BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical device using organic electroluminescence.

2. Description of the Related Art

In recent years, as a display device replacing a liquid crystal display device, organic electroluminescence (organic electro luminescence (EL) (organic light emitting diode (OLED)) has been developed continuously, and a 60-inch large display device (display) has started appearing.

The surface of the organic EL substrate constituting the organic EL display device has a high reflectance. Accordingly, particularly in a bright environment, the surface reflects external light and deteriorates contrast.

Therefore, the surface of the organic EL display device is provided with an antireflection film consisting of a polarizer and a λ/4 plate.

For example, JP2009-259721A describes an organic EL display device comprising an organic EL element portion which consists of a reflecting electrode, an organic EL light emitting layer, and a transparent electrode and a circular polarization plate which consists of a retardation plate and a polarizing plate, in which an antireflection layer having a high reflectance in a wavelength range of complementary color of the color of light reflected from the surface of the circular polarization plate is provided in an air interface of a member closer to an observer than to the circular polarization plate.

Furthermore, JP2017-022016A describes a circular polarization plate for an organic EL display device and an organic EL display device comprising the circular polarization plate, in which the circular polarization plate comprises a polarizer, a retardation layer functioning as a λ/4 plate, a barrier layer, and a pressure sensitive adhesive layer functioning as a barrier in this order, and the barrier layer is thin glass having a thickness of 5 to 100 μm.

SUMMARY OF THE INVENTION

Such an organic EL display device is provided with an antireflection film (circular polarization plate) consisting of a polarizer and a λ/4 plate so as to prevent the reflection of external light and to enable the device to display images with high contrast.

However, the antireflection film consisting of a polarizer and a λ/4 plate also absorbs the light emitted from an organic EL element. Therefore, the conventional organic EL display device has low light use efficiency, and cannot fully demonstrate the performance of the organic EL element.

An object of the present invention is to solve the above problem of the conventional technique and to provide an optical device using organic EL that can accomplish both the effect of preventing external light reflection and the improvement of utilization efficiency of light emitted from an organic EL element.

In order to achieve the object, the optical device according to an embodiment of the present invention has the following constitution.

[1] An optical device including, in the following order, an organic electroluminescent substrate having light emitting portions by organic electroluminescence and a non-light emitting portion which has a metallic reflecting portion, a circularly polarized light-separating layer that is formed using a composition including a liquid crystal compound and has a liquid crystal alignment pattern in which the liquid crystal compound is twisted and aligned along a helical axis extending in a thickness direction and a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in a plane, a λ/4 plate, and a polarizer.

[2] The optical device described in [1], in which the circularly polarized light-separating layer transmits one of left-handed circularly polarized light and right-handed circularly polarized light and reflects the other such that light emitted from the light emitting portions of the organic electroluminescent substrate is separated into right-handed circularly polarized light and left-handed circularly polarized light.

[3] The optical device described in [1], in which the circularly polarized light-separating layer rectilinearly transmits one of right-handed circularly polarized light and left-handed circularly polarized light and refractively transmits the other such that light emitted from the light emitting portions of the organic electroluminescent substrate is separated into right-handed circularly polarized light and left-handed circularly polarized light.

[4] The optical device described in [3], in which the circularly polarized light-separating layer also reverses a sense of rotation of the refractively transmitted circularly polarized light.

[5] The optical device described in any one of [1] to [4], in which the organic electroluminescent substrate has the light emitting portions emitting light having different wavelengths.

[6] The optical device described in [5], in which in a case where a length, over which the direction of the optical axis derived from the liquid crystal compound rotates 180° in one direction along which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in the liquid crystal alignment pattern of the circularly polarized light-separating layer, is regarded as one period, the optical device has a plurality of kinds of circularly polarized light-separating layers whose lengths of the one period varies one another.

[7] The optical device described in [6], in which in the plurality of kinds of the circularly polarized light-separating layer, depending on a wavelength of an incidence ray, the longer the wavelength of the incidence ray incident on a portion, the longer the one period in the portion.

[8] The optical device described in any one of [1] to [7], in which the circularly polarized light-separating layer has an isotropic region in which no liquid crystal compound is aligned.

[9] The optical device described in [8], in which the isotropic region is provided in a region on which light from the light emitting portions of the organic electroluminescent substrate is not incident.

[10] The optical device described in any one of [1] to [9], further having a support, in which one surface of the support is provided with the circularly polarized light-separating layer and the other surface of the support is provided with a λ/4 plate and the polarizer.

According to the optical device of an embodiment of the present invention, in an optical device using organic EL, it is possible to accomplish both the effect of preventing external light reflection and the improvement of utilization efficiency of light emitted from an organic EL element.

