JPS61258718A - Plastic optical apparatus - Google Patents

Abstract

PURPOSE:To obtain the excellent rotational symmetry and high accuracy of surface shape, by arranging a molding gate for injection molding of molten resin in the center of the optical apparatus. CONSTITUTION:A lens body 1 consists of a gate 2, a spool 3 and a lens edge 4 and has a molding hollow 5 where a thin plate 6 such as a decoration plate is attached to cove the gate part 2. The spool 3 is cut from the gate part 2 and the decoration plate 6 is attached to put the cut part out of sight. Molten resin is spread uniformly in forming both convex and concave lenses by arranging the gate in the center of the lens to obtain a plastic lens of excellent uniformity and rotational symmetry without any weld-line.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to plastic optical devices such as plastic lenses used in optical systems used in television projectors, cameras, copying machines, and the like.

Conventional Technology In recent years, plastic molding technology has developed, making it possible to perform high-precision molding that was previously considered impossible.

Due to this, glass was traditionally used for optical devices such as optical lenses that required high precision, but with advances in plastic molding technology, high precision optical devices can now be manufactured by plastic molding. It became possible.

Glass lenses conventionally manufactured by polishing are mostly spherical lenses. Although it is possible to manufacture aspherical glass lenses by polishing, it is extremely difficult to mass produce.
Furthermore, it is expensive and is only used in some expensive equipment.

In comparison, with plastic lenses, both spherical and aspherical surfaces can be produced with no difference in difficulty, and there is no need for the multiple steps of polishing a glass lens, allowing for high precision in a very short period of time. This lens can be manufactured with a high degree of mass production.

Although plastic optical devices have many advantages as described above, in conventional plastic optical devices, a molding gate for injecting molten resin is provided on the outer periphery of the device. (For a conventional example, see Nikkei Mechanical No. 183, No. 10, pages 100-106, "Establishment of mass production technology for aspherical resin lenses, detailed improvements from design to molding") In a molded optical device that has a gate on the outer periphery of the optical device body, when molten resin is injected into the mold space, the molten resin gradually rises from the gate part and fills the mold space. The part located on the opposite side is filled last, completing the process.

This molding method in which the gate is located on the outer periphery has the following drawbacks. First, since the mold temperature is lower than the molten resin temperature, solidification starts from the molten resin injected into the mold space first. In other words, solidification of the resin starts from the resin near the gate, and the solidification of the resin that is later injected into the mold space becomes slower. Therefore, an imbalance occurs in the solidification start and end times, pressure distribution inside the molded product, resin density, etc. between the vicinity of the gate and the opposite side thereof, resulting in a slight difference in the refractive index.

Further, there is a problem in that the surface shape of the lens or the like is unbalanced between the gate portion and the opposite side thereof, or the intermediate portion of the other side, and the rotational symmetry with respect to the central axis is impaired. This rotational symmetry is extremely important and has a large influence on the imaging performance of lenses and the like. If the error occurs isotropically from the center of the lens toward the outer periphery, or if the error occurs rotationally symmetrically,
Compared to the absolute I of the error, the deterioration in imaging performance is small.Also, errors in the air distance between optical devices such as lenses may cause slight fluctuations in focal distance, but they have a very small effect on imaging performance. few. Therefore, rotational symmetry is extremely important in lenses and the like.

Here, FIGS. 3a and 3b show schematic diagrams of a concave lens. 11
1 is a lens body, 12 is a gate, and 13 is a spool.

With such a concave lens, the injected molten resin will
Since the center of the lens is thin, there is a large flow resistance, so it bypasses the center and penetrates υ times on both sides, meeting and joining on the opposite side of the gate. At this bonded portion, the resin is not completely fused and a line called a weld line 14 is generated. This weld line 1
No. 4 significantly impairs the quality of the lens.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a plastic optical device with excellent rotational symmetry and high precision in surface shape.

Means for Solving the Problems In order to solve the above-mentioned problems, the plastic optical device of the present invention has a molding gate for molten resin injection molding arranged in the center of the optical device. be.

According to the present invention, by arranging the molding gate at the center of the optical device as described above, the molten resin is evenly injected from the center toward the outer periphery, and the molten resin is ejected evenly from the center to the positions at equal distances from the gate. Molding is performed under the same conditions at positions where the radius is the same.

Therefore, it is possible to obtain a plastic optical device with extremely high rotational symmetry with the center of the optical device as the origin.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a sectional view of a plastic lens molding apparatus in one embodiment of the present invention. In FIG. 1, 1 is the lens body, 2 is the gate, 3 is the spool, 4 is the edge/scoba part, and 5 is the molded recess to which a thin plate 6 such as a decorative plate is attached to cover the gate part 2. .

FIG. 2 shows a state in which the spool 3 is cut from the gate 2 portion and a decorative plate 6 is applied to the molded recess 5 in order to hide that portion.

For example, if the diameter of the lens is 1001118 and the diameter of the decorative thin plate 6 is 10M, the proportion of the decorative thin plate 6 to the total area of the lens is 1%, and the decrease in brightness of the lens is virtually negligible. It is negligible.

Of course, the gate 2 may be placed on the opposite side.

By arranging the gate at the center of the lens in this manner, the molten resin spreads uniformly around both the concave and convex lenses, resulting in an extremely homogeneous plastic lens with good rotational symmetry and no weld lines.

Furthermore, the present invention is applicable not only to lenses but also to optical devices such as convex mirrors and concave mirrors made by molding. In other words, by vapor-depositing aluminum, chromium, etc. onto the precisely shaped optical device body made by injection molding as described above, spherical and aspherical concave and convex mirrors can be formed easily and accurately. It is possible to manufacture.

Effects of the Invention As described above, according to the present invention, by arranging a gate at the center of a plastic optical device such as a plastic lens, it is possible to obtain an optical device with good rotational symmetry and high surface shape accuracy. It is.

[Brief explanation of drawings]

1... Lens body, 2... Gate, 3
... Spool, 4 ... Lens edge part,
6... Molding recess, 6... Decorative thin plate. Name of agent: Patent attorney Toshio Nakao and 1 other person/
--- Lens failure No. 1 Figure 2 --- Rit 3
--- Nupur 5-11 concave sound p Figure 2 7-1-Lens heather body Otsu -11 Tatsukui City 7 route

Claims (2)

[Claims] (1) A plastic optical device characterized in that a resin injection gate for molding an optical device such as a lens is set in the center of the optical device. (2) The plastic optical device according to claim 1, wherein the resin injection gate provided in the center of the optical device is covered with a thin plate such as a plastic sheet or a thin aluminum plate.