating that made the plastic more durable. Does anyone have an idea of some product or aspect I can use to give it more durability against a scratch?

 

[PratsA]

You're not actually removing a protective coating. The soda blasting is roughening the surface, which then looks dull because of the texture.

Countertop Magic is a paraffin-containing polish that deposits oil and wax into the texture, making it smooth and shiny again. When you scrape your fingernail across it you are not making a new scuff mark. You are removing the Countertop Magic and exposing the rough, soda-blasted surface.

The only reliable methods I know for polishing polycarbonate to a shine involve very careful wet-polishing through a series of grits, ending up with 3-micron or smaller abrasive. It usually takes 45 minutes to an hour per part.

 

[MikeHalloran]

Try a 3M brand headlight lens restoration kit.
No other brand works as quickly or as well, at least on headlights.
It includes a sanding pad for an electric drill, and discs in a coarse grit for cutting the surface down quickly and a superfine grit for restoring the gloss.
Both grit discs are some weird 3M stuff that cuts like crazy but doesn't load up with plastic.





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Mike

Head lights are silane coated to greatly improve scratch resistance and increase surface hardness. I would not expect the same result on untreated PC, however it is still probably the best method.

Regards
Pat
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[hydrive]

Thanks everyone for the info.

PratsA- thats what I initially was thinking, (that there was no protective finish on the plastic) but when thinking about why it leaves so many scratch marks after I clean the plastic, I figured it had to have a protective coating. But now it makes perfect sense that I am simply scraping off the cleaning product, not creating a new scratch.

This AM I did some more research and I also realized I was not drying the plastic long enough before I was testing them. I was cleaning it off with water and drying it on top of a heating pad for about 30 minutes. Today I learned that I should be drying it for 6 hours, with a temp of arround 100-120 F.

As far as the 3m buffing pads go (that are used to restore headlights)I actually did try that in my testing prior to my original post. I used many different cleaning products with the 3M pads, nothing appeared to work. Some products gave it a decent finish however I wasn’t happy with any of them because I thought they all scratched up very easily, but thinking about it now I bet I was just removing the cleaning product again, which gave it the appearance of a scratch.

I plan on retesting many of these again and then letting them dry (with the high temp for 6 hours). Maybe some of the products will absorb better after I use the proper drying method, which may reduce the residual material being scraped away when I scrape it with my fingernail which may (with any luck) give me a durable finish. I also purchased a few more materials to try, such as shoe polish (I was reading another forum where someone said they used shoe polish for black plastic and a few people claim it worked great).

PS- I purchased that 3M headlight kit about a half year ago and I realized the orange sponges are awsome in terms of cleaning other plastics (and a few other items). I tested it on so many things the first day and couldn’t help but to think it was impractical because by the end of the day the sponge took a pretty good beating and the kit sells for around $25, so I went shopping on ebay and purchased 50 orange sponge pads for less then $40. Now that was an awsome find!

Thanks again for the ideas and I will post an update tomorrow.

 

[Demon3]

You can buy polish to remove scratches from CDs in many stores including Best Buy and equivalents. CDs are made of polycarbonate. Just apply to a cloth and rub hard.

I have even seen a machine made to remove scratches from CDs. That's commercial too. DVD rental stores use them.

Chris DeArmitt PhD FRSC CChem

 

[MacGyverS2000]

I use toothpaste (I prefer mint ) to clean CDs. NetFlix is notorious for sending us nasty nasty nasty scratched DVDs that skip. My wife looked at me like I was nuts when I first did it. Pea-sized drop on the disk, rub it in small circles with my finger while slowly changing location, keep going until the stuff dries out too much to continue swirling. Wash with water and wipe dry. The disk will have an overall haze, most likely, but it will play without a hitch.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Demon3]

You have the right nick for that comment!

I saw a commercial for polish for hazy headlights and told my wife that I bet toothpaste would work great at a fraction of the cost. They I googled it and sure enought, it'd been tried and worked great!

Chris DeArmitt PhD FRSC CChem

 

[patprimmer]

I have to admit for yellowed headlights, I used 400 grit, then 1000 grit then 1500, then 2000 grit wet and dry rubbing paper then a fine car polish then a finishing wax. came up looking and performing like new, but as the UV stabilisers are obviously used up, it needs doing every year or so now.

If only someone sold a self healing PU coating heavily loaded with UV absorbers or visible light transparent blockers.

Regards
Pat
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[hydrive]

Well still no luck after lots more trial and error (mostly error). I think the main problem is the original finish is matte, and after using the sand blaster (with baking soda as the media) it leaves the finish to more of a shine.

So I tried another sample with no sandblasting, I only used the 3M pads and it gives it a very shiny finish as well.

Below is a photo,

http://img.photobucket.com/albums/v229/mds33200/DSC01500.jpg

the top of the plastic cover (right side) is the OEM finish, the bottom of the cover (left side) is the polished finish with the 3M pad. The 3M pad makes it so shiny that you can see the reflection of the light in the photo. The OEM finish is so matte that it looks like the light reflection stops right above the OEM area.

So I think I have to roughen it up again after I sand blast it down. I wish I could just treat the scratch instead of the entire plastic cover but the scratch still shows unless I sandblast it and the only way to sandblast it is to process the entire piece so it looks uniform.

Any ideas how to get more of a matte finish?