Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-08-18
2002-10-29
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S220000, C428S316600, C428S323000, C428S331000, C428S458000, C428S480000, C428S910000, C156S224000, C156S218000, C156S217000, C156S221000
Reexamination Certificate
active
06472046
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyester film to belaminated onto a metal plate-and molded. More specifically, it relates to a polyester to be laminated onto a metal plate and molded, which exhibits excellent moldability when laminated onto a metal plate to be subjected to a can making process such as drawing and which can be used to produce metal cans having excellent heat resistance, retort resistance, taste-and-flavor retainabilities and impact resistance, such as drink cans and food cans.
BACKGROUND ART
Metal cans are generally coated on interior and exterior surfaces to prevent corrosion. Recently, the development of methods for obtaining corrosion resistance without using an organic solvent has been promoted for the purpose of simplifying production process, improving sanitation and preventing 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, which comprises laminating a thermoplastic resin film on a plate of a metal such as tin, tin-free steel or aluminum and drawing the laminated metal plate, are under way.
It gradually becomes clear that a copolyester film is suitable for use as this thermoplastic resin film in terms of moldability, heat resistance, impact resistance and taste-and-flavor retainabilities. This polyester film, however, does not always exhibit sufficient taste-and-flavor retainabilities when a can coated therewith contains a drink whose delicate taste is important, such as green tea, or mineral water which must be tasteless and odorless, and changes in flavor and taste of the contents are detected.
JP-A 6-116376 proposes a polyester film to be laminated onto a metal plate and molded, which is made from a copolyester containing alkali-metal elements and a germanium element in specific amounts and which has improved flavor retainabilities When this film is used to coat a can, however, it exhibits excellent taste-and-flavor retainabilities as in a cold pack system in which heat is not applied to the can with contents, whereas it does not always obtain sufficient taste-and-flavor retainabilities as in a retort treatment in which heat is applied to the can with contents.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a polyester film to be laminated onto a metal plate and molded, which solves the above problems of the prior art and which has improved taste-and-flavor retainabilities, particularly taste-and-flavor retainabilities after a retort treatment without losing excellent moldability, heat resistance, impact resistance and retort resistance of a copolyester film.
The 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 onto a metal plate and molded, (A) which comprises a copolyester comprising (a) terephthalic acid in an amount of 82 to 100 mol % and 2,6-naphthalenedicarboxylic acid or a combination of 2,6-naphthalenedicarboxylic acid and other dicarboxylic acid in an amount of 0 to 18 mol % of the total of all dicarboxylic acid components and (b) ethylene glycol in an amount of 82 to 100 mol % and cyclohexanedimethanol or a combination of cyclohexanedimethanol and other diol in an amount of 0 to 18 mol % of the total of all diol components, having (c) a glass transition temperature of 78° C. or more and (d) a melting point of 210 to 250° C., and containing (e) porous silica particles with a pore volume of 0.5 to 2.0 ml/g which are agglomerates of primary particles having an average particle diameter of 0.001 to 0.1 &mgr;m; and
(B) which has the following relationship between the highest peak temperature (Te, °C.) of loss elastic modulus and the glass transition temperature (Tg, °C.):
Te−Tg≦
30.
DETAILED DESCRIPTION OF THE INVENTION
The copolyester in the present invention comprises terephthalic acid in an amount of 82 to 100 mol % and 2,6-naphthalenedicarboxylic acid or a combination of 2,6-naphthalenedicarboxylic acid and other dicarboxylic acid in an amount of 0 to 18 mol % of the total of all dicarboxylic acid components.
Illustrative examples of the other dicarboxylic acid include aromatic dicarboxylic acids such as 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.
The copolyester in the present invention comprises ethylene glycol in an amount of 82 to 100 mol % and cyclohexanedimethanol or a combination of cyclohexanedimethanol and other diol in an amount of 0 to 18 mol % of the total of all diol components.
Illustrative examples of the other diol include aliphatic diols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol and hexanediol; alicyclic diols such as cyclohexanedimethanol; 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.
The above copolyester may comprise at least one or both of 2,6-naphthalenedicarboxylic acid and 1,4-cyclohexanedimethanol as a copolymer component.
It is particularly preferable that all the dicarboxylic acid components of the copolyester consist of terephthalic acid and 2,6-naphthalenedicarboxylic acid and that all the diol components of the copolyester consist of ethylene glycol.
The copolyester in the present invention has a glass transition temperature (Tg) of 78° C. or more and a melting point of 210 to 250° C.
If Tg is lower than 78° C., heat resistance will deteriorate and taste-and-flavor retainabilities after a retort treatment will degrade when the film of the present invention is laminated onto a metal plate and molded into a metal can. To increase the Tg of the copolyester of the present invention to 78° C. or higher, 2,6-naphthalenedicarboxylic acid and cyclohexanedimethanol are used as copolymer components.
The glass transition temperature (Tg) of the copolyester is preferably in the range of 78 to 90° C.
To obtain a Tg of polyester, a 20-mg film sample is placed in a DSC measurement pan, molten by heating on a stage at 290° C. for 5 minutes and solidified by quenching the pan on an aluminum foil laid on ice to obtain a glass transition point at a temperature elevation rate of 20° C./min using the 910 DSC of Du Pont Instruments.
When the melting point is lower than 210° C., the heat resistance of the polymer deteriorates. On the other hand, when the melting point is higher than 250° C., the crystallinity of the polymer becomes too high with the result of impaired moldability.
The melting point of the copolyester is preferably in the range of 210 to 245° C.
The melting point of copolyethylene terephthalate is measured in accordance with a method for obtaining a melting peak at a temperature elevation rate of 20° C./min using the 910 DSC of Du Pont Instruments. The quantity of a sample is 20 mg.
The intrinsic viscosity (orthochlorophenol, 35° C.) of the copolyester is preferably in the range of 0.52 to 1.50, more preferably 0.57 to 1.00, particularly preferably 0.60 to 0.80. When the intrinsic viscosity is lower than 0.52, impact resistance may be insufficient disadvantageously. On the other hand, when the intrinsic viscosity is higher than 1.50, moldability may be impaired.
The content of acetaldehyde in the copolyester is preferably 15 ppm or less, more preferably 12 ppm or less, much more preferably 10 ppm or less.
When the content of the acetaldehyde is larger than 15 ppm, the taste-and-flavor retainabilities of the contents tend to lower disadvantageously.
The concentration of the terminal carboxyl groups of the copolyester is preferably 40 equivalents/10
6
g or less, more preferably 35 equivalents/10
6
g or less, much more preferably 30 equivalents/10
6
g.
When the concentra
Kosuge Masahiko
Kubo Koji
Kurihara Hideshi
Murooka Hirofumi
Sughrue & Mion, PLLC
Teijin Limited
Thibodeau Paul
Zacharia Ramsey
LandOfFree
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