JP2662269B2 - Film manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a film comprising para-aramid. More specifically, the present invention relates to a method for producing a film having excellent mechanical properties and excellent surface properties.

(Conventional technology) An example of molding a para-aramid into a film is shown in
-14567, 57-35088, 59-5407,
No. 57-17866, and the like. Of these, the technique disclosed in JP-B-57-17886 is particularly noticeable because an isotropic film is obtained which is essentially transparent and has excellent mechanical properties. However, the films obtained by the methods disclosed in these documents are not always at a satisfactory level from the viewpoint of surface roughness, and are insufficient for, for example, porcelain tape applications requiring strict surface accuracy. Therefore, for example, Japanese Patent Application Laid-Open No. Sho 62-104714 proposes a technique for improving the surface accuracy of a film based on the technique disclosed in Japanese Patent Publication No. 57-17886.

With a further increase in recording density, a demand for improving the surface accuracy of a base film for a porcelain recording medium has become stronger.

On the other hand, Japanese Patent Application Laid-Open (JP-A) No. 51-132265 describes a method for producing a molded article, particularly a fiber, using a mixture of two or more kinds of poly (p-phenylene terephthalamide) having different degrees of polymerization. According to the publication, it is said that the film has an effect on the mechanical performance and economical efficiency of the obtained fiber, and there is no specific explanation of the film production. Even more, when a specific film production method is adopted, two kinds of raw material polymers are used. There is no description or suggestion about the effect of using the above mixture.

JP-A-62-70450 discloses a poly (p-phenyleneterephthalamide) obtained by substituting chloro-substituted poly (p-phenyleneterephthalamide).
-Phenylene terephthalamide) is disclosed to obtain a film having a high modulus of elasticity by blending in a small amount, but there is no mention or suggestion of surface accuracy at all, and what kind of requirement is selected for the film. No disclosure is made as to whether the surface accuracy is improved.

(Problems to be Solved by the Invention) An object of the present invention is to provide a para-aramid film which is particularly useful as a base film for a high-density magnetic recording medium, has excellent surface accuracy, a high Young's modulus, and has excellent heat resistance. It provides a manufacturing method.

(Means for Solving the Problems) As a result of the above-mentioned intensive studies to obtain a film meeting the purpose, the present inventors have once produced a film from a para-aramid solution and extruded it from a slit die onto a support surface,
When a wet or dry method is employed, when a mixture of two or more para-aramids having substantially different viscosity behaviors is used, the unpredictable effect of reducing the surface roughness of the obtained film is obtained. The present inventors have discovered that they exist, and based on this finding, have conducted further studies to arrive at the present invention.

That is, in the present invention, a para-aramid solution is extruded from a slit die onto a supporting surface, and a wet or dry film is produced so that the average shear rate when passing through the slit is at least 50 sec- ^1. And a mixture of two or more para-aramids having logarithmic viscosities of 0.2 or more and mixed so that the most para-aramid does not exceed 90% by weight of the total. Is the law.

As the para-aramid used in the present invention, a polymer represented by the following formula (I) or (II) or a copolymer thereof is selected.

(Wherein R ₁ , R ₂ and R ₃ are And these hydrogen atoms may be substituted with a functional group such as halogen, methyl, ethyl, methoxy, nitro, and sulfone. m and n are average degrees of polymerization and are about 50 to 1000
It is. The para-aramid used in the present invention may be copolymerized or blended with a polymer other than the above components as long as the amount is about 20 mol% or less. Particularly preferred as the para-aramid is poly (p-phenyleneterephthalamide) or poly (p-benzamide).

When a film is produced from these polymers, dimethylacetamide, N-methylpyrrolidone, hexamethylphosphoramide, tetramethylurea, etc., or a mixed solvent thereof, or lithium chloride, calcium chloride, lithium carbonate, odor, etc. Using a solvent to which an inorganic salt such as lithium chloride is added, a conventional wet or dry method or a combination thereof can be used. In another embodiment, the polymer can be produced from a dope dissolved in sulfuric acid, chlorosulfuric acid, fluorosulfuric acid, or the like. In these dopes, a so-called optically anisotropic dope is sometimes formed. After discharging the dope from a die, the dope is changed to an optically isotropic dope by heating or humidification, and then wet-solidified, and after washing, By biaxial stretching in a wet state, a film having an extremely large Young's modulus can be conveniently produced.

The method of the present invention can be applied to any process, whether dry or wet, but is limited to a process of extruding from a slit die onto a support surface. As a slit die, a so-called T die,
Regardless of the ring die. Film forming methods using these dies are disclosed in JP-B-56-45421 and JP-B-57-35088.
No. 59-5407, JP-A-54-132674,
JP-B-57-17886, J. Appl. Polym. Sci. (Journal of Applied Polymer Science) Vol. 27, N
o.8, p.2965 (1982) and the like, it is applicable to the method for producing a para-aramid film.

In the present invention, it is extremely important that two or more para-aramids differing in logarithmic viscosity by 0.2 or more are used as a mixture. The difference in logarithmic viscosity is more preferably 0.5 or more. In the present invention, the constant viscosity is determined by adding the polymer to 100 ml of 98.5% concentrated sulfuric acid.
It is defined as the value measured at 30 ° C. with 0.5 g dissolved.

There are several embodiments in which two or more para-aramids having logarithmic viscosities different by 0.2 or more are provided, and examples of the two cases are described below.

(A) Polymers of the same or almost the same chemical species but different degrees of polymerization. In this case, a case in which different degrees of polymerization are prepared in the polymerization step is combined with a so-called virgin polymer, which has been newly obtained from the so-called rework polymer and polymerization through the same or similar film manufacturing process. There is a case.

(B) When polymers having different chemical species are used, in this case, they are selected from the above-mentioned polymer groups and used.

The mixing of two or more polymers is performed prior to the preparation of the stock solution (dope) or during the preparation of the stock solution. However, the mixing ratio is such that if a certain component polymer occupies too large a part, the mixing effect is lost. Therefore, the maximum amount of the component polymer is used so as not to exceed 90% of the whole.

In the present invention, the surface effect of the film is improved as an effect of mixing. This is because para-aramid dope (concentrated solution) has unique rheological properties, for example, large flow orientation and oxotropic properties. Despite having a distribution, only films with poor surface accuracy can be obtained, whereas when formed into films by the method of the present invention, flow in a slit die due to mixing of polymers having different rheological properties is achieved. It is presumed that the behavior and the discharge behavior from the die slightly change to improve the surface accuracy of the obtained film.

In the present invention, the extrusion from the slit portion of the die is 50 times.
By setting the average shear rate at a rate of ¹ sec- ¹ or more, and preferably at 100 sec- ¹ , the surface properties of the film are further improved.

In the present invention, it is preferable to perform the film formation step as slowly as possible in order to improve the surface accuracy of the film. For example, in the case of the dry method, the temperature and the temperature are reduced in order to reduce the evaporation rate of the solvent. It is desirable to adjust the degree of decompression and to adopt a low coagulation bath temperature or a high coagulation bath concentration in order to reduce the coagulation rate in the case of the wet method.

Further, in the present invention, it is preferable to stretch the film after film formation in an optional step from the viewpoint of improving the surface accuracy of the film.

(Example) Hereinafter, an example is shown in order to explain this invention in more detail.

In the examples, the logarithmic viscosity ηinh was measured by dissolving 0.5 g of the polymer in 100 ml of 98% sulfuric acid, and at 30 ° C. by a conventional method. The viscosity of the dope was measured using a B-type viscometer at a rotation speed of 1 rpm. The thickness of the film was measured with a dial gauge having a measuring surface having a diameter of 2 mm. For the elongation and modulus, a film sample of 100 m was measured using a constant-speed elongation type elongation measuring instrument.
Cut into a rectangle of mx 10mm, the first grip length 30mm,
The load-elongation curve was drawn five times at a pulling speed of 30 mm / min, and was calculated from this. The surface accuracy of the film was evaluated using a surfcom 3B universal surface profiler manufactured by Tokyo Seimitsu Co., Ltd., and the center line average roughness (Ra) was measured according to JIS B-0601 and JIS B-06.
It was done by measuring according to 51.

Reference Example (Production of Polymer) In a solvent in which lithium chloride is dissolved in N-methylpyrrolidone, terephthalic acid chloride and paraphenylenediamine are reacted to obtain poly (p-phenyleneterephthalamide) (hereinafter referred to as PPTA). Obtained. At this time, by changing the ratio of the monomer to the solvent, ηinh of 6.1, 5.0 and 3.8 were obtained respectively. As diamine monomers, 4,4′-diaminodiphenyl ether and paraphenylenediamine
Using a molar ratio of 3/7, a copolymer of η inh 3.2 was obtained.

Example 1 A film was prepared using PPTA of ηinh 6.1 and 3.8 obtained in Reference Example.

Using two PPTAs with different ηinh almost equally, 99.
The polymer was dissolved in 7% sulfuric acid at a polymer concentration of 11.5% to obtain a dope having optical anisotropy at 60 ° C. When the viscosity of this dope was measured at room temperature, it was 9100 poise. The dope was degassed under vacuum while keeping the dope at about 70 ° C. to facilitate film formation. Also in this case, it has the same optical anisotropy as above,
The viscosity was 3900 poise. The 1.5m curved pipe from the tank through the filter, through the gear pump to the die is maintained at about 70 ° C, and the discharge linear velocity from the slit die at 3.5m / min (950sec- ¹
At an average shear rate of about 90% at a relative humidity of about 65%, cast on a mirror-polished tantalum belt (moving at 12m / min).
The casting dope was optically anisotropic by blowing air at a temperature of ° C., and was introduced into a 30% by weight aqueous sulfuric acid solution at −20 ° C. with a belt to solidify. Next, the coagulated film was peeled off from the belt and washed by running in warm water at about 40 ° C. Roll the roller about 1.in the length direction without drying the washed film.
Stretched 1 time, then using a tenter, first stretched about 1.3 times in the width direction, then dried with hot air at 240 ° C,
Heat treatment was performed at a constant temperature at ℃.

The ηinh of the mixed polymer before the preparation of the dope was 4.9, and the ηinh of the obtained film was 4.4. Table 1 shows the properties of the obtained film.

Comparative Example 1 Example 1 was repeated using PPTA of ηinh 5.0 alone.

Table 1 shows the properties of the obtained film. It can be seen that the mechanical performance is equal to or higher than that of the film of Example 1, but Ra is large (the surface is rough).

Example 2 A PPAT of ηinh5.0 and a copolymer of ηinh3.2 (Reference Example) were mixed at a weight ratio of 2: 1 and a dope was dissolved in concentrated sulfuric acid so as to be 13% by weight. Example 1 was repeated.

Table 1 shows the properties of the obtained film. The film of this example had high tear strength.

Example 3 This example illustrates the so-called rework polymer mixing effect.

The film (ηinh4.5) obtained in Comparative Example 1 was cut into pieces, and a polymer (ηinh4.8) was prepared by mixing about 40% by weight with PPTA of ηinh5.0 of Reference Example 1. The infrared absorption spectrum of the film obtained in Comparative Example 1 was almost the same as PPTA, but there was a slight difference in the so-called shoulder peak.

Dissolve the blended polymer in 99.5% sulfuric acid at 10%
A 7900 poise dope having optical anisotropy at ℃ was obtained. After deaeration and filtration, the dope was cast from a slit die onto a tantalum belt. At this time, the dope discharge linear speed from the die was 3.5 m / min (average discharge shear speed was 670 sec ^-1 ), and the belt moving speed was 10 m / min. The casting dope is converted to a transparent optically isotropic dope by blowing air at about 75 ° C. at a relative humidity of about 80%,
The solution was coagulated with an aqueous sulfuric acid solution at a concentration of 10%. After the coagulated film was removed from the belt, the film was washed with water at room temperature, a 2% aqueous solution of sodium hydroxide, and water at about 30 to 40 ° C. in that order.

The wet film that has been washed and contains about 250 to 350% water is stretched 1.2 times in the length direction and 1.2 times in the width direction with a tenter,
Then, it was dried in another tenter in which hot air circulating at 150 ° C. was stretched 1.05 times only in the width direction.

 Table 1 shows the properties of the obtained film.

(Effect of the Invention) The film obtained by the method of the present invention has very good surface precision in addition to the inherent characteristics of para-aramid film, such as high rigidity, heat resistance, high strength, and chemical resistance. is there. Further, it has been found that despite the good surface accuracy, it has an unexpected property that the slipperiness between films, between films and metal, and between films and ceramics is also good.

The film obtained by the method of the present invention is particularly useful as a base film for a magnetic tape, a base film for a printer, and the like. It is useful as a film, a carrier tape, a barcode printing adhesive tape, and the like.

Claims (1)

(57) [Claims] (1) A method of extruding a para-aramid solution from a slit die onto a support surface to produce a film by a wet or dry method, wherein an average shear rate at the time of passing through the slit is at least.
Extrude the solution to 50 sec- ¹ and mix two or more para-aramids having different logarithmic viscosities of 0.2 or more and mix so that the most para-aramid does not exceed 90% by weight of the whole. Method for producing a film characterized by using