AutowerxDetailing
03-30-2013, 12:16 PM
In various discussions regarding the quality of certain microfiber towels or the softness of a particular type of wash media there seems to be a prevailing idea that one can test their application by use of the surface of a compact disc (CD). The following information is an attempt to understand how a CD’s surface compares to the various types of paint found in typical automotive applications. More importantly the information provided will seek to answer a fundamental question: is the CD test a reliable way of testing the softness of fabric materials for automotive use?
Although there does not appear to be a scientifically acceptable method to performing a CD scratch test for determining a fabric’s softness; the following is a method that can be replicated with a variety of fabrics.
Source a new, unscratched CD and a fabric or wash tool to test. In my test I used a generic CD-R and a CarPro Merino Wool wash mitt.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_22_23.jpg
I performed the test by rubbing the clean, dry wash mitt over the surface of the CD 20 times in a straight line (10 times up and 10 times down). Only slight pressure was used in an attempt to replicate the forces during a normal car wash.
This “dry test” produced a visible scratch pattern that was obviously imparted by the fibers of the wool.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_17_37.jpg
Next I sprayed ONR, diluted to clay lubricant, onto the surface of a new CD and onto the surface of the CarPro mitt.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_19_34.jpg
I performed the test using the same method as before by rubbing the mitt over the CD up and down for 20 strokes. I then washed the CD in water and dried with compressed air to make sure no other fabrics came in contact with the surface. The result was a completely defect free surface.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_22_33.jpg
In my opinion, performing the test “wet” or with some sort of lubricant is a much more reliable way to determine if a particular fabric or wash media is suitable for automotive application.
So, the CarPro mitt passes the CD test with proper lubrication. Nevertheless I was left with the question: why did the dry mitt scratch the surface??? I have never experienced marring on any vehicle I have used the CarPro mitt on… so why did this happen? Which led me to the next question: what are CD’s made out of anyway?
Commercially made CD’s are created in a process by injection molding polycarbonate plastic into a press against a “glass master” disc that has been molded into a positive template of the final CD. A glass master can reliably generate hundreds of thousands of copies before needing to be replaced. Finally a reflective metallic layer is applied and coated with an acrylic varnish for extra protection from corrosion. The most obvious question is how durable is the polycarbonate layer? Why does it seem to be so scratch sensitive?
When comparing the hardness or softness of a surface one can use a pencil test as a way to depict an accurate representation of the general durability of a particular coating. The pencil test involves a testing kit of several pencils with varying degrees of hardness.
A typical pencil hardness testing kit:
http://www.autogeekonline.net/gallery/data/500/Pencils.jpg
To begin a surface hardness test one simply swipes the surface with the softest pencil and checks to see if there is an impression (scratch) in the material. If no scratch is evident, the test is repeated with a harder degree of pencil. The test is complete when the surface is scratched. The hardness of the material can then be rated at the degree of hardness below that which it is scratched.
http://www.autogeekonline.net/gallery/data/500/medium/Mohs_Scale.PNG
Here are some general hardness ratings of various coatings as compared to polycarbonate found in CD’s. I’m not sure exactly what grade of polycarbonate is used in commercial CD production. I'll bet it probably varies depending on the manufacture and the specifications required for that particular disc…
Uncoated Polycarbonate, Sheet Plastic 6B
PC-300™ Polycarbonate, Static Dissipative Plastic B
PC-350™ Polycarbonate, Static Dissipative Plastic 2B
Mar-Con® Polycarbonate, Mar Resistant Plastic H
Mar-Con® Polycarbonate, Mar Resistant Plastic HB
Catalyzed polyester 9H
Catalyzed polyurethane 9H
Catalyzed modified acrylic polyurethane 4H
Catalyzed acrylic polyurethane 2H
Water-based polyurethane 3H
Water-based urethane/isocyanate catalyst 2H
Urethane/nitrocellulose lacquer (after 24 hours) F
Water reducible lacquer 2H
Water-based polyurethane wipe-on finish HB-F
Clear shellac aerosol 3B
Polyurethane/nitrocellulose aerosol HB
Nitrocellulose aerosol 3B
As you can see polycarbonate, of any variety, is an incredibly soft material. Even the “mar resistant” grade is extremely soft. It is much softer than the material found in most types of liquid or aerosol paint coatings. This leads me to believe that using a CD to test the abrasiveness of a particular fabric or wash tool is not reliable and not representative of how the material will perform on an automotive paint finish. The CD test is finally debunked!
Thanks for reading! Questions, comments, feedback appreciated.
References:
ASTM D-3363 Pencil Hardness Scale, SiCron Technologies
http://www.newcyberian.com/cd-manufacturing.pdf
The Pencil Hardness Test (http://www.pencilpages.com/articles/simmons.htm)
Although there does not appear to be a scientifically acceptable method to performing a CD scratch test for determining a fabric’s softness; the following is a method that can be replicated with a variety of fabrics.
Source a new, unscratched CD and a fabric or wash tool to test. In my test I used a generic CD-R and a CarPro Merino Wool wash mitt.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_22_23.jpg
I performed the test by rubbing the clean, dry wash mitt over the surface of the CD 20 times in a straight line (10 times up and 10 times down). Only slight pressure was used in an attempt to replicate the forces during a normal car wash.
This “dry test” produced a visible scratch pattern that was obviously imparted by the fibers of the wool.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_17_37.jpg
Next I sprayed ONR, diluted to clay lubricant, onto the surface of a new CD and onto the surface of the CarPro mitt.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_19_34.jpg
I performed the test using the same method as before by rubbing the mitt over the CD up and down for 20 strokes. I then washed the CD in water and dried with compressed air to make sure no other fabrics came in contact with the surface. The result was a completely defect free surface.
http://www.autogeekonline.net/gallery/data/500/medium/2013-03-29_20_22_33.jpg
In my opinion, performing the test “wet” or with some sort of lubricant is a much more reliable way to determine if a particular fabric or wash media is suitable for automotive application.
So, the CarPro mitt passes the CD test with proper lubrication. Nevertheless I was left with the question: why did the dry mitt scratch the surface??? I have never experienced marring on any vehicle I have used the CarPro mitt on… so why did this happen? Which led me to the next question: what are CD’s made out of anyway?
Commercially made CD’s are created in a process by injection molding polycarbonate plastic into a press against a “glass master” disc that has been molded into a positive template of the final CD. A glass master can reliably generate hundreds of thousands of copies before needing to be replaced. Finally a reflective metallic layer is applied and coated with an acrylic varnish for extra protection from corrosion. The most obvious question is how durable is the polycarbonate layer? Why does it seem to be so scratch sensitive?
When comparing the hardness or softness of a surface one can use a pencil test as a way to depict an accurate representation of the general durability of a particular coating. The pencil test involves a testing kit of several pencils with varying degrees of hardness.
A typical pencil hardness testing kit:
http://www.autogeekonline.net/gallery/data/500/Pencils.jpg
To begin a surface hardness test one simply swipes the surface with the softest pencil and checks to see if there is an impression (scratch) in the material. If no scratch is evident, the test is repeated with a harder degree of pencil. The test is complete when the surface is scratched. The hardness of the material can then be rated at the degree of hardness below that which it is scratched.
http://www.autogeekonline.net/gallery/data/500/medium/Mohs_Scale.PNG
Here are some general hardness ratings of various coatings as compared to polycarbonate found in CD’s. I’m not sure exactly what grade of polycarbonate is used in commercial CD production. I'll bet it probably varies depending on the manufacture and the specifications required for that particular disc…
Uncoated Polycarbonate, Sheet Plastic 6B
PC-300™ Polycarbonate, Static Dissipative Plastic B
PC-350™ Polycarbonate, Static Dissipative Plastic 2B
Mar-Con® Polycarbonate, Mar Resistant Plastic H
Mar-Con® Polycarbonate, Mar Resistant Plastic HB
Catalyzed polyester 9H
Catalyzed polyurethane 9H
Catalyzed modified acrylic polyurethane 4H
Catalyzed acrylic polyurethane 2H
Water-based polyurethane 3H
Water-based urethane/isocyanate catalyst 2H
Urethane/nitrocellulose lacquer (after 24 hours) F
Water reducible lacquer 2H
Water-based polyurethane wipe-on finish HB-F
Clear shellac aerosol 3B
Polyurethane/nitrocellulose aerosol HB
Nitrocellulose aerosol 3B
As you can see polycarbonate, of any variety, is an incredibly soft material. Even the “mar resistant” grade is extremely soft. It is much softer than the material found in most types of liquid or aerosol paint coatings. This leads me to believe that using a CD to test the abrasiveness of a particular fabric or wash tool is not reliable and not representative of how the material will perform on an automotive paint finish. The CD test is finally debunked!
Thanks for reading! Questions, comments, feedback appreciated.
References:
ASTM D-3363 Pencil Hardness Scale, SiCron Technologies
http://www.newcyberian.com/cd-manufacturing.pdf
The Pencil Hardness Test (http://www.pencilpages.com/articles/simmons.htm)