JPWO2016039044A1 - Heat-shrinkable polyester film and package - Google Patents

Abstract

The present invention has sufficient heat shrinkage characteristics in the main shrinkage direction, which is the longitudinal direction, has a low thermal shrinkage rate in the width direction perpendicular to the main shrinkage direction, extremely little scratch on the film surface, and low shrinkage stress, To provide a heat-shrinkable polyester film having high mechanical strength, a small molecular orientation angle difference, and a small thickness unevenness. A heat-shrinkable polyester system comprising ethylene terephthalate as a main constituent, containing 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 as a longitudinal direction. The film has a heat shrink property in the longitudinal direction and the width direction, and a molecular orientation angle difference that is a difference between a molecular orientation angle at one edge in the width direction and a molecular orientation angle at the other edge satisfies a specific range. Heat-shrinkable polyester film.

Description

  The present invention relates to a heat-shrinkable polyester film and a package, and more specifically, suitable for labeling and banding for binding a body and a lid of a lunch box with a belt-like film. Is a polyester-based shrink film with very little.

  In recent years, stretched films made of polyvinyl chloride resin, polystyrene resin, polyester resin, etc. (so-called so-called, Heat-shrinkable film) has been widely used. Among such heat-shrinkable films, the polyvinyl chloride film has problems such as low heat resistance, generation of hydrogen chloride gas during incineration, and dioxin generation. In addition, polystyrene film has poor solvent resistance and must use ink with a special composition during printing, and must be incinerated at a high temperature, and a large amount of black smoke is generated with an unpleasant odor during incineration. There is a problem of doing. Therefore, polyester-based heat-shrinkable films that have high heat resistance, are easy to incinerate, and have excellent solvent resistance are widely used as shrink labels. The usage tends to increase with the increase.

  Moreover, as a normal heat-shrinkable polyester-based film, a film that greatly shrinks in the width direction is widely used. In such a heat-shrinkable polyester film whose width direction is the main shrinkage direction, the film is stretched at a high magnification in the width direction in order to develop shrinkage characteristics in the width direction, but is orthogonal to the main shrinkage direction. As for the longitudinal direction, only low-stretching is often performed, and some are not stretched. As described above, a film that is only stretched at a low magnification in the longitudinal direction or a film that is stretched only in the width direction has a drawback that the mechanical strength in the longitudinal direction is inferior.

  When using it as a banding film that binds the bottle label film or the box and lid of the lunch box with a belt-like film, it must be heat-shrinked in the circumferential direction after the film is annularly attached to the bottle or lunch box container, When mounting a heat-shrinkable film that shrinks in the width direction as a banding film, an annular body is formed so that the width direction of the film is the circumferential direction, and then the annular body is cut into predetermined lengths. It must be attached to the bottle or lunch box by hand. Therefore, it is difficult to attach a label film or a banding film made of a heat-shrinkable film that thermally shrinks in the width direction to a bottle or a lunch box at a high speed. Therefore, recently, there has been a demand for a film that thermally shrinks in the longitudinal direction, which can be wound and mounted directly around a bottle or a lunch box directly from a film roll. The center sealing process for forming and sealing the film tubular body, and processing such as cutting and hand covering are unnecessary, and the film can be mounted at a high speed.

  As a demand for shrinkage, a high shrinkage rate is required. In recent years, due to the diversification of bottle shapes, there are cases where the difference between the maximum and minimum length of the bottle circumference is large (for example, a bottle with a thin cap near the top of the bottle), and the entire bottle is covered with a film. A high shrinkage rate is required in a portion where the bottle body is thin. In order to impart shrinkage, it is common to use a raw material containing an amorphous monomer. Although it is possible to give shrinkage without using amorphous raw materials as much as possible, it is possible by devising film forming conditions, but it is necessary to use amorphous monomers as much as possible and to set the longitudinal draw ratio low. In addition, the maximum shrinkage rate is limited to about 60%, and there is a problem that shrinkage finish performance is deteriorated due to insufficient shrinkage in a thin portion of the bottle.

  The shrinkage rate in the non-shrinkage direction (width direction) is also important in the finish after shrinkage when the film is shrunk to a bottle as a label. The width direction of the film is the vertical direction of the bottle when it is attached to the bottle as a label. However, if the shrinkage rate in the film width direction is high, the film can be pulled in the vertical direction of the bottle (so-called vertical shrinkage). Moreover, since the area of the bottle covered with a film decreases, the area of a required film increases and it is not preferable also in terms of cost. In particular, when the base is attached to a bottle having a square shape (so-called square bottle), vertical shrinkage is conspicuous even in slight contraction in the film width direction, which is not preferable in terms of appearance. Particularly for square bottles, a film having a shrinkage rate in the film width direction very close to 0 or a minus shrinkage rate is preferred. For example, in Patent Document 1, since the shrinkage rate in the film width direction is 0 or more, vertical shrinkage occurs when mounted on a square bottle.

  Moreover, in the request | requirement with respect to the external appearance of the film after shrinkage | contraction, it is calculated | required that there is little distortion after shrinkage | contraction. It is known that distortion after shrinkage is caused by the fact that the main orientation direction of molecules is inclined from the longitudinal direction or the width direction of the film. This tilt is called the molecular orientation angle, but when performing normal biaxial stretching, the mechanical flow direction at the center of the film is 12 o'clock and the angle between the 12 o'clock direction and the molecular chain in the film Although it is close to 0 ° (hereinafter simply referred to as a molecular orientation angle) and there is no difference in molecular orientation in the width direction, the difference in molecular orientation in the width direction is large near the edge of the film. This is because neck-in occurs only in the vicinity of the end portion because the stretching distance is short and abrupt stretching is performed. It is ideal for distortion that the molecular orientation angle is small from the center to the end of the film and that the difference in molecular orientation angle in the width direction is small.

  When the film is shrunk on the bottle or lunch box and attached, deformation of the bottle or lunch box due to shrinkage may be a problem. Since the deformation is caused by the stress of the film generated at the time of shrinkage, it is not preferable that the shrinkage stress is too high. For example, a heat-shrinkable polyester film whose main shrinkage direction is the main shrinkage direction can be formed without using an amorphous component as much as possible. However, since no amorphous component is used, stretching during stretching in the longitudinal direction is possible. The stress is high and the stress during shrinkage is high.

  Further, regarding the appearance of the shrink film, there is a demand for small scratches on the film surface. Scratches on the film surface cause defects such as missing prints when the film is printed. Normally, when the film is heated and stretched, it is necessary to heat the film to Tg or higher.However, when the film reaches a temperature of Tg or higher, friction with the roll or film The film surface is scratched by the displacement. When a general longitudinal stretching machine is used, the film is heated by being brought into contact with a high-temperature roll of Tg or more, so that scratches are likely to occur.

  For example, in Patent Document 1, in a longitudinal stretching machine used for film formation, contact with a plurality of high-temperature rolls having a temperature equal to or higher than Tg of the film causes many scratches on the film surface, which is not preferable in terms of appearance. In addition, since the neck-in occurs rapidly only near the end portion, the difference in molecular orientation angle is large near the end portion, and when the film near the end portion is shrunk because the molecular orientation angle is large, distortion occurs, It is not preferable in appearance.

Japanese Patent No. 4411556

The object of the present invention is to solve the problems of Patent Document 1 and have at least one monomer component that can be an amorphous component in all polyester resin components, and sufficient heat in the main shrinkage direction, which is the longitudinal direction. In the width direction orthogonal to the main shrinkage direction having a shrinkage property, the thermal shrinkage rate is low, the molecular orientation angle difference is small, the shrinkage stress is low, the scratch on the film surface is extremely small, and the mechanical strength is high. 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 configuration.
1. With ethylene terephthalate as the main constituent, it contains more than 5 mol% of one or more monomer components that can be amorphous components in all polyester resin components, and is formed in a long shape with a constant width, A heat shrinkable polyester film having a main shrinkage direction as a longitudinal direction and satisfying the following requirements (1) to (4).
(1) The hot water heat shrinkage in the longitudinal direction when treated for 10 seconds in warm water at 90 ° C is 15% or more and 80% or less
(2) The hot water thermal shrinkage in the width direction perpendicular to the longitudinal direction when treated for 10 seconds in hot water at 90 ° C is -10% or more and 10% or less
(3) The orientation twist index, calculated by converting the molecular orientation angle difference, which is the difference between the molecular orientation angle at one edge in the width direction and the molecular orientation angle at the other edge, per 1 m of film is 15 ° / m or less.
(4) The tensile fracture strength in the width direction, which is the direction perpendicular to the main shrinkage direction, is 80 MPa or more and 200 MPa or less. ^2. The heat-shrinkable polyester film as described in the above item 1, wherein scratches having a depth of 1 μm or more and a length of 3 mm or more existing on the surface are 100 pieces / m ² or less.
3. The heat-shrinkable polyester film as described in 1 or 2 above, 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 as described in any one of 1 to 3 above, wherein the thickness unevenness in the longitudinal direction is 10% or less.
5). 5. The heat-shrinkable polyester film according to any one of the above 1 to 4, wherein the tensile fracture strength in the width direction, which is a direction orthogonal to the main shrinkage direction, is 80 MPa or more and 200 MPa or less.
6). A package comprising the heat-shrinkable polyester film according to any one of the first to fifth aspects as a base material, and a heat-shrinkable covering at least a part of the outer periphery with a label or a banding film.

  According to the present invention, the problems of Patent Document 1 are solved, the heat shrinkage characteristic is sufficient in the main shrinkage direction which is the longitudinal direction, and the heat shrinkage rate is low in the width direction perpendicular to the main shrinkage direction. Thus, it is possible to provide a heat-shrinkable polyester film having a small difference in molecular orientation angle in the width direction, very few scratches on the film surface, low shrinkage stress, high mechanical strength, and small thickness unevenness. Since the heat-shrinkable polyester film of the present invention has very few scratches on the surface, it is possible to obtain 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 mounted very efficiently within a short time. It was possible to obtain a good finish with very little shrinkage, vertical shrinkage, wrinkles, and content popping out. Further, the heat-shrinkable polyester film of the present invention can be suitably used as a banding film that binds the body part and the lid part in a lunch box container or the like. It was possible to obtain a good finish with very little wrinkling, distortion and insufficient shrinkage of the film.

It is a top view which shows the outline of the extending | stretching system A typically. It is a top view which shows the outline of the extending | stretching system B typically. 2 is a plan view schematically showing an outline of a stretching method C. FIG. The plastic container of the lunch box which evaluated the film distortion after shrinkage | contraction is shown. The plastic container of the lunch box which evaluated the deformation | transformation of the container after shrinkage | contraction is shown.

  As a preferable production method for continuously producing the heat-shrinkable polyester film according to any one of the first to fifth aspects, ethylene terephthalate is a main constituent, and an amorphous component in all polyester resin components. A temperature of Tg + Tg + 40 ° C or less at a film Tg + 40 ° C or less with a clip of both ends in the width direction using a simultaneous biaxial stretching machine with a polyester-based unstretched film containing more than 5 mol% of monomer component After stretching in the width direction (transverse stretching) at a magnification of 3.5 times to 6 times, and extending the distance between clips at a temperature of film Tg to Tg + 40 ° C or less, the length is increased from 1.5 times to 6 times. It is to relax in the width direction by narrowing the tenter width by 5% or more and 35% or less after transverse stretching while stretching in the direction (longitudinal stretching) (hereinafter, this stretching method is referred to as “stretching method A”). .

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

  In addition, as one of the manufacturing methods that can obtain the same effects as the above two manufacturing methods, the same polyester-based unstretched film as described above can be obtained by holding the film Tg while holding both ends in the width direction by clips in the tenter. After stretching in the width direction (transverse stretching) at a magnification of 3.5 times or more and 6 times or less at a temperature of Tg + 40 ° C or less, the film is heated again to a temperature of Tg + Tg + 40 ° C or less in another tenter. However, stretching (longitudinal stretching) is 1.5 times or more and 6 times or less in the longitudinal direction 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 a stretching method C).

  Examples of the dicarboxylic acid component constituting the polyester used in the present invention include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and orthophthalic acid, and aliphatics such as adipic acid, azelaic acid, sebacic acid, and 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 by 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 their anhydrides). In a heat-shrinkable polyester film obtained using a polyester containing these polyvalent carboxylic acids, it is difficult to achieve a necessary high shrinkage rate.

  Examples of the diol component constituting the polyester used in the present invention include aliphatic diols such as ethylene glycol, 1-3 propanediol, 1-4 butanediol, neopentyl glycol, and hexanediol, and 1,4-cyclohexanedimethanol. Aromatic diols such as alicyclic diol and bisphenol A can be mentioned.

  The polyester used in 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, and the like), and a polyester having a glass transition point (Tg) 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% of one or more monomer components that can be amorphous components in 100 mol% of the polyhydric alcohol component in the total polyester resin. It is necessary to contain, it is preferably 10 mol% or more, more preferably 15 mol% or more, and particularly preferably 20 mol% or more. Here, examples of the monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanediol, and isophthalic acid.

  In the polyester used in the heat-shrinkable polyester film of the present invention, a diol having 8 or more carbon atoms (for example, octanediol) or a trihydric or higher polyhydric alcohol (for example, trimethylolpropane, trimethylolethane, glycerin) is used. , Diglycerin and the like) are preferably not contained. In the heat-shrinkable polyester film obtained by using polyesters containing these diols or polyhydric alcohols, it is difficult to achieve a necessary high shrinkage rate.

In addition, the heat-shrinkable polyester film of the present invention is a longitudinal direction of the film calculated by the following formula 1 from the length before and after shrinkage when treated in warm water at 90 ° C. for 10 seconds without load. It is preferable that the heat shrinkage rate (that is, hot water heat shrinkage rate of 90 ° C.) is 15% or more and 80% or less.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%) ·· Equation 1

  If the hot-water heat shrinkage in the longitudinal direction at 90 ° C. is less than 15%, it is not preferable because the shrinkage is insufficient when used as a label or a banding film, and wrinkles and tarmi are generated on the label after heat shrinkage. On the other hand, if the thermal contraction rate of hot water in the longitudinal direction at 90 ° C exceeds 80%, when used as a label or banding film, shrinkage distortion tends to occur during heat shrinkage, or so-called "flying up" may occur. It is not preferable. The lower limit of the hot shrinkage in the longitudinal direction at 90 ° C. is preferably 20%, more preferably 25%, and particularly preferably 30%. Further, the upper limit value 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.

  The heat-shrinkable polyester film of the present invention is a film width direction calculated by the above formula 1 from the length before and after shrinkage when treated in warm water at 90 ° C. for 10 seconds without load. It is preferable that the hot water heat shrinkage ratio is -10% or more and 10% or less. If the thermal contraction rate in the width direction at 90 ° C exceeds 10%, it will be unfavorable in appearance due to vertical shrinkage when used as a label or banding film, and the film length will be shortened. . On the other hand, if it is less than -10%, the label length in the direction perpendicular to the main shrinkage direction becomes longer during heat shrinkage, which is not preferable because sagging tends to occur and wrinkles easily occur. 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 further preferably −7% or more and 7% or less. preferable.

  In addition, the heat-shrinkable polyester film of the present invention has an orientation twist obtained by converting a molecular orientation angle difference, which is a difference between a molecular orientation angle at one end edge in the width direction and a molecular orientation angle at the other end edge, into a film width of 1 m. When the index is determined by the following method, the orientation twist index is preferably 15 ° / m or less. The upper limit value of the orientation twist index is more preferably 13 ° / m or less, and further preferably 12 ° / m or less. The orientation twist index is better as it approaches 0 ° / m, but even if it is 1 ° / m, there is no particular problem.

[Measurement method of orientation twist index]
The molecular orientation axis in the present invention is the most when viewed on the XY plane of the film 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. A direction in which the degree of molecular orientation is large is referred to as a molecular orientation axis. The molecular orientation angle means an angle at which the molecular orientation axis when the molecular orientation axis is measured is deviated from the film longitudinal direction or the film width direction. As a method for measuring the molecular orientation angle, first, rectangular samples are collected at the left and right edges facing each other in the width direction of the film. The molecular orientation angle (angle in the molecular orientation axis direction) of the cut film sample is measured with a molecular orientation angle measuring device (MOA-6004) manufactured by Oji Scientific Instruments. The molecular orientation angle is set to 0 degree in the longitudinal direction of the film. When the direction of the molecular orientation axis is smaller than 45 degrees with respect to the longitudinal direction, the difference from 0 degree is obtained, and from 90 degrees when larger than 45 degrees. Find the difference. For the rectangular samples collected 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 between By dividing by the interval in the width direction, the difference in molecular orientation angle per film unit width (1 m) (orientation twist index) is calculated.
Orientation twist index = (absolute value of the difference in orientation angle of each sample sample taken from the left and right edges) ÷ (interval between sample cut-out 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 is shown in the examples. When the shrinkage stress is less than 3 MPa, the film does not come loose and does not adhere when attached to a bottle as a label or a bento as a banding film, which is undesirable in terms of performance and appearance. On the other hand, when the shrinkage stress exceeds 10 MP, the force applied to the bottle or the container is too large when the film is contracted and attached, so that the contents pop out or the container is deformed, which is not preferable. The shrinkage stress is more preferably 4 MPa or more and 9 MPa or less, and further preferably 5 MPa or more and 8 MPa or less.

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

  In addition, the heat-shrinkable polyester film of the present invention preferably has a thickness variation of 10% or less in the longitudinal direction. When the thickness unevenness in the longitudinal direction is more than 10%, it is not preferable because printing spots are likely to occur during printing when creating labels and banding films, and shrinkage spots after heat shrinkage are likely to occur. Absent. The thickness unevenness 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 it approaches 0%, but the lower limit is 2%, which is practically acceptable.

  The heat-shrinkable polyester film of the present invention preferably has a tensile fracture strength in the width direction of 80 MPa to 200 MPa. In addition, the measuring method of tensile fracture strength is demonstrated in an Example. If the tensile fracture strength is less than 80 MPa, the “waist” (stiffness) when wearing as a label or banding film will be weak, and conversely, if the tensile fracture strength exceeds 200 MPa, the label This is not preferable because the cutability (ease of tearing) at the initial stage of tearing becomes poor. The lower limit of 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. Is 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 heat-shrinkable film for labels and banding.

  Further, the heat-shrinkable polyester film of the present invention is not limited in terms of its production method. For example, the above-described polyester raw material is melt-extruded by an extruder to form an unstretched film, and the unstretched film The film can be obtained by biaxial stretching by the method described below.

  When the raw material resin is melt-extruded, the polyester raw material is preferably dried 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. and extruded into a film using an extruder. For this extrusion, any existing method such as a T-die method or a tubular method can be employed.

  And an unstretched film can be obtained by rapidly cooling the sheet-like molten resin after extrusion. In addition, as a method of rapidly cooling the molten resin, a method of obtaining a substantially unoriented resin sheet by casting the molten resin on a rotating drum from a die and rapidly solidifying it can be suitably employed.

  Furthermore, as will be 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. It becomes. Hereinafter, preferable biaxial stretching for obtaining the heat-shrinkable polyester film of the present invention will be described in detail in consideration of the difference from the stretching method of the conventional heat-shrinkable polyester film.

(Preferred drawing method of heat-shrinkable polyester film)
A normal heat-shrinkable polyester film is produced by stretching an unstretched film in the direction in which it is desired to shrink. Although there was a high demand for heat-shrinkable polyester film that shrinks in the longitudinal direction from the past, simply stretching the unstretched film in the longitudinal direction significantly reduces the tensile fracture strength in the width direction. Since a wide film cannot be manufactured, it is not preferable in terms of productivity.

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

  Further, a heat-shrinkable polyester film that shrinks in the longitudinal direction without using an amorphous material as much as possible can be formed by devising the film-forming conditions. However, when an amorphous raw material is not used, since the stretching stress during longitudinal stretching is large, the stress during contraction is also high, and the container is deformed when wound around a lunch container or the like, which is not preferable. In the present invention, by using an amorphous raw material, the stress during stretching can be reduced and the shrinkage stress can be reduced. Furthermore, in the present invention, the stress during stretching can also be lowered 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 slight interval (several mm) between a low-speed roll and a high-speed roll, so the stretching distance is short and the stretching speed is fast, so the stretching stress is high and the shrinkage stress is also high. Become.

  The following explains how to reduce the orientation twist index and eliminate the distortion caused by shrinkage. 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 uniformly causing the neck-in phenomenon that occurs during longitudinal stretching in the film width direction. Neck-in is a phenomenon in which the film contracts in the width direction due to the force generated in the direction (width direction) perpendicular to the stretching direction during longitudinal stretching. In longitudinal stretching with a normal longitudinal stretching machine, stretching is performed with a slight gap (approximately several millimeters) between the low-speed roll and the high-speed roll, so the neck-in effect occurs only near the edge of the film and is abrupt in the longitudinal direction. Therefore, the orientation angle near the end portion is greatly increased, and the orientation twist index is increased. In the present invention, the stretch distance of the longitudinal stretching is greatly increased, so that the influence of neck-in can be generated in the entire width, and the neck-in that is gentle in the longitudinal direction is enabled, and the orientation twist index is reduced. Realized that.

  A method for extending the longitudinal stretch distance while causing a uniform neck-in will be described below. In the stretching method A, the clip interval was widened and the film was stretched in the longitudinal direction, and at the same time, the tenter width was gradually narrowed to allow the neck-in to be performed uniformly. On the other hand, in the stretching method B, since the film is stretched between rolls installed in the vicinity of the tenter outlet 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, since the stretching is performed between the roll near the entrance of the tenter and the roll near the exit, the stretching distance is long and a uniform neck-in can 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.

  The stretching method for greatly reducing scratches generated on the surface will be described below. As a result of research, the present inventor has devised a method for forming a shrink film that is stretched in the longitudinal direction without being brought into contact with a roll of Tg or more of the film, and can greatly reduce scratches on the film surface. As in the above-mentioned stretching method A, after stretching in the longitudinal direction by using a simultaneous biaxial stretching machine and extending in the longitudinal direction by widening the clip interval, sufficient shrinkage without contact with the roll above Tg It was found that a film having a thickness can be formed. Also, as in the above-mentioned stretching method B, even when the clip held inside the tenter is opened after the transverse stretching and stretched in the longitudinal direction by propagating the tension of the roll installed near the tenter outlet, Tg It was found that a shrink film can be formed without contacting the above rolls. In addition, since the position of the roll in the vicinity of the outlet is sufficiently away from the tenter outlet, the temperature of the film is below Tg when the film contacts the roll. Furthermore, as in the above stretching method C, the film is introduced into the tenter without being gripped by the clip, and stretched in the longitudinal direction in the tenter due to the speed difference between the rolls installed near the entrance and the exit of the tenter. It was found that a film having sufficient shrinkage can be formed without contacting the film with the above rolls. In addition, since the position of the roll in the vicinity of the outlet is sufficiently away from the tenter outlet, the temperature of the film is below Tg when the film contacts the roll.

The preferred stretching ratio in the width direction, the stretching ratio in the longitudinal direction, the stretching distance, and the width shrinkage ratio during longitudinal stretching of the heat-shrinkable film of the present invention will be described.
The stretching ratio in the width direction is preferably 2.5 times or more and 6 times or less. When the draw ratio in the width direction is less than 2.5 times, not only the productivity is deteriorated but also the thickness unevenness in the width direction is deteriorated. On the other hand, when the stretching ratio in the width direction exceeds 6 times, breakage tends to occur during stretching, and the shrinkage rate in the width direction becomes too high in the film after longitudinal stretching. More preferably, they are 3 times or more and 5.5 times or less, More preferably, they are 3.5 times or more and 5 times or less.
The draw ratio in the longitudinal direction is preferably 1.5 times or more and 6 times or less. If the draw ratio is less than 1.5 times, the necessary shrinkage cannot be obtained, which is not preferable. If the draw ratio exceeds 6 times, in the case of the drawing method A, the tenter length becomes too long, which is not preferable. In the case of the drawing methods B and C, the width shrinkage during the longitudinal drawing becomes too large and the shrinkage in the width direction. It is not preferable because the rate is greatly negative because it causes defects such as wrinkles when contracted as a bottle label or banding film. More preferably, they are 2 times or more and 5.5 times or less, More preferably, they are 3 times or more and 5 times or less.

  The stretching distance in the longitudinal direction is preferably 1000 mm or more and 7000 mm or less. A longitudinal stretching distance of 1000 mm or less is not preferable because a uniform neck-in does not occur across the entire width during longitudinal stretching. If it exceeds 7000 mm, the neck-in becomes too large, and the shrinkage rate in the width direction is greatly reduced, which is not preferable. More preferably, they are 1500 mm or more and 6500 mm or less, More preferably, they are 2000 mm or more and 6000 mm or less.

The amount of shrinkage in the width direction caused by necking in the longitudinal stretching is described as “width shrinkage ratio during longitudinal stretching”. The width shrinkage ratio at the time of longitudinal stretching is expressed 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 during longitudinal stretching (%) = 100 × (XY) / X ・ ・ ・ Equation 4
The width shrinkage during longitudinal stretching is preferably 5% or more and 35% or less. In the stretching method A, the width reduction ratio during the longitudinal stretching can be adjusted by the tenter width during 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 a pinch roll. In the stretching methods B and C, when the stretching ratio is increased, the width shrinkage ratio during the longitudinal stretching tends to increase, and when the longitudinal stretching distance is increased, the width shrinkage ratio during the longitudinal stretching tends to increase. Further, by using a pinch roll, it is possible to prevent the width shrinkage ratio during longitudinal stretching from becoming larger than necessary. Furthermore, in the stretching methods B and C, it is possible to adjust the width shrinkage ratio during longitudinal stretching by providing a step of heat-treating the film after transverse stretching. The film after transverse stretching has a high shrinkage rate in the width direction, and may shrink more than necessary in the width direction during longitudinal stretching. After transverse stretching, heat treatment is performed with the clip held in the tenter, so that the shrinkage rate in the width direction can be reduced and the width shrinkage rate during longitudinal stretching can be adjusted. In this heat treatment step, the tenter width and the clip interval are not changed. This heat treatment step is for adjusting the width shrinkage ratio at the time of longitudinal stretching, and is not necessarily required, and may not be performed depending on the raw material formulation, the stretching ratio, and the longitudinal stretching distance.
If the width shrinkage ratio during longitudinal stretching is less than 5%, uniform neck-in in the width direction does not occur, 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 to a large minus shrinkage, which is not preferable because it causes defects such as wrinkles. More preferably, they are 7% or more and 33% or less, More preferably, they are 10% or more and 30% or less.
The above pinch roll is a kind of nip roll that sandwiches the film between the rolls and accurately sends the film, pulls both ends of the film outward, and the film is sent to the position at the end of the film so that it is sent outward. Install the two nip rolls symmetrically in the width direction, and slightly tilt it into a letter C.

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

  The banding film and the label can be produced by rounding a rectangular film in the longitudinal direction and overlapping the ends to form a label, or by rolling a film wound in a roll shape in the roll longitudinal direction. It is rounded into two pieces, and the ends are overlapped and adhered to the film, and the tube-shaped body is cut to form a label. The method for adhering the films can be performed using a known method such as fusing sealing, solvent adhesion, adhesion with a hot-melt adhesive, or adhesion with an energy ray curable adhesive.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to 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 composition of the raw materials used in the examples and comparative examples, the film stretching methods and the production conditions in the examples and comparative examples.

Moreover, the evaluation method of a film is as follows.
[Tg (glass transition point)]
It calculated | required according to JIS-K7121-1987 using the differential scanning calorimeter (model | form: DSC220) by Seiko Electronics Industry. An unstretched film (5 mg) was heated from −40 ° C. to 120 ° C. at a temperature rising rate of 10 ° C./min to obtain a temperature rising profile. The temperature at the intersection of the base line extension below the glass transition temperature and the tangent indicating the maximum slope at the transition was taken 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)]
Cut the film into a 10cm x 10cm square, heat-shrink it in warm water with a specified temperature ± 0.5 ° C for 10 seconds under no load condition, measure the vertical and horizontal dimensions of the film, The thermal shrinkage rate was determined according to 1. The direction in which the heat shrinkage rate is large was taken as the main shrinkage direction.

[Orientation twist index]
At the left and right edges in the width direction of the film, a sample of longitudinal direction × width direction = 140 mm × 100 mm was taken. And about these two samples, the molecular orientation angle was measured using the molecular orientation angle measuring apparatus (MOA-6004) by Oji Scientific Instruments. Then, the molecular orientation angle was determined using the following formula 2.
Molecular orientation angle = 90 °-(measurement result) ・ ・ ・ Equation 2
Then, the absolute value of the difference in the molecular orientation angle between these two samples is calculated, and the absolute value of the difference is divided by the interval between the sample cut-out positions (center portions) according to the following formula 3. The difference in molecular orientation angle per width (1 m) was calculated and used as the orientation twist index.
Orientation twist index = (absolute value of difference in orientation angle of each sample molecule) ÷ (interval between sample cut-out positions) ・ ・ ・ Equation 3

[Distortion after contraction]
Wrapped around a plastic container for lunch (side 150 × 150mm, height 100mm) with the container circumferential direction and film shrinking direction so that the body and lid of the container are bound, and fusing at 220 ° C After sealing, it was heated and shrunk in a shrink tunnel with a set temperature of 90 ° C. In FIG. 4, the length from the ground on which the plastic container is placed to the end of the film is length X, and the length X is measured in the circumferential direction (film longitudinal direction) at a pitch of 5 mm. The difference in values was designated as 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 central part and the end part of the produced film roll.

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

[Deformation of container]
Wrapped around a plastic container for lunch (side 150 × 150mm, height 100mm) with the container circumferential direction and film shrinking direction so that the body and lid of the container are bound, and fusing at 220 ° C After sealing, it was heated and shrunk in a shrink tunnel with a set temperature of 90 ° C. Fig. 5 is a top view of the lunch box.Measure the length Y from one side to the other side opposite to the opposite side before installing the film at a 5mm pitch, and shrink the film to install the same length. The thickness Y ′ was measured, and the absolute value of the difference between Y and Y ′ was taken as L. A maximum value Lmax of L calculated at a pitch of 5 mm was obtained, and a large Lmax was judged to have a large deformation of the container, and the standard was as follows.
◎: Lmax ≦ 3mm
○: 3mm <Lmax ≤ 4mm
△: 4mm <Lmax ≤ 5mm
×: 5mm <Lmax

[Scratches on the surface]
(1) Scratch detection Optical defects that were optically recognized as having a size of 50 μm or more were detected on 16 pieces of film.
In the optical defect detection method, a 20 W × 2 fluorescent lamp was installed as a projector at 400 mm below the XY table, and a test piece to be measured was placed on a mask having a slit width of 10 mm provided on the XY table. When light is incident so that the angle formed between the line connecting the projector and the light receiver and the vertical direction of the surface of the test piece is 12 °, if there is a scratch on the test piece at the incident position, that part shines. The amount of light in that part is converted into an electrical signal by a CCD image sensor camera installed 500mm above the XY table, the electrical signal is amplified, differentiated, and compared with a threshold (threshold) level and a comparator to detect optical defects. Output a signal. In addition, a CCD image sensor camera is used to input a flaw image, the video signal of the input image is analyzed according to a predetermined procedure, the size of the optical defect is measured, and the position of the defect of 50 μm or more is displayed. did. Optical defects were detected on both sides of the test piece.
(2) Measurement of scratch size From the optical defects detected in (1) above, defects due to scratches were selected. The above 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 surface of the test piece, and the size of the scratch was measured. When the specimen is observed from the direction perpendicular to the film surface, the unevenness of the scratches close to each other within 50 μm is considered as the same scratch, and the length and width of the rectangle with the smallest area covering the outermost part of those scratches are determined. The length and width of the scratch were taken. The difference in height between the highest and lowest scratches was taken as the depth, and the total number of scratches (pieces / m ² ) with a depth of 1 μm or more and a length of 3 mm or more was determined.

[Tensile fracture strength]
A strip-shaped test piece having a measurement direction (film width direction) of 140 mm and a direction orthogonal to the measurement direction (film longitudinal direction) of 20 mm was produced. Using a universal tensile tester “DSS-100” (manufactured by Shimadzu Corporation), hold both ends of the test piece with a chuck 20 mm each (distance between chucks 100 mm), atmosphere 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 tensile fracture strength.

[Thickness unevenness in the longitudinal direction]
The longitudinal direction of the film was sampled into a long roll of 30 m long × 40 mm wide and measured at a speed of 5 (m / min) using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. In the sampling of the roll-shaped film sample described above, the length direction of the film sample was set 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 (%) ・ ・ Formula 5

  Moreover, the polyester used for the Example and the comparative example is as follows.

・ Polyester 1: Polyester consisting of 70 mol% ethylene glycol, 30 mol% 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% ethylene glycol, 30 mol% 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. And after preheating the unstretched film led to the tenter until the film temperature reaches 90 ° C, it is stretched 4 times at 75 ° C in the transverse direction, and then at 90 ° C in the longitudinal direction by widening the clip interval. Stretched 2.5 times. At this time, the longitudinal stretching distance was 2000 mm. In addition, the film was relaxed in the width direction by narrowing the tenter width by 15% after the transverse stretching during the longitudinal stretching. That is, the width shrinkage ratio 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 made of a heat-shrinkable polyester film. In this series of film stretching processes, the number of rolls having a temperature of Tg or higher was 0. Also, no pinch roll was used in this step. And the characteristic of the obtained film was evaluated by said method. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and few scratches.

(Example 2)
A heat-shrinkable film was continuously produced by the same method 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 unstretched film had a thickness of 160 μm and a Tg of 75 ° C. Further, the width shrinkage ratio during longitudinal stretching was 20%. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and few scratches.

Example 3
A heat-shrinkable film was continuously produced by the same method 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 unstretched film had a thickness of 172 μm and a Tg of 75 ° C. Further, the width shrinkage ratio during longitudinal stretching was 14%. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and 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, this unstretched film was introduced into a transverse stretching machine. The unstretched film led to the tenter was preheated until the film temperature reached 90 ° C, and then stretched 4 times at 80 ° C in the transverse direction. After transverse stretching, the film was heat treated for 2 seconds at a temperature of 100 ° C. while being held by a clip. After the heat treatment, the clip holding the film end was opened in the tenter, and the tension of the roll installed near the tenter outlet was propagated to the film in the tenter. By setting the roll speed in the vicinity of the tenter outlet to 2.5 times the clip speed of the tenter, the film was stretched longitudinally at 90 ° C. by 2.5 times in the tenter. At this time, the distance (longitudinal stretch distance) from the point where the clip was released to the roll near the tenter exit was 4000 mm. Moreover, the pinch roll was used so that it may not shrink too much at the film width direction at the time of longitudinal stretching. The shrinkage ratio in the film width direction during longitudinal stretching was 22%. By cutting and removing 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 processes, the number of rolls having a temperature of Tg or higher was 0. The properties of the obtained film were evaluated by the method described above. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and few scratches.

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

Example 6
A heat-shrinkable film was continuously produced by the same method as in Example 4 except that the thickness of the unstretched film was 230 μm and the longitudinal stretch ratio was changed to 4. The shrinkage ratio in the film width direction during longitudinal stretching was 28%. The properties of the obtained film were evaluated by the same method as in Example 1. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and 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 331 μm and the longitudinal stretch ratio was changed to 6 times. The shrinkage ratio in the film width direction during longitudinal stretching was 31%. The properties of the obtained film were evaluated by the same method as in Example 1. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and few scratches.

Example 8
A heat-shrinkable film was continuously produced by the same method as in Example 4 except that the thickness of the unstretched film was 140 μm and no pinch roll was used during longitudinal stretching. The shrinkage ratio in the film width direction during longitudinal stretching was 30%. The properties of the obtained film were evaluated by the same method as in Example 1. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and few scratches.

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

Example 10
The heat-shrinkable film was continuously applied in the same manner as in Example 4 except that the thickness of the unstretched film was 144 μm and the distance from the point where the clip was opened to the roll near the tenter exit (longitudinal stretching distance) was changed to 6000 mm. Manufactured. The shrinkage ratio in the film width direction during longitudinal stretching was 28%. The properties of the obtained film were evaluated by the same method as in Example 1. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and 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 led to the tenter was preheated until the film temperature reached 90 ° C, and then stretched 4 times at 80 ° C in the transverse direction. The film after transverse stretching was heat-treated at 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 installed at the inlet and outlet. In the second tenter, the end of the film was not gripped with a clip, but heated with hot air, 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 inlet and outlet rolls of the second tenter was 4000 mm, and the shrinkage ratio in the film width direction was 21%. By cutting and removing 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 processes, the number of rolls having a temperature of Tg or higher was 0. The properties of the obtained film were evaluated by the method described above. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, good shrinkage finish, and 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, after leading to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, preheating until the film temperature reaches 90 ° C on 10 preheating rolls, and then stretching 3 times using the roll speed difference did. At this time, the stretching distance was 4 mm, and the shrinkage ratio in the film width direction was 2%. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set at a surface temperature of 25 ° C. In this film stretching process, the number of rolls having a temperature of Tg or higher was 10. This stretching method was designated as a stretching method D, and the properties of the obtained film were evaluated by the methods described above. The evaluation results are shown in Table 2. As a result of the evaluation, the film had sufficient shrinkage, but the thickness unevenness was poor, the tensile strength at break in the width direction was low, and the film had 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 (ordinary 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 transverse direction. Thereafter, heat treatment was performed at a temperature of 130 ° C. for 2 seconds. Furthermore, using a pair of left and right trimming devices provided at the back of the tenter, the edge of the film was cut and the end of the film located outside the cut site was continuously removed. After the film thus transversely stretched, heat-treated and trimmed is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, and preheated until the film temperature reaches 70 ° C. on 10 preheating rolls, The film was stretched 3 times using the roll speed difference. At this time, the stretching distance was 4 mm, and the shrinkage ratio in the film width direction was 2%. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set at 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 processes, the number of rolls having a temperature of Tg or higher was 10. This stretching method was designated as a stretching method E, and the properties of the obtained film were evaluated by the methods described above. The evaluation results are shown in Table 2. As a result of the evaluation, although it has sufficient shrinkability, it was a film having many scratches due to shrinkage distortion occurring in the sample near the end of the film.

[Comparative Example 3]
Thickness is 157μm by putting it into the extruder using only polyester 2, melting the resin at 280 ° C, extruding from T-die, wrapping around a rotating metal roll cooled to a surface temperature of 30 ° C and quenching. An unstretched film was obtained. The Tg of the unstretched film was 75 ° C. Thereafter, the unstretched film was guided to a transverse stretching machine (ordinary tenter). The unstretched film guided to the tenter was preheated until the film temperature reached 100 ° C., and then stretched 4 times at 90 ° C. in the transverse direction. Furthermore, the film that has been laterally stretched and heat-treated in this 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 10 preheating rolls, The film was stretched twice using the roll speed difference. At this time, the stretching distance was 4 mm, and the shrinkage ratio in the film width direction was 2%. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set at 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 made of a heat-shrinkable polyester film. In this series of film stretching processes, the number of rolls having a temperature of Tg or higher was 10. This stretching method was designated as a stretching method E, and the properties of the obtained film were evaluated by the methods described above. The evaluation results are shown in Table 2. As a result of the evaluation, although it has sufficient shrinkability, shrinkage distortion occurred in the sample near the end of the film, and the container was deformed when it was shrink-fitted.

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

1: Tenter 2: Clip opener 3: Clip 4: Stretched film 5: Roll 6: Plastic container (lid)
7: Plastic container (torso)
8: Film 9: Stretching distance

Claims (6)

With ethylene terephthalate as the main constituent, it contains more than 5 mol% of one or more monomer components that can be amorphous components in all polyester resin components, and is formed in a long shape with a constant width, A heat shrinkable polyester film having a main shrinkage direction as a longitudinal direction and satisfying the following requirements (1) to (4).
(1) The hot water heat shrinkage in the longitudinal direction when treated for 10 seconds in warm water at 90 ° C is 15% or more and 80% or less
(2) The hot water thermal shrinkage in the width direction perpendicular to the longitudinal direction when treated for 10 seconds in hot water at 90 ° C is -10% or more and 10% or less
(3) The orientation twist index, calculated by converting the molecular orientation angle difference, which is the difference between the molecular orientation angle at one edge in the width direction and the molecular orientation angle at the other edge, per 1 m of film is 15 ° / m or less.
(4) The tensile fracture strength in the width direction, which is the direction orthogonal to the main shrinkage direction, is 80 MPa or more and 200 MPa or less. ^2. The heat-shrinkable polyester film according to claim 1, wherein scratches having a depth of 1 μm or more and a length of 3 mm or more existing on the surface are 100 pieces / m ² or less.   3. The heat-shrinkable polyester film according to claim 1, 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. The heat-shrinkable polyester film according to claim 1, wherein the thickness unevenness in the longitudinal direction is 10% or less.   5. The heat-shrinkable polyester film according to claim 1, wherein the tensile fracture strength in the width direction, which is a direction perpendicular to the main shrinkage direction, is 80 MPa or more and 200 MPa or less.   A package comprising the heat-shrinkable polyester film according to any one of claims 1 to 5 as a base material, and heat-shrinkable by covering at least a part of the outer periphery with a label or a banding film.

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