JPH03137031A - Method and apparatus for producing glass lens - Google Patents

Abstract

PURPOSE:To easily obtain the lens which is free from sink marks by constituting a lower mold of a specific material to impart prescribed surface roughness to the mold in the apparatus equipped with the upper mold having a glass melting crucible, a molten glass dropping nozzle, the lower mold for receiving a glass drop and an upper mold for compression-molding the glass drop cooperatively with the lower mold. CONSTITUTION:The lower mold 12 for receiving the glass drop is constituted of the material having >=50W/mK thermal conductivity (e.g.: Ag, graphite, SiC, AlN, Si, cemented carbide) and is thereby provided with 0.05 to 0.2muRmax surface roughness in the device equipped with the glass melting crucible 1, the nozzle 4 which is provided in the bottom of the crucible 1 and drops the molten glass 2 as the glass drop 6, the lower mold 12 for receiving the glass drops which receives the glass drops 7, 10 dropped from the nozzle, and the upper mold 13 for compression molding of the dropped glass drop 10 cooperatively with the lower mold 12.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved method and apparatus for forming non-abrasive glass lenses.

Conventional technology The method for producing unpolished glass is the droplet method, in which molten glass is dropped from the tip of a nozzle, the falling glass droplets are received by a lower mold, and press-formed. An excellent method for obtaining lenses free of such defects has been developed by the present inventors and has already been filed (Japanese Patent Application No. 59-267058).

Although the droplet method is an excellent method for producing unpolished glass, several points that need improvement have been discovered. In order to clarify the problems that require such improvement, the droplet method will be explained in more detail with reference to FIG.

The liquid pouring method first involves melting glass (2) in a crucible (1).
into a liquid droplet of a certain size at the tip of the nozzle (4). The area from the crucible (1) to the tip of the nozzle (4) is heated by heaters (5a) to (5d) so that the molten glass does not cool down and become solid. Next, a glass droplet (6) controlled to a predetermined size and temperature is allowed to fall naturally from the tip of the nozzle (4), and is collected in an appropriate mold (12) installed at the point where the glass droplet falls. After collection, it is moved from the point where the glass droplets fall and is pressed with an upper mold (13) to obtain a non-polished glass lens.

However, depending on the above method, so-called "sink marks" may occur depending on the material of the mold (12) that collects the glass droplets. A sink mark can be thought of as a depression that occurs near the center of the lens, as shown in FIG. 2-d. This sink mark is thought to be caused by the mechanism shown in Figures 2-a to 2-d. That is, 2nd-a
The figure shows the state when the dropped glass droplets are collected on the mold.

In the figure, the shaded area indicating the peripheral area where the glass droplet is in contact with the mold is where it solidifies faster than any other part, and after dropping the glass droplet, it solidifies along the shape of the mold. Ru. However, the central part of the glass droplet that is in contact with the mold (the part between the hatched areas) is not completely solidified due to the heat from the remaining high temperature part of the glass droplet that has not yet cooled and is in a softened state. This is thought to be the case, and that portion is pulled upwards due to contraction as the entire glass droplet cools while moving through the mold. As a result, as shown in Figure 2-b, an air pocket is formed in the center of the glass droplet, and in this state, molding is performed with the upper mold as shown in Figure 2-c, resulting in a glass droplet. Whiskers will be formed on the lens.

Another problem is that conventionally, the glass droplet (6) needs to fall until its surface temperature becomes lower than the softening temperature of the glass, so the falling distance (Q) of the glass droplet is Generally, 150 cm to 200 cm or more was required. If the falling distance is long like this, the mold (12
) The position at which the lens falls on the lens is slightly different, and the quality of the mold shape of the resulting lens is also not the same (this failure to faithfully transfer the mold shape is expressed as "poor transferability"). If the falling distance is shortened in order to eliminate poor transferability, the above-mentioned whisker problem will become more noticeable.

Problems to be Solved by the Invention The present invention solves the above-mentioned conventional problems, prevents the generation of whiskers regardless of the type of mold, and prevents deterioration of transferability even if the falling distance of glass droplets is short. An object of the present invention is to provide a method for molding a glass lens and an apparatus for the same in which this is prevented.

A means for solving the problem, that is, the above object of the present invention is to melt and stir glass (for example, SF 1 1) in a crucible to make it uniform, and then to form the glass by appropriately controlling the temperature of the furnace and nozzle (4). This is achieved by receiving the glass droplets (6) in a lower mold having a certain thermal conductivity and surface roughness to produce a glass lens.

Here, the present invention includes a glass melting crucible, a nozzle provided at the bottom of the crucible for dropping glass melted in the crucible as glass droplets, a glass drip tray for receiving glass droplets dropped from the nozzle, a lower mold, and a glass lens manufacturing apparatus comprising an upper mold for compression molding the dropped glass droplet in cooperation with a lower mold, wherein the glass drip dripper has a lower mold that has a thermal conductivity. is composed of a material with a power of 50 W/mK or more, and a resistance of 0.05 μmRmax to 0.2 μmRmax
Provided is an apparatus for manufacturing a glass lens characterized by having a surface roughness of x.

In the present invention, molten glass is dripped from the tip of a nozzle, and the glass droplet is made of a material with a thermal conductivity of 50 W/mK or more and has a surface roughness of 0.05 μmRmax in a lower mold. The present invention provides a method for molding a glass lens, which comprises obtaining a glass lens by compression molding the glass droplets after receiving the glass droplets.

According to the present invention, it is possible to form a glass lens without whiskers, and furthermore, it is possible to receive the glass droplet on the lower mold in a state where the surface temperature is above the softening point, so that the falling distance of the glass droplet can be shortened. This allows glass lenses with good transferability to be manufactured with good reproducibility.

The thermal conductivity that the lower mold of the present invention should have is 50 W.
/mK or more, preferably 80W/mK or more is required. The lower mold requires such thermal conductivity because
This is to prevent the surface roughness of the lower mold, which will be described later, from being transferred during molding, and to form a glass lens having lens surface properties that do not require a polishing step after molding. Thermal conductivity is 50
If it is smaller than W/mK, the surface texture of the mold will be transferred and the resulting lens surface will require polishing.

Examples of materials that can provide such thermal conductivity include silver, aluminum, silicon, graphite, silicon carbide, aluminum nitride, and cemented carbide.

In addition, the surface roughness that the lower mold should have is 0°05~
0.2 pmRmax, preferably 0.1-0.2 μm
Rmax. In this way, by making the surface of the lower mold rougher, the accumulated air (Figure 2-b) that is generated during the shrinking process after the glass drops drop onto the lower mold can be removed through the rough holes during compression molding. Therefore, it is believed that it is possible to prevent the appearance of conventional beards.

If the surface roughness is smaller than 0.05μmRmax, it will not be possible to secure a sufficient path for air to pass through, so whiskers will easily occur, and if it is larger than 0.2μmRmax, the surface roughness will be easily transferred, and the shape accuracy of the mold will be reduced. Errors are likely to occur during measurement.

In addition, the surface roughness referred to in the present invention is JISBO601-1
The values are shown based on 982.

The roughness described above can be imparted to the surface of the lower mold by performing treatments such as blasting, acid etching, and sanding.

Next, the production of glass lenses will be explained, starting with the method of producing glass droplets.

As shown in FIG. 1, glass droplets are produced by allowing glass (2) melted in a crucible (1) to fall naturally from the tip of a nozzle (4).

The crucible and nozzle are preferably made of platinum in order to prevent coloring of the glass, as in the case of ordinary optical glass melting, but the crucible and nozzle are not limited thereto.

The crucible is stirred 1! (3) and heating heater (5a)
It is equipped with

The temperatures of the crucible (1) and nozzle (4) are maintained at desired temperatures by adjusting the heaters (5a, 5b, 5c, 5d). Crucible (1) and nozzle (4)
The temperature can be set depending on the properties of the glass and the size of the glass droplet to be obtained, and is usually 500 to 1400°C.
is within the range of In particular, if the temperature of the lower and upper parts of the nozzle (4) is set high in the lower part and low in the upper part, the glass droplets (6) can be easily dropped. Preferably the lower part is 5
The temperature should be about 0 to 200°C higher than the upper part.

The temperature of the glass droplet varies depending on the falling distance, the ambient temperature, the size of the glass droplet, the temperature, the thermal conductivity of the glass, whether a forced cooling means is provided, etc., and furthermore, the temperature of the glass droplet is collected on the lower mold. Since the subsequent cooling rate of the glass droplet varies depending on the constituent material of the lower mold, the set temperature of the lower mold, etc., when implementing the present invention, the cooling rate is adjusted while taking these conditions into consideration.

Since the above temperature affects the surface tension of the glass, that is, the size of the glass droplet, it is necessary to precisely control this temperature in order to obtain glass droplets with high weight accuracy. In order to precisely control the nozzle temperature and, if necessary, the glass temperature in the crucible, it is preferable to provide means for automatically controlling these temperatures. As a means for this, it is preferable to control the temperature of the glass droplet at the nozzle tip by controlling the time it takes for the glass droplet to form at the nozzle tip and fall. Specifically, for example, a light beam passing through the nozzle tip is emitted by a light emitter (8), and a light receiver (9) for sensing the light is placed opposite to the light emitter with respect to the nozzle tip, and the formation of glass droplets is prevented. The time until the drop is measured, and a signal corresponding to the measured value is sent to a control unit (microcomputer, etc., not shown), which controls the heating provided in the nozzle and, if necessary, in the crucible, depending on the amount of change in time. A method of controlling the amount of electricity supplied to the heaters (5a, 5b, 5c, 5d) may be used. Alternatively, the temperature of the glass droplet may be directly measured using a radiation thermometer or the like instead of the light emitter (8) and the light receiver (9).

The nozzle tip diameter is a factor that affects the weight of the glass droplet. That is, the weight of a glass droplet is approximately expressed in mg "2rrγ (m: weight, r: nozzle tip diameter, γ: surface tension). Generally, the nozzle tip diameter is 0.5 to 15 mm, preferably 0.5 to 10 mm. If the diameter of the nozzle tip is too large, the glass flowing out will overcome the surface tension and the flow will become laminar, making it impossible to obtain glass droplets.

The glass that comes out of the nozzle tip forms a shell shape due to surface tension and falls one after another.

Although not shown in FIG. 1, the falling distance may be adjusted by moving the support base (21) of the lower mold (15) up and down. At this time, using the same control means as used for adjusting the nozzle temperature described above, the control section is activated based on the signal from the light receiver or radiation thermometer to raise and lower the support base and adjust the falling distance. Good too.

The lower mold (11) that collects glass droplets first has a nozzle (4).
), which receives the glass droplet dripping from the tip of the nozzle (4). After the glass droplet drips, it is moved to the molding position, and in cooperation with the upper mold (13), the glass lens is formed by compression molding. to form. At this time, the lower plate (11) only needs to be able to hold the dropped glass liquid in a state with sufficient thickness to obtain the desired lens.

The upper mold (13) may be made of the same material as the lower mold (l l), or may be made of a different material.

Further, the lower mold (l l) for collecting may be convex or concave. The present invention is particularly effective for manufacturing convex lenses using a concave lower mold.

The lower mold (15) has a temperature of 10% higher than the softening temperature of the glass used.
~15000. Preferably, it is heated to a temperature lower by 30 to 100°C.

Usually about 400'04 when using 5FII glass
This is set. By doing so, lenses with high surface precision can be molded, and there is an effect of preventing fusion between the mold and the glass.

The upper mold (18) has a temperature of 10% higher than the softening temperature of the glass used.
It is preferable to keep the temperature heated to a temperature lower than 150°C, preferably 30 to 100°C.

By doing so, it has the same effect as the lower mold.

According to the present invention, various types of lenses such as biconvex, biconcave, planoconvex, planoconcave, and meniscus lenses can be manufactured accurately and efficiently by selecting the upper mold and the lower mold.

Examples and Comparative Examples A droplet method glass lens manufacturing apparatus having the configuration shown in Figure 1 was made of the materials shown in Table 1, and was adjusted to the thermal conductivity and surface roughness shown in Table 1. Using the lower mold, a glass lens was obtained by setting the dropping distance of the glass droplet (from the nozzle tip to the surface of the lower mold) to be 20.50.1001250 cm.

The surface of the lower mold was roughened by blasting, acid etching, sanding, etc. as appropriate.

The mold and the lower surface of the molded lens were measured with a surface roughness meter, and the navel of the lens was measured with a microscope.

Roughness is Rmax based on JIS BO601-1982
The amount of sinkage is the average value of 10 lenses expressed in Newtons. The measurement limit for Ralax is 0.01 μm.

As can be seen from Table 1, the longer the dropping distance, the higher the thermal conductivity of the mold, and the rougher the surface roughness of the mold, the better the shape transferability and no sink marks. Rmax for molds with thermal conductivity of 50W/mK or more
When the diameter is 0.05 μm or less, there is almost no sinkage, and the surface roughness is 0.012 m, which can be ignored in practical terms. Further, when the RmaxO is 80 W/mK or more and RmaxO is 05 μm or less, no sink marks occur and the transferability is good.

Next, the surface roughness of the lens is smaller than that of the mold under any conditions. Furthermore, the longer the dropping distance and the higher the thermal conductivity of the mold, the greater the difference in roughness between the mold and the lens, that is, the better the lens.

First of all, it can be seen from this that, in this method, even the fine surface roughness of the mold is not transferred even when it comes into contact with the mold.

Secondly, since the cooling and solidification of the glass surface after contact with the mold is controlled by the thermal conductivity of the mold, it can be seen that by using a mold with high thermal conductivity, it is possible to suppress the transfer of surface roughness. Furthermore, if we take into account the occurrence of whiskers and the whiskers in the center, we can see that it is possible to prevent the occurrence of sink marks even if the glass droplets are received by the lower mold and molded before they solidify sufficiently with a short falling distance. This is thought to be because the air in the air pockets generated by sink marks during cooling is removed through the gap caused by the difference in roughness between the solidified glass surface and the mold surface during molding.

In the comparative examples, as is clear from Table 1, a dropping distance of 2 m or more is usually required to prevent the occurrence of sink marks. For quartz, whiskers can be seen even at a dropping distance of 250 cm.

Effects of the Invention According to the present invention, by molding dripping glass using a mold with high thermal conductivity and relatively rough surface, it is possible to manufacture good lenses with no sink marks at a shorter dripping distance than before. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a schematic configuration of an apparatus for carrying out the liquid application method of the present invention. FIG. 2 is a second diagram illustrating the mechanism by which beards are produced. Fig. 1, 7, Fig. 2-0, Fig. 2-b, Fig. 2-c, Fig. 2-d, dropping.

Claims (1)

[Scope of Claims] 1. A glass melting crucible, a nozzle provided at the bottom of the crucible for dropping the glass melted in the crucible as glass droplets, and a lower glass droplet receiving mold for receiving the glass droplets dropped from the nozzle. , and an upper mold for compression molding the dropped glass droplet in cooperation with the glass droplet receiver lower mold, wherein the glass droplet receiver lower mold has a thermal conductivity of Constructed of material with a power rating of 50W/mK or more,
A glass lens manufacturing device characterized by having a surface roughness of 0.05 μmRmax to 0.2 μmRmax. 2. After dropping molten glass from the nozzle tip and receiving the glass droplet with a glass droplet receiver lower mold that is made of a material with a thermal conductivity of 50 W/mK or more and has a surface roughness of 0.05 μmRmax. A method for molding a glass lens, which comprises obtaining a glass lens by compression molding the glass droplets.