JPH09254257A - Heat-shrinkable polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the longitudinal sink of a film to make shrink finish appearance beautiful by specifying a shrinkage factor in hot water with specific temp. in one direction and the max. shrinkage rate in one direction in a dry oven. SOLUTION: A polyester heat-shrinkable film 2 is characterized by that a shrinkage factor in hot water of 75 deg.C in one direction is 0.1-30% and the max. shrinkage rate is 0.1-20%/sec at 100 deg.C and 0.1-30%/sec at 140 deg.C. Therefore, the film is pref. drawn by 3.0-6.0 times finally in one direction and pref. drawn by 1.0-1.8 times in the direction right-angled to this direction. Especially, treatment temp. in drawing in a main direction (main shrinkage direction) is set to Tg+0 deg.C-50 deg.C in preheating and gradually raised at a temp. of Tg-20 deg.C-+30 deg.C in drawing and temp. difference is provided to perform drawing. Further, by cooling the film held to an elongated or tensioned state after drawing while applying stress thereto or further succeedingly cooling the film, pre- and post-treatment characteristics become more well.

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 more particularly to vertical shrinkage wrinkles
The present invention relates to a heat-shrinkable polyester film which has very little distortion and shrinkage and is suitable for label applications.

[0002]

2. Description of the Related Art Tubular bodies formed of heat-shrinkable plastic films are, for example, containers, bottles (including plastic bottles), can rods (pipes, rods, wood, various rods), etc. Abbreviated as a category) or for bundling, particularly covering or partially covering these caps, shoulders, torso, etc., and used for the purpose of marking, protection, bundling, improvement of commercial value, etc. It is widely used in fields such as boxes, plates, bottles, rods, notebooks, etc., such as integrated packaging, or skin packs, which are closely adhered to a covered material, and can be used for applications that utilize shrinkage and shrinkage stress. Be expected. Conventionally, films made of polyvinyl chloride, polyethylene, etc. have been mainly used for the above-mentioned applications, but in recent years, heat shrinkage has been caused by the problem of flammability at the time of disposal or the recoverability after mounting in a PET bottle. Polyester film is attracting attention. However, many heat-shrinkable polyester films shrink rapidly, which is not satisfactory as a label shrink film. In order to avoid such a drawback, Japanese Patent Laid-Open No. 1-110931
The publication discloses a method of improving shrinkage finishability by significantly reducing the breaking elongation in the direction orthogonal to the main shrinkage direction. However, the film obtained by the method not only easily breaks when tension is applied in a process such as printing and labeling, but label breakage easily occurs when the normal transportation is performed with the contents filled, so that the label is easily broken. It was a film with very little practicality as a shrink film for automobiles. Further, JP-A-63-309424 discloses a method for obtaining a heat-shrinkable polyester film having improved shrink finish by controlling the shrinkability at 75 ° C.

[0003]

However, the film obtained by this method is not yet satisfactory as a shrink film for labels. For example, in PET bottles, which are the mainstream of recent beverage containers, the shape of the bottle is rapidly changing from a conventional round shape to a square shape in terms of practicality such as storage in a refrigerator. When the heat-shrinkable polyester film disclosed in the above-mentioned JP-A-63-309424 is mounted on this rectangular bottle, the lower part of the label after shrinking is curved in an arched shape (referred to as vertical sink). It has a serious defect as a shrink film for labels in that it is liable to occur. Therefore, in view of the fact that rectangular PET bottles are the mainstream of beverage containers, it is necessary to develop a heat-shrinkable polyester film in which vertical shrinkage is unlikely to occur.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a heat shrinkable polyester film having a certain shrinkage property is less likely to cause vertical shrinkage,
The present invention has been completed. That is, it has been found that a heat-shrinkable polyester film having a certain shrinkage property can suppress vertical shrinkage, which is considered to be caused by a rapid shrinkage in a shrinking tunnel, so that a beautiful shrink finish appearance can be obtained. The polyester-based heat-shrinkable film of the present invention needs to have a shrinkage ratio of 0.1% or more and 30% or less in 75 ° C. hot water in one direction. If the shrinkage ratio in unidirectional hot water at 75 ° C is 0.1% or less, the finish will be poor. On the other hand, when the shrinkage ratio in hot water at 75 ° C. in at least one direction is 30% or more, the shrinkage becomes rapid and shrinkage unevenness and vertical shrinkage increase.

In the polyester-based heat-shrinkable film of the present invention, it is preferable that the shrinkage rate in unidirectional 75 ° C. hot water is 5% or more and 30% or less.
When the shrinkage ratio in the unidirectional hot water at 75 ° C. is 5% or less, the finishability may be slightly insufficient. On the other hand, at least one
If the shrinkage ratio in hot water at 75 ° C in the direction is 30% or more, the shrinkage unevenness and vertical shrinkage increase due to the rapid shrinkage. Further, in the polyester-based heat-shrinkable film of the present invention, it is more preferable that the shrinkage rate in unidirectional 75 ° C. hot water is 10%.
It is necessary to be 30% or less. If the shrinkage ratio in unidirectional hot water at 75 ° C is 10% or less, the finish may be slightly insufficient depending on the conditions. On the other hand, when the shrinkage ratio in hot water at 75 ° C. in at least one direction is 30% or more, the shrinkage becomes rapid and shrinkage unevenness and vertical shrinkage increase.

In the polyester heat-shrinkable film of the present invention, the maximum shrinkage rate at 100 ° C. is 0.1% / sec to 20% / sec, and at 140 ° C. is 0.1% / sec to 30% / sec. It is necessary to be. This maximum contraction rate is 100
When the temperature is 20% / sec or more at ℃, rapid shrinkage causes uneven shrinkage and vertical shrinkage. Even when the maximum shrinkage rate at 140 ° C is 30% / sec or more, the shrinkage becomes sharp and uneven shrinkage and vertical shrinkage increase. On the other hand, at 100 ° C and below 0.1% / sec, sufficient shrinkage cannot be obtained, and the finished product tends to be defective.

In the polyester heat shrinkable film of the present invention, the maximum shrinkage rate is preferably 100 ° C.
1% / sec or more and 20% / sec or less, 140 ° C or more 10% / sec or more 30
% / Sec or less is required. If the maximum shrinkage rate is 20% / sec or more at 100 ° C, rapid shrinkage causes large shrinkage unevenness and vertical shrinkage. Maximum shrinkage rate is 1 at 100 ℃
If it is less than% / sec, the finish may be insufficient depending on the conditions. If the maximum shrinkage rate at 140 ° C is 30% / sec or more, rapid shrinkage causes large shrinkage unevenness and vertical shrinkage. If the maximum shrinkage rate is 140 ° C and 10% / sec or less, the finish may be insufficient depending on the conditions.

In the polyester heat-shrinkable film of the present invention, more preferably, the maximum shrinkage rate is
It should be 5% / sec or more and 20% / sec or less at 100 ° C and 15% / sec or more and 30% / sec or less at 140 ° C. If the maximum shrinkage rate is 20% / sec or more at 100 ° C, rapid shrinkage causes large shrinkage unevenness and vertical shrinkage. Maximum contraction speed is 100
If the temperature is 5% / sec or less at 0 ° C, the finish may be slightly insufficient depending on the conditions. Maximum shrinkage rate at 140 ° C is 30
If it is more than% / sec, rapid shrinkage causes uneven shrinkage and vertical shrinkage. If the maximum shrinkage rate is 140 ° C and 10% / sec or less, the finish may be slightly insufficient depending on the conditions.

The polyester resin used in the heat-shrinkable polyester film of the present invention contains an aromatic dicarboxylic acid or its ester-forming derivative as a dicarboxylic acid component and a polyhydric alcohol component as main components. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalene-1.4- or -2,6-dicarboxylic acid, and the like. Examples of these ester derivatives include derivatives such as dialkyl esters and diaryl esters. Further, an aliphatic dicarboxylic acid can be contained within the range that does not impair the effects of the present invention. Examples of the aliphatic dicarboxylic acid that can be used in the present invention include glutaric acid, adipic acid, sebacic acid, dimer acid, azelaic acid, oxalic acid and succinic acid.

Examples of the polyhydric alcohol component of the polyester resin used in the heat-shrinkable polyester film of the present invention include propylene glycol, triethylene glycol, butylene glycol, diethylene glycol, neopentyl glycol, cyclohexanedimethanol, bisphenol compounds or derivatives thereof. Ethylene oxide adduct, trimethylolpropane, glycerin, pentaerythritol, polyoxytetramethylene glycol, polyethylene glycol and the like. Also,
Although not a polyhydric alcohol, epsilon caprolactone can be used as well.

The polyester resin used in the heat-shrinkable polyester film of the present invention is not limited to the copolymerization component. The polyester may be used alone or in combination of two or more. When two or more kinds are used in combination, it may be a combination of polyethylene terephthalate and a copolyester or a combination of copolyesters. Further, it may be a combination with a homopolyester such as polybutylene terephthalate or polycyclohexylene dimethyl terephthalate. It is more preferable to use two or more kinds of polyester in combination, because a film having various properties can be produced. The polyester can be produced by melt polymerization by a conventional method, but the polyester is not limited to this and may be a polyester obtained by another polymerization method. The degree of polymerization of the polyester is 0.3 in terms of intrinsic viscosity.
It is preferably not less than 1.2 and not more than 1.2.

Further, in the present invention, polyarylate having a Tg of 90 to 160 ° C. may be mixed. Further, if necessary, a lubricant such as titanium dioxide, silica, kaolin, calcium carbonate or the like may be added, and an antistatic agent, an anti-deterioration agent, an anti-UV agent or a dye as a colorant may be added. I can. The intrinsic viscosity of the film base material is preferably 0.50 or more and 1.30 dl / g or less. A film obtained by any method such as an extrusion method or a calender method using such a polymer is finally 2.5 times to 7.0 times in one direction, preferably 3.0 times.
Stretching is performed from double to 6.0, and 1.0 to 2.0 or less, preferably 1.0 to 1.8 in the direction perpendicular to the direction. However, when stretched over 2.0 times,
The heat shrinkage in the direction perpendicular to the main shrinkage direction becomes too large, and the finish becomes wavy. In order to suppress this waviness, it is recommended that the heat shrinkage rate be 15% or less, preferably 9% or less, and more preferably 7% or less. The stretching method is not particularly limited, and stretching methods such as roll stretching, long gap stretching, and tenter stretching are applied, and the shape may be flat or tubular. In addition, sequential biaxial stretching is effective for stretching, and either order may be first. The heat setting in the stretching is carried out according to the purpose, but in order to prevent the dimensional change under high temperature in summer, it is 30 to 1
It is recommended to pass a heating zone at 50 ° C. for about 1 to 30 seconds. Further, before or after such processing, or both may be expanded up to 70%.

In order to exert the preferable characteristics of the present invention,
In addition to the above stretching ratio, it is effective to stretch at a temperature near the average glass transition temperature (Tg) of the polymer composition and in several stages (preferably at least 2 stages). . Especially, in the above-mentioned treatment temperature in the main-direction stretching (main shrinkage direction), the preheating is Tg + 0 ° C to +5
It is important that the stretching is carried out at a temperature difference of 0 ° C. or less so that the temperature gradually rises at a temperature within the range of Tg−20 ° C. to + 30 ° C. Further, it is also effective to stop the stretching at one end during the stretching, provide a relaxation step, and then carry out the second stretching step so that the total stretching ratio becomes a predetermined stretching ratio.

After stretching, the film is cooled while applying tension to the film while keeping the film in a stretched or tensioned state, or by further cooling it, so that the pre- and post-treatment properties become better and more stable. In addition, since the maximum shrinkage speed is reduced by stretching in multiple stages of temperature in this way, a film that is less likely to cause shrinkage unevenness that shrinks with a small speed difference even with respect to temperature unevenness of the heat shrink tunnel is obtained. can get.

The film of the present invention will be described below from the viewpoint of use. Boiling and retorting are performed in packaging applications, especially in packaging of foods and beverages. No existing heat-shrinkable film can withstand these treatments sufficiently. The film of the present invention can withstand heat sterilization by boil treatment or retort treatment, and also the appearance of the original film, and further the finishability by heat shrinkability is also good, and also polyvinyl chloride or polystyrene heat shrink It has a higher heat shrinkage stress than the film, and is also excellent in cohesion. The details will be described below.

(A) Impact resistance One of the roles of the shrink film is to prevent the package from being broken or the load collapsed. For that purpose, it has a high impact resistance and a large shrinkage in the main direction. It is necessary to get a rate. In that respect, the film of the present invention has a high shrinkage ratio and a high impact resistance, so that a beautiful packaging can be obtained, and further, excellent durability is exhibited in terms of protection of an article to be packaged. This tendency is proved by the drop test. (B) Printability The conventional film has inherent drawbacks with respect to the generation of pinholes and the adhesion to ink by halftone printing, but the polyester film has chemical resistance and adhesiveness when made into a copolymer. And the printability was improved. (C) Industrial waste problem In recent years, the use of plastic bottles has been rapidly spreading. When considering the recovery of such a bottle, it is preferable to form the same material, and it is advantageous to apply the film of the present invention to the packaging of a polyester bottle. (D) Shrinkage unevenness The film of the present invention has a high shrinkage ratio and a high shrinkage stress, and since the shrinkage speed is appropriate, shrinkage unevenness does not occur.

EXAMPLES The present invention will be described in detail below by showing Examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. The measuring method used in the present invention is shown below. (1) Maximum shrinkage speed First, a DF-42 type dry oven manufactured by Yamato Co., Ltd. is set in a state where the air volume is set to 0 and the air damper is closed, set to the measurement temperature, and the temperature is raised. Next, the sample size is the main shrinkage direction 5
cm, 4cm in the orthogonal direction, and hang it with a small load of 4.7g. Furthermore, the sample was placed in a dry oven heated to a predetermined temperature for 0 seconds, and the time change of contraction was recorded with a video camera through a window modified to allow external observation, and quantification was performed every second. It was The maximum change in the shrinkage rates with respect to the time thus obtained was defined as the maximum shrinkage rate.

(2) Shrinkage rate of hot water The temperature of the hot water bath is raised to 75 ° C. Next, the sample size is cut out into a square with the main shrinking direction of 10 cm and the orthogonal direction of 10 cm, and it is hung on a jig. Furthermore, it is poured into hot water heated to a predetermined temperature for 0 second, taken out after 10 seconds, and cooled and fixed with water. Quantification was performed by a method of measuring the shrinkage ratio after cooling and fixing.

(3) SH-1500-L made by Tatehike Fuji Astec INC
2L square PET at 1 zone temperature / 2 zone temperature: 85 ° C / 90 ° C with a passage time of 10 seconds using a steam tunnel of
Tests were carried out in bottles (commercial Suntory bottles used in natural waters of the Southern Alps). As for the measurement of vertical sinking, as shown in FIG. 1, in the long side of the bottle, the label lower portion at the bottle end and the label lower portion shift at the central portion were measured. It should be noted that a film in which three colors were printed with grass, gold and white inks manufactured by Toyo Ink Mfg. Co. was used. The measured value was 4 mm or less as a passing level.

(4) Shrinkage Finishability A steam tunnel similar to Tateike and a square PET bottle were subjected to the same test as Tateike and the finish was visually determined. The finish rank is 5
Graded: 5: Best finish 4: Good finish 3: Some shrinkage unevenness (within 2 places) 2: Shrinkage unevenness (3-6 places) 1: Many shrinkage unevenness (6 places or more) 4 The above is the passing level. 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 have a good shrink finish (there are no defects such as wrinkles and insufficient shrinkage), and vertical shrinkage is unlikely to occur. Therefore, it can be said that the heat-shrinkable polyester film for labels has high quality and high practicality. On the other hand, the film obtained in Comparative Example 1 is likely to cause vertical shrinkage, and the film obtained in Comparative Example 2 suffers from insufficient shrinkage, so that it can be said that all of them are inferior in quality as the heat-shrinkable polyester film for labels. Further, the film obtained in Comparative Example 3 has a small effect of improving vertical sinking.

Example 1 Using a stainless steel autoclave, a composition of dimethylene terephthalate 70 mol% as a dibasic acid component, dimethylene naphthalate 30 mol% and ethylene glycol mol% and neopentyl glycol mol% as a glycol component was used. , Glycol was added to be twice the mole of methyl ester, and transesterification was carried out using 0.05 mol of zinc acetate (based on the acid component) as a transesterification catalyst. After that, 0.025 mol of antimony trioxide (based on the acid component) as a catalyst and 0.05 mol (based on the acid component) of an additive were polycondensed.
As a result, 70 mol% of terephthalic acid component, 30 mol% of 2,6 naphthalenedicarboxylic acid component, 50 mol% of ethylene glycol component and 50 mol of neopentyl glycol component.
A polyester consisting of mol% was obtained. This copolymer had an intrinsic viscosity of 0.68 dl / g. This polyester was melt extruded at 280 ° C. to obtain an unstretched film having a thickness of 200 μm. The film was stretched 1.5 times in the machine direction at 120 ° C., then the residual heat was 110 ° C. for 3 seconds, and then the first in the transverse direction.
Gradual stretching was carried out at 110 ° C. for 1.5 times, then at 110 ° C. for a fixed length of 3 seconds, and subsequently stretched to a total of 4.1 times in two zones of 115 ° C. and 120 ° C. Then, heat treatment was performed at 113 ° C. for 5.5 seconds to obtain a heat shrinkable film having a thickness of 40 μm. The physical properties of the obtained film are shown in Table 1.

Example 2 According to the polymerization method of Example 1, 30 mol% of a terephthalic acid component and 70 mol of a 2,6 naphthalenedicarboxylic acid component,
A polyester comprising 40 mol% of ethylene glycol component, 54 mol% of neopentyl glycol component and 6 mol% of polytetramethylene glycol (molecular weight 650) component was obtained. This copolymer had an intrinsic viscosity of 0.71 dl / g. This polyester was melt extruded at 290 ° C. to obtain an unstretched film having a thickness of 180 μm. The film was stretched 1.4 times in the machine direction at 105 ° C, and then the residual heat was 100 ° C.
3 seconds, then the 1st stage stretching in the transverse direction at 88 ° C by 1.5 times,
Then, hold for a fixed length at 88 ° C for 3 seconds, then continue at 95 ° C,
It was divided into two zones of 100 ° C. and stretched to a total of 4.1 times. Then heat treatment at 82 ° C for 5.5 seconds to a thickness of 40 μm.
A heat shrinkable film of The physical properties of the obtained film are shown in Table 1.

Comparative Example 1 By the polymerization method of Example 1, 10 mol% of terephthalic acid component and 90 mol% of 2,6 naphthalenedicarboxylic acid component,
A polyester composed of 45 mol% of ethylene glycol component and 55 mol% of neopentyl glycol component was obtained. This copolymer had an intrinsic viscosity of 0.70 dl / g. This polyester is melt extruded at 295 ° C and the thickness is 180 μm.
Was obtained. Preheat the film to 125 ° C.,
It was stretched for 3 seconds and then transversely at 120 ° C. up to 4 times. Then, heat treatment was performed at 140 ° C. to obtain a heat shrinkable film having a thickness of 40 μm. The physical properties of the obtained film are shown in Table 1.

Comparative Example 2 According to the polymerization method of Example 1, 95 mol% of terephthalic acid component, 5 mol% of 2,6 naphthalene dicarboxylic acid component, 30 mol% of ethylene glycol component, 69 mol% of neopentyl glycol component and polytetra tetracarboxylic acid. A polyester consisting of 1 mol% of a methylene glycol (molecular weight 650) component was obtained. This copolymer had an intrinsic viscosity of 0.69 dl / g. This polyester is melt extruded at 285 ° C. to a thickness of 1
An unstretched film of 80 μm was obtained. Preheat the film 1
It was stretched at 20 ° C. for 3 seconds and then in the transverse direction at 80 ° C. up to 4.1 times. Then, heat treatment was performed at 75 ° C. to obtain a heat shrinkable film having a thickness of 40 μm. Table 1 shows the physical properties of the obtained film.
Shown in

Comparative Example 2 By the polymerization method of Example 1, 90 mol% of terephthalic acid component and 10 mol% of 2,6 naphthalene dicarboxylic acid component,
A polyester comprising 65 mol% of ethylene glycol component and 35 mol% of neopentyl glycol component was obtained. This copolymer had an intrinsic viscosity of 0.71 dl / g. This polyester is melt extruded at 275 ° C and the thickness is 180 μm.
Was obtained. Preheat the film to 125 ° C.,
It was stretched for 3 seconds and then in the transverse direction at 80 ° C. up to 4.0 times.
Then, heat treatment was performed at 92 ° C. to obtain a heat shrinkable film having a thickness of 40 μm. The physical properties of the obtained film are shown in Table 1.

Comparative Example 3 According to the polymerization method of Example 1, 82 mol% of terephthalic acid component, 18 mol% of isophthalic acid component, 95 mol% of ethylene glycol component and 5 mol% of polytetramethylene glycol (molecular weight 1000) component. I got polyester. This copolymer had an intrinsic viscosity of 0.69 dl / g. This polyester is melt extruded at 285 ° C. to a thickness of 1
An unstretched film of 80 μm was obtained. Preheat the film 8
It was stretched at 5 ° C. for 3 seconds and then in the transverse direction at 65 ° C. up to 4.0 times. Then, heat treatment was performed at 60 ° C. to obtain a heat shrinkable film having a thickness of 40 μm. The physical properties of the obtained film are shown in Table 1.

[0027]

[Table 1] As is clear from Table 1, it was found that the film of the present invention had a desired finish.

[0028]

EFFECTS OF THE INVENTION A heat-shrinkable polyester film exhibiting particularly suitable heat-shrinkability in the field of packaging materials such as coating or binding and having good finish is provided.

[Brief description of drawings]

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

[Explanation of symbols]

 1 PET bottle 2 Shrink film 3 Vertical sink

Claims (1)

[Claims] 1. A heat-shrinkable polyester film having a unidirectional shrinkage rate in hot water of 75 ° C. of 0.1% or more and 30% or less and a maximum unidirectional shrinkage rate in a dry oven of 0.1% / 100 ° C. Seconds to 20% / second, 140 ° C
A heat-shrinkable polyester film characterized by being 0.1% / sec or more and 30% / sec or less.