JPH0634817A - Hologram and production of hologram - Google Patents

Abstract

PURPOSE:To effectively decrease only the flare light by gradually annihilating diffraction gratings toward at least one surface from the inside until there are substantially no diffraction gratings on the extreme surface. CONSTITUTION:The diffraction gratings are formed of the laminated structure consisting of hologram material surfaces 1, 2, parts 4 where the refractive index is high and parts 5 where the refractive index is low. The diffraction grating in transition layers 3 disappear gradually toward the surface 2 from the inside. The diffraction gratings do not exist on the extreme surface 2 and a uniform structure is obtd. After the diffraction gratings are produced within the holograms by exposing, etc., the surfaces of the holograms are treated by a solvent as means for gradually annihilating the diffraction gratings from the inside toward the surface 2. The light meeting an incident angle angle transmits the holograms when the light is made incident on the surface 1 side from the outside of a vehicle, but the diffraction and scattering to the surface 2 side do not arise as the pseudo multislits consisting of the terminal ends of the diffraction gratings do not exist on the extreme surface when the holograms are used to head up display for vehicle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram in which flare light during reproduction is reduced and a method for producing the hologram.

[0002]

2. Description of the Related Art A head-up display (HUD) has recently been used as a method of displaying information to a driver in an automobile. This is because the optical information projected from the information projection means such as a liquid crystal display device is projected on a combiner incorporated in the windshield of the automobile so that the driver can read the information from the driving state with almost no movement of the viewpoint. It was done.

Recently, as the above combiner, due to its simplicity as an optical element and the abundance of added functions,
The use of holograms is gaining attention. Since this holographic combiner can have not only a reflection function but also a wavelength selection function, a lens function, etc., it can diffract optical information by light of a limited wavelength in the driver's visual field direction, or It is possible to form an image at a position.

FIG. 2 is an example of a conceptual diagram showing the structure of such a vehicle-mounted HUD. Here, 31 is the observation position of the driver,
32 is a holographic combiner, 33 is a light beam containing information, 34 is a lens system that is a collimator, 35 is a transmissive liquid crystal display element that is a display, 36 is a light source such as a halogen lamp, 37 is a windshield, and 38 is It is a vehicle body.

Light emitted from a light source 36 passes through a transmissive liquid crystal display element 35 via a lens system 34, and a holographic combiner 32 provided on a windshield 37 of a vehicle body.
It is irradiated to the vehicle and is reflected (diffracted) to the driver at the observation position 31.
Is visible at.

In FIG. 2, if the holographic combiner 32 is provided with a lens function, it is possible to form a display image at a distance. Further, the holographic combiner 32 can be provided with the function of the lens system 34 which is the collimator. Further, since the holographic combiner 32 has a wavelength selection function, it is possible to display an image of a color having a desired wavelength. Also, it is possible to make the wavelengths plural.

As such a holographic combiner, a reflection type hologram is usually used. In the production of the reflection hologram, one side of the photosensitive material surface of the hologram is irradiated with reference light and the other side is irradiated with object light. Then, a diffraction grating is manufactured.

When the hologram is a phase type hologram, these two laser beams interfere with each other to produce light and dark interference fringes in the hologram photosensitive material, which are recorded on the photosensitive material. In the case of a photopolymerization type photosensitive material, the monomer is polymerized in the bright part to become a polymer and becomes a part having a high refractive index, and in the dark part, because the polymerization does not occur, it becomes a part having a low refractive index, which is caused by a difference in their refractive index A diffraction grating is created. There is also a photopolymerization type photosensitive material of a type in which a monomer existing in a dark portion diffuses and moves to a bright portion and is polymerized there to form a diffraction grating having a large difference in refractive index. In the photocrosslinkable photosensitive material, the photosensitive side chains of the polymer are crosslinked to form a portion having a high refractive index or a high density in the light portion, and the dark portion is a portion having a low refractive index or a density because no crosslinking occurs. As a result, a diffraction grating based on the difference in their refractive index or density is formed.

In this type of reflection hologram, when the incident angle of the light beam and the reflection diffraction angle are different, the diffraction grating surface is inclined with respect to the hologram material surface and is not parallel to the photosensitive material surface. Therefore, although it is a reflection type hologram, it also has a transmission type hologram property of transmitting light outside the vehicle. Further, since the diffraction grating is exposed on the surface of the photosensitive material, it is considered that the diffraction grating has a structure that can be regarded as a pseudo multiple slit composed of a portion having a high refractive index and a portion having a low refractive index on the surface.

The cross-sectional structure of such a conventional hologram is shown in FIG. 3 (a), and the surface structure is shown in FIG. 3 (b). Figure 3
41 and 42 in (a) are the surface of the hologram material, and 43 and 44 are the high refractive index portion and the low refractive index portion, respectively.
A diffraction grating is formed by these layer structures. In the conventional hologram, the end portions of the diffraction grating are thus exposed on both surfaces 41 and 42. Therefore, the structure of the conventional hologram seen from one surface is as shown in FIG.
A diffraction grating consisting of a high refractive index portion 45 and a low refractive index portion 46 is exposed on the surface, and has a structure that can be regarded as a pseudo multiple slit. FIG. 3B is a view of the conventional hologram as viewed from one surface, but the structure is similar when viewed from the other surface.

[0011]

The hologram as described above also has a transmission type property, and since the end of the diffraction grating is exposed on the surface of the hologram to have a pseudo multiple slit structure, the light from the outside of the vehicle is high. It enters the inside of the vehicle as second-order diffracted light.
Therefore, depending on the angle of incidence of light from the outside of the vehicle, it may appear as bright unevenness or as a spot-like bright spot (hereinafter referred to as flare light), which has an adverse effect such as reducing the visibility of the display image of the HUD. . In addition, it is not preferable in terms of appearance.

[0012]

The present invention has been made to solve the above-mentioned problems, and a diffraction grating having a layered structure composed of a high refractive index portion and a low refractive index portion inclined with respect to the surface is provided. In the hologram formed inside, the diffraction grating gradually disappears from the inside toward at least one surface, the hologram characterized in that the diffraction grating is substantially absent on the outermost surface, and In this method for producing a hologram, after providing a predetermined diffraction grating, at least one surface is treated with a solvent having a property capable of dissolving a hologram material. is there.

FIG. 1 shows an example of a sectional structure of a hologram produced by the method according to the present invention. Reference numerals 1 and 2 denote surfaces of the hologram material, and 4 and 5 denote portions having a high refractive index and a portion having a low refractive index, respectively, and the layer structure forms a diffraction grating.
The refractive index difference between the high and low refractive index parts is usually 0.02.
To about 0.2. 3 is a transition layer on the surface 2 side.
In the transition layer, the diffraction grating gradually disappears from the inside toward the surface 2, and the outermost surface 2 has no diffraction grating and has a uniform structure. In this example,
On the other surface 1 side, the diffraction grating is exposed on the surface 1, but a transition layer similar to 3 can be provided on the surface 1 side.

As described above, the diffraction grating is attached to the surface 2 from the inside.
As a means for gradually disappearing toward the surface, it is possible to employ a method of producing a diffraction grating in the hologram by exposure or the like and then treating the surface of the hologram with an appropriate solvent.

For example, when a hologram is produced by using a vinyl-based or acrylic-based photopolymerizable photosensitive material, a ketone-based solvent such as acetone is used as a solvent (good solvent) having a property of dissolving these materials. Solvents, halogenated hydrocarbon solvents such as dichloromethane, aromatic hydrocarbon solvents such as pyridine and xylene, and other solvents such as ethers and esters can be used. Note that some solvents have a very strong dissolving power, which may destroy the hologram.In such a case, it is possible to dilute the good solvent with a poor solvent having a small dissolving power. preferable. For example, acetone, pyridine and the like have strong solubility in these light-sensitive materials, and therefore they are preferably diluted with a poor solvent such as water or ethanol. Since these solvents have different dissolving powers depending on the photosensitive material, they may be selected according to the materials.

In some photopolymerizable light-sensitive materials, sensitized heating is performed after exposure in order to further increase the difference in refractive index. In that case, the treatment with the solvent is effective even before or after the sensitizing heating. However, since the photosensitive material before heating is easily dissolved, it is necessary to increase the degree of dilution as compared with the case of performing after heating.

Further, not only vinyl type or acrylic type photosensitive materials but also photocrosslinking type photosensitive materials such as negative photoresist and dichromated gelatin can be obtained by using a good solvent for each material. It is possible.

Further, although the reflection hologram has been described above, the same effect can be obtained also in the transmission hologram.

[0019]

When light enters the hologram gram according to the present invention from the outside of the vehicle to the surface 1 side, a part of the light corresponding to the incident angle passes through the hologram gram, but the diffraction grating ends at the outermost surface on the surface 2 side. Since there is no pseudo multiple slit consisting of parts, it is not diffracted or scattered. Therefore, flare light is effectively reduced. On the other hand, the light including information projected from the liquid crystal display device or the like is reflected and diffracted by the diffraction grating inside the hologram and becomes observable by the driver,
Almost unaffected by the transition layer.

If a transition layer is provided on the surface 1 side as well, diffraction and scattering on the surface 1 can be reduced, so that flare light can be further reduced.

As described above, according to the present invention, it is possible to effectively reduce only the flare light with almost no effect on the display image containing information.

[0022]

EXAMPLE A method for producing a hologram of the present invention will be described according to an example. In the present invention, first, the hologram is exposed similarly to the conventional hologram manufacturing method. That is,
By irradiating the reference light from one surface (inside the vehicle) and the object light from the other surface (outside the vehicle) of the photosensitive material, bright and dark interference fringes due to light interference are formed inside the photosensitive material. In the bright part, photopolymerization or photocrosslinking occurs and becomes a high refractive index part, and in the dark part, it does not occur so that it becomes a low refractive index part, and a diffraction grating based on the difference in refractive index is formed. The structure of the hologram manufactured in this manner is a conventional structure as shown in FIGS. 3 (a) and 3 (b). Next, in the present invention, after the exposure for forming a predetermined diffraction grating is performed as described above, one surface is dipped in a solvent having a property of dissolving the hologram photosensitive material, so that the transition as shown in FIG. A layered hologram can be easily produced.

In this example, a hologram was produced using an acrylic photopolymerizable photosensitive material. As the solvent, acetone is 10% with ethanol, 30
%, It is possible to dissolve the surface layer of the hologram using a mixed solvent diluted to 50% to substantially eliminate the diffraction grating on the surface of the hologram, and to form a transition layer of about several μm each. It was

By mounting this on a windshield of an automobile and using it as a combiner for a head-up display, a head-up display in which flare light was effectively suppressed was obtained.

[0025]

According to the present invention, a hologram in which flare during image reproduction is effectively reduced and a method for manufacturing the hologram can be obtained. This is effective for reflection-type and transmission-type holograms using various photosensitive materials.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a hologram of the present invention.

FIG. 2 is a conceptual diagram showing a vehicle-mounted HUD.

FIG. 3 is a sectional view and a plan view showing the structure of a conventional hologram.

[Explanation of symbols]

 1, 2: hologram surface 3: transition layer 4: high refractive index portion 5: low refractive index portion

Claims (2)

[Claims] 1. A hologram in which a diffraction grating is formed by a layer structure composed of a high refractive index portion and a low refractive index portion inclined with respect to the surface, wherein the diffraction grating extends from the inside toward at least one surface. Accordingly, the hologram gradually disappears, and the diffraction grating is substantially absent on the outermost surface. 2. A hologram producing method according to claim 1, wherein after forming a predetermined diffraction grating, at least one surface is treated with a solvent capable of dissolving a hologram material. Of manufacturing.