JPH0740404A - Injection molding of plastic optical element - Google Patents

Abstract

PURPOSE:To produce an optical element deviated in wall thickness with good surface accuracy. CONSTITUTION:After the resin injected into a cavity is cooled to its glass transition point or lower, the surface layer parts of the respective surfaces of a molded product are reheated to the glass transition point or higher to melt the resin of the surface layer parts and subsequently cooled to taking-out temp. to be molded. In reheating, the molded product is heated so that temp. difference is selectively provided to the respective surfaces of the molded product to enhance surface accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of injection molding a plastic optical element.

[0002]

2. Description of the Related Art For molding a plastic optical element, a method of injecting a molten resin into a cavity of a mold kept at a constant temperature and cooling and solidifying the resin is generally used. According to this molding method, in the case of an optical element having a large thickness and a large uneven thickness, a difference occurs in the cooling rate of the resin between the center part and the surface layer part of the molded product and between the thick part and the thin part of the molded product, which causes distortion. Therefore, an optical surface having good surface accuracy cannot be obtained.

As a conventional method for solving this problem, Japanese Patent Publication No. Sho 62-183320 discloses a method in which a surface layer portion of a molded product once cooled and solidified is heated and melted again in a mold and then cooled and solidified again. Has been done. In this method, the surface layer portion of the molded product is remelted uniformly, so that the stress strain retained in the surface layer portion disappears. Further, since the surface layer portion is remelted and recooled in a state where the center portion of the molded product is solidified, distortion may occur in the surface layer portion even if there is solidification shrinkage or restoration expansion of the molded product center portion in the recooling step. Disappears.

[0004]

The above-mentioned conventional method is
The surface layer is re-melted, the resin pressure on each surface of the molded product is made uniform based on the principle of Pascal, and the strain is reduced. However, even if the melted resin is heated until just before the start of physical property deterioration, it has a large viscosity, so that it is difficult to transmit pressure as compared with water. Therefore, for example, as shown in FIGS. 6 and 7, it is possible to make the resin pressure uniform within a surface having no edge portion such as a disk-shaped molding surface or a spherical molding surface shown in FIG. Although it is easy, in the case of the triangular prism shape shown in FIGS. 9 and 10 or the lens shape shown in FIG. 11 in which the left and right ends are linearly cut out, the mutual resin pressures on both sides of the edge portion are Is difficult to make uniform, and a difference in resin pressure occurs between the surfaces on both sides of the edge portion and remains inside the molded product.

Therefore, in the case of molding an optical element such as a triangular prism having an edge portion between the molding surfaces which become the optical surfaces, even if the surface layer portion is reheated, the resin pressure between the respective optical surfaces will be reduced. There is a difference. Therefore, in order to improve the surface accuracy of the specific optical surface, the injection pressure should be adjusted so that the pressure of the resin on the surface layer of the specific optical surface pressing the mold surface when the mold is opened approaches 0 kg / cm ^2. However, there is a problem that sink marks are generated on other optical surfaces when the adjustment is made.

The present invention has been made in view of the above circumstances, and an injection of a plastic optical element capable of improving the surface accuracy of a specific optical surface without causing sink marks on other optical surfaces. An object is to provide a molding method.

[0007]

The manufacturing method of the present invention comprises the following steps. (1) A step of injecting a molten resin into the cavity of the mold. (2) A primary cooling step of cooling the resin in the cavity to a temperature below the glass transition point after injection. (3) After the primary cooling step, a reheating step of heating the resin in the surface layer portion of each surface of the molded product to at least a glass transition temperature or higher to soften the resin. In this reheating step, a surface layer portion of a specific optical surface that requires surface accuracy is heated with a temperature difference so as to have a lower temperature than surface layer portions of other optical surfaces. The temperature difference is set so that the temperature of the nest forming a specific optical surface of the nest forming each surface of the mold cavity is lower than the temperature of the nest forming another optical surface. It can be performed by heating. (4) A secondary cooling step in which the molded product after the reheating step is finished is taken out and cooled to the temperature. In this secondary cooling step, the surface layer portion of the specific optical surface that requires surface accuracy is cooled by providing a temperature difference so as to have a lower temperature than the surface layer portion of the other optical surface. Similar to the reheating step, the temperature difference can be set by cooling so that there is a temperature difference between the insert forming the specific optical surface and the insert forming the other optical surface.

In the above-mentioned structure, in the reheating step, a molten resin layer is formed in the surface layer portion in the state where the center portion of the molded product is solidified. The influence of expansion and contraction of the resin in the central part is eliminated. Further, during the cooling from the reheating step to the vicinity of the glass transition point of the molten resin layer of the surface layer portion in the secondary cooling step, the resin temperature of the surface layer portion of the specific optical surface for which surface accuracy is required,
Since it is lower than the other optical surfaces, the resin pressure on the surface layer portion becomes lower than the resin pressure on the other optical surfaces. Then, the resin pressure of the surface layer portion of each optical surface decreases while maintaining this height difference until it is cooled to the extraction temperature, and converges to a constant pressure.

Therefore, even if the injection pressure is adjusted so that the resin pressure on the surface layer of the optical surface, which requires surface accuracy when the mold is opened, becomes 0 kg / cm ² , the resin pressure at the time of mold opening of the other optical surfaces Is 0 kg / cm ² or more, sink marks do not occur on other optical surfaces.

[0010]

Embodiment 1 FIG. 1 shows a triangular prism 1 manufactured according to Embodiment 1 of the present invention. This triangular prism 1 is composed of five optical surfaces 2, 3 and 4 and side surfaces 5 and 6, and the optical surface 2 has a higher surface accuracy than the other optical surfaces 3 and 4 for reasons of use. Is required. Hereinafter, the optical surface 2 is referred to as an A surface, the optical surface 3 is referred to as a B surface, and the optical surface 4 is referred to as a C surface.

FIG. 2 shows a mold for molding this triangular prism. The cavity 1'is a mold A provided on the A-side insert 7.
Surface 2 ', a mold B surface 3'provided on the B surface insert 8, and C
It is formed by the mold C surface 4 ′ provided on the surface insert 9. A-side insert 7 B-side insert 8 and C-side insert 9 are provided with A-side insert water pipe 10, B-side insert water pipe 11 and C-face insert water pipe 12, respectively, and mold A-face 2 A side insert thermocouple 12, a B side insert thermocouple 14, and a C side insert thermocouple 15 are embedded in the vicinity of ′, the mold B face 3 ′, and the mold C face 4 ′.

The A-side insert water pipe 10 is switchably connected to a A-side insert heating oil tank (not shown) and an A-side insert cooling oil tank (not shown). The sub-water pipe 11 and the C-face insert water pipe 12 are a heating oil tank for BC-face insert (not shown) and a cooling tank for BC-face insert (not shown).
The switch is connected to.

The A-side insert 7, the B-side insert 8, and the C-side insert 9 are embedded in a mold base (not shown), and the resin injected from the molding machine nozzle into the mold base is a gate. It is filled into the cavity 1 ′ via 16.

Next, the manufacturing process according to this embodiment will be described.
FIG. 3 shows the resin temperature in the cavity 1'in the manufacturing process, the characteristic curve 21 shows the temperature of the surface layer portion of the BC surface, and the characteristic curve 22 shows the temperature of the surface layer portion of the A surface.

First, cooling oil is supplied to the A-side nest water pipe 10, the B-side nest water pipe 11 and the C-side nest water pipe 12 from the A-side nest cooling oil tank and the BC-face nest cooling oil tank, respectively. Then, the A-side insert 7, the B-side insert 8 and the C-side insert 9 are brought to the temperature of extraction, and in this state, from the molding machine through the gate 16,
The molten resin is injected and filled in the cavity 1 '. The A-side insert 7, B-side insert 8,
The temperature of the C-face insert 9 rises to the temperature b in FIG.

Next, the resin in the cavity 1'is cooled and solidified to the temperature c shown in FIG. After this, A-side inlet water pipe 10
And heating oil from the heating oil tank for A-side insertion and the heating oil tank for BC-side insertion to the B-side insertion water pipe 11 and the C-side insertion water pipe 12, respectively. Reheating is performed by heating the B-side insert 8 and the C-side insert 9 to at least the glass transition point or higher. At this time, the heating oil in the BC side insert heating tank is kept at a higher temperature than the heating oil in the A side insert heating tank, so that the B side insert is completed at the completion of the reheating process. 8 and the temperature d _BC of the C face insert 9 is the temperature d of the A face insert 7.
Reach higher temperature than _A.

Next, cooling oil is supplied to the A-side insert water pipe 10, the B-side insert water pipe 11 and the C-face insert water pipe 12 from the A-side insert cooling tank and the B _C- face insert cooling tank. Then A
The face insert 7, the B face insert 8 and the C face insert 9 are cooled until the temperature reaches the extraction temperature Te.

In this cooling process, the temperatures of the B-side insert 8 and the C-side insert 9 are A until the A-side insert 7, the B-side insert 8 and the C-side insert 9 are lowered near the glass transition point. Face insert 7
The temperature of the A-side insert 7, the B-side insert 8, and the C-side insert 9 become uniform when the cooling process is completed and the temperature is higher than that of the A-side insert cooling tank. The temperature of the cooling oil in the BC plane insert cooling tank is adjusted. Further, at the time of unloading, the injection pressure in the injection step is set so that the resin pressure of the surface A part 18 (see FIG. 3) is in contact with the surface A of the mold so that the resin pressure of the surface part 18 converges to 0 kg / cm ^2. Make adjustments.

FIG. 4 shows changes in the resin pressure in the above process. The characteristic curve 23 is the resin pressure of the BC surface surface layer portions 19 and 20 (see FIG. 3), and the characteristic curve 24 is the resin pressure of the A surface surface layer portion 18. . Between b and c in FIG. 3 is a cooling step,
In this step, the entire molded product is once cooled and solidified. At this time, the resin pressures of the A-side surface layer portion 18, the B-side surface layer portion 19 and the C-side surface layer portion 20 converge to P _CA and P _C-BC , respectively.
_CA > PC _-BC .

Next, in the reheating step, the central portion 1 of the molded product is
7 (see FIG. 3) is solidified, the A-side surface layer portion 18, the B-side surface layer portion 19 and the C-side surface layer portion 20 are heated to temperatures T _dA and T _d-bc , respectively, but T _dA <T
_{It is d-BC} . At this time, each resin pressure is P
_dA <P _d-BC .

Next, in the secondary cooling step, the A-side surface layer portion 1
By cooling the _No. 8, B-side surface layer portion 19 and the C-side surface layer portion 20 to the extraction temperature Te (see FIG. 3), the respective resin pressures become _PeA and _{Pe -BC} . In addition, at this time, T _dA <T _d-BC near the glass transition point where solidification starts _.
Since the relationship is maintained, the relationship P _eA <P _e-BC occurs. Therefore, even if the injection pressure P _b is adjusted so that P _{eA ≈0} , P _e-BC > 0.

In this embodiment as described above, since the A-side surface layer portion 18, the B-side surface layer portion 19 and the C-side surface layer portion 20 are softened again in the state where the center portion 17 of the molded product is solidified, the molding is performed. Without being affected by the contraction or expansion of the central portion 17 of the product, the stress strain in each is eliminated, and good surface accuracy can be obtained. Further, since the resin pressure P _eA at the time of mold opening of the A-side surface layer portion 18 is lower than the resin pressure P _{e-BC of the} B-side surface layer portion 19 and the C-side surface layer portion, in order to improve the surface accuracy of the optical surface 2. Even if the injection pressure is adjusted so that P _eA becomes equal to 0 kg / cm ² , P _e-BC > 0,
No sink marks are generated on the optical surfaces 3 and 4.

[0023]

Second Embodiment FIG. 5 shows a mold used in a second embodiment of the present invention. In this mold, the A-side insert 7 is arranged in the A-side sleeve 31, and the B-side insert 8 and the C-side insert 9 are BC.
Embedded in the face sleeve 32, these A face sleeves 3
1 and a BC surface sleeve 32 are embedded in a mold base (not shown).

The A-side insert 7, the B-side insert 8 and the C-side insert 9 have an A-side insert heater 35 and a B-side insert heater 3, respectively.
6, the C-side insert heater 37 is embedded, and the A-side sleeve 31 and the B-side sleeve 32 are provided with an A-side sleeve water pipe 33 and a BC-side sleeve water pipe 34, respectively. And these A side sleeve water pipes 23 and BC
A cooling water tank for A surface (not shown) and a cooling water tank for BC surface (not shown) are connected to the surface sleeve water pipe 34.

In such manufacturing using a die,
In the injection process, the primary cooling process, and the secondary cooling process, cooling water is supplied to the A-side sleeve water pipe 33 and the BC-side sleeve water pipe 34 from the A-side cooling tank and the BC-side cooling water tank.
Further, at the time of reheating, this water flow is stopped, and the A-side insert heater 35, the B-side insert heater 36, and the C-face insert heater 37 are energized so that the A-face insert 7, the B-face insert 8 and the C-face insert C The face insert 9 is heated. Other operations are the same as in Example 1.

In this embodiment, the A-side nest heater 35, the B-side nest heater 36, and the C-side nest heater 37 are used to connect the A-side nest 7, the B-side nest 8, and the C-side nest 9. To heat
Reheating can be performed even with a small insert that cannot be provided with a water pipe. Further, in this embodiment, the A-side insert 7, the B-side insert 8 and the C-side insert 9 can be heated to a predetermined temperature in a shorter time than in the first embodiment, and rapid manufacturing is possible.

[0027]

As described above, in the present invention, the thick wall is thick,
Even with an optical element with uneven thickness, it can be manufactured with good surface accuracy, and without sinking in the surface accuracy of other optical surfaces,
It is possible to selectively improve the surface accuracy of a specific optical surface.

[Brief description of drawings]

FIG. 1 is a perspective view of a triangular prism manufactured according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a mold used in Example 1.

FIG. 3 is a characteristic diagram of a resin temperature associated with the production of Example 1.

FIG. 4 is a characteristic diagram of resin pressure in the production of Example 1.

5 is a cross-sectional view of a mold used in Example 2. FIG.

FIG. 6 is a front view of a first example of an optical element.

FIG. 7 is a side view of FIG.

FIG. 8 is a front view of a second example of the optical element.

FIG. 9 is a front view of a third example of the optical element.

FIG. 10 is a front view of FIG. 9.

FIG. 11 is a front view of a fourth example of the optical element.

[Explanation of symbols]

 1 Trigonal prism 2, 3, 4 Optical surface 5, 6 Side surface

Claims (1)

[Claims] 1. An injection step of injecting a molten resin into a cavity of a mold, a primary cooling step of cooling the injected resin, and a resin of a surface layer portion of each surface forming a molded product at least a glass transition point or more. A reheating step of heating the molded article and a secondary cooling step of cooling the molded article to a temperature for removing the molded article are provided. In the reheating step, heating is performed by selectively providing a heating temperature difference to each surface of the molded article. A method for injection-molding a characteristic plastic optical element.