Heat-shrinkable polyester film and method for producing polyester resin film

Abstract

To provide a polyester-based heat-shrinkable film or the like which stably heat-shrinks and exhibits excellent wrinkle resistance even when applied to various PET bottles or the like.SOLUTION: The polyester heat-shrinkable film or the like has the following constitutions (a) to (d). (a) The heat shrinkage ratio A1 in the main shrinkage direction when shrunk in warm water at 80 °C. for 10 seconds is adjusted to a value within the range of 21 to 65%. (b) The heat shrinkage ratio A2 in a case of being shrunk in warm water at 80 °C. for 10 seconds in the direction orthogonal to the main shrinkage direction is set to a value within the range of - 4 to 4%. (c) The absolute ratio (A1 / A2) of the thermal shrinkage A1 to the thermal shrinkage A2 is adjusted to 15 or more. (d) The neck-in rate measured in hot water at 70 °C for 10 seconds is 6% or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a polyester heat-shrinkable film (hereinafter, sometimes simply referred to as a heat-shrinkable film), and a method for producing a polyester resin film. More specifically, the present invention relates to a polyester heat-shrinkable film that exhibits excellent wrinkle resistance and other properties by controlling the neck-in ratio and other factors, even when applied to PET bottles of various different shapes, and a method for producing the same. [Background technology]

[0002] Conventionally, heat-shrinkable films have been widely used as base films for labels on PET bottles, etc. In particular, polyester-based heat-shrinkable films are gaining a growing share of the market as base films for labels due to their excellent strength, transparency, etc. Although polyester heat-shrinkable films have these excellent properties, they have a rapid thermal response when heated, which causes them to shrink unevenly and prone to wrinkling. That is, the heat-shrinkable film is affected by storage conditions, particularly humidity, and the heat shrinkage rate at a given temperature varies, resulting in the problem of wrinkles easily forming when the shrink label is heat-shrunk.

[0003] Therefore, a heat-shrinkable polyester film has been proposed that is a polyester shrink film that has extremely excellent warm water resistance, shrinkage properties, strength, etc., and that can be used for narrow-necked cylindrical heat-resistant PET bottles, etc. (see, for example, Patent Document 1). More specifically, it was a preferred embodiment that the heat-shrinkable polyester film satisfied the following requirements (1) to (3) and also satisfied requirement (4). (1) The thermal shrinkage rate of the film in the main shrinkage direction in an air oven at 100°C for 5 minutes is 20% or more in either the longitudinal or transverse direction. (2) The breaking elongation of the film in the direction perpendicular to the shrinkage direction is within the range of 1 to 100%. (3) The heat of fusion of the film is 8 cal / g or less. (4) The neck-in rate after immersion in 75°C hot water for 5 seconds is 10% or less.

[0004] Furthermore, a heat-shrinkable polyester film has been proposed that is suppressed from wrinkling when used for wrapping labels on lunch boxes, noodle containers, etc. (see, for example, Patent Document 2). More specifically, it is a heat-shrinkable polyester film whose main shrinkage direction is the machine (longitudinal) direction and which satisfies the following requirements (1) to (6). (1) The thermal shrinkage rate in the longitudinal direction after immersion in 80°C hot water for 10 seconds is 35% or more and 70% or less. (2) The thermal shrinkage rate in the direction perpendicular to the longitudinal direction (width direction) after immersion in 80°C hot water for 10 seconds is -8% or more and 7% or less. (3) The film has a constant length, is fixed only in the longitudinal direction, and is held in a state of 90°C hot air for 10 seconds. The film has a widthwise change rate of 5 to 22%. (4) The film is fixed only in the longitudinal direction with 10% slack in the longitudinal direction, and is held under hot air at 90°C for 10 seconds. The rate of change in the film width direction is within the range of 5 to 20%. (5) The maximum heat shrinkage stress in the longitudinal direction measured under hot air at 90°C is within the range of 2 to 10 MPa%. (6) The stress at 10% elongation (so-called F10) measured with hot air at a temperature of 90°C is within the range of 1 to 5 MPa% in the longitudinal direction and within the range of 0.5 to 3 MPa% in the transverse direction.

[0005] Furthermore, a heat-shrinkable film has been proposed that, when applied to a battery cell packaging or the like, has excellent durability and coating retention after coating (see, for example, Patent Document 3). More specifically, a preferred embodiment is a single-layer or multi-layer heat-shrinkable film having a resin layer containing a polyester resin as a main component on at least one side of the film, which satisfies the following requirements (a) to (d) and also satisfies requirement (e). (a) The polyester resin contains a copolymer polyester resin and, in addition to a predetermined copolymerization component, contains at least one selected from the group consisting of 1,4-butanediol, neopentyl glycol, diethylene glycol, etc., and contains 15 mol % or more of a diol component other than ethylene glycol, relative to 100 mol % of the total amount of diol components. (b) When immersed in warm water at 99°C for 10 seconds, the thermal shrinkage rate in the main shrinkage direction is within the range of 40 to 65%. (c) When immersed in warm water at 99°C for 10 seconds, the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction is within the range of 4 to 15%. (d) When immersed in 99°C warm water for 10 seconds, the difference in heat shrinkage between the main shrinkage direction and the direction perpendicular to the main shrinkage direction (heat shrinkage in the main shrinkage direction - heat shrinkage in the direction perpendicular to the main shrinkage direction) is within the range of 30 to 55%. (e) The neck-in rate after immersion in 70°C hot water for 10 seconds is 5% or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 07-77757 (Claims, etc.) [Patent Document 2] WO2020-246420 (Claims, etc.) [Patent Document 3] Patent No. 6791335 (Claims, etc.) Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the case of the heat-shrinkable polyester film disclosed in Patent Document 1, it is necessary to satisfy all of the requirements (1) to (3), which not only makes it difficult to control the manufacturing conditions but also leads to problems such as a low manufacturing yield. Furthermore, requirement (4) states that a neck-in rate of 10% or less after immersion in 75°C hot water for 5 seconds is preferable, but this was only considered to be applicable to standard narrow-necked heat-resistant PET bottles, etc. Therefore, when applied to PET bottles and other bottles whose horizontal cross-sectional shape of the body is not circular but has a complex shape, problems have been observed in that the heat shrinkability tends to be uneven and fine wrinkles are likely to occur.

[0008] Furthermore, in the case of the heat-shrinkable polyester film disclosed in Patent Document 2, in production, an unstretched sheet having a specific polyester composition must be uniaxially stretched in the longitudinal direction and then subjected to a relaxation treatment in the longitudinal direction, which not only makes it difficult to control the production conditions but also leads to problems such as a low production yield. Moreover, all of requirements (1) to (6) had to be met. In particular, requirement (3) required that the film be held at a constant length in the longitudinal direction, fixed only in the longitudinal direction, and held in a 90°C hot air atmosphere for 10 seconds. The rate of change in the film width direction, calculated according to a specified formula, had to be limited to a specified value (5 to 22%). Furthermore, as requirement (4), the film must be fixed only in the longitudinal direction with 10% slack in the longitudinal direction, and held in hot air at 90°C for 10 seconds. The rate of change in the film width direction, calculated according to a specified formula, must be limited to a specified value (5 to 20%), and stable control was not easy. Specifically, when measuring and controlling requirements (3) and (4), it is necessary to fix a specified film in the longitudinal direction, and to adopt heating conditions for 10 seconds under hot air at 90°C, or to reproduce a specified relaxed state, which has resulted in the problem that the obtained values ​​of the rate of change are prone to large variations. Furthermore, its main use is for ribbon labels on lunch box containers, noodle containers, etc., and when applied to PET bottles with complex shapes, there was a problem that the heat shrinkability was prone to being uneven and fine wrinkles were likely to occur.

[0009] Furthermore, in the case of the heat-shrinkable polyester film disclosed in Patent Document 3, it is necessary to satisfy all of the requirements (a) to (d), and not only do the manufacturing conditions, including the selection of raw materials, have to be controlled in an extremely large number of items, but stable control is not easy, and there are problems such as a tendency for the yield during manufacturing to be low. Furthermore, requirement (e) stipulates that the neck-in rate after immersion in 70°C warm water for 10 seconds should be 5% or less. However, this is primarily intended for use in packaging for vehicle battery cells, and when applied to PET bottles or other products with complex shapes, there have been problems with uneven heat shrinkage and the tendency for fine wrinkles to form.

[0010] Therefore, in view of the above problems, the inventors of the present invention have made extensive efforts and have come to solve the conventional problems by limiting the absolute values ​​of the heat shrinkage rates of a heat shrinkable film in the main shrinkage direction and in the direction perpendicular thereto, measured under specified conditions, and the ratio thereof, and by limiting the neck-in ratio measured under specified conditions. In other words, the present invention aims to provide a polyester-based heat-shrinkable film that not only requires few control items and is easy to produce stably, but also stably heat-shrinks and exhibits excellent wrinkle resistance even when applied to PET bottles or the like having complex shapes, and a method for stably producing such a polyester-based resin film. [Means for solving the problem]

[0011] According to the present invention, there is provided a polyester-based heat-shrinkable film derived from a polyester-based resin, characterized in that the polyester-based heat-shrinkable film has the following configurations (a) to (d), which can solve the above-mentioned problems. (a) When the thermal shrinkage rate in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is defined as A1, A1 is set to a value within the range of 21 to 65%. (b) When the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction is A2 when shrunk in 80°C hot water for 10 seconds, A2 is set to a value within the range of -4 to 4%. (c) The absolute value (A1 / A2) of the ratio of the thermal shrinkage rates A1 and A2 is 15 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds shall be 6% or less. That is, by limiting the heat shrinkage rate (a) in the main shrinkage direction under specified conditions, the heat shrinkage rate (b) in the direction perpendicular thereto, the heat shrinkage rates of the heat shrinkable film in the main shrinkage direction and the direction perpendicular thereto measured under specified conditions, and the absolute value (c) of their ratio, and also by limiting the neck-in rate (d) measured under specified conditions, not only can stable production be facilitated, but also excellent wrinkle resistance can be exhibited when applied to various PET bottles, etc.

[0012] Furthermore, in the polyester heat shrinkable film of the present invention, when the maximum shrinkage stress in the main shrinkage direction at a shrinkage temperature of 85° C. is defined as C, it is preferable that C is set to a value within the range of 3 to 10 MPa. In this way, by limiting the maximum shrinkage stress (C) at a predetermined temperature to a predetermined range, it becomes easier to control the neck-in ratio, etc., and excellent wrinkle resistance can be more stably exhibited.

[0013] Furthermore, the polyester heat-shrinkable film of the present invention preferably has a thickness within the range of 10 to 100 μm. By limiting the thickness to a predetermined range in this way, it becomes easier to control the heat shrinkage rate and neck-in rate under predetermined conditions, and as a result, even better wrinkle resistance can be stably exhibited.

[0014] Furthermore, according to the polyester heat-shrinkable film of the present invention, the main shrinkage direction of the polyester heat-shrinkable film is preferably the MD direction. By limiting the main shrinkage direction to the MD in this way, it becomes easier to adjust the manufacturing conditions, particularly for longitudinally shrinkable films, and it also becomes easier to control the heat shrinkage rates (A1 and A2), neck-in ratio, absolute value (A1 / A2), shrinkage stress, etc. under specified conditions, which ultimately makes it possible to exhibit even better wrinkle resistance.

[0015] Furthermore, according to the polyester-based heat-shrinkable film of the present invention, it is preferable that the polyester-based resin is a polyester-based resin derived from a dicarboxylic acid compound and a diol compound as reactive components, and that the diol compound contains at least ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. In this way, by specifically limiting the type of diol compound, which is one of the reaction components, it becomes easier to adjust the heat shrinkage rate (A1 and A2), neck-in rate, absolute value (A1 / A2), shrinkage stress, etc. under specified conditions, and ultimately, even better wrinkle resistance can be exhibited.

[0016] Another aspect of the present invention is a method for producing a polyester resin film derived from a dicarboxylic acid compound and a diol compound as reaction components, the method comprising the following steps 1 and 2: Step 1: A step of preparing a dicarboxylic acid compound and a diol compound as reaction components and reacting them to produce a polyester resin. Step 2: A step of producing a polyester-based heat-shrinkable film having the following configurations (a) to (d) by stretching a polyester-based resin in the TD direction and / or the MD direction. (a) When the thermal shrinkage rate in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is defined as A1, A1 is set to a value within the range of 21 to 65%. (b) When the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction is A2 when shrunk in 80°C hot water for 10 seconds, A2 is set to a value within the range of -4 to 4%. (c) The absolute value (A1 / A2) of the ratio of the thermal shrinkage rates A1 and A2 is 15 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds shall be 6% or less. In other words, by producing a polyester-based heat-shrinkable film in this manner, it is possible to efficiently produce a polyester-based heat-shrinkable film that exhibits excellent wrinkle resistance even when the main shrinkage direction is the so-called horizontal direction (TD direction) or vertical direction (MD direction) and is applied to various PET bottles, etc.

[0017] In carrying out the method for producing a polyester-based heat-shrinkable film of the present invention, it is preferable that the stretching treatment in step 1 is carried out along the MD direction. In this way, by stretching in the MD direction, it becomes easier to adjust the manufacturing conditions, particularly for longitudinally shrinkable films, and it also becomes easier to control the heat shrinkage rates (A1 and A2), neck-in ratio, absolute value (A1 / A2), shrinkage stress, etc. under specified conditions, which ultimately makes it possible to exhibit even better wrinkle resistance. [Brief explanation of the drawings]

[0018] [Figure 1] 1(a) to 1(c) are diagrams illustrating the configuration of each polyester-based heat-shrinkable film. [Figure 2] FIG. 2(a) is a diagram illustrating the relationship between the heat shrinkage rate (A1) in the main shrinkage direction of a polyester-based heat-shrinkable film under predetermined heating conditions (hot water at 80°C for 10 seconds) and the evaluation of shrinkage unevenness (relative value), and FIG. 2(b) is a diagram illustrating the relationship between the heat shrinkage rate (A2) in the direction perpendicular to the main shrinkage direction of a polyester-based heat-shrinkable film under predetermined heating conditions (hot water at 80°C for 10 seconds) and the evaluation of shrinkage unevenness (relative value). [Figure 3] FIG. 3 is a diagram illustrating the relationship between the absolute value (A1 / A2) of the ratio of the heat shrinkage rate (A2) in the perpendicular direction to the heat shrinkage rate (A1) in the main shrinkage direction of a polyester-based heat-shrinkable film, and the evaluation of shrinkage unevenness (relative value). [Figure 4] FIG. 4 is a diagram illustrating the relationship between the neck-in ratio (%) and the evaluation of shrinkage unevenness (relative value) under predetermined heating conditions (hot water 70° C., 10 seconds) for a polyester heat-shrinkable film. [Figure 5]FIG. 5 is a diagram illustrating the relationship between the shrinkage stress (MPa) in the main shrinkage direction of a polyester heat-shrinkable film under predetermined heating conditions (hot water at 85°C for 10 seconds) and the evaluation of shrinkage unevenness (relative value). [Figure 6] Figure 6(a) corresponds to Example 1 and is a diagram (photograph) showing the appearance of a cylindrical label when no shrinkage unevenness occurs, and Figures 6(b) to (d) are enlarged views of areas P, Q, and R of the appearance shown in Figure 6(a). [Figure 7] Figure 7(a) corresponds to Comparative Example 1 and is a diagram (photograph) showing the appearance of a cylindrical label when uneven shrinkage occurs, and Figures 7(b) to (d) are enlarged views of the appearance areas S, T, and U shown in Figure 7(a). [Figure 8] FIG. 8(a) is a diagram provided to explain a measurement sample for measuring the neck-in ratio, FIG. 8(b) is a diagram provided to explain a fixing frame jig for measuring the neck-in ratio, and FIG. 8(c) is a diagram provided to explain a method for measuring the neck-in ratio. DETAILED DESCRIPTION OF THE INVENTION

[0019] [First embodiment] The first embodiment is a polyester-based heat-shrinkable film derived from a polyester-based resin, as illustrated in Figs. 1(a) to (c), and characterized by having the following configurations (a) to (d): (a) When the thermal shrinkage rate in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is defined as A1, A1 is set to a value within the range of 21 to 65%. (b) When the heat shrinkage rate is A2 when the film is heat-shrunk in 80°C hot water for 10 seconds in a direction perpendicular to the main shrinkage direction (hereinafter sometimes simply referred to as the perpendicular direction), A2 is set to a value within the range of -4 to 4%. (c) The absolute value (A1 / A2) of the ratio of the thermal shrinkage rates A1 and A2 is 15 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds shall be 6% or less. Hereinafter, the configuration of the polyester heat-shrinkable film of the first embodiment will be divided into sections, and various parameters and the like will be explained with reference to the drawings as appropriate, while the aspects of the polyester heat-shrinkable film will be specifically explained.

[0020] 1. Polyester resin The polyester resin as the main component may be of any type as long as it is a polyester resin that easily satisfies the above-mentioned structures (a) to (d). However, it is usually preferable that the polyester resin be a polyester resin made of a diol and a dicarboxylic acid, a polyester resin made of a diol and a hydroxycarboxylic acid, a polyester resin made of a diol, a dicarboxylic acid, and a hydroxycarboxylic acid, or a mixture of these polyester resins. Here, examples of diols as raw material components of polyester resins include at least one of aliphatic diols such as ethylene glycol, diethylene glycol, propanediol, butanediol, neopentyl glycol, and hexanediol, alicyclic diols such as 1,4-hexanedimethanol, and aromatic diols. Among these, ethylene glycol, diethylene glycol, and 1,4-hexanedimethanol are particularly preferred. Similarly, examples of dicarboxylic acids as a compound component of polyester resins include at least one of fatty acid dicarboxylic acids such as adipic acid, sebacic acid, and azelaic acid; aromatic dicarboxylic acids such as terephthalic acid, naphthalenedicarboxylic acid, and isophthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and ester-forming derivatives thereof. Among these, terephthalic acid and isophthalic acid are particularly preferred. Similarly, the hydroxycarboxylic acid as a compound component of the polyester resin may include at least one of lactic acid, hydroxybutyric acid, polycaprolactone, and the like.

[0021] A suitable amorphous polyester resin is one composed of a dicarboxylic acid containing at least 80 mol% of terephthalic acid and a diol consisting of 50 to 80 mol% of ethylene glycol and 20 to 50 mol% of one or more diols selected from 1,4-cyclohexanedimethanol, neopentyl glycol, and diethylene glycol. If necessary, other dicarboxylic acids and diols, or hydroxycarboxylic acids, may be used to change or adjust the film properties. These may be used alone or in combination. On the other hand, examples of crystalline polyester resins include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, and polypropylene terephthalate, and it is also preferable to use these either alone or as a mixture.

[0022] Furthermore, when the polyester resin is a mixture of a crystalline polyester resin and a non-crystalline polyester resin, in order to obtain good and appropriate wrinkle resistance, heat resistance, heat shrinkage rate, etc., it is preferable to set the amount of crystalline polyester resin to a value within the range of 10 to 50% by weight relative to the total amount (100% by weight) of the resins constituting the polyester-based heat-shrinkable film. The reason for this is that by setting the blending amount of crystalline polyester resin to a value within the specified range, it is possible to obtain a polyester-based heat-shrinkable film that exhibits good heat-shrinkage properties and exhibits little change in physical properties such as the heat-shrinkage rate at a specified temperature, even under high-humidity conditions. More specifically, if the content of the crystalline polyester resin is less than 10% by weight, it may become difficult to suppress moisture absorption when left in a specified high-humidity environment for a relatively short period of time, and it may become difficult to control the absolute value of the specified heat shrinkage ratio (A1 / A2) within a specified range. On the other hand, if the content of the crystalline polyester resin exceeds 50%, the shrinkage percentage of the resulting polyester-based heat-shrinkable film may be excessively reduced. Therefore, the amount of crystalline polyester resin blended is more preferably within the range of 15 to 45% by weight, and even more preferably within the range of 20 to 40% by weight, relative to the total amount of resin (100% by weight).

[0023] 2.Configuration (a) The constitution (a) is a necessary constitutional requirement that, in a polyester-based heat-shrinkable film, when the heat shrinkage percentage in the main shrinkage direction when shrunk in warm water at 80°C for 10 seconds is A1 (%), the heat shrinkage percentage A1 is a value within the range of 21 to 65%. The reason for this is that if the heat shrinkage rate A1 exceeds this range, the heat shrinkage rate under general heat shrinkage conditions (80°C, 10 seconds) will be insufficient, and the film will not be able to follow the shape of the PET bottle periphery, making it difficult to prevent wrinkles from occurring. More specifically, if the thermal shrinkage rate A1 of such a film is less than 21%, it becomes difficult to limit the numerical value expressed by the absolute value (A1 / A2) described below within a predetermined range, and the balance of the thermal shrinkage rates in the main shrinkage direction and the direction perpendicular thereto becomes poor, which may make it difficult to suppress the occurrence of wrinkles. However, if the thermal shrinkage rate A1 of such a film becomes excessively large, it becomes difficult to limit the numerical value expressed by the absolute value (A1 / A2) within a predetermined range, and the balance between the thermal shrinkage rates in the main shrinkage direction and the direction perpendicular thereto deteriorates, which may make it impossible to suppress the occurrence of wrinkles. Therefore, it is more preferable that the heat shrinkage factor A1 of such a film is set to a value within the range of 25 to 50%, and even more preferably to a value within the range of 30 to 45%. In measuring the above-mentioned heat shrinkage percentage A1, it is more preferable to measure the heat shrinkage percentage A1 in the main shrinkage direction under predetermined conditions before and after leaving the film under high humidity conditions of 20°C and 90% RH for 24 hours. Therefore, unless otherwise specified, it is assumed that the film is left under predetermined conditions and stabilized when measuring the heat shrinkage percentage A1.

[0024] Here, referring to FIG. 2(a), the relationship between the heat shrinkage rate A1 (%) measured under predetermined conditions and the wrinkle resistance property (relative value) will be explained. That is, the horizontal axis of FIG. 2(a) shows the heat shrinkage rate A1 (%) in the main shrinkage direction measured under the heat shrinkage condition of immersion in hot water at 80°C for 10 seconds in the main shrinkage direction, and the vertical axis shows the evaluation (relative value) of the wrinkle resistance property. The wrinkle resistance evaluation (relative value) on the vertical axis is quantified as follows: ⊚ is 5 points, ○ is 3 points, △ is 1 point, and × is 0 point. The data of the characteristic curve in FIG. 2(a) is based on the evaluation results showing the relationship between the heat shrinkage rate in the main shrinkage direction and the wrinkle resistance properties of the polyester heat-shrinkable films of Examples 1, 3 to 7 (however, in FIG. 2(a) Example 2 is omitted from the viewpoint of the manufacturing conditions and is represented as Ex1, 3 to 7) and Comparative Examples 1 to 3 (represented as CE1 to 3 in FIG. 2(a)) described below.

[0025] From the characteristic curve in FIG. 2(a), it can be seen that there is a predetermined relationship between the heat shrinkage rate A1 in the main shrinkage direction measured under predetermined conditions and the wrinkle resistance. More specifically, from the characteristic curve in FIG. 2(a), for example, by limiting the heat shrinkage rate A1 to 55% or less, a good result of at least 4 or more is obtained in the evaluation of wrinkle resistance. Similarly, by limiting the heat shrinkage factor A1 to 50% or less, an even better result of 5 is obtained. However, it has been found separately that if the value of the heat shrinkage rate A1 becomes too small, the adhesion to the adherend such as a PET bottle will be significantly reduced. Therefore, with regard to the structure (a), by setting the heat shrinkage percentage A1 (%) in the main shrinkage direction when shrunk in hot water at 80°C for 10 seconds within a predetermined range, it can be said that good wrinkle resistance can be obtained while maintaining excellent adhesion to adherends such as PET bottles.

[0026] 3. Configuration (b) The constitution (b) is a necessary constitutional requirement that, when a polyester-based heat-shrinkable film is heat-shrunk in 80°C warm water for 10 seconds, the heat shrinkage percentage A2 in the direction perpendicular to the main shrinkage direction is set to a value within the range of -4 to 4%. The reason for this is that if the heat shrinkage rate A2 exceeds the specified range, the heat shrinkage rate under general heat shrinkage conditions (80°C, 10 seconds) may be insufficient, or conversely, the heat shrinkage may be excessive, making it impossible to conform to the shape of the PET bottle's periphery and preventing wrinkles from occurring.

[0027] If the thermal shrinkage rate A2 of such a film is less than -4%, it becomes difficult to limit the numerical value expressed by the absolute value (A1 / A2) described below within a specified range, which in turn reduces the balance between the thermal shrinkage rates in the main shrinkage direction and the direction perpendicular thereto, making it difficult to suppress the occurrence of wrinkles. On the other hand, if the thermal shrinkage rate A2 of such a film becomes excessively large and exceeds 4%, it becomes difficult to limit the numerical value expressed by the absolute value (A1 / A2) within a predetermined range, and as a result, the balance between the thermal shrinkage rates in the main shrinkage direction and the direction perpendicular thereto becomes poor, which may make it difficult to suppress the occurrence of wrinkles.

[0028] In addition, as described above, it is preferable to leave the film under high humidity conditions of 20°C and 90% RH for 24 hours to stabilize it not only before measuring the heat shrinkage rate A1 but also before measuring the heat shrinkage rate A2.

[0029] Here, referring to FIG. 2(b), the relationship between the heat shrinkage rate A2 (%) measured under predetermined conditions and the wrinkle resistance property (relative value in the evaluation) will be explained. That is, the horizontal axis of FIG. 2(b) shows the heat shrinkage rate A2 (%) in the direction perpendicular to the main shrinkage direction measured under heat shrinkage conditions of immersion in 80°C warm water for 10 seconds, and the vertical axis shows the evaluation (relative value) of wrinkle resistance properties. The wrinkle resistance evaluation (relative value) on the vertical axis is quantified with ⊚ being 5 points, ◯ being 3 points, △ being 1 point, and × being 0 point. The characteristic curve in FIG. 2(b) is based on the evaluation results showing the relationship between the heat shrinkage rate in a direction perpendicular to the main shrinkage direction and the wrinkle resistance property in the polyester heat-shrinkable films of Examples 1, 3 to 7 (however, in FIG. 2(b) Example 2 is omitted from the viewpoint of manufacturing conditions and is represented as Ex1, 3 to 7) and Comparative Examples 1 to 3 (represented as CE1 to 3 in FIG. 2(b)). From the characteristic curve in FIG. 2(b), it can be seen that there is a predetermined relationship between the heat shrinkage rate A2 (%) in the direction perpendicular to the main shrinkage direction measured under predetermined conditions and the wrinkle resistance. More specifically, for example, by limiting the heat shrinkage rate A2 to the range of -4 to 4%, a favorable result of at least 3 or more is obtained in the evaluation of wrinkle resistance. In any case, regarding the configuration (b), when the film is heat-shrunk in 80°C hot water for 10 seconds, good wrinkle resistance can be obtained by setting the heat shrinkage rate A2 (%) in the direction perpendicular to the main shrinkage direction to a value within a predetermined range.

[0030] 4. Composition (c) The configuration (c) is a necessary constituent requirement that the absolute value (A2 / A1) of the ratio of the thermal shrinkage percentage A1 in the main shrinkage direction to the thermal shrinkage percentage A2 perpendicular thereto, measured under specified conditions, is 15 or more. The reason for this is that by controlling the numerical value expressed as the absolute value (A2 / A1) in this manner, in combination with other configurations (a) to (b) and (d), etc., a good evaluation of wrinkle resistance properties can be obtained. Conversely, by setting the absolute value (A2 / A1) to a value of 15 or more, the change in the heat shrinkage rate at a specified temperature is small, heat shrinkage can be achieved stably and reproducibly under specified conditions, and excellent wrinkle resistance can be easily exhibited. However, if the absolute value (A2 / A1) becomes too large, the balance between the heat shrinkage rate A1 in the main shrinkage direction and the heat shrinkage rate A2 in the perpendicular direction may be adversely affected, resulting in a decrease in wrinkle resistance. Therefore, in the configuration (c), the absolute value (A2 / A1) is more preferably set to a value within the range of 10-150, and even more preferably set to a value within the range of 15-100.

[0031] Here, referring to FIG. 3, the relationship between the absolute value (A1 / A2) of the ratio of the heat shrinkage percentage (A2) in the direction perpendicular to the main shrinkage direction to the heat shrinkage percentage (A1) in the main shrinkage direction of a polyester heat shrinkable film under predetermined heat shrinkage conditions (immersion in hot water at 80°C for 10 seconds) and shrinkage unevenness will be described. That is, the horizontal axis indicates the absolute value (A1 / A2) of the ratio of the thermal shrinkage rates, and the vertical axis indicates the evaluation value (relative value) of the shrinkage unevenness. From the characteristic curve in FIG. 3, it can be seen that there is an excellent correlation between the absolute value of the ratio of the thermal shrinkage rates (A1 / A2) and shrinkage unevenness. Therefore, it can be said that by limiting the absolute value of the ratio of the thermal shrinkage rates (A1 / A2) to a value within a predetermined range, uneven shrinkage can be controlled with high precision.

[0032] 5.Configuration (d) The constitution (d) is an essential constitutional requirement that the neck-in ratio of the polyester heat-shrinkable film be 6% or less. That is, by taking into consideration the neck-in phenomenon that normally occurs during film production and limiting the neck-in ratio, which simulates this, to a predetermined range, it is possible to achieve excellent wrinkle resistance even when applied to various PET bottles, etc. However, if the neck-in rate is too small, the manufacturing yield and the types of raw materials that can be used may be limited, which may be economically disadvantageous. Therefore, it is more preferable that the neck-in ratio is set to a value within the range of 0 to 5%, and even more preferable that it is set to a value within the range of 0.1 to 3%. The method for measuring the neck-in ratio will be described in detail in Example 1, etc., which will be described later.

[0033] Here, referring to FIG. 4, the relationship between the neck-in ratio (%) measured under predetermined conditions and the wrinkle resistance property (relative value in evaluation) will be explained. That is, the horizontal axis of Figure 4 shows the neck-in ratio (%) measured under the thermal shrinkage conditions of immersion in hot water at 70°C for 10 seconds, and the vertical axis shows the evaluation of wrinkle resistance properties (relative value). The wrinkle resistance evaluation (relative value) on the vertical axis is quantified with ⊚ being 5 points, ◯ being 3 points, △ being 1 point, and × being 0 point. The characteristic curves in Figure 4 are based on the evaluation results of the wrinkle resistance properties of polyester-based heat-shrinkable films of Examples 1, 3 to 7 (however, in Figure 4, Example 2 is omitted from the perspective of manufacturing conditions and is represented as Ex1, 3 to 7) and Comparative Examples 1 to 3 (represented as CE1 to 3 in Figure 4), which will be described later. From the characteristic curve in FIG. 4, it can be seen that there is a predetermined relationship between the neck-in ratio (%) and the wrinkle resistance characteristic (relative value). More specifically, from the characteristic curve in FIG. 4, for example, by limiting the neck-in ratio to a range of 6% or less, a good relative value of at least 3 or more is obtained in the evaluation of wrinkle resistance. Similarly, by limiting the neck-in ratio to a range of 5% or less, an even better result of a relative value of 5 was obtained in the evaluation of wrinkle resistance. In any case, regarding the configuration (d), it can be said that good wrinkle resistance can be obtained by setting the neck-in ratio when heat-shrunk under predetermined conditions to a value of 6% or less.

[0034] 6.Optional configuration requirements (1) Composition (e) Feature (e) is a requirement for the polyester-based heat-shrinkable film of the first embodiment regarding the thickness (average thickness) of the film before heat shrinkage, and is an optional requirement that the thickness be set to a value usually within the range of 10 to 100 μm. In other words, by specifically limiting the thickness of the film before heat shrinkage to a value within a predetermined range in this manner, it becomes easy to control the heat shrinkage rate (A1 and A2), neck-in rate, absolute value (A1 / A2), shrinkage stress, etc. under predetermined conditions. Therefore, the influence of certain factors can be reduced, and uneven shrinkage due to a sudden thermal response can be suppressed in a polyester heat-shrinkable film during heat shrinkage, and as a result, the occurrence of fine wrinkles can also be suppressed. More specifically, if the thickness of the film before heat shrinkage is less than 10 μm or exceeds 100 μm, the polyester heat shrinkable film may not be able to suppress uneven shrinkage due to a sudden thermal response during heat shrinkage, and it may not be possible to suppress the occurrence of fine wrinkles. Therefore, in the configuration (e), the thickness of the film before heat shrinkage is more preferably set to a value within the range of 30 to 80 μm, and even more preferably set to a value within the range of 40 to 60 μm.

[0035] (2) Composition (f) The constitution (f) is an optional constitutional requirement that, in the polyester-based heat-shrinkable film of the first embodiment, when the maximum shrinkage stress in the TD direction or MD direction at a shrinkage temperature of 85°C is C, C is set to a value within the range of 3 to 10 MPa. That is, as shown in FIG. 5, by controlling the maximum shrinkage stress to a value within a predetermined range, effective wrinkle resistance can be exhibited, and even wrinkles that occur due to excess or deficiency of the maximum shrinkage stress during thermal shrinkage can be effectively suppressed. The characteristic curves in Figure 5 are based on the evaluation results of the wrinkle resistance properties of polyester-based heat-shrinkable films of Examples 1, 3 to 7 (however, in Figure 5, Example 2 is omitted due to manufacturing conditions and is represented as Ex1, 3 to 7) and Comparative Examples 1 to 3 (referred to as CE1 to CE3), which will be described later. More specifically, as shown in Figure 5, if the maximum shrinkage stress C exceeds 10 MPa, the maximum shrinkage stress during thermal shrinkage will be excessive, and when attached to a PET bottle or the like, the shape of the PET bottle may be deformed, or wrinkles may occur due to the deformation, resulting in a decrease in wrinkle resistance. On the other hand, as shown in Figure 5, if the value of the maximum shrinkage stress C becomes too small, for example, less than 4 MPa, the maximum shrinkage stress during thermal shrinkage will be insufficient, and a gap will form between the PET bottle and the film, which may actually result in a decrease in wrinkle resistance. Therefore, in the configuration (f), the maximum shrinkage stress C is more preferably set to a value within the range of 4.1 to 8 MPa, and even more preferably set to a value within the range of 5 to 7 MPa.

[0036] (3) Other 1 It is preferable to incorporate various additives into the polyester heat-shrinkable film of the first embodiment, or to attach them to one or both surfaces thereof. More specifically, at least one of a hydrolysis inhibitor, an antistatic agent, an ultraviolet absorber, an infrared absorber, a colorant, an organic filler, an inorganic filler, an organic fiber, an inorganic fiber, and the like is preferably blended in an amount of 0.01 to 10% by weight, more preferably 0.1 to 1% by weight, based on the total amount of the polyester-based heat-shrinkable film.

[0037] As shown in FIG. 1(b), it is also preferable to laminate other resin layers 10a, 10b containing at least one of these various additives on one or both sides of the polyester heat-shrinkable film 10. In this case, when the thickness of the polyester heat-shrinkable film is taken as 100%, the single layer thickness or total thickness of the other resin layers to be additionally laminated is preferably set to a value within the range of 0.1 to 10%.

[0038] The resin as the main component constituting the other resin layer may be a polyester resin similar to that of a polyester-based heat-shrinkable film, or it is preferable that it is at least one of a different acrylic resin, an olefin-based resin, a urethane-based resin, a rubber-based resin, etc.

[0039] Furthermore, it is also preferable to form the polyester heat-shrinkable film into a multilayer structure to further improve the hydrolysis prevention effect and mechanical protection, or to provide a shrinkage rate adjusting layer 10c on the surface of the polyester heat-shrinkable film 10 so that the shrinkage rate of the polyester heat-shrinkable film becomes uniform within the plane, as shown in Figure 1(c). Such a shrinkage adjusting layer can be laminated by using an adhesive, a coating method, or heat treatment depending on the shrinkage characteristics of the polyester heat shrinkable film.

[0040] More specifically, the thickness of the shrinkage rate adjusting layer is in the range of 0.1 to 3 μm, and if the shrinkage rate of the polyester heat-shrinkable film at a specified temperature is excessively large, it is preferable to laminate a shrinkage rate adjusting layer of a type that suppresses this. Furthermore, when the shrinkage rate of a polyester heat-shrinkable film at a predetermined temperature is excessively small, it is preferable to laminate a shrinkage rate adjusting layer of a type that expands the shrinkage rate. Therefore, the present invention aims to obtain a desired shrinkage rate by using a shrinkage rate adjusting layer as a polyester heat-shrinkable film, without producing various heat-shrinkable films with different shrinkage rates.

[0041] (4) Other 2 Next, referring to Figs. 6 and 7, wrinkle resistance properties when a polyester heat-shrinkable film as a cylindrical label is attached to a PET bottle will be specifically described. 6A and 6B are photographs of the appearance of a tubular label without wrinkles, corresponding to Example 1, and Fig. 6A shows the entire body of a PET bottle covered with the tubular label. Figs. 6B to 6D are enlarged views of the upper (area P), middle (area Q), and lower (area R) parts of the body shown in Fig. 7A, respectively, and it can be seen that no wrinkles have occurred in any of the upper to lower parts. On the other hand, Figure 7 shows photographs of the appearance of a tubular label when wrinkles have occurred, corresponding to Comparative Example 1, where Figure 7(a) shows the entire body of a PET bottle covered with the tubular label, and Figures 7(b) to 7(d) are enlarged views of the upper part (area S), middle part (area T), and lower part (area U) of the body shown in Figure 7(a), respectively, and it can be seen that wrinkles have occurred in all parts from the upper part to the lower part. Furthermore, it can be seen from FIG. 7(c) that the plastic bottle itself is also deformed in the central part (area T) of the body of the plastic bottle.

[0042] [Second embodiment] The second embodiment is a method for producing a polyester heat-shrinkable film derived from the dicarboxylic acid compound and diol compound of the first embodiment, and is characterized by having the following steps 1 and 2: Step 1: A step of preparing a dicarboxylic acid compound and a diol compound as reaction components and reacting them to produce a polyester resin. Step 2: A step of producing a polyester-based heat-shrinkable film having the following components (a) to (d) by stretching the polyester-based resin in a predetermined direction. (a) When the thermal shrinkage rate in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is defined as A1, A1 is set to a value within the range of 21 to 65%. (b) When the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction is A2 when shrunk in 80°C hot water for 10 seconds, A2 is set to a value within the range of -4 to 4%. (c) The absolute value (A1 / A2) of the ratio of the thermal shrinkage rates A1 and A2 is 15 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds shall be 6% or less. Hereinafter, the method for producing a polyester-based heat-shrinkable film according to the second embodiment will be specifically described with reference to the drawings as needed.

[0043] 1. Preparation and mixing of raw materials First, it is preferable to prepare the base material and additives such as crystalline polyester resin, non-crystalline polyester resin, rubber-based resin, antistatic agent, and hydrolysis inhibitor. Next, the prepared crystalline polyester resin, amorphous polyester resin, etc. are preferably charged into the stirring vessel while being weighed, and mixed and stirred using a stirring device until homogeneous.

[0044] 2. Raw sheet production process Next, the homogeneously mixed raw materials are preferably dried to an absolutely dry state. Next, typically, it is preferable to carry out extrusion molding to prepare a raw sheet having a predetermined thickness. More specifically, for example, extrusion molding is performed using an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D of 24 and an extrusion screw diameter of 50 mm under conditions of an extrusion temperature of 245°C, to obtain a raw sheet of a predetermined thickness (usually 30 to 1000 μm).

[0045] 3. Preparation of polyester heat-shrinkable film Next, the obtained raw sheet is heated and pressed while being moved over or between rolls using a heat shrinkable film manufacturing device to produce a polyester heat shrinkable film. That is, it is preferable to stretch the film in a predetermined direction while heating and pressing it at a predetermined preheating temperature, stretching temperature, heat setting temperature, and stretching ratio described below, while basically expanding the film width, thereby crystallizing the polyester molecules that make up the polyester-based heat-shrinkable film into a predetermined shape. Then, by solidifying it in this state, a heat-shrinkable polyester heat-shrinkable film that can be used for decoration, labels, etc. can be produced. In producing the heat shrinkable film, the film can be stretched not only in the so-called transverse direction (stretching is performed in the TD direction) but also in the longitudinal direction (stretching is performed in the MD direction). That is, in the case of the present invention, regardless of the direction in which the stretching treatment is performed and the direction is set as the main shrinkage direction, the heat shrinkage rates A1, A2, absolute value (A1 / A2), neck-in rate, heat shrinkage stress (C), etc. can be limited to values ​​within predetermined ranges, and thus the occurrence of fine wrinkles can be suppressed.

[0046] (1) Stretching ratio in MD direction In addition, in the case of so-called transverse stretching, it is usually preferable to set the stretching ratio in the MD direction of the polyester heat-shrinkable film before heat shrinking (sometimes referred to as the average MD stretching ratio or the MD stretching ratio) to a value within the range of 100 to 200%. The reason for this is that by specifically limiting the MD direction stretching ratio to a value within a predetermined range in this manner, the occurrence of fine wrinkles can be suppressed when the produced heat-shrinkable film is heat-shrunk. More specifically, if the MD stretching ratio is less than 100%, it becomes difficult to limit the heat shrinkage ratios A1, A2, B1, the absolute value (A1 / A2), the neck-in ratio, the heat shrinkage stress (C), etc., which may result in a significant decrease in production yield. On the other hand, if the MD stretching ratio exceeds 200%, it may affect the shrinkage rate in the TD, making it difficult to adjust the shrinkage rate itself. Therefore, the MD stretching ratio is more preferably set to a value within the range of 110 to 180%, and even more preferably to a value within the range of 120 to 160%. In the case of so-called longitudinal stretching, the stretching ratio in the MD direction is preferably set to a value within the range of 300 to 600%, and more preferably to a value within the range of 400 to 500%.

[0047] (2) Stretching ratio in TD direction In a preferred embodiment, the stretch ratio in the TD direction of the polyester heat-shrinkable film before heat shrinking (sometimes referred to as the average TD direction stretch ratio or the TD direction stretch ratio) is set to a value within the range of 300 to 600%. The reason for this is that by specifically limiting not only the MD stretch ratio but also the TD stretch ratio to values ​​within a predetermined range, and by specifically limiting the heat shrinkage rates A1, A2, B1, absolute value (A1 / A2), neck-in rate, heat shrinkage stress (C), etc. to values ​​within a predetermined range, it is possible to further suppress the occurrence of fine wrinkles.

[0048] More specifically, if the TD stretching ratio is less than 300%, the shrinkage rate in the TD direction will be significantly reduced, which may excessively limit the applications of the usable polyester heat-shrinkable film. On the other hand, if the TD direction stretching ratio exceeds 600%, the heat shrinkage rate becomes significantly large, which may excessively limit the applications of the polyester heat shrinkable film, or may make it difficult to control the stretching ratio itself at a constant value. Therefore, the TD direction stretching ratio is more preferably set to a value within the range of 350 to 550%, and even more preferably set to a value within the range of 400 to 500%. In the case of so-called longitudinal stretching, the stretching ratio in the TD direction is preferably set to a value within the range of 100 to 200%, and more preferably to a value within the range of 110 to 180%.

[0049] 4. Polyester heat shrink film inspection process It is preferable to provide a predetermined inspection process in which the following properties are measured continuously or intermittently for the produced polyester heat-shrinkable film. That is, by measuring the following characteristics and the like through a predetermined inspection process and confirming that the values ​​fall within the predetermined ranges, a polyester-based heat-shrinkable film having more uniform shrinkage characteristics can be obtained. 1) Visual inspection of the appearance of polyester heat shrinkable film 2) Thickness variation measurement 3) Tensile modulus measurement 4) Tear strength measurement 5) Viscoelasticity measurement using SS curves

[0050] In the production of the polyester-based heat-shrinkable film of the second embodiment, it is essential to measure at least the following components (a) to (d) and confirm that the values ​​are within the predetermined ranges. (a) When the thermal shrinkage rate in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is defined as A1, A1 is set to a value within the range of 21 to 65%. (b) When the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction is A2 when shrunk in 80°C hot water for 10 seconds, A2 is set to a value within the range of -4 to 4%. (c) The absolute value (A1 / A2) of the ratio of the thermal shrinkage rates A1 and A2 is 15 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds shall be 6% or less.

[0051] [Third embodiment] The third embodiment relates to a method for using a polyester heat-shrinkable film. Therefore, any known method for using a heat shrinkable film can be suitably applied. For example, when using a polyester heat-shrinkable film, first, the polyester heat-shrinkable film is cut to an appropriate length and width and formed into a long cylindrical object. The long cylindrical object is then fed to an automatic label attachment device (shrink labeler) and further cut to the required length. Next, the container is fitted onto a PET bottle or the like filled with the contents.

[0052] Next, the polyester heat-shrinkable film fitted onto the PET bottle or the like is subjected to a heat treatment by passing through a hot air tunnel or steam tunnel at a predetermined temperature. These tunnels provide radiant heat such as infrared rays, or heated steam at about 90°C is blown onto the polyester heat-shrinkable film from the surrounding area, thereby uniformly heating the film and causing it to shrink. Therefore, labeled containers can be quickly obtained by adhering them to the outer surface of PET bottles or the like.

[0053] Here, the polyester heat-shrinkable film of the present invention is characterized by satisfying at least the configurations (a) to (d) as described in detail in the first embodiment. By doing so, even when the film is left under high humidity conditions for a relatively short period of time, changes in physical properties due to moisture absorption can be prevented, and a predetermined heat shrinkage rate can be obtained with good reproducibility at each heat treatment temperature. Therefore, even if values ​​such as the thermal shrinkage rate vary to some extent, by reducing the factors that affect the specified factors, it is possible to suppress uneven shrinkage due to a sudden thermal response in a polyester heat-shrinkable film during heat shrinkage, and as a result, it is possible to suppress the occurrence of fine wrinkles.

[0054] Therefore, as shown in Figures 6(a) to (d), even if a label made from this heat-shrinkable film is placed over the body of a bottle and heat-shrunk, it can be attached to the bottle in a manner that conforms to the shape of the bottle, and furthermore, the occurrence of fine wrinkles can be suppressed. On the other hand, if the polyester-based heat-shrinkable film does not satisfy the configurations (a) to (d), uneven shrinkage of the heat-shrinkable film occurs from the top to the bottom of the bottle body, as shown in Figures 7(a) to (d), and wrinkles and bottle deformation are significantly observed. [Example]

[0055] The present invention will be described in detail below based on examples. However, the scope of the present invention is not limited by the descriptions in the examples without any particular reason. The polyester resins used in the examples are as follows:

[0056] (PET1) Dicarboxylic acid: 100 mol% terephthalic acid, diol: 69 mol% ethylene glycol, 6 mol% diethylene glycol, 25 mol% 1,4-cyclohexanedimethanol polyester resin

[0057] (PET2) Dicarboxylic acid: 100 mol% terephthalic acid, diol: polyester resin consisting of 58 mol% ethylene glycol, 5 mol% diethylene glycol, 27 mol% 1,4-cyclohexanedimethanol, and 10 mol% 1,4-butanediol

[0058] (PET3) Dicarboxylic acid: 100 mol% terephthalic acid, diol: 68 mol% ethylene glycol, 12 mol% diethylene glycol, 20 mol% 1,4-cyclohexanedimethanol polyester resin

[0059] (PET4) Dicarboxylic acid: 100 mol% terephthalic acid, diol: 74 mol% ethylene glycol, 5 mol% diethylene glycol, 21 mol% 1,4-cyclohexanedimethanol polyester resin

[0060] (PET5) A polyester resin consisting of dicarboxylic acid: 100 mol% terephthalic acid and diol: 70 mol% ethylene glycol, 2 mol% diethylene glycol, and 28 mol% 1,4-cyclohexanedimethanol.

[0061] (PET6) A polyester resin consisting of dicarboxylic acids: 79 mol% terephthalic acid and 21 mol% isophthalic acid, and diols: 85 mol% ethylene glycol, 2 mol% diethylene glycol, and 13 mol% neopentyl glycol.

[0062] (additives) A silica masterbatch (manufactured by Sumitomo Color Co., Ltd., product name "EPM-7E325") containing 5% by weight of silica relative to 100% by weight of matrix resin (PET resin) and having an average silica particle size of 2.7 μm.

[0063] [Example 1] 1. Preparation of polyester heat-shrinkable film In a stirring vessel, 100 parts by weight of amorphous polyester (PET1) and 1 part by weight of an additive (silica particles) as an antiblocking agent were placed, mixed uniformly, and stirred to prepare the raw materials. Next, after drying the raw material, it was extruded at an extrusion temperature of 260°C using an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D of 24 and an extrusion screw diameter of 50 mm to obtain a raw sheet having a thickness of 150 μm. Next, using a heat-shrinkable film manufacturing device, the raw sheet was longitudinally stretched to produce a 30 μm thick polyester heat-shrinkable film at a preheating temperature of 95°C, a stretching temperature of 85°C, a heat-setting temperature of 84°C, and a stretch ratio (MD direction: 100%, TD direction: 530%).

[0064] 2. Evaluation of polyester heat-shrinkable film (1) Evaluation 1: Heat shrinkage rate A1 The obtained polyester heat-shrinkable film was shrunk in hot water at 80°C for 10 seconds, and the heat shrinkage rate (A1) in the main shrinkage direction was measured and evaluated according to the following criteria. ⊚: The heat shrinkage rate (A1) is within the range of 30 to 50%. Good: The heat shrinkage rate (A1) is in the range of 21 to less than 30%, or more than 50 to 65%. Fair: The heat shrinkage rate (A1) is in the range of 16 to less than 21%, or more than 65 to 70%. ×: The heat shrinkage rate (A1) is less than 16% or more than 70%.

[0065] (2) Evaluation 2: Heat shrinkage rate A2 The obtained polyester heat-shrinkable film was shrunk in 80°C hot water for 10 seconds, and the heat shrinkage rate (A2) in the direction perpendicular to the main shrinkage direction was measured and evaluated according to the following criteria. ⊚: The heat shrinkage rate (A2) is within the range of −3 to 5%. Good: The heat shrinkage rate (A2) is −5 to less than −3%, or is in the range of more than 5 to 10%. Fair: The heat shrinkage rate (A2) is −10 to less than −5%, or is in the range of more than 10 to 12%. ×: The heat shrinkage rate (A2) is less than −10% or more than 12%.

[0066] (3) Evaluation 3: Neck-in rate The neck-in ratio of the obtained polyester heat-shrinkable film was measured under the condition that the main shrinkage direction was fixed, and the film was immersed in hot water at 70°C for 10 seconds, and evaluated according to the following criteria. That is, as shown in FIG. 8(a), a polyester heat-shrinkable film 10 was cut into a long piece having a size of 200 mm or more in the main shrinkage direction and 100 mm in the perpendicular direction to prepare a measurement sample. A mark was drawn in advance at the center of the measurement sample in the main shrinkage direction, in the perpendicular direction, and the length of the mark was designated as L0. Next, as shown in Fig. 8(b), both ends of the measurement sample were fixed to a fixing frame jig having an inner length of 140 mm and a width of 140 mm, with the main shrinkage direction and the inner length direction aligned, i.e., both ends of the measurement sample in the main shrinkage direction were fixed to the fixing frame jig. Meanwhile, the long measurement sample was arranged and fixed so that a predetermined space was left between both sides of the long measurement sample in the orthogonal direction and the fixing frame jig. Next, as shown in FIG. 8(c), the measurement sample attached to the fixing frame jig was immersed in warm water at 70°C for 10 seconds, and then in water at 30°C or lower for 10 seconds, and the maximum thermal shrinkage in the orthogonal direction was measured from the change in the length of the gauge line on the measurement sample. Finally, the obtained thermal shrinkage rate was divided by 2 according to the following formula (1), to obtain the neck-in rate. Neck-in rate (%) = (L0 - L) / 2L0 × 100 (1) L0: Length of the gauge line on the measurement sample before heat treatment L: Length of the gauge line on the measurement sample after heat treatment

[0067] ⊚: The neck-in ratio is within the range of 0 to 4%. Good: The neck-in ratio is within the range of more than 4 to 6%. △: The neck-in ratio is within the range of more than 6 to 8%. ×: The neck-in ratio is greater than 8%.

[0068] (4) Rating 4: Absolute value (A1 / A2) The absolute value (A1 / A2) of the obtained polyester heat-shrinkable film was calculated and evaluated according to the following criteria. ⊚: The absolute value (A1 / A2) is within the range of 10 to 100. Good: The absolute value (A1 / A2) is in the range of 5.5 to less than 10, or more than 100 to 100. Δ: The absolute value (A1 / A2) is 4.5 to less than 5.5, or is in the range of more than 110 to 120. ×: The absolute value (A1 / A2) is less than 4.5 or more than 120.

[0069] (5) Rating 5: Maximum shrinkage stress (C) The obtained polyester heat-shrinkable film was cut into a strip having a width of 25.4 mm in the MD direction and a length of 75 mm in the TD direction to prepare a test piece. Then, the shrinkage stress of the test piece was measured using a strength and elongation measuring device equipped with a heating furnace. More specifically, the heating furnace was preheated to 85°C, the air flow to the heating furnace was stopped, the door of the heating furnace was opened, the test specimen was attached to the chuck of the strength and elongation measuring device, and then the door of the heating furnace was quickly closed and the air flow was resumed. Next, the contractile stress was measured for 30 seconds or more, and the maximum value during the measurement was measured as the maximum contractile stress (C), and evaluated according to the following criteria. ⊚: The maximum shrinkage stress (C) is within the range of 4 to 8 MPa. Good: The maximum shrinkage stress (C) is in the range of 3 to less than 4 MPa, or more than 8 to 10 MPa. △: The maximum shrinkage stress (C) is from 2 to less than 3 MPa, or from more than 10 to 12 MPa. ×: The maximum shrinkage stress (C) is less than 2 MPa or more than 12 MPa.

[0070] (6) Evaluation 6: Wrinkle resistance A cylindrical PET bottle (volume: 500 ml) filled with commercially available drinking water was prepared. Next, a polyester heat-shrinkable film was slit to a width of 26 cm to obtain a long heat-shrinkable film, and 1 mm wide perforations were made along the longitudinal direction of the film, and 1,3-dioxolane was applied to the widthwise edges. Next, the widthwise ends were overlapped and glued together with an overlap of about 1 cm to form a cylindrical label with a diameter of about 8 cm. Further, this cylindrical label was cut into 16 cm pieces in the longitudinal direction to obtain a plurality of cylindrical labels. Next, the tubular label was placed over the body of the prepared cylindrical PET bottle, and then placed on a belt conveyor through a steam tunnel maintained at 85°C and moved at a speed of 6 m / min, causing the tubular label to thermally shrink so that it adhered tightly to the body of the cylindrical PET bottle from the top to the bottom. Finally, the tubular label after heat shrinkage was visually inspected to evaluate its wrinkle resistance based on whether wrinkles of a specified length (1 cm or more) or width (1 mm or more) had occurred, according to the following criteria. ⊚: No wrinkles were observed on any of the five cylindrical labels. ◯: No wrinkles were observed in three or more of the five cylindrical labels. △: No wrinkles were observed in one or more of the five cylindrical labels. ×: The occurrence of predetermined wrinkles was observed in all five of the cylindrical labels.

[0071] [Example 2] In Example 2, as shown in Table 1, PET1 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions for longitudinal stretching were changed to limit the values. That is, in Example 2, a polyester-based heat-shrinkable film having a thickness of 40 μm was produced from the raw sheet at a preheating temperature of 105°C, a stretching ratio (MD direction: 100%, MD direction: 500%), a stretching temperature of 88°C, and a heat setting temperature of 75°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0072] [Example 3] In Example 3, as shown in Table 1, PET2 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions for longitudinal stretching were changed to limit the values. That is, a 25 μm thick polyester heat-shrinkable film was produced from the raw sheet at a preheating temperature of 90°C, a stretch ratio (MD direction: 100%, TD direction: 515%), a stretching temperature of 90°C, and a heat setting temperature of 80°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0073] [Example 4] In Example 4, as shown in Table 1, PET3 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions for longitudinal stretching were changed to limit the values. That is, a 40 μm thick polyester heat-shrinkable film was produced from the raw sheet at a preheating temperature of 90°C, a stretch ratio (MD direction: 400%, TD direction: 100%), a stretching temperature of 82°C, and a heat setting temperature of 80°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0074] [Example 5] In Example 5, as shown in Table 1, PET4 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions for longitudinal stretching were changed to limit the values. That is, a 45 μm thick polyester heat-shrinkable film was produced from the raw sheet at a preheating temperature of 84°C, a stretch ratio (MD direction: 400%, TD direction: 100%), a stretching temperature of 84°C, and a heat setting temperature of 75°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0075] [Example 6] In Example 6, as shown in Table 1, PET4 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions for longitudinal stretching were changed to limit the values. That is, a 50 μm thick polyester heat-shrinkable film was produced from the raw sheet at a preheating temperature of 97°C, a stretch ratio (MD direction: 400%, TD direction: 100%), a stretching temperature of 93°C, and a heat setting temperature of 88°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0076] [Example 7] In Example 7, as shown in Table 1, PET1 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions for longitudinal stretching were changed to limit the values. That is, a 45 μm thick polyester heat-shrinkable film was produced from the raw sheet at a preheating temperature of 70°C, a stretch ratio (MD direction: 420%, TD direction: 100%), a stretching temperature of 85°C, and a heat setting temperature of 83°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0077] [Comparative Example 1] In Comparative Example 1, as shown in Table 1, PET5 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions for longitudinal stretching were changed to limit the values. That is, a 45 μm thick polyester heat-shrinkable film was produced from the raw sheet at a preheating temperature of 75°C, a stretch ratio (MD direction: 100%, TD direction: 500%), a stretching temperature of 75°C, and a heat setting temperature of 50°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0078] Comparative Example 2 In Comparative Example 2, as shown in Table 1, PET6 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions were modified to limit the values. That is, a polyester heat-shrinkable film having a thickness of 47 μm was produced from the raw sheet at a preheating temperature of 75°C, a stretching ratio (MD direction: 100%, TD direction: 500%), a stretching temperature of 75°C, and a heat setting temperature of 50°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0079] Comparative Example 3 In Comparative Example 3, as shown in Table 1, PET6 was used as the polyester resin, and the values ​​of the components (a) to (d) were changed and the manufacturing conditions were modified to limit the values. That is, a polyester heat-shrinkable film having a thickness of 42 μm was produced from the raw sheet at a preheating temperature of 90°C, a stretching ratio (MD direction: 100%, TD direction: 500%), a stretching temperature of 90°C, and a heat setting temperature of 60°C. The produced polyester heat-shrinkable film was then evaluated for wrinkle resistance and other properties in the same manner as in Example 1. The results are shown in Table 2.

[0080] [Table 1]

[0081] [Table 2] [Industrial Applicability]

[0082] The polyester-based heat-shrinkable film of the present invention has at least the following configurations (a) to (c), and therefore can stably heat-shrink and exhibit excellent wrinkle resistance even when applied to various PET bottles, etc. (a) The heat shrinkage percentage A1 in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is set to a value within the range of 21 to 65%. (b) The heat shrinkage percentage A2 in the direction perpendicular to the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is set to a value within the range of -4 to 4%. (c) The neck-in ratio measured in 70°C hot water for 10 seconds shall be 6% or less.

[0083] Furthermore, according to the method for producing a polyester-based heat-shrinkable film of the present invention, by producing a polyester-based heat-shrinkable film having at least the following configurations (a) to (c) in a predetermined process, it is possible to efficiently obtain a polyester-based heat-shrinkable film that stably heat-shrinks and exhibits excellent wrinkle resistance even when applied to various PET bottles, etc.

[0084] In other words, with the polyester-based heat-shrinkable film of the present invention, by controlling not only the heat shrinkage rate (A1 and A2) under specified conditions but also at least the neck-in rate under specified conditions, it is possible to achieve stable heat shrinkage and excellent wrinkle resistance even when applied to PET bottles with complex shapes. Therefore, it can be suitably applied to various PET bottles, outer covering materials for lunch boxes, etc., and its versatility can be significantly expanded, so it can be said that its industrial applicability is extremely high. [Explanation of symbols]

[0085] 10: Polyester heat shrinkable film 10a: Other resin layer 1 10b: Another resin layer 2 10c: Shrinkage rate adjustment layer

Claims

1. A polyester-based heat-shrinkable film derived from a polyester-based resin, characterized in that it has the following configurations (a) to (d): (a) When the thermal shrinkage rate in the main shrinkage direction when shrunk in hot water at 80°C for 10 seconds is defined as A1, A1 is set to a value within the range of 21 to 65%. (b) When the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction is A2 when the film is shrunk in hot water at 80°C for 10 seconds, A2 is set to a value within the range of -4 to 4%. (c) The absolute value (A1 / A2) of the ratio of the thermal shrinkage rates A1 and A2 is set to 15 or more. (d) The neck-in ratio measured in hot water at 70°C for 10 seconds is 6% or less.

2. 2. The polyester-based heat-shrinkable film according to claim 1, wherein C is a value within a range of 3 to 10 MPa, where C is the maximum shrinkage stress in the main shrinkage direction at a shrinkage temperature of 85°C.

3. 2. The polyester heat-shrinkable film according to claim 1, wherein the thickness of the polyester heat-shrinkable film is set to a value within a range of 10 to 100 μm.

4. 2. The polyester heat-shrinkable film according to claim 1, wherein the main shrinkage direction of the polyester heat-shrinkable film is the machine direction.

5. The polyester-based heat-shrinkable film according to claim 1, characterized in that the polyester-based resin is a polyester-based resin derived from a dicarboxylic acid compound and a diol compound as reaction components, and the diol compound contains at least ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol.

6. A method for producing a polyester resin derived from a dicarboxylic acid compound and a diol compound as reaction components, the method comprising the following steps 1 and 2: Step 1: A step of preparing the dicarboxylic acid compound and the diol compound as the reaction components and reacting them to produce a polyester resin. Step 2: A step of producing a polyester-based heat-shrinkable film having the following configurations (a) to (d) by stretching the polyester-based resin in a predetermined direction. (a) When the thermal shrinkage rate in the main shrinkage direction when shrunk in hot water at 80°C for 10 seconds is defined as A1, A1 is set to a value within the range of 21 to 65%. (b) When the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction is A2 when the film is shrunk in hot water at 80°C for 10 seconds, A2 is set to a value within the range of -4 to 4%. (c) The absolute value (A1 / A2) of the ratio of the thermal shrinkage rates A1 and A2 is set to 15 or more. (d) The neck-in ratio measured in hot water at 70°C for 10 seconds is 6% or less.

7. 7. The method for producing a polyester heat-shrinkable film according to claim 6, wherein in step 2, the polyester heat-shrinkable film is stretched along the MD direction, which is the predetermined direction.

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