JP2002046176A - Heat-shrinkable polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film used for a full label of a bottle, especially, for a full label of a PET bottle and extremely reduced in the generation of wrinkles, shrinkage irregularity and strain caused by shrinkage. SOLUTION: In the heat-shrinkable polyester film, the hot water shrinkage factor in the main shrink direction of the film is 5-50% under a treatment condition of 70 deg.C and 5 see and 65-75% under a treatment condition of 85 deg.C and 5 sec, and the hot shrinkage factor in the direction of crossing the main shrink direction of the film at a right angle is 10% or less under the treatment condition of 85 deg.C and 5 sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film suitable for label use. For more information,
The present invention relates to a heat-shrinkable polyester film for full labeling of bottles, particularly for full labeling of PET bottles, which is free from wrinkles, spots and shrinkage due to heat shrinkage.

[0002]

2. Description of the Related Art As a heat-shrinkable film, particularly a heat-shrinkable film for labeling the body of a bottle, a film made of polyvinyl chloride, polystyrene or the like is mainly used. However, for polyvinyl chloride,
The generation of chlorine gas at the time of incineration at the time of disposal poses a problem, and polyethylene has problems such as difficulty in printing. Furthermore, when collecting and recycling PET bottles, it is necessary to separate labels for resins other than PET, such as polyvinyl chloride and polyethylene. For this reason, polyester-based heat-shrinkable films free of these problems have attracted attention.

[0003] In recent years, regarding the recycling of PET bottles, colored bottles are not suitable for recycling, so alternatives have been studied. Use an uncolored bottle in it,
There is a method of shrinking a colored label over the entire bottle.

[0004] However, when used as a full label for a bottle, the conventional heat-shrinkable film may cause a problem in shrink finish due to the complexity and many types of bottles. In particular, in the case of a full label of a beverage bottle or the like having a small mouthpiece and a large difference in the bottle diameter from the body, the conventional heat-shrinkable film causes insufficient shrinkage at the upper neck of the bottle. The heat-shrinkable film used for the full label of such a bottle needs heat-shrinking properties such as a high shrinkage.

[0005] As described above, in the case of full label use of bottles, the performance of conventional polyester heat-shrinkable films was insufficient.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and an object of the present invention is to provide a heat-shrinkable polyester film for full labeling of bottles, particularly for PET bottles. Accordingly, it is an object of the present invention to provide a heat-shrinkable polyester film in which wrinkles, shrinkage spots, and distortion due to shrinkage are extremely small.

[0007]

According to the heat-shrinkable polyester film of the present invention, the hot-water shrinkage of the film in the main shrinkage direction is 5 to 5 at a processing temperature of 70 ° C. and a processing time of 5 seconds.
0%, 65 to 75% at 85 ° C. for 5 seconds, and 10% at 85 ° C. for 5 seconds in a direction orthogonal to the main contraction direction.
A heat-shrinkable polyester film characterized by the following, which solves the above problem.

[0008]

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

The dicarboxylic acid component constituting the polyester used in the present invention includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid and the like. Aliphatic dicarboxylic acids and alicyclic dicarboxylic acids.

Aliphatic dicarboxylic acids (eg adipic acid,
(Sebacic acid, decanedicarboxylic acid, etc.), the content is preferably less than 3 mol%. A heat-shrinkable polyester film obtained using a polyester containing 3 mol% or more of these aliphatic dicarboxylic acids has insufficient rigidity at the time of high-speed mounting.

It is preferable not to contain a trivalent or higher polycarboxylic acid (for example, trimellitic acid, pyromellitic acid and anhydrides thereof). In a heat-shrinkable polyester film obtained by using a polyester containing these polycarboxylic acids, it becomes difficult to achieve a required high shrinkage.

The diol component constituting the polyester used in the present invention includes ethylene glycol, propanediol, butanediol, neopentyl glycol,
Examples thereof include aliphatic diols such as hexanediol, alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatic diols.

The polyester used in the heat-shrinkable polyester film of the present invention contains one or more diols having 3 to 6 carbon atoms (eg, propane diol, butane diol, neopentyl glycol, hexane diol, etc.). , Glass transition point (Tg) 60-75 ° C
Is preferred.

In order to obtain a heat-shrinkable polyester film having particularly excellent shrink finish, neopentyl glycol is preferably used as one of the diol components, and preferably contains at least 16 mol% in the polyester. .

A diol having 8 or more carbon atoms (eg, octanediol) or a polyhydric alcohol having 3 or more carbon atoms (eg, trimethylolpropane, trimethylolethane,
Glycerin, diglycerin, etc.) is preferably not contained. In a heat-shrinkable polyester film obtained by using a polyester containing these diols or polyhydric alcohols, it is difficult to achieve the required high shrinkage.

It is preferable that diethylene glycol, triethylene glycol and polyethylene glycol are not contained as much as possible. In particular, diethylene glycol is likely to be present because it is a by-product component at the time of polymerization of the polyester. However, the polyester used in the present invention preferably has a diethylene glycol content of less than 4 mol%.

The content of the acid component and the diol component of the present invention is the content of the entire polyester with respect to the acid component and the diol component when two or more polyesters are used in combination. It does not matter whether transesterification has taken place after mixing. Further, in order to improve the lubricity of the heat-shrinkable film, for example, an inorganic lubricant such as titanium dioxide, fine-particle silica, kaolin, calcium carbonate, or, for example, may also contain an organic lubricant such as a long-chain fatty acid ester. preferable. If necessary, additives such as a stabilizer, a coloring agent, an antioxidant, an antifoaming agent, an antistatic agent, and an ultraviolet absorber may be contained.

Any of the above polyesters can be produced by polymerization according to a conventional method. For example, a polyester can be obtained by a direct esterification method in which a dicarboxylic acid and a diol are directly reacted, or a transesterification method in which a dimethyl ester of a dicarboxylic acid is reacted with a diol. The polymerization may be performed in any of a batch system and a continuous system.

The heat-shrinkable polyester film of the present invention is treated in hot water with no load, and the heat shrinkage ratio is calculated from the length before and after shrinkage = ((length before shrinkage−length after shrinkage) / The hot water shrinkage rate of the film calculated by the formula of (length before shrinkage) × 100 (%) is a processing temperature of 70 ° C.
The processing time is 5 to 50% for 5 seconds, preferably 10 to 3%.
0%, 65% to 75% at 85 ° C for 5 seconds, preferably 67 to 75%, and 10% or less at 85 ° C for 5 seconds in a direction orthogonal to the main shrinkage direction, preferably Is 6% or less.

When the hot water shrinkage in the main shrinkage direction is less than 5% at 70 ° C. for 5 seconds, the low-temperature shrinkage becomes insufficient, and it is necessary to increase the shrinkage temperature, which is not preferable. On the other hand, if it exceeds 50%, the label jumps up due to heat shrinkage, which is not preferable.

If the shrinkage at 85 ° C. for 5 seconds is less than 65%, the shrinkage at the top of the bottle becomes insufficient, which is not preferable. On the other hand, if it exceeds 75%, the label tends to jump up because it has a further shrinking force even after heat shrinkage.

The shrinkage stress in the main shrinkage direction at 90 ° C. is 0.8
〜1.6 kg / mm ² is preferred. More preferably,
0.9 to 1.5 kg / mm ² . 0.8 shrinkage stress
If it is less than kg / mm ^2, the shrinkage speed may be too slow, resulting in insufficient shrinkage at the top of the bottle. If it exceeds 1.5 kg / mm ² , problems occur such as the liquid level does not drop when the PET bottle is opened.

Although the thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, it is preferably 10 to 200 μm as a heat-shrinkable film for a label.
-100 μm is more preferable.

Next, a specific example of the method for producing the heat-shrinkable polyester film of the present invention will be described, but the present invention is not limited to this method.

The polyester raw material used in the present invention is dried using a drier such as a hopper drier or a paddle drier or a vacuum drier, melted at a temperature of 200 to 300 ° C. and extruded into a film. For extrusion, any existing method such as a T-die method or a tubular method may be employed. After extrusion, it is quenched to obtain an unstretched film.

Next, the obtained unstretched film was subjected to Tg-
At a temperature of 5 ° C. or higher and lower than Tg + 15 ° C., preferably Tg
At a temperature of not less than 0 ° C. and less than Tg + 15 ° C., 3.0 times or more, preferably 3.5 times or more, more preferably 4.times.
Stretch 2 times or more.

Next, if necessary, heat treatment is performed at a temperature of 70 to 100 ° C. to obtain a heat-shrinkable polyester film.

As the stretching method, not only the uniaxial stretching in the horizontal direction by the tenter but also the stretching in the longitudinal direction and the biaxial stretching can be additionally performed. Such biaxial stretching is performed sequentially by biaxial stretching,
Any of the simultaneous biaxial stretching methods may be used, and if necessary, re-stretching may be performed in the machine direction or the transverse direction.

In order to achieve the object of the present invention, the main contraction direction is practically the transverse direction.
The example of the film forming method in the case where the main shrinkage direction is the horizontal direction has been described. However, even when the main shrinkage direction is the vertical direction, except that the stretching direction in the above method is changed by 90 degrees, the operation according to the above method is performed. A film can be formed.

In the present invention, the unstretched film obtained from the polyester is preferably stretched at a temperature of Tg-5 ° C. or more and less than Tg + 15 ° C.

If the film is stretched at a temperature lower than Tg-5 ° C., not only is it difficult to obtain the heat shrinkage, which is a constituent element of the present invention, but also the transparency of the obtained film deteriorates.

On the other hand, when the film is stretched at a temperature of Tg + 15 ° C. or higher, it is not preferable because the obtained film has insufficient stiffness at the time of high-speed mounting and the thickness unevenness of the film is significantly impaired.

In the heat-shrinkable polyester film of the present invention, the thickness distribution of the film calculated from the thickness of the film by the formula: thickness distribution = ((maximum thickness−minimum thickness) / average thickness) × 100 (%) It is preferably at most 6%.
More preferably, it is 5% or less.

Films having a thickness distribution of 6% or less are easy to superimpose colors by, for example, three-color printing carried out at the time of evaluation of shrinkage finish, while films exceeding 6% have a color superimposition. It is not preferable in respect of the point.

In order to make the thickness distribution of the heat-shrinkable polyester-based film uniform, when the film is stretched in the transverse direction using a tenter, the heat transfer coefficient is set at 0.1 in the preheating step performed prior to the stretching step. 0013 calories / cm ²
It is preferable to perform heating at a low wind speed until the film temperature reaches a predetermined value such that the temperature is not more than sec · ° C.

In order to suppress internal heat generation of the film due to stretching and to reduce film temperature unevenness in the width direction,
The heat transfer coefficient of the stretching step is 0.0009 cal / cm ²
· Sec · ° C or higher, preferably 0.0011 to 0.00
The condition of 17 calories / cm ² · sec · ° C is good.

The heat transfer coefficient of the preheating step is 0.0013
If it exceeds calories / cm ² · sec, and the heat transfer coefficient in the stretching step is 0.0009 calories / cm ² · s
When the value is less than ec, the thickness distribution is hard to be uniform, and when the obtained film is subjected to multicolor printing, misregistration occurs due to superposition of multicolors.

[0038]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist.

The evaluation method of the film of the present invention is as follows. (1) Heat shrinkage rate A film is cut into a square of 10 cm × 10 cm, and is subjected to heat shrinkage in hot water at a predetermined temperature of ± 0.5 ° C. under a no-load condition for a predetermined time. Were measured, and the heat shrinkage was determined according to the following equation (1). The direction in which the heat shrinkage was large was defined as the main shrinkage direction.

Heat shrinkage = ((length before shrinkage−length after shrinkage) / length before shrinkage) × 100 (%) (1)

(2) Shrink finish The heat-shrinkable film was previously coated with Toyo Ink Manufacturing Co., Ltd.
Was printed in three colors with grass, gold and white ink.

Using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc, the passage time was 2.5 seconds,
At a zone temperature of 80 ° C., a 500 ml glass bottle (height 2)
The test was carried out using a 0.6 cm, 6.5 cm diameter central part (a bottle manufactured by Yoshino Kogyo Co., Ltd. and used for afternoon tea by Kirin Beverage Co., Ltd.) (measured number = 20).

The evaluation was performed visually, and the criteria were as follows.

No wrinkles, jumping up, or insufficient shrinkage occurred: ○ Wrinkles, jumping up, or insufficient shrinkage occurred: ×

(3) Tg (Glass transition point) DSC (model: DSC22) manufactured by Seiko Instruments Inc.
Using 0), 10 mg of the unstretched film was heated from -40 ° C to 120 ° C at a heating rate of 20 ° C / min, and was obtained from the obtained endothermic curve. A tangent line was drawn before and after the inflection point of the endothermic curve, and the intersection was defined as Tg (glass transition point).

(4) Thickness distribution A contact thickness gauge manufactured by Anritsu Corporation (model: KG60 / A)
Was used to measure the thickness of the sample of 5 cm in the vertical direction and 50 cm in the horizontal direction (the number of measurements = 20), and for each sample, the thickness distribution (variation in thickness) was obtained by the following equation (3). The average value (n = 50) of the thickness distribution was evaluated according to the following criteria.

Thickness distribution = ((maximum thickness−minimum thickness) / average thickness) × 100 (%) (3) 6% or less → ○ More than 6% and less than 10% → △ 10% or more → ×

(5) Shrinkage stress Using a Tensilon (with a heating furnace) high elongation measuring machine manufactured by Toyo Seiki Co., Ltd., a length of 20 mm in the main shrinkage direction from the heat shrinkable film was measured.
When a sample of 0 mm and a width of 20 mm was cut out, the air flow was stopped in an atmosphere preheated to 90 ° C. with an inter-chuck distance of 100 mm, the sample was attached to the chuck, and then immediately the electric furnace door was closed and air blowing was started. The detected shrinkage stress was measured, and the maximum value obtained from the chart was defined as the shrinkage stress (kg / mm ² ).

The polyesters used in the examples are as follows.

Polyester A: Polyethylene terephthalate (intrinsic viscosity (IV) 0.75 dl / g) Polyester B: Polyester (IV 0.72 dl / g) comprising 70 mol% of ethylene glycol, 30 mol% of neopentyl glycol and terephthalic acid Polyester C: polybutylene terephthalate (IV
1.20 dl / g) Polyester D: Polypropylene terephthalate (IV
1.10dl / g)

Example 1 15% by weight of polyester A
Polyester B 75% by weight, Polyester C 10% by weight
Was melted at 280 ° C., extruded from a T-die, and quenched with a chill roll to obtain an unstretched film. The Tg of this unstretched film was 70 ° C.

The unstretched film was heated at a film temperature of 85
After preheating until the temperature reaches 80 ° C,
The film was stretched 5 times at ℃ to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

(Example 2) 10% by weight of polyester A,
80% by weight of polyester B, 10% by weight of polyester C
Was melted at 280 ° C., extruded from a T-die, and quenched with a chill roll to obtain an unstretched film. The Tg of this unstretched film was 69 ° C.

The unstretched film was heated at a film temperature of 84
After preheating until the temperature reaches 80 ° C,
The film was stretched 5 times at ℃ to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

Example 3 15% by weight of polyester A
A polyester obtained by mixing 80% by weight of polyester B and 5% by weight of polyester C was melted at 280 ° C., extruded from a T-die, and rapidly cooled by a chill roll to obtain an unstretched film.
The Tg of this unstretched film was 71 ° C.

Using the unstretched film, a heat-shrinkable polyester film having a thickness of 50 μm was obtained in the same manner as described in Example 1.

Example 4 15% by weight of polyester A
75% by weight of polyester B, 10% by weight of polyester D
Was melted at 280 ° C., extruded from a T-die, and quenched with a chill roll to obtain an unstretched film. The Tg of this unstretched film was 71 ° C.

A 50 μm thick film was obtained from the unstretched film in the same manner as in Example 1.

Example 5 15% by weight of polyester A
60% by weight of polyester B, 25% by weight of polyester C
Was melted at 280 ° C., extruded from a T-die, and quenched with a chill roll to obtain an unstretched film. The Tg of this unstretched film was 62 ° C.

Using the unstretched film, a heat-shrinkable polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 1) A thickness of 50 μm was obtained in the same manner as in Example 1 except that the stretching temperature was 88 ° C.
Was obtained.

(Comparative Example 2) A film was formed in the same manner as in Example 1 except that the stretching temperature was changed to 65 ° C. The film was whitened at the exit of the tenter over the entire width.

Comparative Example 3 A film having a thickness of 50 μm was prepared in the same manner as in Example 5 except that the stretching temperature was changed to 78 ° C.
Was obtained.

(Comparative Example 4) 40% by weight of polyester A,
50% by weight of polyester B, 10% by weight of polyester C
Was melted at 280 ° C., extruded from a T-die, and quenched with a chill roll to obtain an unstretched film.
The Tg of this unstretched film was 69 ° C.

The unstretched film was treated at a film temperature of 87
After preheating until the temperature reaches 80 ° C,
The film was stretched 5 times at ℃ to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

(Comparative Example 5) Except that the stretching ratio was changed to 4.0 times, the thickness was adjusted to 5% in the same manner as in the method described in Example 1.
A 0 μm heat-shrinkable polyester film was obtained.

Table 1 shows the evaluation results of the films obtained in Examples 1 to 5 and Comparative Examples 1 to 5. As is clear from Table 1, the films obtained in Examples 1 to 5 all had good shrink finish. The thickness distribution was also good. The heat-shrinkable polyester film of the present invention has high quality and high practicability, and is particularly suitable for shrink labels.

On the other hand, the heat-shrinkable film obtained in Comparative Example 1 has a poor thickness distribution. Further, the heat-shrinkable films obtained in Comparative Examples 3, 4 and 5 have wrinkles and insufficient shrinkage due to shrinkage, and all have poor shrink finish. As described above, the heat-shrinkable polyester films obtained in Comparative Examples were all inferior in quality and low in practicability.

[0069]

[Table 1]

[0070]

According to the present invention, a heat-shrinkable polyester film suitable for full labeling of bottles, particularly for PET bottles, can be obtained.

When the heat-shrinkable polyester film of the present invention is used as a full label for a bottle, it is possible to obtain a good finish with few wrinkles, uneven spots, distortion and insufficient shrinkage due to heat shrinkage. Very useful as an application.

Claims (3)

[Claims] 1. A heat-shrinkable polyester film, wherein the polyester film has a hot water shrinkage ratio of 5 to 5 at a treatment temperature of 70 ° C. and a treatment time of 5 seconds in the main shrinkage direction.
50%, 65 to 75% at 85 ° C. for 5 seconds, and 10% at 85 ° C. for 5 seconds in the direction orthogonal to the main contraction direction.
% Or less, a heat-shrinkable polyester film. 2. The heat-shrinkable polyester film according to claim 1, wherein the thickness distribution is 6% or less. 3. The heat-shrinkable polyester film according to claim 1, which has a shrinkage stress of 0.8 to 90 ° C.
A heat-shrinkable polyester film having a weight of 1.6 kg / mm ² .