JPH1077335A - Heat shrinkable polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat shrinkable polyester based film excellent in shrinking properties at a low temperature, low in shrinking irregularity, longitudinal sink mark and excellent in resistance to breakage. SOLUTION: This oriented film is formed from a polyester composed of a dicarboxylic acid component, a polyvalent alcohol component containing at least one dimer-diol as a component. In this case, the oriented film has the shrinkage in a hot air at 90 deg.C at least in one direction of 30 to 70%, shrinkage stress of 0.2 to 0.6kg/mm<2> , initial breaking rate of 0%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to cola, juice,
Food and beverages such as beer and cup noodles, pharmaceuticals, sundries,
Regarding industrial materials, stationery, toys, tools, and various other products, the contents of the package and the seller of the product are displayed,
In addition, as a label for packaging products or as a cap seal for containers, foreign substances are prevented from entering the product, dry batteries are prevented, deterioration due to oxidation or moisture absorption of products, safety shields to prevent contamination during product display, or The present invention relates to a heat-shrinkable polyester film used as a packaging material for bundling a plurality of products.

[0002]

2. Description of the Related Art Conventionally, heat shrinkable films have been widely used for applications such as shrink wrapping, shrink labels, and cap seals, utilizing the property of shrinking by heating. And
Conventionally, a uniaxially stretched film made of a vinyl chloride resin, a polystyrene resin, a polyester resin, or the like has been used as a label for various containers such as a polyethylene terephthalate (PET) container and a glass container. Above all, heat-shrinkable vinyl chloride resin films are widely used because of their good low-temperature shrinkage and printability.

However, vinyl chloride resins have problems such as low heat resistance and generation of hydrogen chloride gas during incineration. In addition, heat-shrinkable vinyl chloride resin film
When used as a shrinkable label for an ET container or the like, it is necessary to separate the label from the container when recycling the container.

On the other hand, polystyrene resin and polyester resin films do not generate toxic gases such as hydrogen chloride gas during incineration, and are expected to be used as shrink labels for containers instead of vinyl chloride resin films. .

However, polystyrene resin films are
Although the finish after shrinkage was good, special ink had to be used at the time of printing due to low solvent resistance. In addition, it requires incineration at a high temperature and generates a large amount of black smoke and an unpleasant odor at the time of incineration. As a material capable of solving these problems, a polyester resin film is highly expected, and the amount of use thereof has been remarkably increased.

[0006]

However, the above-mentioned conventional heat-shrinkable polyester films have not been sufficiently satisfactory in heat-shrink properties. In particular, shrinkage unevenness is likely to occur during shrinkage, and when coating and shrinking on containers such as PET bottles, polyethylene bottles, glass bottles, characters and designs printed on the film before shrinkage are distorted after shrinkage, There were problems such as insufficient adhesion.

Further, compared with the heat-shrinkable polystyrene resin film, the shrinkage at a low temperature is inferior. In order to obtain a required amount of shrinkage, the film must be shrunk at a higher temperature.
There were also problems such as deformation of bottles and whitening. In particular, when used as a label for polyethylene bottles, since the polyethylene bottle itself is inferior in heat resistance to PET bottles and the like, it is necessary to perform shrinking work at a lower temperature of, for example, about 70 ° C. Excellent heat shrink films are needed. Further, even in a 2 liter square PET bottle, which has been widely used in recent years, since the heat-shrinkable polyester film has a larger shrinkage stress than the heat-shrinkable polystyrene resin film, the label itself is greatly distorted, and the vertical sink mark and printing at the lower part of the label are printed. It has problems such as poor reproduction of characters. In addition, the heat-shrinkable polyester film has weak orientation in the direction perpendicular to the shrinkage direction because molecules are oriented in the main shrinkage direction. The tear resistance of the film further decreases,
There has been a problem that the film is broken due to tension in a processing step such as printing or tubing processing, and the operability of processing is reduced.

In response to such a demand, Japanese Patent Laid-Open No. 5-305
As described in U.S. Patent No. 663 or JP-A-5-305664, a heat-shrinkable polyester film using a polyester obtained by copolymerizing a specific component and having a shrinkage initiation temperature of 50 ° C or less, or a shrinkage controlled at a shrinkage rate. A heat-shrinkable polyester film with less unevenness has been proposed. However, even with such a heat-shrinkable polyester film, shrinkage unevenness and vertical sink marks cannot be simultaneously solved.

An object of the present invention is to provide a heat-shrinkable polyester-based film having excellent shrinkage characteristics at low temperatures, small shrinkage unevenness and small vertical shrinkage, and excellent tear resistance.

[0010]

In order to achieve the above object, a heat-shrinkable polyester film of the present invention comprises a polyester comprising a dicarboxylic acid component and a polyhydric alcohol component containing at least one dimer diol component. A stretched film having a shrinkage ratio in hot air of 90 ° C. in at least one direction of 30 to 70% and a shrinkage stress of 0.2 to 0.6 in at least one direction.
kg / mm ² , and the initial rupture rate at room temperature is 0%.

The heat-shrinkable polyester film having the above structure has excellent shrinkage characteristics at low temperatures, small shrinkage unevenness and small vertical shrinkage, and excellent tear resistance.

In this case, the polyester of the heat-shrinkable polyester film is composed of a dicarboxylic acid component containing at least one component of a naphthalenedicarboxylic acid component and a polyhydric alcohol component containing at least one component of a dimer diol component. Polyester.

The heat-shrinkable polyester film having the above constitution is particularly excellent in shrinkage characteristics at low temperature and tear resistance.

In this case, at least one of the polyesters of the heat-shrinkable polyester film contains a dimer diol component as one component of a polyhydric alcohol component and a dicarboxylic acid containing at least one naphthalenedicarboxylic acid component as a component. It may be a mixture of a polyester (A) composed of an acid component and a polyester (B) composed of a dicarboxylic acid component containing at least one terephthalic acid component.

The heat-shrinkable polyester film having the above-mentioned structure has a well-balanced shrinkage property and tear resistance particularly at a low temperature.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below.

The polyester constituting the heat-shrinkable polyester film of the present invention is a polyester comprising a dicarboxylic acid component and a polyhydric alcohol component containing at least one dimer diol component, in particular, at least a naphthalenedicarboxylic acid component. Polyester consisting of a dicarboxylic acid component contained as one component and a polyhydric alcohol component containing at least one dimer diol component, more preferably a dicarboxylic acid containing at least a naphthalenedicarboxylic acid component and a terephthalic acid component A polyester comprising an acid component and a polyhydric alcohol component containing at least one dimer diol component.

These polyesters are used alone or as a mixture of two or more polyesters having different compositions.
In particular, it is preferably formed from a mixture of two or more polyethers having different compositions. When using a single polyester, tear resistance may be insufficient if uniform low-temperature shrinkage properties are exhibited, while low-temperature shrinkage may be insufficient if tear resistance is sufficient. Need to be

As the two or more polyesters having different compositions, at least one is composed of a dicarboxylic acid component containing a naphthalenedicarboxylic acid component as at least one component containing a dimer diol component as one component of a polyhydric alcohol component. Of polyester (A) and a polyester (B) comprising a dicarboxylic acid component containing at least one terephthalic acid component.

The dimer diol, which is an essential component of the polyester constituting the film of the present invention, is a derivative of C ₃₆ dimer acid and is a mixture mainly composed of components having the structures of (1) and (2) represented by the following formula. The preferred composition ratio is (1) :( 2) = 10: 90 to 90:10. Further, the dimer diol is preferably washed and purified. Such polyester is less colored and is suitable as a packaging material.

[0021]

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The polyester used in the present invention can be produced by a conventional polyester production method. For example, a method used in a direct esterification method of terephthalic acid and ethylene glycol, or a method produced by a transesterification method of dimethyl terephthalate and ethylene glycol, a third component may be used. Further, the polyester used in the present invention may be a copolymer prepared by mixing a homopolyester or another copolymerized polyester within or outside the range used in the present invention, wherein the third component is 3 to 30 mol%. Any method may be used as long as it is within the range described above.

The dicarboxylic acid component as the third component copolymerized in the polyester used in the present invention includes, for example, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and azelaic acid, isophthalic acid, diphenyldicarboxylic acid, and the like. 5-tertbutyl isophthalic acid, 2,2,6,6
-Tetramethylbiphenyl-4,4-dicarboxylic acid,
Examples thereof include aromatic dicarboxylic acids such as 5-sodium sulfoisophthalic acid, 2,6-naphthalenedicarboxylic acid, and 1,1,3-trimethyl-3-phenylindane-4,5-dicarboxylic acid. Similarly, examples of the polyhydric alcohol component include resin-based diols such as diethylene glycol, propylene glycol, butanediol, and hexanediol, and 1,4-cyclohexanedimethanol;
Xylylene glycol, bis (4-beta-hydroxyphenyl) sulfone, and diols of 2,2 (4-oxyphenyl) propane derivatives can be exemplified. As the third component, 5-sodium sulfoisophthalic acid is particularly preferred. One or more of the above-mentioned copolymerization components other than the third component may be copolymerized as long as the properties imparted by the third component are not impaired.

If necessary, fine particles such as titanium dioxide, fine particle silica, kaolin, and calcium carbonate may be added to the polyester used in the present invention. A dye or the like can be added as a coloring agent. The preferable intrinsic viscosity for forming a film is not particularly limited, but is usually 0.50 to 1.31 dl / g.

An unstretched film obtained by using such a polyester by any method such as an extrusion method and a calendering method is stretched so as to obtain a film having the characteristics of the film of the present invention. Stretching is successive biaxial stretching, coaxial biaxial stretching, longitudinal uniaxial stretching,
It is performed by horizontal uniaxial stretching or a combination thereof. In particular, sequential biaxial stretching is effective, and the stretching order may be either one. When performing the simultaneous biaxial stretching method, longitudinal-preceding and horizontal-preceding stretching may be performed prior to the stretching.

The stretching conditions are as follows: stretching in one direction from 2.5 times to 7.0 times, preferably from 3.0 times to 6.0 times;
The film is stretched 1.0 to 2.0 times or less, preferably 1.1 to 1.8 times in a direction perpendicular to the direction. Stretching in the first direction is mainly performed to obtain a high heat shrinkage ratio, and stretching in the direction perpendicular to the first direction depends on the impact resistance and tear resistance of the film stretched in the first one direction. It is extremely effective in resolving sexual insufficiency. However, when the film is stretched by more than 2.0 times, the heat shrinkage in the direction perpendicular to the main shrinkage direction becomes too large, and the finish after shrinkage becomes wavy. In order to suppress the waving, it is recommended that the heat shrinkage of the obtained film be 15% or less, preferably 8 to 9% or less, more preferably 7% or less. There is no particular limitation on the stretching means, and methods such as roll stretching, long gap stretching, and tenter stretching are applied, and the film may be in any form such as a flat shape or a tube shape.

The heat setting in these stretchings is carried out according to the purpose. In order to prevent dimensional change under high temperature in summer, it is necessary to pass a heating zone of 30 to 150 ° C. for about 1 to 30 seconds. Recommended. Further, the stretching may be performed up to a maximum of 70% before and / or after such processing. In particular, it is preferable to stretch in the main direction and relax in the non-contraction direction (the direction perpendicular to the main contraction direction), and it is better not to perform the expansion in the perpendicular direction.

In order to exhibit the preferable characteristics of the film of the present invention, not only the above-mentioned draw ratio but also a temperature higher than the average glass transition point (Tg) of the polymer composition, for example, Tg + 8
Preheating and stretching at about 0 ° C. is also an effective means. In particular, the processing temperature in the main direction (main shrinkage direction) stretching is to suppress the heat shrinkage in the direction perpendicular to the direction, and to bring the minimum value thereof to a temperature range of 80 ± 25 ° C. as described above. Very important. After stretching, the film is cooled while applying stress to the film while being stretched or tensioned, or by further cooling,
The longitudinal shrinkage characteristics are better and more stable.

Thus, the shrinkage in hot air at 90 ° C. in at least one direction is 30 to 70%, the shrinkage stress is 0.2 to 0.6 kg / mm ² , and the initial rupture rate at room temperature is 0. % Can be obtained.

If the shrinkage ratio of the obtained shrink film in hot air at 90 ° C. is less than 30%, shrinkage is insufficient, and problems such as slack of shrink labels occur. On the other hand, the shrinkage rate is 7
If it exceeds 0%, the shrinkage becomes large, and a force for shrinking acts even after the shrinkable label comes into close contact with the bottle, so that there is a problem that the bottle is deformed in the case of a plastic bottle. When the shrinkage stress is less than 0.2 kg / mm ² , there is a problem that the label is easily moved since the shrinkage stress is small and the tightening force is small even after the label shrinks. On the other hand, when it exceeds 0.6 kg / mm ² , the shrinkage stress is large, so that there is a problem that the vertical sink in a 2-liter square bottle becomes large. If the initial rupture rate at room temperature is high, rupture will already occur when the shrink film is attached.

The plane orientation coefficient of the shrink film is 100 × 10
^-3 or less is preferred. Plane orientation coefficient is 100 × 10 ^-3
This is because when the pressure exceeds, it is easy to be broken by an impact external force, and it is easy to be broken even by a slight injury. On the other hand, the birefringence is preferably 15 × 10 ^{−3 to} 160 × 10 ⁻³ , and if the birefringence is less than 15 × 10 ⁻³ , the heat shrinkage and shrinkage stress in the longitudinal direction are insufficient, and 160 × 10 ⁻³ is insufficient. If it exceeds, the scratch resistance and the impact strength decrease, and even if it becomes a film, its usefulness decreases in practical use.

The thickness of the shrink film of the present invention is 6 to 250.
The range of μm is practical.

The film of the present invention has a 10% relaxation of 50%.
It is useful to have a property of maintaining a residual stress for 2 minutes or more when heat-treated in hot air at 0 ° C. More preferably, it is held for 4 minutes or more. If the retention time of the residual stress is short, secondary thickening occurs. For example, when the bottle is covered with a bottle, a phenomenon such as loosening of the shoulder due to sterilization treatment occurs, which is not preferable.

Next, the film of the present invention will be described in terms of application. Boil treatment and retort treatment are performed for packaging applications, particularly for food and beverage packaging. None of the existing heat-shrinkable films can withstand these treatments sufficiently.
The film of the present invention can withstand heat sterilization by boil treatment or retort treatment, and the original film appearance, furthermore, the finish by heat shrinkage is also good,
It has a higher heat shrinkage stress than a vinyl chloride resin film, and has excellent binding properties.

Therefore, it is possible to provide a strong covering or bundling package that does not cause the load to be dislodged even for a heavy or deformed product. In addition, when the heat shrinkage required for packaging is 50 to 70%, the heat shrinkage in the direction perpendicular to the main shrinkage direction shows the lowest value. The process until the completion is to perform the heat shrink in the temperature region (80 ± 25 ° C.) showing the minimum shrinkage. As a result, a film having the characteristic that the error of the finished dimension was reduced was obtained. In the case of packaging utilizing heat shrinkage, it is necessary to continue heating after completion of heat shrinkage (it must be in a state where it does not shrink any more even if it has the ability to adhere to the package and shrink further). It has become a general procedure, which plays a key role in achieving full shrinkage in response to numerous product variations. At this time, if the shrinkage ability of the film has reached saturation, the film is subsequently linearly expanded by the subsequent heating, and despite the fact that the film has been shrunk exactly, looseness occurs instead. There is a problem.

In the present invention, in order to prevent such a situation from occurring, it is necessary to increase the contraction stress. Further, in order to obtain such a film, it is recommended that the film be further stretched after stretching, as described above.
In this regard, the meaning of the orientation in the present invention exists.

The compatibility of low-temperature shrinkage and tear resistance, which are features of the present invention, is achieved by using the following polymers.
Particularly easily realized. Specifically, a film having both properties can be easily obtained by forming a film with a polymer composition obtained by mixing a polyester obtained by copolymerizing a dimer diol with a polyester having another composition. The cause is considered as follows. The dimer diol copolymer deteriorates the compatibility with the polyester of another composition and causes phase separation to such an extent that the transparency is not deteriorated. Therefore, the low-temperature shrinkage of the low Tg polyester and the tear resistance of the polyester of the other composition are both low. It is thought that can be demonstrated.

[0038]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

1. Shrinkage rate The film was cut to a width of 15 mm and the distance between the sample marks was 2 mm.
The measurement was made at each temperature by taking the sample at 00 mm. For heating, hot air at 80 ° C. and 90 ° C. was used for 1 minute each.

2. Shrinkage stress (kg / mm ² ) Using Tensilon, a sample piece of a sample having a width of 20 mm and a length of 150 mm is collected, a mark of 100 mm is drawn on the film, and the sample piece is mounted on an upper and lower chuck set to 100 mm. The treatment was performed in hot air at 90 ° C., and the maximum contraction stress during the treatment was determined, and the contraction stress was calculated according to the following equation.

Shrinkage stress = (maximum shrinkage force / cross-sectional area)

3. Initial rupture rate According to JIS-C-2318, measurement was performed in the MD direction at n = 20, and the number (x) of samples having a rupture elongation of 5% or less was measured and calculated by the following equation.

Initial rupture rate = (x) × 100

4.2 Vertical sink marks and shrinkage finish on a PET bottle of 2 liter square Print characters and figures on the film with general-purpose ink, cut the film to a predetermined size, and adhere with an impulse sealer. The 2 l-square PET bottle was fitted with the main shrinking direction along the circumferential direction of the bottle, shrunk through a 90 ° C. steam tunnel, the length 3 (mm) in FIG.

The shrinkage finish at that time was evaluated by a sensitivity test.

○: No shrinkage unevenness Δ: 1 to 3 shrinkage unevenness ×: 4 or more shrinkage unevenness (polyester synthesis) Dimethylnaphthalate (DM
N) and ethylene glycol (EG) were charged into a polymerization reactor such that EG was 2.2 times the mole number of DMN, and 0.04 mol% of zinc acetate was used as a transesterification catalyst and trioxidation was used as a polycondensation reaction catalyst. After adding 0.02 mol% of antimony and performing a transesterification reaction by a conventional method, 280
A polycondensation reaction was carried out at a temperature of 0.2 ° C. under a reduced pressure of 0.2 torr to obtain a polyester (A-1) having a reduced viscosity of 0.6.

The dimer diol (DMDO) used in the synthesis of other polyesters is HP-produced by Toagosei Co., Ltd.
1000 was used.

The respective polyesters shown in Table 1 were obtained in the same manner as described above. Note that dimethyl terephthalate (DMT), adipic acid (AA), and butanediol (BD) were also used.

Example 1 Polyester (A) shown in Table 1
-1) 70 wt% and (B-1) 30 wt% are mixed in a resin state and extruded from a T-die with a residence time of 5 minutes using a twin screw extruder set at 280 ° C., and a thickness of 180 μm
Was obtained. 90 ° C in the transverse direction
Then, the film was heat-treated at 90 ° C. for 3 seconds at a constant length, and then cooled under 10% elongation to obtain a film having a thickness of 45 μm. The characteristics are shown in Table 2. It was confirmed that all of the transparency, shrinkage characteristics, and tear resistance were excellent.

Example 2 A film was obtained in the same manner as in Example 1 except that the composition ratio of (A-1) and (B-1) was changed to 50% by weight and 50%. The characteristics are shown in Table 2.
It was confirmed that transparency, shrinkage characteristics, and tear resistance were all excellent.

(Example 3) (A-1) of Example 1 was replaced with (A
A film was obtained in the same manner except that the film was changed to -2). The characteristics are shown in Table 2. It was confirmed that all of the transparency, shrinkage characteristics, and tear resistance were excellent.

(Embodiment 4) (A-1) of Embodiment 2 is replaced with (A
A film was obtained in the same manner except that the film was changed to -2). The characteristics are shown in Table 2. It was confirmed that all of the transparency, shrinkage characteristics, and tear resistance were excellent.

(Comparative Example 1) Only (A-1) was formed in the same manner as in Example 1 to obtain a film. The characteristics are shown in Table 2. It was found that there was no low-temperature shrinkage, the shrinkage stress was large, and the shrink finish was poor.

(Comparative Example 2) Only (B-1) was formed into a film in the same manner as in Example 1 to obtain a film. The characteristics are shown in Table 2. It was found that the tear resistance was insufficient and the shrinkage finish was poor.

(Example 5) (A-1) of Example 1 was replaced with (A
-3) to obtain a film in the same manner as above except for the change.
The characteristics are shown in Table 2. It was confirmed that all of the transparency, shrinkage characteristics, and tear resistance were excellent.

(Embodiment 6) (B-1) of Embodiment 1 is replaced with (B
A film was obtained in the same manner except that the film was changed to -2). The characteristics are shown in Table 2. It was confirmed that all of the transparency, shrinkage characteristics, and tear resistance were excellent.

(Comparative Example 3) (B-1) of Example 1 was replaced with (B
A film was obtained in the same manner except that the film was changed to -4). The characteristics are shown in Table 2. It was confirmed that the low-temperature shrinkage was insufficient and the shrink finish was poor.

(Comparative Example 4) (B-1) of Example 1 was replaced with (B
A film was obtained in the same manner except that the film was changed to -5). The characteristics are shown in Table 2. The tear resistance was insufficient and the vertical sink marks were large.

(Comparative Example 5) A film was obtained in the same manner as in Example 1, except that the transverse stretching temperature was changed to 100 ° C.
The characteristics are shown in Table 2. It was confirmed that tear resistance was insufficient.

(Comparative Example 6) The stretching temperature in Example 1 was set to 100
° C and the heat setting temperature was changed to 100 ° C to obtain a film in the same manner. The characteristics are shown in Table 2. It was confirmed that the tear resistance was insufficient and the shrinkage ratio was small.

(Comparative Example 7) The stretching temperature in Example 1 was set at 85 ° C.
A film was obtained in the same manner except that the film was changed to. The characteristics are shown in Table 2. It was confirmed that the contraction stress was large and the vertical sink was large.

(Comparative Example 8) The stretching temperature in Example 1 was set to 85 ° C.
A film was obtained in the same manner except that the heat setting temperature was changed to 85 ° C. The characteristics are shown in Table 2. Since the shrinkage stress was large, the vertical shrinkage was large, and the shrinkage was large, the bottle was deformed.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

The heat-shrinkable polyester film according to the first aspect of the present invention has excellent shrinkage characteristics at low temperatures, small shrinkage unevenness, small vertical sink marks, and excellent tear resistance.

The heat-shrinkable polyester film according to the second aspect of the invention is particularly excellent in shrinkage characteristics at low temperature and tear resistance.

The heat-shrinkable polyester film according to the third aspect of the invention has a good balance between shrinkage characteristics at low temperatures and tear resistance.

[Brief description of the drawings]

FIG. 1 is a side view showing a vertical sink mark of a heat-shrinkable polyester film after shrinkage in a PET bottle body.

[Explanation of symbols]

 1 PET bottle 2 Shrink film 3 Vertical sink

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B29K 105: 02 B29L 7:00

Claims (3)

[Claims] 1. A stretched film formed from a polyester comprising a dicarboxylic acid component and a polyhydric alcohol component containing at least one dimer diol component, wherein hot stretched at 90 ° C. in at least one direction of the stretched film. A heat-shrinkable polyester film having a shrinkage rate of 30 to 70%, a shrinkage stress of 0.2 to 0.6 kg / mm ² , and an initial rupture rate at room temperature of 0%. 2. The polyester according to claim 1, wherein the polyester comprises a dicarboxylic acid component containing at least one naphthalenedicarboxylic acid component and a polyhydric alcohol component containing the naphthalenedicarboxylic acid component.
The heat-shrinkable polyester film according to the above. 3. A polyester (A) wherein at least one of the polyesters comprises a dicarboxylic acid component containing a naphthalenedicarboxylic acid component as at least one component containing a dimer diol component as one component of a polyhydric alcohol component. 3. The heat-shrinkable polyester film according to claim 1, which is a mixture of a polyester (B) comprising a dicarboxylic acid component containing at least one terephthalic acid component.