Carbon Fiber That Stands Up to the Sun: Long-Lasting Weatherability for CFRP, from Clear Coats to Color Coats

Everlight Chemical Eversorb® CP Series Light Stabilizers for CFRP Coatings — Reducing yellowing and fading, preserving coating adhesion, and extending the appearance lifetime of composites

Carbon fiber reinforced polymer (CFRP) weighs only 30% as much as steel yet can be more than five times harder, and is widely used in automotive, bicycle, wind power and aerospace applications. With JEC holding its first forum in Taipei this year, Taiwan’s role in the global composites supply chain is drawing even more attention.

However, carbon fiber products are mostly used outdoors. Once the clear coat or color coat on the surface yellows, cracks or even peels under UV light, the value of high-end exterior parts is quickly lost.

In accelerated xenon-arc weathering tests (ASTM G155-1), uncoated carbon fiber panels turned severely white after just 150 hours, with a color difference ΔE as high as 15.54. Even with a clear coat, cross-cut adhesion dropped to 1B after 150 hours, with extensive coating delamination. A coating alone cannot protect the appearance of carbon fiber over the long term — the light stabilizer in the coating is the key.

Carbon Fiber Panels After 150 Hours of Weathering

Initial	Uncoated 150 hr	Coated 150 hr	Coated 150 hr Cross-Cut Test
	ΔE 15.54	ΔE 4.29	Cross-cut 1B

※ Test conditions: ASTM G155-1 (Xenon), 150 hours of weathering.

For protective coatings on carbon fiber composites, Everlight Chemical has developed the multifunctional blended light stabilizer Eversorb® CP Series. The liquid formulation is easy to handle, with three grades for different coating types and weatherability requirements:

※ Recommended dosage: 0.5–3% (based on resin solids); especially recommended for acrylic and polyurethane resin systems.

※ Timeline compiled from tests on carbon fiber panels and several clear coat systems; see ①②③ below for test conditions.

① Clear Coat Color Difference: 2,100 Hours

Test conditions | Acrylic polyol clear coat; wet film 70 μm / dry film 30 μm; dosage 2% (based on resin solids); dried at room temperature for 24 hours; ASTM G155-1 (Xenon)

11.1	7	4.5	3.2
Blank	Conventional benzotriazole UVA	Eversorb® CP1	Eversorb® CP2

※ Color difference ΔE after 2,100 hours of weathering; lower is better.

Key Finding

Eversorb® CP1 and Eversorb® CP2 showed less than half the color difference of the blank, clearly outperforming a conventional benzotriazole UV absorber.

Panel Appearance (2,100 hr)

Initial	Blank	Conventional benzotriazole UVA	Eversorb® CP1	Eversorb® CP2
	ΔE 11.1	ΔE 7.0	ΔE 4.5	ΔE 3.2

② Clear Coat Adhesion: 2,500-Hour Cross-Cut Test

Test conditions | Acrylic polyol clear coat; wet film 70 μm / dry film 30 μm; dosage 2% (based on resin solids); dried at room temperature for 24 hours; ASTM G155-1 (Xenon); cross-cut per ASTM D3359

Weathering time (hr)	0	500	1,700	2,100	2,500
Blank	5B	0B	—	—	—
Conventional benzotriazole UVA	5B	5B	0B	—	—
Eversorb® CP1	5B	5B	5B	3B	1B
Eversorb® CP2	5B	5B	5B	4B	4B

※ 5B is best and 0B is worst; “—” indicates the coating had already failed.

Key Finding

Panels with Eversorb® CP2 still maintained 4B after 2,500 hours, with coating delamination significantly suppressed.

Cross-Cut Test Appearance

Blank 500 hr	Conventional benzotriazole UVA 1,700 hr	Eversorb® CP1 2,500 hr	Eversorb® CP2 2,500 hr
0B	0B	1B	4B

Colored carbon fiber finished with transparent color coats is increasingly popular, but the dye molecules in color coats are more easily destroyed by UV light, so they fade and delaminate faster than black carbon weave. Eversorb® CP3 is formulated specifically for transparent color coats on carbon fiber.

④ Color Coat Color Difference: 1,800 Hours

Test conditions | Red transparent color coat, acrylic-PU resin; wet film 180 μm / dry film 90 μm; dosage 1% and 3% (based on resin solids); cured at 80°C for 20 minutes; ASTM G155-1 (Xenon)

12.49	9.35	4.67
Blank	1% Eversorb® CP3	3% Eversorb® CP3

※ Color difference ΔE after 1,800 hours of weathering; lower is better.

Key Finding

The blank faded noticeably by 600 hours, reaching a color difference of 12.5 at 1,800 hours. With 3% Eversorb® CP3, the color difference was only 1.6 at 1,000 hours, and the red appearance was retained at 1,800 hours (ΔE 4.7).

Panel Appearance (Red Transparent Color Coat)

	Initial	600 hr	1,000 hr	1,800 hr
Blank		ΔE 9.1	ΔE 11.0	ΔE 12.5
3% Eversorb® CP3		ΔE 1.2	ΔE 1.6	ΔE 4.7

⑤ Color Coat Adhesion: 1,800-Hour Cross-Cut Test

Test conditions | Red transparent color coat, acrylic-PU resin; wet film 180 μm / dry film 90 μm; dosage 1% and 3% (based on resin solids); cured at 80°C for 20 minutes; ASTM G155-1 (Xenon); cross-cut per ASTM D3359

Weathering time (hr)	0	600	1,000	1,500	1,800
Blank	5B	3B	0B	0B	0B
1% Eversorb® CP3	5B	5B	5B	4B	4B
3% Eversorb® CP3	5B	5B	5B	5B	5B

※ 5B is best and 0B is worst.

Key Finding

The blank dropped to 3B at 600 hours and to 0B at 1,000 hours, with the coating delaminating. With 3% Eversorb® CP3, adhesion remained at the top 5B grade after 1,800 hours.

Cross-Cut Test Appearance (Red Transparent Color Coat)

	Initial	600 hr	1,000 hr	1,800 hr
Blank		3B	0B	0B
3% Eversorb® CP3		5B	5B	5B

⚙ Automotive Carbon Fiber Exterior Parts Hoods, spoilers and aero kits must keep a premium appearance over the long term. An automotive carbon fiber spoiler clear coat has already adopted Eversorb® CP2.		✚ High-End Bicycles / Sporting Goods Carbon fiber bike frames, rackets and golf clubs demand light weight and a premium look, with coatings that keep their color stable over time.
☀ Wind Power & Large Outdoor Composites Wind turbine blades and energy equipment housings need coatings that stay intact under years of sunlight, extending maintenance intervals.		✈ Aerospace & Drones Composite housings and airframe parts are exposed outdoors for long periods. Eversorb® CP Series can be part of the coating weatherability design, while final performance must still be validated against product specifications and certification requirements.

Everlight Chemical Eversorb® CP Series offers a complete line for both clear coats and color coats, providing carbon fiber composites with weatherability solutions that balance performance and value — helping lightweight materials last longer, in line with the long-life principle of sustainable design.

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