JP5381288B2 - Method for producing silica sand for glass production - Google Patents

Description

  The present invention relates to a method for producing silica sand for glass production and a silica sand for glass production produced by the method.

  In recent years, with the improvement in performance of electronic devices, the demand for quality required for glass used in electronic devices and the like has also increased. For example, for glass substrates used in flat panel displays such as liquid crystal displays, there are no undissolved substances or bubbles, and a higher visible light transmittance in the visible light range than ever before. It is strongly demanded.

  In order to improve the quality of glass products, it is important to optimize melting conditions and improve melting equipment, but it is also important to lower the concentration of impurities contained in raw materials used in the manufacture of glass products. . For example, silica sand that is most often used as a raw material for glass usually contains impurities such as iron and titanium. When glass is produced using silica sand that contains a large amount of these impurities, transmission of visible light through the glass is possible. This is because inevitable problems such as a worsening rate occur.

  In view of such problems, for example, the following Patent Documents 1 to 3 disclose glass raw materials for obtaining high-quality glass and methods for producing the same. Specifically, Patent Document 1 discloses a problem caused by a difference in particle diameter of a plurality of raw materials by pulverizing a wet raw material agglomerate among a plurality of types of powdered glass raw materials and mixing them with other glass raw materials. It is disclosed to reduce uniformity.

  Patent Document 2 describes that a direct current is passed through a mineral sand mixed with silica sand ore, fine ferromagnets, and at least one acid, alkali and salt, followed by magnetic separation. Thus, Patent Document 2 describes that impurities can be separated without a complicated process.

In Patent Document 3, as a mixed raw material for glass that can obtain a homogeneous glass article even in a low-temperature melting environment, a mixed raw material for glass that is put into a glass melting furnace, and a plurality of different compositions pulverized after mixing There is disclosed a mixed raw material for glass in which particles of an inorganic raw material having a particle diameter in a particle diameter histogram curve of a granular material are ₉₀ μm or less.

JP 52-92223 A JP 52-56115 A JP 2006-69881 A

  Incidentally, in recent years, not only high performance of electronic devices but also low cost of electronic devices have been strongly demanded. In connection with this, the request | requirement of the cost reduction with respect to the glass used for an electronic device etc. is also increasing. For this reason, not only are there few impurities in glass materials, but there is a strong demand for low cost. Among these, the demand for cost reduction has been greatly increased for the silica sand most frequently used as a glass raw material.

  As an inexpensive silica sand, for example, silica sand composed of sea sand having a plurality of maximum values in the particle diameter distribution in a particle diameter histogram (also referred to as particle diameter frequency distribution) curve (hereinafter referred to as “multiple peak silica sand” in this specification). ). If this multi-peak silica sand can be used as a glass raw material, it is possible to greatly reduce the cost of glass.

  However, when glass melting was performed using a plurality of peak silica sands as a glass raw material, there was a problem that undissolved substances were easily generated. When the glass melting temperature is increased, undissolved materials are reduced, but there is a problem that the visible light transmittance of the glass is lowered. Therefore, when the multi-peak quartz sand is used as it is as a glass raw material, it is difficult to produce high-quality glass.

  Moreover, in order to obtain high-grade silica sand from inexpensive multiple-peak silica sand, it is conceivable to treat the multiple-peak silica sand by the method described in Patent Document 2 described above, but even in that case, undissolved substances are easily generated. This problem cannot be solved.

  This invention is made | formed in view of this point, The objective is to provide the method which can manufacture the silica sand for glass manufacture which an undissolved substance does not produce easily at low cost.

  As a result of intensive research to achieve the above object, the present inventors have a plurality of local maximum values (peaks) in the particle size distribution in the particle size histogram curve, and are silica sand ores (multiple peak silica sands) that are sea sand. It was found that the reason why undissolved substances are likely to occur when glass melting is performed using glass as a glass raw material is that the composition of the particles is different in particle groups having different particle diameter distribution maximum values in the particle diameter histogram curve. .

  That is, silica sand ore with a particle size distribution having a maximum value of 2 or more in the particle size distribution in the particle size histogram curve is collected from, for example, a crust in which natural rocks with different origins are layered with crustal deformation. Or accumulated sand deposited on different coastlines in one place by the action of ocean currents. For this reason, in the particle group from which the maximum value of the particle diameter distribution in a particle diameter histogram curve differs, a particle composition differs. Therefore, when multiple peak silica sand is used as a glass raw material, it has been found that, when glass is melted, particles that are easy to melt tend to melt first and particles that are difficult to melt remain as undissolved materials. Moreover, it discovered that the particle group which has only one maximum value of the particle diameter distribution in the particle diameter histogram curve isolate | separated from multiple peak silica sand has a substantially identical composition. As a result, in order to obtain silica sand in which undissolved substances are unlikely to remain from the multiple peak silica sand, the multiple peak silica sand is classified into a plurality of particle groups having different maximum particle size distribution values in the particle diameter histogram curve before pulverization. Aside from this, the inventors came up with the idea that it is effective to produce silica sand as a glass raw material from only one particle group among a plurality of particle groups.

  That is, the first method for producing silica sand for glass production according to the present invention has a plurality of local maximum values in the particle size distribution in the particle size histogram curve, and the silica sand ore that is sea sand is converted into particles in the particle size histogram curve. A first classification step of classifying the particle distributions into a plurality of different particle groups, a pulverization step of pulverizing one of the plurality of particle groups, and classifying the pulverized particle groups; And a second classification step of extracting silica sand in a predetermined particle diameter range from the pulverized particle group.

  Further, the second method for producing silica sand for glass production according to the present invention has a plurality of maximum values in the particle size distribution in the particle size histogram curve, and the silica sand ore that is sea sand is converted into particles in the particle size histogram curve. This is a method for producing silica sand for glass production using a particle group having only one maximum value of the particle size distribution in a particle diameter histogram curve obtained by classifying into a plurality of particle groups having different maximum values of the diameter distribution. And crushing the particle group having only one maximum value of the particle size distribution, and classifying the pulverized particle group and taking out silica sand in a predetermined particle diameter range from the pulverized particle group. It is characterized by being.

  In the present invention, before pulverizing the plurality of peak silica sands, in the first classification step, the particle size distribution in the particle diameter histogram curve is classified into a plurality of particle groups having mutually different maximum values. Each of the plurality of particle groups has only one maximum value of the particle size distribution in the particle size histogram curve, and has almost the same composition. For this reason, the silica sand for glass manufacture with few composition irregularities between particles can be obtained by obtaining the silica sand for glass manufacture from only one of these particle groups. Therefore, the silica sand for glass production produced according to the present invention does not have a large difference in ease of melting among the particles, and the silica sand for glass production produced according to the present invention contains almost no particles that are difficult to melt. . Therefore, when the silica sand for glass manufacture manufactured by this invention is used, an undissolved substance does not remain easily in glass.

  Moreover, in this invention, since a grinding | pulverization process and a 2nd classification process are performed after a 1st classification process, the silica sand for glass manufacture with a small particle diameter and a small particle diameter distribution width can be obtained. According to the present invention, by carrying out the pulverization step to reduce the particle size, the eutectic reaction with other glass raw materials easily proceeds during glass melting. Further, by performing the second classification step and reducing the particle size distribution width, it is possible to make the easiness of melting the particles uniform. Therefore, it becomes difficult to produce undissolved substances.

From the viewpoint of more effectively suppressing the remaining of undissolved matter, D ₅₀ which is the median diameter of the particles in the particle diameter histogram curve of the particles pulverized in the pulverization step is preferably 200 μm or less, and is 150 μm or less. More preferably, it is more preferably 100 μm or less. By doing in this way, eutectic reaction with other glass raw materials becomes easy to progress at the time of glass melting. Therefore, it becomes difficult to produce undissolved substances. However, since when the median diameter _{D 50} of the particles is too small as 20 [mu] m or less or 10μm or less particles tend to agglomerate, or the median diameter _{D 50} of the particles 20 [mu] m, is preferably is preferably 30μm or more.

  Furthermore, in this invention, since cheap multiple peak silica sand is used as a raw material of the silica sand for glass manufacture, the silica sand for glass manufacture can be manufactured cheaply. Therefore, according to the present invention, silica sand for glass production that hardly causes undissolved material even when the glass melting temperature is lowered can be produced at low cost.

In the present invention, the pulverization step is preferably a step of pulverizing the particle group having the lowest impurity concentration among the plurality of particle groups. In general, the particle group having the largest particle size distribution maximum value in the particle size histogram curve has a lower impurity concentration, and therefore the pulverization process has the largest particle size distribution maximum value in the particle size histogram curve among the plurality of particle groups. A step of pulverizing large particle groups is preferable. By doing in this way, the silica sand for glass manufacture with a low impurity concentration can be manufactured. From the viewpoint of lowering the impurity concentration, the median diameter (D ₅₀ ) of the particles in the particle diameter histogram curve of the particles to be pulverized in the pulverization step is preferably 300 μm or more.

  In general, impurities such as iron and titanium oxide are not uniformly dispersed in the particle, and the particle has a high impurity concentration portion and a low impurity concentration portion. In the case of silica sand, the portion with a lower impurity concentration has a higher particle diameter than the portion with a higher impurity concentration. Accordingly, when the silica sand ore is pulverized, the pulverized product having a larger particle size has a lower impurity concentration, and the impurity concentration tends to increase as the particle size decreases. In view of this, for example, it is also conceivable to manufacture silica sand for glass production by selecting only silica sand having a large particle diameter after pulverizing the plural peak silica sand without performing the first classification step. In this case, since the classification process only needs to be performed once, the manufacturing process can be simplified, and the manufacturing cost of silica sand for glass manufacturing can be reduced.

  However, when only the silica sand having a large particle size is selected after pulverizing the plurality of peak silica sands without performing the first classification step, the obtained silica sand may contain particles having different compositions. Therefore, it becomes difficult to sufficiently suppress the remaining undissolved material.

  Further, when only the silica sand having a large particle size is selected after pulverizing the multiple peak silica sand without performing the first classification step, the impurity concentration cannot be sufficiently lowered.

  Only by performing the first classification step before the pulverization step, taking out only the particle group having a large maximum value of the particle size distribution in the particle size histogram curve, performing the pulverization step, and further classifying the pulverized particle group, Silica sand for producing glass can be produced with little compositional variation between particles and a sufficiently low impurity concentration.

  The silica sand for glass manufacture manufactured by the manufacturing method of this invention is used for manufacture of various glass products, such as glass for electronic components, window glass, and glass for optical members. Window plate glass is plate glass used for the purpose of dividing a space such as laminated plate glass, multilayer plate glass, and tempered plate glass into two. Specific examples of the glass for electronic parts include glass fibers used for printed wiring boards and FRP, tube glass used for flash lamps, xenon lamps, backlights, fluorescent lamps, and the like. Specific examples of the optical member glass include a lens and an optical fiber connecting member.

Among them, the present invention, many content of SiO ₂ component, which is particularly suitable for undissolved easily occurs glassware containing SiO ₂ component. Many content of SiO ₂ component, the undissolved easily occurs glassware containing SiO ₂ component, and a glass substrate for flat panel displays. Specific examples of the glass substrate for flat panel display include a glass substrate for liquid crystal display, a glass substrate for plasma display, and a glass substrate for organic electroluminescence display.

  Moreover, since the glass substrate for flat panel displays is required not only to have undissolved substances but also to have a high transmittance, the present invention that can increase the transmittance is a glass substrate production for flat panel displays. It is particularly useful for the production of silica sand.

  The silica sand ore used in the present invention is not particularly limited as long as it is a sea sand having a plurality of maximum values in the particle size distribution in the particle size histogram curve, but the largest maximum value and the largest among the plurality of maximum values. It is preferable to be sea sand whose difference from the small maximum value is 10 μm or more. In particular, in the present invention, it is preferable to use sea sand having two maximum values separated by 10 μm or more as the quartz sand ore.

  Here, the sea sand refers to a variety of physicochemical actions that the rough ore undergoes in the ground, in particular, silica sand having an external shape whose surface is rounded by a water stream.

Silica sand ore means a raw ore mainly composed of SiO ₂ , and the silica sand ore is not limited to a raw ore consisting only of SiO ₂ . Silica sand ore may contain heavy metal elements such as cobalt, chromium, cadmium and manganese in addition to iron and titanium oxide, but from the viewpoint of producing glass with high visible light transmittance, It is preferable to use a silica sand ore with a low content of heavy metal elements such as cobalt and chromium and iron. Specifically, in the quartz sand ore to be used, Fe ₂ O ₃ is preferably 100 ppm or less in terms of oxide in terms of mass percentage, more preferably 70 ppm or less, and Cr _{2 in} terms of mass percentage in terms of oxide. O ₃ is preferably 3 ppm or less, more preferably 1 ppm or less, and TiO ₂ is preferably 300 ppm or less, more preferably 250 ppm or less in terms of mass percentage in terms of oxide, and cadmium and manganese. Each of them is preferably 10 ppm or less in terms of mass percentage.

  The silica sand ore may contain alkali metal elements such as sodium and potassium, but the content of sodium and potassium in terms of oxides is preferably 100 ppm or less.

  In the present invention, the classification method in the first and second classification steps is not particularly limited as long as it can be efficiently classified, and a dry classification method or a wet classification method may be used. May be. Here, the dry classification method is a method in which an object to be classified is put into an air stream and classified by a weight difference. For example, air, helium, neon, argon, krypton xenon, fluorine, chlorine, bromine, Knox (NOx), sox (SOx), nitrogen, carbon monoxide, carbon dioxide, hydrogen can be used for the dry classification method. , Chlorine, water vapor, or a mixed atmosphere of these gases. The atmospheric pressure is not particularly limited, and the classification step may be performed, for example, under an atmospheric pressure, a reduced pressure atmosphere, or a high pressure atmosphere.

  On the other hand, the wet classification method is a method in which an object to be classified is put into a liquid stream and classified. Examples of the liquid to be used include water, aqueous hydrogen peroxide, an aqueous solution to which a surfactant is added, an aqueous solution containing reactive components such as ions, an acid solution, an alkaline solution, ion-activated water, plasma irradiation water, and carbon dioxide gas saturation. Examples include various gas saturated water such as water, nonpolar organic solvents, and polar organic solvents.

  The particle size distribution measurement method may be based on any principle, but it is a method that can be measured in a state where the raw stone particles are dispersed, and the reproducibility of the measurement result is within 5%. There is preferably used a method that hardly causes individual differences due to handling or the like. As such a method, for example, the particle size of raw sand is measured using a sieve defined in JIS Z8801-1 (2008) “Test sieve—Part 1: Metal sieve” using a reduced sample. The method of doing is mentioned. In the case of measurement using a laser diffraction measurement device or measurement of sintered raw materials, the particle size distribution is measured by using an electron microscope, various fine structure observation devices, and an analysis device for the obtained images. It is also possible to do.

  In the present invention, the particle diameter distribution is measured three times by the above method for the same collected raw material obtained from the raw ore by the reduction operation, and the result is adopted.

  The method for pulverizing the particle group used in the pulverization step of the present invention is not particularly limited as long as the particle group can be efficiently pulverized and foreign particles are not easily mixed into the particle group. Grinding can be performed. The ball used in the ball mill method is preferably formed of a material that does not significantly affect glass melting even when a small amount is mixed in silica sand for glass production. For example, an alumina ball is preferably used. .

  The amount of the ball used when the ball mill method is performed is not particularly limited. For example, it is preferable that the mass ratio of the particle group and the ball mill is about 1: 1.5. Although the diameter of a ball | bowl is not specifically limited, For example, 5 mm-50 mm, Preferably it can be set as about 10 mm-30 mm. Further, the pulverization time can be appropriately set according to the particle diameter to be obtained, and can be, for example, about 1 hour.

  In the present invention, steps other than the first and second classification steps and the pulverization step, for example, a drying step and a further classification step may be appropriately performed according to the characteristics required for silica sand for glass production. Good. For example, before the first classification step, the classification step may be performed using a coarse screen of, for example, 800 μm or more in order to remove foreign substances such as organic substances.

  Moreover, you may perform the process of removing a heavy metal after a grinding | pulverization process or a 2nd classification process. This step can be performed, for example, by a spiral beneficiation method. Spiral beneficiation method means that raw sand is made to flow down by a water stream while turning it 5 times in a spiral trough having an inner slope of 40-45 ° and an outer diameter of about 0.6 m, for example. It is a method for removing heavy metals by collecting and removing them inside the radial direction of the ridges. This spiral beneficiation method may be performed only once or may be repeated a plurality of times. Moreover, it is preferable to dry the particle group from which the heavy metal has been removed by performing sun drying or the like after the spiral beneficiation method.

  In the present invention, an inexpensive plural-peak silica sand is used, and before pulverizing the multiple-peak silica sand, in the first classification step, the particle size distribution in the particle diameter histogram curve is classified into a plurality of particle groups having different local maximum values. Since the particles are classified again after pulverization, the particle size distribution can be reduced and the composition unevenness between the particles can be reduced. Therefore, the silica sand for glass manufacture which an undissolved substance cannot produce easily can be manufactured at low cost.

It is a flowchart showing the manufacturing method of the silica sand for glass manufacture.

  Hereinafter, the present invention will be described in more detail. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without departing from the scope of the present invention.

  Silica sand for glass production was produced based on the flowchart shown in FIG.

  First, in step S1 shown in FIG. Specifically, foreign substances such as organic substances were removed from the quartz sand ore by passing the quartz sand ore through a coarse screen exceeding 800 μm. Here, the silica sand ore used is a particle size distribution in a particle size histogram curve measured using a sieve defined in JIS Z8801-1 (2008) “Sieving for testing—Part 1: Metal sieve”. The first maximum value in the vicinity of the particle diameter of about 460 μm and the second maximum value in the vicinity of the particle diameter of about 170 μm.

  Next, in the first classification step of Step S2, the silica sand ore was classified into a plurality of particle groups having different maximum particle size distribution values in the particle size histogram curve using water flow classification. Specifically, the quartz sand ore was classified into a first particle group having only a local maximum value with a particle size of about 460 μm and a second particle group having only a local maximum value with a particle size of about 170 μm. .

  When the impurity concentration was measured for each of the first particle group and the second particle group, the first particle group having a larger particle diameter was more impurity than the second particle group having a smaller particle diameter. Was low. For this reason, in the present example, the first particle group having a low impurity concentration was selected.

  Next, in step S3, spiral mineral processing was performed. Specifically, the first particle group is caused to flow down by a water stream while swirling five times in a spiral cage having an inner surface inclination of 40 to 45 ° and an outer diameter of about 0.6 m, whereby heavy particles containing heavy metals are collected. Collected radially inside and removed. In this example, this spiral beneficiation was repeated twice.

  Next, in Step S4, the first particle group was sun-dried and dried.

  Next, in the pulverization step of Step S5, alumina balls were used and the first particle group was pulverized by a ball mill. In this pulverization step, the mass ratio between the first particle group and the ball mill was 1: 1.5. The grinding time was 1 hour.

Next, in the second classification step of Step S6, the pulverized first particle group was classified. The median diameter D ₅₀ of the particles measured using a sieve of classified silica sand JIS Z8801-1 (2008) was 90 μm. Moreover, the classified silica sand had only one maximum value of the particle size distribution in the particle size histogram curve, and the maximum value was in the range of 75 to 106 μm. In the classified silica sand, coarse particles having a particle diameter exceeding 250 μm were not observed.

As a result of conducting a chemical analysis on the obtained silica sand, Fe ₂ O ₃ is 45 ppm, TiO ₂ is 240 ppm, Cr ₂ O ₃ is 1 ppm or less in terms of oxide percentage, and other cadmium or cobalt is used. Heavy metal elements were also 10 ppm or less.

  Next, the meltability of the silica sand obtained by the above process was evaluated. Specifically, the silica sand is converted into a non-alkali glass (OA-10 manufactured by Nippon Electric Glass) suitable as a glass substrate for a liquid crystal display, and a chemical conversion raw material such as carbonates of other alkaline earth metal elements, A uniform batch material was prepared by mixing. This batch material was put into a 300 cc platinum crucible, melted at 1550 ° C. for 3 hours, and cast into a carbon frame. As a result of microscopic observation of the obtained glass lump, no undissolved material was observed. From this result, it can be seen that the use of silica sand produced according to the present invention can suppress the generation of undissolved matter.

  Further, a molten glass obtained by melting a batch raw material having the same composition as that described above at 1550 ° C. for 10 hours in the same procedure was cast into a carbon frame in the same manner as described above, and cooled in a slow cooling furnace. Thereafter, a 1 mm thick sample was cut out from the obtained glass plate, and both surfaces were mirror-polished using cerium oxide. And when the measurement of the spectral transmittance of the obtained sample was measured with a double beam scan type spectrophotometer, no decrease in the transmittance due to absorption of impurities or the like was observed in the visible light range. From this result, it is understood that the silica sand produced according to the present invention has a low impurity concentration, and by using this silica sand, glass having a high visible light transmittance can be produced.

Claims (7)

A first classifying a silica sand ore, which is a sea sand, having a plurality of maximum values in a particle size distribution in a particle size histogram curve, into a plurality of particle groups having different particle size distribution maximum values in a particle size histogram curve. Classification process of
A pulverizing step of pulverizing one of the plurality of particle groups;
A method for producing silica sand for glass production, comprising: classifying the pulverized particle group, and taking out a silica sand in a predetermined particle diameter range from the pulverized particle group. Obtained by classifying silica sand ore, which is sea sand, into multiple particle groups with different maximum particle size distributions in the particle size histogram curve, having multiple maximum values in the particle size distribution in the particle size histogram curve. A method for producing silica sand for glass production using a particle group having only one maximum value of the particle size distribution in the obtained particle size histogram curve,
A pulverizing step of pulverizing a particle group having only one maximum value of the particle size distribution;
And a step of classifying the pulverized particle group and taking out the silica sand in a predetermined particle diameter range from the pulverized particle group. The said grinding | pulverization process is a process of grind | pulverizing the particle group with the lowest impurity concentration among these particle groups, The manufacturing method of the silica sand for glass manufacture of Claim 1 or 2. The method for producing silica sand for glass production according to claim 1, wherein the pulverizing step is a step of pulverizing a particle group having a maximum value of a particle size distribution in a particle size histogram curve among the plurality of particle groups. . 5. The method for producing silica sand for glass production according to claim 1, wherein a median diameter (D ₅₀ ) of particles in a particle diameter histogram curve of a particle group pulverized in the pulverization step is 300 μm or more. It is used for manufacture in any one of the glass for electronic components, the window glass, and the glass for optical members, The manufacturing method of the silica sand for glass manufacture as described in any one of Claims 1-5 characterized by the above-mentioned. . It is used for manufacture of the glass substrate for flat panel displays, The manufacturing method of the silica sand for glass manufacture of Claim 6 characterized by the above-mentioned.

Images