JP3074213B2 - Method for producing thermoplastic resin molded article for optical use - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical thermoplastic resin molded article such as an optical component, a preform of a plastic optical fiber, and an optical waveguide.

[0002]

2. Description of the Related Art Optical thermoplastic resin molded articles such as optical parts, plastic optical fiber preforms, and optical waveguides are produced by extrusion molding or injection molding depending on the type of molded article.

However, these conventional methods for producing optical thermoplastic resin molded articles have various disadvantages as described below.

First, when an optical molding is manufactured by an extrusion molding method, a resin passage of an extruder usually has a large number of grooves in which resin easily accumulates. It is formed by the movement of the extruder screw. For this reason, the resin simultaneously supplied from the hopper to the extruder is not simultaneously extruded, but a part of the resin is left on the screw due to convection. When the molding temperature is high, the resin adhering to the screw is deteriorated by the heat of the screw and causes coloring. For this reason, the colored resin is mixed with the resin to be subjected to the subsequent molding and extruded, whereby the molded body is colored.

When an optical molded article is manufactured by an injection molding method, distortion occurs in the resin when the resin is solidified in a molding die. This internal strain makes the obtained molded body easily cracked. For this reason, molded articles having internal distortion are unsuitable for optical products. In addition, the injection molding method
It is unsuitable for the production of an elongated molded article or a resin molded article having a special shape.

In order to solve such a problem, the present inventors have proposed in Japanese Patent Application No. 3-203754 a method of vacuum defoaming molding under heating. However, when this method is applied to a resin that generates a gas, for example, a monomer at the molding temperature, there is a problem that bubbles are generated in the resin molded body.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. Even when the present invention is applied to a resin which generates a volatile substance at a molding temperature, it does not cause internal distortion and has a high molding property. An object of the present invention is to provide a method for producing a thermoplastic resin molded article for optical use, which can produce a resin molded article without coloring even at a temperature.

[0008]

According to the present invention, there is provided a process for supplying a thermoplastic resin into a molding die, wherein the thermoplastic resin is heated at a temperature at which the thermoplastic resin has fluidity by using an inert gas. Pressurizing the molten surface of the plastic resin at a first pressure, gradually cooling the molten surface from a lower portion of the mold while pressurizing the molten surface with an inert gas at a second pressure that is equal to or higher than the first pressure. And obtaining a molded article by subjecting the molded article to a thermoplastic resin molded article for optical use.

Here, the material of the molding die is glass,
Metal, quartz, etc. are used.

As the thermoplastic resin to be used, any of crystalline resins such as polymethylpentene and fluororesin, and non-crystalline resins such as polycarbonate, polyarylate and polysulfone can be used. In the method of the present invention, it is particularly preferable that the molding temperature, which is liable to be oxidatively degraded by the ordinary molding method, is about 200 ° C. or more. In addition,
The thermoplastic resin used in the present invention may contain a volatile component.

When a thermoplastic resin is charged into a molding die, it may be filled with a thermoplastic resin in the form of pellets, powders or flakes at room temperature, or may be filled at a molding temperature or a lower temperature. It may be previously melted and poured in a fluidized state for filling.

As an inert gas for pressurization, argon gas, helium gas, nitrogen gas or the like can be used.
Further, the first pressure is preferably 5 to 70 kgf / cm ² . This is because if the first pressure is less than 5 kgf / cm ² , voids are generated inside the obtained molded body, and the first pressure is 7 kgf / cm ^2.
If the pressure exceeds 0 kgf / cm ² , it takes time for the gas to expel the gas from the inside of the material. Since this pressure is significantly lower than the several hundred kgf / cm ² applied in the conventional injection molding method, when a relatively brittle resin is used for molding or when an elongated molded article is molded, the molded article is cracked. Can be prevented from occurring.

The effect of removing voids in the molded body is greater as the second pressure is higher, but it is 10 to 150 kgf / cm.
It is preferably ² . This means that the second pressure is 10 kg
If the f / cm ^{2 is} less than f / cm ² , the possibility of foaming of the molded article due to volatile matter increases, and if the second pressure exceeds 150 kgf / cm ² , it becomes difficult to degas the molded article after molding. . Note that the relationship between the first pressure and the second pressure may be such that the second pressure is not smaller than the first pressure. This is because if the first pressure is lower than the second pressure, the gas that has been melted at the molding temperature state tends to go outside and foaming occurs. Therefore, the first pressure and the second pressure may be the same. Second on the molten surface of the resin
After applying the pressure, it is preferable to lower the temperature in order to suppress foaming due to volatile components in the resin.

When the obtained resin molded body is subjected to heat spinning in a subsequent step, the resin molded body is previously maintained at a temperature equal to or lower than the glass transition point of the resin molded body material before spinning, and is then subjected to vacuum. It is preferable to dry sufficiently. As a result, even if there is gas dissolved in the molded body, it can be sufficiently removed to the outside. For this reason, foaming during spinning is prevented, and a high-quality resin molded product can be obtained. This is particularly useful when the resin molded product is an optical product.

It is preferable to apply a release agent to the inner surface of the mold so that the molded body after cooling can be easily peeled off. As a material of the release agent, a fluororesin, a ceramic powder or the like can be used. Among these, good smoothness, that is, considering that it can be uniformly applied to the inner surface of the molding die and that there is no adverse optical effect on the obtained resin molded product, it is soluble in a fluorocarbon solvent. Fluororesins, such as fluororesins having a fluorine-substituted alicyclic or heterocyclic group in the main chain, are preferred. As the material of the release agent, a material having a glass transition point higher than the softening point of the thermoplastic resin used for molding is preferable.

These fluororesins are usually dissolved in fluorine-substituted hydrocarbons, so-called fluorocarbons. For this reason, this fluororesin is dissolved in these solvents, applied to the inner surface of the mold, and the solvent is removed to cover the inner surface of the mold.

Since the release agent can be coated in a liquid state, the surface of the molded article is not roughened unlike the case where a fine particle release agent is used. Therefore, for example, when the molded body is a preform of an optical fiber, transmission loss can be suppressed low. In addition, since the inner surface of the mold can be uniformly coated, if the inner surface of the mold is a mirror surface, the film surface of the release agent also becomes a mirror surface, and therefore, the surface of the obtained molded body also has a mirror surface. Become. Further, after the molding of the molded article, the fluororesin coated on the surface of the molding die can be easily removed using a fluorocarbon solvent. In addition,
Since this fluororesin has excellent heat resistance, it exhibits a good releasing effect even when exposed to high temperatures. Therefore, it can be used for a resin molded at a high temperature. Also,
By using such a release agent, it is possible to prevent impurities from the mold from migrating to the resin as the molding material.
Therefore, when the molded product is an optical product, the quality of the product is not adversely affected.

[0018]

The method for producing an optical thermoplastic resin molded article according to the present invention comprises the steps of: pressing a molten surface of a thermoplastic resin with an inert gas at a first pressure at a temperature at which the thermoplastic resin has fluidity; Further, it is characterized in that cooling is gradually performed from the lower part of the mold while pressurizing at a second pressure higher than the first pressure.

By applying pressure at the first pressure, generation of volatiles due to volatile components in the resin is suppressed. Further, by applying the pressure at the second pressure, the bubbles in the molded body can be diffused and made minute, and the molding can be performed without forming a sparse portion inside the molded body, that is, without forming a void inside the molded body.

Also, by gradually cooling from the lower part of the mold, the strain inside the molded body is released from the lower part to the upper part.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

Example 1 A release agent was applied to the inner surface of a cylindrical mold 10 having one end closed as shown in FIG. 1, dried at room temperature, and then placed in a thermostat at 120 ° C. And dried sufficiently to uniformly coat the release agent. At this time, Teflon AF24 was used as a release agent.
A 1% solution obtained by dissolving Fluorinert FC-72 (trade name, manufactured by Sumitomo 3M) as a solvent using 00 (trade name, manufactured by DuPont) was used.

In this mold 10, ZEO as a molding material is used.
NEX280 (trade name, manufactured by Zeon Corporation) was filled and heated to 280 ° C. by heaters H _{1 to} H ₅ .
Was placed in a thermostat 20 shown in FIG. This material was previously vacuum dried at 120 ° C. for 120 hours.

The thermostat 20 comprises a bath main body 21, a mold receiving section 22 inside the tank main body, a lid 23 capable of hermetically sealing the mold receiving section 22, and a heating / cooling area 24. . This heating / cooling area is divided into five zones 24a to 24e. These zones have heaters H1 to H5 and cooling fans F1 to F5, respectively.
And is installed. A conduit is connected to the lid member 23, and the vacuum means I and the inert gas source V (both not shown) are communicated with the mold housing 22 via the switching valve K. In FIG. 2, reference symbol M denotes a pressure gauge, C denotes a water-cooled pipe attached to a side wall of a thermostat, and L denotes a leak valve.

Next, the switching valve B is switched to the inert gas source side, argon gas is introduced into the thermostat 20, and the molten resin surface in the mold 10 is heated at a first pressure of 10 kgf / cm ² for 1 hour. Pressurized. Thereafter, an argon gas is further supplied to the thermostat 20.
And the molten resin surface in the mold 10 is reduced to 70 kgf / cm ^2.
For about 10 minutes. As a result, the molding material in the molding die 10 was molded into an optical molding.

Thereafter, the energization of the lowest heater H1 was stopped, and at the same time the fan F1 was driven.
After 10 minutes, the energization of the heater H2 thereon is stopped and the fan F
2 was driven. Similarly, the energization of the heater and the driving of the fan were sequentially performed to cool the mold 10 sequentially from below.

In this way, after 90 minutes, the leak valve L was opened to bring the mold housing portion 22 of the thermostat 20 to atmospheric pressure, and then the mold 10 was taken out. Further mold 10
3 was taken out from FIG.

The transmittance of the optical molded article 1 thus obtained was measured. As shown in FIG. 4, the transmittance was measured by cutting a molded article for optical use to a length of 10 cm to prepare a test piece 2 and subjecting the end face to a hot plate treatment.
As a result, the light transmittance at a wavelength of 660 nm was 86%, which was good.

The obtained optical molded article was processed into a plastic optical fiber using the apparatus shown in FIG. That is, first, the optical molded body 50 cut out from the optical molded body 1 is vacuum-dried at 120 ° C. for 120 hours, and is placed in a drawing furnace 51. Here, the optical molding 50 is
The thermosetting silicone is melted in the drawing furnace 51, the thermosetting silicone is applied through a thermosetting silicone splitting die 52 installed below the drawing furnace 51, and then the silicone is hardened through a silicone curing furnace 53. It is taken up by a take-up machine 54 installed below the silicone curing furnace 53, and is taken up as a plastic optical fiber by a take-up machine (not shown). The optical characteristics of the obtained plastic optical fiber were measured with a 5 m-1 m cut back. As a result, it was 900 dB / km, and a good result was obtained.

Example 2 An optical molded article was produced in the same manner as in Example 1 except that the first pressure was 10 kgf / cm ² .

The transmittance of the obtained optical molded article 1 was measured in the same manner as in Example 1. As a result, the light transmittance at a wavelength of 660 nm was 86%, which was good.

Comparative Example 1 A release agent was applied to the inner surface of a cylindrical mold 10 having one end closed as shown in FIG. Was filled with a molding material, and this was put into a thermostat 20 shown in FIG. The same release agent and molding material as those used in Example 1 were used.

Next, the switching valve K of the thermostatic bath 20 was switched to the vacuum means side to evacuate. This state was maintained for about 1 hour to defoam the molding material.

Next, the switching valve K is switched to the inert gas source side, argon gas is introduced into the thermostat 20, and the molten resin surface in the mold 10 is pressurized at a pressure of 70 kgf / cm ² for about 10 minutes. did. As a result, the molding material in the molding die 10 was molded into an optical molding. Thereafter, cooling was performed in the same manner as in Example 1. When the molding die 10 was taken out from the thermostat 20 and the optical molded body was taken out from the molding die 10, the volatile component in the molding material was generated as a volatile substance during molding, and the optical molded body was swollen. Was.

Comparative Example 2 As a molding material, ZEONEX280 (manufactured by Zeon Corporation,
The product was injected into a mold 61 having a cavity 60 as shown in FIG. Silicone oil was previously applied to the inner surface of the mold 61 as a release agent, and the temperature of the mold 61 was 270 ° C. After the molding, the mold was cooled, and the optical molded body was taken out.

The transmittance of the obtained optical molded product was measured in Example 1.
As a result, the light transmittance at a wavelength of 660 nm was as low as 58%. Further, when four optical molded products were produced by this method, it was confirmed that one of them had a crack.

[0037]

As described above, the method for producing an optical thermoplastic resin molded article of the present invention can be applied to a resin that generates volatile substances at the molding temperature without causing internal distortion and having a high level. The resin molded article can be produced without coloring even at the molding temperature.

[Brief description of the drawings]

FIG. 1 is a front view showing an example of a mold used in the present invention.

FIG. 2 is a schematic diagram showing an example of a thermostat used in the present invention.

FIG. 3 is a schematic view showing an optical resin molded product obtained by using the molding die shown in FIG. 1;

FIG. 4 is a schematic view showing a test piece obtained by cutting the optical resin molded product shown in FIG. 3 for testing.

FIG. 5 is a schematic view showing an apparatus for spinning an optical resin molded body into a plastic optical fiber.

FIG. 6 is a schematic diagram for explaining a molding die used in a conventional method.

[Explanation of symbols]

1, 50: Optical molded article, 2: Test piece, 10: Mold,
Reference numeral 20: constant temperature bath, 21: bath main body, 22: mold receiving section, 2
3 Lid material, 24 Heating / cooling area, 51 Drawing furnace, 52
... a splitting die for thermosetting silicone, 53 ... a silicone curing furnace, 54 ... a take-off machine, 60 ... a cavity, 61 ... a mold.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI // B29L 11:00 (56) References JP-A-54-90356 (JP, A) JP-A-52-9065 (JP, A JP-A-55-53520 (JP, A) JP-A-5-24050 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29B 11/00-11/12 B29B 13 / 00-13/04 B29C 43/00-43/58 G02B 6/00 G02B 6/10-6/12

Claims (1)

(57) [Claims] A step of supplying a thermoplastic resin into a mold, wherein at a temperature at which the thermoplastic resin has fluidity,
A step of pressurizing the molten surface of the thermoplastic resin in the mold with a first pressure using an inert gas, and a second pressure that is equal to or higher than the first pressure using the inert gas. And gradually cooling from below the mold while obtaining pressure to obtain a molded article.