JP2000000949A - Heat shrinkable polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject film causing no whitening or breaking after heat sterilizing treatment when used as a label or cap of a food container and not also generating shrinkability defect even after long-term preservation. SOLUTION: A heat-shrinkable polyester film comprises a multilayered film consisting of a surface layer comprising polyester containing butylene terephthalate as a main repeating unit and having a glass transition temp. of below 40 deg.C and an m.p. of 170 deg.C or higher and an inner layer comprising modified polyester containing ethylene terephthalate as a main repeating unit, having a glass transition temp. of 50-below 80 deg.C and characterized by that the sum total of terephthalic acid and a component other than ethylene glycol is 5-below 30 mol.% and polyvalent carboxylic acid or three or more valency and polyhydric alcohol of three or more valency is contained within a range of 0.1-below 1.5 mol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film that can be used for labels and caps of food containers involving a heat sterilization step.

[0002]

2. Description of the Related Art Plastic shrink films are used for labels, cap seals, electronic parts and the like of containers. Conventionally, resins made of polyvinyl chloride have been used in many applications as shrink film resins, but resins with low crystallinity such as polyvinyl chloride and polystyrene are required for food applications because heat resistance is required. , Fusion in heat sterilization process,
There is a disadvantage that the film cannot be maintained due to rupture. Polyolefins such as polypropylene and polyethylene are known as resins having crystallinity, but these have insufficient melting points and are difficult to use for food applications.

[0003] On the other hand, polyester has a higher melting point than polystyrene and polyolefin, and thus is suitable for food applications without inconvenience such as fusion and rupture in heat sterilization treatment. There is a problem that whitening occurs due to penetration of moisture into the film by heat sterilization treatment with high-temperature steam. In addition, there is also a problem that oriented crystals grow during stretching in the heat sterilization step, and when used as a label, cracks are caused by external force such as impact or friction.

[0004] Regarding heat-resistant polyester labels for food,
Several proposals have recently been made. For example, JP
In JP-A-278346, deformation during heat sterilization is prevented by using a homo PET layer as an inner layer of a multilayer film.
In JP-A-8-239460, whitening during heat sterilization is suppressed by copolymerizing naphthalenedicarboxylic acid. In JP-A-9-52966, the fusion in the heat sterilization step is suppressed by copolymerizing sulfoisophthalic acid. However, at present, they have not been able to suppress the decrease in strength in the heat sterilization step.

Further, the polyester-based shrink film has a problem that poor shrinkage occurs when the film before shrinkage is stored at room temperature for a long period of time. Polyester shrink films are characterized by a high glass transition temperature and do not shrink at room temperature, unlike polystyrene.However, in food applications, shrinkage due to heat aging, which was not a problem in the past, due to the speeding up of the labeling process It has been known that poor shrinkage occurs due to a rise in temperature and a decrease in shrinkage.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to prevent whitening or breakage after heat sterilization and poor shrinkage even after long-term storage. An object of the present invention is to provide a heat-shrinkable polyester film free from occurrence of cracks.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have made the above object possible by forming a heat-shrinkable film using a polybutylene terephthalate resin having specific physical properties and a polyethylene terephthalate-modified resin. Have been achieved, and the present invention has been achieved.

That is, in the present invention, the main repeating unit is made of butylene terephthalate and has a glass transition temperature of 40.
Polyester having a melting point of less than 170 ° C. and a melting point of 170 ° C. or more is used as the surface layer of the multilayer film, and the main repeating unit is ethylene terephthalate, and the glass transition temperature is 50 ° C. or more.
° C, the total of components other than terephthalic acid and ethylene glycol is 5 mol% or more and less than 30 mol%, and
A heat-shrinkable polyester film comprising a multilayer film having a modified polyester containing 0.1% by mole or more and less than 1.5% by mole of a polyvalent carboxylic acid having a valency of at least 0.1 and less than 1.5% by mole. is there.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polyester resin for a surface layer used in the present invention contains butylene terephthalate as a main repeating unit and has a glass transition temperature (hereinafter abbreviated as Tg) of less than 40 ° C., preferably less than 35 ° C. The melting point is required to be 170 ° C. or higher. T
If the g exceeds 40 ° C., the material tends to crack after retort treatment, and if the melting point is less than 170 ° C., the transparency decreases due to the retort treatment.

In the present invention, the polyester resin for the surface layer has a main repeating unit made of butylene terephthalate. Such polyester may be modified with other components. The third component used to modify polybutylene terephthalate includes:
Examples of the acid component include isophthalic acid and adipic acid, and examples of the glycol component include cyclohexanedimethanol, an ethylene oxide adduct of bisphenol A, and ethylene glycol. Other than these, as the acid component,
For example, known monomers such as 1,4- or 2,6-naphthalenedicarboxylic acid, sebacic acid, azelaic acid, glutaric acid, oxalic acid, succinic acid and the like, and as the glycol component, diethylene glycol, triethylene glycol, Known monomers such as neopentyl glycol are exemplified. The content of these modified components is in the range of 5 to 30 mol% in the polyester whose repeating unit is butylene terephthalate. These modified components are Tg
And the effect of appropriately adjusting the heat shrinkability of the obtained film.

The additives include polyoxyalkylene glycols such as polyoxytetramethylene glycol and polyethylene glycol.

Furthermore, in the present invention, a trihydric or higher polyhydric alcohol such as trimethylolpropane, pentaerythritol, trimellitic acid and pyromellitic acid, and a polybasic acid are used as the third component for the purpose of shortening the polymerization time. May be.

The polyester resin comprising butylene terephthalate as the main repeating unit used in the present invention described above can be produced by a known direct polymerization method or transesterification method, and the degree of polymerization is not particularly limited. However, the intrinsic viscosity (measured at 25 ° C. using a mixed solution of phenol / tetrachloroethane and the like as a solvent, the same applies hereinafter) [η] of 0.5 to
Those having a range of 1.5 dl / g are preferred.

The modified polyester resin for the inner layer used in the present invention is composed of a polyester having ethylene terephthalate as a main repeating unit and has a Tg of 50 ° C. or more and less than 80 ° C. This is because if the Tg is 50 ° C. or lower, the resin having a low Tg in the surface layer causes shrinkage at room temperature to deteriorate dimensional stability, and if the Tg exceeds 80 ° C., shrinkage does not start in a normal labeling step.

Further, in the present invention, the modified polyester resin for the inner layer has a total of 5 mol% of components other than terephthalic acid and ethylene glycol (hereinafter referred to as a third component).
At least 30 mol%, preferably at least 7 mol% and less than 25 mol%, and among these components, a trivalent or higher polyhydric carboxylic acid and / or a trivalent or higher polyhydric alcohol may be used in an amount of 0.1 to 0.1 mol%.
Mol% or more and less than 1.5 mol%, preferably 0.3 mol%
It is necessary that the modified polyester be contained in the range of at least 1.0 mol%.

This is because if the total amount of components other than terephthalic acid and ethylene glycol is less than 5 mol%, shrinkage does not sufficiently occur, and if it exceeds 30 mol%, shrinkage occurs rapidly and causes wrinkles. is there.

In the heat-shrinkable polyester film of the present invention, a tri- or higher polyhydric carboxylic acid and / or a tri- or higher polyhydric alcohol is copolymerized in the third component for modifying the polyethylene terephthalate constituting the inner layer. If not, a change with time such as a decrease in the shrinkage start temperature or a decrease in the shrinkage rate after long-term storage may occur, resulting in poor shrinkage in the high-speed labeling step. If the amount of the third component is less than 0.1 mol%, the effect of suppressing the change with time is small, and if it exceeds 1.5 mol%, the control of the reaction in the polymerization step becomes difficult, and a polymer may not be obtained. It is.

Examples of usable trivalent or higher polycarboxylic acids include trimellitic acid and pyromellitic acid, and examples of polyhydric alcohols include trimethylolpropane and pentaerythritol.

In the present invention, the polyethylene terephthalate modified with the third component as described above may further contain another third component. Other third components include isophthalic acid and adipic acid as acid components, and cyclohexanedimethanol and bisphenol A ethylene oxide adducts as glycol components.
These are effective in making Tg and shrinkage appropriate.
Examples of the acid component other than these include known monomers such as 1,4- or 2,6-naphthalenedicarboxylic acid, sebacic acid, azelaic acid, glutaric acid, oxalic acid, and succinic acid. as,
Known monomers such as butanediol, diethylene glycol, triethylene glycol, and neopentyl glycol are exemplified. These other third components are used in the range of 5 to 30 mol% in the modified polyester whose main repeating unit is polyethylene terephthalate.

In the present invention, a polyoxyalkylene glycol such as polyoxytetramethylene glycol or polyethylene glycol is used to impart flexibility to a modified polyester in which the main repeating unit constituting the inner layer is eletine terephthalate. Can be added in the polymerization step.

In the present invention, the modified polyester resin constituting the inner layer can be produced by a known direct polymerization method or transesterification method, and the degree of polymerization is not particularly limited. From the viewpoint of properties, those having an intrinsic viscosity [η] in the range of 0.5 to 1.5 dl / g are preferred.

The resulting polyester resin for the surface layer and the inner layer is formed into a heat-shrinkable polyester film by the following method, for example. That is, first, the polyester resin is dried and then extruded by an extruder, or extruded by a vented extruder while suppressing a decrease in the degree of polymerization due to hydrolysis. In order to form a multilayer, a multilayer film is formed by a multilayer extruder or an extrusion laminating method.

Next, this raw film is stretched 1.0 to 5.0 times, preferably 1.5 to 4.times. In the vertical or horizontal direction at a temperature higher than the Tg of the modified polyester of the inner layer by 3 ° C. or more.
It is stretched 8 times to give a high shrinkage to the film. Further, if necessary, it is 1.0 to 1.8 in a direction perpendicular to the stretching direction.
Stretching, preferably 1.0 to 1.5 times. This is effective for increasing the strength in the direction perpendicular to the main shrinkage direction of the film and preventing the shrinkage in the stretching direction from unnecessarily shrinking.

The film is stretched by simultaneous biaxial stretching, sequential biaxial stretching, and uniaxial stretching. Either the transverse stretching or the longitudinal stretching may be performed first. The stretched heat-shrinkable film can be used as a product as it is, but may be subjected to heat treatment for several seconds to several tens of seconds in a temperature range of 50 ° C. to 150 ° C. in view of dimensional stability. By performing such a heat treatment, preferable properties such as adjustment of the shrinkage ratio in the shrinkage direction of the polyester film of the present invention, reduction of shrinkage with time of storage of the unshrinkable film, and reduction of shrinkage unevenness can be exhibited.

Although the thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, it is 1-600 μm.
The range is practically used.

In the present invention, the heat-shrinkable film or the polyester resin as a raw material thereof may be blended with various known processings and appropriate additives in order to further impart specific performance. Examples of processing include UV, α
Irradiation of rays, β rays, γ rays or electron beams, corona treatment,
Examples include treatment such as flame treatment, application and lamination of a resin such as vinylidene chloride, polyvinyl alcohol, polyamide, and polyolefin, and vapor deposition of metal.

Examples of the additives include resins such as polyamide, polyolefin, polymethyl methacrylate, and polycarbonate; inorganic particles such as silica, talc, kaolin, and calcium carbonate; pigments such as titanium oxide and carbon black; Mold agents, flame retardants and the like.

The heat-shrinkable polyester film of the present invention is obtained as described above. In order to further develop the film properties aimed at by the present invention, the heat-shrinkable polyester film is heat-treated in saturated steam at 120 ° C. for 1 hour. Haze is 2% / 10
μm or less, the tensile elongation at break in the direction perpendicular to the main shrinkage direction of the heat-treated film is 20% or more, and the shrinkage after immersion in a hot water bath at 80 ° C. for 10 seconds is 3% or more.
It is preferable that the holding ratio of the shrinkage rate after holding at 0 ° C. and 50% RH for 14 days under the same conditions is 90% or more, and the rise in shrinkage start temperature is less than 3 ° C.

When the haze after heat treatment in saturated steam at 120 ° C. for 1 hour exceeds 2% / 10 μm, the effect of suppressing whitening is small and the film after heat treatment is perpendicular to the main shrinkage direction. When the tensile elongation at break in the direction is less than 20%, cracks due to impact, friction, and the like are likely to occur in the area of initial fracture, and when the shrinkage after immersion in a hot water bath at 80 ° C. for 10 seconds is less than 20%, high speed. The shrinkage rate is insufficient in the labeling step of
When the shrinkage rate under the same conditions after holding at 0 ° C. and 50% RH for 14 days is 100% with the shrinkage rate before the treatment, if the holding rate is less than 90%, the shrinkage rate is insufficient. This is because if the rise in the shrinkage start temperature exceeds 3 ° C., the heating may end before the temperature at which a sufficient shrinkage ratio can be obtained, resulting in poor adhesion.

The heat-shrinkable polyester film of the present invention obtained as described above can be suitably used as a label for food containers or a cap label accompanied by a heat sterilization step.

[0031]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. Evaluation of the physical properties in Examples and Comparative Examples was based on the following methods.

(1) Measurement of Tg and melting point (Tm) A resin was melted at 280 ° C. for 5 minutes, and quenched with dry ice, and a differential scanning calorimeter manufactured by Shimadzu Corporation was used. The temperature was measured by (DSC) at a heating rate of 10 ° C./min by nitrogen gasification. Tg was the shoulder value at the baseline, and melting point (Tm) was the peak value of the endothermic change due to melting.

(2) Heat shrinkage rate The film within 24 hours after stretching is stretched 150 m in the stretching direction.
m, cut out to a size of 20 mm in a direction perpendicular to the direction, immersed in a warm water bath at 80 ° C. for 10 seconds with the marking lines provided at intervals of 100 mm, and the length (L0) between the marking lines before contraction and the distance between the marking lines after contraction The length (L0 ') was measured, and the shrinkage ratio (S0) before long-term storage was determined by the following equation.

## EQU1 ## Shrinkage: S0 (%) = ｛(L0−L0 ′) / L
0｝ × 100

(3) Shrinkage unevenness A polyester film cut out to a size of 150 mm in the stretching direction and 20 mm in a direction perpendicular thereto is shrunk into a film when heated and shrunk in hot air at 120 ° C. for 60 seconds with no load. The occurrence of unevenness was visually observed and evaluated in the following two stages. ：: Shrinkage unevenness is hardly observed x: Shrinkage unevenness is significantly generated

(4) Dimensional Stability The stretched film was allowed to stand at a temperature of 30 ° C. for 30 days, and the dimensional retention in the stretching direction after standing was measured and judged according to the following criteria. ：: Dimension retention of 95% or more ×: Dimension retention of less than 95%

(5) Haze after heat sterilization, tensile elongation at break The film is stretched in a glass bottle (diameter 25 mm).
And heat-treated in a saturated steam at 120 ° C. for 1 hour to perform a heat sterilization treatment. The film after the treatment was evaluated for haze and tensile elongation at break by the following methods.

(A) Haze The haze of the film after the heat sterilization treatment was measured using a haze meter, Model TC-HII, manufactured by Tokyo Denshoku Co., Ltd.
I, and measured the haze value of the film with a thickness of 10 μm.
The value was converted to the value per hit and displayed.

(B) Tensile rupture elongation The film after the heat sterilization treatment was cut out to a width of 5 mm in a direction perpendicular to the shrinkage direction, a chuck interval of 30 mm, and a speed of 50 mm.
The tensile elongation at break in mm / min was measured.

(6) Increase in Retention of Shrinkage Ratio and Shrinkage Starting Temperature after Long-Term Storage The film was treated at 30 ° C. and 50% RH for 2 weeks.
The film was evaluated for retention of shrinkage and rise in shrinkage onset temperature by the following method.

(A) Retention of Shrinkage Ratio A film cut out to a size of 150 mm in the stretching direction and 20 mm in a direction perpendicular to the stretching direction is provided with marking lines at intervals of 100 mm and immersed in a hot water bath at 80 ° C. for 10 seconds. The length between the reference lines (L1) and the length between the reference lines after contraction (L1 ') are measured, and the shrinkage ratio (1) after the preservation treatment is determined by the following [Equation 2]. ) Was used to determine the shrinkage retention rate according to the following [Equation 3].

## EQU2 ## Shrinkage: S1 (%) = ｛(L1-L1 ′) / L
1｝ × 100

## EQU3 ## Shrinkage retention ratio (%) = 100 − [− (S0−S)
1) / S0｝ × 100]

(B) Increasing the temperature at which shrinkage starts The film before and after storage is stretched 150 m in the stretching direction.
m, cut out to a size of 20 mm in a direction perpendicular to the direction, provided with marked lines at intervals of 100 mm, and set a temperature range of 50-90 ° C. and 5 ° C.
After immersion in a hot water bath for 10 seconds, the shrinkage ratio at each temperature is obtained by the same method as in the above [Equation 1], and a shrinkage curve with respect to the processing temperature is written. This was determined as the shrinkage onset temperature. Assuming that the shrinkage start temperature before storage is T0 and the shrinkage start temperature after storage is T1, the increase in shrinkage start temperature was determined by the following [Equation 4].

## EQU4 ## Increase in shrinkage start temperature = T1-T0

[Examples 1 to 13] and [Comparative Examples 1 to 6] Polymerization of the resin was carried out as follows. Production of Resin 1-10 A raw material having the composition shown in Table 1 was charged into a reaction vessel equipped with a reflux tower and a stirrer, and 500 ppm based on the raw material.
Was added at a reaction temperature of 140.
The reaction was carried out at a temperature of from 240 ° C. to 240 ° C. while distilling off the methanol by-produced until the methanol distillation amount became 90% of the theoretical amount to obtain an esterified product. While the glycol component by-produced at 250 ° C. is distilled off at a high vacuum of 5 torr or less, the melt viscosity at 250 ° C. becomes the intrinsic viscosity [η].
Was melt-polymerized to a value corresponding to the torque value of PET of 0.7 dl / g at 285 ° C. to obtain a polyester resin.

Production of Resins 11-17 and 19-22 A raw material having the composition shown in Table 1 was placed in a reaction vessel equipped with a reflux tower and a stirrer, and water produced as a by-product was distilled off at 200 to 240 ° C. The reaction was continued until the amount of distilled water reached 90% of the theoretical amount to obtain an esterified product.

Then, 500 ppm of antimony trioxide based on the weight of the raw material was added to the esterified product, and 285
While the glycol component by-produced at 0 ° C. is distilled off under a high vacuum of 5 torr or less, the melt viscosity at 285 ° C. becomes equal to the melt viscosity at 285 ° C. of PET having an intrinsic viscosity [η] of 0.7 dl / g. Melt polymerization was performed to obtain a polyester resin. In addition, as for the resin 22, since the amount of trimethylolpropane was large, the control of the polymerization reaction was not possible, and no resin was obtained.

Production of Resin 18 A raw material having the composition shown in Table 1 was placed in a reaction vessel equipped with a reflux tower and a stirrer, and the content thereof was 600 ppm based on the raw material.
Manganese acetate dihydrate at 140 ° C to 240 ° C
The reaction was carried out at 90 ° C. while distilling off the methanol by-produced until the amount of methanol distilled off reached 90% of the theoretical amount to obtain an esterified product.

Then, 500 ppm of antimony trioxide based on the weight of the raw material was added to the esterified product, and 285
While the glycol component by-produced at 0 ° C. is distilled off under a high vacuum of 5 torr or less, the melt viscosity at 285 ° C. becomes equal to the melt viscosity at 285 ° C. of PET having an intrinsic viscosity [η] of 0.7 dl / g. Melt polymerization was performed to obtain a polyester resin.

Table 2 shows the composition of the polyester resin obtained in each of the above examples. The resin composition was determined by chromatography after hydrolyzing the resin with hydrazine.

[0048]

[Table 1]

[0049]

[Table 2]

The abbreviations in Tables 1 and 2 are as follows. Acid component DMT: dimethyl terephthalate DMI: dimethyl isophthalate NDA: 2,6-naphthalenedicarboxylic acid NDC: 2,6-naphthalenedicarboxylic acid dimethyl ester ADE: 53% by weight of bishydroxyethyl adipate ethylene glycol solution TPA: terephthalic acid IPA: isophthalic acid TMA: trimellitic acid ADA: adipic acid glycol component BDO: 1,4-butanediol BPE: bisphenol A ethylene oxide adduct EG: ethylene glycol TMP: trimethylolpropane PEN: pentaerythritol Other PTMG: polytetramethylene glycol (number average) Molecular weight 1000)

Preparation of Film Each resin obtained was dried under vacuum to reduce the water content to 10%.
It was dried until it became 0 ppm or less.
A three-layer film raw material having a surface layer / inner layer / surface layer was obtained with the structure shown in (1). The thickness ratio was 1/3/1. Extrusion temperature is resin 1
10 was performed at 250 ° C, and resins 11 to 21 were performed at 285 ° C.

The raw film was converted into a polyethylene terephthalate-modified resin of the inner layer by a batch type biaxial stretching machine.
3.8 in the TD (vertical) direction at a temperature 3 ° C. or more higher than
Stretched 1.0 times in MD (horizontal) direction, thickness 40μm
Was obtained. Table 3 shows the results of various evaluations of the physical properties of the obtained film.

[0053]

[Table 3]

[0054]

The heat-shrinkable polyester film of the present invention has sufficient shrinkage, has sufficient transparency and strength even after heat sterilization, and has an increased shrinkage temperature and shrinkage even after long-term storage. The rate of reduction is small, and it can be suitably used for labels and caps for food containers.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 3E067 AA22 AB99 BA03B BB08B BB14A BB14C CA01 EE04 FB01 3E086 AB03 AD16 AD30 BA15 BB22 BB67 CA11 CA40 4F100 AK41A AK41B AL01B AL06B BA02 BA03 BA06 BA10A90J05B00 CF061 CF071 FD010 FD090 GC01 GF00 GG01

Claims (1)

[Claims] 1. A main repeating unit comprising butylene terephthalate, having a glass transition temperature of less than 40 ° C. and a melting point of 1
Polyester having a temperature of 70 ° C. or higher is used as a surface layer, and the main repeating unit is ethylene terephthalate.
And a trivalent or higher polyvalent carboxylic acid and / or
And a heat-shrinkable polyester film comprising a multilayer film having a modified polyester containing trihydric or higher polyhydric alcohol in an amount of 0.1 mol% or more and less than 1.5 mol% as an inner layer.