JP2006096579A - Method for forming optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming an optical element having a stable peripheral ridgeline profile and wall thickness. <P>SOLUTION: In the method for forming an optical element comprises forming a glass material which is softened by heating in a sealed space formed by each forming surface of an upper and a lower die composing a pair of molding dies and a surface of a cylindrical mold, press forming is started at a primary forming pressure. After the start, the speed of a pressing axis is detected, and when the speed is decreased to a predetermined speed or less and a predetermined retention time of the primary forming has elapsed, the primary forming pressure is switched to a secondary forming pressure. The secondary forming pressure is applied until a predetermined retention time of the secondary forming has elapsed so that the optical element has a target profile before cooling. Then, the optical element is cooled to complete forming and removed out of the dies. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for molding an optical element for processing a highly accurate optical element such as an aspheric lens by pressing a heat-softened glass material for molding with a pair of molds.

  Conventionally, there is known a method for obtaining an optical element by press-molding heat-softened glass, but at that time, not only both surfaces of the lens but also the outer diameter side surface are simultaneously molded, and the post-molding centering step is omitted. A method of obtaining a glass optical element has also been performed.

  At this time, the ridgeline formed by the molding surface of the upper and lower molds of the molded optical element and the outer diameter side surface (hereinafter referred to as the outer peripheral ridgeline) may cause burrs and excessive sagging, and thickness accuracy. May not be able to be secured.

  In order to solve such a problem, in Patent Document 1, when a glass material is formed, first, the upper mold is deformed halfway through molding and the movement is restricted by a spacer. A molding method is described in which a cavity is formed and then a glass material is further deformed by a lower mold.

Further, it is desirable that the shape of the outer peripheral ridge line is stable in order to prevent the optical element from being displaced or tilted when assembled into the lens barrel.
JP 2002-249327 A

  However, in the method described in Patent Document 1, the drive shaft must be provided in each of the upper mold and the lower mold, leading to an increase in the size and cost of the apparatus.

  Further, this is not a method for obtaining a glass optical element in which not only the both surfaces of the lens but also the outer diameter side surface are molded at the same time and the centering step after molding is omitted, but Japanese Patent Laid-Open No. 2000-302460 describes the following method. ing. In other words, the upper mold, the lower mold and the glass material are heated while contacting with a low pressure that can be deformed at the molding temperature. Then, after confirming that a predetermined time or more has passed in a state where the molding pressure is balanced, the optical pressure is taken out by switching to the holding pressure and cooling to the transition temperature or lower. However, since the upper mold and the lower mold are in contact with the glass material during heating, surface degradation such as reaction between the glass and the mold at a high temperature occurs, resulting in a problem in durability. In addition, when applied to the method of molding not only both sides of the lens but also the outer diameter side at the same time, molding with a constant molding pressure shortens the molding time. If the molding pressure is set low in order to avoid the generation of burrs, the molding time will be long. In the same publication, there is also described a method of shortening the processing accuracy and processing time by gradually increasing or decreasing the molding pressure according to the deformation speed depending on the characteristics of the glass material in the molding process. However, if this method is applied to the method of molding not only both sides of the lens but also the outer diameter side surface simultaneously, the pressure increases and decreases during molding, so the reaction force that increases as the glass material is filled with deformation in the cavity is increased. It will change, and the condition for maintaining the balance will become difficult, or the condition setting for that will become difficult.

  The present invention has been made in view of the above-described problems, and the glass optical element in which not only the both surfaces of the lens but also the outer diameter side surface are molded at the same time and the centering step after the molding is omitted is large and expensive. It is an object of the present invention to provide a method in which the outer peripheral ridge line has a stable shape without causing burrs or excessive sagging, and can ensure wall thickness accuracy.

  In order to solve the above-mentioned problems and achieve the object, the glass softened by heating in the sealed space formed by the molding surfaces of the upper mold and the lower mold and the surface of the body mold constituting the pair of molds according to the present invention. In the molding method of the optical element that molds the material, the press shaft speed is detected after the press molding is started with the primary molding pressure, and the set primary molding holding time has elapsed after the press shaft speed becomes lower than the set press shaft speed. At that time, the primary molding pressure is switched to the secondary molding pressure, the secondary molding pressure is pressed until the preset secondary molding holding time elapses, the cooling is performed, and the molding is finished. A method for molding an optical element is provided.

  As a result, it is detected that the glass material is filled in the cavity and has left a little deformation by changing the axial speed due to the change in the balance between the reaction force that increases with filling and the primary molding pressure, Since it shape | molds with the secondary shaping pressure to the target shape before cooling, it can be made to make the shape of an outer periphery ridgeline stable and stability of thickness accuracy irrespective of a glass weight.

  Further, in the molding method of the invention, the set press shaft speed is a speed at the time when the glass material is deformed to 110% or less of the optical element design wall thickness by the primary molding pressure under the molding temperature condition. An optical element molding method is provided.

  By appropriately obtaining the speed in a state where a slight deformation is left in advance, the primary molding pressure condition can be set without unnecessarily increasing the molding time.

  Further, in the molding method of the invention, the target shape of the glass material in the passage of the secondary molding holding time is an outer peripheral ridge line formed by each molding surface of the upper mold and the lower mold and the surface of the barrel mold, and an orthogonal cross section. There is provided a method for forming an optical element, characterized in that the radius of curvature of the intersecting line is 1 mm or less and the thickness is in the range of the optical element design thickness to 100 μm thick.

  Thereby, in consideration of deformation due to pressure during cooling to prevent sink due to shrinkage of glass due to cooling, it becomes possible to perform molding within a tolerance range of the design shape.

  Further, in the molding method of the invention, the secondary molding pressure is a preset pressure at which the press shaft speed is 5 μm / second or less when the secondary molding holding time elapses. A forming method is provided.

  Thereby, it is possible to perform molding in which the outer peripheral ridge line does not become burrs or excessively sag within an appropriate molding time.

  According to the glass optical element molding method of the present invention as described above, the final filling shape is obtained by utilizing the balance between the molding pressure and the reaction force accompanying the filling of the glass material into the cavity during molding. Since the outer peripheral ridgeline shape and thickness can be stabilized by switching to a balanced pressure, it is possible to stably produce at a low cost without the need for strict sorting of the glass material weight.

  The glass optical element molding apparatus and molding method of the present invention will be described below based on examples.

  FIG. 1 is a side cross-sectional view of a mold in the molding method of Example 1, and represents the end of molding. The molding surface of the upper mold 1 has a spherical convex shape, and the molding surface of the lower mold 2 has a spherical concave shape, and the value of the spherical surface R is smaller in the lower mold and a meniscus optical element is molded. Yes. A through hole is formed in the body mold 3 so as to communicate with the upper and lower sides, and an upper mold and a lower mold are accommodated. Further, the side surface forming part 3a of the optical element is formed continuously with the hole for housing the lower mold, and the upper mold tip diameter is 30 μm smaller than the diameter of the side surface forming part and inserted into the side surface forming part. A cavity is formed.

  First, a method for setting the deformation speed and the secondary molding pressure for switching from the primary molding pressure to the secondary molding pressure will be described. First, the upper die is raised by a press shaft (not shown) connected to the upper die, and the glass material 4 is supplied to the center of the lower die (FIG. 2). Next, the upper die, the lower die, the barrel die and the glass material are heated to a temperature capable of being molded by a heater (not shown) housed in the barrel die, and the upper die is lowered by the press shaft to perform press molding. In this process, as shown in FIG. 3, the glass material is deformed and filled in the cavity formed by the body mold, the upper mold, and the lower mold, and the optical surfaces of the upper mold and the lower mold and the inner diameter side surface of the cylinder mold are partially. It is transferred and the thickness becomes 110% of the optical element design thickness.

  The pressure (primary molding pressure) at this time is set to a pressure at which the glass material can be molded up to the optical element design thickness in about 10 seconds, and molding is performed at that pressure in advance, and the press shaft speed is obtained from the position information of the press shaft. FIG. 5 schematically shows the axial position graph, where a position where the optical element design thickness is obtained is t0, and a position where the optical element design thickness is 110% is t1. In this example, the speed when the thickness was 110% of the optical element design thickness (press axis position t1) was 30 μm / second from the slope of the graph. Next, the molding pressure is switched from a state where the wall thickness is 110% of the optical element design wall thickness, and the curvature radius of the intersection line between the outer peripheral ridge line and the orthogonal cross section is equal to or less than 1 mm, which is 100 μm thicker than the optical element design wall thickness. Molding to the state (target shape before cooling). FIG. 4 is an enlarged side sectional view of the vicinity of the outer peripheral ridge line of the target shape before cooling. The glass material is deformed and has a thickness of 100 μm thicker than the optical element design thickness, and Ra and Rb of the intersecting line between the outer peripheral ridge line and the orthogonal section are approximately equal in radius of curvature to 1 mm. Here, the secondary molding pressure is changed, and the press shaft speed when the target shape before cooling is obtained is obtained by creating a graph as shown in FIG. From this table, the pressure of 5 μm / sec is determined as 70% of the primary molding pressure. The shape for switching the molding pressure and the target shape before cooling can be adjusted so that the molding cycle, the durability of the molding die, and the like are achieved within an appropriate range.

  Next, a molding method using the set values obtained as described above will be described. Similar to the method for obtaining the set value, the upper die is first raised by the press shaft connected to the upper die, and the glass material is supplied to the center of the lower die (FIG. 2). Next, the upper die, the lower die, the barrel die and the glass material are heated to a temperature at which molding can be performed by a heater housed in the barrel die, and the upper die is lowered by a press shaft to perform press molding at a primary molding pressure. At this time, the press shaft speed is monitored, and after 2 seconds after the press shaft speed reaches 30 μm / sec, the press shaft speed is switched to a secondary molding pressure that is 70% of the primary molding pressure. By waiting for 2 seconds after the press axis speed reaches the set value, even if there is a variation in the weight of the glass material, the molding is surely performed up to a state where the thickness is 110% of the optical element design thickness. Thereafter, the mold is held for 15 seconds and molded to the target shape before cooling, and the mold and the molded optical element 5 are cooled to the transition point while maintaining the pressure (see FIG. 1). Then, the upper die is raised by the press shaft, the optical element on the lower die is taken out, the next glass material is supplied, and the molding is continuously performed (see the process diagram in FIG. 6).

  FIG. 7 is a side sectional view of a molding die in the molding method of Example 2 and represents a molding end point. The molding surface of the upper mold 6 has a spherical concave shape, and the molding surface of the lower mold 7 has a spherical concave shape, so that a double-sided convex optical element is molded. A through hole is formed in the body mold 8 so as to communicate with the upper and lower sides, and an upper mold and a lower mold are accommodated. Further, the side surface forming portion 8a of the optical element is formed continuously with the hole for accommodating the lower mold, and the upper die tip diameter is 50 μm smaller than the diameter of the side surface forming portion and inserted to the side surface forming portion. A cavity is formed.

  First, a method for setting the deformation speed and the secondary molding pressure for switching from the primary molding pressure to the secondary molding pressure will be described. First, the upper die is raised by a press shaft (not shown) connected to the upper die, and the glass material 9 is supplied to the center of the lower die (FIG. 8). Next, the upper die, the lower die, the barrel die and the glass material are heated to a temperature capable of being molded by a heater (not shown) housed in the barrel die, and the upper die is lowered by the press shaft to perform press molding. In this process, as shown in FIG. 8, the glass material is deformed and filled in the cavity formed by the body mold, the upper mold, and the lower mold, and the optical surfaces of the upper mold and the lower mold and the inner diameter side surface of the cylinder mold are partially. It is transferred and the wall thickness is 103% of the optical element design wall thickness.

  The pressure (primary molding pressure) at this time is set to a pressure at which the glass material can be molded up to the optical element design thickness in about 10 seconds, and molding is performed at that pressure in advance, and the press shaft speed is obtained from the position information of the press shaft. The press shaft speed was obtained in the same manner as in Example 1. In this example, the speed when the thickness was 103% of the optical element design thickness was 20 μm / second. Next, the molding pressure is switched from a state where the wall thickness is 103% of the optical element design wall thickness, and the curvature radius of the intersection line between the outer peripheral ridge line and the orthogonal cross section is equal to or less than 0.4 mm. The secondary molding pressure is changed as shown in Table 2 and the pressure at which the press shaft speed is 3 μm / sec is determined as 50% of the primary molding pressure. The shape for switching the molding pressure and the target shape before cooling can be adjusted so that the molding cycle, the durability of the molding die, and the like are achieved in an appropriate range, as in the first embodiment.

  Next, a molding method using the set values obtained as described above will be described. Similar to the method for obtaining the set value, the upper die is first raised by the press shaft connected to the upper die, and the glass material is supplied to the center of the lower die (FIG. 8). Next, the upper die, the lower die, the barrel die and the glass material are heated to a temperature at which molding can be performed by a heater housed in the barrel die, and the upper die is lowered by a press shaft to perform press molding at a primary molding pressure. At this time, the press shaft speed is monitored, and after 5 seconds after the press shaft speed reaches 20 μm / second, the pressure is switched to the secondary forming pressure which is 50% of the primary forming pressure, and the pressure after holding for 20 seconds is changed to the real glass material. The cooling of the mold and the glass material is started at the same time as the pressure is lowered to a low pressure at which deformation of the glass does not occur. In order to prevent sink marks due to the cooling of the glass from the time when the temperature of the mold is lowered by 15 ° C. from the press molding temperature, the mold is pressed again with the secondary molding pressure and cooled to the transition point (see FIG. 9). Then, the upper die is raised by the press shaft, the optical element on the lower die is taken out, the next glass material is supplied, and the molding is continuously performed (see the process diagram in FIG. 10).

  The present invention has the effects described above, and can be expected to be used in an optical element molding method for processing a highly accurate optical element such as an aspheric lens.

2 is a side sectional view of a molding die after molding in Example 1. FIG. 1 is a side sectional view of a mold before molding of Example 1. FIG. FIG. 3 is a side sectional view of a mold during the molding of Example 1. FIG. 3 is an enlarged side cross-sectional view of the vicinity of the outer periphery of the optical element before cooling in Example 1. It is a primary shaping | molding press axial displacement graph. 2 is a molding process diagram of Example 1. FIG. 5 is a side sectional view of a molding die after molding in Example 2. FIG. FIG. 6 is a side sectional view of a molding die before molding in Example 2. FIG. 6 is a side sectional view of a mold during the molding of Example 2. FIG. 6 is a molding process diagram of Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 6 Upper mold | type 2,7 Lower mold | type 3,8 Body type | mold 4,9 Glass material 5,10 Optical element 3a Side surface formation part 8a Side surface formation part Ra Intersection line of an outer periphery ridgeline and an orthogonal cross section Rb Outer periphery ridgeline and an orthogonal cross section Line of intersection

Claims (4)

  In an optical element molding method for molding a heat-softened glass material in a sealed space formed by the molding surfaces of the upper and lower molds constituting the pair of molding dies and the surface of the barrel mold, press molding with primary molding pressure After the press shaft speed is detected, the primary molding pressure is switched to the secondary molding pressure when the set primary molding holding time elapses after the press shaft speed falls below the set press shaft speed. A method for molding an optical element, comprising: pressing after a secondary molding holding time set in advance by a molding pressure, cooling, finishing the molding, and then taking out the optical element.   2. The optical according to claim 1, wherein the set press shaft speed is a speed at the time when the glass material is deformed to 110% or less of an optical element design wall thickness by the primary molding pressure under a molding temperature condition. Element molding method.   The shape of the glass material at the time of the secondary molding holding time is such that the radius of curvature of the line of intersection between the outer peripheral ridge line formed by the molding surfaces of the upper mold and the lower mold and the surface of the barrel mold and the orthogonal cross section is 1 mm or less 3. The method for molding an optical element according to claim 1, wherein the thickness is in the range of not less than the optical element design thickness to not more than 100 μm. The secondary molding pressure is set in advance to a pressure at which a press shaft speed is 5 μm / second or less when the secondary molding holding time has elapsed. 5. 2. A method for molding an optical element according to 1.