Stock material or miscellaneous articles – Web or sheet containing structurally defined element or...
Reexamination Certificate
2002-06-04
2004-07-13
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
C525S437000, C525S439000, C525S444000, C525S445000, C428S357000
Reexamination Certificate
active
06761966
ABSTRACT:
FILED OF INVENTION
The present invention relates to heat-shrinkable polyester films and, in particular, to heat-shrinkable polyester films suitable for label use. More specifically, it relates to heat-shrinkable polyester films for labels on bottles, which films will cause only rare occurrence of wrinkles, shrinkage spots and strains by heat shrinkage.
BACKGROUND OF THE INVENTION
For heat-shrinkable films, particularly heat-shrinkable films for labels on the barrels of bottles, there have mainly been used films made of polyvinyl chloride, polystyrene or other resins. However, for polyvinyl chloride, the evolution of a chlorine-containing gas in its incineration for disposal has become a problem, and for polyethylene, there is a problem that printing is difficult. Further, in the collection and recycling of polyethylene terephthalate (PET) bottles, labels of resins other than PET, such as polyvinyl chloride or polyethylene, should be separated. For these reasons, attention has been paid to heat-shrinkable films made of polyesters involving none of these problems.
In recent years, for the recycling of PET bottles for beverages, labels fitted on the bottles have usually been printed. They without being treated are not suitable for recycling, and therefore, they are often removed before the recycling of the bottles. In this connection, as the means to do so, they may be provided with perforations in a direction perpendicular to the main shrinkage direction.
However, conventional heat-shrinkable polyester films have relatively high resistance to tear propagation in a direction perpendicular to the main shrinkage direction, and they have fault in the cutting properties along perforations when fitted on bottles. Depending on the shapes of bottles or the forms of perforations, labels may be difficult to cut along perforations and may therefore become difficult to remove with bare hands.
Thus, in the case of labels on bottles, the conventional heat-shrinkable polyester films have unsatisfactory cutting properties along perforations.
SUMMARY OF THE INVENTION
The present invention, which can solve the above problems, has been made for the purpose of providing heat-shrinkable polyester films for labels on bottles, particularly for labels on PET bottles, which films will cause only rare occurrence of wrinkles, shrinkage spots and strains by shrinkage as well as which films have excellent tear properties in a direction perpendicular to the main shrinkage direction of the films.
Thus the present invention provides heat-shrinkable polyester films, each having a heat shrinkability of 30% or higher after treatment in hot water at 85° C. for 10 seconds in the main shrinkage direction of the film, and 10% or lower after treatment in hot water at 85° C. for 10 seconds in a direction perpendicular to the main shrinkage direction of the film, the resistance to tear propagation in the direction perpendicular to the main shrinkage direction after the films has been shrunk at 10% in the main shrinkage direction of the film being 1500 mN or smaller.
The heat shrinkability as used herein is defined as follows:
A film is cut into a square shape of 10 cm×10 cm and heat shrunk by immersion under no load in hot water at a prescribed temperature ±0.5° C. for a prescribed time and then measured for side lengths. The heat shrinkability is calculated in the respective directions from the measured values of side lengths by the following equation. The direction of either side corresponding to the larger value of heat shrinkability is referred to as the main shrinkage direction
Heat
shrinkability
=
Side
length
before
shrinkage
-
Side
length
after
shrinkage
Side
length
before
shrinkage
×
100
(
%
)
The resistance to tear propagation as used herein is defined as follows:
A film previously shrunk at 10% is cut into a size of 51 mm in the machine direction×64 mm in the transverse direction, and measured with a light-load tear tester available from TOYO SEIKI SEISAKU-SHO, LTD. The values read from the tester are regarded as the resistance to tear propagation. This measurement is carried out for 5 different samples of each film, and their average value is calculated and presented.
The perforations for label cutting provided on the labels of PET bottles are usually formed in the direction perpendicular to the main shrinkage direction of the labels. The present inventors have found that there is a relation between the cutting properties along perforations and the resistance to tear propagation that lower resistance to tear propagation in the direction perpendicular to the main shrinkage direction of films or labels made of the films will provide more excellent cutting properties along perforations. The control of this relation made it possible to attain the above purpose.
In preferred embodiments, the above heat-shrinkable polyester films are made of polyesters comprising thermoplastic resins incompatible with the polyesters, which is preferred in that regardless of the shapes of bottles or the forms of perforations, there can be provided films and labels made of the films, having excellent cutting properties along perforations.
DETAILED DESCRIPTION OF THE INVENTION
The dicarboxylic acid components constituting polyesters used in the present invention may include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and o-phthalic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid; and alicyclic dicarboxylic acids.
When aliphatic dicarboxylic acids (e.g., adipic acid, sebacic acid, decanedicarboxylic acid) are contained, their contents may preferably be lower than 3 mol %. For heat-shrinkable polyester films obtained by the use of polyesters containing these aliphatic dicarboxylic acids at 3 mol % or higher, their film stiffness in the high-speed fitting is insufficient.
The polyesters may preferably contain no three or more functional polycarboxylic acids (e.g., trimellitic acid, pyromellitic acid, their anhydrides). For heat-shrinkable polyester films obtained by the use of polyesters containing these polycarboxylic acids, their desired high shrinkability can hardly be attained.
The diol components constituting the polyesters used in the present invention may include aliphatic diols such as ethylene glycol, propanediol, butanediol, neopentyl glycol and hexanediol; alicyclic diols such as 1,4-cyclo-hexanedimethanol; and aromatic diols.
The polyesters used in the heat-shrinkable polyester films of the present invention may preferably be those having glass transition temperatures (Tgs) adjusted to 60-75° C. by the incorporation of at least one diol of 3-6 carbon atoms (e.g., propanediol, butanediol, neopentyl glycol, hexanediol).
For the purpose of obtaining heat-shrinkable polyester films exhibiting particularly excellent shrinkage finish, neopentyl glycol may preferably be used as one of the diol components.
The polyesters may preferably contain neither diols of 8 or more carbon atoms (e.g., octanediol), nor three or more functional polyhydric alcohols (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin). For heat-shrinkable polyester films obtained by the use of polyesters containing these diols or polycarboxylic acids, their desired high shrinkability can hardly be attained.
The polyesters may preferably contain none of diethylene glycol, triethylene glycol, and polyethylene glycol, if possible. In particular, diethylene glycol may easily be formed as a by-product component in the polymerization of polyesters and therefore may easily be contained in the polyesters. For the polyesters used in the present invention, the diethylene glycol contents may preferably be lower than 4 mol %.
When two or more polyesters are used in admixture, the acid component contents and the diol component contents
Ito Hideki
Nagano Hiroshi
Tabota Norimi
Acquah Samuel A.
Kenyon & Kenyon
Toyo Boseki Kabushiki Kaisha
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