KR100544770B1 - Process for preparing biaxial drawing polyamide film - Google Patents

Abstract

In the method for producing a polyamide film using the tubular method, the biaxial stretching is carried out simultaneously with the longitudinal and transverse bidirectional stretching ratio of 2.8 to 3.5 times the same as that of the general polyamide film, and after the stretching process, a heat-setting tower is installed before the tenter heat treatment process. Disclosed is a method for producing a biaxially stretched polyamide film, characterized in that the heat treatment is carried out in a bubble state, and the edge part inside the tenter is heat treated at a temperature of 1 ° C. to 20 ° C. higher than the central part. In the method for producing a biaxially stretched polyamide film according to the present invention, the stretching ratio is increased by 2.8 to 3.5 times in both longitudinal and transverse directions, and the strength retention and the removal of shrinkage stress are performed by performing a double heat treatment step in a heat setting tower and a tenter. Two effects can be achieved, and by installing an infrared heater or a hot air device on the edge of the tenter, and installing a shielding plate so that the heat of the edge is not transmitted to the center, the width of the edge is heat treated 1 ℃ to 20 ℃ higher than the central portion. It has the effect of reducing the car.

Polyamide, Edge, Shield, Boeing

Description

Process for preparing biaxially drawn polyamide film

The present invention relates to a method for producing a biaxially stretched polyamide film which is widely used for packaging and the like. The present invention relates to a biaxially stretched polyamide film having a longitudinal and lateral bidirectional draw ratio of 2.8 to 3.5 times the same as that of a general polyamide film, followed by biaxial stretching. The heat-setting tower is installed before the tenter heat treatment process, and the heat treatment is performed in a bubble state, and the edge part of the tenter is heat treated 1 ° C. to 20 ° C. higher than the center part, thereby suppressing the bowing phenomenon generated during heat setting, thereby preventing the physical properties of the film edge and the center part of the film. A method for producing a biaxially stretched polyamide film that effectively solves the problem of difference, bowing and anisotropy.

In general, the biaxially stretched polyamide film has a large molecular orientation difference between the film center portion and the film edge portion, resulting in a difference in physical properties in the width direction, and various problems occur when manufacturing a packaging table using such a film. For example, the printing pitch and the deviation of the pint occurs in the umbilical process, it is difficult to carry out the packaging due to curling in the manufacture of the packaging for high temperature sterilization products such as retort.

In the case of T-Die (T-die) method, the causes of the difference in the physical properties in the width direction in the biaxially stretched polyamide film were examined. The film shrinks due to the stretching stress formed by longitudinal stretching, the shrinkage stress caused by heat, and the shrinkage stress in the heat setting process. The edge of the film is forcibly restrained by the clip, and the center of the film has the restraining force rather than the edge. Due to the weak relationship, the moving speed of the central part is slower than that of the edge part. In the case of the tubular method, unlike the tee-die method, since the interaction of these stresses occurs only in the heat setting process, a relatively small width difference occurs.

Japanese Patent Application No. 35-11774 discloses a method of installing a real cooling step by adding a relaxation step of 20 ° C to 150 ° C between the stretching step and the heat setting step. However, this method also did not express the inhibitory effect of the bowing by the cooling process. In addition, Japanese Patent Application Laid-Open No. 50-73978 discloses a method of providing a nip roll group between a stretching step and a heat setting step. However, the above method has a problem in that the temperature of the intermediate zone where the nip roll is installed is higher than the glass transition temperature (Tg), so that the rigidity of the film at the nip point is lowered and the effect is less. JP-A-63-24459 has a nip roll installed over a narrow range near the center part when the heat setting is performed while the clip is clamped at both ends of the film after stretching is completed, and the center part of the film is not forced behind by the nip roll. A method of advancing has been proposed. However, this method needs to cool the nip roll because the portion where the nip roll is installed is in a tenter in a high temperature region, and the film is hot, so that the roll is scratched, causing limitations in practical terms.

The three-bubble system we have now undergoes a heat-setting process in a tenter, so the bowing phenomenon as described above occurs. As a result, the edge of the film is sold at a low price due to poor quality. Therefore, various efforts have been made to reduce the range of the side where the difference in physical properties is greater than that of the center of the film. One of these efforts is a method of improving boeing by increasing the heat treatment temperature in the third bubble to increase the crystal size to reduce the shrinkage stress due to stretching, and to reduce the shrinkage stress by lowering the heat setting temperature in the tenter. Alternatively, there is a method of compensating the deflection of the center part to some extent by supplementing the air supply device installed in order to prevent the two cut pieces of film from sticking to each other by heat before entering the tenter. However, the effects of the above methods were not great.

The present invention has been made to solve the above problems, an object of the present invention, in the production of a biaxially stretched polyamide film to suppress the bowing phenomenon occurring in the stretching process or heat setting process to uniform the widthwise physical properties It is to provide a method for producing a biaxially stretched polyamide film.

The inventors of the present invention observe the change of the bowing line through the stretching process or the heat setting process in the tenter during the production of the polyamide film using the tubular method, and elucidates the process of the bowing phenomenon obtained in various studies to suppress the bowing phenomenon. Means for reviewing the present invention have been completed, and the present invention has been completed based thereon.

Method for producing a biaxially stretched polyamide film according to the present invention for achieving the above object, in the method for producing a polyamide film using the tubular method, the longitudinal and transverse bi-directional draw ratio of the same as the general polyamide film 2.8 times to 3.5 Simultaneously biaxially stretching, a heat-setting column is installed before the tenter heat treatment step after the stretching step, and the heat treatment is performed in a bubble state, and the inner edge portion of the tenter is heat treated at 1 ° C. to 20 ° C. higher than the central part.

The polyamide resin for film in the present invention is nylon 4, nylon 6, nylon 7, nylon 8, nylon 11, nylon 12, nylon 6.6, nylon 6.9, nylon 6.10, nylon 6.11, nylon 6.22, nylon 6T, nylon 6 / Aliphatic polyamide resins such as 6.6, nylon 6/12, nylon 6 / 6T, nylon 6T / 6I, and polymethacylamides, aromatic nylons obtained from isophthalic acid and hexamethylenediamine, and preferably nylon 6 is used. Can be. Besides, it is possible to use plural kinds of polyamide resins such as copolymers, mixtures and composites. It is preferable that the viscosity of the polyamide resin for films in this invention is 2.8-3.6 with the relative viscosity measured with the 1% polyamide resin solution made with 95% sulfuric acid at 25 degreeC for stable bubble formation.

Polyamide chips for films are prepared by adjusting the content of unreacted lactam to a level of 0.5% through an extraction process after chip polymerization and drying. The chip is then passed through an extruder and melted to form a biaxially stretched nylon film by tubular or tee-die. In the case of the tee-die method, the polyamide resin melt passed through the extruder is processed into a sheet while passing through the tee-die and quenched in a chill roll to form an amorphous undrawn fabric. The unstretched fabric thus formed is stretched by a coaxial biaxial stretching method in longitudinal, transverse sequential stretching or tenter and then heat-set to form a biaxially stretched film. In the tubular process, the polyamide resin melt discharged from a circular die is quenched in a water bath to form an unoriented, amorphous unstretched fabric (first bubble). It undergoes longitudinal stretching by (second bubble). This forcibly stretched film is formed of a biaxially stretched polyamide film having stable form stability by removing the stretching stress while passing through the tenter heat treatment zone.

Compared to the T-die method, the present invention uses a tubular method having excellent physical properties uniformity, anisotropy, and boeing properties over the entire width, and installs a heat-setting tower (third bubble) after the stretching tower. After the rough, a heat treatment enhanced triple bubble system is used, which performs the first heat treatment in the bubble state in the heat-setting column and then performs the second heat treatment in the tenter again.

Looking at the manufacturing process of the biaxially stretched polyamide film having a small boeing rate by the triple bubble system in detail, the undrawn disk discharged through the circular die is forcibly cooled below the glass transition temperature by water circulating in the tank After suppressing crystallization as much as possible, the drawing tower is drawn at a draw ratio of 2.8 to 3.5 times in both longitudinal and transverse directions. In general, in order to reduce the shrinkage stress to improve the heat resistance, the draw ratio is decreased, but in this case, the low molecular orientation causes a decrease in tensile strength and gas barrier properties. In the present invention, by adopting the same draw ratio as the general polyamide film, the reduction of strength and gas barrier property is suppressed, and instead, a separate heat treatment is added to perform double heat treatment to achieve two purposes of maintaining strength and removing shrinkage stress. do. In the stretching conditions, longitudinal stretching by the speed difference of the nip rolls and transverse stretching by the air pressure of the bubbles are simultaneously performed in the stretching section which is set at a temperature of 90 ° C to 150 ° C after preheating at about 60 ° C. The stretched polyamide film is subjected to a heat treatment process to remove the shrinkage stress generated by the forced stretching, in the present invention by performing a uniform heat treatment in a bubble state in the heat-setting column in addition to the conventional tenter single heat treatment, Eliminate shrinkage stress uniformly and effectively by double heat treatment. The temperature of the heat-setting column is preferably 180 ° C. to 210 ° C., and it is important to heat the entire film uniformly by double heating of the infrared heater and the hot air device. If the temperature of the heat-setting tower is less than 180 ℃ less than the physical properties of the desired strength, if it exceeds 210 ℃ smoothness and thickness uniformity is poor and the transparency is not good. Unlike the tenter heat treatment, the bubble heat treatment through the heat-setting column does not distinguish between the edge portion of the film and the center portion of the film, and thus, it is possible to effectively solve the problems of inevitability, bowing and anisotropy, which are inevitably involved in the tenter process. .

Both ends of the primary heat-treated bubble polyamide film are cut and separated into two films. Finally, the second heat treatment is performed in a tenter process, and then wound in a mill roll. At this time, the tenter heat treatment temperature is preferably 190 ℃ to 210 ℃ for effective removal of the residual shrinkage stress. As the tenter heat treatment temperature is lower than 190 ° C, the removal of residual stress is not sufficient, and when the tenter heat treatment temperature is higher than 210 ° C, process problems such as film breakage due to excessive heating conditions are likely to occur.

In addition, the temperature of the film edge portion of the tenter is heat treated 1 to 20 ℃ higher than the central portion. For this purpose, a shielding plate is installed between the edge portion and the center portion of the tenter, and a heater such as an infrared heater or a hot air blower is disposed on the edge portion of the film in the tenter. Install. By doing so, the contraction stress of the edge due to the high temperature is expressed more and the restraint force by the clip is transmitted to the center portion to suppress bowing.

The following three methods are used to confirm the widthwise physical property difference of the polyamide film thus prepared.

First, the widthwise physical property difference can be confirmed by measuring the orientation angle and plane orientation of the molecule using the orientation measurement device. In other words, the polymers are arranged in a uniform form through stretching, and by measuring the orientation angle of the polymer molecular chains arranged in this way, it is possible to evaluate the extent of difference in physical properties. In general, polyamide films produced using the T-die method are susceptible to curling because the molecules are oriented diagonally at about +/- 40 degrees when the orientation angle of the molecules is at the edges. Polyamide films produced using the tubla method are better than those produced by the tee-die method with the edge part of about 60 °. The orientation angle means that the molecules are oriented in the width direction as the absolute value of the measured angle is larger, and thus the workability is better.

Second, the widthwise physical property difference can be confirmed using the slope difference of the heat shrinkage rate. Generally, the heat shrinkage rate is 100 ° C. in a 23 ° × 50% RH atmosphere in a longitudinal direction, 45 °, width direction, and 135 ° direction in 20 mm × 20 mm (L ₀ ). After 30 minutes of heat treatment with water, the surface water is removed, and then left at 23 ° C. × 50% RH, and the length (L ₁ ) is measured in each direction to obtain the following formula.

Thermal Shrinkage (%) = {(L ₀ -L ₁ ) / L ₀ } × 100

On the other hand, the azimuth difference in thermal contraction rate can be obtained through the difference between 45 degrees and 135 degrees of the obtained thermal contraction rates. Films with a large difference in orientation tend to curl when heated to a high temperature.

Third, the widthwise physical property difference can be confirmed by measuring the boeing rate. Boeing means that when a straight line is drawn in the width direction on an unstretched fabric, the straight line is bowed in the final film. It is the boeing factor which quantified this, and the formula is as follows.

Boeing rate (B,%) = (b / W) × 100%

Here, W means film width (mm), b means maximum amount of the bowing line (mm).

The value of the product is increased because it is cut in a straight line when the packing stand made using a film having a small boeing rate is cut in the transverse direction.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereto.

Examples 1 to 3

A polyamide 6 chip for film having a relative viscosity of 3.4 polymerized from caprolactam was introduced into an extruder heated at 260 ° C., melted and heated, and extruded through a circular die, followed by cooling and solidification in a water bath to prepare an unstretched fabric. The prepared unstretched fabric was preheated at 60 ° C. and stretched three times in the longitudinal direction by transverse stretching by air pressure and nip roll speed difference in a bubble column set at 120 ° C., respectively. Thereafter, heat treatment was performed under the conditions shown in Table 1. The heat treated biaxially stretched polyamide film was wound up in a mill roll, and the orientation angles, heat shrinkage difference, and boeing ratio of both sides and the center of the final film were measured and shown in Table 1 below.

Here, the orientation angle was measured using an orientation measuring device called a cobra, and the heat shrinkage ratio was 20 mm in the longitudinal direction, 45 °, width direction, and 135 ° direction at 23 ° C. × 50% RH atmosphere in the center part and both sides of the film. It was cut into x 20 mm (L ₀ ), heated to 100 ° C. boiling water for 30 minutes, harvested, and then the surface water was removed. The resultant was left at 23 ° C. × 50% RH and the final length was measured. The bowing rate was determined by drawing a straight line on the unstretched fabric in the width direction by using a wire, and measuring the maximum amount of the bowing line in the final film.

Comparative Examples 1 and 2

The polyamide 6 chip for film having a relative viscosity of 3.4 polymerized from caprolactam was introduced into an extruder heated at 260 ° C., melted and extruded through a circular die, and then cooled and solidified in a water bath to prepare an unstretched fabric. The prepared unstretched fabric was preheated at 60 ° C. and stretched three times in the longitudinal direction by transverse stretching by air pressure and nip roll speed difference in a bubble column set at 120 ° C., respectively. Then, heat treatment was performed under the conditions shown in Table 1. The measuring method of each physical property was the same as that of Examples 1-3.

Heat-setting tower temperature (℃) Shielding rate of shield plate (%) Heat treatment temperature in the width direction tenter (℃) Orientation Angle by Film Position (°) Boeing rate (%) Heat Shrinkage Rate (%) Breaks Center Stools Edge-center Left medium Ooh Example 1 196 100 210 220 10 -85 88 87 3.9 1.2 0 Example 2 196 100 210 215 5 -83 -87 85 4.2 1.4 0 Example 3 196 50 213 214 One -80 85 82 5.2 1.8 0 Comparative Example 1 200 - 205 205 0 -68 83 70 6.3 2.1 One Comparative Example 2 196 - 210 210 0 -65 -83 72 6.3 2.2 0

As described above, the method for producing a biaxially stretched polyamide film according to the present invention extends the longitudinal and transverse stretching ratios by 2.8 to 3.5 times the same as those of the general polyamide film, and performs a double heat treatment step in a heat setting tower and a tenter. By doing so, it is possible to maintain the strength and lower the shrinkage stress. In addition, by installing an infrared heater or a hot air device on the inner side of the tenter, and installing a shielding plate so that the heat of the side portion is not transmitted to the central portion, there is an effect of reducing the difference in width property by heat treatment the edge portion 1 ℃ ~ 20 ℃ higher than the central portion. As a result, it is possible to solve the problems of printing defects and curling that may occur in the printing or lamination process after pouch manufacturing and to improve the productivity of the film.

Claims (5)

In the method for producing a polyamide film using the tubular method, the biaxial stretching is carried out simultaneously with the longitudinal and transverse bidirectional stretching ratio of 2.8 to 3.5 times the same as that of the general polyamide film, and after the stretching process, a heat-setting tower is installed before the tenter heat treatment process. Heat-treating in a bubble state, wherein the inner part of the tenter is heat-treated at 1 ° C. to 20 ° C. higher than the center part. The method of claim 1, The heat treatment temperature in the tenter heat treatment step is 190 ℃ to 210 ℃ manufacturing method of a biaxially stretched polyamide film, characterized in that. The method of claim 1, In the tenter heat treatment step, a shielding plate is provided between the edge portion of the film in the tenter and the center portion of the film, and is heated by a heater provided at the edge portion of the film in the tenter. The method of claim 3, The heater is a method for producing a biaxially stretched polyamide film, characterized in that the infrared heater or hot air device. The method of claim 1, The temperature of the heat-setting column is 180 ℃ to 210 ℃, the heat treatment in the heat-fixed column of the biaxially stretched polyamide film, characterized in that the entire heating of the film uniformly by the dual heating of the infrared heater and the hot air device. Manufacturing method.