JP2005115165A - Reflection mirror - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain ≥95% reflectance in an optical reflection mirror made of a thermoplastic resin. <P>SOLUTION: In an injection molding mold, the cavity face corresponding to the reflective face of the reflection mirror is formed from ceramics such as zirconia polished to ≤5 nm surface roughness, while other cavity face is formed from a steel material. As the thermoplastic resin, a polyphenylene sulfide resin composition or a cyclic olefin resin is used and injection molded to obtain a reflection mirror body having ≤7 nm surface roughness on the reflective face. The reflectance of ≥95% is obtained by vapor depositing Al as extremely thin as 0.2 μm on the reflective face having the above surface roughness. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reflecting mirror made of a thermoplastic resin having an optical reflecting surface with extremely excellent reflectivity, and a manufacturing method thereof.

  There are various optical reflectors such as optical scanning reflectors used in various optical devices, such as those requiring high accuracy, automobiles, single-vehicle rearview mirrors, etc. that require high reflectivity. Products were made using glass, but those made of thermoplastic resin seem to be used from the standpoints of cost reduction, weight reduction, impact resistance improvement, ease of molding and ease of handling. It has become.

The main body of the thermoplastic resin reflecting mirror is generally molded by an injection molding method. In this molding method, the molten resin plasticized in the cylinder of the molding machine flows through the gates and runners in the mold and enters the cavity that simulates the molded product, where it is cooled through the contact surface between the cavity and the core. It solidifies and becomes a molded product. Explaining the behavior of the molten resin during flow, the resin that contacts the gate, runner and cavity surface rapidly decreases in temperature at the extremely thin surface, loses fluidity and solidifies in situ, forming a surface layer. To do. The molten resin located on the center side of the surface layer is pushed forward from the solidified layer and comes into contact with the cavity surface ahead of the solidified layer, and at the moment, as in the case described above, the solidified layer is formed on the surface. By repeating this filling and solidification, the filling of the cavity is completed, the inside of the molded product is cooled to a predetermined temperature and taken out from the cavity to obtain a molded product. The cooling and filling of the resin during the filling are repeated. The fine flow mark on the surface of the molded product generated by the above will lower the mirror surface accuracy. Further, since the injection molding is performed by heating and cooling the resin as described above, it is inevitable that shrinkage, sink marks, distortion, and the like occur in the molded product.

  The optical reflecting surface is obtained by vapor-depositing a metal such as aluminum (Al) on the surface of the thermoplastic resin reflecting mirror molded in this way. The current reflectivity is not superior to that of conventional glass, and the cause is thought to be due to the surface roughness of the reflector body and the thickness of the metal deposition layer. It is done.

Therefore, the following method has been proposed as a method for obtaining better mirror surface (or transfer) accuracy of a molded product (reflecting mirror body) by injection molding of a thermoplastic resin. No. 1 is one in which a molten resin is injected and filled into a cavity of a mold heated to a glass transition temperature or higher of a thermoplastic resin, and the molded article is taken out by gradually cooling the resin to a temperature equal to or lower than the thermal deformation temperature in the cavity. The second is to inject a molten resin into the cavity and introduce a pressurized fluid into the resin to obtain a hollow molded product (optical reflection member). Part 3 is a cavity piece slidable in the front-rear direction on one of the mold cavity surfaces. After filling the cavity with molten resin, the piece is moved backward to form a gap with the resin and another resin. There are those that reduce the thermal conductivity of one or more resin surfaces of a surface as compared to a resin surface in contact with another mold.

Further, as No. 4, as a molding material for the reflector body, a polyphenylene sulfide resin containing an inorganic filler, a polyether sulfone resin substantially free of a filler, and a polyetherimide resin substantially free of a filler In addition, a technique is disclosed in which a portion of the reflector body that is in contact with the aluminum vapor deposition layer is molded with a mold having a surface roughness Ry of 0.1 μm or less.
JP-A-64-38421 JP 2002-086517 A JP 2001-105449 A JP-A-3-208201

  In one of the above methods for obtaining a better mirror surface of a reflecting mirror base material made of a thermoplastic resin, the stress strain is reduced in the molded product, which is mainly used for molding a plastic lens, but the molding time becomes longer. Not efficient. Part 2 of the molding method is to absorb the sink marks generated in the molded product with a hollow portion formed of a pressurized fluid, thereby eliminating the sink marks on the surface of the molded product that is in close contact with the cavity surface. Although excellent, both the mold structure and molding operation are complex, leading to increased product costs. In the third method, since a gap is provided between one side of the molded article in the cavity, that is, the reflector base and the cavity surface, the resin surface is not cooled by heat conduction. In the same manner as described above, the sink mark is preferentially generated, but the molding shot time becomes longer and the cost is increased. In addition, No. 4 achieves surface smoothness from both sides of the molding material and mold cavity surface, and is excellent. However, there is a flow mark due to cooling of the resin during the flow, which is peculiar to the injection molding method. The current situation is that a sufficient mirror surface cannot be obtained.

The reflecting mirror body in the optical reflecting mirror according to the present invention uses a heat-resistant polyphenylene sulfide resin composition (hereinafter referred to as PPS) that does not contain an internal mold release agent and that contains a spherical inorganic filler. In addition, the fluidity of the resin and the adhesion to the cavity surface are ensured by using the inside of an injection mold with mirror-polished ceramics attached to the required cavity surface, and the mirror surface transferability is good. By using an unplasticized resin material, the quality of the mirror surface was stabilized on the assumption that the plasticizer from the molded product was not volatilized.

In an optical reflector that does not require heat resistance, a cyclic olefin-based resin material was used. By making the thickness of the reflector main body molded with this cyclic olefin-based resin and the above PPS 2 mm or less, molding shrinkage in the thickness direction is minimized, and sink marks are not generated on the reflecting surface.

As a manufacturing method thereof, a part of the cavity surface of the injection mold, that is, the cavity surface that transfers and forms the optical reflecting surface is quenched to a hardness of HRc62 or more, and the surface roughness is reduced to 5 nm or less. A relatively good specularity was also obtained when the mirror-polished steel material was used.

As mentioned above, the optical reflection surface forming part of the cavity is made of ceramics, so that the resin flowing in the cavity is suppressed from heat conduction with the mold, so that early solidified layer formation is suppressed and flow marks are generated. It was to be kept to a minimum. Therefore, the specularity of the optical reflecting surface is improved. Thus, by making the surface roughness of the optical reflector body made of thermoplastic resin 5 nm or less, sufficient gloss can be obtained even if the Al deposition on the surface is extremely thin (0.2 microns or less). As a result, it is possible to obtain a performance with a light reflectance of 95% or more without causing distortion on the reflecting mirror surface. Further, the light reflectance could be further improved by depositing silver on the main body of the optical reflecting mirror.

  The optical reflecting mirror based on the thermoplastic resin according to the present invention comprises a three-way relationship between a thermoplastic resin composition, an injection mold and an Al vapor deposition layer. First, the thermoplastic resin is selected by selecting a PPS resin composition containing an inorganic filler when heat resistance is required under the conditions of use of the optical reflector, and a cyclic olefin resin when heat resistance is not a requirement. Is selected.

  In an injection mold made of steel, it is desirable to embed a ceramic (zirconia-based) block polished in a mirror surface with a surface roughness of 5 nm or less in a cavity to transfer the optical reflecting surface in a nested manner (see FIG. 1). Further, when using a steel material for the cavity surface, stainless steel (SUS), maraging steel, and die steel (SKD) excellent in mirror polishing, corrosion resistance, and quench hardening are selected.

  Al deposited on the reflecting mirror surface of the injection-molded resin reflecting mirror body is 3 microns or less, preferably 2.0 microns or less.

  Examples of the thermoplastic resin reflecting mirror according to the present invention will be described in detail. First, (a) as a molding material for an optical reflector installed in the vicinity of a light source, since heat resistance is required, a commercially available PPS resin is used as a matrix, and an inorganic hollow filler is added to the PPS 70% by weight. As a comparative example, a resin composition in which (b) 20% by weight of a fibrous inorganic filler was kneaded with respect to the PPS was selected. These PPS resin compositions have various required properties such as heat resistance, surface gloss, dimensional stability, and mechanical strength.

  Typical examples of the inorganic hollow filler that can be used include glass balloons, shirasu balloons, alumina silicate balloons, and silica balloons. Any of these hollow bodies can be used, but glass balloons with high burst strength have good wettability to PPS resin and are ideal for obtaining good surface roughness and surface gloss as well as improved strength of molded products. Met. Of course, balloons other than those described above may be used, and a coupling process may be performed.

In the present invention, when a PPS resin that does not contain an internal plasticizer is selected, the plasticizer is not extracted during Al deposition, which is a subsequent process, and is a condition indispensable for improving the light reflectance. I understood that.

As shown in FIG. 1, the mold 1 for injection molding of the reflecting mirror body is provided with a cavity 3 on the movable side mold plate 2, and the stationary side mold plate 4 is nested with a ceramic block in a portion facing the cavity 3. 5 was inserted. The surface of the insert 5 facing the cavity 3 (the cavity surface on the fixed side) has a surface roughness of 5 nm or less. In FIG. 1, 6 is a sprue, 7 is a runner, 8 is a gate, 9 is a nozzle of an injection molding machine, and a mold tube on the movable side and the stationary side is punched with water pipes for adjusting the mold temperature at appropriate positions, or a heater. Is incorporated in the same manner as a general mold.

  The mold was attached to an injection molding machine, and an optical reflector body was molded using the PPS resin compositions (a) and (b) as materials. In this molding, the cylinder temperature was set so that the melting temperature of the resin was 320 ° C., and the temperature of the mold was 140 to 150 ° C. Under this molding condition, the molten resin M injected at a predetermined pressure (primary pressure) from the nozzle 9 of the injection molding machine reaches the cavity 3 through the sprue 6, runner 7 and gate 8 of the mold. Meanwhile, the thin surface layer of the molten resin in contact with the mold surface is cooled by heat conduction with the mold and loses fluidity to become a thin solidified layer. The solidified layer sticks to the mold surface and stops moving forward, and acts to block the heat conduction between the molten resin located on the inner diameter side of the solidified layer and the mold. Therefore, the molten resin on the inner diameter side from the solidified layer is kept warm and pushed forward, and a part of the tip contacts the mold surface in the same manner as above to solidify and form a new heat insulating layer, cooling, The solidification is repeated, and the molten resin M reaches the cavity 3 from the gate 8. Further, on the cavity surface side formed of the steel material of the cavity 3, cooling solidification by contact with the mold surface and further filling are repeated in the same manner as described above. As a result, a fine flow mark F is generated on the surface of the molded product, but the molten resin contacting the other cavity surface, that is, the ceramic nesting surface 5 polished to a surface roughness of 5 nm or less is the thermal conductivity of the ceramic. Since it is extremely small, it does not easily solidify and maintains good fluidity during filling to the end.

  After the filling of the resin into the cavity is completed, a secondary pressure smaller than the primary pressure (also referred to as holding pressure) is usually added to the filled resin by an injection molding machine to replenish the resin for molding shrinkage. did. During this time, the molten resin in the cavity 3 was in close contact with the surface 5 of the ceramic insert until it was cooled by the mold, and after the mold was opened, the molded product was difficult to leave from this surface. Was very good and no flow mark was generated on the surface of the molded product. The shrinkage and sink on the optical reflecting surface side should be 2 mm or less, preferably 1.5 mm or less, for the depth (cavity of the molded product) of the cavity 3 of the mold.

The surface of the molded product that was in contact with the mirror-polished ceramic surface 5 of the optical reflector body thus molded, that is, the optical reflective surface, had a surface roughness of 5 to 7 nm. When 0.2 μm thick aluminum vapor deposition was applied to this surface, the light reflectance of 95% or more was obtained in the molded product made of the material (a), and 93% or higher in the molded product made of the material (b). Obtained. Thus, there was a difference of 1 to 2% in light reflectance between the material (a) and the material (b). In addition, it should be noted that, in the conventional optical reflector made of thermoplastic resin, a reflectance of about 90% was finally obtained by forming an Al deposited layer of 2 to 3 μm, whereas the present invention In this reflector, a light reflectance of 93% or more was obtained with a very thin vapor deposition layer of 0.2 μm, and a smooth surface was obtained by such a thin vapor deposition layer. .

A cyclic olefin resin composition was used as the thermoplastic resin material for the optical reflector body used in applications where there was no problem with heat resistance. Examples of the cyclic olefin-based resin include commercially available products such as TOPAS (manufactured by Ticona, Germany), Apel (manufactured by Mitsui Chemicals), ZEONEX (manufactured by ZEON CORPORATION), ARTON (manufactured by Nippon Synthetic Rubber Company), and the like. Further, JP-A-2003-128865 discloses that a resin composition obtained by grafting and / or copolymerizing an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride with these cyclic olefin resins is blended with the commercially available PPS resin. There are also disclosed resins. Here, TOPAS (manufactured by Ticona) was used as the cyclic olefin resin.

  The above cyclic olefin-based resin was heated by a cylinder of an injection molding machine at a melting temperature of 300 ° C. and injected into a mold heated to 100 to 110 ° C. In this case, the thickness of the cavity portion of the mold was molded into three types of 2.5 mm, 2.0 mm, and 1.5 mm. As a result, the reflecting surface close to the cavity surface 5 made of the ceramics of the mold in the reflecting mirror main body obtained a mirror surface having a surface roughness of 5 nm or less with almost no flow mark. In this case, the mold molded with a cavity portion thickness of 1.5 mm was the best. Furthermore, when an Al vapor deposition layer was formed to a thickness of 0.2 microns on this reflecting surface, a light reflectance of 95% or more was obtained. Also in this case, it was found that the depth of the cavity part 3 (thickness of the molded product) of the mold should be 2 mm (preferably 1.5 mm) or less.

On the other hand, a commercially available cyclic olefin resin (ZEONEX E48R: manufactured by Nippon Zeon Co., Ltd.) was injection molded on the optical reflector body under the same conditions as the cyclic olefin resin composition. In this case, the surface roughness of the optical reflecting surface was slightly roughened to 7 to 9 nm. However, when Al deposition similar to that described above was performed, a light reflectance of 89% or more was obtained.

In addition, a mold formed of a steel material in which the cavity surface for transferring the light reflecting surface is hardened by hardening to a hardness of HRc 62 or more and polished to a surface roughness of 5 nm or less, the optical reflector main body is formed with the above conditions and the resin material. The surface roughness of the optical reflecting surface when molded was slightly worse than that due to the ceramic insert 5, but the light reflectance was 89% by depositing Al of 0.1 micron each of the undercoat and the surface coat. The above reflecting surface was obtained.

  Using a mold whose cavity surface is polished to a mirror surface with a surface roughness of 5 nm or less, injection molding is performed using a PPS resin composition or a cyclic olefin resin as a material, and an Al vapor deposition layer of 0.2 microns or less is formed on the optical reflection surface. A good reflectance can be obtained by the formation. It can be used in various optical devices as a lightweight optical reflector made of a thermoplastic resin composition.

It is the center sectional view showing a part of metallic mold concerning the present invention. It is sectional drawing of the principal part which showed the flow condition of the molten resin within a metal mold | die.

Explanation of symbols

1 Mold 2 Movable mold 3 Cavity 4 Fixed mold 5 Nest 6 Sprue 7 Runner 8 Gate 9 Nozzle

Claims (6)

In the optical reflecting mirror made of thermoplastic resin, the reflecting mirror body uses a polyphenylene sulfide resin composition or a cyclic olefin resin, and the optical reflecting surface of the reflecting mirror body is used for an injection mold for molding the reflecting mirror body. The surface roughness of the cavity surface to be transferred is 5 nm or less, and an aluminum or silver deposition layer is formed to a thickness of 0.2 μ or less on the optical reflecting surface of the reflecting mirror body obtained by injection molding. An optical reflector characterized by that.   In an optical reflector made of a thermoplastic resin, the reflector body is a polyphenylene sulfide resin containing 5-30% by weight of an inorganic hollow filler with respect to 70-95% by weight of polyphenylene sulfide resin and containing no internal plasticizer. The optical reflector body according to claim 1, wherein the composition is a material.   2. The mold for injection molding according to claim 1, wherein the cavity surface of the mold for transferring and forming the optical reflecting surface of the optical reflector body made of thermoplastic resin is formed of ceramics having a surface roughness of 5 nm or less. Mold. The cavity surface for transferring and forming the optical reflecting surface of the reflecting mirror body is formed of a steel material having a hardness of HRc 62 or more and a surface roughness of 5 nm or less. Injection mold.   5. The optical device according to claim 1, wherein a cavity gap of at least a portion forming the light reflecting mirror surface is 2 mm or less in the mold for transferring and forming the optical reflecting surface. Injection mold for reflectors. The optical deposition surface according to claim 1, wherein an aluminum vapor deposition layer is formed to a thickness of 0.2 μm to 0.5 μm on a thermoplastic resin optical reflecting mirror main body having a surface roughness of 5 nm or less. Reflector.

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