Epoxy optical sheet and process for producing the same

Details Epoxy optical sheet and process for producing the same Epoxy optical sheet and process for producing the same

1999-05-06

2002-12-31

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Continuous and nonuniform or irregular surface on layer or...

C428S220000, C428S413000

Reexamination Certificate

active

06500518

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an epoxy optical sheet excellent in optical properties and heat resistance, and a process for producing the epoxy optical sheets at high mass-productivity.
BACKGROUND OF THE INVENTION
Conventional optical sheets made of epoxy resins are those obtained by pouring an epoxy resin into a space of a cast mold followed by hardening (JP-A-6-337408, JP-A-7-28043 and JP-A-7-120741; the term “JP-A” as used herein means an “unexamined published Japanese patent application”). However, it is difficult by this casting method to obtain a sheet having a thickness of 500 &mgr;m or less and being free from any optical strain.
In a method wherein a hardened plate made of an epoxy resin is cut into a sheet, optical strain generates in cutting step when a thickness is 500 &mgr;m or less. As a result, it was also difficult to obtain an optical strain-free sheet by this method. Thus, epoxy optical sheets having high thickness accuracy at a thickness of 500 &mgr;m or less, small retardation and excellent heat resistance have not yet been provided, in spite of a demand therefor.
Moreover, the above-described method suffers from a disadvantage that the complicated steps such as casting and mold opening are required, and this results in poor production efficiency of epoxy optical sheets. Thus, a method is considered, which continuously produces epoxy optical sheets by, for example, a calender method using rolling rolls, a melt extrusion method with T-die or the like, or a flow casting method of a resin solution onto a support, according to the conventional resin sheet production.
However, the epoxy resin involves use as adhesives. Therefore, when the epoxy resin is molded into a sheet by these methods, the epoxy resin adheres to rolls, dies, supports, etc. As a result, it is impossible to easily separate and recover the molded sheets, resulting in breakage of the sheet in separation thereof. In addition, there arises another problem that the thus obtained sheets tend to have uneven surface and thus fail to achieve the required surface smoothness required in optical sheets.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide an epoxy optical sheet having a thickness of 500 &mgr;m or less, an excellent thickness accuracy, a small retardation and a high heat resistance.
Another object of the present invention is to provide a process for producing the epoxy optical sheet at high efficiency.
The present invention provides an epoxy optical sheet comprising a hardened sheet comprising an epoxy resin, and another resin layer formed on one side thereof, wherein the sheet has a retardation of 5 nm or less, an average thickness of 500 &mgr;m or less, a thickness accuracy of ±10% or less, a glass transition temperature of 170° C. or above and a smooth surface.
The present invention further provides a process for continuously producing an epoxy optical sheet, which comprises successively forming a strippable resin layer on a support having a smooth surface, successively spreading an epoxy resin coating solution comprising an epoxy resin, a hardener, a hardening, accelerator and a leveling agent onto the resin layer in the form of a sheet, followed by hardening treatment, thereby forming a hardened sheet adhering to the resin layer; and at the same time, recovering the hardened sheet together with the resin layer from the support.


REFERENCES:
patent: 4321102 (1982-03-01), Drexler et al.
patent: 4576896 (1986-03-01), Suzuki et al.
patent: 6-228274 (1994-08-01), None
patent: 06228274 (1994-08-01), None
Derwent Abstract 1994-299853, abstract of JP 06228274A, Aug. 1994.

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