JPH10296853A - Manufacture of biaxially oriented polyamide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a polyamide film of which an oblique difference in a hot water shrinkage factor is reduced, and which is excellent in dimensional stability under heat. SOLUTION: In a process wherein an unoriented film being amorphous and non-orientated substantially is stretched longitudinally and then stretched laterally by a tenter type laterally stretching machine and thereby a biaxially oriented polyamide film is manufactured sequentially and on the occasion when the opposite ends of this oriented film are released from clips of the tenter type lateral stretching machine after completion of lateral stretch, heat treatment and relaxation treatment and the film is subjected to reheating treatment by flying type heat treatment equipment giving arc-shaped blow of hot air against it, a tensile force (T kg) in the traveling direction of the oriented film at the time of the reheating treatment, a reheating treatment temperature (t deg.C), treatment air velocity (V m/sec) and reheating treatment time (θ sec) are so set as to satisfy the conditions of 0.2<=T<=0.8, 150<=t<=200, 10<=V<=45 and 1.0<=θ<=5.0 respectively in this manufacture. Herein T denotes the tensile force per a thickness 1 μm and a film width 1 m.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a biaxially stretched polyamide film. More specifically, the present invention relates to a method for producing a biaxially stretched polyamide film in which an unstretched polyamide film is first stretched longitudinally and then transversely stretched by a tenter method, and is used for improving anisotropy of heat shrinkage properties of the film. It is about the method.

[0002]

2. Description of the Related Art Biaxially stretched polyamide films have excellent mechanical properties, optical properties, thermal properties, gas barrier properties, wear resistance, impact resistance, pinhole resistance, etc. Widely used as a film for other packaging materials. Further, biaxially stretched polyamide films are widely used as base films for retort food bags (bags for hot water treatment), and such retort food bags are usually heat-sealed to biaxially stretched polyamide films. It is a so-called three-sided seal bag in which various sealants having properties (polyethylene, polypropylene, etc.) are laminated, then folded and heat-sealed on three sides. And, at the stage of actual use, after filling the bag with food and the like, since high-temperature boil treatment is performed,
Dimensional stability at high temperatures is required.

[0003] For example, the direction of 45 ° with respect to the longitudinal direction of a base film (biaxially oriented polyamide film) is 135 °.
If the difference in the degree of hot water shrinkage from the direction of the degree is large (hereinafter referred to as “diagonal difference in hot water shrinkage”), the phenomenon of twisting or curling of the bag occurs, and the appearance of the product is impaired. I do. Also, such a phenomenon, after stretching in the longitudinal direction,
Stretching in the transverse direction is remarkable in the so-called sequential biaxial stretching method, and the influence increases as it is closer to the end, so the polyamide film produced by this sequential biaxial stretching method is used for the above-mentioned applications. It was difficult.

In order to solve such a problem, an arc-shaped floating heat treatment method has been proposed as a method for improving the thermal dimensional stability of a thermoplastic resin film from a stenter. For example, in Japanese Patent Application Laid-Open No. 4-292934, immediately after the film is biaxially stretched in the vertical and horizontal directions, the film is levitated and run so as to draw an arc along the arc surface of the hot air blowing means having an arc vertical cross section. A method is disclosed in which a heat treatment is performed substantially simultaneously in the vertical and horizontal directions of the film during the floating traveling.

However, in this method, it is difficult for the apparatus to control the tension applied in the longitudinal direction of the film, so that the relaxation in the longitudinal direction becomes insufficient, while the width direction (horizontal direction) is practically insufficient. Since it is free, the relaxation treatment is sufficiently performed, and the relaxation effect in each direction becomes non-uniform, and a sufficient effect is obtained with respect to the improvement of the oblique difference in the hot water shrinkage of the finally obtained film. I found that I could not do it.

Further, JP-A-4-292937 discloses that immediately after a film is biaxially stretched in a machine direction and a transverse direction,
There is disclosed a method in which a buoyant steam having an arcuate vertical cross section is used to levitate and travel along an arcuate surface along an arcuate surface, and during the levitating travel, the reheat treatment is performed substantially simultaneously in the longitudinal and lateral directions of the film.

However, this method has a problem that when it is applied to a polyamide film which is liable to undergo dimensional change due to moisture, wrinkles are apt to occur during processing, roll formation is deteriorated, and commercial value is lost. .

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the diagonal difference in shrinkage of hot water, which has been a problem when a polyamide film is produced by a successive biaxial stretching method, by devising production conditions. Things. More specifically, the thermal dimensional stability is excellent, and the diagonal difference in shrinkage ratio of hot water is small,
An object of the present invention is to obtain a biaxially oriented polyamide film having practical strength.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies on a production method capable of reducing the oblique difference in the hot water shrinkage of a successively biaxially stretched polyamide film. It has been found that the above-mentioned problems can be solved by performing re-heat treatment by a floating heat treatment apparatus after the completion of the heat treatment and relaxation treatment, and by setting the running direction tension and the like during the re-heat treatment within an appropriate range. .

That is, the gist of the present invention is as follows. Substantially amorphous, unoriented unstretched film is stretched longitudinally, and then, in the step of manufacturing a biaxially stretched polyamide film by transversely stretching with a tenter type transverse stretching machine,
After the completion of the transverse stretching, heat treatment and relaxation treatment, both ends of the stretched film are released from the clips of the tenter type transverse stretching machine, and when the heat treatment is performed again by the floating heat treatment apparatus, the running direction tension (Tkg) of the stretched film at the time of the reheat treatment , Reheating temperature (t ° C), processing wind speed (Vm / sec) and reheating time (θ
sec) satisfying the following conditions (1) to (4), respectively. 0.2 ≦ T ≦ 0.8 (1) 150 ≦ t ≦ 200 (2) 10 ≦ V ≦ 45 (3) 1.0 ≦ θ ≦ 5.0 (4) where T is a tension per 1 μm in thickness and 1 m in film width.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyamide in the present invention is mainly a polyamide having stretched crystallinity, but is not particularly limited,
Any linear polymer compound having an amide bond in the molecule may be used. That is, starting with nylon 6, polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610), polyundecamide (nylon 11), polylauramide (nylon 12), polymetaxylylene adipamide (MXD6) ) And their copolymers, and nylon 6 which is excellent in cost performance is particularly preferably used.

[0012] If necessary, various additives such as a lubricant, an antistatic agent, an antiblocking agent, and inorganic fine particles can be added to these polyamides as long as they do not adversely affect the performance of the film.

As a specific example of the method for producing a sequentially biaxially stretched polyamide film in the present invention, for example, a polyamide resin extruded from an extruder is discharged from a T-die, and is subjected to an electrostatic imprint casting method or an air knife casting method. It is cooled and solidified on a cooled rotating drum to obtain an unstretched film. Next, the unstretched film is stretched in the machine direction (MD) at a temperature equal to or higher than the glass transition point, and then stretched in the transverse direction (MD) using a tenter type transverse stretching machine. Subsequently, heat treatment and relaxation treatment are performed, and further heat treatment (hereinafter, referred to as re-heat treatment) is performed to reduce residual stress, and the film is wound by a winder.

In the present invention, it is possible to provide moderately stable shrinkage characteristics even if the film has a directionally anisotropic shrinkage characteristic or a somewhat high shrinkage ratio before re-heat treatment. It is.

In the present invention, the stretching ratio MD is 2.6.
Preferably, the TD is in the range of 3.3 to 3.9 times and the TD is in the range of 3.3 to 3.9 times. Since the stretching ratio affects the strength and the heat shrinkage of the film, if the ratio is less than these ranges, the strength cannot be obtained, and if the ratio is larger, the film is cut at the time of stretching and the productivity is deteriorated.

The heat treatment temperature depends on the production rate and the thickness of the film, but is preferably in the range of 205 to 220 ° C. If the temperature is lower than 205 ° C, the dimensional stability of the film is reduced. If the temperature is higher than 220 ° C, the film is deteriorated and the strength is reduced.

The conditions of the heat relaxation treatment (TD direction) for relaxing the internal strain of the film generated in the stretching step include:
The relaxation rate is preferably in the range of 1.0 to 7.0%. Relaxation rate 1.0
%, The internal strain is not sufficiently removed, and if it is more than 7.0%, the thermal shrinkage of the TD becomes smaller than that of the MD,
The balance of the heat shrinkage ratio becomes poor.

The method of performing the reheat treatment in the present invention is a method of blowing hot air in an arc shape (floating heat treatment method). A similar effect can be obtained by using a roll heating method such as a dielectric heating roll as a method of performing the reheat treatment. However, in particular, when the heat treatment is performed at a high temperature, the film and the roll adhere to each other and scratches are generated. There's a problem. Also,
In the reheat treatment step, it is desirable to provide a flow straightening plate and pressure regulating holes in the spray nozzle of the floating heat treatment apparatus so that the hot air can be blown uniformly and perpendicularly to the film surface.

In the reheat treatment step of the present invention,
Since the film edge is not gripped by the chuck, TD
And MD are simultaneously relaxed. At this time, the degree of relaxation treatment of the MD can be adjusted by the magnitude of the tension in the running direction of the film.

In the present invention, it is necessary to satisfy the following conditions (1) to (4) as conditions for the reheat treatment. 0.2 ≤ T ≤ 0.8 (1) 150 ≤ t ≤ 200 (2) 10 ≤ V ≤ 45 (3) 1.0 ≤ θ ≤ 5.0 (4) where T is the thickness of 1 μm and the running direction of the stretched film per 1 m of film width. Tension (Tkg), t is temperature (° C),
V is the velocity of the hot air (m / sec) and θ is the processing time (sec).

When T is less than 0.2 kg, the line tension is insufficient at the commercial production speed of the film, and meandering on a roll and wrinkling at the time of winding are generated. This phenomenon is more likely to occur as the production speed increases, and is not preferable in terms of operability. If T is higher than 0.8 kg, wrinkles are generated in the MD direction, and stress is not relaxed due to high tension, so that a good heat shrinkage cannot be obtained. In order to achieve the object of the present invention, it is particularly important to control the tension in the traveling direction.

Usually, when the film released from the tenter clip is wound by a winder, the film tension is as follows:
Since it is considerably larger than the tension range in the reheat treatment step, it is necessary to perform a tension cut before and after the reheat treatment step in order to control the tension range. As a method of performing the tension cut, a film nip, a suction roll, an S-wrap roll, or the like can be used.

In order to easily control the tension, it is preferable to provide a step of cooling the film below the glass transition point after the re-heat treatment step. this is,
This is for maintaining a good heat shrinkage balance and suppressing the generation of wrinkles in the next winding step, and is also preferable in terms of cooling equipment cost and space. If the film is not cooled before the high tension winding step, the film is stretched, and satisfactory performance cannot be obtained. As a cooling method,
An air knife method or a cooling roll method can be used.

It is necessary that the temperature of the reheat treatment step, the velocity of the hot air, and the processing time simultaneously satisfy the above conditions (2) to (4). The actual film production conditions are adjusted within the above range.However, if the values of the temperature and the processing time are too small, the processing capacity becomes insufficient, and the improvement effect of the hot water shrinkage diagonal difference cannot be obtained. If it is too large, not only is the polymer deteriorated, but the effect of surface treatment such as corona treatment itself is reduced, which is not preferable.

The speed of the hot air is 10 m / sec.
If it is smaller than this, the film will not float and the film will come into contact with the spray nozzle, causing scratches on the film.If it is larger than 45 m / sec, the film tension will increase and the floating balance of the film will become unstable, resulting in wrinkles. More likely to occur.

[0026]

According to the present invention, in the re-heat treatment step, the tension in the TD direction is released without gripping the end portion, and the tension in the MD direction is adjusted appropriately, so that the stress is appropriately moderated in the MD and TD directions. It is considered that the oblique difference in the hot water shrinkage ratio is reduced.

[0027]

Next, the present invention will be described specifically with reference to examples. In addition, the evaluation methods, such as measurement of the following Examples and Comparative Examples, are as follows.

1. Hot water shrinkage (MD, TD) In the center of the entire width of the biaxially stretched polyamide film,
Parallel lines at 100 mm intervals were marked in a predetermined direction with oil-based ink, and these were slit to a width of 10 mm. Temperature of the obtained sample
The humidity was adjusted in an atmosphere of 20 ° C. and a relative humidity of 65% for 2 hours, and the dimension A between marks after the humidity adjustment was measured. This was boiled in hot water at 100 ° C. for 5 minutes, then humidified again in an atmosphere at a temperature of 20 ° C. and a relative humidity of 65% for 2 hours, and then the dimension B between marks was measured. Using these measured values, the hot water shrinkage was calculated by the following equation. Hot water shrinkage = (AB) / A × 100 (%)

2. Hot water shrinkage diagonal difference The difference in hot water shrinkage at 45 ° and 135 ° with respect to the MD direction of the film at 32.5% from the center to the left and right with respect to the entire width of the biaxially stretched polyamide film Was determined, and the average of the left and right values of the film was defined as the difference in shrinkage ratio between hot water.

3. Breaking strength At the center in the width direction of the biaxially stretched polyamide film, samples were taken in the MD and TD directions at a length of 150 mm and a width of 10 mm, respectively, and humidified in an atmosphere at a temperature of 20 ° C. and a relative humidity of 65% for 2 hours. Then, using a Shimadzu Autograph AG-100 Model E, a film conditioned at a temperature of 20 ° C. and a relative humidity of 65% was gripped at a distance between chucks of 100 mm, and measured at a pulling speed of 500 mm / min. did.

Example 1 Nylon 6 (A1030BRF manufactured by Unitika, melting point 220 ° C.) having a relative viscosity of 3.0 (in 95% concentrated sulfuric acid at 25 ° C.) was treated with a 630 mm wide T
The sheet was melt-extruded at 260 ° C. from a die and then rapidly cooled on a rotating drum having a surface temperature of 15 ° C. by an air knife casting method to obtain an unstretched polyamide film having a thickness of 150 μm. Next, the unstretched film was guided to a longitudinal stretching machine composed of a series of heating rollers having different peripheral speeds, and a temperature of 55 ° C.
The film was longitudinally stretched at twice the stretching ratio. Subsequently, the longitudinally stretched film is guided to a tenter-type transverse stretching machine, and is transversely stretched 3.7 times at a temperature of 90 ° C., and then subjected to a heat treatment at 213 ° C.
Was subjected to relaxation treatment. After releasing both ends of the obtained biaxially stretched polyamide film from the tenter clip and trimming the unstretched remaining portion of the end, in a floating heat treatment apparatus,
Reheat temperature 180 ° C, Processing time 2.0 seconds, Processing wind speed 18m / sec
Then, heat treatment was performed at a treatment tension of 3.8 (kg / m / 15 μm), and thereafter, the mixture was immediately cooled with an air knife and a cooling roll to obtain a biaxially stretched polyamide film. As shown in Table 1, the physical properties of the obtained film were good in the difference in oblique hot water shrinkage.

Example 2 The heat treatment temperature in the tenter was set at 210 ° C., the relaxation treatment was set at 3%, and the condition of the reheat treatment by the floating heat treatment apparatus was set at the treatment temperature of 1%.
57 ° C, processing time 1.9sec, processing wind speed 36m / sec, tension 1
A biaxially stretched polyamide film was obtained in the same manner as in Example 1 except that the thickness was 0.2 (kg / m / 15 μm). Table 1 shows the physical properties of the obtained film. As in Example 1, it had an excellent oblique difference in hot water shrinkage.

Comparative Examples 1 to 5 Biaxially stretched polyamide films were obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were used as the reheat treatment conditions in the floating heat treatment apparatus. Table 1 shows the physical properties of the obtained film. In Comparative Example 1, the tension was too low, wrinkles and meandering occurred in the film, and it was not possible to wind up a clean roll in appearance. In Comparative Examples 4 and 5, the heat treatment conditions were too severe, and the strength of the film was reduced.

Comparative Example 6 A biaxially stretched polyamide film was obtained in the same manner as in Example 2, except that the conditions shown in Table 1 were used as the reheat treatment conditions in the floating heat treatment apparatus. Table 1 shows the physical properties of the obtained film.

[0035]

[Table 1]

[0036]

According to the present invention, it is possible to produce a film having excellent dimensional stability and minimizing the difference in oblique hot water shrinkage without breaking, and to produce a successively biaxially stretched polyamide film. As a method, it is extremely effective. Further, since the obtained film has uniform physical properties also in the width direction, the range of use of the biaxially stretched polyamide film, which has been restricted so far, can be expanded.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Fumihiko Hosokawa 31-3 Uji Hinojiri, Uji City, Kyoto Unitika Inside Uji Plastic Factory, Ltd. 3 Unitika Uji Plastic Factory Co., Ltd.

Claims (1)

[Claims] In a process of longitudinally stretching a substantially amorphous, non-oriented, unstretched film and then transversely stretching with a tenter-type transverse stretching machine to successively produce a biaxially stretched polyamide film, transverse stretching and heat treatment are carried out. After the completion of the relaxation treatment, the stretched film is released from the clips of the tenter-type transverse stretching machine at both ends and reheat-treated by a floating heat treatment apparatus that blows hot air in an arc shape. ), Re-heat treatment temperature (t ° C), processing wind speed (Vm /
sec) and the reheat time (θsec) satisfy the following conditions (1) to (4), respectively. 0.2 ≦ T ≦ 0.8 (1) 150 ≦ t ≦ 200 (2) 10 ≦ V ≦ 45 (3) 1.0 ≦ θ ≦ 5.0 (4) where T is a tension per 1 μm in thickness and 1 m in film width.