Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Reshaping running or indefinite-length work
Reexamination Certificate
2001-10-23
2004-02-03
Chen, Vivian (Department: 1773)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Reshaping running or indefinite-length work
C264S280000, C264S288400, C428S480000, C428S910000
Reexamination Certificate
active
06685865
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for the production of a polyester film and more particularly to such a process that can efficiently form, without involving troublesome film breakage, a polyester film having small thickness and great strength in its lengthwise and widthwise directions.
Further, this invention relates to a biaxially oriented polyester film that is obtained by the above process.
BACKGROUND ART
Simultaneous biaxial orientation is known in which a thermoplastic film is allowed to simultaneously stretch both lengthwise and widthwise while it is being clamped at its end portions with clips. The technique of orientation stated here is disclosed for instance in Japanese Unexamined Patent Application Publication No. 49-40369 and No. 49-105877.
However, this conventional simultaneous biaxial orientation has the problem that it fails to give a film having improved strength in its lengthwise and widthwise directions even when a film to be oriented is caused to stretch up to a point directly adjacent to the critical point at which the film breaks, such that the film is made rather thin and very strong in the lengthwise and widthwise directions.
An object of the present invention is to provide a process that can form, without film breakage, a film having small thickness and great strength in its lengthwise and widthwise directions.
DISCLOSURE OF THE INVENTION
In order to solve the foregoing problem, the process for the production of a biaxially oriented polyester film according to the present invention comprises: subjecting a polyester film to simultaneous biaxial stretching in a stretching apparatus constructed to simultaneously stretch the polyester film in the lengthwise and widthwise directions thereof, and subsequently subjecting the polyester film to successive biaxial stretching in the lengthwise direction and successively in the widthwise directions in the same apparatus used in which the simultaneous biaxial stretching was performed.
Namely, in the process according to this invention, a polyester film is simultaneously biaxially stretched lengthwise and widthwise at a relatively low stretch ratio, followed by gradual stepwise biaxial stretching while the stretch temperature is being raised in the same apparatus as used for the simultaneous biaxial stretching while the stretch temperatures are being raised. Thus, a film structured to have enhanced strength in the lengthwise and widthwise directions, or a film structured to have small thickness is stably obtainable with no fear of film breakage.
BEST MODE OF CARRYING OUT THE INVENTION
The polyester used in the present invention is composed predominantly of an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol. Aromatic dicarboxylic acid components are chosen., for example., from terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalene-dicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′diphenyletherdicarboxylic acid and 4,4′-diphenylsulfonedicarboxylic acid. Of these components, terephthalic acid, phthalic acid and 2,6-naphthalene-dicarboxylic acid are preferred. Alicyclic dicarboxylic acid components are chosen for example from cyclohexane-dicarboxylic acid. Aliphatic dicarboxylic acid components are chosen for example from adipic acid, suberic acid, sebacic acid and dodecanedionic acid. The acid components listed here can be used singly, or two or more such components can be used in combination. These components may also be partially copolymerized with an oxy acid such as hydroxyethoxybenzoic acid.
On the other hand, diol components are chosen for example from ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol and 2,2′-bis(4′-&bgr;-hydroxy-ethoxyphenyl) propane, among which ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and diethylene glycol are preferred. Ethylene glycol is a particularly preferable choice. These diol components can be used alone or in combination. The polyester according to this invention may have another monofunctional compound copolymerized in the molecular structure, which compound is trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, 2,4-dioxybenzoic acid, lauryl alcohol or phenylisocyanic acid, when the resulting polymer is substantially linear in nature.
The polyester resin specified above as constituting the polyester film of this invention can be mixed, where desired, with a flame retardant, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a pigment, an organic lubricant such as a fatty acid ester or a wax, or a defoamer. In addition, the polyester resin may contain inorganic particles composed of clay, mica, titanium oxide, calcium carbonate, kaolin, talc, dry- or wet-type silica, colloidal silica, calcium phosphate, barium sulfate, alumina and zirconia, or organic particles composed of acrylic acid and styrene. Alternatively, deposits generally called internal particles may be added, which results from the action of a catalyst used in a polyester polymerization reaction. A surfactant may also be added.
In the present invention, polyethylene tere-phthalate is particularly effective amongst the polyesters mentioned above. Polyesters having polyethylene terephthalate in a content of 70% by mol or more offer noticeable results, but this is not limiting to this invention. Each such polyester may be of a homopolymeric or copolymeric nature, or a simple blend with other components in an arbitrary content of, for example, less than 30% by mol.
Moreover, the polyester film may be single- or multi-layered in structure.
In the present invention, it is desired that the polyester film to be subjected to simultaneous biaxial stretching be a substantially unoriented film with a birefringence of not larger than 0.003. Higher orientation is not favored as it impairs stretchability and invites film breakage during stretching.
The substantially unoriented polyester film stated above can be formed for example by casting a molten polyester film onto the surface of a cooling drum being rotated, which molten film is extruded from a slitted die, and by successively solidifying the cast film on the drum. To enhance casting of the polyester film onto the cooling drum, thereby forming a desired unoriented film, there may be employed a so-called electrostatic casting method in which a high voltage is applied to an electrode straddled between a die and a cooling drum so that a molten film is electrostatically charged, a method in which film bonding is made strong by the surface tension of water spread between a cooling drum and a molten film, or a method in which the principles of the first two methods are combined.
In the process for producing a biaxially oriented polyester film according to the present invention, a polyester film is required to be simultaneously stretched biaxially lengthwise and widthwise in a stretching apparatus constricted to simultaneously stretch a polyester film in its lengthwise and widthwise directions, followed by the successive biaxial stretching of the film in the two directions in the same apparatus as used for the simultaneous biaxial stretching. In the case where the simultaneous biaxial stretching finishes with a polyester film stretched up to a point directly adjacent to the critical point at which the film breaks, no improved strength is found. Even when the simultaneous biaxial stretching is completed and then repeated with a polyester film likewise stretched up to a point near to the film breakage-inducing point, no improved strength is obtained. When a polyester film is stretched monoaxially, that is, in either one of the lengthwise and widthwise directions after completion of the simultaneous biaxial stretching,
Nishibayashi Toshiya
Nishino Satoru
Toyoda Katsuya
Chen Vivian
Piper Rudnick LLP
Toray Industries Inc.
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