TW201302630A - Method for producing granulated bodies, method for producing molten glass, and method for producing glass article - Google Patents

Abstract

Provided is a method for producing granulated bodies that have excellent strength and do not easily generate dust. A method for producing granulated bodies that are used for the production of alkali-free glass, said method comprising: a step for preparing a starting material slurry that contains a glass starting material mixture and water; and a step for producing granulated bodies by spray-drying the starting material slurry. The glass starting material mixture contains at least silica sand, boric acid, a magnesium source and an alkaline earth metal source. At least a part of the magnesium source is a water-soluble magnesium salt, and at least a part of the alkaline earth metal source is a water-soluble alkaline earth metal source. When that total of the molar quantity of the water-soluble magnesium source in terms of MgO and the molar quantity of the water-soluble alkaline earth metal source in terms of oxide in the glass starting material mixture is taken as 1, the relative value of the molar quantity of the water-soluble magnesium source in terms of MgO is 0.05 or more. When the molar quantity of the boric acid in terms of B2O3 in the glass starting material mixture is taken as 1, the relative value of the molar quantity of the water-soluble alkaline earth metal source in terms of oxide is 1.00 or less.

Description

Method for producing granules, method for producing molten glass, and method for producing glass articles Field of invention

The present invention relates to a method for producing a granule used as a raw material of an alkali-free glass, a method for producing a molten glass using the granule obtained by the production method, and a method for producing a glass article using the method for producing the molten glass. The method.

Background of the invention

For various glass substrates for displays, etc., substantially alkali-free glass containing no alkali metal oxide is used. In addition, recently, the alkali-free glass having a composition in which the B ₂ O ₃ content is smaller than that of a conventional one is used because of the diversification of characteristics sought for the alkali-free glass.

Compared with the conventional soda lime glass, the alkali-free glass has a large amount of a raw material having a high melting point and an alkali metal component which does not accelerate the melting of the raw material, and the unmelted raw material is liable to remain. Moreover, the uniformity of the glass composition tends to decrease.

In order to prevent the unmelted raw material from remaining in the inside of the glass substrate, it is presumed that it is effective to atomize the raw material powder. However, when the raw material powder of the fine particles is to be put into the melting kiln, the raw material powder is scattered, and there is a problem that the glass composition is unstable and the raw material is wasted.

As a method for solving such problems, there is a method in which the raw material powder is granulated and used in the production of an alkali-free glass in Patent Documents 1 and 2.

Advanced technical literature Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 51-75711

Patent Document 2: Japanese Laid-Open Patent Publication No. 2009-179508

Summary of invention

However, in the case of granules of the glass raw material powder, if the strength of the granules is insufficient, the granules may be broken during use to produce fine powder. In particular, the fine powder when transporting granules is likely to be a problem. If the fine powder is generated, a problem occurs in which a part of it is scattered. That is, the granules of the glass raw material powder are required to have sufficient strength against the impact applied when the granules are conveyed. Specific impacts can be exemplified by collisions or frictional impacts of granules which are carried by the granules during transportation, impacts of granules colliding with walls of pipes, storage tanks, etc., and granules. Impact caused by friction with the wall surface of piping or feed hopper, etc.

In particular, when a glass article is produced by using a melting furnace in a gas which melts the granules in a gas phase gas atmosphere, the granules are conveyed to the burner by air or the like in a gas-melting furnace, and are flame-treated. The granules are melted and vitrified in the gas. Therefore, if the size of the granule is too large, the glass transition rate becomes low, so it must be small to some extent (for example, the average particle diameter (D50) is about 50 to 700 μm). A granulation method spray drying method suitable for obtaining granules having a small particle diameter as described above.

However, if the strength of the obtained granules is insufficient, it is made in transit. One part of the granules will collapse, or the particles on the surface of the granules will peel off and become micronized. As a result, the fine powder becomes dust, which not only causes the exhaust line of the melting furnace in the gas to be plugged, but also becomes incapable of continuous operation due to frequent clogging such as a bag filter, and the composition of the granules becomes unsuccessful. There are problems such as deviation of the composition of the glass.

The present invention has been made in view of the above circumstances, and is a method for producing a granulated body which is excellent in strength and which is difficult to produce fine powder, and a method for producing a fused glass obtained by using the method, and a glass article. The manufacturing method is for the purpose.

The method for producing a granule of the present invention is a method for producing a granule for producing a glass raw material mixture of an alkali-free glass, and characterized in that the production method has the following steps: a step of preparing a raw material slurry, the raw material The slurry comprises a glass raw material mixture and water; and a step of spray drying the raw material slurry to produce granules; the glass raw material mixture at least containing cerium, boric acid, magnesium source and alkaline earth metal source; and at least the magnesium source a part of the water-soluble magnesium salt, and at least a part of the alkaline earth metal source is a water-soluble alkaline earth metal source; in the glass raw material mixture, the water-soluble magnesium source is converted into MgO molar amount and water-soluble alkaline earth metal source conversion When the total amount of molybdenum of the oxide formed is 1, the relative value of the molar amount of the water-soluble magnesium source converted to MgO is 0.05 or more; and in the glass raw material mixture, the boric acid is converted into the Mo _{2 of} B ₂ O ₃ When the amount is 1, the relative value of the amount of the water-soluble alkaline earth metal source converted into the oxide is 1.00 or less.

The pH of the raw material slurry is preferably 5.5 or more.

The granules in the particle size distribution curve indicate that the D50 of the volume-cumulative median diameter is preferably 50 to 700 μm.

The water-soluble magnesium salt is preferably magnesium sulfate and/or magnesium chloride.

In the glass raw material, the total amount of magnesium sulfate in terms of SO _{3 and} the content of magnesium chloride in terms of Cl is preferably 0.05 to 5% by mass.

The alkali-free glass is preferably borosilicate glass, and has the following composition in terms of oxide: SiO ₂ : 40 to 85% by mass, Al ₂ O ₃ : 0 to 22% by mass, and B ₂ O ₃ : 3 to 20% by mass, MgO: 0.04 to 8% by mass, CaO: 0 to 14.5% by mass, SrO: 0 to 24% by mass, BaO: 0 to 30% by mass, and R ₂ O (R represents alkali metal): 0.1 The mass% or less; however, the total amount of CaO, SrO, and BaO is 5% by mass or more.

The aforementioned raw material slurry preferably further contains a dispersing agent.

The present invention further provides a method for producing molten glass, which is obtained by heating the granules to obtain molten glass.

As a method for producing molten glass, it is preferred to: in a gas phase gas atmosphere At least a part of the granules are melted to be molten glass particles, and the molten glass particles are collected to form a molten glass.

The present invention further provides a method for producing a glass article, which is obtained by molding and cooling the molten glass obtained by the method for producing molten glass.

According to the present invention, granules excellent in strength and difficult to produce fine powder can be obtained. In particular, it is easy to suppress the generation of fine powder when transporting granules.

By using the granules of the present invention, scattering of the raw material powder in the production of molten glass or in the manufacture of glass articles can be prevented. Further, since a glass raw material which is easy to scatter fine powder can be used, a raw material which is hard to melt, such as cerium sand, can be used to increase the melting rate by using a fine powder raw material, and segregation is less likely to occur.

Further, since the strength of the granules is good, generation of fine powder can be suppressed, and molten glass or glass articles having good uniformity and homogeneity of composition can be obtained.

Simple illustration

Fig. 1 is a graph showing the results of measurement of the particle size distribution of Example 1. 0 psi is the particle size distribution in the case where compressed air is not blown, and 50 psi is the particle size distribution in the case where compressed air is blown. (below, the same)

Fig. 2 is a graph showing the results of measurement of the particle size distribution of Example 2.

Fig. 3 is a graph showing the results of measurement of the particle size distribution of Example 3.

Fig. 4 is a graph showing the results of measurement of the particle size distribution of Example 4.

Fig. 5 is a graph showing the results of measurement of the particle size distribution of Example 5.

Fig. 6 is a graph showing the results of measurement of the particle size distribution of Example 6.

Fig. 7 is a graph showing the results of measurement of the particle size distribution of Example 7.

Fig. 8 is a graph showing the results of measurement of the particle size distribution of Example 8.

Fig. 9 is a graph showing the measurement results of the particle size distribution of Comparative Example 1.

Fig. 10 is a graph showing the measurement results of the particle size distribution of Comparative Example 2.

Fig. 11 is a graph showing the results of measurement of the particle size distribution of Comparative Example 3.

Fig. 12 is a graph showing the results of measurement of the particle size distribution of Comparative Example 4.

Fig. 13 is a graph showing the results of measurement of the particle size distribution of Comparative Example 5.

Form for implementing the invention

In the present invention, the "D50" indicating the average particle diameter of the particles means the median diameter of 50% of the volume cumulative in the particle size distribution curve measured by the laser diffraction scattering method. The "D90" is a particle size distribution in which the volume is 90% from the small particle size side in the particle size distribution curve.

The particle size distribution curve of the granules is determined by a dry laser diffraction scattering method, and the particle size distribution curve of the raw material powder used for the manufacture of the granules is based on a wet laser diffraction scattering method. To determine. (Refer to JIS-Z8825-1 (2001) and JIS-Z8819-1 (1999))

In the present invention, the components in the glass are represented by oxides such as B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , MgO, CaO, SrO, BaO, and Na ₂ O, and the contents of the respective components are converted. It is expressed by the mass ratio (% by mass) of the oxide.

In the present invention, the term "alkaline earth metal" means three elements of calcium (Ca), strontium (Sr) and barium (Ba).

<alkali-free glass>

The granules of the present invention (also referred to as "granules" in this specification) In the case of an alkali-free glass (in the present specification, it is also referred to as "glass"). That is, the alkali-free glass can be obtained by heating and melting the granule of the present invention and allowing the vitrification reaction. The granules of the present invention are basically granules comprising all of the raw materials of the alkali-free glass, for example, an alkali-free glass having a predetermined glass composition can be obtained from one granule.

In the present invention, the term "alkali-free glass" means a glass which does not substantially contain an alkali metal oxide. Specifically, the ratio of the alkali metal oxide in the glass composition is preferably 0.1% by mass or less, and particularly preferably 0.02% by mass or less.

The alkali-free glass-based oxide-based glass of the present invention contains cerium oxide as a main component and is a boronic acid glass containing a boron component.

The ideal composition of the alkali-free glass in the present invention is: SiO ₂ : 40 to 85% by mass, Al ₂ O ₃ : 0 to 22% by mass, B ₂ O ₃ : 3 to 20% by mass, and MgO: 0.04 to 8 by mass. %, CaO: 0 to 14.5% by mass, SrO: 0 to 24% by mass, BaO: 0 to 30% by mass, and R ₂ O (R is an alkali metal): 0.1% by mass or less, and an alkaline earth metal oxide amount (CaO) The total amount of SrO and BaO is 5% by mass or more.

The preferred composition of the alkali-free glass is SiO ₂ : 45 to 65 mass %, Al ₂ O ₃ : 0 to 20 mass%, B ₂ O ₃ : 7 to 16 mass%, and MgO: 1 to 6 mass%. CaO: 0 to 7 mass%, SrO: 0 to 11 mass%, BaO: 0 to 15 mass%, and R ₂ O (R system means alkali metal): 0.1 mass% or less, and alkaline earth metal oxide amount (CaO, SrO) The total amount of BaO and the total amount of BaO is 10% by mass or more.

Further, a small amount of a metal oxide other than the above (for example, tin oxide or the like), a non-metal oxide (for example, sulfur oxide or the like), a halogen, or the like may be contained as another component. For example, Fe ₂ O ₃ may be contained as a coloring component.

<Glass raw material mixture>

The glass raw material mixture for producing the granules includes a compound as described above or a compound which can be an oxide as described above by thermal decomposition or the like (the following source, aluminum source, boron source, magnesium source, and alkaline earth metal) Source, etc.).

Each compound constituting the glass raw material mixture is usually used in the form of a powder. The water-soluble compound can also be used in a state of being dissolved in water in advance.

[Source]

The bismuth source is a compound which can be a component of SiO ₂ in the manufacturing step of glass. In the present invention, at least cerium is used as a source of cerium. And all the lines of the source should be sand.

Since the granules of the present invention have good strength, it is also possible to use a small-diameter cerium that has been difficult to use as a glass raw material. The smaller particle size of the cerium in the granules makes it easier to increase the uniformity of the composition in the molten glass or glass article. The cerium may also be used by mixing two or more kinds of average particle diameters. The ceramsite having a small particle size may be obtained by using a cerium having a small average particle diameter, or may be obtained by grinding with a grinder or the like to obtain a smaller average particle diameter.

[aluminum source]

The aluminum source can be a compound of the Al ₂ O ₃ component in the manufacturing step of the glass. Alumina, aluminum hydroxide or the like can be suitably used. These may be used alone or in combination of two or more. Among the usual glass raw materials, the alumina system and the strontium sand are the raw materials which are hard to melt due to the high melting point.

[boron source]

The boron source is a compound which can be a component of B ₂ O ₃ in the production step of glass. In the present invention, at least boric acid is used as a boron source. In the method for producing a granule according to the present invention, boric acid has a function as a binder (binder), which is advantageous for enhancing the strength of the granule. Therefore, it is presumed that boric acid dissolved in the slurry removes moisture in the spray drying step of the slurry, thereby being sent out from the inside of the granule to the surface and deposited on the surface of the granule, and is used as a bond by drying and solidification. The function of the agent.

Examples of the boric acid system include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), and tetraboric acid (H ₂ B ₄ O ₇ ). Among them, orthoboric acid is desirable because it is inexpensive and easy to obtain. These may be used alone or in combination of two or more.

Further, a boron source other than boric acid and boric acid may be used at the same time. Examples of the boron source other than boric acid include boron oxide (B ₂ O ₃ ) and colemanite.

The total amount of boron source in the glass raw material mixture is determined by the composition of the glass to be obtained. When the total of the boron sources is 100% by mass, the proportion of boric acid is preferably 60% by mass or more, more preferably 80% by mass or more, and most preferably 100% by mass.

[magnesium source]

The magnesium source is a compound which can be a component of MgO in the manufacturing step of glass. In the present invention, among the compounds to be added as a clarifying agent, those which can be made into a MgO component in the glass production step are included in the magnesium source. One type of magnesium source may be used or two or more types may be used in combination.

In the present invention, at least a portion of the magnesium source is a water-soluble magnesium salt. The term "water-soluble" in the present invention does not mean a command of several mg in neutral water at normal temperature, but clearly means dissolution. Specifically, it means that 10 g or more is dissolved in 100 mL of water (pH 7) at 20 °C.

Examples of the water-soluble magnesium salt include magnesium chloride (MgCl ₂ ), magnesium sulfate (MgSO ₄ ), and magnesium nitrate (Mg(NO ₃ ) ₂ ). These may also be hydrates. According to the findings of the inventors of the present invention, magnesium chloride (MgCl ₂ ), magnesium sulfate (MgSO ₄ ) or magnesium nitrate (Mg(NO ₃ ) ₂ ) does not form a water-insoluble salt in an aqueous boric acid solution.

Among these, magnesium chloride and magnesium sulfate are also preferred as a clarifying agent component, and it is preferable to increase the content of the water-soluble magnesium salt without changing the glass composition. Any one of magnesium chloride and magnesium sulfate may be used, or both may be used at the same time. It can be inferred that magnesium sulfate will exhibit a clarifying effect at a lower temperature, while magnesium chloride will exhibit a clarifying effect at a higher temperature. Therefore, both should be used at the same time.

In the glass raw material mixture, the content of magnesium sulfate in terms of SO ₃ is preferably 0.05 to 5% by mass, and preferably 0.2 to 2% by mass. If it is more than the lower limit of the said range, sufficient clarification effect can be acquired easily.

If the content of the magnesium sulfate is at most the upper limit of the above range, the desired pH of the raw material slurry can be easily obtained. In other words, when the content of the magnesium sulfate is less than or equal to the upper limit of the above range, the pH of the raw material slurry is likely to be 5.5 or more, and if it is neutral to alkaline, boric acid reacts with the alkaline earth metal carbonate in the slurry to be difficult to form. A water-insoluble salt, and boric acid having a binder function is difficult to be consumed, and sufficient granule strength is easily obtained.

In the glass raw material mixture, the content of magnesium chloride in terms of Cl is preferably 0.05 to 5% by mass, and preferably 0.2 to 3% by mass. When it is more than the lower limit of the above range, a sufficient clarifying effect can be easily obtained in the same manner as described above, and if it is at most the upper limit value, the desired pH of the raw material slurry can be easily obtained as described above.

If magnesium chloride and magnesium sulfate are used in combination as the water-soluble magnesium salt, it is desirable to more easily increase the strength of the granule.

The total content of the water-soluble magnesium salt in the glass raw material mixture can be easily obtained by using the water-soluble magnesium salt, and the strength of the granule can be sufficiently obtained, in terms of oxide (MgO), relative to the glass raw material mixture. The whole is preferably 0.04% by mass or more, and more preferably 3% by mass or more. The upper limit is determined by the amount of MgO in the glass composition to be achieved and the amount of clarifying agent added. The upper limit of the total content of the water-soluble magnesium salt is preferably 5% by mass.

A water-soluble magnesium salt and a water-insoluble magnesium source may also be used together as a magnesium source. By using a water-soluble magnesium salt together with a water-insoluble magnesium source, the pH of the raw material slurry can be easily adjusted to a desired range.

Examples of the water-insoluble magnesium source include magnesium hydroxide (Mg(OH) ₂ ), magnesium carbonate (MgCO ₃ ), magnesium oxide (MgO), and magnesium fluoride (MgF ₂ ). Magnesium fluoride clarifying agent.

Further, dolomite (ideal chemical composition: CaMg(CO ₃ ) ₂ ) can also be used as a water-insoluble magnesium source. The dolomite magnesium source is also an alkaline earth metal source.

Among these, magnesium hydroxide is preferably used insofar as it is easy to obtain a high-purity fine powder material.

It is also desirable to use magnesium hydroxide and dolomite in combination with a point which can more easily increase the strength of the granule.

[Alkaline earth metal source]

The alkaline earth metal source may be a compound of CaO, SrO or BaO in the manufacturing step of glass. In the present invention, a compound added as a clarifying agent may be CaO, SrO or BaO in the glass production step. Those who are included in the alkaline earth metal source. The alkaline earth metal source may be used alone or in combination of two or more.

Specific examples of the alkaline earth metal source include carbonates such as calcium carbonate (CaCO ₃ ), strontium carbonate (SrCO ₃ ), barium carbonate (BaCO ₃ ), and dolomite (ideal chemical composition: CaMg(CO ₃ ) ₂ ); Oxides of calcium oxide (CaO), strontium oxide (SrO) and barium oxide (BaO); calcium hydroxide (Ca(OH) ₂ ), barium hydroxide (Sr(OH) ₂ ) and barium hydroxide (Ba ( OH) ₂ ) and the like hydroxide as an example.

Further, specific examples of the compound which is an alkaline earth metal source and also a clarifier component may be exemplified by sulfate, chloride and fluoride of an alkaline earth metal. And these may also be hydrates.

Among these, the source of the alkaline earth metal which is water-soluble is chloride.

The water-soluble alkaline earth metal source reacts with boric acid in water to form a water-insoluble salt.

In the present invention, the water-soluble alkaline earth metal source which consumes boric acid in the slurry is preferably used in a small amount. It is therefore preferred to use a water-insoluble carbonate.

[铁源]

It can be made to contain Fe ₂ O ₃ as a coloring component. When the content of total iron converted to Fe ₂ O ₃ in the glass is 0.001% by mass or more, it becomes a glass plate having a blue or green color tone that sufficiently penetrates light. When the content of total iron converted to Fe ₂ O ₃ is 5% by mass or less, the visible light transmittance of the glass is good. The content of total iron converted to Fe ₂ O ₃ is preferably 0.005 to 4% by mass, and preferably 0.01 to 3% by mass.

In the present specification, although the total iron content is expressed by the amount of Fe ₂ O ₃ according to the standard analysis method, the iron present in the glass is not always in the form of trivalent iron, and there is also a divalent iron. .

[other ingredients]

The granules may contain a clarifying agent, a coloring agent, a melting aid, an opacifier, or the like as an auxiliary material as needed. These systems can suitably use well-known ingredients.

[Composition of glass raw material mixture]

The boron source is excluded and the composition of the glass raw material mixture is designed to be approximately the same as the composition ratio of the desired glass, in terms of conversion to oxide. The amount of boron source is set to be only the amount of the volatile portion considered to be greater than the boron oxide content of the desired boronic acid glass.

Among the glass compositions, MgO and an alkaline earth metal oxide which are oxides of the elements of Group 2 of the periodic table are components which lower the viscosity of the glass, and these must be contained in a certain amount or more in total. In the present invention, when the water-soluble magnesium source in the glass raw material mixture is converted into the molar amount of MgO and the total amount of the water-soluble alkaline earth metal source converted into the oxide is 1, the water-soluble magnesium source is converted into MgO. The relative value of the molar amount, that is, the molar ratio of {MgO/(MgO+SrO+CaO+BaO)} in the water-soluble component is 0.05 or more, and preferably 0.1 or more, more preferably 0.3 or more, and particularly preferably 0.8 or more. . The upper limit of the molar ratio depends on the composition of the glass to be achieved, but is, for example, 1 or less.

Further, in the glass raw material mixture, when the amount of borax in which boric acid is converted into B ₂ O ₃ is 1, the water-soluble alkaline earth metal source is converted into the relative value of the molar amount of the oxide, that is, the water-soluble component (( The molar ratio of SrO+CaO+BaO)/B ₂ O ₃ } is 1.00 or less, preferably 0.5 or less, and preferably 0.2 or less. The lower molar ratio is also dependent on the composition of the glass to be achieved, but is, for example, 0 (zero) or more, and preferably 0.005 or more.

If the molar ratio of {MgO/(MgO+SrO+CaO+BaO)} in the water-soluble component is at least the lower limit of the above range, and {(SrO+CaO+BaO)/B in the water-soluble component _When the molar ratio of ₂ O ₃ } is at most the upper limit of the above range, granules having excellent strength can be obtained.

According to the findings of the inventors of the present invention, among the water-soluble salts of Mg, Sr, Ca and Ba of the elements of Group 2 of the periodic table, although the water-soluble salts of Sr, Ca and Ba are dissolved in water in the slurry. Boric acid reacts to form a water-insoluble salt, but the water-soluble salt of Mg does not form a water-insoluble salt with boric acid in the slurry, so magnesium ions are present in the slurry. Therefore, it is presumed that the divalent cation (Mg ²⁺ ) of magnesium present in the slurry exerts a function of bringing the inorganic binder closer and bonding the powder particles of the glass raw material mixture to each other, thereby enhancing the strength of the granule. However, it is presumed that the cerium particles which are hydrated in the slurry are charged with a negative ionic ion by the addition of OH ^- , so that two cerium particles are closely connected by the divalent Mg ²⁺ , and the cerium sand particles are connected. The binding force is generated to increase the strength of the granules.

Further, boric acid which has been dissolved in the slurry as described above is useful for enhancing the strength of the granules because it functions as a binder, and it is presumed that the synergistic effect can be favorably obtained. The effect of granule strength.

Therefore, in the present invention, in the total of the water-soluble components (MgO + SrO + CaO + BaO) in the glass raw material mixture, the ratio of MgO which contributes to the strength of the granules is increased, that is, the aforementioned {MgO/ The larger the value of the molar ratio of (MgO + SrO + CaO + BaO)}, the easier it is to obtain the strength-improving effect of the granules brought about by the function of the Mg ²⁺ binder.

Moreover, boric acid is consumed, and the water-soluble alkaline earth metal source is less than boric acid, that is, the smaller the value of the molar ratio of {(SrO+CaO+BaO)/B ₂ O ₃ } is dissolved in the slurry. The presence of boric acid in the state of the body is increased, and the strength enhancement effect of the granules brought about by the function of the binder of boric acid can be easily obtained.

<Method for producing granules>

The method for producing the granule of the present invention is a spray-drying process.

[Preparation of raw material slurry]

First, a slurry of a raw material containing a glass raw material mixture and water is prepared.

Specifically, a powdery glass raw material is mixed with water and used as a raw material slurry. Alternatively, the raw material slurry may be prepared by mixing a powdery glass raw material with a glass raw material which has been previously dissolved in water or in a dispersed state, and if necessary, by adding water. The mixing method can use well-known method techniques. For example, a ball mill, a homogenizer, a stirrer using a stirring wing, a shaker like a "Red Devil", and a device such as a planetary ball mill can be used.

When the particles of the glass raw material powder for modulating the slurry are too large, the composition of each of the particles constituting the granules becomes uneven. Further, when the particles of the glass raw material powder are too large, it takes a lot of time and energy for the vitrification of the granules, and it becomes difficult to form the molten glass particles in the gas phase gas atmosphere. If the glass raw material powder is refined by a ball mill or the like before the preparation of the raw material slurry or during the preparation, the irregularity can be improved. The situation.

The solid content concentration of the raw material slurry is preferably from 10 to 70% by mass, and more preferably from 20 to 60% by mass. When it is at least the lower limit of the above range, the granulated body obtained by spraying the water during drying does not become small, and it is easy to achieve an appropriate production efficiency. Further, the solid content concentration of the raw material slurry is not too low, and it is preferable because the particle size of the granule is small and the particles are formed into dust. If it is less than or equal to the upper limit of the above range, the viscosity of the raw material slurry does not become too high, and good dispersibility is easily obtained. And it is ideal because it is not easy to cause a liquid supply failure.

The pH of the raw material slurry is preferably 5.5 or more, and the raw material slurry may contain a pH adjuster as needed.

The solubility of boric acid depends on the pH of the raw material slurry. A sufficiently high solubility can be easily obtained by setting the pH of the raw material slurry to 5.5 or more. The pH is preferably 7 or more. The higher the solubility of boric acid, the easier it is to obtain the effect of the binder produced by boric acid. Therefore, a good granule strength enhancement effect can be easily obtained by the synergistic effect with the aforementioned effect of the binder produced by Mg ²⁺ .

Further, in the case where the alkaline earth metal carbonate is contained in the glass raw material mixture, if the pH is 5.5 or more, it is also preferable from the point that it is difficult to form the water-insoluble salt of the carbonate and boric acid.

The upper limit of the pH of the raw material slurry is not particularly limited, but the higher the pH, the difficulty in limiting the pH adjuster that can be used. The pH of the raw material slurry of the present invention is preferably 11 or less, and preferably 9 or less.

The pH adjuster is not particularly limited, but it is preferably used in accordance with the use of granules. The type of glass is determined. When an alkali-free borosilicate glass is produced, since it is difficult to use an alkali metal compound as a pH adjuster, it is preferred to use a basic nitrogen compound containing no metal atom. When a highly volatile compound is used as the basic nitrogen compound, the basic nitrogen compound does not remain in the granules. Further, when a low volatility is used as the basic nitrogen compound and the basic nitrogen compound remains in the granules, the basic nitrogen compound decomposes and disappears when the granules are melted.

As the basic nitrogen compound which can be used as a pH adjuster, ammonia or a water-soluble amine compound is preferred. The water-soluble amine compound is preferably a water-soluble alkanolamine or an N-alkyl alkanolamine, and specific examples thereof include monoethanolamine, diethanolamine, and triethanolamine.

Further, although urea is an organic compound, it is decomposed at 133 ° C or higher, so it is almost eliminated in the gas melting furnace, and its taste is not as remarkable as that of ammonia, so it can be suitably used.

The raw material slurry may also contain an appropriate amount of a dispersing agent to stabilize the powdered glass raw material and disperse it, or to stabilize the viscosity of the raw material slurry. As the dispersing agent, for example, "CELUNA D305" (trade name: manufactured by Nakagisa Oil & Fat Co., Ltd.) and "A-6114" (trade name: manufactured by Toagos Corporation), which is a 40% by mass aqueous solution of a polycarboxylate ammonium salt, can be used. )Wait.

In addition to this, it is also possible to contain an additive such as an appropriate viscosity adjuster and a surfactant in the raw material slurry. The amount of the additives to be added is preferably 3% by mass or less based on the total amount of the raw material slurry system, and preferably 2% by mass or less. Moreover, the additives may volatilize or cause due to the melting of the granules. It is decomposed and volatilized, so it does not affect the glass composition.

[spray drying]

Next, the raw material slurry is spray-dried to remove volatile components such as moisture contained in the raw material slurry to produce granules. The granules obtained after spray drying can also be sieved as needed.

Spray drying is also called spray drying granulation method in which a raw material slurry is sprayed and pelletized, that is, water (evaporation) is removed from a raw material slurry to form a particle composed of a solid component of a raw material slurry. One way. As the spray-drying granulation method, a well-known or well-known method can be used.

For the spray drying granulation method, a method of supplying hot air can be used, and the hot air inlet temperature or the outlet temperature of the spray drying device is not limited, but if the hot air inlet temperature is 200 ° C or higher and the outlet temperature is 100 ° C When granulation is carried out in the above state, it is preferable to sufficiently dry the granules. Due to the size of the device, the temperature of the hot air reaches 500 °C.

The spray-drying granulation method as a method for producing granules from a raw material slurry is excellent in mass productivity, and is not only a method capable of controlling the particle size of the granules with high precision, but also can be contained in the raw material slurry. The mixed state of the glass raw material mixture is relatively well maintained, and is a method of producing a granulated body of a homogeneous glass composition.

Further, a spray drying granulation method is suitable for producing granules having a smaller particle size than the above.

[Average particle size of granules]

In the present invention, the average particle size of the granules is in the range of 50 to 700 μm. Preferably, the range of 100 to 500 μm is preferred. When the average particle diameter of the granules is 50 μm or more, the effect of producing the granules can be easily obtained (the scattering of the raw material powder is reduced). Further, since the surface area per unit mass is small, volatilization of boric acid from the surface at the time of melting can be reduced.

On the other hand, when the average particle diameter of the granules exceeds 700 μm, even if the concentration of the raw material slurry is increased or the nozzle pressure is increased, it is actually difficult to form the large particle size by the spray drying granulation method. Granules. When the average particle diameter of the granules is 700 μm or less, when the molten glass is produced by the gas fusion method, it is preferable to ensure the glass transition rate to a certain degree or more.

The average particle size of the granules can be adjusted according to the composition of the glass raw material powder, the pH of the slurry, the mixing method at the time of slurry preparation or the mixing time, the solid concentration of the slurry, the nozzle pressure, and the conditions at the time of spray drying. .

<Method for Producing Molten Glass>

The method for producing molten glass of the present invention is characterized by heating the granule of the present invention and forming a molten glass. The molten glass may be subjected to a common melting method such as a glass melting furnace of a Siemens type, and may be carried out by a gas fusion method. They can all be implemented by a known method.

The method for producing a granule of the present invention is a spray-drying granulation method, and is a method suitable for producing a granule having a relatively small particle diameter as in the gas-melting method.

[Gas fusion method]

In the gas fusion method, at least a part of the granules are melted into a molten glass particle in a gas phase gas atmosphere, and the molten glass particles are collected to obtain a molten glass.

Specifically, the granules are first introduced into the high temperature of the heating device in the gas. In a gas phase gas environment. A well-known thing can be used for the in-air heating apparatus. Since the granules produced by the present invention are excellent in strength, it is possible to suppress the occurrence of fine powder even when particles collide with each other or particles and the inner wall of the conveyance path during transportation or introduction.

Further, the fact that at least a part of the granules are melted means that a part or all of one granule is melted for the individual granules. The state in which one part of the granules has been melted is exemplified by a state in which the surface of the granule is melted and the center portion thereof is not sufficiently melted. In the case of this example, the whole of the (one) molten glass particle type particle is not melted and the part which is not fully melted in the center exists. However, even in the case where there is a portion which is not sufficiently melted, since the particles are heated to be heated during the process of forming the glass melt, a homogeneous glass melt can be obtained when supplied to the forming step.

In the gas-in-melting method, it is preferred to form individual glass particles by melting individual granules in a gas phase gas atmosphere. When a part of the granules are not sufficiently melted in a gas phase gas atmosphere, it is preferable to form a large part of the granules into molten glass particles in a gas phase gas atmosphere. Hereinafter, particles which are generated in a gas phase gas atmosphere together with particles which are not sufficiently melted in a gas phase gas atmosphere are referred to as molten glass particles.

The granules are melted in a gas phase gas atmosphere to obtain molten glass particles, and then the generated molten glass particles are collected to obtain a glass melt, and the molten glass taken out therefrom is supplied to the next molding step. As a method of collecting the molten glass particles, molten glass particles falling in a gas phase environment due to the weight of the body, or molten glass in a gas stream which is carried by the carrier air may be mentioned. The method in which the glass particles are received in a heat-resistant container disposed in a lower portion of the gas phase gas atmosphere and collected is exemplified.

<Method of Manufacturing Glass Articles>

The method for producing a glass article of the present invention is a method for producing a molten glass obtained by the method for producing molten glass of the present invention and cooling it. The term "glass article" refers to an article which is partially or wholly used in a glass which is solid at room temperature and which has substantially no fluidity, and includes, for example, an article obtained by processing a glass surface.

Specifically, first, the molten glass obtained by the method for producing molten glass is molded into a desired shape, and then the glass article is obtained by slow cooling. Thereafter, cutting, grinding, or the like can be carried out as needed, and the glass article can be obtained by post-processing in a known manner.

The forming system can be carried out by a known method such as a floating glass method, a down-draw method, or a melting method. The floating glass plate method is a method of forming molten glass into a plate shape on molten tin.

Slow cooling can also be carried out by a known method.

In the production of molten glass or in the manufacture of glass articles, by using the granules of the present invention, not only the scattering of the raw material powder can be prevented, but also the strength of the granules is good, so that the occurrence of fine powder can be suppressed. A molten glass or glass article having a good uniformity of composition.

Example

The invention will be described in more detail below by way of examples, but the invention is not limited thereto.

In the following examples, the following measurement methods and evaluation methods were used.

[Particle size distribution, average particle size (D50) and D90]

The particle size distribution and average particle size (D50) of the granules, and the average particle size (D50) of the glass raw material powder are obtained by using dry laser diffraction. Scattering particle size. The particle size distribution measured by the particle size distribution measuring apparatus (MICROTRAC MT3200: trade name, manufactured by Nikkiso Co., Ltd.) was determined.

The average particle size (D50) and D90 of the solid components in the slurry are processed by wet laser diffraction. The particle size distribution measured by a scattering particle size distribution measuring apparatus (MICROTRAC MT3300: trade name, manufactured by Nikkiso Co., Ltd.) was determined.

[correlation coefficient]

Further, by measuring the change in the particle size distribution of the granules before and after the collision, the degree of destruction (collapse) of the granules when the granules collided with each other was evaluated. In more detail, first, using the particle size distribution measuring apparatus (MICROTRAC MT3200), the particle size distribution of the granules which are entering the measurement chamber of the particle size distribution measuring apparatus is measured individually: the compressed air is not blown Time (compressed air pressure 0 psi (0 kPa)), and 50 psi compressed air (0.35 MPa). Thereafter, for the particle size distribution at a compressed air pressure of 0 psi (0 kPa) and the particle size distribution at a compressed air pressure of 50 psi (0.35 MPa), the correlation indicating the degree of coincidence in the range of the particle diameter of 0.97 to 996 μm was calculated. coefficient. Specifically, the correlation coefficient of the two is calculated by using the built-in function of the EXCEL2002 SP3, which is a Microsoft Corporation's EXCEL2002SP3, as the cumulative percentage of the obtained two particle size distributions.

When compressed air is blown into the granules, the granules with weak strength will collapse or the surrounding particles will peel off and the fine powder will increase, so the correlation coefficient will change. small. Further, the correlation coefficient is 1 in the case where the compressed air is not blown and the case where the particle size distribution is completely unchanged in the case where the compressed air is blown. The closer the correlation coefficient is to 1, the higher the strength of the granules.

[micronized rate]

For the particle size distribution in the case where 50 psi of compressed air was blown, a volume ratio of less than 50 μm was calculated as the fine powder ratio. The higher the micronized rate, the more easily the granules collapse, or the particles adhering to the granules or the particles constituting the outer periphery of the granules are more likely to peel off.

The average particle diameter (D50) of the glass raw material used in each example and the composition of the glass raw material mixture in each example (unit: mass%) are shown in Tables 1 and 2. The total number of significant figures is also rounded up. The case is not 100.)

Among the glass raw material powders shown in the table, the water-soluble magnesium source is MgCl ₂ ‧6 hydrate and MgSO ₄ ‧ hydrate, and the water-soluble alkaline earth metal source is SrCl ₂ ‧6 hydrate.

In the glass raw material powder, when the total amount of the water-soluble magnesium source converted into MgO and the amount of the water-soluble alkaline earth metal source converted into the oxide are 1 in total, the water-soluble magnesium source is converted into MgO. The relative value of the molar amount (MgO / (MgO + SrO + CaO + BaO) [mole ratio]); in the glass raw material powder, when the boric acid is converted into B ₂ O ₃ molar amount is 1, water solubility The alkaline earth metal source is converted into the relative value of the molar amount of the oxide ((SrO+CaO+BaO)/B ₂ O ₃ [mole ratio]); the content of magnesium chloride in the glass raw material powder (converted into Cl) and magnesium sulfate The content (in terms of SO ₃ ); the content of the dispersant in the raw material slurry and the pH of the raw material slurry; and the solid content concentration of the raw material slurry, D50 and D90 of the solid content of the raw material slurry. In addition, "-" means that it is not measured.

In any of the examples shown in Tables 1 and 2, the glass composition to be achieved is: SiO ₂ : 59.7 mass %, Al ₂ O ₃ : 17.4 mass%, B ₂ O ₃ : 8.0 mass%, MgO: 3.2 mass%, CaO 4.0% by mass, SrO: 7.6% by mass, and total iron in terms of Fe ₂ O ₃ : 0.04% by mass.

[Example 1] (modulation of raw material slurry)

A ball mill container made of polypropylene (PP) having a capacity of 10 L was used, and the container contained a ball having an alumina content of about 50% and having a diameter of about 20 mm.

2.74 kg of glass raw material powder, 3.35 kg of ion-exchanged water, and a polycarboxylic acid ammonium salt aqueous solution as a dispersing agent (manufactured by Nakagisa Oil & Fats Co., Ltd., product name: D-305, solid content concentration 40) were placed in a ball mill container. 1% by mass of 12.5 g, and the mixture was ground and mixed for 6 hours to prepare a raw material slurry having a solid concentration of 45% by mass.

(spray drying)

Using a spray-type spray dryer, the resulting slurry is stirred at room temperature in a non-foaming manner at a temperature of 250 ° C at the inlet and an outlet air temperature of 120 to 150 ° C. The slurry is slurried at the same time at a rate of about 7 kg of granules per hour. And spray drying is carried out.

The obtained granules were sieved through a 1 mm sieve to remove particles having a large particle size.

The average particle diameter, correlation coefficient, and fine powder ratio of the granulated body after sieving were measured. The results are shown in the table (hereinafter, the same). Fig. 1 is a graph showing the measurement results of the particle size distribution. It shows the particle size distribution (0 psi) when the compressed air is not blown and the particle size distribution (hereinafter, the same) when the compressed air (50 psi) has been blown.

[Example 2, Comparative Example 1]

In Example 1, the blending of the glass raw material powder was changed as shown in Table 1. 2.5 kg of a glass raw material powder, 3.75 kg of ion-exchanged water, and 12.5 g of the same dispersing agent (D-305) as in Example 1 were placed, and the mixture was ground and mixed for 6 hours to prepare a raw material slurry having a solid concentration of 40% by mass. .

Granules were produced in the same manner as in Example 1, and measurement of each item was carried out. The measurement results of the particle size distribution of Example 2 are shown in Fig. 2, and the measurement results of the particle size distribution of Comparative Example 1 are shown in Fig. 9.

(result)

Comparative Example 1 is an example in which the glass raw material powder does not contain water-soluble magnesium.

That is, magnesium sulfate was used for Examples 1 and 2, and magnesium sulfate was not used in Comparative Example 1, and more magnesium hydroxide was blended than in Examples 1 and 2.

As shown in Table 1, Examples 1 and 2 and Comparative Example 1 have substantially the same average particle diameter, but the correlation coefficients of Examples 1 and 2 are higher than those of Comparative Example 1, and the fine powder ratio is low. That is, the strength of the granules is high.

Further, in the case of comparing Example 1 with Example 2, the correlation coefficient of Example 2 in which the amount of the water-soluble magnesium salt (magnesium sulfate) is large is high and the fine powder ratio is low. It is presumed that due to the increase in the amount of magnesium ions (Mg ²⁺ ) added, the cerium particles charged with valence ions after hydration pass through the Mg ^{2+ of the} divalent cations to form a binding force. The increase in the place results in an increase in the strength of the granules.

Further, the following experiment was carried out as an additional experiment in which the pH of the monoethanolamine as a pH adjuster was added to the slurry of the slurry of Example 2 (before the ball mill was mixed and polished) to a pH of 9.6. And mixed in the ball mill. The amount of foaming at the time of grinding was less than that of Example 2. It is presumed that this is due to the fact that the water-insoluble salt formed by the reaction of boric acid with CaCO ₃ or SrCO ₃ in an alkaline environment is small. Granules were produced in the same manner as in Example 1 using this slurry. The average particle diameter (D50) of the obtained granules was 81 μm, and the correlation coefficient was 0.995. It is presumed that this is because the formation of a water-insoluble salt of boric acid is suppressed, and the effect of boric acid as a binder is fully exerted, and the strength of the granule is improved.

[Examples 3, 4] (modulation of raw material slurry)

A ball mill container having a capacity of 20 cm ^{3 was} used, and the container contained a ballite having a volume of about 50% and having a vermiculite as a main component and having a diameter of about 60 to 80 mm.

5 tons of glass raw material powder, 5 tons of water, and a polycarboxylic acid ammonium salt aqueous solution as a dispersing agent (product name: A-6114, solid content concentration: 40% by mass) was added to the ball mill container. After 25 hours of grinding and mixing for 12 hours, 5 tons of water was added to prepare a raw material slurry having a solid concentration of 33% by mass.

(spray drying)

The obtained slurry is transferred to a slurry tank, and while stirring, the pump is sent to the spray dryer, and a nozzle type spray dryer is used, and the inlet dry air temperature is 500 ° C and the outlet air temperature is 100 to 200 ° C. Under the conditions, spray drying was carried out at a rate of about 800 kg of granules in one hour. In addition, the yield of the spray dryer is about 80%. The remaining 2% adheres to the inner wall of the dryer, or leaks out of the slurry as the carbon dioxide gas is blown out in the ball mill, is caught by the bag filter, and the slurry adheres to the liquid supply pipe or the slurry tank.

The obtained granules were sieved through a 1 mm sieve to remove particles having a large particle size.

The average particle diameter, correlation coefficient, and fine powder ratio of the granulated body after sieving were measured. The results are shown in Table 1. Further, in the third and fourth figures, a graph showing the measurement results of the particle size distribution is shown.

(result)

Example 3 is an example in which cerium chloride was used as a clarifying agent in addition to magnesium sulfate, and Example 4 was an example in which magnesium chloride was used in addition to magnesium sulfate.

Comparing Example 3 with Example 4, the average particle diameter and the correlation coefficient were substantially equivalent, but the fine powder ratio of Example 4 was remarkably low. In this regard, Examples 3 and 4 have substantially no difference in the solubility of boric acid because the pH of the raw material slurry is substantially equivalent to 7.1 and 6.9. The average particle size (D50) of the granules was about 25 μm larger than that of Example 4, but as a result of the measurement of the particle size distribution, both of the cumulative strains of less than 50 μm in the particle size distribution when no compressed air was blown (0 psi) were 0%. Therefore, the lower fine powder ratio of Example 4 means that the particles which collapsed when 50 psi of compressed air was blown were less in Example 4. That is, the strength of the granules of Example 4 was higher than that of Example 3. Incidentally, the average particle diameter of the solid content in the raw material slurry (after ball mill polishing) was 15 μm with respect to Example 3, and Example 4 was 17 μm, which was approximately equivalent. From this, it is presumed that the number of attachment points of the constituent raw materials is approximately the same, and the van der Waals force is substantially equal.

Therefore, it is presumed that in Example 4, compared with Example 3, since the ratio of the water-soluble magnesium salt (magnesium sulfate and magnesium chloride) in the magnesium source is large, the amount of Mg ions which exhibits the function of the binder is present. Increase to increase the strength of the granules.

[Examples 5 to 8, Comparative Examples 2 to 5]

In this example, granules were produced using cerium having an average particle size difference. Moreover, in order to avoid crushing of the sand, a homogenizer is used, and the raw material is dispersed and mixed only in water. (modulation of raw material slurry)

2 kg of the glass raw material powder and 3 kg of ion-exchanged water having the composition shown in Table 2 were placed in a mixing container of a homogenizer, and the mixture was rotated for 5 minutes per minute by a number of revolutions for 2 minutes to prepare a solid content concentration of 40% by mass. It Raw material slurry. No dispersant was used.

(spray drying)

Using a spray-type spray dryer, the obtained slurry can be obtained at a rate of about 6 to 7 kg of granules per hour at a dry air temperature of 250 ° C and an outlet air temperature of 120 to 150 ° C. Spray dried. The obtained granules were sieved through a 1 mm sieve to remove particles having a large particle size.

The average particle diameter, correlation coefficient, and fine powder ratio of the granulated body after sieving were measured. The results are shown in Table 2. Further, graphs of the measurement results of the particle size distribution are shown in Figs. 5 to 8 and Figs. 10 to 13.

(result)

Water-soluble magnesium sulfate was used in relation to Examples 5 to 8, and Comparative Examples 2 to 5 were not used with magnesium sulfate, and instead were mixed with water-insoluble calcium sulfate (dihydrate gypsum). More magnesium hydroxide than Examples 5-8.

Regardless of the average particle size of the cerium, the average particle size of the granules is approximately equal to about 80 μm.

Comparing Example 5 with Comparative Example 2, Example 6 and Comparative Example 3, Example 7 and Comparative Example 4, and Example 8 and Comparative Example 5, the correlation coefficient is substantially equal or the embodiment is higher, and the micronized ratio is The embodiment is obviously lower. It is presumed that this is an example in which the amount of the water-soluble magnesium salt (magnesium sulfate) is large, and the amount of Mg ²⁺ present in the slurry is increased to increase the granule strength. Further, the same effect can be obtained in a wide range of an average particle diameter of 0.5 to 44.0 μm.

Industrial availability

The granules obtained by the present invention are granules having excellent strength and being difficult to produce fine powder, and in particular, it is suitable for the use of molten glass in the gas fusion method because it is easy to control the generation of fine powder during granule handling. Manufacturing.

In addition, the entire contents of the specification, the scope of the application, the drawings and the abstract of the Japanese Patent Application No. 2011-117149, filed on May 25, 2011, the entire contents of reveal.

Fig. 1 is a graph showing the results of measurement of the particle size distribution of Example 1. 0psi The particle size distribution in the case where compressed air is not blown, and 50 psi is the particle size distribution in the case where compressed air is blown. (below, the same)

Fig. 2 is a graph showing the results of measurement of the particle size distribution of Example 2.

Fig. 3 is a graph showing the results of measurement of the particle size distribution of Example 3.

Fig. 4 is a graph showing the results of measurement of the particle size distribution of Example 4.

Fig. 5 is a graph showing the results of measurement of the particle size distribution of Example 5.

Fig. 6 is a graph showing the results of measurement of the particle size distribution of Example 6.

Fig. 7 is a graph showing the results of measurement of the particle size distribution of Example 7.

Fig. 8 is a graph showing the results of measurement of the particle size distribution of Example 8.

Fig. 9 is a graph showing the measurement results of the particle size distribution of Comparative Example 1.

Fig. 10 is a graph showing the measurement results of the particle size distribution of Comparative Example 2.

Fig. 11 is a graph showing the results of measurement of the particle size distribution of Comparative Example 3.

Fig. 12 is a graph showing the results of measurement of the particle size distribution of Comparative Example 4.

Fig. 13 is a graph showing the results of measurement of the particle size distribution of Comparative Example 5.

Claims (10)

A method for producing a granule, which is a granule for producing a glass raw material mixture, the granulation system for producing an alkali-free glass, and the production method comprising the steps of: preparing a raw material slurry, the raw material slurry containing a glass raw material mixture and water; and a step of spray drying the raw material slurry to produce granules; the glass raw material mixture containing at least a cerium, a boric acid, a magnesium source and an alkaline earth metal source; and at least a part of the magnesium source is water soluble a magnesium salt, and at least a part of the alkaline earth metal source is a water-soluble alkaline earth metal source; in the glass raw material mixture, the water-soluble magnesium source is converted into a MgO molar amount and a water-soluble alkaline earth metal source is converted into an oxide When the total amount of the molar amount is 1, the relative value of the molar amount of the water-soluble magnesium source in terms of MgO is 0.05 or more; and in the glass raw material mixture, the amount of molybdenum converted to B ₂ O ₃ is 1 In the case of the water-soluble alkaline earth metal source, the relative value of the molar amount of the oxide is 1.00 or less. The method for producing a granule according to the first aspect of the invention, wherein the pH of the raw material slurry is 5.5 or more. The method for producing a granule according to the first or second aspect of the invention, wherein the granule has a D50 of a cumulative volume median diameter in the particle size distribution curve of 50 to 700 μm. The method for producing a granule according to any one of claims 1 to 3, wherein the water-soluble magnesium salt is magnesium sulfate and/or magnesium chloride. The method for producing a granule according to the fourth aspect of the invention, wherein the total amount of the content of SO _{3 in terms} of magnesium sulfate and the content of Cl in terms of magnesium chloride is 0.05 to 5% by mass. The method for producing a granule according to any one of claims 1 to 5, wherein the alkali-free glass-based borosilicate glass has the following composition in terms of an oxide: SiO ₂ : 40~ 85 mass%, Al ₂ O ₃ : 0 to 22 mass%, B ₂ O ₃ : 3 to 20 mass%, MgO: 0.04 to 8 mass%, CaO: 0 to 14.5 mass%, and SrO: 0 to 24 mass%, BaO: 0 to 30% by mass, and R ₂ O (R represents an alkali metal): 0.1% by mass or less; however, the total amount of CaO, SrO, and BaO is 5% by mass or more. The method for producing a granule according to any one of claims 1 to 6, wherein the raw material slurry further contains a dispersing agent. A method for producing a molten glass, which is obtained by heating a granule obtained by the production method according to any one of claims 1 to 7 to obtain a molten glass. The method for producing molten glass according to the eighth aspect of the invention, which is characterized in that at least a part of the granules are melted in a gas phase gas atmosphere. The glass particles are melted and the molten glass particles are collected to form a molten glass. A method for producing a glass article, which comprises molding and cooling a molten glass obtained by the method for producing molten glass according to claim 8 or 9.