By Heather Wilson, Technical Writer, and Shawn Small, Owner and Engineer, Ruckus Composites
In this installment of Bike Science Friday, we are going to be paying our first visit to the Ruckus Composites playground of abandoned frames. Here we will witness a smack-down between a highly-engineered tape and the paint on some of the most expensive carbon fiber bikes on the market. The outcome of this fracas will determine who will be crowned King of the Adhesion Mountain.
Why would we sanction such a cruel spectator sport?
We have been wanting to conduct this test for quite some time. In the upwards of 7000 frames that have come through our facility, we have seen just about every paint problem and have even created a few of our own. Every now and then, when we are masking a bike for paint or repair prep, our 3M tapes pull off the original equipment manufacturer paint or clearcoat.
Queue the sad trombone. Wah wah wahhhhhhh . . .
We always fix the issue, but “an ounce of prevention is worth a late night doing paint touch-up,” or however that quote goes.
As we saw in our last installment of Bike Science Friday, surface preparation of carbon fiber composite materials affects surface free energy, and surface free energy is known to affect adherence of coatings such as paint and cleaercoat. We were curious to know how well the paint adhered to carbon fiber frames from a variety of manufacturers, so we employed the cutting-edge technique of scoring the paint with a pen knife and attempting to rip it off with tape.
While this methodology may seem questionable, it conforms to international standards. Honest.
ASTM (American Society for Testing Materials) International has developed over 12,000 standards related to manufacturing processes such as testing, operation, and materials classification. In the coatings industry, adhesion to a surface is rated using ASTM D3359 – 17: Standard Test Methods for Rating Adhesion by Tape Test. In a nutshell, this test involves scoring a grid in the coating, adhering a specific pressure sensitive tape (that conforms to a standard force required for removal) to the grid area, and removal of the tape. The result of the test is classified based on the position and amount of paint removed from the grid (see p.5 of ASTM D3359 – 17 for classification criteria). Standard D3359 was developed to assess adhesion to metallic substrates, but as there is no existing standard for assessing adhesion to carbon fiber composite substrates, we adapted it for our needs.
Bicycles Tested
We chose seven frames to test, representative of a wide range of road, mountain bike, and cyclocross frames with both old and new paint:
- Trek Émonda SL5
- Santa Cruz Stigmata
- S-Works Stumpjumper
- S-Works Roubaix SL4
- Colnago C40
- Bianchi Superleggara
- Pinarello Dogma 60
Testing Procedure
The surface of the frame was wiped with acetone and allowed to dry. A custom adhesive template was applied and a grid with lines spaced 3 mm apart was scored using a pen knife and a straight edge. The grid and surrounding area was lightly sanded using 2,000 grit to remove any lifted edges of clear coat along the score lines. The surface was then wiped with isopropyl alcohol to remove any contaminants and allowed to dry. Before the first frame was tested, two complete rounds were removed from a roll of Elcometer 99 Cross Hatch Adhesion Testing Tape (which meets the standard required by ASTM D3359 – 17) and discarded.
A 3 inch piece of tape was cut and placed over the grid and smoothed on, taking care not to trap air bubbles. The tape was allowed to sit for 90 seconds. The tape was then removed by pulling it quickly back over itself at an angle of 180°. The grid was inspected for removal of clear coat or underlying paint.
Results
We were somewhat disappointed to discover that the tape was no match for the adhesive qualities of the paint in every case — when you’re doing destructive testing of materials not of your own making, at least a little carnage is desirable for entertainment value. Congratulations are due to the manufacturers of these bicycles for utilizing highly effective surface preparation and painting processes.
tape
So naturally we wanted to up the ante, which led to the decision to go ape on the paint by breaking out the Gorilla TapeⓇ. Elcometer 99 tape has a reported adhesive strength of 6.68 N/10mm (0.67 N/mm) whereas Gorilla TapeⓇ has a reported adhesive strength of 31 N/25mm (1.24 N/mm). Using Gorilla TapeⓇ, the results were still less than dramatic, but at least some clear coat/paint was removed from the grid on the Pinarello and Colnago. And the crowd went wild.
It can be slightly disheartening to get a different outcome than expected; but that’s all part of the iterative testing we conduct on our journey of continuous improvement.
The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka! I’ve found it,” but, “That’s funny . . . ”
— Isaac Asimov
Is Elcometer 99 too wimpy to take on the big kids?
In the past, we have witnessed our 3M painter’s tape rip clear coat off a frame when it was covering unpainted carbon fiber composite, so we wanted to validate whether the Elcometer 99 tape is a good choice for testing paint adhesion on carbon fiber composite.
We coated samples of carbon fiber composite that had not undergone any surface preparation treatment with either clear coat or primer and subjected them to the testing described above for the bicycle frames. We chose not to subject the samples to surface preparation because we intentionally wanted to set up a situation where the samples would have relatively low free surface energy leading to relatively poor adhesion of the coatings.
Success! Testing with the Elcometer 99 tape removed a very satisfying patch of clear coat from both the grid and the surrounding area. The primer coating triumphed over the tape and there was almost no primer removed.
What’s Next?
Our next step will be to revisit surface preparation techniques, measurement of water droplet contact angles for assessment of surface free energy, and then follow up with ASTM D3559 – 17 tape testing to determine which preparation techniques produce the best paint adhesion results.
Until then, have faith that your bike frame was well prepared and painted, and is protected in case you encounter a rogue roll of tape in a dark alleyway. If you crash into something else, well, we can fix that for you.