Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Reexamination Certificate
1998-10-16
2001-03-20
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
C264S328160
Reexamination Certificate
active
06203731
ABSTRACT:
A method for injection molding of plastic products, which have excellent transcription properties as well as the metallic mold being used for this injection molding and the manufacturing method of this metallic mold.
FIELD OF THE INVENTION
The present invention relates to the injection molding method for preventing the appearance of transcription defects such as flow marks, weld marks, shrinkage, etc. to the product when the transcription between the metallic mold surface and the product surface has been done sufficiently in injection-molding the plastic products, as well as the metallic mold being used to this injection molding and also the manufacturing method of this metallic mold.
More particularly, this invention relates to the injection molding method capable of sufficiently conducting the transcription and presenting the product of high quality by controlling the temperature of the product visible face side in the metallic mold in order to perform the transcription to a full extent, to the metallic mold being used for this injection-molding and to the manufacturing method of this metallic mold.
BACKGROUND OF THE INVENTION
In the conventional plastic injection molding that is conducted while controlling the entire metallic mold at a low temperature and moreover to a certain temperature, the material resin of molten thermoplastic resin, etc. is speedily cooled down from the surface in contact with the metallic mold and a thick solidified layer is formed, or the transcription between the metallic mold surface and the product surface can not be done sufficiently attributable to the heat shrinkage, and the transcription defects such as flow marks, weld marks, shrinkage, etc. are caused. This is because the hard solidified layer of resin surface hinders the deformation due to the internal pressure of the resin, the resin surface closely adheres to the metallic mold surface and prevents the transcription.
Further, there is such a case of including such filler as glass fiber and beads, and rubber particle as butadiene, etc. into the resin for reinforcing the mechanical strength of the resin, and if these should be contained in the resin, such filler as glass, etc and rubber particle as butadiene, etc. are left over on the resin surface by its thermal shrinkage difference, forming precise irregularities, worsening the transcription properties and damaging the outside appearance of product.
This kind of transcription defect of such product not only damages the outside appearance of product to decrease the product value but also hinders the uniform coating to damage the aesthetic appearance in case of providing the coating on the product surface, and there is such a problem as the cost for repair becomes higher. Further, in an extreme case, the surface smoothness accuracy or the outside appearance being requested as to such product can not be satisfied, thus making the product to be value-less.
This kind of transcription defect can be improved to a certain degree by making the resin pressure inside the metallic mold higher, pressing the resin against the metallic mold surface, by reducing the volume of filler, rubber grain, etc. being contained into the material resin, by making the diameter of grain size smaller, or by improving the material resin itself. However, making the metallic mold internal pressure higher necessitates the use of metallic a mold of higher strength and a large type molding machine capable of generating a high pressure, and causes such new problems as the higher cost, the internal strain of product itself and the generation of deformations. Further, the improvement of the resin itself causes such a problem that the performance of necessary strength and the like can not be satisfied because the serious consideration is taken to the outside appearance.
The highest effect against the transcription defect is to heat the face of metallic mold in contact with the product to the level higher than the glass transfer temperature if the material resin is non-crystal and to heat the said face to the level higher than the fusion temperature if the resin is crystal. This is because the solidified layer of resin in contact with the metallic mold tends to become thinner and deformed and to transcript the surface of metallic mold faithfully by making the surface of the metallic mold higher in temperature.
However, if the surface of metallic mold should simply be heated, the product surface is exposed to a high temperature for a longer period than necessary, there appear such new problems as the appearance of cumber and deformation to the product, and there also appears such an harmful influence that the molding cycle is elongated and the product cost becomes higher. Also, if the necessary high metallic mold surface temperature should not be reached or if the metallic mold surface temperature should be too high, the outside appearance needed to the product and the shape accuracy are damaged, thus causing the loss in production. Therefore, it is essential not only to detect the temperature of the metallic mold surface with high accuracy but also to improve the temperature of the metallic mold, and control the heating and cooling temperatures of metallic mold surface to the targeted temperature and time with high accuracy within a short time based on the detected temperature.
Conventionally, the method for controlling the metallic mold temperature is not to directly detect the surface temperature of metallic mold, but to detect the temperature of heating thermal medium and cooling thermal medium being supplied into the metallic mold using the temperature detection sensor inserted into the medium piping surface or into the piping, thus controlling the medium temperature based on this detection temperature and controlling the metallic mold temperature. Further, as the method for directly detecting the metallic mold surface temperature, such a method is being used as installing the temperature detection sensor inside the metallic mold insert die by the machining, and fitting it into the surface of metallic mold together with this insert die.
Moreover, as the units attempting to improve the responsibility of metallic mold temperature control, to shorten the metallic mold heating time and to raise the control accuracy of metallic mold temperature, a variety of the following units are being proposed.
(1) The unit installing an induction coil around the outer circumference of metallic mold (Gazette of Japan Unexamined Utility Model Publication No. S62-111832).
(2) The unit installing a high frequency induction coil consisting of the copper pipe to the metallic mold to flow the cooling water inside the pipe (Gazette of Japanese Unexamined Patent Publication No. S63-15707).
(3) The unit where the mobile insert die provided with an electric heater can be inserted into or pulled out of the metallic mold (Gazette of Japanese Unexamined Patent Publication No. S63-15719).
(4) The unit where such a device is installed for changing over the speedily heating or cooling of the medium for metallic mold temperature control or the heated or cooled thermal medium and supplying it to the outside of metallic mold, and the heating or cooling thermal medium being supplied can heat or cool the metallic mold through the temperature adjusting medium circulation channel inside the metallic mold (Gazette of Japanese Unexamined Patent Publication No. S62-15707, Gazette of Japanese Unexamined Patent Publication No. S62-208918, Gazette of Japanese Examined Patent Publication No. H7-25115).
As described earlier, the transcription defect of the product can be improved by heating to the high temperature the surface where the material resin of metallic mold flows, but if a long time should be taken to the heating and cooling, then there may appear such new problems that the molding cycle is elongated, the productivity falls down, and the rise of product cost will be invited and the product itself will be cumbered. Further, if the control accuracy of metallic mold surface temperature should be worse, and the moldi
Ishiyama Hideyuki
Kato Tsuyoshi
Suzuki Kiyoshi
Tateyama Hirofumi
Heitbrink Jill L.
McGlew and Tuttle , P.C.
Tohoku Munekata Company Limited
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