JPH0254208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to plastic lenses.

Conventional lenses are typically made by molding and polishing the lens from glass. Therefore, the outer diameter is generally circular for convenience of polishing. Then, the polished lens is attached to a cylindrical mounting frame, and the optical performance is checked to see if it has shifted. If there is any shift, take measures such as rotating the lens to find a good position. I try to do this.

In addition, with conventional plastic molded lenses, parts of the plastic that protrude from the outer diameter of the lens, such as the injection gate part, are cut out, taking care not to distort the lens, and the glass lens is placed in a cylindrical lens holding frame. I am trying to install it in the same way as in the case.

However, in the case of plastic lenses, during injection molding, the plastic is squeezed at the injection gate and then diffused into the cavity where the lens body is to be molded, so optical distortion near the injection gate is avoided. I can't.
In order to reduce this optical distortion as much as possible, efforts are being made to match the shape and size of the gate part to various molding conditions, but it takes time and requires accumulation of experience and experiments, and it is impossible to completely eliminate optical distortion. It's almost impossible to do.

The purpose of the present invention is to prevent the imaging performance of the projection or photographic screen from being adversely affected even if some molding distortion or optical distortion occurs in the lens body when making a plastic lens by injection molding. Our goal is to provide a plastic cleanser made with

The present invention is characterized by focusing on the fact that the screen frames of various optical devices are rectangular in contrast to lenses with circular outer diameters, and that there are four quarter-moon-shaped parts that are not used as lenses. This is because parts that cause optical distortion, such as the injection gate, are arranged in the shaped part.

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

As shown in FIG. 1, the lens 1 is generally made to have a circular outer diameter for manufacturing reasons or for installation into a lens barrel. On the other hand, the actual screen frame of a camera, a copying machine, and various other optical devices is a rectangle, as shown by a two-dot chain line 2 in FIG. This screen frame 2 may be rectangular as shown, or square. In any case, since the screen frame 2 is rectangular, the crescent-shaped parts 1a, 1a, 1b, and 1b, each with one side of the screen frame 2 as a chord, are placed in four locations on the top, bottom, left, and right, and are not used as the screen frame 2. It will occur as a part. Therefore, if parts that cause optical distortion are formed in the crescent-shaped parts 1a, 1a, 1b, and 1b, such as the contact parts of injection gates, flow tabs, positioning pins, and extrusion pins, etc. Even if optical distortion occurs, this optical distortion will not extend within the screen frame 2 and will not have any adverse effect on imaging performance.

FIG. 2 shows an embodiment of the present invention based on such a concept, in which the outer diameter portions of the crescent-shaped parts 1a, 1a having the long sides of the rectangular screen frame 2 as the chords are shown. An injection gate part 3 for plastic molding is formed on the center line Y that bisects the screen frame 2 into left and right halves so as to face one of the long sides of the screen frame 2, and a flow tab 4 is formed at the opposite position. has been done. This flow tab 4 is used for overflow to adjust the flow of resin during plastic injection molding, but it can also be used as is for positioning. The outer diameter portions of the other crescent-shaped portions 1b, 1b, which are on the center line The abutment portions 5, 5 of the push-out pin are formed at antipodal positions. The contact portions 5, 5 can be used as positioning protrusions with respect to the lens mounting frame, as will be described later. Also,
The positioning protrusion 4 can also be used as a contact portion for an extrusion pin during mold release. Although there is a narrow portion 6 between the injection gate 3 and the lens body 1,
This narrow portion 6 is left with a predetermined amount of protrusion or cut off by excessive cutting in order to be used for positioning with respect to the lens mounting frame.

Figure 3 shows an example immediately after molding.
Several injection gate parts 3 protrude radially from one common sprue part 7, and lenses 1 are molded at the tips of these injection gate parts 3, respectively. That is, although this example shows a case where several lenses are molded at once, the present invention does not matter how many lenses are molded at one time, and instead molds one lens at a time. There is no problem.

By the way, as shown in FIG.
, the flow tab 4 and the push-out pin contact portion 5,
Optical distortion 8 occurs around a partially protruding portion such as 5. Particularly in the injection gate section 3, optical distortion is likely to occur because the plastic is squeezed during injection and then diffused into the cavity in which the lens body is to be molded. In addition, in the areas where the flow tab 4 flows out of the molded product, such as the contact areas 5, 5 of the ejector pins, the directionality and density of the resin flow are slightly different. Optical distortion also increases. Furthermore, around the contact parts 5, 5 of the extrusion pin, during demolding, the contact parts 5, 5
Optical distortion is also caused by the application of external force when the material is pushed by the ejection pin of the mold. Also,
For objects that cannot have a large outer diameter, it is also possible to place the push-out pin contact part outside the rectangle of the screen frame and push directly against the lens surface without providing a flow tab or push-out pin contact part. .

With this configuration, even if optical distortion occurs at the injection gate section or the contact section of the ejector pin,
This optical distortion does not extend to the screen frame, and deterioration of imaging performance is prevented.

By the way, even if the injection gate portion determines the arrangement of the positioning protrusions and the like based on how the screen frame will be taken during lens molding, it is not always possible to expect the desired effect if the mounting position with respect to the lens frame is uncertain. That is, the injection gate section or the like may be located on the diagonal of the screen frame, and optical distortion may extend from the corner of the screen frame into the screen frame.

Therefore, when using the plastic lens of the present invention, it is desirable to use it in combination with a predetermined lens mounting frame as shown in FIG. In FIG. 4, the lens mounting frame 10 has positioning grooves formed in its inner peripheral surface in the optical axis direction into which the flow tab 4 of the lens 1, the contact parts 5, 5 of the ejecting pin, and the narrow part 6 of the injection gate are respectively fitted. ing. Therefore, if the lens 1 is fitted in a predetermined position with respect to the mounting frame 10, the relative positional relationship between the lens 1 and the mounting frame 10 will always be constant, and it is possible to avoid the screen frame from being irregular. The effects of the present invention can be exhibited. The lens mounting frame 1 shown in FIG. 4 has a lens receiving part 12 formed at the inner peripheral edge by encircling a circumferential groove 11 around the lens receiving stepped part. It is adapted to receive the surface of the lens 1.

Such a lens mounting frame can be easily made by molding plastic, and by making a mold, it is possible to provide a lens mounting frame at low cost without compromising performance. Furthermore, since the lens mounting position is always constant, there is an advantage that the performance of the assembled lens can be evaluated by simply testing the performance of the molded lens alone. Furthermore, since positioning grooves are provided on the inner circumferential surface of the lens mounting frame, air flows through the grooves when the lens is fitted, and air is compressed and accumulated between the lenses while the lens is being assembled. Inconveniences such as irregular intervals can also be eliminated.

According to the present invention, in a circular plastic lens, the injection gate, the flow tab, and the contact part of the extrusion pin used during mold release, which cause distortion in the lens body during plastic molding, are used as a rectangular screen frame as a lens. Since it is arranged at a position opposite to the side of the injection gate, even if distortion occurs in the injection gate, this distortion is prevented from extending into the screen frame and adversely affects the imaging performance. Can be done. In addition, the above injection gate,
Since the contact parts of the flow tab and the extrusion pin are used as positioning members with respect to the lens mounting frame, the relative positional relationship between the lens mounting frame and the plastic lens can always be kept constant, and the relative positional relationship between the lens mounting frame and the plastic lens can be It is possible to prevent a problem in which a portion such as the injection gate that causes distortion in the lens body during plastic molding enters the rectangular screen frame due to misalignment.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the basic idea of the present invention,
FIG. 2 is a front view showing an embodiment of the present invention, and FIG. 3 is a perspective view showing an example of the manufacturing stage of the lens of the present invention.
FIG. 4 is a front view showing an example of a state in which the lens of the present invention is attached to a mounting frame. 1... Lens, 1a, 1b... Crescent-shaped part,
2... Screen frame, 3... Injection gate, 4... Flow tab, 5... Push-out pin contact portion, 6... Narrow portion, 8... Optical distortion, 10... Lens mounting frame.

Claims (1)

[Claims] 1. A plastic lens whose outer periphery is circular and the part used as the lens is a rectangular screen frame, and an injection gate that causes distortion in the lens body during plastic molding;
The contact portion of the flow tab and the extrusion pin used during mold release is arranged at a position opposite to the side of the rectangular screen frame, and the contact portion of the injection gate, flow tab, and extrusion pin is used as a positioning member with respect to the lens mounting frame. A plastic cleanser featuring: