Polyester film, method for preparing the same, and method for recycling polyethylene terephthalate container using the same

Abstract

Embodiments relate to a polyester film, a method for preparing the same, and a method for recycling polyethylene terephthalate (PET) containers using the same, the polyester film having a crystallization temperature (Tc) that is not measured or is measured to be 70 to 130°C using differential scanning calorimetry such that the crystallinity thereof can be easily controlled. The polyester film thus prepared has excellent shrinkage properties and recyclability, and clumping rarely occurs even when dried for a long time at a high temperature during recycling.

Description

Technical Field

[0001] The embodiments relate to a polyester film, a method for preparing the film, and a method for using the film to recycle polyethylene terephthalate (PET) containers. Specifically, this embodiment relates to a polyester film with excellent recyclability obtained by controlling crystallinity, a method for preparing the film, and a method for using the polyester film to recycle polyethylene terephthalate (PET) containers. Background Technology

[0002] In recent years, with the diversification of beverage and food container manufacturing methods and the increasing use of integrated packaging to attract customers, heat shrink labels and heat shrink packaging materials have received widespread attention. Heat shrink labels or heat shrink packaging materials utilize the properties of polymer films that, once stretched and oriented, tend to shrink into their shape before being stretched at a specific temperature or higher. In a typical heat shrink label or heat shrink packaging process, the heat shrink film is cut, printed into the desired pattern, rolled up, and glued at both ends. It is then loosely wrapped around the container and shrinks as heat is applied.

[0003] Membranes used in the aforementioned shrinkage process need not only basic properties such as heat resistance, chemical resistance, weather resistance, and printability, but also container sealing, uniform heat shrinkage, longitudinal running characteristics, and crack resistance. Traditionally, polyvinyl chloride (PVC), polystyrene (PS), and polypropylene (PP) films have been used in this type of heat shrinkage process. In recent years, polyester films, with properties such as high heat resistance, weather resistance, easy incineration, and excellent printability, have been widely used.

[0004] However, traditional polyester films shrink rapidly and have high shrinkage stress, which can lead to defects due to uneven shrinkage or deformation of plastic containers. To address this, Korean Patent Application 2002-0062838 discloses a method of adding 5% or more of polyester elastomer to heat-shrink polyester film to reduce wrinkles, shrinkage stains, deformation, and other phenomena when the film is used for overall packaging of plastic bottles.

[0005] Therefore, by blending soft components with polyester resins, polyester films for heat-shrinking processes can be prepared with lower crystallinity. Furthermore, they have been developed to possess thermal properties, such as shrinkage rate and shrinkage stress relative to temperature, chemical resistance suitable for bonding processes, and recyclability, which has recently become important due to the issue of waste plastics.

[0006] Furthermore, with increasing attention to environmental issues in recent years, there is a need to address the recycling of products made using thermoplastic polymers. In particular, polyethylene terephthalate (PET), a thermoplastic resin with excellent properties in heat resistance, processability, transparency, and non-toxicity, has been widely used in the production of various products such as films, fibers, bottles, and containers, and efforts are continuously being made to improve its recyclability.

[0007] [Existing Technical Documents]

[0008] [Patent Documents]

[0009] (Patent Document 1) Korean Patent Application 2002-0062838 Summary of the Invention

[0010] Technical issues

[0011] Therefore, the objective of the implementation scheme is to provide a method for preparing a polyester film with excellent shrinkage properties and recyclability obtained by controlling crystallinity, which exhibits minimal uneven agglomeration even under high-temperature and long-term drying during its heat treatment process, as well as a method for using it to recycle polyethylene terephthalate containers.

[0012] Technical solution

[0013] According to one embodiment, a polyester film is provided comprising a copolyester resin copolymerized from a diol and a dicarboxylic acid, wherein the crystallization temperature (Tc) of the film is not measured, or the crystallization temperature measured by differential scanning calorimetry is between 70°C and 130°C, and the agglomeration rate is 10% or less after fragments obtained by crushing a polyethylene terephthalate (PET) container with said polyester film are heat-treated at 210°C for 90 minutes.

[0014] According to another embodiment, a method for preparing a polyester film is provided, comprising preparing a copolyester resin copolymerized from a diol and a dicarboxylic acid; melt-extruding the copolyester resin at 250°C to 300°C to prepare an unstretched sheet; stretching the unstretched sheet at 70°C to 100°C; and then heat-setting it at 65°C to 90°C to prepare a polyester film, wherein the crystallization temperature (Tc) of the film is not measured, or the crystallization temperature measured by differential scanning calorimetry is 70°C to 130°C, and the agglomeration rate is 10% or less after fragments obtained by pulverizing a polyethylene terephthalate (PET) container with the polyester film are heat-treated at 210°C for 90 minutes.

[0015] According to another embodiment, a method for recycling a polyethylene terephthalate (PET) container is provided, comprising providing a PET container with the polyester film, crushing the PET container with the polyester film to obtain fragments, and heat-treating the fragments to obtain recycled polyester fragments, wherein after the fragments are heat-treated at 210°C for 90 minutes, the agglomeration rate is 10% or less, and the fragments include a first fragment obtained by crushing the PET container and a second fragment obtained by crushing the polyester film.

[0016] Advantages of the present invention

[0017] According to one embodiment, the crystallization temperature (Tc) of the polyester film is not measured, or the crystallization temperature measured by differential scanning calorimetry is between 70°C and 130°C, thus its crystallinity can be easily controlled. Therefore, even under prolonged high-temperature drying during the recycling process, uneven agglomeration can be suppressed, allowing it to be used in the recycling process.

[0018] Furthermore, due to the very low agglomeration rate, recyclability can be improved while preventing environmental pollution. The use of the polyester film can improve the quality, yield, and productivity of recycled polyester fragments obtained through recycled polyethylene terephthalate containers.

[0019] Furthermore, the method for regenerating polyethylene terephthalate containers according to embodiments of the present invention does not require separate steps for separating the container and the membrane, thereby saving time and cost and making it more economical. Attached Figure Description

[0020] Figure 1 The image shows the condition of the polyester film applied to the product before and after its heat shrinkage.

[0021] Figure 2 The method for measuring the agglomeration rate of a polyethylene terephthalate container with a polyester film is shown in Test Example 2-1.

[0022] Figure 3 The test examples 1-2 illustrate a method for measuring the heat shrinkage rate of polyester film.

[0023] Figure 4 A method for measuring the adhesive properties of polyester films using solvents is shown.

[0024] Figure 5 A method for measuring the shrinkage stress of a polyester film is shown.

[0025] Figure 6 A method for measuring the skirt ratio of polyester film is shown.

[0026] [Explanation of Reference Figures]

[0027] d: aperture

[0028] x: First dimension

[0029] x1: First size before shrinkage

[0030] x2: First size after shrinkage

[0031] y: Second dimension

[0032] z: Third dimension

[0033] S MAX Maximum stress

[0034] S RES Residual stress

[0035] 1: Products with labels

[0036] 2: Stress tester

[0037] 6: Crusher

[0038] 7: Compressing heavy objects

[0039] 8: sieve

[0040] 10a: Second Fragment

[0041] 10b: Agglomerated mixed fragments

[0042] 11: Tag (before shrinking)

[0043] 11a: Shrinkable label

[0044] 20: Products

[0045] 20a: First Fragment

[0046] 21: Fixture

[0047] 22: Force sensor

[0048] 100: (First) Polyester film (before shrinkage)

[0049] 100a: Shrinked polyester film

[0050] 120: Adhesive Area

[0051] 200: Second polyester film

[0052] The best way to implement an invention

[0053] The present invention will now be described in detail with reference to embodiments. These embodiments are not limited to the following. Rather, they can be modified in various forms without changing the essential points of the invention.

[0054] In this specification, when a component is referred to as "comprising" an element, it should be understood that it may include other elements, rather than exclude other elements, unless otherwise stated.

[0055] Unless otherwise stated, all figures and expressions relating to component quantities, reaction conditions, etc., used herein should be understood as being modified by the term “about”.

[0056] In this specification, terms such as "first" and "second" are used to describe various components, but these components should not be limited by the terms. The purpose of using these terms is merely to distinguish one component from another.

[0057] Heat-shrink labels or packaging materials made of polyester film are difficult to recycle, and despite their excellent thermal properties and chemical resistance, most are discarded after use. This is because when polyester film is incorporated into current recycling processes, i.e., regeneration processes, the prolonged high-temperature treatment causes various process defects, leading to increased costs. Even if polyester film is recyclable, its high crystallinity results in poor adhesive properties when using Variable Sleeve Layout (VSOP) offset printing technology.

[0058] Furthermore, polyethylene terephthalate (PET) containers recycled from consumers undergo liquid gravity separation, dehydration, drying, and / or air gravity separation after washing and shredding to remove significant amounts of film contained in the shredded product. They then undergo additional steps such as granulation to obtain recycled polyester fragments. However, even after these steps, it is difficult to completely remove the film used for PET container labels. The recycled polyester fragments may discolor due to inks contained in the film. Another issue is that, due to the thermal properties of the film, the recycled polyester fragments tend to agglomerate unevenly during the recycling process, especially during heat treatment.

[0059] This led to the proposal of a method using films made of low-density polymers such as polystyrene, polyethylene, and polypropylene as labels for easy gravity separation. However, the low density cannot be effectively achieved due to the ink layer, making complete film separation difficult and failing to address the problem of residual ink staining recycled polyester fragments.

[0060] The polyester film prepared according to the implementation scheme exhibits excellent recyclability through controlled crystallinity, superior shrinkage and adhesion properties in various printing methods, and minimal uneven agglomeration even under prolonged high-temperature drying. Therefore, using this polyester film can improve the quality, yield, and productivity of recycled polyester fragments obtained from recycled polyethylene terephthalate (PET) containers.

[0061] polyester film

[0062] According to one embodiment, a polyester film is provided comprising a copolyester resin copolymerized from a diol and a dicarboxylic acid, wherein the crystallization temperature (Tc) of the film is not measured, or the crystallization temperature measured by differential scanning calorimetry is between 70°C and 130°C, and the agglomeration rate is 10% or less after fragments obtained by crushing a polyethylene terephthalate (PET) container with the polyester film are heat-treated at 210°C for 90 minutes.

[0063] According to one embodiment, the crystallization temperature (Tc) of the polyester film is not measured, or the crystallization temperature measured by differential scanning calorimetry is between 70°C and 130°C. For example, the crystallization temperature (Tc) of the polyester film is not measured, or the crystallization temperature measured by differential scanning calorimetry can be 80°C to 130°C, 85°C to 125°C, 90°C to 123°C, 96°C to 120°C, 98°C to 120°C, or 99.5°C to 118°C. Because the crystallization temperature is adjusted to the above temperature range, the crystallinity of the polyester film can be effectively controlled. In this case, the agglomeration rate of the film or the polyethylene terephthalate (PET) container containing the film is extremely low during the recycling process. Therefore, environmental pollution can be prevented while improving recyclability.

[0064] The differential scanning calorimetry (DSC) can specifically be modulated differential scanning calorimetry (modulated DSC or MDSC), and more specifically, a temperature modulated differential scanning calorimetry (TMDSC).

[0065] Specifically, the crystallization temperature can be measured using differential scanning calorimetry (DSC) at a heating rate of 10°C / min. In the measurement results, the first endothermic temperature is the glass transition temperature (Tg), the exothermic temperature measured after the glass transition temperature is the crystallization temperature (Tc), and the endothermic temperature measured after the crystallization temperature is the melting point (Tm). The integral at Tc is calculated as the heat of crystallization. The larger the value of the heat of crystallization, the faster the crystallization rate and the higher the conversion rate to the crystalline phase.

[0066] Furthermore, when the polyethylene terephthalate (PET) container with the aforementioned polyester film is pulverized and the resulting fragments are heat-treated at 210°C for 90 minutes, the agglomeration rate can be 10% or less. For example, the agglomeration rate can be 8% or less, 6% or less, 5% or less, 4% or less, preferably 3% or less, 2% or less, 1.5% or less, 1% or less, 0.8% or less, or 0.5% or less.

[0067] The agglomeration refers to aggregates that may form during the regeneration process. The size of the aggregates may be at least three times the size of the fragment particles before heat treatment. The agglomeration rate refers to the total mass fraction of the aggregates based on the fragments before heat treatment.

[0068] Specifically, in the regeneration process of polyethylene terephthalate (PET) containers labeled with a membrane, fragments obtained through crushing are passed through a sieve and subjected to heat treatment. During this process, as the fragments clump together, they may form aggregates called clumps. These aggregates are then filtered through the sieve again, and their mass is measured. The agglomeration rate, calculated based on the total mass ratio of the fragments before heat treatment, is used to determine the agglomeration rate. Therefore, the higher the agglomeration rate, the lower the recyclability.

[0069] Because the crystallinity of the polyester film according to one embodiment is effectively controlled, no wrinkles or deformation of the polyethylene terephthalate (PET) container occur when the polyester film is used as a label for the PET container. Furthermore, even when the fragments of the PET container, pulverized together with the used container, are heat-treated during the recycling process, the agglomeration rate is very low. Therefore, both recyclability and the quality, quantity, and yield of recycled polyester fragments manufactured through recycling can be improved.

[0070] If plastic fragments melt and clump together during recycling, various problems can arise. Therefore, clumping rate is assessed according to the standard (APR PET-S-08) being developed by the American Plastics Recycling Association (APR). Specifically, when 3 parts by weight of polyester film and 97 parts by weight of polyethylene terephthalate containers are pulverized into particles with a diameter of 9.5 mm or smaller and heat-treated at 210°C and a pressure of 8.7 kPa (i.e., applying a load of 2.5 kgf to a cylinder with a diameter of 6 cm), the clumping rate is defined as the proportion that fails to pass through an 11.2 mm sieve (or a 0.625 inch (″) sieve).

[0071] Furthermore, based on the results obtained by differential scanning calorimetry, the melting point (T) of the polyester film... m The melting point can be 170°C or higher. For example, the melting point can be 175°C or higher, 180°C or higher, 190°C or higher, 170°C to 240°C, 175°C to 235°C, 180°C to 235°C, 185°C to 230°C, 190°C to 225°C, or 195°C to 225°C.

[0072] If the melting point of the polyester film exceeds the above-mentioned range, the adhesive strength of the polyester film bonded by solvent will decrease, which may make it difficult to use during the bonding process. If the melting point is higher than the above-mentioned range, the agglomeration rate may increase.

[0073] Specifically, if the crystallization temperature of the polyester film is between 96°C and 120°C and its melting point is 170°C or higher, more preferably, if the crystallization temperature of the polyester film is between 96°C and 120°C and its melting point is 190°C or higher, then the agglomeration phenomenon that may occur during the recycling process can be prevented to the greatest extent.

[0074] Furthermore, at the crystallization temperature (T) C The heat of crystallization of polyester films measured at various temperatures can range from 0.01 J / g to 50 J / g. For example, the heat of crystallization of polyester films at crystallization temperatures (T...) can be... C The heat of crystallization measured at [temperature range] can be 0.01 J / g to 40 J / g, 0.05 J / g to 30 J / g, 0.1 J / g to 20 J / g, 0.1 J / g to 10 J / g, 0.1 J / g to 8 J / g, 0.2 J / g to 6 J / g, or 0.3 J / g to 5.7 J / g. Since the heat of crystallization in the embodiments is within the above range, the crystallinity of the polyester film can be effectively controlled. In this case, the agglomeration rate of the film or the polyethylene terephthalate (PET) container containing the film is extremely low during the recycling process. Therefore, environmental pollution can be prevented while improving recyclability.

[0075] Furthermore, in the polyester film according to one embodiment, the shrinkage rate in the main shrinkage direction can be adjusted within a specific range depending on the temperature. For example, the shrinkage rate in the main shrinkage direction of a polyester film heat-treated at X°C for 10 seconds is defined as T. X Shrinkage range T 70 T 80 T 90 and T 100 It can be adjusted. Obtain T X The heat treatment specifically refers to immersing the polyester film in hot water at X°C for 10 seconds.

[0076] Specifically, after heat treatment at 70°C for 10 seconds, the thermal shrinkage rate (T) of the polyester film in the first direction is... 70 It can range from 0% to 50%. For example, T 70 It can be 0% or greater, 5% or greater, 10% or greater, 15% or greater, 20% or greater, 50% or less, 40% or less, 35% or less, 30% or less, 25% or less, or 20% or less.

[0077] In this specification, the first direction can be transverse (TD) or longitudinal (MD), and the second direction is perpendicular to the first direction and can be longitudinal (MD) or transverse (TD). Specifically, the first direction can be the main contraction direction. More specifically, the first direction can be transverse (TD) consistent with the main contraction direction, in which case the second direction can be longitudinal (MD).

[0078] Furthermore, the thermal shrinkage rate (T) of the membrane in the first direction after heat treatment at 80°C for 10 seconds is... 80 It can be 30% or more. For example, T 80 The percentage can be 35% or greater, 45% or greater, 50% or greater, 55% or greater, and can be 30% to 85%, 40% to 80%, 50% to 80%, 55% to 75%, or 58% to 71%. Since the heat shrinkage rate in the first direction after heat treatment at 80°C for 10 seconds is within the above range, it is convenient to label the container while the film is wrapping at least a portion of it. Specifically, when the film is applied as a label to a polyethylene terephthalate (PET) container, no wrinkles or deformation of the PET container will occur.

[0079] The membrane exhibits a thermal shrinkage rate (T) in the first direction after heat treatment at 90°C for 10 seconds. 90 It can be 50% or greater. For example, T 90 The percentage can be 55% or greater, 60% or greater, or 65% or greater, and can be 50% to 90%, 60% to 85%, 65% to 83%, or 69% to 80%. Since the heat shrinkage rate in the first direction after heat treatment at 90°C for 10 seconds is within the above range, it is convenient to label the container while the film is wrapping at least a portion of it. Specifically, when the film is applied as a label to a polyethylene terephthalate (PET) container, no wrinkles or deformation of the PET container will occur.

[0080] The membrane undergoes thermal shrinkage (T) in the first direction after heat treatment at 100°C for 10 seconds. 100 It can range from 40% to 90%. For example, T 100 The shrinkage rate (T) in the first direction after the polyester film is heat-treated at 100°C for 10 seconds can be 40% or greater, 50% or greater, 60% or greater, 70% or greater, 90% or less, 85% or less, 80% or less, 75% or less, or 70% or less. That is, the shrinkage rate (T) in the first direction of the polyester film after heat treatment at 100°C for 10 seconds. 100 It can be 50% to 80%.

[0081] Meanwhile, in the polyester film according to one embodiment, the shrinkage rate in the first direction and the shrinkage rate in the second direction perpendicular to the first direction can be adjusted within a specific range according to the temperature. For example, the shrinkage rate in the second direction of the polyester film heat-treated at X°C for 10 seconds is defined as T. X Shrinkage range T 70 ′、T 75 ′、T 80 ′、T 90 ′ and T 100 ′ can be adjusted. Obtain T XThe heat treatment can specifically refer to immersing the polyester film in hot water at X°C for 10 seconds.

[0082] The polyester film T 70 ′、T 75 ′、T 80 ′、T 90 ′ and T 100 Each can be independently -10% to 10%. For example, the T of the polyester film... 70 ′、T 75 ′、T 80 ′、T 90 ′、T 100 Each of these values ​​can be independently -10% or greater, -8% or greater, -6% or greater, -4% or greater, -2% or greater, or 0% or greater, and can be 10% or less, 8% or less, 6% or less, 4% or less, or 2% or less.

[0083] According to one embodiment, the polyester film can exhibit excellent adhesive strength, i.e., adhesion, when using a solvent.

[0084] For example, after using 1,3-dioxolane bonding, the peel strength of the polyester film can be 300 gf / in or greater. Specifically, the peel strength after using 1,3-dioxolane bonding can be 300 gf / in or greater, 400 gf / in or greater, 500 gf / in or greater, 600 gf / in or greater, or 700 gf / in or greater, or 3000 gf / in or less, 2500 gf / in or less, 2000 gf / in or less, or 1500 gf / in or less. If the peel strength of the polyester film is adjusted to the above range, the polyester film can be used in the bonding process.

[0085] The peel strength can be measured under the following conditions: a solvent is applied to a polyester film, another polyester film is placed on top for lamination, a pressure of 160 Pa is applied to the solvent-applied area for 1 hour, and then the polyester film is delaminated at a speed of 300 mm / min at an angle of 180°.

[0086] Figure 4 A method for measuring the adhesive properties of polyester films using solvents is shown. For example, 1,3-dioxolane is coated onto a strip of first polyester film (100) with a width of 2 mm, forming an area of ​​0.6 cm². 2 The bonding area (120) was covered with a second polyester film (200). A weight of 2 kg was placed on the bonding area (120) and allowed to age for 1 hour. The polyester film was then layered at a speed of 300 mm / min at an angle of 180°, and the maximum force of the polyester film was measured at this time. The polyester film was cut into rectangles with dimensions (x, y) of 9 cm in length and 3 cm in width.

[0087] In a polyester film according to one embodiment, the shrinkage stress in the main shrinkage direction can be adjusted within a specific range. For example, after heat treatment at 90°C for 1 minute, the maximum shrinkage stress of the polyester film in the main shrinkage direction can be 7.0N or 6.0N. Furthermore, after heat treatment at 90°C for 1 minute, the residual stress of the polyester film in the main shrinkage direction can be 6.0N or 5.5N.

[0088] The heat treatment for obtaining shrinkage stress can specifically refer to immersing the polyester film in hot water at 90°C for 1 minute while maintaining the main shrinkage direction. Furthermore, in the stress curve obtained during the shrinkage process as a function of time, the stress at the highest point can be the maximum stress, and the stress at the end of the shrinkage time can be the residual stress.

[0089] Figure 5 A method for measuring the shrinkage stress of a polyester film is shown. For example, after the first polyester film is cut, its first dimension (x) in the measurement direction is 110 mm, its third dimension (z) is 5 mm at each end, and its second dimension (y) in the direction perpendicular to it is 15 mm. Figure 5 (a)). The cut membrane is placed in a stress tester, with both ends of the membrane fixed by clamps (21) and a 100mm gap in the middle. Figure 5 (b) The stress tester containing the membrane was immersed in water at 90°C for 1 minute, and the maximum stress (S) during the contraction process was measured using a force sensor (22). MAX ) and residual stress after shrinkage (S) RES ).

[0090] In the polyester film according to the embodiment, the skirt ratio can be adjusted within a specific range. Specifically, the polyester film is fixed in the main shrinkage direction, and the length before and after shrinkage is measured in a direction perpendicular to the main shrinkage direction of the polyester film. The skirt ratio can be calculated as a ratio obtained by dividing the length difference measured before and after shrinkage (the length difference before and after shrinkage in the direction perpendicular to the main shrinkage direction of the polyester film) by the length of the polyester film in the main shrinkage direction. More specifically, after heat-treating the polyester film at 90°C for 10 seconds, its skirt ratio can be 17.4%.

[0091] Figure 6 A method for measuring the skirt ratio of a polyester film is shown. For example, a polyester film (100) is cut into a first pre-shrinkage dimension (x1) of 60 mm in the direction to be measured and fixed to a heat-setting frame with a width (y) of 115 mm using a clamp (21). Figure 6 (a)). Immerse it in a 90°C water bath for 10 seconds, then measure the first dimension (x2) after shrinkage. Figure 6(b)). In this specification, it is fixed in the transverse direction (TD) as the main contraction direction, and the contracted length in the longitudinal direction (MD) perpendicular to this direction is measured to calculate according to the following equation.

[0092] ΔSR(mm)=x1(mm)–x2(mm)

[0093] SR%(%)=ΔSR(mm) / y(mm)×100

[0094] Furthermore, the glass transition temperature (Tg) of the film, as measured by differential scanning calorimetry, can be 60°C or higher. For example, the glass transition temperature of the film, as measured by differential scanning calorimetry, can be 60°C or higher, 65°C or higher, 70°C to less than 80°C, or 70°C to 75°C.

[0095] The transmittance of the membrane at a wavelength of 550 nm can reach 90% or greater. Specifically, before and after immersion in a 1% sodium hydroxide (NaOH) aqueous solution at 85°C, the transmittance of the membrane measured at a wavelength of 550 nm can be 90.5% or greater, 91% or greater, 92% or greater, or 93% or greater, respectively.

[0096] Furthermore, the change in light transmittance of the membrane before and after immersion in a 1% sodium hydroxide (NaOH) aqueous solution at 85°C can be 0.7% or less. For example, the change in light transmittance before and after immersion can be 0.6% or less, or 0.5% or less.

[0097] The change in transmittance refers to the absolute value of the difference between the transmittance of the membrane before immersion and the transmittance of the membrane after immersion, measured at a wavelength of 500 nm.

[0098] Furthermore, before and after immersing the membrane in a 1% sodium hydroxide (NaOH) aqueous solution at 85°C, the change in Col-L (ΔL) can be 0.7 or less, the change in Col-a (Δa) can be 0.5 or less, and the change in Col-b (Δb) can be 0.5 or less. For example, before and after immersion, the change in Col-L (ΔL) can be 0.65 or less, 0.6 or less, 0.55 or less, or 0.5 or less; the change in Col-a (Δa) can be 0.3 or less, 0.1 or less, 0.08 or less, 0.06 or less, or 0.05 or less; and the change in Col-b (Δb) can be 0.3 or less, 0.1 or less, 0.08 or less, or 0.07 or less.

[0099] The change in Col-L (ΔL) refers to the absolute value of the difference between the Col-L value before immersion and the Col-L value after immersion; the change in Col-a (Δa) refers to the absolute value of the difference between the Col-a value before immersion and the Col-a value after immersion; and the change in Col-b (Δb) refers to the absolute value of the difference between the Col-b value before immersion and the Col-b value after immersion.

[0100] Col-L, Col-a, and Col-b are color coordinates specified by the International Commission on Illumination (CIE), where colors are represented by L (luminance), a (complementary color from green to red), and b (complementary color from yellow to blue). They can be measured using UltraScan PRO (manufacturer: Hunterlab), but are not limited to this.

[0101] According to one embodiment, the polyester film comprises a copolyester resin. Specifically, the copolyester resin may be a resin polymerized from two, three, or more diols and dicarboxylic acids. More specifically, the copolyester resin may be a copolyethylene terephthalate (Co-PET) resin.

[0102] Specifically, the diol may comprise at least one and a combination thereof selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, unsubstituted or alkyl-substituted propylene glycol, unsubstituted or alkyl-substituted butanediol, unsubstituted or alkyl-substituted pentanediol, unsubstituted or alkyl-substituted hexanediol, and unsubstituted or alkyl-substituted octanediol.

[0103] For example, the diol may comprise at least one selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, 1,3-propanediol, 1,2-octanediol, 1,3-octanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,1-dimethyl-1,5-pentanediol.

[0104] The dicarboxylic acid may include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, or their esters.

[0105] For example, the dicarboxylic acid may be terephthalic acid, dimethyl terephthalate, isophthalic acid, naphthalene-dicarboxylic acid, phthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, their esters, or combinations thereof. Specifically, the dicarboxylic acid may contain at least one selected from the group consisting of terephthalic acid, dimethyl terephthalate, naphthalene-dicarboxylic acid, and phthalic acid.

[0106] According to one embodiment, the copolyester resin may be a resin polymerized from two, three, or more diols and dicarboxylic acids. Specifically, the copolyester resin may be a resin polymerized from a diol containing ethylene glycol and at least one comonomer with an aromatic dicarboxylic acid.

[0107] The diol may comprise ethylene glycol and at least one comonomer selected from the group consisting of neopentyl glycol and diethylene glycol.

[0108] Specifically, based on the total molar number of the diol, the diol may contain 50 mol% to 90 mol% of ethylene glycol. For example, based on the total molar number of the diol, the diol may contain 60 mol% to 90 mol%, 65 mol% to 88 mol%, 68 mol% to 85 mol%, 70 mol% to 83 mol%, or 71 mol% to 80 mol% of ethylene glycol.

[0109] Furthermore, the diol may contain 15 mol% or more of at least one comonomer selected from the group consisting of neopentyl glycol and diethylene glycol. For example, based on the total molar number of the diol, the diol may contain 17 mol% or more, 19 mol% or more, 20 mol% or more, 15 mol% to 50 mol%, 15 mol% to 40 mol%, 17 mol% to 35 mol%, 19 mol% to 30 mol%, or 20 mol% to 29 mol% of at least one comonomer selected from the group consisting of neopentyl glycol and diethylene glycol. Because the content of the comonomer of the present invention is within the above range, crystallinity can be effectively controlled while maintaining excellent heat shrinkage rate in the main shrinkage direction.

[0110] Furthermore, if the content of the comonomer is less than the aforementioned range, the heat shrinkage performance of the polyester film may deteriorate. Specifically, at a certain temperature, the heat shrinkage rate of the polyester film in the main shrinkage direction may be insufficient, and the heat shrinkage rate in a second direction perpendicular to the main shrinkage direction may be excessive.

[0111] Specifically, the diol may contain diethylene glycol as a comonomer. For example, the content of diethylene glycol in the diol may be 1 mol% to 10 mol%, 1 mol% to 8 mol%, 3 mol% to 6 mol%, or 3.5 mol% to 5.5 mol%.

[0112] Specifically, the diol may contain neopentyl glycol as a comonomer. For example, the content of neopentyl glycol in the diol may be 5 mol% to 35 mol%, 7 mol% to 33 mol%, 10 mol% to 30 mol%, 13 mol% to 28 mol%, or 15 mol% to 25 mol%.

[0113] Since the content of neopentyl glycol in this invention is within the above range, the heat shrinkage rate in the first direction and the second direction perpendicular to the first direction can be easily adjusted when the film is heat-shrinking, thus more effectively preventing wrinkles and deformation when the film is attached to the container.

[0114] In addition to the diol, the polyester resin may further contain a monohydric alcohol. For example, the monohydric alcohol may be methanol, ethanol, isopropanol, allyl alcohol, or benzyl alcohol. Specifically, based on the total molar number of the diol and the monohydric alcohol, the polyester resin may contain 10 to 30 mol%, 13 to 25 mol%, or 15 to 22 mol% of the monohydric alcohol, but is not limited thereto.

[0115] The dicarboxylic acid may comprise an aromatic dicarboxylic acid. For example, based on the total molar number of the dicarboxylic acid, the dicarboxylic acid may comprise 80 mol% or more, 90 mol% or more, 95 mol% or more, 99 mol% or more, or 100 mol% of terephthalic acid or dimethyl terephthalate.

[0116] The diol and the dicarboxylic acid undergo an ester exchange reaction, followed by polymerization, to form a copolyester resin.

[0117] Specifically, at least one catalyst selected from manganese acetate, calcium acetate, and zinc acetate can be used as the catalyst for the transesterification reaction. Based on the total weight of the dicarboxylic acid, the content of the catalyst can be from 0.02 parts by weight to 0.2 parts by weight, from 0.02 parts by weight to 0.1 parts by weight, or from 0.05 parts by weight to 0.08 parts by weight.

[0118] In addition, after the transesterification reaction is completed, at least one additive selected from the group consisting of silicon dioxide, potassium, and magnesium; stabilizers, such as trimethyl phosphate; and polymerization catalysts, such as antimony trioxide and tetrabutyl titanate, may be selectively added.

[0119] The thickness of the polyester film can be from 10 μm to 100 μm. For example, the thickness of the polyester film can be from 20 μm to 80 μm, 30 μm to 70 μm, 35 μm to 65 μm, 35 μm to 55 μm, 40 μm to 60 μm, or 35 μm to 45 μm.

[0120] Preparation method of polyester film

[0121] According to one embodiment, a method for preparing a polyester film is provided, comprising preparing a copolyester resin copolymerized from a diol and a dicarboxylic acid; melt-extruding the copolyester resin at 250°C to 300°C to produce an unstretched sheet; stretching the unstretched sheet at 70°C to 100°C; and then heat-setting it at 65°C to 90°C to prepare a polyester film, wherein the crystallization temperature (Tc) of the film is not measured, or the crystallization temperature measured by differential scanning calorimetry is 70°C to 130°C, and the agglomeration rate is 10% or less after fragments obtained by pulverizing a polyethylene terephthalate (PET) container with the polyester film are heat-treated at 210°C for 90 minutes.

[0122] The composition and process conditions are adjusted to ensure that the resulting polyester film meets the characteristics described above (crystallization temperature, shrinkage characteristics, etc.). Specifically, to ensure that the final polyester film meets the characteristics described above, the composition of the copolyester resin needs to be adjusted, as well as the extrusion temperature, casting temperature, preheating temperature during stretching, stretch ratio in each direction, stretching temperature, stretching rate, etc. Alternatively, heat treatment and relaxation can be performed after stretching, while simultaneously adjusting the heat treatment temperature and relaxation rate.

[0123] Each step will be described in more detail below.

[0124] First, a copolyester resin is prepared. Details of the copolyester resin are shown above.

[0125] Specifically, the polymerization of the copolymer resin can be carried out through conventional transesterification and polycondensation reactions. In this case, the diols and dicarboxylic acids involved in the reaction, and their contents, are as shown above.

[0126] Subsequently, the copolyester resin is melt-extruded at a temperature of 250°C to 300°C or 260°C to 280°C, and then cooled to obtain an unstretched sheet. The unstretched sheet is preheated in the chamber while being conveyed at a speed of 10 m / min to 110 m / min, 25 m / min to 90 m / min, 40 m / min to 80 m / min, or 50 m / min to 60 m / min.

[0127] The preheating can be carried out at 90°C to 120°C for 0.01 to 1 minute. For example, the preheating temperature (T1) can be 95°C to 115°C or 97°C to 113°C, and the preheating time can be 0.05 minutes to 0.5 minutes or 0.08 minutes to 0.2 minutes.

[0128] The preheated, unstretched sheet is then stretched at a temperature of 70°C to 95°C.

[0129] Specifically, the stretching can be uniaxial or biaxial. More specifically, the stretching can be uniaxial in the transverse (TD) direction or biaxial in the longitudinal (MD) direction followed by the transverse (TD) direction.

[0130] The stretching can be performed at a temperature 10°C to 20°C below the preheating temperature (T1). For example, the stretching can be performed at 70°C to 100°C, 75°C to 100°C, 80°C to 98°C, or 83°C to 96°C.

[0131] Furthermore, if the stretching is uniaxial, it can be performed in the transverse (TD) direction at a stretch ratio of 3.5 to 5, 3.5 to 4.8, or 3.8 to 4.6. Furthermore, if the stretching is biaxial, it can be performed in the longitudinal (MD) direction at a stretch ratio of 1.1 to 2 or 1.1 to 1.5, and then in the transverse (TD) direction at a stretch ratio of 3.5 to 5, 3.5 to 4.8, or 3.8 to 4.6.

[0132] Furthermore, a coating step can be performed after stretching. Specifically, coating can be performed before transverse (TD) stretching in uniaxial stretching or after longitudinal stretching in biaxial stretching and before transverse stretching. More specifically, a coating step can be performed to form a promoting layer that imparts functions such as antistatic properties to the film. The coating step can be performed by spin coating or in-line coating, but is not limited to these methods.

[0133] The stretched sheet is then heat-set at a temperature of 65°C to 90°C to prepare a polyester film.

[0134] The heat setting can be annealing at 65°C to 90°C for 0.01 minutes to 1 minute. For example, the heat setting temperature (T2) can be 65°C to 85°C or 69°C to 81°C, and the heat setting time can be 0.05 minutes to 0.5 minutes or 0.08 minutes to 0.2 minutes.

[0135] Regeneration method for polyethylene terephthalate containers

[0136] According to another embodiment, a method for recycling a polyethylene terephthalate (PET) container is provided, comprising providing a PET container with the polyester film; crushing the PET container with the polyester film to obtain fragments; and heat-treating the fragments to obtain recycled polyester fragments, wherein after heat-treating the fragments at 210°C for 90 minutes, the agglomeration rate is 10% or less, the fragments comprising a first fragment obtained by crushing the PET container and a second fragment obtained by crushing the polyester film.

[0137] According to one implementation, at least one [part / component] was prepared for the purpose of regenerating polyethylene terephthalate (PET) containers. Polyethylene terephthalate (PET) containers encapsulated with the polyester film.

[0138] Traditional methods involve washing recycled waste, where containers, metals, glass, and plastics may be mixed together to sort polyester containers and remove the membranes or similar materials covering the containers to improve their recyclability and quality. These removal steps are performed by mechanically tearing or cutting the membranes or by additional steps such as liquid gravity separation, dehydration, drying, air gravity separation, or granulation.

[0139] However, it is difficult to completely remove the membrane during the above-described removal steps. In particular, it is difficult to improve the quality of the recycled polyester flakes produced due to the residual ink formed on the membrane.

[0140] According to one embodiment, in the method for recycling polyester containers, the additional step of removing the film covering the polyethylene terephthalate (PET) container can be omitted while preparing the recycled polyester fragments, thereby saving costs.

[0141] In the polyethylene terephthalate (PET) container, the polyester film is located on the outer surface of the container. Specifically, the outer surface of the polyethylene terephthalate container is covered with the polyester film, and the film can be shrunk by steam or hot air to cover at least a portion of the outer surface of the polyethylene terephthalate container. For example, the polyester film can serve as a label for the polyethylene terephthalate container as a heat-shrinkable film, but is not limited thereto.

[0142] Details regarding the polyester film are as described above.

[0143] Subsequently, the polyethylene terephthalate (PET) container with the polyester film is crushed to obtain fragments.

[0144] Specifically, at least a portion of the outer surface of the polyethylene terephthalate (PET) container is wrapped with the film, and the container and the film are crushed together to obtain fragments without the need for separating the container and the film.

[0145] That is, the fragments comprise a first fragment obtained by crushing the polyester container and a second fragment obtained by crushing the membrane.

[0146] The particle size of the first fragment can be from 0.1 mm to 25 mm, and the particle size of the second fragment can be from 0.1 mm to 25 mm. For example, the particle size of the first fragment can be from 0.3 mm to 23 mm, 0.5 mm to 20 mm, 1 mm to 20 mm, 0.5 mm to 15 mm, 0.5 mm to 13 mm, 1 mm to 18 mm, 1 mm to 15 mm, 1 mm to 13 mm, or 2 mm to 10 mm, and the particle size of the second fragment can be from 0.3 mm to 23 mm, 0.5 mm to 20 mm, 1 mm to 20 mm, 0.5 mm to 15 mm, 0.5 mm to 13 mm, 1 mm to 18 mm, 1 mm to 15 mm, 1 mm to 13 mm, or 2 mm to 10 mm, but is not limited thereto.

[0147] Subsequently, before proceeding to the heat treatment step, the fragments can be further washed. Specifically, the washing step can be carried out at 85°C to 90°C with a washing solution containing water and / or 1 part by weight of an aqueous sodium hydroxide solution.

[0148] For example, the fragments can be washed first with water, then with the washing solution, and finally with water again. As the washing process continues, impurities that may remain in the fragments can be removed, and ink components can be effectively eliminated. Therefore, the quality and purity of the resulting recycled polyester fragments can be improved, thereby maximizing recyclability.

[0149] In addition, after the washing step, the washed flakes can be dried at a temperature of 60°C to 175°C for 10 to 30 minutes. For example, the drying step can be carried out at 65°C to 175°C, 70°C to 170°C, 90°C to 165°C, 100°C to 165°C, 120°C to 165°C, 140°C to 165°C, or 150°C to 165°C for 10 to 85 minutes, 10 to 70 minutes, or 15 to 30 minutes.

[0150] The washing and drying steps can be repeated one to five times. For example, by repeating the washing and drying steps two to five times or three to five times, impurities remaining in the fragments can be effectively removed.

[0151] Finally, the fragments are heat-treated to obtain recycled polyester fragments.

[0152] Specifically, the fragments comprise a first fragment obtained by crushing the polyethylene terephthalate (PET) container and a second fragment obtained by crushing the polyester film.

[0153] The heat treatment may be performed at a temperature of 200°C to 220°C for 60 to 120 minutes. For example, the heat treatment may be performed at 200°C to 215°C or 205°C to 220°C for 70 to 120 minutes or 80 to 120 minutes.

[0154] Furthermore, after the fragments are heat-treated at 210°C for 90 minutes, the agglomeration rate is 10% or less. Therefore, the recycled polyester fragments exhibit excellent quality due to the low agglomeration rate resulting from the mixing of the first and second fragments. Specifically, since the fragments according to the embodiment include a second fragment obtained by pulverizing the polyester film, the formation of aggregates can be effectively reduced or prevented, thereby improving the quality of the recycled polyester fragments obtained by this method.

[0155] Recycled polyester fragments can be obtained after a heat treatment step. Specifically, recycled polyester fragments comprising a first fragment and a second fragment can be obtained after the heat treatment step. For example, the fragments can be obtained by melt extrusion followed by cutting to obtain recycled polyester fragments, but this is not a limitation.

[0156] Recycled polyester fragments

[0157] According to one embodiment, a method for obtaining recycled polyester fragments using recycled polyethylene terephthalate containers is provided.

[0158] Specifically, the recycled polyester fragments may include a first fragment containing polyethylene terephthalate (PET) and a second fragment containing polyester resin.

[0159] The recycled polyester fragments may have an intrinsic viscosity (IV) of 0.55 dl / g or greater. For example, the recycled polyester fragments may have an intrinsic viscosity (IV) of 0.58 dl / g or greater, 0.59 dl / g or greater, 0.55 dl / g to 3.0 dl / g, 0.55 dl / g to 2.0 dl / g, 0.55 dl / g to 1.0 dl / g, 0.58 dl / g to 0.85 dl / g, or 0.58 dl / g to 0.7 dl / g.

[0160] Furthermore, based on the total weight of the recycled polyester fragments, the recycled polyester fragments may contain 70% to 90% by weight of polyethylene terephthalate and 1% to 30% by weight of copolyester resin. For example, based on the total weight of the recycled polyester fragments, the recycled polyester fragments may contain 80% to 99% by weight, 90% to 99% by weight, or 95% to 99% by weight of polyethylene terephthalate and 1% to 20% by weight, 1% to 10% by weight, and 1% to 5% by weight of copolyester resin. Detailed Implementation

[0161] The invention will be described in more detail below with reference to the following embodiments. However, these examples are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0162] [Example]

[0163] Preparation of polyester film

[0164] Example 1-1

[0165] (1) Preparation of copolyester resin

[0166] Terephthalic acid (TPA) as a dicarboxylic acid, ethylene glycol (EG) and comonomers as diols are added to an autoclave equipped with a stirrer and a distillation column. 0.07 parts by weight of manganese acetate is added to every 100 parts by weight of the dicarboxylic acid as a transesterification catalyst. The mixture is then heated to 220°C to remove the byproduct methanol for the reaction.

[0167] After the transesterification reaction was completed, 0.07 parts by weight of silica with an average particle size of 0.28 μm and 0.4 parts by weight of trimethyl phosphate were added as stabilizers to every 100 parts by weight of the dicarboxylic acid. After 5 minutes, 0.035 parts by weight of antimony trioxide and 0.005 parts by weight of n-butyl titanate were added as polymerization catalysts, and the mixture was stirred for 10 minutes. The reaction mixture was then transferred to a reactor equipped with a vacuum device. The temperature was raised to 285°C while the pressure was gradually reduced, and the polymerization reaction was continued for 210 minutes to obtain the copolyester resin.

[0168] (2) Membrane preparation

[0169] The copolyester resin prepared in step (1) was extruded through a T-die at 270°C and cooled to obtain an unstretched sheet. The unstretched sheet was then conveyed in rollers at a speed of 55 m / min to adjust its thickness. The unstretched sheet was preheated at 105°C for 0.1 min while being conveyed at 55 m / min and stretched transversely (TD) at 83°C with a stretch ratio of 4.3. The stretched sheet was then heat-set at 69°C for 0.1 min to prepare a polyester film with a thickness of 40 μm.

[0170] Examples 1-2 to 1-6 and Comparative Example 1-1

[0171] The preparation method of the polyester film is the same as that in Example 1-1, except that the components, contents and process conditions are changed, as shown in Table 1 below.

[0172] [Table 1]

[0173]

[0174]

[0175] *NPG: Neopentyl Glycol

[0176] *CHDM: 1,4-Cyclohexanediethanol

[0177] *DEG: Diethylene glycol

[0178] Test Example 1-1: T C T m and crystallization temperature

[0179] Four milligrams of polyester film samples prepared in Examples 1-1 to 1-6 and Comparative Example 1-1 were scanned by differential scanning calorimetry (DSC) using a Q2000 (manufacturer: TA Instruments) at a heating rate of 10 °C / min.

[0180] In the measurement results, the first endothermic temperature is the glass transition temperature (Tg), the exothermic temperature measured after the glass transition temperature is the crystallization temperature (Tc), and the endothermic temperature measured after the crystallization temperature is the melting point (Tm). The integral at Tc is calculated as the heat of crystallization. The larger the value of the heat of crystallization, the faster the crystallization rate and the higher the conversion rate to the crystalline phase.

[0181] Test Example 1-2: Heat Shrinkage Rate

[0182] Figure 3 A method for measuring the heat shrinkage rate of polyester film is shown. (Refer to...) Figure 3 The polyester films (100) prepared by Examples 1-1 to 1-6 and Comparative Example 1-1 were each cut into 300 mm pieces in the measurement direction and into 15 mm pieces in the direction perpendicular to the measurement direction. Here, the first dimension (x1) before shrinkage is 300 mm, and the second dimension is 15 mm. Figure 3 (a)).

[0183] The cut polyester film (100) is immersed in a water bath at 80°C or 90°C for 10 seconds. The shrinkage dimension of the polyester film (100a) after shrinkage is measured, that is, the first dimension (x2) after shrinkage. Figure 3 (b) The following equation is used to calculate the thermal shrinkage rate (%) of this test case, obtained in the principal shrinkage direction (TD) of the membrane.

[0184] Heat shrinkage rate (%) = (x1-x2) / x1×100

[0185] [Table 2]

[0186]

[0187] As shown in Table 2, in the polyester films of Examples 1-1 to 1-6, the heat shrinkage rate, crystallization temperature (Tc), heat of crystallization and melting point (Tm) in the main shrinkage direction (TD) at each temperature are all within the preferred range.

[0188] Preparation of recycled polyester flakes

[0189] Example 2-1

[0190] (1) Preparation of polyethylene terephthalate containers with polyester film

[0191] A portion of the outer surface of a polyethylene terephthalate (PET) container (30 g) is wrapped with a polyester film prepared according to Example 1-1. The polyester film is then fixed with an acrylic adhesive. Subsequently, the polyester film prepared according to Example 1-1 is shrunk under hot air conditions at 90°C to obtain a polyethylene terephthalate container with the polyester film.

[0192] (2) Regeneration method for polyethylene terephthalate containers

[0193] The polyethylene terephthalate container with a polyester film obtained in step (1) was pulverized using a pulverizer to obtain fragments. The fragments were first washed with water. Then, the fragments were washed with a washing solution (a mixed solution of 0.3 wt% polyethylene glycol octylphenyl ether (Triton X-100) and 1.0 wt% sodium hydroxide) at 88°C and 880 rpm for 15 minutes with stirring. After the second washing, the fragments were washed a third time with water at room temperature to remove residual washing solution, and then dried at 160°C for 20 minutes.

[0194] The fragments were then heat-treated at 210°C for 90 minutes to obtain recycled polyester fragments.

[0195] Examples 2-2 to 2-8 and Comparative Example 2-1

[0196] The method for preparing recycled polyester fragments is the same as in Example 2-1, except that the polyester film prepared in Example 1-1 is replaced with the polyester film prepared in Example 1-1 by Examples 1-2 to 1-6 and Comparative Example 1-1.

[0197] Test Example 2-1: Agglomeration Rate

[0198] The clumping rate (%) of this invention was measured according to the American Plastics Recycling Association (APR) method for evaluating clumping of polyethylene terephthalate fragments (APR PET-S-08).

[0199] Figure 2 A method for measuring the clumping rate of polyethylene terephthalate (PET) containers with polyester film is shown.

[0200] like Figure 2As shown in (a), an object (1) with a polyethylene terephthalate (PET) container bearing a polyester film label (11a) was crushed by a crusher (6) and passed through a sieve with a pore size of 9.5 mm (a 0.374-inch sieve, not shown in the picture) to obtain 97 g of the first fragment (20a) obtained from crushing the polyethylene terephthalate (PET) container and 3 g of the second fragment (10a) obtained from crushing the polyester film.

[0201] After that, as Figure 2 As shown in (b), the mixed fragments were placed on a cylinder with a diameter of 6 cm and a height of 8 cm, and a 2.5 kg compressed weight (7) was placed on it to apply a load. Subsequently, the cylinder with the compressed weight was heat-treated in a convection oven at 210 °C for 90 minutes, and then cooled at room temperature.

[0202] After that, as Figure 2 As shown in (c), the cooled mixed fragments are filtered through a second sieve (8; 0.625-inch sieve) with an aperture (d) of 11.2 mm, and the aggregates of mixed fragments remaining on the second sieve (8) are collected and weighed.

[0203] Agglomeration rate (%) = Weight of mixed fragment aggregate / Initial weight of mixed fragments × 100

[0204] Test Example 2-2: Intrinsic Viscosity

[0205] The recycled polyester fragments obtained by Examples 2-1 to 2-6 and Comparative Example 2-1 were dissolved in o-chlorophenol at 100°C, and the relative viscosity was measured using an Ostwald viscometer in a constant temperature bath at 35°C. The time it took for the sample to fall was also measured. The intrinsic viscosity (IV) values ​​corresponding to the obtained relative viscosities are then given in Table 3, rounded to three decimal places.

[0206] [Table 3]

[0207]

[0208]

[0209] [Table 4]

[0210]

[0211]

[0212] As shown in Table 4, the recycled polyester fragments in Examples 2-1 to 2-6 meet the specific ranges of crystallization temperature (Tc) and melting point (Tm) in Table 2, and have a very low agglomeration rate compared to Comparative Example 2-1 with similar intrinsic viscosity. They also have an advantage in long-term high-temperature drying during the recycling process, thus improving recyclability.

Claims

1. A polyester film comprising a copolyester resin copolymerized from a diol and a dicarboxylic acid, The crystallization temperature of the membrane was not measured, or the crystallization temperature measured by differential scanning calorimetry was between 70°C and 130°C. The polyester film, after being heat-treated at 80°C for 10 seconds, has a heat shrinkage rate of 30% or more in the first direction. When the fragments obtained by crushing the polyethylene terephthalate container with the polyester film are heat-treated at 210°C for 90 minutes, the agglomeration rate is 10% or less. in, The melting point (T) of the film was measured using differential scanning calorimetry. m ) 190℃ or higher; The dicarboxylic acid comprises terephthalic acid; wherein, based on the total molar number of the diol, the diol comprises 72 mol% to 80 mol% ethylene glycol, 1 mol% to 10 mol% diethylene glycol, and 15 mol% to 25 mol% neopentyl glycol; and Among them, polyester film at crystallization temperature (T) C The heat of crystallization measured at 0.2 J / g to 6 J / g is 0.2 J / g.

2. The polyester film of claim 1, wherein the crystallization temperature of the polyester film, as determined by differential scanning calorimetry, is between 96°C and 120°C.

3. The polyester film of claim 1, wherein the agglomeration rate is 5% or less.

4. A method for preparing the polyester film as described in claim 1, comprising: To prepare a copolyester resin by copolymerization of diols and dicarboxylic acids; The copolyester resin is melt-extruded at 250°C to 300°C to prepare an unstretched sheet; The unstretched sheet is stretched at 70°C to 100°C and then heat-set at 65°C to 90°C to prepare a polyester film. The crystallization temperature of the polyester film was not measured, or the crystallization temperature measured by differential scanning calorimetry was 70°C to 130°C. The polyester film, after being heat-treated at 80°C for 10 seconds, has a heat shrinkage rate of 30% or more in the first direction. When the fragments obtained by crushing the polyethylene terephthalate container with the polyester film are heat-treated at 210°C for 90 minutes, the agglomeration rate is 10% or less. The melting point (T) of the polyester film was measured using differential scanning calorimetry. m ) 190℃ or higher; The dicarboxylic acid includes terephthalic acid; Wherein, based on the total molar number of the diol, the diol comprises 72 mol% to 80 mol% ethylene glycol, 1 mol% to 10 mol% diethylene glycol, and 15 mol% to 25 mol% neopentyl glycol; and Among them, polyester film at crystallization temperature (T) C The heat of crystallization measured at 0.2 J / g to 6 J / g is 0.2 J / g.

5. A method for recycling polyethylene terephthalate containers, comprising: Provide a polyethylene terephthalate container with a polyester film as described in claim 1; The polyethylene terephthalate container with the polyester film is crushed to obtain fragments; and Heat-treating the fragments to obtain recycled polyester fragments. Wherein, after the fragments are heat-treated at 210°C for 90 minutes, the agglomeration rate is 10% or less, and The fragments include a first fragment obtained by crushing a polyethylene terephthalate container and a second fragment obtained by crushing the polyester film.

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