JP5278821B2 - Heat-shrinkable polyester film - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a heat-shrinkable polyester film, a method for producing the same, and a package. Specifically, the present invention relates to a heat-shrinkable polyester film suitable for label applications, a method for producing the same, and a package using a label. Is.

  In recent years, stretched films made of polyvinyl chloride resins, polystyrene resins, polyester resins, etc., for label packaging, cap seals, integrated packaging, etc. that also serve as protection and product display for glass bottles and PET bottles (so-called, Heat-shrinkable film) has been widely used. Among such heat-shrinkable films, a polyvinyl chloride film has low heat resistance and also has problems such as generation of hydrogen chloride gas during incineration and causing 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 having high heat resistance, easy incineration, and excellent solvent resistance have come to be widely used as shrinkage labels, The usage tends to increase with the increase.

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

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

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

  According to the method of Patent Document 1, although the perforation-opening property of the heat-shrinkable polyester film is improved to some extent, it is difficult to say that a heat-shrinkable polyester film having sufficient perforation-opening property is obtained. Moreover, even when the method of Patent Document 1 is adopted, it is not possible to efficiently produce a heat-shrinkable polyester film because it can be stretched only in the width direction during production.

  Also, many of the PET bottles used for carbonated beverages use pressure-resistant bottles, and the positions of these labels are so-called cylinders. It is possible to finish such a small-bore type PET bottle into a label even if the heat shrinkage rate is not high. However, when the heat shrinkage rate is low, the heat shrinkage stress is generally low. When the heat shrinkage stress is low, when the label is made, if the heating time is short in the heat shrinking process, the label does not sufficiently heat shrink, and the label becomes undesirably damaged.

  In addition, recently, labels used for various containers such as PET bottles are expected to have an effect of reinforcing these containers. However, labels obtained from conventional heat-shrinkable polyester films have not been able to satisfy such a reinforcing action.

Japanese Patent Application Laid-Open No. 2002-36312

  The present invention was devised in order to solve the problems of the above-mentioned conventional heat-shrinkable polyester film, and its purpose is to have good shrinkage finish even if the heat shrinkage rate is low, and the perforation. An object of the present invention is to provide a heat-shrinkable polyester-based film having a function capable of reinforcing a shrink-coated container that has very good openability and extremely high productivity.

The first invention of the present invention comprises a polyester resin containing ethylene terephthalate as a main constituent and containing 13 mol% or more of one or more monomer components that can be amorphous components in all polyester resin components. And satisfying the following requirements (1) to (3):
(1) The hot-water heat shrinkage in the film width direction and the longitudinal direction when treated in warm water at 95 ° C. for 10 seconds is 25% or more and 40% or less and 0% or more and 15% or less, respectively;
(2) The maximum heat shrinkage stress in the film width direction at 90 ° C. is 8 MPa or more and 20 MPa or less;
(3) The hot-water heat shrinkage rate in the film width direction in 95 ° C. warm water is X ₀ (%), and the film after being shrunk 10% in the width direction in 80 ° C. warm water in 95 ° C. warm water When the hot water heat shrinkage rate in the width direction is X ₁₀ (%), the heat shrinkage rate difference Δ (= X ₀ −X ₁₀ ) (%) is 10% or more and 20% or less.

Preferred embodiments of the first invention of the present invention are as follows.
(1) The perpendicular tear strength in the longitudinal direction per unit thickness after shrinking 10% in the width direction in warm water at 80 ° C. is 170 N / mm or more and 310 N / mm or less.
(2) The tensile fracture strength in the longitudinal direction is 90 MPa or more and 300 MPa or less.
(3) The main component of the monomer that can be an amorphous component in all the polyester resin components is any one of neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid.

2nd invention of this invention is a manufacturing method for manufacturing the heat-shrinkable polyester film of said 1st invention continuously, Comprising: Each process of following (a)-(g) is included. It is a feature.
(A) After stretching an unstretched polyester film at a temperature of Tg to (Tg + 30 ° C.) and below in the longitudinal direction at a magnification of 2.2 times to 3.0 times, (Tg + 10 ° C.) to (Tg + 40 ° C.) A longitudinal stretching step in which the film is stretched in the longitudinal direction so as to have a total magnification of 2.8 times or more and 4.5 times or less by stretching at a temperature of 1.2 times to 1.5 times in the longitudinal direction;
(B) a first lateral stretching step in which the film after longitudinal stretching is stretched at a magnification of 2 times or more and 3.2 times or less in the width direction in a state where both ends in the width direction are held by clips in the tenter;
(C) Intermediate heat treatment step of heat-treating the film after the first transverse stretching at a temperature of 130 ° C. or higher and 190 ° C. or lower for 5 seconds or longer and 30 seconds or shorter in a tenter with both ends in the width direction held by clips. ;
(D) a natural cooling step of naturally cooling the intermediate heat-treated film by passing it through an intermediate zone that is cut off from the heating zone of each step and does not perform a positive heating operation;
(E) a forced cooling step of actively cooling the film after natural cooling until the surface temperature reaches a temperature of 80 ° C. or higher and 120 ° C. or lower;
(F) a second lateral stretching step in which the film after forced cooling is stretched at a temperature of (Tg + 30 ° C.) or more and (Tg + 55 ° C.) or less in the width direction at a magnification of 1.5 to 2.0 times;
(G) The film after the second lateral stretching is heat-treated at a temperature of 80 ° C. or higher and 130 ° C. or lower for 1.0 second or more and 9.0 seconds or less in a tenter with both ends in the width direction held by clips. Final heat treatment process.

  According to a third aspect of the present invention, there is provided a label having a heat-shrinkable polyester film of the first aspect as a base material, and a perforation or a pair of notches provided on the base material, on at least the outer periphery of the packaging object. It is a package characterized in that it is formed by partially covering and heat shrinking.

  The heat-shrinkable polyester film of the present invention has low shrinkage in the width direction, which is the main shrinkage direction, but has high heat-shrinkage stress and high mechanical strength in the longitudinal direction perpendicular to the width direction. The perforation of the perforation is good, and when opening, it can be cut cleanly along the perforation from the beginning of tearing to the completion of tearing. In addition, the stiffness (the so-called “waist” strength) is high, and the wearability of the label is excellent. In addition, the processing characteristics during printing and tubing are good. Therefore, the heat-shrinkable polyester film of the present invention can be suitably used as a label for containers such as bottles, particularly for PET bottles that are tight like pressure-resistant bottles. The package of the present invention has a good tearing condition of the coated label, can tear the coated label cleanly along the perforation with an appropriate force, and can reinforce the shrink-coated container Have

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

  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 bonded with a solvent. Therefore, it can be suitably used for various coated labels including labels such as PET bottles.

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

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

  When the aliphatic dicarboxylic acid (for example, adipic acid, sebacic acid, decanedicarboxylic acid, etc.) is contained in the polyester, the content is preferably less than 3 mol%. A heat-shrinkable polyester film obtained using a polyester containing 3 mol% or more of these aliphatic dicarboxylic acids has insufficient film stiffness at high-speed mounting.

  Moreover, it is preferable not to make polyester contain trivalent or more polyvalent carboxylic acid (for example, trimellitic acid, pyromellitic acid, and their anhydrides). In a heat-shrinkable polyester film obtained using a polyester containing these polyvalent carboxylic acids, it is difficult to achieve a necessary high shrinkage rate.

  As the diol component constituting the polyester, ethylene glycol, 1-3 propanediol, 1-4 butanediol, neopentyl glycol, aliphatic diol such as hexanediol, alicyclic diol such as 1,4-cyclohexanedimethanol, Examples thereof include aromatic diols such as bisphenol A.

  Polyester is a cyclic diol such as 1,4-cyclohexanedimethanol or a diol having 3 to 6 carbon atoms (for example, 1-3 propanediol, 1-4 butanediol, neopentyl glycol, hexanediol, etc.). The polyester which contained 1 or more types of these and adjusted the glass transition point (Tg) to 60-80 degreeC is preferable.

  Further, the polyester has a total of 13 mol% or more, preferably a total of one or more monomer components that can be amorphous components in 100 mol% of the polyhydric alcohol component or 100 mol% of the polycarboxylic acid component in the total polyester resin. Is at least 15 mol%, more preferably at least 17 mol%, particularly preferably at least 20 mol%. Here, examples of the monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,2- Diethyl 1,3-propanediol, 2-n-butyl 2-ethyl 1,3-propanediol, 2,2-isopropyl 1,3-propanediol, 2,2-di-n-butyl 1,3-propanediol, Examples thereof include 1,4-butanediol and hexanediol. Of these, neopentyl glycol, 1,4-cyclohexanedimethanol, or isophthalic acid is preferably used.

  The polyester preferably does not contain a diol having 8 or more carbon atoms (for example, octanediol) or a trihydric or higher polyhydric alcohol (for example, trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). In the heat-shrinkable polyester film obtained by using polyesters containing these diols or polyhydric alcohols, it is difficult to achieve a necessary high shrinkage rate.

  Further, it is preferable that the polyester does not contain diethylene glycol, triethylene glycol, and polyethylene glycol as much as possible.

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

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

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

In addition, the heat-shrinkable polyester film of the present invention has a heat-shrinkage rate of the film calculated by the following formula from the length before and after shrinkage when treated for 10 seconds in 95 ° C. warm water under no load (that is, , 95 ° C. hot water heat shrinkage ratio) is 25% to 40% in the width direction and 0% to 15% in the longitudinal direction.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%)

  If the hot-water heat shrinkage rate in the width direction at 95 ° C. is less than 25%, the shrinkage amount is small, so wrinkles and tarmi (shrinkage unevenness due to insufficient shrinkage) occur on the label after heat shrinkage. On the other hand, when the hot water heat shrinkage in the width direction at 95 ° C. exceeds 40%, the hot water heat shrinkage can be sufficiently achieved even when the hot water heat shrinkage is low. This is not preferable because distortion is likely to occur at the time of heat shrinkage, or so-called “jumping” may occur. The lower limit of the hot water heat shrinkage in the width direction at 95 ° C. is preferably 26% or more, more preferably 28% or more, and particularly preferably 30% or more. Moreover, the upper limit of the hot water heat shrinkage in the width direction at 95 ° C. is preferably 38% or less, more preferably 36% or less, and particularly preferably 35% or less.

  Also, if the hot water heat shrinkage in the longitudinal direction at 95 ° C. is less than 0% (that is, when stretched by heat treatment), it is not preferable because a good shrink appearance cannot be obtained when used as a bottle label. In addition, if the thermal contraction rate of hot water in the longitudinal direction at 95 ° C. exceeds 15%, it is not preferable because distortion is likely to occur during thermal contraction when used as a label. The hot-water heat shrinkage in the longitudinal direction at 95 ° C. is preferably 1% or more and 13% or less, more preferably 2% or more and 10% or less, and more preferably 3% or more and 8% or less.

The heat-shrinkable polyester film of the present invention has a maximum heat shrinkage stress in the film width direction at 90 ° C. measured by the following method of 8 MPa or more and 20 MPa.
[Measurement method of maximum heat shrinkage stress]
(1) A test piece having a length in the maximum shrinkage direction of 200 mm and a width of 20 mm is cut out from the heat-shrinkable polyester film.
(2) The inside of a heating furnace of a tensile testing machine (for example, “Tensilon” manufactured by Toyo Seiki Co., Ltd.) equipped with a hot air type heating furnace is heated to 90 ° C.
(3) Stop blowing and set the test piece in the heating furnace. The distance between chucks is set to 100 mm (constant), and the test pieces are set so that the length between the chucks of the test pieces and the distance between chucks are 1: 1.
(4) The heating furnace door is quickly closed and air blowing (hot air at a temperature of 90 ° C. and a blowing speed of 5 m / sec) is resumed. Detect and measure the heat shrinkage stress of the specimen.
(5) The maximum value is read from the chart, and this is taken as the maximum heat shrinkage stress value (MPa).

  When the maximum heat shrinkage stress in the film width direction at 90 ° C. is less than 8 MPa, the heat shrinkage rate at the time of heat shrinkage becomes slow, and when it is shrunk to form a PET bottle label, it is heated in a short time of 3 seconds or less. This is not preferable because wrinkles and tarmi are generated on the label. On the other hand, if it 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 maximum heat shrinkage stress in the film width direction at 90 ° C. is preferably 9 MPa or more, more preferably 10 MPa or more, and particularly preferably 11 MPa or more. The upper limit value of the maximum heat shrinkage stress in the film width direction at 90 ° C. is preferably 19 MPa or less, more preferably 18 MPa or less, and particularly preferably 17 MPa or less.

Further, the heat-shrinkable polyester film of the present invention is a film before heat shrinkage, wherein the film before heat shrinkage is X ₀ (%) in the width direction measured by the same method as above at 95 ° C. Was once shrunk in warm water at 80 ° C. for 10% in the width direction, and the heat shrinkage rate in the width direction measured at 95 ° C. by the same method as above was defined as X ₁₀ (%), the difference in heat shrinkage rate Δ (= X ₀ −X ₁₀ ) (%) is 10% or more and 20% or less. If the heat-shrinkable polyester film has a heat shrinkage difference Δ within the above range, a heat-shrinkable label having a reinforcing effect on the coated container can be obtained.

With a heat-shrinkable label obtained from a heat-shrinkable polyester film having a heat shrinkage difference Δ that is less than the above range, the reinforcing effect of the container after coating shrinkage becomes insufficient. In the heat-shrinkable polyester film of the present invention, a preferable heat shrinkage difference Δ is 14% or less. The lower limit of the thermal shrinkage difference Δ is the thermal shrinkage rate X ₁₀ is because a value measured by using a film obtained by 10% heat shrinkage, never below 10%.

  By the way, in a normal heat-shrinkable polyester film, after final heat shrinkage of 10% and then heat shrinkage again, the final heat shrinkage rate (the first heat shrinkage rate of 10% and the second heat shrinkage rate). And the heat shrinkage rate when the film before heat shrinkage is completely shrunk under the same heat shrinkage conditions (that is, the heat shrinkage difference Δ exceeds the above range). End up). In the film of the present invention, as will be described later, the composition of the polyester used in the film is made suitable, and the stretching condition of the film is controlled to ensure the heat shrinkage difference Δ within the above range. .

Further, the thermal shrinkage rate X ₁₀ used to calculate the thermal shrinkage difference Δ is measured as follows. First, a film that is heat-shrinked 10% in the maximum shrinkage direction is produced. A mold having two chucks facing each other is prepared so that only a pair of opposite ends of a rectangular film can be gripped. The heat-shrinkable polyester film is cut into a square or a rectangle parallel to the width direction. The cut film is fixed with the above mold. For fixing, grip both ends of the film perpendicular to the width direction with a chuck, and loosen the film so that the ratio of the film length between chucks and the distance between chucks of the mold is 1: 0.9. Do it. Thereafter, the film fixed to the mold is immersed in hot water at 80 ° C. for 5 seconds in a no-load state and thermally contracted, and then immediately immersed in water at 25 ° C. for 10 seconds in a no-load state and pulled up. The film is removed from the mold and the adhering water is removed to obtain a film thermally contracted by 10% in the maximum shrinkage direction.

A 10 cm × 10 cm sample is cut from the obtained film, the heat shrinkage rate X ₁₀ is measured by the same method as the heat shrinkage rate X ₀ using this sample, and the heat shrinkage is calculated by calculating X ₀ -X _10. The rate difference Δ is calculated.

  In addition, the time from the production process of the film thermally contracted by 10% in the maximum shrinkage direction to the sample cutting process and the time from the sample cutting process to the heat shrinking process should be as short as possible. desirable. In addition, when storing a film that has been heat-shrinked 10% in the maximum shrinking direction until the sample cutting step, and when storing the cut sample until the heat shrinking step, in an airless environment of 25 ° C. or less in an unstrained state. And avoid unnecessary heat shrinkage.

  Further, when the heat-shrinkable polyester film of the present invention was subjected to 10% shrinkage in the width direction in warm water at 80 ° C., when the perpendicular tear strength in the longitudinal direction per unit thickness was determined by the following method, The perpendicular tear strength in the longitudinal direction is preferably 170 N / mm or more and 310 N / mm or less.

[Measurement method of right-angle tear strength]
A film is attached to a short frame having a predetermined length in a state where the film has been loosened in advance (that is, both ends of the film are held by the frame). Then, the film is contracted by 10% in the width direction by being immersed in warm water at 80 ° C. for about 5 seconds until the slack film becomes a tension state in the frame (until the slack disappears). Then, a test piece is created by sampling into the shape shown in FIG. 1 according to JIS-K-7128 (in the sampling, the tearing direction of the test piece is the longitudinal direction). Thereafter, both ends of the test piece are gripped with a universal tensile tester, and the strength at the time of tensile fracture in the longitudinal direction of the film is measured under the condition of a tensile speed of 200 mm / min. And the right angle tear strength per unit thickness is computed using a following formula.
Right angle tear strength = strength at tensile fracture ÷ thickness

  If the right-angled tear strength after shrinking 10% in the width direction in warm water at 80 ° C is less than 170 N / mm, it may be easily broken by impact such as dropping during transportation when used as a label. On the other hand, if the right-angled tear strength exceeds 310 N / mm, the cutting property (easy to tear) at the initial stage of tearing the label becomes poor. The lower limit of the right-angled tear strength is more preferably 175 N / mm or more, more preferably 180 N / mm or more, further preferably 190 N / mm or more, and particularly preferably 200 N / mm or more. Moreover, the upper limit of the right-angled tear strength is preferably 300 N / mm or less, and more preferably 290 N / mm or less. If a cavity is formed in the film by increasing the amount of the additive in the resin, the right angle tear strength can be adjusted low.

  Moreover, the heat-shrinkable polyester film of the present invention preferably has a tensile fracture strength of 90 MPa to 300 MPa when the tensile fracture strength in the longitudinal direction is determined by the following method.

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

  If the tensile fracture strength in the longitudinal direction is less than 90 MPa, the “waist” (stiffness) when the label is attached to a bottle or the like becomes weak. On the contrary, if the tensile fracture strength exceeds 300 MPa, the label This is not preferable because the cutability (ease of tearing) in the initial stage when tearing the film becomes poor. In addition, the lower limit value of the tensile fracture strength is preferably 110 MPa or more, more preferably 130 MPa or more, and particularly preferably 150 MPa or more. Moreover, the upper limit value of the right-angled tear strength is preferably 280 MPa or less, more preferably 260 MPa or less, and particularly preferably 240 MPa or less.

  The above-described heat-shrinkable polyester film of the present invention is formed by melt-extruding the above-described polyester raw material with an extruder to form an unstretched film, and the unstretched film is biaxially stretched by a predetermined method shown below and heat treated. Can be obtained.

  When the raw material resin is melt-extruded, the polyester raw material is preferably dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After the polyester raw material is dried in such a manner, it is melted at a temperature of 200 to 300 ° C. and extruded into a film using an extruder. For this extrusion, any existing method such as a T-die method or a tubular method can be employed.

  And an unstretched film can be obtained by rapidly cooling the sheet-like molten resin after extrusion. As a method for 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 the resin can be employed.

  Further, as will be described later, the obtained unstretched film is stretched in the longitudinal direction under predetermined conditions, and after the longitudinally stretched film is rapidly cooled, it is stretched in the width direction under predetermined conditions and heat-treated. It is possible to obtain the heat-shrinkable polyester film of the present invention by stretching the film again in the width direction under the above conditions and heat-treating it again. Hereinafter, a preferable film forming method for obtaining the heat-shrinkable polyester film of the present invention will be described in detail in consideration of a difference from a conventional heat-shrinkable polyester film forming method.

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

Furthermore, based on the problems in the production of the conventional heat-shrinkable polyester film, the present inventors have further considered about obtaining a heat-shrinkable polyester film having good perforation opening and high productivity. As a result of the progress, the following findings were obtained.
In order to improve the perforation openability when the label is used, it is considered necessary to leave some molecules oriented in the longitudinal direction.
・ In order to achieve a good finish after shrinkage when used as a label, it is indispensable not to develop a contraction force in the longitudinal direction. To that end, the tension state of molecules oriented in the longitudinal direction is eliminated. It is thought that it is necessary to do.

  From the above findings, the present inventors need to have “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” in the film in order to satisfy both the good perforation opening property and the shrinkage finishing property at the same time. I came to think that there is. Then, a trial and error was carried out by paying attention to what kind of stretching would allow “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” to exist in the film. As a result, the film is stretched in the longitudinal direction and then stretched in the width direction, in the case of film production by the so-called longitudinal-lateral stretching method, by subjecting the film after longitudinal stretching to intermediate heat treatment and natural cooling, etc. Realized the existence of “molecules that do not contribute to the shrinking force while being oriented in the longitudinal direction” in the film, and it was found that a heat-shrinkable polyester film satisfying both good perforation opening and shrinkage finishing properties can be obtained. did.

  However, when the film after longitudinal stretching was subjected to an intermediate heat treatment at a high temperature and laterally stretched during film production by the longitudinal-lateral stretching method, a film having a high thermal shrinkage rate in the film width direction was obtained. In order to reduce the thermal shrinkage rate in the film width direction, when the final heat treatment temperature after transverse stretching was increased, the thermal shrinkage rate in the film width direction at 95 ° C. could be adjusted to the target. The 90 ° C. maximum heat shrinkage stress was reduced, and a satisfactory film could not be obtained.

Therefore, the present inventors have made a measure for reducing the thermal shrinkage rate of hot water at 95 ° C. for 10 seconds in the width direction and increasing the maximum heat shrinkage stress in film production by the longitudinal-intermediate heat treatment-lateral stretching method. More about trial and error. In addition, the film after longitudinal stretching is not subjected to an intermediate heat treatment, but the film after longitudinal stretching is subjected to a lateral stretching and then subjected to an intermediate heat treatment, and then subjected to a lateral stretching again at a predetermined magnification. Thus, the shrinkage in the longitudinal direction in the intermediate heat treatment can be reduced and the predetermined heat shrinkage rate and the maximum heat shrinkage stress can be satisfied, and the present invention has been completed. That is, in the production of the heat-shrinkable polyester film of the present invention, it is necessary to take the following means.
(1) Control of longitudinal stretching conditions (2) Lateral stretching after longitudinal stretching (first lateral stretching)
(3) Intermediate heat treatment after first-stage transverse stretching (4) Natural cooling (interruption of heating) between intermediate heat treatment and transverse stretching (second-stage transverse stretching)
(5) Forced cooling of film after natural cooling (6) Control of second-stage transverse stretching conditions Hereinafter, each of the above-described means will be described in sequence.

(1) Control of longitudinal stretching conditions In the production of a film by the longitudinal-lateral stretching method of the present invention, it is necessary to perform longitudinal stretching in two stages in order to obtain the film roll of the present invention. That is, a substantially unoriented (unstretched) film is first longitudinally stretched at a temperature of Tg or higher (Tg + 30 ° C.) to a magnification of 2.2 to 3.0 times (first-stage stretching). Then, without cooling to Tg or less, the film is longitudinally stretched at a temperature of (Tg + 10) or more and (Tg + 40 ° C.) or less so that the magnification is 1.2 to 1.5 times (second-stage stretching). Accordingly, it is necessary to perform longitudinal stretching so that the total longitudinal stretching ratio (that is, the first stage longitudinal stretching ratio × second stage longitudinal stretching ratio) is 2.8 times or more and 4.5 times or less. More preferably, the total longitudinal stretching ratio is longitudinal stretching so that it is 3.0 to 4.3 times.

  In addition, when the film is longitudinally stretched in two stages as described above, the longitudinal refractive index of the film after longitudinal stretching is in the range of 1.600 to 1.630, and the heat shrinkage in the longitudinal direction of the film after longitudinal stretching. It is preferable to adjust the longitudinal stretching conditions so that the stress is 10 MPa or less. By performing longitudinal stretching under such predetermined conditions, it becomes possible to control the degree of orientation in the longitudinal and width directions of the film and the degree of molecular tension during intermediate heat treatment, lateral stretching, and final heat treatment, which will be described later. As a result, the perforation opening property of the final film can be improved.

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

  Furthermore, when the total longitudinal draw ratio is increased, the right-angled tear strength is decreased and the tensile strength in the longitudinal direction is increased. Further, by bringing the total longitudinal draw ratio close to the transverse draw ratio, the Elmendorf ratio can be made close to 1.0, and the perforation opening property when used as a label can be improved. Furthermore, by stretching in the longitudinal direction in two steps, it is possible to increase the longitudinal orientation due to the ability to reduce the stretching stress in the transverse direction, further lowering the right-angled tear strength and the tensile strength in the longitudinal direction. Strength will be greater. Therefore, it is possible to obtain a label having very good perforation tearability by stretching in two stages in the longitudinal direction and increasing the total longitudinal stretching ratio.

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

  In addition, by stretching in two stages in the longitudinal direction, the stretching stress in the longitudinal direction is reduced, so that the thickness unevenness in the longitudinal direction and the thickness unevenness in the width direction tend to increase, but the total longitudinal stretching ratio is increased. Thereby, the thickness unevenness of a longitudinal direction can be made small, and a haze can also be reduced in connection with it. In addition, by increasing the total longitudinal stretching ratio, the stress during transverse stretching increases, so that thickness unevenness in the width direction can also be reduced.

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

(2) Lateral stretching after longitudinal stretching (first lateral stretching)
In the production of a film by the longitudinal-lateral stretching method of the present invention, it is necessary to stretch the film after the longitudinal stretching so as to have a small magnification. That is, the transverse stretching is performed in a state where both ends in the width direction are held by clips in the tenter, preferably at a temperature of 70 ° C. (Tg + 5 ° C.) or more and 135 ° C. (Tg + 70 ° C.) or less, but not less than 2 times and not more than 3.2 times. It is necessary to carry out so that it may become the magnification of.

  As described above, before the intermediate heat treatment after the longitudinal stretching, it is possible to orient the molecules oriented in the longitudinal direction by the longitudinal stretching by adding the transverse stretching at the magnification of the above-mentioned predetermined condition, As a result, the transverse draw ratio in the second stage was reduced, and the hot-water heat shrinkage rate at 95 ° C. for 10 seconds in the width direction could be reduced. In addition, as will be described later, once the film is oriented in the width direction and subjected to intermediate heat treatment in the tenter, the transverse stretching stress during the second transverse stretching increases, and the maximum heat shrinkage stress in the film width direction increases. I understood.

  In addition, the lower limit of the first-stage transverse stretching temperature is preferably 75 ° C. or higher, and more preferably 80 ° C. or higher. Further, the upper limit of the first-stage transverse stretching temperature is preferably 130 ° C. or lower, and more preferably 125 ° C. or lower. On the other hand, the lower limit of the first stage transverse stretching ratio is 2.0 times or more, and more preferably 2.2 times or more. In addition, the upper limit of the first-stage lateral stretching ratio is 3.2 times or less, and more preferably 3.0 times or less.

  As described above, when the stretching temperature is lower than 70 ° C. when stretching in the lateral direction of the first stage, breakage occurs and productivity is deteriorated. When the stretching temperature is higher than 135 ° C, the thickness unevenness in the width direction becomes large, and in the heat treatment zone of the next process, the shrinkage unevenness occurs in the thick and thin portions in the width direction, and the thin portions become whitish and the appearance is poor. Become. Moreover, the thickness in the lateral direction is also deteriorated. In addition, if the first-stage transverse stretch ratio is lower than 2, the orientation in the width direction is insufficient, the stretching stress in the second-stage lateral stretching after the intermediate heat treatment is reduced, and a predetermined maximum heat shrinkage stress is obtained. Can't get. When the lateral magnification of the first stage is higher than 3.2 times, the orientation in the width direction becomes too large, and breakage increases in the second stage of lateral stretching after the intermediate heat treatment.

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

  That is, in the production of a film by the longitudinal-lateral stretching method of the present invention, after stretching an unstretched film longitudinally and laterally stretching, 130 ° C. or more and 190 ° C. in a state where both ends in the width direction are held by clips in the tenter. It is necessary to perform heat treatment (hereinafter referred to as intermediate heat treatment) at a temperature below for 5 seconds to 30 seconds. By performing such an intermediate heat treatment, “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” can be present in the film. As a result, when the label is used, the perforation is good and the shrinkage spots are not generated. A film that does not occur can be obtained. In any case, it is not possible to have “molecules that are oriented in the longitudinal direction but do not contribute to the shrinkage force” in the film, and the predetermined longitudinal stretching described above is performed. Thus, after the intermediate heat treatment, for the first time, “molecules that are oriented in the longitudinal direction and do not contribute to the shrinkage force” can be present in the film. And by carrying out predetermined natural cooling, forced cooling, and transverse stretching (second-stage transverse stretching), which will be described later, the “molecules that are oriented in the longitudinal direction and do not contribute to the shrinkage force” formed in the film are retained. As it is, it becomes possible to orient the molecules in the width direction to express the contraction force in the width direction.

  In addition, the minimum of the temperature of intermediate heat processing is preferable in it being 135 degreeC or more, and it is more preferable in it being 140 degreeC or more. Moreover, the upper limit of the temperature of the intermediate heat treatment is preferably 180 ° C. or less, and more preferably 170 ° C. or less. On the other hand, the time for the intermediate heat treatment needs to be appropriately adjusted in accordance with the raw material composition within a range of 5 seconds to 30 seconds, and is preferably adjusted within a range of 10 seconds to 25 seconds.

  When performing the intermediate heat treatment as described above, by maintaining the treatment temperature at 130 ° C. or higher, it is possible to reduce the stress shrinking in the longitudinal direction, and it is possible to extremely reduce the shrinkage rate in the longitudinal direction. Further, by controlling the temperature of the intermediate heat treatment to 190 ° C. or less, it becomes possible to reduce the variation in the shrinkage rate in the lateral direction.

  Further, by controlling the temperature of the intermediate heat treatment to 190 ° C. or less, it is possible to suppress the film breakage due to the occurrence of film shrinkage spots and maintain good slitting properties. In addition, by controlling the temperature of the intermediate heat treatment to 190 ° C. or lower, it becomes possible to suppress the haze of the film that is increased due to the crystallization of the film.

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

(5) Forced cooling of the film after natural cooling In the production of the film by the longitudinal-lateral stretching method of the present invention, the film naturally cooled as described above is not stretched as it is, but the film temperature is 80 ° C. or higher and 120 ° C. It is necessary to actively cool so that it becomes below ℃. By performing such forced cooling treatment, the stretching stress in the second-stage transverse stretching becomes high, the heat shrinkage stress of the film becomes high, and the reinforcing effect when used as a label can be increased. In addition, the minimum of the temperature of the film after forced cooling is preferable in it being 85 degreeC or more, and more preferable in it being 90 degreeC or more. Further, the upper limit of the temperature of the film after forced cooling is preferably 115 ° C. or lower, and more preferably 110 ° C. or lower.

  When the film is forcibly cooled as described above, if the temperature of the film after forced cooling remains higher than 120 ° C., the shrinkage stress in the width direction of the film becomes low, and the shrinkage rate at the time of forming a label is low. Although sufficient, the shrinkage stress in the width direction of the film can be increased by controlling the temperature of the cooled film to be 120 ° C. or lower.

  In addition, when the film is forcibly cooled, if the temperature of the film after forced cooling remains above 120 ° C., the stress of transverse stretching performed after cooling tends to be small, and the thickness unevenness tends to increase. However, by performing forced cooling so that the temperature of the film after cooling is 120 ° C. or lower, it is possible to increase the stress of transverse stretching performed after cooling and reduce thickness unevenness in the width direction.

  Furthermore, when the film is forcibly cooled, if the temperature of the film after forced cooling remains below 80 ° C., the film tends to break, but the temperature of the film after cooling becomes 80 ° C. or higher. By performing such forced cooling, it becomes possible to suppress breakage of the film.

(6) Control of second-stage transverse stretching conditions In the production of the film by the longitudinal-lateral stretching method of the present invention, the film after longitudinal stretching, first-stage transverse stretching, intermediate heat treatment, natural cooling, forced cooling is subjected to a predetermined process. It is necessary to carry out a final heat treatment by transverse stretching (second-stage transverse stretching) under conditions. That is, the transverse stretching is performed at a temperature of (Tg + 30 ° C.) or more (Tg + 55 ° C.) or less, for example, at a temperature of 95 ° C. or more and 120 ° C. or less, 1.5 times or more in a state where both ends in the width direction are held by clips in the tenter. It is necessary to carry out so that the magnification is 0 or less. By performing the second-stage transverse stretching under such a predetermined condition, it is possible to obtain a film satisfying a good heat shrinkage rate and heat shrinkage stress in the width direction. In addition, the lower limit of the temperature of the second stage transverse stretching is preferably 98 ° C. or higher, and more preferably 101 ° C. or higher. In addition, the upper limit of the second stage transverse stretching temperature is preferably 117 ° C. or lower, and more preferably 114 ° C. or lower. On the other hand, the lower limit of the transverse stretching ratio in the second stage is preferably 1.6 times or more, and more preferably 1.7 times or more. Further, the upper limit of the second-stage transverse stretching ratio is preferably 1.9 times or less, and more preferably 1.8 times or less.

  Moreover, when extending | stretching temperature exceeds 120 degreeC, extending | stretching stress will become small and the maximum thermal contraction stress will become small. By controlling the stretching temperature to 120 ° C. or lower, it is possible to keep the shrinkage stress in the width direction high.

  Further, when the stretching temperature exceeds 120 ° C., the thickness variation in the width direction tends to increase, but by controlling the stretching temperature to 120 ° C. or less, the thickness variation in the width direction can be reduced.

  On the other hand, when the stretching temperature is lower than 95 ° C., the orientation in the width direction becomes too high, and the film tends to be broken at the time of second-stage transverse stretching, or when the film after biaxial stretching is finally wound on a roll However, by controlling the stretching temperature to 95 ° C. or higher, it is possible to reduce breakage during the second-stage transverse stretching and improve the slitting property during winding.

  On the other hand, when the transverse stretch ratio in the second stage exceeds twice, the shrinkage rate in the film width direction becomes high. If the film thermal shrinkage at 95 ° C. for 10 seconds exceeds 50%, it is necessary to increase the final heat treatment temperature in the tenter in order to obtain a predetermined shrinkage. If it does so, the shrinkage stress of the width direction becomes small and is not preferable. Therefore, it is preferable to approximate the predetermined shrinkage rate by the draw ratio.

  On the other hand, when the transverse draw ratio of the second stage is less than 1.5 times, the predetermined shrinkage rate is not achieved, which is not preferable.

  The film after transverse stretching is finally heat-treated at a temperature of 80 ° C. or higher and 130 ° C. or lower for a time of 1.0 second or more and 9.0 seconds or less in a state where both ends in the width direction are gripped in the tenter. It is necessary to When the temperature is higher than 130 ° C., the shrinkage rate and shrinkage stress in the width direction are undesirably lowered. On the other hand, when the temperature is lower than 80 ° C., it cannot relax sufficiently in the width direction, and when the final product is stored at room temperature, shrinkage in the width direction (so-called natural shrinkage) increases with time, which is not preferable. Further, if the heat treatment time is less than 1.0 seconds, the heat treatment may be insufficient, which is not preferable. In addition, if the time exceeds 9.0 seconds, the equipment becomes large, which is not preferable.

[Effects of manufacturing process interaction on film properties]
In producing the heat-shrinkable polyester film of the present invention, any one of the longitudinal stretching step, the first lateral stretching step, the intermediate heat treatment step, the natural cooling step, the forced cooling step, and the second lateral stretching step Only the process can not improve the properties of the film alone, but the longitudinal stretching process, the first horizontal stretching process, the intermediate heat treatment process, the natural cooling process, the forced cooling process, the second horizontal process By performing all of the stretching steps under predetermined conditions, it becomes possible to improve the film properties very efficiently. Among the characteristics of the film, important properties such as thermal shrinkage rate, shrinkage stress, longitudinal right-angled tear strength, and longitudinal tensile fracture strength vary greatly depending on the interaction between specific processes. .

  Therefore, the heat shrinkage rate, heat shrinkage stress, heat shrinkage rate of the heat shrinkable polyester film, the difference between the heat shrinkage rate of the film subjected to 10% heat shrinkage, the perpendicular tear strength in the longitudinal direction, and the tensile fracture strength are within the scope of the present invention. In order to adjust inward, delicate conditions adjustments as described in the above (1) to (6) are required while taking into consideration the interaction between the above-described processes.

  The package of the present invention has a heat-shrinkable polyester film as a base material, and the base material has a perforation or a pair of notches provided on at least a part of the outer periphery of the packaging object. It is formed by heat shrinking. Examples of packaging objects include beverage bottles, various bottles, cans, plastic containers such as confectionery and lunch boxes, and paper boxes. In general, when a label based on a heat-shrinkable polyester film is heat-shrinkable and coated on those packaging objects, the label is heat-shrinked by about 2 to 10% to form a package. Adhere closely. In addition, printing may be given to the label coat | covered with a packaging target object, and it does not need to be printed.

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

  Next, the present invention will be specifically described with reference to examples and comparative examples. However, the present invention is not limited to the mode of the examples, and may be appropriately changed without departing from the gist of the present invention. Is possible. In addition, the evaluation method of a film is shown below.

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

[Maximum heat shrinkage stress]
(1) A test piece having a length in the maximum shrinkage direction of 200 mm and a width of 20 mm is cut out from the heat-shrinkable polyester film.
(2) The inside of a heating furnace of a tensile testing machine (for example, “Tensilon” manufactured by Toyo Seiki Co., Ltd.) equipped with a hot air type heating furnace is heated to 90 ° C.
(3) Stop blowing and set the test piece in the heating furnace. The distance between chucks is set to 100 mm (constant), and the test pieces are set so that the length between the chucks of the test pieces and the distance between chucks are 1: 1.
(4) The heating furnace door is quickly closed and air blowing (hot air at a temperature of 90 ° C. and a blowing speed of 5 m / sec) is resumed. Detect and measure the heat shrinkage stress of the specimen.
(5) The maximum value is read from the chart, and this is taken as the maximum heat shrinkage stress value (MPa).

[Heat shrinkage difference]
For the film before heat shrinkage, the heat shrinkage rate in the width direction measured at 95 ° C. by the same method as described above is X ₀ (%), and the film before heat shrinkage is once 10% in the width direction in 80 ° C. warm water. After shrinkage, when the thermal contraction rate in the width direction measured at 95 ° C. by the same method as described above is X ₁₀ (%), the thermal shrinkage rate difference Δ (%) is expressed as Δ = X ₀ −X ₁₀ ( %).

[Right-angle tear strength]
A film is attached to a short frame having a predetermined length in a state where the film has been loosened in advance (that is, both ends of the film are held by the frame). Then, the film is contracted by 10% in the width direction by being immersed in warm water at 80 ° C. for about 5 seconds until the slack film becomes a tension state in the frame (until the slack disappears). Then, a test piece is created by sampling into the shape shown in FIG. 1 according to JIS-K-7128 (in the sampling, the tearing direction of the test piece is the longitudinal direction). Thereafter, both ends of the test piece are gripped with a universal tensile tester, and the strength at the time of tensile fracture in the longitudinal direction of the film is measured under the condition of a tensile speed of 200 mm / min. And the right angle tear strength per unit thickness is computed using a following formula.
Right angle tear strength = strength at tensile fracture ÷ thickness

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

[Refractive index]
Using an “Abbe refractometer 4T type” manufactured by Atago Co., Ltd., each sample film was measured after being allowed to stand in an atmosphere of 23 ° C. and 65% RH for 2 hours or more.

[Shrinkage distortion at the label]
A cylindrical label (a label with the main shrinkage direction of the heat-shrinkable film as the circumferential direction) was prepared by adhering both ends to the heat-shrinkable film with dioxolane. After that, using a steam tunnel manufactured by Fuji Astec Inc (model: SH-1500-L), passing time 2 seconds, zone temperature 80 ° C, 4% in a 500 ml PET bottle (body diameter 62 mm, attached only to the body winding part) The label was attached by heat shrinking. In addition, as evaluation of the finishing property after shrinkage, the strain in the 360 degree direction on the attached label was measured using a gauge, and the maximum value of the strain was obtained. At that time, evaluation was performed according to the following criteria.
○: Maximum strain less than 2.5 mm ×: Maximum strain 2.5 mm or more

[Label wrinkles]
The label was attached under the same conditions as those described above for measuring shrinkage finish. And it evaluated by the number and the magnitude | size of the wrinkle of the mounted label.
◯: No wrinkles with 2 or less wrinkles and more than 5 mm ×: Wrinkles with 3 or more wrinkles or 1 or more wrinkles greater than 5 mm

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

[Bottle diameter change rate]
The diameter (W ₁ ) of the center of the bottle when a load of 15 kg is applied in the compression mode using “Strograph V10-C” manufactured by Toyo Seiki Co., Ltd. is measured at the center of the side surface of the label-coated bottle. Obtain the bottle diameter change rate (%).
Bottle diameter change rate (%) = 100 × (W ₁ −W ₂ ) / W ₂
Here, W ₂ is the diameter of the front of the bottle central portion to apply a load.
Evaluation was made according to the following criteria.
○: Bottle diameter change rate of less than 7% ×: Bottle diameter change rate of 7% or more

  Next, Tables 1 and 2 show the compositions of the polyester raw materials used in Examples and Comparative Examples, and the resin compositions and production conditions (stretching and heat treatment conditions, etc.) of the films in Examples and Comparative Examples, respectively.

<Preparation of polyester raw material>
In a stainless steel autoclave equipped with a stirrer, thermometer and partial reflux condenser, 100 mol% of dimethyl terephthalate (DMT) as a dibasic acid component and 100 mol% of ethylene glycol (EG) as a glycol component Was added to the molar ratio of 2.2 times that of the methyl ester, and 0.05 mol% of zinc acetate (based on the acid component) was used as the transesterification catalyst while distilling off the methanol produced. A transesterification reaction was performed. Thereafter, 0.025 mol% of antimony trioxide (based on the acid component) was added as a polycondensation catalyst, and a polycondensation reaction was performed at 280 ° C. under a reduced pressure of 26.6 Pa (0.2 Torr). A 0.70 dl / g polyester (A) was obtained. This polyester is polyethylene terephthalate. In the production of the above polyester (A), SiO ₂ (Silicia 266 manufactured by Fuji Silysia) was added as a lubricant at a ratio of 8,000 ppm with respect to the polyester. Further, polyesters (A2, B, C, D) shown in Table 1 were synthesized by the same method as described above. In the table, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and BD is 1,4-butanediol. The intrinsic viscosities of the polyesters A2, B, C, and D were 0.70 dl / g, 0.72 dl / g, 0.80 dl / g, and 1.15 dl / g, respectively. Each polyester was appropriately formed into a chip shape.

[Example 1]
The above-described polyester A, polyester A2, polyester B, and polyester D were mixed at a weight ratio of 10: 20: 60: 10 and charged into an extruder. Thereafter, the mixed resin was melted at 280 ° C., extruded from a T-die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 433 μm. At this time, the take-up speed of the unstretched film (the rotation speed of the metal roll) was about 20 m / min. Moreover, Tg of the unstretched film was 67 degreeC.

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

  As described above, the film immediately after the longitudinal stretching is forcibly cooled at a cooling rate of 40 ° C./second by a cooling roll set at a surface temperature of 30 ° C. (a high-speed roll positioned immediately after the second-stage longitudinal stretching roll). After the cooling, the cooled film is guided to a tenter, preheating zone, first transverse stretching zone, intermediate heat treatment zone, intermediate zone (natural cooling zone), cooling zone (forced cooling zone), second transverse stretching zone, final heat treatment zone. Was passed continuously. In the intermediate zone, when the strip-shaped paper piece is hung in a state where the film is not passed through, the hot air from the intermediate heat treatment zone and the cooling from the cooling zone so that the paper piece hangs almost completely in the vertical direction. The wind and hot air from the transverse stretching zone were shut off.

  Then, the longitudinally stretched film guided to the tenter was first heat-treated at a temperature of 100 ° C. for 10 seconds in the preheating zone, and then stretched 2.2 times while cooling at a temperature of 80 ° C. Then, it was passed in 15 seconds while heating to 145 ° C. in the intermediate heat treatment zone. Thereafter, the film after natural cooling was guided to a cooling zone and forcedly cooled until the surface temperature of the film reached 100 ° C. The film was stretched 1.8 times in the width direction (lateral direction) at a temperature of 105 ° C. in the second transverse stretching zone. (Thus, the total transverse draw ratio was 3.96 times)

  Thereafter, the laterally stretched film is guided to a final heat treatment zone in the tenter with both ends in the width direction held by clips, and is cooled after being heat treated at a temperature of 100 ° C. for 5 seconds in the final heat treatment zone. The biaxially stretched film of about 30 μm was continuously produced over a predetermined length by cutting and removing both edges and winding up into a roll having a width of 400 mm. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film was very favorable overall in terms of preferable heat shrinkage characteristics, preferable cutability and container reinforcing effect.

[Example 2]
In Example 1, the raw material B was replaced with the raw material C. The Tg of the unstretched film was 67 ° C. Other than that, the biaxially stretched film of about 30 micrometers was continuously manufactured over predetermined length by forming into a film on the conditions similar to Example 1, and winding up in roll shape by width 400mm. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film was very favorable overall in terms of preferable heat shrinkage characteristics, preferable cutability and container reinforcing effect.

[Example 3]
An unstretched film having the same resin composition as in Example 1 and a thickness of 460 μm was obtained. The draw ratio of the first step in the transverse drawing step is 2.8 times, which is higher than that of Example 1, and the draw ratio of the second step is 1.5 times, which is lower than that of Example 1. The film was formed under the same conditions as in Example 1 except that it was 20 times higher than in Example 1, and a biaxially stretched film of about 30 μm was continuously formed over a predetermined length by winding it into a roll with a width of 400 mm. Manufactured. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film was very favorable overall in terms of preferable heat shrinkage characteristics, preferable cutability and container reinforcing effect.

[Example 4]
An unstretched film having the same resin composition as in Example 1 and a thickness of 480 μm was obtained. The second stage draw ratio in the transverse stretching step is 2.0 times higher than that in Example 1, and the total transverse stretching ratio is 4.40 times higher than in Example 1. The second stage in the transverse stretching step The film was formed under the same conditions as in Example 1 except that the stretching temperature was 115 ° C., which was higher than that in Example 1. The film was wound into a roll with a width of 400 mm, thereby forming a biaxially stretched film of about 30 μm to a predetermined length. It was manufactured continuously over the entire length. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film was very favorable overall in terms of preferable heat shrinkage characteristics, preferable cutability and container reinforcing effect.

[Example 5]
An unstretched film having the same resin composition as that of Example 1 and a thickness of 464 μm was obtained. In the longitudinal stretching step, the first stage draw ratio is 3.0 times, which is higher than that of Example 1, and the second stage draw ratio is 1.3 times, which is lower than the draw ratio of Example 1. Similar to Example 1 except that the magnification was 3.90 times higher than in Example 1, the intermediate heat treatment temperature in the transverse stretching transverse step was 155 ° C., and the second stage stretching temperature was 115 ° C. higher than in Example 1. A biaxially stretched film of about 30 μm was continuously produced over a predetermined length by forming the film under conditions and winding it into a roll having a width of 400 mm. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film was very favorable overall in terms of preferable heat shrinkage characteristics, preferable cutability and container reinforcing effect.

[Comparative Example 1]
Polyester A, polyester A2, polyester B, and polyester D were mixed at a weight ratio of 10: 50: 30: 10. The Tg of the unstretched film was 67 ° C. The film was formed under the same conditions as in Example 1 except that the second stage stretching temperature in the transverse stretching process was 125 ° C., which was higher than that in Example 1, and wound into a roll with a width of 400 mm. A biaxially stretched film was continuously produced over a predetermined length. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film had a low heat yield and heat shrinkage stress in the width direction, and was slackened when attached to a PET bottle as a label, and was an inappropriate film as a label.

[Comparative Example 2]
An unstretched film having the same raw material composition as in Example 1 and a thickness of 120 μm was obtained. About 30 μm by stretching 4 times at 75 ° C. in the transverse direction without longitudinal stretching, heat treatment for 5 seconds at a temperature of 130 ° C., cooling, cutting off both edges and winding up into a roll with a width of 400 mm A biaxially stretched film was continuously produced over a predetermined length. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained uniaxially stretched film had a low shrinkage stress in the width direction, a high heat shrinkage difference, and a large bottle diameter change rate. Further, the right-angle tear strength was high, and the perforation opening rate was poor.

[Comparative Example 3]
Polyester A, polyester A2, polyester B, and polyester D were mixed at a weight ratio of 10: 10: 70: 10. The unstretched film had a Tg of 67 ° C. and a thickness of 426 μm. In the transverse stretching step, the first stage draw ratio is 1.5 times lower than that of Example 1, the second stage draw ratio is 2.6 times higher than that of Example 1, and the Total draw ratio is 3.90 times. The film was formed under the same conditions as in Example 1 except that it was lower than Example 1 and the second stage stretching temperature in the transverse stretching process was 100 ° C. and lower than Example 1, and was formed into a roll with a width of 400 mm. A biaxially stretched film of about 30 μm was continuously produced over a predetermined length by winding. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film had a low shrinkage stress in the width direction, a high difference in thermal shrinkage, and a large bottle diameter change rate.

[Comparative Example 4]
Polyester A, polyester A2, polyester B, and polyester D were mixed at a weight ratio of 10: 10: 70: 10. The unstretched film had a Tg of 67 ° C. and a thickness of 426 μm. In the transverse stretching step, the first stage draw ratio is 1.5 times lower than that of Example 1, the second stage draw ratio is 2.6 times higher than that of Example 1, and the Total draw ratio is 3.90 times. The film was formed under the same conditions as in Example 1 except that the second stage stretching temperature in the transverse stretching process was 100 ° C. lower than Example 1 and the final heat treatment temperature was 135 ° C. The biaxially stretched film of about 30 μm was continuously produced over a predetermined length by winding it in a roll shape with a width of 400 mm. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The obtained biaxially stretched film had a low shrinkage stress in the width direction, a high difference in thermal shrinkage, and a large bottle diameter change rate.

Table 3 shows the evaluation results of Examples and Comparative Examples.

  Since the heat-shrinkable polyester film of the present invention has excellent processing characteristics as described above, it can be suitably used for labeling applications such as bottles. In particular, it has a beautiful appearance for a package that does not require a high shrinkage rate.

Claims (6)

It comprises a polyester resin containing 50 mol% or more of ethylene terephthalate and containing 13 mol% or more of one or more monomer components that can be an amorphous component in all polyester resin components, and the following (1) to The heat-shrinkable polyester film characterized by satisfying the requirement (3):
(1) The hot-water heat shrinkage in the film width direction and the longitudinal direction when treated in warm water at 95 ° C. for 10 seconds is 25% or more and 40% or less and 0% or more and 15% or less, respectively;
(2) The maximum heat shrinkage stress in the film width direction at 90 ° C. is 8 MPa or more and 20 MPa or less;
(3) The hot water heat shrinkage rate in the film width direction in 95 ° C hot water is X ₀ (%), and the hot water heat shrinkage rate in the width direction in 80 ° C hot water is 10%. When the total hot water heat shrinkage rate of the film formed after shrinking 10% in the width direction and the hot water heat shrinkage rate in the width direction in 95 ° C. warm water is X ₁₀ (%), the difference in heat shrinkage rate Δ (= X ₀ −X ₁₀ ) (%) is 10% or more and 20% or less.   2. The thermal shrinkage according to claim 1, wherein a right-angled tear strength per unit thickness after shrinking in the width direction by 10% in warm water at 80 ° C. is 170 N / mm or more and 310 N / mm or less. Polyester film.   The heat-shrinkable polyester film according to claim 1 or 2, wherein the tensile fracture strength in the longitudinal direction is 90 MPa or more and 300 MPa or less.   The main component of a monomer that can be an amorphous component in all the polyester resin components is any one of neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid. The heat-shrinkable polyester film according to any one of the above. It is a manufacturing method for manufacturing continuously the heat-shrinkable polyester-type film in any one of Claims 1-4, Comprising: Each process of following (a)-(g) is included, The manufacturing characterized by the above-mentioned. Method:
(A) After stretching an unstretched polyester film at a temperature of Tg to (Tg + 30 ° C.) and below in the longitudinal direction at a magnification of 2.2 times to 3.0 times, (Tg + 10 ° C.) to (Tg + 40 ° C.) A longitudinal stretching step in which the film is stretched in the longitudinal direction so as to have a total magnification of 2.8 times or more and 4.5 times or less by stretching at a temperature of 1.2 times to 1.5 times in the longitudinal direction;
(B) a first lateral stretching step in which the film after longitudinal stretching is stretched at a magnification of 2 times or more and 3.2 times or less in the width direction in a state where both ends in the width direction are held by clips in the tenter;
(C) Intermediate heat treatment step of heat-treating the film after the first transverse stretching at a temperature of 130 ° C. or higher and 190 ° C. or lower for 5 seconds or longer and 30 seconds or shorter in a tenter with both ends in the width direction held by clips. ;
(D) a natural cooling step of naturally cooling the intermediate heat-treated film by passing it through an intermediate zone that is cut off from the heating zone of each step and does not perform a positive heating operation;
(E) a forced cooling step of actively cooling the film after natural cooling until the surface temperature reaches a temperature of 80 ° C. or higher and 120 ° C. or lower;
(F) a second lateral stretching step in which the film after forced cooling is stretched at a temperature of (Tg + 30 ° C.) or more and (Tg + 55 ° C.) or less in the width direction at a magnification of 1.5 to 2.0 times;
(G) The film after the second lateral stretching is heat-treated at a temperature of 80 ° C. or higher and 130 ° C. or lower for 1.0 second or more and 9.0 seconds or less in a tenter with both ends in the width direction held by clips. Final heat treatment process.   The heat shrinkable polyester film according to any one of claims 1 to 4 is used as a base material, and a label having a perforation or a pair of notches provided on the base material is coated on at least a part of the outer periphery of the packaging object. And a heat-shrinkable package.

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