JPH10296852A - Manufacture of biaxially oriented polyamide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing stably a biaxially oriented polyamide film having an excellent strength and being excellent in tear linearity in the lengthwise direction of the film. SOLUTION: In a method for manufacturing a biaxially oriented polyamide film wherein a composition of nylon 6(N6)/polymetaxylylene adipamide (MXD6)=80/20-95/5 (weight ratio) used as a material is melted by heating in an extruder and extruded in the shape of a sheet and then oriented in longitudinal and lateral directions, extrusion is conducted under the conditions that the maximum shear rate of a screw metering part in the extruder is 20-50 sec<-1> , that the retention time of resin therein is 1-5 minutes and that the maximum temperature of the resin therein is 260-280 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a biaxially stretched polyamide film having excellent transparency, practical strength, dimensional stability, and excellent straightness when it is torn in the longitudinal direction.

[0002]

2. Description of the Related Art Various plastic film packaging bags are used in large quantities for packaging foods, pharmaceuticals, miscellaneous goods and the like. Usually, a biaxially stretched plastic film is laminated with a heat-sealing non-oriented film. Are often used.

[0003] In particular, a biaxially stretched polyamide film is a suitable packaging material for long-term storage of foods and the like because of its excellent gas barrier properties. As the characteristics required for the packaging bag, it is required that the packaging bag has both the strength and the two characteristics which seem to be incompatible with each other at first glance.
Conventionally, in order to satisfy the easy tearing property, a perforation, a tear tape, or a notch is provided. However, in such a conventional method, it is necessary to add a new processing step, and there is a problem that the strength of the film is reduced. Also, there is a method of laminating a uniaxially stretched polypropylene film,
A trouble often occurs in which a large force is required for tearing, or the packaging bag is not torn linearly. In such a case, if the contents are scattered at the same time as opening, the contents will be wasted, and the clothes and furnishings will be soiled, or if the contents are hot, they may cause burns. Occurs.

As a method of imparting easy tearing property by modifying a polyamide resin, N6 / MXD6 = 85-40 / 15-60
(Weight ratio) by melt extrusion of the mixed polyamide composition, and the longitudinal direction (MD),
There has been proposed an easily tearable film stretched 2.8 times or more in the width direction (TD), and a laminated film in which this easily tearable film is formed as a single layer (Japanese Patent Application Laid-Open Nos. 5-220837 and 5-20837). No. 5-200958).

Also, N6 / MXD6 = 80-95 / 20-5
(Weight ratio), and a biaxially stretched polyamide film having tear straightness in which the shape of the dispersed particles of MXD6 is dispersed in a specific shape has been proposed (JP-A-7-11).
No. 3015).

[0006] However, in the conventional films as described above, there are cases where there is a problem in film formation stability, the thickness unevenness of the film becomes large, the commercial value is reduced, or the tear straightness is insufficient. Was.

[0007]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and has the toughness and excellent transparency and thickness uniformity of a polyamide film, and has a property to be reduced in the longitudinal direction of the film. An object of the present invention is to provide a method capable of stably producing a biaxially stretched polyamide film having excellent straightness upon tearing.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve such problems, and as a result, by using a specific manufacturing method, they have tear straightness and a small thickness unevenness. The inventors have found that a polyamide film can be stably produced, and have reached the present invention.

That is, the gist of the present invention is that N6 / MXD6
= 80/20-95/5 (weight ratio) as a raw material, heated and melted in an extruder, extruded into a sheet, and then stretched in the longitudinal and transverse directions to produce a biaxially stretched polyamide film The method is characterized in that the maximum shear rate of the screw metering section in the extruder is extruded at 20 to 50 sec ^-1 , the residence time of the resin is 1 to 5 minutes, and the maximum temperature of the resin is 260 to 280 ° C. A method for producing a biaxially stretched polyamide film.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polyamide used in the present invention is a mixture of N6 and MXD6. However, as long as the effects of the present invention are not impaired, other polyamides and various inorganic and organic resins commonly used in polyamide resins are used. May be added. Talc, silica, and inorganic additives
Alumina, magnesia, antioxidants such as copper halides and lubricants such as calcium carbonate, and organic additives such as ε-capramide dimer, crystal nucleating agents such as graphite, aromatic amines, hindered phenols and the like Examples include film modifiers such as antioxidants and modified polyolefins.

The relative viscosity of N6 is 2.5-4.0, preferably 2.9-3.3. When the relative viscosity is less than 2.5, the dispersed particle size of MXD6 becomes large, and the tear straightness of the film decreases. On the other hand, when the relative viscosity is more than 4.0, the extrudability of the film decreases, which is not preferable.

The MXD6 in the present invention may contain about 5% or less (% by weight) of a paraxylylene adipamide component as long as the effects of the present invention are not impaired.

The relative viscosity of MXD6 is 2.0-3.0,
Preferably it is 2.3 to 2.5. When the relative viscosity is less than 2.0, the formation of dispersed particles of MXD6 in N6 is inhibited,
The resulting film has poor tear straightness. On the other hand, if the relative viscosity is larger than 3.0, the dispersed particle size of MXD6 becomes large, and the straightness of tearing decreases.

The weight ratio of N6 and MXD6 in the present invention is N6 / MXD6 = 80/20 to 95/5 (weight ratio). If MXD6 is more than 20% by weight, operability problems such as film thickness variation are likely to occur.
When the content of 6 is less than 5% by weight, it is not preferable because the tear straightness cannot be obtained.

In the present invention, the raw resin is heated and melted in an extruder, extruded from a die into a sheet, and then stretched in the longitudinal and transverse directions to produce a biaxially stretched polyamide film. The maximum shear rate of the part is 20 to 50 sec ^-1 , the residence time of the resin is 1 to 5 minutes,
It is necessary that the maximum temperature of the resin satisfies each condition of 260 to 280 ° C.

The screw metering section in the present invention is a portion in front of the screw following the screw supply section and the screw compression section, and is a section for imparting uniform kneading of the molten resin. What is the maximum shear rate of the screw measuring section?
It is the maximum shear rate given to the molten resin at the screw metering section in the extruder. The magnitude of the maximum shear rate is 20-50 sec ^-1 , preferably 30-45 sec ^-1 . If the maximum shear rate is less than 20 sec ^-1 , kneading becomes insufficient, and various performances of the film decrease. Also, 50sec ^-1
If it is larger, the kneading effect is too strong and the tear straightness of the film is undesirably reduced.

The residence time of the resin in the present invention is the time from when the raw material is supplied into the extruder to when it is extruded from the cylinder of the extruder. Residence time is 1-5 minutes,
It is preferably 1 to 3 minutes, and when the residence time is shorter than 1 minute, kneading is insufficient and various performances of the film are reduced,
If the time is longer than 5 minutes, the kneading is too strong and the straightness of tearing of the film decreases, which is not preferable.

In the present invention, the maximum temperature of the resin in the extruder is 260-280 ° C. When the maximum temperature is higher than 280 ° C., the reaction between N6 and MXD6 proceeds to reduce the straightness of tearing of the film, and the thickness of the film tends to be uneven. On the other hand, when the minimum temperature is lower than 260 ° C., the extrusion pressure And the film formation stability decreases.

As the screw used in the present invention, a general screw such as a full flight type or a dam flight type can be used. In the case where a screw to which a kneading portion such as Unimelt or Murdoch is added is used. , N6 and MXD6 are undesirably promoted, and the straightness of tearing of the resulting film may be reduced.

In the method of producing a film according to the present invention, a mixture of N6 and MXD6 is supplied to an extruder, heated and melted under the conditions specified in the present invention, extruded from a die into a sheet, and rotated by a cast roll. Quench on top. Next, the obtained unstretched sheet is biaxially stretched,
As a method of biaxial stretching, tenter type simultaneous biaxial stretching method,
A roll-tenter sequential biaxial stretching method or the like is used.

For example, when the tenter-type simultaneous biaxial stretching method is used, the moisture content of an unstretched sheet is first adjusted to 1 to 6%, and then the sheet is fed to a simultaneous biaxial stretching machine, and the stretching temperature is set to 160.
At ~ 190 ° C, the draw ratio in the longitudinal and transverse directions was 2.8 each.
Simultaneous biaxial stretching with about 3.8 times.

Next, the biaxially stretched film is subsequently subjected to a heat treatment to fix the biaxial stretching. The heat treatment conditions are preferably a temperature of 190 to 220 ° C., a time of 3 to 10 seconds, and a relaxation rate in the width direction of 0 to 10%.

The thickness of the stretched film is not particularly limited as long as it has the strength required for a packaging material, and is usually about 10 to 50 μm.

The biaxially stretched polyamide film obtained by the method of the present invention can be used by laminating another film, paper, cloth, metal or the like, or by vaporizing alumina, silica or the like.

[0025]

The reason that the biaxially stretched polyamide film obtained by the method of the present invention has excellent tear straightness is that the maximum shear rate in the screw measuring section in the extruder, the residence time of the resin and the maximum temperature are controlled. It is inferred that appropriate kneading of N6 and MXD6 for achieving tear straightness was achieved.

[0026]

Next, the present invention will be described in detail with reference to examples and comparative examples. In addition, the evaluation method of each performance of a film is as follows.

(1) Relative viscosity of polyamide [η]: 96%
A sample (1 g) was dissolved in sulfuric acid (100 ml) and measured at 25 ° C. using a Cannon-Fenske viscometer. (2) Shearing speed in the screw measuring section The shearing rate γ (s ^-1 ) in the screw measuring section is determined by the inner diameter D (cm) of the extruder cylinder, the screw rotation speed n
(Rps) and the value of the groove depth H (cm) of the measuring section were obtained from the following equation. γ = π · D · n / H (3) Residence time of the resin in the extruder The time required from the supply of the raw material into the cylinder of the extruder to the extrusion of the resin from the extruder was measured. (4) Maximum temperature of the resin in the extruder A temperature sensor is installed in the extruder cylinder at a position corresponding to the screw supply section, compression section, and metering section so as not to affect screw rotation and resin flow. And measured. (5) Tensile strength Measured according to ASTM-D882 using a sample having a width of 10 mm and a sample length of 100 mm. (6) Film Thickness Variation The thickness of the stretched film was measured in real-time during line running by scanning a radiation type film thickness measuring instrument in the width direction of the film. After traveling 100 m, the measuring instrument is reciprocated 5 times in the film width direction, and the average value of the thickness Da,
From the maximum value Dmax and the minimum value Dmin, the thickness variation rate P (%) was calculated by the following equation. P = [(Dmax-Dmin) / Da] .times.100 A sample having a P of less than 7% was evaluated as .largecircle. (7) Tearing straightness in the longitudinal direction Cuts are made at predetermined intervals (Ws: 20 mm) in the TD direction of the stretched film, and when the film is torn by 200 mm in the MD direction along these cuts, the other end that has no cuts Was measured, and a shift ratio α (%) in tearing was calculated by the following equation. α = We / Ws × 100 This measurement was repeated 10 times, and those having an average value of α of less than ± 10% were evaluated as excellent (very good tear straightness), ± 10% ≦ α ≦ ± 30.
% Was evaluated as ○ (good tear straightness), and those with α exceeding ± 30% were evaluated as × (poor tear straightness).

Example 1 N6 (manufactured by Unitika Ltd., trade name: A1030BRF, relative viscosity 3.1)
0) and MXD6 (manufactured by Mitsubishi Gas Chemical Company, trade name: MX
Nylon S6907, the polyamide compositions were mixed in a weight ratio of relative viscosity 2.40) 80:20, using an extruder equipped with a 200 mm phi dam flight type screw, the maximum shear rate 40 sec ^-1 in the screw metering unit The resin was extruded in a sheet form from a T-die under the conditions that the residence time of the resin in the extruder was 2 minutes and the maximum temperature of the resin in the cylinder was 270 ° C. The extruded unstretched sheet was brought into close contact with a rotating cast roll whose surface temperature was controlled at 15 ° C and quenched.
A μm unstretched sheet was obtained. The obtained unstretched sheet is
After being treated for 1 minute in hot water at a temperature of 200 ° C., it was gripped by clips of a tenter type simultaneous biaxial stretching machine, stretched at a stretching temperature of 185 ° C. and a stretching ratio of 3.0 × 3.3 in the longitudinal and transverse directions, and then stretched for 20 minutes.
Heat treatment was performed at 5 ° C. for 4 seconds to obtain a biaxially stretched film having a thickness of about 15 μm. During the heat treatment, a 5% relaxation treatment was performed in the width direction. The results of measuring the tensile strength, thickness uniformity and longitudinal tear straightness of the obtained biaxially stretched film are as shown in Table 1, and show excellent thickness uniformity and good longitudinal tear straightness. Had.

Examples 2 to 3 A biaxially stretched film was obtained in the same manner as in Example 1 except that the mixing ratio of N6 and MXD6 was changed to the conditions shown in Table 1. Table 1 shows the evaluation results of the properties of the obtained biaxially stretched film.

Examples 4 to 6 The same procedure as in Example 1 was carried out except that the maximum shear rate in the screw metering section, the residence time of the resin in the extruder and the maximum temperature of the resin were changed to the conditions shown in Table 1. A stretched film was obtained. Table 1 shows the evaluation results of the properties of the obtained biaxially stretched film.

Comparative Examples 1-2 A biaxially stretched film was obtained in the same manner as in Example 1 except that the mixing ratio of N6 and MXD6 was changed as shown in Table 1. Table 1 shows the evaluation results of the properties of the obtained biaxially stretched film.

Comparative Examples 3 to 5 The same procedures as in Example 1 were carried out except that the maximum shear rate in the screw measuring section, the residence time of the resin in the extruder and the maximum temperature of the resin were changed to the conditions shown in Table 1, respectively. An axially stretched film was obtained. Table 1 shows the evaluation results of the properties of the obtained biaxially stretched film.

[0033]

[Table 1]

[0034]

According to the method of the present invention, it is possible to stably produce a biaxially stretched polyamide film having excellent strength and excellent tear straightness in the longitudinal direction of the film. Its economic value is extremely large.

Claims (1)

[Claims] 1. A composition comprising nylon 6 (N6) / polymethaxylylene adipamide (MXD6) = 80/20 to 95/5 (weight ratio) is heated and melted in an extruder to form a sheet. In the method of producing a biaxially stretched polyamide film by extruding in the longitudinal and transverse directions,
The maximum shear rate of the screw metering section in the extruder
A method for producing a biaxially stretched polyamide film, wherein the resin is extruded under conditions of 20 to 50 sec ^-1 , a residence time of the resin of 1 to 5 minutes, and a maximum temperature of the resin of 260 to 280 ° C.