Polyester heat shrinkable film

Abstract

To provide a polyester heat-shrinkable film which has improved recyclability and is excellent in wearability and appearance. A polyester-based heat-shrinkable film having (A) a clamping fraction of polyester resin or the like of 1.2% or less, (B) a melting point of 190 to 230°C, (C) a heat of fusion of 25 to 45mJ / mg, (D1) to (D4) heat shrinkage percentages in the main shrinkage direction measured under heat shrinkage conditions of 60, 70, and 80°C for 10 seconds each of 0 to 5%, 25 to 50%, and 55 to 85%, respectively, and a standard deviation of the heat shrinkage percentage values ​​measured at 95 to 100°C for 10 seconds of 1.5% or less.

Description

[Technical Field]

[0001] The present invention relates to a polyester heat-shrinkable film. More specifically, the present invention relates to a polyester heat-shrinkable film that has a good balance between recyclability and heat-shrinkability, can be recycled together with used PET bottles while still attached to them, and has excellent fitability and appearance by correcting the heat-shrinkage rate obtained even if the heat-shrinkage temperature, etc., changes slightly. [Background technology]

[0002] BACKGROUND ART Conventionally, polyethylene resin (HDPE) bottles and polyester resin (PET) bottles (hereinafter sometimes simply referred to as PET bottles) have been widely used as storage containers for beverages, detergents, and the like. PET bottles are particularly popular worldwide as beverage storage containers because they are lightweight, durable, and extremely convenient. On the other hand, these PET bottles are discarded in rivers after use, and then flow into the ocean, causing serious environmental problems. Therefore, in order to solve these environmental problems, active research is being conducted into technologies for collecting and recycling these PET bottles.

[0003] In addition, the PET bottle is covered with a predetermined display label that indicates the name and various information about the contents and also improves decorativeness. That is, it has become common to wrap a display label made of a polyester heat-shrinkable film around the entire surface of a PET bottle. More specifically, in order to obtain good heat shrinkability, polyester-based heat shrinkable films derived from non-crystalline polyester resin (PETG) are widely used.

[0004] However, PETG has the thermal properties of not having a melting point, and there is a problem in that recycled pellets tend to stick together during the recycling process of PET bottles packaged in heat-shrinkable film. That is, when a PET bottle wrapped in heat-shrinkable film is thermally melted during the recycling process, the heat-shrinkable film causes the recycled pellets containing the film to stick together, forming clumps, which can cause clogging in the piping, as shown in Figure 11(a). Therefore, when PET bottles, including the heat-shrinkable film, are melted, the resulting recycled pellets do not stick together, making it difficult to effectively and stably produce pellets of the desired shape using a pelletizer, as shown in Figure 11(b).

[0005] Therefore, in order to achieve various objectives, polyester heat-shrinkable films derived from crystalline polyester resins having a predetermined melting point have been proposed in consideration of recyclability (Patent Documents 1 and 2). That is, Patent Document 1 is a polyester heat-shrinkable film that aims to obtain excellent recyclability while suppressing the adverse effects of residual ink. More specifically, it is a polyester-based heat-shrinkable film that has a heat shrinkage rate of 30% or more in the main shrinkage direction when heat-treated at 80°C for 10 seconds, and a melting point measured with a differential scanning calorimetry (hereinafter sometimes simply referred to as DSC) in the range of 170 to 230°C.

[0006] Patent Document 2 also describes a polyester heat-shrinkable film that aims to achieve excellent recyclability. More specifically, as shown in Figures 12(a) to (b), the invention aims to control the clamping fraction measured under specified conditions to 10% or less, and to control the melting point and crystallization temperature of the polyester heat-shrinkable film, as shown by characteristic curves L6 and L6'. For example, the heat shrinkage rate in the main shrinkage direction at 70°C for 10 seconds is 0% to 50%, the heat shrinkage rate in the main shrinkage direction at 80°C for 10 seconds is 30% to 85%, and the heat shrinkage rate in the main shrinkage direction at 100°C for 10 seconds is in the range of 40 to 90%, and the melting point is limited to a range of 170 to 240°C, etc.

[0007] On the other hand, Patent Document 3 is a polyester heat-shrinkable film that aims to improve the printability of the polyester heat-shrinkable film, limit the rate of change in the heat shrinkage rate for each specified temperature range, and exhibit excellent finish properties when attached to a PET bottle or the like. More specifically, the heat-shrinkable polyester film is characterized in that the rate of change (% / °C) in the heat shrinkage rate in the main shrinkage direction with temperature is 1.5 to 3.0 in the range of 60 to 70°C, 2.5 to 3.5 in the range of 70 to 80°C, 1.0 to 2.0 in the range of 80 to 90°C, and 0.1 to 1.0 in the range of 90 to 100°C. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2020-521823 (Claims, etc.) [Patent Document 2] Patent Publication No. 2022-510146 (Claims, etc.) [Patent Document 3] JP 2011-184690 A (Claims, etc.) Summary of the Invention [Problem to be solved by the invention]

[0009] However, the polyester heat-shrinkable films disclosed in Patent Documents 1 and 2 have aggregation fractions and clumping fractions measured under specified conditions that are below specified values, respectively, and thus have a certain degree of recyclability, but have a problem in that the heat shrinkage values ​​in a specified temperature range tend to vary. In other words, since crystalline polyester resins with a wide range of melting points are used, there was a problem that the heat shrinkage values ​​tended to vary within a specified temperature range (60 to 100°C), particularly in the temperature range around 70°C. As a result, spots and wrinkles tend to occur during heat shrinkage, resulting in poor appearance and wearability, and a good balance between the recyclability and heat shrinkability of polyester heat shrinkable films has not yet been achieved.

[0010] On the other hand, the polyester-based heat-shrinkable film disclosed in Patent Document 3 does not take into consideration the clamping fraction measured under specified conditions, and there was a problem in that when the film was recycled while still attached to a used PET bottle, it was prone to sticking (inter-sticking). Moreover, in all examples (Examples 1 to 4), the heat shrinkage values ​​at 70°C for 10 seconds were in the range of approximately 15 to less than 30%, which was quite low, and therefore the polyester heat shrinkable film was difficult to use and did not provide stable heat shrinkability.

[0011] Therefore, in view of the above problems, the inventors of the present invention have made extensive efforts and have found that the conventional problems can be solved by controlling at least the predetermined properties (A) to (B) such as the clamping fraction of the raw resin as a polyester-based heat-shrinkable film, and the predetermined properties (C) and (D1) to (D4) as a polyester-based heat-shrinkable film, in a polyester-based heat-shrinkable film derived from a polyester resin. In other words, the present invention aims to provide a polyester heat-shrinkable film that can effectively and stably produce pellets of a predetermined shape even when PET bottles coated with a polyester heat-shrinkable film are recycled together, and that can correct the heat-shrinkage rate even if the heat-shrinkage temperature or the like changes and the heat-shrinkage rate does not fall within the desired range, thereby providing a polyester heat-shrinkable film that is excellent in terms of fitability and appearance. [Means for solving the problem]

[0012] According to the present invention, there is provided a polyester-based heat-shrinkable film derived from a polyester resin that is a reaction product of a polycarboxylic acid and a polyalcohol, the polyester-based heat-shrinkable film being characterized by having the following properties (A) to (C) and (D1) to (D4), thereby solving the above-mentioned problems. (A) The clumping fraction (hereinafter sometimes simply referred to as clumping fraction) in a mixture of polyester resin and other PET resin, measured in accordance with APR Document Code: PET-S-08, is set to a value of 1.2% or less. (B) The melting point of the polyester resin measured by DSC is set to a value within the range of 190 to 230°C. (C) The heat of fusion corresponding to the melting peak area at the melting point of the polyester heat-shrinkable film measured by DSC is set to a value within the range of 25 to 45 mJ / mg. (D1) The heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 60°C for 10 seconds is set to a value within the range of 0 to 5%. (D2) The heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 70°C for 10 seconds is set to a value within the range of 25 to 50%. (D3) The heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 80°C for 10 seconds, is set to a value within the range of 55 to 85%. (D4) The standard deviation of the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds is set to 1.5% or less. That is, by mixing other PET resins (recycled PET resins, etc.) with the polyester resin that is the raw material resin of a polyester-based heat-shrinkable film that satisfies the components (A) to (C) and (D1) to (D4) in this way, and then controlling the clamping fraction measured under certain conditions, the melting point of the polyester resin that is the raw material resin, and further the heat of fusion and the heat shrinkage rate at a predetermined temperature within predetermined ranges, it is possible to achieve a good balance between recyclability and heat shrinkability. Therefore, the polyester-based heat-shrinkable film can be recycled together with the specified PET bottle while it is still attached to it, and even if the heat-shrinkage temperature changes from a relatively low temperature condition to a high temperature condition and the heat-shrinkage rate does not fall within the desired range, this can be corrected to provide a polyester-based heat-shrinkable film with excellent attachment properties and appearance.

[0013] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction) measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds is 70% or more as the characteristic (D4'). By controlling the heat shrinkage rate in the high temperature range in this way, it becomes easier to control the heat shrinkage rate in the relatively low temperature range of 60 to 80°C within a desired range, which in turn makes it possible to further improve the wearability and appearance of the film when it is heat-shrunk.

[0014] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction), measured under heat shrinkage conditions of 60 to 80°C for 10 seconds, as property (D5), satisfies the following relational expression (1): In this way, by having the heat shrinkage temperature and the heat shrinkage rate satisfy the predetermined relational expression (1) within a predetermined temperature range, these values ​​can be controlled as a linear function. Therefore, even if the heat shrinkage temperature or the like changes and the heat shrinkage rate does not fall within the desired range, this can be corrected while maintaining good recyclability, and accurate and good heat shrinkability can be obtained.

[0015]

number

[0016] a: Corresponding to the slope of relational expression (1), a value between 3.25 and 4 b: Corresponding to the constant in relational expression (1), a value between 0 and 5

[0017] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction), measured under heat shrinkage conditions of 60 to 80°C for 10 seconds, as characteristic (D5'), satisfies the following relational expression (2): In this way, by having the heat shrinkage temperature and the heat shrinkage rate satisfy the predetermined relational expression (2) within a predetermined temperature range, these values ​​can be controlled linearly within a narrower range while maintaining good recyclability.

[0018]

number

[0019] a´: Corresponding to the slope of relational expression (2), a value between 3.3 and 3.75 b´: Corresponding to the constant in relational expression (2), a value between 0 and 5

[0020] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction), measured under heat shrinkage conditions of 60 to 80°C for 10 seconds, as the characteristic (D5"), satisfies the following relational expression (3): In this way, by making the heat shrinkage temperature and the heat shrinkage rate satisfy the predetermined relational expression (3) within a predetermined temperature range, these values ​​can be controlled linearly within an even narrower range.

[0021]

number

[0022] a´´: Corresponding to the slope of relational expression (3), a value between 3.35 and 3.5 b´´: Corresponding to the constant in relational expression (3), a value between 0 and 5

[0023] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the heat shrinkage rate in the direction perpendicular to the main shrinkage direction (MD direction), measured under heat shrinkage conditions of 70°C and 10 seconds, is within the range of -3 to 5%, as characteristic (D6). By limiting the heat shrinkage rate in the MD direction under specified temperature conditions in this way, the film can be wrapped around a PET bottle and have good fit and appearance even when heat-shrunk at a relatively low temperature. As a result, there is less distortion of letters, figures, etc., making it easier to obtain accurate information, etc. Furthermore, by limiting the heat shrinkage rate in the MD direction in this way, the heat shrinkability of the entire polyester heat shrinkable film can be balanced, and even if it is recycled together with PET bottles, the adhesion, fluidity, etc. can be controlled, making it possible to stably obtain pellets.

[0024] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the average thickness of the film is within the range of 10 to 100 μm, and that the standard deviation of the average thickness measured under specified conditions is 1.7 μm or less. In this way, by limiting the film thickness and the standard deviation as its variation, the balance between recyclability and heat shrinkability is further improved, and a polyester-based heat-shrinkable film can be obtained that has precisely controlled heat shrinkability, transparency, and also excellent mechanical properties.

[0025] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the polyester resin is a mixture of a crystalline polyester resin and a non-crystalline polyester resin, and that the weight blending ratio is within the range of 100:0 to 80:20. By controlling the weight ratio in this way, the balance between recyclability and heat shrinkability is further improved, and a polyester-based heat-shrinkable film can be obtained that has precisely controlled heat shrinkability, wearability, appearance, transparency, and also excellent mechanical properties. [Brief explanation of the drawings]

[0026] [Figure 1] 1(a) to 1(c) are diagrams illustrating the configuration of each polyester-based heat-shrinkable film. [Figure 2] FIG. 2(a) is a diagram illustrating the relationship between the maximum stretching speed and the standard deviation of the heat shrinkage rate in the main shrinkage direction at 100°C for 10 seconds when producing a polyester-based heat-shrinkable film, and FIG. 2(b) is a diagram illustrating the relationship between the maximum stretching speed and the standard deviation of the thickness. [Figure 3] FIG. 3 is a diagram provided to explain the relationship between the standard deviation of the heat shrinkage rate in the main shrinkage direction at 100°C for 10 seconds in a polyester heat-shrinkable film produced at a predetermined maximum stretching speed and the evaluation (relative value) of the clumping fraction. [Figure 4] FIG. 4 is a diagram provided for explaining the relationship between the maximum stretching speed and the amount of heat of crystallization when producing a polyester-based heat-shrinkable film. [Figure 5] FIG. 5 is a diagram provided for explaining the relationship between the maximum stretching speed when producing a polyester-based heat-shrinkable film and the glass transition temperature of the polyester-based heat-shrinkable film. [Figure 6] FIG. 6 is a diagram provided for explaining the relationship between the maximum drawing speed and the heat of fusion. [Figure 7] FIG. 7 is a diagram provided for explaining the region (S1) defined by the relational expression (1) in the present invention. [Figure 8] FIG. 8 is a diagram provided for explaining the region (S2) defined by the relational expression (2) in the present invention. [Figure 9] FIG. 9 is a diagram provided for explaining the region (S3) defined by the relational expression (3) in the present invention. [Figure 10] FIG. 10(a) is a DSC chart of the polyester-based heat-shrinkable film of Example 1, and FIG. 10(b) is a DSC chart of the polyester resin (PET2) used to measure the clumping fraction in Example 1 and the like. [Figure 11]FIG. 11(a) is a conceptual diagram showing the mutual adhesion state of PET bottles coated with a conventional polyester-based heat-shrinkable film, and FIG. 11(b) is a conceptual diagram showing recycled PET resin obtained in a recycling process from PET bottles coated with the polyester-based heat-shrinkable film of the present invention. [Figure 12] FIG. 12(a) is a diagram showing the relationship between the clumping fraction and the melting point in Patent Document 2 (conventional method 2), and FIG. 12(b) is a diagram showing the relationship between the clumping fraction and the heat of crystallization in Patent Document 2. DETAILED DESCRIPTION OF THE INVENTION

[0027] [First embodiment] As shown in FIGS. 1(a) to 1(c), the first embodiment is a polyester-based heat-shrinkable film derived from a polyester resin that is a reaction product of a polycarboxylic acid and a polyalcohol. The present invention provides a polyester heat-shrinkable film that satisfies the following properties (A) to (C) and (D1) to (D4). (A) The clumping fraction in a mixture of polyester resin and other PET resins, measured in accordance with APR Document Code: PET-S-08, shall be 1.2% or less. (B) The melting point of the polyester resin measured by DSC is set to a value within the range of 190 to 230°C. (C) The heat of fusion corresponding to the melting peak area at the melting point of the polyester heat-shrinkable film measured by DSC is set to a value within the range of 25 to 45 mJ / mg. (D1) The heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 60°C for 10 seconds is set to a value within the range of 0 to 5%. (D2) The heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 70°C for 10 seconds is set to a value within the range of 25 to 50%. (D3) The heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 80°C for 10 seconds, is set to a value within the range of 55 to 85%. (D4) The standard deviation of the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds is set to 1.5% or less. Hereinafter, the polyester-based heat-shrinkable film of the first embodiment will be specifically described by dividing it into each constituent element and referring to the drawings as appropriate.

[0028] 1. Polycarboxylic acids The polycarboxylic acid as one of the constituents (raw material components) of the polyester resin is not particularly limited as long as it is a compound that can react with a polyalcohol to form a polyester structure, and examples thereof 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.

[0029] In particular, terephthalic acid is suitable because it has good reactivity with polyalcohol, easily forms a crystalline polyester structure, is relatively inexpensive, and is economically advantageous. Therefore, when the total amount of polycarboxylic acids used is taken as 100 mol %, the amount of terephthalic acid used is preferably 90 mol % or more, and more preferably within the range of 95 to 100 mol %.

[0030] 2. Polyalcohols (1) Type Furthermore, the polyalcohol as one of the constituent components of the polyester resin is not particularly limited as long as it is a compound having multiple reactive hydroxyl groups. For example, it is preferable to blend at least one of an aliphatic diol such as ethylene glycol, diethylene glycol, propanediol, butanediol, neopentyl glycol, or hexanediol, an alicyclic diol other than 1,4-cyclohexanedimethanol, or an aromatic diol. By using such a polyalcohol, it is possible to react it appropriately with the polycarboxylic acid, and it is easy to obtain a polyester resin whose crystallinity and the like are controlled within a predetermined range.

[0031] Among these polyalcohols, it is more preferable to use one or more diols selected from ethylene glycol, diethylene glycol, neopentyl glycol, and the like. That is, by using these specific polyalcohols, the melting point, heat shrinkage rate, heat shrinkage stress, etc. of the polyester resin obtained by reacting with a polycarboxylic acid can be more easily adjusted to values ​​within the specified ranges.

[0032] Therefore, when the total amount of polyalcohols used is taken as 100 mol %, it is preferable to use one or more diols selected from ethylene glycol, diethylene glycol, neopentyl glycol, etc. in an amount of 90 mol % or more, and more preferably in the range of 95 to 100 mol %. If necessary, other dicarboxylic acids and diols, or hydroxycarboxylic acids may be used to change the thermal properties and mechanical properties of the polyester heat-shrinkable film, either alone or in combination as a mixture.

[0033] (2) Reaction amount The amount of polyalcohol reacted is not particularly limited, but it is generally preferable to react 100 moles of a polycarboxylic acid containing 80 mole % or more of terephthalic acid or the like with 130 to 220 moles of polyalcohol, more preferably 150 to 210 moles of polyalcohol, and even more preferably 180 to 200 moles of polyalcohol, and it is also preferable that the polyester resin be obtained by crystallizing these reaction products.

[0034] In this case, as a measure of the crystallinity of the polyester resin, the degree of crystallinity calculated from a DSC curve measured in accordance with JIS K 7122:2012 is preferably a value in the range of 1 to 15%, more preferably a value in the range of 2 to 10%, and even more preferably a value in the range of 3 to 8%. That is, in such a DSC curve, the heat of fusion (ΔHm) obtained from the melting peak area, the heat of crystallization (ΔHc) obtained from the crystallization peak area, and the heat of complete crystallization of the crystallized polyethylene terephthalate (ΔHm 0 ) and the crystallinity of the polyester resin can be calculated according to the following formula (4).

[0035]

number

[0036] ΔHm: Heat of fusion (J / g) ΔHc: Crystallization heat (J / g) ΔHm 0 : 140.1 J / g (heat of complete crystallization of crystalline polyethylene terephthalate)

[0037] 3. Polyester resin (1) Clamping fraction As a characteristic (A) of the polyester resin used as the raw material resin for constituting the polyester-based heat-shrinkable film, the clumping fraction of the polyester resin, which is a mixture of polyester resin and other PET resins, measured in accordance with APR Document Code: PET-S-08, is set to a value of 1.2% or less. The reason for this is that if the clamping fraction exceeds 1.2%, the recyclability may be significantly reduced and the variation in the heat shrinkage rate may become large, making it difficult to prevent the occurrence of spots, wrinkles, etc. during heat shrinkage when the heat shrinkage temperature changes slightly, and to maintain good wearability. However, if the clumping fraction is set to an excessively small value, the yield may be significantly reduced, or the types of ingredients used in the polyester resin may be excessively restricted. Therefore, it is more preferable that the clumping fraction of the polyester resin or the like is set to a value within the range of 0.01 to 1%, and even more preferable that it is set to a value within the range of 0.1 to 0.8%.

[0038] In the case of conventional polyester resins, it is said that the preferred range of heat shrinkage rate for polyester heat shrinkable films made from them is 0% to 50% at 70°C for 10 seconds, and therefore the melting point varies greatly, which in turn makes the S-shaped characteristic curve prone to change. Therefore, in the case of polyester-based heat-shrinkable films derived from conventional polyester resins, the heat-shrinkage temperature varies, and even if the desired heat-shrinkage rate is not obtained, it is not possible to quickly and accurately correct this. In contrast, in the case of the present invention, the heat shrinkage temperature and the heat shrinkage rate change as a linear function. Therefore, even if the heat shrinkage temperature fluctuates and the desired heat shrinkage rate cannot be temporarily obtained, the desired heat shrinkage rate can be stably obtained by controlling the clamping fraction of the polyester resin or the like and in accordance with the relational expressions (1) to (3) described below.

[0039] The clumping fraction of polyester resins and the like, which conforms to APR Document Code: PET-S-08, can be measured under the following measurement conditions. 1) Preheat the oven to 210°C. 2) Next, PET bottles or the like with polyester-based heat-shrinkable film attached are washed, elutriated, and crystallized to obtain PET flakes (corresponding to a mixture of polyester resin and other PET resins) with an initial weight (1 kg) which are placed in a 22 x 33 cm baking pan lined with aluminum foil. 3) Next, the PET flakes contained in the baking pan are heat-treated for 90 minutes using an oven maintained at a predetermined temperature. 4) Then remove the baking pan from the oven and allow it to cool to room temperature. 5) Remove the PET flakes from the baking pan and place them on a sieve with a stainless steel mesh with 12.5 mm openings. 6) The sieve containing the PET flakes is vibrated by hand until all of the PET flakes have been sieved.The PET flakes that pass through the mesh are then collected at the bottom.The PET flakes that do not pass through the mesh and remain on the mesh (agglomerates) are removed as appropriate. 7) Weigh the weight of the agglomerates that cannot pass through the mesh. Also, weigh the PET flakes and residues that are attached to the aluminum foil separately. 8) The clumping fraction is calculated from the weight of PET flakes (agglomerates) and residues that cannot pass through the weighed mesh relative to the initial weight (1 kg).

[0040] (2) Melting point Furthermore, as characteristic (B), the melting point of the polyester resin, which is the raw material resin of the polyester-based heat-shrinkable film, is defined as the temperature showing the maximum value of the melting peak in the DSC curve, and is characterized by being set to a value within the range of 190 to 230°C. The reason for this is that if the melting point is less than 190°C, the display label made of polyester heat-shrinkable film may be prone to melting during the drying process when recycling PET bottles, which may cause the recycled PET bottle pieces to stick together and agglomerate (cluster). On the other hand, if the melting point exceeds 230°C, the amount of heat required for extrusion and stretching of the raw sheet of polyester heat-shrinkable film used for the label becomes too high, which may make processing difficult.

[0041] Therefore, the melting point of the polyester resin is more preferably set to a value within the range of 195 to 225°C, and even more preferably set to a value within the range of 200 to 220°C. In other words, while it is important to control the melting point of the polyester resin, by setting the range (difference between the maximum and minimum values) to 25°C or less, more preferably 15°C or less, a better balance between recyclability and heat shrinkability can be achieved, even when crystalline polyester resin is used as the main component (for example, 80% by weight or more). The melting point of the polyester resin can be measured, for example, as the melting peak temperature (Tpm), which is the peak temperature of the heat of fusion shown as an endothermic reaction in a profile obtained using DSC (the same applies hereinafter). The crystallinity of the polyester resin can be estimated from the area of ​​the peak of the heat of fusion (peak area), half-value width, and the like.

[0042] (3) Average molecular weight It is also preferable that the intrinsic viscosity (IV value) of the polyester resin, which is the average molecular weight of the polyester resin, is set to a value within the range of 0.65 to 0.85 dL / g. The reason for this is that if the intrinsic viscosity is less than 0.65 dL / g, the melt viscosity will be too low, which may cause problems in extrusion moldability. On the other hand, if the intrinsic viscosity exceeds 0.85 dL / g, the melt viscosity becomes too high, which may cause problems in extrusion moldability.

[0043] Therefore, it is more preferable that the intrinsic viscosity be set to a value within the range of 0.68 to 0.83 dL / g, and even more preferable that the intrinsic viscosity be set to a value within the range of 0.7 to 0.8 dL / g. That is, while it is important to control the intrinsic viscosity value of the polyester resin, by setting the range (difference between the maximum and minimum values) to 0.15 dL / g or less, the balance between recyclability and heat shrinkability can be further improved even when crystalline polyester resin is used as the main component (for example, 80% by weight or more). The intrinsic viscosity of the polyester resin can be measured in accordance with JIS K 7390 (the same applies hereinafter).

[0044] (4) Additives It is also preferable to incorporate additives such as antioxidants, weather stabilizers, antistatic agents, antifogging agents, metal soaps, waxes, mildew inhibitors, antibacterial agents, nucleating agents, flame retardants, and slip agents into the polyester resin as needed. In particular, to improve the slipperiness of the film surface, it is preferable to incorporate inorganic slip agents such as calcium carbonate particles, silica particles, or glass particles in an amount of, for example, 0.01 to 10% by weight of the total amount of the film (100% by weight).

[0045] The method of adding the additives is not particularly limited, and any known method can be used, although addition by masterbatch is preferred because it is simple and has excellent uniform mixing properties. For example, a specific example (commercially available product) of a polyester resin masterbatch for blending an antiblocking agent is Anti-Blocking Agent (Contains 20% Silica, manufactured by Sukano Co., Ltd., trade name: G dc S559-E). In addition, it is also preferable to blend other resins within a range that does not impair the physical properties of the heat shrinkable film, particularly the shrinkage rate and heat shrinkage stress.

[0046] (5)Mixture It is also preferred that the polyester resin used as the raw material resin for the polyester-based heat-shrinkable film is a mixture of a crystalline polyester resin and a non-crystalline polyester resin, with the weight blending ratio being within the range of 100:0 to 80:20. The reason for this is that if the weight ratio exceeds 80:20, the balance between recyclability and heat shrinkability becomes poor, making it impossible to stably obtain recycled PET, and the heat shrinkage rate may vary greatly within the desired temperature range. That is, it has generally been said that good shrinkage properties cannot be obtained unless the blending amount of the amorphous polyester resin is at least 60% by weight relative to the total amount (100% by weight) of the polyester resin. However, in the case of the present invention, even when the blending amount of the amorphous polyester resin is set to a value of 20% by weight or less relative to the total amount of polyester resin (100% by weight), good heat shrinkability can be obtained by taking into consideration the clumping fraction, melting point and its variation, heat of fusion and its variation, average molecular weight (intrinsic viscosity and its variation) of the polyester resin, and further the stretching conditions during production (stretching temperature, stretching ratio, thermal process temperature, etc.). Therefore, the weight blending ratio of the crystalline polyester resin to the amorphous polyester resin in the mixture is more preferably set to a value within the range of 99:1 to 85:15, and even more preferably to a value within the range of 98:2 to 90:10.

[0047] 4. Heat of fusion (ΔHm) The polyester heat-shrinkable film is characterized in that its characteristic (C) is that the heat of fusion (sometimes referred to as ΔHm), which corresponds to the melting peak area at the melting point measured by DSC, is within the range of 25 to 45 mJ / mg. The reason for this is that if the heat of fusion of such a polyester-based heat-shrinkable film is less than 25 mJ / mg, crystallization will be insufficient, resulting in a significant decrease in heat resistance and making the polyester-based heat-shrinkable film more likely to melt. On the other hand, if the heat of fusion of such a polyester-based heat-shrinkable film exceeds 45 mJ / mg, although crystallization is sufficient, the amount of heat required for extrusion processing and stretching processing of the raw sheet of polyester-based heat-shrinkable film becomes too high, which may make it difficult to control the manufacturing conditions. Therefore, the heat of fusion of the polyester heat-shrinkable film is more preferably set to a value within the range of 28 to 40 mJ / mg, and even more preferably set to a value within the range of 30 to 35 mJ / mg.

[0048] 5. Thermal properties (1) Heat shrinkage rate D1 under specified measurement conditions (e.g., 60°C) The polyester heat-shrinkable film is characterized in that its characteristic (D1) is that the heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 60°C for 10 seconds, is within the range of 0 to 5%. The reason for this is that if the heat shrinkage rate measured under heat shrinkage conditions of 60°C and 10 seconds exceeds 5%, the storage period of the polyester heat shrinkable film may be shortened or the storage conditions may have to be strictly controlled. On the other hand, if the heat shrinkage rate is negative, the film may not function at all as a heat shrinkable film, or the amount and ratio of the raw material components that can be used may be strictly limited. Therefore, with regard to the characteristic (D1), the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 60°C and 10 seconds is preferably set to a value within the range of 0.1 to 4.5%, and more preferably to a value within the range of 0.5 to 4%.

[0049] (2) Heat shrinkage rate D2 under specified measurement conditions (70°C, etc.) The polyester heat-shrinkable film is characterized in that its characteristic (D2) is that the heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 70°C for 10 seconds, is within the range of 25 to 50%. The reason for this is that if the heat shrinkage rate is less than 25%, the film may not function stably as a heat shrinkable film, or the amounts and ratios of the raw material components that can be used may be strictly limited. On the other hand, if the heat shrinkage rate exceeds 50%, the storage period of the polyester heat shrinkable film will be shortened, or the storage conditions will have to be strictly controlled, and further, when attached to a PET bottle, spots, wrinkles, etc. will be more likely to occur. Therefore, with regard to the characteristic (D2), the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 70°C and 10 seconds is preferably set to a value within the range of 30 to 45%, and more preferably to a value within the range of 35 to 40%.

[0050] (3) Heat shrinkage rate D3 under specified measurement conditions (e.g., 80°C) The polyester heat-shrinkable film is characterized in that its characteristic (D3) is that the heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 80°C for 10 seconds, is within the range of 55 to 75%. The reason for this is that if the heat shrinkage rate is less than 55%, the polyester heat shrinkable film may not function stably, or the amount and ratio of the raw material components that can be used may be strictly limited. On the other hand, if the heat shrinkage rate exceeds 75%, the storage period of the polyester heat shrinkable film may be shortened, or the storage conditions may need to be strictly controlled, and further, when attached to a PET bottle, spots, wrinkles, etc. may be more likely to occur. Therefore, with regard to the characteristic (D3), the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 80°C and 10 seconds is preferably set to a value within the range of 58 to 72%, and more preferably to a value within the range of 60 to 70%.

[0051] (4) Thermal shrinkage (D4') under specified measurement conditions (100°C, etc.) and its standard deviation (D4) (4)-1 Heat shrinkage rate As a characteristic (D4') of the polyester heat shrinkable film, it is preferable that the heat shrinkage rate in the main shrinkage direction (TD) is 70% or more, measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds. The reason for this is that by limiting the thermal shrinkage rate in the TD direction under high temperature conditions in this way, the occurrence of spots, wrinkles, etc. is reduced, and in turn, good appearance and wearability are obtained. In other words, by covering the periphery of a PET bottle and heat-shrinking it not only under high temperature conditions but also at relatively low temperatures, not only does it improve the fit but also the appearance, allowing letters, figures, etc. layered on the surface to be accurately recognized. However, if the heat shrinkage rate (D4') is too large, the yield may be significantly reduced, which may be economically disadvantageous, or the types of components to be used in the polyester resin may be excessively restricted. Therefore, it is more preferable that the heat shrinkage rate (D4') is set to a value within the range of 71 to 90%, and even more preferable that it is set to a value within the range of 72 to 85%.

[0052] (4)-2 Standard deviation of heat shrinkage rate Furthermore, the polyester-based heat-shrinkable film has a characteristic (D4) of having a standard deviation of the heat shrinkage rate in the main shrinkage direction (TD direction) of 1.5% or less, measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds. The reason for this is that if the standard deviation of the heat shrinkage rate exceeds 1.5%, the polyester-based heat shrinkable film may not stably function, or the amount and ratio of the raw material components that can be used may be strictly limited. However, if the standard deviation of the heat shrinkage rate becomes too small, the production yield may be excessively reduced, the types of raw materials that can be used may be excessively limited, and further, storage conditions may need to be strictly controlled. Therefore, with regard to the characteristic (D4), the standard deviation of the heat shrinkage rate in the main shrinkage direction (TD direction), measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds, is preferably set to a value within the range of 0.05 to 1.0%, and more preferably to a value within the range of 0.1 to 0.8%.

[0053] Here, referring to FIG. 2(a), the relationship between the maximum stretching speed when producing a polyester heat-shrinkable film and the standard deviation of the heat shrinkage rate in the main shrinkage direction at 100° C. for 10 seconds will be described. That is, the horizontal axis of Figure 2(a) shows the maximum stretching speed during production of the polyester heat-shrinkable film, and the vertical axis shows the standard deviation of the heat shrinkage rate in the main shrinkage direction measured at 100°C for 10 seconds. From the characteristic curve L1 in Figure 2(a), it can be seen that the standard deviation of the heat shrinkage tends to gradually increase within a range of 0.3 to 0.5% when the maximum stretching speed is 40% / sec or higher, up to approximately 60% / sec. Furthermore, when the maximum stretching speed exceeds 60% / sec, i.e., 67% / sec, the standard deviation of the heat shrinkage tends to increase considerably, from 0.5% to approximately 1.5%. Then, when the maximum stretching speed exceeds 67% / sec, the standard deviation of the heat shrinkage increases even more rapidly, exceeding 1.5%.

[0054] That is, from the characteristic curve L1, it can be understood that in the case of the polyester-based heat-shrinkable film of the present invention, by controlling the maximum stretching speed during production to a value within a predetermined range, the standard deviation of the heat shrinkage rate measured under predetermined conditions can be stably controlled to a desired low value. For example, it is understood that if the maximum stretching speed is at least within the range of 40 to 67% / sec, the standard deviation of the heat shrinkage rate (%) can be controlled to a small value of 1.5% or less. Here, the maximum stretching speed refers to the maximum stretching speed in the main shrinkage direction (TD direction) of the film. When producing a polyester-based heat-shrinkable film, the unstretched film may be stretched at a predetermined speed that is changed, and the maximum stretching speed is defined as the speed at which this speed becomes the maximum. That is, the stretching speed reaches a maximum within a few seconds, for example, 0.1 to 12 seconds, after the start of stretching the unstretched film, and the maximum value of the stretching speed during that time can be regarded as the maximum stretching speed. The stretching speed in the TD direction can be defined by the following formula. Stretching speed in TD direction (% / sec.) = (W t2 -W t1 ) / W t1 ×100 / (t2-t1) W t1 : Width of film (m) t1 seconds after starting stretching of unstretched film W t2 : Width of film (m) t2 seconds after starting stretching of unstretched film (However, t1 <t2、0≦t1、0.1≦t2≦12である。)

[0055] However, in the case of Comparative Example 2 and Comparative Example 3 in FIG. 2(a), it has been found that the clamping fraction is considerably larger than that of the present invention (Example 5, etc.), and it should be noted that, as in the present invention, when the clamping fraction is at least 1.2 or less, the characteristic curve L1 is obtained. On the other hand, as will be described later, by controlling the maximum stretching speed to a value within a predetermined range, the standard deviation of the thickness of the polyester-based heat-shrinkable film can also be stably controlled to a desired value, as shown by the characteristic curve L1' in Figure 2(b). That is, in the case of the characteristic curve L1', even in the cases of Comparative Example 2 and Comparative Example 3 in which the clamping fraction is high, a good correlation with the maximum stretching speed is shown, and it is understood that the standard deviation of the thickness of the polyester-based heat-shrinkable film can be controlled to a predetermined value even if the clamping fraction is not strictly controlled.

[0056] Also, referring to FIG. 3, the relationship between the standard deviation of the heat shrinkage rate in the main shrinkage direction (TD direction) measured under predetermined heat shrinkage conditions (100° C., 10 seconds) and the evaluation of the clumping fraction will be described. That is, the horizontal axis indicates the standard deviation (%) of the thermal shrinkage rate in the main shrinkage direction, and the vertical axis indicates the evaluation results (relative values) of the clumping fraction. From the characteristic curve L2 in FIG. 3, it can be said that the smaller the standard deviation of the thermal shrinkage rate in the main shrinkage direction, the higher the evaluation result (relative value) of the clumping fraction tends to be. More specifically, it is understood that if the standard deviation of the thermal shrinkage rate in the main shrinkage direction is 1.5% or less, a high rating of at least 3 or more can be obtained, and if the standard deviation (%) of the thermal shrinkage rate is 1% or less, a high rating of 5, the highest rating, can be obtained. On the other hand, when the standard deviation of the thermal shrinkage rate in the main shrinkage direction exceeds 1.5%, the evaluation result of the clumping fraction suddenly decreases, and when the standard deviation is 1.9%, the evaluation result of the clumping fraction is 0, and further, when the standard deviation is 2.6%, the evaluation result of the clumping fraction is definitely 0. Therefore, judging from the characteristic curve in FIG. 3, it can be seen that the evaluation result of the clumping fraction can be adjusted by controlling the standard deviation of the thermal shrinkage rate in the main shrinkage direction.

[0057] As shown in Figures 4, 5 and 6, it is presumed that the maximum stretching speed when producing a polyester-based heat-shrinkable film has a predetermined correlation with the heat of crystallization, the glass transition temperature and the heat of fusion, respectively. These will be described in detail in the manufacturing method of the second embodiment.

[0058] (5) Heat shrinkage rate D5 under specified measurement conditions As a property (D5) of the polyester heat-shrinkable film, it is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction) measured under heat shrinkage conditions of 60 to 80°C for 10 seconds satisfies the following relational expression (1). The reason for this is that, by satisfying the predetermined relationship between the heat shrinkage temperature and the heat shrinkage rate within a predetermined temperature range, accurate and favorable heat shrinkability can be obtained even when the blending ratio of the crystalline polyester resin is high, which in turn makes it easier to control the heat shrinkage force.

[0059]

number

[0060] a: Corresponding to the slope of relational expression (1), a value between 3.25 and 4 b: Corresponding to the constant in relational expression (1), a value between 0 and 5

[0061] More specifically, referring to FIG. 7, the relationship between the heat shrinkage rate in the main shrinkage direction (TD) under heat shrinkage conditions of 60 to 80° C. for 10 seconds will be described in relation to relational expression (1). That is, the horizontal axis of FIG. 7 indicates the heat shrinkage temperature (° C.), and the vertical axis indicates the heat shrinkage rate (%) in the main shrinkage direction (TD) of the polyester heat shrinkable film. In FIG. 7, it can be seen that if the shaded area (S1) sandwiched between two straight lines positioned in the vertical direction is within the range defined by the relational formula (1) of the present invention, that is, within the range of at least 60 to 80°C, the heat shrinkage rate increases linearly in response to an increase in the heat shrinkage temperature. Therefore, even if the heat shrinkage temperature varies and the desired heat shrinkage rate cannot be temporarily obtained, it can be said that the heat shrinkage rate (%) of the polyester heat shrinkable film can be controlled to a value within the desired range by controlling the clamping fraction in accordance with the relational expression (1) described below. For example, in controlling the thermal shrinkage at 60, 70 and 80° C. within a predetermined range in the present invention, it is extremely effective to use the relational expression (1) or the like. In FIG. 7, the heat shrinkage rates (%) of the polyester heat shrinkable films of the prior art (Patent Documents 2 and 3) are shown by curves labeled Conventional 2 (Ex. 1) and Conventional 3 (Ex. 1). In the case of the curves D2 and D3, it has been found that the heat shrinkage rate does not decrease linearly in response to a decrease in the heat shrinkage temperature, but rather exhibits an S-shaped curve overall. Furthermore, it is understood that, around 70°C, Conventional 2 (Ex. 1) and Conventional 3 (Ex. 1) fall far outside the range defined by the relational formula (1) of the present invention.

[0062] Furthermore, it is more preferable that the characteristic (D5') be such that the heat shrinkage temperature and the heat shrinkage rate satisfy the predetermined relational expressions (2) and (3), and it is even more preferable that the characteristic (D5'') be such that the heat shrinkage temperature and the heat shrinkage rate satisfy the predetermined relational expression (3). 8 and 9, the shaded areas (S2 and S3) sandwiched between two straight lines positioned vertically are the ranges defined by the relational expressions (2) and (3) of the present invention, respectively. It can be understood that, within the range of at least 60 to 80°C, the heat shrinkage rate increases more precisely in a linear function manner in response to an increase in the heat shrinkage temperature. As in Figure 7, Figures 8 and 9 show the heat shrinkage rates (%) of the polyester heat shrinkable films of the prior art (Patent Documents 2 and 3) as curves labeled Conventional 2 (Ex. 1) and Conventional 3 (Ex. 1), respectively.

[0063]

number

[0064] a´: Corresponding to the slope of relational expression (2), a value between 3.3 and 3.75 b´: Corresponding to the constant in relational expression (2), a value between 0 and 5

[0065]

number

[0066] a´´: Corresponding to the slope of relational expression (3), a value between 3.35 and 3.5 b´´: Corresponding to the constant in relational expression (3), a value between 0 and 5

[0067] (6) Thermal shrinkage rate D6 in the MD direction under specified measurement conditions As a property (D6) of the polyester-based heat-shrinkable film, it is preferable that the heat shrinkage rate in the direction perpendicular to the main shrinkage direction (MD direction), measured under heat shrinkage conditions of 70°C and 10 seconds, is within the range of -3 to 5%. The reason for this is that by limiting the thermal shrinkage rate in the MD direction under specified temperature conditions in this way, the occurrence of spots, wrinkles, etc. is reduced even when the PET bottle is covered and thermally shrunk at a relatively low temperature. Therefore, even with energy-saving heating, good fit and appearance can be easily achieved. Furthermore, by limiting the heat shrinkage rate in the MD direction in this way, the heat shrinkability of the entire polyester heat shrinkable film can be balanced, and even if it is recycled together with PET bottles, the adhesion, fluidity, etc. can be controlled, making it possible to stably obtain pellets. Therefore, as the property (D6), it is more preferable that the heat shrinkage rate in the MD direction is set to a value within the range of −2.5 to 4%, and even more preferably within the range of −2 to 3.5%.

[0068] (7) Thermal shrinkage rate D7 in the MD direction under specified measurement conditions As a characteristic (D7) of the polyester-based heat-shrinkable film, it is preferable that the heat shrinkage rate in the direction perpendicular to the main shrinkage direction (MD direction), measured under heat shrinkage conditions of 60 to 90°C for 10 seconds, has at least one minimum value, and that the minimum value is -3% or more. The reason for this is that by restricting the profile of the heat shrinkage rate in the MD direction under predetermined temperature conditions to have a minimum value of a predetermined magnitude, even if the temperature conditions vary to some extent and the heat shrinkage rate changes, it is possible to correct this and easily obtain a good appearance, accurate information, etc. when heat shrinking, which can be more clearly determined by simple actual measurement of the heat shrinkage curve, TMA measurement, etc. Furthermore, by limiting the heat shrinkage rate in the MD direction within a specified temperature range, the heat shrinkability of the entire polyester heat shrinkable film can be balanced, the generated heat shrinkage stress can be reduced, and pellets can be obtained more stably even when recycled together with PET bottles. Therefore, as the property (D7), the minimum value of the thermal shrinkage rate in the MD direction is more preferably set to a value within the range of −1 to 2%, and even more preferably to a value within the range of −0.5 to 1%.

[0069] (8) Thermal shrinkage rate D8 in the MD direction under specified measurement conditions As a characteristic (D8) of the polyester-based heat-shrinkable film, it is preferable that the heat shrinkage rate in the direction perpendicular to the main shrinkage direction (MD direction) measured under heat shrinkage conditions of 60 to 90°C for 10 seconds has at least one maximum value, and that the maximum value is 3% or less. The reason for this is that by limiting the profile of the heat shrinkage rate in the MD direction under a predetermined temperature condition to have a maximum value of a predetermined magnitude, it becomes easier to obtain a good appearance and accurate information when heat shrinking, and it becomes possible to more clearly determine that the generated heat shrinkage stress is below a predetermined value. In addition, when the profile of the thermal shrinkage rate has a maximum value of a predetermined magnitude, it is preferable that the profile also has a minimum value of the above-mentioned predetermined magnitude. Therefore, as the property (D8), it is more preferable that the maximum value of the thermal shrinkage rate in the MD direction is set to a value within the range of −1 to 2%, and even more preferably within the range of −0.5 to 1.5%.

[0070] 6. Thickness The thickness (average thickness, the same applies hereinafter) of the polyester heat-shrinkable film can be changed depending on the shape of the various PET bottles, but it is usually preferable to set it to a value within the range of 10 to 100 μm. The reason for this is that if the thickness of such a polyester heat-shrinkable film is less than 10 μm, it may become difficult to handle and the breaking strength may be significantly reduced. On the other hand, if the thickness of such a polyester-based heat-shrinkable film exceeds 100 μm, it may not heat-shrink uniformly when heated at a predetermined temperature, or it may be difficult to produce a film with a uniform thickness. Therefore, the thickness of the polyester heat-shrinkable film is more preferably set to a value within the range of 20 to 70 μm, and even more preferably set to a value within the range of 40 to 60 μm. The thickness of the polyester heat-shrinkable film can be measured and calculated in accordance with ISO4593 using a micrometer (manufactured by Mitutoyo Corporation, product name "Thickness Gauge 547-401").

[0071] As described above with reference to FIG. 2(b), it is preferable that the standard deviation, which is the variation in the average thickness of the polyester heat-shrinkable film measured under predetermined conditions, is 1.7 μm or less. The reason for this is that by setting the standard deviation of the average thickness to a predetermined value or less, the balance between recyclability and heat shrinkability becomes even better, even when the polyester-based heat shrinkable film is derived from crystalline polyester resin as the main component (for example, 80% by weight or more). However, if the standard deviation of the average thickness is too small, the yield may be significantly reduced, which may be economically disadvantageous, or the types of components to be used in the polyester resin may be excessively restricted. Therefore, it is more preferable that the standard deviation of the average thickness of the polyester heat-shrinkable film is set to a value within the range of 0.05 to 1.4 μm, and even more preferably to a value within the range of 0.1 to 1.2 μm. The method for measuring the standard deviation of the average thickness will be described in detail in Example 1.

[0072] 7. Functional Layer As long as the object of the present invention is not impaired, the polyester heat-shrinkable film preferably has a functional layer for imparting various functions as required. Such functional layers include a coating layer for imparting surface smoothness, stain resistance, weather resistance, etc., a transfer layer, a print layer for imparting design properties, and the like. Among these, a coating layer using a surfactant is particularly preferred as a functional layer because it contributes greatly to improving antistatic properties and surface smoothness.

[0073] For example, as shown in FIG. 1(b), it is also preferable to laminate other resin layers 10a, 10b containing at least one of these various additives on one or both sides of the polyester heat-shrinkable film 10. In this case, when the thickness of the polyester heat-shrinkable film is taken as 100%, the single layer thickness or total thickness of the other resin layers to be additionally laminated is preferably set to a value within the range of 0.1 to 10%. 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.

[0074] Furthermore, it is also preferable to form the polyester heat-shrinkable film into a multilayer structure to further improve the hydrolysis prevention effect and mechanical protection, or to provide a shrinkage rate adjusting layer 10c on the surface of the polyester heat-shrinkable film 10 so that the shrinkage rate of the polyester heat-shrinkable film becomes uniform within the plane, as shown in Figure 1(c). Such a shrinkage adjusting layer can be laminated as a predetermined layer made of polyester resin or the like by using an adhesive, a coating method, or heat treatment depending on the shrinkage characteristics of the polyester heat shrinkable film.

[0075] 8. Haze value and haze value / thickness (1) Haze value It is also preferable that the haze value of the polyester heat-shrinkable film, measured in accordance with ASTM D1003, is within the range of 2 to 8%. The reason for this is that if the haze value exceeds 8%, the transparency will be poor, which is undesirable as it may result in poor appearance when producing labels. Therefore, the haze value is more preferably 7% or less, and even more preferably 6% or less. The haze value can be measured using a haze meter or the like. Generally, the smaller the value, the higher the transparency and the more preferable it is. However, taking into consideration the necessity of adding a certain amount of lubricant to the film in order to impart the slipperiness required for practical use, the lower limit is about 2%.

[0076] (2) Haze value / thickness It is also preferable that the haze value / thickness of the polyester heat-shrinkable film is 0.15% / μm or less. The reason for this is that if the haze value / thickness exceeds 0.15% / μm, the balance between recyclability and heat shrinkability may be reduced. Therefore, it is more preferable that the haze value / thickness is set to a value of 0.14% / μm or less, and even more preferable that the haze value is set to a value of 0.13% / μm or less. However, if the haze value / thickness becomes too small, the production control of the polyester heat-shrinkable film and the restrictions on the blended materials may become too strict. Therefore, the haze value / thickness is preferably set to a value of 0.03% / μm or more, more preferably to a value of 0.04% / μm or more, and even more preferably to a value of 0.05% / μm or more.

[0077] [Second embodiment] The second embodiment is a method for producing the polyester heat-shrinkable film of the first embodiment. Each step will be described below in detail.

[0078] 1. Preparation and mixing of raw materials As raw materials, recycled crystalline polyester resin pellets as shown in FIG. 11(b), a base material and additives such as a rubber-based resin, an antistatic agent, and a hydrolysis inhibitor are prepared. When preparing such raw materials, it is preferable to heat the recycled crystalline polyester resin pellets, which are the main component, at a predetermined temperature (for example, a temperature 10°C lower than the crystallization temperature) for a predetermined time (for example, 3 to 10 hours) to make them bone dry. Next, recycled crystalline polyester resin pellets and the like are preferably charged into the stirring vessel while being weighed, and mixed and stirred using a stirring device until homogeneous. As the crystalline polyester resin, in addition to recycled crystalline polyester resin pellets, non-recycled crystalline polyester resin pellets may also be used. That is, from an economical point of view, it is preferable to use a relatively large amount of recycled crystalline polyester resin pellets as the crystalline polyester resin, for example, 50% by weight or more of the total amount. On the other hand, in order to easily adjust the clumping fraction, melting point, heat of fusion, haze value, etc. to the desired range, it is preferable to use a relatively large amount of non-recycled crystalline polyester resin pellets, for example, 50% by weight or more of the total amount.

[0079] 2. Raw sheet production process Next, it is preferable to typically carry out extrusion molding (T-die method), inflation molding or cast molding to prepare a raw sheet of a predetermined thickness. More specifically, for example, extrusion molding is carried out using an extruder under the condition of an extrusion temperature of 245° C., and a raw sheet having a predetermined thickness (usually 200 to 300 μm) can be obtained.

[0080] 3. Preparation of polyester heat-shrinkable film Next, the obtained raw sheet is heated and pressed using a heat shrinkable film manufacturing device (tenter) while being moved over or between rolls to produce a polyester heat shrinkable film. However, known stretching methods for developing such shrinkability include inflation, roll stretching, tenter stretching, and combinations thereof. Furthermore, a combination of sheet molding by cast molding and roll stretching and tenter stretching is more preferable because it provides better productivity.

[0081] That is, it is preferable to crystallize the molecules of the polyester resin constituting the polyester-based heat-shrinkable film to a predetermined state by preheating at a predetermined preheating temperature, for example, a temperature in the range of 110 to 150°C, stretching the film in a predetermined direction at a predetermined stretching temperature, at a maximum stretching speed, and at a stretching ratio while basically expanding the film width and while heating and pressing the film. Then, by solidifying the film in this state at a predetermined heat setting temperature, for example, a temperature in the range of 60 to 80°C, a heat-shrinkable polyester heat-shrinkable film for use as decorations, labels, etc. can be produced. That is, after a raw film is produced by a T-die method, an inflation method, or the like, the raw film is usually heated to a temperature equal to or higher than the glass transition temperature of the resin, and stretched at least in the main stretching direction (the width direction of the raw film, i.e., the TD direction) by a factor of 3 to 8, preferably a factor of 4 to 6, at a maximum stretching speed of 40 to 67% / sec, preferably 45 to 62% / sec.

[0082] 4. Effect of maximum drawing speed (1) Relationship with the standard deviation of the specified heat shrinkage rate As shown by the characteristic curve L1 in FIG. 2(a) described above, it has been found that, assuming a predetermined clamping fraction, there is a predetermined correlation between the maximum stretching speed and the standard deviation of the heat shrinkage in the main shrinkage direction at 100°C for 10 seconds. Furthermore, as shown by the characteristic curve L1' in Figure 2(b), it has been found that there is a certain correlation between the maximum stretching speed and the standard deviation of thickness, regardless of whether the film has a certain clumping fraction. From this characteristic curve L1', it can be seen that when the maximum stretching speed is less than 40% / sec, the standard deviation of thickness exceeds at least 1.7 µm.

[0083] (2) Relationship with heat of crystallization Furthermore, as shown by the characteristic curve L3 in FIG. 4, it has been found that there is a predetermined correlation between the maximum stretching speed and the amount of heat of crystallization in the resulting polyester heat-shrinkable film. That is, under certain conditions, by setting the maximum stretching speed within a predetermined range, the value of the heat of crystallization in the resulting polyester heat-shrinkable film can be stably controlled to a value within a desired range. For example, by controlling the maximum stretching speed to within the range of 40 to 65% / sec, the value of the heat of crystallization in the resulting polyester heat-shrinkable film can be controlled to within the range of 12 to 15 mJ / mg.

[0084] (3) Relationship with glass transition temperature Furthermore, as shown by the characteristic curve L4 in FIG. 5, it has been found that there is a predetermined correlation between the maximum stretching speed and the glass transition temperature of the resulting polyester heat-shrinkable film. That is, by setting the maximum stretching speed within a predetermined range under certain conditions, the glass transition temperature of the resulting polyester heat-shrinkable film can be stably controlled to a value within a desired range. For example, by controlling the maximum stretching speed to within the range of 40 to 58% / sec, the glass transition temperature of the resulting polyester heat-shrinkable film can be controlled to around 74.5°C. Furthermore, for example, when the maximum stretching speed is in the range of more than 58% / sec and about 65% / sec, the glass transition temperature of the resulting polyester heat-shrinkable film tends to decrease from around 74.5°C to around 74.3°C. Furthermore, for example, it is understood that when the maximum stretching speed exceeds 65% / sec, the glass transition temperature of the resulting polyester heat-shrinkable film decreases steadily to 74.3°C or less, and this tends to persist.

[0085] (4) Relationship with heat of fusion (ΔHm) Furthermore, as shown by the characteristic curve L5 in FIG. 6, it has been found that there is a predetermined correlation (linear relationship) between the maximum stretching speed and the heat of fusion (ΔHm) of the resulting polyester-based heat-shrinkable film. That is, under certain conditions, by setting the maximum stretching speed within the range of, for example, 40 to 65% / sec, the crystallization temperature and heat of fusion of the resulting polyester-based heat-shrinkable film can be stably controlled to desired values ​​using a linear relationship. Conversely, if the maximum stretching speed exceeds, for example, 65% / sec, the correlation (linear relationship) decreases, and it is understood that it becomes difficult to control the heat of fusion to a desired value.

[0086] 5. Polyester heat shrinkable film inspection process It is preferable to provide a predetermined inspection process in which the following properties are measured continuously or intermittently for the produced polyester heat-shrinkable film. That is, by measuring the following characteristics and the like through a predetermined inspection process and confirming that the values ​​fall within a predetermined range, a polyester heat-shrinkable film having more uniform shrinkage characteristics can be obtained. 1) Visual inspection of the appearance of polyester heat shrinkable film 2) Thickness variation measurement 3) Tensile strength measurement (ASTM D882) 4) Tensile elongation measurement (ASTM D882) 5) Surface slipperiness test (ASTM D1894) 6) Specific gravity measurement (ASTM D792) 7) Ring crush test (TAPPI T882) 8) Tear strength measurement (ASTM D1922) [Example]

[0087] 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 crystalline polyester resin and non-crystalline polyester resin used in Example 1 and the like are as follows. The intrinsic viscosity (IV value) shown in the column for the amorphous polyester resin was measured in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (weight ratio=1 / 1) at a temperature of 30° C. using an Ubbelohde viscometer.

[0088] (PET1) As a crystalline polyester resin, PET1 (manufactured by Eastman Chemical Co., trade name "Embrace Encore"), glass transition temperature (Tg): 74°C, melting point: 217°C, density: 1.3 g / cm 3 ) was prepared. (PET2) As a crystalline polyester resin different from PET1, PET2 (dicarboxylic acid: terephthalic acid 98.6 mol%, isophthalic acid 1.4 mol%, diol: ethylene glycol 97.3 mol%, diethylene glycol 2.7 mol%) was used. The crystalline polyester resin (glass transition temperature (Tg): 78°C, melting point: 251°C, intrinsic viscosity (IV value): 0.72, density: 1.3 g / cm) was used. 3 )) was prepared. Specifically, it was a crystalline polyester resin that was recycled from commercially available PET bottles and pelletized as shown in Figure 11(b). PET2 was used only in Evaluation 1 (clumping fraction) in the examples described below. FIG. 10(b) shows an example of a DSC chart of PET2 obtained by DSC measurement in accordance with JIS K7121:2012. That is, using a DSC device, in Step 1, the temperature of the measurement sample is increased from 30°C to 300°C at a rate of 10°C / min. Next, in Step 2, the temperature is suddenly decreased from 300° C. to 0° C. at a rate of 100° C. / min (not shown in FIG. 10(b)). Furthermore, in Step 3, the temperature is increased from 0°C to 300°C at a rate of 10°C / min. Then, the glass transition temperature, melting peak, etc. that define the properties of PET2 can be accurately determined from the temperature of the specific heat change point and the temperature of the peak point of the DSC curve obtained in Step 1 and Step 3.

[0089] (PETG) As the amorphous polyester resin, PETG (dicarboxylic acid: 100 mol% terephthalic acid, diol: ethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol) was used (manufactured by Eastman Chemical Co., trade name "Embrace LV"; glass transition temperature (Tg): 68.2°C; no melting point; intrinsic viscosity (IV value): 0.7; density: 1.3 g / cm). 3 )) was prepared.

[0090] (additives) As an additive (anti-blocking agent), a silica masterbatch (manufactured by Sukano Corporation, product name "G dc S559-E", containing 20% ​​by weight of silica) was prepared by blending 20 parts by mass of silica with 80 parts by mass of polyethylene terephthalate resin.

[0091] [Example 1] 1. Preparation of polyester heat-shrinkable film As the crystalline polyester resin, the above-mentioned PET1 was prepared. Next, 1000 g of the prepared PET1 was placed in the stirring vessel. In addition, as an anti-blocking agent for the heat shrinkable film, the above-mentioned anti-blocking agent dried under specified conditions was blended in a ratio of 1 part by weight per 100 parts by weight of PET1 to form a raw material for forming the heat shrinkable film.

[0092] Next, this raw material for forming a heat shrinkable film was extruded using a vented twin-screw extruder at an extrusion temperature of 245° C. to obtain a raw sheet having a thickness of 250 μm. Finally, using a heat-shrinkable film manufacturing device, a polyester heat-shrinkable film with a set thickness of 50 μm was produced from the raw sheet at a preheating temperature of 125°C, a maximum stretching speed of 56% / sec, a stretching temperature of 86°C, a heat-setting temperature of 72°C, and a stretching ratio (MD direction: 1.07 times, TD direction: 4.8 times).

[0093] 2. Evaluation of polyester heat-shrinkable film (1) Evaluation 1 (clamping fraction) As shown in Table 1, PET1, PET2, and PETG were appropriately blended to obtain a polyester resin. Next, the clumping fraction of the polyester resin (crystalline polyester resin, amorphous polyester resin, or a mixture thereof) was measured in accordance with APR Document Code: PET-S-08, and evaluated according to the following criteria. ◎: The clumping fraction is 1% or less. ◯: The clumping fraction is 1.2% or less. △: The clumping fraction is 1.4% or less. ×: The clumping fraction is more than 1.4%.

[0094] (2) Evaluation 2 (DSC measurement of polyester heat shrinkable film) The melting point (melting peak temperature) and other properties of the obtained polyester heat-shrinkable film were measured under predetermined conditions using a DSC device (manufactured by Hitachi High-Tech Science Corporation, product name "DSC7000X"). More specifically, a sample of the polyester heat-shrinkable film was dried in a dry oven at 60° C. for 6 hours or more. Next, the sample was set in a differential scanning calorimeter and heated once to a high temperature range in Step 1 (heating rate 10°C / min from 25°C to 250°C). Next, in Step 2, the temperature was lowered to the low temperature range (from 250°C to 25°C at a rate of 10°C / min). Finally, in Step 3, the temperature was raised again to the high temperature range (from 25°C to 250°C at a rate of 10°C / min). Then, as shown in FIG. 10(a), the glass transition temperature, crystallization temperature, heat of crystallization, melting point (melting peak temperature), and heat of fusion (ΔHm) corresponding to the melting peak area were measured from the obtained DSC curve.

[0095] (3) Evaluation 3 (Thermal shrinkage rate) The heat shrinkage rate of the obtained polyester heat shrinkable film was measured in accordance with ASTM D2732-08. That is, it was cut into a rectangular shape having a length of 100 mm along the main shrinkage direction (TD direction) and a length of 100 mm along the non-shrinkage direction (MD direction), and this was used as a measurement sample. The obtained polyester heat-shrinkable film was then immersed for 10 seconds in a thermostatic bath containing hot water at temperatures controlled in 10°C increments of 60, 70, 80, 90, and 100°C, respectively, to cause heat shrinkage. Next, at each temperature, the heat shrinkage rate (%) in the main shrinkage direction (TD) and the non-shrinkage direction (MD) was calculated from the dimensional change before and after the heat treatment according to the following formula (5).

[0096]

number

[0097] (4) Rating 4 (standard deviation of heat shrinkage rate) The heat shrinkage rate of the obtained polyester heat-shrinkable film was measured in accordance with ASTM D2732-08 according to the following procedure, and the standard deviation was calculated. First, eight measurement samples were obtained from the obtained polyester heat-shrinkable film, evenly spaced in the width direction. That is, the sheet was cut into a rectangular shape with a length of 100 mm along the main shrinkage direction (TD direction) and a length of 100 mm along the non-shrinkage direction (MD direction), and eight of these were prepared as measurement samples. Next, as a pretreatment, the eight prepared measurement samples were left in an atmosphere of 23°C and 50% RH for 40 hours or more. Next, each of the eight pretreated measurement samples was immersed for 10 seconds in a thermostatic bath containing temperature-controlled hot water at 100°C, causing thermal shrinkage. Next, the heat shrinkage rate (%) in the main shrinkage direction (TD direction) was calculated from the dimensional changes before and after the heat treatment according to the above formula (5). Next, the standard deviation was further calculated from the calculated thermal shrinkage rates of the eight measurement samples, and evaluated according to the following criteria. ⊚: The standard deviation of the heat shrinkage rate is 1.0% or less. Good: The standard deviation of the heat shrinkage rate is 1.5% or less. △: The standard deviation of the heat shrinkage rate is 2.5% or less. ×: The standard deviation of the heat shrinkage rate exceeds 2.5%.

[0098] (5) Ratings 5 ​​and 6 (thickness and standard deviation) The thickness of the obtained polyester heat-shrinkable film was measured at 20 equally spaced points across the width of the film using a micrometer (manufactured by Mitutoyo Corporation, product name "Thickness Gauge 547-401") in accordance with ISO 4593, and the average value was calculated to be the thickness (average thickness). Furthermore, the standard deviation was further calculated from the 20 measured values ​​used to calculate the thickness (average thickness) of the obtained polyester heat-shrinkable film, and evaluated according to the following criteria. ⊚: The standard deviation of the thickness is 1.4 μm or less. ◯: The standard deviation of the thickness is 1.7 μm or less. △: The standard deviation of the thickness is 2 μm or less. ×: The standard deviation of the thickness is more than 2 μm.

[0099] (6) Rating 7 (Haze value) The haze value of the obtained polyester heat-shrinkable film was measured in accordance with ASTM D1003 using a haze meter (manufactured by BYK, product name "haze-gard dual"), and evaluated according to the following criteria. A: The haze value is 7% or less. Good: Haze value is 8% or less. △: Haze value is 10% or less. ×: The haze value exceeds 10%.

[0100] (7) Rating 8 (wearability / appearance) An eggplant-shaped PET bottle (trade name "Limmi Lemon Juice", volume: 200 ml) filled with commercially available drinking water was prepared. Next, a polyester heat-shrinkable film was slit to a width of 20.5 cm to obtain a long sample, and 1,3-dioxolane was applied to the end portions in the width direction of the sample. Next, the widthwise ends were overlapped and glued together with an overlap of about 1 cm to form a cylindrical label with a diameter of about 6.2 cm. This cylindrical label was then cut into 11 cm pieces in the longitudinal direction to obtain a plurality of cylindrical labels. Next, the tubular label was placed over the body of the prepared, roughly cylindrical PET bottle, and then placed on a belt conveyor through a steam tunnel maintained at 80°C, while being heated and moved for 8 seconds, causing the tubular label to thermally shrink so that it adhered tightly to the body of the roughly cylindrical PET bottle from the top to the bottom.

[0101] Next, the tubular labels after heat shrinkage were visually inspected to see if they were not properly attached to the PET bottle within the specified length (5 mm or more) and width (1 mm or more), or if there were any spots or wrinkles, and the fit was evaluated according to the following criteria. ⊚: No poor attachment, spots or wrinkles were observed in any of the five cylindrical labels. ○: No poor attachment, spots or wrinkles were observed in 3 or more of the 5 cylindrical labels. △: No poor attachment, spots or wrinkles were observed in one or more of the five cylindrical labels. ×: Poor attachment, spots, or wrinkles were observed in all of the five cylindrical labels.

[0102] [Example 2] In Example 2, polyester heat-shrinkable films were prepared and evaluated in the same manner as in Example 1, except that the preheating temperature (°C) and maximum stretching speed (% / sec.) were changed as shown in Table 1. The results obtained are shown in Table 2.

[0103] [Example 3] In Example 3, the polyester heat-shrinkable film was prepared and evaluated in the same manner as in Example 1, except that the set thickness of the polyester heat-shrinkable film was 45 μm and the maximum stretching speed (% / sec.) and other factors were changed as shown in Table 1. The results obtained are shown in Table 2.

[0104] [Examples 4 to 5] In Examples 4 and 5, polyester heat-shrinkable films were prepared and evaluated in the same manner as in Example 1, except that the stretching temperature (°C), heat setting temperature (°C), and maximum stretching speed (% / sec.) were changed as shown in Table 1. The results obtained for each are shown in Table 2.

[0105] [Example 6] In Example 6, a polyester heat-shrinkable film was produced and evaluated in the same manner as in Example 1, except that the above-mentioned PET1 and PETG (blending ratio = 80 / 20) were used as the PET resin as shown in Table 1. The obtained results are shown in Table 2.

[0106] [Comparative Example 1] In Comparative Example 1, a polyester heat-shrinkable film was prepared and evaluated in the same manner as in Example 1, except that the preheating temperature (°C), stretching temperature (°C), and maximum stretching speed (% / sec.) were changed as shown in Table 1. The obtained results are shown in Table 2.

[0107] Comparative Example 2 In Comparative Example 2, a polyester heat-shrinkable film was prepared and evaluated in the same manner as in Example 1, except that the above-mentioned PET1 and PETG (blending ratio = 80 / 20) were used as the PET resin and the preheating temperature (°C), stretching temperature (°C), heat setting temperature (°C), and maximum stretching speed (% / sec.) were changed as shown in Table 1. The obtained results are shown in Table 2.

[0108] Comparative Example 3 In Comparative Example 3, a polyester heat-shrinkable film was prepared and evaluated in the same manner as in Example 1, except that the above-mentioned PET1 and PETG (blending ratio = 60 / 40) were used as the PET resin and the preheating temperature (°C), stretching temperature (°C), heat setting temperature (°C), and maximum stretching speed (% / sec.) were changed as shown in Table 1. The obtained results are shown in Table 2.

[0109] [Table 1]

[0110] [Table 2] [Industrial Applicability]

[0111] According to the present invention, by controlling at least the predetermined properties (A) to (C) such as the clamping fraction and the heat shrinkage rate (D1) to (D4), a good balance between recyclability and heat shrinkability is achieved. In other words, by using a primarily crystalline polyester resin, as in recycled PET, and strictly controlling the specified clamping ratio, etc., it has become possible to effectively prevent the mutual sticking phenomenon even when recycling PET bottles with polyester heat-shrinkable film still attached, and to effectively and stably produce the desired recycled pellets. Furthermore, this has made it possible to reduce variations in the heat shrinkage rate and thickness of polyester heat shrinkable films, and to control the heat shrinkage stress that occurs during heat shrinkage, thereby providing polyester heat shrinkable films that exhibit excellent wearability and appearance over a wide temperature range.

[0112] Furthermore, with the polyester heat-shrinkable film of the present invention, regardless of the thickness, even if the heat-shrinkage temperature or the like changes slightly and the desired heat-shrinkage rate cannot be obtained, it is possible to accurately correct the temperature and control the heat-shrinkage rate within the desired range. Therefore, it can exhibit excellent attachment properties and appearance to various PET bottles, etc., and moreover, it can be recycled together with various PET bottles, etc. while remaining attached, which significantly expands its versatility while maintaining environmental and economical efficiency, and it can be said that its industrial applicability is extremely high. [Explanation of symbols]

[0113] 10: Polyester heat shrinkable film 10a: Other resin layer 1 10b: Another resin layer 2 10c: Shrinkage rate adjustment layer

Claims

1. A polyester-based heat-shrinkable film derived from a polyester resin that is a reaction product of a polycarboxylic acid and a polyalcohol, characterized in that the polyester-based heat-shrinkable film has the following properties (A) to (C) and (D1) to (D4): (A) The clumping fraction in a mixture of the polyester resin and another PET resin, measured in accordance with APR Document Code: PET-S-08, is set to a value of 1.2% or less. (B) The melting point of the polyester resin measured by DSC is set to a value within the range of 190 to 230°C. (C) The heat of fusion corresponding to the melting peak area at the melting point of the polyester heat-shrinkable film measured by DSC is set to a value within the range of 25 to 45 mJ / mg. (D1) The heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 60°C for 10 seconds is set to a value within the range of 0 to 5%. (D2) The heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 70°C for 10 seconds, is set to a value within the range of 25 to 50%. (D3) The heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 80°C for 10 seconds, is set to a value within the range of 55 to 85%. (D4) The standard deviation of the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds is 1.5% or less.

2. (D4') The polyester-based heat-shrinkable film according to claim 1, characterized in that the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 95 ° C to 100 ° C for 10 seconds is 70% or more.

3. (D5) The polyester-based heat-shrinkable film according to claim 1, characterized in that the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 60 to 80°C and 10 seconds satisfies the following relational expression (1): [Equation 1] a: corresponds to the slope of the relational expression (1), and is a value of 3.25 or more and 4 or less b: a constant in the relational expression (1) that is equal to or greater than 0 and equal to or less than 5

4. (D5') The polyester-based heat-shrinkable film according to claim 1, characterized in that the heat shrinkage rate in the main shrinkage direction measured under heat shrinkage conditions of 60 to 80°C and 10 seconds satisfies the following relational expression (2): [Equation 2] a': corresponds to the slope of the relational expression (2), and is a value of 3.3 or more and 3.75 or less b': a constant in the relational expression (2) that is equal to or greater than 0 and equal to or less than 5

5. (D5") The polyester-based heat-shrinkable film according to claim 1, characterized in that the heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 60 to 80°C and 10 seconds, satisfies the following relational expression (3): [Equation 3] a': corresponds to the slope of the relational expression (3), and is a value of 3.35 or more and 3.5 or less b': a constant in the relational expression (3) that is equal to or greater than 0 and equal to or less than 5

6. (D6) The polyester-based heat-shrinkable film according to claim 1, characterized in that the heat shrinkage rate in the direction perpendicular to the main shrinkage direction, measured under heat shrinkage conditions of 70°C and 10 seconds, is set to a value within the range of -3 to 5%.

7. The polyester-based heat-shrinkable film according to claim 1, characterized in that the thickness of the film is set to a value within the range of 10 to 100 μm, and the standard deviation of the thickness measured under specified conditions is 1.7 μm or less.

8. 2. The polyester-based heat-shrinkable film according to claim 1, wherein the polyester resin is a mixture of a crystalline polyester resin and a non-crystalline polyester resin, and the weight blending ratio is within the range of 100:0 to 80:20.

Images