Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work – To degas or prevent gas entrapment
Reexamination Certificate
1999-09-23
2002-07-30
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
To degas or prevent gas entrapment
C264S331180, C264S331210, C215S400000, C428S035700, C428S035800, C428S036900, C428S036920
Reexamination Certificate
active
06426024
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aromatic polyester preform, a blow molded product and a preform production process. More specifically, it relates to a blow molded product having a small content of acetaldehyde, a preform providing the product and a production process for the preform.
BACKGROUND ART
Glass has been heretofore widely used as a material for containers for seasonings, oil, refreshing beverages, beer, Japanese sake, cosmetics, detergents and the like. However, glass is heavy, costly to distribute, and dangerous to handle because of its fragility.
To overcome these defects of glass containers, plastic containers have now been rapidly replacing the glass containers. Of plastic materials for these plastic containers, polyethylene terephthalate is now widely used as a substitute material for glass containers because it has excellent mechanical strength, heat resistance, transparency, gas barrier properties and the like.
However, since a polyethylene terephthalate container may not exhibit a sufficient ultraviolet screening function depending on its application, the irradiation of ultraviolet light from the outside may cause the degeneration of quality and taste of a food contained therein or the discoloration or deterioration of a cosmetic contained therein with the result of a reduction in its trade value. Polyethylene terephthalate itself is a resin having low heat resistance unless it is crystallized, and a polyethylene terephthalate container must be filled with content at a high temperature or showered with hot water after filling for the purpose of sterilization according to the type of the content. Therefore, a material having high heat resistance is desired. High gas barrier properties are also desired to extend the shelf life of content according to the type of the content.
Polyethylene naphthalene dicarboxylate is known as a resin with which the above problems can be overcome.
Polyethylene naphthalene dicarboxylate has higher melt viscosity than polyethylene terephthalate. Therefore, when this resin is molded in accordance with a conventional method for blow molding polyethylene terephthalate into a biaxially oriented bottle, a large content of acetaldehyde is formed and the obtained molded product has a large content of acetaldehyde. Thus, when this molded product is used particularly as a container for a beverage, the flavor of content is spoiled.
It has recently been known that the above problem can be overcome by blending polyethylene naphthalene dicarboxylate with polyethylene terephthalate.
However, when a copolymer resin of ethylene terephthalate and ethylene naphthalene dicarboxylate is produced by a conventionally known copolymerization method, the solid-phase polymerization temperature must be lowered due to a reduction in a melting point, thereby causing a reduction in productivity. This causes not only an increase in costs but also the production of a resin having a different blending ratio for each required quality, thereby increasing production costs and making the control of molding complicated. Since a resin containing 20 to 80 mol % of ethylene naphthalene dicarboxylate is amorphous, handling properties at the time of drying and solid-phase polymerization deteriorate and required physical properties may not be obtained.
As means of obtaining required quality and reducing the production costs of a resin and a molded product, there is proposed a method comprising blending polyethylene naphthalene dicarboxylate with polyethylene terephthalate and molding the blend.
However, since polyethylene terephthalate and polyethylene naphthalene dicarboxylate have low compatibility with each other, a molded product obtained by simply blending these is opaque with low transparency, thereby causing a great reduction its trade value. Even if a transparent molded product can be obtained by selecting severe molding conditions to improve compatibility between them, for example, by raising the injection temperature or increasing the back pressure, a large content of acetaldehyde or oligomers is formed during molding and the oligomers are adhered to the vent portion of the mold of an injection molding machine, thereby causing such problems as burned spot or short shot. In the case of a beverage in particular, the flavor of content is spoiled when the content of acetaldehyde is large.
Since acetaldehyde and oligomers are formed in large quantities during molding, the above problems cannot be solved simply by reducing the content of acetaldehyde or the content of oligomers in a polymer used.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide a process for producing a preform having a small content of acetaldehyde from various aromatic polyester materials, which is accompanied by the formation of acetaldehyde during injection molding as described above.
It is another object of the present invention to provide a process for producing a preform having excellent transparency, a small content of acetaldehyde and a small content of oligomers.
It is still another object of the present invention to provide a preform having a small content of acetaldehyde and excellent transparency, which is produced by the above process of the present invention.
It is still another object of the present invention to provide a biaxially oriented blow molded product obtained by blow molding the above preform of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a process for producing a preform by injection molding an aromatic polyester which comprises at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid and 2,6-naphthalenedicarboxylic acid as a main dicarboxylic acid component and ethylene glycol as a main diol component, wherein injection molding is carried out by an injection molding machine, which has at least one vent at the position of a cylinder between a position where the aromatic polyester is substantially molten in the cylinder of the injection molding machine and the position of the front-end of the metering zone of a screw when the molten aromatic polyester is stored in the front-end portion of the cylinder of the injection molding machine for injection molding, while air is exhausted from the vent under reduced pressure.
According to the present invention, there are further provided a preform produced by the above process and a biaxially oriented blow molded product obtained by blow molding the preform.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The aromatic polyester to which the present invention is directed is a polyester comprising at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid and 2,6-naphthalenedicarboxylic acid as a main dicarboxylic acid component and ethylene glycol as a main glycol component. That is, the above aromatic polyester includes (1) a polyester comprising ethylene-2,6-naphthalene dicarboxylate as a main recurring unit, (2) a polyester comprising ethylene terephthalate as a main recurring unit and (3) a polyester comprising ethylene-2,6-naphthalene dicarboxylate and ethylene terephthalate as main recurring units.
The aromatic polyester comprising ethylene-2,6-naphthalene dicarboxylate as a main recurring unit in the present invention may be a copolymer obtained through copolymerization by substituting part of a 2,6-naphthalene dicarboxylic acid component with at least one member selected from other aromatic dicarboxylic acids such as 2,7-, 1,5- and 1,7-naphthalenedicarboxylic acids, isophthalic acid, terephthalic acid, diphenyldicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid and tetrahydronaphthalene dicarboxylic acid; alicyclic dicarboxylic acids such as hexahydroterephthalic acid, hexahydroisophthalic acid and decahydronaphthalene dicarb
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