Polyester film

Abstract

The present invention relates to a polyester film. The polyester film of the present invention has heat shrinkage and crystallinity, high transparency, and excellent shrinkage and bonding properties, and thus can be suitably used as a material for a heat shrinkage label used in PET containers and the like.

Description

polyester film

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0018834, filed February 7, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a polyester film having heat shrinkability and crystallinity and excellent bonding properties.

[0004]

[0005] Heat-shrinkable films shrink when heated and are used for shrink packaging, shrink labels, and other applications. Examples of heat-shrinkable films include polyvinyl chloride (PVC), polystyrene, and polyester films, and are used for various container labels, cap seals, and direct packaging.

[0006] However, films made of polyvinyl chloride are classified as regulated due to the problem of generating hazardous substances such as hydrogen chloride gas and dioxin when incinerated. While polystyrene film has good workability according to the shrinkage process and the product has a good appearance, it has poor chemical resistance, so special composition inks must be used when printing. In addition, it has the disadvantage of having poor storage stability at room temperature, so it shrinks spontaneously and becomes dimensionally deformed. Furthermore, when polyvinyl chloride film or polystyrene film is used as a shrink label for polyethylene terephthalate containers, there is the inconvenience of having to separate the label and the container during the recycling process for polyethylene terephthalate containers.

[0007] Accordingly, polyester film is attracting attention as a material that is easy to recycle and non-toxic. However, conventional heat-shrinkable polyester film lacks sufficient heat shrinkage, necessitating improved shrinkage properties. Furthermore, amorphous polyester film can adhere to the container during the washing and drying process for recycling polyethylene terephthalate containers, making the container unusable.

[0008] Accordingly, there is a need for the development of a polyester film that has superior shrinkage and bonding properties than existing polyester resins and can improve process convenience by eliminating the need to separate it from the polyethylene terephthalate container before the recycling process.

[0009]

[0010] The present invention aims to provide a polyester film that exhibits sufficient heat shrinkage properties and adhesive properties, and is not fused with polyethylene terephthalate (PET) during the recycling stage of the PET container, so that it can be suitably used as a material for a heat shrinkage label for a PET container.

[0011]

[0012] Accordingly, according to one embodiment of the present invention,

[0013] A polyester film comprising a polyester resin mixture,

[0014] Using a differential scanning calorimeter (DSC), the temperature was increased from 30°C to 280°C at a rate of 10°C / min and maintained at 280°C for 5 minutes (1 st Scan), -300℃ / min to 30℃, then increased to 280℃ at 10℃ / min (2 nd 1 measured from the heat flow obtained when scanning st Heat of fusion in scan and 2 nd Difference in heat of fusion in scan (1 st ΔHm - 2 nd ΔHm) is 2 j / g or more,

[0015] A polyester film is provided, wherein when two sheets of the polyester film are bonded with tetrahydrofuran and one end of the polyester film is pulled at a speed of 200 mm / min using a tensile tester, a peeling force defined as the maximum force when the two sheets of the polyester film are separated is 100 g·f or more.

[0016] The above polyester film may have a shrinkage initiation temperature of 75°C or less.

[0017] The above polyester film may have a maximum shrinkage rate of 40% or more at 95°C.

[0018] The above polyester film may have an intrinsic viscosity of 0.5 to 1.0 dL / g.

[0019] The polyester resin mixture may include a crystalline polyester; and an amorphous polyester having a weight average molecular weight difference of less than 20,000 g / mol from the crystalline polyester.

[0020] At this time, the polyester resin mixture may include 10 to 60 wt% of crystalline polyester and 40 to 90 wt% of amorphous polyester.

[0021] The above polyester resin mixture may contain 8 to 35 mol% of a diol portion derived from 1,4-cyclohexanedimethanol among the total diol portions.

[0022] The above polyester resin mixture may contain 2 to 20 mol% of a diol portion derived from diethylene glycol among the total diol portions.

[0023] The weight average molecular weight of the above crystalline polyester and amorphous polyester may be 60,000 to 150,000 g / mol, respectively.

[0024] In one embodiment, the crystalline polyester can be a polyethylene terephthalate comprising at least 95 mol% of an acid moiety derived from terephthalic acid; and at least 85 mol% of a diol moiety derived from ethylene glycol.

[0025] In one embodiment, the amorphous polyester comprises an acid moiety derived from a dicarboxylic acid or a derivative thereof; and a diol moiety derived from a diol comprising ethylene glycol and a comonomer; wherein the comonomer may comprise 1,4-cyclohexanedimethanol and / or diethylene glycol.

[0026] The above amorphous polyester may contain 20 to 40 mol% of a diol portion derived from 1,4-cyclohexanedimethanol among the total diol portions.

[0027] The above amorphous polyester may contain 10 to 20 mol% of a diol portion derived from diethylene glycol among the total diol portions.

[0028] The polyester film may be a single-layer film, or the polyester film may be a multi-layer film including a core layer and a surface layer formed on one or both sides of the core layer.

[0029] In one embodiment, the core layer may comprise a crystalline polyester and an amorphous polyester in a weight ratio of 0:100 to 60:40, and the surface layer may comprise a crystalline polyester and an amorphous polyester in a weight ratio of 10:90 to 60:40.

[0030] In one embodiment, with respect to the thickness of the polyester film, the percentage of the core layer thickness may be 35% to 92.5%, and the percentage of the surface layer thickness may be 7.5% to 65%.

[0031] According to another embodiment of the present invention, a method for producing a polyester film is provided, comprising: producing a polyester resin mixture comprising a crystalline polyester and an amorphous polyester having a difference in weight average molecular weight of less than 20,000 g / mol; molding the polyester resin mixture to produce an unstretched film; and stretching the unstretched film in at least one direction.

[0032] The above stretching may be uniaxial stretching with a transverse stretching ratio of 2 to 6 times or a longitudinal stretching ratio of 1.1 to 6 times.

[0033] Alternatively, the stretching may be a biaxial stretching with a transverse stretching ratio of 1.5 to 5 times and a longitudinal stretching ratio of 1.1 to 5 times.

[0034]

[0035] The polyester film of the present invention has heat shrinkability and crystallinity, and excellent shrinkage and bonding properties. Therefore, the polyester film can be suitably used as a material for heat shrinkable labels for packaging PET bottles and the like.

[0036] Furthermore, the polyester film of the present invention, due to its crystallinity, does not fuse with PET flakes at high temperatures, allowing it to be recycled while still attached to PET containers. Therefore, using heat-shrinkable labels made with the polyester film minimizes the hassle of having to separate the label and container for recycling, thereby improving the recycling rate.

[0037]

[0038] Figure 1 illustrates a method for preparing a specimen for measuring the adhesive properties (peel strength) of a polyester film.

[0039]

[0040] Unless otherwise specified herein, terminology is used only for the purpose of describing particular embodiments and is not intended to limit the present invention. In addition, singular forms include plural forms unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other particular features, regions, integers, steps, operations, elements, components, and / or groups.

[0041] In this specification, the acid moiety and the diol moiety refer to residues remaining after hydrogen, hydroxyl group or alkoxy group is removed from a dicarboxylic acid or its derivative and a diol by polymerization.

[0042] In this specification, the term 'dicarboxylic acid or a derivative thereof' means one or more compounds selected from dicarboxylic acids and derivatives of dicarboxylic acids. In addition, 'derivatives of dicarboxylic acids' means alkyl esters of dicarboxylic acids (lower alkyl esters having 1 to 4 carbon atoms, such as monomethyl, monoethyl, dimethyl, diethyl or dibutyl esters) or anhydrides of dicarboxylic acids. Accordingly, for example, terephthalic acid or a derivative thereof refers to compounds that react with a diol to form a terephthaloyl moiety, such as terephthalic acid; monoalkyl or dialkyl terephthalates; and terephthalic anhydride.

[0043]

[0044] Hereinafter, the polyester film of the present invention and its manufacturing method will be described in more detail.

[0045]

[0046] polyester film

[0047]

[0048] According to one embodiment of the present invention,

[0049] A polyester film comprising a polyester resin mixture,

[0050] Using a differential scanning calorimeter (DSC), the temperature was increased from 30°C to 280°C at a rate of 10°C / min and maintained at 280°C for 5 minutes (1 st Scan), -300℃ / min to 30℃, then increased to 280℃ at 10℃ / min (2 nd 1 measured from the heat flow obtained when scanning st Heat of fusion in scan and 2 nd Difference in heat of fusion in scan (1 st ΔHm - 2 nd ΔHm) is 2 j / g or more,

[0051] A polyester film is provided, wherein when two sheets of the polyester film are bonded with tetrahydrofuran and one end of the polyester film is pulled at a speed of 200 mm / min using a tensile tester, a peeling force defined as the maximum force when the two sheets of the polyester film are separated is 100 g·f or more.

[0052] The above polyester film exhibits excellent shrinkage ratio while being heat-shrinkable at a low temperature similar to the heat shrinkage temperature of polyvinyl chloride film, and can be used as a heat-shrinkable label for polyethylene terephthalate (PET) containers without deformation or clouding of the PET containers.

[0053] In addition, in the case of amorphous heat shrink labels, there is a problem of them fusing with the PET container during the washing and drying process for recycling the PET container, so they must be removed before being supplied to the recycling stream. However, in the case of a heat shrink label manufactured from a polyester film according to the above embodiment, crystallization is possible even at a high drying temperature, so there is an advantage that they can be supplied to the recycling stream as they are attached to the PET container.

[0054]

[0055] polyester resin mixture

[0056]

[0057] The polyester resin mixture included in the above polyester film may include a crystalline polyester and an amorphous polyester having a difference in weight average molecular weight of less than 20,000 g / mol. By using a polyester resin mixture including a crystalline and amorphous polyester satisfying the difference in weight average molecular weight, a polyester film having crystallinity and exhibiting excellent heat shrinkage properties can be provided.

[0058] The crystalline polyester and the non-crystalline polyester included in the polyester resin mixture each have a structure in which a dicarboxylic acid or a derivative thereof and a diol are polymerized, and an acid moiety derived from the dicarboxylic acid or a derivative thereof and a diol moiety derived from the diol are repeated.

[0059]

[0060] As an example of the above crystalline polyester, polyethylene terephthalate may be used. The polyethylene terephthalate is manufactured by polymerizing a dicarboxylic acid or a derivative thereof with a diol. The dicarboxylic acid or a derivative thereof may be primarily terephthalic acid or a derivative thereof, and the diol may be primarily ethylene glycol.

[0061] The above polyethylene terephthalate may include an acid moiety derived from a comonomer other than terephthalic acid or a derivative thereof. Specifically, the comonomer may be at least one selected from the group consisting of an aromatic dicarboxylic acid having 8 to 14 carbon atoms or a derivative thereof and an aliphatic dicarboxylic acid having 4 to 12 carbon atoms or a derivative thereof. The aromatic dicarboxylic acid having 8 to 14 carbon atoms or a derivative thereof may include an aromatic dicarboxylic acid or a derivative thereof commonly used in the production of a polyester resin, such as isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, naphthalene dicarboxylic acid such as 2,6-naphthalene dicarboxylic acid, dialkyl naphthalene dicarboxylates such as dimethyl 2,6-naphthalene dicarboxylate, and diphenyl dicarboxylic acid. The aliphatic dicarboxylic acid or derivative thereof having 4 to 12 carbon atoms may include cyclohexane dicarboxylic acids such as 1,4-cyclohexane dicarboxylic acid and 1,3-cyclohexane dicarboxylic acid, cyclohexane dicarboxylates such as dimethyl 1,4-cyclohexane dicarboxylate and dimethyl 1,3-cyclohexane dicarboxylate, and linear, branched or cyclic aliphatic dicarboxylic acids or derivatives thereof commonly used in the production of polyester resins, such as sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid and azelaic acid. The above monomer can be used in an amount of 0 to 50 mol%, 0 to 30 mol%, 0 to 20 mol% or 0 to 10 mol% based on the total dicarboxylic acid or its derivative.

[0062] The above polyethylene terephthalate may include a diol moiety derived from a comonomer other than ethylene glycol. Specifically, the comonomer may be an aromatic diol having 8 to 40 or 8 to 33 carbon atoms, an aliphatic diol having 2 to 20 or 2 to 12 carbon atoms, or a mixture thereof. Specific examples of the above aromatic diols include bisphenol A derivatives to which ethylene oxide and / or propylene oxide are added, such as polyoxyethylene-(n)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(n)-2,2-bis(4-hydroxyphenyl)propane or polyoxypropylene-(n)-polyoxyethylene-(n)-2,2-bis(4-hydroxyphenyl)propane (wherein n represents the number of polyoxyethylene or polyoxypropylene units, and may be, for example, 0 to 10), and specific examples of the above aliphatic diols include diethylene glycol, triethylene glycol, propanediol (1,2-propanediol, 1,3-propanediol, etc.), 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, Examples of linear, branched or cyclic aliphatic diols include 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, pentanediol (1,5-pentanediol, 2,4-pentanediol, etc.), 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, hexanediol (1,6-hexanediol, etc.), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and tetramethylcyclobutanediol. In one embodiment, the comonomer may be 1,2-cyclohexanedimethanol or 1,4-cyclohexanedimethanol, preferably 1,4-cyclohexanedimethanol. The comonomer may be used in an amount of 0 to 50 mol%, 0 to 30 mol%, 0 to 20 mol%, or 0 to 10 mol% relative to the total diol.

[0063] Meanwhile, virgin polyethylene terephthalate and / or recycled polyethylene terephthalate may be used as the polyethylene terephthalate.

[0064] Recycled polyethylene terephthalate can be understood to encompass all polyethylene terephthalate collected after use or obtained therefrom. Specifically, the recycled polyethylene terephthalate may be obtained by separating collected waste plastic according to certain standards, crushing and cleaning it, and then melt-extruding it and re-pelletizing it, or by depolymerizing the collected waste plastic to a monomer level and then re-polymerizing it. Depending on the processing method, such recycled polyethylene terephthalate may be re-pelletized and then crystallized for use, or may be crystallized and then further polycondensed in a solid state for use.

[0065] In one embodiment, the crystalline polyester may be a polyethylene terephthalate comprising at least 95 mol% of an acid moiety derived from terephthalic acid; and at least 85 mol% or at least 90 mol% of a diol moiety derived from ethylene glycol.

[0066] Specifically, the acid portion of the polyethylene terephthalate used as the crystalline polyester may be derived from terephthalic acid at 95 mol% or more, 98 mol% or more, or 100 mol%, and the diol portion may be derived from ethylene glycol at 85 mol% or more, 90 mol% or more, 95 mol% or more, or 97 mol% or more, or 100 mol%.

[0067] Meanwhile, the remainder of the acid portion of the polyethylene terephthalate may be derived from at least one selected from the group consisting of naphthalene dicarboxylic acids such as isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalene dicarboxylic acid, dialkyl naphthalene dicarboxylates such as dimethyl 2,6-naphthalene dicarboxylate, and diphenyl dicarboxylic acid, and the remainder of the diol portion may be derived from at least one selected from the group consisting of 1,4-cyclohexanedimethanol, diethylene glycol or triethylene glycol, propanediol (1,2-propanediol, 1,3-propanediol, etc.), 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, It may be derived from at least one selected from the group consisting of 1,4-butanediol, 2,3-butanediol, pentanediol (such as 1,5-pentanediol and 2,4-pentanediol), 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, hexanediol (such as 1,6-hexanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and tetramethylcyclobutanediol.

[0068] For example, the crystalline polyester may include polyethylene terephthalate comprising an acid moiety derived from terephthalic acid at 100 mol%; a diol moiety derived from ethylene glycol at 85 mol% or more, or at 90 mol% or more but not more than 100 mol%, or at 100 mol% or not more than 97.5 mol%, or at 95 mol% or less; and a diol moiety derived from at least one of 1,4-cyclohexanedimethanol and diethylene glycol at 0 mol%, or more than 0 mol%, or at least 2.5 mol%, or at least 5 mol% but not more than 15 mol%, or at most 10 mol%.

[0069] For example, the crystalline polyester may include a polyethylene terephthalate comprising 100 mol% of an acid moiety derived from terephthalic acid; 85 mol% or more, or 90 mol% or more but not more than 100 mol%, or 100 mol% or less, or 97.5 mol% or less, or 95 mol% or less of a diol moiety derived from ethylene glycol; 0 mol%, or greater than 0 mol%, or greater than 1.25 mol%, or greater than 2.5 mol% but not more than 7.5 mol%, or not more than 5 mol% of a diol moiety derived from 1,4-cyclohexanedimethanol; and 0 mol%, or greater than 0 mol%, or greater than 1.25 mol%, or greater than 2.5 mol% but not more than 7.5 mol%, or not more than 5 mol% of a diol moiety derived from diethylene glycol. Meanwhile, the crystalline polyester may be dissolved in orthochlorophenol at a concentration of 1.2 g / dl at 150°C for 15 minutes and have an intrinsic viscosity of 0.50 to 1.2 dl / g or 0.50 to 1.0 dl / g when measured at 35°C. A crystalline polyester satisfying the above intrinsic viscosity range exhibits excellent miscibility with the amorphous polyester described below and exhibits a transparency-enhancing effect, which is preferable.

[0070] In addition, the crystalline polyester may have a melting temperature that satisfies a range of 200°C or higher, or 220°C or higher, or 240°C or higher, and 280°C or lower, or 260°C or lower. When the melting temperature is satisfied, high-temperature drying in the range of 140 to 160°C is possible, thereby achieving a shortened drying time effect.

[0071] The above amorphous polyester is polymerized with a diol containing a dicarboxylic acid or a derivative thereof and ethylene glycol and a comonomer, and has a structure in which an acid portion derived from the dicarboxylic acid or a derivative thereof, a diol portion derived from ethylene glycol, and a diol portion derived from the comonomer are repeated.

[0072] The above dicarboxylic acid or derivative thereof may mainly be terephthalic acid or a derivative thereof, and comonomers that can be used other than the terephthalic acid or a derivative thereof are as described above.

[0073] The type of comonomer included with the above ethylene glycol is not particularly limited, and may be, for example, an aliphatic diol having 2 to 20 carbon atoms or 2 to 12 carbon atoms. Specific examples of the above aliphatic diols include diethylene glycol, triethylene glycol, propanediol (1,2-propanediol, 1,3-propanediol, etc.), 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, pentanediol (1,5-pentanediol, 2,4-pentanediol, etc.), 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, hexanediol (1,6-hexanediol, etc.), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,2-cyclohexanediol, 1,4-cyclohexanediol, Examples of linear, branched or cyclic aliphatic diols include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol and tetramethylcyclobutanediol. In one embodiment, the comonomer may be 1,4-cyclohexanedimethanol and / or diethylene glycol.

[0074] The comonomer included as a diol together with the above ethylene glycol may be included in an amount of 15 mol% or more, or 20 mol% or more, or 30 mol% or more, and 60 mol% or less, or 50 mol% or less, 45 mol% or less, 40 mol% or less, or 35 mol% or less, based on the total diol. If the content of the comonomer is less than 10 mol% based on the total diol, it is unsuitable as an amorphous polyester, and if it exceeds 60 mol%, haze may occur, so it is preferable to satisfy the above range.

[0075] Specifically, the amorphous polyester according to one embodiment of the present invention may contain a diol portion derived from 1,4-cyclohexanedimethanol in an amount of 20 mol% or more, or 25 mol% or more, and 40 mol% or less, or 35 mol% or less, among the total diol portions. By mixing the amorphous polyester, in which the content of the diol portion derived from 1,4-cyclohexanedimethanol among the diol portions satisfies the above range, with the crystalline polyester, a film exhibiting a high shrinkage ratio can be provided.

[0076] Alternatively, the amorphous polyester may contain a diol portion derived from diethylene glycol in an amount of 8 mol% or more, or 10 mol% or more, but 20 mol% or less, or 15 mol% or less, or 13 mol% or less, of the total diol portion. By mixing the amorphous polyester, in which the content of the diol portion derived from diethylene glycol in the diol portion satisfies the above range, with the crystalline polyester, a film exhibiting a high shrinkage ratio can be provided.

[0077] Meanwhile, the diol portion derived from the above diethylene glycol may be introduced by reacting two ethylene glycols to form diethylene glycol during polymerization of the polyester resin, and reacting the diethylene glycol with a dicarboxylic acid or a derivative thereof, or may be formed by adding diethylene glycol as a comonomer other than ethylene glycol during production of the polyester resin.

[0078] Alternatively, the amorphous polyester may contain a diol portion derived from 1,4-cyclohexanedimethanol in an amount of 20 mol% or more, or 25 mol% or more, or 28 mol% or more, but 35 mol% or less, or 33 mol% or less, of the total diol portion, and simultaneously contain a diol portion derived from diethylene glycol in an amount of 8 mol% or more, or 10 mol% or more, but 15 mol% or less, or 13 mol% or less. In this case, the remainder of the total diol portion of the amorphous polyester, excluding the diol portion derived from 1,4-cyclohexanedimethanol and the diol portion derived from diethylene glycol, may be a diol portion derived from ethylene glycol.

[0079]

[0080] The above-described amorphous polyester may have an intrinsic viscosity of 0.45 dl / g or more, 0.55 dl / g or more, or 0.6 dl / g or more, and 1.2 dl / g or less, 1.0 dl / g or less, 0.9 dl / g or less, or 0.8 dl / g or less, when measured at 35°C after dissolving the amorphous polyester in orthochlorophenol at a concentration of 1.2 g / dl for 15 minutes, due to the above-described structure. When this range is satisfied, the amorphous polyester may have an appropriate molecular weight and exhibit excellent mechanical properties.

[0081] The above-described non-crystalline polyester may have a glass transition temperature of 60°C or higher, 65°C or higher, or 70°C or higher, and 80°C or lower, or 75°C or lower, due to the above-described structure. If the glass transition temperature is lower than 60°C, the heat resistance is insufficient, and if it exceeds 80°C, the shrinkage rate of the film decreases, so it is preferable to satisfy the above range.

[0082] When the above polyester resin mixture contains at least one crystalline polyester and at least one amorphous polyester, each of the crystalline polyester and the amorphous polyester satisfies that the difference in weight average molecular weight is less than 20,000 g / mol. The weight average molecular weight of each of the above polyesters can be measured through gel permeation chromatography (GPC) as described later in the examples.

[0083] When the difference in the weight average molecular weight of the crystalline polyester and the non-crystalline polyester satisfies the above range, the mixing property is increased when manufacturing a polyester resin mixture, so that haze does not occur, and when manufacturing a polyester film, high adhesive strength can be achieved.

[0084] In one embodiment, the difference in weight average molecular weight between the crystalline polyester and the amorphous polyester may be 18,000 g / mol or less, or 15,000 g / mol or less. Since the crystalline polyester and the amorphous polyester may have the same weight average molecular weight, the lower limit of the difference in weight average molecular weight is not particularly limited.

[0085] The weight average molecular weight of each of the above crystalline polyester and amorphous polyester may be 60,000 g / mol or more, 70,000 g / mol or more, or 80,000 g / mol or more, and 150,000 g / mol or less, 130,000 g / mol or less, 110,000 g / mol or less, or 100,000 g / mol or less.

[0086] When the above crystalline polyester and the amorphous polyester each satisfy the above weight average molecular weight range and the difference in weight average molecular weight between them is less than 20,000 g / mol, the polyester film can exhibit excellent adhesiveness and excellent blendability.

[0087] The polyester resin mixture included in the polyester film according to one embodiment of the present invention contains 10 to 60 wt% of the crystalline polyester and 40 to 90 wt% of the amorphous polyester, and thus exhibits excellent adhesive properties and heat shrinkage properties.

[0088] From this point of view, the crystalline polyester in the polyester resin mixture may be 10 wt% or more, 12 wt% or more, 15 wt% or more, or 20 wt% or more, but 60 wt% or less, and the remainder other than the crystalline polyester may be an amorphous polyester.

[0089] Meanwhile, since the polyester resin mixture includes a crystalline polyester and an amorphous polyester, the diol portion derived from 1,4-cyclohexanedimethanol may be included in an amount of 8 mol% or more, or 8.5 mol% or more, and 35 mol% or less, or 30 mol% or less, or 25 mol% or less, of the total diol portion. Here, the 'total diol portion of the polyester resin mixture' means the sum of the diol portion of the crystalline polyester and the diol portion of the amorphous polyester included in the polyester resin mixture.

[0090] The above polyester resin mixture exhibits excellent heat shrinkage properties and high adhesive strength as it contains a diol portion derived from 1,4-cyclohexanedimethanol among the total diol portions in the above-described range.

[0091] In addition, the polyester resin mixture may contain 2 to 20 mol% of a diol portion derived from diethylene glycol among the total diol portions, and thus the film may exhibit high shrinkage characteristics. For example, the polyester resin mixture may contain 5 mol% or more, 6 mol% or more, or 7 mol% or more, and 20 mol% or less, 18 mol% or less, 15 mol% or less, or 11 mol% or less of a diol portion derived from diethylene glycol among the total diol portions.

[0092]

[0093] polyester film

[0094]

[0095] A polyester film according to one embodiment of the present invention can exhibit excellent shrinkage properties, bonding properties, and crystallization properties.

[0096] Specifically, the polyester film exhibits excellent adhesive properties, with a peel strength of 100 g·f or more, 120 g·f or more, 130 g·f or more, or 150 g·f or more, as measured after bonding with a tetrahydrofuran solvent. The higher the peel strength, the better it is, and theoretically, there is no upper limit, but for example, it may be 300 g·f or less, 280 g·f or less, or 260 g·f or less.

[0097] The above polyester film is 1 st Heat of fusion in scan and 2 nd Difference in heat of fusion from scan (1 st ΔHm - 2 nd ΔHm) is 2 j / g or more, 2.5 j / g or more, or 3 j / g or more, exhibiting an excellent crystallization effect. The above 1 st Heat of fusion in scan and 2 nd The greater the difference between the melting heat in the scan and the film, the higher the shrinkage rate and the more transparent the film can be while simultaneously exhibiting a crystallization effect.

[0098] The above polyester film has a low shrinkage initiation temperature of 75°C or lower, 72°C or lower, 70°C or lower, 67°C or lower, or 65°C or lower, and can be molded with excellent quality without deformation or clouding of the PET container when used as a heat shrink label for a PET container. The shrinkage initiation temperature may be, for example, 30°C or higher, or 50°C or higher.

[0099] The above polyester film can provide a heat shrinkable film of excellent quality by exhibiting a maximum shrinkage ratio of 40% or more, 45% or more, 48% or more, 55% or more, 60% or more, 65% or more, or 70% or more at 95°C. The upper limit of the maximum shrinkage ratio is not particularly limited, and may be, for example, 85% or less.

[0100] The above polyester film may be dissolved in orthochlorophenol at a concentration of 1.2 g / dl at 150°C for 15 minutes and have an intrinsic viscosity measured at 35°C of 0.5 dL / g or more, 0.6 dL / g or more, or 0.65 dL / g or more, and 1.0 dL / g or less, 0.9 dL / g or less, 0.8 dL / g or less, or 0.75 dL / g or less.

[0101] The above polyester film may be a single-layer film or a multi-layer film comprising two or more layers.

[0102] When the above polyester film is a single-layer film, it may be suitable to exhibit excellent shrinkage properties and adhesive properties to manufacture the single-layer film from a polyester resin mixture containing crystalline polyester in an amount of 10 wt% or more, 15 wt% or more, or 20 wt% or more, but not more than 60 wt%, and containing amorphous polyester as the remainder.

[0103] If the above polyester film is a multilayer film, the multilayer film may include a core layer and a skin layer.

[0104] The surface layer may be formed on one or both sides of the core layer, so that at least one surface of the polyester film may be a surface layer. In this structure, by controlling the types and mixing ratio of crystalline polyester and amorphous polyester so that the core layer exhibits excellent shrinkage characteristics, and controlling the types and mixing ratio of crystalline polyester and amorphous polyester so that the surface layer exhibits crystallinity, a heat shrinkable film having excellent shrinkage characteristics and being recyclable with PET containers without causing a fusion phenomenon even when supplied to PET containers and recycling streams can be provided.

[0105] For example, the core layer may contain crystalline polyester and amorphous polyester in a weight ratio of 0:100 to 60:40, and the surface layer may contain crystalline polyester and amorphous polyester in a weight ratio of 10:90 to 60:40, in which case excellent shrinkage properties, adhesive properties, and crystallinity can be exhibited simultaneously.

[0106] Meanwhile, the polyester film may include two or more core layers and two or more surface layers. For example, the polyester film may have a structure in which a first core layer is formed on a first surface layer, and a second surface layer is formed on the first core layer. As another example, the polyester film may have a structure in which a first surface layer is formed on a first core layer, a second core layer is formed on the first surface layer, and again a second surface layer is formed on the second core layer.

[0107] Regardless of the structure of the polyester film, i.e., whether it is single-layer or multi-layer, the content of crystalline polyester among the polyesters contained in the entire polyester film is adjusted to 10 to 60 wt%, and the content of non-crystalline polyester is adjusted to 40 to 90 wt%, so as to exhibit excellent shrinkage properties, adhesive properties, and crystallinity.

[0108] The thickness of the polyester film is not particularly limited, but may be 3 ㎛ to 350 ㎛. If the polyester film is a multilayer film, the percentage of the core layer thickness to the thickness of the polyester film (thickness of the core layer / thickness of the polyester film X 100) may be 35% to 92.5%, and the percentage of the surface layer thickness to the thickness of the polyester film (thickness of the surface layer / thickness of the polyester film X 100) may be 7.5% to 65%.

[0109]

[0110] Method for manufacturing polyester film

[0111] In one embodiment of the present invention, a method for producing the polyester film is provided. Specifically, the method for producing the polyester film comprises the steps of: producing a polyester resin mixture comprising a crystalline polyester and an amorphous polyester having a difference in weight average molecular weight of less than 20,000 g / mol; melting and extruding the polyester resin mixture to produce an unstretched film; and stretching the unstretched film in one or more directions.

[0112]

[0113] Manufacturing of polyester

[0114]

[0115] The above crystalline and amorphous polyester resins can be commercially available or manufactured using known methods.

[0116] For example, the crystalline and amorphous polyester resins can be produced through an esterification reaction or ester exchange reaction step between the above-described dicarboxylic acid or its derivative and the above-described diol; and a polycondensation reaction step of the esterification or ester exchange reaction product. At this time, the contents of the monomers dicarboxylic acid or its derivative and the diol can be appropriately controlled in consideration of the composition of the acid portion and the diol portion of the desired polyester resin, and the relative reactivity of each monomer.

[0117] In the above esterification reaction or ester exchange reaction, a catalyst is not necessarily required, but a catalyst may be optionally used to shorten the reaction time. Examples of such catalysts include methylates of sodium and magnesium; acetates, borates, fatty acids, and carbonates of Zn, Cd, Mn, Co, Ca, and Ba; oxides of metal Mg; and oxides of Pb, Zn, Sb, and Ge.

[0118] The above esterification reaction or ester exchange reaction can be carried out in a batch, semi-continuous or continuous manner, and each raw material can be introduced separately, but it is preferable to introduce it in the form of a slurry in which a diol is mixed with a dicarboxylic acid or a derivative thereof. The diol can be introduced in a ratio of about 1.2 to 3.0 moles per 1 mole of the dicarboxylic acid or a derivative thereof.

[0119] A polycondensation catalyst, stabilizer, colorant, crystallizer, antioxidant, branching agent, etc. may be added to the slurry before the esterification reaction or ester exchange reaction begins, or to the product after the reaction is completed. However, the timing of adding the above-described additives is not limited thereto, and they may be added at any time during the manufacturing process of the polyester resin.

[0120] As the above polycondensation catalyst, one or more of the usual titanium, germanium, antimony, aluminum, and tin compounds can be appropriately selected and used. Among these, the titanium catalyst can copolymerize a large amount of cyclohexanedimethanol with terephthalic acid or a derivative thereof, and can perform the same level of reaction even when using a small amount compared to the antimony catalyst, and has the advantage of being cheaper than the germanium catalyst. Useful titanium-based catalysts include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate, triethanolamine titanate, acetyl acetonate titanate, ethyl acetoacetic ester titanate, isostearyl titanate, titanium dioxide, titanium dioxide / silicon dioxide coprecipitate, titanium dioxide / zirconium dioxide coprecipitate, etc. The amount of the polycondensation catalyst used may vary depending on the desired color and the stabilizer and coloring agent used, but since it affects the color of the polymerized polyester resin, it may be used so that the amount of titanium element relative to the weight of the polyester resin is about 1 to 100 ppm, more preferably about 1 to 50 ppm. If the amount of the titanium element is less than about 1 ppm, the desired degree of polymerization cannot be achieved, and if it exceeds about 100 ppm, the color of the polyester resin becomes yellow, making it difficult to obtain a transparent polyester film.

[0121] As the above stabilizer, phosphorus compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethylphosphonoacetate can generally be used, and the amount added can be 10 to 200 ppm based on the amount of phosphorus element relative to the weight of the polyester resin. If the amount of the stabilizer added is less than 10 ppm, the stabilizing effect may be insufficient, and the color of the polyester resin may turn yellow. If it exceeds 200 ppm, there is a concern that a polyester resin with a desired high polymerization degree may not be obtained. In addition, examples of coloring agents added to improve the color of the polyester resin include common coloring agents such as cobalt acetate and cobalt propionate, and the amount added can be 10 to 200 ppm based on the amount of cobalt element relative to the weight of the polyester resin. If necessary, anthraquinone compounds, perinone compounds, azo compounds, methine compounds, etc. can be used as organic compound coloring agents, and commercially available products include toners such as Polysynthren Blue RLS from Clarient or Solvaperm Red BB from Clarient. The amount of the organic compound coloring agent added can be adjusted to 0 to 50 ppm based on the weight of the polyester resin. If the coloring agent is used in an amount outside the above range, the yellow color of the polyester resin may not be sufficiently covered or the physical properties may be deteriorated.

[0122] Examples of the crystallizer include a crystal nucleating agent, an ultraviolet absorber, a polyolefin resin, a polyamide resin, and the like. Examples of the antioxidant include a hindered phenol antioxidant, a phosphite antioxidant, a thioether antioxidant, or a mixture thereof. Examples of the branching agent include a typical branching agent having three or more functional groups, such as trimellitic anhydride, trimethylol propane, trimellitic acid, or a mixture thereof.

[0123] The above esterification reaction can be carried out at a temperature of about 200 to 300°C, about 230 to 280°C, about 230 to 265°C, or about 245 to 255°C and a pressure of 0 to 10.0 kgf / cm2 (0 to 7355.6 mmHg), 0 to 5.0 kgf / cm2 (0 to 3677.8 mmHg), 0.1 to 3.0 kgf / cm2 (73.6 to 2206.7 mmHg), or 1.0 to 3.0 kgf / cm2 (736 to 2206.7 mmHg). And, the above ester exchange reaction can be carried out under conditions of a temperature of 150 to 270°C or 180 to 260°C and a pressure of 0 to 5.0 kgf / cm2 (0 to 3677.8 mmHg) or 0.1 to 3.0 kgf / cm2 (73.6 to 2206.7 mmHg). Here, the pressure written outside the parentheses means the gauge pressure (written in kgf / cm2 units), and the pressure written in the parentheses means the absolute pressure (written in mmHg units).

[0124] If the above reaction temperature and pressure are outside the above range, there is a risk that the properties of the polyester resin may deteriorate. The above reaction time (average residence time) is typically 1 to 24 hours or 100 to 300 minutes, and may vary depending on the reaction temperature, pressure, and the molar ratio of the diol to the dicarboxylic acid or its derivative used.

[0125] The product obtained through the above esterification or ester exchange reaction can be manufactured into a polyester resin with a higher degree of polymerization through a polycondensation reaction. Generally, the polycondensation reaction is carried out at a temperature of 150 to 300°C, 200 to 290°C, 260 to 290°C, 260 to 280°C, or 265 to 275°C and a reduced pressure of 400 to 0.01 mmHg, 100 to 0.05 mmHg, or 10 to 0.1 mmHg. Here, the pressure refers to the range of absolute pressure. The reduced pressure condition of 400 to 0.01 mmHg is to remove by-products of the polycondensation reaction such as glycol and unreacted products such as cyclohexanedimethanol. Therefore, if the reduced pressure condition is outside the above range, there is a concern that the removal of by-products and unreacted products may be insufficient. Additionally, if the polycondensation reaction temperature exceeds the above range, there is a risk that the properties of the polyester resin may deteriorate. The polycondensation reaction is carried out for a period of time necessary to reach the desired intrinsic viscosity, for example, for an average residence time of 1 to 24 hours.

[0126] In order to reduce the content of unreacted substances such as cyclohexanedimethanol remaining in the polyester resin, the vacuum reaction can be intentionally maintained for a long time at the end of the esterification reaction or ester exchange reaction or at the beginning of the polycondensation reaction, that is, when the viscosity of the resin is not sufficiently high, so that the unreacted raw materials can flow out of the system. As the viscosity of the resin increases, it becomes difficult for the raw materials remaining in the reactor to flow out of the system. For example, by leaving the reaction product obtained through the esterification reaction or ester exchange reaction before the polycondensation reaction under a reduced pressure condition of about 400 to 1 mmHg or about 200 to 3 mmHg for 0.2 to 3 hours, unreacted substances such as ethylene glycol and cyclohexanedimethanol remaining in the polyester resin can be effectively removed. At this time, the temperature of the product can be controlled to be the same as or between the esterification reaction or ester exchange reaction temperature or the polycondensation reaction temperature.

[0127] By adding a process for discharging unreacted raw materials to the outside of the system as described above, the content of unreacted materials such as cyclohexanedimethanol remaining in the polyester resin can be reduced, and as a result, a polyester resin capable of realizing the desired physical properties at a superior level can be manufactured.

[0128] Meanwhile, the intrinsic viscosity of the polymer after the polycondensation reaction is suitably 0.30 to 1.0 dl / g. If the intrinsic viscosity is less than 0.30 dl / g, the reaction rate in the solid-state reaction is significantly reduced, and if the intrinsic viscosity exceeds 1.0 dl / g, the viscosity of the melt increases during melt polymerization, which increases the possibility of the polymer being discolored due to shear stress between the stirrer and the reactor, and by-reactants such as acetaldehyde also increase.

[0129] The crystalline polyester resin according to the above embodiment can have a higher degree of polymerization by additionally performing a solid-state reaction after the polycondensation reaction, if necessary.

[0130] Specifically, the polymer obtained through the polycondensation reaction is discharged from the reactor and granulated. The granulation method can be the strand cutting method, which extrudes the polymer into a strand shape, solidifies it in a cooling liquid, and then cuts it with a cutter, or the underwater cutting method, which immerses the die hole in a cooling liquid, extrudes it directly into the cooling liquid, and then cuts it with a cutter. In general, in the strand cutting method, the temperature of the cooling liquid must be kept low so that the strand is well solidified to avoid cutting problems. In the underwater cutting method, it is preferable to maintain the temperature of the cooling liquid appropriate for the polymer so that the shape of the polymer is uniform. However, in the case of crystalline polymers, the temperature of the cooling liquid may be intentionally kept high to induce crystallization during discharge.

[0131] Water washing of the granulated polymer can remove unreacted raw materials, such as cyclohexanedimethanol, that are soluble in water. Smaller particles are advantageous because the surface area relative to the particle weight increases with smaller particles. To achieve this goal, the particles can be manufactured to have an average weight of about 15 mg or less. For example, the granulated polymer can be washed by leaving it in water at a temperature equal to or about 5 to 20°C lower than the glass transition temperature of the polymer for 5 minutes to 10 hours.

[0132] For granulated crystalline polymers, a crystallization step is performed to prevent fusion during the solid-state reaction. This can be performed in the air, inert gas, steam, inert gas containing steam, or in a solution, and the crystallization process is performed at 110°C to 210°C or 120°C to 210°C. If the temperature is low, the rate at which crystals are formed in the particles becomes too slow, and if the temperature is high, the rate at which the surface of the particles melts exceeds the rate at which crystals are formed, causing the particles to stick together and fuse. As the particles crystallize, their heat resistance increases, so it is possible to divide the crystallization into several stages and increase the temperature step by step to crystallize.

[0133] The solid-state reaction can be carried out under an inert gas atmosphere such as nitrogen, carbon dioxide, or argon, or under reduced pressure conditions of 400 to 0.01 mmHg and a temperature of 180 to 220°C for an average residence time of 1 to 150 hours. Through this solid-state reaction, the molecular weight is additionally increased, and raw materials that remain unreacted in the melting reaction and cyclic oligomers, acetaldehyde, etc. generated during the reaction can be removed.

[0134] The above crystallized polymer can be solid-phase polymerized by dissolving it in orthochlorophenol at a concentration of 1.2 g / dl at 150°C for 15 minutes, so that the intrinsic viscosity measured at 35°C reaches a value of 0.65 dl / g or more, 0.70 dl / g or more, 0.75 dl / g or more, or 0.80 dl / g or more.

[0135]

[0136] Preparation of polyester resin mixtures

[0137]

[0138] The above polyester resin mixture can be provided by preparing crystalline polyester and amorphous polyester in the form of chips or pellets, drying them, and then mixing them using a stirrer.

[0139] Specifically, the crystalline polyester and the amorphous polyester can be formed into chips or pellets through a twin-screw extruder. Then, the crystalline polyester in the form of chips or pellets can be dried at about 120 to 170°C, and separately, the amorphous polyester in the form of chips or pellets can be dried at about 50 to 75°C, and then the components can be mixed using a stirrer to prepare a polyester resin mixture. Alternatively, the crystalline polyester in the form of chips or pellets and the amorphous polyester in the form of chips or pellets can be dried together at about 50 to 160°C, and then the components can be mixed using a stirrer to prepare a polyester resin mixture.

[0140]

[0141] Manufacturing of unstretched films

[0142]

[0143] Thereafter, the prepared polyester resin mixture can be molded to produce an unstretched film. The polyester resin mixture can be molded at a temperature of about 230°C to 310°C, about 240°C to 300°C, or about 250°C to 290°C to minimize thermal decomposition of the polymer, thereby maintaining the long-chain structure of the polymer, and minimizing damage or breakage of the film during the subsequent stretching process.

[0144] Specifically, a mixture of polyethylene terephthalate and polyester resin in the form of chips or pellets is fed to an extruder, and the temperature of the cylinder is controlled within the above-described range to obtain an unstretched film.

[0145] If the polyester film has a multilayer structure, two or more layers can be formed sequentially or simultaneously. That is, each layer can be formed sequentially by forming one layer and then forming another layer on top of it, or two or more layers can be formed simultaneously by co-extrusion or other methods.

[0146] The unstretched film obtained by the above method can be cooled to an appropriate temperature. Although not particularly limited, the manufactured unstretched film can be pressed against a cooling roll at a temperature of about 10 to 70°C, then wound, and supplied to the next process.

[0147]

[0148] Manufacturing of stretch films

[0149]

[0150] In the step of stretching the above unstretched film, the above unstretched film can be stretched in the longitudinal direction (MD direction) and / or transverse direction (TD direction) to provide a uniaxially stretched film or a biaxially stretched film.

[0151] The stretching temperature of the above-mentioned unstretched film may be a temperature higher than the glass transition temperature of the above-mentioned polyester resin. Specifically, the above-mentioned unstretched film may be stretched at a temperature of 55°C to 180°C or 60°C to 170°C.

[0152] The above unstretched film can be stretched at a high magnification. For example, the above unstretched film can be uniaxially stretched at a transverse stretch ratio of 2 to 6 times or a longitudinal stretch ratio of 1.1 to 6 times. Furthermore, as another example, the above unstretched film can be biaxially stretched at a transverse stretch ratio of 1.5 to 5 times and a longitudinal stretch ratio of 1.1 to 5 times.

[0153]

[0154] The above polyester film can be applied to various technical fields to which the present invention belongs, but is expected to be particularly useful as a heat shrinkable label for PET containers, etc. due to its excellent shrinkage and bonding properties.

[0155]

[0156] Hereinafter, the functions and effects of the invention will be described in more detail through specific examples of the invention. However, these examples are provided merely as examples of the invention and do not define the scope of the invention.

[0157]

[0158] <Method of Measuring Physical Properties>

[0159] The physical properties of each resin or film were measured by the following method.

[0160]

[0161] (1) Differential scanning calorimetry

[0162] The sample was filled in an aluminum pan in a differential scanning calorimeter (DSC, DSC 1 from Mettler Toledo), heated from 30°C to 280°C at a rate of 10°C / min, and maintained at 280°C for 5 minutes (1 st scan), -300℃ / min to 30℃, then increased to 280℃ at 10℃ / min (2 nd The glass transition temperature (Tg), melting temperature (Tm), and heat of fusion (ΔHm) were measured from the heat flow obtained when scanning.

[0163]

[0164] (2) Intrinsic viscosity (IV)

[0165] The resin was dissolved in o-chlorophenol at a concentration of 1.2 g / dl, and the intrinsic viscosity was measured using an Ubbelohde viscometer.

[0166] At this time, when the temperature of the viscosity tube is maintained at 35℃, and the time taken for the solvent to pass between the sections ab inside the viscosity tube (efflux time) is t, and the time taken for the solution to pass is t0, the specific viscosity is defined as in the following mathematical equation 1. Using this specific viscosity, the intrinsic viscosity was calculated using the following mathematical equation 2.

[0167] [Mathematical Formula 1]

[0168]

[0169] [Equation 2]

[0170]

[0171] In the above mathematical expression 2, A is the Huggins constant, which is 0.247, and c is the concentration value, which is 1.2 g / dl.

[0172]

[0173] (3) Weight average molecular weight (Mw)

[0174] The weight average molecular weight of each resin was measured using gel permeation chromatography (GPC) and RI detector from Tosoh.

[0175] A sample was prepared by dissolving 0.03 g of the resin in 3 mL of o-chlorophenol at 150°C for 15 minutes, and then adding 9 mL of chloroform at room temperature. Using 12 mL of a 1:3 (v / v) solution of o-chlorophenol:chloroform as an eluent, the sample was injected at a flow rate of 0.7 mL / min at 40°C for measurement. The Mw value was derived using a calibration curve formed using polystyrene standards. Nine types of polystyrene standards with molecular weights of 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000 (g / mol) were used.

[0176]

[0177] (4) Maximum shrinkage ratio

[0178] Polyester film was cut into a 5 cm X 5 cm square shape, immersed in warm water at 95°C for 10 seconds, and then taken out. Then, the ratio of the reduced length to the initial length was calculated as shown in the following equation, and defined as the maximum shrinkage at 95°C.

[0179] Maximum shrinkage (%) = (Initial length - length measured after immersion) / Initial length Х100

[0180]

[0181] (5) Shrinkage initiation temperature

[0182] Polyester film was cut into a 5 cm × 5 cm square shape, immersed in hot water at each temperature in the temperature range of 55°C to 100°C for 10 seconds, and then taken out. Then, the ratio of the reduced length to the initial length was calculated, and the temperature at which the film shrank by 2% or less was defined as the shrinkage initiation temperature.

[0183]

[0184] (6) Bonding properties

[0185] As shown in Fig. 1, 10 μL of tetrahydrofuran (THF) was applied to the end of a polyester film with a length (l) of 100 mm and a width (w) of 15 mm (the length of the application surface (l) a ) 15 mm, width (w) 15 mm), and a film of the same specification was rolled over the THF-coated surface, and then bonded by applying uniform pressure. The part marked as “B” in Fig. 1 is the part where each polyester film overlaps (THF-coated surface), and the part marked as “A” is the part where each polyester film does not overlap.

[0186] After aging the above-mentioned adhesive films for 10 minutes, the maximum force (gf) at which the heat-shrinkable films separate was measured by pulling one end at a speed of 200 mm / min using a tensile tester (Instron UTM). The peel force was measured three times for each film and the average value was calculated.

[0187]

[0188] (7) Haze (Haze)

[0189] The polyester film was aged for 24 hours in an atmosphere of 23˚C and 65%RH, and then, in accordance with JIS (Japanese Industrial Standards) K7136, the haze (%) was measured at three different locations of the film sample using a haze meter (equipment name: NDH2000, manufacturer: Nippon Denshoku (Japan)), and the average of the individual measurement results was calculated as the result.

[0190]

[0191] <Manufacturing Example: Manufacturing of Crystalline Resin and Amorphous Resin>

[0192]

[0193] Manufacturing Example 1: Manufacturing of Resin 1

[0194] In a 10 L reactor, 100 mol% of terephthalic acid (PTA), 31.5 mol% of 1,4-cyclohexanedimethanol (CHDM), 12 mol% of diethylene glycol (DEG), and 86 mol% of ethylene glycol (EG) were mixed, 0.5 g of tetrabutyl titanate as a catalyst and 0.4 g of triethyl phosphate as a stabilizer were added, and the esterification reaction was performed at atmospheric pressure (760 mmHg) and a temperature of 250 to 260°C. When the production and discharge of water were completed, the contents of the reactor were transferred to a 7 L polycondensation reactor equipped with a stirrer, a cooling condenser, and a vacuum system.

[0195] The polycondensation reaction was carried out at an internal temperature of 240°C to 275°C and a pressure of 50 mmHg in a polycondensation reactor until the intrinsic viscosity (IV) of the reactant became 0.78 dl / g. Thereafter, the reactant was discharged and cut into chips to obtain an amorphous glycol-modified polyethylene terephthalate (PETG) resin 1.

[0196]

[0197] Manufacturing Example 2: Manufacturing of Resin 2

[0198] In a 10 L reactor, 100 mol% of terephthalic acid, 28.5 mol% of 1,4-cyclohexanedimethanol, 13 mol% of diethylene glycol, and 86 mol% of ethylene glycol were mixed, 0.5 g of tetrabutyl titanate as a catalyst and 0.4 g of triethyl phosphate as a stabilizer were added, and the esterification reaction was performed at atmospheric pressure (760 mmHg) and a temperature of 250 to 260°C. When the production and discharge of water were completed, the contents of the reactor were transferred to a 7 L polycondensation reactor equipped with a stirrer, a cooling condenser, and a vacuum system.

[0199] The polycondensation reaction was carried out at an internal temperature of 240°C to 275°C and a pressure of 50 mmHg in a polycondensation reactor until the intrinsic viscosity (IV) of the reactant reached 0.74 dl / g. Thereafter, the reactant was discharged and cut into chips to obtain amorphous glycol-modified polyethylene terephthalate (PETG) resin 2.

[0200]

[0201] Manufacturing Example 3: Manufacturing of Resin 3

[0202] After mixing 100 mol% of terephthalic acid, 5 mol% of 1,4-cyclohexanedimethanol, 2 mol% of diethylene glycol, and 120 mol% of ethylene glycol in a 10 L reactor, an esterification reaction was performed at atmospheric pressure (760 mmHg) and a temperature of 250 to 260°C.

[0203] 0.5 g of tetrabutyl titanate was added as a catalyst and 0.4 g of triethyl phosphate as a stabilizer. After the production and discharge of water were completed, the contents of the reactor were transferred to a 7 L polycondensation reactor equipped with a stirrer, a cooling condenser, and a vacuum system.

[0204] The polycondensation reaction was performed at an internal temperature of 240°C to 275°C and a pressure of 50 mmHg in the polycondensation reactor until the intrinsic viscosity (IV) reached 0.60 dl / g. Thereafter, the reactant was discharged and cut into chips.

[0205] The above chip particles were crystallized in a nitrogen oven at 150°C for 1 hour and then placed in a 20 L solid-state polymerization reactor. Thereafter, solid-state polymerization was performed at 250°C under a nitrogen atmosphere (nitrogen supply rate 50 L / min) while supplying nitrogen at a rate until the intrinsic viscosity (IV) reached 0.80 dl / g, thereby obtaining crystalline 1,4-cyclohexanedimethanol modified polyethylene terephthalate (CHDM modified PET) resin 3.

[0206]

[0207] Manufacturing Example 4: Manufacturing of Resin 4

[0208] Polyethylene terephthalate (PET) containers were crushed to produce flakes. The flakes were fed into an extruder, melted, cooled, and then cut into chips to produce pellets. The pellets were then crystallized in a nitrogen oven at 150°C for 1 hour.

[0209] Next, the above crystallized pellets were placed in a 20 L solid-state polymerization reactor and solid-state polymerization was performed at a temperature of 250°C under a nitrogen atmosphere (nitrogen supply rate 50 L / min) until the intrinsic viscosity (IV) reached 0.73 dl / g, thereby obtaining crystalline reusable PET (post-consumer resin PET, PCR-PET) resin 4.

[0210]

[0211] Manufacturing Example 5: Manufacturing of Resin 5

[0212] Polyethylene terephthalate (PET) containers were crushed to produce flakes. The flakes were fed into an extruder, melted, cooled, and cut into chips to produce pellets. The pellets were then crystallized at 150°C for 1 hour to obtain crystalline PCR-PET resin 5.

[0213]

[0214] Manufacturing Example 6: Manufacturing of Resin 6

[0215] In a 10 L reactor, 100 mol% terephthalic acid, 24 mol% neopentyl glycol (NPG), 8 mol% diethylene glycol, and 100 mol% ethylene glycol were mixed, and 8 g of GeO2 as a catalyst and 0.7 g of triethyl phosphate as a stabilizer were added, and the esterification reaction was performed at atmospheric pressure (760 mmHg) and a temperature of 250 to 260°C. When the production and discharge of water were completed, the contents of the reactor were transferred to a 7 L polycondensation reactor equipped with a stirrer, a cooling condenser, and a vacuum system.

[0216] A polycondensation reaction was performed at an internal temperature of 240°C to 275°C and a pressure of 50 mmHg in a polycondensation reactor. Thereafter, the reactant was discharged and cut into chips to obtain crystalline neopentyl glycol-modified polyethylene terephthalate (NPG-PET) resin 6.

[0217]

[0218] The composition (content of each monomer-derived residue) and physical properties of the diol portion of resins 1 to 6 manufactured according to the above manufacturing examples 1 to 6 are described in Table 1 below.

[0219]

[0220] Unit Resin 1 Resin 2 Resin 3 Resin 4 Resin 5 Resin 6 Type Amorphous PETG Amorphous PETG CHDM modified PETPCR-PETPCR-PETNPG-PET Terephthalic acid Mole% 100 100 100 100 100 Diol composition CHD MMole% 31.5 28.55 000 EGMole% 56.5 58.59 09 7.59 7.37 3 DEGMole% 12 13 52.5 2.78 NP GMole% 00000 19 DSC 2nd Tg℃ 7 17 0 79 80 80 73 Tm℃ None None 24 0 25 0 24 9 None Resin Physical properties IVdL / g0.780.740.800.730.590.66Mwg / mole85,00080,00095,00082,00058,00069,000

[0221]

[0222] <Example>

[0223] Examples 1 to 3 and Comparative Examples 1 to 6: Preparation of single-layer polyester films

[0224] Each resin mixture was prepared using the above resins 1 to 6 with the composition shown in Table 2.

[0225] The polyester resin mixture prepared above was extruded through a die at a temperature of 250°C to 290°C, and then cooled to 20°C to 50°C to produce a single-layer unstretched film. Thereafter, the unstretched film was reheated to 75°C to 90°C and stretched 5 times in the transverse direction to produce a polyester film.

[0226] The thickness of the manufactured polyester film was 50 ㎛.

[0227]

[0228] Examples 4 to 9 and Comparative Examples 7 to 12: Preparation of multilayer polyester films

[0229] Using the above resins 1 to 6, a resin mixture for forming a core layer and a resin mixture for forming a surface layer were prepared with the compositions shown in Table 3.

[0230] A polyester resin mixture for forming a core layer and a polyester resin mixture for forming a surface layer were co-extruded through a die at a temperature of 250°C to 290°C, and then cooled to 20°C to 50°C to produce a three-layer unstretched film having first and second surface layers formed on both sides of the core layer. Thereafter, the unstretched film was reheated to 75°C to 90°C and stretched 5 times in the transverse direction to produce a polyester film.

[0231] The thickness of the core layer of the polyester film of Examples 4 to 6 and Comparative Example 10 was 45 ㎛, and the thickness of each surface layer was 2.5 ㎛.

[0232] The thickness of the core layer of the polyester films of Examples 7 to 9, Comparative Examples 7 to 9, and Comparative Examples 11 to 12 was 40 μm, and the thickness of each surface layer was 5 μm.

[0233]

[0234] The intrinsic viscosity, maximum shrinkage, shrinkage onset temperature, DSC analysis results, adhesive properties, and haze measurement results of the films manufactured in each of the above examples and comparative examples are shown in Tables 2 and 3 below.

[0235]

[0236]

[0237] a Diol composition of the resin mixture

[0238] * ND: Below the quantitative limit (20 g·f), not measurable

[0239] * None: Not observed

[0240]

[0241]

[0242] a Diol composition of the resin mixture

[0243] * ND: Below the quantitative limit (20 g·f), not measurable

[0244] * None: Not observed

[0245]

[0246] Referring to Tables 2 and 3 above, the polyester films of Examples 1 to 9 had a DSC analysis value of 1 st Heat of fusion in scan and 2 nd Difference in heat of fusion in scan (1 st ΔHm - 2 nd It can be confirmed that the film has crystallinity of ΔHm) of 2 j / g or more, has a low shrinkage initiation temperature, has excellent shrinkage and adhesive properties, and exhibits excellent appearance properties without haze.

[0247] On the other hand, it can be confirmed that the polyester films of Comparative Examples 1 to 12 exhibit amorphous properties (neither 1st nor 2nd Tm nor ΔHm are observed in DSC analysis) or have inferior shrinkage properties, adhesive properties, and / or appearance properties compared to Examples 1 to 9.

Claims

1. A polyester film comprising a polyester resin mixture, Using a differential scanning calorimeter (DSC), the temperature was increased from 30°C to 280°C at a rate of 10°C / min and maintained at 280°C for 5 minutes (1 st Scan), -300℃ / min to 30℃, then increased to 280℃ at 10℃ / min (2 nd 1 measured from the heat flow obtained when scanning st Heat of fusion in scan and 2 nd Difference in heat of fusion in scan (1 st ΔHm - 2 nd ΔHm) is 2 j / g or more, When two sheets of the polyester film are bonded with tetrahydrofuran and one end of the polyester film is pulled at a speed of 200 mm / min using a tensile tester, the peeling force, which is defined as the maximum force when the two sheets of the polyester film are separated, is 100 g·f or more. Polyester film.

2. In paragraph 1, The shrinkage initiation temperature is 75 ℃ or lower, Polyester film.

3. In paragraph 1 or 2, With a maximum shrinkage of 40% or more at 95℃, Polyester film.

4. In any one of paragraphs 1 to 3, Having an intrinsic viscosity of 0.5 to 1.0 dL / g, Polyester film.

5. In any one of paragraphs 1 to 4, The above polyester resin mixture, crystalline polyester; and A non-crystalline polyester comprising a difference in weight average molecular weight between the crystalline polyester and the non-crystalline polyester of less than 20,000 g / mol, Polyester film.

6. In paragraph 5, Comprising 10 to 60 wt% of crystalline polyester and 40 to 90 wt% of amorphous polyester, Polyester film.

7. In any one of paragraphs 1 to 6, The polyester resin mixture contains 8 to 35 mol% of a diol portion derived from 1,4-cyclohexanedimethanol among the total diol portions. Polyester film.

8. In any one of paragraphs 1 to 7, The polyester resin mixture contains 2 to 20 mol% of a diol portion derived from diethylene glycol among the total diol portions. Polyester film.

9. In any one of paragraphs 5 to 8, The weight average molecular weights of the above crystalline polyester and amorphous polyester are each 60,000 to 150,000 g / mol. Polyester film.

10. In any one of paragraphs 5 to 9, The above crystalline polyester an acid moiety derived from terephthalic acid of at least 95 mol%; and A polyethylene terephthalate comprising a diol portion derived from ethylene glycol of at least 85 mol%, Polyester film.

11. In any one of paragraphs 5 to 10, The above amorphous polyester comprises an acid moiety derived from a dicarboxylic acid or a derivative thereof; and a diol moiety derived from a diol comprising ethylene glycol and a comonomer; The above monomer comprises 1,4-cyclohexanedimethanol and / or diethylene glycol. Polyester film.

12. In paragraph 11, The above amorphous polyester comprises 20 to 40 mol% of a diol portion derived from 1,4-cyclohexanedimethanol among the total diol portions. Polyester film.

13. In paragraph 11 or 12, The above amorphous polyester contains 10 to 20 mol% of a diol portion derived from diethylene glycol among the total diol portions. Polyester film.

14. In paragraph 1, The above polyester film is a single-layer film, Polyester film.

15. In paragraph 1, The above polyester film is a multilayer film including a core layer and a surface layer formed on one or both sides of the core layer. Polyester film.

16. In paragraph 15, The core layer comprises crystalline polyester and amorphous polyester in a weight ratio of 0:100 to 60:40, The surface layer comprises crystalline polyester and non-crystalline polyester in a weight ratio of 10:90 to 60:

40. Polyester film.

17. In paragraph 15, A polyester film, wherein the percentage of the core layer thickness is 35% to 92.5% and the percentage of the surface layer thickness is 7.5% to 65% with respect to the thickness of the polyester film.

18. A step of preparing a polyester resin mixture including a crystalline polyester and an amorphous polyester having a difference in weight average molecular weight of less than 20,000 g / mol; A step of forming the above polyester resin mixture to produce an unstretched film; and Comprising a step of stretching the above unstretched film in one or more directions, A method for manufacturing a polyester film of claim 1.

19. In paragraph 18, The above stretching is a uniaxial stretching of 2 to 6 times the transverse stretching ratio or 1.1 to 6 times the longitudinal stretching ratio. Method for manufacturing polyester film.

20. In paragraph 18 or 19, The above stretching is a biaxial stretching with a transverse stretching ratio of 1.5 to 5 times and a longitudinal stretching ratio of 1.1 to 5 times. Method for manufacturing polyester film.

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