KR100562468B1 - Manufacturing method of Polyamide film - Google Patents

Abstract

The present invention melt-mixed polyamide homopolymer in an extruder, discharged from a circular die, quenched, and then coaxially stretched in a stretching tower and heat-set with a heater roll and an oven to prepare a biaxially stretched polyamide film. In the drawing, the stretching ratio is 2.35 to 2.80 times at the time of stretching, and the film is formed by heating the heater roll at 160 to 200 ° C. The polyamide film thus formed is prevented from deteriorating physical properties such as tensile strength while lowering the thermal contraction rate. It can be used as a packaging material for steam sterilization.

Packing * Steam Sterilization * Polyamide

Description

Manufacturing method of biaxially oriented polyamide film capable of steam sterilization {Manufacturing method of Polyamide film}

The present invention relates to a method for producing a biaxially stretched polyamide film capable of steam sterilization, and more particularly, by controlling the draw ratio and heat setting temperature appropriately, and having low heat shrinkage, physical properties such as tensile strength are not lowered. A method for producing a biaxially stretched polyamide film useful as a possible packaging material.

In general, the polyamide film is excellent in transparency, pinhole resistance, gas barrier property, heat resistance, oil resistance, etc., and is widely used in food packaging fields such as meat processed food or retort food, and other industrial product packaging fields.

However, a general food packaging polyamide film has a high heat shrinkage rate, particularly in harsh conditions such as steam, and thus is restricted in its application and dimensional deformation may occur, causing defects.

The production of the packaging polyamide film is first polymerized with a polyamide copolymer to make a chip for film production, and then molded into a film by a generally known T-die method or inflation method. For example, the chip is fed into an extruder through a hopper, heated to melt, extruded from an extrusion die, and then cooled and solidified to produce an unstretched fabric, which is then simultaneously co-ordinated in the advancing direction (MD) and width direction (TD) of the film. Alternatively, the film may be prepared by heat-setting after successive stretching.

On the other hand, the stretching method of a polyamide film can be roughly divided into the tubla method and the tenta method. Although the tenta method is an easy method for mass production of films, it is difficult to avoid a lot of investment in processing equipment, and it is difficult to set the processing conditions for stretching the film while maintaining the balance in the width direction and the length direction. In contrast, the tubular method stretches the width direction and the length direction at the same time by the pressure of the fluid introduced into the film, thereby bringing the draw ratios in the width direction and the length direction together, so that the film has excellent glossiness, transparency and strength. Can be obtained. In addition, the tubular method has the advantages of low facility investment cost, installation in a narrow space, and providing a variety of high quality films.

In more detail, the film forming process by the tubular method is performed by melting and mixing the polyamide homopolymer in an extruder, discharging it from a circular die, and quenching with a mandrel and a water bath, followed by stretching ellipses. The film is stretched by coaxial at and heat-fixed with a heater roll and an oven to form a film.

At this time, the film forming conditions of the general food packaging polyamide film is stretched at a draw ratio of 2.8 to 3.2 to improve oxygen barrier properties and mechanical properties, heat-set to a heater roll temperature 170 ~ 190 ℃ and oven temperature 200 ~ 220 ℃.

However, the polyamide homopolymer film obtained in this way has a high heat shrinkage ratio and is not suitable for applications such as steam sterilization.

Accordingly, the present inventors are trying to overcome the limitations of using the polyamide homopolymer film as a steam sterilization packaging material due to its high heat shrinkage ratio, and the draw ratio which is a change factor of the heat shrinkage rate in the use of the tubular method. As a result of lowering and increasing the heat setting temperature, the heat shrinkage rate was found to be low, thus completing the present invention.

Accordingly, an object of the present invention is to provide a method for producing a polyamide film to reduce the dimensional deformation due to heat shrinkage, while preventing the degradation of mechanical properties.

Such a method for producing a polyamide film of the present invention is melt-mixed polyamide homopolymer in an extruder, discharged from a circular die, quenched with a mandrel and a water bath, and then in a stretching tower It is made of a process of forming a film by heat-setting with a heater roll and an oven after stretching by coaxial, the stretching ratio at the time of stretching is 2.35 ~ 2.80 times, characterized in that the temperature of the heater roll is carried out to 160 ~ 200 ℃.

The present invention will be described in more detail as follows.

The method for producing a polyamide film as a steam sterilizing packaging material according to the present invention is in accordance with a conventional tubular method.

First, a polyamide copolymer is produced, and the polymerization process is as follows.

1) First, an aqueous solution of a salt consisting of a mixture of adipic acid and aliphatic diamine is introduced into the reactor. At this time, a mixture of hexamethylenediamine, 2-methylpentamethylenediamine, and metaparaxylenediamine is used as the diamine. Depending on the properties required, 12-aminododecanoic acid or lauryllactam can be added in admixture with the monomers.

2) A proportion of caprolactam is added to the reactor.

3) Pressurize for reaction and maintain constant pressure while releasing water while heating the mixture.

4) The polymerization degree is determined by setting the temperature inside the reactor and the reduced pressure conditions at a level having a relative viscosity of 3.3 to 3.8 and a molecular weight distribution ranging from 2 to 4.

5) The reactor is evacuated to atmospheric pressure and maintained at a constant viscosity.

6) The discharged polymer is made into chips.

7) In order to manage the hot water extract of the polymer to be 0.5% or less, unreacted materials are extracted at the maximum bath ratio and dried to prepare a chip for manufacturing the final polyamide film.

Here, it is preferable that polyamide is polyamide 6.

After preparing a chip for polyamide film production, the chip is fed into an extruder through a hopper, heated to be melted, extruded from an extrusion die, and then cooled and solidified to prepare an unstretched fabric, and then the direction (MD) and width of the film The film may be prepared by simultaneously or sequentially stretching in the direction TD and then heat setting.

In the stretching method after molding the polyamide film, the tubular method is used in the present invention. First, the polyamide homopolymer is melt-mixed in an extruder, discharged from a circular die, and then a mandrel and a water bath. Quench it.

Then, at the stretching tower, the stretching is performed in the simultaneous biaxial. At this time, the stretching ratio is 2.35 to 2.80 times in the present invention. If the draw ratio is less than 2.35, there is a problem that the mechanical strength is poor and the dimensional stability is lowered, and when the draw ratio is larger than 2.80, the heat shrinkage rate is increased.

After stretching at such a draw ratio, the film is produced by heat setting with a heater roll and an oven.

It is preferable that the temperature of a heater roll at the time of heat setting is 160-200 degreeC. If the temperature of the heater roll is lower than 160 ° C., the thermal shrinkage becomes poor. If the temperature of the heater roll is higher than 200 ° C., the appearance and dimensional stability may be deteriorated due to crystal destruction caused by excessive heat.

After the heating rolls, the temperature of the oven is 200-220 ° C. as in the manufacture of general packaging polyamide films.

The biaxially stretched polyamide film obtained as described above is useful for packaging in which steam sterilization is required since the thermal shrinkage of steam or hot water is less than that of general packaging polyamide films, but the physical properties such as tensile strength are not lowered.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Preparation Example: Preparation of Polyamide Copolymer

ε-caprolactam was added and condensation polymerized to make a polymer of 1560 to 200 molecular groups, extruded into a spaghetti, and cut into chips of a predetermined size. In order to remove the unpolymerized material of the nylon itself was extracted with hot water (HOT WATER) and then dried in a wet state to prepare a dry chip.

Examples 1-2 and Comparative Examples 1-3

After the polyamide chips obtained according to the above production examples were prepared for producing polyamide film chips, the chips were fed into an extruder through a hopper, heated and melted at 270 ° C., extruded from an extrusion die, and then cooled and solidified. It was prepared, and then stretched simultaneously or sequentially in the advancing direction (MD) and the width direction (TD) of the film, and then heat-set to produce a film.

After drawing, the heat setting method melt-mixed the polyamide homopolymer in an extruder, discharged from a circular die, and then quenched with a mandrel and a water bath.

Thereafter, the film was stretched coaxially in the stretching tower, and the draw ratios were differently drawn as shown in the following Table 1, and heat-set to the heater roll temperature and the oven temperature as shown in the following Table 1 to obtain a film.

Example Comparative example One 2 One 2 3 Production condition Extension ratio (times) 2.40 2.65 2.30 2.93 3.0 Heating roll temperature (℃) 170 185 160 195 205 Oven Temperature (℃) 205 210 200 215 225

Experimental Example

Tensile strength and thermal contraction rate for steam and hot water were measured for the films obtained according to Examples 1 to 2 and Comparative Examples 1 to 3, and the results are shown in Table 2 below.

Here, the tensile strength was measured according to ASTM D-882, and the heat shrinkage rate for steam was measured after spraying steam at 1 atmosphere for 30 minutes at 130 ° C, and the shrinkage rate for hot water was 30 at 100 ° C hot water. Shrinkage after immersion for minutes is measured.

Example Comparative example One 2 One 2 3 Tensile Strength (kg / ㎡) 24 26 22 30 22 Heat shrinkage (%) steam Longitudinal direction 4.0 4.5 3.0 11.0 3.0 Transverse 3.5 4.0 2.5 10.0 2.5 Hydrothermal Longitudinal direction 1.8 2.0 1.7 3.5 1.7 Transverse 1.5 1.5 1.4 2.5 1.4

From the results in Table 2, as shown in Comparative Example 1, when the thermal contraction rate is low, it can be seen that the dimensional deformation due to thermal contraction is reduced, but the tensile strength is also lowered. In this case, deformation may occur in a post-processing process such as printing, which may cause a defect.

On the other hand, in the case of Comparative Example 2 is excellent in tensile strength, but the heat shrinkage is too large to be applied as a packaging material for steam sterilization.

In the case of Comparative Example 3 it can be seen that the operating property and appearance, mechanical properties are poor due to the temperature of the heat setting beyond the scope of the present invention.

As described in detail above, according to the present invention, the draw ratio is lowered and the heat setting temperature is higher than the general food packaging polyamide film forming during the tubular method, resulting in lower heat shrinkage and lower mechanical properties such as tensile strength. The polyamide film thus prepared is useful for packaging requiring steam sterilization.

Claims (3)

Melt-mixing polyamide homopolymer in an extruder, discharging from a circular die, quenching, and coaxially stretching in a stretching tower, and then heat setting with a heater roll and oven to produce a biaxially stretched polyamide film , The draw ratio at the time of stretching is 2.35 to 2.80 times, the method of producing a steam sterilized biaxially stretched polyamide film, characterized in that the temperature of the heater roll to be carried out to 160 to 200 ℃. The method of claim 1, wherein the film is steam sterilized in a longitudinal direction and a transverse thermal contraction rate of 3 to 7%, respectively. A biaxially stretched polyamide film capable of steam sterilization having a longitudinal and lateral thermal contraction rate of 1.5-2.5% and 1.0-2.0%, respectively, for hot water.