Plastic article or earthenware shaping or treating: apparatus – With mechanical means forming or expanding pores
Reexamination Certificate
2000-06-16
2002-08-20
Kuhns, Allan R. (Department: 1732)
Plastic article or earthenware shaping or treating: apparatus
With mechanical means forming or expanding pores
C425S208000, C425S562000, C425S00400R
Reexamination Certificate
active
06435853
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a method of plasticizing a material for molding thermoplastic resin foam and a plasticizing apparatus. More particular, the present invention relates to a method of plasticizing a material for molding thermoplastic resin foam and a plasticizing apparatus arranged to perform the steps of: rotating a screw disposed in a screw cylinder such that movement in the rotational and axial directions of the screw is permitted to plasticize thermoplastic resin; causing inactive liquid, such as carbon dioxide solution or nitrogen solution in a super critical state to penetrate the molten resin or introducing inactive gas of carbon dioxide or nitrogen, the pressure of which is not lower than the super critical gas pressure into the screw cylinder which is in a hot state, the temperature of which is not lower than the super critical temperature, to create a super critical state in the screw cylinder so as to cause the inactive gas to penetrate the molten resin; and injecting the molten resin for molding a foam member to which the inactive fluid has penetrated into a cavity of a mold so that thermoplastic resin foam is obtained.
2. Related Art
A molding method or a molding apparatus has been disclosed in JP-A-8-258096, JP-A-10-230528 and so forth, in which thermoplastic resin is melted in a heating cylinder of an injection molding machine. Then, inactive liquid, such as carbon dioxide solution or nitrogen solution in a super critical state is caused to penetrate the molten resin. Then, the molten resin for molding a foam member to which the inactive fluid has caused to penetrate is injected into a mold. Thus, a thermoplastic resin foam member is molded. The apparatus for molding a foam member, that is, a manufacturing apparatus disclosed in JP-A-8-258096 incorporates a heating cylinder, a main screw disposed in the heating cylinder, a mixing screw disposed at the leading end of the main screw and an inactive-gas supply unit for supplying the inactive gas or inactive solution to the mixing screw portion. Therefore, when the main screw has been rotated to move the thermoplastic resin in the form of pellet to the leading end of the heating cylinder, the thermoplastic resin in the pellet state is melted owing to a shearing action caused from rotations of the main screw, heat produced owing to friction and heat applied from the outside of the heating cylinder. Then, the molten thermoplastic resin is furthermore uniformly melted by the mixing screw. When carbon dioxide solution in a super critical state is supplied in the foregoing state, the carbon dioxide solution penetrates the molten resin. The molten resin to which the carbon dioxide solution has penetrated is injected into the cavity of a mold by moving the main screw in the axial direction. When the molten resin has been cooled and solidified, the mold is opened. Thus, fine thermoplastic resin foam can be obtained.
The method of manufacturing thermoplastic resin foam disclosed in JP-A-10230528 incorporates two individual units one of which is a continuous plasticizing unit having a heating cylinder and a screw; the other one of which is an injecting unit having a plunger. Therefore, the two units enable the following thermoplastic resin foam to be obtained. That is, thermoplastic resin in the pellet state is supplied to the continuous plasticizing unit. Then, the screw is rotated. Hence it follows that the thermoplastic resin is melted owing to the shearing action caused from rotations of the screw, heat produced owing to the friction and heat applied from the outside of the heating cylinder. When carbon dioxide is supplied into the heating cylinder, a carbon dioxide penetrates the molten resin. The molten resin for molding a foam member to which carbon dioxide has penetrated is supplied to the injecting unit by moving the screw in the axial direction. Then, the plunger is operated to inject the molten resin into the mold so that thermoplastic resin foam is similarly obtained.
Either of the conventional manufacturing apparatuses enables the thermoplastic resin foam to be obtained. However, there are problems to be solved. Since the super critical temperature of carbon dioxide gas is 31° C. and the super critical pressure is 7.4 MPa, there arises a problem of unsatisfactory sealing when carbon dioxide solution in a super critical state, the pressure of which is higher than the foregoing level, is injected into the molten resin in the heating cylinder. That is, since the thermoplastic resin to be supplied to the heating cylinder is in a solid state in the form of pellet, sealing cannot be realized by the thermoplastic resin in the pellet form. Thus, there arises a problem in that injected carbon dioxide solution leaks to the material supply opening. In particular, the foregoing manufacturing apparatus structured such that carbon dioxide solution is injected into the heating cylinder inevitably encounters the problem of unsatisfactory sealing. The reason for this lies in the high pressure of the molten resin in the heating cylinder which is 10 MPa to 30 MPa. Either of the foregoing manufacturing apparatuses cannot overcome the problem of unsatisfactory sealing. The screw of the apparatus for manufacturing fine thermoplastic resin foam disclosed in JP-A-8-258096 is composed of the main screw and the mixing screw disposed at the leading end of the main screw. on the other hand, the apparatus for manufacturing thermoplastic resin foam disclosed in JP-A-10-230528 is composed of the continuous plasticizing unit having the heating cylinder and the screw and the injecting unit having the plunger. Therefore, each of the apparatus must have too complicated structure, causing the cost of the manufacturing apparatus to relatively be enlarged.
SUMMARY OF THE INVENTION
To solve the foregoing problems experienced with the conventional technique, an object of the present invention is to provide a method of plasticizing a material for molding thermoplastic resin foam and a plasticizing apparatus. Specifically, an object of the present invention is to provide a method of plasticizing a material for molding thermoplastic resin foam and a plasticizing apparatus capable of injecting, into a screw cylinder, inactive solution, such as carbon dioxide solution or nitrogen solution in a super critical state or inactive fluid composed of inactive gas, such as carbon dioxide gas or nitrogen gas, the pressure of which is relatively low in spite of a level not lower than the super critical pressure and overcoming the problem of unsatisfactory sealing though inactive fluid, the pressure of which is not lower than the super critical pressure, is injected. Another object of the present invention is to provide a method of plasticizing a material for molding thermoplastic resin foam and capable of using a low-cost plasticizing apparatus having a simple structure.
To achieve the foregoing objects, a plasticizing method according to the present invention uses a screw cylinder having a material supply opening formed at the rear end and an injecting nozzle disposed at the leading end. Moreover, a screw is employed which incorporates a first metallized portion, a pressure-reducing portion and a second metallized portion. The inactive liquid in the super critical state or the inactive solution composed of inactive gas, the pressure of which is not lower than the super critical pressure, is injected to a position corresponding to the pressure-reducing portion of the screw. The injected inactive fluid is sealed by molten resin in the first and second metallized portions.
The foregoing first aspect enables the inactive fluid having a relatively low pressure level to be injected when the pressure is not lower than the super critical pressure. When the inactive fluid having the pressure not lower than the super critical pressure is injected, the sealing effect of the molten resin in the first and second metallized portions causes leakage of injected inactive fluid to the material supply opening or the portion
Ohyabu Hideo
Teraoka Atsuo
Tsuda Fumiaki
Kuhns Allan R.
Sughrue & Mion, PLLC
The Japan Steelworks, Ltd.
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