JPH0495901A - Thin-film optical element, production thereof and head up display using the same - Google Patents

Abstract

PURPOSE:To enhance the uniformity of film thicknesses and to obtain a large area by using high-polymer composition as dielectrics varying in refractive index. CONSTITUTION:High-refractive index materials 3 having the thickness of 1/4 wavelength and low-refractive index materials 2 of 1/4 wavelength are laminated on a base material. The reflected light on the surface of the low-refractive index layers is offset by the reflected light on the boundary between the low- refractive index layers and the high-refractive index layers shifted in phase by 1/2 wavelength and on the boundary between the high-refractive index layers and the base material 1 in this case. The high-polymer composition varying in the refractive index are alternately laminated by >=1 layers each respectively as the low-refractive index layers and the low-refractive index layers on the base material 1 in such a manner and, therefore, the thin-film optical element having the large area is easily obtd.

Description

Detailed Description of the Invention: Industrial Field of Application The present invention relates to an optical thin film formed by providing multiple layers of dielectric materials with different refractive indexes on a substrate, especially when the substrate is made of a highly flexible material such as a plastic film. This invention relates to optical thin films and heads-up displays using them as combiners.

Conventional technologyConventional Optical thin film ζ that exhibits its function by interfering with light of a specific wavelength by laminating inorganic dielectric materials with different refractive indexes Anti-reflection coating and specific wavelengths to improve the transmittance of transparent substrates such as glass It is used as a high-reflection film (dichroic mirror) that reflects or transmits the area, or as a band-pass filter.Also, as a combiner for a head-up display, reflective holograms, semi-transparent mirrors, and dichroic mirrors are used. Other proposals include integrating the combiner with the windshield and inserting the hologram into the laminated glass (Optical Society of Japan Holographic Display Study Group Bulletin January 1990 issue). ).

Problems to be Solved by the Invention In order to form thin films of conventional inorganic dielectric materials, it is necessary to laminate multiple layers. When attempting to obtain a large-area optical thin film, extremely large vacuum equipment is required, and evacuation takes a long time, resulting in problems such as poor productivity and difficulty in obtaining satisfactory film thickness uniformity. In the case of a head-up display, if you try to integrate the windshield and combiner to improve safety, you will need to put the entire windshield into a vacuum device to form a thin film.Also, there will be a hologram sandwiched between the laminated glass. Since it is a reflective type, there are problems in that it is difficult to mass-produce, as it is necessary to expose each sheet one by one, and there is no hologram recording material that can withstand the heat and pressure bonding conditions in the laminated glass manufacturing process. The present invention solves these problems, and aims to provide a large-area thin film optical element and a head-up display that can easily integrate the combiner and the windshield by using this as a combiner. A method for solving the problem is to create a thin film optical element by alternately laminating at least one low refractive index layer and one or more high refractive index layers of polymer compositions having different refractive indexes on a base material. In addition, a selective light reflecting thin film optical element formed by alternately laminating one or more polymer compositions having different refractive indexes on a base material as a low refractive index layer and a high refractive index layer is used as a combiner. Since a polymer composition is used as a dielectric material with different working refractive indexes, it can be laminated by repeating coating and drying in a solution or aqueous dispersion state, and the film thickness is easily highly uniform. By using the thin film optical elements described above as a combiner, it is easy to integrate them with a canopy or windshield, and a head-up display can be provided at low cost. can.

Example general number ζ As a thin film optical element constructed by laminating dielectric materials on a base material.Anti-reflection film Selective light reflection Anti-reflection coatings utilize the reflection of light and the phase difference that occurs when it passes through a dielectric material. (reflection at the interface between the thin film and the base material), by reducing the phase difference of the light to 1/2 wavelength, the reflected light can be mutually canceled, or even if the material has a sufficiently lower refractive index than the base material. Even a single layer has high antireflection ability.There are no organic polymer compounds with such a low refractive index, so it is difficult to construct a single layer with sufficient performance, but two layers There are two methods for anti-reflection coating: one is to stack a quarter-wavelength film, and the other is to stack a film with an undefined thickness. and,
A layer with a low refractive index material having a thickness of 1/4 wavelength, and the interface between the low refractive index layer and the high refractive index layer with a phase shift of 1/2 wavelength to reflect light on the surface of the low refractive index layer. In addition, the reflected light at the interface between the high refractive index layer and the base material cancels each other out.4 Therefore, the reflected light for a single wavelength light incident at 0 degrees becomes zero (if the following formula is satisfied) Here, n・, nl, n2.nl is air, base material,
Low refractive index material High refractive index material refractive index, for example n
5=l, n5=1. 49 (polymethyl methacrylate), rz=1. 39 (poly 2,2°3, 4.4.4-hexafluorobutyl acrylate), n2=1. 70 (poly 2N-rubazolyl acrylate) was obtained, making it possible to use a polymer composition.

The latter ζ is the superposition of the reflected light at the upper interface with the air and the reflected light at the interface between the upper and lower layers and the lower layer and the base material, which have different amplitudes or phases. The design is somewhat difficult, but it is also possible to create an anti-reflection film by laminating more layers.Also regarding multiple reflections of light. However, even if the optimum material composition has been selected through simulation, a selective light reflecting film (as shown in Figure 1, a low refractive index material 2 or 3 on a base material 1) and high refractive index material 3 or 2 at a quarter wavelength.

The reflectance that can be obtained is given by the following equation.

However, nH, nL, and nl are high refractive index layers and low refractive index materials refraction 1. N is the number of laminated layers. For example ('L refractive index 1.6
By laminating 12 layers of trifluoroethyl acrylate/acrylic acid copolymer with a refractive index of 1.42 and pentabromophenyl methacrylate/acrylic acid copolymer with a refractive index of 1°68 on the polyethylene terephthalate film of No. 5, A so-called interference filter such as a band-pass filter that can obtain a reflectance of 50% or more is used.Depending on its characteristics, it is also called a monochromatic filter or a bandpass filter.A monochromatic filter with high wavelength selectivity - 1/4 It can be obtained by accumulating a wavelength laminated film, a half wavelength film, and a quarter wavelength laminated film, and bandpass filters can also be constructed by various combinations (H, A,
Matsufreaud, “Optical Thin Film Elements”, translated by Shigetabe Ogura et al., Nikkan Kogyo Shimbunsha (1969).

The problems that arise when attempting to construct these thin-film optical elements using polymer compositions are that (i) there is no easy lamination method; and (ii) polymer compositions have a large refractive index. In order to obtain an element with sufficiently high performance, the number of laminated layers becomes large.The problem in (a) above is that the form of the polymer composition to be laminated must be selected; In other words, polymer compositions with different refractive indexes are selected from water-insoluble and water-soluble ones, and each is made into a non-aqueous solution or an aqueous solution, or both are made into an aqueous dispersion, and the layers are laminated by repeating coating and drying. is possible and solved.

In addition, the above problem (b) will no longer be a problem due to the simplification of the lamination method itself.4 Next, we will explain the specific manufacturing method and materials for the thin film optical element of the present invention. It is constructed by laminating polymer compositions with different refractive indexes, and the most commonly used base materials include various types of glass, organic glasses such as PMMA, and transparent films such as polyethylene terephthalate. However, there is no particular limitation on the refractive index.Since the difference in the refractive index of the polymer composition is not large, the influence of the refractive index of the base material on the performance of the optical element is not very large, so the degree of freedom is Great strength It is necessary to pay close attention to the adhesion of the laminated polymer composition.Furthermore, when it is constructed on a film-like base material with high flexibility, i! Interference occurs due to multiple reflections within the film itself, so care must be taken with its thickness (~ In the visible light range, if the thickness is 30 microns or more, there will be no effect (as a polymer composition with different refractive index) (It is sufficient if there is a difference in refractive index between the material constituting the low refractive index layer and the material constituting the high refractive index layer.) The polymer composition used may be one containing a polymer compound as a composition, for example, the refractive index A low-molecular-weight compound dissolved in a high-molecular compound for adjustment may also be used (~ If the difference in refractive index of the polymer composition is small, the number of layers required to perform as a thin-film optical element will be large. Therefore, it is preferable to have a refractive index difference of 0.2 or more. 1.Xo Polypentabromophenyl methacrylate (
1,71), polyvinylcarbazole (1,68), polyvinylnaphthalene (1,68), polyethylene terephthalate (1°65), polyα-naphthyl methacrylate (1°64), polyorthochlorostyrene (1,6)
0), aromatic polymers such as polystyrene (1,59), and as polymeric compounds with relatively low refractive index (y) polyhebutafluorobutyl acrylate (1,37), polyfluoroethyl acrylate (1
, 41), polyvinyl acetate (1,47), polymethyl acrylate (1,47
), polyvinyl alcohol (1,49), polymethyl methacrylate (1,49), etc. Of course, other polymers and copolymers are also useful, and other than the addition polymers listed above. Of course, various condensation polymers such as polyamide, polyimide, polyester/k polycarbonate, and polyadducts such as polyurethane can be used, but it is also possible to use polymeric substances produced by reactions such as crosslinking of low-molecular compounds. Needless to say, in addition to the refractive index, points to keep in mind when selecting a polymer compound include the transparency method, temperature characteristics, and adhesion to the base material and other polymer composition. Even if it is sufficiently transparent as a thin film, if it is laminated, the transmittance may not be sufficient due to scattering, or the wavelength selectivity may be poor. Molecular compounds can be used without any particular limitations as long as they suit the purpose.
Compatibility with polymer compounds is related to the bleeding of low-molecular compounds, so care must be taken.
Of course, it is not necessary to use only one type of each type.A Also, in order to ensure adhesion to the base material, the bottom layer should have high adhesion, and in order to increase the surface hardness, only the top layer should be cured. An effective method is to use a plastic resin.

When laminating a polymer composition, the form of the polymer composition (solution or aqueous dispersion) must be selected depending on the water-soluble or water-insoluble nature of the material.Apply as a non-aqueous solution and dry. Materials that dissolve or swell in water or are coated as an aqueous solution are undesirable because they disturb the layer structure and disturb the layer structure even after drying. When the polymer compositions constituting the high refractive index layer are laminated in an aqueous dispersion state, the degree of freedom is large. When aqueous dispersibility is imparted by neutralization, layering is easy because it does not dissolve or disperse even if it comes into contact with an aqueous liquid again after coating and drying. It is necessary to adjust the amount of acid or base component in the polymer compound to coat the polymer composition for lamination.
Dipping methods include spin cord, dropping the coating liquid and then leaving it at an angle. If the base material is film-like and has high flexibility, methods such as gravure coach ink-rod coating and doctor roll coating are used. It is a method of drying the coated material.There are methods of drying with hot air and drying with infrared rays.In terms of mass production, the former is much more advantageous, but the thickness of the layer depends on the target. Settings can be made according to the design of the thin film optical element.The conditions for each lamination process can be determined by changing the conditions for each layer during lamination and measuring the optical properties. It would be effective to measure the optical properties after one layer has been applied and dry, and if there is a deviation, provide feedback to the coating conditions in real time. Binary star The support of the base material must be reliable I, ~
About the drying process after coating L Since the target film thickness is small, the solid content concentration of the coating liquid is small and the viscosity is usually quite low, so the conveyance direction of the substrate coated with the coating liquid should not be changed significantly in the vertical direction. In addition, when coating a long base material with a rod coater or gravure coater, etc., it is necessary to dry quickly. - By processing the film thickness distribution in the direction perpendicular to the coating direction, the curing method when using a curable resin as the top layer of a thin film optical element is as follows: Curing of the curable resin All you have to do is follow the method and irradiate it with ultraviolet rays, heat it for a long time, or irradiate it with an electron beam. X.

If the heat resistance of the layer-constituting material is not sufficient for long periods of time, the layer structure may be disturbed, so it is convenient to use a photocurable resin.

Next, we will explain the head-up display, but as shown in Figure 2, the head-up display is commonly understood.
Fluorescent display t A light-emitting display device 11 such as a CRT, a liquid crystal display element equipped with a light-emitting light source, or a laser scanner transmits external light and reflects light from the light-emitting display device, thereby displaying an external light to the viewer. A combiner 12 installed in front of the canopy or windshield 15, or installed integrally with the canopy or windshield 15, for display superimposed on the front field of view.
Furthermore, depending on the case, the light emitting display device may be composed of optical elements such as a reflecting mirror 13 for changing the optical path and a condenser lens 14 for displaying a display image at a distance from the actual light emitting display device. It is preferable to have a small size, and from the viewpoint of display visibility, one with high brightness is preferable. Possible installation locations include the installation location of instruments in aircraft and automobiles, and above the head of the pilot or driver. There are two main types of combiners: the half-mirror type and the holographic optical element type.

Half mirror type! ,, A highly reflective metal is placed on a transparent base material in a very thin layer to obtain a reflectance or transmittance of about 30 to 70% over the entire visible light range, and the other is a metal with a high reflectance placed on a transparent base material to obtain a reflectance or transmittance of about 30 to 70% over the entire visible light range. 4. Holographic optical element type GEL that obtains high reflectance (low transmittance) in a specific wavelength range and high transmittance (low reflectance) in other wavelength ranges by laminating dielectric materials with different coefficients.
It uses a reflection-type hologram, and it not only has the function of selectively reflecting light, but also has a lens function that changes the position of the virtual image projected via the combiner, so it has a large space-saving effect and is highly functional. Although it is good for
However, it is difficult to reproduce, so each sheet must be exposed and developed, and although it is expensive, the combiner is installed in a position in front of the operator and the driver, and directly in the line of sight of the operator and the driver toward the outside. . As a result, it may be installed on the front side of the canopy or windshield, or the canopy
Although the mainstream method is to integrate it with the canopy or windshield, there are several methods to integrate it with the canopy or windshield.Method of adhering to the surface Method of using the canopy or windshield itself as a base material for thin film optical elements Laminated glass structure In the case of a windshield that has a When standing in front of glass (for example, when glass or organic glass that is thick enough to ensure sufficient rigidity is integrated by gluing or sandwiching) It is advisable to select an adhesive that has flexibility (~especially when adhering to the surface of a canopy or windshield).Polymer film has good workability and is preferable. There are no particular limitations as long as the adhesiveness is sufficient (- Also, when bonding optical elements to make a combiner,
In order to protect the optical element, it is preferable to coat the surface with a photothermal or electron beam curable resin, and the coating method is as shown in Fig. 3, where the curable resin 23 is applied to the area where a thin film is laminated on the base material 21. In order to suppress peeling, it is preferable to use a flat plate when incorporating an optical element between the optical path of the light emitting display device and the combiner. 5. Various types of mirrors and lenses such as concave mirrors and lenses may be used.More specific examples will be shown below.

Example 1 A 2% aqueous solution of polyvinyl alcohol (Kuraray Poval 420) and a 2% tetrahydrofuran solution of polyvinylcarbazole were alternately spin-coated and dried onto a 1 m thick and 10 cm square Pyrex 7740 substrate with a well polished surface.Incidence angle 45 degrees, wavelength 5
Example 2 The reflection U at 45 degrees of incidence of a thin film optical element made in this way, in which a total of 14 layers of quarter wavelength films for 50 nm were laminated, was 40.5%. Transparent film It'- made of polyethylene terephthalate, an aqueous dispersion with a solid content of 2% made by neutralizing a trifluoroethyl acrylate/acrylic acid copolymer with ammonia, and a solid made by neutralizing a naphthyl methacrylate/acrylic acid copolymer with triethylamine. A 2% aqueous dispersion was coated for 1000 m at a speed of 10 m/min using a coater equipped with a coating rod wound with a wire of 50 micron diameter at an incident angle of 2.
Two layers with different refractive indexes with an optical thickness of 1/4 wavelength for 0 degrees and a wavelength of 550 nm were provided.This process was repeated 5 times to create a total of 12 layers of selective light reflection films, resulting in 9 selective light reflections. Variation in center wavelength of light (application width 20cm)
The inner 18cm of m is 10nm above and below.

The average reflectance is 47%, and the variation in this is up and down.
Example 3 After laminating 13 layers of polyvinyl alcohol and polyvinyl carbazole in the same manner as in Example 1, a photocurable resin was finally applied for a quarter wavelength in a nitrogen atmosphere and irradiated with ultraviolet rays. Example 4 The same performance as Example 1 was obtained.The thin film optical element produced in Example 1 was placed in front of the windshield of a car and used as a combiner.The light reflected by the combiner was reflected from the driver's viewpoint. A fluorescent display tube was installed in the same direction as above to create a head-up display.Example 5 The thin optical element film produced in Example 2 was used as a head-up display. Using the thin optical element film of Example 2 as is, the laminated side of the thin optical element film of Example 2 was adhered to the inside of the windshield of a car to prepare a combiner. After applying the photocurable resin, we applied an anaerobic adhesive to the back side of the thin optical element film obtained by irradiating it with ultraviolet rays and curing it, so that it would not stick to the inside of the car windshield. Comparative Example 1 Polytrifluoroethyl Acrylate toluene 2-
I tried to apply a layered mixture of a butanone mixed solution and a 2-butanone solution of polyvinylnaphthalene in the same manner as in Example 1, but when I applied it later, it seemed that the layer under the part where the solution was dropped had dissolved. This results in a layered structure in which the transmitted image is distorted (9) As described above (2) Alternating one or more layers each of polymer compositions with different refractive indexes on a base material as a low refractive index layer and a high refractive index layer. By laminating a thin film optical element with a large area, it is possible to easily obtain a thin film optical element with a large surface area.By laminating one or more layers each of polymer compositions with different refractive indexes on a base material as a low refractive index layer and a high refractive index layer. A selective light reflecting thin film optical element formed by alternately laminating layers is used as a combiner;
Alternatively, the surface of a reflective hologram or thin film optical element made of plastic film can be coated with light or thermosetting resin (by bonding the base material side to a canopy or windshield to form a combiner, It is possible to easily provide a head-up display in which a combiner and a windshield are integrated.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a thin film optical element according to an embodiment of the present invention. Fig. 2 is a component of the head-up display. Fig. 3 is a cross-sectional view of a thin film optical element by plane. Material, 2...Low (high) refractive index material 3
... High (low) refractive index material K 11 ... Light emitting display device 12 ... Combiner, 13 ... Reflection mirror,
14... condenser lens, (15... windshield 21... base material, 22... thin film optical element, 23... curable resin agent name patent attorney Shigetaka Awano) or 1 person Mr. Town 1 (X) Ku Il'T To What Department Figure 2 Light Table 7F, Table I Combiner Anti-Rainbow Mirror - Contemporan Lens Windshield C

Claims (9)

[Claims] (1) A thin film optical element characterized in that one or more polymer compositions having different refractive indexes are alternately laminated on a base material as a low refractive index layer and a high refractive index layer. (2) One of the polymer compositions forming the low refractive index layer and the polymer composition forming the high refractive index layer is a water-insoluble polymer composition, and the other is a water-soluble polymer composition. The thin film optical element according to claim 1, characterized in that it is a molecular composition. (3) The thin film optical element according to claim 1, wherein the polymer composition forming the low refractive index layer and the polymer composition forming the high refractive index layer both contain a water-dispersible resin. (4) The thin film optical element according to claim 1, wherein the polymer composition forming the uppermost layer laminated on the base material contains a resin that is cured by light, heat, or electron beam. (5) A mixture of at least two types of a mixture of a polymer composition and a liquid forming a low refractive index layer and a mixture of a polymer composition and a liquid forming a high refractive index layer is applied onto a substrate. A method for manufacturing a thin film optical element, which comprises alternately coating, drying, and laminating. (6) The method for manufacturing a thin film optical element according to claim 5, wherein one of the mixtures is a non-aqueous solution and the other is an aqueous solution. (7) characterized in that both of the mixtures are aqueous dispersions;
A method for manufacturing a thin film optical element according to claim 5. (8) A selective light reflecting thin film optical element formed by alternately laminating one or more polymer compositions having different refractive indexes as a low refractive index layer and a high refractive index layer on a base material as a combiner. head-up display. (9) A selective light-reflecting thin film optical element in which the base material is a plastic film and the polymer composition constituting the uppermost layer laminated on the base material includes a resin that is cured by light, heat, or electron beam, is attached to the canopy. 9. The head-up display according to claim 8, wherein the head-up display is bonded to the surface of a windshield to form a combiner.