JPH0745329B2 - Glass blank for optical element manufacturing - Google Patents

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 more particularly, to an adhesion force and a frictional force with a mold member at the time of pressing. The present invention relates to a glass blank for lowering and preventing cracking in the cooling process to obtain 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. In some cases, cloudiness may occur, partial fusion with the projecting member may occur, or the frictional force between the glass blank and the mold member may increase 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 in the glass is reduced, coloring is remarkable, and transmittance is reduced.

(D) When an organic thin layer is arranged on the surface of the glass substrate, the organic layer decomposes when heated, and in some cases a corrosive gas (for example, chlorine gas or fluorine gas) is generated,
There is a problem that the press molding device is easily contaminated and the durability of the device including the mold member is easily 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 fusion between the glass blank and the mold member, causes clouding or coloring or cracks or surface accuracy deterioration in the molded product. The purpose is to prevent.

[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. A glass blank for producing an optical element, characterized in that a hydrocarbon coating is applied to the surface on which the functional surface is formed.

Here, by setting the thickness of the hydrocarbon coating to, for example, 10 to 50Å, an extremely small amount of a reaction gas layer is formed at the interface between the mold member and the glass blank, and the adhesive force between the mold member and the glass blank is increased. It is possible to reduce the temperature and prevent fusion and cracking. Compared to the carbon coating layer, the hydrocarbon coating layer contains a large amount of CH ₂ in the film with the same film thickness, so the transmittance of the glass blank does not decrease so much and the fusion and cracking occur. The effect of preventing is an ultra-thin layer (10 to 50Å thickness)
But it is enough.

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.

The surface of the glass substrate 2 on which the optically functional surface is formed (upper and lower surfaces) is coated with a hydrocarbon coating 4. The thickness of the hydrocarbon coating is, for example, 10 to 50Å, preferably 15 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 possibility of film peeling increases. The hydrocarbon coating 4 can be formed using a 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,
It is 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 the present invention.

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, a dome-shaped holder 22 for holding a glass substrate and a heater 24 for heating the glass substrate are provided above.
A quartz film thickness monitor 26 for measuring the coating thickness is arranged. 28 is an antenna for high frequency application. Incidentally, 30 is a glass substrate held by the holder 22.

When the hydrocarbon coating 4 is applied to the surface of the glass substrate 30 (2), the gas is exhausted from the exhaust port 14 to reduce the pressure in the vacuum chamber 12, and then the hydrocarbon gas is supplied from the gas inlet port 16 to, for example, 5 times. It is introduced until it becomes × 10 ^{-2 to} 5 × 10 ^-4 Torr, and a high frequency of 100 to 500 W is applied to the high frequency applying antenna 28,
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 ⁻⁵ 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 degree of vacuum was returned to 1 × 10 ⁻⁵ Torr, and the gas was introduced through the gas inlet 16.
CH ₄ gas was introduced to 1 × 10 ⁻³ Torr. And
A high frequency of 200 W was applied to the high frequency applying antenna 28 for high frequency discharge to form a hydrocarbon coating 4 having a thickness of about 30Å.
The carbon: hydrogen atomic ratio in the hydrocarbon coating 4 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, A1N, 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 member 36 and the lower mold member 38, those made of Si ₃ N ₄ were used, and the surfaces for forming the optical functional surface of these mold members had a surface accuracy within 3 Newtons and a mean line average surface roughness within 0.02 μm. .

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. Moreover, no cracks were formed on the molded product. Further, the surface precision on both surfaces of the lens was good.

[Effect of the Invention] As described above, according to the present invention, at least the surface of the glass substrate on which the optically functional surface is formed is coated with a hydrocarbon to prevent fusion between the glass blank and the mold member. In addition to this, it is possible to prevent clouding, coloring, cracks, and deterioration of 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, 4: Hydrocarbon coating, 12: Vacuum tank, 16: Gas inlet, 24: Heater, 28: High frequency antenna, 30: Glass substrate.

Claims (2)

[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 the glass substrate on which an optical functional surface is formed is coated with a hydrocarbon. 2. The glass blank for producing an optical element according to claim 1, wherein the hydrocarbon coating has a thickness of 10 to 50Å.