KR101214482B1 - Polyester film and preparation method thereof - Google Patents

Abstract

Polyester films, in which polylactic acid is blended with liquid caprolactone polymers, have improved transparency and flexibility, resulting in uniform physical properties throughout the film, specifically uniform flexibility, transparency, strength, elongation and Young's modulus, which can be utilized in various packaging applications. Can be.

Description

Polyester film and manufacturing method thereof {POLYESTER FILM AND PREPARATION METHOD THEREOF}

The present invention relates to a polyester film used as a packaging film and the like and a method of manufacturing the same.

Polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP), general-purpose plastics derived from petroleum, are currently used in various applications, but when incinerated, they generate harmful substances such as dioxins and generate a lot of carbon dioxide. As a result, there is a problem of accelerating the greenhouse gas effect in the atmosphere. In addition, since these plastic films are chemically and biologically stable, they are hardly decomposed, and as a result, they cause global soil pollution, such as shortening the life of landfills.

Recently, in order to fund green growth investment and reduce global greenhouse gas, carbon tax and carbon credit trading system have been actively reviewed. Accordingly, research and development on biopolymers derived from biomass are being actively conducted.

In particular, research and application of polylactic acid (PLA), which is a highly biodegradable aliphatic polyester, are being conducted. Polylactic acid films have excellent mechanical properties and transparency, but have high flexibility due to high crystallinity due to molecular structure. Because of its lack, its use is limited for packaging purposes.

Accordingly, in order to soften the polylactic acid film, poly (butylene adipate-co-tetraphthalate (PBAT), poly (butylene succinate) ): PBS), poly (ε-caprolactone): PCL, poly (butylene adipate-co-succinate): PBAS) or poly ( Although a method of blending solid chips such as poly (butylene adipate) (PBA) has been developed, there is a problem in that haze rises rapidly due to poor compatibility between polylactic acid and the solid chip.

Accordingly, there is a need for developing a polyester film having improved flexibility.

Accordingly, it is an object of the present invention to provide a polyester film having a uniform physical property throughout the film with improved transparency and flexibility and a method for producing the same.

Another object of the present invention is to provide a packaging material comprising the polyester film.

In accordance with the above object, the present invention provides a polyester film in which polylactic acid is blended with a liquid caprolactone polymer.

According to the above another object, the present invention comprises the steps of (a) blending the polylactic acid and the liquid caprolactone polymer to obtain a mixed resin; (b) melting and extruding the mixed resin to obtain an unstretched sheet; And (c) stretching and heat setting the unstretched sheet in at least one of longitudinal and transverse directions.

The present invention also provides a packaging material comprising the polyester film.

The polyester film according to the present invention is made of a biodegradable resin, which is environmentally friendly, has excellent transparency and flexibility, and exhibits uniform physical properties, specifically uniform flexibility, transparency, strength, elongation and Young's modulus.

Hereinafter, the present invention will be described in more detail.

The present invention is to prepare a polyester film, liquefied a paraffinic caprolactone polymer at room temperature, and then mixed with polylactic acid, thereby forming a mixed resin uniformly mixed with polylactic acid resin, through which a uniform film as a whole It is characterized by producing a polyester film having physical properties, specifically uniform flexibility, transparency, strength, elongation and Young's modulus.

That is, the polyester film according to the present invention is made by blending a polylactic acid and a liquid caprolactone polymer.

The caprolactone polymer is prepared by ring-opening a cyclic caprolactone monomer, and has a long alkyl chain (five CH ₂ ) to provide flexibility when added to the polylactic acid film. However, the caprolactone polymer has a low glass transition temperature below 50 ° C., and crystallization proceeds slowly at a temperature above the glass transition temperature and exists in a paraffin phase (semi-solid phase) at room temperature. Therefore, when blending the semi-solid caprolactone polymer with the polylactic acid resin, the physical properties of the final polyester film may be degraded due to uneven mixing. Therefore, after blending the caprolactone polymer completely before blending with the polylactic acid resin, Preference is given to using liquid caprolactone polymers.

In addition, it is preferable to use the caprolactone polymer having a number average molecular weight of 1,000 to 10,000 because it can maximize the flexibility of the polyester film. However, if the number average molecular weight of the caprolactone polymer exceeds 10,000, the kneading and compatibility with the polylactic acid is lowered and the haze is increased, so that the transparency of the film cannot be maintained.

The polylactic acid used in the present invention is a random copolymer of L-lactic acid and D-lactic acid, and having a weight average molecular weight of 80,000 to 500,000 g / mol is preferable in consideration of heat resistance and mechanical properties of the film and film processability.

In addition, the melting temperature of the polylactic acid is preferably 135 ° C or more and 180 ° C or less, and more preferably 140 ° C or more and 180 ° C or less. If the melting temperature is lower than 135 ℃ heat resistance and mechanical properties are not properly expressed is not preferred.

In the production of polyester film, the higher the content of polylactic acid, the more fragile the film and the higher the degree of crystallinity, the more difficult to express flexible properties. Accordingly, the polylactic acid and caprolactone polymer may be included in a weight ratio of 95: 5 to 20:80, and the polylactic acid and caprolactone polymer may be included in a ratio of 95: 5 to improve the fragile properties of the polylactic acid while maintaining the transparency of the film. It is preferably included in the weight ratio of 5 to 60:40.

The polyester film of the present invention as described above is preferably a stretched film produced by stretching in at least one of the longitudinal direction and the transverse direction at a constant stretching temperature.

The polyester film has a heat shrinkage in the longitudinal and transverse directions at 100 ° C. and 5 minutes of hot air condition, respectively, from 0 to 70%, preferably from 1 to 70%, respectively.

In addition, the polyester film exhibits an initial elastic modulus of 100 to 400 kgf / mm 2. If the elastic modulus is less than 100 kgf / mm 2, the resistance to mechanical tension may not be sufficient, leading to breakage during driving, which is not preferable. In addition, when the elastic modulus exceeds 400 kgf / mm 2, it is not preferable because the stiffness of the film is excessively increased and there is a possibility of breaking easily by external impact.

The polyester film exhibits a uniform elastic modulus throughout the film, specifically a variation of ± 15% or less.

Moreover, the number of pinholes after the pinhole resistance test of the said polyester film is 100 or less. If the number of pinholes exceeds 100 or a crack occurs, it is not preferable because the impact resistance is weak and can easily be ruptured when subjected to continuous impact during transportation and handling. In particular, since the film becomes more fragile in winter, pinholes may occur due to repeated wrinkles, which may cause defects. More preferably, the number of pinholes is 15 or less.

In addition, the polyester film exhibits a haze of 30% or less. If the haze is more than 30%, the transparency of the film becomes remarkably turbid so that it cannot be used for packaging applications in which the contents of the inside are visible. More preferably, the haze of the final film is 20% or less, most preferably 10% or less.

The polyester film exhibits a uniform haze throughout the film, specifically with a variation of ± 0.5% or less.

In addition, the polyester film has a strength of 10 to 30 kgf / mm ² , preferably 15 to 25 kgf / mm ² , and exhibits uniform strength of ± 2% or less of variation throughout the film.

In addition, the polyester film has an elongation of 30 to 200%, preferably 90 to 120%, and exhibits uniform elongation of ± 5% or less of variation throughout the film.

In addition, the polyester film preferably has a thickness of 10 to 300 µm, more preferably 10 to 100 µm.

Such a polyester film of the present invention, (a) blending the polylactic acid and the liquid caprolactone polymer to obtain a mixed resin; (b) melting and extruding the mixed resin to obtain an unstretched sheet; And (c) stretching and heat setting the unstretched sheet in at least one of longitudinal and transverse directions.

In the step (a), the mixing ratio of the polylactic acid and the liquid caprolactone polymer is 95: 5 to 60:40 by weight, and the reaction conditions are preferably blended at a temperature of 130 to 200 ° C. for 0.1 to 2 hours under a nitrogen atmosphere. Do. Blending can also be carried out using conventional blending equipment, such as single screw or twin screw type extruders.For more complete mixing of polylactic acid and liquid caprolactone polymers, blending with twin screw type extruders is recommended. desirable.

The liquid caprolactone polymer may be prepared by heating and liquefying the semi-solid caprolactone polymer. If the caprolactone polymer is not completely dissolved and the cosmetic melt remains, the part may be seeded and crystallization may start, so it is preferable to use it after completely liquefying before blending. In addition, when liquefied at an excessively high temperature, thermal degradation may occur and the physical properties of the additive may change, so that the liquefied liquid is gradually melted at a temperature below the thermal decomposition temperature of the caprolactone polymer, preferably at 50 to 80 ° C. Good to do.

In addition, the polylactic acid resin is preferably used after drying for 2 to 5 hours at 80 to 110 ℃ prior to blending with the liquid caprolactone polymer in order to prevent hydrolysis by the residual water.

Melting and extrusion temperature in the step (b) is preferably 180 to 220 ℃.

In addition, in the step (c), the stretching ratio in the longitudinal direction and the transverse direction is 2.5 to 3.5 times and 3.5 to 4.5 times, respectively, and the heat setting temperature is preferably 40 to 250 ° C., specifically, 40 for the heat shrinkable packaging film. To 120 ° C, and in the case of a general packaging film, it is preferably 100 to 250 ° C.

The polyester film according to the present invention prepared by the above method is made of biodegradable resin, and is environmentally friendly and excellent in transparency (90% or more of light transmittance, 30% or less of haze). In addition, the liquid caprolactone polymer is used to maximize the softening properties, while exhibiting uniform physical properties throughout the film. Moreover, since it is manufactured through extending | stretching, it is excellent in strength and elongation.

Accordingly, the polyester film according to the present invention is a general packaging film, high-quality packaging film, general label, heat shrink label, agricultural mulching film, overlapping film, paper lamination, nonwoven lamination, disposable gown, wallpaper It can be used for lamination and flooring lamination.

The present invention also provides a packaging material comprising the polyester film.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are only examples of the present invention and the present invention is not necessarily limited thereto.

Example  One

A polyester film was prepared by performing the composition and process conditions shown in Table 1 below.

Specifically, the caprolactone polymer (PL1000, manufactured by Perstorp) was slowly dissolved in a hot air oven at 50 to 100 ° C. The resulting liquid caprolactone polymer was blended with a polylactic acid resin (4032D, manufactured by NatureWorks) at 200 ° C. using a twin screw type extruder. At this time, the polylactic acid resin was used after drying for 3 hours at 100 ℃ before mixing, the mixing ratio of the liquid caprolactone polymer and polylactic acid resin was 15:85 by weight ratio.

The obtained mixed resin was melted and extruded at 190 ° C., brought into close contact with a casting roll at 15 ° C., stretched at 80 ° C. in 3.0 times in the longitudinal direction, stretched at 100 ° C. in 4.0 times in the transverse direction, and then at 90 ° C. Heat setting was performed to obtain a polyester film having a thickness of 20 μm.

Example  2 and Comparative example  1, 2

A polyester film was prepared in the same manner as in Example 1, except that the composition and process conditions set forth in Table 1 were performed.

division unit Example Comparative example One 2 One 2 article
castle Additive pretreatment Pretreatment No pretreatment additive Caprolactone polymer Caprolactone polymer Number average molecular weight 1,000 2,000 1,000 2,000 content weight% 15 15 15 15 ball
tablet Blending Temperature ℃ 200 200 200 200 Melting and Extrusion Temperature ℃ 190 200 190 200 Stretch
Temperature Longitudinal direction ℃ 80 90 83 92 Lateral direction ℃ 100 95 98 100 Stretching cost 3.0 × 4.0 3.0 × 3.8 3.0 × 4.0 3.0 × 3.9 Heat setting temperature ℃ 90 150 70 180

Test Example

Physical properties of the films prepared in Examples and Comparative Examples were evaluated in the following manner.

(1) Fairness

In the production of the polyester films according to Example 1 and Comparative Example 1, the discharge state, flowability, stretchability, and thickness smoothness of the prepared film were observed, and evaluated according to the following criteria. The results are shown in Table 2 below.

<Evaluation Criteria>

Good processability: Uniform melt state and flowability, uniform elongation and thickness smoothness

Poor processability: Large fluctuation in thickness smoothness due to change of melt flow, non-uniform stretching

Example 1 Comparative Example 1 Fairness Good Bad

As shown in Table 2, the composition of Example 1 blended liquid caprolactone polymer through pretreatment is excellent in uniform discharge state and flowability of the molten resin during the film production, excellent uniform stretchability and thickness smoothness While showing fairness, the composition according to Comparative Example 1, which blended semi-solid caprolactone polymer without pretreatment, had poor processability.

(2) thermal shrinkage of film

Samples of the films prepared in Examples and Comparative Examples were cut into a length of 200 mm and a width of 15 mm in a direction to be measured and held for 5 minutes in an air circulation oven maintained at 100 ° C., followed by measuring the length of the film. The shrinkage in the longitudinal and transverse directions was calculated according to the equation. The results are shown in Table 3 below.

Shrinkage (%) = (length before shrink-length after shrink) / length before shrink x 100

division unit Example Comparative example One 2 One 2 Heat shrinkage
(100 ° C., 5 minutes) Longitudinal direction % 25 5 30 2 Lateral direction % 35 12 50 4

(3) Uniformity Analysis of Film Properties

The film prepared in Examples and Comparative Examples was wound in a continuous process for 6 hours, and the elastic modulus, strength, elongation, and haze were measured by sampling 4 portions of the horizontal 30 cm intervals at the film center at 1 hour intervals after the start of the process. The average value was then taken. Physical property uniformity evaluation results for modulus, strength, elongation, and haze are shown in Tables 4 to 7, respectively.

The elastic modulus was measured using a universal testing machine (UTM 4206-001, INSTRON Co., Ltd.) according to ASTM D 882. After the film was cut to about 100 mm in length and 15 mm in width, it was mounted so that the intervertebral spacing was 50 mm. The experiment was conducted at a tensile speed of 200 mm / min, and the elastic modulus (kgf / mm 2) value of the sample calculated by the program embedded in the installation was obtained.

The elongation and strength of the film was measured using a tensile strength tester (MODEL6021, INSTRON), at least 5 cm in the direction orthogonal to the main shrinking direction of the sample and 15 mm in the main shrinking direction. After mounting, a stress-strain curve was obtained until stretching occurred while stretching at room temperature. The force applied when the fracture occurred was called strength (kgf / mm ² ), and the length magnification increased until the fracture occurred was called elongation (%).

In addition, the haze of the film was measured by a haze meter (SEP-H, Nihon Semitsu Kogaku, Japan) and C-light source was used.

Example Comparative example One 2 One 2 additive 15 wt% PL1000 PL2000 PL1000 PL2000 Elastic modulus
(kgf / mm ² ) 1hr 350 320 420 400 2 hr 345 321 360 360 3hr 347 315 290 260 4hr 352 320 300 350 5hr 349 323 480 330 Average 348.6 319.8 370 340 Standard Deviation 2.701851 2.949576 80.62258 51.47815

Example Comparative example One 2 One 2 additive 15 wt% PL1000 PL2000 PL1000 PL2000 burglar
(kgf / mm ² ) 1hr 19 23 25 26 2 hr 18 19 21 23 3hr 20 20 15 14 4hr 17 18 16 22 5hr 19 21 25 20 Average 18.6 20.2 20.4 21 Standard Deviation 1.140175 1.923538 4.774935 4.472136

Example Comparative example One 2 One 2 additive 15 wt% PL1000 PL2000 PL1000 PL2000 Shinto (%) 1hr 95 108 90 100 2 hr 100 110 100 98 3hr 103 110 120 140 4hr 106 109 106 125 5hr 100 112 110 130 Average 100.8 109.8 105.2 118.6 Standard Deviation 4.086563 1.48324 11.18928 18.70294

Example Comparative example One 2 One 2 additive 15 wt% PL1000 PL2000 PL1000 PL2000 Haze (%) 1hr 4.5 5.5 3 4.1 2 hr 4.2 5.3 4.2 5.2 3hr 4.5 5.5 6.9 7.5 4hr 4.4 5.6 5.5 4.8 5hr 4.5 5.5 4.9 5.3 Average 4.42 5.48 4.9 5.38 Standard Deviation 0.130384 0.109545 1.454304 1.275539

As can be seen in Table 4, the films of Examples 1 and 2 exhibited a uniform elastic modulus throughout the process, but the films of Comparative Examples 1 and 2, which blended semi-solid caprolactone polymer without pretreatment, were mixed with polylactic acid. Due to the unevenness, the elastic modulus was greatly varied during the process. In addition, considering that the lower the initial elastic modulus, the more excellent the flexibility of the film, the results shown in Table 4, it can be seen that the films of Examples 1 and 2 have excellent flexibility compared to the films of Comparative Examples 1 and 2.

In addition, as shown in Tables 5 to 7, the films of Examples 1 and 2 showed uniform physical properties throughout the process also in terms of strength, elongation, and haze, but Comparative Examples 1 and 2 in which semi-solid caprolactone polymers were blended without pretreatment Film 2 had a large change in strength, elongation, and haze physical properties during the process.

In the above, the present invention has been described with reference to the above embodiments, which are only examples, and the present invention will be described below in various modifications and equivalents which are obvious to those skilled in the art. It should be understood that it can be carried out within the scope of the appended claims.

Claims (19)

Polylactic acid and a liquid caprolactone polymer obtained by blending a caprolactone polymer by heating and liquefying,
Polyester film, characterized in that the initial elastic modulus is 100 to 400 kgf / mm2, the deviation is ± 15% or less.
The method of claim 1,
The number average molecular weight of the caprolactone polymer, characterized in that 1,000 to 10,000, polyester film.
The method of claim 1,
The content of the polylactic acid and caprolactone polymer is characterized in that the weight ratio of 95: 5 to 60:40, polyester film.
The method of claim 1,
The film is a polyester film, characterized in that the heat shrinkage in the longitudinal direction and transverse direction at 100 ℃ and hot air conditions of 5 minutes, respectively 0 to 70%.
delete The method of claim 1,
The film has a haze of 30% or less and a deviation of ± 0.5% or less, the polyester film.
The method of claim 1,
The film has a strength of 10 to 30 kgf / mm ² , the deviation is ± 2% or less, polyester film.
The method of claim 1,
The film has an elongation of 30 to 200%, the deviation is ± 5% or less, polyester film.
The method of claim 1,
The film is characterized in that the thickness of 10 to 300 ㎛ polyester film.
(a) blending polylactic acid and liquid caprolactone polymer to obtain a mixed resin;
(b) melting and extruding the mixed resin to obtain an unstretched sheet; And
(c) stretching and heat setting the unstretched sheet in at least one of longitudinal and transverse directions
Including a method of producing a polyester film according to claim 1.
The method of claim 10,
Wherein the liquid caprolactone polymer is prepared by liquefying the caprolactone polymer at a temperature below the pyrolysis temperature.
The method of claim 10,
Wherein said liquid caprolactone polymer is prepared by liquefying a caprolactone polymer at 50 to 80 ° C.
The method of claim 10,
And drying the polylactic acid before blending the polylactic acid with the liquid caprolactone polymer at 80 to 110 ° C. to remove residual water.
The method of claim 10,
Wherein the polylactic acid and the liquid caprolactone polymer are blended in a weight ratio of 95: 5 to 60:40 in step (a).
The method of claim 10,
Blending of the polylactic acid and liquid caprolactone polymer in the step (a) is carried out at a temperature of 130 to 200 ℃ under a nitrogen atmosphere.
The method of claim 10,
Melting and extrusion temperature in the step (b) is characterized in that 180 to 220 ℃.
The method of claim 10,
In the step (c), the draw ratio in the longitudinal direction is 2.5 to 3.5 times, and the draw ratio in the transverse direction is 3.5 to 4.5 times.
The method of claim 10,
Heat-setting temperature in the step (c) is characterized in that 40 to 250 ℃.
Packaging material comprising the polyester film according to claim 1.