JP7119504B2 - Heat-shrinkable polyester film - Google Patents

Description

The present invention relates to a heat-shrinkable polyester film and a package, and more specifically, it is suitable for use as a label for metallic can containers and the like, and contains a large amount of amorphous component as a monomer component constituting polyester. is a heat-shrinkable polyester film using so-called crystalline polyester that does not contain

In recent years, stretched films made of polyvinyl chloride resin, polystyrene resin, polyester resin, etc. (so-called Heat-shrinkable films) have become widely used. Among such heat-shrinkable films, polyvinyl chloride films have problems such as low heat resistance, generation of hydrogen chloride gas during incineration, and generation of dioxins. In addition, polystyrene film has poor solvent resistance, requires the use of ink with a special composition for printing, and must be incinerated at high temperatures. There is a problem that Therefore, polyester-based heat-shrinkable film, which has high heat resistance, is easy to incinerate, and has excellent solvent resistance, has come to be widely used as a shrinkable label. Along with the increase, the usage amount tends to increase.

Moreover, as a normal heat-shrinkable polyester film, a film that is greatly shrunk in the width direction is widely used. Such a heat-shrinkable polyester film whose main shrinkage direction is in the width direction is stretched at a high magnification in the width direction in order to exhibit shrinkage characteristics in the width direction. As for the longitudinal direction, it is often stretched only at a low magnification, and some are not stretched. Thus, a film only stretched at a low magnification in the longitudinal direction or a film stretched only in the width direction has the drawback of being inferior in mechanical strength in the longitudinal direction.

Further, conventional heat-shrinkable polyester films generally use an amorphous polyester raw material (amorphous raw material), as described in Patent Document 1, for example. This is because amorphous molecules are believed to be involved in the development of shrinkage. However, heat-shrinkable polyester films using amorphous raw materials have problems such as low heat resistance and higher raw material costs than crystalline polyester raw materials.

In addition, the heat-shrinkable polyester film described in Patent Document 2 is a heat-shrinkable polyester film that improves the strength in the longitudinal direction of the film and uses a crystalline polyester raw material, but the longitudinal direction is the main shrinkage direction. However, there is no description of a heat shrinkable film whose main shrinking direction is the width direction.
By the way, in order to form a tubular label from a heat-shrinkable film, it is necessary to overlap and fix one widthwise end of the film to the other end. Conventionally, as this fixing method, a solvent bonding method (Patent Document 3), a method using an adhesive (Patent Document 4), and the like have been used. Among them, the solvent bonding method is widely used because it can be processed into tubular labels at high speed.
In the process of processing the heat-shrinkable polyester film sides into tubular labels using this solvent bonding method (tubing process), production efficiency can be improved and costs can be reduced, so many labels are made using this method. It is Moreover, the heat-shrinkable film used in such a tubing process is a film that heat-shrinks in the width direction. This is because the main contraction direction is preferably the direction perpendicular to the tubing direction. Also, if the winding length of tubing is long, a long length is required for high-speed tubing or tubing that can be done at once. Therefore, a film that heat-shrinks in the film width direction is preferable.

Also, from an environmental point of view, there is a high demand for films that use recycled raw materials from PET bottles. Ordinary heat-shrinkable polyester films use raw materials containing a large amount of amorphous components in order to impart heat-shrinkable properties. However, there is a limit to the mixing ratio of recycled raw materials, and it has not been possible to provide a heat-shrinkable polyester film containing a large amount of recycled raw materials. In addition, heat-shrinkable polyester films using a large amount of amorphous raw materials have problems of low heat resistance and uneven thickness.

JP-A-2003-55485 JP 2016-193491 A Japanese Patent No. 3075019 JP 2014-43520 A

An object of the present invention is to solve the problems of the above-mentioned patent documents, and to have sufficient heat shrinkage characteristics with the film width direction as the main shrinkage direction even if it does not contain a large amount of monomer components that can be amorphous components. To provide a heat-shrinkable polyester film having high mechanical strength in the longitudinal direction orthogonal to the direction and having small unevenness in thickness.

The configuration of the present invention is as follows.
1. A heat-shrinkable polyester containing ethylene terephthalate as a main component, containing 0 mol% or more and 5 mol% or less of a monomer component that can be an amorphous component in all polyester resin components, and having a main shrinkage direction in the width direction. A heat-shrinkable polyester film characterized by satisfying the following requirements (1) to (4).
(1) The hot water heat shrinkage in the width direction when treated for 10 seconds in hot water at 90°C is 25% or more and 50% or less.
(2) Hot water heat shrinkage in the longitudinal direction orthogonal to the width direction when treated in hot water at 90°C for 10 seconds is 10% or more and 20% or less.
(3) Tensile breaking strength in the longitudinal direction of the film is 100 MPa or more and 200 MPa or less
(4) The refractive index value in the film longitudinal direction is higher than the refractive index value in the film width direction, which is the main shrinkage direction. 2. The heat-shrinkable polyester film according to 1, wherein the maximum heat-shrinkage stress in the film width direction is 14 MPa or more and 22 MPa or less.
3. 3. The heat-shrinkable polyester film according to 1 or 2, characterized in that thickness unevenness in the longitudinal direction and thickness unevenness in the width direction are both 20% or less.
4. 4. The heat-shrinkable polyester film according to any one of 1 to 3, wherein the heat-shrinkable stress in the width direction of the film after being shrunk by 10% in the width direction is 10 MPa or more and 18 MPa or less.
5. 5. The method for producing a heat-shrinkable polyester film according to any one of 1 to 4, wherein the unstretched film is stretched in the longitudinal direction and then stretched in the width direction.
6. 5. A package comprising the heat-shrinkable polyester film according to any one of 1 to 4 above as a base material, and a label or banding film covering at least a part of the periphery of the package.

According to the present invention, the problem of Patent Document 1 is solved, and even if it does not contain a large amount of monomer components that can be amorphous components, it has sufficient heat shrinkage properties with the film width direction as the main shrinkage direction, and the main shrinkage direction is the film width direction. The heat shrinkage rate in the longitudinal direction perpendicular to the shrinking direction is lower than that in the width direction, which is the main shrinking direction, making it possible to provide a heat-shrinkable polyester film with high mechanical strength in the longitudinal direction and small unevenness in thickness. In addition, since it is not necessary to contain a large amount of monomer components that can become amorphous components in the raw material, it is a highly environmentally friendly heat-shrinkable polyester that contains a large amount of recycled PET bottle polyester and polyester using bio-derived raw materials. made it possible to provide films.
In addition, the heat-shrinkable polyester film of the present invention has high heat-shrinkage stress, and therefore has excellent adhesion to containers.

(Polyester raw material for heat-shrinkable polyester film)
The heat-shrinkable polyester film of the present invention contains ethylene terephthalate as a main component. Here, the main component means that 95 mol % or more of all the polyester components constituting the film is ethylene terephthalate. By using ethylene terephthalate as a main component, excellent mechanical strength and transparency can be obtained.

Ethylene terephthalate may be the entire polyester constituting the film, preferably ethylene terephthalate is 100 mol %. Polymerization methods for such polyethylene terephthalate (hereinafter sometimes simply referred to as PET) include a direct polymerization method in which terephthalic acid and ethylene glycol, and, if necessary, other dicarboxylic acid components and diol components are directly reacted; An arbitrary production method such as a transesterification method in which an acid dimethyl ester (including other dicarboxylic acid methyl esters as necessary) and ethylene glycol (including other diol components as necessary) are transesterified. can be utilized.

The intrinsic viscosity of polyethylene terephthalate is preferably in the range of 0.55 dl/g to 0.8 dl/g. If the intrinsic viscosity is lower than 0.55 dl/g, the film will crystallize upon stretching, resulting in reduced shrinkability. On the other hand, if it is more than 0.8 dl/g, the increase in filtration pressure becomes large, making high-precision filtration difficult, which is not very preferable.

In addition, the present invention can use PET bottle recycled raw materials among PET. (Hereinafter, it may be simply referred to as a recycled raw material). Recycled raw materials generally contain PET as a constituent component in order to improve moldability when made into PET bottles, but generally contain a small amount of isophthalic acid as a monomer component. In the present invention, a large amount of polymer raw materials containing a large amount of monomer components that can be amorphous components are not used in large amounts. It is expressed that the amount is contained in the range of 0 mol % or more and 5 mol % or less.

A typical example of a monomer that can be an amorphous component is isophthalic acid. 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n- Butyl-1,3-propanediol and hexanediol can also be mentioned, and there is no particular problem even if they are contained within the aforementioned content range.

In the polyester raw material used in the present invention, 1,4-butanediol, which is a diol component other than ethylene glycol, may be used as a component other than the ethylene terephthalate and the amorphous component described above. 1,4-butanediol lowers the melting point of the polyester film and is useful as a low Tg component. The content of 1,4-butanediol in all alcohol components and all acid components is preferably 10 mol % or less, more preferably 5 mol % or less, and most preferably 0 mol %.

Moreover, in the present invention, a polyester raw material using ethylene glycol produced from a plant-derived raw material as a glycol component (hereinafter sometimes simply referred to as a biopolyester raw material) can be used.

In order to improve the workability (slipperiness) of the film, it is preferable to add fine particles acting as a lubricant to the polyester raw material. As the fine particles, any fine particles can be selected regardless of the type of inorganic fine particles or organic fine particles. Examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Examples of organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, crosslinked polystyrene particles, and the like. The average particle diameter of the fine particles is preferably in the range of about 0.05 to 3.0 μm when measured with a Coulter Counter.

The method of blending the fine particles in the polyester raw material is not particularly limited, and for example, it can be added at any stage in the production of the polyester resin. It is preferable to add a slurry dispersed in ethylene glycol or the like before starting the reaction to proceed with the polycondensation reaction. In addition, a method of blending a slurry of fine particles dispersed in ethylene glycol or water or the like with a polyester resin raw material using a kneading extruder with a vent; or using a kneading extruder, dried fine particles and a polyester resin raw material. It may be performed by a method of blending and the like.

(Characteristics of the heat-shrinkable polyester film of the present invention)
In addition, the heat-shrinkable polyester film of the present invention is treated in hot water at 90° C. for 10 seconds under no load. is preferably 25% or more and 50% or less.
Thermal shrinkage = {(length before shrinkage - length after shrinkage) / length before shrinkage} x 100 (%) Formula 1

If the hot water heat shrinkage in the width direction at 90°C is less than 25%, the amount of shrinkage is small when used as a heat-shrinkable film. do not have. On the other hand, there is no particular problem even if the hot water heat shrinkage in the width direction at 90° C. exceeds 50%, but in the present invention, 50% is the upper limit of the heat shrinkage. The lower limit of the hot water heat shrinkage in the width direction at 90° C. is preferably 30%, more preferably 35%.

In addition, the heat-shrinkable polyester film of the present invention is treated in hot water at 90 ° C. for 10 seconds under no load, from the length before and after shrinkage, the longitudinal direction of the film calculated by the above formula 1. is preferably 10% or more and 20% or less. If the heat shrinkage in hot water in the longitudinal direction at 90°C exceeds 20%, the length of the film in the direction perpendicular to the shrinking direction becomes short when used as a label or the like, which is not preferable. On the other hand, the shrinkage rate in the longitudinal direction is preferably close to zero, but in the present invention, the lower limit of the heat shrinkage rate is about 10%. The hot water heat shrinkage in the longitudinal direction at 90° C. is preferably 18% or less, more preferably 16% or less.

Moreover, the heat-shrinkable polyester film of the present invention preferably has a tensile strength at break in the longitudinal direction of the film of 100 MPa or more and 200 MPa or less. When the tensile strength at break in the longitudinal direction is 100 MPa or more, troubles such as tearing of the film can be reduced in processing steps such as printing, which is preferable. In addition, it can be suitably used for banding applications where film strength against external force is required. The tensile strength at break in the longitudinal direction is preferably as high as possible, but in the present invention, the upper limit of the tensile strength at break is about 200 MPa. The longitudinal tensile strength at break is preferably 110 MPa or more, more preferably 120 MPa or more.

In addition, the heat-shrinkable polyester film of the present invention preferably has a higher refractive index value in the film longitudinal direction than in the film width direction, which is the main shrinking direction. By setting the refractive index to the value described above, the preferable tensile strength at break in the longitudinal direction of the film can be obtained. The difference in refractive index between the width direction and the longitudinal direction of the film ([longitudinal refractive index] - [width direction refractive index]) is preferably higher than 0, more preferably 0.005 or more.

Moreover, the heat-shrinkable polyester film of the present invention preferably has a maximum heat-shrinkage stress in the film width direction of 14 MPa or more and 22 MPa or less. If the maximum shrinkage stress is higher than 22 MPa, deformation of the container occurs after shrinkage, which is undesirable. A lower maximum heat shrinkage stress in the width direction is preferable for shrink finishability and shrinkage strain, which will be described later, but in the present invention, the lower limit is about 14 MPa. If it is too low, it may not be possible to obtain the preferred thermal shrinkage stress after shrinkage by 10%, which will be described later. The maximum heat shrinkage stress in the width direction is preferably 19 MPa or less, more preferably 18 MPa or less.

The heat-shrinkable polyester film of the present invention preferably has thickness unevenness of 20% or less in both the longitudinal direction and the width direction of the film. If the unevenness in thickness is greater than 20%, it is not preferable because printing omissions or meandering due to wrinkles may occur during processing such as printing. Thickness unevenness in the longitudinal and width directions of the film is preferably as low as possible, but in the present invention, the lower limit of thickness unevenness is about 5%. The thickness unevenness in the longitudinal direction and the width direction is more preferably 18% or less, more preferably 16% or less.

In the heat-shrinkable polyester film of the present invention, the heat-shrinkage stress in the width direction of the film is preferably 10 MPa or more and 18 MPa or less after the film is shrunk by 10%. If the thermal shrinkage stress after shrinking the film by 10% is less than 10 MPa, the tightening of the container after shrinking is insufficient. It is not preferable because the label and the container are idling, making it difficult to open (the fit is poor). If the heat shrinkage stress in the width direction after the film is shrunk by 10% is higher than 18 MPa, deformation of the container occurs, which is undesirable. The heat shrinkage stress in the width direction after shrinking the film by 10% is preferably 11 MPa or more, more preferably 12 MPa or more.

Although the thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, it is preferably 5 to 100 μm, more preferably 10 to 95 μm, as a heat-shrinkable film for label use and banding use.

(Preferred method for producing the heat-shrinkable polyester film of the present invention)
In addition, the heat-shrinkable polyester film of the present invention is not subject to any restrictions on its production method. The film can be obtained by biaxially stretching according to the method shown below.

When the raw material resin is melt-extruded, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer, a paddle dryer, or a vacuum dryer. After the polyester raw material is dried in this manner, it is melted at a temperature of 200 to 300° C. and extruded into a film using an extruder. Any existing method such as a T-die method, a tubular method, or the like can be employed for such extrusion.

Then, an unstretched film can be obtained by rapidly cooling the extruded sheet-like molten resin. As a method for rapidly cooling the molten resin, a method of obtaining a substantially non-oriented resin sheet by casting the molten resin from a nozzle onto a rotating drum and rapidly cooling and solidifying the resin can be suitably employed.

Furthermore, as described later, the obtained unstretched film can be stretched in the width direction under predetermined conditions and then stretched in the longitudinal direction under predetermined conditions to obtain the heat-shrinkable polyester film of the present invention. becomes. Preferred biaxial stretching for obtaining the heat-shrinkable polyester film of the present invention will now be described in detail, taking into consideration the difference from conventional stretching methods for heat-shrinkable polyester films.

(Preferred stretching method for the heat-shrinkable polyester film of the present invention)
A normal heat-shrinkable polyester film is produced by stretching an unstretched film in the desired direction of shrinkage. Although there has been a high demand for a heat-shrinkable polyester film that shrinks in the width direction, simply stretching an unstretched film in the width direction significantly lowers the tensile breaking strength in the longitudinal direction. It is not preferable in terms of productivity because a film with a high production speed cannot be produced. In addition, ordinary heat-shrinkable polyester films use raw materials containing a large amount of amorphous components in order to impart heat-shrinkable properties, so there is a limit to the mixing ratio of recycled raw materials.

As a preferred production method for continuously producing the heat-shrinkable polyester film of the present invention, the unstretched polyester film obtained by the above method is uniaxially stretched in the longitudinal direction of the film at a predetermined draw ratio described later. , The obtained uniaxially stretched film is stretched in the width direction with a tenter at a temperature of Tg or more and Tg + 40 ° C. or less at a predetermined draw ratio described later with clips held at both ends in the same width direction (transverse stretching). method can be adopted.

A preferred draw ratio in the longitudinal direction and a preferred draw ratio in the width direction of the heat-shrinkable film of the present invention will be described.
As a result of research, the present inventor found that a film that does not intentionally use amorphous PET raw materials has a high shrinkage rate in the stretching direction when the stretching ratio is about 2 times, and when the stretching ratio is higher than 3 times, crystallization proceeds in the stretching direction. It was found that the shrinkage rate of A heat-shrinkable polyester film using a conventional amorphous raw material is generally stretched at a temperature from the glass transition temperature (Tg) to Tg + 30 ° C. with a draw ratio of about 3.5 to 5.5 times (final draw It is manufactured by stretching at a magnification). It is believed that the amorphous molecules are oriented under these stretching conditions, and the film is provided with a shrinkage ratio. easier). On the other hand, as in the present invention, when the monomer component (amorphous raw material) that can be an amorphous component is 0 mol % or more and 5 mol % or less and substantially does not contain an amorphous raw material, the same temperature as above, that is, When the film is stretched at a temperature between Tg and Tg + 30°C, the film shrinks if it is stretched at a magnification of 2 to 2.5 times, but it is stretched by the same magnification as above, that is, about 3.5 to 5.5 times. And the shrinkage rate of the film decreases.
From the results of this study, the present inventor found that it is preferable to stretch the film at an initial stretching ratio of 4 times or more and 7 times or less in the longitudinal direction in order to biaxially stretch the film and shrink it in the width direction. If it is less than 4 times, the shrinkage rate in the longitudinal direction becomes high, and defects such as wrinkles occur when the label or banding film is shrunk, which is not preferable. In addition, when the unstretched film is stretched in the width direction without being stretched in the longitudinal direction, thickness unevenness in the width direction becomes large, which is not preferable. There is no upper limit for the draw ratio in the longitudinal direction, but if it is higher than 7 times, it is not preferable because it becomes difficult to draw in the width direction (so-called breakage tends to occur). It is more preferably 4.3 times or more and 6.7 times or less, and still more preferably 4.6 times or more and 6.4 times or less. A preferable stretching temperature in the longitudinal direction is Tg or more of unstretched polyester and Tg + 40°C or less. The draw ratio in the width direction is preferably 1.5 times or more and 2.5 times or less. If it is 1.5 times or less, the heat shrinkage rate in the width direction is insufficient, and if it is 2.5 times or more, the neck-in caused by stretching in the width direction increases the stress applied in the longitudinal direction, and the width shrinkage rate increases. Due to the fact that the thermal shrinkage rate in the direction increases, defects such as wrinkles occur when the film is shrunk as a label or banding film, which is not preferable. It is more preferably 1.6 times or more and 2.4 times or less, and still more preferably 1.7 times or more and 2.3 times or less. A preferable stretching temperature in the width direction is Tg+40° C. or less of the unstretched polyester film. It is preferable to preheat the unstretched polyester film at Tg+40° C. or less before stretching in the width direction. It is preferable to control the preheating time to 2 seconds or more and 10 seconds or less.

The longitudinal stretching and transverse stretching were carried out as described above. If necessary, the film may be heat-treated in a tenter with both ends in the width direction held by clips. Here, heat treatment means heat treatment at a temperature of (Tg−20° C.) or more and Tg or less. Such heat treatment is preferably used because it can suppress a decrease in the thermal shrinkage rate and improve the dimensional stability after storage over time. If the heat treatment temperature is lower than (Tg-20° C.), the above effects of the heat treatment cannot be effectively exhibited. On the other hand, if the heat treatment temperature is higher than Tg, the heat shrinkage in the width direction tends to fall below the lower limit of 50%.

(Package using the heat-shrinkable polyester film of the present invention as a base material)
The package of the present invention is formed by covering at least part of the outer circumference of an object to be packaged with a banding film (and label) obtained from the heat-shrinkable polyester film of the present invention and heat shrinking the film. be. Examples of packaging objects include plastic containers such as lunch boxes (PET bottles for beverages, various bottles, cans, snacks, etc.), paper boxes, and the like. In general, when a label obtained from a heat-shrinkable polyester film is heat-shrunk to cover an object to be packaged, the banding film (and label) is heat-shrunk by about 5 to 50%. Adhere to the package. The banding film (and label) that covers the packaging object may or may not be printed.

As a method for producing a banding film (and label), a rectangular film is rolled in the width direction and the ends are overlapped and glued to form a label, or the film wound into a roll is rolled The roll is rolled in the width direction, the ends are superimposed on the film and adhered to form a tubular body, which is cut into a label shape. Films can be adhered using known methods such as fusion sealing, solvent adhesion, adhesion by hot-melt adhesives, and adhesion by energy ray-curable adhesives.

The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to the aspects of the Examples, and can be modified as appropriate without departing from the scope of the present invention. be. The compositions of raw materials used in Examples and Comparative Examples, film stretching methods and production conditions in Examples and Comparative Examples are shown in the tables.

Moreover, the evaluation method of the film is as follows.
[Tg (glass transition point)]
Using a differential scanning calorimeter (manufactured by Seiko Electronics Co., Ltd., DSC220), put 5 mg of an unstretched film in a sample pan, cover the pan, and heat it from -40 ° C. to 120 ° C. at 10 ° C./ The temperature was raised at a rate of temperature rise of 1 min. Tg (°C) was determined according to JIS-K7121-1987.

[Intrinsic Viscosity (IV)]
0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol/1,1,2,2-tetrachloroethane (60/40 (weight ratio)) and measured at 30°C using an Ostwald viscometer. The unit is dl/g.

[Thermal shrinkage rate (hot water heat shrinkage rate)]
Cut the film into a square of 10 cm × 10 cm, heat it in hot water heated to a predetermined temperature ± 0.5 ° C., treat it for 10 seconds under no load, and then heat shrink the length and width of the film. was measured, and the thermal shrinkage rate was determined according to the following formula 1.
Thermal shrinkage = {(length before shrinkage - length after shrinkage) / length before shrinkage} x 100 (%) (Formula 1)

[Tg (glass transition point)]
Using a differential scanning calorimeter (model: DSC220) manufactured by Seiko Electronics Industry Co., Ltd., 5 mg of an unstretched film is heated from -40 ° C. to 120 ° C. at a temperature increase rate of 10 ° C./min, and the obtained endotherm Obtained from the curve. A tangent line was drawn before and after the inflection point of the endothermic curve, and the intersection point was defined as Tg (glass transition point).

[Method for measuring tensile strength at break]
In accordance with JIS-K7113, a strip-shaped test piece of a predetermined size is prepared, both ends of the test piece are held with a universal tensile tester, and a tensile test is performed at a tensile speed of 200 mm / min. The strength to break was measured.

[Longitudinal thickness unevenness]
The film was sampled into strips of 1 m in the longitudinal direction and 40 mm in the width direction, and a continuous contact thickness meter manufactured by Micron Measuring Instruments Co., Ltd. was used at a speed of 5 (m / min) along the longitudinal direction of the film sample. The thickness was measured continuously. The thickness unevenness of the film was calculated from the following formula 2.
Thickness unevenness = (maximum thickness - minimum thickness) / average thickness x 100 (%) (Formula 2)

[Thickness unevenness in the width direction]
The film was sampled into strips of 0.5 m in the width direction and 40 mm in the longitudinal direction, and a continuous contact thickness meter manufactured by Micron Measuring Instruments Co., Ltd. was used to measure the longitudinal direction of the film sample at a speed of 5 (m / min). The thickness was measured continuously along the The thickness unevenness of the film was calculated from Equation 2 above.

[Melt viscosity]
Capilograph 1D PMD-C Measurement was performed according to JIS K7199 under the conditions of a resin temperature of 250° C. and a shear rate of 6080/S using Toyo Seiki Seisakusho Co., Ltd.

[Thermal shrinkage stress]
A strip-shaped film sample with a length of 150 mm in the width direction and a width of 20 mm is cut out from the heat-shrinkable film, and a strength and elongation measuring machine with a heating furnace manufactured by Toyo Baldwin Co., Ltd. (current company name Orientec) Tesilon universal testing machine PTM-250 ( The shrinkage stress was measured using Orientec's registered trademark). The inside of the heating furnace of the strength and elongation measuring machine was preheated to 90° C., and the distance between chucks for gripping the film sample was set to 100 mm. When attaching the sample to the chuck of the strength and elongation measuring machine, stop the ventilation of the heating furnace once and open the door of the heating furnace. It was set to 100 mm, and the sample was fixed without looseness so that the length direction of the sample was aligned with that between the chucks and the sample was horizontal. After attaching the sample to the chuck, the door of the heating furnace was quickly closed and air blowing was restarted. The time when the heating furnace door is closed and the air blowing is restarted is the start point of measuring the heat shrinkage stress, and the maximum value of the heat shrinkage stress measured up to 30 seconds after the start of measurement is the maximum heat shrinkage stress (maximum heat shrinkage stress (MPa)).

[Thermal shrinkage stress after 10% shrinkage]
A strip-shaped film sample with a length of 161 mm in the width direction and a width of 20 mm was cut out from the heat-shrinkable film, and a strength and elongation measuring machine with a heating furnace manufactured by Toyo Baldwin Co., Ltd. (current company name Orientec) Tesilon universal testing machine PTM-250 ( The shrinkage stress was measured using Orientec's registered trademark). The inside of the heating furnace of the strength and elongation measuring machine was preheated to 90° C., and the distance between chucks for gripping the film sample was set to 100 mm. When attaching the sample to the chuck of the strength and elongation measuring machine, stop the ventilation of the heating furnace once and open the door of the heating furnace. The film length between the chucks was set to 100 mm and the length of the film was set to 111 mm, and the thermal shrinkage stress after 10% shrinkage was measured.

[Refractive index]
Using an Abbe refractometer manufactured by Atago Co., Ltd., and using a sodium lamp as a light source according to JIS K7142, the refractive index of the film was measured.

[Shrinkage finish]
The heat-shrinkable film was previously printed in three colors with grass, gold, and white inks (Toyo Ink Mfg. Co., Ltd.). Then, by bonding both ends of the printed film with phenol, a cylindrical label (a label whose circumferential direction is the main shrinkage direction of the heat-shrinkable film) was produced and cut. The shrink direction diameter of the label was 77 mm. After that, using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc., the passage time is 4 seconds, the zone temperature is 90 ° C., and the label is heat-shrunk into a 350 ml bottle can (body diameter 70 mm) by heat shrinking. I put it on. In addition, at the time of wearing, it was adjusted so that it contracted only to the body. The evaluation of finish after shrinkage was performed visually, and the criteria were as follows.

[Label shrinkage distortion]
As an evaluation of the finish after shrinkage, strain in the 360-degree direction on the top of the attached label was measured using a gauge, and the maximum value of strain was obtained. Evaluation was made according to the following criteria.
○: Maximum strain less than 3.0 mm ×: Maximum strain 3.0 mm or more

[Label fit]
With the bottle-can attached with the label described above, the can bottle was held with one hand and the cap was held with the other hand, and the cap was opened.
○: The attached label and container do not move.
x: The label and the container move, and the label rotates.

Polyesters used in Examples and Comparative Examples are as follows.

・Polyester 1: Polyethylene terephthalate (IV 0.7 dl/g)
・Polyester 2: Polyethylene terephthalate (IV 0.7 dl/g) obtained by adding SiO ₂ (Sylysia 266 manufactured by Fuji Silysia Co., Ltd.) as a lubricant at a rate of 8,000 ppm relative to the polyester during the production of polyester 2 above.
・Polyester 3: Recycled raw material {"Clear Pellets" (IV 0.63 dl/g, manufactured by Yono PET Bottle Recycle Co., Ltd.). %).
・Polyester 4: Bio-polyester raw material using bio-derived ethylene glycol (IV 0.62 dl / g)

Polyester 4 was prepared by the following manufacturing method. Magnesium acetate tetrahydrate was added to a mixture of terephthalic acid refined from petroleum-derived raw materials and ethylene glycol refined from plant-derived raw materials so that the concentration of Mg atoms in the polyester was 70 ppm, and the temperature was 255°C under normal pressure. was subjected to an esterification reaction. After that, antimony trioxide was added in an amount of 280 ppm in the polyester as Sb atoms and trimethyl phosphate in an amount of 40 ppm in the polyester as P atoms, and the mixture was further reacted at a temperature of 260°C. Subsequently, the reaction product was transferred to the polycondensation reaction layer, and the reaction system was gradually depressurized while heating to raise the temperature, and polycondensation was performed by a conventional method at 280°C under a reduced pressure of 133 Pa (1 mmHg), IV = 0.62. dl/g polyester chips were obtained. When the biomass degree was measured, the biomass degree was 17%.

[Example 1] (Hereinafter, Example 1 is read as Reference Example 1)
The above polyester 1 and polyester 2 were mixed at a weight ratio of 93:7 and fed into an extruder. Thereafter, the mixed resin was melted at 280° C., extruded through a T-die, wound around a rotating metal roll cooled to a surface temperature of 30° C., and quenched to obtain an unstretched film having a thickness of 300 μm. At this time, the take-up speed of the unstretched film (rotational speed of the metal roll) was about 8 m/min. The Tg of the unstretched film was 75°C.
After that, the unstretched film was preheated with metal rolls of a longitudinal stretching device until the film temperature reached 80°C, stretched by a factor of 5 using the speed difference of the rolls, and then cooled with a cooling roll at 30°C.
The film stretched in the longitudinal direction is preheated with a transverse stretching machine (tenter) until the film temperature reaches 100°C, then stretched twice at 100°C, and the length in the width direction is fixed and heat-treated at 95°C. It cooled until the film temperature became 50 degrees C or less.
By cutting and removing both edges after the tenter, a biaxially stretched film with a thickness of 30 μm is continuously formed over a predetermined length, and a film roll made of a heat-shrinkable polyester film with a width of 2 m is obtained. Obtained.
Then, the properties of the obtained film were evaluated by the methods described above. Table 3 shows the evaluation results.
As a result of the evaluation, it was found to be a film having sufficient shrinkability and a good finish after shrinkage.

[Example 2] (Hereinafter, Example 2 will be read as Reference Example 2)
A heat-shrinkable film was continuously produced in the same manner as in Example 1, except that polyester 3 and polyester 2 were mixed at a weight ratio of 93:7 and put into the extruder. The Tg of the unstretched film was 75°C. Then, the properties of the obtained film were evaluated in the same manner as in Example 1. Table 3 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkage and good shrinkage finish.

[Example 3] (Hereinafter, Example 3 will be read as Reference Example 3)
A heat-shrinkable film was continuously produced in the same manner as in Example 1, except that polyester 4 and polyester 2 were mixed at a weight ratio of 93:7 and put into the extruder. The Tg of the unstretched film was 75°C. Then, the properties of the obtained film were evaluated in the same manner as in Example 1. Table 3 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkage and good shrinkage finish.

[Example 4]
A heat-shrinkable film was continuously produced in the same manner as in Example 1, except that the vertical draw ratio was changed from 5 times to 4.5 times and the horizontal draw ratio was changed from 2 times to 2.2 times. did. A film roll made of a heat-shrinkable polyester film having a width of 2.2 m was obtained. Table 3 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkage and good shrinkage finish.

[Example 5] (Hereinafter, Example 5 is read as Reference Example 4)
A heat-shrinkable film was continuously produced in the same manner as in Example 1, except that the vertical draw ratio was changed from 5 times to 5.5 times and the horizontal draw ratio was changed from 2 times to 1.8 times. manufactured. A film roll made of a heat-shrinkable polyester film having a width of 1.8 m was obtained. Table 3 shows the evaluation results. As a result of the evaluation, it was found to be a film having sufficient shrinkability and a good finish after shrinkage.

[Comparative Example 1]
The above polyester 1 and polyester 2 were mixed at a weight ratio of 93:7 and fed into an extruder. Thereafter, the mixed resin was melted at 280° C., extruded through a T-die, wound around a rotating metal roll cooled to a surface temperature of 30° C., and quenched to obtain an unstretched film having a thickness of 60 μm.
The obtained unstretched film is preheated with a transverse stretching machine (tenter) until the film temperature reaches 100° C., stretched twice at 100° C., and heat-treated at 95° C. with the length in the width direction set to a constant length, It cooled until the film temperature became 50 degrees C or less.
By cutting and removing both edges after the tenter, a uniaxially stretched film with a thickness of 30 μm is continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester film with a width of 2 m. rice field.
Then, the properties of the obtained film were evaluated by the methods described above. Table 3 shows the evaluation results. As a result of the evaluation, the tensile strength at break in the longitudinal direction was low and the thickness unevenness was high. In addition, since the shrinkage stress after 10% shrinkage was low, the fit of the label was poor.

[Comparative Example 2]
The above polyester 1 and polyester 2 were mixed at a weight ratio of 93:7 and fed into an extruder. Thereafter, the mixed resin was melted at 280° C., extruded from a T-die, wound around a rotating metal roll cooled to a surface temperature of 30° C., and quenched to obtain an unstretched film having a thickness of 450 μm. At this time, the take-up speed of the unstretched film (rotational speed of the metal roll) was about 8 m/min. The Tg of the unstretched film was 75°C.
After that, the unstretched film was preheated with metal rolls of a longitudinal stretching device until the film temperature reached 80°C, stretched by a factor of 5 using the speed difference of the rolls, and then cooled with a cooling roll at 30°C. .
A film stretched in the longitudinal direction is preheated with a transverse stretching machine (tenter) until the film temperature reaches 100 ° C., then stretched 3 times at 100 ° C., and the length in the width direction is fixed and heat-treated at 95 ° C. , until the film temperature was 50° C. or lower.
By cutting and removing both edges after the tenter, a biaxially stretched film with a thickness of 30 μm is continuously formed over a predetermined length, and a film roll made of a heat-shrinkable polyester film with a width of 3 m is obtained. Obtained.
Then, the properties of the obtained film were evaluated by the methods described above. Table 3 shows the evaluation results. The shrinkage ratio in the width direction was insufficient, and the film was unsuitable as a label.

[Comparative Example 3]
The above polyester 1 and polyester 2 were mixed at a weight ratio of 93:7 and fed into an extruder. Thereafter, the mixed resin was melted at 280° C., extruded through a T-die, wound around a rotating metal roll cooled to a surface temperature of 30° C., and quenched to obtain an unstretched film having a thickness of 180 μm. At this time, the take-up speed of the unstretched film (rotational speed of the metal roll) was about 8 m/min. The Tg of the unstretched film was 75°C.
Thereafter, the unstretched film was preheated with metal rolls of a longitudinal stretching device until the film temperature reached 80°C, stretched by a factor of 3 using the speed difference of the rolls, and then cooled with a cooling roll at 30°C.
A film stretched in the longitudinal direction is preheated with a transverse stretching machine (tenter) until the film temperature reaches 100°C, then stretched 3 times at 100°C, and the length in the width direction is fixed and heat-treated at 95°C. It cooled until the film temperature became 50 degrees C or less.
By cutting and removing both edges after the tenter, a biaxially stretched film with a thickness of 30 μm is continuously formed over a predetermined length, and a film roll made of a heat-shrinkable polyester film with a width of 2 m is obtained. Obtained.
Then, the properties of the obtained film were evaluated by the methods described above. Table 3 shows the evaluation results. The shrinkage rate in the longitudinal direction was high, and the shrink finish was poor, making the film unsuitable as a label.

Since the heat-shrinkable polyester film of the present invention has excellent properties as described above, it can be suitably used for bottle labeling and banding. The film has a sufficient heat shrinkage rate in the width direction even with an extremely low content of monomer components that can become amorphous components in polyester, so the recycled raw material ratio can be increased and the film is also suitable for the environment. is.

Claims (6)

A heat-shrinkable polyester containing ethylene terephthalate as a main component, containing 0 mol% or more and 5 mol% or less of a monomer component that can be an amorphous component in all polyester resin components, and having a main shrinkage direction in the width direction. A heat-shrinkable polyester film for a banding film, which is a film and satisfies the following requirements (1) to (4).
(1) The hot water heat shrinkage in the width direction when treated for 10 seconds in hot water at 90°C is 25% or more and 50% or less.
(2) Hot water heat shrinkage in the longitudinal direction perpendicular to the width direction when treated in hot water at 90°C for 10 seconds is more than 12% and 20% or less.
(3) Tensile breaking strength in the longitudinal direction of the film is 100 MPa or more and 200 MPa or less
(4) The refractive index value in the film longitudinal direction is higher than the refractive index value in the film width direction, which is the main shrinkage direction. 2. The heat-shrinkable polyester film according to claim 1, wherein the maximum shrinkage stress in the film width direction is 14 MPa or more and 22 MPa or less. 3. The heat-shrinkable polyester film according to claim 1, wherein the thickness unevenness in the longitudinal direction and the thickness unevenness in the width direction are both 20% or less. 4. The heat-shrinkable polyester film according to any one of claims 1 to 3, wherein the heat-shrinkage stress in the width direction of the film after the film is shrunk by 10% in the width direction is 10 MPa or more and 18 MPa or less. 5. The method for producing a heat-shrinkable polyester film according to any one of claims 1 to 4, wherein the unstretched film is stretched in the longitudinal direction and then stretched in the width direction. A package comprising the heat-shrinkable polyester film according to any one of claims 1 to 4 as a base material, and at least part of the outer periphery of the package being covered with a banding film.