"A new material that changed watches": A new generation of carbon that overcomes deterioration over time, and various methods

In recent years, "new materials" have become widespread in the watch market. The use of unconventional materials for the exterior and movement of watches has brought about major changes not only in terms of design, such as shape and color, but also in performance. Issue 112 of Chronos Japan featured such "new materials" as "New Materials That Have Changed Watches," and we've republished this article on webChronos. This time, we'll introduce brands that have tackled the issue of carbon fiber, which is used for watch cases but has a problem with deterioration over time, and the methods they used to overcome this challenge.

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Issues with carbon cases

　Carbon composites, originally derived from the aerospace and motorsports industries, are now used in bicycle frames and sports equipment. It wasn't until the late 1990s and early 2000s that they made their way into the luxury watch industry. Initially, carbon cases suffered from the problem of deterioration due to the material itself. However, this problem has now been overcome and carbon composites are gaining popularity as a counter-material that adds character to watch cases.

Countertop material that overcomes the problem of deterioration over time

　Carbon-based composite materials began to be used in the aerospace industry around the 1970s. Their raw material, carbon fiber, is made by carbonizing acrylic fiber or pitch at high temperatures, but it is rarely used on its own; it is used as a composite material combined with a base material such as synthetic resin. Carbon fiber is very light, with a specific gravity of 2.25g/cm3, and has excellent tensile strength in the fiber direction, so it is well known as a structural material for aircraft and F1 cars.

　The method of extracting carbon fiber, the main raw material, was invented in 1959 by the American company National Carbon, which invented a technology to graphitize rayon, but this method is now obsolete, and the mainstream is now the aforementioned acrylic fiber-based (PAN-based carbon fiber) or pitch-based (pitch-based carbon fiber). Both of these technologies were invented in Japan, and Japanese companies, led by Toray and Teijin, boast the largest market share.

　The most common method for making carbon fiber composite materials is "laminated carbon," in which prepregs (woven sheets of carbon fiber impregnated with resin) are layered and baked together. When people simply say CFRP (Carbon Fiber Reinforced Plastics), they are usually referring to this laminated carbon. It was introduced to the Swiss watch industry in the late 1990s and early 2000s, and has enjoyed steady popularity due to its unique surface patterns and light weight. However, it is also true that the very first carbon cases showed noticeable signs of aging, such as surface fraying and yellowing. If you immediately understand the reason for this, you may be quite a car enthusiast.

　This is a bit of a digression, but when considering the deterioration of carbon parts, the most familiar example would be a car hood. Many aftermarket parts for cars and motorcycles are made with dry carbon fiber exteriors to reduce weight, but if these are installed as bare carbon fiber, they will fall apart within a few years. This is because ultraviolet rays cause the base resin to deteriorate rapidly. The deterioration of carbon fiber parts equals the deterioration of resin, and this is no different for watch cases. Richard Mille was one of the first to notice this and begin working to improve the quality of carbon fiber materials.

　From the very beginning of development, it was decided that Richard Mille's first model, the RM 001 Tourbillon, would feature a carbon baseplate. However, as is well known, this carbon baseplate was not ready in time for the first launch, and it would later reappear as the V2. Why was the production of the carbon baseplate delayed? Giulio Papi of APRP (now Audemars Piguet Le Locle), who co-developed the watch, explained the following in a 2015 interview with this magazine:

"We decided early on that the movement would have the look of a 'black F1 engine,' but the problem was whether carbon fiber suitable for luxury watches existed. Normal carbon contains about 20% resin, but if the resin content is too high, there are concerns that it will deteriorate due to UV rays, and we also had to check its compatibility with the cleaning solution used during overhauls. While it is possible to make a base plate using carbon fiber with a 20% resin content, it is not a method used in luxury watches. We spent about five years searching for the right material, and eventually came across carbon fiber with a 2% resin content, which was being produced in the United States at the time."

　Richard Mille subsequently collaborated with Swiss company North Thin Ply Technology (NTPT) to radically improve the quality of laminated carbon fiber. This began with "NTPT® Carbon" (now Carbon TPT®), which dramatically increased theoretical strength by stacking unidirectional carbon fiber tapes, known as UD tapes, offset by 45 degrees. At the same time, the brand developed a technology for laminating UD tapes made of other materials, such as quartz fiber, successfully diversifying the appearance of carbon composites. The resin used as the "bond" presented a challenge, but NTPT at the time developed a new "white resin" that was resistant to UV rays, solving the problem of aging. Richard Mille is also experimenting with incorporating advanced materials such as carbon nanotubes and graphene to further refine the carbon fiber itself.

　Another carbon-based composite material commonly used in the watch industry is "forged carbon." This method is characterized by the use of molds to manufacture the case ébauche. Finely chopped carbon fibers are infused with resin, then randomly arranged in a mold and fired under high pressure. The random orientation of the carbon fibers results in high strength, and by mixing in various materials, it is possible to add texture to the case and bezel. Examples abound, including the luminous material Super-LumiNova used by Zenith and Corum, the microfiber nonwoven fabric used by Hublot to increase case strength, and Corum's 18K gold powder. Furthermore, both laminated carbon and forged carbon are extremely hard materials, requiring advanced cutting techniques for their processing.

　Finally, while I haven't seen the actual watch, Oris's ProPilot Altimeter is an intriguing new trend. The PEKK resin, a type of high-molecular polymer, is layered using 3D printing technology developed by the Swiss 9T Laboratory to create a texture resembling the so-called "carbon fiber eye." Even the movement holder is molded as a single piece, suggesting high precision in the 3D printer. I'm curious about how the carbon fiber is used; it's likely that powdered carbon is mixed into the PEKK material. The advantage of using carbon as a structural material is its high tensile strength relative to its specific gravity, but this would only be possible if the carbon were in fibrous form. However, such strength isn't necessary for a watch case; a hard, lightweight surface is sufficient. This suggests that carbon-based composite materials and 3D printers are an excellent match, particularly in the watch industry.