JPS63278945A - Porous membrane - Google Patents

Abstract

PURPOSE:To obtain a porous membrane having a high water flux, excelling in heat resistance, chemical resistance, storage stability and handleability and suited for treatment of condensate, treatment of water for supercritical pressure boilers, comprising a mixture of a specified polyether-imide with a polybutadiene. CONSTITUTION:A saturated vapor or mist-containing vapor of a poor solvent which is miscible with component B and does not dissolve component A (e.g., water) is fed at a rate of 0.1-1,000mg/sec.cm<2> and forcibly contacted with at least either surface of a thin-film object formed from a 2-40wt.% concentration polymer solution formed by dissolving a mixture (A) of 99-90pts.wt. polyether-imide (a) having a weight-average MW >=30,000 and repeating units of the formula (wherein n is 1-7), obtained by polycondensing phenoxyphenyldicarboxylic acid with phenylenediamine, with 1-10pts.wt. polybutadiene (b) of a weight-average MW of 1,000-10,000 in a good solvent (B) such as N-methylpyrrolidone to obtain a porous membrane of an average pore diameter <=0.20mu, a thickness >=50mu and a water flux >=25ml/cm<2>.min.10psi.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a porous membrane that is effective for filtering fine particles present in a fluid.

[Conventional technology]

The applications of filtration techniques using porous membranes are expanding year by year, and as a result, porous membranes with various functions have been required.

For example, in water treatment such as water treatment for supercritical boilers, porous membranes that can block small particles, have a high water flux, and are heat resistant are required.

Traditionally, porous membranes for removing particulates from fluids include:
Cellulose acetate, polysulfone, polyethylene and the like are known, but these have drawbacks in mechanical properties, solvent resistance, and heat resistance.

In order to solve these problems, porous membranes made of polyetherimide (Japanese Patent Laid-Open No. 60-5150
3) has been proposed.

[Problem that the invention seeks to solve]

However, the polyetherimide porous membrane described above has the following problems.

That is, the problem is that a porous polyetherimide film obtained by a normal wet film forming method has a small water flux because of the presence of a non-porous dense layer.

Porous membranes manufactured using metal salts such as lithium chloride or swelling agents such as ethylene glycol have been proposed, but the swelling agent remains in such porous membranes. However, there is a problem that it elutes during use. In addition, the problem with porous membranes made by this method is that when the water physis is large, the average pore diameter of the pores is large, and when the pores have a small average pore diameter, the water 7 lux is small. There are no known porous membranes that have a small average pore diameter and a large water flux.

In view of this situation, the present inventors have developed a material with excellent mechanical properties.
We conducted extensive research to develop a porous membrane that has good heat resistance and solvent resistance, a small particle inhibition diameter, and a high water content.
The invention has been completed.

[Means for solving the problems] The gist of the present invention is to provide a polyetherimide 9 having a repeating unit represented by the following general formula [where n is an integer of 1 to 7].
It consists of a mixture of 9-90 parts by weight of polybutadiene and 1-10 parts by weight, the average pore diameter is 0.20 μm or less, the film thickness is 50 μm or more, and the water flux is 25 wl/c.
rIL'', min -10p,s,i or more.

The polyetherimide represented by the above general formula is a polymer obtained by condensation polymerization of phenoxyphenyldicarboxylic anhydride and phenylenediamine, and CnH,H
The group can have a linear or branched structure.

A typical example of the polymer is 2,2-bis[4-(3,4
-dicarboxyphenoxy)phenyl] obtained by a polycondensation reaction of propane anhydride and meta-72-diamine. The polymer represented by the above general formula has excellent mechanical properties, solvent resistance, and heat resistance, and is the most suitable polymer as a material for the porous membrane of the present invention, which requires these properties.

The porous membrane of the present invention is composed of a mixture of 99 to 90 parts by weight of polyetherimide represented by the above general formula and 1 to 10 parts by weight of polybutadiene.

Here, polybutadiene refers to a polymer represented by the general formula 0 (where m and n are arbitrary integers). The state of dispersion of polybutadiene in the porous membrane is not particularly limited, and is preferably in the form of molecular dispersion, but as long as the overall homogeneity is not significantly impaired, two or more molecules may form aggregates, may be in a dispersed state.

The porous membrane of the present invention contains 1 to 10% by weight of polybutadiene, but if the polybutadiene content is within this range, uniform dispersion is possible, so the various properties of polyetherimide are impaired. It is possible to obtain a porous membrane with a small average pore diameter and a large water flux. On the other hand, if the polybutadiene content deviates from this range, the water flux in the porous membrane cannot be increased, and if it exceeds 10% by weight, it becomes difficult to uniformly disperse the polybutadiene.

The porous membrane of the present invention has pores with an average diameter of 0.20 μm or less. The average pore diameter here refers to the rejection rate of polymer latex (usually polystyrene latex) particles of 9.
This value is expressed as a particle size corresponding to 0%, and is a value expressed as a particle size corresponding to 0%.
, 01 wt% aqueous dispersion) can be determined from a curve showing the relationship between the polymer latex particle diameter and the rejection rate.

The average pore diameter of the pores is 0.20 μm or less, and is more preferably 0.15 μm or less for applications that require higher filtration accuracy.

The pore structure of the porous membrane is not particularly limited; for example, it may have a homogeneous or heterogeneous sponge-like structure as a whole, or a structure consisting of a sponge-like structure with an average pore diameter of 0.20 μm or less and a finger-like structure with a larger average pore diameter. can be taken. or,
The porous membrane can take any shape such as a flat membrane, hollow fiber membrane, or tubular membrane.

The thickness of the porous membrane of the present invention is 50 μm or more. This film thickness is set from the point of view of practical performance such as ease of handling, and films with a film thickness of less than 50 μm generally have a problem of poor mechanical strength and being easily damaged during handling. Although the upper limit of the film thickness is not particularly limited, it is preferably about 150 μm or less.

The water flux of the porous membrane of the present invention is 25 go/22·mi
n −10p,s,1 or more. That is, it is characterized in that it has a small average pore diameter of 0.20 μm or less, and has a high water latex despite having a thick film thickness of 50 μm or more. Water flux is 25 #/an”,
min, 10 pog, i or more, it has the advantage that a sufficient amount of water to be treated per unit membrane area can be secured. If the water flux is smaller than this, a sufficient amount of treated water cannot be secured, which is not preferable. Water 7 lux is 3
0 d/crrL" 1w1n -10p, s, 1
It is more preferable that it is above.

Next, the method for manufacturing the porous membrane of the present invention will be described. Although various methods can be adopted as a film forming method, the following steam coagulation method can be mentioned as a preferable method.

Here, the vapor coagulation method means that the good solvent and It refers to a film forming method in which saturated vapor or mist-containing vapor of a poor solvent that is compatible and does not dissolve the polymer is forced into contact with the polymer. Compared to the group film forming method, the vapor coagulation method can lengthen the time between the start of phase separation of the polymer-solvent system in a thin film and the subsequent start of coagulation of the polymer. It is believed that a porous membrane without a non-porous layer (dense m) can be obtained because the solidification rate of coalescence is slow.

The degree of polymerization of polyetherimide is not particularly limited, but in consideration of film forming properties, heat resistance, etc., it is preferable to use a polyetherimide having a weight average molecular weight of about 30,000 or more. Further, the degree of polymerization of polybutadiene is not particularly limited, but the weight average molecular weight is approximately 1,000 to 10,000 seconds at 20°C.
It is preferable to use one having a viscosity of approximately 1.5 to 1000 voids. It is thought that by using polybutadiene with such a low molecular weight, it is possible to delay the onset of coagulation of the entire polymer, and it is possible to obtain a porous membrane with a large water flux.

Examples of good solvents for polymers include N-methylpyrrolidone, dimethylacetamide, dimethylsulfoxide, 1,4-dioxane, and trichlorethylene. A polymer solution is prepared by dissolving polyetherimide and polybutadiene in a solvent such that the weight composition ratio of polyetherimide and polybutadiene is 99-90:1-10.

The content of the polymer in the polymer solution is determined by the porosity of the porous membrane,
Although the optimum content changes depending on the type of solvent since it affects the pore size distribution, etc., it is preferably about 2 to 40% by weight, and more preferably 5 to 30% by weight.

The thickness of the thin film prepared from the polymer solution may be set as appropriate depending on the thickness of the intended porous membrane, but usually it is approximately 50 to 2000 μm. , can be obtained by casting or coating on objects with smooth surfaces such as metal plates, polymer films, rotating drums, endless belts, etc. However, as long as the smoothness of the thin film is not impaired, porous Porous objects such as polymeric films can also be used.

Further, a hollow fiber-like thin film can also be obtained by appropriately selecting the polymer concentration in the polymer solution and spinning using a hollow fiber nozzle.

Furthermore, by allowing the polymer solution to flow down through the slit-like grooves, a sheet-like thin film can be formed without using a support.

Normally, thin film-like materials are brought into contact with steam immediately after they are made, but
It may be brought into contact with steam after some time has elapsed.

In the steam coagulation method, saturated steam or mist-containing steam is used, and although the mist-containing steam may be unsaturated steam, saturated steam is preferable.

The liquid to generate such saturated vapor or vapor containing mist may be any liquid as long as it is a poor solvent for the polymer, and a typical example thereof is water. Examples include organic solvents with a low boiling point that easily generate vapor, such as carbon dioxide, methyl alcohol, ethyl alcohol, methyl ethyl ketone, acetone, tetrahydrofuran, and methyl acetate. However, in consideration of ease of handling, working environment, safety, economy, etc., it is preferable to use water.

Here, as a representative example, a manufacturing method will be described in which saturated steam or steam containing mist is supplied to the surface of a thin film-like material made of a polymer solution. Water vapor can be supplied by adjusting the temperature and concentration using a known device, but usually a method is adopted in which saturated steam at diffused pressure is ejected from a nozzle and supplied to the surface of the thin film-like material.

Since the solidification rate and solidification behavior of a single polymer vary depending on the concentration of the polymer solution, the thickness of the thin film, the boiling point of the good solvent, the compatibility of the good solvent with water, etc., the temperature, concentration, supply rate, and supply time of water vapor vary. By appropriately selecting such conditions, the pore diameter, pore diameter distribution, porosity, etc. can be controlled to preferable values.

The amount of saturated steam or steam containing mist supplied to the surface of the thin film is approximately 0.1 to 1000 ■/l・c
It is preferable that it is approximately 0.5
It is more preferable that the amount of water vapor, etc. to be supplied is approximately 10089/I@g+, C1l".
0 minutes or less is sufficient.

Although the direction in which the water vapor is supplied to the surface of the thin film-like material is not particularly limited, it is preferable to supply the water vapor from the vertical direction in consideration of the supply efficiency of the water vapor.

By supplying water vapor to the surface of a thin film made of a polymer solution, the polymer components are solidified and a porous structure is formed. In this case, from the viewpoint of promoting coagulation of the polymer and preventing re-dissolution, it is preferable to remove a good solvent from the thin film-like material or the porous polymer during or after supplying water vapor. The good solvent can be removed by evaporation or by running off as an aqueous solution of condensed water.

If a good solvent or the like remains inside the porous membrane obtained after coagulating the polymer, it may be removed by drying, washing with water, etc., if necessary.

〔Example〕

The present invention will be explained below with reference to Examples.

In the examples, the rejection rates of air 7lux, water 72lux, and polymer latex particles were measured by the following method. In addition, in the examples, all amounts of each component used are shown in parts by weight.

Air 7 Lux has a porous membrane punched out to a diameter of 255 m and is assembled into a membrane filter holder, and
It was determined by supplying clean air at a transmembrane pressure of 10 p, s, and measuring the permeation flow rate.

For the water flux, a porous membrane punched to a diameter of 25 mm was immersed in ethanol, then replaced with water to guide the water into the micropores, and then incorporated into a membrane filter holder in the same way, and clarified water at 20°C. The transmembrane pressure difference is 10 p, s, i
The permeation flow rate was measured.

In addition, 0.01 tvt% aqueous solutions of polystyrene latex with various particle sizes were prepared, and the permeate and stock solutions obtained by pressure filtration at a differential pressure of 0.1 to 7 cm were
: The absorbance of each can was measured by UV absorbance method (wavelength: 2.75 parts m), and the rejection rate of the polymer latex particles was calculated from the difference between the two.

Example 1 Polyetherimide (UL'rEM1000 manufactured by G, Company B)
) was dissolved in 900 parts by weight of dimethylacetamide, and liquid polybutadiene (Nippon Zeon Co., Ltd.) was dissolved in 900 parts by weight of dimethylacetamide.
manufactured by Polyyoil 110, viscosity 7.5 voids, 20
℃) was added and sufficiently stirred to prepare a polymer solution.

This solution was cast onto a glass plate to a thickness of 127 μm using a film-forming applicator to form a thin film of polymer solution.

Next, the pulp in the pipe containing 3 kg f/crIL'' of saturated steam was opened, and the polymer was solidified by supplying saturated steam to the surface of the thin film for 4 minutes from a nozzle with a diameter of 5 cm.

The thin film material was placed vertically at a distance of 30 m (1 m) from the nozzle.

Water vapor was supplied under the same conditions, and 1 c
The temperature at the rIL position was measured to be 83°C.

In addition, the actual measured value of the water vapor flow rate is 267P/min,
Spraying at a position 30cm from the nozzle (direct @ 15cmφ)
The amount of water vapor supplied per unit area calculated from the area of 177 (m") was 25 m97 sec - (-) Next, the coagulated polymer was peeled off from the glass plate, and after washing with running water for about 1 hour, It was dried with ventilation at 45° C. for about 12 hours.

The thickness, air flux, water flux, and rejection rate of polymer latex particles of the porous membrane thus obtained were measured and shown in Table 1.

In addition, the content of polybutadiene in the porous membrane is ')I
- It was determined by measuring the aromatic ring peak of polyetherimide and the proton peak bonded to the carbon of the carbon-carbon double bond of polybutadiene by NMR method.

Further, when the porous membrane was observed using a scanning electron microscope, a substantially porous sponge-like structure was observed on the surface layer, and a finger-like structure was observed from the inside to the back surface.

Example 2 Example 1 except that the amount of polybutadiene added was 5 parts.
Film formation was carried out in the same manner. The properties of the obtained film are shown in Table 1. When observed with a scanning electron microscope, Example 1
A similar structure was observed.

Example 3 Example 1 except that the amount of polybutadiene added was 11 parts.
Film formation was carried out in the same manner. The properties of the obtained film are shown in Table 1. When observed with a scanning electron microscope, Example 1
A similar structure was observed.

Comparative Example 1 120 parts of polyetherimide was dissolved in 880 parts of N-methyl-2-pyrrolidone at 95°C over 4 hours to give a coating thickness of 100 μm, and immediately dissolved in water at 22°C for 3 hours.
It was immersed for 0 minutes to solidify. Subsequently, in the same manner as in Example 1, washing with running water and ventilation drying were performed.

The properties of the obtained film are shown in Table 1. As a result of observation with a scanning electron microscope, the surface layer was covered with a skin layer that was not substantially porous, and a finger structure was observed inside.

Comparative Example 2 A film was formed in the same manner as Comparative Example 1, except that 100 parts of polyetherimide was dissolved in a mixed solvent consisting of 400 parts of N-methyl-2-pyrrolidone and 500 parts of tetrahydro7ran, and the coating thickness was 127 μm. I did ゛.

The properties of the obtained film are shown in Table 1. As a result of observation with a scanning electron microscope, the surface layer was covered with a skin layer that was not substantially porous, and a finger-shaped structure was observed inside.

Comparative Example 3 25 parts of polyetherimide was added with 115 parts of N-methyl-2-pyrrolidone and ethylene carbonate, and further heated at 80°C.
After stirring for 4 hours, the polymer solution was cast onto a glass plate to a thickness of 127 μm using a film-forming applicator to form a thin film of the polymer solution. Then 15 parts of water at 20°C, N
-Methyl-2-pyrrolidone (42.5 parts) and ethylene carbonate (42.5 parts) for 30 minutes to coagulate the polymer.

Next, the coagulated polymer was peeled off from the glass plate, washed with running water for about 1 hour, and then dried with ventilation at 45° C. for about 12 hours.

The properties of the obtained film are shown in Table 1. As a result of observation using a scanning electron microscope, it was found to have a homogeneous spongy structure with substantially porous surfaces and insides.

Comparative Example 4 A polymer solution prepared in the same manner as Comparative Example 1 was coated with a film thickness of 1
2711m, water vapor amount 17.2 a97s@e-α1
A film was formed in the same manner as in Example 1 except that the water vapor supply time was 5 minutes.

〔Effect of the invention〕

The porous membrane of the present invention has the following excellent effects.

(1) Excellent heat resistance and chemical resistance. ,(2)
Despite the small particle size that can be blocked, it has a significantly high water flux.

(3) It has good storage stability and is easy to handle because the porous IX structure does not change even when stored in a dry state.

The porous membrane of the present invention having the above-mentioned excellent performance,
It can be applied to various fields including water treatment for supercritical boilers, nuclear power generation, post-water treatment for thermal power generation, and production of ultrapure water in electronic circuit manufacturing.

Claims (1)

[Claims] Polyetherimide 9 having a repeating unit represented by the following general formula ▲ Numerical formula, chemical formula, table, etc. ▼ [However, n represents an integer from 1 to 7]
Consisting of a mixture of 9 to 90 parts by weight and 1 to 10 parts by weight of polybutadiene, the average pore diameter is 0.20 μm or less, the film thickness is 50 μm or more, and the water flux is 25 ml/cm.
^2・min. 10p. s. A porous membrane characterized in that it is more than or equal to i.