JP2007090605A - Heat-shrinkable polyester film and heat-shrinkable label - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film which has excellent heat shrinkability and solvent adhesion, causes no breaking troubles in post-processes, e.g. printing or a label processing and exerts excellent breaking resistance during long storage of the film. <P>SOLUTION: Among all the polyester resin components, layers (A) consisting of a polyester resin containing less than 72 mol% of ethylene terephthalate units are arranged on both sides of a layer (B) consisting of a polyester resin containing at least 70 mol% of ethylene terephthalate units. The film has a heat shrinkage in the maximum shrinking direction of ≥50% when immersed in warm water of 95°C for 10 s and can be adhered with a non-chlorine type organic solvent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

Heat-shrinkable plastic films are widely used for applications such as shrink wrapping, shrinkage labels, cap seals, etc. by utilizing the property of shrinking by heating. Among them, stretched films such as polyvinyl chloride films, polystyrene films, and polyester films are used for labels, cap seals, and integrated packaging in various containers such as polyethylene terephthalate (PET) containers, polyethylene containers, and glass containers. Has been.

  However, the polyvinyl chloride film has problems such as low heat resistance, generation of hydrogen chloride gas during incineration, and dioxin. Further, when a heat-shrinkable vinyl chloride resin film is used as a shrink label for a PET container or the like, there is a problem in that the label and the container must be separated when the container is recycled.

  On the other hand, a polystyrene film can be evaluated for its good finished appearance after shrinkage, but it is poor in solvent resistance, so an ink with a special composition must be used for printing. In addition, heat-shrinkable films have recently been used in hot beverage PET bottle labels, but when stored in warming equipment such as hot-warmers, the heat-shrinkable polystyrene film comes into contact with hot wires that have become hot. There is a problem that the shrinkage label melts instantly. Furthermore, the polystyrene resin needs to be incinerated at a high temperature, and has a problem that a large amount of black smoke and off-flavor are generated at the time of incineration.

  Polyester films without these problems (excellent in solvent resistance, heat resistance, and environmental suitability) are highly expected as shrink labels to replace polyvinyl chloride films and polystyrene films. Along with the increase, the usage amount is also increasing.

  However, the conventional heat-shrinkable polyester film has also been required to have further improvement in shrinkage characteristics. When the degree of stretching is increased in order to ensure the shrinkage rate, the film is likely to break in the direction perpendicular to the shrinkage direction, which may cause troubles in the printing process, the label processing process, or the film after shrinkage. This breaking trouble is likely to occur when stored for a long time in a relatively high temperature atmosphere of 30 ° C. or higher, and improvement of this breaking trouble has been desired.

As disclosed in Patent Document 1, a polyester film with an increased content of ethylene terephthalate units becomes tough, difficult to tear, and yield point stress increases. Can be obtained.
JP-A-9-239833

  By the way, when using a heat-shrinkable film for coating a real container, after performing a printing process as necessary, it is processed into a form such as a label (tubular label) or a tube, and these processed films Is attached to the container and is heat-shrinked so as to be closely attached to the container. In the tube processing, depending on the composition of the polyester film, there is often a problem that the adhesiveness is insufficient.

  When a label is produced from a heat-shrinkable polyester film, it is often adhered using a solvent. For this adhesion, it is preferable that a solvent such as 1,3-disoxolane or tetrahydrofuran is applied to one surface of the film and the other surface of the film is pressure-bonded to the applied surface. If the adhesive strength is insufficient, the label mounting part may be peeled off when the label is heat-shrinked or when the beverage bottle is handled. However, when the content of the ethylene terephthalate unit is increased, there is a tendency that the solvent adhesion due to application of a non-chlorinated solvent (1,3-dioxolane, tetrahydrofuran, etc.) or pressure bonding is lowered.

  The present invention has been made in view of the above circumstances, and has excellent heat shrinkability, excellent solvent adhesiveness, less breakage troubles in subsequent processes such as printing and labeling, and a film for a long period of time. It is an object to provide a heat-shrinkable polyester film having excellent tear resistance even when stored.

In the heat-shrinkable polyester film of the present invention, the layer (A) composed of a polyester resin having less than 72 mol% of ethylene terephthalate units in all polyester resin components has 70 mol% of ethylene terephthalate units in all polyester resin components. Located at both outer layers of the polyester resin layer (B), the hot water shrinkage in the maximum shrinkage direction is 50% or more at 95 ° C., and the thermal shrinkage in the direction orthogonal to the maximum shrinkage is 4 % Heat-shrinkable polyester film characterized in that it can be bonded with a non-chlorine organic solvent.
That is, two polyester resin mixtures (A ′) whose ethylene terephthalate units are less than 72 mol% in all polyester resin components and two resin mixtures (B ′) whose ethylene terephthalate units are 70 mol% or more in all polyester resin components Are melted and co-extruded using an extruder, and (A) is laminated as an outer layer and (B) is an inner layer to obtain an unstretched polyester film having at least two types and three layers, uniaxially stretched, or A heat-shrinkable polyester film obtained by biaxial stretching and a method for producing the same, and a heat-shrinkable polyester film excellent in solvent adhesion and processing suitability when used as a label can be provided. .

The “maximum shrinkage direction” means the direction in which the sample is most contracted, and the thermal shrinkage rate in the maximum shrinkage direction is determined by the shrinkage rate in the vertical direction or the horizontal direction of the square sample. That is, the heat shrinkage rate (%) in the maximum shrinkage direction was measured by measuring the length of the film in the vertical and horizontal directions after immersing a 10 cm × 10 cm sample in 95 ° C. ± 0.5 ° C. water for 10 seconds under no load. By doing so, it can be obtained by the following equation.
Heat shrinkage rate (%) = 100 × (length before shrinkage−length after shrinkage) ÷ (length before shrinkage)

  The heat-shrinkable polyester film of the present invention has excellent heat-shrinkage properties and solvent adhesion, and is excellent in shrink finish, and can maintain excellent cutting resistance even when the film is stored for a long period of time. Therefore, it can be suitably used for applications such as shrink labels, cap seals, shrink wrapping and the like.

  The heat-shrinkable polyester film of the present invention is obtained by pulling up a sample cut into a 10 cm × 10 cm square shape by immersing it in 95 ° C. warm water for 10 seconds and then immersing it in 25 ° C. water for 10 seconds. The heat shrinkage rate in the maximum shrinkage direction must be 50% or more. If the film has a heat shrinkage rate of less than 50%, the film heat shrinkage rate is insufficient, and when the film is covered and shrunk to a container or the like, the film does not adhere to the container and an appearance defect occurs. A more preferable heat shrinkage rate is 52% or more, and further preferably 55% or more. On the other hand, if the thermal shrinkage rate is excessively high, an appearance defect such as jumping of the label occurs due to abrupt shrinkage when the container is covered and contracted. The heat shrinkage rate is preferably 80% or less, more preferably 78% or less, and still more preferably 76% or less. Further, the heat shrinkage rate in the maximum shrinkage direction when immersed in warm water of 75 ° C. for 10 seconds and then pulled up in water of 25 ° C. for 10 seconds must be 20% or more. When the film has a thermal shrinkage rate of less than 20%, when the container is coated and shrunk, the shrinkage rate is insufficient at a low temperature, so the shrinkage is insufficient, and it is necessary to raise the temperature excessively. It is unfavorable because it shrinks rapidly and tends to cause wrinkles and shrinkage spots. A more preferable heat shrinkage rate is 25% or more, and further preferably 30% or more. Further, if the thermal shrinkage rate becomes too high, the shrinkage is abrupt even at a low temperature, resulting in poor appearance such as jumping of the label. The heat shrinkage rate is preferably 45% or less, more preferably 43% or less, and still more preferably 41% or less.

  The thermal shrinkage rate in the direction perpendicular to the maximum shrinkage direction when immersed in warm water at 95 ° C. for 10 seconds and then pulled up in water at 25 ° C. for 10 seconds is 4% or more, and 5% The above is more preferable. If the thermal contraction rate in the direction orthogonal to the maximum shrinking direction is less than 4%, it is not preferable that the container has a three-dimensional shape, because loosening occurs when a label is attached, and a horizontal reed tends to enter. The upper limit value of the heat shrinkage rate in the direction orthogonal to the maximum shrinkage direction is preferably 11% or less, and more preferably 9% or less. When the heat shrinkage rate exceeds the above-mentioned preferable upper limit value, there arises a drawback that the vertical shrinkage of the label becomes large during shrinkage.

  The maximum value of the shrinkage stress in the main shrinkage direction at 90 ° C. is 12 MPa or less, and more preferably 10 MPa or less. When the pressure is 12 MPa or more, the container is too tight and the liquid level rises and may be spilled when the lid is opened. On the other hand, when the pressure is 4 MPa or less, tightening becomes too weak, and depending on the shape of the container, idle rotation occurs, which is not preferable. More preferably, it is 4.5 MPa or more.

  Moreover, in this invention, it is suitable that it can adhere | attach with a non-chlorine-type solvent. The label is rolled into a cylindrical shape so that the maximum shrinkage direction of the heat-shrinkable polyester film of the present invention is the circumferential direction, and the ends are bonded to each other to create a tubular body. It is created by cutting. Adhesive solvents include 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; 1,3-dioxolane. Organic solvents such as oxolanes are used, but in consideration of the generation of toxic substances caused by halogens such as chlorine atoms, it is preferable that they can be bonded with non-chlorine organic solvents, and in particular, from the viewpoint of safety Therefore, it is desirable to use tetrahydrofuran and 1,3-dioxolane.

  Adequate heat shrinkage rate in the main shrinkage direction and the direction perpendicular to the main shrinkage direction of the film and the adhesiveness of the film with a non-chlorine solvent should adopt the following preferable raw material composition, laminated structure, and film forming conditions. It is possible to secure by.

  Next, the preferable composition of the heat-shrinkable polyester film of the present invention will be described. Examples of the polyester as the main constituent of the present invention include ethylene terephthalate, ethylene naphthalate, and ethylene isophthalate. Among them, ethylene terephthalate is mainly used from the viewpoint of film tear resistance, heat resistance, shrink finish, cost, and the like. It is preferable to contain the other monomer component mentioned later as a structural component. As other dicarboxylic acid components constituting the polyester, aromatic dicarboxylic acids or their ester-forming derivatives, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and the like can be used. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalene-1,4- or -2,6-dicarboxylic acid, and 5-sodium sulfoisophthalic acid. Examples of these ester derivatives include derivatives such as dialkyl esters and diaryl esters. Examples of the aliphatic dicarboxylic acid include dimer acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, oxalic acid, and succinic acid. Examples of the alicyclic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid. It is done. Further, an oxycarboxylic acid such as p-oxybenzoic acid, and a polyvalent carboxylic acid such as trimellitic anhydride or pyromellitic anhydride may be used in combination as necessary.

  Examples of the diol component constituting the polyester used in the present invention include ethylene glycol, diethylene glycol, 1,3-propanediol, triethylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, , 6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 1,9-nonanediol, 1,10 -Ether glycols such as alkylene glycol such as decanediol, polyoxytetramethylene glycol, polyethylene glycol, alkylene oxide adduct of bisphenol compound or derivatives thereof, dimer diol and the like are included. Trihydric or higher alcohols include trimethylolpropane, glycerin, pentaerythritol and the like. Among the polyhydric alcohol components, neopentyl glycol component, 1,4-cyclohexanedimethanol component and the like are useful components for amorphizing the film and can be used because the heat shrinkability of the film can be increased. It is preferable. The preferred amount of use is 5 to 40 mol%, more preferably 10 to 35 mol% with respect to 100 mol% of the diol component in the entire film, and in both outer layers (A), the solvent adhesion is ensured. From the point, it is 18 mol% to 40 mol%, more preferably 20 mol% to 35 mol%. Further, the 1,4-butanediol component, the 1,3-propanediol component, and the like are useful components for lowering the glass transition temperature of the film and enabling heat shrinkage even at a low temperature. It is a preferred embodiment of the present invention to contain these components that lower the glass transition temperature, and in particular the 1,4-butanediol component is preferably 2 mol% or more with respect to 100 mol% of the diol component in the entire film, More preferably 4 mol% or more, and still more preferably 6 mol% or more.

  The polyester composition used in the present invention further includes, for example, inorganic lubricants such as titanium dioxide, fine-particle silica, kaolin, and calcium carbonate, and, for example, long chains to improve the slipperiness of the heat-shrinkable film. It is also preferable to contain an organic lubricant such as a fatty acid ester.

  In the heat-shrinkable polyester film of the present invention, inorganic particles, organic salt particles and crosslinked polymer particles can be added as a lubricant.

  Inorganic particles include calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, riotium fluoride, etc. Is mentioned.

  In particular, in order to obtain a film with a lower haze while obtaining good handling properties, the inorganic particles are preferably agglomerated silica particles formed by agglomerating primary particles.

  Examples of the organic salt particles include terephthalate such as calcium oxalate, calcium, barium, zinc, manganese, and magnesium.

  Examples of the crosslinked polymer particles include homopolymers or copolymers of vinyl monomers such as divinylbenzene, styrene, acrylic acid or methacrylic acid. In addition, organic particles such as polytetrafluoroethylene, benzoguanamine resin, thermosetting urea resin, and thermosetting phenol resin may be used.

  Examples of the method for adding the lubricant include a method in which the lubricant is dispersed in the polymerization step of the polyester used as the film raw material, a method in which the polyester after polymerization is melted again, and the like. In order to disperse the lubricant uniformly in the film roll, after the lubricant is dispersed in the polyester by any of the methods described above, the shape of the polymer chip in which the lubricant is dispersed is matched and the raw material segregation in the hopper It is preferable to suppress this phenomenon. Taking polyester as an example, a polyester chip that is taken out in a molten state from a polymerization apparatus in a molten state after polymerization and immediately cooled with water and then cut with a strand cutter has a cylindrical shape with an elliptical bottom surface. It is preferable to use different raw material chips in which the average size of the major axis, minor axis, and cylindrical height of the elliptical bottom surface is within the range of the chip size ± 20% of the raw material species with the highest usage ratio, More preferably, the size is within a range of ± 15%.

  Moreover, a ultraviolet absorber, an antistatic agent, a coloring agent, an antibacterial agent, etc. can also be added as needed. The preferred intrinsic viscosity for forming the film is not limited, but is usually 0.30 to 1.30 dl / g.

The polyester contained in the raw material composition is composed of the acid component and the diol component. In order to adjust the polyester, one or more acid components are used to improve the properties as a heat-shrinkable film. Or it is preferable to use combining a diol component, and the kind and content of the monomer component combined are suitably determined based on a desired film characteristic and economical characteristic.
The raw material composition contains one or more polyesters. When two or more kinds of polyesters are mixed, a mixture having a desired composition of a copolyester and a homopolyester is prepared. In general, copolyester has a low melting point, so it is difficult to handle at the time of drying, so homopolyester (polyethylene terephthalate, polyethylene naphthalate, poly (1,4-cyclohexene diethylene terephthalate), etc.) and copolyester are used. It is preferable to use a mixture.
As a preferred embodiment, any one or more of an ethylene terephthalate unit, a unit consisting of neopentyl glycol and terephthalic acid, 1,4-cyclohexanedimethanol and terephthalic acid unit, butylene terephthalate, propylene terephthalate, and ethylene isophthalate are used. In a more preferable embodiment, the polyester contains ethylene terephthalate and a unit composed of neopentyl glycol and terephthalic acid, a unit composed of 1,4-cyclohexanedimethanol and terephthalic acid, and a butylene terephthalate unit or propylene terephthalate. It contains a unit.
As an influence on the film physical properties when the content of the ethylene terephthalate unit is increased, there is an effect of making the film tough and not easily torn. Further, when the yield point stress is increased and the container is mounted on a container or the like, adhesion to the container can be obtained. However, by increasing the amount, there is a tendency to reduce the solvent adhesion due to the application of a solvent such as 1,3-dioxolane and tetrahydrofuran and pressure bonding.

  In the present invention, the above-described constituent components can be used, but it is necessary that the ethylene terephthalate unit unit is 70 mol% or more based on the entire film. By setting the ethylene terephthalate unit to 70 mol% or more, an effect of increasing the yield point stress by strengthening the film in the future can be obtained, and the processing stability of the film can be enhanced. The ethylene terephthalate unit is preferably 71% by mole or more, and more preferably 72% by mole or more. The upper limit of the ethylene terephthalate unit is not particularly limited, but is preferably 80 mol% or less from the viewpoint of ensuring solvent adhesion and an appropriate heat shrinkage rate. The ethylene terephthalate unit is preferably 79 mol% or less, and more preferably 78 mol% or less.

  Furthermore, in the present invention, it is preferable that one side and the other side of the film can be solvent-bonded. The solvent adhesiveness can be ensured by the film composition, the layer structure described later, the film forming method and the like. In the present invention, being capable of solvent bonding means that the solvent bonding strength is 3 N / 15 mm or more in the evaluation method of the examples.

  Furthermore, in the present invention, after the film was stored for 2 weeks under an environment of a temperature of 30 ° C. and a relative humidity of 85%, a tensile test was performed in a direction perpendicular to the maximum shrinkage direction of the film after storage in accordance with JIS K7127. It is preferable that the percentage of the number of test pieces having an elongation of 5% or less with respect to the total number of test pieces (20 pieces) is 10% or less. 5% or less is more preferable, and 0% is more preferable. By setting it as the said characteristic range, processing stability which does not generate | occur | produce defects, such as a fracture | rupture at the time of a process, can be obtained even after storing a film for a long period of time.

  Furthermore, in the present invention, it is preferable that the yield point stress value in the tensile stress-strain curve when the tensile test is performed in the maximum shrinkage direction of the film is 5.0 MPa or more according to JIS K7127. By setting the yield point stress value to 5.0 MPa or more, adhesion to the container can be obtained when the yield point stress value is attached to the container or the like. The yield point stress value is preferably 5.5 MPa or more, and more preferably 6.0 MPa or more.

  Furthermore, in this invention, it has the layer (A) which consists of a polyester resin whose ethylene terephthalate unit is less than 72 mol% in all the polyester resin components in a film double-sided outer layer side, and an ethylene terephthalate unit is 70 in all the polyester resin components. It is necessary to have a laminated structure of at least three layers having a layer (B) made of a polyester resin of mol% or more on the inner layer side.

  The ethylene terephthalate unit in the (A) layer is preferably 69 mol or less, more preferably 68 mol or less, and the ethylene terephthalate unit in the (B) layer is preferably 72 mol% or more, more preferably 74 mol% or less.

  A preferred laminated structure is (A) / (B) / (A). The ratio of the thickness of the (A) layer and the (B) layer is preferably 25/50/25 to 10/80/10. If the thickness of the (B) layer is less than 50%, the tear resistance, strength, heat resistance and the like are insufficient, such being undesirable. Further, when the thickness of the layer B) exceeds 80%, the solvent adhesive strength is lowered, which is not preferable.

  The production method of the polyester is not particularly limited, but a so-called direct polymerization method in which an oligomer obtained by directly reacting a dicarboxylic acid and a glycol is polycondensed, and a dimethyl ester of dicarboxylic acid and a glycol are transesterified. Examples include a so-called transesterification method in which polycondensation is performed later, and any production method can be applied.

  The polyester raw material used for this invention is dried using dryers, such as a hopper dryer and a paddle dryer, or a vacuum dryer, and it extrudes in the form of a film at the temperature of 200-300 degreeC. Alternatively, an undried polyester raw material is similarly extruded into a film while removing moisture in a vented extruder. At this time, it is preferable to take measures to reduce the composition fluctuation of the polymer component described above. When extruding, any existing method such as a T-die method or a tubular method may be adopted. After extrusion, it is cooled rapidly to obtain an unstretched film. Stretching is performed on the unstretched film, but in order to achieve the object of the present invention, the lateral direction is practical as the main shrinking direction. For example, when the main shrinkage direction is the longitudinal direction, the film can be formed in accordance with a normal operation in addition to changing the stretching direction in the following method by 90 degrees.

In addition, when paying attention to uniforming the thickness distribution of the desired heat-shrinkable polyester film, the thermal conductivity coefficient is preliminarily applied in the preheating step prior to the stretching step when stretching in the transverse direction using a tenter. Is preferably heated at a low wind speed of 0.0013 calories / cm ² · sec · ° C. or less until the film temperature reaches Tg−20 ° C. to Tg + 60 ° C. Stretching in the transverse direction is 2.3 to 7.3 times, preferably 3.5 to 6.0 times at a temperature of Tg-30 ° C to Tg + 40 ° C, more preferably at a temperature of Tg-25 ° C to Tg + 35 ° C. . Thereafter, heat treatment is performed at a temperature of 60 ° C. to 8 ° C. while stretching 0 to 15% or relaxation of 0 to 15%. If necessary, heat treatment is further performed at a temperature of 40 ° C. to 100 ° C. to cause heat shrinkage. A conductive polyester film is obtained. In this transverse stretching process, it is preferable to take measures to suppress temperature fluctuations in the aforementioned process.

As a stretching method, not only horizontal uniaxial stretching with a tenter, but also stretching in the longitudinal direction is 1.03 times or more, preferably 1.05 times to 1.2 times. The biaxial stretching may be either sequential biaxial stretching or simultaneous biaxial stretching, and may be re-stretched as necessary. Further, in 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 may be used. Even when these longitudinal stretching steps or biaxial stretching steps are adopted, the film roll of the present invention is subject to fluctuations in the film surface temperature measured at a fixed position in the preheating step, stretching step, etc., similarly to the transverse stretching. Within the range of the distance in the flow direction corresponding to the film winding length, the average temperature is preferably within ± 1 ° C, and more preferably within the average temperature ± 0.5 ° C. From the viewpoint of suppressing the internal heat generation of the film accompanying stretching and reducing the film temperature unevenness in the width direction, the heat transfer coefficient in the stretching process is preferably 0.0037 J / cm ² · sec · ° C. or more. More preferably, the condition of 0.00544 to 0.00837 J / cm ² · sec · ° C. is good.

  Furthermore, the heat shrinkage rate in the direction of the main shrinkage of the film and the direction perpendicular to the main shrinkage direction is set by setting the heat transfer coefficient in the preheating step and the drawing step within the above preferable range among the above-described drawing conditions. It becomes easy to control the adhesiveness of the film with a non-chlorine solvent to a more appropriate range.

  Next, the present invention will be described in more detail using examples and comparative examples, but is not limited to the following examples. Moreover, the measuring method of the physical property of the film obtained by the Example and the comparative example is shown below.

(1) Composition A sample (chip or film) is dissolved in a solvent in which chloroform D (manufactured by Usolip) and trifluoroacetic acid D1 (manufactured by Usolip) are mixed at a ratio of 10: 1 (volume ratio) to prepare a sample solution. , NMR (“GEMINI-200”; manufactured by Varian) was used to measure the proton NMR of the sample solution under the measurement conditions of a temperature of 23 ° C. and an integration count of 64 times. Based on the peak intensity of protons measured by NMR measurement, the composition ratio of monomers constituting the sample was calculated.

(2) Heat shrinkage rate The film was cut into a 10 cm × 10 cm square, heat-shrinked in warm water at a measurement temperature of ± 0.5 ° C. under no load for 10 seconds, and then 25 ° C. ± 0.5 ° C. After being immersed in water for 10 seconds, the length of the sample in the vertical and horizontal directions was measured, and the thermal shrinkage rate was determined according to the following formula.
Heat shrinkage rate (%) = (length before shrinkage−length after shrinkage) ÷ length before shrinkage × 100

(3) Yield point stress Using TENSILON / UTM-IIIL (TOYO MEASRING INSTRMMENTS CO. LTD), in a direction orthogonal to the main stretching direction (maximum shrinkage direction) of the film, the ambient temperature is 23 ° C., and the gap between the chucks is 100 mm. A film test piece having a width of 15 mm was subjected to a tensile test at a tensile speed of 200 mm / min, and a stress-strain curve was prepared.

(4) The film is stored for 2 weeks in an environment with a tear resistance temperature of 30 ° C. and a relative humidity of 85%. According to JIS K7127, a tensile test is performed in a direction orthogonal to the maximum shrinkage direction of the film after storage. The number of test specimens was 20. The test piece length was 200 mm, the distance between chucks was 100 mm, the test piece width was 15 mm, the temperature was 23 ° C., and the tensile speed was 200 mm / min. The test variables that broke at an elongation of 5% or less were counted, and the percentage of the total number of specimens (20) was determined to determine the tear resistance (%).

(5) Solvent adhesion 1,3-Dioxolane was applied to the stretched film with a cotton swab at a coating amount (5 ± 0.3) g / m ² and a coating width of 5 ± 1 mm, and two sheets were bonded together to provide a seal. did. The seal part is cut to a width of 15 mm in the direction perpendicular to the main stretching direction (maximum shrinkage direction) of the film, and is set in a universal tension tester STM-50 manufactured by Baldwin Co., Ltd. Measured at / min.

(6) Heat shrinkage stress Using a Tensilon (with heating furnace) strong elongation measuring machine manufactured by Toyo Seiki Co., Ltd., a sample having a length of 200 mm in the main shrinkage direction and a width of 20 mm was cut out from the heat shrinkable film, and the distance between chucks was 100 mm. , Stop the air blowing in an atmosphere preheated to 90 ° C., attach the sample to the chuck, then quickly close the heating furnace door and measure the stress detected when the air blowing (blowing air speed 5 m / sec) is started, The maximum value obtained from the chart was defined as heat shrinkage stress (MPa).

(Synthesis of polyester)
(Synthesis Example 1)
A stainless steel autoclave equipped with a stirrer, a thermometer and a partial recirculating cooler contains 100 mol% of dimethyl terephthalate (DMT) as a dicarboxylic acid component and 100 mol% of ethylene glycol (EG) as a polyhydric alcohol component. The polyhydric alcohol was charged so that the molar ratio was 2.2 times that of the methyl ester. The transesterification reaction was carried out while adding methanol (to the acid component) and distilling off the produced methanol out of the system. Thereafter, a polycondensation reaction was performed at 280 ° C. under a reduced pressure condition of 26.7 Pa to obtain a polyester (A) having an intrinsic viscosity of 0.75 dl / g. The composition is shown in Table 1.

(Synthesis Examples 2-3)
By the same method as in Synthesis Example 1, polyesters (B) to (C) shown in Table 1 were obtained. In the table, NPG is neopentyl glycol, BD is 1,4-butanediol, and DEG is diethylene glycol. The intrinsic viscosity of each polyester was (B): 0.77 dl / g, (C): 0.72 dl / g. Each polyester was chipped. Table 1 shows the composition of each synthesis example.

  In addition, as for the inorganic lubricant, a master batch was prepared by adding 0.7% by mass of the inorganic lubricant used in the polyester (A) to the polyester (A), and the required amount was used. The lubricant was added in advance by dispersing the lubricant in ethylene glycol and polymerizing by the above method.

Example 1
Polyester composition (A) in which 15 wt% of polyester A shown in Table 1 and 75 wt% of B and 10 wt% of C are mixed, and 65 wt% of polyester A, 25 wt% of B and C The polyester composition (B) mixed with 10 wt% is supplied to two different extruders, melt extruded at 275 ° C., and the (A) layer becomes the outer layer and the (B) layer becomes the inner layer by the multi-manifold die method. Thus, the layers were laminated at a ratio of 1: 2: 1, extruded as two types and three layers, and rapidly cooled on a chill roll having a surface temperature of 25 ° C. to obtain an unstretched film having a thickness of 180 μm. This unstretched film was continuously led to a tenter and preheated until the film temperature reached 70 ° C, and then stretched 4.0 times in the transverse direction at a temperature of 78 ° C. Next, heat treatment was performed at 80 ° C. for 14 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. At this time, the heat transfer coefficient in the preheating step was 0.0009 calories / cm ² · sec · ° C., and the heat transfer coefficient in the stretching step was 0.0056 J / cm ² · sec · ° C. The physical properties of the obtained film are shown in Table 2.

(Example 2)
Polyester composition (A) in which 20 wt% of polyester A shown in Table 1 and 70 wt% of B and 10 wt% of C are mixed, and 60 wt% of polyester A, 30 wt% of B and C A heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the polyester composition (B) mixed with 10 wt% was supplied to two different extruders.

(Comparative Example 1)
The polyester compositions (A) and (B) were both heat-shrinkable polyester films in the same manner as in Example 1 except that 65 wt% polyester A, 25 wt% B and 10 wt% C were mixed. Got.
The physical properties of this film are shown in Table 2.

(Comparative Example 2)
Both polyester compositions (A) and (B) were heat-shrinkable polyester films in the same manner as in Example 1 except that 15 wt% of polyester A, 75 wt% of B, and 10 wt% of C were mixed. Got.
The physical properties of this film are shown in Table 2.

(Comparative Example 3)
Both polyester compositions (A) and (B) were heat-shrinkable polyester films in the same manner as in Example 1 except that polyester A was mixed with 40 wt%, B was mixed with 50 wt%, and C was mixed with 10 wt%. Got.
The physical properties of this film are shown in Table 2.

(Comparative Example 4)
A heat-shrinkable polyester film was obtained in the same manner as in Example 1 except that the layers (A) were outer layers and the (B) layer was an inner layer, except that the layers were laminated at a ratio of 4: 42: 4.
The physical properties of this film are shown in Table 2.

  The heat-shrinkable polyester film of the present invention maintains an excellent appearance, has excellent processability such as label processing, has excellent solvent adhesiveness when used as a label, and has a film for a long period of time. Even when stored, it has excellent tear resistance, is suitable for label use, and has high industrial utility value.

Claims (6)

  Polyester having a layer (A) composed of a polyester resin having an ethylene terephthalate unit of less than 72 mol% in all polyester resin components on the outer side of both sides of the film, and having an ethylene terephthalate unit of 70 mol% or more in all polyester resin components A film composed of at least three layers having a resin layer (B) on the inner layer side, and the thermal shrinkage rate in the maximum shrinkage direction when immersed in warm water of 95 ° C. for 10 seconds is 50% or more, A heat-shrinkable polyester film characterized by having a heat shrinkage rate of 4% or more in a direction perpendicular to the maximum shrinkage direction and capable of being bonded with a non-chlorine organic solvent.   Elongation when the film is stored for 14 days in an environment of temperature 30 ° C and relative humidity 85% and then subjected to a tensile test in a direction perpendicular to the known maximum shrinkage direction after storage according to JIS K7127. The heat-shrinkable polyester film according to claim 1, wherein the number of test pieces of 5% or less is 10% or less with respect to the total number of test pieces (20 pieces).   According to JIS K7127, the yield point stress value in the tensile stress-strain curve when the tensile test is performed in the direction orthogonal to the maximum shrinkage direction of the film is 5.0 MPa or more. A heat-shrinkable polyester film according to claim 1.   The method for producing a heat-shrinkable polyester film according to any one of claims 1 to 3, wherein the heat shrinkage rate in the maximum shrinkage direction when immersed in warm water of 75 ° C for 10 seconds is 20% or more. .   The heat-shrinkable polyester film according to any one of claims 1 to 4, wherein the maximum value of shrinkage stress in the main shrinkage direction at 90 ° C is 12 MPa or less.   The heat-shrinkable label produced from the heat-shrinkable polyester film in any one of Claims 1-5.