JPH0628903B2 - Method for producing biaxially stretched nylon 6 film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for producing a biaxially stretched nylon 6 film, and can be used in the fields of food packaging, industrial materials and the like.

BACKGROUND ART A nylon film produced by simultaneous biaxial stretching by a tubular method has an excellent feature that mechanical and optical properties such as strength and transparency are good.

[Problems to be Solved by the Invention] A biaxially stretched nylon film obtained by a conventional tubular method generally has low thickness accuracy, so that the winding shape is deteriorated, and the secondary shape such as printing, laminating, and bag making. Due to the occurrence of defects during processing, their use as packaging and industrial films has been limited. This is because even if the thickness accuracy is adjusted with an extrusion die when the original film for stretching is produced,
This is because, in addition to the occurrence of thickness unevenness of about 2 to 6%, according to the conventional tubular method, the thickness unevenness is further deteriorated by a factor of 2 or more during stretching. In addition, according to the conventional method, the bubbles are not stable during stretching and deformation, so that there is a possibility that the bubbles may roll laterally or sometimes break.

According to Japanese Patent Publication No. 49-47269, poly-
A tubular film obtained by melt-extruding an ε-capramide resin is rapidly cooled and solidified to obtain a poly-ε-capramide resin tubular film which is substantially amorphous and has substantially no hydrogen bond, in which the water content is less than 2%. To 45 ~ before stretching.
A bi-axially molecularly oriented poly-ε-capramide resin, which is characterized by performing tube stretching at a temperature of 70 ° C. and biaxially stretching at a stretching ratio of 2.0 to 4.0 times in each length and width. A method of manufacturing a film has been proposed. Also,
According to Japanese Patent Publication No. 53-15914, after heating the polyamide unstretched tubular film to a temperature of 50 to 90 ° C., the ambient temperature between the stretching start point and the stretching end point is 180.
The stretching start point is fixed by maintaining the temperature at 250 ° C. to 250 ° C., and the final stretching ratio difference between the transverse direction and the longitudinal direction is maintained in the range of 0.2 to 0.6, and 2.5 to 3.7 in the longitudinal direction by the gas pressure. Double
A tubular biaxial stretching method for a polyamide film has been proposed which is characterized in that simultaneous biaxial stretching is performed in the transverse direction at a magnification of 3.0 to 4.0 times.

However, according to the production method based on such control of the draw ratio or the draw temperature, it is not always possible to precisely specify the molding conditions for obtaining a good film.

The present invention relates to a biaxially stretched nylon film produced by a tubular method, particularly a biaxially stretched nylon 6 film,
It is an object of the present invention to provide a manufacturing method capable of stabilizing the molding state during stretching and improving the thickness accuracy of the obtained film.

[Means for Solving the Problems] In the method for producing a biaxially stretched nylon 6 film by the tubular method, the present invention has confirmed various parameters involved in the stretching by experiments, and as a result, the maximum of the moving direction (MD) of the film was obtained. It was found that good results can be obtained by taking the stretching stress as σ _MD and the maximum stretching stress in the width direction (TD) of the film as σ _TD , and setting the manufacturing conditions based on this. That is, the present invention is characterized in that σ _MD and σ _TD are set to 600 kg / cm ² ≦ σ _MD ≦ 1300 kg / cm ² 600 kg / cm ² ≦ σ _TD ≦ 1300 kg / cm ² , respectively.

However, σ _MD and σ _TD are respectively expressed by the following equations.

σ _MD = (F × B _MD ) / A F = T / r where F is the stretching force (kg), B _MD is the stretching ratio in the MD direction, A is the cross-sectional area of the original film (cm ² ), T Is the rotating torque (kg-cm) of the nip roll, and r is the radius (cm) of the nip roll.

σ _TD = (ΔP × R) / t where ΔP is the bubble internal pressure (kg × cm ² ), R is the bubble radius (cm), and t is the film thickness (cm).

If σ _MD and σ _TD exceed 1300 kg / cm ² , continuous production will not be possible due to frequent bubble breakage during expansion. When σ _MD and σ _TD are less than 600 kg / cm ² , bubbles in the process of stretching become unstable, resulting in poor film thickness accuracy and no commercial value. Further, both σ _MD and σ _TD preferably have an upper limit of 120.
The lower limit is set to 0 kg / cm ² and the lower limit is set to 700 kg / cm ² .

[Examples] Example 1 Nylon 6 having a relative viscosity η _r = 3.7 (Ube Industries, Ltd.)
Extruded from an annular die (diameter: 75 mm) using a product manufactured by K.K. Next, as shown in FIG. 1, after the raw film 1 was inserted between a pair of nip rolls 2, it was heated by a heater 3 (set temperature of 310 ° C.) while pressurizing a gas therein, and a stretching start point. Simultaneously biaxial stretching was carried out by blowing air 5 (air volume of 15 m ² / min) from the air ring 4 to expand the bubbles 6 and taking them with a pair of downstream nip rolls 7. The stretching ratio was 3.0 times in the moving direction (MD) of the film and 3.2 times in the width direction (TD) of the film.

During the simultaneous biaxial stretching, the pressure in the bubble 6, the radius of the bubble 6, the number of revolutions of the nip rolls 1 and 7, the load of the drive motor, the torque, etc. are set to specific values to obtain the moving direction of the film ( adjusting the maximum draw stress sigma _TD of the maximum draw stress sigma _MD and the width direction of the film (TD) of the MD).

In this example, the maximum stretching stress σ _{MD in} the moving direction (MD) of the film was 950 kg / cm ² , and the maximum stretching stress σ _{TD in} the width direction (TD) of the film was 960 kg / cm ² . In addition, these σ _MD and σ _TD are calculated by the following equation.

σ _MD = (F × B _MD ) / A F = T / r T = [97,450 × (I−I _o ) × 0.22] / N where F is a stretching force of 108 kg, and B _MD is a stretching ratio in the MD direction. 3.0, A is 0.34 cm in cross section of the original film
² , T is a rotational torque of 539 kg-cm, and r is a nip roll radius of 5 cm. In the above formula for obtaining T, I is the motor current during operation, 3.67 A, I _o is the motor current during idle operation, 1.80 A, and N is the rotation speed of the nip roll, 74.5 rpm. The specific value of the torque T is related to the specific nip roll according to the embodiment.

σ _TD = (ΔP × R) / t where ΔP is the bubble internal pressure 900 × 10 ⁻⁴ kg / c
m ² and R are bubble radii 14.4 cm, and t is film thickness 13.5 × 10 ^-4 cm. Pressure in this bubble ΔP
Is a value measured using a digital manometer.
Further, the film thickness t is the thickness of the original film / (M
It is a value calculated from (D stretch ratio × TA stretch ratio).

In the production of the biaxially stretched nylon 6 film according to the present example in which σ _MD and σ _TD were set as described above, continuous production was performed for 24 hours, and the bubble 6 at the time of stretching deformation did not roll. The biaxially stretched nylon 6 film 8 was stable, and the thickness variation was ± 4%, which was very good in thickness accuracy.

Examples 2 to 10 In the same manner as in Example 1 above, biaxially stretched nylon 6 film 8 according to Examples 2 to 10 was manufactured. However, MD
Regarding the draw ratio, the TD draw ratio, the air volume of the air ring 4, and the set temperature of the heater 3, the conditions were changed as follows.

Regarding the MD stretch ratio, the values in Examples 2 to 8 and 10 were 3.
0 and Example 9 were set to 3.4.

Regarding the TD stretch ratio, Examples 2 to 6, 9 and 10 were set to 3.2, Example 7 was set to 3.0, and Example 8 was set to 3.4.

Regarding the air volume of the air ring 4, the second, third, and seventh embodiments are described.
10 to 15 m ³ / min, Example 4 to 5 m ³ / min, Example 6 to 4
It was set to 5 m ³ / min.

Regarding the set temperature of the heater 3, the second embodiment is set to 330 ° C.,
Example 3 was set to 280 ° C, Examples 4 to 9 were set to 310 ° C, and Example 10 was set to 370 ° C.

The cooling water in the cooling tanks was set at 15 ° C.

In the simultaneous biaxial stretching, the maximum stretching stress σ _{MD in} the moving direction (MD) of the film and the maximum stretching stress σ _{TD in} the width direction (TD) of the film are approximately equal and appropriate values for each example. The pressure in the bubble 6, the radius of the bubble 6, the number of revolutions of the nip rolls 1, 7, the load of the drive motor, the torque, etc. were set to specific values so that

In the production of the biaxially stretched nylon 6 film 8 according to each example in which σ _MD and σ _TD were set to appropriate values, continuous production was performed for 24 hours, and bubbles 6 were stretched and deformed.
Table 1 below shows the results of observing and evaluating the stability of the biaxially stretched nylon 6 film 8, and measuring and evaluating the thickness accuracy of the obtained biaxially stretched nylon 6 film 8, and performing the comprehensive evaluation. .

Comparative Examples 1 to 8 Biaxially stretched nylon films according to Comparative Examples 1 to 8 were manufactured in the same manner as in the above Examples. However, the MD stretch ratio and the TD stretch ratio, the air volume of the air ring 4, the set temperature of the heater 3, and the water temperature of the cooling water were changed as follows.

Regarding the MD stretch ratio, Comparative Examples 1 to 4 and 8 are 3.0,
Comparative Example 5 was 3.6, Comparative Example 6 was 2.4, and Comparative Example 7 was 3.
It was set to 4.

Regarding the TD stretch ratio, 3.2 in Comparative Examples 1 to 6 and 8,
Comparative Example 7 was set to 3.4.

Regarding the air volume of the air ring 4, Comparative Examples 1, 2, 5
8 to 15 m ³ / min, Comparative Example 3 to 0 m ³ / min, Comparative Example 4 to 55
m ³ / min.

Regarding the temperature of the heater 3, Comparative Example 1 was set to 400 ° C., Comparative Example 2 was set to 260 ° C., and Comparative Examples 3 to 8 were set to 310 ° C.

Regarding the water temperature of the cooling water, Comparative Examples 1 to 7 were set to 15 ° C, and Comparative Example 8 was set to 45 ° C.

Further, at the time of simultaneous biaxial stretching, the pressure inside the bubble 6, the radius of the bubble 6, etc. are set so that σ _MD and σ _TD become appropriate values which are substantially equal in each comparative example, as in the above-mentioned examples. Was set to a specific value.

In the production of the biaxially stretched nylon 6 film according to each comparative example in which σ _MD and σ _TD are set to appropriate values,
After continuously manufacturing for 24 hours, the stability of bubbles during stretching deformation was observed and evaluated, and the thickness accuracy of the obtained biaxially stretched nylon 6 film was measured, evaluated, and comprehensively evaluated. It is also shown in Table 1.

In this table, ◎, ◯, △ and × of the molding stability have a variation width of the folding diameter of 1% or less, 2% or less, 5% or less and 5%, respectively.
Indicates that the value exceeds. In addition, thickness accuracy ◯, △ and ×
Indicates 6% or less, 10% or less and more than 10%, respectively. And ◎ of the comprehensive evaluation is most suitable for industrial production,
◯ indicates that it is suitable for industrial production, Δ indicates that industrial production is possible, but some troubles occur, and × indicates industrial production is impossible.

From the examples and comparative examples in this table, the maximum stretching stress σ _{MD in} the moving direction (MD) of the film and the width direction (T
When the maximum stretching stress σ _TD of D) is 600 kg / cm ² or more and 1300 kg / cm ² or less, good molding stability of the bubble 6 and good thickness accuracy of the biaxially stretched nylon 6 film 8 are obtained. It can be seen that

[Effects of the Invention] According to the present invention, since good molding stability can be obtained during stretch deformation of a biaxially stretched nylon 6 film, continuous production can be carried out without trouble. Further, since the thickness accuracy of the obtained biaxially stretched nylon 6 film is improved,
It is possible to provide products of good quality.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus used in the manufacturing method according to the embodiment. 1 ... Original film, 3 ... Heater, 4 ... Air ring, 6 ... Bubble, 8 ... Biaxially stretched nylon 6 film.

Claims (1)

[Claims] 1. A biaxially stretched nylon 6 produced by a tubular method.
In the method for producing a film, when the maximum stretching stress in the moving direction (MD) of the film is σ _MD and the maximum stretching stress in the width direction (TD) of the film is σ _TD , σ _MD and σ _TD are each 600 kg / cm ² ≦ σ _MD ≦ 1300 kg / cm ² 600 kg / cm ² ≦ σ _TD ≦ 1300 kg / cm ^{2 A} method for producing a biaxially stretched nylon 6 film. However, the σ _MD and σ _TD are respectively expressed by the following equations. σ _MD = (F × B _MD ) / A F = T / r where F is the stretching force (kg), B _MD is the stretching ratio in the MD direction, A is the cross-sectional area of the original film (cm ² ), T Is the rotating torque (kg-cm) of the nip roll, and r is the radius (cm) of the nip roll. σ _TD = (ΔP × R) / t where ΔP is the bubble internal pressure (kg / cm ² ), R is the bubble radius (cm), and t is the film thickness (cm).