1. TOP
  2. Product information  Fine Materials
  3. Polyester (OKP Optical Plastic)

Polyester (OKP Optical Plastic): For injection molding, raw material of the film

OKP is a special polyester for optical use arising from coal chemistry. OKP has a high refractive index of 1.6 or more, extremely low birefringence, and high fluidity. Therefore, it is easy to obtain high performance injection-molded objects and films.


  • High refractive index
  • Low birefringence
  • Low Abbe number
  • High fluidity

Example of usage

  • Various optical lens
  • Various optical films
  • Other optical elements

Comparison of birefringence

OKP4 Image

PMMA (methyl methacrylate resin) Image
PMMA (methyl methacrylate resin)

Polycarbonate resin Image
Polycarbonate resin

COP (cyclo-olefin polymer) Image
COP (cyclo-olefin polymer)

Abbe number

Abbe number

Physical properties

Properties Unit,Conditions OKP4 OKP4HT OKP-1 Reference
(Optical grade)
Physical properties
Glass transition temperature 121 142 132 145 139
Heat distortion temperature ℃,1.80MPa 106 123 115 123 122
Linear expansion coefficient ×10-5/℃ 7.2 6.9 7.1 7.0 6.0
Optical properties
Refractive index (D line) - 1.607 1.632 1.642 1.585 1.531
Abbe number νD 27 23 22 29 56
Birefringence ×10-4,OGC method < 5 55 < 5 128 53
Coefficient of temperature dependence of refractive index ×10-5/℃ -13 -11 -12 -12 -10

∗ Values of other resins indicated for comparison are quoted form catalogs and published documents.

New development product

Optical films (OKP-F)

Optical film can be produced by the melt extrusion method. It's a very low birefringence, orientation birefringence does not occur mostly by stretched.

OKP-F Image

OKP particles

OKP particles is high refractive index polyester resin. It stabilizes to water. Particle sizes can be controlled.

OKP particles Image