JP2004306259A - Heat-shrinkable polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film having high shrinkability, excellent not only in shrink finish but also in perforation properties and suppressed in shrink stress. <P>SOLUTION: The heat-shrinkable polyester film comprises 70-90 wt.% of a copolyester resin (A), wherein a dicarboxylic acid component is terephthalic acid, a diol component is ethylene glycol and a copolymerizable component is 20-50 mol% of 1,4-dicyclohexanedimethanol, and 10-30 wt.% of a copolymerized polybutylene terephthalate resin (B) wherein a dicarboxylic acid component is terephthalic acid, a diol component is 1,4-butanediol and a copolymerizable component is 5-20 mol% of isophthalic acid. In this heat-shrinkable polyester film, the maximum shrink stress (85°C silicone bath immersion) in the main shrink direction of the film is 5.5 MPa or below and the shrinkage factor of the film after treatment in hot water at 80°C for 10 sec is 35-50% in the main shrink direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３９】
表１から本発明の実施例１〜３はいずれの特性にも優れていることが分かる。これに対して、収縮応力が大き過ぎる比較例１、比較例３、４及び比較例８では内容物飛び出しの問題があり、共重合ポリエステル樹脂Ａと共重合ポリブチレンテレフタレート樹脂Ｂの比率が範囲外である比較例２ではミシン目適性に劣ることが分かる。また、延伸倍率が低い比較例５、６は厚み振れが大きく、主収縮方向の収縮率が小さい比較例７では収縮仕上がりが劣ることが分かる。
【００４０】
【発明の効果】
本発明によれば、高収縮性を有し収縮仕上がりに優れるとともに、収縮応力を抑えた熱収縮性ポリエステル系フィルムであって、ミシン目適性も優れており、特にホット飲料用ＰＥＴボトルの収縮ラベルとして好適に使用できる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film that can be suitably used as a shrink label for a PET bottle for hot beverage.
[0002]
[Prior art]
Heat-shrinkable films are widely used in shrink wrapping, shrink-wrapping wrapping, plastic container labels, glass container destruction and scattering prevention packaging, labels, cap seals, and the like.
Therefore, for such coated label applications, etc., a beautiful shrink finish after shrinkage due to excellent heat shrinkability is required as a function of the film.
[0003]
As the material of the heat-shrinkable film, polyvinyl chloride (PVC), styrene-butadiene block copolymer (SBS), and polyester resin are best known. However, although PVC and SBS have less shrinkage spots and wrinkles during heat shrinkage and are excellent in shrink finish, both PVC and SBS have a natural shrinkage of the film (which is slightly higher than normal temperature, for example, in summer, Shrinks before use). Therefore, a polyester film having a small natural shrinkage, a high shrinkage, and a good heat resistance is suitably used as a heat shrinkable label for a hot beverage PET bottle.
[0004]
[Problems to be solved by the invention]
However, the heat-shrinkable polyester-based film has a very low natural shrinkage and is easy to obtain high shrinkage. However, for example, if the PET bottle is covered with the contents in a state of being filled, the contents easily pop out when the bottle is opened. There is a problem. In addition, there is a problem that shrinkage spots and wrinkles are easily generated during heat shrinkage, and the bottle is deformed due to high stress at the time of shrinkage.
In recent years, demand for PET bottles for hot beverages, so-called PET bottles for hot beverages, housed in hot benders or hot warmers for the purpose of warming beverages such as coffee or tea as contents has been increasing. In a bottle containing a hot beverage, there is a problem that the hot beverage of the contents pops out due to shrinkage of the label particularly when the cap is opened.
[0005]
Further, usually, the shrinkable label is provided with a perforation at a constant pitch so that the label can be easily cut off after the label is attached. The heat-shrinkable polyester-based film has a problem that it is harder to cut along the perforation than the heat-shrinkable film of PVC or SBS, and is inferior in perforation suitability.
Therefore, a heat-shrinkable polyester-based film having high shrinkage, excellent shrinkage finish and reduced shrinkage stress, and further having excellent perforation suitability are desired.
Here, a heat-shrinkable polyester film in which the characteristics of shrinkage and shrinkage stress are specified has been proposed (for example, see Patent Document 1). However, the film described in Patent Literature 1 has a problem that it is not possible to satisfy all of the above characteristics including improvement of perforation suitability.
[0006]
The present invention has been made in view of the above-described conventional problems, and has an object to increase the shrinkage rate and suppress the stress at the time of shrinking of the film to be low, so that there is no problem of popping out of the contents and excellent in shrinkage finish. Another object of the present invention is to provide a heat-shrinkable polyester film excellent in perforation suitability.
[0007]
[Patent Document 1]
JP-A-2002-46177
[Means for Solving the Problems]
The present invention has found a heat-shrinkable polyester film capable of solving the above problems, and the gist thereof is as follows.
The dicarboxylic acid component is terephthalic acid, the diol component is ethylene glycol, and the copolymerization component is 1,4-cyclohexanedimethanol, 20 to 50 mol%. % By weight, 10 to 30% by weight of a copolymerized polybutylene terephthalate resin (B) in which the dicarboxylic acid component is terephthalic acid, the diol component is 1,4-butanediol, and the copolymerization component is 5 to 20% by mole of isophthalic acid. A heat-shrinkable polyester film comprising: a maximum shrinkage stress in the main shrinkage direction (immersion in a 85 ° C. silicone bath) of 5.5 MPa or less, and shrinkage of the film after treatment in hot water at 80 ° C. for 10 seconds. The heat-shrinkable polyester film having a percentage of 35% to 50% in the main shrinkage direction. That.
Here, the film preferably has a draw ratio in the main shrinkage direction of 4.0 to 4.7 times, and can be suitably used for shrink labels of PET bottles for hot beverages.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
The resin composition used in the heat-shrinkable polyester film of the present invention is obtained by mixing a copolymerized polyester resin (A) having a specific composition and a copolymerized polybutylene terephthalate resin (B) having a specific composition at a specific ratio. There is a need to.
The copolymerized polyester resin (A) is an ethylene terephthalate-based copolymerized polyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component, and uses 1,4-cyclohexanedimethanol as a copolymerization component. Use the copolyester that was used.
[0010]
In the copolymerized polyester resin (A) used in the present invention, in order to suppress crystallization when forming into a film and to impart excellent toughness, 1,4 of the copolymerized component in 100 mol% of the diol component is used. -The content of cyclohexanedimethanol is 20 to 50 mol%, preferably 25 to 40 mol%.
[0011]
The copolymerized polybutylene terephthalate resin (B) is a polybutylene terephthalate-based copolymer polyester containing terephthalic acid as a dicarboxylic acid component and 1,4-butanediol as a diol component as main components, and isophthalic acid as a copolymerization component. Is used.
Isophthalic acid is used in an amount of 5 to 20% by mole, preferably 5 to 15% by mole, based on 100% by mole of the dicarboxylic acid component. Copolymerized polyester of less than 5% by mole has high crystallinity when formed into a film. In addition, there is a problem that the shrinkage stress is too large, and that there is a problem that the suitability for perforation is poor. If it exceeds 20 mol%, there are problems such as poor cutting properties of the polymer particles and fusion of the particles to make production difficult.
[0012]
In the present invention, it is necessary to mix the copolymerized polyester resin (A) and the copolymerized polybutylene terephthalate resin (B) at a specific ratio,
The copolymerized polyester resin (A) is 70 to 90% by weight, preferably 75 to 90%, and the copolymerized polybutylene terephthalate resin (B) is 10 to 30% by weight, preferably 15 to 25% by weight. Is less than 70% by weight, there is a problem that the suitability for perforation is inferior, and if it exceeds 90% by weight, the shrinkage stress becomes too large.
In the polyester resin used in the present invention, in addition to the above components (A) and (B), other polyester resins and various additives such as a stabilizer, an ultraviolet absorber, and the like, as long as the object of the present invention is not impaired. A lubricant, a coloring agent and the like may be blended.
[0013]
The film of the present invention is obtained by stretching an unstretched film made of the above resin composition in at least one direction, and satisfies specific maximum shrinkage stress and shrinkage ratio characteristics.
The maximum shrinkage stress (85 ° C. silicone bath immersion) must be 5.5 MPa or less, and if it exceeds 5.5 MPa, the contents will pop out when used as a shrink label for hot beverage PET bottles. easy.
As for the shrinkage characteristics, the shrinkage ratio of the film after treatment in hot water at 80 ° C. for 10 seconds needs to be 35% to 50% in the main shrinkage direction. If the ratio exceeds, there is a problem that the shrinkage finish is inferior.
The intrinsic viscosity of the film of the present invention is 0.5 or more, preferably 0.6 or more. If the intrinsic viscosity of the film is less than 0.5, the rupture resistance tends to decrease.
[0014]
Next, the method for producing the film of the present invention will be specifically described, but is not limited to the following production method. The copolymerized polyester obtained by the polycondensation reaction is mixed and melt-extruded at a temperature of 200 to 320 ° C. At the time of extrusion, a method such as a T-die method or a Cubra method may be employed.
[0015]
In the present invention, it is preferable that the unstretched film before stretching is stretched in at least one direction in a range of 4.0 to 4.7 times, and when it is less than 4.0 times, the thickness unevenness becomes large and 4.7 times. If it exceeds, the shrinkage stress tends to be too large.
Here, when the T-die method is used, after extrusion, it is quenched on a casting drum having a surface temperature of 15 to 80 ° C. to form an unstretched film having a thickness of 30 to 300 μm. The obtained unstretched film is stretched 1.0 to 1.3 times, preferably 1.0 to 1.1 times at a roll temperature of 60 to 120 ° C. using a heated longitudinal stretching roll. After the longitudinal stretching, the film is stretched 4.0 to 4.7 times at a stretching temperature of 60 to 120 ° C using a tenter, and is heat-treated at a temperature of 55 to 100 ° C and wound up.
[0016]
Here, among the various characteristics of the film, since the shrinkage characteristics mainly depend on the stretching ratio and the stretching temperature, from the viewpoint of increasing the shrinkage in the main shrinking direction, high-magnification and low-temperature stretching are preferable. On the other hand, the shrinkage stress mainly depends on the stretching temperature, and the shrinkage stress increases as the stretching ratio and the stretching temperature are low, and there is also an influence of the heat treatment after the stretching (annealing, particularly the relaxation heat treatment). In order to set the temperature dependence of the shrinkage rate more smoothly, one method is to adjust the draw ratio while performing stretching at a relatively high temperature, and to improve the flatness of the film after stretching and adjust the shrinkage rate. Therefore, when heat treatment is performed, the heat treatment is performed at a low temperature that does not promote crystallization of the polyester. As a result, it is possible to suppress the shrinkage stress that largely affects the behavior of the film at the time of heat shrinkage, and to obtain a film exhibiting gentle shrinkage characteristics. Specific temperature conditions can be appropriately set according to the type of polyester used.
[0017]
Further, in the present invention, it is also possible to improve the adhesiveness of the film to the printed layer by subjecting one or both surfaces of the film to a surface activation treatment such as a corona discharge treatment before, after or after the stretching step. It is. In addition, during the stretching step, before or after the stretching, it is also possible to improve the adhesiveness, antistatic property, sliding property, light-shielding property and the like of the film. Further, for example, a laminated film may be formed by a co-extrusion method or the like, for example, by using the polyester resin for the core layer and providing a copolymerized polyester resin layer having a lower crystallinity than the polyester resin for the surface layer.
[0018]
【Example】
(Examples and Comparative Examples)
Hereinafter, Examples and Comparative Examples will be described, but the present invention is not limited thereto.
[0019]
(Sample preparation)
[Example 1]
The dicarboxylic acid component is terephthalic acid, the diol component is ethylene glycol, and the copolymerization component is a copolymerized polyester resin containing 1,4-cyclohexanedimethanol 32 mol%, and amorphous silica having an average particle size of 2.4 μm (manufactured by Fuji Silysia Chemical Ltd.) , Silysia 320) in an amount of 0.05% by weight, and a copolymerized resin in which the dicarboxylic acid component is terephthalic acid, the diol component is 1,4-butanediol, and the copolymerization component is isophthalic acid 10 mol%. Butylene terephthalate resin B was mixed at a ratio of 85:15, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. The obtained unstretched film is uniaxially stretched by a tenter in a transverse direction at a stretching temperature of 84 ° C. at a stretching ratio of 4.5 times, and then heat-treated at 91 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0020]
[Example 2]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 75:25, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film is uniaxially stretched by a tenter in an atmosphere at a stretching temperature of 80 ° C. at a stretching ratio of 4.5 times in the transverse direction, and then heat-treated at 94 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0021]
[Example 3]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 85:15, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film is uniaxially stretched by a tenter in a transverse direction at a stretching temperature of 84 ° C. at a stretching ratio of 4.1 times, and then heat-treated at 91 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0022]
[Comparative Example 1]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 95: 5, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film is uniaxially stretched by a tenter in an atmosphere at a stretching temperature of 88 ° C. at a stretching ratio of 4.5 times in the transverse direction, and then heat-treated at 90 ° C. for 6 seconds to obtain a film having a thickness of 50 μm. Got.
[0023]
[Comparative Example 2]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 65:35, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film is uniaxially stretched by a tenter in an atmosphere at a stretching temperature of 76 ° C. at a stretching ratio of 4.5 times in the transverse direction, and then subjected to a heat treatment at 95 ° C. for 6 seconds to obtain a film having a thickness of 50 μm. Got.
[0024]
[Comparative Example 3]
A copolyester resin A and a polybutylene terephthalate resin C in which the dicarboxylic acid component is terephthalic acid and the diol component is 1,4-butanediol are mixed at a ratio of 85:15, and biaxial extrusion is performed in the same direction while pulling a vacuum vent. After being melt-extruded at 270 ° C. in a machine, it was rapidly cooled to obtain an unstretched film. The obtained unstretched film is uniaxially stretched by a tenter in a transverse direction at a stretching temperature of 84 ° C. at a stretching ratio of 4.5 times, and then heat-treated at 91 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0025]
[Comparative Example 4]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 85:15, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film was uniaxially stretched by a tenter in a transverse direction at a stretching temperature of 84 ° C. at a stretching ratio of 5.0 times, then heat-treated at 91 ° C. for 6 seconds, and then heat-treated. A film having a thickness of 50 μm was obtained.
[0026]
[Comparative Example 5]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 85:15, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film is uniaxially stretched by a tenter in a transverse direction at a stretching temperature of 84 ° C. at a stretching ratio of 3.8 times, and then heat-treated at 91 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0027]
[Comparative Example 6]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 85:15, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film is uniaxially stretched by a tenter in a transverse direction at a stretching temperature of 84 ° C. at a stretching ratio of 3.5 times, and then heat-treated at 91 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0028]
[Comparative Example 7]
The copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B are mixed at a ratio of 85:15, melt-extruded at 270 ° C. with a biaxial extruder in the same direction while pulling a vacuum vent, and then rapidly cooled to obtain an unstretched film. Got. The obtained unstretched film is uniaxially stretched by a tenter in a transverse direction at an stretching temperature of 84 ° C. at a stretching ratio of 4.5 times, and then heat-treated at 96 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0029]
[Comparative Example 8]
The dicarboxylic acid component is terephthalic acid, the diol component is ethylene glycol, the copolymerization component is 1,4-cyclohexanedimethanol 18 mol%, and the copolymerization polyester resin having 10 mol% diethylene glycol is amorphous silica having an average particle size of 2.4 μm (Fuji A copolyester resin D containing 0.05 wt% of Silysia Chemical Co., Silysia Chemical Co., Ltd.) and a copolymerized polybutylene terephthalate resin B are mixed in a ratio of 85:15, and a coaxial twin screw extruder is pulled while a vacuum vent is pulled. After melt extrusion at 270 ° C., the mixture was quenched to obtain an unstretched film. The obtained unstretched film is uniaxially stretched at a stretching ratio of 4.5 times in a transverse direction at a stretching temperature of 81 ° C. in an atmosphere of a tenter, and then heat-treated at 90 ° C. for 6 seconds to obtain a 50 μm thick film. Got.
[0030]
(Evaluation of film properties)
The properties of the films obtained in the preparation of the samples were evaluated. The evaluation of the film is as follows.
[0031]
・ Shrinkage rate in main shrinkage direction:
A polyester film cut into a size of 150 mm in the stretching direction and 25 mm in a direction perpendicular to the stretching direction was immersed in warm water of 80 ° C. for 10 seconds at intervals of 100 mm with marked lines, and determined by the following formula.
Shrinkage (%) = {(LL ′) / L} × 100
L: distance between mark lines before contraction (mm) L ': distance between mark lines after contraction (mm)
[0032]
・ Shrinkage stress:
Each film was cut out in the TD direction to a width of 10 mm and a length of 70 mm, chucked at 50 mm, and fixed to the load cell so that there was no tarmi. Thereafter, the sample was immersed in a silicon bath at 85 ± 0.5 ° C., and the initial shrinkage stress at that time was measured. The shrinkage stress was calculated by applying the following equation.
Shrinkage stress (MPa) = stress applied to load cell (N) / cross-sectional area of specimen (mm ² )
[0033]
・ Perforation evaluation:
A perforated film with a pitch of 0.7 × 0.7 mm is formed into a cylindrical shape, covered over the entire surface of the neck of the 280 ml plastic bottle, immersed in a hot water bath at 85 ° C. for 10 seconds, and perforated vertically after shrink mounting. Was evaluated. The one that cuts along the perforation to the lower part without any problem (○), the one that cuts to some extent along the perforation, the one that peels the apple before reaching the lower part (△), almost along the perforation The sample which was not cut and became peeled from the apple was designated as (x).
[0034]
・ Thickness deviation:
The sample was cut into a width of 5 cm in the MD direction and a width in which the product could be collected in the TD direction excluding the ears, to obtain a sample. The thickness of each sample was measured using a contact thickness meter (model: KG601A) manufactured by Anritsu Corporation, and the thickness fluctuation (thickness variation) was determined by the following equation.
Thickness deviation R = {(maximum thickness)-(minimum thickness)} (μm)
R ≦ 5 was (○) 5 <R ≦ 7 was (△) R> 7 was (×).
[0035]
・ Shrink finish evaluation:
The film with the grids was formed into a cylindrical shape, covered all over the neck of the 500 ml PET bottle, passed through a steam shrink tunnel and mounted on the bottle, and the shrink appearance was evaluated. The temperature of the steam shrink tunnel was set at 80 to 85 ° C. Labels with no lattice distortion and excellent adhesion, with a beautiful finish (）), those with slight distortion and wrinkles but no practical problems (△), poor shrinkage or poor finish Those that did not reach the practical level at all were marked (x).
[0036]
-Contents jump out:
Pour water up to a height of 5 mm from the mouth into a 500 ml PET bottle (using a bottle of "Marocha 500 ml" manufactured by Nippon Coca-Cola Co., Ltd.), cover the entire surface of the bottle with a cylindrical film up to the neck of the bottle, and pass through the steam shrink tunnel several times. Evaluation was made based on whether or not the contents jumped out of the mouth when sequentially passed and shrunk. Those that barely popped out (（), those that occasionally popped out (△), and those that popped out quite frequently were (x).
[0037]
Table 1 shows the evaluation results of the samples of each of the examples and the comparative examples.
[0038]
[Table 1]

[0039]
From Table 1, it can be seen that Examples 1 to 3 of the present invention are excellent in all characteristics. On the other hand, in Comparative Examples 1, 3, 4 and 8 in which the shrinkage stress is too large, there is a problem of the contents jumping out, and the ratio of the copolymerized polyester resin A and the copolymerized polybutylene terephthalate resin B is out of the range. It can be seen that Comparative Example 2, which is inferior, is inferior in perforation suitability. Further, it can be seen that Comparative Examples 5 and 6 where the stretching ratio is low have large thickness fluctuation, and Comparative Example 7 where the contraction rate in the main contraction direction is small has inferior shrinkage finish.
[0040]
【The invention's effect】
According to the present invention, a heat-shrinkable polyester film having high shrinkage property and excellent shrinkage finish, and suppressed shrinkage stress, excellent perforation suitability, and particularly shrinkable labels for PET bottles for hot beverages It can be suitably used as

Claims (3)

The dicarboxylic acid component is terephthalic acid, the diol component is ethylene glycol, the copolymer component is 70 to 90% by weight of a copolymerized polyester resin (A) containing 20 to 50 mol% of 1,4-cyclohexanedimethanol, and the dicarboxylic acid component is A heat-shrinkable polyester system comprising 10 to 30% by weight of a copolymerized polybutylene terephthalate resin (B) having terephthalic acid and a diol component of 1,4-butanediol and a copolymerization component of 5 to 20 mol% of isophthalic acid The film has a maximum shrinkage stress in the main shrinkage direction (85 ° C. silicone bath immersion) of 5.5 MPa or less and a shrinkage ratio of the film after treatment in hot water of 80 ° C. for 10 seconds of 35% in the main shrinkage direction. A heat-shrinkable polyester film characterized by being 50% or less. The heat-shrinkable polyester film according to claim 1, wherein the stretch ratio in the main shrinkage direction is in a range of 4.0 to 4.7 times. 3. The heat-shrinkable polyester film according to claim 1, wherein the heat-shrinkable polyester film is used for a shrink label of a PET bottle for hot beverage.