JP2004170634A - Heat-shrinkabile cylindrical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable cylindrical film which less influences environments and whose perforation part can be prevented from being torn owing to vibration, a shock, etc. <P>SOLUTION: The heat-shrinkable cylindrical film has perforations 5 and is formed of a bioerodible heat-shrinkable film and individual holes forming the perforations 5 are round even before heat shrinkage. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a heat-shrinkable tubular film that is put on various containers such as bottles, cans, and PET bottles and is attached by heat treatment.
[0002]
[Prior art]
Generally, various heat-shrinkable tubular films are attached to containers such as PET bottles (bottles made of polyethylene terephthalate). For example, there are a shrink label attached to the body of a plastic bottle, a cap seal for sealing the mouth of the container, and the like. In these heat-shrinkable tubular films, it is necessary to provide perforations for breaking. That is, the shrink label is provided with perforations for separating it from the plastic bottle during recycling, and the cap seal is provided with perforations for opening.
[0003]
These perforations are formed, for example, by pressing a perforation forming blade such as a Thomson blade having a continuous concave and convex shape against the film. Each of the perforations formed by the protrusions of the cutting edge of the forming blade is formed in a slit shape having a predetermined length along the perforation forming direction. As described above, since the perforations are usually provided along the axial direction of the tubular film, the slit-shaped holes also extend in the axial direction of the tubular film.
[0004]
On the other hand, these tubular films are made of a uniaxially stretched polyester film or the like so as to be mainly thermally contracted in the circumferential direction. However, since this kind of tubular film is discarded immediately after use, it is desired to use a biodegradable heat-shrinkable film instead of the conventional polyester film from an environmental problem. .
[0005]
[Problems to be solved by the invention]
However, when a biodegradable heat-shrinkable film is provided with perforations and heat-shrinked, there is a problem that the film is easily broken at the perforations. The biodegradable heat-shrinkable film is brittle as compared to a normal heat-shrinkable polyester film, and has a property of being easily torn in the longitudinal direction. A tensile force due to heat shrinkage acts in a direction (circumferential direction) orthogonal to the slit-shaped hole, and the slit-shaped hole is pushed and expanded by the tensile force, so that stress concentration occurs on the film at both ends of the slit-shaped hole. appear. As a result, it is considered that cracks tend to occur at the perforations due to vibrations and impacts, particularly when dropped or transported.
[0006]
The present invention has been completed by the inventor of the present invention as early as possible to address the problems that occur when such a biodegradable heat-shrinkable film is applied to a perforated tubular film. An object of the present invention is to provide a heat-shrinkable tubular film which has little effect on the environment and can prevent tearing of a perforated portion due to vibration and impact.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and the heat-shrinkable tubular film according to the present invention is a heat-shrinkable tubular film having perforations, and a biodegradable heat-shrinkable film , And the individual holes constituting the perforations are round before heat shrinkage.
Note that the round shape includes not only a perfect circle but also an elliptical shape and an oblong shape.
[0008]
In the heat-shrinkable tubular film having the above structure, since it is constituted by a biodegradable heat-shrinkable film, unlike a conventional polyester film, after being discarded, it is decomposed by microorganisms over time. Therefore, the impact on the environment is small. In addition, the biodegradable heat-shrinkable film is hard and brittle as compared with a conventional polyester film such as polyethylene terephthalate. Even when a tensile force acts on the film, stress concentration is less likely to occur around the hole compared to a conventional slit-shaped hole, and therefore, cracking of the film due to vibration or impact is prevented. .
In addition, since the shape of the perforated hole is deformed by heat shrinkage, for example, a substantially circular shape before heat shrinkage generally becomes a flat shape such as an oval shape after heat shrinkage. However, the degree of deformation before and after thermal contraction differs depending on the amount of contraction. Therefore, the degree of deformation varies depending on the film portion, and the shape before heat shrinkage may be substantially maintained in a place where the amount of shrinkage is small.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the heat-shrinkable tubular film of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a cap seal 1 attached to the mouth of a container (bottle) as a heat-shrinkable tubular film in the present embodiment. The cap seal 1 is formed by forming a horizontal uniaxially stretched film into a cylindrical shape so that the lateral direction is the circumferential direction. The horizontal uniaxially stretched film may be any film that is substantially uniaxially stretched, and may be slightly stretched in the vertical direction. The cap seal 1 is preformed in a tapered shape in which the upper end 2 is bent inward and the diameter increases downward. However, a flat (tube-shaped) one folded flat may be directly mounted on the container without being preformed.
[0010]
At a predetermined position on the lower end 3 of the cap seal 1, a knob 4 is provided so as to project downward. Further, two perforations 5 are formed substantially parallel to the entire length of the cap seal 1 in the axial direction from the base of the knob portion 4.
[0011]
The cap seal 1 is heat-shrinked after being fitted to the opening 11 of the container 10, and is tightly attached to the container 10 along the shape of the opening 11 as shown in FIG. 2. A stopper 12 is provided at the mouth 11 of the container 10, and the outer periphery of the stopper 12 is covered by the upper end 2 of the cap seal 1 from above to prevent the stopper 12 from falling out of the mouth 11. I do.
Then, as shown in FIG. 3, the knob 4 can be easily opened by pulling the knob 4 upward. That is, the film between the two perforations 5 is cut off from the other portion in a tape shape, so that the tubular cap seal 1 can be easily broken in the longitudinal direction and opened.
[0012]
Here, a biodegradable heat-shrinkable film is used as a film constituting the cap seal 1. As the biodegradable heat-shrinkable film, for example, a film using polylactic acid is used. This polylactic acid is naturally hydrolyzed in soil and water and decomposed by microorganisms. In detail, it is a transverse uniaxially stretched film containing a polylactic acid-based polymer as a main component. Lactic acid includes two kinds of optical isomers, L-lactic acid and D-lactic acid. Therefore, the polylactic acid-based polymer includes poly (L-lactic acid) whose structural unit is L-lactic acid, poly (D-lactic acid) whose structural unit is D-lactic acid, and L-lactic acid and D-lactic acid whose structural units are L-lactic acid. Poly (DL-lactic acid), which is lactic acid, or a mixture thereof is used as a main component. The composition ratio of D-lactic acid and L-lactic acid is preferably in the range of 100: 0 to 85:15 by weight, or in the range of 0: 100 to 15:85. Here, the composition ratio is, when D-lactic acid and L-lactic acid are mixed, the weight ratio of each, and in the case of DL-lactic acid, the weight of the D-lactic acid component and the L-lactic acid component in the copolymer. The ratio refers to the ratio of the total weight of D-lactic acid to the total weight of L-lactic acid when they are mixed.
[0013]
Further, a copolymer with a hydroxycarboxylic acid, an aliphatic diol, or an aliphatic dicarboxylic acid may be used.
Examples of hydroxycarboxylic acids include optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid), glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, Bifunctional aliphatic hydroxycarboxylic acids such as hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycaproic acid, caprolactone, and butyrolactone And lactones such as valerolactone.
Examples of the aliphatic diol include ethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol.
Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecandioic acid and the like.
However, when a copolymer with these is used, the polylactic acid-based polymer is contained in an amount of 50% by weight or more so as not to impair the properties of the polylactic acid.
[0014]
In addition, as a small amount of a copolymer component, a non-aliphatic dicarboxylic acid such as terephthalic acid or a non-aliphatic diol such as an ethylene oxide adduct of bisphenol A is used to improve heat resistance, or a diisocyanate compound or an epoxy compound. , A molecular weight may be increased by using a small amount of a chain extender such as an acid anhydride, and a heat stabilizer, a light absorber, a slipping agent, a plasticizer, an inorganic filler, a colorant, a pigment, etc. It may be added. The weight average molecular weight is preferably in the range of 50,000 to 400,000.
[0015]
Incidentally, by appropriately selecting the stretching conditions and the crystallinity of polylactic acid, the shrinkage starting temperature of the film is set in the range of 50 to 63 ° C., and the shrinkage in the transverse direction when immersed in hot water of 65 ° C. for 10 seconds is reduced. It can be set to be 10% or more. When set in this manner, a film having a low shrinkage start temperature and a small natural shrinkage ratio is obtained. The preferable heat shrinkage is about 60 to 70% when immersed in 90 ° C. hot water for 10 seconds.
[0016]
Since the cap seal 1 is made of a biodegradable heat-shrinkable film, the influence on the environment is smaller than that of a conventional polyester film or the like. In particular, since this type of cap seal 1 is separated from the container 10 by opening and immediately discarded, the effect of using a biodegradable heat-shrinkable film having a small effect on the environment is great.
[0017]
On the other hand, in the case of a biodegradable heat-shrinkable film, the film is hard and brittle, and the heat shrinkage further increases the hardness and brittleness. For this purpose, the shape of each hole 5a constituting the perforation 5 is devised. That is, instead of the slit shape as in the related art, the shape is a round shape as shown in FIGS. 1, 3 and 4. The hole 5a of the perforation 5 is a through hole, but may not be completely penetrated.
[0018]
The size of the hole 5a of the perforation 5 is, for example, 0.05 to 2 mm, and the pitch (the interval between the adjacent holes 5a) is 0.1 to 5 mm. For example, when the thickness of the film is 50 μm, the hole 5a of the perforation 5 has a diameter of 0.4 mm and a pitch of 1 mm.
[0019]
As a method for forming such perforations 5 in a film, there are mainly a method using a laser and a method using a needle having a round cross section.
First, in the case where the former laser is used, the film is irradiated with a laser beam using a laser beam irradiation device such as a carbon dioxide laser beam, an argon laser beam, or a YAG laser beam. For example, in a center sealing step or the like for forming a cylinder, a long film being continuously transferred is irradiated with a laser beam. When the film is irradiated with a beam, the irradiated minute area instantaneously melts and evaporates. When the beam is scanned while being turned on and off along a direction (longitudinal direction) crossing (orthogonal to) the stretching direction of the film, the beam is intermittently irradiated, and round holes 5a are formed at regular intervals. At the same time, a thick portion 5b (shown by a two-dot chain line in FIG. 4) that rises in the thickness direction is formed around the hole 5a. By controlling the beam irradiation conditions such as the beam output, the depth of the beam focus, the beam scanning speed, and the ON / OFF cycle of the beam, the diameter and pitch of the hole 5a, the shape and thickness of the thick portion 5b, etc. Can be set. In the case of beam irradiation as described above, micro-cracks do not occur in the film when the perforations 5 are formed, and therefore, it is preferable. Further, since the thick portion 5b is formed around the hole 5a, cracks starting from the periphery of the hole 5a are particularly unlikely to occur.
[0020]
On the other hand, when the latter needle is used, for example, a disk having a large number of the needles protruding from the outer peripheral portion is used. By pressing the rotating disk against the film to be conveyed, it is possible to continuously form the circular holes 5a at regular intervals in the film with the needle at the outer periphery. As described above, when the perforation 5 is formed using a needle having a round cross section, the apparatus is simple, and therefore, there is an advantage that the manufacturing cost can be suppressed. When the perforation 5 is formed using a needle, the thick portion 5b is not formed around the hole 5a of the perforation 5 to be formed as in the case of laser.
In addition, the shape of the hole 5a becomes elliptical or oblong because the hole 5a is deformed in a direction to close the hole 5a after the needle is removed. When the diameter of the hole 5a is about 1 to 2 mm, the hole 5a can be formed by a circular punching blade or the like instead of the needle. In this case, it is possible to form the hole 5a which is almost a perfect circle.
[0021]
In any case, since the individual holes 5a constituting the perforations 5 are formed in a round shape instead of a slit shape as in the related art, even if a hard and brittle biodegradable heat-shrinkable film is used, Cracks hardly occur around the hole 5a. Therefore, even if the container 10 is transported or dropped after the heat shrinkage, even if the container 10 is subjected to vibration or impact, the film at the perforation 5 can be prevented from breaking.
Moreover, when the biodegradable film is broken by hand, the biodegradable film is fragile (especially, it has a property of tearing in the longitudinal direction while being uniaxially stretched in the transverse direction). Even if there is, it can be broken smoothly. In particular, even a hole 5a having a thick portion 5b formed around it by laser beam irradiation is preferable because it can be broken.
[0022]
Although the cap seal 1 has been described above as an example, the same applies to a shrink label.
[0023]
The number of perforations 5 is not limited to two, but may be one. Further, the perforation 5 may be formed in the circumferential direction or obliquely, in addition to the one along the axial direction of the tubular film.
[0024]
【The invention's effect】
As described above, in the heat-shrinkable tubular film according to the present invention, the influence on the environment can be reduced by using the biodegradable heat-shrinkable film, and individual holes constituting perforations can be formed. The round shape can prevent the perforated portion from being broken by vibration, impact, or the like, even with a relatively fragile biodegradable heat-shrinkable film.
Furthermore, even if it is a horizontal uniaxially stretched film, since it is a film having a tearing property in the vertical direction, perforations formed of round holes can be smoothly broken.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a cap seal to which a heat-shrinkable tubular film of one embodiment of the present invention is applied.
FIG. 2 is a cross-sectional view showing a state where the cap seal is attached to a container.
FIG. 3 is a perspective view showing a state when the cap seal is opened from the container.
FIG. 4 is an enlarged view of a perforated portion of the cap seal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cap seal (heat-shrinkable cylindrical film), 2 ... Upper end part, 3 ... Lower end part, 4 ... Knob part, 5 ... Perforation, 5a ... Hole, 5b ... Thick part, 10 ... Container, 11 ... Port Part, 12 ... plug

Claims (1)

A heat-shrinkable tubular film having perforations, comprising a biodegradable heat-shrinkable film, wherein individual holes constituting the perforations are round before heat-shrinkage. Tubular film.

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