Polyester (OKP Optical Plastic)--Fluorene derivative--Fine materials business/Osaka Gas Chemicals Co., Ltd.

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.

Basic structure and advantages

High refractive index
Low birefringence
Low Abbe number
High fluidity

Example of usage

Optical imaging lens
Various optical films
Sensor cover

Comparison of birefringence

OKP4	PMMA (methyl methacrylate resin) Polycarbonate resin COP (cyclo-olefin polymer)

Abbe number

Abbe number Image

Physical properties

Characteristics		Test method	Condition	Unit	OKP4	OKP4HT	(For reference) PC (for optics)	(For reference) COP	PMMA
Physical property	Specific gravity	Density method	—	g/cm³	1.22	1.26	1.2	1.01	1.19
	Water absorption	JIS K7209	—	%	0.2	0.2	0.2	< 0.01	0.3
	Glass transition temperature	DSC	—	℃	121	143	145	138	110
	Heat distortion temperature	JIS K7207	18.5kgf/cm²	℃	105	128	126	123	100
	Coefficient of thermal expansion	JIS K7197	30〜120℃	10^-5/K	7.2	6.9	7	7	6
Optical properties	Light transmittance	JIS K7105	700nm, 3mmT	%	90	90	89	92	93
	Refractive index (nd)	Abbe refractometer	589nm(20℃)	—	1.607	1.632	1.585	1.525	1.49
	Temperature dependence coefficient	Abbe refractometer	—	10^-5/K	-13	-11	-12	-10	-10
	Abbe number	Abbe refractometer	—	—	27	23	29	56	58
Mechanical properties	Tensile strength	JIS K7113	—	MPa	71	65	52	59	73
	Tensile elongation	JIS K7113	—	%	9	10	110	40	5
	Flexural modulus	JIS K7203	—	MPa	2.7	2.5	2.4	2.1	3.3
	Flexural strength	JIS K7203	—	MPa	120	115	96	94	120
	Impact strength	ASTM D256	—	J/m	58	43	78	24	15.7
	Pencil hardness	JIS K5401	—	—	2H	H	B	H	2H
Moldability properties	MFR	JIS K6719	230℃, 2.16kg	g/10min	12	3	65 (300℃, 1.2kg)	21 (280℃, 2.16kg)	2 (230℃, 3.8kg)

∗Physical properties of other resins are quoted from catalogs and the literature.

New development product

●Optical film grade (OKP-F)
Extremely low birefringence makes it possible to create optical films by the melt extrusion method. birefringence does not occur even if the film is extended.

Optical film grade (OKP-F) Image

●High performance grade
We have been developing more grades that have a further excellent high refractive index, low birefringence, and environmental resistance to cover high-level requirements and wider use.

High performance grade Image