Sealing material paste

Abstract

To provide an environmentally friendly sealing material paste that does not easily thicken over time. [Solution] A sealing material paste comprising a sealing material, a resin binder, and a solvent, characterized in that the sealing material comprises at least glass powder and lead-free refractory filler powder, and the moisture content of the sealing material is 0.2% by mass or less.

Description

[Technical Field]

[0001] The present invention relates to a sealing material paste, and more specifically to a sealing material paste suitable for sealing soda glass plates together in display tubes such as fluorescent display tubes. [Background technology]

[0002] Fluorescent display tubes generally have a structure in which two soda glass plates (cover glass and base glass) are arranged at a predetermined distance apart, and their outer edges are sealed with a sealing material. The soda glass plate that serves as the base glass often has a frame formed on its outer edge to accommodate the element. In addition, side spacers made of soda glass may be placed on the outer edge of the soda glass plate (see Patent Documents 1-3).

[0003] The sealing materials used include resin-based adhesives, metal solder, and composite inorganic powders containing glass powder and refractory filler powder.

[0004] Resin-based adhesives include epoxy, silicone, polyurethane, polyethylene, polyester, and other materials, either individually or in mixtures of two or more of these. Additives such as plasticizers and tackifiers, as well as mica, alumina, glass beads, and carbon fibers, are also used. However, resin-based adhesives have the problem of not being able to completely block moisture intrusion, making it difficult to maintain airtightness inside fluorescent display tubes, and the resin is susceptible to degradation due to ultraviolet light and moisture.

[0005] Furthermore, as metal solder, pastes and rods mainly composed of Pb-Sn-Sb-Zn alloy, Bi-Sn-Ti alloy, Bi-Sn-Zn-Cu-Ag alloy, etc., are used. However, metal solder has the problem of poor durability of the sealing part, as well as difficulty in increasing the productivity of fluorescent display tubes.

[0006] On the other hand, if a composite inorganic powder containing glass powder and refractory filler powder is used as the sealing material, the intrusion of gas can be completely blocked and the soda glass plates can be firmly sealed together, thus maintaining the airtightness inside the fluorescent display tube over a long period of time.

[0007] When using a composite inorganic powder as the sealing material, the fluorescent display tube is manufactured as follows. First, the sealing material, resin binder, and solvent are kneaded together to form a sealing material paste, which is then put into a dispenser device. The sealing material paste is then applied in a linear fashion to the outer edge of a soda glass plate from the dispenser nozzle, and the resulting coating film is dried. Next, this coating film is fired to form a glaze layer on the outer edge of the soda glass plate. After that, two soda glass plates are stacked with the glaze layer in between, and then fired in an electric furnace or the like to seal the two soda glass plates. Furthermore, an exhaust pipe attached to one of the soda glass plates is connected to a vacuum pump or the like, the pressure between the two soda glass plates is reduced, and the exhaust pipe is sealed with a burner or the like to obtain the fluorescent display tube. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 08-017362 [Patent Document 2] Japanese Patent Publication No. 2005-213125 [Patent Document 3] Japanese Patent Publication No. 2006-012429 [Overview of the project] [Problems that the invention aims to solve]

[0009] Incidentally, conventional sealing pastes used lead-based glass powder as a low-melting-point glass and lead titanate as a refractory filler. Due to recent legal revisions, lead titanate has been designated as a hazardous substance, and environmental regulations such as REACH have also been strengthened, making it strongly required to use substances other than lead titanate as refractory fillers.

[0010] However, when using a substance other than lead titanate as the refractory filler, there was a problem that the sealing material paste thickened over time, making it difficult to discharge the sealing material paste from the dispenser nozzle.

[0011] An object of the present invention is to provide a sealing material paste that is environmentally friendly and difficult to thicken over time.

Means for Solving the Problems

[0012] The sealing material paste of the present invention is a sealing material paste containing a sealing material, a resin binder, and a solvent, wherein the sealing material contains at least glass powder and lead-free refractory filler powder, and the moisture content of the sealing material is 0.2% by mass or less.

[0013] In the sealing material paste of the present invention, the lead-free refractory filler powder is preferably willemite.

[0014] In the sealing material paste of the present invention, the moisture content of the lead-free refractory filler powder is preferably 0.1% by mass or less.

[0015] In the sealing material paste of the present invention, the specific surface area of the lead-free refractory filler powder is preferably 0.7 m , ,

[0018] / g or less.

[0016] In the sealing material paste of the present invention, the glass powder preferably contains, as a glass composition, 75 to 95% by mass of PbO and 5 to 20% by mass of B2O3.

[0017] According to the present invention, it is possible to provide a sealing material paste that is environmentally friendly and difficult to thicken over time.

Mode for Carrying Out the Invention

[0018] The sealing material paste of the present invention is a sealing material paste containing a sealing material, a resin binder, and a solvent, wherein the sealing material contains at least glass powder and lead-free refractory filler powder. The sealing material is added to seal soda glass plates. The resin binder is added for the purpose of adjusting the viscosity of the paste. The solvent is added to disperse the sealing material in the paste. Further, if necessary, a surfactant, a thickener, etc. can also be added.

[0019] (Sealing material paste) In the sealing material paste of the present invention, at a shear rate of 4 (sec -1 ), the viscosity during production at 40°C is preferably 180 Pa·s or less, particularly preferably 170 Pa·s or less, and especially preferably 75 to 160 Pa·s. If the viscosity during production at 40°C at a shear rate of 4 (sec -1 ) is too high, it becomes difficult to discharge the sealing material paste from the dispenser nozzle. Note that if the viscosity during production at 40°C at a shear rate of 4 (sec -1 ) is too low, the sealing material paste is likely to separate, so the sealing material paste is likely to clog in the dispenser nozzle. Note that the "viscosity during production" is the viscosity of the sealing material paste measured immediately after manufacturing the sealing material paste.

[0020] In the sealing material paste of the present invention, at a shear rate of 4 (sec -1 ), the viscosity after 7 days at 40°C is preferably 200 Pa·s or less, particularly preferably 190 Pa·s or less, and especially preferably 75 to 180 Pa·s. If the viscosity after 7 days at 40°C at a shear rate of 4 (sec -1 ) is too high, it becomes difficult to discharge the sealing material paste from the dispenser nozzle. Note that if the viscosity after 7 days at 40°C at a shear rate of 4 (sec -1 ) is too low, the sealing material paste is likely to separate, so the sealing material paste is likely to clog in the dispenser nozzle. Note that the "viscosity after 7 days" is the viscosity of the sealing material paste measured after 7 days have elapsed since the production of the sealing material paste.

[0021] In the sealing material paste of the present invention, the viscosity after 7 days - the viscosity at the time of production (shear rate 4 (sec -1 ), the value obtained by subtracting the viscosity at the time of production at 40°C from the viscosity after 7 days at 40°C (shear rate 4 (sec -1 )) is preferably 40 Pa·s or less, 30 Pa·s or less, particularly 20 Pa·s or less. The smaller this value, the less likely the sealing material paste is to thicken over time, meaning that the sealing material paste can be easily discharged from the dispenser nozzle even after changes over time.

[0022] (Sealing material) The content of the sealing material is preferably 90.0 to 99.9% by mass, 90.5 to 97.5% by mass, particularly 91.0 to 95.0% by mass. If the content of the sealing material is too low, the proportion of the solid content of the coating film will be low, so the coating film is likely to shrink in the subsequent drying process and firing process, and cracks in the glaze layer are likely to occur. On the other hand, if the content of the sealing material is too high, the content of the resin binder and solvent will be relatively low, making it difficult to form a paste.

[0023] The moisture content of the sealing material is 0.2% by mass or less, preferably 0.18% by mass or less, particularly 0.15% by mass or less. If the moisture content of the sealing material is too high, the sealing material paste is likely to thicken over time.

[0024] The thermal expansion coefficient of the sealing material is 50×10 -7 ~85×10 -7 / °C, 55×10 -7 ~80×10 -7 / °C, particularly preferably 60×10 -7 ~77×10 -7 / °C. If the thermal expansion coefficient of the sealing material is outside the above range, when the object to be sealed is soda-lime glass, inappropriate stress will remain in the sealed part, so there is a risk that the sealed part will be stress-damaged by mechanical impact or the like.

[0025] The softening point of the sealing material is preferably 450°C or lower, 435°C or lower, and particularly preferably 350-425°C. If the softening point of the sealing material is too high, it becomes difficult for the sealing material to soften and flow, making it difficult for the sealing shape to become a meniscus shape, and the sealing strength between the two soda glass plates tends to decrease.

[0026] (Glass powder) The glass powder is preferably lead-based glass. Lead-based glass has a low melting point and readily reacts with the surface layer of the soda glass plate during firing, which is advantageous for improving sealing strength.

[0027] Lead-based glass preferably contains PbO 75-95% and B2O 35-20% by mass as its glass composition. The reasons for limiting the content range of each component are explained below. In the explanation of the glass composition range of lead-based glass, the % indicates mass %.

[0028] PbO is a component that lowers the softening point, and its content is preferably 75-95%, 80-92%, and especially 83-88%. If the PbO content is too low, the softening point becomes too high, and the softening fluidity tends to decrease. On the other hand, if the PbO content is too high, the glass tends to devitrify during firing, and this devitrification tends to decrease the softening fluidity.

[0029] B2O3 is an essential component for glass formation, and its content is preferably 5-20%, 8-17%, and especially 10-15%. If the B2O3 content is too low, the glass network will not form easily, and the glass will be prone to devitrification during firing. On the other hand, if the B2O3 content is too high, the viscosity of the glass will increase, and its softening and fluidity will decrease.

[0030] In addition to the above ingredients, the following ingredients may also be added.

[0031] SiO2 is a component that enhances water resistance, and its content is preferably 0-5%, 0-3%, and especially 0.1-1.5%. If the SiO2 content is too high, the softening point may rise unduly. Also, the glass may become more prone to devitrification during firing.

[0032] Al2O3 is a component that enhances water resistance, and its content is preferably 0-5%, 0-3%, and especially 0.1-1.5%. If the Al2O3 content is too high, the softening point may rise unduly.

[0033] Li2O, Na2O, and K2O are components that reduce resistance to devitrification. Therefore, the content of Li2O, Na2O, and K2O is 0-5%, 0-3%, and especially less than 0-1%, respectively.

[0034] MgO, CaO, SrO, and BaO are components that enhance devitrification resistance, but they also increase the softening point. Therefore, the content of MgO, CaO, SrO, and BaO is 0-5%, 0-3%, and especially 0-1%, respectively.

[0035] ZnO is a component that reduces the coefficient of thermal expansion, and its content is preferably 0-5%, 0-3%, and especially 0-1.5%. If the ZnO content is too high, the glass is more likely to devitrify during firing.

[0036] P2O5 is a component that enhances resistance to devitrification, but if its content is high, the glass is more likely to separate into phases during melting. Therefore, the P2O5 content is preferably 2.5% or less, and particularly preferably 1% or less.

[0037] ZrO2 is an ingredient that enhances acid resistance, and its content is preferably 0-5%, 0-3%, and especially 0-1.5%. If the ZrO2 content is too high, the glass is more likely to devitrify during firing.

[0038] TiO2 is an ingredient that enhances acid resistance, and its content is preferably 0-5%, 0-3%, and especially 0-1.5%. If the TiO2 content is too high, the glass is more likely to devitrify during firing.

[0039] (Lead-free refractory filler powder) The lead-free refractory filler powder is preferably willemite. Using willemite as the lead-free refractory filler powder reduces the viscosity of the sealing material paste over time. Furthermore, willemite has a low coefficient of thermal expansion, high mechanical strength, and good compatibility with lead-based glass. However, using cordierite as the lead-free refractory filler powder makes the sealing material paste more prone to viscosity increase over time.

[0040] The moisture content of the lead-free refractory filler powder is preferably 0.1% by mass or less, 0.09% by mass or less, and particularly preferably 0.08% by mass or less. If the moisture content of the lead-free refractory filler powder is too high, the sealing material paste will tend to thicken over time.

[0041] The specific surface area of ​​the lead-free refractory filler powder is 0.7 m². 2 It is preferable that the amount be less than or equal to / g. If the specific surface area of ​​the lead-free refractory filler powder is too large, the moisture content of the lead-free refractory filler powder tends to increase.

[0042] Furthermore, willemite produced by the melting method tends to have a low moisture content and a small specific surface area.

[0043] In the sealing material according to the present invention, the content of lead-free refractory filler powder is preferably 20 to 50 volume%, 25 to 45 volume%, and particularly preferably 30 to 40 volume%. If the content of refractory filler powder is too low, the thermal expansion coefficient of the sealing material may become unduly high. On the other hand, if the content of refractory filler powder is too high, the softening and flowability of the sealing material may become unduly low.

[0044] In addition to glass powder and refractory filler powder, the sealing material may also contain, for example, glass beads to provide a spacer function, or pigments to blacken it.

[0045] (Resin binder) In the sealing material paste, the resin binder content is preferably less than 0.6% by mass, 0.15 to 0.55% by mass, and particularly preferably 0.2 to 0.5% by mass. If the resin binder content is too high, the debinding properties tend to decrease, and bubbles and other debris tend to remain in the sealed area after firing. If the resin binder content is too low, the sealing material paste tends to separate, making it prone to clogging in the dispenser nozzle. Also, the dried film tends to crack.

[0046] Suitable resin binders include acrylic acid esters (acrylic resins), ethyl cellulose, polyethylene glycol derivatives, nitrocellulose, polymethylstyrene, polyethylene carbonate, and methacrylic acid esters. Acrylic acid esters and ethyl cellulose are particularly preferred because they exhibit good thermal decomposition properties and can increase viscosity with small additions.

[0047] (solvent) In the sealing material paste, the solvent content is preferably 5-9.5% by mass, 5.5-9% by mass, and particularly 6-9% by mass. If the solvent content is too low, it becomes difficult to disperse the sealing material in the paste. On the other hand, if the solvent content is too high, the sealing material paste tends to separate, making it more likely to clog the dispenser nozzle.

[0048] The boiling point of the solvent is preferably 250°C or lower, 100-230°C, and particularly 150-210°C. If the boiling point of the solvent is too high, the coating film will be difficult to dry. If the boiling point of the solvent is too low, the solvent will evaporate easily, causing the sealing material paste to clog the dispenser nozzle.

[0049] Suitable solvents include N,N'-dimethylformamide (DMF), α-terpineol, higher alcohols, γ-butyllactone (γ-BL), tetralin, butylcarbitol acetate, butyl acetate, ethyl acetate, isoamyl acetate, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, benzyl alcohol, toluene, 3-methoxy-3-methylbutanol, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, propylene glycol methyl ether (PM), dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, propylene carbonate, dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone. Dipropylene glycol monomethyl ether and tripropylene glycol monobutyl ether are particularly preferred due to their high viscosity and good solubility of resin binders and the like.

[0050] The sealing material paste of the present invention can be applied by various methods, but as described above, it is preferable to apply it with a dispenser.

[0051] As described above, the sealing paste of the present invention is suitable for sealing soda glass plates together, but is also suitable for sealing soda glass plates with exhaust pipes and soda glass plates with side spacers. Furthermore, it is also suitable as a sealing paste for vacuum insulated glass or for solar collector panels. [Examples]

[0052] The present invention will be described in detail below based on the following examples. Note that the following examples are merely illustrative. The present invention is not limited in any way to the following examples.

[0053] Table 1 shows examples of the present invention (samples No. 1 to 4) and comparative examples (sample No. 5).

[0054] [Table 1]

[0055] The lead-based glass powders listed in the table were prepared as follows. First, a glass batch was prepared by mixing various raw materials to obtain lead-based glass having the following glass composition, and this was placed in a platinum crucible and melted at 900-1000°C for 1-2 hours. During melting, the mixture was stirred with a platinum rod to homogenize the molten glass. Next, a portion of the obtained molten glass was poured between water-cooled twin rollers and formed into a film. The lead-based glass contains, by mass%, PbO 86%, B2O 313%, and SiO 21%.

[0056] Next, the obtained glass film was crushed in a ball mill. A portion of the glass powder was then classified using a 350-mesh sieve to obtain fine glass powder, while the remaining glass powder was classified using a 100-mesh sieve to obtain coarse glass powder. Finally, the coarse and fine glass powders were mixed as needed to obtain glass powder.

[0057] Next, sealing materials were prepared by mixing the glass powder and lead-free refractory filler powder listed in the table in the proportions indicated in the table. The moisture content and specific surface area of ​​the lead-free refractory filler powder, as well as the moisture content of the sealing material, were measured. Note that "WIL" in the table refers to willemite.

[0058] The moisture content was measured using the Karl Fischer method.

[0059] The specific surface area was measured using the BET method.

[0060] Next, the sealing material, resin binder, and solvent listed in the table were mixed in the proportions shown in the table, and then kneaded in a stirrer to prepare a sealing material paste. Here, dipropylene glycol monomethyl ether (boiling point 190°C) was used as the solvent. Ethyl cellulose was used as the resin binder. The shear rate of the obtained sealing material paste was 4 (sec -1The viscosity of the product was measured at 40°C at the time of manufacture and 7 days later using a rotational viscometer (Brookfield). Subsequently, the viscosity at the time of manufacture was calculated by subtracting the viscosity at 7 days later. The results are shown in Table 1.

[0061] As is clear from Table 1, samples No. 1 to 4 had low viscosity (viscosity after 7 days - viscosity at time of manufacture) of 19 Pa·s or less. On the other hand, sample No. 5 had a high viscosity (viscosity after 7 days - viscosity at time of manufacture) of 71 Pa·s.

Claims

1. A sealing material paste containing a sealing material, a resin binder, and a solvent, The sealing material comprises at least glass powder and lead-free refractory filler powder. A sealing material paste characterized by having a moisture content of 0.2% by mass or less.

2. The sealing material paste according to claim 1, characterized in that the lead-free refractory filler powder is willemite.

3. The sealing material paste according to claim 1 or 2, characterized in that the moisture content of the lead-free refractory filler powder is 0.1% by mass or less.

4. The specific surface area of ​​the lead-free refractory filler powder is 0.7 m². ２ The sealing material paste according to claim 1 or 2, characterized in that it is less than or equal to / g.

5. The glass powder has a glass composition of PbO 75-95% by mass, B ２ O ３ The sealing material paste according to claim 1 or 2, characterized by containing 5 to 20%.

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