JP3320513B2 - Injection molding method of plastic optical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for 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 maintained at a fixed 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 thickness deviation, a difference occurs in the cooling rate of the resin between the central portion and the surface layer of the molded product, and between the thick portion and the thin portion of the molded product. , An optical surface having good surface accuracy cannot be obtained.

As a conventional method for solving this problem, Japanese Patent Application Laid-Open No. 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. It has been disclosed. According to this method, the surface layer of the molded article is uniformly re-melted, so that the stress strain retained in the surface layer disappears. In addition, since the surface layer portion is re-melted and re-cooled in a state where the center portion of the molded product is solidified, distortion occurs in the surface layer portion even when the molded product central portion undergoes solidification shrinkage or restoration expansion in the re-cooling step. Disappears.

[0004]

SUMMARY OF THE INVENTION The above-mentioned conventional method has the following problems.
The surface layer is re-melted, and the resin pressure on each surface of the molded article is made uniform based on the principle of Pascal to reduce distortion. However, even if the molten resin is heated until just before the deterioration of physical properties is started, pressure transmission is less likely to be performed as compared with water or the like because it has a large viscosity. 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 a triangular prism shape shown in FIGS. 9 and 10 or a lens shape shown in FIG. It is difficult to make the resin uniform, and a difference in resin pressure occurs on both sides of the edge portion, which remains inside the molded product.

For this reason, when molding an optical element such as a triangular prism having an edge between molding surfaces to be optical surfaces, even if the surface layer is reheated, the resin pressure between the optical surfaces is reduced. There is a difference. Therefore, for the purpose of improving the surface accuracy of the specific optical surface, the injection pressure is set so that the pressure at which the resin on the surface layer of the specific optical surface presses the mold surface when the mold is opened approaches 0 kg / cm ^2. In the case where is adjusted, sinking occurs on another optical surface.

The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances, and has been made in consideration of the above subject matter. It is an object to provide a molding method.

[0007]

The injection molding method of the present invention comprises the following steps. (1) A step of injecting a molten resin into a cavity of a mold. (2) A primary cooling step of cooling the resin in the cavity to a temperature lower than the glass transition point after injection. (3) After the primary cooling step, a reheating step of heating and softening the resin on the surface layer of each surface of the molded article to at least a temperature equal to or higher than the glass transition point. In this reheating step, the surface layer of a specific optical surface requiring surface accuracy is heated with a temperature difference so as to be lower than the surface layer of the other optical surface. The setting of the temperature difference is such that the temperature of the nest forming a specific optical surface among the nests forming each surface of the mold cavity is lower than the temperature of the nest forming the other optical surfaces. It can be performed by heating. (4) A secondary cooling step of taking out the molded article after the reheating step and cooling it down to the removal temperature. In the secondary cooling step, a surface layer of a specific optical surface requiring surface accuracy is cooled by providing a temperature difference so as to be lower than a surface layer of another optical surface. As in the case of the reheating step, the temperature difference can be set by cooling such that a temperature difference occurs between the insert forming the specific optical surface and the insert forming the other optical surface.

In the above-described configuration, in the reheating step, a molten resin layer is formed on the surface layer in a state where the center of the molded article is solidified. The influence of expansion and contraction of the resin at the center 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 in the secondary cooling step, the resin temperature of the surface layer of the specific optical surface where surface accuracy is required,
Since it is lower than the other optical surfaces, the resin pressure on the surface portion becomes lower than the resin pressure on the other optical surfaces. Then, before being cooled to the take-out temperature, the resin pressure of the surface layer of each optical surface decreases while having this level difference, 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 at the time of opening the mold becomes 0 kg / cm ² , the resin pressure at the time of opening the mold of the other optical surface is reduced. Is larger than 0 kg / cm ² , sink does 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. The triangular prism 1 is composed of five optical surfaces 2, 3, 4 and side surfaces 5, 6, and the optical surface 2 has a higher surface accuracy than the other optical surfaces 3, 4 for reasons of use. Is required. Hereinafter, the optical surface 2 is referred to as an A surface, the optical surface 3 as a B surface, and the optical surface 4 as a C surface.

FIG. 2 shows a mold for molding the triangular prism. The cavity 1 'is a mold A provided in the A-plane insert 7.
Surface 2 ′, a mold B surface 3 ′ provided on the B surface insert 8,
It is formed by the mold C surface 4 ′ provided on the face insert 9. The A-plane insert 7, the B-plane insert 8, and the C-plane insert 9 are provided with an A-plane insert water pipe 10, a B-plane insert water pipe 11, and a C-plane insert water pipe 12, respectively. Surface 2 'and mold B
In the vicinity of the surface 3 'and the mold C surface 4', the A-plane insert thermocouples 13 and B
A faceted thermocouple 14 and a C-faced thermocouple 15 are embedded.

The A-plane nesting water pipe 10 is switchably connected to a heating oil tank (not shown) for A-plane nesting and a cooling oil tank (not shown) for A-plane nesting. The sub water pipe 11 and the C-plane insertion water pipe 12 are switchably connected to a BC plane insertion heating oil tank (not shown) and a BC plane insertion cooling oil tank (not shown).

The A-plane insert 7, the B-plane insert 8, and the C-plane insert 9 are buried in a mold base (not shown), and the resin injected from the molding machine nozzle into the mold base is gated. The cavity 16 is filled through the space 16.

Next, a manufacturing process according to this embodiment will be described.
FIG. 3 shows a change in the resin temperature in the cavity 1 'in the manufacturing process. The characteristic curve 21 shows the temperature of the surface layer on the BC surface, and the characteristic curve 22 shows the temperature of the surface layer on the A surface. Further, the switching of each operation performed on the mold is entered in FIG. 3 as b, c, d, and e as a time scale.

First, cooling oil is supplied to the A-plane nesting water pipe 10, the B-plane nesting water pipe 11, and the C-plane nesting water pipe 12 from the cooling oil tank for the A-plane nesting and the BC-plane nesting cooling oil tank, respectively. Then, the A-plane insert 7, the B-plane insert 8, and the C-plane insert 9 are taken out at the same temperature as Te, and in this state, the molten resin is injected from the molding machine through the gate 16 into the cavity 1 '. Fill.
The temperature of the A-plane insert 7, the B-plane insert 8, and the C-plane insert 9 rises due to the filled molten resin, and reaches the temperature Tb in FIG.

Next, as a primary cooling step, the resin in the cavity 1 'is cooled and solidified for a predetermined time to obtain a temperature Tc shown in FIG. 3, which is lower than the glass transition point. This temperature Tc
Is set to be the same as the take-out temperature Te. Thereafter, the heating oil from the heating oil tank for nesting the A plane and the heating oil tank for nesting the BC plane is supplied to the A-plane nesting water pipe 10, the B-plane nesting water pipe 11, and the C-plane nesting water pipe 12. Then, for the reheating step of heating the A-plane insert 7, the B-plane insert 8, and the C-plane insert 9 at least to the glass transition point or higher, reheating is performed for a predetermined time. At this time, the heating oil in the heating tank for the insertion of the BC plane is maintained at a higher temperature than the heating oil in the heating tank for the insertion of the A plane. 8 and the temperature Td- _BC of the C-plane insert 9 reach a temperature higher than the temperature Td- _A of the A-plane insert 7, and both are higher than the glass transition point.

Next, cooling oil is supplied to the A-plane insert water pipe 10, the B-plane insert water pipe 11 and the C-plane insert water pipe 12 from the A-plane insert cooling tank and the BC-plane insert cooling tank. , A
Cooling is performed for a predetermined time until the temperatures of the face insert 7, the B face insert 8 and the C face insert 9 reach the removal temperature Te in the secondary cooling step.

In this cooling step (secondary cooling step),
Until the A-plane insert 7, the B-plane insert 8 and the C-plane insert 9 fall near the glass transition point, the temperatures of the B-plane insert 8 and the C-plane insert 9 are higher than the temperature of the A-plane insert 7. Temperature, and when this cooling step is completed, the cooling tank for the A-plane insert and the BC-plane insert so that the temperatures of the A-plane insert 7, the B-plane insert 8 and the C-plane insert 9 become uniform. The temperature of the cooling oil in the cooling tank is adjusted respectively. At the time of removal, A
The injection pressure in the injection step is adjusted so that the resin pressure of the surface layer 18 converges to 0 kg / cm ² while the surface layer 18 (see FIG. 2) is in contact with the A surface 2 ′ of the mold.

FIG. 4 shows the change of the resin pressure in the mold in the above-mentioned process, and the switching of each operation performed on the mold is set as a time scale in correspondence with b, c, and b in FIG.
The characteristic curve 23 is indicated by d and e, the characteristic curve 23 is the resin pressure of the BC surface surface portions 19 and 20 (see FIG. 2), and the characteristic curve 24 is A
This is the resin pressure of the surface layer portion 18. Time b in FIG.
FIG. 3 shows a state in which the molten resin is injected into the cavity 1 ′ to complete the filling, and a cooling step (primary cooling step) is performed from b to c. In this step, the entire molded article is once cooled and solidified. You. At this time, the surface layer 18 of the surface A and the surface layer 1 of the surface B
Each 9 and the resin pressure of the C-plane surface portion 20 _{P C-A,} P
_Although it converges to _C-BC , PC _-A > PC _-BC .

Next, in the reheating step, the central part 1
7 (see FIG. 2), the surface layer 18 of the surface A, the surface layer 19 of the surface B, and the surface layer 20 of the C surface
_d-A and _Td-BC , but _Td-A
< _Td-BC . At this time, each resin pressure is _Pd-A < _Pd-BC .

Next, in the secondary cooling step, the surface layer 1
8, by cooling the surface layer portion 19 on the B side and the surface layer portion 20 on the C surface to the removal temperature Te (see FIG. 3), the respective resin pressures at the time of removal (time e) are _Pe-A , P
_e-BC . Further, in the vicinity of the glass transition point at which solidification starts (see FIG. 3), T _d−A <T _d−BC
Since the relationship is maintained, a relationship of _Pe-A < _Pe-BC occurs. Therefore, even if the injection pressure _Pb is adjusted so that P _e−A ≒ 0, P _e−BC > 0.

In the present embodiment as described above, the surface portion 18 of the surface A, the surface portion 19 of the surface B, and the surface portion 20 of the C surface are softened again while the center portion 17 of the molded product is solidified. Without being affected by contraction or expansion of the center portion 17 of the product, stress distortion in each of them is eliminated, and excellent surface accuracy can be achieved. Also, since the resin pressure _PeA at the time of opening the surface layer 18 of the surface A is lower than the resin pressure _{Pe-BC of the} surface layer B 19 and the surface layer C, the surface accuracy of the optical surface 2 is improved. Even if the injection pressure is adjusted so that P _eA is equal to 0 kg / cm ² , P _e-BC > 0, and
No sink marks occur on the optical surfaces 3 and 4.

[0023]

Embodiment 2 FIG. 5 shows a mold used in Embodiment 2 of the present invention. In this mold, the A-side insert 7 is disposed in the A-side sleeve 31, and the B-side insert 8 and the C-side insert 9 are BC
These A-side sleeves 3 are embedded in the
1 and a BC surface sleeve 32 are embedded in a mold base (not shown).

The A-plane insert 7, the B-plane insert 8 and the C-plane insert 9 have an A-plane insert heater 35 and a B-plane insert heater 3 respectively.
6, a C-plane insertion heater 37 is embedded, and an A-side sleeve water pipe 33 and a BC-side sleeve water pipe 34 are provided in the A-side sleeve 31 and the B-side sleeve 32, respectively. Then, these A-side sleeve water pipe 33 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 the production using such a mold,
In the injection step, the primary cooling step, and the secondary cooling step, 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.
At the time of reheating, this water flow is stopped, and the A-plane insertion heater 35, the B-plane insertion heater 36, and the C-plane insertion heater 37 are energized, so that the A-plane insertion 7, the B-plane insertion 8, and C The face insert 9 is heated. Other operations are performed in the same manner as in the first embodiment.

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

[0027]

As described above, in the present invention, the thickness is large,
Even with an optical element with uneven thickness, it can be manufactured with good surface accuracy, and without causing sink marks on the surface accuracy of other optical surfaces,
The surface accuracy of a specific optical surface can be selectively improved.

[Brief description of the 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 sectional view of a mold used in the first embodiment.

FIG. 3 is a characteristic diagram of a resin temperature during production in Example 1.

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

FIG. 5 is a sectional view of a mold used in the second embodiment.

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

FIG. 7 is a side view of FIG. 6;

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 Triangular prism 2, 3, 4 Optical surface 5, 6 Side surface

Claims (1)

(57) [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 of each surface forming a molded product is at least a glass transition point or higher. A reheating step of heating the molded article, and a secondary cooling step of cooling the molded article to the take-out temperature, wherein in the reheating step, heating is performed by selectively providing a heating temperature difference to each surface of the molded article. Characteristic injection molding method for plastic optical elements.