JPH02133434A - Highly slippery polyamide film and its production - Google Patents

Abstract

PURPOSE:To obtain a polyamide film excellent in slipperiness and smoothness by making an optically anisotropic dope of a p-substituted aromatic polyamide, converting this dope into an optically isotropic one and coagulating the resulting dope into a film. CONSTITUTION:An optically anisotropic dope is obtained by reacting a p- substituted aromatic polyamide (A) of an inherent viscosity number >=3.5 [e.g., poly(p-phenyleneterephthalamide)] with sulfuric acid of a concentration >=95wt.% and 0.1-2wt.%, based component A, inorganic particles (e.g., SiO2) of a mean particle diameter of 0.11-0.50mum. This dope kept in an optically anisotropic state is cast over the surface of a support in an average shear rate >=50sec<-1>, converted into an optically isotropic one by moisture absorption and/or heating an coagulated in a 30wt.% or higher aqueous sulfuric acid solution kept at 10 deg.C or below, washed, stretched at a draw ratio >=1.1, and dried to obtain a polyamide film having a tensile elongation >=8% in all directions and having 10<4>-10<5>/mm<2> of 0.06-0.25mum-high protrusions of the inorganic particles on the film surface.

Description

[Detailed Description of the Invention] [Industrial Application Field] A film made of a para-aromatic polyamide represented by t'-invention C, f, S (p-phenylene terephthal 7mide) (hereinafter referred to as PPTA) In more detail, the longitudinal direction of the film (hereinafter referred to as 4D direction)
The present invention also relates to a para-aromatic polyamide film that exhibits excellent mechanical properties in both the width direction (hereinafter abbreviated as TD force direction) and has both excellent slipperiness and good smoothness.

[Conventional technology]

Para-aromatic polyamide has particularly excellent crystallinity and high melting point, and due to its rigid molecular structure, it has heat resistance and high mechanical strength, and is a polymer material that has attracted particular attention in recent years. It is. It has also been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus (Young's modulus), and are already being used industrially. There are few proposals for application examples.

Problems with para-aromatic polyamides include the fact that their useful high molecular weight polymers are poorly soluble in organic solvents, and it is necessary to use strong inorganic acids such as concentrated sulfuric acid as a solvent. Therefore, for example,
In Publication No. 45421, a unit in which a halogen group is introduced into the aromatic nucleus of a para-aromatic polyamide is copolymerized with an aromatic polyamide other than PPTA that does not have a substituent on the aromatic group to make it soluble in an organic solvent, and then Attempts are being made to obtain the film. However, since the monomer is expensive, this increases the cost and has the drawback of impairing the heat resistance and crystallinity of the para-aromatic polyamide.

For this reason, several methods have been disclosed for obtaining films by extruding and coagulating optically anisotropic dopes of para-aromatic polyamides having no substituents (Japanese Patent Publication No. 59-1
4567, JP 57-35088, JP 59-5407, and JP 54-13267.
Publication No. 4).

However, these methods are difficult to use as a practical industrial method for producing films because 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 by heating an optically anisotropic dope of para-aromatic polyamide until it becomes optically isotropic immediately before solidifying it, and then solidifying it, it is transparent and has isotropic mechanical properties. It is described that a film with a high target value can be obtained. 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 as relaxing the axial orientation, the liquid crystal domain structure of the optically anisotropic dope remains even after the dope is extruded and is successfully avoided from solidifying into an opaque film.

The para-aromatic polyamide film produced by this method has excellent mechanical properties, heat resistance, chemical resistance, dimensional stability, etc., so it can be used for magnetic tapes, photographic films, capacitor films, etc. It is expected to be used as a material for air insulation films, ink ribbons for thermal printers, films for flexible printed wiring boards, etc.

However, in order to smoothly produce para-aromatic polyamide films and apply them to the above uses, it is necessary to improve the slipperiness of para-aromatic polyamide films. In other words, if the film does not have sufficient slipperiness, especially in the case of a thin film, it will seriously impede operations such as winding, rewinding, coating, and slitting.
For example, it causes problems in the process, such as the occurrence of wrinkles and the attraction of dust due to static electricity.

In order to improve the slipperiness of such films,
No. 2-119024 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, it has problems with contact with high-temperature objects such as thermal transfer printer tape and slipperiness during high-speed running, and the surface smoothness is relatively poor, making it difficult to maintain a high-precision surface. However, it has not been possible to satisfactorily meet the quality requirements for magnetic recording media, etc., which require the following. That is, at present, a film that has both high slipperiness and excellent smoothness has not yet been obtained.

[Problem to be solved by the invention]

An object of the present invention is to provide a high-performance film using a para-aromatic polyamide, which has even greater slipperiness and smoothness than conventional polyamide films, and a method for producing the same.

[Means for Solving the Problems] As a result of extensive research to obtain a para-aromatic polyamide film that meets the above objectives, the present inventors have developed the technology disclosed in, for example, Japanese Patent Publication No. 17886/1986, In other words, when obtaining a para-aromatic polyamide film by first making an optically anisotropic dope of para-aromatic polyamide and coagulating it by optical isostatic ratio, a specific shape is formed on the film surface using inorganic particles. They discovered that by adding a specific number of protrusions to the surface of the film, a film with easy slipping properties could be obtained.After further research, the present invention was completed.

That is, the first aspect of the present invention is a film made of a para-aromatic polyamide having a logarithmic viscosity of 3.5 or more, which has a tensile elongation of 8% or more in all directions, and has a film surface containing inorganic particles. Formed height 0.06-0.25μm
The second aspect of the present invention is a highly slippery polyamide film characterized by the presence of 104 to 105 protrusions/mm. 95% by weight or more of sulfuric acid and 0.1 to 2% by weight of para-aromatic polyamide with an average particle size of 0.
An optically anisotropic dope consisting essentially of fine inorganic particles of 11 to 0.50 μm is cast onto a supporting surface while maintaining optical anisotropy so that the average shear rate is 50 sec-1 or more. After converting the acid dope into optical isotropy by moisture absorption and/or heating, it is coagulated in a 30% by weight or more sulfuric acid aqueous solution maintained at 10'C or less, then washed, and the film is further heated to 1.1% by weight. This is a method for producing a polyamide film, which is characterized by drying while stretching the film to more than double the amount.

The para-aromatic polyamide used in the present invention means that the amide bond is at the para-position of the aromatic ring or with an orientation value (
4,4"-biphenylene, 1,5 naphthalene, 2,6-
PPTA, poly(p-benzamide), poly(4,4'-benzamide), poly(4,4'-benzamide), etc. anilide terephthalamide), poly(p-phenylene-4,4"-biphenylene dicarbonamide), poly(p-phenylene-2,6-
Examples include aromatic polyamides having a structure of a para-orientation type or a structure close to a para-orientation type, such as naphthalene dicarbonamide). These polyamides are conveniently produced from aromatic diamines and aromatic dicarboxylic acid chlorides by conventionally known low temperature solution polymerization methods. In particular, PPTA is preferable from an industrial standpoint because it can be polymerized from simple monomers and is therefore inexpensive.

If the degree of polymerization of the polymer of the present invention is too low, a film with good mechanical properties cannot be obtained, so the logarithmic viscosity η1nh (100 m
Poly in j2? The degree of polymerization is selected to give a value of -0.5 g dissolved at 30°C).

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 films with an elongation smaller than 8% tend to tear easily and are not practical. The tensile elongation is preferably 10% or more. On the other hand, the PPTA film made by the method described in Japanese Patent Publication No. 55-14170 has a low elongation in the MD force direction of 4 to 6%.
However, 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 with a height of 0.06 to 0.25 μm formed from inorganic particles on the surface of the film.
There must be 10'pieces/mm''.

Here, on the surface of the protruding portion, the inorganic particles may be exposed, or the para-aromatic polyamide may cover the inorganic particles and the inorganic particles may be present inside. The height of the protrusion is 0.
If it exceeds 25 μm, the surface accuracy will be poor although the sliding properties will be good, so 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 0.06 μm, sufficient slipperiness cannot be obtained. There is a tendency for the slipperiness to improve as the number of protrusions increases, but 105 protrusions/m m2
If the number exceeds 105 pieces/m2, the slip property will not improve any further and troubles such as a decrease in stretchability will easily occur during manufacturing, so the number should be 105 pieces/mm2 or less.

On the other hand, if the number is less than 104 pieces/mm'', sufficient slipperiness cannot be obtained.

In the present invention, the shape of the protrusion is preferably spherical or cylindrical;
The presence of such homogeneous protrusions makes it possible to improve slipperiness while maintaining smoothness.

The inorganic particles used in the present invention are selected from those that are substantially inactive towards concentrated sulfuric acid, such as SiOz
, T i Ox , Ca304, etc. are used.

The shape of the inorganic particles is generally spherical, and for example, spherical SiO2 Seahoster KE (manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) obtained by emulsion polymerization is used.

The content of the inorganic particles is appropriately determined from both the performance of the film (slidability, mechanical performance, etc.) and the operability in film production (dope viscosity, 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/mm 2 or more. This condition is closely related to the deformation resistance of the film. The Young's modulus in at least one direction is preferably 1,300 kg/mm 2 or more, and most preferably 1,500 kg/mm 2 or more, which is related to jitter characteristics when used as a magnetic tape, for example. There are two aspects of the film of the present invention; one is a balance type in which the vertical and horizontal Young's moduli are approximately equal to 1000 kg/mm" or more, and the other is a balance type in which either the vertical or horizontal Young's modulus is It is a tensilized type that is thick and has a weight of 1000 kg/mm2 or more.

The films of the present invention are preferably thin films of about 12 μm or less. Particularly preferably, the thickness is 10 μm or less.

For example, when used as a videotape, the bulkiness per length increases in proportion to the thickness, so it meets the needs of being small, lightweight, and long in 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 1.3
It ranges from 70 to 1.420 g/ci. This density value was determined at 30°C by density gradient tube method using carbon tetrachloride-toluene.

This density range is 1 to 4 that of known PPTA fibers.
This value is considerably smaller than that of noni, which ranges from 3 g/ci to 1.46 g/cA. The density is 1.370
If it is less than g/crd, the mechanical properties will deteriorate and it will be 1.42
If it exceeds 0 g/ci, the film will have planar orientation and therefore will have poor isotropy in mechanical properties.

In any case, having such a low density results in a light and high-strength film.

Next, a method for obtaining such a para-aromatic polyamide film will be explained.

In the method of the present invention, it is first necessary to prepare an optically anisotropic dope of para-aromatic polyamide.

A suitable solvent for 3JIWing the dope used for molding the para-aromatic polyamide film of the present invention is sulfuric acid with a concentration of 95 or more. If the sulfuric acid content is less than 95% by weight, it may be difficult to dissolve the dope, or the dope may have an abnormally high viscosity 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 concentration of 100% by weight or more, from the viewpoint of stability and solubility of the polymer, the concentration should be 98 to 100% by weight.
Weight % concentrations are preferably used.

The polymer 4 degree in the dope used in the present invention is at room temperature (
A concentration that exhibits optical anisotropy at a temperature of about 20 to 30° C. or higher is preferably used, specifically about 10% by weight or more, preferably about 12% by weight or more. At a polymer concentration lower than this, that is, at a polymer concentration that does not exhibit optical anisotropy at room temperature or higher temperatures, the molded para-aromatic polyamide film often does not have desirable mechanical properties. The upper limit of the polymer concentration in the dope is not particularly limited; however, it is usually 20% by weight or less, and preferably 18% by weight or less for particularly high ηlnh para-aromatic polyamides, and more preferably 18% by weight or less. is 16% by weight or less.

In the present invention, the dope has an average particle diameter of 0.11 to 0.
．． It is necessary to add inorganic particles with a diameter of 50 μm, and particles having a spherical shape are preferably used.

When the average particle diameter is 0.50 μm or more, the film has large protrusions, which impairs smoothness, and when it is 0.11 μm or less, sufficient slipperiness cannot be obtained.

Inorganic particles can be added to sulfuric acid before adding para-aromatic polyamide, added at the same time as para-aromatic polyamide, added after forming an optically anisotropic dope, or added to some para-aromatic This can be carried out by any method such as adding after dissolving the group polyamide and then adding the remaining para aromatic polyamide. In order to prevent inorganic particles from agglomerating and improve dispersibility,
For example, one of the preferred embodiments is to use a homogenizer or a static mixer. In addition, in the case of a method in which inorganic particles are added after creating an optically anisotropic dope,
Prior to addition, it is preferable to remove as much insoluble dust, foreign matter, etc. as possible by filtration, etc., and to remove gases such as air generated or entrained during dissolution. Degassing can be carried out after preparing the dope, or it can be carried out in a vacuum (
This can also be achieved by conducting the process under reduced pressure.

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 in the range of 0.1 to 2% by weight, preferably 0.2 to 1% by weight, based on the para-aromatic polyamide.

The dope of the present invention may also contain other conventional additives, such as fillers, anti-glare agents, UV stabilizers, heat stabilizers, antioxidants, pigments, solubility aids, etc.

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. , depends on the polymer concentration, degree of polymerization of the polymer, content of non-solvent, etc., so by investigating these relationships in advance, an optically anisotropic dope can be created, and by changing the conditions for an optically isotropic dope, the optical It is possible to change from anisotropy 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 casting, it is important to set the discharge rate from the die such that the average shear rate when passing through the die is 50 seconds-1 or more. When the time is less than 50 seconds-1, irregularities often occur in the formation of protrusions, probably due to insufficient dispersion of the inorganic particles. The shear rate is preferably 100 sec-1 or higher.

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 do so.

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 can be surface finished, such as glass, Hastelloy, Kuntal, gold, platinum, etc.
Fully bent materials plated with titanium nitride or the like are preferably used, and these materials are particularly 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. Change the solubility and polymer concentration to transition to the optically isotropic region, or increase the temperature of the dope by heating to transition the dope phase to the optically isotropic region, or simultaneously or sequentially absorb moisture and heat. This can be achieved by using them together. In particular, methods that utilize moisture absorption, including methods that use heating in combination, are useful because they can efficiently achieve the optical isopotency ratio of optical anisotropy without causing decomposition of the para-aromatic polyamide.

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 atomized 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 preferable because it often contains large particles of condensed water. The suction field is usually room temperature to about 180°C, preferably 50 to 150°C.
This is done using humidified air.

In the case of a method using heating, the heating means is not limited to 1Y, and includes methods such as applying the above-mentioned stale and excited air to the casting dope, irradiating with an infrared lamp, and using dielectric heating.

The optically cast dope on the support surface then undergoes solidification. In the present invention, an aqueous sulfuric acid solution of 30% by weight or more can be used as the dope coagulation liquid. If the sulfuric acid aqueous solution is less than 30% by weight, 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 sulfuric acid 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 less, more preferably 0 to -40°C.

Since the coagulated film as it is contains acid, it is necessary to wash and remove the acid content 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 washing with water. Cleaning is carried out, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid.

The cleaned film then needs to be stretched in the wet state before being subjected to drying. Stretching is performed in two directions at a stretching ratio of 1.1 times or more. At this time, it is often observed that the moisture contained within the film comes out like sweat. The stretching ratio may be different in the MD force direction 1"D direction, but it is important to stretch at least 1.1 times or more in order to improve the surface precision of the film. Preferably 1.15 times or more. It is better to use a stretching ratio of

Stretching in two directions may involve simultaneous biaxial stretching, or sequential stretching in one direction.
It may be stretched axis by axis. Since the para-aromatic polyamide molecular chains can be oriented in the stretching direction by stretching, mechanical properties and surface precision are improved.

Drying must be carried out under tension, at a constant length, or with slight stretching so that the film does not shrink. If a film that has a tendency to shrink upon removal of the cleaning liquid (e.g. water) is dried without any shrinkage restriction, micro-inhomogeneous structure formation (crystallization, etc.) will occur, which may result in 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. There are no particular restrictions on other conditions for drying, and methods include methods using heated gas (air, nitrogen, argon, etc.) or room temperature gas, methods using radiant heat such as electric heaters and infrared lamps, and dielectric heating methods. The drying temperature can be freely selected, and the drying temperature is not particularly limited as long as it is at room temperature or above. 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. Although the maximum temperature for drying is not particularly limited, it is preferably 500'C or less in consideration of drying energy and decomposability of the polymer.

〔Example〕

Examples are shown below, but these examples are intended to illustrate the present invention, and are not intended to limit the invention. In addition, unless otherwise specified in the examples, weight parts or weight %
shows. The logarithmic viscosity ηinh is 98% sulfuric acid 100mf and poly? -0.5g was dissolved and measured at 30'C in a conventional manner.

The viscosity of the dope was measured using a B-type viscometer at a rotation speed of 1 rpm. The thickness of the film is 2 m in diameter.
Measurements were made using a dial gauge with a measuring surface of m. Strength and elongation and Young's modulus were measured by cutting a film sample into a rectangle of 100 mm x 10 mm using a constant speed extension type strength and elongation measuring machine, and drawing a load-elongation curve 5 times at an initial grip length of 30 mm and a tensile speed of 30 kites/min. , calculated 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 photograph taken at a magnification of 3500 times using a scanning electron microscope manufactured by JEOL Ltd., and calculating the number per mm''.

Example 1 5 in2 particles with a primary particle size of 0.20 pm were added to 99.6% sulfuric acid and stirred vigorously. PP of SiO□
The proportion to TA was set at 0.1% by weight. Next, PPTA having an ηin h of 5.8 was dissolved in this dispersion to give a polymer concentration of 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, to a die, through a 1.5m curved tube kept at about 70'C, and polished to a mirror finish from a die with a 0.15mm x 250a+m slit. The cast dope was cast onto a tantalum heddle at a shear rate of 750 seconds, and air at about 90°C with a relative humidity of about 85% was blown to make the cast dope optically isotropic. It was guided inside and solidified.

The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C. The washed film was stretched 1.15 times in the MD and TD using a tenter, and then dried with hot air at 200°C. It was heat treated at C. The results are shown in Table 1.

Example 2.3.4 and Comparative Example 1.2.3 Films were produced in the same manner as in Example 1 by changing the size and amount of SiOz particles added to the dope. Table 1 shows the results.

〔Effect of the invention〕

As shown in the examples, the film of the present invention has good mechanical properties such as high strength and high Young's modulus that are not found in commercially available films, and also has a surface with very good surface precision and easy to use. It also has a smooth surface. In addition to these properties, it also has excellent electrical insulation, heat resistance, oil resistance,
It has pressure resistance, resistance to chemicals other than strong acids, and a dense structure.

Therefore, the film of the present invention can be suitably used for insulating materials and magnetic tapes for electrical equipment that rotates at high speed, flexible printed wiring boards, tapes for thermal transfer printers, wire coating materials, filtration membranes, etc. Due to its excellent transparency, it is used as packaging materials, plate-making materials,
It is also useful for photographic films and the like.

In particular, the film of the present invention has a high Young's modulus, strong tear resistance, high slipperiness and smoothness, so it can be used for videotapes, computer tapes, audio tapes, floppy disks, various cards (telephones, train tickets, etc.). It is useful as a magnetic tape for things such as commuter passes, etc., and is particularly useful as a high-quality videotape with excellent image clarity and stability.

Claims (2)

[Claims] (1) A film made of para-aromatic polyamide with a logarithmic viscosity of 3.5 or more and a tensile elongation of 8 in all directions.
% or more, and the protrusions with a height of 0.06 to 0.25 μm formed from inorganic particles on the film surface are 10^4 to 1
A highly slippery polyamide film characterized by the presence of 0^5 pieces/mm^2. (2) A para-aromatic polyamide with a logarithmic viscosity of 3.5 or more, sulfuric acid with a concentration of 95% by weight or more, and an average particle diameter of 0.1 to 2% by weight relative to the para-aromatic polyamide.
An optically anisotropic dope consisting essentially of fine inorganic particles of 11 to 0.50 μm is applied onto the supporting surface while maintaining optical anisotropy so that the average shear rate is 50 seconds^-^1 or more. 30% by weight maintained at 10°C or less after casting and converting the dope to optically isotropic by moisture absorption and/or heating.
A method for producing a polyamide film, which comprises coagulating it in the above sulfuric acid aqueous solution, washing it, and drying it while stretching the film to 1.1 times or more.