WO2015011786A1

WO2015011786A1 - Optical component having nanoparticle thin film and optical application device using same

Info

Publication number: WO2015011786A1
Application number: PCT/JP2013/069944
Authority: WO
Inventors: 平田　浩二
Original assignee: 日立マクセル株式会社
Priority date: 2013-07-23
Filing date: 2013-07-23
Publication date: 2015-01-29
Also published as: JPWO2015011786A1

Abstract

An optical component has a thin film formed from inorganic nanoparticles (silicate, titanium oxide, and the like) with a particle diameter of substantially 15 nm or less on the surface of a base material containing plastic. The particle diameter of the nanoparticles within the thin film becomes smaller moving from the interface with the base material toward the surface of the thin film. The relative density of the nanoparticles is reduced moving from the interface with the base material toward the surface of the thin film by holes present within the thin film. By making the relative density of the nanoparticles on the surface of the thin film substantially 40% or less, the effective refractive index at the surface of the thin film is made smaller than the refractive index of the base material. Thus, an optical component having both abrasion resistance and water resistance as well as an antireflective effect is provided.

Description

Optical component having nanoparticle thin film and optical application apparatus using the same

The present invention relates to an optical component such as a lens having a nanoparticle thin film such as a silicate nanoparticle, and an optical application apparatus using this optical component.

In a projection-type image display device, which is one of optical application devices, the image displayed on a small image display element (liquid crystal panel or DMD (Digital Mirror Device: Texas Instruments Inc.)) is enlarged and projected onto a screen or the like with a projection lens. To do. In this case, an aspheric plastic lens is used as a projection lens in order to correct an aberration generated in an enlarged image projected on a screen (see Patent Document 1). Furthermore, there is also known a projection lens in which a plastic lens having a free-form surface having a large design freedom with respect to an aspheric surface is applied.

On the other hand, in recent vehicle lamps, a configuration in which an LED (Light Emitting Diode) is used as a light source and a light distribution characteristic is controlled using a plastic optical lens and a reflector (reflecting mirror) is becoming mainstream (Patent Document 2). ).

In addition, in a projection display apparatus using the above-described liquid crystal panel as an image display element, inorganic polarizing plates are provided on the incident side and the exit side of the liquid crystal panel in order to increase the brightness and contrast of the image. (See Patent Document 3)
JP 2006-78949 A JP 2003-317513 A JP 2009-3106 A

In the plastic lenses of Patent Documents 1 and 2, (1) the lens surface has low hardness and is easily damaged, (2) the plastic expands in volume and the refractive index changes, and (3) light on the lens surface. There are problems such as the occurrence of reflection loss. As a countermeasure, it is effective to form a protective film (antireflection film) on the surface of the plastic lens. However, when forming the protective film, it is necessary to evaporate below the heat distortion temperature of the plastic. An expensive manufacturing facility is required as compared with the vapor deposition apparatus.

On the other hand, the inorganic polarizing plate used in Patent Document 3 is generally a grid structure of a metal (aluminum) material, and (4) the polarization property changes due to moisture adhering to the metal surface due to condensation or the like (depending on the polarization) There is a problem that the characteristics are impaired. In addition, the plastic lens used in the vehicle lamp has a new problem due to the use environment such as (5) dirt on the surface of the vehicle, such as exhaust gas and dust, and the transmittance decreases. Also for these, it is required to form a protective film with simple equipment.

An object of the present invention is to provide an optical component in which a protective film having a desired performance is formed with simple equipment in order to solve the above-described problems.

In order to solve the above problems, the optical component of the present invention has a thin film made of inorganic nanoparticles having a particle size of approximately 15 nm or less on the surface of the substrate, and the particle size of the nanoparticles in the thin film is from the interface with the substrate It is characterized by decreasing toward the surface of the thin film and decreasing the relative density of the nanoparticles from the interface with the substrate toward the surface of the thin film due to pores existing in the thin film.

Further, the thin film has an effective refractive index depending on the relative density of the nanoparticles at each film thickness position, the relative density of the nanoparticles on the surface of the thin film is approximately 40% or less, and the effective refractive index on the surface of the thin film is It is characterized by being smaller than the refractive index of the substrate.

According to the present invention, it is possible to provide an optical component in which a protective film having a desired performance is formed with simple equipment.

The principal part sectional drawing which shows one Example of the optical component which has a nanoparticle thin film. The figure which shows the particle size distribution of the inorganic nanoparticle in a thin film. The figure which shows the effective refractive index of a silicate nanoparticle thin film. The figure which shows the effective refractive index of a titanium oxide nanoparticle thin film. The figure which shows the spectral transmittance of the plastic lens which formed the silicate nanoparticle thin film. The figure which shows the example of the optical system of the projection type video display apparatus 30 as an application example of an inorganic nanoparticle thin film. FIG. 7 is an enlarged cross-sectional view of the exit lens 34 in FIG. 6. The expanded sectional view of the reflective mirror 35 in FIG. The figure which shows the example of the lens for headlights used for a vehicle lamp as an application example of an inorganic nanoparticle thin film. The figure which shows the example of application to the Fresnel lens of an inorganic nanoparticle thin film. The figure which shows the example of application to the inorganic polarizing plate of an inorganic nanoparticle thin film.

Hereinafter, the present embodiment will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of an essential part showing an embodiment of an optical component having a nanoparticle thin film. Here, the structure of a thin film made of inorganic nanoparticles formed on a substrate of an optical component is schematically shown. The base material 10 is a plastic material for plastic lenses, for example, and a thin film 20 made of inorganic nanoparticles 21 is formed on the surface of the base material 10. The inorganic nanoparticles 21 are fine particles having high hardness such as silicate (silicate) and titanium oxide, and have a predetermined particle size distribution (average particle size 5-10 nm) with a particle size of approximately 15 nm or less. A first layer (L1) to which particles having a relatively large particle size are attached is formed at the interface with the substrate 10, and a second layer (L2) to which particles having a medium particle size are attached is formed thereon, A third layer (L3) to which particles having a small particle size are attached is formed on the surface portion in contact with air to form a laminated structure. Note that particles having a small particle diameter exist not only in the L3 layer but also in the gap between the L1 layer and the L2 layer.

There are gaps (holes) between the fine particles after adhering to the substrate 10, and the ratio of the holes (porosity) increases from the substrate to the surface (from the L1 layer to the L3 layer). ing. In other words, the volume density of the particles decreases from the substrate toward the surface. Hereinafter, the volume density is referred to as “relative density”. Here, the adhesion structure of the nanoparticles is schematically described, and since the particle size is continuously distributed, it is not necessarily separated into the L1 layer to the L3 layer and aligned and adhered as illustrated. The number of layers is also arbitrary.

Although the antireflection effect is obtained by the nanoparticle thin film as will be described later, the film thickness t of the thin film 20 is set to the vicinity of t = λ / 4 with respect to the wavelength λ of light in order to promote the effect. Thereby, the reflected light of the thin film surface and the reflected light of the base material interface cancel each other, and the reflectance can be reduced.

The formation of a thin film composed of such inorganic nanoparticles is performed as follows. Inorganic nanoparticles (silicate or titanium oxide) having a particle size of 15 nm or less are melted in a liquid containing volatile alcohol. The solution containing the nanoparticles is applied to the surface of the substrate, or the substrate is dipped in the solution. Thereafter, the film is dried to vaporize the volatile solvent, thereby forming a thin film in which nanoparticles are laminated and attached to the surface of the substrate. At this time, since particles having a large particle size are preferentially adsorbed to the substrate, the particle size decreases from the substrate toward the air interface as shown in FIG. 1, and the relative density of the nanoparticles changes. A film is formed. In this way, since the thin film is formed by a wet method such as coating or dipping, even a base material having low heat resistance such as plastic can be handled with simpler equipment than the vapor deposition method.

FIG. 2 is a diagram showing the particle size distribution of inorganic nanoparticles in the thin film. The horizontal axis is the particle size of inorganic nanoparticles (silicate, titanium oxide), and the vertical axis is the cumulative frequency. Since the cumulative frequency on the vertical axis is represented by the cumulative value of the detected particle volume (measured in the direction from small particle size to large particle size), the apparent frequency increases as the particle size increases. From this particle size distribution, it can be said that there are many particles having an average particle size of 5 to 10 nm (average particle size).

The optical component thus formed with the inorganic nanoparticle coating film has the following characteristics.
(1) By forming a high-hardness nanoparticle thin film on the surface of the substrate, the scratch resistance of the substrate (particularly plastic) is improved.
(2) By forming a dense nanoparticle thin film on which water molecules do not pass on the surface of the substrate, moisture absorption is prevented and volume expansion of the substrate (particularly plastic) is prevented.
(3) By reducing the relative density of the portion close to the surface (air interface) of the nanoparticle thin film, the effective refractive index can be reduced and the antireflection effect can be obtained. Hereinafter, the antireflection effect by the nanoparticle coating film will be mainly described.

FIG. 3 is a diagram showing the effective refractive index of the silicate nanoparticle thin film. The horizontal axis represents the relative density of nanoparticles (silicate), and the vertical axis represents the effective refractive index. Since the thin film formed as described above has vacancies, the effective refractive index in the thin film is the refraction index of the nanoparticles (silicate) (N1 = 1.42) and the refraction of the vacancies (air). It becomes an intermediate value of the rate (N0 = 1.0). Hereinafter, this refractive index is referred to as “effective refractive index”. For example, the effective refractive index when the relative density is 40% is Na = 1.3. That is, if the relative density in the thin film is changed in the film thickness direction and the relative density on the surface is 40%, the effective refractive index on the surface of the thin film is Na = 1.3.

In this case, the reflectance Ra on the thin film surface depends on the effective refractive index Na on the thin film surface,
Ra = {(Na−N0) / (Na + N0)} ² = 0.017 (1.7%)
It becomes.

On the other hand, if the refractive index of the plastic as the base material is 1.5, the reflectance without a thin film is 0.04, and the reflectance when the thin film is 100% of nanoparticles (silicate) is 0.03. It becomes. Therefore, the reflectance of the optical component (base material) can be greatly reduced by forming a thin film having a relative density on the surface of 40% or less.

Similarly, FIG. 4 is a diagram showing the effective refractive index of the titanium oxide nanoparticle thin film. The horizontal axis represents the relative density of nanoparticles (titanium oxide), and the vertical axis represents the effective refractive index. Also in this case, the effective refractive index is an intermediate value between the refractive index of the nanoparticles (titanium oxide) (N2 = 2.5) and the refractive index of the air holes (air) (N0 = 1.0). For example, when the relative density = 5%, the effective refractive index is Nb = 1.3.

In this case, the reflectance Rb on the thin film surface depends on the effective refractive index Nb on the thin film surface,
Rb = {(Nb−N0) / (Nb + N0)} ² = 0.017 (1.7%)
It becomes. Since the reflectance when the thin film is 100% of nanoparticles (titanium oxide) is 0.18, the reflectance of the optical component can be reduced by forming the nanoparticle thin film.

FIG. 5 is a diagram showing the spectral transmittance of a plastic lens formed with a silicate nanoparticle thin film. The horizontal axis represents wavelength and the vertical axis represents transmittance. In the absence of a thin film, the transmittance is about 92%, but by forming a silicate nanoparticle thin film, the reflectance can be reduced and the transmittance of the lens can be increased to about 98%. In this case, the transmittance in the region of 500 to 550 nm is improved as the wavelength dependency.

Next, some examples of optical components on which nanoparticle thin films are formed will be described.
FIG. 6 is a diagram showing an example of an optical system of the projection display apparatus 30 as an application example of the inorganic nanoparticle thin film. Reference numeral 31 denotes a liquid crystal panel as an image display element, 32 denotes a cross prism, 33 denotes a projection lens group composed of a plurality of lenses, 34 denotes an exit lens as the final stage of the

projection lens group

33, and 35 denotes a reflection mirror. The image light flux formed by the liquid crystal panel 31 is enlarged by the projection lens group 33 and is emitted from the exit lens 34. The emitted image light beam is reflected by the reflection mirror 35 and projected onto a screen or the like. In this example, the inorganic nanoparticle thin film is applied to the exit lens 34 and the reflection mirror 35 exposed to the outside air.

FIG. 7 is an enlarged cross-sectional view of the exit lens 34 in FIG. The exit lens 34 is a plastic lens, and silicate nanoparticle

thin films

20a and 20b are formed on the incident side and the exit side. As a result, the outgoing lens 34 is prevented from being scratched and moisture-absorbed, and the transmittance is improved by reducing the reflection loss on the surface as shown in FIG.

FIG. 8 is an enlarged cross-sectional view of the reflection mirror 35 in FIG. The reflection mirror 35 has a structure in which an aluminum metal film 12 is formed on a plastic or glass substrate 11, and the silicate nanoparticle thin film 20 is formed on the metal film 12. Thereby, the reflection mirror 35 can be prevented from being scratched and absorbing moisture.

FIG. 9 is a diagram showing an example of a headlight lens used in a vehicle lamp as an application example of an inorganic nanoparticle thin film. For example, the LED light source 13 was used and the silicate nanoparticle thin film 20 was formed on the emission surface of the plastic projection lens 14. This prevented the projection lens 14 from being damaged and absorbs moisture, and improved the transmittance by reducing the reflection loss on the surface as shown in FIG.

Note that the vehicular lamp is used in an environment where the optical characteristics are likely to deteriorate due to dust adhering to the lens surface or sulfide in the air. In such a case, by using titanium oxide as inorganic nanoparticles, in addition to the above effects, a unique effect of photocatalytic action by ultraviolet rays (self-purifying action by reacting with water molecules in the air) can be obtained and transmitted. It is possible to prevent a decrease in the rate, that is, a decrease in the intensity of the projection light.

FIG. 10 is a diagram showing an application example of an inorganic nanoparticle thin film to a Fresnel lens. The silicate nanoparticle thin film 20 was formed on the emission surface of the plastic Fresnel lens 15. Also in this case, the transmittance can be improved by preventing the Fresnel lens 15 from being scratched and absorbing moisture and reducing the reflection loss on the surface as shown in FIG.

FIG. 11 is a diagram showing an application example of an inorganic nanoparticle thin film to an inorganic polarizing plate. The inorganic polarizing plate 16 has a structure (wire grid structure) in which fine metal wires (aluminum) 18 are arranged at a predetermined interval on a glass substrate 17. And the silicate nanoparticle thin film 20 was formed in these surfaces. Thereby, damage and moisture absorption of the inorganic polarizing plate 16 can be prevented. In particular, deterioration of the surface of the fine metal wire 18 due to condensation (hydrolysis caused by moisture adhering to change polarization characteristics) is prevented, and reliability is improved. For example, when the endurance time until the thin metal wire 18 peeled in the boiling test was examined, the inorganic polarizing plate having the conventional structure without a thin film had an endurance time of about 40 minutes, whereas the inorganic polarizing plate of this example In 12 hours, the durability was significantly improved. In addition, although the inorganic polarizing plate 16 shown here is a reflection type, the same effect can be obtained by an absorption type structure in which a light absorbing material is provided on the upper part of the thin metal wire 18.

In the above embodiments, silicate or titanium oxide is used as the inorganic nanoparticle material. However, the material is not limited to this, and a high-hardness oxide or nitride can be appropriately used, or a composite material thereof may be used.

According to the above embodiment, a protective film made of silicate nanoparticles or titanium oxide nanoparticles can be formed on the surface of a light transmissive member including a plastic lens or an inorganic polarizing plate by a simple method and process using a wet method. By forming such a nanoparticle thin film, it is possible to provide an optical component having both scratch resistance, waterproofness and antireflection effect. Furthermore, by using such an optical component, it is possible to realize an optical application device such as a projection image display device having high luminance and high reliability.

DESCRIPTION OF

SYMBOLS

10,11 ... Base material, 12 ... Metal film, 13 ... LED light source, 14 ... Projection lens, 15 ... Fresnel lens, 16 ... Inorganic polarizing plate, 17 ... Crow base material, 18 ... Metal fine wire, 20 ... Inorganic nanoparticle coating Thin film, 21... Inorganic nanoparticles, 30... Projection type image display device, 31... Liquid crystal panel, 32.

Claims

Having a thin film made of inorganic nanoparticles having a particle size of approximately 15 nm or less on the surface of the substrate;
The particle size of the nanoparticles in the thin film decreases from the interface with the substrate toward the surface of the thin film,
An optical component having a nanoparticle thin film, wherein the relative density of the nanoparticles decreases from the interface with the substrate toward the surface of the thin film due to pores present in the thin film.
An optical component having the nanoparticle thin film according to claim 1,
The thin film has an effective refractive index depending on the relative density of the nanoparticles at each film thickness position,
An optical having a nanoparticle thin film, wherein the relative density of the nanoparticles on the surface of the thin film is approximately 40% or less, and the effective refractive index on the surface of the thin film is smaller than the refractive index of the substrate. parts.
An optical component having the nanoparticle thin film according to claim 2,
An optical component having a nanoparticle thin film, characterized in that the reflectance on the surface of the thin film is smaller than the reflectance of the substrate.
An optical component having the nanoparticle thin film according to claim 2,
An optical component having a nanoparticle thin film, wherein the thickness t of the thin film is formed to be approximately t = λ / 4 with respect to a wavelength λ of light used in the optical component.
An optical component having the nanoparticle thin film according to any one of claims 1 to 4,
An optical component having a nanoparticle thin film, wherein the inorganic nanoparticles include silicate or titanium oxide.
An optical component having the nanoparticle thin film according to any one of claims 1 to 4,
An optical component having a nanoparticle thin film, wherein the substrate includes plastic.
An optical component having the nanoparticle thin film according to any one of claims 1 to 6,
An optical component having a nanoparticle thin film, wherein the optical component is any one of a lens, a reflection mirror, and an inorganic polarizing plate.
An optical application apparatus using the optical component having the nanoparticle thin film according to any one of claims 1 to 7.