JPH02245702A - Anti-reflection film and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain an antireflection film of a large area at a low cost by laminating coating layers different from each other an mixing ratio between the constituents to form a film whose refractive index changes continuously. CONSTITUTION:A glass substrate, MgF2 as a substance having the lowest refractive index and a substance having a refractive index between the refractive index of the glass substrate and that of MgF2, e.g., SiO2 are prepd. Superfine SiO2 particles 2 are mixed with superfine MgF2 particles 1 and the glass substrate 3 is coated with the mixture while changing the mixing ratio in the direction of the thickness of the resulting film. The amt. of the SiO2 particles 2 is gradually reduced from the surface of the substrate toward the surface of the film and the malt of the MgF2 particles 1 is gradually increased. The change of refractive index at the interface between the film and the glass substrate is made gradual, a significant antireflection effect is produced and an antireflection film of a large area is formed at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus using an ultrafine particle film, and particularly to a film effective as an antireflection film for cathode ray tubes.

[Conventional technology]

Research on films that reduce the reflectance of glass surfaces (anti-reflection films) has been going on for a long time, and they have been used in lenses for cameras and glasses. There are various types of anti-reflection films used in anti-reflection filters to reduce reflected light from VDTs, but the ones currently in use are mainly multilayer films and non-uniform films. It is a membrane.

A multilayer structure is a structure in which low refractive index materials and high refractive index materials are alternately laminated on the glass surface, and its antireflection effect is the overall effect of optical interference between each layer. Regarding multilayer films, Physics of Spin Film No. 2 (1
964) Section 243 (Physics of Th1
n Fil+ms 2 , (1964) P.

243-P, 284) to 284.

Further, a film having a refractive index distribution in the thickness direction of the film is called an inhomogeneous film, but if the average refractive index of this film is lower than that of the substrate glass, it becomes an antireflection film. Inhomogeneous membranes generally have a porous glass surface. A method of reducing reflectance by forming an inhomogeneous film by forming fine irregularities by sputter etching after forming an island-shaped metal vapor deposited film on the glass surface is described in Upward Physics Letter No. 36 (1980). Paragraphs 727 to 730 (Appl, Phys,
Lett.

36 (1980) P, 727-P, 730). In addition, 5iOz of Zodarime glass
Solar Energy, 6
(1980), paragraphs 28 to 34 (Solar
Energy 6 (1980) P.

28-P, 34).

[Problem to be solved by the invention]

In the prior art, the multilayer film can be formed only by sputtering or vacuum evaporation, and requires highly accurate control of the film thickness, so there are problems in that it is expensive and difficult to increase in area. The method of forming a heterogeneous film by sputter etching also has the problems of high cost and difficulty in increasing the area.

The method of forming a heterogeneous film by immersing it in a HzSiFe solution and making the surface porous makes it difficult to form fine irregularities and does not provide a sufficient antireflection function. At the same time, there was a problem in that the transmittance also decreased.

An object of the present invention is to form an antireflection film that is low cost and easy to increase in area.

[Means to solve the problem]

Reflection of light occurs at an interface where the refractive index changes suddenly, so if the refractive index changes gradually at the interface, reflection will no longer occur.Normally, the most effective way to prevent reflection of soda glass (refractive index of approximately 1.53) is to Substance with low reflectance Magnesium fluoride (Mg
Mg
The antireflection effect is not sufficient because the refractive index changes suddenly at the interface between the Fz film and air (refractive index approximately 1.0).Therefore, the refractive index gradually changes from a refractive index close to that of the glass substrate to a refractive index close to that of air. If a film can be formed, an effective antireflection effect can be obtained.

Therefore, a substance with a refractive index between that of a glass substrate and MgFs, for example, ultrafine particles of 5ift (refractive index 1.46) and ultrafine MgFz particles are mixed and coated on a glass substrate, and the mixing ratio is adjusted in the film thickness direction. In other words, by gradually decreasing the mixing ratio of 5iOz ultrafine particles and increasing the mixing ratio of MgFx ultrafine particles from the glass substrate surface to the coating film surface, the refractive index change at the interface between the coating surface and the glass substrate becomes more gradual. Therefore, an effective antireflection effect can be achieved. Moreover, by this method, a large-area antireflection film can be formed at low cost.

[Effect]

A substance with a refractive index close to that of the glass substrate (e.g. 5iOz)
and a substance with a refractive index close to that of air (e.g. MgFz)
By using ultrafine particles when mixing both substances, it is possible to uniformly mix both substances at a level smaller than the wavelength of light. Therefore, its refractive index becomes an average refractive index corresponding to the volume fraction of 5ift and MgFx. That is, 5if
In an ultrafine particle film in which t ultrafine particles and M g F x ultrafine particles are mixed, the average refractive index n (x) at a position in the film thickness direction Then, n(x)=1.46X
It can be shown as V(s)+1.38X(1-v(s)). Therefore, if the mixing ratio is changed in the film thickness direction, the refractive index will also change correspondingly, and the refractive index change at the interface between the glass substrate and the coating film will be gradual.

Furthermore, by stacking coating films having different mixing ratios, it is possible to form a film whose average refractive index gradually carbonizes as a whole.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a cross-sectional view when an ultrafine particle film of the present invention is formed on a glass substrate, and FIG. 2 is a diagram showing changes in the average refractive index of the ultrafine particle film in the film thickness direction.

First, 5iOz ultrafine particles were added to a solvent in which ethyl silicate (Si(OCzHδ)4) was dissolved in ethanol, water, nitric acid, isopropyl alcohol, and acetylacetone were added, and the particles were thoroughly dispersed by ultrasonic vibration.
The amount of S x Oz ultrafine particles is, relative to the above solvent IQ,
After dispersing the a SiOx ultrafine particles to 25 g, citraconic acid was further added and sufficiently dissolved. The amount of citraconic acid was expressed as a log of the above solvent IQ. Thereafter, ultrasonic vibration was further applied, and the solvent was designated as solvent A after 0 or more mixing was completed in order to achieve sufficient dispersion of the 5ift ultrafine particles and sufficient mixing of each component.

Solvent B, in which M g F x ultrafine particles and ethyl silicate had been previously dispersed in ethanol, was added to the above solvent A and mixed uniformly by ultrasonic vibration. The amount of M g F x ultrafine particles in solvent B is approximately 25 g relative to solvent IQ.
It is. By changing the mixing ratio of solvent A and solvent B, 5iOa
The mixing ratio of ultrafine particles and M g F z ultrafine particles is changed.

First, a mixture of solvent A and solvent B was dropped onto the glass plate surface so that the volume fraction of 5i01L ultrafine particles and M g F z ultrafine particles was 7:3, and the mixture was evenly applied using a spinner. Thereafter, the coating film was dried by keeping it at 40° C. for about 10 minutes in air. After drying, a solvent containing 5 iOz ultrafine particles and M g F z ultrafine particles mixed at a volume fraction of 1:1 was further added dropwise and uniformly applied using a spinner. after that.

The a M g F z ultrafine particles and 5ift ultrafine particles obtained by firing in air at 160°C for 45 minutes to thermally decompose ethyl silicate and 5ift ultrafine particles are firmly fixed on the glass substrate by 5i (lz) generated by thermal decomposition. Ru.

When the cross section of the ultrafine particle film thus formed was observed with an electron microscope, as shown in Figure 1, the ratio of 5iOz ultrafine particles to MgF'2 ultrafine particles was 7:3, and the PPI <first layer) was approximately 0. .1μm, 1:1 layer (second layer) is about 0.1μm, total film thickness is about 0.2μm, 5ins ultrafine particles and MgFx ultrafine particles are uniformly mixed, and the densely deposited film is N1. ! It was noticed.

Figure 2 shows the results of calculating the change in average refractive index in the film thickness direction of the above ultrafine particle film from the volume fractions of 5iOz ultrafine particles and M g Fx ultrafine particles, where a is the refractive index of air and is approximately 1. .0b is the refractive index of the first layer, which is approximately 1.42, and C is the refractive index of the second layer, which is approximately 1.44.degree.d is the refractive index of soda glass, which is approximately 1.53.

Since the refractive index of the film as a whole changes gradually, it has the effect of reducing the reflectance at the interface between the coating film and the glass substrate. Furthermore, since the film is formed of ultrafine particles, minute irregularities occur on the surface of the coated film, resulting in a reduction in reflection on the surface of the coated film.

A wavelength of 400 to 700 was applied at an incident angle of 5° to the glass substrate on which the above ultrafine particle film was formed and the untreated glass substrate.
3 nm light was incident, and its reflectance was measured, and the results are shown in Figure 3. In IIA, ■ is the reflection characteristic of the glass plate on which the above ultrafine particle film was formed, and ■ is the reflection characteristic of the untreated glass plate. It is.

In the entire wavelength range, the antireflection film of the present invention has a reflectance reduced to about 1/4 of that of an untreated glass plate.

Furthermore, when the transmittance is expressed as an integral value between wavelengths of 400 to 700 nm, the untreated glass plate has a transmittance of 92%, whereas the glass plate coated with the antireflection film of the present invention has a transmittance of about 86%. VDT (
It is suitable as an antireflection coating for visual display terminals).

In this example, two layers were used with different mixing ratios, but if more layers were used and the average refractive index was changed in smaller increments, the antireflection effect would further increase.

〔Effect of the invention〕

According to the present invention, it is possible to form a film with a continuously changing refractive index by repeating a simple coating method, so that an anti-reflection film can be manufactured at low cost, and furthermore, a large-area anti-reflection film can be easily formed. There is.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an antireflection film according to an embodiment of the present invention, and FIG.
The figure shows the change in refractive index of the anti-reflection film in the film thickness direction, and Figure 3 shows the reflectance between the anti-reflection film of one embodiment of the present invention and an untreated glass plate in the wavelength range of 400 to 700 nm. FIG.

Claims (1)

[Scope of Claims] 1. An antireflection film mainly composed of ultrafine particles, characterized in that two or more types of ultrafine particles coexist, and the mixing ratio thereof changes in the film thickness direction. 2. In an antireflection film mainly composed of ultrafine particles, there are two thin layers in which two or more types of ultrafine particles coexist and their mixing ratios differ.
An antireflection film characterized by being formed of more than one layer. 3. In the method of forming an anti-reflection film mainly composed of ultrafine particles, two or more types of ultrafine particles are mixed, and thin layers with different mixing ratios are laminated to vary the mixing ratio of the ultrafine particles in the film thickness direction. A method for producing an antireflection film characterized by: