JPH0381338A - Thermally shrinkable polyester film - Google Patents

Abstract

PURPOSE:To improve the shrinkability at a low temp. and heat resistance by forming a compsn. comprising polyethylene terephthalate and two specific (co) polyesters into a film and stretching the resulting film. CONSTITUTION:A compsn. is prepd. by compounding: 30-70wt.% polyethylene terephthalate having an intrinsic viscosity of 0.55-1.3dl/g; 20-70wt.% (co)polyester having an intrinsic viscosity of 0.50-1.3dl/g and a glass transition point of 35 deg.C or higher; 1-30wt.% (co)polyester having an intrinsic viscosity of 0.50-1.3dl/g and a glass transition point of 34 deg.C or lower, and if necessary other additives. The compsn. is formed into a film; the film is stretched 3.0 to 7.0-fold in a predetermined direction and 1.0 to 2.0-fold in the direction vertical to the predetermined direction and, if necessary, is heat set, thereby, producing a thermally shrinkable film which has a shrinkage factor in the predetermined direction of 20% or higher at 80 deg.C and 40% or higher at 100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-shrinkable polyester film suitable as a packaging material used for covering, bundling, packaging, etc. In particular, it relates to a polyester film that exhibits excellent heat shrinkage properties even when shrunk at low temperatures.

(Prior Art) Heat-shrinkable films are used for various containers such as bottles (including glass and plastic bottles) and cans, and long objects (
It is used for covering, binding, or exterior of pipes, rods, wood, various rod-shaped bodies, etc. For example, signs,
It is used to cover part or all of a bottle's cap, shoulder, and body for purposes such as protection, binding, and improving product value. Furthermore, it is also used for packaging a plurality of boxes, bottles, boards, sticks, notebooks, etc., as well as packaging items by bringing the film into close contact with the film (skin packaging).

All of the above uses utilize the heat shrinkability and shrinkage stress of the film. Usually, packaging or bundling is performed by forming a heat-shrinkable film into a tube shape, covering it over, for example, a bottle or a collection of vibrators, and then heat-shrinking the film. Therefore, these heat-shrinkable films must withstand processing for heat-shrinking. Also,
When used to coat bottles, it must have heat resistance to the extent that it can be subjected to boiling or retort treatment after coating. In particular, when used in plastic products such as bottles made of polyethylene or polyethylene terephthalate (pH! Ru.

As the material for the heat-shrinkable film, polyvinyl chloride, polystyrene, polypropylene, etc. are used. However, such films generally have poor heat resistance and cannot withstand boiling or retort processing. Films made of polyvinyl chloride tend to produce gel-like substances from polymers and additives during heat shrinkage, and when printed, pinholes occur on the printed surface. Furthermore, there is the problem that chlorine gas is generated during incineration. Films made of polystyrene have poor weather resistance and solvent resistance, and are prone to cracking. Furthermore, the dimensions of the film are not stable. Polypropylene has poor shrinkage characteristics at low temperatures, and wrinkles and spots tend to form in the shrinkage area.

(Problems to be Solved by the Invention) Compared to such conventional heat-shrinkable films, polyester films have excellent heat resistance, weather resistance, and solvent resistance. On the other hand, it has poor heat shrinkage characteristics (low temperature shrinkability) when contracted at low temperatures.

It has not been put to practical use because it tends to cause wrinkles and spots in high-shrinkage areas.

To solve these problems, a heat-shrinkable polyester film made of a mixture of copolymerized polyester and/or polyethylene terephthalate and copolymerized polyester (Japanese Patent Application Laid-open No. 156833/1983), which has a glass transition temperature of 35°C or higher, has been developed. Heat-shrinkable polyester films containing polyester and/or copolymerized polyester and other polymers have been proposed (Japanese Patent Laid-Open Nos. 62-32028 and 62-121732).

However, it still had insufficient low-temperature shrinkability, making it difficult to use it for plastic products.

The present invention is intended to solve the above-mentioned conventional problems, and its purpose 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 contains 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. .

The composition comprises a composition containing 1 to 30% by weight of a polyester and/or a copolyester having a glass transition temperature of 34° C. or less, thereby achieving the above object.

The amount of polyethylene terephthalate contained in the composition is preferably 30 to 70% by weight.

More preferably, it is 40 to 60% by weight. 30% by weight
If it is below , the heat resistance and impact strength of the obtained film will decrease. Conversely, when it exceeds 70% by weight, the residual shrinkage stress of the film during heat shrinkage decreases. Therefore, for example, when boiling is performed, high shrinkage areas become loose. In addition, the intrinsic viscosity of the polyethylene terephthalate is preferably 0.55 to L3di/g,
More preferably 0.63 to 1.2 J! /g.

The amount of polyester and/or copolyester having a glass transition temperature of 35° C. or higher contained in the composition is preferably 20 to 1%.

More preferably, it is 30 to 50% by weight. 20% by weight
When the value is less than , the residual shrinkage stress of the film during heat shrinkage decreases. Therefore, for example, when boiling is performed, the high shrinkage portions become loose. On the other hand, if it exceeds 70% by weight, the heat resistance and impact strength of the resulting film will decrease. Furthermore, the temperature sensitivity during heat shrinkage increases, and the shrinkage speed becomes faster. Therefore, shrinkage spots are likely to occur. In addition, the intrinsic viscosity of the above polyester and copolymerized polyester is preferably 0.50 to 1.3 d/g, more preferably 0.60 to 1.2 d1/g.

Examples of the polyester and copolyester 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. Copolymerized polyester.

For example, it is a polyester containing terephthalic acid and ethylene glycol as main components, and containing other acid components and/or other glycol components as copolymer components. Other acid components include aliphatic dibasic acids (e.g., adipic acid, sepathic acid, azelaic acid) and aromatic dibasic acids (e.g., isophthalic acid, diphenyldicarboxylic acid, 5-tert-butyl isophthalic acid, 2.2.6.6-tetramethylbiphenyl-4,4-dicarboxylic acid, 2,6-natutalenicalphone M,1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid) used.

Glycol components include aliphatic diols (e.g.

Neopentyl glycol, diethylene glycol.

propylene glycol, butanediol, hexanediol), alicyclic diols (e.g. 1,4-cyclohexane dimetatool) or aromatic diols (e.g. xylylene glycol, 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 composition is preferably 1 to 30% by weight.

More preferably, it increases by 3 to 20%. When it exceeds 30% by weight, the residual shrinkage stress of the film during heat shrinkage decreases. Therefore, for example, when boiling is performed, the high shrinkage portions become loose. Furthermore, although the low-temperature shrinkability is greatly improved, the rate at which the printed film naturally shrinks during storage increases, causing problems such as a decrease in printing pitch. The intrinsic viscosity of the above polyester and copolyester is preferably 0.
50 to 1.3 d/g''c, more preferably 0.60 to 1.2 d/g''c.

Examples of the polyester and copolyester having a glass transition temperature of 34°C or less 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. Copolymerized polyester.

For example, the main components are terephthalic acid and/or isophthalic acid and ethylene glycol, and other acid components and/or
Or it is a polyester containing other glycol components as a copolymer component. As other acid components, aliphatic dibasic acids (eg, adipic acid, sepathic acid, azelaic acid, isophthalic acid), etc. are used. As other glycol components, aliphatic diols (eg, neopentyl glycol, butanediol, hexanediol), etc. are used. Alternatively, block copolymers of these polyesters and polyethers (eg, polyethylene oxide, polypropylene oxide) may be used.

The polyesters and polyester copolymers described above may be manufactured 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 and a glycol component are reacted, etc. can be used.

In the above composition, in addition to the polyester component.

Various additives may be contained as necessary.

Additives include lubricants (eg titanium dioxide).

(particulate silica, kaolin, calcium carbonate), antistatic agents, antiaging agents, ultraviolet inhibitors, 9 coloring agents (for example, dyes), and the like.

The above composition can be prepared by 9 known methods such as extrusion.

The base is shaped into a film using the calendar method.

The shape of the film is, for example, planar or tubular, and is not particularly limited. The resulting film is 9. For example,
It is stretched in a predetermined direction in a range of 3.0 times to 7.0 times, preferably 4.0 times to 6.0 times, under predetermined conditions described below. 1.0 times to 2 times in the direction perpendicular to this direction.
．． It is stretched 0 times, preferably in the range of 1.1 times to 1.8 times. The order of this stretching may be either first.

By stretching in the direction orthogonal to the main stretching direction, the impact resistance of the obtained stretched film is improved and the tendency to tear in one direction is alleviated. If the stretching ratio in the above-mentioned orthogonal direction exceeds 2.0, the heat shrinkability in the direction orthogonal to the main shrinkage direction becomes too large, and the finish when heat shrinking is uneven and wavy.

As the stretching method, one usual method is adopted.

For example, roll stretching method, long gap stretching method.

There are tenter drawing method and tubular drawing method. 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 lateral directions may be performed simultaneously.

Sequential biaxial stretching, in which one direction is performed first, is effective, and either direction in the vertical and horizontal directions may be used first.

Preferably, the above-mentioned stretching is performed in a second step.

For example, first, the above-mentioned film is preheated to a temperature higher than the glass transition temperature (Tg) of the polymer composition constituting the film, for example, about Tg+80'C. Here 2
The glass transition temperature of a polymer composition means the average value of the glass transition temperatures of each polyester fraction, weighted by its content. And 9/1 of the entire stretching process
0 or less, stretching is performed at a temperature of Tg 10 (approximately 1°C).

In the remaining steps of 1710 and above, Tg + 60°C or less.

Preferably, stretching is performed at a temperature of Tg + 50°C or lower.

If the treatment is performed within the above temperature range during stretching in the main direction (main shrinkage direction), thermal shrinkage in a direction perpendicular to the main direction can be suppressed.

Heat setting is usually performed during these stretching steps.

For example, after stretching, it is recommended to pass through a heating zone at 30"C to 150C for about 1 second to 60 seconds.

By performing heat setting, it is possible to prevent dimensional changes in the obtained heat-shrinkable film under high temperature conditions in summer.

Furthermore, after the above-mentioned stretching, the heat shrinkage properties of the resulting film can be improved by cooling the film while maintaining it in a tensioned state and applying stress to the film, or by continuing to cool it even after releasing the tensioned state following the treatment. , 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 one predetermined direction, and The heat shrinkage rate is 40% or more. The thermal 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 relatively low temperatures and does not generate wrinkles or spots. For example, when used for plastic bottles such as polyethylene bottles and PET bottles, the film can be heat-shrinked at a low temperature, so the bottle itself will not be deformed. Further, there is no need to lengthen the processing time for heat shrinkage in order to prevent the occurrence of wrinkles, spots, etc.

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

The measurement method used in the examples is as follows.

(1) Heat shrinkage rate A heat-shrinkable polyester film was cut into strips with a width of 20 mm to prepare samples, and marked lines were marked at intervals of 200 am in the longitudinal direction. This sample is heated by applying hot air at 80°C or 100°C for 10 seconds, and the shrinkage rate is measured.

(2) Maximum thermal contraction rate Using the same sample as in (1) above, continue heating by applying hot air at 100'C, and define the contraction rate at the point of maximum contraction as the maximum thermal contraction rate.

(3) Impact strength heat shrinkable polyester film 10m wide and 10cm long
A sample is cut into a strip of m length. After this sample was left for 24 hours under conditions of a temperature of 23° C. and a relative humidity of 65%, the impact strength was measured using a tensile impact tester (manufactured by Toyo Seiki).

(4) Heat-resistant tubular heat-shrinkable polyester film
cc PUT bottle and heat-shrink it at 150"C for 10 seconds. Leave the bottle in hot water at 90°C for 30 minutes and check whether the heat-shrinked film has loosened.

(5) Glass transition temperature JIS-7121 Based on.

by differential scanning calorimeter Measure.

(Margin below) Tai Feng Group 1 First, 100 mol% of terephthalic acid was used as the acid component.

A copolyester composition was prepared using 80 mol% of ethylene glycol and 20 mol% of neopentyl glycol as glycol components. The resulting copolymerized polyester A had a glass transition temperature of 69°C and an intrinsic viscosity of 0.
．． It was 67di/g.

Further, copolymerized polyester B was prepared using 70 mol% of terephthalic acid and 30 mol% of sepathic acid as acid components, and 45 mol% of ethylene glycol and 55 mol% of neopentyl glycol as glycol components. The resulting copolymerized polyester B had a glass transition temperature of 7° C. and an intrinsic viscosity of 0.70 d/g.

The heat-shrinkable film of this example was prepared in the following manner using the thus obtained copolymerized polyesters A and B as polyester components. Copolymerized with 50% by weight of polyethylene terephthalate (intrinsic viscosity 0.70 d/g) as a polyester component with a glass transition temperature of 35°C or higher.35% by weight of polyester A as a polyester component with a glass transition temperature of 34°C or lower. Polyester B was mixed in a proportion of 15% by weight. Furthermore, 0.05% by weight of silicon dioxide, based on the total weight of the mixture, was added to this mixture as an additive to obtain a polyester composition. This polyester composition was melt extruded at 290''C to obtain a film with a thickness of 190 μm.

After preheating this unstretched film at 120'C for 6 seconds,
It was stretched 4.7 times in one predetermined direction. The temperature conditions during stretching were set to 80°C up to A in the entire stretching process, and 70''C for the remaining A. After stretching, the temperature was cooled to 40°C while maintaining the tension state. The shrinkable film had a thickness of 40 μ-, and the heat shrinkage rates at 80° C. and 100° C. were 31% and 52%, respectively.Other physical properties are shown in Table 1.

Form this heat-shrinkable film into a tube.

After getting the shrink label and putting it on the PET bottle, 150
It was heat-shrinked by heating at ℃ for 10 seconds. The label shrunk uniformly throughout, and no spots were observed on the shoulder of the bottle, no wrinkles were observed on the high shrinkage area, and no looseness was observed at the end of the label. Further, no deformation of the bottle was observed. Based on these results and the physical property values shown in Table 1.

It can be seen that the heat-shrinkable film of this example has excellent low-temperature shrinkability and heat resistance.

Polyethylene phthalate (intrinsic viscosity 0.70 cd/g)
) 50% by weight and copolymerized polyester A (50% by weight), and the stretching ratio was set to 4.9 so that the maximum heat shrinkage rate was partially equal to that of the heat-shrinkable film of Example 1. A heat-shrinkable film was obtained in the same manner as in Example 1. The heat shrinkage at 80°C and 100'C was 16% and 50%, respectively. Other physical properties are shown in Table 1.
Shown below.

20Mold the heat-shrinkable film into a tube shape to obtain a shrink label, cover it with a PET bottle, and then heat it at 150°C for 1 hour.
Heat shrinkage was achieved by heating for 0 seconds. The label did not shrink uniformly and wrinkles remained in the high shrinkage areas. Also, 17
When the bottle was heat-shrinked by heating at 0''C for 10 seconds, some deformation was observed in the bottle.

Comparison team main polyethylene terephthalate (intrinsic viscosity 0.70d/g
) 50% by weight and 850% by weight of copolymerized polyester, except that the stretching ratio was set to 4.8 so that the maximum heat shrinkage rate matched that of the heat-shrinkable film of Example 1. A heat-shrinkable film was obtained in the same manner as in Example 1.

The heat shrinkage rate at 80℃ and 100℃ is 4
8% and 49%.

Other physical property values are shown in Table 1.

This heat-shrinkable film was formed into a tube shape to obtain a shrinkable label, which was placed over a PET bottle and then heated at 150°C for 10 minutes.
Heat shrinkage was achieved by heating for a second. Spotting occurred in one area due to non-uniform and rapid shrinkage of the label. When the heat shrinkage was performed by changing the heating time to 30 seconds, two spots did not occur, but loosening occurred in the high shrinkage portion at the top of the shrunk label.

Furthermore, when the label was heat-shrinked by heating at 130°C for 10 seconds, the label still did not shrink uniformly.

Wrinkles remained in high shrinkage areas. As described above, the heat-shrinkable films of the nine comparative examples had a high shrinkage speed.

Good shrinkage characteristics could not be obtained because the residual shrinkage stress rapidly decreased.

First, 80 mol% of terephthalic acid and 1.
Copolymerized polyester C using 20 mol% of 3-trimethyl-3-phenylindene-4,5-dicarboxylic acid and 100 mol% of ethylene glycol as the glycol component.
was prepared. The resulting copolymerized polyester C had a glass transition temperature of 98°C and an intrinsic viscosity of 0.69 dl/g.
Met.

Further, copolymerized polyester D was prepared 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 copolymerized polyester D is -20°C,
The intrinsic viscosity was 0.90 dJl/g.

The heat-shrinkable film of this example was prepared in the following manner using the thus obtained copolymerized polyesters C and D as polyester components. Copolymerized with 50% by weight of polyethylene terephthalate (intrinsic viscosity 0.70 di/g) as a polyester component with a glass transition temperature of 35°C or higher.40% by weight of polyester C as a polyester component with a glass transition temperature of 34°C or lower. Polyester D was mixed at a ratio of 1% per coat. Additionally, 0.05% by weight of silicon dioxide, based on the total weight of the mixture.

It was added to this mixture as an additive to obtain a polyester composition. This polyester composition was melt-extruded at 290°C to obtain a film with a thickness of 210 μm.

After preheating this unstretched film at 120° C. for 7 seconds, it was stretched 5.2 times in one predetermined direction. The temperature conditions during stretching were set to 90°C up to A in the entire stretching process, and 70°C for the remaining %. After stretching, the film was cooled to 50°C while maintaining tension. The obtained heat-shrinkable film is
At a thickness of 40 us, the heat shrinkage rates at 80''C and 100''C were 29% and 53%, respectively.

Form this heat-shrinkable film into a tube shape.

After getting the shrink label and putting it on the PET bottle, 15
Heat-shrinked by heating at 0'C for 10 seconds.

Good results as shown in Table 1 were obtained.

Comparison group main polyethylene phthalate (intrinsic viscosity 0.70di/g
) 5% by weight and 50% by weight of copolymerized polyester C, and the stretching ratio was set to 5.3 so that the maximum heat shrinkage rate matched the heat shrinkable film of Example 2. A heat-shrinkable film was obtained in the same manner as in Example 2.

The heat shrinkage rates at 80"C and 1oo"C were 8% and 48%, respectively. Other physical property values are shown in Table 1.

This heat-shrinkable film was formed into a tube shape to obtain a shrinkable label, which was placed over a PET bottle and heated at 15°C for 10 minutes.
Heat shrinkage was achieved by heating for a second. The label did not shrink uniformly and wrinkles remained in the high shrinkage areas. Also, 1
When thermal shrinkage was performed by heating at 70'C for 10 seconds, deformation was observed in a portion of the bottle.

Five-year-old polyethylene terephthalate (intrinsic viscosity 0.70 dl/
g) A mixture of 50% by weight and 50% by weight of copolymerized polyester D was used, except that the stretching ratio was set to 5.4 so that the maximum heat shrinkage rate corresponded to the heat-shrinkable film of Example 2. A heat-shrinkable film was obtained in the same manner as in Example 2. The heat shrinkage rates at 80°C and 100°C were 42% and 47%, respectively.

Other physical property values are shown in Table 1.

This heat-shrinkable film was shaped into a tube to obtain a shrinkable label, which was placed over a PET bottle and heated to 150°C for 10 hours.
Heat shrinkage was achieved by heating for a second. The label did not shrink uniformly and wrinkles appeared in the high shrinkage areas. In addition, when the heating time was changed to 30 seconds to eliminate one spot, loosening occurred in the high shrinkage area.

(Hereinafter, blank spaces) (Effects of the Invention) The heat-shrinkable polyester film of the present invention has excellent low-temperature shrinkability and heat resistance as described above.

Such a heat-shrinkable film provides a beautiful appearance and a strong packaging state when plastic products such as polyethylene or PET bottles are wrapped or bundled. Furthermore, when printing is performed, the stability of the printing pitch is excellent. The heat-shrinkable polyester film of the present invention is useful in a wide variety of packaging materials fields.

Highly useful.

that's all

Claims (1)

[Claims] 1. A heat-shrinkable polyester film made of a composition containing the following polyester components: 30 to 70% by weight of polyethylene terephthalate; 35°C
20 to 70% by weight of polyester and/or copolymerized polyester having a glass transition temperature or higher; and 34
Polyester and/or having a glass transition temperature below ℃
Or copolymerized polyester 1 to 30% by weight. 2. The heat shrinkage rate at 80℃ in one predetermined direction of the film is 20
% or more and has a heat shrinkage rate at 100° C. of 40% or more.