JPH0655842B2 - Polyamide film and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyamide film consisting essentially of polyparaphenylene terephthalamide (hereinafter referred to as PPTA) and a process for producing the same, and more specifically, it is transparent. And due to the excellent surface orientation, the film length direction (hereinafter,
Excellent mechanical properties in both the MD direction and the width direction (abbreviated as the TD direction), with a small change in water absorption.
The present invention relates to a PPTA film and a manufacturing method for obtaining the same.

(Prior art and its problems) A linearly coordinated aromatic polyamide represented by PPTA has particularly excellent crystallinity and high melting point, and because of its rigid molecular structure, it has high heat resistance and high mechanical strength. In recent years,
It is a polymer material that has received particular attention. Further, it has been reported that fibers spun from a concentrated solution exhibiting its optical anisotropy exhibit high strength and module, and it has already been industrially implemented, but there are few proposals for application to films. .

For example, in JP-B-53-44957, a unit in which a halogen group is introduced into an aromatic nucleus of a linear coordination aromatic polyamide and PP
Aromatic polyamides that are soluble in organic solvents by copolymerizing aromatic polyamide units having no substituents on aromatic nuclei other than TA are disclosed as the main technology, and they are obtained from organic dopes of the polyamides. It is said that the dimensional change due to moisture absorption is significantly reduced when the film is heated under tension while maintaining the planar molecular orientation, and the film is heated to a certain density or more. However, this is disadvantageous in that the cost is high because the monomer is expensive, and the heat resistance, chemical resistance and crystallinity of the linearly coordinated aromatic polyamide are impaired.

In Example 4 of the publication, a PPTA film is disclosed. However, since the dope is adjusted at a high temperature of 120 ° C. for 1.5 hours, the degree of polymerization of PPTA is significantly lowered, and the dope concentration is high. The weight percentage was about 17%, and as in the example, the polymer solution was cast on a glass plate heated to 120 to 150 ° C. without cooling and immediately cooled to 0 to 3 ° C. When immersed in water, only the devitrified film can be obtained because it solidifies while leaving the optical anisotropy of the dope, and even if this film is heat-treated, only a film with low elongation that easily tears in one direction is obtained. Absent.

On the other hand, JP-B-57-17886 discloses a method of optically isotropically heating an optically anisotropic dope of a polyamide such as PPTA using concentrated sulfuric acid or the like as a solvent, followed by solidification, washing and drying.・ It is said that a transparent film having excellent mechanical properties in the MD direction can be obtained, but it has the drawback that only a film with a small elongation and a large dimensional change rate due to water absorption can be obtained in the dry state.

(Object of the invention) The object of the present invention is to overcome such drawbacks, and in PPTA,
It is an object of the present invention to provide a film which is excellent in transparency, has a high strength and elongation in both longitudinal and lateral directions and a modulus, and has a small dimensional change due to water absorption, and a method for producing the film.

(Means for Solving the Problems) As a result of intensive studies on the method for obtaining a film like the above, the present inventors have found that the optically anisotropic dope of PPTA is cast on a support surface and then the optical or the like is obtained by humidification. To obtain a film by sterilizing and then coagulating and washing, and the PP thus obtained
It has been found that the above object can be achieved by combining the special heat treatment of the TA film, and the present invention has been completed based on this finding.

(Structure and Action of the Invention) That is, the present invention consists essentially of polyparaphenylene terephthalamide having a logarithmic viscosity ηinh of 2.5 or more, a crystallinity of 75% or more as measured by reflection X-ray diffraction, and a long It is a transparent polyamide film characterized by having an elongation of 9% or more in both the length and width directions.

Further, the method for producing a film of the present invention is characterized in that an optically anisotropic dope consisting essentially of polyparaphenylene terephthalamide and one or more solvents selected from concentrated sulfuric acid, chlorosulfuric acid and fluorosulfuric acid is used as a support surface. The film obtained by casting on top, then optically isotropy by humidification, coagulation and washing, was used at 300 ° C-5 ° C.
Heat treatment under tension at 00 ° C.

The PPTA used in the present invention is substantially It is a polymer represented by the following formula, and it is convenient to produce it from a conventionally known paraphenylenediamine and terephthaloyl dichloride by a low temperature solution polymerization method.

If the degree of polymerization of the polymer of the present invention is too low, a film having good mechanical properties, which is the object of the present invention, cannot be obtained. Therefore, the logarithmic viscosity ηinh of 2.5 or more, preferably 3.5 or more (sulfuric acid 100 ml) Dissolve 0.2g of polymer in 30
A polymer having a degree of polymerization giving a value (measured at ° C) is selected.

The PPTA film of the present invention must have an apparent crystallinity by X-ray diffraction as described below of 75% or more. This is because if the apparent crystallinity is less than 75%, the crystallinity is not sufficient and water is easily absorbed (moisture absorption), and accordingly, the dimensional change of water absorption is large, and such a film is simply dried without being subjected to the heat treatment described later. Obtained when the degree of film or heat treatment is low. The upper limit of the apparent crystallinity is not particularly specified, but if it is too large, the film becomes brittle, so 85% or less is usually preferable.
The apparent crystallinity can be obtained by chopping the film into about 1 mm and drawing a diffraction intensity curve by the reflection method. For example, Rigaku Denki X-ray generator (RU-200γ
A) Carry out using a goniometer (PMG-RA) and scintillation counter (SC30). For the measurement, monochromatic CuKd (λ = 1.5418Å) is used. The cut film is set in a glass sample holder, and 40 KV ・
Operate the X-ray generator at 120 mA and use the scintillation counter to make step scan.
Step width 2θ = 0.02 degrees, time constant = 1
The second, the divergence slit = 1 °, the skittling slit = 1 ° and the receiving slit = 0.15 mm, the diffraction intensity at 2θ = 10 ° to 34 ° is recorded. The diffraction intensity curves between 2θ = 14 ° and 34 ° are connected to form a baseline, and the crystallinity is the ratio of the upper part of the baseline to the total area of the diffraction intensity curve between 2θ = 10 ° to 34 ° ( %).

The elongation of the film of the present invention must be 9% or more,
It is more preferably at least 12%. The PPTA films obtained in JP-B-57-17886 and JP-B-53-44957 have an elongation of about 3 to 4%, and are weak in bending and twisting, so that their use is limited.

The film of the present invention preferably has a light transmittance of 55% or more, more preferably 70% or more.
It has a transparency not found in PPTA films.

The light ray drop rate is measured as follows. Attach a film to the place where the liquid cell of a normal photoelectric photometer (or spectrophotometer) is set, select visible light with a wavelength of 600 nm,
The drop rate is measured. One of the important features of the film according to the invention is its transparency. As described above, the film obtained by directly extruding the optically anisotropic dope into the coagulation bath through a slight air gear is devitrified, and the light transmittance is usually 10% or less. This light drop rate naturally decreases as the thickness of the film increases, but the film according to the present invention has a transparency sufficiently higher than 55% up to the normally used thickness of about 200 μm.

The film of the present invention has a small dimensional change rate due to water absorption or moisture absorption, and specifically, it is preferably 5 × 10 ⁻⁵ mm / mm.
/% RH or less, water absorption dimensional change rate, and more preferably 3 x 10 ^-5 mm / mm /% RH or less. The water absorption dimensional change rate is measured as follows. The sample is dried at 100 ° C in a nitrogen atmosphere, cooled to room temperature, and then the elongation of the sample is measured in water (room temperature) using TMA (thermomechanical measuring device, TMA-30 manufactured by Shimadzu Corporation). It was calculated.

The size of the sample at the time of measurement was 2 mm in width and 8 mm in effective gripping length.

Next, a method for obtaining the PPTA film of the present invention will be described.

In carrying out the present invention, it is first necessary to prepare an optically anisotropic dope of PPTA.

Suitable solvents for preparing the dope used for molding the PPTA film of the present invention include sulfuric acid, chlorosulfuric acid, fluorosulfuric acid or a mixture thereof at a concentration of about 96% by weight or more. Sulfuric acid may be 100% or more, that is, fuming sulfuric acid, or trihalogenated acetic acid,
You may mix and use it in the range which does not impair the effect of this invention.

The concentration of the polymer in the dope used in the present invention is preferably such that it exhibits optical anisotropy at room temperature (about 20 ° C. to 30 ° C.) or higher, specifically about 10% by weight. Above, preferably about 11% by weight or more. At polymer concentrations lower than this, that is, at polymer concentrations that do not exhibit optical anisotropy at room temperature or higher, the molded PPTA film often does not have desirable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 20% by weight or less, and 16% by weight or less is preferably used for PPTA having a particularly high ηinh.

The dope of the present invention may be mixed with usual additives such as extenders, delusterants, UV stabilizers, heat stabilizers, antioxidants, pigments and solubilizers.

Whether the dope is glossy anisotropic or optically isotropic can be examined by a known method, for example, the method described in Japanese Patent Publication No. 50-8474, the critical point of which is the type of solvent, temperature and polymer. Since it depends on the concentration, the degree of polymerization of the polymer, the content of the non-solvent, etc., by investigating these relationships in advance, an optically anisotropic dope is formed, and by changing the conditions to be an optically isotropic dope, The optical anisotropy can be changed to an optical method.

The method for obtaining a transparent film having excellent mechanical properties of the present invention is such that, after casting the dope on the support surface, the dope is converted from optical anisotropy to optical isotropic by moisture absorption prior to solidification. It is a thing.

To change the optical anisotropy from optical anisotropy, specifically, the optically anisotropic dope formed into a film on the supporting surface is solidified prior to solidification to reduce the concentration of the solvent that forms a dope to reduce the concentration of the solvent. The temperature of the dope is increased by heating it in addition to the change in the optically anisotropic region of the dope due to moisture absorption or by the change of the dissolution capacity and polymer concentration of the dope. Can be achieved by optically transforming to.

Absolute humidity of about 20g
This can be achieved by passing an atmosphere of (water) / Kg (dry air) or more. Absolute humidity 20g (water)
If it is less than Kg (dry air), it is not practical because the moisture absorption rate is slow. Especially, when changing from an optically anisotropic dope to an optically isotropic dope only by absorbing moisture at around room temperature, 30 g (water) / Kg
(Dry air) or more is preferable. Further, the idea of more aggressively humidifying the normal humidity atmosphere is a desirable embodiment because the time until it becomes optically isotropic is short, and the heating temperature can be lowered when heating is also used.

In addition, in the method of simultaneously using moisture absorption or rapid heating after combined use, for example, when nitric acid is used as a solvent, the optical anisotropy substantially disappears, and the temperature at which the dope is converted into an optically isotropic polymer is Although it varies depending on the concentration, the degree of polymerization of the polymer, the concentration of sulfuric acid, the thickness of the dope, and the degree of moisture absorption, a temperature of about 45 ° C or higher is usually preferred, and the upper limit is generally too low when considering the degradability of the polymer. It is desirable that the temperature is not high, and it is desirable that the temperature of the film-shaped dope is selected not to exceed 200 ° C.

In the present invention, as the coagulating liquid of the dope, for example, dilute sulfuric acid containing about 70% by weight or less of water, about 20% by weight is used.
The following are sodium hydroxide aqueous solution and aqueous ammonia, and about 50 wt% or less sodium chloride aqueous solution and calcium chloride aqueous solution. The temperature of the coagulation bath is not particularly reduced and is usually in the range of about -5 ° C to 50 ° C.

Since the coagulated film contains acid as it is, it is necessary to wash and remove the acid component as much as possible in order to produce a film in which mechanical properties are not significantly deteriorated by heating. Specifically, it is desirable to remove the acid content up to about 500 ppm, and more desirably 200 ppm or less. Water is usually used as the cleaning liquid, but if necessary, it may be washed with warm water, or may be neutralized with an alkaline aqueous solution and then washed with water or the like. The cleaning is performed by, for example, running a film in the cleaning liquid or spraying the cleaning liquid.

The washed film is then subjected to a heat treatment, but the film to be heat treated may be preliminarily wet-stretched, and a film containing water or a film once dried is used.

The heat treatment atmosphere may be in air, but preferably, for example,
An inert gas such as nitrogen or argon is preferable. The heat treatment method may be treatment on a heating roll, treatment in a heating atmosphere with a tenter, treatment in silicone oil, fixing to a metal frame, or the like, but wrinkles may be generated in the heating atmosphere. In order to prevent it, it is necessary to limit the contraction of the film under tension. The term "under tension" includes three modes of contraction under constant length, contraction to the extent that wrinkles do not occur, and stretching slightly.

The heat treatment temperature is preferably higher than 300 ° C., more preferably 350 ° C. or higher in order to increase the crystallinity or reduce the dimensional change rate due to water absorption.

The maximum temperature of heat treatment should be 500 ° C or less in consideration of heat treatment energy, polymer decomposability, and reduction of film elongation. The heat treatment time depends on the heat treatment temperature, the capacity of the heat treatment machine, the amount of water contained in the film before the heat treatment, and the like, but is usually selected from the range of 5 seconds to 1 hour. If it is shorter than 5 seconds, the heat treatment effect is not sufficient and the crystallinity is small,
Water absorption and dimensional change of water absorption are large, and if it exceeds 1 hour, the polymer is decomposed and the elongation is extremely lowered, which is not preferable. The heat treatment time is preferably 15 seconds to 2000 seconds.

It is preferable to shorten the treatment time by increasing the heat treatment temperature.

In producing a film by the method of the present invention, all the above steps may be carried out batchwise or continuously. Further, the heat treatment may be performed in two or more steps at different temperatures, for example.

(Examples) Examples and reference examples (PPTA production examples) are shown below.
These Reference Examples and Examples illustrate the present invention and do not limit the present invention. In the examples, unless otherwise specified, parts by weight or% by weight is shown. The logarithmic viscosity η inh was measured by dissolving 0.2 g of the polymer in 100 ml of 98% sulfuric acid at 30 ° C. by a conventional method. The viscosity of the dope was measured with a B-type viscometer at a rotation speed of 1 rpm. The film thickness was measured with a dial gauge having a measuring surface with a diameter of 2 mm. For strength and elongation, a constant-speed elongation type strength and elongation measuring machine cuts a film sample into a rectangle of 100 mm x 10 mm, and draws a load-stretch curve 5 times at an initial grip length of 30 mm and a pulling speed of 30 mm / min. , Calculated from this.

Reference Example (Production of PPTA) PPTA was obtained by the constant temperature solution polymerization method as follows. Tokusho
In a polymerization apparatus disclosed in Japanese Patent Laid-Open No. 53-43986, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 of paraphenylenediamine was dissolved therein. After cooling to 8 ° C., 91.4 parts of terephthaloyl dichloride was added at once in powder form. After a few minutes, the polymerization reaction product solidified into a cheese, so the polymerization reaction product was discharged from the polymerization device according to the method described in JP-B-53-43986, and immediately transferred to a twin-screw closed type kneader. The polymerization reaction product was finely pulverized. Next, the finely pulverized product was transferred into a Hensiel mixer, added with approximately the same amount of water and further pulverized, then washed several times in warm water and dried in hot air at 110 ° C. ηinh is 6.5
95 parts of a pale yellow PPTA polymer were obtained. The polymers having different ηinh can be easily obtained by changing the ratio of N-methylpyrrolidone and the monomers (paraphenylenediamine and terephthalic acid dichloride) or / and the ratio between the monomers.

Example 1 PPTA having an ηinh of 5.0 was dissolved in 99.7% sulfuric acid at a polymer concentration of 13.0% to obtain a dope having optical anisotropy at 50 ° C. The viscosity of this dope at room temperature was 14,000 poise. This dope was placed in a beaker and kept at about 70 ° C. to facilitate film formation. At that time as well, the dope exhibited optical anisotropy and the viscosity was 9000 poise. This dope was applied on a glass plate at 30 ° C. with an applicator having a step of 0.1 mm. The glass plate was allowed to stand while being kept at 60 ° C. in the air kept at a temperature of 60 ° C. and an absolute humidity of 35 g (water) / Kg (dry air).

After about 30 seconds, it became transparent, and the glass plate was immersed in a water bath at 10 ° C. The film solidified from this was transparent as a result of conversion from optical anisotropy to optical isotropic at the dope stage. The coagulated film was washed with water and then heat-treated under various conditions under constant length to obtain a film having the properties shown in Table 1. Here, the heat treatment at 550 ° C. for 1 minute is a comparative example outside the present invention.

Example 2 Table 2 shows the result of heat-treating the film obtained by drying the water-washed film in Example 1 once in an oven at 120 ° C. under a fixed length.

Comparative Examples 1 and 2 The washed film of Example 1 was placed in an air oven at 120 ° C.
The properties of the film obtained by drying overnight (Comparative Example 1) and the film obtained by heat treatment at 250 ° C. for 1 hour (Comparative Example 2) are summarized in Table 3.

Example 3 The dry film of Comparative Example 1 was attached to a metal frame so as not to shrink the film, and heat-treated for 30 minutes in 300 ° C. silicone oil, resulting in a crystallinity of 77.5%,
Elongation 20%, water absorption dimension change MD direction 5.3 × 10 ^-5 mm /
A film having a property of 5.9 × 10 ⁻⁵ mm / mm /% RH in the TD direction was obtained.

(Effect of the invention) The film of the present invention, as shown in the examples, has good mechanical performance, in particular, high elongation, and has a small dimensional change rate due to water absorption / moisture absorption in both TD and MD directions. PP
It has features not found in TA film. Not only these characteristics, but also excellent heat resistance, electrical insulation, oil resistance,
It has pressure resistance, chemical resistance, and dense structure. For this reason,
INDUSTRIAL APPLICABILITY The film of the present invention is used as a material suitable for a dielectric for capacitors, an insulating material for high-speed rotating electrical equipment, a magnetic tape, a flexible printed wiring board, an electric coating material, and the like, especially in a region where water absorption is a problem. It

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Claims (2)

[Claims] 1. A reflection method X comprising a polyparaphenylene terephthalamide having a logarithmic viscosity ηinh of 2.5 or more.
The apparent crystallinity measured by line diffraction is 75% or more,
A transparent polyamide film characterized by an elongation of 9% or more in both the long and width directions 2. An optically anisotropic dope consisting essentially of polyparaphenylene terephthalamide and one or more solvents selected from concentrated sulfuric acid, chlorosulfuric acid and fluorosulfuric acid is cast on a support surface. After that, it becomes optically isotropic by coagulation
A method for producing a polyamide film, which comprises heat-treating the washed film at 300 ° C to 500 ° C under tension.