JPS5910895B2 - Polyamide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stretching an aromatic polyamide film, and particularly to a method for stretching a film made of polymetaphenylene isophthalamide.

Since polymetaphenylene isophthalamide is infusible and cannot be melt-molded, it is generally cast-molded as a solution in an amide solvent.

The film obtained by casting is usually heat treated at a temperature of 250°C or higher to improve its physical properties, but at this time it is more desirable to heat it while being stretched or stretched in one or two directions. . However, since the molecules of cast-formed, unoriented polymetaphenylene isophthalamide film have a rigidity of 10, the stress required for hot stretching is extremely large even if the film is heated above 270°C, which is the softening point of the polymer. However, because the maximum stretching ratio is low, sufficient molecular orientation is not achieved, and this poses a major problem in improving mechanical and electrical performance through stretching. In addition, when polymetaphenylene isophthalamide film is stretched using a normal stretching method, so-called netting occurs, so when the film is stretched, the entire film does not stretch uniformly, resulting in two phases, a stretched phase and a non-stretched phase, resulting in cracks between the two phases. A phenomenon is observed in which the curvature progresses toward the non-stretched phase as a result of stretching. This phenomenon is caused by the stretching temperature,
Although it is affected by the water content of the film, the stretching speed of the film, etc., it is difficult to eliminate the occurrence of this phenomenon only by selecting these conditional factors. Naturally, it is difficult to obtain a stretched film with uniform physical properties and thickness from an unoriented film that causes netting upon stretching. As a result of intensive research to solve the above-mentioned problems caused by the adoption of conventional stretching methods, the present inventors have identified a specific aqueous solution for use in an unoriented film made of polymetaphenylene isophthalamide. If pre-stretching is carried out in a state containing a certain amount, and then hot-stretching in the same direction as the pre-stretching, the total stretching ratio can be dramatically increased to 4 to 6 times, and the mechanical performance of the pool is also almost proportional to the stretching ratio of 35. The present invention was completed based on the discovery that netting did not occur during stretching and that the thickness variation rate of the stretched film could be kept within 5% based on the stress strain curve obtained. It came to this.

That is, in the present invention, when stretching a film made of an aromatic polyamide in which at least 50 mol% of substantially unoriented repeating structural units are represented by The compound is pre-stretched by 1.1 times or more in at least one direction with an aqueous solution containing 5% by weight or more, and then 2
This is a method for stretching an aromatic polyamide film, which is characterized by hot stretching in at least one direction that is the same as the preliminary stretching at a temperature of 00° C. or higher.

In the present invention, the aromatic polyamide in which at least 50 mol% of repeating structural units is represented by This means that it is a polymer obtained by copolymerizing other copolymerization components within a range that does not impair heat resistance. If the content of the copolymer component in the copolymer exceeds 50 mol%, its heat resistance will decrease, so the content must be less than 50 mol%, and is preferably 20 mol% or less. Such aromatic polyamides can be synthesized by conventionally known methods as described in, for example, Japanese Patent Publication No. 35-13247 and Japanese Patent Publication No. 35-14399.

In order to produce the substantially unoriented film used in the present invention from such an aromatic polyamide, for example, a solution consisting of the polyamide and an amide solvent is cast, and the solvent is removed by heating in air. What is necessary is to remove it, and furthermore, what is necessary is to remove a certain amount of the solvent by heating and then wash with water.

As the amide solvent applicable to the present invention, any solvent that can dissolve the polyamide can be used, but
In particular N-N-dimethylformamide, N-N-dimethylacetamide, N-methyl-2-pyrrolidone, N-N
-N'-N'・N] (-hexamethylphosphoramide,
N-N-NINI-tetramethylurea is preferred, 1
It can be used as a species or as a mixture of two or more.

Some of these amide solvents are also used as polymerization solvents for the aromatic polyamide used in the present invention, and a stock solution for casting molding can be obtained by performing low-temperature solution polymerization in these solvents. If obtained directly, it will form part of the polymer solution. Lithium chloride, calcium chloride, magnesium chloride, and zinc chloride are particularly suitable as ionic inorganic compounds to be applied to the present invention, and these can be used alone or in combination of two or more.

These ionic inorganic compounds are used as auxiliaries to improve the solubility of amide solvents, and are also formed by neutralizing the acid produced after the polymerization reaction. be. To prepare an unoriented film containing 5% by weight or more of an aqueous solution of an amide solvent or an aqueous solution containing an amide solvent and an ionic inorganic compound,
It can be obtained by drying a cast film, or by washing and scouring the film after drying, or by immersing the film after washing in water in the above aqueous solution without drying. It can also be obtained by washing with water, immediately drying it, and then immersing it in the above aqueous solution again.

In the method of the present invention, an unoriented film containing an aqueous solution of an amide solvent or an aqueous solution containing an amide solvent and an ionic inorganic compound in an amount of 1.1 times or more in at least one direction is prepared. After stretching, it is hot stretched at a temperature of 200° C. or higher in at least one direction that is the same as the preliminary stretching.

It is necessary that the stretching ratio of the preliminary stretching is 1.1 times or more, and it is particularly preferable that it is about 1.1 times to 2 times.

If the stretching ratio in the preliminary stretching is less than 1.1 times, the subsequent hot stretching cannot be carried out effectively. The maximum stretching ratio at room temperature is about 2.5 times, and if the pre-stretching temperature is increased, the maximum possible stretching ratio will further increase, but in terms of the physical performance of the resulting film, it is about 1.5 times. 5
After pre-stretching by ~2.0 times, it is preferable to hot-stretch at 250°C to 350°C in the same direction as the preliminary stretching. As described above, there is an optimum value for the stretching ratio between preliminary stretching and hot stretching, and the preliminary stretching ratio is approximately 0.5 of the hot stretching ratio.
It is preferable to set it to about 1.5 times. If the content of the aqueous solution contained in the unoriented film is too small, effective preliminary stretching cannot be performed.

In order to carry out effective preliminary stretching, the content of the aqueous solution in the unoriented film must be 5% by weight or more, preferably 10% by weight or more, and more preferably 20% by weight or more.

Further, the concentration of the amide solvent in the aqueous solution of the amide solvent is preferably 80% by weight or less.

When an aqueous solution containing more than 80% by weight of an amide solvent is contained, it is not preferable because the effect of swelling the film is large and the effect of preliminary stretching is reduced.

When using an aqueous solution containing an amide solvent exceeding 80% by weight, the content in the film is 5 to 60% by weight,
In particular, a range of 10 to 40% by weight is preferred.

Further, even if the content of the ionic inorganic compound in the film is small, it is effective, and even if it is contained in an amount of 5% by weight or more, the effect hardly changes. The stretching method of the present invention is characterized in that an unoriented film containing the above aqueous solution is first pre-stretched in at least one direction, and then further hot-stretched in the same direction as the pre-stretching direction. Although a two-stage stretching method is employed, this two-stage stretching method may be carried out only in one axial direction, or may be carried out sequentially in two axial directions or simultaneously in two axial directions.

In hot stretching, it is necessary to set the stretching ratio to 1.1 times or more at 200° C. or higher. Stretching is difficult at temperatures below 200°C, and when the stretching ratio is less than 1.1 times, it is impossible to obtain a film having the desired excellent mechanical properties.

The film containing the above aqueous solution is in a moderately plasticized state, and the rigid aromatic polyamide is kept in a mobile state, making it possible to carry out effective pre-stretching. It is thought that as a medium for bonding with the aromatic polyamide, the salts plasticize the aromatic polyamide more effectively than in the absence of the salt. In addition, the preliminary stretching of the film pre-orientates the plasticized aromatic polyamide molecules while disentangling them, and the subsequent hot stretching enables uniform orientation of the aromatic polyamide molecules in the same direction without netting. Conceivable. In this manner, the aromatic polyamide molecules are given a nearly ideal orientation by the subsequent hot stretching, and crystallization is promoted by the thermal effect, greatly improving the performance of the resulting film. it is conceivable that. As described above, according to the method of the present invention, a film with excellent mechanical performance and less uneven thickness can be easily produced.

Next, the present invention will be described in more detail with reference to Examples.

Example 1 Polymetaphenylene isophthalamide (0% in 96% sulfuric acid)
．． 57/100m11 Intrinsic viscosity at 25℃ is 1.6
N-N-dimethylacetamide (hereinafter abbreviated as DMA) containing 20% by weight of 7) and 9.3% by weight of calcium chloride.

) The solution was uniformly applied to a thickness of 500 μm on a glass plate and dried by heating to obtain a film. The obtained film was washed for 60 minutes in an aqueous solution containing 10% by weight of calcium chloride, a part of the film was cut out while still wet for compositional analysis, and the remaining film was washed in one direction for 1.5 min at room temperature.
After pre-stretching 8 times, then drying with hot air at 80°C for 5 minutes, in the same direction as the pre-stretching in an oven at 300°C,
The film was hot stretched 2.5 times at a stretching speed of 0.00%/min, then washed with water and dried to obtain a transparent film. The average thickness of the obtained film was 22 μm, and the thickness variation was 1 μm.

In addition, the strength of the stretched film is 31.6 kg/in the stretching direction.
Md and elongation were 13%. According to the composition analysis results of the unstretched film, the moisture content is 50.1% by weight, and the DMA is 2.3%.
% by weight and 6.1% by weight of calcium chloride. Example 2 An unstretched film was formed using the same polymer solution as in Example 1 and in the same manner as in Example 1. After drying at room temperature for about 20 minutes, a part of the film was cut and a compositional analysis was performed.
The remaining film was sequentially pre-stretched by 1.5 times in both the vertical and horizontal directions.

After leaving the pre-stretched film to dry at room temperature for 3 hours,
A highly transparent film was obtained by sequentially carrying out hot stretching by 1.2 times in both the vertical and horizontal directions in an oven at 00°C, followed by washing with water and drying. The strength of this film in the vertical direction is 24.8kg/Mdl, and the elongation is 33%, and the strength in the horizontal direction is 25.1kg/M7! ! , the elongation was 38%. Further, the film thickness was 28μ±1μ. The unstretched film contained 23% by weight of water, 3.1% by weight of DMA, and 7.0% by weight of calcium chloride. Example 3 The same polymer solution as used in Example 1 was cast onto a running endless belt and dried with hot air to continuously obtain an unstretched film with a thickness of 450 μm.

Next, the obtained unstretched film was washed with water for 30 minutes in a 40°C scouring tank containing an aqueous calcium chloride solution with a concentration of 5% by weight, and immediately stretched vertically and horizontally at room temperature in a simultaneous biaxial stretching machine with a set of tenters without drying. Each was pre-stretched twice, and then stretched once in two axial directions at the same time in an air atmosphere at 340°C.
．． The film was hot stretched 5 times, washed with water, dried, and continuously wound into a film. The strength of the obtained film in the vertical direction is 2
3.21<9/i1 elongation 10%, strength in the horizontal direction is 22
．． The weight was 4 kg/ml and the elongation was 25%.

Further, the film thickness was 50μ±1.5μ. In addition, 48% by weight was contained in the unstretched film subjected to preliminary stretching.
of water, 3.0% by weight of DMA, and 2.8% by weight of calcium chloride. Comparative Example 1 Using the same polymer solution as used in Example 1, a thickness of 5
A thin film of 00 μm was uniformly cast on a glass plate and dried by blowing hot air. The obtained film was washed in hot water at 40°C for 45 minutes, and then dried at 50°C for 2 hours to obtain a water content of 0.3 weight. % unstretched film was obtained.

This film was sequentially hot-stretched in both the vertical and horizontal directions in an oven at 320° C., and the stretching ratio until breakage was measured five times. As a result, the average stretching ratio was only 1.6 times in both the vertical and horizontal directions. The strength of this film in the vertical direction is 8.5k
g/Md elongation is 53%, strength in the horizontal direction is 7.8 kg/
Md and elongation were 55%.

Observation of the film during stretching revealed that in the longitudinal direction, a slight netting phenomenon occurred during stretching by 1.2 to 1.4 times, and in the horizontal direction, the netting phenomenon occurred constantly during stretching. I found out.

The thickness of the film after stretching was 40μ±20μ, and the thickness accuracy was extremely low, and the film was also inferior in strength. Examples 4 to 7, Comparative Examples 2 to 3 Using the same polymer solution as that used in Example 1,
Films were produced under the conditions shown in Table 1.

The film stretching conditions, the physical properties of the obtained film, and the film thickness accuracy are as shown in Table 1. In each example, unstretched films with the compositions shown in Table 1 were obtained by immersing the dried films, which had been cast and scoured in hot water at 30 to 50°C, into baths of various compositions. .

Claims (1)

[Scope of Claims] 1. At least 50% of the repeating structural units are substantially unoriented.
When stretching a film made of an aromatic polyamide whose mol% is represented by ▲numerical formula, chemical formula, table, etc.▼, an aqueous solution of an amide solvent or an aqueous solution containing an amide solvent and an ionic inorganic compound is applied to the film. 1.1 in at least one direction with a content of 5% by weight or more
1. A method for stretching an aromatic polyamide film, which comprises pre-stretching an aromatic polyamide film by at least twice as much, and then hot-stretching it at a temperature of 200° C. or higher in at least one direction identical to the pre-stretching.