Synthetic quartz glass tube for ultraviolet light and method for manufacturing the same

Abstract

The present invention provides a synthetic quartz glass tube for ultraviolet irradiation in which the generation of distortion during ultraviolet irradiation is suppressed, and a method for manufacturing the same. [Solution] A synthetic quartz glass tube for ultraviolet light, wherein the synthetic quartz glass tube has an OH group concentration of 5 to 500 wt.ppm, and in the OH group concentration distribution in the thickness direction of the tube, the position of the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of the depth from the outer surface, and when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt.ppm], the OH group concentrations A, B, and C satisfy the following formulas (1) and (2). B≧C>A························· Formula (1) BA≧20[wt.ppm]...Formula (2)

Description

Technical Field

[0001] The present invention relates to a synthetic quartz glass tube for ultraviolet rays and a method for manufacturing the same.

Background Art

[0002] Synthetic quartz glass transmits light well from the ultraviolet region to the vacuum ultraviolet region. Therefore, for example, it is used in discharge tubes such as excimer lamps. However, due to defects such as ODC (Oxygen Deficient Center) and compaction (increase in density and volume shrinkage due to ultraviolet irradiation) caused by ultraviolet rays emitted from the lamp, distortion (strain) occurs, and in severe cases, it may be damaged. This is particularly prominent when using vacuum ultraviolet rays of 200 nm or less as a light source, and with the recent increase in size and high output of excimer lamps, it has become an even more serious problem.

[0003] It is known that defects in synthetic quartz glass generated during ultraviolet irradiation can be repaired by containing a predetermined amount of OH groups. Also, doping synthetic quartz glass with fluorine is known as one method for suppressing the generation of defects itself. This is a method of stabilizing the overall structure by previously cutting unstable three-membered and four-membered ring structures in synthetic quartz glass having distorted Si-O-Si bonds that are prone to generating defects with fluorine.

[0004] Patent Document 1 proposes an optical glass for ultraviolet light with an F (fluorine) concentration of 1% or more and an OH group concentration of 10 ppm or more, suggesting that doping with both F and OH groups can more effectively suppress the generation of defects than doping with each of them alone. Also, Patent Document 2 describes quartz glass with an F concentration of 1 to 1500 ppm and an OH group concentration of 110 to 500 ppm, but an upper limit is set because when the F concentration exceeds 3000 ppm, the illuminance maintenance rate of the excimer lamp is lower than that of conventional products.

[0005] As described in Patent Document 3, the presence of F and OH groups is known to affect compaction; the higher the OH group concentration, the greater the compaction, and conversely, the higher the F concentration, the less compaction occurs. For this reason, an OH group concentration of 100 ppm or less is preferred, and 10 ppm or less is particularly preferred, while an F concentration of 100 ppm or more is preferred, and 1000 ppm or more is particularly preferred. As this preferred range indicates, the OH group concentration has a greater impact on compaction than the F concentration, even at low concentrations or with only slight differences in concentration. Therefore, controlling the OH group concentration distribution inside the synthetic quartz glass is important to suppress strain.

[0006] Patent Document 4 proposes a synthetic quartz glass in which there is a region with a maximum OH group concentration in the center, and the OH group concentration gradually decreases towards the outer edge from this region. However, it is manufactured using the VAD method, and the core must be removed when used in the shape of a glass tube. As a result, the OH group concentration distribution in the thickness direction of the final glass tube is such that the OH group concentration increases from the outside to the inside of the glass tube. In this case, when irradiated with ultraviolet light, the inside, which has a smaller diameter, experiences a larger volume contraction than the outside, making the entire tube prone to distortion.

[0007] Therefore, in order to reduce the overall distortion of the glass tube during UV irradiation, it is considered ideal for the volume to shrink in the direction that reduces the overall size of the tube. Specifically, it is desirable for the volume shrinkage to decrease from the outside to the inside of the glass tube, that is, for the OH group concentration to decrease. Patent document 4 proposes a synthetic quartz glass in which there is a region with a minimum OH group concentration in the center, and the OH group concentration gradually increases from this region toward the outer edge. However, because it is manufactured by a direct method, the OH group concentration exceeds 500 ppm, resulting in large distortion.

[0008] In any case, since the above is a glass mass, the relationship between the OH group concentration distribution in the tubular shape and the strain generated during ultraviolet irradiation has not been well understood until now. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 8-67530 [Patent Document 2] Japanese Patent Publication No. 2004-319200 [Patent Document 3] Japanese Patent Publication No. 2003-321230 [Patent Document 4] Japanese Patent Publication No. 2002-128536 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] This invention has been made in view of the above-mentioned problems, and aims to provide a synthetic quartz glass tube for ultraviolet irradiation in which the generation of distortion during ultraviolet irradiation is suppressed. [Means for solving the problem]

[0011] The present invention has been made to solve the above problems, and provides a synthetic quartz glass tube for ultraviolet light, wherein the synthetic quartz glass tube has an OH group concentration of 5 to 500 wt.ppm, and in the OH group concentration distribution in the thickness direction of the tube, the position of the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of a depth from the outer surface, and when the OH group concentration of the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration of the outer surface of the synthetic quartz glass tube is C [wt.ppm], the respective OH group concentrations A, B, and C satisfy the following formulas (1) and (2). B≧C>A························· Formula (1) BA≧20[wt.ppm]...Formula (2)

[0012] Such synthetic quartz glass tubes for UV irradiation can be manufactured in a way that suppresses the generation of distortion during UV irradiation by controlling the OH group concentration distribution.

[0013] In this case, it is preferable that the concentration of fluorine contained in the synthetic quartz glass tube for ultraviolet light is 10 to 2500 wt.ppm.

[0014] By including fluorine at this concentration, an even greater strain suppression effect can be obtained.

[0015] Furthermore, the present invention provides an ultraviolet synthetic quartz glass member characterized by comprising any of the above-described ultraviolet synthetic quartz glass tubes and a reflective film that covers at least a portion of the surface of the ultraviolet synthetic quartz glass tube.

[0016] The present invention can be suitably applied to a synthetic quartz glass component for ultraviolet light, which is equipped with a reflective film in addition to a synthetic quartz glass tube for ultraviolet light.

[0017] Furthermore, the present invention relates to a method for manufacturing a synthetic quartz glass tube for ultraviolet light, comprising the steps of: supplying a silicon compound as a raw material onto a rotating target; flame hydrolysis of the silicon compound with an oxyhydrogen flame to deposit cylindrical silica soot; heating the cylindrical silica soot by a zone melting method to obtain cylindrical transparent quartz glass; and heating and stretching the cylindrical transparent quartz glass to produce a synthetic quartz glass tube; and obtaining from the manufactured synthetic quartz glass tube the OH group concentration is 5 to 500 wt.ppm, and the OH group concentration distribution in the direction of the tube wall thickness is The present invention provides a method for manufacturing a synthetic quartz glass tube for ultraviolet light, comprising the step of selecting a tube in which the OH group concentrations A, B, and C satisfy the following formulas (1) and (2), where the position with the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface, and the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt.ppm], and thereby a synthetic quartz glass tube for ultraviolet light is manufactured. B≧C>A························· Formula (1) BA≧20[wt.ppm]...Formula (2)

[0018] Furthermore, the present invention relates to a method for manufacturing a synthetic quartz glass tube for ultraviolet light, comprising the steps of: supplying a silicon compound as a raw material onto a rotating target; flame hydrolysis of the silicon compound with an oxyhydrogen flame to deposit cylindrical silica soot; heating the cylindrical silica soot by a zone melting method to obtain cylindrical transparent quartz glass; and heating and stretching the cylindrical transparent quartz glass to produce a synthetic quartz glass tube, wherein the OH group concentration distribution in the cylindrical transparent quartz glass is measured after obtaining the cylindrical transparent quartz glass but before the heating and stretching; and in the synthetic quartz glass tube produced by heating and stretching the cylindrical transparent quartz glass, the OH group concentration in the synthetic quartz glass tube is 5 to 500 wt.ppm. The present invention provides a method for manufacturing a synthetic quartz glass tube for ultraviolet light, characterized by further comprising the step of selecting cylindrical transparent quartz glass in which, in the OH group concentration distribution in the thickness direction of the tube, the position of the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 depth from the outer surface, and when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt.ppm], the respective OH group concentrations A, B, and C are estimated to satisfy the following formulas (1) and (2), and then heating and stretching the selected cylindrical transparent quartz glass to produce a synthetic quartz glass tube. B≧C>A························· Formula (1) BA≧20[wt.ppm]...Formula (2)

[0019] By manufacturing synthetic quartz glass tubes for UV irradiation using these methods, the OH group concentration distribution can be controlled, and synthetic quartz glass tubes for UV irradiation with suppressed distortion during UV irradiation can be produced.

[0020] Also, in this case, when it is estimated from the result of measuring the OH group concentration distribution in the cylindrical transparent quartz glass that, in the OH group concentration distribution in the tube wall thickness direction of the synthetic quartz glass tube, the position where the maximum OH group concentration is present does not exist within the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface, by grinding the outer circumference of the cylindrical transparent quartz glass, a method can be further provided that includes a step of making the position where the maximum OH group concentration is present within the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface in the OH group concentration distribution in the tube wall thickness direction.

[0021] Also, when it is estimated from the result of measuring the OH group concentration distribution in the cylindrical transparent quartz glass that, in the OH group concentration distribution in the tube wall thickness direction of the synthetic quartz glass tube, the OH group concentrations A, B, and C satisfy B > A > C, by grinding the outer circumference of the cylindrical transparent quartz glass, a method can be further provided that includes a step of making the OH group concentrations A, B, and C satisfy the formula (1) in the OH group concentration distribution in the tube wall thickness direction.

[0022] According to these methods, even when it is estimated that the conditions of the synthetic quartz glass tube for ultraviolet rays of the present invention are not satisfied, the OH group concentration distribution can be controlled, and a synthetic quartz glass tube for ultraviolet rays in which the generation of strain during ultraviolet irradiation is suppressed can be manufactured.

[0023] Also, in the manufacturing method of any of the above synthetic quartz glass tubes for ultraviolet rays, after the step of depositing the cylindrical silica soot, a step of doping the cylindrical silica soot with fluorine is included, and it is preferable to heat the fluorine-doped cylindrical silica soot by the zone melting method.

[0024] By adding fluorine in this way, a further strain suppression effect can be obtained.

Effects of the Invention

[0025] The synthetic quartz glass tube for ultraviolet light of the present invention is a synthetic quartz glass tube for ultraviolet light in which the OH group concentration distribution in the thickness direction is controlled, and therefore such a synthetic quartz glass tube suppresses the generation of distortion when irradiated with ultraviolet light. Furthermore, such a synthetic quartz glass tube for ultraviolet light can be manufactured using the manufacturing method of the present invention. [Brief explanation of the drawing]

[0026] [Figure 1] This is a schematic cross-sectional view showing the regional divisions in an example of a synthetic quartz glass tube for ultraviolet light according to the present invention. [Figure 2] This is a schematic cross-sectional view showing the regional divisions in another example of the synthetic quartz glass tube for ultraviolet light of the present invention, where (a) is an example where the cross-section is elliptical, (b) is an example where the cross-section is flattened, and (c) is another example where the cross-section is flattened. [Figure 3] This graph shows a schematic example of the OH group concentration distribution in the synthetic quartz glass tube for ultraviolet light according to the present invention. [Figure 4] This graph shows a schematic representation of another example of the OH group concentration distribution in the synthetic quartz glass tube for ultraviolet light according to the present invention. [Figure 5] This is a flowchart illustrating an example of a method for manufacturing a synthetic quartz glass tube for ultraviolet light according to the present invention. [Figure 6] This is a flowchart showing another example of the method for manufacturing a synthetic quartz glass tube for ultraviolet light according to the present invention. [Figure 7] This graph shows the OH group concentration distribution in the synthetic quartz glass tubes for ultraviolet light of Examples 4 and 5 and Comparative Example 3. [Modes for carrying out the invention]

[0027] To overcome the above-mentioned problems, the inventors diligently conducted research and discovered that by adjusting the dehydration method during glass production, the heating conditions during vitrification, and the amount of outer circumference grinding after vitrification, and thereby controlling the OH group concentration distribution in the wall thickness direction of the synthetic quartz glass tube, it was possible to suppress the generation of distortion throughout the tube when the OH group concentration difference was set to a certain value or higher. This led to the present invention.

[0028] The present invention will be described in more detail below. The present invention is a synthetic quartz glass tube for ultraviolet light, and has the following features (i) to (iii) (definition of OH group concentration and OH group concentration distribution). (i) The synthetic quartz glass tube has an OH group concentration of 5 to 500 wt.ppm, (ii) In the distribution of OH group concentration in the thickness direction of the synthetic quartz glass tube, the position with the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface, (iii) A synthetic quartz glass tube for ultraviolet light, characterized in that when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt.ppm], the respective OH group concentrations A, B, and C satisfy the following formulas (1) and (2). B≧C>A························· Formula (1) BA≧20[wt.ppm]...Formula (2)

[0029] The synthetic quartz glass tube for ultraviolet light according to the present invention will be described in more detail with reference to the drawings.

[0030] Figure 1 shows a schematic cross-sectional view illustrating the regional divisions in an example of the synthetic quartz glass tube for ultraviolet light according to the present invention. Although Figure 1 shows the regional divisions of the tube for the convenience of explaining the present invention, the synthetic quartz glass tube for ultraviolet light according to the present invention is a continuous body of synthetic quartz glass, and there are no visible boundaries.

[0031] As shown in Figure 1, the UV-emitting synthetic quartz glass tube 10 is a hollow tube shape and has an inner surface 11 and an outer surface 17. For explanatory purposes, the UV-emitting synthetic quartz glass tube 10 is divided into an inner 1 / 3 portion (inner region) 12, an intermediate 1 / 3 portion (intermediate region) 14, and an outer 1 / 3 portion (outer region) 16. The dashed lines in Figure 1 indicate the thickness direction of the UV-emitting synthetic quartz glass tube 10. The inner region 12 occupies the inner 1 / 3 of the thickness of the inner surface 11 and the outer surface 17, and is the area between the inner surface 11 and a depth of 1 / 3 of the thickness. The outer region 16 occupies the outer 1 / 3 of the thickness of the inner surface 11 and the outer surface 17, and is the area between the outer surface 17 and a depth of 1 / 3 of the thickness. The intermediate region 14 is the portion other than the inner region 12 and the outer region 16.

[0032] Figure 1 shows a cylindrical synthetic quartz glass tube 10 for ultraviolet light with a circular cross-section. However, the present invention does not necessarily require a circular cross-section; it can be applied to any hollow tube having a curved portion (having a radius). For example, it may have an elliptical cross-section or a flattened shape (a shape having both a straight and a curved portion in its cross-section). Figures 2(a) to 2(c) show synthetic quartz glass tubes 20 for ultraviolet light with an elliptical or flattened cross-section. In all of the shapes shown in Figures 2(a) to 2(c), similar to the synthetic quartz glass tube 10 for ultraviolet light in Figure 1, the area between the inner surface 21 and the outer surface 27 can be divided for explanatory purposes into an inner 1 / 3 portion (inner region) 22, an intermediate 1 / 3 portion (intermediate region) 24, and an outer 1 / 3 portion (outer region) 26. Figure 2(b) shows an example of a tube cross-sectional shape consisting of four straight sections and four curved sections, and Figure 2(c) shows an example of a tube cross-sectional shape consisting of two straight sections and two curved sections.

[0033] The present invention will be described with reference to Figure 1. The synthetic quartz glass tube 10 for ultraviolet light according to the present invention has an OH group concentration of 5 to 500 wt. ppm. In other words, the OH group concentration of the entire synthetic quartz glass tube 10 for ultraviolet light is 5 to 500 wt. ppm, without distinguishing between the inner region 12, the intermediate region 14, and the outer region 16. If this OH group concentration exceeds 500 wt. ppm, the strain becomes large. If the OH group concentration is less than 5 wt. ppm, the defect repair capability cannot be obtained.

[0034] Furthermore, in the synthetic quartz glass tube 10 for ultraviolet light of the present invention, the position where the maximum OH group concentration is located in the OH group concentration distribution in the thickness direction of the tube is located in the range between the outer surface of the synthetic quartz glass tube 10 and a depth of 2 / 3 from the outer surface. This means that the position where the maximum OH group concentration is located is within the combined range of the outer region 16 and the intermediate region 14 in Figure 1.

[0035] Furthermore, in the synthetic quartz glass tube 10 for ultraviolet light of the present invention, when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt.ppm], each OH group concentration A, B, and C satisfies the following formulas (1) and (2). B≧C>A························· Formula (1) BA≧20[wt.ppm]...Formula (2)

[0036] The OH group concentration A [wt.ppm] on the inner surface of the synthetic quartz glass tube represents the OH group concentration near the inner surface 11 in Figure 1. Specifically, it is the OH group concentration at a location 10 μm in from the inner surface 11. This is because the OH group concentration on the surface itself cannot be measured. Similarly, the OH group concentration C [wt.ppm] on the outer surface of the synthetic quartz glass tube represents the OH group concentration near the outer surface 17 in Figure 1, specifically, the OH group concentration at a location 10 μm in from the outer surface 17. Furthermore, the maximum OH group concentration B [wt.ppm] indicates the OH group concentration at the same location as the maximum OH group concentration mentioned above. The location with the maximum OH group concentration B is located in the range between the outer surface of the synthetic quartz glass tube 10 and a depth of 2 / 3 from that outer surface.

[0037] The OH group concentration distribution and the respective OH group concentrations A, B, and C in the synthetic quartz glass tube for ultraviolet light of the present invention will be explained with reference to Figures 3 and 4. In both Figures 3 and 4, the horizontal axis represents the distance from the inner surface 11 in the thickness direction of the synthetic quartz glass tube 10 for ultraviolet light, and the vertical axis represents the OH group concentration. Figure 3 shows the case where B>C>A in equation (1) B≧C>A. Figure 4 shows the case where B=C>A in equation (1) B≧C>A.

[0038] The OH group concentration distribution of the UV-resistant synthetic quartz glass tube 10 of the present invention is typically B>C>A as shown in Figure 3, but B and C may coincide, resulting in B=C>A, as shown in Figure 4. B=C means that the OH group concentration is maximum near the outer surface 17 of the UV-resistant synthetic quartz glass tube 10. As shown by the dashed line in Figure 4, there may be areas in the UV-resistant synthetic quartz glass tube 10 where the OH group concentration is lower than the OH group concentration A on the inner surface.

[0039] In the synthetic quartz glass tube 10 for ultraviolet light of the present invention, it is also necessary that the relationship between the OH group concentrations A and B satisfies formula (2) BA ≥ 20 [wt.ppm].

[0040] The synthetic quartz glass tube 10 for ultraviolet light, in which the OH group concentration distribution in the thickness direction is controlled according to the present invention, can suppress the generation of distortion during ultraviolet irradiation. The reason for this is as follows.

[0041] In synthetic quartz glass tubes for UV irradiation, it is ideal for the overall size of the tube to shrink in order to minimize the strain on the entire tube during UV irradiation. Furthermore, the volume contraction of synthetic quartz glass is greater the higher the OH group concentration during UV irradiation. Therefore, it is desirable for the OH group concentration to decrease from the outside to the inside of the glass tube (i.e., an OH group concentration distribution as shown in Figure 4). However, when manufacturing synthetic quartz glass tubes using a manufacturing method that involves a soot body, OH groups inevitably leach out from the soot surface during the dehydration process, resulting in a distribution within the glass tube where the maximum value (maximum OH group concentration B) is located (i.e., an OH group concentration distribution as shown in Figure 3). If this maximum value (maximum OH group concentration B) is in the inner region 12 in Figure 1, the volume contraction inside the synthetic quartz glass tube 10 will be large, resulting in increased strain. Therefore, it must be located within 2 / 3 of the depth from the outside (i.e., either the outer region 16 or the intermediate region 14). Furthermore, in the synthetic quartz glass tube 10 for ultraviolet light, the outer volume is relatively larger than the inner volume, so it can withstand some difference in volume contraction between the outer and inner parts of the tube.

[0042] In this invention, the concentration of fluorine contained in the synthetic quartz glass tube for ultraviolet light is preferably 10 to 2500 wt.ppm. A fluorine concentration (F concentration) of 10 wt.ppm or higher provides a more effective distortion suppression effect. Furthermore, by setting the fluorine concentration to 2500 wt.ppm or lower, the distortion suppression effect can be obtained while sufficiently maintaining the illuminance retention rate of ultraviolet lamps such as excimer lamps.

[0043] Furthermore, the present invention also provides an ultraviolet synthetic quartz glass member comprising the above-mentioned ultraviolet synthetic quartz glass tube 10 and a reflective film that covers at least a portion of the surface of the ultraviolet synthetic quartz glass tube 10 (at least one of the inner surface 11 and the outer surface 17). The lamps in which such an ultraviolet synthetic quartz glass member is used are not particularly limited as long as they emit ultraviolet light, and the ultraviolet synthetic quartz glass tube and ultraviolet synthetic quartz glass member of the present invention can be applied to excimer lamps, mercury lamps, xenon lamps, etc.

[0044] The synthetic quartz glass tube 10 for ultraviolet light of the present invention can be manufactured, for example, by the following manufacturing methods (first embodiment, second embodiment). Both the first embodiment and the second embodiment are based on a method called the OVD (Outside Vapor Deposition) method.

[0045] (First aspect) The first embodiment is a method for producing synthetic quartz glass tubes and selecting synthetic quartz glass tubes for ultraviolet light that have a specific OH group concentration distribution. The first embodiment is shown in Figure 5.

[0046] First, as shown in S11 of Figure 5, the silicon compound, which is the raw material, is supplied onto a rotating target, and the silicon compound is subjected to flame hydrolysis with an oxyhydrogen flame to deposit cylindrical silica soot (step S11).

[0047] After the step of depositing cylindrical silica soot (step S11), a step of doping the cylindrical silica soot with fluorine (not shown) may be provided. In this case, in step S12, described later, the fluorine-doped cylindrical silica soot is heated by the zone melt method.

[0048] Next, as shown in S12 of Figure 5, cylindrical silica soot is heated by the zone melt method to obtain cylindrical transparent quartz glass (step S12).

[0049] Next, as shown in S13 of Figure 5, a synthetic quartz glass tube is fabricated by heating and stretching a cylindrical transparent quartz glass (step S13).

[0050] Next, as shown in S14 of Figure 5, synthetic quartz glass tubes are selected from the fabricated tubes if they have an OH group concentration of 5 to 500 wt.ppm, the position of the maximum OH group concentration in the OH group concentration distribution in the tube wall thickness direction is located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of the depth from the outer surface, and when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt.ppm], then tubes in which each OH group concentration A, B, and C satisfy the above formulas (1) and (2) are selected (step S14). This allows for the manufacture of synthetic quartz glass tubes for ultraviolet light.

[0051] In the OVD method, the soot is prepared as in step S11 above. Since the soot produced by the OVD method is a hollow soot, OH groups are removed from both the inside and outside of the soot during dehydration. Furthermore, as in step S12 above, vitrification occurs gradually from the outside by the zone melt method, so by adjusting the temperature and traverse rate conditions, it is possible to create a situation where the inside is heated for a long time, thereby reducing the OH group concentration on the inside. In addition, if fluorine is present, Si-OH is replaced with Si-F, which further promotes dehydration and increases the difference in OH group concentration on the inside.

[0052] Through the above process, a synthetic quartz glass tube for ultraviolet light that satisfies the provisions (i) to (iii) of the OH group concentration and its distribution in the present invention can be manufactured. Furthermore, if a synthetic quartz glass tube for ultraviolet light that satisfies the provisions (i) to (iii) of the OH group concentration and its distribution in the present invention is obtained under specific manufacturing conditions, the same manufacturing conditions can be used in subsequent manufacturing of synthetic quartz glass tubes for ultraviolet light that repeatedly satisfy the provisions of the OH group concentration and its distribution in the present invention.

[0053] (Second aspect) The second embodiment is basically the same as the first embodiment, but involves measuring the OH group concentration distribution at the cylindrical transparent quartz glass stage to select cylindrical transparent quartz glass that yields a synthetic quartz glass tube with a specific OH group concentration distribution. The second embodiment is shown in Figure 6.

[0054] First, as shown in S21 of Figure 6, the silicon compound, which is the raw material, is supplied onto a rotating target, and the silicon compound is flame-hydrolyzed with an oxyhydrogen flame to deposit cylindrical silica soot (step S21). Next, as shown in S22 of Figure 6, the cylindrical silica soot is heated by the zone melt method to obtain cylindrical transparent quartz glass (step S22). Steps S21 and S22 are the same as steps S11 and S12 of the first embodiment. Alternatively, a step of doping the cylindrical silica soot with fluorine may be added after the step of depositing the cylindrical silica soot (step S21), in which case heating the fluorine-doped cylindrical silica soot by the zone melt method in step S22 is also the same as in the first embodiment.

[0055] In the second embodiment, after obtaining cylindrical transparent quartz glass in step S22 and before heat stretching (step S24 described later), the OH group concentration distribution in the cylindrical transparent quartz glass is measured as shown in S23 of Figure 6. Cylindrical transparent quartz glass is selected (step S23) in which, when the cylindrical transparent quartz glass is heat stretched to produce a synthetic quartz glass tube, the OH group concentration in the synthetic quartz glass tube is estimated to be between 5 and 500 wt.ppm, the position of the maximum OH group concentration in the OH group concentration distribution in the thickness direction of the tube is located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of the depth from the outer surface, and when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt.ppm], the maximum OH group concentration is B [wt.ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt.ppm], the OH group concentrations A, B, and C are estimated to satisfy the above formulas (1) and (2).

[0056] Next, as shown in S24 of Figure 6, the cylindrical transparent quartz glass selected in step S23 is heated and stretched to produce a synthetic quartz glass tube, thereby manufacturing a synthetic quartz glass tube for ultraviolet light (step S24).

[0057] By the process described above, a synthetic quartz glass tube for ultraviolet light that satisfies the specified OH group concentration and distribution of the present invention can be manufactured. Furthermore, similar to the first embodiment, if a synthetic quartz glass tube for ultraviolet light that satisfies the specified (i) to (iii) of the specified OH group concentration and distribution of the present invention is obtained under specific manufacturing conditions, the same manufacturing conditions can be used in subsequent manufacturing of synthetic quartz glass tubes for ultraviolet light to repeatedly produce tubes that satisfy the specified OH group concentration and distribution of the present invention.

[0058] Furthermore, in a second embodiment, if, based on the results of measuring the OH group concentration distribution in the cylindrical transparent quartz glass performed in step S23, it is estimated that the OH group concentration distribution in the wall thickness direction of the synthetic quartz glass tube does not satisfy the conditions for the ultraviolet synthetic quartz glass tube 10 of the present invention, the conditions for the ultraviolet synthetic quartz glass tube 10 of the present invention can be satisfied by performing outer circumference grinding on the cylindrical transparent quartz glass.

[0059] First, if the measurement results of the OH group concentration distribution in the cylindrical transparent quartz glass indicate that the position with the maximum OH group concentration when it is considered as a synthetic quartz glass tube 10 for ultraviolet light does not exist in the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface, then the outer circumference of the cylindrical transparent quartz glass can be ground. This makes it possible to ensure that the position with the maximum OH group concentration in the OH group concentration distribution in the wall thickness direction of the synthetic quartz glass tube 10 exists in the range between the outer surface of the synthetic quartz glass tube 10 and a depth of 2 / 3 from the outer surface.

[0060] Furthermore, even if the measurement results of the OH group concentration distribution in the cylindrical transparent quartz glass do not satisfy equation (1) in the OH group concentration distribution in the thickness direction of the synthetic quartz glass tube, and it is estimated that the OH group concentrations A, B, and C are B>A>C, the outer circumference of the cylindrical transparent quartz glass can still be ground. This makes it possible to ensure that the OH group concentrations A, B, and C in the thickness direction of the UV synthetic quartz glass tube 10 satisfy equation (1).

[0061] These methods allow for the control of the OH group concentration distribution even when it is estimated that the conditions for the synthetic quartz glass tube for ultraviolet light of the present invention are not met. Generally, when manufacturing synthetic quartz glass tubes, the surface layer becomes contaminated during dehydration and vitrification processes, and therefore, outer surface grinding is sometimes performed to remove the contaminated portion. The outer surface grinding performed in the present invention to control the OH group concentration distribution in the thickness direction has a different purpose than the outer surface grinding performed for normal contamination removal.

[0062] While it is possible to obtain synthetic quartz glass tubes for ultraviolet light that satisfy provisions (i) to (iii) of the present invention by other methods (for example, by preparing a glass mass with an OH group concentration distribution that increases from the center outwards and selecting the cutting site), these methods have the following disadvantages. Specifically, the VAD (Vapor phase Axial Deposition) method can produce glass masses (not glass tubes) with an OH group concentration distribution that falls within the scope of the present invention, but the core must be removed to make it a glass tube, which is disadvantageous in terms of cost. Furthermore, in the case of the direct method, the OH group concentration is generally 500 ppm or more, making it difficult to obtain synthetic quartz glass tubes for ultraviolet light according to the present invention.In addition, in the case of the electrofusion method, the OH group concentration is less than 20 ppm, and a difference of 20 ppm or more in the OH group concentration distribution does not occur, making it impossible to satisfy equation (2). [Examples]

[0063] The present invention will be described in detail below with reference to examples and comparative examples, but these are not intended to limit the present invention.

[0064] (Example 1) A cylindrical silica soot with an outer diameter of 400 mm (inner diameter of 60 mm) and a length of 3000 mm was fabricated using the Outside Vapor Deposition (OVD) method. The obtained cylindrical silica soot was placed in a dehydration furnace and dehydrated by heating at an arbitrary temperature below 1200°C. Next, it was cooled to room temperature, and after removing the silica soot from the dehydration furnace, vitrification was performed by the zone melt method at an arbitrary temperature below 1600°C. The OH group concentration distribution in the wall thickness direction was controlled by adjusting the dehydration conditions and the heating conditions during vitrification. Finally, the obtained cylindrical transparent quartz glass was heated and stretched to obtain a synthetic quartz glass tube with an outer diameter of 40 mm and a wall thickness of 3 mm.

[0065] (Examples 2-5, Comparative Examples 2-4) A cylindrical silica soot with an outer diameter of 400 mm (inner diameter of 60 mm) and a length of 3000 mm was fabricated by the OVD method. The obtained cylindrical silica soot was placed in a dehydration furnace and dehydrated by heating at an arbitrary temperature below 1200°C. Next, it was cooled to room temperature and doped with fluorine by reacting with a predetermined amount of SiF4 gas. Subsequently, the silica soot was removed from the dehydration furnace and vitrified by the zone melt method at an arbitrary temperature below 1600°C. The OH group concentration distribution in the wall thickness direction was controlled by adjusting the dehydration conditions and heating conditions during vitrification. Finally, the obtained cylindrical transparent quartz glass was heated and stretched to obtain a synthetic quartz glass tube with an outer diameter of 40 mm and a wall thickness of 3 mm.

[0066] (Example 6) A cylindrical silica soot with an outer diameter of 400 mm (inner diameter of 60 mm) and a length of 3000 mm was fabricated by the OVD method. The obtained cylindrical silica soot was placed in a dehydration furnace and dehydrated by heating at an arbitrary temperature below 1200°C. Next, it was cooled to room temperature and doped with fluorine by reacting with a predetermined amount of SiF4 gas. Subsequently, the silica soot was removed from the dehydration furnace and vitrified by the zone melt method at an arbitrary temperature below 1600°C. The OH group concentration distribution in the wall thickness direction was controlled by adjusting the dehydration conditions, heating conditions during vitrification, and the amount of outer perimeter grinding after vitrification. The amount of outer perimeter grinding at this time was set to 10 mm. The amount of outer perimeter grinding was determined by cutting out a portion of the obtained cylindrical transparent quartz glass and measuring the OH group concentration distribution in the wall thickness direction using FT-IR. Finally, the cylindrical transparent quartz glass was heated and stretched to obtain a synthetic quartz glass tube with an outer diameter of 40 mm and a wall thickness of 3 mm.

[0067] (Comparative Example 1) A cylindrical silica soot with a diameter of 350 mm and a length of 1500 mm was prepared using the VAD (Vapor Phase Axial Deposition) method. Next, vitrification was performed at an arbitrary temperature of 1600°C or lower while the material was left to stand. Subsequently, a hole was drilled through the center of the diameter of the cylindrical transparent quartz glass mass in the longitudinal direction to form a cylindrical transparent quartz glass. Finally, the obtained cylindrical transparent quartz glass was heated and stretched to obtain a synthetic quartz glass tube with an outer diameter of 40 mm and a wall thickness of 3 mm.

[0068] [Evaluation Method] (F concentration measurement) A 3g sample was cut from a sample with an outer diameter of 40mm and a wall thickness of 3mm, and measured using ICP-QMS (quadrupole ICP mass spectrometer).

[0069] (OH group concentration measurement) A synthetic quartz glass tube with an outer diameter of 40 mm, a wall thickness of 3 mm, and a length of 3 mm was prepared and divided into four sections in the cross-sectional direction. Two of the curved surfaces of the cross-sections were then mirror-polished. Next, measurements were taken using a micro-FT-IR at 10 μm intervals from the inside to the outside of the tube, and the reading was 3673 cm⁻¹. -1The OH group concentration was calculated from the peak height. The innermost measurement point was designated as the inner OH group concentration A, the maximum value as the maximum OH group concentration B, and the outermost measurement point as the outer OH group concentration C. As shown above, the maximum OH group concentration B and the outer OH group concentration C may coincide.

[0070] (Position of maximum OH group concentration) From the OH group concentration distribution measured by the above method, it was determined whether the maximum OH group concentration was located within 2 / 3 of the wall thickness from the outside of the tube (i.e., either the outer region 16 or the intermediate region 14 in Figure 1). A circle (○) was used if it was within 2 / 3 of the wall thickness, and a cross (×) was used otherwise.

[0071] (Measurement of distortion after UV irradiation) A synthetic quartz glass tube with an outer diameter of 40 mm, a wall thickness of 3 mm, and a length of 30 mm was prepared and divided into four sections in the cross-sectional direction. Next, it was heated at 1000°C for 24 hours to remove the strain. Subsequently, half of the 20 x 30 mm surface of the synthetic quartz glass tube was covered with aluminum foil and subjected to a 180 mW / cm² heating. 2 The sample was irradiated at 172 nm with the specified irradiation energy for 1000 hours. The birefringence (strain) at a wavelength of 632.8 nm was measured at a 20 × 30 mm surface of the obtained sample using a birefringence measuring instrument EXICOR350AT (Hinds). Birefringence was measured at multiple arbitrary positions measurable by the measuring instrument, and the highest birefringence was defined as the maximum birefringence (maximum strain). A value of 100 nm / cm or less was considered acceptable.

[0072] The results for each example and comparative example are shown in Table 1. Figure 7 shows graphs illustrating the OH group concentration distribution in the synthetic quartz glass tubes for ultraviolet light in Examples 4 and 5 and Comparative Example 3.

[0073] [Table 1]

[0074] As can be seen from Table 1, Examples 1 to 6, which satisfy formulas (1) and (2), showed low maximum birefringence after 1000 hours of UV irradiation, resulting in good synthetic quartz glass tubes for UV irradiation with suppressed distortion during UV irradiation. On the other hand, Comparative Examples 1, 3, and 4 did not satisfy either or both of formulas (1) and (2), and as a result, the maximum birefringence after 1000 hours of UV irradiation exceeded 100 nm / cm, and good synthetic quartz glass tubes for UV irradiation could not be obtained. In Comparative Example 2, the position with the highest OH group concentration was not located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of the depth from the outer surface, but was located on the inside. As a result, the maximum birefringence after 1000 hours of UV irradiation exceeded 100 nm / cm, and good synthetic quartz glass tubes for UV irradiation could not be obtained.

[0075] As shown in Figure 7, in Examples 4 and 5, the location of the maximum OH group concentration is within the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface. In Comparative Example 3, the location of the maximum OH group concentration is also within the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface, but Comparative Example 3 is an example that does not satisfy equation (1).

[0076] Furthermore, in Examples 2 to 6, which were doped with fluorine, the generation of strain was suppressed more than in Example 1, which was not doped with fluorine.

[0077] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are merely illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0078] 10, 20... Synthetic quartz glass tubes for UV light, 11, 21... Inner surface of synthetic quartz glass tube for UV light, 12, 22... The inner 1 / 3 portion (inner region) of the synthetic quartz glass tube for UV light, 14, 24... The middle 1 / 3 portion (intermediate region) of the synthetic quartz glass tube for UV light. 16, 26... The outer 1 / 3 portion (outer region) of the synthetic quartz glass tube for UV light. 17, 27... Outer surface of synthetic quartz glass tube for UV light.

Claims

1. A synthetic quartz glass tube for ultraviolet light, The aforementioned synthetic quartz glass tube has an OH group concentration of 5 to 500 wt. ppm. In the OH group concentration distribution in the wall thickness direction of the synthetic quartz glass tube, the position with the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and a depth of 2 / 3 from the outer surface. A synthetic quartz glass tube for ultraviolet light, characterized in that when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt. ppm], the maximum OH group concentration is B [wt. ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt. ppm], each OH group concentration A, B, and C satisfies the following formulas (1) and (2). B≧C>A・・・・・・・・・・Formula (1) B-A≧20 [wt. ppm]...Formula (2)

2. The synthetic quartz glass tube for ultraviolet light according to claim 1, characterized in that the concentration of fluorine contained in the synthetic quartz glass tube for ultraviolet light is 10 to 2500 wt. ppm.

3. A synthetic quartz glass tube for ultraviolet light according to claim 1 or claim 2, A reflective film covering at least a portion of the surface of the aforementioned synthetic quartz glass tube for ultraviolet light, A synthetic quartz glass component for ultraviolet light, characterized by being composed of the following:

4. A method for manufacturing synthetic quartz glass tubes for ultraviolet light, The process involves supplying a silicon compound, which is the raw material, onto a rotating target, and depositing a cylindrical silica soot by flame hydrolysis of the silicon compound with an oxyhydrogen flame. The steps include heating the cylindrical silica soot by a zone melting method to obtain cylindrical transparent quartz glass, The steps include: heating and stretching the cylindrical transparent quartz glass to produce a synthetic quartz glass tube; From the synthetic quartz glass tubes prepared as described above, the OH group concentration is 5 to 500 wt. ppm, and in the OH group concentration distribution in the thickness direction of the tube, the position of the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of a depth from the outer surface, and when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt. ppm], the maximum OH group concentration is B [wt. ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt. ppm], the step of selecting those in which each OH group concentration A, B, and C satisfies the following formulas (1) and (2). A method for manufacturing a synthetic quartz glass tube for ultraviolet light, characterized by having a [specific component], thereby enabling the production of a synthetic quartz glass tube for ultraviolet light. B≧C>A・・・・・・・・・・Formula (1) B-A≧20 [wt. ppm]...Formula (2)

5. A method for manufacturing synthetic quartz glass tubes for ultraviolet light, The process involves supplying a silicon compound, which is the raw material, onto a rotating target, and depositing a cylindrical silica soot by flame hydrolysis of the silicon compound with an oxyhydrogen flame. The steps include heating the cylindrical silica soot by a zone melting method to obtain cylindrical transparent quartz glass, The steps include: heating and stretching the cylindrical transparent quartz glass to produce a synthetic quartz glass tube; It has, The process further includes a step of selecting cylindrical transparent quartz glass that, after obtaining the cylindrical transparent quartz glass but before the heat stretching, measures the OH group concentration distribution in the cylindrical transparent quartz glass, and, when the cylindrical transparent quartz glass is heat stretched to produce a synthetic quartz glass tube, the OH group concentration in the synthetic quartz glass tube is estimated to be between 5 and 500 wt. ppm, and in the OH group concentration distribution in the thickness direction of the tube, the position of the maximum OH group concentration is located in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of the depth from the outer surface, and when the OH group concentration on the inner surface of the synthetic quartz glass tube is A [wt. ppm], the maximum OH group concentration is B [wt. ppm], and the OH group concentration on the outer surface of the synthetic quartz glass tube is C [wt. ppm], then it is estimated that each OH group concentration A, B, and C satisfies the following formulas (1) and (2). A method for producing a synthetic quartz glass tube for ultraviolet light, characterized by manufacturing a synthetic quartz glass tube for ultraviolet light by heating and stretching the selected cylindrical transparent quartz glass to produce a synthetic quartz glass tube. B≧C>A・・・・・・・・・・Formula (1) B-A≧20 [wt. ppm]...Formula (2)

6. The method for manufacturing a synthetic quartz glass tube for ultraviolet light according to claim 5, further comprising the step of grinding the outer circumference of the cylindrical transparent quartz glass so that the position with the maximum OH group concentration in the OH group concentration distribution in the thickness direction of the synthetic quartz glass tube does not exist in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of a depth from the outer surface, if, as a result of measuring the OH group concentration distribution in the cylindrical transparent quartz glass, it is estimated that the position with the maximum OH group concentration in the OH group concentration distribution in the thickness direction of the synthetic quartz glass tube exists in the range between the outer surface of the synthetic quartz glass tube and 2 / 3 of a depth from the outer surface.

7. The method for manufacturing a synthetic quartz glass tube for ultraviolet light according to claim 5, further comprising the step of grinding the outer circumference of the cylindrical transparent quartz glass so that the OH group concentrations A, B, and C in the OH group concentration distribution in the thickness direction of the synthetic quartz glass tube satisfy formula (1) when, based on the results of measuring the OH group concentration distribution in the cylindrical transparent quartz glass, it is estimated that B > A > C in the OH group concentration distribution in the thickness direction of the synthetic quartz glass tube,

8. After the step of depositing the cylindrical silica soot, The step of doping the cylindrical silica soot with fluorine is included. A method for manufacturing a synthetic quartz glass tube for ultraviolet light according to any one of claims 4 to 7, characterized in that the fluorine-doped cylindrical silica soot is heated by the zone melt method.

Images