Polyester heat shrink films with improved shrink properties

Abstract

By adjusting the dynamic viscoelasticity before and after shrinkage to a specific range, the polyester thermal shrinkage film can have more excellent shrinkage rate and shrinkage uniformity at high temperature. Therefore, the heat shrink film can be used for packaging and labeling containers or bottles so as to improve the quality.

Description

Technical Field

[0001] This invention relates to a heat-shrinkable polyester film with enhanced shrinkage properties. Background Technology

[0002] Polyesters, a type of polymer, possess excellent mechanical strength, heat resistance, transparency, and gas barrier properties, making them suitable for use in various fields. In particular, heat-shrinkable films prepared from polyester resins exhibit high heat resistance and a suitable heat shrinkage rate; therefore, they are suitable for packaging materials and / or labels for plastic containers such as PET bottles.

[0003] The labeling or packaging process using heat shrink film involves first placing the heat shrink film, cut to the appropriate size and shape, onto a clean and dried container or bottle; then shrinking the film through a high-temperature heat treatment process to tightly fit the shape of the container or bottle. If the film shrinks too little or unevenly during this process, it may break, potentially leading to poor printability in subsequent printing processes.

[0004] The shrinkage characteristics of heat-shrinkable films, such as shrinkage rate and shrinkage uniformity at high temperatures, are related to the crystallinity of the polymer constituting the film. Crystallinity can vary depending on the polymer composition or the stretching and heat treatment processes used in film preparation. Therefore, to obtain the desired shrinkage characteristics of the heat-shrinkable film, the composition of the polymer resin can be adjusted, or the stretching and heat treatment conditions during film preparation can be appropriately modified.

[0005] For example, Korean Patent No. 0785251 discloses a technique in which 5% by weight or more of polyester elastomer is incorporated into the preparation of a heat shrink film to suppress the generation of wrinkles, shrinkage stains, twisting, etc. when the film is used for full packaging of plastic bottles.

[0006] [Existing technical documents]

[0007] [Patent Literature]

[0008] (Patent Document 1) Korean Patent No. 0785251 (December 5, 2007). Summary of the Invention

[0009] Technical issues

[0010] The shrinkage characteristics of heat shrink film can vary not only depending on the raw material resin, but also on the film preparation process, making them difficult to control.

[0011] The inventors have discovered that when the ratio of tan δ before and after shrinkage of the heat-shrinkable film is controlled within a specific range, the shrinkage characteristics are enhanced.

[0012] Therefore, one object of the present invention is to provide a heat-shrinkable polyester film that is controlled to have a high shrinkage rate and uniform shrinkage.

[0013] Solution to the problem

[0014] This invention provides a heat-shrinkable film comprising a copolyester resin containing a diol component and a dicarboxylic acid component, wherein when the film is cut along the main shrinkage direction, mounted on a stretching jig, and measured using a dynamic mechanical analyzer (DMA) at a frequency of 1 Hz under heating conditions from 30°C to 150°C at a rate of 3°C / min, the temperature (°C) at which tan δ is 1 or greater is in the range of 65°C to 100°C, and the maximum ratio of tan δ calculated by the following equation is 50% or greater.

[0015] The maximum ratio of Tan to δ is given by: (tan δ [1]max / tan δ [2]max) × 100

[0016] Here, tan δ [1]max is the maximum value of tan δ when the heat shrink film is measured under the above heating conditions, tan δ [2]max is the maximum value of tan δ when the heat shrink film is shrunk for 30 seconds at 95℃ and measured under the above heating conditions, and tan δ is G″ / G′, where G″ is the loss modulus and G′ is the storage modulus.

[0017] Beneficial effects of the invention

[0018] According to the present invention, the dynamic viscoelasticity before and after shrinkage, specifically the ratio of tanδ, is controlled within a specific range; therefore, the shrinkage rate and shrinkage uniformity at high temperatures can be effectively controlled.

[0019] Because of its excellent shrinkage rate and shrinkage uniformity, as well as its excellent stretchability and printability, this heat shrink film can be used for packaging and labeling containers or bottles, thereby improving quality. Detailed Implementation

[0020] Best Implementation of the Invention

[0021] In this specification, the terms used to refer to the various components are used to distinguish them from each other and are not intended to limit the scope of the embodiments. Furthermore, in this specification, singular expressions are also construed to cover plural forms unless the context otherwise requires.

[0022] In this specification, the terms first, second, etc., are used to describe various components. However, these components should not be limited by these terms. These terms are used to distinguish one element from another.

[0023] In this specification, the term "comprising" is intended to specify a particular feature, region, step, method, element, and / or component. Unless otherwise expressly stated, the presence or addition of any other feature, region, step, method, element, and / or component is not excluded.

[0024] Within the numerical ranges of limiting component size and physical properties described in this specification, when examples are given of numerical ranges limited only by the upper limit and numerical ranges limited only by the lower limit, it should be understood that numerical ranges combining these upper and lower limits are also included within the scope of the present invention.

[0025] Properties of heat shrink film

[0026] According to the present invention, the dynamic viscoelasticity of the heat-shrinkable polyester film, particularly its properties related to tan δ, is controlled within a specific range. As a result, a heat-shrinkable polyester film with high shrinkage rate, uniform shrinkage, and tensile strength can be provided.

[0027] Tan δ (tan δ) is defined as the loss modulus (G″) divided by the storage modulus (G′) (i.e., tan δ = G″ / G′), which can be an important indicator for confirming the membrane shrinkage characteristics. The loss modulus represents viscous behavior and indicates how much energy is lost, while the storage modulus represents elastic behavior and indicates how much energy is stored.

[0028] Since tan δ represents the energy lost due to internal friction associated with molecular rearrangement when stress is applied to a polymer, it can be considered an indicator of the polymer's damping performance. Even if the polymers constituting the membrane have the same composition, the membrane's tan δ will vary due to changes in elasticity and viscosity caused by molecular orientation during stretching.

[0029] For example, tan δ can be measured using a dynamic mechanical analysis (DMA) apparatus. First, the sample is cut to a suitable size and mounted on the DMA's clamps or holder. Then, periodic stress or strain is applied while the sample is heated or cooled. In the DMA, the phase difference between the periodic stress and the response is measured, thereby obtaining the sample's loss modulus and storage modulus, and then tan δ is calculated.

[0030] Specifically, the heat-shrinkable film can be cut in the main shrinkage direction and mounted on a stretching fixture to measure tanδ using a dynamic mechanical analysis (DMA) device under heating conditions of 3°C / min from 30°C to 150°C at a frequency of 1 Hz.

[0031] In the tan δ curve of temperature obtained from DMA, the maximum peak can appear near the glass transition temperature (Tg), the height of the peak can indicate the number of molecular chains that have moved relative to the temperature, and the full width at half maximum (FWHM) of the peak can provide information about the chain segment movement.

[0032] When the peak temperature or peak height in the tan δ curve is high, it means that the membrane is flexible and has a structure that easily absorbs shocks. This is thought to be due to a decrease in the crystallinity of the resin or a reduction in the crystal size.

[0033] In particular, the temperature range where tan δ is 1 or greater is the range where viscosity is high relative to elasticity; therefore, it can be interpreted as the temperature range in which the heat-shrinkable film exhibits high shrinkage properties.

[0034] According to the present invention, the temperature (°C) at which the heat shrink film has a tan δ of 1 or greater is 65°C or higher. Furthermore, the temperature (°C) at which the heat shrink film has a tan δ of 1 or greater can be 100°C or lower.

[0035] If the temperature at which tan δ is 1 or greater, measured in the main shrinkage direction of the heat-shrinkable film, is below 65°C, the crack resistance at room temperature deteriorates, and the film properties may change over time. Furthermore, if the temperature at which tan δ is 1 or greater, measured in the main shrinkage direction of the heat-shrinkable film, exceeds 100°C, it becomes difficult to achieve the high shrinkage characteristics required by this invention.

[0036] According to one implementation, when the heat shrink film is cut in the main shrinkage direction and installed on a stretching fixture, a dynamic mechanical analysis (DMA) device is used to measure tan δ at a heating rate of 3°C / min, from 30°C to 150°C, and a frequency of 1Hz. The temperature (°C) at which tan δ is 1 or greater is in the range of 65°C to 100°C.

[0037] For example, the temperature (°C) at which the heat shrink film has a tan δ of 1 or greater can be 65°C or higher, 68°C or higher, 70°C or higher, 73°C or higher, or 75°C or higher, and can be 100°C or lower, 95°C or lower, 90°C or lower, or 85°C or lower. As a specific example, the temperature (°C) at which the heat shrink film has a tan δ of 1 or greater can be 65°C to 100°C or 68°C to 100°C.

[0038] In particular, according to the present invention, the tan δ characteristics of the heat-shrinkable film before and after shrinkage are jointly controlled.

[0039] According to one embodiment, the heat-shrinkable film can be a film stretched in the main shrinkage direction; therefore, tan δ before shrinkage can refer to the tan δ of the stretched film, and tan δ after shrinkage can refer to the tan δ of both the stretched and shrunken films. Meanwhile, since the shrunken film is very similar to the film in its unstretched state, the tan δ after shrinkage can also be considered as the tan δ of the unstretched film.

[0040] As mentioned above, considering the tanδ before and after membrane shrinkage allows for more effective control of membrane shrinkage characteristics.

[0041] According to one embodiment, when the heat shrink film shrinks for 30 seconds at 95°C, the temperature (°C) with tan δ of 1 or greater can be measured under the above-mentioned heating conditions, which is within the range of 65°C to 85°C.

[0042] For example, the temperature (°C) at which the tan δ of the shrunken heat shrink film is 1 or greater can be 65°C or higher, 68°C or higher, 70°C or higher, 73°C or higher, or 75°C or higher, and can be 85°C or lower, 83°C or lower, 80°C or lower, or 77°C or lower. As a specific example, the temperature (°C) at which the tan δ of the shrunken heat shrink film is 1 or greater can be between 65°C and 85°C or between 68°C and 85°C.

[0043] Specifically, shrinkage rate and shrinkage uniformity can be effectively controlled when the ratio of the maximum tanδ values ​​of the film before and after shrinkage is adjusted to a specific range. Specifically, the shrinkage rate and shrinkage stress caused by the crystallinity of the resin itself or by crystallinity occurring during stretching are reflected in the film's tanδ. These can be effectively controlled by adjusting the ratio of the maximum tanδ values ​​of the film before and after shrinkage to a specific range.

[0044] According to one implementation, when a heat-shrinkable film is cut in the main shrinkage direction and mounted on a stretching fixture, and tanδ is measured using a dynamic mechanical analysis (DMA) device at a heating rate of 3°C / min, from 30°C to 150°C, and a frequency of 1Hz, the maximum ratio of tanδ calculated by the following equation is 50% or greater.

[0045] The maximum ratio of Tan to δ is given by: (tan δ [1]max / tan δ [2]max) × 100

[0046] Here, tan δ [1]max is the maximum value of tan δ when the heat shrink film is measured under the above heating conditions, and tan δ [2]max is the maximum value of tan δ when the heat shrink film is shrunk at 95°C for 30 seconds and measured under the above heating conditions.

[0047] Conversely, if the maximum ratio of tan δ is less than 50%, the polyester constituting the heat shrink film has excessively high crystallinity, which may cause whitening due to partial crystallization during the heat shrinking process, and the adhesion between films may become poor or impossible.

[0048] For example, the maximum ratio of tan δ can be 50% or greater, 55% or greater, 60% or greater, 65% or greater, 70% or greater, or 75% or greater, and can be 120% or less, 100% or less, 95% or less, 90% or less, 85% or less, or 80% or less. As a specific example, the maximum ratio of tan δ can be 50% to 120%, 50% to 100%, 50% to 95%, 55% to 100%, or 55% to 95%.

[0049] Furthermore, according to one embodiment of the heat-shrinkable film, the temperature at which the pre-shrink film has a tan δ of 1 or greater can be higher than the temperature at which the post-shrink film has a tan δ of 1 or greater. This is attributed to the orientation of the polymer chains during the stretching process of the film, and the different degree of movement of the oriented chains relative to temperature compared to the post-shrink film.

[0050] In one specific implementation, the heat shrink film can satisfy the following relationship (a).

[0051] Tmax [1] > Tmax [2] (a)

[0052] Here, Tmax [1] is the highest temperature (°C) of tan δ of 1 or greater when the heat shrink film is measured under the above heating conditions, and Tmax [2] is the highest temperature (°C) of tan δ of 1 or greater when the heat shrink film is measured under the above heating conditions after shrinking at 95°C for 30 seconds.

[0053] In another specific implementation, the heat shrink film can satisfy the following relationship (a').

[0054] Tmin[1]> Tmin[2] (a')

[0055] Here, Tmin [1] is the lowest temperature (°C) of the temperature at which tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions, and Tmin [2] is the lowest temperature (°C) of the temperature at which tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions after shrinking at 95°C for 30 seconds.

[0056] Furthermore, in a heat-shrinkable film according to one embodiment, the size of the temperature range in which tan δ is 1 or greater can be controlled within a specific range.

[0057] The temperature range where tan δ is 1 or greater varies depending on the degree of crystal orientation of the polymer chains during stretching. As crystal orientation increases, the temperature range where tan δ is 1 or greater also increases. Therefore, if the temperature range where tan δ is 1 or greater is too large, it may be difficult to achieve a high shrinkage rate during shrinkage due to the increased crystal orientation. On the other hand, if the temperature range where tan δ is 1 or greater is too small, the polymer chains may not be sufficiently oriented due to the decreased crystal orientation, which may make it difficult to achieve uniform shrinkage during the shrinkage process.

[0058] In one specific implementation, the heat shrink film can satisfy the following relationship (b).

[0059] 10°C ≤ Tmax [1] – Tmin [1] ≤ 30°C (b)

[0060] Here, Tmax [1] is the highest temperature (°C) of the temperature at which tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions, and Tmin [1] is the lowest temperature (°C) of the temperature at which tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions.

[0061] For example, the calculated value of Tmax[1]–Tmin[1] in relation (b) can be 10°C to 30°C, 15°C to 30°C, 10°C to 25°C, 15°C to 25°C, 15°C to 20°C or 10°C to 20°C.

[0062] In another specific implementation, the heat shrink film can satisfy the following relationship (b').

[0063] 1°C ≤ Tmax [2] – Tmin [2] ≤ 20°C (b')

[0064] Here, Tmax [2] is the highest temperature (°C) of the heat shrink film when measured under the above-mentioned heating conditions after shrinking for 30 seconds at 95°C, with tan δ of 1 or greater, and Tmin [2] is the lowest temperature (°C) of the heat shrink film when measured under the above-mentioned heating conditions after shrinking for 30 seconds at 95°C, with tan δ of 1 or greater.

[0065] For example, the calculated value of Tmax[2]–Tmin[2] in relation (b') can be 1°C to 20°C, 1°C to 15°C, 5°C to 20°C, 5°C to 15°C, 1°C to 10°C, or 5°C to 10°C.

[0066] Furthermore, in a heat-shrinkable film according to one embodiment, the temperature range in which tan δ is 1 or greater before shrinkage can be larger to a certain extent or greater than that after shrinkage. A difference in tan δ between the stretched and shrink films reaching a certain level or greater indicates the orientation of the polymer chains. When a certain level or greater chain orientation occurs, it can exhibit high shrinkage rate and uniform stretching, which are characteristics of heat-shrinkable films.

[0067] In one specific implementation, the heat shrink film can satisfy the following relationship (c).

[0068] 3°C ≤ (Tmax [1] – Tmin [1]) – (Tmax [2] – Tmin [2]) (c)

[0069] Here, Tmax [1] is the highest temperature (°C) among the temperatures (°C) where tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions, and Tmin [1] is the lowest temperature (°C) among the temperatures (°C) where tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions. Tmax [2] is the highest temperature (°C) among the temperatures (°C) where tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions after shrinking at 95°C for 30 seconds, and Tmin [2] is the lowest temperature (°C).

[0070] For example, the calculated value of (Tmax[1]–Tmin[1]–(Tmax[2]–Tmin[2]) in relation (c) can be 3°C or higher, 5°C or higher, 7°C or higher, or 10°C or higher, and can be 30°C or lower, 25°C or lower, 20°C or lower, or 15°C or lower.

[0071] Furthermore, in a heat-shrinkable film according to one embodiment, the stiffness ratio before and after shrinkage can be adjusted to a specific range, thereby producing excellent tensile properties.

[0072] Specifically, heat shrink film can have a stiffness ratio of 150% or greater, as defined by the following equation.

[0073] Stiffness ratio = (Stiffness[2] / Stiffness[1]) × 100

[0074] Here, stiffness[1] is the measured stiffness of the heat shrink film (N / m), and stiffness[2] is the measured stiffness of the heat shrink film after shrinking at 95°C for 30 seconds (N / m). The stiffness is measured at a temperature where the tan δ of the heat shrink film is 1.

[0075] Within the aforementioned preferred range, the orientation of the polymer constituting the film can be appropriately adjusted to improve tensile strength.

[0076] For example, the stiffness ratio can be 150% or greater, 200% or greater, 250% or greater, 300% or greater, 350% or greater, or 400% or greater, and can be 700% or less, 600% or less, or 500% or less. As a specific example, the stiffness ratio can be 150% to 700%, 150% to 600%, or 150% to 500%.

[0077] Furthermore, in a heat-shrinkable film according to one embodiment, the shrinkage rate relative to temperature can be controlled within a specific range of the heat-shrinking process temperature range.

[0078] Specifically, when the heat-shrinkable film is cut to 15.5 cm along the main shrinkage direction and installed on the film stretching fixture, and when the temperature is increased from 65°C to 85°C at a rate of 5°C / min and held at 5°C intervals for 1 minute, the shrinkage that occurs during the heating process can be from -0.3 cm / °C to -0.7 cm / °C.

[0079] As mentioned above, a high shrinkage rate relative to temperature of -0.3 cm / °C or higher allows for sufficient shrinkage. A shrinkage rate relative to temperature variation of -0.7 cm / °C or lower is suitable to ensure uniform shrinkage relative to temperature changes.

[0080] Therefore, heat shrink film has a lower risk of breaking due to tension during processing, which may reduce the operability of processing.

[0081] More specifically, the shrinkage rate can be -0.3 cm / °C to -0.7 cm / °C, -0.4 cm / °C to -0.7 cm / °C, -0.5 cm / °C to -0.7 cm / °C, -0.3 cm / °C to -0.6 cm / °C, -0.3 cm / °C to -0.5 cm / °C, or -0.4 cm / °C to -0.6 cm / °C.

[0082] Heat shrink film can exhibit a certain or even higher shrinkage rate at high temperatures. For example, under conditions of 90°C and 15 seconds, heat shrink film can have a shrinkage rate of 60% or greater in the main shrinkage direction. Specifically, under conditions of 90°C and 15 seconds, the heat shrinkage rate of heat shrink film in the main shrinkage direction can be 60% to 80%.

[0083] According to one embodiment, the heat shrinkable film can be a film stretched in at least one direction. The heat shrinkable film can be a film uniaxially stretched in the longitudinal (MD) or transverse (TD) direction, or biaxially stretched in both directions.

[0084] As one example, the heat shrink film may be a film stretched 1 to 5 times or 1.1 to 4.5 times in the longitudinal (MD) direction. As another example, the heat shrink film may be a film stretched 1.5 to 6 times or 2.5 to 5.5 times in the transverse (TD) direction. As yet another example, the heat shrink film may be a film stretched 1 to 5 times in the longitudinal (MD) direction and 1.5 to 6 times in the transverse (TD) direction.

[0085] In heat shrink film, the longitudinal (MD) or transverse (TD) direction can be the primary shrinkage direction. Specifically, the stretch ratio of the heat shrink film in the primary shrinkage direction can be 1.5 to 6 times. More specifically, the heat shrink film can be a film in which the transverse (TD) direction is the primary shrinkage direction.

[0086] Components of heat shrink film

[0087] The heat-shrinkable film according to the present invention comprises a copolyester resin, which comprises a diol component and a dicarboxylic acid component.

[0088] In addition, at least one of the diol component and the dicarboxylic acid component may contain recycled monomers.

[0089] According to the present invention, the diol component may be a diol component used to prepare a copolyester resin.

[0090] Specifically, the diol component may be at least one selected from the group consisting of: bis(2-hydroxyethyl) terephthalate (BHET), isosorbide, neopentyl glycol, ethylene glycol, cyclohexanediol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-Dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylethanol.

[0091] Preferably, when considering the crystallinity, heat shrinkage, and economic benefits of the heat-shrinkable polyester film, the diol component may include two or more (specifically, three or more, four or more, or five or more) selected from the group consisting of: bis(2-hydroxyethyl) terephthalate, isosorbide, ethylene glycol, cyclohexanediol, neopentyl glycol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylethanol.

[0092] Furthermore, the diol component may include ethylene glycol and at least one selected from the group consisting of (specifically, two or more, three or more, or four or more): bis(2-hydroxyethyl) terephthalate, isosorbide, cyclohexanediol, neopentyl glycol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylethanol as comonomers.

[0093] When the glycol component contains ethylene glycol and comonomer, there are no particular restrictions on the amount of these components used. However, based on the total weight of the glycol component, the amount of ethylene glycol can be 10% by weight to less than 100% by weight, 15% by weight to 90% by weight, 20% by weight to 85% by weight, 30% by weight to 85% by weight, 50% by weight to 80% by weight, or 50% by weight to 85% by weight, and the amount of comonomer can be greater than 0% by weight to 90% by weight, greater than 0% by weight to 85% by weight, 1% by weight to 90% by weight, 1% by weight to 50% by weight, 2% by weight to 50% by weight, 10% by weight to 85% by weight, 15% by weight to 80% by weight, 15% by weight to 70% by weight, or 15% by weight to 50% by weight.

[0094] Based on the total weight of the glycol components, the amount of isosorbide used as a comonomer can be 0% to 30% by weight, 0% to 10% by weight, 0% to 3% by weight, 0.1% to 20% by weight, 0.5% to 10% by weight, 0.5% to 5% by weight, 0.5% to 3% by weight, or 1% to 3% by weight. Based on the total weight of the glycol components, the amount of 1,4-cyclohexanediol used as a comonomer can be 0% to 50% by weight, 0% to 40% by weight, 1% to 50% by weight, 2% to 50% by weight, 3% to 45% by weight, 4% to 40% by weight, or 5% to 35% by weight. Based on the total weight of the glycol components, the amount of neopentyl glycol used as a comonomer can be 0% to 50% by weight, 0% to 30% by weight, 1% to 50% by weight, 2% to 50% by weight, 3% to 45% by weight, 4% to 40% by weight, or 5% to 35% by weight. Based on the total weight of the diol component, the amount of diethylene glycol used as a comonomer can be 0% to 50% by weight, 1% to 50% by weight, 1% to 30% by weight, 1% to 15% by weight, 2% to 50% by weight, 3% to 45% by weight, 4% to 40% by weight, 5% to 35% by weight, 5% to 25% by weight, or 5% to 15% by weight.

[0095] The polyester resin according to the invention may contain structural units derived from isosorbide as copolymerizing units in amounts ranging from 0 mol% to 30 mol%, 0 mol% to 10 mol%, 0 mol% to 3 mol%, 0.1 mol% to 20 mol%, 0.5 mol% to 10 mol%, 0.5 mol% to 5 mol%, 0.5 mol% to 3 mol%, or 1 mol% to 3 mol%. The polyester resin according to the invention may contain structural units derived from 1,4-cyclohexanediol as copolymerizing units in amounts ranging from 0 mol% to 50 mol%, 0 mol% to 35 mol%, 1 mol% to 50 mol%, 2 mol% to 50 mol%, 3 mol% to 45 mol%, 4 mol% to 40 mol%, or 5 mol% to 35 mol%. The polyester resin according to the present invention may contain structural units derived from neopentyl glycol as copolymerizing units in amounts of 0 mol% to 50 mol%, 0 mol% to 30 mol%, 1 mol% to 50 mol%, 2 mol% to 50 mol%, 3 mol% to 45 mol%, 4 mol% to 40 mol%, or 5 mol% to 35 mol%. The polyester resin according to the present invention may contain structural units derived from diethylene glycol as copolymerizing units in amounts of 0 mol% to 50 mol%, 1 mol% to 50 mol%, 2 mol% to 50 mol%, 3 mol% to 45 mol%, 4 mol% to 40 mol%, or 5 mol% to 35 mol%.

[0096] According to the present invention, the dicarboxylic acid component can be a common dicarboxylic acid component.

[0097] Specifically, the dicarboxylic acid component may include at least one selected from the group consisting of: isophthalic acid, terephthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylic acid, diphenyl dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylic acid, dimethyl 1,3-cyclohexanedicarboxylic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid.

[0098] Preferably, when considering the crystallinity and heat shrinkage of the stretched polyester film, the dicarboxylic acid component may include at least one selected from the group consisting of isophthalic acid, terephthalic acid, dimethyl phthalate and dimethyl isophthalate.

[0099] Furthermore, the dicarboxylic acid component may contain recovered monomers obtained through the depolymerization of waste polyester. As a specific example, the dicarboxylic acid component may include at least one recovered monomer selected from recovered dicarboxylic acids and recovered dicarboxylic acid derivatives. As a more specific example, the dicarboxylic acid component may include at least one recovered monomer selected from, but not limited to, the group consisting of recovered isophthalic acid, recovered terephthalic acid, recovered dimethyl isophthalate, and recovered dimethyl phthalate.

[0100] As mentioned above, the recovered monomers obtained through the depolymerization of waste polyester need to be understood as different from the original monomers or pure monomers. Specifically, the recovered monomers may contain reagents or solvents used in various chemical steps during the depolymerization process of waste polyester, or byproducts formed from their side reactions. Therefore, monomers recovered through ordinary depolymerization processes contain organic and inorganic impurities in addition to monomer compounds as the main component; thus, their purity is not high. For this reason, the recovered monomers can also be considered as a composition containing two or more components.

[0101] According to the present invention, the intrinsic viscosity (IV) of the polyester resin at 35°C may be 0.5 dl / g or greater or 0.6 dl / g or greater, and may be 1.2 dl / g or less, 1.1 dl / g or less, 1.0 dl / g or less, 0.9 dl / g or less or 0.8 dl / g or less.

[0102] According to one specific embodiment, the intrinsic viscosity of the copolyester resin at 35°C can be from 0.5 dl / g to 0.9 dl / g. Within this preferred range of intrinsic viscosity, this is beneficial for ensuring the processing performance of the copolyester resin. Specifically, the polyester resin is dissolved in o-chlorophenol (OCP) at a concentration of 0.12% at 100°C, and the intrinsic viscosity is measured using an Ubbelohde viscometer in a thermostat at 35°C.

[0103] Preparation method of heat shrink film

[0104] The method for preparing the heat-shrinkable film according to the present invention includes: preparing a polyester resin by using a diol component and a dicarboxylic acid component (S-1); preparing a stretched sheet from the polyester resin (S-2); and heat-setting the stretched sheet.

[0105] In step (S-1), the diol component and the dicarboxylic acid component are polymerized to prepare a polyester resin (polymer). Since the diol component and dicarboxylic acid component used in the polymerization reaction are the same as those described above, their description is omitted.

[0106] The polymerization of the diol and dicarboxylic acid components can be carried out by conventionally known methods (e.g., liquid-phase polymerization, solid-phase polymerization, etc.). The polymerization reaction can be carried out in a batch reactor or a continuous reactor. Specifically, the polymerization reaction may include an esterification reaction (transesterification reaction) to prepare an oligomer by reacting the diol component with the dicarboxylic acid component, and a polycondensation reaction of the oligomer.

[0107] There are no particular limitations on the temperature of the esterification reaction, but considering the physical properties of the polyester resin and the stretched polyester film, the temperature can be 230°C to 270°C, 235°C to 268°C, 240°C to 265°C, or 240°C to 260°C. Furthermore, there are no particular limitations on the duration of the esterification reaction, but it can be 1 hour to 24 hours, 2 hours to 22 hours, 3 hours to 20 hours, or 4 hours to 18 hours. Additionally, there are no particular limitations on the pressure during the esterification reaction, but it can be 0 kgf / cm². 2 Up to 5.0 kgf / cm 2 0.1 kgf / cm 2 Up to 4.5 kgf / cm 2 0.1 kgf / cm 2 Up to 4.0 kgf / cm 2 Or 0.1 kgf / cm 2 Up to 3.0 kgf / cm 2 .

[0108] There are no particular restrictions on the temperature for the polycondensation reaction, but considering the physical properties of the polyester resin and the stretched polyester film, the temperature can be 245°C to 290°C, 250°C to 285°C, 255°C to 280°C, or 255°C to 270°C. Furthermore, there are no particular restrictions on the duration of the polycondensation reaction, but it can be 1 hour to 24 hours, 2 hours to 24 hours, 5 hours to 22 hours, or 7 hours to 20 hours.

[0109] Meanwhile, additives may be used in the polymerization reaction, which include at least one selected from the group consisting of catalysts, stabilizers, colorants, crystallizers, antioxidants and branching agents.

[0110] There are no particular limitations on the catalyst, but it can specifically be methylates of sodium and magnesium; acetates, borates, fatty acid salts, and carbonates of zinc, cadmium, manganese, cobalt, calcium, and barium; and oxides or hydrates of magnesium, lead, manganese, titanium, zinc, antimony, and germanium. For example, the catalyst can be tetraethyl titanate, triacetyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octyl glycol titanate, triethanolamine titanate, acetylacetone titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, germanium dioxide, germanium tetrachloride, germanium glycol, germanium acetate, or combinations thereof.

[0111] There are no particular restrictions on the choice of stabilizer, but phosphorus-based compounds such as phosphoric acid, trimethyl phosphate, and triethyl phosphate can be used.

[0112] There are no particular restrictions on colorants, but organic compounds such as cobalt-based compounds, anthraquinone-based compounds, cyclic ketone-based compounds, azo compounds, and methine compounds (e.g., cobalt acetate, cobalt propionate, Clarient's Polysynthren Blue RLS, and Clarient's Solvaperm Red BB toner) can be used.

[0113] There are no particular restrictions on crystallizing agents, but crystal nucleating agents, ultraviolet absorbers, polyolefin resins, polyamide resins, etc., can be used.

[0114] There are no particular restrictions on the choice of antioxidants; hindered phenolic compounds, phosphites, thioethers, etc., can be used.

[0115] There are no particular restrictions on branching agents; trimellitic anhydride, trimethylolpropane, trimellitic acid, etc., can be used.

[0116] In step (S-2), a stretched sheet is prepared from the polyester resin obtained in step (S-1). The stretched sheet can be prepared using conventional methods. Specifically, the stretched sheet can be prepared by a polyester resin melting and casting step, a uniaxial or biaxial stretching step, etc.

[0117] The melting and casting steps of the polyester resin can be carried out using an extruder. In this case, there are no particular limitations on the melt extrusion temperature, but it can be 180°C to 310°C, 200°C to 310°C, 230°C to 310°C, 240°C to 300°C, 250°C to 290°C, 250°C to 280°C, or 250°C to 275°C. An unstretched sheet can be obtained through this process, and the resulting unstretched sheet can then be transferred to a stretching step. Before the stretching step, the unstretched sheet can be preheated to a predetermined temperature (e.g., 90°C to 120°C).

[0118] The uniaxial or biaxial stretching step may include stretching an unstretched sheet obtained through a melting and casting step in the longitudinal (MD), transverse (TD) direction, or both. Longitudinal stretching may be performed at 55°C to 180°C, 60°C to 170°C, or 75°C to 90°C at a stretch ratio of 1 to 5 times or 1.1 to 4.5 times. Transverse stretching may be performed at 55°C to 180°C, 60°C to 170°C, 60°C to 130°C, 60°C to 90°C, 60°C to 85°C, 75°C to 90°C, or 75°C to 85°C at a stretch ratio of 1.5 to 6 times, 2.5 to 5.5 times, 3.5 to 6 times, 4 to 6 times, 4.5 to 6 times, 4.5 to 5.5 times, or 3.5 to 5.5 times.

[0119] In step (S-3), the stretched sheet obtained in step (S-2) is heat-set. There are no particular limitations on the heat-setting temperature of the stretched sheet, but it can be similar to or higher than the temperature of the stretching step. Specifically, the heat-setting temperature can be 60°C to 200°C, 65°C to 190°C, 65°C to 180°C, or 65°C to 170°C. When the heat-setting temperature is within the above range, a stretched polyester film with high crystallinity and high mechanical strength can be prepared.

[0120] Implementation schemes of the present invention

[0121] [Example]

[0122] Below, a preferred embodiment is given to facilitate understanding of the invention. However, the following embodiments are provided only to help readily understand the invention, and the scope of the invention is not limited thereto.

[0123] <Preparation of heat shrink film>

[0124] Example 1

[0125] (1) Preparation of copolyester resin

[0126] A reactor equipped with a column and a water-cooled condenser was charged with terephthalic acid (TPA, 3,846.5 g), isosorbide (ISB, 48.3 g), ethylene glycol (EG, 1,300.6 g), 1,4-cyclohexanediethanol (CHDM, 778.6 g), diethylene glycol (DEG, 375.5 g), germanium catalyst (GeO2, 1.0 g), titanium catalyst (1.0 g), phosphoric acid (1.5 g), blue toner (0.005 g), and red toner (0.003 g). Subsequently, after raising the reactor temperature, the mixture was subjected to a pressure 2 kgf / cm² higher than atmospheric pressure. 2 Under pressure, an esterification reaction was carried out at 265°C to obtain a transparent reactant.

[0127] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 270°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.77 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0128] (2) Preparation of heat shrink film

[0129] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 270°C, and cast at 40°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 80°C and stretched only 5 times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0130] Example 2

[0131] (1) Preparation of copolyester resin

[0132] A reactor equipped with a column and a water-cooled condenser was charged with terephthalic acid (TPA, 3,831.6 g), ethylene glycol (EG, 1,672.8 g), 1,4-cyclohexanediol (CHDM, 627.8 g), neopentyl glycol (NPG, 53.3 g), diethylene glycol (DEG, 374.2 g), a CHDM derivative (123.7 g), a titanium catalyst (1.0 g), phosphoric acid (1.5 g), a blue toner (0.005 g), and a red toner (0.005 g). Subsequently, after raising the reactor temperature, the mixture was subjected to a pressure 1 kgf / cm² higher than atmospheric pressure. 2 Under pressure, an esterification reaction was carried out at 255°C to obtain a transparent reactant.

[0133] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 285°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.65 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0134] (2) Preparation of heat shrink film

[0135] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 260°C, and cast at 25°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 80°C and stretched only 4.5 times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0136] Example 3

[0137] (1) Preparation of copolyester resin

[0138] In a reactor equipped with a column and a water-cooled condenser, terephthalic acid (TPA, 2,949.8 g), recovered bis(2-hydroxyethyl) terephthalate (r-BHET, 1,128.4 g), ethylene glycol (EG, 412.2 g), 1,4-cyclohexanediethanol (CHDM, 1,243.9 g), diethylene glycol (DEG, 277.0 g), germanium catalyst (1.0 g), phosphoric acid (1.5 g), a blue toner (0.005 g), and a red toner (0.005 g) were charged. Subsequently, after raising the reactor temperature, an esterification reaction was carried out at 273°C under atmospheric pressure to obtain a transparent reactant.

[0139] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 275°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.80 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0140] (2) Preparation of heat shrink film

[0141] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 260°C, and cast at 68°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 78°C and stretched only 4.5 times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0142] Example 4

[0143] (1) Preparation of copolyester resin

[0144] A reactor equipped with a column and a water-cooled condenser was charged with terephthalic acid (TPA, 3,959.2 g), ethylene glycol (EG, 2,040.3 g), 1,4-cyclohexanediethanol (CHDM, 534.2 g), diethylene glycol (DEG, 416.4 g), germanium catalyst (1.0 g), phosphoric acid (1.5 g), blue toner (0.025 g), and red toner (0.010 g). Subsequently, after raising the reactor temperature, the mixture was subjected to a pressure 1 kgf / cm² higher than atmospheric pressure. 2 Under pressure, an esterification reaction was carried out at 260°C to obtain a transparent reactant.

[0145] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 275°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.78 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0146] (2) Preparation of heat shrink film

[0147] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 275°C, and cast at 35°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 78°C and stretched only 5 times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0148] Example 5

[0149] (1) Preparation of copolyester resin

[0150] A reactor equipped with a column and a water-cooled condenser was charged with terephthalic acid (TPA, 4,139.7 g), ethylene glycol (EG, 2,216.1 g), neopentyl glycol (NPG, 432.3 g), diethylene glycol (DEG, 155.5 g), germanium catalyst (1.0 g), phosphoric acid (1.5 g), cobalt acetate (0.2 g), blue toner (0.015 g), and red toner (0.005 g). Subsequently, after raising the reactor temperature, the mixture was subjected to a pressure 1 kgf / cm² higher than atmospheric pressure. 2 Under pressure, an esterification reaction was carried out at 250°C to obtain a transparent reactant.

[0151] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 285°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.70 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0152] (2) Preparation of heat shrink film

[0153] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 270°C, and cast at 36°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 85°C and stretched only 4.5 times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0154] Example 6

[0155] (1) Preparation of copolyester resin

[0156] A reactor equipped with a column and a water-cooled condenser was charged with terephthalic acid (TPA, 2,291.3 g), recovered bis(2-hydroxyethyl) terephthalate (r-BHET, 1,144.2 g), ethylene glycol (EG, 369.7 g), 1,4-cyclohexanediol (CHDM, 720.8 g), neopentyl glycol (NPG, 650.7 g), diethylene glycol (DEG, 196.6 g), germanium catalyst (1.0 g), phosphoric acid (1.5 g), cobalt acetate (0.2 g), blue toner (0.015 g), and red toner (0.005 g). Subsequently, after raising the reactor temperature, the mixture was subjected to a pressure 2 kgf / cm² higher than atmospheric pressure. 2 Under pressure, an esterification reaction was carried out at 265°C to obtain a transparent reactant.

[0157] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 270°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.78 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0158] (2) Preparation of heat shrink film

[0159] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 260°C, and cast at 38°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 85°C and stretched only 4.5 times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0160] Comparative Example 1

[0161] (1) Preparation of copolyester resin

[0162] A reactor equipped with a column and a water-cooled condenser was charged with terephthalic acid (TPA, 3,280.6 g), recovered bis(2-hydroxyethyl) terephthalate (r-BHET, 1,254.9 g), ethylene glycol (EG, 1,487.6 g), 1,4-cyclohexanediethanol (CHDM, 395.3 g), diethylene glycol (DEG, 154.0 g), titanium catalyst (1.0 g), phosphoric acid (1.5 g), blue toner (0.005 g), and red toner (0.005 g). Subsequently, after raising the reactor temperature, the mixture was subjected to a pressure 1 kgf / cm² higher than atmospheric pressure. 2 Under pressure, an esterification reaction was carried out at 263°C to obtain a transparent reactant.

[0163] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 285°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.70 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0164] (2) Preparation of heat shrink film

[0165] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 280°C, and cast at 25°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 90°C and stretched only 4.5 times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0166] Comparative Example 2

[0167] (1) Preparation of copolyester resin

[0168] In a reactor equipped with a column and a water-cooled condenser, terephthalic acid (TPA, 3,259.2 g), recovered bis(2-hydroxyethyl) terephthalate (r-BHET, 554.1 g), ethylene glycol (EG, 971.5 g), 1,4-cyclohexanediethanol (CHDM, 349.0 g), diethylene glycol (DEG, 272.0 g), titanium catalyst (1.0 g), phosphoric acid (1.5 g), blue toner (0.010 g), and red toner (0.005 g) were charged. Subsequently, after raising the reactor temperature, an esterification reaction was carried out at 263°C under atmospheric pressure to obtain a transparent reactant.

[0169] Subsequently, the reactants were transferred to a polycondensation reactor and polycondensation was carried out at 275°C while maintaining the pressure in the polycondensation reactor below normal pressure. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.78 dl / g, the mixture was discharged outside the polycondensation reactor to form strips, which were then solidified with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0170] (2) Preparation of heat shrink film

[0171] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 270°C, and cast at 25°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 85°C and stretched only four times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0172] Comparative Example 3

[0173] (1) Preparation of copolyester resin

[0174] A reactor equipped with a column and a water-cooled condenser was charged with terephthalic acid (TPA, 3,316.3 g), ethylene glycol (EG, 122.2 g), 1,4-cyclohexanediethanol (CHDM, 2,237.5 g), diethylene glycol (DEG, 49.8 g), titanium catalyst (1.0 g), phosphoric acid (1.5 g), blue toner (0.005 g), and red toner (0.005 g). Subsequently, after raising the reactor temperature, the mixture was subjected to a pressure 1 kgf / cm² higher than atmospheric pressure. 2 Under pressure, an esterification reaction was carried out at 263°C to obtain a transparent reactant.

[0175] The resulting material was then transferred to a polycondensation reactor and subjected to a polycondensation reaction at 275°C while maintaining the pressure in the reactor below normal. When the intrinsic viscosity (IV) of the mixture in the polycondensation reactor reached 0.70 dl / g, the mixture was discharged outside the reactor to form strips, which were then cured with a coolant and granulated to an average weight of approximately 12 mg to 14 mg to prepare polyester resin (copolymer) chips.

[0176] (2) Preparation of heat shrink film

[0177] The polyester resin chips prepared in the above preparation examples were fed into an extruder, melt-extruded at 290°C, and cast at 40°C to prepare an unstretched polyester sheet. Subsequently, the unstretched sheet was heated to 95°C and stretched only four times in the transverse (TD) direction to prepare a stretched polyester sheet. The stretched polyester sheet was heat-set to prepare a stretched polyester film with a thickness of 50 μm.

[0178] <Evaluation of Heat Shrink Film>

[0179] Test Example 1: tan δ (DMA)

[0180] The tan δ of the heat shrink films prepared in the examples and comparative examples was measured respectively.

[0181] (1) Tanδ-stretch membrane

[0182] - Sample: Each membrane with a thickness of approximately 50 μm, stretched in the TD direction, is cut in the width direction (TD).

[0183] - The stretched film sample was mounted on a stretching fixture, and the tan δ curve (tanδ = E' / E”, where E' is the storage modulus and E” is the loss modulus) was obtained at a frequency of 1 Hz using a Dynamic Mechanical Analysis (DMA) device (TA Q800) under the condition of heating from 30°C to 150°C at a rate of 3°C / min.

[0184] - In temperatures where tan δ≥1, the minimum temperature (min) and the maximum temperature (max) are obtained, and their difference (max–min) is calculated.

[0185] (2) Tan δ- after contraction

[0186] - Sample: Each membrane with a thickness of approximately 50 μm, stretched in the TD direction, is cut in the width direction (TD) and shrunken at 95°C for 30 seconds.

[0187] - The tan δ curve of the shrunken membrane sample was obtained in the same manner as in Part (1) above.

[0188] - In temperatures where tan δ≥1, the minimum temperature (min) and the maximum temperature (max) are obtained, and their difference (max–min) is calculated.

[0189] (3) Tan δ interval

[0190] The temperature interval (max–min) of tanδ≥1 for the stretched membrane in Part (1) and the temperature interval (max–min) of tanδ≥1 for the shrunken membrane in Part (2) were measured respectively, and the difference between the two (i.e., the value of (1)–(2)) was obtained.

[0191] (4) The ratio of the maximum value of Tan δ

[0192] The ratio of the maximum value of tan δ of the stretched membrane measured in Part (1) above to the maximum value of tan δ of the shrunken membrane measured in Part (2) above (i.e., the value of (1) / (2)) was obtained.

[0193] Test Example 2: Stiffness

[0194] The stiffness of the membranes prepared in the examples and comparative examples was measured respectively.

[0195] (1) Stiffness - Stretch membrane

[0196] - Sample: Each membrane with a thickness of approximately 50 μm, stretched in the TD direction, is cut in the width direction (TD).

[0197] - The stretched film sample was mounted on a stretching fixture, and the tan δ curve (tanδ = E' / E”, where E' is the storage modulus and E” is the loss modulus) was obtained at a frequency of 1 Hz using a Dynamic Mechanical Analysis (DMA) device (TA Q800) under the condition of heating from 30°C to 150°C at a rate of 3°C / min.

[0198] (2) Stiffness after contraction

[0199] - Sample: Each membrane with a thickness of approximately 50 μm, stretched in the TD direction, is cut in the width direction (TD) and shrunken at 95°C for 30 seconds.

[0200] - The stiffness after shrinkage is measured in the same manner as in section (1) above.

[0201] (3) Stiffness ratio

[0202] The ratio of the stiffness of the stretched film after shrinkage, measured in Part (2) above, to the film stiffness measured in Part (1) above (i.e., the value of (2) / (1)) was obtained. The stiffness was measured at a temperature where the tan δ of the heat-shrinkable film was 1.

[0203] Test Example 3: Shrinkage Uniformity

[0204] Shrinkage uniformity of each membrane prepared in the test examples and comparative examples.

[0205] - Sample: Each membrane, approximately 50 μm thick and stretched in the TD direction, will be cut to an initial dimension of 15.5 cm in the width direction (TD).

[0206] - When a stretched film sample is mounted on a stretching fixture, and the temperature is increased from 65°C to 85°C at a rate of 5°C / min and held at 5°C intervals for 1 minute, the shrinkage (cm) during the heating process is measured. The shrinkage rate (cm / °C) relative to temperature is calculated based on the measurements to evaluate the uniformity of shrinkage.

[0207] Test Example 4: Intrinsic Viscosity

[0208] The polyester resins prepared in the examples were each dissolved in o-chlorophenol (OCP) at 100°C at a concentration of 0.12%, and their intrinsic viscosity (IV, dl / g) was measured using an Ubbelohde viscometer in a constant temperature bath at 35°C. The results confirmed that the intrinsic viscosity of the polyester resins obtained in the examples was in the range of 0.5 dl / g to 0.9 dl / g at 35°C.

[0209] The test results are shown in Tables 1 and 2 below.

[0210] [Table 1]

[0211] [Table 2]

[0212] [Table 3]

[0213] [Table 4]

[0214] [Table 5]

[0215] The test results above show that the heat-shrinkable films of Examples 1 to 6 exhibit tanδ and stiffness characteristics controlled within an ideal range before and after shrinkage. Consequently, their shrinkage uniformity is excellent, ranging from -0.3 cm / °C to -0.7 cm / °C at temperatures between 65°C and 85°C.

[0216] Conversely, the heat-shrinkable films of Comparative Examples 1 to 3 exhibit tan δ characteristics and stiffness properties outside the desired range. In particular, the films of Comparative Examples 1 and 3 do not have a temperature range with tan δ of 1 or greater. As a result, the films of Comparative Examples 1 to 3 are evaluated to have poor shrinkage uniformity.

Claims

1. A heat-shrinkable film comprising a copolyester resin, said copolyester resin comprising a diol component and a dicarboxylic acid component, in, When the membrane is cut along the main contraction direction, mounted on a stretching fixture, and measured using a dynamic mechanical analysis (DMA) device at a frequency of 1 Hz under heating conditions from 30°C to 150°C at a rate of 3°C / min, the maximum tan δ ratio calculated by the following equation is 50% or greater in the range of 65°C to 100°C for temperatures (°C) where tan δ is 1 or greater. The maximum ratio of Tan to δ is given by: (tan δ [1]max / tan δ [2]max) × 100 Wherein, tan δ [1]max is the maximum value of tan δ when the heat shrink film is measured under the above heating conditions, tan δ [2]max is the maximum value of tan δ when the heat shrink film is measured under the above heating conditions after shrinking for 30 seconds at 95°C, and tan δ is G″ / G′, where G″ is the loss modulus and G′ is the energy storage modulus.

2. The heat-shrinkable film according to claim 1, wherein, When the heat-shrinkable film shrinks for 30 seconds at 95°C, the temperature (°C) with tan δ of 1 or greater is in the range of 65°C to 85°C when measured under the above-mentioned heating conditions.

3. The heat-shrinkable film according to claim 1, wherein, The heat-shrinkable film satisfies the following relationship (a): Tmax [1] > Tmax [2] (a) Wherein, Tmax [1] is the highest temperature (°C) of tan δ of 1 or greater when the heat shrink film is measured under the above heating conditions, and Tmax [2] is the highest temperature (°C) of tan δ of 1 or greater when the heat shrink film is measured under the above heating conditions after shrinking at 95°C for 30 seconds.

4. The heat-shrinkable film according to claim 1, wherein, The heat-shrinkable film satisfies the following relationship (b): 10°C ≤ Tmax [1] – Tmin [1] ≤ 30°C (b) Wherein, Tmax [1] is the highest temperature (°C) among the temperatures (°C) where tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions, and Tmin [1] is the lowest temperature (°C) among the temperatures (°C) where tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions.

5. The heat-shrinkable film according to claim 1, wherein, The heat-shrinkable film satisfies the following relationship (c): 3°C ≤ (Tmax [1] – Tmin [1]) – (Tmax [2] – Tmin [2]) (c) Wherein, Tmax [1] is the highest temperature (°C) among the temperatures (°C) where tan δ is 1 or greater when measuring the heat shrink film under the above heating conditions, and Tmin [1] is the lowest temperature (°C). Tmax [2] is the highest temperature (°C) among the temperatures (°C) where tan δ is 1 or greater when the heat shrink film is shrunk at 95°C for 30 seconds under the above heating conditions, and Tmin [2] is the lowest temperature (°C).

6. The heat-shrinkable film according to claim 1, wherein, The stiffness ratio of the heat-shrinkable film is 150% or greater, as defined by the following equation: Stiffness ratio = (Stiffness[2] / Stiffness[1]) × 100 Among them, stiffness[1] is the stiffness measurement value (N / m) of the heat shrink film, and stiffness[2] is the stiffness measurement value (N / m) of the heat shrink film after shrinking at 95°C for 30 seconds, wherein the stiffness is measured at a temperature where the tan δ measurement value of the heat shrink film is 1.

7. The heat-shrinkable film according to claim 1, wherein, The stretch ratio of the heat shrink film in the main shrinkage direction is 1.5 to 6 times.

8. The heat-shrinkable film according to claim 1, wherein, When the heat-shrinkable film is cut to 15.5 cm in the main shrinkage direction and mounted on a film stretching fixture, and when the temperature is increased from 65°C to 85°C at a rate of 5°C / min and held at 5°C intervals for 1 minute, the shrinkage rate during the heating process is -0.3 cm / °C to -0.7 cm / °C.

9. The heat-shrinkable film according to claim 1, wherein, The diol component is at least one selected from the group consisting of: bis(2-hydroxyethyl) terephthalate (BHET), isosorbide, neopentyl glycol, ethylene glycol, cyclohexanediol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2 -Dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylethanol; and The dicarboxylic acid component is selected from at least one of the following groups: isophthalic acid, terephthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylic acid, diphenyl dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylic acid, dimethyl 1,3-cyclohexanedicarboxylic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid.

10. The heat-shrinkable film according to claim 1, wherein, At least one of the diol component and the dicarboxylic acid component contains a recovered monomer.

11. The heat-shrinkable film according to claim 1, wherein, The intrinsic viscosity of the copolyester resin at 35°C is 0.5 dl / g to 0.9 dl / g.

Images