JPH04323601A - Production of base body of lightweight reflection mirror - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing a reflector used in, for example, astronomical observation, beam focusing, or the space industry. The present invention relates to a method for manufacturing a reflecting mirror substrate having superior 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 condensing of light, such as a mirror, is made of a bubble-free reflector plate made of quartz glass or high silicic acid lath, etc., and has a vapor-deposited metal film such as aluminum as an optical reflective layer on the surface of the bubble-free reflector plate. This is supported by an operating support base 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 practical requirements, many proposals have been made, particularly regarding support members for large reflecting mirror plates, for maintaining sufficient support strength and achieving weight reduction.

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. In addition, such a reflecting mirror material has extremely low strength in the surface direction of the reflecting mirror, and cannot be said to be a satisfactory support member for polishing the 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 and later causes changes over time such as mirror waviness, which is a major factor in the deterioration of reflector performance. 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 quartz glass plate is fixedly connected between a front plate and a rear plate made of quartz glass. This article describes a lightweight astronomical mirror with a support grid made of fused and integrated. This support grid consists of plate-like and/or tubular members of quartz glass placed on a support plate, each containing granules, tubules, etc. 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 under a non-oxidizing atmosphere. It is also disclosed that the support grid, heated to a temperature and thus formed, is immovably connected to the front and rear plates by heat fusion.

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 method is difficult to adopt 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, it is an object of the present invention to provide a practically desirable lightweight reflecting mirror base which is excellent in operability and whose reflecting mirror surface does not suffer from distortion due to temperature changes. . 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. Yet another object is to provide an industrially advantageous manufacturing method for such a lightweight reflecting mirror base.

[0009]

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

[0010] A reflector is a reflector that collects or scatters light, such as sunlight or laser beams, and is particularly useful for astronomical objects and the space industry. It can also be used for condensing light or utilizing solar heat, and the reflective surface of the silicon oxide transparent bubble-free plate that forms the mirror surface is formed into a curved surface depending on the purpose of use. In addition, an appropriate metal film is formed on that surface depending on the type of light to be used. 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, such as a substantially bubble-free transparent plate made of high-purity high silicic acid lath or quartz glass. 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, and it will not be satisfactory. It also doesn't provide the operability that it should.

[0012] It is preferable that such a foam is mainly composed of closed cells, and a porous material having a high content of closed cells that forms a three-dimensional lattice structure network can be High compressive strength can be obtained. Since such 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 pressing force applied to the reflector plate surface during polishing. Since it provides excellent resistance strength, it is extremely desirable as a holding member for a reflecting mirror plate.

[0013] Such a foam can be produced, for example, by heat-reacting powder of hydroxyl-containing quartz glass made of silicon oxide in an ammonia atmosphere, molding it into a desired shape, and sintering it;
The shaped and sintered product is heated and reacted in an ammonia atmosphere to produce an ammoniated sintered body, and then the sintered body is heated and melted at a temperature of 1500 to 1800°C in an electric furnace, for example. The gas leaving the glass effectively makes it possible to obtain a foam consisting mainly of closed cells. Alternatively, it can be manufactured by mixing a powder that reacts and sublimates at a predetermined temperature with silica powder and heat-sealing the mixture. In the production of this heated foam, foaming conditions are selected so as to form cells of an appropriate diameter and to prevent the formation of open cells due to excessive heating.

The porous foam produced in this way is cut into a desired shape, for example, a disc or a rectangular plate depending on the size and shape of the reflecting mirror. A plate of transparent bubble-free quartz glass or high silicate glass is fused and integrated with a plate of quartz glass or high silicate glass, which does not require very high purity, on the other side as a rear plate. In this integration operation, silica powder having a softening point lower than that of the porous foam is applied over the entire surface between the bonding surface between the upper surface of the porous foam layer and the back surface of the reflective disk. For example, by spreading the silica powder thinly to form 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, it is effective. 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 which is fused and integrated with one surface of the foam layer is a transparent plate made of highly purified quartz glass or high silicate glass and which does not substantially contain air bubbles. It is. This is because even the presence of minute bubbles causes undesirable conditions such as distortion and distortion in the reflector, making it impossible to create a highly accurate reflector. 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 made of quartz. It is important that the plate is made of glass or high silicate glass.

[0017] In the method of the present invention, the laminate in which both plates are integrally joined to the foam layer is then hermetically sealed around the entire circumference, but the airtight seal is Preferably, the circumferential surfaces, in particular all sides of the foam layer, are first smoothed and finished. The smooth finishing treatment may be performed by finishing to form an airtight seal film appropriately, and may be carried out by commonly known methods such as smooth polishing with a grinder or baking with a fire such as a hydrogen-oxygen combustion flame. This can be done by

Next, the smoothed peripheral surface is hermetically sealed. As the sealing agent for the airtight seal, for example, a silicone rubber sealing agent that is curable at room temperature or curable under heat is conveniently used. Coating with this sealant can be easily done by coating while extruding from the tube. Although this airtight seal does not necessarily require high airtightness, it has been found that it is important in obtaining a highly flat polished finish in the subsequent precision smoothing of the surface of the reflector plate. That is, in the absence of a seal, a satisfactory flat surface could not be obtained by precision polishing. The reason for this is not clear, but perhaps in aqueous polishing, the intrusion of fine powder abrasives and water into the porous foam layer of the substrate and the interfaces between the upper and lower plates, which can be ignored, has a subtle effect on the precision polishing of the surface. It is presumed that as a result, it is not possible to form an optically excellent reflective film of vapor-deposited aluminum metal or silver.

The laminate whose circumferential side surface is hermetically sealed is then subjected to precision polishing on the surface of the reflector plate on which the metal film for the reflector is deposited. The polishing is performed by using, for example, an aqueous abrasive and highly precise polishing into a flat or predetermined curved surface by a commonly known precision polishing method, thereby completing the lightweight reflector base of the present invention.

A lightweight reflecting mirror substrate manufactured by the method of the present invention will be explained with reference to the accompanying drawings. FIG. 1 is a perspective view of an example of a rectangular lightweight reflecting mirror substrate manufactured by the method of the present invention, with the airtight seal layer on the circumferential side thereof partially removed for ease of understanding. It is shown in the same condition. In the figure, a reflective mirror plate 2 made of transparent bubble-free high-purity quartz glass is placed on one side of a plate-like porous foam layer 1 made of silica glass, and a reflective plate 2 made of quartz glass is placed on the other side of the foam layer. board 3
are fused and integrated, and then a silicone rubber sealant layer 4 is hermetically sealed over the entire circumferential surface of the integrated laminate, and the surface 2' of the transparent bubble-free board is precisely sealed. It is polished to form a flat polished surface for an optically superior reflector.

[0021]

[Function] The substrate for a lightweight reflector produced by the method of the present invention is lightweight, the porous foam layer that stably supports the reflector quartz glass plate has sufficient three-dimensional strength, and the reflector surface Since it is formed with an excellent flat polished surface, it is possible to obtain excellent optical precision and high operability as a large reflecting mirror.

[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 hydrolyzed with a flame to produce a quartz glass glass body.
After reacting the ammonia gas at a temperature of 1,600 °C for 2 hours, the ammonia atmosphere gas was expelled, and the mixture was foamed by heating to a temperature of 1,600 °C to obtain a porous silica glass foam with an apparent density of about 0.3 g/cm3. Ta. 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 0.5 mm was placed thereon, and a thin layer of fine silica powder was spread over the entire surface as a fusing agent between the two, and heat-sealed at a temperature of about 1300°C. that time,
The bottom surface of the porous disk has a diameter of 500 mm and a thickness of 0.5 mm.
A quartz glass disk was used as a rear plate, and a thin layer of fine silica powder was similarly applied as a fusion agent, and these were kept in contact and melted by heating to simultaneously integrate them. In the structure obtained in this way, the porous foam layer and the bubble-free transparent quartz glass plate are welded together over the entire surface, so uneven welding causes distortion in the quartz glass plate and impairs the light reflection characteristics. There was no disadvantage of deterioration, and there was no fear that the surface would be deformed or damaged even if stress, such as pressure during polishing, was applied to the surface, and it had sufficient strength as a lightweight reflecting mirror base.

[0024] Next, the surface of the foam layer exposed on the peripheral side of this structure is smoothed and polished all around with a grinder, and the peripheral side is coated with a room temperature curing silicone rubber sealant. was completely covered to form an airtight sealing layer. The surface of the transparent bubble-free quartz glass plate of the structure with the circumferential side hermetically sealed was precisely polished using an aqueous polishing liquid, and the flatness of this surface was examined using optical interference fringes. It was confirmed that the interference fringes were parallel and the entire surface had an extremely high degree of flatness. This precision polished surface provides an excellent reflective surface for laser light, etc. by forming an aluminum vapor deposited film thereon, for example. Therefore, such a precision-polished structure is extremely desirable as a lightweight reflecting mirror base that has far superior optical properties compared to conventionally known lightweight reflecting mirrors.

[0025]

Effects of the Invention According to the method of the present invention, compared to conventionally known substrates for large reflecting mirrors, the porous support is lightweight and
Provides a reflective mirror with excellent dimensional pressure strength and high optical precision using metal vapor deposition. In addition, the lightweight reflector has excellent operability even if it is large, and is particularly desirable as it has extremely high practical value as a large reflector for astronomical objects. Furthermore, the substrate obtained by the method of the present invention is provided at a much lower cost than similar conventional substrates for reflecting mirrors, and is therefore extremely advantageous industrially.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a lightweight reflecting mirror substrate manufactured by the method of the present invention with an airtight seal layer on the circumferential side partially removed.

[Explanation of sign]

1... Plate-shaped porous foam layer made of silica glass 2... Reflector plate 2' made of transparent, bubble-free, high-purity quartz glass...
Surface of transparent bubble-free plate 3... quartz glass plate

Claims (3)

[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 plate of quartz glass or high silicate glass is fused and integrated on the other side of the transparent plate, and then the integrated laminate is airtightly sealed over the entire peripheral surface, and then the transparent bubble-free plate is sealed. A method for manufacturing a lightweight reflecting mirror substrate, which is characterized by precisely polishing the surface. Claim 2: The airtight seal is a silicone rubber seal.
2. The method of claim 1, wherein the method is provided by coating with a ring agent. 3. The manufacturing method according to claim 1, wherein, prior to said airtight sealing, the surface of the foam layer is smoothed over the entire circumferential surface.