KR100265927B1 - Polyester film and method for manufacturing the same - Google Patents

Abstract

The present invention discloses a polyester film having excellent thermal adhesiveness and mechanical strength, and having excellent lamination processing properties with a film made of another resin and a metal plate without undergoing a separate post-processing process such as adhesive application. More than 90% by weight of the polyester film according to the present invention consists of ethylene terephthalate, the ultimate viscosity is 0.55-0.75 ㎗ / g and the melting temperature is 240-260 ℃ of the first polyester resin and the degree of crystallinity A first film layer having at least 40%, and an ethylene terephthalate unit in the repeating unit: a second polyester resin having an ethylene isophthalate unit content of 88:12-76:24 wt% and a melting temperature of 190-215 캜. And it is characterized in that it comprises a second film layer of 13% or less crystallinity formed on any one surface of the first film layer.

Description

Polyester film and its manufacturing method

The present invention relates to a polyester film and a method of manufacturing the same, and more particularly, to a polyester film excellent in thermal adhesion between the film and the film and can be laminated on a metal plate such as aluminum without using an adhesive, and a method of manufacturing the same. It is about.

Polyester resins, especially polyethylene terephthalate resins, are physicochemically stable, have high mechanical strength, and are excellent in heat resistance, chemical resistance, and electrical insulation, making them suitable for medical, industrial, magnetic recording media, capacitors, packaging, photographic films, and labels. It is widely used for manufacturing various molded articles. In particular, the polyester resin is excellent in light weight, food hygiene and ease of handling has been widely used to replace the glass container with containers such as various foods, natural drinks, carbonated drinks, cosmetics.

However, since the film made of polyester resin is not heat-adhesive in itself, it is generally laminated with a polyolefin film and is widely used for packaging purposes. In this case, the laminated composite polyester film has to go through at least one polyolefin lamination post-processing, and thus an increase in manufacturing cost is inevitable. In addition, since the polyolefin film layer finally becomes a contact surface with food, there is a problem that excellent food hygiene of the polyester film cannot be utilized.

On the other hand, recently, co-polyester films which have been somewhat improved in thermal adhesive properties of polyester films have been studied, but they are easily used due to their weak peel strength indicating thermal adhesive properties, so they are easily used for food packaging. It is not.

In addition, in food packaging containers such as metal cans, the polyester film is heat-bonded and post-processed with an adhesive or the like for the purpose of environmental protection by utilizing the food hygiene of polyester, simplifying the painting process, and excluding the use of solvents. Although used as a laminate layer, there is a problem in that at least one adhesive coating process must be performed like the polyolefin laminate film.

Accordingly, the technical problem to be achieved by the present invention is to provide a polyester film having excellent lamination processing characteristics with a film made of another resin and a metal plate without undergoing a separate post-processing process such as adhesive application due to excellent thermal adhesiveness and mechanical strength. have.

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, more than 90% by weight of the repeating unit is made of ethylene terephthalate, the ultimate viscosity is 0.55-0.75 ㎗ / g made of a first polyester resin having a melting temperature of 240-260 ℃ A first film layer having a crystallinity of 40% or more; And an ethylene terephthalate unit in the repeating unit: an ethylene isophthalate unit content of 88:12-76:24 wt% and a second polyester resin having a melting temperature of 190-215 ° C, wherein the first film layer It provides a polyester film comprising a second film layer having a crystallinity of 13% or less formed on any one surface of the film.

In order to achieve the above technical problem, the present invention (a) more than 90% by weight of the repeating unit is made of ethylene terephthalate, the ultimate viscosity is 0.55-0.75 ㎗ / g and the melting temperature is 240-260 ℃ first polyester The melt of the resin is extruded to form a first film layer, and at the same time, the content of ethylene terephthalate unit in the repeating unit: ethylene isophthalate unit is 88:12-76: 24% by weight and the melting temperature is 190-215 캜 Forming a melt of the second polyester resin on one surface of the first film layer and co-extruding the second film layer to produce an unstretched film having two layers; And (b) stretching the unstretched film 2.5 to 4.5 times in the longitudinal direction and 2.5 to 4.5 times in the transverse direction and at a heat treatment temperature T _t satisfying the following formula:

T _c -10 <T _t <T _m -20

Where T _c is a cooling crystallization temperature and T _m is a melting temperature, respectively. The heat treatment is performed for 2 to 4 seconds to give a crystallinity of 40% or more and a crystallinity of 13% or less of the second film layer. It provides a method for producing a polyester film, characterized in that it comprises a step to be.

In the present invention, the thickness of the second film layer preferably accounts for 5-40% of the total thickness of the polyester film.

In the present invention, the thermal adhesive peel strength between the second film layer is 500 gf / inch or more, the breaking strength of the total polyester film is preferably 16 kgf / mm ² or more.

In the present invention, a third film layer made of the second polyester resin may be further formed on the first film layer opposite to the surface on which the second film layer is formed, in which case (a In the step of co-extrusion, a third film layer made of the second polyester resin is further formed at the same time on the first film layer on the opposite side of the second film layer.

The polyester film according to the present invention has excellent thermal adhesiveness and mechanical strength, and has excellent lamination processing properties with a film made of another resin and a metal plate without undergoing a separate post-processing process such as adhesive application.

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

In the first polyester resin forming the first film layer of the polyester film according to the present invention, at least 90% by weight of the repeating unit is made of ethylene terephthalate. The ethylene terephthalate unit may be formed by a direct esterification reaction of terephthalic acid and ethylene glycol or a transesterification reaction of dimethyl terephthalate and ethylene glycol. As the remaining 10% by weight or less of the copolymer component, both an acid component and an alcohol component can be used. Examples of the acid component include isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-sodium sulfopropoxyisophthalic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid and diphenoxy Ethanedicarboxylic acid, α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylic acid, trimellitic acid, pyromellitic acid, adipic acid, azelaneic acid And bifunctional or polyfunctional aromatic or aliphatic basic acids such as sebacic acid and cyclohexanedicarboxylic acid. Examples of the alcohol component include trimethylene glycol, diethylene glycol, 2,2-dimethyl-1,3-propanediol, tetramethylene glycol, pentamethylene glycol, neopentyl glycol, hexamethylene glycol, cyclohexylene glycol, 1,4- Bifunctional aromatic or aliphatic alcohols such as cyclohexanedimethanol, 5-sodium sulforesosinol, p-xylene glycol, polyethylene glycol and the like.

The intrinsic viscosity of the first polyester resin is 0.55-0.75 dl / g and the melting temperature is preferably in the range of 240-260 ℃ to maintain the mechanical strength of the entire polyester film according to the present invention.

The second polyester resin constituting the second film layer and the third film layer of the polyester film according to the present invention has an ethylene terephthalate unit in the repeating unit: the content of ethylene isophthalate unit 88:12-76:24 weight It consists of%. The ethylene terephthalate unit may be formed by a direct esterification reaction of terephthalic acid and ethylene glycol or a transesterification reaction of dimethyl terephthalate and ethylene glycol.

In addition, the ethylene isophthalate unit may be formed by a direct esterification reaction of isophthalic acid and ethylene glycol or a transesterification reaction of dimethyl isophthalate and ethylene glycol.

When the content of the ethylene isophthalate unit is less than 12% by weight, the crystallization rate of the second polyester resin is increased, resulting in poor thermal adhesiveness. If the content exceeds 24% by weight, crystallization of the second polyester resin becomes difficult, resulting in fusion between the second polyester resin chips in the drying process, resulting in unstable manufacturing process and excessively low melting temperature. In this case, the viscosity of the second film layer and the third film layer is smaller than the viscosity of the first film layer, so that curling occurs at the exit of the Ti-die in the coextrusion step and between the two resin layers in the feed block. There is a problem that the flow of the contact surface of the unstable phenomenon occurs, as a result of which the thickness of the polyester film is uneven.

It is preferable that the melting temperature of the said 2nd polyester resin which comprises the 2nd film layer and 3rd film layer of the polyester film which concerns on this invention is 190-215 degreeC. If the melting temperature is less than 190 ° C., the viscosity of the second film layer and the third film layer is smaller than the viscosity of the first film layer, so that the thickness of the polyester film described above is uneven. In addition, when the melting temperature exceeds 215 ° C crystallization of the second film layer and the third film layer is rapidly progressed, there is a problem that the heat adhesion is poor.

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 respectively dried under a nitrogen atmosphere. Subsequently, the melt of the first polyester resin is extruded to form a first film layer, and at the same time, the melt of the second polyester resin is formed on one surface of the first film layer so as to become a second film layer. Co-extrusion is performed using a T-die equipped with two extruders and a feeder block to prepare an unstretched film composed of two layers. Subsequently, the unstretched film is stretched 2.5 to 4.5 times in the longitudinal direction and 2.5 to 4.5 times in the transverse direction, and has a temperature range of 10 ° C. lower than the cooling crystallization temperature (T _c ) to 20 ° C. lower than the melting temperature (T _m ). By heat treatment at a heat treatment temperature (T _t ) for 2-4 seconds, the crystallinity of the first film layer is 40% or more, the crystallinity of the second film layer is 13% or less, and the heat between the second film layers The adhesive peel strength is 500 gf / inch or more, and the breaking strength of the entire polyester film is adjusted to 16 kgf / mm ² or more.

When the crystallinity of the first film layer is less than 40%, the breaking strength of the film is lowered. When the crystallinity of the second film layer is more than 13%, thermal adhesiveness is poor.

On the other hand, in the polyester manufacturing process, the thickness of the second film layer is preferably adjusted to occupy 5-40% of the total thickness of the polyester film, more preferably adjusted to 10-30%.

If the thickness of the second film layer is less than 5%, there is a problem that the thickness of the second film layer is too thin, resulting in poor thermal adhesiveness. If the thickness of the second film layer is greater than 40%, the thickness of the first film layer is relatively thin, resulting in the total polyester film. Not only the mechanical strength of the resin is lowered but also the amount of use of the second polyester resin, which is more expensive than the first polyester resin increases, the problem that the manufacturing cost of the entire polyester film rises more than necessary.

Meanwhile, in the polyester film according to the present invention, a third film layer made of the second polyester resin may be further formed on the first film layer opposite to the surface on which the second film layer is formed. In this case, in the coextrusion step, a third film layer made of the second polyester resin should be further formed at the same time on the first film layer on the opposite side of the second film layer.

In addition, the polyester resin of the first to third film layer is a known additive, for example, a heat stabilizer, a dispersant, an electrostatic agent, a crystallization accelerator, an antiblocking agent, a nucleating agent, and other inorganic lubricants, etc. It can be included within a range that does not damage.

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) extreme 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 35 ° C., and then extrapolated to infinite lean concentration.

(2) melting temperature and cooling crystallization 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.

The cooling crystallization temperature of the resin was measured while melting the sample by raising the temperature to 300 ° C. (heating rate: 20 ° C./min) with the differential thermal analyzer, and then cooling (cooling rate: 20 ° C.).

(3) Heat adhesive peel strength

Peel strength was measured by pressing the second film layer of the film to face each other on a bar heated to 140 ℃ and pressed for 1 second at a pressure of 40psi and then 180 ° peeling test.

(4) adhesion of steel sheet

The TFS (Tin Free Steel) plate heated to 200 ° C. and the second film layer were faced to each other, pressed for 2 seconds with a heat-resistant rubber roller, and then quenched by water cooling to complete lamination. Thus, scratches (5 mm x 5 mm) were cut out with a razor on the film portion of the plate plated on the iron plate and heated in boiling water at 100 ° C. for 2 hours, and then the flaw portions were peeled off.

At this time, it was judged to be defective if peeling easily occurred, and evaluated as good if peeling did not occur.

(5) crystallinity of film

After separating the inner and outer surfaces of the film and measuring the density by the density gradient pipe method (JIS K7112, ASTM D1505), the crystallinity of the film was measured using the following equation.

Where X _c represents the crystallinity of the film, d _c represents the density of 100% crystals (1.445), d _a represents the density of 100% amorphous (1.335), and d represents the density of the measured sample, respectively.

(6) breaking strength of film

It measured by the method of ASTM D882.

Example 1

After terephthalic acid and ethylene glycol were mixed in a 1: 2 equivalent ratio, 0.1 wt% of trimethyl phosphate as a thermal stabilizer, 0.05 wt% of antimonitriacetate as a polymerization catalyst, and 0.1 wt% of silicon oxide having an average particle diameter of 3 μm as an inorganic lubricant. After the addition and polycondensation reaction, a first polyester resin chip having an intrinsic viscosity of 0.65 dl / g, a melting temperature of 256 ° C., and a cooling crystallization temperature of 198 ° C. was prepared.

After mixing the acid component consisting of 80% by weight of terephthalic acid and 20% by weight of isophthalic acid and the diol component of ethylene glycol in a 1: 2 equivalent ratio, 0.1% by weight of trimethyl phosphate as a heat stabilizer and 0.05% by weight of antimonitriacetate as a polymerization catalyst A second polyester resin chip having an intrinsic viscosity of 0.66 dl / g and a melting temperature of 200 ° C. was prepared by adding a polycondensation reaction.

Subsequently, the first polyester resin chip was dried at 120 ° C. for 120 minutes and at 170 ° C. for 180 minutes under a nitrogen atmosphere. In addition, the second polyester resin chip was dried at 80 ° C. for 100 minutes, 105 ° C. for 100 minutes, and 160 ° C. for 150 minutes under a nitrogen atmosphere.

Subsequently, the first polyester resin is used as the first film layer by using a TiDY equipped with two extruders and a feeder block, in which a thickness ratio of the first film layer and the second film layer is 80:20. After melt | dissolving polyester resin as a 2nd film layer, it coextruded and stuck to the cooling roll cooled at 30 degreeC, and obtained the unstretched film.

The unstretched film thus obtained was stretched 3.5 times in the longitudinal direction and 3.5 times in the transverse direction using a conventional biaxial stretching apparatus, and then heat-treated at 190 ° C. for 2 seconds to obtain a 53% crystallinity of the first film layer (specific gravity = 1.396). ), The crystallinity degree 6.3% (specific gravity = 1.342) of the 2nd film layer, and the biaxially-stretched bilayer polyester film of 50 micrometers in thickness were obtained.

The thickness of the first film layer was 40.4 μm, and the thickness of the second film layer was 9.6 μm when the polyester film was measured by a scanning electron microscope (SEM).

Table 1 shows the results of measuring the thermal adhesion peel strength, the steel sheet adhesion strength and the breaking strength of the polyester film thus obtained. Referring to Table 1, the thermal adhesive peel strength of the polyester film was good at 960 gf / inch, the steel sheet adhesion was at a good level, and the breaking strength was 19.4 kgf / mm ² , which was a fairly good level.

Examples 2 to 13

The melting temperature of the second polyester resin was changed by adjusting the isophthalic acid content of the second polyester resin forming the second film layer as shown in Table 1 while fixing the overall film thickness to 50 μm. In addition, the polyester film was manufactured while changing the biaxial draw ratio and heat treatment temperature such that the crystallinity of the first film layer and the crystallinity of the second film layer were changed.

Referring to Table 1, in Examples 2 to 12 included in the claims of the present invention, the thermal adhesive peeling strength, the steel sheet adhesive strength, and the breaking strength of the prepared polyester film were generally good.

Comparative Examples 1 to 8

The melting temperature of the second polyester resin was changed by adjusting the isophthalic acid content of the second polyester resin forming the second film layer as shown in Table 1 while fixing the overall film thickness to 50 μm. In addition, the polyester film was manufactured while changing the biaxial draw ratio and heat treatment temperature such that the crystallinity of the first film layer and the crystallinity of the second film layer were changed.

Referring to Table 1, in the case of Comparative Examples 1, 2, 4, 6 and 7, which are not included in the claims of the present invention, the thermal adhesive peeling strength, the steel sheet adhesive strength and the breaking strength of the polyester film produced are generally poor. It was.

In addition, in the case of Comparative Example 3, in which the content of isophthalic acid in the second polyester resin was excessively 27 wt%, the film was not entangled with each other due to the fusion characteristics of the chips themselves when dried in a nitrogen atmosphere. In the case of Comparative Example 5 in which the longitudinal stretching ratio and the lateral stretching ratio were stretched by 4.8 times, the film itself could not be formed due to breakage due to excessive stretching ratio. In addition, in the case of the comparative example 8 which performed the heat processing temperature at 240 degreeC, the 2nd film layer melted and entangled due to excessive heat processing temperature, and the favorable film was not obtained.

Second film layer Biaxial drawing condition Film Crystallinity Film properties Isof deoxidation content ^a Melting temperature Draw ratio ^b Heat treatment temperature First film layer Second film layer Breaking strength Heat adhesive peel strength ^c Steel plate ^d adhesion unit weight% ℃ Pear ℃ % % kg / mm ² gf / inch - Example 1 20 200 3.5 × 3.5 190 53 6.3 19.4 960 Good Example 2 15 212 3.5 × 3.5 190 53 10.2 19.7 810 Good Example 3 18 204 3.5 × 3.5 190 53 8.2 19.5 850 Good Example 4 22 196 3.5 × 3.5 190 53 5.5 19.2 1250 Good Example 5 20 200 2.8 × 2.8 190 51 5.8 17.1 1010 Good Example 6 20 200 3.0 × 3.0 190 52 6.0 17.9 990 Good Example 7 20 200 3.8 × 3.8 190 53 8.7 19.9 880 Good Example 8 20 200 4.1 × 4.1 190 54 11.0 21.6 850 Good Example 9 20 200 3.5 × 3.5 195 53 6.0 19.6 960 Good Example 10 20 200 3.5 × 3.5 200 54 5.8 20.4 1030 Good Example 11 20 200 3.5 × 3.5 210 55 6.1 20.7 990 Good Example 12 20 200 3.5 × 3.5 220 55 6.0 21.7 1030 Good Example 13 20 200 3.5 × 3.5 225 55 6.1 21.1 970 Good Comparative Example 1 10 228 3.5 × 3.5 190 53 18.2 20.0 350 Bad Comparative Example 2 12 224 3.5 × 3.5 190 53 16.5 19.8 400 Bad Comparative Example 3 27 182 3.5 × 3.5 190 - - - - - Comparative Example 4 20 200 2.2 × 2.2 190 50 5.5 11.7 1050 Good Comparative Example 5 20 200 4.8 × 4.8 190 - - - - - Comparative Example 6 20 200 3.5 × 3.5 170 47 18.1 17.7 370 Bad Comparative Example 7 20 200 3.5 × 3.5 180 48 16.9 18.2 390 Bad Comparative Example 8 20 200 3.5 × 3.5 240 - - - - -

Isophthalic acid content ^a : Content based on the total weight of the 2nd polyester resin which comprises a 2nd film layer.

Draw ratio ^b : longitudinal draw ratio x transverse draw ratio

Thermal adhesive peel strength ^c : thermal adhesive peel strength between second film layers

Steel plate adhesive force ^d : Peeling state after adhering the second film layer and the steel plate

As described above, the polyester film according to the present invention has excellent thermal adhesiveness and mechanical strength, and has excellent lamination processing properties with a film made of another resin and a metal plate without undergoing a separate post-processing process such as adhesive application. Therefore, the polyester film according to the present invention is suitable for the use of the film for food packaging and the inner adhesive film of the metal can for beverage.

Claims (8)

At least 90% by weight of the repeating unit is made of ethylene terephthalate, the ultimate viscosity is 0.55-0.75 ㎗ / g and the melting temperature is 240-260 ℃ of the first polyester resin, the first film layer having a crystallinity of 40% or more; And Ethylene terephthalate unit in the repeating unit: the content of ethylene isophthalate unit is 88:12-76: 24% by weight and the second polyester resin having a melting temperature of 190-215 ℃ and of the first film layer A polyester film comprising a second film layer having a crystallinity of 13% or less formed on any one surface. The thickness of the second film layer, Polyester film, characterized in that 5 to 40% of the total thickness of the polyester film. The polyester film of claim 1, wherein the thermal adhesive peel strength between the second film layers is 500 gf / inch or more, and the breaking strength of the entire polyester film is 16 kgf / mm ² or more. The polyester film according to claim 1, wherein a third film layer made of the second polyester resin is further formed on the first film layer on the side opposite to the surface on which the second film layer is formed. . (a) 90% by weight or more of the repeating unit is composed of ethylene terephthalate and has an intrinsic viscosity of 0.55-0.75 dl / g and a melt of the first polyester resin having a melting temperature of 240-260 캜 to extrude the first film layer. At the same time, the melt of the second polyester resin having an ethylene terephthalate unit: ethylene isophthalate unit content of 88:12-76: 24% by weight in the repeating unit and a melting temperature of 190-215 ° C is prepared. Forming an unstretched film composed of two layers by coextrusion to one side of the first film layer to form a second film layer; And (b) stretching the unstretched film 2.5 to 4.5 times in the longitudinal direction and 2.5 to 4.5 times in the transverse direction and at a heat treatment temperature T _t satisfying the following formula: T _c -10 <T _t <T _m -20 Where T _c is a cooling crystallization temperature and T _m is a melting temperature, respectively. The heat treatment is performed for 2 to 4 seconds to give a crystallinity of 40% or more and a crystallinity of 13% or less of the second film layer. Method for producing a polyester film, characterized in that it comprises a step to be. The method of claim 5, wherein the thickness of the second film layer, Method for producing a polyester film, characterized in that 5 to 40% of the total thickness of the polyester film. The method of claim 5, wherein the thermal adhesive peel strength between the second film layer is 500 gf / inch or more, and the breaking strength of the entire polyester film is 16 kgf / mm ² or more. The method of claim 5, wherein in the coextrusion of step (a), And simultaneously forming a third film layer made of the second polyester resin on the first film layer on the opposite side of the second film layer.