JPH0476932B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a mold for molding lenses by press molding and lenses molded by this mold, and more specifically, the present invention relates to a mold for molding lenses by press molding and lenses molded by this mold. The present invention relates to a lens molding mold that does not cause defects and a lens molded by this mold. (Prior art) In recent years, by press-molding a glass material in a mold with a predetermined surface precision,
Methods have been developed for forming highly accurate optical elements that do not require post-processing such as grinding and polishing. This type of molding method will be explained using FIGS. 3 and 4. Fig. 3 shows a state in which a softened glass material is housed in a mold and press-molded, and Fig. 4 shows a cross-sectional view of a glass molded product formed by the mold shown in Fig. 3. . The mold shown in the figure includes an upper mold 16 and a lower mold 17.
and a body mold 18, an upper mold 16 and a lower mold 17.
Each molding surface 16a, 17a is mirror-finished with high precision. A softened glass material 14 is supplied onto the lower mold 17 of this mold, and then the upper mold 16 is lowered and pressed by the pressure rod 15. This pressed state is maintained for a sufficient period of time for the surface shapes of the molding surfaces 16a and 17a to be transferred to the glass material 14, and then the entire mold is cooled as it is, and then the upper mold 16 is raised to form a glass molded product. Take out 14a. By the way, since there is some variation in the weight of the glass material supplied for such press molding, in order to obtain a glass molded product of a constant weight,
Surplus glass material 19 on the inner periphery of the upper end of the body mold 18
A relief part 13 is provided to release the glass material, and a surplus portion 19 of the glass material generated during press molding is extruded into the relief part to adjust the weight of the glass molded product. Note that the surplus portion of the outer periphery of the glass molded product constitutes a non-functional surface that does not need to function optically, and can be used, for example, as a mounting and holding portion for an optical lens. (Problem to be Solved by the Invention) The formed lens thus formed has an optically functional surface 14b formed by pressure transfer between the molding surfaces 16a and 17a, and an excess portion 19 of the glass material on its outer periphery. Molded optical non-functional surface 19
It has a. However, cracks 20 may occur in the resulting molded product at the boundary 20a between the functional surface 14b and the non-functional surface 19a. As for the cause of this, the present inventors believe that as the glass material inside the mold cools after press forming, a force acts to shrink the entire glass material in the mold toward its center, but the excess glass material 19 extruded into the relief part 13 , upper mold 16
Unable to follow the shrinkage of the glass material between the and lower mold 17,
For this reason, we have come to believe that the tensile stress concentrates on the boundary portion 20 where the stress is the weakest, causing local destruction of that portion. Such a phenomenon is particularly noticeable in the case of a lens shape in which the thickness of the excess glass material increases from the inner circumferential side toward the outer circumferential side, and can also occur when the thickness is the same. (Means for Solving the Problems) The above-mentioned problems are achieved by press-molding a glass material between an upper mold and a lower mold, forming an optically functional surface on the molding surface of each mold, and A glass material is placed on the outer periphery of the cavity formed by the upper mold, the lower mold, and the trunk mold so that an optically non-functional surface surrounding the optically functional surface is formed between the trunk mold surrounding the mold and the other mold. In a mold forming a relief part that receives a surplus portion of Part width...T Outer circumferential width in the optical axis direction of the relief part...T', (T-T')/(D'-D) Set so that the reduction rate expressed by the above formula is greater than 0.1. This problem is solved by a mold for molding a lens, which is characterized by: (Function) As described above, in the lens molding mold of the present invention, the relief portion through which the excess glass material is extruded during pressing is provided on the outer periphery of the cavity between the upper mold and the lower mold. The part formed by the relief part functions as a non-functional surface of the lens. Therefore, by making the above-mentioned relief part into a shape in which the area between the upper mold and the lower mold gradually decreases, the area between the upper mold and the lower mold including the body mold is designed to gradually decrease from the inner circumference to the outer circumference of the lens formed by this relief part. The shape is such that the thickness gradually decreases, and it easily follows the shrinkage of the glass material toward the center during cooling after pressing, and no stress concentration occurs at the boundary between the functional and non-functional surfaces. No cracks occur at the border of the lens. (Example) Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the lens molding die of this example, and FIG. 2 is an optical lens molded by the molding die shown in FIG. 1. The mold shown in FIG. 1 consists of an upper mold 2 and a lower mold 3.
The molding surfaces 2a and 3a of the upper mold 2 and lower mold 3 are mirror-finished to a predetermined shape corresponding to the functional surface of the optical lens to be molded. Further, a relief portion 5 is formed on the inner periphery of the upper end portion of the body mold 4. The relief portion 5 is shaped such that the groove depth gradually decreases from the inner circumferential side toward the outer circumferential side. The glass formed in this relief portion functions as a non-functional surface of the optical lens. In order to press mold an optical lens using this mold, the upper mold 2 is raised, a softened glass material is placed on the lower mold 3, and then the upper mold 2 is lowered to place the softened glass material on the lower mold 3. The mold 2 is pressed for a sufficient time to transfer the shape of the molding surfaces 2a, 3a onto the glass material 14, and then, after cooling the entire mold as it is, the upper mold 2 is raised to take out the glass molded product 6. In this way, a glass molded article 6 as shown in FIG. 2 is obtained. The mold of this embodiment as described above is shaped such that the groove depth of the relief portion 5 forming the lower non-functional surface 6b of the optical lens 6 gradually decreases from the inner surface to the outer surface, Moreover, since the shape is smooth from the relief part 5 to the forming surface 3a of the lower mold 3, when the glass in the mold as a whole contracts toward the center as it cools after press molding, the glass at the time of this contraction It is possible to easily follow the shrinkage of the glass on the molding surfaces 2a and 3a without hindering the movement of the glass, so that stress concentration does not occur at the boundary portion 6a, and an optical lens without cracks in this portion can be obtained. The above molding mold is composed of an upper mold, a lower mold, and a body mold, but the lower mold has the function of a body mold, and the lower mold has the above-mentioned relief. Even if a section is formed, the effect will not change in any way. More specific embodiments of the present invention will be described below. In the mold shown in the above embodiment, the upper mold 2
The radius of curvature R of the molding surface 2a of the lower mold 3 is 19.5 mm, the outer diameter of the lower mold 2 is 20 mm, and the upper mold 2 is lowered to contact the body mold. The width of the upper mold 2 at the innermost periphery 5a of the relief part 5 at the upper end of the body mold 4 is 1.2 mm, and the width of the upper mold 2 at the outermost periphery 5b of the relief part 5 is 1.0 mm. Using SF8 as the glass material, this spherical material with a diameter of 8 mm was supplied onto the lower mold 3, heated to 540°C in an N ₂ atmosphere, and 500 kg was released from the top of the upper mold 2.
Pressure was applied for 3 minutes, and then the mold was left as it was to cool the entire mold, thus obtaining the desired optical lens 6. No cracks were observed at the boundary 6a between the functional surface and the non-functional surface of the obtained optical lens, and the properties of the functional surface were also good. Incidentally, the width between the innermost periphery 5a of the relief part 5 of the body mold 4 when it contacts the upper end of the body mold of the upper mold 2 of the molding mold is 1.2 mm, and the width of the relief part 5 of the mold 4 is 1.2 mm. The width from the upper part 2 at the outermost circumference 5b of
When press molding was performed under the above conditions with a thickness of 1.3 mm, cracks were generated at the boundary portion 6a of the obtained optical lens. Here, in the mold shown in Fig. 1, the diameter of the outermost circumference of the relief part is D, the diameter between the innermost circumference of the relief part is D',
The width of the innermost peripheral part 5a of the relief part 5 when the upper mold 2 contacts the upper end of the body mold 4 is T, and the width of the outermost peripheral part 5b of the relief part 5 is T'. The radius of curvature of the functional surface is 31.5 mm, and the radius of curvature of the optical functional surface of the lower mold 3 is 19.5 mm. is "Yes" or "No"
) are listed in Table 1. In this table, the reduction rate indicated by * is the value obtained by (T-T')/(D'-D), that is, the non-functional surface 6b of the lens 6.
means the rate at which the lens thickness gradually decreases from the inner circumferential side to the outer circumferential side.

[Table] (Effects of the Invention) As explained above, according to the lens mold of the present invention, when the glass material shrinks during cooling after pressing, there is an excess of glass material that is formed at the relief part. Since the parts contract and move smoothly, stress concentration does not occur at the boundary between the functional and non-functional surfaces. Furthermore, the lens obtained using such a mold has no defects such as cracks at the boundary between the functional surface and the non-functional surface, and can be used as an optical lens with good surface precision.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the lens molding mold of the present invention, Figure 2 is a molded lens molded by the mold shown in Figure 1, and Figure 3 is a glass material softened by a press molding device. FIG. 4 shows a sectional view of a molded lens molded by the molding apparatus shown in FIG. 3. 2... Upper mold, 3... Lower mold, 4... Trunk mold, 5...
Relief part, 5a... Innermost circumferential part of the escape part, 5b... Outermost circumferential part of the escape part, 6... Molded lens, 6a... Boundary part.

Claims (1)

[Claims] 1 A glass material is press-molded between an upper mold and a lower mold, and an optically functional surface is formed on the molding surface of each mold, and a body mold surrounding one mold and the other mold are formed. A relief portion for receiving an excess portion of the glass material is formed on the outer periphery of the cavity formed by the upper mold, the lower mold, and the body mold so as to form an optically non-functional surface surrounding the optically functional surface between the molds. In the mold, the relief portion has the following characteristics: Outermost circumferential dimension of the relief portion...D' Innermost circumferential dimension of the relief portion...D Inner circumferential width in the optical axis direction of the relief portion...T Optical axis direction of the relief portion Molding of a lens characterized in that the reduction rate expressed by the above formula is set to be greater than 0.1, where outer peripheral width...T' is (T-T')/(D'-D) Usage type.