Production method for glass powder

Abstract

A production method for a glass powder having an average particle size of 1.5 μm or less, said method including: a dry-grinding step for dry-grinding glass gobs and obtaining a roughly ground powder; a classification step for classifying the roughly ground power and obtaining a classified powder from which glass particles with diameters of greater than 10 μm have been removed; and a wet-grinding step for wet-grinding the classified powder and obtaining the glass powder.

Description

Method for producing glass powder

[0001] The present invention relates to a method for producing glass powder.

[0002] Glass powder is used in various applications. For example, in the dental field, glass powder is blended as a filler into dental compositions such as composite resins.

[0003] Since the particle size distribution of glass powder affects the properties of the composition to be blended, glass powder with a controlled particle size distribution is required. For example, Patent Document 1 discloses a method for producing glass powder in which a pulverized slurry containing wet-pulverized pulverized glass is passed through a net and / or a sieve, and particles having a particle size exceeding 10 μm are removed by separation.

[0004] Japanese Patent No. 5997488

[0005] Conventional methods for producing glass powder classify the glass powder after wet pulverization. However, since the glass powder after wet pulverization has fine particles that tend to aggregate, sufficient classification cannot be achieved, and the productivity of glass powder is low.

[0006] An object of the present invention is to provide a method for producing glass powder that can improve productivity.

[0007] One aspect of the present invention is a method for producing glass powder having an average particle size of 1.5 μm or less, the method including a dry pulverization step of dry pulverizing a glass mass to obtain coarsely pulverized powder, a classification step of classifying the coarsely pulverized powder to obtain classified powder from which glass powder having a major axis exceeding 10 μm has been removed, and a wet pulverization step of wet pulverizing the classified powder to obtain the glass powder.

[0008] According to one aspect of the present invention, it is possible to provide a method for producing glass powder that can improve productivity.

[0009] It is a figure which shows the process of the manufacturing method of the glass powder by embodiment. It is a figure which shows the SEM image of Example 1. It is a figure which shows the SEM image of Comparative Example 1.

[0010] Embodiments of the present invention will be described in detail below. The method for producing glass powder according to this embodiment is a method for producing glass powder having an average particle size of 1.5 μm or less. In this specification, glass powder refers to powdered glass. The average particle size means the particle diameter (median diameter: D50) at 50% of the cumulative value in the particle size distribution (volume basis) measured by laser diffraction scattering method.

[0011] The method for producing glass powder according to this embodiment includes a dry grinding step S1, a classification step S2, and a wet grinding step S3, as shown in Figure 1.

[0012] In the dry grinding step S1, the glass lumps are dry-ground to obtain coarse powder. Here, the glass lumps are the starting material in the glass powder manufacturing method. The glass lumps represent glass in a state where molten glass has solidified and lost its fluidity.

[0013] Examples of glass compositions include lanthanum glass, barium glass, strontium glass, silicate glass, borate glass, phosphate glass, or fluoroaluminosilicate glass. These glasses may be used individually or in combination of two or more. Among these, lanthanum glass, barium glass, and strontium glass are particularly suitable for dental glass where radiopaque properties are required.

[0014] The morphology of the glass chunks is not particularly limited, but is preferably granular or flake-like. When the glass chunks are granular, the average particle size is, for example, 50 μm or more and 5000 μm or less, preferably 100 μm or more and 1000 μm or less, and more preferably 200 μm or more and 500 μm or less.

[0015] In this specification, dry grinding refers to a process of grinding a solid, such as a powder, in a gas phase without the interposition of a liquid substance. In dry grinding, a ball-shaped or bead-shaped grinding medium is used. In the dry grinding step S1, glass or ceramics are used as the grinding medium, and zirconia is preferably used. The size of the grinding medium is, for example, 0.5 mm or more and 20 mm or less in diameter, preferably 1 mm or more and 10 mm or less, and more preferably 2 mm or more and 5 mm or less.

[0016] The coarsely ground powder is glass powder with a larger average particle size than the glass powder obtained in the wet grinding process described later. The average particle size of the coarsely ground powder is, for example, 1 μm to 50 μm, preferably 1 μm to 40 μm, and more preferably 1 μm to 30 μm.

[0017] In classification step S2, the coarsely ground powder is classified to obtain classified powder from which glass powder with a major axis exceeding 10 μm has been removed. In this specification, classification refers to the process of classifying the target particles according to their particle size. Examples of classification methods include sieving and wind-powered classification (hereinafter referred to as wind-powered classification), with wind-powered classification being preferred. The major axis refers to the maximum length at any two points on the contour of the particle.

[0018] The classification in classification step S2 may be carried out continuously with or discontinuously with the dry grinding in dry grinding step S1.

[0019] The glass powder removed by classification in classification step S2 is preferably glass powder with a major diameter of 8 μm or more, more preferably glass powder with a particle size of 7 μm or more, and even more preferably glass powder with a particle size of 5 μm or more.

[0020] In the wet grinding step S3, the classified powder is wet-ground to obtain glass powder with an average particle size of 1.5 μm or less.

[0021] In this specification, wet grinding refers to a process of grinding a solid, such as a powder, while it is dispersed in a dispersion medium. The dispersion medium refers to a solvent used to disperse the solid, such as a powder. In wet grinding step S3, it is preferable to use water, alcohol, or a mixture thereof as the dispersion medium.

[0022] A dispersant may optionally be added to the dispersion medium. A dispersant is an additive that, when a powder and a liquid are mixed, prevents particle aggregation and disperses the particles into individual particles. Examples of dispersants include inorganic dispersants such as sodium hexametaphosphate and sodium tripolyphosphate, and organic dispersants such as polycarboxylic acid type dispersants.

[0023] In wet grinding, ball-shaped or bead-shaped grinding media are used. In wet grinding step S3, it is preferable to use zirconia or glass beads as the grinding media. The size of the grinding media is, for example, a diameter of 0.1 mm to 10 mm, preferably 0.1 mm to 5 mm, and more preferably 0.1 mm to 3 mm.

[0024] The average particle size of the glass powder obtained in the wet grinding step S3 is preferably 0.05 μm or more and 1.5 μm or less, more preferably 0.1 μm or more and 1.3 μm or less, and even more preferably 0.1 μm or more and 1 μm or less.

[0025] In this embodiment, a drying step may be included after the wet grinding step S3. In the drying step, the glass powder obtained in the wet grinding step S3 is dried. By performing a drying step after the wet grinding step, the dispersion medium adhering to the glass powder can be removed.

[0026] Drying can be carried out using known methods such as heat drying, low-temperature drying, forced-air drying, reduced-pressure drying, freeze-drying, spray drying, and natural drying.

[0027] In this embodiment, as described above, by performing the dry grinding step S1, the classification step S2, and the wet grinding step S3, classification is performed after dry grinding and before wet grinding, and not after wet grinding.

[0028] Conventional wet-milled powders become too fine, increasing their cohesiveness and making classification processes such as sieving and air classification difficult. However, dry-milled powders, as in this embodiment, do not become too fine, making classification processes such as sieving and air classification easy. Therefore, the glass powder manufacturing method of this embodiment can improve the productivity of glass powder production.

[0029] Furthermore, in this embodiment, as described above, wind classification can be used in the classification process, making it easier to remove glass powder with a major axis exceeding 10 μm. Therefore, the glass powder manufacturing method of this embodiment can further improve the productivity of glass powder.

[0030] Furthermore, in this embodiment, as described above, by using zirconia or glass beads as the grinding medium in the dry grinding process, high grinding efficiency can be obtained, thus shortening the grinding time. In addition, because zirconia as a grinding medium has high wear resistance, the inclusion of impurities in the ground powder can be suppressed.

[0031] Furthermore, glass beads have high sphericity and minimal variation in specific gravity, allowing for stable grinding and dispersion efficiency in the dry grinding process. Additionally, because glass is transparent, it helps to minimize the reduction in transparency due to impurity contamination.

[0032] Furthermore, in this embodiment, as described above, by using zirconia or glass beads as the grinding medium in the wet grinding process, high grinding efficiency can be obtained, thus shortening the grinding time. In addition, because zirconia as a grinding medium has high wear resistance, the inclusion of impurities in the ground powder can be suppressed.

[0033] Furthermore, glass beads have high sphericity and minimal variation in specific gravity, allowing for stable grinding and dispersion efficiency in wet grinding processes. Additionally, because glass is transparent, it helps to minimize the reduction in transparency due to impurity contamination.

[0034] Furthermore, in this embodiment, as described above, by using water, alcohol, or a mixture thereof as a dispersion medium in the wet grinding process, the glass is hydrolyzed and becomes easier to grind. Also, when water is used as a dispersion medium, freeze-drying becomes easier because water freezes easily. Moreover, when alcohol is used as a dispersion medium, the drying process after wet grinding becomes easier because alcohol evaporates easily.

[0035] Furthermore, in this embodiment, as described above, by obtaining classified powder from which glass powder with a major diameter exceeding 10 μm has been removed in the classification process, the average particle size of the pulverized powder after wet grinding becomes even smaller. Therefore, according to the glass powder manufacturing method of this embodiment, glass powder with an average particle size of 1.5 μm or less can be obtained with high precision.

[0036] The glass powder obtained by the manufacturing method of this embodiment is not particularly limited in its use, but can be used, for example, in dental materials. Examples of dental materials to which such glass powder can be applied include dental composite resins, dental cements, dental adhesives, dental temporary filling materials, dental primers, dental coating materials, dental hard resins, dental cutting resin materials, dental temporary restorative materials, dental fillings, and toothpastes.

[0037] The present invention will be further described below with reference to examples. Various tests and evaluations will be conducted according to the methods described below.

[0038] <Preparation of Glass Powder> Barium glass ingots were placed in a dry ball mill as the starting material, and dry grinding was performed using zirconia as the grinding medium. Then, a rotor-type air classifier was used to obtain only powder with a particle size below the size required for the classification conditions. The obtained classified powder was placed in a wet bead mill for nano-dispersion and production, and wet grinding was performed using zirconia as the grinding medium and water as the dispersion medium. The obtained glass powder was heated and dried.

[0039] <Particle Size (Particle Size Distribution)> The particle size (particle size distribution) of the glass obtained during the glass powder production process was confirmed as median diameter (D50), 10% diameter (D10), 90% diameter (D90), and 99% diameter (D99) after dry grinding, classification, and wet grinding. Note that the 10% diameter (D10), 90% diameter (D90), and 99% diameter (D99) represent the particle sizes at the 10%, 90%, and 99% cumulative values, respectively, of the particle size distribution (volume basis) measured by laser diffraction scattering. The particle size distribution was measured using a laser diffraction / scattering particle size analyzer, with the glass dispersed in a 0.1 mass% sodium hexametaphosphate aqueous solution.

[0040] <Preparation of Dental Composite Resin Hardened Body>After hydrophobic treatment of 7 g of the obtained glass powder with 0.2 g of γ-methacryloyloxypropyltriethoxysilane, 3 g of a thermosetting resin was mixed and placed in a furnace in which nitrogen with a concentration of 99.9% was controlled to 0.3 MPa and the oxygen concentration was less than 1.0%. Then, nitrogen was sealed and the pressure was increased to 2.0 MPa. Simultaneously with the completion of the pressure increase, the temperature inside the furnace was raised to 120 °C and polymerized and cured for 1 hour to prepare a dental composite resin.

[0041] <SEM Observation>Regarding the hardened body of the obtained dental composite resin, a range of φ15 mm polished with SiC of particle size #4000 was observed with a scanning electron microscope (SEM). The SEM images of Example 1 and Comparative Example 1 are shown in FIGS. 2 and 3. The SEM images in FIGS. 2 and 3 are enlarged 1000 times.

[0042] <Flexural Strength>A CAD / CAM block of the dental composite resin was prepared, and the flexural strength was measured according to JIS T6517:2011. The evaluation criteria for the flexural strength were that 230 MPa or more was good and less than 230 MPa was bad.

[0043] [Example 1] After dry grinding, glass powder with a major diameter of 10 μm or more was removed with an air classifier. The results of SEM observation are shown in FIG. 2. The particle size (μm) of the glass obtained in the process of producing the glass powder is shown in Table 1. The results of the flexural strength are shown in Table 2.

[0044] [Comparative Example 1] After dry grinding, glass powder with a major diameter of 125 μm or more was removed with a sieve. The results of SEM observation are shown in FIG. 3. The results of the flexural strength are shown in Table 2.

[0045]

[0046]

[0047] From Table 1, in Example 1, the median diameter after wet grinding was 1.5 μm or less. Also, from Table 2 and FIG. 2, Example 1 was a glass powder that did not contain glass powder with a major diameter of 10 μm or more, and the flexural strength was good (230 MPa or more).

[0048] On the other hand, as shown in Figure 3 and Table 2, Comparative Example 1 was a glass powder containing glass powder with a major axis of 10 μm or more, and its bending strength was poor (less than 230 MPa).

[0049] These results show that by dry-grinding glass ingots to obtain coarse powder, classifying the resulting powder to remove glass particles with a major diameter exceeding 10 μm, and then wet-grinding the classified powder to produce glass powder, the productivity of glass powder production can be improved while controlling the average particle size of the resulting glass powder to 1.5 μm or less.

[0050] The embodiments disclosed above include, for example, the following aspects:

[0051] <1> A method for producing glass powder having an average particle size of 1.5 μm or less, comprising: a dry grinding step of dry grinding a glass lump to obtain coarse ground powder; a classification step of classifying the coarse ground powder to obtain classified powder from which glass powder with a major diameter exceeding 10 μm has been removed; and a wet grinding step of wet grinding the classified powder to obtain the glass powder.

[0052] <2> The method for producing glass powder according to <1>, wherein wind classification is used in the classification step.

[0053] <3> The method for producing glass powder according to <1> or <2>, wherein zirconia or glass beads are used as the grinding medium in the dry grinding step.

[0054] <4> The method for producing glass powder according to any one of <1> to <3>, wherein zirconia or glass beads are used as the grinding medium in the wet grinding step.

[0055] <5> The method for producing glass powder according to any one of <1> to <4>, wherein in the wet grinding step, water, alcohol, or a mixture thereof is used as a dispersion medium.

[0056] <6> The method for producing glass powder according to any one of <1> to <5>, wherein in the classification step, a classified powder is obtained from which glass powder with a major diameter exceeding 8 μm has been removed.

[0057] Although embodiments of the present invention have been described above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the invention as described in the claims.

[0058] This application claims priority based on Japanese Patent Application No. 2025-014816, filed on 31 January 2025, the entire contents of which are incorporated herein by reference.

Claims

1. A method for producing glass powder having an average particle size of 1.5 μm or less, comprising: a dry grinding step of dry grinding a glass mass to obtain coarse ground powder; a classification step of classifying the coarse ground powder to obtain classified powder from which glass powder with a major diameter exceeding 10 μm has been removed; and a wet grinding step of wet grinding the classified powder to obtain the glass powder.

2. The method for producing glass powder according to claim 1, wherein wind classification is used in the classification step.

3. The method for producing glass powder according to claim 1, wherein zirconia or glass beads are used as the grinding medium in the dry grinding step.

4. The method for producing glass powder according to claim 1, wherein zirconia or glass beads are used as the grinding medium in the wet grinding step.

5. The method for producing glass powder according to claim 1, wherein water, alcohol, or a mixture thereof is used as a dispersion medium in the wet grinding step.

6. The method for producing glass powder according to claim 1, wherein in the classification step, glass powder with a major diameter exceeding 8 μm is removed to obtain classified powder.

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