Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common...
Reexamination Certificate
2001-06-13
2003-05-20
Walker, W. L. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
C264S001100, C264S328800, C264S572000, C425S112000, C425S555000, C425S808000, C425S812000, C425SDIG004
Reexamination Certificate
active
06565346
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens, mirror, prism, or similar plastic molded article or product produced by injection molding and included in an optical device, e.g., a copier, laser printer, facsimile apparatus, or similar image forming apparatus, and a method and apparatus for producing the same. More particularly, the present invention is concerned with a plastic molded article or product having, e.g., mirror surfaces and a fine undulation pattern transferred thereto with high accuracy by injection molding, and a method and apparatus for producing the same.
2. Discussion of Background
For injection molding, it is a common practice to use a mold assembly including an inner mold surface forming a cavity having a preselected volume, a transfer surface formed on the inner mold surface for transferring a mirror surface to a molded article or product, and a gate or sprue open at the inner mold surface and having a preselected opening area. Molten resin is injected into the cavity via the gate or sprue and then cooled. The resulting molded article or product is taken out by opening the mold assembly. While such a molded article or product, particularly a mirror, lens, prism, or similar optical element, is required to have an accurate mirror surface and a uniform refractive index, the mirror surface needing a high surface accuracy is caused to sink because the molten resin contracts at the time of solidification.
Injecting molding methods for solving the above-described problem are taught in, e.g., Japanese Patent Laid-Open Publication Nos. 3-128218, 8-234005, 3-151218, and 3-281213 (hereinafter “Prior Art 1”). In Prior Art 1, either a non-transfer surface, or a mold surface which faces a transfer surface, is formed with, e.g., a roughened mirror surface or a surface treated so as to have a lower wettability, or else use is made of a porous material. Injection is stopped just before a cavity is filled up with molten resin. Then, the molten resin is solidified by cooling without any dwelling. As a result, the roughened surface is caused to sink due to a difference in adhering force between the molten resin, the transfer surface, and the roughened surface. This prevents the mirror surface of the molded article or product from sinking. Alternatively, an overflow portion for receiving excess molten resin is located outside of the cavity. When the overflow portion begins to be filled, injection is stopped. Then, the molten resin is solidified by cooling without any dwelling. This also allows the roughened surface to sink due to a difference in adhering force between the resin, the transfer surface, and the roughened surface.
An injection molding method disclosed in Japanese Patent Laid-Open Publication No. 2-175115 (hereinafter “Prior Art 2”) injects molten resin into a cavity in which a porous member, which communicates with a compressed gas such as air, is provided on an inner mold surface so as to contact the non-transfer surface of a molded article or product. While dwelling and cooling are under way after the injection of the molten resin, air is fed to the non-transfer surface of the molded article or product via the porous member. With this method, a side of a cylindrical thin lens (i.e., the molded article or product) may be caused to sink.
Japanese Patent Laid-Open Publication No. 6-304973 (hereinafter “Prior Art 3”) proposes an injection molding method in which a non-transfer surface communicates with the outside air via a vent hole. During an interval between the beginning and the end of the injection of molten resin into a cavity, a pressure difference is generated between the transfer surface and the non-transfer surface of the resin. As a result, the non-transfer surface of the resin is caused to sink. Specifically, air is brought into contact with the molten resin, on a surface other than the mirror surface of the molded article or product transferred from the transfer surface of the mold assembly, via the vent hole and a bore communicating therewith, so that the cooling speed of the molten resin is lowered. At the same time, a preselected air pressure is fed to the vent hole in order to generate a preselected pressure difference between the mirror surface of the molded article or product and the vent hole. This allows only the portion of the resin facing the vent hole to sink, i.e., prevents the mirror surface of the molded article or product from sinking. In addition, because only the portion of the resin facing the vent hole sinks, a molded article or product can be produced by simple control over the amount of the molten resin to be injected into the cavity and without any strain being generated in the resin. The resulting molded article or product is therefore free from an internal strain and is provided with an accurate mirror surface.
Prior Art 3 further teaches that the vent hole may communicate with a compressor so as to apply a preselected air pressure to the portion of the resin facing the vent hole. With this configuration, it is possible to generate any desired pressure difference between the mirror surface of the molded article or product and the portion of the resin facing the vent hole, thereby causing the portion of the resin facing the vent hole to sink. In addition, the pressure difference is readily adjustable in order to further enhance the accuracy of the mirror surface without any internal strain.
Japanese Patent Laid-Open Publication No. 6-315961 (hereinafter “Prior Art 4”) teaches an injection molding method causing the non-transfer surface of resin to sink. In accordance with this method, the transfer surface of a mold assembly is heated to and held at a high temperature. The transfer surface side of the resin is heated to a high temperature until the injection of molten resin into a cavity ends.
However, the above-described injection molding methods of Prior Art 1, Prior Art 2, Prior Art 3, and Prior Art 4 have some drawbacks. More particularly, Prior Art 1, which relies on any one of the roughened surface, surface treatment, or porous material, results in an expensive mold assembly. Moreover, stopping the injection just before the cavity is filled up with the molten resin is extremely difficult. Should the correct timing for stopping the injection of molten resin not be realized, the relationship in the adhering forces between the transfer surface and the roughened surface would be inverted and would thereby cause the mirror surface of the molded article or product to sink or else result in a shortage of resin. In addition, because sinking cannot be provided with directionality and because setting the molding conditions is difficult, the configuration of the molded article or product is critically limited. It is more preferable that the injection of the molten resin be stoppable at any time within a broader range of times. However, in this case, the overflow portion, which is formed integrally with the molded article or product, must be removed by an extra step. Moreover, if the area of the opening of the gate or sprue for feeding the molten resin to the overflow portion is excessively small, the relationship in adhering force between the transfer surface and the roughened surface would also be inverted and would thereby cause the mirror surface of the molded article or product to sink. Also, there would not be enough of the molten resin.
Prior Art 1 can be implemented as a mirror or similar optical element needing a single mirror surface, because it roughens the mold surface facing the transfer surface. However, Prior Art 1 cannot produce a lens, prism, or similar optical element, because the number and positions of the mirror surfaces are limited. In addition, the relationship in adhering force is inverted and causes the mirror surface of the molded article or product to sink, depending on the material constituting the transfer surface and roughened surface and the kind of resin used.
Prior Art 2 increases the cost of the mold assembly due to the porous member and provides more sophi
Fukushima Akira
Kanematsu Toshihiro
Murai Motoyasu
Sawada Kiyotaka
Yamanaka Yasuo
Luk Emmanuel S.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
Walker W. L.
LandOfFree
Plastic molded article or product and method and apparatus... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plastic molded article or product and method and apparatus..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plastic molded article or product and method and apparatus... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3058508