JPH10176041A - Thermally shrinkable polyester film for sealing cap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject film comprising terephthalic acid and ethylene glycol as main constituents and further containing a bisphenol-A/ethylene oxide adduct in an addition ratio and capable of expressing good shrinkability and excellent tearability. SOLUTION: This film is produced from a polyester resin comprising (A) terephthalic acid and (B) ethylene glycol as main constituents and further containing (C) a bisphenol-A/ethylene oxide adduct as a constituent in an amount of 5-25mol.% based on the glycol constituent. The film preferably has a shrinkage degree of 10-45% at least in one direction at 80 deg.C, when immersed in warm water for 1min. Thereby, a shrinkage degree sufficient as a thermally shrinkable film and a tearing property excellent on employment as a cap-sealing film can be expected.

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 used in a packaging material, particularly for use as a cap seal, and more particularly to a film having good heat-shrinkability and a property of easily tearing when used as a cap seal. Things.

[0002]

2. Description of the Related Art Heat-shrinkable plastic films are used for marking, protecting, binding and improving the added value of products such as containers, fishing rods, condensers, fluorescent fluorescent lamps, etc., as well as for packaging and close-packing of books and notebooks. Used. At present, in various fields, development of various applications utilizing the shrinkage and shrinkage stress of this heat-shrinkable plastic film is expected.

Heretofore, resins such as polyvinyl chloride, polystyrene, and polyolefin have been used as materials for heat-shrinkable plastic films. However, such resins have problems in heat resistance, weather resistance, chemical resistance and the like.

For example, a polyvinyl chloride film can be made into a heat-shrinkable film having various shrinkage characteristics. However, since fish eyes are apt to occur frequently, when a printed material is used as a packaging material, printing omissions occur and the commercial value is low. It was easy to be. Further, in order to obtain a heat-shrinkable film free of fish eyes, there is a problem that excessive quality control is required, so that the film production cost is significantly increased. Furthermore, polyvinyl chloride generates harmful gas when incinerated at the time of disposal, and the plasticizer in the resin bleeds out with the passage of time to cause contamination due to dust and the like, and is not preferable in terms of safety.

On the other hand, a shrink film obtained from polystyrene has a good finish after shrinkage but has low solvent resistance, so that a special ink must be used for printing, and spontaneous shrinkage occurs even at room temperature. Had to be stored in a cold place in order to. In addition, there is also a great problem in the disposal, such as the necessity of incineration at a high temperature and the generation of a large amount of black smoke and offensive odor during incineration.

[0006] As a material capable of solving these problems, a polyester film is expected very much, and its use amount has been remarkably increased.

The heat-shrinkable polyester film has been developed as a film having good heat-shrinkability and various performances by copolymerization and film forming techniques, utilizing the excellent mechanical properties, heat resistance, chemical resistance, etc. of PET. ing.

Uses of the heat-shrinkable polyester film include bottle labels, covering of electronic parts, sealing of caps (sealing caps) of seasoning bottles and the like.

[0009]

SUMMARY OF THE INVENTION A shrink film comprising a polyester resin in which a bisphenol A ethylene oxide adduct is copolymerized as a glycol component has been reported in JP-A-5-301287 and JP-A-6-8322. I have.

The polyester resin of the shrinkable film described in JP-A-5-301287 is copolymerized with isophthalic acid in addition to bisphenol A ethylene oxide adduct, but is torn by copolymerizing isophthalic acid. Worse.

In the polyester resin described in JP-A-6-8322, polytetramethylene oxide is copolymerized with bisphenol A ethylene oxide, but this also results in poor tearability.

Therefore, it has been difficult to use such a shrink film made of a polyester resin as a cap seal which requires good tearing properties in at least one direction.

An object of the present invention is to solve the difficulty of tearing a polyester-based heat-shrinkable film, which is required for a cap seal application of the heat-shrinkable film.

[0014]

Means for Solving the Problems In view of such a problem, the present inventors have made intensive studies on the tearability of a polyester film and have reached the present invention.

That is, the gist of the present invention is that a polyester resin containing terephthalic acid and ethylene glycol as main constituents and bisphenol A ethylene oxide adduct as a constituent unit in the range of 5 to 25 mol% of the glycol component. Heat-shrinkable polyester film for cap seals.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester resin used in the polyester film of the present invention contains terephthalic acid and ethylene glycol as main constituents, and bisphenol A ethylene oxide adduct is 5 to 5 of the glycol component.
It is contained as a constituent unit in the range of 25 mol%.

The polyester resin used in the polyester film of the present invention preferably contains bisphenol A ethylene oxide adduct as a constituent unit of the polyester resin in a range of 5 to 25 mol% of the glycol component. Preferably, it is contained in the range of 7 to 20 mol%.

When the content of the ethylene oxide adduct of bisphenol A in the glycol component is less than 5 mol%, tearing is not easily obtained, and when it exceeds 25 mol%, crystallinity is completely lost and crystallization occurs in a drying step before melt extrusion. A problem arises that drying at a high temperature cannot be carried out.

The main component of the glycol component of the polyester resin used in the polyester film of the present invention is ethylene glycol, and 65% of the total glycol component.
Preferably, it is about 95 mol%.

Bisphenol A ethylene oxide adduct and glycol components other than ethylene glycol include neopentyl glycol, diethylene glycol,
Examples thereof include 1,4-cyclohexanedimethanol, propylene glycol, 1,4-butanediol, trimethylene glycol, and hexamethylene glycol, and copolymerization can be performed for various purposes within a range that does not impair the tearing property.

The main acid component constituting the polyester resin used in the present invention is terephthalic acid, and its amount is preferably at least 90 mol% of all the acid components. Acid components other than terephthalic acid include 2,6 naphthalenedicarboxylic acid, oxalic acid, malonic acid, succinic acid,
Examples thereof include phthalic acid, azelaic acid, adipic acid, and sebacic acid, and can be copolymerized according to various purposes within a range that does not impair the tearability.

[0022] Additives can be added to the polyester resin of the present invention for various purposes. Examples of additives include a flame retardant, an ultraviolet absorber, a lubricant, and an antistatic agent.

The polyester resin used for the shrink film of the present invention can be synthesized by a conventional method. That is, the synthesis of an intermediate by a transesterification method or a direct esterification method, a polycondensation of this intermediate, and if necessary, the degree of polymerization by solid phase polymerization is increased.

Although the degree of polymerization of the resin is not particularly limited, the intrinsic viscosity (measured at 25 ° C. in a mixed solution of phenol / tetrachloroethane and the like) at 0.5 to 1. A range of 2 is preferred.

The obtained polyester resin is dried to a moisture content of 50 ppm or less by a conventional method such as hot air drying using a dehumidified air flow or vacuum drying, and then dried as a film raw material by a known film forming method such as a casting roller method or a calendar method. It is formed into a film. Next, the raw film is 1.5 to 5.0 times, preferably 1.times. In the film forming direction or at right angles thereto at a temperature higher than the glass transition temperature of the polyester resin by 3 ° C. or more, preferably 5 ° C. or more. 5-4.8
The film is stretched twice to give a high shrinkage to the film. Further, if necessary, the film is stretched 1.0 to 1.8, preferably 1.0 to 1.5 times in the direction perpendicular to the stretching direction. This is effective for preventing the film from shrinking in the stretching direction more than necessary. The stretching of the film is performed by a method such as simultaneous biaxial stretching, sequential biaxial stretching, or uniaxial stretching, and the stretching in the film forming direction and the direction perpendicular thereto may be performed first.

The stretched heat-shrinkable polyester film can be used as a product as it is, but may be subjected to a heat treatment at a temperature of 50 to 150 ° C. for several seconds to several tens of seconds in view of dimensional stability and the like. By performing such a heat treatment, preferable properties such as adjustment of the shrinkage ratio in the shrinkage direction of the polyester film, reduction of shrinkage with time during storage of the unshrinkable film, and reduction of shrinkage unevenness can be exhibited.

The thickness of the heat-shrinkable film of the present invention is not particularly limited, but a thickness of 1 to 600 μm is practically used.

In the present invention, in order to further impart specific performance, conventionally known various processings can be performed, and various additives can be added. Examples are UV, α
Irradiation of rays, γ rays, β rays or electron beams, corona treatment,
Plasma irradiation treatment Flame treatment, etc., vinylidene chloride,
Examples include application and lamination of a resin such as polyvinyl alcohol, polyamide, and polyolefin, and vapor deposition of a metal. Examples of additives include polyamide, polyolefin, polymethyl methacrylate, resins such as polycarbonate, silica, talc, kaolin, inorganic particles such as calcium carbonate, titanium oxide, pigments such as carbon black,
UV absorbers, release agents, flame retardants and the like.

The heat-shrinkable polyester film of the present invention thus obtained can be used for a cap seal. When used for a label, the label is easily torn, and the label may be broken and the appearance may be poor.

The heat-shrinkable polyester film of the present invention preferably has a shrinkage of 10 to 45% at 80 ° C. in at least one direction when immersed in warm water for 1 minute.

If the shrinkage at 80 ° C. is less than 10%, the shrinkage cannot be used as a cap seal because the shrinkage is insufficient. To increase the shrinkage, the processing temperature must be higher than the deformation temperature of the bottle. This is for copying. If the shrinkage ratio exceeds 45%, the shrinkage occurs rapidly, which causes poor appearance such as uneven shrinkage and wrinkles due to the heat treatment.

The heat-shrinkable film of the present invention preferably has a tear strength in a direction perpendicular to the main shrinkage direction of less than 6 kgf / mm. Normally, the cap sealing shrink film is sealed in such a manner that the shrink film shrinks in the winding direction. Therefore, the tearing direction of the cap seal is perpendicular to the shrinking direction.

If the tear strength in the direction perpendicular to the main shrinkage direction exceeds 6 kgf / mm, when used as a container seal, it is difficult to tear when opened.

As described above, the heat-shrinkable polyester film obtained by the present invention, when used for sealing a container or the like, is a film that easily tears when opened and has a sufficient shrinkage.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the examples.

[0036]

【Example】

(Examples 1 to 3, Comparative Examples 1 to 3) The monomers shown in Table 1 were placed in a reaction vessel equipped with a reflux tower and a stirrer, and the reaction temperature was 26.
An esterified product was obtained at 0 ° C. while distilling off by-produced water.
Then, the esterified product was polymerized by melt polymerization while adding 450 ppm of antimony trioxide to the acid component as a polymerization catalyst and distilling off ethylene glycol by-produced at 280 ° C. under a high vacuum of 5 torr or less to obtain a polyester resin. .

After drying the obtained polyester resin by vacuum drying, it was melt-extruded at 270 ° C. to prepare a raw film. This film is stretched 3.8 times in the TD direction at a temperature higher than the glass transition temperature by 3 ° C. or more, and has a thickness of 40 μm.
Was obtained.

Table 1 shows the shrinkage ratio, the appearance after shrinkage, and the tear strength in the direction perpendicular to the stretching direction of the obtained film.
Shown in

The method for measuring the shrinkage and tear strength and the appearance observation after shrinkage will be described below.

(Shrinkage Ratio) Marked lines are provided at intervals of 100 mm on a polyester film cut out to a size of 150 mm in the stretching direction and 20 mm in a direction perpendicular thereto, and immersed in warm water at 80 ° C., and the length between the marked lines after 1 minute I asked for it.

Shrinkage (%) = {(L−L ′) / L} × 100 L: length before shrinkage L ′: length after shrinkage (tear strength) Tear perpendicular to stretching direction Measure strength. The measuring method used was the A method of JIS K7128.

(Appearance after Shrinkage) The appearance after shrinkage was visually observed and evaluated as follows. ○-Good appearance ×-Bad appearance

[0043]

[Table 1]

[0044]

The polyester film of the present invention has a sufficient shrinkage rate as a heat-shrinkable film and excellent tearability when used as a cap seal.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FIB29L 7:00 C08L 67:00

Claims (2)

[Claims] 1. A heat-shrinkable resin for a cap seal comprising a polyester resin containing terephthalic acid and ethylene glycol as main constituents and a bisphenol A ethylene oxide adduct as a constituent unit in the range of 5 to 25 mol% of the glycol component. Polyester film. 2. The shrinkage when immersed in warm water for one minute is 10 to 45% at 80 ° C. in at least one direction, and the tear strength in the direction perpendicular to the main shrinkage direction is 6 kgf /.
The heat-shrinkable polyester film for a cap seal according to claim 1, which is not more than mm.