KR20060118355A - Biodegradable aliphatic polyester film and preparation thereof - Google Patents

Abstract

Provided are a biodegradable aliphatic polyester film that is superior in heat resistance, mechanical properties, and optical properties, has low specific gravity, high whiteness, and high porosity, and is usable as environment-friendly packing materials, and a preparation thereof. The biodegradable aliphatic polyester film is prepared from a polylactic acid polymer resin having a melting temperature of 135‹C or higher. The polyester film has a specific gravity of 1.18 or less, a whiteness of 50% or more, a porosity of 5% or more, a biodegradation ratio of 90% or more, a degree of crystallinity of 25-65%, a dynamic frictional coefficient of 1.0 or less, F-5 of 7kgf/mm^2, the modulus of elasticity of 200-500kgf/mm^2, and a coefficient of linear expansion at 60‹C of 0-2micron/cmÀ‹C.

Description

Biodegradable Aliphatic Polyester Film {BIODEGRADABLE ALIPHATIC POLYESTER FILM AND PREPARATION THEREOF}

1 is a schematic view showing a specimen and a torsional packaging thereof for measuring a torsional fixation rate of a film prepared in an embodiment of the present invention.

The present invention relates to a biodegradable aliphatic polyester film, and more particularly, to an aliphatic polyester film having excellent whiteness and porosity and low specific gravity, as well as heat resistance, mechanical properties, optical properties, biodegradability, and torsional fixation rate. It is about.

Plastic films frequently used for packaging include cellophane, polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), nylon, polyethylene terephthalate (PET), and the like. However, since cellophane film causes severe environmental pollution during the manufacturing process, it is regulated by the production itself, and polyvinyl chloride film has a lot of restrictions in use due to the generation of harmful substances such as dioxins during incineration. In addition, the polyethylene film is too low heat resistance and mechanical properties is limited to use other than the low-end packaging bags.

Polypropylene, nylon, polyethylene terephthalate, etc. may be mentioned as a film having a relatively stable molecular structure and having good mechanical properties. However, when used for packaging purposes, the film is buried and accumulated due to chemical and biological stability. In addition, shorter landfills have caused shorter lives and problems with global soil pollution.

In order to compensate for the disadvantages of plastics that do not decompose, a film made of 20% to 40% of a decomposable resin such as starch in a hardly decomposable plastic is decomposed after a certain period of time. However, such a film is deteriorated in mechanical properties under the influence of the mixed decomposable resin, there is a disadvantage that there is no heat resistance. Further, after a certain period of time, only the degradable resin mixed in the film is selectively decomposed, and in the case of the overall film, there is a disadvantage in that it accumulates in the soil as it is only physically chopped.

Therefore, in recent years, much research has been conducted on polylactic acid, which is an aliphatic polyester having high biodegradability of the resin itself.

Polylactic acid, an aliphatic polyester, is a polymer made by condensation polymerization of lactic acid. Lactic acid is an optical isomer of L-lactic acid and D-lactic acid, so polylactic acid is generally present as a random copolymer between two optical isomers. Since the random copolymer does not have crystallinity, the random copolymer may be manufactured as a blown film in an amorphous state and used for a general encapsulation, which does not require heat resistance and mechanical properties.

In addition, a stretched film may be prepared by adding a large amount of inorganic material or a large amount of nanocomposite in order to give crystallinity to the random copolymer, but it is not easy to properly control the degree of crystallization, and optical properties such as transparency There is a problem that becomes extremely bad. In addition, due to the large amount of inorganic materials and nanocomposites, the flexibility of the stretched film is lowered and the film is in a stiff state with low mechanical properties. Therefore, there is a problem in using a good packaging film and the biodegradability is also worsened.

On the other hand, polymers made of L-lactic acid alone or D-lactic acid alone may be useful raw materials that can be used as stretched films as semi-crystalline resins having a high melting temperature (near 180 ° C) and controlling the crystallinity to some extent. The lack of flexibility of the film and the stiff technical disadvantages have not been completely solved, and the production cost of pure homopolymers is so high that there are many problems for practical use.

In addition, the film with low specific gravity can be used for packaging to reduce the weight of the final product and can be easily separated when recycling the packaging material due to the difference in specific gravity between the product and the packaging film, thereby increasing the area ratio to the unit weight, thereby increasing the yield in the post-processing process. Films with excellent whiteness can produce a white printing effect without any other printing process, and have a color similar to paper, which is very useful as a special packaging film or a twisted film, and a high porosity film has a high oxygen and gas permeability. It is better than the film and is well ventilated, so it can be usefully used as a hygiene product.

Accordingly, an object of the present invention is to provide an aliphatic polyester film having a low specific gravity, excellent whiteness, and high porosity while using a polylactic acid, which is a random copolymer, without a decrease in flexibility and biodegradation rate, and a method for producing the same.

In order to achieve the above object, in the present invention, a polylactic acid-based polymer resin having a melting temperature (T _m ) of 135 ° C. or more and has a specific gravity of 1.18 or less, a whiteness of 50% or more, a porosity of 5% or more and a biodegradation rate of 90% or more Provided is a biodegradable aliphatic polyester film.

In the present invention,

a) extruding the melting temperature (T _m ) polylactic acid copolymer resin at a temperature of T _m + 100 ° C. to T _m + 40 ° C. and then cooling it at a temperature of 30 ° C. or lower;

b) The sheet obtained is preheated at a temperature in the range of T _m -100 ° C. to T _m -85 ° C., followed by longitudinal stretching at a temperature in the range of T _m -85 ° C. to T _m -75 ° C., followed by a minimum of two steps. At the same temperature as the scene, later stages of transverse stretching at a temperature ranging from T _m -80 ° C to T _m -70 ° C; And

c) heat setting the stretched film at a temperature ranging from T _m -60 ° C to T _m -30 ° C.

It provides a method for producing a biodegradable aliphatic polyester film comprising a.

The present invention will be described in more detail below.

In the present invention, a polylactic acid polymer which is an aliphatic polyester can be used alone or in combination with a small amount of other hydroxy carboxylic acid units as a copolymer resin.

It is preferable that melt temperature of a polylactic acid-type polymer is 135 degreeC or more and less than 180 degreeC, and 140 degreeC or more is more preferable. If the melting temperature is lower than 135 ℃ heat resistance and mechanical properties are not properly expressed because it is not preferable.

In addition, the polylactic acid polymer is a polymer obtained by condensation of lactic acid made from vegetable raw materials such as corn, which is a random copolymer of L-lactic acid and D-lactic acid, and has a weight average molecular weight of 80,000 g / mol to 500,000 g / mol. It is preferable. When the weight average molecular weight is less than 80,000, heat resistance and mechanical properties are not properly expressed, and when the weight average molecular weight is greater than 500,000, the viscosity is too high to process a proper biaxially stretched film.

Small amounts of hydroxy carboxylic acid units that can be used in the present invention include glycolic acid or 2-hydroxy-3,3-dimethylbutyl acid, and the like in an amount of 5% by weight or less based on the total copolymerized resin. Can be used.

In addition, a normal electrostatic agent, an antistatic agent, a sunscreen, an antiblocking agent, and other inorganic lubricants may be added to the copolymerized resin of the present invention within a range that does not impair the effects of the present invention.

In order to increase the biodegradation rate and porosity of the film, the amount of the inorganic substance contained in the resin is preferably 5% by weight or less, preferably 3% by weight or less, based on the total resin weight.

In the present invention, in order to control the crystallinity, friction coefficient, specific gravity, F-5, elastic modulus, linear expansion coefficient, whiteness, porosity and biodegradation rate of the film, the extrusion temperature of the extruder during melt extrusion of the resin is T _m +100 ℃ It is preferable to set it as the range of -T _m + 40 degreeC, and to make a cooling roll in a casting process after melt extrusion into 30 degreeC or less. Moreover, it is preferable to make the preheating temperature in longitudinal stretch be T _m- 100 degreeC-T _m -85 degreeC, and let longitudinal stretch temperature be T _m -85 degreeC-T _m -75 degreeC.

The transverse stretching temperature, i.e., the temperature in the section where transverse stretching occurs in the tenter, is divided into at least two stages, i.e., early and late, so that the initial stretching temperature is the same as the initial stretching temperature, and later, T _m -80 ° C to T _m -70 ° C. It is preferable that the residence time in the later stage of the transverse stretch be at least 15% of the total transverse stretch time and the residence time in the later stage of the transverse stretch at least 50% of the total transverse stretch time. It should be set at least 5 ℃ higher than the initial one. Moreover, it is preferable that heat setting temperature shall be T _m -60 degreeC-T _m -30 degreeC.

The aliphatic polyester film of the present invention prepared according to the above is characterized by specific gravity of 1.18 or less, whiteness of 50% or more, porosity of 5% or more, and biodegradation rate of 90% or more.

If the specific gravity is greater than 1.18, the area ratio to the unit weight is increased, which lowers the yield in the post-processing process, and the price of the product is also high. When the whiteness is less than 50%, the white effect is produced when the special packaging film or the special twist film is applied. For this purpose, white printing is required, and when the porosity is less than 5%, oxygen and gas permeability are reduced, and the ventilation is poor.

In addition, the aliphatic polyester film of the present invention prepared according to the above has a crystallinity of 25% to 65%, the coefficient of kinetic friction of 1.0 or less, F-5 of 7 kgf / mm ² or more, elastic modulus of 200 to 500 kgf / mm ^The coefficient of linear expansion in the temperature range of ² and 25 degreeC-60 degreeC is 0-2.0 micrometers / cm * degreeC.

When the crystallinity of the film is lower than 25%, the heat resistance of the film is poor and the mechanical properties are significantly lowered. When the crystallinity is higher than 65%, the flexibility of the film is excessively low, resulting in a deterioration in mechanical properties. In addition, the higher the degree of crystallinity of the film, the stronger the binding force between the molecular chains to extend the period of decomposition of the film, the lower the biodegradation rate of the film.

When the coefficient of dynamic friction of the film exceeds 1.0, the handling performance deteriorates in the film production process and the post-processing process such as printing, which significantly reduces the production and post-processing yield.

When the film has an F-5 of less than 7 kgf / mm ² and an elastic modulus of less than 200 kgf / mm ² , the film is stretched even at a small force, and it is difficult to be used for good packaging applications such as deformation easily, and the film has an elastic modulus of 500 Exceeding kgf / mm ² makes the film too strong and stiff, making it difficult to use for good packaging applications.

In addition, when the coefficient of linear expansion in the temperature range of 25 ℃ to 60 ℃ is less than 0, the shrinkage of the film occurs at the temperature, if the coefficient of linear expansion exceeds 2.0 ㎛ / cm · ℃ the film is excessively stretched at the temperature to wrap You cannot use it for a purpose.

In the present invention, in order to control the birefringence and the light transmittance of the film, in addition to the above extrusion process, casting process, longitudinal stretching process, transverse stretching process and heat setting process conditions, respectively in the longitudinal direction and transverse direction when stretching the film It is preferable to extend | stretch 3 times or more, and the draw ratio in one direction should not exceed 2 times the draw ratio in the other direction.

The film of the present invention prepared according to the above has a birefringence of 0.01 or less and a light transmittance of 80% or more.

If the birefringence of the film is 0.01 or less, the degree of orientation of the molecular chains in the longitudinal and transverse directions of the film is in harmony with each other and may exhibit uniform mechanical and optical properties in both directions. However, it is not preferable because almost no orientation occurs in one direction of the transverse direction and excessive orientation in the other direction causes mechanical and optical properties of the film to be asymmetrically expressed.

In addition, when the light transmittance is less than 80%, the film is not relatively transparent and the appearance is not beautiful, it is not preferable because the printed pattern is clearly visible from the outside.

The aliphatic polyester film of the present invention has a torsional fixation rate of at least one direction of 57% or more. A torsional fixation rate of 57% means that when used for the twisted packaging of common candies, twisting to 630 degrees (1.75 wheels) preserves 360 degrees (one wheel) even after 24 hours of standing. At this time, if one wheel is not preserved, it cannot be used for good twist packaging. This torsional fixation rate is closely related to the crystallinity and elasticity modulus, and the lower the crystallinity of the film, the better the torsional fixation rate.

The film produced according to the present invention is not only excellent in heat resistance, mechanical properties, optical properties and biodegradability, but also excellent in torsional fixing rate, which is very useful as an environmentally friendly packaging material and individual twisted packaging material. In addition, since the specific gravity is 1.18 or less, it is light and the area ratio to the unit weight is increased to increase the yield in the post-processing process. The film is opaque, clean, beautiful in appearance and beautiful in appearance with a whiteness of 50% or more. Very useful as packaging film and special twisted packaging.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are not intended to limit the present invention, but are not limited thereto. Measurement of physical properties and various performance evaluations of the films prepared in Examples and Comparative Examples of the present invention were performed by the following method.

(1) Melting temperature (T _m, ℃)

Using a differential scanning thermal analyzer (Perkin Elmer, DSC-7), the crystal melting temperature was measured at a rate of 20 ° C. per minute.

(2) Dynamic friction coefficient (μk)

According to the standard measurement method of ASTM D1894, two sheets of 15 mm x 15 mm film were stacked, 150 g of weight was placed thereon, and the force generated when sliding at a speed of 20 mm / min was applied to the friction surface. Calculated by dividing by the force acting perpendicular to.

(3) biodegradation rate (%)

The ratio of the biodegradability value measured by KS M3100-1 (2003) for 180 days with the standard was calculated according to the following equation.

(4) crystallinity (%)

Crystal melting energy (Hc, J / g) measured at a heating rate of 20 ° C. per minute using a differential scanning thermal analyzer (PerkinElmer, DSC-7) and crystal generation energy generated at elevated temperature (Ha, J / It was calculated from g) according to the following formula.

(5) F-5 (kgf / mm ² )

Using a UTM (Instron, model name 4206-001) according to the standard measurement method of ASTM D882, the 100 mm long and 15 mm wide samples were stretched at a rate of 200 mm / min at room temperature and the strength at 5% elongation was measured. Measured.

(6) modulus of elasticity (kgf / ㎜ ² )

Initial elastic modulus was calculated according to the following formula using UTM (Instron, Model No. 4206-001) according to the standard measurement method of ASTM D882.

(7) linear expansion coefficient (µm / cm 占 폚)

Using a heat deflection analyzer (TA, TMA 2940) at a temperature rise rate of constant load 0.05 N and 10 ℃ / min was measured at 25 ℃ to 60 ℃ was calculated according to the following formula.

(8) birefringence

After measuring the refractive index in the longitudinal direction and the transverse direction using an Abbe refractometer, it was calculated according to the following equation.

(9) Light transmittance (%)

According to the standard measurement method of ASTM D1003 it was measured at a diameter of 25 mm and scattering angle of 2.5 degrees.

(10) specific gravity

It was measured according to the density gradient pipe method (ASTM D1505, JIS K7112).

(11) whiteness (%)

It was measured according to the standard measurement method of ASTM E313-96.

(12) torsional fixed rate (%)

After putting candy (hard candy) on the specimen of 10 cm × 7 cm, holding the middle part (candy) as shown in Fig. 1, and wrapping it by 630 degrees (1.75 wheels) left and right, respectively, and then preserving the torsion after standing at room temperature for 24 hours. The angle was measured and calculated according to the following formula. (However, in Fig. 1, when the 10 cm direction is the longitudinal direction, it is referred to as the longitudinal torsion fixed rate, and when the 10 cm direction is the transverse direction, it is called the transverse twist fixed rate.)

(13) Porosity (%)

The porosity of the film was calculated according to the following formula.

Example 1

A random copolymer of L-lactic acid and D-lactic acid, 97 wt% of polylactic acid resin (Cargill Dow) having a weight average molecular weight of 220,000 and a melting temperature of 149 ° C., and silicon dioxide having an average particle diameter of 2 μm prepared by a master batch method. 3 wt% of the same polylactic acid resin containing 1 wt% was mixed to prepare a mixed resin having a total silicon dioxide content of 0.03 wt%.

After melt-extruding the said mixed resin through the extruder whose melt extrusion temperature is 225 degreeC, it adhered to the cooling roll cooled at 20 degreeC, and obtained the sheet | seat. The sheet thus obtained was immediately preheated to 60 ° C., and then longitudinally stretched 3.5 times by passing through a 68 ° C. stretching roll.

The stretched film was 4.0 times transversely stretched in the transverse stretching section of the tenter, which was divided into 2 zones, with the average temperature of the initial 20% section being 68 ° C and the average temperature of the late 80% section being 75 ° C.

The sheet was heat-set at 106 ° C. in the heat treatment section of the tenter to prepare a polylactic acid biaxially oriented film of aliphatic polyester having a thickness of 20 μm.

The crystallinity, birefringence, light transmittance, dynamic friction coefficient, linear expansion coefficient, F-5, elastic modulus, torsional fixed ratio, specific gravity, whiteness, porosity, and biodegradability of the film were measured and shown in Table 1 below.

Comparative Example 1

After preheating the melt-extruded and cooled sheet to 65 ° C, it is stretched 3.5 times by passing through a 75 ° C stretching roll, and the average temperature of the initial 20% section is 80 ° C, and the average temperature of the later 80% section is 88 ° C. After stretching 4.0 times in the transverse stretching section of the tenter divided into 2 sections, the tenter is divided into 2 zones in which the average temperature of the initial 25% section is 115 ℃ and the average temperature of the late 75% section is 132 ℃. A polylactic acid biaxially oriented film having a thickness of 20 μm was manufactured in the same manner as in Example 1, except that the heat setting was performed in the heat treatment section. The properties of the film were measured and shown in Table 1 below.

Comparative Example 2

The melt extrusion temperature of the resin is 260 ° C., the temperature of the cooling roll is 40 ° C., the temperature of the longitudinal drawing section is 85 ° C., the temperature of the transverse drawing section is 90 ° C. without distinction between the initial and the latter, and the temperature of the heat treatment section. A polylactic acid biaxially oriented film having a thickness of 20 μm was prepared in the same manner as in Comparative Example 1, except that the initial and late stages were 115 ° C., and the characteristics of the film are shown in Table 1 below.

Comparative Example 3

90% by weight of polylactic acid resin and 10% by weight of silicon dioxide prepared by the master batch method are mixed to prepare a mixed resin having a total silicon dioxide content of 10% by weight, and the temperature of the transverse stretching and heat treatment sections is divided into the initial and the later stages. A polylactic acid biaxially oriented film having a thickness of 20 μm was prepared in the same manner as in Comparative Example 1, except that 88 and 132 ° C., respectively, and the properties of the film are shown in Table 1 below.

As shown in Table 1, the polyester film of Example 1 according to the present invention is excellent in biodegradation rate, while maintaining excellent properties of all of heat resistance, mechanical properties and optical properties, while having a small specific gravity and excellent whiteness and porosity. It can be seen.

Aliphatic polyester film according to the present invention is excellent in heat resistance, mechanical properties, optical properties and biodegradation can be used as an environmentally friendly packaging material. In particular, since the film according to the present invention has excellent torsional fixing rate, it is very useful as an individual twist packaging material such as chocolate and candy, and has a low specific gravity, high whiteness and high porosity, and can be used for high quality packaging applications with a beautiful appearance.

Claims (10)

A biodegradable aliphatic polyester film, which is made of a polylactic acid polymer resin having a melting temperature of 135 ° C. or higher and has a specific gravity of 1.18 or less, a whiteness of 50% or more, a porosity of 5% or more, and a biodegradation rate of 90% or more. . The method of claim 1, Crystallinity of 25% to 65%, dynamic friction coefficient of 1.0 or less, F-5 of 7 kgf / mm ² or more, elastic modulus of 200 to 500 kgf / mm ² and 0 to 2 μm / cm Biodegradable aliphatic polyester film, characterized in that it has a coefficient of linear expansion. The method according to claim 1 or 2, A biodegradable aliphatic polyester film having a birefringence of 0.01 or less and a light transmittance of 80% or more. The method according to claim 1 or 2, A biodegradable aliphatic polyester film, characterized in that the torsion fixation rate in at least one direction is 57% or more. The method of claim 3, wherein A biodegradable aliphatic polyester film, characterized in that the torsion fixation rate in at least one direction is 57% or more. a) extruding a polylactic acid copolymer resin having a melting temperature (T _m ) of 135 ° C. or higher at a temperature of T _m + 100 ° C. to T _m + 40 ° C. and then cooling it at a temperature of 30 ° C. or lower; b) The sheet obtained is preheated at a temperature in the range of T _m -100 ° C. to T _m -85 ° C., followed by longitudinal stretching at a temperature in the range of T _m -85 ° C. to T _m -75 ° C., followed by a minimum of two steps. At the same temperature as the scene, later stages of transverse stretching at a temperature of T _m -80 ° C to T _m -70 ° C, and c) heat-setting at a temperature of T _m -60 ° C. to T _m -30 ° C., wherein the biodegradable aliphatic polyester film is prepared. The method of claim 6, The temperature of the laterally laterally stretched process is 5 degreeC or more higher than the initial temperature. The method of claim 6, The residence time in the initial transverse stretching period is at least 15% of the total transverse stretching time, the residence time in the later section is at least 50% of the total transverse stretching time. The method of claim 6, Longitudinal stretching and transverse stretching are each carried out at a draw ratio of three times or more. Packaging material comprising a biodegradable aliphatic polyester film according to claim 1.

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