JPH01168438A - Manufacture of plastic lens - Google Patents

Abstract

PURPOSE:To manufacture a plastic lens having high quality in a high cycle by dividing the lens into two pieces, forming them from a center gate, and binding them by refilling resin. CONSTITUTION:In order to divide a lens into two lens pieces each having one side plane and 2mm of central thickness, cam grooves to be engaged with cams 9, 10, 11, 12 of elements 5, 6 and sleeves 7, 8 are formed on guide plates 13, 14, 15, 16. The temperature of a center gate jig 1 is held constantly at 150 deg.C by an inner heater 3, and the elements 5, 6 and the sleeves 7, 8 are held constantly at 120 deg.C by the heater. The temperature of a nozzle 21 is set to 240 deg.C, resin is filled for 5sec, and it is held in this state for 1min. In case of refilling the resin to bind the divided lens pieces, a nozzle 25 held at 270 deg.C is completed by disposing the elements 5, 6 and the sleeves 7, 8, then moving a molding machine, touching the nozzle 25 to nozzle retainers 23, 24 and filling it. A molding cycle includes 65sec of a filling step, 15sec of a refilling step, and approx. 10sec of moving and removing steps, thereby molding it in a high cycle of 2min or less.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a plastic lens a! In particular, the present invention relates to a manufacturing method that is highly accurate, high cycle, high quality, and suitable for preventing the occurrence of fold lines in concave lenses.

[Conventional technology]

Plastic lenses have the advantage of being able to reduce the number of lenses, reduce size, and produce aspherical lenses in large quantities at low cost. However, the reason why no progress has been made in realizing this technology is that it is difficult to maintain a high degree of shape accuracy and shorten the molding cycle at the same time.

Conventionally, the manufacturing method for obtaining a high degree of shape accuracy is
As described in Japanese Unexamined Patent Publication No. 57-187232, by making the cavity volume constant when the resin temperature in the mold reaches a predetermined temperature, the specific volume of the resin in the mold can be reduced to at least A method is disclosed in which the temperature is maintained constant until the temperature drops to a predetermined value.

However, in the above method, the molding cycle becomes longer as the lens thickness increases and as the ratio of the maximum thickness to the minimum thickness of the primary lens increases. No consideration has been given to this molding cycle. In order to shorten the molding cycle, if the temperature of the pot mold is lowered by a certain level, the thin wall portion will solidify first, and the above molding method will cause significant internal distortion. It turns out.

On the other hand, in a concave lens, weld lines occur due to its shape. As a method for preventing this, there is a method of raising the temperature of the mold during filling to a temperature higher than the temperature at which the fluidity of the resin changes significantly. However, this method results in a delay in the bottom cycle. Another method is a forming method using a center gate. However, lenses with a high degree of phase change leave gate marks, making them practically unusable.

On the other hand, when a lens is molded using a side gate, orientation due to the shear stress of the resin during filling occurs inside the lens. However, no solution has been found so far. One possible method is to use a center gate, but this method cannot be put to practical use for the reasons mentioned above.

[Problem that the invention seeks to solve]

The purpose of the present invention is to produce a high-precision plastic lens in a high cycle and with high quality without internal distortion, which is impossible to achieve with conventional side gates, and to eliminate the occurrence of 1st line, which is a technical problem unique to concave lenses. An object of the present invention is to provide a method of manufacturing a plastic lens that can prevent the above problems.

[Ninth way to solve the problem]

The above purpose is to understand the accuracy factors of plastics.
Koyoshi is bottomed out.

First, it was found that the conventional molding methods using side gates and high filling pressure to reduce thermal shrinkage each have their own drawbacks. Since it is not possible to deal with the gate marks properly with a center gate, it was natural to use a side gate. However, in reality, 200℃
If the front and rear high-temperature resin is to be filled into the lens cavity, which is at least around 50 degrees Celsius, high pressure is required at the side gate to fill the entire lens, and due to the shear stress when passing through the gate, The physical properties of the lens are different in the gate direction and in the direction perpendicular to the gate direction. This resulted in two drawbacks. One is a sturdy mold structure that can withstand high filling pressures, which increases heat mass and inevitably delays the molding cycle.

Another reason is that the physical properties of the lens are different in the gate direction and in the direction perpendicular to it, which causes a difference in the amount of elastic recovery after being removed from the mold, resulting in the lens having an asymmetrical shape. It is easy to obtain high accuracy. In order to overcome this problem, methods of increasing the mold temperature and lengthening the molding cycle were unavoidable in order to ensure accuracy.

The present invention first began with a study on how to fill the center gate. As a result, it was found that filling from inside the lens is a good way to eliminate the gate marks on the center gate. Actually, I found out that I could split the intended plastic lens into two parts, open the center gate, and glue the two lenses together. Furthermore, in consideration of the centering accuracy, molding cycle, etc. during bonding, it has been found that it is efficient to perform this bonding while the two lenses are in the lens cavity. In summary, the feature of the present invention is to simultaneously create half of the intended lens in separate cavities on the center gate, and with the lenses in these two cavities, to reconnect the cavities and the lenses. The point is to join the two lenses together by refilling with resin.

[Effect]

The operation of the present invention will be explained with reference to FIG. FIG. 4 shows a cross section of the mold during filling. 1Fi, a precise center gate jig that fills two cavities at the same time. 2
is a sprue, and 4 is a gate.

Center gate jig 1 is used for lens cavities 19 and 20.
It is composed of an input piece 5.6 and a sleeve 7.8.

In FIG. 4, if only the upper half and lower half of the center gate jig 1 are viewed, it is similar to molding using a conventional center gate. However, the major difference from the conventional method is that the surface formed by the center gate jig 1 is refilled with resin in the next step, so there is no need to increase precision. This brings great benefits to ensuring the accuracy of the lens surface formed by the insert pieces 5 and 6 and to the mold structure. The most important point in improving the accuracy of blinds and plastic lenses is how to reduce uneven sink marks caused by heat shrinkage.In the present invention, all the sink marks caused by heat shrinkage can be eliminated using the center gate jig. It can be concentrated on the surface formed by 1. One way to do this is to raise the center gate jig above a temperature at which the fluidity of the resin changes significantly. The principle of this method is that even if the area around the lens surface formed by the insert pieces 5 and 6 shrinks due to heat, the resin around the center gate jig 1 will continue to flow and compensate for the sink mark around the lens surface. It is in. In addition, in the mold structure of the present invention, there is no need to fill with high filling pressure to reduce heat shrinkage as in conventional methods, so it is possible to minimize the amount of lens cavity molding required. . Furthermore, since the lens is originally created by dividing the entire lens into two parts, the lens thickness is halved and the molding cycle is reduced to about one-fourth in terms of heat conduction. Furthermore, since it is a center gate, there is no weld line in a concave lens, and since the inside of the lens has isotropic physical properties and is filled with low pressure, internal distortion due to filling is significantly reduced. It is easy to infer that this is the case.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 shows a cross section of the mold during filling.

1 is a center gate jig for filling two cavities at the same time, and a heater 3 is incorporated therein. 2 is a sprue and 4 is a gate.

The lens cavities 19 and 20 are each composed of a center gate jig 1, an insert piece 5.6, and a sleeve 7.8. The insert pieces 5, 6 and the sleeve 7.8 are each fitted with a cam portion 9.10.11.12 for sliding and positioning.

The sleeve 8 is provided with a gel 22 for refilling. 17 is 2 pins for pulling out sprue 2, 18
is a drive section for the Z pin 17, which is connected to the center gate jig 1.

21 is a nozzle of a molding machine (not shown).

Next, the operation will be explained. The nine lenses we created are made of polycarbonate, a biconcave lens with a curvature of 70m and radius of 90cm, the center thickness is 4.5m, the outside diameter is φ90tm, the lens outside diameter is φ80m, and the brim thickness is 5mm. . First, in order to divide this lens into two single-plane lenses with a center wall thickness of 2 mm, insert the insert piece 5.6 and the cam portion 9. of the sleeve 7.8.
10.11.12 The cam groove that engages with the guide plate 13.14
．． 15.1<S. (Please note that the information board is 15°16/
Nozzle receivers 23, 24 are provided for moss refilling. ) Also, at this time, the float of the center gate jig 1 is
0mg+'f: Consideration has been given to ensuring availability in advance.

The details of the sliding and positioning of the insert piece and the sleeve will be explained later.

The heaters 3 in the center gate jig 1 are arranged in a circular shape to prevent uneven temperature distribution within the lens, as shown in FIG. 1 (6). The temperature of center gate jig 1 is determined by heater 6.
The temperature is kept constant at 150°C. The input piece 5.6 and sleeve 7.8 are heated to 120°C by an internal heater (not shown).
The temperature of the nozzle 21, which is kept constant, is 240°C.

Filling was carried out in 5 seconds and held in the state shown in Figure 1 for 1 minute.

Next, a second refilling process is performed to combine the divided lenses.
This will be explained using figures. In Figure 2, input J1i1i15
, 6, the sleeve 7.8 forms a 0.5-connection part as shown in the figure by the cam groove of the cam part 9.10.11.12 and the guide plate 1!1.14.15.16. will be placed in

However, the nozzle receiver 23.24 and sleeve 8I installed on the guide plate 15.1+5 are provided with a fixed gate 22.
It is now ready for filling. For filling, after arranging the nozzle 25, which is maintained at a high temperature of 270° C., the inserting piece 5.6 and the sleeve 7.8 as shown in FIG. 2, the molding machine (not shown) is moved. Place the nozzle 25 into the nozzle receiver 2
5.24 After completing the filling by touching the nozzle 25, immediately move the molding machine and place the nozzle 25 into the nozzle receiver 25.2.
The ratio is not subtracted from 4. The time from when the nozzle 25 is touched to when it is removed is within 5 seconds. Then, 10 seconds after the above-mentioned refilling was completed, the cysts 5 and 6 and the sleeve 7 and 8 were all moved to take out the lenses.

Next, the input piece 5.6 in filling, refilling, and taking out the lens.
The operating system for sliding and positioning the sleeve 7.8 will be explained with reference to FIG. In (α) of FIG. 3, A is a filling process, B is a refilling process, and C is a lens removal process.

30.31 is a cam groove of the guide plate that engages with the cam portion 9.10 of the input piece 5.6, and 52.degree. 36 is a cam groove of the guide plate that engages with the cam portion of the sleeve 7.8. The cam grooves are provided in the guide plate with appropriate inclinations so that the inserting piece 5.6 and the sleeve 7.8 are positioned at respective positions in the process. FIG. 3(b) is a manual view of the mold, in which the sleeve 7.8 is held on the frame 34.35,
The frame 34.55 is connected to a cylinder 36.37, and as the cylinders 66, 37 are moved by a cylinder drive 58.59, the insert pieces 5, 6 and the sleeve 7.8 move towards the cam part 9.
, 10.11.12 and the cam grooves 30.31.32.33 are arranged at the positions for each process shown in the third factor (α) above.

The above is an explanation of the operating system for sliding and positioning the insert piece and the sleeve.

Next, the lens created in this example has an input frame of 5.6
The mold was designed to be 0.6% larger in order to compensate for the thermal shrinkage between the lens take-out temperature of 120°C and the usage temperature of 20°C. Therefore, the obtained lens was measured with a laser interferometer, and the radius of curvature error was ±10 μm from the designed 1 m.
The spherical precision that can be read from the interference fringes is less than 0.3 μm, which is accurate enough to be used in high-end lens systems such as projection televisions and video cameras. In addition, the state of internal strain was observed using a polarimeter, and it was found that the state of the internal strain was almost zero. Also, although it was a roar, there was no weld line. The molding cycle is filling process 65 seconds, refilling process 1
It took about 5 seconds to move and take out, and it took about 10 seconds to move and take out, and it was possible to mold in a high tickle time of 2 minutes or less.

In this embodiment, a polycarbonate cleft-concave lens was used for explanation, but the lens shape and material are not limited to other convex or meniscus shapes, or acrylic or polystyrene. However, in the case of a meniscus lens, it may not be possible to divide it into two depending on the radius of curvature.

〔Effect of the invention〕

According to the present invention, the originally intended lens is divided into two parts,
The molding cycle, which involves creating each part using a center gate and refilling it with resin to bond it together, is one-fourth of the conventional molding cycle. High-cycle molding becomes possible, making it possible to obtain high-quality plastic lenses with no internal distortion, high precision, and no weld lines in concave lenses.

[Brief explanation of the drawing]

Fig. 1 is a sectional view and front view of an embodiment of the present invention, Fig. 2 is a sectional view of an embodiment of the invention, Fig. 3 is a model sectional view of an embodiment of the invention, and Fig. 4 is a sectional view of an embodiment of the invention. FIG. 2 is a cross-sectional view of a model explaining the present invention in detail. 1... Center gate jig, 2... Sprue, 3...
・Heater, 4... Gate, 5.6... Entering piece, 7.8
...Sleeve, 9. IQ, 11.12...Cam part, 13.14.15.15...Guide plate, 17...
・Z bin, 30.31.32.33...cam groove, 34
゜35... Frame, 56.57... Cylinder. t; Seven Shifu γ Ni Fjf Job 4/Gate 7; Sleeve. 2z 87° le j' enter A9 R: '73'
, He 7 6: It q: η＾f
f. Figure 2

Claims (1)

[Claims] 1. A plastic lens can be obtained by separately creating halves of a plastic lens using two divided cavities using a center gate, then filling with resin again, and combining the lenses created using the two cavities. Characteristic plastic lens manufacturing method.