JP2824104B2 - Film manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a film from a polymer liquid crystal, and more particularly, to a film in a longitudinal direction (hereinafter abbreviated as an MD direction) and a width direction (TD). Direction) The present invention relates to a method for producing a film which exhibits excellent mechanical properties in both directions and has excellent surface smoothness and has no streaks and little thickness unevenness.

[Conventional technology]

Attempts have been made to obtain a high-performance polymer film by utilizing the easy orientation of polymer liquid crystals. However, since the polymer liquid crystal is easily oriented in the direction in which the force is applied, a special device is required for the production of a film that requires a balance between vertical and horizontal properties. For example, there are a method using a conical mandrel, an inflation method, a method in which shear is applied in the lateral direction, a method in which a liquid crystal is once converted into a non-liquid crystal and then solidified.

These methods basically solved the problem of vertical and horizontal balance of film physical properties, and resulted in films with excellent mechanical performance. The film is rough and causes microscopic thickness unevenness, streaks, and poor surface smoothness of the film.

In general, a doctor blade method, a manifold die method, a circular die method, or the like is used as a method for forming a film. When forming a polymer liquid crystal film, the manifold die method and the circular die method are mainly used due to the high viscosity of the solution and the like. Has come to be used.

Further, in the manifold die method, as a method of supplying the resin to the die manifold, there are a T-die method in which the resin is supplied to the center of the manifold from the back or above the die, and an I-die method in which the resin is supplied from the side of the die manifold. . In the I-die method, since the resin is supplied from the side of the die in relation to the joining position with the resin supply machine, the communication path can be short, the resin is less decomposed, and the structure is simple, but the thickness accuracy is secured. For this reason, the T-die is becoming more common. When a T-die is used in order to obtain a film having a high thickness accuracy as described above, when a film is formed from a polymer liquid crystal, the characteristic of the polymer liquid crystal that tends to flow in one direction remains, and a central portion (that is, a die) is formed. Near the polymer liquid crystal supply inlet)
Local unevenness of thickness occurred and could not be eliminated. Further, it has been very difficult to obtain a film having no spider mark even in a circular die.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a high-quality film having excellent mechanical properties, a smooth surface and no thickness unevenness, from a polymer liquid crystal.

[Means for solving the problem]

The present inventors have conducted studies from various angles in order to solve the above-mentioned problems.As a result, it was unexpectedly possible to eliminate unevenness in film thickness due to the property of polymer liquid crystal that easily flows in one direction. It was found that it was effective to insert from the side of the die, and to obtain a high degree of thickness accuracy, it was found that the lip adjustment interval of the thickness adjustment was reduced.
The cause of the surface roughness of the film was found to be related to the thixotropic and domain-like heterogeneous dispersion of the polymer liquid crystal. In order to prevent such a property of the polymer liquid crystal from being caused as a rough surface of the film, it is effective to increase the flow velocity when the polymer liquid crystal is discharged from the die, that is, the shear rate to a certain value or more. This has led to the present invention.

That is, the present invention relates to a method for producing a film from a polymer liquid crystal, wherein a molten or solution-like polymer liquid crystal is supplied from the side of the die, extruded from a die having a lip adjustment bolt pitch of 30 mm or less, and extruded. Wherein the average extruding speed of the film is an average shearing speed not lower than an inflection point in the relationship between the viscosity of the polymer liquid crystal and the shearing speed.

In the present invention, the polymer liquid crystal is a thermotropic,
The present invention is not limited to either lyotropic mode, and is applicable to any type of polymer liquid crystal of nematic, cholesteric and smectic. Examples of such a high-molecular liquid crystal include aromatic polyester, aromatic polyazomethine, hydroxypropylcellulose (above thermotropic liquid crystal), aromatic polyamide-strong acid solution, hydroxypropylcellulose-water solution, cellulose derivative-acid or organic solvent. A solution, a polypenzopisthiazole-acid solution,
Polybenzobisoxazole-acid solution (the above is lyotropic liquid crystal).

Next, a discharge molding method from a polymer liquid crystal, which is particularly important in carrying out the present invention, will be described.

The molding die used in the present invention must be adapted to supply the resin from the side of the manifold type die.
The method of supplying the resin from the side is not limited, but is usually supplied to the manifold through a side plate. In the method of supplying from the middle of the manifold type die, that is, the commonly used T-die method, due to the characteristic of polymer liquid crystal that easily flows in one direction, the part where the resin is supplied and flows linearly, and the liquid crystal in the manifold is There is a boundary between the flow and the portion spreading in the width direction, and it is not possible to obtain a film having a value of (maximum thickness−minimum thickness) ÷ average thickness × 100 of 3% or less. Also, the circular die requires a structurally supporting part for the mandrel, so it is not possible to eliminate the spider marks due to the property that the liquid crystal easily flows in one direction, and the thickness unevenness generated in this part is 3% or less. The film cannot do it.

It is desirable that the die lip contact portion of the die used in the present invention is finished to a mirror surface. Further, the so-called loose land length of the lip contact portion is preferably relatively short, such as about 0.5 to 3 mm, in order to obtain a high shear rate described later. In addition, the gap of the lip is also important in implementing the present invention,
In order to increase the shear rate, it is preferable to reduce the value.
It is preferably used at a thickness of 3 mm or less, particularly 0.1 mm or less, because a high shear rate can be easily obtained. The smaller the gap of the lip is, the better the mechanical grinding precision allows.

Since the die used in the present invention is a method of supplying the resin from the side of the manifold type die, it is difficult to make the thickness with high precision, particularly when the slit width is long, so the die lip adjustment is performed. Pitch must be less than 30mm. In practicing the present invention, it is preferable to reduce the gap between the lips, and the lip adjustment pitch when the gap is reduced is important. The necessary deflection of the lip material cannot be corrected. The smaller the lip adjustment pitch, the better, but it is preferably about 15 to 25 mm due to manufacturing restrictions.

In recent years, in general, in the production of a polymer film, the shear rate at the time of ejection has been reduced as much as possible in order to obtain a film having less unevenness in thickness and good surface smoothness. However, it has been found that a film obtained by extruding a polymer liquid crystal at a low shear rate has a large surface roughness and uneven thickness. Therefore, in order to investigate the chicken sootropic property, domain viscoelasticity, and the like, which are considered to be the cause, the relationship between the viscosity (η) and the shear rate (γ) was plotted using both logarithms, and as shown in FIG. It has been found that there is an inflection point (hereinafter, point a) at which the viscosity sharply drops below a certain shear rate.

A feature of the present invention is that, in the method for producing a film from a polymer liquid crystal, when the polymer liquid crystal is discharged from a die, the polymer liquid crystal is extruded at a speed such that the average shear rate is equal to or higher than the point a. The film obtained by being discharged is
It has been found that the surface roughness and unevenness of thickness are significantly reduced as compared with a film obtained by discharging at a low average shear rate below the point a.

Hereinafter, in order to explain the present invention in more detail, poly (P
-Phenylene terephthalamide (hereinafter abbreviated as PPTA) in a concentrated sulfuric acid solution as an example of a polymer liquid crystal.
Although the case where a film is manufactured from a slit I die is described, it should be understood that the technology of the present invention can be similarly applied to the above-described polymer liquid crystal-based and other liquid crystal-based film forming methods.

PPTA is virtually And is conveniently produced from a conventionally known paraphenylenediamine and terephthaloyl chloride by a low-temperature solution polymerization method.

If the degree of polymerization of the polymer is too low, a film having good mechanical properties cannot be obtained.
A polymer having a degree of polymerization that gives a logarithmic viscosity ηinh of 4.5 or more (a value measured by dissolving 0.2 g of the polymer in 100 ml of sulfuric acid at 30 ° C.) is selected.

In the method of the present invention, first, it is necessary to prepare an optically anisotropic dope (liquid crystal dope) of PPTA.

A suitable solvent for preparing the dope used for forming the PPTA film is sulfuric acid at a concentration of 95% by weight or more. With less than 95% by weight of sulfuric acid, it is difficult to dissolve or the dope after dissolution becomes abnormally high in viscosity. Chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid and the like may be slightly mixed in the dope. Sulfuric acid may be 100% by weight or more, but a concentration of 98 to 100% by weight is preferably used from the viewpoint of stability and solubility of the polymer.

The concentration of the polymer in the dope is not less than a concentration exhibiting optical anisotropy at room temperature (about 20 ° C. to 30 ° C.) or higher, and specifically about 10% by weight or more, preferably about 11% by weight or more.
Used in weight percent or more. At a polymer concentration lower than this, that is, a polymer concentration that does not show optical anisotropy at room temperature or higher, the molded PPTA film often does not have favorable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually
It is preferably used in an amount of 20% by weight or less, particularly 18% by weight or less, and more preferably 16% by weight or less, based on PPTA of ηinh.

The dope may contain ordinary additives, for example, extenders, delusterants, ultraviolet stabilizers, heat stabilizers, antioxidants, pigments, dissolution aids, lubricants and the like.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, for example, the method described in Japanese Patent Publication No. 50-8474, but its critical point is determined by the type of solvent, temperature, and polymer. It depends on the concentration, the degree of polymerization of the polymer, the content of the additive, etc.
By making an optically anisotropic dope and changing the condition to be an optically isotropic dope, it is possible to change from optically anisotropic to optically isotropic.

The dope used in the present invention should remove insoluble dust and foreign matter as much as possible by filtration or the like prior to molding and solidification, and remove gases such as air generated or entrained during melting. Is preferred. Degassing can be performed after the dope is once prepared, or can be achieved by performing it under vacuum (reduced pressure) from the stage of charging the raw materials for preparation. The preparation of the dope can be performed continuously or batchwise.

Examination of the relationship between the viscosity and the shear rate of the optically anisotropic dope prepared as described above, that is, the liquid crystal dope, shows the results as shown in FIG. 1, and there is a point a where the viscosity sharply decreases. The optically anisotropic dope having such a property is discharged from a slit I die having a lip adjustment pitch of 20 mm and cast on a support surface. In carrying out the present invention, the special die described above is discharged. The shear rate at the time is important, and it is necessary to perform the shear rate at or above the point a in FIG. 1; below this, microscopic roughness occurs on the film surface, causing uneven thickness.

The land length of the lip portion of the die of the present invention is preferably 0.5 to 3 mm in order to obtain a film with even higher surface accuracy, and the surface of the lip contacting portion is preferably polished to a mirror surface. Rmax used in mechanical design
It is a mirror surface finished to 0.8S or less, more preferably 0.4S or less. In a preferred embodiment, the lip contact portion is made of a corrosion-resistant material such as tantalum.

A method for obtaining a transparent PPTA film with excellent mechanical properties and good surface accuracy is to cast the dope on a support surface and then convert the dope from optical anisotropy to optical isotropic before solidification. .

To make the optically anisotropic from optical anisotropy, specifically, prior to solidification of the optically anisotropic dope cast on the support surface, reduce the concentration of the solvent that forms the dope by absorbing moisture, The dope is transferred to the optically isotropic region by the change of the dissolving ability and the polymer concentration of the polymer, or the dope is raised by heating, and the phase of the dope is transferred to the optically isotropic, or the moisture absorption and the heating are performed simultaneously or sequentially. It can be achieved by using them together. In particular, the method utilizing moisture absorption, including the method using heating in combination, is effective in making the optical anisotropy optical isotropic and efficient
This is useful because it does not cause TA decomposition.

In order to absorb the dope, air at a normal temperature and humidity may be used, but preferably humidified or heated and humidified air is used. The humidified air may contain water in the form of mist exceeding the saturated vapor pressure, or may be so-called steam. However, supersaturated steam at about 45 ° C. or lower is not preferable because it often contains large granular condensed water. The moisture absorption is usually performed by humidified air at room temperature to about 180 ° C, preferably 50 to 150 ° C.

In the case of the heating method, the heating means is not particularly limited, and includes a method of applying the heated air to the casting dope, a method of irradiating an infrared lamp, and a method of dielectric heating.

The casting dope optically isotropic on the support surface is then subjected to solidification. Water, which can be used as a dope coagulating liquid,
An aqueous solution of sulfuric acid, an aqueous solution of sodium hydroxide, an aqueous solution of sodium sulfate, and the like, preferably an aqueous solution of sulfuric acid of 20 to 70% by weight. The temperature of the coagulating liquid is preferably 10 ° C. or lower, more preferably 5 ° C. or lower.

Since the coagulated film contains an 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 the mechanical properties are hardly reduced by heating. Specifically, it is desirable to remove the acid content to about 500 ppm or less. Water is usually used as a washing liquid, but if necessary, washing may be performed with warm water, or after neutralizing and washing with an aqueous alkaline solution, washing with water or the like. The cleaning is performed by, for example, running the film in the cleaning liquid or spraying the cleaning liquid.

The washed film may then be stretched in the wet state, if necessary, but the stretching allows the PPTA molecular chains to be oriented in the stretching direction, thereby improving the mechanical properties.

Drying is performed under tension, under constant length, or while stretching slightly while restricting shrinkage of the film. If the cleaning liquid (eg water)
If the film which has a tendency to shrink with the removal of the film is dried without any restriction of shrinkage, it may be due to non-uniform microstructure formation (such as crystallization) or the light transmittance of the resulting film Becomes smaller. Further, the flatness of the film may be impaired or curled. In order to dry while limiting shrinkage, for example, a tenter drier or drying by sandwiching between metal frames can be used. Other conditions relating to the drying are not particularly limited, and include a method using a heated gas (air, nitrogen, argon, etc.) or a normal temperature gas, a method using radiant heat such as an electric heater or an infrared lamp, and a method using a dielectric heating method. The drying temperature can be freely selected, and the drying temperature is not particularly limited, as long as the temperature is equal to or higher than normal temperature. However, in order to increase the mechanical strength, a higher temperature is preferable, and 100 ° C or higher. More preferably, 200 ° C. or higher is used. The maximum drying temperature is not particularly limited, but is preferably 500 ° C. or lower in consideration of drying energy and decomposability of the polymer.

In order to obtain a film having excellent transparency, that is, a film having an extremely high light transmittance, it is obvious that the dope is not limited to dust, dust such as a gas for absorbing moisture, a gas for heating, a support surface, a coagulating liquid, a cleaning liquid, a dry gas, and dust. It is preferable to reduce the content of as much as possible, and in this regard, producing a film in a so-called clean room or clean water is also one of the preferred embodiments.

〔Example〕

Examples are shown below, but these examples illustrate the present invention and do not limit the present invention.
In the examples, unless otherwise specified, parts by weight or weight%
Is shown. Logarithmic viscosity ηinh is 98% 98% sulfuric acid 100ml polymer 0.2g
Was dissolved and measured at 30 ° C. by a conventional method.

The relationship between the viscosity of the dope and the shear rate was determined by a conventional method at a constant temperature while flowing dry nitrogen through a measuring section of a rheometer (RM-1) manufactured by Shimadzu Corporation to prevent moisture absorption of the dope. In addition, the average shear rate (γ) of the discharge part during film forming is:
It was determined by the following general formula.

(Here, Q indicates the discharge amount, W indicates the slit width, and H indicates the slit gap.) The elongation and modulus are cut out of a film sample into a rectangle of 100 mm × 10 mm from a constant-speed elongation type elongation meter. ,
A load-elongation curve was drawn five times at an initial grip length of 30 mm and a pulling speed of 30 mm / min, and was calculated by this.

Rt (maximum height according to roughness curve) and Ra (center line surface roughness) representing the surface roughness of the film were measured with a surface roughness meter of Surfcom 550 manufactured by Tokyo Seimitsu Co., Ltd. (measurement length 4 mm, cut 0.8mm off).

The thickness of the film was determined by arbitrarily measuring ten points with a dial gauge having a measuring surface of 2 mm in diameter, and calculating the average of eight points excluding the largest and smallest ones. The thickness unevenness of the film is the same dial gauge, and 1 mm at 1 cm intervals in the width direction of the film.
Zero point measurement was obtained by the following equation.

Examples 1-2 A PPTA polymer having a η inh of 5.8 was dissolved in 99.5% sulfuric acid at a polymer concentration of 12% to obtain a dope having optical anisotropy at 60 ° C. When the relationship between the viscosity (η) and the shear rate (γ) was measured with a rheometer while maintaining the dope at 60 ° C., the results shown in FIG. 2 were obtained. That is, the shear rate 75se
There was an inflection point at c- ¹ . Put this dope in a tank,
Degassed under vacuum while keeping at ° C. After degassing, keep the 1.5m curved pipe from the tank to the die through the gear pump and the filter at about 60 ° C, with the slit gap shown in Table 1 and the lip adjustment screw spacing 20mm with a 260mm wide slit side slit. The formula I die is maintained at 60 ° C., extruded with γ shown in Table 1, cast on a mirror-polished endless belt made of tantalum,
The casting dope was optically isotropic by blowing air at about 120 ° C. with a dew point of 28 ° C., and was introduced together with a belt into a 40% by weight sulfuric acid aqueous solution at 3 ° C. for coagulation. Next, the coagulated film was peeled off from the belt and washed by running in water at room temperature. The dried film is stretched by two nip rolls with different peripheral speeds without drying, then put in a tenter, stretched in the width direction until it enters the drying section, and is then run at a constant length of 200 ° C with a tenter. And dried with hot air. afterwards,
Heat treatment at a constant length of 390 ° C. was carried out while sandwiching the tenter.

 Table 1 shows the results of the obtained films.

Comparative Example 1 A film was manufactured in exactly the same manner as in Example 2 except that the I-die of Example 2 was replaced with a T-die having the same lip adjusting screw interval of 20 mm and a slit width of 260 mm.

 Table 1 shows the results of the obtained films.

Limit value 3 where thickness unevenness becomes considerably large and can be used practically
%.

Comparative Example 2 The T-die of Comparative Example 1 was replaced with a T-die having a lip adjusting screw interval of 50 mm and a slit width of 260 mm, and a film was produced in the same manner with the slit gap and γ shown in Table 1.

 Table 1 shows the results of the obtained films.

[Effect of the Invention] The film obtained by the method of the present invention is a good machine represented by a high strength and a high Young's modulus which are not seen in a commercially available film, reflecting the easiness of orientation of the polymer liquid crystal. It has excellent properties, and has very little surface unevenness with little unevenness in thickness. Obtaining such a film excellent in both mechanical performance and surface precision from a polymer liquid crystal has been achieved for the first time by the present invention. For this reason, the film obtained by the present invention can be used as an insulating material for electric equipment rotating at high speed, a magnetic tape, a base film for a ribbon for a printer, a flexible printed wiring board, a wire covering material, a filtration membrane, a capacitor film, an electric insulating film, and the like. It can be suitably used and is useful for packaging materials, plate making materials, photographic films and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the relationship between the viscosity of a polymer liquid crystal and the shear rate. FIG. 2 shows the relationship between the viscosity of the dope of Example 1 (PPTA-sulfuric acid-based liquid crystal) and the shear rate.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 47/00-47/96

Claims (1)

(57) [Claims] In a method for producing a film from a polymer liquid crystal, a molten or solution polymer liquid crystal is supplied from the side of a die, and extruded from a die having a lip adjusting bolt pitch of 30 mm or less and extruded. A method for producing a film, characterized in that the average extrusion rate at the time is an average shear rate not lower than the inflection point in the relationship between the viscosity of the polymer liquid crystal and the shear rate.