KR100271925B1 - Polyester film and method for manufacturing the same - Google Patents

Abstract

The present invention discloses a polyester film for metal cans and a method of manufacturing the same. A polyester film laminated on a metal plate used to make a three piece metal can for storing food and beverages, the extraction amount of the oligomer is less than 1.0% when boiled for 48 hours in xylene at atmospheric pressure, 138 ℃, intrinsic viscosity 0.01-5 of microparticles | fine-particles with an average particle diameter of 0.01-5.0 micrometers among the 1st film layer which consists of a 1st polyester resin of 0.63-0.68 dl / g, and the 2nd polyester resin with an intrinsic viscosity of 0.62-0.64 dl / g The polyester film according to the present invention comprises a second film layer formed on any one surface of the first film layer by dispersing it in a weight%, and is excellent in impact resistance, heat resistance, and moldability and taste retention. Can be improved.

Description

Polyester film and its manufacturing method

The present invention relates to a polyester film and a method for manufacturing the same, and more particularly, to barrier properties, winding properties, heat resistance, impact resistance, and molding processability, and preserves the flavor of food and beverages such as soft drinks and tea well. The polyester film for three-piece metal cans which can be made, and its manufacturing method are related.

In order to prevent corrosion treatment on a three-piece metal can consisting of a conventional food and beverage storage body, an upper lid, and a lower lid, a thermosetting paint such as lacquer is applied to an inner surface of the food and beverage to prevent corrosion of the metal plate. However, in the case of the conventional three-piece metal can, there is a problem that environmental hormones such as bisphenol-A are eluted as food and drink from the paint and threaten human health.

In addition, the method of applying the thermosetting paint has a problem that requires a large number of processing steps in addition to the pollution problem because the heat treatment at high temperature for a long time to apply the paint dissolved in the organic solvent to the steel sheet and to cure it. In addition, since the organic solvent is not completely removed and always remains in a small amount, when the food and beverages are stored in the three-piece metal can, the organic solvent is eluted to the food and beverages, and the taste of the food and beverages may be deteriorated or an unpleasant smell may occur. .

In recent years, attempts have been actively made to laminate resin films instead of a method of applying a paint to the inner surface of a three-piece metal can to improve the above problem.

For example, a method of manufacturing a three-piece metal can using a steel sheet laminated with a polyolefin-based film such as polyethylene and polypropylene has been tried experimentally. However, this method is difficult to be laminated on a three-piece metal can for food and beverages because it is easy to peel off during heat treatment due to the lack of heat resistance of the polyolefin-based film, and an excessive amount of low-molecular substances such as oligomers are eluted when the food and beverages are stored.

Thus, attempts have been made to laminate polyester films instead of polyolefin films. As such resin films (hereinafter referred to as "films for metal cans"), polyester films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and the like are heat-resistant, chemical-resistant, lightweight, food hygienic and It is easy to handle and is widely used as a film for metal cans for storing natural drinks, carbonated drinks, and the like. However, since films made of polyester resins such as PET and PBT are not self-adhesive, they need to be adhered to a metal plate using an adhesive. Therefore, a large number of steps are required to prepare a metal can, and a residual solvent from the adhesive Elution as a food and beverage has a problem that threatens the health of the human body.

In order to solve the above problems, Japanese Patent Laid-Open No. 5-162244 proposes a method of manufacturing a three-piece metal can with a steel sheet laminated with a film made of a block copolymer of polyester and polyether using a thermosetting adhesive. have. However, in this method, since the film is made of copolyester, elution of low molecular weight substances such as oligomers is reduced, and heat resistance to withstand heat treatment such as retort processing is developed, but preference beverages such as coffee and tea should not have subtle taste changes. To be used for storage, there is a problem in poor taste retention and impact resistance.

Japanese Patent Laid-Open No. 10-139897 discloses a polyester film in which 1.5 wt% of inorganic fine particles and crosslinked polymer particles are added to a film in order to improve scratch resistance. However, when the excessive amount of the crosslinked polymer particles is added, the crosslinked polymer particles and the inorganic fine particles contained in the film in contact with the food and beverage are exposed to the food, causing chemical changes with them, resulting in a change in taste and smell. There is a problem that must be limited.

Accordingly, the technical problem to be achieved by the present invention is to provide a polyester film for three-piece metal can that can be excellent in impact resistance, heat resistance, winding properties and molding processability and improve taste retention in order to solve the above problems.

Another object of the present invention is to provide a method for producing the polyester film.

In order to achieve the above technical problem, the present invention is a polyester film laminated on a metal plate used to produce a three piece metal can for food and beverage storage, when boiled for 48 hours in xylene at atmospheric pressure, 138 ℃ A first film layer made of a first polyester resin having an oligomer extraction amount of less than 1.0% and an intrinsic viscosity of 0.63-0.68 dl / g; And 0.01 to 5 wt% of fine particles having an average particle diameter of 0.01 to 5.0 μm in a second polyester resin having an intrinsic viscosity of 0.62 to 0.64 dl / g, the second formed on one surface of the first film layer. It provides a polyester film comprising a film layer.

In order to achieve the above another technical problem, the present invention provides a method for producing a polyester film laminated on a metal plate used to manufacture a three piece metal can for storing food and beverages, (a) in xylene at atmospheric pressure of 138 ° C. When boiled for 48 hours, the amount of the oligomer extracted is less than 1.0% and the melt of the first polyester resin having an intrinsic viscosity of 0.63-0.68 dl / g is extruded to form a first film layer, and at the same time, the intrinsic viscosity is 0.62-0.64 A melt formed by dispersing 0.01 to 5% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm in a second polyester resin having a dl / g is laminated on any one surface of the first film layer and co-extruded to form a second film layer. Preparing an unstretched film composed of two layers; And (b) stretching the unoriented film at 2.0-4.0 times in the longitudinal direction at 75-120 ° C., 2.0-4.0 times in the transverse direction at 100-140 ° C., and heat-treating at 200-240 ° C. for 5 to 10 seconds. It provides a method for producing a polyester film comprising a.

In the polyester film and the manufacturing method thereof according to the present invention, it is preferable that the first and second polyester resins are 70 mol% or more of the repeating units made of ethylene terephthalate units.

In the polyester film according to the present invention and a method for producing the same, the fine particles in the group consisting of silica, calcium carbonate, calcium phosphate, calcium terephthalate, magnesium carbonate, sodium fluoride, aluminum hydroxide, alumina, talc, titanium dioxide, and mica It is preferably at least one selected.

The polyester film for three-piece metal cans according to the present invention is excellent in impact resistance, heat resistance, and moldability and can improve taste retention.

In order to facilitate the winding in producing the polyester film, the surface roughness of the film must be increased to some extent by adding fine particles to reduce the friction between the film and the winding roller. However, in the case of the film for metal cans, the film which does not contain microparticles | fine-particles is advantageous from a viewpoint of barrier property and impact resistance. Particularly, if inorganic fine particles are included on the surface of the film in contact with food, these films protrude on the surface of the film and cause chemical reaction with the food, thereby altering the taste of the food. Therefore, a film containing no inorganic fine particles is desirable on the film surface in contact with food. Do. In addition, if the polymer used on the film surface in contact with food contains a lot of monomers or low molecular weight oligomers used for polymerization of the polymer, they may elute during storage of the food and may alter the taste of the food and give off an unpleasant odor. . Therefore, for food preservation of food, the film in contact with food should be made of a polymer containing as little monomer or oligomer as possible.

Therefore, in order to satisfy the above conditions, the polyester film for metal cans according to the present invention has no surface particles added, but the first film layer made of a polyester resin having a small content of oligomer and the second surface having fine particles added to increase surface roughness. It consists of a film layer. Therefore, the polyester film for metal cans according to the present invention can exhibit proper winding property during the manufacturing process by the second film layer, and is easy to handle, and the first film layer is laminated so that the second film layer is in contact with the metal plate. By contacting the food and beverages can be improved barrier properties, impact resistance and taste retention.

In addition, since the first film layer and the second film layer are generally made of a polyester resin having the same composition, the degree of interlayer crystallinity does not change due to heat and pressure applied in a process of forming a metal can after being laminated to a metal plate. There is an advantage that no delamination occurs.

Hereinafter, the polyester film for three-piece metal can and the manufacturing method thereof according to the present invention will be described in detail.

As mentioned above, polyester resins having the same composition are usually used for the first film layer and the second film layer of the polyester film according to the present invention. However, since the first polyester resin of the first film layer in contact with the food and drink is subjected to solid phase polymerization after the main polymerization in order to minimize the residual content of monomers and oligomers, intrinsic viscosity is generally higher than that of the second polyester resin of the second film layer. Becomes high.

It is preferable that 70 mol% or more of a repeating unit of the said 1st and 2nd polyester resin consists of ethylene terephthalate units. If the content of the ethylene terephthalate units in the repeating units of the first and second polyester resin is less than 70 mol%, there is a problem in that heat resistance and steering resistance are poor.

The ethylene terephthalate component in the repeating unit is obtained by directly esterifying terephthalic acid and ethylene glycol first, or transesterifying dimethyl terephthalate and ethylene glycol, followed by further condensation polymerization under high temperature and high pressure.

The first and second polyester resins may contain copolyester components other than the ethylene terephthalate component within 30 mol% of the repeating unit. Acid components used to form the copolyester component include isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, cyclohexane dicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-sodium sulfopropoxyisophthalic acid, Diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxyethanedicarboxylic acid, α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylic acid, anthracene dica Bifunctional or polyfunctional aromatic or aliphatic basic acids such as carboxylic acid, trimellitic acid, pyromellitic acid, adipic acid, azelaic acid, sebacic acid, cyclohexanedicarboxylic acid, and the like. .

Alcohol components used to form the copolyester component include trimethylene glycol, diethylene glycol, 2,2-dimethyl-1,3-propanediol, tetramethylene glycol, pentamethylene glycol, neopentyl glycol, hexamethylene glycol, Bifunctional aromatic or aliphatic alcohols such as cyclohexylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, 5-sodium sulforesorcinol, polyethylene glycol and the like.

It is preferable that the intrinsic viscosity of the said 1st polyester resin is 0.63-0.68 dl / g. It is preferable that the intrinsic viscosity of the said 2nd polyester resin is 0.62-0.64 dl / g. When the intrinsic viscosity of the second polyester resin is less than 0.62 dl / g, the crystallization of the film is too fast and the post-processability such as tearing of the film when forming into a metal can after heat bonding to the metal plate is not only poor, but also diethylene glycol or acet By-products of low molecular weight, such as aldehydes are included in the film, there is a problem that can later be eluted as food and beverage.

In particular, the first polyester resin in contact with the food and beverage is subjected to solid-phase polymerization to minimize the elution of oligomers, such as by-products of low molecular weight, such as diethylene glycol or acetaldehyde. As such, the first polyester resin that has undergone the solid phase polymerization is generally higher in intrinsic viscosity than the second polyester resin, but preferably not to exceed 0.68 dl / g. When the intrinsic viscosity of the first polyester resin exceeds 0.68 dl / g, the difference in viscosity with the second polyester resin becomes large, and it is difficult to control the extrusion amount, so that there is a problem that it is difficult to form a film having a uniform thickness of each layer.

Melting points of the first and second polyester resins of the present invention prepared in this way is in the range of 200 ~ 240 ℃.

As mentioned above, in the polyester film according to the present invention, fine particles are not added to the first film layer in contact with the food and beverage, in order to reliably isolate the metal plate and the food and beverage, and to increase impact resistance and taste preservation, but to the second film layer. The fine particles are added to increase the so as to facilitate the handling of the polyester film.

The average particle diameter of the fine particles is preferably 0.01 to 5.0 µm, more preferably 0.05 to 4.0 µm. If the average particle diameter of the fine particles is less than 0.01㎛, the effect on the surface roughness is insignificant, not only the winding property is poor, the productivity is lowered, but also the production of oligomers during the manufacturing process increases, if the surface diameter of the film exceeds 5.0㎛ There is a problem that excessively roughened film defects increase.

It is preferable that the addition amount of microparticles | fine-particles is 0.01 to 5 weight%. If the amount of fine particles is less than 0.01% by weight, it contributes little to the roughening of the film surface, and the effect of addition is insignificant. If the amount of fine particles is more than 5% by weight, defects in the film such as voids increase and a large amount of pinholes are generated after lamination. There is a problem that the film is deteriorated physical properties.

The fine particles are preferably chemically inert compounds selected from oxides or inorganic salts of Group 2-4 elements on the periodic table, such as wet or dry silica, synthetic or natural calcium carbonate, calcium phosphate, terephthalate, magnesium carbonate, Sodium fluoride, aluminum hydroxide, alumina, talc, titanium dioxide, mica, and the like. Of these, silica, calcium carbonate, calcium phosphate, sodium fluoride or titanium dioxide are particularly preferred.

One or two or more kinds of the fine particles may be used, but in order to improve the barrier property and to suppress the generation of pinholes during molding into a metal can, the microparticles have a good affinity with the polyester resin to almost form voids. It is preferable to use monodisperse fine particles having excellent impact resistance.

Hereinafter, the manufacturing method of the polyester film according to the present invention will be described in detail.

First, the first and second polyester resins prepared by conventional methods are dried under a nitrogen atmosphere. Subsequently, a melt obtained by melting the first polyester resin in a first extruder at a temperature about 30 ° C. higher than the melting point of the resin is supplied to a feed block to form a first film layer, and at the same time, the second extruder is used in a second extruder. A second film obtained by supplying a melt obtained by melting a resin containing 0.01 to 5% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm in a polyester resin at a temperature about 30 ° C. higher than the melting point of the resin to the feed block. It is made up of layers. In the feed block, the first film layer and the second film layer are laminated and discharged through an extrusion die to prepare an unstretched film composed of two layers. Subsequently, the cooling film is cooled while electrostatically applying the second film layer as the drum face in the cooling drum.

Subsequently, the unstretched film is stretched 2.0 to 4.0 times in the longitudinal direction at 75 to 120 ° C. If the longitudinal stretching temperature is less than 75 ° C, the stretching becomes uneven or the molecular orientation is excessive, and if it exceeds 120 ° C, the stretching becomes uneven or the thermal adhesion is significantly lowered. Next, extending | stretching is performed in a horizontal direction. The stretching temperature in the transverse direction should be in harmony with the stretching temperature in the longitudinal direction, preferably stretching from 2.0 to 4.0 times in the transverse direction at 100 to 140 ° C.

Subsequently, the stretched film is opened and fixed. The heat setting step is carried out in order to maintain the crystallinity at a desirable level, which is very important for the thermal stability, dimensional stability, and taste preservation of the film, preferably heat treatment at 200-240 ° C. for 5-10 seconds.

The polyester film according to the present invention includes a heat stabilizer of a phosphate-based or phosphite-based compound. The thermal stabilizer functions to prevent the formation of a complex or thermal decomposition by a metal catalyst and to decompose a peroxide causing a secondary thermal oxidation reaction. By using the heat stabilizer, it is possible to prevent deterioration such as viscosity decrease, color change of the resin due to thermal decomposition, and thermal deformation through a manufacturing process of the copolyester resin and a molding process into a metal can.

In addition to the above heat stabilizer, the copolyester resin may include known additives such as dispersants, antistatic agents, crystallization accelerators, antiblocking agents, and nucleating agents within a range that does not impair the effects of the present invention. .

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples. In Examples and Comparative Examples of the present invention, various performance evaluation of the produced film was carried out by the following method.

(1) intrinsic viscosity

According to the three-point method, 0.05 g, 0.10 g, 0.20 g of the polymer was dissolved in 25 ml of ο-chlorophenol, and the relative viscosity was measured at 30 ° C., and then extrapolated to infinite lean concentration.

(2) melting temperature

The melting temperature of the resin was measured by using a differential thermal analyzer (model name: DSC-7, Perkin Elmer, USA) to raise the temperature to 300 ° C, melt the sample, and then rapidly cool the temperature and increase the temperature (temperature rising rate: 20 ° C / min). It was.

(3) amount of oligomer extracted

The film prepared in the following example was thermally laminated using an epoxy adhesive so that the second film layer was in contact with both sides of the tin steel sheet, respectively. The tin steel sheet in which the films were laminated on both surfaces was quenched to obtain a disc. A disc of 30 mm in width and 30 mm in length was placed in 150 g of xylene and the amount of oligomer was extracted by using a soxhlet device while maintaining the boiling point of xylene (138 ° C.).

(4) heat resistance

After the three-piece welded tube manufactured by using the disc of (3) was exposed to steam at about 125 ° C, it was tested whether the welded tube and the film were peeled off and the results were evaluated as follows.

Yu: When whitening occurs on the film or the film peels off at the edges.

None: When neither bleaching nor peeling occurs

(5) impact resistance

The disc was deformed by dropping a 1 kg balance weight onto the steel sphere at 10 cm with the film surface abutting on a silicon rubber having a thickness of 3 mm and a hardness of 50 ° and placing a 5/8 inch steel sphere. Subsequently, the impact resistance of the weld tube was evaluated by connecting the (+) terminal and the (-) terminal to the inner and outer surfaces of the disc of the deformed portion, and measuring the current value flowing through the conductor by applying a voltage of 6 V as follows. It was.

(Double-circle): When all 10 welded pipes measured are 1 mA or less (very good).

○: When 7 to 9 of the 10 welded tubes were 1 mA or less (good)

(Triangle | delta): When 4-6 of 10 measured weld tubes are 1 mA or less (defect)

X: 3 or less of 10 measured weld tubes are 1 mA or less (not possible)

Example 1

After mixing terephthalic acid and ethylene glycol in a molar ratio of 1: 2, 0.04% by weight of antimonitriacetate as a polymerization catalyst and bis-2,4-di-t-butylpentaerythritol diphosphate as a thermal catalyst were added to the mixture. 0.01 wt%, and 0.01 wt% of triphenylphosphate were added thereto, the polycondensation reaction was carried out, and solid phase polymerization was performed to prepare a first polyester resin chip having an intrinsic viscosity of 0.68 dl / g.

On the other hand, during the condensation polymerization of the first polyester resin, the same method as the preparation method of the first polyester resin was carried out except that 0.07% by weight of silica having an average particle diameter of 1.5 μm was further added and solid phase polymerization was not performed. To prepare a second polyester resin chip having an intrinsic viscosity of 0.62 dl / g.

Subsequently, each of the first polyester resin chip and the second polyester resin chip was dried at 200 ° C. for 5 hours under a nitrogen atmosphere. Subsequently, the first polyester resin and the second polyester resin were each melted at about 30 ° C. higher than the melting temperature of each resin using two extruders, and then extruded. Subsequently, the melt of the first polyester resin becomes the first film layer, the melt of the second polyester resin becomes the second film layer by using the feed block and the T-die attached to the tip of the two extruders. It coextruded so that the thickness ratio of a 1st film layer and a 2nd film layer might be (2) :( 1). Next, it adhered to the cooling roll cooled at 30 degreeC so that a 2nd film layer might become a contact surface, and obtained the unstretched film.

The unstretched film thus obtained was stretched 3.7 times in the longitudinal direction at 95 ° C. and 4.0 times in the transverse direction at 125 ° C. using a conventional biaxial stretching apparatus, and was heat-treated at 220 ° C. for 5 seconds to give a first film layer of 8 μm. The biaxially stretched bilayer polyester film of 12 micrometers in total thickness whose 2nd film layer is 4 micrometers was obtained.

The thickness of the first film layer was 21 μm, and the thickness of the second film layer was 4 μm when the polyester film was measured by a scanning electron microscope (SEM).

Table 1 shows the results of measuring the refractive index, molding processability, and heat resistance of the polyester film thus obtained. Referring to Table 1, the molding processability, heat resistance, and impact resistance of the polyester film of Example 1 were very good.

Examples 2-6

The intrinsic viscosity after the first polyester resin solid phase polymerization, the intrinsic viscosity of the second polyester resin, and the average particle diameter and amount of silica added thereto, as shown in Table 1, with the entire film fixed at 12 μm, were claimed. The polyester film was manufactured using the method similar to the method of Example 1 except having changed within the range.

Table 1 shows the results of measuring the amount, heat resistance, impact resistance and the like of the extraction oligomer of the obtained polyester film. Referring to Table 1, it can be seen that the polyester films of Examples 2 to 6 have good film forming, heat resistance, and impact resistance, and the amount of oligomers extracted is very small, thereby improving taste preservation of stored foods and beverages. .

Comparative Examples 1 to 5

The intrinsic viscosity after the first polyester resin solid phase polymerization, the intrinsic viscosity of the second polyester resin, and the average particle diameter and amount of silica added thereto, as shown in Table 1, with the entire film fixed at 12 μm, were claimed. The polyester film was manufactured using the method similar to the method of Example 1 except having changed so that it might not belong to the range.

Table 1 shows the results of measuring the amount, heat resistance, impact resistance and the like of the extraction oligomer of the obtained polyester film. Referring to Table 1, the polyester films of Comparative Examples 1 to 5 are generally poor in film forming, heat resistance, and impact resistance, and the amount of the extracted oligomer may increase, resulting in a polyester film for three-piece metal cans. It was found to be inappropriate to use.

On the other hand, in Comparative Example 3 in which the fine particles were not added to the second film layer, the heat resistance, the amount of the extraction oligomer, and the impact resistance were all very good, but the winding properties were poor. In addition, in the case of Comparative Example 1 in which the intrinsic viscosity of the first polyester resin was too high, the intrinsic viscosity of the second polyester resin could not be produced with a film of uniform thickness.

First film layer Second film layer Filmmaking Volume of extracted oligomers (%) Heat resistance Impact resistance Comprehensive Evaluation Intrinsic viscosity of the second polyester Average particle size (㎛) Addition amount (% by weight) Intrinsic viscosity of the first polyester Example One 0.68 0.62 1.5 0.07 Good 0.37 radish ◎ Good 2 0.64 0.62 2.3 0.05 Good 0.58 radish ◎ Good 3 0.67 0.63 3.2 0.07 Good 0.42 radish ◎ Good 4 0.63 0.62 0.1 1.5 Good 0.73 radish ◎ Good 5 0.67 0.62 5.0 0.03 Good 0.43 radish ◎ Good 6 0.66 0.63 1.0 0.06 Good 0.51 radish ◎ Good Comparative example One 0.75 0.62 1.5 0.08 Thickness 0.23 radish ◎ Bad 2 0.66 0.63 2.3 6 Good 0.41 radish △ Bad 3 0.65 0.62 - 0 Winding 0.49 radish ◎ Bad 4 0.67 0.63 5.5 0.03 Good 0.39 radish △ Bad 5 0.62 0.62 3.2 0.07 Good 1.32 U △ Bad

As described above, the polyester film according to the present invention is composed of a first film layer having little oligomer content and no second particles added, and a second film layer having increased surface roughness by adding fine particles. Therefore, the polyester film according to the present invention can exhibit proper winding property during the manufacturing process by the second film layer, and is easy to handle, and the first film layer containing no fine particles and low oligomer content is used for food and beverages. Since it comes in contact with the heat resistance, impact resistance, and barrier properties can be improved and taste retention is improved.

Claims (6)

A polyester film laminated to a metal plate used to make a three piece metal can for food and beverage storage, A first film layer composed of a first polyester resin having an extraction amount of less than 1.0% and an intrinsic viscosity of 0.63-0.68 dl / g when boiled in xylene at 138 ° C. for 48 hours; And A second film formed by dispersing 0.01 to 5% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm in a second polyester resin having an intrinsic viscosity of 0.62 to 0.64 dl / g, wherein the second film is formed on one surface of the first film layer. A polyester film comprising a layer. The polyester film of claim 1, wherein at least 70 mol% of the repeating units are polyester resins each comprising ethylene terephthalate units. The method of claim 1, wherein the fine particles are any one or more selected from the group consisting of silica, calcium carbonate, calcium phosphate, calcium terephthalate, magnesium carbonate, sodium fluoride, aluminum hydroxide, alumina, talc, titanium dioxide, and mica. Polyester film. A method for producing a polyester film laminated on a metal plate used to make a three piece metal can for storing food and beverages, (a) The first film layer is obtained by extruding a melt of a first polyester resin having an oligomer extraction amount of less than 1.0% and an intrinsic viscosity of 0.63-0.68 dl / g when boiled in xylene at 138 캜 for 48 hours. At the same time, a melt formed by dispersing 0.01-5 wt% of fine particles having an average particle diameter of 0.01-5.0 μm in a second polyester resin having an intrinsic viscosity of 0.62-0.64 dl / g is formed on either surface of the first film layer. Stacking on and co-extrusion to a second film layer to produce an unstretched film composed of two layers; And (b) stretching the unoriented film at 2.0-4.0 times in the longitudinal direction at 75-120 ° C., 2.0-4.0 times in the transverse direction at 100-140 ° C., and heat-treating at 200-240 ° C. for 5 to 10 seconds. The manufacturing method of the polyester film containing what is included. The polyester film of claim 4, wherein the first and second polyester resins are polyester resins in which at least 70 mol% of the repeating units are made of ethylene terephthalate units. The method of claim 4, wherein the fine particles are any one or more selected from the group consisting of silica, calcium carbonate, calcium phosphate, calcium terephthalate, magnesium carbonate, sodium fluoride, aluminum hydroxide, alumina, talc, titanium dioxide, and mica. Polyester film.