JPH10114531A - Production of forming die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a glass forming die usable to form an optical glass element from high-temp. glass at the time of forming a forming die to be used for compression-molding a lens from an optical glass perform by producing a master die from a material having a specified high temp. Tg. SOLUTION: The optical glass perform has 400-850 deg.C Tg and a specified thermal expansion coefficient and determines the surface shape of a lens to be formed. A forming die preform is formed from a base material as a mixture of aluminosilicate glass and quartz having >=900 deg.C Tg and the specified thermal expansion coefficient for the forming die and the formed lens to separate from each other. The surface shaped for the master die and that for the forming die are calculated from the surface shape and thermal expansion coefficient of an optical element, the thermal expansion coefficient of the master die, the temp. to form the forming die and the temp. at which the lens is formed, and a forming die preform is formed by the master die to obtain the forming die.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to molding optical glass lenses, and more particularly, to making glass molds for molding optical glass elements.

[0002]

BACKGROUND OF THE INVENTION Various methods and apparatus for compression forming glass optical elements are well known in the prior art. In these methods and apparatus, an optical element preform, referred to as a mass, is compression molded at an elevated temperature to form a glass lens element. The basic process and apparatus for forming a glass optical element is taught in a series of patents granted to the present applicant (Eastman Kodak Company). Such patents include U.S. Patents 3,833,347,
U.S. Pat. No. 4,139,677 and U.S. Pat. No. 4,168,961.
These patents disclose various materials suitable for constructing a molding insert used to form the optical surface of the formed optical element. Suitable materials for constructing these molded inserts include glassy or vitreous carbon, silicon carbide, silicon nitride, and mixtures of silicon carbide and carbon. In the practice of the process disclosed in these patents, a glass preform or lump is inserted into a molding space with a mold formed from one of the materials described above. The mold is held in a chamber that is held in a non-oxidizing atmosphere during the molding process. The preform is then softened by increasing the temperature of the mold to increase the glass transition temperature (Tg) by 100 ° C for the particular type of glass from which the preform is made. Pressure is applied to the mold to form the preform into the shape of the mold. Next, the mold and the preform can be cooled below the transition temperature of the glass.
The pressure is released from the mold. The temperature is further reduced,
The finished molded lens is taken out.

[0003]

SUMMARY OF THE INVENTION U.S. Pat. No. 4,897,101
No. 4,964,903 suggests a method and apparatus for forming optical glass elements using a formed glass mold. According to this method and apparatus, a metal master mold is first manufactured. Suitable materials for forming such a master mold include Inconel 78, stainless steel type 420, tungsten carbide, and the like. The master surface is coated or plated to minimize deterioration of the molding surface due to chemical attack, corrosion, dents, abrasion, and adhesion of the molding sale material. The lens design data is used to calculate the master type profile. It is described that a difference in thermal expansion coefficient between a lens material and a material of a mold is compensated at a molding temperature to obtain a required molded shape. Since a metal master mold is used, the above processes and methods have a temperature limit. Glass forming mold formed by metal master mold, relatively low Tg
(Temperatures below 500 ° C.) can only be formed. As a result, a lens molded using such a glass mold has a lower Tg than that of the glass mold. In order to use such a glass mold, a glass having a Tg of 402 ° C. or less is considered to be acceptable. Accordingly, the commercial potential of such methods and apparatus is limited, at the maximum, to the type of glass utilized to form optical glass elements using such methods and apparatuses. In practice, there are very few types of commercially available glasses that can actually use such methods and apparatus. There was a need to develop new glass compositions that could use the above methods and apparatus.

[0004] The prior art is from 900 ° C to 1500 ° C.
Does not suggest a method of forming a glass mold formed from a high-temperature glass having a Tg in the range from the master mold.
Accordingly, the prior art does not suggest a process for making optical glass elements moldable from a variety of commercially available glasses having a Tg in the range of 400 ° C. to 850 ° C.

It is an object of the present invention to provide a method of forming a glass mold that can be used to form an optical glass element from high temperature glass. Further, the present invention provides
It is intended to make an amorphous base material for forming a mold that can be used to mold for optical gases from glass having a Tg in the range of 400 ° C to 850 ° C.

Still another object of the present invention is a method for producing a glass mold used before molding an optical glass element, wherein the base material used for molding the glass mold is 50 × 10 ^{−. 7} / ° C to 100 × 10 ^-7 / °
It is to provide a method having a coefficient of thermal expansion of C. Further, another object of the present invention is to provide a method in which 700 ° C. to 900 ° C.
It is an object of the present invention to provide a method for molding a mold from an amorphous material having a Tg in the range of ° C.

[0007]

Other features, objects, and advantages of the present invention will become apparent from the description of the specification and the drawings. These features, objectives and advantages are, first, from 1000 ° C to 25 ° C.
This is achieved by fabricating the master mold from a material having a Tg in the range of 00 ° C. A preferred material for this purpose is silicon carbide produced by chemical vapor deposition. Other materials that can be used to make the master mold include vicol and fused quartz. The master mold is manufactured by a very high-precision (ｐλ / 4p-v) computer controlled grinding and polishing apparatus. This master type is
Used in glass forming processes to produce molds with opposite curved surfaces. This mold is then used in a production mode to produce the final product, an optical glass lens. The method includes a calibration of the curved surface and a two-step molding process, where the three materials (master mold, mold, lens) have different coefficients of thermal expansion and two different temperatures (mold mold process and , Lens manufacturing process). This is especially important for aspheric surfaces. This system requires glass stratification so that the glass mold has a strain point above the process temperature of the lens glass. If the strain point of the mold is lower than the process temperature of the lens glass, the mold slightly deforms in each molding cycle, and curved surface creep occurs. An appropriate release agent is required.

[0008] As mentioned above, once the master mold has been manufactured, it is used to mold the mold. The lens to be finally molded using this mold is 400 °
It has a Tg in the range of C to 850 ° C,
The mold should be at least 100 ° C below the Tg of the glass lens
Must have a higher Tg. This is achieved by making an amorphous base material containing 50% to 75% quartz by weight. This is achieved by mixing quartz with the aluminosilicate glass.
Amorphous base materials are used to form molded preforms. A first surface shape for the optical element molded by the mold is determined. From the first surface shape and the coefficient of thermal expansion of the optical element, the coefficient of thermal expansion of the master mold, the predetermined coefficient of thermal expansion of the mold, the temperature at which the mold is molded, and the temperature at which the lens is molded, A second surface shape and a third surface shape for the mold are calculated. The second mold is formed by grinding and polishing the master mold. A release agent coating is applied to the star mold.

[0009] Predictive glass forming for high quality lens applications has two major limitations in its high value implementation. The first limitation is that the mold is expensive, and the second is that the life of the mold is short. Although a number of methods and apparatus have been described for producing very high precision molded glass lenses in a laboratory environment, implementation of the industrially feasible high-volume manufacturing process involves these two. Limited by factors. The essential motivation for the glass mold used to mold the lens is to reduce the cost per mold, as well as to make the mold quickly and relatively simply. In addition, the master mold may be iteratively adjusted or changed based on test feedback, so that one may seek to draw high precision from the master mold molding system. As a result, it is possible to improve the molding dies that are sequentially created by using such a master die.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a mold assembly 10, shown in cross section, is used to manufacture the glass mold of the present invention. The mold assembly 10 includes a lower mold housing 12 and an upper mold housing 14. A mold bottom plate 16 is provided at the lower end of the lower mold housing 12. Mold bottom plate 16 in lower mold housing 12
A spacer sleeve 18 is supported on the top. Also,
A ring mold 20 mounted in a spacer plate 18 is supported on the mold bottom plate 16. Ring type 2
0 has a cylindrical space 22. The central axis of the cylindrical space 22 substantially coincides with the central axis of the ring mold 20.
The ring mold 20 has an upper counterbore and a lower counterbore having a central axis coinciding with the central axis of the cylindrical space 22, thereby forming an upper annular shoulder 24 and a lower annular shoulder 26. (See FIG. 2). Master mold 28 in ring mold 20
Is supported. The master mold 28 has an annular flange 30. The annular flange 30 extends radially and engages the upper annular shoulder 24 so that the master mold 28 depends within the ring mold 20. A molding surface 32 is formed at the lower end of the master mold 28. Thus, a molding space 34 is formed. The lower end of the molding space 34 is the mold bottom plate 16.
As a result, the side surface is formed by the ring mold 20, and the upper end is formed by the molding surface 32.
Is formed.

The upper housing 14 has a cylindrical member 36. The cylindrical member 36 is provided concentrically with the lower housing 12. The pusher plate 3 is attached to the cylindrical member 36.
8 is attached.

The glass preform is inserted into the molding space 34, and the master mold 28 is inserted into the ring mold 20. Drive means (not shown) for pushing down the upper mold housing 14 causes the pusher plate 38 to engage the upper surface of the master mold 28. The glass preform and mold assembly have already been heated to a temperature above the glass transition temperature Tg of the glass used to make the glass preform. In this way, the glass preform is forced to conform to the shape of the molding space 34.

[0013] If the elements of the mold are not precisely positioned with respect to each other, a precise surface will not be formed on the molded article. This is particularly problematic, especially for aspheric surfaces, where repositioning the lens assembly does not completely eliminate the error. In this regard, a molding system using a master mold for molding a mold requires more difficult work than directly molding a lens element. Nevertheless, very good results can be obtained by properly managing the molds and maintaining tolerances.

The spacer sleeve 18 is custom made for a given master mold 28 and glass mold to be molded. In this way, the spacer sleeve 18
The same mold assembly 10 can be used for different sized ring dies 20 and different sized master dies 28.

[0015] The material of the mold bottom plate 16 is selected by heat conduction properties, whereas the pusher plate 38 is selected by mechanical strength. Many materials are conceivable for that, but the preferred material for the mold bottom plate 16 is a carbonaceous material (eg, P-03 graphite from Pure Carbon Company, Pennsylvania), and the preferred material for the pusher plate 38 is It is steel.

[0016] The release of the formed glass mold is a problem. The ring mold 20 is made of carbonaceous material (P-03 graphite), that is, Vycor (trademark), and has a cylindrical space 22.
Must coincide with the central axis of the master mold 28 and the central axis of the glass mold formed in the molding space 34. In use, the mold assembly 10 is assembled as in FIG. 1 except that the glass preform is placed on the mold bottom plate 16 below the ring mold 20. Next, a master mold 28 is placed on the glass preform in the ring mold 20. The mold assembly is heated and pushed closed after reaching the appropriate temperature. FIG. 1 shows the mold assembly in the solution position after pressing. A slot 35 is provided at the top of the ring mold 20 (see FIG. 3). Slot 35 is flange 30
Extends from the ring mold 20 to the master mold 28.
Can be removed. The master mold 28, the glass molding mold 40 and the ring mold 20 molded together with the master mold,
It is removed from the mold assembly 10 after cooling. Master type 28
Is pulled out, and the glass mold 40 is pushed out from the bottom of the ring mold 20 (if necessary). At this point, the mold assembly 10 is ready for the next use.

Referring to FIG. 4, an example of a glass forming mold 40 formed by the mold assembly 10 of FIG. 1 is shown in a partial cross section. The glass mold 40 has a molding surface 42. The molding surface 42 can be aspheric. The glass mold 40 further has an annular flange portion 44 extending radially from the glass mold.

A second embodiment of the present invention will be described with reference to FIGS. The mold assembly 100 includes a lower mold housing 112 and an upper mold housing 114. A mold bottom plate 116 is provided at the lower end of the lower mold housing 112. Ring mold 1 on mold bottom plate 116
20 are supported. Ring mold 120 is mounted within spacer sleeve 118. The ring mold 120 has a cylindrical space 22. The central axis of the cylindrical space 122 substantially coincides with the central axis of the ring mold 120.
A master mold 128 is supported in the ring mold 120 (see FIGS. 6 to 8). The master mold 128 has an annular flange 130. The annular flange 130 extends in the radial direction, and when the master mold 120 is completely inserted into the cylindrical space 122, the annular upper end surface 124 of the ring mold 120
Engages. A molding surface 132 is formed at the lower end of the master mold 128. Thus, a molding space 134 is formed. The lower end of the molding space 134 is the mold bottom plate 116.
The side surface is formed by the ring mold 120 and the upper end is formed by the molding surface 1.
32. Upper housing 114
Has a cylindrical member 136. The cylindrical member 136 is disposed so that the central axis thereof coincides with the lower molding die 112. The mold assembly 100 differs from the mold assembly 10 in the shape of the ring mold 120 and the mold bottom plate 116. A recess 140 is formed in the mold bottom plate 116 to enable a flange to be formed at the bottom of the glass mold. Then, from the annular flange 130, the master mold 1
Hanging 28 allows ring mold 120 to have a simple cylindrical shape having a cylindrical space 122 therethrough.

In use, a generally cylindrical preform 150 is inserted into the cylindrical space 122 and the mold bottom plate 1
16. Next, the master mold 128 is placed so that the molding surface 132 is placed on the preform 150.
Is inserted into the cylindrical space 122 (see FIG. 7). After the mold is heated to a predetermined temperature, the upper mold housing 114 moves downward in the vertical direction, and the pusher plate 132 tilts to the upper surface of the master mold 128. The master mold 128 is thus pushed down into the cylindrical space 122 until the flange 130 engages the annular upper surface 124 of the ring mold 120.
This forces the preform 150 to conform to the shape of the molding space 134 (see FIG. 8). The preform 150 becomes a glass mold 160 having an annular flange 162 and a concave molding surface.

The method of the present invention produces a glass mold using a master mold molding system. Glass molds are ultimately used to mold optical glass elements. The master mold 28 is manufactured with very high precision (≒ λ / 4p−v) by a computer controlled grinding machine. The master mold 28 is then polished with a suitable sander to reduce surface roughness. Once manufactured, the master mold 28 is then used in the glass forming process on the same forming machine that manufactures the final product, the glass optical element. Thus, the master mold 28 is used to manufacture the glass mold 40. The glass mold 40 has a molding surface 42 having a curved surface opposite to the molding surface 32 of the master mold 28. The glass mold 40 is then used to manufacture a lens that is the final product in a product manufacturing mode.

Calibration of the curved surface is performed for the two-step molding process. The master mold 28, the glass mold 40, and the final lens are formed from three different materials having different coefficients of thermal expansion. Furthermore, different operating temperatures are involved. The temperature at which the master mold 28 is used to mold the glass mold 40 must be higher than the temperature at which the glass mold 40 will mold the final lens. For aspheric surfaces, calibration of the curved surface is practically important, and in the system of the present invention, the material of the glass mold 40 is hierarchically arranged so that it has a higher strain point than the process temperature at which the final lens is molded. It is necessary to attach. If not, the creep of the curved surface causes the molding surface 42 to deform slightly in each molding cycle. In the molding operation, an appropriate release agent is required.

The calibration of curved surfaces (lenses and molding surfaces) is based on a simple first-order approximation theory of expansion and the assumption of material isotropicity. Empirical data on materials and processes, namely the coefficient of thermal expansion applied to the process temperature and the design factor of the desired curved surface of the lens.

According to the first order expansion theory, the fractional change rate of the linear dimension of an object is directly proportional to the temperature change. That is, the following equation holds. ΔL / L ₀ = α · ΔT (1) Here, the proportionality constant is called a linear coefficient of thermal expansion (CTE) and is measured by an experiment. ΔL is the change in length, L ₀ is the initial length, and ΔT is the temperature change from process to ambient. For many optical glasses, it has been experimentally confirmed that this temperature change for the glass forming process is preferably 40 ° C. below the process temperature. 20 ° C of which corresponds to the surroundings (room temperature to 20 ° C
), And the remaining 20 ° C. can be considered a temperature drop from the forming temperature to a temperature at which the glass has structural integrity. In other words, the temperature at which the glass has a surface that can support itself without a mold. α has a reciprocal unit of temperature.

If ΔL = L−L ₀ , equation (1)
Can be rewritten into the following equation. L = L ₀ (1 + α · ΔT) (2) where L is the length at the final temperature. This applies to all linear dimensions of isotropic materials whose temperature-controlled behavior can be described by a constant CTE. It is not necessary to consider the expansion behavior at intermediate temperatures. Only the expansion behavior at the temperature at both ends matters. Therefore, α need not be a value published in the handbook, but is determined so as to satisfy Expression (2). Since the radius is a linear dimension, it is described by equation (2). Therefore, RT = RL (1 + αG · ΔT) (3) Where RT is the radius of the lens at the operating temperature of the process, RL is the desired radius of the lens at ambient temperature, αG is the equivalent linear thermal expansion coefficient of the glass, and ΔT is the temperature difference (from process to ambient). This is used with (1) similar equations for mold materials and (2) with the understanding that reproducibility is high at elevated temperatures rather than ambient temperatures. RT = RN (1 + αN · ΔT) (4) where RN is the radius at ambient temperature and αN is the CTE of the material of the manufactured mold. Then, RN = RL ・ (1 + αG ・ ΔT) / (1 + αN） ΔT) (5) or RN = RL ・ KLN (6)

With respect to the aspherical surface, a correction is made on the basis of the dimensional revision. For example, a typical design equation for an aspheric surface is given by: ^{X = CY 2 / (1+ (} 1- (K + 1) C 2 Y 2) 1/2 + DY 4 + EY 6 + FY 8 + GY 10 (7) wherein, X is a semi - Anatatejiku (half aperture ordinate) slack in Y , K are conic constants (dimensionless shape coefficients), D, E, F and G are so-called aspheric deformation constants, C is vertex curvature and vertex radius ( vertex radiu
s) The reciprocal of R. In order to convert equation (7) from an equation describing a lens surface to an equation describing a Nabin surface, KLN of equation (6) is used according to the dimension of the converted constant. K
Is a dimensionless shape coefficient. Therefore, it is maintained as it is (the parabola is maintained as a parabola). C has a reciprocal unit of length. Therefore, it is converted by dividing by KLN. D has the unit of the reciprocal of the cube of the length. Therefore, it is converted by dividing by KLN to the third power, and so on.

In a molding system using a master mold, this calibration is performed in another stage. That is, the master mold becomes a mold, and the mold becomes a pseudo glass lens. Different material and temperature constants are used in this iteration.

Since the method of the present invention involves making a glass optical element from a glass preform, the glass mold 4
A Tg of 0 must be at least 100 ° C. higher than the Tg of the optical glass preform. The optical glass preform used in the present invention is from 400 ° C to 850 °
Since it has a Tg in the range of C, the glass mold 40 must be molded from a material with a relatively high Tg. As a material of the glass mold 40, Vicol (trade name Vy
cor) and modified aluminosilicate glasses. Bicol is a 96% quartz structural glass. Examples of aluminosilicate glass include Corning 1723, General Electric GE-180, Sem-Com SCE
-3. In order to mold the glass mold 40 from bicol or modified aluminosilicate glass, the master mold 28 must not deform at a temperature substantially higher than the Tg of bicol or modified aluminosilicate glass. A preferred material for making master mold 28 is silicon carbide made by chemical vapor deposition. In order to manufacture the glass mold 40 from a modified aluminosilicate glass, a fine-grained ceramic having a high temperature property such as fused quartz, bicol or zirconia can be used.

As mentioned above, two different molding operations require a release agent system. The release agent system is a direct function of the two materials involved and the temperature at which the two materials premature each other. For flint glass, the forming temperature is on the order of 500 ° C. For crown glass, the forming temperature is on the order of 700 ° C. The forming temperature of the modified aluminosilicate glass is on the order of 900 ° C. For fused quartz (ie, Vicol), the molding temperature is on the order of 1500 ° C. Silicon carbide manufactured by chemical vapor deposition retains its structural integrity up to 2600 ° C. (in a nitrogen atmosphere).

For most combinations of glass and silicon carbide described above, several types of carbon coatings can be used as release agents. Various carbon coating release agents are well known in the prior art. However, carbon coating release agents generally cannot be used with flint glass. The carbon coating and the oxygen adsorbed on the surface produce carbon monoxide, which acts as an oxidizing agent to reduce lead oxide (a major component of flint glass) on the surface to elemental lead. This reducing action causes undesirable distortion and deformation of the molding surface 42 and the glass mold 40.
Therefore, in the case of flint glass containing lead oxide, the forming surface must be coated with tin oxide in combination with appropriate preform glass cleaning. Preformed glass elements are typically ultrasonically cleaned prior to molding. During the ultrasonic cleaning process, lead is chemically extracted from the surface of the glass preform using an aqueous solution of ethylenediaminetetraacetic acid. Extraction of lead from the surface of the glass preform promotes prevention of reaction between the lead oxide in the glass preform and the carbon coating of the mold. Another method for extracting lead from the surface of a glass preform is disclosed in Japanese Patent Publication No. 21606/1992.
No. 207728).

A preferred coating technique for applying tin oxide is sol-gel spin coating followed by baking. There are several tin oxide precursors that can be used in this method. The gel phase allows the use of minor additives for individual glass tuning. In addition, the spin coating technique is less susceptible to pinholes that occur in evaporative coating, for example. Further, sputtering can be used to apply a tin oxide release agent.

The carbon coating can be performed by various methods. The preferred method of carbon coating is the pyrolysis of a simple hydrocarbon gas such as methane or acetylene. Furthermore, there is a method in the prior art for producing diamond-like carbon. It is preferred to place the release agent in the mold method rather than in the preform. This is because the preform surface is remapped in the pressing process. If the molding process is performed correctly, the curved surface of the preform will always be larger than the curved surface. In this way, the lens produced always has a larger surface area than the surface of the mold produced thereby. Further, both the preform and the mold may be coated with carbon.

Within the scope of the method of the present invention, the glass mold 40 can be made from commercially available materials. For example, the glass mold 40 can be made from aluminosilicate glass such as Corning 1723. The glass mold 40 is manufactured to have a spherical surface,
Used to press typical high temperature glass such as Hoya TaC-4. After carefully examining the lens at regular intervals (approximately 100), interference fringes can be used to determine if the curve has creeped (changed with slope).
Therefore, aluminosilicate glass is not suitable because a stable system cannot be produced. Attempts were made to make glass molds from Bicol (Corning 7913). This material is a special borosilicate glass manufactured by Corning, whose temperature characteristics are close to fused quartz. For example, Vicol forms at about 1400 ° C, but does not creep at the forming temperature of optical glass except for fused quartz itself. The use of Vicol to make glass molds has been technically successful. But
The harsh environment required of molding equipment to actually produce glass molds from Bicol is not a desirable solution for actual production. Furthermore, bicol creates another problem with very low thermal expansion properties.

Other glass materials having sufficiently high Tg at moldable temperatures have been considered. Glasses investigated include Corning 1731, Sem-Com SCE-3, General Electric GE-180, and Corning 9754. These glasses were unsuitable. It is not necessary to select an optical glass for the material. In fact, it may be opaque as long as the temperature characteristics allow it to meet the molding requirements of the method of the present invention without creep. (Maintain amorphous)
Truly amorphous materials are preferred over any material containing a crystalline structure because of the isotropic and reproducible properties as well as the final surface quality achieved thereby.

A number of optical and structural glasses have been evaluated on paper for use in making glass molds 40 in the method of the present invention. Also, some optical and structural glasses were evaluated experimentally. It was confirmed that an ideal glass was not commercially available. Aluminosilicate glass was mixed with quartz to produce a glass having a sufficiently high Tg at moldable temperatures. Specifically, Corning 1723 was mixed with quartz. Corning 172 of powder
3 was added with 5%, 10%, and 20% by weight of quartz to perform three test melting operations. There was no need to start with the powder composition and stir. Furthermore, no fining agent was required. All melts were clear and available. The glass mold 40 is
Manufactured from each of the melts shown in Examples A, B and C in the table below. All of the glass molds 40 made from Examples A, B and C passed the creep test and the molding test. A useful and interesting by-product of these tests is obtained when the coefficient of thermal expansion is derived from the spherical test data of the glass mold 40 made from Examples A, B and C and of the lenses molded thereby. Was. Contrary to the concept envisaged, the thermal expansion increased without decreasing with the addition of quartz. Table 例 Example Quartz CTE Tg% (× 10 ^-7 / ° C ) ──────────────────────────────────── A571> 700 ° C B1087> 725 ° C C 2099> 750 ° C Corning 1723 −−46 {665 ° C} ───

Thermal expansion increases as the amount of added quartz increases
The results obtained can be useful in many contexts. First, phosphorus
It can be used to improve the release characteristics from the mold 20.
Second, the overall tolerance of the mold assembly 10 can be reduced.
You. Third, the thermal expansion coefficient of glass for manufacturing a lens.
Depending on the number and whether the surface is positive or negative
It is possible to select the material for manufacturing the glass mold 40
It works. For example, regarding the release from the ring mold 20,
46 × 10 graphite molded ring^-7/ ° C CTE
And the glass mold is 71 × 10^-7/ ° C CTE
If it has, when cooled after pressing,
The mold is separated from the ring mold 20 and can be easily separated.
Regarding the strictness of the dimensional tolerance of the mold assembly 10, for example,
Practical Tolerance Limits Usable for Mold Assembly 10
Is a certain value at ambient temperature,
If the materials are similar, the molding temperature
The chain of other tolerances for one side is not improved. Naturally
And the glass mold is the same as the ring mold 20 and the master mold 28.
If the assembly expands too much, the assembly
At high molding temperatures,
Can produce better finished parts. Lens glass
Used to make glass mold 40 by CTE
The intended level in terms of the choice of materials to be
75 × 10 ^-7/ ° C Positive meniscus lens
Base material for manufacturing the convex side glass mold 40
The glass of Example A above as a starting material and the concave glass
As described above as a base material for manufacturing the mold 40
It is desirable to use Example B. In this way, Len
The cold glass always separates from the mold glass during cooling.
The mold is promoted and damaged by removing the tendency to engage
Can be made as small as possible.

From the foregoing, it will be seen that the present invention is clear and suitable for obtaining all the above objects and conclusions, together with other advantages which are essential to the invention. Certain features and sub-combinations are useful and can be used with other features and sub-combinations. This is planned and lies within the scope of the claims.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a ring type.

FIG. 3 is a top view of a ring type.

FIG. 4 is a half sectional view of a glass mold.

FIG. 5 is a sectional view of a second embodiment of the present invention.

FIG. 6 is a sectional view of a second embodiment of the present invention.

FIG. 7 is a sectional view of a second embodiment of the present invention.

FIG. 8 is a sectional view of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Mold assembly 12 ... Lower mold housing 14 ... Upper mold housing 16 ... Mold bottom plate 18 ... Spacer sleeve 20 ... Ring mold 28 ... Master mold 32 ... Molding surface 34 ... Molding space 40 ... Glass molding mold

Claims (3)

[Claims] 1. A method of making a mold for use in a compression molding process for molding a lens from an optical glass preform, the method comprising: (a) forming the optical glass preform from 400 ° C to 8 ° C;
Determining a first surface shape of a lens to be molded in a mold having a Tg of 50 ° C. and a first coefficient of thermal expansion; and (b) a predetermined amount of quartz in the aluminosilicate glass. Is mixed with the base material, that is, a Tg of at least 900 ° C.
Producing a base material having a predetermined second coefficient of thermal expansion such that the mold and the lenses molded by the mold are separated from each other during a cooling step of the compression molding process; Forming a mold preform from the base material; and (d) molding the first surface profile and coefficient of thermal expansion of the optical element, the coefficient of thermal expansion of the master mold, the predetermined coefficient of thermal expansion of the mold, and the mold. From the temperature and the temperature at which the lens is molded,
Calculating a second surface shape for the master mold and a third surface shape for the mold; and (e) grinding and polishing the master mold to obtain a second surface shape; (F) forming a mold preform with the master mold to form a mold. 2. The method of claim 1 further comprising the step of coating the mold preform with pyrolytic carbon prior to molding the mold. 3. A method of making a mold for use in a compression molding process for molding a lens from an optical glass preform having a Tg of 400 ° C. to 850 ° C. and a first coefficient of thermal expansion, the method comprising: (A) including quartz in a range of 50% to 75% by weight,
At least 100 above the Tg of the optical glass preform
° C high Tg and 50 × 10 ^-7 / ° C to 100 × 10
Making an amorphous base material having a coefficient of thermal expansion of ^-7 / ° C; (b) forming a mold preform from said base material; and (c) first forming a lens to be molded in the mold. Determining a surface shape; and (d) a first surface shape and a coefficient of thermal expansion of the optical element, a coefficient of thermal expansion of the master mold, a predetermined coefficient of thermal expansion of the mold, a temperature at which the mold is molded, and the lens is molded. From the temperature
Calculating a second surface shape for the master mold and a third surface shape for the mold; and (e) grinding and polishing the master mold to obtain a second surface shape; (F) applying a release agent coating to a master mold; and (g) molding a mold preform with the master mold to form a mold.