JPH11240966A - Thermally shrinkable polyester-based film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermally shrinkable polyester-based film scarcely generating longitudinal bright specks, wrinkles, irregular shrinkage and strains after the shrinkage of the film, and suitable in the use of labels. SOLUTION: This thermally shrinkable polyester-based film comprises a stretched film produced from a polyester comprising >=70 mol.% of terephthalic acid component and >=70 mol.% of ethylene glycol component, and has a thermal shrinkage factor of >=15% in the main shrinking direction at 85 deg.C and an Er/σ max ratio of >=200 wherein the Er is the Young's modulus of the film in the main shrinking direction at 85 deg.C, and the σ max is the maximum value of shrinking stress expressed for a minute from a heating-start time at 85 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polyester film and a method for producing the same. The present invention relates to a suitable heat-shrinkable polyester film and a method for producing the same.

[0002]

2. Description of the Related Art In the field of heat-shrinkable films, particularly shrinkable films for labeling bottle body, films made of polyvinyl chloride, polyethylene, etc. have been mainly used. There are problems such as the generation of chlorine-based gas during incineration, the problem of difficulty in printing polyethylene, and the additional problem of collecting PET bottles, such as the necessity to separate labels of resin other than PET. Shrinkable polyester films have attracted attention. However, many of the heat-shrinkable polyester films shrink rapidly, and are not satisfactory as shrink films for labels, such as wrinkles, spots of shrinkage, and distortion remaining after shrinkage. In order to avoid some of these drawbacks, Japanese Patent Application Laid-Open No. 1-110931 discloses a method of improving the shrink finish by remarkably reducing the elongation at break in the direction perpendicular to the main shrink direction. However, the film obtained by this method is not only easily broken when tension is applied in the steps of printing and labeling, etc., and label is easily broken if normal transportation is carried out with the contents filled. The film was poor in practical use as a shrink film for use. Also, in Japanese Patent Application Laid-Open No. 63-309424, 75 ° C.
A method is disclosed for obtaining a heat-shrinkable polyester film having improved shrink finish by controlling the shrinkage characteristics of the polyester film.

[0003]

However, the film obtained by the above method has not yet been satisfactory as a shrinkable film for labels. In PET bottles, which are the mainstream of recent beverage containers, the shape of the bottles has been rapidly switched from a conventional round type to a square type in view of the storability in refrigerators. When a cylindrical label made of a heat-shrinkable polyester film disclosed in the official gazette is attached to the body of a rectangular bottle, a flat portion other than the corner of the bottle is curved into an arch after shrinkage (referred to as "Tatehike"). Disadvantage). Square PE
Since T bottles are becoming the mainstream of beverage containers, it is necessary to develop a heat-shrinkable polyester-based film that is less likely to cause vertical shrinkage when used as a label for the bottles. In addition to these, it is an object of the present invention to provide a heat-shrinkable polyester film suitable for label use, which has a shrink finish, that is, very little wrinkles, spots, and distortions after shrinkage.

[0004]

In order to achieve the above object, a heat-shrinkable polyester film according to the present invention comprises a terephthalic acid component in a dicarboxylic acid component of 70 mol% or more and an ethylene glycol component in a diol component of 70 mol%. A stretched film made of polyester which is
The heat shrinkage in the main shrinkage direction after treatment in hot water at 85 ° C. for 10 seconds is 15% or more, and was measured with a dynamic viscoelasticity measuring device 8
The ratio (Er) between the Young's modulus (Er) in the main shrinkage direction at 5 ° C. and the maximum value (σmax) of the shrinkage stress in the main shrinkage direction in the air oven at 85 ° C. from 1 minute after the start of heating.
/ Σmax) is 200 or more.

The heat-shrinkable polyester film of the present invention having the above constitution has a stable heat-shrinkability, no shrinkage after shrinkage, and extremely few wrinkles, shrinkage spots and distortions. It is a heat-shrinkable film suitable for label applications.

Further, the method for producing a heat-shrinkable polyester film of the present invention mainly comprises an unstretched polyester film in which a terephthalic acid component in a dicarboxylic acid component is at least 70 mol% and an ethylene glycol component in a diol component is 70 mol%. Tg (glass transition point) -2 in the direction of shrinkage
The film is stretched at a stretching temperature of 0 to Tg + 40 ° C. and a stretching ratio of 2.5 to 6.0 times, and then heat-treated at 70 to 100 ° C. while stretching 3 to 15%.

The method for producing a heat-shrinkable polyester film according to the present invention having the above-mentioned structure provides a film suitable for label use, which has very little occurrence of vertical shrinkage, wrinkles, shrinkage spots and distortion after shrinkage of the heat-shrinkable film. The present invention relates to a method for producing a heat-shrinkable polyester film excellent in shrink finish by selecting stretching conditions and keeping shrink characteristics in a certain range. Further, in the present invention, it is preferable that the main shrinkage direction is the width direction (lateral direction) at the time of film production from the viewpoint of convenience when using the heat shrinkable film.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be specifically described below. The polyester used in the present invention is a polyester in which the terephthalic acid component in the dicarboxylic acid component is 70 mol% or more and the ethylene glycol component in the diol component is 70 mol%. More specifically, as a dicarboxylic acid component other than terephthalic acid, one of known dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and naphthalenedicarboxylic acid Or two or more types,
Further, as a glycol component other than ethylene glycol, one of known diols such as propylene glycol, neopentyl glycol, tetramethylene glycol, hexamethylene glycol, trimethylene glycol, diethylene glycol, polyalkylene glycol, and 1,4-cyclohexanedimethanol, or Two or more types can be shown. In order to obtain a heat-shrinkable polyester film having particularly excellent shrink finish, it is preferable to use polyester in which neopentyl glycol is the remaining component of the glycol component. Moreover, Tg is 90-150.
It is also preferable to mix the polyarylate at 15 ° C. by 15 to 40%.

The terephthalic acid component in the dicarboxylic acid component in the polyester used in the present invention is 70 mol%.
As described above, a polyester in which the ethylene glycol component in the diol component is 70 mol% or more refers to a dicarboxylic acid in the entire polyester irrespective of whether transesterification has been performed after mixing when two or more polyesters are used in combination. The ratio of terephthalic acid in the components and the ratio of ethylene glycol in the glycol components are shown.

The polyester constituting the heat-shrinkable film of the present invention has a terephthalic acid component in the dicarboxylic acid component of 7%.
0% by mole or more, and a polyester in which the ethylene glycol component in the diol component is 70% by mole. Terephthalic acid and ethylene glycol are each a dicarboxylic acid component,
If the amount is less than 70 mol in the diol component, the resulting heat-shrinkable film will have a reduced rupture resistance after shrinkage.

Further, it is preferable to include an inorganic lubricant and an organic lubricant in order to improve the lubricity of the heat-shrinkable film. Further, if necessary, additives such as a stabilizer, a coloring agent, an antioxidant, an antifoaming agent, and an antistatic agent may be contained. The limiting viscosity of the polyester constituting the heat-shrinkable film of the present invention is preferably 0.50 or more.
It is more preferably at least 60, particularly preferably at least 0.65. The limiting viscosity of the polyester constituting the film is 0.
If it is less than 50, the direction orthogonal to the main shrinkage direction is apt to be torn and the workability is lowered, which is not preferable.

The heat-shrinkable film of the present invention has a property that the heat-shrinkage rate in the main shrinkage direction (direction having the largest shrinkage rate) after treatment in hot water at 85 ° C. for 10 seconds is 15% or more. If the shrinkage in the main shrinkage direction is less than 15%, the amount of shrinkage when shrinking as a label becomes insufficient, and the film does not adhere sufficiently to the container or wrinkles easily form in the film, which is not preferable.

The heat-shrinkable film of the present invention has a Young's modulus (Er) of 85 ° C. in the main shrinkage direction measured by a dynamic viscoelasticity measuring apparatus and a temperature of 1 ° C. from the start of heating in an 85 ° C. air oven.
The ratio (Er / σmax) with respect to the maximum value (σmax) of the contraction stress in the main contraction direction which is developed until after minutes is 200 or more. When Er / σmax is less than 200, vertical shrinkage tends to increase, which is not preferable. Although each of the maximum value of the Young's modulus and the contraction stress is not particularly limited, the maximum value of the contraction stress is preferably 0.4 or more. If the maximum value of the shrinkage stress is less than 0.4, the direction orthogonal to the main shrinkage direction is apt to be torn, which is not preferable because the workability is reduced. The upper limit of Er / σmax is not particularly limited, but is about 500.

The thickness of the heat-shrinkable film of the present invention is not particularly limited, but is preferably 10 to 200 μm, more preferably 20 to 100 μm, as a shrinkable film for labels.

Although the heat shrinkage of the heat shrinkable film of the present invention in the direction orthogonal to the main shrinkage direction is not particularly limited, the heat shrinkage after treatment in hot water of 95 ° C. for 10 seconds is 1%.
It is preferably at most 5%, more preferably at most 10%.

The polyester raw material used in the present invention is dried using a drier such as a hopper drier or a paddle drier, or a vacuum drier, and extruded into a film at a temperature of 200 to 300 ° C. For extrusion, any existing method such as a T-die method or a tubular method may be employed. After extrusion, it is quenched to obtain an unstretched film. The stretching process is performed on the unstretched film. However, in order to achieve the object of the present invention, the transverse direction is practical as the main shrinking direction. In the case where the main shrinkage direction is the longitudinal direction, the film can be formed according to a normal operation, except that the stretching direction in the following method is changed by 90 degrees.

Further, if attention is paid to making the thickness distribution of the intended heat-shrinkable polyester film uniform,
When the film is stretched in the transverse direction using a tenter, the heat transfer coefficient is set at 0.00 in a preheating process performed prior to the stretching process.
It is preferable to perform heating at a low wind speed of 13 calories / cm ² · sec · ° C. or less until a predetermined film temperature is reached.
The stretching in the transverse direction is performed at a temperature of Tg-20 ° C. to Tg + 40 ° C. by 2.5 to 6.0 times, preferably 3.0 to 5.5 times. Thereafter, a heat-shrinkable polyester film is obtained by performing heat treatment at 70 to 100 ° C. while elongating at 3 to 15%. As a stretching method, not only a uniaxial stretching in a tenter but also a slight stretching in a longitudinal direction is possible.
The biaxial stretching may be either sequential biaxial stretching or simultaneous biaxial stretching, and may be performed again if necessary.
Focusing on suppressing the internal heat generation of the film due to stretching and reducing the film temperature unevenness in the width direction, the heat transfer coefficient of the stretching step is 0.0009 calories / cm ² · sec · ° C.
As described above, the condition of 0.0011 to 0.0017 calories / cm ² · sec · ° C. is preferable.

[0018]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist. In addition, in this invention, the evaluation method of a film is as follows.

(1) Heat Shrinkage Rate The film was cut into a square of 10 cm × 10 cm, treated in hot water at a predetermined temperature of ± 0.5 ° C. for 10 seconds under no load, and heat shrunk. The lateral dimension was measured, and the heat shrinkage was determined according to the following equation (1). The direction in which the heat shrinkage was large was defined as the main shrinkage direction. Heat shrinkage = (length before shrinkage-length after shrinkage / length before shrinkage) x 100 (%) Formula (1)

(2) Maximum value of shrinkage stress Using a Tensilon (model: UTM-4L) with an air oven manufactured by Toyo Seiki Co., Ltd., the distance between the chucks is 50 mm, the sample shape is the main shrinkage direction: 10 cm, and the main shrinkage direction. And the orthogonal direction: 2 cm, the force developed when heated in a 90 ° C. air oven for 1 minute was recorded on a recorder, the maximum value was read, and the maximum value of the shrinkage stress was determined according to the following equation (2). The maximum value of shrinkage stress = (reading / sample cross-sectional area of the ^{pre-heating) (Kg / mm 2) (} 2) Formula

(3) Shrink finish finish Steam tunnel manufactured by Fuji Astec INC (model: SH-1)
500-L), a transit time of 10 seconds, and a zone temperature /
2-zone temperature: set to 85 ° C / 90 ° C, 900 cc square PET bottle (height 25.5 cm, central section vertical 7.1 cm, horizontal 7.1 cm) (Blendy manufactured by AGF Corporation) (The number of samples = 10) was tested using the bottles used for the above. In addition, the heat shrinkable film includes
Three colors were printed in advance using grass, gold, and white inks of Toyo Ink Manufacturing Co., Ltd. The evaluation was performed visually, and the criteria were as follows. No wrinkles, color spots, or insufficient shrinkage → ○ Color spots → △ Crater-like wrinkles or insufficient shrinkage → ×

(4) Young's Modulus Dynamic Viscoelasticity Measurement Device (Model:
DJA-225) at a frequency of 10 Hz and a heating rate of 5
It was measured in the range of -50 ° C to 150 ° C at a rate of ° C / min, and the Young's modulus at 85 ° C was determined from the chart.

(5) Vertical tunnel Steam tunnel manufactured by Fuji Astec INC (model: SH-
1500-L), 1 zone temperature / 2 zone temperature: 85 ° C./90° C., 2 L square PET bottle at a passage time of 10 seconds (a bottle used for natural water of Minami Alps manufactured by Suntory Limited) ). In the measurement of vertical shrinkage, as shown in FIG. 1, in the width direction of the bottle (--cm), the difference between the lower part of the label at the corner of the bottle and the lower part of the label at the center was obtained. A film printed in three colors with grass, gold, and white inks of Toyo Ink Manufacturing Co., Ltd. was used.

(6) Tg (glass transition point) DSC (model: DSC22) manufactured by Seiko Denshi Kogyo KK
Using 0), a tangent was drawn to an endothermic curve obtained when 10 mg of the unstretched film was heated from -40 ° C. to 120 ° C. at a rate of 20 ° C./min, and the intersection was defined as Tg (glass transition point). And

The polyesters used in the examples are as follows. Polyester A: Polyethylene terephthalate Polyester B: Polyester composed of 70 mol% of ethylene glycol, 30 mol% of neopentyl glycol and terephthalic acid Polyester C: Ethylene oxide adduct of bisphenol compound

[0026]

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Polyethylene terephthalate polyester D: polyethylene naphthalate polyester E: polybutylene terephthalate copolymerized with 20 mol% of

[0028]

EXAMPLES Example 1 35% by weight of polyester A,
2% polyester mixed with 65% by weight of polyester C
It was extruded and quenched at 80 ° C. to obtain an unstretched film.
The unstretched film is 2.0 times further at 94 ° C.
The film was stretched 2.0 times at 6 ° C. and then heat-treated for 20 seconds while stretching at 5% at 89 ° C. to obtain a heat-shrinkable polyester film having a thickness of 45 μm. (Example 2) A polyester obtained by mixing 35% by weight of polyester A, 35% by weight of polyester B and 30% by weight of polyester D was extruded and rapidly cooled at 280 ° C to obtain an unstretched film. 94 ° C. in the transverse direction
And stretched 4.0 times at 89 ° C., and stretched at 89 ° C. for 5% while stretching at 20 ° C.
Heat treatment was performed for 2 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. (Example 3) Polyester containing 35% by weight of polyester A, 55% by weight of polyester B and 10% by weight of polyester E was extruded at 280 ° C and rapidly cooled to obtain an unstretched film. The unstretched film is stretched 1.1 times in the machine direction at 75 ° C., then 2.5 times in the transverse direction at 88 ° C. and 2.0 times in 72 ° C. Heat treatment was performed for 2 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. Comparative Example 1 A polyester obtained by mixing 35% by weight of polyester A, 45% by weight of polyester B and 20% by weight of polyester C was extruded at 280 ° C. and rapidly cooled to obtain an unstretched film. 94 ° C. in the transverse direction
And stretched 4.0 times at 89 ° C., and stretched at 89 ° C. for 5% while stretching at 20 ° C.
Heat treatment was performed for 2 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. (Comparative Example 2) A polyester obtained by mixing 10% by weight of polyester A and 90% by weight of polyester C was extruded at 280 ° C and rapidly cooled to obtain an unstretched film. After stretching the unstretched film 4.0 times in the transverse direction at 97 ° C,
And a heat-shrinkable polyester film having a thickness of 45 μm was obtained. (Comparative Example 3) A heat-shrinkable polyester film was obtained in the same manner as in Example 3, except that 5% elongation was not performed during the heat treatment.

Table 1 shows the evaluation results of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 3. As is clear from Table 1, all of the films obtained in Examples 1 to 3 show a good shrinkage finish (there are no defects such as wrinkles and insufficient shrinkage), and hardly cause vertical shrinkage. Thus, the heat-shrinkable polyester film of the present invention has high quality and high practicability, and is particularly excellent for shrink labels. On the other hand, the film obtained in Comparative Example 1 is apt to cause vertical shrinkage, and the film obtained in Comparative Example 2 suffers from insufficient shrinkage. Therefore, it can be said that all of the films are inferior in quality as heat-shrinkable polyester films for labels. In addition, the film obtained in Comparative Example 3 has a small vertical shrinkage improving effect.

[0030]

[Table 1]

[0031]

The heat-shrinkable polyester film of the present invention according to the first aspect is less likely to cause vertical shrinkage and has less wrinkles, shrinkage spots and distortion after shrinkage. Further, according to the method for producing a heat-shrinkable polyester film of the present invention described in claim 2, a heat-shrinkable polyester film which is less likely to cause vertical shrinkage and has less wrinkles, shrinkage spots and distortion after shrinkage can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing shrinkage of a shrinkable film in a PET bottle body after shrinkage.

[Explanation of symbols]

 1 PET bottle 2 Shrink film 3 Tatehike

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67:02 (72) Inventor Shinichiro Okumura 344 Maehata, Kizu-shi, Inuyama-shi, Aichi Pref. Inventor Hiroaki Ezaki 344 Maebata, Kizu, Inuyama-shi, Aichi Prefecture Inuyama Plant of Toyobo Co., Ltd.

Claims (2)

[Claims] 1. A stretched film comprising a polyester in which a terephthalic acid component in a dicarboxylic acid component is 70 mol% or more and an ethylene glycol component in a diol component is 70 mol%, after being treated in hot water at 85 ° C. for 10 seconds. Has a thermal shrinkage rate of 15% or more in the main shrinkage direction, and has a Young's modulus (E
r) and the maximum value of the shrinkage stress (σ) in the main shrinkage direction which develops from 1 minute after the start of heating in an air oven at 85 ° C.
max) is 200 or more (Er / σmax). 2. An unstretched polyester film in which the terephthalic acid component in the dicarboxylic acid component is 70 mol% or more and the ethylene glycol component in the diol component is 70 mol% is stretched by Tg-20 to Tg + 40 ° C. in the direction of the main shrinkage direction. Stretching at a stretching ratio of 2.5 to 6.0 times at a temperature,
A method for producing a heat-shrinkable polyester film, wherein the heat treatment is performed at 70 to 100 ° C. while elongating by 3 to 15%.