JP6519720B2 - White heat-shrinkable polyester film - Google Patents

Description

  The present invention relates to a white heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film suitable for label applications. More specifically, the present invention relates to a white heat-shrinkable polyester film which is for a plastic bottle label and can have a beautiful appearance without curling or the like when the label is shrunk into the plastic bottle.

  As a heat-shrinkable film, particularly a heat-shrinkable film for a label of a bottle barrel, a film made of polyvinyl chloride, polystyrene or the like is mainly used. However, polyvinyl chloride has recently been associated with problems such as generation of chlorine-based gas when incinerated at the time of disposal, and polystyrene has problems such as difficulty in printing. Films have attracted attention. However, polyester films have a heavy specific gravity of about 1.4. Moreover, since a general heat-shrinkable polyester film is transparent, it has a high light transmittance and is not suitable for protection of contents. Therefore, there is a great demand for a white heat-shrinkable polyester film in which the specific gravity is reduced and the light transmittance is reduced by forming a cavity.

  Therefore, white heat-shrinkable polyester films have been studied. The method (patent document 1) of mixing an incompatible thermoplastic resin in the main raw material of a heat-shrinkable polyester film is proposed.

JP 2002-36356 A

  According to the method of mixing a thermoplastic resin immiscible with polyester in the main material of the heat-shrinkable polyester film described in Patent Document 1 described above, the thermoplastic resin immiscible with polyester is mixed into the main material As a result, a white heat-shrinkable polyester film can be formed, and the apparent specific gravity can be made less than 1.00 by increasing the proportion of the thermoplastic resin incompatible with the polyester. Also, it is described that there is no problem in printing by turning the non-foamed layer to the outside.

In recent years, production has been generally increased by increasing speed for cost and efficiency. In uniaxial stretching in the width direction, which is a general method for producing heat-shrinkable polyester films, in order to accelerate, it is necessary to increase the speed in the process of solidifying the molten resin discharged from the die in the extrusion process with a cooling roll. There is.
However, when the solidification speed of the cooling roll is increased, the difference in the cooling speed is increased in the surface not in contact with the surface in contact with the cooling roll. As a result, there is a problem that the film as a product curls.

  Further, in the layer configuration of three or more layers including the foam layer (void-containing layer) and the non-foam layer (non-void-containing layer), the shrinkage behavior at the time of heat contraction between the foam layer and the non-foam layer is different. The foamed layer generally has a slower shrinking speed because foaming inhibits shrinkage, and the non-foamed layer has a faster shrinking speed than the foamed layer. Therefore, if the shrinkage behavior of the non-foamed layers on both sides in the film thickness direction is different, wrinkles and the like are likely to occur at the time of shrinkage finishing, which is not preferable. Therefore, in order to reduce the contraction speed difference between the two outer sides, it is desirable that the difference between the non-foamed layers on both the outer sides be small. For this purpose, it is desirable that the thickness difference between the non-foamed layers on both sides be small, the difference in the degree of crystallization such as density be small, and the deviation of the raw material composition be small.

  In addition, since the white heat-shrinkable polyester film has a low light transmittance and is excellent in shielding properties, it is possible to protect the contents, for example, by covering the entire container with a PET bottle for beverage. Therefore, there is a demand for a film having a high shrinkage rate to cover the entire container. As described above, when the shrinkage rate is high, the shrinkage speed difference between the non-foamed layers on both sides of the film becomes important in order to finish shrinking the appearance well.

  The object of the present invention is to solve the problems of the above-mentioned conventional white heat-shrinkable polyester-based film, to enable high-speed production, and to produce white heat-shrinkability having good shrinkage finish without causing curling due to heat contraction. It is in providing a polyester-type film.

MEANS TO SOLVE THE PROBLEM The present inventors came to complete this invention, as a result of earnestly examining, in order to solve said subject. That is, the present invention comprises the following constitution.
The first invention of the present invention is a white heat-shrinkable material comprising at least one polyester-based resin layer having titanium oxide particles and at least two layers sandwiching at least the titanium oxide particle-containing layer. It is a polyester-type film, Comprising: It is a white heat-shrinkable heat-shrinkable polyester-type film characterized by satisfy | filling the following requirements (1)-(7).
(1) Thermal contraction rate in the main shrinkage direction by hot water treatment at a treatment temperature of 90 ° C. and treatment time of 10 seconds is 30% or more and 85% or less (2) The gloss of both sides of the film measured at an angle of 60 ° is 40 % And 150% or less (3) thickness difference of both outermost layers of film is 2 μm or less (4) Both thickness of both outermost layers of film are 3 μm or more and 12 μm or less (5) density difference of both outermost layers of film is 0. 005 g / cm ³ or less (6) The difference in the number of moles of noncrystalline components in both outermost layers of the film is 1 mol% or less (7) light transmittance is 40% or less It is a white heat-shrinkable polyester film according to the first invention, wherein the maximum value of the heat-shrink stress is 9 MPa or less.
A third invention of the present invention is the white heat-shrinkable polyester system according to any one of the first to second inventions characterized in that the solvent adhesive strength is 2N / 15 mm width or more and 10N / 15 mm width or less. It is a film.
A fourth invention of the present application is a heat-shrinkable label using the white heat-shrinkable polyester film according to any of the first to third inventions.
A fifth invention of the present application is a package in which the heat-shrinkable label of the fourth invention is coated on at least a part of the outer periphery of the object to be packaged.
The sixth invention of the present application is the process according to any one of the first to third inventions of actively cooling both outermost layers to reduce the density difference between both outer layers in the step of producing an unstretched film from a molten resin. It is a manufacturing method of a white heat-shrinkable polyester film.
In the seventh invention of the present application, as a method of positively cooling both outermost layers in the step of producing an unstretched film from a molten resin, the layer on one side is cooled by a cooling roll and the layer on the other side has a longitudinal wind speed difference Manufacturing the white heat-shrinkable polyester film of any one of the first to third inventions, wherein cooling is performed by applying a cooling air using an apparatus adjusted to have a wind speed difference of 1 m / sec or less It is a method.

The white heat-shrinkable polyester film of the present invention has high shrinkability in the width direction, which is the main shrink direction, and good shrink finish when forming into a label. In addition, when forming a non-oriented film, it is possible to make the difference in thickness and density between both layers on the outer side of the film and the difference between noncrystalline materials small, and to make the shrinkage finish after drawing good.
Usually, when the laminated structure is extruded and solidified at a high speed by a cooling roll, the difference in density (difference in crystallinity) of the outer layer of the non-foamed layer contributing to the shrinkage finish differs and the shrinkage behavior differs and the shrinkage finish worsens. In particular, such problems are likely to occur because, in recent years, the solidification speed of the cooling roll has become faster due to an increase in production amount (production at increased speed) for the purpose of cost reduction and the like. In the present invention, when producing a white heat-shrinkable polyester film at high speed, it is possible to reduce the difference in density between both outer non-foamed layers of the non-oriented film. As a result, good shrink finish is obtained, and it is possible to obtain a beautiful appearance when it is used as a PET container label.
Therefore, according to the present invention, it is possible to provide a white heat-shrinkable polyester film capable of high-speed production, having no heat-shrinkage and no curling, and having good shrink finish and having good printability. Become.

  The white heat-shrinkable polyester film of the present invention is excellent in appearance, has a light ray-cut property without printing or processing, and has an excellent appearance even when printing is performed.

  In addition, the white heat-shrinkable polyester film of the present invention has high adhesion when the front and back (or the same surface) are adhered by a solvent. Therefore, it can be used suitably for various coated labels etc. including labels, such as a PET bottle.

The white heat-shrinkable heat-shrinkable polyester film of the present invention comprises at least one polyester-based resin layer containing titanium oxide particles and at least two layers sandwiching the titanium oxide particle-containing layer. It is a white heat-shrinkable polyester film which is characterized by satisfying the following requirements (1) to (7).
(1) Thermal contraction rate of 30% to 85% in the main shrinkage direction due to warm water treatment at a treatment temperature of 90 ° C and treatment time of 10 seconds (2) The gloss of the film measured at an angle of 60 degrees is 40% or more 150% or less (3) thickness difference of both outermost layers of the film is 2 μm or less (4) thickness of both outermost layers of the film is 3 μm or more and 12 μm or less (5) the density difference of both outermost layers of the film is 0.005 g / ( ³ ) The embodiment of the present invention will be specifically described in the case where the difference in the number of moles of amorphous components in both outermost layers of the (6) film is 1 mol% or less and (7) the light transmittance is 40% or less.

  In the heat-shrinkable polyester film of the present invention, a polyester composed of a dicarboxylic acid component and a polyvalent glycol component is melt-extruded from an extruder and cooled by a conductive cooling roll (such as a casting roll) to form a film Thus, the unstretched film can be obtained.

  The heat-shrinkable polyester film is formed into a film by cooling a polyester composed of a dicarboxylic acid component and a polyhydric glycol component from an extruder by melt extrusion, a conductive cooling roll (such as a casting roll). An unstretched film can be obtained.

In addition, in the case of the said extrusion, in order to provide a required heat-shrinkage characteristic to a film, copolyester is extruded independently, or several polyester (copolyester, homo polyester, etc.) is mixed and extruded. That is, the film is a second alcohol which gives the film a non-crystalline property different from that of the base unit (such as a crystalline unit such as polyethylene terephthalate) and the polyhydric glycol component (such as an ethylene glycol component) constituting the base unit. Contains ingredients. As a main acid component which comprises the said base unit, a terephthalic acid is preferable and ethylene glycol is preferable as a main diol component.
In addition, the content rate of the acid component of this invention and a diol component is a content rate with respect to the acid component of the whole polyester, and a diol component, when using 2 or more types of polyester in mixture. It does not matter whether transesterification has been done after mixing.

  Any of the above polyesters may be produced by polymerization by conventional methods. For example, the polyester can be obtained using a direct esterification method in which a dicarboxylic acid and a diol are directly reacted, and a transesterification method in which a dicarboxylic acid dimethyl ester and a diol are reacted. The polymerization may be carried out either batchwise or continuously.

  When a polyester-based film containing a second alcohol component other than ethylene glycol is stretched, a heat-shrinkable polyester-based film can be easily obtained.

  As the above-mentioned second alcohol component that imparts non-crystallinity, a diol component and a trivalent or higher alcohol component can be used. The diol component includes ethylene glycol, 1,3-propanediol, 1,4-butanediol, 2,2-diethyl-1,3-propanediol, 1,6-hexanediol, 3-methyl-1,5- Alkylene glycols such as pentanediol, 2-methyl-1,5-pentanediol, 1,9-nonanediol, 1,10-decanediol; cyclic alcohols such as 1,4-cyclohexanedimethanol; diethylene glycol, triethylene glycol, Ether glycols such as polypropylene glycol, polyoxytetramethylene glycol, and alkylene oxide adducts of bisphenol compounds or derivatives thereof; dimer diols and the like. Trihydric or higher alcohols include trimethylolpropane, glycerin, pentaerythritol and the like.

  The total amount of one or more monomer components that can be an amorphous component in 100 mol% of the polyhydric alcohol component in the entire polyester resin is preferably 14 mol% or more, and more preferably 16 mol% or more. In particular, it is preferably 18 mol% or more. Here, examples of the monomer which can be an amorphous component include neopentyl glycol and 1,4-cyclohexanediol.

  Further, in order to make the heat shrinkable polyester film particularly excellent in shrink finish and improve the shrink finish with a high heat shrinkage rate, the polyhydric alcohol component 100 in all the polyester resins as described above is used. The amount of neopentyl glycol or 1,4-cyclohexanedimethanol component in the mol% is preferably 14 mol% or more, more preferably 16 mol% or more, and particularly preferably 18 mol% or more. The upper limit of the component is not particularly limited, but if the amount of the component is too large, the heat shrinkage may be excessively high or the breakage resistance of the film may be deteriorated. Is preferably, 35 mol% or less is more preferable, and 30 mol% or less is particularly preferable.

In order to improve the shrinkage finish, the polyester elastomer content is preferably 3% by mass or more. Here, the polyester elastomer is a polyester block copolymer comprising, for example, a high melting point crystalline polyester segment (Tm 200 ° C. or higher) and a low melting point soft polymer segment (Tm 80 ° C. or lower) having a molecular weight of 400 or more, preferably 400 to 800. And polyester-based elastomers using a polylactone such as poly-.epsilon.-caprolactone as the low melting point soft polymer segment.
Moreover, it is possible to make shrinkage ratio of the direction orthogonal to the main shrinkage direction appropriate by making polyester elastomer into the said range and combining with the below-mentioned preferable manufacturing method and conditions.

  It is preferable not to contain an aliphatic linear diol having 8 or more carbon atoms (eg, octanediol etc.) or a polyhydric alcohol having 3 or more valences (eg, trimethylolpropane, trimethylolethane, glycerin, diglycerin etc.) . In the heat-shrinkable polyester-based film obtained by using a polyester containing such a diol or a polyhydric alcohol, it becomes difficult to secure the necessary contraction rate in the main contraction direction.

  Moreover, it is preferable not to contain diethylene glycol, triethylene glycol and polyethylene glycol as much as possible. In particular, diethylene glycol is easily present because of a by-product component during polyester polymerization, but in the polyester used in the present invention, the content of diethylene glycol is preferably less than 4 mol%.

  In the present invention, in order to adjust the total light transmittance of the film to a specific small range and to impart light ray cutting properties to the film, for example, particles of inorganic particles, organic particles, etc. On the other hand, 0.1 to 20% by mass, preferably 1 to 15% by mass is preferably contained. When the content of the particles is less than 0.1% by mass, for example, it is likely to be difficult to obtain sufficient light ray-cutting properties, which is not preferable. On the other hand, if it exceeds 20% by mass, for example, the film strength is lowered and the film formation tends to be difficult.

  The particles may be added before polyester polymerization, but are usually added after polyester polymerization. The inorganic particles to be added include, for example, kaolin, clay, calcium carbonate, silicon oxide, calcium tephthalate, aluminum oxide, titanium oxide, calcium phosphate, known inactive particles such as carbon black, and insoluble when melt-forming a polyester resin The high melting point organic compound, the cross-linked polymer, and the metal compound catalyst used at the time of polyester synthesis, for example, an alkali metal compound, an alkaline earth metal compound, etc. can be internal particles formed inside the polymer at the time of polyester production. Among these, titanium oxide particles are preferable from the viewpoint of imparting the required light ray-cutting property.

  The average particle size of the particles contained in the film is in the range of 0.001 to 3.5 μm. Here, the average particle size of the particles is measured by the Coulter counter method. The average particle diameter of the particles is preferably 0.001 μm or more and 3.5 μm or less, more preferably 0.005 μm or more and 3.0 μm or less. It is not preferable that the average particle diameter of the particles is less than 0.001 μm, for example, because it becomes difficult to obtain the required light ray-cut property. When the average particle diameter of the particles exceeds 3.5 μm, the smoothness of the film surface is inferior, and defects such as print defects are likely to occur, which is not preferable. The average particle size of the anatase form is generally 2.0 μm or less, and the average particle size of the rutile form is 2.0 μm or more. In order to conceal visible light, a particle diameter of 2.0 to 3.0 μm is the most efficient, and rutile titanium oxide generally has higher concealability than anatase.

  Titanium oxide particles are classified into crystal forms of anatase type and rutile type. Both are used for plastic kneading applications. Anatase is easy to cause yellowing and deterioration of resin due to direct sunlight etc. When used outdoors, the surface of titanium oxide is treated specially (alumina, silica, organic etc.) or rutile is selected. There are many.

  In the present invention, in order to make the apparent specific gravity of the entire film be less than 1.00, for example, it is preferable to contain fine cavities inside. For example, although a foam material or the like may be mixed and extruded, a preferable method is to obtain a cavity by mixing an incompatible thermoplastic resin in polyester and stretching in at least one axial direction. Specific examples of resins incompatible with polyester include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins.

  The content of the resin incompatible with polyester is preferably in the range of 5 to 30% by weight or less in terms of a film. If the amount of the incompatible resin is less than 5% by weight, for example, the amount of formation of voids in the film decreases, and the effect of lowering the apparent specific gravity tends to be insufficient, which is not preferable. When the incompatible resin exceeds 30% by weight, for example, kneading in the extrusion step tends to be uneven, and it is difficult to obtain a stable film, which is not preferable.

  Polystyrene-based resin refers to a thermoplastic resin containing polystyrene structure as a basic component, and homopolymers such as atactic polystyrene, syndiotactic polystyrene, isotactic polystyrene, and other components are grafted or block copolymerized. It includes a mixture of a modified resin, such as impact-resistant polystyrene resin and modified polyphenylene ether resin, and a thermoplastic resin compatible with these polystyrene resins, such as polyphenylene ether.

As polyolefin resin, cyclic polyolefin is preferable. As a cycloolefin unit of cyclic polyolefin resin, it is preferable to have norbornene and a tetracyclo dodecane unit. Moreover, it is preferable to have a non-cyclic olefin monomer unit as a copolymerization unit, Especially preferably, it is an ethylene unit. Particularly preferable cycloolefin copolymers are norbornene-ethylene copolymer and tetracyclododecane-ethylene copolymer. Among them, cyclic polyolefin resins containing 5 to 80% by weight, preferably 10 to 60% by weight of ethylene units are particularly preferable.

  The cyclic polyolefin resin usually has a glass transition temperature of -20 to 400 ° C, but the cyclic polyolefin resin used in the present invention needs to be 100 to 230 ° C, preferably 130 to 200 ° C. When the glass transition temperature is less than 100 ° C., Tg may be lower than the temperature at the time of unstretched film stretching, which is not preferable because it becomes difficult to foam at the time of film stretching. When the Tg is higher than 230 ° C., uniform mixing of the polymer in the extruder becomes difficult, and it becomes difficult to extrude the polymer mixture, for example, the film characteristics become nonuniform.

  In preparation of the polymer mixture formed by mixing the polyester and the incompatible resin, for example, chips of each resin may be mixed, melt-kneaded and extruded in an extruder, or both resins may be preliminarily mixed using a kneader The kneaded product may be further melt-extruded from an extruder. Further, in the step of polymerizing the polyester, a resin incompatible with the polyester such as a polystyrene resin may be added, and the chip obtained by stirring and dispersing may be melt extruded.

  The film in the present invention is preferably provided with an A layer substantially free of voids, in addition to the B layer containing a large number of fine voids inside. In order to make this configuration, different raw materials are charged into different extruders A and B, respectively, melted, bonded in a molten state in front of the T-die or inside the die, and cooled by a conductive cooling roll (casting roll etc.) By forming into a film, an unstretched film can be obtained.

The stretching is preferably uniaxial stretching, but may be biaxial stretching by stretching at a lower magnification in a direction different from the direction of the uniaxial stretching (film width direction). At this time, it is preferable not to contain an incompatible resin in the layer A as a raw material. By doing this, there is no void in layer A, and a film that can maintain the strength after printing can be obtained. In addition, since there is no cavity, the film does not weaken and becomes a film excellent in mounting properties.
In addition, since the formation of the cavity has an effect of reducing the contraction rate, the provision of the layer without the cavity can provide a high thermal contraction rate.

  Furthermore, in the film of the present invention, it is particularly preferable to use a B layer containing a large number of cavities inside as an intermediate layer, and provide both layers (both outermost layers) with a void-free A layer. By adding a polystyrene resin, smoke is generated during melt extrusion, which contaminates the process and causes the deterioration of operability. By making the layer B an intermediate layer, the problem of smoke is eliminated, and stable production for a long time can be implemented. In this case, the fact that the layer A is the surface layer (the outermost layer) also includes the case where the surface of the layer A is subjected to the corona treatment or coating treatment described later.

  Furthermore, if necessary, additives such as stabilizers, colorants, antioxidants, antifoaming agents, antistatic agents, UV absorbers and the like may be contained. In addition, a fluorescent whitening agent may be added to improve the whiteness of the film.

  The heat-shrinkable polyester film of the present invention desirably has an intrinsic viscosity of 0.60 dl / g or more. If the intrinsic viscosity of the heat-shrinkable film is too low, the molecular weight of the polyester constituting the film is lowered, so the durability of the shrinkage stress at the time of heat shrinkage decreases, and defects such as shrinkage whitening and shrinkage spots occur. It becomes easy, and it becomes inferior to shrinkage finish and appearance. In addition, when the molecular weight of the polyester decreases, the mechanical strength and tear resistance of the film are reduced.

  The intrinsic viscosity is preferably 0.60 dl / g or more, more preferably 0.63 dl / g or more.

  As a method of increasing the intrinsic viscosity of a film, for example, a method of using a high molecular weight polyester as polyester which is a raw material of the film (for example, the intrinsic viscosity is 0.63 dl / g or more, preferably 0.68 dl / g Method of using polyester of at least 0.70 dl / g or more, (2) a method of suppressing thermal decomposition and hydrolysis at the time of forming a film by extruding polyester (for example, polyester raw material as a preliminary) Method of extrusion to a moisture content of 100 ppm or less, preferably 50 ppm or less after drying, (3) A method of using a hydrolysis resistant polyester as the polyester (for example, the acid value is 25 eq / ton or less) Method of using polyester), (4) Antioxidant to polyester (eg 0.01 to 1 quality) Such as% of content) is a method to the like.

  As the polymerization catalyst for polyester, various conventional catalysts can be used. For example, titanium-based catalyst, antimony-based catalyst, germanium-based catalyst, tin-based catalyst, cobalt-based catalyst, manganese-based catalyst, etc., preferably titanium-based catalyst (titanium catalyst Examples include tetrabutoxide and the like, an antimony-based catalyst (such as antimony trioxide), a germanium-based catalyst (such as germanium dioxide), and a cobalt-based catalyst (such as cobalt acetate).

  Furthermore, it is possible to subject the white heat-shrinkable polyester film of the present invention to corona treatment, coating treatment, flame treatment or the like in order to improve the adhesion of the film surface.

  The white heat-shrinkable polyester film of the present invention is treated in warm water at 90 ° C. in a no-load state for 10 seconds and the heat shrinkage ratio = ((Length before shrinkage−length after shrinkage) It is preferable that the thermal contraction rate in the width direction of the film calculated by the equation of length) / shrinkage) × 100 (%) is 30% or more and 85% or less. The lower limit value is more preferably 35% or more, still more preferably 40% or more. The upper limit value is more preferably 82% or less, still more preferably 80% or less.

  If the hot water heat shrinkage rate in the width direction at 90 ° C. is less than 30%, the shrinkage of the label occurs and it is unsuitable as a shrinkable film. On the other hand, if it exceeds 85%, the shrinkage ratio is large, which is not preferable because problems such as the occurrence of label jump during shrinkage processing easily occur. The reason for adopting a temperature of 90 ° C is that the boiling point of water is 100 ° C when it is determined how much the heat shrinkage potential of the film is maximum, assuming that the label is attached in a steam tunnel or the like. It is often evaluated at a temperature relatively close to

  The white heat-shrinkable polyester film of the present invention preferably has a gloss of 40% or more and 150% or less measured at an angle of 60 degrees. If it is less than 40%, ink loss occurs at the time of printing, and a beautiful appearance can not be obtained. The lower limit value is more preferably 43% or more, still more preferably 46% or more. The upper limit is preferably as high as possible for better printability, but in the case of a white heat-shrinkable polyester film, the upper limit is 150%.

  The thickness of the white heat-shrinkable polyester film of the present invention is not particularly limited, but is preferably 30 μm to 60 μm assuming a heat-shrinkable film for labels as a use. In addition, although the thickness of each layer of the white heat-shrinkable polyester film of the present invention is not particularly limited, it is preferably 3 μm or more.

  In order to satisfy the above characteristics, when the film of the present invention is a non-foamed layer A and a foamed layer B, the layer configuration is A / B / A or A / C / B / C / A, etc. Yes. By setting it as this layer structure, the curl at the time of heat contraction can be suppressed compared with other layer structure. The thickness ratio of the layer A to the layer B is preferably B / A = 2/1 or more, more preferably 3/2 or more. If the thickness ratio of the B layer is small and B / A is less than 1/1, it is difficult to achieve both a low apparent specific gravity and a good appearance.

It is desirable that the thickness difference between the outermost layers of the film which is the non-foamed layer of the white heat-shrinkable polyester film of the present invention is 2 μm or less. Since the non-foamed layer has a large influence on shrinkage, if the difference in thickness between the two non-foamed layers is large, problems of curling and finishing defects tend to occur at the time of heat shrinkage. The upper limit value of the thickness difference between both outermost layers of the film which is the non-foamed layer is more preferably 1.5 μm or less, still more preferably 1 μm or less. The lower limit value is preferable because the lower one is free from curling and finishing defects, and the ideal thickness difference is 0 μm.

The thickness of both outermost layers of the non-foamed layer of the white heat-shrinkable polyester film of the present invention is preferably 3 μm or more and 12 μm or less. The thickness of the non-foamed layer is related to the unevenness of the film surface and to the printability. When the thickness is too thick, the film specific gravity is high, which is not preferable as a white film. The lower limit value of the thickness of the non-foamed layer on the film outer side is more preferably 3.5 μm or more, still more preferably 4 μm or more. The upper limit value is more preferably 11.5 μm or more, and still more preferably 11 μm or more.

The difference in density between the outermost layers of the film of the non-foamed layer of the white heat-shrinkable polyester film of the present invention is preferably 0.005 g / cm ³ or less. Since the non-foamed layer has a large influence on shrinkage, if the difference in the density (crystallization degree) of the non-foamed layer is large, problems of curling and finishing defects are likely to occur at the time of heat shrinkage. The upper limit of the density difference of the film outside of both layers of non-foam layer, more preferably 0.004 g / cm ³ or less, more preferably 0.003 g / cm ³ or less. The lower limit value is preferable because the lower one is free from curling and poor finishing, and the ideal density difference is 0 g / cm ³ .

It is desirable that the difference in the content of the amorphous component of the film outermost layers, which is the non-foamed layer of the white heat-shrinkable polyester film of the present invention, be 1 mol% or less. Since the non-foamed layer has a large influence on the shrinkage, if the difference in the content of the amorphous component contributing to the shrinkage of the non-foamed layer is large, problems of curling and finishing defects are likely to occur at the time of heat shrinkage. The upper limit value of the difference between the contents of amorphous components in both outermost layers of the film of the non-foamed layer is more preferably 0.8 mol% or less, still more preferably 0.6 mol% or less. The lower limit value is preferable because the lower one is free from curling and poor finishing, and the difference in the number of moles of the ideal amorphous component is 0 mol%.

  In the present invention, the total light transmittance of the film 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 not be visible or the appearance may be inferior, which is not preferable. 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 and may be inferior in appearance such as invisibility of printed matter, which is not preferable.

  In the present invention, it is desirable that the maximum value of the thermal contraction stress in a 90 ° C. hot air of the film is 9 MPa or less. When the pressure is higher than 9 MPa, the shrinkage rate becomes fast, and the shrinkage finish tends to be deteriorated. The upper limit value is more preferably 8 MPa or less, still more preferably 7 MPa or less. The lower limit is preferably low, but if it is too low, the slack in the label after thermal contraction will be large, so the lower limit is more preferably 1 MPa or more, further preferably 1.5 MPa or more.

  The white heat-shrinkable polyester film of the present invention preferably has a solvent adhesive strength of 2 N / 15 mm or more and 10 N / 15 mm. If the solvent adhesive strength is less than 2N / 15 mm width, it is not preferable because the label is easily shrunk from the solvent-bonded portion after the heat shrinkage. The lower limit value is more preferably 3 N / 15 mm or more, still more preferably 4 N / 15 mm or more. The solvent adhesive strength is preferably large, but the solvent adhesive strength is currently considered to be about 10 (N / 15 mm) or less in view of the performance of the film forming apparatus. In addition, when the solvent adhesive strength is too high, when two films are solvent-bonded to form a label, it is likely to be adhered to unnecessary films, which may reduce the productivity of the label. As it is, it may be 7 (N / 15 mm) or less for practical use.

    Next, the method for producing the white heat-shrinkable polyester film of the present invention will be described by way of specific examples, but it is not limited to this production method.

  In the white heat-shrinkable polyester film of the present invention, the apparent specific gravity of the film is preferably 1.20 or less. The low specific gravity of the film and its light weight are great advantages in mass production. When the apparent specific gravity of the film is less than 1.00, when the film is used as a PET bottle label, it is easy to separate the bottle and the label by water, which is more preferable. More preferably, it is 0.95 or less. However, if the apparent specific gravity of the film is too small, the strength of the film is easily impaired, so the apparent specific gravity is preferably 0.75 or more. More preferably, it is 0.80 or more.

  The polyester raw material used in the present invention is dried using a hopper dryer, a dryer such as a paddle dryer, or a vacuum dryer, melted at a temperature of 200 to 300 ° C., and extruded as a film. When extruding, any existing method such as T-die method or tubular method may be adopted. After extrusion, quenching is performed to obtain an unstretched film.

  Moreover, it is preferable to carry out in 250 degreeC-290 degreeC regarding extrusion temperature. If the extrusion temperature is less than 250 ° C., for example, the load will be excessive and normal extrusion will be difficult. When the extrusion temperature exceeds 290 ° C., for example, the polyester resin is apt to be thermally deteriorated in the extruder, resulting in a failure such as showing a decrease in mechanical strength of the obtained film.

  In addition, it is important that the extrusion temperature of the non-foamed layer A be ± 10 ° C. or less than the extrusion temperature of the foamed layer B. When the extruded resin temperatures of the A layer and the B layer are extremely different, the difference in melt viscosity becomes large, and the layer ratio of the A layer and the B layer in the width direction of the non-oriented film becomes different.

Also, at least two extruders are required to extrude the layers A and B. In addition, the layer A of the non-foamed layer may be discharged by one extruder, and the foam layer B may be sandwiched by the feed block in front of the die. At that time, by making the diameter, angle, and volume in the pipe of the feed block divided after the A layer enters the feed block the same, it is possible to reduce the difference in ratio of non-crystalline materials with small thickness difference.
In addition, the layer A may be a layer on the outer side of the film sandwiching the layer B by using two extruders. However, in this case, it is necessary to design so that the ratio of raw materials entering the extruder is uniform. When mixing different raw materials, it is necessary to install a stirrer on the hopper just before entering the extruder to mix the raw materials. In addition, it is necessary to make the piping from the hopper to the extruder a straight piping so that the raw material composition that has been stirred does not shift in the raw material composition when it enters the extruder. Furthermore, it is important to adjust the temperature of the molten resin in the extruder so that the difference in resin pressure between the two A layers is ± 3% or less before the feed block joined with the B layer. When the resin pressure is high by one side, the layer thickness of the one with high resin pressure is high, and the layer thickness ratio of the non-oriented film in the width direction of one side is high, and the other is an end. When the layer thickness ratio of is increased, problems occur. If the discharge of the two extruders in layer A is the same, and the pipe diameter and volume of the feed block are the same, the difference in resin temperature between the two extruders should be ± 1 ° C. or less. It is possible that the difference in resin pressure is ± 3% or less.

Next, it is common to solidify the molten resin with a cooling roll from an extruder to form an unstretched film. However, the inventors of the present invention generate a difference in the degree of crystallization (density) of each surface of the unstretched film on the cooling roll surface side and the non-cooling roll surface side in this step, which causes curling during heat shrinkage. I found out. More specifically, the cooling rate of the surface not in contact with the cooling roll is reduced, the degree of crystallization of the non-contacting surface is increased, and the difference in the degree of crystallinity occurs between the contact surface to the cooling roll and the non-contacting surface. This phenomenon becomes more pronounced when the cooling roll is rotated at high speed in an attempt to increase productivity.
Therefore, the inventors succeeded in reducing the degree of crystallization of the non-contact surface by applying cold air to the non-contact surface after contacting the cooling roll, and suppressing the occurrence of curling at the time of heat shrinkage.
It is preferable to use a device capable of supplying a wide width of cold air so that the cold air impinges in the entire film width direction. Further, since the unstretched film end is necked in when the molten resin is discharged from the die and the thickness is thicker than the central portion, it is preferable to adjust the end so that the cooling air velocity becomes high. The adjustment of the wind speed is carried out using, for example, a punching plate, and although the wind speed is high at the end, it is more preferable to adjust the central part so that the wind speed difference in the width direction is 5% or less.

In the longitudinal direction, it is preferable to control and cool the cold air with a wind speed difference such that the wind speed difference is 1 m / sec or less. If the variation in the longitudinal wind speed is larger than 1 m / sec, the thickness difference occurs due to the strength of the wind speed in the unstretched film. The thickness difference causes thickness unevenness in the longitudinal direction, and a difference occurs in the degree of crystallization of each surface.
The temperature of the cold air is preferably set to a temperature 3 to 15 ° C. lower than the temperature of the cooling roll. Since the heat transfer coefficient of cold air is lower than that of the cooling roll, the temperature is preferably lower than the temperature of the cooling roll. Further, if the temperature of the cold air is lower than the temperature of the cooling roll by 16 ° C. or more, dew condensation occurs on the cooling roll, which is not preferable.
Moreover, although the wind speed of cold wind is based also on the speed | rate of cooling solidification, 4 m / s or more and 25 m / s or less are preferable. If the wind speed is lower than 4 m / sec, the cooling effect is reduced, which is not preferable. If the wind speed is higher than 25 m / sec, the cooling effect is enhanced, but the point of arrival of the molten resin on the cooling roll is different, which causes uneven thickness and a difference in the degree of crystallization of each surface.

The unstretched film is then stretched in at least one direction. As mentioned above, uniaxial stretching in the width direction of the film is preferred. When stretching the unstretched film, first, preheating is performed. The temperature of the preheating is in the range of Tg + 10 ° C to Tg + 30 ° C of the unstretched film. Then, stretching is performed. The stretching ratio is 3.4 times to 7.0 times, preferably 3.6 times to 6.5 times that of the unstretched film. The stretching temperature is a predetermined temperature within the range of Tg-5 ° C to Tg + 15 ° C.
The lower the preheating temperature or the stretching temperature, the higher the stress at the time of stretching, so that it is possible to make the cavity larger and to lower the apparent density. The same applies to the draw ratio, and the higher the draw ratio, the higher the stress at the time of drawing, the larger the cavity can be made, and the apparent density can be lowered. However, if the stress at the time of stretching is too high, breakage occurs and productivity is deteriorated. Therefore, the above-mentioned range is optimal in order to achieve both the condition for reducing the apparent density and the productivity.

Next, heat setting of the film is preferably performed. The heat setting temperature is in the range of Tg + 5 ° C. to Tg + 50 ° C. In addition, heat setting may be performed in a state in which the film is stretched in the stretching direction. The tension rate at that time is preferably 6% or less.
When the heat setting temperature is higher than Tg + 50 ° C., the shrinkage in the film width direction is small, and the cavity is crushed to cause an apparent density to be high.

  From the viewpoint of controlling the heat shrinkage stress of the film, it is preferable that the number of drawing steps is large, but if the number of steps is too large, the design of drawing equipment in industrial production becomes difficult. It is desirable to have four stages or less.

  The package of the present invention is formed by covering at least a part of the outer periphery with a label provided with a perforation having the above-mentioned white heat-shrinkable polyester film as a base material, and thermally shrinking the package. Examples of the objects include plastic bottles for beverages, various bottles, cans, plastic containers such as confectionery and lunch boxes, paper boxes, etc. (hereinafter, these are collectively referred to as objects to be packaged) . In the case where a label comprising a white heat-shrinkable polyester film as a base material is thermally shrunk and covered with such a packaging object, the label is thermally shrunk by about 2 to 15% to be packaged Adhere to In addition, printing may be given to the label coat | covered by a packaging target object, and printing does not need to be given.

  As a method of producing a label, an organic solvent is applied to the inside slightly from the end of one side of a rectangular film, the film is immediately rolled up, the ends are overlapped and adhered to form a label, or a roll Apply the organic solvent a little inside from the end of one side of the wound film, round the film immediately, overlap the ends and adhere, and cut the tube-like body into a label . As the organic solvent for adhesion, cyclic ethers such as 1,3-dioxolane or tetrahydrofuran are preferable. Besides these, 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 Next, the present invention will be specifically described using Examples and Comparative Examples, but the present invention is not limited to the embodiments of the Examples in any way, and within the scope of the gist of the present invention, as appropriate. It is possible to change.

  The evaluation method used in the present invention is as follows.

Thermal contraction rate in the main contraction direction
The film is cut into a square of 10 cm × 10 cm and treated for 10 seconds in a no-load state in hot water at a hot water temperature of 90 ° C. ± 0.5 ° C. for heat shrinkage, and then the film in the transverse direction (main shrinking direction) The dimensions were measured, and the heat shrinkage was determined according to the following equation (1).
Thermal contraction rate = ((length before contraction−length after contraction) / length before contraction) × 100 (%) (1)

[Total light transmittance]
The total light transmittance was determined with NDH-1001DP manufactured by Nippon Denshoku Kogyo Co., Ltd.

[gross]
According to JIS K 874, it measured at an angle of 60 degrees using a gloss meter "VG 2000" (manufactured by Nippon Denshoku Kogyo Co., Ltd.).

[Thickness of film outer layer, thickness difference]
After cutting the film cross section, the thickness of each layer was measured using a scanning electron microscope "JSM-6510A type" (manufactured by JEOL Ltd.). And the thickness difference of each layer was determined.

[Density difference]
Only the film outer layer was scraped and sampled with a razor blade. After placing the sample in the liquid for 24 hours using a density gradient tube containing a liquid (a calcium nitrate aqueous solution) having a continuous density gradient in the tube, the sampled film is placed in the liquid from a stationary equilibrium position. The density of the sample was read. The density of each of the outer layers was determined, and the difference was taken as the density difference.

[Difference in amorphous component content]
Only the film outer layer was scraped and sampled with a razor blade. About 5 mg of the sampled film was dissolved in 0.7 ml of a mixed solution of heavy chloroform and trifluoroacetic acid (volume ratio 9/1), and determined using 1 H-NMR (Varian, UNITY 50). The content (number of moles) of each amorphous component of the outer layer was determined, and the difference was taken as the difference between the content (number of moles) of the amorphous component. In all of the examples of the present application, the neopentyl glycol content was determined as the amorphous component content.

[Heat shrinkage stress]
A sample with a length of 160 mm in the main shrinkage direction and a width of 20 mm is cut out from the heat-shrinkable film using a Tensilon (with heating furnace) strength and elongation measurement machine made by Orientec Co., and the film chucking position is 30 mm × 28 mm cardboard pieces Hold the sample in the atmosphere heated to 90 ° C in advance with an interval of 100 mm between the chucks, attach the sample to the chuck, and then immediately close the door of the heating furnace and start blowing (blowing wind speed 5 m / sec) detection The stress applied was measured for 30 seconds, and the maximum value obtained from the chart was taken as the heat shrinkage stress (MPa).

[Apparent specific gravity of film]
One piece of the film was cut out into A4 size (21.0 cm × 29.7 cm) to prepare a sample. The thickness of each sample was measured at 10 points using a micrometer with four significant figures using a micrometer, and the average value of the thickness (t: μm) was determined. The mass (w: g) of one sample of this sample was measured using an automatic upper balance with four significant figures, and the apparent specific gravity was determined from the following equation (2). The apparent specific gravity was rounded to two decimal places.
Apparent specific gravity = w / (21.0 × 29.7 × t × 10 ⁻⁴ ) = w × 100 / t
... Formula (2)

Solvent adhesive strength
The heat-shrinkable film was coated with 1,3-dioxolane at a coating amount of 5 ± 0.3 g / m ² and a coating width of 5 ± 1 mm, and a seal was obtained by bonding two sheets. Thereafter, the seal direction is cut to a width of 15 mm in a direction perpendicular to the sealing direction, and it is set at 20 mm between chucks in universal tensile tester STM-50 manufactured by Baldwin Co., Ltd. and subjected to tensile peeling at a tensile speed of 200 mm / min. Peel resistance was measured. And the strength at that time was taken as the solvent adhesive strength.

[Shrink finish]
The heat-shrinkable film was previously printed in two colors with the Toyo Ink Mfg. Co., Ltd.'s grass-gold ink. And the cylindrical label (The label which made the main contraction direction of the heat-shrinkable film the circumferential direction) was created by adhering the both ends of the printed film with dioxolane. After that, using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc., using a 500 ml PET bottle (body diameter 70 mm, minimum diameter 25 mm at the neck) at a zone temperature of 90 ° C. Tested (number of measurements = 20).
In addition, at the time of mounting | wearing, in the neck part, it adjusted so that the part of 30 mm in diameter might become one end of a label.
The evaluation was performed visually, and the criteria were as follows.
○: none of wrinkles, jump up and contraction was not generated ×: wrinkle, jump up or contraction was generated

[Shrinkage distortion at label]
As an evaluation of finish after shrinkage, the strain in the direction of 360 degrees on the attached label was measured using a gauge to determine the maximum value of the strain. At that time, the criteria were as follows.
○: maximum strain less than 1.5 mm.
X: Maximum distortion 1.5 mm or more.

[curl]
As an evaluation of the curl after contraction, the curl was measured using a gauge in the direction of 360 degrees at the top of the attached label (neck). At that time, the criteria were as follows.
○: Maximum curl less than 0.5 mm. And no curl.
X: Maximum curl 0.5 mm or more.

[Label adhesion]
The label was attached under the same conditions as the measurement conditions of shrinkage finish described above. Then, when the attached label and the plastic bottle were lightly twisted, if the label did not move, it was evaluated as ○, or if the label and the bottle were misaligned, it was marked as x.

The polyesters used in the examples are as follows.
Polyester a: polyethylene terephthalate (intrinsic viscosity 0.75 dl / g)
Polyester b: Polyester consisting of 30 mol% neopentyl glycol, 10 mol% diethylene glycol, 60 mol% ethylene glycol and terephthalic acid (intrinsic viscosity 0.78 dl / g)
Polyester c: Polyester raw material consisting of 50% by weight of polyester a and 50% by weight of titanium oxide (manufactured by Nippon Pigment Co., Ltd. Product name: ET550)
Polyester d: polybutylene terephthalate (intrinsic viscosity 1.3 dl / g)
Raw material e: Cyclic polyolefin resin (manufactured by Polyplastics Co., Ltd. Product name: Topas (registered trademark) 6017)
Raw material f: Amorphous polystyrene resin (Nippon Polystyrene Co., Ltd. product name: G797N)

Example 1
5% by weight of polyester a as layer A, 75% by weight of polyester b, 20% by weight of polyester c, 65% by weight of polyester b as layer B, 15% by weight of polyester c, 20% by weight of raw material e, layer C As a polyester with 5% by weight of polyester a, 75% by weight of polyester b, and 20% by weight of polyester c, A layer and C layer melt at 265 ° C., B layer melt at 280 ° C., layer Coextrusion was performed from a T-die such that the thickness ratio was A layer / B layer / C layer = 20/60/20, and quenched with a chill (chill) roll to obtain an unstretched multilayer film with a thickness of 200 μm. The temperature of the cooling roll at this time is in contact with the layer A at 25 ° C. In the C layer opposite to the cooling roll, cold air at 10 ° C. was blown at a central portion of 8 m / s and an end portion of 10 m / s using a multi-duct.

  The unstretched film was preheated to a film temperature of 80 ° C., and then stretched in the width direction with a tenter. The stretching was 5.5 times at 75 ° C. Next, the film was heat-set at 82 ° C. while holding the film width at the end of stretching to obtain a white heat-shrinkable polyester film.

  The evaluation results of the obtained film are shown in Table 3. A film with good shrink finish was obtained.

(Example 2)
A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the material e of the B layer was changed to the material f. The evaluation results of the obtained film are shown in Table 3. A film with good shrink finish was obtained.

(Example 3)
Co-extrusion from T die so that the layer thickness ratio becomes A layer / B layer / C layer = 30/40/30 by changing the discharge amount of the extruder, and quenching with a chill (chill) roll to form a 200 μm thick film. A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the stretched multilayer film was changed. The evaluation results of the obtained film are shown in Table 3. Although the gloss and the apparent specific gravity were high, a film having a good shrink finish was obtained.

(Example 4)
5% by weight of polyester a as layer A, 95% by weight of polyester b, 80% by weight of polyester b as layer B, 10% by weight of polyester c, 10% by weight of raw material e, 5% by weight of polyester a as layer C A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that 95% by weight of polyester b was mixed. The evaluation results of the obtained film are shown in Table 3. Although the shrinkage rate and shrinkage stress of the hot water in the width direction were high, a film with good finish was obtained.

(Example 5)
A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that 55% by mass of polyester b, 15% by mass of polyester c and 30% by mass of raw material e were mixed as the layer B. The evaluation results of the obtained film are shown in Table 3. Although the gloss and the apparent specific gravity became lower, a film having a good finish was obtained.

(Comparative example 1)
A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the cooling air was not blown to the C layer opposite to the cooling roll using a multiduct. The evaluation results of the obtained film are shown in Table 3. A difference in density between the A layer and the C layer occurs, causing a slight curl, resulting in a film inferior in shrinkage strain.

(Comparative example 2)
Co-extrusion from the T die so that the layer thickness ratio becomes 5/90/5 by changing the discharge amount of the extruder, and quenching with a chill (chill) roll to form a 200 μm thick film. A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the stretched multilayer film was changed. The evaluation results of the obtained film are shown in Table 3. The layer thickness of the A layer and the C layer was thin and the film became inferior in gloss.

(Comparative example 3)
Co-extrusion from the T die so that the layer thickness ratio becomes A layer / B layer / C layer = 15/60/25 by changing the discharge amount of the extruder, and quenching with a chill roll to form a 200 μm thick film. A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the stretched multilayer film was changed. The evaluation results of the obtained film are shown in Table 3. The layer thicknesses of the A layer and the C layer were different, and curling occurred after shrinkage, resulting in a film having poor shrink finish.

(Comparative example 4)
A white heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the C layer was changed to a mixture of 5% by weight of polyester a, 71% by weight of polyester b, and 24% by weight of polyester c. The evaluation results of the obtained film are shown in Table 3. Amorphous mole% of A layer and C layer is different (A layer 22.5 mol%, C layer 21.3 mol%). The number of moles of non-crystalline components in the A layer and the C layer was different by 1.2 mol%, and after shrinkage, curling occurred slightly, resulting in a film having poor shrink finish.

  The white heat-shrinkable polyester film of the present invention has high quality and high practicability, and it is possible to obtain a beautiful shrink finish even at high speed production, and is particularly suitable for shrink labels.

Claims (7)

A white heat-shrinkable polyester-based stretched film comprising at least one polyester-based resin layer containing titanium oxide particles, and at least two layers sandwiching the titanium oxide particle-containing layer, comprising: A white heat-shrinkable polyester-based stretched film characterized by satisfying the requirements (1) to (7).
(1) Thermal contraction rate in the main shrinkage direction by hot water treatment at a treatment temperature of 90 ° C. and treatment time of 10 seconds is 30% or more and 85% or less (2) The gloss of both sides of the film measured at an angle of 60 ° is 40 % And 150% or less (3) thickness difference of both outermost layers of film is 2 μm or less (4) Both thickness of both outermost layers of film are 3 μm or more and 12 μm or less (5) density difference of both outermost layers of film is 0. 005 g / cm ³ or less (6) The difference in the number of moles of amorphous components of both outermost layers of the film is 1 mol% or less (7) The light transmittance is 40% or less The white heat-shrinkable polyester-based stretched film according to claim 1, wherein the maximum value of the heat-shrink stress in a hot air at 90 ° C is 9 MPa or less. The white heat-shrinkable polyester-based stretched film according to any one of claims 1 to 2, wherein the solvent adhesive strength is 2 N / 15 mm width or more and 10 N / 15 mm width or less. The heat-shrinkable label using the white heat-shrinkable polyester-based stretched film according to any one of claims 1 to 3.   A package in which the heat-shrinkable label according to claim 4 is coated on at least a part of the outer periphery of the object to be packaged. The white heat-shrinkability according to any one of claims 1 to 3, characterized in that, in the step of producing an unstretched film from a molten resin, both outermost layers are positively cooled to reduce the density difference between both outer layers. Method for producing polyester-based oriented film. In the process of making an unstretched film from a molten resin, as a method of actively cooling both outermost layers, the layer on one side is cooled by a cooling roll, and the layer on the other side has a wind speed difference of 1 m / sec or less in longitudinal direction The method for producing a white heat-shrinkable polyester-based stretched film according to any one of claims 1 to 3, wherein cooling is performed by applying a cooling air using an apparatus adjusted to be a difference.