Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2000-10-03
2002-09-10
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S034900, C428S910000, C106S013000
Reexamination Certificate
active
06447925
ABSTRACT:
FILED OF INVENTION
The present invention relates to heat-shrinkable polyester films and more particularly to heat-shrinkable polyester films that are useful as wrapping materials, mainly as covering materials for the openings of vessels used for packing noodles, puddings, salads, and other foods.
BACKGROUND OF THE INVENTION
For heat-shrinkable films, particularly shrinkable films as the labels on the bodies of bottles, polyvinyl chloride films, polystyrene films, and other polymer films have been widely used. Some problems, however, have been raised, including the evolution of chlorine-containing gases in the incineration of waste polyvinyl chloride films, difficulty in printing on polystyrene films, and need of separating the labels of resins other than polyethylene terephthalate (PET) in the recycling of PET bottles. Heat-shrinkable polyester films therefore have lately drawn considerable attention.
The polyester heat-shrinkable films have higher strength than the films of other materials, but on the other hand, they exhibit great shrinkage stress when shrunk, so that they may often deform objects to be brought into close contact therewith, such as plastic vessels or aluminum vessels, by heat shrinkage. In particular, when heat-shrinkable polyester films are used as covering materials on vessels, there has been raised a problem that the vessels are easily deformed, if the shrinkage characteristics of the films exhibit a great anisotropy between the direction of extrusion (i.e., the machine direction) and the direction perpendicular to the machine direction (i.e., the transverse direction) in the extrusion of the films.
Heat-shrinkable films are often used as covering materials for chilled or frozen foods. In this case, low temperatures may cause the condensation of water in the contents on the film surface, resulting in the fogging of the films, and even when transparent films are used, the view of the contents may sometimes be obstructed. Further, when the films are used as covering materials, they are cut into a prescribed shape and then layered, from which state they are taken one by one before placement on the vessels and covering for closure. At that time, the layered films become difficult to come off by static electricity, which may cause a deterioration of workability.
SUMMARY OF THE INVENTION
Under these circumstances the present inventors extensively studied to develop a heat-shrinkable polyester film that will cause very few occurrence of wrinkles, shrinkage spots, and strains after heat shrinkage and that can therefore prevent the deformation of applied objects by shrinkage stress. As a result, they have found that such a heat-shrinkable polyester film can be obtained by the control of heat shrinkage to occur evenly in all the directions, more particularly by the control of shrinkability and shrinkage stress to become substantially even in all the directions, thereby completing the present invention.
Thus the present invention provides a heat-shrinkable polyester film having a shrinkability in hot water (hereinafter referred to as a hot-water shrinkability) at 95° C. for 10 seconds ranging from 30% to 50% in at least one direction (hereinafter referred to as direction (A)) and ranging from 25% to 45% in a direction (hereinafter referred to as direction (B)) perpendicular to said at least one direction, wherein a difference &Dgr;HS between said hot-water shrinkability in direction (A) and said hot-water shrinkability in direction (B) (ie., &Dgr;HS=|hot-water shrinkability in direction (A)—hot-water shrinkability in direction (B)|) is 10% or smaller.
DETAILED DESCRIPTION OF THE INVENTION
The polyester used in the heat-shrinkable polyester film of the present invention is not particularly limited, but it may include polyesters obtained by the reaction of acid components such as terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acids with diol components such as propanediol, butanediol, hexanediol, ethylene glycol, neopentyl glycol, and 1,4-cyclohexane dimethanol. The polyester may preferably contain as the diol components at least one of the diols containing 3 to 6 carbon atoms, such as propanediol, butanediol, hexanediol and neopentyl glycol, and particularly for the purpose of improving shrinkage finish, the polyester may preferably contain neopentyl glycol as one kind of the diol components. Further, the polyester may preferably have a glass transition temperature (Tg) adjusted to 60° C. to 75° C.
The polyester may preferably contain none of diols containing 8 or more carbon atoms, such as octanediol, polyhydric diols such as trimethylolpropane, trimethylolethane, glycerin and diglycerin, and polycarboxylic acids such as trimellitic acid and pyromellitic acid, including their anhydrides. The heat-shrinkable polyester films made of polyesters containing these diols and/or carboxylic acids are difficult to have high heat shrinkability.
Further, when aliphatic carboxylic acids such as adipic acid, sebacic acid and decanedicarboxylic acid are contained as the acid components, the content of aliphatic carboxylic acids may preferably be lower than 3 mol % in all the acid components. The heat-shrinkable polyester films made of polyesters containing these aliphatic carboxylic acids at 3 mol % or higher in all the acid components exhibit a deterioration of toughness needed in the high-speed wrapping.
The polyester may further preferably contain none of diethylene glycol, triethylene glycol and polyethylene glycol as the diol components. In particular, diethylene glycol may often exist as a by-product component in the polymerization of the polyester. In the polyester used in the present invention, the content of at least diethylene glycol may preferably be reduced to lower than 4 mol %.
For the polyester used in the heat-shrinkable polyester film of the present invention, one kind of the above polyesters may be used alone, or two or more kinds of the above polyesters may be used in admixture. In the present invention, when the polyester contains two or more kinds of acid components and/or diol components, the content of these acid components or diol components indicates, whether ester interchange is achieved or not after mixing, the content of acid components or diol components in the polyester as a whole. It is the same with the case where two or more kinds of polyesters are used.
The polyester used in the heat-shrinkable polyester film of the present invention may contain other ingredients to such an extent that they are not harmful to the effects of the present invention, including inorganic and organic lubricants to improve smoothness, colorants, antioxidants, compatibilizers, antistatic agents, ultraviolet light absorbers, and other additives
The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but it is preferably 10 to 200 &mgr;m, more preferably 20 to 100 &mgr;m, when the film is used as a shrinkable film for labels.
In the heat-shrinkable polyester film of the present invention, the hot-water shrinkability at 95° C. for 10 seconds in at least one direction (A) should be 30% to 50% and the hot-water shrinkability at 95° C. for 10 seconds in direction (B) perpendicular to the above direction (A) should be 25% to 45%, and &Dgr;HS (where &Dgr;HS=|hot-water shrinkability in direction (A)—hot-water shrinkability in direction (B)|) should be 10% or smaller. If &Dgr;HS is higher than 10%, unevenness of shrinkage occurs in the heat shrinkage to cause the deformation of vessels or other objects for which the heat-shrinkable polyester film of the present invention is used. When the heat-shrinkable polyester film of the present invention is prepared in film shape by extrusion, in which the direction of extrusion in the preparation of said film is taken as the machine direction and the direction perpendicular to the machine direction is taken as the transverse direction, the hot-water shrinkability at 95° C. for 10 seconds may preferably be 30% to 50% in the transvers
Hashimoto Masatoshi
Nagano Hiroshi
Ohtsuka Atsuhiko
Tabota Norimi
Takabayashi Seizo
Chen Vivian
Morrison & Foerster / LLP
Toyo Boseki Kabushiki Kaisha
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