Polyester heat-shrinkable film and storage method for polyester heat-shrinkable film

Abstract

To provide a polyester-based heat shrink film that exhibits excellent mechanical properties even when frozen and stored under predetermined conditions.SOLUTION: The polyester-based heat shrink film satisfies the following configurations (a), (b), and (i) when the main shrink direction is the TD direction and the direction orthogonal thereto is the MD direction. Configuration (a): The tensile fracture nominal strain C1 in the MD direction of the polyester-based heat shrink film frozen and stored at 0°C or less for one month or more, as measured in accordance with JIS K 7127:1999, is 300% or more. Configuration (b): When the tensile fracture nominal strain in the MD direction before frozen storage is C2, C1 / C2 is 0.85 or more. Configuration (i): A mixture comprising a recycled crystalline polyester resin is used, and its blending amount is 10 to 30 wt.%.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a polyester heat-shrinkable film and a method for storing the polyester heat-shrinkable film. More specifically, the present invention relates to a polyester heat-shrinkable film (hereinafter sometimes simply referred to as a heat-shrinkable film) that stably exhibits mechanical properties, etc. even after storage under specified conditions, and to a method for storing such a heat-shrinkable film. [Background technology]

[0002] Conventionally, heat-shrinkable films have been widely used as base films for labels on PET bottles, etc. In particular, heat-shrinkable films made of polystyrene resin or polyester resin are widely used due to their excellent transparency and strength. Here, depending on the order quantity of the heat shrinkable film, etc., a plurality of types of heat shrinkable film manufactured at different times are stored in the same warehouse for a predetermined period after manufacturing. Therefore, although they are usually stored at room temperature (23°C), they deteriorate during storage, and it has been confirmed that polyester heat-shrinkable films in particular tend to break easily when used.

[0003] Therefore, a heat-shrinkable laminated film has been proposed, which has a heat-shrinkable film structure of at least three layers, A layer, B layer, and C layer, each of which has a predetermined composition as the main component, and has a light transmittance of 5% or less for rays of 300 nm or less, and a ratio TTD / TMD of the tear strength TTD in the main shrinkage direction of the heat-shrinkable film to the tear strength TMD in the direction perpendicular to the main shrinkage direction, as measured in accordance with JIS K 7128-3, of 0.4 or more and 1.6 or less (see Patent Document 1). Layer A: An amorphous polyester resin composition containing polycarboxylic acid residues and polyhydric alcohol residues. Layer B: A styrene-based resin composition. Layer C: A resin composition containing a copolymer of a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon or a hydrogenated derivative thereof, in which the content of the styrene-based hydrocarbon in the copolymer or hydrogenated derivative is 5% by mass or more and 40% by mass or less. The heat-shrinkable film has a tensile breaking elongation at -5°C in a direction perpendicular to the main shrinkage direction of the heat-shrinkable film of 100% or more after storage at 30°C for 30 days, as measured in accordance with JIS K 7127.

[0004] It has also been proposed to evaluate heat-shrinkable polyester films stored for 48 hours in an atmosphere of 55°C and 35% RH (see Patent Document 2). More specifically, it is a heat-shrinkable polyester film containing polyethylene terephthalate as a main constituent component, and characterized by satisfying the following requirements (1) to (3). (1) The hot water shrinkage rate in the main shrinkage direction when immersed in 70°C hot water for 10 seconds is 20% or more and 60% or less. (2) The natural shrinkage rate in the main shrinkage direction when stored for 48 hours in an atmosphere of 55°C and 35% RH is less than 6%. (3) The predetermined refractive index difference is 0.06 or more.

[0005] Also, a heat-shrinkable laminated film has been proposed, characterized in that a film made of the following resin composition A is used as an intermediate layer (A) and films made of resin composition B are used as both outer surface layers (B) (see Patent Document 3). <Resin Composition A> 45 to 65 mass% of metallocene-catalyzed linear low-density polyethylene resin, 5 to 25 mass% of low-density polyethylene resin, 5 to 15 mass% of cyclic olefin resin, and 5 to 25 mass% of petroleum resin. <Resin composition B> 70 to 90% by mass of cyclic olefin resin and 10 to 30% by mass of linear low-density polyethylene resin. The resulting labeled and packaged PET bottles are then filled with water and frozen at -5°C for 24 hours. After confirming that they are frozen, the perforations are visually inspected to see if they have broken. In other words, if there is any break in the label-fastened packaging at that point, it is evaluated as a problem (×), and if there is no break, it is evaluated as no problem (◯).It is a subjective evaluation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-160543 A (Claims, etc.) [Patent Document 2] JP 2017-024382 A (Claims, etc.) [Patent Document 3] JP 2006-027052 A (Claims, etc.) Summary of the Invention [Problem to be solved by the invention]

[0007] However, conventional storage conditions for heat-shrinkable films are subject to strict restrictions on the type and form of the heat-shrinkable film, and evaluations are limited to mechanical properties and heat shrinkage rates over a relatively short period of time. Although there are many evaluation items, there is still a problem in that the evaluations are unreliable. For example, Patent Document 1 uses the tensile breaking elongation at -5°C of a heat-shrinkable film with a three-layer structure (layers A to C) after storage at 30°C for 30 days as an evaluation criterion, and requires that the tensile breaking elongation be measured under low-temperature conditions, which requires the adoption of a complicated measurement method and has the problem that the values ​​are prone to variability. Furthermore, of the three-layer structure, Layer A must be formed from a specific amorphous polyester resin composition, Layer B from a styrene resin composition, and Layer C from a resin composition such as a copolymer of a styrene hydrocarbon and a conjugated diene hydrocarbon or a hydrogenated derivative thereof, which poses a problem of extremely large restrictions on the shape of the measurement sample.

[0008] In addition, Patent Document 2 uses as evaluation criteria (a) the shrinkage rate in the main shrinkage direction of a heat-shrinkable polyester film when immersed in warm water at 70°C for 10 seconds, (b) the natural shrinkage rate in the main shrinkage direction of a heat-shrinkable polyester film when stored in an atmosphere at 55°C and 35% RH for 48 hours, and further (c) a predetermined refractive index of the heat-shrinkable polyester film. That is, (b) was based on the evaluation criteria such as the natural shrinkage rate, which has a considerable degree of variability.

[0009] Furthermore, Patent Document 3 employs a method in which a three-layer heat-shrinkable laminated film made of a specified resin is frozen at -5°C for 24 hours and then evaluated for the presence or absence of breakage at the perforations when frozen. This method requires a complicated measurement method and has the problem that the evaluation results are highly variable. Furthermore, of the three-layer structure, both outer layers (B) must be formed from a resin composition consisting of a specified ratio of cyclic olefin resin and linear low-density polyethylene resin, and the middle layer (A) must be formed from a resin composition consisting of a specified linear low-density polyethylene resin, a low-density polyethylene resin, a cyclic olefin resin, and a petroleum resin, which has the problem of extremely severe restrictions on the form of the measurement sample.

[0010] Furthermore, in the case of conventional heat-shrinkable films, even polyester-based heat-shrinkable films come in a wide variety of types and structures, and are stored in the same warehouse or the like for a certain period of time from production until actual use. Differences in storage time have been seen to lead to large variations in the mechanical properties of the heat-shrinkable films. That is, in the case of a plurality of types of polyester-based heat-shrinkable films, particularly single-layer polyester-based heat-shrinkable films, which are produced in roll form at different production times and stored in the same warehouse, the evaluation criteria of Patent Documents 1 to 3 above are unreliable and therefore cannot be used, and new evaluation criteria have been required.

[0011] Therefore, the inventors of the present invention have found that even in the case of a polyester heat-shrinkable film, the degree of deterioration can be detected with high accuracy by controlling the value of the nominal tensile break strain (C1) in the MD direction of the heat-shrinkable film after a predetermined time has elapsed since production at a predetermined temperature, and the ratio (C1 / C2) of this C1 to the nominal tensile break strain (C2) in the MD direction measured immediately after production, and have completed the present invention. In other words, the present invention aims to provide a heat-shrinkable film that can eliminate deteriorated polyester heat-shrinkable films under simple conditions and that stably exhibits excellent mechanical properties, etc., and a method for storing such a heat-shrinkable film. [Means for solving the problem]

[0012] According to the present invention, when the main shrinkage direction of a polyester heat-shrinkable film obtained by freezing and storing the film at a predetermined temperature for a predetermined time is defined as the TD direction and the direction perpendicular thereto is defined as the MD direction, there is provided a polyester heat-shrinkable film that satisfies the following properties (a), (b), and (i), thereby solving the above-mentioned problems. Structure (a): When the nominal tensile strain at break in the MD direction measured in accordance with JIS K 7127:1999 for a polyester heat-shrinkable film that has been frozen and stored at a predetermined temperature of 0°C or lower for a predetermined period of time ranging from one month to six months from the time immediately after production is defined as C1, C1 is set to a value of 382.5% or more. Structure (b): When the nominal tensile strain at break in the MD direction of a polyester heat-shrinkable film immediately after production and before frozen storage, as measured in accordance with JIS K 7127:1999, is C2, C1 / C2 is a value of 0.85 or more, and C2 is a value within the range of 450 to 600%. Structure (i): The polyester resin used as the constituent resin of the polyester-based heat-shrinkable film is a mixture of an amorphous polyester resin and a recycled crystalline polyester resin, and when the entire mixture is taken as 100% by weight, the amount of the recycled crystalline polyester resin is set to a value within the range of 10 to 30% by weight. That is, by controlling the ratio (C1 / C2) of the nominal tensile break strain in the MD direction (C1) after the polyester heat-shrinkable film is produced and then frozen and stored under specified conditions to the nominal tensile break strain in the MD direction (C2) immediately after production and before frozen storage (usually within 24 hours after production) within a specified range, it is possible to eliminate deteriorated polyester heat-shrinkable films under simple conditions and effectively prevent tensile breakage, etc. More specifically, there is a good correlation between the specified ratio (C1 / C2) and the mechanical properties, and the polyester heat-shrinkable film can stably exhibit excellent mechanical properties, etc., regardless of variations in storage conditions (temperature, time, etc.) of the polyester heat-shrinkable film or the shape of the heat-shrinkable film.

[0013] Furthermore, when constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that the predetermined time for measuring C1 in the structure (a) is set to a value of 3 months or more and 12 months or less, with the time immediately after production as the standard (usually within 24 hours after production). By limiting the storage time in this manner, it becomes easier to remove deteriorated heat shrinkable films, although this depends on the storage temperature, and tensile breakage and the like can be effectively prevented regardless of the type or form.

[0014] In forming the polyester heat-shrinkable film of the present invention, it is preferable that the predetermined temperature for freezing and storing the film is set to a value of −30° C. or lower. By limiting the predetermined temperature in this way, it becomes easier to remove deteriorated heat shrinkable films over a long period of time, and tensile breakage and the like can be effectively prevented regardless of the type or form.

[0015] In constructing the polyester heat-shrinkable film of the present invention, it is preferable that the polyester heat-shrinkable film further satisfies the following requirement (c). Configuration (c): The coefficient of dynamic friction measured in accordance with JIS K 7125:1999 is set to a value within the range of 0.15 to 0.6. By controlling the dynamic friction coefficient in this way, even when the heat shrinkable film is processed into a roll, it exhibits better handling properties and the heat shrinkage rate can be easily controlled.

[0016] Furthermore, in constructing the polyester-based heat-shrinkable film of the present invention, when the polyester-based heat-shrinkable film is shrunk in the TD direction in warm water or boiling water at 70°C, 80°C, and 100°C for 10 seconds, the heat shrinkage rates are designated as A1 to A3. It is preferable that A1 is 10% or more, A2 is 30% or more, and A3 is 60% or more. When configured in this manner, it is possible to compare the heat shrinkage characteristics of a heat shrinkable film, which are typically evaluated at 70°C to 100°C for 10 seconds, and determine the correspondence with the present invention. The heat shrinkage rates A1 to A3 of the heat shrinkable film preferably satisfy the predetermined values ​​not only before a predetermined time has elapsed since the time of production, but also after the predetermined time has elapsed.

[0017] Furthermore, in constructing the polyester-based heat-shrinkable film of the present invention, it is preferable that, with respect to the endothermic heat of the melting peak measured using DSC, when the endothermic heat before the lapse of a predetermined time is set to 100%, the change in endothermic heat after the lapse of a predetermined time is set to a value within the range of 0 to 25%. By configuring it in this manner, by limiting the change in the amount of heat absorption due to enthalpy relaxation in the heat-shrinkable film, it is possible to estimate the deterioration of the heat-shrinkable characteristics, etc., and ultimately to quantitatively confirm the deterioration of the heat-shrinkable film.

[0018] In forming the polyester heat-shrinkable film of the present invention, it is preferable that the haze of the polyester heat-shrinkable film before heat shrinkage is 10% or less as measured in accordance with JIS K 7136:2000. Such a configuration increases the versatility of the heat shrinkable film, allowing it to be used in a wide range of applications. It is preferable that the heat shrinkable film has a predetermined haze value not only before a predetermined time has elapsed since the time of production, but also after the predetermined time has elapsed.

[0019] Another aspect of the present invention is a method for storing a polyester heat-shrinkable film by freezing and storing it for a predetermined time at a predetermined temperature, characterized in that when the main shrinkage direction of the polyester heat-shrinkable film is defined as the TD direction and the direction perpendicular to the TD direction is defined as the MD direction, the polyester heat-shrinkable film satisfies the following properties (a), (b), and (i): Structure (a): When the nominal tensile strain at break in the MD direction measured in accordance with JIS K 7127:1999 for a polyester heat-shrinkable film that has been frozen and stored at a predetermined temperature of 0°C or lower for a predetermined period of time ranging from one month to six months from the time immediately after production is defined as C1, C1 is set to a value of 382.5% or more. Structure (b): When the nominal tensile strain at break in the MD direction of a polyester heat-shrinkable film immediately after production and before frozen storage, as measured in accordance with JIS K 7127:1999, is C2, C1 / C2 is a value of 0.85 or more, and C2 is a value within the range of 450 to 600%. Structure (i): The polyester resin used as the constituent resin of the polyester-based heat-shrinkable film is a mixture of amorphous polyester resin and recycled crystalline polyester resin, and when the entire mixture is taken as 100% by weight, the amount of recycled crystalline polyester resin blended is within the range of 10 to 30% by weight. In this way, by storing the heat shrinkable film in a frozen state so as to satisfy the specified conditions, not only does it become easier to identify defective products, but it also allows the heat shrinkable film to retain its specified thermal and mechanical properties with good reproducibility even after storage in the same warehouse for a short period of time, such as one month, or even after storage for a long period of time, such as six months or more. [Brief explanation of the drawings]

[0020] [Figure 1]1(a) to 1(c) are diagrams provided to explain the shape of the heat shrinkable film. [Figure 2] 2(a) and 2(b) are diagrams provided to explain the method for measuring the nominal tensile strain at break in the MD direction of a heat shrinkable film, and the resulting SS chart (stress-strain curve). [Figure 3] FIG. 3 is a diagram for explaining the relationship between the nominal tensile break strain (C1) in the MD direction and the elapsed time (months) for a polyester heat-shrinkable film when the storage temperature conditions are changed (23°C, 0°C, -35°C, -60°C). [Figure 4] FIG. 4(a) is a diagram illustrating the relationship between the ratio of nominal tensile strain at break in the MD direction (C1 / C2) and the elapsed time (months) when the storage conditions are changed for a heat-shrinkable film, and FIG. 4(b) is a diagram illustrating the relationship between the ratio of nominal tensile strain at break in the MD direction (C1 / C2) and the film breakage rate (relative value) when the storage conditions are changed. [Figure 5] 5(a) and 5(b) are diagrams for explaining the method for measuring the dynamic friction coefficient of a heat-shrinkable film and the measurement results. [Figure 6] FIG. 6 is a diagram for explaining the relationship between the dynamic friction coefficient and the elapsed time due to differences in storage conditions of the heat shrinkable film. [Figure 7] FIG. 7 shows DSC charts of the heat shrinkable film before frozen storage and after frozen storage at −60° C. and 23° C. for 12 months, respectively. [Figure 8] 8(a) to 8(c) are diagrams (photographs) provided to explain the frozen storage state of the heat-shrinkable film. DETAILED DESCRIPTION OF THE INVENTION

[0021] [First embodiment] The first embodiment is a polyester heat-shrinkable film 10 illustrated in Figs. 1(a) to (c), which is characterized in that when the main shrinkage direction of the polyester heat-shrinkable film obtained by freezing and storing it for a predetermined time at a predetermined temperature is defined as the TD direction and the direction perpendicular thereto is defined as the MD direction, the polyester heat-shrinkable film satisfies the following properties (a), (b), and (i): Structure (a): When the nominal tensile break strain in the MD direction measured in accordance with JIS K7127:1999 for a polyester heat-shrinkable film that has been frozen and stored at a predetermined temperature of 0°C or lower and for a predetermined time period of one month or more, based on the time immediately after production, is defined as C1, C1 is set to a value of 300% or more. Structure (b): When the nominal tensile strain at break in the MD direction of a polyester heat-shrinkable film immediately after production and before frozen storage, as measured in accordance with JIS K 7127:1999, is C2 (hereinafter sometimes referred to as the initial value), C1 / C2 is a value of 0.85 or more. Structure (i): The polyester resin used as the constituent resin of the polyester-based heat-shrinkable film is a mixture of amorphous polyester resin and recycled crystalline polyester resin, and when the entire mixture is taken as 100% by weight, the amount of recycled crystalline polyester resin blended is within the range of 10 to 30% by weight. Hereinafter, the configuration of the heat shrinkable film of the first embodiment will be specifically described with reference to the drawings as needed.

[0022] 1. Resin composition (1) Type As the constituent resin of the heat shrinkable film, any resin containing polyester resin as the main component can be used as appropriate. Therefore, since the heat shrinkability, heat resistance, mechanical strength, transparency, etc. are superior, the polyester resin content is preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 95% by weight or more of the total amount.

[0023] (2) Polyester resin When a polyester resin is used as the constituent resin of the heat-shrinkable film, the type of polyester resin is not fundamentally important, but it is usually preferable that the polyester resin be a polyester resin composed of a diol and a dicarboxylic acid, a polyester resin composed of a diol and a hydroxycarboxylic acid, a polyester resin composed of a diol, a dicarboxylic acid, and a hydroxycarboxylic acid, or a mixture of these polyester resins.

[0024] Here, examples of the diol as a compound component of the polyester resin include at least one of aliphatic diols such as ethylene glycol, diethylene glycol, propanediol, butanediol, neopentyl glycol, and hexanediol, alicyclic diols such as 1,4-hexanedimethanol, and aromatic diols. Among these, ethylene glycol, diethylene glycol, and 1,4-hexanedimethanol are particularly preferred.

[0025] Similarly, examples of dicarboxylic acids as a compound component of polyester resins include at least one of fatty acid dicarboxylic acids such as adipic acid, sebacic acid, and azelaic acid; aromatic dicarboxylic acids such as terephthalic acid, naphthalenedicarboxylic acid, and isophthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and ester-forming derivatives thereof.

[0026] Among these, terephthalic acid is particularly preferred. Similarly, the hydroxycarboxylic acid as a compound component of the polyester resin may include at least one of lactic acid, hydroxybutyric acid, polycaprolactone, and the like.

[0027] Furthermore, as the amorphous polyester resin, for example, an amorphous polyester resin composed of a dicarboxylic acid consisting of at least 80 mol% terephthalic acid and a diol consisting of 50 to 80 mol% ethylene glycol and 20 to 50 mol% of one or more diols selected from 1,4-cyclohexanedimethanol, neopentyl glycol, and diethylene glycol can be preferably used. If necessary, other dicarboxylic acids and diols or hydroxycarboxylic acids may be used to change the properties of the film. These may be used alone or in combination.

[0028] On the other hand, examples of crystalline polyester resins include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, and polypropylene terephthalate, and these may be used alone or in combination.

[0029] Furthermore, when the polyester resin is a mixture of an amorphous polyester resin and a crystalline polyester resin, in order to obtain good heat resistance, shrinkage rate, etc., the amount of amorphous polyester resin is preferably in the range of 90 to 100% by weight, more preferably 91 to 100% by weight, relative to the total amount of resin constituting the polyester-based heat-shrinkable film.

[0030] 2. Configuration (a): Tensile fracture nominal strain C1 In the configuration (a), when the nominal tensile strain at break in the MD direction of a heat-shrinkable film after storage at a predetermined temperature (e.g., 23°C) for a predetermined time (e.g., one month or more) after production is C1, as measured in accordance with JIS K 7127:1999, C1 is set to a value of 300% or more. That is, a dumbbell-shaped test piece is stored under specified conditions, and then a tensile load is applied. The maximum load at which the test piece breaks is divided by the cross-sectional area, which is defined as the tensile breaking stress, and the maximum load at which the test piece yields is divided by the cross-sectional area, which is defined as the tensile yield stress. Therefore, the phenomenon when the test piece breaks in this way corresponds to the nominal tensile strain at break in the MD direction of the heat shrinkable film, and can be compared with the specified heat shrinkage characteristics. Therefore, it is more preferable that the nominal tensile strain at break C1, which is the configuration (a), is set to a value within the range of 310 to 800%, and even more preferably within the range of 320 to 600%.

[0031] Here, with reference to FIGS. 2(a) and 2(b), a method for measuring the nominal tensile strain at break in the MD direction of a heat shrinkable film will be described based on JIS K 7127:1999. That is, FIG. 2(a) is a schematic diagram of a tensile tester conforming to JIS K 7721:2009. A heat-shrinkable film serving as a measurement sample (with a predetermined dumbbell shape) is sandwiched between two vertical chucks 12a and 12b attached near the center of a bar attached parallel to the main body, and chuck 12a is raised at a predetermined speed (for example, 300 mm / min). The load cell 12c connected to the chuck 12a measures the stress corresponding to the elongation (strain) of the test sample, and outputs the measured stress to the outside using a measuring device (not shown).

[0032] Next, using the tensile tester shown in FIG. 2(a), an SS curve (stress-strain curve) for the measurement sample can be obtained as shown in FIG. 2(b). The nominal tensile strain at break in the MD direction of the heat shrinkable film (initial value is C1) can be defined as the stress at which the measurement sample on the SS curve breaks.

[0033] Next, referring to FIG. 3, the relationship between the nominal tensile strain at break (C1) in the MD direction of the heat shrinkable film and the elapsed time (months) will be described. That is, the horizontal axis of FIG. 3 shows the elapsed time under different storage conditions, and the vertical axis shows the nominal tensile strain at break (C1) in the MD direction of the polyester heat-shrinkable film. In FIG. 3, line A1 corresponds to a storage temperature condition of -60°C, line B1 corresponds to a storage temperature condition of -35°C, line C1 corresponds to a storage temperature condition of 0°C, and further, line D1 corresponds to a storage temperature condition of 23°C. Comparing the profile changes of these lines A1 to D1, it is clear that differences in the nominal tensile fracture strain (C1) in the MD direction begin to appear after at least 1 to 3 months due to differences in storage temperature conditions, and more specifically, the lower the storage temperature conditions, the more likely it is that the initial value before storage is maintained. Next, after 6 months, a clear difference in the nominal tensile break strain (C1) in the MD direction due to the difference in storage temperature conditions was confirmed, and at least under storage temperature conditions of 0°C, -35°C, and -60°C, there was a tendency for the nominal tensile break strain (C1) to maintain 85% or more of the initial value before storage. Furthermore, after 12 months, the nominal tensile strain at break (C1) tends to remain at least 50% of the initial value before storage under storage temperatures of -35°C and -60°C. Therefore, if the storage temperature condition is within the range of 0°C to approximately -60°C, more preferably within the range of -35°C to -60°C, and particularly preferably around -60°C, it can be said that the degree of deterioration of the nominal tensile strain at break (C1) of the polyester heat-shrinkable film can be confirmed after at least 1 to 3 months have passed, and the deterioration state of the polyester heat-shrinkable film can be estimated.

[0034] 3. Configuration (b): Ratio of tensile fracture nominal strain (C1 / C2) The configuration (b) is a configuration in which, when the nominal tensile strain at break in the MD direction of the heat-shrinkable film measured in accordance with JIS K 7127:1999 before storage for a predetermined time under predetermined conditions, i.e., immediately after production, is defined as C2, the ratio C1 / C2 is 0.85 or more. That is, when a tensile load is applied, the maximum load at which the test piece breaks is divided by the cross-sectional area, which is the tensile breaking stress, and the maximum load at which the test piece yields is divided by the cross-sectional area, which is the tensile yield stress. Therefore, the phenomenon when the test piece breaks in this way corresponds to the nominal tensile strain at break in the MD direction of the heat shrinkable film, and can be compared with the specified heat shrinkage characteristics. In addition, taking into consideration the numerical value or ratio of C1 after storage for a predetermined time under predetermined conditions, and furthermore practical usability and application, specifically, it is preferable that C2 be a value of 300% or more, more preferably a value in the range of 400 to 800%, and even more preferably a value in the range of 450 to 600%.

[0035] Here, referring to FIG. 4(a), the relationship between the ratio of nominal tensile break strains in the MD direction (C1 / C2) and the elapsed time in a polyester heat-shrinkable film will be described. That is, the horizontal axis of Figure 4(a) shows the elapsed time (months) at different storage temperatures (including examples other than Examples 1-2 and Comparative Examples 1-2), and the vertical axis shows the ratio (C1 / C2) of the nominal tensile break strain in the MD direction of the heat-shrinkable film. In Figure 4(a), characteristic curve A2 is the characteristic curve when the heat-shrinkable film is stored at a temperature of -60°C for different elapsed times, and characteristic curve B2 corresponds to the same case when the heat-shrinkable film is stored at a temperature of 23°C for different elapsed times. Comparison of these characteristic curves A2 and B2 reveals that due to differences in storage temperature, differences begin to appear in the ratio of nominal tensile break strain in the MD direction (C1 / C2) after 1 to 3 months, and after 6 months a clear difference can be confirmed, and after 12 months an even clearer difference can be confirmed.

[0036] Therefore, although it depends on the storage temperature, etc., if the elapsed time is at least 1 to 3 months, it is possible to determine the difference in the ratio of the nominal tensile breakage (C1 / C2) of the heat-shrinkable film, and it is possible to accurately estimate the degree of deterioration of the heat-shrinkable film. The change in the ratio (C1 / C2) of the nominal tensile break strength of the heat shrinkable film is thought to be caused by the migration of antiblocking agents and low molecular weight substances to the surface of the heat shrinkable film, and it is also presumed that the influence of changes in the crystalline state is one of the causes.

[0037] Next, referring to FIG. 4(b), the relationship between the ratio (C1 / C2) of nominal tensile strain at break in the MD direction of a polyester heat-shrinkable film and the relative evaluation based on the film breakage rate (%) will be explained. That is, the horizontal axis of Figure 4(b) shows the ratio of nominal tensile break strains in the MD direction (C1 / C2), which includes examples other than Examples 1-2 and Comparative Examples 1-2, and the vertical axis shows the relative evaluation (-) based on the film breakage rate (%).

[0038] According to the characteristic curve in FIG. 4(b), when the ratio of C1 / C2 is between about 0.1 and 0.8, the relative evaluation based on the film breakage rate (%) is 0, which is an extremely poor evaluation result. Next, when the C1 / C2 ratio is approximately 0.8 to 0.83, the relative evaluation based on the film breakage rate (%) is 1, which is still an insufficient evaluation result. In contrast, it can be seen that when the ratio of C1 / C2 becomes 0.85 or more, the relative evaluation based on the film breakage rate (%) suddenly becomes favorable. Furthermore, it is understood that when the C1 / C2 ratio is 0.95 or more, the relative evaluation based on the film breakage rate (%) reaches the maximum score of 5. Therefore, from the tendency of this characteristic curve, it can be said that in order to obtain a good film breakage rate (%), it is preferable to set the C1 / C2 ratio to a value of 0.85 or more. Conversely, on the premise that the nominal tensile strain at break in the MD direction during manufacturing is set to a predetermined value (300% or more), by setting the C1 / C2 ratio to a predetermined value (0.85 or more), the film breakage rate (%) can be reduced and stable mechanical strength can be controlled.

[0039] 4. Configuration (c): Coefficient of kinetic friction The configuration (c) relates to the coefficient of dynamic friction of a polyester heat-shrinkable film after storage at a predetermined temperature for a predetermined time, as measured in accordance with JIS K 7125:1999, and it is preferable that the coefficient of dynamic friction is set to a value within the range of 0.15 to 0.6. The reason for this is that if the dynamic friction coefficient is less than 0.15, the surface becomes excessively slippery, making it difficult to handle or to roll up. On the other hand, if the dynamic friction coefficient exceeds 0.6, the surface smoothness decreases, and it may become difficult to adjust values ​​such as the thermal shrinkage rate. Therefore, it is more preferable that the dynamic friction coefficient is set to a value within the range of 0.25 to 0.55, and even more preferable that the dynamic friction coefficient is set to a value within the range of 0.3 to 0.5. Regarding the constitution (c), it is preferable that the coefficient of dynamic friction of the polyester heat-shrinkable film before being stored in a frozen state at a predetermined temperature for a predetermined time also be set to a value within the range of 0.15 to 0.6. That is, even when frozen storage is performed at a predetermined temperature for a predetermined time, it is preferable that the dynamic friction coefficient does not change before and after the storage. More specifically, the ratio of the dynamic friction coefficient after frozen storage to the dynamic friction coefficient before frozen storage is preferably 0.5 to 1.2, more preferably 0.8 to 1.1, and even more preferably 0.9 to 1.05.

[0040] As shown in FIG. 5(a), the dynamic friction coefficient is measured by using a load cell 24 to measure the friction coefficient when a sliding piece 16 carrying a load 18 of 200 g is slid on the polyester heat-shrinkable film 10 to be measured at a speed of 100 mm / min. In the case of the dynamic friction coefficient, unlike the static friction coefficient, the spring 22 is not used to absorb the shock when the load cell 24 starts to move, and the peak of the static friction force is ignored. As shown in Figure 5(b), the average load from the start of the relative slippage between the contact surfaces up to 60 mm is the friction force F D Specifically, the dynamic friction coefficient μ D (-) can be found.

[0041]

number

[0042] μD : Coefficient of dynamic friction (-) F D :Dynamic friction force (N) F P :Normal force generated by the weight of the sliding piece (1.96N)

[0043] Here, referring to FIG. 6, the relationship between the coefficient of dynamic friction and the elapsed time in a polyester heat-shrinkable film will be explained. That is, the horizontal axis of FIG. 6 indicates the elapsed time (months), and the vertical axis indicates the dynamic friction coefficient (-) of the heat shrinkable film. The characteristic curve A3 corresponds to the storage condition at -60°C, and the characteristic curve B3 corresponds to the storage condition at room temperature (23°C). For both characteristic curves A3 and B3, differences begin to appear in the dynamic friction coefficient after about 1 to 3 months have passed, and after 6 months a clear difference from the initial value can be confirmed. Therefore, regardless of differences in storage conditions, as long as the elapsed time is at least three months or more, it is possible to accurately estimate the degree of deterioration of the heat-shrinkable film by determining the difference between the initial value and the dynamic friction coefficient after a specified time has elapsed.

[0044] 5. Compositions (d) to (f) (Heat shrinkage rate) (1) Furthermore, the configurations (d) to (f) are typical heat shrinkage rates evaluated for heat shrinkable films. Therefore, for the heat-shrinkable film after storage for a predetermined time, the heat shrinkage rates (A1, A2, A3) at 70°C for 10 seconds, 80°C for 10 seconds, and 100°C for 10 seconds can be measured using the following formula (2), and compared with the heat shrinkage rates of other heat-shrinkable films.

[0045]

number

[0046] L: Measurement sample length before heat treatment (cm) L0: Measurement sample length after heat treatment (cm)

[0047] (2) Composition (g): Haze The constitution (g) is a constitutional requirement that the haze of the polyester heat-shrinkable film after storage for a predetermined time, as measured in accordance with JIS K 7136:2000, is 10% or less. The reason for this is that by limiting the haze to a value equal to or less than a predetermined value, the transparency of the heat shrinkable film can be easily controlled quantitatively, and since the transparency is good, the versatility can be further enhanced.

[0048] More specifically, if the haze before heat shrinkage exceeds 10%, the transparency decreases, which may make it difficult to apply the film to decorative applications such as PET bottles. On the other hand, if the haze before heat shrinkage is too small, it becomes difficult to control stably, and the production yield may decrease significantly. Therefore, as the configuration (g), it is more preferable that the haze of the film after storage for a predetermined time be set to a value within the range of 0.1 to 7%, and even more preferably to a value within the range of 0.5 to 3%.

[0049] (5) Composition (h): Enthalpy change Furthermore, the configuration (h) is a configuration requirement that the change in endothermic heat (sometimes referred to as enthalpy change) corresponding to the endothermic peak based on enthalpy relaxation (crystalline melting) measured using a DSC (differential scanning calorimeter) for the heat-shrinkable film after storage for a predetermined time is a value within the range of 0 to 25%, when the endothermic heat before the predetermined time has elapsed is set to 100%. That is, the state of deterioration of the heat-shrinkable film can be determined by measuring the enthalpy value of the endothermic peak in an air stream at a temperature rise rate of 10°C / min using a DSC.

[0050] Here, referring to FIG. 7, the relationship between the enthalpy value corresponding to the endothermic peak measured by DSC and the elapsed time in a polyester heat-shrinkable film will be described. That is, in FIG. 7, line L1 is a DSC curve corresponding to the polyester heat-shrinkable film (corresponding to Example 1) immediately after production (usually within 24 hours). Similarly, line L2 is a DSC curve corresponding to a polyester-based heat-shrinkable film after storage at -60°C for 12 months from immediately after production, and line L3 is a DSC curve corresponding to a polyester-based heat-shrinkable film after storage at 23°C for 12 months from immediately after production. It is clear that the DSC curve of line L2 does not have a significant difference in shape, including the endothermic peak, from the DSC curve of line L1, but it is understood that the shape of the endothermic peak of the DSC curve of line L3 changes near the crystal transition, and the predetermined enthalpy value also changes slightly. Therefore, the state of deterioration of such a heat-shrinkable film can be estimated from the DSC curve measured by DSC and the enthalpy value corresponding to the endothermic peak. Therefore, it can be said that the change in endothermic amount at the endothermic peak corresponding to the endothermic peak measured by DSC is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less, when the change immediately after production is taken as 100%.

[0051] (6) Other 1 It is preferable to incorporate various additives into the heat shrinkable film of the first embodiment, or to attach them to one or both surfaces thereof. More specifically, at least one of a hydrolysis inhibitor, an antistatic agent, an ultraviolet absorber, an infrared absorber, a colorant, an organic filler, an inorganic filler, an organic fiber, an inorganic fiber, and the like is preferably blended in an amount of 0.01 to 10% by weight, more preferably 0.1 to 1% by weight, based on the total amount of the polyester-based heat-shrinkable film.

[0052] 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%.

[0053] The resin as the main component constituting the other resin layer may be a polyester resin similar to that of the heat-shrinkable film, or preferably at least one of a different acrylic resin, an olefin resin, a urethane resin, a rubber resin, etc.

[0054] Furthermore, it is also preferable to form the 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 heat-shrinkable film becomes uniform within the plane, as shown in Figure 1(c). Such a shrinkage adjusting layer can be laminated by using an adhesive, a coating method, or a heat treatment depending on the shrinkage characteristics of the heat shrinkable film.

[0055] More specifically, the thickness of the shrinkage rate adjusting layer is in the range of 0.1 to 3 μm, and if the shrinkage rate of the heat shrinkable film at a specified temperature is excessively large, it is preferable to laminate a shrinkage rate adjusting layer of a type that suppresses this. Furthermore, if the shrinkage rate of the heat shrinkable film at a predetermined temperature is excessively small, it is preferable to laminate a shrinkage rate adjusting layer of a type that expands the shrinkage rate. Therefore, the shrinkage rate adjusting layer is used to obtain a desired shrinkage rate without producing various types of heat shrinkable films with different shrinkage rates.

[0056] (7) Other 2 The method for producing the heat shrinkable film of the first embodiment is not particularly limited, but it is typically preferable to produce it in accordance with the following steps.

[0057] 1) Preparation and mixing of raw materials First, it is preferable to prepare the base material and additives such as crystalline polyester resin, non-crystalline polyester resin, rubber-based resin, antistatic agent, and hydrolysis inhibitor. Next, the prepared crystalline polyester resin, amorphous polyester resin, etc. are preferably charged into the stirring vessel while being weighed, and mixed and stirred using a stirring device until homogeneous.

[0058] 2) Raw sheet production process Next, the homogeneously mixed raw materials are preferably dried to an absolutely dry state. Next, typically, it is preferable to carry out extrusion molding to prepare a raw sheet having a predetermined thickness. More specifically, for example, extrusion molding is performed using an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D of 24 and an extrusion screw diameter of 50 mm under conditions of an extrusion temperature of 260°C, and a raw sheet of a predetermined thickness (usually 10 to 300 μm) can be obtained.

[0059] 3) Creating heat shrinkable film Next, the obtained raw sheet is heated and pressed while being moved over or between rolls using a heat shrinkable film manufacturing device to produce a heat shrinkable film (polyester heat shrinkable film, etc.). That is, it is preferable to stretch the film in a predetermined direction while heating and pressing it at a predetermined stretching temperature and stretching ratio, while basically expanding the film width, thereby crystallizing the molecules that make up the heat-shrinkable film into a predetermined shape. Then, by solidifying it in this state, a heat-shrinkable film that can be used for decoration, labels, etc. can be produced.

[0060] 4) Heat shrink film inspection process It is preferable to provide a predetermined inspection process in which the following characteristics are measured continuously or intermittently for the produced 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, it is possible to obtain a heat shrinkable film with more uniform shrinkage characteristics and the like. Visual inspection of the appearance Thickness variation measurement Glass transition temperature measurement Melting point and heat of fusion measurement Tensile modulus measurement -Tear strength measurement Viscoelasticity measurement using SS curves

[0061] (8) Other 3 The embodiment regarding the method of using the heat shrinkable film is not particularly limited, and any known method of using a heat shrinkable film can be suitably applied. For example, when using a heat shrinkable film, first, the heat shrinkable film is cut to an appropriate length and width and formed into a long cylindrical object. The long cylindrical object is then fed to an automatic label attachment device (shrink labeler) and further cut to the required length. Next, the container is fitted onto a PET bottle or the like filled with the contents.

[0062] Next, the heat-shrinkable film wrapped around the PET bottle or the like is subjected to a heat treatment by passing it through a hot air tunnel or steam tunnel at a predetermined temperature. The heat-shrinkable film is uniformly heated and thermally shrunk by radiant heat such as infrared rays or by blowing heated steam at about 90°C onto it from the surrounding area. Therefore, labeled containers can be quickly obtained by adhering them to the outer surface of PET bottles or the like.

[0063] The heat shrinkable film of the present invention is characterized by satisfying at least the following requirements (a) and (b). By doing so, the heat shrinkable film can be kept stable for a considerably long period of time under certain conditions when it is heat shrunk. Therefore, even if a label made from this film is placed over the body of a bottle and heat-shrunk, it can be attached to the bottle while conforming to the shape of the bottle periphery, and furthermore, the occurrence of fine wrinkles can be suppressed.

[0064] [Second embodiment] The second embodiment is a method for storing a polyester heat-shrinkable film by storing it in a frozen state at a predetermined temperature for a predetermined time, characterized in that, when the main shrinkage direction of the polyester heat-shrinkable film is defined as the TD direction and the direction perpendicular to the TD direction is defined as the MD direction, the polyester heat-shrinkable film satisfies the following properties (a), (b), and (i): Structure (a): When the nominal tensile strain at break in the MD direction measured in accordance with JIS K 7127:1999 for a polyester heat-shrinkable film that has been frozen and stored at a predetermined temperature of 0°C or lower for a predetermined period of time ranging from one month to six months from the time immediately after production is defined as C1, C1 is set to a value of 382.5% or more. Configuration (b): When the nominal tensile break strain in the MD direction of the polyester heat-shrinkable film immediately after production and before frozen storage, as measured in accordance with JIS K 7127:1999, is C2, C1 / C2 is set to a value of 0.85 or more, and C2 is set to a value within the range of 450 to 600%. Structure (i): The polyester resin used as the constituent resin of the polyester-based heat-shrinkable film is a mixture of an amorphous polyester resin and a recycled crystalline polyester resin, and when the entire mixture is taken as 100% by weight, the amount of the recycled crystalline polyester resin is set to a value within the range of 10 to 30% by weight. Hereinafter, the method for storing the polyester heat-shrinkable film of the second embodiment will be described in more detail with reference to FIGS. 8(a) to 8(c) as needed.

[0065] 1. Heat shrink film preparation process As described in the first embodiment, it is preferable to manufacture and prepare the heat shrinkable film according to a predetermined process. That is, through the steps of preparing and mixing raw materials, creating a raw sheet, and creating a heat-shrinkable film, a shrinkable heat-shrinkable film having predetermined heat-shrinkage characteristics and mechanical properties can be created. In the case of freezing and storing, it is preferable to insert the heat shrinkable film prepared as shown in FIG. 8(a) into a bag-shaped covering material made of a moisture-proof material.

[0066] 2.Storage process of heat shrink film (1)Storage temperature Next, the heat shrinkable film is preferably stored at a storage temperature of 0°C or lower. That is, as shown in FIG. 4(a), if the temperature is below a predetermined temperature, the degree of deterioration of the heat-shrinkable film is low even after a predetermined period of time (for example, six months or less) has passed, and it can be said that there are few practical problems. Conversely, even if the storage conditions are at a specified temperature and the storage period is 1 to 6 months, if C1 / C2 is less than 0.85 due to variations in temperature conditions, storage time, etc., it can be determined that the heat-shrinkable film has deteriorated. When the film is stored at 0°C or below and C1 / C2 becomes less than 0.85, the deteriorated portion can be removed from the heat-shrinkable film, or the roll of heat-shrinkable film containing the deteriorated portion can be removed, thereby providing a heat-shrinkable film that exhibits excellent breaking strength.

[0067] On the other hand, if it is desired to maintain the initial mechanical properties immediately after production, it is preferable to carry out the storage process by setting the storage temperature of the heat-shrinkable film to a value within the range of -60°C to -30°C. That is, it is preferable to prepare a freezer stocker or the like as shown in Figures 8(b) to (c), and store the heat-shrinkable film inserted into the covering material by controlling its internal temperature (freezer storage temperature) to a value within the range of -60°C to -30°C. The reason for this is that if the storage temperature exceeds -30°C, the heat shrinkable film may deteriorate somewhat over time, although this is affected by the amount of oxygen and moisture in the surroundings. On the other hand, if the storage temperature falls below -60°C, the load on the freezer storage equipment may increase and storage costs may become higher. Therefore, although it depends on the type and application of the heat shrinkable film, the storage temperature is more preferably set within the range of -55°C to -35°C, and even more preferably within the range of -50°C to -40°C. Furthermore, when the storage temperature reaches approximately -60°C, the heat shrinkable film is effectively frozen, and the moisture contained therein is also frozen. Therefore, it is preferable to return the temperature of the heat shrinkable film to room temperature before performing various measurements.

[0068] (2) Storage time The storage time after production of the heat shrinkable film is preferably one month or more at a predetermined temperature (-60°C to 0°C). The reason for this is that, conversely, if the storage period is less than one month, the produced heat-shrinkable film is less likely to deteriorate, depending on the storage temperature, and there is little point in limiting C1 / C2 to the specified range. That is, as shown in Figures 3 and 4(a), even if the storage temperature is between 0°C and room temperature (23°C), the heat shrinkage properties and mechanical properties of the heat shrinkable film tend to deteriorate to a certain extent after one month or more has passed. However, if the storage time is too long, it may become very costly to maintain and manage the storage temperature. Therefore, after production of the heat shrinkable film, the storage time at a predetermined temperature is more preferably 1.5 to 12 months, and even more preferably within the range of 2 to 6 months.

[0069] (3) Storage device Furthermore, the type and configuration of the storage device (including the storage method) are not particularly limited, but in the case of frozen storage, it is preferable to use, for example, a freezer stocker as shown in Figures 8(b) to (c), a freezer warehouse that maintains the entire product at a specified temperature, or a method of spraying cooled air or a cooled liquid or immersing the product in such a method. If such a storage device is a freezer stocker, it can maintain a more uniform low temperature and may be relatively easy to make the device smaller. Therefore, it is suitable for measuring and inspecting storage conditions and heat-shrinkable films housed inside. Furthermore, a refrigerated warehouse has a larger storage area and can store and transport a relatively large amount of heat shrinkable film easily. Therefore, even if the heat shrinkable film is in roll form, a considerable amount can be stored in a limited space.

[0070] On the other hand, although not shown, methods such as spraying cooling air or cooling liquid (including mist) or immersion in them are relatively inexpensive and economically advantageous. However, in the case of storage for a relatively long period of time, it is preferable to use a general freezer warehouse or refrigerator from the viewpoint of space and economy, provided that the environmental temperature does not fluctuate much. In order to further prevent deterioration of the heat shrinkable film due to variations in the environmental temperature, etc., it is preferable to continuously or intermittently record and manage the environmental conditions such as temperature and humidity in the warehouse.

[0071] (4) Storage method If necessary, it is preferable to store the product in an inert gas atmosphere or in air containing a predetermined amount or more of an inert gas. That is, if the storage temperature is within the range of -60°C to 0°C, the relative humidity is usually 0%, and even if a polyester heat-shrinkable film or the like is used, it can be said that there is almost no deterioration due to hydrolysis or the like. However, if the storage device is a refrigerated warehouse or the like, it may be opened and closed many times during the storage period to load stored heat shrinkable films and load newly manufactured heat shrinkable films. Therefore, in order to ensure a more complete and stable storage condition for the heat-shrinkable film, it is preferable to mix an inert gas, such as nitrogen, with at least air, at a concentration of 25 vol% or more per unit volume, more preferably 30 vol% or more, and even more preferably 50 vol% or more.

[0072] 3. Returning the heat shrink film to room temperature When the storage temperature is within the range of -60°C to 0°C, from the viewpoint of cost, etc., it is preferable to return the polyester heat-shrinkable film to room temperature under conditions of, for example, room temperature (23°C), 50% RH, and 24 hours. Furthermore, when the heat-shrinkable film is returned to room temperature under the above conditions, condensation or moisture absorption may occur, resulting in a deterioration in the heat-shrinkability and mechanical properties of the heat-shrinkable film. Therefore, it is more preferable to return the heat shrinkable film from the predetermined storage temperature to room temperature, usually over a period of 12 to 24 hours. That is, the temperature gradient when returning to room temperature is preferably within the range of -60°C / 12 hours to 0°C / 24 hours, and more preferably within the range of -40°C / 12 hours to -5°C / 24 hours. Furthermore, to prevent the effects of condensation due to moisture in the air, it is generally preferable to return the temperature to room temperature in an environment with a relative humidity of 0 to 30%, and more preferably to return the temperature to room temperature in an environment with a relative humidity of 0 to 20%. Therefore, when the heat-shrinkable film is in a roll form and has a considerable volume, it is preferable to cover the entire or part of the heat-shrinkable film with a moisture-proof material or moisture-proof member (including a desiccant, etc.), and then return it to room temperature while blowing dry air, etc.

[0073] 4. Heat shrink film inspection process As explained in detail in the first embodiment, it is necessary to carry out at least the following steps (a) to (c). That is, in step (a), depending on the type of heat shrinkable film, C1, which is the nominal tensile strain at break in the MD direction, of the heat shrinkable film after storage for a predetermined time under predetermined conditions, is measured. Next, in step (b), C1 / C2, which is the ratio of C1 to the nominal tensile strain at break C2 in the MD direction of the heat-shrinkable film before the lapse of a predetermined time for measuring C1, is measured. Next, in step (c), the coefficient of dynamic friction is measured.

[0074] 5.Other inspection processes for heat shrinkable film Next, as described in the first embodiment, it is preferable to carry out an inspection step in which predetermined heat shrinkage characteristics and mechanical properties of the heat shrinkable film are measured continuously or intermittently in addition to steps (a) to (c) to confirm that they are within predetermined ranges. 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, it is possible to obtain a heat shrinkable film with more uniform shrinkage characteristics and the like. [Example]

[0075] 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 resins used in the examples are as follows:

[0076] (PETG1) Dicarboxylic acid: 100 mol% terephthalic acid, diol: 67 mol% ethylene glycol, 19 mol% 1,4-cyclohexanedimethanol, 11 mol% diethylene glycol Amorphous polyester resin (glass transition temperature: 69°C)

[0077] (PETG2) Dicarboxylic acid: 100 mol% terephthalic acid, diol: amorphous polyester consisting of 63 mol% ethylene glycol, 24 mol% 1,4-cyclohexanedimethanol, and 13 mol% diethylene glycol (glass transition temperature: 69°C)

[0078] (PETG3) Amorphous polyester (glass transition temperature: 69°C) consisting of dicarboxylic acid: 100 mol% terephthalic acid, diol: 59.9 mol% ethylene glycol, 27.7 mol% 1,4-cyclohexanedimethanol, and 12.4 mol% diethylene glycol.

[0079] (PETG4) Dicarboxylic acid: 100 mol% terephthalic acid, diol: amorphous polyester consisting of 70 mol% ethylene glycol, 28 mol% neopentyl glycol, and 2 mol% diethylene glycol (glass transition temperature: 69°C)

[0080] (APET) Dicarboxylic acid: 100 mol% terephthalic acid, diol: 100 mol% ethylene glycol crystalline polyester resin (glass transition temperature: none, intrinsic viscosity: 0.65 dL / g)

[0081] (PCR) Dicarboxylic acid: 98.6 parts by weight of terephthalic acid, 1.4 parts by weight of isophthalic acid; diol: 97.3 parts by weight of ethylene glycol, 2.7 parts by weight of diethylene glycol. Recycled crystalline polyester resin (glass transition temperature: none, intrinsic viscosity: 0.72 dL / g)

[0082] (PBT) A crystalline polyester resin consisting of 100 parts by weight of dicarboxylic acid: terephthalic acid and 100 parts by weight of diol: 1,4-butanediol

[0083] (additives) Silica masterbatch consisting of PET matrix resin, 5% silica by weight, and an average silica particle size of 2.7 μm

[0084] [Example 1] 1. Creating heat shrinkable film 100 parts by weight of amorphous polyester resin (PETG1) and 1 part by weight of additive were placed in a stirring vessel, and the raw material was dried. After that, it was extruded at an extrusion temperature of 260°C using an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D of 24 and an extrusion screw diameter of 50 mm to obtain a raw sheet having a thickness of 100 μm. Next, using a heat-shrinkable film manufacturing device under the conditions shown in Table 1, a 40 μm thick polyester heat-shrinkable film was produced from a 200 μm thick raw sheet at a stretching temperature of 82°C and a stretch ratio (MD direction: 101%, TD direction: 500%). The obtained polyester heat-shrinkable film was sealed in a covering material and stored in a freezer stocker (JMCC-60, manufactured by JCM) at −60° C. for 6 months to prepare a test sample.

[0085] 2. Evaluation of heat shrinkable film (test piece) (1) Rating 1: C1 The polyester heat-shrinkable film was removed from the freezer and stored at 23°C and 50% RH for 24 hours. Next, in accordance with JIS K 7127:1999, the nominal tensile break strain (C1) in the MD direction of the polyester heat-shrinkable film was measured under a specified temperature condition (-60°C), with the value immediately after production as the reference value, after storage for a specified period (6 months).

[0086] (2) Rating 2: C2 The nominal tensile strain at break (C2) in the MD direction of the obtained polyester heat-shrinkable film was measured within 24 hours in accordance with JIS K 7127:1999, with the value immediately after production being used as the initial value.

[0087] (3) Rating 3: C1 / C2 From C1 obtained in Evaluation 1 and C2 obtained in Evaluation 2, the value of C1 / C2, which indicates the rate of change in the nominal tensile strain at break in the MD direction of the obtained polyester heat-shrinkable film, was calculated.

[0088] (4) Evaluation 4: Film breakage rate The obtained test samples (number of samples=5) were taken out of the freezer and stored at 23° C. and 50% RH for 24 hours. Thereafter, in accordance with JIS K 7127:1999, a tensile tester was used to measure the SS curve, and the percentage of films that broke in the elastic region was counted and evaluated according to the following criteria. ◎: Less than 5%. ○: The value is 20% or less. △: Value is 60% or less. ×: Value is over 60%.

[0089] (5) Evaluation 5: Coefficient of dynamic friction The obtained test samples were taken out of the freezer and stored at 23°C and 50% RH for 24 hours. Thereafter, the dynamic friction coefficient of the test sample was measured in accordance with JIS K 7125:1999.

[0090] (6) Rating 6 to 8: Heat shrinkage rate The obtained test samples were removed from the freezer and stored at 23°C and 50% RH for 24 hours, and then immersed in hot water or boiling water at 70°C, 80°C, and 100°C in a thermostatic chamber for 10 seconds each to cause thermal shrinkage. Next, the heat shrinkage rates (A1, A2, A3) were calculated from the dimensional changes (TD direction) before and after the heat treatment at each temperature according to formula (2).

[0091] (7) Rating 9: Haze The obtained test samples were taken out of the freezer and stored at 23°C and 50% RH for 24 hours. Thereafter, the haze value was measured in accordance with JIS K 7136:2000 and evaluated according to the following criteria. ◎: The value is 3% or less. ○: The value is 7% or less. △: Value is 10% or less. ×: Value exceeds 10%.

[0092] (8) Rating 10: Enthalpy change The obtained test samples were taken out of the freezer and stored at 23°C and 50% RH for 24 hours. Thereafter, the enthalpy value was measured using DSC, and the enthalpy change (change in endothermic amount) was evaluated according to the following criteria, with the enthalpy value within 24 hours after production being taken as 100%. ◎: Value is 15% or less. ○: The value is 25% or less. △: Value is 50% or less. ×: Value exceeds 50%.

[0093] [Example 2] In Example 2, a polyester heat-shrinkable film was prepared under the conditions shown in Table 1, and evaluated in the same manner as in Example 1, except that the storage conditions were -60°C and 12 months. The results obtained are shown in Table 2.

[0094] [Examples 3 to 12] In Examples 3 to 12, as shown in Table 1, polyester heat-shrinkable films were produced in the same manner as in Example 1, except that the types and compounding ratios of the PET resins used and some of the production conditions were changed. Next, after storing the specimens in a frozen state under predetermined conditions, the nominal tensile strain at break (C1) in the MD direction was evaluated. The results are shown in Table 2.

[0095] [Comparative Example 1] In Comparative Example 1, a polyester heat-shrinkable film was prepared under the conditions shown in Table 1 and evaluated in the same manner as in Example 1, except that the storage conditions were room temperature (23°C) and 6 months. The obtained results are shown in Table 2.

[0096] Comparative Example 2 In Comparative Example 2, a polyester heat-shrinkable film was prepared under the conditions shown in Table 1 and evaluated in the same manner as in Example 1, except that the storage conditions were room temperature (23°C) and 12 months. The obtained results are shown in Table 2.

[0097] [Table 1]

[0098] [Table 2] [Industrial Applicability]

[0099] According to the present invention, by controlling the ratio (C1 / C2) between the nominal tensile break strain (C1) of a polyester heat-shrinkable film after frozen storage for a predetermined time immediately after production (usually within 24 hours) as the configuration (a) and the nominal tensile break strain (C2) immediately after production, i.e., before frozen storage as the configuration (b), within a predetermined range, deterioration of the polyester heat-shrinkable film can be prevented, and film breakage and the like can be effectively prevented. Furthermore, according to the present invention, in addition to the configurations (a) and (b), as the configuration (c), by controlling the predetermined dynamic friction coefficient within a predetermined range, it is possible to further detect deterioration of the heat shrinkable film, and effectively prevent film breakage and surface deterioration. Therefore, the polyester heat-shrinkable film of the present invention satisfies the simple configuration (a) and the like, and can be safely and suitably applied to labels on various PET bottles, etc., even at room temperature, even after a predetermined time has passed, and therefore it can be said that its industrial applicability is extremely high.

[0100] Additionally, although the present invention relates to a polyester-based heat-shrinkable film, it has been found that the same effects can be obtained with a polystyrene-based heat-shrinkable film derived from polystyrene resin. That is, by controlling the ratio (C1 / C2) of the nominal tensile break strain (C1) of a polyester heat-shrinkable film after frozen storage for a predetermined time from immediately after production (usually within 24 hours) to the nominal tensile break strain (C2) immediately after production, i.e., before frozen storage, within a predetermined range, it has become possible to prevent deterioration of the polystyrene heat-shrinkable film and effectively prevent film breakage, etc. [Explanation of symbols]

[0101] 10: Polyester heat shrinkable film 10a: Other resin layer 1 10b: Another resin layer 2 10c: Shrinkage rate adjustment layer 16: Slider 18: Load 24: Load cell

Claims

1. When the main shrinkage direction of a polyester heat-shrinkable film obtained by freezing and storing it for a predetermined time at a predetermined temperature is defined as the TD direction and the direction perpendicular thereto is defined as the MD direction, The polyester heat-shrinkable film is characterized in that the polyester heat-shrinkable film satisfies the following requirements (a), (b), and (i): Configuration (a): When the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film measured in accordance with JIS K 7127:1999 is C1, the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film is C1, the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film measured in accordance with JIS K 7127:1999, the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film ... Structure (b): When the nominal tensile break strain in the MD direction of the polyester heat-shrinkable film immediately after production and before frozen storage, as measured in accordance with JIS K 7127:1999, is C2, C1 / C2 is set to a value of 0.85 or more, and C2 is set to a value within the range of 450 to 600%. Structure (i): The polyester resin constituting the polyester-based heat-shrinkable film is a mixture of a non-crystalline polyester resin and a recycled crystalline polyester resin, and the amount of the recycled crystalline polyester resin is set to a value within the range of 10 to 30% by weight when the entire mixture is taken as 100% by weight.

2. 2. The polyester-based heat-shrinkable film according to claim 1, wherein the predetermined time for measuring C1 in the configuration (a) is a value of at least three months, with the time immediately after production as the reference.

3. 3. The polyester heat-shrinkable film according to claim 1, wherein the predetermined temperature is set to a value of −30° C. or less.

4. 3. The polyester heat-shrinkable film according to claim 1, further satisfying the following requirement (c): Configuration (c): The dynamic friction coefficient measured in accordance with JIS K 7125:1999 is set to a value within the range of 0.15 to 0.

6.

5. 3. The polyester-based heat-shrinkable film according to claim 1 or 2, wherein when the polyester-based heat-shrinkable film is shrunk in hot water or boiling water at 70°C, 80°C, and 100°C for 10 seconds in the TD direction, the heat shrinkage rates are designated as A1 to A3, where A1 is a value of 10% or more, A2 is a value of 30% or more, and A3 is a value of 60% or more.

6. 3. The polyester-based heat-shrinkable film according to claim 1, wherein, with respect to the endotherm of the melting peak measured using DSC, when the endotherm before the predetermined time has elapsed is set to 100%, a change in the endotherm after the predetermined time has elapsed is set to a value within a range of 0 to 25%.

7. 3. The polyester heat-shrinkable film according to claim 1, wherein the haze of the polyester heat-shrinkable film before heat shrinkage is 10% or less as measured in accordance with JIS K 7136:2000.

8. A method for storing a polyester heat-shrinkable film, comprising freezing and storing the film at a predetermined temperature for a predetermined time, A method for storing a polyester-based heat-shrinkable film, characterized in that, when the main shrinkage direction of the polyester-based heat-shrinkable film is defined as the TD direction and the direction perpendicular to the TD direction is defined as the MD direction, the polyester-based heat-shrinkable film satisfies the following configurations (a), (b), and (i): Configuration (a): When the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film measured in accordance with JIS K 7127:1999 is C1, the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film is C1, the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film measured in accordance with JIS K 7127:1999, the nominal tensile break strain in the machine direction of the polyester heat-shrinkable film ... Structure (b): When the nominal tensile break strain in the MD direction of the polyester heat-shrinkable film immediately after production and before frozen storage, as measured in accordance with JIS K 7127:1999, is C2, C1 / C2 is set to a value of 0.85 or more, and C2 is set to a value within the range of 450 to 600%. Structure (i): The polyester resin constituting the polyester-based heat-shrinkable film is a mixture of a non-crystalline polyester resin and a recycled crystalline polyester resin, and the amount of the recycled crystalline polyester resin is set to a value within the range of 10 to 30% by weight when the entire mixture is taken as 100% by weight.

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