KR100389295B1 - 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 beverage, comprising a first polyester resin having an intrinsic viscosity of 0.64 to 0.70 dl / g and an acetaldehyde content of 20 ppm or less. A first film layer having _a center line average roughness Ra of 10 nm or less; And 0.01 to 2.0% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm, and comprising a second polyester having an intrinsic viscosity of 0.62 to 0.64 dl / g, which is formed on one surface of the first film layer. In addition, the polyester film according to the present invention is characterized in that it comprises a second film layer having _a center line average roughness (R _a ) of 10 to 200 nm at the same time barrier, heat resistance, impact resistance, taste preservation, hygiene and molding processability It is excellent and can preserve the flavor of food and beverages such as soft drinks and tea well.

Description

Polyester film and method for manufacturing the same

The present invention relates to a polyester film and a method of manufacturing the same, and more particularly, the barrier (barrier), heat resistance, impact resistance, taste preservation, hygiene and molding processability at the same time, and the flavor of food and beverages such as soft drinks and tea A polyester film for three-piece metal cans that can be well preserved and a method for producing the same.

In order to prevent corrosion treatment of a three-piece metal can consisting of a body, an upper lid, and a lower lid, conventionally, a thermosetting paint such as lacquer is applied to an inner surface in contact with food and drink 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 solvents are eluted to the food and beverages, and the taste of the food and beverages may be altered or may cause an unpleasant smell. .

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 preservation and hygiene 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.

Therefore, the technical problem to be achieved by the present invention is to solve the above problems, at the same time excellent barrier property, heat resistance, impact resistance, taste preservation, hygiene and molding processability and can preserve the flavor of food and beverages such as soft drinks and tea well To provide a polyester film for a three-piece metal can.

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 a metal plate used to manufacture a three-piece metal can for food and beverage storage, intrinsic viscosity is 0.64 ~ 0.70 ㎗ / g and acetaldehyde content is 20ppm or less, and the low made of one of polyester resin, the center line average roughness (R _a) is 10nm or less the first film layer; And 0.01 to 2.0% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm, and comprising a second polyester having an intrinsic viscosity of 0.62 to 0.64 dl / g, which is formed on one surface of the first film layer. And it provides a polyester film comprising a second film layer having _a center line average roughness (R _a ) of 10 to 200nm.

In order to achieve the above another technical problem, the present invention is a method of manufacturing a polyester film laminated on a metal plate used to manufacture a three piece metal can for storing food and beverages, (a) intrinsic viscosity is 0.64 ~ 0.70 A melt of the first polyester resin having a content of acetaldehyde of 20 ppm or less is extruded to be the first film layer, and at the same time, the average particle diameter is 0.01 to the second polyester resin having an intrinsic viscosity of 0.62 to 0.64 dl / g. Preparing an unstretched film composed of two layers by laminating a melt formed by dispersing 0.01 μm to 2.0 wt% of particles having 5.0 μm on one surface of the first film layer to coextrude the second film layer; And (b) stretching the unoriented film 2.0 to 4.0 times in a first direction at 75 to 120 ° C., 2.0 to 4.0 times in a second direction perpendicular to the first direction at 100 to 140 ° C., and 200 to 240 ° C. in the heat-treated for 5 to 10 seconds the first and the 10nm below the center line average roughness (R _a) of the first film layer and comprising a center line average roughness (R _a) of the second film layer such that 10 ~ 200nm It provides a method for producing a polyester film, characterized in that.

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 polyester resins in which at least 70 mol% of the repeating units are made of ethylene terephthalate units.

In the polyester film according to the present invention and a method for producing the same, the fine particles are silica, calcium carbonate, calcium phosphate, terephthalate, magnesium carbonate, sodium fluoride, aluminum hydroxide, alumina, talc, titanium dioxide, kaolin, barium sulfate, zeolite And mica is preferably any one or more selected from the group consisting of.

In the polyester film and the manufacturing method thereof according to the present invention, the difference in intrinsic viscosity between the first and the second polyester resin is preferably 0.02 ~ 0.1 dl / g.

Polyester film for three-piece metal cans according to the present invention is excellent in barrier properties, heat resistance, impact resistance, taste preservation, hygiene and molding processability and can preserve the flavor of food and beverages such as soft drinks and tea well.

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 is a microparticle-free first film layer and the fine particles made of a polyester resin having a small content of by-products such as acetaldehyde and oligomers, without the addition of fine particles. Is added to form a second film layer with increased surface roughness. 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, taste retention, hygiene can be improved.

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 beverage is subjected to solid phase polymerization after the main polymerization in order to minimize the residual content of by-products such as acetaldehyde and oligomers, the second polyester of the second film layer is usually Intrinsic viscosity is higher than resin.

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.

The intrinsic viscosity of the first polyester resin is 0.64 to 0.70 dl / g, the intrinsic viscosity of the second polyester resin is 0.62 to 0.64 dl / g, and the intrinsic viscosity between the first and second polyester resins It is preferable that the difference is 0.02 to 0.1 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 in order to minimize elution of oligomers such as by-products of low molecular weight such as diethylene glycol or acetaldehyde and to improve taste preservation and hygiene. As described above, the first polyester resin that has undergone the solid phase polymerization has a higher intrinsic viscosity than the second polyester resin, but it is preferable that the difference of the intrinsic viscosity with the second polyester resin is 0.02 to 0.1 dl / g. . If the difference in intrinsic viscosity is more than 0.1 dl / g, it is difficult to precisely control the amount of extrusion and there is a problem that it is difficult to mold into a film having a uniform thickness of each layer.

Solid phase polymerization is not particularly limited in any way, but the difference in intrinsic viscosity with that of the second polyester resin is 0.02 to 0.1 dl / g by controlling the reaction time at a temperature of 20 to 30 ° C. lower than the melting temperature of the polymer under vacuum or nitrogen atmosphere. And the acetaldehyde content is adjusted to 20 ppm or less. When the content of acetaldehyde exceeds 20 ppm, there is a problem that the taste of the contents stored in the metal can is changed.

On the other hand, the melting point of the first and second polyester resin of the present invention prepared in this way is preferably adjusted to the range of 240 ~ 260 ℃.

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, taste retention, and hygiene. Particulates are added to increase the coilability and to facilitate 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 2.0 weight%. If the amount of fine particles added 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 the fine particles is more than 2.0% 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, kaolin or mica. Among them, silica, calcium carbonate, calcium phosphate, sodium barium fluoride, zeolite 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 2.0% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm in a polyester resin at a temperature of about 30 ° C. higher than the melting point of the resin to the feed block. It is made into 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.

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 in order to maintain the thermal stability, crystallinity, and heat adhesion of the film to a desirable level, it is preferable to heat treatment for 5 to 10 seconds at 200 ~ 240 ℃. In this way the first is adjusted so that the center line average roughness (R _a) is 10nm or less and is 10 ~ 200nm center line average roughness (R _a) of the second film layer of the first film layer.

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) acetaldehyde content

1.5 g of the first polyester resin chip was frozen and ground, and then heated and vaporized acetaldehyde was measured using high performance gas chromatography equipped with a head space sampler (JAI Co., Ltd.) capable of collecting at -40 ° C.

(4) surface roughness

The surface roughness (R _a ) was measured on the conditions of cut-off 0.25mm using the contact type two-dimensional surface roughness meter (SE-30D, Kosaka, Japan).

(5) heat resistance

After exposing the three-piece metal cans prepared according to the methods described in the Examples and Comparative Examples below 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

(6) 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. The impact resistance was evaluated as follows by connecting the positive and negative terminals to the inner and outer surfaces of the deformed portion and measuring the current value flowing through the conductor with a voltage of 6V.

(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 terephthalic acid was used as an acid component and ethylene glycol: 1,4-butanediol = 97: 3 mol% mixture was used as a glycol component, the acid component: glycol component was mixed in a molar ratio of 1: 2, and then a polymerization catalyst was prepared for the mixture. 0.04% by weight of antimonitriacetate, 0.01% by weight of bis-2,4-di-t-butylpentaerythritol diphosphate, and 0.01% by weight of triphenylphosphate were added as a heat stabilizer, and the polycondensation reaction was carried out. The polymerization was carried out to prepare a first polyester resin chip having an intrinsic viscosity of 0.67 dl / g.

In the meantime, 0.07% by weight of calcium carbonate having an average particle diameter of 2.8 μm was added during the polycondensation of the first polyester resin, and the same method as the method for preparing the first polyester resin was used except that the 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 feed block and the T-die attached to the tip of the two extruders were used to co-extrude the melt of the first polyester resin to be the first film layer and the melt of the second polyester resin to be the second film layer. It was. 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 3.8 times in the longitudinal direction at 95 ° C. and 4.0 times in the transverse direction at 120 ° 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 polyester film thus obtained was coated with an epoxy adhesive, and a laminated film was obtained by laminating a polyester film on both sides of a 0.21 mm thick tin steel sheet using a thermal lamination method so as to contact the second film layer. Subsequently, a three-piece metal can was manufactured using the laminate.

Table 1 shows the results of measuring film forming property, impact resistance, acetaldehyde content, surface roughness and heat resistance using the obtained polyester film and metal can. Referring to Table 1, the polyester film of Example 1 was very good in film forming property, heat resistance, and impact resistance. In addition, since the surface roughness of the second film layer is 68 nm, the surface roughness is appropriate, so that it is easy to handle the film such as winding property, and the content of acetaldehyde of the first polyester resin is very small (14 ppm), which may improve taste preservation and hygiene. And it was found.

Examples 2-6

As shown in Table 1 with the total thickness of the film fixed at 12 μm, the intrinsic viscosity after the solid phase polymerization of the first polyester resin, the intrinsic viscosity of the second polyester resin, the average particle diameter and the amount of the fine particles added thereto, and the surface roughness thereof, A polyester film was prepared using the same method as in Example 1 except for changing within the claims of the present invention.

Table 1 shows the results of measuring film forming property, impact resistance, acetaldehyde content, surface roughness and heat resistance using the obtained polyester film and metal can. Referring to Table 1, the polyester films of Examples 2 to 6 were very good in film forming property, heat resistance, and impact resistance. In addition, since the surface roughness of the second film layer is 34 to 84 nm, the surface roughness is appropriate, so that it is easy to handle the film such as winding property, and the content of acetaldehyde of the first polyester resin is 20ppm or less, which improves taste preservation and hygiene. Could be found.

Comparative Examples 1 to 5

Intrinsic viscosity after solid state polymerization of 1st polyester resin, the intrinsic viscosity of 2nd polyester resin, and the average particle diameter, addition amount, and surface roughness of 1st polyester resin solid-state polymerization as shown in Table 1, fixing the whole film thickness to 12 micrometers A polyester film was prepared using the same method as in Example 1, except that one or more were changed so as not to fall within the claims of the present invention.

Table 1 shows the results of measuring film forming property, impact resistance, acetaldehyde content, surface roughness and heat resistance using the obtained polyester film and metal can. 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 tend to increase the content of acetaldehyde, which is used as a polyester film for three-piece metal cans. It was found to be inappropriate for the following. On the other hand, in Comparative Example 3 in which the fine particles were not added to the second film layer, the heat resistance and the acetaldehyde content, heat resistance, and impact resistance in the first polyester resin (first film layer) were all good, but the surface of the second film layer was good. Low roughness resulted in poor windability.

First film layer Second film layer Intrinsic Viscosity Difference Between First and Second Film Layers Filmmaking Heat resistant Impact resistance Species Intrinsic viscosity (㎗ / g) AA ¹⁾ Content (ppm) Intrinsic viscosity (㎗ / g) Particle Type Average particle size (㎛) Addition amount (% by weight) R _a (nm) Example One 0.67 14 0.62 Calcium carbonate 2.8 0.07 68 0.05 Good radish ◎ Good 2 0.70 12 0.63 Silica / titanium dioxide 1.6 / 3.2 0.02 / 0.08 84 0.07 Good radish ◎ Good 3 0.68 20 0.62 Silica 2.45 0.12 65 0.06 Good radish ◎ Good 4 0.68 16 0.64 Titanium dioxide 2.1 0.07 57 0.04 Good radish ◎ Good 5 0.70 13 0.63 Silica 0.9 0.15 34 0.07 Good radish ◎ Good 6 0.68 19 0.62 Calcium Carbonate / Silica 1.6 / 2.1 0.02 / 0.09 73 0.06 Good radish ◎ Good Comparative example One 0.74 9 0.61 Silica 1.6 0.1 48 0.13 Thickness radish ◎ Bad 2 0.68 19 0.64 Calcium carbonate 3.2 2.5 250 0.04 Good radish × Bad 3 0.68 18 0.62 - - 0 5 0.06 Winding radish ◎ Bad 4 0.64 42 0.63 Titanium dioxide 2.1 0.07 54 0.01 Good U ○ Bad 5 0.62 83 0.62 Titanium dioxide / silica 2.3 / 3.2 0.03 / 0.05 76 0.00 Good U ○ Bad

AA = acetaldehyde

As described above, the polyester film according to the present invention is composed of a first film layer having a small content of acetaldehyde without fine particles added and a second film layer having increased surface roughness by adding fine particles. Accordingly, the polyester film according to the present invention may exhibit proper winding property during the manufacturing process by the second film layer, and thus, the first film layer which is easy to handle, and which does not contain fine particles and contains less acetaldehyde, Since it comes in contact with food and beverages, it has excellent heat resistance, impact resistance, barrier properties, taste preservation, and hygiene.

Claims (8)

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 having an intrinsic viscosity of 0.64 to 0.70 dl / g and a first polyester resin having an acetaldehyde content of 20 ppm or less and having a center line average roughness (R _a ) of 10 nm or less; And It contains 0.01 to 2.0% by weight of fine particles having an average particle diameter of 0.01 to 5.0 μm, and is composed of a second polyester having an intrinsic viscosity of 0.62 to 0.64 dl / g, and is formed on one surface of the first film layer. And a second film layer having _a center line average roughness (R _a ) of 10 to 200 nm. 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 selected from the group consisting of silica, calcium carbonate, calcium phosphate, calcium terephthalate, magnesium carbonate, sodium fluoride, aluminum hydroxide, alumina, talc, titanium dioxide, kaolin, barium sulfate, zeolite and mica. Polyester film characterized in that at least one. The polyester film according to claim 1, wherein a difference in intrinsic viscosity between the first and second polyester resins is 0.02 to 0.1 dl / g. 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) Extrusion of a melt of a first polyester resin having an intrinsic viscosity of 0.64 to 0.70 dl / g and an acetaldehyde content of 20 ppm or less to form a first film layer, and at the same time a second having an intrinsic viscosity of 0.62 to 0.64 dl / g A melt formed by dispersing 0.01 to 2.0% 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 coextruded to form a second film layer. Preparing a new 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., at 200 to 240 ° C. in that it comprises a step such that 5-10 seconds heat treatment to the first and is 10nm or less the center line average roughness (R _a) of the first film layer, is 10 ~ 200nm center line average roughness (R _a) of the second film layer while The manufacturing method of the polyester film characterized by the above-mentioned. 6. The method of claim 5, 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 5, wherein the fine particles are any selected from the group consisting of silica, calcium carbonate, calcium phosphate, calcium terephthalate, magnesium carbonate, sodium fluoride, aluminum hydroxide, alumina, talc, titanium dioxide, kaolin, barium sulfate, zeolite and mica. Method for producing a polyester film, characterized in that at least one. The method of claim 5, wherein the difference in intrinsic viscosity between the first and the second polyester resin is 0.02 ~ 0.1 dl / g.