JP2001096616A - Heat-shrinkable polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable film containing a polyester resin as a main raw material in which the generation of wrinkles, distortion, shrinkage spots, etc. is minimized. SOLUTION: In a heat-shrinkable polyester film, the shrinkage rate in the main shrinkage direction of the film at 70 deg.C for 10 sec in hot water is at least 15%, the shrinkage rate at 80 deg.C for 10 sec in hot water is at least 35%, the difference between the above shrinkage rates is 25% or below, the average shrinkage rate in the direction perpendicular to the main shrinkage direction at 70-90 deg.C is 10% or below, and the maximum shrinkage stress in the main shrinkage direction measured in 80 deg.C silicone oil is 40-95 kg/cm2.

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 which can be suitably used as a shrinkable label for bottles and the like. An object of the present invention is to provide a heat-shrinkable film containing a polyester resin as a main raw material, which prevents deformation and shrinks slowly to suppress wrinkles, distortions, shrinkage spots, and the like of the film.

[0002]

2. Description of the Related Art A heat-shrinkable film widely used for shrink wrapping, shrink-wrapping wrapping, plastic container labels, glass container destruction and scattering prevention packaging, labels, cap seals, etc. Vinyl (hereinafter sometimes referred to as "PVC") is best known and has been used. This is because a heat-shrinkable film made of PVC satisfies user requirements relatively widely, including practical properties such as mechanical strength, rigidity, optical properties, shrinkage properties, and cost. However, P
Although VC has excellent practical properties and cost performance as a heat-shrinkable film, it generates toxic gas containing chlorine when incinerated after disposal. It has become

As one of the materials other than PVC, a styrene-butadiene block copolymer (hereinafter referred to as "S
A heat-shrinkable polystyrene film whose main material is sometimes referred to as "BS" has been proposed and used, but this polystyrene-based film has less shrinkage spots and wrinkles during heat shrinkage, and has excellent shrink finish. Although,
Poor rigidity at room temperature, high natural shrinkage (slightly higher than normal temperature, for example, the film shrinks slightly before use in summer), and has problems such as poor rupture resistance. ing.

Further, as a material other than PVC, a heat-shrinkable polyester film using a polyester resin as a main material has been proposed and used. Although this heat-shrinkable polyester film has a very low rigidity at room temperature and a very low natural shrinkage rate, it tends to cause uneven shrinkage and wrinkles during heat shrinkage and tends to be inferior in shrink finish compared to a film made of PVC or SBS. Can be For plastic bottle labels and the like, for which demand is expected to increase more and more in recent years, a heat-shrinkable polyester film capable of obtaining a highly shrink-finished appearance in a relatively short time and at a relatively low temperature has been desired.

[0005]

According to the present invention, as a result of various studies for solving the above problems, it has been found that the above problems can be solved by imparting specific shrinkage characteristics to a polyester film. It has been reached. That is, the gist of the present invention is that, in a heat-shrinkable polyester film, the shrinkage rate in hot water of 70 ° C. for 10 seconds in the main shrinkage direction of the film is 15% or more,
The shrinkage for 10 seconds in hot water at 80 ° C. is 35% or more, the difference in the shrinkage is 25% or less, and the average shrinkage in the direction perpendicular to the main shrinkage direction at 70 ° C. to 90 ° C. is 10%. % Or less, and the maximum shrinkage stress in the main shrinkage direction measured in silicone oil at 80 ° C. is 40 to 95 kg.
/ Cm ^2, which is a heat-shrinkable polyester film.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. In the film of the present invention, the shrinkage of the film needs to be in the following range. The shrinkage rate in hot water of 70 ° C. in the main shrinkage direction for 10 seconds is 15% or more, preferably 20% or more,
The shrinkage for 10 seconds in hot water at ℃ is 35% or more, more preferably 40% or more, and the difference in the shrinkage must be 25% or less. Further, it is important that the average shrinkage in the longitudinal direction at 70 ° C. to 90 ° C. is 10% or less, more preferably 7% or less. In recent labeling processes for heat-shrinkable films, shrinking the film after filling the contents into a container is becoming the mainstream.In this method, in order to avoid quality deterioration due to temperature rise of the contents, There is a need to lower the temperature.

Therefore, it is necessary to start shrinking at a temperature as low as possible. However, a conventional heat-shrinkable polyester film has a problem that shrinkage and wrinkles occur in the finished product after heat shrinkage since shrinkage starts sharply from a low temperature, and the commercial value is reduced. In the film of the present invention, it is important to provide the above-mentioned shrinkage ratio in order to provide a film free from shrinkage spots and wrinkles even at a low temperature. By giving the above shrinkage,
Upon entering the shrinker, the film begins to shrink in the cold state, and gradually shrinks as the temperature increases during passage. 70 ° C and 8
It is important that the difference in the shrinkage at 0 ° C. is 25% or less. Even if the low-temperature shrinkability is greatly imparted, if the material shrinks rapidly without going through a smooth shrinking process, it is difficult to obtain a good shrink finish.

Further, when the film shrinks in the direction perpendicular to the main shrinkage direction of the film in the shrinkage temperature range, shrinkage occurs in the label vertical direction, and particularly, the average shrinkage in the vertical direction at 70 ° C. to 90 ° C. exceeds 10%. In addition, uneven spots and wrinkles are generated in the shrink finish, and the commercial value is reduced. further,
The shrinkage stress at the time of shrinkage also greatly affects the finish.
The maximum shrinkage stress in the main shrinkage direction of the film of the present invention measured in silicone oil at 80 ° C. is 40.
It must be in the range of 95 kg / cm ² . If the maximum shrinkage stress exceeds 95 kg / cm ² , uneven shrinkage of the film during heating will cause uneven shrinkage and wrinkles to occur extremely easily. Conversely, if it is less than 40 kg / cm ² , the wrapped body lacks the binding property. Since shrinkage spots and wrinkles are more likely to occur in the case of hot air shrinkers than in the case of steam shrinkers, it is preferable to set the maximum shrinkage stress low even in the above range when using hot air shrinkers.

In the heat-shrinkable polyester film of the present invention, it is necessary to devise material properties in order to exhibit the above-mentioned shrinkage properties. Originally, a polyester resin is a crystalline resin, and is oriented and crystallized by stretching a film. Therefore, it is necessary to lower the crystallinity of the constituent material itself. However, if the constituent resin is made completely amorphous, it becomes difficult to sufficiently satisfy the required properties as a heat-shrinkable film. Therefore, it is important to impart appropriate crystallinity. An amorphous polyester film has an abrupt rise of a shrinkage curve and a very high shrinkage stress according to its viscoelastic properties. On the other hand, by imparting appropriate crystallinity, the shrinkage rate at high temperature is reduced, and as a result, it is expected that the shrinkage curve curve becomes gradual and the shrink finish is improved. Further, by imparting crystallinity, the thickness accuracy of the stretched film is affected.
Although there are several methods for improving the thickness accuracy depending on the stretching conditions, the crystallinity of the constituent material resin most affects the thickness accuracy.

When the film to be heated is partially viewed at an early stage of the stretching process, the film may show an uneven temperature distribution. In this case, stretching starts at a higher temperature. When the resin used is an amorphous resin,
The stretched and thinned portions are further stretched, and the entire film becomes unevenly stretched. On the other hand, when there is crystallinity, the initially stretched portion becomes thinner and the stretching stress increases due to the orientation crystallization, so that the non-stretched portion is easily stretched, and as a result, the film is uniformly stretched over the entire film, thereby increasing the thickness. Accuracy improves.

As the polyester resin used as a material of the film of the present invention, an ethylene terephthalate copolymer polyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component as a main component is preferably used. As the copolymerization component, isophthalic acid, adipic acid, sebacic acid and the like as dicarboxylic acids, neopentyl glycol, diethylene glycol as diol components,
Copolymerized polyesters using 1,4-cyclohexanedimethanol, 1,4-butanediol, and the like can be easily obtained industrially and have good shrinkage, which is preferable. In the copolyester used in the present invention, 100 mol% of a dicarboxylic acid component and 100 mol% of a diol component
Of the total amount of 200 mol% of the copolymer component is 20 mol%
It is more preferably at least 30 mol%.
Copolymerized polyesters having a total copolymerization component of less than 20 mol% are not preferred because the crystallinity when formed into a film is high, the shrinkage finish is poor, and the solvent sealing property is inferior.

It is preferable to mix a butylene terephthalate other than the ethylene terephthalate polyester and a copolymer thereof with the polyester. The most common method is to incorporate polybutylene terephthalate. Since polybutylene terephthalate has high crystallinity, even a small addition amount tends to impart crystallinity to the entire film. However, it has the effect of lowering the glass transition temperature (Tg) of the entire film. Therefore, the blending amount of polybutylene terephthalate is preferably 5 to 40% by weight. If the amount is less than 5% by weight, the effect of lowering the Tg and the imparting of crystallinity are insufficient. If the amount exceeds 40% by weight, the crystallinity becomes too high, and the shrinkage is reduced to a practical level or more, and the solvent sealing property and ink adhesion are reduced. It is easy to adversely affect the properties. As a measure of the crystallinity, the measurement result of the calorific value (ΔHm) required to melt all the crystals when the film is heated at a heating rate of 10 ° C./min by a differential scanning calorimeter (DSC) is 30.
It is preferable to adjust to a range of J / g or less.

In the film of the present invention, it is preferable to blend polybutylene terephthalate obtained by copolymerizing polyether in order to impart the above-mentioned shrinkage characteristics. Polybutylene terephthalate itself has a very low Tg, and the effect of lowering Tg by blending can be expected to be sufficient.However, only the amount of polybutylene terephthalate added, in order to impart more low-temperature shrinkage, as described above, Crystallinity will rise too much, solvent sealing properties,
Ink adhesion tends to decrease. It is preferable to use polybutylene terephthalate copolymerized with a polyether in order to further exhibit the effect of lowering Tg. In particular, among polyethers, polytetramethylene glycol is the best in terms of polymerization and quality. The content of polytetramethylene glycol in the polybutylene terephthalate is preferably from 0.3 to 10 mol%, more preferably from 0.5 to 3 mol%, in the diol component. If the polytetramethylene glycol unit is less than 0.3 mol%, the physical properties do not change as in the case of polybutylene terephthalate alone. On the other hand, if it exceeds 10 mol%, the compatibility with other mixed resins is deteriorated and the transparency tends to be lowered.

The intrinsic viscosity of the film of the present invention is 0.5
Above, preferably 0.6 or more. If the intrinsic viscosity of the film is less than 0.5, the rupture resistance tends to decrease. Further, in the film of the present invention, in order to improve the lubricity of the film, organic lubricants, fine particles such as inorganic lubricants may be contained, and an antistatic agent or the like may be applied by a kneading method or a coating method. It is possible. The raw materials used in the present invention are not limited to being used in a state where a polyester resin having each component is mixed, but it is also possible to prepare and use a polyester equivalent to the above contents in a polymerization stage.

Next, the method for producing the film of the present invention will be described specifically, but it is not limited to the following method. The copolymerized polyester obtained by the polycondensation reaction was mixed, and 200
Melt extrude at a temperature of ~ 320 ° C. When extruding, T
A method such as a die method or a tubular method may be employed. T
When the die method is used, the material is rapidly cooled on a casting drum having a surface temperature of 15 to 80 ° C. after extrusion to a thickness of 30 to 300 μm.
m of unstretched film. The obtained unstretched film is rolled at a roll temperature of 60 to 1 using a heated longitudinal stretching roll.
1.0-2.0 times, preferably 1.0-1.
Stretching 5 times, after longitudinal stretching, stretching temperature 6 using a tenter
Stretched 1.7 to 7.0 times at 0 to 120 ° C,
Heat treatment at a temperature of 0 ° C. and winding.

Here, among the various characteristics of the film, the shrinkage ratio mainly depends on the stretching ratio and the stretching temperature. Therefore, from the viewpoint of increasing the shrinkage ratio in the main shrinking direction, high-magnification and low-temperature stretching are preferred. On the other hand, the shrinkage stress also depends mainly on the stretching temperature, and the shrinkage ability increases as the stretching ratio increases and the stretching temperature decreases, and there is also the effect of the heat treatment (annealing, particularly relaxation heat treatment) after the stretching. In order to set a gentler value than the shrinkage ratio, one method is to adjust the draw ratio while stretching at a relatively high temperature, and perform a heat treatment to improve the flatness of the film after stretching and to adjust the shrinkage ratio. In this case, it is performed at a low temperature which does not promote crystallization of the polyester. As a result, it is possible to obtain a film exhibiting a gradual shrinkage characteristic while suppressing the shrinkage stress, which greatly affects the behavior of the film at the time of heat shrinkage, at a low level. Specific temperature conditions can be appropriately set according to the type of polyester used.

Further, in the present invention, during the stretching step,
Before or after stretching, one or both surfaces of the film may be subjected to a surface activation treatment such as corona discharge treatment to improve the adhesiveness of the film to the printed layer.
In addition, during the stretching step, before or after the stretching, it is possible to improve the adhesiveness, antistatic property, slipperiness, light-shielding property and the like of the film. Furthermore, for example, using the above polyester resin for the core layer, providing a copolymerized polyester resin layer having a lower crystallinity than the polyester resin in the surface layer,
It can also be a laminated film by a co-extrusion method or the like.

[0018]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples. The method for evaluating the characteristics of the film is as follows. 1) Shrinkage rate The shrinkage rate in the main shrinkage direction and the vertical direction was measured by the following method. The film was cut out to a size of 150 mm in the measurement direction and 25 mm in the vertical direction to prepare a sample, and marked with 100 mm intervals in the sample measurement direction.
It was immersed in a warm water bath at 80 ° C. and 80 ° C. for 10 seconds, and determined by the following equation. Shrinkage = [(100−L) / 100] × 100 (%) (L is the distance between marked lines after shrinkage; unit: mm) The average shrinkage in the vertical direction is 70 ° C., 75 ° C.
The degree of shrinkage when immersed in a warm water bath at 80 ° C, 80 ° C, 85 ° C, and 90 ° C for 10 seconds was averaged.

2) Heat Shrinkage Stress A sample cut into a strip having a width of 15 mm and set in a 150 mm-spaced chuck so that the main shrinkage direction is the longitudinal direction is immersed in silicone oil at 80 ° C. The maximum shrinkage stress was measured.

3) DSC measurement Differential thermal scanning calorimeter DSC-7 manufactured by PerkinElmer Co., Ltd.
From the peak area of the thermograph at the time of the first scan when the film was heated at a heating rate of 10 ° C./min using a mold, the heat quantity ΔHm required to melt all the crystals was determined.

4) Shrinkage Appearance The film with lattices was formed into a cylindrical shape, covered with a PET bottle, passed through a steam shrink tunnel, and attached to the bottle, and the shrinkage appearance was evaluated. The temperature of the steam shrink was 65 ° C, 70 ° C, 75 ° C, and 80 ° C. Labels with no lattice distortion and excellent adhesion and a beautiful finish (○), insufficient shrinkage, distortion and wrinkles, etc., but not practically hindered (△) to (○), insufficient shrinkage ,
Those with little distortion and wrinkles but not complete but having some problem in practical use were rated (△), and those with insufficient shrinkage or finished properties that did not completely reach the practical level were rated (x).

(Examples 1 to 4, Comparative Examples 1 to 5) A dicarboxylic acid component comprising 90 mol% of terephthalic acid and isophthalic acid (I
PA) 10 mol%, the diol component is ethylene glycol 80 mol%, and 1.4-cyclohexanedimethanol 20
Modified polybutylene terephthalate composed of terephthalic acid as a dicarboxylic acid component, 97 mol% of a diol component and 3 mol% of polytetramethylene glycol (molecular weight: about 1000) in a copolyester composed of arbitrary moles. And melt-extruded at 270 ° C. to obtain an unstretched film. The obtained unstretched film was uniaxially stretched in the transverse direction by a tenter under the conditions shown in Table 1, and then heat-treated to obtain a film having a thickness of 50 µm. Note that only Comparative Example 1 was stretched 1.4 times in the machine direction. Table 2 shows the evaluation results of the characteristics of each film.

[0023]

[Table 1]

[Table 2]

Regarding Examples 1 to 4 and Comparative Examples 1 to 5, when the film shrinkage at 70 ° C. and 80 ° C. and the maximum shrinkage stress in the main shrinkage direction at 80 ° C. are all within the specified ranges, good results are obtained. It can be seen that a shrink finish is obtained. Also, it can be seen that the above shrinkage property can be provided by blending polybutylene terephthalate copolymerized with polytetramethylene glycol.

[0025]

According to the present invention, it is possible to obtain a film which can sufficiently cope with a low-temperature shrinker, has very little wrinkles, strains and shrinkage during shrinkage, and has excellent shrinkage characteristics.

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Claims (3)

[Claims] 1. A heat-shrinkable polyester film which is heated in hot water at 70 ° C. in the main shrinkage direction of the film.
The shrinkage rate per second is 15% or more, and the shrinkage rate for 10 seconds in hot water at 80 ° C is 35% or more, and the difference in the above shrinkage rates is 25% or less, with respect to the main shrinkage direction from 70 ° C to 90 ° C. A heat-shrinkable polyester film characterized by having an average shrinkage in the vertical direction of 10% or less and a maximum shrinkage stress in the main shrinkage direction of 40 to 95 kg / cm ² measured in silicone oil at 80 ° C. 2. The heat-shrinkable polyester film according to claim 1, wherein a copolymerized polybutylene terephthalate containing 0.3 to 10 mol% of a polyether is blended. 3. The heat-shrinkable polyester film according to claim 1, wherein the polyether is polytetramethylene glycol.