DE3803191A1 - Glass article, and process for the production thereof - Google Patents

Abstract

The present invention relates to a glass article moulded from a soda-lime-silica glass whose surface has been modified in such a way that the sodium ions are replaced by other ions. The invention also relates to a process for the production of the glass article in which a soda-lime-silica glass moulding is brought into contact with a molten salt at from 430 to 490 DEG C for from 0.5 to 4 hours.

Description

The present invention relates to a glass article, which protects against discoloration by electron beams which is for use as a glass sheet or plate a cathode ray tube (hereinafter abbreviated as CRT), which is irradiated with electron beams is suitable and also a process for its manufacture.

The glass plate of a CRT changes color (also below) referred to as brown coloring) by bombardment with Electron beams. To fix this problem, the Glass plate made of glass of a specific composition, containing Sr, Ba, Ce, etc. The Manufacturing process includes melting the glass, feeding the drop, pressing the drop and crushing the glass plate.

This manufacturing process has the disadvantage that a special furnace for melting the glass one specific composition is necessary and that also a crushing or grinding stage after Press molding is required. This leads to high ones Production costs and low productivity.

Furthermore, the known glass plate must be considerable Have thickness so that they have a pressure greater than Withstands 3 kg · f / cm² (29.4 N / cm²). This leads to a Weight gain.

On the other hand, it is possible to make the glass plate of a CRT a sodium carbonate) calcium oxide (lime) silica glass plate to build. This glass plate is made by Irradiation with electron beams, however, colored brown.  

The discoloration of a sodium carbonate-calcium oxide-silica glass by irradiation with electron beams probably by the following mechanism evoked. Electrons on the glass plate impact, penetrate into the surface layer of the Glass plate in relation to the acceleration voltage of the electrons and the electrons stay in it and form an electric field. This electric field causes sodium ions to come off the surface layer move into the inner layer. These form sodium ions Colloids made from sodium metal atoms in glass are composed.

In Japanese patent application 1 05 705/1975 a method of manufacturing a glass that is against Discoloration due to electron beam radiation is protected. This procedure is therefore characterized in that lithium ions or sodium ions, which in the surface layer of the glass with Is irradiated by electron beams at least one kind of ions from potassium ions, Rubidium ions, cesium ions and hydrogen atoms be replaced. This ion exchange process is however not very effective in preventing one Brown color.

In Japanese patent application 1 53 148/1987 a method to prevent discoloration of glass disclosed by irradiation with electron beams. According to This process uses sodium ions in the Surface layer of the sodium carbonate-calcium oxide-silica glass plate a CRT that with Electron rays are irradiated by potassium ions exchanged. The ion exchange is done by immersion  a sodium carbonate-calcium oxide-silica glass plate in potassium nitrate at 440 to 480 ° C for 0.5 to 3 h carried out. As a result of the ion exchange, the Formation of colloids reduced by sodium atoms. Potassium ions from the surface layer in the Inner layer migrate, however, form colloids Potassium atoms are composed, which causes discoloration of glass is only slightly reduced.

The object of the present invention is a To provide glass object that is at Irradiation with electron beams hardly turns brown.

Another object of the present invention is a Glass object with high strength available too put.

Another object of the present invention is a Process for the manufacture of the glass object to provide low manufacturing costs.

The present invention includes the following seven Embodiments:

• (1) A glass article made of a sodium carbonate-calcium oxide-silica glass molded body respectively. -form has been molded, its surface is modified so that sodium ions through it Lithium ions and at least one type of ion, selected from potassium ions, rubidium ions and Cesium ions.
• (2) A process for producing this glass article, in which a sodium carbonate-calcium oxide-silicon dioxide glass molding  or molded body with a molten salt, the lithium ion and at least a kind of ions chosen from potassium ions, Rubidium ions and cesium ions, contains, at 430 to 490 ° C is brought into contact over 0.5 to 4 h.
• (3) A glass object made from a glass molding, composed of 69 to 73% SiO₂, 0.5 to 1.5% Al₂O₃, 0 to 0.15% Fe₂O₃, 7 to 14% CaO, 0 to 4.5% MgO, 12 to 16% Na₂O, 0 to 1.5% K₂O, 0 to 0.1% TiO₂, 0 to 0.5% SO₃ and 0.2 to 1.5% Li₂O, each in wt .-%, with its surface so is modified that sodium ions in it Potassium ions are exchanged.
• (4) A method of manufacturing this glass article, in which a glass molding or body of this Composition with a molten salt, the Contains potassium ions in contact at 430 to 490 ° C brought.
• (5) A method of manufacturing a glass article, against discoloration caused by radiation Electron beams is protected, at which a Sodium carbonate-calcium oxide-silicon dioxide glass molding with a molten salt containing potassium ions and at least one type of ions selected from Contains calcium ions, barium ions and strontium ions, is brought into contact so that the Glass molding one surface layer Has composition by a molar ratio from 0.4 to 0.65 is defined for Na₂O / (Na₂O + K₂O), wherein the surface layer has a depth in which the irradiated electrons can penetrate (This depth is called the maximum range below  specified).
• (6) A method of manufacturing a glass article, in which a sodium carbonate-calcium oxide-silicon dioxide glass molding with a molten salt, containing potassium ions and lithium ions in contact is brought and then the glass molding one Heat treatment is suspended so that the Surface layer from the surface to the Maximum range has a composition that by a molar ratio of 0.4 to 0.65 for Na₂O / (Na₂O + K₂O) and by a molar ratio of 0.05 to 0.3 for Li₂O / (total amount of alkali metal oxides) defined is.
• (7) A method of manufacturing a glass article, in which a sodium carbonate-calcium oxide-silicon dioxide glass molding with a molten salt, containing potassium ions, is brought into contact and then the glass molding of a heat treatment is exposed so that the surface layer of the Surface up to the maximum area one Has composition by a molar ratio from 0.4 to 0.65 for Na₂O / (Na₂O + K₂O) is defined.

Fig. 1 is a cross sectional view of a CRT glass plate, which refers to an inventive embodiment.

Fig. 2 is a graph showing the molar ratio of Na₂O / (Na₂O + K₂O) in the surface layer of the glass plate. (The solid line indicates the data of Example 7 and the broken line indicates the data of Comparative Example 5.)

Fig. 3 is a graph showing the molar ratio of Na₂O / (Na₂O + K₂O) in the surface layer of the glass plate. (The solid line indicates the data of Example 8 and the broken line indicates the data of Comparative Example 6.)

Fig. 4 is a graph showing the molar ratio of Li₂O / (Li₂O + Na₂O + K₂O) in the surface layer of the glass plate of Example 8.

The glass article according to the first invention Embodiment is made of a molten glass plate known sodium carbonate-calcium oxide-silica glass, its surface, which with electron beams is irradiated, is modified so that sodium ions therein by lithium ions and at least one type of ion, selected from potassium ions, rubidium ions and cesium ions, are exchanged.

The partial exchange of sodium ions by lithium ions and at least one type of ion selected from potassium ions, Rubidium ions and cesium ions, provides the "mixed Alkali effect ", which turns the glass plate brown reduced by irradiation with electron beams and forms a compressed layer in the glass surface, which leads to increased glass strength.

The lithium ions that exchange the sodium ions lie in the form of lithium oxide in the glass. The average content of glass of lithium oxide should preferably 0.1 to 3% by weight at a depth of 10 μm, in the electron beams from the irradiated surface  penetrate, amount. With an average salary of lithium oxide of more than 3% by weight Glass molding has low strength and exhibits extreme Show a cloudy surface and fine surface cracks.

The exchange of sodium ions with potassium ions, Rubidium ions and cesium ions should preferably be in one Depth of 5 to 20 µm from the surface. The Exchange in an extremely flat or deep layer does not prevent browning.

The sodium carbonate-calcium oxide-silicon dioxide glass molding is through a swimming or float process produced. It is made of 69 to 73 wt .-% SiO₂, 0.5 to 1.5 wt .-% Al₂O₃, 0 to 0.15% by weight Fe₂O₃, 7 to 14% by weight CaO, 0 to 4.5 wt .-% MgO, 12 to 16 wt .-% Na₂O, 0 to 1.5% by weight K₂O, 0 to 0.1% by weight TiO₂ and 0 to 0.5% by weight SO₃ composed. Furthermore, it is desirable that the surface of the glass molding that with Electron beams are irradiated, the side with molten tin in the float or swimming pool in Contact comes, is opposite. If not is the ion exchange on the surface of the Molded body slowly and the tin on it the glass surface may turn brown.

The glass article according to the first invention Embodiment is carried out by the method according to the second Embodiment according to the invention produced. After this The process is a CRT glass plate with the desired shape from a sodium carbonate-calcium oxide-silicon dioxide glass formed, and the molding obtained is in a molten salt, the lithium ion and at least one Kind of ions selected from potassium ions, rubidium ions and Contains cesium ions at 430 to 490 ° C for 0.5 to 4 h  immersed so that the sodium ions in the surface of the Glass moldings by lithium ions and at least one kind of ions selected from potassium ions, rubidium ions and Cesium ions.

According to the method according to the second invention The embodiment should include the amount of lithium ions in the molten salt bath, based on the total amount Ions from at least one type of potassium ion, Rubidium ions and cesium ions, preferably 0.04 to 0.4 mol% be. If the amount of lithium ions is greater than Is 0.4 mol%, the glass article obtained has one low strength and, in extreme cases, cloudy Surface and fine surface cracks.

If the glass molding by molding a glass plate is made, it is possible to finish the glass surface without Keep grain and polish flat.

The glass article according to the first invention Embodiment is characterized in that its Surface is treated so that the sodium ions in it partly by lithium ions and at least one kind of Ions selected from potassium ions, rubidium ions and Cesium ions, partially exchanged. The so treated glass surface changes color when irradiated barely brown with electron beams. This leads to that Advantage that a commercially available sodium carbonate-calcium oxide-silica glass plate as starting material can be used for the CRT glass plate, and that the Glass plate without grain and polishing level and thus at can be manufactured at low cost.

The glass plate produced according to the invention has a increased strength and can therefore with less  Thickness can be made because of the glass surface Compressed surface layer, which by the Partial exchange of sodium ions in the surface layer by at least one kind of ions selected from Potassium ions, rubidium ions and cesium ions.

The glass article according to the third invention Embodiment is characterized in that the Surface that is irradiated with electron beams, so is modified that the sodium ions by potassium ions are exchanged. It is made out of a glass plate 69 to 73 wt .-% SiO₂, 0.5 to 1.5 wt .-% Al₂O₃, 0 to 0.15% by weight Fe₂O₃, 7 to 14% by weight CaO, 0 to 4.5% by weight MgO, 12 to 16 wt .-% Na₂O, 0 to 1.5 wt .-% K₂O, 0 to 0.1% by weight of TiO₂, 0 to 0.5% by weight of SO₃ and 0.2 to 1.5% by weight Li₂O is composed, manufactured.

The third embodiment according to the invention is based on the following finding. The brown color caused by Electron beam is taking place because the alkali ions in the outermost layer of glass move inside when the glass with electron beams is irradiated, and turns into metallic alkali atoms change to a depth of 0.5 to 8 µm from the surface. It it is known that when two or more types of alkali are used in Glass, this is a brown color due to the Prevent mixed alkali effects. A brown color can be prevented even more effectively if 0.2 up to 1.5 wt .-% Li₂O added to Na₂O and K₂O will. If the amount of Li₂O is less than 0.2% by weight browning is not effectively prevented. If the amount of Li₂O is greater than 1.5 wt .-%, the No effect of preventing browning reinforced. The weight ratio of Na₂O / (Na₂O + K₂O) should be 0.2 to 0.6. Outside this area  is the effect on preventing one Brown coloration only slight.

The depth of the layer in which discoloration occurs Irradiation with electron beams takes place through the distance the electron beams penetrate, certainly. The depth is given by the following formula expressed (Thomson - Widington law):

wherein

D (cm) means the depth of the glass into which the electron beams penetrate;
V (volts) is the acceleration voltage of the electron beams;
d (g / cm³) is the density of the glass and
β is 6.2 × 10¹¹ volt² · cm² / g.

Therefore, when the accelerating voltage V (volt) of the electron beams is 10 kV, 20 kV and 30 kV, the electron beams penetrate to a depth of 0.62 µm, 2.48 µm and 5.58 µm, respectively. It has been found experimentally that electron beams penetrate to a depth of 0.5 to 1.5 µm, 0.75 to 4 µm and 2.0 to 6.5 µm, respectively, when the electron beam hits a surface of a sodium carbonate-calcium oxide-silica -Glass emits at an acceleration voltage of 10 kV, 20 kV and 30 kV.

This fact means that when the Composition of the surface layer of a Glass molds into which the irradiated Electron beams penetrate such that the content of Li₂O 0.2 to 1.5 wt .-% and the weight ratio of Na₂O / (Na₂O + K₂O) is 0.2 to 0.6, the glass object protected against browning by electron beams is and has a high strength.

The glass molding according to the third invention Embodiment should therefore be the following Have composition:

A Li₂O content in the surface layer deeper than 0.4 µm from 0.2 to 1.5% by weight, the weight ratio of Na₂O / (Na₂O + K₂O) is 0.2 to 0.6.

Such a glass object is made according to the method the fourth embodiment of the invention. According to this method, a glass plate made of 69 up to 73% by weight SiO₂, 0.5 to 1.5% by weight Al₂O₃, 0 to 0.15% by weight Fe₂O₃, 7 to 14 wt .-% CaO, 0 to 4.5 wt .-% MgO, 12 up to 16% by weight Na₂O, 0 to 1.5% by weight K₂O, 0 to 0.1% by weight TiO₂, 0 to 0.5 wt .-% SO₃ and 0.2 to 1.5 wt .-% Li₂O is composed, formed in a desired shape, and the glass plate is placed in a molten salt bath, the Contains potassium ions at 430 to 490 ° C over a prescribed time immersed so that the sodium ions in the surface layer partly due to potassium ions be replaced.

Better results are obtained when using a glass plate  the above composition by a Float has been formed into a process CRT glass plate is molded and the glass plate in one molten salt bath containing potassium ions at 430 is immersed up to 490 ° C, so that sodium ions in the Surface layer of the glass plate partially through Potassium ions are exchanged. The ion exchange protects the glass plate against brown coloring Electron beams and causes a compression voltage in the glass surface, which increases the glass strength becomes.

An advantage of the ion exchange process is that that it is possible to determine the depth of the surface layer, in which the ion exchange takes place by adjusting the Time during which the glass plate is melted Control salt bath immersed. Therefore can the immersion time for the ion exchange to suitable Way according to the acceleration voltage of a CRT can be set.

The above glass composition (69 to 73% by weight SiO₂, 0.5 to 1.5 wt .-% Al₂O, 0 to 0.15 wt .-% Fe₂O₃, 7th up to 14% by weight CaO, 0 to 4.5% by weight MgO, 12 to 16% by weight Na₂O, 0 to 1.5 wt .-% K₂O, 0 to 0.1 wt .-% TiO₂, 0 to 0.5 wt .-% SO₃ and 0.2 to 1.5 wt .-% Li₂O) can under Use of an oven to manufacture a Sodium carbonate, calcium oxide, silicon dioxide glass be preserved. The glass article according to the invention can therefore manufactured without using a special oven will. This reduces the manufacturing cost. If the glass object according to the invention from a glass plate, the has been produced by a float process, is manufactured, it also has a smooth Surface, and there is no polishing after molding  necessary.

If a suppression of browning by immersing one commercially available Sodium carbonate-calcium oxide-silica glass plate in a molten salt that contains both potassium ions as well as contains lithium ions, the Glass strength due to the exchange of lithium Sodium are reduced. This requires an increase the thickness of the glass plate when the glass plate as Vacuum container, such as used as a CRT. An increase the thickness is disadvantageous in terms of production costs and a reduction in weight of the CRTs.

In comparison, the item according to the third and fourth embodiment of the invention advantages. The partial exchange of sodium ions by potassium ions makes the glass against a brown color of the Electron beams due to the mixed alkali effect resistant. Furthermore, a compressed layer of Glass surface is formed, and this is the Glass strength increased.

The glass article according to the fourth invention Embodiment is made from a glass plate that from 69 to 73% by weight SiO₂, 0.5 to 1.5% by weight Al₂O₃, 0 to 0.15% by weight Fe₂O₃, 7 to 14 wt% CaO, 0 to 4.5 wt% MgO, 12 to 16% by weight Na₂O, 0 to 1.5% by weight K₂O, 0 to 0.1% by weight TiO₂, 0 to 0.5% by weight SO₃ and 0.2 to 1.5% by weight Li₂O is composed, being made Surface is modified so that sodium ions in it are partially replaced by potassium ions. He will therefore hardly brown when irradiated with electron beams colored. In addition, it has an improved strength  due to the ion exchange, and therefore the plate be made with a smaller thickness. He can using an oven to make a Obtained sodium carbonate-calcium oxide-silica glass will. The glass article according to the invention can therefore can be made without using a special oven. This is advantageous in terms of production costs. If the glass object according to the invention from a glass plate, which was produced by a float process, is produced, it has a smooth surface, and no polishing after molding is required.

According to the fifth embodiment of the present invention a method of manufacturing a glass article which protected against discoloration by electron beams is provided. According to this procedure a glass molding made of sodium carbonate-calcium oxide-silica glass has been formed into a molten salt bath, the potassium ion and at least one Type of ions selected from calcium ions, barium ions and Strontium ions, contains, immersed so that sodium ions in its surface layer partly due to potassium ions be replaced. The ion exchange is up to one to such an extent that the molar ratio of Na₂O / (Na₂O + K₂O) 0.4 to 0.65 in the surface layer to a depth of the maximum area from the surface is.

If the sodium carbonate-calcium oxide-silica glass in contact with a molten salt bath, the Potassium ions and at least one kind of ions selected from Contains calcium ions, barium ions and strontium ions, is brought, the exchange of sodium ions through Potassium ions from the action of at least one ion the group of calcium ions, barium ions and  Suppresses strontium ions. This makes it possible Molar ratio of Na₂O to the total amount of Na₂O and K₂O to check at 0.4 to 0.65.

As mentioned above, the glass depth (Maximum range) in which the electron beams penetrate through the acceleration voltage of the Electron beams determined, and it is known that the Depth through the formula

can be expressed in what

D (cm) means the depth of the glass into which the electron beams penetrate;
V (volts) means the acceleration voltage of the electron beams;
d (g / cm³) means the density of the glass; and
β is 6.2 × 10¹¹ volt² · cm² / g.

Therefore, when the accelerating voltage V (volt) of the electron beams is 10 kV, 20 kV and 30 kV, the electron beams penetrate to a depth of 0.62 µm, 2.48 µm and 5.58 µm, respectively. It has been found that electron beams penetrate to a depth of 0.5 to 1.5 µm, 0.75 to 4 µm and 2.0 to 6.5 µm, respectively, when the electron beam hits a surface of a sodium carbonate-calcium oxide-silicon dioxide. Glases strikes at an acceleration voltage of 10 kV, 20 kV and 30 kV.

The time for treatment in a molten salt bath should be in relation to the acceleration voltage of the Electron beams or the maximum range selected will. It is therefore necessary to treat with a Salt containing potassium ions and strontium ions, etc. so that the surface layer within the Maximum range has a composition that by a molar ratio of Na₂O to the total amount Na₂O and K₂O is defined from 0.4 to 0.65.

According to the fifth embodiment of the present invention the molten salt used to treat the Sodium carbonate, calcium oxide, silicon dioxide glass 99.90 to 99.99 mol% of a salt is used Contains potassium ions. Treatment with the molten salt should preferably be at 440 to 480 ° C be carried out over 0.5 to 4 h.

According to a sixth embodiment of the invention is a method of manufacturing a glass article, against discoloration by electron beams is protected. According to this The process becomes a glass molding that consists of a Sodium carbonate-calcium oxide-silicon oxide glass formed in a molten salt bath containing potassium ions and contains lithium ions immersed so that sodium ions through in the surface layer of the glass molding Potassium ions and lithium ions are exchanged. The treated Glass object continues to experience one Heat treatment. The heat treatment can be carried out when the item is in a heating process (such as a sealing or baking process) during a Manufacturing process of a CRT is. The  Treatment procedures can be carried out by yourself. The Ion exchange is to such an extent carried out that the molar ratio of Na₂O / (Na₂O + K₂O) 0.4 to 0.65 and the molar ratio of Li₂O / (total amount the alkali metal oxides) 0.05 to 0.3 in Surface layer almost to the depth of the maximum area from the surface.

If the molar ratio of Na₂O / (Na₂O + K₂O) 0.4 to 0.65 the sodium ions and potassium ions move with it a lower diffusion rate than others Molar ratios, the alkali ions changing so slowly move that the formation of colloids is prevented and the discoloration of the glass object decreases. An encore of Li₂O in a molar ratio of 0.05 to 0.3 reduces the rate of diffusion, causing the Glass object further less discolored. A molar ratio of Li₂O of less than 0.5 or more than 0.3 increases the Diffusion rate and the glass can become discolor.

When in contact with a molten salt, the potassium ions and contains lithium ions, the surface layer experiences of sodium carbonate-calcium oxide-silica glass one Change in composition. That is, 70 to 100% of the Sodium ions in the surface layer are caused by Potassium ions and lithium ions exchanged. The subsequent heat treatment causes sodium ions and potassium ions to the depth of the maximum range from that Diffuse surface. As a result, the Composition in the surface layer of this depth a composition by a molar ratio of Na₂O to the total amount of Na₂O and K₂O from 0.4 to 0.65 and by a molar ratio of Li₂O to the total amount Alkali metal oxides is defined from 0.05 to 0.3.  

As mentioned above, the depth of the glass (Material area) into which the electron beams penetrate through the acceleration voltage of the Electron beams determined.

When the accelerating voltage V (volts of the electron beams is 10 kV, 20 kV and 30 kV, the electron beams penetrate to a depth of 2.5 µm, 4.5 µm and 7.5 µm, respectively. It has been found experimentally that electron beams in penetrate to a depth of 0.5 to 1.5 µm, 0.75 to 4 µm or 2.0 to 6.5 µm if they hit a surface of a sodium carbonate-calcium oxide-silica glass at an acceleration voltage of 10 kV, 20 kV and 30 kV hit.

The appropriate temperature and time for treatment should be in Dependence on the desired acceleration voltage of electron beams and the conditions of the Ion exchange can be set so that the Molar ratio of Na₂O to the total amount of Na₂O and K₂O Is 0.4 to 0.65. Generally require the Ion exchange and heat treatment a higher Temperature and a longer time when the desired Accelerating voltage of the electron beams increases.

According to the sixth embodiment of the present invention potassium nitrate and lithium nitrate are melted Salt containing potassium ions and lithium ions is used. In this case, the molten salt should preferably be kept at 440 to 480 ° C, and the immersion time should preferably be 0.5 to 4 hours. The Heat treatment should be at 440 to 480 ° C for 1 to 10 h be performed.  

According to the seventh embodiment of the present invention a method of manufacturing a glass article which protected against discoloration by electron beams is provided. According to this procedure a glass molding made from a Sodium carbonate-calcium oxide-silica glass formed in a molten salt bath containing potassium ions contains, immersed so that sodium ions in the Surface layer of the glass molding due to potassium ions be replaced. The treated glass object experiences continue a heat treatment. The ion exchange will to such an extent that the Molar ratio of Na₂O / (Na₂O + K₂O) 0.4 to 0.65 in the surface layer to the depth of the maximum area from the surface.

When in contact with a molten salt, the potassium ions contains, the surface layer of the Sodium carbonate-calcium oxide-silica glass one Change their composition. That is, 70 to 80% Sodium ions in the surface layer are caused by Potassium ions exchanged, and the surface layer contains both sodium ions and potassium ions. The subsequent heat treatment causes sodium ions and potassium ions to the depth of the maximum range from that Diffuse surface. As a result, the Composition in the surface layer of this depth a composition by a molar ratio of Na₂O to the total amount of Ma₂O and K₂O from 0.4 to 0.65 is defined.

As mentioned above, the depth of the glass (Maximum range) into which the electron beams penetrate  by the acceleration voltage of the electron beams, expressed by the formula

certainly.

Therefore, when the accelerating voltage V (volt) of the electron beams is 10 kV, 20 kV and 30 kV, the electron beams penetrate to a depth of 0.62 µm, 2.48 µm and 538 µm, respectively.

The appropriate temperature and time for treatment should depend on the desired Accelerating voltage of the electron beams and the Conditions of ion exchange can be chosen so that the molar ratio of Na₂O to the total amount of Na₂O and K₂O is 0.4 to 0.65. Generally require the ion exchange and heat treatment a higher one Temperature and a longer time if the desired Accelerating voltage of the electron beams increases.

According to the seventh embodiment of the present invention Potassium nitrate as a molten salt, the potassium ion contains, used. In this case, the melted one Salt are preferably kept at 440 to 480 ° C, and the immersion time should preferably be 0.5 to 4 hours, and the heat treatment should be at 440 to 480 ° C above 1 up to 10 hours.

According to the fifth, sixth and seventh embodiment of the invention, sodium carbonate-calcium oxide-silica glass is used. The preferred composition of the glass is shown in Table 1.
Component weight%

SiO₂50-75 Al₂O₃0.5-2.5 MgO0-4.5 CaO5.0-14.0 Na₂O5.0-16.0 K₂O0-2.0 Fe₂O0-1.0 TiO₂0-0.5 SO₃0-0.5

According to the fifth, sixth and seventh Glass used in the embodiment of the invention should have such a composition that the Alkali metal oxide 5% by weight or more, preferably 10% by weight or more in the glass and that that Sodium oxide 65% by weight or more, preferably 80% by weight or more of the alkali metal oxide. When a Composition is used outside this range the glass has poor resistance to discoloration due to electron beams.

According to the fifth embodiment of the present invention the surface layer of the glass to a depth of Maximum range modified so that the molar ratio of Na₂O to the total amount of Na₂O and K₂O 0.4 to 0.65 is. The sodium ions and potassium ions combined in the surface layer are less mobile in the glass and therefore hardly form colloids of Alkali metal atoms. For this reason, the Glass object according to the invention against discoloration protected by electron beams.

When sodium ions, potassium ions and lithium ions together are present in the surface layer, the discolors Glass object less than when two kinds of alkali ions present together in it.

According to the invention, it is not necessary to have a glass to use special composition that is a great Amount of potassium oxide contains to prevent Discoloration due to electron beams. The production of the Glass article according to the invention therefore does not require any special oven or an expensive raw material. The glass object according to the invention is in its Resistance to discoloration  glass object according to the invention is in its Resistance to discoloration Electron beams compared to known glass for Superior picture tubes from color TVs.

The following examples illustrate the invention.

Examples 1 to 3 and Comparative Example 1

A glass plate with a width of 300 mm, a length of 370 mm and a height of 50 mm with a flat surface as shown in Fig. 1 was made of a sodium carbonate-calcium oxide-lithium dioxide glass plate, which was formed by a float process had been produced by heating and vacuum molding in combination with presses. After pretreatment at about 200 ° C for about 30 minutes, the glass plate was immersed in a molten salt bath composed of potassium nitrate and lithium nitrate at 460 ° C for 2 hours. The content of lithium nitrate in the molten salt bath was 0 mol% in Comparative Example 1, 0.04 mol% in Example 1, 0.15 mol% in Example 2 and 0.04 mol% in Example 3. After immersion the glass plate was washed.

Table 2 shows the average concentration (Wt .-%) of lithium oxide in the surface layer up to a depth of 10 µm from the surface of the glass plate. Table 2 also shows the molar ratio of Na₂O / (Na₂O + K₂O) in the same surface layer.

The glass plate obtained by the above method was irradiated with electron beams for 300 hours using an electron gun (cathode voltage: 21 kV, cathode current: 30 µA and surface current density: 100 µA / cm²). The glass plate was then checked for light transmission at a wavelength of 400 nm. The change in absorbance ln (T ₀ / T) is shown in Table 2. (T ₀ and T mean the light transmission before and after irradiation with electrode beams.)

From Table 2 it can be seen that the brown color in the Examples 1 to 3 (wherein the concentration of Lithium nitrate is 0.04 to 0.4 mol%) is less than in Comparative Example 1 (which does not contain lithium nitrate is). It was found that the surface layer of the Glass plate has a compression voltage, which causes the Glass plate has an increased strength.  

Table 2

Examples 4 to 6 and Comparative Examples 2 and 3

A glass plate with a width of 300 mm, a length of 370 mm and a height of 50 mm with a flat surface as shown in Fig. 1 was made from a glass plate having the composition shown in Table 3 by heating and vacuum molding in combination with Presses. After pretreatment at about 200 ° C for about 30 minutes, the glass plate was immersed in a molten salt of potassium nitrate at 460 ° C for 2 hours. After immersion, the glass plate was washed. For comparison, the same glass plate made of glass for color television picture tubes was made with the brown color resistant composition shown in Table 4 (Comparative Example 3).

Table 3 (% by weight)

Component weight%

SiO₂56.8 Al₂O₃2.07 MgO 0.83 CaO 0.23 SrO9.1 BaO11.5 ZnO2.41 Li₂O0.41 Na₂O7.2 K₂O7.23 CeO₂0.63 TiO₂0.57 ZrO₂1.73 Fe₂O₃0.035 Sb₂O₃0.14

Table 5 shows the weight ratio of Na₂O / (Na₂O + K₂O) up in the same surface layer of the glass plate to a depth of 2.5 µm from the surface.

A test piece cut out from the glass plate obtained by the above method was irradiated with electron beams for 300 hours using an electron gun (cathode voltage: 20 kV, cathode current: 300 µA and surface current density: 1.00 µA / cm²). The glass plate was then checked for light transmission at a wavelength of 400 nm. The change in absorbance ln (T ₀ / T) is shown in Table 5. (T ₀ and T mean the light transmission before and after irradiation with electron beams.)

From Table 5 it can be seen that the glass plates of Examples 4 to 6 (wherein the concentration of lithium oxide 0.2 to 1.0 wt .-%) is a good resistance have a brown color. It was found, that a compression tension (80 kg / cm²) in the Surface layer of the glass plate is present, whereby the Glass plate has an increased strength.  

Table 5

Example 7 and Comparative Examples 4 and 5

A 3 mm thick glass plate, which had been formed by a float process and had the composition shown in Table 6, was subjected to ion exchange. The glass plate was irradiated with electron beams. The discoloration caused by the irradiation was evaluated by measuring the change in permeability.
Component weight%

SiO₂72.92 Al₂O₃1.70 MgO3.83 CaO7.52 Na₂O13.38 K₂O0.70 Fe₂O₃0.08 SO₃0.30

The ion exchange was carried out under the following conditions carried out:

molten salt: potassium nitrate (purity 99.9%): 99.975 mol%
Strontium nitrate: 0.025 mol% bath temperature: 460 ° C immersion time: 1 h

The radiation with electron beams was among the following conditions:

Acceleration voltage: 10 kV Surface current density: 2.0 µA / cm² Radiation time: 200 h

The test piece thus obtained was placed on its Light transmission with a wavelength of 400 nm checked. The results are shown in Table 7.  

Table 7

The molar ratio of Na₂O / (Na₂O + K₂O) in the surface layer of the aforementioned glass plate was measured using an X-ray microanalyzer (XMA). The results are shown in Fig. 2 (solid line).

In Comparative Example 4, the above glass plate was treated with molten potassium nitrate at 480 ° C for 1 hour, and the treated glass plate was checked for its light transmittance (400 nm) before and after irradiation with electron beams. In Comparative Example 5, a commercially available glass plate for color picture tubes was checked for its light transmittance (400 nm) before and after irradiation with electron beams. The results are shown in Table 7. The molar ratio of Na₂O / (Na₂O + K₂O) in the surface layer of the plate of Comparative Example 5 was measured. The results are shown in Fig. 2 (broken line). From Table 7 and Fig. 2 it can be seen that the transparency of the glass plate according to the invention decreases less after irradiation with electron beams than that of Comparative Examples 4 and 5.

Example 8 and Comparative Examples 6 and 7

A 3 mm thick glass plate, formed by a Float method, with that given in Table 6 Composition was one ion exchange and one then subjected to heat treatment. The glass plate was irradiated with electron beams. The through the Irradiation discoloration was determined by measuring the Change in light transmittance rated.

The ion exchange was carried out under the following conditions carried out:

molten salt: potassium nitrate (purity 99.9%): 99.9% by weight
Lithium nitrate: 0.1% by weight bath temperature: 460 ° C immersion time: 3 h heat treatment: at 460 ° C for 4 h.

The radiation with electron beams was among the following conditions:

Acceleration voltage: 10 kV Surface current density: 35 µA / cm² Irradiation time: 20 h

The test piece thus obtained was placed on its Light transmission at a wavelength of 400 nm checked. The results are shown in Table 8.  

Table 8

The molar ratio of Na₂O / (Na₂O + K₂O) in the surface layer of the aforementioned glass plate was measured using an X-ray microanalyzer (XMA). The results are shown in Fig. 3 (solid line). Fig. 4 shows the molar ratio of Li₂O / (Li₂O + Na₂O + K₂O) in Example 8.

In Comparative Example 6, the above glass plate was subjected to ion exchange, but no heat treatment. In Comparative Example 7, a commercially available glass plate for color picture tubes had the composition shown in Table 4. The glass plates of Comparative Examples 4 and 7 were checked for their light transmittance (400 nm) before and after irradiation with electron beams. The results are shown in Table 8. The molar ratio of Na₂O / (Na₂O + K₂O) in the surface layer of the plate of Comparative Example 6 was measured. The results are shown in Fig. 3 (broken line). From Table 8 and Fig. 3 it can be seen that the glass plate according to the invention decreases in light transmission after irradiation with electron beams less than that of Comparative Examples 6 and 7.

Example 9 and Comparative Examples 8 and 9

A 3 mm thick glass plate, formed by a Float method, with that given in Table 6 Composition was an ion exchange and Subsequent heat treatment exposed. The glass plate was irradiated with electron beams. The through the Irradiation discoloration was determined by measuring the Change in light transmittance rated.

The ion exchange was carried out under the following conditions carried out:

molten salt: potassium nitrate: (purity 99.9%) Bath temperature: 460 ° C Immersion time: 2 h Heat treatment: at 460 ° C for 4 h.

The radiation with electron beams was among the following conditions:

Acceleration voltage: 10 kV Surface current density: 2.0 µA / cm² Irradiation time: 200 h

The test piece thus obtained was placed on its Light transmission at a wavelength of 400 nm checked. The results are shown in Table 9.

Table 9

The molar ratio of Na₂O / (Na₂O + K₂O) in the surface layer of the aforementioned glass plate was measured using an X-ray microanalyzer (XMA). The results are almost the same as the solid line shown in Fig. 3).

In Comparative Example 8, the above glass plate was subjected to ion exchange but no heat treatment. In Comparative Example 9, a commercially available glass plate for color picture tubes had the composition shown in Table 4. The glass plates of Comparative Examples 8 and 9 were checked for their light transmittance (400 nm) before and after irradiation with electron beams. The results are shown in Table 9. The molar ratio of Na₂O / Na₂O + K₂O) in the surface layer of the plate of Comparative Example 8 was measured. The results are almost the same as shown in Fig. 3 (broken line). From Table 9 and Fig. 3 it can be seen that the glass plate according to the invention decreases in its light transmission after irradiation with electron beams much less than that of Comparative Examples 8 and 9.

Claims (27)

1. Glass object which is protected against discoloration by electron beams, characterized in that it has been formed from a sodium carbonate-calcium oxide-silica glass, with a part of its surface which is irradiated with electron beams is modified so that the sodium ions therein are replaced by lithium ions and at least one type of ions selected from potassium ions, rubidium ions and cesium ions. 2. Glass article according to claim 1, characterized characterized that part of the surface that with Electron beams are irradiated, so modified is that the average content of Li₂O about a depth of 10 µm in the surface layer 0.1 is up to 3% by weight. 3. Glass article according to claim 1, characterized characterized in that the sodium carbonate-calcium oxide-silica glass through a float process has been produced and from 69 to 73 wt .-% SiO₂, 0.5 to 1.5 wt .-% Al₂O₃, 1 to 0.15 wt .-% Fe₂O₃, 7th up to 14% by weight CaO, 0 to 4.5% by weight MgO, 12 to 16% by weight Na₂O, 0 to 1.5% by weight K₂O, 0 to 0.1% by weight TiO₂ and 0 to 0.5 wt .-% SO₃ is composed, being the surface covered with electron beams is irradiated, the surface covered with melted Tin of the float bath during manufacture Contact is opposite. 4. Glass article according to claim 1, characterized characterized in that the ions from at least one  Type of ions selected from potassium ions, rubidium ions and calcium ions, in the surface layer in one Penetrate depth of 5 to 20 µm. 5. A method of manufacturing a glass article which against discoloration by electron beams is protected, characterized in that a Glass molding made of sodium carbonate-calcium oxide-silicon dioxide glass in a molten salt, containing lithium ions and at least one type of ion from the group of potassium ions, rubidium ions and Cesium ions, at 430 to 490 ° C for 0.5 to 4 h is immersed, causing the sodium ions in the Surface layer of the glass molding through Lithium ions and at least one type of ion from the Group consisting of potassium ions, rubidium ions and Cesium ions. 6. The method according to claim 5, characterized in that the molten salt is lithium ion in an amount from 0.04 to 0.4 mol%, based on the total amount on potassium ions, rubidium ions and cesium ions, contains. 7. The method according to claim 5, characterized in that that the glass molding is a sodium carbonate-calcium oxide-silica glass plate is. 8. Glass object that is resistant to discoloration Is protected by electron beams characterized in that part of its surface, the is irradiated with electron beams, so modified is that the sodium ions are replaced by potassium ions be replaced, with the glass object off  a glass plate made of 69 to 73 wt .-% SiO₂, 0.5 to 1.5 wt .-% Al₂O₃, 0 to 0.15 wt .-% Fe₂O₃, 7th up to 14% by weight CaO, 0 to 4.5% by weight MgO, 12 to 16% by weight Na₂O, 0 to 1.5% by weight K₂O, 0 to 0.1% by weight TiO₂, 0 to 0.5% by weight SO₃ and 0.2 to 1.5% by weight Li₂O is composed, is formed. 9. Glass article according to claim 8, characterized characterized that part of the surface that with Electron beams are irradiated, so modified is that the Li₂O content 0.2 to 1.5 wt .-% and the weight ratio of Na₂O / (Na₂O + K₂O) 0.2 to 0.6 over a depth of 0.5 µm or more in the Surface layer is. 10. Glass object that is resistant to discoloration Is protected by electron beams characterized that he by immersing a Containing glass moldings in a molten salt Potassium ions, at 430 to 490 ° C over a prescribed time, causing sodium ions in its Surface partially replaced by potassium ions have been obtained and that the glass molding from a glass plate, composed of 69 to 73% by weight SiO₂, 0.5 to 1.5% by weight Al₂O₃, 0 to 0.15% by weight Fe₂O₃, 7 to 14 wt .-%, CaO, 0 to 4.5 wt .-% MgO, 12 to 16% by weight Na₂O, 0 to 1.5% by weight K₂O, 0 to 0.1 wt .-% TiO₂, 0 to 0.5 wt .-% SO₃ and 0.2 to 1.5 wt .-% Li₂O, is formed. 11. A method of manufacturing a glass article according to Claim 10, characterized in that it Glass molding into a molten salt over such is immersed in a period of time that part of the Surface that is irradiated with electron beams  is modified so that the content of Li₂O 0.2 to 1.5 wt .-% and the weight ratio of Na₂O / (Na₂O + K₂O) 0.2 to 0.6 over a depth of 0.5 µm or more in the surface layer. 12. A method of manufacturing a glass article, the against discoloration by electron beams is protected, characterized in that a Sodium carbonate-calcium oxide-silicon dioxide glass molding with a melted salt that Potassium ions and at least one type of ion, selected from calcium ions, barium ions and Strontium ions, so brought into contact, that its surface layer at a depth into which the electron beams penetrate, one Has composition by a molar ratio from 0.4 to 0.65 for Na₂O / (Na₂O + K₂O) is defined. 13. The method according to claim 12, characterized in that that the sodium carbonate-calcium oxide-silica glass from 50 to 75% by weight Si₂O, 0.5 to 2.5% by weight Al₂O₃, 0 to 1.0% by weight Fe₂O₃, 5.0 to 14.0% by weight CaO, 0 to 4.5% by weight MgO, 5.0 to 16.0% by weight Na₂O, 0 to 2.0% by weight K₂O, 0 to 0.5% by weight TiO₂ and 0 to 0.5 wt .-% SO₃ is composed. 14. The method according to claim 12, characterized in that that the molten salt is 99.90 to 99.99 mol% Contains salts that contain potassium ions. 15. The method according to claim 12, characterized in that the glass molding in the molten salt bath 440 to 480 ° C is immersed for 0.5 to 4 h.   16. A method of manufacturing a glass article which against discoloration by electron beams is protected, characterized in that a Sodium carbonate-calcium oxide-silicon dioxide glass molding with a molten salt that potassium ions and contains lithium ions so contacted will that natrimions in the surface layer exchanged with potassium ions and lithium ions be, and then the glass molding one Heat treatment is suspended so that the Surface layer at a depth to which the Electron beams penetrate, a composition has by a molar ratio of 0.4 to 0.65 for Na₂O / (Na₂O + K₂O) and a molar ratio of 0.05 up to 0.3 for Li₂O / total amount of alkali metal oxides) is defined. 17. The method according to claim 16, characterized in that that the sodium carbonate-calcium oxide-silica Glass from 50 to 75 wt .-% SiO₂, 0.5 up to 2.5 wt .-% Al₂O₃, 0 to 1.0 wt .-% Fe₂O₃, 5.0 to 14% by weight CaO, 0 to 4.5% by weight MgO, 5.0 to 16.0% by weight Na₂O, 0 to 2.0% by weight K₂O, 0 to 0.5% by weight TiO₂ and 0 to 0.5 wt .-% SO₃ is composed. 18. The method according to claim 17, characterized in that that the sodium carbonate-calcium oxide-silica glass has such a composition that the Content of the alkali metal oxides 5% by weight or more and the ratio of Na₂O in the alkali metal oxides 65% by weight or more. 19. The method according to claim 16, characterized in that that the molten salt is potassium nitrate and Is lithium nitrate and the glass molding in it  molten salt at 440 to 480 ° C for 0.5 to 4 h is dipped. 20. The method according to claim 16, characterized in that that the glass molding undergoes a heat treatment at 440 exposed to 480 ° C for 1 to 10 h. 21. The method according to claim 16, characterized in that that the glass molding in the molten salt so is immersed that 70 to 100% of the sodium ions in its surface layer by potassium ions and Lithium ions are exchanged. 22. A method of manufacturing a glass article which against discoloration by electron beams is protected, characterized in that a Sodium carbonate-calcium oxide-silicon dioxide glass molding with a molten salt that contains potassium ions contains, is brought into contact so that Sodium ions in its surface layer Potassium ions are exchanged and that subsequently the glass molding is subjected to a heat treatment is so that the surface layer thereof in one Depth into which the electron beams penetrate, a Has composition by a molar ratio from 0.4 to 0.65 for Na₂O / (Na₂O + K₂O) is defined. 23. The method according to claim 22, characterized in that that the sodium carbonate-calcium oxide-silica glass from 50 to 75% by weight SiO₂, 0.5 to 2.5% by weight Al₂O₃, 0 to 1.0% by weight Fe₂O₃, 5.0 to 14.0% by weight CaO, 0 to 4.5% by weight MgO, 5.0 to 16.0% by weight Na₂O, 0 to 2.0% by weight K₂O, 0 to 0.5% by weight TiO₂ and 0 to 0.5 wt .-% SO₃ is composed.   24. The method according to claim 22, characterized in that that the sodium carbonate-calcium oxide-silica glass has such a composition that the Content of the alkali metal oxides 5% by weight or more and the ratio of Na₂O in the alkali metal oxides 65% by weight or more. 25. The method according to claim 22, characterized in that the molten salt is potassium nitrate and the Glass molding into the molten salt at 440 to 480 ° C is immersed for 0.5 to 4 h. 26. The method according to claim 22, characterized in that the glass molding undergoes a heat treatment at 440 exposed to up to 480 ° C or 1 to 10 h. 27. The method according to claim 22, characterized in that the glass molding in the molten salt so is immersed that 70 to 80 wt .-% of Sodium ions in its surface due to potassium ions be replaced.