TWI499563B - Method for producing glass preform, and - Google Patents

Description

Glass preform and manufacturing method thereof

The present invention relates to a glass preform for producing an optical glass such as a lens obtained by press molding, and a method of manufacturing the same.

In recent years, with the expansion of the use of digital cameras and the increase in functionality, the shape of lenses used has also been diversified, and the expectation of asphericalization of lenses of various shapes which have been increased in the past has been increasing. Further, for a convex shaped lens for an optical pickup, a steeply curved shape having a small radius of curvature is also required.

In order to produce such a lens, if only a glass preform having a spherical shape or an elliptical shape is used, the amount of deformation of the glass by pressing becomes large, so that it is difficult to obtain a desired shape with high precision. Therefore, in order to reduce the amount of deformation of the glass, a glass preform having a shape similar to the shape of the final lens has been proposed. Previously, such a lens-approximate shape glass preform was produced by grinding and grinding a glass cut out from a glass ingot, or by a simple pressing after manual pressing. In addition, a direct pressing method in which a high-temperature glass blank is press-formed can be cited (for example, refer to Patent Document 1).

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Special Publication No. 7-29781

When manufacturing a glass preform, it is necessary to accurately produce a size of a plurality of portions such as a thickness, a diameter, and a curvature of the target lens. In the case where a glass preform having a complicated shape is produced by grinding or grinding, variations in size are liable to occur, and there is a problem that the volumetric accuracy which is the most important characteristic of the glass preform is changed. Further, in the case of being produced by polishing, the grinding surface remains on the side surface, and dust such as glass frit is generated from the surface, thereby affecting the mirror quality of the lens. Moreover, when the grinding surface reaches the effective surface of the lens when pressing, there is also a problem that it becomes defective. Further, the steps in the method are complicated, and the amount of waste glass due to grinding and grinding increases, which causes problems in terms of cost or environment.

In the case where a glass preform is produced by manual pressing, it is necessary to apply a release agent to the stamper. The release agent is liable to adhere to the glass, and it is necessary to perform polishing in order to remove the release agent after pressing. In this case, the same problems as those described by grinding and grinding are also caused.

In the direct press manufacturing method, since the glass frit having a high temperature is in contact with the mold at a low temperature, only the portion of the glass blank that is in contact with the mold is quenched, and the deformation is insufficient, and the surface is likely to wrinkle. Further, since the glass blank is cut when the glass blank is supplied to the mold, there is a problem that it is necessary to remove the cut by polishing after pressing.

The present invention has been made to solve the above problems, and an object of the invention is to provide a glass preform having high volume accuracy, excellent surface quality, and low cost.

The inventors of the present invention have found that the above-mentioned problems can be solved by a glass preform obtained by subjecting a glass block to a specific step, and have been proposed as the present invention.

That is, the present invention relates to a glass preform characterized by comprising a molded body of a glass block, and the surface is not ground.

Since the glass preform of the present invention is produced by press molding using a mold, even when a complicated shape such as an aspherical surface is formed on the surface of the glass, the dimensional deviation is small (excellent in volume accuracy). Further, since the grinding and polishing steps after the press molding can be omitted, the surface precision is high (for example, the number of linear grooves due to polishing or the like is small). Further, the glass preform of the present invention is different from those previously produced by direct pressing, and has no defects such as wrinkles or cuts on the surface, and thus is excellent in surface quality. Therefore, in the lens obtained by press molding the glass preform, the optical image is hardly disturbed.

Further, since there is no problem of dust such as glass frit generated by grinding or polishing, it is possible to eliminate the production failure caused by the dust.

Second, the glass preform of the present invention is characterized by having a lens approximation shape selected from any one of a biconvex, a biconcave, a concavo-convex, a plano-convex, and a plano-concave.

Thus, the glass preform has a shape similar to the shape of the target lens, whereby the amount of glass deformation at the time of press molding can be reduced. Therefore, a lens having a desired shape can be obtained with high precision.

Third, the glass preform of the present invention is characterized in that the optical effective surface is aspherical.

When a glass preform having an optically effective surface having an aspherical shape is used, when the aspherical lens is produced, the amount of deformation of the glass during press forming can be small, so that the press forming time is shortened and the dimensional accuracy is improved. Advantage.

Fourth, the glass preform of the present invention is characterized in that the glass transition point of the glass block is 700 ° C or less.

By using a glass block having a relatively low glass transition point of 700 ° C or less, press molding becomes easy, and the glass preform of the present invention can be easily obtained.

Fifth, the glass preform of the present invention is characterized in that a rough surface derived from a stamper is transferred onto the surface of the glass preform.

Sixth, the glass preform of the present invention is characterized in that a rough surface derived from a stamper is transferred at a position other than the optical effective surface.

By press molding using the glass preform of this configuration, it is also easy to form a rough surface at a position other than the optical effective surface (for example, the top side of the lens) in the lens to be produced. Therefore, it is preferable that the black surface to be applied to the side surface of the lens to prevent the intrusion of external light from being easily adhered by the light diffused by the rough surface.

Seventh, the glass preform of the present invention is characterized in that the boundary portion between the optical effective surface and the side surface portion is convex curved.

In the glass preform, if a corner portion is formed at a boundary portion between the optical effective surface and the side surface portion, when an impact is applied from the outside, the stress applied to the corner portion becomes large and breaks. Even a small breakage may cause deterioration in volumetric accuracy, or the damaged glass piece may become dust, which may cause deterioration of the quality of the glass preform. Further, although the method of removing the corners by chamfering may be considered, when the method is employed, the number of steps is increased, resulting in an increase in production efficiency or cost. Moreover, the volumetric accuracy of the glass preform is lowered.

Eighth, the glass preform of the present invention is characterized in that a compressive stress layer is formed on the surface.

When a compressive stress layer is formed on the surface of the glass preform, the glass preform is strengthened by the difference in compressive stress between the surface and the inside, so that breakage during handling can be reduced.

Ninth, the present invention relates to a lens characterized by molding any one of the above glass preforms.

Tenth, the lens of the present invention is characterized in that a rough surface derived from a stamper is transferred at a position other than the optical effective surface.

Eleventh, the present invention relates to a method of producing a glass preform, comprising: forming a molten glass to produce a glass block of a specific shape; and molding the glass block using a mold having at least a concave portion or a convex portion.

Twelfth, the method for producing a glass preform of the present invention is characterized in that the glass block is heated to have a viscosity of 10 ⁹ dPa‧s or less before the press molding.

When the glass block is set in the mold in the cold room, and the glass block and the mold are heated, and the temperature rises to the vicinity of the softening point of the glass block, the press forming is performed, and each time the press forming requires heating and cooling of the glass block and the mold, and press forming is performed. It takes a long time. On the other hand, in the method for producing a glass preform of the present invention, the glass block is heated in advance to have a specific viscosity before the press molding, so that the time required for press forming can be greatly shortened.

The glass preform of the present invention can exhibit the following remarkable effects even when a complicated shape is formed on the surface of the glass: the volume precision is excellent, and the surface precision is high due to the omission of the grinding and grinding steps after the press forming, and There are defects such as wrinkles or cuts and the surface quality is excellent. Therefore, in the lens obtained by press molding the glass preform, the optical image is hardly disturbed. Further, in the glass preform of the present invention, since the grinding and polishing steps after the press molding can be omitted, the cost or environmental problems caused by the waste of the glass can be solved.

The glass preform of the present invention is characterized in that it is formed by molding a glass block, and is not subjected to a grinding treatment after press molding. The shape of the glass block is not particularly limited, but a glass preform having a desired shape can be easily obtained in an elliptical shape or a substantially spherical shape, which is preferable.

The shape of the glass preform of the present invention is not particularly limited, but is preferably a lens approximate shape selected from any one of a double convex shape, a double concave shape, a concave-convex shape, a flat convex shape, and a flat concave shape. The shape of the glass preform may be appropriately selected as long as it corresponds to the lens shape of the target.

Fig. 1 shows an embodiment of a glass preform of the present invention. Fig. 1(a) is a view showing a lenticular glass preform, (b) is a view showing a biconcave glass preform, and (c) is a view showing a embossed glass preform, (d) It is a figure which shows the glass preform of a flat convex shape, (e) is a figure which shows the glass preform of the flat-concave shape.

Further, as described above, the lens in which the glass preform of the present invention is molded is preferably formed with a rough surface derived from a stamper at a position other than the optical effective surface (for example, a side surface portion of the lens). Here, in the glass preform, a rough surface derived from the stamper may be formed at a position other than the optical effective surface, whereby a lens forming a desired rough surface can be easily produced. The rough surface formed here is formed by the polishing of the surface of the mold or the like, and the rough surface can be transferred to the glass surface at the time of press molding, and thus is formed by a dot-like or linear projection. On the other hand, in the case where the rough surface of the glass preform is formed by grinding, a dot or a line having a concave shape is formed. For example, in each of the glass preforms 1 of Fig. 1, a rough surface may be formed on the side surface portion S. Furthermore, the side portion S may have a curved shape.

The optically effective surface of the glass preform is preferably an aspherical shape. Examples of the aspherical shape include those in which the longitudinal cross-sectional shape is a secondary curve. Specifically, when the optical axis of the optical effective surface portion is aligned with the Z axis of the three-axis orthogonal XYZ coordinate system, the shape represented by the following formula (1) is usually used. Here, k is a conic constant that determines the shape of the secondary curve, and c is the central curvature (R is the central radius of curvature).

[Number 1]

In the glass preform in which the optical effective surface is expressed by the formula (1), the shape becomes the aspherical shape of the spheroidal surface by making the conic constant k satisfy the range of -1 < k < 0, especially -1 < k < -0.7.

The glass transition point of the glass block is preferably 700 ° C or lower, 650 ° C or lower, or 640 ° C or lower, and particularly preferably 630 ° C or lower from the viewpoint of easy press molding.

Preferably, the boundary portion B between the optical effective surface L of the glass preform and the side surface portion S is convex curved. The radius of curvature of the convex curved surface is preferably 10 μm or more, 100 μm or more, 500 μm or more, and more preferably 1 mm or more. When the radius of curvature of the convex curved surface is too small, when an impact is applied from the outside, the stress applied to the boundary portion B becomes large and breaks. The boundary portion B can be formed into a convex curved shape by, for example, the shape of the mold at the time of press molding of the glass preform.

Preferably, a compressive stress layer is formed on the surface of the glass preform. The compressive stress in the compressive stress layer is preferably 0.1 MPa or more, 1 MPa or more, 10 MPa or more, and more preferably 40 MPa or more. If the compressive stress is too small, it becomes easily broken during handling.

The material of the glass block is not particularly limited, and examples thereof include SiO ₂ -B ₂ O ₃ based glass, B ₂ O ₃ -ZnO-La ₂ O ₃ based glass, and TeO ₂ -B ₂ O ₃ -WO ₃ -La ₂ O. ₃ series of glass and the like. In addition, "~-glass" means a glass containing this component as an essential component.

However, in the glass preform of the present invention, there is a case where a rough surface, that is, a dot-like or linear protrusion is formed on the surface. In this case, the polishing damage formed on the surface of the mold is equivalent to the transfer to the glass surface at the time of press molding, and can be said to be a feature of the glass preform manufactured by press molding. The shape of the protrusion is 0.001 to 10 μm in line width and the height of the protrusion is 0.001 to 5 μm. If it is a dot, the diameter is 0.001 to 10 μm and the height is 0.001 to 5 μm. The projections present on the optically effective surface are preferably small, and the line width and diameter are preferably 2 μm or less, further 1 μm or less, and more preferably 0.5 μm or less. The rough surface derived from the stamper is preferably transferred to the glass preform except for the optical effective surface.

Next, a method of manufacturing the glass preform of the present invention will be described.

First, a glass raw material prepared to have a desired composition is melted to become molten glass. Next, the molten glass is formed into an ingot to obtain a glass material. Further, the obtained glass material is cut and polished to produce a glass block having a specific shape (for example, a substantially spherical shape).

It is preferred to preheat the glass block using an electric furnace or the like before performing press molding. The heating of the glass block is preferably carried out at a temperature at which the viscosity of the glass is 10 ⁹ dPa‧s or less, 10 ^7.6 dPa‧s or less, 10 ⁶⁵ dPa‧s or less, especially 10 ^5.4 dPa‧s or less. If the viscosity of the glass is too high, the time required for press molding tends to be long. On the other hand, if the viscosity of the glass is too low, the glass preform becomes high temperature, and the mold also becomes high temperature at the same time, and is easily deteriorated. Next, the heated glass block is filled in a mold having at least a concave portion or a convex portion heated to the vicinity of the softening point of the glass, and a pressing force is applied until a desired shape is formed, and press molding is performed. Here, in order to prevent deterioration caused by oxidation of the mold, the environment at the time of press molding is preferably vacuum or non-oxidation. Examples of the non-oxidizing gas include a reducing gas such as hydrogen or an inert gas such as nitrogen or argon. Among them, nitrogen can be preferably used because it is relatively easy to handle and inexpensive. After the press molding, the glass preform of a specific shape was obtained by slowly cooling to room temperature.

Further, in addition to the above-described production method, the glass block may be formed by dropping the molten glass onto a reverse conical mold and cooling it to form a substantially spherical shape such as a sphere or an ellipsoidal shape. At this time, in addition to cooling the glass which has been formed by dropping to room temperature, it is heated again until the viscosity of the glass becomes 10 ⁹ dPa ‧ or less and is supplied to the mold, and may be used in the cooling process of the glass formed by dropping. When the viscosity of the glass is 10 ⁹ dPa ‧ or less, the time is transferred to the mold and supplied to the press molding method.

The glass preform of the present invention is used for press molding, whereby a lens can be obtained. Here, the press molding method is not particularly limited, and the same method as the above-described press molding used in the method for producing a glass preform can be mentioned.

As a material of the stamper, a superhard metal such as SUS (Stainless Steel) or carbide, a Co-based or a carbon-based alloy can be used. When a mold release film is necessary, a carbon-based or nitride-based release film such as a noble metal such as Pt or a DLC (Diamond-like carbon) can be used.

Example

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to the examples.

(Example 1)

The glass raw material was blended to have a composition of SiO ₂ -B ₂ O ₃ system, and melted at 1300 ° C for 2 hours using platinum rhodium. After melting, the glass melt is formed into a pellet and annealed. After measuring the glass transition point of the obtained ingot, it was 500 °C.

The ingot is cut and ground to a desired size to produce a spherical glass block having a mirror surface. The glass block was heated in an electric furnace until the viscosity became 10 ^5.3 dPa ‧ and filled in a mold having a concave-convex shape until the viscosity of the glass became 10 ^10.3 dPa ‧ in a nitrogen atmosphere The press molding is performed by applying pressure until the desired shape is formed. After the press molding, the glass preform was obtained by slowly cooling to room temperature to obtain a concavo-convex shape as shown in Fig. 1 (c).

The shape and dimensions of the glass preform produced were as follows.

Outer diameter: 20.0 mm

Thickness (center): 3.0 mm

Radius of curvature 1 (concave): -20.0 mm

Curvature radius 2 (convex): -30.0 mm

Radius of curvature 3 (boundary part B): 700 μm

After measuring the volume deviation of 10 glass preforms produced in the same order, it was within ±0.1%.

Further, the compressive stress in the compressive stress layer on the surface of the glass preform was 48 MPa. The measurement of compressive stress is determined by photoelastic method.

The surface of the obtained glass preform is mirror-finished, and the surface undulations such as cuts or wrinkles are not present. Further, a linear protrusion caused by the polishing marks of the mold is formed on the surface of the glass preform. It has a line width of 0.5 μm and a height of 0.1 μm. Since the surface of the mold contacting the side surface is a mirror surface, the side portion of the obtained glass preform also becomes a mirror surface.

Using the obtained glass preform, press molding was carried out in the same manner as described above to obtain a lens having a concavo-convex shape. At this time, insufficient filling or cracking at the time of press molding did not occur. Further, the side portion of the obtained lens also becomes a mirror surface.

(Example 2)

The glass raw material is blended to form a composition of SiO ₂ -B ₂ O ₃ system and melted, and the glass melt is dropped from the nozzle onto the mold having an inverted conical shape, and cooled to be formed into an elliptical shape. The obtained ellipsoidal glass block was heated in an electric furnace until the viscosity became near 10 ^4.8 dPa ‧ and filled with a lenticular shape when heated to a temperature at which the viscosity of the glass became 10 ^8.6 dPa ‧ s In the mold of the shape, press molding is performed until pressure is applied under a nitrogen atmosphere until a shape is formed. After the press molding, it was slowly cooled to room temperature to obtain a lenticular glass preform as shown in Fig. 1 (a). Defects such as insufficient filling or cracking during molding, and fusion of glass and mold did not occur.

The shape and dimensions of the glass preform produced were as follows.

Outer diameter: 25.0 mm

Thickness (center): 5.0 mm

Curvature radius 1: 50.0 mm

Curvature radius 2: -50.0 mm

Radius of curvature 3 (boundary part B): 1400 μm

After measuring the volume deviation of 10 glass preforms produced in the same order, it was within ±1%.

Furthermore, the compressive stress in the compressive stress layer on the surface of the glass preform was 12 MPa.

The surface of the obtained glass preform is mirror-finished, and the surface undulations such as cuts or wrinkles are not present. Further, a linear protrusion caused by the polishing marks of the mold is formed on the surface of the glass preform. It has a line width of 0.1 μm and a height of 0.05 μm. Since the surface of the mold contacting the side surface is a rough surface, the side portion of the obtained glass preform also becomes a rough surface. The linear marks forming the rough surface are transferred to the mold surface by pressing, and have a convex shape.

Using the obtained glass preform, press molding was carried out in the same manner as described above to obtain a biconvex lens. At this time, insufficient filling or cracking at the time of press molding did not occur. Further, the side portion of the obtained lens also becomes a rough surface.

(Example 3)

The glass block obtained in Example 1 was subjected to press molding under the same conditions as in Example 1 except that the glass block was heated in an electric furnace until the viscosity of the glass became near the temperature of 10 ^4.6 dPa ‧ s. Glass preforms. At this time, a mold which is processed into an aspherical shape corresponding to the position of the optical effective surface is used so that the surface is formed with an aspherical shape.

The shape and dimensions of the glass preform produced were as follows.

Outer diameter: 20.0 mm

Thickness (center): 3.0 mm

Radius of curvature 1 (concave): -20.0 mm

Curvature radius 2 (convex): -30.0 mm

Cone constant k: -0.790

After measuring the volume deviation for each of the ten glass preforms produced in the same order, it was within ±1%.

The surface of the obtained glass preform is mirror-finished, and the surface undulations such as cuts or wrinkles are not present. Further, a linear protrusion caused by the polishing marks of the mold is formed on the surface of the preform. It has a line width of 0.1 μm and a height of 0.05 μm. Since the surface of the mold contacting the side of the glass preform is a rough surface, the side portion of the obtained glass preform also becomes a rough surface. The linear marks forming the rough surface are transferred to the mold surface by pressing, and have a convex shape.

Using the obtained glass preform, press molding was carried out in the same manner as described above to obtain a lens having an aspherical uneven shape. At this time, insufficient filling or cracking at the time of press molding did not occur. Further, the side portion of the obtained lens also becomes a rough surface.

The present invention has been described in detail with reference to the specific embodiments thereof, and it is understood that various changes or modifications may be added without departing from the spirit and scope of the invention.

The present application is based on Japanese Patent Application No. 2010-001123, filed on Jan. 6, 2010, and Japanese Patent Application No. 2010-261896, filed on The form is incorporated herein.

Industrial availability

According to the present invention, even when a complicated shape is formed on the surface of the glass, the glass preform having excellent surface quality can be obtained because of excellent volume accuracy, high surface precision, and defects such as wrinkles or cuts. Further, in the manufacturing step of the glass preform of the present invention, since the grinding and polishing steps after the press molding can be omitted, the cost or environmental problems caused by the waste glass can be solved. Further, it is also possible to obtain a lens in which the optical image is hardly disturbed by press molding the glass preform of the present invention.

1. . . Glass preform

B. . . Boundary part

L. . . Optical effective surface

S. . . Side section

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view showing an embodiment of a glass preform of the present invention. (a) a glass preform having a biconvex shape, (b) a glass preform having a biconcave shape, (c) a glass preform showing a concavo-convex shape, and (d) a glass preform having a plano-convex shape, (e) A glass preform that represents a flat concave shape.

1. . . Glass preform

B. . . Boundary part

L. . . Optical effective surface

S. . . Side section

Claims (12)

A glass preform comprising a molded body of glass blocks and having a surface that is not ground. A glass preform according to claim 1, which has a lens approximation shape selected from any one of a biconvex, a biconcave, a concavo-convex, a plano-convex, and a plano-concave. A glass preform according to claim 1 or 2, wherein the optically effective surface is aspherical. The glass preform of claim 1 or 2, wherein the glass transition point of the glass block is 700 ° C or less. A glass preform according to claim 1 or 2, wherein a rough surface derived from the stamper is transferred onto the surface of the glass preform. A glass preform according to claim 1 or 2, wherein a rough surface derived from the stamper is transferred at a position other than the optical effective surface. The glass preform of claim 1 or 2, wherein the boundary portion between the optical effective surface and the side portion is convex curved. A glass preform according to claim 1 or 2, wherein a compressive stress layer is formed on the surface. A lens formed by molding a glass preform according to any one of claims 1 to 8. A lens according to claim 9, wherein the rough surface derived from the stamper is transferred at a position other than the optical effective surface. A method of manufacturing a glass preform, comprising: forming a molten glass And manufacturing a glass block of a specific shape; and molding the glass block using a mold having at least a concave portion or a convex portion. The method of manufacturing the glass preform of claim 11, comprising: heating the glass block to a viscosity of 10 ⁹ dPa before performing the press forming. s below.