Polyester-based heat-shrinkable film and method for producing polyester-based resin film

Abstract

Provided is a polyester-based heat-shrinkable film or the like that, even when used in various types of PET bottles and the like, thermally shrinks stably and exhibits excellent wrinkle resistance characteristics.　This polyester-based heat-shrinkable film or the like has the following features (a)-(d). (a) The heat shrinkage rate A1 in the main shrinkage direction when being shrunk in hot water at 80°C at a condition of 10 seconds is set to a value within the range of 21-65%. (b) The heat shrinkage rate A2 in a direction orthogonal to the main shrinkage direction when being shrunk in hot water at 80°C at a condition of 10 seconds is set to a value within the range of -5% to 10%. (c) The absolute value (A1 / A2) of the ratio of the heat shrinkage rates A1 and A2 is 5.5 or more. (d) The neck-in rate measured in hot water at 70°C at a condition of 10 seconds is set to 6% or less.

Description

Polyester-based heat-shrinkable film and method for manufacturing polyester-based resin film

[0001] The present invention relates to a polyester heat-shrinkable film (hereinafter sometimes simply referred to as 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 even when applied to PET bottles of various shapes by controlling the neck-in ratio and other properties, and a method for producing the same.

[0002] Heat-shrinkable films have traditionally been widely used as base films for labels on PET bottles and the like. 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, and other properties. Although polyester-based heat-shrinkable films have these excellent properties, they have a tendency to shrink unevenly and wrinkle when heated due to their rapid thermal response. That is, the heat-shrinkable film is affected by storage conditions, particularly humidity, and the like, resulting in variations in the heat-shrinkage rate at a given temperature. Consequently, there has been a problem in that wrinkles are likely to occur when the shrink label is heat-shrunk.

[0003] Therefore, a heat-shrinkable polyester film has been proposed that is a polyester shrink film with excellent hot water resistance, shrinkage characteristics, and strength, and that can be applied to thin-necked cylindrical heat-resistant PET bottles, etc. (see, for example, Patent Document 1). More specifically, a heat-shrinkable polyester film that satisfies the following requirements (1) to (3) and also satisfies requirement (4): (1) The heat shrinkage rate in the main shrinkage direction of the film after 5 minutes in an air oven at 100°C 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 a value 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 ratio after immersion in 75°C warm water for 5 seconds is 10% or less.

[0004] Furthermore, a heat-shrinkable polyester film that suppresses wrinkles when used for packaging applications such as ribbon labels for lunch boxes and noodle containers has been proposed (see, for example, Patent Document 2). More specifically, this heat-shrinkable polyester film has a longitudinal (longitudinal) direction as its primary shrinkage direction, and satisfies the following requirements (1) to (6): (1) The heat 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 heat 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 rate of change in the width direction of the film, determined by fixing the film in the longitudinal direction only while maintaining a constant length and holding it in 90°C hot air for 10 seconds, is a value within the range of 5 to 22%. (4) The film width direction change rate, measured by fixing only the longitudinal direction with 10% slack in the longitudinal direction and holding it under hot air at 90°C for 10 seconds, 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 under 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 exhibits excellent durability and coating retention after coating when used in battery cell packaging, etc. (see, for example, Patent Document 3). More specifically, a single-layer or multilayer heat-shrinkable film having a resin layer containing a polyester resin as a primary 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) The heat shrinkage percentage in the main shrinkage direction when immersed in 99°C warm water for 10 seconds is a value within the range of 40 to 65%. (c) The heat shrinkage percentage in the direction perpendicular to the main shrinkage direction when immersed in 99°C warm water for 10 seconds is a value within the range of 4 to 15%. (d) When immersed in 99°C hot 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 ratio after immersion in 70°C hot water for 10 seconds is 5% or less.

[0006] Japanese Patent Publication No. 07-77757 (Claims, etc.) WO2020-246420 (Claims, etc.) Japanese Patent Publication No. 6791335 (Claims, etc.)

[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 requires strict control of the manufacturing conditions but also tends to result in low manufacturing yields. Furthermore, although requirement (4) stipulates that the neck-in ratio after immersion in 75°C hot water for 5 seconds should be 10% or less, this requirement was only intended for application to standard narrow-necked heat-resistant PET bottles, etc. Therefore, when the film is applied to PET bottles, etc., whose horizontal cross-sectional shape of the body is not circular but has a complex shape, the heat shrinkability tends to be non-uniform and fine wrinkles tend to occur.

[0008] Furthermore, in the case of the heat-shrinkable polyester film disclosed in Patent Document 2, an unstretched sheet having a specific polyester composition must be uniaxially stretched in the longitudinal direction and then relaxed in the longitudinal direction during production, which not only requires strict control of production conditions but also tends to result in low production yields. Furthermore, all of requirements (1) to (6) must be satisfied. In particular, requirement (3) requires that the film be held in a fixed length state, fixed only in the longitudinal direction, and held in a 90°C hot air atmosphere for 10 seconds, and the film width direction change rate calculated according to a predetermined formula must be limited to a predetermined value (5 to 22%). Furthermore, requirement (4) requires that the film be held in a 10% slack state, fixed only in the longitudinal direction, and held in a 90°C hot air atmosphere for 10 seconds, and the film width direction change rate calculated according to a predetermined formula must be limited to a predetermined value (5 to 20%), making stable control difficult. Specifically, when measuring and controlling requirements (3) and (4), it is necessary to fix a predetermined film in the longitudinal direction, and to employ conditions such as heating for 10 seconds in hot air at 90°C, or to reproduce a predetermined relaxed state, which poses a problem that the obtained values ​​of the rate of change are prone to large variations. Furthermore, when the film is applied to PET bottles and the like having complex shapes, which are primarily used for band labels for lunch boxes and noodle containers, the heat shrinkability tends to be non-uniform, and fine wrinkles tend 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 are there an extremely large number of control items for the manufacturing conditions, including the selection of raw materials, but stable control is not easy, and there are problems that the manufacturing yield is likely to be low. Furthermore, although the requirement (e) is that a neck-in ratio of 5% or less after immersion in 70°C hot water for 10 seconds is preferable, this film is mainly intended for use in packaging for vehicle battery cells, and when used in PET bottles and the like having complex shapes, there are problems that the heat shrinkability is likely to be non-uniform and fine wrinkles are likely to occur.

[0010] Therefore, in view of the above problems, the inventors of the present invention have made extensive efforts and have solved the conventional problems by limiting the heat shrinkage rates of a heat shrinkable film in the main shrinkage direction and the direction perpendicular thereto, measured under specified conditions, and the absolute value of the ratio between these, and by limiting the neck-in rate measured under specified conditions. That is, an object of the present invention is to provide a polyester heat shrinkable film which not only requires few control items and is easy to produce stably, but also heat shrinks stably and exhibits excellent wrinkle resistance even when applied to PET bottles and the like having complex shapes, and a method for stably producing such a polyester resin film.

[0011] According to the present invention, there is provided a polyester-based heat-shrinkable film derived from a polyester-based resin, characterized by having the following configurations (a) to (d), which can solve the above-mentioned problems. (a) When the heat shrinkage percentage A1 in the main shrinkage direction is measured in hot water at 80°C for 10 seconds, A1 is set to a value within the range of 21 to 65%. (b) When the heat shrinkage percentage A2 in the direction perpendicular to the main shrinkage direction is measured in hot water at 80°C for 10 seconds, A2 is set to a value within the range of -5 to 10%. (c) The absolute value (A1 / A2) of the ratio of the heat shrinkage percentages A1 and A2 is set to a value of 5.5 or more. (d) The neck-in ratio measured in hot water at 70°C for 10 seconds is set to a value of 6% or less. That is, by limiting the heat shrinkage rate (a) in the main shrinkage direction under predetermined 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 predetermined conditions, and the absolute value (c) of their ratio, and also by limiting the neck-in rate (d) measured under predetermined 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 be a value within the range of 3 to 10 MPa. By limiting the maximum shrinkage stress (C) at a predetermined temperature to a predetermined range in this way, it becomes easier to control the neck-in ratio and the like, 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 this range, it becomes easier to control the heat shrinkage rate and neck-in rate under predetermined conditions, and furthermore, it becomes possible to stably exhibit even better wrinkle resistance.

[0014] Furthermore, according to the polyester-based heat-shrinkable film of the present invention, it is preferable that the main shrinkage direction of the polyester-based heat-shrinkable film is the MD direction. By restricting the main shrinkage direction to the MD direction in this way, it becomes easy to adjust the production conditions, particularly for the longitudinally shrinkable film, and it also becomes easy to control the heat shrinkage rates (A1 and A2), neck-in ratio, absolute value (A1 / A2), shrinkage stress, etc. under predetermined conditions, and ultimately it is possible to exhibit even more excellent wrinkle resistance.

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

[0016] Another aspect of the present invention is a method for producing a polyester-based 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: Preparing a dicarboxylic acid compound and a diol compound as reaction components and reacting them to produce a polyester-based resin. Step 2: Stretching the polyester-based resin in the TD direction, the MD direction, or either one of them to produce a polyester-based heat-shrinkable film having the following configurations (a) to (d): (a) When the heat shrinkage percentage A1 is determined in the main shrinkage direction when the film is shrunk in 80°C hot water for 10 seconds, A1 is set to a value within the range of 21 to 65%. (b) When the heat shrinkage percentage A2 is determined in the direction perpendicular to the main shrinkage direction when the film is shrunk in 80°C hot water for 10 seconds, A2 is set to a value within the range of -5 to 10%. (c) the absolute value of the ratio of the heat shrinkage rates A1 and A2 (A1 / A2) is 5.5 or more. (d) the neck-in ratio measured in hot water at 70°C for 10 seconds is 6% or less. That is, by producing a polyester-based heat-shrinkable film in this manner, it is possible to efficiently produce a polyester-based heat-shrinkable film whose main shrinkage direction is the so-called transverse direction (TD direction) or longitudinal direction (MD direction) and which exhibits excellent wrinkle resistance even when 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 to carry out the stretching treatment along the MD direction in step 1. By stretching in the MD direction in this way, it becomes easier to adjust the production conditions, particularly for the longitudinally shrinkable film, 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 predetermined conditions, and ultimately it becomes possible to exhibit even more excellent wrinkle resistance.

[0018] Figures 1(a) to 1(c) are diagrams illustrating the configuration of polyester-based heat-shrinkable films. Figure 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). Figure 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 is a diagram illustrating the relationship between the absolute value (A1 / A2) of the ratio of the heat shrinkage rate (A2) in the direction perpendicular to the main shrinkage direction of a polyester-based heat-shrinkable film to the heat shrinkage rate (A1) in the main shrinkage direction, and the evaluation of shrinkage unevenness (relative value). Fig. 4 is a diagram illustrating the relationship between the neck-in ratio (%) and the evaluation (relative value) of shrinkage unevenness for a polyester-based heat-shrinkable film under predetermined heating conditions (70°C hot water, 10 seconds). Fig. 5 is a diagram illustrating the relationship between the shrinkage stress (MPa) in the main shrinkage direction and the evaluation (relative value) of shrinkage unevenness for a polyester-based heat-shrinkable film under predetermined heating conditions (85°C hot water, 10 seconds). Fig. 6(a) is a diagram (photograph) showing the appearance of a cylindrical label corresponding to Example 1 when no shrinkage unevenness occurs, and Figs. 6(b) to 6(d) are enlarged views of the appearance regions P, Q, and R shown in Fig. 6(a). Fig. 7(a) is a diagram (photograph) showing the appearance of a cylindrical label corresponding to Comparative Example 1 when shrinkage unevenness occurs, and Figs. 7(b) to 7(d) are enlarged views of the appearance regions S, T, and U shown in Fig. 7(a). 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.

[0019] [First Embodiment] The first embodiment is a polyester-based heat-shrinkable film derived from a polyester-based resin, as illustrated in Figures 1(a) to 1(c), characterized by the following configurations (a) to (d): (a) When the heat shrinkage percentage A1 in the main shrinkage direction is measured in 80°C hot water for 10 seconds, the heat shrinkage percentage A1 is set to a value within the range of 21 to 65%. (b) When the heat shrinkage percentage A2 in the direction perpendicular to the main shrinkage direction (hereinafter sometimes simply referred to as the perpendicular direction) is measured in 80°C hot water for 10 seconds, the heat shrinkage percentage A2 is set to a value within the range of -5 to 10%. (c) The absolute value (A1 / A2) of the ratio of the heat shrinkage percentages A1 and A2 is set to a value of 5.5 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds is set to a value of 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 serving as the main component can be of any type as long as it satisfies the above-described requirements (a) to (d). However, typically, polyester resins composed of diols and dicarboxylic acids, polyester resins composed of diols and hydroxycarboxylic acids, polyester resins composed of diols, dicarboxylic acids, and hydroxycarboxylic acids, or mixtures of these polyester resins are preferred. Examples of diols used as raw material components for 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 aliphatic 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, examples of hydroxycarboxylic acids as a compound component of polyester resins include at least one of lactic acid, hydroxybutyric acid, and polycaprolactone.

[0021] Furthermore, a suitable amorphous polyester resin is, for example, a dicarboxylic acid containing at least 80 mol% terephthalic acid and a diol consisting of 50 to 80 mol% 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 mixtures. On the other hand, examples of crystalline polyester resins include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, and polypropylene terephthalate. It is also preferable to use these alone or in mixtures.

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

[0023] 2. Structure (a) Structure (a) is a necessary constituent requirement that, for a polyester-based heat-shrinkable film, when the heat shrinkage percentage A1 (%) in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds is defined as a value within the range of 21 to 65%. The reason for this is that if the heat shrinkage percentage A1 exceeds this range, the heat shrinkage percentage under general heat shrinkage conditions (80°C, 10 seconds) will be insufficient, and the film will be unable to conform to the shape of the periphery of a PET bottle, making it difficult to suppress the occurrence of wrinkles. More specifically, if the heat shrinkage percentage A1 of such a film is less than 21%, it will be difficult to limit the numerical value expressed by the absolute value (A1 / A2) described below within a predetermined range, which will result in a poor balance between the heat shrinkage percentages in the main shrinkage direction and the direction perpendicular thereto, making it difficult to suppress the occurrence of wrinkles. However, if the heat shrinkage ratio A1 of such a film becomes excessively large, it becomes difficult to limit the numerical value expressed by the absolute value (A1 / A2) within the specified range, and the balance between the heat shrinkage ratios in the main shrinkage direction and the direction perpendicular thereto becomes poor, which may result in failure to suppress the occurrence of wrinkles. Therefore, it is more preferable to set the heat shrinkage ratio A1 of such a film to a value within the range of 25 to 50%, and even more preferably to set it to a value within the range of 30 to 45%. When measuring the heat shrinkage ratio A1 described above, it is more preferable to measure the heat shrinkage ratio A1 in the main shrinkage direction under specified 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 the specified conditions and stabilized when measuring the heat shrinkage ratio A1.

[0024] Here, referring to Fig. 2(a), the relationship between the heat shrinkage percentage A1 (%) measured under predetermined conditions and the wrinkle resistance property (relative value) will be explained. That is, in Fig. 2(a), the horizontal axis represents the heat shrinkage percentage 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 represents the evaluation of the wrinkle resistance property (relative value). The evaluation of the wrinkle resistance property (relative value) on the vertical axis is quantified, with ◎ being 5 points, ○ being 3 points, △ being 1 point, and × being 0 points. 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 property in 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 production 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] The characteristic curve in FIG. 2( a) shows 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, the characteristic curve in FIG. 2( a) shows that, for example, limiting the heat shrinkage rate A1 to 55% or less results in a favorable wrinkle resistance evaluation of at least 4. Similarly, limiting the heat shrinkage rate A1 to 50% or less results in an even better result of 5. However, it has been found that excessively low heat shrinkage rates A1 significantly reduce adhesion to adherends such as PET bottles. Therefore, with regard to configuration (a), by setting the heat shrinkage rate A1 (%) in the main shrinkage direction when shrunk in 80°C hot water for 10 seconds to a value within the range of 21 to 55%, it can be said that excellent adhesion to adherends such as PET bottles can be obtained while maintaining excellent adhesion.

[0026] 3. Structure (b) Structure (b) is a necessary constituent requirement that, in a polyester heat-shrinkable film, when heat-shrinking is performed in hot water at 80°C for 10 seconds, the heat-shrinkage percentage A2 in the direction perpendicular to the main shrinkage direction is within the range of -5 to 10%. The reason for this is that if the heat-shrinkage percentage A2 exceeds the predetermined range, the heat-shrinkage percentage under general heat-shrinkage conditions (80°C, 10 seconds) may be insufficient or, conversely, may be excessively heat-shrunk, making it impossible to conform to the shape of the PET bottle and preventing wrinkles from occurring.

[0027] If the heat shrinkage ratio A2 of the film is less than -5%, it becomes difficult to limit the numerical value expressed by the absolute value (A1 / A2) described below within a predetermined range, which in turn reduces the balance between the heat shrinkage ratios 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 heat shrinkage ratio A2 of the film is excessively large and exceeds 10%, it becomes similarly difficult to limit the numerical value expressed by the absolute value (A1 / A2) within a predetermined range, which in turn reduces the balance between the heat shrinkage ratios in the main shrinkage direction and the direction perpendicular thereto, making it difficult to suppress the occurrence of wrinkles. Therefore, it is more preferable to set the heat shrinkage ratio A2 of the film in the direction perpendicular thereto within a range of -4 to 8%, and even more preferable to set it within a range of -3 to 5%.

[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 the film 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 percentage A2 (%) measured under predetermined conditions and the wrinkle resistance property (relative value in the evaluation) will be explained. That is, in Fig. 2(b), the horizontal axis represents the heat shrinkage percentage 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 represents the evaluation (relative value) of the wrinkle resistance property. The evaluation (relative value) of the wrinkle resistance property 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 evaluation results showing the relationship between the heat shrinkage rate in a direction perpendicular to the main shrinkage direction and wrinkle resistance for polyester heat-shrinkable films of Examples 1, 3 to 7 (however, Example 2 is omitted in FIG. 2(b) 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)), which will be described later. 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 a range of -5 to 10%, good results of at least 3 or more were obtained in the evaluation of wrinkle resistance. Similarly, by limiting the heat shrinkage rate A2 to a range of -5 to 5%, good results of 5 or more were obtained in all cases. In any case, with regard to the configuration (b), when the film is heat-shrunk in hot water at 80°C 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. Structure (c) Structure (c) is a necessary constituent requirement that the absolute value (A2 / A1) of the ratio of the heat shrinkage percentage A1 in the main shrinkage direction to the heat shrinkage percentage A2 in the direction perpendicular thereto, measured under specified conditions, be 5.5 or greater. This is because controlling the absolute value (A2 / A1) in this manner, in conjunction with other structures (a), (b), and (d), results in a favorable evaluation of wrinkle resistance. Conversely, by setting the absolute value (A2 / A1) to 5.5 or greater, the change in the heat shrinkage percentage at a specified temperature is minimal, heat shrinkage can be achieved stably and reproducibly under specified conditions, and excellent wrinkle resistance can be achieved. However, if the absolute value (A2 / A1) is excessively large, the balance between the heat shrinkage percentage A1 in the main shrinkage direction and the heat shrinkage percentage A2 in the perpendicular direction may be impaired, resulting in a deterioration in wrinkle resistance. Therefore, in the configuration (c), it is more preferable that the absolute value (A2 / A1) is set to a value within the range of 10 to 150, and even more preferable that it is set to a value within the range of 15 to 100.

[0031] Here, referring to Figure 3, the relationship between shrinkage unevenness and the absolute value (A1 / A2) of the ratio of the heat shrinkage rate (A2) in the direction perpendicular to the main shrinkage direction to the heat shrinkage rate (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) will be explained. That is, the horizontal axis shows the absolute value (A1 / A2) of the heat shrinkage rate ratio, and the vertical axis shows the evaluation value (relative value) of shrinkage unevenness. From the characteristic curve in Figure 3, it can be seen that there is an excellent correlation between the absolute value (A1 / A2) of the heat shrinkage rate ratio and shrinkage unevenness. Therefore, it can be said that shrinkage unevenness can be accurately controlled by limiting the absolute value (A1 / A2) of the heat shrinkage rate ratio to a value within a predetermined range.

[0032] 5. Structure (d) Structure (d) is a necessary constituent requirement for a polyester-based heat-shrinkable film to have a neck-in ratio of 6% or less. That is, by taking into account the neck-in phenomenon that typically occurs during film production and limiting the neck-in ratio, which simulates this phenomenon, to a predetermined range, excellent wrinkle resistance can be achieved even when applied to various PET bottles, etc. However, if the neck-in ratio is excessively small, it may limit the manufacturing yield and the types of raw materials that can be used, which may be economically disadvantageous. Therefore, it is more preferable to set the neck-in ratio to a value within the range of 0 to 5%, and even more preferable to set it 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., described below.

[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 the evaluation) will be explained. That is, in FIG. 4 , the horizontal axis represents the neck-in ratio (%) measured under heat shrinkage conditions of immersion in hot water at 70°C for 10 seconds, and the vertical axis represents the evaluation (relative value) of the wrinkle resistance property. The evaluation (relative value) of the wrinkle resistance property 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. 4 is based on the evaluation results of the wrinkle resistance property of polyester heat shrinkable films of Examples 1 and 3 to 7 (however, in FIG. 4 , 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 CE3) described below. 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 property (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 is obtained in the evaluation of the wrinkle resistance property. Similarly, by limiting the neck-in ratio to a range of 5% or less, an even better result of a relative value of 5 is obtained in the evaluation of the wrinkle resistance property. In any case, with regard to the configuration (d), it can be said that good wrinkle resistance property can be obtained by setting the neck-in ratio to a value of 6% or less when heat-shrunk under predetermined conditions.

[0034] 6. Optional Feature (1) Feature (e) Feature (e) is a feature related to the thickness (average thickness) of the polyester-based heat-shrinkable film of the first embodiment before heat shrinkage, and is an optional feature that typically sets the thickness within a range of 10 to 100 μm. Specifically, by specifically limiting the thickness of the film before heat shrinkage to a value within a predetermined range, it becomes easier to control the heat shrinkage rate (A1 and A2), neck-in ratio, absolute value (A1 / A2), shrinkage stress, and other factors under predetermined conditions. This reduces the influence of certain factors, thereby suppressing uneven shrinkage due to a sudden thermal response in the polyester-based heat-shrinkable film during heat shrinkage, and as a result, the occurrence of fine wrinkles. More specifically, if the thickness of the film before heat shrinkage is less than 10 μm or more than 100 μm, it may be impossible to suppress uneven shrinkage due to a sudden thermal response in the polyester-based heat-shrinkable film during heat shrinkage, making it impossible to suppress the occurrence of fine wrinkles. Therefore, as the configuration (e), it is more preferable that the thickness of the film before heat shrinkage is set to a value within the range of 30 to 80 μm, and even more preferably to a value within the range of 40 to 60 μm.

[0035] (2) Structure (f) Structure (f) is an optional structural requirement of the polyester-based heat-shrinkable film of the first embodiment, where C is the maximum shrinkage stress in the TD direction at a shrinkage temperature of 85°C, and C is 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 caused by excessive or insufficient maximum shrinkage stress during heat shrinkage can be effectively suppressed. The characteristic curve in FIG. 5 is based on the evaluation results of the wrinkle resistance of the polyester-based heat-shrinkable films of Examples 1 and 3 to 7 (however, in FIG. 5 , Example 2 is omitted from the perspective of production 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, and wrinkles may occur due to this deformation, resulting in a deterioration of wrinkle resistance. On the other hand, as shown in Figure 5, if the value of the maximum shrinkage stress C is excessively small, for example, less than 4 MPa, the maximum shrinkage stress during thermal shrinkage will be insufficient, causing a gap to form between the PET bottle and the film, which may in turn result in a deterioration of wrinkle resistance. Therefore, as for configuration (f), it is more preferable to set the maximum shrinkage stress C to a value within the range of 4.1 to 8 MPa, and even more preferably within the range of 5 to 7 MPa.

[0036] (3) Others 1 It is preferable to blend various additives into the polyester-based 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 blended preferably 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] 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-based heat-shrinkable film 10. In this case, when the thickness of the polyester-based heat-shrinkable film is taken as 100%, it is usually preferable that the single layer thickness or total thickness of the other resin layers to be laminated is a value within a 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 Fig. 1(c). Such a shrinkage rate adjusting layer can be laminated by an adhesive, a coating method, heat treatment, or the like, 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 predetermined temperature is excessively large, it is preferable to laminate a shrinkage rate adjusting layer of a type that suppresses this. Also, if the shrinkage rate of the 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 increases it. Thus, the shrinkage rate adjusting layer is used to obtain a desired shrinkage rate for the polyester heat-shrinkable film, without having to prepare various heat-shrinkable films with different shrinkage rates.

[0041] (4) Other 2 Next, referring to Figures 6 and 7, we will specifically explain the wrinkle resistance properties when a polyester heat-shrinkable film serving as a tubular label is attached to a PET bottle. That is, Figure 6 corresponds to Example 1, and is a photograph of the appearance of the tubular label when no wrinkles occur, and Figure 6(a) shows the entire body of the PET bottle covered with the tubular label. Figures 6(b) to 6(d) are enlarged views of the upper (region P), middle (region Q), and lower (region R) of the body shown in Figure 6(a), respectively, and it can be seen that no wrinkles occur in any of the upper to lower regions. Meanwhile, Figure 7 corresponds to Comparative Example 1, and is a photograph of the appearance of the tubular label when wrinkles occur, and Figure 7(a) shows the entire body of the PET bottle covered with the tubular label. 7(b) to 7(d) are enlarged views of the upper (region S), middle (region T), and lower (region U) parts of the body shown in Fig. 7(a), and it can be seen that wrinkles have occurred in all parts from the upper to the lower parts. Furthermore, Fig. 7(c) shows that the PET bottle itself has also deformed in the middle part (region T) of the body of the PET bottle.

[0042] [Second Embodiment] The second embodiment is a method for producing a polyester-based heat-shrinkable film derived from the dicarboxylic acid compound and diol compound of the first embodiment, characterized by 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-based resin. Step 2: A step of stretching the polyester-based resin along a predetermined direction to produce a polyester-based heat-shrinkable film having the following configurations (a) to (d). (a) When the heat shrinkage percentage A1 is determined in the main shrinkage direction when the film is shrunk in 80°C hot water for 10 seconds, the value of A1 is set to a value within the range of 21 to 65%. (b) When the heat shrinkage percentage A2 is determined in the direction perpendicular to the main shrinkage direction when the film is shrunk in 80°C hot water for 10 seconds, the value of A2 is set to a value within the range of -5 to 10%. (c) The absolute value (A1 / A2) of the ratio of the heat shrinkage percentages A1 and A2 is set to a value of 5.5 or more. (d) The neck-in ratio measured in hot water at 70°C for 10 seconds is 6% or less. The method for producing a polyester-based heat-shrinkable film of the second embodiment will now be described in detail with reference to the drawings as appropriate.

[0043] 1. Preparation and Mixing of Raw Materials First, it is preferable to prepare the raw materials, such as base materials and additives, such as crystalline polyester resin, amorphous polyester resin, rubber-based resin, antistatic agent, hydrolysis inhibitor, etc. Next, it is preferable to charge the prepared crystalline polyester resin, amorphous polyester resin, etc. into a stirring vessel while weighing them, and mix and stir them using a stirring device until they become uniform.

[0044] 2. Raw Sheet Production Process Next, the uniformly mixed raw materials are preferably dried to an absolutely dry state. Next, typically, extrusion molding is performed to produce a raw sheet of 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-Based Heat-Shrinkable Films Next, the obtained raw sheet is heated and pressed while moving on or between rolls using a heat-shrinkable film manufacturing device to produce a polyester-based 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 essentially expanding the film width, thereby crystallizing the polyester molecules constituting the polyester-based heat-shrinkable film into a predetermined shape. Then, by solidifying it in this state, a heat-shrinkable polyester-based heat-shrinkable film for use as decoration, labels, etc. can be produced. Note that when producing the heat-shrinkable film, the film can be stretched not only transversely (stretched in the TD direction) but also longitudinally (stretched 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 as a result, the occurrence of fine wrinkles can be suppressed.

[0046] (1) MD Stretching Ratio

[0044] Furthermore, in the case of so-called transverse stretching, it is usually preferable to set the MD stretching ratio 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 stretching ratio to a value within a predetermined range, 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, absolute value (A1 / A2), neck-in ratio, and heat shrinkage stress (C), which can significantly reduce production yield. On the other hand, if the MD stretching ratio exceeds 200%, it can affect the shrinkage ratio in the TD direction, making it difficult to adjust the shrinkage ratio itself. Therefore, the MD stretching ratio is more preferably in the range of 110 to 180%, and even more preferably in the range of 120 to 160%. In the case of so-called longitudinal stretching, the MD stretching ratio is preferably in the range of 300 to 600%, and more preferably in the range of 400 to 500%.

[0047] (2) Stretching Ratio in TD Direction In a preferred embodiment, the stretching ratio in the TD direction of the polyester heat-shrinkable film before heat shrinking (sometimes referred to as the average TD stretching ratio or the TD stretching 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 stretching ratio described above but also the TD stretching ratio to values ​​within a predetermined range, and by specifically limiting the heat shrinkage ratios A1, A2, B1, absolute value (A1 / A2), neck-in ratio, heat shrinkage stress (C), etc. to values ​​within their respective predetermined ranges, the occurrence of fine wrinkles can be further suppressed.

[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 stretching ratio exceeds 600%, the heat shrinkage rate will be significantly increased, which may excessively limit the applications of the usable polyester heat-shrinkable film, or it may become difficult to control the stretching ratio itself to a constant value. Therefore, it is more preferable to set the TD stretching ratio to a value within the range of 350 to 550%, and even more preferable to set it to a value within the range of 400 to 500%. In addition, when so-called longitudinal stretching is performed, it is preferable to set the TD stretching ratio to a value within the range of 100 to 200%, and more preferably to set it to a value within the range of 110 to 180%.

[0049] 4. Inspection process for polyester heat-shrinkable film 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 properties in the predetermined inspection process and confirming that they fall within the predetermined range, it is possible to obtain a polyester heat-shrinkable film with more uniform shrinkage properties. 1) Visual inspection of the appearance of the polyester heat-shrinkable film 2) Measurement of thickness variation 3) Measurement of tensile modulus 4) Measurement of tear strength 5) Measurement of viscoelastic properties using an SS curve

[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 heat shrinkage percentage in the main shrinkage direction is A1, which is measured when the film is shrunk for 10 seconds in 80°C hot water, A1 is set to a value within the range of 21 to 65%. (b) When the heat shrinkage percentage in the direction perpendicular to the main shrinkage direction is A2, which is measured when the film is shrunk for 10 seconds in 80°C hot water, A2 is set to a value within the range of -5 to 10%. (c) The absolute value (A1 / A2) of the ratio of the heat shrinkage percentages A1 and A2 is set to 5.5 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds is set to 6% or less.

[0051] [Third Embodiment] The third embodiment relates to a method for using a polyester-based heat-shrinkable film. Therefore, any known method for using a heat-shrinkable film can be suitably applied. For example, when carrying out the method for using a polyester-based heat-shrinkable film, the polyester-based heat-shrinkable film is first 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. The long cylindrical object is then fitted onto a PET bottle or the like filled with a content.

[0052] Next, the polyester heat-shrinkable film fitted around the PET bottle or the like is heated by passing it through a hot air tunnel or steam tunnel at a predetermined temperature. The polyester heat-shrinkable film is uniformly heated and heat-shrunk by radiant heat such as infrared rays or heated steam at about 90°C blown onto it from the surroundings, as provided in these tunnels. Thus, the polyester heat-shrinkable film can be adhered to the outer surface of the PET bottle or the like, and a labeled container can be quickly obtained.

[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. This prevents changes in physical properties due to moisture absorption, even when the film is left for a relatively short period of time under high-humidity conditions, and allows a predetermined heat shrinkage rate to be obtained with good reproducibility at each heat treatment temperature. Therefore, even if the values ​​of the heat shrinkage rate and the like vary somewhat, the factors that influence the predetermined conditions can be reduced, and non-uniform shrinkage due to a sudden thermal response can be suppressed in the polyester heat-shrinkable film during heat shrinkage, thereby suppressing the occurrence of fine wrinkles.

[0054] Therefore, as shown in Figures 6(a) to (d), when 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 while conforming to the shape of the bottle periphery, and the occurrence of fine wrinkles can also be suppressed. On the other hand, if a polyester-based heat-shrinkable film does not satisfy the features (a) to (d), uneven shrinkage of the heat-shrinkable film will occur from the top to the bottom of the bottle body, as shown in Figures 7(a) to (d), and the occurrence of wrinkles and deformation of the bottle will be clearly observed.

[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: polyester resin consisting of 69 mol% ethylene glycol, 6 mol% diethylene glycol, and 25 mol% 1,4-cyclohexanedimethanol

[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: polyester resin consisting of 68 mol% ethylene glycol, 12 mol% diethylene glycol, and 20 mol% 1,4-cyclohexanedimethanol

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

[0060] (PET5) Dicarboxylic acid: 100 mol% terephthalic acid, diol: 70 mol% ethylene glycol, 2 mol% diethylene glycol, 28 mol% 1,4-cyclohexanedimethanol polyester resin

[0061] (PET6) A polyester resin composed 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] (Additive) A silica masterbatch (manufactured by Sumika 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-based heat-shrinkable film 100 parts by weight of amorphous polyester (PET1) and 1 part by weight of an additive (silica particles) as an antiblocking agent were placed in a stirring vessel, uniformly mixed and stirred, and used as raw materials. Next, after this raw material was dried, it was extruded 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 the conditions of an extrusion temperature of 260 ° C. to obtain a raw sheet with a thickness of 150 μm. Next, using a heat-shrinkable film manufacturing device, the raw sheet was longitudinally stretched 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%) to produce a polyester-based heat-shrinkable film with a thickness of 30 μm.

[0064] 2. Evaluation of Polyester-Based Heat-Shrinkable Films (1) Evaluation 1: Heat Shrinkage A1 The obtained polyester-based heat-shrinkable films were shrunk in 80°C hot water for 10 seconds, and the heat shrinkage (A1) in the main shrinkage direction was measured and evaluated according to the following criteria: ◎: The heat shrinkage (A1) was a value in the range of 30 to 50%. ○: The heat shrinkage (A1) was a value in the range of 21 to less than 30%, or more than 50 to 65%. △: The heat shrinkage (A1) was a value in the range of 16 to less than 21%, or more than 65 to 70%. ×: The heat shrinkage (A1) was a value less than 16% or more than 70%.

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

[0066] (3) Evaluation 3: Neck-in Ratio The neck-in ratio of the obtained polyester heat-shrinkable film was measured for 10 seconds in 70°C hot water with the main shrinkage direction fixed, and evaluated according to the following criteria. Specifically, as shown in FIG. 8( a), a polyester heat-shrinkable film 10 was cut into a long piece measuring 200 mm in the main shrinkage direction and 100 mm in the perpendicular direction to prepare a measurement sample. A reference line 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 reference line was designated L0. Next, as shown in FIG. 8( b), the measurement sample was attached to a fixing frame jig with an inner length of 140 mm and a width of 140 mm, with both ends of the measurement sample fixed in the main shrinkage direction and the inner length direction aligned. The long measurement sample was then positioned and fixed so that a predetermined space was left between both ends of the long measurement sample in the perpendicular direction and the fixing frame jig. Next, as shown in Figure 8(c), the measurement sample attached to the fixing frame jig was immersed in hot water at 70°C for 10 seconds, and then in water at 30°C or less for 10 seconds, and the maximum thermal shrinkage in the orthogonal direction was measured from the change in the length of the marked line on the measurement sample. Finally, the neck-in ratio was determined by dividing the obtained thermal shrinkage ratio by 2 according to the following formula (1): Neck-in ratio (%) = (L0 - L) / 2L ０ × 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 a value within the range of 0 to 4%. ◯: The neck-in ratio is a value within the range of more than 4 to 6%. △: The neck-in ratio is a value within the range of more than 6 to 8%. ×: The neck-in ratio is a value exceeding 8%.

[0068] (4) Evaluation 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 a value in the range of 10 to 100. ◯: The absolute value (A1 / A2) is a value in the range of 5.5 to less than 10, or a value in the range of more than 100 to 110. △: The absolute value (A1 / A2) is a value in the range of 4.5 to less than 5.5, or a value in the range of more than 110 to 120. ×: The absolute value (A1 / A2) is less than 4.5 or a value in excess of 120.

[0069] (5) Evaluation 5: Maximum Shrinkage Stress (C) The obtained polyester heat-shrinkable film was cut into strips measuring 25.4 mm in width in the MD direction and 75 mm in length in the TD direction to prepare test specimens. The shrinkage stress of the test specimens was then measured using a strength-strain measurement device equipped with a heating furnace. More specifically, the heating furnace was preheated to 85°C, the airflow from the heating furnace was temporarily stopped, the door of the heating furnace was opened, and the test specimen was attached to the chuck of the strength-strain measurement device. The door of the heating furnace was then promptly closed and airflow was resumed. The shrinkage stress was then measured for 30 seconds or more, and the maximum value during the measurement was recorded as the maximum shrinkage stress (C), and the results were evaluated according to the following criteria: ⊚: The maximum shrinkage stress (C) was within the range of 4 to 8 MPa. ◯: The maximum shrinkage stress (C) was within the range of 3 to less than 4 MPa, or greater than 8 to 10 MPa. △: The maximum shrinkage stress (C) is 2 to less than 3 MPa, or is in the range of more than 10 to 12 MPa. ×: The maximum shrinkage stress (C) is less than 2 MPa or exceeds 12 MPa.

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

[0071] [Example 2] In Example 2, as shown in Table 1, PET1 was used as the polyester resin, and the values ​​of components (a) to (d) were changed to restrict the production conditions for longitudinal stretching. That is, in Example 2, a 40 μm thick polyester heat-shrinkable film was produced from a raw sheet at a preheating temperature of 105°C, a stretch ratio (MD direction: 100%, TD 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 components (a) to (d) were changed to restrict the production conditions for longitudinal stretching. That is, a polyester-based heat-shrinkable film having a thickness of 25 μm was produced from an original 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-based 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 components (a) to (d) were changed to restrict the production conditions for longitudinal stretching. That is, a 40 μm thick polyester heat-shrinkable film was produced from an original 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 components (a) to (d) were changed to restrict the production conditions for longitudinal stretching. That is, a polyester-based heat-shrinkable film having a thickness of 45 μm was produced from an original 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-based 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 components (a) to (d) were changed to restrict the production conditions for longitudinal stretching. That is, a polyester-based heat-shrinkable film having a thickness of 50 μm was produced from an original 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-based 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 components (a) to (d) were changed to restrict the production conditions for longitudinal stretching. That is, a polyester-based heat-shrinkable film having a thickness of 45 μm was produced from an original 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-based 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 components (a) to (d) were changed to restrict the production conditions for longitudinal stretching. That is, a 45 μm thick polyester heat-shrinkable film was produced from an original 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 components (a) to (d) were changed and the manufacturing conditions were modified to restrict the properties. That is, a 47 μm thick polyester heat-shrinkable film was produced from an original 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.

[0079] Comparative Example 3 In Comparative Example 3, as shown in Table 1, PET6 was used as the polyester resin, and the values ​​of components (a) to (d) were changed and the manufacturing conditions were modified to restrict the properties. That is, a 42 μm thick polyester heat-shrinkable film was produced from an original sheet at a preheating temperature of 90°C, a stretch 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]

[0081]

[0082] The polyester heat-shrinkable film of the present invention, which has at least the following configurations (a) to (c), 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 55%. (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 -5 to 10%. (c) The neck-in ratio measured in 70°C hot water for 10 seconds is set to a value of 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] That is, with the polyester heat-shrinkable film etc. of the present invention, by controlling not only the heat shrinkage rates (A1 and A2) under predetermined conditions but also at least the neck-in rate under predetermined conditions, it is possible to stably heat-shrink and exhibit excellent wrinkle resistance even when applied to PET bottles of complex shapes, etc. Therefore, it can be suitably applied to various PET bottles, outer wrapping materials for lunch boxes, etc., and its versatility can be significantly expanded, so it can be said that its industrial applicability is extremely high.

[0085] 10: Polyester-based heat-shrinkable film 10a: Other resin layer 1 10b: Other resin layer 2 10c: Shrinkage rate adjusting layer

Claims

1. A polyester-based heat-shrinkable film derived from a polyester-based resin, characterized by having the following configurations (a) to (d): (a) When the heat shrinkage percentage in the main shrinkage direction is A1, which is measured in 80°C hot water for 10 seconds, A1 is set to a value within the range of 21 to 65%. (b) When the heat shrinkage percentage in the direction perpendicular to the main shrinkage direction is A2, which is measured in 80°C hot water for 10 seconds, A2 is set to a value within the range of -5 to 10%. (c) The absolute value (A1 / A2) of the ratio of the heat shrinkage percentages A1 and A2 is 5.5 or more. (d) The neck-in ratio measured in 70°C hot water for 10 seconds is 6% or less.

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

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

4. 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. A 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-based heat-shrinkable film from a polyester-based resin derived from a dicarboxylic acid compound and a diol compound as reactive components, the method comprising the following steps 1 and 2: Step 1: Preparing the dicarboxylic acid compound and the diol compound as reactive components and reacting them to produce a polyester-based resin; Step 2: Stretching the polyester-based resin in a predetermined direction to produce a polyester-based heat-shrinkable film having the following configurations (a) to (d): (a) When the heat shrinkage percentage A1 is determined in the main shrinkage direction by shrinking the film in 80°C hot water for 10 seconds, A1 is set to a value within the range of 21 to 65%; (b) When the heat shrinkage percentage A2 is determined in the direction perpendicular to the main shrinkage direction by shrinking the film in 80°C hot water for 10 seconds, A2 is set to a value within the range of -5 to 10%; and (c) The absolute value (A1 / A2) of the ratio of the heat shrinkage percentages A1 and A2 is set to a value of 5.5 or greater. (d) The neck-in ratio measured in hot water at 70°C for 10 seconds is 6% or less.

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

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