JPH1149876A - Highly rigid heat-resistant aramide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject film capable of maintaining the flatness and straight property of the film and controlling the deterioration of mechanical and electrical properties and adhesivity due to moisture and heat and useful for magnetic tapes, etc., by reducing a washed and extracted chlorine content in a specific range. SOLUTION: This highly rigid and heat-resistant aramide film has a Young's modulus of 700-2500 kg/mm<2> and controlled to a washed extracted chlorine content of 0.001-8 ppm. The film is obtained e.g. by forming a film from an aramide by a dry method or a wet method. When an acid such as hydrogen chloride as a polymerization by-product or sulfuric acid as a solvent is left in the film, the film is neutralized and washed with an excessive amount of an alkali until to leave the solvent in an amount of <=1000 ppm. The film is further subjected to an ultrasonic washing treatment using >=50 deg.C hot water to reduce the washed and extracted chlorine content to a prescribed value, and subsequently subjected to a wet-drawing treatment at an orientation speed of <=50%/sec so as to give an area orientation ratio of 0.9-5.0 times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-rigid heat-resistant aramid film, and more particularly, to a high-rigid heat-resistant aramid film having excellent moisture and heat resistance because of special requirements as a film. is there.

[0002]

2. Description of the Related Art Aramid films are attracting attention as high-rigidity heat-resistant films having a high Young's modulus, such as magnetic tapes, ink sheets for printers, base films for solar cells, films for flexible printed wiring boards, and films for electrical insulation. Practical use has begun as an acoustic material.

In some of these applications, the aramid film may be used in a high temperature and high humidity environment, but the conventional aramid film may not be used in such an environment or / and after use in such an environment. -In many cases, the electrical properties are reduced, the adhesive strength to other materials is reduced, and the flatness and straightness of the film are often impaired, so that use of the film has been limited.

JP-A-50-102650 and JP-A-51-81854 disclose that the content of an ionic inorganic compound is reduced in order to obtain an aramid film having less curl, that is, good flatness. I have. However, these are related to flatness in a normal state, and are not intended to improve wet heat resistance. Actually, various heat treatments cause a large decrease in performance.

JP-A-63-141207 discloses a method for improving the heat resistance and tear resistance of an aramid film.
An aramid film in which the total content of chlorine chemically bonded to aramid and chlorine contained without chemical bonding is equal to or less than a specific value is disclosed. However, the films disclosed therein are not intended to improve the wet heat resistance, and in fact, have insufficient wet heat resistance.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a film in which the disadvantages of the conventional aramid film, in particular, the resistance to moisture and heat, have been eliminated, that is, even if the film itself is subjected to a wet heat treatment, the mechanical properties of the film itself are reduced. An object of the present invention is to provide a high-rigidity heat-resistant film in which the properties, electrical properties, and adhesion to other materials are hardly reduced, and the flatness and straightness of the film are maintained.

[0007]

The inventors of the present invention have studied from various viewpoints to solve this problem. As a result, the moisture and heat resistance strongly involves chlorine, which is often contained in a small amount in the aramid film. In particular, the present inventors have discovered an unexpected fact that the effect of a trace amount of chlorine not chemically bonded to the aramid molecule is large, and reached the present invention after further detailed investigation.

That is, according to the present invention, the Young's modulus is 700 to
A high-rigidity heat-resistant aramid film characterized in that the amount of chlorine extracted and washed in a 2500 kg / mm ² aramid film is 0.001 to 8 ppm. Hereinafter, the present invention will be described in detail.

The aramid used in the present invention is substantially composed of units selected from the group consisting of the following structural units. —NH—Ar ₁ —NH— (1) —CO—Ar ₂ —CO— (2) —NH—Ar ₃ —CO— (3) where Ar ₁ , Ar ₂ and Ar ₃ are at least one aromatic ring And may be the same or different. Representative examples thereof include those represented by the following formula.

[0010]

Embedded image

[0011] Further, those in which a part of hydrogen on the ring of these aromatic rings is substituted with a halogen group, a nitro group, an alkyl group, an alkoxy group or the like are also included. X is -O-,
—CH ₂ —, —SO ₂ —, —S—, —CO— and the like.
In particular, an aramid in which 80 mol% or more of all the aromatic rings are bonded at the para position is preferable.

The aramid film of the present invention may contain a lubricant, an antioxidant, other additives, etc. as long as the physical properties of the film are not impaired or the object of the present invention is not adversely affected, that is, unless a chlorine compound is contained. , And other polymers may be included. The Young's modulus of the film of the present invention is 700 to 2
Should be 500 kg / mm ² , preferably 900 to
2500 kg / mm ² . Young's modulus is 700kg /
This is because a film having a size of less than mm ² is no longer a film in the category of a highly rigid film. On the other hand, 25
This is because an aramid film exceeding 00 kg / mm ² is easily torn and brittle, and its usefulness as a film is reduced.

The film having a high Young's modulus of the present invention can be realized by increasing the number of para-oriented components in the molecular structure and by applying a relatively high stretching ratio at the time of production to make the molecular chains highly oriented. The present invention can be applied not only to a so-called balance type in which the physical properties are constant in all directions in the film plane, but also to a tensile type in which the length direction or the width direction is reinforced.

In the present invention, it is important that the amount of chlorine contained in the film to be washed and extracted is 0.001 to 8 ppm. Here, the chlorine extracted by washing is chlorine that is not chemically bonded to the aramid polymer, and is the chlorine present in the film in the form of hydrogen chloride, sodium chloride, lithium chloride, calcium chloride, magnesium chloride, etc. Refers to the total amount. Aramid is generally obtained by a polycondensation reaction of by-produced hydrogen chloride from an aromatic diamine and an aromatic dicarboxylic acid chloride, so that hydrogen chloride is separated by ordinary industrial neutralization, washing and extraction after the reaction is completed. ,
Chlorine remains unavoidable even after removal, about 20 ppm
It is extremely difficult to achieve the following non-polymerizable chlorine content: For this reason, it is necessary to perform a special treatment described later in order to make the chlorine content in the above range that is extracted by washing. If the chlorine content of the film to be washed and extracted exceeds 8 ppm, the wet heat resistance of the film is extremely reduced. That is, when the film is subjected to wet heat treatment, for example, 50 ° C., 8
When left at 0% RH for 1 week or at 100 ° C. and 90% RH for 1 day, the mechanical properties of the treated film are reduced, the adhesive strength is reduced, the flatness (flatness) is deteriorated, and the linearity is reduced. Deterioration (curvature of the film) and the like occur.

[0015] The upper limit of the chlorine content of the film to be washed and extracted is preferably 5 ppm. The lower the chlorine content of the film extracted and washed, the better the moist heat resistance, but the lower limit is set at 0.0 from the limit of industrial practice.
01 ppm. The film of the present invention preferably has a density in the range of 1.40 to 1.47 g / cm ³ in order to further increase the wet heat resistance. In the aramid film, having a density in this range means that the film is highly crystalline and dense. The density can be measured, for example, by a so-called density gradient tube method at 25 ° C. in carbon tetrachloride / toluene. In fact, all the films of Examples of the present invention described below have a density of 1.41 to 1.46 g / cm ³ . Had a density.

It is preferable that the variation in the density of the film be 0.01 or less in order to keep the flatness of the film after the wet heat treatment in a good state. The density varied from 0 to 0.01 g / cm ³ . The variation in density is defined as the difference between the maximum value and the minimum value at 10 measured values measured at an arbitrary position on the film.

According to the present invention, the average thickness is about 1 to 1000 μm.
However, the ratio of the thickness variation to the average thickness is preferably 0 to 5%. More preferably, this ratio is 0-4%. If the ratio exceeds 5%,
This is because, when the film is wound up in a roll, the winding appearance of the film becomes poor, and the release itself from the roll and the workability of the film after the release become poor.

The film of the present invention preferably has a thickness of 30 to
It has a strength of 80 kg / mm ² , which is considerably higher than that of a general film, and is one of the features related to a high-rigidity film. The films of the present invention also preferably have an elongation of 15 to 100%.
This is because films with an elongation of less than 15% are often found to be brittle. On the other hand, it is generally desirable that the elongation is large.
% Is the upper limit. The elongation can be achieved by adjusting the degree of polymerization, the degree of stretching orientation, the degree of crystallization, and the like of the polymer.

The film of the present invention further preferably has a coefficient of hygroscopic expansion in the film surface direction of 0 to 40 ppm /% RH, more preferably 0 to 25 ppm /% RH. If the coefficient of hygroscopic expansion in the direction of the film surface is too large, the dimensional change with respect to the change in humidity increases, which is not preferable because the handling of the film, the processability, and the performance in each application change.

It was also found that the coefficient of hygroscopic expansion in the film thickness direction is preferably 0 to 600 ppm /% RH. More preferably, 0 to 500 ppm
/% RH. If the coefficient of hygroscopic expansion in the thickness direction of the film is too large, the rolled form of the film may be poor, resulting in poor flatness and poor workability of the film. The reduction of the coefficient of hygroscopic expansion can be achieved by selecting the type of polymer, adjusting the degree of stretching orientation, the degree of crystallinity, and the polymer end group.

The film of the present invention preferably has a heat shrinkage at 200 ° C. of 0 to 0.5%. The reason is that if the heat shrinkage is large, the flatness of the film may be reduced when the film is subjected to a high-temperature history in the film processing step or the like. The reduction of the heat shrinkage rate depends on the choice of polymer type,
This can be achieved by heat setting or the like. Further, it is desirable that the variation in the heat shrinkage is not more than 0.1% in order to maintain the uniformity and flatness of the film after the wet heat treatment at a favorable level. The variation in the heat shrinkage is defined by the difference between the maximum value and the minimum value of 10 points measured at an arbitrary position on the film. In order to reduce the variation in the heat shrinkage, it is important to suppress the fluctuation in the width direction and the time in the process conditions of stretching, drying, heat treatment, and heat setting in the film manufacturing process.

The film of the present invention preferably has a coefficient of dynamic friction with a metal mirror surface in the range of 0.02 to 0.25,
More preferably, it is 0.02 to 0.15. If the coefficient of friction is too small, handling in the processing step becomes unstable, and if it is too large, wrinkling, distortion and damage are increased in the processing step. Adjustment of friction coefficient depends on the amount of lubricant
This can be achieved by selecting the type, particle size, degree of dispersion, etc., and preferably 0.01 to 3% by weight of a lubricant is added.

The film of the present invention further comprises IEC-11
2 has a tracking resistance (CTI) of preferably 200 to 1,000. This indicates that the electrical insulation is excellent even in an ionic environment. The film of the present invention preferably has a thickness of 0.1 mm.
Substantially no surface coarse protrusions having a height of 8 μm or more. This characteristic of the film can be achieved by selecting the particle size and dispersity of the lubricant.

The method of producing the film of the present invention is not particularly limited, but it is necessary to satisfy the requirement of increasing the Young's modulus and taking special measures to reduce the chlorine content which can be extracted by washing. . As for aramid, if it is soluble in an organic solvent, it is polymerized directly in a solvent, or once a polymer is isolated and redissolved to form a solution, and then formed into a film by a dry method or a wet method. Those which are hardly soluble in an organic solvent such as paraphenylene terephthalamide (PPTA) are dissolved in concentrated sulfuric acid or the like to form a solution, and then formed into a film by a dry method or a wet method.

In the dry method, the solution is extruded from a die, cast on a support such as a metal drum or an endless belt, and the solvent is removed until the cast solution forms a self-supporting film. In the wet method, the solution is extruded directly from a die into a coagulating liquid, or cast on a metal drum or an endless belt as in the dry method, and then coagulated in the coagulating liquid. If the polymer solution is optically anisotropic, it needs to be converted to an optically isotropic solution before solidifying the polymer solution. If the film is coagulated with the optical anisotropy remaining, the resulting film tends to tear in one direction and cannot be used as a film. Conversion to optical isotropicity is preferably performed after casting on a support.

In both the dry method and the wet method, a solvent, an inorganic salt, and the like in the film are washed, and a process such as stretching, drying, and heat treatment is performed. In obtaining the film of the present invention, the film washing step is important. Since aramid is a highly polar polymer, ionic compounds and low-molecular organic polar compounds are easily coordinated.
This is because it is difficult to reduce the residual amount to 0 ppm or less. In the study of the present inventors, the film of the present invention was obtained only by combining a special washing method.

That is, when hydrogen chloride as a by-product of the polymerization remains or / and when an acid such as sulfuric acid is used as a solvent, it is important to first make the neutralization with an alkali in excess of the equivalent amount. is there. In addition, about 1000
After the residual solvent amount becomes less than ppm, it is necessary to thoroughly reduce the residual amount of solvent, salt, alkali, etc. by washing with hot water of 50 ° C. or more and washing while applying ultrasonic waves. It is. However, a method other than the above method is not excluded.

After the washing is completed, the film is wet-drawn. In order to secure the Young's modulus of the film of the present invention, in any of the film forming methods, the area stretching ratio is 0.9.
It is preferably set to be up to 5.0 times, more preferably 1.
It is 0 to 4.0 times. At an area stretch ratio of less than 0.9,
The Young's modulus becomes insufficient. In order to reduce the variation in the density of the film and to improve the flatness and uniformity of the film after the wet heat treatment, the stretching speed is preferably set to about 50% / second or less.

Drying and heat treatment are generally performed at 100 to 600
It is performed under heating conditions of ° C. Of these, drying and heat treatment are preferably performed separately. When the film is dried, if it is heated too rapidly, voids are formed in the film, resulting in a decrease in surface smoothness and a decrease in elongation at break, resulting in a decrease in flatness and linearity due to an increase in density variation of the film. 100-300 ° C, especially 1
It is preferable to carry out under heating conditions of 50 to 250 ° C. The heat treatment of the film is preferably performed at 300 to 550 ° C. for the purpose of improving Young's modulus and thermal dimensional stability. As the heat treatment method, any of a contact type and a non-contact type may be used,
For example, a method of contacting a roll with temperature control,
Infrared heating, a method of heating in a non-contact manner between plate heaters, and the like are available.

The film of the present invention may be subjected to a modification treatment on the film surface in order to improve the affinity and adhesion between the film surface and other materials. As the surface modification treatment,
Corona discharge treatment, plasma treatment and the like are known. In order to improve the slipperiness of the films or to prevent the blocking phenomenon, a method of mixing fine particles into the film is usually employed, and the fine particles are also referred to as a lubricant. The fine particles include organic compounds and inorganic compounds. Usually, for example, SiO ₂ , TiO ₂ , ZnO, Al ₂ O ₃ , CaSO ₄ , B
aSO ₄ , CaCO ₃ , carbon black, zeolite,
Other inorganic compounds such as metal powders are used, but what is important is that they contain substantially no chlorine compounds. . The particle size is 0.01 to 2 μm, and the amount added is 0.03 to
It is often chosen as 5% by weight. That is, it is produced by mixing the fine particles in an aramid solution and forming a film of the solution. At this time, in order to improve the dispersion of the fine particles, a homogenizer of an ultrasonic system or a stirring system is preferably used.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the measuring method of the characteristic value in an Example is as follows. (1) Method of measuring film thickness, strength, elongation and Young's modulus The film thickness is measured with a dial gauge having a measurement surface of 2 mm in diameter.

The strength, elongation and Young's modulus are constant-speed elongation
Using a measuring machine, measuring length 100mm, pulling speed 50mm
/ Min, measured in the longitudinal direction of the film and its right angle
Expressed as the average value with the direction. (2) Method of measuring heat shrinkage A 2 cm × 5 cm sample piece was cut out from a film and
Scratches 5mm and 45mm from one end of the test piece with a blade
Attach it as a label and put it in advance in an atmosphere of 23 ° C. and 55% RH.
After standing for 72 hours, the distance between the signs (L₀)
And a hot-air oven at 200 ° C
And left at 23 ° C.
After leaving for 72 hours in an atmosphere of 55% RH,
Distance (L ₁) Is measured with a “reading microscope”
Shrinkage (%) = ｛(L₀-L₁) / L₁｝ × 100
Was. Variations in heat shrinkage can be arbitrarily sampled from the film.
Difference between maximum and minimum values for 10 ringed samples
Indicated by

(3) Method for measuring the amount of chlorine extracted by washing The film was cut into pieces, placed in a Soxhlet extractor, and subjected to Soxhlet extraction with ion-exchanged water for 3 hours.
It was quantified by ion chromatography manufactured by NEX. (4) Method for measuring coefficient of hygroscopic expansion in the film surface direction Thermodynamic property measuring instrument (TMA, TM7 manufactured by Vacuum Riko Co., Ltd.)
000 type), a sample with a width of 5 mm was attached, and a load of 0.
Under 3 g, the temperature was once raised to 300 ° C., then cooled under a dry nitrogen stream, the humidity change between dry nitrogen and air at 23 ° C., and the dimensional change of the film were measured and calculated by the following formula, I asked.

[(F _A −F _N ) / F _N ] × [1 / (M _A −M _N )] where F _A = dimension of film in air F _N = dimension of film in dry nitrogen M _A = Humidity of air M _N = Humidity of dry nitrogen (5) Measurement method of tracking resistance (CTI value) According to IEC-112, a NH ₄ Cl aqueous solution is dropped on a film to which voltage is applied stepwise in advance, and tracking is performed. The maximum applied voltage at which the number of drops indicating destruction became 50 or more was determined and defined as the CTI value.

(6) Method of Measuring Moisture Heat Resistance As a wet heat treatment, the film was allowed to stand in an atmosphere of 50 ° C. and 80% RH for 7 days, and the film characteristics before and after that were compared. (7) Method of measuring adhesive strength A film subjected to corona discharge treatment was dried at 150 ° C. for 3 minutes, and then a copper-clad laminate was prepared using a copper foil having a thickness of 35 μm and an adhesive (TB1650 manufactured by Three Bond Co.)
Cured for 2 hours at 150C and then for 3 hours at 150C. This sample was cut to a width of 1 cm, and a tensile tester was used to obtain a tensile speed of 50 cm.
Peeling was performed at 180 ° at mm / min, and the resistance was defined as the adhesive strength.

(8) Evaluation of flatness When the film was spread on a horizontal surface and lightly tensioned by hand, the film was compared with the flatness relative to the film. △, those with large undulations were represented by ×. (9) Method of measuring linearity A film having a length of 1 m is sampled in the longitudinal direction, placed on a horizontal plane, and a line segment between adjacent curved vertexes in the longitudinal direction caused by the curvature of the film is drawn. Measure the maximum distance that the minute deviates from the arc inside the curve. This was performed between all adjacent vertices, and the maximum value was defined as the amount of film bending. The intuition of the film is represented by a small amount of bending.

[0037]

Comparative Example 1 Example 1 of JP-A-63-141207 was additionally tested. 11. Polybaraphenylene terephthalamide (PPTA) in 99.1% sulfuric acid with a polymer concentration of 12.
Dissolved at 5% to obtain a dope having optical anisotropy at 70 ° C.
Vacuum degassed for 5 hours. The dope kept at 70 ° C. was cast from a die having a slit of 0.6 mm at an ejection linear speed of 3.5 m / min onto an endless belt made of mirror-polished tantalum, and blown with air at 85% relative humidity and 90 ° C. Then, the casting dope is made optically isotropic and, together with the belt,
The solution was introduced into a 30% aqueous sulfuric acid solution at 5 ° C. for coagulation.

Next, the coagulated film was peeled off from the belt and washed by running in hot water at 40 ° C. The washed film is guided to a tenter and shrunk to 90% in both the running direction of the film and the direction perpendicular to the running direction.
It was dried with hot air at 0 ° C., and was heat-treated by contacting with a hot plate at 280 ° C. at the exit of the tenter. The film thus obtained was designated as Film A, and the properties thereof are shown in Table 1.

Next, the properties of the film obtained by setting the slit of the die to 0.8 mm and performing drying under stretching of 1.05 times as Film B are shown in Table 1.

[0040]

Example 1 PPTA was dissolved in 99.8% sulfuric acid so as to have a polymer concentration of 12%, and cast on an endless belt from a die having a slit interval of 0.3 mm.
In the sulfuric acid, 0.04 μm silica particles were previously dispersed by an ultrasonic stirrer so as to be 0.3% by weight with respect to PPTA. Moisture absorption treatment at the same time as heating on the belt,
After inverting the dope from the liquid crystal phase to the isotropic phase, 45 ° C.
Coagulated in 5% sulfuric acid. The film drawn from the coagulation bath is immersed in an aqueous solution of caustic soda to neutralize excessively until the pH becomes about 8, and then washed with water to obtain a pH of 7.0 to 7.0.
After being adjusted to 7.1, washing was further performed while applying ultrasonic waves in hot water at 60 ° C.

Next, the wet film is moved in the longitudinal direction by 1.1.
After stretching twice, it was stretched transversely to 1.1 times by a clip tenter, and then dried with hot air at 150 ° C. while maintaining a constant length state.
After a tension heat treatment at 400 ° C. and a free heat treatment at 300 ° C., it was rolled up. Here, the stretching speed is about 20
% / Sec. In order to prevent temperature unevenness of 5 ° C. or more from occurring in the width direction of the film during transverse stretching and drying, the cooling and heating of the tenter clip are sufficiently performed with a specially added device. In order to prevent the temperature distribution of the heater from having a difference of 5 ° C. or more between the center portion and the end portion, heat retention was added to prevent heat radiation at the end portion.

P obtained in a width of 500 mm and a length of 300 m
The PTA film had an average thickness of 25 μm, and there was almost no difference in physical properties in the longitudinal direction and the width direction, as shown in Table 1. Compared to the film of Comparative Example 1, the amount of chlorine extracted and washed was significantly smaller, and the film properties were not substantially reduced by the wet heat treatment.

[0043]

[Table 1]

[0044]

Example 2 Example 1 was the same as Example 1 except that the slit interval of the die was 0.1 mm, the stretching ratio was 1.2 in both length and width, and the stretching speed was changed to about 35% / sec. did. The physical properties of the obtained film were balanced vertically and horizontally, and as shown in Table 2, the amount of chlorine extracted and washed was extremely small, and there was no problem with the heat and humidity resistance.

[0045]

Comparative Example 2 In Example 2, neutralization with caustic soda and irradiation with ultrasonic waves were stopped, and washing with water at room temperature was carried out.
Thoroughly performed so as to be 6.9 or more, and the other steps were the same as in Example 2. Table 2 shows the physical properties of the obtained film.
As shown in the figure, elongation, adhesive strength, straightness, etc. were considerably reduced by the wet heat treatment.

[0046]

EXAMPLE 3 Polyparaphenylene-2-chloroterephthalamide (PPClTA) was added at a polymer concentration of 13% by weight.
And cast on an endless belt from a die with a slit spacing of about 0.4 mm. For concentrated sulfuric acid, fine titanium oxide particles of 0.02 μm
A was dispersed by an ultrasonic dispersing machine so that the content of A was 0.2% by weight. The same operation as in Example 1 was performed to prepare a film.

A film having balanced properties in the vertical and horizontal directions was obtained, and is shown in Table 2.

[0048]

[Table 2]

[0049]

According to the present invention, it is possible to obtain an aramid film having no performance deterioration even when subjected to a wet heat treatment. That is, the conventional aramid film not only deteriorates mechanical properties such as high elongation, electric insulation, adhesive strength, etc., but also reduces flatness and straightness of the film due to wet heat treatment. However, the film of the present invention has eliminated such disadvantages.

Therefore, when the film of the present invention is used for a base film of a magnetic tape, an ink sheet for a printer, a solar cell substrate, a base film for a flexible printed wiring board, an acoustic material, an electric insulating material, etc. Even in harsh usage environments, the reliability as a material is far superior to conventional aramid films, and coupled with the inherent properties of aramid films, such as high heat resistance, high Young's modulus, and good dimensional stability, Very useful for applications.

Claims (1)

[Claims] 1. A Young's modulus of 700 to 2500 kg / mm
^2. The high-rigidity heat-resistant aramid film according to ² , wherein the amount of chlorine extracted by washing is 0.001 to 8 ppm.