Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under...
Reexamination Certificate
1998-04-06
2002-04-30
Silbaugh, Jan H. (Department: 1732)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
C425S568000, C425S570000, C425S572000, C264S328800, C264S328120, C249S060000
Reexamination Certificate
active
06379143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to molds and molded articles, and more particularly, to molds for forming molded plastic articles which can be used as an oil or air filter used in a car or electronic equipments, a filter used in daily necessities including kitchen utensils and articles used in a bathroom or a toilet, various filters used for straining, draining, and other various purposes, a cover for thin case, a partition, and the like, and the molded articles.
2. Description of the Related Art
Conventionally, molded plastic articles such as a meshed plastic filter or a molded thin plastic plate having a frame were produced by an insert molding instead of an one-piece molding in order to avoid difficulties in molding. But, the insert molding demands too many processes and high cost. In performing the insert molding, bonding of a meshed net to the frame is important. Thus, skilled workers, expensive positioning apparatus and expensive welding apparatus are required for the bonding process.
The attempt at the one-piece molding encountered the following drawbacks:
(1) If molten plastic material is injected into net rib grooves at a low injection pressure, the material can not reach to the end of the grooves and it is likely that there would be some of the net ribs missing or some parts of plate distorted especially at distant locations from a gate.
(2) If a high pressure injection is applied, there would be no ribs missing or plate distorted. But, large-sized equipments are needed for a high injection pressure. In case of net ribs, the space between the ribs would be closed, resulting possibility of fail to serve as a filter or a net. Further, regulation of the pressure is complicated.
(3) It is a fatal drawback that, in the conventional technology, net ribs were produced only by too fine latticed grooves through which molten resin should be compelled to flow. And, since gas or air produced from hot molten resin might stay within the mold, the molten resin could not uniformly reach to the end of the fine grooves even under the sufficiently high injection pressure.
(4) The fine grooves have the latticed shape. Thus, the molten resin stream might come into collision with one another. This fact would also lead to the result that the molten resin could not uniformly reach to the end of the fine grooves even under the sufficiently high injection pressure.
In order to solve the drawbacks (1) to (3), the applicant of this invention has already suggested an improved plastic filter having a guide or an improved mold having a guide groove in the followings:
Japanese Patent Publication No. Pei 7(1995)-20677, Japanese Non-examined Patent Publication Nos. Pei 6(1994)-126784, 6(1994)-155531, 7(1995)52164, 7(1995)-137166 and 7(1995)-284617.
But, further study is necessary to obtain perfectly molded articles having good plasticity and yield without any defect such as burr or weld.
As shown in
FIGS. 66
to
69
, those suggestions have the problems that flowability of the molten resin is degraded at the points remote from a gate through which the molten resin is injected, and short portions
26
are appeared by the influence of gas or air produced within the mold. Even in case of using the principle of the guide suggested by the applicant of this invention, it is likely that there are short portions
26
at the points beyond the effect of the guide.
The applicant of the present invention noticed that a mold structure which can provide good flowability of the molten resin is more advantageous than the conventional mold having the meshed net formed by the latticed fine grooves. The advantageous mold structure can be obtained by fine grooves each of which extends in one direction and does not have any intersection. The present invention provides a fine meshed filter formed by using the fine grooves each of which are formed by an upper mold and a lower mold which can be fitted together by pressing.
Various products such as plastic baskets and waste baskets used in drain-outlets as a kitchen utensil were produced by the conventional technology. But, all of those was produced by using the grooves formed in one-piece mold. Those could not offer the functions or effects of the present invention. Further, all of those obtained by the conventional technology was formed by using large and wide grooves, and did not applicable to the fine meshed product having the groove interval or the groove width of 1 mm or less.
SUMMARY OF THE INVENTION
There are following problems to be solved in injection molding of an article having a fine-pitch net structure, for example a filter for air conditioner or oil filter, by the one-piece molding;
(1) Mold structure within which little amount of gas or air is produced,
(2) Mold structure which can provide generally uniform flow of the molten resin,
(3) Mold structure which can improve flowability of the molten resin, and
(4) Mold structure which can improve flowability of the molten resin and can prevent missing of rib at the point to which the molten resin can hardly reach, or molding defect in the thick portions.
To solve the above problems, it is an objective of the present invention to provide a mold apparatus which can overcome the disadvantages in the prior art.
Accordingly, to achieve the above objective, the invention provides an injection molding apparatus for molding a plastic articles having a frame by fitting an upper mold and a lower mold by press, and injecting molten resin through a gate, wherein the improvement comprises:
(a) a net groove formed in stripes by a plurality of fine grooves extended only in one direction in each of the upper mold and the lower mold, the fine grooves in the upper mold and the lower mold being faced with each other,
(b) at least one passage groove having a large diameter or a large width for facilitating the entrance of the molten resin, one or more of the passage grooves intersecting the fine grooves being formed on the fine grooves of the upper mold and/or the lower mold and formed;
(c) at least one gate formed on the passage groove for injecting the molten resin into the mold; and
(d) a frame groove formed to surround the fine grooves in the upper mold and/or the lower mold.
Further, the passage groove is communicated with the frame groove through a sharp-pointed end of the passage groove, in order to prevent the molten resin from being entered through the passage groove into the frame groove without any obstacle.
In addition, the passage groove is communicated with the frame groove through a constricted end of the passage groove and the end of the passage groove connected to the frame groove has a large diameter or a large width, in order to prevent the molten resin from being entered through the passage groove into the frame groove without any obstacle.
Also, the passage groove comprises a plurality of constricted portions to form a plurality of divided parts, and gates are formed on each of the divided parts of the passage groove for injecting the molten resin into the mold, in order to prevent the molten resin from being entered through the passage groove into the frame groove without any obstacle and facilitate the entrance of the molten resin into the fine grooves.
Still further, the passage groove is formed as a guide groove having a large diameter or a large width, both ends of which are not directly connected to the frame groove, in order that the molten resin injected through the gate into the mold can be entered into the fine grooves after the pressure of the molten resin is accumulated.
Additionally a band-shaped groove having a large diameter or a large width is formed at an end of the guide groove in a direction intersecting the guide groove to form a substantially T-shaped end of the guide groove, in order that the molten resin injected through the gate into the mold can be entered into the fine grooves in a wide range after the pressure of the molten resin is accumulated.
Also a band-shaped groove having a large diameter or a large width is formed in a directi
Daisan Kanagata Seisakusyo Ltd.
Dellett and Walters
Silbaugh Jan H.
Staicovici Stefan
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