JP2001158033A - Manufacturing method of resin optical component and injection mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably manufacture an optical part made of a resin made free from strain by short-time treatment and excellent in optical characteristics. SOLUTION: A molten resin molded article is held within a mold in a molten state for a predetermined time while the shape thereof is kept. By holding the resin molded article in a molten state, the internal strain of the resin molded article can be perfectly eliminated and the strain of the resin molded article can be eliminated. Since the resin molded article is held in the mold in a molten state, the shape of the molding surface of the mold can be accurately transferred.

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 a resin optical component such as an optical disk and a lens, and a mold for injection molding used therefor, and more particularly to a method for producing a resin optical component having excellent optical characteristics. The present invention relates to a method and an injection mold used for the method.

[0002]

2. Description of the Related Art Recent advances in digital technology and laser technology have resulted in compact discs (CD), laser discs (LD), digital video discs (DVD) or mini discs (MD) as recording media for various types of information.
Such optical disks are widely used. Also, due to advances in molding technology and material technology, resin-made Fresnel lenses and the like have been widely used in place of glass-made lenses.

[0003] Optical components such as optical disks and Fresnel lenses are required to have excellent light transmission and to have fine irregularities on the surface. Therefore, these optical components are generally manufactured by injection molding, which uses a transparent resin such as polycarbonate with excellent translucency and can accurately transfer the mold surface shape by pressing the mold surface with high pressure. It is.

[0004] For example, an optical disk material is formed on a surface thereof by injection molding from a transparent resin such as polycarbonate.
Forming a base material with fine pits with a depth of about 1 μm,
A reflective film is formed on the surface by aluminum evaporation, and a transparent protective film is further formed on the surface.

However, in a resin molded product formed by injection molding, internal stress is generated by the action of high pressure at the time of injection, so that distortion remains. And when a molded product having such residual strain is used as an optical component,
There was a problem that high-precision optical characteristics could not be obtained.
For example, when irradiating a laser beam in an attempt to read information from a DVD, if the disc has distortion, the light is birefringent, so that information cannot be read accurately.

Therefore, in a conventional method of manufacturing a resin optical component, an annealing process is performed in which a molded product after injection molding is held at a temperature lower than the melting point by 5 to 10 ° C. for several tens to several hours and then cooled. ing. Since the internal stress of the molded product is removed by this annealing treatment, residual distortion is reduced, and a resin optical component with improved optical characteristics can be manufactured.

[0007]

However, in the conventional annealing process, a processing time of several hours is required in some cases, so that there is a problem that the processing time is long and the productivity is low. If the processing time is short, distortion remains and high-precision optical characteristics cannot be obtained. Further, although the processing time can be shortened by increasing the processing temperature, a jig may be required to prevent deformation, and the number of steps is increased. Further, there is also a disadvantage that the fine irregularities on the surface are deformed by the deformation, and the optical characteristics are deteriorated.

The present invention has been made in view of such circumstances, and eliminates distortion with a short processing time.
It is an object of the present invention to stably produce a resin optical component having excellent optical characteristics.

[0009]

A feature of the method of manufacturing a resin optical component of the present invention that solves the above-mentioned problems is that a pressure is applied to a resin in a molten state to form a molten resin molded article having a predetermined shape.
It is an object of the present invention to hold a molten resin molded product in a molten state for a predetermined time while maintaining its shape in a mold, and then to cool and solidify it.

The method of manufacturing a resin optical component according to the present invention, which further embodies the above invention, is characterized by an injection step of injecting and filling a resin in a molten state into a mold to obtain a molten resin molded article; It comprises a holding step of heating the molded article in the mold and holding it in a molten state for a predetermined time, and a releasing step of releasing the molten resin molded article from the mold after cooling and solidifying.

A feature of the injection mold of the present invention that can carry out the above-mentioned manufacturing method is an injection mold for molding a resin optical component, wherein the resin injected and filled in the cavity has a melting point or higher. It is to have a heating means for heating at a high temperature.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the manufacturing method of the present invention, a molten resin molded product is held in a molten state for a predetermined time while maintaining its shape in a mold. By maintaining the molten state in this manner, the internal stress can be completely eliminated, and the distortion can be eliminated. Furthermore, since it is held in a molten state in the mold, the mold surface shape can be accurately transferred.
Therefore, the resin optical component obtained by the present invention is:
Exhibits excellent optical properties. The time for maintaining the molten state varies depending on the type of resin, but about several seconds is sufficient. Therefore, the productivity is improved in a very short time as compared with the annealing.

In the production method of the present invention, first, a pressure is applied to a resin in a molten state to obtain a molten resin molded article having a predetermined shape. For this purpose, various molding methods such as press molding, extrusion molding and injection molding can be used.

The obtained molten resin molded product is placed in a mold, heated, and held in a molten state for a predetermined time.
In this step, the molten resin molded product formed by the above-described molding method may be cooled once and then placed in a mold and heated to be melted, or the formed molten resin molded product is cooled and solidified. It is also possible to keep the molten state in the mold without melting. If cooling and solidifying is performed halfway, the loss of thermal energy is large. Therefore, it is desirable that the formed molten resin molded product be melted and held in a mold in a molten state without being cooled and solidified.

For example, when manufacturing a resin optical component by injection molding, first, a molten resin is injected into a mold. Since the injected molten resin is cooled from the surface in contact with the mold, it is preferable that the molten resin be heated immediately after injection and filled to maintain the molten state. To do so, the mold may be formed so as to be heatable, and the mold may be heated in advance before injection, or the mold may be heated immediately after injection and filling.

In order to heat the molten resin molded article and hold it in a molten state, the mold can be heated to indirectly heat the molten resin molded article. To heat the mold,
Heating means such as a method of arranging a heater in a mold and energizing the heater to heat it, and a method of arranging a conductor in the mold and heating the conductor by dielectric heating by irradiating a high frequency wave can be adopted. it can. In order to efficiently heat the molten resin molded product, it is desirable to arrange a heater and a conductor near the mold surface.

Examples of the heater include a thin-film surface heater, an embedded heater, a nichrome wire, and the like, and any conductor such as iron that generates an eddy current by high-frequency irradiation can be used. It is desirable to provide a cooling means such as a cooling water passage in the mold. By driving the cooling means after holding the molten state for a predetermined time, the time required for cooling and solidifying can be reduced, and the productivity is further improved.

There is a relationship between the holding temperature when the molten resin molded article is held in a molten state and the holding time required for eliminating distortion, and the holding time can be shortened as the holding temperature increases. However, the difference is about 1 second at most when the holding temperature is near the melting point of the molten resin molded article or near the decomposition temperature. Therefore, if the holding temperature is arbitrarily selected within the range from the melting point to the decomposition temperature, the residual strain can be eliminated by holding for a few seconds at most.

[0019]

The present invention will be specifically described below with reference to Test Examples and Examples.

(Test Example) Using the mold shown in FIG. 1, a laser beam was applied to the molten resin in the mold while the molten resin molded product filled in the mold was held in a molten state during injection molding. And the light intensity of the transmitted light transmitted through the molten resin was measured. Polystyrene (PS) was used as a sample.

A slit-shaped cavity 200 having a thickness of 3 mm and a width of 20 mm is provided between the fixed mold 100 and the movable mold 101.
Is formed, and a runner 103 that connects the cavity 200 and the injection port 102 is formed in the fixed mold 100.
The lower end of the cavity 200 is open to the outside in the cross-sectional shape of the cavity 200. As shown in FIG. 2, eight heaters 104 are buried in the vicinity of the divided surface of the fixed die 100 and the movable die 101, and the die surface is heated to a predetermined temperature by energization.

The fixed mold 100 and the movable mold 101 are each provided with a 90-degree regular-angle prism 105, and the 90-degree regular-angle prism 105 is opposed to each other via a sapphire window 106 arranged on the mold surface. Sapphire window 106
Are provided at substantially the center of the cavity 200. The fixed mold 100 has an optical path (not shown) for irradiating the 90-degree regular-angle prism 105 with laser light.

This mold was mounted on an injection molding machine, and the light intensity of transmitted light was measured by a test device shown in FIG. In this test apparatus, the He-Ne laser light emitted from the light source 300 passes through the polarizer 301 and enters an optical path (not shown) provided in the fixed mold 100. The laser light incident on the optical path is bent by a 90-degree regular-angle prism 105 in the fixed mold 100, passes through the molten resin in the cavity 200 from the sapphire window 106, and passes through the sapphire window 106 of the movable mold 101. The beam is bent again by the 90-degree regular-angle prism 105 and passes through the pinhole 302. The transmitted light that has passed through the analyzer 303 is detected by a detector 304 at a light intensity of a specific wavelength. The detection signal is the OP amplifier 3
The signal is amplified at 05 and input to the computer 307 via the A / D converter 306 to be processed.

In this test, the molten resin injected from the injection port 102 passes through the runner 103 and passes through the cavity 2.
00, and flows out from the lower end opening. When the injection is stopped, the molten resin stays in the cavity 200 due to the viscosity and the atmospheric pressure of the molten resin, and the flow stops. Therefore, the light intensity is measured in the initial stage in which the molten resin fills the cavity 200, the middle stage in which the molten resin flows out of the lower end opening as a steady flow after filling the cavity 200, and the flow after the injection is stopped. Was measured at each of the later stages when the test stopped. FIG. 3 shows an example of the obtained measured values.

In FIG. 3, the horizontal axis represents the elapsed time immediately after the emission, and the vertical axis represents the relative light intensity of the detected light. The relative light intensity is a relative value when the maximum light intensity is set to 1.0. Although the molten resin is filled in advance and the transmitted light intensity is not detected in a stationary state before the start of the injection, the transmitted light intensity is observed when the injection is started. This is because the resin flows to generate anisotropy and exhibit birefringence. The light transmitted through the molten resin is split into two plane polarized lights that vibrate in two directions perpendicular to each other, pass through the sample at each speed, and a phase difference is generated. If the light intensity is detected via the analyzer 303, the relative speed and the phase difference of the light in the two principal stress directions have the relationship of the expression (1).

Relative intensity = sin ² (phase difference (δ) / 2) (1) The relative velocity is minimum when 2nπ (n = 0, 1, 2,...), And (2n + 1) π (n = 0, 1, 2,...), And the true phase difference is obtained by reading the maximum and minimum repetition n and adding n × π. From this phase difference, birefringence can be calculated from equation (2).

Birefringence = (phase difference (δ) × wavelength of light) /
(2π × thickness of slit) (2) As can be seen from FIG. 3, the light intensity greatly changes in the initial stage (A) and is complicated, but is almost stable in the steady flow state in the middle stage (B). The light intensity is shown. Then, in the latter stage (C), the relative light intensity decreases rapidly by repeating the maximum and the minimum of the light intensity, becomes almost zero within two seconds after the flow stops, and the birefringence becomes almost zero. Therefore, it is clear that the distortion of the molten resin can be reduced to almost zero only by maintaining the molten state for about 2 seconds after the flow stops.

Using the test apparatus described above, a test was performed while controlling the temperature of the molten resin from the injection molding machine and the temperature of the mold to be the same. The test temperature is 185 ° C,
Four levels of 200 ° C., 215 ° C. and 225 ° C. were used, and the flow rate of the steady flow in the middle stage was constant at 3.30 cm ³ / sec. The results of the latter stage (C) at each level are shown in FIGS. Further, the amount of change in the birefringence in the latter stage (C) was determined from each result, and the results are shown in FIG.

From FIGS. 4 to 7, it can be seen that the relative light intensity becomes zero only by maintaining the molten state for about 2 seconds after stopping the flow, regardless of the melting temperature. Further, from FIG. 8, regardless of the melting temperature, the birefringence is zero only by maintaining the molten state for about 2 seconds after the flow stops. That is, it is apparent that the distortion of the molten resin can be reduced to almost zero simply by maintaining the molten state for about 2 seconds after the flow stops, regardless of the melting temperature.

Next, the test temperature was fixed at 200 ° C., and the flow rate of the steady flow in the middle stage (B) was 0.70 cm ³ /
Seconds, 1.43 cm ³ / sec, 3.30 cm ³ / sec and 5.
Four levels of 45 cm ³ / sec were selected and the relative light intensity was measured in the same manner. Then, the amount of change in the birefringence in the latter stage (C) was obtained from each result, and the results are shown in FIG.

FIG. 9 shows that the birefringence is zero only by maintaining the molten state for about 2 seconds after the flow stops, regardless of the flow velocity of the steady flow. This means that the birefringence becomes zero just by maintaining the molten state for about 2 seconds after the flow is stopped regardless of the injection pressure, and that the present invention is satisfied even by a molding method in which various pressures act. ing. In other words, not only injection molding, but also molded products formed by low-pressure molding methods such as press molding and extrusion molding, the birefringence can be reduced to zero by holding the molten state for about 2 seconds, and the distortion can be reduced. Can be eliminated.

That is, according to the results of the above test examples, a pressure is applied to the resin in the molten state to form a molten resin molded article having a predetermined shape. It is clear that distortion can be eliminated by holding the time. Since the distortion has already been eliminated in the molten state, it is possible to produce a molded article having no residual distortion even after cooling and solidification.

(Example 1) FIG. 10 is a sectional view of an injection molding die used in this example. This mold includes a fixed mold 1, a movable mold 2 and a spacer 20, and a cavity 10 is formed between the mold surfaces of the fixed mold 1 and the movable mold 2. The fixed mold 1 has a runner portion 11 communicating with the cavity 10.
Are formed. In the vicinity of the mold surfaces of the fixed mold 1 and the movable mold 2, thin-film surface heaters 3 are respectively embedded. A heat insulating layer 4 made of a heat insulating material such as asbestos is arranged on the back surface of the surface heater 3, and the heat of the surface heater 3 is mainly supplied to the mold surface side. Further, a cooling water passage (not shown) is formed inside the fixed mold 1 and the movable mold 2 so that the mold surface can be cooled by flowing the cooling water.

Using this mold, a Fresnel lens was molded from a polystyrene resin. The temperature of the molten resin at the time of injection is 2
The temperature was set to 00 ° C., and the injection pressure was about 4 MPa. Then, in the pressure-compressed state immediately after the cavity 10 is filled with the molten resin, the surface heater 3 is energized to set the mold surface temperature to 200 ° C.
This state was maintained for 2 seconds. Thereby, the cavity 10
The molten resin molded article in the inside is heated to 200 ° C., and the whole becomes a molten state and is held for about 1 second. Thereafter, the power supply to the surface heater 3 was stopped, and cooling water was circulated through a cooling water passage (not shown) to cool the mold and cool the molten resin molded product.

The obtained Fresnel lens exhibited excellent optical properties equal to or better than those of the conventional annealed Fresnel lens, and no distortion was observed. The fine groove shape on the surface was a fine one to which the shape of the mold surface was reliably transferred.

(Embodiment 2) In the above-described mold, the surface heater 3 was used as a heating means. However, even if a mold having a structure as shown in FIG. Can be molded.

This mold uses an iron plate 5 instead of the surface heater 3.
Are embedded, and on the back surface of the iron plate 5, the same heat insulating layers 4 as in the first embodiment are respectively arranged. A cooling water passage 6 and a high-frequency oscillator 7 are arranged on the back of the heat insulating layer 4.

In this mold, the high-frequency oscillator 7 is driven at a frequency of 0.5 KHz to several MHz in a pressure-compressed state immediately after the cavity 10 is filled with the molten resin. As a result, an eddy current is generated in the iron plate 5 and the iron plate 5 is dielectrically heated, and the heat can heat the molten resin molded product in the cavity 10. By maintaining the state for about one second, the molten resin molded product is maintained. Can be eliminated.

[0039]

According to the method for manufacturing a resin optical component and the injection mold of the present invention, a resin optical component having no residual distortion can be easily and reliably manufactured.
Therefore, the conventional annealing treatment is not required, and the number of steps can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a metal mold used in a test example, partially cut away.

FIG. 2 is an explanatory diagram illustrating a configuration of a test apparatus used in a test example.

FIG. 3 is a graph showing a relationship between elapsed time after injection and relative light intensity measured in a test example.

FIG. 4 is a graph showing the relationship between the elapsed time after stopping the flow at 185 ° C. and the relative light intensity.

FIG. 5 is a graph showing the relationship between the elapsed time after stopping the flow at 200 ° C. and the relative light intensity.

FIG. 6 is a graph showing the relationship between the elapsed time after stopping the flow at 215 ° C. and the relative light intensity.

FIG. 7 is a graph showing the relationship between the elapsed time after stopping the flow at 225 ° C. and the relative light intensity.

FIG. 8 is a graph showing the relationship between the elapsed time after stopping the flow and the birefringence at each temperature when the flow velocity is constant.

FIG. 9 is a graph showing the relationship between the birefringence and the elapsed time after stopping the flow of the molten resin flowing at each flow rate when the temperature is constant.

FIG. 10 is a sectional view of an injection mold used in Example 1.

FIG. 11 is a sectional view of an injection mold used in Example 2.

[Explanation of symbols]

1: fixed type 2: movable type 3: surface heater 4: heat insulating layer 10: cavity

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[Submission date] December 3, 1999 (1999.12.
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 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Minoru Komada 1 Nagahata, Ochiai, Kasuga-cho, Nishikasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. 1 Toyota Gakuen Toyota Technical University F-term (reference) 4F202 AH73 AR06 CA11 CB01 CN01 CN21

Claims (3)

[Claims] 1. A pressure-applied pressure is applied to a resin in a molten state to form a molten resin molded article having a predetermined shape, and the molten resin molded article is held in a molten state for a predetermined time while maintaining its shape in a mold. A method for producing a resin optical component, comprising cooling and solidifying. 2. An injection step of injecting and filling a resin in a molten state into a mold to form a molten resin molded article, and heating the molten resin molded article in the mold to hold the molten state in a molten state for a predetermined time. A method for producing a resin optical component, comprising: a holding step; and a release step of releasing the molten resin molded product from the mold after cooling and solidifying. 3. An injection molding die for molding a resin optical component, comprising a heating means for heating the resin injected into the cavity to a temperature equal to or higher than its melting point. .