JP2020049947A - Heat-shrinkable polyester film roll - Google Patents

Abstract

To provide a heat-shrinkable polyester film that comprises: a sufficient heat-shrinkage property in a main shrinkage direction being the longitudinal direction; a low heat shrinkage in the width direction orthogonal to the main shrinkage direction; extremely few scratching on a film surface; a low shrinkage stress; a high mechanical strength; a small difference in molecular orientation angle; and a small thickness unevenness.SOLUTION: There is provided a heat-shrinkable polyester film roll obtained by winding a heat-shrinkable polyester film into a roll, the heat-shrinkable polyester film that contains: ethylene terephthalate as a main component; more than 5 mol% of a monomer component that can be an amorphous component in all polyester resin components; and that has a main shrinkage direction in the longitudinal direction, and that satisfies in a specific range of: a heat shrinkage property in the longitudinal direction and the width direction; and a molecular orientation angle difference that is a difference between a molecular orientation angle in the vicinity of the single edge and a molecular orientation angle in the vicinity of the other edge in the width direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat-shrinkable polyester film and a package. More specifically, the present invention is suitable for labeling, banding for binding a body and a lid of a lunch box or the like with a band-shaped film, and a flaw on the film surface. Is a polyester-based shrink film having a very small content.

  In recent years, stretched films made of polyvinyl chloride-based resin, polystyrene-based resin, polyester-based resin, etc. have been used for label packaging, cap sealing, integrated packaging, etc., which also serve as protection of glass bottles and PET bottles and display of products. Heat-shrinkable films) have become widely used. Among such heat-shrinkable films, polyvinyl chloride-based films have problems such as low heat resistance, generation of hydrogen chloride gas during incineration, and generation of dioxin. In addition, polystyrene-based films have poor solvent resistance, require the use of inks with special compositions when printing, and require incineration at high temperatures. There is a problem of doing. Therefore, polyester-based heat-shrinkable films having high heat resistance, easily incinerated, and having excellent solvent resistance have come to be widely used as shrink labels. With the increase, the usage amount tends to increase.

  Further, as a general heat-shrinkable polyester film, a film which largely shrinks in the width direction is widely used. The heat-shrinkable polyester film in which the width direction is the main shrinkage direction is stretched at a high magnification in the width direction in order to exhibit shrinkage characteristics in the width direction, but is orthogonal to the main shrinkage direction. In the longitudinal direction, stretching is often performed only at a low magnification, and some are not stretched. Thus, a film that has been stretched only at a low magnification in the longitudinal direction or a film that has been stretched only in the width direction has a disadvantage that the mechanical strength in the longitudinal direction is inferior.

  When used as a banding film that binds the bottle label film and the lunch box body and lid with a band-shaped film, the film must be heat-shrinked in the circumferential direction after being attached to the bottle or lunch container in an annular shape, When attaching a heat-shrinkable film that shrinks in the width direction as a banding film, after forming an annular body so that the width direction of the film is the circumferential direction, the annular body is cut at predetermined lengths. Must be worn over bottles and lunch containers. Therefore, it is difficult to attach a label film or a banding film made of a heat-shrinkable film that shrinks in the width direction to a bottle or a lunch container at a high speed. Therefore, in recent years, there has been a demand for a film that is heat-shrinkable in the longitudinal direction and can be wound around a bottle or a lunch box directly from a film roll and mounted. A center sealing step of forming and sealing a film tubular body, and processing such as cutting and covering, are not required, and mounting at a high speed is possible.

  As a demand for shrinkability, a high shrinkage rate is required. In recent years, due to the diversification of bottle shapes, there is also a case where the difference between the maximum and minimum lengths of the waist of the bottle is large (for example, a bottle with a thin cap near the top of the bottle). On the other hand, a high shrinkage ratio is required in a portion where the body of the bottle is thin. In order to impart shrinkage, it is common to use a raw material containing an amorphous monomer. Although it is possible to impart shrinkage without using amorphous raw materials indefinitely by devising film forming conditions, it is necessary to use amorphous monomers infinitely and set the longitudinal stretching ratio low. In addition, the maximum shrinkage rate is limited to about 60%, and there is a problem that shrinkage is insufficient in a thin portion of the bottle due to insufficient shrinkage.

  The shrinkage in the non-shrinkage direction (width direction) is also important for the finish after shrinking when the film is shrunk as a label into a bottle and attached. When the film is attached to a bottle as a label, the width direction of the film is the lengthwise direction of the bottle. However, if the shrinkage in the width direction of the film is high, the film can be pulled in the lengthwise direction of the bottle (so-called vertical shrinkage). In addition, the area of the bottle covered with the film is reduced, so that the required area of the film increases, which is not preferable in terms of cost. In particular, in the case of mounting on a bottle having a square bottom (so-called square bottle), even a slight shrinkage in the film width direction is noticeable, and the vertical shrinkage is conspicuous, which is not preferable in appearance. In particular, for a square bottle, a film having a shrinkage rate extremely close to 0 or a negative shrinkage rate in the film width direction is preferable. For example, in Patent Document 1, since the shrinkage in the film width direction is 0 or more, vertical shrinkage occurs when mounted on a square bottle.

  Further, in the demand for the appearance of the film after shrinkage, it is required that distortion after shrinkage is small. It is known that distortion after shrinkage occurs because the main orientation direction of molecules is inclined from the longitudinal direction or width direction of the film. This tilt is called the molecular orientation angle.When normal biaxial stretching is performed, the angle between the 12 o'clock direction and the molecular chains in the film when the machine flow direction is 12 o'clock in the center of the film. (Hereinafter simply referred to as molecular orientation angle) is close to 0 °, and there is no difference in molecular orientation in the width direction, but the difference in molecular orientation in the width direction is large near the end of the film. This is because neck-in occurs only in the vicinity of the end portion because the stretching distance is short and rapid stretching is performed. It is ideal for distortion that the molecular orientation angle is small from the center to the edge of the film and the difference in the molecular orientation angle in the width direction is small.

  When shrinking and attaching a film to a bottle or lunch container, deformation of the bottle or lunch container due to shrinkage may be a problem. Since the deformation is caused by the stress of the film generated during shrinkage, it is not preferable that the shrinkage stress is too high. For example, it is possible to form a heat-shrinkable polyester film having a longitudinal direction as a main shrinkage direction without using an amorphous component as much as possible, but since an amorphous component is not used, stretching at the time of stretching in the longitudinal direction is possible. High stress and high stress during shrinkage.

  Furthermore, with respect to the appearance of the shrink film, there is a demand for less scratches on the film surface. Scratches on the film surface cause defects such as missing prints when printing is performed on the film. Usually, when a film is stretched by heating, it is necessary to heat the film to a temperature of Tg or higher.However, when the film has reached a temperature of Tg or higher, the friction with the roll and the The shift causes scratches on the film surface. When a general longitudinal stretching machine is used, the film is heated by being brought into contact with a roll having a high temperature of Tg or more, and therefore, the film is easily scratched.

  For example, in Patent Document 1, in a longitudinal stretching machine used for film formation, when a plurality of high-temperature rolls having a temperature equal to or higher than the Tg of the film are brought into contact, many scratches are generated on the film surface, which is not preferable in appearance. Also, since neck-in occurs sharply only near the end, the difference in the molecular orientation angle near the end is large, and when the film near the end is shrunk because the molecular orientation angle is large, distortion occurs, Not desirable in appearance.

Japanese Patent No. 411556

An object of the present invention is to solve the problem of Patent Document 1 and have at least one kind of monomer component which can be an amorphous component in all polyester resin components, and have sufficient heat in a main shrinkage direction which is a longitudinal direction. It has shrinkage properties, has a low heat shrinkage in the width direction orthogonal to the main shrinkage direction, a small difference in molecular orientation angle, low shrinkage stress, extremely small scratches on the film surface, and high mechanical strength. An object of the present invention is to provide a heat-shrinkable polyester film having a small thickness unevenness.

That is, the present invention has the following configurations.
1. Ethylene terephthalate as the main component, contains more than 5 mol% of one or more monomer components that can be an amorphous component in all polyester resin components, and is formed in a long shape with a constant width, A heat-shrinkable polyester film whose main shrinkage direction is the longitudinal direction, wherein the heat-shrinkable polyester film satisfies the following requirements (1) to (4): Polyester film roll.
(1) The hot water heat shrinkage in the longitudinal direction when treated in hot water at 90 ° C for 10 seconds is 15% or more and 80% or less.
(2) The hot water heat shrinkage in the width direction orthogonal to the longitudinal direction when treated in hot water at 90 ° C for 10 seconds is -10% or more and 10% or less.
(3) Orientation twist index calculated by converting the molecular orientation angle difference, which is the difference between the molecular orientation angle near one edge in the width direction and the molecular orientation angle near the other edge, per 1 m of the film is 15 ° / m or less and 1 ° or more. Being
(4) The tensile fracture strength in the width direction that is orthogonal to the main shrinkage direction is 80 MPa or more and 200 MPa or less. The heat of claim 1, wherein the surface of the heat-shrinkable polyester film has flaws having a depth of 1 μm or more and a length of 3 mm or more are 100 / m ² or less and 15 / m ² or more. Shrinkable polyester film roll.
3. The heat-shrinkable polyester film roll according to the above 1 or 2, wherein the maximum heat shrinkage stress in the longitudinal direction of the film at 90 ° C is 3 MPa or more and 10 MPa or less.
4. 4. The heat-shrinkable polyester film roll according to any one of the first to third aspects, wherein the thickness unevenness in the longitudinal direction of the heat-shrinkable polyester film is 10% or less and 4% or more.
5. The heat according to any one of claims 1 to 4, wherein a tensile fracture strength in a width direction which is a direction orthogonal to a main shrinkage direction of the heat-shrinkable polyester film is 80 MPa or more and 200 MPa or less. Shrinkable polyester film roll.

  According to the present invention, it solves the problem of Patent Document 1, has a sufficient heat shrinkage property in the main shrinkage direction which is the longitudinal direction, and has a low heat shrinkage in the width direction orthogonal to the main shrinkage direction. In addition, it is possible to provide a heat-shrinkable polyester film having a small difference in molecular orientation angle in the width direction, extremely small scratches on the film surface, low shrinkage stress, high mechanical strength, and small thickness unevenness. The heat-shrinkable polyester film of the present invention has an extremely small number of scratches on the surface, and thus has an excellent appearance. The heat-shrinkable polyester film of the present invention can be suitably used for a film label of a bottle, and can be attached very efficiently within a short time. In addition, it was possible to obtain a good finish with very little shrinkage, vertical shrinkage, wrinkles, and protrusion of the contents. In addition, the heat-shrinkable polyester film of the present invention can be suitably used as a banding film that binds a trunk and a lid in a lunch container or the like. Thus, it was possible to obtain a good finish with very little wrinkles, distortion and insufficient shrinkage of the film.

It is a top view which shows the outline of the stretching system A typically. It is a top view which shows the outline of the extending method B typically. It is a top view which shows the outline of the stretching method C typically. 3 shows a plastic container of a lunch box for evaluating film distortion after shrinkage. Fig. 4 shows a plastic container of a lunch box for evaluating the deformation of the container after shrinkage.

  As a preferred production method for continuously producing the heat-shrinkable polyester film according to any one of the above first to fifth, ethylene terephthalate is used as a main component, and an amorphous component is formed in all the polyester resin components. Using a simultaneous biaxial stretching machine, a polyester-based unstretched film containing more than 5 mol% of a monomer component is held at both ends in the width direction by clips, and a temperature of not less than Tg and not more than Tg + 40 ° C. The film is stretched in the width direction (horizontal stretching) at a magnification of 3.5 times or more and 6 times or less, and then the length of the film is extended at a magnification of 1.5 times or more to 6 times or less by expanding the interval between clips at a temperature of Tg or more and Tg + 40 ° C or less. While stretching in the direction (longitudinal stretching), the tenter width is relaxed in the width direction by narrowing the tenter width by 5% or more and 35% or less from after the transverse stretching (hereinafter, this stretching method is referred to as stretching method A). .

  Further, the same effect as the above-mentioned production method is obtained, as one of the production methods, the same polyester-based unstretched film as described above, a film Tg or more in a state where both ends in the width direction are gripped by clips in a tenter, After stretching in the width direction (transverse stretching) at a temperature of Tg + 40 ° C or less and a magnification of 3.5 or more and 6 times or less, the clip holding the film end is opened in the tenter, and the film in the tenter is removed. The tension of the roll installed near the exit of the tenter is propagated, and the film is stretched 1.5 times or more and 6 times or less in the longitudinal direction at a temperature of the film Tg or more and Tg + 40 ° C or less due to the speed difference between the tenter clip and the roll near the exit ( Longitudinal stretching). Since the film is stretched longitudinally without being held in the width direction, the width of the film is reduced by 5% or more and 35% or less. (Hereinafter, this stretching method is referred to as stretching method B)

  In addition, the same effect as the above two production methods is obtained.One of the production methods is a film Tg in a state in which the same polyester unstretched film as described above is gripped by clips at both ends in the width direction in a tenter. After stretching in the width direction (transverse stretching) at a temperature of 3.5 to 6 times at a temperature of Tg + 40 ° C or less, heat the film again to a temperature of Tg to Tg + 40 ° C or less in another tenter. Meanwhile, stretching (longitudinal stretching) in the longitudinal direction by 1.5 times or more and 6 times or less due to the speed difference between the rolls installed at the entrance and the exit of the tenter. Since the film is stretched longitudinally without being held in the width direction, the width of the film is reduced by 5% or more and 35% or less (hereinafter, this stretching method is referred to as stretching method C).

  As the dicarboxylic acid component constituting the polyester used in the present invention, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, aromatic dicarboxylic acid such as orthophthalic acid, adipic acid, azelaic acid, sebacic acid, aliphatic such as decanedicarboxylic acid Examples thereof include dicarboxylic acids and alicyclic dicarboxylic acids.

  When an aliphatic dicarboxylic acid (for example, adipic acid, sebacic acid, decanedicarboxylic acid, etc.) is contained, the content is preferably less than 3 mol%. A heat-shrinkable polyester film obtained using a polyester containing 3 mol% or more of these aliphatic dicarboxylic acids has insufficient film stiffness during high-speed mounting.

  Further, it is preferable not to contain a trivalent or higher polyvalent carboxylic acid (for example, trimellitic acid, pyromellitic acid and anhydrides thereof). In a heat-shrinkable polyester film obtained by using a polyester containing these polycarboxylic acids, it becomes difficult to achieve a required high shrinkage.

  As the diol component constituting the polyester used in the present invention, ethylene glycol, 1-3 propanediol, 1-4 butanediol, neopentyl glycol, aliphatic diols such as hexanediol, 1,4-cyclohexanedimethanol and the like Examples thereof include alicyclic diols and aromatic diols such as bisphenol A.

  The polyester used for the heat-shrinkable polyester film of the present invention is a cyclic diol such as 1,4-cyclohexanedimethanol or a diol having 3 to 6 carbon atoms (for example, 1-3 propanediol, 1-4 butanediol). , Neopentyl glycol, hexanediol, etc.), and a polyester whose glass transition point (Tg) is adjusted to 60 to 80 ° C is preferable.

  The polyester used in the heat-shrinkable polyester film of the present invention contains more than 5 mol% in total of at least one monomer component which can be an amorphous component in 100 mol% of polyhydric alcohol components in all polyester resins. It must be contained, and is preferably at least 10 mol%, more preferably at least 15 mol%, and particularly preferably at least 20 mol%. Here, examples of the monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanediol, and isophthalic acid.

  The polyester used for the heat-shrinkable polyester film of the present invention includes a diol having 8 or more carbon atoms (eg, octanediol) or a polyhydric alcohol having 3 or more carbon atoms (eg, trimethylolpropane, trimethylolethane, glycerin). , Diglycerin, etc.). In the case of a heat-shrinkable polyester film obtained using a polyester containing these diols or polyhydric alcohols, it is difficult to achieve the required high shrinkage.

Further, when the heat-shrinkable polyester film of the present invention is treated in hot water at 90 ° C under no load for 10 seconds, the longitudinal direction of the film calculated from the length before and after shrinkage by the following formula 1 Is preferably 15% or more and 80% or less.
Heat shrinkage = {(length before shrinkage-length after shrinkage) / length before shrinkage} x 100 (%)

  If the hot water heat shrinkage in the longitudinal direction at 90 ° C. is less than 15%, the shrinkage becomes insufficient when used as a label or a banding film, and the label after heat shrinkage is undesirably wrinkled or thickened. On the other hand, if the hot water heat shrinkage in the longitudinal direction at 90 ° C exceeds 80%, shrinkage distortion is likely to occur during heat shrinkage when using as a label or banding film, or so-called “fly-up” may occur. Not preferred. The lower limit of the hot water heat shrinkage in the longitudinal direction at 90 ° C. is preferably 20%, more preferably 25%, and particularly preferably 30%. The upper limit of the hot water heat shrinkage in the longitudinal direction at 90 ° C. is preferably 75% or less, more preferably 70% or less, and particularly preferably 65% or less.

Further, when the heat-shrinkable polyester film of the present invention is treated in hot water at 90 ° C. for 10 seconds under no load, the width direction of the film calculated from the length before and after shrinkage by the above formula 1 The hot water heat shrinkage of the hot water is preferably -10% or more and 10% or less. When the hot water heat shrinkage in the width direction at 90 ° C exceeds 10%, when used as a label or banding film, vertical shrinkage occurs during heat shrinkage, which is not preferable in appearance, and the length of the film is short, which is not preferable. . On the other hand, if it is less than -10%, the label length in the direction perpendicular to the main shrinkage direction becomes longer at the time of heat shrinkage, so that the label tends to be slack and wrinkled easily. The hot water heat shrinkage in the width direction at 90 ° C. is preferably -9% or more and 9% or less, more preferably -8% or more and 8% or less, and more preferably -7% or more and 7% or less. preferable.

  Further, the heat-shrinkable polyester film of the present invention has a molecular orientation angle difference, which is a difference between the molecular orientation angle at one edge and the molecular orientation angle at the other edge in the width direction, and the orientation twist is calculated per film width 1 m. When the index is determined by the following method, the orientation twist index is preferably 15 ° / m or less. The upper limit of the orientation twist index is more preferably 13 ° / m or less, and further preferably 12 ° / m or less. The orientation twist index is preferably as close to 0 ° / m as possible, but 1 ° / m is no problem.

[Method of measuring orientation twist index]
The molecular orientation axis in the present invention, when the longitudinal direction of the film is the X axis, the width direction of the film is the Y axis, and the thickness direction of the film is the Z axis direction, when viewed on the XY plane of the film, The direction in which the degree of molecular orientation is large is called the molecular orientation axis. The molecular orientation angle means an angle at which the molecular orientation axis measured from the molecular orientation axis is shifted from the longitudinal direction of the film or the width direction of the film. As a method for measuring the molecular orientation angle, first, a rectangular sample is collected at the left and right edges facing each other in the width direction of the film. The molecular orientation angle (the angle of the molecular orientation axis direction) of the cut-out film sample is measured by a molecular orientation angle measuring device (MOA-6004) manufactured by Oji Scientific Instruments. The molecular orientation angle is 0 degree in the longitudinal direction of the film, and the direction of the molecular orientation axis is a difference from 0 degree when the direction is smaller than 45 degrees with respect to the longitudinal direction, and 90 degrees when the direction is larger than 45 degrees. Find the difference between For a rectangular sample taken from the left and right edges facing each other in the width direction of the film, the molecular orientation angle is measured by the above method, and the absolute value of the difference is calculated according to the following equation 2 between the cut-out positions (central portions) of the sample. The difference between the molecular orientation angles per unit width (1 m) of the film (orientation torsion index) is calculated by dividing by the width direction interval.
Orientation torsion index = (absolute value of the difference between the orientation angles of sample molecules taken from the left and right edges) ÷ (interval between sample cutting positions) ・ ・ ・ Equation 2

  The heat-shrinkable polyester film of the present invention preferably has a shrinkage stress of 3 MPa or more and 10 MPa or less. The method for measuring the shrinkage stress will be described in Examples. When the shrinkage stress is less than 3 MPa, the film is not loosely adhered when attached to a bottle as a label or when attached to a lunch box as a banding film, which is not preferable in terms of performance and appearance. On the other hand, if the shrinkage stress exceeds 10 MP, when the film is shrunk and mounted, the force applied to the bottle or container is too large, so that the contents pop out or the container is undesirably deformed. The shrinkage stress is more preferably 4 MPa or more and 9 MPa or less, further preferably 5 MPa or more and 8 MPa or less.

A film that has reached a temperature of Tg or more during film formation causes scratches on the film surface due to friction with the roll and displacement of the film when the film contacts a roll of a film forming machine. In the heat-shrinkable polyester film of the present invention, it is preferable that flaws having a depth of 1 μm or more and a length of 3 mm or more on the surface are 100 pieces / m ² or less. If the number of scratches exceeds 100 / m ² , the appearance of the film, such as design, is impaired, which is not preferable. The number of scratches is more preferably 90 / m ² or less, further preferably 80 / m ² or less, and the lower limit is, of course, 0 / m ² .

  In addition, the heat-shrinkable polyester film of the present invention preferably has a thickness unevenness in the longitudinal direction of 10% or less. When the thickness unevenness in the longitudinal direction is more than 10%, printing unevenness is likely to occur at the time of printing when producing a label or a banding film, or shrinkage unevenness after heat shrinkage is likely to occur. Absent. The uneven thickness in the longitudinal direction is more preferably 9% or less, further preferably 8% or less, and particularly preferably 7% or less. The thickness unevenness in the longitudinal direction is better as approaching 0%, but the lower limit is 2%, which is practically acceptable.

  The heat-shrinkable polyester film of the present invention preferably has a tensile breaking strength in the width direction of 80 MPa or more and 200 MPa or less. The method for measuring the tensile fracture strength will be described in Examples. If the tensile breaking strength is less than 80 MPa, the "stiffness" (stiffness) when mounting as a label or banding film is weakened, which is not preferable. It is not preferable because the cuttability (teariness) in the initial stage of tearing becomes poor. Incidentally, the lower limit of the tensile fracture strength is more preferably 100 MPa or more, more preferably 110 MPa or more, particularly preferably 120 MPa or more, and the upper limit is more preferably 190 MPa or less, further preferably 180 MPa or less, and 170 MPa or less. Particularly preferred.

  The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 95 μm as a label or banding heat-shrinkable film.

  Further, the heat-shrinkable polyester film of the present invention is not limited at all with respect to the production method, for example, melt extruding the above polyester raw material by an extruder to form an unstretched film, the unstretched film It can be obtained by biaxially stretching the film by the method described 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 or a paddle dryer, or a vacuum dryer. After the polyester raw material is dried in such a manner, it is melted at a temperature of 200 to 300 ° C. using an extruder and extruded into a film. For such extrusion, any existing method such as a T-die method and a tubular method can be employed.

  Then, an unstretched film can be obtained by rapidly cooling the extruded sheet-like molten resin. In addition, as a method of rapidly cooling the molten resin, a method of casting a molten resin from a die on a rotating drum and rapidly cooling and solidifying the molten resin to obtain a substantially unoriented resin sheet can be suitably adopted.

  Further, as described later, the obtained unstretched film is stretched in the width direction under predetermined conditions, and then stretched in the longitudinal direction under predetermined conditions, to thereby obtain the heat-shrinkable polyester film of the present invention. Becomes Hereinafter, preferred biaxial stretching for obtaining the heat-shrinkable polyester film of the present invention will be described in detail in consideration of a difference from a conventional method for stretching a heat-shrinkable polyester film.

[Preferred stretching method for heat-shrinkable polyester film]
An ordinary heat-shrinkable polyester film is manufactured by stretching an unstretched film in a direction in which the film is to be shrunk. Although the demand for a heat-shrinkable polyester film that shrinks in the longitudinal direction has been high conventionally, simply stretching the unstretched film in the longitudinal direction will significantly reduce the tensile fracture strength in the width direction. A wide film cannot be manufactured, which is not preferable in terms of productivity.

  Patent Literature 1 discloses a method in which an unstretched film is stretched under predetermined conditions in the order of transverse stretching, heat treatment, and longitudinal stretching in order to improve mechanical properties in a longitudinal direction and a width direction. However, this method is not preferable because the orientation twist index is large and the orientation angle is large at the end, so that when it is wound around a container such as a lunch box and contracted, distortion occurs. Furthermore, in longitudinal stretching, since a plurality of rolls contact the roll having a temperature equal to or higher than the film Tg of the longitudinal stretching machine, there is a problem that a number of scratches occur on the surface due to friction or displacement with the film.

  In addition, a heat-shrinkable polyester film that shrinks in the longitudinal direction without using an amorphous raw material indefinitely can be formed by devising film forming conditions. However, when an amorphous raw material is not used, since the stretching stress during longitudinal stretching is large, the stress at the time of shrinkage is also high, and the container is deformed when shrunk around a lunch box container or the like, which is not preferable. In the present invention, by using an amorphous raw material, it is possible to reduce the stress at the time of stretching and reduce the shrinkage stress. Further, in the present invention, the stress at the time of stretching can be reduced by making the longitudinal stretching distance much longer than usual, and the shrinkage stress can be reduced. In stretching using a normal longitudinal stretching machine, stretching is performed at a small interval (about several mm) between the low-speed roll and the high-speed roll, so the stretching distance is short, and the stretching speed is high, so the stretching stress is high and the shrinkage stress is high. Become.

  A method of reducing the orientation twist index and eliminating distortion due to shrinkage will be described below. As a result of research, the present invention has made it possible to lower the orientation twist index by making the longitudinal stretching distance much longer than usual and causing the neck-in phenomenon that occurs during longitudinal stretching to occur uniformly in the film width direction. Neck-in is a phenomenon in which a film shrinks in the width direction due to a force generated in a direction (width direction) orthogonal to the stretching direction during longitudinal stretching. In longitudinal stretching using a normal longitudinal stretching machine, stretching is performed with a small gap (about several mm) between the low-speed roll and the high-speed roll, so the effect of neck-in occurs only near the edge of the film and sharply in the longitudinal direction. Therefore, the orientation angle near the end greatly increases and the orientation twist index increases. In the present invention, the effect of neck-in can be caused over the entire width by significantly increasing the stretching distance of the longitudinal stretching, and a gentle neck-in can be performed in the longitudinal direction, and the orientation twist index is reduced. That was realized.

  A method of extending the stretching while generating a uniform neck-in by greatly increasing the stretching distance in the longitudinal direction will be described below. In the stretching method A, it was possible to stretch the clips in the longitudinal direction by increasing the clip interval, and at the same time, to gradually narrow the tenter width, thereby enabling uniform neck-in. On the other hand, in the stretching method B, since the film is stretched between the rolls installed near the exit of the tenter from the time when the film is released from the clip in the tenter, the stretching distance is long, and a uniform neck-in can be generated. became. Also in the stretching method C, the stretching was performed between the roll near the entrance of the tenter and the roll near the exit, so that the stretching distance was long and a uniform neck-in could be generated. Drawing method A is shown in FIG. 1, drawing method B is shown in FIG. 2, and drawing method C is shown in FIG.

  A stretching method for greatly reducing scratches on the surface will be described below. As a result of the research, the present inventor has devised a method for producing a shrinkable film that is stretched in the longitudinal direction without contacting the film with a roll having Tg or more, and has made it possible to significantly reduce scratches on the film surface. After the transverse stretching using a simultaneous biaxial stretching machine as in the above stretching method A, by stretching in the longitudinal direction by increasing the clip interval, sufficient shrinkage without contact of the film with a roll of Tg or more It was found that a film having the following can be formed. Further, as in the above-mentioned stretching method B, when the clip gripped inside the tenter is opened after the transverse stretching and the film is stretched in the longitudinal direction by propagating the tension of the roll installed near the exit of the tenter, Tg It was found that a shrink film could be formed without contacting the above roll. Since the position of the roll near the outlet is sufficiently far from the tenter outlet, the temperature of the film is at or below Tg when the film comes into contact with the roll. Furthermore, as in the above stretching method C, the film is introduced into the tenter without being gripped by the clip, and is stretched in the longitudinal direction in the tenter by the speed difference between the rolls installed near the entrance and the exit of the tenter, thereby obtaining a Tg. It was found that a film having sufficient shrinkage could be formed without the film contacting the roll described above. Since the position of the roll near the outlet is sufficiently far from the tenter outlet, the temperature of the film is at or below Tg when the film comes into contact with the roll.

Preferred stretching ratios in the width direction, stretching ratios in the longitudinal direction, stretching distances, and width reduction ratios in the longitudinal stretching of the heat-shrinkable film of the invention are described.
The stretching ratio in the width direction is preferably 2.5 times or more and 6 times or less. When the stretching ratio in the width direction is less than 2.5 times, not only productivity is deteriorated, but also unevenness in thickness in the width direction is unfavorably deteriorated. On the other hand, if the stretching ratio in the width direction exceeds 6 times, breakage is likely to occur at the time of stretching, and the shrinkage in the width direction of the film after longitudinal stretching becomes too high, which is not preferable. More preferably, it is 3 times or more and 5.5 times or less, and still more preferably, 3.5 times or more and 5 times or less.
The stretching ratio in the longitudinal direction is preferably 1.5 times or more and 6 times or less. If the stretching ratio is less than 1.5 times, the required shrinkage cannot be obtained, which is not preferable. When the stretching ratio is more than 6 times, the stretching method A is not preferable because the tenter length becomes too long.In the case of the stretching methods B and C, the width shrinkage during longitudinal stretching becomes too large, and the width direction shrinks. It is not preferable because the rate becomes largely negative, which causes defects such as wrinkles when shrinking as a bottle label or a banding film. More preferably, it is 2 times or more and 5.5 times or less, and still more preferably 3 times or more and 5 times or less.

  The stretching distance in the longitudinal direction is preferably from 1000 mm to 7000 mm. If the longitudinal stretching distance is 1000 mm or less, uniform neck-in over the entire width during longitudinal stretching is not preferable. If it exceeds 7000 mm, the neck-in becomes too large and the shrinkage in the width direction is greatly reduced, which is not preferable. It is more preferably 1500 mm or more and 6500 mm or less, and still more preferably 2000 mm or more and 6000 mm or less.

The amount of shrinkage in the width direction caused by the neck-in of the longitudinal stretching is described as “width shrinkage ratio during longitudinal stretching”. The width shrinkage ratio during longitudinal stretching is represented by the following formula 4, where X is the width of the film before stretching and Y is the width of the film after stretching.
Width shrinkage ratio during longitudinal stretching (%) = 100 × (XY) / X ・ ・ ・ Equation 4
The width shrinkage ratio during longitudinal stretching is preferably 5% or more and 35% or less. In the stretching method A, the width reduction ratio in the longitudinal stretching can be adjusted by the tenter width in the longitudinal stretching, and in the stretching methods B and C, it can be adjusted by the stretching ratio, the longitudinal stretching distance, and the presence or absence of the pinch roll. In the stretching methods B and C, when the stretching ratio is increased, the width reduction ratio in the longitudinal stretching tends to increase, and when the longitudinal stretching distance is increased, the width reduction ratio in the longitudinal stretching tends to increase. In addition, by using a pinch roll, it is possible to prevent the width shrinkage ratio during longitudinal stretching from becoming unnecessarily large. Further, in the stretching methods B and C, by providing a step of heat-treating the film after the transverse stretching, the width shrinkage ratio in the longitudinal stretching can be adjusted. The film after transverse stretching has a high shrinkage in the width direction, and may shrink more than necessary in the width direction during longitudinal stretching. After the transverse stretching, by performing a heat treatment while holding the clip in the tenter, the shrinkage in the width direction can be reduced, and the width shrinkage during longitudinal stretching can be adjusted. In this heat treatment step, the tenter width and the clip interval are not changed. Note that this heat treatment step is for adjusting the width shrinkage ratio during the longitudinal stretching, and is not always necessary, and may not be performed depending on the raw material formulation, the stretching ratio, and the longitudinal stretching distance.
If the rate of width shrinkage during longitudinal stretching is less than 5%, uniform neck-in does not occur in the width direction and the orientation twist index cannot be reduced, which is not preferable. On the other hand, if it exceeds 35%, the shrinkage rate in the width direction is greatly reduced, resulting in a large negative shrinkage. More preferably, it is 7% or more and 33% or less, and further preferably 10% or more and 30% or less.
The above-mentioned pinch roll is a type of nip roll that sandwiches the film between the rolls and accurately sends the film, and pulls both ends of the film outward, so that the film is sent outward, at the position of the film end. Attach the two nip rolls symmetrically in the width direction and incline slightly but in a C shape.

  The package of the present invention is formed by covering at least a part of the outer periphery of an object to be packaged and thermally shrinking the banding film and the label obtained from the heat-shrinkable polyester film of the present invention. Examples of the packaging object include plastic containers such as lunch boxes (including PET bottles for beverages, various bottles, cans, and confectionery), paper boxes, and the like. In general, when a label obtained from a heat-shrinkable polyester film is coated on the object to be packaged by heat-shrinking, the banding film and the label are heat-shrinked by about 5 to 70% to form a package. In close contact. In addition, the banding film and the label to be coated on the packaging object may be printed, or may not be printed.

  As a method for producing a banding film and a label, a rectangular film is rolled in the longitudinal direction, the ends are overlapped and adhered to form a label, or a film wound in a roll is rolled in the roll longitudinal direction. Then, the end is superimposed on the film and adhered, and the tube is cut into a label. As a method of bonding the films, a known method such as fusing seal, solvent bonding, bonding with a hot melt adhesive, bonding with an energy ray-curable adhesive, or the like can be used.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the embodiments of the examples, and can be appropriately changed without departing from the spirit of the present invention. is there. Table 1 shows the compositions of the raw materials used in the examples and comparative examples, the film stretching methods and production conditions in the examples and comparative examples.

The method for evaluating the film is as follows.
[Tg (glass transition point)]
It was determined according to JIS-K7121-1987 using a differential scanning calorimeter (model: DSC220) manufactured by Seiko Electronics Industries, Ltd. 5 mg of the unstretched film was heated from -40 ° C to 120 ° C at a heating rate of 10 ° C / min to obtain a heating profile. The temperature at the intersection of the extension line of the baseline below the glass transition temperature and the tangent line showing the maximum slope at the transition part was defined as the glass transition temperature.

[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.

[Heat shrinkage (hot water heat shrinkage)]
The film is cut into a square of 10 cm x 10 cm, treated with no load in hot water at a specified temperature of ± 0.5 ° C, heat-shrinks it for 10 seconds, and measures the vertical and horizontal dimensions of the film. In accordance with No. 1, the heat shrinkage was determined. The direction in which the heat shrinkage was large was defined as the main shrinkage direction.

[Orientation twist index]
At the left and right edges in the width direction of the film, samples of length direction × width direction = 140 mm × 100 mm were collected. And about these two samples, the molecular orientation angle was measured using the molecular orientation angle measuring device (MOA-6004) made by Oji Scientific Instruments. Then, the molecular orientation angle was determined using the following equation 2.
Molecular orientation angle = 90 °-(measurement result) ・ ・ ・ Equation 2
Then, the absolute value of the difference between the molecular orientation angles of the two samples is calculated, and the absolute value of the difference is divided by the interval between the cutout positions (central portions) of the samples according to the following equation 3, thereby obtaining a unit: The difference between the molecular orientation angles per width (1 m) was calculated and used as the orientation twist index.
Orientation torsion index = (absolute value of the difference between the orientation angles of each sample molecule) ÷ (interval between sample cutting positions) ・ ・ ・ Equation 3

[Distortion after shrinkage]
A plastic container for lunch (side 150 x 150 mm, height 100 mm) is wrapped around the body of the container and the lid with the circumferential direction of the film shrinking so that the film is bound, and blown at 220 ° C. After sealing, heat shrinkage was performed in a shrink tunnel at a set temperature of 90 ° C. In FIG. 4, the length from the ground on which the plastic container is placed to the edge of the film is defined as length X, and the length X is measured in the circumferential direction (the longitudinal direction of the film) at a pitch of 5 mm. The difference between the values was R. _R. Large ones, it is determined that distortion after shrinkage is large, criteria were as follows.
◎: R ≦ 1mm
○: 1mm <R ≤ 2mm
△: 2mm <R ≤ 3mm
×: 3mm <R
The above evaluation was performed on two samples of the manufactured film roll, that is, the center part and the end part.

[Shrinkage stress]
A sample having a length of 200 mm and a width of 20 mm was cut out from the heat-shrinkable film, and a toughness elongation measuring machine with a heating furnace manufactured by Toyo Baudwin (currently Orientec) (Tensilon (registered trademark of Orientec)) ). The heating furnace was previously heated to 90 ° C., and the distance between the chucks was 100 mm. The ventilation of the heating furnace was once stopped, the door of the heating furnace was opened, the sample was attached to the chuck, and then the door of the heating furnace was closed immediately and the ventilation was restarted. The shrinkage stress was measured for 30 seconds or more, and the maximum value during the measurement was defined as the shrinkage stress (MPa).

[Deformation of container]
Wrap the plastic container (box 150 × 150mm, height 100mm) in the lunch box with the circumferential direction of the container in the shrinking direction of the film so that the film binds the body and lid of the container, and cut at 220 ° C After sealing, heat shrinkage was performed in a shrink tunnel at a set temperature of 90 ° C. Fig. 5 is a view of the lunch container seen from above.The length Y from one side to the other side is measured at a pitch of 5 mm before mounting the film, the film is shrunk and the length of the same portion is similarly measured after mounting. The measured Y ′ was measured, and the absolute value of the difference between Y and Y ′ was defined as L. The maximum value Lmax of L calculated at a pitch of 5 mm was determined, and the one with the larger Lmax was determined to be large in the deformation of the container, and the criteria were as follows.
◎: Lmax ≦ 3mm
○: 3mm <Lmax ≤ 4mm
△: 4mm <Lmax ≦ 5mm
×: 5mm <Lmax

[Scratch on the surface]
(1) Detection of Scratches For 16 pieces of film, optical defects that are optically recognized as having a size of 50 μm or more were detected.
In the optical defect detection method, a fluorescent lamp of 20 W × 2 was installed 400 mm below the XY table as a projector, and a test piece to be measured was placed on a mask with a slit width of 10 mm provided on the XY table. When light is incident so that the angle between the line connecting the light emitter and the light receiver and the vertical direction of the surface of the test piece becomes 12 °, if there is a flaw in the test piece at the incident position, that part shines. The light quantity of that part is converted to an electric signal by a CCD image sensor camera installed 500 mm above the XY table, the electric signal is amplified, differentiated, and compared with a threshold level to detect optical defects Output a signal. In addition, using a CCD image sensor camera, input the image of the flaw, analyze the video signal of the input image according to a predetermined procedure, measure the size of the optical defect, and display the position of the defect of 50 μm or more did. Optical defects were detected on both sides of the test piece.
(2) Measurement of size of flaw A defect due to a flaw was selected from the optical defects detected in the above (1). The test piece was cut into an appropriate size, and observed using a three-dimensional shape measuring device TYPE550 manufactured by Micromap Co., Ltd., from the direction perpendicular to the test piece surface, and the size of the scratch was measured. When the test piece, that is, when observed from the direction perpendicular to the film surface, the unevenness of the scratches approaching within 50 μm is considered as the same scratch, and the length and width of the rectangle having the smallest area covering the outermost of the scratches are The length and width of the scratch were determined. The difference between the height of the highest point and the lowest point of the flaw was defined as the depth, and the number of all flaws having a depth of 1 μm or more and a length of 3 mm or more (pieces / m ² ) was determined.

[Tensile fracture strength]
A strip-shaped test piece having a measurement direction (film width direction) of 140 mm and a direction perpendicular to the measurement direction (film longitudinal direction) of 20 mm was prepared. Using a universal tensile tester “DSS-100” (manufactured by Shimadzu Corporation), grip both ends of the test piece with chucks at 20 mm each side (distance between chucks: 100 mm), ambient temperature 23 ° C, tensile speed 200 mm / A tensile test was performed under the condition of min, and the strength (stress) at the time of tensile fracture was defined as the tensile fracture strength.

[Thickness unevenness in the longitudinal direction]
The film was sampled in the form of a long roll having a length of 30 m and a width of 40 mm in the longitudinal direction of the film, and measured at a speed of 5 (m / min) using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. In the above-described sampling of the roll-shaped film sample, the length direction of the film sample was defined as the main shrinkage direction of the film. The maximum thickness at the time of measurement was Tmax., The minimum thickness was Tmin., And the average thickness was Tave.
Thickness unevenness = ｛(Tmax.−Tmin.) / Tave.｝ × 100 (%) ・ ・ Equation 5

  The polyesters used in Examples and Comparative Examples are as follows.

・ Polyester 1: Polyester consisting of 70 mol% of ethylene glycol, 30 mol% of neopentyl glycol and terephthalic acid (IV 0.72 dl / g)
・ Polyester 2: polyethylene terephthalate (IV 0.75 dl / g)
・ Polyester 3: Polyester consisting of 70 mol% of ethylene glycol, 30 mol% of 1,4-cyclohexanedimethanol and terephthalic acid (IV 0.75 dl / g)

(Example 1)
The above-mentioned polyester 1 and polyester 2 were mixed at a weight ratio of 60:40 and charged 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 rapidly cooled to obtain an unstretched film having a thickness of 170 μm. The Tg of the unstretched film was 75 ° C. Thereafter, the unstretched film was guided to a simultaneous biaxial stretching machine. Then, after preheating the unstretched film led to the tenter until the film temperature reaches 90 ° C, the film is stretched 4 times in the horizontal direction at 75 ° C, and then the clip interval is increased to 90 ° C in the vertical direction. Stretched 2.5 times. At this time, the longitudinal stretching distance was 2000 mm.
Further, the film was relaxed in the width direction by reducing the tenter width by 15% from that after the transverse stretching in the longitudinal stretching. That is, the width contraction rate during longitudinal stretching was 15%. By cutting and removing both edges after the tenter, a biaxially stretched film of about 20 μm was continuously formed over a predetermined length to obtain a film roll composed of a heat-shrinkable polyester film. In this series of film stretching film forming steps, the number of rolls having a temperature of Tg or higher was 0. No pinch roll was used in this step. Then, the characteristics of the obtained film were evaluated by the above methods. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

(Example 2)
A heat-shrinkable film was continuously produced in the same manner as in Example 1, except that polyester 1 and polyester 2 were mixed at a weight ratio of 90:10 and charged into an extruder. The thickness of the unstretched film was 160 μm, and Tg was 75 ° C. Further, the width shrinkage ratio during longitudinal stretching was 20%. Then, the characteristics of the obtained film were evaluated by the same method as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

(Example 3)
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 60:40 and charged into an extruder. The thickness of the unstretched film was 172 μm, and Tg was 75 ° C. In addition, the width contraction rate during longitudinal stretching was 14%. Then, the characteristics of the obtained film were evaluated by the same method as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

(Example 4)
The above-mentioned polyester 1 and polyester 2 were mixed at a weight ratio of 60:40 and charged 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 rapidly cooled to obtain an unstretched film having a thickness of 156 μm. The Tg of the unstretched film was 75 ° C. Thereafter, the unstretched film was introduced into a transverse stretching machine. The unstretched film guided to the tenter was preheated until the film temperature reached 90 ° C, and then stretched 4 times in the transverse direction at 80 ° C. After the transverse stretching, the film was heat-treated at a temperature of 100 ° C. for 2 seconds while being held by clips. After the heat treatment, the clip holding the end of the film was opened in the tenter, and the tension of the roll installed near the exit of the tenter was transmitted to the film in the tenter. By setting the roll speed near the exit of the tenter to 2.5 times the clip speed of the tenter, the film was longitudinally stretched 2.5 times at 90 ° C. in the tenter. At this time, the distance (longitudinal stretching distance) from the point where the clip was released to the roll near the exit of the tenter was 4000 mm. In addition, a pinch roll was used so as not to shrink too much in the film width direction during longitudinal stretching. The shrinkage in the film width direction during longitudinal stretching was 22%. By cutting off both edges after longitudinal stretching, a biaxially stretched film of about 20 μm was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester film. In this series of film stretching film forming steps, the number of rolls having a temperature of Tg or higher was 0. The properties of the obtained film were evaluated by the methods described above. Table 2 shows the evaluation results.
As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

(Example 5)
A heat-shrinkable film was continuously produced in the same manner as in Example 4, except that the thickness of the unstretched film was changed to 170 μm and the longitudinal stretching ratio was changed to 2. The shrinkage in the film width direction during longitudinal stretching was 15%. The properties of the obtained film were evaluated in the same manner as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

[Example 6]
A heat-shrinkable film was continuously produced in the same manner as in Example 4, except that the thickness of the unstretched film was changed to 230 µm and the longitudinal stretching ratio was changed to 4 times. The shrinkage in the film width direction during longitudinal stretching was 28%. The properties of the obtained film were evaluated in the same manner as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

[Example 7]
A heat-shrinkable film was continuously produced in the same manner as in Example 4, except that the thickness of the unstretched film was changed to 331 μm and the longitudinal stretching ratio was changed to 6. The shrinkage in the film width direction during longitudinal stretching was 31%. The properties of the obtained film were evaluated in the same manner as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

Example 8
A heat-shrinkable film was continuously produced in the same manner as in Example 4, except that the thickness of the unstretched film was 140 μm and a pinch roll was not used during longitudinal stretching. The shrinkage in the film width direction during longitudinal stretching was 30%. The properties of the obtained film were evaluated in the same manner as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

[Example 9]
The heat-shrinkable film was continuously formed in the same manner as in Example 4 except that the thickness of the unstretched film was changed to 150 μm, and the distance from the point where the clip was released to the roll near the exit of the tenter (longitudinal stretch distance) was changed to 5000 mm. Manufactured. The shrinkage in the film width direction during longitudinal stretching was 25%. The properties of the obtained film were evaluated in the same manner as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

[Example 10]
A heat-shrinkable film was continuously formed in the same manner as in Example 4 except that the thickness of the unstretched film was changed to 144 μm, and the distance from the point where the clip was released to the roll near the exit of the tenter (longitudinal stretch distance) was changed to 6000 mm. Manufactured. The shrinkage in the film width direction during longitudinal stretching was 28%. The properties of the obtained film were evaluated in the same manner as in Example 1. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

[Example 11]
The above-mentioned polyester 1 and polyester 2 were mixed at a weight ratio of 60:40 and charged 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 rapidly cooled to obtain an unstretched film having a thickness of 158 μm. The Tg of the unstretched film was 75 ° C. Thereafter, the unstretched film was introduced into a transverse stretching machine (first tenter). The unstretched film guided to the tenter was preheated until the film temperature reached 90 ° C, and then stretched 4 times in the transverse direction at 80 ° C. The film after the transverse stretching was heat-treated at a temperature of 100 ° C. for 2 seconds while being held by the clip. After transverse stretching and heat treatment in the first tenter, the film was guided to a tenter with rolls capable of applying tension at the entrance and exit. In the second tenter, the end of the film was heated by hot air without holding the end of the film with a clip, and the film in the second tenter was stretched longitudinally at 90 ° C. due to the difference in speed between the inlet and outlet rolls. The speed difference was 2.5 times, and a pinch roll was used so as not to shrink too much in the film width direction. The distance (longitudinal stretching distance) between the rolls at the entrance and exit of the second tenter was 4000 mm, and the shrinkage in the film width direction was 21%. By cutting off both edges after longitudinal stretching, a biaxially stretched film of about 20 μm was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester film. In this series of film stretching film forming steps, the number of rolls having a temperature of Tg or higher was 0. The properties of the obtained film were evaluated by the methods described above. Table 2 shows the evaluation results. As a result of the evaluation, the film had sufficient shrinkability, had good shrink finish, and had few scratches.

(Comparative Example 1)
The above-mentioned polyester 1 and polyester 2 were mixed at a weight ratio of 60:40 and charged 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 rapidly cooled to obtain an unstretched film having a thickness of 60 μm. The Tg of the unstretched film was 75 ° C. After that, it was led to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, pre-heated on 10 pre-heated rolls until the film temperature reached 90 ° C, and then stretched 3 times using the difference in roll speed did. At this time, the stretching distance was 4 mm, and the shrinkage in the film width direction was 2%. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25 ° C. In this film stretching step, the number of rolls having a temperature of Tg or higher was ten. This stretching system was designated as stretching system D, and the characteristics of the obtained film were evaluated by the above-described methods. Table 2 shows the evaluation results. As a result of evaluation, the film had sufficient shrinkage, but had poor thickness unevenness, low tensile breaking strength in the width direction, and many scratches.

(Comparative Example 2)
Polyester 1 and polyester 2 were mixed at a weight ratio of 90:10 and charged 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 rapidly cooled to obtain an unstretched film having a thickness of 157 μm. The Tg of the unstretched film was 75 ° C. Thereafter, the unstretched film was guided to a transverse stretching machine (normal tenter). The unstretched film guided to the tenter was preheated until the film temperature reached 90 ° C., and then stretched 4 times at 75 ° C. in the horizontal direction. Thereafter, heat treatment was performed at a temperature of 130 ° C. for 2 seconds. Further, using a pair of left and right trimming devices provided behind the tenter, the edge of the film was cut off, and the end of the film located outside the cut portion was continuously removed. Such a transverse stretching, heat treatment, the trimmed film is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, and after preheating until the film temperature reaches 70 ° C. on ten preheating rolls, The film was stretched three times using a difference in roll speed. At this time, the stretching distance was 4 mm, and the shrinkage in the film width direction was 2%. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25 ° C. Then, the cooled film is guided to a tenter (second tenter), heat-treated in an atmosphere of 90 ° C. for 2 seconds in the second tenter, cooled, and both edges are cut and removed. A 20 μm biaxially stretched film was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester film. In this series of film stretching film forming steps, the number of rolls at which the temperature was Tg or higher was ten. This stretching method was referred to as a stretching method E, and the characteristics of the obtained film were evaluated by the methods described above. Table 2 shows the evaluation results. As a result of the evaluation, although the film had sufficient shrinkability, the sample near the edge of the film had shrinkage distortion and had many scratches.

[Comparative Example 3]
It is put into an extruder using only polyester 2, the resin is melted at 280 ° C., extruded from a T-die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to a thickness of 157 μm. Was obtained. The Tg of the unstretched film was 75 ° C. Thereafter, the unstretched film was guided to a transverse stretching machine (normal tenter). Then, the unstretched film guided to the tenter was preheated until the film temperature reached 100 ° C, and then stretched 4 times in the transverse direction at 90 ° C. Furthermore, the film stretched in the transverse direction in such a manner is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, and after preheating until the film temperature reaches 90 ° C. on ten preheating rolls, The film was stretched twice by using the difference in speed between the rolls. At this time, the stretching distance was 4 mm, and the shrinkage in the film width direction was 2%. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25 ° C. Then, the cooled film was guided to a tenter (second tenter), and subjected to 5% relaxation in the width direction while being heat-treated in an atmosphere of 90 ° C. for 8 seconds in the second tenter. By cutting and removing both edges after the second tenter, a biaxially stretched film of about 20 μm was continuously formed over a predetermined length to obtain a film roll composed of a heat-shrinkable polyester film. In this series of film stretching film forming steps, the number of rolls at which the temperature was Tg or higher was ten. This stretching method was referred to as a stretching method E, and the characteristics of the obtained film were evaluated by the methods described above. Table 2 shows the evaluation results. As a result of the evaluation, although the sample had sufficient shrinkage, shrinkage distortion occurred in the sample near the film edge, and the container was deformed when shrink-fitted, resulting in a film with many scratches.

  Since the heat-shrinkable polyester film of the present invention has the excellent characteristics as described above, it can be suitably used for a banding film used for a labeling purpose of a bottle or a bundling purpose such as a lunch box. However, the package used as a label or a banding film has a beautiful appearance. The film has a sufficient heat shrinkage in the longitudinal direction, has a low shrinkage in the width direction, does not cause deformation or shrinkage distortion in the container, has very little scratches on the film surface, and has excellent appearance.

1: Tenter 2: Clip opener 3: Clip 4: Stretched film 5: Roll 6: Plastic container (lid)
7: Plastic container (body)
8: Film

Claims (5)

Ethylene terephthalate as the main component, contains more than 5 mol% of one or more monomer components that can be an amorphous component in all polyester resin components, and is formed in a long shape with a constant width, A heat-shrinkable polyester film whose main shrinkage direction is the longitudinal direction, wherein the heat-shrinkable polyester film satisfies the following requirements (1) to (4): Polyester film roll.
(1) The hot water heat shrinkage in the longitudinal direction when treated in hot water at 90 ° C for 10 seconds is 15% or more and 80% or less.
(2) The hot water heat shrinkage in the width direction orthogonal to the longitudinal direction when treated in hot water at 90 ° C for 10 seconds is -10% or more and 10% or less.
(3) Orientation twist index calculated by converting the molecular orientation angle difference, which is the difference between the molecular orientation angle near one edge in the width direction and the molecular orientation angle near the other edge, per 1 m of the film is 15 ° / m or less and 1 ° or more. Being
(4) The tensile fracture strength in the width direction that is orthogonal to the main shrinkage direction is 80 MPa or more and 200 MPa or less. The heat according to claim 1, wherein the flaw having a depth of 1 μm or more and a length of 3 mm or more present on the surface of the heat-shrinkable polyester film is 100 pieces / m ² or less and 15 pieces / m ² or more. Shrinkable polyester film roll.   3. The heat-shrinkable polyester film roll according to claim 1, wherein the heat-shrinkable polyester film has a maximum heat-shrinkage stress in a longitudinal direction of the film at 90 ° C. of 3 MPa or more and 10 MPa or less.   4. The heat-shrinkable polyester film roll according to claim 1, wherein the thickness unevenness in the longitudinal direction of the heat-shrinkable polyester film is 10% or less and 4% or more.   The heat according to any one of claims 1 to 4, wherein the heat-shrinkable polyester film has a tensile fracture strength in a width direction that is a direction orthogonal to a main shrinkage direction of 80 MPa or more and 200 MPa or less. Shrinkable polyester film roll.