JPH11207819A - Heat shrinkable polyester-based film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep stably a beautiful appearance by making great a heat shrinkage coefficient to prevent an unevenness in shrinkage by a method wherein the heat shrinkage coefficient in one direction of a film and a moisture content of the film at a specific temperature are allowed to have specific values. SOLUTION: A heat shrinkage coefficient in one direction of a film at 100 deg.C is set to 40% or over, and a moisture content of the film is set to 1000 to 10000 ppm. As a dicarboxylic acid composition comprising a polyester in a raw material composition, excepting a terephthalic acid comprising an ethylene terephthalate unit, either of an aromatic dicarboxylic acid and a cyclic dicarboxylic acid is acceptable. The raw material composition is molded in, for example, a film state or a tube state by, for example, an extrusion method or a calendar method. Further, as the control of the moisture content, for example, a method wherein an extruded film-shaped molded product is dipped in warm water or in water before drawing, a method wherein heated steam is jetted to the film, a method of passing through wet atmosphere, a method of using a wet drawing machine, or the like are adopted.

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 suitable as a packaging material used for coating, bundling, exterior and the like. In particular, the present invention relates to a heat-shrinkable polyester film which has a small shrinkage unevenness, gives excellent shrinkage results with excellent heat resistance, and can stably maintain a beautiful finished appearance.

[0002]

2. Description of the Related Art Heat-shrinkable films are available in various containers such as bottles (including glass and plastic bottles) and cans.
For covering long objects (various rods such as pipes, rods, wood, etc.)
It is used for binding or exterior. For example,
It is used to cover a part or the whole of a cap, a shoulder, and a body of a bottle for the purpose of displaying, protecting, binding, improving commercial value, and the like. Further, it is also used for applications such as packing a plurality of boxes, bottles, plates, sticks, notebooks, and the like, and for packaging skins in which a film is brought into close contact with an object to be packaged. These applications make use of the shrinkage and shrinkage stress of the film.

[0003] As a material of the above-mentioned film, polyvinyl chloride, polystyrene, polyethylene, hydrochloride rubber and the like have been used. Usually, these films are formed into a tube shape, and are wrapped or bound by, for example, covering a bottle or accumulating pipes and the like, followed by heat shrinkage.

However, the conventional film has poor heat resistance and cannot withstand boil or retort treatment at a high temperature. Therefore, sterilization at a high temperature cannot be performed. Has a problem that it is damaged during processing.

[0005] Further, conventional films, for example, polyvinyl chloride films are difficult to print due to poor adhesiveness to ink, and are liable to produce gels derived from additives, so that pinholes are formed on the printed surface. Is easy to occur. In addition, conventional films shrink over time after production,
There is a problem that the printing pitch changes due to shrinkage, and high-precision printing cannot be performed.

On the other hand, the amount of plastic bottles used has increased rapidly in recent years, and it has been called for to collect the bottles for the protection of the global environment. If a different kind of film is used, there is a problem that the film cannot be collected and reused. In addition, polyvinyl chloride film has the problem of incinerator corrosion and air pollution caused by chlorine gas.
In addition, a problem of acid rain due to hydrogen chloride gas has occurred, and a heat-shrinkable film that does not cause waste pollution is desired.

In order to solve the above-mentioned problems of the conventional film, there has been proposed a heat-shrinkable film using a polyester which is excellent in heat resistance, weather resistance and solvent resistance and does not easily cause waste pollution. This heat-shrinkable polyester film has problems such as insufficient heat shrinkage in a desired direction and inability to control the heat shrinkage in a direction perpendicular to the desired direction to an appropriate value. there were. However, it has been found that this problem can be solved by optimizing the copolymer composition of the raw material polyester resin.
No. 6833 and the like.

However, the film obtained by the above method is
Because the shrinking speed is too fast, there is a problem that uneven shrinkage that sharply reflects the uneven temperature distribution that occurs in the shrinking process occurs.In addition, boiling and retorting at high temperature after coating the container is required. When performing or filling the container with a high-temperature substance such as hot water, the heat resistance problem that the film does not break but newly sags still remains.

[0009]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems of the polyester-based heat-shrinkable film. An object of the present invention is to provide a heat-shrinkable polyester film which does not cause unevenness in shrinkage of the film, has a beautiful appearance, and can stably maintain its appearance even under high temperature conditions experienced after finishing.

[0010]

According to the present invention, which has solved the above-mentioned problems, a heat-shrinkable polyester film has a temperature of 100 ° C.
The heat shrinkage in one direction of the film is 40% or more, and the moisture content of the film is 1000 ppm or more.
It has a gist where it is less than 000 ppm.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The essential requirement of the present invention is that the heat-shrinkable polyester film has a heat shrinkage in one direction of not less than 40% at 100 ° C. and a water content of less than 1,000 to 10,000 ppm. That is. If the water content is less than 1000 ppm, it is difficult to sufficiently reduce the shrinkage speed, and as a result, uneven shrinkage tends to occur due to the influence of the non-uniformity of the temperature distribution in the shrinkage step. Although it is not clear why the film shrinkage characteristics can be controlled by optimizing the water content as described above, it is presumed that the heat shrinkage characteristics change due to the interaction between water molecules and polyester molecular chains. Is done.

The dicarboxylic acid component constituting the polyester in the raw material composition used for the heat-shrinkable polyester film of the present invention includes terephthalic acid constituting an ethylene terephthalate unit, aromatic dicarboxylic acid and alicyclic dicarboxylic acid. Any of the acids can be used.

As the aromatic dicarboxylic acid, isophthalic acid, orthophthalic acid, 5-tert-butylisophthalic acid,
Benzenecarboxylic acids such as 5-sodium sulfoisophthalic acid; naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid; 4,4′-dicarboxydiphenyl, 2,2,6,6-tetramethylbiphenyl-4,
Dicarboxybiphenyls such as 4'-dicarboxylic acid;
1,1,3-trimethyl-3-phenylindene-4,
5-dicarboxylic acid and a substituted product thereof; 1,2-diphenoxyethane-4,4′-dicarboxylic acid and a substituted product thereof.

The fatty acid carboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, pimelic acid, suberic acid, undecanoic acid, dodecanedicarboxylic acid, brassic acid, tetradecanedicarboxylic acid, Tapsinic acid, nonadecanedicarboxylic acid, docosandicarboxylic acid, and substituted products thereof,
4,4′-dicarboxycyclohexane and substituted products thereof are exemplified.

As the diol component of the polyester contained in the raw material composition, any of aliphatic diols, alicyclic diols, and aromatic diols can be used in addition to ethylene glycol constituting the polyethylene terephthalate unit. obtain.

As the aliphatic diol, diethylene glycol, propylene glycol, butanediol, 1,1,
6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,
3-propanediol, 2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol and the like. As the alicyclic diol,
Examples include 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol. Examples of the aromatic diol include an ethylene oxide adduct of a bisgenol compound such as 2,2-bis (4′-β-hydroxyethoxyphenyl) sulfone; xylylene glycol; Polyalkylene glycols such as polyethylene glycol and polypropylene glycol can also be used as the diol component.

The polyester contained in the raw material composition is composed of the above-mentioned acid component and diol component. To adjust the polyester, one or more polyesters are required to improve the properties as a heat-shrinkable film. It is preferable to use an acid component or a diol component in combination, and the type and content of the monomer component to be combined may be appropriately determined based on desired film properties, economy, and the like.

The raw material composition contains one or more polyesters. When one kind of the polyester is contained, the copolymer is a polyester containing an ethylene terephthalate unit. When two or more polyesters are mixed, a mixture having a desired composition of a copolymerized polyester and a homopolyester is obtained.
In general, the copolyester has a low melting point and has problems such as difficulty in handling during drying. Therefore, homopolyester (polyethylene terephthalate, polyethylene naphthalate, poly (1,4-cyclohexenediethylene terephthalate), etc.) and copolyester are used. It is preferable to use a mixture. However, when the heat-shrinkable polyester film is used, it is preferable that 1 to 2 mol% of the entire polyester is an aliphatic dicarboxylic acid unit. By controlling the temperature within this range, the onset temperature of heat shrinkage can be controlled within a preferable range.

Any of the polyesters in the above raw material composition can be produced by a conventional method. For example, a direct esterification method in which a dicarboxylic acid and a diol are directly reacted;
The polyester is prepared using an ester exchange method in which dimethyl dicarboxylate is reacted with a diol. The adjustment may be performed in any of a batch system and a continuous system.

In the raw material composition, various known additives may be added as required in addition to the polyester. Examples of additives include lubricants such as titanium dioxide, fine-particle silica, kaolin, and calcium carbonate; antistatic agents;
Antioxidants; ultraviolet absorbers; coloring agents (dyes and the like).

The raw material composition can be prepared by a known method (for example,
Extrusion, calendering) to form a film. The shape of the film is, for example, a flat shape or a tube shape, and is not particularly limited. As the stretching method, for example, a known method such as a roll stretching method, a long gap stretching method, a tenter stretching method, and a tubular stretching method can be adopted. In any of these methods, stretching may be performed by sequential biaxial stretching, simultaneous biaxial stretching, monoaxial stretching, or a combination thereof. In the biaxial stretching, stretching in the longitudinal and transverse directions may be performed simultaneously, but sequential biaxial stretching in which one of them is performed first is effective, and the order of the longitudinal and transverse directions may be any. The stretching ratio is arbitrarily set in the range of 1.0 to 7.0 times, and if the predetermined unidirectional magnification is 3.5 times or more, preferably 4.5 times or more, the heat shrinkage ratio is 40%. Can be achieved.

In the stretching step, preheating is preferably performed at a temperature not lower than the glass transition temperature (Tg) of the polymer constituting the film and not higher than Tg + 80 ° C., for example. In the heat set at the time of stretching, for example, it is recommended to pass through a heating zone at 30 to 150 ° C. for about 1 to 30 seconds after stretching. Further, after stretching the film, before or after performing the heat setting, the stretching may be performed at a predetermined degree. Further, after the stretching, a step of cooling while applying stress to the film while maintaining the stretched or tensioned state, or a cooling step may be added after the tension is released following the treatment. The thickness of the obtained film is preferably in the range of 6 to 250 μm.

In the present invention, the moisture content of the heat-shrinkable polyester film must be less than 1,000 to 10,000 ppm. The control of the water content is achieved by adjusting the water content in any of the above steps, and is particularly preferably performed before or during the stretching step. Moisture control can be performed by any method, for example, a method of immersing the extruded film-shaped molded product in warm water or water before stretching, a method of spraying heated steam on the film, a method of passing through a humid atmosphere, A method using a wet stretching machine is exemplified, but the method is not limited thereto.

The heat-shrinkable polyester film of the present invention thus obtained has a lower shrinkage speed than the conventionally proposed heat-shrinkable polyester film, and is less likely to cause uneven shrinkage when shrunk. It has a beautiful appearance and can stably maintain its appearance even under various high-temperature conditions which will be experienced later.

[0025]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which do not limit the present invention.
Modifications and alterations that do not depart from the spirit described below are all included in the technical scope of the present invention. Measurements used in Examples
The evaluation method is as follows.

(1) Moisture content in film Karl Fischer moisture meter (KYOTO Electr)
nics, MKC-210) was used and the sample weight was 1 g and the sample heating temperature was 230 ° C.

(2) Shrinkage unevenness The film is subjected to metallic printing for shrinkage labeling, formed into a cylindrical tube, covered with a 1.5 liter square PET bottle, and passed through a shrink tunnel. The conditions of the shrink tunnel were as follows: the first zone: 100 ° C. × residence time 4.5 seconds, and the second zone: 140 ° C. × residence time 5 seconds. The presence or absence of print shading due to uneven shrinkage of the obtained label was visually judged. A: Very good without uneven shrinkage. ：: There is no unevenness in shrinkage, but relatively good. C: Shrinkage unevenness was observed, and it was almost defective. X: There is much unevenness in shrinkage, which is poor.

(3) Boil treatment The film was made into a shrink label, put on a bottle filled with water, and shrunk in hot water at 80 ° C. This was immersed again in hot water at 80 ° C. for 30 minutes, and the state of the label slack was visually judged. A: Very good without sagging. ：: Not too much slack but relatively good. Δ: Sag is observed and almost defective. X: There is much sagging and it is bad.

(4) Appropriate Filling of High-Temperature Substance The film is made into a shrink label, and shrink-fitted to a bottle by the method used for judging uneven shrinkage. The bottle was filled with hot water at 87 ° C., and after 6 minutes, the state of the label slack after water cooling was visually judged. A: Very good without sagging. ：: Not too much slack but relatively good. Δ: Sag is observed and almost defective. X: There is much sagging and it is bad.

(5) Heat Shrinkage The film is cut so as to have a long side in a direction in which the film shrinks and a width of 15 mm. Mark lines are drawn at 200 mm intervals in the long side direction. The sample is heated by blowing hot air of 100 ° C. for 1 minute, and the amount of change in the distance between the marked lines is measured. The percentage of this change with respect to the original length was defined as the heat shrinkage (%).

(6) Shrinking speed The shrinking film was cut into a suitable size, immersed in an oil bath at 80 ° C. for 1 second, and immediately cooled by air, and the percentage of the amount of change in the main shrinkage direction relative to the original length was calculated. The evaluation characteristics of the shrinkage speed were used.

EXAMPLE 1 95.4 mol% of terephthalic acid as a dicarboxylic acid component
And 4.6 mol% of sebacic acid, 74.5 mol% of ethylene glycol and 25.5 mol% of neopentyl glycol as glycol components, and an average particle size of 2.4 μm.
Using a copolyester composition containing 0.05% by weight of m 2 silicon dioxide as a raw material, it was melt-extruded at 290 ° C. to obtain a film having a thickness of 190 μm. The obtained film was treated in hot water at 80 ° C. for 20 seconds to remove water adhering to the film surface. At this time, the water content in the film was 8,200 ppm. This unstretched film is
After preheating at 10 ° C. for 6 seconds, the film was stretched 4.8 times in a predetermined direction at a temperature of 70 ° C. After stretching, heat set at 40 ° C. for 5 seconds while maintaining the tension state, to a thickness of 40 ° C.
A μm heat-shrinkable film was obtained. At this time, the moisture content in the film was 3,600 ppm.

Examples 2 and 3 The same copolyester composition as in Example 1 was treated with hot water at 60 ° C. for 30 seconds (Example 2) and at 40 ° C. for 60 seconds (Example 3). A heat-shrinkable film was obtained in the same manner as in Example 1 except for performing the above. At this time, the water content in the unstretched film was 5800 ppm and 4600 ppm, respectively, and the water content after stretching was 2700 ppm and 1800 ppm, respectively.

Example 4 An unstretched film obtained by using the same copolymerized polyester composition as in Example 1 was placed in hot water at 80 ° C. for 20 minutes.
After preheating for 4.8 seconds, 4.8 in a predetermined direction in hot water of 65 ° C.
The film was stretched twice and the surface was dried to obtain a heat-shrinkable film having a thickness of 40 μm. At this time, the moisture content of the film was 25
It was 00 ppm.

Comparative Example A heat-shrinkable film was obtained in the same manner as in Example 1 except that the same copolymer polyester composition as in Example 1 was not used and the treatment with hot water was not performed. At this time, the water content after stretching and film formation was 600 ppm. The properties of the obtained heat-shrinkable film are summarized in Table 1.

[0036]

[Table 1]

[0037]

The heat-shrinkable polyester film of the present invention has a sufficiently high heat-shrinkage rate for practical use. When it is heat-shrinked and used for coating or bundling, the temperature gradient and non-uniformity in the shrinking step are reduced. Irrespective of the high-temperature conditions that the film experiences after shrinkage, such as giving a uniform shrinkage result and applying high-temperature sterilization treatment (for example, retort treatment, boil treatment) after coating or bundling, or filling a coated container with a high-temperature substance, etc. Also has no sagging or wrinkles, and is highly useful in a wide range of packaging materials.

Claims (1)

[Claims] 1. A heat-shrinkable polyester film characterized in that the heat shrinkage in one direction of the film at 100 ° C. is 40% or more, and the water content of the film is 1000 ppm or more and less than 10000 ppm.