Silica glass and its manufacturing method

Abstract

To improve transmittance of silica glass across a broad range of wavelengths.SOLUTION: As slurry, a glass raw material solution containing silica glass powder, a solvent, a dispersant and a curable resin is prepared. Next, a curing agent is added to the slurry, which is poured into a molding die to be cured. The cured molded body is dried and degreased, then subjected to chlorination and sintering. At that time, the temperature of the chlorination should be, preferably, 800°C or higher and 1200°C or lower, and more preferably, 950°C or higher and 1000°C or lower. The duration of the chlorination should be, preferably, 1 hour or longer and 6 hours or shorter, and more preferably, 2 hours or longer and 3 hours or shorter. In this manner, silica glass having a transmittance of 80% or more in the range of 170-3500 nm can be produced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to silica glass and a method for producing the same. [Background technology]

[0002] Silica glass is used in a variety of applications, including optical fibers, LEDs, and lenses (for medical and imaging applications, etc.). In order to transmit light efficiently in these applications, it is desirable for silica glass to have high light transmittance. Various techniques have been proposed to increase transmittance. Patent Document 1 discloses a technique that incorporates a purification step in which Al, Na, Fe, etc. are removed by treating the material in a hydrogen chloride gas atmosphere at a heating temperature of 1,000 to 1,500°C for 0.5 to 5 hours before the sintering step. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7101156 Summary of the Invention [Problem to be solved by the invention]

[0004] Optical fibers made of silica glass are used not only for transmitting information but also for transmitting light and energy. To increase the versatility of optical fibers, there has been a demand in recent years for high transmittance across a wide wavelength range. In particular, there is a growing demand for high transmittance in the wavelength range of 200 nm or less, known as the vacuum ultraviolet range, and in the wavelength range of 1000 to 3500 nm, known as the infrared range. The same is true for lenses (for medical and imaging applications, etc.). While there have traditionally been materials with high transmittance in the vacuum ultraviolet or infrared ranges, there have been no materials with high transmittance across both wavelength ranges. In view of the above problems, an object of the present invention is to provide silica glass having high transmittance from the vacuum ultraviolet region to the infrared region. [Means for solving the problem]

[0005] The present invention provides A method for producing silica glass by hardening and sintering a slurry, comprising: (a) preparing a slurry containing silica glass powder; (b) mixing the slurry with a curing agent and curing the mixture to form a compact; (c) sintering the molded body to obtain silica glass; The manufacturing method may be such that step (c) includes a chlorine treatment in which sintering is performed in a chlorine gas atmosphere at a temperature of 800° C. to 1200° C. for 0.5 hours to 6 hours.

[0006] Chlorine treatment has traditionally been used as a means of removing metal impurities and OH groups and improving the transmittance of silica glass. However, if the chlorine treatment time is short, metal impurities and the like cannot be sufficiently removed, and if the chlorine treatment time is long, structural defects occur in the silica glass, where the Si-O-Si structure becomes Si-Si or Si-OO-Si. Furthermore, if the temperature during chlorine treatment is low, the reaction does not occur easily, and metal impurities and the like cannot be sufficiently removed. That is, in order to ensure high transmittance from the vacuum ultraviolet region to the infrared region, it is important to sufficiently remove metal impurities, etc. while avoiding structural defects. As a result of experiments, the inventors of the present application have found that by performing chlorine treatment within the above-mentioned temperature range and treatment time, silica glass having high transmittance from the vacuum ultraviolet region to the infrared region can be produced.

[0007] In the production method of the present invention, It is more preferable that the chlorine treatment is carried out at a temperature in the range of 900°C or higher and 1050°C or lower.

[0008] In addition, in the production method of the present invention, It is more preferable that the chlorine treatment is carried out at a temperature of 900° C. or higher and 1000° C. or lower for a period of 1 hour or higher and 4 hours or lower.

[0009] In addition, in the production method of the present invention, It is more preferable that the chlorine treatment is carried out at a temperature of 950° C. or higher and 1000° C. or lower for a period of 2 hours or higher and 3 hours or lower.

[0010] In the present invention, the slurry containing silica glass powder may contain a curable resin, a dispersant, and a solvent in addition to the silica glass powder. Silica glass powder of various particle sizes can be used, for example, 0.1 to 2 μm. The curable resin may be, for example, an epoxy resin. The dispersant may be, for example, a tetramethylammonium hydroxide solution. The solvent may be, for example, distilled water. In the present invention, triethylenetetramine or the like can be used as the curing agent.

[0011] In the present invention, before sintering the molded body, a step of drying the molded body to remove the solvent and a step of degreasing the molded body to remove the curable resin may be added. Drying can be performed under various temperature conditions and for various times.

[0012] The present invention is not limited to the manufacturing method and can take various forms. The silica glass may have a transmittance of 70% or more at a thickness of 3 mm or less in the wavelength range of 170 nm or more and 220 nm or less, and a transmittance of 90% or more at a thickness of 3 mm or less over the entire wavelength range of 220 nm or more and 2600 nm or less.

[0013] The silica glass of the present invention is Silica glass having a transmittance of 79% or more in a wavelength band of 170 nm or more and 220 nm or less at a thickness of 3 mm or less may also be used.

[0014] The silica glass of the present invention is Furthermore, silica glass having a transmittance of 80% or more in a wavelength band of 2600 nm or more and 3500 nm or less at a thickness of 3 mm or less may be used.

[0015] The silica glass of the present invention is Silica glass having a transmittance of 80% or more in the entire wavelength band of 170 nm or more and 3500 nm or less at a thickness of 3 mm or less may also be used.

[0016] The aforementioned manufacturing method can produce the above-mentioned silica glass having a transmittance different from conventional silica glass. Such silica glass has the advantage of being able to efficiently transmit light with high transmittance from the vacuum ultraviolet region to the infrared region. Utilizing such silica glass can realize highly versatile optical fibers and lenses (for medical use, imaging, etc.). [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a process diagram showing a molded body manufacturing process. [Figure 2] 1 is a graph showing the transmittance of Example 1. [Figure 3] 10 is a graph showing the transmittance of Example 2. [Figure 4] 10 is a graph showing the transmittance of Example 3. [Figure 5] 10 is a graph showing the transmittance of Example 4. [Figure 6] 10 is a graph showing the transmittance of Example 5. [Figure 7] 10 is a graph showing the transmittance of Example 6. [Figure 8] 10 is a graph showing the transmittance of Example 7. [Figure 9] 10 is a graph showing the transmittance of Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1 is a process diagram showing a process for producing a green body, which shows a process for producing a green body by a slurry casting method. In the slurry casting method, first, a slurry is prepared (step S1). In this step, a glass raw material solution containing silica glass powder, a solvent, a dispersant, and a curable resin is mixed in a ball mill for a predetermined time. Distilled water or the like can be used as the solvent. This glass raw material solution may contain various additives and impurities.

[0019] Next, a curing agent is added to the prepared slurry, which is then poured into a mold and cured (step S2). The molded product may have a dense structure, or may have a structure for photonic crystal fiber, in which holes and high-refractive-index glass are regularly arranged in the cross section of the optical fiber. In the case of a molded product for photonic crystal fiber, wires or the like for forming the holes are set in the mold, and the slurry is then poured in and cured. To harden the product, it can be left at room temperature, but heating is also acceptable.

[0020] Once the molded body has hardened, it is removed from the mold (step S3) and dried to remove the solvent from the molded body (step S4). The curable resin in the molded body is then removed by degreasing. Degreasing can be performed under various conditions, but may be performed at a temperature of about 850°C, for example.

[0021] The molded body that has been degreased in this way is then subjected to chlorine treatment and sintering (step S6), thereby obtaining a transparent glass sintered body. Chlorination and sintering are both a series of treatments carried out at high temperatures. Chlorination involves heating the compact in a chlorine gas atmosphere. The temperature conditions and treatment time for the chlorine treatment are preferably in the range of 0.5 to 6 hours, in which the chlorine treatment is performed at a temperature of 800° C. to 1200° C. in a chlorine gas atmosphere for sintering. It is more preferable that the temperature condition be in the range of 900°C or higher and 1050°C or lower. It is more preferable that the chlorine treatment is carried out at a temperature of 900° C. or higher and 1000° C. or lower for a period of 1 hour or higher and 4 hours or lower. Furthermore, it is more preferable to carry out the chlorine treatment at a temperature of 950° C. or higher and 1000° C. or lower for a period of 2 hours or higher and 3 hours or lower.

[0022] Examples of the molded body will be described below. In these examples, examples and comparative examples were prepared by varying the temperature conditions and time of chlorine treatment. The molded body was cylindrical with an outer diameter of 30 mm and a thickness of 3 mm. The manufacturing process was as described above. Silfil (registered trademark) from Tokuyama Corporation was used as the silica glass powder, but it is not limited to this. The curable resin used was SR-4GL, an epoxy resin manufactured by Sakamoto Pharmaceutical Co., Ltd. The dispersant used was a 25% tetramethylammonium hydroxide solution, and the curing agent used was triethylenetetraamine. These are merely examples, and the materials used are not limited to these.

[0023] A list of examples is shown in the table below. The transmittance was measured for light of various wavelengths using a molded body having a thickness of 3 mm as a test piece. In Examples 1, 2, and 8, the transmittance in the range of 2600 nm to 3500 nm was not measured. [Table 1]

[0024] The transmittance of the silica glass of Examples 1 to 8 is shown in Figures 2 to 9, respectively. In each figure, Figure (a) shows the transmittance in the range of 140 to 300 nm, Figure (b) shows the transmittance in the range of 300 to 2600 nm, and Figure (c) shows the transmittance in the range of 2600 nm (2.6 μm) to 5000 nm (5.0 μm). For Examples 1, 2, and 8, the transmittance in the range of 2600 nm to 3500 nm was not measured, so Figures 2, 4, and 9 only show Figures (a) and (b). 2 to 9, it was confirmed that the transmittance of the silica glass of Examples 1 to 8 changed continuously over the entire measured wavelength band, and no sudden spike-like or pulse-like changes occurred.

[0025] According to Examples 1 to 8, the transmittance in the wavelength band of 170 nm or more and 220 nm or less was 70% or more, and the transmittance was 90% or more over the entire wavelength band of 220 nm or more and 2600 nm or less, and it was found that high transmittance was achieved over a wide range. In these examples, the chlorine treatment is carried out for 0.5 to 6 hours. Chlorine treatment can be carried out in a chlorine gas atmosphere at a temperature of 800 to 1200°C, and therefore, it is considered preferable to carry out the chlorine treatment under such temperature conditions and time range. Specifically, in Examples 1 to 8, the chlorine treatment was carried out in the range of 900° C. or higher and 1050° C. or lower, and it can be said that it is more preferable to carry out the chlorine treatment under such temperature conditions.

[0026] Next, according to Examples 2 to 5, 7, and 8, the transmittance at a thickness of 3 mm or less in the wavelength band of 170 nm or more and 220 nm or less was even higher at 79% or more, and the transmittance was 90% or more over the entire wavelength band of 220 nm or more and 2600 nm or less, and it was found that high transmittance was achieved over a wide range. In these examples, the chlorine treatment was carried out at 900° C. or higher and 1000° C. or lower for 1 hour or longer and 4 hours or shorter, and therefore, it can be said that the production method in which such chlorine treatment is carried out is more preferable.

[0027] On the other hand, it is also possible to employ embodiments that place more importance on the transmittance in the range of 2600 nm to 3500 nm. According to embodiments 3, 4, 6, and 7, the transmittance in the wavelength range of 170 nm to 220 nm is 70% or more, and the transmittance in the wavelength range of 2600 nm to 3500 nm is 80% or more, and it was found that high transmittance can be achieved over a wide range. In these examples, the chlorine treatment was carried out at 900° C. or higher and 1050° C. or lower for 1 hour or longer and 6 hours or shorter, and therefore, it can be said that the production method in which such chlorine treatment is carried out is more preferable.

[0028] Furthermore, according to Examples 3, 4, and 7, the transmittance was 80% or more in the entire wavelength band of 170 nm or more and 3500 nm or less, and it was found that high transmittance was achieved over a wide range. In these examples, the chlorine treatment was carried out at 950° C. or higher and 1000° C. or lower for 2 hours or longer and 3 hours or shorter, and therefore, it can be said that the production method in which such chlorine treatment is carried out is more preferable.

[0029] The above results are for a limited number of materials, but since the temperature and time of chlorine treatment are what primarily affect transmittance, it is believed that similar results will be obtained for other materials as well. The present invention is not limited to the above-described embodiment, but can be realized using various materials and chlorine treatment conditions. [Industrial Applicability]

[0030] The present invention can be used to ensure high transmittance in silica glass from the vacuum ultraviolet region to the infrared region, and is particularly useful in optical fibers, lenses (for medical use, imaging, etc.), etc.

Claims

1. A method for producing silica glass by hardening and sintering a slurry, comprising: (a) preparing a slurry containing silica glass powder; (b) mixing the slurry with a curing agent and curing the mixture to form a compact; (c) sintering the molded body to obtain silica glass; The manufacturing method includes, in the step (c), a chlorine treatment in which sintering is performed in a chlorine gas atmosphere at a temperature of 900° C. or more and 1000° C. or less for 1 hour or more and 4 hours or less.

2. The manufacturing method according to claim 1, The manufacturing method includes carrying out the chlorine treatment at a temperature of 950°C or higher and 1000°C or lower for a period of 2 hours or higher and 3 hours or lower.

3. Silica glass having a transmittance of 79% or more at a thickness of 3 mm in the wavelength band of 170 nm or more and 220 nm or less, a transmittance of 90% or more at a thickness of 3 mm over the entire wavelength band of 220 nm or more and 2600 nm or less, and a transmittance of 75% or more at a thickness of 3 mm over the entire wavelength band of 2600 nm or more and 2800 nm or less.

4. The silica glass according to claim 3, Furthermore, the silica glass has a transmittance of 80% or more at a thickness of 3 mm in the wavelength band of 2600 nm or more and 3500 nm or less.

5. The silica glass according to claim 3, Silica glass having a transmittance of 80% or more at a thickness of 3 mm over the entire wavelength band of 170 nm to 3500 nm.

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