JPS62179913A - Molding of plastic lens - Google Patents

Abstract

PURPOSE:To prevent weld line from developing by a method wherein the predetermined amount of resin material is poured under the state that the mold space is kept to be open at a specified size. CONSTITUTION:The amount of retreat of a top force 1 to form a cavity between the top and bottom forces is set in terms of the amount of opening of a mold space to be opened so as to let the ratio of the thickness at the center to that at the peripheral edge of a molded lens at 1/2.5 or more. When the top force 1 is shifted in the direction to close the cavity opening so as to compress the resin after molten resin material is poured so as to arrive at the center of the cavity, the development of weld line becomes difficult, because the resin flows quicker at the center of the cavity than at the remaining portion of the cavity during the flow process of the resin. In addition, the residual strain of the molded part is reduced when the resin is poured in the cavity by injection under the state that the forces are heated in advance up to a temperature, which exceeds the glass transition point and is below the melting point of the resin material. The usable thermoplastic resin materials is preferably monopolymer such as polymethyl methacrylate, polycarbonate, polystyrene or the like, copolymer mainly consisting of the above-mentioned monopolymers or the like.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for molding a plastic lens made of thermoplastic resin. The present invention relates to a plastic lens molding method that prevents weld lines from forming in the molding method.

[Prior Art] Conventionally, a method of molding a plastic lens by injection molding using thermal IT (qj resin material) is to construct a cavity as a so-called high-grade ωF polished metal alloy mold, and to A common molding method was to inject a tungsten-molten resin.

In such a molding method, as a method to compensate for shape defects such as sink marks and deformation that occur due to cooling shrinkage of the injected resin, the mold is slightly moved after the resin is injected into the cavity. A method has been proposed to reduce the cavity volume to compensate for volumetric shrinkage due to cooling shrinkage and to prevent shape defects from occurring. (Unexamined Japanese Patent Publication No. 58-te't
(See TS3 Publication, 58-167135 Publication) Also, as a method of forming a strong concave lens, cutting oil [J
discloses a lens molding method that does not generate weld lines by placing a lens blank that is close to the final shape in a mold as a nest, and injecting resin into the gap formed by the nest and the cavity. ing. (Refer to Japanese Unexamined Patent Publication No. 57-173138.) [Problems to be Solved by the Invention] When molding a strong concave lens using the general injection molding method or the method of slightly moving the mold, the lens The thickness ratio between the center thickness (tc) and the peripheral thickness (te) increases, and therefore the mold cavity into which the resin is injected is narrower at the center and wider at the periphery, so injection is injected from one side. The resin flows in a branched state along the periphery where flow resistance is low, and merges on the opposite side of the injection inlet, which does not completely fuse and remains as a weld line.There is no way to prevent this. It was difficult. In addition, air bubbles may remain in the molded product as residual air bubbles. These will be described in detail later.

・On the other hand, the method of injecting resin into the gap of the cavity using an insert f can prevent the occurrence of sink marks, but it requires an additional process of preforming and processing the blank. However, there is a problem in that it is complicated, such as requiring a holding mechanism for the nest within the mold.

Step F to solve problem E] The present invention is based on the findings obtained by elucidating the mechanism by which weld lines occur in the molding of strong concave plastic lenses made from thermoplastic resin. This was achieved by finding suitable cavity spacing settings and a mold operating mechanism that can prevent the occurrence of weld lines.

1! According to the present invention, in a method for molding a strong concave plastic lens by injection molding a thermoplastic resin material, the mold spacing constituting the cavity is set such that the ratio of the center thickness of the lens to the peripheral thickness is 1/2.5 or more. This method of molding a plastic lens is characterized in that the mold is opened until the mold becomes 1-, and a resin material t1 of a predetermined value is injected, and then the mold is closed to form the final lens shape.

In the present invention, a strong concave plastic lens having a focal length of -50 cm or less and a diopter of -2.0 or more is suitable for molding such a lens.

FIG. 2 is a conceptual diagram of the process of filling a resin material into a cavity when a concave plastic lens is molded by normal injection molding. As shown in Figure 2, in normal injection molding, weld lines cannot be prevented if the ratio of the center thickness (tc) to the peripheral thickness (te) of the molded product is less than 1/2.5. . This is, for example, a concave lens made of polymethyl methacrylate (optical refractive index no = 1.492) with a center thickness of 1.71 m and an outer diameter of 70 m, and the weld line when molding a lens with a focal length of 157 c+s or less. It is shown that this occurs, and it is virtually impossible to mold a strong concave lens. In this case, it is possible to change the ratio L by changing injection molding conditions, gate shape selection, mold temperature adjustment, etc., but the degree of change is extremely small.

On the other hand, FIG. 3 is a conceptual diagram showing the filling process when the molten resin material is injected to the center of the cavity and then the mold is moved in the direction in which the cavity opening is closed to compress the injected resin. As shown in Figure 3, when the resin is compressed while being injected into a part of the cavity, the flow process is different from that during injection injection, and the flow is faster in the center, so weld lines do not occur. It becomes difficult.

The present invention is based on the knowledge described in item 1, and the mold spacing constituting the cavity is determined by the ratio of the center thickness of the lens to the peripheral thickness, 140, and the ratio of the small to medium part of the mold to the peripheral part.
It is characterized by injection injection with a ratio of 1/2.5 to 12.

That is, at least one mold is retracted into a cavity formed by retracting the desired mold spacing for molding the desired lens shape until the ratio of the center thickness to the peripheral thickness of the lens becomes 1/2.5 or more. A plasticized molten resin material is injected in a plasticized molten state in an amount sufficient to form a lens molded product of a predetermined shape. Therefore, the resin material injected into the cavity formed by this opened mold becomes undershot. Then,
The reason why it is better to open the mold to a ratio of 1/2.5 or more between the center thickness and the peripheral thickness of the lens is because it can be commonly applied to strong concave lenses with short focal lengths, as mentioned above. , which was newly discovered and whose ratio is 1/2
．． 5 or less, for example 1/3.0, weld lines naturally occur, and residual air bubbles are also observed.
It becomes impossible to prevent them. Also 1/2.5
For example, l/2.4. l/2.3...1/2.0
．． Setting it to 1/1.9 means that there is no difference in the mold spacing between the center and the periphery, which means that the mold spacing is wide, and if it is too wide, it will affect the molding conditions in injection molding. affect Therefore, the limit is determined by the performance and capacity of the injection molding machine, but in normal injection molding it is 1/2.
It is suitable that it is in the range of 5 to 1/2.0.

Next, the mold is closed after injection and injection. The most suitable timing for this is at the end of injection injection.
A slight shift back and forth is not a particular problem; however, if the closing timing is delayed, a cooling line may remain at the part where the mold and the end of the resin material are in contact at the time of the injection path r, and a significant delay is undesirable. Further, it is desirable that the mold closing speed is 0.5 to 10 m/sec. It is preferable that the time required to completely close the final molded product shape is 0.01 to 1 second. Therefore, in the molding method of the present invention, the mold is heated in advance to a temperature above the glass transition point or melting point of the resin material. Injection injection is performed by heating the following:
This is preferable in terms of reducing the residual strain of the molded product, and the time required to completely close the mold in such a case is 0.
．． 05 to 5 seconds is suitable.

The mold is preferably made of glass, particularly tempered glass, because the transfer surface can be easily processed and polished, and the area density of the molded product can be improved. However, the material of the forming mold is not particularly limited.

In the molding method of the present invention, the number of molds used is not limited to one set, and a molding method using an injection port-tarika type in which multiple sets are attached may also be suitably employed. However, the injection molding and compression process to prevent weld lines must be performed in the injection zone, and the subsequent cooling [
Therefore, it is necessary to use a rotary table to remove the molded product from the mold.

Any material is not particularly limited as long as it can be used in the molding method of the present invention to form a thermoplastic resin shape, or preferably,
Polymers of polymethyl methacrylate, polycarbonate, polystyrene, etc., copolymers having these as main components, etc. Furthermore, polyacrylonitrile-styrene copolymers, polybutadiene-styrene copolymers may be used. . The material is preferably in the form of normal granules, so-called pellets.

Furthermore, the molding method of the present invention is particularly suitable for molding spherical or aspherical eyeglass lenses that require high precision in single-strength concave plastic lenses.

The molding method of the present invention is extremely useful in preventing the occurrence of weld lines for strong concave plastic lenses as molded products. It can be applied to injection compression molding as a method of , and other molding methods. For example, the injection compression molding method has seven −
1 I l″IFIIIFI 1 I-ni, insects
a-Ljl Ifhi (■ ÷・1 Yut, i
f , 'AIl / L a 114 By applying high pressure to the mold in advance, only the volume corresponding to the thermal expansion' is applied to the mold for minute stroke compression, or the final stroke is It can be applied to necessary high pressure applications.

[Example] Example 1 A cross-sectional view showing the configuration of an injection molding machine used for molding in an example is shown in FIG. In Figure 1, the upper mold l
is attached to a hydraulic piston 3 that allows the mold to move in the 7F direction. By filling the pressure oil chamber 4 of the hydraulic component block 8 with pressure oil, the L mold l is moved backward. IIf retreats to the position set in
It is Noh. The lower mold 2 is fixed, and when the L mold 1 retreats, a cavity is formed between both molds. The plasticized and melted resin material is injected into the cavity from the injection injection lower at a predetermined interval of 14 minutes. When the resin material 1 is injected into the cavity, pressure oil is put into the pressure oil chamber 5 of the hydraulic component block 8, and the upper mold 1 moves forward to compress the resin material in the cavity until it reaches its final shape. . In such a molding machine, the receding profile of the L mold 1 is such that the ratio of the center thickness to the peripheral thickness of the molded lens is 1/2.5 as an opening 14 where the mold interval is widened.
It is necessary to set it so that E.

Using the molding machine described above, the center thickness is 1.7cm, the peripheral thickness is 8cm.
．． 5+sm, inner surface R71, Ela layer layer, outer surface R
2+341111, a concave plastic lens with a diameter of 70-■ is made of polymethyl methacrylate (minute 7-Q20,0
00) according to the primary procedure.

First, the upper mold 1 is further set back by 3.00 mm from a position sufficient to mold a lens having the required shape shown in L. As a result, the mold interval is opened so that the ratio of the center thickness to the peripheral edge thickness of the lens becomes 1/2.44. In other words, the mold spacing is 4.7 am (1.7 mm + 3.0 mm) in the center.
, Peripheral part is 11.5 seconds (8.5 feet + 3.0 seconds)
Therefore, the ratio is 1/2.44.

Inside this cavity, there is a space corresponding to the amount of molded lens.
The measured amount of molten polymethyl methacrylate is injected from the injection injection lower, and the upper mold 1 is compressed and lowered at the same timing as the end of injection injection, compressing the resin material in the cavity into the final lens shape. did.

The molding conditions were as follows: ηf/ψ temperature of polymethyl methacrylate was set at 240°C, mold surface temperature was set at 60°C,
Injection pressure is 800kg/crn', injection time 0.5~1
seconds, and the compression time was set to 0.5 seconds. The compression pressure per mold surface was 500 kg/cm'. After compression, the molded product was cooled for 90 seconds and taken out from the mold.

The concave plastic lens obtained as a molded product was molded according to the specified 1-method based on the design values, and there were no weld lines or residual bubbles, and it was homogeneous, had low distortion, and was of excellent quality. there were.

Example 2 Using the same injection molding machine as in Example 1, the center thickness 1.
7■, peripheral thickness 9.88m+s, inner surface R63,84
+em, outer surface R2O2mm, diameter 70+s+s concave plastic lens made of polycarbonate (molecular weight 22
．． 000) according to the following procedure.

The mold l is moved back 4.0 hm from a position sufficient to mold a predetermined lens shape. As a result, the mold is opened so that the ratio of the center thickness of the lens to the peripheral thickness is 1/2.43.
The mold spacing is 5.7mm in the center (J, 7mm+4
．． 0011! I), the peripheral edge is 13.8Eimm (9,
86m layer + 4.00m layer).

Molten polycarbonate was injected into the formed cavity in the same manner as in Example 1, the upper mold was compressed and lowered, and after cooling, the molded product was ejected from the mold.

The molding conditions were as follows: The total iq rYfj temperature of polycarbonate was set at 70°C, the mold surface temperature was set at 80”C,
Injection pressure was 1,400kg/crn', injection time was 0.
5 to 1 second, and the compression time was 0.5 seconds. The compression pressure per mold surface is 700 kg/cm'. Cooling after compression is 80 seconds.

The concave plastic lens obtained as a molded product was molded to the specified dimensions based on the design values, and there were no weld lines or residual bubbles, and it was homogeneous and had low distortion, indicating excellent quality. .

Comparative Example 1 Using the same injection molding machine as in Example 1, a concave plastic lens in the same shape as in Example 1 was made of polymethyl methacrylate (molecular weight 20.000), and the upper mold was molded to form a lens in the desired shape. Further from the position sufficient to form
1.8 The intestinal layer is retracted, thereby opening the center thickness of the lens and the peripheral part to 1/3.08, and the mold spacing is set to 3.3 mm (1.7 mm + 1.8 mm) at the center and 10 mm at the peripheral part. The molding was performed in the same manner as in Example 1, except that the thickness was changed to .1 mm (8.5 mm + 1.8 mm).

The concave plastic lens as a molded product obtained is the fourth
As shown in the figure, a weld line was observed on the side opposite to the injection port.

Comparative Example 2 Using the same injection molding machine as in Example 1, a concave plastic lens in the same shape as in Example 1 was molded using polymethyl methacrylate (molecular weight 20.000) to form a lens in the desired shape. Molding was carried out in the same manner as in Example 1, except that the 1-nimold was not moved back to provide a sufficient position.

The concave plastic lens as the obtained molded product is the fifth
As shown in the figure, a weld line and residual air bubbles were observed on the side opposite to injection injection [1], and the dimensional accuracy was poor, and the product was determined to be a defective molded product in terms of quality.

Examples 3 to 4 The upper mold setback in Example 1 was set to 4 am and 5 layers, and the mold spacing was opened so that the ratio of the center thickness of the lens to the peripheral edge was 1/2.19 and 1/2.01. Other than that, 20 lenses were each made using the same procedure as in Example 1.
It was molded into a sheet.

The number of defective molded lenses produced is shown in the table below, and no defective products were observed.

Example Lens center thickness and defective/peripheral thickness ratio
Good product (pieces) 3 1/ 2.19 0/ 204
1/2.0I Q/20 Comparative Example 3 The upper mold in Example 1 was set back to 2 layers, and the mold spacing was opened so that the ratio of the center thickness of the lens to the peripheral edge was 1/2.83. Twenty lenses were molded using the same procedure as in Example 1.

The number of defective lenses produced is shown in Table 1. Weld lines and residual air bubbles were observed in all of the lenses.

Comparative example Lens center thickness and defective/peripheral thickness ratio
Good product 3 1/ 2.83 20/ 0
[Effects of the Invention] Conventionally, injection molding of concave plastic lenses using 81'I■ plastic resin materials for strength, that is, short focal length, has the disadvantage that weld lines occur on the lens as a molded product, which deteriorates the quality. This had the serious problem of lowering the energy consumption.

However, since the molding method of the present invention adopts a new single-stage opening/closing mechanism for the mold during injection molding, there is no weld line or other defects such as those shown in L. Is recognized. In particular, from the point of view of preventing the occurrence of defects in molded products when using the conventional injection molding method, there is no impact on the manufacturing cycle or cost. It has the effect of becoming right-handed.

The molding method of the present invention is useful for injection molding of strong concave plastic lenses, but it goes without saying that lenses of even better quality can be obtained by applying the method to this method.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the configuration of the injection molding machine used in the examples, and Figure 2 is a conceptual diagram showing the process of filling the resin material into the cavity when a concave plastic lens is molded by normal injection molding. Figure 3 is a conceptual diagram showing the filling process in the cavity when the mold is moved in the direction of closing the cavity and the injected resin material is compressed in injection molding. Figure 5 shows comparative example 2.
FIG. 2 is an explanatory diagram showing the occurrence of defects in an injection-molded plastic lens in FIG. l Nidmold, 2: Lower mold 3: Hydraulic piston, 4.5: Pressure oil chamber 6: F, mold retraction 1 (setting bolt 7: injection inlet, 8: Hydraulic configuration pronk No. 1, Fig. 3)

Claims (4)

[Claims] (1) In a method of molding a strong concave plastic lens by injection molding a thermoplastic resin material, the mold spacing constituting the cavity is adjusted so that the ratio of the lens center thickness to the peripheral thickness is 1.
A method for molding a plastic lens, which comprises opening the mold until the mold is 2.5 or more, injecting a predetermined amount of resin material, and then closing the mold to form the final lens shape. (2) The molding method according to claim 1, wherein the mold is heated in advance to a temperature higher than the glass transition point of the resin material and then injected. (3) The thermoplastic resin material is polymethyl methacrylate,
The molding method according to claim 1, wherein the molding method is a homopolymer of polycarbonate or polystyrene, or a copolymer having these as main components. (4) The molding method according to claim 1, wherein the plastic lens is a spectacle lens.