JPH0249617B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a plastic lens obtained by injection molding, injection compression molding, etc., in which a gate is bonded to a collar provided on the outer periphery of the lens part.
In particular, it concerns the shape of the brim.

[Background of the invention]

In recent years, plastic lenses have come to be used instead of glass lenses as constituent lenses in optical equipment such as video camera lenses. Such plastic lenses are made from thermoplastic plastics such as polymethyl methacrylate and polystyrene, and are made by injection molding or injection compression molding.
Lenses with a desired shape can be easily obtained with high precision, and productivity is improved compared to glass lenses, making it possible to reduce the cost and weight of lenses.

However, on the other hand, since the plastic material is heated during molding, residual stress cannot be avoided, and in order to form relatively high-precision lenses such as camera lenses, It is necessary to increase the roundness of the outer periphery of the lens to minimize the clearance with the lens barrel.

When a plastic lens is molded by injection molding or the like, the portion where internal stress occurs is near the gate that is integrally bonded to the plastic lens. For this reason, there is a lot of residual stress in the vicinity of the gate, and when a molded plastic lens is annealed, this residual stress causes deformation in the vicinity of the gate.

Therefore, in order to eliminate the influence of such residual stress, as shown in FIG. 1, a collar 2 is provided on the outer periphery of the lens portion 1, and a runner 3 is connected to the outer periphery of this collar 2 with a gate 3'. There is. According to such a conventional plastic lens, there is a lot of residual stress in the part of the collar 2 where the gate 3' is connected.
Residual stress in the lens portion 1 becomes extremely small. Therefore, even if annealing treatment is performed, almost no deformation occurs in the lens portion 1.

However, when cutting the gate 3' from the molded plastic lens, a tool such as a heated nipper is used to prevent the plastic lens from cracking.
As shown in FIG. 3, the cut portion 4 swells and deforms due to heat, resulting in a portion that protrudes by an amount a in the width direction and by an amount b in the thickness direction from other portions of the collar 2. . 2 is a plan view of the plastic lens shown in FIG. 1 after the gate is cut, and FIG. 3 is a cross-sectional view taken along the dashed line xx' in FIG.
Parts corresponding to those in FIG. 1 are given the same reference numerals.

Furthermore, since there is a lot of residual stress near the gate, when the molded plastic lens is annealed, the part of the collar 2 near the gate will deform, and the edge thickness of this part of the collar 2 will change. .

In this way, changes in the edge thickness of the flange near the gate and bulges at the cut portion of the gate impair the roundness of the outer diameter of the plastic lens due to the flange, making it difficult to attach such a plastic lens to a lens barrel. This caused the plastic lens to become eccentric or fall over.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
This prevents residual stress in the vicinity of the gate of the flange provided on the outer periphery of the lens portion, and the effects of deformation due to gate cutting, greatly improving the roundness of the lens outer periphery and the parallelism of the flange surface, allowing the lens barrel to be assembled with high precision. To provide a plastic lens that can be attached to, etc.

[Summary of the invention]

In order to achieve this object, the present invention makes the part of the collar near the gate joint part thinner than other parts of the collar, in response to the bulging deformation during gate cutting and the deformation due to residual stress during annealing. It is characterized by its narrow width.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a plan view showing an embodiment of the plastic lens according to the present invention, and FIG. 5 is a sectional view taken along the dashed line x-x' in FIG. Corresponding parts are given the same reference numerals.

In FIGS. 4 and 5, the collar 2 provided on the lens portion 1 consists of a portion where the gate 3' is joined and another portion, and the outer periphery of this other portion is set with a high degree of roundness. , the thickness is set to a constant value with high precision, and the two surfaces in the thickness direction maintain high parallelism.

On the other hand, the part where the gate 3' of the collar 2 is connected is
The width of the collar 2 other than this part is made narrower by A than the other parts, and the part including the gate 3' of the runner 3 is made thinner than the other parts to form a thin part 5. These A and B are 100μm
As shown in Figures 2 and 3, this is because the bulging deformation a and b when the gate is cut are 50 to 100 μm, respectively, and the deformation due to residual stress during annealing. This is because the only way to prevent this is to relieve the residual stress. That is, in consideration of the bulging deformation of the gate 3' when it is cut and the deformation due to residual stress, the gate 3' is attached at least 100 μm inward from the outer periphery of the collar 2, and the edge thickness of the thin part 5 is made smaller than that of the collar 2.
The thickness is 200 μm or more.

As mentioned earlier, the residual stress is caused by the gate 3'
(Fig. 4), the degree of residual stress due to photoelasticity is measured, and depending on the spread of residual stress, part or all of the thin wall portion 5 is quickly cut using a tool heated to around 200°C. do.

Fig. 6 is a plan view showing the plastic lens after the gate has been cut in this way, and Fig. 7 is a plan view showing the plastic lens after the gate has been cut in this way.
It is a cross-sectional view taken along the dashed line xx' in the figure, and 4 is a bulge, and parts corresponding to those in FIG. 4 are given the same reference numerals.

In FIG. 6, a bulge 4 is generated in the thin portion 5 due to the gate cutting of the thin portion 5, but the deformation in the lens radial direction is less than 100 μm.
It does not protrude from the surface including the outer peripheral surface of the collar 2, and since the deformation of the bulge 4 in the thickness direction of the collar 2 is 200 μm or less, it does not protrude from the surface including the surface of the collar 2.

In this way, the plastic lens after cutting the gate 3 is free of undesirable protrusions, and
Since the thin wall portion 5 is heated because a heated tool is used to switch the gate 3, the residual stress in the thin wall portion 5 is almost eliminated, and almost no annealing deformation occurs even when annealing is performed. do not have. Therefore, it is possible to obtain a highly accurate plastic lens that can be incorporated into a lens barrel with minimal clearance without eccentricity or tilting.

〔Effect of the invention〕

As explained above, according to the present invention, the outer diameter roundness and the edge thickness of the flange can be maintained with high accuracy without being affected by bulging deformation during gate cutting or deformation due to residual stress during annealing treatment. This makes it possible to provide a plastic lens with excellent functionality without the drawbacks of the prior art described above.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an example of a conventional plastic lens, Fig. 2 is a plan view showing the plastic lens shown in Fig. 1 after the gate is cut, and Fig. 3 is taken along the dashed line x-x' in Fig. 2. 4 is a plan view showing an embodiment of the plastic lens according to the present invention, FIG. 5 is a sectional view taken along the dashed line x-x' in FIG. 4, and FIG. 6 is a plan view of the plastic lens of FIG. FIG. 7 is a sectional view taken along the dashed line xx' in FIG. 6. FIG. 1...Lens part, 2...Brim, 3'...Gate,
4...Swelling part, 5...Thin part.

Claims (1)

[Claims] 1. A collar is provided on the outer periphery of the lens portion, and a runner gate is bonded to the collar by injection molding, injection compression molding, etc., and the gate is cut and heated. In the plastic lens obtained by the method, the portion of the brim to which the gate is bonded is narrower than the portion of the brim other than the portion to which the gate is bonded, and the gate is thinner than the brim. , the gate cut portion at the brim, which bulges and deforms when the gate is cut and deforms during the heat treatment, protrudes from a surface including the surface of the portion of the brim other than the portion to which the gate is bonded; A plastic cleanser characterized by being configured so as to prevent the above.