Injection compression molding method of a spectacle lens

Abstract: In an injection compression molding method of a lens, in which a mold is closed to preserve a predetermined compressing margin in a cavity (3) for a lens, molten resin is injected and fed into the cavity (3) for the lens, and compressed for the aforementioned predetermined compressing margin before or after the injection and the feed of the molten resin is completed, the predetermined compressing margin (the degree of slightly opening S (-) ) for producing a minus lens is molded is defined to be larger than the predetermined compressing margin (the degree of slightly opening S (+) ) for producing a plus lens is molded. As a result, even when the minus lens is molded, the larger area of the cavity can be ensured and a flow property of the molten resin in the cavity is improved, so that the molten resin reaching the inside of the cavity (3) flows through the central portion of the cavity (3) into the peripheral portion, with the result that the appearance of a weld mark in the central portion is avoided.

Description: This invention relates to an injection compression molding method of a spectacle lens, in which the spectacle lens is obtained by injecting, compressing and molding a thermoplastic resin, and a spectacle lens produced by using the injection compression molding method. More specifically, this invention relates to an injection compression molding method of a spectacle lens, being capable of molding a plus lens and a minus lens with high-precision and high-quality. As a molding method for obtaining a lens from a thermoplastic resin, an injection compression molding method is well-known (e.g: Japanese Patent Application Laid-open No. Sho 2-26723, Japanese Utility Model Application Publication No. Hei 6-9826 and so on). The spectacle lens, within the range of +4.00 Diopter to -8.00 Diopter of the lens power, is preferably used for the molding method. The injection compression molding method is a method that, in order to obtain uniform high-precise of the configuration by correcting shrinkage of molten resin, the mold is closed to retain a compressing margin in a cavity for lens, and the molten resin is injected to feed into the cavity for lens, and then compressed for the compressing margin to obtain lens. Provided that the lens has the different thickness so that the lens is brought about the different thickness when the curvature between the rear face and front face of the lens is different, the lens has two kinds of a plus lens, which the thickness of the central portion is thicker than the peripheral portion, and a minus lens, which the thickness of the central portion is thinner than the peripheral portion. Further, the thickness of the lens is different dependent upon a design of an optical lens, for example, an aspherical lens, having approximate 1.50 of index of refraction, can be adjusted to designing values of 4.2 mm of the thickness of the central portion and 1.0mm of the thickness of the peripheral portion in the case of +2.00 Diopter of the degree of lens, and of 1.4mm of the thickness of the central portion and 7.9mm of the thickness of the peripheral portion in the case of -4.00 Diopter of the lens power. However, when the above lenses are molded to be compressed under the same conditions, the following disadvantages are produced by the difference of a shape properties. In the molding of the minus lens, the central portion of the lens is thinner than the peripheral portion thereof, so that the central portion of the cavity has a large flow-resistance. Therefore, the molten resin injected into the cavity hardly flows in the central portion of the cavity, so that the resin flows around from the peripheral portion to the central portion by separately flowing, resulting in a disadvantage that a lot of weld marks are easily produced in the central portion. Further, in the molding of the plus lens, when the difference between the volume of the cavity and the quantity of the fed molten resin is extremely big, the flow property of the molten resin is reduced, and naturally, a non-fed part is produced, with the result that a flow mark is easily produced on the lens after molding. It is an object of the present invention to provide an injection compression molding method of a spectacle lens, in which a lens having a different thickness regardless of the shape properties of lens, namely a plus lens and a minus lens, can be molded with a high degree of precision and high quality. It is another object of the present invention to provide an injection compression molding method of a spectacle lens, in which a plus lens and a minus lens can be efficiently molded from an injecting process to a process for removing from the mold. It is still an object of the present invention to provide a spectacle lens being outstanding for uniform optical properties with a high degree of precision and high quality. EP 0339642 discloses a mold assembly, and methods of mounting and removing insert thereof, and ejecting the 5 insert. US 4184835 discloses a mold apparatus, comprising injection and compression mold blocks for use in molding parts from thermoplastic resins. SPIE - Ophthalmic lens design and fabrication Vol. 1529 July 1991 (pp.13-21) G. Galic and S. Maus "Improved Plastic Molding Technology for Ophthalmic Lens & Contact Lens", discloses an injection molding technique for producing high minus lenses and reviews molding technology at the time of publication. According to the present invention, an injection compression molding method of a spectacle lens having a meniscus-shape using an injection compression moulding apparatus having a function for setting a predetermined compression margin for molding a lens, in which a mould is closed to preserve a predetermined compressing margin previously adjusted in a cavity for a lens, formed with an optical insert exchanged as necessary, and a molten resin is injected and fed into the cavity for the lens, compressed for said predetermined compressing margin at least from at the time before the injection of the molten resin is completed, is characterised by adjusting said predetermined compressing margin for producing a minus lens having a thinner central portion than a peripheral portion thereof to be larger than said predetermined compressing margin for producing a plus lens having a thicker central portion than a periphery portion thereof, wherein the predetermined compressing margin for producing the minus lens is above 0.8 mm and is determined according to lens power, and the predetermined compressing margin for producing the plus lens is less than 0.8mm, the compression margin being established in accordance with lens power of the plus lens and the minus lens, and wherein, after completion of injection of the molten resin, a nozzle is shut to define a closed space of the lens cavity and a sprue and a runner for supplying the molten resin into the cavity to prevent back flow of molten resin during compression, wherein the adjustment of the predetermined compressing margin for producing the plus lens is carried out by opening the mould at the predetermined compressing margin after the mould is closed from the initial position where a compressing margin in the cavity for the lens is maximum until a position where the compressing margin is disappeared; and wherein the adjustment of the predetermined compressing margin for producing the minus lens is carried out by closing the mould from the initial position where the compressing margin in the cavity for the lens is maximum until a position where the predetermined compressing margin is preserved. Here, the meaning of "at least from at the time before the injection of the molten resin is completed" includes "at the time before the injection is completed" or "after the injection is completed". In the aforementioned molding method, the predetermined compressing margin for producing the minus lens is adjusted to be larger than the predetermined compressing margin for producing the plus lens, so that the larger space in the cavity can be ensured and the flow properties of the molten resin in the cavity is improved, therefore, in producing the minus lens, the molten resin reaching the inside of the cavity flows through the central portion of the cavity into the peripheral portion without separately flowing. As a result, the appearance of a weld mark in the central portion can be avoided, and sufficient pressurizing force is retained in an intensity lens, resulting in the improvement of transfer properties with the mold. From the reason, regardless of shape-properties of lens, the plus lens and the minus lens can be formed with a high degree of precision and high quality. In the aforementioned injection compression molding method, it is considered that the predetermined compressing margin for producing the minus lens is needed to be adjusted to be larger than the predetermined compressing margin for producing the plus lens. At the time, the adjustment of the predetermined compressing margin for producing the minus lens carried out by opening the mold for the predetermined compressing margin after the mold is closed from the initial position where the compressing margin in the cavity for lens is maximum until a position where the predetermined margin is disappeared, like the adjustment of the predetermined compressing margin for producing the plus lens, it causes a disadvantage of inferior efficiency as for time from a view of a long distance which the mold is opened for the predetermined compressing margin. More specifically, in the present invention, the predetermined compressing margin in the case of the plus lens is not large and is defined as less than 0.8 mm, for example 0.1-0.2 mm is sufficient for a lens having +1.00 to +3.00 Diopter. In a control for closing the mold, from a view of a structure of a molding apparatus, it takes much time to control the movement from the maximum compressing position to upward at 0.1 mm of pitch because of necessity of sophisticated control, for example, it takes approximately 10 seconds for moving 5 mm. The movement of the mold from top to bottom is easy, it takes less than one second, even for 15 mm. Therefore, in the injection compression molding method of the spectacle lens according to the present invention, the adjustment of the predetermined compressing margin for producing the plus lens is carried out by opening the mold at the predetermined compressing margin after the mold is closed from the initial position where a compressing margin in the cavity for a lens is maximum until a position where the compressing margin is disappeared; and the adjustment of the predetermined corresponding margin for producing the minus lens is carried out by closing the mold from the initial position where the compressing margin in the cavity for the lens is maximum until a position where the predetermined compressing margin is preserved. By adjusting as described above, the predetermined compressing margin for producing the minus lens is adjusted by closing the mold from the initial position where the compressing margin in the cavity for lens is maximum until the position where the predetermined compressing margin is preserved, namely, the operation in which the mold is opened for the compressing margin as a long distance is not needed, resulting in the swift adjustment of the predetermined compressing margin with a high degree of precision. Further, the predetermined compressing margin for producing the plus lens is adjusted by opening the mold for the predetermined compressing margin of a short distance after the mold is closed from the initial position where the compressing margin in the cavity for lens is maximum until the position where the compressing margin is disappeared, resulting in the swift adjustment of the predetermined compressing margin with a high degree of precision as in the case of the minus lens. In the aforementioned injection compression molding method, the predetermined compressing margin for producing the minus lens is defined to be larger than the predetermined compressing margin for producing the plus lens, so that the flow of the molten resin is stopped while a large non-fed part is retained in the cavity for lens at the time the injection of the molten resin is completed, therefore, it is considered to occur a disadvantage that feed history of resin, called as a flow mark, is easily appeared in a critical portion of the fed portion and the non-fed portion in the molded lens after the pressurizing process. For the above points, the injection compression molding method of the' spectacle lens according to the present invention can further improve the flow properties and the transfer properties of the resin by starting compressing for the predetermined compressing margin for producing the minus lens before the injection of the molten resin is completed, and starting compressing for the predetermined compressing margin for producing the plus lens after the injection of the molten resin is completed. That is to say, when the minus lens is molded, the compression for the predetermined compressing margin is started before the injection of the molten resin is completed and the volume of the cavity for lens becomes smaller, so that the flow properties of the molten resin is improved, therefore, the large non-fed part is not much retained in the cavity for lens at the time the injection of the molten resin is completed, resulting in avoidance of the appear of the flow mark. Here, provided that, in producing the minus lens, a spure, a runner, and the cavity for the lens are to be a sealed space just after the injection of the molten resin is completed, further in producing the plus lens, the spure, the runner, and the cavity for lens are to be a sealed space before the compression for the predetermined compressing margin is started, the molten resin does not back-flow to out of the sprue, the runner and the cavity for lens although the molten resin in the cavity for lens is pressurised by the compression, resulting in the lens superior to the transfer properties of the mold, without a striae, feed history or the like, and with a high degree of precision and high quality. According to the above molding method, the following effects are expected, in addition to the effect that the plus lens and the minus lens, regardless of the shape-properties of lens, can be formed with a high degree of precision and high quality to avoid appearance of the weld in the central portion. That is to say, the holding member is moved to be pushed toward the stationary die by the eject pin when the die fitting member of the movable die is retreated, thereby the insert is advanced toward the stationary die relatively to the die fitting member of the movable die, so that the space, having the same degree as the degree of the retreating movement of the die fitting member, is not formed between the lens-molding in the cavity and the insert, therefore, the compressed air can be controlled to produce excessively, and the influence of the pressure of the compressed air upon the lens-molding can be avoided, resulting in the molding having the high precision of molding, without parts of molded in the spure or the runner are bent or fault brought when the molding is removed from the mold, such as the displacement of the molding to the mold is produced. Here, when the insert is advanced toward the stationary die relatively to the die fitting member of the movable die by moving the holding member to be pushed by the eject pin when the die fitting member of the movable die is retreated, the degree of the advancing movement may be the same as the degree of the retreating movement (the degree of slightly opening) of the die fitting member, and may be larger than the degree of the retreating movement, but it is preferable to be smaller. Provided that the degree of the advancing movement is defined to be smaller than the degree of the retreating movement, the space can be formed between the insert and the lens-molding, so that the lens-molding does not fall from the cavity even when the movable die is separated from the stationary die, with the result that the lens-molding is prevented from damage caused by falling. Especially, it is advisable that the space between the insert and the lens-molding is formed at 1-4 mm. The space formed at less than 1 mm causes the fall of the lens-molding upon occasion, and the space formed at more than 4 mm causes inferior effect of controlling to excessively produce the compressed air. More specifically, release of clamping force after closing the mold is rapidly and greatly retreated for the compressing margin adjusted large, so that, especially, the conditions (mainly, temperature) for molding the convex face of the lens are greatly changed. Therefore, phenomenons, for example, fault, brought when the molding is removed from the mold, arises by strongly exerting force of removing from the mold on a part of the lens or the spure or the runner is broken, occur. Hence, by providing a mid-ejecting function with the adjustment of the aforementioned space, it is avoided that the partially strong force of removing from the mold is excessively exerted on a part of the molding. Especially, when the plus lens is molded, the strength of the connecting part with the runner is not strong in structure for the thinner peripheral portion of the lens, so that the aforementioned ejecting method is effective. Here, the lens is the spectacle lens having a meniscus-shape. In the accompanying drawings:- Fig. 1 is a sectional view showing a mold for molding with injection and compression according to a preferable embodiment of the present invention; Fig. 2 is a sectional view taken along the II - II line in Fig. 1; Fig. 3 is a flow chart showing molding processes in the above embodiment; Fig. 4 is a drawing showing a state before molten resin is injected and fed when a plus lens is formed in the above embodiment; Fig. 5 is a drawing showing a state after the molten resin is compressed when the plus lens is formed in the above embodiment; Fig. 6 is a drawing showing a state before the molten resin is injected and fed when a minus lens is formed in the above embodiment; Fig. 7 is a drawing showing a state after the molten resin is compressed when the minus lens is formed in the above embodiment; Fig. 8 is a drawing showing a state in which, in the above embodiment, a die fitting member of a upper die is lifted up from a die body at the degree of slightly opening, and an insert of the upper die is moved downward relatively to the die fitting member with an eject pin; and Fig. 9 is a drawing showing a state in which the upper die and a lower die are opened to separate from the state of Fig. 8. The preferred embodiment according to the present invention will be explained in detail below with reference to the attached drawings. Fig. 1 is a sectional view of a mold for molding with injection and compression which is used in an injection compression molding method of a spectacle lens (a spectacle lens having a meniscus shape; fixed focus, multifocus, progressive multifocus) according to the embodiment, and further Fig. 2 is a sectional view taken along the II-II line in Fig. 1. Incidentally, materials of the spectacle lens molded here is a thermoplastic resin, such as PMMA (poly methyl methacrylate), PC (polycarbonate) or the like. In the embodiment, in order to prevent striae, optical distortion or the like, the injection is carried out at low output. As shown in Fig. 1, the aforementioned mold for molding with the injection and compression is a mold for molding two lenses, in which cavities 3 for the two spectacle lenses are formed between a upper die 1 and a lower die 2, caused by dividing the mold in the vertical direction at a parting line PL. The upper die 1, which is a movable die opening and closing for the lower die 2 as a stationary die in the vertical direction, includes a die fitting member 16 and a die body 4 attached to the die fitting member 16 to be able to move toward the lower die 2. In turn, the die fitting member 16 is composed of a upper member 16A and a lower member 16B. the die body 4 is composed of an insert guide 5 and die plates 6 and 7. The lower die 2 includes a die body 8, composed of an insert guide 9 and a die plate 10, and a die fitting member 15 for attaching the die body 8. Inside of each of the insert guides 5 and 9, inserts 11 and 12 forming the cavity 3 are held to be capable of sliding in a direction at right angles to the parting line PL. The die body 4 of the upper die 1 is connected to the die fitting member 16 with a bolt 17 shown in Fig. 2, and a plate spring 17A, inserted on the outer circumference of the bolt 17, is provided to connect between the die body 4 and the die fitting member 16. Incidentally, the die fitting member 16 is adopted to be moved in the vertical direction by a clamping cylinder (not shown). A space S is formed between the die body 4 and the die fitting member 16, in which the die body 4 and the die fitting member 16 are opened and closed at the space S in the vertical direction while being guided with a guide pin 18. A slightly opening cylinder (not shown) is arranged downward the die fitting member 15 to cause the die fitting member 16 to lift up in opposition to clamping force caused by the clamping cylinder, thereby the space S is formed. A hydraulic cylinder 19, placed with the bottom up, is provided in the die fitting member 16 to move in the vertical direction. A piston rod 21, connected to a piston 20 of the hydraulic cylinder 19, is passed through a back insert 22 fixed on the lower face of the cylinder 19 and provided with a T-shaped clamping member 23 at the end of the piston rod 21. The T-shaped clamping member 23 is detachably engaged with a T-shaped groove formed on the upper end face of the insert 11. A hydraulic cylinder 26, placed with the top down, is provided in the die fitting member 15. A piston rod 28, connected to a piston 27 of the hydraulic cylinder 26, is passed through the die fitting member 15 and includes a T-shaped clamping member 29 at the end. The T-shaped clamping member 29 is detachably engaged with a T-shaped groove formed on the lower end face of the aforementioned insert 12. On the upper end of the aforementioned hydraulic cylinder 19, a pressure receiving portion 32 is fixed. Whereupon the pressure receiving portion 32 is pushed down by an eject pin 34 inserted from a hole 33 formed in the die fitting member 16, the hydraulic cylinder 19, the back insert 22 and the insert 11 are also pushed down, thereby a lens-molding molded in the cavity 3 is pushed out when the upper die 1 is opened from the lower die 2. In the aforementioned portion, a holding member, for holding the insert 11 by the back insert 22, the hydraulic cylinder 19 and the pressure receiving portion 32, is structured. At the central portion of the die fitting member 16 of the upper die 1, an eject bar 35 is arranged to be able to move in the vertical direction. On the upper end of the eject bar 35, a pressure receiving portion 36 is fixed. Whereupon the pressure receiving portion 36 is pushed down by an eject pin 38 inserted from a hole 37 formed in the die fitting member 16, the eject bar 35 is pushed down. To the pressure receiving portion 32, spring force caused by a spring 40, wound on the outer circumference of an eject return-pin 39, acts upward. Incidentally, spring force caused by a spring (not shown), wound on the outer circumference of an eject return-pin, acts upward to the pressure receiving portion 36. Therefore, provided that the eject pins 34 and 38 are lifted up, the pressure receiving portions 32 and 36 are also lifted up to return to original positions. In the aforementioned portion, a holding member, structured with the back insert 22, the hydraulic cylinder 19 and the pressure receiving portion 32, is abutted to die fitting member 16 to be supplied with elastic urging force in the opposite direction to the lower die 2 by the spring 40 as an elastic member all the time. Operation in the embodiment will be explained below. First, responsive to kinds of lens intended to be molded, the inserts 11 and 12 are changed. When the inserts 11 and 12 are changed, the upper die 1 including the die fitting member 16 is lifted up to separate from the lower die 2. Further, by lifting the piston rod 21 of the hydraulic cylinder 19 down and lifting the piston rod 28 of the hydraulic cylinder 26 up, the T-shaped clamping members 23 and 29, attached at the end of the piston rods 21 and 28, are projected from the insert guides 5 and 9. The inserts 11 and 12, newly placed to the die bodies 4 and 8 of the upper die 1 and the lower die 2, are horizontally delivered while being held with arms of a robot (not shown), the T-shaped grooves 24 and 30 of the inserts 11 and 12 are engaged with the T-shaped clamping members 23 and 29. After that, the piston rod 21 of the hydraulic cylinder 19 is lifted up to pull the insert 11 up, and the piston rod 28 of the hydraulic cylinder 26 is lifted down to pull the insert 12 down. As a result, the inserts 11 and 12 are inserted into the insert guides 5 and 9. As described thus far, the inserts are changed to the inserts 11A and 12A as shown in Figs. 4 and 5 when the plus lens (a lens having the thicker central portion than the peripheral portion) is molded, and the inserts are changed to the inserts 11B and 12B as shown in Figs. 6 and 7 when the minus lens (a lens having the thicker central portion than the peripheral portion). When the lens is molded, operation is advanced along a flow chart shown in Fig. 3. First, the mold is closed as a state shown in Figs. 1 and 2. That is to say, the upper die 1 is lifted down by the clamping cylinder to touch the die plate 6 of the upper die 1 to the die plate 10 of the lower die 2 and to close the mold with a state the plate spring 17A is not compressed. In this state, the space S is adjusted at the maximum degree of slightly opening (approximate 15 mm). Next, the degree of slightly opening (a predetermined compressing margin) is adjusted. At this time, less than 0.8 mm of the degree of slightly opening S (+) is adjusted when the plus lens is molded. More than 5 mm of the degree of slightly opening S (-) is adjusted when the minus lens is molded. More specifically, the predetermined compressing margin for producing the minus lens is adjusted larger than the predetermined compressing margin for producing the plus lens. Here, when the plus lens is molded, namely, when less than 0.8 mm of the degree of slightly opening S (+) is adjusted, as shown in Fig. 4, the die fitting member 16 is further lifted down by the clamping cylinder (at this time, the plate spring 17A is compressed), and after the space S is completely disappeared, the die fitting member 16 is lifted up at the aforementioned degree of slightly opening S (+) in opposition to clamping force of the clamping cylinder by the slightly-opening cylinder to adjust the degree of slightly opening S (+) . And when the minus lens is molded, namely, when more than 5 mm of the degree of slightly opening S (-) is adjusted, as shown in Fig. 6, the die fitting member 16 is lifted down until a position, where the aforementioned degree of slightly opening S (-) is preserved, by the clamping cylinder (at this time, the plate spring 17A is compressed), and is stopped at the position to adjust the degree of slightly opening S (-) Next, the molten resin is injected and fed. The molten resin is injected from a nozzle of the injection molding apparatus connected to a sprue bush 57 and fed through a sprue 58 and a runner 59 into the cavity 3. At this time, in the case the plus lens is molded (Fig. 4), the thickness of the central portion of the cavity 3 (the central portion of the lens) is larger, so that the molten resin reaching the inside of the cavity 3 reaches the peripheral portion through the central portion of the cavity 3 (the central portion of the lens). And in the case the minus lens is molded, the degree of slightly opening S (-) is adjusted at more than 5 mm, namely, the thickness of the central portion of the cavity 3 is adjusted to be large, so that the molten resin reached the inside of the cavity 3 reaches the peripheral portion through the central portion of the cavity 3 without separately flowing. Therefore, in any cases, a weld mark in the central portion is controlled. Further, in the case the plus lens is molded (Fig. 4), after the molten resin is completed being injected, a space including the cavity 3, the runner 59 and the sprue 58 is to be a sealed space by closing the nozzle, and continuously, the molten resin is pressurized (compressed). That is to say, as shown in Fig. 5, the die fitting member 16 is lifted down at the degree of slightly opening S (+) by the clamping cylinder. And in the case the minus lens is molded (Fig. 6), the molten resin is started being pressurized (compressed) before being completed being injecting. More specifically, when approximate 90-95 % of the molten resin injected is injected, the pressurization is started by the clamping cylinder, and as shown in Fig. 7, the die fitting member 16 is lifted down at the degree of slightly opening S (-) . At this time, the nozzle is closed just after the molten resin is completed being injected to cause the space including the cavity 3, the runner 59 and the sprue 58 to be the sealed space. Then, after the plus lens or the minus lens is molded as described thus face, the lens is ejected. The die fitting member 16 of the upper die 1 is lifted up by the clamping cylinder, namely, is lifted up from the lower die 2, to open the degree of slightly opening S between the die body 4 and the die fitting member 16. At this time, the eject pin 34 is lifted down by the eject cylinder to cause the pressure receiving portion 32 to move to press downward from the die fitting member 16 by the eject pin 34. The degree of pressured movement is smaller than the degree of slightly opening S, for example, when the degree of slightly opening S is 15 mm, the degree of pressured movement is 13 mm. In other words, when the die fitting member 16 is lifted up, the insert 11 is lifted down toward the lower die 2 relatively to the die fitting member 16. As a result, the degree of the upward-movement of the insert 11, which should be, originally, lifted up at the same degree as when the die fitting member 16 is lifted up at the degree of slightly opening S, is controlled to be smaller, for example, in molding the minus lens, as shown in Fig. 8, the insert 11 is a slightly space A, which is 2 mm when the degree of slightly opening and the degree of the pressured movement are values as described above, distant from the spectacle lens 44A as the lens-molding 44 molded in the cavity 3. As shown in Fig. 9, the die fitting member 16 and the die body 4 of the upper die 1 are lifted up by the clamping cylinder so as to open the upper die 1 from the lower die 2 at the parting line PL. After that, a part of the lens-molding 44 exposed from the lower face of the upper die 1 is gripped by a gripping device, and further, the eject pins 34 and 38 are lifted down by each eject cylinder, thereby the pressure receiving portions 32 and 36 are moved to be pressed, naturally, the lens-moldings 44 are pushed out with the insert 11 and the eject bar 35. At this time the lens-molding 44 is pushed out, the insert 11 is only the space A distant from the spectacle lens 44A of the lens-molding 44, so that air entering the space A is not compressed until becoming large pressure by the insert 11, with the result that the lens-molding 44 can be pushed out from the upper die 1 without the influence of the large pressure of the compressed air upon the spectacle lens 44A. More specifically, when the die fitting member 16 of the upper die 1 is lifted up at the degree of slightly opening S from the die body 4, the pressure receiving portion 32 is not moved downward to be pressed by the eject pin 34, and further when the insert 11 is not lifted down relatively to the die fitting member 16, the space having the same degree as the degree of slightly opening S is formed between the spectacle lens 44A of the lens-molding 44 and the insert 11, so that the excessive high-pressure air influences the spectacle lens 44A as a precise molding portion by greatly compressing air in the space when the spectacle lens 44A is pushed out with the insert 11, however, in the embodiment according to the present invention, a slight space A is formed between the spectacle lens 44A and the insert 11, so that the molding 44 can be pushed out with controlling to excessively produce the compressed air when the spectacle lens 44A of the lens-molding 44 is pushed out with the upper insert 11, with the result that the precise molding state of the spectacle lens 44A is ensured without parts of molded in the spure or the runner are bent or fault brought when the molding is removed from the mold, such as the displacement of the molding to the mold is produced. According to the embodiment, the degree of slightly opening S (-) for producing the minus lens is adjusted to be larger than the degree of slightly opening S (+) for producing the plus lens, thereby the molten resin reached the inside of the cavity 3 flows through the central portion of the cavity 3 into the peripheral portion without separately flowing when the minus lens is molded, so that appearance of a weld mark in the central portion is avoided. Therefore, the plus lens and the minus lens, regardless of kinds of lens, can be molded with a high degree of precision and high quality. At this time, the degree of slightly opening S (-) for producing the minus lens is needed to be adjusted to be larger than the degree of lightly opening S (+) for producing the plus lens, but by lifting the die fitting member 16 of the upper die 1 down from the initial position where the degree of slightly opening S is maximum until the position where the degree of slightly opening S (-) is preserved, the degree of slightly opening S (-) is adjusted; with the result that the degree of slightly opening S (-) can be swiftly adjusted with a high degree of precision. Further, the degree of slightly opening S (+) for producing the plus lens is smaller than the degree of slightly opening S (-) producing the minus lens, therefore the die fitting member 16 of the upper die 1 is opened at the degree of slightly opening S (+) after being lifted down from the initial position where the degree of slightly opening S is maximum until the position where the degree of slightly opening S is disappeared, thereby the degree of slightly opening S (+) is adjusted, with the result that the degree of slightly opening S (+) can be swiftly adjusted with a high degree of precision. In molding the minus lens, due to the fact that the volume in the cavity 3 becomes reduced before the injection of the molten resin is completed by starting compressing for the degree of slightly opening S (-) before the injection of the molten resin is completed, a large non-fed part in the cavity is not much retained at the time the injection and feed of the molten resin is completed, therefore the appearance of the flow mark is avoided. That is to say, provided that the degree of slightly opening S (+) is adjusted to be large, the flow of the molten resin is stopped while the large non-fed part is retained in the cavity at the time the injection and feed of the molten resin is completed, thereby a disadvantage that a flow mark is easily appeared on a critical portion of a fed part and the non-fed part is considered, however, with the processes of the embodiment, the appearance of the flow mark is avoided. When the die fitting member 16 of the upper die 1 is lifted up from the lower die 2, the holding member, holding the insert 11 provided in the die body 4 of the upper die 1 is moved to be pressed toward the lower die 2 with the eject pin 34 to cause the insert to lift down toward the lower die 2 relatively to the die fitting member 16, so that when the lens-molding 44 is pushed out with the insert 11, it can be pushed out while the product of the compressed air is controlled, therefore, the pressure of air compressed with high-pressure has an influence on the lens-molding 44, with the result that the lens-molding 44 can be pushed out while a molding precision of the lens-molding 44 molded with a high degree of precision is ensured. In the case that the die fitting member 16 of the upper die 1 is lifted up from the die body 4 at the degree of slightly opening S, when the insert 11 is lifted down relatively to the die fitting member 16 by moving the pressure receiving portion 32 to press downward with the eject pin 34, the degree of the downward-movement is defined to be smaller than the degree of the upward-movement (the degree of slightly opening S) of the die fitting member 16, so that the space can be formed between the insert 11 and the spectacle lens 44A of the lens-molding 44. Therefore, even when the upper die 1 is opened from the lower die 2, the lens-molding 44 does not fall from the cavity 3, resulting in the prevention of damaging the lens-molding 44 by falling. Furthermore, in the embodiment, the two cavities 3 are formed by the insert 11 and the like, and the holding member of the insert 11, composed of the back insert 22, the hydraulic cylinder 19 and the pressure receiving portion 32, is supplied with the elastic urging force upward by the spring 40 to be independent of each insert 11, therefore even when the spring 40 of each insert 11 has a different force caused by the spring, the structure is not under the influence of the force caused by the spring, however, the eject pin 34 is provided to each insert 11, namely, each holding member of the insert 11, so that the holding member independent of one another can be moved to be pressed downward with the specified way by the eject pin 34, with the result that two spectacle lenses 44A of the lens-moldings 44 can be pushed out with the two inserts 11. In the embodiment described thus far, it is intended that the predetermined compressing margin is adjusted dependent upon the degree of slightly opening which is formed between the die body 4 and the die fitting member 16, but another mold may be used. For example, a mold, having a structure in which the predetermined compressing margin is adjusted from the position of a cavity core provided to be projected into the cavity 3, and the compression is carried out by projecting the cavity core into the cavity 3. And, in the aforementioned embodiment, it is intended that the compression for the degree of slightly opening S (-) is started at the time approximate 90-95 % of the molten resin is injected when the minus lens is molded, but this percentage may be selectively defined dependence upon the volume of the cavity 3, kinds of resin, the lens power and so on. Further, in the aforementioned embodiment, it is intended that the eject pin 34 is moved downward in two steps to be simultaneous with when the die fitting member 16 of the upper die 1 is lifted up from the die body 4 at the degree of slightly opening S and when the mold is opened to separate the die body 4 from the lower die 2, but when the movement for slightly opening the die fitting member 16 by the clamping cylinder and the movement for opening the mold to separate the die body 4 from the lower die 2 are continuously carried out, the eject pin 34 is continuously moved downward, thereby the degree of the downward-movement of the insert 11 against the die fitting member 16 is defined to be larger, and the lens-molding 44 may be pushed out as it is. According to the injection compression molding method of the spectacle lens of the present invention, the predetermined compressing margin for producing the minus lens is adjusted to be larger than the predetermined compressing margin for producing the plus lens, with result that the appearance of the weld mark in the central portion is avoided even when the minus lens is molded, and naturally, the plus lens and the minus lens can be molded with a high degree of precision and with high quality, regardless of the shape properties of the lens. The predetermined compressing margin for producing the minus lens is adjusted by closing the mold from the initial position, where the compressing margin in the cavity 3 is maximum, until the position, where the aforementioned compressing margin is preserved, resulting in prosecution of the efficient adjustment. Further, when the minus lens is molded, the compression of the aforementioned compressing margin is started before the injection of the molten resin is competed, so that the large non-fed part is not much retained in the cavity at the time the injection of the molten resin is completed, therefore, the appearance of the flow mark can be avoided. When the die fitting member of the movable die is retreated from the stationary die, the holding member, holding the insert provided in the die body of the movable die, is moved to be pressed toward the stationary die with the eject pin to cause the insert to advance toward the stationary relatively to the die fitting member, so that the lens-molding can be pushed out while the product of the compressed air is controlled when the lens-molding is pushed out with the insert. Therefore, the pressure of air compressed with high pressure does not have influence on the lens-molding, with the result that the operation the lens-molding is pushed out can be carried out while a molding precision of the lens-molding 44 molded with a high degree of precision is ensured. Naturally, the processes from the injection to the removal from the mold can be efficiently carried out. Further, the spectacle lens is obtained by using the injection compression molding, in which the spectacle lens is molded with the injection and the compression to define the predetermined compressing margin for producing the minus lens, having the thinner central portion than the peripheral portion, to be larger than the predetermined compressing margin for producing the plus lens, having the thicker central portion than the peripheral portion, resulting in the spectacle lens superior to the optical properties with a high degree of precision, high quality and uniform quality.

Claims: An injection compression moulding method of a spectacle lens (44A) having a meniscus-shape using an injection compression moulding apparatus having a function for setting a predetermined compression margin for moulding a lens, in which a mould is closed to preserve a predetermined compressing margin(S) previously adjusted in a cavity (3) for a lens (44A), formed with an optical insert (11, 12) exchanged as necessary, and a molten resin is injected and fed into the cavity for the lens, compressed for the predetermined compressing margin at least from at the time before the injection of the molten resin is completed, characterised by : adjusting the predetermined compressing margin (S) for producing a minus lens having a thinner central portion than a peripheral portion thereof to be larger than said predetermined compressing margin for producing a plus lens having a thicker central portion than a periphery portion thereof, wherein the predetermined compressing margin for producing the minus lens is above 0.8mm and is determined according to lens power, and the predetermined compressing margin for producing the plus lens is less than 0.8mm, the compression margin being established in accordance with lens power of the plus lens and the minus lens, and wherein, after completion of injection of the molten resin, a nozzle is shut to define a closed space of the lens cavity and a sprue and a runner for supplying the molten resin into the cavity to prevent back flow of molten resin during compression, wherein the adjustment of the predetermined compressing margin (S) for producing the plus lens is carried out by opening the mould at the predetermined compressing margin (S) after the mould is closed from the initial position where a compressing margin in the cavity (3) for the lens is maximum until a position where the compressing margin is disappeared; and wherein the adjustment of the predetermined compressing margin for producing the minus lens is carried out by closing the mould from the initial position where the compressing margin in the cavity for the lens is maximum until a position where the predetermined compressing margin is preserved.

Inventors: ASAMI HIROSHI, NISHIMOTO TATSUO, SAITO KIYOHIRO, ASAMI, HIROSHI, NISHIMOTO, TATSUO, SAITO, KIYOHIRO
Applicants: HOYA CORP, HOYA CORPORATION
Application year: 1996
Main classification: B29C45
IPC codes: B29C45, B29D11