KR101012167B1 - Bidirectional shrinkable biodegradable film and preparation method thereof - Google Patents

Abstract

The present invention relates to a biodegradable bidirectional shrinkage film and a method for manufacturing the same, wherein the biodegradable bidirectional shrinkage film of the present invention having a polylactic acid resin containing 80% by weight or more of L-lactic acid is 100 ° C. in a hot air oven for 10 minutes. The shrinkage in both directions is 10 to 50% at the time of shrinkage, the initial elastic modulus is 50 to 350 kgf / mm2 on the strain-stress curve, and the elongation reduction rate of the film after shrinking at 120 ° C. for 10 seconds in a hot air shrinkage tunnel (ΔE ) Is 0 to 70%, the film of the present invention is uniformly shrinkable and not easily broken by external impact during transportation / storage, thereby exhibiting excellent flexibility and breaking strength.

Biodegradation, Bidirectional Shrinkage, Film, Polylactic Acid, Stretching, Packaging Materials, Elastic Modulus

Description

Biodegradable bidirectional shrink film and its manufacturing method {BIDIRECTIONAL SHRINKABLE BIODEGRADABLE FILM AND PREPARATION METHOD THEREOF}

The present invention relates to a biodegradable bidirectional shrinkage film and a method for manufacturing the same, and more particularly, to a biodegradable bidirectional shrinkage film for overlapping and having a uniform shrinkage and excellent flexibility and breaking strength.

As general-purpose heat shrink films, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyester film (PET) and the like derived from petroleum are widely used. In order to use the heat-shrinkable film for various shrink packaging materials or overlaps, basic properties such as shrinkage, printability, transparency, solvent resistance, heat resistance, and post-processing aptitude, as well as safety in transportation and storage after shrinkage, impact resistance, and the like are required. Although petroleum-based films may partially satisfy the above required characteristics, polyvinyl chloride film (PVC) generates many harmful substances such as dioxins when incinerated, and thus, many polyvinyl chloride films (PS) are printed. It is difficult to use the ink for general film due to the poor properties and has a large natural shrinkage, there is a difficulty in storage, polyethylene (PE) and polypropylene (PP) has a problem of poor heat resistance and too flexible to post-processability. Shrinkable polyethylene terephthalate (PET) is excellent in heat resistance, weather resistance, and shrinkage uniformity, but it is accumulated without being decomposed upon disposal, shortening the life of landfills and causing global soil pollution.

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

Japanese Patent Application Laid-Open No. 2002-113775 proposes a heat shrinkable film mainly based on polylactic acid. However, the film has a low heat shrinkage ratio, so that shrinkage does not occur completely even when shrinked. There is a problem that falls significantly.

In addition, US Patent Publication Nos. 2007/0003774 and 2007/0116909 propose heat-shrinkable biodegradable polylactic acid based films prepared in a blown manner. However, the film made by this method has a significantly lower strength and elongation, indicating a deteriorated mechanical property, and crystallization is accelerated when shrinking in the shrinking tunnel, so that the film is easily broken as the elongation is sharply dropped.

Accordingly, it is an object of the present invention to provide a biodegradable bidirectional shrinkage film having a uniform shrinkage property and excellent properties such as impact resistance, flexibility, transparency, as well as suitable properties for packaging applications, and a method of manufacturing the same.

In order to achieve the above object, in the present invention, a biaxially stretched biodegradable film containing polylactic acid resin as a main component, the polylactic acid resin containing 80% by weight or more of L-lactic acid; The bidirectional shrinkage at 100 ° C. for 10 minutes in a hot air oven is 10 to 50%; The initial elastic modulus on the strain-stress curve is 50 to 350 kgf / mm 2; It provides a biodegradable bidirectional shrinkage film and a packaging material comprising the same, characterized in that the elongation reduction rate (ΔE) of the film after shrinking for 10 seconds at 120 ℃ in a hot air shrink tunnel.

In addition, the present invention, melt-extruded raw material resin containing a polylactic acid resin containing 80% by weight or more of L-lactic acid as a main component; Stretching the melt-extruded unstretched film 2 to 7 times in the longitudinal and transverse directions, respectively, at a temperature of 0 to 40 ° C. higher than the glass transition temperature of the raw material resin; Heat-setting the biaxially stretched film at a temperature of 50 to 100 ° C. lower than the melting temperature of the raw material resin; And it provides a method for producing a biodegradable bi-directional shrinkage film of the present invention comprising the step of cooling the film while giving a relaxed or static relaxed to the heat-set film.

Biodegradable bi-directional shrink film of the present invention has a uniform shrinkage and excellent basic properties such as impact resistance, flexibility, transparency, as well as low initial shrinkage speed can be shrunk uniformly in the shrink tunnel, external impact during transportation / storage Since it is not easily broken by having excellent flexibility and breaking strength, it can be usefully used for overlapping purposes.

Hereinafter, the biodegradable bidirectional shrink film of the present invention will be described in detail.

The biodegradable bidirectional shrinkage film of the present invention is a biaxially oriented film having a polylactic acid resin as a main component as a raw material resin, and particularly includes a polylactic acid resin containing 80% by weight or more of L-lactic acid. When the L-lactic acid content is 80% by weight or less, the crystallinity is too low, there is a problem that the heat resistance is significantly lowered and the shrinkage rate is faster due to the high shrinkage stress, there is a problem that the shrinkage uniformity. Preferably the L-lactic acid content is at least 90% by weight.

In addition to the polylactic acid resin, an aliphatic or aliphatic aromatic polyester resin having a glass transition temperature of -80 to 60 ° C may be used as the raw material resin.

The aliphatic or aliphatic polyester resin may be obtained by polycondensing an aliphatic dicarboxylic acid or a derivative thereof and a diol component, and terephthalic acid, phthalic acid, isophthalic acid, naphthalene 2,6-dicarboxyl in a range that does not impair biodegradability. At least one dicarboxylic acid selected from the group consisting of an acid, diphenylsulfonic acid dicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxyethanedicarboxylic acid, and cyclohexanedicarboxylic acid can be further used. . At this time, as the aliphatic dicarboxylic acid or derivatives thereof, at least one selected from the group consisting of succinic acid, glutaric acid, malonic acid, oxalic acid, adipic acid, sebacic acid, azelaic acid, and nonanedicarboxylic acid may be used. Ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, propylene glycol, 1,4-cyclohexanediol, hexamethylene glycol, polyethylene glycol, triethylene One or more types selected from the group consisting of glycol, neopentyl glycol and tetramethylene glycol can be used.

The glass transition temperature is preferably from 1 to 30% by weight, based on the total weight of the raw material resin of the aliphatic or aliphatic aromatic polyester resin having a glass transition temperature of -80 to 60 ° C. It is difficult to form a sheet during extrusion processing due to poor property, and easily decomposes, and there is a problem in that the final film is opaque due to poor compatibility. More preferably 5 to 20% by weight.

The biodegradable bidirectional shrink film of the present invention has the following physical properties in order to be optimized for various shrink packaging materials or overlap applications.

First, when the biodegradable bidirectional shrinkage film is shrunk in a hot air oven at 100 ° C. for 10 minutes, the bidirectional shrinkage rate needs to be 10 to 50%. When the bidirectional shrinkage is less than 10%, there is a problem that the shrinkage is too small to be applied to a container having various shapes, and there is a problem in that the appearance is not tight and wrinkles occur even when shrinking. This is because when the bidirectional shrinkage exceeds 50%, the contraction speed is so fast that the contraction shape is distorted or the focus is shifted in the contraction tunnel.

And the initial elastic modulus on the strain-stress curve needs to be 50 to 350 kgf / mm 2. When the elastic modulus is less than 50 kgf / mm2, the resistance to mechanical tension is not sufficient in the printing and laminating processes, such as wrinkles in the driving direction, causing printing problems or breaking during driving. Not. On the contrary, when it exceeds 350 kgf / mm 2, it is not preferable because the stiffness of the film rises and is easily broken or broken by an external impact. More preferably, the range of 150-300 kgf / mm <2> is good.

Moreover, the elongation reduction rate (ΔE) of the film after shrinking for 10 seconds at 120 ° C. in a hot air shrinkage tunnel needs to be 0 to 70%. Since all shrink films do not completely induce crystallization, there is a stress to return to the state before stretching when heat is applied, and crystallization of the film proceeds by heat. As the crystallization progresses, the film properties after shrinking are changed, in particular, the elongation decreases drastically. When the elongation reduction rate (ΔE) after shrinkage exceeds 70%, a problem arises in that the film is cracked due to products colliding during transportation, and thus the film cannot serve as a packaging film. Preferably, the elongation reduction rate (ΔE) is 50% or less.

And the impact absorption energy of the film is preferably 5 kgf-cm or more, more preferably 5 to 30 kgf-cm. Shock absorption energy is a measure of the force that can absorb shock at high speed when the film ruptures. If the impact absorption energy is less than 5 kgf-cm, the film may be damaged by small impact during transportation / handling / storage. Because it is not desirable.

In addition, the Elmendorf tear strength of the film is preferably 3.0 kgf / μm or more, more preferably 3.0 to 10.0 kgf / μm. In general, the slower the rate of tear propagation after the film is ruptured, the more flexible and impact-resistant the film is. If the Elmendorf tear strength is less than 3.0 kgf / ㎛, the tearing area after the tear is much higher. There is a problem that is damaged.

And it is preferable that the haze of a film is 30% or less. If the haze exceeds 30%, the transparency of the film becomes remarkably turbid so that the film cannot be used for packaging purposes requiring transparency. More preferably, the haze of the final film may be 20% or less.

Next, the process for producing the biodegradable bidirectional shrink film of the present invention will be described in detail. The film manufacturing process according to the invention is briefly, (1) melt-extruded raw material resin; (2) biaxially stretching the melt-extruded unstretched film vertically and horizontally; (3) heat setting the biaxially stretched film; And (4) cooling the heat-set film.

In the present invention, a polylactic acid resin containing 80% by weight or more of L-lactic acid is used as the main raw material resin, and in addition, an aliphatic or aliphatic aromatic polyester resin having a glass transition temperature of -80 to 60 ° C is compared with the total weight of the raw material resin. It can be used by mixing in 1 to 30% by weight.

In addition, additives such as a crosslinking agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antiblocking agent, an inorganic lubricant, and an antistatic agent may be added to the raw material resin in a conventional manner without departing from the object of the present invention.

After melt-extruding the raw material resin, it is brought into close contact with the casting roll and biaxially stretched vertically and horizontally. In this case, the casting roll temperature is 0 to 30 ° C. because the casting roll temperature is lowered as much as possible to increase the crystallization rate. It is preferable and it is especially preferable that it is 10-20 degreeC.

In addition, the stretching temperature in the longitudinal and transverse directions in the stretching step is preferably a temperature of 0 to 40 ℃ higher than the glass transition temperature of the raw material resin. This is because when the stretching temperature is lower than the glass transition temperature of the raw material resin, the stretching stress is high, so that the frequency of break in the process is high and the orientation crystallization is severe, and thus it is well broken in the turbidity and the winding process. On the other hand, when the stretching temperature is higher than the glass transition temperature +40 ℃ temperature, the high temperature stretching tends to cause adhesion between the roll and the film, the film thickness smoothness is poor, and there is a difference in the shrinkage ratio for each part.

In addition, the stretching ratio in the longitudinal and transverse directions needs to be 2 to 7 times, preferably 3 to 5 times. When the stretching is less than 2 times, the orientation crystallization by the stress induction is not performed, the shrinkage property does not come out, there is a problem in the shrinkage uniformity is not preferable.

Next, in the heat setting step, the heat setting is carried out at a temperature of 50 to 100 ℃ lower than the melting temperature of the raw material resin. When heat setting at a temperature lower than the above range, thermal crystallization by heat proceeds to obtain sufficient shrinkage characteristics, and the crystallinity is increased, which is not preferable in terms of flexibility and impact strength of the film. On the contrary, when heat setting is performed at a temperature higher than the above range, crystallization does not occur, and thus the initial shrinkage speed is increased, making it difficult to handle in the post-processing process. Preferably, the heat setting is preferably performed at a temperature of 50 to 80 ° C. lower than the melting temperature of the raw material resin.

Finally, in the cooling step, to balance the shrinkage in both directions, it is necessary to give 0.01-5% of the relaxation that rearranges the state of the relaxed or oriented molecules. If reverse relaxation is desired, it is not preferable because only the transverse shrinkage increases.

The biodegradable bidirectional shrink film of the present invention prepared in such a process is excellent in shrinkage, impact resistance, flexibility, transparency, etc., so that the packaging material including this is not easily broken by external impact during transport / storage as well as excellent flexibility And the breakband strength.

The present invention will be described in more detail with reference to the following examples. However, the following examples are merely examples of the technical idea of the present invention and the present invention is not limited thereto.

Example

In the following examples and comparative examples, the polylactic acid resin was obtained by product name 4042D (melting temperature 150 ° C, L-lactic acid content 95.5%, Tg = 60 ° C) or product name 4032D (melting temperature 170 ° C) purchased from NatureWorks LLC. , L-lactic acid content 98.5%, Tg = 62 ℃) polylactic acid resin was used.

Example 1

A master batch was added to polylactic acid resin (4042D, NatureWorks), which is a raw material resin, to add 0.02% by weight of silicon dioxide having an average particle diameter of 2 µm to the final film. Drying was performed to remove moisture. It was melt-extruded at 240 degreeC, closely contacted with the casting roll of 25 degreeC, and extended | stretched 3.0 times at 75 degreeC in the longitudinal direction, and extended at 4.0 degreeC at 90 degreeC in the horizontal direction. It was heat-set at 80 ° C. and cooled while giving no relaxation to prepare a biodegradable bidirectional shrink film having a thickness of 20 μm.

Example 2

The master batch mixed with polylactic acid resin (4032D, NatureWorks), which is a raw material resin, was added so that 0.07 wt% of silicon dioxide having an average particle diameter of 2 μm was added to the final film and dried at 110 ° C. for 2 hours using a hot air dryer. Was removed. It melt-extruded at 240 degreeC, contacted with the casting roll of 25 degreeC, extended | stretched 2.5 times at 75 degreeC in the longitudinal direction, and extended | stretched 3.7 times at 90 degreeC in the horizontal direction. It was heat-set at 90 ° C. and cooled while giving no relaxation to prepare a biodegradable bidirectional shrink film having a thickness of 20 μm.

Example 3

As raw material resin Except for blending polylactic acid resin (4032D, NatureWorks) and polybutylene adipate coterephthalate resin (PBAT, G8060, Chemistry) with a glass transition temperature of -30 ° C in a weight ratio of 90:10. In the same manner as in Example 1, a biodegradable bidirectional shrink film having a thickness of 20 μm was prepared.

Comparative Example 1

The master batch mixed with polylactic acid resin (4032D, NatureWorks), which is a raw material resin, was added so that 0.07 wt% of silicon dioxide having an average particle diameter of 2 μm was added to the final film and dried at 110 ° C. for 2 hours using a hot air dryer. Was removed. This was melt-extruded at 240 ° C., brought into close contact with a casting roll at 25 ° C., stretched 3.0 times at 80 ° C. in the longitudinal direction, and 4.0 times at 90 ° C. in the transverse direction. It was heat-set at 150 ° C. and cooled while giving no relaxation to prepare a biodegradable bidirectional shrink film having a thickness of 20 μm.

Comparative Example 2

The master batch mixed with polylactic acid resin (4042D, NatureWorks), which is a raw material resin, was added so that 0.07 wt% of silicon dioxide having an average particle diameter of 2 μm was added to the final film, and dried at 110 ° C. for 2 hours using a hot air dryer. Was removed. This was melt-extruded at 240 ° C., brought into close contact with a casting roll at 25 ° C., stretched 1.5 times at 60 ° C. in the longitudinal direction, and stretched 5.0 times at 100 ° C. in the transverse direction. It was heat set at 50 ° C. and cooled while giving reverse relaxation to prepare a biodegradable bidirectional shrink film having a thickness of 20 μm.

Comparative Example 3

Polylactic acid resin (4032D, Nature Works) and polybutylene succinate resin (PBS, G4560, Chemistry) with a glass transition temperature of -20 ° C. were blended at a weight ratio of 40:60, and then dried at 70 ° C. with a dehumidifying dryer for 5 hours. Dry to remove moisture. This was melt-extruded at 220 ° C., brought into close contact with a casting roll at 25 ° C., stretched 2.8 times at 80 ° C. in the longitudinal direction, and 5.5 times at 105 ° C. in the transverse direction. It was heat-set at 60 ° C. and cooled while giving reverse relaxation to prepare a biodegradable bidirectional shrink film having a thickness of 20 μm.

Test Example

The properties of the film were measured for the polyester films prepared in Examples 1 to 3 and Comparative Examples 1 to 3, and are shown in Table 1 below. At this time, the characteristic measurement of the film was performed by the following method.

(1) the composition of the film

Each characteristic peak obtained by dissolving a film in a solvent (4: 1 mixture solution of chloroform and trifluoroacetic acid substituted with deuterium) using H-NMR (model name: JSM-LA300) manufactured by Jeol, Japan The composition of the film was shown using the area ratio of.

(2) Polarimeter

Automatic Polarimeter (Model: P-1020) of Jasco, Japan, was used, and the L-lactic acid content (% by weight) was calculated using software as a sodium lamp. Indicated.

(3) Thermal Characteristic Analysis (Tg, Tm, ΔHm)

Using a Perkin-Elmer differential scanning thermal analyzer (DSC) was measured at a temperature rising rate of 10 ℃ / min. At this time, the initial endothermic change was the glass transition temperature (Tg, ° C), and the peak point of the following exothermic curve was the crystallization temperature (Tc, ° C), and the peak point of the endothermic curve which appeared subsequently was the melting point (Tm) of the film. , ° C).

(4) initial elastic modulus

Measured according to ASTM D 882, the film prepared using an Instron universal testing machine (UTM, model name: 4206-001), after cutting to about 100 mm in length, 15 mm in width, the interval between the intervertebral The test was carried out at a rate of 200 mm / min of tensile speed by mounting 50 mm. Then, the initial modulus of elasticity (kgf / mm 2) calculated by the program embedded in the facility was obtained. Lower initial elastic modulus provides greater flexibility.

(5) shrinkage (%)

The main shrinkage was heat treated in a hot air oven maintained at a temperature of 100 ° C. for a length of 200 mm and a width of 15 mm in the direction to measure the sample, and then the length was calculated by the following equation.

Shrinkage (%) = (length before heat treatment-length after heat treatment) / length before heat treatment X 100

(6) Elongation reduction rate (%)

Measured according to ASTM D 882, the film produced using the universal testing machine (UTM, model name 4206-001) manufactured by INSTRON (UTM, model name 4206-001) after cutting to about 100 mm in length, 15 mm in width, the interval between the chuck is 50 mm The test was carried out at a rate of 200 mm / min of tensile speed by mounting as much as possible. Thereafter, the elongation value before shrinkage was obtained by a program built in the facility, and the sample obtained in the shrinkage characteristic evaluation of (11) was obtained in the above manner to obtain the elongation value after shrinkage, and the elongation reduction rate was calculated by the following equation.

% Elongation (△ E) = (Elongation before contraction-Elongation after contraction) / Elongation before contraction X 100

(7) impact absorption energy

The measurement was performed according to ASTM D3420, and a device was used as a Film Impact Tester manufactured by Toyoseiki, Japan. The pendulum tip used a hemispherical shape having a diameter of 0.5 inches, and the sample film was mounted on a sample stage having a circular hole having a diameter of about 50 mm. The measured value was defined as impact absorption energy (kgf-cm). Ten times were measured for each sample, and the average value was taken.

(8) Elmendorf Tear Strength

Measured according to ASTM D1922, the device measures the tearing force of the film by raising the pendulum oscillating at a constant speed to a certain position using an Elmendorf Tear Tester tester It was set as Elmendorf tear strength (kgf / micrometer).

(9) Haze

Haze meter (model name: SEP-H) of Nihon Semitsu Kogaku of Japan was measured, and haze was measured using C-light source.

(10) film forming stability

According to the fracture properties and flatness of the stretched film was evaluated as follows:

○ (good): when there is no break, there is no stretched mura in the final film, and the smoothness is excellent;

Δ (comparatively good): no breakage, but cloudy and stretch swarm in the final film; And

× (Poor): When production is difficult for a long time due to fusion of a roll or breaking of a film.

(11) Shrinkage Evaluation

Hot air tunnels were used to open and close the hot air nozzles as needed, and to rotate the vessel while passing through the tunnel. In order to determine the uniform shrinkage, a label, such as a graph paper, was printed on the label with an appropriate width. This label is placed on the upper body so that it rises about 2 cm above the shoulder of a 1.5 L square heat-resistant PET bottle commonly used as a juice drink container, and the shrinkage state of the label is evaluated as shown below when passed through a 120 ° C. hot air for 10 seconds. Was:

(Circle): When it contracts uniformly after contraction and the appearance is beautiful;

(Triangle | delta): When a contraction | contraction is oriented to one side and a crater-shaped nonuniform contraction appears; And

X: When it does not shrink well and does not adhere to a bottle, but is excited.

From the results of Table 1, in the embodiment according to the present invention can obtain a film having excellent physical properties, such as uniform shrinkage, impact resistance, flexibility, transparency, etc. of the present invention, while in the scope of the present invention In the case of the comparative example deviating it can be seen that such general physical properties are inferior to the film of the present invention.

Claims (10)

In the biaxially stretched biodegradable film containing polylactic acid resin as a main component, Polylactic acid resin and SiO ₂ containing at least 80% by weight of L-lactic acid; The bidirectional shrinkage ratio at the time of shrinking in a hot air oven at 100 DEG C for 10 minutes is 10 to 50%; The initial elastic modulus on the strain-stress curve is 50 to 350 kgf / mm 2; Biodegradable bidirectional shrink film, characterized in that the elongation reduction rate (ΔE) of the film after shrinking for 10 seconds at 120 ℃ in a hot air shrink tunnel. The method of claim 1, In addition to the polylactic acid resin, a biodegradable bidirectional shrink film comprising an aliphatic or aliphatic aromatic polyester resin having a glass transition temperature of -80 to 60 ℃ in an amount of 1 to 30% by weight based on the total weight of the raw material resin. The method of claim 1, Biodegradable bidirectional shrink film, characterized in that the film has a shock absorption energy of more than 5 kgf-cm. The method of claim 1, Biodegradable bi-directional shrink film, characterized in that the film has an Elmendorf tear strength of 3.0 kgf / ㎛ or more. The method of claim 1, Biodegradable bidirectional shrink film, characterized in that the film has a haze of 30% or less. (1) blending raw material resin containing polylactic acid resin containing 80 wt% or more of L-lactic acid with SiO ₂ , followed by hot air drying to remove moisture and melt extrusion; (2) stretching the melt-extruded unstretched film 2 to 7 times in the longitudinal and transverse directions, respectively, at a temperature of 0 to 40 ° C. higher than the glass transition temperature of the raw material resin; (3) heat-setting the biaxially stretched film at a temperature of 50 to 100 ° C. lower than the melting temperature of the raw material resin; And (4) A method for producing the biodegradable bidirectional shrink film of claim 1, comprising the step of cooling the film while giving no relaxation or static relaxation for the heat-set film. The method of claim 6, Method of producing a biodegradable bi-directional shrinkage film characterized in that the biaxially stretched 3 to 5 times in the longitudinal and transverse directions, respectively in the step (2). The method of claim 6, Biodegradable, characterized in that the raw material resin of step (1), in addition to the polylactic acid resin, in an amount of 1 to 30% by weight of an aliphatic or aliphatic aromatic polyester component having a glass transition temperature of -80 to 60 ℃. Method of producing a bidirectional shrink film. The method of claim 6, Method for producing a biodegradable bi-directional shrink film, characterized in that the stretching step of step (2) is carried out in a casting roll of 0 to 30 ℃. A packaging material comprising the biodegradable bidirectional shrink film of claim 1.