JP5945680B2 - Mold release method for plastic lenses - Google Patents

Description

  The present invention relates to a method for releasing a plastic lens in which a liquid curable plastic material is filled in a cavity of a lens molding unit and cured to form a plastic lens and then taken out.

Conventionally, as one of the means for producing a plastic lens, a lens molding unit is prepared, and the cavity (space) is mainly filled with a thermosetting plastic material, subjected to heat treatment with a predetermined heating history, and cured. There is a manufacturing method in which a molded plastic lens is taken out thereafter.
In general, a lens molding unit has a convex mold and a concave mold arranged at a predetermined interval so as to form a cavity inside using a ring-shaped gasket or an adhesive tape (this state is referred to as a mold set). Sometimes called). When a gasket is used, from the inlet, when an adhesive tape is used, a plastic material (generally referred to as a monomer) that is adjusted by piercing a filling tube is partially filled. I am doing so. The lens molding unit filled with the plastic material is allowed to stand for several hours to several tens of hours in a heating atmosphere such as a heating furnace, and the plastic material is cured to mold the plastic lens. Patent document 1 is shown as an example of such a conventional manufacturing method.

A plastic lens obtained by using such a lens molding unit is in close contact with the convex mold and the concave mold constituting the lens molding unit. Therefore, in order to separate (release) the plastic lens from the mold, the lens molding unit is set in a press device, and the plastic lens is bent by pressing. The mold release procedure is performed as follows.
A. Gasket type lens molding unit b) Remove the gasket b) Place the unit between the pressing surfaces of the press device c) Press the lens part and bend it to release it from the mold d) Remove the mold Adhesive tape type lens molding unit a) Remove the adhesive tape b) Place the unit between the pressing surfaces of the press machine c) Press the lens part and bend it to release it from the mold d) Remove the mold Plastic molded products have different expansion rates, so they may be released in the process of naturally lowering the temperature after heat curing without being forced to release in this way (although not necessarily neatly) .

JP-A-8-244048 JP-A-9-136327

By the way, in the above-mentioned mold release operation, there has been a problem of cracking (penetration) of conventionally molded plastic lenses. Basically, the molded plastic lens is planned to have a few millimeters of extra portion around the edge when releasing, and the portion where can occurs after removal from the mold after release. A product that is made one size smaller by grinding the periphery including However, there are cases where cracks intrude into the relatively inner direction of the lens. If such a crack penetrates deeply, it remains even if the lens periphery is ground, and the commercial value of such a lens is lost. In addition, since the portion where the can is generated is chipped and sticks to the mold side, it must be cleaned so that the chipped portion does not remain when the mold is used again.
For this reason, in order to reduce chipping and cracking, for example, as in Patent Document 2, the mold set is filled with resin, cured, and then peeled off, and then subjected to steam treatment to mold and plastic molding. Means have been proposed for promoting moisture release by penetrating moisture between the product (plastic lens).
However, in such a method, the mold and the plastic molded product are naturally released as moisture penetrates, and the mold that has slipped off may damage the plastic molded product. For this reason, partitioning each mold set so that the mold does not shift reduces the number of mold sets accommodated in a furnace having the same volume as compared with the case where the mold sets are arranged close to each other. Also, peeling the adhesive tape may cause the mold to release spontaneously (not necessarily clean) due to the difference in expansion rate as described above. There was also a request to remove it. In addition, when the mold set is immersed in water in order to permeate the water, so-called water-burning (water droplets) can be obtained when the water is dried on the plastic molded product that has been removed unless the water is high-purity water such as pure water. This is not preferable because a trace component in the water is whitened after the evaporation of water and a phenomenon of sticking to the surface) occurs.
From the various problems as described above, there has been a demand for means for promoting mold release without peeling off the adhesive tape at the time of mold release as in Patent Document 2.
The present invention has been made paying attention to such problems existing in the prior art. Its purpose is to allow moisture to penetrate into the interface between the molded plastic lens and the mold without removing the holding means such as adhesive tape, and to promote the release of the plastic lens and the mold. The object is to provide a method for releasing a plastic lens.

In order to solve the above problem, in the invention of claim 1, a convex mold having a first lens molding surface for forming the concave surface side of the lens, and a second lens for forming the convex surface side of the lens A concave mold having a molding surface is arranged at a predetermined interval so that the lens molding surfaces face each other, and a moisture-permeable holding member is held while maintaining the interval between the two molds along the outer peripheral edge of the two molds. A lens molding unit in which a cavity surrounded by the two molds and the moisture-permeable holding member is formed is prepared, and a liquid thermosetting plastic material is filled in the cavity. After the plastic material is cured and a plastic lens is molded in the cavity, the lens molding unit is placed in a humidified atmosphere for a predetermined time. The moisture in the humidified atmosphere breathable holding member is introduced into the cavity, and its gist in that so as to facilitate release from the both mold of the plastic lens.
The gist of the invention of claim 2 is that, in addition to the configuration of the invention of claim 1, the moisture-permeable holding member is an adhesive tape.

In such a configuration, first, a liquid thermosetting plastic material is filled into a cavity surrounded by both molds of the lens forming unit and the moisture-permeable holding member. The filled plastic material is cured in a predetermined curing process to form a plastic lens. Since it is a thermosetting plastic material, it is cured over time with a predetermined heating history by applying heat from outside or irradiating microwaves or ultraviolet rays.
When the plastic lens is molded, the lens molding unit is placed in a humidified atmosphere without removing the moisture-permeable holding member. As a result, moisture enters the cavity from the moisture-permeable holding member and penetrates into the interface between the mold and the plastic lens. This promotes release of the molded plastic lens from the mold. After being placed in a humidified atmosphere for a predetermined time, the moisture-permeable holding member is removed and the mold release work is performed. At this time, pressing is performed with a large force without using a press device for mold release. Even if it is not necessary, it is possible to release it neatly.

Here, the “lens molding unit” refers to a combined state in which a cavity is formed by being surrounded by both molds and a moisture-permeable holding member regardless of whether or not the curable plastic material is filled.
The humidified atmosphere may be realized by heating the water and releasing the vapor into the sealed space, and is realized by releasing water molecules in the sealed space in the form of a mist by the ultrasonic vibration of the ultrasonic generator. May be. Further, even if the forced saturated water vapor state is not used, a high humidity state may be created by natural evaporation of water in the sealed space when the outside air temperature is high.
Higher humidity and temperature are preferable. This is because, at the same humidity, the higher the temperature, the greater the amount of water vapor contained in the air, and the surface tension of the water is lowered, making it easier to penetrate the interface between the mold and the plastic lens. However, if the temperature is too high, it causes discoloration (yellowing) due to deterioration of the resin of the molded plastic lens. Therefore, the temperature in the humidified atmosphere is preferably about 20 to 60 ° C.
In general, an adhesive tape or a gasket is used as the moisture-permeable holding member constituting the lens molding unit. However, as a material having sufficient moisture permeability, an adhesive tape is most preferable in the present invention.

  In the invention of each of the above claims, it is possible to promote the release by allowing water to penetrate into the interface between the molded plastic lens and the mold without removing the holding means such as an adhesive tape. Even if it is not used, even if it is used, it is possible to release it neatly without pressing it with great force.

(A) And (b) is a perspective view explaining the construction process of the lens shaping | molding unit used for the Example of this invention. (A) of the same lens shaping | molding unit is a front view longitudinal cross-sectional view explaining a monomer injection | pouring state, (b) is a longitudinal cross-sectional view explaining the state by which the plastic lens was shape | molded. Explanatory drawing explaining the process of immersing the same lens shaping | molding unit in the aqueous solution with a temperature difference in order. Explanatory drawing explaining the state which is releasing the plastic lens from the same lens shaping | molding unit with a vice.

Hereinafter, a specific method for releasing a plastic lens of the present invention will be described with reference to the drawings.
First, the lens molding unit 1 used for manufacturing a plastic lens will be described. As shown in FIGS. 1 and 2, the lens molding unit 1 includes a convex mold 2, a concave mold 3 and a moisture-permeable adhesive tape 4. Both molds 2 and 3 are made of heat-resistant glass. The surface of the convex mold 2 is a first lens molding surface 5 formed of a predetermined curved surface for molding the back surface (eyeball side) of the plastic lens to be molded, and the back surface of the concave mold 3 is molded. The second lens molding surface 6 is formed of a predetermined curved surface for molding the front surface (object side) of the plastic lens.
The adhesive tape 4 is a wide flexible film made of polyethylene terephthalate (PET) that has been bi-stretched and has an adhesive layer 4a made of a silicone adhesive on the entire surface. The PET film retains the inherent moisture permeability of the PET film without applying a moisture-proof coating.
The convex mold 2 and the concave mold 3 are arranged slightly spaced apart with the first lens molding surface 5 and the second lens molding surface 6 facing each other, and straddle the outer peripheral end surfaces 7 of both molds 2 and 3. As shown, the adhesive tape 4 is wound. A cavity 8 is formed inside the lens molding unit 1 in a state where the adhesive tape 4 is wound.

  As shown in FIG. 2 (a), the cavity 8 of the lens molding unit 1 configured in this way is filled with a monomer as a curable plastic material adjusted inward by protruding the injection nozzle 11 against the side surface of the adhesive tape 4. Then, the monomer is cured by heating in a heating atmosphere such as a heating furnace with a heating history according to a conventional method. As shown in FIG. 2B, the plastic lens 10 is molded inside the lens molding unit 1 by curing the monomer. As shown in FIG. 2B, the front and back surfaces of the plastic lens 10 are in close contact with the first and second lens molding surfaces 5 and 6 of both molds 2 and 3 at the stage of completion of molding, Adheres closely to the adhesive tape 4.

Next, based on the block diagram of FIG. 3, the process from the lens molding unit 1 in which the plastic lens 10 is molded as described above to the production of a lens will be described.
First, an example of a humidification process for promoting the release of the plastic lens 10 in the lens molding unit 1 will be described. In the present embodiment, the pressure-sensitive adhesive tape 4 is not peeled off from the lens molding unit 1 and left in a high humidity condition furnace for 6 hours.
After the humidification process is completed, the process proceeds to the mold release process. At this stage, the adhesive tape 4 is peeled off. And it sets to the vice 21 as a press apparatus as shown in FIG. The vice 21 includes a fixed wall portion 22 and a movable wall portion 23, and the movable wall portion 23 connected to the tip of the screw rod 24 moves forward and backward by rotating the screw rod 24 supported by the bearing 24. It is configured.
According to such a vice 21, the lens molding unit 1 is disposed between the fixed wall portion 22 and the movable wall portion 23, and the screw rod 24 is rotated by the handle 25 so that the movable wall portion 23 is fixed to the fixed wall portion 22. By moving the plastic lens 10 in the direction and thus pressing the plastic lens 10 in the diametrical direction, the plastic lens 10 can be bent in the direction of the recess, and the interfaces between the molds 2 and 3 can be shifted and released. In some cases, the lens molding unit 1 does not require a mold release process because the mold may naturally be released when the adhesive tape 4 is peeled off before being set on the vice 21.

In the post-processing step after the mold release step, the edge of the plastic lens 10 after the mold release is cut to produce a so-called round lens as a product. Then, it is cleaned with an appropriate cleaning agent and pure water, dried, and inspected. The lens may be a round lens as it is, but it is provided with various coating layers on one or both sides and delivered to the user (glasses shop). Examples of the coating layer include a primer layer, a hard coat layer, an antireflection layer, an antifogging coat layer, and an antifouling coat layer. Although only one such coating layer may be formed, two or more types of layers may be laminated to form a multilayer coating layer.
On the other hand, the molds 2 and 3 after the mold release are washed and used again for the lens molding unit 1.
With this configuration, the following effects are combined in the present embodiment.
(1) Since it is easy to release, not only productivity is good, but also defects such as cracks and hooks are less likely to occur than in the past.
(2) Conventionally, there is a high possibility that a part of the edge of the plastic lens 10 is left inside the molds 2 and 3 when the molds are released, so the molds 2 and 3 themselves are also water with high pressure for deburring. Although it had to be washed, the present invention eliminates the necessity because it can be neatly released.
In addition, it is free to implement this invention in the aspect which does not deviate from the meaning of this invention.

Next, examples carried out according to the above steps will be described.
First, the moisture permeability of the pressure-sensitive adhesive tape used in the following examples was examined. The pressure-sensitive adhesive tape used in this example was a highly moisture-permeable PET film having a thickness of 0.04 mm that had not been subjected to a moisture-proof coating treatment (hereinafter referred to as tape A). For comparison, two types of pressure-sensitive adhesive tapes in which a moisture-proof coating was applied to a PET film having a thickness of 0.04 mm were also used (hereinafter, tapes B and C). The lens molding unit was not filled with the monomer, and instead, silica gel was sealed, and moisture permeability was determined from the increase in weight. As a lens molding unit, a flat plate mold having a diameter of 80 mm is arranged to face each other at intervals of 10 mm, and tapes A to C are wound to enclose 3.5 g of silica gel in each internal cavity (Wako Pure Chemical Industries, Ltd. silica gel, medium Granular (blue) is used). This was left to stand for 24 hours in an atmosphere of 60 ° C., 99% humidity and a temperature condition. Five lens molding units were prepared for each type of tape, and the average value of the weight increase rate of silica gel was determined. The weight increase rate indicates how much moisture the silica gel has absorbed, and the larger the value, the more moisture the tape has penetrated. The results are shown in Table 1.
As shown in Table 1, in the lens molding unit using the tape A in this example, the weight increase rate of the silica gel is much larger than the lens molding unit using the tapes B and C having the moisture-proof coating. That is, it can be said that the tape A has extremely high moisture permeability.

Next, the case where the tape A was used about the mold release performance was examined in comparison with the tapes B and C. The lens molding unit 1 was used, and the tapes A to C were used as the adhesive tape 4. A lens molding unit 1 filled with a monomer and cured according to a conventional method was allowed to stand for 6 hours in an atmosphere of 35 ° C. and 80% humidity as humidification and temperature conditions. This releasability
X: There is power when releasing. And even if you are careful, can easily occur.
Δ: Power is present at the time of mold release, but it is difficult for the can to enter if careful.
○: No force is required during mold release. In addition, it is difficult for cans to occur.
It was evaluated in three stages. The results are also shown in Table 1. It can be seen that the releasability when tape A is used is the best. From this result, it can be determined that there is a positive correlation between the moisture permeability and releasability of the tape.

Next, Table 2 shows the average can rate of the examples which were carried out by changing the temperature and humidity using the tape A. In each example, a plastic lens was molded under the common conditions A to C below, and only the humidification and temperature conditions were changed to be examples. The can occurrence rate in the examples is a value when plastic lenses of at least 300 or more are actually molded under each condition.
A) Lens molding unit conditions The lens molding unit 1 was used, and the tape A was used in Examples 1 to 4 as the adhesive tape 4 and the tape C was used only in Example 5.
B) About the prepared monomer 7 parts by weight of sulfur powder was added to 93 parts by weight of bis (β-epithiopropyl) sulfide and stirred at 50 ° C., and the sulfur powder was completely dissolved. 0.4 part by weight of (n-butyl) phosphonium bromide was added, and the mixture was sufficiently stirred and dissolved to adjust the monomer component.
The monomer was degassed at 10 hPa for 30 minutes, and the injection nozzle was pushed up to the side of the adhesive tape as described above to fill the inside of the lens molding unit.
C) Heating temperature history After being placed in a lens molding unit heating furnace filled with the monomer of A) and held at 30 ° C for 10 hours, the temperature was continuously raised from 30 ° C to 100 ° C over 10 hours, The mixture was kept at 100 ° C. for 1 hour, and then the heating was terminated and the mixture was naturally cooled to room temperature. Then, it moved to the furnace for giving predetermined humidification and temperature conditions, and left still for 6 hours.

1) Example 1
The humidification and temperature conditions were 35 ° C. and humidity 20%.
2) Example 2
The humidification and temperature conditions were 35 ° C. and humidity 50%.
3) Example 3
The humidification and temperature conditions were 35 ° C. and humidity 65%.
4) Example 4
The humidification and temperature conditions were 35 ° C. and humidity 80%.
5) Example 5
The humidification and temperature conditions were 35 ° C. and humidity 50%.

(result)
In Table 2, it can be seen that compared to Example 5 in which the humidity and temperature conditions are the same as those of Example 2, the use of tape A having high moisture permeability is less likely to generate cans. This is probably because the moisture permeability is higher when the moisture penetrates into the cavity, and as a result, more moisture penetrates into the interface between the mold and the plastic lens. Moreover, in Examples 1-4, it turns out that it becomes difficult to generate | occur | produce a can as the humidity is high, and it is thought that this is because a lot of moisture permeates the interface between the mold and the plastic lens as the humidity is high. That is, it is understood that it is more preferable to place the lens molding unit in an atmosphere with high humidity.

  DESCRIPTION OF SYMBOLS 1 ... Lens molding unit, 2 ... Convex mold, 3 ... Concave mold, 4 ... Adhesive tape as a moisture-permeable holding member, 5 ... 1st lens molding surface, 6 ... 2nd lens molding surface, 8 ... Cavity, 10: Plastic lens.

Claims (2)

A convex mold having a first lens molding surface for forming the concave surface side of the lens and a concave mold having a second lens molding surface for forming the convex surface side of the lens The two molds and the moisture-permeable holding member are disposed by being spaced apart from each other by a predetermined distance so as to face each other, and disposing the moisture-permeable holding member while maintaining the distance between the two molds along the outer peripheral edge of the two molds. Prepare a lens molding unit with a cavity surrounded by a liquid, fill the cavity with a liquid thermosetting plastic material, cure the plastic material in a predetermined curing process, and mold a plastic lens in the cavity Then, the lens molding unit is placed in a humidified atmosphere for a predetermined time to capture moisture in the humidified atmosphere from the moisture-permeable holding member. It was introduced into the tee, releasing method for a plastic lens which is adapted to facilitate release from the both mold of the plastic lens. The method for releasing a plastic lens according to claim 1, wherein the moisture-permeable holding member is an adhesive tape.

Images