JPH0649785B2 - Heat shrinkable polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-shrinkable polyester film suitable as a packaging material used for coating, bundling, exterior, and the like. In particular, the present invention relates to a polyester film that exhibits excellent heat shrinkage properties even when it is shrunk at a low temperature.

(Prior Art) A heat-shrinkable film is used for coating various containers such as bottles (including glass and plastic bottles) and cans, and long objects (pipes, rods, wood, various rods, etc.), and binding. It is used for exterior or exterior. For example, it is used to cover a part or the whole of the cap, shoulder, and body of a bottle for the purpose of marking, protection, bundling, and improvement of commercial value. Further, it is also used for the purpose of accumulating and packaging a plurality of boxes, bottles, plates, rods, notebooks, etc., or for the purpose of bringing a film into close contact with an object to be packaged (skin package).

All of the above applications utilize the heat shrinkability and shrinkage stress of the film. Usually, a heat-shrinkable film is formed into a tube shape, and, for example, a bottle or an accumulated pipe is covered with the heat-shrinkable film, and then heat-shrinkable, whereby packaging or bundling is performed. Therefore, these heat-shrinkable films must withstand the process for heat shrink. When used for coating a bottle, it must have heat resistance to the extent that boil treatment or retort treatment can be performed after coating. In particular, when used for plastic products such as polyethylene and polyethylene terephthalate (PET) bottles, it is required that they can be sufficiently shrunk at a low temperature in order to avoid deformation of the plastic due to heating.

Polyvinyl chloride, polystyrene, polypropylene, etc. are used as the material of the heat-shrinkable film. However, such a film generally has poor heat resistance and cannot withstand boil treatment or retort treatment. Films made of polyvinyl chloride tend to form gels of polymers and additives during heat shrinkage, and when printed, pinholes appear on the printed surface. Further, there is a problem that chlorine gas is generated during incineration. A film made of polystyrene is inferior in weather resistance and solvent resistance, and cracks easily occur. Furthermore, the dimensions of the film are not stable. Polypropylene has poor shrinkage properties at low temperatures, and wrinkles and spots are likely to occur in the shrinkage area.

(Problems to be Solved by the Invention) In contrast to such a conventional heat-shrinkable film, a polyester film is excellent in heat resistance, weather resistance, and solvent resistance. On the other hand, it has not been put to practical use because it has poor heat shrinkage characteristics (low temperature shrinkability) when it is shrunk at a low temperature, and wrinkles and spots easily occur in the high shrinkage part.

To solve these problems, a heat-shrinkable polyester film made of a mixture of copolyester and / or polyethylene terephthalate and copolyester (Japanese Patent Laid-Open No. 63-156833), glass transition temperature
Heat-shrinkable polyester film prepared by blending polyester and / or copolyester having a temperature of 35 ° C. or higher with another polymer (Japanese Patent Laid-Open No. 62-32028 and Japanese Laid-Open Patent No. 62-121732).
No.) etc. have been proposed. However, the low temperature shrinkage is still insufficient and it was difficult to use it for plastic products.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a heat-shrinkable polyester film having excellent low-temperature shrinkability and heat resistance.

(Means for Solving the Problems) The heat-shrinkable polyester film of the present invention comprises 30 to 70% by weight of polyethylene terephthalate and 20 to 70% by weight of polyester and / or copolyester having a glass transition temperature of 35 ° C. or higher. , A polyester having a glass transition temperature of 34 ° C. or less and / or 1 to 30% by weight of a copolyester, thereby achieving the above object.

The amount of polyethylene terephthalate contained in the composition is preferably 30 to 70% by weight, more preferably 40 to 60% by weight. If the amount is less than 30% by weight, the heat resistance and impact strength of the obtained film deteriorate. On the other hand, if it exceeds 70% by weight, the residual shrinkage stress of the film during heat shrinkage decreases. Therefore, for example, when the boil process is performed, the high shrinkage portion is loosened. The intrinsic viscosity of the polyethylene terephthalate is preferably
0.55 to 1.3 dl / g, more preferably 0.63 to 1.2
dl / g.

The amount of polyester and / or copolyester having a glass transition temperature of 35 ° C. or higher contained in the above composition is
It is preferably 20-70% by weight, more preferably 30-
50% by weight. When it is less than 20% by weight, the residual shrinkage stress of the film during heat shrinkage decreases. Therefore,
For example, when boiled, loosening occurs in the high shrinkage area. On the other hand, if it exceeds 70% by weight, the heat resistance and impact strength of the obtained film deteriorate. In addition, the temperature sensitivity during heat shrinkage increases, and the shrinkage speed increases. Therefore, contraction unevenness is likely to occur. The intrinsic viscosity of the above polyester and copolyester is preferably 0.50 to 1.3 dl
/ G, and more preferably 0.60 to 1.2 dl / g.

Examples of polyesters and copolyesters having a glass transition temperature of 35 ° C. or higher used in the present invention include the following. First, any polyester may be used as long as it has a glass transition temperature of 35 ° C or higher. The copolyester is, for example, a polyester containing terephthalic acid and ethylene glycol as main components and other acid components and / or other glycol components as copolymerization components. Other acid components include aliphatic dibasic acids (eg, adipic acid, sebacic acid, azelaic acid) and aromatic dibasic acids (eg, isophthalic acid, diphenyldicarboxylic acid, 5-tert-butylisophthalic acid, 2,2,6,6
-Tetramethylbiphenyl-4,4-dicarboxylic acid, 2,6
Naphthalenedicarboxylic acid, 1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid) are used.
Examples of the glycol component include aliphatic diols (eg, neopentyl glycol, diethylene glycol, propylene glycol, butanediol, hexanediol), alicyclic diols (eg, 1,4-cyclohexanedimethanol) or aromatic diols (eg, xylyl diol). Lenglycol, bis (4-β-hydroxyphenyl)
Sulfone, 2,2- (4-hydroxyphenyl) propane derivative) is used.

The amount of polyester and / or copolyester having a glass transition temperature of 34 ° C. or less contained in the above composition is
It is preferably 1 to 30% by weight, more preferably 3 to
20% by weight. If it exceeds 30% by weight, the residual shrinkage stress of the film during heat shrinkage decreases. Therefore, for example, when the boil process is performed, the high shrinkage portion is loosened. Further, although the low temperature shrinkability is greatly improved, the rate at which the printed film naturally shrinks during storage increases, and the printing pitch decreases. The intrinsic viscosity of the polyester and the copolyester is preferably 0.50 to 1.3 dl / g,
More preferably, it is 0.60 to 1.2 dl / g.

Examples of polyesters and copolymerized polyesters having a glass transition temperature of 34 ° C. or lower used in the present invention include the following. First, any polyester may be used as long as it has a glass transition temperature of 34 ° C or lower. The copolyester is, for example, a polyester containing terephthalic acid and / or isophthalic acid and ethylene glycol as main components and other acid components and / or other glycol components as copolymerization components. Other acid components include aliphatic dibasic acids (eg adipic acid,
Sebacic acid, azelaic acid, isophthalic acid, etc. are used. Other glycol components include aliphatic diols (eg, neopentyl glycol, butanediol,
Hexanediol) or the like is used. Alternatively, block copolymers of these polyesters and polyethers (eg, polyethylene oxide, polypropylene oxide) can be used.

The polyesters and polyester copolymers described above can be prepared by conventional methods. For example, a direct esterification method in which an acid component and a glycol component are directly reacted, a transesterification method in which an ester as an acid component is reacted with a glycol component, and the like can be used.

In addition to the polyester component, the above composition may contain various additives as required. As the additive, a lubricant (for example, titanium dioxide, fine particle silica, kaolin, calcium carbonate), an antistatic agent, an antiaging agent, an anti-UV agent, a coloring agent (for example, a dye) and the like are used.

The above composition is formed into a film by a known method (for example, an extrusion method or a calender method). The shape of the film is, for example, a plane shape or a tube shape, and is not particularly limited. The obtained film is, for example, stretched in a predetermined direction in a predetermined direction in the range of 3.0 to 7.0 times, preferably 4.0 to 6.0 times. 1.0 to 2.0 times in the direction orthogonal to this direction, preferably 1.1 times
Stretched in the range of double to 1.8 times. Either may be first in the order of this stretching. By stretching in the direction orthogonal to the main stretching direction, the impact resistance of the obtained stretched film is improved and the property of being easily torn in one direction is relaxed. When the draw ratio in the above-mentioned right angle direction exceeds 2.0,
The heat shrinkage becomes too large in the direction orthogonal to the main shrinkage direction, and the finish when heat shrinks becomes uneven in a wavy state.

A usual method is adopted as the stretching method. These include, for example, roll drawing, long gap drawing, tenter drawing, and tubular drawing. In any of these methods, the stretching may be performed by sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. In the above-mentioned biaxial stretching, stretching in the longitudinal and transverse directions may be performed simultaneously, but sequential biaxial stretching in which either one is performed first is effective, and the longitudinal and transverse directions may be performed first.

Preferably, the above stretching is performed in the following steps.
For example, first, the film is preheated at a temperature not lower than the glass transition temperature (Tg) of the polymer composition constituting the film, for example, a temperature of about Tg + 80 ° C. Here, the glass transition temperature of the polymer composition means a value obtained by averaging the glass transition temperatures of the respective polyester components by weighting the contents thereof. And, in the process of 9/10 or less of the total drawing process, the drawing is carried out at a temperature of about Tg + 80 ° C and the remaining
In the process of 1/10 or less, Tg + 60 ° C or less, preferably
Stretching is performed at a temperature of Tg + 50 ° C. or lower. If the treatment is carried out within the above temperature range during the stretching in the main direction (main shrinkage direction), heat shrinkage in the direction orthogonal to this direction can be suppressed.

During these stretching, heat setting is usually performed.
For example, it is recommended to pass a heating zone at 30 ° C to 150 ° C for about 1 to 60 seconds after stretching. By performing heat setting, it is possible to prevent dimensional change of the obtained heat-shrinkable film under high temperature in summer. Furthermore, after the stretching, the film is cooled while keeping the film in a tension state while applying stress, or by cooling the film continuously after releasing the tension state after the treatment, thereby obtaining a heat shrinkage property of the obtained film. , It will be better and more stable.

The heat-shrinkable polyester film of the present invention thus obtained has a heat shrinkage rate of 20% or more, preferably 30% or more in an atmosphere of 80 ° C in a predetermined direction,
The heat shrinkage rate in the atmosphere is 40% or more. The heat shrinkage rate in the direction orthogonal to this direction is extremely small.
Therefore, the heat-shrinkable polyester film of the present invention exhibits sufficient heat-shrinkability at a relatively low temperature and does not cause wrinkles or spots. For example, when used in plastic bottles such as polyethylene bottles and PET bottles, the film itself can be shrunk at a low temperature, so the bottle itself does not deform. Further, it is not necessary to lengthen the treatment time for heat shrinkage in order to prevent the generation of wrinkles and spots.

(Examples) Examples of the present invention will be described below.

The measuring method used in the examples is as follows.

(1) Heat shrinkage rate A heat-shrinkable polyester film is cut into strips with a width of 20 mm to make samples, and marked lines are drawn at intervals of 200 mm in the longitudinal direction. Apply 80 ° C or 100 ° C hot air to this sample for 10 seconds to heat it, and measure the shrinkage.

(2) Maximum heat shrinkage Using the same sample as in (1) above, continue heating by blowing hot air at 100 ° C, and set the shrinkage at the time of the most shrinkage as the maximum heat shrinkage.

(3) Impact strength A heat-shrinkable polyester film is cut into strips with a width of 10 mm and a length of 10 cm to obtain samples. Temperature this sample to 23
After leaving it for 24 hours under the condition of ℃ and relative humidity of 65%, measure the impact strength using Tensil Impact Tester (manufactured by Toyo Seiki).

(4) Heat resistance 300cc of tubular heat-shrinkable polyester film
Cover with a PET bottle and heat shrink at 150 ° C for 10 seconds. Let this bolt stand in hot water at 90 ° C for 30 minutes, and check whether the heat-shrinked film is loose.

(5) Glass transition temperature Measured by a differential scanning calorimeter based on JIS-K7121.

Example 1 First, a copolyester A was prepared using 100 mol% of terephthalic acid as an acid component, 80 mol% of ethylene glycol and 20 mol% of neopentyl glycol as a glycol component. The copolymerized polyester A thus obtained had a glass transition temperature of 69 ° C. and an intrinsic viscosity of 0.67 dl / g.

Further, a copolymerized polyester B was prepared using 70 mol% of terephthalic acid and 30 mol% of sebacic acid as acid components, and 45 mol% of ethylene glycol and 55 mol% of neopentyl glycol as glycol components. The glass transition temperature of the obtained copolyester B was 7 ° C. and the intrinsic viscosity was 0.70 dl / g.

The heat-shrinkable film of this example was prepared as follows, using the copolymerized polyesters A and B thus obtained as the polyester component. 50% by weight of polyethylene terephthalate (intrinsic viscosity 0.70 dl / g), 35% by weight of copolyester A as a polyester component having a glass transition temperature of 35 ° C or higher, and a glass transition temperature of 34 ° C
Copolymerized polyester B as the following polyester component
Mixed at a rate of 15% by weight. Further, 0.05% by weight of silicon dioxide based on the total weight of the mixture was added as an additive to the mixture to obtain a polyester composition. This polyester composition was melt extruded at 290 ℃, and the thickness was 190μm.
I got a film of.

This unstretched film was preheated at 120 ° C. for 6 seconds and then stretched 4.7 times in one predetermined direction. In addition, the temperature condition during stretching is 80 ° C until half of the whole stretching process, and the other half is
It was set at 70 ° C. After stretching, keep the tension at 40 ℃
Cooled to. The resulting heat-shrinkable film has a thickness of 40μ
m, the thermal shrinkages at 80 ° C and 100 ° C are
31% and 52%. Other physical property values are shown in Table 1.

This heat-shrinkable film was formed into a tube to obtain a shrinkable label, which was covered with a PET bottle and then heat-shrinked by heating at 150 ° C for 10 seconds. The label contracted uniformly over the whole area, and no spots were found on the shoulders of the bottles, no wrinkles were formed on the highly contracted parts, and no loose edges were found. No deformation of the bottle was observed. From these results and the physical properties shown in Table 1, it can be seen that the heat-shrinkable film of this example is excellent in low-temperature shrinkability and heat resistance.

Comparative Example 1 A mixture of 50% by weight of polyethylene phthalate (intrinsic viscosity 0.70 dl / g) and 50% by weight of copolyester A was used so that the maximum heat shrinkage rate was in agreement with that of the heat shrinkable film of Example 1. Example 1 except that the draw ratio was 4.9
A heat-shrinkable film was obtained in the same manner as. 80 ° C and 100
The heat shrinkages at ℃ were 16% and 50%, respectively. Other physical property values are shown in Table 1.

This heat-shrinkable film was formed into a tube to obtain a shrink label, which was covered with a PET bottle and then heat-shrinked by heating at 150 ° C for 10 seconds. The label did not shrink uniformly, and wrinkles remained in the high shrinkage area. Moreover, when heat-shrinking was performed by heating at 170 ° C for 10 seconds, some deformation of the bolt was observed.

Comparative Example 2 A mixture of 50% by weight of polyethylene phthalate (intrinsic viscosity 0.70 dl / g) and 50% by weight of copolyester B was used so that the maximum heat shrinkage was in agreement with that of the heat shrinkable film of Example 1. Example 1 except that the draw ratio was 4.8
A heat-shrinkable film was obtained in the same manner as. 80 ℃ and 100
The heat shrinkages at ℃ were 48% and 49%, respectively. Other physical property values are shown in Table 1.

This heat-shrinkable film was formed into a tube to obtain a shrink label, which was covered with a PET bottle and then heat-shrinked by heating at 150 ° C for 10 seconds. The label contracted unevenly and rapidly, resulting in partial spots. Heating time
When changed to 30 seconds and heat-shrinked, no spots occurred, but looseness occurred in the high-shrinkage part of the shrunken label. When heat-shrinked by heating at 130 ° C for 10 seconds, the label did not shrink uniformly, and wrinkles remained in the high-shrinkage area. As described above, the heat-shrinkable film of this comparative example had a high shrinkage rate and the residual shrinkage stress rapidly decreased, so that good shrinkage characteristics could not be obtained.

Example 2 First, 80 mol% of terephthalic acid and 1,3-as acid components
Trimethyl-3-phenylindene-4,5-dicarboxylic acid
20 mol%, ethylene glycol as glycol component 10
Copolyester C was prepared using 0 mol%.
The glass transition temperature of the obtained copolyester C is 98%.
And the intrinsic viscosity was 0.69 dl / g.

Further, Copolyester D was prepared by using 50 mol% of terephthalic acid and 50 mol% of adipic acid as acid components, and 42 mol% of ethylene glycol and 58 mol% of butanediol as glycol components. The glass transition temperature of the obtained copolyester D is -20 ° C and the intrinsic viscosity is
It was 0.90 dl / g.

The heat-shrinkable film of this example was prepared as follows using the thus obtained copolymerized polyesters C and D as the polyester component. 50% by weight of polyethylene terephthalate (intrinsic viscosity 0.70 dl / g), 40% by weight of copolymerized polyester C as a polyester component having a glass transition temperature of 35 ° C or higher, and a glass transition temperature of 34 ° C
Copolymerized polyester D as the following polyester component
Mixed at a rate of 10% by weight. Further, 0.05% by weight of silicon dioxide based on the total weight of the mixture was added as an additive to the mixture to obtain a polyester composition. This polyester composition was melt extruded at 290 ℃ and the thickness was 210μ.
m film was obtained.

This unstretched film was preheated at 120 ° C for 7 seconds and then stretched 5.2 times in one predetermined direction. The temperature conditions during stretching are 90 ° C for up to half of the entire stretching process, and the remaining 1/2 for
It was set at 70 ° C. After stretching, while maintaining tension, 50 ℃
Cooled to. The resulting heat-shrinkable film has a thickness of 40μ
m, the thermal shrinkages at 80 ℃ and 100 ℃ are respectively
29% and 53%.

This heat-shrinkable film was molded into a tube to obtain a shrink label, which was then covered with a PET bottle and then heat-shrinked by heating at 150 ° C for 10 seconds, with good results as shown in Table 1. Was obtained.

Comparative Example 3 A mixture of 50% by weight of polyethylene phthalate (intrinsic viscosity of 0.70 dl / g) and 50% by weight of copolyester C was used, and the maximum heat shrinkage ratio was matched with that of the heat shrinkable film of Example 2. Example 2 except that the draw ratio was 5.3
A heat-shrinkable film was obtained in the same manner as. 80 ℃ and 100
The heat shrinkages at ℃ were 8% and 48%, respectively. Other physical property values are shown in Table 1.

This heat-shrinkable film was molded into a tube to obtain a shrinkable label, which was covered with a PET bottle and then heat-shrinked by heating at 150 ° C for 10 seconds. The label did not shrink uniformly, and wrinkles remained in the high shrinkage area. When heat-shrinking was performed by heating at 170 ° C for 10 seconds, a part of the bottle was deformed.

Comparative Example 4 Polyethylene terephthalate (intrinsic viscosity 0.70 dl / g) 50
Same as Example 2 except that a mixture of 50% by weight and 50% by weight of copolyester D was used, and the stretching ratio was 5.4 so that the maximum heat shrinkage rate was in agreement with the heat shrinkable film of Example 2. To obtain a heat-shrinkable film. 80 ℃ and
The heat shrinkages at 100 ℃ were 42% and 47%, respectively. Other physical property values are shown in Table 1.

This heat-shrinkable film was formed into a tube to obtain a shrink label, which was covered with a PET bottle and then heat-shrinked by heating at 150 ° C for 10 seconds. The label did not shrink uniformly, and wrinkles occurred in the high shrinkage area. Also, when the heating time was changed to 30 seconds to eliminate spots, loosening occurred in the high shrinkage area.

(Effect of the Invention) The heat-shrinkable polyester film of the present invention thus has excellent low-temperature shrinkability and heat resistance. Such a heat-shrinkable film gives a beautiful appearance and a strong packaging state when covering or bundling plastic products such as polyethylene and PET bottles. Further, when printing is performed, the stability of the printing pitch is excellent. Therefore, the heat-shrinkable polyester film of the present invention is useful and has high utility value in a wide range of packaging material fields.

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Claims (2)

[Claims] 1. A heat-shrinkable polyester film comprising a composition containing the following polyester components: Polyethylene terephthalate 30 to 70% by weight; Polyester having a glass transition temperature of 35 ° C. or higher and / or copolymerized polyester 20 to 70% by weight And 1 to 30% by weight of polyester and / or copolyester having a glass transition temperature of 34 ° C. or lower. 2. The film has a heat shrinkage of 20% or more at 80 ° C. and a heat shrinkage of 40% at 100 ° C. in a predetermined direction.
The heat-shrinkable polyester film according to claim 1, which is the above.