JPS6253811B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrode substrate used in optical display devices and the like, and particularly to an electrode substrate having a thin film obtained by coating and heating a condensed silicate compound. It is a well-known fact that in recent years, silicon oxide or a film similar to silicon oxide has been used for insulating films of semiconductor devices, insulating films of liquid crystal display devices, or alignment control films. In particular, in the case of a liquid crystal display element, it consists of a pair of electrode substrates in which a transparent conductor thin film and an organic or inorganic compound film are sequentially formed on an insulating substrate, and the surface on which the organic or inorganic compound film is formed is covered with a spacer. They are combined facing each other with a liquid crystal sealed inside. In this case, the orientation of the organic or inorganic compound film with respect to the liquid crystal is directly utilized.
DSM tires and phase transition type display methods are available.
Further, a display method is known in which the alignment of liquid crystal in contact with the organic or inorganic compound film is controlled to be twisted nematic by rubbing the organic or inorganic compound film in a specific direction. The organic or inorganic compound films formed in this manner generally require good adhesion with the base insulating film and transparent conductor thin film, no pinholes in the film itself, and uniformity over the entire film. It has good insulation properties and excellent insulation properties. Furthermore, when used as a display substrate, it is desirable that the film itself be as transparent as possible, and uniformity in film thickness is required. Further, it is desirable that the method for forming the thin film be mass-produced as much as possible. As a method for forming the organic or inorganic compound on the electrode forming substrate, a method of sputtering or vapor depositing a metal oxide, a method of coating an organic substance or an organometallic compound, etc. are employed. There is a method of coating a metal oxide by sputtering, but if the metal oxide is deposited on a substrate with electrodes by sputtering or vapor deposition, the step between the underlying insulating substrate and the electrode will not be filled and will remain sharp. This not only causes a decrease in insulation properties, but also causes non-uniform alignment at the stepped portions when used as a liquid crystal display substrate, which has a significant adverse effect on the display characteristics of the display device. In order to reduce such a steep difference in level between the underlying insulating substrate and the electrode, it is necessary to dissolve an organic substance, a substance that will form an organic polymer film such as polyvinyl alcohol in an appropriate solvent, and apply it on the electrode-attached substrate. This can be achieved by However, when such organic material films are used, they generally cannot be expected to have insulating properties, and when used as display substrates such as liquid crystal display elements, airtight sealing treatments, such as glass sealing at around 500°C, are required. It is impossible to produce a reliable display device because it cannot withstand the process. Furthermore, the situation is similar when an organometallic compound such as a silicon derivative film is dissolved in an appropriate solvent and applied to a substrate with electrodes. It is impossible to achieve an airtight seal. Furthermore, the inorganic film obtained by dissolving the organometallic compound in a suitable solvent and coating it on the electrode-forming substrate and then heating to volatilize or burn off the organo group has a non-uniform surface and significant irregularities. Further, the inorganic film formed in this manner does not have strong adhesion to the electrode-forming substrate regardless of the film thickness, and peeling may occur. The reason for these is thought to be that gas generated when the organo group is volatilized or burnt out by heating moves or passes through the coating film. Therefore, in order to form an inorganic film with a smooth film surface and high adhesion to the surface of the electrode-forming substrate, large groups (organo groups) must be formed during the heating process, such as in organometallic compounds. It is desirable not to use, as a coating liquid, a compound that breaks chemical bonds and volatilizes in large quantities, or a solution prepared by dissolving the compound in an appropriate solvent.
In other words, even if the constituent compound of the film to be formed on the electrode forming substrate or its precursor compound is dissolved or dispersed in an appropriate solvent and applied, the chemical bonds may change slowly or in small amounts during the solvent drying or heating process after coating. It is desirable to select a substance that causes a change in chemical species. From this point of view, for silicon compound films, condensed silicate compounds [general formula: S _io O _o-1 (OH) _2o
+2 :n≧1] is dissolved in an appropriate solvent and applied to an electrode-forming substrate.
At this time, the selection of the condensed silicate compound and the selection of the solvent are important factors, and the desired silicon compound can be obtained from a solution containing 50 mol% or more of orthosilicate Si(OH) ₄ as the condensed silicate compound. I can't. That is, even if an alcohol solution of orthosilicic acid is applied to an electrode forming substrate, the adhesion between the thin film and the insulating substrate and transparent electrode is poor, and a homogeneous film cannot be formed under any coating and baking conditions. Therefore, as a general conventional coating liquid, the degree of condensation has advanced to a certain degree and the condensed silicate compound [average degree of condensation 4 to 10] is mixed with methyl alcohol, ethyl alcohol, iso-propyl alcohol, n-propyl alcohol, or iso-butyl alcohol. and a mixed solvent of low viscosity alcohols such as n-butyl alcohol and low viscosity esters such as methyl acetate, ethyl acetate and ethyl ester. Generally, in order to suppress gelation, the condensed silicic acid compound concentration is used at 20% or less, but the initial viscosity of the solution using the low viscosity solvent at such a concentration or less is 10 centipoise or less. Although such a low viscosity solution is suitable when using a spin coating method or a dip coating method, it cannot be applied to a print coating method, which allows mass production to be several steps higher than these coating methods. It is clear that by using the print coating method, it is possible to selectively form a thin film only on the necessary portions of the substrate, and therefore the mass productivity is greater than the spin coating method, dip coating method, and spray coating method. The purpose of the present invention is to select an appropriate solvent, create a solution containing a condensed silicate compound suitable for printing, and apply it on a substrate on which electrodes are formed. An object of the present invention is to provide an electrode substrate on which a thin film is formed by heating after coating, with good mass productivity. In order to form a thin film on a substrate on which electrodes are formed by a printing coating method, even if an offset printing method is used, which allows the application of a solution with a relatively wide viscosity range by changing the printing jig, it is necessary to use the printing ink solution. The viscosity must be 10 centipoise or higher. As a method for producing a condensed silicate compound solution with a high viscosity of 10 centipoise or more, firstly, the condensed silicate compound concentration is increased or a condensed silicate compound having a large degree of condensation is used, and the second method is to use a condensed silicate compound solution with a high viscosity of 10 centipoise or more. It is conceivable to use a solvent with high viscosity that is compatible with the compound, but as described above, when the former is used, partial gelation occurs in the solution, which is undesirable in terms of storage. When using the latter, in addition to ensuring that the condensed silicate compound is sufficiently dissolved in the latter solvent or a mixed solvent with an appropriate other solvent, the solvent must be heated at a relatively low temperature, preferably below 400°C. It is necessary for the gas to volatilize. However, it is desirable that it be relatively difficult to volatilize at room temperature. As a result of considering many compounds that should be used as solvents based on these required criteria, we found that glycerin, polyethylene glycol, polyvinyl alcohol, and nitrocellulose alone or as a mixture thereof, or these compounds together with the above-mentioned alcohols and esters, etc. The film obtained by applying a solution of a condensed silicic acid compound dissolved in a solvent mixed with the above-mentioned electrode forming substrate and heating it has good adhesion, good uniformity, and a desired film thickness. It became clear that it was possible to obtain The viscosity of the solution can be adjusted from 10 to 10 by appropriately selecting the mixing ratio of the solvent and the condensed silicate compound concentration depending on the printing jig and desired film thickness.
It is possible to make it 300000 centipoise. The present invention will be described below with reference to Examples. Example 1 First, a low viscosity solution containing a condensed silicate compound is synthesized. Ethyl silicate 40 [general formula S _io O _o-1
(OC ₂ H ₅ ) _2o+2 : mixture where n≧1] 20g, water 5g,
Charge 50g of ethyl alcohol, 24.8g of ethyl acetate, and 0.2g of phosphoric acid into a reaction vessel, and heat at 60°C.
Allow the reaction to run for 3.0 hours. After confirming by gas chromatography that no ethyl silicate remains, the reaction is terminated. When this liquid was analyzed by liquid chromatography, it was found that orthosilicic acid S _i
It was confirmed that the amount of (OH) ₄ present was less than 10%, and most of the silicic acid compounds were high-order condensed compounds [general formula S _io O _o-1 (OH) ₄ :n≧2]. You can see that Also, the initial viscosity of this solution is approximately 2
It's Centipoise. For the sake of the following explanation, this solution will be referred to as a condensed silicate compound raw solution for convenience. Next, 30 g of the condensed silicate compound stock solution was collected and mixed with 70 g of glycerin in a beaker with stirring. The solution obtained after stirring is clear,
It has a viscosity of approximately 130 centipoise. Next, ethyl alcohol was added using a rotary evaporator.
Easily volatile components such as ethyl acetate were removed to form a solution with a viscosity of approximately 2000 centipoise. This solution is transparent and homogeneous with no segregation of components. As shown in the block diagram in the figure, the above solution is printed on a glass substrate on which electrodes have been formed in advance using an offset proofing machine. To explain the outline of the printing method, in Fig. 1, the display surface area is 12×
A 47mm LCD display electrode pattern is formed on the top.
Each of the lower glass substrates is used as a printing medium 5. The printing machine is equipped with a manual offset proofing machine, and the thickness
Wrap a 1.65mm blanket seal 6b (K-110 type, manufactured by Kinyosha) around the fuselage core 6a, and place a 11.9x
A relief plate 3 made of ethylene propylene terpolymer (hereinafter referred to as EPT) cut to 46.9 mm is pasted with adhesive to form a blanket body 6. As the ink stand 7, a glass plate on which indium oxide is vapor-deposited is used. The condensed silicate compound solution, which is a printing ink, is coated on the indium oxide vapor-deposited surface of the ink bed 7 using a roll coater, and then applied to the ink bed 7 of the rubber blanket cylinder 6 and the printing material 5.
The printing pressure is 0.5Kg/cm ² . Under these conditions, the printed layers printed on the top and bottom glass plates of the liquid crystal display were heated at 120°C for 30 minutes, and then heated at 500°C for 30 minutes to remove organic components. Promote volatilization and silicon oxidation. As a result, the film thickness
A thin film of 1500 ű100 Å is formed. This thin film contains about 4% by weight of SiOH bonds, and it is confirmed from the infrared absorption spectrum that the composition is close to SiO ₂ . Next, the surface of the thin film is rubbed using a cotton cloth. The directions of this rubbing are different for the upper glass plate and the lower glass plate, and are perpendicular to each other. Then, after printing glass paste containing spacers such as glass beads except for the small part of the liquid crystal sealing port so as to keep the gap between the upper and lower glass plates at 10 μm, a load was applied.
The seal is fired at 450℃. A thin Cr--Ni--Au layer is then formed around the sealing port by vapor deposition. This forms the envelope of the liquid crystal display device. Then, a biphenyl liquid crystal E-7 (Merck & Co., Ltd.) is sealed in the surrounding air under reduced pressure, and the filling opening is sealed with solder. When the liquid crystal display device thus produced is observed using two polarizing plates, it is observed that the liquid crystal layer is oriented in a twisted manner over the entire surface. The film formed to orient the liquid crystal in this way is called an alignment film. Next, the lifespan (operating lifespan) until the alignment of the liquid crystal deteriorates after the operation test of the liquid crystal display device under high temperature and high humidity was investigated. For comparison, as shown in Table 1, in addition to the display device (Table 1 sample No.),
A display device using a film formed by a spin coating method (Sample No. in Table 1) and a display device bonded with an epoxy resin adhesive instead of a glass seal were created. For sample No. in Table 1, the above condensed silicate compound stock solution having a viscosity of about 2 centipoise was used as the solution to be applied, and the solution was applied by rotation at 1700 revolutions/minute while dropping the solution using a spinner. The subsequent preparation procedure follows the sample No. above. The film thickness is
It is 1500 ű300 Å. For sample No. in Table 1, the preparation procedure for sample No. is followed except for the sealing method.
All samples had good initial characteristics. The operating test conditions are to apply a 12V, 32Hz pulse to drive the device in a thermostatic chamber at 70°C and 90% relative humidity. The degree of alignment deterioration of the liquid crystal is determined by microscopic observation.

[Table] As a result, as shown in Table 1, even though the alignment film is printed and coated with an epoxy resin adhesive, when observed under a microscope with a magnification of 10 times, it was found that approximately 500
After some time has elapsed, alignment deterioration of the liquid crystal begins to be observed. Further, even if a glass seal is applied, when an alignment film formed by a spin coating method is used, deterioration in the alignment of the liquid crystal begins to be observed after about 2000 hours of operation. For those that use an alignment film made by printing and applying a glass seal, no abnormalities such as alignment deterioration are observed even after 3,000 hours of operation. The reason for the short operating life of LCD devices sealed with epoxy adhesives is that the epoxy adhesives are not sufficiently airtight, allowing moisture from the outside air to enter the display device, causing electrochemical reactions that cause the liquid crystal to deteriorate. This is thought to be due to deterioration. In addition, the reason why an alignment film formed by printing coating method has a longer operating life than one formed by spin coating method is as follows.
This is presumably because a dense film with good adhesion is formed on the electrode and glass surface because the solution is printed while applying pressure in a direction perpendicular to the surface of the printing material. In addition, compared to the spin coating method, the printing coating method does not have a large difference in film thickness between the center and periphery of the substrate.
Since a uniform electric field is applied across the entire substrate,
Uniform display is guaranteed over the entire surface of the display device. Example 2 50g of condensed silicate compound stock solution used in Example 1
was collected and mixed with 50 g of polyethylene glycol 600 in a beaker with stirring. The solution obtained after stirring is homogeneous and transparent. Next, volatile components are partially removed using a rotary evaporator to form a solution with a viscosity of approximately 120 centipoise, which is used as printing ink. The same printing machine and blanket seal 6b as in Example 1 are used. As the material of the convex plate 8, Bright (main component: butyl rubber) with a rubber hardness of 50 is used. The thickness of the convex plate is approximately 0.5 mm, and V-shaped grooves with a depth of 0.1 mm are cut vertically and horizontally on the surface of this convex portion at a pitch of 0.2 mm. The ink stand 7 is placed on a 1 mm thick glass plate with a thickness of 0.2 mm.
A material with a Pyflon (polyamide resin) film of mm is used. The condensed silicate compound solution, which is the printing ink, is coated onto the pyflon film of the ink bed using a roll coater, and the printing pressure on the ink bed 7 of the rubber blanket cylinder 6 and the printing material 5 is set to 1 kg/cm. ² . Under these conditions, the printed layers printed on the upper and lower glass substrates of the liquid crystal display were heated at 120°C for 30 minutes, then at 500°C for 1 hour.
Heat for a period of time to form a thin film. As a result, the chemical composition of the film obtained is the same as that of Example 1, and the film thickness is 1300 ű100 Å. Further, according to microscopic observation, there are no defects such as pinholes over the entire film surface. Next, in the same manner as in Example 1, rubbing was performed to form an envelope with the upper and lower substrates, and Example 1
A liquid crystal is sealed in the envelope. Even in the liquid crystal display device constructed in this manner, it was observed that the liquid crystal layer was arranged in a twisted manner over the entire surface. In addition, the operating life under the same operating test conditions as Example 1 is
More than 3000 hours. Example 3 A solution is prepared in which 5 g of nitrocellulose is dissolved in 95 g of diethylene glycol acetate mono-n-butyl ether. Next, 50 g of the condensed silicate compound stock solution used in Example 1 was collected and mixed with 50 g of the nitrocellulose solution by thorough stirring in a beaker. The solution obtained after stirring was transparent, indicating that they were homogeneous and compatible. Next, volatile components are partially removed using a rotary evaporator to form a solution with a viscosity of approximately 8,000 centipoise, which is used as printing ink. Printing was carried out under the same conditions as in Example 1 except that the printing pressure was 1 Kg/cm ² , and the printing layer 4 was heated at 120°C for 30 minutes, then at 250°C.
℃ for 20 minutes and further heated at 500℃ for 1 hour to form a thin film. As a result, the chemical composition of the film obtained is the same as that of Example 1, and the film thickness is 1600 ű200 Å. According to microscopic observation, the film surface was as good as in Examples 1 and 2, and there were no defects such as pinholes. In addition, the film has good adhesion and MIL
As a result of visually observing the presence or absence of damage in the Standard C-6-75A rubber rubbing test (eraser: JIS standard S-50), it was found that there was no damage at all, and a dense film was formed with good adhesion. . Then, rubbing was performed in the same manner as in Example 1,
The upper and lower substrates constitute an envelope, and the liquid crystal of Example 1 is sealed in the envelope. In the liquid crystal display device of this example as well, it was observed that the liquid crystal was arranged in a twisted manner over the entire surface. Further, the operating life under the same operating test conditions as in Example 1 is 3000 hours or more. Although the case where polyvinyl alcohol is used is omitted in this example, the effect is almost the same as in Example 3. From the viewpoint of mass production, the above examples mainly focused on the printing coating method, but by appropriately selecting the composition of the solution, it is possible to have a viscosity of 10 centipoise to 300,000 centipoise using any of the above solvents. is possible, and the optimum viscosity can be selected depending on the coating method, and the coating method is not necessarily limited. Further, although a liquid crystal display device has been described in the embodiment, the present invention is not limited to this.

[Brief explanation of the drawing]

The figure is a diagram illustrating an outline of a method of applying a condensed silicate compound solution according to the present invention using an offset proofing machine. 1... plate plate, 2... printing plate, 3... letterpress,
4... Printing ink, 5... Printing material, 6... Rubber blanket cylinder, 6a... Body part, 6b... Rubber blanket body core, 7... Ink stand.

Claims (1)

[Claims] 1 A condensed silicate compound (general formula: S _io O _o-1 (OH) _2o+2 : n≧1), glycerin, and polyethylene are placed on an insulating substrate with an electrode including an insulating substrate and an electrode formed on the insulating substrate. Contains one or more compounds selected from glycol, polyvinyl alcohol and nitrocellulose, with a viscosity of 10 to
An electrode substrate characterized in that it has a thin film obtained by applying and heating a solution of 300,000 centipoise.