Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-09-14
2002-05-07
Ramsey, Kenneth J. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S402000
Reexamination Certificate
active
06384523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color selection electrode (color selection mask) having a finer pitch of apertures, a method of producing the same, and a cathode ray tube using the same.
2. Description of the Related Art
Picture tubes, called Braun tubes or CRTs (cathode ray tubes), are being widely used as television receivers or computer displays.
FIG. 8
is a cross-sectional view of a cathode ray tube. A container or tube comprises a panel
11
, a funnel
12
and an neck, and the inside of the container is vacuumed. In the neck part, an electron gun
14
is positioned which generates electron beam
15
. On the inside surface of the panel
11
, a phosphor screen
16
is formed. Inside the container, a color selection electrode
17
is placed before the phosphor screen
16
. A color picture tube has a color selection mask and a three-color (red, green, and blue) phosphor screen corresponding to the individual apertures on the color selection mask. The different color phosphors selectively emit light for color selection by the angle of incidence of an electron beam emitted from the electron gun to the color selection mask.
The color selection masks in actual use may be roughly classified according to the shape of the perforations into shadow masks having circular perforations and aperture grilles having slit-shaped (rectangular) openings, but are often also known generically as “shadow masks”.
For general television use, aperture grilles with slits of a width of about 200 to 250 &mgr;m arranged at a pitch of about 0.5 to 1.0 mm are often used (Trinitron system: Trade Mark of SONY CORPORATION).
In the case of a shadow mask, dot-shaped circular perforations of a diameter of about 200 to 250 &mgr;m are arranged regularly at about a 0.6 mm pitch. The smaller the pitch of the perforations, the higher the resolution, so as a color selection mask for a high definition cathode ray tube, a shadow mask with a pitch reduced to about 0.2 mm is used.
The ordinary method of-manufacturing a color selection mask will be explained below.
First, a resist is coated on an iron-alloy plate of about 100 to 300 &mgr;m thickness to form a resist film. Next, the resist is exposed and developed in accordance with the pattern of the color selection mask for resist patterning. The resist is then used as a mask for etching the iron-alloy plate to open the required apertures, then the resist is removed.
After the color selection mask is perforated by the etching, it is worked to shape it to a curved surface having a predetermined radius of ourvation. Next, it is heated at 400 to 500° C. and oxidized by reactive gas to blacken the surface. The blackening is to prevent random reflection.
The color selection mask manufactured by the above method is placed about 10 mm before the phosphor screen (electron gun side).
In the conventional method of manufacturing a color selection mask explained above, the mask is only perforated by the etching method. The general limit in fine working in the case of the etching method is about the same as the thickness of the worked plate in the case of the pitch of perforations and about 15% of the designated dimension in the case of the working precision.
Accordingly, when manufacturing a mask for a high definition cathode ray tube by the conventional method of manufacturing a color selection mask, the limit of fining of the pitch of the mask perforations becomes about the same as the thickness of the iron-alloy plate, that is, about 0.2 mm.
When manufacturing a mask for a high definition cathode ray tube by the above conventional method, since the limit of fining of the pitch of the mask perforations becomes about the thickness of the iron-alloy plate of the mask, finer mask perforations are generally formed by the method of making the thickness of the iron-alloy plate being worked thinner.
If just making a thin film, the instead of the conventional method of perforating a iron-alloy plate of a predetermined thickness by etching, it would be possible to make fine perforations precisely by forming a metal layer on portions other than the mask perforations by electrofineforming.
Japanese Unexamined Patent Publication (Kokai) No. 60-30038 discloses a shadow mask of a 100 &mgr;m thickness of the iron-alloy plate and about a 0.2 mm pitch of perforations manufactured only by electrofineforming without perforation by etching.
However, the mask apertures of the color selection mask must be tapered in cross-section so as not to obstruct a passing electron beam. When forming a color selection mask only by electrofineforming, it is difficult to give the fine mask apertures a tapered cross-sectional shape in a mask for a high definition cathode ray tube with a pitch of apertures narrower than the shadow mask described in the above Japanese Unexamined Patent Publication (Kokal) No. 60-30038. As shown in
FIG. 9
, the narrower the taper width (shown by “A” in
FIG. 9
) of the mask apertures and the closer the side walls of the mask apertures to perpendicular, the easier the occurrence of scattered electrons (halation) due to the random reflection of the electron beam at the inside surfaces of the mask perforations.
On the other hand, in the one-side etching method of etching from the side of the color selection mask which becomes the phosphor screen side, openings having the predetermined precision are formed by etching with slight over etching. As a result, especially when making the iron-alloy plate thin, the taper width shown in
FIG. 9
tends to become narrower.
Even if the taper width becomes narrower, not that much of the disadvantage arises in a color selection mask having a pitch of apertures of 0.6 mm or more, but in a color selection mask having a pitch of apertures of 0.4 mm or less, if the taper width becomes narrow, the above-mentioned halation may occur.
When making the iron-alloy plate of the mask thin, as explained above, not only does it become difficult to finely taper the cross-sectional shape of the mask apertures, but the disadvantage also arises in the mechanical strength of the mask member. It is also necessary to make the iron-alloy plate of the mask maintain tension when welding the color selection mask to the picture tube frame.
According to the conventional method of manufacture, there is a certain limit to thinning the color selection mask in order to avoid uneven etching when making the mask apertures and improve the uniformity. It is difficult to make the thickness less than 80 &mgr;m.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a color selection electrode (a color selection mask) with a finer pitch of apertures free from limitations due to the thickness of the metal substrate.
Another object of the present invention is to provide a method producing the above color selection electrode.
Still another object of the present invention is to provide a CRT using the color selection electrode.
According to the present invention, there is provided a method of producing a color selection electrode used for a cathode ray tube including an electron gun and a phosphor screen, the color selection electrode being positioned between the electron gun and the phosphor screen and having apertures through which electron beam generated from the electron gun selectively passes to the phosphor screen, the method comprising the steps of: depositing a first resist on both surfaces of a metal substrate, a first plane of the substrate directing to the electron gun and a second plane of the substrate directing to the phosphor screen, and patterning the same by photolithography; electrodepositing a metal on portions of the first plane of the substrate where the first resist is not formed to form an electrodeposited metal layer; depositing a second resist on the entire surface of the substrate which is directed to the first plane to cover the first resist and the electrodeposited metal layer; using the first resist as a mask and etching the second plane of the substrate; and removing the first resist an
Rader & Fishman & Grauer, PLLC
Ramsey Kenneth J.
Sony Corporation
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