JP2000348643A - Glass panel for cathode-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fatigue fracture and realize weight reduction, by providing a specific relationship between a maximum compressive stress σC developed on a surface out of a face by reinforcement and a maximum tensile stress σT developed in a glass. SOLUTION: This physically reinforced glass panel has a relationship of an expression: 3.3σT<=|σC|<=5σT between the maximum compressive stress σC developed on a glass surface out of a face where the maximum tensile vacuum stress is developed after at least assembling of a cathode-ray tube, more specifically, near the end of a screen end on the surface out of the face, and a maximum tensile stress σT developed in a glass. The physical reinforcement satisfying this expression can be provided by a heat treatment of rapidly cooling the glass from higher temperature and a temperature operation in a gradual cooling initial stage, comparing with a reinforcing method having a relation σC=|2σT|. The maximum tensile stress σT developed in the glass is preferably not more than 10 MPa for suppressing crack or splitting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass panel for a cathode ray tube used mainly for receiving television broadcasts.

[0002]

2. Description of the Related Art A cathode ray tube used for receiving a television broadcast or the like is a glass having a panel portion (hereinafter referred to as a glass panel) for displaying an image and a funnel-shaped funnel portion having a neck portion for storing an electron gun at one end. The outer shell is constituted by the valve. The glass panel has a substantially box-shaped structure, and includes a substantially rectangular face portion on which a screen is formed and a skirt portion forming a side wall thereof. The screen is formed by applying a fluorescent film on the inner surface of the face portion, and has a substantially rectangular shape including four sides parallel to the major axis and the minor axis orthogonal to the center of the face portion.

When a cathode-ray tube using such a glass panel is subjected to a pressure difference of 1 atm between the inside and outside, a screen end portion on a short axis or a long axis has an asymmetric structure different from a spherical shell. On the outer surface of the skirt portion near the blend R portion, which is the joint portion between the face portion and the skirt portion, a region of a large tensile stress (+ sign) exists in a relatively wide range together with the compressive stress (-sign). When the glass panel and the funnel are compared, a larger tensile stress is generated in the glass panel.

FIG. 4 shows a distribution of stress generated in a glass bulb in the most general cathode ray tube. Here, σ _{1 in} FIG. 4 indicates a stress along the paper surface, and σ ₂ indicates a stress component in a direction perpendicular to the paper surface. The numbers along the stress distribution in FIG. 4 indicate the stress value at that position.

Looking at this from the viewpoint of a glass panel, a two-dimensional stress distribution exists on the surface of the glass panel, and the maximum value of the tensile vacuum stress is usually determined by the screen end of the face portion or the skirt of the glass panel. Exists in the department. Therefore, if the tensile vacuum stress of the glass panel is large, if the structural strength of the glass panel is not sufficient, static fatigue failure due to atmospheric pressure occurs and the glass panel does not function as a cathode ray tube.

As a guarantee for preventing such destruction, taking into account the degree of damage to the glass surface generated in the process of assembling the glass panel and the cathode ray tube and the practical service life of the cathode ray tube, etc. An external pressure load test is performed by pressing a glass panel uniformly damaged with emery paper to determine a pressure difference between the inside and outside when the glass panel is broken, and the pressure difference is made to withstand about 3 atm.

The structural breaking strength of such a damaged glass panel is two-dimensional because the tensile vacuum stress existing in the outer surface layer of the glass panel depends on the structure of the glass bulb. Therefore, it is not uniquely determined, and is in a range of at most a minimum value of 18.6 MPa and an average of about 24.5 MPa. Also, the starting point of the fatigue fracture due to the vacuum stress has a high probability of being present in a region where the maximum value σ _Vmax of the tensile vacuum stress exists. Therefore, σ _Vmax is changed from 6 MPa to 12
The thickness and shape of the glass panel are determined so as to keep the glass panel in the range up to MPa. In other words, the vacuum stress is reduced by providing the face portion with a certain curvature and thickness.

However, if the radius of curvature of the outer surface of the face portion is increased while maintaining the thickness difference between the center thickness and the screen edge for the purpose of improving visibility, for example, a 29-inch glass panel can be made into a flat face portion. When the maximum tensile vacuum stress is suppressed within the range, the face portion has a thickness of 18.
Increase to 5 mm. For this reason, Japanese Patent No.
As shown in the figure, effective strengthening is performed in the region where the tensile vacuum stress is maximized, and the thickness is reduced while securing the strength.

In general, in the physical strengthening method used for glass, an effective temperature difference in the thickness direction between the surface and the inside of the glass is at least in a temperature range in which molecules constituting the glass can be rearranged after molding. As it is generated, it is rapidly cooled to a temperature range in which the molecules cannot be rearranged, and then cooled and strengthened at such a rate that it does not crack to room temperature. For example, in the strengthening of a relatively simple two-dimensionally shaped sheet glass, a heat treatment for quenching both sides almost uniformly forms a compressive stress layer from both sides to a depth of about 1/6 of the glass thickness, and 2 / At a thickness of about 3, a tensile stress layer is formed. Although the relationship between the maximum compressive stress σ _C and the maximum tensile stress σ _T of the compressive stress layer and the tensile stress layer is approximately | σ _C | = 2σ _T , the stress distribution may show a parabolic shape. Are known.

[0010]

[0007] When using the reinforcing method as described above, = sigma increasing the _C σ _T | σ _C | becomes larger sigma _T in / 2 relationship. Once when a crack has reached the penetrating tension layer compression layer, progress of the cracks is dependent on the size of the sigma _T, more or crack free running while attempting to free the strain energy large, branched fine It becomes easier to fragment.

[0011] Therefore, when a crack occurs in the glass panel of the cathode ray tube which has stored a large strain energy due to the strengthening, it self-detonates instantaneously in an attempt to eliminate the internal and external pressure difference of 1 atm. In the case of destruction during the assembly of a cathode ray tube, fragmentation of fragments causes a problem of causing contamination of the process.
When σ _T is excessively large, the amount of shrinkage of the glass generally generated during the heat treatment for assembling the cathode ray tube increases, and the phosphor formed on the inner surface of the face and the shadow through which electrons pass before the heat treatment. The relative positions of the holes in the mask become inconsistent and lose practicality. Conventionally, due to these problems, the practical range of the compressive stress formed on the surface of the physically strengthened glass panel is extremely limited.

As another method for improving the surface strength of glass, it is conceivable to strengthen the surface of glass by ion exchange treatment. This method is a method in which alkali ions in glass are replaced with larger ions at a temperature lower than a slow cooling region, and a compressive stress is generated on the surface by increasing the volume. In this case, since the compressive stress layer is formed only on the very surface, the tensile stress layer inside the glass formed so as to cancel the compressive stress layer becomes extremely thick as compared with the physical strengthening.

In this ion exchange treatment, for example, SiO ₂ —Sr containing 5 to 8% of Na ₂ O and 5 to 9% of K ₂ O is used.
_{O-BaO-Al 2 O 3} -ZnO 2 based glass panel (manufactured by Asahi Glass Co. 5001 glass), and held at about 450 ° C. KNO
₃ Obtained by immersion in the melt for about 4 to 6 hours. Due to this processing, 150
A relatively large compressive stress of about 300 MPa is formed. On the other hand, the tensile stress value is so small that it cannot be measured.

Therefore, even if a large compressive stress is formed on the surface in the ion exchange treatment, no self-destruction occurs due to the tensile stress inside the glass. However, the depth of the compressive stress layer is at most about 30 μm, which is too small as compared with the maximum depth of damage of 100 to 200 μm that occurs during manufacturing or use, and is not sufficiently practical. .

As described above, conventionally, in order to reduce the weight of the glass panel, the glass panel is strengthened and σ
_When forming _C , sufficient research has not been performed on the relationship between σ _C and σ _T that is safe even if σ _C is increased. For this reason,
The safety of the cathode ray tube has been ensured by keeping σ _C below a certain value so that σ _T does not exceed a predetermined range, or by increasing the glass thickness without increasing σ _C.

The present invention focuses on the constraints and problems in strengthening a glass panel as described above, and makes it possible to reduce the tensile residual stress formed inside the glass to an allowable range while maintaining the practical strength of the compressive stress on the glass surface. The present invention has created a glass panel for a cathode ray tube which has a strengthened stress distribution whose range is expanded as compared with the conventional case and which can be reduced in weight with safety.

[0017]

That is, the present invention relates to a glass panel for a cathode ray tube comprising a substantially rectangular face portion on which a screen is formed and a skirt portion forming a side wall thereof, wherein at least the face portion is physically reinforced. A compressive stress layer is formed, and at least in the vicinity of the screen end where the maximum tensile vacuum stress is formed after assembling the cathode ray tube at the rectangular face portion, the maximum compressive stress σ _C formed on the outer surface of the face portion by the reinforcement. Between the maximum tensile stress σ _T formed inside the glass and 3.3 σ _T
Provided is a glass panel for a cathode ray tube, characterized by having a relationship of ≦ | σ _C | ≦ 5σ _T.

The present invention also relates to a glass panel for a cathode ray tube comprising a substantially rectangular face portion on which a screen is formed and a skirt portion forming a side wall thereof, wherein at least the face portion has a glass thickness by physical strengthening and chemical strengthening. Is formed on the outer surface of the face by the reinforcement at least in the vicinity of the screen end where the maximum tensile vacuum stress is formed after assembling the cathode ray tube in the rectangular face at least. Provided is a glass panel for a cathode ray tube, wherein a relationship of 3.3σ _T ≦ | σ _C | ≦ 5σ _T is established between the maximum compressive stress σ _C and the maximum tensile stress σ _T formed inside the glass. .

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION A physically reinforced glass panel according to a preferred embodiment of the present invention is provided at least on a face outer surface where a maximum tensile vacuum stress is generated after assembling a cathode ray tube, and more specifically, on a face outer surface. Maximum compressive stress σ _C formed on the glass surface near the screen edge
And the maximum tensile stress σ _T formed inside the glass has a relationship of 3.3σ _T ≦ | σ _C | ≦ 5σ _T.

In the physical strengthening in which σ _C and σ _T have the above-mentioned specific relationship, compared with the conventional strengthening method having the relationship of σ _C = | 2σ _T | It is obtained by performing a temperature operation in stages.

In general, if the thickness of the compressive stress layer is sufficient compared to the depth of the damage that occurs during manufacturing or use, the degree of thinning of the glass increases as the reinforcing stress increases. Can be. However, glass panels are usually susceptible to optical defects on the glass surface during press forming.Therefore, after strengthening, polishing is performed to remove such optical defects, and the high optical quality required for image display may be ensured. is there. For this reason, it is desirable that the compressive stress layer before polishing be at least about 1 mm.

When | σ _C |> 5σ _T , the thickness of the compressive stress layer is reduced to less than 1/12 of the glass thickness, and when the surface of the glass panel is polished, the compressive stress layer is formed. Most or all of the strengthening effect is lost because the surface layer is removed by polishing. Further, in order to obtain such a stress relationship, excessive quenching processing is required, and in combination with the box-shaped structure of the glass panel, a shift in cooling between the skirt portion and the face portion tends to increase. Due to the large temperature difference between the portions, unnecessary tensile residual stress different from the essential reinforcing stress is generated in the face portion. This tensile residual stress acts to offset the compressive stress obtained by the reinforcement and significantly impairs the effect of the reinforcement.

On the other hand, when 3.3 σ _T > | σ _C |, it is difficult to sufficiently increase the strengthening compressive stress on the glass surface within the allowable range of σ _T. As a result, in order to obtain more strength in the glass panel, it is necessary to rely exclusively on the thickness of the glass, so it is difficult to increase only the strength without changing the thickness of the glass or to make the glass thinner. As a result, the weight of the glass panel cannot be reduced. In particular, in terms of workability of physical strengthening, strength and weight reduction and safety of the glass panel, it is desirable that 3.6σ _T ≦ | σ _C | ≦ 4.5σ _T.

When σ _C and σ _T are strengthened so as to satisfy the above-mentioned specific relationship, the maximum tensile stress σ _T formed inside the glass should be 10 MPa or less to suppress crack flakes. Above. It is more preferable that the pressure is 8 MPa or less from the viewpoint of suppressing the generation of unnecessary tensile residual stress different from the essential reinforcing stress. Further, σ _C formed on the glass surface is desirably 15 MPa or more in order to suppress crack generation and propagation at the time of impact. Further, in order to prevent fatigue fracture and achieve effective weight reduction, 20 MPa is required. It is more desirable that the above is satisfied.

The specific relationship between σ _C and σ _T in the present invention is:
It is important that the condition is satisfied at least in the face portion where the maximum tensile stress is formed after assembling the cathode ray tube. In a normal cathode ray tube, since the maximum tensile stress is formed near the screen edge on the outer surface of the face on the short axis, in this case, the compressive stress σ _{C of the} outer surface of the face near the screen edge on the short axis is obtained. The tensile stress σ _T inside the glass must satisfy 3.3σ _T ≦ | σ _C | ≦ 5σ _T.

FIG. 2 shows the vicinity of the screen edge.
Will be described. FIG. 2 is a plan view when the glass panel 1 is viewed from the outside of the face portion 2. The screen 3 is formed in a rectangular shape on a main portion of the face portion 2 as shown by a dotted line. Therefore, the end of the screen 3, that is, the peripheral contour thereof is located near the blend R of the face portion. The vicinity of the screen end is a region near the peripheral edge of the screen within the range of the screen 3, and the range is a portion where the maximum tensile vacuum stress is locally largely distributed.

In general, a larger compressive stress is often formed near the screen edge on the outer surface of the face portion where the maximum tensile vacuum stress is formed to strengthen the glass panel. As a result, the tensile stress inside the glass in this portion also increases, so that it is extremely effective to emphasize σ _C and σ _{T at} this position. In other areas, the maximum tensile vacuum stress is relatively small, and it has been theoretically and empirically confirmed that the safety of the cathode ray tube is maintained.

However, the present invention is not necessarily limited to the position where the maximum tensile vacuum stress is formed. In other regions, naturally, even if 3.3σ _T ≦ | σ _C | ≦ 5σ _T , there is no problem. Particularly, when σ _{C in the} region is large, the above relationship is set to suppress the excessive increase of σ _T. It is desirable to be established. Further, the compressive stress is also formed on the inner surface of the face portion by the reinforcement, but since it can be considered to be substantially the same as the other regions described above, detailed description will not be given.

Furthermore, for example, when a mechanical shock is applied to the outer surface of the cathode ray tube, if the face corner area where the implosion is most likely to occur is strengthened by the above-described specific relationship between σ _C and σ _T , the strengthening is performed. The presence of compressive stress suppresses the growth of cracks and lowers the probability of implosion, and even if the cracks reach the tensile layer, the existing tensile stress is small, so the self-propelled crack can be suppressed and the danger of implosion Can be avoided.

Another embodiment of the present invention is a glass panel in which at least the outer surface of the face portion is physically reinforced and ion exchange reinforced (chemically reinforced). This glass panel incorporates the advantages of physical and chemical strengthening,
The thickness of the compressive stress layer is about 1/12 of the glass thickness. In this glass panel as well, the maximum tensile stress σ _C formed in the surface layer near the screen edge where the maximum tensile vacuum stress is formed after assembling the cathode ray tube and the maximum tensile stress σ _T formed in the glass are 3. 3σ _T ≦ | σ _C | ≦
It is desirable to have a relationship of 5σ _T.

In this case, chemical strengthening is used as an auxiliary means of physical strengthening to more effectively increase the surface compressive stress. Therefore, in consideration of economy, it is desirable that the chemical strengthening process be performed simultaneously with the physical strengthening process,
The range in which the chemical strengthening treatment is performed may be limited to a region that is particularly easily damaged or a region where the maximum tensile vacuum stress is formed.

In the present invention, the skirt portion is also usually reinforced, and especially in the case of physical strengthening, although the degree of reinforcement is different from that of the face portion, the skirt portion is strengthened at the same time as the face portion. A layer is formed. But,
Since the reinforcement of the skirt portion is not directly related to the present invention, the reinforcement is not necessarily required. When enhanced, the relationship between σ _C and σ _{T at} the selected location is 3.3 σ _T
≦ | σ _C | ≦ 5σ _T may or may not be satisfied.

[0033]

EXAMPLES Examples of the present invention are shown in Table 1 together with comparative examples. The glass panel used was a 34-inch one having an aspect ratio of 4: 3, a glass thickness of 17.5 mm at the center of the face portion, and a glass edge of 19.50 at the short axis.
3 mm, thinner than normal one. The position where the maximum tensile vacuum stress of these glass panels is formed is
Near the short screen edge. The same glass panel was used in both Examples and Comparative Examples.

The heat treatment for strengthening was performed on the glass panel 40 seconds after it was taken out of the mold after molding, and the temperature of the face portion (screen end) at the start was about 500 ° C. As the quenching means, a method of cooling at least the screen end on the short axis with air at room temperature of about 20 ° C. was used. However, Comparative Example 2 was the same as Comparative Example 1 except that the quenching means was not used, but a method of increasing the compressive stress on the surface by operating slow cooling conditions was adopted.

For each of the examples and comparative examples, the glass panel was strengthened under the respective heat treatment conditions, and the maximum compressive stress σ _C and the maximum tensile stress σ _T were reduced by the shortest outer surface of the face portion where the maximum tensile vacuum stress was formed. Measured at the screen end of the shaft. The measurement was performed by measuring the short axis end of the glass panel including the skirt portion in a width of 13 to 15 mm and a length of about 1 mm.
Cut out as a 50 mm measuring test piece 4 (see FIG. 2),
After the measurement pieces shown in FIG. 3 were manufactured, the stress at the screen edge on the outer surface of the face portion was measured for each measurement piece by the Babinet compensator method. The thickness of the compression layer was measured by photographing a stress pattern obtained by the Babinet compensator method. σ _C ,
Regarding the σ _T and the compression layer, three arbitrary samples were extracted from the samples obtained under the respective strengthening conditions, measured, and evaluated by the average value.

With respect to the compressive strength, five samples were taken out of the samples obtained under the respective strengthening conditions, and a glass bulb uniformly damaged with # 150 emery paper was pressurized by water pressure to perform an external pressure load test, which led to destruction. The pressure difference between inside and outside at the time was obtained and evaluated by an average value. The explosion-proof test was performed by the missile method at an energy of 20 J commonly used in this field for any 10 samples obtained under each strengthening condition.

As is apparent from these examples, | σ _C /
Examples 1, 2, and 3 in which σ _T | is in the range of 3.3 to 5 are as follows:
All samples were acceptable except that one of them failed in Example 1. Further, the σ _T of the glass panel of each embodiment was 1
It was 0 MPa or less. In contrast, | of Comparative Examples 1 and 2
σ _C / σ _T | 2.5, Comparative Example 3 | σ _C / σ _T | 5.5
And the rejection rates are all high.

[0038]

[Table 1]

[0039]

According to the present invention, the practical range of the strengthening compressive stress formed in the surface layer of the glass panel is increased as compared with the conventional strengthening without increasing the tensile stress formed inside the glass panel by physical strengthening. Since the stress distribution, that is, only the reinforcing compressive stress can be increased, there is an effect of reducing the weight while preventing fatigue fracture.

Furthermore, when a mechanical shock is applied to the outer surface of the cathode ray tube, the presence of a high reinforcing compressive stress according to the present invention has the effect of suppressing the growth of cracks and lowering the probability of implosion, and at the same time, the cracks are pulled at the center of glass. Even if the stress layer is reached, the tensile stress inside the glass is kept small by the present invention, so that there is an effect that the self-propelled crack can be suppressed and the risk of implosion can be avoided. By these effects, a strong and lightweight cathode ray tube glass bulb that does not cause implosion due to mechanical shock or thermal shock during assembling the cathode ray tube or fatigue fracture after completion can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a stress distribution in a sectional direction of a glass panel of the present invention.

FIG. 2 is a plan view of the face portion of the glass panel of the present invention as viewed from the outside.

FIG. 3 is an explanatory sectional view of a measurement test piece.

FIG. 4 is an explanatory diagram of a stress distribution generated in a glass bulb of a cathode ray tube.

[Explanation of Signs] 1: Glass panel 2: Face 3: Screen 4: Measurement test piece

Claims (3)

[Claims] 1. A glass panel for a cathode ray tube comprising a substantially rectangular face portion on which a screen is formed and a skirt portion forming a side wall thereof, wherein a compressive stress layer is formed on at least the face portion by physical strengthening. At least in the vicinity of the screen edge where the maximum tensile vacuum stress is formed after assembling the cathode ray tube of the rectangular face portion, the maximum compressive stress σ _C formed on the outer surface of the face portion by the strengthening and the maximum tensile stress formed inside the glass due to the strengthening. between _{σ T, 3.3σ T ≦ | σ} C | ≦ 5σ T becomes a cathode ray tube glass panel and having a relationship. 2. A glass panel for a cathode ray tube comprising a substantially rectangular face portion on which a screen is formed and a skirt portion constituting a side wall thereof, wherein at least the face portion is made to be 1/12 of the glass thickness by physical strengthening and chemical strengthening. The above-mentioned compressive stress layer is formed, and at least in the vicinity of the screen end where the maximum tensile vacuum stress is formed after assembling the cathode ray tube in the rectangular face portion, the maximum compressive stress σ formed on the outer surface of the face portion by the reinforcement. _2. between _C and the maximum tensile stress σ _T formed inside the glass;
_{3σ T ≦ | σ C | ≦} 5σ T becomes a cathode ray tube glass panel and having a relationship. 3. The glass panel for a cathode ray tube according to claim 1, wherein a maximum compressive stress σ _C is 15 MPa or more and a maximum tensile stress σ _T is 10 MPa or less.