JP2004307329A - Insulating material for display tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulating material for a display tube, which does not cause the reduction of brightness or the insulation failure of the display tube and is free of lead, and in which the stability of glass is high. <P>SOLUTION: The insulating material for the display tube contains a glass powder. The glass powder contains, by molar percentage, 5-25% SiO<SB>2</SB>, 25-55% B<SB>2</SB>O<SB>3</SB>, 20-45% ZnO, 0.1-7% TiO<SB>2</SB>, 0-10% Al<SB>2</SB>O<SB>3</SB>, 2-20% of Li<SB>2</SB>O + Na<SB>2</SB>O + K<SB>2</SB>O, and 0-20% of MgO + CaO + SrO + BaO, with the proviso that the molar ratio of B<SB>2</SB>O<SB>3</SB>to SiO<SB>2</SB>is ≤3.5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an insulating material for a display tube mainly used for an insulating coating of a plasma display panel (PDP), a fluorescent display tube (VFD), a field emission display (FED), and the like. The insulating coating in the PDP corresponds to protection of the address electrodes formed on the back plate and protection of the transparent electrodes formed on the front plate, which are generally referred to as a dielectric material for protecting the address electrodes and a transparent dielectric material, respectively. Is called. In the present invention, for the sake of convenience, a wiring including an electrode is also referred to as a wiring, and a dielectric material is treated as being synonymous with an insulating material.

For insulation coating of wiring such as PDP, VFD, FED, etc., an insulating material having characteristics of a firing temperature of 500 to 600 ° C. and a coefficient of thermal expansion of about 60 to 100 × 10 ⁻⁷ / ° C. is used.

Conventionally, as this kind of insulating material, a powder material mainly composed of lead-containing glass (PbO—B ₂ O ₃ ) that can be fired at a low temperature has been widely used. However, recently, from the viewpoint of environmental problems, an insulating material containing no lead has been demanded, and a material using an SiO ₂ —B ₂ O ₃ —ZnO-based glass containing an alkali component has been proposed. (For example, Patent Documents 1 to 3)
JP-A-11-250809 JP 2000-226232 A JP 2001-146436 A

  However, since the material proposed in Patent Document 1 has poor stability of glass, it tends to be devitrified at the time of firing, and it is difficult to obtain characteristics as designed. Further, the materials disclosed in Patent Documents 2 and 3 do not sufficiently consider the reduction in brightness of the display tube due to volatilization from glass and the poor insulation of the insulating film due to foaming during firing.

  An object of the present invention is to provide an insulating material for a display tube which does not cause a decrease in luminance or insulation failure of the display tube, has high glass stability, and does not contain lead.

The insulating material for a display tube of the present invention is an insulating material for a display tube containing glass powder, wherein the glass powder is represented by mol%, 5 to 25% of SiO _2, 25 to 55% of B ₂ O _{3, and} 20 to 45 of ZnO. %, TiO ₂ 0.1 to 7%, Al ₂ O ₃ 0 to 10%, Li ₂ O + Na ₂ O + K ₂ O 2 to 20%, MgO + CaO + SrO + BaO 0 to 20%, and a molar ratio of B ₂ O ₃ / SiO ₂ It is characterized by being made of glass satisfying ≦ 3.5.

  By using the insulating material of the present invention, it is possible to perform the insulating coating of the aluminum wiring without lowering the brightness of the display tube or causing insulation failure. Further, since the glass has high stability and does not contain lead, it is suitable as an insulating material for a display tube.

The following mechanism causes a reduction in the brightness of the display tube and poor insulation that occur when an insulating material containing a SiO ₂ —B ₂ O ₃ —ZnO-based glass powder is used.

When the moisture contained in the glass is volatilized during firing, the volatilization of B ₂ O _{3 and} other easily volatilizable components is promoted. Volatilized B ₂ O _{3 and the} like have an adverse effect on the electron-emitting portion of the display tube, and this is considered to cause a reduction in luminance. Therefore, the lower the water content in the glass and the lower the content of B ₂ O ₃ , the less the brightness of the display tube is reduced.

Moisture is also a cause of generation of bubbles that cause insulation failure. Bubbles that cause insulation failure mainly occur on the aluminum wiring, and the bubbles are generated by reducing the moisture in the glass with aluminum. Aluminum is a material having a very high reducing ability, and easily reduces moisture in glass. Therefore, if the glass coated on the wiring contains a large amount of moisture,
2H ₂ O → 2H ₂ + O ₂
Reaction occurs, resulting in significant foaming. Therefore, as the amount of water in the glass is smaller, insulation failure is less likely to occur. The above reaction can be explained by the theory of priority of oxidation-reduction by Ellingham diagram (Chemistry of Glasses, A Paul). The Ellingham diagram shows the redox priorities among the materials. The likelihood of a redox reaction between the materials is proportional to the distance between the reaction lines of each material on the Ellingham diagram, and the greater the distance, the easier the reaction occurs. From this theory, it can be seen that aluminum, which is a wiring material, is much lower than H ₂ O on the Ellingham diagram, and easily reduces H ₂ O, which is higher.

Therefore, in the present invention, in a SiO ₂ —B ₂ O ₃ —ZnO-based glass which is a main constituent material of an insulating material, a predetermined amount of TiO ₂ is introduced into the glass composition, and the value of B ₂ O ₃ / SiO ₂ is strictly adjusted. It is characterized by being adjusted to.

TiO ₂ is a component that densifies the glass structure and makes it difficult to contain moisture. SiO ₂ also has the same effect, and the glass structure is further densified by increasing the amount of SiO ₂ relative to B ₂ O ₃ . As a result, the glass is less likely to volatilize. Moreover, since the content of B ₂ O ₃ relatively decreases, the amount of B ₂ O ₃ in the glass decreases, and the volatilization amount of B ₂ O ₃ decreases. In addition, since the B ₂ O ₃ raw material has a high water content, the amount of water brought into the glass decreases with a decrease in the B ₂ O ₃ content.

  Due to these synergistic effects, it is possible to obtain an insulating material that does not easily cause a decrease in luminance or insulation failure.

If the amount of SiO ₂ relative to B ₂ O ₃ is relatively increased, the glass becomes harder, and it becomes difficult to fire at a temperature of 500 to 600 ° C. Therefore, in the present invention, an alkali component is further introduced to reduce the viscosity of the glass.

  Hereinafter, the reasons for limiting the glass powder composition contained in the insulating material for a display tube of the present invention will be individually described in detail.

SiO ₂ is a component that forms the skeleton of glass, and is a glass-forming oxide. Also, when the content of SiO ₂ is increased, the glass structure becomes denser, and the amount of water in the glass tends to decrease. Also, the thermal expansion decreases. In the composition of the present invention, if the content of SiO ₂ is more than 25 mol%, the viscosity of the glass becomes high and the firing temperature in the insulating coating step becomes too high. On the other hand, if the content is less than 5 mol%, the glass becomes unstable and easily devitrifies during firing. When the glass is devitrified, it becomes difficult to obtain the characteristics as designed. In particular, the desired fluidity and thermal expansion coefficient cannot be obtained. Since it is preferable that the insulating material be fired at a lower temperature, SiO ₂ is preferably at most 20 mol%, and more preferably at least 10 mol% from the viewpoint of glass stability.

B ₂ O ₃ is a component that forms the skeleton of glass, and is a glass-forming oxide. It is a component that lowers the melting temperature and softening point of glass. On the other hand, it causes a decrease in luminance due to volatilization, and the raw material is a main water supply source into glass. When the content of B ₂ O ₃ is less than 25 mol%, the above effect is poor. When the content is more than 55 mol%, the glass is separated and the softening point does not become 630 ° C. or lower. For this reason, when firing at a temperature of 600 ° C. or less, a fired film having a smooth surface cannot be obtained, and the insulating property deteriorates. Further, the brightness of the display tube may be reduced due to the volatilization of B ₂ O ₃ from the glass. Further, the B ₂ O ₃ raw material brings a large amount of water into the glass, causing foaming. The content of B ₂ O ₃ is preferably 35 to 45 mol%.

  ZnO is an intermediate oxide, and is a component that lowers the coefficient of thermal expansion without significantly increasing the melting temperature and softening point of glass. If ZnO is less than 20 mol%, the effect is not sufficient, and if it is more than 45 mol%, crystals are precipitated at the time of sintering and a homogeneous glass cannot be obtained. The content of ZnO is preferably 25 to 45 mol%.

TiO ₂ is an intermediate oxide and is a characteristic component of the present invention. The general effect of TiO ₂ is to lower the coefficient of thermal expansion without significantly increasing the melting temperature and softening point of the glass, as in ZnO, but in the present invention, in addition to this, it densifies the glass structure and increases the water content. Is difficult to include. Since TiO ₂ is relatively easily reduced by aluminum, TiO ₂ also has an effect of reducing the amount of reduction of water in glass. Note that titanium metal precipitated by reduction has low elution properties and is difficult to grow, and thus does not cause insulation failure. If the content of TiO ₂ is less than 0.1 mol%, the above effects cannot be sufficiently obtained. On the other hand, if the content is more than 7 mol%, the glass becomes unstable and easily devitrifies during firing. For this reason, it becomes difficult to obtain the characteristics as designed, and for example, it becomes impossible to obtain desired fluidity and thermal expansion coefficient. The preferred range of TiO ₂ is 0.5 to 7 mol%, in particular 1.5 to 5 mol%.

Al ₂ O ₃ is an intermediate oxide, and is a component that suppresses and stabilizes the phase separation of glass. It also has the effect of lowering the coefficient of thermal expansion. If the content of Al ₂ O ₃ is more than 10 mol%, the viscosity of the glass becomes high, so that an appropriate fluidity cannot be obtained. Further, the glass transition point is undesirably high. The preferred range is 0.1 to 10 mole% Al ₂ O _3, more preferably 0.5 to 5 mol%.

Li ₂ O is an alkali metal oxide, Na ₂ O and K ₂ O is a component to lower the melting point of lowering the softening point of the glass, the content thereof in total 2 to 20 mol%, preferably 7 ~ 15 mol%. When the amount is less than 2 mol%, the above effects are poor, and when the amount is more than 20 mol%, the thermal expansion coefficient increases and the electrical insulation decreases.

The contents of Li ₂ O, Na ₂ O and K ₂ O are respectively 0 to 6 mol% (particularly 2 to 3 mol%) of Li ₂ O and 0 to 10 mol% (particularly 3 to 6 mol%) of Na ₂ O. , K ₂ O is preferably 0 to 10 mol% (particularly 3 to 5 mol%). If each component is too large, the coefficient of thermal expansion becomes too large. It is desirable to use two or more, particularly all three, of the alkali metal oxides in combination. By mixing and using an alkali metal oxide, the temperature of the glass can be easily lowered without increasing the thermal expansion coefficient due to the alkali mixing effect.

  Alkaline earth metal oxides such as MgO, CaO, SrO, and BaO are components that improve water resistance and chemical resistance. In particular, BaO and SrO are effective for improving the stability of the present composition. The alkaline earth oxide is preferably added in a total amount of 3 mol% or more in order to obtain the above effect, but from the viewpoint of stability and expansion of the glass, the total amount is 20 mol% or less, preferably 15 mol%. The following should be restricted:

  The contents of MgO, CaO, SrO, and BaO are respectively 0 to 10 mol% (particularly 0 to 5 mol%), 0 to 10 mol% (particularly 0 to 5 mol%), and 0 to 10 mol% of SrO ( It is preferable that the content of BaO is 0.1 to 5 mol%, and the content of BaO is 0.1 to 10 mol% (particularly 1 to 5 mol%). If each component is too large, the coefficient of thermal expansion becomes too high, causing inconvenience such as poor adhesion to the substrate.

Further, the glass according to the present invention is characterized in that the molar ratio of B ₂ O ₃ / SiO ₂ is 3.5 or less. As described above, in the case of insulating coating of a display tube, when the composition of the glass is volatilized, the brightness of the display tube is reduced as described above. However, the SiO ₂ —B ₂ O ₃ —ZnO-based glass has phase separation. Prone to quasi-unstable glass with tendency. In such a glass, a composition component tends to be easily volatilized. Therefore, by increasing the ratio of SiO ₂ to B ₂ O ₃ in the composition, the phase separation tendency of the glass can be reduced, and a decrease in the brightness of the display tube can be prevented. Further, when the amount of SiO ₂ relative to B ₂ O ₃ is relatively increased, the glass structure becomes denser, and the glass becomes less likely to contain moisture. Moreover, since the content of B ₂ O ₃ is relatively reduced, the volatilization amount of B ₂ O ₃ is reduced. In addition, the amount of moisture brought into the glass can be reduced as the B ₂ O ₃ content decreases. The preferred ratio of B ₂ O ₃ / SiO ₂ is B ₂ O ₃ / SiO ₂ ≦ 3.0.

Further, the glass in the present invention preferably has a molar ratio of ZnO / SiO ₂ ≦ 3. By limiting the ratio of SiO _{2 to} ZnO to the above range, the phase separation tendency of the glass can be further reduced, and the luminance of the display tube can be further stabilized. More preferred ratio of ZnO / SiO ₂ is a ZnO / SiO ₂ ≦ 2.5.

In addition to the above components, other components can be added as long as the effects of the present invention are not impaired. For example, ZrO ₂ may be added up to 5 mol% to improve water resistance and chemical resistance, and P ₂ O ₅ may be added up to 10 mol% to stabilize glass.

However, it is desirable that halogen (particularly, fluorine F ₂ and chlorine Cl ₂ ) and SO ₃ are not substantially contained. Halogen and SO ₃ volatilize during firing and contaminate the cathode (cathode), which is an electrode that emits electrons, and the anode (anode), which donates electrons, and hinder the transfer of electrons. As a result, the brightness of the display tube is reduced. Therefore, it is necessary to reduce these components to a level at which deterioration in luminance due to volatilization during firing does not pose a problem. More specifically, it is desirable that the total amount of halogen is 100 ppm or less and that of SO ₃ is 10 ppm or less. In order to reduce the chlorine and sulfur contents in the glass, a glass raw material having a small absolute amount of these impurities may be selected. By doing so, the glass obtained does not contain impurities in excess of the theoretical amount. In practice, the content of these impurities is usually less than half the theoretical amount. In order to further reduce the amount of impurities, (1) at the time of glass melting, the melting temperature is raised by 50 ° C. or higher than usual, or the melting time is lengthened. (2) Oxygen gas or inert gas (nitrogen gas) at the time of glass melting And (3) glass melting in a vacuum. These methods can be appropriately selected to obtain a glass having a very small impurity content.

  The insulating material for a display tube of the present invention is basically composed of a glass powder having the above composition. Powder such as zinc may be added in a total amount of 15% by volume or less.

  Next, a method for producing the insulating material for a display tube of the present invention will be described.

  First, a glass raw material is prepared so as to have the above composition, mixed, and then melted. Subsequently, the molten glass is formed, pulverized and classified to obtain a glass powder. Further, if necessary, ceramic powder is added to obtain the display tube insulating material of the present invention.

  Subsequently, a method of using the display tube insulating material of the present invention will be described.

  The insulating material for a display tube of the present invention can be used, for example, in the form of a paste. When used in the form of a paste, a binder, a solvent and the like are used together with the insulating material. The content of the insulating material in the paste is generally about 50 to 95% by mass.

  The binder is a component used for adjusting the viscosity of the paste, and its content is generally about 0.1 to 20% by mass. As the binder, polybutyl methacrylate, polyvinyl butyral, polymethyl methacrylate, polyethyl methacrylate, ethyl cellulose and the like can be used, and these can be used alone or in combination.

  The solvent is a material for making the material into a paste, and its content is generally about 10 to 30% by mass. As the solvent, for example, terpineol, diethylene glycol monobutyl ether acetate, 2,2,4-trimethyl-1,3-pentadiol monoisobutyrate, or the like can be used alone or as a mixture.

  The paste is produced by kneading the prepared insulating material, binder, plasticizer, solvent and the like at a predetermined ratio.

  In order to form an insulating film using such a paste, first, these pastes may be applied by a screen printing method, dried, and fired at a temperature of about 500 to 600 ° C. The form in which the material of the present invention is used is not limited to the paste form, but may be in the form of a green sheet, for example.

  When manufacturing a display tube such as a PDP, VFD, or FED, an insulating film made of the above-mentioned material may be formed using the above-described method at a place where the insulating tube is to be coated. Obtainable.

Hereinafter, the present invention will be described based on examples.

  Table 1 shows examples of the present invention (samples Nos. 1 to 5), and Table 2 shows comparative examples (samples Nos. 6 and 7).

Each sample was prepared as follows. First, raw materials such as various oxides and carbonates were prepared so as to have the compositions shown in Tables 1 and 2, mixed uniformly, put into a platinum crucible, and melted at 1250 ° C. for 1 to 2 hours in air. Next, the molten glass was passed through a water-cooled roller to be formed into a thin plate, pulverized by a ball mill for 5 hours, and air-classified to obtain a glass powder having an average particle size of about 4 μm. In addition, the content of halogen such as F ₂ and Cl ₂ and SO _{3 in} the glass was adjusted so that the total amount of halogen was 100 ppm or less and SO ₃ was 10 ppm or less in each sample by selecting raw materials.

  About the obtained sample, the glass transition point, the thermal expansion coefficient, the insulating property, the stability of the glass, and the volatility of the glass component were evaluated.

  As a result, no devitrification was observed in the glass during firing for each sample, and it was confirmed that the glass was stable. In addition, the luminance and the insulating properties were at levels that did not cause any practical problems in each sample. In particular, no. The samples Nos. 1 to 3 were very excellent in both insulating and volatile properties.

  On the other hand, the sample No. In No. 6, a glass component is volatilized in a large amount, and it is expected that a fluorescent display tube manufactured using this material will have low luminance. No. 7 had poor insulation.

  The glass transition point was determined by differential thermal analysis (DTA), and the coefficient of thermal expansion was determined by a push-rod type thermal expansion measuring device.

The insulation was measured by applying a pasted sample on a soda plate on which aluminum wiring was applied, baking it at 560 ° C. for 15 minutes to give an insulation coating of about 25 μm, and then observing a cross section with an electron microscope (1000 ×). ) Was performed and the state of the foam was observed. As a result, those having a width of 100 μm on the photograph and in which no foaming was observed in the insulating film were evaluated as ◎, those in which foaming was observed but 1 to 4 were evaluated as ○, and those exceeding 5 / cm ² were evaluated as ×. evaluated. The paste used was a sample powder, ethyl cellulose, and terpineol kneaded at a ratio of 80% by mass, 1% by mass, and 19% by mass, respectively.

  The stability of the glass was obtained by visually observing the state of phase separation during melting and the presence or absence of devitrification during firing of the powder, and ◎ indicates that neither phase separation nor devitrification was observed. The evaluation at the time of firing was performed by observing the sample surface used for the evaluation of the insulating property.

  The evaluation of the volatility of the glass was performed as follows. First, for the sample powder to be evaluated, the weight corresponding to the density was measured, and a green compact having a diameter of 20 mm was produced by an air press. This green compact was placed on a soda glass plate (FIG. 1), and a quartz glass tube was installed so as to surround the green compact (FIG. 2). Further, another soda glass plate was placed on the tube, and the tube was covered (FIG. 3). Subsequently, it was placed in an electric furnace in this state and baked at 560 ° C. for 30 minutes. After firing, dirt due to volatile components adhering to the covered glass plate was observed and evaluated. As a result of the observation, "◎" indicates that no dirt was observed, "O" indicates that dirt was observed only with a microscope of 50 times magnification, and "X" indicates that dirt was visually observed. For example, in the case of a fluorescent display tube application, if a filament serving as a cathode (cathode) is contaminated with a volatile component generated from a material (glass), the brightness is considered to be reduced.

4 is a photograph showing a state in which a compact is placed on a soda glass plate for evaluation of volatility. It is a photograph which shows the state which installed the quartz glass tube around the green compact for evaluation of volatility. It is a photograph which shows the state covered with the soda glass plate for evaluation of volatility.

Claims (8)

An insulating material for a display tube comprising a glass powder, in the glass powder _{mol%, SiO 2 5~25%, B 2} O 3 25~55%, ZnO 20~45%, TiO 2 0.1~7 %, Al ₂ O ₃ 0 to 10%, Li ₂ O + Na ₂ O + K ₂ O 2 to 20%, MgO + CaO + SrO + BaO 0 to 20%, and a glass whose molar ratio is B ₂ O ₃ / SiO ₂ ≦ 3.5. An insulating material for a display tube, comprising: Glass powder, an insulating material for a display tube according to claim 1, characterized in that it consists of glass ZnO / SiO ₂ is 3 or less in molar ratio. Glass _{powder, Li 2 O 0~6%, Na} 2 O 0~10%, K 2 insulating material for a display tube according to claim 1, characterized in that it consists O 0% content to glass. _{2. The} insulating material for a display tube according to claim 1, wherein the glass powder is made of glass containing two or more kinds selected from Li ₂ O, Na ₂ O and K ₂ O as essential components. Glass powder, halogen and an insulating material for a display tube according to claim 1, the SO _3, characterized in that it consists of a glass that is substantially free.   An insulating paste comprising the display tube insulating material according to claim 1.   An insulating film obtained by firing the insulating material according to claim 1.   An insulating film obtained by firing the insulating paste according to claim 6.