Polyester film having improved smoothness

Abstract

An embodiment provides a polyester film having a waviness index of 20 mm or less. The waviness index is the maximum value from among the heights of parts that rise above a flat surface when the polyester film that was wound in a roll is unrolled on the flat surface. The polyester film of the embodiment has a low occurrence of bends, wrinkles, sagging and the like and is relatively flat when the polyester film that was wound in a roll form is unrolled.

Description

Polyester film with improved smoothness

[0001] The embodiment relates to a polyester film with improved smoothness, and relates to a polyester film having relatively flat characteristics and having less occurrence of bending, wrinkling, stretching, etc. when the polyester film wound in a roll shape is unfolded.

[0002]

[0003] Polyester films have high mechanical strength, excellent chemical resistance, and transparency, and are widely used in construction, automobiles, electronics, and packaging.

[0004] Films are typically transported in coiled rolls. Therefore, polyester film is considered easy to use and of high quality only when the rolls are clean and the unrolled film is smooth.

[0005] The background technology described above is technical information that the inventor possessed for the purpose of deriving the present invention or acquired in the process of deriving the present invention, and cannot necessarily be considered as publicly known technology disclosed to the general public prior to the application for the present invention.

[0006] Related prior art includes domestic patent publication no. 10-2014-0103103, graphite film and method for producing graphite film, and publication no. 10-2023-0019950, film, film roll and method for producing film.

[0007]

[0008] The purpose of the embodiment is to provide a polyester film with improved smoothness that has relatively flat characteristics and is less prone to bending, wrinkling, and stretching when the polyester film is rolled into a roll shape and spread out.

[0009]

[0010] To achieve the above purpose, a polyester film according to one or more embodiments has a waviness index that is the maximum value among the heights of a portion floating on a flat surface when the polyester film is spread out in a roll state wound on a flat surface, and the waviness index of the polyester film is 20 mm or less.

[0011] The polyester film may have an end sagging index of 0 mm or more and 20 mm or less at the first end and the second end.

[0012] The larger value between the sagging of the first side end and the sagging of the second side end may be 25 mm or less.

[0013] The tensile modulus in the winding direction is the tensile modulus measured in the longitudinal direction along which the polyester film is wound.

[0014] The lateral tensile modulus is the tensile modulus measured in the longitudinal direction when the polyester film is wound.

[0015] The coiling tensile modulus ratio is the ratio of the coiling direction tensile modulus based on the lateral direction tensile modulus.

[0016] The above polyester film may have a winding tensile modulus ratio of 1 to 1.8.

[0017] The difference in the tensile modulus of elasticity in the winding direction is the absolute value of the difference between the tensile modulus in the lateral direction and the tensile modulus in the winding direction.

[0018] The above polyester film has a difference in the tensile modulus of the above winding of 75 kg / mm 2 Up to 250 kg / mm 2 It could be.

[0019] The above polyester film may not exhibit any external shading or deformation after 7 days when rolled onto a 6-inch core.

[0020] The above polyester film may include any one selected from the group consisting of recycled polyester resin, plant-derived polyester resin, and combinations thereof.

[0021] In order to achieve the above purpose, a polyester film according to one or more embodiments has a length in the winding direction of 3 m or more and, when the polyester film is pulled at a speed of 20 m / min with a tension of 10 kgf on a guide roll arranged at intervals of 1.2 m, a difference in sagging between the lateral edges on both sides based on the lateral center of the polyester film is 0 mm or more and 20 mm or less.

[0022]

[0023] The polyester film of the embodiment has a relatively flat characteristic and is less prone to bending, wrinkling, or stretching when the polyester film is rolled up in a roll shape and unfolded, thereby improving smoothness.

[0024] The polyester film of the embodiment has a flat surface with minimal curvature, allowing for immediate processing upon unrolling from the roll, resulting in excellent workability. Furthermore, in a continuous process where tension is applied, the degree of sagging at both ends is similar, further enhancing processability.

[0025]

[0026] Figure 1 is a drawing schematically illustrating the appearance of a polyester film unfolded in a roll state.

[0027] Figure 2 is a conceptual diagram illustrating a method for evaluating a wave curvature index in an implementation example.

[0028] Figure 3 is a conceptual diagram illustrating a device for evaluating end deflection in an implementation example.

[0029] Figures 4a and 4b are conceptual diagrams illustrating the type of sagging in the cross-section of the film taken along the line AA' of Figure 3.

[0030]

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Like reference numerals designate similar parts throughout the specification.

[0032] In this specification, the term "combination of these" included in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including one or more selected from the group consisting of the components.

[0033] In this specification, the description of “A and / or B” means “A, B, or A and B.”

[0034] Throughout this specification, terms such as "first" and "second" are used to distinguish between identical terms. Furthermore, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0035] Unless otherwise specified in this specification, ppm is based on weight.

[0036] In this specification, the numerical limits of A to B described without special mention mean A or more and B or less, and include the numerical boundary values ​​even without special mention.

[0037] The drawings may be presented with exaggerated or omitted configurations for illustrative purposes, and the scope of the implementation examples shall not be construed as being limited thereby.

[0038]

[0039] Film sag is a factor in evaluating film rollability, and it's related to deformation. Ideally, film distributed in rolled form should be flat and free of wrinkles or creases when unrolled after distribution and storage, just like before unwinding. However, film unrolled after winding can sometimes exhibit partial creases or wrinkles, or even unevenness throughout. Reducing or eliminating these creases, creases, and undulations is a key element of high-quality film.

[0040] The inventors improved the properties related to flattening of the film when the wound film is unrolled, such as wrinkles, creases, and bends, by applying methods such as controlling temperature changes during the manufacturing process and controlling tensile modulus according to the direction of the film, and explained this in detail with an implementation example.

[0041]

[0042] Fig. 1 is a schematic diagram illustrating a polyester film rolled out in a roll state, and Fig. 2 is a conceptual diagram illustrating a method for evaluating a wave curvature index in an embodiment. Fig. 3 is a conceptual diagram illustrating a device for evaluating end sag in an embodiment, and Figs. 4a and 4b are conceptual diagrams illustrating the types of sag in the cross-section of the film taken along the line AA' of Fig. 3.

[0043] The implementation examples are described in more detail below with reference to FIGS. 1 to 4b.

[0044] In one or more embodiments, the polyester film (30) has a waviness index of 20 mm or less.

[0045] The polyester film (30) above can be moved or stored in a rolled state. Referring to Fig. 1, the rolled state is a state in which the film is rolled starting from one end and toward the other end with a cylindrical core (5) as the center, wherein the one end is in contact with the core (5), the other end corresponds to the central end (35), and the ends of the film on both sides in the direction from the one end to the other end are referred to as the first side end (31) and the second side end (33), respectively. In addition, the direction from the core (5) to the central end (35) is referred to as the winding direction (Dr) of the polyester film (30), and the direction that connects the first side end (31) and the second side end (33) and is substantially orthogonal to the winding direction is referred to as the side direction (Ds) of the polyester film (3).

[0046] Referring to Fig. 2, the wave curvature index (W) is the maximum value among the heights of the floating portions on a flat surface (10: example, shelf) when the polyester film (20) is spread out on a flat surface (10: example, shelf) in a rolled state.

[0047] The waviness index is evaluated by placing a film rolled up in a roll shape on a flat surface (10) such as a shelf to determine how much it is waviness when unfolded. The height of the film surface is measured using a measuring sensor (not shown) placed on the shelf, and the height difference (W) between the flat surface (100) and the surface of the polyester film (30) is evaluated as the waviness index. In this specification, mm is used as the unit.

[0048] As one or more embodiments, the waviness index (W) of the polyester film (30) may be 18 mm or less, 16 mm or less, 14 mm or less, or 12 mm or less. The waviness index may be 0 mm or more, 1 mm or more, 2 mm or more, or 3 mm or more. The polyester film (30) having the waviness index has excellent flatness when the film is rolled up and stored, and thus has excellent usability.

[0049] Referring to Fig. 3, the edge sagging index (d-SI) of the film is a value that represents the difference between the sagging lengths of both ends of the film measured in mm when the polyester film (30) is run while applying tension (P) over two guide rolls (first guide roll: 71, second guide roll: 72) at intervals of about 1.2 M. The both ends are the degree of sagging measured at the midpoint (A-A') of the two guide rolls. For example, the tension is applied at about 10 kgf, and the running speed is applied at about 20 m / min.

[0050] Referring to Figures 4a and 4b, the shape and degree of sagging that occurs in the polyester film (30) at the point AA' will be described. The polyester film (30) running between two guide rolls is subject to tension (P) as it moves, but its height in the lateral direction (Ds) at the point AA' may not be constant.

[0051] For example, Fig. 4a shows a shape in which both ends sag downward compared to the center portion, and the second end sags more than the first end. For example, Fig. 4b shows a shape in which both ends sag downward compared to the center portion, and the first end sags more than the second end. For example, a shape in which the center sags downward compared to both ends, and a shape in which the first end sags more than the second end when comparing the ends may also occur (not shown). For example, a shape in which the center and the other end sag downward compared to one end, and a shape in which the second end sags more than the first end when comparing the ends may also occur (not shown). Although shapes such as A are described as examples, sagging may occur in other shapes besides those described, and the scope of the rights is not limited on the grounds that the sagging shapes of the film cross sections in A-A' are different. Additionally, it will be understood by those skilled in the art that the degree of sagging shown in the drawing has been exaggerated for explanatory purposes, and the scope of the rights is not limited for this reason.

[0052] In one or more embodiments, the edge sagging index (difference in sagging between the two ends, d-SI) of the polyester film (30) is 0 mm or more and 20 mm or less. The edge sagging index may be 20 mm or less, 18 mm or less, 16 mm or less, 14 mm or less, or 12 mm or less. The edge sagging index may be 0 mm or more, 1 mm or more, 2 mm or more, or 3 mm or more. Such a film has a well-controlled edge sagging degree, so that workability is improved when applied to continuous processes such as winding, rewinding, reprocessing, or cutting the film, and an excellent polyester film with fewer defects can be provided.

[0053] The above-mentioned end sagging index is calculated by using the difference between the heights measured at both ends using a sensor based on the relatively flat part in the center. The height of the central flat part is the reference for height measurement, and the point where sagging is 0 mm, which is the reference for the sagging value at each end described below. If sagging occurs, the result is used to indicate the sagging of the end, with a positive number, and if it is located higher than the exact center, a negative number.

[0054] In one or more embodiments, the sagging of the first side end of the polyester film (30) may be 25 mm or less. Specifically, the sagging of the first side end may be 25 mm or less, 23 mm or less, 20 mm or less, 18 mm or less, or 15 mm or less. The sagging of the first side end may be greater than -5 mm, greater than 0 mm, greater than 1 mm, or greater than 2 mm.

[0055] In one or more embodiments, the sagging of the second side end of the polyester film (30) may be 25 mm or less. Specifically, the sagging of the second side end may be 25 mm or less, 23 mm or less, 20 mm or less, 18 mm or less, or 15 mm or less. The sagging of the second side end may be greater than -5 mm, greater than 0 mm, greater than 1 mm, or greater than 2 mm.

[0056] The larger value of the sagging of the first side end and the sagging of the second side end may be 25 mm or less. The larger value may be 25 mm or less, 23 mm or less, 20 mm or less, 18 mm or less, or 15 mm or less. The larger value may be greater than 0 mm, greater than 1 mm, or greater than 2 mm.

[0057] When the sagging of the first side end or the sagging of the second side end of the polyester film (30) is within the above range, workability is improved when applied to a continuous process of reprocessing or cutting the film, and an excellent polyester film with fewer defects can be provided, and inconveniences that may occur during the process, such as a portion of the film being caught on a roll or rolled while being folded, can be reduced.

[0058] In one or more embodiments, the thickness of the polyester film (30) may be 5 μm or more. The thickness may be 5 μm or more, 10 μm or more, or 20 μm or more. The thickness may be 300 μm or less, for example, but is not limited thereto. The polyester film (30) of the embodiments may have excellent processability even though it is thin, and may have excellent end sagging index characteristics, wave curvature index characteristics, etc. compared to other polyester films of the same thickness.

[0059]

[0060] The inventors determined that the sagging or waviness index-related characteristics of a polyester film are characteristics related to the morphological behavior of the film in an environment where a constant tension is applied, such as during a winding process or a processing process utilizing the film. For example, they considered that there is an effect of the force applied or remaining on the film when tension is applied at one or more points or three or more points from one end of the film (center end: 35 in Fig. 1). In order to substantially reduce this effect, the inventors determined that the ratio of the tensile modulus of the polyester film (30) in the winding direction (Dr) and the lateral direction (Ds) is important.

[0061] The roll-up tensile modulus ratio is the ratio of the lateral tensile modulus to the roll-up tensile modulus. In other words, the roll-up tensile modulus ratio is obtained by dividing the lateral tensile modulus by the roll-up tensile modulus.

[0062] The winding direction tensile modulus is the tensile modulus measured in the longitudinal direction in the direction in which the polyester film is wound, and the lateral direction tensile modulus is the tensile modulus measured in the longitudinal direction in the lateral direction when the polyester film is wound.

[0063] In one or more embodiments, the polyester film (30) may have a take-up tensile modulus ratio of 1 to 1.8. The take-up tensile modulus ratio may be 1 or more, 1.1 or more, 1.15 or more, or 1.2 or more. The take-up tensile modulus ratio may be 1.8 or less, 1.6 or less, 1.5 or less, or 1.4 or less. When the polyester film has such a take-up tensile modulus ratio, it may be helpful in maintaining the sagging index or the waviness index within a desired range, and may reduce the occurrence of wrinkles, folds, etc. that may occur during take-up, and may improve the convenience of work utilizing the polyester film.

[0064] The difference in the tensile modulus of elasticity in the winding direction is the absolute value of the difference between the tensile modulus in the lateral direction and the tensile modulus in the winding direction.

[0065] In one or more embodiments, the polyester film (30) has a difference in the tensile modulus of the winding of 75 kg / mm. 2 Up to 250 kg / mm 2 The above difference in tensile modulus of the coiling is 75 kg / mm 2 Above, 82 kg / mm 2 or more than 88 kg / mm 2 It can be ideal. The above difference in tensile modulus is 250 kg / mm 2 Below 220 kg / mm 2 Below, 190 kg / mm 2 Below 140 kg / mm 2 or less, or 120 kg / mm 2This may be as follows. When there is such a difference in the tensile modulus of elasticity during winding, it may be helpful in maintaining the sagging index or the wave curvature index within the desired range, reduce the occurrence of wrinkles and folds that may occur during winding, and improve the convenience of working with the polyester film.

[0066] In one or more embodiments, the polyester film (30) has a tensile modulus in the winding direction of 330 kg / mm 2 It can be ideal. The tensile modulus in the winding direction is 330 kg / mm. 2 Above, 360 kg / mm 2 or 375 kg / mm 2 It can be ideal. The tensile modulus in the winding direction is not particularly limited, but is 600 kg / mm 2 or less, or 500 kg / mm 2 Polyester films having these characteristics can have improved workability.

[0067] In one or more embodiments, the polyester film (30) has a lateral tensile modulus of 400 kg / mm 2 Above, 450 kg / mm 2 or more than 500 kg / mm 2 It may be ideal. The lateral tensile modulus is not particularly limited, but is 700 kg / mm 2 or less, or 650 kg / mm 2 Polyester films having these characteristics can have improved workability.

[0068] In one or more embodiments, the polyester film (30) has a length in the winding direction of 3 m or more, and when the polyester film is pulled at a speed of 20 m / min with a tension of 10 kgf on guide rolls arranged at intervals of 1.2 M, the difference in sagging between the lateral edges of the polyester film relative to the lateral center of the polyester film may be 0 mm or more and 20 mm or less.

[0069] The above end sagging index may be 20 mm or less, 18 mm or less, 16 mm or less, 14 mm or less, or 12 mm or less. The above end sagging index may be 0 mm or more, 1 mm or more, 2 mm or more, or 3 mm or more. Such a film has a well-controlled end sagging degree, and thus has improved workability when applied to continuous processes such as winding, rewinding, reprocessing, or cutting the film, and can provide an excellent polyester film with fewer defects.

[0070]

[0071] In one or more embodiments, the polyester film (30) comprises a diol residue and a dicarboxylic acid residue.

[0072] The above diol residue is a linear or branched aliphatic C2 to C 10 It may be a diol residue. The diol residue may further include an alicyclic diol or an aromatic diol.

[0073] For example, the diol residue may be an ethylene glycol residue, a diethylene glycol residue, a neopentyl glycol residue, a 1,3-propanediol residue, a 1,2-octanediol residue, a 1,3-octanediol residue, a 2,3-butanediol residue, a 1,3-butanediol residue, a 1,4-butanediol residue, a 1,5-pentanediol residue, a 2-butyl-2-ethyl-1,3-propanediol residue, a 2,2-diethyl-1,5-pentanediol residue, a 2,4-diethyl-1,5-pentanediol residue, a 3-methyl-1,5-pentanediol residue, a 1,1-dimethyl-1,5-pentanediol residue, a 1,6-hexanediol residue, a 2-ethyl-3-methyl-1,5-hexanediol residue, It may include a 2-ethyl-3-ethyl-1,5-hexanediol residue, a 1,7-heptanediol residue, a 2-ethyl-3methyl-1,5-heptanediol residue, a 2-ethyl-3-ethyl-1,6-heptanediol residue, a 1,8-octanediol residue, a 1,9-nonanediol residue, a 1,10-decanediol residue, or two or more thereof.

[0074] Specifically, the diol residue may include any one selected from the group consisting of an ethylene glycol residue, a diethylene glycol residue, a neopentyl glycol residue, a cyclohexanedimethanol residue, and combinations thereof.

[0075] The polyester resin may contain 30 mol% to 100 mol% of ethylene glycol residues based on the total number of moles of the diol residues. For example, the polyester resin may contain 40 mol% to 100 mol%, 50 mol% to 100 mol%, or 65 mol% to 100 mol% of ethylene glycol residues based on the total number of moles of the diol residues.

[0076] The above dicarboxylic acid residue may be an aromatic dicarboxylic acid residue such as a terephthalic acid residue, a dimethylterephthalic acid residue, an isophthalic acid residue, a naphthalenedicarboxylic acid residue, an orthophthalic acid residue; an aliphatic dicarboxylic acid residue such as an adipic acid residue, an azelaic acid residue, a sebacic acid residue, a decanedicarboxylic acid residue; an alicyclic dicarboxylic acid residue; an ester residue thereof; or a combination of two or more thereof.

[0077] Specifically, the dicarboxylic acid residue may include any one selected from the group consisting of a terephthalic acid residue, a dimethylterephthalic acid residue, an isophthalic acid residue, a naphthalenedicarboxylic acid residue, an orthophthalic acid residue, and combinations thereof.

[0078] Specifically, the dicarboxylic acid residue may include any one selected from the group consisting of a terephthalic acid residue, a dimethylterephthalic acid residue, an isophthalic acid residue, and combinations thereof.

[0079] The polyester film may contain 0 mol% to 10 mol% of the isophthalic acid residues based on the total dicarboxylic acid residues. The polyester film may contain 0 mol% or more, 0.01 mol% or more, 0.05 mol% or more, 0.1 mol% or more, or 0.13 mol% or more of the isophthalic acid residues based on the total dicarboxylic acid residues. The polyester film may contain 10 mol% or less, 8 mol% or less, 6 mol% or less, 4 mol% or less, or 3 mol% or less of the isophthalic acid residues based on the total dicarboxylic acid residues. When the polyester film contains the isophthalic acid residues in the above content, it may be helpful in controlling the degree of crystallization of the polymer even when there is a rapid change in temperature during the film manufacturing process.

[0080] The polyester film may contain 90 mol% to 100 mol% of terephthalic acid residues, dimethylterephthalic acid residues, or a combination thereof based on the total dicarboxylic acid residues. Specifically, it may contain 90 mol% or more, 92 mol% or more, 94 mol% or more, 96 mol% or more, or 97 mol% or more. In addition, it may contain 100 mol% or less, 99.99 mol% or less, 99.95 mol% or less, 99.9 mol% or less, or 99.87 mol% or less.

[0081] The above polyester resin synthesis method can be applied without limitation to any conventional polyester resin synthesis method. For example, a polyester resin can be synthesized by mixing a monomer capable of forming a dicarboxylic acid residue and a monomer capable of forming a diol residue, and then inducing an esterification reaction or a condensation reaction. At this time, a catalyst can be introduced to improve the efficiency of the reaction. The catalyst can be a titanium-based catalyst, an antimony-based catalyst, etc., but is not limited thereto.

[0082]

[0083] In one or more embodiments, the polyester film (30) may comprise a recycled polyester resin.

[0084] Polyester resin, particularly polyethylene terephthalate resin, is a widely used plastic used in containers for beverages and other liquids (PET bottles) and films. PET bottles, in particular, are a clean and recyclable material, and recycling technologies are being researched and utilized.

[0085] The recycled polyester resin may be a physically recycled resin, a chemically recycled resin, or a mixture thereof.

[0086] Physical recycling involves crushing and washing collected polyester products (mainly PET bottles) to obtain polyester resin in the form of chips, flakes, or pellets. Chemical recycling involves collecting polyester products, removing foreign substances, and then chemically decomposing and resynthesizing the products into monomers (e.g., terephthalic acid, ethylene glycol, bis(hydroxyethyl) terephthalate). Various decomposition methods, including glycolysis, methanolysis, hydrolysis, and ammonolysis, can be applied. Recycled resins are commercially available from companies such as Sinopec, SK Chemicals, and Custom Polymers.

[0087] Physically recycled resins or chemically recycled resins are theoretically expected to have substantially equivalent properties to non-recycled resins (virgin resins). However, in practice, some samples exhibit properties that are somewhat inferior to those obtained using conventional resins. The inventors speculate on various reasons for this, including limitations in foreign material removal, the generation of carbon-based foreign materials during processing, increased metallic foreign material content, agglomeration of foreign materials, damage to polymer chains during recycling, and differences in polymer chain size distribution. However, they recognize that proving the cause or clearly identifying a causal relationship is practically difficult.

[0088] In one or more embodiments, the polyester film (30) may contain 10 wt% to 100 wt% of the recycled resin based on the total polyester resin. Specifically, the recycled resin may be contained in the polyester film in an amount of 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, or 70 wt% or more, based on the total polyester resin applied to the polyester film. In addition, the recycled resin may be contained in an amount of 100 wt% or less, 98 wt% or less, 95 wt% or less, 93 wt% or less, or 90 wt% or less. It has been experimentally confirmed that the polyester film of the embodiments can excellently obtain intended properties such as the appearance, sagging property, rollability, and waviness index of the film even when the recycled resin is applied in a significant amount as described above.

[0089] The polyester resin may have an intrinsic viscosity (IV) of about 0.58 dl / gr to about 0.90 dl / gr. The intrinsic viscosity may be about 0.58 dl / gr or more, or about 0.60 dl / gr or more. The intrinsic viscosity may be about 0.90 dl / gr or less, about 0.85 dl / gr or less, about 0.80 dl / gr or less, or about 0.75 dl / gr or less. When the polyester resin has this intrinsic viscosity range, it is relatively easy to control crystallinity in the manufacturing process described below, and a polyester film having a certain level or more of mechanical strength can be obtained.

[0090]

[0091] The above polyester film (30) may further include additives such as antioxidants, activators, and inorganic particles.

[0092] The above antioxidant may include a phenol-based antioxidant, a phosphorus-based antioxidant, and / or a sulfur-based antioxidant.

[0093] The phenolic antioxidant may be, for example, tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; benzeneformanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy, alkyl ester (alkyl is 7 or 9 carbon atoms); triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate; tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate; 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; or a combination thereof.

[0094] The above-mentioned antioxidant may be, for example, 3,9-bis(2,4-dicumylphenoxy)-2,4,8,10-tetraoxa-3,9-iphosphaspiro[5.5]undecane [3,9-Bis(2,4-dicumylphenoxy)-2,4,8,10-tetraoxa-3,9-iphosphaspiro[5.5]undecane]; bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite; bis(2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite; tetrakis(2,4-di-tert-butylphenyl)4,4'-biphenylene diphosphonite; or a combination thereof.

[0095] The above sulfur-based antioxidant may be dilauryl-3,3'-thiodipropionic acid ester; dimyristyl-3,3'-thiodipropionic acid ester; distearyl-3,3'-thiodipropionic acid ester; laurylstearyl-3,3'-thiodipropionic acid ester; pentaerythrityl tetrakis(3-laurylthiopropion ester); or a combination thereof.

[0096] The above antioxidant can be applied in an amount of 0.01 to 3 parts by weight based on 100 parts by weight of the polyester resin.

[0097] The above-mentioned activator may be a salt of an alkali metal or a salt of an alkaline earth metal, and contributes to the sheet formation of the extruded resin in the silom manufacturing process. For example, the activator may be a magnesium-based compound or a potassium-based compound, and specifically, magnesium acetate, potassium acetate, or a mixture thereof may be used.

[0098] The above-mentioned agent can be applied in an amount of 100 to 3000 ppm (by weight) based on 100 parts by weight of the polyester resin.

[0099] Examples of the above inorganic particles include, but are not limited to, silica, calcium carbonate, and talc.

[0100] In one or more embodiments, the polyester film (30) may be wound on a 6-inch core roll without any external shading or deformation after 7 days. The polyester film may be easily wound with excellent quality, and may be stored in a wound state with little or no substantial damage to the film.

[0101]

[0102] In one or more embodiments, the polyester film (30) can be manufactured by a method for manufacturing a polyester film.

[0103] There are no special limitations on the manufacturing method of polyester film, but the description is based on the melt extrusion method.

[0104] The method for manufacturing a polyester film includes a preparation step, a forming step, and a stretching step.

[0105] The preparation step is a step of preparing a polyester composition containing the polyester resin and additives described above.

[0106] The molding step is a step for manufacturing the polyester composition into a polyester resin composition sheet. Specifically, the method using the melt extrusion method is described. The polyester composition is placed in an extruder and melt extruded. Melting can be performed by heating to a temperature of about 260°C to about 320°C. The melting can be performed at a temperature of about 270°C to about 290°C.

[0107] The molten composition is extruded and rapidly cooled through a T-die to produce a polyester resin composition into a sheet. A casting roll may be used, but is not limited thereto.

[0108] The stretching step includes the process of stretching and heat-fixing the above sheet.

[0109] The above stretching can be applied using a biaxial stretching method.

[0110] Specifically, the sheet may be stretched a first time in a first direction and then a second time in a second direction. The first and second directions are substantially perpendicular. The first direction may be the machine direction and the second direction may be the width direction.

[0111] The first extension may be applied at an extension ratio of 2 to 4 times, or may be applied at an extension ratio of 2 to 3.5 times, 2.5 to 3.5 times, or 2.8 to 3.2 times.

[0112] The second extension may be applied at an extension ratio of 3 to 5 times, or may be applied at an extension ratio of 3 to 4.5 times, 3.5 to 4.5 times, or 3.8 to 4.2 times.

[0113] However, the above description is not intended to exclude biaxial stretching in which primary and secondary stretching are performed simultaneously.

[0114] The above heat fixation is performed in the order of heat treatment and cooling.

[0115] The above heat treatment can be carried out at a temperature of 210°C to 250°C, or at a temperature of 220°C to 240°C. When heat treatment is carried out at such a temperature, it can help the polyester film to have excellent dimensional stability.

[0116] The above cooling can be carried out at a temperature of 30°C to 70°C, and can be carried out at a temperature of 35°C to 65°C. When such cooling temperatures are applied, the polyester film can have better sagging properties and a superior wave curvature index.

[0117] The cooling rate applied during cooling after the heat treatment may be 10°C / sec to 150°C / sec, and the cooling rate may be 10°C / sec or more, 13°C / sec or more, 20°C / sec or more, 25°C / sec or more, 30°C / sec or more, or 35°C / sec or more. In addition, the cooling rate may be 130°C / sec or less, 125°C / sec or less, or 120°C / sec or less. Specifically, the cooling rate may be 30°C / sec to 44°C / sec, or 32°C / sec to 42°C / sec. When such a cooling rate is applied, it may help the polyester film to have better sagging characteristics and a superior waviness index.

[0118] The difference between the heat treatment temperature and the cooling temperature may be 145°C to 205°C. Specifically, the difference may be 145°C or more, 150°C or more, 155°C or more, or 160°C or more. The difference may be 205°C or less, 200°C or less, or 195°C or less. When the heat setting and cooling are performed within this temperature range, the polyester film may have better sagging properties and a superior waviness index. If the difference exceeds 205°C, the cooling may proceed at too fast a rate, so that the residual stress within the polyester film is not properly relieved, and the surface of the polyester film may become uneven. In addition, distortion may occur in the arrangement of polymers within the film, which may cause waviness at the edges or on the film surface when the film is rolled and then unrolled. In addition, if the difference is less than 145°C, workability may deteriorate during the manufacturing process.

[0119] The manufactured polyester film can be wound into a roll and stored and transported.

[0120] The polyester film of the embodiment can provide a polyester film that has relatively flat characteristics and is less prone to bending, wrinkling, stretching, etc. when the polyester film rolled into a roll shape is unfolded.

[0121]

[0122] Hereinafter, a more detailed explanation will be given through specific examples. The following examples are merely illustrative examples to aid understanding of the present invention and are not intended to limit the scope of the present invention.

[0123]

[0124] (1) Manufacturing of polyester resin

[0125] 1) Terephthalic acid as a dicarboxylic acid and ethylene glycol as a diol were introduced into an autoclave equipped with a stirrer and a distillation tower, and triethyltin as an ester exchange catalyst was introduced in an amount of about 100 to 500 ppm (by weight) based on the total monomer content, and then the temperature was raised to 220°C to remove methanol as a byproduct and to proceed with an ester exchange reaction, thereby producing a polyester resin.

[0126] 2) Discarded polyester film was depolymerized and then polymerized to produce chemically recycled polyester resin. The polymerization was performed by adding terephthalic acid and BHET (bis-hydroxyethyl terephthalate) ethylene glycol using the glycolysis method, and this was subjected to an ester exchange reaction in a similar manner to 1) to obtain recycled polyester resin.

[0127]

[0128] (2) Manufacturing of polyester film

[0129] A polyester film was manufactured from a composition containing a polyester resin using the contents and process conditions presented in Table 1 below. The composition contained approximately 100 ppm (by weight) of silica based on the entire polyester resin, and 350 ppm (by weight) of magnesium acetate and 50 ppm (by weight) of potassium acetate as additives.

[0130] The above composition was manufactured into a polyester film by melt extrusion and then molding using a casting roll. The manufactured film had a thickness of approximately 75 μm. The manufactured film was cut to a width of 1,500 mm and then wound to a length of approximately 2,000 m to manufacture it into a roll shape.

[0131] Polyester resin stretching heat treatment / cooling temperature (℃) Virgin resin Recycled resin Plant-derived resin #IV* MD stretching ratio TD stretching ratio Heat treatment temperature Cooling temperature Heat treatment temperature - Cooling temperature Cooling speed (℃ / sec) Example 1 100--0.61 2.9 3.9 2 2 5 6 0 16 5 3 4 Example 2 100--0.61 3.0 3 8 2 2 5 4 0 18 5 3 8 Example 3 100--0.61 2.9 3.9 2 3 5 6 0 17 5 3 6 Example 4 100--0.61 2.8 4 0 2 3 5 4 0 19 5 4 0 Example 5 1090-0.62 8 3.9 2 3 5 6017536Example 63070-0.63.03.92356017536Example 710-900.852.93.92356017536Comparative Example 1100--0.612.93.92483321545Comparative Example 28020-0.612.34.02483321529Comparative Example 3100--0.612.84.02107014029Comparative Example 4100--0.612.34.02103317724Comparative Example 5100--0.612.34.02356017523

[0132] # The plant-derived resin was applied by purchasing Lotte Chemical's PET Bio product (polyester resin).

[0133] * IV refers to the intrinsic viscosity of the film, and its measurement was performed by dissolving each film (10 mg) in ortho-chlorophenol at 100°C, and then measuring the relative viscosity by obtaining the falling time of the sample using an Ostwald viscometer in a constant temperature bath at 35°C. The obtained relative viscosity was converted to intrinsic viscosity (IV) based on the relative viscosity-intrinsic viscosity conversion table, and the value rounded to the third decimal place was presented.

[0134]

[0135] (3) Evaluation of physical properties of polyester film

[0136] 1) Measurement of tensile modulus

[0137] The manufactured polyester film was cut into 10 mm wide and 10 cm long pieces in the winding and lateral directions, respectively, to prepare measurement samples. Each of the samples was mounted on a universal material testing machine (UTM, INSTRON-34TM) and the magnitude of force according to deformation was measured when pulling at a speed of 200 mm / min. The magnitude of force when the strain rate was 5% was defined as the tensile modulus, and five samples cut in the winding and lateral directions were measured, and the average value was taken.

[0138] 2) End sagging index (d-SI, mm)

[0139] The film roll (20) cut to a constant width is unrolled again so that the film (30) is pulled at a constant tension (P) and driven over two guide rolls (71, 73) spaced 1.2 m apart. At this time, the film cut at the midpoint of the two guide rolls is driven, and the extent to which the cross-sections of both feet are stretched compared to the reference line is measured in mm, and the difference in the extent of stretching on the left and right sides is defined as the end sagging index (see Fig. 3). In the embodiment, the film cut to a width of 1500 mm is driven while being pulled at a tension of 10 kgf and a speed of 20 m / min, and at this time, the length by which the cross-sections on both sides are stretched compared to the center is measured using a laser distance meter.

[0140] 3) Wave curvature index

[0141] When a 2 m long film was spread on a flat shelf, the maximum height of the part that was not in contact with the shelf but was lifted from the side was measured (see Fig. 2).

[0142] 4) Roll appearance evaluation

[0143] A roll with a length of 2000 m was manufactured by winding it on a 6-inch core, and the appearance of the roll was observed after 7 days to evaluate the appearance quality step by step as follows.

[0144] Grade 1 (◎): There are no special defects in the appearance of the roll and it maintains a uniform appearance.

[0145] Grade 2 (○): Some shading was observed on some parts of the roll, but no deformation occurred and it was released smoothly.

[0146] Grade 3 (△): Dark shades are observed in several areas of the roll, and it is unevenly loosened.

[0147] Out of Grade (X): The roll is wound unevenly and cannot be manufactured.

[0148]

[0149] The evaluation results are shown in Table 2 below.

[0150] Tensile modulus (kg / mm) 2 ) End sagging (mm) Roll appearance Waviness index Lateral direction Winding direction Tensile modulus Difference ratio (lateral direction / winding direction) Winding direction Left Winding direction Right End sagging index (mm) Example 15 2 2 4 1 8 1 0 4 1.2 5 5 1 4 ◎ 3 Example 25 4 8 4 5 5 9 3 1.2 1 3 7 ◎ 6 Example 3 4 9 7 4 0 8 8 9 1.2 2 9 7 ◎ 6 Example 4 5 16 3 9 7 1 1 9 1.3 1 7 3 1 4 ○ 9 Example 5 4 8 2 3 7 6 1 0 6 1.2 8 1 5 3 1 2 ◎ 6 Example 6 4 9 7 4 0 9 8 8 1.2 2 1 0 1 3 3 ◎ 8 Example Example 7521426951.229178○12Comparative Example 1513420931.2228424△14Comparative Example 25773092681.8731823△23Comparative Example 3485416691.17541935X31Comparative Example 45642862781.9729-736X24Comparative Example 55592892701.9334430△22

[0151] Referring to Tables 1 and 2 above, the samples of Examples 1 to 7 showed lower values ​​in the wave flexure index compared to the samples of Comparative Examples 1 to 5. In addition, the roll appearance also showed results of grade 1 or higher. The end sag index of the examples also showed better results than the comparative examples. Examples 1 and 6 using recycled resin and Example 7 using plant-derived resin also showed excellent wave flexure index and end sag index.

[0152]

[0153] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0154] (Explanation of symbols)

[0155] 5: Core

[0156] 71: First guide roll 73: Second guide roll

[0157] 20: Polyester film in roll form

[0158] 31: First side section 33: Second side section

[0159] 35: Central end

[0160] Dr: Winding direction Ds: Lateral direction

[0161] S: Sensor P: Tension

[0162] d-SI: End sagging index

Claims

1. The wave curvature index is the maximum value of the height of the floating part on the flat surface when the polyester film is spread out in a roll state wound on a flat surface. A polyester film having a wave curvature index of 20 mm or less.

2. In paragraph 1, The above polyester film is a polyester film, wherein the end sagging index at the first end and the second end is 0 mm or more and 20 mm or less.

3. In paragraph 2, A polyester film, wherein the larger value between the sagging of the first side end and the sagging of the second side end is 25 mm or less.

4. In paragraph 1, The tensile modulus in the winding direction is the tensile modulus measured in the longitudinal direction along which the polyester film is wound. The lateral tensile modulus is the tensile modulus measured in the longitudinal direction when the polyester film is wound. The coiling tensile modulus ratio is the ratio of the coiling direction tensile modulus based on the lateral direction tensile modulus, The above polyester film is a polyester film having a tensile modulus ratio of 1 to 1.

8.

5. In paragraph 1, The tensile modulus in the winding direction is the tensile modulus measured in the longitudinal direction along which the polyester film is wound. The lateral tensile modulus is the tensile modulus measured in the longitudinal direction when the polyester film is wound. The difference in the tensile modulus of elasticity in the winding direction is the absolute value of the difference between the tensile modulus in the lateral direction and the tensile modulus in the winding direction. The above polyester film has a difference in the tensile modulus of the above winding of 75 kg / mm 2 Up to 250 kg / mm 2 In, polyester film.

6. In paragraph 4 or 5, The tensile modulus in the winding direction is 330 kg / mm 2 Ideal, polyester film.

7. In paragraph 1, A polyester film that does not show any external shading or deformation after 7 days of being rolled onto a 6-inch core.

8. In paragraph 1, The above polyester film is a polyester film comprising any one selected from the group consisting of recycled polyester resin, plant-derived polyester resin, and combinations thereof.

9. The length of the polyester film in the winding direction is 3 m or more, When the polyester film is pulled at a speed of 20 m / min with a tension of 10 kgf on guide rolls arranged at intervals of 1.2 m, A polyester film, wherein the difference in sagging between the lateral edges of the polyester film relative to the lateral center of the polyester film is 0 mm or more and 20 mm or less.

10. In paragraph 9, The tensile modulus in the winding direction is the tensile modulus measured in the longitudinal direction along which the polyester film is wound. The lateral tensile modulus is the tensile modulus measured in the longitudinal direction when the polyester film is wound. The coiling tensile modulus ratio is the ratio of the coiling direction tensile modulus based on the lateral direction tensile modulus, The above polyester film is a polyester film having a tensile modulus ratio of 1 to 1.8.

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