KR19990042593A - Method for producing biaxially oriented nylon film - Google Patents

Abstract

According to the present invention, in manufacturing a biaxially oriented crystalline nylon film, the molten tubular film discharged from the annular die is rapidly cooled and then reheated to inflate air therein, thereby simultaneously compressing the biaxially stretched film to substantially MD (film movement). Direction) and TD (direction perpendicular to the moving direction of the film), after pre-heating at the film temperature (80 to 120 ° C) or higher and 30 ° C or lower at the time of biaxial stretching in a tensionless state, the tube heat treatment oven The tubular film, which was introduced into the tube and re-expanded by internal air, was heated from 25 to 35 ° C below the melting point of the crystalline polymer resin by far-infrared radiation heating and hot air from the outside. After forced air cooling, both sides of the folded tubular film are slitted or trimmed, separated into two sheets of film, and in parallel with a small amount of air interposed between the films. It is introduced into a tenter-type oven, and the film is held in parallel with the creep chain spacing, and during this time, the film temperature is heated to a temperature lower than the melting point of the crystalline polymer resin by 2 to 15 ° C., followed by secondary heat setting, followed by forced air cooling. The present invention provides a method for producing a biaxially oriented nylon film, wherein the nylon film produced by the present invention has almost no thickness variation and has excellent heat-setting properties. Lamination properties have excellent advantages.

Description

Method for producing biaxially oriented nylon film

The present invention relates to a method for producing a biaxially oriented nylon film, and more particularly, to continuously produce a film oriented biaxially by inflation of a tube-type crystalline polymer resin at an arbitrary magnification. By the heat treatment method, there is little variation in the thickness of the film, the shrinkage difference between the heat shrinkage rate and the film width direction is small, and the flatness of the film is also excellent. The present invention relates to a method for producing a nylon film.

Biaxially oriented nylon film has excellent gas barrier properties, pinhole resistance, cold resistance, heat resistance, and the like, and is widely used as a packaging material for food packaging materials such as processed foods and retort foods, and various industrial products.

It is well known that the crystalline polymer resin film is stretched in a controlled state at a predetermined temperature condition to produce molecular orientation, thereby improving the physical properties of the film such as tensile strength, impact strength, and chemical resistance. .

However, these molecular orientations can lead to microstructural changes that are susceptible to other properties of the film, particularly the drawback of unstable dimensions due to temperature. That is, the oriented film shrinks in the orientation direction by temperature, and in particular, causes shrinkage remarkably at a temperature higher than the orientation temperature received to achieve the softening temperature or molecular orientation of the resin film. Significant shrinkage in the post-processing process impairs the appearance and thus becomes a barrier to declining commodity value.

It is therefore well known to stretch an oriented film and then crystallize it by heating it to a temperature higher than the stretched temperature in general to stabilize it against shrinkage, which is called tension heat treatment or heat setting. Generally, there are three ways to heat-set a stretched film as follows.

The first method is to heat-treat a flat film on a heat roll or heat belt and heat-treat it. Since this method basically does not involve bending in the film during heat setting, the film after heat setting Has the advantage that it does not involve anisotropy in thermal contraction rate and other mechanical properties. However, it is difficult to completely remove the shrinkage in the width direction (TD) of the film during heat setting, that is, it is difficult to completely prevent the slight shrinkage from occurring at both ends of the film, and to achieve local anisotropy such as thickness deviation and dynamic characteristics. There is a limit that cannot be prevented from occurring.

Secondly, it is a method of heating and setting heat by blowing hot air while holding and driving a flat film on the clip chain which runs using a tenter. However, this method produces significant anisotropy in the film during heat setting, anisotropy in the heat shrinkage and other mechanical properties, and causes defects such as uneven shrinkage in the printing process and the laminating process and distortion of the bag during boiling sterilization. There is a problem.

The third method is a method proposed in Japanese Patent Laid-Open No. 3-106635, which re-expands the tubular film in a cylindrical oven and runs it, and blows and blows hot air to heat and fix the film. The Ying phenomenon does not occur, and no local anisotropy as occurs in the first method.

However, by this method, since the film heating method in the heat treatment oven is only caused by hot air, the periodic fluctuation of the bubble diameter at the time of heat setting at a high temperature near the melting point of the film, for example (below 10 to 30 ° C below the melting point), Bubble fluctuation occurs and satisfactory heat setting is impossible. In particular, as shown in Fig. 1A, when one portion of the tubular film fluctuates slightly, the film there is close to the discharge port of the hot air, so that the temperature rises and the softening progresses, thereby increasing the unbalanced expansion gradually.

Moreover, since the amount of air in the tube is constant, the diameter of the film on the top of the unbalanced inflation portion is small, which results in the periodic variation of the bubble diameter, which usually proceeds for a long time and does not stop easily. In addition, this phenomenon occurs because the film temperature occurs at a high temperature below the melting point of 40 ℃, as a result, it becomes impossible to heat-set at such a high temperature, resulting in insufficient heat-setting and the residual heat shrinkage rate is not sufficiently lowered. Under such conditions, the bubble fluctuation phenomenon as shown in FIG. 1B appears, and heat setting cannot be sufficiently performed.

An object of the present invention is to overcome the problems of the prior art as described above, there is little variation in the thickness of the film, the shrinkage difference in the heat shrinkage rate and film width direction is small, and at the same time excellent in the flatness of the film (printing, laminating) And a method for producing a biaxially oriented nylon film that can be used without deformation in a sterile packaging process.

1 (a) is an explanatory diagram showing a state of a film in a tubular hot stove according to the prior art;

1 (b) is an explanatory view showing the state of a film in a tubular hot stove according to the prior art which shows bubble fluctuations;

2 is a schematic diagram of a tubular heat treatment apparatus used in the present invention,

3 (a) and 3 (b) illustrate a method of measuring a boeing rate,

4 is a schematic view of a planarity measuring device.

* Description of the symbols for the main parts of the drawings *

1. Film in a tubular hot stove 2. Hot air entrance

3. Hot air outlet 4. Far infrared heater

5. L = line of predetermined width in the direction perpendicular to the moving direction

6. Δｂ = deflection amount of L after stretching and heat treatment

7. ℓ = width of L after stretching and heat treatment

8. ｈ = distance drooping from the horizontal

That is, according to the present invention, when the melt-extruded molten tubular film discharged from the annular die is rapidly cooled and reheated, the film is simultaneously biaxially stretched by injecting air into the inside to substantially biaxially stretch the film in the tensionless state of MD and TD. After preheating to above the film temperature (80 ~ 120 ℃) and below 30 ℃ higher temperature, it is introduced into the tubular heat treatment oven divided into 4 sections, and the film temperature (80 ~ 120 at the time of biaxial stretching in the first section) ℃) and above, the hot air of 40 ℃ or less higher temperature and far-infrared radiation heating is performed in parallel, and the temperature of the hot air in the remaining sections is 20 ~ 70 ℃ lower than the film temperature, forced convection film for far-infrared radiation heating While cooling, the film temperature is finally heated to a temperature lower than the melting point of the crystalline polymer resin by 5 to 25 ° C. to perform heat setting, and after cooling by forced air, it is characterized by cutting and winding up. It is to provide a method for producing a biaxially oriented crystalline nylon film.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

When the biaxially oriented crystalline nylon film is manufactured according to the present invention, preheating may be performed during stretching to further improve the effect of the present invention. Specifically, the biaxially oriented film is folded before being introduced into a tubular heat treatment oven. A tubular film in a state is put into a rectangular parallelepiped preheating oven to blow hot air to a temperature above biaxial stretching temperature (80 to 120 ° C.), 30 ° C. or higher, that is, a temperature at which the film heat shrinkage stress reaches a maximum, 30 ° C. or higher. At a high temperature or less, the MD (Machine Direction) tension of the film is significantly suppressed, while the TD (Traverse Direction) is substantially tensionless, and thus preliminary heat treatment can be performed.

This preliminary heat treatment causes the film in the state where the maximum shrinkage stress is lowered to enter the tubular heat treatment oven, and the temporary shrinkage of the bubble diameter caused by the heat shrinkage stress when heat-setting in the tubular swelling state is remarkably alleviated. The change in bubble diameter in the oven (i.e., the change in re-expansion after shrinking once) improves the stability of the bubble so that it is hardly seen. Therefore, the film can be sufficiently heat set at a high temperature up to 5-25 ° C. below the melting point, and the residual heat shrinkage can be lowered by that much.

The preliminary heat treatment apparatus used in the present invention is one in which a plurality of holes or slits are designed on a plurality of air rolls or air pipe surfaces. Hot air is blown into this hole or slit so that the film heats this air or the air pipe group when running in a floating state, so that wrinkles do not occur in the film.

In the present invention, the heat setting by the tubular method is performed by a tubular heat treatment oven as shown in FIG. 2, wherein the heating is mainly performed by far-infrared conduction heat by the far-infrared heater 4 and at the same time hot air discharge of a constant temperature. It is sprayed through (3) and performed.

In the present invention, the tubular heat treatment oven used for heat setting by the tubular method is divided into four sections. In the first section, the film temperature (80-120 ° C.) or more at the time of biaxial stretching is 40 ° C. or higher. The heating is performed in parallel with the hot wind and the far-infrared radiant heating, and the temperature of the hot air in the remaining sections is 20 to 70 ° C. lower than the film temperature, and is heat-set while forcing the convective cooling of the film to the far-infrared radiant heating.

In the first section, because the film near the room temperature enters the heat treatment oven, the heat shrink stress is rapidly strong while reaching the maximum temperature (80 ~ 120 ℃), that is, the biaxial stretching temperature. Since there is almost no risk of expansion, the hot air temperature does not necessarily need to be lower than the film temperature, and hot air can be sprayed at a temperature higher than the temperature (80 to 120 ° C) at which the heat shrinkage stress is maximized and a temperature higher than 40 ° C. That is, the film in this zone is heated by far infrared radiation heating and hot air. When hot air is sprayed at a temperature exceeding 40 ° C. than the temperature at the time of biaxial stretching, the film temperature rises rapidly above the biaxial stretching temperature, and thus the film bubble fluctuates due to rapid film shrinkage.

Heating in the remaining sections is mainly carried out by radiant conduction heat by far-infrared rays, and at the same time, by blowing hot air at a temperature of 20 ° C. to 70 ° C. below the film surface temperature along the bubble film to cool the film, abnormal expansion of the bubble and periodic bubble It was possible to suppress fluctuations such as hardness fluctuations and to raise the film surface temperature to a temperature lower than the film melting point by 5 to 25 ° C to complete the heat setting.

In such a heating method, even if the initial stage of abnormal expansion starts in any part of the bubble film, the forced convection cooling is prevented by hot air at a temperature lower than the film surface temperature by 20 ° C or more, and thus the progress of abnormal expansion is prevented, resulting in periodic fluctuations in the bubble diameter. Back bumps do not occur.

If the difference between the film temperature and the hot air temperature is less than 20 ° C., the effect of preventing the abnormal expansion of the bubble is not sufficient. On the other hand, if the temperature difference exceeds 70 ° C., the effect of preventing the abnormal expansion of the bubble, that is, the bubble stabilization effect, is improved. In order to increase the surface temperature gradually, far-infrared radiation energy must be significantly increased, which is undesirable in terms of energy efficiency.

The residual heat shrinkage rate of the film can be lowered to the minimum limit in practice as described above. However, if there is a slight problem in the planarity of the film after heat setting, the film is put in a tenter and 5 to 15 above the melting point. The film which has favorable planarity can be obtained by carrying out secondary heat setting at the low temperature of ° C. In this way, when performing the second heat setting by the tenter, the film temperature at the time of the first heat setting in the tubular heat setting oven, which is the previous step, does not necessarily have to be raised to the temperature of 5 to 25 ° C. or lower, or lower than the melting point, 25 to 25. Sufficiently, even at the temperature of 35 degreeC, it confirmed experimentally.

In order to explain the present invention more specifically, the production of a nylon 6 resin film will be described as an example.

In general, the nylon 6 resin used in the production of biaxially stretched films contains several kinds of additives, a small amount of monomers and oligomers, and thus the actual melting point is about 215 ° C. The nylon 6 resin is melt kneaded with an extruder and extruded from a circular die, and the cylindrical molten film is rapidly cooled by using cooling water to prepare an unstretched fabric, and then the unstretched fabric is put into a stretching machine to be reheated, and the air inside. It is press-inflated by and re-expanded, and simultaneously biaxially stretched about 3 times MD and TD, respectively, and a stretched film is obtained. The film temperature during the simultaneous biaxial stretching, that is, the stretching temperature has a temperature gradient from the stretching start point to the stretching end point, but is approximately 80 to 120 ° C. The film beyond the stretching end point is immediately cooled by cold air, and exits the stretching apparatus through the folding device. Thus, since it cools immediately after completion | finish of extending | stretching, most of the film deformation stress at the time of extending | stretching is frozen and remains in a film as internal stress.

When the biaxially oriented film is re-expanded by adding air inside without preheating, and when it is put into a tubular heat treatment oven and subjected to heat treatment, the film is heated inside the oven, and the film temperature is gradually raised to raise the maximum temperature above the melting point. The internal stress is removed by raising the temperature to 5 ~ 30 ℃ lower, that is, 180 ~ 200 ℃. At this time, the shrinkage stress is rapidly expressed in the first section until the film put into the oven reaches 80 to 120 ° C. from the room temperature to the temperature at which the shrinkage stress becomes the maximum. As a result, the diameter of the film bubble is slightly reduced. do.

In addition, as the film temperature rises, the internal stress gradually relaxes, that is, the shrinkage stress drops and the bubble diameter of the film decreases rapidly.Because of the internal air pressure, the bubble diameter passes the second section of expansion and restoration, and the film temperature reaches the maximum temperature of 185. After exiting from the oven after passing through the third and fourth sections in a state of rising to ˜210 ° C., it is forcedly cooled by cold air and folded into a plate shape.

The hot air spraying temperature of the first section is 110-160 ° C, the reaching temperature of the film is 120-160 ° C, the hot-air spraying temperature is 130-155 ° C, and the reaching temperature of the film is 160-185 ° C in the second section. Hot air spraying temperature in the third section is 130 ~ 180 ℃, the surface temperature of the film is 185 ~ 210 ℃, after staying at this temperature for at least 1 to 3 seconds, the film hot air spraying temperature is 140 ~ 185 ℃, the film After remaining in the fourth zone having a surface temperature of 190 to 210 ° C. for at least 1 to 3 seconds, it is derived and cooled by cold air.

In the first section, the film is heated in parallel with the far-infrared radiant energy and the heat energy of the hot wind at the same time, but the far-infrared radiant energy in the second, third and fourth sections always keeps the film against the forced convection cooling by the hot wind. Gradually raising the temperature, the insufficient energy is to supply the film.

Under such conditions, problems such as abnormal expansion of bubbles, periodic diameter fluctuations, and fluctuations are hardly seen. However, after being forced out of the heat treatment oven and forced air-cooled, the thermal contraction rate of the film folded into a plate shape was 3 to 4% (average of MD and TD), showing that the heat setting was sufficiently completed.

When the film is heated to a uniform hot air temperature regardless of the section, it is very difficult to prevent periodic fluctuations and fluctuations in the bubble diameter, and under these conditions, the maximum temperature of the film is to operate while suppressing periodic fluctuations and fluctuations in the bubble diameter. It should be limited to below 175 ℃. In addition, the produced film is not sufficiently heat set, the heat shrinkage rate (115 ℃) is about 5% or more, the film thickness variation occurs and the post-processing printing or lamination properties are not good.

The case where the preheating process is added in order to further improve the said improvement effect using nylon 6 resin is demonstrated.

In other words, before the biaxially stretched nylon film is introduced into the main heat treatment oven, the pre-heat treatment apparatus of the rectangular parallelepiped preheating oven or the air floating method using the air pipe, air roll, etc. is introduced. Substantially no tension, MD is in a very low tension state, that is substantially free shrinkage, the film temperature is 80 ~ 150 ℃, that is, the film temperature at the time of biaxial stretching, that is, the temperature at which the heat shrinkage stress of the biaxially stretched film is maximum, By heating below 30 degreeC high temperature, the residual heat shrink stress of a film is dropped, and it heats up by putting into a main heat processing oven, and performing heat setting. When the pre-heat treatment temperature is lower than the film stretching temperature, the effect of eliminating the residual heat shrinkage stress is small, and the film shrinks at a temperature higher than the temperature 30 ℃ higher than the stretching film, which is not good for the heat setting process.

In the case of performing the preliminary heat treatment as described above, since the stability of the bubble is further improved, the periodic diameter fluctuation and fluctuation of the bubble are suppressed even when the maximum attainable temperature of the film is raised to 5 to 10 ° C, that is, to 190 to 210 ° C. As a result, the thermal contraction rate (115 ° C.) of the product film is reduced to 2-3%, and a product that can withstand high temperature sterilization such as retort sterilization is obtained.

In the example in which the nylon 6 resin is used as described above, even if preheating is performed or not, bowing of the film hardly occurs. Therefore, even if any part of the TD direction of a film is sampled, anisotropy, especially anisotropy of a thermal contraction rate and a thermal contraction rate does not appear. In the hot water voile sterilization and retort sterilization process of the laminated umbilical cord product, neither the distortion of the bag nor the nonuniform shrinkage occurs.

Although the heat-setting biaxially oriented nylon 6 film obtained in the above process can be sufficiently provided for practical use, in order to improve the planarity of the film to an extreme level, a tenter type secondary heat setting may be performed subsequent to the tubular heat treatment oven process. It may be.

In the second heat setting, after passing through a tubular treatment oven, passing the accentuated air-cooled cylindrical film into a plate, and folding the folded film into two sheets by slitting or edge trimming, and then a small amount of The film is placed in a parallel tenter oven with air interposed therebetween, and the film is advanced by reducing the gap between the tenter clips in parallel or with the progress of the clips. After forced cooling, the film is taken out of the clip and wound up.

The maximum reached temperature of the film in the tenter oven was 200-210 ° C., and the flatness of the treated film was at the highest level, and troubles such as the occurrence of defects and wrinkles in printing or lamination processes were hardly generated. In addition, when performing tenter oven heat treatment under such conditions, the highest film surface temperature of the film in a tubular heat treatment oven is not necessarily high temperature such as 190 to 210 ° C., and sufficient to be about 180 to 190 ° C. is sufficient for the measurement of thermal shrinkage rate. It was confirmed by

However, when the maximum temperature of the film in the tube heat treatment oven is lower than 180 ° C., the residual heat shrinkage stress of the film that has passed through the tube heat treatment oven is not sufficiently lowered, and thus the film bowing in the tenter oven This is not preferable because it appears to a degree that can not be ignored, because anisotropy such as heat shrinkage rate, heat shrinkage rate and the like occurs.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided only for illustrating the present invention, and the present invention is not limited by the following Examples.

Example 1

Using a polyamide-based nylon 6 (relative viscosity 3.6) as the crystalline thermoplastic resin, extruded from a circular die having a diameter of 70 mm, followed by quenching in 18 ° C cooling water, and a cylindrical nylon film having a diameter of 77 mm and a thickness of 120 µm (shrinkage) Start temperature 45 degreeC, melting | fusing point 215 degreeC) was produced. This raw film was continuously supplied to a U-shaped guide plate to obtain a two-ply plate-like film. Continuously feeding and heating this plate-like film into a tubular oven using both hot air and infrared heaters to draw magnification MD (moving direction of film) / TD (orthogonal to film moving direction) = 2.9 / 3.1. Simultaneous biaxial stretching was performed. The biaxially stretched film which consists of two layers of plate shape was obtained through the U-shaped board comprised of 16 sets of guide rolls. Subsequently, the plate-shaped stretched nylon film was subjected to preheat treatment at 105 ° C. for 4 seconds in a rectangular parallelepiped preheating oven. This was driven into a tubular heat treatment oven designed in four sections to enable temperature control by hot air and infrared heaters. In this case, the temperature of the infrared heater in the first section was 280 ° C, the temperature of hot air was 130 ° C, and finally the surface temperature of the film was 130 ° C. In the second section, the temperature of the infrared heater was 275 ° C, the temperature of the hot air was 150 ° C, and the surface temperature of the film was 175 ° C. In the third section, the temperature of the infrared heater was 260 ° C, the temperature of the hot product was 160 ° C, and the surface temperature of the film was 187 ° C. The temperature of the infrared heater in the last 4 section was 275 degreeC, the temperature of hot air was 160 degreeC, and the surface temperature of the film was 190 degreeC. After heat setting, the film was cut and wound up. For the obtained nylon film, shrinkage (95 ° C., 115 ° C.), planarity, boeing rate, and bubble diameter variation were measured and shown in Table 1 below.

Example 2

After passing through a tubular heat treatment oven as in Example 1, forced air cooling and trimming the folded film past the U-shaped guide plate to make two pieces, and interposed a small amount of air between the two-phase film in a parallel tenter oven After the heat treatment, the maximum surface temperature of the film was 210 ° C. and the second heat setting was performed, except that the film was wound, and then processed in the same manner as in Example 1 to prepare a nylon film, and the physical properties thereof were measured. Together.

Example 3

The stretched film of Example 1 was produced through the following heat setting without preheating. The temperature of the infrared heater in the 1st section of the tube heat treatment oven was 280 degreeC, the temperature of hot air was 130 degreeC, and the surface temperature of the film was 130 degreeC finally. In the second section, the temperature of the infrared heater was 280 ° C, the temperature of the hot air was 155 ° C, and the surface temperature of the film was 177 ° C. In the third section, the temperature of the infrared heater was 280 ° C, the temperature of the hot air was 160 ° C, and the surface temperature of the film was 195 ° C. The temperature of the infrared heater in the last 4 section was 280 degreeC, the temperature of hot air was 165 degreeC, and the surface temperature of the film was 205 degreeC. After the heat setting, the film was cut and wound to prepare a nylon film, and the physical properties were measured and the results are shown in Table 1 together.

Comparative Example 1

Using a polyamide-based nylon 6 (relative viscosity 3.6) as the crystalline thermoplastic resin, extruded from a circular die having a diameter of 70 mm, followed by quenching in 18 ° C cooling water, and a cylindrical nylon film having a diameter of 77 mm and a thickness of 120 µm (shrinkage) Start temperature 45 degreeC, melting | fusing point 215 degreeC) was produced. This raw film was continuously supplied to a U-shaped guide plate to obtain a two-ply plate-like film. The plate-shaped raw film is continuously introduced into a tubular oven using hot air and infrared heaters, and heated to draw a stretch ratio of MD (moving direction of film) / TD (orthogonal to film moving direction) = 2.9 / 3.1. Simultaneous biaxial stretching was performed. The biaxially stretched film which consists of two layers of plate shape was obtained through the U-shaped board comprised of 16 sets of guide rolls. This was run inside the tubular heat treatment oven. In the tubular heat treatment oven, the nylon film was first heat-fixed at 180 ° C. with uniform hot air regardless of the section, and the nylon film was secondly heat-fixed at 210 ° C. with hot air in a tenter oven to wind the film to prepare a nylon film. Various physical properties were measured and the results are shown in Table 1 together.

Comparative Example 2

Nylon film was prepared in the same manner as in Comparative Example 2, except that the nylon film was first heat-fixed at 150 ° C. in a tubular heat-treatment oven, and secondly heat-fixed at 210 ° C. in a tenta oven. The results are shown together in Table 1 below.

[Property evaluation method]

* Heat shrinkage rate was measured by ASTM D 2838 method.

* Boeing rate: Draw a standard line (L) of a predetermined width in the direction perpendicular to the moving direction on the raw nylon film as shown in Figure 3a, and the amount of deflection of the line L after stretching and heat setting as shown in Figure 3b ( (B) and the width (L) of L after extending | stretching and heat processing were measured, and the bowing rate was calculated | required from baud rate = (triangle | delta) b / Lx100%. Since the bowing rate after stretching is 0%, only the bowing rate after heat setting is shown.

* Planarity: As shown in Fig. 4, the full width of the final heat-treated film was placed over a rod bar 3m away, and the deflection distance (h) based on the horizontal was used as a criterion for measurement evaluation. Was suspended to add a constant tension. And the measurement of the bubble diameter fluctuation was evaluated by measuring the width fluctuation value (taken 5 times the average value at 5M intervals) when the cylindrical film is folded in a plate shape.

division Heat Shrinkage (%) Flatness (mm) Boeing rate (%) Bubble diameter change (mm) 95 ℃ (MD / TD) 115 ° C (MD / TD) Example 1 1.9 / 1.8 2.5 / 2.6 27 2.7 4.5 Example 2 1.8 / 1.7 2.3 / 2.5 21 2.4 4.5 Example 3 2.0 / 2.1 3.4 / 3.5 28 3.6 11 Comparative Example 1 2.4 / 2.3 4.2 / 4.3 28 5.0 27 Comparative Example 2 2.4 / 2.4 4.6 / 4.8 29 5.3 21

The nylon film produced by the method of the present invention has almost no thickness variation and has excellent heat-setting properties, and thus can be used without deformation since it has excellent printing properties or lamination properties during post-processing of the film, and thus is used in various food packaging materials such as retort food. Is possible.

Claims (4)

The molten tubular film discharged from the annular die is rapidly cooled and then reheated to pressurize air into the inside to simultaneously draw the biaxially stretched film in MD (direction of film movement) and TD (direction perpendicular to the direction of film movement). Pre-heat treatment is carried out at film temperature (80 ~ 120 ℃) above 30 ℃ higher than biaxial stretching in tensionless state, and then introduced into the tubular heat treatment oven divided into 4 sections to obtain the hot air temperature of the first section. When biaxial stretching, the film temperature (80 ~ 120 ℃) or more, less than 40 ℃ high temperature, in parallel to the far-infrared radiation heating is performed in parallel, the temperature of the hot air of the remaining sections is 20 ~ 70 ℃ lower temperature than the film temperature While the film is forced to convection cooling for far-infrared radiant heating, the film temperature is finally heated to a temperature of 5-25 ° C lower than the melting point of the crystalline polymer resin, and heat-setting is performed. The method of passport face biaxially wherein taking the crystalline nylon film. The molten tubular film discharged from the annular die was quenched and then reheated to pressurize the air into the inside to simultaneously introduce a biaxially stretched film into the tubular heat treatment oven divided into four sections. At the time of axial stretching, the film is heated above the film temperature (80 ~ 120 ℃) and below 40 ℃, and heated in parallel with the far-infrared radiation heating, and the temperature of the hot air in the remaining sections is 20 ~ 70 ℃ lower than the film temperature. While the film is forced convection cooling with heating, the film temperature is finally heated to a temperature of 5-25 ° C. lower than the melting point of the crystalline polymer resin, followed by heat setting, followed by forced air cooling, followed by cutting and winding up. Method for producing a fragrance crystalline nylon film. When the molten tubular film discharged from the annular die is rapidly cooled and then reheated, the air is compressed into the inside to simultaneously compress the biaxially stretched film. After preheating below 30 ℃ higher, it is introduced into a tubular heat treatment oven divided into four sections, and the temperature of the hot air in the first section is greater than or equal to the film temperature (80 ~ 120 ℃) at the time of biaxial stretching. Below the high temperature, heating is performed in parallel with the far-infrared radiation heating, and the temperature of the hot air in the remaining sections is 20 to 70 ° C lower than the film temperature, forcing the convection cooling of the film to the far-infrared radiation heating, and finally, the film temperature. The first heat setting is performed by raising the temperature to 25 ~ 35 ° C. below the melting point of the crystalline polymer resin, and after forced air cooling, slitting or trimming both ends of the folded tubular film. The film is separated into two films, introduced into a parallel tenter oven with a small amount of air interposed between the films, and the film is held in parallel with the creep chain spacing, while the film temperature is crystalline. A method for producing a biaxially oriented crystalline nylon film, characterized in that the film is heated to a temperature lower than the melting point of the polymer resin by 5 to 15 ° C, secondary heat-setting, and forced air cooling. After quenching and solidifying the molten tubular film discharged from the annular die, reheating and injecting air into the inside, the simultaneous biaxially stretched film was introduced into a tubular heat treatment oven divided into four sections. At the time of axial stretching, the film is heated above the film temperature (80 ~ 120 ℃) and below 40 ℃, and heated in parallel with the far-infrared radiation heating, and the temperature of the hot air in the remaining sections is 20 ~ 70 ℃ lower than the film temperature. While heating the film by forced convection with heating, the film temperature is finally raised to a temperature 25-35 ° C. lower than the melting point of the crystalline polymer resin, and the first heat setting is performed. After forced air cooling, the both ends of the folded tubular film are slit. By dipping or trimming into two films and introducing them into a parallel tenter oven with a small amount of air interposed between the films, The film is held in parallel at intervals, and during this time, the film temperature is heated to a temperature of 5 to 15 ° C. lower than the melting point of the crystalline polymer resin, followed by secondary heat setting, followed by forced air cooling, followed by winding up. Method for producing a fragrance crystalline nylon film.