Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With reshaping or surface embossing of formed article
Reexamination Certificate
1999-02-11
2001-07-03
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
With reshaping or surface embossing of formed article
C264S109000, C264S328200
Reexamination Certificate
active
06254814
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique for molding and obtaining a biodegradable article such as seed-rasing container, an non-electrostatic article such as packaging container for delivering a compact disc, a tray for an IC and the like, which comprises papers such as waste papers, wood-pulp papers and the like.
(1) Molding Compound
Hitherto, when an article including a waste paper was molded by using a conventional molding composition, there was a problem during the kneading step that the molding compound is easy to stick onto a wall of a kneader, a die and the like, resulting in poor workability.
Also in a step of drying and solidifying the molding compound charged in a cavity of a mold, the surface of the composition in contact with the wall of the cavity is dried and solidified first to form a surface layer. Further, since the surface layer is very thin immediately after completion of the charging, there is a possibility that the surface layer adheres to the wall of the cavity when a vapor pressure or a charging pressure is applied to the surface layer. In such a case, water added into the molding compound is vaporized by the mold which is heated to a high temperature. And it is difficult to discharge the water vapor by a degassing means through the interface between the wall of the cavity and the surface layer.
Further, if the surface layer adheres onto the wall of the cavity, there is a problem of crack development in the molded article due to frictional resistance with the wall of the cavity when a solidified molded article is released.
Namely, it is eagerly desired that a molding compound is not liable to stick onto a wall of a kneader during the kneading step and is facilitating water discharge during the molding step. Further, it is required that the molding compound provides a molded article which is easily released from the mold and does not generate a crack.
(2) Molding Method
In the conventional method of molding an article including a cellulose fiber, a molding compound obtained by adding and kneading a pulverized waste paper, starch and water is charged into a cavity of a heated mold and, then, dried and solidified by discharging a water vapor from the molding composition.
As means for discharging the water vapor, there is suggested a flash-type mold which is provided with degassing means with micro pores in the wall of the cavity (for example, refer to JP-A-9-76213). When the molding is conducted with such a flash-type mold, it is suggested that the charging pressure is increased to obtain a molded article having superior transferring property, dimensional accuracy, low air permeability and high density (for example, refer to JP-A-9-109113). In such case, a positive mold is employed to prevent the molding compound from flowing out from the cavity even if the mold is opened slightly. And, after charging the molding compound while opening the positive mold slightly, a part of the water vapor is discharged by means of degassing means. Then, the remaining water vapor is discharged after the mold is closed.
Further, a method for discharging the water vapor without providing degassing means when an article including a cellulose fiber is molded (for example, refer to JP-A-10-29250). In this method, it is suggested to open the mold to form a gap of about 1 mm and to discharge the water vapor through the gap in the drying step. It is noted that the molding compound comprising 3 to 100 parts by weight of gluten as a binder and 20 to 150 parts by weight of water per 100 parts by weight of raw paper material is used.
In the method of molding by employing the mold provided with degassing means having micropores, if the cavity has a portion to mold a thin molded article or a narrow groove to mold a rib, it is necessary to increase flowability of the molding compound in the cavity by applying a high charging pressure in order to charge the molding compound into a cavity uniformly.
On the other hand, the molding compound charged in the cavity is heated and dried from the surface portion which is in contact with the wall of the cavity having a high temperature. Therefore, a solidified surface layer (hereinafter, referred to simply as “surface layer”) is formed on the surface portion of the molding compound. But, since heat transfer is delayed in the center portion of the molding compound, the molding compound is in the flowable state with a relatively low viscosity in the center portion. Since the surface layer formed of the molding compound is soft in the form of thin film, the surface layer is easily fractured due to an increased charging pressure and the flowable molding compound in the center portion flows into micropores of the degassing means to close the micro pore. Namely, there is a problem that it becomes difficult to dry and solidify the molding compound rapidly because the discharge of the water vapor is inhibited.
Further, in order to shorten the period of time for drying the molding compound, it is necessary to set the temperature of the mold to not lower than 120° C., preferably not lower than 130° C. to facilitate the generation of the water vapor. However, in the method wherein the water vapor is discharged by opening the mold to form the gap of about 1 mm without providing the degassing means having micropores, the molding compound flows into the large gap of the mold and a flash is easily formed due to the water vapor pressure when the temperature of the mold is set to not lower than 120° C. Also, there is a tendency that a void is easily generated in the cavity because of the lack of the molding compound. The thickness of the molded article obtained by employing such a kind of a cellulose fiber is usually so thin that it is really disadvantageous if a flash or a void of about 1 mm is formed in such thin molded article.
On the other hand, when the temperature of the mold is not higher than 120° C., it is necessary to increase an adding amount of water to make gluten perform the binding property and to give flowability to the molding compound. However, even if the amount of water per the solid content of cellulose fiber and gluten is decreased, the molding compound has flowability and the flash is liable to be developed. Therefore, if the amount of water is large, there are problems that the flash is further easily formed and that the molding cycle may not be shortened because the temperature of the mold is low and the drying period of time becomes longer.
Namely, it is eagerly expected that the molding method can be conducted without providing the degassing means with micropores and without generating the flash wherein the water vapor can be discharged smoothly and reliably in a short period of time and the charging pressure can be increased.
(3) Mold
Hitherto, when a molded article is molded, the shape of a cavity of a mold is fabricated on the basis of the outer shape of the article to be obtained and the molding compound is charged into the cavity, followed by solidifying the molding compound.
Apart from the case wherein the surface is treated by forming an irregularity, the wall of the cavity in a general mold is made smooth by grinding or is made mirrorlike by mirror polishing in order for the charged molding composition is liable to flow.
When the molding compound is charged into the conventional cavity with a smoothed surface or mirrorlike surface, the molding compound is cooled from the interface between the wall of the cavity and the molding compound in the case that the molding compound comprises a thermoplastic resin. Therefore, as described above, there is formed a solidified surface layer at the surface portion of the molding compound and, the inner portion of the molding composition wherein heat transfer from the wall of the cavity is delayed is in the flowable state with a relatively low viscosity. Since the surface layer formed on the surface portion of the molding compound is adhesive to the cavity wall, the molding compound is charged as the fountain-flow as shown in
FIG. 1
to provide a homogeneously mo
Funaki Masahiko
Higaki Seio
Sudo Manabu
Ueda Seiichi
Yagi Kousuke
Daiho Industrial Co., Ltd.
McDermott & Will & Emery
Theisen Mary Lynn
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