JP2000128571A - Glass composition for cathode ray tube and cathode ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass compsn. which is economically excellent, which has >=50 cm-1 absorptivity for 0.1 nm X-rays although containing no lead, and which is used for a cathode ray tube of a low anode voltage of 15 kV, and to provide a cathode ray tube using this glass compsn. SOLUTION: A glass compsn. for a cathode ray tube is by mass 55 to 75% SiO2, 0 to 5% Al2O3, 0 to 2% Li2O, 3 to 12% Na2O, 3 to 12% K2O, 3 to 10% CaO, 2 to 13% BaO, 1 to 10% ZnO, 15 to 35% K2O+CaO+BaO+ZnO, 0 to 5% MgO, 0 to 3% SrO, 0 to 3% B2O3, and 0 to 1% Sb2O3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass composition for a cathode ray tube having a low anode voltage (15 kV or less) and a cathode ray tube having an envelope formed of the glass composition.

[0002]

2. Description of the Related Art Glass parts of a color picture tube (cathode tube) conventionally used as a cathode ray tube include a panel, a funnel, a neck tube, and the like.
Glass is used according to the required characteristics at each location.

A phosphor emitting three primary colors of red, green and blue is applied to the inner surface of the panel glass, and an electron beam emitted from an electron gun sealed in a neck tube emits this phosphor through a shadow mask. An image is formed by letting the user make an image. Since the electron beam is braked by the shadow mask and the phosphor, X-rays are generated. Therefore, the glass constituting the envelope of the cathode ray tube must absorb the X-rays sufficiently so that there is no danger to the human body.

Therefore, the funnel and the neck tube include:
Lead glass containing a large amount of PbO having a large X-ray absorption capacity is used. On the other hand, since PbO is reduced by irradiation of electron beams or X-rays to reduce coloration of the panel, lead glass is not used, and glass containing SrO or BaO having relatively high X-ray absorption capacity is used. Can be

[0005] These glasses have a wavelength of 0.06 nm.
The near X-ray absorption capacity is high. This is because the wavelength of the generated X-rays depends on the applied anode voltage, and the generated X-rays have an anode voltage of 20 kV or more applied with a conventional color picture tube.
This is because the peak wavelength of the line is around 0.06 nm.
PbO has a particularly high X-ray absorption capacity in this wavelength range, and SrO contained in panel glass also has a relatively high X-ray absorption capacity in this wavelength range.

By the way, it is needless to explain again the harmfulness of lead, but the regulation of harmful substances on environmental problems in recent years is no exception for lead glass. For example, lead glass bulbs are used in small automotive light bulbs, but since this lead glass bulb elutes lead during shredding, a notice has been issued to reduce the amount of lead used. Lead-free is being promoted.

[0007] Glass for cathode ray tubes has the problem of X-ray shielding described above, and lead-free has not progressed very much because there are few effective substitute oxides for PbO. At present, recycling as cullet is considered as an environmental measure on a trial basis, but 100% recycling is impossible from the beginning. Therefore, most waste CRTs are landfilled, and glass containing lead, unlike stable landfill disposal of general glass, is required to have a controlled landfill that blocks groundwater.

[0008] In view of the above, in order to prevent environmental pollution, it is desirable to reduce the amount of lead used as much as possible or to use lead-free glass. This is the same even when considering the health risks given to workers in the process of manufacturing and processing lead glass.

[0009]

In order to lead-free a funnel glass or a neck tube glass which requires a high X-ray absorbing ability, the contained PbO component is replaced by another component having a high X-ray shielding ability. Need to be replaced.

Examples of such lead-free glass for a cathode ray tube include, in addition to the panel glass described above, a funnel glass for a beam index type cathode ray tube (Japanese Patent Laid-Open No. 8-3).
No. 1343, JP-A-8-31344) are disclosed. Each of these glasses has a large amount of SrO, BaO
Addition enhances X-ray absorption near the wavelength of 0.06 nm.

[0011] However, there is a drawback that an increase in expensive components of these raw materials increases the cost of glass and deteriorates economic efficiency. In addition, there are some black and white CRT glasses as other lead-free CRT glasses,
It contains a large amount of BaO and is not necessarily economical, including the fact that a small amount of a coloring inhibitor such as CeO ₂ is added.

Further, Bi ₂ O ₃ has a high X-ray absorption coefficient at a wavelength of 0.06 nm, and proposes a new glass in which PbO is replaced by Bi ₂ O ₃ (Japanese Patent Laid-Open Nos. 7-206471 and 9-1).
No. 42873), but it has not been put to practical use, including the fact that the raw materials are very expensive. When replacing PbO with SrO or BaO contained in panel glass, a large amount of SrO, B is required to achieve a high X-ray absorption coefficient required for a funnel glass for a CRT.
aO is required, the glass is devitrified, and is not practical.

Under such circumstances, for example, Japanese Patent Laid-Open No.
No. 36363, Japanese Patent Application Laid-Open No. 6-338272, and the like, a new thin flat type cathode ray tube having an anode voltage value as low as 15 kV or less as compared with a conventional cathode ray tube is being developed. In this type of cathode ray tube, the wavelength of the generated X-ray shifts to a longer wavelength side (around 0.1 nm) as compared with a conventional cathode ray tube. For this reason, the components of the glass necessary to sufficiently absorb X-rays have a wavelength of 0.0
Different components can be used as compared to the case of 6 nm.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a cathode ray tube having a low anode voltage value of 15 kV without using lead and having a wavelength of 0.1 n.
It is an object of the present invention to provide a glass composition having an absorption coefficient of 50 cm ^-1 or more for X-rays of m and excellent in economical efficiency, and a cathode ray tube using the same.

[0015]

According to the present invention, in order to attain the above object, the present invention does not substantially contain PbO,
X-ray absorption coefficient at a wavelength of 0.1nm is not less 50 cm ^-1 or more, represented by mass%, SiO ₂ 55 to 75%, Al
₂ O ₃ 0-5%, Li ₂ O 0-2%, Na ₂ O 3-1
_{2%, K 2 O 3~12%} , CaO 3~10%, Ba
O 2-13%, ZnO 1-10%, K ₂ O + CaO
+ BaO + ZnO 15-35%, MgO 0-5%, S
_{rO 0~3%, B 2 O 3} 0~3%, Sb 2 O 3 0~1
% Of a glass composition for a low voltage cathode ray tube.

In the present invention, the present inventors consider that K ₂ O + CaO + BaO + Z is more preferable than SrO + BaO in order to increase the X-ray absorption capacity near the wavelength of 0.1 nm in consideration of economy.
The inventors have found that nO is effective, and specifically, by using the above-described composition in terms of mass%, it is more economical than conventional glass and has a wavelength of 0.1 n without containing PbO.
m X-rays have an absorption coefficient of 50 cm ^-1 or more (0.1 n
m) was obtained.

The function of each component of the glass constituting the present invention and the reason why the composition range is limited as described above will be described below. SiO ₂ is a main component forming the skeleton of glass, and if its content is less than 55%, the glass becomes unstable and easily devitrifies. If it exceeds 75%,
Melting and molding becomes difficult because the viscosity of the glass is too high. Therefore, the range of 60 to 70% is preferable.

Al ₂ O ₃ can be added to enhance the chemical durability and mechanical strength of the glass. Preferably 0.5 to
Although it is in the range of 3.5%, if it exceeds 5%, the melting property of the glass deteriorates.

Li ₂ O has an effect of lowering the viscosity of glass, and can be added up to 2% in the present invention.
If the content exceeds 2%, the cost is increased and the thermal expansion coefficient of the glass becomes too large.

Na ₂ O has an effect of improving the melting property of the glass. In the present invention, Na ₂ O is contained in an amount of 3% or more, but if it exceeds 12%, the chemical durability and electric resistance deteriorate. K
₂ O has the same effect as Na ₂ O, and has a wavelength of 0.1
It is an essential component for increasing the X-ray absorption coefficient in nm, but if it is less than 3%, its effect is small, and if it exceeds 12%, the thermal expansion coefficient becomes too large. Therefore, the range of 4 to 10% is preferable.

Like K ₂ O, CaO is an X-ray absorbing component having a wavelength of 0.1 nm, and is an essential component for increasing the electrical resistance of glass. If it exceeds, the glass tends to be devitrified. Therefore, the range of 4 to 8% is preferable.

BaO is an essential component having a very high X-ray absorption coefficient at a wavelength of 0.1 nm, and contains 2% or more. If the content is less than this, X-ray absorption becomes insufficient and
If it exceeds 3%, the glass tends to be devitrified.

ZnO also has an extremely high X-ray absorption coefficient at a wavelength of 0.1 nm and an effect of increasing water resistance, and is an essential component in the present invention. In order to sufficiently bring out the effect, it is desirable to contain 1% or more.
However, since the raw material of ZnO is expensive, excessive addition causes an increase in cost, and glass is easily crystallized. Therefore, the content of ZnO should be kept to a necessary minimum, and its maximum limit is 10%, preferably 1 to 8%.
Range.

As described above, the X-ray absorption component in the present invention is a combination of K ₂ O + CaO + BaO + ZnO, and is contained in the range of 15 to 35%. If the content of these components is less than 15%, the X-ray absorption coefficient at a wavelength of 0.1 nm will be less than 50 cm ^-1, which is not preferable. If the content exceeds 35%, the economic efficiency will deteriorate. Preferably it is in the range of 18 to 32%.

MgO can be contained up to 5% for adjusting the viscosity curve of the glass. 5% addition of MgO
If the ratio exceeds, devitrification tends to occur, which is not preferable.
SrO can be added up to 3% for adjusting the viscosity curve of the glass. Addition of more than 3% is not preferable because it increases the cost.

B ₂ O ₃ has the effect of lowering the viscosity of the glass and increasing the meltability. The content is preferably in the range of 0.5 to 2%, and if it exceeds 3%, the chemical durability deteriorates. Sb ₂ O ₃ has an effect as a fining agent for glass, and can be added up to 1% in the present invention. However, if it exceeds 1%, the glass tends to be devitrified, which is not preferable. As fining agents, other than Sb ₂ O ₃ , AS ₂ O ₃ , F, SO ₃
Etc. can be used. These fining agents are Sb
_Since all substances including ₂ O ₃ are environmental pollutants, it is desirable not to use them at all if possible, but if they are used, they should be kept to the minimum necessary.

The setting of the X-ray absorption coefficient of glass is important for reducing the amount of X-ray leakage from a color picture tube.
According to the Japan Electronic Machinery Manufacturers Association (EIAJ), the X-ray absorption coefficient of funnel glass in a color CRT is 62 cm.
^-1 (wavelength 0.06 nm). X that occurs
The intensity of the line increases in proportion to the square of the anode voltage. However, in a color picture tube in which the anode voltage value is as low as 15 kV or less, the generated X-ray intensity itself becomes low. When this is converted into the X-ray absorption coefficient of glass, It is possible to reduce the standard value of 62 cm ^-1 of the conventional color picture tube to about 50 cm ^-1 .
Therefore, the X-ray absorption coefficient of the glass in the present invention is 50
cm ^-1 or more. If the X-ray absorption coefficient is lower than this, the amount of transmitted X-rays may increase, which is not preferable.

FIG. 1 shows the wavelength dependence of main X-ray absorption components in the present invention. From this figure, SrO, which is the main X-ray absorption component in the current panel glass, has a wavelength of 0.07.
It can be seen that the K-shell absorption edge is at 7 nm, and the absorption coefficient for X-rays with a wavelength of 0.1 nm is lower than that of K ₂ O or CaO. In the wavelength range shown in FIG. 1, since the X-ray absorption coefficients of K ₂ O and CaO are almost equal, these characteristic lines are shown overlapping.

Although not shown in FIG. 1, BaO has an L-shell absorption edge at a wavelength of 0.207 to 0.236 nm,
K ₂ O has a wavelength of 0.344 nm, and CaO has a wavelength of 0.34 nm.
307 nm and ZnO are K
There is a shell absorption edge. PbO and SrO shown
As can be seen from the absorption edge of the above, when this wavelength is exceeded, the mass absorption coefficient is remarkably reduced. Therefore, the X-ray absorption coefficient of glass must be set in accordance with the anode voltage of the cathode ray tube.

That is, the design of the bulb glass in the conventional cathode ray tube is performed at 0.06 nm (anode voltage: 20 kV), and the mass absorption coefficient of the main glass component is PbO>
While SrO>ZnO>BaO> K ₂ O ≒ CaO, at 0.095 nm (anode voltage 13 kV), Z
nO>BaO>PbO> K ₂ O ≒ CaO> SrO, and the composition dependency on the X-ray absorption coefficient of the glass changes rapidly.

In the present invention, X-rays having a wavelength of 0.1 nm have been focused on in the case of a cathode ray tube having an anode voltage of 10 to 15 kV.
Is valid.

[0032]

Embodiments of the present invention will be described below in detail. FIGS. 2 and 3 show the glass composition, the coefficient of thermal expansion α, the glass transition point Tg, the softening point Ts, the specific gravity, and the X at a wavelength of 0.1 nm in Examples and Comparative Examples of the present invention.
The linear absorption coefficient and batch cost are shown.

Glass was prepared by mixing raw materials so as to have the composition shown in the figure, and was melted in an electric furnace using a platinum crucible at 1450 ° C. for 5 hours. Stirring was performed in order to homogenize the glass during melting, and after defoaming, poured into a metal mold and cooled to obtain a sample.

The coefficient of thermal expansion is measured in the range of 0 to 300 ° C., the specific gravity is measured by Archimedes' method, and the X-ray absorption coefficient is the mass absorption coefficient of the glass component oxide at a wavelength of 0.1 nm and the specific gravity of the glass. From the calculation. Since the glass batch cost varies depending on the raw material used, the values in the figure are not absolute, but here the commonly used raw materials (silica sand, aluminum hydroxide, lithium carbonate, soda ash, potassium carbonate, calcium carbonate) , Dolomite, strontium carbonate, barium carbonate, zinc white, zirconium oxide, boric acid, titanium oxide, cerium oxide, and antimony oxide).

2 and 3, reference numerals 1 to 20 denote examples of the present invention, and reference numerals 21 to 26 denote comparative examples. In addition, 21 and 22 are color CRT panel glass, 23 is a black and white CRT glass, 24 is a glass composition of a known example, 25 and 26 are X-ray absorbing components, although the content of each component is within the range of the present invention. (K ₂ O + CaO + BaO +
Examples of glasses whose total content of ZnO) is out of the range of the present invention are shown.

In this example and Comparative Examples 21 to 24, the X-ray absorption coefficient 50 required for the funnel glass was
cm ^-1 or more (at 0.1 nm), but according to the comparison of batch costs, the present example is less than 40 yen in all cases, whereas the comparative example is more than 40 yen in all cases. It is clear that this embodiment is excellent in economy.

As apparent from FIG. 3, when the total content of the X-ray absorption components (K ₂ O + CaO + BaO + ZnO) is less than 15% (Comparative Example 25), the batch cost is low, but the X-ray absorption coefficient is low. Is as low as about 42 cm ^-1 and 35
% (Comparative Example 26), the batch cost becomes high, and the economic efficiency becomes poor.

The thermal expansion coefficient α of each glass in this embodiment
Is in the range of 80 to 110 × 10 ⁻⁷ / ° C., but in the glass of the present invention, the coefficient of thermal expansion is not limited to the above value. As described above, a glass part for a cathode ray tube is a combination of a panel, a funnel, and a neck tube, and these are welded to form an envelope. In addition, a metal material is welded to the glass as a jig for attaching parts such as a shadow mask. In these combinations, it is necessary to match the coefficients of thermal expansion of each other in order to reduce distortion during welding. Therefore, the coefficient of thermal expansion of the glass may be arbitrarily selected depending on the combination of materials used, and when the coefficient of thermal expansion needs to be adjusted, the content of the alkali component may be adjusted.

It is more important to match not only the coefficient of thermal expansion of the funnel glass but also the transition point, strain point, annealing point, and softening point according to the glass material of the panel and neck tube. Further, by using lead-free glass for the panel and neck tube glass, it is possible to obtain a glass for the envelope of the cathode ray tube, which is less environmentally pollutable and easy to recycle.

FIGS. 4 and 5 show an embodiment in which the glass composition of the above embodiment is applied to a 21-inch thin flat cathode ray tube. According to this cathode ray tube, a substantially rectangular flat face plate 31 and a substantially rectangular flat rear plate 32 are opposed to each other via a side wall 33, and a plurality of apertures 3 formed in the rear plate are formed.
A plurality of funnels 35 are joined around 4 to form a vacuum envelope 36.

A phosphor screen 37 having an integrated structure is formed on the inner surface of the face plate 31.
A shadow mask 35 is provided in the vacuum envelope so as to face the phosphor screen. In addition, each funnel 3
A deflection yoke 38 is mounted on the outer side of 5, and an electron gun 40 is disposed in the neck 39 of each funnel 35.

Further, in order to support the atmospheric pressure load applied to the vacuum envelope 36, the face plate 31 and the rear plate 3
A plurality of support members 41 are arranged between the two.
The base end of each support member 41 is fixed to the rear plate 32 using a method such as sealing with frit glass or laser welding, and the front end is processed into a wedge shape to be applied to the black light absorbing layer of the phosphor screen 37. In contact.

In the cathode ray tube configured as described above, the electron beam emitted from the electron gun 40 is deflected in the horizontal and vertical directions by the magnetic fields generated by the corresponding deflection yokes 38, and the fluorescent screen 37 is moved to the corresponding pluralities. Scanning is performed by dividing the region into five regions R1 to R20 in this example, five in the horizontal direction and four in the vertical direction. The image drawn on the phosphor screen 37 by the divided scanning is the electron gun 4
By controlling the signals applied to the zero and the deflecting device 38, the connection is made, and one large image without breaks or overlaps is reproduced on the entire surface of the phosphor screen 37.

In the cathode ray tube having the above structure, the same 2
1 inch conventional cathode ray tube (approximately 450mm in length,
(A deflection angle of 90 degrees and a neck diameter of 29 mm) can reduce the anode voltage. Hereinafter, the anode voltage will be described in detail.

In the cathode ray tube according to the present embodiment, the value of the anode voltage Eb greatly changes in accordance with the change, and important factors in the characteristics are the deflection power and the focus characteristics of the electron beam. First, the deflection power P is generally approximately proportional to the average diameter R of the deflection coil, the average diameter r of the core, the anode voltage Eb, and the sine square of half the value of the deflection angle θ. When the relative value is considered here, the average diameter R of the deflection coil and the average diameter r of the core can be approximated by replacing the average diameter R of the deflection coil with the neck diameter φ, and P∝φ ² × EbXsin ² θ / 2.

From the above equation, since the neck diameter of the cathode ray tube according to the present embodiment is 13 mm, considering that the number of divided scans is 20, when the deflection angle is 60 degrees and the anode voltage is about 16 kV or less. If this is the case, the deflection power can be reduced to the level of a conventional cathode ray tube or less. In this case, the depth of the cathode ray tube is about 180 mm, and the depth can be reduced to a little less than about 1/3 as compared with the conventional cathode ray tube.

On the other hand, the focus characteristic of the electron beam can be represented by the magnification M of the electric field lens. Assuming that the distance from the electric field lens to the phosphor screen 35 is Li, the distance from the virtual crossover to the electric field lens is Lo, and the voltage at the virtual crossover is Eo, the magnification of the electric field lens is M = (Li / Lo) × √ (Eo
/ Eb). To prevent this value from becoming higher than that of the conventional cathode ray tube, the anode voltage of the cathode ray tube in the present embodiment may be set to about 10 kV or more.

From the above, according to the present embodiment, 21
For an inch-size cathode ray tube, the cathode voltage is
From V, it becomes possible to make it about 10 to 16 kV. By conducting similar studies on cathode ray tubes of other screen sizes, the anode voltage of a thin flat type cathode ray tube can be set to 10 to 15 kV.
In the present embodiment, the anode voltage is set to 13 kV in consideration of both the electron beam focus characteristics and the deflection power. In this case, the shortest wavelength of the generated X-ray is about 0.095.
and leaked X-rays can be sufficiently suppressed by using the glass having the above composition.

In the embodiment described above, the anode voltage is 13 k
The purpose is to improve the X-ray absorption coefficient for X-rays having a wavelength of 0.1 nm in the case of V. However, when the anode voltage further decreases, the shortest wavelength of the generated X-rays shifts to the longer wavelength side. It is possible to cope by changing the balance of the contents in consideration of the absorption edge position of each component of the glass.

For example, as another example of a thin flat type cathode ray tube, there is one using a cold cathode element as a cathode. This type of cathode ray tube has a low-voltage operation with an anode voltage of several tens to several hundreds of volts and a high-voltage operation of several kV. The latter type has recently become mainstream. The specific anode voltage is described in SID Seminar Sexual Notes Vol. 1 5/18 (SID
SEMINAR LECTURE NOTES Vol
According to Ume1 MAY18), 4.5 to 6 kV (M
-1) and 8 kV (M-5). Therefore, in this case, the shortest wavelength of the generated X-rays is about 0.15 to 0.28 nm, and by forming the vacuum envelope using the composition glass of the present embodiment described above,
Leaked X-rays can be suppressed sufficiently.

[0051]

As described above, the glass composition for a cathode-ray tube according to the present invention is suitable for use in a cathode-ray tube having an anode voltage as low as 15 kV or less, and is compared with a case where conventional glass is diverted. It is highly economical and can reduce the cost of glass parts. Further, since this glass composition does not contain lead, it contributes not only to improvement in occupational health in the working environment at the time of glass production, but also to global environmental protection, and is preferable in terms of environmental protection. The present glass composition is suitable for use as a funnel for a cathode ray tube having a low anode voltage because the characteristics of the glass composition do not deteriorate for use in a cathode ray tube.

Therefore, according to the present invention, there is provided a glass composition which can sufficiently absorb X-rays having a wavelength of 0.1 nm without containing lead and which is excellent in economic efficiency, and a cathode ray tube provided with the glass composition. Can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing mass absorption coefficients of main components of a glass for a cathode ray tube.

FIG. 2 shows glass compositions, thermal expansion coefficients, glass transition points, softening points, and the like of various glass compositions according to the embodiment of the present invention.
The figure which shows specific gravity, the X-ray absorption coefficient of 0.1 nm wavelength, and batch cost.

FIG. 3 shows a glass composition, a thermal expansion coefficient, a glass transition point, a softening point, a specific gravity, and a wavelength of 0.1 n of various glass compositions according to the embodiment of the present invention and a glass composition according to a comparative example.
The figure which shows the X-ray absorption coefficient of m, and a batch cost.

FIG. 4 is a perspective view showing a cathode ray tube according to the embodiment of the present invention.

FIG. 5 is a sectional view taken along the line AA in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 31 ... Face plate 32 ... Rear plate 33 ... Side wall 35 ... Funnel 36 ... Vacuum envelope 37 ... Phosphor screen 38 ... Deflection yoke 39 ... Neck 40 ... Electron gun

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01J29 / 29 / H01J / 29 / Z (72) Inventor Takashi Nishimura 1-9-2 Hara-cho, Fukaya-shi, Saitama Co., Ltd. Inside Toshiba Fukaya Electronic Factory (72) Inventor Makoto Shiratori 5358-3, Kawajiri, Yoshida-cho, Harihara-gun, Shizuoka Prefecture Inside (72) Inventor Takao Omori 5-558-3, Kawajiri, Yoshida-cho, Harihara-gun, Shizuoka Prefecture F term (reference) 4G062 AA03 BB01 DA06 DA07 DB01 DB02 DB03 DC01 DC02 DC03 DD01 DE03 DF01 EA01 EA02 EA03 EB03 EB04 EC03 EC04 ED01 ED02 ED03 EE03 EF01 EF02 EF03 EG03 EG04 FA01 FF01 F01 FF01 F01 FF01 GA01 GA10 GB01 GC01 GD01 GE01 HH01 HH03 HH05 HH07 HH09 HH11 HH13 HH15 HH17 HH20 JJ01 JJ03 JJ04 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK07 KK10 MM25 NN14 5C032 AA02 BB01 BB10

Claims (3)

[Claims] (1) When expressed in terms of% by mass, 55 to 75% of SiO ₂ ,
l ₂ O ₃ 0-5%, Li ₂ O 0-2%, Na ₂ O 3 ~
_{12%, K 2 O 3~12%} , CaO 3~10%, B
aO2~13%, 1~10% ZnO, K 2 O + CaO
+ BaO + ZnO 15-35%, MgO 0-5%,
_{SrO 0~3%, B 2 O 3} 0~3%, Sb 2 O 3 0~
A glass composition for a cathode ray tube having a composition of 1%. 2. A cathode ray tube having an envelope made of at least glass, wherein the anode voltage is 15 kV or less, and wherein the glass composition according to claim 1 is used for the envelope. 3. The cathode ray tube according to claim 2, wherein the X-ray absorption coefficient at a wavelength of 0.1 nm is 50 cm ⁻¹ or more.