JP2943178B2 - Heat-shrinkable polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a heat-shrinkable polyester film (including a sheet; the same applies hereinafter) exhibiting particularly suitable properties in the field of packaging materials such as coating or bundling. About.

In particular, the present invention relates to a polyester film which gives a beautiful finished appearance without partially whitening the heat shrunk film.

(Prior Art) A tubular body formed from a heat-shrinkable plastic film is, for example, a container, a bottle (including a plastic bottle), a can-bar (pipes, bars, wood, various bars) (hereinafter referred to as a container). For covering or bundling, in particular, covering a part or the whole of these caps, shoulders, trunks, etc., and used for the purpose of marking, protection, bundling, improving the commercial value, etc. In addition, it is widely used in the field of packaging, such as boxes, bottles, boards, sticks, notebooks, etc., or in close contact with an object to be packaged, such as a skin pack, and uses shrinkage and shrinkage stress. Application development is expected.

Conventionally for the above-mentioned applications, use a heat-shrinkable film such as polyvinyl chloride, polystyrene, polyethylene, and hydrochloric acid rubber, and cover it with the above-mentioned containers after forming it into a tubular body,
It was heat shrunk by stacking and packaging.

However, these films have poor heat resistance, and have a drawback in that when they are subjected to a boil treatment or a retort treatment, they melt or burst and cannot maintain a film-like body.

In applications that require printing, printing pinholes (fine irregularities due to fish eyes due to additives or polymer gels in the film) due to poor ink transfer are observed. In addition, there is also a problem that the film shrinks (shrink at room temperature) to cause a dimensional change in the printing pitch. On the other hand, a tube using a polyester-based heat shrinkable film has been made on a trial basis, but the heat shrinkage rate in a desired direction cannot be sufficiently increased, or the above-mentioned direction cannot be attained. There is a problem that it is not possible to reduce the heat shrinkage in a direction perpendicular to the above, and it has been difficult to develop the above application.

These drawbacks can be solved by optimizing the copolymer composition of the raw material polyester resin as disclosed in, for example, JP-A-63-156833. 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.

(Problems to be Solved by the Invention) The present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to have a sufficiently large heat shrinkage and uniform shrinkage to partially whiten. It is an object of the present invention to provide a heat-shrinkable polyester film which gives a beautiful finished appearance without any problem.

(Means for Solving the Problems) The heat-shrinkable polyester film of the present invention comprises a composition of polyethylene terephthalate having a diethylene glycol content of more than 2.5 to 20 mol% and a copolymerized polyester, and 50 to 90 of the constituent components. A film in which the mol% is composed of ethylene terephthalate units, and the total diethylene glycol content in the composition is 2.5 to 20 mol%, and the heat shrinkage in hot air at 100 ° C. is in a predetermined direction of the film. 30% or more, thereby achieving the above object.

The composition of the present invention is composed of polyethylene terephthalate and a copolymerized polyester, and 50 to 90 of its constituent components.
It is necessary that the mole% is composed of ethylene terephthalate units and that the content of diethylene glycol is 2.5 to 20 mole%. If the content of the ethylene terephthalate unit is less than 50 mol%, the heat resistance of the film is lowered, and it is not possible to withstand high-temperature boil treatment or retort treatment, and the production cost is undesirably increased.

Conversely, if it exceeds 90 mol%, the one-way shrinkage decreases,
The retention time of the residual stress during the heat treatment is shortened. For example, when the bottle is coated, a phenomenon such as loosening of the shoulder due to the sterilization treatment is caused, which is not preferable.

When the amount of diethylene glycol is less than 2.5 mol%, the shrinked film is partially whitened when the film is thermally shrunk, and the appearance of the product is poor, which is not preferable. Conversely, if it exceeds 20%, the stability of the film, particularly the weather resistance, or the heat resistance is lowered, and it is not preferable because the film cannot withstand high-temperature boil treatment or retort treatment. There is also a problem that the degree of coloring increases.

 Particularly preferred is 3 to 10 mol%.

The present invention is characterized in that the composition is composed of polyethylene terephthalate and a copolymerized polyester, and that the content of diethylene glycol is more than 2.5 to 20 mol% as polyethylene terephthalate.

In general, copolymer resins have a low melting point and thus are difficult to handle in drying the resin and the like. Therefore, it is preferable to use polyethylene terephthalate to reduce the use ratio of the copolymer resin. Since polyethylene terephthalate resin is produced in large quantities and the production cost is low,
The use of polyethylene terephthalate also has an advantage in terms of economy.

Usually, polyethylene terephthalate is contained in the produced polyester by-product of the condensation reaction of ethylene glycol during the production process without adding diethylene glycol during the production.

The content varies depending on the polyester production method, production conditions and the catalyst used in the production, etc.
Generally, the products on the market are between 1.0 and 2.5 mol%. As for the heat-shrinkable polyester film, for example, Example 1 of JP-A-63-150331 discloses that a copolymer resin containing 2 mol% of diethylene glycol is used.

The polyethylene terephthalate of the present invention is greatly characterized in that it is used in a range of more than 2.5 to 20 mol%, which is larger than the amount of diethylene glycol so as to be contained as a by-product when produced by a usual method. A range of 3 to 10 mol% is particularly preferred.

The control of the diethylene glycol content in the polyethylene terephthalate may be performed by optimizing the production conditions and the catalyst, or may be performed by adding a predetermined amount of diethylene glycol during the transesterification reaction or the esterification reaction.

In the method of the present invention, the content of diethylene glycol in the copolymerized resin is not particularly limited, and can be arbitrarily set as long as the total amount of diethylene glycol in the composition is in the range of 2.5 to 20 mol%. It may be 2.5 mol% or 2.5 mol% or more.

The copolymerized polyester of the present invention is not particularly limited as long as it contains a unit other than the ethylene terephthalate unit. Acid composition other than terephthalic acid used in the copolymerized polyester, isophthalic acid, phthalic acid,
Naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid; dicarboxybiphenyls such as 4,4'-dicarboxydiphenyl; substituted phthalic acids such as 5-tert-butylisophthalic acid; 2,2,6,6- Substituted dicarboxylic biphenyls such as tetramethylbiphenyl-4,4'-dicarboxylic acid, 1,1,3-trimethyl-3-phenylindene-
4,5-dicarboxylic acid and its substituted products, aromatic dicarboxylic acids such as 1,2-diphenoxyethane-4-, 4'-dicarboxylic acid and its substituted products, oxalic acid, malonic acid, succinic acid, glutaric acid, Aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, pimelic acid, suberic acid, undecanoic acid, dodecanedicarboxylic acid, brassic acid, tetradecanedicarboxylic acid, tapsinic acid, nonadecanedicarboxylic acid, docholinedicarboxylic acid, and the like, and substitution thereof. And alicyclic dicarboxylic acids such as 4,4'-dicarboxycyclohexane and substituted products thereof.

As the glycol component used in the copolymerized polyester, ethylene glycol, diethylene glycol,
Triethylene glycol, propylene glycol, butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,3-propanediol, 2-diethyl-1,3- Fatty acid diols such as propanediol and 2-ethyl-2-n-butyl-1,3-propanediol; alicyclic diols such as 1,3 cyclohexanedimethanol 1,4-dichlorohexanedimethanol; 2,2 -Bis (4'-β-hydroxyethoxydidiphenyl) propane, bis (4'-β
And ethylene oxide adducts of bisphenol compounds such as (-hydroxyethoxyphenyl) sulfone and aromatic diols such as xylylene glycol.

It is preferable to use one or more of these copolymer components from the viewpoint of balancing the properties as a heat-shrinkable film. The type and content of these copolymer components can be arbitrarily selected based on film characteristics, economic efficiency, and the like.

One type of the copolymer resin may be used, or two or more types may be used in combination.

These polyethylene terephthalates and copolymerized polyesters can be produced by a conventional polyester production method. For example, prepared by a direct esterification method in which a dicarboxylic acid component and a glycol component are directly reacted to perform polycondensation; or a transesterification method in which a dimethyl ester of the dicarboxylic acid component is reacted with a glycol component to perform transesterification. Is done. The preparation may be performed in any of a batch system and a continuous system.

If necessary, a lubricant such as titanium dioxide, fine particle silica, kaolin, or calcium carbonate may be added. Further, a dye or the like may be added as an antistatic agent, an antioxidant, an ultraviolet inhibitor, or a colorant. I can do it. In addition, the preferable intrinsic viscosity as a film base material is 0.50 to 1.3 dl / g.

A film obtained by an arbitrary method such as an extrusion method or a calendering method using such a polymer is stretched in one direction by 2.5 to 7.0 times, preferably 3.0 to 6.0 times, and is stretched by 1.0 in a direction perpendicular to the direction.
The film is stretched from 1 to 2.0 times, preferably from 1.1 to 1.8 times. Stretching in the first direction is performed to obtain a high heat shrinkage rate, and stretching in the direction perpendicular to the first direction depends on the impact resistance and tear resistance of the film stretched in the first direction. It is extremely effective in solving badness.

However, when the film is stretched beyond 2.0 times, the heat shrinkage in the direction perpendicular to the main shrinkage direction becomes too large, and the finish becomes wavy. To suppress this waving, set the heat shrinkage to 15%
Or less, preferably 8 to 9% or less, more preferably 7% or less.
It is recommended that: There is no particular limitation on the stretching means, and methods such as roll stretching, long gap stretching, and tenter stretching are applied.
It does not matter whether it is tubular or the like.

Stretching is carried out by sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching or a combination thereof. The film of the present invention is stretched, for example, uniaxially in the longitudinal direction, uniaxially in the horizontal direction, biaxially in the vertical and horizontal directions, and sometimes the biaxial stretching is performed in either the longitudinal or lateral direction. It is valid, and the order can be either. When the simultaneous biaxial stretching method is performed, the stretching order may be any of vertical and horizontal simultaneous, vertical and horizontal advance. The heat setting in the stretching is performed according to the purpose, but it is recommended to pass through a heating zone of 30 to 150 ° C. for about 1 to 30 seconds in order to prevent dimensional change under high temperature in summer. Also, before or after such treatment, stretching may be performed up to a maximum of 70%. Especially stretched in the main direction, non-shrink direction (direction perpendicular to the main shrink direction)
Is preferably relaxed, and it is better not to perform the extension in the direction immediately after.

In order to exert the preferable characteristics of the present invention, it is effective to preheat and stretch at a temperature higher than the average glass transition temperature (Tg) of the polymer composition, for example, at about Tg + 80 ° C., in addition to the stretching ratio described above. Means. In particular, the processing temperature in the main direction stretching (main shrinkage direction) is extremely low in order to suppress the heat shrinkage in the direction perpendicular to the direction and bring the minimum value to the temperature range of 80 ± 25 ° C. as described above. is important. Further, after stretching, the film is cooled while applying stress to the film while being stretched or tensioned, or by further cooling, the front-rear shrinkage property becomes better and more stable.

The plane orientation coefficient of the film thus obtained is 100 × 10
^-3 or less is preferred. If the plane orientation coefficient exceeds 100 × 10 ⁻³ , it is easily broken by an external impact force, and easily broken even by a small amount of damage. On the other hand, the birefringence is preferably 15 × 10 ^-3 ~ 160 × 10 ^-3 , the birefringence is 15 × 10
^If it is less than ^-3 , the heat shrinkage and shrinkage stress in the longitudinal direction are insufficient, and
If it exceeds 0 × 10 ⁻³ , the scratch resistance and the impact strength are reduced, and the usefulness of the film is reduced even if it becomes a film.

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) An example is described below, but the measuring method used in the example is as follows.

1. Heat shrinkage ratio The distance between the sample marks was set to 200 mm, the film was cut to a width of 15 mm, and each was heated for 1 minute using 100 ° C. hot air and measured.

2. Heat shrinkage residual stress retention time (50% relaxation etc.) Using Tensilon, sample a sample of width 20mm and length / 50mm, mark the line of 100mm on the film of the sample and set it to 50mm Attach the 100mm mark line to the upper and lower chucks,
The treatment is performed in hot air at 00 ° C., and the time until the shrinkage stress becomes zero is determined.

3. Partial whitening The roll film obtained by film formation was stored at 40 ° C. for 3 days, and then the film was cut into 230 mm width and processed into a tube by using a tube forming apparatus. The tubular body was cut into a length of 140 mm, covered with a glass bottle of a single service size, and thermally shrunk at 130 ° C. by a hot air method for 5 seconds. The heat shrunk film is visually observed to determine the presence or absence of a whitened portion.

4. Diethylene glycol content After methanol decomposition of polyester under high temperature and pressure,
Quantify by gas chromatography.

Example 1 Polyethylene terephthalate containing 3.5 mol% of diethylene glycol produced by adding diethylene glycol in a polyester production process and terephthalic acid / ethylene glycol sebacate / diethylene glycol / neopentyl glycol = 85/1546/4/50 (molar ratio)
Was uniformly blended at a weight ratio of 80:20, and was extruded at 300 ° C. to obtain an unstretched film having a thickness of 180 μm. The film was stretched 1.2 times in the machine direction, then stretched 4.1 times in the transverse direction, and then cooled under stretching in the transverse direction by about 20% to obtain a stretched film of 40 μm. Table 1 shows the characteristic values of the obtained stretched film.

The film obtained by the method of the present invention has excellent one-way shrinkability, and is of high quality in which no partial whitening occurs in the shrunk film.

Comparative Example 1 In the method of Example 1, the diethylene glycol content of the polyethylene terephthalate and the copolymer resin was changed to 2.
Table 1 shows the properties of the stretched film obtained by the same method as in Example 1 except that the content was 0 mol%.

Although the film obtained in this comparative example has excellent one-way shrinkability, the shrinkage of the shrinkable film is high, and the whitening occurs on the shoulder portion of the bottle, resulting in poor aesthetics.

Comparative Example 2 Table 1 shows the properties of the stretched film obtained by the same method as in Example 1 except that only the copolymerized resin was used without using polyethylene terephthalate in the method of Example 1.

The film obtained in this comparative example has excellent one-way shrinkability, and does not cause partial whitening in the shrunk film, but has a short residual stress holding time when heat-treated, and is, for example, a bottle. However, there is a problem that the sterilization treatment causes a phenomenon such as loosening of the shoulder portion.

Comparative Example 3 Table 1 shows the properties of the stretched film obtained by the same method as in Example 1 except that polyethylene terephthalate alone was used without using the copolymerized resin in the direction of Example 1.

The film obtained in this comparative example is inferior in terms of one-way shrinkage, partial whitening, and residual stress holding time, and is of low quality.

Examples 2 to 7 Table 1 shows the properties of the stretched films obtained by using the polyesters shown in Table 1 in the same manner as in Example 1. All of the films obtained in these examples are of high quality.

Comparative Example 4 The procedure of Example 3 was repeated except that only the copolymerized polyester was used without using polyethylene terephthalate.
Table 1 shows the properties of the stretched film obtained by the same method as in Example 1.

The film obtained in this comparative example is inferior in the residual stress holding time when heat-treated.

Comparative Example 5 Table 1 shows the properties of the stretched film obtained by the same method as in Example 4 except that the content of diethylene glycol in the polyethylene terephthalate and the copolyester was 2.0 mol%.

The film obtained in this comparative example is inferior in that whitening occurs partially in the shrunk film.

(Effect of the Invention) Since the film of the present invention is constituted as described above, stable heat shrinkage in a specific direction is exhibited, and a beautiful and strong packaging state can be given in a coated package or a bundled package. In addition, it has various effects such as improvement of printing pitch stability and heat resistance, and exhibits excellent utility value in a wide range of fields without causing partial whitening phenomenon in shrinked films.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI B29K 105: 02 B29L 7:00 (56) References JP-A-1-258935 (JP, A) JP-A-1-160632 (JP, A) JP-A-3-29763 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 61/06-61/10 C08J 5/18 C08L 67/02

Claims (1)

(57) [Claims] (1) a diethylene glycol content of more than 2.5 to 20;
Mole percent of a composition of polyethylene terephthalate and copolymerized polyester, 50 to 90 mole% of the constituents
Is a film comprising ethylene terephthalate units and having a total diethylene glycol content of 2.5 to 20 mol% in the composition, wherein the polyester film has a heat shrinkage in hot air at 100 ° C. of a predetermined value. A heat-shrinkable polyester film that is 30% or more in the direction.