JP2012153039A - Injection mold, method for injection molding and lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection mold which can prevent the deterioration of productivity while preventing the deterioration of optical characteristics caused by a weld line, in regard to a thin concave lens formed of resin.SOLUTION: Heat insulating layers 14 and 24 having lower heat conductivity than that of a mold are provided on molding surfaces of a lens molding space 3. In the lens molding space 3, molten resin passing on the right side of an optical function molding portion 31 of a flange molding part 32 and molten resin passing on the left side of the optical function molding portion 31 of the flange molding part 32 out of the molding resin flowing in from gates 61 and 62 are made to associate with each other at the side of the flange molding part 32 opposite to gates 61 and 62. At this time, setting is performed so that the molten resin passing through the optical function molding portion 31 including the thinnest portion from the flange molding part 32 out of the molten resin made to flow into the lens molding space 3 from the gates 61 and 62 may reach the flange molding part 32 beyond a boundary between the optical function molding portion 31 and the flange molding part 32 at a side opposite to the gates 61 and 62.

Description

  The present invention relates to an injection mold for molding a thin resin lens, an injection molding method using the injection mold, and a thin resin lens.

  Currently, small cameras with high resolution are built in mobile phones and smartphones. Also, you can take a picture of the back of the car, take pictures of obstacles in front of the car, record an accident, etc. A small, high-resolution camera may be used as the camera or the like.

  In these cameras, a lens unit in which a plurality of lenses are arranged and fixed in the optical axis direction is used. For example, when such a lens unit is incorporated in a thin device such as a mobile phone or a smartphone, the length of the lens unit along the optical axis direction is limited. Therefore, it is required to reduce the thickness of each lens in the lens unit. For example, the concave lens used in the lens unit can reduce the thickness of the entire lens by making the thickness of the thinnest part (thickness along the optical axis direction) as thin as possible.

Therefore, there is a demand for a resin concave lens that is as thin as possible in the center.
In the injection molding of such a resin (thermoplastic resin) lens, a temperature considerably higher than the glass transition temperature of the molten resin so that the molten resin injected into the injection mold has fluidity. On the other hand, the injection mold is set to a temperature lower than the glass transition temperature described above in order to cool and cure the lens at least before removing the molded lens from the mold. Here, the injection mold has, for example, a movable mold and a fixed mold each having a cavity filled with molten resin, and the movable mold is separated from the fixed mold after molding. Thus, the molded lens can be taken out.

In forming a concave lens as thin as possible, the temperature of the cavity portion of the mold is set to a temperature lower than the glass transition temperature of the injected molten resin, and the thickness along the optical axis direction of the thinnest thinnest portion is set. It has been found that the following problems arise when trying to mold a lens of 0.4 mm or less.
That is, when the lens is injection-molded using an injection mold in which the thickness of the thinnest part of the concave lens is 0.4 mm or less, a weld line is generated in the molded lens.
As a cause of the occurrence of this weld line, the present inventors have found that a concave lens using a mold having a mold temperature that is lower by, for example, about 5 ° C. to 10 ° C. than the molding temperature of normal resin molding, that is, the glass transition temperature of the molten resin. In the injection molding, when the thickness along the optical axis direction of the thinnest part of the mold cavity becomes 0.4 mm or less, it was found that the flow rate of the molten resin in that part becomes extremely slow.

  When the above-mentioned molten resin is in contact with the inner surface of the cavity lower than its glass transition temperature, heat is conducted to the mold at the portion close to the inner surface of the molten resin cavity and the fluidity of the molten resin is lowered. It becomes a state. On the other hand, at a position away from the inner surface of the cavity of the molten resin to some extent, the heat conduction is suppressed by the molten resin existing between the inner surface of the cavity and the fluidity is maintained. It becomes possible to flow at a flow rate.

  That is, the fluidity of the molten resin is maintained at a position away from the inner surface of the cavity by 0.2 mm or more, but when closer to the inner surface of the cavity than that, the molten resin rapidly dissipates heat to the mold side. It seems that the temperature is lowered and the fluidity of the molten resin is greatly reduced. Accordingly, when the distance between the inner surfaces of the opposing cavities becomes narrower than 0.4 mm, which is twice as large as 0.2 mm, the fluidity of the molten resin in the section from the opposing inner surface to 0.2 mm is low in the cavity cross section. As a result, there is no portion where the fluidity of the molten resin is maintained.

As a result, as described above, when the thickness of the cavity (that is, the distance between the inner surfaces) becomes 0.4 mm or less, the flow rate of the molten resin is clearly slowed down, and the flow of the molten resin may eventually stop. There is. When the flow of the molten resin stops in the cavity, the molten resin dissipates heat to the mold and is immediately cured.
In this case, the flow velocity of the molten resin flowing on the outer peripheral side of the central portion is faster than the flow velocity of the molten resin flowing through the portion where the thickness of the central portion of the cavity is 0.4 mm or less.
As a result, the molten resin flowing through the central part of the cavity out of the molten resin flowing into the cavity from the gate is in a state where the flow becomes extremely slow or stopped at the central part of the cavity. The molten resin that flows to the left and right from the central portion flows to the left and right of the molten resin that is substantially stopped at the central portion, and flows around the central portion to a portion that is opposite to the gate of the cavity. At this time, since the flow rate of the molten resin that flows to the left and right of the central portion is faster than the molten resin at the central portion of the cavity, the central portion is not yet flowed to the portion where the molten resin still flows. The molten resin that flows to the left and right of the part flows backward, and the gap is filled with the molten resin that flows backward.

Here, when the central portion of the concave lens is sufficiently thick, the molten resin is substantially uniform from the gate side portion of the cavity to the opposite side portion of the gate of the cavity without causing a large speed difference between the central portion and the outer peripheral portion. When it flows, the flow direction of the molten resin is also substantially uniform, and it is difficult for molten resins having different flow directions to associate with each other. However, as described above, when the molten resin flows differently in the central portion and the left and right sides thereof, the molten resin that has flowed through the left and right sides of the central portion from the gate side of the cavity is associated with each other on the opposite side of the gate of the cavity, Furthermore, as described above, the molten resin that has flowed back is associated with the molten resin that has flowed slowly or stopped in the central portion.
In this way, when molten resins having different flow directions are associated with each other in the cavity, there is a high possibility that a weld line is generated because the molten resins that have flowed and associated while lowering the temperature are not uniformly integrated. In particular, between the molten resin flowing in the central portion and the molten resin flowing backward, there is a possibility that the molten resin flowing in the central portion is already cured as described above, and a weld line is generated.

  Here, as a general weld line prevention method, for example, when the molten resin is injected, the temperature of the cavity portion of the injection mold is raised higher than the glass transition temperature of the molten resin, Prevents the glass transition point temperature from being touched by the mold, and then cures the molten resin in the cavity by lowering the temperature of the cavity part of the injection mold and lowering it below the glass transition temperature. There is a way to make it.

  In this method, since the temperature of the cavity portion of the mold is rapidly changed greatly, the configuration of the injection mold becomes complicated and the equipment cost increases. In addition, since heating and cooling time for the mold is required, the time required for one molding (cycle time) in the injection molding in which the molding and the taking-out of the molded product are repeated sequentially becomes long, and the productivity is low. Become.

In addition, as a method of obtaining a product without a weld line that occurs when the thickness of the central portion of the cavity is thin as described above, a lens molding space constituted by a cavity of an injection mold is prevented so that a weld line is not generated. The lens is made thicker than the target lens, thereby forming a preform lens without a weld line. By increasing the thickness of the lens, the molten resin is prevented from being brought into an associated state, thereby preventing the occurrence of weld lines. Since the lens of the molded preform is thicker than the target lens, it is compression-molded while being reheated to obtain a lens having a thickness as an actual product.
In this method, a compression molding machine is required separately from the injection molding machine, and the equipment cost is increased. Also, in addition to the time required for injection molding, time required for compression molding is required, and it is necessary for lens molding even if injection molding and compression molding are performed in parallel when producing lenses continuously. Time is increased and productivity is reduced.

It has been proposed to prevent the weld line as follows in the injection molding of the lens of the vehicle lamp, that is, the transparent cover of the lamp portion of the vehicle, instead of the small thin concave lens for the small camera described above ( For example, see Patent Document 1).
The lens of this vehicle lamp has an opening. In the cavity of the mold for molding this lens, there is an obstacle part where the molten resin cannot enter in order to form the opening. A line is formed. Therefore, by forming a heat insulating layer on the inner surface of the mold cavity, the molten resin in contact with the mold is prevented from being rapidly cooled to form a thick skin layer, and the generation of weld lines caused by the association of the skin layers. Is preventing.

  In addition, there has been proposed one that prevents the generation of weld lines by combining heating above the glass transition temperature of the mold as described above and the heat insulating layer formed on the inner surface of the cavity (for example, , See Patent Document 2).

JP 2003-111826 A JP 2001-113580 A

  By the way, when combining a heat insulation layer and the heating of a metal mold | die, the same problem as the case where a metal mold | die is heated more than the above-mentioned glass point transfer arises. In other words, equipment for controlling the mold temperature in a short time from a temperature higher than the glass transition temperature of the molten resin to a temperature lower than the glass transition temperature is expensive, and the cycle time of molding the lens is increased. This leads to a decrease in productivity.

Therefore, without controlling the temperature of the mold abruptly across the glass transition temperature of the molten resin (control to keep the mold within a predetermined temperature range is performed), the generation of the weld line is prevented only by the heat insulating layer. It is preferable.
However, as described above, in the concave lens with the thinnest part having a thickness of 0.4 mm or less, the heat insulating layer prevents the fluidity from being lowered due to heat radiation to the mold of the molten resin adjacent to the cavity inner surface, and the central part of the cavity However, even if the molten resin flows at a certain flow rate, the flow rate of the molten resin flowing through the thick outer peripheral portion on the left and right of the central portion is higher than the flow velocity of the molten resin flowing through the thin central portion. There is a high possibility of speeding up, and at the opposite side of the gate of the cavity, the molten resin flowing through the central portion of the cavity and the molten resin flowing through the left and right sides of the central portion of the cavity are associated with each other.

In this case, since the thickness of the cavity is thin even at a portion that is not the thinnest portion of 0.4 mm or less, the thickness of the associated molten resin is reduced, and the temperature is likely to decrease due to heat dissipation. Therefore, it is difficult to prevent the occurrence of weld lines. However, if the temperature of the molten resin is further suppressed by reducing the temperature of the molten resin due to heat radiation to the mold by increasing the thickness of the heat insulating layer, the molten resin will associate in the cavity as described above. Even so, there is a possibility that the occurrence of weld lines can be prevented when the temperature of the associated molten resin is higher than the glass transition temperature of the molten resin, for example.
However, in this case, the thick heat insulating layer keeps the molten resin at a high temperature, and after the molten resin is filled in the cavity, it takes time until the molten resin is cooled and cured to such an extent that it can be removed from the mold. It will take. As a result, the cycle time for sequentially molding the lenses becomes longer, and the productivity is lowered.

  That is, by reducing the thickness of the lens basically, the cycle time, in particular, the time required for cooling after molding in the cycle time should be shortened, but a heat insulating layer with extremely high heat insulating performance is provided. Therefore, there is a problem that the cooling time becomes long, the cycle time cannot be shortened, and the productivity is lowered.

  The present invention has been made in view of the above circumstances, and in a resin-made thin concave lens whose thinnest part is 0.4 mm or less, it is possible to prevent a decrease in optical characteristics due to a weld line and to reduce productivity. An object of the present invention is to provide an injection mold, an injection molding method, and a lens that can be prevented.

In order to achieve the above object, an injection mold according to claim 1 is for injection molding in which a lens molding space part in which a molten resin injected and a lens is molded is composed of at least a pair of molds. Mold,
The lens molding space includes an optical function molding unit that molds an optical function unit having an optical function as the lens, and a flange that is provided around the optical function unit and molds a flange unit used for fixing the lens. With a molding part,
The thickness along the optical axis direction of the lens at the thinnest thinnest part of the optical function molded part is 0.4 mm or less, and along the optical axis direction of the thickest thickest part of the flange molded part Is thicker than the thickness of the thinnest part of the optical function molded part,
The molding surface that is the inner surface of the lens molding space is provided with a heat insulating layer having a lower thermal conductivity than the mold,
At least the optical function molding portion is provided with a surface molding layer that covers the heat insulating layer and contacts the molten resin to be injected,
The material and thickness of the heat insulating layer are:
Of the molten resin that has flowed into the lens molding space from a gate connected to the flange molding part, a molten resin that passes through the right side of the optical function molding part of the flange molding part, and the optical function of the flange molding part When the molten resin that has passed through the left side of the molded part meets on the side of the flange molded part facing the gate,
Of the molten resin that has flowed into the lens molding space from the gate, the molten resin that has passed through the optical function molding part including the thinnest part from the flange molding part has the optical function on the side facing the gate. It is set so as to reach the flange molded part beyond the boundary between the molded part and the flange molded part,
A weld line is formed only in the flange forming portion.

In the first aspect of the present invention, the lens molding space (cavity) configured with at least a pair of molds and molding the lens has an optical function molding unit that molds an optical function unit having an optical function of the lens, and And a flange forming part for forming a flange part used for fixing the lens around the optical function part of the lens.
In the lens molding space, the thickness of the thinnest part of the optical function molding part is 0.4 mm, and the thickest part of the flange molding part is thicker than that.

A heat insulating layer is formed on the inner surface of the lens molding space, and a surface molding layer in contact with the molten resin is provided on the heat insulating layer at least in the optical function molding portion of the lens molding space.
Due to the heat insulating layer, the temperature of the molten resin injected into the lens molding space is conducted to the mold and the temperature decreasing rate when the temperature of the molten resin decreases is slowed down. Thereby, the fluidity | liquidity fall of the part close | similar to the said inner surface of the molten resin which contacts the inner surface of a lens shaping | molding space part is suppressed.

  Therefore, in the thinnest part of the optical function molded part having a thickness of 0.4 mm or less, the thickness of the part where the fluidity is greatly reduced is less than 0.2 mm from the molding surface, and the minimum is 0.4 mm or less. There will be a portion where the flow velocity is fast at the center of the thin portion.

  This heat insulating layer increases the flow rate of the molten resin through the optical function molding part including the thinnest part, so that the flange molding part around the optical function molding part of the molten resin flowing through the lens molding space part is divided into right and left. When the leading edges of the molten resin that flow through each other meet on the opposite side of the lens molding space (on the side facing the gate), the leading edge of the molten resin that passes through the optical function molding portion is on the side facing the gate. The flange is formed so as to reach the flange forming part side beyond the boundary between the optical function forming part and the flange forming part.

In this case, the leading edge of the molten resin flowing on the left and right sides of the flange molding part around the optical function molding part and the leading edge of the molten resin flowing through the optical function molding part are the flange molding part outside the optical function molding part. Will meet. Thereby, the weld line which arises when molten resin associates is formed only in a flange molding part, and is not formed in an optical function molding part.
Since the lens molded with this injection mold has no weld line in the optical function part, the optical characteristics of the optical function part are not greatly deteriorated by the generation of the weld line.

  Here, if the heat insulating performance of the heat insulating layer is high, the temperature of the molten resin is kept high by the heat insulating layer when the molten resin is filled into the space finally remaining in the lens molding space when the molten resin is filled. There is a high possibility that the occurrence of weld lines can be prevented. However, in this case, it takes time to cool the molded lens, the cycle time for molding the lens becomes long, and the productivity of the lens decreases.

  On the other hand, by setting the heat insulation performance of the heat insulation layer to such an extent that the weld line remains in the flange portion, it is possible to suppress the time required for cooling the molded lens from increasing, and to shorten the lens molding cycle time. Thus, productivity can be improved.

  The injection mold according to claim 2 is the invention according to claim 1, wherein the thickness along the optical axis direction of the thickest portion of the flange molding portion is the thinnest portion of the optical function molding portion. The thickness is 1.5 times or more of the thickness along the optical axis direction.

  In the invention of claim 2, the molten resin that passes through the thinnest part even if a heat insulating layer is provided by the flange molding part being 1.5 times or more thicker than the thinnest part of the optical function molding part. There is a high possibility that the flow rate of the molten resin passing through the flange portion side becomes higher, and it becomes more difficult to suppress the occurrence of the weld line. Therefore, when the structure capable of completely suppressing the generation of the weld line is used, the lens molding cycle time becomes longer. On the other hand, by generating the weld line only in the flange molding portion outside the optical function molding portion as described above, the cycle time can be shortened and the lens productivity can be improved.

  The injection mold according to claim 3 is the invention according to claim 1 or 2, wherein the pair of molds includes a sprue, a runner, and a runner as a resin passage through which resin flows into the lens molding space. The gate is provided, and the heat insulating layer is provided on an inner surface of the sprue, the runner, and the gate that is in contact with the molten resin.

  In the invention according to claim 3, when the molten resin passes through the sprue, runner and gate before reaching the lens molding space of the pair of molds, the temperature is lowered by conducting heat to the mold side. It is possible to prevent overdoing. In order to increase the flow rate of the molten resin at the thinnest part of the optical function molding portion of the lens molding space, it is preferable that the temperature of the molten resin is as low as possible, and a heat insulating layer is also provided on the inner surface of the sprue, runner and gate. Thus, the flow rate of the molten resin in the thinnest part can be reliably increased, and a weld line can be prevented from occurring in the optical function molded part.

  The injection molding method according to claim 4 is an injection molding method using the injection mold according to any one of claims 1 to 3, wherein the temperature of the mold is set during the injection molding. The temperature is set so as to be kept within a predetermined temperature range lower than the glass transition temperature of the molten resin.

In the invention according to the fourth aspect, the same effects as the inventions according to the first to third aspects can be achieved.
Further, since the temperature range of the mold at the time of injection molding is maintained in a predetermined temperature range lower than the glass transition temperature of the molten resin, the mold is made of the molten resin glass when the lens is continuously molded. After raising the temperature above the transition point temperature, it is not necessary to lower the temperature below the glass transition temperature of the molten resin, and it is possible to prevent the cycle time from becoming longer. Further, it is possible to prevent an increase in equipment cost without requiring complicated equipment for rapidly raising and lowering the mold with the glass transition temperature of the molten resin interposed therebetween.

The lens according to claim 5 is a resin lens provided with an optical function part having an optical function, and a flange part provided around the optical function part and used for fixing,
The thickness along the optical axis direction of the thinnest thinnest part of the optical function part is 0.4 mm or less, and the thickness of the thickest thickest part of the flange part along the optical axis direction is It is thicker than the thickness of the thinnest part of the optical function part,
A weld line is formed only in the flange portion outside the optical function portion.

  In the invention described in claim 5, in the lens in which the thickness of the thinnest portion of the optical function portion is 0.4 mm or less and the flange portion is thicker than that, a weld line is formed only in the flange portion. As a result, it is possible to shorten the lens molding cycle time and improve the productivity of the lens, compared with the case where the lens is not produced during the injection molding. Further, since no weld line is formed in the optical function portion of the lens, it is possible to prevent the lens optical characteristics from being degraded by the weld line formed.

  The lens according to claim 6 is the lens according to claim 5, wherein the thickness of the thinnest portion of the flange portion along the optical axis direction is the light of the thinnest portion of the optical function portion. The thickness is 1.5 times or more of the thickness along the axial direction.

  In the lens according to claim 6, since the flange portion is 1.5 times or more thicker than the thinnest portion of the optical function portion, it is more difficult to suppress the generation of the weld line at the time of manufacturing, and the generation of the weld line is generated. If this is completely suppressed, the lens molding cycle time becomes longer. On the other hand, by generating a weld line only in the flange portion outside the optical function component, the cycle time can be shortened and the productivity of the lens can be improved. Moreover, even if the thinnest part of the optical function part is thinned, the strength of the lens can be secured by the flange part.

According to a seventh aspect of the present invention, in the invention of the fifth or sixth aspect, an optical function molding portion that molds the optical function portion, and the flange portion provided around the optical function molding portion. Injection molding with an injection mold having a lens molding space having a flange molding part to be molded,
Of the molten resin that has flowed into the lens molding space from a gate connected to the flange molding part, a molten resin that passes through the right side of the optical function molding part of the flange molding part, and the optical function of the flange molding part When the molten resin that has passed through the left side of the molded part meets on the side of the flange molded part facing the gate,
Of the molten resin that has flowed into the lens molding space from the gate, the molten resin that has passed through the optical function molding part including the thinnest part from the flange molding part has the optical function on the side facing the gate. A weld line is formed only in the flange portion because the flange formed portion is reached beyond the boundary between the formed portion and the flange formed portion.

  In the lens according to claim 7, the molten resin that has passed through the right side of the optical function molding portion of the flange molding portion of the molten resin that has flowed in from the gate and the optical function of the flange molding portion in the lens molding space at the time of manufacture. The molten resin that has passed through the left side of the molding part meets on the side facing the gate of the flange molding part. At this time, of the molten resin that has flowed into the lens molding space portion from the gate, the molten resin that has passed through the optical function molding portion including the thinnest portion from the flange molding portion faces the optical function molding portion and the flange on the side facing the gate. Molded by reaching the flange molding part beyond the boundary with the molding part. As a result, the weld line is formed only in the flange portion, and the same effects as those of the invention of claim 5 can be achieved.

  According to the injection mold, the injection molding method and the lens of the present invention, when an extremely thin concave lens is injection-molded, the optical characteristics are deteriorated by the weld line while preventing the molding cycle time of the lens from becoming long. Can be prevented.

It is principal part sectional drawing which shows the injection mold of embodiment of this invention. It is a principal part front view which shows the movable metal mold | die of the said injection mold. It is a principal part schematic sectional drawing which shows the runner of the said injection mold for demonstrating the thermal radiation of molten resin, (a) is a figure which shows the case where there is no heat insulation layer, (b) has a heat insulation layer. FIG. It is a top view which shows the molded concave lens before cut | disconnecting a gate, and shows the flow process of molten resin in case there exists a heat insulation layer. It is sectional drawing which shows the shape | molded concave lens before cut | disconnecting a gate. It is a perspective view which shows the concave lens which cut | disconnected the gate. It is a top view which shows the molded concave lens before cut | disconnecting a gate, and shows the flow process of molten resin when there is no heat insulation layer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 to 3, the injection mold according to the first embodiment is a mold used in a known injection molding machine, and a fixed mold (first mold) 1 is used as a pair of molds. And a movable mold (second mold) 2. FIG. 1 shows a cavity plate portion having a molding surface for molding the lens of each of the fixed mold 1 and the movable mold 2.

  These cavity plates are provided with a plurality of sets of cavities 11 and 21 so that a plurality of lenses can be taken (FIG. 1 shows only one set of cavities 11 and 21, and FIG. Only one is shown). When the cavity plate of the fixed mold 1 and the cavity plate of the movable mold 2 are abutted, the cavity 11 of the fixed mold 1 and the cavity 21 of the movable mold 2 are abutted to form a lens comprising these cavities 11 and 21. A space (cavity) 3 is formed. In this example, as shown in FIG. 1, the main part of the lens molding space 3 is formed by a cavity 21 on the movable mold 2 side.

Further, the cavities 11 and 21 of the fixed mold 1 and the movable mold 2 are respectively concave lenses 4 (an optical function part 41 having an optical function and a flange part 42 provided around the optical function part 41 and used for positioning and fixing). (Shown in FIGS. 4 and 5). The concave lens 4 has a rotationally symmetric shape around the central axis (optical axis) of the optical function unit 41.
Corresponding to the concave lens 4 to be molded, the lens molding space 3 is provided around the optical function molding unit 31 for molding the optical function unit 41 of the concave lens 4 and the flange of the concave lens 4. And a flange forming part 32 for forming the part 42.

  The fixed mold 1 and the movable mold 2 are respectively formed with cylindrical holes 13 and 23 into which the inserts 12 and 22 are inserted in portions corresponding to the optical function molding portion 31 of the cavity plate. Cylindrical inserts 12 and 22 are rotatably inserted into the holes 13 and 23, respectively. The front end surfaces of the nestings 12 and 22 are formed with molding surfaces for molding the optical function part 41 of the concave lens 4 by the optical function molding part 31.

  Further, the central axis of the optical function molding portion 31 and the central axes of the inserts 12 and 22 are made to coincide with each other. The diameters of the nests 12 and 22 are larger than the diameter of the optical function molding part 31, and the tip surfaces of the nests 12 and 22 are the molding surfaces of the optical function part 41 of the concave lens 4 at the optical function molding part 31 as described above. And the molding surface of the inner peripheral side portion of the flange portion 42 around the optical function portion 41. Further, the periphery of the nestings 12 and 22 on the front end surfaces of the cavity plates of the fixed mold 1 and the movable mold 2 correspond to the outer peripheral side portion of the flange molding portion 32, and the outer peripheral portion of the flange portion 42 of the concave lens 4. It is designed to be molded.

In order to mold the concave lens 4, the optical function molding unit 31 forms a distance between the inner surface on the fixed mold 1 side and the inner surface on the movable mold 2 side (the concave lens to be molded) from the outer peripheral side toward the center side. 4) (distance along the optical axis direction 4). In the center of the optical function molding part 31, the above-mentioned distance is the shortest.
The distance between the inner surfaces is defined as the thickness of the lens molding space 3, and the portion at the approximate center of the optical function molding portion 31 is the thinnest portion with the smallest thickness. The thickness along the axial direction of the concave lens 4 to be molded at the thinnest part of the optical function molding portion 31 of this embodiment is set to 0.4 mm or less, for example.

  When the concave lens 4 is combined with another lens and incorporated in a thin device, the concave lens 4 is preferably as thin as possible, and the thickness of the thinnest portion of the optical function molding portion 31 may be 0.3 mm or less. By thinning the thinnest thinnest part of the optical function part 41, the optical characteristics as a concave lens can be satisfied even if the thickest part of the optical function part 41 is thinned. That is, by reducing the thinnest thinnest part of the optical function unit 41, the thickness of the entire concave lens 4 can be reduced.

  The flange molding part 32 is a part for molding the flange part 42 that is the outer peripheral part of the concave lens 4, and has the same thickness as the thickest part along the optical axis direction of the optical function molding part 31. . Basically, the thickness of the flange forming portion 32 is substantially uniform. The flange portion 42 of the concave lens 4 may be provided with a concave portion or a notch portion, or may be provided with a convex portion, and the thickness of the flange forming portion 32 may not be uniform.

  The thickness along the optical axis direction of the concave lens 4 to be molded, which is the thickest thickest part of the flange molding part 32, is the optical axis direction of the concave lens 4 to be molded of the thinnest thinnest part of the optical function molding part. It is more than 1.5 times the thickness along. In addition, although it may be 2 times or more or 3 times or more, in order to reduce the thickness of the concave lens 4, it is preferable that the flange forming portion 32 is thin. However, even if it is thinner than the thickest part of the optical function molding portion 31, the thickness of the thickest part of the concave lens 4 is not reduced.

The fixed mold 1 and the movable mold 2 are provided with runners 51 and 52 into which molten resin injected through a sprue (not shown) provided in the fixed mold 1 flows. Gates 61 and 62 are provided between 11 and 21. The main parts of the gates 61 and 62 are provided on the movable mold 2 side.
And the heat insulation layers 14, 15, 16, 17, 24, 25, 26, and 27 are all formed in the portions of the fixed mold 1 and the movable mold 2 that are in contact with the molten resin.

  That is, the heat insulating layers 14 and 24 are formed on the tip surfaces of the inserts 12 and 22. Further, heat insulating layers 15 and 25 are provided at portions corresponding to the outer peripheral portion of the flange forming portion 32 of the cavity plate of the fixed mold 1 and the movable mold 2. Further, heat insulating layers 17 and 27 are provided at portions corresponding to the runners 51 and 52 of the cavity plate of the fixed mold 1 and the movable mold 2. Further, heat insulating layers 16 and 26 are provided at portions corresponding to the gates 61 and 62 of the cavity plate of the fixed mold 1 and the movable mold 2. A heat insulating layer is also formed on the inner surface of the sprue (not shown).

  In the nestings 12 and 22, surface molding layers 18 and 28 are further provided on the surfaces of the heat insulating layers 14 and 24 described above. The surface molding layers 18 and 28 are formed not only from the distal end surfaces of the inserts 12 and 22 but also from the distal end surface to the outer peripheral surface of the distal end portion.

The heat insulating layer may be made of, for example, a thermoplastic polyimide resin, a thermosetting epoxy resin, or a ceramic such as zirconium oxide, aluminum oxide, titanium oxide, or chromium oxide. May be used. However, when considering the durability of the fixed mold 1 and the movable mold 2, it is preferable that the heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 are made of ceramics instead of resin.
In this embodiment, zirconia (ZrO2) ceramics is used, and the portions of the fixed mold 1 and the movable mold 2 on which the above-described heat insulating layers 14, 15, 16, 17, 24, 25, 26, 27 are formed are sprayed. The heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 are formed.

  The thickness of the heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 is such that when the concave lens 4 is molded, a weld line is generated only in the flange portion 42 outside the optical function portion 41 of the concave lens 4. Set to do. For example, data is obtained by experiment or the like, and a weld line is provided on the flange portion 42 outside the optical function portion 41, and the molding cycle time of the concave lens 4 is set as short as possible. The optimum heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 may be different in thickness depending on the synthetic resin used as the material of the concave lens 4.

Here, for example, when the heat insulating layers 14, 15, 16, 17, 24, 25, 26, 27 are made of zirconia ceramics formed by thermal spraying, the heat insulating layers 14, 15, 16, 17, 24, 25, 26 are used. , 27 is preferably 100 μm to 1.0 mm.
By setting the thickness of the heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 to 100 μm or more, the thickness of the thinnest portion of the optical function molding portion 31 of the lens molding space portion 3 is increased as described above. Even if the thickness of the flange molding part 32 of the lens molding space part 3 is 0.4 mm or less and is 1.5 times or more the thickness of the thinnest part of the optical function molding part 31, the optical function part of the concave lens 4 It is possible to prevent a weld line from being generated at 41, and a weld line is generated only at the flange portion.

Further, by setting the thickness of the heat insulating layers 14, 15, 16, 17, 24, 25, 26, 27 to 1.0 mm or less, the thinnest portion of the optical function molding portion 31 of the lens molding space 3 as described above. The concave lens 4 is 0.4 mm or less, and the thickness of the flange molding portion 32 of the lens molding space 3 is 1.5 times or more the thickness of the thinnest portion of the optical function molding portion 31. It is possible to prevent a weld line from occurring only in the flange portion 42 and an increase in the cycle time of the concave lens 4.
Moreover, it is more preferable that the thickness of the heat insulation layers 14, 15, 16, 17, 24, 25, 26, and 27 be 150 μm to 500 μm. Furthermore, it is more preferable that the thickness of the heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 is 200 μm to 300 μm. In the above example, the heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 are made of zirconia ceramics. Although the required thickness of the heat insulating layer varies depending on the type of the heat insulating layer and the molding temperature, the thickness of the heat insulating layer is determined in consideration of the thermal conductivity of the heat insulating layer.
The thermal conductivity of the heat insulating layer is preferably in the range of 0.1α to 0.01α when the thermal conductivity of the mold is α (W / (m · k)). That is, the thermal conductivity of the heat insulating layer is preferably 1/10 or less and 1/100 or more of the thermal conductivity of the mold.

  It is to be noted that the nests 12 and 22 are formed on the front end surfaces of the nests 12 and 22, and the nests 12 of the cavity plates of the fixed mold 1 and the movable mold 2 are formed by the heat insulating layers 14 and 24 for mainly molding the optical function portion 41 of the concave lens 4. , 22 around the heat insulating layers 15 and 25 for forming the flange portion 42 of the concave lens 4 and the inner surfaces of the gates 61 and 62 of the fixed mold 1 and the movable mold 2 around the concave lens 4. Layers 16 and 26, heat insulating layers 17 and 27 formed on the inner surfaces of runners 51 and 52 of fixed mold 1 and movable mold 2, and heat insulating layers formed on the inner surface of a sprue (not shown) have different thicknesses. It is good.

For example, with respect to the heat insulating layers 14, 15, 24, 25 on the lens molding space 3 side, the heat insulating layers 16, 17, 26, 27 on the side for guiding the molten resin to the lens molding space 3 (heat insulating layers on the inner surface of the sprue) It is good also as what thickens. In this case, if the thickness of the heat insulating layers 14, 15, 24, 25 is within the above range, the heat insulating layers 16, 17, 26, 27 (including the heat insulating layer on the inner surface of the sprue) have the above thickness. It may be thicker than the range.
By adopting such a configuration, the temperature of the molten resin before reaching the lens molding space 3 is reliably prevented from being lowered, and the formation of a weld line in the optical function portion 41 is further suppressed. be able to.

  The surface molding layers 18 and 28 are, for example, portions that are mirror-finished in order to mold the optical function portion 41 of the concave lens 4, and are plated with an alloy such as a nickel-based alloy, for example. In this embodiment, nickel and phosphorus are plated. Further, when a fine shape is formed in the optical function portion 41, the surface molding layers 18 and 28 may be subjected to fine processing transferred to the surface of the optical function portion 41. Moreover, it is preferable that the thickness of the surface molding layers 18 and 28 is 100 micrometers-200 micrometers, for example.

  In such an injection molding method using an injection mold, the molten resin injected into the lens molding space 3 formed by the fixed mold 1 and the movable mold 2 is sprue, runners 51 and 52 and a gate. 61 and 62 will flow in. At this time, the temperature of the molten resin is set to a temperature range higher than the glass transition temperature of the injected molten resin so that the molten resin has fluidity. The injection molding can be performed by setting the range.

  The injection amount (flow velocity) of the molten resin at the time of injection is the tip edge of the molten resin when it flows in the lens molding space 3 from the gate 61, 62 side to the opposite side of the gate 61, 62 side. However, it is preferable to set so as to make it difficult to be V-shaped as described later.

  The temperature of the fixed mold 1 and the movable mold 2 during the injection molding is changed from the molten resin through the heat insulating layers 14, 15, 16, 17, 24, 25, 26, 27 to the fixed mold 1 and the movable mold. Based on the fact that the fluidity of the molten resin is reduced due to the heat radiation to 2, the molten resin is substantially filled in the lens molding space 3 at a temperature higher than the temperature at which a weld line is not generated in the optical function molding portion. Later, it is necessary to quickly reach a temperature at which the molten resin can be cured. The temperature of the fixed mold 1 and the movable mold 2 may be set in a temperature range lower by 5 ° C. to 10 ° C. than the glass transition temperature of the molten resin as in the conventional case, but is fixed to speed up the cycle time. The temperatures of the mold 1 and the movable mold 2 are preferably set in a temperature range that is 10 ° C. to 20 ° C. lower than the glass transition temperature.

  Here, in this embodiment, even if the temperature of the fixed mold 1 and the movable mold 2 is lower than the conventional temperature, the heat insulating layers 14 and 24 are formed on the tip surfaces of the inserts 12 and 22, and the fixed mold 1 and the movable mold 1 are movable. Since the heat insulating layers 15 and 25 are provided in the portion corresponding to the outer peripheral portion of the flange forming portion 32 of the cavity plate of the mold 2, that is, the heat insulating layers 14, 15 and 24 are provided on the inner peripheral surface of the lens forming space portion 3. , 25 are formed, it is possible to prevent the molten resin from being rapidly cooled when it contacts the inner peripheral surface of the lens molding space 3, and a weld line is formed only in the flange portion 42 as described above. It is possible to be done.

  In particular, in this embodiment, the heat insulating layers 17 and 27 are provided not only on the inner peripheral surface of the lens molding space 3 but also on the portions corresponding to the runners 51 and 52 of the cavity plates of the fixed mold 1 and the movable mold 2. In addition, since the heat insulating layers 16 and 26 are provided in the portions corresponding to the gates 61 and 62, and the heat insulating layer is also provided on the inner peripheral surface of the sprue, the fixed mold 1 and the movable mold 2 as described above. Even if the temperature is lower than the conventional temperature, it is possible to prevent the temperature from decreasing more than necessary before the molten resin reaches the lens molding space 3. Thereby, as described above, it is possible to form a weld line only in the flange portion 42.

  Further, the temperature control is performed such that the temperature of the fixed mold 1 and the movable mold 2 is increased so as to be higher than the glass transition temperature of the molten resin, and the temperature is decreased so as to be lower than the glass transition temperature of the molten resin after the temperature increase. For example, control of maintaining the temperature of the fixed mold 1 and the movable mold 2 within the above-described temperature range lower than the glass point transfer temperature of the molten resin by a known mold temperature controller, basically, Is only controlled to maintain a substantially constant temperature lower by a predetermined temperature difference from the glass transition temperature of the molten resin. Therefore, it is not necessary to increase or decrease the temperature of the fixed mold 1 and the movable mold 2 in the lens molding cycle time. Moreover, the equipment for performing temperature rising / falling rapidly is not required.

The concave lens 4 molded by the above-described injection molding method by the above-described injection molding method has a shape in which an annular flange portion 42 is provided around a circular optical function portion 41 as shown in FIGS. It has become. In addition, the dashed-two dotted line in FIG. 4 shows the flow process (position of the front-end edge of the flowing molten resin) of the molten resin at the time of injection molding in steps.
4 and 5 illustrate a state in which the gate portion 43 formed by the gates 61 and 62 and the runner portion 44 formed by the runners 51 and 52 are not removed from the concave lens 4.

This concave lens 4 has a thickness along the optical axis direction of the concave lens 4 at the thinnest thinnest part of the optical function part 41 of 0.4 mm or less, and is the smallest of the flange part 42 formed around the optical function part 41. The thickness of the thickest pressure part is 1.5 times or more the thickness of the thinnest part of the optical function part 41.
Moreover, in the optical function part 41, the center part of the optical function part 41 is the thinnest, and the outermost periphery of the optical function part 41 is the thickest. Further, the flange portion 42 has a substantially uniform thickness, and the thickness thereof is substantially the same as that of the outermost peripheral portion (the boundary between the optical function portion 41 and the flange portion 42), which is the thickest in the optical function portion 41. Has been.

Further, in the concave lens 4 formed by the injection molding method using the above-described injection molding die, the optical function part 41 having a concave surface and actually having optical characteristics as a concave lens has no weld line, and the weld line. Therefore, the optical characteristics are not deteriorated.
Further, a weld line is generated in the flange portion 42.

  As the material of the concave lens 4, for example, polymethylene methacrylate resin (PMMA), cycloolefin polymer resin (COP), cyclic olefin copolymer resin (COC), polycarbonate resin (PC), polyester resin (PE) and the like are suitable. However, the present invention is not limited to these.

In the injection molding method of the concave lens 4 using the above-described injection molding die, the molten resin having a set temperature is injected into the sprue, and the molten resin passes from the sprue through the runners 51 and 52 to the gates 61 and 62. Then, it flows into the lens molding space 3 as a cavity.
Here, as shown in FIG. 1, the heat insulating layer 14 is formed on the inner surface of the sprue, the runners 51 and 52, the gates 61 and 62, the optical function molding portion 31 and the flange molding portion 32 of the lens molding space 3, as described above. , 15, 16, 17, 24, 25, 26, 27 are formed. Therefore, for example, as shown in FIG. 3A, for example, the molten resin P passing through the runners 51 and 52 is a molten resin in the case of the fixed mold 1a and the movable mold 2a without the heat insulating layers 17 and 27. As shown by the arrows from the molten resin P, a large amount of heat is radiated from the molten resin P to the fixed mold 1a and the movable mold 2a, which are lower than the glass transition temperature of P and have high thermal conductivity, and the inner surfaces of the molten resin runners 51 and 52 The fluidity of the portion adjacent to (a portion indicated by a two-dot chain line) is greatly reduced. On the other hand, by providing the heat insulating layers 17 and 27 on the inner surfaces of the runners 51 and 52, the heat radiation indicated by the arrows from the molten resin P to the fixed mold 1 and the movable mold 2 is weakened by the heat insulating layers 17 and 27. Moreover, the fluidity | liquidity of a grade which is also a part close | similar to the inner surface of the runners 51 and 52 of the molten resin P can be given. Alternatively, the thickness of the portion where the fluidity is lowered can be reduced.

  Thus, the heat insulation layers 14, 15, 16, 17, 24, 25, 26, and 27 can slow down the temperature drop rate of the molten resin, and can delay the decrease in fluidity of the molten resin. Further, in the thinnest portion where the thickness of the optical function molding portion 31 is 0.4 mm or less and in the vicinity thereof, the molten resin includes the molten resin that is in contact with the fixed mold 1 and the movable mold 2 in direct contact with each other. It is possible to prevent the molten resin in the vicinity of the fixed mold 1 and the movable mold 2 from being lowered in temperature by large heat dissipation and greatly reducing the fluidity of the portion. Thereby, even the thinnest part of the optical function molding part 31 maintains the fluidity of the molten resin and can flow.

  The resin that has flowed into the lens molding space 3 passes through the substantially disk-shaped lens molding space 3 from the connection portion of the gates 61 and 62 to the opposite side of the gates 61 and 62 of the lens molding space 3 (opposite the gates 61 and 62). To the side). At this time, the leading edge of the molten resin that flows while flowing to the left and right corresponding to the lateral width of the substantially disc-shaped lens molding space 3 reaches the opposite side of the gates 61 and 62 of the lens molding space 3. As a result, the lens molding space 3 is filled with the molten resin.

  The cause of the weld line at this time is that when the molten resin is filled into the lens molding space 3, the leading edges of the flowing molten resin come into contact with each other. For example, when molding a circular convex lens, the central part of the disk-shaped lens molding space is the thickest, so the leading edge of the flowing molten resin becomes convex because the central part advances faster than the outside. When the molten resin reaches the side facing the land, the molten resin is unlikely to be associated from two directions, and a weld line is unlikely to occur.

  In the case of the concave lens 4 with respect to such a convex lens, the weld line w is likely to be generated. FIG. 7 shows the concave lens 4 in a state in which the gate portion 43 is not cut, and illustrates the filling state of the molten resin (the position of the leading edge of the flowing molten resin) stepwise by the two-dot chain lines a to d. It is. Moreover, in the concave lens 4 shown in FIG. 7, the alternate long and two short dashes lines a to d indicate the filling state of the molten resin when the heat insulating layer is not provided in the injection mold or when the heat insulating performance of the heat insulating layer is not sufficient. In the comparative example, the weld line w is formed from the optical function part 41 to the flange part 42.

  In the case of the concave lens 4, particularly when there is a thick flange portion 42 on the outer peripheral portion, for example, as shown by a two-dot chain line a in FIG. 7, almost immediately after the molten resin starts flowing into the lens molding space portion 3. Since the molten resin flows into the flange molding portion 32 that forms the flange portion 42 having a uniform thickness, the leading edge of the molten resin that basically flows has a convex curve.

Next, when the center part of the front end edge of the molten resin enters the optical function forming part 31 for forming the optical function part 41, the thickness of the center part becomes thinner. As indicated by a chain line b, the flow velocity at the center portion becomes slower than the flow velocity at the outer peripheral portion of the relatively thick optical function portion 41, and becomes a concave curve.
Furthermore, when the center part of the front end edge of the molten resin passes through the center part as the thinnest part where the thickness of the optical function molded part 31 is 0.4 mm or less, the front end edge of the molten resin is a two-dot chain line. As shown by c, the flow velocity at the center portion is further slowed down, and the portion left and right of the center portion is considerably advanced and protrudes with respect to the center portion that is greatly depressed.

Here, since the flow velocity is slow at the center portion of the two-dot chain line c, the left and right protrusions of the two-dot chain line c are the center portion, whereas the flow rate is slightly advanced with respect to the center position of the optical function unit 41. As shown by a two-dot chain line d, the leading edge of the molten resin becomes substantially V-shaped, and the leading edges of the left and right molten resins meet. Thus, a weld line w is formed.
At this time, from the stage shown by the two-dot chain line c to the stage shown by the two-dot chain line d, the center part of the leading edge of the molten resin corresponding to the center part of these two-dot chain lines flows only slightly, Even at the stage indicated by the alternate long and two short dashes line d, it is still in the optical function part 41 and does not reach the flange part 42. In this state, the molten resins forming the left and right projecting portions meet as indicated by a two-dot chain line d to form a weld line w. As a result, a part of the weld line w is formed in the optical function unit 41. In the two-dot chain line d, the tip edge of the molten resin is substantially V-shaped, but if the flow of the resin is delayed at the center of the tip edge of the molten resin indicated by the two-dot chain line d, Even after the left and right projecting portions contact each other on the further front side, a portion that is not filled with the molten resin remains on the optical function portion 41 side, and the molten resin that is associated with each other moves toward the center of the optical function portion 41 so that the molten resin flows backward. In some cases, the molten resin is filled in a portion of the optical function portion that is not yet filled with the resin.
In this case, the weld line w may include a plurality of curved lines instead of a single straight line.

On the other hand, in the molding of the concave lens 4 of the embodiment shown in FIG. 4, the heat insulating performance of the heat insulating layers 14, 15, 16, 17, 24, 25, 26, 27 is necessary and sufficient. FIG. 7 shows the progress of the central portion of the front end edge of the molten resin indicated by the two-dot chain line c, in particular, in the step edge of the molten resin indicated by the two-dot chain lines a to d. Is getting faster.
Thereby, as shown by a two-dot chain line d, when the tip edge of the molten resin is substantially V-shaped, the position of the portion that becomes the vertex of the V-shape at the center of the V-shaped tip edge is It becomes the outer flange portion 42 side of the optical function portion 41. Thereby, it is possible to prevent the weld line w from being formed on the optical function unit side.

  In other words, the flow of the molten resin in the lens molding space 3 passes through the right side of the optical function molding portion 31 of the flange molding portion 32 of the molten resin flowing in from the gates 61 and 62 in the lens molding space 3. The molten resin and the molten resin passing through the left side of the optical function molding part 31 of the flange molding part 32 meet on the side of the flange molding part 32 facing the gates 61 and 62.

  At this time, as shown in FIG. 7, the molten resin that has flowed from the gates 61 and 62 into the lens molding space 3 through the flange molding part 32 through the optical function molding part 31 including the thinnest part is melted. If the resin does not exceed the boundary between the optical function molding part 31 and the flange molding part 32 on the side facing the gates 61 and 62, the molten resin flowing from the left and right associates in the optical function molding part 31 as described above. The molten resin associated at the flange molding part 32 flows back to the gap side remaining in the optical function molding part 31. In this case, a weld line is formed in the optical function molding portion 31.

However, in this embodiment, the heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 described above suppress heat dissipation from the molten resin to the fixed mold 1 and the movable mold 2 to achieve fluidity. Therefore, it is possible to prevent the weld line w from being generated on the optical function unit 41 side as shown in FIG.
That is, when the front edge of the molten resin becomes V-shaped as indicated by a two-dot chain line d, the vertex of the V-shaped portion is not the optical function portion 41 but the boundary between the optical function portion 41 and the flange forming portion 42. Over the flange forming portion 42 side.
In other words, the molten resin that passes through the right side of the optical function molding part 31 of the flange molding part 32 and the molten resin that passes through the left side of the optical function molding part 31 of the flange molding part 32 are converted into the gate 61, When meeting on the side facing 62, the molten resin flowing from the gates 61, 62 into the lens molding space 3 through the flange molding part 32 through the optical function molding part 31 including the thinnest part is melted. On the side of the resin facing the gates 61 and 62, the resin extends beyond the boundary between the optical function molding portion 31 and the flange molding portion 32 and reaches the flange molding portion 32.

In the concave lens 4 of this embodiment, since the thinnest part is 0.4 mm or less, it is difficult to make the left and right protrusions of the front end edge of the molten resin not meet, so that the weld line is eliminated. For this, it is necessary to raise the temperature of the molten resin in contact with or close to the mold when the leading edges of the molten resin are associated with each other than the glass transition temperature of the molten resin.
In this case, it can be considered that the temperature at the time of filling the molten resin in the fixed mold 1 and the movable mold 2 is higher than the glass transition temperature of the molten resin. In addition, by providing a heat insulating layer with extremely high heat insulating performance, even when the temperature at the time of filling the molten resin of the fixed mold 1 and the movable mold 2 is set lower than the glass transition temperature of the molten resin, the molten filling is performed. It is conceivable that the temperature of the resin does not become lower than the glass transition temperature during filling. Or it is possible to combine these methods. In these cases, it takes time to cool the molten resin to a temperature at which it can be taken out from the stationary mold 1 and the movable mold 2, and the molding cycle time of the concave lens 4 becomes longer, and the productivity is lowered.

Therefore, in the present invention, by setting a state in which a weld line is generated in the flange portion 42 as described above, it is possible to suppress an increase in the cooling process in the molding of the concave lens 4, shorten the cycle time, and improve productivity. We are trying to improve.
That is, in this embodiment, when the lens molding space 3 is filled with the molten resin as described above, the temperature of the molten resin is reduced by the heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27. By preventing the fluidity of the molten resin, the top edge of the molten resin becomes substantially V-shaped as shown by the two-dot chain line d in FIG. The optical function molding part 31) is positioned on the outer flange part 42 (flange molding part 32) side.

  The heat insulating layers 14, 15, 16, 17, 24, 25, 26, and 27 have a temperature when the leading edges of the molten resin meet higher than the temperature at which the weld line is generated (temperature higher than the glass transition point of the molten resin). ) Before the left and right portions of the molten resin front edge meet each other, or before the molten resin front edge becomes substantially V-shaped (the center of the concave portion of the front edge is concave) The center of the front edge of the molten resin (the front edge of the molten resin that has passed through the optical function molded part 31 including the thinnest part) is on the opposite side of the gates 61 and 62 when It extends beyond the optical function part 41 (optical function molding part 31) to the flange part 42 (flange molding part 32).

  Accordingly, it is possible to prevent a weld line from being generated in the optical function unit 41 and to deteriorate the optical characteristics of the concave lens 4, and it is possible to shorten the lens molding cycle time and improve productivity.

In addition, since the non-product part (gate part 43, runner part 44, etc.) formed by the above-mentioned gates 61, 62 is connected to the concave lens 4 as a molded product, it is necessary to cut this. There is. At this time, since the outer peripheral surface of the flange portion 42 may be used for positioning when fixing the concave lens 4, it is preferable that the remaining non-product portion cut from the outer peripheral surface of the flange portion 42 does not protrude.
For this reason, the part which the non-product part of the flange part 42 is connected to is cut linearly on the flange part 42 side.

In addition, the position where the non-product portion of the flange portion 42 is connected is formed into a shape cut in a straight line in advance, so that the position where the non-product portion is connected enters slightly inside the virtual circle overlapping the outer peripheral surface of the flange portion 42. It is good also as a structure which makes it a shape and cuts a non-product part in the part inside the said virtual circle of this flange part 42. FIG. That is, the shape of the concave lens 4 and the lens molding space 3 may not be a shape in which the outer peripheral surface is a circle, but a shape in which a part of the circle is cut into a straight line.
Further, the concave lens can be applied to a lens having a concave surface on one side and a flat surface on the other side, or a lens having both surfaces concave.
As described above, the concave concave lens has been described. However, the present invention is not limited to this. For example, the present invention can be applied to a thin meniscus lens having a central portion.

1 Fixed mold (mold)
2 Movable mold (mold)
3 Lens molding space (cavity)
31 Optical function molding part 32 Flange molding part 4 Concave lens (lens)
41 Optical function part 42 Flange part 51, 52 Runner 61, 62 Gate 14, 15, 16, 17, 24, 25, 26, 27 Heat insulation layer 18, 28 Surface molding layer w Weld line

Claims (7)

An injection molding mold comprising at least a pair of molds as a lens molding space where the injected molten resin flows and the lens is molded,
The lens molding space includes an optical function molding unit that molds an optical function unit having an optical function as the lens, and a flange that is provided around the optical function unit and molds a flange unit used for fixing the lens. With a molding part,
The thickness along the optical axis direction of the lens at the thinnest thinnest part of the optical function molded part is 0.4 mm or less, and along the optical axis direction of the thickest thickest part of the flange molded part Is thicker than the thickness of the thinnest part of the optical function molded part,
The molding surface that is the inner surface of the lens molding space is provided with a heat insulating layer having a lower thermal conductivity than the mold,
At least the optical function molding portion is provided with a surface molding layer that covers the heat insulating layer and contacts the molten resin to be injected,
The material and thickness of the heat insulating layer are:
Of the molten resin that has flowed into the lens molding space from a gate connected to the flange molding part, a molten resin that passes through the right side of the optical function molding part of the flange molding part, and the optical function of the flange molding part When the molten resin that has passed through the left side of the molded part meets on the side of the flange molded part facing the gate,
Of the molten resin that has flowed into the lens molding space from the gate, the molten resin that has passed through the optical function molding part including the thinnest part from the flange molding part has the optical function on the side facing the gate. It is set so as to reach the flange molded part beyond the boundary between the molded part and the flange molded part,
An injection mold, wherein a weld line is formed only in the flange molding portion.   The thickness along the optical axis direction of the thickest part of the flange molding part is 1.5 times or more the thickness along the optical axis direction of the thinnest part of the optical function molding part. The mold for injection molding according to claim 1.   The pair of molds is provided with a sprue, a runner and the gate as a resin passage for allowing the resin to flow into the lens molding space, and the heat insulation is provided on inner surfaces of the sprue, the runner and the gate which are in contact with the molten resin. The injection mold according to claim 1 or 2, wherein a layer is provided. An injection molding method using the injection mold according to any one of claims 1 to 3,
An injection molding method characterized in that the temperature of the mold is set to be kept in a predetermined temperature range lower than the glass transition temperature of the molten resin during injection molding. A resin lens provided with an optical function part having an optical function, and a flange part provided when being fixed around the optical function part,
The thickness along the optical axis direction of the thinnest thinnest part of the optical function part is 0.4 mm or less, and the thickness of the thickest thickest part of the flange part along the optical axis direction is It is thicker than the thickness of the thinnest part of the optical function part,
A lens in which a weld line is formed only in the flange portion outside the optical function portion.   The thickness of the flange portion along the optical axis direction of the thickest portion is 1.5 times or more the thickness of the optical function portion along the optical axis direction of the thinnest portion. The lens according to claim 5. Injection molding with an injection mold having a lens molding space having an optical function molding part for molding the optical function part and a flange molding part provided around the optical function molding part to mold the flange part And
Of the molten resin that has flowed into the lens molding space from a gate connected to the flange molding part, a molten resin that passes through the right side of the optical function molding part of the flange molding part, and the optical function of the flange molding part When the molten resin that has passed through the left side of the molded part meets on the side of the flange molded part facing the gate,
Of the molten resin that has flowed into the lens molding space from the gate, the molten resin that has passed through the optical function molding part including the thinnest part from the flange molding part has the optical function on the side facing the gate. The weld line is formed only in the flange portion because the flange formed portion is reached beyond the boundary between the formed portion and the flange formed portion. lens.

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