[Business solutions] Development of a semiconductive sheet

  • Challenge for whole new development

  • Pursuing perfection

  • Design with consideration given to usage

We are also trying to make strides in a new field in addition to electric insulation materials.
~ Development of a semiconductive sheet ~


The composition elements of electric equipment include a conductor that can conduct electricity, an insulation that cannot conduct electricity, and a semiconductor that has electrical resistance intermediate between former two elements. Electric equipment may obtain the best performance by using these elements within a certain balance.
Okabe Mica had long-standing proven results as a manufacturer of electric insulation, but entered a new field to improve the characteristics of customers’ products.


Because a generator has a large potential difference inside, any failures (voids) may cause various electrical discharges, resulting in insulation degradation. Eliminating such defects and suppressing the potential differences will contribute to extending the life of the generator and improving its reliability.

Internal structure of the generator’s coils


Mica products have excellent electrical insulation, however, to produce a better generator, relying on only electrical insulation materials with excellent dielectric strength is not enough.

Conventional Roebel transposition stuffing may easily cause failures (voids) and carry the risk of easily causing damage (electrical tree) due to electrical discharge.
Providing semiconductivity to this part may improve coil performance.


We developed a sheet with semiconductivity instead of using conventional Roebel transposition stuffing. Additionally, in order to easily fill the gaps of the Roebel transposition part of the generator coils, we made a semi-cured adhesive to improve fluidity.

Newly-developed product: Semiconductive sheet

Newly-developed product using conductive material: semiconductive sheet with Roebel transposition stuffing having semiconductivity

Followability to the Roebel transposition part

Because of its semi-cured product character, an adhesive may flow and follow even in the Roebel transposition part that has uneven narrow gaps after heat pressing.

  • 01

    Set the sheet on uneven parts of strand wires at the Roebel transposition part

  • 02

    Hold the sheet with molds and perform heat pressing

  • 03

    Completion of the process

Stable semiconductivity appeared after heat pressing

Study and development for material composition with stable semiconductivity even at the high temperature part in coils.


Taking advantage of our advanced know-how of electrical insulators, we succeeded in developing semiconductive products, a new field. We achieved a successful outcome by cultivating our creativity day by day to create new benefit-oriented value.