JPH05318588A - Heat shrinkable polyester series film - Google Patents

Abstract

PURPOSE:To provide a heat shrinkable polyester series film having beautiful finish and external appearance without disadvantages such as wrinkling, distortion, shrinkage spots, partial whitening, etc. CONSTITUTION:The heat shrinkable polyester series film contains 40-80mole% of ethylene terephthalate unit, and has 30% or more of heat shrinkability at 100 deg.C and 1.32g/cm<3> or less of a density after it is thermally shrinked.

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 gives a beautiful finished appearance with very few defects such as wrinkles, distortion, and whitening of shrinkage spots when heat-shrinked.

[0002]

2. Description of the Related Art Heat-shrinkable films are used for coating various containers such as bottles (including glass and plastic bottles) and cans, and long objects (pipes, rods, wood, various rod-shaped bodies), and binding. It is used for exterior or exterior.
For example, it is used to cover a part or the whole of the cap portion, shoulder portion, and body portion of a bottle for the purpose of marking, protection, bundling, and improvement of commercial value. In addition, boxes, bottles,
It is also used for the purpose of accumulating and packaging a plurality of plates, sticks, notebooks, etc., and for the purpose of closely adhering a film to an object to be packaged and packaging it with the film (skin package). The above applications make use of the shrinkage and shrinkage stress of the film. As the material of the film, polyvinyl chloride, polystyrene, polyethylene, rubber hydrochloride, etc. are used. Usually, these films are formed into a tube shape, for example, after covering a bottle or accumulating pipes,
Packaging or binding is performed by heat shrinking. However, since the conventional film has poor heat resistance and cannot withstand any high temperature boil treatment or retort treatment, it cannot be sterilized at high temperature. For example, when a retort process is performed, the conventional film is damaged during the process.

Further, when a conventional film, for example, a polyvinyl chloride film is printed, its adhesion to ink is poor. Furthermore, since vinyl chloride lacks heat resistance, a gel of a polymer or an additive is likely to be partially formed during film formation. Because of this gel-like material, pinholes are likely to occur on the printed surface. Since the above-mentioned conventional film shrinks with time after manufacturing, the printing pitch changes due to shrinkage, and high-precision printing cannot be performed. On the other hand, a heat-shrinkable film using a polyester having excellent heat resistance, weather resistance and solvent resistance has been proposed. This polyester heat-shrinkable film has problems that the heat shrinkage in the desired direction is insufficient and the heat shrinkage in the direction orthogonal to the direction cannot be reduced. However, such a problem is found in, for example, Japanese Patent Laid-Open No. 63-156.
This can be solved by optimizing the copolymerization composition of the raw material polyester resin as disclosed in, for example, Japanese Patent No. 833. However, the films obtained by these methods also have problems such as an excessively fast shrinkage rate, and defects such as wrinkles, distortions, shrinkage spots, and partial whitening of the film when heat-shrinked are beautiful. There is a drawback that it is difficult to obtain a good appearance.

[0004]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems of the prior art. The object of the present invention is to make the heat shrinkage sufficiently large and to shrink uniformly. It is an object of the present invention to provide a heat-shrinkable polyester film which gives a beautiful appearance without defects such as wrinkles, distortions, shrinkage spots, and partial whitening of the film when exposed.

[0005]

The heat-shrinkable polyester film of the present invention is a heat-shrinkable polyester film containing at least one polyester, and 40 to 80 mol% of the total polyester contained. An ethylene terephthalate unit, wherein the polyester film has a heat shrinkage ratio at 100 ° C. of 30% or more in one predetermined direction of the film, and the density of the film after the heat shrinkage treatment is 1.32 or less. This is a heat-shrinkable polyester film.

The dicarboxylic acid component constituting the polyester contained in the composition used in the thermoplastic polyester film of the present invention includes terephthalic acid constituting an ethylene terephthalate unit, an aromatic dicarboxylic acid,
Both aliphatic and alicyclic dicarboxylic acids can be used. As aromatic dicarboxylic acids, benzenedicarboxylic acids such as isophthalic acid, orthophthalic acid and 5-tert-butylisophthalic acid; naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid;
4,4'-dicarboxydiphenyl, 2,2,6,6-
Dicarboxybiphenyls such as tetramethylbiphenyl-4,4'-dicarboxylic acid; 1,1,3-tolumethyl-3-phenylindene-4,5-dicarboxylic acid and its substitution product; 1,2-diphenoxyethane- 4,4'-
There are dicarboxylic acids and their substitution products. Examples of the aliphatic dicarboxylic acid 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, taposic acid. , Nonadecane dicarboxylic acid, docosane dicarboxylic acid, and substituted products thereof, 4,4′-dicarboxycyclohexane and substituted products thereof.

As the diol component of the polyester contained in the above composition, there is ethylene glycol which constitutes a polyethylene terephthalate unit, and in addition to this, any of aliphatic diol, alicyclic diol and aromatic diol can be used. Examples of the aliphatic diol include diethylene glycol propylene glycol, butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,3-propanediol, 2-ethyl- 2-n-
Butyl-1,3-propanediol and the like. Examples of the alicyclic diol include 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol.
Aromatic dicarboxylic acids include 2,2-bis (4'-β
Ethylene oxide adducts of bisphenol compounds such as -hydroxyethoxydiphenyl) propane and bis (4'-β-hydroxyethoxyphenyl) sulfone; polyalkylene glycols such as xylylene glycol, polyethylene glycol and polypropylene glycol.

The polyester contained in the composition used in the film of the present invention can be formed from the above-mentioned acid component and diol component. In order to prepare the polyester, it is usually preferable to use one or more acid components or diol components in combination, which can improve the properties as a heat-shrinkable film. The type and content of the monomer components used in combination can be appropriately determined based on desired film properties, economic efficiency and the like.

The heat-shrinkable polyester film of the present invention is a heat-shrinkable polyester film comprising a composition containing at least one type of polyester as described above, and the total polyester content is 40 to 80 mol. %
Must be an ethylene terephthalate unit.
40 to 75 mol% is preferable, and 40 to 70 mol% is more preferable. When the ethylene terephthalate unit is less than 40 mol%, the heat resistance of the film is low and it cannot withstand high temperature boil treatment or retort treatment. further,
The manufacturing cost is also high. On the other hand, if it exceeds 80 mol%, it is difficult to reduce the density of the film after heat shrinkage to 1.32 or less, and therefore wrinkles, distortions, shrinkage spots, and partial whitening occur on the film when heat shrinked. This is not preferable because defects such as the above occur and a beautiful appearance cannot be obtained. The ethylene terephthalate unit here means a value obtained by integrating the amount of terephthalic acid residues and the amount of ethylene glycol residues of the final composition.

The heat-shrinkable polyester film of the present invention is a preferred embodiment in which 1 to 10 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.

A heat-shrinkable polyester film of the present invention, which has a heat of fusion measured by DSC of 1 cal / g or less, preferably an amorphous polyester in which the heat of fusion cannot be observed is a preferred embodiment. The characteristics can be achieved by controlling the amount of ethylene terephthalate unit described above.

Any of the polyesters contained in the above composition can be produced by conventional methods. For example,
A direct esterification method in which a dicarboxylic acid and a diol are directly reacted; a dicarboxylic acid dimethyl ester and a diol;
A (copolymerization) polyester is prepared using a transesterification method of reacting The preparation may be performed by either a batch method or a continuous method. The polyester composition constituting the film of the present invention contains one or more polyesters. When one type of polyester is contained, it is a copolyester that satisfies the content ratio conditions of the ethylene terephthalate unit and the polyethylene glycol and / or polyethylene glycol copolymer unit. If more than one, it is a desired mixture of two or more of copolyesters and homopolyesters,
The mixture satisfies the above conditions. 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 dimethylene terephthalate) and a copolyester are preferably mixed and used.
In particular, the method of mixing polyethylene terephthalate and copolyester is preferable from the economical point of view because polyethylene terephthalate can be obtained at a low cost.

The polyester composition constituting the film of the present invention contains various additives as required in addition to the above polyester. Examples thereof include lubricants such as titanium dioxide, fine particle silica, kaolin, and calcium carbonate; antistatic agents; antiaging agents; ultraviolet ray inhibitors; coloring agents (dyes, etc.). The intrinsic viscosity when the above polyester and various components of the polyester composition containing various additives as necessary are mixed is preferably 0.50 to 1.
3d / g.

The heat-shrinkable polyester film of the present invention needs to have a density of 1.32 or less after heat shrinking. When the density of the film after heat shrinkage exceeds 1.32, defects such as wrinkles, distortions, shrinkage spots, and partial whitening occur in the film when heat shrinked, and a beautiful appearance cannot be obtained, which is preferable. Absent. The major technical point for making the density of the film after the heat shrinkage below 1.32 is:
As described above, the amount of polyethylene terephthalate cot in the polyester composition is regulated to a smaller amount than the conventionally known method. It is not clear why the film has a beautiful appearance without the above-mentioned defects by setting the density of the film after the heat shrinkage to 1.32 or less, but the heat shrinkage rate is appropriate and the film is slightly heated. This is because even if there is temperature unevenness during shrinking, uniform shrinkage occurs, and even if some shrinkage unevenness occurs during shrinking, the shrinkage unevenness is corrected in the heat shrink furnace by the thermal stress of the film itself. I think that the.

The heat-shrinkable polyester film of the present invention preferably has a density before heat shrinkage of less than 1.32. More preferably, it is 1.30 or less. That is, it is a preferred embodiment that the density of the film is low before and after the heat shrinkage, and the change in the film density is reduced by the heat shrinkage. The density before the heat shrinkage was 1.
In order to make it less than 32, in addition to optimizing the polyester composition as described above, in the manufacturing process for manufacturing the heat-shrinkable film, the stress of the film generated in the stretching process is moderately relaxed by means such as heat setting. It can be achieved by doing. For example, one way is to raise the heat setting temperature. Further, one means is to devise so that excessive stress is not generated in the film in the stretching step, and for example, stretching at high temperature is one means, but it is not necessary to be particular about these means.

The above polyester composition is formed into a film by a known method (for example, extrusion method, calender method). The shape of the film is, for example, a plane shape or a tube shape, and is not particularly limited. The obtained film is stretched, for example, in a predetermined one direction (main stretching direction) in a range of 2.5 to 7.0 times, preferably 3.0 to 6.0 times under a predetermined condition described later. To be done. 1.0 to 2.0 times in the direction orthogonal to the direction, preferably 1.
Stretching is performed in the range of 1 to 1.8 times. Either may be the first in the order of this stretching. Stretching in the main stretching direction is
This is done to obtain a high heat shrinkage ratio in this direction. By stretching in the direction orthogonal to the main stretching direction, the impact resistance of the obtained film is improved and the property of being easily torn in one direction is relaxed. The draw ratio in the above-mentioned right angle direction is 2
When it exceeds twice, the heat shrinkability in the direction orthogonal to the main shrinkage direction becomes too large, and the finish when heat shrinks becomes uneven in a wavy state. The film stretched at the above ratio usually has a shrinkage in the direction orthogonal to the shrinkage in the main direction of 15% or less, preferably 8 to 9%, and more preferably 7% or less. Such a film has a uniform finish when subjected to heat treatment.

As a stretching method, a usual method is adopted. Examples thereof include roll stretching method, long gap stretching method, tenter stretching method, and tubular stretching method. In any of these methods, the stretching is performed by sequential biaxial stretching and simultaneous biaxial stretching.
Axial stretching, uniaxial stretching, and combinations thereof can be performed. In the above-mentioned biaxial stretching, stretching in the longitudinal and transverse directions may be performed simultaneously, but sequential biaxial stretching in which either one is performed first is effective, and the longitudinal and transverse directions may be performed first. Preferably, the above stretching is performed in the following steps. For example, first, the film is preheated at a temperature not lower than the average glass transition temperature (Tg) of the polymer constituting the film, for example, Tg + 80 ° C. or lower. When preheating is performed in the above temperature range during stretching in the main direction (main shrinkage direction), heat shrinkage in the direction orthogonal to the direction can be suppressed. Moreover, by performing the heating within the temperature range of 80 ± 25 ° C., the heat shrinkage ratio in the orthogonal direction becomes almost minimum.

During these stretching, heat setting is usually performed. For example, after stretching, 30 ° C. to 150 ° C.
It is recommended to pass a heating zone at 0 ° C. for about 1 to 30 seconds. By performing heat setting, dimensional change of the obtained film under high temperature in summer can be prevented. The stretching may be performed to a predetermined degree after the film is stretched and before or after the heat setting. In that case, extension is performed at a rate of up to 70% of the film length. In particular, it is better to extend in the main direction and not extend in the non-contraction direction (direction orthogonal to the main contraction direction). Furthermore, after the stretching, a step of cooling while keeping the stretched or tensioned state while applying stress to the film, or adding a step of continuously cooling after releasing the tensioned state after the treatment is obtained. The shrinkage property of the film by heating becomes better and more stable.

The plane orientation coefficient of the film thus obtained is preferably 100 × 10 ^-3 or less. When the plane orientation coefficient exceeds 100 × 10 ⁻³ , the strength is lowered and the surface is liable to be broken even by a small amount of external damage. For example, even if it is wrapped around the outer surface of a bottle and used as a reinforcing material, the reinforcing effect is low. The birefringence is preferably 15 × 10 ^{−3 to} 160 × 10 ⁻³ . When the birefringence is less than 15 × 10 ⁻³ , the shrinkage rate and shrinkage stress in the main shrinkage direction are low. On the other hand, if it exceeds 160 × 10 ⁻³ , it is easily broken by external damage and the impact strength is low, so that it is not practical. The resulting film thickness is 6
The range of ˜250 μm is preferable.

EXAMPLES The present invention will be described below with reference to examples. The measuring method used in the examples is as follows. Heat shrinkage film is cut into a width of 15 mm to make a sample, and a marked line is drawn in a space of 200 mm in the longitudinal direction. Hot air having a predetermined temperature (90 ° C.) is applied to this sample for 1 minute to heat it, and the shrinkage rate is measured. Film Density The density was measured at 25 ° C. using a density gradient tube composed of a mixed solution of n-heptane and carbon tetrachloride. The density after heat shrinkage is measured for a film that has been shrunk by heating with hot air at 90 ° C. for 1 minute. The shrink-finished film was subjected to metallic printing as a shrink label and tubed into a cylindrical shape, and then covered with a 1.5-inch rectangular PET bottle and passed through a shrink tunnel. The condition of the shrink tunnel is 100 ° C in the first zone and the residence time is 4.5.
Second, the second zone was 140 ° C. and the residence time was 5 seconds. The finish of shrinkage of the obtained label was visually judged with respect to wrinkles, print distortion, and print shading due to shrinkage unevenness.

EXAMPLE 1 83 mol% of terephthalic acid as dicarboxylic acid, 14 mol% of isophthalic acid and 3 mol% of sebacic acid, 70 mol% of ethylene glycol, 3 mol% of diethylene glycol and 27 mol% of neopentyl glycol as diol components. And silicon dioxide with an average particle size of 2.4 μm 0.0
Copolymerized polyester containing 5% by weight and having an intrinsic viscosity of 0.70 d / g was melt extruded at 290 ° C. to give a thickness of 190 μm.
I got a film. This unstretched film is heated at 120 ° C for 6
After anticipating for a second, it was stretched 4.7 times in one predetermined direction.
The temperature condition during stretching is 80 until the half of all steps.
The other half was set to 90 ° C. After stretching, while maintaining a tension state, it was cooled to 40 ° C. to obtain a heat-shrinkable film having a thickness of 40 μm. The properties of the heat-shrinkable film thus obtained are shown in Table 1. The heat-shrinkable film obtained in this example had a low density after shrinkage, had a good shrinkable finish as a shrinkable label, and was highly practical.

Examples 2 to 3 Polyethylene terephthalate and copolymerized polyester were mixed at the compounding ratios shown in Table 1 to obtain a heat-shrinkable film in the same manner as in Example 1.
Shown in. Like the heat-shrinkable film obtained in Example 1, the heat-shrinkable film obtained in these Examples has a low density after shrinkage, has a good shrink finish as a shrink label, and is highly practical. It was a thing.

Comparative Examples 1 to 4 As shown in Table 1, Example 1 was modified by increasing the polyethylene terephthalate units in the polyester composition.
The characteristics of the heat-shrinkable film obtained in the same manner as in Table 1 are shown in Table 1. The heat-shrinkable films obtained in these comparative examples are
The film after heat-shrinking had a high density, and the shrinkable finish as a shrinkable label was poor, and the practicality was low.

[0024]

EFFECT OF THE INVENTION The shrink film of the present invention is a film which gives a beautiful appearance with very few defects such as wrinkles, distortions and shrinkage spots when it is heat-shrinked, and it is widely used for label shrink films. It is useful in the packaging material field and has high utility value.

[0025]

[Table 1]

[0026]

[Table 2]

Claims (1)

[Claims] 1. A heat-shrinkable polyester film containing at least one polyester, wherein 40 to 80 mol% of the total polyester contained is an ethylene terephthalate unit, and the polyester film at 100 ° C. A heat-shrinkable polyester film having a heat shrinkage of 30% or more in a predetermined direction of the film and a density of the film after heat shrinkage of 1.32 g / cm ³ or less.