JP2008062349A - Method of washing glass sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of washing the surface of a glass sheet, which removes foreign matter on the surface of the glass sheet derived from metal tin, so as to be used for a glass substrate for a flat panel display used in a plasma display, a liquid crystal display and so on. <P>SOLUTION: The method of washing the surface of glass sheet, which is obtained by forming glass ribbon like a plate on a molten metal tin, includes a process of injecting particles with the Moh's hardness of 3 or less, and with the average particle diameter of 5 to 50 μm to make the particles collide with the surface of the glass sheet, thereby removing foreign matter on the surface of the glass sheet due to molten metal tin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for cleaning the surface of a glass plate obtained by a float process.

  The mainstream of the current glass plate manufacturing method is the “float method”. In this method, molten glass is continuously supplied to a bath filled with molten metal tin, called a tin bath, to form a glass ribbon, and the glass ribbon is floated on the surface of the tin bath. This is a method of forming a plate-like glass, and can stably produce a large amount of glass plates having excellent flatness.

  However, in this float method, a tin-based foreign matter originating from the molten metal tin may be formed on the glass plate surface and recognized as a defect. In particular, when a glass type produced by the float process has a high annealing point, the volatilization of the molten metal is likely to occur during the production process, and as a result, the occurrence of tin-based foreign matters due to the molten metal is likely to occur on the glass plate surface. .

  Applications of glass plates include automotive and architectural window fields, electronic materials, display fields, etc., and these applications require optical transparency and surface flatness. Accordingly, there is a demand for minimizing tin-based foreign matter defects as described above. Above all, in the case of glass substrates for flat panel displays used for plasma displays, liquid crystal displays, etc., even fine defects may cause problems, so the above-mentioned glass surface defects may be eliminated. Particularly desired.

  As a method for removing tin-based foreign matter from the glass surface produced by the float process, a method in which a glass substrate is immersed in an acidic aqueous solution to dissolve and remove the foreign matter has been proposed. For example, Patent Document 1 discloses nitric acid and hydrochloric acid. Soaking in a mixed acid, Patent Documents 2 and 3 disclose soaking in an inorganic acid solution containing divalent chromium ions. In addition, Patent Document 4 discusses a method in which tin-based fine foreign matter on the surface of a glass plate is removed by decomposition and volatilization by sublimating ammonium halide at a high temperature in the vicinity or in contact therewith.

On the other hand, it is known to blast the surface in order to remove and clean contaminants such as organic substances and oxides present on the surface of the object to be processed. For example, Patent Document 5 discloses a technique for removing organic substances from the surface by causing particles such as dry ice to collide with the surface of the glassy liquid crystal display panel from which the film has been peeled off, and then supplying plasma.
Japanese Patent Laid-Open No. 2-88445 JP-A-9-295832 JP-A-9-295833 Japanese Patent Laid-Open No. 10-85684 JP 2002-144231 A

  The present invention relates to a method for cleaning the surface of a glass plate obtained by forming a glass ribbon into a plate shape on molten metal tin, so that the glass plate can be provided for applications requiring optical transparency and surface flatness. In particular, to provide a method for cleaning a glass plate surface capable of removing foreign substances on the surface of a glass plate derived from metal tin so that it can be used for a glass substrate for a flat panel display used in a plasma display, a liquid crystal display, etc. Is an issue.

  In the present invention, a method for cleaning the surface of a glass plate obtained by forming a glass ribbon into a plate shape on molten metal tin was investigated, and a method for blasting the surface for cleaning was unexpectedly investigated. The present inventors have obtained knowledge that they are effective in removing metallic foreign substances formed on the surface of oxides such as glass, and have made the present invention.

  The glass plate surface cleaning method of the present invention is a glass plate surface cleaning method obtained by forming a glass ribbon into a plate shape on molten metal tin, and has a Mohs hardness of 3 or less and an average particle size of 5 to 50 μm. A foreign matter on the glass plate surface caused by the molten metal tin is removed by performing a blasting process in which the particles are jetted to cause the particles to collide with the glass plate surface.

  The Mohs hardness of the glass plate is 5-6. It is important to select the particle hardness and particle size to be sprayed on the glass plate surface to prevent the generation of scratches on the glass plate surface while removing foreign matter on the glass plate surface caused by molten metal tin by blasting. It is. From this viewpoint, the hardness of the particles injected onto the glass plate surface is 3 or less, preferably 2 or less, more preferably 1 or more.

  Further, if the particle size of the particles sprayed on the glass plate surface becomes too large, the glass plate may be damaged by an impact at the time of collision with the glass plate surface. On the other hand, when the particle size is small, it is difficult to remove foreign matters caused by molten metal tin. In the present invention, in consideration of this, the average particle size is set to 5 to 50 μm. In consideration of the above points, the average particle size is preferably 10 to 40 μm, more preferably 15 to 35 μm.

  In addition, the average particle diameter in this invention is defined as a value of the average particle diameter obtained by the method based on JIS H0554 (1995). And it measures by the method based on this method, and the particle | grains which have the above-mentioned particle diameter are applied to this invention.

  Furthermore, in this invention, it is preferable to perform the acid treatment which makes the glass plate surface contact with 0.1-30 normal acid aqueous solution by oxidation-reduction titration before or after making particles collide with the glass plate surface. In the present invention, the combined use of blasting and acid treatment was examined. When the acid treatment was performed before the blasting treatment, the removal of foreign matters on the surface of the glass plate caused by molten metal tin was remarkably effective. And it is preferable to use inorganic acid with strong acidity, such as nitric acid, a sulfuric acid, and hydrochloric acid, as this acidic aqueous solution.

  And it is preferable to use at least 1 sort (s) chosen from ice and dry ice for the particle | grains used for injection by the blasting process of this invention. If the particles are ice, it is preferable that the particles do not remain on the substrate surface and the subsequent cleaning is light. Further, if the particles are dry ice having sublimation properties, solid particles do not remain on the glass surface after the injection, and subsequent cleaning or the like is unnecessary. Considering this, it is more preferable that the particles used for injection are dry ice.

  The glass plate surface cleaning method of the present invention efficiently removes foreign matter on the glass plate surface caused by molten metal tin. Therefore, the glass plate whose surface is cleaned by the method of the present invention can be suitably provided for applications requiring optical transparency and surface flatness, and in particular, flat panels used for plasma displays, liquid crystal displays, and the like. It can be suitably used as a glass substrate for display.

  The glass plate surface cleaning method of the present invention is a glass plate surface cleaning method obtained by forming a glass ribbon into a plate shape on molten metal tin, and has a Mohs hardness of 3 or less and an average particle size of 5 to 50 μm. A foreign matter on the glass plate surface caused by the molten metal tin is removed by performing a blasting process in which the particles are jetted to cause the particles to collide with the glass plate surface.

  Examples of particles having a Mohs hardness of 3 or less in the present invention are ice, dry ice, calcium carbonate, gypsum, and talc. Among them, it is preferable to use ice and dry ice as described above.

  An apparatus for performing blasting has a mechanism for injecting a carrier gas in which a group of particles as described above is dispersed. When the particles to be ejected are dry ice, the apparatus for performing the blast treatment may have a mechanism for vaporizing liquid or supercritical carbon dioxide in a supercritical state. When carbon dioxide is vaporized, 20 to 40% by weight becomes dry ice. Therefore, when a mechanism for vaporizing liquid or supercritical carbon dioxide is provided, the carrier gas source and the particle source can be made the same.

  The carrier gas at the time of blasting is preferably 0.1 to 1 MPa, preferably 0.3 to 0.8 MPa, more preferably a gas compressed to 0.4 to 0.6 MPa. In addition, it is preferable to use a gas such as air or nitrogen, and the gas is preferably dried.

  Then, the particles are sprayed on the glass plate surface for 3 to 30 seconds, preferably 5 to 20 seconds, and the particles are preferably sprayed at an angle of 45 degrees from the vertical to the glass plate surface, and are sprayed substantially vertically. It is more preferable.

  The glass plate surface cleaning method of the present invention is a glass type produced by a float process, particularly a glass type having an annealing point of 600 ° C. or higher, particularly 600 to 800 ° C., particularly alkali ions. It is particularly effective for cleaning the surface of silicate glass species having alkaline earth ions, so-called high strain point glass. These high strain point glasses are suitably used for display applications such as plasma displays and liquid crystal displays, and since the glass has a high annealing point, tin tends to volatilize from the tin bath in the manufacturing process. It is because the foreign-material defect of the glass plate surface resulting from molten metal tin becomes easy to generate | occur | produce. The annealing point is obtained by a method based on JIS R3103-2 (2001) “Viscosity of glass and viscosity fixed point—Part 2: Measurement method of annealing point and strain point by fiber stretching method”. Is.

  Next, foreign substance types on the surface of the glass plate caused by molten metal tin will be described. The foreign matter includes a top spec that can be formed on the top surface side of the glass plate surface (the side opposite to the surface formed in contact with the molten tin), a tin falling object, and a bottom surface side of the glass plate surface (molten tin). Can be classified into dross caused by transfer from the conveyance roll deposits that can be formed on the surface formed in contact with the surface.

  The top spec is a fall deposit from the upper part of the tin bath, and is formed with a length of 1 to 5 μm, particularly 2 to 4 μm in the thickness direction of the glass plate, and 1 to 200 μm in the surface direction of the glass plate. The fallen tin can be formed with a length of 0.1 to 1 μm, particularly 0.2 to 0.5 μm in the thickness direction of the glass plate, and 1 to 100 μm in the surface direction of the glass plate. The dross is described as having a length of 0.1 to 1 μm, particularly 0.2 to 0.5 μm in the thickness direction of the glass plate and 100 to 400 μm in the surface direction of the glass plate. it can.

  And the difficulty of removing a foreign substance from a glass plate is in the order of “top spec> dross> tin fallen object”. This is because the temperature when foreign matter is generated is higher in the order of “top spec> dross> tin fallen object”. The cleaning method of the present invention is also effective for removing the top spec.

Example 1
Both surfaces of a glass plate (1000 mm × 1000 mm × 2.8 mmt) having a composition shown in Table 1 and an annealing point of 631 ° C. produced by the float method were visually observed, and as a tin-based foreign matter,
3 top specs
3 dross
Those having 4 falling tins were selected as glass plates to be cleaned. Using a blast cleaning device (dry ice blast cleaning device, powder shot, manufactured by Taiyo Nippon Sanso Co., Ltd.) on the glass plate, particles are jetted for 10 seconds using a carrier gas to the portion where tin-based foreign matter is present. A blasting process was performed. In this injection, the injection angle with respect to the glass plate surface was 90 °, and the distance from the particle injection portion to the glass plate surface was 10 mm.

  In the blast cleaning apparatus, gaseous carbon dioxide is injected at 0.25 kg / min from a mechanism for vaporizing carbon dioxide in a liquid or supercritical state. 30% by weight of it becomes dry ice. In this example, the average particle size of dry ice having a Mohs hardness of 2 is set to 30 μm, and the flow rate of gaseous carbon dioxide containing 30 wt% dry ice particles (the carbon dioxide is the carrier gas). Is performed at 300 l / min. No scratches were observed on the glass plate surface after blasting. After cleaning, the number of tin-based foreign matters present on the surface of the glass plate was observed, and the results were as follows.

2 top specs
1 dross
0 falling tin objects

Example 2
As a tin-based foreign material,
3 top specs
3 dross
Select a glass plate to be washed with 5 falling tin objects as a glass plate to be cleaned, and perform acid cleaning except showering for 60 seconds with a 40% -18% nitric acid aqueous solution (3N) before blasting. The procedure was the same as in Example 1.

  No scratches were observed on the glass plate surface after cleaning. And when the number of the tin-type foreign material which exists in the glass plate surface was observed, it became as follows.

Top spec 1
0 dross
Tin fallen object 0 Example 3
As a tin-based foreign material,
4 top specs
3 dross
A procedure similar to that of Example 2 was adopted except that a glass plate having four falling tins was selected as the glass plate to be cleaned and the order of the blast treatment and the acid treatment was reversed.

  No scratches were observed on the glass plate surface after cleaning. And when the number of the tin-type foreign material which exists in the glass plate surface was observed, it became as follows.

2 top specs
1 dross
0 falling tin objects Comparative Example 1
As a tin-based foreign material,
4 top specs
3 dross
A procedure having the same procedure as in Example 2 was performed except that a glass plate to be cleaned having 5 tin falling objects was selected and blasting was not performed.

  No scratches were observed on the glass plate surface after cleaning. And when the number of the tin-type foreign material which exists in the glass plate surface was observed, it became as follows.

4 top specs
3 dross
Tin falling object 1 [comparison of cleaning methods of each example and comparative example]
Table 3 shows the removal rate of each tin-based foreign substance in the glass plate cleaning performed in each of the examples and the comparative example. From this, it can be seen that the blast treatment is effective in removing tin-based foreign matters, particularly in removing dross and top peck. Moreover, it became clear by this invention that each tin type foreign material can be removed more efficiently by performing acid treatment before blasting or after blasting.

  The effect of removing the top specs by the blasting process performed in the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a surface state after a portion where the top spec is present on the surface of the glass plate is blasted under the conditions of this embodiment. And FIG. 22 has shown the surface state of the part in which the top specification of the glass plate before a blast process exists. It is confirmed that there is no scratch on the surface of the glass plate due to the blasting process, and that the top spec is removed by the blasting process.

  In the present embodiment, the blasting process is performed in a spot-like manner on a portion where foreign matter is present. However, in addition to this, the entire glass plate surface may be blasted at once, or the glass plate may be blasted linearly in the length direction of the glass and the glass plate moved during the blasting. The entire surface of the glass plate may be blasted by scanning a member to be blasted.

  After the glass plate cleaning method shown in the present invention is carried out, a glass substrate suitably used for display applications such as a plasma display and a liquid crystal display is obtained through a polishing process and the like.

It is a figure (photograph) which shows the surface state after carrying out the blast process of the part in which the top specification existed on the glass plate surface on the conditions of a present Example. The length of the bar in the figure represents 100 μm. It is a figure (photograph) which shows the surface state of the part in which the top specification of the glass plate before blasting exists. The length of the bar in the figure represents 100 μm.

Claims (4)

A method for cleaning a glass plate surface obtained by forming a glass ribbon into a plate shape on molten metal tin, and spraying particles having a Mohs hardness of 3 or less and an average particle size of 5 to 50 μm on the glass plate surface A method for cleaning the surface of a glass plate, characterized by having a step of removing foreign matter on the surface of the glass plate caused by the molten metal tin by causing collisions. The glass plate surface according to claim 1, further comprising a step of bringing the glass plate surface into contact with an acidic aqueous solution of 0.1 to 30 N by oxidation-reduction titration before or after the particles collide. Cleaning method. The method for cleaning a surface of a glass plate according to claim 1 or 2, wherein the particles are at least one selected from ice and dry ice. A method for producing a glass substrate, comprising the step of cleaning the surface of the glass plate by the method according to claim 1.