JPH076612A - Multilayer film reflecting mirror - Google Patents

Abstract

PURPOSE:To have a characteristic excellent in heat resistance and moisture resistance, and make a mirror be applied to a high-output and long-life type light source. CONSTITUTION:The thin film of zinc sulfide as a high-refractive index film and the thin film of strontium fluoride as a low-refractive index film, are alternately laminated to form a ZnS-SrF2 multilayer film 4 filmed on a reflecting mirror 5 adopted. This constitution can provide the reflecting mirror 5 having a characteristic excellent in heat resistance and moisture resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer film reflecting mirror used for floodlighting and the like, and more particularly to a multilayer film reflecting mirror having improved durability.

[0002]

2. Description of the Related Art Conventionally, a multilayer film which is coated as a thin film on the inner surface side of a glass substrate in a reflector for a halogen light bulb has a high refractive index film formed of zinc sulfide (ZnS) which is easy to obtain uniformity and is fluorinated. A low-refractive index film is formed of magnesium (MgF ₂ ) or silicon dioxide (SiO ₂ ), and an alternating layer in which these are alternately laminated is adopted as a multilayer film of a reflecting mirror, and is mounted as a light source in the center of a halogen bulb. Visible light from the halogen lamp is reflected by the reflecting mirror, and heat rays are transmitted through the reflecting mirror.

By the way, since a ZnS-MgF ₂ -based multilayer film is excellent in moisture resistance but inferior in heat resistance, it has a relatively low heat load and a long life, such as a light source with a low output and a long life. Has been applied to. In addition, ZnS-Si
Since the O ₂ -based multilayer film has excellent heat resistance but poor moisture resistance, it is applied to a light source that has a high heat load and a short life, such as a high-output / short-life halogen lamp.

[0004]

However, the above-mentioned multilayer film reflecting mirror is suitable according to the performance of the light source because the multilayer film has a defect in either heat resistance or moisture resistance. There is a problem that it is necessary to select and use one, and in recent years, as the output of light sources and the lifespan of light sources have increased, multilayer films excellent in both heat resistance and moisture resistance have been developed. It has been requested.

The present invention has been made in view of the above circumstances, and provides a multilayer-film reflective mirror which has excellent heat resistance and moisture resistance and can be applied to a high-power long-life light source. With the goal.

[0006]

In order to achieve the above object, the present invention provides a thin film of zinc sulfide as a high refractive index film and a thin film of strontium fluoride as a low refractive index film on a reflective substrate having a curved surface. Is alternately laminated.

[0007]

Since the present invention is constituted as described above, the multilayer-film reflective mirror has excellent heat resistance and humidity resistance, and can be sufficiently applied to a high output / long life type light source.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 is a glass substrate, for example, a glass substrate of a reflector for a halogen light bulb, and one surface is formed by a concave surface 2 which is a paraboloid of revolution. A halogen lamp 3 is installed as a light source in the center of the concave surface 2.
Further, a multi-layer film 4 as a highly durable thin film is coated on the concave surface 2 to form a reflecting mirror 5. The visible light emitted from the halogen lamp 3 is reflected by the multilayer film 4 coated on the reflecting mirror 5, and the multilayer film 4 through which the heat rays pass through the reflecting mirror 5 is
It is a ZnS-SrF ₂ based multilayer film in which 21 layers of a high refractive index film (H) made of zinc sulfide (ZnS) and a low refractive index film (L) made of strontium fluoride (SrF ₂ ) are alternately laminated. That is, at a design wavelength of λ ₁ = 600 nm, a total of 12 layers of H ₁ and L ₁ having an optical film thickness of ¼ λ are alternately laminated, for a total of 12 layers, and then on top of this, a design wavelength of λ ₂ = 450 nm is used. This is a multilayer film 4 in which H ₂ and L ₂ having a film thickness of ¼λ are alternately laminated in a total of 8 layers of 4 layers each, and further 1 layer of H ₂ is further added to laminate a total of 21 layers. This multilayer film 4 is formed by a vacuum evaporation method. (1) Degree of vacuum 1 × 10 ^{−4 to} 5 × 10 ⁻⁴ Torr (2) Substrate temperature 150 to 250 ° C. (3) Evaporation source Electron beam (electron gun) evaporation conditions It was formed into a film.

Then, after the vapor deposition of the multilayer film 4 is completed, the multilayer film 4 is
The reflecting mirror 5 on which is vapor-deposited is heated from 400 ° C to 520
Heat resistance and humidity resistance were evaluated for the one obtained by curing the multilayer film 4 by performing a baking treatment for 1 hour in an oxidizing atmosphere at a temperature of 20 ° C. in the temperature range up to ° C. The ZnS-MgF ₂ -based multilayer film and the ZnS-SiO ₂ -based multilayer film are also formed in the same manner. Since the ZnS-SiO ₂ -based multilayer film is easily oxidized, the ZnS-MgF ₂ -based multilayer film is easily oxidized. The same evaluation was performed by performing the firing treatment in each of the reducing atmospheres. The evaluation results are shown in Table 1.

[0011]

[Table 1] The evaluation shown in Table 1 was performed by the following evaluation method.
That is, the heat resistance is allowed to stand in an electric furnace having a temperature of 440 ° C., and the film peeling occurrence time is investigated. Moisture resistance: left in an atmosphere of temperature 50 ° C, humidity 90%,
Investigate the peeling occurrence time of the film. These evaluations are shown in Table 1 in terms of film peeling occurrence time.

As is clear from Table 1, ZnS-SrF
_{The 2} type multi-layer film 4 is superior in heat resistance to the ZnS-MgF ₂ type multi-layer film, and is superior in moisture resistance to the ZnS-SiO ₂ type multi-layer film. It was found that it is excellent in both heat resistance and moisture resistance.

Further, regarding the ZnS-SrF ₂ -based multilayer film 4, the one which can obtain a durability of at least 100 hours in the heat resistance and humidity resistance test is set as a good product having no practical problem,
In order to establish the optimum firing temperature and time for obtaining this durability, the firing temperature range is expanded and the firing time is changed to 30, 60 and 90 minutes for each firing temperature. The heat resistance and humidity resistance were evaluated in detail by the same evaluation method. The evaluation results are shown in Table 2.

[0014]

[Table 2] In Table 2, those fired at 550 ° C. were excellent in heat resistance and humidity resistance, but film cracking was observed, so it was judged that there was a problem in practical use.

Therefore, as is clear from Table 2, although the temperature is slightly lower than the set standard in the baking treatment at the temperature of 400 ° C. for 30 minutes and 60 minutes, it is recognized as the error range of the test, and therefore, the optimum baking treatment condition is set. Firing temperature 400
It was found that a temperature of ℃ to 520 ℃ was established.

Next, with respect to the firing treatment of the ZnS—SrF ₂ -based multilayer film 4 in the atmosphere, that is, the firing treatment in the acidic atmosphere and the reducing atmosphere, ZnS—Sr was subjected to the same evaluation as above.
The heat resistance and moisture resistance of the F ₂ -based multilayer film 4 were evaluated, and the evaluation results are shown in Table 3.

[0017]

[Table 3] As is clear from Table 3, the evaluation results show that there is almost no difference in durability between firing in an oxidizing atmosphere and firing in a reducing atmosphere. In other words, it can be said that the ZnS—SrF ₂ -based multilayer film 4 is stable in firing in either atmosphere and more stable than the crystal system of the ZnS—MgF ₂ -based multilayer film or the ZnS—SiO ₂ -based multilayer film.

By the way, fluoride is generally oxidized by firing. For example, since MgF ₂ is oxidized into MgO, it has to be fired in a reducing atmosphere. However, since SrF ₂ has a stable crystal system and has a chemical characteristic that it is difficult to oxidize at 1000 ° C. or lower, it can be fired not only in a reducing atmosphere but also in an oxidizing atmosphere. It was confirmed from the above evaluation results. ZnS (refractive index 2.3) is an oxide ZnSO ₄ (refractive index 1.6) when fired in an oxidizing atmosphere.
However, it has been found that its oxidation does not affect the optical properties, while
It has also been found that the adhesion between thin films is enhanced.

As described above, the ZnS--SrF ₂ system multilayer film 4
Was found to be stable even when fired in an oxidizing atmosphere.

Further, ZnS has a characteristic that the wraparound is extremely good as compared with other high refractive index materials in the design of the multilayer film, and therefore even the glass substrate 1 having a curved surface is provided. A multilayer film 4 having a uniform thickness can be obtained. Moreover, Zn with a stable refractive index is used in electron deposition.
S and SrF ₂ are obtained, and Z having stable optical characteristics is obtained.
An nS-SrF ₂ -based multilayer film 4 is formed.

In the above embodiment, ZnS-SrF ₂
The system-based multilayer film 4 is applied to the reflecting mirror 5 for a halogen light bulb, but the present invention is not limited to this, and it is needless to say that it is also applicable to an optical multilayer film such as a bandpass filter, a cold mirror, and a color filter.

Further, although the coating film of the multilayer film 4 was formed by the vacuum vapor deposition method, the present invention is not limited to this, and other methods such as a sputtering method and an ion plating method may be used, and the same effect can be obtained. .

Further, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0024]

As described above in detail, according to the multilayer mirror of the present invention, the thin film of zinc sulfide as the high refractive index film and the thin film of strontium fluoride as the low refractive index film are alternately laminated. It has excellent characteristics in both heat resistance and humidity resistance, and has an effect that it can be sufficiently applied to a high-output, long-lifetime light source.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view of a halogen light bulb to which a multilayer-film reflective mirror of the present invention is applied.

[Explanation of symbols]

 4 ... Multilayer film 5 ... Reflecting mirror (multilayer film reflecting mirror)

Claims (1)

[Claims] 1. A multilayer-film reflective mirror, characterized in that a thin film of zinc sulfide as a high refractive index film and a thin film of strontium fluoride as a low refractive index film are alternately laminated on a reflective substrate having a curved surface.