Pursuing higher performance with advanced surface treatment technology. The company’s core sealing products, including oil seals and O-rings, are expected to deliver both airtight performance that prevents leaks and low friction that improves energy efficiency in machinery. These two qualities are often in tension, but NOK continues to refine both through ongoing R&D focused on surface functionality, materials, and component design, centered at its Shonan R&D Center in Fujisawa, Kanagawa. In recent years, this work has expanded to include polymer brushes, a surface treatment technology gaining attention worldwide. Rather than focus solely on short-term gains, NOK is pursuing mid to long-term research to improve the performance of its sealing products.

Polymer brushes: Unlocking new possibilities

Polymer brushes work at the molecular scale. The basic building blocks of rubber and plastic are monomers, and they can be linked together into long chains called polymers. A polymer brush forms when these chains are densely grafted onto the surface of materials like rubber or metal, creating a brush-like structure just tens to hundreds of nanometers thick (a nanometer is one-billionth of a meter). This ultra-thin layer can dramatically change how surfaces behave.

What kind of surface properties can polymer brushes provide? According to Takeya Aoki of NOK's Materials Research Section, Technology Research Department, polymer brushes can alter how easily fine particles mix, how readily other molecules adhere, and the level of friction. Leveraging these effects, it's possible to create materials that, for example, are resistant to dirt buildup.

Although research into polymer brushes has a long history, one technical challenge has been improving the material's durability. That required growing the polymer chains more densely, evenly, and to greater lengths. This was achieved by a research group led by Professor Yoshinobu Tsujii at the Institute for Chemical Research, Kyoto University. Their breakthrough came through a method known as living radical polymerization under high pressure, which enabled the creation of concentrated polymer brushes (CPB) with extremely high density and a film thickness on the order of several micrometers (a micrometer is one-millionth of a meter). This advancement rapidly accelerated efforts toward practical application. In the latest findings, the group demonstrated that surfaces treated with CPB are resistant to snow, ice, and frost buildup and identified the mechanism behind it.

Since 2016, NOK has been involved in an industry-academia research and development project led by Professor Tsujii. Today, the company continues that work through a consortium focused on the practical use of polymer brush materials.

Toward low-friction applications

NOK aims to use polymer brushes as a coating material to further reduce friction on the surface of its sealing products. "Polymer brushes are highly compatible with sealing products," explains Aoki. These products must minimize friction while maintaining strong sealing performance. Concentrated polymer brushes, in particular, appear well suited to achieving both goals, which previous surface treatment technologies for seals had been unable to do.

However, achieving low friction alone isn't enough. "Unless we can clearly explain why a seal exhibits low friction, we can't apply it to actual products," says Aoki. That's why NOK is drawing on its strengths in visualization technology, materials expertise, and tribology know-how to advance foundational research into polymer brushes as low-friction sealing materials.

At the Shonan R&D Center, there’s a demonstration device designed to simulate a rotary-motion seal, allowing visitors to experience the low-friction effect of polymer brushes firsthand. It compares a sample with a polymer brush coating to one without. When turned by hand, the coated sample rotates smoothly with minimal effort, while the uncoated one resists movement unless force is applied. The benefit of polymer brushes for reducing surface friction in seals is clear, but the precise conditions and mechanisms behind that effect are still not fully understood.

Polymer brushes have a property known as swelling. Think of how a toothbrush retains water when you rinse it. In a similar way, the brush-like structure of a polymer brush can hold liquid within its bristles. This is believed to allow for the formation of a thicker lubricating film between two contacting surfaces, thereby reducing friction.

Concentrated polymer brushes, NOK's primary focus, are particularly effective at forming thick films and have high swelling capacity. Since conventional sealing products have not used coatings or surface treatments with such high swelling properties, it's all the more important to clarify exactly how the brush structure contributes to sealing performance.

Future research could also uncover properties beyond friction reduction, and expectations for this line of study remain high.

A deeper understanding of the sealing mechanism of concentrated polymer brushes

NOK has a long history of researching materials, including rubber, metal, and lubricants. By visualizing surface and internal structures at various scales, nanometers, micrometers, and millimeters, the company has built a body of knowledge on material behavior and used that to explain the mechanisms behind real-world product phenomena.

Now, NOK is applying those visualization technologies to polymer brushes as well. One such method, currently being explored in collaboration with Kyoto University, uses Förster resonance energy transfer (FRET) to evaluate polymer brush performance. A fluorescent agent is attached to the material that comes into contact with the tip of the polymer brush, and the change in fluorescence intensity as the distance between them decreases is used to observe the brush and contact surface during sliding. “In past sealing research, we used fluorescence to evaluate oil film conditions at the microscale,” says Aoki, who believes this is an area where NOK's strengths can shine. For polymer brushes, the company is now working to develop measurement techniques at the nanoscale and use them to evaluate sealing performance.

Mid to long-term research with an eye on future value

 NOK’s commitment to polymer brush research reflects a corporate belief that a deep understanding of mechanisms will be key to differentiating the company from its competitors. Maintaining a leading market share in the highly competitive sealing industry requires constantly embracing new technologies and a challenger spirit.

Research into polymer brushes for sealing applications still has a long way to go, not only in unraveling the mechanisms but also in developing methods for applying polymer brushes to materials such as rubber and plastic and creating low-cost, mass-production systems. It’s not something NOK can accomplish alone. That’s why NOK believes it’s essential to raise awareness of polymer brushes. By increasing participation in Professor Tsujii’s consortium and accelerating joint research and development, NOK hopes to generate new ideas and insights through collaboration. This, in turn, could lead to broader application of polymer brushes across different materials and enable the discovery of entirely new functional properties.

Takeya Aoki

Materials Research Section, Technology Research Department, NOK Group R&D, NOK Corporation

Since joining NOK in 2019, Aoki has been engaged in friction research on rubber materials. In 2020, he began working on the development of low-friction materials.

All data, titles, and affiliations in this article are as of June 2025.

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