JPH05148383A - Polysulfone-based porous film and its preparation - Google Patents

Abstract

PURPOSE:To prepare the subject film excellent in the resistances to heat, acid, and alkali and suitable for a filtration membrane a separator of a cell, etc., by dissolving a polysulfone polymer in a specific solvent and forming the resulting soln. into a film in a coagulating bath. CONSTITUTION:A polysulfone polymer (pref. one having repeating units of the formula) is dissolved in gamma-butyrolactone or sulfonate in a concn. of 5-15wt.%. The resulting soln. is formed into a film a coagulating liq. consisting mainly of water in a coagulating bath. The obtd. film has a pore diameter (d) calculated from the means pore diameter pressure of 0.5mum or lower, a thickness (D) of the dense layer of 20mum or lower, an air passability expressed by a Gurley value (A) of 100sec/50cc or lower, and a void content (phi) of 40-95vol%, is excellent in the resistances to heat, acid, and alkali, and effectively prevents the formation of dendrite when used as a separator of a cell.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a filtration membrane, a battery separator, a sustained release carrier, and a novel polysulfone-based porous membrane having excellent heat resistance, acid resistance, alkali resistance and chemical resistance, which are particularly suitable. Manufacturing method

[0002]

2. Description of the Related Art Conventionally, a polymer solution prepared by dissolving a polysulfone resin and a nonionic surfactant in a hydrophilic organic solvent is soaked in a non-solvent such as water, and treated with the nonionic surfactant to give a microporous property. Japanese Unexamined Patent Publication (Kokai) No. 2-276153 proposes that a membrane is regenerated to produce an alkaline battery separator.

[0003]

In the alkaline battery separator obtained by the above method, the interface resistance of the separator film as the battery separator is small. However, when it is used as a separator of a system in which dendritic electrodeposition (dendrites) occurs in alkaline batteries, especially nickel-zinc batteries, etc., the dense layer (micropore layer) thickness D is 20 μm.
Since the thickness is thinner than m, the dendrite generation is not sufficiently suppressed, and the cycle life is short, such as several hundreds of cycles, and there is a problem that the battery life is short in practical use.

In order to suppress the generation of dendrites, it is considered desirable to reduce the pore diameter of the porous membrane or to increase the membrane thickness, but on the contrary, the resistance of the membrane increases and the conductivity of ions and Since the mobility of gas decreases, it is expected that a high-performance separator satisfying both of them will appear.

As a result of intensive investigations aimed at solving these problems, the present inventors have found a novel polysulfone-based porous membrane and a method for producing the same, and completed the present invention.

[0006]

Means for Solving the Problems The gist of the present invention is composed of a polysulfone-based polymer and has a pore diameter d converted from an average pore diameter pressure, a dense layer thickness D, a Gurley value A indicating air permeability, and a porosity φ. Is in a polysulfone-based porous membrane satisfying the following formula. d ≦ 0.5 (μm) (1) 20 ≦ D (μm) (2) A ≦ 100 (sec / 50cc) (3) 40 ≦ φ ≦ 95 (volume%) (4)

Further, the polysulfone-based polymer is dissolved in 5 to 15% by weight of γ-butyrolactone or sulfolane and then formed into a film in a coagulation bath containing water as a main component to produce a polysulfone-based porous film.

The polysulfone polymer of the present invention has a repeating unit structure

[Chemical 1] Any compound having the formula can be used, and among them, those represented by the following general formula are preferably used.

[Chemical 2] The porous membrane of the present invention has a structure in which mesh-like voids are three-dimensionally communicated with each other.

In the present invention, when the pore size d converted from the average pore size pressure exceeds 0.5 μm, there is a problem that dendrites are not sufficiently blocked when used as a battery separator, which is not preferable. d is 0.5μ
It is preferably m or less, more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

In the present invention, the dense layer (microporous layer) means
Of the layers in which the three-dimensional network structure is continuously formed, the converted diameter when the network void is approximated to a circle is D ₀
As a unit of 0.1 μm, D ₀ is 0.5 μm
The following part refers to a layer in which at least one film surface is continuously formed inside.

When the thickness D of the dense layer (micropore layer) is less than 20 μm, dendrites are not sufficiently blocked when used as a battery separator, and the cycle life which is one of the battery life is practically insufficient. It is not preferable because there is a problem that

D is preferably 20 μm or more,
The thickness is more preferably 60 μm or more, and particularly preferably 100 μm or more.

The structure of the membrane is a dense layer (microporous layer) as a whole or adjacent to the dense layer (microporous layer) in order to maintain mechanical strength and retain electrolyte. It may be composed of a portion having a large pore diameter (support layer).

Although there is a problem that the Gurley value A increases as the overall film thickness increases, the film thickness is greater than the thickness D of the dense layer (micropore layer) and satisfies the condition of 100 sec / 50 cc or less. If it is good.

The Gurley value A of the present invention depends on the pore diameter d converted from the average pore diameter pressure of the membrane, the dense layer (fine pore layer) thickness D, the porosity φ and the like. When the Gurley value A is larger than 100 sec / 50 cc, resistance during mass transfer in the film is large, which is not preferable.

The porosity φ of the present invention is a ratio of the volume of pores to the apparent volume of the porous membrane, expressed as a percentage.

The porosity φ of the present invention is 40 to 95% by volume. If it is less than 40% by volume, the resistance is remarkably large during various mass transfer, which is not preferable, and if it is more than 95% by volume, the mechanical strength is large. It is not preferable because it extremely decreases. A more preferable porosity is usually about 60 to 80% by volume.

The method for producing the polysulfone type porous membrane of the present invention will be described below. First, a polysulfone-based polymer is dissolved in a solvent to prepare a polymer solution. In this case, it is preferable to use, as the good solvent for the polysulfone-based polymer, a solvent that is replaced with the coagulating liquid when immersed in the coagulating bath, that is, a polar solvent that is compatible with the coagulating liquid.

Examples thereof include dioxane, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, morpholine, γ-butyrolactone and sulfolane, but γ-butyrolactone is more preferable for obtaining the porous membrane of the present invention. , Sulfolane is particularly preferred.

Further, the third component may be appropriately added to the polymer solution as long as the structure of the present invention is maintained. The polysulfone-based polymer concentration of the polymer solution is preferably 5 to 15% by weight, and if it exceeds 15% by weight, the resistance to mass transfer in the obtained porous membrane becomes so large that it has no practical meaning. If the concentration is less than 5% by weight, a porous film having sufficient mechanical strength cannot be obtained.

The composition of the coagulation bath is water, methanol,
Any alcohol, such as ethanol and butanol, glycols such as ethylene glycol and diethylene glycol, ethers, aliphatic hydrocarbons such as n-hexane and n-heptane, glycerols such as glycerin, can be used as long as it does not dissolve the polymer. I can, but
Water is more preferable as the coagulation bath for obtaining the porous membrane of the present invention, and a mixture of water and glycerin is particularly preferable.
If it is within the range that does not inhibit the coagulation action of the present invention,
You may add a component suitably.

The porous membrane of the present invention may be used alone or as a laminate of a plurality of sheets. Further, another porous material such as a nonwoven fabric or a film may be laminated as a support layer or an active layer.

[0023]

The present invention will be specifically described with reference to the following examples.

"Converted pore size d from average pore size pressure" is AS
It is measured by the air flow method described in TMF316 and gives the average value of the minimum pore diameters of the channels penetrating the membrane surface. Specifically, diameter 2
A 5 mm punched porous membrane is dipped in mineral oil for 5 minutes, then installed in a membrane filter holder, and one side of the porous membrane is filled with clean air at 20 ° C per minute 1 kg / cm.
^By supplying pressure while increasing the pressure linearly in ² , the air starts to permeate to the opposite side of the porous membrane, then the amount of air permeation increases and the amount of air permeation is 1 when it is not immersed in mineral oil. The differential pressure when it reached / 2 was defined as the average pore diameter pressure.

The average pore diameter d was obtained from the following equation.

[Equation 1] However, γ is the surface tension of liquid (34dy for mineral oil)
ne / cm), θ is the contact angle, ΔP is the average pore diameter pressure, co
s θ = 1.

The "dense layer thickness D" was determined by observing and measuring with a scanning electron microscope.

"Gurley value A indicating air permeability" is based on JIS
A value measured by the air permeability test method described in P8117, in which a porous membrane punched out to a diameter of 47 mm is installed in an air permeability tester (B type), and an area of 645 mm ² is passed by 50 cc of air. It was determined by measuring the time (sec).

The "porosity" was measured by the mercury porosimeter method. The "battery cycle life" was measured by the following method. Between a known sintered nickel positive electrode having nickel hydroxide as an active material and a zinc negative electrode having zinc as an active material,
An alkaline zinc battery was prepared by arranging a porous membrane. The electrolytic solution used was a 9N potassium hydroxide solution to which 1 molar zinc oxide powder was added.

The cycle life of the alkaline zinc battery was measured by charging the above battery at 0.17 C for 4 hours,
A continuous cycle test was performed under the charge and discharge conditions of discharging at 0.3C and stopping the discharge when the battery voltage reached 1.3V, and the cycle when the discharge capacity reached 75% of the initial capacity. It is shown by the number. "Part" means "part by weight".

Example 1 Polysulfone polymer (manufactured by Nissan Chemical Industries, Ltd., Ude
l P-3500) 7 parts in γ-butyrolactone 93 parts to prepare a polymer solution, followed by a film-making applicator to give a thickness of 18
It was casted to 0 μm to form a thin film of the polymer solution.

Then, the polymer was coagulated by immersing it in water at 25 ° C. in a coagulation bath for 300 seconds. Next, after removing the residual solvent by immersing in warm water of 80 ° C and washing, 60 ° C
And dried with hot air for 1 hour to obtain a porous membrane. The physical properties are shown in Table 1.

Examples 2 to 8 The composition ratio of the polysulfone polymer and γ-butyrolactone was [8/92] (Example 2), [9/91] (Example 3), [10/90] (Example 4). ), [11/89]
(Example 5), [12/88] (Example 6), [13 /
87] (Example 7) and [14/86] (Example 8), except that the same procedure as in Example 1 was carried out to produce a porous membrane. The physical properties are shown in Table 1.

Examples 9 to 11 The water temperature in the coagulation bath was [0 ° C] (Example 9), [60 ° C].
A porous membrane was produced in exactly the same manner as in Example 4, except that (Example 10) and [90 ° C] (Example 11) were used. The physical properties are shown in Table 1.

Example 12 Polysulfone polymer (manufactured by Nissan Chemical Industries, Ltd., Ude
The polymer solution was prepared by dissolving 8 parts of 1 P-3500) in 92 parts of sulfolane, and then cast on a glass plate to a thickness of 250 μm using an applicator for making a film to form a thin film of the polymer solution. An object was formed.

Then, the polymer was coagulated by immersing it in water at 25 ° C. in a coagulation bath for 300 seconds. Next, after removing the residual solvent by immersing in warm water of 80 ° C and washing, 60 ° C
And dried with hot air for 1 hour to obtain a porous membrane. The physical properties are shown in Table 1.

Examples 13 to 14 The composition ratio of polysulfone polymer and sulfolane was set to [10/9].
0] (Example 13) and [12/88] (Example 14), and a porous membrane was produced in exactly the same manner as in Example 12. The physical properties are shown in Table 1.

Example 15 Polysulfone polymer (manufactured by Nissan Chemical Industries, Ltd., Ude
A polymer solution was prepared by dissolving 10 parts of 1P-3500) in 90 parts of sulfolane, and subsequently using a film-making applicator, a thickness of 250 μm on a glass plate.
To form a thin film of the polymer solution.

The polymer was then coagulated by dipping it in water / glycerin (75 parts / 25 parts) at 25 ° C. in a coagulation bath for 300 seconds. Next, the residual solvent and the like were removed by immersing in warm water of 80 ° C and washing, and then dried with hot air at 60 ° C for 1 hour to obtain a porous membrane. The physical properties are shown in Table 1.

Examples 16 to 19 The composition ratio of polysulfone polymer and sulfolane was [12/8].
8] (Example 16), [13/87] (Example 17),
A porous membrane was produced in exactly the same manner as in Example 15, except that [14/86] (Example 18) and [15/85] (Example 19) were used. The physical properties are shown in Table 1.

The membranes of Examples 1 to 19 all satisfy the formulas (1), (2), (3) and (4) specified by the present invention and have a cycle life of 1000 times or more, which is practically sufficient. Met.

Comparative Example 1 A polymer solution was prepared by dissolving 10 parts of a polysulfone polymer in 90 parts of dioxane, and then using a film-making applicator, a glass plate having a thickness of 300 μm was prepared.
Then, it was cast into a thin film of a polymer solution. Then, it was immersed in water at 25 ° C. in a coagulation bath for 300 seconds to form a polymer.

Next, the residual solvent and the like were removed by immersing in warm water at 80 ° C. and washing, and then dried with hot air at 60 ° C. for 1 hour to obtain a porous film. The physical properties are shown in Table 1. The obtained membrane had a high Gurley value A and a large resistance of the membrane, so the ion conductivity and the gas mobility were low, and practical performance as a battery was not exhibited.

Comparative Examples 2 to 5 The solvents were [dimethylformamide] (Comparative Example 2), [dimethylacetamide] (Comparative Example 3) and [n-methyl-2-].
Pyrrolidone] (Comparative Example 4) and [Morpholine] (Comparative Example 5) were used, and a porous membrane was produced in exactly the same manner as Comparative Example 1. The physical properties are shown in Table 1. The resulting membrane is
The dense layer (micropore layer) thickness D was less than 20 μm, and the cycle life was less than 230 times, which was insufficient for practical use.

Comparative Example 6 A porous membrane was produced in exactly the same manner as in Example 1 except that the composition ratio of the polysulfone polymer and γ-butyrolactone was set to [16/84]. The physical properties are shown in Table 1. The obtained membrane had a high Gurley value as in Comparative Example 1, and did not exhibit practical performance as a battery.

Comparative Example 7 The composition of the polymer solution was polysulfone polymer / dimethylformamide / polyoxyethylene (20) sorbitan monolaurate (manufactured by Wako Pure Chemical Industries, Ltd.) (15/82/3 weight ratio). Except for the above, a porous membrane was produced in exactly the same manner as in Example 1. The physical properties are shown in Table 1.

Comparative Examples 8 to 11 Polyoxyethylene (20) sorbitan laurate
[Polyoxyethylene (20) sorbitan monooleate] (Comparative example 8), [Polyoxyethylene (20) sorbitan palmitate] (Comparative example 9), [Polyoxyethylene (20) sorbitan monostearate] (Comparative example 1
0), [polyoxyethylene (20) sorbitan trioleate] (Comparative Example 11), except that Comparative Example 7
A porous membrane was produced in exactly the same manner as in. The physical properties are shown in Table 1.

The films of Comparative Examples 7 to 10 had a dense layer (microporous layer) thickness D of less than 20 μm in total and a cycle life of less than 300 times, which was not practically sufficient. Comparative Example 1
The film No. 1 had a high Gurley value A, and practical performance as a battery was not exhibited.

[0048]

[Table 1]

[0049]

The porous membrane of the present invention has heat resistance, acid resistance, and
It has excellent alkali resistance and can effectively suppress the generation of dendrites when used as a battery separator.

Claims (4)

[Claims] 1. A polysulfone-based porous material comprising a polysulfone-based polymer and having a pore diameter d converted from an average pore diameter pressure, a dense layer thickness D, a Gurley value A indicating air permeability, and a porosity φ satisfying the following expressions: film. d ≦ 0.5 (μm) (1) 20 ≦ D (μm) (2) A ≦ 100 (sec / 50cc) (3) 40 ≦ φ ≦ 95 (volume%) (4) 2. The polysulfone-based porous membrane according to claim 1, wherein the dense layer has a thickness D of D ≧ 60 (μm). 3. A polysulfone-based polymer is contained in an amount of 5 to 15% by weight.
A method for producing a polysulfone-based porous film, which comprises dissolving the film in γ-butyrolactone and then forming the film in a coagulation bath containing water as a main component. 4. A method for producing a polysulfone-based porous membrane, which comprises dissolving the polysulfone-based polymer in sulfolane and then forming the membrane in a coagulation bath containing water as a main component.