JP2932596B2 - Heat shrinkable polyester film - Google Patents

Description

Description: TECHNICAL FIELD 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 polyester film in which a heat-shrinkable film gives a beautiful finished appearance without partial whitening.

(Prior art) Heat-shrinkable films are used for covering and binding various containers such as bottles (including glass and plastic bottles) and cans and long objects (pipes, rods, wood, various rods, etc.). Or for exterior use. 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 marking, protecting, binding, improving commercial value, and the like. Further, it is also used for applications such as stacking and packaging a plurality of boxes, bottles, boards, sticks, notebooks, and the like, and for packaging a skin by tightly attaching a film to an object to be packaged (skin package). The above application utilizes the shrinkage and shrinkage stress of the film.

As the material of the film, polyvinyl chloride, polystyrene, polyethylene, hydrochloride rubber and the like are 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 then heat shrinking.

However, the conventional film has poor heat resistance and cannot withstand boil treatment or retort treatment at any high temperature, and thus cannot be sterilized at high temperature. For example, when a retort process is performed, the conventional film breaks during the process.

Further, when a conventional film is printed on, for example, a polyvinyl chloride film, 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 easily generated on the printing surface.

Since the above-mentioned conventional film shrinks with time after production, the printing pitch changes due to the shrinkage, and high-precision printing cannot be performed.

On the other hand, a heat-shrinkable film using a polyester excellent in heat resistance, weather resistance and solvent resistance has been proposed. This polyester heat-shrinkable film has heretofore had problems such as an insufficient heat shrinkage in a desired direction and an inability to reduce the heat shrinkage in a direction orthogonal to the desired direction. However, such a problem, for example, as disclosed in JP-A-63-156833 and the like,
This can be solved by optimizing the copolymer composition of the raw polyester resin. However, even when the film obtained by this method is shrunk by hot air, for example, a portion that shrinks sufficiently and a portion that shrinks insufficiently occur, and a patchy pattern (shrinkage spot) is likely to be generated on the film surface. Further, there is a drawback that a particularly shrinked portion of the heat shrunk film is whitened, which impairs the appearance of the product.

(Problem to be Solved by the Invention) The present invention is to solve the above conventional problems,
It is an object of the present invention to provide a heat-shrinkable polyester film which has a sufficiently high heat shrinkage and does not partially whiten because it shrinks uniformly and gives a beautiful finished appearance.

(Means for Solving the Problems) The heat-shrinkable polyester film of the present invention is a heat-shrinkable polyester film containing at least two kinds of polyesters, and one of the contained polyesters is 50 to 90 moles in total. % Is an ethylene terephthalate unit and 0.05 to 10 mol% is a polyethylene glycol unit and / or a polyethylene glycol copolymer, and the heat shrinkage of the polyester film at 100 ° C is 100%. The heat shrinkage is 30% or more in one predetermined direction of the film, thereby achieving the above object.

As the dicarboxylic acid component constituting the polyester contained in the composition used in the thermoplastic polyester film of the present invention, in addition to terephthalic acid constituting an ethylene terephthalate unit, aromatic dicarboxylic acid, aliphatic dicarboxylic acid and alicyclic dicarboxylic acid Can be used. As aromatic dicarboxylic acids, isophthalic acid,
Orthophthalic acid, benzenedicarboxylic acids such as 5-tert-butylisophthalic acid; naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid; 4,4'-dicarboxydiphenyl, 2,2,6,6-tetramethylbiphenyl- 4,4 '
-Dicarboxybiphenyls such as dicarboxylic acids; 1,1,3
-Tolumethyl-3-phenylindene-4,5-dicarboxylic acid and its substituted products; 1,2-diphenoxyethane-4,
4'-dicarboxylic acid and its substituted products. Aliphatic dicarboxylic 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, tapsin Acids, nonadecanedicarboxylic acid, docosandicarboxylic acid, and substituted products thereof, such as 4,4'-dicarboxycyclohexane and substituted products thereof.

As the diol component of the polyester contained in the composition, there are ethylene glycol and diethylene glycol constituting the polyethylene terephthalate unit, and in addition, any of aliphatic diol, alicyclic diol and aromatic diol can be used. As the aliphatic diol, propylene glycol, butanediol,
1,6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,3-
There are propanediol, 2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol and the like. Examples of the alicyclic diol include 1,3-cyclohexaneditamenol and 1,4-cyclohexanedimethanol. As aromatic dicarboxylic acids, 2,2
-Ethylene oxide adducts of bisphenol compounds such as -bis (4'-β-hydroxyethoxydiphenyl) propane and bis (4'-β-hydroxyethoxyphenyl) sulfone; xylylene 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. The above components are appropriately selected and used so as to satisfy the amounts of the ethylene terephthalate unit and the polyethylene glycol and / or polyethylene glycol copolymer unit in the composition described below. In order to prepare a polyester, it is usually preferable to use one or more acid components or diol components in combination, whereby the properties of the heat-shrinkable film can be improved. The kind and content of the monomer components used in combination can be appropriately determined based on desired film properties, economic efficiency, and the like.

As described above, the heat-shrinkable polyester film of the present invention is a heat-shrinkable polyester film comprising a composition containing at least two kinds of polyesters, wherein one of the contained polyesters is 50 to 90 moles in total. % Are ethylene terephthalate units. If the ethylene terephthalate unit is less than 50 mol%, the heat resistance of the film is low, and the film cannot withstand high-temperature boil treatment or retort treatment. Further, the manufacturing cost is high. vice versa,
If it exceeds 90 mol%, the one-way shrinkage decreases, and the retention time of residual stress during heat treatment becomes short. Therefore, for example, when a bottle is covered with such a film and subjected to a heat sterilization treatment, the shoulder is loosened.

One of the polyesters contained in the heat-shrinkable polyester film of the present invention comprises 0.05 to
10 mol%, preferably 0.2 to 5 mol%, is polyethylene glycol and / or polyethylene glycol copolymer units. When the content of the polyethylene glycol and / or polyethylene glycol copolymer unit is less than 0.05 mol%, when the obtained film is thermally shrunk, the degree of shrinkage becomes non-uniform, and as a result, partial shrinkage occurs. And the appearance becomes poor. Conversely, if it exceeds 10 mol%, the stability of the film, particularly the weather resistance and heat resistance, will be poor. Therefore, it cannot withstand boil processing and retort processing at high temperature. When the film is colored, there is also a problem that the color of the film after shrinking becomes dark.

The molecular weight of the polyalkylene glycol and the polyalkylene glycol copolymer unit used in the present invention is not particularly limited, but is 150 to 200,000, preferably 200 to 20,
000 are preferred.

In the case of a copolymer, the copolymer component includes propylene glycol, tetramethylene glycol and the like.

Any of the polyesters contained in the composition can be produced by a conventional method. For example, a (copolymerized) polyester is prepared using a direct esterification method in which a dicarboxylic acid and a diol are directly reacted; a transesterification method in which a dicarboxylic acid dimethyl ester is reacted with a diol. The preparation may be carried out in any of a batch mode and a continuous mode.

The polyester composition constituting the film of the present invention contains two or more polyesters. It is a mixture of two or more desired copolyesters and homopolyesters, which satisfies the above conditions. In general, copolymerized polyesters have a low melting point, so there are problems such as difficult handling during drying.
It is preferable to use a mixture of a homopolyester (polyethylene terephthalate, polyethylene naphthalate, poly (1,4-cyclohexene dimethylene terephthalate)) and a copolymerized polyester. By using a mixture of polyesters having different glass transition temperatures, the heat shrinkage properties of the obtained film are improved. In particular, a method of mixing polyethylene terephthalate and a copolymerized polyester is preferable in terms of economy because polyethylene terephthalate can be obtained at low cost.

The polyester composition constituting the film of the present invention contains various additives as required in addition to the polyester described above. They include, for example, lubricants such as titanium dioxide, particulate silica, kaolin, calcium carbonate, etc .; antistatic agents; antioxidants; ultraviolet inhibitors; coloring agents (dyes, etc.).

The intrinsic viscosity when mixing the above polyester and various components of the polyester composition containing various additives as necessary is preferably 0.50 to 1.3 dl / g.

The polyester composition is formed into a film by a known method (for example, an extrusion method or a calender method).
The shape of the film is, for example, a flat shape or a tube shape, and is not particularly limited. The obtained film is, for example,
Under predetermined conditions described later, the film is stretched in a predetermined direction (main stretching direction) in a range of 2.5 to 7.0 times, preferably 3.0 to 6.0 times. 1.0 times in the direction perpendicular to the direction
The film is stretched 2.0 times, preferably 1.1 to 1.8 times. This stretching may be performed in any order. Stretching in the main stretching direction is performed to obtain a high heat shrinkage in this direction. Stretching in the direction perpendicular to the main stretching direction improves the impact resistance of the obtained film and alleviates the property that the film is easily torn in one direction. If the stretching ratio in the perpendicular direction exceeds twice, the heat shrinkability in the direction perpendicular to the main shrinkage direction becomes too large, and the finish after the heat shrinkage becomes uneven in a wavy state. The film stretched at the above ratio usually has a shrinkage in the direction perpendicular to the main shrinkage of 15% or less, preferably 8 to 9% or less, more preferably 7% or less with respect to the shrinkage in the main direction.
Such a film has a uniform finish when subjected to a heat treatment.

As a stretching method, an ordinary method is employed. For example, there are a roll stretching method, a long gap stretching method, a tenter stretching method, and a tubular stretching method. In any of these methods, stretching can be performed by sequential biaxial stretching, simultaneous biaxial stretching, monoaxial stretching, and combinations thereof. In the biaxial stretching described above, stretching in the vertical and horizontal directions may be performed simultaneously, but sequential biaxial stretching in which one of them is performed first is effective, and the order of the vertical and horizontal directions may be any.

Preferably, the stretching is performed in the following steps. For example, first, the above film, the average glass transition temperature (Tg) or more of the polymer constituting it, for example,
Preheat at a temperature of Tg + 80 ° C or less. When preheating is performed in the above temperature range at the time of main direction stretching (main shrinkage direction), heat shrinkage in a direction orthogonal to the direction can be suppressed. And 80 ±
By performing the heat treatment in a temperature range of 25 ° C., the heat shrinkage in the orthogonal direction is almost minimized.

At the time of stretching, heat setting is usually performed.
For example, after stretching, it is recommended to pass through a heating zone of 30C to 15C for about 1 to 30 seconds. By performing the heat setting, it is possible to prevent a dimensional change of the obtained film under a high temperature in summer. After the stretching of the film and before or after performing the heat setting, the stretching may be performed at a predetermined degree. In that case, elongation is performed at a rate up to 70% of the film length. In particular, it is better to extend in the main direction and not to extend in the non-contraction direction (the direction orthogonal to the main contraction direction).

Further, after the stretching, the film can be obtained by adding a step of cooling while applying stress to the film while maintaining the stretched or stretched state, or adding a step of continuously cooling after releasing the strained state following the treatment. The shrinkage characteristics of the resulting film upon heating become better and more stable.

The plane orientation coefficient of the film thus obtained is 100 × 10
It is preferably ^-3 or less. Plane orientation coefficient is 100 × 10 ^-3
When it exceeds, the strength is reduced, and it becomes easy to be torn even by a slight injury. For example, even if it is wound around the outer surface of a bottle and used as a reinforcing material, the reinforcing effect is low.

The birefringence is preferably from 15 × 10 ^{−3 to} 160 × 10 ⁻³ . If the birefringence is less than 15 × 10 ⁻³ , the contraction rate and contraction stress in the main contraction direction will be low. Conversely, if it exceeds 160 × 10 ⁻³ , it is liable to be torn by an external injury and the impact strength is low, so that the practicality is low. The thickness of the resulting film is 6-250
The range of μm is preferred.

The heat-shrinkable polyester film of the present invention thus obtained does not cause partial whitening of the film even if it is shrunk with hot air after storage at 40 ° C. for 3 days.
The film of the present invention is printed on its surface as required. By heat shrinking, it is used for various applications such as coating, bundling, and exterior.

(Example) Hereinafter, the present invention will be described with reference to examples. The measuring method used in the examples is as follows.

(1) Heat shrinkage The film is cut to a width of 15 mm to make a sample, and the film is cut in the longitudinal direction.
Mark lines at 200mm intervals. Hot air at a predetermined temperature (100 ° C.) is applied to the sample for 1 minute to heat the sample, and the shrinkage is measured.

(2) Heat shrinkage residual stress retention time (at 50% relaxation) A film is a test piece of 20 mm width and 150 mm length, and marked lines are drawn at 100 mm intervals in the longitudinal direction. The distance between the pair of upper and lower chucks of Tensilon is set to 50 mm, and the film is fixed to these chucks at the positions indicated by the marked lines. To this 100
The film is shrunk by applying hot air at a temperature of ° C., and the time until the shrinkage stress becomes zero is determined.

(3) Partial whitening The film is stored at 40 ° C. for 3 days while being wound on a roll. This is cut into a width of 230 mm, processed by a tube forming apparatus, and processed into a tube shape. 140mm length of the tube
Cut, cover with a single service size glass bottle, expose to hot air of 130 ° C for 5 seconds, and heat shrink. The heat shrunk film is visually observed to determine the presence or absence of a whitened portion.

EXPERIMENTAL EXAMPLE 1 A copolymerized polyester consisting of 100 mol% of terephthalic acid, 0.5 mol% of polyethylene glycol having a molecular weight of 1000, 8.75 mol% of ethylene glycol, 2 mol% of diethylene glycol and 10 mol% of neopentyl glycol was prepared.
The mixture was melt extruded at a temperature of 180 ° C. to obtain an unstretched film having a thickness of 180 μm. This film was stretched 1.2 times in the machine direction and then 4.1 times in the transverse direction. Then, the film was further cooled while being stretched in the transverse direction by about 20% to obtain a stretched film having a thickness of 40 μm. The characteristics of the obtained film were measured in Examples 2 to 7 described below.
Table 1 shows the results of Comparative Examples 1 to 8.

Comparative Example 1 A stretched film was prepared in the same manner as in Experimental Example 1 except that instead of blending polyethylene glycol in the method of Experimental Example 1, a copolymerized polyester in which the proportion of ethylene glycol was increased by a considerable number of moles was used. .

Table 1 shows the properties of the obtained film. When the film thus obtained was subjected to a partial whitening test, partial whitening was observed at the shoulder of the bottle with a high film shrinkage.

Comparative Example 2 A stretched film was produced in the same manner as in Experimental Example 1 except that the blending ratio of neopentyl glycol was 50 mol% and the ratio of ethylene terephthalate unit was 45.5 mol% outside the scope of the present invention. Prepared. Table 1 shows the properties of the obtained film. Table 1 shows the characteristics of the obtained film. The film obtained here has a short residual stress holding time when heat-treated, and tends to be loosened by the heat treatment.

Examples 1 to 6 Polyethylene terephthalate and various copolymerized polyesters containing polyethylene glycol or polyethylene glycol copolymer were uniformly blended in the proportions shown in Table 1, and a stretched film was prepared in the same manner as in Experimental Example 1. .

 Table 1 shows the properties of the obtained film.

Comparative Examples 3 to 8 In place of blending polyethylene glycol or a polyethylene glycol copolymer in the copolymerized polyester in the method of Examples 1 to 6, a copolymerized polyester in which the proportion of ethylene glycol is increased by a considerable number of moles is used. Table 1 shows the characteristics of the films prepared in the same manner as in Examples 1 to 6 except for the above.

In all of the films obtained in these comparative examples, partial whitening was observed at the shoulder of the bottle having a high film shrinkage in the partial whitening test.

From Table 1, the heat-shrinkable films of the present invention were obtained in Examples 1 to
As shown in Fig. 6, it has an excellent heat shrinkage of 58% or more in the main shrinkage direction and 2.5% or less in the direction perpendicular thereto. The residual stress retention time during heat treatment is also sufficiently long, for example, when coated on a bottle,
There is no loosening of the shoulder during heat treatment for sterilization. Furthermore, the shrunk film has a beautiful appearance without partial whitening.

(Effect of the Invention) According to the present invention, a heat-shrinkable polyester film having sufficient heat-shrinkability in a predetermined direction and uniformly shrinking is obtained. When this film is used, a strong packaging state can be given in the covering packaging or the binding packaging. Furthermore, the shrinkable film does not partially whiten, and packaging with a beautiful appearance is possible. Therefore, the film of the present invention can be suitably used in a wide range of fields.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification code FI B29L 7:00 C08L 67:00 (58) Investigated field (Int.Cl. ⁶ , DB name) C08J 5/00-5/02 C08J 5/12-5/22 B29C 61/06 B29C 55/02

Claims (1)

(57) [Claims] 1. A heat-shrinkable polyester film containing at least two polyesters, wherein one of the polyesters contains 50 to 90 mol% of ethylene terephthalate units, and 0.05 to 10 mol%. % Is a polyester comprising a polyethylene glycol unit and / or a polyethylene glycol copolymer, and the heat shrinkage at 100 ° C. of the polyester film is 30% or more in one predetermined direction of the film. Heat shrinkable polyester film.