JP5761282B2 - Method for producing white heat-shrinkable polyester film, white heat-shrinkable polyester film, and package - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a white heat-shrinkable polyester film, a method for producing the same, and a package, and more specifically, a white heat-shrinkable polyester-based film having light-cutting properties and suitable for label applications, and the production thereof. The present invention relates to a package using a method and a label.

  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.

  In addition, as the heat-shrinkable film, a film that is largely shrunk in the width direction is generally used from the viewpoint of handling during label production. Therefore, the conventional heat-shrinkable polyester film has been produced by stretching at a high magnification in the width direction in order to develop a sufficient shrinkage force in the width direction during heating.

  However, since the conventional heat-shrinkable polyester film is hardly stretched in the longitudinal direction perpendicular to the main shrinkage direction, the mechanical strength is low, and when it is covered by being shrunk on a plastic bottle or the like as a label, There is a defect that the label cannot be torn well along the perforation (that is, the perforation opening is poor). In addition, when the film is stretched in the longitudinal direction during production in order to improve the perforation opening of the heat-shrinkable polyester film, the mechanical strength increases and the perforation opening improves to some extent, but in the longitudinal direction. Since the shrinkage force is expressed, when a plastic bottle or the like is shrunk as a label and coated, a problem that the appearance (shrinking finish) is very poor is exposed.

  Therefore, in order to improve the perforation openability of the heat-shrinkable polyester film, a method of mixing an incompatible thermoplastic resin into the main raw material of the heat-shrinkable polyester film (Patent Document 1) is also proposed. .

Japanese Patent Application Laid-Open No. 2002-36312

  According to the method of mixing an incompatible thermoplastic resin into the main raw material of the heat-shrinkable polyester film as described in Patent Document 1, the perforation opening property of the heat-shrinkable polyester film is improved to some extent, but is not necessarily perforated. It is difficult to say that a heat-shrinkable polyester film having sufficient openability is obtained. Moreover, even when the method as disclosed in Patent Document 1 is adopted, the heat-shrinkable polyester film cannot be efficiently produced because it can be stretched only in the width direction during production.

  An object of the present invention is to provide a white heat-shrinkable polyester film having a very good perforation-opening property and a highly productive manufacturing method thereof, which solves the problems of the conventional heat-shrinkable polyester film. It is in.

  Another object of the present invention is to provide a lightweight white heat-shrinkable polyester film having light-cutting properties without printing or processing, and having an excellent aesthetic appearance even when printing is performed. is there.

That is, the present invention has the following configuration.
1. The following requirements (1) to (5 ) comprising a polyester-based resin containing ethylene terephthalate as a main constituent and containing at least 15 mol% of at least one monomer component that can be an amorphous component in all polyester resin components. A white heat-shrinkable polyester-based film that continuously includes the following steps (a) to (f): Production method.
(1) The hot-water heat shrinkage in the width direction when treated in warm water at 90 ° C. for 10 seconds is 40% or more and 80% or less.
(2) The hot water thermal contraction rate in the longitudinal direction when treated in hot water at 90 ° C. for 10 seconds is from 0% to 15%.
(3) The perpendicular tear strength in the longitudinal direction per unit thickness after shrinking in the width direction by 10% in warm water at 80 ° C. is 90 N / mm or more and 200 N / mm or less.
(4) The tensile fracture strength in the longitudinal direction is 100 MPa or more and 250 MPa or less. ( 5 ) It has a Y layer having fewer cavities than the X layer on at least one side of the X layer having many cavities inside, and has a whiteness. (A) An unstretched film is stretched at a magnification of 2.2 times or more and 3.0 times or less in the longitudinal direction at a temperature of Tg or more and Tg + 30 ° C., and then at a temperature of Tg + 10 ° C. or more and Tg + 40 ° C. or less. Longitudinal stretching step (b) Longitudinal stretching in which the film is stretched at a magnification of 1.2 to 1.5 times in the longitudinal direction so that the total magnification is 2.8 to 4.5 times. An intermediate heat treatment step in which the subsequent film is heat-treated at a temperature of 130 ° C. or higher and 190 ° C. or lower for a time of 1.0 second or more and 9.0 seconds or less in a state where both ends in the width direction are held by clips in the tenter. c) Intermediate heat treatment The natural cooling process in which the film is naturally cooled by passing through an intermediate zone that is shielded from the front and rear zones and does not perform an active heating operation. (D) The surface temperature of the film after natural cooling is 80 ° C. Active cooling step of actively cooling until reaching a temperature of 120 ° C. or lower (e) The film after the active cooling is 2.0 times or higher and 6.0 times or lower in the width direction at a temperature of Tg + 10 ° C. or higher and Tg + 40 ° C. or lower. Transverse stretching step of stretching at a magnification (f) 1.0 to 9.0 seconds at a temperature of 80 ° C. or higher and 100 ° C. or lower with the film after the horizontal stretching held in the tenter by clips at both ends in the width direction Final heat treatment process for heat treatment for the following time
2 . 2. The method for producing a white heat-shrinkable polyester film according to the first aspect, wherein the shrinkage stress in the width direction when heated to 90 ° C. is 3 MPa or more and 15 MPa or less.
3 . The method for producing a white heat-shrinkable polyester film according to the first or second aspect, wherein the thickness unevenness in the width direction is 1.0% or more and 12.0% or less.
4 . The method for producing a white heat-shrinkable polyester film according to any one of the first to third aspects, wherein the thickness unevenness in the longitudinal direction is 1.0% or more and 12.0% or less.
5. The method for producing a white heat-shrinkable polyester film according to any one of the first to fourth aspects, wherein the solvent adhesive strength is 2 N / 15 mm width or more and 15 N / 15 mm width or less.
6). The method for producing a white heat-shrinkable polyester film according to any one of the first to fifth aspects, wherein the dynamic friction coefficient is 0.1 or more and 0.55 or less.
7). Main component of the monomer that can be the amorphous component in the whole Porisuteru resin component is, neopentyl glycol, 1,4-cyclohexanedimethanol, the first to be characterized by either of the isophthalic acid 6 The manufacturing method of the white heat-shrinkable polyester-type film in any one of.
8). An apparent density is 1.2 g / cm < ³ > or less, The manufacturing method of the white heat-shrinkable polyester film in any one of said 1st- 7th characterized by the above-mentioned.
9. A white heat-shrinkable polyester film produced by the method for producing a white heat-shrinkable polyester film described in any one of the first to eighth .
10. A package comprising the white heat-shrinkable polyester film as described in the above item 9 as a base material, and heat-shrinkable by covering at least part of the outer periphery with a label having a perforation or a pair of notches. body.

  The white heat-shrinkable polyester film of the present invention is highly shrinkable in the width direction, which is the main shrinkage direction, has high mechanical strength in the longitudinal direction perpendicular to the width direction, and has a perforation opening property when used as a label. When opening, it can be cut neatly along the perforation from the beginning of tearing to the completion of tearing. In addition, the stiffness (so-called “waist strength”) is high, and the wearability when the label is used is excellent. In addition, the processing characteristics during printing and tubing are good. Therefore, the white heat-shrinkable polyester film of the present invention can be suitably used as a label for a container such as a bottle. When used as a label, the white heat-shrinkable polyester film can be very efficiently used in a container such as a bottle within a short time. It can be worn, and when it is heat-shrinked after wearing, it can express a good finish with very little wrinkles and insufficient shrinkage, and the attached label expresses very good perforation opening Become. The package of the present invention has a good tearing condition of the coated label, and can be torn the coated label cleanly along the perforation with an appropriate force.

  The white heat-shrinkable polyester film of the present invention is lightweight and excellent in aesthetics, has light-cutting properties without printing or processing, and has excellent aesthetics even when printed.

  In addition, the white heat-shrinkable polyester film of the present invention can be produced very efficiently because it is produced by being stretched biaxially and vertically.

It is explanatory drawing which shows the shape of the test piece in the measurement of a right-angled tear strength (In addition, the unit of the length of each part of the test piece in a figure is mm).

  The polyester used in the present invention is mainly composed of ethylene terephthalate. That is, it contains 50 mol% or more, preferably 60 mol% or more of ethylene terephthalate. Other dicarboxylic acid components constituting the polyester of the present invention include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, And alicyclic dicarboxylic acid.

  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 white heat-shrinkable polyester film obtained by using a polyester containing 3% by mole or more of these aliphatic dicarboxylic acids has insufficient film stiffness during high-speed wearing.

  Further, it is preferable not to contain a trivalent or higher polyvalent carboxylic acid (for example, trimellitic acid, pyromellitic acid, and their anhydrides). In the white heat-shrinkable polyester film obtained by using the 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 for the white 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 butane). A polyester having a glass transition point (Tg) adjusted to 60 to 80 ° C. by containing one or more of diol, neopentyl glycol, hexanediol and the like.

  The polyester used in the white heat-shrinkable polyester film of the present invention is one or more kinds that can be an amorphous component in 100 mol% of the polyhydric alcohol component or 100 mol% of the polyvalent carboxylic acid component in the total polyester resin. The total of the monomer components is preferably 15 mol% or more, more preferably 17 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-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,2- Diethyl 1,3-propanediol, 2-n-butyl 2-ethyl 1,3-propanediol, 2,2-isopropyl 1,3-propanediol, 2,2-di-n-butyl 1,3-propanediol, Among them, 1,4-butanediol and hexanediol can be mentioned. Among them, neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid are preferably used.

  In the polyester used in the white 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, It is preferable not to contain glycerin, diglycerin and the like. 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.

  Moreover, it is preferable not to contain diethylene glycol, triethylene glycol, and polyethylene glycol as much as possible in the polyester used for the white heat-shrinkable polyester film of the present invention.

  In addition, in the resin forming the white heat-shrinkable polyester film of the present invention, various additives, for example, waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents are used as necessary. Further, a heat stabilizer, a coloring pigment, an anti-coloring agent, an ultraviolet absorber and the like can be added. In the resin forming the white heat-shrinkable polyester film of the present invention, it is preferable to improve the workability (slidability) of the polyethylene terephthalate resin film by adding fine particles as a lubricant. Any fine particles can be selected. Examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Examples of the organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and crosslinked polystyrene particles. The average particle size of the fine particles can be appropriately selected as necessary within a range of 0.05 to 3.0 μm (when measured with a Coulter counter).

  As a method of blending the above particles into the resin forming the white heat-shrinkable polyester film, for example, it can be added at any stage of producing the polyester resin, but it can be added at the esterification stage or transesterification. After completion of the reaction, it is preferable to add as a slurry dispersed in ethylene glycol or the like at the stage before the start of the polycondensation reaction to advance the polycondensation reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water using a vented kneading extruder and a polyester resin material, or a dried particle and a polyester resin material using a kneading extruder It is also preferable to carry out by a method of blending and the like.

  In the present invention, in order to obtain an appropriate whiteness, for example, it is preferable to contain fine cavities inside. For example, a foam material or the like may be mixed and extruded, but a preferable method is to obtain a cavity by mixing an incompatible thermoplastic resin in polyester and stretching it in at least one axial direction. The thermoplastic resin incompatible with the polyester used in the present invention is arbitrary, and is not particularly limited as long as it is incompatible with the polyester. Specific examples include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, a polystyrene resin or a polyolefin resin such as polymethylpentene or polypropylene is preferable because of the formation of cavities.

  Polystyrene resin refers to a thermoplastic resin containing a polystyrene structure as a basic component, and grafted or block copolymerized with other components in addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene. Modified resins, such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and mixtures of thermoplastic resins having compatibility with these polystyrene resins, such as polyphenylene ether, are included.

  The polymethylpentene-based resin is a polymer having units derived from 4-methylpentene-1 at 80 mol% or more, preferably 90 mol% or more, and other components include ethylene units, propylene units, Examples include units derived from butene-1 units, 3-methylbutene-1, and the like. The melt flow rate of such polymethylpentene is preferably 200 g / 10 min or less, more preferably 30 g / 10 min or less. This is because when the melt flow rate exceeds 200 g / 10 min, it is difficult to obtain the effect of reducing the weight of the film.

  The polypropylene resin in the present invention also includes modified resins obtained by grafting or block copolymerizing other components in addition to homopolymers such as isotactic polypropylene and syndiotactic polypropylene.

  In preparing a polymer mixture obtained by mixing the polyester and the incompatible resin, for example, the chips of each resin may be mixed and melt-kneaded in an extruder and then extruded, or both resins may be preliminarily mixed by a kneader. The kneaded product may be further melt extruded from an extruder. Further, a chip obtained by adding a polystyrene resin in the polyester polymerization step and stirring and dispersing may be melt-extruded.

The film in the present invention is preferably provided with a Y layer having fewer cavities than the X layer on at least one side of the X layer containing a large number of cavities inside. In order to achieve this configuration, different raw materials are charged into different extruders for X and Y, melted, bonded together in a molten state before or in a T-die, and solidified in close contact with a cooling roll, which will be described later. It is preferable to stretch by the method. At this time, it is preferable that the amount of incompatible resin in the Y layer as a raw material is smaller than that in the X layer. By doing so, there are few cavities in the Y layer, the surface roughness is reduced, and the film does not impair the aesthetics of printing. In addition, since there are portions where there are not many cavities in the film, the film does not become weak and the film has excellent wearability.

  Furthermore, the white heat-shrinkable polyester film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion of the film surface.

In addition, the white heat-shrinkable polyester film of the present invention has a film width calculated by the following formula 1 from the length before and after shrinkage when treated for 10 seconds in 90 ° C. warm water under no load. The heat shrinkage rate in the direction (that is, the hot water heat shrinkage rate at 90 ° C.) is preferably 40% or more and 80% or less.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%)
... Formula 1

  If the hot water thermal shrinkage in the width direction at 90 ° C. is less than 40%, the shrinkage amount is small, so it is not preferable because wrinkles and tarmi are generated on the label after heat shrinkage, and conversely, the width direction at 90 ° C. If the hot-water heat shrinkage rate exceeds 80%, it is not preferable because when used as a label, the shrinkage tends to occur during heat shrinkage, or so-called “jumping” occurs. In addition, the lower limit of the hot water temperature thermal contraction rate in the width direction at 90 ° C. is preferably 45% or more, more preferably 50% or more, and particularly preferably 55% or more. Further, the upper limit value of the hot water thermal contraction rate in the width direction at 90 ° C. is preferably 75% or less, more preferably 70% or less, and particularly preferably 65% or less.

  In addition, the white heat-shrinkable polyester film of the present invention has a film length calculated by the above formula 1 from the length before and after shrinkage when treated for 10 seconds in 90 ° C. warm water without load. The heat shrinkage rate in the direction (that is, the hot water heat shrinkage rate at 90 ° C.) is preferably 0% or more and 15% or less, more preferably 13% or less, still more preferably 12% or less, and 11%. Or less, more preferably 9% or less.

  It is preferable that the hot water thermal shrinkage in the longitudinal direction at 90 ° C. is less than 0% (that is, the shrinkage is a negative value) because a good shrink appearance cannot be obtained when used as a bottle label. On the other hand, if the hot water thermal contraction rate in the longitudinal direction at 90 ° C. exceeds 15%, it is not preferred because distortion tends to occur during thermal contraction when used as a label. The lower limit of the hot water heat shrinkage in the longitudinal direction at 90 ° C. is preferably 1% or more, more preferably 2% or more, and particularly preferably 3% or more.

  The white heat-shrinkable polyester film of the present invention preferably has a shrinkage stress in the width direction of 3 MPa or more and 15 MPa or less when heated to 90 ° C. If the shrinkage stress in the width direction when heated to 90 ° C is less than 3 MPa, it is not preferable because a good shrinkage appearance cannot be obtained when used as a label on a bottle, and conversely, the width when heated to 90 ° C. When the shrinkage stress in the direction exceeds 15 MPa, when used as a label, distortion tends to occur during heat shrinkage, which is not preferable. In addition, the lower limit value of the shrinkage stress in the width direction when heated to 90 ° C. is more preferably 4 MPa or more, further preferably 5 MPa or more, and particularly preferably 6 MPa or more. Further, the upper limit value of the shrinkage stress in the width direction when heated to 90 ° C. is more preferably 15 MPa or less, further preferably 13 MPa or less, further preferably 11 MPa or less, and particularly preferably 9 MPa or less. .

  Moreover, when the white heat-shrinkable polyester film of the present invention was subjected to 10% shrinkage in the width direction in warm water at 80 ° C., the right angle tear strength in the longitudinal direction per unit thickness was determined by the following method. The right-angled tear strength in the longitudinal direction is preferably 90 N / mm or more and 200 N / mm or less.

[Measurement method of right-angle tear strength]
The film is shrunk 10% in the width direction in hot water adjusted to 80 ° C., and then sampled as a test piece of a predetermined size according to JIS-K-7128. Thereafter, both ends of the test piece are gripped with a universal tensile tester, and the strength at the time of tensile fracture in the longitudinal direction of the film is measured under the condition of a tensile speed of 200 mm / min. Then, the right angle tear strength per unit thickness is calculated using the following equation 2.
Right angle tear strength = strength at tensile failure ÷ thickness ・ ・ ・ Equation 2

  When the right-angled tear strength after shrinking 10% in the width direction in warm water at 80 ° C is less than 90 N / mm, it may be easily broken by impacts such as dropping during transportation when used as a label. On the other hand, when the right-angled tear strength exceeds 200 N / mm, the cutting property (easy to tear) at the initial stage of tearing the label becomes poor. In addition, the lower limit of the right-angled tear strength is more preferably 110 N / mm or more, and further preferably 130 N / mm or more. Further, the upper limit value of the right-angled tear strength is more preferably 190 N / mm or less, and further preferably 180 N / mm or less. Creating a cavity in the film by increasing the amount of the additive in the resin can be said to be a device for further adjusting the right-angled tear strength.

  The white heat-shrinkable polyester film of the present invention preferably has a tensile fracture strength of 100 MPa to 250 MPa when the tensile fracture strength in the longitudinal direction is determined by the following method.

[Measurement method of tensile fracture strength]
In accordance with JIS-K7113, a strip-shaped test piece of a predetermined size is prepared, and both ends of the test piece are gripped by a universal tensile tester, and a tensile test is performed under a condition of a tensile speed of 200 mm / min. The strength (stress) at the time of tensile fracture in the longitudinal direction of the film is calculated as the tensile fracture strength.

  If the tensile fracture strength in the longitudinal direction is less than 100 MPa, the “waist” (stiffness) when labeling and attaching to a bottle or the like is weakened. On the contrary, if the tensile fracture strength exceeds 250 MPa, the label This is not preferable because the cutability (ease of tearing) in the initial stage when tearing the film becomes poor. In addition, the lower limit value of the tensile fracture strength is preferably 120 MPa or more, more preferably 140 MPa or more, and particularly preferably 150 MPa or more. Further, the upper limit value of the right-angled tear strength is preferably 240 MPa or less, more preferably 230 MPa or less, and particularly preferably 220 MPa or less.

  The white heat-shrinkable polyester film of the present invention preferably has a thickness variation in the width direction (thickness variation when the measurement length is 1 m) of 12% or less. If the thickness unevenness in the width direction is more than 12%, it is not preferable because printing spots are likely to occur during printing at the time of label production or shrinkage spots after heat shrinkage are likely to occur. The thickness variation in the width direction is more preferably 10% or less, and particularly preferably 8% or less. Although the thickness variation in the width direction is preferably as small as possible, the lower limit of the thickness variation is considered to be about 1% from the viewpoint of the performance of the film forming apparatus.

  Furthermore, the thickness of the white heat-shrinkable polyester film of the present invention is not particularly limited, but it is preferably 5 to 200 μm, more preferably 10 to 70 μm, as the heat-shrinkable film for labels.

  The white heat-shrinkable polyester film of the present invention preferably has a thickness variation in the longitudinal direction (thickness variation when the measurement length is 10 m) of 12% or less. When the thickness unevenness in the longitudinal direction is more than 12%, it is not preferable because printed spots are likely to occur during printing at the time of label production or shrinkage spots after heat shrinkage are likely to occur. In addition, the thickness variation in the longitudinal direction is more preferably 10% or less, and particularly preferably 8% or less. Moreover, although the thickness variation in the longitudinal direction is preferably as small as possible, the lower limit of the thickness variation is considered to be about 1% from the viewpoint of the performance of the film forming apparatus.

  Furthermore, the white heat-shrinkable polyester film of the present invention preferably has a solvent adhesive strength of 2 (N / 15 mm) or more, and more preferably 4 (N / 15 mm) or more. If the solvent adhesive strength is less than 4 (N / 15 mm), it is not preferable because the label is easily peeled off after the heat shrinkage. The solvent adhesive strength is more preferably 6 (N / 15 mm) or more, and particularly preferably 8 (N / 15 mm) or more. The higher the solvent adhesive strength, the better. However, the upper limit of the solvent adhesive strength is considered to be about 15 (N / 15 mm) in view of the performance of the film forming apparatus.

  In addition, the white heat-shrinkable polyester film of the present invention has a dynamic friction coefficient (dynamic friction coefficient when the front and back surfaces of the heat-shrinkable polyester film are bonded) of 0.1 or more and 0.55 or less. preferable. If the dynamic friction coefficient is less than 0.1 or more than 0.55, it is not preferable because the processing characteristics at the time of processing into a label deteriorate. In addition, the lower limit value of the dynamic friction coefficient is more preferably 0.15 or more, and particularly preferably 0.2 or more. Further, the upper limit value of the dynamic friction coefficient is more preferably 0.50 or less, and particularly preferably 0.45 or less.

In the present invention, the apparent density of the film is preferably 1.2 g / cm ³ or less, more preferably 1.18 g / cm ³ or less, and still more preferably 1.16 g / cm ³ or less. The fact that the apparent density is small and light is a great advantage in mass production, and the white heat-shrinkable polyester film of the present invention has a cavity inside, so that preferable light weight can be realized. In particular, by adopting the longitudinal-transverse stretching method described later, a larger area stretching ratio can be employed as compared with a conventional uniaxially stretched film having a cavity, and a smaller apparent density can be obtained. However, if the apparent density is too small, the strength of the film itself is impaired. Therefore, the apparent density is preferably 0.6 g / cm ³ or more, and more preferably 0.7 or more.

  The molecular orientation ratio (MOR) in the present invention is preferably 1.05 or more and 3 or less. When the molecular orientation ratio is larger than 3, the longitudinal orientation is low, and it is difficult to satisfy the perpendicular tear strength in the longitudinal direction of the film. The preferred molecular orientation ratio is 2.8 or less, more preferably 2.6 or less. The molecular orientation ratio is preferably closer to 1, but it may be 1.05 or more.

[Measurement method of molecular orientation ratio]
A sample of the film in the longitudinal direction × width direction = 140 mm × 100 mm was taken. And about the sample, molecular orientation ratio (MOR) was measured using the molecular orientation angle measuring apparatus (MOA-6004) by Oji Scientific Instruments.

  In order to satisfy the above characteristics, the film of the present invention may be composed of a single layer, but the layer structure is preferably X / Y, Y / X / Y, or Y / X / Z. The thickness ratio between the X layer and the Y layer is preferably X / Y = 2/1 or more, more preferably 4/1 or more, and even more preferably 6/1 or more. If it is less than 1/1, it is difficult to achieve both the aesthetics of printability and the reduction in density. Y / X / Y is preferable for suppressing undesirable curling after the shrinkage treatment.

When the Z layer is provided, the content of the cavities is arbitrary, but it is possible to add particles for controlling slippage between the bottle and the film during shrinkage.
The film of the present invention has a cushion rate of 10% or more, preferably 20% or more. If the cushion rate is low, the effect of preventing the bottle or bottle from being damaged is lowered.

  In addition, when the white heat-shrinkable polyester film of the present invention has a laminated structure, the thickness of each layer is not particularly limited, but is preferably 2 μm or more.

  In the present invention, the total light transmittance is 40% or less, preferably 35% or less, more preferably 30% or less, and still more preferably 20% or less. If it exceeds 40%, the contents may be seen through or the printed matter may be difficult to see, which may be inferior in appearance. In the present invention, the whiteness is 70 or more, preferably 75 or more, more preferably 80 or more. If it is less than 70, the contents may be seen through or the printed matter may be difficult to see, and the appearance may be inferior.

  The film obtained by this invention can be made into a tube shape, and a film edge part can be joined. In that case, 1,3-dioxolane or a mixed solution with an organic solvent compatible with 1,3-dioxolane or a solvent or a swelling agent having a solubility parameter in the range of 8.0 to 13.8 is applied. It is preferable to bond by drying at a temperature of 70 ° C. or lower to obtain a tubular body before drying. Examples of the solubility parameter include those described in a solvent handbook (edited by the Japan Adhesive Association, published by Nikkan Kogyo Shimbun). The joint portion in the tube may have a width as narrow as possible from 50 mm or more and, of course, is appropriately determined according to the size of the container. A width of 5 mm is standard. Further, the joining portion may be joined in a single line shape, or may be formed by forming a plurality of linear joints over two or more. Since these joints do not damage the film base material, they retain the properties of the polyester polymer as they are and have protective properties such as impact resistance and bottle breakage resistance. It is good without a decrease in the degree of orientation due to shrinkage and no embrittlement phenomenon due to the subsequent heat treatment.

  The attachments using this tube include containers, bottles (including plastic bottles), and can sticks (pipes, sticks, wood, various sticks), preferably attached to bottles mainly composed of polyethylene terephthalate. Thus, recovery is facilitated, and even if a trace amount is mixed with the bottle raw material when the polyethylene terephthalate bottle is reused, it is effective because it is difficult to color.

  Moreover, although the manufacturing method of the white heat-shrinkable polyester film of this invention is not specifically limited, an example is given and demonstrated. The above-mentioned polyester raw material can be obtained by melting and extruding with an extruder to form an unstretched film, biaxially stretching the unstretched film by a predetermined method shown below, and heat-treating it. A plurality of resin composition raw materials can be coextruded in order to obtain a laminated unstretched film as necessary.

  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 is stretched in the longitudinal direction under predetermined conditions, and after the longitudinally stretched film is rapidly cooled, it is once heat-treated, and the heat-treated film is subjected to predetermined conditions. After cooling in step 1, it is possible to obtain the white heat-shrinkable polyester film of the present invention by stretching in the width direction under a predetermined condition and heat-treating again. Hereinafter, a preferable film forming method for obtaining the white heat-shrinkable polyester film of the present invention will be described in detail in consideration of a difference from a conventional heat-shrinkable polyester film forming method.

[Method for Forming White Heat-Shrinkable Polyester Film of the Present Invention]
As described above, the heat-shrinkable polyester film is usually produced by stretching only in the direction in which the unstretched film is desired to be shrunk (that is, the main shrinkage direction, usually the width direction). As a result of studying the conventional production method by the present inventors, it has been found that there are the following problems in the production of a conventional heat-shrinkable polyester film.
If the film is simply stretched in the width direction, as described above, the mechanical strength in the longitudinal direction is reduced, and the perforation opening property when the label is used is deteriorated. In addition, it is difficult to increase the line speed of the film forming apparatus.
-If the method of extending | stretching to a longitudinal direction is employ | adopted after extending | stretching to the width direction, the contraction force of the width direction cannot fully be expressed, no matter what extending | stretching conditions are employ | adopted. In addition, the contraction force in the longitudinal direction is expressed at the same time, and when finished as a label, the finish after the shrinkage attachment becomes worse.
・ If a method of stretching in the width direction is used after stretching in the length direction, the contraction force in the width direction can be expressed, but the contraction force in the length direction is expressed at the same time. The finish of becomes worse.

Furthermore, based on the problems in the production of the above conventional heat-shrinkable polyester film, the present inventors further consider obtaining a white heat-shrinkable polyester film having good perforation opening and high productivity. As a result, the following findings were obtained.
・ In order to improve the perforation of the perforated label, it is considered necessary to leave some molecules oriented in the longitudinal direction. In order to make it good, it is indispensable not to develop a contraction force in the longitudinal direction, and for that purpose, it is considered necessary to eliminate the tension state of molecules oriented in the longitudinal direction. When the portion having the above is provided, it works more advantageously with respect to the perforation opening, and unlike the uniaxially stretched film having a simple cavity, the area stretch ratio can be increased by the special longitudinal-lateral stretch method described below, and its effect That is expected to expand

From the above findings, the present inventors need to have “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” in the film in order to satisfy both the good perforation opening property and the shrinkage finishing property at the same time. I came to think that there is. Then, a trial and error was carried out by paying attention to what kind of stretching would allow “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” to exist in the film. As a result, at the time of film production by the so-called longitudinal-lateral stretching method, which is stretched in the longitudinal direction after being stretched in the longitudinal direction, “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” by taking the following means: It is possible to obtain a white heat-shrinkable polyester film that simultaneously satisfies good perforation opening properties and shrink finish properties, and has devised the present invention.
(1) Control of longitudinal stretching conditions (2) Intermediate heat treatment after longitudinal stretching (3) Natural cooling (interruption of heating) between intermediate heat treatment and transverse stretching
(4) Forced cooling of the film after natural cooling (5) Control of transverse stretching conditions Hereinafter, each of the above-described means will be sequentially described.

(1) Control of longitudinal stretching conditions In the production of a film by the longitudinal-lateral stretching method of the present invention, longitudinal stretching is preferably performed in two stages in order to obtain the film roll of the present invention. That is, a substantially unoriented film is longitudinally stretched at a temperature of Tg or more and Tg + 30 ° C. or less to a magnification of 2.2 to 3.0 times (first-stage stretching), and cooled to Tg or less. Without stretching at a temperature of not less than Tg + 10 and not more than Tg + 40 ° C. to a magnification of 1.2 times or more and 1.5 times or less (second stage stretching), the total longitudinal stretching ratio (that is, the first stage stretching) Is preferably 2.8 times to 4.5 times, and the total longitudinal drawing ratio is 3.0 times to 4.3 times. More preferably, it is longitudinally stretched so as to be as follows.

  Moreover, it is preferable to adjust the conditions of longitudinal stretching so that the thermal shrinkage stress in the longitudinal direction of the film after longitudinal stretching is 10 MPa or less. By performing longitudinal stretching under such predetermined conditions, it becomes possible to control the degree of orientation in the longitudinal and width directions of the film and the degree of molecular tension during intermediate heat treatment, lateral stretching, and final heat treatment, which will be described later. In addition, it is possible to improve the perforation-opening property of the final film by acting that the film is provided with a cavity.

  When stretching in the longitudinal direction as described above, if the total longitudinal stretching ratio increases, the contraction rate in the longitudinal direction tends to increase, but by stretching in two stages in the longitudinal direction as described above, The stretching stress in the direction can be reduced, and the shrinkage in the longitudinal direction can be kept low. In addition, when the total longitudinal stretching ratio is high, the stress at the time of stretching in the width direction tends to be high, and it tends to be difficult to control the final shrinkage in the lateral direction, but by stretching in two stages, The stretching stress in the transverse direction can be reduced, and the shrinkage rate in the transverse direction can be easily controlled.

  Furthermore, when the total longitudinal draw ratio is increased, the right-angled tear strength is decreased and the tensile strength in the longitudinal direction is increased. Further, by making the total longitudinal draw ratio close to the transverse draw ratio, it is possible to improve the perforation openability when the label is used. Furthermore, by stretching in the longitudinal direction in two steps, it is possible to increase the longitudinal orientation due to the ability to reduce the stretching stress in the transverse direction, further lowering the right-angled tear strength and the tensile strength in the longitudinal direction. Strength will be greater. Therefore, it is possible to obtain a label having very good perforation tearability by stretching in two stages in the longitudinal direction and increasing the total longitudinal stretching ratio.

  On the other hand, if the total longitudinal draw ratio exceeds 4.5 times, the orientation in the longitudinal direction becomes high and the solvent adhesive strength becomes low, but by controlling the total longitudinal draw ratio to 4.5 times or less, It is possible to suppress the orientation in the width direction and keep the solvent adhesive strength high, and when the total longitudinal draw ratio exceeds 4.5 times, the roughness of the surface layer decreases, so the dynamic friction coefficient However, by controlling the total longitudinal draw ratio to 4.5 times or less, it is possible to suppress the decrease in surface roughness and keep the coefficient of dynamic friction low.

  In addition, stretching in the longitudinal direction in two stages reduces the stretching stress in the longitudinal direction, and thus tends to increase the thickness unevenness in the longitudinal direction and the thickness unevenness in the width direction, but increases the total longitudinal stretching ratio. Thereby, the thickness unevenness of a longitudinal direction can be made small. In addition, by increasing the total longitudinal stretching ratio, the stress during transverse stretching increases, so that thickness unevenness in the width direction can also be reduced.

  In addition, by increasing the total longitudinal stretching ratio, the orientation in the longitudinal direction can be increased, and the slit property when the film after biaxial stretching is finally wound on a roll can be improved. .

(2) Intermediate heat treatment after longitudinal stretching As described above, in order to make “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” exist in the film, it is preferable to thermally relax the molecules oriented in the longitudinal direction. However, conventionally, in the biaxial stretching of the film, if the film is subjected to a high temperature heat treatment between the first axis stretching and the second axis stretching, the film after the heat treatment is crystallized, so that the film is further stretched. It was technical common sense in the industry that it was not possible. However, as a result of trial and error by the inventors, in the longitudinal-transverse stretching method, longitudinal stretching is performed under certain conditions, intermediate heat treatment is performed under predetermined conditions according to the state of the film after the longitudinal stretching, and By applying transverse stretching under predetermined conditions according to the state of the film after the intermediate heat treatment, “molecules that are oriented in the longitudinal direction and do not contribute to the shrinkage force” are generated in the film without causing breakage during transverse stretching. The surprising fact that it can be present.

  That is, in the production of a film by the longitudinal-lateral stretching method of the present invention, after longitudinally stretching an unstretched film, a temperature of 130 ° C. or higher and 190 ° C. or lower in a state where both ends in the width direction are held by clips in the tenter. It is preferable to perform heat treatment (hereinafter referred to as intermediate heat treatment) over a period of 1.0 second to 9.0 seconds. By performing such an intermediate heat treatment, “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” can be present in the film. As a result, when the label is used, the perforation is good and the shrinkage spots are not generated. A film that does not occur can be obtained. In any case, it is not possible to have “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” in the film, and the predetermined longitudinal stretching described above is performed. Thus, after the intermediate heat treatment, for the first time, “molecules that are oriented in the longitudinal direction and do not contribute to the shrinkage force” can be present in the film. Then, by performing the predetermined natural cooling, forced cooling, and transverse stretching described later, the molecules are oriented in the width direction while retaining the “molecules that do not contribute to the shrinkage force while being oriented in the longitudinal direction” formed in the film. It is possible to develop a contraction force in the width direction.

  In addition, the minimum of the temperature of intermediate heat processing is preferable in it being 140 degreeC or more, and it is more preferable in it being 150 degreeC or more. Moreover, the upper limit of the temperature of the intermediate heat treatment is preferably 180 ° C. or less, and more preferably 170 ° C. or less. On the other hand, the time for the intermediate heat treatment is preferably adjusted as appropriate depending on the raw material composition within a range of 1.0 second to 9.0 seconds, and is preferably adjusted to 3.0 seconds to 7.0 seconds. .

  Moreover, when performing the intermediate heat treatment as described above, it is preferable to adjust the conditions for the intermediate heat treatment so that the heat shrinkage stress in the longitudinal direction of the film after the intermediate heat treatment is 0.5 MPa or less. Furthermore, it is preferable to adjust the conditions of the intermediate heat treatment so that the tensile fracture elongation in the longitudinal direction of the film after the intermediate heat treatment is 100% or more and 170% or less. By performing an intermediate heat treatment under such predetermined conditions, it becomes possible to control the degree of orientation in the longitudinal direction and width direction of the film and the degree of molecular tension during transverse stretching and final heat treatment, and thus the final film. It becomes possible to make the perforation openability of this. In addition, when the tensile fracture elongation in the longitudinal direction of the film after the intermediate heat treatment is less than 100%, the film is fragile, so that the transverse stretchability is poor, and breakage is likely to occur during transverse stretching. On the other hand, if the tensile elongation at break in the longitudinal direction of the film after the intermediate heat treatment exceeds 170%, it becomes difficult to obtain a film with good perforation openability even if the conditions of transverse stretching and final heat treatment are adjusted. .

  Furthermore, when performing the intermediate heat treatment as described above, it is preferable to adjust the conditions for the intermediate heat treatment so that the perpendicular tear strength in the longitudinal direction of the film after the intermediate heat treatment is 200 N / mm or less. By performing an intermediate heat treatment under such a predetermined condition, it becomes possible to suppress a rapid increase in the right-angled tear strength in the longitudinal direction during transverse stretching, and to improve the perforation opening property of the final film. It becomes possible.

  When the intermediate heat treatment is performed as described above, by maintaining the treatment temperature at 130 ° C. or higher, it is possible to reduce the stress that shrinks in the longitudinal direction, and the shrinkage rate in the longitudinal direction can be extremely reduced. Also, if the intermediate heat treatment temperature is higher than 190 ° C, the variation in the shrinkage rate in the lateral direction will increase, but by controlling the intermediate heat treatment temperature to 190 ° C or less, the variation in the shrinkage rate in the horizontal direction will be reduced. It becomes possible to do.

  Further, when the treatment temperature exceeds 190 ° C. during the intermediate heat treatment, the surface layer of the film is crystallized and the solvent adhesive strength is lowered, but by controlling the temperature of the intermediate heat treatment to 190 ° C. or less, It is possible to suppress the crystallization of the surface layer and keep the solvent adhesive strength high. In addition, by maintaining the treatment temperature at 130 ° C. or higher, the surface roughness of the surface layer can be increased appropriately, thereby reducing the friction coefficient.

  Further, when the heat treatment temperature exceeds 190 ° C. during the intermediate heat treatment, shrinkage spots are generated on the film, which tends to increase the thickness unevenness in the longitudinal direction and the thickness unevenness in the width direction. By controlling the temperature to 190 ° C. or lower, the thickness unevenness in the longitudinal direction can be kept small. In addition, during the intermediate heat treatment, if the treatment temperature exceeds 190 ° C., the film will crystallize, and the thickness variation in the width direction tends to increase due to variations in stress during transverse stretching. By controlling the temperature of the intermediate heat treatment to 190 ° C. or less, it becomes possible to suppress crystallization of the film and keep the thickness variation in the width direction small.

  Further, when the intermediate heat treatment is performed, if the treatment temperature exceeds 190 ° C., shrinkage spots are generated on the film, so that the slit property of the film is deteriorated during production or the film is easily broken. However, by controlling the temperature of the intermediate heat treatment to 190 ° C. or less, it becomes possible to suppress the film breakage and maintain good slitting properties.

(3) Natural cooling (interruption of heating) between intermediate heat treatment and transverse stretching
In the production of a film by the longitudinal-lateral stretching method of the present invention, as described above, it is preferable to perform an intermediate heat treatment after the longitudinal stretching. It is preferable to pass through an intermediate zone where no aggressive heating operation is performed for a time of less than a second. That is, an intermediate zone is provided in front of the transverse stretching zone of the tenter for transverse stretching, the film after longitudinal stretching is guided to the tenter, and after passing through the intermediate zone for a predetermined time, the transverse stretching is performed. Is preferred. In addition, in the intermediate zone, when the strip-shaped piece of paper is suspended without passing through the film, the accompanying flow and cooling zone accompanying the flow of the film so that the piece of paper hangs down almost completely in the vertical direction. It is preferable to block the hot air from. If the time for passing through the intermediate zone is less than 0.5 seconds, the transverse stretching becomes high-temperature stretching, and the shrinkage rate in the transverse direction cannot be sufficiently increased. On the contrary, it is sufficient that the time for passing through the intermediate zone is 3.0 seconds, and setting it longer than that is not preferable because it wastes equipment. The lower limit of the time for passing through the intermediate zone is preferably 0.7 seconds or more, and more preferably 0.9 seconds or more. Further, the upper limit of the time for passing through the intermediate zone is preferably 2.8 seconds or less, and more preferably 2.6 seconds or less.

(4) Forced cooling of the film after natural cooling In the production of the film by the longitudinal-lateral stretching method of the present invention, the naturally cooled film is not directly stretched as it is, but the film temperature is 80 ° C. or higher and 120 ° C. It is preferable to quench rapidly so that it becomes below ℃. By performing such a rapid cooling treatment, it becomes possible to obtain a film having good perforation opening properties when used as a label. In addition, the lower limit of the temperature of the film after quenching is preferably 85 ° C or higher, and more preferably 90 ° C or higher. Moreover, the upper limit of the temperature of the film after rapid cooling is preferably 115 ° C. or less, and more preferably 110 ° C. or less.

  When the film is rapidly cooled as described above, if the temperature of the film after rapid cooling remains above 120 ° C., the shrinkage rate in the width direction of the film becomes low, and the shrinkability when used as a label is insufficient. However, by controlling the temperature of the cooled film to be 120 ° C. or lower, it is possible to maintain a high shrinkage rate in the width direction of the film.

  In addition, when the film is rapidly cooled, if the temperature of the film after quenching remains higher than 120 ° C., the film crystallizes, the tensile strength in the longitudinal direction decreases, and the solvent adhesive strength tends to decrease. However, it is possible to keep the tensile strength in the longitudinal direction and the solvent adhesive strength high by performing rapid cooling so that the temperature of the cooled film becomes 120 ° C. or less.

  Furthermore, when the film is rapidly cooled, if the temperature of the film after quenching remains higher than 120 ° C., the stress of transverse stretching performed after cooling tends to be small, and the thickness unevenness in the width direction tends to increase. By performing rapid cooling so that the temperature of the film after cooling is 120 ° C. or lower, it is possible to increase the stress of transverse stretching performed after cooling and reduce thickness unevenness in the width direction.

  In addition, when the film is rapidly cooled, if the temperature of the film after quenching remains higher than 120 ° C., the film is likely to be crystallized due to crystallization. By subjecting the film to rapid cooling so that the temperature of the film becomes 120 ° C. or lower, it is possible to suppress the breakage of the film.

(5) Control of transverse stretching conditions In the production of a film by the longitudinal-lateral stretching method of the present invention, it is preferable to transversely stretch the film after longitudinal stretching, intermediate heat treatment, and rapid cooling under predetermined conditions. That is, the transverse stretching is performed so that the magnification is 2.0 times or more and 6.0 times or less at a temperature of Tg + 10 ° C. or more and Tg + 40 ° C. or less in a state where both ends in the width direction are held by clips in the tenter. preferable. By performing transverse stretching under such predetermined conditions, the molecules are oriented in the width direction while maintaining the “molecules that do not contribute to the shrinkage force while being oriented in the longitudinal direction” formed by longitudinal stretching and intermediate heat treatment. Thus, it is possible to obtain a film having good perforation opening properties when used as a label. Further, by adopting the longitudinal-transverse stretching method, it is possible to give a larger area stretch ratio than a heat-shrinkable film having a simple uniaxially stretched cavity, and to further improve perforation opening. This improvement in perforation opening shows a good correspondence with a decrease in right-angled tear strength. The lower limit of the transverse stretching temperature is preferably Tg + 15 ° C. or more, and more preferably Tg + 20 ° C. or more. Moreover, the upper limit of the temperature of transverse stretching is preferably Tg + 35 ° C. or less, and more preferably Tg + 30 ° C. or less. On the other hand, the lower limit of the transverse stretching ratio is preferably 2.5 times or more, and more preferably 3.0 times or more. Further, the upper limit of the transverse stretching ratio is preferably 5.5 times or less, and more preferably 5.0 times or less. Adopting the longitudinal-transverse stretching method and making the area stretch ratio larger than that of the conventional uniaxial stretching method is preferable from the viewpoint of obtaining a smaller apparent density.

  When stretching in the transverse direction as described above, if the stretching temperature is increased when stretching in the transverse direction, the tensile strength in the longitudinal direction increases, the perpendicular tearing strength in the longitudinal direction decreases, and the label is formed. The perforation openability is improved.

  Further, when the stretching temperature exceeds Tg + 40 ° C., the shrinkage rate in the longitudinal direction becomes high and the shrinkage rate in the width direction becomes low. By controlling the stretching temperature to Tg + 40 ° C. or less, the shrinkage rate in the longitudinal direction Can be kept low, and the shrinkage rate in the width direction can be kept high.

  Further, when the stretching temperature in the lateral stretching increases, the lateral orientation decreases, the solvent adhesive strength increases, the crushing of the lubricant can be prevented, and the friction coefficient can be kept low.

  Further, when the stretching temperature exceeds Tg + 40 ° C., the thickness variation in the width direction tends to increase, but by controlling the stretching temperature to Tg + 40 ° C. or less, the thickness variation in the width direction can be reduced.

  On the other hand, when the stretching temperature is lower than Tg + 10 ° C., the orientation in the width direction becomes too high, and it becomes easy to break at the time of transverse stretching, or the slit property when the film after biaxial stretching is finally wound on a roll. Although it becomes worse, by controlling the stretching temperature to Tg + 10 ° C. or higher, it is possible to reduce the fracture during transverse stretching and improve the slit property during winding.

[Effects of manufacturing process interaction on film properties]
In the production of the white heat-shrinkable polyester film of the present invention, only one of the longitudinal stretching step, intermediate heat treatment step, natural cooling step, forced cooling step, and transverse stretching step is a film alone. However, it is extremely efficient by performing all of the longitudinal stretching process, intermediate heat treatment process, natural cooling process, forced cooling process, and transverse stretching process under predetermined conditions. Further, it is considered that the film characteristics can be improved. In addition, among the characteristics of the film, important characteristics such as longitudinal tear strength in the longitudinal direction, tensile fracture strength in the longitudinal direction, thickness variation in the width direction, dynamic friction coefficient, thickness variation in the longitudinal direction are The value fluctuates greatly depending on the interaction.

  That is, the white heat-shrinkable polyester film of the present invention adjusts the perpendicular tear strength in the longitudinal direction to 90 N / mm or more and 200 N / mm or less, more preferably 130 N / mm or more and 180 N / mm or less. The interaction between the longitudinal stretching process and the intermediate heat treatment process has a great influence on the perpendicular tear strength in the longitudinal direction. Moreover, if a cavity is made by increasing the amount of additives in the resin as described above, the right-angled tear strength in the longitudinal direction can be adjusted small.

  Further, the white heat-shrinkable polyester film of the present invention preferably has a tensile strength in the longitudinal direction adjusted to 100 MPa or more and 250 MPa or less. The interaction of the three processes, the heat treatment process and the transverse stretching process, has a great influence.

  Further, the white heat-shrinkable polyester film of the present invention is preferably adjusted to have a thickness variation in the width direction of 1.0% or more and 12.0% or less. The interaction of the three processes, the heat treatment process and the transverse stretching process, has a great influence.

  In addition, the white heat-shrinkable polyester film of the present invention is preferably adjusted to have a dynamic friction coefficient of 0.1 or more and 0.55 or less, but the dynamic friction coefficient has an interaction between the longitudinal stretching step and the intermediate heat treatment step. It has a huge impact.

  The white heat-shrinkable polyester film of the present invention is preferably adjusted to have a thickness variation in the longitudinal direction of 1.0% or more and 12.0% or less. The interaction with the heat treatment process has a great influence.

  Therefore, in order to adjust the right-angled tear strength in the longitudinal direction of the white heat-shrinkable polyester film, the tensile fracture strength, the thickness variation in the width direction, the dynamic friction coefficient, and the thickness variation in the longitudinal direction within the scope of the present invention, as described above. It is preferable to perform delicate condition adjustments as described in the above (1) to (5) while considering the interaction between the processes.

  The package of the present invention is formed by heat-shrinking at least a part of the outer periphery with a label provided with perforations based on the polyester film as a base material. Examples include plastic bottles for beverages, various bottles, cans, plastic containers such as confectionery and lunch boxes, paper boxes, and the like (hereinafter collectively referred to as packaging objects). In general, when a label based on a white heat-shrinkable polyester film is coated on these packaging objects by heat-shrinking, the label is heat-shrinked by about 2 to 15%. Adhere to. In addition, printing may be given to the label coat | covered with a packaging target object, and it does not need to be printed.

  The label can be made by applying an organic solvent slightly inside from the edge of one side of the rectangular film, and immediately rolling the film and bonding the edges together to form a label, or roll Apply the organic solvent slightly inside from the edge of one side of the film wound up in the shape of a film, immediately roll up the film, overlap the edges and adhere, cut the tube to make a label . As the organic solvent for adhesion, cyclic ethers such as 1,3-dioxolane or tetrahydrofuran are preferable. In addition, aromatic hydrocarbons such as benzene, toluene, xylene and trimethylbenzene, halogenated hydrocarbons such as methylene chloride and chloroform, phenols such as phenol, and mixtures thereof can be used.

  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.

  The evaluation method of the film is as follows.

[Thermal shrinkage (hot water thermal shrinkage)]
The film is cut into a 10 cm × 10 cm square, heat-shrinked by treatment in warm water at a predetermined temperature ± 0.5 ° C. for 10 seconds under no load condition, and then measured in the vertical and horizontal dimensions of the film. According to the following formula 1, the thermal shrinkage rate was obtained. The direction in which the heat shrinkage rate is large was taken as the main shrinkage direction.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%)
... Formula 1

[Maximum heat shrinkage stress value]
The stretched film was cut into a size of main shrinkage direction (width direction) × direction perpendicular to the main shrinkage direction (longitudinal direction) = 200 mm × 15 mm. Then, after adjusting Baldwin's universal tensile testing machine STM-50 to a temperature of 90 ° C., the cut film was set, and the stress value in the main shrinkage direction when held for 10 seconds was measured.

[Measurement method of right-angle tear strength]
The film is shrunk 10% in the width direction in hot water adjusted to 80 ° C., and then sampled as a test piece of a predetermined size according to JIS-K-7128. Thereafter, both ends of the test piece are gripped with a universal tensile tester, and the strength at the time of tensile fracture in the longitudinal direction of the film is measured under the condition of a tensile speed of 200 mm / min. Then, the right angle tear strength per unit thickness is calculated using the following equation 2.
Right angle tear strength = strength at tensile failure ÷ thickness ・ ・ ・ Equation 2

[Tensile fracture strength]
In accordance with JIS-K7113, a strip-shaped test piece of a predetermined size is prepared, and both ends of the test piece are gripped by a universal tensile tester, and a tensile test is performed under a condition of a tensile speed of 200 mm / min. The strength (stress) at the time of tensile fracture in the longitudinal direction of the film was calculated as tensile fracture strength.

[Whiteness]
Whiteness was performed using Nippon Denshoku Industries Co., Ltd. Z-1001DP according to the JIS-L1015-1981 method.

[Total light transmittance]
The total light transmittance was calculated | required by Nippon Denshoku Industries Co., Ltd. product NDH-1001DP.

[Thickness unevenness in the width direction]
The film was sampled into a wide band with a length of 40 mm and a width of 1.2 m, and was measured in the width direction of the film sample at a speed of 5 (m / min) using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. The thickness was continuously measured along (measurement length was 500 mm). The maximum thickness at the time of measurement was Tmax., The minimum thickness was Tmin., The average thickness was Tave.
Thickness unevenness = {(Tmax.−Tmin.) / Tave.} × 100 (%) Expression 3

[Longitudinal thickness unevenness]
The film was sampled into a long roll of 12 m long × 40 mm wide, and along the longitudinal direction of the film sample at a speed of 5 (m / min) using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. The thickness was continuously measured (measurement length was 10 m). The maximum thickness at the time of measurement was Tmax., The minimum thickness was Tmin., And the average thickness was Tave.

[Solvent adhesive strength]
Sealing was performed by applying 1,3-dioxolane to the stretched film and bonding the two together. Thereafter, the seal portion is cut to a width of 15 mm in a direction orthogonal to the main shrinkage direction of the film (hereinafter referred to as the orthogonal direction), and set in a universal tension tester STM-50 manufactured by Baldwin Co., Ltd. A 180 ° peel test was performed at 200 mm / min. And the tensile strength at that time was made into solvent adhesive strength.

[Dynamic friction coefficient]
Based on JIS K-7125, the dynamic friction coefficient (micro | micron | mu) d at the time of joining the surface of a film and a back surface was calculated | required in 23 degreeC and 65% RH environment using the tensile tester (ORIENTEC company make Tensilon). The weight of the thread (weight) wound with the upper film was 1.5 kg, and the size of the bottom area of the thread was 63 mm long × 63 mm wide. In addition, the tensile speed at the time of friction measurement is 200 mm / min. Met.

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

[Apparent density of film]
Four films were cut into 5.0 cm squares and used as samples. Four samples of this sample were overlapped, and the total thickness was measured at 10 points using a micrometer with four significant figures, and the average value of the total thickness was determined. The average value was divided by 4 and rounded to 3 significant figures to obtain an average thickness t (μm) per sheet. The mass w (g) of the four samples was measured using an automatic upper balance with four significant digits, and the apparent density was calculated from the following equation 4. The apparent density was rounded to 3 significant figures.
Apparent density (g / cm ³ ) = w / (5.0 × 5.0 × t × 10 ⁻⁴ × 4)
= W × 100 / t Equation 4

[Molecular orientation ratio]
A sample of the film in the longitudinal direction × width direction = 140 mm × 100 mm was taken. And about the sample, molecular orientation ratio (MOR) was measured using the molecular orientation angle measuring apparatus (MOA-6004) by Oji Scientific Instruments.

[Shrink finish]
The heat-shrinkable film was preliminarily printed in three colors with grass, gold, and white ink from Toyo Ink Manufacturing Co., Ltd. And the both ends of the printed film were adhere | attached with the dioxolane, and the cylindrical label (The label which made the main shrink direction of the heat-shrinkable film the circumferential direction) was created. After that, using a Fuji Astec Inc steam tunnel (model: SH-1500-L), a 500 ml PET bottle with a transit time of 2.5 seconds and a zone temperature of 80 ° C. (body diameter 62 mm, minimum neck diameter 25 mm) The label was attached by heat shrinking. At the time of mounting, the neck portion was adjusted so that a portion with a diameter of 40 mm was one end of the label. The finish after shrinkage was evaluated visually, and the criteria were as follows.
◎: No wrinkles, jumping up, insufficient shrinkage, and no color spots are observed ○: Wrinkles, jumping up, or insufficient shrinkage cannot be confirmed, but some color spots are seen △: Jumping Neither ascending nor insufficient shrinkage has occurred, but spots on the neck are observed. ×: Wrinkles, jumping up, insufficient shrinkage occurred

[Label adhesion]
The label was attached under the same conditions as those described above for measuring shrinkage finish. Then, when the attached label and the PET bottle were lightly twisted, it was evaluated as “◯” if the label did not move, or “x” if it slipped through or the label and the bottle were displaced.

[Perforation opening]
A label having a perforation in a direction perpendicular to the main shrinkage direction in advance was attached to a PET bottle under the same conditions as those for measuring the shrinkage finish. However, the perforations were formed by putting holes having a length of 1 mm at intervals of 1 mm, and two perforations were provided in the longitudinal direction (height direction) of the label over a width of 22 mm and a length of 120 mm. The bottle is then filled with 500 ml of water, refrigerated to 5 ° C., tearing the perforation of the bottle label immediately after removal from the refrigerator with the fingertips, tearing it cleanly along the perforation in the vertical direction, and removing the label from the bottle The number that could be removed was counted, and the ratio (%) to 50 samples was calculated.

  Tables 1 and 2 show the properties, compositions, examples, and film production conditions (stretching / heat treatment conditions, etc.) of the polyester raw materials used in the examples and comparative examples, respectively.

<Preparation of polyester raw material>
In a stainless steel autoclave equipped with a stirrer, thermometer and partial reflux condenser, 100 mol% of dimethyl terephthalate (DMT) as a dibasic acid component and 100 mol% of ethylene glycol (EG) as a glycol component Was added to the molar ratio of 2.2 times that of the methyl ester, and 0.05 mol% of zinc acetate (based on the acid component) was used as the transesterification catalyst, and the methanol produced was distilled off the system. The transesterification reaction was carried out. Thereafter, 0.025 mol% of antimony trioxide (based on the acid component) was added as a polycondensation catalyst, and a polycondensation reaction was performed at 280 ° C. under a reduced pressure of 26.6 Pa (0.2 Torr). Polyester A of 70 dl / g was obtained. This polyester is polyethylene terephthalate. Further, polyesters (B, C, D) shown in Table 1 were synthesized by the same method as described above. In the table, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and BD is 1,4-butanediol. The intrinsic viscosity of each polyester was 0.72 dl / g for B, 0.80 dl / g for C, and 1.15 dl / g for D. Each polyester was appropriately formed into a chip shape.

[Example 1]
The above-mentioned polyester A, polyester B, and polyester D were mixed at a weight ratio of 10:80:10 to obtain a raw material for the Y layer. The raw material for the X layer is the same as described above, when polyester A, polyester B and polyester D are mixed at a weight ratio of 10:80:10, and further 10% by weight of polystyrene resin (G797N made by Nippon Polystyrene) and titanium dioxide (TA-300 made by Fuji Titanium). ) 10 wt% was added and mixed. The raw materials of the X layer and Y layer are put into separate twin screw extruders, mixed, melted and joined together with a feed block, melt extruded at 280 ° C from a T-die, and cooled to a surface temperature of 30 ° C. The film was wound around a rotating metal roll and rapidly cooled to obtain an unstretched film having a thickness of 484 μm and a Y / X / Y laminated structure (Y / X / Y = 121 μm / 242 μm / 121 μm). At this time, the take-up speed of the unstretched film (rotational speed of the metal roll) is about 20 m / min. Met. Moreover, Tg of the unstretched film was 67 degreeC.

  Then, the unstretched film obtained as described above was led to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, and stretched in two stages in the longitudinal direction using a difference in the rotational speed of the rolls. That is, after preheating an unstretched film on a preheating roll until the film temperature reaches 78 ° C., a low-speed rotating roll set at a surface temperature of 78 ° C. and a medium-speed rotating roll set at a surface temperature of 78 ° C. The film was stretched 2.6 times using the rotational speed difference (first-stage longitudinal stretching). Further, the longitudinally stretched film is longitudinally stretched 1.4 times using a rotational speed difference between a medium-speed rotating roll set at a surface temperature of 95 ° C. and a high-speed rotating roll set at a surface temperature of 30 ° C. Stretched (second-stage longitudinal stretching) (therefore, the total longitudinal stretching ratio was 3.64 times).

  As described above, the film immediately after the longitudinal stretching is forcibly cooled at a cooling rate of 40 ° C./second by a cooling roll set at a surface temperature of 30 ° C. (a high-speed roll positioned immediately after the second-stage longitudinal stretching roll). After that, the cooled film is guided to the tenter, and the intermediate heat treatment zone, the first intermediate zone (natural cooling zone), the cooling zone (forced cooling zone), the second intermediate zone, the transverse stretching zone, and the final heat treatment zone are continuously formed. I let it pass. In the tenter, the length of the first intermediate zone is set to about 40 cm, between the intermediate heat treatment zone and the first intermediate zone, between the first intermediate zone and the cooling zone, and between the cooling zone and the second intermediate zone. Shielding plates were provided between the intermediate zone and between the second intermediate zone and the transverse stretching zone, respectively. Further, in the first intermediate zone and the second intermediate zone, when the strip-shaped paper piece is hung in a state where the film is not passed through, the paper piece from the intermediate heat treatment zone is almost completely hung down in the vertical direction. Hot air, cooling air from the cooling zone, and hot air from the transverse stretching zone were blocked. In addition, when passing the film, the film and the shielding plate are arranged so that most of the accompanying flow accompanying the film flow is blocked by the shielding plate provided between the intermediate heat treatment zone and the first intermediate zone. Adjusted the distance. In addition, when passing the film, most of the accompanying flow accompanying the film flow is blocked by the shielding plate at the boundary between the intermediate heat treatment zone and the first intermediate zone and at the boundary between the cooling zone and the second intermediate zone. The distance between the film and the shielding plate was adjusted so as to be blocked.

  Then, the longitudinally stretched film led to the tenter is first heat treated at a temperature of 160 ° C. for 5.0 seconds in the intermediate heat treatment zone, and then the film after the intermediate heat treatment is led to the first intermediate zone. Natural cooling was achieved by passing through the zone (passing time = approximately 1.0 second). After that, the film after natural cooling is guided to the cooling zone, and is actively cooled by blowing low temperature air until the surface temperature of the film reaches 100 ° C., and the cooled film is guided to the second intermediate zone. Then, it was naturally cooled again by passing through the zone (passing time = about 1.0 second). Further, the film after passing through the second intermediate zone is guided to the transverse stretching zone, preheated until the surface temperature of the film reaches 95 ° C., and then 4.0 times in the width direction (lateral direction) at 95 ° C. Stretched.

  Thereafter, the laterally stretched film is guided to the final heat treatment zone, where it is heat treated at a temperature of 85 ° C. for 5.0 seconds and then cooled, and both edges are cut and removed to obtain a width of 500 mm. The biaxially stretched film of about 40 μm was continuously produced over a predetermined length by winding in a roll. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3.

[Example 2]
In Example 1, white heat shrinkage was performed in the same manner as in Example 1 except that 10% by weight of the polystyrene resin added to the raw material of the X layer was changed to 10% by weight of crystalline polypropylene resin (FO-50F ground polymer). Film was continuously produced. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3. It was a good film as in Example 1.

[Example 3]
The polyester A, polyester B, polyester C, and polyester D described above were mixed so that the weight ratio was 10: 15: 65: 10 to obtain the raw material polyester of the X layer and the Y layer, and each was put into an extruder. . At the time of mixing, 10% by weight of polystyrene resin (G797N manufactured by Nippon Polystyrene) and 10% by weight of titanium dioxide (TA-300 manufactured by Fuji Titanium) were added to the X layer raw material in the same manner as in Example 1. Thereafter, each of the mixed resins was melt extruded under the same conditions as in Example 1 to form an unstretched film. The Tg of the unstretched film was 67 ° C. By forming the unstretched film under the same conditions as in Example 1, a biaxially stretched film of about 40 μm was continuously produced with a width of 500 mm. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 4]
The above polyester A, polyester C, and polyester D were mixed so that the weight ratio was 10:80:10 to obtain raw material polyesters for the X layer and the Y layer, and each was put into an extruder. At the time of mixing, 10% by weight of polystyrene resin (G797N manufactured by Nippon Polystyrene) and 10% by weight of titanium dioxide (TA-300 manufactured by Fuji Titanium) were added to the X layer raw material in the same manner as in Example 1. Thereafter, each of the mixed resins was melt extruded under the same conditions as in Example 1 to form an unstretched film. The Tg of the unstretched film was 67 ° C. By forming the unstretched film under the same conditions as in Example 1, a biaxially stretched film of about 40 μm was continuously produced with a width of 500 mm. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 5]
Example 1 except that the amount of discharge was adjusted to Example 1 and the film thickness was changed to an unstretched film (Y / X / Y = 133 μm / 266 μm / 133 μm) having a film thickness of 532 μm and a Y / X / Y laminated structure In the same manner as in Example 1, an unstretched film was obtained. The unstretched film was subjected to a first stage longitudinal stretching ratio of 2.9 times, and the total longitudinal stretching ratio was changed to 4.06 times, and at an intermediate heat treatment zone at a temperature of 170 ° C. for 8.0 seconds. A biaxially stretched film having a thickness of about 40 μm was continuously produced with a width of 500 mm by forming a film under the same conditions as in Example 1 except that the heat treatment was performed. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 6]
An unstretched film (Y / X / Y = 100 μm / 200 μm / 100 μm) was obtained in the same manner as in Example 1, except that the film thickness was 400 μm and a Y / X / Y laminated structure was obtained. A stretched film was obtained. Example 1 except that the unstretched film was heat-treated at a temperature of 155 ° C. in an intermediate heat treatment zone by changing the first-stage longitudinal stretch ratio to 2.2 times and changing the total longitudinal stretch ratio to 2.94 times. A biaxially stretched film having a thickness of about 40 μm was continuously produced with a width of 500 mm. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 7]
By forming a film under the same conditions as in Example 1 except that the amount of addition of titanium dioxide (TA-300 Fuji Titanium) in the X layer is changed to 14% by weight with respect to Example 1, a film thickness of about 40 μm is obtained. An axially stretched film was continuously produced with a width of 500 mm. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Comparative Example 1]
When the same polyester raw material as in Example 1 is melt-extruded in the same manner as in Example 1, an unstretched film having a thickness of 480 μm and a Y / X / Y laminated structure (Y / X / Y = 120 μm / 240 μm) / 120 μm), the discharge amount of the extruder was adjusted. Other than that was carried out similarly to Example 1, and obtained the unstretched film. Then, the unstretched film is vertically increased by a factor of 3.7 using a rotational speed difference between a medium-speed rotating roll set at a surface temperature of 82 ° C and a high-speed rotating roll set at a surface temperature of 30 ° C. Stretched. Thereafter, the film was subjected to natural cooling, forced cooling, transverse stretching, and final heat treatment as in Example 1 except that a temperature of 125 ° C. was applied by an intermediate heat treatment, and about 40 μm was obtained by cutting and removing both edges. The biaxially stretched film was continuously produced with a width of 500 mm. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Comparative Example 2]
An unstretched film (Y / X / Y = 36 μm / 72 μm / 36 μm) having a Y / X / Y laminated structure with a film thickness of 144 μm obtained in the same manner as in Example 1 except that the discharge amount was changed, After preheating until the surface temperature of the film reached 75 ° C., the film was stretched uniaxially at 75 ° C. in the width direction (lateral direction) 4.0 times. Thereafter, the laterally stretched film is guided to the final heat treatment zone, where it is heat treated at a temperature of 85 ° C. for 5.0 seconds and then cooled, and both edges are cut and removed to obtain a width of 500 mm. The film was rolled into a roll shape to continuously produce a laterally uniaxially stretched film having a thickness of about 40 μm over a predetermined length. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

  As is clear from Table 3, the films obtained in Examples 1 to 7 all have high shrinkage in the width direction, which is the main shrinkage direction, and the shrinkage in the longitudinal direction perpendicular to the main shrinkage direction is high. It was very low. In addition, the films obtained in Examples 1 to 7 all have sufficient light-cutting properties, high solvent adhesive strength, small longitudinal thickness unevenness, and label adhesion when used as labels. It was good, no shrinkage spots were seen, and the perforation openability was good. Furthermore, wrinkles did not occur in the film rolls obtained in Examples 1 to 7. That is, all of the white heat-shrinkable polyester films obtained in the examples had high label quality and were extremely practical.

  On the other hand, the heat-shrinkable film obtained in Comparative Example 1 had a high heat shrinkage rate in the longitudinal direction, and shrinkage spots occurred when used as a label. Further, since the film obtained in Comparative Example 2 has a large molecular orientation ratio (MOR), the right-angle tear strength is large, the tensile fracture strength in the orthogonal direction (longitudinal direction) is small, and the perforation openability is not good. It was. That is, the heat-shrinkable polyester film obtained in the comparative example was inferior in quality as a label and low in practicality.

  Since the white heat-shrinkable polyester film of the present invention has excellent properties such as perforation cutability, light cutability, and light weight, it can be suitably used for labeling bottles.

  F ・ ・ Film

Claims (10)

The following requirements (1) to (5 ) comprising a polyester-based resin containing ethylene terephthalate as a main constituent and containing at least 15 mol% of at least one monomer component that can be an amorphous component in all polyester resin components. A white heat-shrinkable polyester-based film that continuously includes the following steps (a) to (f): Production method.
(1) The hot-water heat shrinkage in the width direction when treated in warm water at 90 ° C. for 10 seconds is 40% or more and 80% or less.
(2) The hot water thermal contraction rate in the longitudinal direction when treated in hot water at 90 ° C. for 10 seconds is from 0% to 15%.
(3) The perpendicular tear strength in the longitudinal direction per unit thickness after shrinking in the width direction by 10% in warm water at 80 ° C. is 90 N / mm or more and 200 N / mm or less.
(4) The tensile fracture strength in the longitudinal direction is 100 MPa or more and 250 MPa or less. ( 5 ) It has a Y layer having fewer cavities than the X layer on at least one side of the X layer having many cavities inside, and has a whiteness. (A) An unstretched film is stretched at a magnification of 2.2 times or more and 3.0 times or less in the longitudinal direction at a temperature of Tg or more and Tg + 30 ° C., and then at a temperature of Tg + 10 ° C. or more and Tg + 40 ° C. or less. Longitudinal stretching step (b) Longitudinal stretching in which the film is stretched at a magnification of 1.2 to 1.5 times in the longitudinal direction so that the total magnification is 2.8 to 4.5 times. An intermediate heat treatment step in which the subsequent film is heat-treated at a temperature of 130 ° C. or higher and 190 ° C. or lower for a time of 1.0 second or more and 9.0 seconds or less in a state where both ends in the width direction are held by clips in the tenter. c) Intermediate heat treatment The natural cooling process in which the film is naturally cooled by passing through an intermediate zone that is shielded from the front and rear zones and does not perform an active heating operation. (D) The surface temperature of the film after natural cooling is 80 ° C. Active cooling step of actively cooling until reaching a temperature of 120 ° C. or lower (e) The film after the active cooling is 2.0 times or higher and 6.0 times or lower in the width direction at a temperature of Tg + 10 ° C. or higher and Tg + 40 ° C. or lower. Transverse stretching step of stretching at a magnification (f) 1.0 to 9.0 seconds at a temperature of 80 ° C. or higher and 100 ° C. or lower with the film after the horizontal stretching held in the tenter by clips at both ends in the width direction Final heat treatment process for heat treatment for the following time 2. The method for producing a white heat-shrinkable polyester film according to claim 1 , wherein the shrinkage stress in the width direction when heated to 90 ° C. is 3 MPa or more and 15 MPa or less. 3. The method for producing a white heat-shrinkable polyester film according to claim 1, wherein thickness unevenness in the width direction is 1.0% or more and 12.0% or less. The method for producing a white heat-shrinkable polyester film according to any one of claims 1 to 3 , wherein the thickness unevenness in the longitudinal direction is 1.0% or more and 12.0% or less. Method for producing a white heat-shrinkable polyester film according to any one of claims 1 to 4, solvent adhesive strength is equal to or less than 2N / 15 mm width or higher 15N / 15 mm width. The method for producing a white heat-shrinkable polyester film according to any one of claims 1 to 5 , wherein a coefficient of dynamic friction is 0.1 or more and 0.55 or less. Main component of the monomer that can be the amorphous component in the whole Porisuteru resin component is, neopentyl glycol, 1,4-cyclohexanedimethanol, according to claim 1-6, characterized in that either of the isophthalic acid The manufacturing method of the white heat-shrinkable polyester film in any one. Method for producing a white heat-shrinkable polyester film according to any one of claims 1 to 7, an apparent density is equal to or is 1.2 g / cm ³ or less. A white heat-shrinkable polyester film produced by the method for producing a white heat-shrinkable polyester film according to any one of claims 1 to 8 . A package comprising the white heat-shrinkable polyester film according to claim 9 as a base material, and a heat-shrinkable covering at least part of the outer periphery with a perforation or a label provided with a pair of notches. body.