JPH0352417B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a press mold used for molding glass lenses such as lenses for optical equipment such as cameras, or pick-up lenses for compact discs.

[Conventional technology]

In recent years, glass lens forming methods that directly press-form glass and eliminate the need for subsequent cold grinding and polishing have been widely used (for example, Japanese Patent Laid-Open Publication No. 171233/1983, Showa 60-
Publication No. 171236).

FIG. 7 shows an example of such a press molding apparatus. A softened glass material 10 is supplied to a lower mold 1, and an upper mold 2 is lowered thereon along a guide mold 3.
Press and press to form a glass lens into a predetermined shape. Next, the upper mold 2 is raised and a glass lens 4 as shown in FIG. 8 is taken out.

[Problem that the invention seeks to solve]

The glass lens 4 formed in this way is
Spherical or aspherical curved surface portion 5 effective as a lens
and a flat portion 6 made of surplus glass material located outside of the flat portion 6, but cracks 7 are likely to occur at the boundary between the two, which causes a drop in optical accuracy. This is because the curved surface portion 5 and the flat surface portion 6 are formed at a relatively small angle α according to the shape of the boundary between the curved surface processed portion 7 and the flat surface processed portion 8 of the lower die 1. This is thought to be due to large stress being concentrated in this area during the process, and the mold itself was also prone to breakage at the boundary.

[Means for solving problems]

In the present invention, the boundary between the curved surface processed portion of the mold and the flat surface processed portion located outside the curved surface processed portion is chamfered.

Chamfering may be performed on either a flat surface or a curved surface.

[Effect]

Since there are no sharp corners between the curved surface processed part and the flat processed part, the mold itself is less likely to be damaged, and such corners are not transferred to the glass lens to be formed, so that no significant stress concentration occurs.

〔Example〕

FIG. 1a is a sectional view showing an embodiment of the present invention, and FIG. 1b is a partially enlarged view thereof. The mold of this embodiment is composed of a lower mold 11, an upper mold 12, and a guide mold 13. The molding surface of the lower mold 11 consists of a spherical curved surface processed part 14 and a flat processed part 15 that constitutes the outer edge. A sloped surface 16 having an inclination of θ=30° is formed. Note that the curved surface processing portion 14 may be an aspherical surface depending on the desired lens surface. Upper mold 11, lower mold 12 and guide mold 13
is made of tungsten carbide (WC).

In the above configuration, the preform 1 is attached to the lower die 11.
7 is placed and the guide mold 13 is set, the entire mold is heated to soften the preform 17. In this state, the upper mold 12 is lowered and press molding is performed as shown in FIG. As the upper mold 12 descends, the preform 17, which is softening, has a curved surface portion 18 made of a spherical surface effective as a lens, a sloped surface 19, and a horizontal portion 20 in this order according to the shape of the molding surface of the lower mold 11. The shape of the glass lens is obtained.

FIG. 3 shows a glass lens 21 formed in this manner. Dimensions of each part are outer diameter D1 = 6.5mm,
The effective diameter of the curved surface portion 18, that is, the diameter of the effective portion through which light passes, is D2 = 4.6 mm, and the radius of curvature of the curved surface portion 18 is R1.
= 3.7 mm, center wall thickness t1 = 2.5 mm, wall thickness difference between the outer edge and center t2 = 1.2 mm, and θ with respect to the flat part 20.
It has a built-up portion 22 that forms a slope surface 19 of =30°. As the glass material, heavy flint optical glass SF6 (manufactured by HOYA Corporation; transition temperature 435°C) was used.

The angle α at which the tangent planes of the curved surface portion 18 and the plane portion 20 intersect, and the angle β at which the planes tangent to the curved surface portion 18 and the sloped surface 19 intersect, and the planes tangent to the slope surface 19 and the plane portion 20 intersect. Both angles γ (=180° - θ) are larger, and therefore, stress concentration is alleviated compared to a lens molded using a conventional mold in which the curved surface portion 18 and the flat portion 20 directly intersect. Ru. This also applies to the mold itself, and by chamfering this part, damage such as chipping is less likely to occur. As the radius of curvature of the curved surface processed portion 14 is smaller, the curved surface processed portion 14 and the flat surface processed portion 15 intersect at a sharper angle, so the effectiveness of chamfering increases.

The inclination θ of the sloped surface 14 is not limited to 30°, but is appropriately set depending on the radius of curvature of the curved surface processing portion 12 in particular. For example, when the radius of curvature is small, it is desirable to make the slope of the slope surface 14 relatively large.

Moreover, chamfering is not limited to chamfering on a flat surface such as the sloped surface 14. FIG. 4 shows a lower die 11A having a spherical surface 23 with a radius of curvature R2=1.0 mm. In this case, the angles formed by the tangent planes of the curved surface processing section 14 and the spherical surface 23, and between the spherical surface 23 and the plane processing section 15 are as follows:
In both cases, the maximum angle is 180°, and the effect of alleviating stress concentration is the most excellent. The rest of the structure is the same as that shown in FIG. 1, and a glass lens can be formed that differs only in the shape of the built-up portion 22 in FIG. 3.

The above description has been made using a mold for a plano-convex lens as an example, but it goes without saying that the present invention can also be applied to a mold for a biconvex lens. Similarly, for example, the fifth
By combining an upper mold 12B having a convex spherical molding surface 24 as shown in the figure with a lower mold as described above, a meniscus-shaped glass lens 21B as shown in FIG. 6 can also be molded. .

Further, the glass material is not limited to those mentioned above, and the present invention can be similarly applied to molding of a glass lens using a glass material having other components.

In addition to the above-mentioned tungsten carbide, the mold can also be made of glass materials such as silicon carbide (SiC), zirconium oxide (ZrO ₂ ), stainless steel, cermet, silicon nitride (Si ₃ N ₄ ), etc. It may be selected appropriately depending on the relationship.

〔Effect of the invention〕

According to the present invention, by chamfering the boundary between the curved surface processed portion and the planar processed portion, this portion is strong against impact and is less likely to be damaged. Generally, molds for glass lenses are expensive, but according to the present invention, the life of the mold can be extended. In addition, in the glass lens to be molded, stress concentration in the portion where the boundary portion is transferred is alleviated, the occurrence of cracks is prevented, and a glass lens with high optical precision can be obtained.

[Brief explanation of drawings]

FIG. 1a is a cross-sectional view showing an embodiment of the present invention, FIG. 1b is a partially enlarged view thereof, FIG. 2 is a cross-sectional view showing a press-molded state, and FIG. FIG. 4 is a cross-sectional view of a main part showing another embodiment of the present invention, FIG. 5 is a cross-sectional view showing still another embodiment of the present invention, FIG. 6 is a cross-sectional view of a lens to be molded, and FIG. FIG. 8 is a sectional view showing a conventional example, and FIG. 8 is a sectional view of a lens to be molded. 11, 11A... lower mold, 14... curved surface processing section,
15... Plane processed part, 16... Gradient surface (chamfered part), 23... Spherical surface (chamfered part).

Claims (1)

[Claims] 1. In a glass lens mold that presses the glass to be molded with opposing surfaces of the first and second molds and transfers the surface shape of each opposing surface to both main surfaces of the glass lens to be molded, the first and second molds A curved surface-processed part and a flat-processed part located outside the curved-surface-processed part are provided on at least one of the opposing surfaces, and a boundary between the curved-surface processed part and the flat-processed part is chamfered. Glass lens mold.