JPH06339989A - Heat-shrinkable polyester-based film - Google Patents

Abstract

PURPOSE:To provide a heat-shrinkable polyester-based film which has a sufficiently large rate of heat shrinkage and causes no shrinkage unevennesses when the film is thermally shrunk and an outward appearance is stably maintained even under the conditions of high temperature after finishing by specifying both a unidirectional rate of heat shrinkage at the specified temperature and a moisture content respectively. CONSTITUTION:A heat-shrinkable polyester-based film is applied to covering, binding and packing material such as outer packaging. In the case, the unidirectional rate of heat shrinkage of the film at 100 deg.C is set to >=40% and also moisture content is set in a range within 1,000-10,000ppm. Thereby such a film is obtained as has a sufficiently large rate of heat shrinkage and causes no shrinkage unevennesses when the film is thermally shrunk and the film has a pretty outward appearance and also the outward appearance is stably maintained even under the conditions of high temperature after finishing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polyester film which is suitable as a packaging material used for coating, binding, exterior packaging and the like. In particular, the present invention relates to a heat-shrinkable polyester film which has less shrinkage unevenness, gives a shrinkage result excellent in heat resistance, and can stably maintain a beautiful finished appearance.

[0002]

2. Description of the Related Art Heat-shrinkable films are used for various containers such as bottles (including glass and plastic bottles) and cans,
For coating long items (pipes, rods, various rods such as wood),
It is used for bundling or as an exterior. For example,
It is used to cover part or all of the bottle cap, shoulder, and body for the purposes of labeling, protection, bundling, and improvement of commercial value. Further, it is also used for the purpose of accumulating and packaging a plurality of boxes, bottles, plates, rods, notebooks, etc., and for the purpose of skin package for adhering a film to an object to be packaged for packaging. These applications make use of the shrinkage and shrinkage stress of the film.

Polyvinyl chloride, polystyrene, polyethylene, rubber hydrochloride and the like have been used as the material of the film. Usually, these films are formed into a tube shape, for example, by covering them with a bottle, accumulating pipes and the like, and then heat-shrinking them for packaging or bundling.

However, since the conventional film has poor heat resistance and cannot withstand boil treatment or retort treatment at a high temperature, it cannot be sterilized at a high temperature. Had the problem of being damaged during processing.

In addition, conventional films, such as polyvinyl chloride films, have poor adhesion to ink and are difficult to print, and further, gel-like substances derived from additives are likely to be formed, so that pinholes are formed on the printed surface. Is likely to occur. In addition, since conventional films shrink over time after production,
There is a problem that the printing pitch changes due to the contraction, and high-precision printing cannot be performed.

On the other hand, in recent years, the amount of plastic bottles used has rapidly increased, and the necessity of collecting the bottles has been exclaimed to protect the global environment. In particular, polyvinyl chloride and polystyrene are used for coating polyester bottles. If a different type of film is used, there is a problem that it cannot be subjected to recovery and reuse. In addition, the polyvinyl chloride film has the problems of corrosion of the incinerator and air pollution due to chlorine gas,
Further, there is a problem of acid rain due to hydrogen chloride gas, and a heat-shrinkable film which does not cause waste pollution is desired.

In order to solve the above problems of the conventional film, a heat-shrinkable film using a polyester, which is excellent in heat resistance, weather resistance and solvent resistance and hardly causes waste pollution, has been proposed. This heat-shrinkable polyester film has problems such as insufficient heat shrinkage in the desired direction and inability to control the heat shrinkage in the direction orthogonal to the desired direction to an appropriate value. there were. However, this problem can be solved by optimizing the copolymerization composition of the raw material polyester resin.
No. 6833 is disclosed.

However, the film obtained by the above method is
Since the shrinking speed is too fast, there is a problem that uneven shrinkage that reflects the uneven temperature distribution that occurs in the shrinking process sharply occurs, and boil treatment or retort treatment at high temperature after coating the container is required. When it is carried out or when the container is filled with a high temperature substance such as hot water, the problem of heat resistance still remains that the film is not damaged but newly sags.

[0009]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems of the polyester heat-shrinkable film. The object of the present invention is to obtain a sufficiently high heat-shrinkage rate and to provide a heat-shrinkable film. It is an object of the present invention to provide a heat-shrinkable polyester film that does not have uneven shrinkage and is finished with a beautiful appearance, and that the appearance can be stably maintained even under high temperature conditions experienced after finishing.

[0010]

According to the present invention, which is capable of solving 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 water content of the film is 1000 ppm or more 10
It has a gist when it is less than 000 ppm.

[0011]

The essential requirement of the present invention is that the heat shrinkable polyester film at 100 ° C. has a heat shrinkage in one direction of 40% or more and a water content of 100%.
It is 0 to less than 10000 ppm. If the water content is less than 1000 ppm, it becomes difficult to sufficiently reduce the shrinkage rate, and thus unevenness in shrinkage tends to occur under the influence of the non-uniformity of temperature distribution in the shrinking step. It is not clear why the shrinkage properties of the film can be controlled by optimizing the water content as described above, but it is presumed that the heat shrinkage properties are changed by the interaction between water molecules and polyester molecular chains. To be 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 the 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 its substituted product; 1,2-diphenoxyethane-4,4'-dicarboxylic acid and its substituted product, and the like.

As the fatty acid carboxylic acid, 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, docosanedicarboxylic acid, and substitution products thereof,
4,4'-dicarboxycyclohexane and its substitution products and the like can be mentioned.

As the diol component of the polyester contained in the raw material composition, not only ethylene glycol which constitutes the polyethylene terephthalate unit but also other aliphatic diols, alicyclic diols and aromatic diols are used. obtain.

As the aliphatic diol, diethylene glycol, propylene glycol, butanediol, 1,
6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,
There are 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 aromatic diols include ethylene oxide adducts of bisgenol compounds such as 2,2-bis (4′-β-hydroxyethoxyphenyl) sulfone; xylylene glycol and the like. Further, polyalkylene glycol such as polyethylene glycol or 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, and in order to adjust the polyester, one or more kinds are used in order to improve the properties as a heat-shrinkable film. It is preferable to use the acid component or the 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 also contains one or more polyesters. When only one type of polyester is contained, it is a copolyester containing an ethylene terephthalate unit. When two or more polyesters are mixed, a mixture of the copolymerized polyester and the homopolyester having a desired composition is used.
Generally, copolyesters have a low melting point, and therefore have problems such as being difficult to handle during drying. Therefore, homopolyesters (polyethylene terephthalate, polyethylene naphthalate, poly (1,4-cyclohexene diethylene terephthalate), etc.) and copolyesters are recommended. It is preferable to use them as a mixture. However, when the heat-shrinkable polyester film is used, it is preferable that 1 to 2 mol% of the whole polyester is an aliphatic dicarboxylic acid unit. By controlling in this range, the start temperature of heat shrinkage can be controlled in 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 a transesterification method or the like in which a dicarboxylic acid dimethyl ester is reacted with a diol. The adjustment may be performed by either a batch method or a continuous method.

In addition to the above polyester, various known additives may be added to the raw material composition, if necessary. Examples of the additives include lubricants such as titanium dioxide, fine particle silica, kaolin, calcium carbonate; antistatic agents;
Antiaging agents; ultraviolet absorbers; coloring agents (dyes, etc.).

The above raw material composition can be prepared by a known method (for example,
It is formed into a film by an extrusion method or a calendar method). The shape of the film is, for example, a plane shape or a tube shape, and is not particularly limited. As the stretching method, a known method such as a roll stretching method, a long gap stretching method, a tenter stretching method, or a tubular stretching method can be employed. In any of these methods, sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, and a combination of these may be performed. In the above-mentioned biaxial stretching, stretching in the longitudinal and transverse directions may be carried out simultaneously, but sequential biaxial stretching in which either one is carried out first is effective, and the longitudinal and lateral directions may be carried out first. The stretching ratio is arbitrarily set in the range of 1.0 to 7.0, and if the predetermined unidirectional ratio is 3.5 times or more, preferably 4.5 times or more, the heat shrinkage rate is 40%. Can be achieved.

In the stretching step, preheating is preferably carried out 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 heat setting during stretching, for example, it is recommended to pass a heating zone at 30 to 150 ° C. for about 1 to 30 seconds after stretching. Further, after the film is stretched, it may be stretched to a predetermined degree before or after heat setting. Further, after the stretching, a step of cooling the film while applying a stress to the film while keeping the stretched or tensioned state, or a cooling step after the tensioned state is released following the treatment, may be added. The thickness of the obtained film is preferably in the range of 6 to 250 μm.

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

The heat-shrinkable polyester film of the present invention thus obtained has a smaller shrinkage rate than the conventionally proposed heat-shrinkable polyester film, and uneven shrinkage is less likely to occur in the film when it is shrunk. In addition to being finished with a beautiful appearance, the appearance can be stably maintained even under various high temperature conditions that will be experienced later.

[0025]

The present invention will be described in more detail with reference to the following examples, but the following examples do not limit the present invention.
All modifications and implementations that do not depart from the spirit of the description below are included in the technical scope of the present invention. Measurements used in the examples
The evaluation method is as follows.

(1) Moisture content in film Karl Fischer moisture meter (KYOTO Electr)
MikC-210 manufactured by Onics Co., Ltd. was used, and the weight of the sample was 1 g and the sample heating temperature was 230 ° C. (2) Shrinkage unevenness Metallic printing for shrinkage labels is applied to the film to form a tube into a cylindrical shape, which is then covered with a 1.5-liter rectangular PET bottle and passed through a shrink tunnel. The conditions of the shrink tunnel were as follows: First zone: 100 ° C. × retention time 4.5 seconds, Second zone: 140 ° C. × retention time 5 seconds. The presence or absence of print shading due to uneven contraction of the obtained label was visually judged. ⊚: Very good without uneven shrinkage. ◯: Shrinkage unevenness is not complete, but relatively good. B: Shrinkage unevenness is recognized, which is close to a defect. X: There are many uneven shrinkages and it is defective.

(3) Boil treatment The film was used as a shrink label, covered with a bottle containing water, and shrinked in hot water at 80 ° C. This was immersed again in hot water at 80 ° C. for 30 minutes, and the slack state of the label was visually judged. A: Very good with no slack. ○: There is no slack, but it is relatively good. Δ: Sagging is recognized and it is close to defective. X: Lots of slack and defective. (4) Proper filling of high-temperature substance The shrink film is used as a shrink label, and the bottle is shrink-mounted by the method used to determine uneven shrinkage. This bottle was filled with hot water at 87 ° C., and after 6 minutes, the state of slack of the label after water cooling was visually judged. A: Very good with no slack. ○: There is no slack, but it is relatively good. Δ: Sagging is recognized and it is close to defective. X: Lots of slack and defective.

(5) Heat Shrinkage The film is cut out so that the shrinking direction is the long side and the width is 15 mm. Marks are drawn at intervals of 200 mm in the long side direction. The sample is heated with hot air of 100 ° C. for 1 minute to measure the amount of change in the distance between the marked lines. The percentage of this change amount to the original length was defined as the heat shrinkage rate (%). (6) Shrinkage rate The shrinkage film is cut into an appropriate size, immersed in an oil bath at 80 ° C for 1 second, and immediately air-cooled, and the percentage of the change amount in the main shrinkage direction to the original length is calculated as The evaluation characteristics were used.

Example 1 As dicarboxylic acid component, 95.4 mol% of terephthalic acid
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 diameter of 2.4 μ.
Using a copolymerized polyester composition containing 0.05% by weight of silicon dioxide of m as a raw material, melt extrusion was performed 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 the water adhering to the film surface. At this time, the water content in the film was 8200 ppm. This unstretched film 1
After preheating at 10 ° C. for 6 seconds, it 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 to give a thickness of 40
A heat shrinkable film having a thickness of μm was obtained. The water content in the film at this time was 3600 ppm.

Examples 2 and 3 Using the same copolyester composition as in Example 1, the treatment with hot water was carried out at 60 ° C. for 30 seconds (Example 2), 40 ° C. for 60 seconds (Example 3), respectively. A heat shrinkable film was obtained in the same manner as in Example 1 except for the above. The water content in the unstretched film at this time 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 copolyester composition as in Example 1 was heated in hot water at 80 ° C. for 20 days.
After preheating for 2 seconds, 4.8 in the prescribed direction in hot water at 65 ° C
The film was stretched twice and the surface was dried to obtain a heat-shrinkable film having a thickness of 40 μm. The water content of the film at this time is 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 copolyester composition as in Example 1 was used and no treatment with hot water was carried out. At this time, the water content after stretching film formation was 600 ppm. The properties of the obtained heat-shrinkable film are summarized in Table 1.

[0033]

[Table 1]

[0034]

EFFECT OF THE INVENTION The heat-shrinkable polyester film of the present invention has a practically sufficient heat-shrinkage rate, and when it is heat-shrinked and used for coating or binding, the temperature gradient and nonuniformity in the shrinking process. In the high temperature conditions that the film experiences after shrinking, such as high temperature sterilization treatment after coating or bundling (eg retort treatment, boil treatment), filling of the coated container with high temperature substance, etc. Also, it has no slack or wrinkles and is highly useful in a wide range of packaging material fields.

Claims (1)

[Claims] 1. A heat-shrinkable polyester film, wherein the heat shrinkage in one direction of the film at 100 ° C. is 40% or more, and the water content of the film is 1,000 ppm or more and less than 10,000 ppm.