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] This invention relates to a polyester-based heat-shrinkable film. More specifically, this invention relates to a polyester-based heat-shrinkable film that offers a good balance between recyclability and heat shrinkability, can be recycled together with used PET bottles while still attached, and adjusts the resulting heat shrinkage rate even if the heat shrinkage temperature changes slightly, resulting in excellent attachability and appearance. [Background technology]

[0002] Traditionally, polyethylene (HDPE) bottles and polyester (PET) bottles (hereinafter sometimes simply referred to as PET bottles) have been widely used as beverage storage containers, detergent storage containers, and the like. In particular, PET bottles are widely used worldwide as beverage storage containers due to their lightweight nature, excellent durability, and high level of convenience. On the other hand, these PET bottles are discarded into rivers after use, and their subsequent runoff into the ocean and other areas is causing serious environmental problems. Therefore, in order to solve these environmental problems, research into collection and recycling technologies for PET bottles is being actively conducted.

[0003] Furthermore, PET bottles are covered with a designated label to display various information about their name and contents, and to improve their decorative appearance. In other words, the mainstream practice is to use a heat-shrinkable polyester film as a label, and to completely wrap the PET bottle with a label. More specifically, polyester-based heat-shrinkable films derived from amorphous polyester resin (PETG) are widely used to obtain good heat shrinkability.

[0004] However, PETG has a problem in that it does not have a melting point due to its thermal properties, and in the recycling process of PET bottles wrapped in heat-shrinkable film, it is prone to causing the recycled pellets to stick together. In other words, when PET bottles packaged in heat-shrinkable film were subjected to thermal melting during the recycling process, as shown in Figure 11(a), a problem was observed where the heat-shrinkable film caused the recycled pellets containing the film to stick together, forming clumps and causing blockages in the piping. Therefore, when PET bottles, including the heat-shrinkable film, are melted, the resulting recycled pellets do not adhere to each other, making it difficult to effectively and stably produce pellets of a predetermined shape using a pelletizer, as shown in Figure 11(b).

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

[0006] Furthermore, Patent Document 2 also describes a polyester-based heat-shrinkable film aimed at obtaining excellent recyclability and other properties. More specifically, as shown in Figures 12(a) and 12(b), this invention aims to control the melting point and crystallization temperature of the polyester heat-shrinkable film by controlling the clamping fraction measured under predetermined conditions to 10% or less, as shown by characteristic curves L6 and L6'. For example, this is a polyester heat-shrinkable film in which 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%, 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 the range of 170 to 240°C.

[0007] On the other hand, Patent Document 3 describes a polyester heat-shrinkable film that aims to improve printability and other properties for polyester heat-shrinkable films, and to limit the rate of change in the heat shrinkage rate for each predetermined temperature range, thereby exhibiting excellent finish when attached to PET bottles and the like. More specifically, the heat-shrinkable polyester film is characterized by the temperature-dependent change rate (% / °C) of the heat shrinkage rate in the main shrinkage direction being 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] Japanese Patent Publication No. 2020-521823 (Claims, etc.) [Patent Document 2] Japanese Patent Publication No. 2022-510146 (Claims, etc.) [Patent Document 3] Japanese Patent Publication No. 2011-184690 (Claims, etc.) [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, while the polyester heat-shrinkable films disclosed in Patent Document 1 and Patent Document 2 achieve reasonable recyclability by keeping the aggregation fraction and clamping fraction values ​​measured under predetermined conditions below predetermined values, they exhibit a problem in that the value of the heat shrinkage rate in a predetermined temperature range tends to vary. In other words, because crystalline polyester resins with a wide range of melting points are used, a problem was observed in all cases where the value of the thermal shrinkage rate tended to vary within a specified temperature range (60-100°C), particularly in the temperature range around 70°C. Therefore, unevenness and wrinkles are more likely to occur during heat shrinkage, resulting in poor appearance and ease of attachment. As a result, a good balance between the recyclability and heat shrinkability of polyester heat shrinkable films has yet to be achieved.

[0010] On the other hand, the polyester heat-shrinkable film disclosed in Patent Document 3 does not take into account the clamping fraction measured under predetermined conditions, and when recycled while still attached to used PET bottles, it is prone to adhesion (mutual adhesion). Furthermore, in all the examples (Examples 1-4), the heat shrinkage rate at 70°C for 10 seconds was in the range of approximately 15-30%, which is considerably low. This resulted in problems with the usability of the polyester heat shrinkable film and the inability to obtain stable heat shrinkage.

[0011] Therefore, in view of the above problems, the inventors of the present invention have made diligent efforts and have found that the conventional problems can be solved by using a polyester-based heat shrinkable film derived from polyester resin, and by controlling at least predetermined characteristics (A) to (B) such as the clamping fraction of the raw material resin, and predetermined characteristics (C), (D1) to (D4) as a polyester-based heat shrinkable film. 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 any changes in the heat shrinkage temperature, etc., that cause the heat shrinkage rate to fall outside the desired range, thereby providing a polyester heat-shrinkable film with excellent attachability 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 which is a reaction product of a polyvalent carboxylic acid and a polyalcohol, characterized by having the following characteristics (A) to (C) and (D1) to (D4), and the above-described problems can be solved. (A) The clamping fraction (hereinafter, may be simply referred to as the clamping fraction) in a mixture of a 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 measured by DSC of the polyester resin 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 measured by DSC of the polyester-based heat-shrinkable film 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 value 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 a value of 1.5% or less. That is, by satisfying the configurations (A) to (C) and (D1) to (D4) in this way, for the polyester resin which is the raw material resin of the polyester-based heat-shrinkable film, another PET resin (such as recycled PET resin) is mixed, and the clamping fraction measured under certain conditions, the melting point of the polyester resin as the raw material resin, further, the heat of fusion, and the heat shrinkage rate at a predetermined temperature are controlled within a predetermined range, so that the balance between recyclability and heat shrinkability can be made good. Therefore, even when the polyester-based heat-shrinkable film is attached to a predetermined PET bottle and recycled together, and even when the heat shrinkage temperature or the like changes from a relatively low temperature condition to a high temperature condition and the heat shrinkage rate does not fall within the desired range, it can be corrected to provide a polyester-based heat-shrinkable film excellent in attachment properties and appearance properties.

[0013] Further, in forming the polyester-based heat-shrinkable film of the present invention, as the characteristic (D4'), it is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction) measured under the heat shrinkage conditions of 95°C to 100°C for 10 seconds is 70% or more. By controlling the heat shrinkage rate in such a high temperature range as well, it becomes easier to control the value of the heat shrinkage rate at 60 to 80°C in a relatively low temperature range to the desired range accordingly, and thus, the attachment properties and appearance properties during heat shrinkage of the film can be further improved.

[0014] Further, in forming the polyester-based heat-shrinkable film of the present invention, as the characteristic (D5), it is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction) measured under the heat shrinkage conditions of 60 to 80°C for 10 seconds satisfies the following relational expression (1). By making the heat shrinkage temperature and the heat shrinkage rate satisfy the predetermined relational expression (1) in such a predetermined temperature range, their values can be controlled linearly. Therefore, even when the heat shrinkage temperature or the like changes and the heat shrinkage rate does not fall within the desired range while maintaining good recyclability, it can be corrected to obtain accurate and good heat shrinkage properties.

[0015]

Number

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

[0017] Furthermore, in constructing the polyester 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 60-80°C and 10 seconds, satisfies the following relational expression (2). In this way, within a predetermined temperature range, the thermal shrinkage temperature and the thermal shrinkage rate satisfy a predetermined relation (2), allowing their values ​​to be controlled linearly within a narrower range while maintaining good recyclability.

[0018]

number

[0019] a': Corresponds to the slope of relation (2), and is a value between 3.3 and 3.75. b': Corresponds to the constant in relation (2), and is a value between 0 and 5 (inclusive).

[0020] Furthermore, in constructing the polyester 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 60-80°C and 10 seconds, satisfies the following relational expression (3). In this way, within a predetermined temperature range, the thermal shrinkage temperature and the thermal shrinkage rate satisfy a predetermined relation (3), allowing their values ​​to be controlled linearly within an even narrower range.

[0021]

number

[0022] a'': Corresponds to the slope of relation (3), and is a value between 3.35 and 3.5. b'': Corresponds to the constant in relation (3), and is a value between 0 and 5 (inclusive).

[0023] Furthermore, in constructing the polyester heat-shrinkable film of the present invention, it is preferable that the characteristic (D6) is such 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%. By limiting the thermal shrinkage rate in the MD direction under predetermined temperature conditions, even when coating the PET bottle and thermal shrinking it at relatively low temperatures, the fit and appearance are improved. As a result, deformation of letters and figures is reduced, making it easier to obtain accurate information. Furthermore, by restricting the thermal shrinkage rate in the MD direction in this way, the overall thermal shrinkage properties of the polyester-based heat-shrinkable film can be balanced, and even when recycled together with PET bottles, the adhesiveness and fluidity can be controlled, allowing for the stable production of pellets.

[0024] Furthermore, when constructing the polyester heat-shrinkable film of the present invention, it is preferable that the average thickness of the film be within the range of 10 to 100 μm, and that the standard deviation of the average thickness measured under predetermined conditions be 1.7 μm or less. By limiting the film thickness and its standard deviation, the balance between recyclability and heat shrinkability is further improved, making it possible to obtain a polyester-based heat shrinkable film with precisely controlled heat shrinkability, transparency, and excellent mechanical properties.

[0025] Furthermore, in constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the polyester resin is a mixture of crystalline polyester resin and amorphous polyester resin, with a weight mixing ratio within the range of 100:0 to 80:20. By controlling the weight-to-weight ratio in this way, the balance between recyclability and heat shrinkability can be further improved, resulting in a polyester-based heat-shrinkable film with precisely controlled heat shrinkability, ease of attachment, appearance, transparency, and excellent mechanical properties. [Brief explanation of the drawing]

[0026] [Figure 1] Figures 1(a) to 1(c) are diagrams illustrating the morphology of polyester heat-shrinkable films. [Figure 2] Figure 2(a) is provided to illustrate the relationship between the maximum stretching speed when creating 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, and Figure 2(b) is provided to similarly illustrate the relationship between the maximum stretching speed and the standard deviation of the thickness. [Figure 3] Figure 3 is provided to illustrate the relationship between the standard deviation of the heat shrinkage rate in the main shrinkage direction at 100°C and 10 seconds in a polyester heat shrinkable film prepared at a predetermined maximum stretching speed, and the evaluation (relative value) of the clamping fraction. [Figure 4] Figure 4 illustrates the relationship between the maximum stretching speed and the amount of heat required for crystallization when creating a polyester heat-shrinkable film. [Figure 5] Figure 5 is provided to illustrate the relationship between the maximum stretching speed when creating a polyester heat-shrinkable film and the glass transition temperature of the polyester heat-shrinkable film. [Figure 6] Figure 6 is provided to illustrate the relationship between the maximum stretching rate and the heat of fusion. [Figure 7] Figure 7 is provided to illustrate the region (S1) defined by relation (1) in the present invention. [Figure 8] Figure 8 is provided to illustrate the region (S2) defined by relation (2) in the present invention. [Figure 9] Figure 9 is provided to illustrate the region (S3) defined by relation (3) in the present invention. [Figure 10] Figure 10(a) is a DSC chart of the polyester heat shrink film of Example 1, and Figure 10(b) is a DSC chart of the polyester resin (PET2) used when measuring the clamping fraction in Example 1, etc. [Figure 11]Figure 11(a) is a conceptual diagram showing the bonding state of a conventional PET bottle coated with a polyester heat-shrinkable film, and Figure 11(b) is a conceptual diagram showing recycled PET resin obtained in the recycling process, derived from a PET bottle coated with the polyester heat-shrinkable film of the present invention. [Figure 12] Figure 12(a) is a diagram showing the relationship between clamping fraction and melting point in Patent Document 2 (Conventional 2), and Figure 12(b) is a diagram showing the relationship between clamping fraction and heat of crystallization in the same Patent Document 2. [Modes for carrying out the invention]

[0027] [First Embodiment] The first embodiment is a polyester-based heat-shrinkable film derived from a polyester resin, which is a reaction product of a polycarboxylic acid and a polyalcohol, as illustrated in Figures 1(a) to (c). Furthermore, a polyester-based heat-shrinkable film is provided that satisfies the following characteristics (A) to (C) and (D1) to (D4). (A) The clamping 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, as measured by DSC, shall be within the range of 190 to 230°C. (C) The amount of heat of fusion corresponding to the melting peak area at the melting point measured by DSC of the polyester heat shrink film shall be a value within the range of 25 to 45 mJ / mg. (D1) The thermal shrinkage rate in the main shrinkage direction, measured under thermal shrinkage conditions of 60°C for 10 seconds, shall be within the range of 0 to 5%. (D2) The thermal shrinkage rate in the main shrinkage direction, measured under thermal shrinkage conditions of 70°C for 10 seconds, shall be within the range of 25-50%. (D3) The thermal shrinkage rate in the main shrinkage direction, measured under the thermal shrinkage conditions of 80°C for 10 seconds, shall be within the range of 55-85%. (D4) The standard deviation of the thermal shrinkage rate in the main shrinkage direction, measured under thermal shrinkage conditions of 95°C to 100°C for 10 seconds, shall be 1.5% or less. The polyester heat-shrinkable film of the first embodiment will be described in detail below, divided into its constituent elements, with reference to the drawings as appropriate.

[0028] 1. Polycarboxylic acid As a polycarboxylic acid used as one of the constituent components (raw material components) of polyester resin, there are no particular limitations as long as it is a compound that can react with polyalcohol to form a polyester structure. Examples include at least one of the following: 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; or ester-forming derivatives thereof.

[0029] In particular, terephthalic acid is preferred because it reacts well with polyalcohols, readily forms a crystalline polyester structure, and is relatively inexpensive, making it economically advantageous. Therefore, when the total amount of polycarboxylic acid used is 100 mol%, it is preferable to use terephthalic acid at a value of 90 mol% or more, and more preferably at a value within the range of 95 to 100 mol%.

[0030] 2. Polyalcohol (1) Types Furthermore, the polyalcohol used as one of the components of the polyester resin is not particularly limited as long as it is a compound having multiple reactive hydroxyl groups. However, it is also preferable to include at least one of the following: aliphatic diols such as ethylene glycol, diethylene glycol, propanediol, butanediol, neopentyl glycol, and hexanediol, or alicyclic diols other than 1,4-cyclohexanedimethanol, or aromatic diols. This is because using such polyalcohols makes it easier to obtain polyester resins with controlled crystallinity and other properties within a predetermined range by reacting them appropriately with polycarboxylic acids.

[0031] Furthermore, it is more preferable to use one or more diols selected from ethylene glycol, diethylene glycol, neopentyl glycol, etc., in these polyalcohols. In other words, by using these specific polyalcohols, the melting point, thermal shrinkage rate, thermal shrinkage stress, etc., of the polyester resin obtained by reacting it with a polycarboxylic acid can be more easily adjusted to values ​​within a predetermined range.

[0032] Therefore, when the total amount of polyalcohol used is 100 mol%, it is preferable to use one or more diols selected from ethylene glycol, diethylene glycol, neopentyl glycol, etc., at a value of 90 mol% or more, and more preferably at a value within the range of 95 to 100 mol%. Furthermore, other dicarboxylic acids and diols, or hydroxycarboxylic acids, may be used as needed to alter the thermal and mechanical properties of the polyester heat-shrinkable film, either individually or in combination as a mixture.

[0033] (2) Amount of reaction Furthermore, while there are no particular restrictions on the amount of polyalcohol to be reacted, it is generally preferable to react 100 moles of a polycarboxylic acid containing 80 mol% or more of terephthalic acid with 130 to 220 moles of polyalcohol, more preferably 150 to 210 moles, and even more preferably 180 to 200 moles. In addition, it is preferable that the resulting product be a polyester resin obtained by crystallizing these reactants.

[0034] In that case, as a guideline for the crystallinity of the polyester resin, it is preferable that the degree of crystallinity calculated from the DSC curve measured in accordance with JIS K 7122:2012 be in the range of 1 to 15%, more preferably in the range of 2 to 10%, and even more preferably in the range of 3 to 8%. In other words, in such a DSC curve, the heat of fusion (ΔHm) obtained from the melting peak area and the heat of crystallization (ΔHc) obtained from the crystallization peak area are used, and the heat of complete crystallization of crystallized polyethylene terephthalate (ΔHm) is used. 0 From this, the degree of 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 a raw material for the polyester heat-shrinkable film, the clamping fraction of the polyester resin, etc., which is 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. The reason for this is that if the clamping fraction exceeds 1.2%, recyclability may be significantly reduced, or the variation in the rate of heat shrinkage may increase. As a result, it becomes difficult to suppress the occurrence of unevenness or wrinkles during heat shrinkage when the heat shrinkage temperature changes slightly, and to maintain good fit. However, if the clamping fraction is set to an excessively small value, the yield may decrease significantly, or the types of compounding components that can be used in the polyester resin may be excessively restricted. Therefore, it is more preferable to set the clamping fraction of polyester resin, etc., to a value in the range of 0.01 to 1%, and even more preferable to set it to a value in the range of 0.1 to 0.8%.

[0038] In the case of conventional polyester resins, the polyester heat-shrinkable films constructed from them are preferably characterized by a heat shrinkage rate of 0% to 50% at 70°C for 10 seconds. As a result, the melting point varies considerably, and consequently, the S-shaped characteristic curve tends to change easily. Therefore, in the case of conventional polyester heat-shrinkable films derived from polyester resin, the heat shrinkage temperature varied, and even if the desired heat shrinkage rate could not be obtained, it was not possible to correct this quickly and accurately. In contrast, in the present invention, since the thermal shrinkage temperature and thermal shrinkage rate change linearly, even if the thermal shrinkage temperature fluctuates and the desired thermal shrinkage rate cannot be obtained temporarily, the clamping fraction of polyester resin, etc., can be controlled, and the desired thermal shrinkage rate can be stably obtained in accordance with the relational equations (1) to (3) described later.

[0039] Furthermore, the clamping fraction of polyester resin, etc., in accordance with APR Document Code:PET-S-08, can be measured under the following measurement conditions. 1) Preheat the oven to 210°C. 2) Next, PET flakes (corresponding to a mixture of polyester resin and other PET resins) with an initial weight (1 kg), obtained by washing, elutriating, and crystallizing PET bottles, etc., with the polyester heat shrink film attached, are placed in a 22 x 33 cm baking pan lined with aluminum foil. 3) Next, the PET flakes placed in the baking pan are heated in an oven maintained at a predetermined temperature for 90 minutes. 4) Next, remove the baking pan from the oven and let it cool to room temperature. 5) Remove the PET flakes from the baking pan and place them on a sieve with a stainless steel mesh opening of 12.5 mm. 6) The sieve containing the PET flakes is vibrated by hand until all of the PET flakes have been sieved through. The flakes that pass through the mesh are then collected below. Any PET flakes that do not pass through the mesh and remain on the mesh (aggregates) are removed as appropriate. 7) Weigh the aggregates that cannot pass through the mesh. Also, weigh the PET flakes attached to the aluminum foil and any residue separately. 8) The clamping fraction is calculated from the weight of PET flakes (aggregates) 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 for the polyester heat-shrinkable film, is defined as the temperature at which the maximum value of the melting peak in the DSC curve is shown, and is characterized by being set to a value within the range of 190 to 230°C. The reason for this is that when the melting point is below 190°C, the labels made of polyester heat-shrinkable film may easily melt during the drying process when recycling PET bottles. This can cause the recycled PET bottle fragments to stick together and aggregate (clump). On the other hand, if the melting point exceeds 230°C, the amount of heat required for extrusion and stretching of the polyester heat-shrinkable film raw material used for labels becomes too high, which can make processing difficult.

[0041] Therefore, it is more preferable to set the melting point of the polyester resin to a value in the range of 195 to 225°C, and even more preferable to set it to a value in the range of 200 to 220°C. In other words, while controlling the melting point of the polyester resin is important, by setting its range (the difference between the maximum and minimum values) to 25°C or less, and more preferably to 15°C or less, an even better balance between recyclability and heat shrinkability can be achieved, even when crystalline polyester resin is the main component (for example, 80% by weight or more). Furthermore, the melting point of polyester resin can be measured, for example, as the peak melting 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 hereafter). Furthermore, the crystallinity of the polyester resin can be estimated from the area at the peak of the heat of fusion (peak area) and the full width at half maximum (FMAX).

[0042] (3) Average molecular weight Furthermore, it is preferable that the intrinsic viscosity (IV value), which is the average molecular weight of the polyester resin, be within the range of 0.65 to 0.85 dL / g. The reason for this is that if the intrinsic viscosity falls below 0.65 dL / g, the melt viscosity becomes too low, which can cause problems with extrusion moldability. On the other hand, if the intrinsic viscosity exceeds 0.85 dL / g, the melt viscosity becomes too high, which can cause problems with extrusion moldability.

[0043] Therefore, it is more preferable to have an intrinsic viscosity within the range of 0.68 to 0.83 dL / g, and even more preferable to have a value within the range of 0.7 to 0.8 dL / g. In other words, while controlling the intrinsic viscosity of the polyester resin is important, by setting its range (the 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 the main component (for example, 80% by weight or more). The intrinsic viscosity of polyester resin can be measured in accordance with JIS K 7390 (the same applies hereafter).

[0044] (4) Additives Furthermore, it is preferable to incorporate additives such as antioxidants, weather stabilizers, antistatic agents, antifogging agents, metal soaps, waxes, antifungal agents, 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, and glass particles in an amount ranging from 0.01% to 10% by weight of the total amount of film (100% by weight).

[0045] Furthermore, the method of adding the additive is not particularly limited, and known methods can be used. However, addition by masterbatch is preferred because it is simple and provides excellent uniform mixing. For example, a specific example (commercial product) of a polyester resin-based masterbatch used when formulating an antiblocking agent is Anti-Blocking Agent (Contains: 20% Silica, manufactured by Sukano, product name: G dc S559-E). In addition, it is preferable to blend other resins, provided that they do not impair the physical properties of the heat-shrinkable film, particularly its shrinkage rate and thermal shrinkage stress.

[0046] (5)Mixture Furthermore, it is preferable that the polyester resin used as the raw material for the polyester heat-shrinkable film is a mixture of crystalline polyester resin and amorphous polyester resin, with a weight mixing ratio within the range of 100:0 to 80:20. The reason for this is that if the weight-to-weight ratio exceeds 80:20, the balance between recyclability and heat shrinkage becomes poor, making it difficult to obtain stable recycled PET, and potentially leading to large variations in the heat shrinkage rate within the desired temperature range. In other words, it was generally said that good shrinkage could not be obtained unless the amount of amorphous polyester resin blended was at least 60% by weight relative to the total amount of polyester resin (100% by weight). However, in the present invention, even when the amount of amorphous polyester resin blended is 20% by weight or less relative to the total amount of polyester resin (100% by weight), good thermal shrinkage can be obtained by considering the clamping fraction, melting point and its variation, heat of fusion and its variation, average molecular weight (intrinsic viscosity and its variation), and furthermore, the stretching conditions during manufacturing (stretching temperature, stretching ratio, heat process temperature, etc.). Therefore, it is more preferable that the weight ratio of the mixture of crystalline polyester resin and amorphous polyester resin be within the range of 99:1 to 85:15, and even more preferable that it be within the range of 98:2 to 90:10.

[0047] 4. Heat of fusion (ΔHm) The characteristic (C) of the polyester heat shrinkable film 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 when the heat of fusion of such polyester heat-shrinkable films falls below 25 mJ / mg, crystallization becomes insufficient, significantly reducing heat resistance and potentially making the polyester heat-shrinkable film more prone to melting. On the other hand, if the heat of fusion of such polyester heat-shrinkable film exceeds 45 mJ / mg, crystallization may be sufficient, but the amount of heat required for extrusion and stretching of the raw material sheet of polyester heat-shrinkable film becomes too high, making it difficult to control the manufacturing conditions. Therefore, it is more preferable that the heat of fusion of the polyester heat-shrinkable film be in the range of 28 to 40 mJ / mg, and even more preferable that it be in the range of 30 to 35 mJ / mg.

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

[0049] (2) Thermal shrinkage rate D2 under specified measurement conditions (e.g., 70°C) The properties (D2) of the polyester heat-shrinkable film are characterized by having a heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 70°C and 10 seconds, within the range of 25 to 50%. The reason for this is that if the thermal shrinkage rate falls below 25%, the film may not stably perform its function as a thermal shrink film, or the amount and ratio of usable raw material components may be strictly limited. On the other hand, if the heat shrinkage rate exceeds 50%, the storage period of the polyester heat shrink film will be shortened, or the storage conditions will have to be strictly controlled, and furthermore, when attached to a PET bottle, it will be more prone to developing blemishes or wrinkles. Therefore, with respect to characteristic (D2), it is preferable that the thermal shrinkage rate in the main shrinkage direction, measured under thermal shrinkage conditions of 70°C for 10 seconds, be in the range of 30 to 45%, and more preferably in the range of 35 to 40%.

[0050] (3) Thermal shrinkage rate D3 under specified measurement conditions (80°C, etc.) The properties (D3) of the polyester heat-shrinkable film are characterized by a heat shrinkage rate in the main shrinkage direction, measured under heat shrinkage conditions of 80°C and 10 seconds, being within the range of 55 to 75%. The reason for this is that if the heat shrinkage rate falls below 55%, the polyester heat shrink film may not function stably, or the amount and ratio of usable raw material components may be strictly limited. On the other hand, if the heat shrinkage rate exceeds 75%, the storage period of the polyester heat shrink film will be shortened, or storage conditions will need to be strictly controlled, and furthermore, when attached to a PET bottle, unevenness and wrinkles may easily occur. Therefore, with respect to characteristic (D3), it is preferable that the thermal shrinkage rate in the main shrinkage direction, measured under thermal shrinkage conditions of 80°C for 10 seconds, be in the range of 58 to 72%, and more preferably in the range of 60 to 70%.

[0051] (4) Thermal shrinkage rate (D4') and its standard deviation (D4) under specified measurement conditions (e.g., 100°C) (4)-1 Thermal 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 direction), measured under heat shrinkage conditions of 95°C to 100°C for 10 seconds, be 70% or more. The reason for this is that by limiting the thermal shrinkage rate in the TD direction under high-temperature conditions, the occurrence of unevenness and wrinkles is reduced, resulting in better appearance and fit. In other words, by covering the PET bottle, not only is the ease of attachment improved, but the appearance is also enhanced, and letters, figures, etc., laminated on the surface can be recognized with high accuracy, even when heat-shrinking at relatively low temperatures as well as high-temperature conditions. However, if the thermal shrinkage rate (D4') is made excessively large, the yield will decrease significantly, which may be economically disadvantageous, or the types of compounding components that can be used in the polyester resin may be excessively restricted. Therefore, it is more preferable that the thermal shrinkage rate (D4') be in the range of 71 to 90%, and even more preferable that it be in the range of 72 to 85%.

[0052] (4)-2 Standard deviation of thermal shrinkage Furthermore, the polyester heat-shrinkable film is characterized by having a standard deviation of 1.5% or less 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, as a characteristic (D4). The reason for this is that if the standard deviation of the heat shrinkage rate exceeds 1.5%, the polyester heat shrinkable film may not be able to stably perform its function, or the amount and ratio of usable raw material components may be strictly limited. However, if the standard deviation of the thermal shrinkage rate becomes excessively small, it may lead to an excessive decrease in manufacturing yield, an excessive restriction on the types of raw materials that can be used, and even require strict control of storage conditions. Therefore, with respect to characteristic (D4), it is preferable that the standard deviation of the thermal shrinkage rate in the main shrinkage direction (TD direction), measured under thermal shrinkage conditions of 95°C to 100°C for 10 seconds, be within the range of 0.05 to 1.0%, and more preferably within the range of 0.1 to 0.8%.

[0053] Here, referring to Figure 2(a), we will explain the relationship between the maximum stretching speed when creating 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. Specifically, the horizontal axis of Figure 2(a) represents the maximum stretching speed during the creation of the polyester heat-shrinkable film, and the vertical axis represents 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 when the maximum stretching speed exceeds 40% / sec. and reaches approximately 60% / sec., the standard deviation of the thermal shrinkage rate tends to gradually increase within the range of 0.3 to 0.5%. Furthermore, when the maximum stretching speed exceeds 60% / sec. and reaches 67% / sec., the standard deviation of the thermal shrinkage rate increases at a considerable rate, tending to be between 0.5% and approximately 1.5%. And when the maximum stretching speed exceeds 67% / sec., the standard deviation of the thermal shrinkage rate increases even more rapidly, exceeding 1.5%.

[0054] In other words, from the characteristic curve L1, it can be understood that, in the case of the polyester heat-shrinkable film of the present invention, by controlling the maximum stretching speed during its creation 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 low desired value. For example, if the maximum stretching rate is within the range of at least 40-67% / sec., it is understood that the standard deviation of the thermal 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 manufacturing polyester heat-shrinkable films, the unstretched film may be stretched at a predetermined speed, and this value is defined as the speed at which that maximum stretching speed occurs. In other words, the stretching speed is maximum within a few seconds after the start of stretching of the unstretched film, for example, within 0.1 to 12 seconds. Therefore, the maximum stretching speed during that period can be considered the maximum stretching speed. The elongation rate in the TD direction can be defined by the following formula. Stretching rate in the TD direction (% / sec.) = (W t2 -W t1 ) / W t1 ×100 / (t2-t1) W t1 : The width (m) of the film at t1 seconds after the start of stretching of the unstretched film. W t2 : The width (m) of the film after t2 seconds following the start of stretching of the unstretched film. (However, t1 <t2、0≦t1、0.1≦t2≦12である。)

[0055] However, it should be noted that in the case of Comparative Examples 2 and 3 in Figure 2(a), the clamping fraction is considerably larger compared to the present invention (Example 5, etc.), and characteristic curve L1 is obtained when the clamping fraction is at least 1.2 or less, as in the present invention. 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 heat-shrinkable film can also be stably controlled to the desired value, as shown by the characteristic curve L1' in Figure 2(b). In other words, in the case of characteristic curve L1', even in the case of Comparative Examples 2 and 3, where the clamping fraction is high, a good correlation with the maximum stretching speed is observed. Therefore, it can be understood that the standard deviation of the thickness of polyester heat-shrinkable films can be controlled to a predetermined value even if the clamping fraction is not strictly controlled.

[0056] Furthermore, referring to Figure 3, we will explain the relationship between the standard deviation of the thermal shrinkage rate in the main shrinkage direction (TD direction), measured under specified thermal shrinkage conditions (100°C, 10 seconds), and the evaluation of the clamping fraction. Specifically, the horizontal axis shows the standard deviation (%) of the thermal shrinkage rate in the main shrinkage direction, and the vertical axis shows the evaluation result (relative value) of the clamping fraction. From the characteristic curve L2 in Figure 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 clamping 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 is obtained, and if the standard deviation (%) of the thermal shrinkage rate is 1% or less, a high rating of 5, the highest possible rating, is 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 clamping fraction rapidly decreases. At a standard deviation of 1.9%, the evaluation result of the clamping fraction is 0, and at a standard deviation of 2.6%, the evaluation result of the clamping fraction is definitely 0. Therefore, judging from the characteristic curve in Figure 3, it can be understood that the evaluation results of the clamping 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 inferred that the maximum stretching speed when creating a polyester 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 explained in detail in the manufacturing method of the second embodiment.

[0058] (5) Thermal shrinkage rate D5 under specified measurement conditions As a characteristic (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 60-80°C and 10 seconds, satisfies the following relational expression (1). The reason for this is that, within a predetermined temperature range, the thermal shrinkage temperature and the thermal shrinkage rate satisfy the predetermined relationship equation (1), making it possible to obtain accurate and good thermal shrinkage even when the proportion of crystalline polyester resin is high. Consequently, controlling the thermal shrinkage force also becomes easier.

[0059]

number

[0060] a: Corresponds to the slope of relation (1), and is a value between 3.25 and 4. b: Corresponds to the constant in relation (1), and is a value between 0 and 5 (inclusive).

[0061] More specifically, with reference to Figure 7, the relationship between the thermal shrinkage rate in the main shrinkage direction (TD direction) under thermal shrinkage conditions of 60-80°C and 10 seconds will be explained in relation to equation (1). Specifically, the horizontal axis of Figure 7 shows the heat shrinkage temperature (°C), and the vertical axis shows the heat shrinkage rate (%) in the main shrinkage direction (TD direction) of the polyester heat shrinkable film. In Figure 7, if the shaded area (S1) between the two straight lines located vertically is within the range defined by relation (1) of the present invention, and is at least in the range of 60 to 80°C, then it is understood that the thermal shrinkage rate increases linearly in response to an increase in thermal shrinkage temperature. Therefore, even if the heat shrinkage temperature varies and the desired heat shrinkage rate cannot be obtained temporarily, 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 relational equation (1) described later. For example, when controlling the thermal shrinkage rate at 60, 70, and 80°C within a predetermined range in the present invention, it is extremely effective to use relational formula (1), etc. In Figure 7, the thermal shrinkage rate (%) of the polyester heat-shrinkable films of the prior art (Patent Documents 2 and 3) is shown by curves labeled Conventional 2 (Ex.1) and Conventional 3 (Ex.1). In the case of these D2 and D3 curves, it has been found that the thermal shrinkage rate does not decrease linearly in response to the decrease in thermal shrinkage temperature, but rather takes on a so-called S-shape overall. Furthermore, it is understood that around 70°C, Conventional 2 (Ex.1) and Conventional 3 (Ex.1) fall significantly outside the range defined by relation (1) of the present invention.

[0062] More preferably, as characteristic (D5'), the thermal shrinkage temperature and thermal shrinkage rate satisfy predetermined relational equations (2) and, even more preferably, as characteristic (D5''), the predetermined relational equation (3) is satisfied. In other words, in Figures 8 and 9, the shaded areas (S2 and S3) enclosed by the two straight lines located vertically, respectively, represent the ranges defined by relational equations (2) and (3) of the present invention, respectively. Furthermore, it is understood that, at least within the range of 60 to 80°C, the thermal shrinkage rate increases more accurately and linearly in response to an increase in the thermal shrinkage temperature. Similar to Figure 7, Figures 8 and 9 show curves labeled Conventional 2 (Ex.1) and Conventional 3 (Ex.1), respectively, representing the thermal shrinkage rate (%) of conventional polyester heat-shrinkable films (Patent Documents 2 and 3).

[0063]

number

[0064] a': Corresponds to the slope of relation (2), and is a value between 3.3 and 3.75. b': Corresponds to the constant in relation (2), and is a value between 0 and 5 (inclusive).

[0065]

number

[0066] a'': Corresponds to the slope of relation (3), and is a value between 3.35 and 3.5. b'': Corresponds to the constant in relation (3), and is a value between 0 and 5 (inclusive).

[0067] (6) Thermal shrinkage rate D6 in the MD direction under predetermined measurement conditions As a characteristic (D6) of the polyester heat-shrinkable film, it is preferable that the heat shrinkage rate in the direction perpendicular to the principal shrinkage direction (MD direction), measured under heat shrinkage conditions of 70°C and 10 seconds, be within the range of -3 to 5%. The reason for this is that by limiting the thermal shrinkage rate in the MD direction under these predetermined temperature conditions, even when coating the PET bottle and thermal shrinking it at a relatively low temperature, the occurrence of blemishes, wrinkles, and other defects is reduced. Therefore, even with energy-saving heating, it becomes easier to achieve good installation and appearance. Furthermore, by restricting the thermal shrinkage rate in the MD direction in this way, the overall thermal shrinkage properties of the polyester-based heat-shrinkable film can be balanced, allowing for stable pellet production by controlling properties such as tackiness and fluidity, even when recycled together with PET bottles. Therefore, as a characteristic (D6), it is more preferable that the thermal shrinkage rate in the MD direction be within the range of -2.5 to 4%, and even more preferable that it be within the range of -2 to 3.5%.

[0068] (7) Thermal shrinkage rate D7 in the MD direction under predetermined measurement conditions As a characteristic (D7) of the polyester heat shrinkable film, the heat shrinkage rate in the direction perpendicular to the principal shrinkage direction (MD direction), measured under heat shrinkage conditions of 60-90°C and 10 seconds, preferably has at least one minimum value, and it is preferable that this minimum value is -3% or greater. The reason for this is that by restricting the thermal shrinkage profile in the MD direction under predetermined temperature conditions to have a predetermined minimum value, even if the temperature conditions vary somewhat and the thermal shrinkage rate changes, it becomes easier to correct and perform thermal shrinkage, resulting in a better appearance and more accurate information. This can be more clearly determined by simple measurement of thermal shrinkage curves or TMA measurements. Furthermore, by limiting the thermal shrinkage rate in the MD direction within a predetermined temperature range, the overall thermal shrinkage properties of the polyester-based heat-shrinkable film can be balanced, reducing the generated thermal shrinkage stress, and allowing for more stable pellet production even when recycled together with PET bottles. Therefore, as a characteristic (D7), it is more preferable that the minimum value of the thermal shrinkage rate in the MD direction be within the range of -1 to 2%, and even more preferable that it be within the range of -0.5 to 1%.

[0069] (8) Thermal shrinkage rate D8 in the MD direction under predetermined measurement conditions The properties (D8) of the polyester heat-shrinkable film include the heat shrinkage rate in the direction perpendicular to the principal shrinkage direction (MD direction), measured under heat shrinkage conditions of 60-90°C and 10 seconds, which preferably has at least one maximum value, and this maximum value is 3% or less. The reason for this is that by restricting the thermal shrinkage profile in the MD direction under predetermined temperature conditions to have a maximum value of a predetermined size, it becomes easier to obtain a good appearance and accurate information during thermal shrinkage, and it becomes clearer that the generated thermal shrinkage stress is below a predetermined value. Furthermore, in the thermal shrinkage profile, it is preferable that when there is a maximum value of a predetermined size, there is also a minimum value of the predetermined size as described above. Therefore, as a characteristic (D8), it is more preferable that the maximum value of the thermal shrinkage rate in the MD direction be within the range of -1 to 2%, and even more preferable that it be within the range of -0.5 to 1.5%.

[0070] 6. Thickness Furthermore, the thickness of the polyester heat-shrinkable film (average thickness, the same applies hereinafter) can be changed to accommodate the various shapes of PET bottles, but it is generally preferable to use a value within the range of 10 to 100 μm. The reason for this is that when the thickness of such polyester heat-shrinkable film is less than 10 μm, it becomes difficult to handle, and its tensile strength and other properties may decrease significantly. On the other hand, if the thickness of such polyester heat-shrinkable film exceeds 100 μm, it may not shrink uniformly when heated at a predetermined temperature, or it may become difficult to manufacture it to a uniform thickness. Therefore, it is more preferable to set the thickness of the polyester heat-shrinkable film to a value in the range of 20 to 70 μm, and even more preferable to set it to a value in the range of 40 to 60 μm. The thickness of the polyester heat-shrinkable film can be measured and calculated in accordance with ISO 4593 using a micrometer (Mitutoyo Corporation, product name "Thickness Gauge 547-401").

[0071] Furthermore, as described above based on Figure 2(b), it is preferable that the standard deviation of the variation in the average thickness of the polyester heat-shrinkable film measured under predetermined conditions be 1.7 μm or less. The reason for this is that by keeping the standard deviation of the average thickness below a predetermined value, even when a polyester-based heat-shrinkable film is made with crystalline polyester resin as the main component (for example, 80% by weight or more), the balance between recyclability and heat shrinkability becomes even better. However, if the standard deviation of the average thickness becomes excessively small, the yield may decrease significantly, leading to economic disadvantages, or the types of compounding components that can be used in the polyester resin may be excessively restricted. Therefore, it is more preferable to set the standard deviation of the average thickness of the polyester heat-shrinkable film to a value within the range of 0.05 to 1.4 μm, and even more preferable to set it 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 explained in detail in Example 1.

[0072] 7. Functional Layer Within the limits that do not impair the objectives of the present invention, it is also preferable that the polyester heat-shrinkable film has a functional layer for imparting various functions as needed. Examples of such functional layers include coating layers, transfer layers, and printing layers for providing surface smoothness, stain resistance, weather resistance, etc. Among these, a coating layer using a surfactant is particularly preferable as a functional layer because it greatly contributes to improving antistatic properties and surface lubricity.

[0073] For example, as shown in Figure 1(b), it is also preferable to laminate other resin layers 10a, 10b containing at least one of these various additives onto one or both sides of the polyester heat-shrinkable film 10. In that case, when the thickness of the polyester heat-shrinkable film is set to 100%, it is preferable that the single-layer thickness or total thickness of the additional resin layers to be laminated is usually within the range of 0.1 to 10%. Furthermore, the resin that constitutes the other resin layers may be a polyester resin similar to that used in polyester heat-shrinkable films, or it is preferable that it be at least one of the following: an acrylic resin, an olefin resin, a urethane resin, a rubber resin, etc.

[0074] Furthermore, it is preferable to create a multilayer structure for the polyester heat shrink film to further enhance hydrolysis prevention and mechanical protection, or, as shown in Figure 1(c), to provide a shrinkage rate adjustment layer 10c on the surface of the polyester heat shrink film 10 so that the shrinkage rate of the polyester heat shrink film becomes uniform across the surface. Such a shrinkage rate adjustment layer can be laminated as a predetermined layer made of polyester resin or the like, depending on the shrinkage characteristics of the polyester heat-shrinkable film, by means of an adhesive, coating method, or heat treatment.

[0075] 8. Haze value and haze value / thickness (1) Haze value Furthermore, it is preferable that the haze value of the polyester heat-shrinkable film, measured in accordance with ASTM D1003, be 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 may result in an unattractive appearance when creating labels, and is therefore undesirable. Therefore, such a 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, etc. Generally, a smaller value is preferable as it indicates higher transparency. However, considering that a certain amount of lubricant must be added to the film to provide the necessary slipperiness for practical purposes, the lower limit is around 2%.

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

[0077] [Second Embodiment] The second embodiment is a method for manufacturing a polyester heat-shrinkable film according to the first embodiment. The process will be described in detail below, step by step.

[0078] 1. Preparation and mixing of raw materials As raw materials, the main components and additives, such as recycled crystalline polyester resin pellets, rubber-based resin, antistatic agents, and hydrolysis inhibitors, are prepared as shown in Figure 11(b). When preparing the 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 bring them to an extremely dry state. Next, it is preferable to weigh the recycled crystalline polyester resin pellets, etc., into the stirring container and mix and stir them using a stirring device until they become uniform. Furthermore, in addition to recycled crystalline polyester resin pellets, non-recycled crystalline polyester resin pellets may also be used as the crystalline polyester resin. In other words, economically speaking, 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 clamping 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. Process for creating the raw material sheet Next, it is preferable to produce a raw material sheet of a predetermined thickness, typically by extrusion molding (T-die method), inflation molding, or casting molding. More specifically, for example, by extruding the material using an extruder at an extrusion temperature of 245°C, a raw material sheet of a predetermined thickness (typically 200-300 μm) can be obtained.

[0080] 3. Preparation of polyester heat-shrinkable film Next, the obtained raw material sheet is heated and pressed using a heat-shrinkable film manufacturing device (tenter) while moving it on and between rolls to create a polyester heat-shrinkable film. However, known stretching methods for achieving such shrinkage include the inflation method, the roll stretching method, the tenter stretching method, and combinations thereof. Furthermore, due to better productivity, a combination of sheet forming by cast molding and roll stretching and tenter stretching is even more preferable.

[0081] In other words, it is preferable to preheat the film at a predetermined preheating temperature, for example, within the range of 110 to 150°C, and then stretch it in a predetermined direction while basically expanding the film width at a predetermined stretching temperature, maximum stretching speed, and stretching ratio, and while heating and pressing, thereby crystallizing the molecules of the polyester resin constituting the polyester heat-shrinkable film into a predetermined state. Then, by solidifying it at a predetermined heat-fixing temperature, for example, within the range of 60 to 80°C, a heat-shrinkable polyester-based heat-shrinkable film can be created for use as decoration or a label. In other words, it is preferable to manufacture a film roll by a T-die method or inflation method, then heat the film roll to a temperature above the glass transition temperature of the resin, and stretch it to a value of at least 3 to 8 times, preferably 4 to 6 times, in the main stretching direction (the width direction of the film roll, i.e., the TD direction) at a maximum stretching speed of 40 to 67% / sec., preferably 45 to 62% / sec.

[0082] 4. Effect of maximum elongation speed (1) Relationship with the standard deviation of the specified thermal shrinkage rate As already shown by the characteristic curve L1 in Figure 2(a) above, assuming a predetermined clamping fraction, a predetermined correlation has been found between the maximum stretching speed and the standard deviation of the thermal shrinkage rate in the main shrinkage direction at 100°C for 10 seconds. Furthermore, as shown by the characteristic curve L1' in Figure 2(b), a predetermined correlation has been found between the maximum stretching rate, the standard deviation of the thickness, and the clamping fraction, regardless of the predetermined clamping fraction. From this characteristic curve L1', it can be understood that when the maximum stretching rate falls below 40% / sec., the standard deviation of the thickness exceeds at least 1.7 μm.

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

[0084] (3) Relationship with glass transition temperature Furthermore, as shown by the characteristic curve L4 in Figure 5, a predetermined correlation has been found between the maximum stretching speed and the glass transition temperature of the resulting polyester-based heat-shrinkable film. In other words, 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 desired range. For example, by controlling the maximum stretching speed to a range of 40-58% / sec. or less, the glass transition temperature of the resulting polyester heat-shrinkable film can be controlled to around 74.5°C. Furthermore, for example, in the range where the maximum stretching speed exceeds 58% / sec. and is around 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, it is understood that, for example, in the range where the maximum stretching speed exceeds 65% / sec., the glass transition temperature of the resulting polyester heat-shrinkable film reliably decreases to 74.3°C or below and tends to remain so.

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

[0086] 5. Inspection process for polyester heat-shrinkable film It is preferable to continuously or intermittently measure the following properties of the prepared polyester heat-shrinkable film and to establish a predetermined inspection process. In other words, by measuring the following characteristics through a predetermined inspection process and confirming that they fall within a predetermined range, a polyester heat-shrinkable film with more uniform shrinkage characteristics can be produced. 1) Visual inspection of the appearance of polyester heat shrinkable film 2) Measurement of thickness variation 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) [Examples]

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

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

[0089] (PETG) As an amorphous polyester resin, PETG (amorphous polyester consisting of dicarboxylic acid: 100 mol% terephthalic acid, diol: ethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol) (manufactured by Eastman Chemical, trade name "Embrace LV", glass transition temperature (Tg): 68.2℃, no melting point, intrinsic viscosity (IV value): 0.7, density: 1.3 g / cm³) 3 I prepared )).

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

[0091] [Example 1] 1. Preparation of polyester heat-shrinkable film As the crystalline polyester resin, PET1 as described above was prepared. Next, 1000g of the prepared PET1 was added to the stirring container. Furthermore, as an anti-blocking agent for the heat-shrinkable film, the above-mentioned Anti-Blocking Agent, dried under predetermined conditions, was blended at a ratio of 1 part by weight per 100 parts by weight of PET1, and used as a raw material for forming the heat-shrinkable film.

[0092] Next, this heat-shrinkable film-forming raw material was extruded using a vented twin-screw extruder at an extrusion temperature of 245°C to obtain a raw sheet with a thickness of 250 μm. Finally, using a heat-shrinkable film manufacturing apparatus, a polyester heat-shrinkable film with a set thickness of 50 μm was fabricated from a raw sheet using a preheating temperature of 125°C, a maximum stretching speed of 56% / sec., a stretching temperature of 86°C, a heat-fixing 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 films (1) Evaluation 1 (Clamping fraction) As shown in Table 1, PET1, PET2, and PETG were appropriately blended to obtain polyester resin. Next, in accordance with APR Document Code:PET-S-08, the clamping fraction of the polyester resin (crystalline polyester resin, amorphous polyester resin, or mixture thereof) was measured and evaluated according to the following criteria. ◎: The clamping fraction is 1% or less. ○: The clamping fraction is 1.2% or less. △: The clamping fraction is 1.4% or less. ×: The clamping fraction is greater than 1.4%.

[0094] (2) Evaluation 2 (DSC measurement of polyester heat shrink film) The obtained polyester heat-shrinkable film was measured for its melting point (peak melting temperature) and other properties under predetermined conditions using a DSC device (manufactured by Hitachi High-Tech Science Corporation, product name "DSC7000X"). More specifically, samples of polyester heat-shrinkable film were dried in a dry oven at 60°C for more than 6 hours. Next, the sample was placed in a differential scanning calorimeter and heated to a high temperature range in Step 1 (heating rate of 10°C / min, from 25°C to 250°C). Next, in Step 2 (cooling from 250°C to 25°C at a cooling rate of 10°C / min), the temperature was temporarily lowered to the low-temperature range. Finally, in Step 3 (heating from 25°C to 250°C at a heating rate of 10°C / min), the temperature was raised again to the high-temperature range. Then, as shown in Figure 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) Rating 3 (Thermal shrinkage rate) The heat shrinkage rate of the obtained polyester heat shrinkable film was measured in accordance with ASTM D2732-08. Specifically, the material 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 this was used as the measurement sample. Next, the obtained polyester heat-shrinkable film was immersed for 10 seconds in a constant-temperature bath containing hot water, each at a temperature controlled to 60, 70, 80, 90, and 100°C in 10°C increments, to heat-shrink it. Next, at each temperature, the thermal shrinkage rate (%) in the main shrinkage direction (TD direction) and the non-shrinkage direction (MD direction) was calculated according to formula (5) below, based on the dimensional changes before and after the heat treatment.

[0096]

number

[0097] (4) Rating 4 (Standard deviation of thermal shrinkage rate) The heat shrinkage rate of the obtained polyester heat shrinkable film was measured and the standard deviation was calculated according to ASTM D2732-08 using the following procedure. First, eight measurement samples were obtained from the resulting polyester heat-shrinkable film, uniformly distributed in the width direction. Specifically, the material was cut into squares 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 sample samples were left in an atmosphere of 23°C and 50% RH for more than 40 hours. Next, the eight pre-treated samples were each immersed for 10 seconds in a constant-temperature bath containing temperature-controlled hot water at 100°C to induce thermal shrinkage. Next, the thermal shrinkage rate (%) in the main shrinkage direction (TD direction) was calculated from the dimensional changes before and after the heat treatment, according to equation (5) above. Next, the standard deviation was calculated from the thermal shrinkage rates of the eight measured samples, and evaluated according to the following criteria. ◎: The standard deviation of the thermal shrinkage rate is 1.0% or less. ○: The standard deviation of the thermal shrinkage rate is 1.5% or less. △: The standard deviation of the thermal shrinkage rate is 2.5% or less. ×: The standard deviation of the thermal shrinkage rate is greater than 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 points at equal intervals in the width direction of the film using a micrometer (Mitutoyo Corporation, product name "Thickness Gauge 547-401") in accordance with ISO 4593, and the average value was calculated to determine the thickness (average thickness). Furthermore, the standard deviation was calculated from the 20 measurement points used to determine 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 greater than 2 μm.

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

[0100] (7) Rating 8 (Ease of wearing / Appearance) We prepared an eggplant-shaped PET bottle (product name "Limmi Lemon Juice", volume: 200ml) filled with commercially available drinking water. Next, 1,3-dioxolane was applied to the ends in the width direction of the elongated sample obtained by slitting a polyester heat-shrinkable film to a width of 20.5 cm. Next, the ends in the width direction were overlapped and glued together so that there was an overlap of approximately 1 cm, creating a cylindrical label with a diameter of approximately 6.2 cm. Furthermore, this cylindrical label was cut into 11 cm intervals along its length to obtain multiple cylindrical labels. Next, the cylindrical label was placed over the body of a roughly cylindrical PET bottle, and the bottle was moved through a steam tunnel maintained at 80°C on a conveyor belt, heating it for 8 seconds while moving. This process caused the cylindrical label to heat-shrink so that it tightly adhered to the body of the roughly cylindrical PET bottle from top to bottom.

[0101] Next, the heat-shrinkable cylindrical labels were visually inspected to check for any improper adhesion to the PET bottles, such as failure to adhere properly to the label within the specified length (5 mm or more) or width (1 mm or more), or for any unevenness or wrinkles. The adhesion was then evaluated according to the following criteria. ◎: Of the five cylindrical labels, no improper attachment, blemishes, or wrinkles were observed in any of them. ○: Of the five cylindrical labels, no improper attachment, blemishes, or wrinkles were observed in three or more. △: Out of 5 cylindrical labels, no improper attachment, blemishes, or wrinkles were observed in one or more. ×: All five cylindrical labels showed signs of improper attachment, blemishes, or wrinkles.

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

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

[0104] [Examples 4-5] 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-fixing 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, as shown in Table 1, a polyester heat-shrinkable film was prepared and evaluated in the same manner as in Example 1, except that PET1 and PETG (mixing ratio = 80 / 20) were used as the PET resin. The results obtained are shown in Table 2.

[0106] [Comparative Example 1] In Comparative Example 1, as shown in Table 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. The results obtained are shown in Table 2.

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

[0108] [Comparative Example 3] In Comparative Example 3, as shown in Table 1, the above-mentioned PET1 and PETG (mixing 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, but otherwise, a polyester heat-shrinkable film was prepared and evaluated in the same manner as in Example 1. The results obtained are shown in Table 2.

[0109] [Table 1]

[0110] [Table 2] [Industrial applicability]

[0111] According to the present invention, by controlling at least predetermined characteristics (A) to (C), such as the clamping fraction, and (D1) to (D4), which relate to the thermal shrinkage rate, a good balance between recyclability and thermal shrinkage is achieved. In other words, by primarily using crystalline polyester resin, such as recycled PET, and strictly controlling the predetermined clamping fraction, it has become possible to effectively prevent the bonding phenomenon even when recycling PET bottles with the polyester heat-shrinkable film still attached, and to effectively and stably produce the desired recycled pellets. Furthermore, this reduces variations in the heat shrinkage rate and thickness of polyester heat shrinkable films, and controls the heat shrinkage stress generated during heat shrinkage, making it possible to provide polyester heat shrinkable films that exhibit excellent attachability and appearance over a wide temperature range.

[0112] Furthermore, with the polyester heat-shrinkable film of the present invention, even if the thickness is not affected and the heat shrinkage temperature and other factors change slightly, making it difficult to obtain the desired heat shrinkage rate, it is now possible to accurately correct and control the heat shrinkage rate within the desired range. Therefore, it can be attached to various types of PET bottles and exhibits excellent fit and appearance, and moreover, it can be recycled together with the PET bottles while still attached. As a result, it can significantly expand its versatility while maintaining environmental friendliness and economic efficiency, and its industrial applicability is extremely high. [Explanation of symbols]

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

Claims

1. A polyester-based heat-shrinkable film derived from a polyester resin, which is a reaction product of a polycarboxylic acid and a polyalcohol, characterized in that it has the following properties (A) to (C) and (D1) to (D4). (A) The clamping fraction in the mixture of the polyester resin and other recycled PET resin, as measured in accordance with APR Document Code:PET-S-08, shall be 1.2% or less. (B) The melting point of the polyester resin, as measured by DSC, shall be within the range of 190 to 230°C. (C) The amount of heat of fusion corresponding to the melting peak area at the melting point of the polyester heat shrink film measured by DSC shall be a value within the range of 25 to 45 mJ / mg. (D1) The thermal shrinkage rate in the TD direction, which is the main shrinkage direction, measured under thermal shrinkage conditions of 60°C for 10 seconds, shall be a value within the range of 0 to 5%. (D2) The thermal shrinkage rate in the TD direction, which is the main shrinkage direction, measured under thermal shrinkage conditions of 70°C for 10 seconds shall be within the range of 33.0% or more and 42.5% or less. (D3) The thermal shrinkage rate in the TD direction, which is the main shrinkage direction, measured under thermal shrinkage conditions of 80°C for 10 seconds shall be within the range of 66.0% or more and 80.0% or less. (D4) The standard deviation of the thermal shrinkage rate in the TD direction, which is the main shrinkage direction, measured under thermal shrinkage conditions of 95°C to 100°C for 10 seconds shall be 1.5% or less. The polyester heat-shrinkable film according to claim 1, characterized in that the heat shrinkage rate in the TD direction, which is the main shrinkage direction, measured under the heat shrinkage conditions of (D5') 60 to 80°C for 10 seconds, satisfies the following relational expression (2). [Math 1]

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

3. The polyester heat shrinkable film according to Claim 1, characterized in that (D2') the heat shrinkage rate in the TD direction, which is the main shrinkage direction, measured under the heat shrinkage conditions of 70°C for 10 seconds is within the range of 33.5% or more and 40.0% or less, (D3') the heat shrinkage rate in the TD direction, which is the main shrinkage direction, measured under the heat shrinkage conditions of 80°C for 10 seconds is within the range of 67.0% or more and 75.0% or less, and (D5'') the heat shrinkage rate in the TD direction, which is the main shrinkage direction, measured under the heat shrinkage conditions of 60 to 80°C for 10 seconds satisfies the following relational expression (3). [Math 2]

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

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

6. The polyester-based heat-shrinkable film according to claim 1, characterized in that the polyester resin is a mixture of a crystalline polyester resin and an amorphous polyester resin, with a weight mixing ratio in the range of 100:0 to 80:

20.

7. A method for producing a polyester heat-shrinkable film according to any one of claims 1 to 6, characterized in that, after preparing a raw material sheet derived from polyester resin, the maximum stretching speed when producing a polyester heat-shrinkable film from the raw material sheet is set to a value of 40 to 65% / second.

8. The method for producing a polyester heat-shrinkable film according to claim 7, characterized in that the maximum stretching speed is adjusted to control the value of the heat of crystallization in the polyester heat-shrinkable film to be within the range of 12 to 15 mJ / mg.

Images