JPH04335301A - Production of base body of reflection mirror - Google Patents

Abstract

PURPOSE:To improve strength and accuracy and to reduce costs as well as to obtain excellent operability by fusing and forming a glass sealing layer on the peripheral side face of a laminate formed by using a quartz glass or high silicate glass sheet to a porous foam layer. CONSTITUTION:The disk-shaped porous foam 1 which is the quartz glass or high silicate glass consisting of silicon oxide and has 0.1 to 1g/cm<2> apparent density is used as a supporting member for a reflection mirror plate. This porous foam 1 is cut to a desired plate of a disk or square shape according to the size and shape of the reflection mirror. The transparent foamless quartz glass or high silicate glass sheet 2 for the reflection mirror is fused and integrated to the one surface thereof and a glass sheet 3 which does not require high purity as the rear sheet is fused and integrated to the other surface. After both sheets are joined to both surfaces of the foam layer 1, a slender sealing layer 4 of the quartz glass or high silicate glass is fused and formed on the peripheral side face of this laminate. The entire side face of the foam layer 1 is preferably finished smooth before the formation of the sealing layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing a reflecting mirror useful for astronomical observation, beam focusing, space industry, etc.
In particular, the present invention relates to a method for manufacturing a reflecting mirror substrate that is lightweight, has excellent operability, and has high structural strength and optical properties.

0002

[Prior Art] Conventionally, astronomical reflectors and high-energy beams have been used.
For example, a reflector used for optical convergence such as a mirror is made of a bubble-free reflector plate made of quartz glass, high silicate glass, etc., with a vapor-deposited metal film such as aluminum as an optical reflective layer. It is supported on an operating support and can be rotated freely. Such a base for a reflecting mirror is required to maintain accuracy without being affected by the temperature of the reflecting surface or internal force changes. Until now, such a reflector had a diameter of 5
Small ones of ~20cm were the mainstream, but in recent years,
In order to obtain a high light condensing efficiency, large diameter devices of 30 cm to 1 m or more are now required and put into practical use. However, since such large objects are extremely heavy, changes in the supporting posture such as the support angle of the reflector can easily cause deformation due to its own weight, causing waviness on the mirror surface and impairing the optical performance of the reflector. There were problems such as deterioration.

[0003] As the size increases, the mirror surface waviness changes due to subtle volume changes and deformations of the reflector base due to radiation of the focused beam and changes in environmental temperature, and these changes affect the reflection. Since this degrades mirror performance, quartz glass and high silicate glass, which have small thermal expansion changes, have come to be used as materials for reflective mirrors. However, these glasses make the reflector base heavy and reduce the operability of the reflector, so in order to improve the operability, it is required to reduce the weight of the base as much as possible. In line with such practical requirements, many proposals have been made to maintain sufficient support strength and to achieve weight reduction, particularly regarding support members for large reflecting mirror plates.

For example, Japanese Patent Publication No. 63-57761 discloses a transparent reflector plate (front plate) as a lightweight reflector material for celestial bodies.
and the rear plate, a supporting grid of quartz glass or the like consisting of several rows of tubes, staggered so that each tube in the row has a contact line or zone with two tubes in an adjacent row. Discloses a special tube construction in which the thickness of the tube wall in the area of the line of contact etc. is reduced compared to the rest of the wall and the tubes are further welded together along the line of contact etc. has been done. However, such a specially constructed astronomical reflector material is not only complicated in construction but also difficult to manufacture, which is extremely disadvantageous from an industrial standpoint. Moreover, such a reflecting mirror material has extremely low strength in the plane direction of the reflecting mirror, and cannot be said to be a support member that is satisfactory for polishing the flat or curved surface of an integrated reflecting mirror plate.

Furthermore, when manufacturing this reflecting mirror material, it is difficult to keep the effective height of the tube material, which is the supporting grid, constant in a strict sense. The unevenness remains as distortion, which later causes changes over time such as mirror waviness, which is a major factor in degrading the performance of the reflecting mirror. In addition, due to its structure, the rigidity of the support grid against its own weight changes when the mirror surface is placed horizontally and perpendicularly to gravity, resulting in subtle changes in surface accuracy depending on the posture of the mirror surface. It is difficult to use it for applications that require ease of use.

[0006] Furthermore, the technique disclosed in Japanese Patent Publication No. 61-26041 relates to a lightweight mirror, and in particular, a support grid made of quartz glass is movable between a front plate (reflector plate) and a rear plate made of quartz glass. It describes a lightweight astronomical mirror that is fused and integrated so that it does not occur. This support grid consists of plate-like and/or tubular members of quartz glass placed on a support plate, each containing granules and tubules in the space remaining between the two members. The material to be sintered consisting of pieces, small particles, platelets or mixtures thereof is filled, this arrangement is held together by graphite rings, and these are then sintered in a furnace in a non-oxidizing atmosphere. It is also disclosed that the supporting grid thus formed is heated to a freezing temperature and heat-fused to the front plate and the rear plate so as not to move, thereby firmly connecting them.

However, in this method, a large number of plate-shaped members or tubular members of appropriate shapes are prepared in advance, and predetermined spaces arranged in parallel are filled with sintered material, or reinforcing tubular members filled with sintered material are used. This is extremely disadvantageous industrially because it requires a complicated operation, labor, and time to properly arrange the front plate and the rear plate and fuse them together. In addition, this method of using a tubular member is not sufficient for reducing weight, and the portion of the front plate of the reflector where the tubular support member is fused is distorted, making it difficult to polish flat, which is fatal as optical accuracy is impaired. There was a problem.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lightweight reflecting mirror base with excellent operability in which the reflecting mirror surface does not become distorted due to temperature changes or deform due to its own weight. Another object of the present invention is to provide a highly practical foamable porous support member for a reflective mirror plate that is lightweight and has excellent three-dimensional strength even in a direction orthogonal to the supporting direction of the reflective mirror plate. Still another object is to provide a reflector base which is practically hermetically sealed and is extremely useful in practice, and which is not contaminated by mirror polishing or other processing or handling.

[0009]

SUMMARY OF THE INVENTION The gist of the present invention is a method for manufacturing a lightweight reflecting mirror base comprising the constituent elements set forth in claim 1 of the appended claims of the specification.

[0010] A reflecting mirror is a reflecting mirror that collects or scatters light, such as sunlight or beams, and is particularly useful for astronomical objects and the space industry. This is a reflecting mirror that can also be used to utilize light and solar heat, and the reflecting surface of the silicon oxide transparent bubble-free plate that forms the mirror surface is formed into a flat surface or a predetermined curved surface depending on the purpose of use. Furthermore, a metal vapor deposition film appropriate for the type of light to be used is formed on that surface. In either method of use, the reflecting mirror is required to have high optical reflection accuracy and easy operability. Therefore, it is important that the reflective surface is made of a material that does not substantially deform due to temperature changes.The reflective surface should be made of a material that does not substantially deform due to temperature changes. A board is used.

In the method of the present invention, the member supporting such a reflecting mirror plate is preferably made of silica glass or high silicate glass comprising 99% by weight or more of silicon oxide, and whose apparent density is 0.1. A disc-shaped porous foam with ˜1 g/cm 3 is used. If the apparent density of the porous foam is less than 0.1 g/cm3, the support strength for supporting the reflector plate will be weak, and if it exceeds 1 g/cm3, the weight reduction will be insufficient, and the tendency to deform due to its own weight will increase, making it unsatisfactory. I can't get the operability I should have.

[0012] It is preferable that such a foam is mainly composed of closed cells, and a porous body having a three-dimensional lattice structure network formed by such closed cells can be High compressive strength is guaranteed. Since such a porous foam supports the reflector plate uniformly over the entire surface, it not only has excellent resistance to the pressing force applied to the reflector plate surface during polishing, but also has excellent resistance to the pressure applied to the surface of the reflector plate during polishing. It also provides excellent resistance strength, making it extremely desirable as a holding member for a reflecting mirror plate.

Such a foam can be produced, for example, by subjecting a hydroxyl group-containing quartz glass powder made of silicon oxide to an ammonification reaction under heating in an ammonia atmosphere, molding it into a desired shape and sintering it, or by molding and sintering it. This is heated and reacted in an ammonia atmosphere to produce an ammoniated glass sintered body, and then the sintered body is heated to a temperature of 1500 to 180
It is easily manufactured by heating and melting the glass to a temperature of 0°C and generating gas from the glass. At this time, by preventing the gas bubbles generated in the molten glass from bursting, a foam mainly consisting of closed cells can be effectively obtained. Foams can also be produced by mixing powder components that react and sublimate at the melting temperature of glass with silica powder and fusing them with heat. Foaming conditions are selected to ensure and prevent the formation of open cells due to overheating.

The porous foam thus produced can be shaped into a desired shape depending on the size and shape of the reflecting mirror, for example.
It is cut into a disc or square plate as appropriate, and one side has a transparent bubble-free quartz glass or high silicate glass plate for the reflective mirror, and the other side has a back plate of quartz glass or a plate of not very high purity. High silicate glass plates are fused and integrated. In this integration operation, a silica powder having a softening point lower than that of the porous foam layer is applied between the bonding surface between the upper surface of the porous foam layer and the back surface of the reflector disk. It is effective by spreading it thinly over the entire surface, for example, forming a layer of about 1 mm over the entire surface, holding it in a bonded state through this, and heating it to a temperature above the softening point of the silica powder for about 1 to 4 hours. can be fused and integrated.

If the softening point of the silica powder is equal to or higher than the softening point of the supporting member, the porous supporting member will soften and melt during heating and integration, causing undesirable problems such as rupturing of closed cells and deformation of the substrate surface. This is inconvenient because it causes a phenomenon that should not occur. In general, those obtained by the sol-gel method or the thermochemical vapor phase method have a relatively low melting point, so their pulverized products can be suitably used as the above-mentioned silica powder. Further, the finer the silica powder is, the more homogeneous the fusion bonding layer is formed, so it is preferable, and for example, a particle size of 10 μm or less is extremely desirable in practice. According to this integration method, the area of fusion bonding is greatly increased, and the reflecting mirror plate is more stably fixed to the foam layer. In this joining, the back surface of the reflecting mirror plate and the surface of the porous body to be joined are formed in advance into the same surface shape so that they are in contact with each other over substantially the entire surface.

[0016] The reflecting mirror plate that is fused and integrated with one surface of the foam layer is a transparent plate that is made of quartz glass or high silicate glass of the highest possible purity and that does not substantially contain air bubbles. It is the body. Even if this reflective plate contains minute air bubbles, it is not preferable to include air bubbles because it will cause undesirable conditions such as distortion and distortion on the reflecting surface, making it impossible to create a highly accurate reflecting mirror. In addition, the plate that is melted and integrated with the other side does not need to have the same high purity and transparency as a reflective mirror plate, and it is okay for the plate to contain some air bubbles or lose its transparency, but It is important that the plate is made of quartz glass or high silicate glass that does not substantially affect changes.

In the method of the present invention, after both plates are integrally joined to the foam layer, a sealing layer of quartz glass or high silicate glass is fused and formed on the circumferential side of the laminate. Although this sealing layer does not necessarily have to be completely airtight, it is preferable that the peripheral surfaces, especially all the sides of the foam layer, be smoothed prior to forming the sealing layer. The smooth finishing treatment can be performed by a commonly known method such as smooth polishing using a grinder or baking using a fire such as a hydrogen-oxygen combustion flame.

Next, a sealing layer of quartz glass or high silicate glass is fused and formed on the circumferential side of the laminate which has been smoothed.
Glass powder may be attached to the surface to be sealed and heated and melted to form a glass seal layer, but a glass plate corresponding to the width and length of the circumferential surface may be It is practical to fuse and integrate them sequentially on the circumferential side. The reflector base on which such a glass seal layer is formed is
For example, in mirror polishing using a water-based abrasive, not only can contamination of the substrate from the sides by the finely divided aqueous abrasive be virtually completely prevented, but the physical strength of the reflector base can be greatly improved, allowing precision polishing. The mirror surface can be kept stable for a long period of time.

As described above, the surface of the transparent reflective mirror plate of the laminate whose circumferential surface is glass-sealed is polished to a flat or flat surface by a commonly known precision polishing method using, for example, an aqueous abrasive. The mirror is precisely polished to a predetermined curved surface, and a thin film of a metal for a reflective mirror, such as aluminum or silver, is formed on the polished surface by vapor deposition or other means, resulting in a lightweight, large-sized reflective mirror. In addition, when forming a metal thin film on a mirror surface, it is exposed to high temperatures and the circumferential seal is damaged due to the expansion of gas inside the base.
If there is a concern that the layer may be damaged, it is desirable to provide one or more small holes in the circumferential surface of the layer.

The method of the present invention will be explained in more detail with reference to the accompanying drawings. FIG. 1 is a partially cutaway perspective view of an example of a disc-shaped, lightweight, large-sized reflecting mirror substrate manufactured by the method of the present invention. In the figure, a reflective plate 2 made of transparent, bubble-free, high-purity quartz glass is placed on one side of a disc-shaped porous foam layer 1 made of silica glass, and a translucent plate 2 made of quartz glass is placed on the other side. The plates 3 are fused and integrated, and then elongated quartz glass plates 4 are sequentially fused and integrated from one end to the peripheral side of the integrated laminate to form a sealing layer. The lightweight and large reflecting mirror base of the present invention obtained in this way has a highly accurate reflecting mirror surface 2 whose mirror surface is precisely polished and flat.
A glossy reflective film is further formed on the polished surface by metal vapor deposition or the like, thereby providing an optically excellent reflective mirror.

[0021]

[Operation] The method of the present invention effectively provides a lightweight substrate on which a flat or curved mirror is formed that is stable and has excellent optical surface precision on its reflective mirror surface. In addition, the large reflecting mirror obtained by the method of the present invention has excellent structural strength despite its light weight, and its high-precision mirror surface is stably maintained over a long period of time. Usability is extremely high.

[0022]

EXAMPLES Next, the present invention will be explained in more detail using specific examples. Example 1 Silicon tetrachloride was supplied to an oxyhydrogen flame burner and flame-hydrolyzed to produce a quartz glass soot body, which was heated to 1000°C.
After reacting the ammonia gas for 2 hours at a temperature of . This foam was cut to create a disk with a diameter of 350 mm and a thickness of 25 mm.

[0023] On the front surface of this porous disk, a diameter of 350 mm is provided.
, a transparent, bubble-free quartz glass disk with a thickness of 3 mm was mounted,
In the meantime, a thin layer of fine silica powder was spread over the entire surface as a fusing agent, and the film was heat-sealed at a temperature of about 1300°C. At that time, a quartz glass disk with a diameter of 350 mm and a thickness of 3 mm was used as a back plate on the lower surface of the porous disk, and a thin layer of silica powder was similarly spread as a fusion agent, and these were kept in contact and heat fused together. A laminate was obtained. Next, 30mm x 1mm thick
A 1100mm long quartz glass plate is used as an oxygen-hydrogen burner.
A sealing layer was formed by fusion-bonding and integrating on the circumferential side of the laminate.

The flat surface of the transparent bubble-free quartz glass plate of the large reflector base thus obtained was precision polished using an aqueous polishing liquid. When we investigated the flatness of this surface using optical interference fringes, we found that the interference fringes were parallel.
It was confirmed that the entire surface had extremely high flatness. By further depositing a thin aluminum film on this precision polished surface, a highly precise flat reflective surface suitable for use with laser beams etc. was obtained. A large-sized reflecting mirror on which a vapor-deposited film is formed is extremely desirable because it is much lighter and has superior optical properties compared to conventionally known lightweight reflecting mirrors.

[0025]

Effects of the Invention: A large reflecting mirror substrate formed by surrounding a porous foam layer with a quartz glass plate obtained by the method of the present invention has a structure in which the porous foam layer is composed of a cell-free transparent quartz glass reflecting plate and a quartz glass plate. The rear plate facing the front plate is welded and integrated over the entire surface, and the glass seal layer on the peripheral side is melted and integrated, so it has extremely high structural strength despite being lightweight and has excellent operability. For example, there is no risk of deformation or breakage even if stress is applied such as pressure during polishing, and there is no problem of deterioration of light reflection characteristics due to distortion of the quartz glass reflector plate, making it highly practical. has real value.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of an example of a disc-shaped, lightweight, large-sized reflecting mirror substrate manufactured by the method of the present invention.

[Explanation of sign]

1... Disc-shaped porous foam layer made of quartz glass 2...
Reflector plate 2' made of transparent bubble-free high purity quartz glass...
・Precision polished surface of 2 3... Quartz glass plate 4... Quartz glass seal layer

Claims (2)

[Claims] Claim 1: A reflective mirror made of transparent bubble-free quartz glass or high silicate glass on one side of a porous foam layer made of silica glass or high silicate glass having an apparent density of 0.1 to 1 g/cm3. A quartz glass or high silicate glass plate is fused and integrated on the other side of the quartz glass or high silicate glass plate, and then a quartz glass or high silicate glass sealing layer is fused and formed on the peripheral side of the quartz glass or high silicate glass plate. Method for manufacturing a reflecting mirror base. 2. The manufacturing method according to claim 1, wherein the sealing layer is fused and integrated with the elongated glass plate.