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

Abstract

Provided is a polyester-based heat-shrinkable film or the like excellent in wrinkle resistance.　The present invention provides a polyester-based heat-shrinkable film or the like that is characterized by satisfying the following configurations (a)-(d) when a main shrinkage direction is defined as a TD direction and a direction orthogonal to the main shrinkage direction is defined as an MD direction. (a) A 2θ value obtained by an X-ray diffraction measurement device includes a crystal peak indicating the maximum value at a diffraction angle (a section of 42° or greater and less than 44°) of the (-105) plane, and the half value width of the crystal peak is set to a value of 7° or less; (b) the crystallite size of the (-105) plane obtained by the X-ray diffraction measurement device is set to a value of 2.5 nm or less; (c) the thermal shrinkage rate A1 in the TD direction is set to a value within the range of 25-65% under a condition of 10 seconds in hot water of 80°C; and (d) the refractive index in the TD direction is set to a value within the range of 1.58-1.66.

Description

Polyester heat-shrinkable film and method for producing the same

[0001] The present invention relates to a polyester heat-shrinkable film and a method for producing the same, and more particularly to a polyester heat-shrinkable film (hereinafter sometimes simply referred to as "heat-shrinkable film") having excellent wrinkle resistance and having a half-width of a crystalline peak controlled using an X-ray diffraction analyzer (hereinafter sometimes referred to as "XRD"), and an efficient method for producing the same.

[0002] Conventionally, heat-shrinkable films have been widely used as base films for labels on PET bottles and the like, and are made of various materials, including polyester resins. These heat-shrinkable films are thermally shrunk by passing them through a tunnel that generates hot air or steam, and then attached to the container. However, uneven shrinkage (non-uniformity) may occur during the heat shrinkage, resulting in wrinkles and color unevenness. Therefore, various heat-shrinkable films have been proposed to prevent the occurrence of wrinkles and color unevenness due to uneven shrinkage (non-uniformity) during the heat shrinkage.

[0003] For example, a polyester-based heat-shrinkable film has been proposed that exhibits a high heat shrinkage rate in the width direction and a low heat shrinkage rate in the longitudinal direction, high mechanical strength in the longitudinal direction, good perforation tearability, and excellent shrinkage finish (see Patent Document 1). More specifically, the polyester resin is made of a polyester resin, and the proportion of acid components other than terephthalic acid in all acid components (A mol %) and the proportion of alcohol components other than ethylene glycol in all alcohol components (B mol %) are in the ranges of 5 mol %≦A+B≦40 mol %. The polyester-based heat-shrinkable film is characterized in that the total acid components contain 1 to 30 mol % of a naphthalenedicarboxylic acid component and 0.3 to 3 mol % of an alkali metal salt of sulfobenzenedicarboxylic acid.

[0004] Furthermore, a polyester-based heat-shrinkable film has been proposed in which the amount of amorphous components in the total polyester resin components is strictly controlled, and the hot water heat shrinkage rate at 80°C and 90°C in the longitudinal direction of the film and the hot water heat shrinkage rate at 90°C in the width direction of the film are limited (see Patent Document 2). More specifically, the film contains ethylene terephthalate as the main constituent component and one or more monomer components that can become amorphous components in the total polyester resin components, the total of which is 15 mol% or more. The polyester-based heat-shrinkable film is characterized by having a hot water heat shrinkage rate in the longitudinal direction of the film of 30% or more at a treatment temperature of 80°C for a treatment time of 10 seconds, and 40% or more at a treatment temperature of 90°C for a treatment time of 10 seconds, and a hot water shrinkage rate in the width direction of the film of 10% or less at 90°C for a treatment time of 10 seconds.

[0005] JP 08-027259 A (claims, etc.) JP 2007-016120 A (claims, etc.)

[0006] However, in all of the heat-shrinkable films described in Patent Documents 1 and 2, although the heat shrinkage rate at a predetermined temperature and in a predetermined shrinkage direction is limited to a predetermined range, no consideration is given to controlling the half-width of the crystalline peak, etc. Therefore, in the case of PET bottles and the like in which the bottle diameter of the body is not uniform and the horizontal cross-sectional shape of the body is not circular in some parts but has a complex shape, the heat shrinkability is likely to be non-uniform, which has caused the problem that it is extremely difficult to suppress the occurrence of fine wrinkles.

[0007] The inventors of the present invention have found that by limiting the half-width of the crystal peak corresponding to the (-105) plane and the crystallite size to values ​​within a predetermined range through measurements using an X-ray diffraction measurement device (transmitted light), etc., it is possible to quantitatively suppress the occurrence of fine wrinkles even when the film is applied to various PET bottles, etc., and have completed the present invention. That is, an object of the present invention is to provide a polyester heat-shrinkable film that can be obtained through simple and precise measurements, etc., and that accurately exhibits excellent wrinkle resistance even when applied to various PET bottles, etc., and an efficient method for producing such a heat-shrinkable film.

[0008] According to the present invention, there is provided a polyester-based heat-shrinkable film derived from a polyester-based resin, characterized in that, when the main shrinkage direction is the TD direction and the direction perpendicular to the main shrinkage direction is the MD direction, the film satisfies the following requirements (a) to (c), thereby solving the above-mentioned problems: (a) the 2θ value obtained using an X-ray diffraction measurement device (usually a transmission X-ray diffraction measurement device; the same applies hereinafter) includes a crystalline peak (including a crystalline domain; the same applies hereinafter) showing a maximum value at a diffraction angle of the (-105) plane (in the range of 42° or more to less than 44°), and the half-width of the crystalline peak is 7° or less; (b) the crystallite size of the (-105) plane obtained using the X-ray diffraction measurement device is 2.5 nm or less; and (c) when the heat shrinkage ratio A1 is determined by heat shrinking in the TD direction in 80°C hot water for 10 seconds, the A1 is within the range of 25 to 65%. That is, by accurately limiting the half-width of a predetermined crystal peak and the crystallite size by XRD, which is a simple and precise measurement, and satisfying the features (a) to (c), the occurrence of fine wrinkles can be quantitatively and effectively suppressed even when the product is applied to various PET bottles, etc.

[0009] In constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the following requirement (d) be satisfied: (d) The refractive index in the main shrinkage direction (usually the TD direction) is set to a value within the range of 1.58 to 1.66. By limiting the refractive index in this way, the half-width of the crystalline peak and the crystallite size can be determined with greater precision, and even when the film is applied to various PET bottles, the occurrence of fine wrinkles can be quantitatively and more accurately suppressed.

[0010] In constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the following requirement (e) be satisfied: (e) When the heat shrinkage percentage A2 is determined by heat shrinking in the TD direction in 70°C hot water for 10 seconds, A2 is set to a value within the range of 3 to 40%. By limiting the heat shrinkage percentage A2 in this manner, the film can be applied to various PET bottles and the like, and even when a wide range of heat shrinkage temperatures is applied, the occurrence of fine wrinkles and the like can be more accurately suppressed.

[0011] In constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the following requirement (f) be satisfied: (f) When the heat shrinkage rate A3 is determined by heat shrinking in the TD direction in hot water at 100°C for 10 seconds, A3 is set to a value within the range of 30 to 80%. By limiting the heat shrinkage rate A3 in this manner, the film can be applied to various PET bottles and the like, and even when a wide range of heat shrinkage temperatures is applied, the occurrence of fine wrinkles and the like can be more accurately suppressed.

[0012] In constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the following requirement (g) be satisfied: (g) The haze value measured in accordance with JIS K 7136:2000 is 10% or less. By controlling the haze value within this predetermined range, not only is excellent transparency achieved, but also excellent printability and uniform heat shrinkability can be exhibited.

[0013] In constructing the polyester-based heat-shrinkable film of the present invention, it is preferable to set the thickness within the range of 10 to 100 μm. By limiting the thickness in this way, handling and production control become easier, and the film can be applied to various PET bottles, etc., and even if the heat-shrinkage temperature varies, the occurrence of fine wrinkles can be suppressed.

[0014] Another aspect of the present invention is a method for producing a polyester-based heat-shrinkable film derived from a polyester-based resin, the method comprising at least 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 exhibiting the following configurations (a) to (c): (a) The 2θ value obtained by an X-ray diffraction measurement device includes a crystalline peak showing a maximum value at a diffraction angle of the (-105) plane (in the range of 42° or more to less than 44°), and the half-width of the crystalline peak is 7° or less; (b) The crystallite size of the (-105) plane obtained by an X-ray diffraction measurement device is 2.5 nm or less; and (c) When the thermal shrinkage percentage A1 is defined as the percentage when the film is shrunk in 80°C warm water for 10 seconds, the A1 is set to a value within the range of 25 to 65%. By producing in this manner, it is possible to effectively produce a polyester-based heat-shrinkable film that quantitatively suppresses the occurrence of fine wrinkles, etc., even when applied to various PET bottles, etc.

[0015] When carrying out the method for producing a polyester-based heat-shrinkable film of the present invention, it is preferable to measure at least the components (a) and (b) in-line in step (2). By measuring at least the components (a) and (b) of the polyester-based heat-shrinkable film in-line in this way, the quality of the polyester-based heat-shrinkable film can be easily and effectively determined in the production process.

[0016] FIGS. 1(a) to 1(c) are diagrams illustrating the morphology of polyester-based heat-shrinkable films. FIG. 2 is a diagram illustrating the relationship between the half-width (°) obtained from the XRD measurement chart of a polyester-based heat-shrinkable film and the crystallite size (nm). FIG. 3 is a diagram illustrating the relationship between the half-width (°) obtained from the XRD measurement chart of a polyester-based heat-shrinkable film and the refractive index (-). FIGS. 4(a) to 4(c) are diagrams illustrating the relationship between the half-width (°) obtained from the XRD measurement chart of a polyester-based heat-shrinkable film and the 80°C heat shrinkage rate A1 (%), the 70°C heat shrinkage rate A2 (%), and the 100°C heat shrinkage rate A3 (%). FIG. 5 is a diagram illustrating the relationship between the half-width (°) obtained from the XRD measurement chart of a polyester-based heat-shrinkable film and the haze (relative value). FIG. 6 is a diagram illustrating the relationship between the crystallite size (nm) obtained from the XRD measurement chart of a polyester-based heat-shrinkable film and the refractive index (-). 7(a) to 7(c) are diagrams provided to explain the relationship between the crystallite size (nm) obtained from the XRD measurement chart for a polyester-based heat-shrinkable film and the 80°C heat shrinkage rate A1 (%), the 70°C heat shrinkage rate A2 (%), and the 100°C heat shrinkage rate A3 (%). Fig. 8 corresponds to Example 1 and is a diagram (photograph) showing the appearance of a cylindrical label when no wrinkles have occurred, and Figs. 8(b) to 8(d) are enlarged views of the appearance regions P, Q, and R shown in Fig. 8(a). Fig. 9(a) corresponds to Comparative Example 1 and is a diagram (photograph) showing the appearance of a cylindrical label when wrinkles have occurred, and Figs. 9(b) to 9(d) are enlarged views of the appearance regions S, T, and U shown in Fig. 9(a).

[0017] [First Embodiment] The first embodiment is a polyester-based heat-shrinkable film 10 derived from a polyester-based resin, as exemplified in FIG. 1( a) and the like. When the main shrinkage direction is the TD direction and the direction perpendicular to the main shrinkage direction is the MD direction, the polyester-based heat-shrinkable film 10 is characterized by satisfying the following characteristics (a) to (c): (a) The 2θ value obtained by an X-ray diffraction measurement device includes a crystalline peak showing a maximum value at a diffraction angle of the (-105) plane (in the range of 42° or more to less than 44°), and the half-width of the crystalline peak is 7° or less. (b) The crystallite size of the (-105) plane obtained by an X-ray diffraction measurement device is 2.5 nm or less. (c) When the heat shrinkage percentage A1 is defined as the percentage A1 when heat-shrunk in 80°C hot water for 10 seconds, the A1 is within the range of 25 to 65%. The polyester-based heat-shrinkable film of the first embodiment will now be described in detail with reference to the drawings.

[0018] 1. Polyester Resin The type of polyester resin constituting the polyester-based heat-shrinkable film of the first embodiment is not particularly limited, but it is preferably derived from a polyester-based resin composition containing, when the total amount of polyester resins is taken as 100% by weight, typically 30 to 100% by weight of a non-crystalline polyester resin and 0 to 70% by weight of a crystalline polyester resin.

[0019] (1) Amorphous polyester resins can be used as amorphous polyester resins, as long as they are basically polymers derived from polyalcohols and dicarboxylic acids and are amorphous at room temperature. Therefore, amorphous polyester resins made from polyalcohols and hydroxycarboxylic acids, amorphous polyester resins made from polyalcohol dicarboxylic acids and hydroxycarboxylic acids, or mixtures of these polyester resins are preferred. Whether a resin is an amorphous polyester resin can be determined by the absence of a melting peak of the crystalline portion in a DSC curve obtained by DSC (differential scanning calorimetry).

[0020] Here, examples of polyalcohols that are raw material components of amorphous polyester resins include at least one diol, such as aliphatic diols such as ethylene glycol, diethylene glycol, propanediol, butanediol, neopentyl glycol, and hexanediol, alicyclic diols such as 1,4-hexanedimethanol, and aromatic diols. Therefore, among these polyalcohols, ethylene glycol, diethylene glycol, and 1,4-hexanedimethanol are particularly preferred. This is because the use of such polyalcohols allows for an appropriate reaction with a polycarboxylic acid, making it easier to obtain an amorphous polyester resin whose amorphousness is controlled to a desired state.

[0021] Similarly, examples of dicarboxylic acids as raw material components 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 is particularly preferred. Similarly, examples of hydroxycarboxylic acids as compound components of polyester resins include at least one of lactic acid, hydroxybutyric acid, and polycaprolactone.

[0022] (2) Crystalline polyester resin On the other hand, as the crystalline polyester resin, basically, any polyester resin having a crystalline portion at room temperature can be used. Therefore, polyester resins consisting of polyalcohol and dicarboxylic acid, polyester resins consisting of polyalcohol and hydroxycarboxylic acid, polyester resins consisting of polyalcohol dicarboxylic acid and hydroxycarboxylic acid, or mixtures of these polyester resins are preferred. Whether a resin corresponds to a crystalline polyester resin can be determined by the fact that a melting peak of the crystalline portion basically appears in a predetermined temperature range in the DSC curve obtained by DSC (differential scanning calorimetry).

[0023] Here, the polyalcohol, which is a compound component of the polyester resin, is similar to the reactive components of the amorphous polyester resin, and examples thereof include at least one diol, such as an aliphatic diol (e.g., ethylene glycol, diethylene glycol, propanediol, butanediol, neopentyl glycol, or hexanediol), an alicyclic diol (e.g., 1,4-hexanedimethanol), or an aromatic diol. Among these, ethylene glycol, diethylene glycol, and 1,4-hexanedimethanol are particularly preferred. Similarly, examples of the dicarboxylic acid, which is a reactive component of the polyester resin, are similar to the reactive components of the amorphous polyester resin, and examples thereof include at least one of aliphatic dicarboxylic acids (e.g., adipic acid, sebacic acid, or azelaic acid), aromatic dicarboxylic acids (e.g., terephthalic acid, naphthalenedicarboxylic acid, or isophthalic acid), alicyclic dicarboxylic acids (e.g., 1,4-cyclohexanedicarboxylic acid), or ester-forming derivatives thereof.

[0024] Therefore, examples of crystalline polyester resins include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polypropylene terephthalate, etc., and these may be used alone or in combination. In particular, as an example of a crystalline polyester resin, a crystalline polyester resin containing 100 parts by weight of terephthalic acid and 100 parts by weight of ethylene glycol in the total amount of reaction components can be suitably used.

[0025] (3) Blend Ratio The polyester resin composition constituting the polyester heat-shrinkable film preferably contains, relative to the total amount (100 wt%), 20 to 100 wt% of amorphous polyester resin and 0 to 80 wt% of crystalline polyester resin. The reason for this is that by limiting the blending amounts of the amorphous polyester resin and the crystalline polyester resin in this way, they may be homogeneously mixed while undergoing partial phase separation, making it difficult to adjust viscoelastic properties such as the loss factor. Therefore, it is possible to more easily adjust the heat shrinkage rate and maximum shrinkage stress near the shrinkage temperature to within the desired range, and it is also easier to quantitatively control the haze value and other properties.

[0026] More specifically, if the content of the amorphous polyester resin is less than 20% by weight, it becomes difficult to adjust viscoelastic properties such as the loss coefficient, which may make it difficult to control the heat shrinkage rate and mechanical strength near the shrinkage temperature of the polyester heat-shrinkable film, or the maximum shrinkage stress, etc. Therefore, it is more preferable that the polyester heat-shrinkable film contains 50 to 90% by weight of the amorphous polyester resin and 10 to 50% by weight of the crystalline polyester resin, and even more preferable that the polyester heat-shrinkable film contains 70 to 90% by weight of the amorphous polyester resin and 10 to 30% by weight of the crystalline polyester resin, based on the total amount.

[0027] 2. Structure (a) Structure (a) of the polyester-based heat-shrinkable film is characterized in that (a) the 2θ value obtained by an X-ray diffraction measurement device includes a crystalline peak that exhibits a maximum value at a diffraction angle (between 42° or more and less than 44°) of the (-105) plane, and the half-width of the crystalline peak is 7° or less. This is because the half-width of the crystalline peak corresponding to the (-105) plane can be limited to a narrow value of 7° or less using an X-ray diffraction measurement device (transmitted light), which is a simple and precise measurement method. Therefore, even when applied to various PET bottles, the occurrence of fine wrinkles can be quantitatively suppressed. Conversely, if the half-width of the crystalline peak exceeds 7° in the char measured by an X-ray diffraction measurement device (transmitted light), it becomes difficult to control the heat shrinkability and quantitatively suppress the occurrence of fine wrinkles. However, excessively narrowing the half-width of the crystalline peak may significantly reduce production yield or excessively limit the types of polyester resins that can be used. Therefore, it is more preferable to limit the half-width of such a crystal peak to a value within the range of 1 to 6.5°, and even more preferable to limit it to a value within the range of 2 to 6°.

[0028] Here, referring to FIG. 2, the relationship between the half-width (°) of the crystal peak and the crystallite size (nm) will be explained. That is, from the characteristic curve in FIG. 2, it can be seen that there is a correlation such that the crystallite size decreases in inverse proportion as the half-width increases. More specifically, when the half-width is 3 to 5°, the crystallite size is in the range of 1.5 to 2.5 nm, and when the half-width exceeds 5°, it becomes 1.5 nm or less, and further, when the half-width exceeds 7°, it can be seen that the crystallite size tends to be below 1 nm. In fact, in the examples described below, when the half-width is in the range of 3.25 to 5.07°, a crystallite size of 1.75 to 2.74 nm is obtained. Therefore, by controlling the half-width of the crystal peak within a predetermined range in a measurement chart obtained with an X-ray diffraction measurement device, the desired crystallite size (2.5 nm or less) can be obtained, although there is also a relationship with other influencing factors.

[0029] Next, referring to FIG. 3 , the relationship between the half-width (°) of the crystal peak and the refractive index (−) in the TD direction (hereinafter sometimes simply referred to as the refractive index) in a measurement chart obtained with an X-ray diffraction measurement device will be described. That is, judging from the characteristic curve in FIG. 3 , it can be seen that there is a correlation in which the refractive index value exponentially decreases as the half-width increases. In fact, in the examples described below, a refractive index of approximately 1.60 to 1.67 (−) is obtained when the half-width is in the range of 3.25 to 5.07°, and a refractive index of approximately 1.5 to 1.58 (−) is obtained when the half-width exceeds 7°. Therefore, by controlling the half-width of the crystal peak in a measurement chart obtained with an X-ray diffraction measurement device to a predetermined range (e.g., 3 to 5°), a desired refractive index (a refractive index in the TD direction of 1.58 to 1.66) can be obtained, although other influencing factors may also be involved.

[0030] Next, referring to Figures 4(a) to (c), the relationship between the half-width (°) of the crystalline peak and the 80°C heat shrinkage A1 (%), 70°C heat shrinkage A2 (%), and 100°C heat shrinkage A3 (%) will be explained. That is, from the characteristic curves in Figures 4(a) to (c), it can be seen that the respective heat shrinkages increase as the half-width increases, and then tend to gradually decrease once the half-width exceeds 5 to 6°. In fact, in the examples described below, for the 80°C heat shrinkage A1, values ​​of approximately 30 to 60% were obtained by setting the half-width to 4° or more. Similarly, for the 70°C heat shrinkage A2, values ​​of approximately 15 to 35% were obtained by setting the half-width to 4° or more. Furthermore, similarly, for the 100°C heat shrinkage A3, values ​​of approximately 50 to 80% were obtained by setting the half-width to 4° or more. Therefore, by controlling the half width of the crystal peak in a measurement chart obtained by an X-ray diffraction measurement device to a predetermined range (for example, 3 to 5°), it can be said that the heat shrinkage rate at 70°C to 100°C can be controlled to a value within a desired range, although there is also a relationship with other influencing factors.

[0031] Next, referring to FIG. 5 , the relationship between the half-width (°) of the crystalline peak and the haze (%) in a measurement chart obtained with an X-ray diffraction measurement device will be described. That is, judging from the characteristic curve in FIG. 5 , it can be seen that there is a correlation such that when the half-width is in the range of 3 to 5°, the haze value tends to increase slightly in the range of about 1 to 5%, but when the half-width exceeds 5° and is in the range of 8°, the haze value drops to 3% or less. In fact, in the examples described below, when the half-width is in the range of 3.25 to 5.07°, a haze of about 1.60 to 5.2% is obtained, and when the half-width exceeds 7°, a haze of about 1.8% is obtained. Therefore, although there are other influencing factors involved, a desired haze can be obtained by controlling the half-width of the crystalline peak within a predetermined range (e.g., 3 to 5°) in a measurement chart obtained with an X-ray diffraction measurement device.

[0032] 3. Structure (b) Furthermore, structure (b) of the polyester-based heat-shrinkable film is characterized in that the crystallite size of the (-105) plane measured by an X-ray diffraction measurement device is 2.5 nm or less. This is because the crystallite size of the (-105) plane can be limited to a relatively small value of 2.5 nm or less using an X-ray diffraction measurement device (transmitted light), which is a simple and precise measurement method. Therefore, even when applied to various PET bottles, the occurrence of fine wrinkles can be quantitatively suppressed. Conversely, if the crystallite size exceeds 2.5 nm, it becomes difficult to control the heat shrinkability, making it difficult to quantitatively suppress the occurrence of fine wrinkles. However, attempting to control the crystallite size too small may significantly reduce production yield or excessively limit the types of polyester resins that can be used. Therefore, it is more preferable to limit the crystallite size to a value within the range of 0.5 to 2.3, and even more preferable to limit it to a value within the range of 1.3 to 2.1.

[0033] Here, referring to Figure 6, the relationship between crystallite size (nm) and refractive index (-) will be explained. That is, judging from the characteristic curve in Figure 6, it can be seen that when the crystallite size is in the range of about 1.2 to 2.5 nm, the refractive index increases proportionally, and when the crystallite size exceeds 2.5 nm, the refractive index value also tends to be almost saturated. In fact, in the case of the examples described below, when the crystallite size is 1.2 to 2.45 nm, a refractive index of about 1.5 to 1.65 is obtained, and when the crystallite size exceeds 2.5 nm and becomes 2.74 nm, the refractive index value increases to about 1.67. Therefore, by limiting the crystallite size to a value within a predetermined range (e.g., 2.5 nm or less), a desired refractive index value (e.g., 1.58 to 1.66) can be obtained.

[0034] Next, referring to FIG. 7, the relationship between the crystallite size (nm) and the 80°C heat shrinkage rate A1 (%), the 70°C heat shrinkage rate A2 (%), and the 100°C heat shrinkage rate A3 (%) will be explained. That is, judging from the characteristic curves in FIG. 7, when the crystallite size is in the range of 1 to 2 μm, the heat shrinkage rate from 70°C to 100°C increases gradually or remains approximately the same, while when the crystallite size exceeds 2 μm, the heat shrinkage rate from 70°C to 100°C tends to decrease rapidly. For example, in the examples described below, by setting the crystallite size to about 1 to 2.5 nm, a value in the range of about 30 to 60% is obtained for the 80°C heat shrinkage rate A1. Similarly, by setting the crystallite size to about 1 to 2.5 nm, a value in the range of about 3 to 35% is obtained for the 70°C heat shrinkage rate A2. Furthermore, the 100°C heat shrinkage A3 is within a range of approximately 40 to 80% by setting the crystallite size to approximately 1 to 2.5 nm. Therefore, it can be said that by limiting the crystallite size to a predetermined range (e.g., 2.5 nm or less), the heat shrinkage from 70 to 100°C can also be limited to a desired range.

[0035] 4. Structure (c) Structure (c) of the polyester-based heat-shrinkable film is characterized in that, when heat-shrunk in TD direction in 80°C hot water for 10 seconds, the heat shrinkage percentage A1 is set to a value within the range of 25 to 65%. The reason for this is that, under such heat-shrinkage temperature conditions, by controlling the desired heat shrinkage percentage at a commonly used temperature of 80°C, it is possible to quantitatively suppress the occurrence of fine wrinkles. Conversely, if the crystallite size exceeds 2.5 nm, it becomes difficult to control the heat shrinkability, making it difficult to quantitatively suppress the occurrence of fine wrinkles. However, if the heat shrinkage percentage A1 is less than 25% or, conversely, exceeds 65%, the manufacturing yield may be significantly reduced or the types of polyester resins that can be used may be excessively limited. Therefore, it is more preferable to limit the heat shrinkage percentage A1 to a value within the range of 35 to 55%, and even more preferable to limit it to a value within the range of 38 to 50%.

[0036] 5. Structure (d) Structure (d) of the polyester-based heat-shrinkable film is characterized in that the refractive index in the TD direction is set to a value within the range of 1.58 to 1.66. The reason for this is that by limiting the refractive index in the TD direction to a relatively narrow range using a refractometer or the like, which is a simple and precise measurement method, the occurrence of fine wrinkles and the like can be quantitatively suppressed even when the film is applied to various PET bottles and the like. Conversely, if the refractive index is less than 1.58 or exceeds 1.66, it becomes difficult to control the heat shrinkability and quantitatively suppress the occurrence of fine wrinkles and the like. Therefore, it is more preferable to limit the refractive index to a value within the range of 1.59 to 1.66, and even more preferable to limit it to a value within the range of 1.61 to 1.64.

[0037] 6. Structure (e) In structure (e) of a polyester-based heat-shrinkable film, when the heat shrinkage percentage A2 is determined by heat shrinking in 70°C hot water for 10 seconds in the TD direction, it is preferable that A2 be set to a value within the range of 3 to 40%. The reason for this is that by limiting the 70°C heat shrinkage percentage, a good heat shrinkage percentage can be obtained in the polyester-based heat-shrinkable film during heat shrinkage, and thus the maximum shrinkage stress can also be easily obtained. Therefore, it is more preferable to set the 70°C heat shrinkage percentage in the TD direction to a value within the range of 5 to 30%, and even more preferably to a value within the range of 10 to 20%.

[0038] 7. Structure (f) In structure (f) of a polyester-based heat-shrinkable film, when the heat shrinkage percentage A3 is determined by heat shrinking in boiling water at 100°C for 10 seconds in the TD direction, it is preferable that A3 be set to a value within the range of 30 to 80%. The reason for this is that by limiting the heat shrinkage percentage at 100°C, a good heat shrinkage percentage can be obtained in the polyester-based heat-shrinkable film during heat shrinkage, and thus the maximum shrinkage stress can also be easily obtained. Therefore, it is more preferable to set the 100°C heat shrinkage percentage in the TD direction to a value within the range of 40 to 75%, and even more preferably to a value within the range of 45 to 73%.

[0039] 8. Feature (g) Feature (g) is preferably a haze value of 10% or less, measured in accordance with JIS K 7136:2000. By controlling the haze value within a predetermined range in this manner, not only is transparency excellent, but printability and uniform heat shrinkability can also be achieved. However, if the haze value is made too small, the types and amounts of usable polymerization components are limited, making control difficult during production and resulting in excessively low production efficiency. Therefore, it is more preferable to set the haze value within the range of 1 to 8%, and even more preferably within the range of 2 to 5%.

[0040] 9. Thickness It is usually preferable to set the thickness of a polyester heat-shrinkable film to a value within the range of 10 to 100 μm. The reason for this is that by specifically limiting the film thickness before heat shrinkage to a value within a predetermined range, it becomes easier to produce a film with a uniform thickness, and it also becomes easier to control the heat shrinkage rate and the maximum shrinkage stress, making it easier to prevent uneven shrinkage. Therefore, it is more preferable to set the film thickness before heat shrinkage to a value within the range of 20 to 60 μm, and even more preferably to a value within the range of 30 to 50 μm.

[0041] 10. Other Thermal Properties, etc. (1) MD Heat Shrinkage 1 In a polyester-based heat-shrinkable film, the MD direction is the direction perpendicular to the main shrinkage direction, and this is a constituent requirement that the heat shrinkage (B1) in the MD direction when shrunk at 80°C for 10 seconds is 5% or less. The reason for this is that by limiting the 80°C heat shrinkage in the MD direction to a value of 5% or less, the polyester-based heat-shrinkable film can achieve a good heat shrinkage in the main shrinkage direction during heat shrinkage, and therefore the maximum shrinkage stress can also be easily achieved. Therefore, it is more preferable to limit the 80°C heat shrinkage in the MD direction to a value within the range of 3% or less, and even more preferable to limit it to a value of 1% or less.

[0042] (2) MD Heat Shrinkage 2 In a polyester heat-shrinkable film, the MD direction is the direction perpendicular to the main shrinkage direction, and this is a constituent requirement that the heat shrinkage (B2) in the MD direction when shrunk at 90°C for 10 seconds is 10% or less. The reason for this is that by limiting the 90°C heat shrinkage in the MD direction to a value of 10% or less, the polyester heat-shrinkable film can achieve a good heat shrinkage during heat shrinkage, and therefore the maximum shrinkage stress can also be easily obtained. Therefore, it is more preferable to limit the 90°C heat shrinkage in the MD direction to a value of 8% or less, and even more preferable to limit it to a value of 5% or less.

[0043] (3) Constitution of Polyester-Based Heat-Shrinkable Film It is preferable to blend or attach various additives to the polyester-based heat-shrinkable film, or to one or both sides 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, etc. is blended in an amount of preferably 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.

[0044] 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 set to a value within the range of 0.1 to 10%.

[0045] 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.

[0046] 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 adjustment layer 10c on the surface of the polyester heat-shrinkable film 10, as shown in Fig. 1(c), so that the shrinkage rate of the polyester heat-shrinkable film becomes uniform within the plane. Such a shrinkage rate adjustment 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.

[0047] 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.

[0048] [Second Embodiment] The second embodiment is a method for producing a polyester-based heat-shrinkable film 10 as exemplified in FIG. 1(a) and the like, characterized by comprising at least 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 10 exhibiting the following configurations (a) to (c). (a) The 2θ value obtained by an X-ray diffraction measurement device includes a crystalline peak showing a maximum value at a diffraction angle of the (-105) plane (in the range of 42° or more to less than 44°), and the half-width of the crystalline peak is 7° or less. (b) The crystallite size of the (-105) plane obtained by an X-ray diffraction measurement device is 2.5 nm or less. (c) When the heat shrinkage rate when shrunk in 80°C warm water for 10 seconds is defined as A1, A1 is set to a value within the range of 25 to 65%. Hereinafter, the method for producing a polyester-based heat-shrinkable film of the second embodiment will be specifically described with reference to the drawings as appropriate.

[0049] 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.

[0050] 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 230 to 270°C, to obtain a raw sheet of a predetermined thickness (usually 30 to 1000 μm).

[0051] 3. Preparation of Polyester-Based Heat-Shrinkable Film 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 basically expanding the film width, thereby crystallizing the polyester molecules that make up the polyester-based heat-shrinkable film into a predetermined shape. Next, by solidifying it in that state, a heat-shrinkable polyester-based heat-shrinkable film that can be used for decoration, labels, etc. can be produced.

[0052] 4. Next, it is preferable to provide an inspection process to confirm whether the polyester heat-shrinkable film exhibits the characteristics (a) to (c). That is, a predetermined polyester heat-shrinkable film is prepared as the object to be measured, and an X-ray diffraction measurement device is used to inspect and confirm that the half-width of the crystalline peak, the crystallite size, and even the heat shrinkage rate under predetermined heat-shrinkage conditions are within predetermined ranges. This can suppress the occurrence of fine wrinkles, even when the film is applied to various PET bottles, etc. Furthermore, because the characteristics (a) to (b) can be inspected using an X-ray diffraction measurement device, it is also possible to measure and manage these characteristics in-line during the manufacturing process of the polyester heat-shrinkable film. In this case, it is also preferable to confirm that the thickness of the polyester heat-shrinkable film is within the predetermined range.

[0053] 5. Others The obtained polyester heat-shrinkable film is immersed in hot water maintained at a predetermined temperature for a predetermined time using a predetermined heating device, or is heat-treated to heat-shrink the polyester heat-shrinkable film, and the heat shrinkage rate is measured. It is also preferable to measure the haze, glass transition point, and various thermal properties of the polyester heat-shrinkable film and check that they are within predetermined ranges. The obtained polyester heat-shrinkable film is then attached to an adherend such as a PET bottle, and heat-treated in that state under predetermined conditions, and the uniform shrinkage of the polyester heat-shrinkable film is evaluated.

[0054] It is preferable to provide an inspection process in which the produced polyester heat-shrinkable film is continuously or intermittently measured for the following properties and the like to confirm that they are within the specified ranges. That is, by measuring the following properties and the like in such a predetermined inspection process and confirming that they fall within the specified ranges, more uniform heat-shrinkable properties and the like can be exhibited, and quality control can be performed quantitatively even when the heat-shrinkage conditions vary. 1) Visual inspection of the appearance of the polyester heat-shrinkable film 2) Measurement of thickness variation 3) Haze measurement 4) Measurement of glass transition point 5) Measurement of melting point and heat of fusion 6) Measurement of tensile modulus 7) Measurement of tear strength 8) Measurement of SS curve

[0055] [Third Embodiment] The third embodiment relates to a method for using the polyester-based heat-shrinkable film of the first embodiment. That is, 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, first, the polyester-based heat-shrinkable film is cut to an appropriate length and width, and a long cylindrical object is formed. Next, the long cylindrical object is fed to an automatic label attachment device (shrink labeler), further cut to the required length, and further fitted onto a PET bottle or the like filled with contents.

[0056] Next, the polyester heat-shrinkable film wrapped around the PET bottle or the like is heated by passing it through a hot air tunnel or steam tunnel at a predetermined temperature. These tunnels provide radiant heat such as infrared radiation or heated steam at approximately 80°C, which is blown onto the polyester heat-shrinkable film from the surroundings, uniformly heating it and causing it to shrink. Therefore, when the half-width of the crystalline peak is 7° or less, the label can be quickly attached to the outer surface of the PET bottle or the like, as shown in Figures 8(a) to 8(d). On the other hand, when the half-width of the crystalline peak exceeds 7°, regions are formed in the bottle body from the top to the bottom where the label cannot conform to the shape of the bottle, and wrinkles are also significantly observed, as shown in Figures 9(a) to 9(d).

[0057] The present invention will be described in detail below based on examples. However, the scope of the present invention will not be narrowed by the description of the examples without any particular reason. The polyester resins used in Example 1 and the like are as follows.

[0058] (PETG1) Amorphous polyester consisting of dicarboxylic acid: 100 mol% terephthalic acid, diol: 69 mol% ethylene glycol, 20 mol% 1,4-cyclohexanedimethanol, and 11 mol% diethylene glycol. (PETG2) Amorphous polyester (glass transition point: 69°C) consisting of dicarboxylic acid: 100 mol% terephthalic acid, diol: 63 mol% ethylene glycol, 24 mol% 1,4-cyclohexanedimethanol, and 13 mol% diethylene glycol. (APET) A crystalline polyester (glass transition point: none, intrinsic viscosity: 0.65 dL / g) consisting of dicarboxylic acid: 100 mol% terephthalic acid, and diol: 100 mol% ethylene glycol. (Additive) A silica masterbatch (manufactured by Sumika Color Co., Ltd., product name "EPM-7E325") consisting of PET, silica content: 5% by mass, and average silica particle size: 2.7 μm was used.

[0059] [Example 1] 1. Preparation of polyester-based heat-shrinkable film 70 parts by weight of amorphous polyester resin (PETG1) (equivalent to 70% by weight when the total amount of the mixture is 100% by weight) and 30 parts by weight of crystalline polyester resin (APET1) (equivalent to 30% by weight when the total amount of the mixture is 100% by weight) 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 at an extrusion temperature of 260 ° C. using an extruder with an L / D of 24 and an extrusion screw diameter of 50 mm (manufactured by Tanabe Plastic Machinery Co., Ltd.) to obtain a raw sheet.

[0060] Next, using a heat-shrinkable film manufacturing device, a polyester-based heat-shrinkable film having a thickness of 40 μm was produced from the raw sheet at a preheating temperature of 75°C, a stretching temperature of 75°C, a stretching ratio (MD direction: 100%, TD direction: 500%), and a heat setting temperature of 60°C.

[0061] 2. Evaluation of Polyester-Based Heat-Shrinkable Films (1) Evaluation 1: Half-Width On a chart obtained using an X-ray diffraction measurement device (Rigaku Corporation, RINT-RAPID, transmission method), the half-width of the crystalline peak showing the maximum 2θ value at the diffraction angle of the (-105) plane (the range of 42° or more to less than 44°) was measured. The results are shown in Table 2.

[0062] (2) Evaluation 2: Crystallite Size The crystallite size of the (-105) plane was measured from the chart obtained using the X-ray diffraction measurement device. The results are shown in Table 2.

[0063] (3) Evaluation 3: Heat Shrinkage Ratio (A1) The heat shrinkage ratio A1 was measured when the film was heat shrunk in the TD direction in hot water at 80°C for 10 seconds, and the heat shrinkage ratio (A1) was calculated according to the following formula. The results are shown in Table 2. Heat shrinkage ratio = (length of film before heat shrinkage - length of film after heat shrinkage) / length of film before heat shrinkage x 100

[0064] (4) Evaluation 4: Refractive Index The refractive index of the film in the TD direction was measured using a refractometer in accordance with JIS K7142: 2014. The results are shown in Table 2.

[0065] (5) Evaluation 5: Heat Shrinkage Ratio (A2) In Evaluation 5, the heat shrinkage ratio (A2) in the TD direction of the polyester heat-shrinkable film was measured in the same manner as in Evaluation 3, except that the heat shrinkage conditions of 80°C and 10 seconds were changed to 70°C and 10 seconds. The results are shown in Table 2.

[0066] (6) Evaluation 6: Heat Shrinkage Ratio (A3) In Evaluation 6, the heat shrinkage ratio (A3) in the TD direction of the polyester heat-shrinkable film was measured in the same manner as in Evaluation 3, except that the heat shrinkage conditions of 80°C and 10 seconds were changed to 100°C and 10 seconds. The results are shown in Table 2.

[0067] (7) Evaluation 7: Haze Value The haze value of the obtained polyester heat-shrinkable film was measured in accordance with JIS K 7136: 2000. The results are shown in Table 2.

[0068] (8) Evaluation 8: Wrinkle Resistance In Evaluation 8, the wrinkle resistance (sometimes referred to as adhesion evaluation) of the polyester-based heat-shrinkable film after heat shrinkage was measured and evaluated according to the following criteria. Specifically, a cylindrical PET bottle (volume: 500 ml) filled with commercially available drinking water was prepared. Next, the polyester-based 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. 1,3-dioxolane was then applied to the widthwise edges. The widthwise edges were then overlapped and adhered together with an overlap of approximately 1 cm to obtain a cylindrical label with a diameter of approximately 8 cm. This cylindrical label was then cut longitudinally at 16 cm intervals to obtain multiple cylindrical labels. The tubular label was then placed over the body of the prepared cylindrical PET bottle and moved through a steam tunnel maintained at 85°C on a belt conveyor at a speed of 6 m / min. The tubular label was then heat-shrunk so that it adhered tightly to the body of the cylindrical PET bottle from top to bottom. The heat-shrunk tubular label was then visually inspected to determine whether wrinkles of a specified length (1 cm or more) or width (1 mm or more) had occurred, according to the following criteria. The wrinkle resistance was evaluated based on the presence or absence of wrinkles. The results are shown in Table 2. Excellent: No wrinkles were observed in any of the five tubular labels. Average: No wrinkles were observed in any of the five tubular labels. Wrinkles were observed in all of the five tubular labels.

[0069] [Examples 2 to 5] In Examples 2 to 5, various polyester-based heat-shrinkable films were prepared in the same manner as in Example 1, except that the type of polyester resin used and the production conditions were changed as shown in Table 1, and the half-width of the crystalline peak, the crystallite size, the heat shrinkage rates (A1 to A3), etc. were measured in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0070] [Comparative Examples 1 and 2] In Comparative Examples 1 and 2, various polyester-based heat-shrinkable films were prepared in the same manner as in Example 1, except that the type of polyester resin and the production conditions were changed as shown in Table 1, and the half-width of the crystalline peak, the crystallite size, the heat shrinkage rate (A1 to A3), and the like were measured.

[0071]

[0072] Evaluation 1: Half width Evaluation 2: Crystallite size Evaluation 3: Heat shrinkage rate (A1) Evaluation 4: Refractive index Evaluation 5: Heat shrinkage rate (A2) Evaluation 6: Heat shrinkage rate (A3) Evaluation 7: Haze value Evaluation 8: Wrinkle resistance

[0073] According to the present invention, in a polyester heat-shrinkable film derived from a predetermined polyester resin composition, the half-width of the crystalline peak showing the maximum 2θ value at a predetermined diffraction angle, the crystallite size, and the heat shrinkage rate are measured on a chart obtained using an X-ray diffraction measurement device (transmission method), and by controlling each within a predetermined range, it has become possible to efficiently and accurately control the heat shrinkage properties, wrinkle resistance, etc. Therefore, the polyester heat-shrinkable film of the present invention can be applied to various PET bottles, etc., significantly expanding its versatility and can be said to have extremely high industrial applicability.

Claims

1. A polyester-based heat-shrinkable film derived from a polyester-based resin, characterized in that, when the main shrinkage direction is the TD direction and the direction perpendicular to the main shrinkage direction is the MD direction, the film satisfies the following requirements (a) to (c): (a) the 2θ value obtained with an X-ray diffraction measurement device includes a crystalline peak showing a maximum value at a diffraction angle of the (-105) plane (in the range of 42° or more to less than 44°), and the half-width of the crystalline peak is 7° or less; (b) the crystallite size of the (-105) plane obtained with the X-ray diffraction measurement device is 2.5 nm or less; (c) when the heat shrinkage ratio A1 is determined when the film is heat-shrunk in the TD direction in 80°C hot water for 10 seconds, A1 is a value within the range of 25 to 65%.

2. The polyester heat-shrinkable film according to claim 1, characterized in that it satisfies the following requirement (d): (d) the refractive index in the machine direction, measured in accordance with JIS K7142:2014, is a value within the range of 1.58 to 1.

66.

3. The polyester heat-shrinkable film according to claim 1, characterized in that it satisfies the following requirement (e): (e) When the heat shrinkage rate A2 is set as the rate when the film is heat-shrunk in the TD direction in 70°C warm water for 10 seconds, A2 is set to a value within the range of 3 to 40%.

4. The polyester heat-shrinkable film according to claim 1, characterized in that it satisfies the following requirement (f): (f) When the heat shrinkage rate A3 is set as the rate when the film is heat-shrunk in the TD direction in 100°C hot water for 10 seconds, the value A3 is within the range of 30 to 80%.

5. The polyester heat-shrinkable film according to claim 1, which satisfies the following requirement (g): (g) the haze value measured in accordance with JIS K 7136:2000 is 10% or less.

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

7. A method for producing a polyester heat-shrinkable film derived from a polyester resin, 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 the polyester resin; Step (2): stretching the polyester resin along a predetermined direction to produce a polyester heat-shrinkable film exhibiting the following configurations (a) to (c): (a) the 2θ value obtained by an X-ray diffraction measurement device includes a crystalline peak showing a maximum value at a diffraction angle of the (-105) plane (in the range of 42° or more to less than 44°), and the half-width of the crystalline peak is 7° or less; (b) the crystallite size of the (-105) plane obtained by the X-ray diffraction measurement device is 2.5 nm or less; and (c) when the thermal shrinkage percentage A1 when shrunk in 80°C warm water for 10 seconds is defined as A1, the value being within the range of 25 to 65%.

8. The method for producing a polyester-based heat-shrinkable film according to claim 7, characterized in that in step (2), the structures (a) and (b) are measured in-line.

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