KR100271928B1 - 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. Condensation polymerization of at least one glycol component selected from the group consisting of an acid component consisting of 20 to 5 mol% of terephthalic acid, at least one of isophthalic acid and phthalic acid, and an aliphatic glycol having 2 to 8 carbon atoms, and has an intrinsic viscosity of 0.62 -The average particle diameter of 0.01-5.0 in the first film layer which consists of co-polyester resin which is 0.68 dl / g and the extraction amount of an oligomer is 1.0% or less when boiled for 48 hours in xylene at normal pressure and 138 degreeC. The polyester film according to the present invention comprises a second film layer formed on one surface of the first film layer by dispersing the microparticles having a thickness of 0.01 to 0.5% by weight, and the barrier (barrier) resistance, heat resistance, It is suitable as a polyester film for metal cans due to its excellent impact resistance, taste preservation, hygiene and molding processability.

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 a polyester can for a metal can and a method for producing the same, having excellent barrier resistance, heat resistance, impact resistance, taste retention, hygiene and molding processability. will be.

In conventional metal cans for food and beverage storage, a coating such as lacquer is applied to an inner surface of the food and beverage storage to prevent corrosion of the metal plate. However, in the case of such a conventional 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 order to prevent this, attempts have been actively made to laminate resin films without applying a paint on the inner surface of the metal can. As such a resin film (hereinafter referred to as a film for metal cans), a polyester film such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or the like is used for heat resistance, chemical resistance, light weight, food hygiene and handling. Because of its ease of use, it is widely used as a film for metal cans for storing natural beverages, carbonated beverages, etc. However, films made of polyester resins such as PET, PBT, etc. are not self-adhesive. Since it is necessary to adhere to the metal plate, a large number of processes are required to manufacture the metal can, and there is a problem that residual solvents, etc., from the adhesive are eluted into the food and drink, which threatens human health.

Therefore, recently, polyester films for metal cans that can be easily thermally bonded to metal plates have been actively studied. However, the improvement in terms of metal plate corrosion prevention function, forming processability, thermal stability, barrier property (characteristics that can reliably isolate food and gas from metal plate), impact resistance and hygiene, which are essential characteristics of polyester film for metal cans There are many problems to do.

For example, when polymerizing a PET resin, a film using a polyester resin copolymerized with tetramethylene glycol in addition to ethylene glycol as a glycol component or a resin blended with PET and PBT has a low melting point, and thus has good thermal adhesiveness but a high crystallization rate. Therefore, when the metal plate on which the film is laminated is formed into a metal can, cracks or whitening are severely generated in the film, resulting in poor workability.

In addition, Japanese Patent Application Laid-open No. Hei 5-301978 discloses a polyester resin obtained by copolymerizing trimethylene glycol as an acid component and glycol component consisting of 20 to 5 mol% of isophthalic acid or sebacic acid and 95 to 80 mol% of terephthalic acid. The polyester resin has a problem that deterioration occurs in the film during post-processing with heat, such as retort processing, because of poor thermal stability, even if normally formed into a metal can after lamination on a metal plate because the glass transition temperature is too low.

JP-A 3-110124 and JP-A 7-207040 disclose a polyester resin obtained by copolymerizing an acid component consisting of terephthalic acid and isophthalic acid and a glycol component consisting of ethylene glycol and polyoxyalkylene glycol, and adding monodisperse inorganic fine particles. To compensate for the disadvantage that the impact resistance is poor, but there is a problem that the adhesive must be used because the barrier property is poor to apply to the positive pressure pipe for carbonated beverage storage.

Japanese Patent Laid-Open Publication Nos. 5-154971, 6-39979, and 6-218893 disclose co-extruded polyester films, but the problem is that the residual orientation is significantly reduced in the upper layer having a low melting point due to the high melting point of the adhesive layer, PBT, etc. There are problems that whitening phenomenon occurs severely during heat treatment, including a large number of resins having a high crystallization rate, and crystallinity between film layers is different, so that separation between film layers is likely to occur when an impact is applied after heat treatment.

Therefore, there are many problems in using the polyester film as a film for commercial food storage metal cans.

In addition, there are many patents that disclose films made of various copolyester resins, and patents that disclose polyester films to which various inorganic fine particles are added as polyester films for metal cans.

However, they cannot satisfy all the required characteristics according to the metal can forming method or the applied food, and in particular, they need to be improved in terms of impact resistance, heat resistance, taste preservation, hygiene and molding processability, which are important characteristics of the metal can film. I'm leaving a lot.

Accordingly, the technical problem to be achieved by the present invention is to improve the impact resistance, heat resistance, molding processability to solve the above problems, and above all for positive pressure pipes that require particularly better barrier properties such as carbonated beverages with excellent taste preservation and hygiene It is to provide a polyester film for a metal can that can be laminated without an adhesive.

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, in the polyester film laminated on the metal plate used to manufacture metal cans for food and beverage storage, 80 to 95 mol% of terephthalic acid and at least one of isophthalic acid and phthalic acid 20 to 5 Condensation polymerization of at least one glycol component selected from the group consisting of an acidic component consisting of mole% and an aliphatic glycol having 2 to 8 carbon atoms, in which the intrinsic viscosity is 0.62 to 0.68 ㎗ / g and boiled for 48 hours in xylene at atmospheric pressure at 138 ° C. A first film layer composed of a copolymerized polyester resin having an amount of extraction of oligomer of 1.0% or less; And a second film layer formed by dispersing 0.01 to 0.5% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm in the copolymerized polyester resin and formed on one surface of the first film layer. Provide a film.

In the polyester film according to the present invention, the refractive index of the polyester film is 1.61 to 1.66 in any one direction at any one point of the film, and also at any one point of the film It is preferable that the difference in refractive index in the other two directions is 0 to 0.02.

In order to achieve the above another technical problem, the present invention provides a polyester film laminated on a metal plate used to manufacture a metal can for food and beverage storage, comprising: (a) 80 to 95 mol% of terephthalic acid and isophthalic acid and phthalic acid; Condensation polymerization of at least one glycol component selected from the group consisting of 20 to 5 mole% of acid and aliphatic glycols having 2 to 8 carbon atoms, intrinsic viscosity of 0.62 to 0.68 dl / g, normal pressure of 138 ℃ When the mixture was boiled for 48 hours at 100%, the melt of the copolymerized polyester resin having an oligomer extraction amount of 1.0% or less was extruded to form a first film layer, and at the same time, 0.01 to 5.0 μm of fine particles having an average particle diameter of 0.01 to 5.0 μm were included in the copolymerized polyester resin. Even if the melt formed by dispersing 0.5 wt% is laminated on any one surface of the first film layer to form a second film layer Rock co-extrusion to produce an unstretched film composed of two layers; And (b) stretching the unstretched film from 2.0 to 4.0 times in the first direction at 75 to 120 ° C., 2.0 to 4.0 times in the second direction perpendicular to the first direction at 100 to 140 ° C., and 180 to 230 ° C. It provides a method for producing a polyester film comprising the step of heat treatment for 5 to 10 seconds.

In the method for producing a polyester film according to the present invention, the refractive index of the polyester film is 1.61 to 1.66 in any one direction at any one point of the film, and at any one point of the film It is preferable that the difference in refractive index in any two different directions is 0 to 0.02.

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, taste preservation property, hygiene, and impact resistance. In particular, in the case of a polyester film laminated on a metal can for storing carbonated beverages, a film containing no fine particles is preferable because there is a possibility that the taste of the carbonated beverage may change due to the fine particles protruding on the surface of the film.

By the way, the polyester film according to the present invention consists of a first film layer is not added fine particles and a second film layer is added to increase the surface roughness. Therefore, the film of 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 a metal plate such as a tin-free steel sheet. It is excellent in barrier property, taste preservation, hygiene and impact resistance by making it contact with food and beverage.

In addition, since the first film layer and the second film layer are made of a copolyester resin having the same composition, the interlayer crystallinity does not change due to heat and pressure applied in a process of forming a metal can after laminating it on a metal plate. Does not happen.

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

As mentioned above, a copolyester resin having the same composition is used for the first film layer and the second film layer of the polyester film according to the present invention. The copolymerized polyester resin is a terephthalic acid (or dimethyl terephthalate) and isophthalic acid (or dimethyl isophthalate) and in order to increase the heat adhesion to the metal plate, such as a tin-free steel sheet and moldability to the metal can Direct esterification or transesterification of one or more glycol components selected from the group consisting of an acid component composed of one or more selected from phthalic acid (or dimethyl phthalate) and an aliphatic glycol having 2 to 8 carbon atoms, followed by further condensation polymerization under high temperature and high pressure Obtained. Examples of the glycol component include ethylene glycol, trimethylene glycol, diethylene glycol, 2,2-dimethyl-1,3-propanediol, tetramethylene glycol, pentamethylene glycol, neopentyl glycol, hexamethylene glycol, 1,4-cyclohexane Diol, 1, 4- cyclohexane dimethanol, etc. are mentioned.

In order for the polyester film according to the present invention to be easily and strongly heat-bonded to a metal plate, the content of terephthalic acid in the acid component is preferably 80 to 95 mol%, more preferably 85 to 92 mol%, and The content of at least one selected from phthalic acid and phthalic acid is preferably 20 to 5 mol%, more preferably 15 to 8 mol%.

When the content of isophthalic acid and / or phthalic acid is maintained in the above range, not only the heat adhesion to a substrate such as a metal plate for a metal can is easy, but also the substrate and the film may be firmly adhered after the heat adhesion.

If the content of any one or more selected from isophthalic acid and phthalic acid is less than 5 mol%, a large amount of heat is required when heat-bonding the metal plate, and crystallization of the film is accelerated during molding into a metal can, so that peeling from the metal plate tends to occur. If the content of any one or more selected from isophthalic acid and phthalic acid is more than 20 mol%, the viscosity and melting point of the polyester resin may be too low, resulting in a significant decrease in film formation and barrier properties.

It is preferable that the intrinsic viscosity of the said polyester resin is 0.62-0.68 dl / g. If the intrinsic viscosity is less than 0.62 dl / g, the crystallization of the film is too fast and heat-bonded to the metal plate, resulting in poor post-processability such as tearing of the film when forming into a metal can, and low molecular weight such as diethylene glycol or acetaldehyde. Since by-products can be included in the film and later eluted into food and beverages, it is necessary to increase the intrinsic viscosity by performing solid phase polymerization. If it exceeds 0.68㎗ / g, the polymerization time is long and the viscosity is too high, so that the film has a uniform thickness. Hard to mold

Melting point of the polyester resin thus produced is in the range of 200 ~ 240 ℃. In addition, the polyester resin is subjected to solid phase polymerization to minimize the elution of oligomers, such as by-products such as diethylene glycol or acetaldehyde, and the extraction amount of the oligomer when boiled for 48 hours in xylene at atmospheric pressure, 138 ℃ It is preferable to adjust so that it may be 1.0% or less. Thereby, the polyester film which concerns on this invention improves taste retention and hygiene. On the other hand, the polyester resin used for the 2nd film layer which does not directly contact a food-drinks does not need to go through solid state polymerization.

As mentioned above, in the polyester film according to the present invention, the first film layer in contact with the food and drink is not added with fine particles to reliably isolate the metal plate and the food and drink and increase impact resistance, taste preservation, and hygiene, but the second film Particulates are added to the layer to increase the coilability. That is, in order to facilitate the handling of the polyester film, the second film layer should have an average roughness Ra of 0.005 to 0.1 μm. In order to achieve this, the present invention has an average particle diameter of 0.01 to 5.0 in the second film layer. 0.01-0.5 weight% of microparticles | fine-particles which are micrometers are added. When the average particle diameter of the fine particles is less than 0.01 μm, the effect on the surface roughness is insignificant, and when the average particle size exceeds 5.0 μm, defects in the film increase. In addition, when the addition amount is less than 0.01% by weight, the addition effect is insignificant, and when the addition amount is more than 0.5% by weight, there is a problem in that defects in the film such as voids increase and a large amount of pinholes are generated after lamination.

Examples of fine particles that can be used include titanium dioxide, barium sulfate, calcium carbonate, silica, kaolin, talc and zeolites. One or two or more kinds of these fine particles may be used, but in order to improve barrier properties and suppress pinholes from being formed into metal cans, they have good affinity with polyester resins 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 copolyester resin prepared by a conventional method is dried under a nitrogen atmosphere. Subsequently, a melt obtained by melting the copolyester resin at a temperature of about 30 ° C. higher than the melting point of the resin in a first extruder is supplied to a feed block to form a first film layer, and at the same time, the copolyester in a second extruder. A melt of a resin in which 0.01 to 0.5% by weight of fine particles having an average particle diameter of 0.01 to 5.0 µm is dispersed in the resin is supplied to the feed block to form a second film layer. 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.

The draw ratio is set in accordance with the degree of orientation, strength, elastic modulus, etc. of the film, but usually 2 to 4 times is appropriate. In the case of transverse stretching after longitudinal stretching according to sequential stretching, the longitudinal stretching temperature is preferably 75 to 120 ° C. If the stretching temperature is less than 75 ℃, the stretching becomes uneven or the molecular orientation is excessive, and if it exceeds 120 ℃ stretching becomes uneven or the thermal adhesive strength is significantly reduced. Although extending | stretching temperature at the time of carrying out a lateral stretch following longitudinal extending | stretching should harmonize suitably with the extending | stretching temperature of a longitudinal direction, it is preferable that it is 100-140 degreeC.

Subsequently, the stretched film is opened and fixed. The heat setting step is carried out to maintain the thermal stability, crystallinity, and thermal adhesion of the film to a desirable level, it is preferable to heat treatment for 5 to 10 seconds at 180 ~ 230 ℃.

The refractive index of the polyester film for metal cans according to the present invention thus obtained is preferably adjusted to 1.61 to 1.66 in any one direction at any one point of the film, more preferably 1.63 to 1.65. The refractive index is a measure of molecular orientation. If the refractive index is less than 1.61, the moldability of the film is excellent, but the heat resistance and barrier resistance are greatly reduced. If the refractive index exceeds 1.66, moldability is poor. In particular, when a deep can is manufactured from a metal plate on which the film is laminated, the film exhibits whitening as the elongation of the film increases. In some cases, metal cans that are deep (tall) cannot be manufactured.

Meanwhile, in addition to controlling the refractive index of the film to the above range, the drawing process and the stretching process during the metal can manufacturing process (both processes have a cup shape having a height of about the tuna can first of a metal plate cut in a circular shape). In the process of manufacturing a metal can deep by punching after molding to a depth), since the deformation of the film should be constant in all directions, it should be adjusted so that the difference in refractive index in different directions is small.

In the case of the film according to the present invention, the difference in refractive index in any two different directions at any one point of the film is adjusted to 0.02 or less, more preferably 0.015 or less through the stretching step and heat setting. If the difference in refractive index is greater than 0.02, there is a problem in that cracking or breaking occurs in the film during the drawing and stretching process, thereby making it impossible to manufacture a deep metal can. On the other hand, a perfect isotropic film having a zero difference in refractive index in two different directions in this respect is most ideal, but there is a problem in that manufacturing cost is so high that manufacturing speed decreases and manufacturing yield of the manufacturing line decreases.

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) Copolymerization Ratio of Copolyester Resin

The copolymerization ratio was determined by analyzing ¹³ C-NMR spectral obtained using a nuclear magnetic resonance spectroscopy (JEOL, model name: JNM-LA300).

(4) refractive index

The maximum and minimum values were obtained by measuring 12 times at intervals of 15 degrees at any one point using an Abbe refractometer (Atagoshi, Japan). In this way, after measuring five times in different places, the average value of the maximum value and the average value of the minimum value were obtained.

(5) amount of oligomer extracted

The laminate prepared according to the method described in the Examples and Comparative Examples below was cut into 30 mm long and 30 mm long pieces and placed in 150 g of xylene, while maintaining the boiling point of xylene (138 ° C.) in a soxhlet. The oligomer was extracted using the apparatus and the amount thereof was measured.

(6) Moldability

1% saline solution was put into a metal can manufactured according to the method described in the following Examples and Comparative Examples, and the positive and negative terminals were connected to the inner and outer surfaces of the metal can, respectively, and the voltage was applied at 6V. By measuring the current value flowing therein, the lamination defects generated during molding into the metal can were evaluated as follows.

(Double-circle): When all 10 metal cans measured are 1 mA or less (very good)

○: When 7 to 9 out of 10 measured metal cans are 1 mA or less (good)

(Triangle | delta): When 4-6 out of 10 metal cans measured are 1 mA or less (defective)

X: 3 or less of 10 metal cans measured are 1 mA or less (not possible)

(7) heat resistance

After the metal cans prepared according to the methods described in Examples and Comparative Examples below were exposed to steam at about 120 ° C., the heat resistance was evaluated as follows based on the change of the film and whether the film was peeled off.

Yu: When whitening or peeling of the film occurs

No: Whitening does not occur on the film and no peeling of the film occurs

(8) impact resistance

Laminated plates prepared in Examples and Comparative Examples below were placed on a silicon rubber with a thickness of 3 mm and a hardness of 50, and a steel sphere 5/8 inches in diameter was placed thereon. A 1 kg weighing weight was then dropped onto the steel sphere at 40 cm above to deform the laminate. At this deformation site, impact resistance was evaluated by measuring the current value using the method and reference described in (6).

Example 1

The acid component was composed of terephthalic acid and isophthalic acid at a molar ratio of 88 mol%: 12 mol%, and ethylene glycol was composed of a glycol component, and the acid component: glycol component was mixed at a molar ratio of 1: 2. 0.04% by weight of antimonitriacetate as a polymerization catalyst, 0.01% by weight of bis-2,4-di-t-butylpentaerythritoldiphosphate as a heat stabilizer, and triphenylphosphate, based on the total weight of the mixture, with respect to the mixture 0.01 wt% was added, the polycondensation reaction was carried out, and solid phase polymerization was carried out to prepare a mono-copolymer polyester resin chip having an intrinsic viscosity of 0.68 dl / g.

In the meantime, 0.07% by weight of silica having an average particle diameter of 2.3 µm was added during condensation polymerization of the first copolymerized polyester resin, and the same method as the method for producing the first copolymerized polyester resin was carried out except that no solid phase polymerization was performed. Using the method, a second co-polyester resin chip having an intrinsic viscosity of 0.62 dl / g was prepared.

Subsequently, each of the first copolyester polyester chip and the second copolyester polyester chip was dried at 200 ° C. for 5 hours under a nitrogen atmosphere. Then, two extruders were used to melt and extrude the first copolyester polyester resin and the second copolyester polyester resin, respectively. Subsequently, the melt of the first copolyester polyester resin becomes the first film layer and the melt of the second copolyester polyester resin becomes the second film layer by using the feed block and the Ti-die attached to the tip of the two extruders. And coextruded so that the thickness ratio of a 1st film layer and a 2nd film layer might be 8: 2. 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 3.2 times in the longitudinal direction at 90 ° C. and 3.2 times in the transverse direction at 120 ° C. using a conventional biaxial stretching apparatus and heat-treated at 200 ° C. for 5 seconds to give a biaxially stretched thickness of 25 μm 2 A layer polyester film was obtained.

The thickness of the first film layer was 20.8 μm, and the thickness of the second film layer was 4.2 μm when the polyester film was measured by a scanning electron microscope (SEM).

The two-layer polyester film was laminated on a 0.17 mm thick tin-free steel sheet (TFS plate: tin free steel plate) heated to 230 ° C. to manufacture a laminated plate, and then the laminated plate was drawn and stretched to a metal can having a diameter of 82 mm. (Commonly referred to as "Draw & Thin Redraw can") were made.

Table 1 shows the results of measuring the refractive index, molding processability, and heat resistance of the two-layer 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 content of isophthalic acid or phthalic acid mixed with terephthalic acid in the acid component, the content of tetramethylene glycol or cyclohexanedimethanol mixed with ethylene glycol in the glycol component, as shown in Table 1, with the total thickness of the film fixed at 25 μm. Example 1 except that the intrinsic viscosity of the first polyester resin constituting the film layer, the content of silica fine particles having an average particle diameter of 2.3 μm in the second film layer, and the refractive index were changed within the claims of the present invention. The polyester film was manufactured using the same method as the method.

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 films of Examples 2 to 6 were very good.

Comparative Examples 1 to 5

The content of isophthalic acid or phthalic acid mixed with terephthalic acid in the acid component, the content of tetramethylene glycol or cyclohexanedimethanol mixed with ethylene glycol in the glycol component, as shown in Table 1, with the total thickness of the film fixed at 25 μm. Except having changed the intrinsic viscosity of the 1st polyester resin which comprises a film layer, the content of silica microparticles with an average particle diameter of 2.3 micrometers in a 2nd film layer, or refractive index so that it does not belong to the claim of this invention. To prepare a polyester film using the same method as in Example 1.

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, it was found that the molding processability, heat resistance, and impact resistance of the polyester films of Comparative Examples 1 to 5 were generally poor, and therefore, they were not suitable for use as a polyester film for metal cans.

On the other hand, in Comparative Example 2, the molding processability, heat resistance, and impact resistance were all very good, but the film forming processability was poor due to the large difference in intrinsic viscosity between the first and second polyester resins.

Composition of First and Second Polyester Resins First Polyester Resin 2nd polyester resin Refractive Index (Max / Min) Moldability Heat resistance Impact resistance Comprehensive Evaluation Acid component ¹⁾ Glycol ²⁾ component Intrinsic Viscosity (g / ㎗) Extract oligomer amount (% by weight) Intrinsic Viscosity (g / ㎗) Silica Content (wt%) Example One 12 mole% of IPA - 0.68 0.42 0.62 0.07 1.642 / 1.624 ◎ radish ◎ Good 2 10 mole% of IPA BD 2 mol% 0.66 0.51 0.62 0.05 1.638 / 1.622 ◎ radish ◎ Good 3 IPA 8 mol% CHDM 3 mol% 0.68 0.43 0.61 0.07 1.657 / 1.643 ◎ radish ◎ Good 4 12 mole% of IPA - 0.65 0.64 0.62 0.1 1.616 / 1.623 ◎ radish ◎ Good 5 10 mol% of PA BD 2 mol% 0.64 0.73 0.61 0.05 1.642 / 1.658 ◎ radish ◎ Good 6 12 mol% of PA - 0.67 0.48 0.62 0.12 1.662 / 1.642 ◎ radish ◎ Good Comparative example 1` 4 mol% of PA BD 10 mol% 0.66 0.53 0.62 0.07 1.643 / 1.646 △ U △ Bad 2 10 mole% of IPA CHDM 3 mol% 0.75 0.23 0.61 0.1 1.613 / 1.627 ◎ radish ◎ Bad 3 IPA 22 mol% - 0.68 0.84 0.62 0.07 1.613 / 1.622 ○ U ○ Bad 4 10 mole% of IPA BD 3 mol% 0.66 0.46 0.62 0.6 1.623 / 1.646 ○ radish × Bad 5 12 mole% of IPA - 0.62 1.17 0.61 0.12 1.662 / 1.671 ◎ U ◎ Bad

IPA: isophthalic acid PA: phthalic acid BD: 1,4-butanediol

CHDM: cyclohexanedimethanol

1) rest terephthalic acid 2) rest ethylene glycol

As described above, the polyester film according to the present invention comprises a first film layer to which fine particles are not added and a second film layer to which surface roughness is increased 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 thus is easily handled. It is excellent in taste preservation, and hygiene. In addition, the polyester film of the present invention has excellent molding processability, heat resistance, impact resistance, and heat adhesion to the metal can, and thus can be laminated on a metal plate without using an adhesive. It is suitable as a polyester film for metal cans because there is no fear of spilling environmental hormones such as bisphenol-A from food and beverages.

Claims (4)

In the polyester film laminated on a metal plate used to manufacture metal cans for food and beverage storage, Condensation polymerization of at least one glycol component selected from the group consisting of 20 to 5 mol% of terephthalic acid, at least one of isophthalic acid and phthalic acid, and an aliphatic glycol having 2 to 8 carbon atoms. A first film layer of copolymerized polyester resin having an extraction amount of oligomer of 1.0% or less when boiled for 48 hours in xylene at atmospheric pressure, 138 ° C. at 0.68 dl / g; And A polyester film comprising 0.01 to 0.5% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm in the copolymerized polyester resin and comprising a second film layer formed on one surface of the first film layer. . The method of claim 1, wherein the refractive index of the polyester film is 1.61 to 1.66 in any one direction at any one point of the film, and also in any two different directions at any one point of the film The difference in refractive index of the polyester film is 0 to 0.02. In the method for producing a polyester film laminated on a metal plate used to produce a metal can for food and beverage storage, (a) 80 to 95 mole percent terephthalic acid, at least one of isophthalic acid and phthalic acid, at least one glycol component selected from the group consisting of 20 to 5 mole% of acid and aliphatic glycols having 2 to 8 carbon atoms, When the viscosity is 0.62 to 0.68 dl / g and boiled for 48 hours in xylene at atmospheric pressure and 138 ° C., the melt of the copolymerized polyester resin having an oligomer extraction amount of 1.0% or less is extruded to form a first film layer. A melt formed by dispersing 0.01 to 0.5% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm in a polyester resin is laminated on any one surface of the first film layer and co-extruded to form a second film layer into two layers. Preparing an unstretched film; And (b) stretching the unoriented film 2.0 to 4.0 times in a first direction at 75 to 120 ° C. and 2.0 to 4.0 times in a second direction perpendicular to the first direction at 100 to 140 ° C., and then at 180 to 230 ° C. Method for producing a polyester film comprising the step of heat treatment for 5 to 10 seconds. The method of claim 3, wherein the refractive index of the polyester film is 1.61 to 1.66 in any one direction at any one point of the film, and also in any two different directions at any one point of the film The difference of the refractive index of is 0-0.02, The manufacturing method of the polyester film characterized by the above-mentioned.