JPH02235722A - Manufacture of biaxially orientated nylon 6 film - Google Patents

Abstract

PURPOSE:To enable continuous production to be achieved without difficulty, while the excellent forming stability in orientating and deforming the title film is obtained by setting a maximum orientation stress in the moving direction and one in the axial direction of the film each to a specified value. CONSTITUTION:A blank film 1 passes between the nip rolls 2 of a pair, and then while the film is heated by a heater 3 (set temperature of 300 deg.C) with the gas injected thereinto, it is expanded into a bubble 6 by blowing air (air volume of 15m<3>/min) from an air ring 4 at the beginning point of orientation. Said film is biaxially oriented simultaneously by taking up it with a pair of nip rolls 7 downstream. The maximum orientation stress sigmaMD in the moving direction(MD) of the film, and the maximum orientation stress sigmaTD in the axial direction(TD) of the film are respectively set in 600kg/cm<2=sigmaTD<=1300kg/cm<2> and 600kg/cm<2=sigmaMD<=1300kg/cm<2>. When sigmaMD and sigmaTD exceed 1300kg/cm<2>, since the bubble in orientating is often broken, its continuous production is not achieved. When sigmaMD and sigmaTD are lower than 600kg/cm<2>, since the bubble in orientating becomes unstable, the thickness accuracy of the film is reduced, where the value of a commodity is lost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a biaxially stretched nylon 6 film, and can be used in the food packaging field, industrial materials field, etc. [Background Art] Nylon films produced by simultaneous biaxial stretching using the tubular method have excellent mechanical and optical properties such as strength and transparency. [Problems to be Solved by the Invention] Biaxially stretched nylon films obtained by the conventional tubular method generally have low thickness accuracy, resulting in poor winding appearance and problems with secondary processes such as printing, laminating, and bag making. Defects occur during processing, which limits its use as packaging and industrial films. This is because even if the thickness accuracy is adjusted using the extrusion die when producing the original film for stretching,
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 worsened by more than twice as much during stretching.

In addition, according to the conventional method, the bubbles are not stable during stretching and deformation, so there is a risk that the bubbles may sway and sometimes break. According to Japanese Patent Publication No. 49-47269, a tubular film obtained by melt-extruding a poly-ε-capramide resin is rapidly cooled and solidified to produce a poly-ε-capramide resin which is substantially amorphous and substantially free of hydrogen bonds. The Bramide resin tubular film was maintained at a moisture content of less than 2% and 45 to 40% before stretching.
Poly-6-capramide with biaxial molecular orientation, characterized by carrying out tube stretching at a temperature of 70°C, and carrying out biaxial stretching at a stretching ratio of 2.0 to 4.0 times in the longitudinal and lateral directions. A method for manufacturing resin film has been proposed. According to Japanese Patent Publication No. 53-15914, after heating an unstretched polyamide tubular film to a temperature of 50 to 90°C, the atmospheric temperature between the stretching start point and the stretching end point is adjusted to 1.
The stretching start point is fixed by maintaining the temperature at 80 to 250°C, and while maintaining the final stretching ratio difference between the transverse and longitudinal directions in the range of 0.2 to 0.6, the stretching ratio is 2.5 to 3. 7
A method of biaxially stretching a polyamide film in the shape of a tube has been proposed, which is characterized by carrying out simultaneous biaxial stretching at a magnification of 3.0 to 4.0 times in the transverse direction.

However, depending on the manufacturing method based on controlling the stretching ratio or stretching temperature, it has not always been possible to accurately define molding conditions to obtain a good film. The present invention relates to biaxially stretched nylon 6 films produced by the tubular method, particularly biaxially stretched nylon 6 films.
The purpose of the present invention is to provide a manufacturing method that can stabilize the forming state during stretching and improve the thickness accuracy of the obtained film. [Means for Solving the Problems] The present invention provides a method for producing biaxially stretched nylon 6 film using the tubular method, and as a result of conducting experiments to determine various parameters involved in stretching, The maximum stretching stress is expressed as σl and the width direction of the film (
It has been found that good results can be obtained by taking the maximum stretching stress of TD) as a parameter and setting the manufacturing conditions based on this. That is, in the present invention, σ. and σ? . respectively, 600 kg/cd≦era”1300
kg/c4600kg/cj≦σ. ≦1300kg/C
It is characterized by being set to l&. However, σ. and σ. are respectively expressed by the following formulas.

σno=(FXB,lo)/AF=T
/ r Here, F is the stretching force (ICg), BMII is the stretching ratio in the MD direction, A is the cross-sectional area of the original film (aa), T
is the rotational torque of the nip roll (kg-cm), and r is the radius of the nip roll (C11).

σ,,1(ΔPxR)/t Here, ΔP is the bubble internal pressure (kg/CI1), R is the bubble radius (cm), and t is the film thickness (elm). σ. and σa. If it exceeds 1300 kg/d,
Continuous production is no longer possible due to frequent bubble breakage during stretching. Also, σ. and σ. If it is less than 600 kg/cd, the bubbles in the process of stretching become unstable, resulting in poor film thickness accuracy and no commercial value.
And σ. and σi1 preferably have an upper limit of 1200 kg/cd and a lower limit of 700 kg/c.
Let it be d. [Example] . Nylon 6 (manufactured by Ube Industries, Ltd.) with a relative thickness η of -3.7 was extruded from an annular die (diameter 75 m), then cooled in a cooling tank (water temperature 15"C) to a thickness of 120 μm. Next, as shown in Fig. 1, this raw film 1 was passed between a pair of nip rolls 2, and after compressing gas inside it, it was heated to a heater 3 (at a set temperature). 3
At the same time, air 5 (air flow rate 15 i/min) is blown from the air ring 4 to the stretching start point to expand it into bubbles 6, which are taken up by a pair of nip rolls 7 on the downstream side, thereby simultaneously biaxially stretching. Stretching was performed. The stretching ratio was 3.0 times in the film movement direction (MD) and 3.2 times in the film width direction (TD). During this simultaneous biaxial stretching, the pressure inside the bubble 6, the radius of the bubble 6, the rotation of the Ninpro roll 1.7, the load and torque of the drive motor, etc. are set to specific values, and the direction of movement of the resulting film ( MD) maximum stretching stress σ. And the maximum stretching stress σ, D in the width direction (TD) of the film was adjusted.

In this example, the maximum stretching stress σ in the moving direction (MD) of the film. is 950 kg/cd, and the maximum stretching stress in the width direction (TD) of the film is σ7. is 960kg
/cd. In addition, these σllゎ and σTD are
This is calculated from the second part.

6 HB= (FX B.e) / AF - T
/ r T = [97.450X (1 - 1.)
0.22] /N where F is stretching force (kg), BH6
is the stretching ratio in the MD direction, A is the cross-sectional area of the original film (c
j), T is the torque (kg-cm), r is the radius of the nip roll (cm), I is the motor current during operation (A), I
. is the motor current (A) during idle operation, and N is the rotation speed (rps) of the nip roll. Note that the specific numerical value of the torque T mentioned above is related to a specific nip roll according to an example. σ,. = (ΔP x R ) / t Here, ΔP is the bubble internal pressure (kg/eta), R is the bubble radius (am), and t is the film thickness (1). σ,． and σT. In the production of the biaxially stretched nylon 6 film according to this example with the conditions set in this way, 24
When continuous manufacturing was performed, bubbles 6 during stretching deformation were observed.
The film was stable with no horizontal vibration, and the thickness variation of the obtained biaxially stretched nylon 6 film 8 was ±4%, which showed very good thickness accuracy. 2-10 Biaxially stretched nylon 6 films 8 according to Examples 2-10 were produced in the same manner as in Example 1 above. However, MD
The conditions for the stretching ratio and TD stretching ratio, the air volume of the air ring 4, and the set temperature of the heater 3 were varied as follows. Regarding the MD stretching ratio, Examples 2 to 8.10 were set to 3.0.
, Example 9 was set as 3.4. Regarding the TD stretching ratio, Examples 2 to 6, 9, and 10 were
．． 2. Example 7 was set as 3.0, and Example 8 was set as 3.4. Regarding the air volume of the air ring 4, Examples 2.3, 7 to
10 at 15 I/min, Example 4 at 5 I/min, Example 6 at 4
The rate was set at 5 points/minute. Regarding the set temperature of the heater 3, Example 2 was set to 330°C;
Example 3 was heated to 280°C, Examples 4 to 9 were heated to 310°C, and Example 10 was heated to 370°C. The temperature of the cooling water in the cooling tank was 15°C. In addition, during simultaneous biaxial stretching, the maximum stretching stress σ in the moving direction (MD) of the film was determined for each example. The pressure inside the bubble 6, the radius of the bubble 6, the rotational speed of the nip roll 1.7, the load of the drive motor, and the torque are adjusted so that the maximum stretching stress σTll in the width direction (TD) of the film is approximately equal to the appropriate value. etc. were set to specific values.

σ. and σ? . In manufacturing the biaxially stretched nylon 6 film 8 according to each example in which the conditions were set to appropriate values, continuous manufacturing was performed for 24 hours, and the bubble 6 during stretching deformation was carried out.
The results of observing and evaluating the stability of the obtained biaxially stretched nylon 6 film 8, measuring and evaluating the thickness accuracy, that is, the thickness accuracy, and comprehensive evaluation are summarized in Table 1 below. ．． Kamikasa ■Upper 2l Biaxially stretched nylon films according to Comparative Examples 1 to 8 were produced in the same manner as in the above Examples. However, the following conditions were used for the MD draw ratio and TD draw ratio, the air volume of the air ring 4, the set temperature of the heater 3, and the temperature of the cooling water. Regarding the MD stretching ratio, Comparative Examples 1 to 4.8 were 3.0,
Comparative Example 5 was 3.6, Comparative Example 6 was 2.4, and Comparative Example 7 was 3.6.
I gave it a 4. Regarding the TD stretching ratio, Comparative Examples 1 to 6.8 were 3.2,
Comparative Example 7 was set to 3.4. Regarding the air volume of air ring 4, Comparative Examples 1, 2, 5 to
8 at 15 po/min, Comparative Example 3 at 0 po/min, Comparative Example 4 at 55
Port/minute. Regarding the temperature of the heater 3, Comparative Example 1 was set at 400°C, Comparative Example 2 was set at 260"C5, Comparative Examples 3 to 8 were set at 310°C. Regarding the temperature of the cooling water, Comparative Examples 1 to 7 were set at 15°C, Comparative Example The temperature was set at 45°C. In addition, during simultaneous biaxial stretching, as in the above-mentioned examples, for each comparative example, the inside of the bubble 6 was adjusted so that the vibration and σ? The pressure, the radius of bubble 6, etc. were set to specific values. In the production of biaxially stretched nylon 6 film according to each comparative example in which σ and σTD were set to appropriate values, continuous production for 24 hours was carried out. The stability of the bubbles during stretching deformation was observed and evaluated, and the resulting biaxially stretched nylon 6
The results of measuring and evaluating film thickness accuracy and comprehensive evaluation are also shown in Table 1 below. In this table, ◎, O, △, and × for forming stability indicate the fluctuation range of fold diameter of 1% or less, 2% or less, 5% or less, and 5%, respectively.
This shows that it exceeds . Also, ○, Δ, and × for thickness accuracy indicate 6% or less, 10% or less, and more than 10%, respectively. And the overall evaluation ◎ is suitable for industrial production, O
indicates that industrial production is possible, Δ indicates that industrial production is possible but some trouble may occur, and × indicates that industrial production is impossible. From the examples and comparative examples in this table, the moving direction of the film (MD
) maximum stretching stress σl411 and film width direction (T
The maximum stretching stress σTD of D) is 600 k in both cases.
It can be seen that when the weight is greater than or equal to g/cd and less than or equal to 1300 kg/cj, not only good molding stability of the bubble 6 but also good thickness accuracy of the biaxially stretched nylon 6 film 8 can be obtained. Ru. Furthermore, since the thickness accuracy of the resulting biaxially stretched nylon 6 film is improved, it is possible to provide a product with good quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the apparatus used in the manufacturing method according to the example. DESCRIPTION OF SYMBOLS 1... Raw film, 3... Heater, 4... Air ring, 6... Bubble, 8... Biaxially stretched nylon 6 film. Applicant Idemitsu Petrochemical Co., Ltd.

Claims (1)

[Claims] (1) In the manufacturing method of biaxially stretched nylon 6 film using the tubular method, the maximum stretching stress in the film movement direction (MD) is σ_M_
D, the maximum stretching stress in the width direction (TD) of the film is σ_T
When __D, σ_M_D and σ_T_D are each 600 kg/cm^2≦σ_T_D≦1300 kg/c
m^2600kg/cm^2≦σ_M_D≦1300k
A method for producing a biaxially stretched nylon 6 film, characterized in that the film is set at g/cm^2. However, σ_M_D and σ_T_D are each expressed by the following formulas. σ_M_D=(F×B_M_D)/A F=T/r Here, F is the stretching force (kg), B_M_D is the stretching ratio in the MD direction, A is the cross-sectional area of the raw film (cm^2), and the rotation of the nip roll. T is the torque (kg-cm), and r is the radius of the nip roll (cm). σ_T_D=(ΔP×R)/t Here, ΔP is the bubble internal pressure (kg/cm^2), R is the bubble radius (cm), and t is the film thickness (cm).