JPH1119956A - Method for molding plastic lens and plastic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily alleviate a strain in the inside of a plastic lens in a short treating time in the case of molding the lens. SOLUTION: A protrusion 20A located out of an optical surface effective range is heated by a rod heater 14 set to a critical temperature or higher of generating shrink. Then, thermoplastic resin molding material is compression molded to intentionally generate the shrink at the protrusion 20A by releasing a tensile stress in a molding 20 in its later cooling step. Thus, since the stress in the molding 20 is released, a strain in the molding 20 can be easily disappeared or reduced in a short treating time without annealing in a long time as prior art.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic lens molding method and a plastic lens, and more particularly to compression molding of a thermoplastic resin molding material in a mold and gradually compressing the compression molded thermoplastic resin molding material. The present invention relates to a plastic lens molding method for molding a plastic lens by cooling, and a plastic lens obtained by the molding method. In addition, shrinkage is a phenomenon in which a molded product made of a thermoplastic resin molding material or the like is a phenomenon in which the surface of the molded product is pulled and dented due to shrinkage of a portion of the molded product that is delayed in cooling, such as a central portion or a thick portion. Means

[0002]

2. Description of the Related Art In recent years, plastic lenses molded from a thermoplastic resin molding material have been widely used for optical components such as fθ lenses installed in image writing units such as copying machines and laser beam printers.

In such a plastic lens, a thermoplastic resin molding material is supplied to a mold having a predetermined shape, the thermoplastic resin molding material is compression-molded with the mold, and then the compression-molded thermoplastic resin molding material is formed. Is generally molded by taking out of the mold and gradually cooling it.

In the plastic lens molded in this way, when the compression molded thermoplastic resin molding material is removed from the mold, the thermoplastic resin molding material is rapidly cooled from the mold temperature to room temperature. A temperature difference occurs between the inside and the surface, and the surface solidifies first. After that, the inside of the thermoplastic resin molding material also solidifies gradually,
Tensile stress sometimes remains inside a plastic lens molded from the thermoplastic resin molding material. The residual tensile stress causes distortion in the plastic lens, and the distortion deteriorates the optical characteristics of the plastic lens.

As a technique for preventing the occurrence of such distortion, Japanese Patent Application Laid-Open No. Hei 5-329863 discloses a technique in which the temperature of a mold is set to be equal to or higher than the glass transition point of the resin molding material, and the mold is filled with the resin molding material. Techniques have been proposed for cooling slowly to minimize the occurrence of distortion. In addition, the applicant of the present invention provides a molded product after completion of molding at a temperature equal to or lower than the glass transition point (glass transition point −25 ° C. to −55 ° C.) for about 2 hours to 15 hours.
A technology for releasing residual strain by annealing for a time or a technology for releasing residual stress by applying an external force to a molded product after completion of molding at the time of mounting are proposed.

[0006]

However, the above-mentioned various techniques have a problem in that the processing time required for a cooling process and an annealing process for minimizing the generation of distortion becomes long, There is a problem that it is not easy to apply an appropriate external force to the product, and there is still room for improvement.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a plastic lens molding method capable of easily relieving distortion in a short processing time and a plastic lens molded by the molding method. The purpose is to provide.

[0008]

According to a first aspect of the present invention, there is provided a method for molding a plastic lens, wherein a thermoplastic resin molding material is compression-molded in a mold, and the compression-molded thermoplastic resin molding material is formed. By gradually cooling
A plastic lens molding method for molding a plastic lens, wherein a sink is intentionally generated in a predetermined portion of a thermoplastic resin molding material during the compression molding.

That is, in the method of molding a plastic lens according to the first aspect, when a thermoplastic resin molding material is compression-molded with a mold, a sink is intentionally generated in a predetermined portion of the thermoplastic resin molding material. Then, a plastic lens is molded by gradually cooling the compression molded thermoplastic resin molding material.

FIG. 2 shows that APO (a copolymer of ethylene and a bicycloalkene or a cyclic olefin such as a tricycloalkene using a coordination catalyst of a soluble vanadium and an organoaluminum compound) generates relatively large distortion. 3 shows a temperature-specific volume (volume per gram) characteristic curve of the combined sample. FIG. 3 shows a temperature-specific volume (volume per gram) characteristic curve of PMMA used as an optical plastic material with little distortion.

From FIGS. 2 and 3, the change in the specific volume (volume per gram) of each material which occurs during the cooling of the molded product from immediately after removing the mold to room temperature is 0.04% for APO.
52 cm ³ / g compared to 0.028 for PMMA
cm ³ / g. In other words, it can be seen that the greater the change in specific volume, the more strain is generated.

From this, it is presumed that distortion occurs due to the following mechanism. 1) After removal of the mold, the plastic lens molded product comes into contact with the environmental temperature, so that a temperature difference occurs between the surface and the inside of the plastic lens molded product. 2) begin to solidify from the surface that first comes into contact with the ambient temperature. 3) Even after the surface has solidified, the temperature of the interior that has not yet solidified falls. 4) The specific volume inside the plastic lens molded product changes (the volume tends to decrease). 5) Since the internal volume tends to be smaller than the solidified surface, a tensile stress acts on the surface. 6) When the inside solidifies while the tensile stress is acting,
Tensile stress remains in the plastic lens molded product, causing distortion (see FIG. 4A).

Thus, it can be seen that the cause of the distortion in the plastic lens molded product is the tensile stress inside the molded product.

On the other hand, as shown in FIG. 4B, when the surface of the plastic lens molded product has a large tensile stress and the surface is deformed and sink marks occur, the tensile stress inside the molded product is released. The occurrence of distortion is reduced.

FIGS. 5 (A) and 5 (B) show that sink and sink occur due to shrinkage caused during cooling. When the sink rate is large when finally settled to room temperature (not shown in FIG. 5A, for example, the sink rate is -1 m).
m), the color of the distortion becomes orange and the distortion is reduced. On the other hand, when the amount of sink when finally settling down to room temperature is small (at the time of −0.3 mm or less shown in FIG. 5A), the color of the distortion is blue and the distortion is the largest.

From the above, it can be seen that by generating sink marks in a plastic lens molded product, the tensile stress inside the molded product can be released and the occurrence of distortion can be reduced.

[0017] Therefore, as in the method for molding a plastic lens according to the first aspect, a predetermined portion of the thermoplastic resin molding material is intentionally shrunk at the time of compression molding, thereby releasing the tensile stress inside the plastic molded product. And
Distortion can be easily eliminated or reduced. In addition, since an annealing step after molding is not required, there is an advantage that the molding processing time of the plastic lens can be significantly reduced.

The predetermined portion of the thermoplastic resin molding material that causes sink marks should be set to a portion other than the portion functioning as a lens (ie, outside the effective range of the optical surface). Is desirable.

By the way, in order to intentionally generate a sink in a predetermined portion of the thermoplastic resin molding material at the time of compression molding, the plastic lens molding method according to claim 3 is employed. can do.

In the plastic lens molding method according to the third aspect, the thermoplastic resin molding material is supplied to a mold, and the mold is used to heat a predetermined portion of the thermoplastic resin molding material to a temperature higher than a critical temperature at which sink occurs. Then, the thermoplastic resin molding material is compression-molded into a predetermined shape. As a result, sink marks occur at predetermined portions of the thermoplastic resin molding material. After that, the compression molded thermoplastic resin molding material is gradually cooled to form a plastic lens having a predetermined shape.

In this manner, the plastic lens according to claim 5, that is, the thermoplastic resin molding material is supplied to a mold, and the mold is used to cause a predetermined portion of the thermoplastic resin molding material to exceed a critical temperature at which sinking occurs. After heating, the thermoplastic resin molding material is compression-molded into a predetermined shape, and the compression-molded thermoplastic resin molding material is gradually cooled to complete a plastic lens.

The mold used in the plastic lens molding method according to the third aspect of the present invention is, as described in the fourth aspect, provided that any part of the supplied thermoplastic resin molding material is at or above the critical temperature at which sinking occurs. It is desirable that the material can be heated to a high temperature. By using such a mold, it is possible to generate sink marks in an arbitrary portion (for example, a portion other than a portion functioning as a lens) regardless of the shape of the molded plastic lens. The degree of freedom is improved.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the plastic lens molding method according to the present invention will be described below.

[Device configuration for generating sink marks] As described above, the present invention is characterized by intentionally generating sink marks during molding of a plastic lens. Will be described.

FIGS. 6A and 6B are schematic views of a mold slide piece 12 used in the present embodiment. The arrow W direction indicates the longitudinal direction of the molded thermoplastic resin molding material (hereinafter, referred to as molded article) 20. An arrow X direction indicates a beam transmission direction of the plastic lens obtained from the molded product 20, and an arrow Y direction orthogonal to the beam transmission direction indicates a beam non-transmission direction of the plastic lens.

As shown in FIGS. 6A and 6B,
Two rod heaters 14 are provided on the slide piece 12 by arrows W.
It is buried along the direction. The temperature of the rod heater 14 is adjusted by a temperature adjustment unit (not shown).

The slide piece 12 is provided with a concave portion 12A whose depth is in the direction of arrow Y. Therefore, the molded product 20 has a convex portion 20 corresponding to the concave portion 12A.
A will be formed. Since the protrusion 20A protrudes in the beam non-transmission direction (the direction of the arrow Y), the influence of the provision of the protrusion 20A on the optical characteristics of the plastic lens is avoided.

The dimensions of the molded product 20 are shown in FIG.
The dimension t in the direction of the arrow Y including the projection 20A shown in FIG.
Is set to be larger than the dimension CT in the arrow X direction. This has the advantage that even if the amount of sink marks increases, there is no possibility that the sink marks will affect the optical characteristics.

[Plastic lens molding process] Next, a plastic lens molding process based on the plastic lens molding method according to the present invention will be described with reference to FIG.

In step 1 of FIG. 1, the thermoplastic resin molding material is supplied to the mold, and in the next step 2, the thermoplastic resin molding material is molded into a predetermined shape by the holding pressure or compression pressure of the mold.

In the present embodiment, in the molding step of step 2, the temperature of the rod heater 14 shown in FIG. The molded article 20 is obtained by molding the plastic resin molding material into a predetermined shape. Then, the molded product 20 is gradually cooled for a predetermined time.

In the process of gradually cooling the molded product 20 as described above, the molded product 20 solidifies from the surface thereof, and even after the surface is solidified, the temperature inside the molded product 20 decreases. The specific volume inside the molded product 20 decreases, and the molded product 2
Inside 0, tensile stress acts on the already solidified surface.

In this embodiment, since the protrusion 20A is heated by the heat of the rod heater 14 set to a temperature higher than the critical temperature at which sinkage occurs, the tensile stress on the surface of the protrusion 20A is smaller than the tensile stress on other portions. 6C, and sink marks occur on the surface of the projection 20A as shown in FIG. Due to the occurrence of the sink mark, the tensile stress inside the molded article 20 is released, and the distortion inside the molded article 20 is eliminated or reduced.

By the way, since the projection 20A protrudes in the beam non-transmission direction (the direction of arrow Y), even if the projection 20A has sink marks as shown in FIG. The plastic lens 20B does not enter the portion of the plastic lens obtained from the molded product 20 which functions as a lens (the area below the dotted line K in FIG. 6C), and the influence on the optical characteristics of the plastic lens is avoided. .

Thereafter, in step 3, the molded product is removed from the mold, and the appearance of the removed molded product is checked. This external appearance check is carried out visually, and checks for voids and foreign matter, and checks for distortion due to a polarizing plate, etc. With respect to the molded product determined to have no abnormality by such an appearance check, the profile, distortion, and transmittance are measured in step 4 after 24 hours, the measurement results are evaluated, and the plastic lens molding process is completed. .

According to the embodiment described above, the convex portion 20A is heated by the rod heater 14 set at a temperature higher than the critical temperature for sinkage in the plastic lens molding step, so that the convex portion 20A is cooled in the subsequent cooling process. Since the sink occurs in the 20A, the tensile stress inside the molded product 20 can be easily released in a short processing time without performing long-time annealing or the like as in the prior art, and the distortion inside the molded product 20 can be eliminated or eliminated. Can be reduced.

The rod heater 14 shown in FIG.
Alternatively, a heater capable of heating an arbitrary portion of the supplied thermoplastic resin molding material to a temperature higher than the critical temperature at which sink occurs may be used. In this case, regardless of the shape of the plastic lens to be molded, an arbitrary portion of the thermoplastic resin molding material can be heated to a temperature higher than the critical temperature for sink generation, and sink can be generated in the portion. This has the advantage that the degree of freedom of the process for intentionally generating the is improved.

[0038]

As described above, according to the present invention,
An excellent effect is obtained that the distortion inside the plastic molded article can be easily eliminated or reduced in a short processing time.

In particular, according to the fourth aspect of the present invention, since a mold capable of heating an arbitrary portion of the supplied thermoplastic resin molding material to a temperature higher than a critical temperature at which sink occurs is used, a molded plastic lens is used. Whatever the shape,
A sink can be generated in an arbitrary portion (for example, a portion other than a portion functioning as a lens), and there is an advantage that a degree of freedom of processing is improved.

[Brief description of the drawings]

FIG. 1 is a process diagram showing a process of injection molding a plastic lens.

FIG. 2 is a graph showing a temperature-specific volume characteristic of APO.

FIG. 3 is a graph showing temperature-specific volume characteristics of PMMA.

4A and 4B are conceptual diagrams showing the occurrence of distortion and sink marks in a plastic lens, wherein FIG. 4A shows a case where stress is small on the surface and distortion occurs, and FIG. It is a figure which each shows the case which arises.

FIG. 5 (A) is a graph showing the relationship between the cooling time after removal of a molded product and the sink mark amount in the case where the sink amount is small when the temperature finally drops to room temperature, and FIG. FIG. 7 is a diagram showing that distortion occurs in the case of FIG.

6A is a schematic configuration diagram of a slide piece according to an embodiment of the present invention, FIG. 6B is a cross-sectional view taken along line 6-6 in FIG. 6A, and FIG. It is a figure which shows the plastic lens molded article in which sink occurred using the slide top.

[Explanation of symbols]

 12 Slide top 14 Rod heater 20 Molded product 20A Convex part

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29C 45/78 B29C 45/78 // B29K 101: 12 B29L 11:00

Claims (5)

[Claims] 1. A plastic lens molding method for molding a thermoplastic lens by compression-molding a thermoplastic resin molding material with a mold and gradually cooling the compression-molded thermoplastic resin molding material. A method for molding a plastic lens, characterized in that sinking is intentionally generated in a predetermined portion of a thermoplastic resin molding material during molding. 2. The plastic lens molding method according to claim 1, wherein the predetermined portion of the thermoplastic resin molding material is set to a portion other than a portion functioning as a lens. 3. A thermoplastic resin molding material is supplied to a mold, and a predetermined portion of the thermoplastic resin molding material is heated by the mold to a temperature not lower than a critical temperature at which sinking occurs. A plastic lens molding method in which a material is compression-molded into a predetermined shape and the compression-molded thermoplastic resin molding material is gradually cooled. 4. The plastic lens molding method according to claim 3, wherein the mold can heat any part of the supplied thermoplastic resin molding material to a temperature higher than a critical temperature at which sink occurs. 5. A method for supplying a thermoplastic resin molding material to a mold,
A predetermined portion of the thermoplastic resin molding material is heated by the mold to a temperature not lower than the critical temperature at which sinkage occurs, and then the thermoplastic resin molding material is compression-molded into a predetermined shape, and the compression-molded thermoplastic resin molding material is gradually reduced. The plastic lens obtained by cooling.