Fine chemical materials


Fine chemical materials

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 121 142 133 145 139
Heat distortion temperature ℃,1.80MPa 103 119 112 123 122
Linear expansion coefficient ×10-5/℃ 7.4 6.3 6.5 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

∗ 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