JP4473692B2 - Manufacturing method of molded products - Google Patents

Description

  The present invention relates to a method for manufacturing a molded article such as a lens, which includes press-molding an optical element such as a meniscus lens having a highly difficult surface shape with high accuracy. In particular, the present invention relates to a method of manufacturing a molded article such as a lens including a step of more efficiently and highly accurately producing a press mold.

As a method of molding an optical element, a glass material is sandwiched between a pair of mold members having a molding surface that has a surface shape having a predetermined surface accuracy corresponding to the shape of the optical element to be obtained. Press molding in a temperature range in which the viscosity of the glass material is 10 ⁸ dPaS or less, then cool the glass material and mold member, and mold the optical in the temperature range where the glass material is near the glass transition point A molding method for taking out an element from a mold member is known. (Patent Document 1)

In addition, there is known a method in which the molding surface of the mold member is processed so as to cancel the risk that occurs due to variations in the cooling rate and temperature distribution during molding in advance (Patent Document 2). This optical element molding method is a method of manufacturing an optical element by storing a molding glass material in a pair of molds and press molding under heating. A first step of setting a molding condition including a condition considering the cooling rate and temperature distribution at the time of cooling after press molding so that a constant assist is stably formed on the optical functional surface of the optical element; And a second step of molding an optical element using a molding die member having a molding surface processed into a shape that cancels the fixed assist.
Japanese Patent Publication No. 61-32263 JP-A-8-337426

  However, in the example of Patent Document 1, for example, when trying to process an optical element whose shape is difficult to obtain, such as a concave meniscus lens, (1) heating temperature, pressing pressure, press In addition to time, it is extremely difficult to select the range of (2) cooling speed after molding, (3) press pressure during cooling after molding, and (4) temperature difference between upper and lower molds during cooling after molding, etc. Other factors that affect accuracy will need to be scrutinized. Furthermore, even if these various molding conditions are set to optimum ones, there are many cases where it is difficult to satisfy the required surface accuracy, and there is a problem that the yield decreases and the manufacturing cost increases.

In the molding method according to Patent Document 2,
(1) It is necessary to set the molding conditions so that a certain shape can be formed stably.
(2) It was necessary to correct the surface shape of the molding surface for each optical functional surface of the optical element.

  In particular, in the case of a concave meniscus lens, the shape after molding is unstable on both the concave and convex surfaces, and it is difficult to set molding conditions so that a certain shape can be stably obtained. For example, even if the molding conditions are set so that a certain shape is stably formed in advance, if the mold shape on the concave surface side is corrected, the shape obtained by molding becomes unstable. Therefore, when “(2) Mold correction” is performed, it is necessary to also perform correction of “(1) Molding conditions”. Furthermore, if the mold shape on the concave side is corrected, the convex side is also affected. Therefore, not only correction of the mold shape and molding conditions on the concave surface side, but also correction of “(1) molding conditions” and “(2) mold correction” on the convex surface side is necessary. Then, the correction on the convex surface side affects the concave surface side again. In this way, in the correction of (1) molding conditions and (2) mold correction of concave meniscus lenses, it is necessary to alternately correct the concave side and the convex side, and the number of corrections increases. This was a serious obstacle to mass production.

  Therefore, the present invention provides a method that can improve the accuracy of mold correction when producing a mold for press molding, and as a result, can produce a mold that can mold a lens having a desired shape with a small number of corrections. To provide a method for producing a molded product such as a meniscus lens, particularly a concave meniscus lens having extremely good productivity and good shape accuracy, surface accuracy, and surface roughness, using a mold produced by this method. Objective.

The present invention for solving the above problems is as follows.
[Claim 1 ]
A first surface including a concave shape, comprising pressing a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape; and a convex shape In a manufacturing method for obtaining a molded article having a second surface including:
The mold is produced by the following steps (1) and (2).
(1) Based on the shape of the first surface (curvature radius R1 _LT0 at room temperature T0) and the second surface (curvature radius R2 _LT0 at room temperature T0) of the desired molded product, the shape of the first surface and the second surface Correction step of determining the shape of the first molding surface (curvature radius R1 _MT0 at room temperature T0) and the second molding surface (curvature radius R2 _MT0 at room temperature T0) by correcting
However, the correction coefficient for determining the first molding surface shape of the molding die by correcting the shape of the first surface is r1, and the second molding surface of the molding die is corrected by correcting the shape of the second surface. Let r2 be a correction coefficient for determining
When
And, and
Correction coefficients r1 and r2 are set within the following ranges,
(2) A molding die producing step for producing the molding die according to the determined shapes of the first molding surface and the second molding surface.
[Claim 2]
A first surface including a concave shape, comprising pressing a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape; and a convex shape In a manufacturing method for obtaining a molded article having a second surface including:
The mold is produced by the following steps (1) and (2).
(1) Based on the shape of the first surface (curvature radius R1 _LT0 at room temperature T0 ) and the second surface (curvature radius R2 _LT0 at room temperature T0 ) of the desired molded product, the shape of the first surface and the second surface Correction step of determining the shape of the first molding surface (curvature radius R1 _MT0 at room temperature T0 ) and the second molding surface (curvature radius R2 _MT0 at room temperature T0 ) by correcting
However, the correction coefficient for determining the first molding surface shape of the molding die by correcting the shape of the first surface is r1, and the second molding surface of the molding die is corrected by correcting the shape of the second surface. Let r2 be a correction coefficient for determining
When
And the correction coefficient r1 is 0.980 to 0.999 times the correction coefficient r2.
(2) A molding die producing step for producing the molding die according to the determined shapes of the first molding surface and the second molding surface.
[Claim 3]
The manufacturing method according to claim 2, wherein the correction coefficients r1 and r2 are set within the following ranges, respectively.
[Claim 4 ]
A first surface including a concave shape, comprising pressing a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape; and a convex shape In a manufacturing method for obtaining a molded article having a second surface including:
The mold is produced by the following steps (1) and (2).
(1) Based on the shapes of the first and second surfaces of the desired molded product, the shapes of the first and second molding surfaces are determined by correcting the shapes of the first and second surfaces. Correction process,
However, the correction coefficient for determining the first molding surface shape of the molding die by correcting the shape of the first surface is r1, and the second molding surface of the molding die is corrected by correcting the shape of the second surface. Let r2 be a correction coefficient for determining
When the first surface of the desired molded article has an aspheric surface represented by the following formula:
The shape of the first molding surface is an aspherical expression that converts an arbitrary point (x1, y1) on the aspherical surface of the first surface of the desired molded product into (r1, X1, r1, Y1).
(Where K ₁ = K ₂ )
Furthermore,
When the second surface of the desired molded article has an aspheric surface represented by the following formula:
The shape of the second molding surface is an aspherical expression that converts an arbitrary point (x2, y2) on the aspherical surface of the second surface of the desired molded product into (r2, X2, r2, Y2).
(Where K ₃ = K ₄ ), but
R _LT0 is the radius of curvature of the desired molded product at room temperature T0 , R _MT0 is the radius of curvature of the molding surface at room temperature T0 ,
(2) A molding die producing step for producing the molding die by the determined aspherical shape of the first molding surface and the second molding surface.
[Claim 5 ]
The manufacturing method according to claim 4 , wherein the correction coefficients r1 and r2 are set within the following ranges, respectively.
[Claim 6 ]
6. The manufacturing method according to claim 4, wherein the correction coefficient r1 is 0.980 to 0.999 times the correction coefficient r2.
[Claim 7 ]
In press molding, after the first pressurization with a predetermined load is applied to the softened molding material, the molding material is cooled to a temperature lower than that at the start of the first pressurization and is smaller than the first pressurization. The manufacturing method according to any one of claims 1 to 6 , wherein a second pressure is applied by a load.
[Claim 8 ]
The molded article is a concave meniscus lens, a manufacturing method according to any one of claims 1-7.
[Claim 9 ]
The manufacturing method according to any one of claims 1 to 8 , wherein the molded product is a molded product having a free surface on an outer peripheral portion, and the molded product is subjected to a centering step to obtain a concave meniscus lens.

In the method for molding a concave meniscus lens according to the present invention (reference embodiment) , the difference in shrinkage between the concave surface and the convex surface of the provisional lens press-molded by using a mold is grasped. The number of corrections of “molding conditions” and “(2) mold correction” can be reduced, and an optical element having high surface accuracy can be processed. In the method according to the reference aspect, the number of corrections can be minimized. However, the number of corrections may be two or more.

Further , according to the method of the present invention, the convex-side correction coefficient r1 and the concave-side correction coefficient r2 in the molding die are set within appropriate ranges based on the desired lens shape without actually forming the provisional lens. By determining the shape of the mold, the same effect as described above can be obtained. That is , the method of the present invention is an epoch-making method that does not require even provisional lens molding.

  According to the present invention, it is not necessary to select complicated molding conditions such as alternately correcting the convex surface side and the concave surface side of the molding die, and a high-precision molding die can be easily manufactured.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Press molding equipment)
FIG. 1 is a cross-sectional view showing a configuration of a molding apparatus employed for press-molding a concave meniscus lens according to the present invention in a second molding step. FIG. 1 shows a state in which the press molding operation to the glass material 20 by the upper mold 11 and the lower mold 12 is almost completed.

  As shown in FIG. 1, it is preferable to design the mold so that a free surface is formed on the outer periphery of the molded article. That is, the outer periphery of the molded product has a surface formed without contacting the mold through the molding process, that is, a free surface. This is because when the outer periphery of the molded product comes into contact with the mold member during the molding process and is regulated, the molded product's molding surface [when the molded product is a lens] This is because the contraction of the lens surface (convex surface, concave surface) may become uneven. Furthermore, when some variation in volume occurs in the molding material (such as a glass preform preformed in a preliminary volume described later), unevenness in thickness occurs during press molding due to a decrease in the supply accuracy of the molding material to the mold. Even in this case, if the molding is performed so that a free surface is formed, the occurrence of surface accuracy defects due to the non-uniform shrinkage is avoided, which is advantageous. In this case, even if the molded product is apparently uneven in thickness, the surface accuracy satisfies the required performance, and therefore, a satisfactory molded product can be obtained through the centering step.

  In FIG. 1, the body mold 13 constituting the outer shell portion of the mold 10 is formed in a cylindrical shape having a small-diameter portion 13 a on the inner side, and a cylindrical shape is formed in the upper through hole of the body mold 13. In a state where the formed upper mold 11 is fitted, it is inserted so as to be slidable in the vertical direction. The upper mold 11 is formed with a disk-like flange portion 11a at the upper end thereof. In addition, a first molding surface 14 including a convex shape is formed on the lower surface of the upper mold 11 to press the glass material 20 and transfer a desired shape to the surface thereof to form an optical functional surface. ing.

  Further, above the upper mold 11, a cylinder 33 for generating a press pressure to be applied to the glass material 20 and a support base 31 that presses the upper bottom surface of the upper mold 11 as the cylinder 33 moves are arranged. Yes. Therefore, when the cylinder 33 is operated and the support base 31 is pushed downward, a pressing pressure is applied to the glass material 20. When the upper mold 11 is pushed downward and the upper surface of the upper mold and the upper surface of the body mold form the same surface, the press stroke downward of the upper mold 11 is once defined. Thereafter, when the upper surface of the upper mold and the upper surface of the body mold are formed on the same surface so that it can be further lowered following the contraction of the molded body due to cooling, a gap is formed between the flange portion 11a and the body mold small diameter portion 13a. In addition, it is preferable to determine the shapes and dimensions of the flange portion 11a and the trunk-shaped small diameter portion 13a.

  On the other hand, similarly to the upper mold 11, the lower mold 12 formed in a columnar shape is inserted into the lower through hole on the lower side of the trunk mold 13 in a fitted state. A flange 12 a on a circular plate is formed at the lower part of the lower mold 12, and the lower surface of the flange 12 a is in contact with the upper surface of the support substrate 32. The support substrate 32 receives a downward pressing pressure applied from the upper mold 11 to the lower mold 12 through the glass material 20. On the upper end surface of the lower mold 12, a second molding surface 15 including a concave shape for transferring a desired shape to the lower surface of the glass material 20 to form an optical functional surface is formed.

  By the press operation, the surface shape of the first molding surface 14 of the upper mold 11 is transferred to the upper surface of the glass material 20 to form an optical functional surface (concave surface), and on the lower surface of the glass material 20, The surface shape of the second molding surface 15 of the lower mold 12 is transferred to form an optical function surface (convex surface).

  In addition, around the molding apparatus 10, the body mold 13, the upper mold 11, and the lower mold 12 are heated, and the glass material 20 is heated through the body mold 13, the upper mold 11, and the lower mold 12. A heating means (not shown) is arranged.

(Molding material)
Although there is no restriction | limiting in particular in the shaping | molding raw material applied to the manufacturing method of this invention, A glass raw material is used suitably. For example, an optical constant having a refractive index (nd) of 1.55 or more and an Abbe number (υd) of 20 to 65 is generally usefully used as the concave meniscus lens according to the present invention. The glass having these optical constants is dropped or flown down from a molten state to a receiving mold and preformed into a predetermined volume and a predetermined shape, or glass preformed by a process such as cold grinding or polishing. It can be used as a molding material.
Further, a molding material having a volume larger than that of a desired lens can be used. At this time, it can press-mold so that the outer edge part of a shaping | molding material may become a free surface, and can perform the centering process of removing the outer edge part of a molded object after said 2nd shaping | molding process.

(Press molding process)
Next, a procedure for molding a concave meniscus lens using the molding die 10 configured as described above will be described.

(A) Mold Preheating Step The upper and lower molds 11 and 12 are preheated to a predetermined temperature by heating means such as a high frequency induction coil. The preheating temperature of the mold is, for example, 10 ⁸ to 10 ¹² dPaS equivalent in terms of glass viscosity. Regarding the mold temperature, if the temperature is excessively high, there is a problem of fusing to the molding surface of the glass. If the temperature is too low, there is a problem that the deformation of the glass material becomes insufficient. At this time, the temperature setting values of the upper and lower molds may be the same, and a temperature difference may be provided depending on the shape and size of the molded lens.

(B) Glass material supply process A glass material is conveyed between the preheated upper and lower molds, and is supplied and arranged on the molding surface of the lower mold. As the glass material, a glass material (preform) preformed in a predetermined shape with an appropriate volume (generally larger than the volume of the lens as the final product) is usually used. Such a glass material can be supplied to the mold after being softened to a viscosity suitable for molding. Alternatively, a glass material having a temperature lower than the temperature corresponding to the viscosity suitable for molding can be supplied between the upper and lower molds and further heated to a viscosity suitable for molding between the upper and lower molds. In addition, the temperature of the glass material when it is supplied to the mold is preferably 10 ^5.5 to 10 ¹² dPaS in terms of glass viscosity, and more preferably 10 ^5.5 to 10 ^8.5 dPaS.

  When the softened glass material is transported and placed on the lower mold, if the glass material comes into contact with the transport member and a defect occurs on the surface, the surface shape of the optical lens to be molded is affected. Therefore, it is preferable to use a jig that transports the softened glass material in a state of being floated by gas and drops and supplies the glass material onto the lower mold surface.

(C) Press molding process When the upper and lower molds and the glass material are each at a predetermined temperature, and the glass material is heated and softened, the lower mold is raised (or the upper mold is lowered) to press the glass material, and the upper and lower molds are formed. By transferring the molding surface shape of the mold, an optical element (for example, a concave meniscus lens) having a predetermined surface shape is molded. The lower mold is raised by operating a driving means (for example, a servo motor) connected to the cylinder, and the glass material is pressurized by raising the lower mold by a predetermined stroke. The pressurization schedule can be arbitrarily set according to the shape and size of the optical element to be molded.

  In the present invention, when forming a concave meniscus lens, it is a multi-stage press in which the pressure of the glass material is divided into two or more times, and cooling is started at the start of pressurization or in the middle of pressurization. A concave meniscus lens having accuracy is more preferable for obtaining an advantageous molding cycle time. For example, the cooling can be started after the first pressurization is performed with a predetermined load immediately after the glass material is supplied between the upper and lower molds or simultaneously with the first pressurization. Thereafter, secondary pressurization with a load smaller than the primary pressurization may be performed, and after the first pressurization, the load is once reduced or released, and the temperature is lowered to a predetermined temperature and then pressurized again ( (Secondary pressurization) may be performed.

The primary pressurizing load is suitably 30 to 300 kg / cm ² from the viewpoint of glass viscosity and prevention of breakage during deformation. The load of the second pressurization is preferably smaller than the load of the primary pressurization, for example, 10 to 80% of the primary pressurization, and preferably 20 to 150 kg / cm ² . By setting this range, it is preferable that a secondary pressure drop can be satisfactorily obtained and there is no possibility that the lens is broken.

(D) Cooling / mold release step While performing the above-described pressurization schedule and maintaining the adhesion between the molded optical element and the mold while cooling to a temperature equivalent to 10 ¹² dPaS by the viscosity of the glass, Release the press-molded product. The mold release temperature is preferably 10 ^12.5 to 10 ^13.5 dPaS.

  In addition, the cooling rate of a shaping | molding die can be 10-400 degreeC / min, for example. If the cooling rate is too slow, the cooling time becomes long and the production efficiency is lowered, and if the cooling rate is too fast, surface accuracy tends to deteriorate and cracks occur. In some cases, the upper and lower molds may be cooled at different cooling rates.

(E) Extraction step After the mold release, the press-molded product (optical element) on the lower mold surface is automatically extracted by, for example, an extraction arm having an adsorbing member.

(F) Centering step The released press-molded product can be subjected to a centering step as necessary. In particular, when molding is performed such that a free surface is formed on the outer periphery of the press-molded product, a concave meniscus lens having a desired shape can be obtained through a centering step.

(Making mold)
In the production method of the reference embodiment of the present invention,
A first molding step of obtaining a temporary molded product by press molding a molding material softened by heating using a primary mold having a first molding surface including a convex shape and a second molding surface including a concave shape;
A step of grasping the shrinkage rate on the first molding surface side and the shrinkage rate on the second molding surface side in the temporary molding product from the difference between the shape of the temporary molding product and the molding surface shape of the primary molding die, and
Based on the determined shape, the shapes of the first molding surface including the convex surface shape and the second molding surface including the concave surface shape of the secondary mold for obtaining the desired molded product based on these shrinkage rates are determined. A secondary mold production process for producing a secondary mold;
After that, a secondary mold, that is, a mold for product molding is produced,
Using the secondary mold, the molding material is press-molded to obtain a final product (second molding step).

(First molding process)
In the first molding step, a provisional molded product is obtained by press molding a molding material softened by heating using a primary molding die having a first molding surface including a convex shape and a second molding surface including a concave shape. The primary molding die is preferably produced based on the shapes of the first surface and the second surface of the molded product to be obtained. The primary mold is suitably made of the same material as the secondary mold. The press molding method and conditions are as described above.

(Shrinkage rate grasping process)
In the shrinkage rate grasping step, the shrinkage rate on the first molding surface side and the shrinkage rate on the second molding surface side in the temporary molded product are grasped from the difference between the shape of the temporary molding product and the molding surface shape of the primary mold. The shrinkage rate can be grasped based on the rate of change of the radius of curvature of the surface of the provisional lens molded by the molding surface with respect to the radius of curvature of the molding surface of the primary mold when the shape of the molding surface is spherical. . This point will be further described in the embodiments described later. When the molding surface shape is an aspherical surface, the contraction rate can be grasped by using the paraxial curvature radius instead of the curvature radius.

(Secondary mold making process)
In the secondary mold making process, the second mold surface including the convex shape and the second mold surface including the concave shape of the secondary mold for obtaining the desired molded product based on the shrinkage rate obtained in the above step. Each shape is determined, and a secondary mold is produced based on the determined shape. For both the primary mold and the secondary mold described above, the conventional method can be used as it is for producing the mold itself. Only the method of determining the shape of the first molding surface including the convex shape and the shape of the second molding surface including the concave shape may be performed by the method of the present invention.

(Second molding process)
In the second molding step, the molding material is press-molded using a secondary molding die to obtain a final product. The press molding method and conditions are basically as described above. Moreover, in this invention, if a secondary shaping | molding die can be produced, press molding of a shaping | molding raw material can be repeatedly performed using it, and a final product can be obtained continuously.

In the above reference embodiment, the shapes of the first molding surface and the second molding surface of the molding die are determined by molding the provisional lens. However, it is also possible to determine the shapes of the first molding surface and the second molding surface of the mold by correcting the shape based on the desired lens shape without molding the provisional lens. Hereinafter, this method (second embodiment (present invention) ) will be described.

  This method press-molds a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape, and a first surface including a concave shape; A manufacturing method including obtaining a meniscus lens having a second surface including a convex shape, wherein the molding die is manufactured by the following steps (1) and (2): .

(1) Based on the shape of the first surface (curvature radius R1 _LT0 at room temperature T0) and the second surface (curvature radius R2 _LT0 at room temperature T0) of the desired lens, the first molding surface and the second molding of the mold A correction step for determining the shape of the surface;
(2) A mold making step for producing a mold having the shape of the determined first molding surface (curvature radius R1 _MT0 at room temperature T0) and second molding surface (curvature radius R2 _MTO at room temperature T0).
A lens having a predetermined optical performance can be obtained by press-molding a glass material using the mold thus obtained. Press molding of the glass material can be performed in the same manner as described above.

The above method is based on the knowledge that the following relationship is approximately established as a result of the study by the present inventors.
(R _LT : Lens curvature radius at temperature T at which the lens is released from the mold after press molding
R _LT0 : radius of curvature of lens at room temperature T0 α _L : coefficient of thermal expansion of molding material at temperatures T0 to T)
(R _MT : Mold surface curvature radius at temperature T at which the lens is released from the mold after press molding
R _MT0 : radius of curvature of molding surface at room temperature T0 α _M : coefficient of thermal expansion of mold material at temperatures T0 to T)

At this time,
Then,
1 <r1 <r2
Holds.

Furthermore, the values of r1 and r2 are
Then, the present inventors have also found that a lens having excellent surface accuracy (for example, surface accuracy with asperity and habit within one Newton ring) can be obtained.

  Further, the present inventors have found that the above effect can be obtained when r1 is 0.980 to 0.999 times r2.

  When obtaining a lens having an aspheric surface on the first surface or the second surface, when determining the molding surface shape for molding the aspheric surface, in the above, the “curvature radius” is defined as the aspheric surface. A similar method can be performed by substituting an aspherical "paraxial radius of curvature", and such a method is also included in the present invention. Furthermore, by correcting the aspherical surface that defines the aspherical surface of the first surface or the second surface of the lens to be obtained, an aspherical surface that defines the shape of the molding surface that molds the aspherical surface is obtained. Is also possible. Hereinafter, this method (third aspect) will be described.

  The method includes pressing a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape, and the first surface including a concave shape. And a manufacturing method for obtaining a molded product having a second surface including a convex shape, wherein the molding die is produced by the following steps (1) and (2).

(1) Based on the shapes of the first and second surfaces of the desired molded product, the shapes of the first and second molding surfaces are determined by correcting the shapes of the first and second surfaces. Correction process,
However, the correction coefficient for determining the first molding surface shape of the molding die by correcting the shape of the first surface is r1, and the second molding surface of the molding die is corrected by correcting the shape of the second surface. Let r2 be a correction coefficient for determining
When the first surface of the desired lens has an aspheric surface represented by the following formula:
The shape of the first molding surface is an aspherical surface that converts an arbitrary point (x1, y1) on the aspherical surface of the first surface of the desired lens into (r1 · X1, r1 · Y1).
(Where K ₁ = K ₂ )
Furthermore,
When the second surface of the desired lens has an aspheric surface represented by the following formula:
The shape of the second molding surface, aspheric expression to convert an arbitrary point of (x2, y2) on the second surface of the aspheric the desired lens (r2 · X2, r2 · Y2 )
(Where K ₃ = K ₄ ), but
Is,
(2) A molding die producing step for producing the molding die by the determined aspherical shape of the first molding surface and the second molding surface.

  A lens (molded product) having a predetermined optical performance can be obtained by press-molding a glass material using the mold thus obtained. Press molding of the glass material can be performed in the same manner as described above.

  In the above aspheric expression, x is the distance in the optical axis direction from the tangent plane of the aspherical vertex to a point on the aspheric surface at a height y from the optical axis, R is the paraxial radius of curvature, and K is The conic constants B, C, D, and E are aspheric coefficients.

Also in the third aspect, the values of r1 and r2 are
Then, the present inventors have also found that a lens (molded product) having excellent surface accuracy (for example, surface accuracy equivalent to that of aston and habit within one Newton ring) can be obtained. Further, the present inventors have found that the above effect can be obtained when r1 is 0.980 to 0.999 times r2.

  Note that this method can also be applied to the case where either the first surface or the second surface of the lens to be obtained is a spherical surface, and such a case is also included in the present invention. That is, when determining the shape of the molding surface on the spherical surface side, it can be applied as a case where the coefficient is zero in the aspherical formula.

  Hereinafter, the production of a mold according to the present invention, particularly the production method of the present invention, will be described in more detail with reference to examples. The following examples are examples for explaining the present invention, and the present invention is not limited to these examples.

Reference example 1
Here, regarding the manufacturing procedure of the mold used for press-molding a desired concave meniscus lens, the lens diameter as shown in FIG. 2 is φ16.2 mm, the radius of curvature of the lens concave surface is 8.970 ± 0.005 mm, and the lens convex surface A concave meniscus lens with a side curvature radius of 48.980 ± 0.010 mm was press-molded using a borosilicate glass system (Tg = 500 ° C, Ts = 540 ° C, nd = 1.583, vd = 59.5) as a glass material. This will be described based on a reference example.

  First, a temporary lower mold having a temporary upper mold having a first molding surface including a convex shape and a second molding surface including a concave shape was prepared as a primary molding die (preparation of a first molding die). The radius of curvature of the convex surface of the temporary upper mold is the same as that of the concave surface of the lens to be obtained (8.970 mm), and the radius of curvature of the concave surface of the temporary lower mold is the radius of curvature of the convex surface of the lens to be obtained (48.980 mm). ).

Using these temporary mold and temporary mold (first mold), the glass material was subjected to primary molding under the following press conditions (primary molding step).
・ First press condition
Temperature: 600 ° C, Pressing force: 100kgf, Pressing time: 30 seconds ・ Cooling rate: -60 ° C / min, no temperature difference between upper and lower molds ・ Pressing condition in cooling process (second pressing condition)
Temperature: 530 ° C ~ 500 ° C, Pressing force: 50kgf
When the shape (curvature radius) of the provisional lens obtained by the primary molding process was measured, the curvature radius of the concave surface of the provisional lens was 8.940 mm and the curvature radius of the convex surface was 48.681 mm, as shown in Table 1. .

Here, the contraction coefficient ε of the provisional lens with respect to the primary mold surface can be calculated by Expression 1 shown below.

  When the contraction coefficient ε1 on the first molding surface side (the concave surface of the provisional lens) and the contraction coefficient ε2 on the second molding surface side (the convex surface of the provisional lens) are calculated from Equation 1, the contraction coefficient ε1 is 0.00334 respectively. (0.334%) and the shrinkage coefficient ε2 was 0.00610 (0.610%).

  Here, the term “shrinkage” refers to a change in the surface shape caused by the volume shrinkage of the molded body due to cooling, and the shrinkage coefficient means the degree of this change. That is, the contraction coefficient is grasped by the degree of change (decrease) in the radius of curvature of the surface of the provisional lens formed by the molding surface with respect to the radius of curvature of the molding surface of the primary mold. In the case of an aspheric lens, the paraxial radius of curvature can be used as the radius of curvature here.

As a result of grasping the contraction behavior, the inventors have found that when the concave meniscus lens is press-molded, the contraction coefficient ε1 on the concave surface side of the lens is always smaller than the contraction coefficient ε2 on the convex surface side. That is, in producing a secondary mold for obtaining a desired lens shape (curvature radius), the respective curvature radii of the first mold surface (convex surface side) and the second mold surface (concave surface side) of the first mold. As a result of examining how much is set, the shape of the secondary molding die is determined using the shrinkage coefficient ε or the correction coefficients r1 and r2 (the correction coefficient for the first molding surface and the correction coefficient for the second molding surface). Can be determined. Here, the correction coefficient is defined as follows.

  In the present invention, since the correction coefficient indicates the shrinkage behavior of the molding material, it is also referred to as a shrinkage rate.

A correction coefficient r1 for correcting the first molding surface of the primary mold and obtaining a desired lens shape, and a correction coefficient for correcting the second molding surface of the primary mold and obtaining a desired lens shape r2 has the following relationship between the contraction coefficient ε1 on the concave surface side of the lens and the contraction coefficient ε2 on the convex surface side.

  When the contraction coefficient ε1 = 0.00334 and the contraction coefficient ε2 = 0.00610 calculated by the above equation 1, the correction coefficients are r1 = 1.00335 and r2 = 1.00614, respectively.

  Here, in the case of a concave meniscus lens, the relationship between r1 and r2 is 1 <r1 <r2.

In the reference embodiment of the present invention, the radius of curvature of the secondary mold for press molding the concave meniscus lens to be finally obtained, the correction coefficient thereof, and the first molding surface (convex surface) of the primary mold. And a value obtained by multiplying the curvature radius of the second molding surface (concave surface) of the primary mold. That is, in this reference example, the radius of curvature of the first molding surface (convex surface) of the secondary molding die is 9.000 mm, and the radius of curvature of the second molding surface (concave surface) of the secondary molding die is 49.281. Produced (secondary mold making process).

  The glass material is press-molded under the same molding conditions as in the first molding step using the secondary molding die thus produced (the second molding step), and the resulting concave meniscus lens shape is obtained using a Fizeau interferometer. The results of the investigation are summarized in Table 2. For both concave and convex surfaces of the lens, the curvature relationship falls within the desired specification, and both the ass (non-axisymmetric shape error around the optical axis) and habit are within one Newton ring (this is an OK product). It can be seen that extremely good surface accuracy is obtained.

The concave meniscus lens press-molded in this reference example is a molded article having an outer diameter of φ16.2 mm as shown in FIG. In the figure of this molded product, a region outside the dotted line can be subjected to centering to obtain a concave meniscus lens whose outer peripheral portion is the processed surface.

Reference Examples 2-4
As in Example 1, except that the glass material, press conditions and lens shape were changed as shown in Table 3, the correction coefficient of the concave mold surface was selected within a predetermined range as the correction coefficient of the convex mold surface. A good concave meniscus lens was obtained.

In this reference example, an example of a spherical concave meniscus lens was introduced, but the reference aspect of the present invention can be similarly applied to an aspheric concave meniscus lens.

Example 5
The desired lens was a double aspherical concave meniscus lens, and a good lens was obtained by the following method.

  The desired lens shape was as shown in Table 4. Here, the correction coefficients of the first surface and the second surface are 1 <r1 <r2, specifically r1 = 1.003 and r2 = 1.008, respectively, and the coordinates of an arbitrary point on the aspherical surface of the first surface. Convert (x1, y1) to (r1, X1, r1, Y1), and convert the coordinates (x2, y2) of any point on the aspherical surface of the second surface to (r2, X2, r2, Y2) Such an aspherical expression was determined by calculation for each of the first surface and the second surface. This aspherical formula is shown in Table 5. And the shaping | molding die which has the shape shown to this Table 5 in each aspherical type of the 1st surface and the 2nd surface was produced, and the concave meniscus lens was press-molded using this.

The molding material used is the same borosilicate glass system (Tg = 500 ° C., Ts = 540 ° C., nd = 1.583, vd = 59.5) as in Reference Example 1, and the lens diameter is φ15.2 mm. With respect to the obtained lens, the shape error of the lens surface (PV value of the difference between the desired lens shape and the obtained lens shape) measured with a palpation type shape measuring instrument was within 0.3 μm.

* Here, each coefficient represents a coefficient of the following aspherical expression.
X = (Y ² / R) / [1+ [1- (1 + K) (Y / R) ² ] ^1/2 ] + BY ⁴ + CY ⁶ + DY ⁸ + EY ¹⁰

  Furthermore, the same results were obtained even when the glass material was fluorine-containing glass, high refractive low dispersion glass not containing lead, or the like. Needless to say, the present invention can be similarly applied to molding using other molding materials. Further, although the fifth embodiment has been described for both aspherical concave meniscus lenses, the present invention can also be applied to a concave meniscus lens having one aspherical surface and one spherical surface.

As described above, according to the molding method of the optical element as shown in the embodiments, it is not necessary to control the molding conditions with high accuracy by using a very basic apparatus similar to the conventional one. Thus, it becomes possible to mold an optical element having a shape difficult to mold with high accuracy.
Of course, the present invention can be applied to a modified or modified embodiment without departing from the spirit of the present invention.

  The present invention is as described above. When a concave meniscus lens is press-molded, the concave side and the convex side are corrected when the mold shape is corrected in advance to cope with the contraction of the lens from the press molding temperature to room temperature. By grasping the difference in shrinkage rate, it is possible to reduce the molding conditions and the number of times of mold correction, to obtain a predetermined surface shape relatively easily with high accuracy. As a result, troublesome processes leading to optimization of various conditions related to press molding such as cooling rate are shortened and tact time can be shortened. Can be mass-produced well. Also, if the behavior of the lens material in the cooling process after press molding is known in advance, it is possible to set the correction coefficient without actually performing the calculation process after molding the provisional lens. There is. Even in such a case, the predetermined surface accuracy can be obtained without repeating complicated steps by setting the concave-side correction coefficient and the convex-side correction coefficient in a predetermined relationship.

  The present invention can be used in the field of manufacturing lenses using a molding material such as glass.

It is sectional drawing which shows the structure of the shaping | molding apparatus employ | adopted in order to press-mold the concave meniscus lens concerning this invention in a 2nd shaping | molding process. Sectional drawing of a concave meniscus lens.

Claims (9)

A first surface including a concave shape, comprising pressing a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape; and a convex shape In a manufacturing method for obtaining a molded article having a second surface including:
The mold is produced by the following steps (1) and (2).
(1) Based on the shape of the first surface (curvature radius R1 _LT0 at room temperature T0) and the second surface (curvature radius R2 _LT0 at room temperature T0) of the desired molded product, the shape of the first surface and the second surface Correction step of determining the shape of the first molding surface (curvature radius R1 _MT0 at room temperature T0) and the second molding surface (curvature radius R2 _MT0 at room temperature T0) by correcting
However, the correction coefficient for determining the first molding surface shape of the molding die by correcting the shape of the first surface is r1, and the second molding surface of the molding die is corrected by correcting the shape of the second surface. Let r2 be a correction coefficient for determining
When
And, and
Correction coefficients r1 and r2 are set within the following ranges,
(2) A molding die producing step for producing the molding die according to the determined shapes of the first molding surface and the second molding surface.   A first surface including a concave shape, comprising pressing a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape; and a convex shape In a manufacturing method for obtaining a molded article having a second surface including:
  The mold is produced by the following steps (1) and (2).
(1) First surface of desired molded product (curvature radius R1 at room temperature T0) _LT0 ) And the second surface (radius of curvature R2 at room temperature T0) _LT0 ) Based on the shape of the first and second surfaces by correcting the shape of the first and second surfaces (the radius of curvature R1 at room temperature T0) _MT0 ) And the second molding surface (curvature radius R2 at room temperature T0) _MT0 Correction process for determining the shape of
However, the correction coefficient for determining the first molding surface shape of the molding die by correcting the shape of the first surface is r1, and the second molding surface of the molding die is corrected by correcting the shape of the second surface. Let r2 be a correction coefficient for determining
When
And the correction coefficient r1 is 0.980 to 0.999 times the correction coefficient r2.
(2) A molding die producing step for producing the molding die according to the determined shapes of the first molding surface and the second molding surface.   The manufacturing method according to claim 2, wherein the correction coefficients r1 and r2 are set within the following ranges, respectively.
A first surface including a concave shape, comprising pressing a molding material softened by heating using a mold having a first molding surface including a convex shape and a second molding surface including a concave shape; and a convex shape In a manufacturing method for obtaining a molded article having a second surface including:
The mold is produced by the following steps (1) and (2).
(1) Based on the shapes of the first and second surfaces of the desired molded product, the shapes of the first and second molding surfaces are determined by correcting the shapes of the first and second surfaces. Correction process,
However, the correction coefficient for determining the first molding surface shape of the molding die by correcting the shape of the first surface is r1, and the second molding surface of the molding die is corrected by correcting the shape of the second surface. Let r2 be a correction coefficient for determining
When the first surface of the desired molded article has an aspheric surface represented by the following formula:
The shape of the first molding surface is an aspherical expression that converts an arbitrary point (x1, y1) on the aspherical surface of the first surface of the desired molded product into (r1, X1, r1, Y1).
(Where K ₁ = K ₂ )
Furthermore,
When the second surface of the desired molded article has an aspheric surface represented by the following formula:
The shape of the second molding surface is an aspherical expression that converts an arbitrary point (x2, y2) on the aspherical surface of the second surface of the desired molded product into (r2, X2, r2, Y2).
(Where K ₃ = K ₄ ), but
R _LT0 is the radius of curvature of the desired molded product at room temperature T0 , R _MT0 is the radius of curvature of the molding surface at room temperature T0 ,
(2) A molding die producing step for producing the molding die by the determined aspherical shape of the first molding surface and the second molding surface. The manufacturing method according to claim 4 , wherein the correction coefficients r1 and r2 are set within the following ranges, respectively.
6. The manufacturing method according to claim 4, wherein the correction coefficient r1 is 0.980 to 0.999 times the correction coefficient r2. In press molding, after the first pressurization with a predetermined load is applied to the softened molding material, the molding material is cooled to a temperature lower than that at the start of the first pressurization and is smaller than the first pressurization. The manufacturing method according to any one of claims 1 to 6 , wherein a second pressure is applied by a load. The molded article is a concave meniscus lens, a manufacturing method according to any one of claims 1-7. The manufacturing method according to any one of claims 1 to 8 , wherein the molded product is a molded product having a free surface on an outer peripheral portion, and the molded product is subjected to a centering step to obtain a concave meniscus lens.