JP2009151140A - Liquid crystal fresnel lens and manufacturing method thereof - Google Patents

Abstract

Disclosed is a liquid crystal Fresnel lens capable of obtaining good lens characteristics without unevenness by changing the material and structure of the Fresnel lens.
An opposing transparent substrate having a lens substrate having a Fresnel lens formed on one side thereof, a transparent electrode disposed so as to oppose the lens substrate, and opposed to the Fresnel lens, and the lens substrate In the liquid crystal Fresnel lens in which the liquid crystal is arranged between the transparent substrate and the counter transparent substrate, since the Fresnel lens is formed of a light-transmitting conductive material, the liquid crystal Fresnel can obtain good lens characteristics without unevenness. lens.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal Fresnel lens, and more particularly, to a technique by which a liquid crystal Fresnel lens can obtain good lens characteristics without unevenness.

  In recent years, a mechanism for connecting a plurality of focal points with a single lens unit, such as a zoom mechanism of a camera, has been used in various apparatuses. This mechanism has a plurality of lenses in one lens unit, and the focal point is varied by varying the distance between the lenses. However, the lens unit requires a plurality of lenses and the distance between the lenses. Could not be made thinner.

  On the other hand, in the bifocal glasses, a multifocal lens having a plurality of curvatures in one lens and changing a focus depending on a viewing place in the lens is used. Although such a lens can be made thin, since the focal point is different in the entire lens, the focal point has a problem that the field of view becomes narrow. In view of this, a variable focus lens using a liquid crystal whose refractive index can be changed by voltage has been studied. A variable focus lens combining a Fresnel lens and a liquid crystal has been proposed (for example, see Patent Document 1).

  This method is called a liquid crystal Fresnel lens. FIG. 4 shows a cross-sectional structure diagram of the liquid crystal Fresnel lens. In the liquid crystal Fresnel lens 1, the Fresnel lens 3 is formed on the first substrate 2, the first transparent conductive film 18 is formed thereon, and further on the first transparent conductive film 18. The first alignment film 6 is formed to constitute the lens substrate 7. A liquid crystal 8 is filled on the lens substrate so as to cover the Fresnel lens 3. A second base material 11 on which a second alignment film 9 and a second transparent conductive film 10 are formed is disposed so as to face the Fresnel lens 3, thereby forming a counter transparent substrate 12. Around the liquid crystal 8, a sealing agent 13 mixed with a spacer is disposed in order to prevent leakage of the liquid crystal 8 and to keep the first base material 2 and the second base material 11 uniform. General nematic liquid crystal has anisotropy in refractive index in the long side direction and short side direction of liquid crystal molecules, and has a refractive index of about 1.7 in the long side direction and about 1.5 in the short side direction. ing. When there is no potential difference between the first transparent conductive film 18 and the second transparent conductive film 10, the liquid crystal 8 is aligned along the rubbing direction of the alignment film. At this time, the light passes through the liquid crystal Fresnel lens 1. When transmitted, the light incident in parallel with the rubbing direction has the same lens effect as when passing through a Fresnel lens having a refractive index difference of 0.2 when the refractive index of the Fresnel lens 3 is 1.5. When there is a certain potential difference between the first transparent conductive film 18 and the second transparent conductive film 10, the liquid crystal 6 rises. Since the refractive index of the liquid crystal at this time is 1.5, it becomes the same as the refractive index of the Fresnel lens 3, and the lens effect disappears. Accordingly, when only the light incident in the rubbing direction is taken out by the polarizing plate 14, a liquid crystal Fresnel lens capable of changing the focus can be manufactured by the potential difference between the first transparent conductive film and the second transparent conductive film.

For the Fresnel lens of the liquid crystal Fresnel lens, an optically transparent resin is usually used, and an indium oxide-based transparent conductive thin film (hereinafter referred to as ITO) is used for the transparent conductive film. When ITO is formed on a resin by a thin film method, the adhesive force is poor, and when the stress concentration occurs due to thermal distortion or external force in the Fresnel lens during post-processing or use, the conductivity decreases due to peeling of the transparent conductive film, A continuity failure occurs. For this reason, in Patent Document 2, an organopolysiloxane film is formed as the adhesion layer 19 between the Fresnel lens and the transparent conductive film to increase the adhesion (see, for example, Patent Document 1).
JP-A-4-322214 JP-A-63-89334

  However, in the above-described conventional configuration, the adhesion layer 19 is formed by spin-coating the adhesion layer material liquid and then baking it. However, the adhesion layer material liquid is formed in the groove portion 20 of the Fresnel lens when the adhesion layer material liquid is applied. It accumulates due to surface tension. For this reason, the thickness of the adhesion layer of the groove portion 20 of the Fresnel lens is changed, light passing through the groove portion 20 of the Fresnel lens is scattered, and concentric stripes appear on the liquid crystal Fresnel lens. Had.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a liquid crystal Fresnel lens that can obtain good lens characteristics without unevenness by changing the material and structure of the Fresnel lens.

In order to solve the above-described conventional problems, the liquid crystal Fresnel lens of the present invention is disposed so as to face the lens substrate, the lens substrate on which the Fresnel lens is formed on one side, and opposed to the Fresnel lens. In the opposite transparent substrate having a transparent conductive film, and a liquid crystal Fresnel lens in which liquid crystal is disposed between the lens substrate and the opposite transparent substrate,
The Fresnel lens is formed of a light-transmissive conductive material, and is formed flat between the Fresnel lens and the transparent substrate, and a flat conductive layer formed of the same material as the Fresnel lens is formed. It is characterized by being.

  According to the liquid crystal Fresnel lens of the present invention, since the adhesion layer can be eliminated by forming the Fresnel lens with a light-transmitting conductive material, it occurs when the thickness of the adhesion layer in the groove portion of the Fresnel lens changes. Thus, the concentric stripe unevenness of the liquid crystal Fresnel lens can be eliminated, and good lens characteristics can be obtained without unevenness.

  Hereinafter, embodiments of the liquid crystal Fresnel lens of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a sectional structural view of a liquid crystal Fresnel lens according to Embodiment 1 of the present invention. The structure of the liquid crystal Fresnel lens 1 in the first embodiment will be described with reference to FIG. A Fresnel lens 3 made of a light-transmitting conductive material is formed on a light-transmitting first base material 2 serving as a base material. Between the Fresnel lens 3 and the first substrate 2, a flat conductive layer 4 made of the same material as that of the Fresnel lens 3 is formed via an adhesive layer 5. A first alignment film 6 is formed on the Fresnel lens 3 in order to align the directions of the liquid crystals, thereby forming a lens substrate 7. On the first alignment film 6, a liquid crystal 8 is disposed. Further thereon, a second alignment film 9 having the same function as the first alignment film is disposed. Further thereon, a second transparent conductive film made of ITO serving as a counter electrode of the Fresnel lens 3 is formed on a light transmissive second base material 11 to constitute a counter transparent substrate 12.

  When no electric field is applied to the liquid crystal, the liquid crystal molecules are aligned along the alignment direction of the alignment film, but the first alignment film and the second alignment film are aligned so that the liquid crystal molecules are aligned in the same direction. Has been. Around the liquid crystal, a sealant 13 mixed with a spacer is disposed in order to prevent leakage of the liquid crystal and to keep the distance between the lens substrate and the counter transparent substrate uniform. On the opposing transparent substrate 12, a polarizing plate 14 having slits is disposed in the same direction as the alignment direction of the first alignment film and the second alignment film, and the direction in which the liquid crystal behaves as a high refractive index material. Only the light is incident on the liquid crystal Fresnel lens 1.

  In the conventional structure shown in FIG. 4, an ITO film is formed on a Fresnel lens made of an insulating resin. However, since the adhesion between ITO and resin is weak, an adhesion layer is formed between the Fresnel lens and ITO. It was. The adhesion layer was formed by spin-coating the adhesion layer material liquid and then baking it. However, the adhesion layer material liquid collected in a curved line due to surface tension in the groove portion of the Fresnel lens when the adhesion layer material liquid was applied. . For this reason, the light passing through the groove of the Fresnel lens is scattered by the adhesion layer, and concentric stripes appear on the liquid crystal Fresnel lens. In the structure of the Fresnel lens of the present invention, since the Fresnel lens itself has conductivity, it is not necessary to form a transparent conductive film on the Fresnel lens. For this reason, the adhesion layer is not necessary, and the concentric stripe unevenness of the liquid crystal Fresnel lens due to the thickness variation of the adhesion layer can be eliminated.

  A method for manufacturing a conductive Fresnel lens will be described with reference to FIGS. In order to produce a conductive Fresnel lens, the height from the top of the Fresnel lens to the first substrate is required in units of μm, which is difficult by the thin film method. Therefore, a conductive Fresnel lens was fabricated using the coating method this time. First, transparent conductive ink 17 (X-100, manufactured by Sumitomo Metal Mining Co., Ltd.), which is a solution mainly composed of ITO fine particles, was dropped onto the Fresnel lens molding die shown in FIG. Since the transparent conductive ink 17 contains a solvent, it was dried at 40 ° C. for about 20 minutes and then cured at 100 ° C. for 20 minutes. Then, as shown in FIG. 2B, the transparent conductive ink is reduced. The Fresnel lens molding die 15 is provided with a Fresnel lens molding die frame 16 so as to surround a region where the Fresnel lens is transferred. The frame portion 16 of the Fresnel lens molding die can be removed.

  A cross-sectional perspective structure of this Fresnel lens molding die is shown in FIG. When the transparent conductive ink 17 is cured, the ink contracts, so that the liquid level of the transparent conductive ink is lowered, and transfer to the first substrate becomes difficult. Therefore, the frame portion 16 of the Fresnel lens molding die is removed. Next, the adhesive layer 5 is formed on the first substrate. In the present embodiment, a light-transmitting optical double-sided pressure-sensitive adhesive sheet is attached. Then, as shown in FIG. Next, the transparent conductive ink 17 was pressed against the adhesive layer and transferred together with the Fresnel lens molding die. In this state, the Fresnel lens was removed from the Fresnel lens molding die to obtain a conductive Fresnel lens and a flat conductive layer as shown in FIG. The lens substrate was completed by rubbing the substrate. The Fresnel lens mold used in the present embodiment has a Fresnel lens diameter of 10 mm, a groove height 21 serving as a Fresnel lens tooth, 5 μm, a Fresnel lens mold mold frame thickness 22 of 15 μm, and a transparent conductive material. For the part that comes into contact with the ink, an oil-repellent-coated one was used. The completed lens substrate had a Fresnel lens tooth height of 5 μm and a conductive flat layer thickness of 5 μm.

  In this embodiment, the ITO fine particle ink is used as the transparent conductive ink, but a transparent conductive polymer ink or the like may be used. Further, the adhesive layer may be formed by applying a curing liquid such as a photo-curable adhesive.

  By the way, since the general transparent conductive ink has a higher electric resistance than the ITO thin film, even if only the Fresnel lens is made conductive, the electric resistance is too high to be used for the liquid crystal Fresnel lens. Therefore, in order to reduce the electrical resistance of the Fresnel lens, a transparent conductive flat conductive layer made of the same material as the Fresnel lens is provided between the Fresnel lens and the adhesive layer. By increasing the thickness of this conductive flat layer, the electrical resistance value of the Fresnel lens is reduced. The flat conductive layer is actually formed at the same time because the Fresnel lens molding die has a frame portion of the Fresnel lens molding die. Therefore, it is possible to reduce the electrical resistance without increasing the number of steps.

  In order to confirm the effect of the conductive Fresnel lens of the first embodiment, as a comparative example, the same Fresnel lens molding die was used, and a lens substrate was manufactured using a non-conductive ultraviolet curable resin. For the adhesion layer, an organopolysiloxane solution was applied by spin coating, and after curing, an ITO thin film was formed by sputtering.

  Two types of liquid crystal Fresnel lenses were manufactured using the lens substrate of Embodiment 1 manufactured by the above method and the lens substrate of Comparative Example 1, and the operation was compared. In the liquid crystal Fresnel lens using the lens substrate of Comparative Example 1, concentric white stripes were generated due to the change in the thickness of the adhesion layer in the groove portion of the Fresnel lens. In the liquid crystal Fresnel lens using the lens substrate of Embodiment 1, no concentric white stripes were seen, and a clear image could be obtained.

  As described above, when a liquid crystal lens was produced using the Fresnel lens using the conductive material of this example, white stripes disappeared and good lens characteristics were obtained.

  The liquid crystal Fresnel lens and the manufacturing method thereof according to the present invention have an effect of obtaining good lens characteristics without unevenness, and are useful as a variable focus lens such as a zoom lens of a camera or a pair of glasses for both perspective.

1 is a cross-sectional structure diagram of a liquid crystal Fresnel lens according to Embodiment 1 of the present invention. Manufacturing process diagram of lens substrate of liquid crystal Fresnel lens according to Embodiment 1 of the present invention Sectional perspective view of the Fresnel lens molding die of Embodiment 1 of the present invention Cross-sectional structure of a conventional liquid crystal Fresnel lens

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal Fresnel lens 2 First base material 3 Fresnel lens 4 Flat conductive layer 5 Adhesive layer 6 First alignment film 7 Lens substrate 8 Liquid crystal 9 Second alignment film 10 Second transparent conductive film 11 Second base material DESCRIPTION OF SYMBOLS 12 Opposite transparent substrate 13 Sealant 14 Polarizing plate 15 Fresnel lens molding die 16 Fresnel lens molding die frame part 17 Transparent conductive ink 18 First transparent conductive film 19 Adhesion layer 20 Fresnel lens groove part 21 Fresnel lens tooth Groove height 22 Frame thickness

Claims (4)

A counter transparent substrate having a lens substrate having a Fresnel lens formed on one side thereof, a transparent conductive film disposed to face the lens substrate and disposed to face the Fresnel lens; and the lens substrate and the counter substrate In a liquid crystal Fresnel lens with a liquid crystal arranged between a transparent substrate,
The Fresnel lens is formed of a light-transmissive conductive material, and is formed flat between the Fresnel lens and the transparent substrate, and a flat conductive layer formed of the same material as the Fresnel lens is formed. Liquid crystal Fresnel lens. The adhesive layer for adhere | attaching the said flat conductive layer and said 1st transparent substrate is formed between the said flat conductive layer and the 1st transparent substrate which is a base material of the said lens substrate. The liquid crystal Fresnel lens described. The liquid crystal Fresnel lens according to claim 2, wherein ITO conductive particles are used as the conductive material. A lens molding step of forming a Fresnel lens molding by dripping and applying a solution containing light-transmitting fine particles as a main component to a Fresnel lens molding die;
A drying step of drying the Fresnel lens molding in the Fresnel lens molding mold after the lens molding step;
Forming an adhesive layer on a light-transmitting substrate;
A transfer step of transferring the light-transmitting base material formed with the adhesive layer to a molded product in the Fresnel lens molding die;
A method for producing a liquid crystal Fresnel lens, comprising the step of taking out the molded product from the Fresnel lens molding die.

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