Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-09-26
2002-04-16
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S335000, C428S323000, C428S330000, C428S331000, C428S458000, C428S480000, C428S910000, C428S304400, C428S307300, C528S302000, C528S305000, C528S308000, C528S308600
Reexamination Certificate
active
06372326
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a biaxially oriented polyester film to be molded and laminated on a metal sheet. More specifically, it relates to a biaxially oriented polyester film to be molded and laminated on a metal sheet, which exhibits excellent moldability when it is laminated on a metal sheet and subjected to a can making process such as drawing and from which metal cans having excellent heat resistance, retort resistance, taste and odor retention properties, impact resistance and corrosion prevention properties, such as drink cans and food cans, can be produced.
PRIOR ART
Metal cans are generally coated on interior and exterior surfaces to prevent corrosion. Recently, the development of methods for obtaining corrosion prevention properties 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 sheet of a metal such as tin, tinfree steel or aluminum and drawing the laminated metal sheet are under way. A polyolefin film or polyamide film has been tried as this thermoplastic resin film but does not satisfy all 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 which is accompanied by large deformation, moldability, retort resistance, and taste and odor retention properties become unsatisfactory.
A copolyester film has been studied as a film which is satisfactory in terms of moldability, heat resistance, impact resistance, and taste and odor retention properties. JP-A 5-339348 discloses a polyester film to be molded and laminated on a metal sheet, which comprises 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 molded and laminated on a metal sheet, on which a copolyester having a specific melting point and glass transition temperature is laminated. However, studies conducted by the present inventors have revealed that when cans covered with these films are used as drink containers, a change in odor 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 molded and laminated on a metal sheet, 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 odor retention properties in a system in which it is not heated while containing contents, such as a cold pack system, but does not always obtain sufficient taste and odor retention properties in a system in which it is heated while containing contents, such as a retort treatment.
JP-A 7-70340 proposes a copolyester film containing lubricant particles having an average particle diameter of 1.0 &mgr;m or less and specifying the density of agglomerates of the particles in the film as a material having pinhole resistance. JP-A 8-269215 proposes a polyester film which specifies the degree of deformation of particles contained in the film as a material having pinhole resistance. When a metal sheet is deformed more than usual, sufficient can making properties cannot be obtained from the films because the particles may fall off from these films, taste and odor retention properties may deteriorate and the heat resistance of the particles may lower.
It is an object of the present invention to provide a biaxially oriented polyester film to be molded and laminated on a metal sheet, which eliminates the defects of the prior art and has improved pinhole resistance and deep drawability while retaining excellent heat resistance, impact resistance, taste and odor retention properties, and corrosion prevention properties of a copolyester film.
It is another object of the present invention to provide an industrially advantageous process for producing a polyester as a raw material for the biaxially oriented polyester film of the present invention.
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 molded and laminated on a metal sheet,
(A) which comprises a copolyester comprising (a) terephthalic acid and isophthalic acid as dicarboxylic acid components, terephthalic acid being contained in an amount of 82 mol % or more and isophthalic acid or a combination of isophthalic acid and other dicarboxylic acid being contained in an amount of 18 mol % or less based on the total of all the dicarboxylic acid components, and (b) ethylene glycol in an amount of 82 to 100 mol % and other diol in an amount of 0 to 18 mol % based on the total of all the diol components as diol components, having (c) a glass transition temperature of 70° C. or higher and lower than 78° C., (d) a melting point of 210 to 250° C., (e) an intrinsic viscosity of 0.50 to 0.80 dl/g, and containing (f) porous particles having an average particle diameter of 0.1 to 2.5 &mgr;m, a pore volume of 0.05 to 2.5 ml/g, a specific surface area of 50 to 600 m
2
/g and a compressive resistance of 1 to 100 MPa, and;
(B) which contains agglomerates of the porous particles having a particle diameter of 20 &mgr;m or more at a density of no more than 10/mm
2
.
The copolyester used in the present invention consists of terephthalic acid and isophthalic acid as dicarboxylic acid components, and terephthalic aid is contained in an amount of 82 mol % or more and isophthalic acid or a combination of isophthalic acid and other dicarboxylic acid is contained in an amount of 18 mol % or less based on the total of all the dicarboxylic acid components as specified in (a). Illustrative examples of the other dicarboxylic acid other than terephthalic acid and isophthalic acid include aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic 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 is preferred from the viewpoints of flavor retention properties and impact resistance.
As specified in (b), the copolyester comprises ethylene glycol in an amount of 82 to 100 mol % and other diol in an amount of 0 to 18 mol % based on the total of all the 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 cylohexane 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, triethylene glycol, cyclohexane dimethanol, neopentyl glycol and diethylene glycol are preferred from the viewpoints of flavor retention properties and moldability.
When one of these ethylene glycols is contained as the main glycol component, diethylene glycol is preferably copolymerized, more preferably copolymerized in an amount of 5 mol % or less, particularly preferably 4 mol % or less based on the total of all the glycol. When the amount of diethylene glycol is larger than 5 mol %, heat resistance may lower. This diethylene glycol component
Kosuge Masahiko
Kurihara Hideshi
Chen Vivian
Sughrue & Mion, PLLC
Teijin Limited
LandOfFree
Biaxially oriented polyester film to be molded and laminated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Biaxially oriented polyester film to be molded and laminated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Biaxially oriented polyester film to be molded and laminated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2852157