Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-09-07
2003-09-09
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S328000, C428S329000, C428S330000, C428S331000, C428S458000, C428S480000, C428S910000, C524S323000, C524S327000, C524S394000, C524S398000, C528S302000, C528S305000, C528S308000, C528S308600
Reexamination Certificate
active
06617006
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyester film to be laminated on a metal plate and molded. More specifically, it relates to a polyester film to be laminated on a metal plate and molded, which exhibits excellent moldability when it is laminated on a metal plate and subjected to a can making process such as drawing and from which metal cans having excellent heat resistance, retort resistance, taste and flavor retention properties, impact resistance and corrosion resistance, such as drink cans and food cans, can be produced.
DESCRIPTION OF THE PRIOR ART
Metal cans are generally coated on the interior and exterior sides to prevent corrosion. Recently, the development of methods for obtaining corrosion resistance without using an organic solvent has been promoted to simplify production process, improve sanitation and prevent pollution. One of the methods is to coat a metal can with a thermoplastic resin film. That is, studies on a method for making cans by laminating a thermoplastic resin film on a metal plate such as a tin, tin-free steel or aluminum plate and drawing the laminated metal plate are under way. A polyolefin film or polyamide film has been tried as this thermoplastic resin film but does not satisfy all the requirements such as moldability, heat resistance, impact resistance, and taste and odor retention properties.
Then, a polyester film, particularly a polyethylene terephthalate film attracts much attention as a film having well-balanced properties and there have been made some proposals based on this film (JP-A 56-10451, JP-A 64-22530, JP-A 1-192545, JP-A 1-192546 and JP-A 2-57339) (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). However, studies conducted by the present inventors have revealed that, in the case of molding accompanied by large deformation, the film does not satisfy all the requirements such as moldability, retort resistance, and taste and flavor retention properties.
A copolyester film has been studied as a film which is satisfactory in terms of moldability, heat resistance, impact resistance, and taste and flavor retention properties. JP-A 5-339348 discloses a polyester film to be laminated on a metal plate and molded, which is made from a copolyester having a specific melting point, glass transition temperature and terminal carboxyl group concentration. JP-A 6-39979 proposes a polyester film to be laminated on a metal plate and molded, which is a copolyester laminate film having a specific melting point and glass transition temperature. However, studies conducted by the present inventors have clarified that when cans covered with these films are used as drink containers, a change in flavor or taste is detected according to the type of a drink as disclosed by JP-A 55-23136.
JP-A 6-116376 proposes a polyester film to be laminated on a metal plate and molded, which is made from a copolyester containing specific amounts of elemental alkali metals and elemental germanium. When this film is used, it exhibits excellent taste and flavor retention properties in a process in which it is not heated while containing contents, such as a cold pack system, but does not always achieve sufficient taste and flavor retention properties in a process in which it is heated while containing contents, such as a retort treatment.
JP-A 8-40437 discloses a polyester film which contains specific amounts of an oligomer and elemental alkali metals and JP-A 9-241361 and JP-A 10-231413 propose a film made from a copolyester which has specific contents of alkali metals and a catalytic metal compound and contains a phosphorus compound in a specific ratio. Even when these films are used, they are still unsatisfactory in terms of polyester productivity and heat deterioration during the production of a biaxially oriented film. Further improvement in performance has been desired.
Moreover, JP-A 9-70934 proposes a laminated polyester film which contains a specific amount of a specific metal but this film is unsatisfactory in terms of resistance to hydrolysis in a process in which a heat treatment is carried out after contents are packed like a retort treatment and cannot always achieve satisfactory taste and flavor retention properties.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polyester film to be laminated on a metal plate and molded, which has overcome the defects of the prior art, has improved resistance to hydrolysis and taste and flavor retention properties and higher productivity while retaining the excellent heat resistance, impact resistance, deep drawability and corrosion resistance of a polyester film, and is inexpensive and preferred from the viewpoint of sanitation.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, the above objects and advantages of the present invention are attained by a biaxially oriented polyester film to be laminated on a metal plate and molded, which comprises an aromatic polyester composition comprising:
(A) an aromatic polyester which comprises ethylene terephthalate as the main recurring unit and a titanium compound and a phosphorus compound both of which satisfy at least one of the following expressions (1) and (2):
0.1≦Ti/P≦3.0 (1)
5≦Ti+P≦60 (2)
wherein Ti is the amount (mmol %) of elemental titanium of the titanium compound contained in this aromatic polyester and P is the amount (mmol %) of elemental phosphorus of the phosphorus compound contained in the aromatic polyester, and the following expression (3):
2≦Ti≦20 (3)
wherein Ti is as defined hereinabove, and which contains alkali metal compounds, a germanium compound and an antimony compound in a total amount of not more than 3 ppm in terms of the total of elemental alkali metals, elemental germanium and elemental antimony; and
(B) 0.05 to 5.0 wt % based on the aromatic polyester composition of inert fine particles having an average particle diameter of 2.5 &mgr;m or less.
THE PREFERRED EMBODIMENT OF THE INVENTION
The present invention will be described in detail hereinbelow.
The aromatic polyester in the present invention is a polyester comprising ethylene terephthalate as the main recurring unit. The aromatic polyester is preferably copolyethylene terephthalate obtained by copolymerizing a third component other than the ethylene terephthalate unit as a constituent component from the viewpoints of heat resistance and moldability. The above third component (comonomer) may be either a dicarboxylic acid component or a glycol component. Examples of the dicarboxylic acid component preferably used as the third component include aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, isophthalic acid and phthalic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid; and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. They may be used alone or in combination of two or more. Out of these, 2,6-naphthalenedicarboxylic acid and isophthalic acid are preferred. Examples of the glycol component preferably used as the third component include aliphatic diols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol and hexanediol; alicyclic diols such as cyclohexane dimethanol; aromatic diols such as bisphenol A; and polyalkylene glycols such as polyethylene glycol and polypropylene glycol. They may be used alone or in combination of two or more. Out of these, diethylene glycol is preferred. The aromatic polyester of the present invention is preferably selected from the following three copolyesters:
(a) a copolyester which comprises 82 mol % or more of terephthalic acid and 18 mol % or less of isophthalic acid as dicarboxylic acid components and 82 to 100 mol % of ethylene glycol and 0 to 18 mol % of a diol other than ethylene glycol as diol components;
(b) a copolyester which comprises 82 mol % or more of terephthalic acid and 18 mol
Hasegawa Kinji
Kosuge Masahiko
Kubo Koji
Kubota Shunsuke
Minobe Nobuo
Chen Vivian
Teijin Limited
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