JP2011016671A - Method for manufacturing glass lens by hot-imprinting process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding a glass lens having sufficient properties without producing a void in the glass lens by a hot-imprinting process of pressing a heated glass plate material from the upper and lower direction using a side opening type mold.SOLUTION: The method for manufacturing the glass lens 5 from a glass plate material 1 includes a step of pressing the side opening type mold 2 to the glass plate material 1 at a temperature equal to or above a glass transition point that the glass plate material 1 exhibits to mold the glass plate material 1 into the glass lens 5 and the thickness of the glass plate material is controlled to ≥3 mm.

Description

  The present invention relates to a method of forming a glass lens from a glass plate material by a thermal imprint method.

  Currently, many electronic devices equipped with lenses such as digital cameras and mobile phones are on the market. Glass lenses and resin lenses are known as lenses. Although glass lenses are excellent in heat resistance, chemical stability, and optical characteristics, many low-cost resin lenses are used in general-purpose consumer equipment from the viewpoint of cost.

  Glass lenses are mainly manufactured by a press molding method in which a spherical or flat spherical preform whose volume and mass are controlled is heated and molded using a closed mold.

  On the other hand, as an efficient and economical technique for forming fine patterns, an attempt was made around 1995 to form a submicron-sized concavo-convex pattern on a semiconductor substrate in advance and press-transfer it directly or via a resist or the like. It was. This print transfer technique is called an imprint method, and has attracted attention in various fields since the beginning of the 21st century (see, for example, Non-Patent Document 1).

  The imprint method is capable of batch transferring fine uneven patterns from submicron to nanometer scale onto the substrate surface, and has been widely studied as a method for forming nano patterns on the surface of polymer materials. However, it is also expected as a technique for forming a fine uneven pattern on a glass material (see, for example, Patent Document 1).

  As one of the methods for forming a fine pattern on the glass surface using the imprint process, a thermal imprint method for transferring a fine pattern by pressing a mold against glass heated to a temperature higher than the softening point has been studied. ing.

JP 2009-107878 A

Masao Nakao, “Nanoprint and Nanoimprint Technology (Overview)”, Optronics, Optronics, Inc., July, 2006, No. 295, p. 136-137

  The present inventor aims to reduce the cost of glass lens molding compared to conventional glass lens press molding, and uses a side-open mold, and by a thermal imprint system that pressurizes a heated glass plate material from above and below. Glass lens molding was studied.

  However, it has been found that when a glass lens is molded by the above method, a gap is generated in the vicinity of the apex and the center of the bottom surface of the glass lens. This void was thought to be caused by the glass overflowing to the side of the mold.

  In view of the present situation, the present invention provides a method capable of forming a glass lens having sufficient properties without generating voids in the glass lens by a thermal imprint method in which a heated glass plate material is pressed from above and below. The purpose is to provide.

  As a result of various studies to solve the above-mentioned problems, the present inventors have used a glass plate material as a raw material having a thickness of 3 mm or more, so that a glass lens can be produced without generating voids in the glass lens. The inventors have found that it can be molded and have arrived at the present invention.

That is, the present invention is a method for producing a glass lens from a glass plate material,
Including a step of forming the glass plate material into a glass lens by pressing a side-open mold against the glass plate material at a temperature equal to or higher than the glass transition point of the glass plate material;
It is a manufacturing method of the glass lens whose thickness of the said glass plate material is 3 mm or more.

  According to the present invention, a glass lens having sufficient properties can be formed without generating voids by a thermal imprint method in which a heated glass plate material is pressurized from above and below.

Schematic which shows one Embodiment which concerns on the manufacturing method of this invention. Partially enlarged side view of the lens surface for conceptually showing an antireflective structure

Hereinafter, the embodiment of the present invention will be described in detail with reference to FIG.
First, the glass plate material 1 is prepared. The glass referred to in the present invention may be glass that can be used for a glass lens, and generally means silicate glass. Specific examples include BK7 (registered trademark) manufactured by HOYA and Tempax manufactured by SCHOTT.

BK7 has a composition of SiO ₂ : 69%, B ₂ O ₃ : 10%, Na ₂ O: 8%, K ₂ O: 8%, BaO: 3% (more than weight%), and softening point Is 724 ° C., the glass transition point is 580 ° C., and the coefficient of thermal expansion is 72 to 89 × 10 ⁻⁷ / ° C. On the other hand, Tempax is composed of SiO ₂ : 81%, B ₂ O ₃ : 13%, Na ₂ O: 4%, K ₂ O: 8%, Al ₂ O ₃ : 2% (more than weight%). The softening point is 820 ° C., the glass transition point is 525 ° C., and the coefficient of thermal expansion is 3.3 × 10 ⁻⁶ / ° C.

  The glass plate material is a glass material having a plate-like shape having a certain thickness. The shape of the glass plate material is not particularly limited. In the present invention, the glass plate material has a thickness of 3 mm or more as indicated by an arrow in FIG. Use of a glass plate having a thickness of less than 3 mm is not preferable because a gap is generated in the vicinity of the center of the glass lens after molding according to the present invention. By setting the thickness to 3 mm or more, the outflow of glass to the side of the mold can be suppressed, so it is considered that the voids are not generated. The upper limit of the thickness is not particularly limited, and can be set as appropriate depending on the usage status of the glass lens to be molded, and may be, for example, about 10 mm or less, or about 20 mm or less.

  The prepared glass plate material is loaded on the holding table 4 (FIG. 1A). The holding table 4 faces the plate 3 of the press machine. The plate 3 is connected to a driving device (not shown) that drives the plate 3 in the vertical direction, and pressure can be applied to the glass plate material 1 loaded on the holding body 4. Each of the holding table 4 and the plate 3 is designed so that the temperature can be controlled, and the plate 3 is designed so that the pressure applied to the glass plate 1 can be controlled. A mold 2 is mounted on the surface of the plate 3 facing the holding table 4.

  The mold 2 is a mold used to mold a desired glass lens, and holds the transferred concave mold facing the glass plate material 1. In the mold of FIG. 1A, a concave lens shape 2a is engraved at the center of the mold, and a planar region 2b is formed around it. The mold may have fine processing on the lens surface. With such a mold, a non-reflective structure or the like can be applied to the surface of the glass lens to be molded. According to this, a non-reflective structure can be provided on the lens surface simultaneously with convex or concave glass lens molding. As shown in FIG. 2, the non-reflective structure is formed by providing fine sawtooth irregularities on the lens surface. The distance between adjacent apexes (arrows in FIG. 2) is on the order of the wavelength of light, and the presence of such fine irregularities on the lens surface diffuses the reflected light, causing reflections and reflections. Can be prevented.

  The mold is required not to melt at a high temperature when a glass plate material is formed by a thermal imprint method. Since silicate glass has a high glass transition point, it is preferable to use a mold made of silicon carbide (SiC) ceramics having a very high melting point of about 2000 ° C. The mold may be made of single crystal silicon carbide or may be made of silicon carbide obtained by reaction sintering, but from the viewpoint of manufacturing cost, it is made of reaction sintered silicon carbide. Those are preferred.

  The surface of the mold is preferably coated with diamond-like carbon (DLC), metal such as gold or molybdenum, boron nitride, or the like in order to improve releasability from the molded glass lens. If such a surface treatment is not performed, the mold and the glass adhere and cannot be released. Although the thickness of the coating layer can be determined as appropriate, when fine processing for a non-reflective structure or the like is provided on the mold surface, the coating layer is provided so as to be sufficiently thinner than the size of the fine processing. For example, the thickness of the coating layer is preferably about 1/10 or less of the size of the fine processing. A specific numerical value of the thickness is about several μm.

  The shape of the mold can be produced by mechanical cutting, dry etching using a reactive gas, or the like.

  In a state where the glass plate material 1 and the mold 2 in FIG. 1A are not in contact with each other, the temperature of both the plate 3 and the holding table 4 is increased so that the glass plate material 1 and the mold 2 are equal to or higher than the glass transition point of the glass plate material 1. Heat to temperature. All of these are performed under vacuum conditions.

  In consideration of the glass transition point of the glass, it is preferable that the temperature at the time of heating is sufficiently high so that good transferability can be obtained. However, if it is too high, it is not preferable from the viewpoint of energy cost. Determine in consideration of When the glass is BK7, the heating temperature is preferably 700 ° C. or higher.

  Next, the plate 3 is driven downward to bring the surface of the glass plate 1 into contact with the planar region 2b of the edge of the mold 2 (FIG. 1B).

  Furthermore, when a predetermined pressure is applied to the glass plate material by the plate 3, the glass plate material is deformed along the shape of the mold, and the glass plate material 1 is formed into the glass lens 5 (FIG. 1 (c)). In the present invention, since the mold is of a side opening type, the surface of the holding body 4 and the flat surface 2b of the edge portion of the mold 2 do not adhere to each other at the time of pressurization, and the glass flows out from directly below the mold. become.

  After being molded, heating of the mold is stopped while maintaining this position and pressure. Thereby, the temperature of the glass lens is lowered. The holding time at this time is about 10 seconds to 2 minutes.

  When the temperature of the glass lens is lowered to below the glass transition point of the glass material, when the pressing is stopped and the plate 3 is driven upward, the molded glass lens is released (FIG. 1 (d)). . It is preferable that the temperature of the glass material at the time of mold release is a temperature lower by about 50 ° C. to 100 ° C. than the glass transition point. In this temperature range, it is possible to release the mold without affecting the properties of the glass lens.

  The obtained glass lens 5 has a convex lens portion 5a at the center and a parallel portion 5b around the lens portion 5a. The parallel portion 5b is a region formed by being sandwiched between the planar region 2b of the edge portion of the mold 2 and the surface of the surface of the holding body 4, and the thickness of the parallel portion 5b indicated by the arrow in FIG. Is thinner than the thickness of the glass plate 1. Further, around the parallel part 5b, a burr 5c is formed, which is formed by glass flowing out from directly under the side-open mold. FIG. 1D illustrates a state where the height of the burr is larger than the thickness of the parallel portion 5b, but the height of the burr is not limited to this.

  Optimum conditions regarding the temperature during heating, the degree of pressurization, and the holding time of heating and pressurization vary depending on the glass transition temperature, thickness, size, and the like of the glass plate used. Therefore, it is preferable to produce a stress / strain curve for each glass plate material by thermomechanical analysis (TMA), and to determine optimum molding conditions based on this.

  Although a convex glass lens can be manufactured by the above, the parallel part 5b and the burr | flash 5c can be suitably removed.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Example)
As a material of the mold, a reaction sintered silicon carbide plate (□ 30 mm, thickness 3 mm) manufactured by Nippon Fine Ceramics Co., Ltd. was used.

  A concave toric surface (R130 mm, R65 mm, maximum depth 0.5 mm) was ground on one surface of the silicon carbide plate. For grinding, an ultra-precision CNC grinder SGU52SXSN4 (manufactured by Nagase Integrex) was used.

  A concave mold was produced by coating a diamond-like carbon film having a film thickness of 1 μm by a conventional method on the concave toric surface of the ground mold.

As the glass plate material, BK7 (□ 30 mm, thickness 2 mm) manufactured by HOYA was used.
An imprint apparatus Reprina-T50 (manufactured by Origin Electric Co., Ltd.) is used as a molding machine. A concave mold is used as an upper jig in the vacuum chamber, and a concave toric surface coated with a diamond-like carbon film is directed downward. A flat mold (holding stand) was installed on the lower jig. A glass plate was loaded on the flat mold.

  First, after reducing the pressure until the degree of vacuum in the vacuum chamber reached 50 Pa, the upper and lower jigs were simultaneously heated to 700 ° C. under the vacuum. After reaching the target temperature, the upper jig was slid downward, and a preload of about 50 N was applied to the glass plate for 60 seconds. Then, it was pressed for a predetermined time (600 seconds or 1800 seconds) with a set load (1 kN, 2 kN, or 3 kN) and molded into a glass lens.

  After pressing, heating was stopped with the arrangement of the jigs fixed, and the mold was released after the temperature dropped to 550 ° C. Mold release was easily performed. After cooling to room temperature, the molded glass lens and mold were removed from the vacuum chamber.

  The cooling method includes furnace cooling (natural cooling) in the range of 400 ° C. or higher, air cooling in the range of less than 400 ° C. and 250 ° C. or higher, water cooling in the range of less than 250 ° C., and cooling by opening to the atmosphere in less than 100 ° C. Was also implemented.

  Under the above-described load and time conditions, the glass lens was molded without any problem. The thickness of the parallel portion 5b of the glass lens obtained under the conditions of 1 kN and 600 seconds was 1.7 mm. Further, the thickness of the parallel portion 5b is 1.4 mm under the conditions of 2 kN and 600 seconds; the thickness is 1.1 mm when the conditions are 3 kN and 600 seconds; the thickness is 1.2 mm when the conditions are 1 kN and 1800 seconds; A 0.8 mm glass lens was obtained.

  When the roughness of the molding surface of each glass lens was measured by Talisafe CCI6000 manufactured by Taylor Hobson, the roughness was 2 nmRa and 10 nmRz. That is, the molding surface of the glass lens could be finished to a mirror surface without voids.

  However, a concave mold in which the diamond-like carbon film was not coated on the concave toric surface was used, and the lens was molded under the same conditions. However, the mold and glass adhered, and the mold could not be easily released.

(Comparative example)
A glass lens was molded under the same conditions as in the examples except that the thickness of the glass plate used was 2 mm. Although a glass lens was formed, a minute gap was included in the vicinity of the center of the top and bottom of the lens, and it was not usable as a lens.

  From the above, it can be seen that by setting the thickness of the glass plate material to 3 mm or more, it is possible to mold a glass lens that does not include voids.

  According to the method of the present invention, there is a possibility that a large number of glass lenses can be formed at once from a simple glass plate material, and continuous production of glass lenses can be expected as in the case of progressive press forming of a metal plate material. For this reason, it becomes possible to mold a glass lens at a lower cost than the press molding method in which a hermetic mold is used.

1 Glass 2 Mold 3 Plate 4 Holding stand

Claims (3)

A method for producing a glass lens from a glass plate material,
Including a step of forming the glass plate material into a glass lens by pressing a side-open mold against the glass plate material at a temperature equal to or higher than the glass transition point of the glass plate material;
The manufacturing method of the glass lens whose thickness of the said glass plate material is 3 mm or more.   The method for manufacturing a glass lens according to claim 1, wherein the mold is made of silicon carbide ceramics. The glass mold manufacturing method according to claim 2, wherein a surface of the mold that is in contact with the glass plate is coated with diamond-like carbon, gold, molybdenum, or boron nitride.

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