JP2956129B2 - Microporous film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a microporous film having excellent heat resistance, a small moisture absorption coefficient, and a small coefficient of humidity expansion.

[Prior Art] Polyolefin-based films such as polypropylene are known as microporous films, but have poor heat resistance and chemical resistance. Further, an aromatic polyamide film is known as a film excellent in both heat resistance and chemical resistance, and a method for producing a porous aromatic polyamide film is also described in JP-B-59-14494 and 59-36939. .

[Problems to be Solved by the Invention] However, even a porous aromatic polyamide film produced by the method is not sufficient in heat resistance, and has a large humidity expansion coefficient and a high moisture absorption rate, and lacks dimensional stability against humidity change. ing.

An object of the present invention is to provide a microporous film having excellent heat resistance, a small moisture absorption coefficient, a small coefficient of humidity expansion, and excellent dimensional stability against changes in humidity.

[Means for Solving the Problems] The present invention relates to an aromatic polyamide and a resin other than the aromatic polyamide, wherein the solvent is one in which the aromatic polyamide is dissolved.
A film having fine pores, comprising a blended resin with a resin that dissolves in an amount of 5% by weight or more (hereinafter, simply referred to as a soluble resin), wherein the amount of the aromatic polyamide is 5% of the blended resin.
The present invention relates to a microporous film having a porosity of not less than 20% by weight and a porosity of the film of not less than 20% and a moisture absorption of the film of not more than 5%.

The aromatic polyamide of the present invention is one or more of the general formula Those containing 50 mol% or more of the repeating unit represented by are preferable, and those containing 70 mol% or more are more preferable.

Here, Ar ₁ and Ar ₂ are composed of one or more structures containing at least one aromatic ring, and may have the same composition or different ones. Representative examples thereof include the following.

Also, part of the hydrogen on these aromatic rings are halogen (especially chlorine), a nitro group, an alkyl group of C ₁ -C ₃ (especially methyl), such as alkoxy groups C ₁ -C ₃ Also includes those substituted with a substituent. X represents —O—, —CH _{2
-, - SO 2 -, -} S -, - CO- , and the like. These are included in the form of homopolymer or copolymer.

From the viewpoint of improving the heat resistance which is the object of the present invention, Ar ₁ ,
Ar ₂ preferably has a rigid structure mainly in a para-orientation, and those having a substituent such as a halogen group or an alkyl group on the aromatic ring are more preferable because of high solubility in a solvent and compatibility with a soluble resin. Further, a halogen group is preferable because it improves the humidity characteristics of the obtained film.

Further, solubility in solvents, from the viewpoint of compatibility with the improved resin is _{high, -O -, - CH 2 -} , - SO 2 -, - S -, - CO- 2 aromatic rings, such as over a It is also preferable that the structure in which is bonded is copolymerized. However, if the amount is too large, heat characteristics, mechanical characteristics, and humidity characteristics will be deteriorated.

_{That, Ar 1: (Ar 3)} a (Ar 4) b (Ar 5) c Ar 2: (Ar 6) d (Ar 7) e , however, a + b + d + e > 0.5 b + e> 0.5 c <0.4 Ar ₄ , Ar ₇ : Ar ₃ , Ar ₆ nucleus-substituted (halogen, etc.) group Is preferable. Ar ₁ , Ar ₂
The groups other than Ar ₃ , Ar ₄ , Ar ₅ , Ar ₆ , and Ar ₇ constituting the above are not particularly limited as long as the above formula is satisfied.

For example, A solution of one or more aromatic polyamides represented by, for example, a soluble resin, the pot life is extremely stable even when stored for a long time, and the obtained microporous film is also tough and has good heat resistance and good humidity characteristics. It will be.

It is needless to say that one kind or two or more kinds of the soluble resins of the present invention may be used. As a solvent for dissolving both the aromatic polyamide and the soluble resin, an organic solvent is preferable in consideration of ease of handling and the like, and N-methyl-2-pyrrolidone, dimethylacetamide, hexamethylenephosphoramide, dimethylformamide, dimethylformamide Examples thereof include amide polar solvents such as imidazolidinone and dimethyl sulfone.
Mixtures of pyrrolidone and N-methyl-2-pyrrolidone with other amide polar solvents are preferred. Particularly when these solvents are used, polycarbonate, polyvinylidene fluoride, polymethyl methacrylate, polystyrene, polyvinyl alcohol, polyether sulfone, polysulfone, polyarylate, polysulfide sulfone, and polyetherimide are preferable, and the mechanical properties at high temperatures are preferable. Amorphous resins which are remarkably improved and have excellent humidity characteristics, such as polycarbonate, polyether sulfone, polysulfone, polyarylate, and polysulfide sulfone, are more preferable. Especially, Since the resin having both the basic skeleton A and the structure of C = 0 is very compatible with the aromatic polyamide, a blend solution obtained by dissolving the aromatic polyamide and the soluble resin in the above-mentioned solvent has a long term. It is more preferable because a film having excellent storage stability and excellent mechanical properties can be obtained. For example, polycarbonate, polyarylate and the like can be mentioned, and polycarbonate is more preferred from the viewpoint of economy. The basic skeleton A may have a substituent, such as a halogen group. Further, another resin as the third component is preferably added to the blended resin of the aromatic polyamide and the soluble resin, preferably at 40% by weight of the soluble resin.
Or less, more preferably 30% by weight or less, still more preferably
20% by weight or less may be added. For example, when polycarbonate is used as the soluble resin, adding polyethersulfone, polysulfone, or the like thereto improves mechanical properties. Further, in addition to the above solvents, good solvents for soluble resins, for example, dioxane, tetrahydrofuran, methylene chloride, chloroform, 1,1,2-trichloroethane,
Triclen, acetone, toluene, etc., within a range that does not prevent the soluble resin and the aromatic polyamide from being compatible with each other, preferably within 20% by weight of the total solvent amount, more preferably within 15% by weight. I can't support it.

A film made of the blend resin is obtained by forming the above-mentioned blend solution into a solution.

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, and has a porosity of 20% or more and 90% or less, preferably 30% or more and 80% or less.

It is necessary that the amount of the aromatic polyamide in the film of the present invention is in the range of 5% by weight to 90% by weight of the blend resin. When the amount of the aromatic polyamide is less than this range, the effect of improving the heat resistance is no longer observed, and the mechanical properties at high temperatures are extremely deteriorated. It is preferably at least 7% by weight, more preferably at least 10% by weight. On the other hand, if the amount of the aromatic polyamide is larger than this range, there is no economic merit and the humidity characteristics are deteriorated. Preferably
It is at most 70% by weight, more preferably at most 50% by weight.

The heat shrinkage at 200 ° C. in at least one direction of the film obtained in the present invention is preferably 40% or less. It is more preferably at most 30%, further preferably at most 20%. 40%
If it is larger, the dimensional stability is poor, and it is not practical.

The moisture absorption of the film is 5% or less, more preferably 3% or less, and still more preferably 1% or less. If it is more than 5%, the dimensional change due to moisture absorption becomes large, and it is not practical.

The film of the present invention has an elongation at break in at least one direction of 5
% Or more is preferable. It is more preferably at least 10%, further preferably at least 15%. If it is less than 5%, the film will be broken during handling and processing of the film, which is not practical. Further, the strength in at least one direction is preferably 1 kg / mm ² or more, more preferably 3 kg / mm ² or more, and further preferably 5 kg / mm ² or more. The Young's modulus in at least one direction is preferably 50 kg / mm ² or more, more preferably 100 kg / mm 2
² or more.

The thickness of the film of the present invention is preferably 2 to 200 μm,
5-100 μm is more preferred. The density of the film is preferably ^{0.5~1.5g / cm 3, 0.7~1.3g / cm} 3 is more preferable.

Next, a method for producing the microporous film of the present invention will be described, but is not limited thereto.

The aromatic polyamide of the present invention is obtained by reacting a diisocyanate with a dicarboxylic acid or a diacid chloride with a diamine. In the case of diacid chloride and diamine, N
It is synthesized by solution polymerization in an amide-based polar solvent such as -methyl-2-pyrrolidone or dimethylacetamide, or by interfacial polymerization using an aqueous medium. Diacid chloride and diamine are mixed at low temperature (usually 50
C., preferably 30.degree. C. or lower) for 1 to 2 hours with stirring. The order of adding the monomers is not particularly limited. Hydrochloric acid generated after the polymerization is neutralized with an inorganic alkali or an organic neutralizing agent. The reaction between the diisocyanate and the dicarboxylic acid is carried out in an amide-based polar solvent in the presence of a catalyst, usually at a high temperature (50 to 200 ° C.). These polymer solutions may be directly used as stock solutions for blending,
Alternatively, the polymer may be isolated once and then redissolved in a solvent to prepare a stock solution for blending. In some cases, an inorganic salt such as calcium chloride or magnesium chloride is added to the stock solution for blending as a solubilizing agent. Polymer concentration is 0.
It is preferably from 5 to 40% by weight, more preferably from 2 to 20% by weight.

In order to improve the mechanical properties of the heat-resistant film, it is necessary to keep the molecular weight of the polymer at a certain level or more, and it is convenient to _{express the} intrinsic viscosity (η _inh ) as a measure for this. That is, the intrinsic viscosity is preferably 1.0 to 10.0.
0, more preferably 1.5 to 9.0.

As a method of blending the aromatic polyamide and the soluble resin, a method of separately preparing a stock solution of each of the aromatic polyamide and the soluble resin and blending the stock solutions with each other, an amide polar solvent solution in which the soluble resin is dissolved is used. In this method, the aromatic polyamide is polymerized, and the polymerization and the blending are performed simultaneously. The apparent intrinsic viscosity obtained from the membrane-forming solution thus obtained is preferably 0.1 to 8.0, more preferably 0.2 to 8.0.
~ 5.0.

Next, production of a microporous film is performed by a so-called wet film formation method. The wet bath may be any bath in which the polymer is insoluble and the solvent is soluble, but water is usually preferred from the viewpoint of easy handling. The water bath may contain an inorganic salt such as lithium chloride or another solvent soluble in water. Thereby, the pore diameter and the porosity can be controlled. This stock solution is cast on a support such as a metal drum or endless metal belt and introduced into the water together with the support, or immediately immersed in the water as it is from a base in the water or on the surface of the water, and then immediately vertically. In the direction
Stretch 1.01-1.5 times. Thereafter, when the inorganic salt is added, until the inorganic salt completely disappears from the film,
Water is passed until the residual ratio of the aprotic polar solvent becomes 5% or less. The water temperature is preferably from 0 ° C to 90 ° C, more preferably from 20 ° C to 80 ° C. The pore diameter and porosity can also be controlled by changing the water temperature. By longitudinal stretching in water, the pore size could be changed, and the amount of residual inorganic salts could be reduced to 10 ppm or less.
Thereafter, drying is performed at 100 to 250 ° C. It is preferable to adjust the polymer concentration and the temperature of the film forming stock solution so that the viscosity during film formation is 5 to 50,000 poise. More preferably,
100 to 10,000 poise. Here, the viscosity refers to a value measured with a rotary B-type viscometer under the same conditions (concentration and temperature) as during film formation. When cast on a support such as a metal drum or an endless metal belt, it may be dried here and then guided into water. At this time, it is necessary to adjust the solvent so that it does not suddenly scatter and cause surface roughness.
C., preferably at 50-250.degree. C. within 60 minutes. Area magnification is preferably 0.8 to 5.0 times, more preferably
Stretch or relax at 1.1-3.0 times. The area ratio refers to the product of the stretching ratio in the film longitudinal direction (MD direction) and the stretching ratio in the width direction (TD direction). The hole diameter can be freely changed by adjusting the area magnification.

Uses of the microporous film of the present invention thus obtained include electrolytic capacitors, battery separators, and the like. Particularly, use of capacitors is desirable.

[Characteristics evaluation method] (1) Mechanical properties (strength, elongation, Young's modulus) Test width 1 in Tensilon type tensile tester according to ASTM-D-882
Set to 0mm, test length 50mm, pulling speed 300
Measure the strength and elongation when the film is broken by pulling at mm / min. The atmosphere is 25 ° C. and 55% RH.

(2) Intrinsic viscosity (η _inh ) The intrinsic viscosity was measured using an Ubbelohde viscometer under the conditions of 0.5 g / 100 ml and 30 ° C. using N-methyl-2-pyrrolidone as a solvent according to the following equation.

(3) Solution Viscosity (Poise) Measured at a temperature of 30 ° C. using a rotary B-type viscometer (Tokyo Keiki).

(4) Thermal Shrinkage Rate A film was cut out so as to have a test width of 10 mm and a test length of 200 mm, heated in an oven at 200 ° C. for 10 minutes, taken out of the test piece, allowed to cool, and calculated by the following formula.

Heat shrinkage (%) = (Test length-Length after heating) / Test length x 100 (5) Moisture absorption Film is cut out to about 100mm x 100mm, dried in a 150 ° C oven for 1 hour, and then dried. The temperature is lowered in a desiccator and the weight at the time of dehumidification is measured. After leaving this film in 75% RH for 48 hours, the film is taken out, weighed after saturation, and calculated by the following equation.

Moisture absorption (%) = (weight when moisture is absorbed-weight when dehumidified) / weight when dehumidified x 100 (6) Porosity A sample (10 x 10 cm) is immersed in liquid paraffin for 24 hours.
It is determined by the following formula from the weight after sufficiently wiping the liquid paraffin of the surface layer and the weight before immersion.

(7) Pore size Mercury porosimeter (MICROMERITICS PORE SIZER 93
00), the pore diameter distribution was measured, and the number average was defined as the pore diameter.

[Effect of the Invention] The microporous film obtained by the present invention has a humidity characteristic (particularly hygroscopicity), which is said to be the greatest drawback of aromatic polyamide.
Is improved, the moisture absorption is low, and the heat resistance is high. Therefore, when used as separators for batteries, electrolytic capacitors, electric double layer capacitors, etc., the dimensional change is small even in a humid atmosphere, and wrinkles etc. do not occur, so that the performance does not deteriorate and the film is stored in a roll form for a long time. In this case, a good winding shape can be maintained. In particular, it is effective when an aqueous electrolyte such as a nickel-cadmium battery is used. In addition, since the surface of the film is slightly hydrophilized due to the presence of the aromatic polyamide, it is not necessary to perform a hydrophilization treatment unlike polypropylene and the like, and the process can be omitted.

Furthermore, it does not flow even at a temperature higher than the softening pour point of the soluble resin, has a small heat shrinkage at high temperatures, and has excellent dimensional stability. Deterioration does not occur and is particularly effective. In addition, it exhibits excellent properties for micro filters, moisture permeable and waterproof applications.

Further, since a relatively inexpensive soluble resin is used, the production cost of the microporous film can be reduced.

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

Example 1 100 mol% of 4,4'-diaminodiphenylmethane and 100 mol% of 2-chloroterephthalic acid chloride (hereinafter abbreviated as CTPC)
In N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP)
The reaction was performed at 0 ° C. or lower to obtain an NMP solution of an aromatic polyamide. This solution was poured into a large amount of water, reprecipitated and dried to obtain a powdery polymer. 20 parts of this polymer was dissolved in 100 parts of NMP, and the polyether sulfone prepared separately
200 parts of an NMP solution containing 30 parts were added to obtain a blend solution.
The intrinsic viscosity was 1.0 and the solution viscosity was 100 poise.

When this stock solution for film formation is cast on a glass plate and immersed in water together with the glass plate, it comes off naturally from the glass plate. Furthermore, after immersing in water for 15 minutes, it is dried at 170 ° C. for 2 minutes. The properties were excellent as shown in Table 1.

Example 2 As in Example 1, 300 parts of an NMP solution containing 15 parts of an aromatic polyamide obtained from 100 mol% of 2-chloroparaphenylenediamine (hereinafter abbreviated as CPA) and 100 mol% of CTPC, and NMP containing 35 parts of polycarbonate. Blend 250 parts of the solution, cast on a rotating metal drum with the lower half in water, guide it into water at 25 ° C, peel off from the drum when it became self-supporting, stretched 1.2 times in the longitudinal direction After passing through water until the residual solvent in the film became 5% or less, the film was stretched 1.3 times in the transverse direction while drying at 200 ° C. with a tenter to obtain a film. The film had excellent characteristics as shown in Table 1.

Example 3 In the same manner as in Example 1, 350 parts of an NMP solution containing 10 parts of an aromatic polyamide obtained from the reaction of 85 mol% of CPA, 15 mol% of 4,4'-diaminodiphenyl ether and 100 mol% of CTPC, and 40 parts of polycarbonate are prepared. did. Solution viscosity is 30
It was 80 poise at ° C. Use this blend stock solution 100m wide
m, continuously extruded into the water from the base of slit 0.1mm,
The film was stretched 1.05 times in water in the longitudinal direction and 1.3 times in the transverse direction at 180 ° C. to obtain a microporous film. As shown in Table 1, the film was very excellent.

Comparative Example 1 An NMP solution of polycarbonate was cast on a glass plate.
The properties of the microporous film consisting of only polycarbonate obtained by immersing it in water for 30 minutes and drying at 120 ° C. for 6 minutes were very poor as shown in Table 1.

Comparative Example 2 A solution obtained by reacting 100 mol% of CPA with 100 mol% of CTPC and neutralizing with lithium carbonate was cast on glass,
Soaked in water. The film obtained after 20 minutes and dried at 220 ° C. was a microporous film having excellent mechanical strength but poor humidity characteristics.

As described above, films out of the range of the present invention were inferior in either of the heat characteristics and the humidity characteristics.

Continuation of the front page (56) References JP-A-52-42559 (JP, A) JP-A-56-154051 (JP, A) JP-B-59-14494 (JP, B2) (58) Fields investigated (Int) .Cl. ⁶ , DB name) B29C 55/02 C08J 9/28 CFG

Claims (1)

(57) [Claims] 1. An aromatic polyamide and a resin other than the aromatic polyamide, wherein the solvent in which the aromatic polyamide is dissolved is 1
A microporous film comprising a resin blended with a resin that dissolves at least 5% by weight of the blended resin, wherein the amount of the aromatic polyamide ranges from 5% by weight to 90% by weight of the blended resin; A microporous film having a porosity of 20% or more and a moisture absorption of the film of 5% or less.