JPH021741A - Readily slipping polyamide film and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject film having protrusions of inorganic particles on the surface thereof by casting an optically isotropic dope consisting of poly(p- phenylene terephthalamide), sulfuric acid and fine particulate inorganic particles onto a support surface, converting the above-mentioned dope into an isotropic dope and carrying out coagulating, washing and drying of the resultant dope. CONSTITUTION:An optically anisotropic dope consisting of poly(pphenylene terephthalamide) having >=3.5 intrinsic viscosity, sulfuric acid in >=95wt.% concentration and fine particulate inorganic particles (e.g., consisting of SiO2) having 10-100mum average particle diameter is cast onto a support surface, converted into an isotropic dope by moisture absorption and/or heating and coagulated in an aqueous solution of sulfuric acid in >=30wt.% concentration at <=10 deg.C, washed and dried by limiting shrinkage of the film to afford the objective film having >=8% tensile strength in all the directions, 10<5>-10<6> protrusions of 0.01-0.05mu height/mm<2> due to the inorganic particles present on the surface, excellent in mechanical characteristics and surface properties and especially suitable as video tapes, etc.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a polyamide film, particularly a film made of poly(p-phenylene terephthalamide) (hereinafter referred to as PPTA). The present invention relates to a PPTA film that exhibits excellent mechanical properties in both the MD force direction (hereinafter abbreviated as MD force direction) and the width direction (TD force direction), and also has excellent surface properties and slipperiness.

[Conventional technology]

PPTA has particularly excellent crystallinity and a high melting point, and because of its basic molecular structure, it has heat resistance and high mechanical strength, and is a polymer material that has attracted particular attention in recent years.

It has also been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus, and have already been implemented industrially. No examples are known yet.

The problem with PPTA is that its useful high molecular weight polymer is poorly soluble in organic solvents, and strong inorganic acids such as concentrated sulfuric acid must be used as a solvent. , for example, Special Public Interest Publication No. 56-4
No. 5421 discloses that a linearly coordinated aromatic polyamide having a halogen group introduced into its aromatic nucleus is copolymerized with an aromatic polyamide other than PPTA that has no substituent on the aromatic group, thereby making it soluble in organic solvents. , attempts have been made to obtain films from it. However, since the monomer is expensive, this increases the cost and has the drawback of impairing the heat resistance and crystallinity of the linearly coordinated aromatic polyamide.

For this reason, several methods have been disclosed for obtaining films by extrusion solidification of optically anisotropic dopes of linearly oriented aromatic polyamides that do not have substituents (Japanese Patent Publication No. 59-14567, Japanese Patent Publication No. 59-14567, No. 57-35088, Japanese Patent Publication No. 59-5407, and Japanese Patent Application Laid-open No. 54-1
32674), however, these methods
This method is difficult to use as an industrial method for producing a practical film due to the fact that the anisotropy of the physical properties of the obtained film is too large and the production method is complicated.

Japanese Patent Publication No. 57-17886 discloses that an optically anisotropic dope of a linearly coordinated aromatic polyamide is heated until it becomes optically isotropic immediately before solidification, and then solidified to produce a transparent material with mechanical properties. It is described to obtain films that are isodirectional. This method is an original method that goes against the conventional concept of achieving high performance by utilizing optically anisotropic doping. At the same time, it has been successfully avoided that the liquid crystal domain structure of the optically anisotropic dope remains even after the dope is extruded and solidifies as it is, resulting in an opaque film.

The aramid film produced by this method has excellent mechanical properties, heat resistance, chemical resistance, dimensional stability, etc.
magnetic deso, photographic film, capacitor film,
It is expected to be used as a material for electrical insulation films, ink ribbons for thermal printers, films for flexible printed wiring boards, etc.

However, in order to smoothly produce polyamide films and apply them to the above uses, it is necessary to improve the slipperiness of polyamide films.

In other words, if the slipperiness of the film is insufficient, especially in the case of a thin polyamide film, it will cause serious problems such as winding, rewinding, coating, slitting, etc., and will cause process problems such as the occurrence of winding wrinkles and the attraction of dust due to static electricity. becomes an obstacle.

In order to improve the slipperiness of such a polyamide film, JP-A-62-119024 describes a film to which inorganic particles are added and a method for producing the same. However, although this film has a low coefficient of friction, its surface smoothness is relatively poor, and it has not been able to satisfactorily meet the quality requirements for applications such as magnetic recording media, which require highly precise surface properties.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a high-performance film using PPTA, particularly a polyamide film with excellent smoothness and ease of slipping.

[Means for solving problems]

As a result of extensive research to obtain a PPTA film that meets the above objectives, the present inventors have discovered, for example,
When obtaining a PPTA film using the technique disclosed in Japanese Patent No. 886, in which an optically anisotropic dope of PPTA is firstly doped and solidified using an optically isotropic ratio,
They discovered that by adding a specific number of protrusions to the surface of the film using inorganic particles, the film could become slippery, and after further research, they completed the present invention.

That is, the first aspect of the present invention is poly(
(p-phenylene terephthalamide), the tensile elongation in all directions is 8% or more, and the film surface has a height of 0.01 to 0.5% formed from inorganic particles.
The second aspect of the present invention is an easily slippery polyamide film characterized by the presence of 10' to 10':+/nun'' protrusions of 05 μm in diameter. amide), 95% by weight or more of sulfuric acid, and an optically anisotropic dope consisting essentially of fine inorganic particles with an average particle size of 10 to 100 mμ are cast onto a support surface while maintaining optical anisotropy, 3. After converting the gutter to optically isotropic by moisture absorption and/or heating, it was kept at 10°C or less.
This method of producing a polyamide film is characterized by coagulating it in an aqueous sulfuric acid solution of 0% by weight or more, then washing, and drying while limiting shrinkage of the film.

The PPTA used in the present invention is substantially (-CO+C
It is a polymer represented by 0IIN+Ni1-)n, and is conveniently produced from conventionally known paraphenylenediamine and terephthaloyl chloride by a low-temperature solution polymerization method.

The degree of polymerization of the polymer of the present invention is 3.5 or more, since if it is too low, a film with good mechanical properties cannot be obtained.
Logarithmic viscosity η1nh (sulfuric acid 100
Value measured at 30°C by dissolving 0.5g of polymer in d)
The polymerization degree that gives the following is selected.

The film of the present invention can achieve its purpose only if it satisfies the following two requirements.

First of all, the film of the present invention needs to have a tensile elongation of 8% or more in all directions. This is because a film having an elongation smaller than 8% is easily torn and is not practical. The tensile elongation is preferably 10% or more. On the contrary,
The PPTA film made by the method described in Japanese Patent Publication No. 55-14170 has a high elongation in the MD force direction of 4 to 6%.
In addition, the elongation in the TD force direction is less than 1%, making it extremely easy to tear.

The high elongation of the film of the present invention is related to the process of casting an optically anisotropic dope onto a support surface and then making it optically isotropic.

Second, the film of the present invention has protrusions of 10' to 10' in height formed from inorganic particles on its surface with a height of 0.01 to 0.05 μm.
0hp/ff1fllt must exist.

Here, on the surface of the protruding portion, the inorganic particles may be exposed, or the inorganic particles may be coated with PPTA and the inorganic particles may be present inside. When the height of the protrusions exceeds 0.05 μm, although the slipperiness is good, the surface precision deteriorates, so that, for example, in magnetic recording media applications, noise such as dropouts increases and performance deteriorates. On the other hand, if the height of the protrusions is less than 0.01 μm, sufficient slipperiness cannot be obtained. As the number of protrusions increases, the slipperiness tends to improve, but once the number of protrusions increases, the slipperiness does not improve any further, and problems such as reduced stretchability are likely to occur during manufacturing. Therefore, 10”: +/11+11
On the other hand, if it is less than 105 g/mm2, sufficient slipperiness cannot be obtained.

The shape of the protrusion can be arbitrary, such as spherical, pleated, mountain range, etc.

The inorganic particles used in the present invention are selected from those that are substantially inactive to concentrated sulfuric acid, such as Sing.
, Ti(h), Ca5Oa, etc. are used.

The amount of inorganic particles contained in the film of the present invention is PPTA
It is preferably in the range of 0.01 to 5% by weight, more preferably in the range of 0.05 to 1% by weight.

The content of inorganic particles is determined by film performance (slidability, mechanical performance, etc.) and film manufacturing operability (dope viscosity,
It should be determined from both factors (dischargeability, etc.). The film of the invention preferably also has the following properties:

For example, the film of the present invention has a Young's modulus in at least one direction of 1000 kg/lo'' or more.

This condition is closely related to the deformation resistance of the film. For example, it is related to jitter characteristics when used as a magnetic tape, and more preferably, the Young's modulus in at least one direction is 1300 kg/ms" or more,
Most preferably, it is 1500 kg/mm" or more. The film of the present invention has two aspects. One is a balanced type in which vertical and horizontal Young's moduli are approximately equal to 1000 kg/mm2 or more, and the other is a balanced type. For one, the Young's modulus is larger in either the vertical or horizontal direction.1000 kg
/cm" or more, and is a tensilized type.

The films of the present invention are preferably thin films of about 12 μm or less. Particularly preferably, the length is 1011 m or less. For example, when used as a videotape, the bulkiness per length increases in proportion to the thickness;
This is because it meets the needs of being lightweight and having a long recording time.

The film of the present invention is also preferably substantially void-free.

Furthermore, the film of the present invention typically has a density of 1.37.
It is in the range of 0 to 1.420 g/cm'. This density value was measured at 30° C. by density gradient tube method using carbon tetrachloride-toluene. This density range is
That of known PPTA fibers is 1.43g/cm' to 1
．． This is a small value compared to the range of 46 g/cm'. When the density is less than 1.370 g/cm', the mechanical properties deteriorate, and 1.420 g/cm:I
If the film exceeds this value, the film will have planar orientation and will therefore have poor isotropy in mechanical properties. In any case, this low density results in a light and high-strength film. The film of the present invention preferably has plane orientation defined by the crystal orientation angle determined by X-ray diffraction as described below. That is, the crystal orientation angle with respect to the 2θ-23° peak due to X-rays incident at right angles to the film surface is 30° or more, and the crystal orientation angle with respect to the 2θL = 18' peak due to X-rays incident parallel to the film surface is 30° or more. Preferably, the angle is 60° or less. When X-rays are incident at right angles to the film surface (hereinafter referred to as
(referred to as the TV direction) and cases in which the light is incident parallel to the surface (hereinafter referred to as the S■ force direction).

The film of the present invention has 2θL=
, has a large diffraction peak at 23″, but this 2θζ23
The crystal orientation angle at S is preferably 30° or more, more preferably 50° or more.
A large diffraction peak of 2θζ18° appears on the equator line due to incidence from the force direction, and it is preferable that the crystal orientation angle at 2θζ18° is 60° or less. When both of these crystal orientation angles are satisfied, it can be said that the film of the present invention has a so-called plane-oriented structure, and the film has high mechanical properties both in the drawing direction and in the direction perpendicular thereto. It is highly preferred because it has high tear strength.

A known method can be used to measure the crystal orientation angle.
For example, the following method is used.

Place the counter at a predetermined 2θ angle and rotate the film 180°.
By rotating, a diffraction intensity curve is obtained. In addition, TV
In , rotation is made between 90 degrees forward and backward, centering on the highest strength. The value of the arc length in degrees in the diffraction photograph corresponding to the point showing half the intensity of the highest intensity of this curve with respect to the baseline drawn between the lowest intensity points (i.e., 50% of the baseline of the highest intensity) angle with respect to a point)
is measured and taken as the crystal orientation angle of the sample. During the measurement, the diffraction intensity can be measured by stacking several films if necessary.

Next, a method for obtaining such a PPTA film will be explained.

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

A suitable solvent for preparing the gutter used for forming the PPTA film of the present invention is sulfuric acid at a concentration of 95% by weight or more. Sulfuric acid containing less than 95% by weight may be difficult to dissolve;
The dope becomes extremely viscous after being dissolved.

The dope of the present invention may contain a small amount of chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid, and the like. Although it is possible to use sulfuric acid with a weight of 100 or more, from the viewpoint of stability and solubility of the polymer, the
Weight % concentrations are preferably used.

The polymer concentration in the dope used in the present invention is at room temperature (
A concentration that exhibits optical anisotropy at a temperature of about 20° C. to 30° C. or higher is preferably used, and specifically, about 10% by weight or more, preferably about 12% by weight or more. At polymer concentrations below this, ie, polymer concentrations that do not exhibit optical anisotropy at room temperature or higher temperatures, the formed PPTA film often does not have desirable mechanical properties. The upper limit of the polymer concentration in the dope is not particularly limited, but is usually 20%.
Hereinafter, for PPTA with particularly high ηinh, the amount used is preferably 18% by weight or less, more preferably 16% by weight or less.

In the present invention, the dope has an average particle diameter of 10 to 100
It is necessary to add mμ inorganic fine particles.

If the average particle diameter is 100 mμ or more, the film will have large protrusions and the smoothness will be impaired, and if it is less than 10 mμ, sufficient slipperiness will not be obtained.

The inorganic particles are added to the sulfuric acid before adding PPTA,
Adding at the same time as PPTA, adding after forming an optically anisotropic dope, adding and dissolving a portion of PPTA, adding inorganic particles, and then adding the remaining PPTA. I can do it. In order to prevent agglomeration of inorganic particles and improve dispersibility, it is also a preferred embodiment to use, for example, a homogenizer or a static mixer. In addition, in the case of a method in which inorganic particles are added after making an optically anisotropic dope, it is necessary to remove as much insoluble dust and foreign matter as possible by filtration, etc. prior to addition, and to remove any particles generated during dissolution. It is preferable to remove entrained gas such as air. Degassing can be carried out after preparing the dope, or
This can also be achieved by performing the process under vacuum (reduced pressure) from the stage of preparing raw materials for preparation. Preparation of the dope can be carried out continuously or batchwise.

In the present invention, the amount of inorganic particles added to the dope is preferably about 0.001 to 1% by weight (based on the total amount of dope).

The dope of the present invention may also contain other conventional additives, such as fillers, light removers, UV stabilizers, heat stabilizers, antioxidants, pigments, solubilizing agents, and the like.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, such as the method described in Japanese Patent Publication No. 50-8474, but the critical point depends on the type of solvent, temperature, polymer Since it depends on the concentration, degree of polymerization of the polymer, content of non-solvent, etc., optically anisotropic dope can be created by investigating these relationships in advance, and by changing the conditions for optically isotropic dope. It is possible to change from optical isotropy to optical isotropy.

The dope thus prepared is cast onto a support surface from a die, for example a slit die, while maintaining its optical anisotropy. In addition, in the laboratory, it can be cast onto a glass plate using a doctor knife. In the present invention, even if steps such as casting and subsequent conversion to optical isotropy, coagulation, washing, stretching, and drying are performed continuously, all or part of these steps may be performed intermittently, that is, batchwise. You may go. Preferably, the casting process is carried out continuously, and moreover, the moving speed of the support surface on which the dope is cast is at least twice the linear speed at which the dope is discharged from the die.

The support surface used in the present invention is in the form of a belt or drum, or is used as a plate. The material is not particularly limited as long as it is acid resistant and has a surface finish.
For example, plated metals such as glass, Hastelloy, tantalum, gold, platinum, and titanium nitride are preferably used, and sometimes these materials are preferably finished with a so-called mirror finish.

The method for obtaining the film of the present invention is to cast the dope onto a supporting surface and then convert the dope from optically anisotropic to optically isotropic prior to solidification.

To change optical anisotropy to optical isotropy, specifically, before solidifying an optically anisotropic dope cast on a support surface, the concentration of the solvent forming the dope is lowered by absorbing moisture. Transform the dope into an optically isotropic region by changing the solubility and polymer concentration, or increase the temperature of the dope by heating to transform the dope phase to optically isotropic, or absorb moisture and heat simultaneously or sequentially. This can be achieved by using them together. First, methods using moisture absorption, including methods that use heating in combination, are effective in increasing the optical isopotency ratio of optical anisotropy and P
This is useful because it can be done without causing decomposition of PTA.

To make the dope absorb moisture, air at normal temperature and humidity may be used, but humidified or heated and humidified air is preferably used. The humidified air may contain mist-like moisture exceeding the saturated vapor pressure, and may be so-called water vapor. However, supersaturated steam at a temperature of about 45°C or lower is not preferred because it often contains large particles of condensed water. Moisture absorption is usually carried out by humidified air at room temperature to about 180°C, preferably 50 to 150°C.

In the case of a heating method, the heating means is not particularly limited;
A method of applying humidified air as described above to the casting dope,
Methods include irradiation with an infrared lamp and dielectric heating.

The optically cast dope on the supporting surface is then subjected to solidification. In the present invention, an aqueous sulfuric acid solution of 30% by weight or more can be used as the dope coagulation liquid. 30%
If the sulfuric acid aqueous solution is less than 100%, it becomes difficult to obtain a film with excellent surface precision, probably because the coagulation rate of the dope including water is too high. The coagulation bath is preferably a 40-70% by weight aqueous solution.

In the present invention, the temperature of the coagulating liquid needs to be 10°C or less. This is because it has been found that the lower the temperature, the lower the solidification rate and the tendency for the film to contain fewer voids, thus improving the surface precision of the film.

The coagulation bath temperature is preferably 5°C or lower, more preferably 0°C to -40°C.

Since the coagulated film as it is contains acid, it is necessary to wash and remove the acid as much as possible in order to produce a film whose mechanical properties are less likely to deteriorate due to heating. Specifically, it is desirable to remove the acid content to about 500 ppm or less.

Water is usually used as the cleaning liquid, but if necessary, hot water may be used, or washing may be performed by neutralizing with an alkaline aqueous solution and then using water or the like. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid.

The washed film may then be stretched in the wet state if desired before being subjected to drying. Stretching is performed in one direction or two directions at a stretching ratio of 1.05 times or more. At this time,
It is often observed that the moisture contained within the film comes out as sweat. For stretching in one direction, MD
Stretching may be carried out either in the direction of the force or in a direction perpendicular thereto, and preferably about 1.1 to 1.7 times. 2
The stretching in the directions may be simultaneous biaxial stretching or sequential stretching one axis at a time. In the case of bidirectional stretching, it is preferably carried out at a stretching ratio of about 1.07 to 1.5 times. Since the PPTA molecular chains can be oriented in the stretching direction by stretching, mechanical properties are improved.

Drying must be carried out under tension, at a constant length, or with slight stretching to limit shrinkage of the film.

If a film that has a tendency to shrink upon removal of the cleaning liquid (e.g., water) is dried without any restriction on shrinkage, it may not be profitable due to the formation of microscopically non-uniform structures (crystallization, etc.). The light transmittance of the film will be reduced.

Furthermore, the flatness of the film may be impaired or the film may curl. To dry while limiting shrinkage, for example, a tenter dryer or drying between metal frames can be used. Other conditions related to drying are not particularly limited, and may include methods using heated gas (air, nitrogen, argon, etc.) or room temperature gas, methods using radiant heat such as electric heaters or infrared lamps, dielectric heating methods, etc. It can be freely selected, and the drying temperature is not particularly limited as long as it is room temperature or higher. However, in order to increase the mechanical strength, a high temperature is preferable, and a temperature of 100°C or higher, more preferably 200°C or higher is used. The maximum temperature for drying is not particularly limited, but in consideration of drying energy and decomposability of the polymer, it is preferably 500° C. or lower.

〔Example〕

Examples and reference examples (manufacturing examples of PPTA) are shown below, but these reference examples and examples are for explaining the present invention, and are not intended to limit the present invention. In the examples, parts by weight or weight % are shown unless otherwise specified. The logarithmic viscosity ηinh was measured by a conventional method at 30° C. by dissolving 0.5 g of the polymer in 98% sulfuric acid 100+ffi.

The viscosity of the dope was measured using a B-type viscometer at a rotation speed of 1 rptg. The thickness of the film is 2 diameter
Measurement was performed using a dial gauge with a nm measurement surface. Strength and elongation and Young's modulus are measured using a constant speed extension type strength and elongation measuring machine.
Cut the film sample into a rectangle of 100fIIIXIOIII11, with an initial grip length of 30fffffi,
The load-elongation curve was drawn five times at a tensile rate of 30/min, and the calculation was made from this.

The size of the protrusions on the film surface and the surface roughness (Ra) were measured using a three-dimensional surface shape measuring device (Surfcom 55) manufactured by Tokyo Seimitsu Co., Ltd.
0). The number of protrusions was determined by counting the number of protrusions within a certain area using a scanning electron microscope manufactured by JEOL, using a photograph with the highest shadow magnified at 3,500 times, and calculating the number of protrusions within a certain area. +11111"
The number of hits was calculated.

Example 1 SiO□ having a primary particle size of 40 mμ was added to 99.6% sulfuric acid and vigorously stirred. At this time, the ratio of SiO□ to sulfuric acid was set at 0.01%. Next, I) PTA having ηinh = 5.8 was dissolved in this dispersion so that the polymer concentration was 12% by weight to obtain a dope having optical anisotropy at 60°C. This dope has a temperature of 9
．． It was 600 voices. The dope was degassed under vacuum at 55-65°C for about 4 hours.

This dope is passed from the tank through a static mixer, through a gear pump, and into a die, through a 1.5m curved pipe kept at about 70°C, and then passed through a gou with a 0.15mm x 300mm slit to a mirror surface. The cast dope was cast onto a polished tantalum belt, blown with air at about 90°C with a relative humidity of about 85% to make the cast dope optically isotropic, and then placed together with the belt in a 30% aqueous sulfuric acid solution at -20°C. The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C. After washing the film,
It was dried with hot air at 240° C. under a fixed length using a tenter. The results are shown in Table 1. Examples 2 and 3, Comparative Examples 1 and 2 Table 1 shows the results of producing a film in the same manner as in Example 1 by changing the size and amount of SiO□ particles added to the dope. show.

Margins below [Effects of the Invention] As shown in the examples, the film of the present invention has good mechanical properties as expressed by high strength and high Young's modulus, which are not found in commercially available films, and also has surface precision. It has both very good properties and easy slipping properties. In addition to these properties, it also has excellent electrical insulation, heat resistance, oil resistance, pressure resistance, resistance to chemicals other than strong acids, and dense structure. Therefore, the film of the present invention can be suitably used as an insulating material for high-speed rotating electrical equipment, magnetic tape, flexible printed circuit boards, thermal transfer printers, wire coating materials, filtration membranes, etc. Because of its excellent transparency, it is also used in packaging materials, plate-making materials, photographic films, etc.

In particular, the film of the present invention has a high Young's modulus, strong tear resistance, high surface precision, and slipperiness. , commuter passes, etc.), and is particularly useful as a high-quality videotape with excellent image clarity and stability.

Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Claims] (1) A film made of poly(p-phenylene terephthalamide) with a logarithmic viscosity of 3.5 or more, a tensile elongation in all directions of 8% or more, and a film made of inorganic particles on the film surface. A slippery polyamide film (2) characterized by the presence of protrusions with a height of 0.01 to 0.05μ at a rate of 10^5 to 10^6/mm^2, and a logarithmic viscosity of 3.
5 or more poly(p-phenylene terephthalamide) and 9
5% by weight or more of sulfuric acid and an average particle size of 10 to 100 mμ
An optically anisotropic dope consisting essentially of fine inorganic particles was cast onto a support surface while maintaining its optical anisotropy, and the dope was converted to optically isotropic by moisture absorption and/or heating. A method for producing a polyamide film, which is then coagulated in an aqueous solution of 30% by weight or more of sulfuric acid maintained at 10°C or lower, then washed, and further dried while limiting shrinkage of the film.