JPH0211666B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a synthetic resin curved mirror, and more particularly, to a method for manufacturing a synthetic resin curved mirror with good shape stability. Synthetic resin mirrors are used in the fields of displays, interiors, and miscellaneous goods because they are lighter than conventional ones, hard to break, and easy to machine. Furthermore, recently, as vehicles such as automobiles become lighter, there has been a demand for practical use of synthetic resin mirrors for vehicles that are lighter and more difficult to break than conventional glass mirrors. Such mirrors made of synthetic resin, for example, are made by thoroughly cleaning the surface of a methacrylic resin plate, then vacuum-depositing a metal such as aluminum on the surface, and applying synthetic resin paint to protect the vacuum-deposited film. It is obtained by coating. If necessary, the substrate may be subjected to surface hardening treatment in advance to prevent scratches from wiping dirt such as fingerprints, dust, and mud with a cloth, making it difficult to see the mirror. However, unlike non-moisture-permeable glass mirrors, conventional synthetic resin mirrors are mainly affected by the temperature and humidity of the environment in which they are used, making it difficult to maintain a constant radius of curvature. The area has not been reached. That is, as shown in FIG. 1, a hardened surface film 2 is formed on the outer surface of the mirror body 1 to prevent scratches on the mirror body, and a reflective film 3 made of aluminum or the like is provided on the back surface.
A back coat film 4 is provided to prevent aluminum from being attacked by moisture, air, and chlorides. This back coat film also covers the end portion 3' of the reflective film 3 to form a coating film 4'. When the mirror body 1 is made of a transparent synthetic resin material such as acrylic resin, it is generally hygroscopic and the side provided with the back coat film 4 has high moisture resistance. Moisture is absorbed only from other surfaces, and the surface expands and warps convexly, changing its shape. For example, in the case of a convex mirror, the radius of curvature r shown in Fig. I have a problem getting the . In view of this situation, the inventors of the present invention focused on the fact that the radius of curvature changes due to the absorption of moisture from one direction from the surface other than the back coat film of a synthetic resin mirror, and formed a thin metal film on top of it. Before forming the back coat film, the synthetic resin substrate is molded into the desired shape and has a low moisture content by avoiding heat treatment by surface hardening, and is then conditioned to have the equilibrium moisture content of the environment in which it will be used. The present invention was completed by discovering that the problem of variations in the radius of curvature of hygroscopic transparent synthetic resin mirrors can be solved. An object of the present invention is to provide a method for manufacturing a synthetic resin mirror with good shape retention. In manufacturing a synthetic resin curved mirror, the present invention includes:
A curved surface made of synthetic resin characterized by forming a curved surface made of synthetic resin into a desired shape, conditioning the surface of the curved surface, forming a metal thin film on the surface of the curved surface substrate, and subsequently forming a back coat film. This is a method for manufacturing mirrors. The synthetic resins used in this invention include acrylic resin, polycarbonate, styrene-methyl methacrylate resin, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene resin, etc., but they have high transparency and other optical properties and heat resistance. Acrylic resin and polycarbonate, which have excellent properties, are most suitable. for example
50℃95% in JISD5705 vehicle mirror performance test
In the humidity resistance test of RH96Hr and the hot water resistance test at 90°C for 1Hr, the mirror substrate absorbs moisture and softens, and the variation in the radius of curvature of the convex mirror in particular increases, so ASTMD648 18.6
Kg/cm ² Resin with a heat distortion temperature of 90℃ or higher under load is suitable, but acrylic resin with a heat distortion humidity of 100℃,
From this point of view, polycarbonate having a heat distortion temperature of 120°C is preferred. The mirror substrate can be obtained by processing a casting plate or an extrusion plate into a desired shape by vacuum forming, press molding cutting, etc., or by injection molding a molding material pellet, or by other known methods. The quality of surface accuracy, plate thickness dimension, shape dimension, and radius of curvature is stable,
Injection molding is preferred because it has good productivity and is advantageous in terms of cost. General injection molding methods can be used, but in order to minimize molding distortion and obtain molded products with highly accurate dimensions and radius of curvature, it is recommended to use a precision mold temperature controller. . The mold used for molding is preferably corrected in advance in anticipation of variations in the radius of curvature of the curved mirror. For example, as shown in Fig. 1, when the amount of change over time in the radius of curvature r of an acrylic resin convex mirror after vacuum deposition and back coating is △r, the radius of curvature R of the convex mirror mold should be R = r + △r. preferable. △r
The value of can be determined by the amount of change in the radius of curvature over time, depending on the synthetic resin used, the molding machine, and the molding conditions. Next, the mirror substrate is subjected to surface hardening treatment. As the curable coating material, known hardening agents such as silicone, polyfunctional acrylic, urethane, and acrylic-urethane can be used, but scratch resistance is Excellent silicone-based and polyfunctional acrylic-based materials are desirable. The coating composition can be applied to the surface of the mirror substrate by a known method such as spray coating, cast coating, brush coating, or dip coating. If the surface of the mirror base material is cleaned by degreasing with an organic solvent, ultrasonic cleaning, etc. before painting, a mirror with a good appearance and no blemishes can be obtained. Drying is generally carried out by a thermosetting method, and takes 30 to 120 minutes at 60 to 130°C. The preferred thickness of this coating is 1 to 30 microns, more preferably 3 microns.
~15 microns. If it is less than 1 micron, the wear resistance will not be sufficient, and if it is more than 30 microns, cracks will easily occur. Humidity control in the present invention is a relative humidity of 50-95%, more preferably 60-80%, and a temperature of 10°C.
-80°C, more preferably 20°C - 50°C. If the relative humidity is below 50%, the radius of curvature will fluctuate greatly and the effect will be small; if the humidity is above 95%, dew will condense on the surface-hardened substrate, and if vacuum evaporated onto this substrate, it will not be possible to obtain a product with a beautiful appearance. If the temperature is below 10°C, the radius of curvature will fluctuate greatly and there will be no effect, and if it is above 80°C, the substrate will deform, which is not preferable. The metal thin film coating is performed by vacuum evaporation, ion plating, sputtering, or the like. For example, after coating the surface with a hardened film, the humidity-controlled substrate is placed in a vacuum deposition tank.
^10-4 to ^10-5 torr vacuum and aluminum at 100Å
Deposit to a thickness of ~500 Å. Although pretreatment is not particularly necessary, it is preferable to do so because dust may adhere to the reflective film or a rough surface like orange skin may occur on the reflective film, making it impossible to obtain a high-quality mirror. A curable resin film is coated on the surface of a thin metal film, and cured by irradiation with an active energy source such as ultraviolet rays, electron beams, or heat. The coating may be applied by brush coating, spray coating, curtain flow coating, etc., but is preferably applied to a film thickness of 10 to 50 μm. An embodiment of the present invention will be described with reference to the drawings. Acrylic resin for injection molding (Parapet HR manufactured by Kyowa Gas Chemical Industry Co., Ltd.) was injection molded using a 3 mm thick convex mirror mold with a radius of curvature of 1300 mm. Next, the molded product is immersed in a silane-based surface hardening solution, pulled up gently, placed in a hot air constant temperature bath at 85℃ for 120 minutes to crosslink and cure, forming a coating film with a thickness of 10μ, and then heated at 30℃ and 80%RH. The humidity was controlled for 40 hours under these conditions. Next, put it in a vacuum evaporation tank ^and
Aluminum is vapor-deposited in a vacuum to form a film approximately 0.02μ thick. Next, back coat paint is spray-painted onto the thin aluminum film and heated at 75°C for 24 hours to form a film approximately 30μ thick. , we obtained a convex mirror. FIG. 2 shows the change over time in the amount of variation (Δr) in the radius of curvature of the convex mirror manufactured by the above procedure. The equilibrium value in the above example is 150 mm, but if the humidity adjustment step is omitted from the above procedure, the equilibrium value is 300 mm, and the amount of variation in the radius of curvature (△r) is reduced to about 1/2 by the humidity adjustment. There is. As described above, a curved mirror with good shape and dimension retention can be obtained by the procedure of surface hardening, humidity control, and vacuum deposition, and this point will be explained below together with the manufacturing method.
Table 1 is an explanatory diagram of the manufacturing process of the present invention,

[Table] Even if the humidity is controlled, a curved mirror with good shape and dimension retention cannot be obtained. In the manufacturing process, the moisture content of the substrate increases due to humidity conditioning, and cracks occur during the subsequent surface hardening treatment due to the solvent in the hardening solution, making it impossible to obtain a curved mirror with a good appearance. In the manufacturing process, the radius of curvature fluctuates greatly due to unilateral absorption of moisture from surfaces other than the reflective film surface of the curved mirror, making it impossible to obtain a precise curved mirror. According to the manufacturing process of the method of the present invention, a curved mirror with good shape and dimension retention can be obtained.
Figure 3 shows that the amount of change over time △r in the radius of curvature of the convex mirror made of a rubber-based soft protective film in the present invention is 100.
This shows that a good convex mirror of less than mm was obtained, and a comparison shows that a mirror with better shape and dimensions than a convex mirror made of a hard protective film made of unsaturated polyester resin was obtained. The soft protective film in the present invention is formed from a rubber-based protective paint, and such paints include:
Examples include those containing polybutadiene-based, polyisoprene-based, or soft vinyl chloride-based soft resins. Table 2 shows the polycarbonate convex mirror of the present invention, and the amount of change in the radius of curvature over time Δr is
100mm, indicating that a good mirror can be made. In this example, surface hardening treatment was performed using a primer paint for polycarbonate and an organosiloxane curing liquid for polycarbonate.

[Table] The present invention has a structure as explained above, and in particular, a curved mirror base made of a transparent synthetic resin material such as acrylic resin that is molded into a desired shape and surface hardened is coated with a thin metal film or a back coat. Because it has a humidity-controlling structure, it can significantly reduce shape changes due to moisture absorption, resulting in a lightweight synthetic resin curved mirror that has scratch resistance and optical properties comparable to those of inorganic glass curved mirrors, and is resistant to breakage. It has the advantages of easy shape and size control and efficient manufacturing. Although the curved mirror of the present invention has been described as a convex mirror in the above embodiments, it may be a concave mirror, and can be applied not only to vehicle outside mirrors but also to decorative mirrors and curved mirrors.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a synthetic resin convex mirror, Figure 2 is a diagram showing the effect of humidity control on changes in the radius of curvature of the convex mirror over time, and Figure 3 is a diagram showing soft protection against changes in the radius of curvature of the convex mirror over time. It is a figure showing the effect of a film.

Claims (1)

[Scope of Claims] 1. In manufacturing a synthetic resin curved mirror, a thin metal film is formed on the surface of a curved synthetic resin substrate that has been molded into a desired shape and surface hardened, after which the humidity is controlled. A method for manufacturing a curved mirror made of synthetic resin, which method comprises the steps of: and subsequently forming a back coat film. 2. The manufacturing method according to claim 1, wherein the synthetic resin is an acrylic resin or a polycarbonate. 3. The manufacturing method according to claim 1, wherein the radius of curvature of the mold used for molding is corrected in advance in anticipation of variations in the radius of curvature of the curved mirror. 4. The manufacturing method according to claim 1, wherein the back coat film is a soft synthetic resin.