Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-05-25
2002-10-08
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S198000
Reexamination Certificate
active
06462167
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing blow moldings through gas assist resin injection, to blow moldings, and to a polycarbonate resin composition for gas assist injection molding suitable to the production method. More precisely, the invention relates to a method for producing blow moldings having the advantages of good moldability and wall thickness uniformity even when the percentage of hollowness of the moldings is relatively high, in particular to a method for producing ribbed blow moldings.
BACKGROUND ART
As having the advantages of impact resistance, heat resistance, good electric properties and dimensional stability, polycarbonate resins have many applications in various fields of, for example, OA (office automation) appliances, information and communication appliances, electric and electronic appliances for industrial use and household use, automobile parts and building materials. However, there are some problems with polycarbonate resins in that they require high molding and working temperatures and their melt flowability is low. On the other hand, moldings for housings and parts for OA appliances and information and communication appliances such as typically duplicators and facsimiles and for other electric and electronic appliances are now required to have a complicated shape with local projections or depressions, for example, having ribs or bosses therewith, and to be lightweight and thin-walled from the viewpoint of resources saving. Therefore, desired are polycarbonate resins and polycarbonate resin compositions having increased melt flowability, or that is, having increased injection moldability.
Compositions of polycarbonate resins, to which are added styrenic resins such as acrylonitrile-butadiene-styrene resins (ABS resins), rubber-modified polystyrene resins (HIPS), acrylonitrile-styrene resins (AS resins) or the like for improving the melt flowability of the compositions, are known as polymer alloys, and have many applications in the field of moldings as having good heat resistance and impact resistance. Polycarbonate resins are self-extinguishable. However, their polymer alloys for OA appliances, information and communication appliances and other electric and electronic appliances are required to have higher flame retardancy of not lower than a predetermined level so as to ensure and increase the safety of their moldings for those applications.
To meet the requirements, various polycarbonate resin compositions have heretofore been proposed. Concretely, Japanese Patent Laid-Open No. 55145/1986 discloses a thermoplastic resin composition comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an AS resin, (D) a halogen compound, (E) a phosphate, and (F) a polytetrafluoroethylene component. Japanese Patent Laid-Open No. 32154/1990 discloses a molding polycarbonate composition with high flame retardancy and high impact resistance, which comprises (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an As resin, (D) a phosphate, and (E) a polytetrafluoroethylene component.
A method of injection molding is excellent in that its productivity is high and its design latitude is broad. Therefore, the above-mentioned polycarbonate resin compositions comprising, as the essential ingredient, a polycarbonate resin are formed into various moldings according to such an injection molding method. However, some problems are pointed out with the injection molding method in that the moldings produced are often burred owing to high injection-molding pressure applied thereto and the burrs often damage the molds used. Another problem with it is that the moldings produced are often warped owing to the residual strain thereof caused by high dwell pressure in cooling them. Still another problem is that the moldings, especially thick-wall parts thereof are often shrunk to have shrink marks. Because of these problems, use of injection moldings in the field in which their outward appearance is considered important is restricted.
On the other hand, the social desire for saving resin and for lightweight moldings is much increasing for saving natural resources. For lightweight moldings, their walls may be thinned, which, however, is naturally limitative in view of the melt flowability of resin for them, the applicability of the method to large-size moldings, and the mechanical strength and the toughness of such thin-walled moldings. Also for lightweight moldings, they may be foamed. However, use of foamed moldings is limited in view of their mechanical strength and appearance. Still another method for lightweight moldings is blow-molding to produce hollow articles, a-type of blow moldings.
The blow-molding method comprises blowing a molten parison with air being applied inside it to thereby transfer the mold profile onto the thus-blown parison. The method is characterized in that the percentage of hollowness of the moldings produced therein can be relatively freely varied. However, this is problematic in that the parison being blown is often unstable, the wall thickness of the moldings produced is often uneven and the mechanical strength and the toughness of the moldings could not be increased with ease. For increasing the mechanical strength and the toughness of the moldings, one modification of blow molding has been proposed, which comprises forming ribs inside the blow moldings. In this modification, the ribs are formed inside the blow moldings, depending on the profile of the mold used. Accordingly, the moldings produced shall have recesses formed on their surface, and are therefore problematic in that they could not be used in some applications.
For still another modification of producing blow moldings, a gas assist injection molding method is much used in the field of various moldings. This method comprises injecting a resin melt into an injection mold, followed by blowing the resin melt with a pressure gas forcedly applied thereinto to thereby form a hollow inside the thus-blown resin melt. The gas assist injection molding method is characterized in that the pressure for resin injection into the mold may be relatively low, that the percentage of hollowness of the blow moldings to be produced can be controlled in any desired manner, and that the hollow can be selectively formed in the thick-wall part of the moldings. The other characteristics of the gas assist injection molding method are that the blown resin melt is not shrunk while it is solidified to be a molding (this is because, in the gas assist injection molding method, the pressure in the mold is well kept as it is owing to the pressure gas therein while the blown resin melt is cooled), and that the residual strain of the moldings is low and the moldings are not warped (this is because the molding pressure is relatively low). Because of such excellent characteristics, the method produces good blow moldings.
In the gas assist injection molding method, used are polypropylene resins, rubber-modified polystyrene resins, ABS resins, etc. In addition, polycarbonate resin moldings producing in a mode of such gas assist blow molding have been proposed. For example, Japanese Patent Laid-Open No. 70852/1997 discloses polycarbonate resin blow moldings, which are produced in a mode of blow injection molding of a polycarbonate resin and for which the polycarbonate resin comprises, as the essential ingredient, a chloride ion-free polycarbonate having an alkali metal and/or alkaline earth metal content of from 1 to 800 ppb, an aromatic monohydroxy compound content of from 1 to 200 ppm, a content of the oligomer component having a molecular weight of at most 1000 and the residual monomer of from T
1
to T
2
% by weight (T
1
=1,130,000×(weight-average molecular weight of the polycarbonate)
−1.60
; T
2
=1,520,000×(weight-average molecular weight of the polycarbonate)
−1.44
), and a terminal hydroxyl content of from 1 to 30 mol %. They say that the blow injection molding method which they employed is to form a hollow inside the blow molding owing to t
Hara Kouichi
Mitsuta Naoki
Nodera Akio
Boykin Terressa M.
Idemitsu Petrochemical Co. Ltd.
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