JPH02222430A - Microcellular aromatic polyamide film - Google Patents

Abstract

PURPOSE:To obtain the subject film, having continuous micropores with specific values or below of humidity expansion coefficient and shrinkage stress in the longitudinal direction of the film and hardly any dimensional change, excellent in heat, chemical resistance, etc., and useful as electrolytic capacitors, etc. CONSTITUTION:The objective film, obtained by dissolving 2-40wt.% aromatic polyamide consisting of a polymer preferably containing >=50mol% recurring units expressed by the formula (p+q>=1), etc., and 0-100wt.% (based on the polymer) inorganic salt (e.g. calcium chloride) in an aprotic polar solvent (e.g. dimethylformamide) to provide a film-forming stock solution, regulating the resultant stock solution so as to afford 100-10000P viscosity, casting the regulated solution onto a support, such as a metallic drum, longitudinally drawing the film in water at 0 to <=90 deg.C by a wet film-forming method (preferably in a water bath) to prepare a microporous film and having <=50X10<-6>cm/cm/% RH humidity expansion coefficient and <=2kg/mm<2> shrinkage stress in the longitudinal direction thereof within a temperature range of 100-300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a microporous aromatic polyamide film having excellent heat resistance, humidity stability, and chemical resistance.

[Conventional technology] Polyolefin-based films such as polypropylene are known as microporous films, but they have poor heat resistance and chemical resistance, and their dimensions at higher temperatures are increasing year by year when used as separators in electrolytic capacitors, for example. Stability has been required, and problems have arisen with these films, such as a lack of long-term reliability due to film deterioration due to changes over time.

Aromatic polyamide film is known as a film that is excellent in both heat resistance and chemical resistance, and a method for producing porous aromatic polyamide film was also published in Japanese Patent Publication No. 1983-
14494 and 59-36939.

[Problems to be Solved by the Invention] However, there is a tendency for electrolytic capacitors to be used at higher temperatures, and even films produced by this method have insufficient heat resistance.
When used as a separator for electrolytic capacitors, it lacks long-term stability as it tends to curl or sag, resulting in conductivity. Furthermore, it has become clear that they have large humidity expansion coefficients and moisture absorption rates, lack dimensional stability, and cannot be used in applications that use aqueous electrolytes.

An object of the present invention is to provide a microporous aromatic polyamide film that has excellent heat resistance, chemical resistance, and humidity dimensional stability.

[Means for Solving the Problems] The present invention provides an aromatic polyamide film having continuous micropores, the film having a humidity expansion coefficient of at least 50 in the longitudinal direction.
The present invention relates to a microporous aromatic polyamide film having a shrinkage stress of 2 kg/mm2 or less in a temperature range of 100 to 300° C. in at least the longitudinal direction.

The aromatic polyamide of the present invention is preferably a polymer containing 50 mol% or more of repeating units represented by the general formula %.

Here, Arl and Ar2 contain at least one aromatic ring and may be the same or different, and representative examples thereof include the following.

It also includes those substituted with substituents such as a halogen group (especially chlorine), a nitro group, an 01-C1 alkyl group (especially a methyl group), and a C□-C5 alkoxy group. Also, X is
-0--CH2- -5o2-, -s-, -co-, etc. These may be included alone or in copolymerized form.

Polymers having an alkyl group or -CH2- are preferred because their solubility in a polymer solution is improved over those without substituents, their compatibility with inorganic salts is good, and very fine pores can be obtained. Moreover, those having a halogen group are particularly preferable because they have a low moisture absorption rate.

For example, (here I)+Q≧1) Also, if some of the hydrogens on the aromatic rings are (here Q=O~4) (here q=-Q~4), etc., 50 mol % or more.

The present invention comprises 50 basic structural units represented by the above general formula.
It is necessary to contain at least 70 mol%, preferably at least 70 mol%. If it is less than the above range, the heat resistance will deteriorate and the object of the present invention cannot be achieved. The copolymerization component of less than 50 mol% is not particularly limited, and may contain ester bonds, urethane bonds, imide bonds, heterocyclic bonds, and the like. In order to obtain a film with excellent mechanical properties and heat resistance, the intrinsic viscosity of the polymer (0.5 g of the polymer is dissolved in 100 ml of N-methylpyrrolidone containing 2.5% by weight of lithium bromide at 30° C. The value measured in ) is preferably 0.5 to 6.0.

Further, the aromatic polyamide of the present invention may be blended with lubricants, antioxidants, other additives, and other polymers to the extent that the physical properties of the film are not impaired.

The microporous film of the present invention has a pore diameter of 0.1 nm or more and 100 μm or less, preferably 1 nm or more and 10 μm or less,
The porosity is 20% or more and 90% or less. Continuous pores mean that pores are continuous on the front and back sides of the film, and mean that the liquid paraffin permeation time is 0.5 seconds or more and 5 seconds or less.

In addition, the microporous film of the present invention must have a humidity expansion coefficient of 50 X 10-6 cm/cm/%RH or less in the vertical direction, and a humidity expansion coefficient of 20 X 10-6 cm/cm/%R.
H or less is preferable. If it is larger than this, for example, when the film is used in a wound manner, the film may be wrinkled due to changes in humidity, causing deterioration of electrical characteristics.

Further, the moisture absorption rate of the film is preferably 5% or less, more preferably 4% or less. If it is larger than this, the electrical characteristics will deteriorate due to the influence of moisture.

Further, the shrinkage stress in the temperature range of 100 to 300°C in the longitudinal direction at least needs to be 2 kg/mm' or less. If it is larger than this, the film will wrinkle when used at high temperatures, deteriorating its electrical properties. Preferably l k
g/mm2 or less. Also, the coefficient of thermal expansion is 5 x
l Q-6cm/cm/℃ or more 50X10-6cm/c
The temperature is preferably 0+/°C or lower. Outside this range, the film will wrinkle due to temperature changes, deteriorating its electrical properties, and if it is wound with metal foil such as aluminum foil, the difference in thermal expansion coefficient will be too large, causing wrinkles. Further, the heat shrinkage rate at 250°C in at least one direction is preferably 5%.
It is preferably 2% or less. If it is larger than this, the dimensional change will be large when used at high temperatures and the electrical characteristics will deteriorate.

Furthermore, the strength of the film is preferably 3 kg/mm2 or more in at least one direction, more preferably 5 kg/mm2.
It is 2 or more. The elongation is preferably 5% or more in at least one direction, more preferably 10% or more.

Further, since the film of the present invention has high strength, it can be easily made into a thin film, and the film thickness can be 3 μm or more, and preferably 5 μm or more and 500 μm or less.

The film obtained by the present invention preferably has a strength retention rate of 80% or more when immersed in a 10% by weight NaOH aqueous solution at 25° C. for 5 days.

Next, the manufacturing method will be explained. The film of the present invention is produced by adding an inorganic salt to the polymer in a solution of an aromatic polyamide.
~100% by weight is present, and this solution (film forming stock solution) is formed by wet film forming. First, regarding the membrane forming stock solution, the solvent is preferably an aprotic polar solvent such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, hexamethylphosphoramide, and the like. Preferred inorganic salts include calcium chloride, lithium chloride, and magnesium chloride. As the film-forming stock solution, a solution obtained by dissolving the above-mentioned aromatic polyamide in the above-mentioned aprotic polar solvent at a concentration of 2% by weight or more and 40% by weight or less can be used. The solution may be used as it is synthesized in an organic polar solvent, or it may be isolated and redissolved. For example, when it is obtained from the reaction of acid chloride and diamine, it can be synthesized by solution polymerization in an aprotic organic polar solvent such as N-methylpyrrolidone, dimethylacetamide, or dimethylformamide, or by interfacial polymerization using an aqueous medium. be done. Hydrogen chloride is produced as a by-product when acid chloride and diamine are used as monomers in the polymer solution. To neutralize this, an inorganic neutralizing agent such as calcium hydroxide or an organic neutralizing agent such as ethylene oxide is used to neutralize the hydrogen chloride. Add. Further, the reaction between isocyanate and carboxylic acid is carried out in an aprotic organic polar solvent in the presence of a catalyst. A poor solvent may be added to the film-forming stock solution to the extent that the polymer does not precipitate.

This may allow the pore diameter to be controlled. Examples of the poor solvent in this case include, but are not limited to, water, methanol, ethanol, chloroform, and the like.

Next, a microporous film is produced by a so-called wet film forming method. The wet bath may be one in which the polymer is insoluble and the solvent is soluble, but water is usually preferred from the viewpoint of ease of handling.

The water bath may also contain an inorganic salt such as lithium chloride or other water-soluble solvent. Thereby, the pore diameter and porosity can be controlled. This film-forming stock solution is cast onto a support such as a metal drum or an endless metal belt and introduced into the water together with the support, or it is immediately immersed vertically into the water from a nozzle above the water or the water surface. Stretch 1.01 to 185 times in the direction.

Thereby, the shrinkage stress and humidity expansion coefficient can be set within the desired range. Thereafter, if an inorganic salt is added, water is passed through the film until the inorganic salt is completely removed from the film and until the residual rate of the aprotic polar solvent becomes 5% or less. The water temperature is preferably 0°C or more and 90°C or less, and more preferably 20°C or more and 80°C or less. Pore diameter and porosity can also be controlled by changing the water temperature. after that,
Drying, stretching, relaxing, and heat treatment are performed in the same way as in normal film formation. These treatments are generally carried out at temperatures between 100 and 500°C.
It will be held in By longitudinally stretching in water, the pore diameter can be changed, and the amount of residual inorganic salt can be reduced to 10 ppm or less. The viscosity during film formation is 100~
It is preferable to adjust the polymer concentration and temperature of the film-forming stock solution so that the poise becomes 100 poise. The viscosity here refers to a value measured using a rotating B-type viscometer under the same conditions (concentration, temperature) as during film formation.

When cast onto a support such as a metal drum or an endless metal belt, it may be dried here and then introduced into water. At this time, it is necessary to control so that the solvent does not suddenly scatter and cause surface roughening, and the treatment is generally carried out at room temperature to 300°C, preferably 50 to 250°C, within 60 minutes. Stretching or relaxing is performed at an area magnification of preferably 0.8 to 5.0 times, more preferably 1°1 to 3.0 times.

The areal magnification is the product of the stretching ratio in the longitudinal direction (MD force direction) of the film and the stretching ratio in the transverse direction (TD force direction).

The pore diameter can also be freely changed by adjusting the surface magnification.

[Method for evaluating properties] (1) Mechanical properties (strength, elongation) The specimen was set in a tensilon type tensile tester according to ASTM-D-882 with a test width of 10 mm and a test test of 50 mm, and pulled at a pulling speed of 300 mm/min. Measure the strength and elongation when the film breaks. Atmosphere is 25℃, 55
%RH.

(2) Heat shrinkage rate A film was cut out to a test width of 10 mm and a test width of 200 mm, heated in an oven at 250° C. for 10 minutes, and then the test piece was taken out and allowed to cool, and then calculated using the formula below.

Heat shrinkage rate (%) = (length after heating - trial) / trial × 10
0 (3) Shrinkage stress A sample was cut out with a trial width of 10 mm and a trial width of 100 mm, and an initial load of 0.25 kg/mm2 was applied.
Keep it at a constant length. Heat this in a heating furnace at a heating rate of 10℃/min for 2 hours.
Raise the temperature to 50°C and write the stress on a chart. Determine the shrinkage stress with the zero point before applying the initial load.

(4) Coefficient of thermal expansion In order to eliminate the effects of thermal contraction and moisture absorption and desorption, the film is
80-15 when heated to 0℃ and gradually cooled.
Calculated from dimensional changes in the 0°C region. The amount of dimensional change was measured using a thermomechanical analyzer (TMA).

(5) Humidity Expansion Coefficient Set in a constant temperature and humidity chamber with a trial width of 1 cm and a trial width of 15 cm, dehumidify to a constant humidity (approximately 30% RH), and after the film length becomes constant, humidify (approximately 80% RH). %RH), it begins to elongate due to moisture absorption. After about 24 hours, moisture absorption reaches equilibrium and film elongation also reaches equilibrium. Calculate from the amount of elongation at this time using the formula below.

Humidity expansion coefficient (cm/cm/%RH) = Amount of elongation/(Attempt x Humidity difference) (6) Cut the moisture absorption film to approximately 100 mm x 100 mm, and
After dehumidifying by heating in an oven at 50°C for 1 hour, the temperature is lowered in a dry desiccator, and the weight after dehumidification is measured. This film is 75
After being left in %RH for 48 hours, the sample was taken out, the weight after saturation was measured, and the weight was calculated using the following formula.

Moisture absorption rate (%) = (Weight at moisture absorption - Weight at dehumidification) / Weight at dehumidification x 100 (7) Porosity Sample (10 x 10 cm) was immersed in liquid paraffin for 24 hours, and the liquid paraffin on the surface layer was immersed in liquid paraffin for 24 hours. Calculate the weight after wiping thoroughly and the weight before soaking using the formula below.

Porosity (%) = (weight after immersion - weight before immersion) / (apparent volume x density of liquid paraffin) x 100 (8) Pore diameter mercury porosimeter (M I CROMERI T I
C8 company PORE 5IZER9300) i, :, J
: The distribution of pore diameters was measured, and the number average was taken as the pore diameter.

(9) Liquid paraffin permeation time Using liquid paraffin with a viscosity of 77 ± 1 centistokes at 37.8°C as specified in JIS K 9003, after holding the liquid paraffin and sample at an ambient temperature of 25°C for 24 hours, Place the sample on a horizontal surface,
Add liquid paraffin from a height of 5 to 20 mm above the sample.
,03-0.06g is allowed to fall naturally. At this time, the time from when the liquid paraffin comes into contact with the sample surface until it passes through the sample surface and wets the opposite surface is measured, and this is defined as the liquid paraffin permeation time.

(10) Chemical resistance (strength retention) After being immersed in a 10% by weight NaOH aqueous solution at 25° C. for 5 days, the strength is measured using the method described above and calculated using the formula below.

Strength retention rate (%) = Strength after immersion / Strength before immersion x 10
(11) Element winding test method A sample film is slit to a width of 4 mm, and anode chemical aluminum foil and cathode aluminum foil are alternately stacked on the sample film to produce an element winding. After storing this element roll at 200° C. for 24 hours, the sample film was unwound and observed. The evaluation was based on the following criteria.

・Those with no change at all 20.Things that have changed to the extent that there is no practical problem: ○・Things that have wrinkles in the film or aluminum foil that may pose a practical problem: X [ Effects of the Invention] The microporous film obtained by the present invention has a small humidity expansion coefficient and moisture absorption rate, so when used for batteries, electrolytic capacitors, separators for electric double layer capacitors, etc., dimensional changes are small even in a humid atmosphere. Since wrinkles do not occur, there is no deterioration in performance, and even when the film is stored in roll form for a long period of time, it can maintain a good rolled shape. This is particularly effective when an aqueous electrolyte is used, such as in nickel-cadmium batteries. Furthermore, because the shrinkage stress at high temperatures is small, even when used at high temperatures of 100°C or higher,
Since wrinkles do not occur, there is no deterioration in performance, making it particularly effective. It also has excellent mechanical properties and can be made into a thin film, which has the effect of making it more compact for the above-mentioned applications. Furthermore, it exhibits excellent properties in microfilters, moisture permeable and waterproof applications, etc.

[Examples] Next, Examples will be shown to explain the present invention more specifically, but the present invention is not limited thereto.

Example 1 4.4'-diaminodiphenylmethane (DAM) and 2-
A polymer solution synthesized from chloroterephthalic acid chloride (CTPC) was reprecipitated in water, washed, dried, and the isolated polymer was dissolved in N,N-dimethylacetamide at a concentration of 20% by weight to obtain a film-forming stock solution. This stock solution was cast onto a rotating metal drum with the lower half submerged in water and heated to 25°C.
As soon as it became self-supporting, it was peeled off from the drum and stretched 1.4 times in the machine direction. Further, the film was passed through water until the residual solvent in the film became 5% or less, and then stretched 1.5 times in the transverse direction while drying at 280° C. using a tenter.

Thickness 20μm 1 pore diameter 0. A microporous film with a porosity of 7 μm and 70% was obtained, and as shown in Table 1, the shrinkage stress was 0.
．． 7 kg/mm2, humidity expansion coefficient 30 x 10-
The film had excellent dimensional stability with respect to 'cm/cm/%RH, heat, and humidity. Moreover, the element winding test was also good.

Example 2 2-chloro-p- in NMP (N-methylpyrrolidone)
Phenylenediamine (CPA) and 2-chloroterephthalic acid chloride (CTPC) were reacted and neutralized with lithium carbonate, and the resulting solution was used as a membrane-forming stock solution (concentration: 10% by weight). This film-forming stock solution was extruded through a nozzle 2 cm above the water surface, introduced into water at 50°C, immediately stretched 1.2 times, and treated in the same manner as in Example 1 to obtain a microporous film. As shown in Table 1, the film had excellent heat and humidity dimensional stability. Furthermore, very excellent results were obtained in the element winding test.

Example 3 A polymer obtained by interfacial polycondensation of isophthalic acid chloride (IPC) and metaphenylenediamine (MA) was
It was dissolved in NMP at % by weight, and calcium chloride was added thereto in an amount of 20% by weight based on the polymer to obtain a membrane-forming stock solution. This was longitudinally stretched 1.5 times in the same manner as in Example 2 to obtain a microporous film. It had excellent properties as shown in Table 1.

Comparative Example 1 A film was obtained in the same manner as in Example 3 except that stretching in water was not performed. Thickness 40μm 1 pore diameter 0.1μm 1
A microporous film with a porosity of 53% was obtained, and as shown in Table 1, the shrinkage stress was as small as 0°4 kg/mm2, but the humidity expansion coefficient was 95 x 10-6 cm/cm/%RH. The film had very poor dimensional stability under humidity.

Comparative Example 2 The film forming stock solution used in Example 3 was cast on a glass plate,
The mixture was solidified in a nitrogen atmosphere at -70°C, and the whole glass plate was immersed in a dry ice-methanol bath (-74°C) for extraction for 4 hours. Then, after further desalting and desolvation in water at room temperature,
A microporous film was obtained by drying. Although the thickness was 50 μm, the pore diameter was 0.09 μm, and the porosity was 46%, the humidity expansion coefficient was 77×10-' cm/cm/%RH, which was very poor in humidity dimensional stability, and the shrinkage stress was 1. It was a large film at 2 kg/mm2. In addition, wrinkles appeared in the element winding test, and it is considered that it cannot withstand practical use.

Claims (1)

[Claims] An aromatic polyamide film having continuous micropores and having a humidity expansion coefficient of at least 50 x 10^- in the longitudinal direction.
^6cm/cm/%RH or less, at least 10 in the vertical direction
Shrinkage stress in the temperature range of 0 to 300℃ is 2kg/m
A microporous aromatic polyamide film characterized by having a diameter of m^2 or less.