JPH0745330B2 - Glass blank for optical element manufacturing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a glass blank used as a molding material in press molding of an optical element such as a lens, and in particular, it prevents a reaction with a mold member at the time of pressing and adheres closely. The present invention relates to a glass blank for reducing a force and a frictional force to prevent cracks from being generated in a cooling process and obtaining a good optical element.

[Problems to be Solved by the Related Art and Invention] Conventionally, in order to obtain a good molded product in a glass reheat press, it is necessary to prevent fusion between the material glass for molding and the molding die member. It was a big challenge. Therefore, various techniques for improving the mold member have been proposed in the past, and in recent years, improvement of the molding material has been started to prevent the fusion. As a proposal for improving such a molding material, for example, Japanese Patent Publication No. 2-1778, Japanese Patent Publication No. 2-1779, Japanese Patent Publication No. 2-1780, and Japanese Patent Publication No. 61-29890 disclose glass substrates. Coating the surface of the glass with a glass transition temperature higher than that of the glass substrate,
It is disclosed to provide a silicon oxide coating or a carbon coating. Further, JP-A-1-264937 discloses disposing a thin layer of an organic substance on the surface of a glass substrate.

Although the above-mentioned improvements have the effect of preventing fusion with the mold member, the method disclosed in the above publication has the following problems.

(A) When a glass coating having a glass transition temperature higher than that of the glass substrate is applied to the surface of the glass substrate, the coating glass layer is cracked by the press pressure, and the substrate glass oozes out from the glass substrate to partially cover the surface. There is a case where cloudiness occurs or partial fusion with the mold member occurs, or the frictional force between the glass blank and the mold member increases during the cooling process, causing cracks in the glass.

(B) When a silicon oxide coating is applied to the surface of the glass substrate, it is the same as in (a) above. Especially, since silicon oxide is well compatible with the mold member, cracks are likely to occur during the cooling process, and Since the thermal expansion coefficient of silicon oxide is significantly lower than that of ordinary optical glass constituting a glass substrate, the coating is likely to be cracked when heated.

(C) When the carbon coating is applied to the surface of the glass substrate to be thicker than necessary, since carbon is a reducing agent, it reacts with oxygen in the glass to reduce the glass component and color the glass brown. In particular, when lead-containing glass is used as the glass substrate, PbO is reduced in the glass, coloring is remarkable, and transmittance is lowered.

(D) When an organic thin layer is disposed on the surface of the glass substrate, the organic thin layer decomposes when heated, and in some cases, a corrosive gas (for example, chlorine gas or fluorine gas) is generated, and the press is performed. There is a problem that the molding device is easily contaminated and the durability of the device including the mold member is impaired. Further, since the above-mentioned decomposition occurs partially randomly, the surface accuracy may decrease.

Therefore, in view of the problems of the above-mentioned conventional techniques, the present invention, in addition to preventing the reaction between the glass blank and the mold member and preventing the clouding of the molded product, the fusion of the molded product and the mold member. The purpose is to prevent cracking and coloration.

[Means for Solving the Problems] According to the present invention, a glass blank used as a molding material for producing an optical element by press molding, wherein at least an optical component of a glass substrate is provided. There is provided a glass blank for producing an optical element, characterized in that a reaction-preventing coating and a hydrocarbon coating are provided in this order on the surface on which a functional surface is formed.

Here, the reaction-preventing coating is, at the molding temperature, in order to prevent the glass blank and the mold member from reacting with each other to prevent the glass blank from becoming cloudy, a substance having a higher melting point than the glass blank is effective, for example, Al ₂ It is O ₃ , SiO ₂ , MgF ₂ or glass for vapor deposition. Further, the thickness of the reaction-preventing coating is a lower limit of the film thickness at which the glass component does not reach the mold member surface by diffusing the reaction-preventing coating layer at the molding temperature, and the upper limit of the thickness at which cracks do not occur during molding, 100-500Å
Is.

Further, the hydrocarbon coating, by forming a very small amount of reaction gas layer at the interface between the mold member and the glass blank,
The adhesive force between the mold member and the glass blank is reduced to prevent fusion and cracking. For this purpose, the thickness of the hydrocarbon coating is, for example, 10 to 50Å. If the thickness of the hydrocarbon coating layer is too thin, a sufficient effect of lowering the adhesive strength cannot be obtained, and if the thickness of the hydrocarbon coating layer is too thick, the molded product is markedly colored and the transmittance is reduced. For this reason,
If the thickness is made too thick, it is necessary to remove the hydrocarbon film remaining on the surface of the glass blank after molding and the reaction product between the hydrocarbon film and the glass by a post-process such as an annealing process.

Compared with the carbon coating layer, the hydrocarbon coating layer contains a large amount of CH _{2 in} the same film thickness, so the transmittance of the glass blank does not decrease so much and the fusion and cracking The effect of preventing is also sufficient with an ultrathin layer (10 to 50Å thickness).

Further, the method for forming the hydrocarbon coating layer, a high-frequency discharge treatment of hydrocarbon gas, ion gun treatment or direct current discharge treatment, it is possible to use a good method of covering the glass blank, and the above method is There is an advantage that it is a low-cost processing method.

[Examples] Specific examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of a glass blank according to the present invention. In this embodiment, the optical element is a biconvex lens.

In FIG. 1, 2 is a glass substrate which is a material for press molding. As the glass substrate, an optical glass having a refractive index value and a dispersion value necessary for obtaining a lens having desired optical characteristics is used. The glass substrate 2 is finished in a shape and dimensions similar to a desired lens shape.

A reaction-preventing coating 3 and a hydrocarbon coating 4 are provided in this order on the surface (upper and lower surfaces) of the glass substrate 2 on which the optically functional surface is formed.

Examples of the reaction prevention coating 3 include Al ₂ O ₃ , SiO ₂ and MgF ₂
Alternatively, glass for vapor deposition can be used. The thickness of the reaction preventive coating 3 is, for example, 100 to 500Å. The reaction preventive coating 3 can be formed using a thin film deposition technique such as vacuum deposition.

The hydrocarbon coating has a thickness of, for example, 10 to 50Å, preferably 13 to 35Å. If the thickness of the hydrocarbon coating is too thin, the effect will not be sufficient, and if it is too thick, the transmittance of the molded article will be significantly reduced, and an annealing step will be required. The hydrocarbon coating 4 can be formed using a simple thin film deposition technique such as plasma treatment or ion gun treatment. The atomic ratio of carbon: hydrogen in the hydrocarbon coating 4 is, for example, 10/6 to 10
/0.5, and particularly preferably 10/5 to 10/1.

FIG. 2 is a schematic diagram showing a schematic configuration of a thin film deposition apparatus used for manufacturing the glass blank of the above embodiment. Less than,
An example of blank production will be described with reference to this drawing.

In FIG. 2, 12 is a vacuum chamber, and 14 is an exhaust port formed in the vacuum chamber. The exhaust port is connected to a vacuum exhaust source (not shown). Reference numeral 16 is a gas introduction port for introducing gas into the vacuum chamber 12. The gas inlet is connected to a gas source (not shown).

Inside the vacuum chamber 12, an evaporation source 18 and a shutter 20 are arranged in the lower part, and a dome-shaped holder 22 for holding the glass substrate, a heater 24 for heating the glass substrate and a coating thickness measurement in the upper part. A quartz film thickness monitor 26 is arranged. 28 is an antenna for high frequency application. Incidentally, 30 is a glass substrate held by the holder 22.

When the reaction-preventing coating 3 and the hydrocarbon coating 4 are applied to the surface of the glass substrate 30 (2) in this order, gas is exhausted from the exhaust port 14 to reduce the pressure in the vacuum chamber 12 and then from the evaporation source 18. The reaction-preventing coating-forming material is evaporated, and then the gas inlet
Hydrocarbon gas is introduced from 16 to 5 × 10 ^{−2 to} 5 × 10 ⁻⁴ Torr, for example, and is fed to the antenna 28 for high frequency application to 100 ×
A high frequency of ~ 500 W is applied to form a hydrocarbon plasma.

Examples of the hydrocarbon gas introduced into the vacuum chamber 12 include methane, ethane, propane, ethylene, propylene and acetylene.

Since the carbon: hydrogen atomic ratio in the hydrocarbon coating 4 changes depending on the deposition conditions, the conditions are set so that a desired atomic ratio can be obtained.

Next, an actual example of manufacturing the glass blank of the above-mentioned embodiment using the above-mentioned apparatus will be described.

A glass substrate 30 made by polishing a flint optical glass (SF8) into a predetermined shape was washed and set in a holder 22. After heating to 300 ° C. with the heater 24 and exhausting from the exhaust port 14 until the degree of vacuum in the vacuum chamber 12 becomes 1 × 10 ⁻³ Torr or less,
Ar gas was introduced from the gas inlet 16 to 5 × 10 ⁻⁴ Torr. Then, a high frequency of 300 W was applied to the high frequency applying antenna 28, high frequency discharge was performed, and plasma cleaning of the glass substrate 30 was performed. After that, the introduction of Ar gas was stopped, the vacuum degree of 1 × 10 ⁻⁵ Torr was returned, and the vapor deposition glass was evaporated from the evaporation source 18 to form a reaction prevention coating (vapor deposition glass layer) 3 of about 300 Å thickness. did. Next, the evaporation from the evaporation source 18 is stopped, and CH ₄ gas is supplied from the gas inlet 16 to 1 × 10 ⁻³ Torr.
It was introduced until. Then, the high frequency applying antenna 28
A high-frequency discharge of 400 W was applied to discharge high-frequency electricity to form a hydrocarbon coating 4 having a thickness of about 30 Å. The above hydrocarbon coating 4
The carbon: hydrogen atomic ratio in was about 10/2 as a result of measurement by infrared spectroscopy.

FIG. 3 is a cross-sectional view showing an example of an apparatus in which press molding is carried out using the glass blank obtained as described above.

In FIG. 3, 32 is a vacuum chamber body, and 34 is its lid. Reference numerals 36, 38, and 40 are an upper mold member, a lower mold member, and a body member for press-molding a lens, respectively. 42 is a die holder, and 44 is an upper die member retainer. Reference numeral 46 is a heater, 48 is a push-up rod for pushing up the lower mold member, and 50 is a cylinder for operating the push-up rod.
52 is a vacuum pump, 54, 56, 58, 60 are valves, 62 is a pipe for introducing non-oxidizing gas such as nitrogen gas, 64 is a leak pipe, and 66 is a valve. .
68 is a temperature sensor and 70 is a water cooling pipe. 72 is a vacuum chamber support member.

As the upper mold member 36, the lower mold member 38 and the body mold member 40,
For example, a base material made of cemented carbide, Si ₃ N ₄ ,, SiC, sialon, cermet, Al ₂ O ₃ , ZrO ₂ , Cr ₂ O _3, etc. may have Si ₃ N ₄ , TiN, TaN, It is possible to use those coated with BN, AlN, SiC, TaC, WC, platinum alloy or the like.

Next, an actual example of press molding using the glass blank of the above example in the above apparatus will be described.

As the upper mold member 36 and the lower mold member 38, those made of Si ₃ N ₄ are used, and the surfaces for forming the optical functional surface of these mold members have a surface accuracy within 3 Newtons and a center line average surface roughness of 0.02 μm.
Within

Place a glass blank in the mold and move inside the vacuum chamber to 1 x 10 ^-2 To
The gas was evacuated to rr or less, and then nitrogen gas was introduced into the vacuum chamber.

After heating to 530 ℃, operate the cylinder 50 to 100Kg
Pressed at a pressure of / cm ² for 5 minutes. Then, it was gradually cooled to 200 ° C. or lower.

Then, air was introduced into the vacuum chamber, the mold was opened, and the molded product was taken out.

As described above, 100 lenses were molded. When the functional surface of the obtained lens was observed with a scanning electron microscope at a magnification of 3750, no surface defect was observed, and neither surface was colored or clouded. Further, fusion with the mold member did not occur at all, and cracking of the molded product did not occur at all. Further, the surface precision on both surfaces of the lens was good.

[Effects of the Invention] As described above, according to the present invention, a glass blank and a mold member are provided by applying a reaction-preventing coating and a hydrocarbon coating in this order on at least the surface of the glass substrate on which the optically functional surface is formed. In addition to preventing the reaction with and preventing fusion, it is possible to prevent clouding, coloring, cracks and deterioration of the surface accuracy of the molded product.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a glass blank according to the present invention. FIG. 2 is a schematic diagram showing a schematic configuration of a thin film deposition apparatus used for manufacturing the glass blank of the above embodiment. FIG. 3 is a sectional view showing an example of an apparatus for performing press molding. 2: Glass substrate, 3: Reaction prevention coating, 4: Hydrocarbon coating, 12: Vacuum tank, 16: Gas inlet, 18: Evaporation source, 24: Heater, 28: High frequency applying antenna, 30: Glass substrate.

Claims (4)

[Claims] 1. A glass blank used as a molding material for producing an optical element by press molding, comprising:
A glass blank for producing an optical element, characterized in that at least a surface of a glass substrate on which an optical functional surface is formed is coated with a reaction-preventing coating and a hydrocarbon coating in this order. 2. The glass blank for producing an optical element according to claim 1, wherein the reaction preventing coating is Al ₂ O ₃ , SiO ₂ , MgF ₂ or glass for vapor deposition. 3. The glass blank for producing an optical element according to claim 1, wherein the thickness of the reaction preventing coating is 100 to 500Å. 4. The glass blank for producing an optical element according to claim 1, wherein the hydrocarbon coating has a thickness of 10 to 50 Å.