KR100348157B1 - Nylon tubular film and preparation thereof - Google Patents

Abstract

The present invention is directed to improving the mechanical properties, chemical properties and post-processing properties of the nylon tubular film by improving the initial MD modulus, and ultimately the added value of the product. The unstretched sheet obtained by extruding and quenching the molten nylon is stretched at a magnification of 2.5 to 3.5 times in the machine direction (MD) and 2.5 to 3.5 times in the transverse direction (TD) in the temperature range of Tg to Tcc and tenter in the tenter heat treatment section. Elongation is 2.5 to 7.0%, and applying this method, it is possible to produce a high quality nylon tubular film having an initial MD modulus of 320 to 420 kg / mm 2.

Description

Nylon tubular film and preparation method thereof

FIELD OF THE INVENTION The present invention relates to the manufacture of nylon films, and more particularly to nylon tubular films having improved initial tensile machine direction (MD) modulus and methods of making the same.

Nylon film has excellent gas barrier properties compared to other films, and is mainly used for packaging materials such as vacuum packaging and gas substitution packaging. Most of these films are nylon 6, and some nylon 66 is used. In general, these manufacturing methods include a coaxial biaxial tenter method, a sequential biaxial tenter method, a coaxial biaxial tubular method, and the like.

Table 1 briefly compares the manufacturing process and quality characteristics of nylon coaxially oriented films by conventional tubular and tenter methods.

division Coaxial Tubular Method Coaxial tenter method 1. Process Comparison die Circular-die T-die Stretch Air injected into the bubble-low temperature Tenter-High Temperature Stretching Heat treatment Roll, tenter Tenter 2. Product Characteristics Balance sex Very good Good Thickness uniformity Bad Very good Flatness Normal to good Very good Moisture resistance Bad Very good Initial MD Modulus 290 ~ 310㎏ / ㎡ 340-370kg / mm2

Films made by the coaxial tubular method (hereinafter referred to as "tubular films") have a very weak thickness uniformity and moisture resistance compared to films made by the tenter method, and the initial machine direction (MD) modulus is relatively 10-20% lower. This difference comes from the difference in stretching process.

Low initial machine direction (MD) modulus can cause many problems in post processing. That is, problems such as pint out in the printing process and cutting and elongation in the gold and silver yarn manufacturing process occur. The initial MD modulus of the tubular film was lower than that of the tenter film because the coaxial biaxial tubular method showed that the quenched unstretched sheet had no main orientation axis in the temperature range between Tg and Tcc. It is stretched to the alignment structure and is a low-temperature stretching method, and undergoes heat setting process through heat treatment. In this process, the orientation crystals and small crystals melt to cause modulus reduction, while the co-axial tenter method is more than Tcc and less than Tm. This is because the stretching is carried out in the tenter at temperature, and thus the modulus is relatively higher than the tubular method with a very uniform alignment crystal having a main alignment axis. Due to this fundamental film production method, it is difficult for the biaxial tubular method to overcome the simultaneous biaxial tenter method.

Therefore, the present invention is to provide a nylon tubular film of high quality excellent in mechanical properties, chemical properties and post-processing in view of the problems of the prior art as described above.

In the study to solve the above problems, the present inventors can significantly improve the initial tensile mechanical direction (MD) modulus of the nylon tubular film by the special design of the stretching and heat treatment process in the film forming process by the tubular method. I learned.

Therefore, according to the present invention, the molten nylon is extruded through an annular die and quenched to prepare an unstretched sheet in a tubular state, and the unstretched sheet is cold crystallization temperature above a glass transition temperature (Tg). : Stretched at a magnification of 2.5 to 3.5 times in the machine direction (MD) and 2.5 to 3.5 times in the transverse direction (TD) in a temperature section of Tcc) or less, and a tenter elongation of 2.5 to 7.0% in the tenter heat treatment section. A method of making a nylon tubular film is provided.

In addition, according to the present invention there is provided a nylon film, characterized in that the MD modulus is 320 to 420 kg / mm2 produced by the above-described method.

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

The method for producing a nylon film according to the present invention consists of extrusion of molten nylon in an annular die, quenching, coaxial stretching, heat treatment in a heat treatment roll, heat treatment and stretching in a tenter. The present invention has a main feature in improving the initial tensile mechanical modulus (MD) modulus of nylon tubular film by specially managing the processes of coaxial stretching, heat treatment in a heat treatment roll, heat treatment and stretching in a tenter. .

In this production method, the tube-shaped unstretched sheet is heated in the temperature range of Tg to Tcc, and air is injected to simultaneously biaxially stretch at a magnification of 2.5 to 3.5 times in the machine direction (MD) and 2.5 to 3.5 times in the transverse direction (TD). do. In general, in the case of a biaxially stretched film, the breaking strength is controlled in the stretching direction, but the modulus is controlled by hydrogen bonding rather than the orientation above a certain draw ratio. That is, when the degree of orientation increases in one direction, the modulus increases in the vertical direction of the direction in which the orientation is increased. This is because the effect of narrowing the distance between molecules easily occurs due to the hydrogen bond in the orientation of the molecules. If the draw ratio is increased too much, breakage occurs, which is disadvantageous to the application of the site, and therefore, an appropriate draw ratio is required.

The biaxially stretched film as described above undergoes a heat treatment process. Heat treatment process is divided into roll heat treatment and tenter heat treatment.

It is preferable that roll heat processing maintains the temperature of about 150-190 degreeC. If the temperature is lower than this temperature, heat shrinkage is insufficient and the heat shrinkage rate is increased to 4% or more. If the temperature is higher than the ionicity, breakage occurs when stretching is performed in the tenter. In other words, if the crystal structure is controlled by α-crystal due to heat treatment of molecules oriented in the machine direction (MD), breakage occurs due to excessive increase of stress when stretching is performed in the tenter. That is, crystallization at an easy stretch level should proceed under moderate stress.

The tenter heat treatment process is as follows. In the conventional tubular process, the quench sheet was performed only in the temperature range of Tg to Tcc, and the tenter was heat-treated only. In the present invention, when the tenter elongation is increased by 2.5 to 7% with respect to the tenter inlet film width while heat-treated at a temperature of 217 ° C. or lower in the tenter heat treatment section, the transverse direction ( TD) increases hydrogen bonding. In the tenter, since the orientation crystal is formed by tenter stretching the polymer chain remaining in the amorphous state after the heat treatment, the initial machine direction (MD) modulus can be improved.

The present invention is applicable to all nylon films that can be produced by the tubular method, and particularly advantageously to nylon 6 and nylon 66 films. In addition, although not particularly limited, the thickness of the film can be prepared by using a suitable thickness within the range of 5 to 50㎛ usually produced.

The present invention will be described in more detail by the following examples. However, the following examples are only examples of the present invention and the present invention is not limited thereto.

Various performance evaluations of the films and processability of the films prepared in Examples and Comparative Examples of the present invention were carried out by the following measuring method.

-Tensile strength, elongation: measured according to American Standard Test Method (ASTM) D-882. Model Name-Instron 1123, Measurement Conditions-Drawing Speed 300mm / min, Grip Distance 100mm, Temperature 23 ℃, Relative Humidity 50%, Specimen Size-Width 10mm, Length 100mm,

Tensile modulus: measured according to ASTM D-882. Model Name-Instron 1123, Measurement Conditions-Drawing Speed 100mm / min, Grip Distance 100mm, Temperature 20 ℃, Relative Humidity 65%, Specimen Size-Width 10mm, Length 100mm

-Density: Measured using density gradient tube method in accordance with ASTM D-1507.

-Degree of crystallinity: density of the sample ( ), The density of the amorphous region ( ) And the density of the crystal regions ( ) Is calculated by substituting Based on nylon α-crystal Is 1.084, Calculated by 1.235.

-Hot air shrinkage: Measured after change of temperature at 150 ℃ for 30 minutes according to JIS C-2318.

Example 1

The molten nylon 6 was extruded through an annular die at 260 ° C., quenched to form an unstretched sheet in an amorphous tubular state, and co-axial stretching was performed by injecting air into the tube while heating the unstretched sheet to 80 ° C. At this time, the MD draw ratio was 2.95 times and the TD draw ratio was 2.95 times. Next, the heat treatment roll was passed through a heat treatment at 150 to 170 ° C., and the tenter elongation was increased to 5.15% in this tenter heat treatment section while performing heat treatment at 198 to 215 ° C. in the tenter.

Example 2

Among the treatment conditions, the same procedure as in Example 1 was repeated except that the heat treatment roll temperature was changed to 155 to 175 ° C, the tenter temperature was 198 to 217 ° C, and the tenter elongation was changed to 2.94%.

Example 3

The same procedure as in Example 2 was repeated except that the heat treatment roll temperature was changed to 155 to 180 ° C and the tenter temperature to 201 to 215 ° C.

Example 4

The same procedure as in Example 2 was repeated except that the roll heat treatment temperature was changed to 155 to 185 ° C and the tenter heat treatment temperature to 195 to 215 ° C.

Example 5

The same procedure as in Example 1 was repeated except that the MD draw ratio was 3.1 and the TD draw ratio was 2.95 times, the heat treatment roll temperature was increased from 150 to 180 ° C., the tenter heat treatment temperature was increased from 190 to 215 ° C., and the tenter elongation was 3.68%. .

Example 6

The same procedure as in Example 4 was repeated except that the tenter heat treatment temperature was changed to 195-210 ° C.

Comparative Example 1

The same procedure as in Example 1 was repeated except that the tenter heat treatment temperature was increased from 215 to 217 ° C and the tenter elongation was increased by 4.41%.

Comparative Example 2

The same procedure as in Example 1 was repeated except that the roll heat treatment temperature was 155 to 186 占 폚, the tenter heat treatment temperature was 201 to 214 占 폚, and the tenter elongation was increased by 0.73%.

Comparative Example 3

The MD draw ratio was 3.1 times, and the roll heat treatment method was repeated with the same procedure as in Example 4 except that the heat treatment was performed by tension heat treatment.

The film forming process conditions of the Examples and Comparative Examples are summarized in Table 2, the physical properties of the nylon film prepared in each example was measured and the results are shown in Table 3.

division Exam conditions Extension section Extension ratio (times) Roll heat treatment method Heat treatment temperature (℃) Tenter elongation (%) MD TD Roll heat treatment Tenter heat treatment Example 1 2.95 2.95 relaxation 150/170 198/215/208 4.41 Example 2 2.95 2.95 relaxation 155/175 198/205/217 2.94 Example 3 2.95 2.95 relaxation 155/180 195/215/215 2.94 Example 4 2.95 2.95 relaxation 155/185 190/212/215 2.94 Example 5 3.10 2.95 relaxation 150/180 190/215/205 3.68 Example 6 3.10 2.95 relaxation 150/180 195/215/210 3.68 Comparative Example 1 2.95 2.95 relaxation 150/170 215/217/215 5.15 Comparative Example 2 3.10 2.95 Tension 155/180 190/205/205 2.94 Comparative Example 3 3.10 2.95 Tension 156/187 190/212/215 2.94 Comparative Example 4 3.10 2.95 Tension 150/175 190/210/215 2.94 Comparative Example 5 2.95 2.95 relaxation 155/186 201/212/214 0.73 Comparative Example 6 3.10 2.95 Tension 155/186 201/212/214 0.73

※ Tenter elongation: Maximum elongation compared to the tenter width

division Film properties Strength (kg / mm2) Initial Modulus (㎏ / ㎠) Elongation (%) Heat Shrinkage (%) Crystallinity (%) density Planarity (Appearance) MD TD MD TD MD TD MD TD Example 1 29.3 31.6 326 348 154 147 2.80 2.10 43.37 1.1495 Very good Example 2 28.8 31.9 323 297 167 157 2.65 2.25 44.23 1.1508 Very good Example 3 29.6 32.0 325 303 165 152 2.55 2.15 44.63 1.1514 Very good Example 4 28.9 28.6 327 311 153 151 2.80 2.00 44.37 1.1510 Very good Example 5 33.5 31.1 329 346 137 137 3.30 1.95 44.03 1.1505 Very good Example 6 33.1 31.3 333 352 130 143 3.40 2.15 43.64 1.1499 Very good Comparative Example 1 26.5 27.3 295 306 164 167 1.80 1.95 44.76 1.1516 Bad Comparative Example 2 30.1 29.8 307 296 156 160 2.75 1.65 43.44 1.1496 Bad Comparative Example 3 33.0 30.6 303 347 138 163 3.25 1.65 42.45 1.1481 Extremely poor

As can be seen from Table 3, the nylon tubular film produced by the method of Examples 1 to 4 according to the present invention has an initial machine direction (MD) modulus of about 20 to about 20 parts of the nylon film produced by the general tubular method. It showed an increase of about 30%, and the heat shrinkage rate was also less than 3.5%, which was stable to hot water. In addition, in Examples 5 to 6, the machine direction (MD) draw ratio was increased to 3.1 times, and the elongation was decreased by increasing the machine direction (MD) draw ratio, and the machine direction (MD) breaking strength was increased by about 10%. The degree of machine direction (MD) modulus was improved. This can be explained by showing the effect of hydrogen bonding in the direction perpendicular to the stretching direction mentioned earlier. However, in Comparative Example 1, although the tenter elongation was set to 5.15%, the improvement in machine direction (MD) modulus was small. This results in the effect of partial melting of the orientation crystals due to the high temperature in the stretched tenter width, and the reduction of the orientation effect is very effective in inhibiting the initial mechanical direction (MD) modulus, although the heat shrinkage rate is very good. One result was shown. Comparative Examples 2 to 3 showed no TD stretching to 0.73% of tenter stretching, so that there was no improvement in machine direction (MD) modulus.

As described above, the present invention is a novel useful invention that improves the mechanical properties, chemical properties and post-processability of the nylon tubular film by improving the initial mechanical direction (MD) modulus, and eventually greatly increases the added value of the product.

Claims (2)

In manufacturing the nylon tubular film, the unstretched sheet obtained by extruding and quenching molten nylon through an annular die was 2.5 to 3.5 times in the machine direction (MD) and 2.5 in the transverse direction (TD) at a temperature range of Tg to Tcc. A method for manufacturing a nylon tubular film, comprising stretching at a magnification of ˜3.5 times and having a tenter elongation of 2.5 to 7.0% in the tenter heat treatment section. The nylon tubular film, wherein the initial machine direction (MD) modulus is 320 to 420 kg / mm 2.