Polyester-based shrink film

Abstract

The present application provides a polyester shrink film with excellent wrinkle resistance. The polyester shrink film satisfies the following (a) to (c) configurations. (a) When the main shrink direction is set as the TD direction, the heat shrinkage rate in the TD direction under the condition of 90°C hot water for 10 seconds is set as A2, A2 is a value of 53% or more, (b) the maximum shrinkage stress in the TD direction at a shrinkage temperature of 90°C is set as B, B is a value in the range of 2 to 10 MPa, (c) according to B and A2, the value represented by B / A2 is a value in the range of 0.08 to 0.15 MPa / %.

Description

Technical Field

[0001] This invention relates to polyester shrink film.

[0002] More specifically, this relates to polyester shrink films with excellent wrinkle resistance for use in PET bottles and the like. Background Technology

[0003] Shrink film has long been widely used as a substrate film for labels on PET bottles and other products. In particular, due to the advantages of polyester shrink film in terms of strength and transparency, its proportion as a substrate film for labels is constantly increasing.

[0004] Although polyester shrink film has such excellent properties, it suffers from uneven shrinkage and wrinkles due to its rapid thermal response when heated.

[0005] Therefore, it has been proposed to suppress the formation of wrinkles by controlling the thermal shrinkage rate and thickness distribution at multiple specified temperatures (for example, see Patent Document 1).

[0006] More specifically, a heat-shrinkable plastic resin film is characterized in that the film's hot water shrinkage rate is 5-50% in the main shrinkage direction at 70°C and after 5 seconds of treatment, and is more than 65% at 85°C and after 5 seconds of treatment; and is less than 10% in the direction orthogonal to the main shrinkage direction at 85°C and after 5 seconds of treatment.

[0007] Furthermore, a heat-shrinkable plastic resin film is characterized by a thickness distribution of less than 6%.

[0008] Existing technical documents

[0009] Patent documents

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2002-011790 (Patent Claims, etc.). Summary of the Invention

[0011] However, while the heat-shrinkable plastic resin film described in Patent Document 1 limits the heat shrinkage rate to a specified range within a specified temperature and shrinkage direction, it does not consider the maximum shrinkage stress or the ratio of the maximum shrinkage stress to the heat shrinkage rate. Therefore, when this film is used in various PET bottles, there is a problem that the formation of tiny wrinkles cannot be suppressed during the heat shrinkage process.

[0012] In particular, in the case of PET bottles with inconsistent bottle diameters and complex cross-sectional shapes in some parts, the formation of micro-wrinkles cannot be suppressed due to uneven shrinkage.

[0013] In response, the inventors of this invention discovered that by limiting the specified heat shrinkage rate and the maximum shrinkage stress to specified ranges, and by limiting the ratio of the maximum shrinkage stress to the heat shrinkage rate to specified ranges, a shrink film capable of suppressing the generation of micro-wrinkles can be obtained even when applied to various PET bottles, etc., thus completing this invention.

[0014] That is, the purpose of this invention is to provide a polyester shrink film that can exhibit excellent wrinkle resistance even when applied to various PET bottles, etc.

[0015] According to the present invention, a polyester-based shrink film derived from polyester resin is provided, characterized in that it satisfies the following (a) to (c) configurations, thereby solving the above-mentioned problems.

[0016] (a) When the main shrinkage direction is set to the TD direction (the same applies below), and the heat shrinkage rate in the TD direction under the condition of shrinking in warm water at 90°C for 10 seconds is set to A2 (%), A2 is a value of 53% or more.

[0017] (b) The maximum shrinkage stress at a shrinkage temperature of 90°C in the TD direction is set as B (MPa), where B is a value in the range of 2 to 10 (MPa).

[0018] (c) According to B and A2, the value represented by B / A2 is in the range of 0.08 to 0.15 MPa / %.

[0019] That is, by satisfying configuration (a), the polyester shrink film can obtain a good heat shrinkage rate during heat shrinkage, and thus also a good maximum shrinkage stress.

[0020] Furthermore, by satisfying the requirements of the polyester shrink film obtained in configuration (b), the maximum shrinkage stress is controlled to a value within a specified range, and wrinkles that may occur due to excessive or insufficient maximum shrinkage stress can be suppressed.

[0021] Furthermore, by satisfying configuration (c), even when there is a slight deviation between the heat shrinkage rate of configuration (a) and the maximum shrinkage stress of configuration (b), it is possible to reduce the elements of the specified influencing factors and suppress uneven shrinkage caused by the rapid thermal response in the polyester shrink film during heat shrinkage, thereby also suppressing the generation of micro wrinkles.

[0022] Therefore, by limiting the heat shrinkage rate A2, the maximum shrinkage stress B, and B / A2 to values ​​within a specified range, a shrink film with excellent wrinkle resistance can be provided.

[0023] It should be noted that, for example, in Evaluation 9 of Example 1, if three or more of the five cylindrical labels made with the polyester shrink film of the present invention under specified conditions do not produce visually observable specified wrinkles, they are considered to have good wrinkle resistance.

[0024] Furthermore, when constructing the polyester shrink film of the present invention, it is preferable to further satisfy the following (d) configuration.

[0025] (d) Let the thickness of the polyester shrink film before shrinkage be t (μm). According to B and t, the value of B / t is in the range of 0.05 to 0.4 MPa / μm.

[0026] By specifically limiting the value represented by B / t to a specified range, it is easy to control the value represented by B / A2 to a specified range.

[0027] Therefore, it can further improve wrinkle resistance.

[0028] Furthermore, when constructing the polyester shrink film of the present invention, the thickness t of the polyester shrink film before shrinkage is preferably set to a value in the range of 15 to 45 μm.

[0029] By specifically limiting the thickness of the polyester shrink film before shrinkage to a specified range, it is easier to control the values ​​represented by the heat shrinkage rate A2, maximum shrinkage stress B, B / A2, and B / t to a specified range.

[0030] In addition, when constructing the polyester shrink film of the present invention, the heat shrinkage rate in the TD direction under the condition of shrinking in 80°C warm water for 10 seconds is set as A1 (%), and A1 is preferably a value in the range of 40 to 70%.

[0031] By limiting the heat shrinkage rate A1 to a specified range, it is easy to control the heat shrinkage rate A2 to a specified range.

[0032] Furthermore, when constructing the polyester shrink film of the present invention, the stretch ratio of the polyester shrink film in the MD direction before shrinkage is preferably a value in the range of 100% to 200%.

[0033] By specifically limiting the stretch ratio of the polyester shrink film in the MD direction to a specified range, and by specifically limiting the values ​​represented by A1, A2, B, B / A2 and B / t, as well as the heat shrinkage rates A′1 and A′2 (described later), to specified ranges, the generation of micro-wrinkles can be suppressed.

[0034] Furthermore, when constructing the polyester shrink film of the present invention, it is preferable that the stretch ratio of the polyester shrink film before shrinkage in the TD direction is set to a value in the range of 300 to 600%.

[0035] By specifically limiting the stretch ratio of the polyester shrink film in both the MD and TD directions to a specified range, and by specifically limiting the values ​​represented by A1, A2, B, B / A2 and B / t, as well as the heat shrinkage rates A′1 and A′2 (described later), to a specified range, the generation of micro-wrinkles can be suppressed.

[0036] Furthermore, when constructing the polyester shrink film of the present invention, the haze value of the pre-shrink film, as measured according to the JIS K 7105 standard, is preferably 5% or less.

[0037] By specifically limiting the haze value to a specified range, it is easy to quantitatively control the transparency of polyester shrink film, and the good transparency further improves its versatility.

[0038] Furthermore, when constituting the polyester shrink film of the present invention, the content of amorphous polyester resin is preferably in the range of 90 to 100% by weight of the total resin.

[0039] By specifically limiting the content of amorphous polyester resin in this way, it is easier to adjust the heat shrinkage rate and maximum shrinkage stress near the shrinkage temperature (e.g., 80–90°C, hereinafter the same) to the desired range, and it is also easier to quantitatively control the haze value, etc.

[0040] It should be noted that the balance of amorphous polyester resin in the total resin content is contributed by crystalline polyester resin and resins other than polyester resin. Attached Figure Description

[0041] Figure 1 (a) to (c) are diagrams illustrating the morphology of polyester shrink films.

[0042] Figure 2 This is a graph illustrating the relationship between the shrinkage rate (A2) of polyester shrink film under specified heating conditions (warm water 90°C, 10 seconds) and the maximum shrinkage stress (B) under specified heating conditions (hot air 90°C, 30 seconds or more).

[0043] Figure 3 This is a graph used to illustrate the relationship between the maximum shrinkage stress (B) of polyester shrink film under specified heating conditions (hot air at 90°C for more than 30 seconds) and the shrinkage rate (A2) under specified heating conditions (warm water at 90°C for 10 seconds) and the evaluation of wrinkle resistance.

[0044] Figure 4This is a graph used to illustrate the relationship between the ratio of maximum shrinkage stress (B) to shrinkage rate (A2) of polyester shrink film under specified heating conditions (hot air at 90°C for more than 30 seconds) and the ratio of maximum shrinkage stress (B) to thickness (t) under specified heating conditions (hot air at 90°C for more than 30 seconds).

[0045] Figure 5 This is a graph used to illustrate the relationship between the ratio of maximum shrinkage stress (B) / thickness (t) of polyester shrink film under specified heating conditions (hot air at 90°C for more than 30 seconds) and the evaluation of wrinkle resistance.

[0046] Figure 6 (a) Corresponding to Example 1, this is a diagram (photograph) showing the appearance of the cylindrical label when no wrinkles have formed. Figure 6 (b) to (d) are respectively Figure 6 (a) is an enlarged view of regions P, Q, and R in the appearance shown.

[0047] Figure 7 (a) Corresponding to Comparative Example 1, is a diagram (photograph) showing the appearance of the cylindrical label when wrinkles are formed. Figure 7 (b) to (d) are respectively Figure 7 (a) is an enlarged view of regions S, T, and U in the appearance shown.

[0048] Figure 8 This is a graph showing the change in shrinkage stress of polyester shrink film over time under specified heating conditions (hot air at 90°C for more than 30 seconds). Detailed Implementation

[0049] [First Implementation]

[0050] The first implementation method is Figure 1 The polyester shrink film derived from polyester resin shown is characterized by satisfying the following (a) to (c) configurations.

[0051] (a) If the main contraction direction is TD, and the contraction rate in the TD direction under the condition of contraction in warm water at 90°C for 10 seconds is set as A2, then A2 is a value of 53% or more.

[0052] (b) The maximum shrinkage stress at a shrinkage temperature of 90°C in the TD direction is set as B, where B is a value in the range of 2 to 10 MPa.

[0053] (c) According to B and A2, the value represented by B / A2 is a value in the range of 0.08 to 0.15 MPa / %.

[0054] Hereinafter, the composition of the polyester shrink film of the first embodiment will be described separately and appropriately referred to. Figure 1(a) to (c) provide specific explanations of various parameters, etc.

[0055] 1. Polyester resin

[0056] Basically, there are no restrictions on the type of polyester resin, but polyester resins composed of diols and dicarboxylic acids, polyester resins composed of diols and hydroxycarboxylic acids, polyester resins composed of diols, dicarboxylic acids and hydroxycarboxylic acids, or mixtures of these polyester resins are generally preferred.

[0057] Here, the diols that are the compound components of polyester resins can include at least one of aliphatic diols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, neopentyl glycol, and hexanediol, alicyclic diols such as 1,4-hexanediethanol, and aromatic diols.

[0058] Moreover, ethylene glycol, diethylene glycol and 1,4-hexanediethanol are particularly preferred.

[0059] In addition, dicarboxylic acids that are also components of polyester resins can include fatty acid dicarboxylic acids such as adipic acid, sebacic acid, and azelaic acid; aromatic dicarboxylic acids such as terephthalic acid, naphthalic acid, and isophthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; or at least one of their esterifying derivatives.

[0060] Moreover, terephthalic acid is particularly preferred among these.

[0061] In addition, regarding hydroxycarboxylic acids, which are also compound components of polyester resins, at least one of lactic acid, hydroxybutyric acid, polycaprolactone, etc. can be cited.

[0062] Additionally, as an amorphous polyester resin, for example, an amorphous polyester resin composed of the following components is preferably used: a dicarboxylic acid consisting of at least 80 mol% terephthalic acid, 50-80 mol% ethylene glycol, and a diol consisting of 20-50 mol% of one or more diols selected from 1,4-cyclohexanediol, neopentyl glycol, and diethylene glycol. Other dicarboxylic acids and diols, or hydroxycarboxylic acids, may also be used to modify the properties of the membrane, as needed. Alternatively, they may be used individually or in mixtures.

[0063] On the other hand, as crystalline polyester resins, there are polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, and polypropylene terephthalate, which can be used individually or as mixtures.

[0064] In addition, when the polyester resin is a mixture of amorphous polyester resin and 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 relative to the total amount of resin constituting the polyester shrink film, and more preferably in the range of 91 to 100% by weight.

[0065] 2. Composition (a)

[0066] The essential component (a) is that, in the polyester shrink film of the first embodiment, the main shrinkage direction is set to the TD direction, and the heat shrinkage rate in the TD direction under the condition of shrinking in warm water at 90°C for 10 seconds is set to A2, and the heat shrinkage rate A2 is a value of 53% or more.

[0067] The reason is that by specifically limiting the heat shrinkage rate A2 at 90°C to a specified value, a good heat shrinkage rate can be obtained in the polyester shrink film during heat shrinkage, and thus the maximum shrinkage stress can also be obtained.

[0068] More specifically, when the 90°C heat shrinkage rate A2 of the film is less than 53%, due to insufficient heat shrinkage, it sometimes becomes unable to follow the shape of the bottle's outer perimeter for PET bottles with complex shapes, and cannot suppress the formation of wrinkles.

[0069] Therefore, as a configuration (a), it is more preferable to set the lower limit of the heat shrinkage rate A2 at 90°C to a value of 56% or more, and even more preferably to set it to a value of 59% or more.

[0070] On the other hand, if the above-mentioned 90°C heat shrinkage rate A2 value is too large, the film will shrink unevenly due to the rapid thermal response during heat shrinkage, making it prone to wrinkles.

[0071] Therefore, as a component (a), the upper limit of the heat shrinkage rate A2 at 90°C is preferably 85% or less, more preferably 80% or less.

[0072] It should be noted that in the shrink film of the first embodiment, the heat shrinkage rate is defined by the following formula.

[0073] Shrinkage rate (%) = (L0 - L1) / L0 × 100

[0074] L0: Dimensions of the sample before heat treatment (long side or width direction)

[0075] L1: Size of the sample after heat treatment (same direction as L0)

[0076] 3. Composition (b)

[0077] Component (b) is a necessary component, the main point of which is to set the maximum shrinkage stress of the polyester shrink film of the first embodiment in the TD direction at a shrinkage temperature of 90°C as B, where B is a value in the range of 2 to 10 MPa.

[0078] The reason is that by specifically limiting B to a value within a specified range, wrinkles caused by excessive or insufficient maximum shrinkage stress can be suppressed.

[0079] More specifically, when the maximum shrinkage stress B is less than 2 MPa, the maximum shrinkage stress becomes insufficient, and the wrinkle resistance is reduced because the excessive wrinkles generated by the PET bottle at the initial shrinkage stage cannot be eliminated during the shrinkage process.

[0080] In addition, when the maximum shrinkage stress B is above 10 MPa, the maximum shrinkage stress becomes too large, and the bottle will deform when it shrinks.

[0081] Therefore, as a configuration (b), the maximum shrinkage stress B is more preferably a value in the range of 3 to 9 MPa, and even more preferably a value in the range of 4 to 8 MPa.

[0082] Here, for Figure 2 The relationship between the heat shrinkage rate A2 under specified heating conditions (warm water 90°C, 10 seconds) and the maximum shrinkage stress B under specified heating conditions (hot air 90°C, 30 seconds or more) in polyester shrink film is explained.

[0083] That is, when Figure 2 When the measurement data shown satisfies configurations (a) and (b), it can be seen that there is a very good correlation (correlation coefficient (R) of 0.81) between the heat shrinkage rate A2 and the maximum shrinkage stress B. Therefore, according to the purpose of this application, by limiting the heat shrinkage rate A2 to a value within a specified range, the maximum shrinkage stress B can be controlled to a value within a specified range.

[0084] 4. Composition (c)

[0085] Component (c) is a necessary component, the main point of which is that, based on the maximum shrinkage stress B and the thermal shrinkage rate A2, the value expressed by B / A2 is in the range of 0.08 to 0.15 MPa / %.

[0086] The reason is that by specifically limiting B / A2 to a value within a specified range, even if there is a slight deviation from the values ​​of composition (a) and composition (b), the factors that influence the specified factors can be reduced, and the uneven shrinkage caused by the rapid thermal response in the polyester shrink film during heat shrinkage can be suppressed, thereby suppressing the generation of micro-wrinkles.

[0087] More specifically, when the value represented by B / A2 is less than 0.08 MPa / % or greater than 0.15 MPa / %, the polyester shrink film cannot suppress uneven shrinkage caused by the rapid thermal response during heat shrinkage, thus resulting in the inability to suppress the generation of micro-wrinkles.

[0088] Therefore, as component (c), the value represented by B / A2 is more preferably a value in the range of 0.09 to 0.14 MPa / %, and even more preferably a value in the range of 0.10 to 0.13 MPa / %.

[0089] Next, in Figure 3 The text further illustrates the relationship between the numerical value represented by B / A2 and the evaluation of wrinkle resistance.

[0090] Right now, Figure 3 The horizontal axis represents the B / A2 value (MPa / %) in the polyester shrink film, and the vertical axis represents the evaluation of wrinkle resistance (relative value), thus representing the characteristic curve M. The evaluation of wrinkle resistance (relative value) on the vertical axis is numerically obtained by assigning ◎ as 5, ○ as 3, △ as 1, and × as 0.

[0091] As can be seen from the characteristic curve M, if the value represented by B / A2 is in the range of 0.08 to 0.15 MPa / %, then the wrinkle resistance evaluation (relative value) is 3 or above, and a good wrinkle resistance evaluation (relative value) can be obtained.

[0092] Conversely, if the value represented by B / A2 is greater than 0.15 MPa / %, the evaluation of wrinkle resistance (relative value) decreases sharply, and it cannot exert sufficient wrinkle resistance.

[0093] 5. Arbitrary constituent elements

[0094] (1) Composition (d)

[0095] Configuration (d) is a component in which the ratio of maximum shrinkage stress B to thickness t (μm) in the polyester shrinkage film of the first embodiment is expressed as B / t, which is a value in the range of 0.05 to 0.4 MPa / μm.

[0096] The reason is that by specifically limiting B / t to a value within a specified range, it is easier to control the value represented by B / A2 to be within the specified range, reducing the factors that affect the specified shrinkage. In polyester shrink films during heat shrinkage, it is possible to suppress uneven shrinkage caused by rapid thermal response, thereby suppressing the generation of micro-wrinkles.

[0097] More specifically, when the value of B / t is less than 0.05 MPa / μm or greater than 0.4 MPa / μm, the uneven shrinkage caused by the rapid thermal response in the polyester shrink film during heat shrinkage cannot be suppressed, thus resulting in the inability to suppress the generation of micro-wrinkles.

[0098] Therefore, as a component (d), the value of B / t is more preferably a value in the range of 0.06 to 0.35 MPa / μm, and even more preferably a value in the range of 0.07 to 0.30 MPa / μm.

[0099] Next, Figure 4 The diagram shows the relationship between the values ​​represented by B / A2 and the values ​​represented by B / t.

[0100] Right now, Figure 4 The horizontal axis represents the value of B / A2 in polyester shrink film (MPa / %), and the vertical axis represents the value of B / t (MPa / μm), thus representing the characteristic curve N.

[0101] As shown by the characteristic curve N, a shaded area is formed by setting the value of B / A2 to the range of 0.08–0.15 MPa / %, and the value of B / t to the range of 0.05–0.40 MPa / μm. Within this area, good wrinkle resistance with a relative value of 3 or higher can be obtained.

[0102] Next, Figure 5 The figure shows the relationship between the value expressed by B / t and the evaluation of wrinkle resistance.

[0103] Right now, Figure 5 The horizontal axis represents the B / t value (MPa / μm) in polyester shrink film, and the vertical axis is... Figure 3 The same value represents the wrinkle resistance evaluation (relative value), which is represented by the characteristic curve X. The wrinkle resistance evaluation (relative value) on the vertical axis is obtained by numericalizing ◎ as 5, ○ as 3, △ as 1, and × as 0.

[0104] As can be seen from the characteristic curve X, if the value represented by B / t is in the range of 0.05 to 0.40 MPa / μm, then a good wrinkle resistance rating (relative value) of 3 or above can be obtained.

[0105] In contrast, when the value represented by B / t is greater than 0.40 MPa / μm, the wrinkle resistance evaluation (relative value) is less than 3, which means that it cannot exert sufficient wrinkle resistance.

[0106] Next, for Figure 6 and Figure 7 Please provide an explanation.

[0107] Right now, Figure 6 Corresponding to Example 1, this is a photograph of the appearance of the cylindrical label without wrinkles. Figure 6 (a) shows the entire body of the PET bottle covered by the cylindrical label. Furthermore, Figure 6 (b) to (d) are respectively Figure 6 (a) shows an enlarged view of the upper (P region), middle (Q region), and lower (R region) parts of the bottle body. It can be seen that no wrinkles are produced at any part from the top to the bottom.

[0108] on the other hand, Figure 7 Corresponding to Comparative Example 1, here is a photograph of the appearance of the cylindrical label when wrinkles have formed. Figure 7 (a) shows the entire body of the PET bottle covered by the cylindrical label. Furthermore, Figure 7 (b) to (d) are respectively Figure 7 (a) shows an enlarged view of the upper (S region), middle (T region), and lower (U region) parts of the bottle, revealing that wrinkles are present at any point from the top to the bottom.

[0109] It should be noted that, Figure 6 and Figure 7 In the image, the blacked-out parts represent the printed content on the label and do not affect the evaluation of the wrinkles.

[0110] Furthermore, it was clarified that in PET bottles with inconsistent bottle diameters and complex cross-sectional shapes (non-circular) at different locations, even when using... Figure 6 The cylindrical label is also less prone to wrinkling.

[0111] (2) Composition (e)

[0112] The configuration (e) is as follows: the thickness (average thickness) of the polyester shrink film of the first embodiment is generally preferably a value in the range of 15 to 45 μm.

[0113] The reason is that by specifically limiting the thickness t to a value within a specified range, it is easier to control the values ​​represented by heat shrinkage rates A2, B, B / A2, and B / t to values ​​within the specified range. Therefore, the factors influencing the heat shrinkage can be reduced, and uneven shrinkage caused by the rapid thermal response in the polyester shrink film during heat shrinkage can be suppressed, thereby inhibiting the formation of micro-wrinkles.

[0114] More specifically, when the thickness represented by t is less than 15 μm or greater than 45 μm, it cannot suppress the uneven shrinkage caused by the rapid thermal response in the polyester shrink film during heat shrinkage, thus resulting in the inability to suppress the generation of micro wrinkles.

[0115] Therefore, as a component (e), the thickness represented by t is more preferably a value in the range of 20 to 43 μm, and even more preferably a value in the range of 25 to 40 μm.

[0116] (3) Composition (f)

[0117] The composition (f) is as follows: the heat shrinkage rate A1 of the polyester shrink film when it shrinks in warm water at 80°C for 10 seconds is preferably a value in the range of 40% to 70%.

[0118] The reason is that by specifically limiting the heat shrinkage rate A1 at 80°C to a value within a specified range, it is easier to control the heat shrinkage rate A2 at 90°C to a value within a specified range.

[0119] More specifically, when the 80°C heat shrinkage rate A1 is less than 40% or greater than 70%, the 90°C heat shrinkage rate A2 cannot be controlled within the specified range, thus failing to suppress the formation of wrinkles.

[0120] Therefore, as a component (f), the heat shrinkage rate A1 at 80°C is preferably a value in the range of 42% to 68%, and more preferably a value in the range of 45% to 65%.

[0121] (4) Composition (g)

[0122] The configuration (g) comprises the following components: the direction orthogonal to the TD direction of the polyester shrink film is designated as the MD direction, and the heat shrinkage rate in the MD direction under the condition of shrinking in warm water at 80°C for 10 seconds is designated as A′1, preferably a value of 10% or less.

[0123] The reason is that by specifically limiting the heat shrinkage rate A′1 at 80°C to a specified value, it is easier to control the heat shrinkage rate A′2 at 90°C, which will be described later, to a value within the specified range.

[0124] More specifically, when the 80℃ heat shrinkage rate A′1 is greater than 10%, the 90℃ heat shrinkage rate A′2 cannot be controlled within the specified range, and wrinkles cannot be suppressed during the heat shrinkage of the film.

[0125] Therefore, as component (g), the heat shrinkage rate A′1 at 80°C is more preferably a value in the range of 1 to 9%, and even more preferably a value of 2 to 8% or less.

[0126] (5) Composition (h)

[0127] The configuration (h) is based on the following components: the direction orthogonal to the TD direction of the polyester shrink film is defined as the MD direction, and the heat shrinkage rate in the MD direction under the condition of shrinking in warm water at 90°C for 10 seconds is set as A′2, preferably a value in the range of 1.5 to 15%.

[0128] The reason is that by specifically limiting the 90℃ heat shrinkage rate A′2 to a value within a specified range, the influence factors on the values ​​represented by B / A2 and B / t are reduced, thus the film can achieve better wrinkle resistance during heat shrinkage.

[0129] More specifically, when the 90℃ heat shrinkage rate A′2 is less than 1.5% or greater than 15%, the influence of the values ​​represented by B / A2 and B / t cannot be reduced, and therefore good wrinkle resistance cannot be obtained during film heat shrinkage.

[0130] Therefore, as a component (h), the heat shrinkage rate A′2 at 90°C is more preferably a value in the range of 3 to 12%, and even more preferably a value in the range of 4 to 11%.

[0131] (6) Composition (i)

[0132] The component (i) is the stretch ratio of the polyester shrink film in the MD direction before shrinkage (average MD stretch ratio, sometimes simply referred to as MD stretch ratio).

[0133] Furthermore, the stretching ratio in the MD direction is preferably a value in the range of 100% to 200%.

[0134] The reason is that by specifically limiting the stretching ratio in the MD direction to a specified range, and by specifically limiting the values ​​represented by A1, A2, A′1, A′2, B, B / A2, and B / t to a specified range, the generation of micro-wrinkles can be suppressed.

[0135] More specifically, when the MD stretch ratio is less than 100%, the manufacturing yield is significantly reduced.

[0136] On the other hand, when the stretch ratio in the MD direction is greater than 200%, it can sometimes affect the shrinkage rate in the TD direction, making it difficult to adjust the shrinkage rate itself.

[0137] Therefore, as a configuration (i), the stretching ratio in the MD direction is more preferably a value in the range of 110 to 180%, and even more preferably a value in the range of 120 to 160%.

[0138] (7) Composition (j)

[0139] Additionally, component (j) comprises the following constituent elements: the stretch ratio of the pre-heat-shrink polyester shrink film in the TD direction (average TD stretch ratio, sometimes simply referred to as TD stretch ratio).

[0140] Furthermore, the stretch ratio in the TD direction is preferably a value in the range of 300 to 600%.

[0141] The reason is that by specifically limiting the stretching ratio in the TD direction to a specified range, and by specifically limiting the values ​​represented by A1, A2, A′1, A′2, B, B / A2, and B / t to a specified range, the generation of micro-wrinkles can be suppressed.

[0142] More specifically, when the TD stretch ratio is less than 300%, the shrinkage rate in the TD direction is sometimes significantly reduced, excessively limiting the applications of polyester shrink films.

[0143] On the other hand, when the TD stretch ratio is greater than 600%, the shrinkage rate may increase significantly, which may excessively limit the use of polyester shrink film or make it difficult to control the stretch ratio itself consistently.

[0144] Therefore, as a configuration (j), the stretching ratio in the TD direction is more preferably a value in the range of 350 to 550%, and even more preferably a value in the range of 400 to 500%.

[0145] (8) Composition (k)

[0146] In addition, the composition (k) is any compositional element, the main point of which is: the haze value of the polyester shrink film before heat shrinkage, as measured according to JIS K 7105, is 5% or less.

[0147] The reason is that by specifically limiting the haze value to a specified range, the transparency of polyester shrink film can be quantitatively controlled, and the good transparency further improves its versatility.

[0148] More specifically, when the haze value of the film before heat shrinking is greater than 5%, the transparency decreases, making it sometimes unsuitable for applications such as decorative PET bottles.

[0149] On the other hand, when the haze value of the film before heat shrinkage becomes too small, it is sometimes difficult to control stably, which can significantly reduce the yield of finished products.

[0150] Therefore, as a component (k), the haze value of the heat-shrinkable pre-film is more preferably in the range of 0.1% to 3%, and even more preferably in the range of 0.5% to 1%.

[0151] (9) Composition (m)

[0152] Furthermore, the composition (m) is any compositional element, the main point of which is that the polyester shrink film of the first embodiment contains an amorphous polyester resin in the range of 90 to 100% by weight.

[0153] The reason is that by specifically limiting the content of amorphous polyester resin in this way, it is easier to adjust the heat shrinkage rate and maximum shrinkage stress near the shrinkage temperature to the desired range, and it is also easier to quantitatively control the haze value, etc.

[0154] More specifically, when the content of amorphous polyester resin is less than 90% by weight, it is sometimes difficult to control the shrinkage rate and maximum shrinkage stress near the shrinkage temperature of the polyester shrink film.

[0155] In addition, if the content of crystalline polyester resin becomes too high, the range of factors that can reduce the specified influencing factors may become significantly narrower.

[0156] Therefore, as a component (m), the content of crystalline polyester resin is more preferably in the range of 91 to 100% by weight of the total amount, and even more preferably in the range of 92 to 100% by weight.

[0157] (10) Other

[0158] It is preferred that various additives be incorporated into or attached to one or both sides of the polyester shrink film of the first embodiment.

[0159] More specifically, generally, relative to the total amount of polyester shrink film, at least one of the following is preferably added in the range of 0.01 to 10% by weight, more preferably in the range of 0.1 to 1% by weight.

[0160] In addition, such as Figure 1 As shown in (b), it is also preferable that other resin layers 10a and 10b containing at least one of these various additives are laminated on one or both sides of the polyester shrink film 10.

[0161] At this point, when the thickness of the polyester shrink film is set to 100%, the thickness of the single layer or the total thickness of the additional resin layers is usually preferably in the range of 0.1% to 10%.

[0162] Furthermore, the resin that forms the main component of the other resin layers can be the same polyester resin as the polyester shrink film, or at least one of the following: acrylic resin, olefin resin, polyurethane resin, rubber resin, etc., which are different from it.

[0163] Furthermore, it is preferable to make the polyester shrink film a multi-layered structure to further achieve waterproofing and mechanical protection, or as... Figure 1 As shown in (c), a shrinkage adjustment layer 10c is provided on the surface of the polyester shrink film 10 in order to make the shrinkage rate of the polyester shrink film uniform in the plane.

[0164] This shrinkage adjustment layer can be laminated using adhesives, coating methods, or heat treatment, depending on the shrinkage characteristics of the polyester shrink film.

[0165] More specifically, the thickness of the shrinkage adjustment layer is in the range of 0.1 to 3 μm. When the shrinkage rate of the polyester shrink film at a specified temperature is too large, it is preferable to use a shrinkage adjustment layer of the type that inhibits shrinkage.

[0166] In addition, if the shrinkage rate of the polyester shrink film at the specified temperature is too small, it is preferable to laminate a shrinkage rate adjustment layer of the type that expands the shrinkage rate.

[0167] Therefore, as a polyester shrink film, instead of producing shrink films with various shrinkage rates, the desired shrinkage rate is obtained through a shrinkage rate adjustment layer.

[0168] [Second Implementation]

[0169] The second embodiment relates to an embodiment of a method for manufacturing a polyester shrink film according to the first embodiment.

[0170] 1. Raw material preparation and mixing process

[0171] First, as raw materials, it is preferable to prepare crystalline polyester resin, amorphous polyester resin, rubber resin, antistatic agent, hydrolysis inhibitor and other main agents and additives.

[0172] Next, preferably, the prepared crystalline polyester resin, amorphous polyester resin, etc. are weighed and added into the mixing container, and then mixed and stirred until uniform using a stirring device.

[0173] 2. Fabrication process of blanks

[0174] Next, it is preferable to dry the uniformly mixed raw materials to an absolutely dry state.

[0175] Next, typically, extrusion molding is preferred to produce blanks of a specified thickness.

[0176] More specifically, for example, extrusion molding can be performed using an L / D24 extruder with a screw diameter of 50 mm (manufactured by TANABE PLASTICS MACHINERY Co., Ltd.) at an extrusion temperature of 180°C to obtain a preform of a specified thickness (usually 10 to 100 μm).

[0177] 3. Preparation of polyester shrink film

[0178] Next, the obtained blank is heated and pressed while being moved on or between rollers using a shrink film manufacturing device to produce a polyester shrink film.

[0179] That is, preferably, the film width is substantially increased while heating and pressing, and stretched in a specified direction at a specified stretching temperature and stretching ratio, thereby causing the polyester molecules constituting the polyester shrink film to crystallize into a specified shape.

[0180] Then, by curing it in this state, it is possible to produce heat-shrinkable polyester shrink films for use as decorations, labels, etc.

[0181] 4. Inspection procedures for polyester shrink film

[0182] For the manufactured polyester shrink film, it is preferable to continuously or intermittently measure the following characteristics and set up a prescribed inspection procedure.

[0183] That is, by conducting a prescribed inspection process and measuring the following characteristics, and confirming that the values ​​fall within the prescribed range, polyester shrink film with more uniform shrinkage characteristics can be produced.

[0184] 1) Visual inspection of the appearance of polyester shrink film

[0185] 2) Thickness deviation measurement

[0186] 3) Determination of tensile modulus of elasticity

[0187] 4) Tear strength test

[0188] 5) Viscoelasticity determination based on SS curve

[0189] Furthermore, in the manufacture of the polyester shrink film of the second embodiment, it is necessary to measure and calculate the following (a) to (c).

[0190] (a) Assuming the main contraction direction is the TD direction, the thermal shrinkage rate A2 when contracting in the TD direction under the condition of 90°C warm water for 10 seconds.

[0191] (b) The maximum shrinkage stress B under conditions of hot air at 90°C for more than 30 seconds in the TD direction;

[0192] (c) The value represented by B / A2.

[0193] [Third Implementation]

[0194] The third embodiment relates to an embodiment of a method of using polyester shrink film.

[0195] Therefore, the commonly known methods of using shrink film are generally applicable.

[0196] For example, when implementing the method of using polyester shrink film, firstly, the polyester shrink film is cut into appropriate lengths and widths and formed into long cylindrical objects.

[0197] Next, the long cylindrical object is supplied to an automatic labeling device (shrink labeling machine) for further cutting into the required length.

[0198] Next, it is embedded in PET bottles filled with contents, etc.

[0199] Next, as a heat treatment for polyester shrink film embedded in PET bottles, etc., it is passed through the interior of a hot air channel and a steam channel at a specified temperature.

[0200] Then, by blowing infrared radiation and heating steam at around 90°C into these channels, the polyester shrink film is uniformly heated and thermally shrunk.

[0201] Therefore, it can be attached tightly to the outer surface of PET bottles and other containers to quickly obtain labeled containers.

[0202] Here, the polyester shrink film according to the present invention is characterized in that it at least satisfies the composition (a) to (c).

[0203] In this way, a good heat shrinkage rate and maximum shrinkage stress can be obtained in the polyester shrink film during heat shrinkage.

[0204] In addition, by controlling the maximum shrinkage stress to a value within a specified range, it is possible to obtain a polyester shrink film that can suppress the formation of wrinkles caused by excessive or insufficient maximum shrinkage stress.

[0205] Furthermore, even with slight deviations in the values ​​of heat shrinkage rate and maximum shrinkage stress, the factors that influence the specified shrinkage can be reduced. In polyester shrink films during heat shrinkage, uneven shrinkage caused by rapid thermal response can be suppressed, thereby suppressing the formation of micro-wrinkles.

[0206] Therefore, as Figure 6 As shown in (a) to (d), the label made of this film is covered on the bottle and heat-shrinks, so that it can be installed according to the shape of the bottle's outer surface, and can also suppress the formation of tiny wrinkles.

[0207] On the other hand, if at least the conditions of (a) to (c) are met, such as Figure 7 As shown in (a) to (d), from the top to the bottom of the bottle, there is an area where the label cannot follow the shape of the bottle's outer perimeter, and wrinkles can be clearly seen.

[0208] It should be noted that the polyester shrink film of the present invention does not actually contain structural units derived from lactic acid, and therefore also has the advantage of not requiring strict humidity control during storage.

[0209] [Example]

[0210] The present invention will now be described in detail based on embodiments. Unless otherwise specified, the scope of the present invention is not limited to the descriptions in the embodiments.

[0211] It should be noted that the resin used in the embodiments is as follows.

[0212] (PETG1)

[0213] An amorphous polyester composed of 100 mol% dicarboxylic acid (terephthalic acid) and 70 mol% ethylene glycol, 25 mol% 1,4-cyclohexanediethanol, and 5 mol% diethylene glycol.

[0214] (PETG2)

[0215] An amorphous polyester composed of dicarboxylic acid (100 mol%), diols (72 mol%), neopentyl glycol (25 mol%), and diethylene glycol (3 mol%).

[0216] (APET)

[0217] A crystalline polyester composed of 100 mol% dicarboxylic acid: terephthalic acid and 100 mol% glycol: ethylene glycol

[0218] (PBT)

[0219] A crystalline polyester composed of 100 mol% dicarboxylic acid: terephthalic acid and 100 mol% diol: 1,4-butanediol

[0220] [Example 1]

[0221] 1. Preparation of polyester shrink film

[0222] Use 100 parts by weight of amorphous polyester resin (PETG1) in the mixing container.

[0223] Next, after the raw material is dried, it is extruded at an extrusion temperature of 180°C using an extruder with an L / D24 and an extrusion screw diameter of 50 mm (manufactured by TANABE PLASTICS MACHINERY Co., Ltd.) to obtain a preform with a thickness of 100 μm.

[0224] Next, using a shrink film manufacturing apparatus, a polyester shrink film with a thickness of 40 μm is produced from the preform at a stretching temperature of 83°C and a stretching ratio (MD direction: 105%, TD direction: 480%).

[0225] 2. Evaluation of polyester shrink film

[0226] (1) Evaluation 1: Thickness deviation

[0227] The thickness of the polyester shrink film obtained by measuring with a micrometer (based on a desired value of 40 μm) is evaluated according to the following criteria.

[0228] ◎: The thickness deviation is within the range of ±0.1μm of the reference value.

[0229] 〇: The thickness deviation is within the range of ±0.5μm of the reference value.

[0230] △: The thickness deviation is within the range of ±1.0μm of the reference value.

[0231] ×: The thickness deviation is within the range of ±3.0μm of the reference value.

[0232] (2) Evaluation 2: Thermal shrinkage rate 1 (A1)

[0233] The obtained polyester shrink film (TD direction) was immersed in warm water at 80°C for 10 seconds using a constant temperature bath to cause it to shrink.

[0234] Next, the thermal shrinkage rate (A1) is calculated based on the dimensional changes before and after heat treatment at a specified temperature (80°C warm water) according to the following formula, and evaluated according to the following criteria.

[0235] Heat shrinkage rate = (Length of film before heat shrinkage - Length of film after heat shrinkage) / Length of film before heat shrinkage × 100

[0236] ◎: The heat shrinkage rate (A1) is in the range of 45% to 65%.

[0237] 〇: The heat shrinkage rate (A1) is in the range of 40% to 70% and is outside the range mentioned above.

[0238] △: The heat shrinkage rate (A1) is in the range of 35% to 75% and is outside the range of 0 mentioned above.

[0239] ×: The heat shrinkage rate (A1) is a value of less than 35% or greater than 75%.

[0240] (3) Evaluation 3: Thermal shrinkage rate 2 (A2)

[0241] The obtained polyester shrink film (TD direction) was immersed in warm water at 90°C for 10 seconds using a constant temperature bath to cause it to shrink.

[0242] Next, the thermal shrinkage rate (A2) is calculated based on the dimensional changes before and after heat treatment at a specified temperature (90°C warm water) according to the following formula, and evaluated according to the following criteria.

[0243] Heat shrinkage rate = (Length of film before heat shrinkage - Length of film after heat shrinkage) / Length of film before heat shrinkage × 100

[0244] ◎: The heat shrinkage rate (A2) is in the range of 56% to 80%.

[0245] 〇: The heat shrinkage rate (A2) is in the range of 53% to 85% and is outside the range mentioned above.

[0246] △: The heat shrinkage rate (A2) is within the range of 50% to 90% and is outside the range of 0 mentioned above.

[0247] ×: The heat shrinkage rate (A2) is a value of less than 50% or greater than 90%.

[0248] (4) Evaluation 4: Thermal shrinkage rate 3 (A′1)

[0249] The obtained polyester shrink film (MD direction) was immersed in warm water at 80°C for 10 seconds using a constant temperature bath to cause it to shrink.

[0250] Next, the thermal shrinkage rate (A′1) is calculated based on the dimensional changes before and after heat treatment at a specified temperature (80°C warm water) according to the following formula, and evaluated according to the following criteria.

[0251] Heat shrinkage rate = (Length of film before heat shrinkage - Length of film after heat shrinkage) / Length of film before heat shrinkage × 100

[0252] ◎: The heat shrinkage rate (A′1) is less than 8%.

[0253] 〇: The heat shrinkage rate (A′1) is less than 10%.

[0254] △: Values ​​with a heat shrinkage rate (A′1) of less than 12%.

[0255] ×: The heat shrinkage rate (A′1) is greater than 12%.

[0256] (5) Evaluation 5: Thermal shrinkage rate 4 (A′2)

[0257] The obtained polyester shrink film (MD direction) was immersed in warm water at 90°C for 10 seconds using a constant temperature bath to cause it to shrink.

[0258] Next, the thermal shrinkage rate (A′2) is calculated based on the dimensional changes before and after heat treatment at a specified temperature (90°C warm water) according to the following formula, and evaluated according to the following criteria.

[0259] Heat shrinkage rate = (Length of film before heat shrinkage - Length of film after heat shrinkage) / Length of film before heat shrinkage × 100

[0260] ◎: The heat shrinkage rate (A′2) is a value in the range of 2 to 12%.

[0261] 〇: The heat shrinkage rate (A′2) is in the range of 1.5% to 15% and is outside the range mentioned above.

[0262] △: The heat shrinkage rate (A′2) is within the range of 1 to 18% and is outside the range of 0 mentioned above.

[0263] ×: The heat shrinkage rate (A′2) is a value of less than 1% or greater than 18%.

[0264] (6) Evaluation 6: Maximum shrinkage stress 1 (B)

[0265] The obtained polyester shrink film was cut into strips with a width of 25.4 mm in the MD direction and a length of 75 mm in the TD direction, which were used as test pieces.

[0266] Next, the shrinkage stress of the prepared test piece is measured using a tensile strength measuring machine equipped with a heating furnace.

[0267] More specifically, preheat the furnace to 90°C, stop the furnace air supply, open the furnace door, install the test piece on the chuck of the tensile strength measuring machine, then quickly close the furnace door and turn the air supply back on.

[0268] Next, measure the shrinkage stress for more than 30 seconds, and take the maximum value of the measurement as the maximum shrinkage stress B, and evaluate it according to the following criteria.

[0269] It should be noted that the measured change in shrinkage stress over time is as follows: Figure 8 The characteristic curve V is shown in the figure.

[0270] More specifically, the shrinkage stress reached its maximum value of 6.13 MPa 6.6 seconds after the start of the measurement.

[0271] ◎: Values ​​in the range of 3 to 9 MPa.

[0272] 〇: Values ​​within the range of 2 to 10 MPa and outside the range mentioned above.

[0273] △: Values ​​within the range of 1 to 11 MPa and outside the range of 0 mentioned above.

[0274] ×: Values ​​less than 1 MPa or greater than 11 MPa.

[0275] (7) Evaluation 7: Maximum shrinkage stress 2 (B / A2)

[0276] Based on the maximum shrinkage stress B and heat shrinkage rate A2 of the obtained polyester shrink film, calculate B / A2 (MPa / %) and evaluate it according to the following criteria.

[0277] ◎: Values ​​within the range of 0.09~0.14MPa / %.

[0278] 〇: Values ​​within the range of 0.08 to 0.15 MPa / % and outside the range mentioned above.

[0279] △: Values ​​outside the above range of 0 within the range of 0.07~0.16MPa / %

[0280] ×: Values ​​less than 0.07 MPa / % or greater than 0.16 MPa / %

[0281] (8) Evaluation 8: Maximum shrinkage stress 3 (B / t)

[0282] Based on the maximum shrinkage stress B of the obtained polyester shrink film and the film thickness t, B / t (MPa / μm) is calculated and evaluated according to the following criteria.

[0283] ◎: Values ​​in the range of 0.06 to 0.35 MPa / μm.

[0284] 〇: Values ​​within the range of 0.05 to 0.4 MPa / μm and outside the range mentioned above.

[0285] △: Values ​​within the range of 0.04 to 0.45 MPa / μm and outside the range of 0 mentioned above.

[0286] ×: Values ​​less than 0.04 MPa / μm or greater than 0.45 MPa / μm.

[0287] (9) Evaluation 9: Anti-wrinkle properties

[0288] Cylindrical PET bottles (capacity: 500ml) filled with beverage water are ready for sale.

[0289] Next, on a strip of shrink film obtained by cutting the polyester shrink film into a strip with a width of 26cm, a 1mm wide seam is set along the long side, and 1,3-dioxolane is coated at the end in the width direction.

[0290] Next, the ends are overlapped and glued together with an overlap of approximately 1 cm in the width direction to create a cylindrical label with a diameter of approximately 8 cm. This cylindrical label is then cut every 16 cm along its length to obtain multiple cylindrical labels.

[0291] Next, the cylindrical label is placed over the prepared cylindrical PET bottle, placed on a conveyor belt, and moved at a speed of 6 m / min in a steam channel maintained at 85°C, causing the cylindrical label to heat-shrink and seal tightly against the cylindrical PET bottle from top to bottom.

[0292] Next, visually inspect the heat-shrinked cylindrical label and evaluate its wrinkle resistance based on whether wrinkles of a specified length (more than 1 cm) and a specified width (more than 1 mm) are produced, according to the following criteria.

[0293] ◎: Of the 5 cylindrical labels, none of them showed the required wrinkles.

[0294] 〇: Of the 5 cylindrical labels, no prescribed wrinkles were observed in 3 or more.

[0295] △: Of the 5 cylindrical labels, more than 1 did not show the required wrinkles.

[0296] ×: Of the 5 cylindrical labels, all 5 were found to have the specified wrinkles.

[0297] (10) Rating 10: Haze

[0298] According to JIS K 7105, the haze value of the polyester shrink film is measured and evaluated according to the following criteria.

[0299] ◎: Values ​​below 1%.

[0300] 〇: Values ​​below 3%.

[0301] △: Values ​​below 5%.

[0302] ×: Values ​​greater than 5%.

[0303] [Examples 2-5]

[0304] In Examples 2-5, as shown in Table 1, various polyester shrink films were produced by changing the values ​​of components (a) to (c) respectively, in the same manner as in Examples 1. Except for this, the maximum shrinkage stress 1 (B), maximum shrinkage stress 2 (B / A2), etc., were evaluated in the same way as in Example 1. The results are shown in Table 2.

[0305] That is, in Example 2, a polyester shrink film with a thickness of 25 μm was prepared using amorphous polyester resin (PETG1) as raw material and by changing the extrusion conditions. Otherwise, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0306] In addition, in Example 3, a polyester shrink film with a thickness of 40 μm was prepared using amorphous polyester resin (PETG1) as raw material and by changing the extrusion conditions. Otherwise, the evaluation was carried out in the same manner as in Example 1.

[0307] In addition, in Example 4, a polyester shrink film with a thickness of 25 μm was prepared by mixing 90 parts by weight of amorphous polyester resin (PETG1) and 10 parts by weight of crystalline polyester resin (PBT) as raw materials and changing the extrusion conditions. Otherwise, the evaluation was carried out in the same manner as in Example 1.

[0308] In addition, in Example 5, a polyester shrink film with a thickness of 39 μm was prepared using amorphous polyester resin (PETG2) as raw material and by changing the extrusion conditions. Otherwise, the evaluation was carried out in the same manner as in Example 1.

[0309] [Comparative Example 1]

[0310] In Comparative Example 1, as shown in Table 1, polyester shrink films that did not meet the constituent requirements (b) and (c) were prepared and evaluated in the same manner as in Example 1. The results are summarized in Table 2.

[0311] That is, a polyester shrink film with a thickness of 30 μm that does not meet the constituent requirements (b) and (c) is produced by mixing 90 parts by weight of amorphous polyester resin (PETG1) and 10 parts by weight of crystalline polyester resin (APET) as raw materials and changing the extrusion conditions.

[0312] It should be noted that the measured change in shrinkage stress over time is as follows: Figure 8 The characteristic curve W is shown in the figure.

[0313] More specifically, the shrinkage stress reached its maximum value of 13.74 MPa 14 seconds after the start of the measurement.

[0314] [Comparative Example 2]

[0315] In Comparative Example 2, as shown in Table 1, polyester shrink films that did not meet the constituent requirements (a) to (c) were prepared and evaluated in the same manner as in Example 1. The results are summarized in Table 2.

[0316] That is, using only amorphous polyester resin (PETG2) as raw material, and changing the extrusion conditions, a polyester shrink film with a thickness of 22 μm that does not meet the constituent requirements (a) to (c) is produced.

[0317]

[0318]

[0319] Industrial availability

[0320] According to the present invention, the disadvantages of existing heat-shrinkable thermoplastic resin films, especially polyester shrink films, are eliminated. By limiting the heat shrinkage rate A2, the maximum shrinkage stress B, and B / A2 to values ​​within a specified range, polyester shrink films with excellent wrinkle resistance can be effectively provided.

[0321] Therefore, the polyester shrink film according to the present invention can be applied to various PET bottles, etc., which can significantly expand its versatility, and its industrial applicability is very high.

Claims

1. A polyester-based shrink film containing 90 to 100% by weight of an amorphous polyester in the total amount of the resin, and satisfying the following (a) to (c), (f), (k), and (m): (a) when a main shrinkage direction is set as a TD direction, and a heat shrinkage rate in the TD direction at a condition of 90°C hot water for 10 seconds is set as A2, the A2 is a value of 53% or more; (b) a maximum shrinkage stress in the TD direction at 90°C is set as B, and the B is a value in a range of 2 to 10 MPa; (c) a value represented by B / A2 according to the B and the A2 is a value in a range of 0.08 to 0.15 MPa / %, (f) a heat shrinkage rate in the TD direction at a condition of 80°C hot water for 10 seconds is set as Al, and the Al is a value in a range of 40 to 70%; (k) a haze value of the polyester-based shrink film before shrinkage measured in accordance with JIS K 7105 is a value of 5% or less; and (m) 90 to 100% by weight of the amorphous polyester in the total amount of the resin. Further satisfying the following (d): (d) a thickness of the polyester-based shrink film before shrinkage is set as t, and a value represented by B / t according to the B and t is a value in a range of 0.05 to 0.40 MPa / μm. The thickness t of the polyester-based shrink film before shrinkage is a value in a range of 15 to 45 μm. A stretch ratio in an MD direction of the polyester-based shrink film before shrinkage is a value in a range of 100 to 200%. A stretch ratio in the TD direction of the polyester-based shrink film before shrinkage is a value in a range of 300 to 600%. ​ ​ ​ ​ ​ ​ 2. The polyester-based shrink film according to claim 1, characterized by ​ ​ 3. The polyester-based shrink film according to claim 2, characterized by ​ 4. The polyester-based shrink film according to claim 1 or 2, characterized by ​ 5. The polyester-based shrink film according to claim 1 or 2, characterized by ​

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