Fresnel lens and optical device provided with same
Provided is a Fresnel lens which has excellent heat resistance and which can covert light even from a poor-quality semiconductor light sources into uniform, high-quality light and can disperse the resulting light without lowering the central illuminance. The Fresnel lens according to the present invention includes two or more sawtooth prisms in a surface thereof and is made of a cured product of a curable composition containing an epoxy compound (A). Of the sawtooth prisms, a sawtooth prism having a longest inclined side in a cross section has a roughened surface, where the cross section is given by cutting the Fresnel lens in a plane which passes through the center of the Fresnel lens and which is perpendicular to a reference plane of the Fresnel lens.
1. A Fresnel lens comprising two or more sawtooth prisms in a surface thereof,
wherein the Fresnel lens is made of a cured product of a curable composition containing (A) an epoxy compound,
wherein, of the sawtooth prisms, only a sawtooth prism having a longest inclined side in a cross section has a roughened surface having an arithmetic mean surface roughness (Ra) of 1 to 30 μm, where the cross section is given by cutting the Fresnel lens in a plane which passes through a center of the Fresnel lens and which is perpendicular to a reference plane of the Fresnel lens.
2. The Fresnel lens according to claim 1 ,
wherein the epoxy compound (A) comprises a compound represented by Formula (a):
wherein R 1 to R 18 are each, identically or differently, selected from hydrogen, halogen, an optionally oxygen- or halogen-containing hydrocarbon group, and optionally substituted alkoxy; and X is selected from a single bond and a linkage group.
3. The Fresnel lens according to claim 1 , wherein the curable composition further comprises:
(B) an oxetane compound; and
(C) a cationic-polymerization initiator,
in addition to the epoxy compound (A).
4. The Fresnel lens according to claim 1 ,
wherein the Fresnel lens has a glass transition temperature of 100° C. or higher.