Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1998-11-25
2001-09-04
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C359S360000, C359S580000, C359S586000, C359S588000, C359S589000, C428S212000, C428S216000, C428S336000, C428S343000, C428S344000, C428S428000, C428S697000, C428S699000, C428S701000, C428S702000
Reexamination Certificate
active
06284382
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an antireflection film and a manufacturing method thereof, and particularly to an antireflection film formed by stacking silicon oxide films and indium tin oxide films in multilevels, and a manufacturing method thereof.
In general, an antireflection film of a stacked structure having conductive films has been formed by alternately stacking, on a base film, films each having a larger refractive index and films each having a small refractive index. In many cases, the film having a small refractive index has been made from silicon dioxide (hereinafter, referred to as “SiO
2
”) and the film having a larger refractive index and an electric conductivity has been made from indium tin oxide (hereinafter, referred to as “ITO”). For example, there has been known an antireflection film formed by stacking, on a resin base film, an ITO film, a SiO
2
film, an ITO film, a SiO
2
film, and a contamination preventive film in this order.
However, the antireflection film used to be stuck on the surface of a glass panel of a CRT (Cathode Ray Tube), for example, a Braun tube, is required to satisfy the following characteristics:
(1) The adhesive strength to a resin base film must be sufficient large. In this case, the adhesive strength is measured for the antireflection film after being left for two hours in an atmosphere in a high temperature (for example, 60° C.) and a high humidity (98%) or after being repeatedly subjected to five cycles of heat history between +70° C. (five hours) and −40° C. (five hours).
(2) The reflectance characteristic (average reflectance to light having a wavelength of 450 nm to 650 nm) must be as sufficiently small as 0.6% or less.
(3) The electric resistance (to ensure electromagnetic shielding and antistatic characteristic) must be 500 &OHgr;/□ or less.
(4) The transparency must be large. More specifically, the total light transmittance (to light having a wavelength of 450 nm to 650 nm) must be 90% or more.
In summary, the antireflection film used for a glass panel of a CRT is required to simultaneously satisfy the above inconsistent characteristics (1) to (4).
The above-described related art antireflection film having the stacked structure of ITO/SiO
2
/ITO/SiO
2
is generally difficult to simultaneously satisfy the items (1) to (4). To be more specific, the related art antireflection film allowing to satisfy them can be manufactured at the expense of the manufacturing yield, which results in the increased manufacturing cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an antireflection film which is stuck on the surface of a glass panel of a CRT, and which can be inexpensively manufactured at a high productivity while satisfying all of requirements regarding its adhesive strength, reflectance characteristic, electric resistance and total light transmittance, and to provide a manufacturing method thereof.
To achieve the above object, according to a first aspect of the present invention, there is provided an antireflection film including: silicon oxide films and indium tin oxide films stacked on a base film in multilevels, wherein the thickness of the uppermost silicon oxide film of the antireflection film is thicker than that of the indium tin oxide film directly under the uppermost silicon oxide film. In the above antireflection film, preferably, the lowermost silicon oxide film, positioned at the interface with the base film, of the antireflection film is a SiO
x
film where the value x is in a range of 0.5 to 1.9.
In the above antireflection film, since the thickness of the uppermost silicon oxide film is thicker than that of the indium tin oxide film directly under the silicon oxide film, light absorption of the indium tin oxide film becomes small, so that a reduction in total light transmittance becomes small. As a result, it becomes easy for the antireflection film to ensure the total light transmittance capable of satisfying an allowable value (for example, 90% or more). Also since the SiO
x
film is provided as the lowermost film, positioned at the interface with the base film, of the antireflection film and the value x of the SiO
x
film is specified to be in a range of 0.5 to 1.9, it is possible to suppress a reduction in total light transmittance in a range of about 0.5% to 2.5% while ensuring a sufficient adhesive strength of the antireflection film.
According to a second aspect of the present invention, there is provided a method of manufacturing an antireflection film, including the step of: stacking silicon oxide films and indium tin oxide films on a base film in multilevels, wherein the thickness of the uppermost silicon oxide film of the antireflection film is thicker than the indium tin oxide film directly under the uppermost silicon oxide film. The above method preferably further includes the step of forming the lowermost silicon oxide film of the antireflection film while controlling the degree of oxidation of silicon by measuring light absorption of the silicon oxide film. Also the above method preferably further includes the step of allowing, before formation of the lowermost silicon oxide film, the surface of the base film on which the lowermost silicon oxide film is to be formed to undergo surface activation treatment due to glow discharge using an aluminum electrode. In the method, preferably, the films constituting the antireflection film are formed using a dual magnetron type sputtering system.
In the above manufacturing method, since the silicon oxide (SiO
x
) film is formed while the degree of the oxidation of silicon is controlled by measuring light absorption of the silicon oxide film, it is possible to ensure a sufficient adhesive strength to the base film and also keep the total light transmittance of the antireflection film at a specific value or more. Also since before formation of the SiO
x
film, the surface of the base film on which the SiO
x
film is to be formed is subjected to glow discharge treatment using an aluminum electrode, it is possible to enhance the adhesive strength of the antireflection film to the base film. Further, since the films constituting the antireflection film are formed using a dual magnetron type sputtering system, each film thus formed is of a multilayer structure in which thin layers each containing oxygen in a large amount and thin layers each containing oxygen in a small amount are stacked densely in multilayers. As compared with a multilayer structure in which layers each containing oxygen in a large amount and layers each containing oxygen in a small amount are coarsely stacked in multilayers or a multilayer structure having layers each containing oxygen in the same amount, the above multilayer structure according to the present invention is advantageous in that stress is easily dispersed and propagation of breakage is obstructed by the interface of each layer, with a result that the film having such a multilayer structure is less susceptible to breakage. On the other hand, in the multilayer structure in which the layers are coarsely stacked or where the layers each contain the same amount of oxygen, since stress is less dispersed, the film, as a result, is susceptible to breakage.
Accordingly, since the antireflection film of the present invention can satisfy all of requirements regarding its adhesive strength, reflectance characteristic, electric resistance, and total light transmittance, it contributes to manufacture of a high quality CRT.
Further, according to the present invention, the antireflection film capable of satisfying all of requirements regarding its adhesive strength, reflectance characteristic, electric resistance, and total light transmittance can be manufactured at a high yield as compared with a related art method. This contributes to manufacture of a high quality CRT at a low cost.
REFERENCES:
patent: 5362552 (1994-11-01), Austin
patent: 5972517 (1999-10-01), Kondo et al.
Honjo Yoshiharu
Ishikawa Hiroichi
Kaneko Koichi
Kobayashi Tomio
Lippey Barret
Jones Deborah
Kananen Ronald P.
Miranda Lymarie
Rader Fishman & Grauer
Sony Corporation
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