KR810001847B1 - Method of preparing poly hexamethylen adipamid filn - Google Patents

Abstract

Polyhexamethylene adipamide film, useful as packing, was prepd. by extrusion of polyhexamethylene adipamide followed by sliding-contacted cooling and drawing biaxially. The relative viscosity(η rel) of polyhexamethylene adipamide was 3.3 -5.0 at 25≰C and 96% H2SO4. The relation of cooling velocity(X ≰C) and relative viscosity was as follow. -100 Xη rel + 1200 < X < -170 Xηrel + 2150.

Description

Method for producing polyhexamethylene adipamide film

1 is a diagram showing a two-side tubular stretching machine, in which (1) an unstretched film (2) is a nip roller (3) is a cooling ring and (4) is a seal Deshielding elastomer, (5) hot air blowing ring, (6) heat adjustment hood, (7) deflator, (8) nip towler, (9) stretching Film,

2 is a cross-sectional view of the film bubble (P) is the starting point of the TD yarn, (Q) is the draw ratio of r to 1/2 of the final draw ratio of TD, (R) is the TD draw Indicates the ending point,

3 is a drawing showing elongation with respect to relative viscosity and cooling rate.

TECHNICAL FIELD This invention relates to the manufacturing method of the polyhexamethylene adipamide film which hardly exhibits anisotropy. The anisotropic polyhexamethylene adiamide film of the present invention has improved toughness and dimensional stability against hot water, and has the feature of being used as a packaging film material for packaging bags that can withstand high temperatures. Instead of the term “packaging bags that can withstand high temperatures”, the term “packaging bags that can withstand short periods of time at high temperatures”, sometimes used instead of the term “heat resistant packaging bags”, is used for simplicity.

Conventionally, many polymers such as polyolefins, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polyesters, and nylon-6 (poly-epsilon-capramide) have been used as packaging film materials. Among these packaging film materials, nylon-6 and polyethylene terephthalate are extremely satisfactory in toughness, gas barrier properties, transparency, gloss and heat resistance, so biaxially stretched nylon-6 and polyethylene phthalate films are used as food packaging materials. It has been. In recent years, there has been a great demand for a method for giving improved toughness and heat resistance in the production of packaging films for preparing food packaging materials. In the field of packaging films, penetration forces (i.e., stress breakdown resistance measured by penetrating a loaded perforation through the film) are a measure of the film's resistance to breakage and penetration during handling and transport of the package. It is known that it is important as. Therefore, the terms “toughness” and “toughness” used herein mean “stress breakdown resistance” and “stress breakdown resistance”.

Dimensional stability against hot water or steam is important in the thermal resistance of the packaging film, and the poor dimension stability against hot water or steam means that the packaging film is preferable when the food packaging material is exposed to high temperature such as hot water or steam. Large dimensional change (or shrinkage), i.e., the shape of the packaging material is crushed and sometimes destroyed.

Conventional biaxially stretched nylon-6 films are not very satisfactory as films of heat-resistant packaging bags because they are highly shrinkable upon exposure to high temperatures and are not very robust for use in bulky and heavy packages. Conventional biaxially stretched polyethylene terephthalate films have no problem with dimensional stability against hot water or steam, but are far less robust than the nylon-6 films described above.

Biaxially stretched nylon-66 films are described in US Pat. Nos. 3,794,547 and 3,50,766 and Japanese Patent Application No. 50-61. In the United States patent, the film is stretched by a tenter, and in the Japanese patent, the film is stretched using a tubular biaxial stretcher. However, these patent specifications do not clearly describe biaxially stretched nylon-66 films, only the biaxially stretched nylon-6 films are described in detail.

A method for producing a biaxially stretched polyhexamethylene adipamide film is already disclosed in Japanese Patent Application No. 49,268 / 1976. According to this method, the unstretched polyhexamethylene adiamide film is continuously stretched in the transverse direction and the machine direction, that is, the longitudinal direction. However, the biaxially stretched polyhexamethylene adiamide film obtained in this way is not very satisfactory in terms of stress fracture resistance and dimensional stability against hot water or steam and in particular the isotropy of these properties. This is because the molecular orientation tendency of the stretched film produced when the unstretched polyhexamethylene adipamide film is continuously stretched in the transverse and longitudinal directions is not simultaneously stretched. This is because it is difficult to obtain an exact balance between the transverse direction and the longitudinal direction of the orientation.

It is generally said that films made of polymers with flexible molecular structures are more rigid than films made of polymers with rigid molecular structures. However, the inventors have found that although polyhexamerene adiamide film has a more balanced molecular orientation than polycapramide film, in particular, biaxially stretched polyhexamethylene adiamide film is superior in toughness to polycapramide film. To their surprise.

In addition, polyhexamethylene adipamide films having substantially complete isotropy of molecular orientation in polyhexamethylene adipamide films and polyhexamethylene adipamide films having a lower degree of polymerization are somewhat superior in obtaining desirable toughness. I found out that.

Even when the unstretched polyhexamethylene adiamide film is simultaneously stretched by a conventional method using a long cloth, so-called bowing phenomenon always occurs, so that the resulting film has isotropic stability. Lack. In addition, even when the unstretched polyhexamethylene adipamide film is stretched using a biaxial tubular stretching machine, it is difficult to prepare a substantially amorphous unstretched polyhexamethylene adipamide film. This is because polyhexamethylene adipamide has a higher melting point, higher crystallization rate than polycapramide, and also has considerably more low melting materials such as oligomers.

One of the important objects of the present invention is to provide a biaxially stretched polyhexamethylene adipamide which exhibits improved stress fracture resistance and improved dimensional stability against hot water or steam and improved isotropy in these properties.

Another object of the present invention is to provide a biaxially stretched polyhexamethylene adipamide film having improved toughness and low shrinkage against hot water or steam, and particularly effective as a packaging film material for packaging bags that can withstand high temperatures. To provide.

One of the objects of the present invention is a birefringence of 0.006 or less measured at any point of crystallinity of 35 to 45% and total surface area by measuring at a temperature of 25 ° C., 96% sulfuric acid solution and measuring at a relative viscosity of 3.2 or more and an inclined tube density measurement method. Iv) to provide a biaxially stretched polyhexamethylene adipamide film having an initial modulus of at least 230 kg / mm 2 with respect to tension as measured in any direction of Δn and full area.

The film of the invention preferably has a thickness of 5 to 60 microns, more preferably 10 to 25 microns thick.

The film of the present invention (measured by the method described below) ideally has a penetrating force of 0.6 kg or more, more preferably 0.7 kg or more for a 15 micron film thickness. However, the most robust commercially available biaxially stretched nylon-6 film on the market has a penetration of approximately 0.55 kg at most for a 15 micron film thickness. In addition, the film of the present invention preferably has a shrinkage of 5% or less as measured by exposure to steam at a temperature of 135 ° C. for 10 minutes, more preferably 3% or less.

Moreover, the film of this invention has a gas barrier property normally, and the air flow rate with respect to oxygen molecule is 50 cc / m <^2> .day.atm or less in 15 micron film thickness.

The film of the present invention consists of polyhexamethylene adipamide, but its main component is hexamethylenediamine, adipic acid and a small amount of one or more comonomer components (another diamine and / or dibasic acid). Hexamethylene adipamide, ie, condensate. The amount of mixed content to be contained in the comonomer and the weight mixture in the empty hexamethylene adipamide should normally be approximately 10% by weight. A small amount of conventional additives such as lubricants, stabilizers, pigments, and dyes may be mixed and used in the polyhexamethylene adipamide forming the film.

In obtaining the desired penetration, it is very important that the relative viscosity (nrel; measured at 25 ° C in 96% sulfuric acid solution) of 3.2 or more. If the relative viscosity is less than 3.2, it is difficult and impossible to produce a film having a penetration of more than 0.6 kg for a 15 micron film thickness, even if all other requirements are met. It is desirable to set the relative viscosity within the range of 3.2 to 5.0.

In obtaining the desired penetration force, it is also important to make the birefringence (Δn) at any point in the film entire area equal to or less than 0.006 and the initial elastic modulus with respect to the tension in any direction among the film overall areas to be 230 kg / mm 2 or more. The above requirement means that the polymer film of the present invention exhibits a high degree of neutralization, and that the oriented molecules are very irregularly distributed over the entire surface of the film.

The term birefringence described above means Δn defined by the following equation.

Δn〓1nx―ny1

Where nx and ny refer to the refractive indices respectively measured in the longitudinal direction (ie, the machine direction) and the transverse direction (ie, the direction perpendicular to the longitudinal direction). Refractive index is measured using a polarizing microscope with a Berek correction plate.

The irregular distribution of molecules oriented over the film surface area means that the film has improved stress breakthrough penetration, wear resistance and flex weakness. Therefore, such a film is not easily broken or pinholes are easily generated.

It is desirable to make the film of the present invention have an initial modulus of from 230 to 350 kg / mm 2 for birefringence and tension of 0.000 to 0.006.

In addition, the film of the present invention has a crystallinity of 35% to 45% by measuring the heat-treated film by the inclined tube density measurement method. The degree of crystallinity is closely related to the dimensional stability under conditions exposed to high temperature, and also to the phenomenon that the film of the heat-resistant packaging bag becomes undesirably whitened, which is thought to occur due to oxidative decomposition of the film. If the degree of crystallinity is less than 35%, under conditions exposed to high temperature, the shrinkage of the film is actually less than the lower range than the desired range, that is, less than about 5%. On the contrary, when the degree of crystallinity is 45% or more, the shrinkage of the film exposed to high temperature may be satisfactorily reduced, but the film exposed to high temperature turns white.

Crystallinity is measured as follows. The film sample immediately after biaxial stretching is placed in a desiccator and subjected to heat treatment. After 24 hours, the density of the film sample is measured using an inclined density tube filled with a carbon tetrachloride-toluene mixture maintained at 25 °. The crystallinity (X) is calculated by the following equation.

The term `` penetration force '' is used here as a measure of resistance to stress breakdown, that is, whether or not pinholes form on the film, and can withstand the Japanese National Ministry of Agriculture, Publication No. 1019-High Temperature of October 23, 1975. The maximum load per kg measured according to the Japanese agricultural standard described in the edible packaging bag as follows: In other words, while applying a load having a diameter of 1 mm and a radius of curvature of 0.5 mm at one end, the perforation is extended by dropping the perforation downward at a constant speed of 50 mm per minute on the elongated film sample. The relationship between the elongated length of the film sample and the load is plotted on the graph to indicate the maximum load on the graph.

In the present specification, the dimensional stability of the film against hot water or steam is expressed as the shrinkage percentage (%) of the film measured as follows. A 10-cm-wide and 1-cm-long film specimen is placed in a retreat, exposed to superheated steam or pressurized hot water at 135 ° C for 10 minutes, and then the film specimen is placed in a water bath for 5 minutes. Cool and dry. Measure the length (1: cm) of the dry film specimen and calculate the shrinkage of the film by the following equation.

The film of the present invention preferably has a shrinkage of 0.5% to 5% as measured according to the method described above.

Another object of the present invention is to extrude the melted polyhexamethylene adipamide into a circular mold and to cool the mold under the following conditions by contacting the molded tubular extrudate with the outer surface of the inner mandrel. Relative viscosity of polyhexamethylene adipamide polymer having a relative viscosity (ηrel) of 3.3 to 5.0 measured at 25 ° C in 96% sulfuric acid solution at a cooling rate (X ° C / sec) to satisfy Provided is a method for producing a biaxially stretched polyhexamethylene adiamide film in which a tubular extrudate molded into a mold is cooled by a cooling process at 250 ° C. to 150 ° C., and then biaxially stretches a tubular film obtained simultaneously. It is.

Expression: -100 × ηrel + 1,200 <× <-170 × ηrel + 2,150

Polyhexamethylene adipamides having a relative viscosity? Rel of 3.3 to 5.0, preferably 3.5 to 4.8, are used. The polyhexamethylene adipamide is dissolved in a conventional manner, preferably from 280 ° C. to 300 ° C., and the melt is extruded into a mold having a circular spacing, and the tubular extrudate circulates through the liquid and cooling liquid medium for cooling. It is cooled by inclined contact with the outer surface of the inner mandrel to control the temperature. The inner mandrel is normally assembled where the mandrel side has a circular gap and is perpendicular to the mold surface passing through the center of the circular gap.

Of the production methods described above, the cooling rate for the tubular extrudate is most important. The spherical formation rate resulting from the process of solidifying the dissolved polyhexaethylene adipamide is much faster than that of the dissolved poly-epsilon-caprimid. That is, the maximum spherical formation rate of polyhexamethylene adipamide was determined by B.B.Burnett & W.F.Mc Dessit; As described in J.appln, physics, page 28 1101, it is 4.7 times the maximum spheroid formation rate of pliexilon-capramide. Therefore, when the dissolved polyhexamethylene adipamide is cooled by a conventional method which is often used in the production of poly-epsilon-capramide, the resultant cooled film has a considerable amount of spherical content, and thus it is not evenly stretched. Becomes difficult.

In the production process of the present invention the cooling rate is important for obtaining the desired amorphous unstretched film. The cooling rate can be measured at the contact by directly contacting the film with a thermocouple or thermistor, which has a low calorific value.

The importance of the cooling rate can be seen from the following examples. Four polyhexamethylene adipamide resins having a relative viscosity of 3.5, 3.8, 4.2 and 4.7 were molded by melt extrusion at 285 ° C. into circular molds, respectively. Each of the tubular extrudate was obliquely contacted with the outer surface of the mold inner mandrel having an outer diameter of 155 mm to obtain a cooled unstretched tubular film having a thickness of 120 microns and a cross-sectional homogeneity of ± 3%. The cooling rate of each tubular extrudate was adjusted as shown in Table 1 by varying the cooling rate and temperature of the cooling water circulated in the inner mandrel. Each unstretched film was simultaneously used in the longitudinal terms (ie, machine direction, hereinafter referred to as MD) and transverse (hereinafter referred to as `` TD '') using the biaxial tubular expander shown in FIG. It extended | stretched biaxially. In M.D and T.D, the stretching temperature and the stretching ratio were both 100 ° C. and 3.0. Film formability is shown below the first table, and elongation is shown in the first table and FIG.

TABLE 1

A: The film bubble was stable for a long time, and stretching could be performed without any difficulty.

B: Film bubble was unstable, film was broken frequently.

As can be seen from Tables 1 and 3, when the cooling rate is lower than (-110 x ηrel + 1,200) ° C / sec, it is difficult to stretch the film that is not stretched smoothly and uniformly. On the contrary, when the cooling rate exceeds (-170 × ηrel + 2,150) ° C./sec, air is undesirably introduced into the space between the flimm and the inner mandrel, so that the temperature nonuniformity and the thickness of the tubular compact can be reduced as much as possible. A faint white antigum is produced on the film in the process of solidifying the melted tubular compact even at the smallest size, making it difficult to obtain a uniform unstretched film having a good appearance.

The cooling rate of the film can be controlled by selecting the internal mandrel, the flow rate and temperature of the cooling liquid circulated in the mandrel, and the temperature of the film in contact with the mandrel. It can also be blown to the outside of the tubular extrudate.

As the inner mandrel member, a metal material having good thermal conductivity, good machinability, and a moderate hardness, for example, iron and alloys thereof, such as carbon steel, aluminum and alloys thereof such as duralumin, and copper such as bronze and brass and the like Alloys and the like can be used.

It is surprising that the suitable cooling rate of the film varies with the relative viscosity of the polymer, ie the degree of polymerization. It is assumed that this is unique to the cooling process using the inner mandrel, which is closely related to the fact that the tension of the melt on the tubular extrudates in contact with the mandrel changes with the degree of polymerization and that the crystallization rate changes with the degree of polymerization. do.

The unstretched tubular film is biaxially stretched using, for example, a conventional biaxial mandarin stretching machine having the form shown in FIG. In FIG. 1, the unstretched tubular film 1 passes between two of the lower speed pairs of nips and then through the cooling ring 3 to fix the draw start point. The tubular film is blown through the hot air blowing ring to the film and heated by hot air flowing down the inside of the heat regulation hood 6. The shielding elastomer plate 5 is between the cooling ring 3 and the hot air blowing ring 5. The heated tubular film is biaxially stretched by M.D due to the speed difference between the high speed nip roller 8 and the low speed nip roller 2 and the T.D by the gas bubble. The bubbles come out of the stretched film 9 in oblique contact with the walls of the interior of the deflator 7.

The stretching temperature indicates the hot air temperature blown through the ring 5 of the stretching machine shown in FIG. 1, and a temperature range of 70 ° C to 180 ° C is preferable.

Elongations X and Y in M.D and T.D are each within a range from 0.5 to 4.0, and the difference IX-YI between the two elongations is preferably 0.5 or less. When elongation X and Y are 2.5 or less, desired elasticity in tension cannot be obtained and such a film lacks penetration force. When the elongation rates X and Y exceed 4.0, the film tends to break, making it difficult to stretch uniformly.

Neckimg tends to occur in the peripheral direction in biaxially stretching the polyhexamethylene adiamide film. This necking results in uneven film transparency even if the film thickness is uneven. In order to prevent the above necking phenomenon or to minimize the smoothing and smooth the stretching, it is preferable to set the parameter? Α ＂as defined below to 2.5 or more and less than 8.0. When the parameter α is 2.5 or less, necking is generated around the film around the point at which T.D stretching is started, and this necking causes non-uniformity of the transparency of the stretched film. If the parameter α is 8.0 or more, the film bubble is unstable, and the variation in the elongation of T.D is quite significant.

The parameter ＂α＂ is defined by

Parameter α = L / r

As shown in FIG. 2 showing the hex-section of the film bubble, L is the length of the vertical line between the point P where the drawing of TD begins and the point Q where the drawing ratio of r is 1/2 of the final drawing ratio of TD , 1/4 of the length difference between the tubular film diameter at the point R at which TD stretching ends and the tubular film diameter at the point where TD stretching has not yet started. Both L and r are obtained by measuring photographs of film bubbles.

The parameter α varies depending on the diameter and length of the hood, the hot air temperature blown through the tubular extrudate, the elongation and the amount of air in the bubble.

The importance of the parameter α can be seen from the following examples. Polyhexamethylene adipamide having a relative viscosity of 3.8 (25 ° C. 96% H ₂ SO ₄ ) was melt-extruded at 280 ° C. with a circular mold having a diameter of 160 mm, and the tubular extrudate was beveled with an inner mandrel having a diameter of 150 mm. Contacted. The cooling rate was 1050 ° C./sec and the speed of drawing out was 4.5 m / min. The thickness of the non-stretched film obtained as described above was 110 microns, and the biaxial portion shown in FIG. 1 at the speed of 4.5 m / min for the unstretched film was injected into the tubular expander under the conditions shown in Table 2 below. The film was simultaneously drawn by MD and TD. The inner diameter of the heat adjusting hood was 580 mm. The transparency non-uniformity and stretching characteristics of the stretched film are shown in Table 2 below.

TABLE 2

The biaxially stretched film is usually subjected to heat treatment in order to give the film satisfactory dimensional stability, which is particularly effective as a packaging material for heat resistant packaging bags. However, polyhexamethylene adipamide tends to be oxidatively decomposed more than poly-epsilon-capramide, and therefore, heat treatment is preferably performed under the following conditions.

fT(℃)＜240-78.9Logt＋268

fT(℃)

f-106.8Logt＋388190

fT (° C) <240-78.9Logt + 268

fT (℃)

f-106.8Logt + 388

Where T is the heating temperature ° C and is the heating cycle in seconds. When these conditions are satisfied, heat processing is performed by a conventional method.

The importance of the above-described heat treatment can be seen from the following examples. Both ends of the biaxially stretched film sample were fixed by creep, and the samples fixed by creep were subjected to heat treatment in a hot blast furnace under the conditions shown in Table 3 below. For each film sample, tension was applied in the longitudinal direction while limiting the shrinkage in the transverse direction of the film sample to 5% or less. The heat treated film samples were exposed to steam for 10 minutes at a temperature of 135 ° C. to test their shrinkage. The change in appearance of the film sample was also observed after exposure to steam. The results of these experiments are shown in Table 3 below.

TABLE 3

In the present invention, the film is exposed to steam at 135 ° C. for 10 minutes, and when the shrinkage in any direction of the film is 5% or less, it can be satisfactorily used in the preparation of edible packaging bags that can withstand a desired high temperature. If the shrinkage is less than 3%, it is considered to be very satisfactory. As can be seen from Table 3, when the film under the above-described conditions is subjected to heat treatment, the heat treated film shows a satisfactory shrinkage ratio and does not become white.

As described above, the film of the present invention has improved toughness, dimensional stability, and gas barrier properties, and therefore, heat-resistant packaging bags of curry sauce, hamburgers and meatballs, and frozen food packaging of shrimp and sea crab before instant cooking. And soup packaging materials for instant noodle and food packaging materials for large and small packaging materials of liquid and fish jelly foods such as bean paste and cognac paste. Since polyhexamethylene adipamide is inherently good in oil resistance, the film of the present invention is effective as a transport packaging material such as gasoline and kerosene. The film of the present invention is also effective as a packaging material for high explosive abnormalities and machine tools. In addition to the packaging material, the film of the present invention can also be used as a base for metal deposition films, adhesives, and electrically insulating films.

The present invention will be described through the following examples.

Example 1

Polyhexamethylene adipamide having a relative viscosity (ηrel) of 3.6 was measured in a 25 ° C, 96% sulfuric acid solution and injected into an extruder, melted at a temperature of 280 ° C, and extruded into a circular mold having a diameter of 160 mm to produce a tubular extrudate. An oblique contact was made with the outer surface of the mandrel having a diameter of 155 mm and a surface roughness of 1 S. In order to cool the tubular extrudate, hot water was circulated therein to cool the interior to a temperature of 40 ° C. The rate of pulling out the tubular extrudate was 5 m / min and the cooling rate from 250 ° C. to 150 ° C. was 1050 ° C./sec. This gave an undrawn film with a thickness of 110 microns.

Using an unstretched film using a biaxial stretching machine similar to that shown in Figure 1, the elongation at 100 ° C. and longitudinal (ie, machine direction, abbreviated as MD) is outlined in 3.0 and transverse direction (hereinafter TD). The biaxial stretching was carried out simultaneously with an elongation of 3.1. Parameter α was 3.0.

The stretched film is flattened using a deflector, and is placed in a furnace equipped with a hot air blower capable of crimping both ends of a flat film of a predetermined length and feeding both outer surfaces above and below the flat film. The film was preheated at 150 ° C. for 2 seconds and then heated at 230 ° C. for 6 seconds. The shrinkage of T.D was fixed at 4%. The thickness of the heat treated film was 14.2 microns and the properties of this film are shown in Table 4 below.

TABLE 4

Example 2

A biaxially stretched polyhexamethylene adipamide film was prepared under the methods and conditions described in Example 1. However, instead of the relative viscosity 3.6, polyhexamethylene adipamide having a relative viscosity of 3.2, 3.5 and 3.6 was used. The properties of the film obtained as described above are shown in Table 5 below.

TABLE 5

Example 3

Biaxially stretched polyhexamethylene adipamide films were prepared under similar methods and conditions as described in Example 1 except for the following.

It shows in Table 6 when the characteristic of the film obtained by making it above is shown.

TABLE 6

Example 4

Under the methods and conditions described in Example 1, only the stretching and heat treatment conditions were changed as shown in Table 7 to prepare biaxially stretched polyhexamethylene adipamide. The stretched film was preheated to 100 ° C. and heat treated at 150 ° C. During the heat treatment, the shrinkage of the film with respect to T.D was limited to 5% or less, and the film was tensioned only with M.D. The results for these are shown in Table 7 below. Penetration in Table 7 is for the thickness of the 15 micron film.

TABLE 7

As can be seen from Table 7, the birefringence (Δn) for the film should be greater than or equal to 0.0006 to achieve the desired improved stress breakdown resistance and penetration.

Example 5

This example is a comparative example, in which the present invention continuously stretches the polyhexamethylene adipamide film not stretched according to the method described in JP 49,268 / 1976, instead of simultaneously stretching it in the biaxial direction.

Polyhexamethylene adipamide having a relative viscosity (? Rel) of 3.6 was melt-extruded in a similar manner as described in the Examples to form an amorphous unstretched film having a thickness of 150 microns, and the unstretched film was The film was first stretched in the transverse direction at a temperature of 80 캜 and an elongation of 2.9, and then stretched in the longitudinal direction at an elongation of 3.5 as a roller stretching machine while maintaining the temperature of the film at the point of stretching using an infrared heater at 120 캜. The drawing speed of the roller stretching machine was 120,000% / min, and in the drawing in the longitudinal direction, the drawing was not smooth at the drawing rate of 3.3. The shrinkage ratio of the film to T.D was limited to 3% and the biaxially stretched film (2.9T.D × 3.5M.D) was heat-treated at 220 ° C. using a heating roller while applying the film tension only to the M.D. The properties of the film obtained as described above are shown in Table 8 below.

Example 6

This example is a comparative example. In this comparative example, a biaxially stretched polyethylene derephthalate film and a nylon-6 film that can be used commercially were tested. The commercially available biaxially stretched film tested was as follows.

(1) a biaxially stretched polymethylene terephthalate film having a thickness of 12 microns and (2) a nylon-6 film A having a thickness of 15 microns biaxially drawn at the same time with a wrapping machine and (3) a tubular stretching method Nylon-6 film B having a thickness of 15 microns biaxially stretched by the axial stretching method, the penetration force and shrinkage in vapor for these films are shown in Table 8.

TABLE 8

As can be seen from Table 8, commercially available biaxially stretched polyhexamethylene adipamide film and polystyrene terebutanate film are not satisfactory at least in terms of toughness and dimensional stability to hot water.

Example 7

Various biaxially stretched polyhexamethylene adipamide films were prepared in the same manner as described in Example 1, except that the relative viscosity of the polymer, film formation, film stretching and film heat treatment conditions were shown in Table 9. Prepared under conditions. Each stretched film was preheated at 150 ° C. for 2 seconds and then heat treated. During the heat treatment, the shrinkage of the film with respect to T.D was limited to 4% and the film was tensioned only with M.D. In the film samples, the film samples of Experiment Nos. 3 and 6 did not undergo heat treatment for these two films because they had very poor stretchability and large unevenness in transparency.

The properties of the film obtained above are shown in Table 9. Penetration here is for the film thickness of 15 microns.

TABLE 9

Claims (1)

A biaxially stretched polyhexamethylene adipamide film was prepared by sliding contact cooling the tubular extrudates formed by melting molten polyhexamethylene adipamide through an annular mold gap. In the process, polyhexamethylene adipamide having a relative viscosity (? Rel) of 3.3-5.0 as measured at 25 ° C. and 96% sulfuric acid is used, and in the step in which the tubular extrudate is cooled from 250 ° C. to 150 ° C. A method for producing a polyhexamethylene adiamide film, characterized in that the tubular film obtained after cooling at a cooling rate (X ° C / sec) satisfying the following formula with respect to the relative viscosity is simultaneously stretched biaxially. -100 × ηrel + 1,200 <× <-170 × ηrel + 2,150

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