JPS6238308B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sealing material whose main component is low-melting glass, which is used to airtightly seal the envelopes of various display devices such as fluorescent display tubes and liquid crystal display tubes, and other packages such as semiconductor devices. The present invention relates to a sealing material that contains fine particles of metal oxide and has excellent chemical resistance and water resistance, as well as excellent printability. The present invention can be used for sealing envelopes and packages of various display devices made of glass or ceramics, and an embodiment of a fluorescent display tube will be described below. As shown in FIG. 1, a conventional fluorescent display tube has an insulating substrate 1 made of glass or ceramics.
A wiring conductor 2 and an insulating layer 3 provided with through holes.
An anode conductor 4 which is electrically connected to the wiring conductor 2 through a through hole, and a phosphor layer 5 deposited on the upper surface of the anode conductor 4 are laminated by a printing method.
A control electrode 6 is provided above the phosphor layer 5.
Further above, a filament-shaped cathode 7 is disposed. A front envelope 8 made of a glass plate formed into the shape of a flat-bottom boat is fixed to the substrate 1 by overlapping with the sealing material 9 so as to cover these electrodes. The type in which the envelope is composed of the base plate 1 and the flat-bottomed boat-shaped front envelope 8 is referred to as a molded front type. In other types of fluorescent display tubes, as shown in FIG. 2, a glass substrate 1 has a wiring conductor 2 and an insulating layer 3 provided with through holes, as in the molded front type.
It has a structure in which an anode conductor 4 and a phosphor layer 5 are laminated. However, the front enclosure 10 includes a front plate 10a made of glass, and a front plate 10a made of glass.
Side plate 1 also made of glass around 0a
This structure is formed by joining and assembling 0b with a sealing material and surrounding it. The front enclosure 10 is bonded and fixed to the substrate 1 with a sealing material 9. The type in which the envelope is composed of the front envelope 10 assembled with the base plate 1, the front plate 10a, and the side plate 10b is called an assembled front type. A sealing material containing low-melting point glass as a main component was formed into a paste form and printed on the sealing parts of both types of envelopes, and each part was polymerized for 400 min.
It was heat treated at ~500°C to bond and seal. In conventional sealing materials, in addition to the main component, low-melting glass, the substances shown in Table 1 are added as fillers in powder form. The reason for adding this filler is that the main component, low melting point glass, has a coefficient of thermal expansion of 100~
Since this is a relatively large value of 115×10 ^-7 /℃, the envelope of the fluorescent display tube, which is composed of a glass plate with a coefficient of thermal expansion of 85 to 95×10 ^-7 /℃, is made mainly of low-melting glass. When sealed with a sealing material that has the following properties, there is a drawback that the sealed portion may break or crack due to thermal stress due to the difference in coefficient of thermal expansion. In order to eliminate this drawback, a sealing material with a small coefficient of thermal expansion has been obtained by dispersing in the form of particles a substance with a coefficient of thermal expansion smaller than that of the low-melting glass. The names and thermal expansion coefficients of the materials used as the filler are shown in Table 1.

[Table] In addition, low melting point glass uses PbO as the main raw material.
It is a lead-boric acid glass with B ₂ O ₃ and ZnO added to it, and an example of a conventional composition is as follows. PbO...77-83Wt% B ₂ O ₃ ...7-11 ZnO...7-12 SiO ₂ ...1-3 The PbO component, which is the main raw material among the above components, is slightly unstable chemically. B 2 O 3 had the property of easily combining with solvents, etc., and B ₂ O ₃ had the property of easily absorbing moisture compared to air. Therefore, conventional low-melting glass has the disadvantage that it adsorbs moisture in the atmosphere and reacts with water and oxygen, causing deterioration. In addition, the substances mentioned above as fillers are effective in reducing the coefficient of thermal expansion, but they are not effective in reducing water resistance, and moisture adsorbed to the filler and particles on the surface of the low-melting glass reacts with the low-melting glass. This resulted in a phenomenon in which the water content was difficult to evaporate even during heat treatment during sealing, and remained in the form of bubbles in the sealing material of the fluorescent display tube. When this phenomenon occurs, moisture and gas are generated within the display tube after it is formed in the fluorescent display tube, causing problems such as lowering the brightness of the fluorescent display tube and shortening its life. In addition, as a method for applying the sealing material, it is generally applied around the substrate 1 by screen printing, and a paste is formed by mixing low melting point glass and filler in a vehicle in which ethyl cellulose is dissolved in a terpineol solution. let When printing with this paste, if the viscosity of the paste is lowered, printability will improve, but after printing, the paste will sag or run, resulting in poor printing accuracy. Another problem was that increasing the viscosity of the paste made it difficult for the paste to come out of the screen, resulting in poor printability. The present invention has been made in view of the above-mentioned circumstances, and is a method of coating the surface of low-melting glass, which is weak in chemical resistance and water resistance, with ultrafine particles of SiO ₂ that have good adsorption and release _properties . Forms a protective layer to prevent moisture and chemicals from directly adhering to the low melting point glass, and prevents reactions with the low melting point glass by releasing it during heat treatment during sealing.
Another object of the present invention is to provide a sealing material with excellent printing properties due to the thixotropic effect produced by the ultrafine particle paste. EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the present invention shown in the drawings will be described in detail. FIG. 3 is an enlarged view of the sealing material of the present invention.
11 are particles of low melting point glass, and 12 are particles of filler material. Ultrafine particles 13 of metal oxide, for example silicon dioxide, are attached to the surfaces of these particles of low melting point glass 11 and filler 12. In addition, the composition of the blending amount of each component is, in terms of weight percent, low melting point glass is 60 to 85%, filler with a coefficient of thermal expansion is 14 to 38%, and average particle size is 1.
It is composed of 0.05 to 15% of ultrafine particles of metal oxide of micrometer or less. Low melting point glass has a softening point of glass below 450℃, and is a lead-boric acid based low melting point glass powder whose main material is PbO. An example of the components of the low melting point glass is as follows. Each component is expressed in weight percent. PbO...77~83% _{B2O3 ...} 7~11 _{Al2O3 ...3} ~8 SiO2 _... 1~3 The above components were melted in a platinum crucible, cooled, and ball milled. Grind to a particle size that passes 150 mesh. Therefore, the maximum particle size is approximately 100μ
m, and the average particle size is 10 to 20 μm. As mentioned above, the chemical properties of this low-melting glass were that it had poor chemical resistance and water resistance. The thermal expansion coefficient of this low melting point glass is a relatively large value of about 100 to 115×10 ^-7 /°C. However, the coefficient of thermal expansion of the glass plate used for the envelope of a fluorescent display tube is approximately 85 to 95 × 10 ^-7 /℃, so if the low melting point glass is used as it is, the difference in the coefficient of thermal expansion will be too large, and the sealed part will be damaged. It cannot be used because it is destroyed or cracked. Therefore, a filler is mixed in to reduce the coefficient of thermal expansion. Materials that can be used as the filler are those shown in Table 1 above, which have a small coefficient of thermal expansion. The particle size of these fillers is almost the same as that of the previous low melting point glass, and the average particle size is within the range of 5 to 15 μm. The materials to be mixed as filler are lead titanate,
One type of substance selected from substances having a coefficient of thermal expansion such as zirconium silicate, β-spodiumene, β-eucryptite, cordierite, quartz glass, or aluminum titanate, or two.
Use a mixture of more than one type of substance in a predetermined ratio. The metal oxide is formed by forming at least one substance selected from silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), etc. into ultrafine particles with a particle size of 1 μm or less. As an example, the case of silicon dioxide will be explained. The raw material is silicon tetrachloride (Si Cl ₄ ), which is synthesized by hydrolyzing this Si Cl ₄ in an oxyhydrogen flame to aggregate silicon dioxide. When silicon dioxide is synthesized by the gas phase reaction as described above, ultrafine particles with an average particle size in the range of 10 to 20 millimicrons are formed. This is how it was made
SiO ₂ is amorphous silicon dioxide, has a wide specific surface area of approximately 200 m ² /g, and has a huge number of particles of 10 ¹⁷ per gram. Furthermore, silicon dioxide has silanol groups (SiOH) on its surface, and water molecules gather at the silanol groups of silicon dioxide, allowing it to absorb up to about 40 Wt% of water. However, this moisture can be easily released by heating silicon dioxide. The temperature range for the release of this physically adsorbed moisture is 100
Adsorbed water is released at temperatures ranging from around 200°C to around 200°C. Furthermore, even when heated, the specific surface area does not decrease until 550°C, which is the first time it decreases around 550°C. Therefore, by coating the surface of the particles of the low melting point glass with the fine particles of silicon dioxide to form a protective layer, moisture is absorbed by the silicic acid and does not come into direct contact with the low melting point glass. It does not react with melting point glass and has the effect of preventing deterioration of low melting point glass. Furthermore, since the adsorbed water is easily released from the silicon dioxide by heating during sealing, it does not remain in the sealing material layer. In addition to the above-mentioned protective effect, silicon dioxide has the effect of adjusting the softening point, and if too much silicon dioxide is added, the softening point of the glass will become too high, which is not preferable. Therefore, in order to cover the entire surface of the particles of low melting point glass with a small amount, it is necessary to reduce the particle size and increase the specific surface area. Therefore, the average particle size was set to 1 μm or less. Furthermore, if a large amount of fine particles is added, the bulk specific gravity as a frit increases, and when heated and melted, the volume decreases greatly, making it undesirable as a sealing material. Therefore, the maximum is 15%. It is also known that ultrafine silicon dioxide particles have silanol groups (SiOH) on their surfaces. The silanol groups on this surface tend to form hydrogen cross-links and bond with each other, but since these hydrogen bonds are in a weak state, applying only a slight external force causes them to separate again, resulting in a decrease in viscosity. When the external force is removed and the material is allowed to stand still, the silicon dioxide particles bond together again. This phenomenon is called the thixotropic effect and has the effect of improving printing characteristics. In other words, when printing a paste containing ultrafine particles of silicon dioxide, when it passes through the mesh of the screen, an external force is applied by the squeegee, which breaks the bonds and reduces the viscosity, improving fluidity and allowing it to pass through even a fine mesh. do. However, when the paste passes through the screen and is printed on the substrate, it remains stationary, so hydrogen bonds occur and the viscosity increases, making it possible to print with high precision without the paste dripping or flowing out. The thixotropic effect is also present in ultrafine particles of aluminum oxide and titanium oxide, which, like silicon dioxide, have the effect of improving printing characteristics. Example 1 Low melting point glass powder 1500g 68.0Wt% Lead titanate 700g 31.7 Ultrafine particles - SiO ₂ 700g 0.3 The low melting point glass used had the following composition. PbO 83Wt% B ₂ O ₃ 9 〃 SiO ₂ 3 〃 Al ₂ O ₃ 5 〃 The low melting point glass consisting of the above components is formed into a powder form, and a 150-mesh pass-through product is used. The average particle size is 5 to 10 μm, and the maximum particle size is about 100 μm. The melting point is below 450°C. Weigh 1500g of this low melting point glass. Lead titanate is used as a type of filler. The average particle size of 10 μm is adjusted to the above ratio.
Weigh 700g. Ultrafine silicon dioxide particles are obtained by weighing 7.4 g of amorphous fine particles with an average particle size of 0.01 μm and thoroughly mixing them in a mixer or disperser to form a low melting point glass 11, as shown in the enlarged view of Figure 3. Ultrafine particles of silicon dioxide are attached to the surface of the material to coat the surface. At the same time, the surface of lead titanate, which is a filler, is also coated, but it does not affect the effect of lowering the expansion coefficient in any way, and in the case of amorphous silicon dioxide, the coefficient of thermal expansion is 5 × 10 ^-7 / Since the value is as small as °C, it can also effectively reduce the coefficient of thermal expansion. Pigments may also be added to add color. 230 g of vehicle is added to the sealing material mixed as described above to form a paste. The vehicle contains 1 to 2 wt% of cellulose binder such as ethyl cellulose or methyl cellulose.
It is composed of 98 to 99 Wt% of alcohol, such as terpineol, which is a binder solvent. This vehicle is applied to the sealing material at 8~
Add at a rate of 10Wt% and make into a paste. The sealing material paste thus formed has thixotropic properties and excellent printing properties. Example 2 Low melting point glass 79wt% Lead titanate 10 〃 Zirconium silicate silicon dioxide 10 〃 Ultrafine particle silicon dioxide 1 〃 In this example, a two-component substance with a low expansion coefficient of lead titanate and zirconium silicate was added as a filler. and 1Wt% ultrafine silicon dioxide.
This is an example in which the effects of preventing deterioration of low melting point glass and improving thixotropy were greater than those of Example 1. The only difference from Example 1 is the ratio of the ingredients, and the rest is the same as Example 1, so the explanation will be omitted. The present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist thereof. As explained above, according to the sealing material of the present invention, ultrafine silicon dioxide particles are attached to the low melting point glass particles, which are the main components of the sealing material, so that the protective layer of the chemically weak low melting glass acts as a protective layer. without moisture or chemicals directly adhering to the low melting point glass.
Further, it can be released by heat treatment during sealing. Therefore, it has the effect of providing a sealing material with strong chemical resistance and water resistance. Furthermore, since the silicon dioxide is made into ultrafine particles of 1 μm or less, it has thixotropic properties and has the effect of significantly improving printing characteristics.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of a general fluorescent display tube, and FIG. 3 is an enlarged view of the sealing material of the present invention. 11...Low melting point glass, 12...Filler material, 13...Ultrafine particle SiO ₂ .

Claims (1)

[Claims] 1. A filler with a low expansion coefficient of 14 to 38% is uniformly dispersed in a lead-boric acid based low melting point glass with a softening point of 60 to 85% of 450°C or less expressed as weight %. , 0.05~
A sealing material characterized in that 15% of ultrafine metal oxide particles with an average particle size of 1 μm or less adhere to almost the entire surface of low melting point glass and filler. 2 The low expansion coefficient filler is lead titanate,
The sealing material according to claim 1, comprising at least one substance selected from zirconium silicate, β-spodiumene, β-eucryptite, cordierite, etc. 3. The sealing material according to claim 1, wherein the metal oxide is made of at least one substance selected from silicon dioxide, aluminum oxide, and titanium oxide.