JP2009160788A - Heat-shrinkable polyester film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film which has good solvent adhesiveness in coating PET bottles with the film as a label, good perforation opening properties when shrinked and applied to bottles and controlled possibility of electrostatic troubles. <P>SOLUTION: The heat-shrinkable polyester film is composed of a polyester type resin comprising ethylene terephthalate as main structural units and specified amounts of units derived from amorphous monomers. A specified anionic antistatic agent is present at least in one side of the film. The number of test specimens of ≤25% which have a breaking elongation in the direction perpendicular to the principal shrinkage direction of ≤5%, with the test carried out under prescribed conditions. The film has a solvent adhesion strength of 2-15 N/15 mm, a solvent permeation resistance index of ≤0.2 N/15 mm, a warm water shrinkage in the principal shrinkage direction of 50-80% in warm water at 95°C and a tear propagation resistance ratio of 3.5-6.0 in the direction perpendicular to the principal shrinkage direction of the film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat-shrinkable polyester film and a method for producing the same, and more particularly to a heat-shrinkable polyester film suitable for labeling and a method for producing the same.

  In recent years, stretching made of polyvinyl chloride resin, polystyrene resin, polyester resin, etc. for applications such as label packaging, cap seals, integrated packaging, etc. that also serve as protection and product display for glass bottles and PET (polyethylene terephthalate) bottles Films (so-called heat shrinkable films) have been used. Among these heat-shrinkable films, the polyvinyl chloride film has problems such as low heat resistance and generation of hydrogen chloride gas during incineration and dioxins. 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. Along with the increase, the usage amount tends to increase (Patent Documents 1, 2, etc.).
JP-A-9-239833 JP 7-138388 A

  However, since the conventional heat-shrinkable polyester film is almost unstretched in the direction orthogonal to the main shrinkage direction (ie, the longitudinal direction), when it is shrunk to a PET 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).

  Further, since the conventional polyester film is an insulator, there is a problem that static electricity is easily generated and accumulated. Static electricity makes processing difficult, such as film wrapping around a roll or shocking the human body in contact with the film during processing, for example, the manufacturing process, printing, bonding, and other secondary processing processes. This is a factor that lowers work efficiency. In addition, there are problems such as generation of so-called printing whiskers, poor openability after labeling, and contamination of the film surface, resulting in a reduction in commercial value.

  Paying attention to these situations, the present invention eliminates the problems of the conventional heat-shrinkable polyester film, and has a good perforation opening property when it is shrunk to a PET bottle or the like as a label and covered. An object of the present invention is to provide a heat-shrinkable polyester film in which troubles due to static electricity are suppressed and a method for producing the same.

The heat-shrinkable polyester film of the present invention that has solved the above problems is a polyester resin in which ethylene terephthalate is the main constituent unit, and in all polyester resin components, the unit derived from an amorphous monomer is 15 mol% or more. A heat-shrinkable polyester film having a thickness of 25 μm or more and 60 μm or less, and an anionic antistatic agent having an alkyl group having 10 to 20 carbon atoms on at least one surface of the heat-shrinkable polyester film. It is characterized by being present and satisfying the following requirements (1) to (5).
(1) After storing the film in an atmosphere of 30 ° C. and 85% relative humidity for 672 hours or more, when a tensile test is performed in the direction orthogonal to the main shrinkage direction, the number of test pieces having a breaking elongation of 5% or less 25% or less of the total number of test pieces,
(2) The adhesive strength after 1 hour has passed since the surface and the back surface of the film are solvent-bonded with tetrahydrofuran, and is 2N / 15mm or more and 15N / 15mm or less.
(3) After dropping 1,3-dioxolane onto a predetermined number of films, a predetermined number of films are stacked on the dropping portion to form a film laminate, and the film laminate is subjected to a predetermined pressure over a predetermined time. After compression, the adhesive strength between the film on which 1,3-dioxolane is dropped and the film located thereunder, and the adhesion between the film superimposed on the film on which 1,3-dioxolane is dropped and the film located on the upper side When the strength is measured, both of these two adhesive strengths are 0.2 N / 15 mm or less.
(4) The hot water shrinkage rate in the main shrinkage direction when treated for 10 seconds in warm water at 95 ° C. is 50% or more and 80% or less,
(5) The tear propagation resistance ratio in the direction orthogonal to the main shrinkage direction of the film is 3.5 or more and 6.0 or less.

  The amorphous monomer component is preferably composed mainly of one selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid.

  Moreover, the heat-shrinkable polyester film of the present invention preferably has a core layer and a laminated structure in which skin layers are laminated on both surfaces of the core layer. The polyester resin material constituting the core layer is preferably made of a material having an intrinsic viscosity (IV) lower than that of the polyester resin constituting the skin layer, and further the polyester constituting the core layer. It is recommended that the ratio of the unit derived from the amorphous monomer contained in the resin material is lower than the ratio of the unit derived from the amorphous monomer contained in the polyester resin material constituting the skin layer. .

  The production method of the present invention is a method for producing the heat-shrinkable polyester film, and a sheet forming step for forming an unstretched sheet by melt-extruding a polyester resin material from an extruder, and a sheet The unstretched sheet obtained in the forming step includes at least a stretching step in which the unstretched sheet is stretched in the transverse direction, and the sheet forming step is characterized in that the following requirements (a) to (f) are satisfied.

(A) Two or more kinds of polyester resins having different intrinsic viscosities (IV) are melt-extruded from a plurality of extruders by a co-extrusion method, and a core layer made of a low IV resin and a skin layer made of a high IV resin Is a step of forming an unstretched sheet laminated with
(B) The ratio of the unit derived from the amorphous monomer contained in the core layer is lower than the ratio of the unit derived from the amorphous monomer in the skin layer.
(C) The moisture content of the polyester resin chips supplied to the hopper of the extruder is 10 ppm or more and 50 ppm or less.
(D) It is performed while cooling the screw of each extruder.
(E) The preheating temperature of the extruder is 200 ° C. or more and 270 ° C. or less, and the temperature of the compression zone of each extruder is 290 ° C. or more and 310 ° C. or less.
(F) The temperature of the extruder for extruding the core layer is higher than the temperature of the extruder for extruding the skin layer, and the difference is 5 ° C. or more and 15 ° C. or less.

  The polyester resin raw material includes two or more polyethylene terephthalate resins having different IVs, and the difference between the maximum IV and the minimum IV of the polyethylene terephthalate resin IV is 0.04 dl / g or more. It is preferable to set it as 13 dl / g or less.

  The method for producing the heat-shrinkable polyester film of the present invention includes an anionic system having an alkyl group having 10 to 20 carbon atoms on at least one side of the unstretched sheet or the uniaxially stretched polyester film. A method of applying a coating solution containing an antistatic agent and then biaxially stretching or uniaxially stretching the coated film is also included.

  The heat-shrinkable polyester film of the present invention has good perforation-opening properties when it is shrunk onto a non-covered material such as a PET bottle. In addition, the heat-shrinkable polyester film of the present invention has an extremely high adhesive force when the front and back surfaces (or the same surface) are adhered to each other with a solvent, and also has excellent antistatic properties. It can be suitably used for various coated labels including the above label.

  The heat-shrinkable polyester film of the present invention comprises ethylene terephthalate as a main constituent unit, and a heat-shrinkable polyester film comprising a polyester-based resin in which the unit derived from an amorphous monomer is 15 mol% or more in all polyester resin components. It is. First, the polyester constituting the heat-shrinkable polyester film of the present invention will be described.

[About polyester]
The heat-shrinkable polyester film of the present invention uses a polyester composed of a polyvalent carboxylic acid and a polyhydric alcohol as a raw material, and the polyhydric alcohol component constituting this includes ethylene glycol, propylene glycol, triethylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2-methyl-1,5-pentanediol, 2,2-diethyl-1,3- Propanediol, 1,9-nonanediol, aliphatic diol such as 1,10-decanediol, alicyclic diol such as 1,4-cyclohexanedimethanol, trimethylolpropane, glycerin, pentaerythritol, diethylene glycol, dimer diol, Polyoxytetramethylene Call, like bisphenol compounds or alkylene oxide adducts of derivatives thereof.

  Examples of the polyvalent carboxylic acid component constituting the polyester used in the present invention include aromatic dicarboxylic acids and ester forming derivatives thereof, and aliphatic dicarboxylic acids. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalene-1,4- or -2,6-dicarboxylic acid, 5-sodium sulfoisophthalic acid, and the like. Examples of the aromatic dicarboxylic acid ester derivatives include the above-mentioned aromatic dicarboxylic acid derivatives such as dialkyl esters and diaryl esters. Examples of the aliphatic dicarboxylic acid include glutaric acid, adipic acid, sebacic acid, azelaic acid, oxalic acid, succinic acid and the like, and an aliphatic dicarboxylic acid usually called dimer acid. Furthermore, an oxycarboxylic acid such as p-oxybenzoic acid, a trivalent or higher polyvalent carboxylic acid such as trimellitic anhydride or pyromellitic anhydride may be used in combination as necessary.

  In addition, although not polyhydric alcohols or polycarboxylic acids, lactones typified by ε-caprolactone can be used in part. Lactones are those that ring-open to become units having ester bonds at both ends, and a unit derived from one lactone can be considered to be a carboxylic acid component and an alcohol component. Therefore, when lactones are used, the amount of the polyhydric alcohol component is calculated assuming that the amount obtained by adding the unit amount derived from the lactone to the amount of the polyhydric alcohol component is 100 mol%. Also, when calculating the amount of each polycarboxylic acid component, the amount obtained by adding the unit amount derived from the lactone to the amount of the polyvalent carboxylic acid component is 100 mol%.

  The heat-shrinkable polyester film of the present invention has an ethylene terephthalate unit as a main constituent unit. “Main” means 50 mol% or more in 100 mol% of all units constituting the polyester. The ethylene terephthalate unit is a component that contributes to the tear resistance, strength, heat resistance, etc. of the film. In the present invention, the ethylene terephthalate unit is 50 mol% in 100 mol% of the constituent unit of the heat-shrinkable polyester film. Select to be above. The ethylene terephthalate unit is preferably 55 mol% or more, more preferably 60 mol% or more.

  The preferred constituent unit other than the ethylene terephthalate unit contained in the heat-shrinkable polyester film of the present invention is a unit derived from a polyhydric alcohol other than ethylene glycol and / or a unit derived from a polyvalent carboxylic acid other than terephthalic acid, In the heat-shrinkable polyester film, one that can be an amorphous component is preferably used. By including the amorphous component, the high crystallinity derived from the ethylene terephthalate unit can be lowered, so that the heat shrinkage property, tear resistance and solvent adhesion of the film can be improved in a balanced manner. A specific unit derived from a polyhydric alcohol other than ethylene glycol is an ester unit composed of the above-mentioned polyvalent carboxylic acid component exemplified as an amorphous monomer component and, for example, ethylene glycol, and a unit other than terephthalic acid. The unit derived from a monovalent carboxylic acid means an ester unit composed of the polyhydric alcohol component exemplified as the amorphous monomer component and terephthalic acid, for example.

  Examples of the amorphous monomer component that can be an amorphous component include isophthalic acid, naphthalene-1,4- or -2,6-dicarboxylic acid for the polyvalent carboxylic acid component, neopentyl glycol for the polyhydric alcohol component, 1 1,4-cyclohexanedimethanol and 1,4-butanediol are preferable. Of these, neopentyl glycol or 1,4-cyclohexanedimethanol is preferred for polyhydric alcohols, and isophthalic acid is preferred for polyvalent carboxylic acids. Particularly preferred is neopentyl glycol or 1,4-cyclohexanedimethanol.

  Such amorphous monomer-derived units are preferably 15 mol% or more in the total polyester resin component. More preferably, it is 15.3 mol% or more, and further preferably 15.5 mol% or more. From the viewpoint of solvent adhesiveness, it is desirable to use a polyester containing the above preferred amorphous component in at least a part of the polyester raw material constituting the layer that becomes the surface of the film. Preferably, the ratio of the unit derived from the amorphous monomer is 26 mol% or less, more preferably 25 mol% or less, and still more preferably 23 mol% or less.

  The intrinsic viscosity of the polyester raw material used in the present invention is preferably selected so that the intrinsic viscosity (IV) of the film formed from the polyester is 0.62 dl / g or more. If the intrinsic viscosity of the film is 0.62 dl / g or more, it is possible to secure the tear resistance of the film, and it is possible to reduce the occurrence of troubles and defects such as breakage during printing and solvent bonding. It is.

  Moreover, in this invention, you may mix a recycled raw material (recycle raw materials, such as a PET bottle) with a normal polyester raw material as a polyester raw material of a heat-shrinkable polyester film. In general, recycled materials tend to reduce the intrinsic viscosity of the film. Therefore, when using the recycled material, it is preferable to select a polyester material other than the recycled material so that the intrinsic viscosity of the film is 0.62 dl / g or more. Specifically, considering the decrease in intrinsic viscosity due to melt extrusion, the intrinsic viscosity of other polyester raw materials is preferably 0.68 dl / g or more, more preferably 0.70 dl / g or more, and still more preferably It is 0.72 dl / g or more. In addition, the more preferable minimum of the intrinsic viscosity as a film is 0.63 dl / g, More preferably, it is 0.64 dl / g.

  The polyester resin constituting the heat-shrinkable polyester film of the present invention can be produced by melt polymerization according to a conventional method. As the polymerization method, a so-called direct polymerization method in which an oligomer obtained by directly reacting a polyvalent carboxylic acid and a polyhydric alcohol is polycondensed, a transesterification reaction between the methyl ester of the polyvalent carboxylic acid and the polyhydric alcohol is performed. Arbitrary polymerization methods can be selected from so-called transesterification and other known polymerization methods in which polycondensation is performed after the polymerization. As the polymerization catalyst, a conventional catalyst can be used. For example, a titanium-based catalyst (such as titanium tetrabutoxide), an antimony-based catalyst (such as antimony trioxide), a germanium-based catalyst (such as germanium dioxide), or a cobalt-based catalyst (such as cobalt acetate). Etc.

  Further, fine particles may be added as a lubricant to the polyester resin. By including a lubricant and fine particles, the slipperiness of the film produced using the polyester resin is improved, and the workability when producing the film is improved. 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 diameter of the fine particles may be appropriately selected as necessary within a range of 0.05 to 3.0 μm (when measured with a Coulter counter). Furthermore, various additives such as waxes, antioxidants, crystal nucleating agents, thinning agents, heat stabilizers, coloring pigments, anti-coloring agents, ultraviolet absorbers and the like can be added as necessary. .

  An anionic antistatic agent having an alkyl group having 10 to 20 carbon atoms is present on at least one surface (preferably both surfaces) of the heat-shrinkable polyester film of the present invention. The presence of a specific anionic antistatic agent reduces the surface resistivity of the film and improves the antistatic property, resulting in the generation of static electricity that causes various problems during secondary processing of the film. -Accumulation is suppressed.

  Examples of the anionic antistatic agent include higher alcohol sulfuric acid ester salts, sulfuric acid ester salts of alkylphenol ethylene oxide adducts, sulfuric acid and sulfonic acid derivatives such as alkyl sulfonates and alkyl allyl sulfonates, and the like. Those having ~ 20 alkyl groups. More specifically, alkyl sulfonate, alkyl benzene sulfonate, alkyl sulfate ester salt, alkyl ethoxy sulfate ester salt, alkyl phosphate ester salt and the like having an alkyl group having 10 to 20 carbon atoms can be mentioned. Among them, preferred are dodecyl sulfonate, dodecyl benzene sulfonate, and the like.

  In the present invention, an anionic antistatic agent having an alkyl group having 10 to 20 carbon atoms is used even when the film is subjected to heat during film processing (during film production and secondary processing). This is because the antistatic agent is prevented from scattering and disappearing from the film surface, and the antistatic effect is more reliably ensured. If the number of carbon atoms is less than the above range, the rate of scattering / disappearing from the film becomes very large due to heat received during film processing, and the effect of the antistatic agent may not be sufficiently obtained. On the other hand, when the number of carbons exceeds the above range, the antistatic effect becomes insufficient, and the effect of using the antistatic agent may not be sufficiently obtained. In addition, it is preferable that carbon number of an anionic antistatic agent is 12 or more and 18 or less.

The amount of the anionic antistatic agent present on the surface of the heat-shrinkable polyester film of the present invention is preferably 0.001 to 0.5 g / m ² . If the amount of the anionic antistatic agent is less than the above range, the antistatic effect may not be sufficiently secured. On the other hand, when the amount of the anionic antistatic agent exceeds the above range, the transparency and blocking resistance of the film may be lowered.

  From the viewpoint of maintaining good antistatic properties on the film surface, the surface specific resistance value of the film is preferably 13 Ω · cm or less. More preferably, it is 12 ohm * cm or less, More preferably, it is 11 ohm * cm or less.

[Requirement (1)]
In the heat-shrinkable polyester film of the present invention, the film is stored in an atmosphere of 30 ° C. and 85% relative humidity for 672 hours (28 days), and then the direction perpendicular to the main shrinkage direction (maximum shrinkage direction) of the film ( When a tensile test is performed in the (orthogonal direction), the number of test pieces having a breaking elongation of 5% or less needs to be 25% or less of the total number of test pieces (hereinafter, this value is referred to as an initial breaking rate). The initial breaking rate refers to a tensile test in a direction perpendicular to the main shrinkage direction of a plurality of film test pieces after storage under the above conditions, a test piece length of 200 mm, a distance between chucks of 100 mm, a test piece width of 15 mm, and a temperature of 23 This is the ratio (percentage) of the number of test pieces having a breaking elongation of 5% or less when it is carried out at a temperature of 200 ° C. and a tensile speed of 200 mm / min. When the initial breaking rate exceeds 25%, troubles and defects such as breakage are likely to occur due to a decrease in the tear resistance of the film when the film is processed after long-term storage. The initial breaking rate is preferably 20% or less, and more preferably 15% or less. In order to set the initial breaking rate to 25% or less, it is preferable to set the intrinsic viscosity of the film to 0.62 dl / g or more and to control the molecular orientation of the film within a certain high range. As an index of the molecular orientation of the film, a heat shrinkage stress value in the main shrinkage direction (for example, a shrinkage stress in the main shrinkage direction when heated to 90 ° C. described later) can be used. It is preferable to control the numerical value within the range. In addition, in order to control the molecular orientation (thermal shrinkage stress) of the film, a method of forming a film with an appropriate stretching stress can be suitably used with the stretching ratio and the stretching temperature as appropriate conditions.

[Requirement (2)]
The heat-shrinkable polyester film of the present invention has a solvent adhesive strength measured in accordance with a method described later of 2 N / 15 mm or more. If the solvent adhesive strength is less than 2 N / 15 mm, the label formed from this film is likely to be peeled off from the solvent-adhered portion after being thermally contracted, which is not preferable. The solvent adhesive strength is more preferably 4 N / 15 mm or more, and particularly preferably 6 N / 15 mm or more. The higher the solvent adhesive strength, the better. However, at the present stage, 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.

[Requirement (3)]
In the heat-shrinkable polyester film of the present invention, 1,3-dioxolane is dropped on the uppermost film of a film laminate in which a predetermined number of films are stacked, and then a predetermined number of films are formed on the dropping portion. And after compressing the laminate of these films at a predetermined pressure for a predetermined time, the adhesive strength between the film in which 1,3-dioxolane was dropped and the film positioned therebelow, and 1, When the adhesive strength between the film superposed on the film on which 3-dioxolane was dropped and the film located on the lower side was measured, the two adhesive strengths (hereinafter referred to as the solvent penetration index, The characteristic may be referred to as solvent penetration resistance), but both must be 0.2 N / 15 mm or less (detailed measurement method will be described later). When the solvent penetration resistance index is less than 0.2N / 15mm, when two films are bonded to each other with a solvent, a label may be bonded to an unnecessary film. Since it falls, it is not preferable. The solvent penetration resistance index is preferably as low as possible, and most preferably 0 (N / 15 mm), which is not detected as a numerical value by a tensile tester.

[Requirement (4)]
The heat-shrinkable polyester film of the present invention is the main shrinkage of the film calculated by the following formula 1 from the length before and after shrinkage when treated in warm water at 95 ° C. for 10 seconds under no load. The heat shrinkage rate in the direction (95 ° C. hot water shrinkage rate) needs to be 50% or more and 80% or less.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%).

  If the hot-water heat shrinkage rate in the main shrinkage direction at 95 ° C is less than 50%, the shrinkage amount is too small, and thus wrinkles and tarmi are generated on the label after heat shrinkage. If the hot water shrinkage rate in the shrinking direction exceeds 80%, it is not preferable because when used as a label, the shrinkage tends to occur during heat shrinkage, or so-called “jumping” may occur. The hot water shrinkage rate in the main shrinkage direction at 95 ° C. is preferably 53% or more, more preferably 56% or more, and further preferably 59% or more. Further, the hot water shrinkage rate in the main shrinkage direction at 95 ° C. is preferably 75% or less, more preferably 70% or less, and further preferably 65% or less.

  The heat-shrinkable polyester film of the present invention is a main shrinkage of the film calculated from the length before and after shrinkage by the above formula 1 when treated for 10 seconds in 95 ° C. warm water under no load. The hot water shrinkage in the direction orthogonal to the direction (hereinafter simply referred to as the orthogonal direction) is preferably 0% or more and 15% or less.

  If the hot water shrinkage in the orthogonal direction at 95 ° C. is less than 0% (that is, the shrinkage is a negative value), a good shrink appearance cannot be obtained when used as a bottle label. On the other hand, when the hot water shrinkage rate in the orthogonal direction at 95 ° C. exceeds 15%, it is not preferable because distortion tends to occur during heat shrinkage when used as a label. The hot water shrinkage in the orthogonal direction at 95 ° C. is preferably 1% or more, more preferably 2% or more, further preferably 3% or more, preferably 17% or less, and 13% or less. More preferably, it is 11% or less.

[Requirement (5)]
In the heat-shrinkable polyester film of the present invention, the tear propagation resistance ratio in the direction orthogonal to the main shrinkage direction of the film is 3.5 or more and 6.0 or less. When the tear propagation resistance ratio in the orthogonal direction is less than 3.5, it is not preferable because it is difficult to tear straight along the perforation when used as a label. On the other hand, if the tear propagation resistance ratio in the orthogonal direction exceeds 6.0, it is not preferable because it is easy to tear at a position off the perforation. The tear propagation resistance ratio in the orthogonal direction is preferably 3.7 or more, more preferably 3.9 or more, and further preferably 4.1 or more. Further, the upper limit of the tear propagation resistance ratio in the orthogonal direction is preferably 5.8, more preferably 5.6 or less, and even more preferably 5.4 or less.

  The heat-shrinkable polyester film of the present invention preferably has a shrinkage stress in the main shrinkage direction of 3 MPa to 20 MPa when heated to 90 ° C. When the shrinkage stress in the main shrinkage direction is less than 3 MPa when heated to 90 ° C., it may be difficult to obtain a good shrink appearance when used as a bottle label. When the shrinkage stress in the main shrinkage direction exceeds 20 MPa, when used as a label, distortion tends to occur during heat shrinkage, which is not preferable. In addition, the lower limit of the shrinkage stress in the main shrinkage direction when heated to 90 ° C. is more preferably 4 MPa, further preferably 5 MPa or more, and particularly preferably 6 MPa or more. The upper limit of the shrinkage stress in the main shrinkage direction when heated to 90 ° C. is more preferably 18 MPa, even more preferably 16 MPa or less, still more preferably 14 MPa or less, and particularly preferably 12 MPa or less.

  Furthermore, it is preferable that the heat-shrinkable polyester film of the present invention does not detect the endothermic curve peak during melting point measurement in differential scanning calorimetry (DSC). By making the polyester constituting the film amorphous, the peak of the endothermic curve at the time of measuring the melting point becomes more difficult to express. By highly amorphous to the extent that the endothermic curve peak at the time of melting point measurement does not appear, the heat shrinkage rate and the maximum heat shrinkage stress value can be increased together with the solvent adhesive strength. It becomes easy to control within the range.

  The heat-shrinkable polyester film of the present invention preferably has a thickness of 25 μm or more and 60 μm or less. For example, when used for label applications, it is recommended that the overall thickness be 30 μm or more and 50 μm or less. In addition, when the heat-shrinkable polyester film of the present invention has a laminated structure, the thickness of each layer is not particularly limited, but is preferably 10 μm or more.

[Film Production Method]
The heat-shrinkable polyester film of the present invention is obtained by melting and extruding the above-described polyester raw material with an extruder to form an unstretched sheet, and stretching the unstretched sheet by a predetermined method.

  When the polyester-based resin material is melt-extruded, the polyester-based resin material is preferably dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. Thus, after drying a polyester raw material, it is preferable to employ | adopt the method of using an extruder and fuse | melting at the temperature of 200-300 degreeC, and extruding in a sheet form. For this extrusion, any existing method such as a T-die method or a tubular method can be employed.

  From the viewpoint of obtaining a film having the above-described various characteristics, the heat-shrinkable polyester film of the present invention is preferably a multilayer film having a multilayer structure. For the production of such a laminated film, a method (so-called co-extrusion method) in which resin raw materials melted by a plurality of extruders are co-extruded is preferably used. At this time, when a recycled raw material is used as a part of the raw material resin, it is preferable to appropriately adjust the amounts of the recycled raw material and the other polyester resin raw materials in the resin raw material constituting each layer. In addition, it is preferable to use the chip-shaped thing wash | cleaned and grind | pulverized by the well-known method as recycling raw materials, such as a PET bottle recycling raw material.

  And an unstretched sheet is obtained by quenching the extruded sheet-like molten resin. 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. When casting on a rotating drum and quenching and solidifying, an electrode is disposed between the extruder and the rotating drum, a voltage is applied between the electrode and the rotating drum, and the film is electrostatically It is preferable to employ a method of closely contacting the rotating drum since the uneven thickness of the film is reduced.

  As described above, in the production of the heat-shrinkable polyester film of the present invention, a conventionally known method can be adopted, and in particular, tearability and heat-shrinkage characteristics in a label obtained from the heat-shrinkable polyester film of the present invention. From the viewpoint of ensuring the above, the present inventors have found that the sheet forming step desirably satisfies the following requirements. The requirements will be described below.

[Preferred production method of heat-shrinkable polyester film (sheet forming step)]
As described above, the heat-shrinkable polyester film of the present invention is mainly composed of polyethylene terephthalate. Usually, when a film using polyethylene terephthalate as a main raw material is used as a label, the tearability when tearing along a sewing machine and opening the film is not good. As a result of the present inventors' research and development to improve the drawbacks of such heat-shrinkable polyester film, when producing a heat-shrinkable film from polyethylene terephthalate resin, a polyethylene terephthalate raw material having a low IV ( Hereinafter, it was found that the above-mentioned tearability can be improved by adding a large amount of low IV-PET raw material. However, when a large amount of the low IV-PET raw material is added, it has become clear that undesirable phenomena such as deterioration in solvent adhesion and shrinkage finish and increase in the initial fracture rate occur.

  From these findings, the present inventors can adjust the kind and amount of the amorphous component added to the low IV-PET raw material, thereby improving the heat shrinkability of all of the tearability, solvent adhesion, and shrinkage finish. It was examined whether a film could be obtained. However, the single-layer heat-shrinkable film has a limit in achieving a good balance of good tearability, solvent adhesion, shrinkage finish, and initial fracture characteristics. Therefore, the applicants are not a single-layer heat-shrinkable film, but a layer made of a low IV-PET material (hereinafter simply referred to as a low IV layer) and a layer made of a high IV-PET material (hereinafter simply referred to as a high IV layer). In order to improve the solvent adhesion, shrink finish, and initial breakage rate of heat-shrinkable film with low IV-PET raw material added, we conducted intensive studies. It was.

  At the beginning of the study, there was a concern that sufficient heat shrinkage characteristics could not be obtained by laminating the low IV layer and the high IV layer, but the laminating method, laminating mode of the low IV layer and the high IV layer, As a result of investigating the relationship between the tearability, solvent adhesion, shrinkage finish, and initial fracture characteristics of the laminated film in detail, the shrinkage characteristics when the low IV layer and the high IV layer were laminated, contrary to the initial prediction. It has become clear that additivity holds. And by laminating the low IV layer and the high IV layer by the specific method (coextrusion method) shown below, it becomes possible to supplement the characteristics of the low IV layer with the high IV layer, with good tearability, It has been found that the conflicting properties of good solvent adhesion, shrink finish, and low initial fracture rate can be satisfied simultaneously. In addition, by laminating a layer made of a low IV-PET raw material and a layer made of a high IV-PET raw material by a specific method, solvent penetration resistance (solvent penetration) and adhesion in a short time It has also been found that the strength is dramatically improved. Hereinafter, a film forming method for efficiently producing the heat-shrinkable polyester film of the present invention will be described.

In order to obtain the heat-shrinkable polyester film of the present invention, it is necessary to take the following means (a) to (f) in the sheet forming step. By taking such means, it becomes possible to obtain a heat-shrinkable polyester film that satisfies both good tearability, good solvent adhesion, shrinkage finish, and low initial breaking rate at the same time, and has no other problems.
(A) Adjustment of layer structure (b) Adjustment of amorphous component ratio in core layer and skin layer (c) Adjustment of moisture content in raw material chip (d) Cooling of screw of extruder (e) Preheating of extruder (F) Temperature Adjustment of Core Layer Forming Extruder and Skin Layer Forming Extruder Hereinafter, each of the above-mentioned means will be sequentially described.

(A) Adjustment of layer structure In order to obtain the heat-shrinkable polyester film of the present invention, when two or more kinds of polyethylene terephthalate resins having different IV are melt-extruded from a plurality of extruders by a co-extrusion method, the film It is necessary to make a layered structure in which a core layer containing a resin having a low IV is formed and a skin layer containing a resin having a high IV is laminated on both sides thereof. By adopting such a laminated structure, it is possible to simultaneously develop the good solvent adhesion inherent in low IV-PET, the good shrinkage finish property of high IV-PET, and the low initial breaking rate. . In addition, if the layer structure of a film has laminated | stacked the skin layer containing resin with high IV on both surfaces of the core layer containing resin with low IV, the skin layer has a laminated structure which consists of several layers. There may be.

  In addition, you may use raw material resin which has comparable IV for a core layer and a skin layer, In such a case, the layer skin layer containing raw material resin which has higher IV, or raw material which has lower IV A layer containing a resin may be a core layer. Further, when the raw material resin constituting each layer includes two or more kinds of polyethylene terephthalate resins, the difference between the maximum IV and the minimum IV of the polyethylene terephthalate resins is 0.04 dl / g or more and 0.13 dl. / G or less. More preferably, it is 0.05 dl / g or more and 0.12 dl / g or less, More preferably, it is 0.06 dl / g or more and 0.11 dl / g or less. The polyethylene terephthalate resin means that the amount of ethylene terephthalate units in the raw material chip is 50 mol% or more.

(B) Adjustment of Amorphous Component Ratio in Core Layer and Skin Layer In order to obtain the heat-shrinkable polyester film of the present invention, the unit amount derived from the amorphous monomer in the core layer is changed to the non-layer content in the skin layer. It is necessary to make it lower than the ratio of the unit amount derived from the crystalline monomer. If the ratio of the amount of the unit derived from the amorphous monomer in the core layer is large, it is not preferable because permeation blocking easily occurs after solvent adhesion processing.

  In addition, the ratio of the unit derived from the amorphous monomer contained in the core layer is 8 to 12 mol%, more preferably 7 to 11 mol% with respect to the unit amount derived from the amorphous monomer in the entire film. Is preferred.

(C) Adjustment of moisture content in raw material chips In the method of the present invention, it is necessary to adjust the moisture content of the polyester resin raw material chips before being supplied to the hopper of each extruder to 10 ppm to 50 ppm in the sheeting step. is there. If the moisture content of the chip exceeds 50 ppm, it is not preferable because defects such as poor mechanical strength of the obtained film occur. Conversely, if the moisture content of the chip is less than 10 ppm, it is difficult to stretch during production. Therefore, it is not preferable. In addition, the various dryers mentioned above can be used for adjustment of the moisture content in a raw material chip | tip.

(D) Cooling of screw of extruder In the sheeting process according to the method of the present invention, it is necessary to cool the screw of each extruder. When the screw of the extruder is not cooled, the polyester chip containing the amorphous component sticks to the screw feed portion, and there is a case in which a problem such as failure of normal extrusion may occur, which is not preferable. The method for cooling the screw is not particularly limited, but is preferable because a method of circulating cooling water inside the screw is easy.

(E) Adjustment of the temperature of the preheated portion of the extruder and the compression zone Further, in the sheeting process according to the method of the present invention, the temperature of the preheated portion of each extruder is adjusted to 200 ° C. or higher and 270 ° C. or lower. It is necessary to adjust the temperature of the compression zone to 290 ° C. or more and 310 ° C. or less. If the temperature of the preheated part of each extruder is less than 200 ° C and more than 270 ° C, there will be a situation where normal extrusion cannot be performed due to poor biting due to slipping of the polyester-based resin chip or sticking to the screw. This is not preferable. Moreover, when the temperature of the compression zone of each extruder is less than 290 ° C. and more than 310 ° C., it is not preferable because problems such as discharge of unmelted resin and progression of thermal degradation of the raw material resin in the extruder occur.

(F) Temperature adjustment of the extruder for forming the core layer and the extruder for forming the skin layer In addition, in the sheeting step according to the method of the present invention, the temperature of the extruder for extruding the core layer is set to the extrusion for extruding the skin layer. The temperature needs to be higher than the temperature of the machine, and the difference must be 5 ° C. or more and 15 ° C. or less. In this way, when the extrusion temperature of the core layer is made higher than the extrusion temperature of the skin layer and the difference between the extrusion temperatures is 5 ° C. or more and 15 ° C. or less, problems such as an increase in the load on the extrusion motor occur. This is because it can be prevented and normal extrusion can be carried out.

  Only one of the means (a) to (f) described above does not effectively contribute to the tearability of the film (label), good solvent adhesion, shrinkage finish, and low initial breaking rate, By combining and using the means of (a) to (f), it is considered that a heat-shrinkable polyester film satisfying the above properties at the same time and having no other problems can be obtained very efficiently.

  Next, the unstretched sheet obtained through the sheet forming step is stretched. The stretching treatment may be performed continuously after cooling with the rotating drum or the like, or may be wound up into a roll after cooling and then performed. It is most practical in terms of production efficiency of the heat-shrinkable polyester film of the present invention that the unstretched sheet is stretched in the transverse (width) direction of the film and the main shrinkage direction is the transverse (width) direction of the film. Therefore, in the following, the stretching method when the main shrinkage direction is the transverse direction will be mainly described. Even when the main shrinkage direction is the longitudinal (longitudinal) direction of the film, the film is stretched according to the stretching operation when the main shrinkage direction is the transverse direction of the film by changing the stretching direction by 90 ° in the following method. be able to.

The transverse stretching is performed at a predetermined temperature in the range of Tg-20 ° C to Tg + 40 ° C, and the stretching ratio is preferably 2.3 to 7.3 times, more preferably 2.5 to 6.0 times. In addition, after transverse stretching, heat treatment is performed at a predetermined temperature in the range of 50 ° C. to 110 ° C. while applying 0 to 15% elongation or 0 to 15% relaxation, and 40 ° C. to 100 ° C. as necessary. It is preferable to perform the heat treatment again at a predetermined temperature within the range. In order to reduce the uneven thickness of the film after transverse stretching, it is preferable to perform a preheating step prior to the transverse stretching step. In this preheating step, the heat transfer coefficient is 0.00544 J / cm ² · sec · It is preferable to perform heating at a low wind speed until the film surface temperature reaches a certain temperature within the range of Tg + 0 ° C. to Tg + 60 ° C. so as to be equal to or lower than 0 ° C. (0.0013 calories / cm ² · sec · ° C.).

In the transverse stretching step, it is preferable to use equipment that can reduce the fluctuation of the film surface temperature. That is, the stretching process includes a preheating process before stretching, a stretching process, a heat treatment process after stretching, a relaxation process, a restretching process process, and the like. In particular, the preheating process, the stretching process, and the heat treatment process after stretching. In this case, it is preferable to adjust so that the fluctuation range of the surface temperature of the film measured at an arbitrary point is within the average temperature ± 1 ° C., and more preferably within the average temperature ± 0.5 ° C. When the fluctuation range of the surface temperature of the film is small, the film is stretched or heat-treated at the same temperature over the entire length of the film, so that the heat shrinkage behavior and other physical properties become uniform. Equipment that can reduce fluctuations in the film surface temperature includes, for example, equipment that can suppress fluctuations in wind speed by an inverter for controlling the wind speed of hot air that heats the film, and a low pressure of 500 kPa or less (5 kgf / cm ² or less) as the heat source. The equipment etc. which can suppress the temperature fluctuation of the hot air using steam can be mentioned.

  Further, as a method for stretching the film, not only a method of stretching uniaxially with a tenter, but also a method of adding a stretching of 1.0 to 4.0 times, preferably 1.1 to 2.0 times in the longitudinal direction. It is also possible to adopt. When performing such biaxial stretching, both sequential biaxial stretching and simultaneous biaxial stretching can be employed, and re-stretching may be performed as necessary. In the case of sequential biaxial stretching, any of stretching methods such as vertical and horizontal, horizontal and vertical, vertical and horizontal and horizontal and vertical and horizontal directions can be adopted. In the case where the film is stretched in the machine direction, it is preferable to minimize the fluctuation of the film surface temperature as much as possible in the preheating process, the stretching process, etc., similarly to the transverse stretching.

  The heat-shrinkable polyester film of the present invention has a specific anionic antistatic agent on its surface. The anionic antistatic agent can be present on the film surface by applying a coating solution containing the antistatic agent on the film surface (coating method), kneading the antistatic agent in the raw material resin for forming the film, However, in the present invention, it is preferable to employ the above coating method.

  Usually, in a film employing a kneading method, the antistatic effect is exhibited by the antistatic agent oozing out from the inside of the film. However, in the case of a polyester-based film, since the glass transition temperature of polyester is generally high, the antistatic agent hardly oozes out on the film surface at a temperature near room temperature, and the antistatic effect tends to be insufficient. Polyester films have a relatively high film-forming temperature, and the reactivity of polar groups of the polyester is also high. If an antistatic agent is blended in the raw material resin, the polyester will deteriorate during film formation. When prompted, it may cause a decrease in physical properties or coloration.

  On the other hand, in the case of the coating method, since the antistatic agent is directly present on the film surface, the antistatic effect is effectively exhibited regardless of the high glass transition temperature of the polyester, and the introduction of the antistatic agent is effective. Film deterioration and coloring can also be prevented.

  The timing for applying the coating solution containing the antistatic agent to the film surface according to the present invention is not particularly limited, and it may be applied to an unstretched sheet after melt extrusion and before stretching, and a film after stretching (after uniaxial stretching or It may be applied to the film after biaxial stretching.

  In the coating solution applied to the film, a mixed solvent of a lower alcohol having 1 to 3 carbon atoms and water is preferably used as a solvent. As the lower alcohol having 1 to 3 carbon atoms, those that can be mixed with water at an arbitrary ratio, such as methanol, ethanol, n-propanol, and isopropanol, are preferable. Alcohols having a large number of carbon atoms (4 to 18 carbon atoms) are not preferred because they are phase-separated from water when preparing a coating solution, and application of such coating solutions tends to cause coating spots. However, a higher alcohol having a large number of carbon atoms may be used in combination with a lower alcohol having 1 to 3 carbon atoms as long as it does not cause phase separation.

  The amount of the lower alcohol used is preferably 10% by mass or more in the coating solution. When the amount of the lower alcohol is less than 10% by mass, the surface tension of the coating solution is increased, the wettability to the film is lowered, and coating spots are easily generated. The reason is unknown, but in the heat-shrinkable film obtained by applying the coating liquid to the film surface and then drying, when the temperature and humidity change suddenly, the transparency of the film decreases and it is practical May be impaired.

  Moreover, it is preferable that the amount of lower alcohol in a coating liquid is 60 mass% or less. When the amount of lower alcohol exceeds 60% by mass, the amount of organic solvent in the coating solution increases. Therefore, when applying the coating liquid during the film manufacturing process (after melt extrusion and unstretched sheet before stretching), it is necessary to take explosion-proof measures because of the danger of explosion. In addition, when using alcohol with many carbon atoms simultaneously with lower alcohol, it is recommended that the total amount of alcohol in a coating liquid shall be 60 mass% or less.

The amount of the anionic antistatic agent present on the film surface by application of the coating solution is preferably 0.001 to 0.5 g / m ² . More preferably, it is 0.1 g / m < ² > or less, More preferably, it is 0.01 g / m < ² > or less. If the amount of the anionic antistatic agent is below the above range, the antistatic effect may not be sufficiently secured. On the other hand, when the amount of the anionic antistatic agent exceeds the above range, the transparency and blocking resistance of the film may be lowered.

[Label production method]
In order to use the heat-shrinkable polyester film of the present invention as a heat-shrinkable label, for example, the heat-shrinkable film before shrinkage is taken out after being stored in a temperature / humidity controlled environment for a predetermined time, and a known tube shape is obtained. Using a molding device, apply the adhesive solvent to the inner side slightly from the edge of one side of the film at a certain width. Immediately roll up the film, bond the ends overlap, and process the tube. A method of cutting to a predetermined length to obtain a heat-shrinkable label can be suitably employed.

  For the adhesion of the film when forming the label, a melt adhesion method in which a part of the film is melted may be adopted, but from the viewpoint of suppressing fluctuations in the thermal shrinkage characteristics of the label, solvent adhesion using a solvent. The method is preferably adopted. In this case, usable solvents include, for example, aromatic hydrocarbons such as benzene, toluene, xylene and trimethylbenzene; halogenated hydrocarbons such as methylene chloride and chloroform; phenols such as phenol; furans such as tetrahydrofuran; Examples include organic solvents such as oxolanes such as 1,3-dioxolane; among these, it is desirable to use 1,3-dioxolane or tetrahydrofuran with high safety. The heat-shrinkable label formed as described above can be coated on a container if it is attached to a container such as a PET bottle and then thermally contracted by a known heat-shrinking means (hot air tunnel, steam tunnel, etc.).

  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. In addition, "ppm" used in a present Example is a mass reference | standard. Moreover, the measuring method of the physical property of the film obtained by the Example and the comparative example is as follows.

[Film composition]
The film was dissolved in a solvent in which chloroform D (manufactured by Yurisop) and trifluoroacetic acid D1 (manufactured by Yurisop) were mixed at 10: 1 (volume ratio) to prepare a sample solution, and NMR (“GEMINI-200”) was prepared. NMR of the sample solution was measured under the measurement conditions of a temperature of 23 ° C. and an integration count of 64 times. From the obtained chart, the composition ratio of the components constituting the film was calculated based on the peak intensity of a predetermined proton.

[Intrinsic viscosity]
0.1 g of a sample (chip or film) was precisely weighed and dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane = 3/2 (mass ratio), and then measured with an Ostwald viscometer at 30 ± 0.1 ° C. The intrinsic viscosity [η] is determined by the following formula (Huggins formula).

Here, η _SP is the specific viscosity, t ₀ is the drop time of the solvent using the Ostwald viscometer, t is the drop time of the tip solution using the Ostwald viscometer, and C is the concentration of the tip solution. In the actual measurement, the intrinsic viscosity was calculated by the following approximate equation with k = 0.375 in the Huggins equation.

ここで、η_rは、相対粘度である。

Here, η _r is a relative viscosity.

[Initial breaking rate]
A tensile test was performed according to JIS K 7127 in the direction perpendicular to the main shrinkage direction of the heat-shrinkable polyester film after being stored for 672 hours (28 days) in an atmosphere of 30 ° C. and 85% relative humidity. The tensile test was performed under the conditions of a test piece length of 200 mm, a chuck-to-chuck distance of 100 mm, a test piece width of 15 mm, a temperature of 23 ° C., and a pulling speed of 200 mm / min. Then, the number of test pieces fractured at an elongation of 5% or less was counted, and the percentage (%) with respect to all the test pieces (20 pieces) was obtained to obtain the initial fracture rate (%).

[Solvent adhesive strength]
On the film surface of 10 cm × 10 cm, 1,3-dioxolane was applied at a coating amount of 3 ± 0.5 g / m ² and a coating width of 3 cm in the central portion of the film in parallel to the direction perpendicular to the main shrinkage direction of the film. The two films were laminated and bonded so that the back surface of the other film was in contact with the solvent-coated surface. After 1 hour has elapsed from the bonding of the film, a measurement sample having a film length (film main shrinkage direction) of 50 mm and a width of 15 mm was cut out so that the bonding portion was in the center, and this was cut into a universal tensile testing machine (STM -50, manufactured by Baldwin Co., Ltd.), and a 90 ° peel test was performed under the condition of a tensile speed of 200 mm / min. The tensile strength when the other film peeled from one film was defined as the solvent adhesive strength.

[Solvent penetration resistance]
The film was cut to prepare 10 samples of size 5 cm × 5 cm, and 5 sheets were stacked so that the inner surface of the roll (the surface that becomes the core side when winding the stretched film) was on the upper side (lower sample film) 1-5). One drop (approximately 18 μl) of 1,3-dioxolane is dropped on the uppermost central portion (lower film 5) of the stacked films, and immediately, five sheets are placed so that the inner surface of the roll is upward. The samples were stacked (upper sample film 6 to 10, upper sample film 6 was in contact with lower sample film 5), and the whole was wrapped with aluminum foil and sealed. Next, after being stored at 40 ° C. for 24 hours under a load of 2 kg, after opening and confirming the number of sheets infiltrated with the solvent, the first and second sheets (ie, 1,3- The adhesive strength between the lower sample film 5 on which dioxolane was dropped, the lower sample film 4 below it, and the upper sample films 6 and 7) was measured by the same method as the above-mentioned solvent adhesive strength, and evaluated according to the following criteria.
○: Adhesive strength is less than 0.2 N / 15 mm Δ: Adhesive strength is 0.2 N / 15 mm or more and less than 0.5 N / 15 mm ×: Adhesive strength is 0.5 N / 15 mm or more

[95 ° C hot water heat shrinkage]
The film was cut into a 10 cm × 10 cm square, immersed in warm water at 95 ° C. ± 0.5 ° C. for 10 seconds in a no-load state and heat-shrinked, and immediately immersed in water at 25 ° C. ± 0.5 ° C. After dipping for a second, the lengths of the sample in the vertical and horizontal directions were measured, and the thermal shrinkage rate (%) was calculated according to the following formula 1. The direction with the largest shrinkage rate was defined as the main shrinkage direction.
Thermal shrinkage rate (%) = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 Formula 1

[Tear propagation resistance ratio]
Two types of samples, a main shrinkage direction 51 mm × orthogonal direction 64 mm sample and a main shrinkage direction 64 mm × orthogonal direction 51 mm sample, are cut out from the film, and each resistance value when tearing these two types of samples conforms to JIS P 8116. Then, measurement was performed using a light load tearer manufactured by Toyo Seiki Co., Ltd., and the obtained measurement values were taken as tear propagation resistance values in the main shrinkage direction and the orthogonal direction, respectively. Then, the tear propagation resistance ratio was calculated from each measured value by the following formula 2. The measurement of the tear propagation resistance value was repeated five times in both the orthogonal direction and the main shrinkage direction, and the average value of the five tear propagation resistance ratios was taken as the tear propagation resistance ratio.
Tear propagation resistance ratio = Tear propagation resistance value in the orthogonal direction ÷ Tear propagation resistance value in the main shrinkage direction ... Equation 2

[Maximum heat shrinkage stress value]
It measured using the tensile tester with a heating furnace ("Tensilon" by Toyo Seiki Co., Ltd.). A sample with a length in the main shrinkage direction of 200 mm and a width of 20 mm was cut out from the film before heat shrinkage, the blowing of the tensile tester heated in advance to 90 ° C. was stopped, and the distance between the chucks was set to 100 mm. After being attached to the chuck, the heating furnace door is immediately closed, and air blowing (hot air at a temperature of 90 ° C. and a blowing speed of 5 m / second is supplied from the back, left and right directions) is detected. The shrinkage stress was measured, and the maximum heat shrinkage stress value (MPa) was determined from the measurement chart.

[Shrink finish]
The heat-shrinkable film was preliminarily printed in three colors with grass, gold, and white ink from Toyo Ink Manufacturing Co., Ltd. A cylindrical label (the main shrinkage direction of the heat-shrinkable film is taken as the circumferential direction) was prepared by adhering both ends of the printed film with dioxolane.

Next, using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc., spraying water vapor with a passage time of 2.5 seconds and a zone temperature of 80 ° C. with a vapor pressure of 1 kg / cm ² (pressure gauge display: 98 kPa). The label was attached by heat shrinking to a 500 ml PET bottle (body diameter: 62 mm, minimum neck diameter: 25 mm). In addition, when mounting | wearing, it adjusted so that the 40 mm diameter part of a neck part might become one end of a 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 up nor contraction has occurred, but spots are seen on the neck. ×: Wrinkles, jumping up, insufficient contraction has occurred.

[Perforation opening]
A label having a perforation in advance in a direction perpendicular to the main shrinkage direction was attached to a PET bottle under the same conditions as those for measuring the shrinkage finish, and heat-shrinked. For the perforation, two holes having a length of 1 mm were formed at intervals of 1 mm over a length (120 mm) in the vertical direction (height direction) of the label (distance 22 mm between the two). The notch was provided on the upper side of the label when the bottle was raised.

The perforation is formed by placing two 1 mm thick cardboards under a folded label, using a perforation blade having a shape corresponding to the size and spacing of the perforation holes, and a gauge pressure of 2 kg. A perforation was put on the label at 5 mm from the end of the label folded in half by crimping a perforation blade to the label at / cm ² .

  After that, the bottle with the label is filled with 500 ml of water, refrigerated at 5 ° C for 24 hours, tear the perforation of the label on the bottle immediately after taking out from the refrigerator with your fingertips, and tear it cleanly along the perforation in the vertical direction The number of labels that could be removed from the bottle was counted, and 30 or more were evaluated as “◯” and less than 30 were evaluated as “×”.

[Surface specific resistance]
Using a surface resistivity measuring instrument (main body: R8340, sample box: R12704) manufactured by Advantest Corporation, measurement was performed in an atmosphere of an applied voltage of 100 V, 23 ° C., 65% RH, and the reading value of the measuring instrument was defined as the surface resistivity. Those having a surface resistivity of 13 Ω · cm or less were evaluated as having excellent antistatic properties.

  Table 1 shows properties and compositions of polyesters A to F used in Examples and Comparative Examples. Furthermore, the composition of the polyester resin in Examples and Comparative Examples, and the film compositions obtained in Examples and Comparative Examples are shown in Table 2, and the film production conditions in Examples and Comparative Examples are shown in Table 3. In Tables 1 and 2, “TPA” is terephthalic acid, “EG” is ethylene glycol, “BD” is 1,4-butanediol, “NPG” is neopentyl glycol, “CHDM” is 1 , 4-cyclohexanedimethanol means each.

[Preparation of anionic antistatic coating solution]
Coating liquid 1
It diluted by adding 63 mass% of water to 2 mass% of dodecyl sulfonate and further adding 35 mass% of isopropanol to prepare a coating solution having a solid content concentration of 2 mass%.
Coating liquid 2
It diluted by adding 63 mass% of water to 2 mass% of dodecylbenzenesulfonate, and further adding 35 mass% of isopropanol to prepare a coating solution having a solid content concentration of 2 mass%.

[Example 1]
Resin for core layer formation is melted in a single screw extruder (first extruder), and a resin for skin layer formation is melted in a single screw extruder (second extruder). Using a co-extrusion method, the molten resin was laminated and extruded in a three-layer T die, and then rapidly cooled to obtain an unstretched sheet having a thickness of 175 μm consisting of a three-layer structure of skin layer / core layer / skin layer. It was.

  In addition, as resin for core layer formation, polyester A (IV = 0.70 dl / g): 9 mass%, polyester B (IV = 0.70 dl / g): 31 mass%, polyester C (IV = 1. 20 dl / g): 10% by mass, polyester D (IV = 0.65 dl / g): a polyester resin mixed with 50% by mass was used. Moreover, as resin for skin layer formation of both front and back, the polyester-type resin which mixed polyester A: 15 mass%, polyester B: 75 mass%, and polyester C: 10 mass% was used.

  In the preparation of the unstretched sheet described above, each polyester resin chip before being supplied to the hopper provided in each of the first extruder (for core layer formation) and the second extruder (for skin layer formation). The moisture content of each was adjusted to 30 ppm or less. Further, the screws of the first and second extruders were cooled with circulating water. Furthermore, while adjusting the preheating temperature of each extruder to 265 degreeC, the temperature of the compression zone of each extruder was adjusted to 300 degreeC. In addition, in the production of the unstretched sheet described above, the temperature of the first extruder for core layer extrusion was adjusted to 280 ° C., and the temperature of the second extruder for skin layer extrusion was adjusted to 275 ° C. (both Difference: 5 ° C.).

An anionic antistatic agent coating solution 1 prepared in advance was applied to one side of the obtained unstretched sheet by an air knife method, preheated at 88 ° C. for 10 seconds, and then in a tenter at 80 ° C. in the lateral direction. Stretched 9 times, followed by heat treatment at 78 ° C. for 10 seconds, thickness 45 μm (skin layer / core layer / skin layer thickness: 11.25 μm / 22.5 μm / 11.25 μm), coat amount 0.004 g A heat-shrinkable polyester film of / m ² was obtained. In addition, the fluctuation | variation of the surface temperature of the film in each process of an extending process was settled in the range of +/- 0.5 degreeC. Table 3 shows the film production conditions, and Tables 4 and 5 show the characteristics of the films evaluated by the above evaluation methods.

[Example 2]
Polyester which forms the skin layer by changing the mixing ratio of the polyester resin forming the core layer to 16% by mass of polyester A, 31% by mass of polyester B, 10% by mass of polyester C, and 43% by mass of polyester D The thickness is the same as in Example 1 except that the mixing ratio of the polyester resin is changed to 8% by mass of polyester A, 75% by mass of polyester B, 10% by mass of polyester C, and 7% by mass of polyester D. A heat-shrinkable polyester film having a thickness of 45 μm (each thickness of skin layer / core layer / skin layer: 11.25 μm / 22.5 μm / 11.25 μm) was obtained. In Example 2, as in Example 1, the variation in the surface temperature of the film in each step of the stretching process was within a range of ± 0.5 ° C. The film production conditions are shown in Table 3, and the characteristics of the film evaluated by the above evaluation method are shown in Table 4.

[Example 3]
The mixing ratio of the polyester resin forming the core layer is 31% by mass of polyester B, 10% by mass of polyester C, 50% by mass of polyester D, and 9% by mass of polyester F (IV = 0.60 dl / g). In the same manner as in Example 1 except that the mixing ratio of the polyester resin forming the skin layer was changed to 75% by mass of polyester B, 10% by mass of polyester C, and 15% by mass of polyester F, A heat-shrinkable polyester film having a thickness of 45 μm (each thickness of skin layer / core layer / skin layer: 11.25 μm / 22.5 μm / 11.25 μm) was obtained. In Example 3, as in Example 1, the variation in the surface temperature of the film in each step of the stretching process was within a range of ± 0.5 ° C. The film production conditions are shown in Table 3, and the characteristics of the film evaluated by the above evaluation method are shown in Table 4.

[Example 4]
The mixing ratio of the polyester resin forming the core layer is 9% by mass of polyester A, 10% by mass of polyester C, 50% by mass of polyester D, and 31% by mass of polyester E (IV = 0.70 dl / g). The mixing ratio of the polyester resin forming the skin layer was changed to 15% by weight of polyester A, 10% by weight of polyester C, and 75% by weight of polyester E, the stretching temperature was changed to 83 ° C., and heat treatment was performed. Except that the temperature was changed to 80 ° C., the heat shrinkage was 45 μm (skin layer / core layer / skin layer thickness: 11.25 μm / 22.5 μm / 11.25 μm) in the same manner as in Example 1. A conductive polyester film was obtained. In Example 4, as in Example 1, the variation of the film surface temperature in each step of the stretching process was within the range of ± 0.5 ° C. The film production conditions are shown in Table 3, and the characteristics of the film evaluated by the above evaluation method are shown in Table 4.

[Comparative Example 1]
The mixing ratio of the polyester resin forming the core layer was changed to 55% by weight of polyester B, 10% by weight of polyester C, and 35% by weight of polyester D, and the mixing ratio of the polyester resin forming the skin layer was changed. Polyester A: 35% by mass, Polyester B: 55% by mass, Polyester C: Thickness 45 μm (skin layer / core layer / skin layer thickness) in the same manner as in Example 1 except that the content was changed to 10% by mass. : 11.25 μm / 22.5 μm / 11.25 μm) heat-shrinkable polyester film. In Comparative Example 1, as in Example 1, the variation in the surface temperature of the film in each step of the stretching process was within a range of ± 0.5 ° C. The film production conditions are shown in Table 3, and the characteristics of the film evaluated by the above evaluation method are shown in Table 4.

[Comparative Example 2]
The mixing ratio of the polyester resin that forms the core layer is changed to 30% by mass of polyester B, 10% by mass of polyester C, and 60% by mass of polyester D, and the mixing ratio of the polyester resin that forms the skin layer is Polyester B: 90% by mass, Polyester C: Changed to 10% by mass, except that the heat treatment temperature was changed to 81 ° C., the thickness was 45 μm (skin layer / core layer / skin layer). A heat-shrinkable polyester film having a thickness of 11.25 μm / 22.5 μm / 11.25 μm was obtained. In Comparative Example 2, as in Example 1, the variation in the surface temperature of the film in each step of the stretching process was within a range of ± 0.5 ° C. The film production conditions are shown in Table 3, and the characteristics of the film evaluated by the above evaluation method are shown in Table 4.

[Comparative Example 3]
The mixing ratio of the polyester resin that forms the core layer is changed to 10% by mass of polyester C, 15% by mass of polyester D, and 75% by mass of polyester E, and the mixing ratio of the polyester resin that forms the skin layer is changed. Polyester A: 15% by mass, polyester C: 10% by mass, polyester E: 75% by mass, stretching temperature is changed to 85 ° C., heat treatment temperature is changed to 81 ° C., and anionic antistatic agent coating solution Heat shrinkability of 45 μm (skin layer / core layer / skin layer thickness: 11.25 μm / 22.5 μm / 11.25 μm) in the same manner as in Example 1 except that No. 1 was not applied. A polyester film was obtained. In Comparative Example 3, as in Example 1, the variation in the surface temperature of the film in each step of the stretching process was within a range of ± 0.5 ° C. And the characteristic of the obtained film was evaluated by the same evaluation method as Example 1. The evaluation results are shown in Table 4.

[Comparative Example 4]
When the core layer and the skin layer were co-extruded by the same single screw extruder as in Example 1, the temperatures of the preheating portion and the compression zone of the first extruder and the second extruder were 280 ° C. and 285 ° C., respectively. The core layer extrusion temperature and skin layer extrusion temperature were both changed to 275 ° C. And although it tried to melt-extrude the polyester-type resin similar to Example 1 without cooling a screw, normal melt-extrusion cannot be performed and the unstretchable sheet | seat which can be extended | stretched can be obtained. There wasn't.

  From Table 4, it can be seen that the film of each example is very good in both perforation opening and solvent adhesion. In addition, it can be seen that the film of each example exhibits good solvent penetration resistance (good solvent penetration index). On the other hand, it can be seen that the film of each comparative example has poor perforation-opening properties, solvent adhesion, and solvent penetration resistance (solvent penetration index).

[Example 5, Comparative Examples 5-6]
Heat shrinkability in the same manner as in Example 1, except that the coating amount of the anionic antistatic agent coating solution 1 was changed so that the amount of the anionic antistatic agent present on the film surface was the amount shown in Table 5. A polyester film was obtained. In Comparative Example 6, no anionic antistatic agent coating solution was applied. The properties of the obtained film are shown in Table 5.

From Table 5, it can be seen that when the amount of the antistatic material present on the surface of the heat-shrinkable polyester film is 0.002 g / m ² or more, good antistatic properties are exhibited.

  As described above, the heat-shrinkable polyester film of the present invention has excellent properties such as perforation opening, solvent adhesion, shrink finish, solvent penetration resistance, and troubles caused by static electricity are suppressed. Therefore, it can be suitably used for bottle labeling and the like.

Claims (8)

It is a heat-shrinkable polyester film composed of a polyester resin in which ethylene terephthalate is the main constituent unit, and the unit derived from an amorphous monomer is 15 mol% or more in all polyester resin components,
The thickness is 25 μm or more and 60 μm or less,
An anionic antistatic agent having an alkyl group having 10 to 20 carbon atoms is present on at least one surface of the heat-shrinkable polyester film,
A heat-shrinkable polyester film characterized by satisfying the following requirements (1) to (5).
(1) After storing the film in an atmosphere of 30 ° C. and 85% relative humidity for 672 hours or more, when a tensile test is performed in the direction orthogonal to the main shrinkage direction, the number of test pieces having a breaking elongation of 5% or less 25% or less of the total number of test pieces,
(2) The adhesive strength after 1 hour has passed since the surface and the back surface of the film are solvent-bonded with tetrahydrofuran, and is 2N / 15mm or more and 15N / 15mm or less.
(3) After dropping 1,3-dioxolane onto a predetermined number of films, a predetermined number of films are stacked on the dropping portion to form a film laminate, and the film laminate is subjected to a predetermined pressure over a predetermined time. After compression, the adhesive strength between the film on which 1,3-dioxolane is dropped and the film located thereunder, and the adhesion between the film superimposed on the film on which 1,3-dioxolane is dropped and the film located on the upper side When the strength is measured, both of these two adhesive strengths are 0.2 N / 15 mm or less.
(4) The hot water shrinkage rate in the main shrinkage direction when treated for 10 seconds in warm water at 95 ° C. is 50% or more and 80% or less,
(5) The tear propagation resistance ratio in the direction orthogonal to the main shrinkage direction of the film is 3.5 or more and 6.0 or less.   The heat-shrinkable polyester film according to claim 1, wherein the amorphous monomer is mainly composed of one selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid.   The heat-shrinkable polyester film according to claim 1 or 2, wherein the heat-shrinkable polyester film has a laminated structure in which a core layer and skin layers are laminated on both surfaces of the core layer.   The thermal contraction according to any one of claims 1 to 3, wherein the polyester resin material constituting the core layer is made of a material having a lower intrinsic viscosity (IV) than the polyester resin constituting the skin layer. Polyester film.   The ratio of the unit derived from the amorphous monomer contained in the polyester resin raw material constituting the core layer is lower than the ratio of the unit derived from the amorphous monomer contained in the polyester resin raw material constituting the skin layer. The heat-shrinkable polyester film according to any one of claims 1 to 4. A method for producing the heat-shrinkable polyester film according to claim 1,
Including a sheeting step of forming an unstretched sheet by melt-extruding a polyester-based resin raw material from an extruder, and a stretching step of stretching the unstretched sheet obtained in the sheeting step at least in the lateral direction,
The method for producing a heat-shrinkable polyester film, wherein the sheet forming step satisfies the following requirements (a) to (f).
(A) Two or more kinds of polyester resins having different intrinsic viscosities (IV) are melt-extruded from a plurality of extruders by a co-extrusion method, and a core layer made of a low IV resin and a skin layer made of a high IV resin Is a step of forming an unstretched sheet laminated with
(B) The ratio of the unit derived from the amorphous monomer contained in the core layer is lower than the ratio of the unit derived from the amorphous monomer in the skin layer.
(C) The moisture content of the polyester resin chips supplied to the hopper of the extruder is 10 ppm or more and 50 ppm or less.
(D) It is performed while cooling the screw of each extruder.
(E) The preheating temperature of the extruder is 200 ° C. or more and 270 ° C. or less, and the temperature of the compression zone of each extruder is 290 ° C. or more and 310 ° C. or less.
(F) The temperature of the extruder for extruding the core layer is higher than the temperature of the extruder for extruding the skin layer, and the difference is 5 ° C. or more and 15 ° C. or less.   The polyester resin raw material includes two or more kinds of polyethylene terephthalate resins having different IVs, and the difference between the maximum IV and the minimum IV of the polyethylene terephthalate resin IV is 0.04 dl / g or more and 0.13 dl. / G or less, The manufacturing method of the heat-shrinkable polyester film of Claim 6.   After applying a coating solution containing an anionic antistatic agent having a C10-20 alkyl group to at least one surface of the unstretched sheet or the uniaxially stretched polyester film, the coated film is biaxially stretched or The method for producing a heat-shrinkable polyester film according to claim 6, which is uniaxially stretched.